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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
POSTER ABSTRACTSMembrane NA+ - K + - 2CI- cotransport and anion exchanger inhibition by soy isoflavonoids
MARTINEZ, RM; GIMENEZ, I;, LOU,M; MAYORAL, JA; ALDA, JO
Department of Pharmacology and Physiology, Faculty of Medicine and Department of Organic Chemistry, Faculty of Sciences, Zaragoza (SPAIN).
INTRODUCTION
Screening rat urine for the presence of membrane transport inhibitors, we found equol is a potent inhibitor of the Na+ - K+ - 2CI- cotransport (Alda et al. Biochem. Biophys. Res. Commun. 1996, 221: 279-285). The purpose of this work was to characterize the inhibitory profile of equol, genistein and daidzein on ion transport systems.
METHODS
Na+ - K+ - 2 CI - cotransport, Na + -K+ pump and Na+/H+ countertransport were measured in LLC-PK1 (a continuous cell line of renal origin) monolayers, as the bumetanide sensitive Rb+ influx, the ouabain-sensitive Rb+ influx, and the amoloride sensitive Li+ influx, respectively. In lithium loaded human red blood cells, HCO3-/CI- anion exchanger activity was equated to the DIDS (4.4'- diisothiocyna-2,2'- disulfonic stilbene)-sensitive Li+efflux.
Dose - effect curves for genistein (from SIGMA), equol and daidzein (synthetized by one of us: J.A.M.) were obtained by addition of the substance dissolved in DMSO (DMSO final concentration < 0.5%).
RESULTS
Na+ - K +- 2CI- cotransport half-maximal inhibitory concentrations (IC50):
Drug IC50mM (mean (DS) n
Furosemide 10.26(2.74 5
Equol 23.6(3.62 5
Genistein 34.75(2.62 5
Daidzein 140(24.04 4
HCO3-/CI- anion exchanger half-maximal inhibitory concentrations (IC50):
Drug IC50mM(mean (DS) n
DIDS 0.407(0.004 3
Equol 60.42(3.2 3
Genistein 98.73(4.5 3
Daidzein 294.11(14.7 4
Other membrane transport systems
Isoflavonoids did not show any effect on other transports (Na + - K+ pump and Na+/H+ countertransport).
CONCLUSIONS
Tested isoflavonoids showed inhibitions of two ion transport systems: Na+-K+-2CI- cotransport and the HCO3-CI- anion exchanger. Equol and genistein inhibited cotransport with an IC50 closed to that of furosemide, a widely used drug in renal and cardiovascular disorders. Like furosemide and other looop diuretics, isoflavonoids were also weak inhibitors of the anion exchanger. Relative inhibitory potency between equol, genistein and daidzein was the same on both transports. These results offers a new perspective in the search for biological activities of soy isoflavonoids.
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