(P03-004-23) Onion Peel Extract Prevents Intestinal Inflammation via AMP-Activated Protein Kinase

Objectives: Obesogenic diets cause intestinal inflammation and dysfunction, accelerating the development of obesity. Reducing inflammation is an effective strategy to prevent obesity. Some polyphenols have the potential to reduce inflammation. Due to their instability during the intestinal digestive process, their anti-inflammatory effects tested in in vitro system may not be reliable. Therefore, the objective of our study was to investigate the anti-inflammatory effect of onion peel and its major bioactive compound, quercetin in the intestine and further examine the effect of intestinal digestion on their anti-inflammatory effect.

Methods: Onion peel extract was prepared using 70% aqueous ethanol (v/v) by a liquid-liquid extraction method, whereas quercetin was purchased from Sigma-Aldrich. Onion peel extract and quercetin were digested using intestinal digestive enzymes in vitro. To mimic the human intestinal epithelium, the Caco-2, and HT-29 co-culture was used. Cells were inflamed with lipopolysaccharide for 12 h after they are pretreated with onion peel extract and quercetin with or without digestion for 12 h. Genes and proteins related to tight junction and inflammation were determined using real-time PCR and western blot, respectively. Epithelial integrity was determined by measuring trans-epithelial electrical resistance (TEER) and absorption of florescent dye.

Results: Onion peel extract and quercetin with or without digestion increased tight junction genes, zonula occludens, and claudin1, with the highest increase by digested onion peel extract, supported by increased TEER and decreased fluorescent dye absorption. These samples also decreased inflammatory genes, cyclooxygenase-2 and tumor necrosis factor-alpha. AMP-activated protein kinase (AMPK) was activated, which deactivated its downstream protein, nuclear factor kappa B (NF-κB).

Conclusions: Onion peel extract and quercetin with or without digestion have anti-inflammatory effect via AMPK-NF-κB signaling in intestinal cells, despite the better anti-inflammatory effect of the extract than quercetin. Overall, the consumption of onion peel and quercetin may attenuate obesity-induced intestinal inflammation.

Funding Sources: USDA AFRI