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Letters to the Editor |
Departments of1
Pharmacology and
2 Faculty of Chemical Technology University of Split Split, Croatia
3 Physiology and Biophysics School of Medicine and
aAddress correspondence to this author at: Department of Pharmacology University of Split School of Medicine, Soltanska 2, 21000 Split, Croatia. Fax 38-52-1465073; e-mail mboban{at}bsb.mefst.hr.
To the Editor:
The acute increase in serum antioxidant capacity after red wine consumption was initially attributed to polyphenolics in the wine (1)(2). However, polyphenolics are poorly absorbed, and their plasma concentrations after wine consumption are insufficient to explain the observed increase in antioxidant capacity (3). Red wine consumption is also linked to the acute increase in serum urate concentration that significantly contributes to the observed increase in serum antioxidant capacity (4)(5). However, the exact wine compounds responsible for the increase in urate have not been determined.
For our study, 9 healthy male nonsmoking volunteers (25–40 years of age) randomly consumed 4 beverages (3 mL/kg of body weight) in a cross-over design after an overnight fast, over the period of 4 weeks, 1 beverage per week. The following beverages were consumed: red wine, polyphenolics-stripped red wine, ethanol–water solution (water containing 14% ethanol by volume), and water. Beverages were consumed over 5 min. The University of Split School of Medicine’s Ethics Committee approved the study. Blood samples were drawn before and 30, 60, 90, 120, and 180 min after consumption into heparin-containing Vacutainers. We measured plasma antioxidant capacity (as ferric-reducing antioxidant power) (6) and the concentrations of catechin, as a representative of wine polyphenolics (by HPLC coupled with fluorescence detector), and urate (by the uricase method). Removal of polyphenolics was achieved by use of polyvinylpolypyrrolidone (7) and confirmed by the Folin–Ciocalteau method (8).
Only wine consumption caused an increase in plasma catechin values. In contrast to ethanol and water, consumption of both wine and polyphenolics-stripped wine produced increases in plasma urate concentrations and antioxidant capacity, reaching peak values after 60 min (Fig. 1
). Other constituents, administered in the concentrations found in red wine, were subsequently tested to precisely identify the one causing the increased plasma urate concentration and antioxidant capacity. We successfully replicated this increase with a mixture of 8 g/L glycerol in ethanol–water solution (Fig. 1
). There was no glycerol effect if ethanol was removed from the solution. Consumption of organic acids (mixture containing 1 g/L each of lactic, malic, tartaric, acetic, and citric acid) or sugars (mixture containing 2 g/L each of glucose and fructose) in ethanol–water solution had no effect.
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Our results indicate that the increase in plasma urate after red wine consumption is polyphenolics-independent and that the combination of glycerol and ethanol is responsible for the urate-related increase in plasma antioxidant capacity. This phenomenon could be linked to the finding that significant depletion of ATP and adenine nucleotides (which may indicate that they had been metabolized to urate) occurred only in rat liver slices incubated in a medium containing both glycerol and ethanol (9). The detailed mechanism by which this effect occurs is yet to be elucidated.
Our finding that glycerol and ethanol interact in modulating urate production and the related increase in plasma antioxidant capacity provides a novel experimental direction for clarifying the biological effects of red wine.
Acknowledgments
This work was supported by a grant from the Ministry of Science, Education and Sport, Republic of Croatia. We thank Ivica Brizic and Jonatan Vukovic for their assistance.
References
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) and antioxidant capacity (
) 60 min after consumption of red wine (RW), polyphenolics-stripped red wine (PSRW), ethanol–water solution (water containing 14% ethanol by volume; ET), water, and a combination of ethanol–water solution and 8 g/L glycerol (ET + glycerol).