Beneficial effects of silymarin on estrogen-induced cholestasis in the rat: a study in vivo and in isolated hepatocyte couplets.
The effect of silymarin (SIL) on 17alpha-ethynylestradiol (EE)-induced cholestasis was evaluated in rats. EE (5 mg/kg, subcutaneously, daily, for 5 days) decreased both the bile-salt-dependent and the bile-salt-independent fractions of the bile flow. The decrease in the former was associated to a reduction in the bile salt pool size (-58%), and this effect was completely prevented by SIL. This compound also counteracted the inhibitory effect induced by EE on HCO(3)(-) but not glutathione output, 2 major determinants of the bile-salt-independent bile flow. EE decreased the secretory rate maximum (SRM) of tauroursodeoxycholate, (-71%) and bromosulfophthalein (BSP; -60%), as well as the expression of the BSP canalicular carrier, mrp2; SIL failed to increase mrp2 expression, and had only a marginal beneficial effect on both tauroursodeoxycholate and BSP SRM values. However, the two-compartment model-based kinetic constant for BSP canalicular transfer was significantly improved by SIL (+262%). SIL decreased rather than increased CYP3A4, the cytochrome P450 isoenzyme involved in the oxidative metabolism of EE, and had no inhibitory effect on the UDP-glucuronosyltrasferase isoforms involved in the formation of its 17beta-glucuronidated, more cholestatic metabolite. Pretreatment of isolated rat hepatocyte couplets with silibinin, the major, active component of SIL, counteracted the estradiol 17beta-glucuronide-induced decrease in the percentage of couplets secreting apically the fluorescent bile acid analogue, cholyl-lysyl-fluorescein. These results show that SIL protects against EE-induced cholestasis by normalizing mainly the decrease in the bile salt pool size and HCO(3)(-) output, and probably by counteracting the cholestatic effect of its cholestatic, glucuronidated metabolite.
Crocenzi
F A
FA
Instituto de Fisiología Experimental (IFISE)-Facultad de Ciencias Bioquímicas y Farmacéuticas (CONICET - U.N.R.), Rosario, Argentina.
Sánchez Pozzi
E J
EJ
Pellegrino
J M
JM
Favre
C O
CO
Rodríguez Garay
E A
EA
Mottino
A D
AD
Coleman
R
R
Roma
M G
MG
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D001646:Bile / Q000187:drug effects / Q000502:physiology; D001647:Bile Acids and Salts / Q000037:antagonists & inhibitors / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects; D002779:Cholestasis / Q000139:chemically induced* / Q000517:prevention & control*; D004548:Elasticity; D045166:Estradiol Congeners / Q000494:pharmacology; D004997:Ethinyl Estradiol / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D051381:Rats; D017208:Rats, Wistar; D012838:Silymarin / Q000494:pharmacology*
D018435:ATP Binding Cassette Transporter, Subfamily B; D000469:Alkaline Phosphatase; D001647:Bile Acids and Salts; D045166:Estradiol Congeners; D004997:Ethinyl Estradiol; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012838:Silymarin; C421109:multidrug resistance-associated protein 1