Flavone sulfates

Figure 7.2 Paper electrophoresis for the detection of flavonoid glucuronides (pH 4.4) and sulfates (pH 2.2). (A) Extract containing flavone sulfates (B) extract containing flavone glucuronides (C) Extract containing flavone glucosides. The glucuronides and sulfates move toward the anode at pH 4.4. Sulfates keep migrating toward the anode at pH 2.2, but not glucuronides.

These metabolites represent a specific group of flavonoids which are linked covalently via hydroxyl groups to SOj", thus forming ester moieties mono-, di-, tri-, and even tetrasulfates were discovered. In 1975 a first review on flavonoid sulfates was published by Harbome (Harbome 1975) which documented the presence of such metabolites in over 160 species from nine dicotyledonous and seven monocotyle-donous families. It was followed by an update of Barron et al. (1988) which listed in all known flavonoid sulfates, i.e., 56 flavanol sulfates as well as 45 flavone sulfates. They were usually isolated as their potassium salts. Such metabolites were found in at least 250 species belonging to 17 dicotyledonous and 15 monocotyle-donous families. They were assumed to have no overall systematic significance, since many of these families are widely separated from each other. However, a general point was that they were found only in families which were herbaceous and/or morphologically advanced. Furthermore, this review included information on position-specific flavonol sulphotransferases. 

However, the effect of piperine on SULT and flavonoid status across the life cycle remains to be investigated. Induction of phase II metabolism appears to decrease the bioavailability and accelerate the excretion of flavonoids. For example, Siess et al.115 and Walle et al.116 reported flavones induced rat hepatic UGT activity in HepG2 and Caco-2 cells. This induction of UGT enhanced quercetin glucuronidation in Caco-2 cells. In addition to inducing UGT activity, the flavone chrysin inhibits hepatic SULT-mediated sulfation of acetaminophen and minoxidol." The impact of chrysin on the capacity of COMT action toward flavonoids has not been examined. Further, the effect of age on phase II modulation by piperine and chrysin has not been reported. Thus, information on the relationship between age and intake of flavonoids and other phytochemicals that also affect phase II metabolism is required. 

Acetyltrisulfate quercetin] (sulfated flavone) Acteoside (= Verbascoside Kusaginin)... 

Ferric nitrate, 107 Ferrous sulfate, 237 Fischer esterification, 248 Flavones, 13, 14,424 Fluoranthene picrate, 391 Fluorene-9-carboxylic acid, 101 Fluorenol, 455, 506... 

The threat of nuclear fallout from atomic weapons testing was the impetus for a large number of studies that investigated methods to prevent absorption of radiostrontium, while not adversely affecting the absorption of calcium. Reasonably effective strategies have included alginates, aluminum phosphate, and sulfates. Less effective or less practical strategies have included cold, diet, dietary fiber, flavones, and stable strontium. 

Glycosides of flavonoid sulfates occur in a number of plants (Fig. 11.12) (Harbome, 1991). More than 100 flavone and flavonol sulfates from more than 250 species and 30 families have been characterized compounds of this type may be recognized by examination of their UV spectra before and after addition of HCl and aryl-sulfatase (Barron and Ibrahim, 1988 Harbome, 1991 Varin, 1992). 

The number and the position of hydroxyl groups attached even in the same class of flavonoids can influence the lipophilicity of the flavonoids. Octanol-water partition coefficient (log P) values were reported for flavonoids from the flavone, flavonol, and flavanone [11], showing that aglycones are more lipophilic than any glycosylated or sulfated conjugates. However, there is not a trend of retention time of the flavonoid with respect to the log P (Table 69.1). Despite having the same number and position of hydroxyl substituents in luteolin (flavone) and eriodictyol (flavanone), they have different log P values but similar retention times. 

A third group of potential MRP substrates are sulfated, i.e. flavonoids which are common in Asteraceae. Although transport experiments with sulfated flavonoids have not yet been performed, indirect evidence suggests that a directly energized transporter is responsible for vacuolar uptake of sulfated compounds because directly energized uptake of the disulfonated fluorescent tracer Lucifer Yellow CH into rye mesophyll vacuoles was strongly inhibited by sulfated flavones (Klein et al, 1997). 

Baba M, Nakajima M, Schols D et al (1988) Pentosan polysulfate, a sulfated oligosaccharide, is a potent and selective anti-HIV agent in vitro. Antiviral Res 9 335-343 Brinkworth RI, Stoermer Ml, Fairlie DP (1992) Flavones are inhibitors of HIV-1 proteinase. Biochem Biophys Res Commun 188 631-637... 

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