Trans Fat in Foods

What are trans-fats? Where are they formed? How are they formed?

Trans Fats in Foods

Metabolism of natural 20-carbon polyunsaturated fatty acids like arachidonic acid results in the biosynthesis of mediators with potent physiological effects such as prostaglandins, prostacyclins, thromboxanes, leukotrienes, and lipoxins. These substances are known collectively as eicosanoids because they contain 20 carbon atoms (Greek eikosi = 20). However, polyunsaturated trans fatty acids cannot be used to produce useful mediators because the molecules have unnatural shapes that are not recognized by enzymes such as cyclooxygenase and lipoxygenase.  Although low levels of trans-vaccenic acid occur naturally in some animal food products, partially hydrogenated oils contain a large proportion of diverse trans fatty acids. Trans fatty acids that are incorporated into the cell membranes create denser membranes that alter the normal functions of the cell.

Effect of trans fats on the heart.

Dietary trans fats raise the level of low-density lipoproteins (LDL or "bad lipoproteins") increasing the risk of coronary heart disease. Trans fats also reduce high-density lipoproteins (HDL or "good lipoproteins"), and raise levels of triglycerides in the blood. Both of these conditions are associated with insulin resistance which is linked to diabetes, hypertension, and cardiovascular disease. 

Researchers have reported that people who ate partially hydrogenated oils, which are high in Trans fats, worsened their blood lipid profiles and had nearly twice the risk of heart attacks compared with those who did not consume hydrogenated oils. Because of the overwhelming scientific evidence linking trans fats to cardiovascular diseases, the Food and Drug Administration started requiring all food labels to disclose the amount of trans fat per serving in 2006.

Effect of trans fats on the brain. 

Trans fats also have a detrimental effect on the brain and nervous system. Neural tissue consists mainly of lipids and fats. Myelin, the protective sheath that covers communicating neurons, is composed of 30% protein and 70% fat. Oleic acid and DHA are two of the principal fatty acids in myelin. Studies show that trans fatty acids in the diet get incorporated into brain cell membranes, including the myelin sheath that insulates neurons.[10]  These synthetic fats replace the natural DHA in the membrane, which affects the electrical activity of the neuron. 

 

Trans fatty acid molecules alter the ability of neurons to communicate and may cause neural degeneration and diminished mental performance. Neurodegenerative disorders such as multiple sclerosis (MS), Parkinson's Disease, and Alzheimer's Disease appear to exhibit membrane loss of fatty acids.

Unfortunately, our ingestion of trans fatty acids starts in infancy. A Canadian study showed that an average of 7.2% of the total fatty acids of human breast milk consisted of trans fatty acids which originated from the consumption by the mothers of partially hydrogenated vegetable oils. Baby milk formulas have violated rules and exceeded the amount of trans fats allowed. Baby milk formulas are thus a source of trans fats in babies.

Source: http://www.scientificpsychic.com/fitness/fattyacids2.html

Fat-free Craze vs Fat Awareness

Why are people crazy about oily and fatty foods? Should people be concerned?

The Fat Free Craze

The concept that some fats are essential for good health is just emerging in the awareness of the general public, but the aversion to fat resulting from many years of indoctrination against fat has resulted in great consumer demand for low-fat or nonfat products.

 

Some manufacturers, eager to increase their sales, concoct products that use monoglycerides, diglycerides, or fatty acid esters of polyglycerol, and argue that these products are "Fat Free" because only triglycerides are fats. Average consumers eat these products under the illusion that they are low in calories because the manufacturers do not disclose the calories of these components in the Nutrition Facts. 

 

In addition, most products containing monoglycerides, diglycerides, or artificial fats do not state whether the constituent fatty acids are saturated or hydrogenated. 

 

New regulations are often adopted as a reaction to abuses like this, but it is a slow process that may be further delayed by lobbying and enables manufacturers to continue reaping profits in the meantime.

Source: http://www.scientificpsychic.com/fitness/fattyacids2.html

Hydrogenation and Trans Fats

What is hydrogenation? What are trans fats? What are hydrogenated fats?

Hydrogenated fats

By now, it is a well-established fact that trans fats are harmful and are responsible for causing thousands of deaths per year from cardiovascular diseases, but hydrogenated fats continue to be added to so many food products that it almost impossible to avoid them. Frequently, even lard is hydrogenated! Why aren't these products banned? Because manufacturers with a lot of political influence don't want to lose money on products that might turn rancid before they are sold. Fast modern distribution methods, good packaging, and controlled temperature storage could solve this problem and deliver healthier products to the consumers, but it would increase costs. One of the latest trends used by manufacturers is to avoid the word "hydrogenated" and to obtain oils from foreign sources where our regulations do not apply. Some products use "Modified Palm Oil" without mentioning the process used to modify the oil. The modification could be a simple fractionation to separate high-melting from low-melting triglycerides, but it could involve hydrogenation.

 

Sources: http://www.scientificpsychic.com/fitness/fattyacids2.html

Nota: Inilah cara menulis rencana bagi menjatuhkan nama baik Malaysia, dan eksport minyak kelapa sawitnya, dengan memburukkan amalan industri. Mereka boleh semak Sijil ISO daripada menuduh tanpa citation yang munasabah. Tak baik tulis berlapik macam ni.

Cholesterol

What is cholesterol?

(1) Structure of Cholesterol

Cholesterol has a total of 27 carbon (C) atoms. Cholesterol is a sterol as it has a hydroxyl (-OH) group at carbon #3 (C3) - only this hydroxyl group is hydrophilic in cholesterol. Cholesterol is a stable molecule as it has a rigid hydrophobic steroid nucleus (rings A, B, C and D) which is not easily degraded by human enzymes. It is  has an aliphatic hydrophobic tail with eight carbons (8C). It has a carbon-carbon double bond between carbon #5 and carbon #6 (C5=C6). It has 5 methyl (-CH3) groups at C18, C19, C21, C26 and C27. 

(2) Function of Cholesterol

Cholesterol is produced by the liver and is found in all body tissues. It helps to organize cell membranes and control their permeability, and therefore avoid cancer formation. Cholesterol derivatives in the skin are converted to vitamin D when the skin is exposed to sunlight. Vitamin D₃ mediates intestinal calcium absorption and bone calcium metabolism. Cholesterol is a precursor to many physiologically important steroids, such as bile acids & salts and steroid hormones. Examples of steroid hormones are testosterone, progesterone, and cortisol.

(3) Cholesterol Synthesis

Cholesterol synthesis occurs in the liver. Cholesterol synthesis initially involves the conversion of acetate to mevalonic acid. The rate-limiting step is catalysed by enzyme beta-hydroxy-beta-methyl glutaryl coenzyme A reductase (HMGCoA reductase). HMGCoA reductase is the rate-limiting enzyme in cholesterol synthesis. The activity of HMGCoA reductase is controlled by negative feedback by the intracellular cholesterol concentration (cholesterol pool). 

(4) Storage of Cholesterol

About two-thirds of the plasma cholesterol is esterified with fatty acids to form cholesteryl esters (CE). Cholesteryl esters are storage forms of cholesterol. The active form of cholesterol is free cholesterol (FC).

(5) Determination of Plasma Cholesterol

Assays in routine use measure the plasma total cholesterol concentrations and do not distinguish between the unesterified and esterified forms. To obtain a measurement for CE separate from FC, HPLC will need to be used. HPLC is high-performance liquid chromatography - it separates the 2 forms of cholesterol (FC, CE) and they can then be determined separately.

When performing cholesterol screening, clinical cholesterol assays measure the Total Cholesterol (TC). Total Cholesterol is the sum of all the cholesterol in all the lipoproteins present in blood.

Unlike that of triglyceride, plasma concentration of cholesterol does not rise after a fatty meal. This means, the subject or patient (or you) does not have to fast 12 hours before a cholesterol test.

(6) High Plasma Cholesterol and Heart Disease

A high level of cholesterol in the blood is considered to be a risk factor for cardiovascular diseases. High blood serum cholesterol levels are associated with increased risk of cardiovascular diseases.

Cholesterol and lipoprotein levels can be normalized through exercise and dietary changes. Dietary changes include reduced Calorie diets that eliminate hydrogenated fats and add sources of polyunsaturated fatty acids (PUFA) such as grape seed oil. 

Blood cholesterol levels can be lowered by reducing the sources of dietary cholesterol, increasing the amount of fiber in the diet, and by consuming oils high in polyunsaturated fatty acids while reducing the intake of saturated fats.

Research on dietary fats by Hegsted and others has shown that myristic acid (C14:0), and palmitic acid (C16:0) increase cholesterol levels, whereas polyunsaturated fats such as linoleic acid (C18:2) reduce cholesterol levels. 

(7) Reduced Absorption of Cholesterol

Sterols of vegetable origin are called "phytosterols". They have the same basic structure as cholesterol, but differ in the side chains attached to carbon 17. Phytosterols, such as stigmasterol from soybean oil, are of current interest because they lower blood cholesterol levels. Sterols that are fully saturated (no double bonds) are called "stanols". For example, stigmastanol has the same structure as stigmasterol, but without the double bonds. When fatty acids react with the hydroxyl at carbon 3 they form "sterol esters".

References:
Clinical Chemistry in Diagnosis and Treatment. Sixth edition, 1994. Philip D Mayne. page 225
http://www.scientificpsychic.com/fitness/fattyacids2.html

Plasma lipids and lipoproteins

Taken from: http://ethesis.helsinki.fi/

2.1. Plasma lipids and lipoproteins

Lipids play very important roles in maintaining the structure of cell membrane (cholesterol, phospholipids), cell growth (cholesterol), steroid hormone synthesis (cholesterol), and energy metabolism (triglycerides). Since lipids are highly hydrophobic, they have to be packed into lipoproteins as water-soluble particles in blood circulation (Gotto et al. 1986). A lipoprotein is a particle consisting of a core of hydrophobic lipids, i.e., triglycerides (TG), cholesteryl esters (CE), surrounded by a polar layer of phospholipids (PL), unesterified cholesterol (FC), and apolipoprotein(s) (Ginsberg 1990). Plasma lipoproteins are usually classified into five major subfractions based on their density (d), particle size, flotation rate (Sf), and electrophoretic mobility in agarose gel. Routinely, the lipoproteins are separated by sequential ultracentrifugation (Havel et al. 1955).

Table 1. Properties and apolipoprotein composition of the major human plasma lipoproteins

CMs are derived from dietary lipids (exogenous pathway) and assembled in the intestinal epithelial cells. TGs are the major constituents of the CM particles. The TGs in CM are hydrolyzed in the peripheral tissues by lipoprotein lipase (LPL) to form the CM remnants which are taken up by the liver in a process that probably involves apolipoprotein E (apoE) on the surface of the remnants and a hepatic receptor called LDL receptor-related protein (LRP) (Beisiegel 1995). VLDL particles are synthesized in the liver (endogenous pathway). They are the main liver-derived TG-rich lipoproteins and in circulation, their TGs are hydrolyzed by LPL and the VLDLs are then degraded into CE-enriched particles called IDL (Gotto et al. 1986). About half of the IDL particles are taken up by the liver via LDL receptor and remnant receptor (van Berkel et al. 1995), whereas the other half are converted into LDL by hepatic lipase (HL) (Taskinen and Kuusi 1987). LDLs are the major carriers of cholesterol in plasma. LDL metabolism is discussed in more detail in Section 2.2.2. Lipoprotein (a) [Lp(a)], which consists of an LDL particle covalently attached to apolipoprotein (a) [apo(a)], is a distinct class of CE-rich plasma lipoprotein. It can bind weakly to LDL receptors and play a role in the genesis of atherosclerosis (Jauhiainen et al. 1991).

HDLs consist of apoAI and apoAII as the main apolipoprotein constituents and carry about 20% cholesterol, most of which are CE (Ginsberg 1990). HDLs are synthesized in the liver and intestine (Franceschini et al. 1991). Also HDLs can be generated following the lipolysis of TG-rich lipoproteins whereafter plasma phospholipid transfer protein (PLTP) facilitates the transfer of phospholipids and some cholesterol into HDL pool (Eisenberg 1984, Jiang et al. 1999). In addition, the lecithin-cholesterol acyltransferase (LCAT) has a crucial role in the maturation of HDL particles. LCAT can catalyze the formation of CE which are then incorporated into the core of discoidal nascent HDL (Franceschini et al. 1991). HDLs (especially preß-mobile HDL) play a major role in the transport of cholesterol from peripheral tissues to the liver, a process known as reverse cholesterol transport (Tall 1990). HDL CE are transfered by cholesteryl ester transfer protein (CETP) to apoB-containing particles which are finally removed from the circulation by the liver (Tall 1993). In addition, HDLs can be taken up by class B scavenger receptor (SR-BI)-mediated process in certain cells where this receptor mediates selective CE uptake leaving the HDL particles largely intact (Acton et al. 1996, Krieger 1998), or directly removed by the liver (Tall 1992).

LDL and atherogenesis

Taken from: http://ethesis.helsinki.fi/

2.2.1. LDL and atherogenesis

LDLs transport about 75% of the total cholesterol in blood circulation. Evidence exists that LDL cholesterol is a critical atherogenic factor (Grundy 1995,1997, Frishman 1998). A large number of epidemiologic studies have demonstrated a strong positive correlation between elevated LDL cholesterol levels and the development of coronary artery disease (CAD) (Kannell et al 1979, Krauss 1987, Genest and Cohn 1995, Frishman 1998). Genetic studies have also documented that inheritable hypercholesterolemias (familial hypercholesterolemia, familial defective apoB-100), mainly with elevated levels of LDL cholesterol, are the primary cause of premature CAD (Goldstein et al. 1973, Tybjaerg-Hansen et al. 1992). In addition, apoB and LDL particles have been identified in atherosclerotic plaques (Hoff et al. 1979a, Hoff et al. 1979b) and in vitro studies have shown that elevated LDL levels damage endothelial cell (EC) layer and penetrate into the arterial intima. The accumulation of LDL in the arterial wall initiates monocyte and smooth muscle cell migration and transforms macrophages and smooth muscle cells into cholesterol-loaded foam cells, which are the major cell components found in the plaque (Goldstein et al 1979, Brown and Goldstein 1983). Furthermore, pathological studies have demonstrated that the lowering of LDL-cholesterol is associated with reduced severity of atherosclerotic lesion and improvement of cardiac functional parameters (Zambon and Hokanson 1998). For example, reduction in cholesterol levels may reduce the susceptibility of LDL to oxidation which is a causal factor for the initiation and progression of atherosclerosis. Protection of LDL from oxidation could increase nitric oxide bioavailability and improve endothelium-dependent vasomotor, anti-inflammatory, and anticoagulant properties of the endothelium (Guetta and Cannon 1996). Finally, clinical studies have shown that lowering of LDL cholesterol has been associated with the reduction of CAD morbidity and mortality (Gotto 1995). The Scandinavian Simvastatin Survival Study (4S) showed that the lipid-lowering agent simvastatin significantly reduced the risk of coronary death and major coronary events in 4444 patients with coronary disease over the median follow-up period of 5.4 years (Scandinavian Simvastatin Survival Study Group 1994). These effects were presumed to be due to the beneficial reduction of serum lipids and lipoproteins, in which LDL cholesterol was reduced by 35%. The best evidence supporting lipid-lowering therapy for primary prevention comes from the West of Scotland Study (Shepherd et al. 1995). In this study, treatment with pravastatin resulted in significant reduction in nonfatal myocardial infarctions and death due to CAD. Taken together, these studies strongly support the importance of LDL in atherogenesis.

LDL (apoB-100,E) receptor mediated uptake

Taken from: http://ethesis.helsinki.fi/

2.2.2. LDL and receptor mediated metabolism

LDL is the most abundant cholesterol-carrying lipoprotein in plasma. CE, located in the hydrophobic core of LDL, is the main form of cholesterol carried in LDL. CE is supposed to be too hydrophobic to pass through cell membranes. The question is how can esterified cholesterol be delivered into cells for their use? The delivery problem is solved by the LDL receptors. The LDL receptors bind LDL and CE packed into LDL particles is delivered into the cell by receptor-mediated endocytosis. The receptor-mediated removal of LDL cholesterol occurs mostly via classical LDL receptors that have been observed in all mammalian cells tested except erythrocytes (Brown and Goldstein 1986) (Fig. 1). The liver plays a crucial role in receptor mediated uptake of LDL: about 75% of the LDL particles removed from the circulation are mediated by the liver. Of these, 75% of the clearance is LDL receptor-mediated, the remainder is by a nonspecific, receptor-independent low affinity process (Pittman et al. 1982, Billheimer et al. 1984). Also SR-BI mediates LDL binding but only CE is selectively delivered to the cell especially in non-placental steroidogenic tissues (van Berkel et al. 1995).

Figure 1. Steps in the LDL pathway in cultured human fibroblasts.  

HMG CoA reductase, 3-hydroxy-3-methylglutaryl CoA reductase; ACAT, acyl CoA:cholesterol acyltransferase (Brown and Goldstein, 1986).

The LDL receptor is a cell surface glycoprotein with a molecular weight of 164 kDa, with a coding gene on chromosome 19 (Francke et al. 1984). It is present on both hepatic and extrahepatic cells. The high binding interaction between LDL apoB and the LDL receptor is responsible for the receptor-mediated uptake and clearance of LDL from the circulation. The ApoE on apoE-containing lipoproteins (VLDL, IDL) is also capable of interacting with the LDL receptors and regulating the metabolism of these lipoproteins (Mahley 1990). Following the binding of LDL to its receptors, the lipoprotein is internalized and delivered into lysosomes where its CE is hydrolyzed. The liberated cholesterol is then used by the cell for the synthesis of plasma membranes, bile acids, and steroid hormones, or stored in the ester form. The increased intracellular cholesterol level will, in return, down regulate the LDL receptor activity, i.e., receptor synthesis. Subsequently, the number of the LDL receptors synthesized decreases when the cellular cholesterol content increases, and vice versa (Brown and Goldstein 1986). Therefore, cellular cholesterol content is the major LDL receptor regulator. ApoB-100, one of the largest monomeric proteins known, is the major protein component of LDL and acts as a ligand for the LDL receptor. 

ApoB-100 is a large (513 kDa), single chain glycoprotein composed of 4536 amino acid residues with a coding gene residing on the short arm of chromosome 2 (Knott et al. 1986, Yang et al. 1986). There is only one apoB-100 molecule in each LDL particle (Tikkanen and Schonfeld 1985, Cladaras et al 1986). ApoB-100 also is not transfered between lipoprotein particles during the metabolic conversion of VLDL into LDL. It is presumed that the apoB-100 binding site resides in the carboxyterminal portion of the molecule. However, the region assumed to be involved in LDL binding is not yet clear. So far three apoB mutations, called familial defective apolipoprotein B-100 (FDB) (Arg3500®Gln, Arg3500®Trp, Arg3531®Cys) have been reported to be related to hypercholesterolemia (Soria et al. 1989, Gaffney et al. 1995, Pullinger et al. 1995). However, none of these mutations have been found in Finland (Hämäläinen et al. 1990). 

LDL structure (general)

Taken from: http://ethesis.helsinki.fi/

2.2.3. LDL particle structure

In blood circulation, TG and CE are packed into LDL particles forming a hydrophobic core surrounded by a surface monolayer of polar PL together with unesterified cholesterol (FC) and apoB. LDL normally also contains lipophilic antioxidants, mainly Vitamin E and ß-carotene. LDL is a large spherical particle, molecular weight of about 3 x 106 Da, with a diameter of 22-28 nm and density between 1.019-1.063 g/ml. The core is composed of some 1,600 molecules of CE (long chain fatty acid) and 170 molecules of TG. The CE is the main lipid of the lipoprotein core with the most fatty acyl chain in these esters being linoleate (Krieger et al. 1978). This core is shielded by a layer of PL (700 molecules), FC (600 molecules), and 1 molecule of apoB-100 (Steinberg 1997b, Stryer 1988, Yang et al. 1989). In the percent mass composition, each LDL particle consists of 35-45% CE, 7-10% FC, 7-10% TG, 15-20% PL, and 20-25% protein (Deckelbaum et al. 1987, Schultz and Liebman 1997). 

Figure 2. Schematic model of LDL particle.

Overall structure of the LDL particle is shown in Fig. 2. The PLs are arrayed so that their hydrophilic heads are on the outside, allowing the LDL to be dissolved in the blood or intercellular fluid. Embedded in this hydrophilic coat is one apoB-100 molecule. Effective and efficient binding for apoB-100 to the LDL receptor is the prerequisite for cholesterol delivery into cells. In principle, LDL can also transport other lipophilic biosubstances into cells under the direction of apoB-100. On the other hand, apoB-100 gene mutation or conformational changes may affect LDL metabolism and plasma cholesterol levels (Innerarity et al. 1987, Aviram et al. 1988, Chen et al. 1994).

Ox-LDL structure

Taken from: http://ethesis.helsinki.fi/

2.2.4. Oxidative modification of LDL

There is much evidence indicating that oxidized LDL (Ox-LDL) is present in atherosclerotic lesions in vivo (Ylä-Herttuala 1998). First of all, LDL isolated from atherosclerotic lesions is in part oxidatively modified (Ylä-Herttula et al. 1989). Second, immunological techniques have demonstrated that atherosclerotic lesions contain materials reactive with antibodies generated against Ox-LDL (Haberland et al. 1988, Palinski et al. 1989, Rosenfeld et al. 1990). Third, serum contains autoantibodies against Ox-LDL (Palinski et al. 1989, Salonen et al. 1992). Fourth, treatment with antioxidants can prevent the development or slow the progression of atherosclerosis (Carew et al. 1987, Kita et al. 1987, Steinberg 1997a). 

In principle, any modified LDL in plasma could be rapidly removed by hepatic sinusoidal cells (Kupffer cells), which contain abundant scavenger receptors. Moreover, a variety of antioxidants remain in plasma. Therefore, it was presumed that Ox-LDL mainly occurred locally in the arterial wall after entrance of normal LDL, whereby it was sequestered from antioxidants in plasma (Steinberg et al. 1989, Witztum and Steinberg 1991). However, recent studies have suggested that very small amounts of Ox-LDL are also present in plasma (see review from Nielsen 1999). These changes could have occurred elsewhere, or during a previous transient passage through the artery wall. Such minimally modified LDL might then be "primed" for more rapid oxidative modification on a subsequent entry into the intima. Therefore, Ox-LDL in the arterial wall can be derived both from normal LDL oxidized locally in the arterial intima and from Ox-LDL in plasma (Nielsen 1999). 

Lipid peroxidation presumably starts in the polyunsaturated fatty acids (PUFA) forming an ester bond with LDL-surface PLs, and then propagates to core lipids, resulting in oxidative modification not only of the PUFA, but also of the cholesterol moiety (mostly CE) and modification and degradation of apoB (Witztum 1994). 

Therefore, a wide variety of biologically active molecules can be formed, including oxidized sterols, oxidized fatty acids, and PL and protein derivatives generated by adduct formation with breakdown products of oxidized fatty acids. For example, malondialdehyde and 4-hydroxynonenal can subsequently react with lysine residues in apoB. Such adducts, and others, presumably create the epitopes on apoB that lead to recognition by scavenger receptors on macrophages.

In culture, all the vascular cells can initiate oxidation of LDL, but the relative contributions of ECs, monocytes and macrophages, or smooth muscle cells (SMC) to such modification in vivo are unknown (Heinecke 1998, Ylä-Herttuala 1998). In vitro, LDL can bind to copper which can promote rapid lipid peroxidation. However, it is not known whether sufficient free copper and iron, or complexes of these metals, exist in vivo to promote LDL peroxidation, although intact ceruloplasmin can act as a prooxidant. 

Therefore, several mechanisms are probably involved, and even the same cell type may use different pathways. For example, release of superoxide anion from ECs or SMCs might be responsible for initiation of oxidation in some settings, and thiols in others (Heinecke et al. 1986). 

In macrophages, enhanced 15-lipoxygenase activity could generate increased cellular lipid hydroperoxides, which could be transferred to extracellular LDL, providing the "seed" that would lead to enhanced lipid peroxidation (Heinecke 1998). 

The antioxidant defences that prevent oxidation of LDL need to be defined. The antioxidant content of the LDL particle is critical for its protection (Esterbauer et al. 1992) and, theoretically, if sufficient lipophilic antioxidants were present, the LDL particles would be protected from even profound oxidant challenge. In vivo, whether or not LDL becomes oxidized is a question of the balance between the extent of the prooxidant challenge and the capacity of the antioxidant defenses. 

Although Ox-LDL is found in man, there are no conclusive intervention studies in man to support a quantitatively important role for this process. The ongoing antioxidant trials will no doubt add more beneficial evidence in the role of atherosclerosis prevention. 

LDL oxidation (test methods)

Taken from: http://ethesis.helsinki.fi/

2.2.5. Determination of lipoprotein oxidation

LDL oxidation is a lipid peroxidation chain reaction driven by free radical intermediates, which is accompanied by characteristic changes of chemical, physiochemical, and biological properties. Therefore, a variety of methods may be used for determining the rate and extent of oxidation in vitro (Puhl et al. 1994) and in vivo (Jialal and Devaraj 1996).

For in vivo LDL oxidation determination, the immunological method for autoantibody to Ox-LDL has been widely used (Jialal and Devaraj 1996), while a recent developed baseline diene conjugation measurement is a promising method for estimating LDL oxidation in vivo (Ahotupa et al. 1998). 

The in vitro estimation of LDL oxidation includes measurement of the increase of thiobarbituric acid-reactive substances (TBARS), total lipid hydroperoxides, defined lipid hydroperoxides, hydroxy- and hydroperoxy fatty acids, conjugated dienes (CD), oxysterols, lysophospholipids, aldehydes, fluorescent chromophores, measurement of disappearance of endogenous antioxidants and PUFA, oxygen uptake, and total peroxyl radical trapping potential (TRAP) (Puhl et al. 1994, Valkonen and Kuusi 1997). 

A convenient and very frequently used method for continuously monitoring the process of copper-induced LDL oxidation is to measure the conjugated diene formation at 234 nm as a time course in a UV spectrophotometer (Esterbauer et al. 1989).

Ox-LDL metabolism

Taken from: http://ethesis.helsinki.fi/

2.2.6. Metabolism of oxidized LDL

Ox-LDL particles are taken up by so-called scavenger receptors (Fig. 3). In the liver, Kupffer cells are the main site for mediating the in vivo uptake of Ox-LDL from the circulation and might thus protect against circulating Ox-LDL (van Berkel et al. 1995). 

Increased LDL levels in plasma lead to an increase entry of LDL into the intima through the injured endothelium, resulting in accumulation of LDL in the intima. 

LDL in the artery wall can be oxidatively modified by all the major cells of the arterial wall, i.e. ECs, SMCs, monocytes/macrophages, and in cell-free system by transition metals, lipoxygenase, myeloperoxidase, and nitric oxide (NO). 

Ox-LDL is taken up by a family of scavenger-receptors (SR) on the surfaces of cells such as macrophages, platelets, and ECs. However, which part of the Ox-LDL particle is being recognized by scavenger receptors is not fully understood (Greaves et al. 1998).

Certainly, both the lipids and the protein are oxidized under the oxidative condition. It was shown that the modified apolipoproteins extracted from Ox-LDL particles were efficiently internalized and degraded by macrophage scavenger receptors (Parthasarathy et al. 1987), while the oxidized lipids extracted from Ox-LDL were also recognized by scavengers (Terpsta et al. 1998). 

During the oxidation of LDL, the PUFA are broken down to smaller fragments and become conjugated with the -amino groups of lysine residues. Therefore, Steinberg (1997b) proposed that the recognition of Ox-LDL by scavenger receptors appears to be due to the masking of lysine -amino groups and subsequent changes in protein charge and configuration. 

The SRs mediate the endocytosis of the Ox-LDL, where the process is not down regulated. Increasing uptake of Ox-LDL via scavenger receptors certainly promotes cholesteryl ester accumulation and conversion to lipid-droplet filled foam cell formation which is the hallmark of fatty streaks and atherosclerotic plaques. 

The SR activity on the macrophages exhibits a remarkable broad binding specificity (Goldstein et al. 1979, Brown and Goldstein 1983); they not only recognize Ox-LDL but also other chemically modified proteins such as acetyl LDL (Ac-LDL), methylated LDL, suggesting they are multiligand receptors. So far, there are more than six classes of SRs (10 types) that have been shown to be responsible for endocytosis of Ox-LDL (Krieger 1997). 

Figure 3. Scheme depicting the uptake of native and Ox-LDL by macrophage receptors (Steinberg 1997a). 

Atherogenicity of oxidized LDL (ox-LDL)

Taken from: http://ethesis.helsinki.fi/

2.2.7. Atherogeneity of oxidized LDL

In the early stages, uptake of Ox-LDL by macrophage may be protective. When too much Ox-LDL accumulates in macrophage, irreversible damage occurs, resulting in foam cell formation, cell death, and release of many modified molecules with diverse effects (Witztum et al. 1991, Witztum 1994). As a result of accumulation of lipid deposits in foam cells, the arterial wall evolves from the initial fatty streak to form the lipid-rich atheromatous core and an overlying dense fibrocellular layer, comprising primarily of SMCss. 

Ox-LDL is the prerequisite for macrophage uptake and cellular cholesterol accumulation (Steinberg et al. 1989). Therefore, it has potential atherogenic properties in the initiation and development of the atherosclerotic lesion (Ross 1993, Steinberg 1997b). 

In addition to the foam cell formation, Ox-LDL can also play other roles. It promotes atherosclerosis by recruitment and retention of monocytes and T cells in the intima, migration of SMC from media into intima where these cells will become foam cell-like after having taken up Ox-LDL, by its cytotoxicity toward EC and by stimulating monocyte adhesion to the endothelium. In addition, the Ox-LDL or its products may induce cellular expression of potent chemotactic factors, such as monocyte chemotactic protein 1, and secretion of colony-stimulating factors, such as macrophage colony-stimulating factor, which can stimulate SMC proliferation and differentiation of monocytes into macrophages. 

Ox-LDL is also immunogenic with antibodies to epitopes of Ox-LDL found in plasma and in lesions associated with immune complexes. In addition, CD4+ T cells have been isolated from human atherosclerotic plaques and up to 10% of these clones proliferate and release cytokines on exposure to Ox-LDL. This response is dependent on autologous antigen-presenting cells and restricted by HLA-DR. Thus there is both a humoral and a cell-mediated immune response, typical of an inflammatory lesion (Witztum 1994). 

Ox-LDL enhances platelet adhesion and aggregation, which may stimulate macrophage foam cell formation and SMC proliferation.

Ox-LDL may alter other vital properties of the arterial wall with clinical or fatal consequences such as impairing vasodilation (Holvoet and Collen 1998). 

Ox-LDL can induce vascular cell apoptosis which is involved in atherosclerosis formation (Nishio et al. 1996, Li et al. 1998).

Ox-LDL, or its products, can profoundly impair the nitric-oxide-mediated vasorelaxation of coronary arteries in response to agents such as acetylcholine. 

Hypercholesterolaemia, by generation of more Ox-LDL in the intima or by creation of a prooxidant environment that stimulates EC to release more superoxide anion, may contribute importantly to vasospasm even in the absence of significant lesions.

Certain products of Ox-LDL, such as oxysterols, are highly toxic to EC and could initiate breaks in endothelial integrity. 

Other products may stimulate tissue-factor release and initiate coagulation and thrombosis. 

Because the shoulder regions of even established lesions are rich in macrophage-filled foam cells containing Ox-LDL (it is at these sites that plaque rupture and thrombotic events occur), Ox-LDL probably participates in this late stage as well. 

Thus, Ox-LDL may contribute to atherogenesis and CHD by mechanisms other than macrophage foam-cell formation alone. 

The pathological process of Ox-LDL initiated atherosclerotic lesion formation is shown in Fig. 4. Accordingly, the intervention and prevention of Ox-LDL should be the primary goal of therapy.

Figure 4. Pathway for Ox-LDL initiated atherosclerotic lesion formation. 

EC: Endothelial cells, M: monocytes, SMC: smooth muscle cells

LDL structure (detailed)

Taken from: http://ethesis.helsinki.fi/

2.2.8. LDL composition, oxidizability, and endogenous antioxidants

In LDL particle, cholesteryl linoleate represents quantitatively the single most important polyunsaturated fatty acid (PUFA) which is the substrate for peroxidation. If PUFA becomes oxidized to lipid hydroperoxides, their isolated carbon-carbon double bonds are converted to conjugated double bonds showing a strong UV-absorption at 234 nm, designated as conjugated diene (CD) formation (Esterbauer et al 1993). Therefore, its content in LDL may influence the determination of oxidation resistance measured by CD or TBARS formation (Ziouzenkova et al. 1996). 

Reaven et al. (1993) reported that LDL particles rich in PUFA are more readily oxidized than LDL particles enriched in saturated fatty acids or monounsaturated fatty acids. In addition, elevated levels of preformed lipid hydroperoxides and cholesterol in LDL were associated with increased oxidation susceptibility (Frei and Gaziano 1993). Studies have shown that monoenic fatty acids enriched LDL, for example oleic acid was remarkably resistant to oxidative modification as measured by decreased formation of CD and TBARS (Parthasarathy et al. 1990). 

The 3-hydroxy-3-methylglutaryl-coenzyme A (HMG CoA) reductase inhibitors reduced the susceptibility of LDL to oxidation by altering the LDL particle composition containing less lipid relative to protein (Lavy et al. 1991) or preserve endogenous antioxidants (Chen et al. 1997). In deed, most of these HMG-CoA reductase inhibitors themselves are antioxidants and could become bound to lipoprotein in the circulation to protect them against oxidation (Lennernas and Fager 1997, Girona et al. 1999). 

LDL particle size could also influence its oxidation susceptibility. For example, small, dense LDL particles displayed diminished resistance to oxidative stress in vitro (Tribble et al. 1992, de Graaf et al. 1991). 

Since LDL is the major extracellular transport vehicle for lipid-soluble antioxidants, it contains relatively large amounts of a-tocopherol, g-tocopherol, b-carotene, and ubiquinol-10 and among them a-tocopherol is the most important antioxidant known with 6 molecules per LDL particle (Esterbauer et al. 1995). As the oxidation goes on, a-tocopherol is the first and b-carotene is the last endogenous antioxidant in LDL particles to be depleted (Esterbauer et al. 1992). 

The endogenous antioxidants contained in LDL particles might influence oxidation resistance (Tribble et al. 1994). Dietary antioxidant supplementation could increase their content in LDL and therefore, increase oxidation resistance of lipoproteins (Nyyssonen et al. 1994, Jialal et al. 1995). The composition of native LDL and the antioxidants contained in LDL are listed in Tables 2 and 3.

Table 2. Composition of human LDL

Table 3. Antioxidants in native human LDL

Antioxidants in LDL

Taken from: http://ethesis.helsinki.fi/

2.2.9. Antioxidants in the pathogenesis of atherosclerosis

As discussed in section 2.2.7, Ox-LDL is involved in several steps of atherosclerosis. It is believed that antioxidants can interfere to different extents with these steps (Faggiotto et al. 1998). Kleinveld et al. (1993) reported that 18 weeks of pravastatin or simvastatin administered to 23 hypercholesterolemic patients (15 men, 8 women) decreased LDL cholesterol levels by 36% and significantly reduced the rate and extent of copper-catalyzed LDL oxidation. LDL particles after therapy were changed in composition to contain less lipid relative to protein, possibly rendering the particle less susceptible to oxidation (Lavy et al. 1991). HMG-CoA reductase inhibitors rather than reducing LDL levels and changing its particle composition, may also be of antioxidant importance. In this regard, Giroux et al. (1993) reported that simvastatin diminished superoxide anion formation and LDL oxidation by human macrophages in tissue culture. Fruebis et al. (1994) have found that atherosclerosis in WHHL rabbits is inhibited by probucol (a potent antioxidant) but not by its analogue with similar structure. Thus, for any given prooxidant stress, there may be a threshold of protection that must be achieved. Protection of LDL from oxidation could increase nitric oxide bioavailability and improve endothelium-dependent vasomotor, anti-inflammatory, and anticoagulant properties of the endothelium (Guetta and Cannon 1996). Recently, Yasunari et al. (1999) observed that antioxidants probucol and vitamin E prevent smooth muscle cell migration and proliferation via reducing intracellular oxidative stress. Since endogenous antioxidants (superoxide dismutase, H₂O₂-removing enzymes, and metal binding proteins) may become inadequate to prevent LDL oxidation, exogenous antioxidants (diet-derived or supplemented) would seem, therefore, important to maintain such effect in vivo. The direct provision of lipophilic antioxidants into the LDL particle should be the most effective strategy. The most abundant natural antioxidant in LDL is a-tocopherol (Esterbauer et al. 1992), and supplementation of the diet with vitamin E can increase the vitamin E content of LDL and lead to enhanced protection of such LDL from in vitro oxidation. The vitamin E content in LDL particles is positively correlated with oxidation resistance (Tesoriere et al. 1998). However, in man, supplementation at about 1.2 g per day saturates the LDL, and at this degree of enrichment (about a 2 1/2-fold increase) the lag time for CD formation, a sensitive index of susceptibility to lipid peroxidation, is only prolonged by 50% (Reaven and Witztum 1996). Tikkanen et al. (1998) have observed that soybean phytoestrogen intake prolonged the lag time by 20 min. However, we do not know if this degree of lag time prolongation is sufficient to protect LDL under all conditions and its correlation to the prevention of CAD. For example, in hypercholesterolaemia, the residence of LDL in the artery is prolonged. If the pro-oxidant stress is continuous, more potent antioxidant activity would be required. Beta-carotene is the next most common antioxidant in LDL (Esterbauer et al. 1992) and theoretically should provide enhanced antioxidant protection. However, data have not supported this effect even when the b-carotene content was increased more than 20-fold by dietary enrichment (Heinecke 1998, Anderson et al. 1998). By contrast, the administration of probucol to volunteers, such that the probucol content of the LDL is 2-4 mg/mg of LDL protein, can lead to near-total protection against oxidative stress for as long as 16 hours. Vitamin C, a water-soluble antioxidant, also provides significant protection for LDL in vitro, presumably by maintaining or regenerating vitamin E in the LDL particle in its reduced antioxidant state.

Another strategy to protect LDL against oxidation is to reduce its content of PUFA by dietary substitution with oleic acid (Reaven et al. 1993). The diet-enriched flavonoids and isoflavonoids, may have great nutritional benefits against atherosclerosis as they appear to constitute a major source of dietary antioxidants (Hertog et al. 1993).

A reduction in prooxidant activity can also be achieved by enhancing the antioxidant content of cells, for example, by enriching them with ascorbate, or with vitamin E or b-carotene. Navab et al (1991) have developed a co-culture of ECs and SMCs that can oxidatively modify LDL. Enrichment of this culture with vitamin E, or b-carotene, decreases the ability of the cells to modify LDL.

In theory, antioxidant protection could be achieved with changes in lifestyle, diet and even with pharmacological approach. Despite the impressive ability of lipid-soluble antioxidants to block atherosclerosis in hypercholesterolemic animals, some studies are controversial because these antioxidants may have other antiatherogenic effects such as a hypolipidemic effect which may confound the conclusion. However, randomized clinical trials will eventually resolve the question as to whether these antioxidants deserve greater importance in inhibition of atherosclerosis.

Clinical Chemistry in Diagnosis and Treatment (1994) Philip D Mayne

Call No: QY90 Z69 1994 

Author: Philip D. Mayne
Publisher: Oxford Univ Pr
Publication Date: 1994-01-01
Language: English
Format: Paperback
ISBN-10: 0340576472
ISBN-13: 9780340576472
Product ID: EPID48049310

Topics of interest

Chapter 11: Plasma Lipids and Lipoproteins (pages 223-241)
Terminology (page 224)
Plasma Lipids (pages 224-5)
- Fatty acids
- Triglycerides
- Phospholipids
- Cholesterol
- Fig 11.1: Chemical structure of lipids present in plasma
- Table 11.1: Fatty acids present in plasma


Lipoproteins (pages 225-6; 227)
- Chylomicrons
- VLDL
- IDL
- LDL
- HDL
- Table 11.2: The composition and electrophoretic mobility of the main lipoprotein particles
- Table 11.3: WHO (Fredrickson) classification of hyperlipidaemia, based on the electrophoretic pattern of the lipoproteins 
- Table 11.4: The main apolipoproteins and their known functions (page 227)
- Fig 11.2: Exogenous pathway of lipid metabolism (page 228)
- Fig 11.3: Endogenous pathway of lipid metabolism (page 229)
- Fig 11.4: The relation between the cellular uptake of LDL and the endogenous synthesis of cholesterol (page 230)


Metabolism of Lipoproteins (pages 227-231)
- Exogenous Lipid Pathways
- - Chylomicron Metabolism
- Endogenous Lipid Pathways
- - VLDL Metabolism
- - LDL Metabolism
- - Factors Influencing Plasma LDL Concentrations
- Role of HDL


Disorders of Lipid Metabolism (pages 232-236)
- Clinical Manifestation of Hyperlipidaemia
- - arterial walls, subcutaneous tissue, tendons, cornea
- Lipid and Cardiovascular Disease
- Predominant Hypercholesterolaemia
- - What is hypercholesterolaemia?
- - Causes of hypercholesterolaemia
- - - Secondary hypercholesterolaemia
- - - - Table 11.5: The effect of some drugs on plasma lipid concentrations
- - - Primary hypercholesterolaemia
- - - - Familial combined hyperlipidaemia
- - - - Familial (monogenic) hypercholesterolaemia
- Predominant Hypertriglyceridaemia
- - Table 11.6: Some important causes of secondary hypertriglyceridaemia
- - Familial combined hyperlipidaemia
- - Familial endogenous hypertriglyceridaemia
- Mixed Hyperlipidaemia
- Rare Disorders Associated With Lipid Metabolism


Principles of Treatment of Hyperlipidaemia (pages 236-7)
- General Measures
- - Hypercholesterolaemia
- - - Restriction of dietary animal fats, eggs and dairy products
- - - Drug treatment
- - Hypertriglyceridaemia
- - - Dietary restriction
- - - Fibric acid derivatives 


Summary (page 238)


Investigation of Lipid Disorders (pages 239-241)
- Plasma Sampling
- Investigation of Suspected Hyperlipidaemia
- Is The Cause Primary Or Secondary?
- What Is The Nature Of The Abnormality?
- Family Studies
- Treatment

Clinical Chemistry in Diagnosis and Treatment (1994) Philip D Mayne

Call No: QY90 Z69 1994 

Author: Philip D. Mayne
Publisher: Oxford Univ Pr
Publication Date: 1994-01-01
Language: English
Format: Paperback
ISBN-10: 0340576472
ISBN-13: 9780340576472
Product ID: EPID48049310

Topics of interest

Chapter 10: Carbohydrate Metabolism (pages 195-222)
- Table 10.1: Common reducing and non-reducing sugars (page 196)

- The Importance of Extracellular Glucose Concentrations (page 196-7)
- Maintenance of Extracellular Glucose Concentrations (page 197)

- - Hormones concerned with glucose homeostasis (page 197)
- - - Insulin; Structure of proinsulin (Fig 10.1, page 197)
- - - Circulating C-peptide
- - - Glucagon
- - - Table 10.2: Action of hormones that affect intermediary metabolism (page 198)

- Control of plasma glucose concentration (page 198-9)
- - The Liver (page 198-200)
- - Fig 10.2: Postprandial metabolism of glucose (page 199)
- - Table 10.3: Metabolism of the carbon skeleton of some amino acids to either carbohydrate (glycogenic) or fat (ketogenic) (page 200)
- Systemic effects of a glucose load (page 200)

- Ketosis (pages 201-2)
- - Adipose Tissue and the Liver
- - Fig 10.3: Intermediary metabolism during fasting: ketosis (page 201)
- - Table 10.2: Action of hormones that affect intermediary metabolism (page 198)

- Lactate Production  and Lactic Acidosis (pages 202-5)
- - Striated muscle and the liver (page 202-3)
- - Fig 10.4: Intermediary metabolism during muscular contraction: the Cori cycle (page 203)
- - Pathological lactic acidosis (pages 203- 205)
- - Tissue hypoxia (pages 203-4)
- - Fig 10.5: Metabolic pathways during tissue hypoxia (page 204)

- Urinary Glucose (page 205)
- - Glycosuria
- - Reducing substances 
- - - Table 10.1: Common reducing and non-reducing sugars (page 196)
- - - Table 10.4: Reducing substances in urine ... (page 105) 


Hyperglycaemia and Diabetes Mellitus (pages 206-211)
- Diabetes mellitus
- Impaired Glucose Tolerance (IGT)
- Subjects as risk of developing diabetes mellitus (page 207)

- Clinical and Metabolic Features of IDDM (page 207)
- - Long-term effects

- Principles of Management of Diabetes Mellitus (pages 208)
- - Blood glucose concentrations
- - Glycated hemoglobin (HbA1c)


- Acute Metabolic Complications of Diabetes Mellitus (pages 208- 210)
- - Diabetic Ketoacidosis
- - Hyperosmolal Non-Ketotic Coma
- - Other causes of coma in patients with diabetes mellitus

- Principles of Treatment of Diabetic Coma (pages 210-211)
- - Diabetic ketoacidosis
- - Hyperosmolal nonketotic coma


- Hypoglycemia (page 211-212)
- - Table 10.6: Principal causes of fasting hypoglycaemia in adults
- - Table 10.7: Substances that may provoke hypoglycaemia


- Hypoglycaemia, Particularly in Adults (pages 212-213)
- - Insulin- or other drug-induced hypoglycaemia
- - - Table 10.8: Results of plasma insulin and C-peptide estimations during hypoglycaemia (spontaneous or after a prolonged fast)
- - Insulinoma (page 212-3)
- - Alcohol-induced hypoglycaemia
- - During prolonged fasting (page 213)
- - Non-pancreatic tumours
- - Reactive (functional) hypoglycaemia
- - Endocrine causes
- - Impaired liver function


- Hypoglycaemia in Infants and Chilldren (pages 213-5)
- - Neonatal Period
- - Early Infancy
- - - Glycogenoses
- - - Hereditary fructose intolerance
- - Later Infancy
- - - Idiopathic hypoglycaemia of infancy
- - - Leucine sensitivity


- Treatment of Hypoglycemia (page 215)
-  Summary (216)


- Investigation of Disorders of Carbohydrate Metabolism
- Estimation of Plasma or Blood Glucose
- Collection of Urine Sample for Glucose Estimation


Investigation of Suspected Diabetes Mellitus (pages 217-220)
- Initial investigations
- Table 10.10: Interpretation of fasting and random plasma glucose concentrations
- Oral Glucose Tolerance Test / OGTT (pages 218-219)
- Table 10.12: Interpretation of oral glucose tolerance (page 218)
- Initial investigation of a diabetic patient presenting in coma (page 219-220)
- Table 10.13: Clinical and biochemical features of a diabetic presenting in coma (page 219)


Investigations of Hypoglycaemia (pages 220-222)
- Insulin Suppression Test
- Glycosuria
- - Reducing substances 
- - - Glucose
- - - Glucuronates
- - - Galactaose
- - - Fructose
- - - Lactose
- - - Pentoses
- - - Homogentisic acid


- Ketonuria (page 222)

Clinical Biochemistry for Medical Students (1996) M.F. Laker - Chapter 1: Carbohydrate Metabolism

Call No: QY 90 L192 1996

Good Topics in this book:

Chapter 1: Carbohydrate Metabolism

- Blood glucose homeostasis (pages 1-4)
- Fig 1.1: Origins of blood glucose & maintenance of blood glucose by glycogen breakdown & synthesis from lactate, alanine and glycerol (gluconeogenesis) (pages 2-3)

- Hormonal regulation of blood glucose (pages 3-4)
- - Insulin; Principle actions of insulin (page 4, Fig 1.2)
- - Glucagon
- - Growth Hormone
- - Adrenaline
- - Cortisol


- Interrelation of glucose, nonesterified fatty acid and ketone body metabolism (pages 4-5)
- Fig 1.3: Control of ketogenesis (page 5)

Various types of diabetes: (pages 6-7)
- Diabetes mellitus (pages 6-14)
- - Table 1.1: Clinical classification of diabetes mellitus (page 6) 
- - Table 1.2: Typical features of IDDM and NIDDM
- Insulin-Dependent (Type I) Diabetes / IDDM (page 6)
- Non-Insulin-Dependent (Type 2) Diabetes / NIDDM (page 6)
- Malnutrition-Related Diabetes Mellitus (page 7)
- Secondary Diabetes (page 7)
- Gestational Diabetes Mellitus (page 7)

- Impaired Glucose Tolerance / IGT (page 7)
- Diagnosis of Diabetes and Impaired Glucose Tolerance (page 8)
- Table 1.3: Indications, protocol and factors influencing the oral glucose tolerance test (OGTT) (page 8)
- Table 1.4: Diagnostic criteria for diabetes mellitus and impaired glucose tolerance (page 8)

- Glucose Estimation (page 9)
- Blood Glucose Analysis; Blood Glucose Monitoring (page 9)

- Urine Testing, Urine Analysis (page 9)

- Management of Diabetes (page 9)
- Glycated Proteins (page 10)

- Metabolic Complications - diabetic ketoacidosis & hypoglycemia (page 10)
- Table 1.5: Causes of impaired consciousness in diabetic patients (page 10)

- Diabetic Ketoacidosis (page 10)
- Fig 1.4: Major changes in fuel metabolism in diabetic ketoacidosis (page 11)
- Fig 1.5: Major changes in water and electrolyte metabolism in diabetes mellitus (page 12)
- Hyperosmolar Nonketotic Coma (page 13)
- Lactic Acidosis (page 13)

- Long-term Complications of Diabetes (page 13)
- - Table 1.6: Long-term complications in diabetes mellitus (page 14)
- Proteinuria in Diabetes (page 14)
- Hypoglycemia (pages 14-18)
- - Table 1.7: Causes of hypoglycemia (page15)

- Investigation of Hypoglycemia in Adults (page 17)
- Hypoglycemia in Infancy & Childhood (page 17)

- Inherited Metabolic Disorders of Carbohydrate Metabolism (page 18)
- - Glycogen Storage Disease (Glycogenoses) (pages 18-19)
- - - Fig 1.6: Glycogen metabolism (page 18)
- - - Table 1.8: Features of glycogen storage diseases (page 19)
- - Galactosemia (page 19)
- - - Fig 1.7: Pathway for the conversion of galactose to glucose (page 20)
- - Disorders of Fructose Metabolism (page 20)
- - - Hereditary Fructose Intolerance (page 20)
- - - Essential Fructosuria (page 20)

Cases

Case 1.1: Gestational Diabetes Mellitus
Case 1.2: IDDM
Case 1.3: Recurrent hypoglycemic episodes (C-peptide 0 pmol/L)

PowerPoints

Metabolism of Carbohydrates

http://slideplayer.com/search/metabolism+of+carbohydrates/

http://slideplayer.com/slide/3863013/#

http://slideplayer.com/slide/4450277/#

http://slideplayer.com/slide/686291/

http://slideplayer.com/slide/3362469/#

http://slideplayer.com/slide/3387511/

http://slideplayer.com/slide/3768633/

Viral infection of the heart (viral myocarditis)

Case study: A 49-year old lady suffered a viral infection for about 3 weeks before she succumbed to a fatal acute viral myocarditis. Discuss her case in the light of technological advances we have today to diagnose her cause of death.

Myocarditis is inflammation of the heart muscle. Myocarditis may occur after a viral, fungal, or bacterial infection, such as diphtheria, rheumatic fever, or tuberculosis.

Viral causes of myocarditis 1948-2007

Diagnosis and treatment of viral myocarditis

Myocarditis is an important and often unrecognized cause of dilated cardiomyopathy (DCM). It is defined as inflammation of the heart muscle that may be identified by clinical or histopathologic criteria. 

Recent developments in the diagnosis and treatment of patients with suspected myocarditis include improved histologic criteria and use of cardiac magnetic resonance imaging (MRI). 

Treatment for myocarditis includes evaluation and treatment of the underlying cause of the inflammation. Treatment may require use of antibiotics, if a bacterial infection is the cause, and medications to relieve pain and inflammation. Lifestyle changes, including increased rest and a low-salt diet, may be part of the treatment.

Sources:

http://www.ivillage.com/myocarditis/4-y-102098

http://www.mayoclinicproceedings.com/content/84/11/1001/T1.expansion.html

PatientsLikeMe

PatientsLikeMe is a good website to see the extent of sufferings of people affected by a variety of diseases. It has a lot of details and is quite easy to select a few cases for study. Most cases are real even though the names and images are unreal.

Source: http://www.patientslikeme.com/patients

Why does coffee cause nausea, headache and sweaty palms?

Umi Nadhirah Binti Rokhibi commented on your Wall post.

Umi Nadhirah wrote "bila minum satu sachet kopi (Nescafe,Ali Cafe,etc.),tiba-tiba jadi pening,nausea,tapak tgn berpeluh,kenapa ya?"

Faridah Abdul Rashid: nausea - as coffee is bitter and does initiate nausea; sounds more like onset/aura of migraine; maybe nervousness or stress response.

Blood glucose or blood sugar?

Blood sugar is the layman's term for blood glucose.

In medicine, we will use blood glucose.

In daily coversation, we can use blood sugar.

Please avoid using blood sugar in exams. Glucose is a specific blood sugar; glucose is a monosaccharide. All saccharides fall under the general term "sugar".

Physiological condition/state

What is meant by physiological condition or physiological state?
What does physiological condition mean?

- the condition or state of the body or bodily functions

The physiological condition or state needs to be clearly stated or described in order to avoid ambiguity.

It can refer to the fed or fasted state, postprandial state (soon after eating), fasting condition, prolonged fasting leading to starvation, starved condition, starvation or extreme starvation, exercise, exercising condition, exertion or prolonged exercise leading to sustained demand on energy resources and oxygenation, etc. It can mean conscious state, unconscious state or fainted.

Where weight is not stated, it can refer to normal BMI, overweight or obesity.

In surgical patients, it can mean pre-surgical or post-surgical.

In males, it can mean young boy, puberty, teenagers, young adult men, working men, active old men or inactive old men.

In females, it can mean young girl, puberty, teenagers, young adult women, pregnancy, lactating, perimenopausal or postmenopausal.

Gluconeogenesis Maintains Blood Glucose

Endocrine and Metabolism Block, MD Phase I 2010/2011

SLU: Endocrine and Metabolism - Discuss the role of gluconeogenesis in maintaining blood glucose level

Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

1. Discuss the role of gluconeogenesis in maintaining blood glucose level.

Reference:
Clinical Biochemistry for Medical Students, M.F. Laker (1996) - page 3

Gluconeogenesis

- Other compounds which are gluconeogenic substrates are also converted to glucose in the liver; lactate, glycerol and amino acids, particularly alanine (Ala).
- Lactate is continually produced by partial oxidation of glucose in muscle and erythrocytes and is reconverted to glucose in the liver by the Cori cycle.
- Alanine is formed in muscle by transamination of pyruvate (pyruvate is derived from glucose by partial glycolysis). The liver has a high capacity to extract alanine from blood.

Reference:
Clinical Chemistry in diagnosis and treatment, Philip D Mayne (1994) - page 200

Under normal aerobic conditions the liver can synthesize glucose by gluconeogenesis using the metabolic products from other tissues, such as glycerol, lactate or the carbon chains resulting from deamination of certain amino acids (mainly alanine) (Table 10.3)

Table 10.3: Metabolism of the carbon skeleton of some amino acids to either carbohydrate (glycogenic) or fat (ketogenic)

- Glycogenic: Ala, Arg, Gly, His, Met, Ser, Val

- Glycogenic & Ketogenic: Ile, Lys, Phe, Tyr

- Ketogenic: Leu

SLU: Endocrine & Metabolism - Discuss the covalent modification regulatory mechanism in glycogen metabolism

Endocrine and Metabolism Block, MD Phase I 2010/2011
Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

2. Discuss on the covalent modification regulatory mechanism in glycogen metabolism.




-

Types of Metabolic Regulation

Endocrine and Metabolism Block, MD Phase I 2010/2011

SLU: Endocrine & Metabolism - Describe briefly the different types of metabolic regulation and provide examples

Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

3 cyan. Describe briefly the different types of metabolic regulation, with examples.

SLU: Endocrine & Metabolism - Explain the changes in carbohydrate metabolism in this patient which lead to hyperglycemia

Endocrine and Metabolism Block, MD Phase I 2010/2011
Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

4. A 12-year old boy is a known diabetic due to deficiency of insulin. His blood glucose level was found to be very high, i.e., 25 mmol/L. (Normal fasting blood glucose level: 3.5-5.5 mmol/L)

a. Explain the changes in carbohydrate metabolism in this patient which lead to hyperglycemia.




-

SLU: Endocrine & Metabolism - Explain the changes expected in triglycerides, free fatty acids and ketones in this (diabetic) patient

Endocrine and Metabolism Block, MD Phase I 2010/2011
Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

4. A 12-year old boy is a known diabetic due to deficiency of insulin. His blood glucose level was found to be very high, i.e., 25 mmol/L. (Normal fasting blood glucose level: 3.5-5.5 mmol/L)

b. Based on the above information, explain the changes expected in triglycerides, free fatty acids and ketones in this patient.





-

SLU: Endocrine & Metabolism - State the changes in protein metabolism

Endocrine and Metabolism Block, MD Phase I 2010/2011
Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

4. A 12-year old boy is a known diabetic due to deficiency of insulin. His blood glucose level was found to be very high, i.e., 25 mmol/L. (Normal fasting blood glucose level: 3.5-5.5 mmol/L)

c. State the changes in protein metabolism.





-

SLU: Endocrine & Metabolism - Explain briefly the changes expected in acid-base balance

Endocrine and Metabolism Block, MD Phase I 2010/2011
Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

4. A 12-year old boy is a known diabetic due to deficiency of insulin. His blood glucose level was found to be very high, i.e., 25 mmol/L. (Normal fasting blood glucose level: 3.5-5.5 mmol/L)

d. Explain briefly the changes expected in acid-base balance.




-

Insulin Deficiency vs Starvation

Endocrine and Metabolism Block, MD Phase I 2010/2011

SLU: Endocrine and Metabolism - Insulin deficiency: Compare the condition of this patient with a person undergoing starvation with respect to carbohydrate, lipid, protein metabolism and acid base balance

Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan and Professor Faridah Abdul Rashid
27-28 February 2011

4. A 12-year old boy is a known diabetic due to deficiency of insulin. His blood glucose level was found to be very high, i.e., 25 mmol/L. (Normal fasting blood glucose level: 3.5-5.5 mmol/L)

e. Compare the condition of this patient with a person undergoing starvation with respect to carbohydrate, lipid, protein metabolism and acid-base balance.

Pathways of Lipoprotein Metabolism

Endocrine and Metabolism Block, MD Phase I 2010/2011

SLU: Endocrine and Metabolism Block - Describe briefly the exogenous and endogenous pathways of lipoprotein metabolism

Prepared by Dr Julia Omar, Assoc Prof Dr KNS Sirajudeen, Dr Win Mar Kyi, Dr Zulkarnain Mustapha, Dr Aini Suzana Adenan & Professor Faridah Abdul Rashid
27 & 28 February 2011

5. Describe briefly the exogenous and endogenous pathways of lipoprotein metabolism.

Reference:
Clinical Chemistry in Diagnosis and Treatment (1994) Philip D Mayne - pages 227-230

Exogenous Lipid Pathways

(1) Digestion and Absorption of Dietary Fats

Fatty acids and cholesterol, released by digestion of dietary fat together with cholesterol from the bile, are absorbed into the intestinal mucosal cells (enterocytes) where they are re-esterified to form triglycerides and cholesteryl esters. These, together with phospholipids, apoA and apoB-48, are secreted from cells into the lymphatic system as chylomicrons. This secretion depends on the presence of apoB-48 (in the case of chylomicrons). Chylomicrons enter the systemic circulation by the thoracic duct. ApoC and apoE, both derived from HDL, are added to them in both lymph and plasma.

(2) Chylomicron Metabolism

Chylomicrons are metabolized in adipose tissue and muscle. The enzyme, lipoprotein lipase, located on capillary walls, is activated by apoC-II and hydrolyses triglyceride to glycerol and fatty acids. The fatty acids are either taken up by adipose or muscle cells or are bound to albumin in the plasma. The glycerol enters the hepatic glycolytic pathway. As the chylomicron shrinks, surface material containing apoA and some apoC and phospholipid is released and incorporated into HDL (this is the source of HDL from lipolysis).

The small  chylomicron remnants are composed mainly of cholesterol, apoB-48 and apoE. They rapidly bind to hepatic chylomicron-remnant receptors, which recognize the constituent apoE. The remnants then enter the liver cells where the protein is catabolized and the cholesterol released. The uptake of chylomicron remnants, unlike that of LDL, is not influenced by the amount of cholesterol in hepatic cells.

CM metabolism (Source: http://bit.ly/f31SPa)

At the end of this pathway dietary triglycerides have been delivered to adipose tissue and muscle, and cholesterol to the liver.

Endogenous Lipid Pathways

(1) Sources and Synthesis of Hepatic Lipids

The liver is the main source of endogenous lipids. Triglycerides are synthesized from glycerol and fatty acids in the smooth endoplasmic reticulum (SER), which may reach the liver from the fat stores in adipose tissues or from glucose. Hepatic cholesterol may be synthesized locally or be derived from lipoproteins, such as chylomicron remnants, after they have been taken up by liver cell. These lipids are transported in blood from the liver in VLDL. 

(2) VLDL Metabolism

VLDL is a large triglyceride-rich particle incorporating apoB-100, apoC and apoE. After secretion it incorporates more apoC from HDL. In peripheral tissues triglycerides are removed after hydrolysis by lipoprotein lipase (LPL). Up to this stage the metabolism of VLDL is similar to that of chylomicrons, although it occurs more slowly. However, the disposal of the resulting remnant particle differs.

VLDL metabolism (Source: http://bit.ly/f31SPa)

(3) IDL Metabolism

The VLDL remnant or IDL, which contains both triglycerides and cholesterol, as well as apoB-100 and apoE, has 2 fates - it is either (i) rapidly taken up by the liver and acted upon by hepatic triglyceride lipase (HTGL) to form LDL, or (ii) it loses the remaining triglycerides and apoE intravascularly  by  further LPL action to become LDL. LDL contains only apoB-100 and is formed in 2 ways - HTGL action in liver and LPL action in the blood capillaries.

IDL metabolism (Source: http://bit.ly/f31SPa)

(4) LDL Metabolism

LDL is a small cholesterol-rich lipoprotein containing only apoB-100. It has a longer half-life in blood than its precursors (VLDL and IDL). VLDL and IDL account for approximately 70% of the total cholesterol in plasma. It is taken up by specific receptors located on cell surfaces (LDL receptors or apoB/E receptors). Although these receptors are present on all cells, they are most abundant in the liver. They recognize apoB and apoE and so can take up either LDL or IDL. After entering cells LDL particles are broken down by lysosomes; much of the released cholesterol contributes to membrane formation or, in the adrenal cortex and gonads, to steroid synthesis. 

(5) LDL-Receptor Mediated Regulated Cholesterol Uptake

Most cells can synthesize cholesterol but several feedback mechanisms prevent its intracellular accumulation. Cholesterol, taken up by receptors, inhibits intracellular cholesterol synthesis and prevents further uptake by reducing the rate of synthesis of LDL receptors. Most of the plasma LDL is removed by LDL receptors.

(6) Unregulated Cholesterol Uptake

If plasma concentrations are high some may also enter cells by a passive, unregulated route, via the scavenger receptors which are present on macrophages. These scavenger receptors take up oxidized small LDL which are formed during prolonged lipaemia as occurs in diabetes. 

(7) Atherogenic Lipoproteins

Atherogenic lipoproteins are from 2 sources - exogenous and endogenous lipoprotein metabolism. Chylomicron remnants are atherogenic. LDL are highly atherogenic. Because of their small size LDL particles can infiltrate tissues, such as those of the arterial wall, and cause damage.

PowerPoints

http://slideplayer.com/search/lipoprotein+metabolism/

http://slideplayer.com/slide/2071777/

http://slideplayer.com/search/cholesterol/