Relationship between serum complement and different lipid disorders

Inflammatory and lipid factors share an important role in atherosclerosis. Recent studies showed the concomitant presence and increase of complement components and lipids both in the atherosclerotic plaque and the circulating blood. The aim of this study was to examine the relationship between the complement system and lipid disorders. We evaluated the circulating complement terminal complex C5b-9, a clear sign of complement activation, in three groups of 30 patients the first with hypercholesterolemia, the second with hypertriglyceridemia (associated with low values of HDL-cholesterol), the third with low levels of HDL-cholesterol compared with an equivalent group of matched normolipemic subjects. We found a significant increase of sC5b-9 in each group of patients compared with controls. The mean sC5b-9 level in the hypercholesterolemic population was 366.2 +/- 141.2 ng/ml (P<0.01), 395.4 +/- 118.2 ng/ml in the hypertrygliceridemic group (P<0.01), 414.8 +/- 126.4 ng/ml in the low HDL-chol subjects (P<0.01), and 182.0 +/- 40.8. ng/ml in the control group. Regression analysis showed a significant direct correlation between sC5b-9 and triglycerides (r=0.64), and a significant inverse correlation between sC5b-9, HDL-chol (r=-0.74), and apo-A1 (r=-0.68); no significant relationship was found between sC5b-9 and cholesterol. We suggest that complement activation is associated with the various lipid disorders and is more important in those dyslipidemic conditions in which other factors may be involved. In particular, hypertriglyceridemia may be associated with endothelial and fibrinolytic disturbances, and the decrease of HDL may induce the failure of the regulatory proteins transported by the same HDL.