Monoammonium glycyrrhizinate improves antioxidant capacity of calf intestinal epithelial cells exposed to heat stress in vitro

Dairy calves are highly susceptible to the negative effects of heat stress, which can cause organ hypoxia after blood redistribution, damage the intestinal barrier, and trigger intestinal oxidative stress. This study aimed to investigate the antioxidant effects of monoammonium glycyrrhizinate (MAG) on calf small intestinal epithelial cells under heat stress in vitro. Small intestinal epithelial cells were isolated from a 1-day-old healthy calf and purified by differential enzymatic detachment. The purified cells were divided into seven groups. The control group was cultured with DMEM/F-12 at 37℃ for 6 h, and the treatment groups were cultured with 0, 0.1, 0.25, 0.5, 1, or 5 μg/mL MAG at 42℃ for 6 h. Heat stress causes oxidative damage to cells. Adding MAG in the medium can significantly improve cell activity and reduce cellular oxidative stress. Monoammonium glycyrrhizinate significantly increased the total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity caused by heat stress, and significantly decreased malondialdehyde (MDA) and nitric oxide (NO) levels. The MAG treatment also reduced lactate dehydrogenase (LDH) release, increased mitochondrial membrane potential (MMP), and decreased apoptosis under heat stress. MAG also upregulated the expression of the antioxidant-related genes, Nrf2 and GSTT1, in heat-stressed intestinal epithelial cells and significantly downregulated the expression of the heat shock response-related proteins, MAPK, HSP70, HSP90, and HSP27. From the above results, we conclude that 0.25 μg/mL MAG improves the capability of the antioxidant system in small intestinal epithelial cells to eliminate reactive oxygen species by activating antioxidant pathways, improving the oxidant/antioxidant balance, lowering excessive heat shock responses, and reducing intestinal oxidative stress.