Synergistic-antagonistic interaction of traditional herbs Acalypha indica, Centella asiatica, and Sesbania grandiflora: In antifungal-demelanising activities and nitric oxide immunomodulatory responses

Abstract

Aims:The oriental-based herbs Acalypha indica (AI), Centella asiatica (CA), and Sesbania grandiflora (SG) possess a broad range of undisclosed therapeutic activities which are edible and easily available throughout the year. To convert the herb extracts into a potential drug form, aqueous (A) and methanol (M) extracts of herbs were assessed alone and in combination for their antifungal-demelanising activity and nitric oxide (NO) immunomodulatory responses. A new bioactive synergistic and antagonistic assessments approach was made on these herbs to identify which extract combination qualifies as a natural drug candidate. Methodology and results: Via micro-dilution technique, methanol extract of A. indica (AI-M) showed the strongest antifungal activity against Aspergillus niger, with a minimum inhibitory concentration (MIC) of 50 mg/mL and a minimum fungicidal concentration (MFC) of 100 mg/mL. Sublethal (50 mg/mL) and subinhibitory (25 mg/mL) doses of AI-M produced the optimal black pigmentation reduction to demelanise A. niger. The combinations AI-M+CA-M, AI-M+SG-M, and CA-M+SG-M showed similar antifungal activities (MIC = 100 mg/mL). At 500 µg/mL, CA-A and the combination CA-A+SG-A successfully induced RAW264.7 cells to produce NO at 17.85 µM and 40.84 µM, respectively. The combination of herbs extract showed synergistic interaction towards stimulation of NO production. In contrast, they demonstrated antagonism towards antifungal-demelanising properties. Compound identification of AI-M, SG-M, and SG-A were performed using a UHPLC-QTrap-MS/MS system, which detected phenolic compounds from various groups (cinnamic acids, benzoic acids, and flavonoids). Conclusion, significance and impact of study: The combination of herb extracts showed better stimulation of NO production while the single herb extracts demonstrated good antifungal-demelanising activity. These findings help in the selection of herbs combination for potential natural drug discovery. A good combination of herbs demonstrated synergism to execute better bioactivities compared to individual herb extracts.