Metabolism of apolipoproteins CII, CIII1, CIII2 and VLDL-B in human subjects consuming high carbohydrate diets.

Simultaneous kinetics of apoproteins CII, CIII1 and CIII2 and VLDL-B were determined in six normal subjects initially while consuming a control diet and subsequently while consuming a high carbohydrate diet. Mean triglyceride levels in plasma and VLDL were significantly increased, from 110 to 173 mg/dl and 40 to 114 mg/dl respectively, by the high carbohydrate diet. Specific radioactivity of each C peptide was determined, following injection of 125I-VLDL, in both VLDL and HDL from plasma samples taken over 48 hr using a technique involving analytical isoelectric focusing. Specific activity vs time curves for VLDL and HDL were almost superimposable on either diet, suggesting that CII, CIII1 and CIII2 were catabolized as a group. The high carbohydrate diet resulted in a significant increase in the mass of each C peptide which was brought about by an increase in production since no change in fractional removal rate (FRR) was observed. The pool size of VLDL apo B was also significantly increased and was a function of both increased production as well as decreased FRR. The proportion of CIII2 mass relative to those of CII and CIII1 was lower in both VLDL and HDL with the high carbohydrate diet. These observations indicate that the metabolism of the B and C apoproteins are independent of each other and do not respond in the same manner to changes in VLDL triglyceride and that increased triglyceride synthesis and secretion stimulates C apoprotein production.