Glutathione content in feline oocytes during in vitro maturation in the presence of thiol compounds

In a previous study we demonstrated that the presence of cysteine in the culture medium significantly enhanced intracellular glutathione (GSH) content of feline oocytes after 48 h of culture (1). Glutathione is known to play an important role in protecting the cells from oxidative stress. Feline oocytes are more likely to be very sensitive to oxidative damage due to their high lipid content. The biosynthesis of GSH increases during oocyte maturation and depends on the availability of cysteine in the extracellular environment (2). However, cysteine is very unstable and rapidly oxidized to cystine. It has been reported in other species that the presence in the culture medium of low molecular weight thiol compounds, such as -mercaptoethanol (BME) and cysteamine (CSH), reduces cystine to cysteine, promotes cysteine uptake and enhances GSH synthesis in the oocytes (2). The aim of the present study was to evaluate the effect of the association of cysteine with CSH or BME on intracellular GSH content during meiotic progression of feline oocytes. Our results indicate that the presence of thiols in the maturation medium impedes a depletion of the endogenous pool of GSH in feline oocytes, and promotes GSH increase concurrently with the progression of meiotic maturation. However, in these cultural conditions no clear evidence of an enhancement of GSH synthesis is demonstrated by the contemporary presence of cysteine and its reductor compounds.