CELLULAR ANTIOXIDANT PROPERTIES AND EFFECTS OF PHENOLIC-RICH EXTRACTS OF PEPPER (Capsicum spp) FRUITS ON SOME BIOMOLECULES IMPLICATED IN ALZHEIMER’S DISEASE

Abstract

This study investigated the neuroprotective properties of Capsicum spp on some biomolecules implicated in Alzheimer’s Disease pathology. Ripe and unripe pepper fruits [Capsicum annuum var. accuminatum (chilli/sombo); Capsicum annuum var. grossuum (bell pepper/tatase); Capsicum chinense (habanero/ata rodo)] were lyophilised and then pulverized. These fruits were thereafter extracted with a solvent mixture of 1M HCl and methanol (1:1, v/v). The total phenol and total flavonoid contents as well as the antioxidant activities in neuronal SH-Sy5y and endothelial Ea.Hy 926 cells were determined. The effects of the phenolic extracts on beta secretase, 3-hydroxy-3-methylglutaryl–coenzyme A reductase (HMGR), acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), glutathione peroxidase (GPx), glutathione reductase (GR) activities and amyloid aggregation were also determined. Phenolic constituents of the Capsicum spp were characterized using high performance liquid chromatography coupled with a diode array detector (HPLC-DAD). Total phenol contents of the ripe Capsicum spp, which ranged from 84.00±1.49mg/g (ata rodo) to 127.06±9.14mg/g (sombo) were significantly (P<0.05) higher than the unripe fruits [63.10±1.83mg/g (sombo) –76.69±1.80mg/g (tatase)], while the flavonoid contents of the ripe [18.11±2.74mg/g (sombo) – 43.89±0.78mg/g (tatase)] were significantly (P<0.05) lower than the unripe [34.73±1.48mg/g (sombo) – 46.31±1.48mg/g (tatase)]. The phenolic extracts had antioxidant activities in the neuronal and endothelial cells as typified by the cellular antioxidant activity; and also increased the activities of intracellular GPx and GR in both cell lines. Furthermore, the extracts inhibited beta secretase, AChE, BuChE and HMGR activities. Similarly, the phenolic extracts inhibited amyloid aggregation and also destabilized preformed amyloid fibrils. Quercetin and its glycosides were revealed by HPLC-DAD as being the most predominant phenolic compounds in Capsicum spp. The inhibitory effects of Capsicum spp on some of the key enzymes and biomolecules involved in AD pathology is an indication of their potential as nutraceuticals/functional food in the management of AD