To test whether DHEA and Metformin can improve the quality of zygotes from mice with antiphospholipid syndrome (APS). Cardiolipin, the major phospholipid in mitochondrial membrane, regulates the stability of respiratory supercomplex. Lycat is a enzyme that converts the cardiolipin precursor to mature form. This remodeling process shows prompt responses to oxidative stress. Transgenic mice overexpressing Lycat recapitulated APS-related recurrent pregnancy failure. Oxidative stress induced by high AP-abs impairs the differentiation of extraembryonic tissues. Exogenous DHEA at low doses inhibits lipid peroxidation and restores oxidative balance. Similarly, Metformin (Met) reduces DNA damage-induced aneuploidy in reproduction by attenuating reactive oxygen species (ROS) production. 1) ROS detection. Ovaries from 2-month old Lycat-Tg (n=8) and WT (n=6) mice were collected for cryosectioning. Rehydrated tissue sections were incubated with 10 μM fluorogenic H2DCF for 20 min. After DAPI counter staining, ROS+ cells were photographed (Ex/Em = 468/560 nm) and quantified by NIH ImageJ. Data were presented as percentage of ROS+ cells among total cells on each section.2) Quantifing mitochondrial (mt) copy number and In Vitro rescue. One-cell embryos (n=111) from Tg ♂ x Tg ♀s matings were collected and cultured in M16 supplemented with 10 nM DHEA + 5 μM Met to blastocysts (DM-Tg); among them, 71 embryos were pooled for SYBR green Q-PCR on an ABI-7900HT. A 650pb DNA fragment encoding NADH Dehydrogenase Subunit I was amplified. Absolute mtDNA copy number in a single blastocyst was derived by a linear regression model using standard curves calculated between Ct and the logarithm of the concentration of standards.Effects of DHEA/Met on embryo quality was further tested in vivo by uterine transfer of the remaining DM-Tg embryos to WT foster females at 10 embryos/mouse with 4 repeats. Pregnancy was verified on day 12.5 p.c. Comparable numbers of WT and untreated Tg blastocysts were included as controls in each assay. Unpaired t-test was used for statistical analysis. DCF-staining showed that elevated Lycat led to ovarian hypersensitivity (WT, 11.3±5.3 vs. Tg, 28.7±6.0%; p=0.01) to ROS. Unlike the untreated Tg controls that showed a 27% decrease in mitochondrial biogenesis (WT, 3.42±0.54 x 105 vs Tg 2.48±0.64 x 105 copies/blastocyst; p<0.01), the DM-Tg embryos showed no difference in mtDNA copy number as compared with the WT controls (WT, 3.42±0.54 x105 vs. DM-Tg 3.30±0.60 x105; p=0.6). Moreover, in vitro cultivation of Tg embryos to blastocyst stage, in the presence of DHEA/Met, did enhance the viability of the embryos (DM-Tg, 7.3±1.0 vs. Tg, 4.8±1.0 pups/litter; p=0.008), resulting in an implantation rate comparable to WT embryos (DM-Tg 7.3±1.0 vs. WT, 8.5±1.3; p=0.17). Beneficial effects of DHEA/Met cocktail on embryo viability are, at least in part, achieved by preventing premature mitochondria degradation.