[Lipoprotein (a)--a mysterious factor in atherogenesis]

Etiopathogenesis of arterial hypertension and coronary disease involves interaction of numerous exogenous factors which determine the clinical course and therapeutic response in genetically predisposed individuals. The role of numerous cardiovascular risk factors has been reevaluated during the past few years, yet some unresolved issues and gaps still remain. One of the still insufficiently studied factors is lipoprotein (a) [Lp (a)] which belongs to a subclass of LDL lipoproteins. Its important component is apolipoprotein (a) which is structurally similar to plasminogen. This characteristic can be followed through evolution and is probably crucial for its physiologic but also pathophysiologic role. Actually, through its competition with plasminogen, Lp (a) interferes with the process of fibrinolysis and may contribute to tissue healing and restoration but also support and accelerate atherothrombotic process. Lp (a) concentration is stable and genetically determined in an individual and the indication that persons with elevated levels are permanently exposed to increased risk is supported by the data on twofold incidence of myocardial infarction in mothers of children with highest Lp (a) concentrations. Apart from competing with plasminogen via apolipoprotein (a), Lp (a) increases the activity of inhibitors of plasminogen-I activator and reduces the activity of transforming growth factor-beta. This results both in the absence of fibrinolysis and promotion of migration and proliferation of media smooth muscle cells, which are important in the onset of atherosclerotic process. Lp (a) binds to elastin via apolipoprotein B, resulting in oxidation and facilitated entry into macrophages and their transition into the so-called foam cells, also an important sign of early atherosclerosis. Although many pathophysiologic processes by which Lp (a) contributes to atherosclerosis have also been confirmed by animal experiments as well as by the presence of histologic evidence, clinical significance of elevated Lp (a) concentration is still questionable. However, results of prospective studies and metaanalyses were published few months ago and identified decisively Lp (a) as a factor that increases cardiovascular risk primarily in patients in whom other risk factors were also present. According to currently prevailing attitude, routine determination of Lp (a) is not justified and, according to most authors, its determination is useful in patients who had a cardiovascular incident at the age under 55 years, in those with recurrent coronary stenosis, or those with positive family history of such incidents. As Lp (a) is genetically determined, its detection in the early stages of essential hypertension might be a useful prognostic marker but a period of observation is still necessary for correct selection of hypertensive patients. Apart from the observation that hormone replacement therapy significantly decreases the Lp (a) level, there is currently no information on the effectiveness of either dietary or drug therapy. Due to Lp (a) antifibrotic effects, small aspirin doses may be beneficial to these patients, as well as B complex vitamins since hyperhomocysteinemia enhances atherogenicity of Lp (a). Therapeutic approach to patient with increased Lp (a) levels is currently based on as strict regulation of arterial pressure, glycemia and other dislipidemias as possible. In the present clinical practice, the elevated level of this lipoprotein indicates a patients with elevated cardiovascular risk, regardless of the fact whether Lp (a) is only a marker or an active factor of pathophysiologic process. Increased Lp (a) concentration may refer to the need for therapy, frequent monitoring and determination of even stricter aims for these individuals by selecting metabolically neutral and best tolerated drugs.