In vitro and acute in vivo toxicity of the aqueous and chloroformic extracts of Rapanea melanophloeos (L) Mez

Abstract

This study was conducted to generate a toxicological profile of Rapanea melanophloeos, a medicinal plant widely utilized in traditional medicine to treat helminthiasis,using brine shrimp (Artemia salina) and Sprague Dawley (SD) rats. The aqueous extract showed potent in vitro toxicity to brine shrimp with a median lethal concentration (LC50) of 59.37μg/ml, while the extract chloroformic extract did not exhibit potent in vitro toxicity (LC50 of 1250 μg/ml), after exposure for 24 h. The acute toxicity study in rats indicated the no-observed-adverse-effect-level (NOAEL) and the lowest-observed-adverse-effect-level (LOAEL) of the aqueous extract to be 300mg/kg and 500mg/kg respectively, 24 h after single dosing. These values were lower than those of the chloroformic extract which had a NOAEL of 500mg/kg and a LOAEL of 1000mg/kg. The median lethal doses (LD50) of both extracts were above 7500mg/kg. The most overt signs of toxicity for both the aqueous and chloroformic extracts were depression, inactivity and somnolence, delayed reaction to stimuli, lethargy, piloerection and lackluster eyes. Recovery was complete in 24 h. Necropsy of the animals that died at the highest dose of both extracts revealed general congestion and enlargement of the liver, spleen and kidneys. There was mucoid content in the gastrointestinal tract of the animals dosed with the aqueous extract. At histopathology, the aqueous extract caused modest congestion of the kidney, liver and lungs, while the chloroformic extract did not change the histological appearance of any of the organs.The study shows that both extracts are harmless at the therapeutic doses and the plant is therefore unlikely to cause single dose toxicity at the curative doses used. This supports safe medicinal use of Rapanea melanophloeos and there is need to study prolonged toxicity of the plant.

Key words: In vitro toxicity, in vivo toxicity, LOAEL, NOAEL.