Abstract
Inflammatory bowel disease (namely, colitis) severely impairs human health. Isoleucine is reported to regulate immune function (such as the production of immunoreactive substances). The aim of this study was to investigate whether l-isoleucine administration might alleviate dextran sulfate sodium (DSS)-induced colitis in rats. In the in vitro trial, IEC-18 cells were treated by 4 mmol/L l-isoleucine for 12 h, which relieved the decrease of cell viability that was induced by TNF-α (10 ng/ml) challenge for 24 h (P <0.05). Then, in the in vivo experiment, a total of 44 Wistar rats were allotted into 2 groups that were fed l-isoleucine-supplemented diet and control diet for 35 d. From 15 to 35 d, half of the rats in the 2 groups drank the 4% DSS-adding water. Average daily gain, average daily feed intake and feed conversion of rats were impaired by DSS challenge (P <0.05). Drinking the DSS-supplementing water also increased disease activity index (DAI) and serum urea nitrogen level (P <0.05), shortened colonic length (P <0.05), impaired colonic enterocyte apoptosis, cell cycle, and the ZO-1 mRNA expression (P <0.05), increased the ratio of CD11c-, CD64-, and CD169-positive cells in colon (P <0.05), and induced extensive ulcer, infiltration of inflammatory cells, and collagenous fiber hyperplasia in colon. However, dietary l-isoleucine supplementation attenuated the negative effect of DSS challenge on growth performance (P <0.05), DAI (P <0.05), colonic length and enterocyte apoptosis (P <0.05), and dysfunction of colonic histology, and downregulated the ratio of CD11c-, CD64-, and CD169-positive cells, pro-inflammation cytokines and the mRNA expression of TLR4, MyD88, and NF-κB in the colon of rats (P <0.05). These results suggest that supplementing l-isoleucine in diet improved the DSS-induced growth stunting and colonic damage in rats, which could be associated with the downregulation of inflammation via regulating TLR4/MyD88/NF-κB pathway in colon.
Highlights
Gut functions and integrity play a vital role for health and growth in humans and animals [1]
Many previous studies have shown that isoleucine administration may regulate the generation of immunoreactive substances [12]
We found that lisoleucine administration could influence the mRNA expression and concentration of inflammation-related cytokines of ileal mucosa in weaned piglets [13]
Summary
Gut functions and integrity play a vital role for health and growth in humans and animals [1]. Isoleucine, known as one of branched chain amino acids, is important for some physiological functions of humans and animals [8,9,10,11]. Through reviewing the previous studies, it is found that isoleucine is important to maintain immunity in the in vivo and in vitro trials, which is involved into the regulation of immune organs, immune cells, and immunoreactive substances (such as immunoglobulins, cytokines, and host defense peptides) [12]. Our recent study showed that l-isoleucine administration could relieve rotavirus infection via affecting immune response, namely, the mRNA expression and concentration of inflammationrelated cytokines in the ileal mucosa of weaned piglets [13]. Lisoleucine administration could regulate the inflammatory response, and be used to control and cure DSS-induced colitis.
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