β2GPI pretreated with TRX-1 protects human endothelial cells and EAhy 926 cells from oxidative stress–induced cell death. (A) EAhy926 cells were exposed to various concentrations of H₂O₂ for 20 minutes at 37°C, and a cell viability dose-response curve was constructed (n = 3). (B) Cells were incubated with nβ2GPI (2 μM) with or without pretreatment with DTT-activated TRX-1 (3.5μM) or with TRX-1 alone for 20 minutes at 37°C, then with 13mM H₂O₂ for 20 minutes at 37°C. After overnight incubation with media, cell viability was determined and expressed as fold increase in cell viability over H₂O₂-only–treated cells (n ≥ 5). (C) HUVECs were exposed to various concentrations of H₂O₂ for 40 minutes at 37°C, and a cell viability dose-response curve was constructed (n = 5). (D) HUVECs incubated with nβ2GPI (1μM) pretreated with TRX-1 (1.75μM) were activated by TRX-R/NADPH for 20 minutes at 37°C and then incubated with 4mM H₂O₂ for 40 minutes at 37°C. No difference between H₂O₂-only–treated cells and β2GPI/NADPH, β2GPI alone, and TRX-1/TRX-R/NADPH alone was observed (n = 3). For all panels, ***P < .001, **P ≤ .01, and *P ≤ .05.