Apolipoprotein (a) levels and phenotypes in NIDDM patients with microalbuminuria and albuminuria

Abstract

This study was conducted to determine whether circulating levels of lipoprotein (a), an independent risk factor of macrovascular disease, are increased in non-insulin-dependent diabetes mellitus (NIDDM) patients with microalbuminuria who have an increased risk of cardiovascular mortality. Apolipoprotein (a) [apo(a)] levels and phenotypes, and other circulating lipid levels were determined in 227 Chinese NIDDM patients with varying stages of diabetic nephropathy. None was on lipid-lowering therapy. Apo(a) levels in normoalbuminuric (geometric mean 166 U/L; 95% confidence intervals 137, 200; n = 105) and microalbuminuric patients (162; 132, 209; n = 77) were similar to values in controls (166; 143, 193, n = 168). Albuminuric patients, however, higher apo(a) levels than both normoalbuminuric and controls (242; 184, 317 n = 45; P < 0.05). The overall size range of the apo(a) phenotypes and the frequency of having at least one small isoform, i.e. < 700 kDa, were similar among the four groups of subjects. A positive correlation was found between log apo(a) and log plasma creatinine levels (P < 0.01). Compared to normoalbuminuric patients, both microalbuminuric and albuminuric patients were older (P < 0.01) and had higher HbAlc (P < 0.01), greater BMI(P < 0.05) and longer disease duration (P < 0.05) compared to normoalbuminuric patients. Nevertheless, using multiple linear regression analysis, it was found that the presence of nephropathy conferred an independent influence on increasing total cholesterol (P < 0.001), triglyceride (P < 0.001) and apoB (P < 0.01), and decreasing HDL cholesterol (P < 0.05) levels even when only the normoalbuminuric and microalbuminuric groups were analysed. The prevalence of macrovascular disease was significantly increased in microalbuminuric and albuminuric patients (45.1 and 48.7% respectively vs 20.2% in normoalbuminuric patients, P < 0.01). It is concluded that circulating apo(a) levels were not increased in Chinese NIDDM patients with microalbuminuria. However, atherogenic changes in other lipid and lipoprotein levels may contribute to an increased risk of macrovascular disease in these patients.