α-Bisabolol, a Dietary Bioactive Terpene Attenuates Oxidative Stress and Inflammation in Colonic Mucosa of Acetic Acid-Induced Colitis in Rats

Inflammatory bowel diseases (IBDs), such as ulcerative colitis, and Crohn's disease are chronic idiopathic inflammatory diseases of the gastrointestinal system involving interaction between genetic and environmental factors mediating the occurrence of oxidative stress and inflammation. There is no permanent cure for IBD except long-term treatment or surgery (resection of the intestine), and the available agents in the long term appear unsatisfactory and elicit numerous adverse effects. To keep the disease in remission, prevent relapses and minimize adverse effects of currently used medicines, novel dietary compounds of natural origin convincingly appear to be one of the important therapeutic strategies for the pharmacological targeting of oxidative stress and inflammation. Therefore, it is imperative to investigate plant-derived dietary agents to overcome the debilitating conditions of IBD. In the present study, the effect of α-Bisabolol (BSB), a dietary bioactive monoterpene commonly found in many edible plants as well as important components of traditional medicines, was investigated in acetic acid (AA)-induced colitis model in rats. BSB was orally administered to Wistar male rats at a dose of 50 mg/kg/day either for 3 days before or 30 min after induction of IBD for 7 days through intrarectal administration of AA. The changes in body weight, macroscopic and microscopic analysis of the colon and calprotectin levels in the colon of rats from different experimental groups were observed on day 0, 2, 4, and 7. The levels of myeloperoxidase (MPO), a marker of neutrophil activation, reduced glutathione (GSH) and malondialdehyde (MDA), a marker of lipid peroxidation, and the levels of pro-inflammatory cytokines were measured. AA caused a significant reduction in body weight and induced macroscopic and microscopic ulcers, along with a significant decline of endogenous antioxidants (superoxide dismutase (SOD), catalase, and GSH), with a concomitant increase in MDA level and MPO activity. BSB significantly improved the AA-induced reduction in body weight, colonic mucosal histology, inhibited MDA formation, and restored antioxidant levels along with a reduction in MPO activity. AA also induced the release of pro-inflammatory cytokines such as interleukin-1 (IL-1), interleukin-23 (IL-23) and tumor necrosis factor-α (TNF-α). Furthermore, AA also increased levels of calprotectin, a protein released by neutrophils under inflammatory conditions of the gastrointestinal tract. BSB treatment significantly reduced the release of calprotectin and pro-inflammatory cytokines. The findings of the present study demonstrate that BSB has the potential to improve disease activity and rescue colonic tissues from damage by inhibiting oxidative stress, lipid peroxidation and inflammation. The findings are suggestive of the benefits of BSB in IBD treatment and substantiate its usefulness in colitis management, along with its gastroprotective effects in gastric ulcer.