[Lower levels of HDL2 cholesterol are associated with microalbuminuria in patients with type 1 diabetes].

OBJECTIVE

Lipoproteins may contribute to diabetic nephropathy. Although elevated total HDL cholesterol levels have been shown to protect from coronary artery disease and nephropathy in many studies, HDL can be subdivided into at least two major subclasses, which are thought to differ in the ability to protect against atherosclerosis. The objective of this study was to determine the relationship between serum lipids and HDL subclasses with albuminuria in patients with type 1 diabetes.

METHODS

We analyzed lipid profiles of 259 patients with type 1 diabetes and normal thyroid function. Patients were classified as normoalbuminuric (albumin excretion rate < 30 mg/24 h, n = 215) and microalbuminuric (albumin excretion rate 30-300 mg/24 h, n = 44) in at least two urine collections. None showed signs of adrenal, thyroid, renal or cardiovascular disease, or received drugs, apart from insulin, that could attenuate glucose metabolism, serum lipids or renal function. Total, LDL, HDL, HDL2, HDL3, VLDL cholesterol and triglycerides were measured by an enzymatic colorimetric method and urinary albumin concentration was determined by an immunoturbidimetric assay.

RESULTS

Patients with microalbuminuria had higher levels of total cholesterol (5.07 vs. 5.02 mmol/L, Mann Whitney=6874, P = 0.666), LDL cholesterol (2.81 vs. 2.80 mmol/L, Mann Whitney = 6964, P = 0.778), VLDL cholesterol (0.57 vs. 0.48 mmol/L, Mann Whitney = 6268, P = 0.151) and triglycerides (1.27 vs. 1.08 mmol/L, Mann Whitney = 6283, P = 0.158), and lower levels of HDL cholesterol (1.68 vs. 1.73 mmol/L, Mann Whitney = 6501, P = 0.293) and HDL3 cholesterol (1.15 vs. 1.16 mmol/L, Mann Whitney = 6991, P = 0.812); however, these differences were not statistically significant. In contrast, HDL2 cholesterol levels were significantly lower in those who had microalbuminuria compared with those who had normoalbuminuria (0.50 vs. 0.57 mmol/L, Mann Whitney = 5600, P = 0.01).

CONCLUSIONS

Microalbuminuria is the earliest clinical indicator of diabetic nephropathy. Clustering of coronary artery disease with nephropathy has been shown previously in patients with type 1 diabetes. Specific effects of HDL subclasses on cardiovascular disease have also been observed, i.e. a protective effect of large HDL subfractions (HDL2) and an increased risk for small HDL particles (HDL3). Results of the present study showed that lower levels of HDL2 cholesterol were associated with microalbuminuria in patients with type 1 diabetes. Whether higher HDL2 cholesterol levels may be protective against the development of microalbuminuria in patients with type 1 diabetes can only be determined in long-term studies.