Evaluation of the Inhibitory Effects of Quercetin-Related Flavonoids and Tea Catechins on the Monoamine Oxidase-A Reaction in Mouse Brain Mitochondria

Abstract

Quercetin, a typical dietary flavonoid, is thought to exert antidepressant effects by inhibiting the monoamine oxidase-A (MAO-A) reaction, which is responsible for regulation of the metabolism of the neurotransmitter 5-hydroxytryptamine (5-HT) in the brain. This study compared the MAO-A inhibitory activity of quercetin with those of O-methylated quercetin (isorhamnetin, tamarixetin), luteolin, and green tea catechins ((-)-epicatechin, (-)-epicatechin gallate, (-)-epigallocatechin, and (-)-epigallocatechin gallate) by measuring the formation of the oxidative deamination product of 5-HT, 5-hydroxyindole aldehyde (5-HIAL), in mouse brain mitochondria. Quercetin was inferior to luteolin in the inhibition of MAO-A activity, whereas isorhamnetin, tamarixetin, and tea catechins scarcely exerted inhibitory activity. Quercetin did not affect MAO-A activity in mouse intestinal mitochondria, indicating that it does not evoke side effects on the metabolism of dietary monoamines in the gut. These data suggest that quercetin is a weak (but safe) MAO-A inhibitor in the modulation of 5-HT levels in the brain.

Extraction, partial purification and characterisation of vanillic acid decarboxylase fromAlicyclobacillus acidoterrestrisDSM 3923

“…When the concentration increased to 1.0 mmol L −1 , VAD activity was completely inhibited by cinnamic acid, ferulic acid, resveratrol, quercetin and rutin. Polyphenols, especially flavonoids, were described to inhibit numerous unrelated enzymes . The inhibition mechanism may be due to the binding of these molecules to enzymes through hydrogen bonding, hydrophobic interactions, metal chelation and ππ ‐stacking …”

Isoquercetin Could Protect Against Ovariectomy-Induced Neuronal Changes in Rats

“…These results are in accordance with [41] who concluded that quercetin can protect against CNS toxicity by reverting dopamine activity. On the other hand [44] suggest that isoquercetin is a weak (but safe) MAO-A inhibitor in the modulation of 5-HT levels in the brain. Moreover [42] indicate that piperine can enhance the antioxidant and antiinflammatory properties of isoquercetin, and exhibits strong neuroprotective effects against neurotoxicity.…”

Protective action of green tea catechins in neuronal mitochondria during aging

“…The H 2 O 2 produced during dopamine oxidation may interact with free iron to form highly reactive hydroxyl radicals that can damage nucleic acids, proteins and membrane lipids, and lead to neuronal degeneration (6). Interestingly, EGCG has been reported to be an effective MAO B inhibitor in adult rat brain (111), although neither EC, EGC, ECG nor EGCG affect MAO A activity in mouse brain mitochondria (112). This inhibition of MAO B activity may well underlie part of the neuroprotective effects of EGCG.…”