Differential associations of serum amyloid A and pentraxin-3 with allele-specific lipoprotein(a) levels in African Americans and Caucasians

Lipoprotein(a) [Lp(a)] is a cardiovascular disease (CVD) risk factor, where inflammation impacts levels differentially across ethnicity. We investigated the effect of systemic [serum amyloid A (SAA)] and vascular [pentraxin-3 (PTX-3)] inflammation on Lp(a) levels across different apolipoprotein(a) [apo(a)] sizes in a biethnic population. Lp(a) and allele-specific apo(a) levels, apo(a) sizes, SAA, and PTX-3 levels were determined in 336 Caucasians and 224 African Americans. We dichotomized subjects into 2 groups using the respective median SAA (29.8 and 41.5 mg/dL for Caucasians and African Americans, respectively) or PTX-3 levels (1.6 and 1.1 ng/mL for Caucasians and African Americans, respectively). Among African Americans, but not in Caucasians, Lp(a) levels were increased (146 vs 117 nmol/L, P = 0.024) in the high versus low SAA group. No difference was observed across PTX-3 groups. Furthermore, among African Americans with smaller (<26 K4 repeats) apo(a) sizes, allele-specific apo(a) levels (111 vs 79 nmol/L, P = 0.020) were increased in the high versus low SAA group. Again, no difference was observed for PTX-3. We did not find any significant associations between allele-specific apo(a) and SAA or PTX-3 levels among Caucasians with smaller (<26 K4) apo(a) sizes. In conclusion, increased levels of SAA, but not PTX-3, were associated significantly with higher Lp(a) levels for smaller (<26 K4) apo(a) sizes in African Americans. Our results implicate that a proinflammatory stimulus may result in an increased cardiovascular risk through a selective increase in Lp(a) levels among African Americans who carry a smaller apo(a) size.