IN VITRO AND IN VIVO EVALUATION OF ANTI TRYPANOSOMAL EFFECTS OF THREE TROPICAL MEDICINAL PLANTS

Abstract

Trypanosomosis is a fatal and chronic disease that is a threat to human and animal health caused by species of Trypanosoma. In Africa, trypanosomes are transmitted cyclically by about 30 species and sub species of tsetse fly (Glossina spp) or occasionally, mechanically by biting flies (Tabanus). Due to high cost of developing and licensing new drugs, international pharmaceutical companies have shown little interest in the development of new trypanocide. In this vein some workers have suggested the use of locally produced trypanocides. Hence, the objective of this study; which is to analyze the trypanocidal efficacy of some selected plants against Trypanosoma brucei infection in vitro and in vivo and also to study the phytochemical properties, free radical scavanging activities and toxicity of the selected plants. Six plant extracts from three tropical medicinal plants (Spondia mombin, Hura creptan and Ceiba pentandra) traditionally used for treatment of malaria in Nigeria were investigated in this study. Preliminary phytochemical screening and DPPH (1,1-dipheny 1-2-picrylhydrazyl) free radical scavenging activities of all extracts was performed by standard procedures. Acute toxicity test and LD50 dose determination procedure was performed for the extracts. All six extracts were investigated for their in vitro antitrypanosomal activities against Trypanosoma brucei. The best two extracts with the most efficacious in vitro activity were subjected to in vivo evaluation in Wistar albino rats. Ethanolic extracts of the leaves and methanolic extracts of the stem bark of each plant were obtained. Saponin and glycosides were present in all extracts except Hura creptan bark. Alkaloids, flavonoids, and tannins were present in all extracts except Ceiba pentandra bark. Phenols and carbohydrates were present in all extracts, however proteins were absent in Hura creptan bark and leaves but present in the others. The percentage scavenging activity of DPPH radical was found to be highest in Spondia mombin leaves (87.03%), followed by Ceiba pentandra leaves (86.50%), Spondia mombin bark (83.93%), Hura creptan leaves (83.93%) and Hura creptan bark (80.59%) in that order. The least percentage scavenging activity of DPPH radical for extracts tested was recorded in Ceiba pentandra bark with 39.13%. The methanolic extract of Spondia mombin bark has the highest LD50 value of 5000 mg/kg while Spondia mombin leaves has the value of 1788.85 mg/kg. Ethanolic extract of Ceiba pentandra leaves and methanolic extract of Hura creptan bark has LD50 values of 774.59 mg/kg and 470 mg/kg respectively. Hura creptan leaves has value of 178.88 mg/kg, while methanolic extract of Ceiba pentandra bark has the least LD50 value of 141.42mg/kg. All six extracts tested, except methanolic extract of Hura creptan bark showed varying degree of in vitro antitrypanosomal activity which was concentration-dependent. Ethanolic extracts of Spondia mombin leaves and methanolic extracts of Spondia mombin bark showed the best in vitro results and were thus subjected to in vivo analysis. Extracts of Spondia mombin leaves exhibited in vivo antitrypanosomal effect at 225 mg/kg body weight while doses 890 mg/kg and 450 mg/kg of the extracts were able to clear parasites from circulation within 3 and 5 days of treatment, respectively. Extracts of Spondia mombin bark showed antitrypanosomal effects at 2500 mg/kg and 1250 mg/kg but could not clear the parasites completely. In both extracts tested in vivo, there was prolongation of survival period of up to eleven (11) days for ethanolic extracts of Spondia mombin leaves and nine (9) days for methanolic extract of Spondia mombin bark as compared to three (3) days observed in the untreated control group in this experiment. Histopathological changes were observed in all infected groups with the lesions being more prominent and irreversible in infected untreated group (untreated control) and being lesser in group treated with Diminanene aceturate at 3.5 mg/kg, as well as in group treated with Spondia mombin leaves at 890 mg/kg. The study therefore showed that extracts of Spondia mombin are relatively safe, has high radical scavenging activity and demonstrated high degree of in vitro and in vivo antitrypanosomal effect against Trypanosoma brucei in rat models. This plant may therefore add to the arsenals of botanical antitrypanosomal agents.