N-Acetyl Cysteine Inhibits Weaning Stress-Induced Intestinal Cell Cycle Arrest in Piglets through Decreasing ERK, JNK, and p38 Phosphorylation

Objectives: Weaning induces oxidative stress in pigs, increasing the risk of diarrhea and death. Intestinal damage is associated with obstructed intestinal cell cycles. To stop damage caused by reactive oxygen species (ROS), N-acetyl cysteine (NAC) has been widely employed. In this study, we examined changes in the intestinal cyclin of weaning piglets and assessed the impact of NAC on intestinal cell cycle arrest and intracellular signaling pathways. Methods: We conducted two animal experiments. In the first, we divided 12 litters of 120 newborn piglets into two groups: a control group and a weaning group. The control piglets were allowed to suckle normally. The weaning group was weaned after 3 weeks and fed a normal diet for piglets. We slaughtered six piglets from the control group and six from the weaning group. We observed cyclin changes and intestinal development at days 0, 1, 4, and 7 after weaning. In the second experiment, we divided 15 litters of 150 piglets that were 2 weeks old into three groups: the control group, the weaning group, and the NAC group. Control piglets were allowed to suckle normally. Piglets in the weaning and NAC groups were weaned when they were 21 days old. The NAC group was fed a basal diet supplemented with 500 mg/kg NAC, and the weaning group was fed the basal diet alone. The experimental period was 14–25 days of age. Four days after weaning, we slaughtered one piglet from each litter. We then analyzed intestinal cell cycle indexes, intestinal oxidative stress, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 phosphorylation. Results: Weaning decreased the piglets’ feed intake and daily gain, reduced the serum antioxidant capacity, and increased the intestinal ROS level. Furthermore, the jejunum histology and barrier development of the jejunum exhibited damage after weaning, the microvilli displayed hypoplasia, and the p21 and p27 protein expression levels of the jejunum were significantly elevated. We did not observe any significant differences in cyclin D and E after days 1, 4, and 7 post-weaning compared with the control group. We observed, however, significantly increased cyclin D and E expression, lower ERK, JNK, and p38 kinase phosphorylation; villus atrophy alleviation; decreased p21 and p27 expression; and increased average daily intake of feed and weight gain. Conclusion: This research demonstrates that weaning stress inhibits piglet intestinal proliferation by reducing cyclin D and cyclin E expression. NAC downregulates p21 and p27 through modulating mitogen-activated protein kinases (MAPKase) phosphorylation, thereby promoting cell proliferation. The results indicate that NAC promotes intestinal function and the integrity of enterocytes and holds promise as a new feed additive for animal health.