Oxydation of Quercetin by Salivary Components II. Effects of Quercetin on Reactive Oxygen Metabolism by Salivary Polymorphonuclear Leukocytes.

Abstract

Salivary polymorphonuclear leukocytes (SPMN) produce O 2-and H 2 O 2 reducing molecular oxygen, and quercetin is a phenolic compound found in vegetables and fruits. The aim of the present study was to elucidate the interaction between SPMN and quercetin. The oxygen consumption by SPMN, which was stimulated by phorbol myristate acetate (PMA), was suppressed by quercetin. Half-inhibition was observed at about 20 M quercetin. During inhibition of the oxygen uptake, quercetin was oxidized; the oxidation was inhibited by superoxide dismutase and enhanced by horseradish peroxidase. We showed previously that when onion soup is ingested, quercetin glucosides in the soup are hydrolyzed to quercetin in the oral cavity to bind to the epithelial tissues, and that quercetin can be a hydrogen donor to peroxidase in saliva to scavenge H 2 O 2 (Hirota et al., 2001). It was discussed then that the H 2 O 2 scavenging function may be important when H 2 O 2 production is enhanced. The enhancement of H 2 O 2 production is possible by the stimulation of leukocytes in the oral cavity. H 2 O 2 formation usually accompanies the formation of O 2 -and it is known that flavonol aglycones like kaempferol and quercetin reduce O 2 -to H 2 O 2 (Takahama 1983(Takahama , 1987Bors et al., 1997).Blackburn Jr. et al. (1987) reported that quercetin can inhibit O 2 -production, degranulation and phosphorylation of specific proteins, which are observed in plasma neutrophils when stimulated. The inhibition of O 2 -production may be in part due to inhibition of the NADPH oxidase system of leukocytes that is located on the cell membranes (Tauber et al., 1984). In addition, quercetin can also inhibit the activation of phospholipases that is induced on the stimulation of leukocytes (Takemura et al., 1997;Tordera et al., 1994). Berton et al. (1980) discussed that quercetin can regulate inflammatory processes taking account of quercetin-dependent inhibition of O 2 -production by stimulated leukocytes. It is known that some flavonoids including quercetin have an anti-inflammatory function (Pietta, 1997;Tordera et al., 1994). These reports using plasma leukocytes prompted us to study the effects of quercetin which can stay in the oral cavity for 4-5 h after ingestion of onion soup (Hirota et al., 2001), on the stimulation of salivary polymorphonuclear leukocytes (SPMN) and on the scavenging of O 2 -and H 2 O 2 that are formed by SPMN. In addition, as some phenolics might decrease the risk of caries (Haslam, 1998), the effects of quercetin on bacteria which cause caries and periodontal diseases were also studied. The results obtained in this study are quercetin-dependent inactivation of SPMN, scavenging of O 2 -and H 2 O 2 generated by SPMN and inhibition of the growth of P. gingivalis. These results suggest that quercetin might suppress the growth of P. gingivalis attenuating the production of reactive oxygen species by stimulated SPMN in the oral cavity and tissues. Materials and MethodsReagents Quercetin and 3,4-dihydroxybenzoic acid were obtained from Wako ...

Quercetin and the Glucosides Inhibit Nitration of a Salivary Component 4-Hydroxyphenylacetic Acid Catalyzed by Salivary Polymorphonuclear Leukocytes

“…It has been suggested that the H 2 O 2 /MPO system oxidizes nitrite (van der Vliet et al, 1997) and that polyphenols inhibit acidic nitritedependent nitration of tyrosine by scavenging nitrogen oxides (Oldreive et al, 1998). Quercetin was also oxidized by SPMN in the absence (Hirota et al, 2002) and presence of NaNO 2 (data not shown). Furthermore, it has been reported that quercetin (20-30 M) inhibits the oxygen consumption catalyzed by PMA-activated SPMN by 50% (Hirota et al, 2002).…”

“…4-Hydroxyphenylacetic acid (HPA) is also a component in the oral cavity although its origin remains to be elucidated . Since stimulated plasma polymorphonuclear leukocytes nitrate HPA to 4-hydroxy-3-nitrophenylacetic acid (NO 2 HPA) in the presence of nitrite (Halliwell et al, 1999;van der Vliet et al, 1997) and SPMN produces H 2 O 2 by stimulation (Hirota et al, 2002;Yamamoto et al, 1991), nitration of salivary HPA is probable if SPMN is accumulated and activated in the oral cavity.…”

“…It has been reported that quercetin and the glucosides are present in the saliva after ingestion of onion soup, and that the flavonols remained in the oral cavity for several hours after the ingestion (Hirota et al, 2001). The importance of the phenolics as antioxidants in the oral cavity is deduced from the report that polyphenols can scavenge reactive oxygen species generated by SPMN (Hirota et al, 2002). The importance is also deduced from the result that polyphenols can inhibit myeloperoxidase (MPO)-and acidic nitrite-dependent nitration of free tyrosine and tyrosine residues in proteins (Halliwell et al, 1999;van der Vliet et al, 1997;Oldreive et al, 1998;Oldreive & Rice-Evans, 2001) and can protect DNA bases against deamination by nitrous acid (Oldreive et al, 1998;Zhao et al, 2001).…”

“…Reactions were started by adding H 2 O 2 . Absorbance decrease by oxidation of quercetin was recorded by double beam mode at 370 nm (Hirota et al, 2002).…”

“…This result suggests that SPMN in SCS was stimulated in the absence of PMA and that PMA further stimulated the SPMN. It has been reported that isolated SPMN produces O 2 Ϫ and H 2 O 2 (Yamamoto et al, 1991;Al-Essa et al, 1994) absorbing molecular oxygen (Hirota et al, 2002) in the absence of stimuli. Figure 1 shows the time courses of nitration of 0.1 mM HPA to NO 2 HPA by isolated SPMN in the presence of 1 mM NaNO 2 .…”