PHENOLIC CHARACTERIZATION, ANTI-INFLAMMATORY ACTIVITIES AND ANTI-NEUROPATHIC POTENTIALS OF STEM BARK EXTRACT OF AFRICAN BIRCH (Anogeissus leiocarpus DC. Guill & Perr.)

Abstract

Inflammation is a sequence of events that occurs in response to noxious stimuli, infection, trauma, or injury in the living tissues. Neuropathic pain can be defined as an abnormal pain state that arises from a damaged peripheral nervous system (PNS) or central nervous system (CNS). Osteoarthritis is a chronic inflammatory disease and it is also one of the leading causes of chronic morbidity in the developed world, mostly affecting the work force population throughout the world. Nonsteroidal anti-neuropathic and anti-inflammatory drugs including diclofenac, indomethacin are currently used for management of neuropathic pain and inflammatory disorders. These drugs have adverse side effects including gastrointestinal bleeding and peptic ulcers. Therefore, there is need to explore other sources especially of plant origin for new production of anti-inflammatory drugs that are readily available, more effective and less toxic than the synthetic drugs. The present research characterized the phenolic constituents, assessed the antioxidant, anti-inflammatory and anti- neuropathic potentials of stem bark extract of Anogeissus leoicarpus DC. Guill & Perr. Phytochemical screening, characterization of the bioactive constituents was carried out using High Performance Liquid Chromatography with Diode-Array Detection (DAD)-Mass Spectrometry (HPLC-DAD-MS), detection of saponins by NMR. In vitro antioxidant activity of stem bark extract of Anogeissus leoicarpus was also carried out using standard methods. Acute toxicity study using standard methods was performed to establish the LD50 of the extract. Rats were administered varying doses of stem bark extract of Anogeissus leoicarpus for 14 days followed by biochemical and haematological evaluations to assess sub chronic toxicity. The anti-inflammatory and anti-neuropathic potentials of stem bark extract of Anogeissus leoicarpus were carried out in formalin-induced inflammation in rats model and also in mono-iodo-acetate (MIA)-induced osteoarthritis in rats model. Male wistar rats were randomly distributed into normal control, induced control andformalin induced rats co-administered with hexane and ethanolic stem bark extract of Anogeissus leoicarpus (75, 150 or 300 mg/kg) and ibuprofen (400 mg/kg) ibuprofen serving as the reference group. After the treatments, assays for plasma biochemical parameters, tissue oxidative stress markers, pro-inflammatory markers levels of tumour necrosis factor alpha (TNF-α), interleukin-6 and interleukin-1β and histological examination were performed. For rat model of mono-iodo-acetate (MIA)-induced osteoarthritis, treatment was carried out based on the results generated from HPLC-DAD analysis. After the treatment, neurobehavioral effects, serum cytokine levels associated with osteoarthritis and histopathological examination were carried out. The results showed that study plant revealed the presence of flavonoids, tannins, terpenoids, sterols and saponins. According to Lorke’s method, the studied plant was safe and non-toxic to rats. (LD50 ≥ 5000 mg/kg). Anogeissus leoicarpus stem bark extract demonstrated high antioxidant capacity and radical scavenging ability in vitro. The results revealed that hexane extract has higher antioxidant and radical scavenging ability in vitro than ethanolic extract. HPLC analyses of the extract revealed a total of 59 compounds including 43 ellagitannins and 16 triterpenoids. The study plant is a good source of bioactive compounds (castalagin, ellagic acid, gallic acid, triterpenoids, saponins) that have been proven to have anti-inflammatory and neuroprotective potentials. The study plants reduced oxidative stress and improved biochemical and neurochemical dysfunction in formalin induced inflammation in wistar rats as well as in mono-iodo-acetate (MIA)-induced osteoarthritis in rats through its antioxidant, anti-inflammatory activities and anti-neuropathic potentials.