The present study was to investigate the sialylation of apolipoprotein CIII (apo CIII) in very low density lipoproteins (VLDL) and its effects on lipid and lipoprotein metabolism in diabetes mellitus.
The composition of apo C subgroup in VLDL has been determined by polyacrylamide isoelectric focusing and scanning densitometry. As apo CIII0 contains no sialic acid, apo CIII1 one sialic acid and CIII2 two sialic acid as their molecular components, the extent of sialylation of apo CIII was characterized by (apo CIII1+apo CIII2)/apo CIII0, expressed as VLDL apo CIII sialylation index.
This index was correlated negatively to plasma triglyceride and LDL cholesterol and positively to HDL cholesterol and showed strong correlation (p<0.02) to atherogenic index, (Plasma cholesterol-HDL cholesterol)/HDL cholesterol.
VLDL apo CIII sialylation index was lower in oral hypoglycemic drug group than in diet and insulin therapy group, and was significantly low in type IV hyperlipidemic diabetics compared with in normolipidemic diabetics. This index was also significantly low in poor controled diabetics, whose hemoglobin AI were above 10%, however, this index showed no correlation to hemoglobin AI value.
On heparin administration (N=19), VLDL apo CIII Sialylation index increased signicantly, 5.30±2.81 to 6.44±2.94 (p<0.05) and changes in VLDL triglyceride concentration by heparin administration showed negative correlation to the value of VLDL apo CIII sialylation index of the sample before heparin administration. These two results revealed the extent of sialylation of apo CIII carried on VLDL may influence the lypolysis of VLDL.
Preliminary study of VLDL subfractionation by Geon-Pevicon electrophoresis also showed the extent of sialylation of apo CIII in VLDL presumably affects the charge of VLDL particle and its electromobility in electrophoresis.
