LDL-UNBOUND APOLIPOPROTEIN(A) AND CAROTID ATHEROSCLEROSIS IN HEMODIALYSIS-PATIENTS

High lipoprotein(a) [Lp(a)] plasma concentrations, which are genetical ly determined by apo(a) size polymorphism, are directly associated wit h an increased risk for atherosclerosis, Patients with end-stage renal disease (ESRD), who show an enormous prevalence of cardiovascular dis ease, have elevated plasma concentrations of Lp(a). In recent studies we were able to show that apo(a) size polymorphism is a better predict or for carotid atherosclerosis and coronary artery disease in hemodial ysis patients than concentrations of Lp(a) and other lipoproteins. Les s than 5% of apo(a) in plasma exists in a low-density lipoprotein (LDL )-unbound form. This ''free'' apo(a) consists mainly of disintegrated apo(a) molecules of different molecular weight, ranging from about 125 to 360 kDa. LDL-unbound apo(a) molecules are elevated in patients wit h ESRD. The aim of this study was therefore to investigate whether the LDL-unbound form of apo(a) contributes to the prediction of carotid a therosclerosis in a group of 153 hemodialysis patients. The absolute a mount of LDL-unbound apo(a) showed a trend to increasing values with t he degree of carotid atherosclerosis, but the correlation of Lp(a) pla sma concentrations with atherosclerosis was more pronounced. In multiv ariate analysis the two variables were related to neither the presence nor the degree of atherosclerosis. Instead, the apo(a) phenotype took the place of Lp(a) and LDL-unbound apo(a). After adjustment for other variables, the odds ratio for carotid atherosclerosis in patients wit h a low molecular weight apo(a) phenotype was about 5 (p < 0.01). This indicates a strong association between the apo(a) phenotype and the p revalence of carotid atherosclerosis. Finally, multivariate regression analysis revealed age, angina pectoris and the apo(a) phenotype as th e only significant predictors of the degree of atherosclerosis in thes e patients. In summary, it seems that LDL-unbound apo(a) levels do not contribute to the prediction of carotid atherosclerosis in hemodialys is patients. However, this does not mean that ''free'', mainly disinte grated, apo(a) has no atherogenic potential.