Protective effects of fermented onion juice containing higher amount of querectin aglycone against oxidative stress by 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) treatment in Sprague–Dawley rats

It has been reported on beneficial effects of onion extracts containing a large amount of quercetin glucosides for several decades. This study was performed to investigate antioxidative and hepatoprotective effects of fermented onion (Allium cepa L.) extracts containing higher amount of quercetin aglycone (FOQ) against oxidative stress by 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) treatment in rats. RP-HPLC analysis elucidated that the fermented onions contain larger amount of quercetin aglycone than that of fresh onions, and the content of quercetin aglycone in 1.0 kg of fresh and fermented onion pickles was 261.34 ± 19.47 and 360.25 ± 27.32 mg, respectively. In vitro free radical scavenging assay showed potently radical-quenching ability of FOQ against reactive oxygen species (ROS) such as hydroxyl, superoxide, and carbon-centered radical using electron spin resonance (ESR) spectroscopy. Biological parameters in plasma and liver tissue were evaluated with 36 healthy Sprague–Dawley rats in the experimental groups (n = 6); control (basal diet), AAPH treated, quercetin aglycone treated, ascorbate-AAPH treated, quercetin aglycone-AAPH treated and FOQ-AAPH treated group. The results revealed that quercetin aglycone or FOQ intakes could increase the level of glutathione (GSH), enzymatic activity of glutathione reductase (GSSG-R), and catalase (CAT), but could decrease the level of glutamate oxaloacetic transaminase (GOT), glutamate pyruvate transaminase (GPT), thiobarbituric acid reactive substance (TBARS) production with the abnormal levels caused by AAPH induced oxidative stress. Moreover, histological study for central vein (CV) area of hepatic lobule was illustrated that cytoplasmic phase near the CV in the qurecetin and FOQ pretreated before AAPH injection could be maintained with normal morphology like that of the control. The present study illustrated that the fermented onion extracts containing larger amount of quercetin aglycone (FOQ) have antioxidative activities against AAPH-induced carbon-centered radical, and its activity can present the protective effect against hepatic damage by oxidative stress similar with the ability of ascorbate (vitamin C).