L-Proline Supplementation Alleviates Lipopolysaccharide-Induced Intestinal Inflammation in Weaned Rabbits by Modulating Mucosal Barrier Function and Gut Microbiota.

L-proline (Pro) is a conditionally essential amino acid that has been reported to exert protective effects on intestinal health. This research investigated whether Pro supplementation reduces intestinal inflammation in weaned rabbits, and whether this effect involves the maintenance of the intestinal mucosal barrier and the composition of gut microbiota. A total of thirty weaned New Zealand White rabbits were randomly divided into five groups: a control group, an LPS-challenged model group, and three LPS-challenged groups receiving 0.5%, 1% or 2% Pro in their drinking water. Following the overall results of the study, 1% Pro was chosen for further investigation. Notably, 1% Pro supplementation significantly decreased the spleen index, alleviated colonic histopathological injury, enhanced the expression of the tight junction proteins Occludin and Zonula Occludens-1 (ZO-1), restored the population of goblet cells, decreased the colonic mRNA levels of the pro-inflammatory cytokines IL1B and IL6, and increased the expression of the anti-inflammatory cytokine IL10. Microbiome analysis revealed that Pro supplementation was associated with alterations in the dysbiotic gut ecosystem, including increased relative abundances of potentially beneficial genera such as Ruminococcus, Christensenellaceae_R-7_group, and Lachnospiraceae_NK4B4_group, and decreased the relative abundance of opportunistic pathogens like Escherichia-Shigella. Overall, these results suggest that Pro functions as a microbiota-modulating immunonutrient that mitigates intestinal inflammation and supports the integrity of the mucosal barrier, likely through changes in gut microbial composition.