Cysteine reduces oxidative damage induced by heat stress in dromedary camel oocytes during <i>in vitro</i> maturation.

Abstract

<h4>Background</h4>Assisted reproductive technologies (ARTs), including <i>in vitro</i> maturation (IVM), hold promise for improving reproductive efficiency in dromedary camels, especially under challenging environmental conditions.<h4>Aim</h4>This study aimed to evaluate the potential effects of cysteine supplementation in IVM medium on nuclear maturation, mitochondrial activity, antioxidant status, oocyte ultrastructure, and heat stress marker genes expression using a dromedary camel oocyte model.<h4>Methods</h4>Two experiments were conducted. In Experiment 1, cumulus-oocyte complexes (COCs) were collected and matured <i>in vitro</i> using varying cysteine concentrations (0.0, 0.8, 1.6, and 2.4 mM) under standard conditions (38.5°C, 5% CO2, 40 hours) to identify the optimal concentration. Experiment 2 evaluated the protective effect of the selected concentration (1.6 mM) during heat stress, where COCs were exposed to 40.5°C for the first 24 hours of maturation, followed by exposure to 38.5°C for 16 hours. Three groups were compared: control, heat-stressed without cysteine, and heat-stressed with cysteine. We evaluated oocyte nuclear maturation, mitochondrial intensity, adenosine triphosphate (ATP) content, the activity of antioxidant markers, and oocyte ultrastructure. We used RT-quantitative real-time PCR to assess the mRNA expression of cumulus expansion, oxidative stress, and mitochondrial health-related genes.<h4>Results</h4>Results showed that heat stress conditions significantly reduced nuclear maturation, mitochondrial activity, ATP and antioxidant levels, and the mRNA expression levels of antioxidant, anti-apoptotic, cumulus expansion, and oocyte quality markers, while increasing pro-apoptotic <i>CASP3</i> transcription level (<i>p</i> <; 0.05). Conversely, cysteine administration markedly reversed heat stress-induced detrimental effects by restoring oocyte maturation and ultrastructure, mitochondrial intensity, ATP content, antioxidant balance, and gene expression profile modulation.<h4>Conclusion</h4>Supplementation with 1.6 mM cysteine during IVM of camel oocytes effectively improves oocyte quality and mitigates heat stress-related damage. This research supports the practical application of cysteine as a supplement to IVM media, specifically to enhance oocyte developmental competence and improve ART success rates in camels exposed to thermal stress.