Chemical composition and Toxicological evaluation of the aqueous leaf extracts of Plectranthus amboinicus Lour. Spreng

Abstract

Ethnopharmacological relevance: Plectranthus amboinicus is used in traditional medicine to treat several diseases and ailments including opportunistic infections associated with HIV/AIDS. However, there is little insight as to the possible toxic effects of this herbal formulation on major organ systems of the body. This study was designed to assess the acute and sub acute toxic effects of the aqueous leaf extract of P. amboinicus on the histology of tissues, biochemical (liver and kidney functions) as well as hematological indices in albino swiss mice and wistar rats respectively. Materials and methods: In this study, phytochemical screening of the aqueous extracts of P. amboinicus was carried out using standard qualitative and quantitative (SPME and GCMS) analytical methods. The extracts were tested for acute toxicity in mice and for sub acute toxicity in Wistar rats according to the OECD guidelines No 425. In acute toxicity test, the dose of 5000 mg/kg was used as the limit dose test. The sub acute toxicity test was evaluated through biochemical, hematological, histopathological and body weight of rats using daily doses of 2500 mg/kg, 1250 mg/kg and 625 mg/kg of the aqueous extract for 28 days. Any signs of toxicity were recorded. Histopathological examination was done on the liver, kidneys, lungs and intestines. Body weight changes were measured weekly for 28 days of daily single dose of extract administration. Results: Phytochemical screening of the aqueous extracts revealed the presence of tannins, saponins, flavonoids, steroid glycosides and polyuronides. GCMS analysis revealed the presence of 11 chemical compounds constituting 97.6% of the total extract composition. The principle constituents include linalool (50.3 %), nerol acetate (11.6%), geranyl acetate (11.7 %) and carvacrol (14.3%). In acute toxicity, the extracts did not cause any mortality or evidence of adverse effects following oral administration of the highest dose of 10,000 mg/kg of crude extract in both mice. In sub acute study, normal body weight gains were observed during the study period compared to the control group. The kidney function parameters (Urea, creatinine, uric acid) were significantly increased following administration of extract. Histopathological examination of extract treated groups showed necrosis of hepatic cells with generalized congestion in the renal cortex, pneumonitis and sloughing of intestinal villi. Conclusion: The aqueous extract is rich in phytochemical compounds that are of therapeutic value. No mortalities were observed during acute and sub acute toxicity study period. These finding indicate that the extract caused treatment- related toxicological abnormalities which increased with dosage. The aqueous extract of P. amboinicus is safe to use as indicated by the high LD50 value, but should be used with caution at high doses.