Director: Laboratory for Clinical Biochemistry Research

Tracy Bio

Research
Cardiac disease is the greatest killer of Americans, responsible for approximately 43% of deaths in the last few years. This disease, in its many forms, results from a complex set of interacting variables including diet, lipid metabolic factors, genetic factors and thrombotic factors. This last area is where we have been focusing our attention for the last few years. While it is clear that plasma lipid levels are important in the development of atherosclerosis, the precipitating event in a myocardial infarction ("heart attack") is a thrombotic event, i.e., the formation of a blood clot in one of the small arteries which feed the heart muscle, causing a lack of oxygen and other nutrients. There are also some data which suggest that blood clotting is important earlier in the disease process, much as lipids are.

Our overall hypothesis is that individuals vary in their propensity to form blood clots much as they vary in their lipid metabolism, and that this variation is important in determining an individual's risk for cardiovascular disease. This variation may be due to environmental or genetic factors, or to the interplay of genes and environment. We use a variety of immunoassay and functional assay techniques to probe plasma samples from large populations in epidemiological studies aimed at understanding the difference between people in their ability to form blood clots, and what this difference might mean in terms of cardiovascular risk. In recent years, it has been shown that fibrinogen, a major procoagulant protein important in the formation of blood clots, is an independent risk factor, much like plasma cholesterol. Other procoagulant factors which have been implicated, and are under active investigation, include factor VII, factor X and factor V. The procoagulant system is balanced by an anticoagulant system, and factors here have been implicated as well: protein C, protein S and antithrombin III. Once a clot has formed, it is likely that the ability to remove the clot may play a crucial role in determining the overall effect of the clot. Profibrinolytic factors are responsible for clot removal, and antifibrinolytic factors regulate this response. Candidates for factors with key roles, and ones we are currently investigating,include tissue-type plasminogen activator and plasminogen activator inhibitor-1. Also, a plasma lipid which may have important antifibrinolytic capacity is Lp(a), a Low Density Lipoprotein-like particle, which we are also studying. We study these factors in several multicenter projects, including the Cardiovascular Health Study (older persons over 65 years), the Strong Heart Study (Native Americans), the Cardiovascular Risk factor Study of Young Adults (persons aged 18-28). To date, over 23,000 individuals have been studied in our laboratory, and we have a plasma sample repository (-70oC freezers) with approximately 500,000 individual aliquots, which maybe used for future studies.

Our laboratory is deeply involved in the generation of new assays in this area, with much work ongoing in the area of direct measurement of thrombin, plasmin and other enzymes. These factors are difficult to measure directly, and several methods are currently being investigated, including specific monoclonal antibody-based assays, and two-site immunoassays which make use of specific antibodies and direct active site labelling using biotinylated active site specific reagent such D-Phe-Pro-Arg Chloromethyl Ketone. We are also interested in a finding developed from our epidemiological studies, i.e., plasma lipids and coagulation factors appear to be tightly co-regulated in a manner that is unclear. Physical biochemical studies of plasma, as well as diet studies, are planned, to investigate this finding.