Polyphenols in red pepper [Capsicum annuum var. aviculare (Tepin)] and their protective effect on some pro-oxidants induced lipid peroxidation in brain and liver

Polyphenols exhibit a wide range of biological effects because of their antioxidant properties. The study sought to carry out a comparative studies on the protective ability of free and bound polyphenol extracts of red Capsicum annuum var. aviculare (Tepin) on brain and liver - in vitro. Free polyphenols of red Capsicum annuum var. aviculare (Tepin) were extracted with 80% acetone, while the bound polyphenols were extracted with ethyl acetate from acid and alkaline hydrolysed residue from free polyphenols extract. The phenol content, Fe(II) chelating ability, OH radical scavenging ability and protective ability of the extract against some pro-oxidant (25 μM Fe(II), 7 μM sodium nitroprusside and 1 mM quinolinic acid)-induced lipid peroxidation in brain and liver was subsequently determined. The results of the study revealed that the free polyphenols (218.2 mg/100 g) content of the pepper were significantly higher (P<0.05) than the bound polyphenols (42.5 mg/100 g). Furthermore, the free polyphenol extract had a significantly higher (<0.05) Fe(II) chelating ability, OH radical scavenging ability than the bound polyphenols. In addition, both extracts significantly inhibited (P<0.05) basal and the various pro-oxidant (25 μM Fe(II), 7 μM sodium nitroprusside and 1 mM quinolinic acid)-induced lipid peroxidation in rat's brain and liver in a dose-dependent manner. However, the free polyphenols caused a significantly higher inhibition in the MDA (malondialdehyde) production in the brain and liver homogenates than the bound phenols. In conclusion, Capsicum annuum var. aviculare (Tepin) contains 83.7% free soluble polyphenol and 16.3% bound polyphenols. In addition, both polyphenolic extracts inhibit the various pro-oxidant agents (Fe²⁺, sodium nitroprusside and quinolinic acid) induced lipid peroxidation in brain and liver tissues in a doe-dependent manner. However, the free polyphenols had higher protective ability than the bound polyphenols. The main mechanism through which they are carry out their protective effect against lipid peroxidation in the brain and the liver is by Fe(II) chelating ability, OH and NO radicals scavenging ability and inhibition of over-stimulation of NMDA receptor.