NEUROPROTECTIVE PROPERTY OF AIDAN (TETRAPLEURA TETRAPTERA TAUB.) IN TRANSIENT, PERMANENT AND IN VITRO CEREBRAL ISCHEMIA EXPERIMENTAL MODELS OF CEREBROVASCULAR ACCIDENT

Abstract

Cerebrovascular accident (stroke) remains a leading cause of death and morbidity worldwide with no effective therapeutic drug despite decades of intensive research. However, emerging trends show that medicinal plants could be promising sources of effective bioactive agents for the management of the disease. This study evaluated the effects of Tetrapleura tetraptera fruit extract, ethnomedicinally used for the management of epilepsy and convulsion, in in vitro and in vivo models of stroke. Methanol extract of Tetrapleura tetraptera fruit (TT) was prepared by maceration, qualitatively and quantitatively screened for phytoconstituents and tested for in vitro antioxidant activity, followed by toxicity profiling in male Wistar rats. In transient stroke model, male Wistar rats were pretreated with TT 50, 100 and 200 mg/kg TT (represents 1/10th, 1/50th and 1/100th of the LD50, respectively) for 7 days before 30 min of bilateral common carotid artery occlusion and 24 h of reperfusion (BCCAO/R). Animals were assessed for neurobehavioural deficits and biochemical estimations of markers of redox status, inflammation, ion dyshomeostasis, mitochondrial dysfunction, excitotoxicity and neurotransmitter dysregulation were performed on cortex, striatum and hippocampus of the brain, with the assessment of hippocampal histoarchitecture. In the permanent model, mice were pretreated with TT for 7 days before 15 min photothrombotic lesion (PTL) of the somatosensory cortex, followed by 3 days of post-treatment with TT. The expression of glutamate and neuromodulator receptors, as well as calcium binding protein and glial fibrillary acidic protein (GFAP) were evaluated by protein immunoblotting, while reactive GFAP astrocytes were evaluated immunohistochemically. In the in vitro model, primary astrocytes were treated with TT prior to hypoxia, and cell viability and mitochondrial membrane potential of astrocytes were evaluated. Chromatographic and spectroscopic analysis were carried out on TT to isolate bioactive compounds. Phytochemical screening revealed the presence of saponins, tannins, polyphenols, terpenoids and sterols and HPLC-DAD fingerprinting shows the presence of the marker compound, aridanin (0.36 ± 0.00 mg/g). TT demonstrated appreciable in vitro antioxidant capacity and radical scavenging activity compared with reference standards. With LD50 greater than 5000 mg/kg b.wgt, TT was not toxic after oral administration of varying dosages. In transient experimental stroke, BCCAO/R caused neurobehavioral deficits, with over 50% decreased level/activity of GSH, catalase, superoxide dismutase, lipid peroxidation, xanthine oxidase, myeloxyperoxidase and LDH which were ameliorated by treatment with TT at all tested doses in all brain regions (p<0.05). Alterations to level/activity of Na+, K+, Na+/K+ ATPase, complex I, glutamine synthetase, acetylcholinestrase and dopamine metabolism in rats subjected to BCCAO/R were significantly amended by treatment with TT. In permanent stroke model, PTL caused over 50% decreased expression of GluR1, NMDAR1, TrkB and increased expression of calbindin D28K and GFAP, which was reversed by treatment with TT (p<0.05). In in vitro stroke model, TT significantly protected astrocytes from cell death and prevented alteration in mitochondrial integrity after hypoxia. Aridanin, egosterols and sucrose were characterized from TT. These results suggest TT elicited neuroplastic response to pathophysiologies occasioned by ischemia/reperfusion injury. Therefore, Tetrapleura tetraptera could be a source of new therapeutic agents for treating ischemic stroke.