Beneficial effects of silymarin on estrogen-induced cholestasis in the rat: A study in vivo and in isolated hepatocyte couplets

Abstract

The effect of silymarin (SIL) on 17␣-ethynylestradiol (EE)-induced cholestasis was evaluated in rats. EE (5 mg/kg, subcutaneously, daily, for 5 days) decreased both the bilesalt-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 17␤-glucuronidated, more cholestatic metabolite. Pretreatment of isolated rat hepatocyte couplets with silibinin, the major, active component of SIL, counter- Estrogens are well known to cause intrahepatic cholestasis in susceptible women during pregnancy, administration of oral contraceptives, and postmenopausal replacement therapy. 1 Given these clinical implications, experimental cholestasis induced by estrogen administration in rodents, mainly 17␣-ethynylestradiol (EE), has been widely used as an experimental model to assess the mechanisms involved in estrogeninduced cholestasis. These studies have shown that estrogens induce cholestasis by reducing both the bile-salt-dependent fraction of the bile flow (BSDF) and the bile-salt-independent fraction of the bile flow (BSIF). 1,2 The model in rats, however, requires estrogen dosages much greater than those required to induce cholestasis in susceptible women and fails to fully reproduce the pathology in humans in that little if any effect on serum parameters of hepatic damage, e.g., bile salt and bilirubin levels, is recorded. 3,4 The mechanism involved in the impairment of the BSDF is multifactorial. EE decreases sinusoidal uptake of bile acids, 5 at least in part by inducing down-regulation of the expression of the sodium-taurocholate cotransporting polypeptide protein, ntcp. 6 At the canalicular level, EE was shown to decrease the ATP-dependent taurocholate transport in hepatocyte canalicular membrane preparations, 5 which is thought to be due, at least in part, to an impairment in the expression of the canalicular bile salt export pump at a posttranscriptional level 7 ; this contributes to explain the decrease in the secretory rate maximum (SRM) of taurocholate, a parameter that is thought to evaluate the canalicular, rate-limiting transfer of bile salts in vivo...

Silymarin and epithelial cancer chemoprevention: How close we are to bedside?

“…Similarly, silymarin was found to retard collagen accumulation associated with both early and advanced biliary fibrosis in experimental model of complete bile duct occlusion induced by Ethibloc in rats (Luper, 1998). In experimental model of choleostasis induced by 17α-ethynylestradiol (EE) in rats, silymarin exerted protective effects by normalizing the EE-induced decrease in bile salt pool size and HCO 3 − , and by counteracting cholestatic effect of its glucuronidated metabolite (Crocenzi et al, 2001). In yet another study conducted by the same group, hepatoprotective effects of silymarin were observed in monohydroxylated bile salt (BS) taurolithocholate (TLC)-induced choleostatsis in rats by preventing the impairment of both BS-dependent and -independent fractions of the bile flow (Crocenzi et al, 2003).…”

Silibinin improves hepatic and myocardial injury in mice with nonalcoholic steatohepatitis

“…Although being used in clinical practice worldwide, its therapeutic efficacy has been questioned for years. Potent scavenging properties have been demonstrated in vitro and in vivo, in different hepatic and non-hepatic cells [18,19]; and strong evidences for silibinin therapeutic efficacy have been reported in different types of experimental liver injury [20][21][22].…”

Regulation of Expression and Activity of Rat Intestinal Multidrug Resistance-Associated Protein 2 by Cholestatic Estrogens

“…EE-treated rats were administered EE dissolved in propylene glycol (33.7 mM), at a daily dose of 5 mg/kg b.wt. s.c. for 5 consecutive days (Crocenzi et al, 2001). Control rats received injections of vehicle (propylene glycol; 0.5 ml/kg b.wt.…”

“…Estrogens contribute to the pathogenesis of both oral contraceptive-induced cholestasis and cholestasis of pregnancy (Vore, 1987;Reyes and Simon, 1993). Ethynylestradiol (EE), a synthetic estrogen, decreases bile flow formation in experimental animals, thus representing a useful model to study both estrogen-and drug-induced cholestasis (Crocenzi et al, 2001). In the rat, EE-induced decreases in both bile salt-dependent and -independent bile flow are attributed to decreased expression and activity of the canalicular bile salt export pump (Abcb11) and Mrp2 (Trauner et al, 1997;Lee et al, 2000) and concomitant impairment in biliary excretion of bile salts and Mrp2 substrates, such as glutathione species.…”