Eicosapentaenoic acid (EPA) inhibited lipoprotein(a) [Lp(a)] oxidation and its effects on expression of oxidative stress and pro-inflammatory proteins in endothelial cells

Background Elevated Lp(a) increases cardiovascular (CV) risk, and while the precise mechanism for this risk is incompletely understood it may be related to oxidation of Lp(a) components. Lp(a) can bind oxidized phospholipids that increase its susceptibility to oxidation, enhancing its ability to elict endothelial cell (EC) inflammation. The omega-3 fatty acid eicosapentaenoic acid (EPA) delivered as icosapent ethyl (4 g/d) reduced CV events in high-risk patients with elevated Lp(a) (REDUCE-IT). A mechanism of EPA action may include attenuation of Lp(a) oxidation due to its potent free radical scavenging capacity. Purpose We assessed the effects of Lp(a) ± EPA on protein expression in ECs during conditions of oxidative stress. Methods Lp(a) enriched to 62% of total ApoB-containing particles (the remaining 38% being LDL) from patients with elevated levels following isopycnic centrifugation. Lp(a) was incubated with EPA (50 µM) or equivolume vehicle at 37°C for 30 min. Oxidation was then initiated using copper sulfate (20 µM). After 2 h, human umbilical vein ECs (HUVECs) were incubated with Lp(a) (150 µg/mL by ApoB protein) for 8 h. Cell lysate samples were then analyzed by global LC/MS-based proteomics. Significant changes (p<0.05) in expression between treatment groups >1-fold were further analyzed. Heme oxygenase-1 (HO-1), which is known to be increased with EPA treatment, and intercellular adhesion molecule-1 (ICAM-1) were also analyzed by Western blot. Results EPA attenuated oxidation in Lp(a)-enriched fractions through 2 h by 61% compared with vehicle-treated controls (p<0.001). A total of 239 proteins were significantly modulated by oxLp(a) compared with Lp(a) + EPA (145 increased, 94 decreased). Proteins with the most significant changes in expression with oxLp(a) relative to EPA + Lp(a) included those associated with cellular stress such as heat shock protein 70 kDa protein 1B (HSPA1B), which increased 3.4-fold (p = 1.46 × 10-6), HSP1H (1.5-fold, p = 5.14 × 10-5) and HSP86 (1.4-fold, p = 0.013). Lp(a) + EPA treatment significantly increased expression of PPARγ which can suppress inflammatory signaling. Western blot revealed levels of HO-1 were significantly increased by Lp(a) + EPA compared to oxLp(a) (p<0.01). ICAM-1 was also increased significantly with oxLp(a) but not Lp(a) + EPA (p<0.01). Conclusions EPA attenuated Lp(a) oxidation and its effects on oxidative stress and pro-inflammatory protein expression. Inhibition of Lp(a) oxidation by EPA may thereby reduce endothelial dysfunction and inflammation in the presence of elevated Lp(a), thereby contributing to the reduction of CV events in patients with elevated Lp(a) levels.