We investigated the effect of oxidative stress induced by hydrogen peroxide (H2O2) on lipid peroxide (LPO) level and nuclear maturation in porcine oocytes cultured with or without cumulus cells. After 22h of pre-culture, oocytes with attached cumulus cells (COC group) or denuded oocytes (DO group) were cultured with H2O2, and intra-oocyte H2O2 and LPO levels were quantitatively analyzed using immunofluorescence. This is the first report evaluating LPO levels in porcine oocytes. After H2O2 supplementation, the DO group showed severe accumulation of H2O2 and LPO in the oocytes. Similarly, while inhibition of progression of nuclear maturation was observed in both groups, the effect was more severe in the DO group. These results demonstrate that cumulus cells reduce the accumulation of H2O2 stress in oocytes. Furthermore, we attempted to reduce the oxidative stress by H2O2 with L-carnitine, a H2O2 scavenger. L-carnitine decreased H2O2 and LPO levels in the oocytes in both groups, and improvement in the progression of impaired nuclear maturation was observed. These effects were different by the presence of cumulus cells. Our results provide that L-carnitine is useful for alleviating H2O2-induced oxidative stress by reducing LPO levels and improving the progression of nuclear maturation.
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