Aqueous fraction of Alstonia boonei de Wild leaves suppressed inflammatory responses in carrageenan and formaldehyde induced arthritic rats.

Alstonia boonie de Wild is an ethnomedical plant used as therapy against inflammatory disorders. This study evaluated the most active anti-inflammatory and anti-oxidant fraction of A. boonei leaves using in vitro and in vivo models. Quantitative phytochemical analysis, anti-protein denaturation and hypotonicity-induced hemolysis of human red blood cell membrane (HRBC), radical scavenging activity assays, carrageenan and formaldehyde-induced inflammation models were carried out. Results showed that aqueous and ethyl acetate fractions of 70% methanol extract of A. boonie leaves contained high quantities of total phenolic and flavonoid compounds compared with hexane and butanol fractions. Aqueous fraction of A. boonie leaves significantly (P<0.05) inhibited heat-induced protein denaturation, stabilized hypotonicity-induced hemolysis of HRBC, scavenged DPPH, NO and H2O2 radicals in a concentration-dependent manner compared with other fractions in vitro. In addition, orally administered 50-250-mg/kg body weight (b.w.) aqueous fraction of A. boonei leaves suppressed carrageenan-induced rat paw edema thickness by 74.32%, 79.22% and 89.86% respectively at 6th h in a dose-dependent manner comparable with animals treated with standard diclofenac sodium (88.69%) in vivo. Furthermore, investigation of formaldehyde-induced inflammation in rats showed that 50-250 mg/kg b.w. aqueous fraction of A. boonei reduced plasma alanine aminotransferase and aspartate aminotransferase activities. Aqueous fraction of A. boonei also suppressed eosinophils, monocytes and basophils, total white blood cell, total platelet, neutrophil and lymphocyte counts and modulated plasma lipid profile compared with control group. Aqueous fraction of A. boonei leaves exhibited substantial active anti-inflammatory and antioxidant activities. Hence, an aqueous fraction of A. boonei leaves could be channeled towards pharmaceutical drug development. In addition, this study provided scientific insight to account for the traditional use of A. boonei leaves in ethnomedical practice.