Lipoprotein(a) and apolipoprotein(a) isoforms and proteinuria in patients with moderate renal failure

Background. Atherosclerotic diseases are a major cause of death in patients with renal failure. Increased serum concentrations of lipoprotein(a) [Lp(a )] have been established as a genetically controlled risk factor for these diseases and have been demonstrated in patients with moderate renal failure , suggesting that this lipoprotein contributes to the increased cardiovascu lar risk seen in these patients. Variable alleles at the apolipoprotein(a) [apo(a)] gene locus are the main determinants of the serum Lp(a) level in t he general population. The purpose of this study was to investigate apo(a) isoforms in patients with moderate renal failure and mild proteinuria (less than 1.0 g/day). Methods. In 250 consecutive subjects recruited at a hypertension clinic: we assessed the renal function by 24-hour creatinine clearance, proteinuria, and microalbuminuria, as well as the prevalence of atherosclerotic disease, and we also measured apo(a) isoforms, serum albumin, and Lp(a) concentrati ons. Results. Moderate impairment of renal function (creatinine clearance, 30 to 89 ml/min per 1.73 m(2) of body surface area) was found in 97 patients, Lp (a) levels were significantly greater in patients with moderate renal failu re (21.7 +/- 23.9 mg/dl) as compared with patients with normal renal functi on (15.6 ri: 16.4 mg/dl, P < 0,001), and an inverse correlation was observe d between log Lp(a) and creatinine clearance (r -0.181, Pt 0.01). However, no difference was found in the frequency of low molecular weight apo(a) iso forms between patients with normal (25.5%) and impaired (27.5%) renal funct ion. Only patients with the smallest size apo(a) isoforms exhibited sig,;si gnificantly elevated levels of Lp(a), whereas the large-size isoforms had s imilar concentrations in patients with normal and impaired renal function. No significant relationship was found between serum Lp(a) and proteinuria. Clinical and laboratory evidence of one or more events attributed to athero sclerosis was found in 9.8% of patients with normal renal function and 25.8 % of patients with moderate renal failure (P < 0.001). Conclusions. These results indicate that renal failure per se or other gene s beside the apo(a) gene locus are responsible for the elevation of serum L p(a) levels in patients with moderate impairment of renal function. The ele vation of Lp(a) levels occurs independently of the level of proteinuria and may contribute to the risk for atherosclerotic disease in these patients.