Vitamin D3 (VD3) induces intestinal CYP3A that metabolizes orally administered anti-leukemic chemotherapeutic substrates dexamethasone (DEX) and dasatinib potentially causing a vitamin-drug ...interaction. To determine the impact of VD3 status on systemic exposure and efficacy of these chemotherapeutic agents, we used VD3 sufficient and deficient mice and performed pharmacokinetic and anti-leukemic efficacy studies. Female C57BL/6J and hCYP3A4 transgenic VD3 deficient mice had significantly lower duodenal (but not hepatic) mouse Cyp3a11 and hCYP3A4 expression compared to VD3 sufficient mice, while duodenal expression of Mdr1a, Bcrp and Mrp4 were significantly higher in deficient mice. When the effect of VD3 status on DEX systemic exposure was compared following a discontinuous oral DEX regimen, similar to that used to treat pediatric acute lymphoblastic leukemia patients, male VD3 deficient mice had significantly higher mean plasma DEX levels (31.7 nM) compared to sufficient mice (12.43 nM) at days 3.5 but not at any later timepoints. Following a single oral gavage of DEX, there was a statistically, but not practically, significant decrease in DEX systemic exposure in VD3 deficient vs. sufficient mice. While VD3 status had no effect on oral dasatinib’s area under the plasma drug concentration-time curve, VD3 deficient male mice had significantly higher dasatinib plasma levels at t = 0.25 hr. Dexamethasone was unable to reverse the poorer survival of VD3 sufficient vs. deficient mice to BCR-ABL leukemia. In conclusion, although VD3 levels significantly altered intestinal mouse Cyp3a in female mice, DEX plasma exposure was only transiently different for orally administered DEX and dasatinib in male mice. Likewise, the small effect size of VD3 deficiency on single oral dose DEX clearance suggests that the clinical significance of VD3 levels on DEX systemic exposure are likely to be limited.
Vitamin D.sub.3 (VD.sub.3) induces intestinal CYP3A that metabolizes orally administered anti-leukemic chemotherapeutic substrates dexamethasone (DEX) and dasatinib potentially causing a vitamin-drug ...interaction. To determine the impact of VD.sub.3 status on systemic exposure and efficacy of these chemotherapeutic agents, we used VD.sub.3 sufficient and deficient mice and performed pharmacokinetic and anti-leukemic efficacy studies. Female C57BL/6J and hCYP3A4 transgenic VD.sub.3 deficient mice had significantly lower duodenal (but not hepatic) mouse Cyp3a11 and hCYP3A4 expression compared to VD.sub.3 sufficient mice, while duodenal expression of Mdr1a, Bcrp and Mrp4 were significantly higher in deficient mice. When the effect of VD.sub.3 status on DEX systemic exposure was compared following a discontinuous oral DEX regimen, similar to that used to treat pediatric acute lymphoblastic leukemia patients, male VD.sub.3 deficient mice had significantly higher mean plasma DEX levels (31.7 nM) compared to sufficient mice (12.43 nM) at days 3.5 but not at any later timepoints. Following a single oral gavage of DEX, there was a statistically, but not practically, significant decrease in DEX systemic exposure in VD.sub.3 deficient vs. sufficient mice. While VD.sub.3 status had no effect on oral dasatinib's area under the plasma drug concentration-time curve, VD.sub.3 deficient male mice had significantly higher dasatinib plasma levels at t = 0.25 hr. Dexamethasone was unable to reverse the poorer survival of VD.sub.3 sufficient vs. deficient mice to BCR-ABL leukemia. In conclusion, although VD.sub.3 levels significantly altered intestinal mouse Cyp3a in female mice, DEX plasma exposure was only transiently different for orally administered DEX and dasatinib in male mice. Likewise, the small effect size of VD.sub.3 deficiency on single oral dose DEX clearance suggests that the clinical significance of VD.sub.3 levels on DEX systemic exposure are likely to be limited.
The subarachnoid space, where cerebrospinal fluid (CSF) flows over the brain and spinal cord, is lined on one side by arachnoid barrier (AB) cells that form part of the blood-CSF barrier. However, ...despite the fact that drugs are administered into the CSF and CSF drug concentrations are used as a surrogate for brain drug concentration following systemic drug administration, the tight-junctioned AB cells have never been examined for whether they express drug transporters that would influence CSF and central nervous system drug disposition. Hence, we characterized drug transporter expression and function in AB cells. Immunohistochemical analysis showed P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in mouse AB cells but not other meningeal tissue. The Gene Expression Nervous System Atlas (GENSAT) database and the Allen Mouse Brain Atlas confirmed these observations. Microarray analysis of mouse and human arachnoidal tissue revealed expression of many drug transporters and some drug-metabolizing enzymes. Immortalized mouse AB cells express functional P-gp on the apical (dura-facing) membrane and BCRP on both apical and basal (CSF-facing) membranes. Thus, like blood-brain barrier cells and choroid plexus cells, AB cells highly express drug transport proteins and likely contribute to the blood-CSF drug permeation barrier.
Abcg2/Bcrp and Abcb1a/Pgp are xenobiotic efflux transporters limiting substrate permeability in the gastrointestinal system and brain, and increasing renal and hepatic drug clearance. The systemic ...impact of Bcrp and Pgp ablation on metabolic homeostasis of endogenous substrates is incompletely understood. We performed untargeted metabolomics of cerebrospinal fluid (CSF) and plasma, transcriptomics of brain, liver and kidney from male Sprague Dawley rats (WT) and Bcrp/Pgp double knock-out (dKO) rats, and integrated metabolomic/transcriptomic analysis to identify putative substrates and perturbations in canonical metabolic pathways. A predictive Bayesian machine learning model was used to predict in silico those metabolites with greater substrate-like features for either transporters. The CSF and plasma levels of 169 metabolites, nutrients, signaling molecules, antioxidants and lipids were significantly altered in dKO rats, compared to WT rats. These metabolite changes suggested alterations in histidine, branched chain amino acid, purine and pyrimidine metabolism in the dKO rats. Levels of methylated and sulfated metabolites and some primary bile acids were increased in dKO CSF or plasma. Elevated uric acid levels appeared to be a primary driver of changes in purine and pyrimidine biosynthesis. Alterations in Bcrp/Pgp dKO CSF levels of antioxidants, precursors of neurotransmitters, and uric acid suggests the transporters may contribute to the regulation of a healthy central nervous system in rats. Microbiome-generated metabolites were found to be elevated in dKO rat plasma and CSF. The altered dKO metabolome appeared to cause compensatory transcriptional change in urate biosynthesis and response to lipopolysaccharide in brain, oxidation-reduction processes and response to oxidative stress and porphyrin biosynthesis in kidney, and circadian rhythm genes in liver. These findings present insight into endogenous functions of Bcrp and Pgp, the impact that transporter substrates, inhibitors or polymorphisms may have on metabolism, how transporter inhibition could rewire drug sensitivity indirectly through metabolic changes, and identify functional Bcrp biomarkers.
The effects of vitamin A and/or vitamin D deficiency were studied in an Arf
BCR-ABL acute lymphoblastic leukemia murine model. Vitamin D sufficient mice died earlier (p = 0.003) compared to vitamin D ...deficient (VDD) mice. Vitamin A deficient (VAD) mice fared worst with more rapid disease progression and decreased survival. Mice deficient for vitamins A and D (VADD) had disease progression similar to VAD mice. Regulatory T cells, previously shown to associate with poor BCR-ABL leukemia control, were present at higher frequencies among CD4
splenocytes of vitamin A deficient vs. sufficient mice. In vitro studies demonstrated 1,25-dihydroxyvitamin D (1,25(OH)
VD
) increased the number of BCR-ABL ALL cells only when co-cultured with bone marrow stroma. 1,25(OH)
VD
induced CXCL12 expression in vivo and in vitro in stromal cells and CXCL12 increased stromal migration and the number of BCR-ABL blasts. Vitamin D plus leukemia reprogrammed the marrow increasing production of collagens, potentially trapping ALL blasts. Vitamin A (all trans retinoic acid, ATRA) treated leukemic cells had increased apoptosis, decreased cells in S-phase, and increased cells in G
/G
. ATRA signaled through the retinoid X receptor to decrease BCR-ABL leukemic cell viability. In conclusion, vitamin A and D deficiencies have opposing effects on mouse survival from BCR-ABL ALL.
Variation in the CYP3A enzymes, which act in drug metabolism, influences circulating steroid levels and responses to half of all oxidatively metabolized drugs. CYP3A activity is the sum activity of ...the family of CYP3A genes, including CYP3A5, which is polymorphically expressed at high levels in a minority of Americans of European descent and Europeans (hereafter collectively referred to as 'Caucasians'). Only people with at least one CYP3A5*1 allele express large amounts of CYP3A5. Our findings show that single-nucleotide polymorphisms (SNPs) in CYP3A5*3 and CYP3A5*6 that cause alternative splicing and protein truncation result in the absence of CYP3A5 from tissues of some people. CYP3A5 was more frequently expressed in livers of African Americans (60%) than in those of Caucasians (33%). Because CYP3A5 represents at least 50% of the total hepatic CYP3A content in people polymorphically expressing CYP3A5, CYP3A5 may be the most important genetic contributor to interindividual and interracial differences in CYP3A-dependent drug clearance and in responses to many medicines.
CYP2B6 metabolizes many drugs, and its expression varies greatly. CYP2B6 genotype-phenotype associations were determined using human livers that were biochemically phenotyped for CYP2B6 (mRNA, ...protein, and CYP2B6 activity), and genotyped for CYP2B6 coding and 5'-flanking regions. CYP2B6 expression differed significantly between sexes. Females had higher amounts of CYP2B6 mRNA (3.9-fold, P < 0.001), protein (1.7-fold, P < 0.009), and activity (1.6-fold, P < 0.05) than did male subjects. Furthermore, 7.1% of females and 20% of males were poor CYP2B6 metabolizers. Striking differences among different ethnic groups were observed: CYP2B6 activity was 3.6- and 5.0-fold higher in Hispanic females than in Caucasian (P < 0.022) or African-American females (P < 0.038). Ten single nucleotide polymorphisms (SNPs) in the CYP2B6 promoter and seven in the coding region were found, including a newly identified 13072A>G substitution that resulted in an Lys139Glu change. Many CYP2B6 splice variants (SV) were observed, and the most common variant lacked exons 4 to 6. A nonsynonymous SNP in exon 4 (15631G>T), which disrupted an exonic splicing enhancer, and a SNP 15582C>T in an intron-3 branch site were correlated with this SV. The extent to which CYP2B6 variation was a predictor of CYP2B6 activity varied according to sex and ethnicity. The 1459C>T SNP, which resulted in the Arg487Cys substitution, was associated with the lowest level of CYP2B6 activity in livers of females. The intron-3 15582C>T SNP (in significant linkage disequilibrium with a SNP in a putative hepatic nuclear factor 4 (HNF4) binding site) was correlated with lower CYP2B6 expression in females. In conclusion, we found several common SNPs that are associated with polymorphic CYP2B6 expression.
We have investigated several in silico and in vitro methods to improve our ability to predict potential drug interactions of antibiotics. Our focus was to identify those antibiotics that activate ...pregnane X receptor (PXR) and induce CYP3A4 in human hepatocytes and intestinal cells. Human PXR activation was screened using reporter assays in HepG2 cells, kinetic measurements of PXR activation were made in DPX-2 cells, and induction of CYP3A4 expression and activity was verified by quantitative polymerase chain reaction, immunoblotting, and testosterone 6beta-hydroxylation in primary human hepatocytes and LS180 cells. We found that in HepG2 cells CYP3A4 transcription was activated strongly (> 10-fold) by rifampin and troleandomycin; moderately (> or = 7-fold) by dicloxacillin, tetracycline, clindamycin, griseofulvin, and (> or = 4-fold) erythromycin; and weakly (> 2.4-fold) by nafcillin, cefaclor, sulfisoxazole, and (> 2-fold) cefadroxil and penicillin V. Similar although not identical results were obtained in DPX-2 cells. CYP3A4 mRNA and protein expression were induced by these antibiotics to differing extents in both liver and intestinal cells. CYP3A4 activity was significantly increased by rifampin (9.7-fold), nafcillin and dicloxacillin (5.9-fold), and weakly induced (2-fold) by tetracycline, sufisoxazole, troleandomycin, and clindamycin. Multiple pharmacophore models and docking indicated a good fit for dicloxacillin and nafcillin in PXR. These results suggest that in vitro and in silico methods can help to prioritize and identify antibiotics that are most likely to reduce exposures of medications (such as oral contraceptive agents) which interact with enzymes and transporters regulated by PXR. In summary, nafcillin, dicloxacillin, cephradine, tetracycline, sulfixoxazole, erythromycin, clindamycin, and griseofulvin exhibit a clear propensity to induce CYP3A4 and warrant further clinical investigation.
The ABC transporter, Mrp4, transports the sulfated steroid DHEA-s, and sulfated bile acids interact with Mrp4 with high affinity.
Hepatic Mrp4 levels are low, but increase under cholestatic ...conditions. We therefore inferred that up-regulation of Mrp4 during
cholestasis is a compensatory mechanism to protect the liver from accumulation of hydrophobic bile acids. We determined that
the nuclear receptor CAR is required to coordinately up-regulate hepatic expression of Mrp4 and an enzyme known to sulfate
hydroxy-bile acids and steroids, Sult2a1. CAR activators increased Mrp4 and Sult2a1 expression in primary human hepatocytes
and HepG2, a human liver cell line. Sult2a1 was down-regulated in Mrp4 -null mice, further indicating an inter-relation between Mrp4 and Sult2a1 gene expression. Based on the hydrophilic nature of sulfated bile acids and the Mrp4 capability to transport sulfated steroids,
our findings suggest that Mrp4 and Sult2a1 participate in an integrated pathway mediating elimination of sulfated steroid
and bile acid metabolites from the liver.
Sister of P-glycoprotein (SPGP) is the major hepatic bile salt export pump (BSEP). BSEP/SPGP expression varies dramatically among human livers. The potency and hierarchy of bile acids as ligands for ...the farnesyl/bile acid receptor (FXR/BAR) paralleled their ability to induce BSEP in human hepatocyte cultures. FXR:RXR heterodimers bound to IR1 elements and enhanced bile acid transcriptional activation of the mouse and human BSEP/SPGP promoters. In FXR/BAR nullizygous mice, which have dramatically reduced BSEP/SPGP levels, hepatic CYP3A11 and CYP2B10 were strongly but unexpectedly induced. Notably, the rank order of bile acids as CYP3A4 inducers and activators of pregnane X receptor/steroid and xenobiotic receptor (PXR/SXR) closely paralleled each other but was markedly different from their hierarchy and potency as inducers of BSEP in human hepatocytes. Moreover, the hepatoprotective bile acid ursodeoxycholic acid, which reverses hydrophobic bile acid hepatotoxicity, activates PXR and efficaciously induces CYP3A4 (a bile-metabolizing enzyme) in primary human hepatocytes thus providing one mechanism for its hepatoprotection. Because serum and urinary bile acids increased in FXR/BAR −/− mice, we evaluated hepatic transporters for compensatory changes that might circumvent the profound decrease in BSEP/SPGP. We found weak MRP3 up-regulation. In contrast, MRP4 was substantially increased in the FXR/BAR nullizygous mice and was further elevated by cholic acid. Thus, enhanced hepatocellular concentrations of bile acids, due to the down-regulation of BSEP/SPGP-mediated efflux in FXR nullizygous mice, result in an alternate but apparent compensatory up-regulation of CYP3A, CYP2B, and some ABC transporters that is consistent with activation of PXR/SXR by bile acids.
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