Inhibition of proinflammatory enzymes and attenuation of IL-6 in LPS-challenged RAW 264.7 macrophages substantiates the ethnomedicinal use of the herbal drug Homalium bhamoense cubitt & W.W.Sm

Abstract

Commonly used to treat skin injuries in Asia, several Homalium spp. have been found to promote skin regeneration and wound healing. While ethnobotanical surveys report the use of H. bhamoense trunk bark as a wound salve, there are no studies covering bioactive properties. As impaired cutaneous healing is characterized by excessive inflammation, a series of inflammatory mediators involved in wound healing were targeted with a methanol extract obtained from H. bhamoense trunk bark. Results showed concentration-dependent inhibition of hyaluronidase and 5-lipoxygenase upon exposure to the extract, with IC50 values of 396.9 ± 25.7 and 29.0 ± 2.3 µg mL−1, respectively. H. bhamoense trunk bark extract also exerted anti-inflammatory activity by significantly suppressing the overproduction of interleukin 6 (IL-6) in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages at concentrations ranging from 125 to 1000 µg mL−1, while leading to a biphasic effect on nitric oxide (NO) and tumor necrosis factor alpha (TNF-α) levels. The phenolic profile was elucidated by HPLC-DAD, being characterized by the occurrence of ellagic acid as the main constituent, in addition to a series of methylated derivatives, which might underlie the observed anti-inflammatory effects. Our findings provide in vitro data on anti-inflammatory ability of H. bhamoense trunk bark, disclosing also potential cutaneous toxicity as assessed in HaCaT keratinocytes.