Abstract
The mutagenicity of ten flavonoids was assayed by the Ames test, in Salmonella typhimurium strains TA98, TA100 and TA102, with the aim of establishing hydroxylation pattern-mutagenicity relationship profiles. The compounds assessed were: quercetin, kaempferol, luteolin, fisetin, chrysin, galangin, flavone, 3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone. In the Ames assay, quercetin acted directly and its mutagenicity increased with metabolic activation. In the presence of S9 mix, kaempferol and galangin were mutagenic in the TA98 strain and kaempferol showed signs of mutagenicity in the other strains. The absence of hydroxyl groups, as in flavone, only signs of mutagenicity were shown in strain TA102, after metabolization and, among monohydroxylated flavones (3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone), the presence of hydroxyl groups only resulted in minor changes. Luteolin and fisetin also showed signs of mutagenicity in strain TA102. Finally, chrysin, which has only two hydroxy groups, at the 5-OH and 7-OH positions, also did not induce mutagenic activity in any of the bacterial strains used, under either activation condition. All the flavonoids were tested at concentrations varying from 2.6 to 30.7 nmol/plate for galangin and 12.1 to 225.0 nmol/plate for other flavonoids. In light of the above, it is necessary to clarify the conditions and the mechanisms that mediate the biological effects of flavonoids before treating them as therapeutical agents, since some compounds can be biotransformed into more genotoxic products; as is the case for galangin, kaempferol and quercetin.
Highlights
In recent years, there has been a growing academic and industrial interest in the health benefits of flavonoids [1]
Its mutagenicity in strain TA98 increases in the presence of metabolic activation in a dose-dependent manner, with a mutagenic index higher than 2.0 at 147.8 nmol/plate
In the TA100 strain, quercetin induced an increase in the number of revertant colonies relative to the negative control in the absence of metabolic activation, with a mutagenic index of 2.0 at the concentration of 98.4 nmol/plate, indicating the direct mutagenic activity for this strain
Summary
There has been a growing academic and industrial interest in the health benefits of flavonoids [1]. Flavonoids are low-molecular-weight secondary metabolites of plants that, unlike primary metabolites, are not essential to their survival They are bioactive across kingdoms with over 9,000 structural variants known [2,3]. The basic molecular skeleton of flavonoid compounds (Figure 1) consists of two fused aromatic carbon rings, constituting benzopyran rings (A and C), and a benzene ring (B). These compounds can be divided into various sub-groups based on the degree of oxidation of the C-ring, the hydroxylation pattern of the ring structure and the substituent at position 3 [7], including chalcones, flavones, flavonols, flavanones, anthocyanins, and isoflavonoids [3]
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