Potential role of trans-inhibition of the bile salt export pump by progesterone metabolites in the etiopathogenesis of intrahepatic cholestasis of pregnancy
Introduction
Intrahepatic cholestasis of pregnancy (ICP) appears during the second or third trimester of gestation and disappears spontaneously shortly after delivery [1]. In general, the manifestations of ICP are not severe for the mother [2], but often serious for the fetus [3].
The etiology of ICP is not well understood. This is probably multifactorial, involving predisposing dietary and genetic factors. The steroid profiles in the serum are profoundly altered [4] and ICP has been associated with an abnormal reaction of the maternal liver to endogenous sex steroids or their metabolites [2], [5]. Whether abnormal steroid metabolism is primary or secondary to the cholestasis is not clear. The rise in the serum concentrations of progesterone metabolites (PMs), mostly sulfated derivatives, has been associated with impaired biliary excretion of these compounds [6], [7]. However, it has also been proposed that one of the primary changes would be an increase in the reductive biotransformation of progesterone, resulting in increased formation of PMs [8]. In both cases, the accumulation of PMs was suggested to occur first in the mother, whereas alterations in steroid metabolism in the feto-placental unit are regarded as secondary to maternal disease [6], [9].
The cholestatic effect of certain steroids, such as estradiol 17β-d-glucuronide (E217βG), has been suggested to be due to trans-inhibition of the major mechanism accounting for bile acid (BA) transport across the canalicular membrane of hepatocytes, i.e. the bile salt export pump (BSEP, gene symbol ABCB11) [10], [11]. Whether PMs are able to induce a similar effect is not known.
In the absence of clinical manifestations, some apparently normal pregnancies presented the so-called asymptomatic hypercholanemia of pregnancy (AHP) [12], which probably reflects a continuum between normal pregnancy and overt disease (ICP), and which is accompanied by decreased serum concentrations of progesterone, but increased levels of several PMs, such as 5α-pregnan-3α-ol-20-one (PM4) [12]. Similarly, PM4 is one of the most abundant PMs accumulated in the serum of ICP patients [4], and their fetuses [6], [9]. These findings support the hypothesis that alterations in progesterone metabolism could be an important primary event in the etiology of ICP. Therefore, the aim of the present study was to investigate whether PMs might play a role in BA retention in AHP, which might be also involved in the etiopathogenesis of ICP.
Section snippets
Materials
Cholic acid (CA), chenodeoxycholic acid (CDCA), CA methyl ester (ME), sodium taurocholate (TC), estradiol 17β-d-glucuronide (E217βG), rifampicin, cyclosporin A (CsA) and potassium cyanide (KCN) were from Sigma Aldrich (Madrid, Spain). Progesterone and progesterone metabolites (PMs): 5β-pregnan-3α,20α-diol (PM3), 5α-pregnan-3α-ol-20-one (PM4), 5α-pregnan-3β-ol-20-one (PM5) and their sulfated derivatives (PM4-S and PM5-S) were from Steraloids, Inc. (Newport, RI, USA). [14C]-CA (48.6 mCi/mmol) was
Cholestatic effect on isolated perfused rat liver
When added to the perfusion medium at initial concentrations that can be regarded as moderately elevated as compared with values found in the serum of patients with ICP [4], [6] PM4, as well as progesterone, did not impair basal bile flow (Fig. 1A) or BA output (Fig. 1B). In contrast, both E217βG and PM4-S induced a persistent decrease in bile flow (Fig. 1A) and BA output (Fig. 1B). GC–MS analysis revealed that PM4-S (the mass spectrum of the non-sulfated form is shown in Fig. 2A) and E217βG
Discussion
PMs have been suggested to play an even more important role than estrogens [10], [22], [23] in the etiology of ICP [24]. The present study provides information regarding the mechanisms of cholestasis induced by these compounds, in particular some of the PMs that are elevated in the serum of women with AHP [12] or ICP [4], [6]. The present study suggests that inhibition of BA secretion into bile, mainly mediated by BSEP [25], may play an important role in the cholestatic effect induced by
Acknowledgements
The authors thank Dr Peter J. Meier, Bruno Stieger and Bruno Hagenbuch (University Hospital, Zurich, Switzerland) and Dr M. Eileen Dolan (Section of Hematology/Oncology, University of Chicago, IL, USA) for their generous supply of recombinant plasmids containing the cDNA of rat BSEP and human CES1, respectively. Secretarial help by M.I. Hernandez, technical help by E. Flores and supervision of the English version of the submitted manuscript by N. Skinner are gratefully acknowledged. This study
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