We continued studying atherogenic plasma constituents and markers with respect to analytical and diagnostic performance and clinical utility of the respective methods. Since plasma high-density lipoprotein (HDL) is known to be protective against coronary artery disease and plasma low-density lipoprotein (LDL) is atherogenic, measurement of the cholesterol (C) content of these lipoproteins is important for assessing cardiovascular risk, diagnosing lipid disorders and monitoring lipid-modifying interventions. We assessed the analytical performance of a recently available homogeneous HDL-C (EZ-HDL) and LDL- C (EZ LDL) methods in human sera. Compared to conventional heterogeneous (pretreatment and electrophoretic) lipoprotein- cholesterol methods, these new homo-geneous methods exhibited similar or greater precision but biases between them and the old methods suggested unsatisfactory standardization. Further, we observed that lipemia has more pronounced effect on these homogeneous methods than that described by the manufacturer. Analysis of serum lipid and lipoprotein constituents is not always possible in freshly collected specimens and published data often are conflicting or not available for newer methods. This prompted us to further examine possible storage effects on these analytes. In ongoing long-term storage studies we are monitoring the effect of both storage temperature (+4oC and -70oC) and repeat freezing-thawing on various serum lipids and lipoprotein cholesterol fractions as measured with a variety of methods. In collaboration with one group of investigators of the Cardiology Branch of the NHLBI, we evaluated the effects of quinapril, estrogen, cholesterol-lowering therapies (statins), antioxidants (vitamin E), and L-arginine, the natural precursor of nitric oxide, on various plasma lipids, lipopro-teins, apolipoproteins, markers of fibrinolysis (e.g., D-dimer) and inflammation (e.g., C-reactive protein, CRP), and/or homocysteine in postmenopausal women and/or patients with coronary artery disease (CAD). In another collaboration, we continued studying the clinical significance of viral and bacterial infections in the development and progression of atherosclerosis. Further investigations on a possible relationship between apolipoprotein(a) isoforms and athero-thrombotic phenomena in patients with systemic lupus erythematosus (SLE), and on the effect of interleukins on plasma lipids, lipoproteins and apolipoproteins, and on the possible effect of fre-quent blood donations (reduced iron load) on various atherosclerotic factors and markers, and on the atherosclerotic process itself are still in progress.
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