Association between low-density lipoprotein composition and its metabolism in non-insulin-dependent diabetes mellitus

Abstract

Atheroma is related to low-density lipoprotein (LDL) composition, LDL in diabetic patients—a group with increased risk of severe atheroma—has been shown by our group and others to have various compositional alterations that are potentially atherogenic. Little is known about the relationship between LDL turnover and composition. This study examined the relationship between LDL composition and turnover in non-insulin-dependent diabetes mellitus (NIDDM) patients. Twenty-two NIDDM patients with a mean plasma cholesterol of 6.6 ± 1.5 mmol/L were studied. Twelve subjects were hypercholesterolemic (mean cholesterol, 7.7 ± 0.8 mmol/L), and eight of these agreed to be studied a second time after 4 weeks of treatment with simvastatin. LDL was isolated by density gradient ultracentrifugation, iodinated, and reinjected into the patient. LDL turnover was determined by measuring the clearance of [ 125I]-LDL from plasma over a 10-day period. The LDL residence time, determined using a biexponential model, correlated negatively with the body mass index (BMI) ( r = −.73, P < .001) and serum triglycerides ( r − .57, P < .01). There was a significant inverse correlation between LDL residence time and the LDL esterified to free cholesterol ratio in hypercholesterolemic subjects ( r = −.94, P < .001). There was a significant inverse relationship between LDL residence time and both hemoglobin A 1c (HbA 1c and fasting blood glucose in these subjects before treatment ( P < .005). After simvastatin therapy, the relationships were no longer significant. Simvastatin treatment was associated with a shorter LDL residence time ( P < .01) and a decrease in LDL glycation ( P < .001) with virtually no change in diabetic control (HbA 1c, 6.0% ± 3.1% v 6.3% ± 3.3%, NS). This study suggests that a decrease in residence time by upregulation of the LDL receptor with simvastatin alters LDL composition in a way that is likely to render the particle less atherogenic.