Acute Oral-toxicity, Anti-inflammatory and Analgesic Effects of Aqueous and Methanolic Bark Extracts of Piliostigma Thonningii (Schum) in Mice

Abstract

Aqueous and methanolic extracts of some medicinal plants in African have been shown to have anti-inflammatory and analgesic effects. Previous studies have documented diverse ethno-medical applications of various plants, including Piliostigma thonningii, a leguminous herb in the family Caesalpiniacea. As a way of establishing the scientific justification for the ethno-medical use of Piliostigma thonningii (Schum) bark extracts, the current study was designed to evaluate acute oral toxicity, anti-inflammatory and analgesic effects of aqueous and methanolic stem bark extracts of P. thonningii. In this study, fresh stem barks of P. thonningii were obtained from Kiangombe forest in Embu County, where the plant grew naturally with the help of a renowned herbalist. Voucher specimen was prepared and authenticated by a taxonomist at the East Africa herbaria at the National Museums of Kenya. Methanolic extracts were prepared by cold maceration using analytical grade methanol whereas aqueous extracts were obtained through the freeze-drying process according to standard phytochemical methods. The extracts were stored in refrigerator set at 4oC and retrieved only during use. Acute oral toxicity was investigated according to the Up-and-Down-Procedure described by the OECD/OCDE document number 425 guidelines. Anti-inflammatory effects of the aqueous and methanolic stem bark extracts of P. thonningii were done using the xylene-induced ear-oedema in Swiss albino mice. Peripheral analgesic effects of the aqueous and methanolic stem bark extracts of P. thonningii were performed using the acetic acid induced writhing technique on mice. Acute oral toxicity data was analyzed and interpreted according to the OECD guidelines. Anti-inflammatory and analgesic assay data were descriptively analysed and the expressed as Mean±SEM. One-way ANOVA was done to determine differences among means followed by Tukey’s post hoc test, or un-paired student t-test were performed appropriately for pairwise comparison and separation of means at α=0.05. The acute oral toxicity assay results revealed that all the studied plant extracts were safe with LD50 value of >2000 mg/Kg BW. Anti-inflammatory results showed that, the aqueous extract at a dose levels of 100 mg/Kg BW and 500 mg/Kg BW and the methanolic extract at a dose of 500 mg/Kg BW caused significantly higher percentages of xylene-induced oedema in mice than that caused by the reference drug, dexamethasone (p<0.05). A comparison between the effects of the two studied plant extracts on xylene-induced ear oedema in mice showed that the aqueous stem bark extract of P. thonningii at all the studied dose levels produced significantly higher percentage inhibition of oedema as compared with the percentage inhibitions caused by the methanolic extract at the same dose levels (p<0.05). On the other hand, analgesic activity data revealed that the aqueous extract at the highest dose of 500 mg/Kg BW reduced acetic acid induced writhing frequency significantly more than the standard drug, Acetylsalicylic acid (p<0.05). A comparison between the percentage inhibitions of writhing frequencies in mice treated with the studied plant extracts was done. The aqueous stem bark extract treated mice, at all doses exhibited significantly lower writhing frequencies compared with the frequencies recorded by mice that received the methanolic stem extract (p<0.05). The remarkable anti-inflammatory and analgesic effects of these extracts could be attributed to the presence of active phytochemicals, which target various pathways leading to mitigation and modulation of these conditions. Furthermore, the safety of these extracts could be due to low concentration/absence of toxic phytocompounds. This in part explains the use of this plant in the traditional management of pain and inflammatory disorders. From the obtained results, the aqueous and methanolic stem bark extracts of P. thonningii possess anti-inflammatory and analgesic properties and are safe. Further studies aimed at isolating and characterizing active compounds responsible for the reported activities are recommended.