Melatonin Supplementation during In Vitro Maturation of Porcine Oocytes Alleviates Oxidative Stress and Endoplasmic Reticulum Stress Induced by Imidacloprid Exposure

SIMPLE SUMMARY: The residue of chemicals can affect the maturation of livestock oocytes, thereby affecting the quality of embryos. Research has shown that imidacloprid, a systemic neonicotinoid insecticide widely used in agriculture, can damage the reproductive system of mammals, and it is unclear whether imidacloprid will affect oocyte maturation and how to reduce its toxicity. The results of this study show that imidacloprid can affect oocyte maturation, and melatonin supplementation can restore oocyte maturation by alleviating oxidative stress and endoplasmic reticulum stress, and offset the toxic effect of imidacloprid on pig oocytes, which indicates that Melatonin may be a promising drug to improve the quality of oocytes exposed to imidacloprid in animals. ABSTRACT: Imidacloprid (IMI) is an endogenous neonicotinoid insecticide widely used in agriculture and has attracted researchers’ attention because of its risks to the environment and human health. Melatonin (MT) is an antioxidant hormone produced by the pineal gland of the brain. Studies have shown that it has a variety of physiological functions and plays a crucial role in the development of animal germ cells and embryos. The potential protective effects of MT against oocyte damage caused by neonicotinoid pesticide toxicity remain unclear. In this study, we report the toxicity of IMI against, and its effects on the quality of, porcine oocytes and the protective effect of MT on IMI-exposed oocytes. The results show that IMI exposure adversely affected oocyte maturation, while MT supplementation ameliorated its toxic effects. Specifically, IMI exposure increased oxidative stress (OS), endoplasmic reticulum stress (ERS), and apoptosis, which may affect polar body expulsion rates and blastocyst formation. Also, IMI exposure reduced oocyte cleavage rates and the number of cells in blastocysts. However, all of these toxic effects can be restored after a melatonin supplementation treatment. In conclusion, these results suggest that melatonin has a protective effect on IMI-induced defects during porcine oocyte maturation.