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Cysteine reduces oxidative damage induced by heat stress in dromedary camel oocytes during in vitro maturation
Nasser Ghanem1, Mohamed Eleam2, Gamal Shawki2
1Animal Production Department, Faculty of Agriculture, Cairo University, Giza, Egypt.
Background:
Assisted reproductive technologies (ARTs), including in vitro maturation (IVM), hold promise for improving reproductive efficiency in dromedary camels, especially under challenging environmental conditions.
Aim:
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.
Methods:
Two experiments were conducted. In Experiment 1, cumulus-oocyte complexes (COCs) were collected and matured in vitro 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.
Results:
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 CASP3 transcription level (p <; 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.
Conclusion:
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.
