Synergistic Antimicrobial and Antioxidant Properties of Coccinia grandis (L.) Voigt, Clerodendrum inerme (L.) Gaertn. and Acanthus ebracteatus Vahl. Extracts and Their Potential as a Treatment for Xerosis Cutis

Abstract

Background: A common health condition among older persons is xerosis cutis. Topical corticosteroid treatments are ­associated with side effects. There is an unmet need for her­bal treatment alternatives. Coccinia grandis, Clerodendrum inerme and Acanthus ebracteatus are used to treat skin con­ditions in Thai traditional medicine. This study aimed to investigate their antimicrobial and antioxidant properties, synergistic properties as well as their cytotoxicity. Methods: ­Ethanolic herbal extracts were used to perform minimal ­inhibitory (MIC) and minimal bactericidal concentration (MBC) assays on common skin pathogens. Synergistic anti­microbial activity was evaluated by a chequerboard assay. Antioxidant and synergistic properties were assessed by a 1,1-diphenyl-2-picrylhydrazyl assay. Cytotoxicity was tested on normal adult human primary epidermal keratinocytes. Results: All extracts showed an inhibitory effect on growth of all microorganisms tested. MIC and MBC values ranged from 0.0625 to 32 mg/mL and from 0.0625 to >256 mg/mL, respectively. A. ebracteatus extract markedly demonstrated bactericidal activity against an methicillin-resistant Staphylococcus aureus strain. Additive antimicrobial activity was observed (fractional inhibitory concentration index values: 0.75–1). All extracts possessed antioxidant properties (IC₅₀ values: 0.12–0.25 mg/L). However, antagonism was observed with paired extract combinations (combination index values: 1.025–1.455). The cell viability assay confirmed that herbal extracts were not cytotoxic. Conclusions: Our results provide early findings of pharmacological activities to support a novel choice of herbal combinations as potential local skin treatment options for xerosis cutis.