Recovery effect of onion peel extract against H2 O2 -induced inhibition of gap-junctional intercellular communication is mediated through quercetin.
Cellular oxidative damage mediated by reactive oxygen species has been reported to inhibit gap-junctional intercellular communication (GJIC). In turn, the inhibition of GJIC can be attenuated by functional food compounds with antioxidant properties. In this study, we compared the protective effects of onion peel extract (OPE) and onion flesh extract (OFE) on oxidative stress-mediated GJIC inhibition, and investigated the mechanisms of action responsible. OPE restored H2 O2 -induced GJIC inhibition to a higher degree than OFE in WB-F344 rat liver epithelial cells. OPE was found to inhibit H2 O2 -induced phosphorylation of ERK1/2 and Cx43. A radical scavenging assay demonstrated superiority of OPE over OFE, suggesting that the observed effects might be mediated via an antioxidant mechanism. Quercetin is the major compound that is likely to be responsible for the protective effect against H2 O2 -mediated GJIC inhibition. This study suggests that OPE, a material often discarded, may be of value for the future development of functional food products.


CONCLUSIONS
This study demonstrates that onion peel extract (OPE) exhibits a protective effect against the inhibition of gap-junctional intercellular communication (GJIC) mediated by H2 O2 , which is likely to occur via its antioxidant activity. OPE contains significant concentrations of bioactive phenolic compounds. Reductions in oxidative stress can lead to recovery of GJIC, which has been reported to be implicated in the prevention and treatment of cancers. These findings suggest that onion peel, a common waste product, could be used as potential resources for functional food development. Onion peel could be processed into a quercetin-rich powder or a pill for the prevention of cancer and other oxidative stress-related diseases.
Dept. of Agricultural Biotechnology, Seoul Natl. Univ, Seoul 151-921, Republic of Korea; Food Safety Center, Ottogi Corp, Gyeonggi-Do 431-070, Republic of Korea.
Young-Jun
YJ
Kim
Sang Gwon
SG
Seo
Keunhwa
K
Choi
Jong Eun
JE
Kim
Heerim
H
Kang
Min-Yu
MY
Chung
Ki Won
KW
Lee
Hyong Joo
HJ
Lee
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002450:Cell Communication / Q000187:drug effects*; D018031:Connexin 43 / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D017629:Gap Junctions / Q000187:drug effects* / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D019697:Onions / Q000737:chemistry*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D010766:Phosphorylation / Q000187:drug effects; D018517:Plant Roots; D011794:Quercetin / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344
D000975:Antioxidants; D018031:Connexin 43; D011794:Quercetin; D048052:Mitogen-Activated Protein Kinase 3
connexin (Cx) 43; gap-junctional intercellular communication (GJIC); onion peel extract (OPE); quercetin; reactive oxygen species (ROS)