Antimicrobial constituents of Artemisia afra Jacq. ex Willd. against periodontal pathogens

Abstract

The phytochemical investigation of an ethanol extract of Artemisia afra, led to the isolation of six known compounds, Acacetin (1) 12α,4α-dihydroxybishopsolicepolide (2), Scopoletin (3) α-amyrin (4), Phytol (5) and a pentacyclic tri-terpenoid Betulinic acid (6). The isolated compounds were evaluated for their anti-microbial activity against Gram positive (Actinomyces naeslundii, Actinomyces israelii and Streptococcus mutans), Gram negative bacteria (Privotella intermedia, Porphyromonus gingivalis and Aggregatibacter actinomycetemcomitans previously known as Actinobacillus actinomycetemcomitans) and Candida albicans. The crude extract of A. afra inhibited the growth of all tested microbial species at concentration range of 1.6 mg/ml to 25.0 mg/ml. The compounds 1-6 also showed activity range at 1.0 mg/ml to 0.25 mg/ml. Three best compounds which showed good activity were selected for further studies. Cytotoxicity of the extract and compounds was determined using the XTT (Sodium 3’-[1-(phenyl amino-carbonyl)-3,4-tetrazolium]-bis-[4-methoxy-6-nitro] benzene sulfonic acid hydrate) cell proliferation kit. The antioxidant activity of the extract and compounds was done using the DPPH scavenging method. The extract showed good antioxidant activity with an IC50 value of 22.2 μg/ml. Scopoletin had a strong transformation of the DPPH radical into its reduced form, with an IC50 value of 1.24 μg/ml which was significant to that of vitamin C (1.22 μg/ml). Acacetin and Betulinic acid exhibited a decreased scavenging activity with the IC50 of 2.39 and 2.42 _g/ml, respectively. The extract and compounds showed moderate toxicity on McCoy fibroblast cell line and the extract influenced the release of cytokine against Hep2 cells. Scopoletin was relatively non-toxic with an IC50 value of 132.5 μg/ml. Acacetin and betulinic acid also showed a smooth trend of non-toxic effects at lower concentrations and toxic at higher concentrations with IC50 values of 35.44 and 30.96 μg/ml. The obtained results in this confirmed the use of A. afra in the treatment of microbial infections.