Oxidized Information and Courses from MediaLab, Inc.

The product profile for Ictotest® points out that bilirubin is very light sensitive, so urine specimens should be protected from excessive light exposure and examined as quickly as possible when received in the laboratory. On standing, bilirubin, which has a goldish color, is oxidized to biliverdin, which is a green color. Many of the procedures used to detect bilirubin will not react with biliverdin, so false-negative results may occur if urine is not fresh when tested.

We have listed the 'classic' cardiovascular risk markers as LDL-C, HDL-C and triglycerides. But there are many more cardiovascular risk markers as well as cardiovascular risk factors. A cardiovascular risk factor is a condition (not a laboratory analyte) that is associated with an increased risk of developing cardiovascular disease. Examples include: Age Gender (males are at increased risk) Heredity Hypertension Cigarette Smoking Obesity Diabetes StressThere are also negative risk factors, factors which decrease a person's risk of cardiovascular disease. Examples include: Optimal HDL-C concentration Exercise Estrogen Moderate alcohol intakeThis course will not focus on cardiovascular risk factors. Instead we will focus on newer, emerging cardiovascular risk markers. There are well over twenty well-studied cardiovascular risk markers; in this course we will focus on some of the more established markers and the ones which are becoming more commonly measured in the clinical laboratory. These include apolipoprotein A1/apolipoprotein B100, Lp(a), oxidized LDL, LpPLA2, hsCRP and lipoprotein particle size and concentration.It is important to remember that the association between a cardiovascular risk marker and actually having or developing cardiovascular disease is a statistical one. The fact that a patient has a particular risk marker which is abnormal simply increases the probability of developing cardiovascular disease, it does not mean that he or she is certain to develop cardiovascular disease. Conversely, if an individual does not have a particular cardiovascular risk marker present it does not guarantee protection against cardiovascular disease. We must always remember that some percentage of individuals who have heart attacks or strokes will not have abnormal risk markers present.

LpPLA2 refers to lipoprotein-associated phospholipase A2. This enzyme is also known as platelet-activating factor acetylhydrolase(PAF). The LpPLA2 enzyme is a lipase found predominantly on the surface of LDL particles. Note that LpPLA2 is a lipase enzyme and not an apolipoprotein. LpPLA2 is made by inflammatory cells (T cells, mast cells, macrophages) and then integrated onto the surface of lipoprotein particles. The enzymatic function of LpPLA2 is to hydrolyze oxidized phospholipids in LDL.LpPLA2 plays a corrective role in removing oxidized phospholipids. Thus, it might seem that having high levels of LpPLA2 would be good. However, although LpPLA2 has a positive role in removing oxidized lipids, it also generates inflammatory products in the process. So in fact, high levels of LpPLA2 are associated with increased cardiovascular risk. Researchers have identified high amounts of LpPLA2 in human atherosclerotic lesions. The LpPLA2 that accumulates in the vessel wall can come from LDL (which can carry LpPLA2 on its surface) or it can come from immune cells that have invaded the vessel wall. Since Lp-PLA2 is produced or localized in the plaque itself, it may be a more specific marker of cardiovascular function compared to systemic, more general inflammatory markers like hs-CRP.

Free radicals are well known to occur in biological systems. A free radical is an atom or small molecule with unpaired electrons. These unpaired electrons make the atom or molecule highly reactive and unstable. Free radicals are produced constantly via metabolic processes. They are also released by immune cells. Immune cells can undergo 'oxidative bursts' (also called respiratory bursts) to help fight pathogens. Oxidative bursts can help degrade pathogens phagocytosed by immune cells and therefore free radicals have an important role in immune system function.However, free radicals also have detrimental effects on surrounding cells. When LDL is co-localized with cells or tissues that are releasing free radicals (such as in an inflamed vessel wall) the free radicals can chemically modify the phospholipids and other components of the lipoprotein. The LDL becomes oxidized and the modification makes the LDL more atherogenic.

There are currently two antibodies that have been developed that target oxidized lipids; the 4E6 antibody and EO6 antibody. The 4E6 antibody is directed against an oxidized epitope on the ApoB-100 protein on LDL. The EO6 antibody recognizes oxidized phospholipids and the assay measures the content of these oxidized phospholipids on lipid particles that contain ApoB-100.