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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #109082
Title: STRUCTURE-ACTIVITY RELATIONSHIPS OF QUERCETIN IN ANTAGONIZING HYDROGEN PEROXIDE-INDUCED CALCIUM DYSREGULATION IN PC12 CELLS

Author
item WANG - HNRCA-TUFTS
item Joseph, James

Submitted to: Free Radicals in Biology and Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/1999
Publication Date: N/A
Citation: WANG, .H., JOSEPH, J.A. STRUCTURE-ACTIVITY RELATIONSHIPS OF QUERCETIN IN ANTAGONIZING HYDROGEN PEROXIDE-INDUCED CALCIUM DYSREGULATION IN PC12 CELLS. FREE RADICALS IN BIOLOGY AND MEDICINE.

Interpretive Summary: Oxidative stress can induce neurotoxic insults by increasing intracellular calcium (Ca2+), which has been implicated in various neurodegenerative diseases in aging. Previously, we showed that the hydrogen peroxide- induced calcium dysregulation in PC12 cells including: 1) increased in calcium baselines; 2) decreased depolarization-induced calcium influx; and 3) failure to recover the Ca2+ levels. In the present experiments, we investigated whether a dietary flavonoid, quercetin, can antagonize these effects and its possible structure-activity relationships by comparing the results with four other flavonoids. Each flavonoid has slightly different structures from quercetin and its efficacy was examined in same cell model. Our results indicated that two structural components, including: 1) 3', 4'-hydroxyl (OH) groups in the B ring; 2) 2,3-double bond in conjugation with a 4-oxo group in C ring along with the polyphenolic structures were crucial for the protection. These structural components are found in quercetin, and this compound was also the most efficacious in reducing the H2O2-induced Ca2+ dysregulation in cells, as well as oxidative stress assessed via the dichlorofluorescein assay. Collectively, these data indicated that the particular polyphenolic structural components in quercetin provided its strong antioxidant property in protecting cells against H2O2-induced oxidative stress and calcium dysregulation.

Technical Abstract: The mechanisms of H2O2-induced elevated calcium baselines in PC12 cells wer investigated in the present study by using fura-2-fluorescent imaging analysis. The results showed that while the calcium comes from both intracellular and extracellular sources, only the extracellular calcium influx was responsible for the sustained post-H2O2-exposure increases. This scalcium influx was partially blocked by calcium channel antagonists [verapamil (L-type) or mibefradil (non-selective)], and was more effectively blocked by sodium channel antagonist, tetrodotoxin (TTX). Membrane depolarization following H2O2 exposure, as measured by using a membrane potential sensitive dye, DiBac4(3), contributed to the opening of the ion channels. The H2O2-induced calcium influx was blocked by TTX even in a sodium-free buffer indicating that calcium directly fluxed through sodium channels. Sodium-calcium exchangers (NCX) did not play a role since using a specific reverse mode NCX inhibitor, No. 7943, was ineffective to block the influx. The H2O2-induced calcium influx can be mimicked by using a thiol selective oxidizing reagent, 2',2'-dithiodipyridine, and in both situations, the calcium levels were completely reversed by a thiol selective reducing reagent, dithiothreitol. Our results indicated that mechanisms of oxidant induced elevated calcium baselines in PC 12 cells involved calcium influx through sodium and calcium channels that may be directly or indirectly attributed to thiol oxidation.