Chemical Composition and Biological Activities of the Essential Oil of Plectranthus caninus Roth

Abstract:

The essential oil from the aerial parts of Plectranthus caninus Roth (Lamiaceae), obtained by hydro-distillation was analyzed by gas chromatography/mass spectrometry (GC /MS) and evaluated for antimicrobial, free radical scavenging and anti-inflammatory activities. Thirty-four compounds representing 91.02% of the total oil were identified. The major constituents of the oil were camphor (22.36%) and α-thujene (14.48%). The oil was tested against 21 bacterial and 4 fungal strains using disc diffusion method and found to be active against a broad spectrum of pathogens including Gram-positive and Gram-negative bacteria as well as some fungal strains. The minimum inhibitory concentrations (MICs) of the oil against the bacterial strains tested ranged from 10 to 400 μg/ml, and from 800 to 1000 μg/mL against the fungal strains employed. The in vitro antioxidant activity was assessed using 2,2-diphenyl- 1‑picrylhydrazil (DPPH) radical scavenging assay. The oil reduced DPPH in a concentration dependent manner with an EC ₅₀ value of 3.5 μl/ml. The in vivo anti-inflammatory activity was evaluated on the basis of inhibition of carrageenaninduced mouse hind paw oedema whereby doses of 200 and 300 mg/kg were found to inhibit significantly increase in paw volume during the late phase of inflammation. The study provides evidence for the broad-spectrum antimicrobial, significant antioxidant and anti-inflammatory effect of Plectranthus caninus essential oil, a possible explanation for the traditional use of the plant in the treatment of cold, teeth and gum disorders which may be related to microbial infections and inflammation.

Key words: Anti-inflammatory activity, antimicrobial activity, camphor, free radical scavenging activity, hydro-distillation.