Toxicity and Antiviral Activities of Some Medicinal Plants Used by Traditional Medical Practitioners in Zimbabwe

Abstract

Genital herpes, usually caused by Herpes Simplex Virus type-2 (HSV-2), is the commonest sexually transmitted disease especially amongst rural women in Southern Africa including Zimbabwe. This predisposes them to HIV/AIDS infection, cancer and opportunistic infections (OIs). Current antiviral treatments are often cytotoxic and/or ineffective. This motivates active research to find alternative safer drugs or lead drugs from traditional medicinal sources. Twenty six (26) methanol extracts from commonly used and often endangered plant species (14) used by communities and traditional medical practitioners for treating illnesses and sexually transmitted diseases from 5-selected districts of Zimbabwe were investigated for toxicity by Brine shrimp lethality test (BSLT) and by 50% Cytopathic effect on VERO cultured cells. The extracts were also tested for antiviral activity against Herpes Simplex Virus-2 (HSV-2) by the End Point Titration Technique (EPTT) and Neutralisation Test (NT) on VERO cells. Results from the BSLTs ranged 66.66 - 4304 μg/ml; 50% Cytopathic effect from 19.53 - 312 μg/ml whilst the NT ID 50 values ranged from 10.41 - 125 μg/ml. The antiviral EPTT reduction factor (RF) was 1 - 10 4 with 13 extracts showing RF ≥ 10 3 . All the plant extracts had moderate to high toxicity (LC 50 , 789 - 66 μg/ml) in the BSLT. Six extracts had LC 50 values greater than 1000 μg/ml. All 26 extracts were cytotoxic with CC 50 values < 500 ug/ml of which 19 were more toxic CC 50 < 100 ug/ml. Nine extracts had in vitro therapeutic indexes ≥ 3.7. Cassia abbreviata , Dichrostachys cinerea and Hypoxis hemerocallidea had therapeutic indexes (TI) 7.5 - 15.0. The more active plant extracts were from roots and root tubers. The results confirm the rationale for the use of traditional medicinal plants by traditional medical practitioners for treating various diseases and could bring awareness for their better use and improve conservation. The results also provide an opportunity to develop more efficacious drugs by isolating lead compounds and determining their mode of action.