INCREASED HEPATIC SECRETION OF VERY-LOW-DENSITY LIPOPROTEIN APOLIPOPROTEIN B-100 IN NIDDM

We measured the hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 (VLDL apoB) using a stable isotope gas-chromatography mass-spectrometry method in six patients with non-insulin-dependent diabetes mellitus (NIDDM) (four males, two females, age 57.5+/-2.2 years (mean+/-SEM), weight 88.2+/-5.5 kg, glycated haemoglobin (HbA(1)) 8.5+/-0.5%, plasma total cholesterol concentration 5.7+/-0.5 mmol/l, triglyceride 3.8+/-0.9 mmol/l, high-density lipoprotein (HDL) cholesterol 1.0+/-0.1 mmol/l) and six non-diabetic subjects matched for age, sex and weight (four males, two females, age 55.7+/-2.8 years, weight 85.8+/-5.6 kg, HbA(1) 6.5+/-0.1%,plasma total cholesterol concentration 5.7+/-0.5 mmol/l, triglyceride 1.2+/-0.1 mmol/l, HDL cholesterol 1.4+/-0.1 mmol/l). HbA(1), plasma triglyceride and mevalonic acid (an index of cholesterol synthesis in vivo) concentrations were significantly higher in the diabetic patients than in the non-diabetic subjects (p = 0.006, p = 0.02 and p = 0.004, respectively), VLDL apoB absolute secretion rate was significantly higher in the diabetic patients compared with the non-diabetic subjects (2297+/-491 vs 921+/-115 mg/day, p < 0.05), but there was no significant difference in the fractional catabolic rate of VLDL apoB. There was a positive correlation between VLDL apoB secretion rate and (i) fasting C-peptide (r = 0.84, p = 0.04) and (ii) mevalonic acid concentration (r = 0.83, p < 0.05) in the diabetic patients but not in the non-diabetic subjects. There was also a significant positive association between plasma mevalonic acid and plasma C-peptide (r = 0.82, p < 0.05) concentrations in the diabetic patients. We conclude that in NIDDM, there is increased hepatic secretion of VLDL apoB which may partly explain the dyslipoproteinaemia seen in this condition. We suggest that increased secretion of this apolipoprotein may be a consequence of resistance to the inhibitory effect of insulin on VLDL apoB secretion. Insulin resistance may also be the mechanism by which cholesterol synthesis, a regulator of apoB secretion, is increased in NIDDM.