Phytochemical Insights and Bioactive Potentials of Alstonia scholaris, a Variety from Mizoram, India: Studies of the Antioxidant and Anti-Infective Properties

Abstract

A distinct variety of Alstonia scholaris in Mizoram, Northeast India, is a medicinal plant applied in the remedy of various ailments, including diarrhoea, dysentery, gastrointestinal infections, malaria and wounds. To evaluate A. scholaris bark for its secondary metabolite components, antioxidant, antibacterial, antifungal and anthelmintic properties. The chloroform extract of A. scholaris was chemically assessed for its phytocompounds. Antioxidant content was evaluated using phenol, flavonoid and total antioxidant estimations. Antioxidant reaction was determined using DPPH (2,2-diphenyl-1-picrylhydrazyl)-scavenging and ferric-reducing activities. Antimicrobial susceptibility assays were performed against bacteria and fungi. Anthelmintic activity was examined on a parasitic tapeworm of chicken. Carbohydrates, reducing sugars, phytosterols and saponins were detected as the main bioactive secondary metabolites. The plant extract possesses appreciable amounts of antioxidants, with the total phenolic content of 11.42±0.08 mg GAE/g (gallic acid equivalent), the total flavonoid content of 57.87±3.53 mg QCE/g (quercetin equivalent) and the total antioxidant capacity of 7.22±0.01 mg AAE/g (ascorbic acid equivalent). Free radical-scavenging estimation against DPPH (2,2-diphenyl-1-picrylhydrazyl) indicated a half-maximal Inhibitory Concentration (IC50) value of 28.96 µg/mL. The Ferric-Reducing Antioxidant Power (FRAP) assay showed a linear concentration-dependent antioxidation reaction similar to the standard ascorbic acid. It effectively inhibited Gram-positive bacteria (Bacillus cereus, Enterococcus faecalis and two strains of Staphylococcus aureus), as well as Gram-negative species (Escherichia coli and Salmonella typhi). A notable observation was its effectiveness against an antibiotic-resistant S. aureus. The antifungal efficacy against three pathogenic species was in the order Fusarium keratoplasticum<Aspergillus fumigatus<Candida albicans. It was highly effective against an intestinal tapeworm, causing structural damages in all vital parts of the parasite body as revealed by histology and scanning electron microscopy. The findings indicate that A. scholaris bark contains important bioactive compounds that are health benefit, antimicrobial and anthelmintic in nature. This is the first report on the broad-spectrum anti-infective potential of A. scholaris and provides an evident-based therapeutic value of the plant.

Keywords: Anthelmintic; Antifungal; Antibacterial; Antioxidant; Medicinal plant