title: Genistein inhibits glucose and sulphate transport in isolated rat liver lysosomes.
abstract: Genistein and daidzein are known to have both beneficial and adverse effects on human health due to their many biological actions at the cellular level. Both isoflavones have been shown to inhibit GLUT-mediated glucose transport across the plasma membrane of mammalian cells. Since lysosomal membrane transport is essential for maintaining cellular homeostasis, the present study examined the effects of genistein and daidzein on glucose and sulphate transport in isolated rat liver lysosomes. Both genistein and daidzein significantly inhibited lysosomal glucose uptake. Genistein was a more potent glucose transport inhibitor than daidzein, with a half-maximum inhibitory concentration (IC(50)) of 45 micromol/l compared with 71 micromol/l for daidzein. Uptake kinetics of d-glucose showed a significant decrease in Vmax (control:genistein treat = 1489 (sem 91):507 (sem 76) pmol/unit of beta-hexosaminidase per 15 s) without a change in K(m). The presence of 50 microm-genistein in the medium also reduced glucose efflux from lysosomes preloaded with 100 mm-d-glucose. Genistein also inhibited lysosomal sulphate transport. Similar to its effects on glucose uptake kinetics, genistein treatment caused a significant decrease in sulphate uptake V(max) (control:genistein treat = 87 (sem 4):59 (sem 5) pmol/unit of beta-hexosaminidase per 30 s), while the K(m) was not affected. The evidence provided by the present study suggests that the most likely mechanism of lysosomal glucose transport inhibition by genistein is via direct interaction between genistein and the transporter, rather than mediation by tyrosine kinase inactivation. Genistein likely has a similar mechanism of directly inhibiting sulphate transporter.
authors.affiliation: Department of Biochemistry, School of Medicine, Tzu-Chi University, No. 701, Section 3, Chung-Yan Road, Hualien, Taiwan, ROC. hfy@mail.tcu.edu.tw
authors.forename: Hsu-Fang
authors.initials: HF
authors.lastname: Chou
authors.forename: Kun-Hung
authors.initials: KH
authors.lastname: Chuang
authors.forename: Yi-Shan
authors.initials: YS
authors.lastname: Tsai
authors.forename: Yi-Ju
authors.initials: YJ
authors.lastname: Chen
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002942:Circular Dichroism; D005260:Female; D019833:Genistein / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism*; D007529:Isoflavones / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013431:Sulfates / Q000378:metabolism*
chemical_list: D007529:Isoflavones; D013431:Sulfates; C004742:daidzein; D019833:Genistein; D005947:Glucose; D000117:Acetylglucosamine