Intracellular flavonoids as electron donors for extracellular ferricyanide reduction in human erythrocytes

Nitric Oxide (NO) Scavenging and NO Protecting Effects of Quercetin and Their Biological Significance in Vascular Smooth Muscle

“…The plasma concentrations of quercetin in humans on a normal diet are in the low micromolar range (0.3-2.2 M; Scalbert and Williamson, 2000), but quercetin rapidly penetrates the plasma membrane, reaching intracellular concentrations about 10-fold higher than those in the extracellular medium (Fiorani et al, 2002). However, these concentrations are still lower than those of oxyhemoglobin, which are in the high micromolar/low millimolar range.…”

“…Quercetin produced a characteristic 5,5-dimethyl-1-pyrroline-N-oxide-OH radical, indicating O 2 -derived radical production, that was detectable only at pH values Ն9 and auto-oxidation, measured by O 2 consumption, at pH values Ն8 (Canada et al, 1990 Interestingly, quercetin was much less effective in scavenging NO at pH 7 (i.e., the intracellular pH), suggesting a reduced NO consumption by quercetin intracellularly. On the other hand, quercetin rapidly accumulates intracellularly (Fiorani et al, 2002). In the cytosol, NO binds to the heme of soluble guanylate cyclase with very rapid kinetics (Ͼ1.4 ϫ 10 8 M Ϫ1 s Ϫ1 ), effectively competing with intracellular scavengers (Zhao et al, 1999).…”

Redox Reactions and Electron Transfer Across the Red Cell Membrane

“…RBC readily take up both of these flavinoids. The degree of enhancement cannot be explained by direct reaction with extracellular ferricyanide (29). Therefore, these flavinoids may also act as intracellular donors for this redox activity.…”

“…The latter observation is more likely to reflect endofacial NADH reductase activity or direct reduction of ferricyanide by NADH, rather than a lack of inhibition of NADH-dependent ferricyanide reductase activity. pCMBS inhibits the flavinoid-enhanced ferricyanide reduction (29) but not the fast phase of NADH-dependent ferricyanide reductase activity (7); an indication that this phase might be mediated by a different type of membrane reductant(s) rather than membrane protein sulfhydryls. The variability in sensitivity to sulfyhdryl agents is a good indication of the existence of a number of different membrane electron transport systems mediated by different processes, at least some involving membrane proteins.…”

Análise dos efeitos da epigalocatequina-3-galato (EGCG) de Camellia sinensis (chá verde) em modelo de hepatotoxicidade química experimental induzida pela Dietilnitrosamina (DEN)

“…A capacidade dos polifenóis vegetais em atuar como antioxidantes nos sistemas biológicos já foi reconhecida nos anos trinta (BENTHSATH, 1936), entretanto, este mecanismo antioxidante foi ignorado até pouco tempo. Para alguns derivados de ácidos fenólicos, tem sido relatada a excelente propriedade de quelação do ferro e de outros metais de transição, e neutralização da ação oxidativa dos radicais livres (FIORANI et al, 2002). Estudos realizados demonstraram que os polifenóis presentes no chá verde apresentam bioatividades importantes em certas patologias como: diabetes mellitus, cardiopatias, infecções virais, inflamações e em doenças degenerativas, como o câncer e o envelhecimento.…”