Cytotoxic and anti-inflammatory effects of onion peel extract on lipopolysaccharide stimulated human colon carcinoma cells

The present study investigated the cytotoxic activity of ethanol extract of onion peel (OPE) in HT-29 human colon carcinoma cells. High-performance liquid chromatography (HPLC) analysis was performed to determine the amounts of phenolic acids and flavonoids in OPE. In addition, the influence of OPE on antioxidant- and inflammation-associated gene expression was also determined in a model of lipopolysaccharide (LPS)-stimulated HT-29 cells. HPLC analysis showed that OPE contained well-known antioxidant compounds, including p-coumaric acid, vanillic acid, epicatechin, and morin. After incubation with OPE, HT-29 cells showed either a loss of normal nuclear architecture or detachability from each other. The cytotoxic effects of OPE on HT-29 cells were confirmed by MTT and LDH release assays. LPS-induced oxidative conditions effectively downregulated TNF-α mRNA expression in OPE pretreated HT-29 cells compared with cells only stimulated with LPS. In addition, the expression of heme oxygenase-1 (HO-1) and glutathione S-transferase (GSTs) detoxification genes (i.e., GSTM1, GSTT1, and GSTP1) was upregulated after treatment with LPS at sublethal concentrations. However, the LPS-induced mRNA expression of HO-1 and GSTs was significantly attenuated by treatment with OPE. Therefore, onion peel extract is a promising component of future nutraceuticals and value-added products.