The compositional abnormalities of lipoproteins in diabetic renal failure

Diabetic nephropathy (DN) is a common cause of chronic renal failure (CRF). Patients with DN have abnormal lipoprotein metabolism that can be influenced by both the impairment of renal function and the metabolic control of diabetes. The aim of the study was to explore the specific compositional lipoprotein abnormalities in patients with insulin-dependent DN in comparison with diabetic patients without nephropathy and non-diabetic CRF patients.

The lipid and apolipoprotein (apo) composition of major lipoprotein density classes was determined in 20 patients with insulin-dependent diabetes mellitus and nephropathy and compared with that in seven diabetic patients without nephropathy, 20 patients with non-diabetic CRF, and nine healthy control subjects. Lipoproteins isolated by preparative ultracentrifugation were very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

Patients with DN had a plasma lipid and apolipoprotein profile characteristic of renal dyslipoproteinaemia with increased concentrations of triglycerides and cholesterol, reduced levels of apoA-I and apoA-II and increased levels of apoB, apoC-II, apoC-III and apoE. These changes were more pronounced in diabetic than in non-diabetic patients with comparable degrees of renal failure. All density classes were characterized by abnormal concentration and composition of some lipid and apolipoprotein constituents. DN patients had a more than four-fold increase of VLDL mass, a three-fold increase of IDL mass, and a significant reduction of HDL mass compared to control subjects. They also had significantly higher concentrations of apoB, apoC-peptides and apoE particularly in VLDL and IDL, and to some extent in LDL. In HDL, DN patients had lower cholesterol, apoA-I, apoA-II and apoC-II levels than controls. The major compositional change in DN patients was a significant increase in the relative content of apoC-peptides in IDL and LDL. The lipoprotein abnormalities were more pronounced in patients with high HbA1c values. In addition, lower GFR and increased proteinuria were associated with higher concentrations of triglycerides and apoC peptides in VLDL, IDL, and LDL in DN patients.

The results indicate that patients with DN share the characteristic features of dyslipidaemia of CRF with accumulation of intact or partially delipidized apoB-containing lipoproteins enriched in apoC-peptides and apoE, which are present not only in VLDL and IDL but also in LDL density range. The alterations are more marked in DN than in nondiabetic CRF patients reflecting the additional impact of metabolic control. Increased levels of these lipoproteins may represent risk factors for the accelerated development of atherosclerotic vascular disease in these patients.