1,8‐Cineole, a bioactive monoterpenoid, mitigates colon inflammation by stimulating colon PPAR‐γ transcription factor
Authors: Subramanya Sandeep B. , Venkataraman Balaji , Almarzooqi Saeeda , Raj Vishnu , Subramanian Veedamali S. , Bhongade Bhoomendra A. 
Published: May 2022

Introduction

Peroxisome proliferator‐activated receptor gamma (PPAR‐γ) plays a vital role in regulating intestine inflammation. PPAR‐γ is highly expressed in the adipose tissue and the colon. Therefore, PPAR‐γ ligands offer a drug‐targeting system that can be exploited to treat inflammatory bowel diseases (IBDs), especially in ulcerative colitis. IBD prevalence is on the rise globally. Current mainstream therapies for IBD offer protection but with many side effects; therefore, up to 30% of IBD patients turn to alternate therapy using bioactive phytochemicals. 1,8‐cineole (eucalyptol), a naturally occurring monoterpenoid in many aromatic plants, possesses potent anti‐inflammatory properties. The docking studies reveal that, it is a potent activator of the PPAR‐γ transcription factor. Therefore, in this study, we investigated the role of 1,8‐cineole modulating colon epithelial PPAR‐γ transcription in colon inflammation.

Aim

This study aims to investigate 1,8‐cineole’s anti‐inflammatory properties using both in vivo and in vitro models of colon inflammation.

Methodology

C57BL/6J black mice were administered 2% dextran sodium sulfate (DSS) 1,8‐cineole administered at concentrations of 100 & 200mg/kg body. The DAI, colon length, MPO, and histology changes were determined. Proinflammatory cytokines (IL‐1β, IL‐6, TNF‐α, & IL17A) were measured using ELISA and mRNA using real‐time PCR. PPAR‐γ expression and phosphoNF‐κB/NF‐κB expression were estimated. RAW (264.7) macrophages cultured in DMEM and pretreated with different concentrations (µM) 1,8‐cineole before the LPS (1µg/ml culture media) stimulation. Proinflammatory cytokine responses (IL‐1β, IL‐6, and TNF‐α) and PPAR‐γ protein expression determined. HT‐29 cells were cultured in DMEM media and were stimulated using TNF‐α (1ng/ml). CXCL‐1, IL‐8, mRNA level determined using real‐time PCR after 1,8‐cineole co‐treatment. 1,8‐cineole effect on PPAR‐γ promoter activity was determined using full length promoter transfection studies.

Results

1,8‐cineole treatment significantly (p<0.01) decreased DAI, MPO level, and restored colon length dose‐dependently in DSS treated group. Histological scoring for colonic inflammation was significantly (p<0.001) improved upon 1,8‐cineole treatment. 1,8‐cineole treatment also inhibited the proinflammatory cytokines (IL‐1β, IL‐6, TNF‐α, & IL17A) significantly (p<0.01) both at protein and mRNA levels. 1,8‐cineole significantly inhibited COX‐2 and iNOS both at protein and mRNA levels. 1,8‐cineole also activated PPAR‐γ protein expression dose‐dependently and also inhibited NF‐κB expression in DSS‐administered and LPS‐stimulated RAW macrophages. 1,8‐cineole significantly (p<0.01) decreased proinflammatory cytokine (CXCL‐1, & IL‐8) mRNA expression when HT‐29 cells were challenged with TNF‐α. 1,8‐cineole also increased PPAR‐γ promoter activity.

Conclusion

1,8‐cineole mitigates colon inflammation by stimulating colon PPAR‐γ transcription factor.