Roles of Nuclear Receptors in the Gene Expression of Drug-metabolizing Enzymes under Various Physiological Conditions

Inhibitory effect of 5β-pregnane-3α,20β-diol on transcriptional activity and enzyme activity of human bilirubin UDP-glucuronosyltransferase

Prolonged unconjugated hyperbilirubinemia in infants associated with breast milk feeding is a common pediatric problem known as breast milk jaundice (BMJ). A polymorphic mutation (G71R) of bilirubin UDP-glucuronosyltransferase (UGT1A1) is a known cause of BMJ on the infantile side, but the responsible components of breast milk are not currently known. We analyzed the inhibitory effect of 5β-pregnane-3α,20β-diol (pregnanediol) on transcriptional activity and enzyme activity of UGT1A1. To this end, we constructed two types of expression vectors. One type comprised vectors including the upstream enhancer-promoter sequence of UGT1A1 for WT and variant type (-3279T>G with A(TA)7TAA), used in studying transcriptional regulation. The other type comprised vectors including cDNA of UGT1A1 for WT and the G71R variant, used in studying enzyme activity. In an in vitro expression study, pregnanediol did not affect the transcriptional activity of UGT1A1 enhancer-promoter complex of WT and variant type, even with coexistence of transcriptional factors such as constitutive androstane receptor or pregnane X receptor. In contrast, in the presence of 100 μM pregnanediol, bilirubin glucuronidation of G71R-UGT1A1 was reduced to 51% of WT. We suggest that pregnanediol is a cause of breast milk jaundice in carriers of G71R.

Control of hepatic differentiation via cellular aggregation in an alginate microenvironment

Integral to the development of embryonic stem cell therapeutic strategies for hepatic disorders is the identification and establishment of a controllable hepatic differentiation strategy. In order to address this issue we have established an alginate microencapsulation approach which provides a means to modulate the differentiation process through changes in key encapsulation parameters. We report that a wide array of hepatocyte specific markers is expressed by cells differentiated during a 23-day period within an alginate bead microenvironment. These include urea and albumin secretion, glycogen storage, and cytochrome P450 transcription factor activity. In addition, we demonstrate that cellular aggregation is integral to the control of differentiation within the bead environment and this process is mediated by the E-cadherin protein. The temporal expression of surface E-cadherin and hepatocyte functional expression occur concomitantly and both cellular aggregation and albumin synthesis are blocked in the presence of anti E-cadherin immunoglobulin. Furthermore, by establishing a compartmental model of differentiation, which incorporates this aggregation phenomenon, we can optimize key encapsulation parameters.