Anti-inflammatory, analgesic and antioxidant properties of Newbouldia Laevis (P. BEAUV.) stem bark extract

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Newbouldia laevis (fam. Bignoniaceae) commonly called the fence tree or African border tree is used traditionally in Ghana and other parts of Africa for the management of various inflammatory and pain conditions. This study evaluated the anti-inflammatory properties of hydro-alcoholic stem bark extract and reference drugs (diclofenac and dexamethasone) in acute inflammation using carrageenan-induced foot edema iii the 7- day-old chick (prophylactic and curative) and mouse (prophylactic). Adjuvant-induced arthritis in rat (prophylactic) was used to evaluate the effect of the extract and reference drugs (diclofenac and dexamethasone) in chronic inflammation. The antioxidant potential was evaluated using total phenol test, reducing power test, DPPH radical scavenging assay, and assay of lipid peroxidation. The analgesic effect of the extract was evaluated using the rat formalin test. Diclofenac and dexamethasone dose dependently inhibited carrageenan-induced foot edema in the 7-day old chick (prophylactic and curative) and mice (prophylactic). Similarly the extract (50-400 mg kg’ p.o.) dose dependently inhibited foot edema in the chicks with maximal inhibitions of 70.02± 5.05 and 51.73 ±6.91% for the prophylactic and curative protocols respectively. In the mice carrageenan-induced edema (prophylactic), the extract (30-300 mg kg-1 p.o.) produced a maximal inhibition of 75.51±10.07%. Diclofenac (10-100 mg kg-1 i.p.) and dexamethasone (0.3-3.0 mg kg-1 i.p.) caused significant inhibitions in both the acute and polyarthritic phase edema of the rat adjuvant-induced arthritis. On the contrary, the extract (10-100 mg kg’ p.o.) did not cause significant inhibition of the acute phase edema, but inhibited the polyarthritic phase edema by 25.30±2.53 - 28.11±2.02% in U-shaped fashion, The rank order of potency defined by ED50 values (in mg kg-1 was: dexamethasone> diclofenac> extract for all models of inflammation used. In the test for antioxidant properties, the extract showed a concentration dependent increase in phenol content expressed as tannic acid equivalent. The extract showed a concentration dependent reduction of Pe3+ to Fe2+ in the reducing power test, concentration dependent de-colorization of DPPH free radical solution, and a dose dependent inhibition of ascorbic acid/Fe3 induced lipid peroxidation in rat brain homogenate. The extract (10-300 mg kg-1 p.o.) and morphine (1-10 mg kg-1 i.p.) dose-dependently decreased formalin evoked nociceptive behaviour in both the first and second phases. Contrary to extract and morphine, diclofenac did not show any significant inhibition in the first phase, but dose dependently decreased nociceptive behaviour in the second phase. The potency of the drugs (defined by ED50 in mg kg-1) was in the order; morphine> extract> diclofenac for the first and morphine> extract > diclofenac for the second phase. All together, the observations of this study has shown that the hydro-alcoholic stem bark extract of N. leavis has anti-inflammatory and analgesic activities in animal models, and antioxidant properties which may play a significant role in its anti-inflammatory effects.
A thesis submitted to the Department of Pharmacology in partial fulfilment of the requirements for the degree of Master of Philosophy, 2006