Intestinal Protective Effects of a Pomegranate Peel Extract in In Vitro and Ex Vivo Studies

Recovery of nutritional and bioactive molecules by pomegranate peel (PP) has found wide applications in food and pharmaceutical industries. We investigated protective effects of a PP extract (PPE) from Mediterranean (Mazara del Vallo, Italy) on intestinal inflammation by using in vitro and ex vivo models. Reactive oxygen species (ROS) and lactate dehydrogenase (LDH) levels, as well as tight junction protein-1 (ZO-1) expression, were determined in lipopolysaccharide (LPS)-injured Caco-2 cells treated with PPE. We evaluated anti-inflammatory and antioxidant effects of PPE in isolated colon specimens of adult male mouse (C57/BL6) stimulated by LPS. Cyclooxygenase-2 (COX-2), nuclear factor-kB (NF-kB), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), as well as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), and inducible nitric oxide synthase (i-NOS) gene expression was determined. We also characterized phytochemical composition of the extract through chromatographic (HPLC-UV) and spectrophotometric techniques. PPE was rich in punicalagins A and B, along with other polyphenols such as hydroxytyrosol (HT), catechin, p-coumaric acid, and rosmarinic acid. In Caco-2 cells, PPE reduced ROS generation and LDH release, restoring intestinal barrier integrity by upregulating ZO-1 expression. In addition, PPE increased SOD, CAT, and GPX and suppressed COX-2, NF-kB, TNF-α, IL-1β and i-NOS LPS-induced gene expression in colon. PPE mitigates inflammation and oxidative stress, restoring intestinal barrier function. The beneficial effects induced by the extract could be related to the pattern of polyphenolic composition, with particular regard to HT, rosmarinic acid, p-coumaric acid, catechin, as well as punicalagins A and B.