Apolipoprotein assays: methodological considerations and studies in non-insulin-dependent diabetes treated by diet, glibenclamide and insulin.

The effect of sample pre-treatment as a source of variability of apolipoprotein (apo) AI, AII and B assays was demonstrated with lipid dissociating agents. The average mean percentage change ranged from -58 to +133% compared with untreated samples. The apolipoprotein method selected was validated by comparing their concentrations with their corresponding lipoprotein lipid or protein in normal controls and Type 2 (non-insulin-dependent) diabetic patients. The coefficient of variation was maintained below 3.5% for apo AI, AII, B and HDL2-apo AI. The apolipoprotein concentrations of fasting plasma lipoproteins were determined in a cross-sectional study of non-obese (body-mass index less than or equal to 30) patients with Type 2 diabetes mellitus. Compared with normal subjects matched for sex, age, body-mass index, exercise, alcohol consumption and smoking. Type 2 patients at diagnosis showed reduced apo AI and HDL2-apo AI concentrations, lowered apo AI:B ratio and increased concentrations of apo B. Type 2 patients treated by diet alone (for 6-72 months) and diet plus glibenclamide (2.5-15 mg/day for 6-48 months) exhibited similar abnormalities of plasma apolipoprotein concentration to Type 2 patients at diagnosis. However, in Type 2 patients treated with insulin (25-65 U/day for 8-144 months) concentrations of apo AI and HDL2-apo AI, and the apo AI:B ratio were normal. Apo B concentrations were generally lower compared with all groups of non-insulin treated patients. These abnormalities of apolipoprotein metabolism, which are associated with premature coronary disease, are still evident in patients treated by diet and diet plus glibenclamide, but are not seen in Type 2 patients treated with insulin.