Mechanisms of oxidative stress in porcine oocytes and the role of anti-oxidants

Abstract

The mechanisms of oxidative stress in in vitro maturing porcine oocytes and the effects of anti-oxidant supplementation of the medium in ameliorating these effects were investigated in the present study. In addition to intracellular reduced glutathione (GSH) concentrations and DNA fragmentation, the present study focused on superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase activity. The anti-oxidants used were N-acetylcysteine (NAC) and its derivative NAC-amide (NACA). The results indicate that when SOD is inhibited, supplementation of the maturarion medium with 1.5 mm NAC or NACA compensates for the decrease in SOD activity by reducing the degree of DNA fragmentation (P < 0.05). When GPx is inhibited, supplementation of the maturarion medium with 1.5 mm NAC alleviates the effects of no GPx activity, as indicated by a decrease in the degree of DNA fragmentation (P < 0.05). When the maturarion medium was supplemented with 1.5 mm NACA, intracellular GSH concentrations decreased (P < 0.05) and SOD and catalase activities increased (P < 0.05) along with the degree of DNA fragmentation. These results indicate that the mechanisms of alleviating oxidative stress in porcine oocytes are very complex and supplementing maturing oocytes with anti-oxidants may enhance enzyme activities and eliminate free radicals.

Effects of oxygen concentration on in vitro maturation of canine oocytes in a chemically defined serum-free medium

“…In order to recover GSH, oocytes use another enzyme, glutathione reductase (GSR), to reduce the GS-SG (oxidized form of GSH) back to GSH (Guerin et al 2001). Because of lower levels of GSH within in vitro matured canine oocytes (!8 pMol/oocyte) in comparison with in vivo (19.2 pMol/oocyte) (Kim et al 2007), high levels of H 2 O 2 and ROS within COCs during IVM can severely impair maturation and increase degeneration rates (Whitaker & Knight 2008). These studies showed that the H 2 O 2 level in oocytes is a good indication of oxidative stress.…”

“…2B). It is noteworthy that H 2 O 2 is a byproduct of the ROS protection system in which SOD enzymes transform damaging oxygen-free radicals into less aggressive H 2 O 2 molecules (Whitaker & Knight 2008). As oxidative stress is introduced to oocytes immediately after mechanical extraction till the end of the culture period via various sources of free radicals, light and physical trauma (Guerin et al 2001, Menezo et al 2010, it is necessary to provide these cells with least amount of Effects of oxygen level on canine oocyte maturation stressors.…”

“…However, presence of these abundant lipid droplets in ooplasm has an impeccable influence on predisposition of cumulus oocyte complexes (COCs) to oxidative stress by reactive oxygen species (ROS; Wakefield et al 2008, Whitaker & Knight 2008, Tao et al 2010. Oxygen concentration during the IVM culture period can contribute to the extent and velocity of this oxidative stress of which oocyte nuclear and cytoplasmic maturation and development pattern may perturb (Kim et al 2007, Whitaker & Knight 2008.…”

“…GSH becomes a substrate of glutathione peroxidase (GPX) in alliance with catalase (CAT), which degrades hydrogen peroxide (H 2 O 2 ) to water and oxygen (Whitaker & Knight 2008). H 2 O 2 itself is the resulting product in neutralization of ROS by superoxide dismutases (SOD) (cytosolic SODZ Cu-Zn SOD1, mitochondrial SODZMn-SOD2) (Guerin et al 2001).…”

Endoplasmic Reticulum-Derived Multilamellar Bodies in Oocytes of Mouse Follicle Cultures under Oxidized Low-Density Lipoprotein Treatment

“…It occurs during oocyte maturation in vitro and seems to be the motor of ovulation in vivo [Martin-Romero et al, 2008;Whitaker and Knight, 2008;Spanel-Borowski, 2011a]. It also appears that it is not the oxidative stress but rather a physiological production and action of ROS that evolves as a signaling factor to induce ovulation [Shkolnik et al, 2011].…”