Microwave-assisted extract of rhodomyrtone from <i>rhodomyrtus tomentosa</i> leaf: Anti-inflammatory, antibacterial, antioxidant, and safety assessment of topical rhodomyrtone formulation

Abstract

Series of works on the biological properties of rhodomyrtone, a major active component of Rhodomyrtus tomentosa leaf has been reported. In this study, rhodomyrtone-rich microwave-assisted extract from R. tomentosa leaf (RT-MAE) before formulation was profiled for phytochemical composition using gas chromatography-mass spectrometry (GC-MS) and targeted for anti-inflammatory activity with topical application. The formulation was assessed for bioactivity, biocompatibility, and safety on human volunteers. The GC-MS spectra indicated a rich content of phytosterols, sesquiterpenes, and acylphloroglucinols. At concentrations 50–600 ng/mL, RT-MAE before formulation treated macrophages showed >86% cell viability. Nitric oxide production significantly decreased by 19.26–88.36% following the treatment with 50–600 ng/mL RT-MAE before formulation (p < 0.001). Moreover, a significant (p < 0.01) concentration-dependent downregulation of lipopolysaccharide-induced IL-6, IL-1β, iNOS, and COX-2 mRNA was observed in RT-MAE before formulation treated macrophages. The extract demonstrated minimum inhibitory (MIC) and minimum bactericidal concentration (MBC) at 0.25–4 and 1–16 μg/mL, respectively. The antioxidant activity of RT-MAE before formulation indicated IC50 of 0.16 and 0.06 ug/mL for DPPH and ABTS assays, respectively. Ex-vivo diffusion of rhodomyrtone from formulation showed steady-state flux 64.935 ng/cm2 h, with >80% viability on HaCaT cells. Safety assessment of formulation containing RT-MAE after formulation was conducted on healthy volunteers. Hematological and biochemical analysis showed no significant difference between test and baseline (p < 0.05). The results suggested that the formulation can be effectively employed as a topical inflammatory agent.