α‐Bisabolol, a bioactive dietary sesquiterpene alleviates colon inflammation by regulating PPAR‐γ transcription factor

Abstract

Introduction Peroxisome proliferator activated receptor gamma (PPAR‐γ) plays an important role in regulating intestinal inflammation. PPAR‐γ is expressed in many tissues in the body but high amount is found in adipose tissue and colon. Therefore, PPAR‐γ ligands offer drug‐targeting system that can be exploited for treating inflammatory bowel diseases (IBDs). IBD prevalence is on the rise globally. Current mainstream therapies for IBD offer protection but with many side effects, therefore, up to 30% IBD patients turn to alternate therapy using dietary phytochemicals. α‐Bisabolol, a naturally occurring dietary sesquiterpene, isolated from Matricaria chamomilla has been demonstrated to have anti‐inflammatory properties. Initial docking studies reveal that it is a potent activator of PPAR‐γ transcription factor. Aim Therefore, the main aim of this study was to investigate α‐Bisabolol’s anti‐inflammatory property using both in vivo and in vitro experimental models of colon inflammation. Methodology C57BL/6J black mice were administered with 2% dextran sodium sulfate (DSS) in drinking water for 7days to induce colitis. The treatment group received α‐Bisabolol at 50 & 100 mg/kg body wt and compared with control and DSS along with a positive control drug. The disease activity index (DAI), colon length, myeloperoxidase (MPO) and histology was performed. Pro‐inflammatory cytokines (IL‐1β, IL‐6, and TNF‐α) level was measured using ELISA, and mRNA using real time PCR. Pro‐inflammatory mediators such as Cox‐2, iNOS expression was also measured at both protein and mRNA levels. PPAR‐γ and NF‐κB interaction were evaluated using colonic epithelial cell cytoplasm and nuclear fractions. Human colon carcinoma cell line, HT‐29 was used for in vitro studies. HT‐29 cells were cultured in 10% FBS containing DMEM media and were stimulated using TNF‐α (1ng/ml) to mimic inflammation. Various concentrations of α‐Bisabolol effect was evaluated on pro‐inflammatory cytokines such as GRO‐α, IL‐8, TNF‐α, COX‐2, and iNOS mRNA levels using real time PCR. Results α‐Bisabolol treatment significantly (p<0.01) decreased DAI, MPO level and restored colon length in a dose dependent manner in DSS treated group. Histological scoring for colonic crypt damage and inflammation was significantly (p<0.001) improved upon α‐Bisabolol treatment. α‐Bisabolol treatment also inhibited the pro‐inflammatory cytokines (IL‐1β, IL‐6 and TNF‐α) significantly (p<0.01) both at protein and mRNA level. α‐Bisabolol significantly inhibited COX‐2, and iNOS both at the protein and mRNA levels. α‐Bisabolol also activated PPAR‐γ protein expression in a dose dependent manner and also inhibited NF‐κB expression. α‐Bisabolol significantly (p<0.01) decreased pro‐inflammatory cytokine (GRO‐α, IL‐8, TNF‐α, COX‐2, and iNOS) mRNA expression when HT‐29 cells were challenged with TNF‐α. Support or Funding Information This study is supported by United Arab Emirates University, Zayed Center for Health Sciences, Center Based Interdisciplinary grant awarded to Dr Sandeep B Subramanya. Grant #31R230