Low density lipoprotein cholesterol, lipoprotein(a), and apo(a) isoforms in the elderly: Relationship to fasting insulin

Background and Aim: Insulin resistance/hyperinsulinemia ave often associate d with aging and could play an important role in the development of glucose intolerance and dyslipidemia in the elderly We investigated the relationsh ip between plasma fasting insulin with total cholesterol (TC) and low densi ty lipoprotein LDL cholesterol (LDL-C), triglycerides (TG), lipoprotein(a) [Lp(a)] levels apolipoprotein (a) [apo (a)] isoforms in 100 free-living "he althy" octo-nonagenarians. Methods and Results: Fasting insulin was positiv ely correlated with TG, whereas a negative relation was found with TC and L DL-C (r=-0.29 and r=-0.28 respectively; p<0.01), LDL-C/apo B, HDL-C and apo A-I levels. Fasting insulin was also inversely correlated with Lp(a) level s (r=-0.22; p<0.03), whereas the latter were significantly related with TC and LDL-C (r=0.30 and r=0.31; p<0.005), TG (r=0.21; p<0.05) and apo B (r=0. 26; p<0.02). There was a negative relation between Lp(a) levels and apo(a) isoforms: the greater the apo(a) molecular weight, the lower the Lp(a) leve l (p<0.0001). Fasting insulin increased with apo(a) size, though the differ ence in insulin levels among apo(a) isoforms was not significant (p=0.4). M ultiple regression analysis showed that fasting insulin was the best predic tor of LDL-C (R-2=0.14; p=0.002) irrespective of age gender, BMI, waist cir cumference and TG, while apo(a) isoform size, BMI and waist circumference w ere related with Lp(a) irrespective of TC and LDL-C, TC and apo B (R-2=0.35 to 0.37; p<0.0001). Conclusions: These results suggest that fasting insuli n levels significantly influence LDL-C metabolism in old age. Lp(a) levels seem to be very strongly related to genetic background, although an indirec t relation with insulin through adiposity and/or other associated lipid abn ormalities cannot be ruled out.