Quercetin inactivation

Two series of experiments were carried out to evaluate the influence of temperature on quercetin inactivation. In the first, quercetin solutions were kept for three hours at pH 7.5 in the temperature range 0 to 75 c in the presence of oxygen. Table 4 shows that temperature had only a minor influence on the mutagenic activity of quercetin at pH 7.5. 

A kinetic study was performed at pH 7.5 and 9.0 to ascertain the dependence of quercetin inactivation on time at 37 C. Table 6 shows that at pH 7.5, inactivation starts after about 4 hours and is complete after about 12 hours. In contrast, inactivation at pH 9.0 starts within minutes and is complete after about two hours. Time of exposure also appears to be an important variable governing quercetin inactivation. 

Miura, T. Muraoka, S. Fujimoto, Y. Inactivation of creatine kinase induced by quercetin with horseradish peroxidase and hydrogen peroxide pro-oxi-dative and anti-oxidative actions of quercetin. Food Chem. Toxicol., 41, 759-765 (2003)... 

Unlike genistein (42), quercetin (29) [308,309] and myricetin (31) [310] enhanced the calcium current carried by L-type calcium channels of the myocytes from rat tail artery. The character of voltage-, concentration-, and frequency-dependent calcium current changes induced by myricetin (31) [310] allowed the conclusion that this flavonoid exerted its effect on L-type calcium channels by binding preferentially to the channels in the inactivated state. Quercetin stimulated L-type calcium channels in rat pituitary GH3 cells in a dose-dependent manner [309]. The EC50 value was about 7 xM, and many facts suggested direct interaction between ion channels and flavonoid. In NG 108-15 neuronal cells quercetin (29) caused inhibition of TTX-sensitive sodium current. 

The compound does not directly inactivate the virus, but it was most effective when present in the early stages of virus replication. Although T2 was not active in vivo, its diacetyl derivative 1 (Ro 09-0298) was orally effective in protecting mice from lethal Infections with coxsackievirus B1.53 The closely related natural product, quercetin, has antiviral activity both in vitro and in vivo.5 1 Additional studies with quercetin against Mengo M virus Infected mice have confirmed previous reports of its oral... 

FACTORS WHICH FACILITATE INACTIVATION OF QUERCETIN MUTAGENICITY... 

Since it was necessary to use ethanol to keep quercetin in solution, we tested effects of ethanol on tyrosinase activity with its usual substrate, tyrosine (Worthington, 1982). The following results were obtained (in units/mg) pH 6.5 Tris buffer, 3,000 50% pH 6.5 buffer-50% ethanol, 700 pH 7.0 buffer, 2,500 50% pH 7.0 buffer-50% ethanol, 1,000 pH 7.5 buffer, 2,650 50% pH 7.5 buffer-50% ethanol, 1,100. Although ethanol suppresses tyrosinase activity, it does not completely inactivate the enzyme under conditions of the present study. Additional studies revealed that the extent of suppression is directly related to the amount of ethanol in the mixed solvent. 

Several factors expected to modify quercetin mutagenicity were, therefore, studied to establish optimal conditions for inactivating or suppressing the mutagenic potential of quercetin. 

Exposure of quercetin to buffers in an oxygen atmosphere had no observable effect on quercetin mutagenicity in the pH range 2 to 5. The transition point for the pH-oxygen inactivation appears to be near pH 6.5, since the number of revertants at this pH was about 440 compared to about 1000 at the lower pH values. Complete inactivation, where the number of revertants equals that observed with buffer controls, took place at pH values above 8. 

To assess whether compounds formed during the inactivation process adversely affected the activity of the Salmonella typhimurium TA98 strain employed in this study, quercetin was first inac-tivated at 37°C for 24 hours by exposure to pH 8, 9, 10 buffers in the presence of oxygen. The pH of each solution was then adjusted to 7.5 with 1 HCl before the Ames test was run. Parallel inactivated samples were spiked with a second dose of quercetin immediately before the Ames test was conducted. 

Table 2 shows that the spiked samples were fully active. The microsomes and bacteria were not affected by the reaction medium or by inactivated quercetin products. 

Table 3. Monreversibility of quercetin in 100 ml 50% ethanol-buffer inactivation at 37 C (15 mg 24 hours). See text. ...

In contrast exposure of quercetin to identical conditions but at pH 9.0 led to complete inactivation in the entire temperature range with one exception. Inactivation at 0 C proceeded to about 70% of the original value at pH 9.0. 

Table 5 shows that exposure of 15 mg of quercetin in 100 ml of pH 7.5 ethanol-buffer for 24 hours at 37 C produced an inactive product. However, activity was retained when the concentration of quercetin was increased to 30, 60, 75 mg in 100 ml of ethanol-buffer. In contrast, at pH 9.0, inactivation took place at all four concentrations. These results suggest that, in addition to the paramount importance of hydroxide ions in the destruction of quercetin, quercetin oxidation appears to be governed by concentration, at least at low concentrations. 

A possible explanation for the apparent non-dependence of the inactivation at pH 7.5 on quercetin concentration, is that destruction of part of the quercetin at the high concentrations still leaves enough quercetin to produce the maximum number of rever-tants. Additional studies are needed to define the dependence of the inactivation on concentration at different pH values. 

Figure 2- suggest that these expectations were indeed observed. Both absorption maxima decreased with increasing pH on exposure of an oxygen-saturated solution of quercetin to tyrosinase. The extent of the decrease in the absorption maximum near 370 nm correlated with decreased mutagenicity. Spectroscopy may therefore be useful for monitoring the mutagenic inactivation of quercetin and possibly other flavonoids. 

Table 7 shows that (a) copper, ferrous and ferric sulfates have the ability to inactivate quercetin mutagenicity at pH 7, even in a... 

Reversibility of copper sulfate and ferrous sulface catalyzed inactivation of quercetin mutagenicity . 

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