Vitamin E alleviates ammonia‑nitrogen and hypoxia co-exposure-induced intestinal damage in grass carp (Ctenopharyngodon idella) by modulating mitochondrial function, cellular autophagy and apoptosis

Abstract

Vitamin E is an essential fat-soluble vitamin with strong antioxidant properties and anti-inflammatory effects. However, whether vitamin E mitigates the combined effects of ammonia‑nitrogen and hypoxia on grass carp intestine remains unclear. Therefore, we investigated the effects of vitamin E on intestinal damage, mitochondrial dysfunction, autophagy, and apoptosis induced by ammonia‑nitrogen and hypoxia co-exposure in grass carp. Grass carp were fed with diets containing different levels of vitamin E (5.44, 52.07, 96.85, 141.71, 185.66, and 230.12 mg/kg diet, added in the form of DL-α-tocopherol acetate) for 9 weeks, followed by a 10-d ammonia‑nitrogen and hypoxia co-exposure test. A total of nine fish were chosen for each treatment group. The results showed that vitamin E improved the width of intestinal folds and reduced mitochondrial damage from co-exposure to ammonia‑nitrogen and hypoxia. Additionally, vitamin E up-regulated the protein levels of mitochondrial respiratory complex (I-V) subunits and the mRNA expression of mitochondrial biogenesis-related genes (ppargc1α, nrf1/2, tfam) and fusion-related genes (mfn1, mfn2, opa1). Conversely, it down-regulated mitophagy-associated proteins (Pink1 and Parkin) and the mitochondrial fission gene (drp1). Furthermore, vitamin E reduced the expression of autophagy-associated genes (lc3, atg5, atg12, becn1, ulk1) and apoptosis-associated genes (casp3, casp9, bax), along with the protein levels of Bax and Lc3. In contrast, vitamin E increased the mRNA expression of bcl2 and sqstm1 and elevated the protein levels of Sqstm1. In summary, vitamin E can mitigate damage caused by ammonia‑nitrogen and hypoxia co-exposure in the intestine by improving mitochondrial function and decreasing apoptosis and autophagy.