Dexamethasone Induces Pregnane X Receptor and Retinoid X Receptor-α Expression in Human Hepatocytes: Synergistic Increase of CYP3A4 Induction by Pregnane X Receptor Activators

Abstract

In this report we show that submicromolar concentrations of dexamethasone enhance pregnane X receptor (PXR) activatormediated CYP3A4 gene expression in cultured human hepatocytes. Because this result is only observed after 24 h of cotreatment and is inhibited by pretreatment with cycloheximide, we further investigated which factor(s), induced by dexamethasone, might be responsible for this effect. We report that dexamethasone increases both retinoid X receptor-␣ (RXR␣) and PXR mRNA expression in cultured human hepatocytes, whereas PXR activators such as rifampicin and clotrimazole do not. Accumulation of RXR␣ and PXR mRNA reaches a maximum at a concentration of 100 nM dexamethasone after treatment for 6 to 12 h and is greatly diminished by RU486. A similar pattern of expression is observed with tyrosine aminotransferase mRNA. Moreover, the effect of dexamethasone on PXR mRNA accumulation seems to be through direct action on the glucocorticoid receptor (GR) because the addition of cycloheximide has no effect, and dexamethasone does not affect the degradation of PXR mRNA. Furthermore, dexamethasone induces the accumulation of a RXR␣-immunoreactive protein and increases the nuclear level of RXR␣:PXR heterodimer as shown by gel shift assays with a CYP3A4 ER6 PXRE probe. This accumulation of latent PXR and RXR␣ in the nucleus of hepatocytes explains the synergistic effect observed with dexamethasone and PXR activators together on CYP3A4 induction. These results reveal the existence of functional cross talk between the GR and PXR, and may explain some controversial aspects of the role of the GR in CYP3A4 induction.

Addition of Dexamethasone Alters the Bile Acid Composition by Inducing CYP8B1 in Primary Cultures of Human Hepatocytes

“…24 To determine if the effect was mediated through GR, primary hepatocytes from 4 donor cases were treated with dexamethasone in combination with RU486, a GR antagonist. 25 When cells were treated with dexamethasone only, the expression of CYP7A1 increased, but addition of RU486 inhibited the dexamethasone CYP7A1 induction, Figure 4A.…”

A mechanism-based pharmacokinetic/pharmacodynamic model for CYP3A1/2 induction by dexamethasone in rats

“…In the PD study, 84 rats were randomly sorted into DEX or control (corn oil only) treatment groups. The treated rats were anesthetized with 60 mg/kg pentobarbital sodium and sacrificed at 0, 1,2,4,8,12,16,24,30,36,42,48,54, and 60 h (n=3 per time point). For the CYP3A1/2 enzyme activity assays, approximately 4 g of liver was rapidly excised for the preparation of liver microsomes.…”

“…For the PK analysis, serial blood samples were collected from three treated rats at various times after dosing (0.083, 0.25, 0.5, 0.75, 1,2,3,4,6,8,12,16,24,30,36, and 48 h). The collected blood was centrifuged at 3000×g at 4 °C for 10 min.…”

“…Briefly, the mechanism of rat CYP3A1/2 induction involves the binding of an inducer to PXR, the formation of an inducer-bound PXR/RXR (retinoid X-receptor) complex, translocation of the complex to the nucleus, and binding of the complex to DNAresponsive elements in the 5'-regulatory region of target genes (ie, CYP3A1/2) thereby triggering the transcription of these genes. Many drugs that induce CYP3A1/2 are PXR ligands Dexamethasone (DEX) has been widely used to treat patients with inflammatory and autoimmune conditions [5][6][7] , and it has been reported to be a remarkable inducer of both human CYP3A4 and rat CYP3A1/2 [8][9][10] . Recently, multiple in vitro and in vivo studies have demonstrated that the pharmacodynamics (PD) of CYP3A1/2 induction by DEX are doseand time-dependent [11][12][13] .…”

Inflammation et métabolisme des médicaments

“…Notamment, nous avons observé que l'expression et l'activité des récepteurs CAR et PXR sont étroitement régulées par des médiateurs pro-et anti-inflammatoires. En effet, alors que l'expression des gènes PXR et CAR est augmentée par les glucocorticoïdes lors de l'activation du récepteur GR (glucocorticoid receptor) [15,16] Le rôle pivot de la famille NF-kB : inhibition de l'activité transcriptionnelle de PXR La famille NF-κB a un rôle pivot dans la régulation de la réponse immunitaire. Sous leurs formes inactives, les dimères NF-κB p65 RelA:p50 sont retenus dans le cytoplasme par leur association avec les protéines inhibitrices IκB.…”