L-carnitine improves hydrogen peroxide-induced impairment of nuclear maturation in porcine oocytes

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.