Abstract 1595: Decreased LCAT Protein and Increased Activated Complement Fragments in the Dysfunctional HDL of Individuals With Diabetes and the Hp 2–2 Genotype
Objective: To characterize LCAT and activated complement proteins in the HDL of Hp 2–2 DM individuals.
Background: The Hp gene is polymorphic with two common alleles denoted 1 and 2 which encode protein products with dramatically different structures and functions. In six independent longitudinal studies the Hp genotype has been demonstrated to be predictive of incident CVD with DM individuals with the Hp 2–2 genotype having a 3–5 fold increased risk of CVD as compared to DM individuals without the Hp 2–2 genotype. We have recently provided a plausible mechanism for the increased CVD in Hp 2–2 via an interaction between the Hp protein and HDL. Specifically, we have demonstrated that the Hp 2–2 protein binds to ApoA1 and thereby tethers the potent oxidant hemoglobin to HDL resulting in increased HDL lipid peroxidation and the loss of the ability of Hp 2–2 HDL to promote cholesterol efflux from macrophages. The key complement protein C3 has recently been shown to be associated with the HDL of individuals with CAD and may bind to and be activated by oxidized lipids. We therefore hypothesized that the HDL of Hp 2–2 individuals may have more activated complement. Furthermore, based on the binding site of Hp on ApoA1 we proposed that the interaction of Hp 2–2 with ApoA1 would interfere with HDL LCAT activity.
Method: HDL was purified from DM individuals with the Hp 1–1, Hp 2–1 or Hp 2–2 genotype by affinity chromatography. HDL lipid peroxidation was assessed spectrophotometrically. C3 associated with HDL was assessed by western blot. LCAT activity and protein were assessed by TLC and western blot respectively.
Results: We found a graded effect of the amount of HDL oxidation associated with the number of Hp 2 alleles (Hp 2–2>Hp 2–1>Hp 1–1) in DM individuals. LCAT activity was Hp dependent with markedly less LCAT activity in Hp 2–2 which appears to be due to a decrease in the amount of the LCAT protein associated with HDL in Hp 2–2 individuals. An increase in C3 protein was found in the HDL of Hp 2–2 DM individuals.
Conclusion: The dysfunctional HDL of Hp 2–2 DM individuals is associated with structural changes in component proteins that may affect HDL functional maturation and transform HDL into a proinflammatory agent.