xact direction nor the magnitude of a modify in such activity is usually precisely predicted around the sole basis on the chemical nature of a flavonoid [98], theoretically, it may be anticipated that nu blocking by means of methylation, sulfation or glucuronidation, 1 or additional of its redox-active phenolic groups, for instance, a single phenolic, catechol or galloyl in ring B, would compromise the flavonoid’s original antioxidant properties [61,99,100]. InAntioxidants 2022, 11,6 ofAntioxidants 2022, 11, x FOR PEER REVIEW6 offact, most studies indicate that when such a sort of metabolites are assayed in vitro for their ROS-scavenging/reducing activity, these have either considerably lost or only marginally HDAC1 Synonyms retained the antioxidant activity of their precursors, but that in no case have they undergone liver by means of the portal vein, they circulate in systemic blood nearly exclusively as O-glucua substantial acquire of such activity [74,96,10112]. Basically, equivalent in vitro outcomes have ronide, O-sulphate and/or O-methyl ester/ether metabolites (generally in this order of not too long ago been reported regarding the capacity of some flavonoids’ phase II-conjugation abundance) [69,90]. metabolites to upregulate (via an indirect action) the cell’s endogenous antioxidant capacity [80,11315] (Table 1). It needs to be noted, however, that in some distinct situations, Table 1. Phenol-compromising reactions. As exemplified for quercetin (Q), the principle reactions that influence the redox-active phase I and/or II biotransformation metabolites have been shown to exert a variety of phenol moieties of quercetin are listed. Furthermore, the chemical nature of a number of the formed metabolites and also the influence other, not necessarily the antioxidant properties biological actions that could that the phenol-compromising reactions can have onantioxidant-dependent, on the metabolites are described. drastically contribute for the health-promoting effects of their precursor flavonoids [79,116,117]. Phenol Effect on Metabolites Compromising Reactions Table 1. Phenol-compromising reactions. As exemplified for quercetin (Q), the principle reactions that Antioxidant Abl Compound potency impact the redox-active phenol moieties of quercetin are common, these metabolites have much less of Glycosides (e.g. Q-3-O-glucoside; Q-4-OIn listed. In addition, the chemical nature O-Glycosylation a number of the formed metabolites Q-5-O-glucoside the ROS-scavenging potency than their on plus the impact that phenol-compromising reactions can have glucoside; three,4-O-diglucoside; (in plants) the antioxidant properties of your metabolites are described. and Q-7-O-glucoside) corresponding aglycones The ROS-scavenging potency of OPhenol O-Deglycosylation Quercetin O-deglycosylated in C3, C4 C5 or Impact on Compromising Metabolites deglycosylated metabolites is, in most Antioxidant Potency (in human intestine/colon) C7 Reactions instances, significantly higher These Normally, these metabolites have much less metabolites have, in general, much less O-Glycosylation Glycosides (e.g., Q-3-O-glucoside; Q-4 -O-glucoside; ROS-scavenging potency than their Glucuronides (e.g. Q-3-O- and Q-7-O(in plants) 3,four -O-diglucoside; Q-5-O-glucoside and Q-7-O-glucoside) ROS scavenging/reduction potency but in Biotransformation corresponding aglycones glucuronides) some distinct situations are capable to up(in human intestine/ O-Deglycosylation The ROS-scavenging potency of Sulphates (e.g. Q-3-O-andin C3, C4 , C5 or C7 Q-3′-O-sulphates) (in human Quercetin O-deglycosylated O-deglycosylated meta
