Age-dependent Participation of Apolipoprotein C-II in Lipoprotein Metabolism, an Observation in Healthy Adults

Apolipoprotein C-II is generally accepted as the major activator of lipoprotein lipase which is considered to be a key enzyme in the hydrolysis of triglyceride from chylomicron and VLDL. Recent biochemical advances have made it possible to determine easily the concentration of serum apolipoprotein C-II in clinical practice. The recently developed analytical method will promote further clinical studies on participation of apolipoproteins in lipoprotein metabolism relating to atherogenesis. This study was intended to clarify clinically the agedependent difference of lipoprotein metabolism in association with apolipoprotein C-II.A hundred and thirty-nine healthy adults with normal physical findings, blood pressures, urinalysis, blood sedimentation rates, chest films, ECGs and liver function tests were selected for this study in the annual screening for circulatory diseases. Fasting blood specimens were drawn early in the morning. Serum apolipoprotein C-II level was determined by single radial immunodiffusion method using agar plate containing specific antiserum. Mean values and standard deviations of serum apolipoprotein C-II in healthy subjects aged 20 to 39 were 2.9±0.77mg/dl in 14 males and 3.1±0.86mg/dl in 29 females. Neither of age groups indicated significant sex difference. The highest levels in males and females were exhibited in subjects aged 40 to 59 and in those aged over 60 years respectively.The significant correlation between apolipoprotein C-II and triglyceride was displayed in subjects aged 20 to 39 and 40 to 59 years. In subjects aged above 60 years, apolipoprotein C-II was directly proportional to total cholesterol, phospholipid, apolipoprotein A-I and A-II, showing no significant correlation between this apolipoprotein and triglyceride, and phospholipid correlated positively to total cholesterol, apolipoprotein A-I and A-II.In present results, direct relationship between apolipoprotein C-II and triglyceride in young age groups confirms the generally recognized property of apolipoprotein C-II which plays an important role in the hydrolysis of triglyceride by lipoprotein lipase. Apolipoprotein C-II is an obligatory factor of phaspholipase A1 activity on lipoprotein lipase, close associations of apolipoprotein C-II with total cholesterol, phospholipid, apo A-I and A-II in aged subjects suggest strongly the participation of apolipoprotein C-II in action of phospholipase A1 as apolipoprotein C-II does not correlate to triglyceride. These results reveal clearly the agedependent diversity of apolipoprotein C-II in lipoprotein metabolism. Therefore, in conclusion, clinical observation of lipoprotein metabolism should be performed taking the age difference into account.