Anti-inflammatory effects of characterized orange peel extracts enriched with bioactive polymethoxyflavones

In view of the potential of polymethoxyflavones (PMFs) and hydroxylated PMFs (OH-PMFs) as bioactives against inflammation, we prepared six different orange peel extracts (OPEs). The major compounds of these extracts were characterized and quantified by high performance liquid chromatography (HPLC). Effects on inflammation were analyzed by nutrigenomics using a human cell-based TPA-induced monocyte–macrophage differentiation model employing U-937 cells and inflammatory surrogate genes. Dose response and kinetics analysis of OPEs with different chemical profiles revealed less cytotoxic effects of PMFs as compared to OH-PMFs as demonstrated by the MTT-method. Noteworthy, a comparison of two PMF members such as 3,5,6,7,3′,4′-hexamethoxyflavone (HexaMF) and 3,5,6,7,8,3′,4′-heptamethoxyflavone (HeptaMF) exhibited less cytotoxic effects of HeptaMF as compared to HexaMF. A specific OPE enriched with HeptaMF, PMFs and OH-PMFs at low concentrations (10 μg/mL) significantly down-regulated the expression of a panel of genes involved in inflammatory response, including COX-2, TNF-α, ICAM-1, NFκB, IL-1β, IL-6, and IL-8 with an inflammatory index of −0.55. The strong anti-inflammatory effects were then validated in a mouse carrageenan-induced paw edema model. Oral intake of OPE reduced paw edema significantly in a dose-dependent manner. Importantly, a dosage of 250 mg/kg gave an anti-inflammatory effect comparable to ibuprofen. A preliminary clinical study showed that OPE was well tolerated showing no adverse side effects. In summary, enrichment of phyto extracts such as OPEs with specific polymethoxyflavones as anti-inflammatory bioactives is a promising strategy to find naturally derived extracts that are effective against diseases associated with inflammation.