Brain integrity is altered by hepatic APOE ε4 in humanized-liver mice

Liver-generated plasma apolipoprotein E (apoE) does not enter the brain but nonetheless correlates with Alzheimer's disease (AD) risk and AD biomarker levels. Carriers of APOEε4, the strongest genetic AD risk factor, exhibit lower plasma apoE and altered brain integrity already at mid-life versus non-APOEε4 carriers. Whether altered plasma liver-derived apoE or specifically an APOEε4 liver phenotype promotes neurodegeneration is unknown. Here we investigated the brains of Fah-/-, Rag2-/-, Il2rg-/- mice on the Non-Obese Diabetic (NOD) background (FRGN) with humanized-livers of an AD risk-associated APOE ε4/ε4 versus an APOE ε2/ε3 genotype. Reduced endogenous mouse apoE levels in the brains of APOE ε4/ε4 liver mice were accompanied by various changes in markers of synaptic integrity, neuroinflammation and insulin signaling. Plasma apoE4 levels were associated with unfavorable changes in several of the assessed markers. These results propose a previously unexplored role of the liver in the APOEε4-associated risk of neurodegenerative disease.

Procurement and Evaluation of Hepatocytes for Transplantation From Neonatal Donors After Circulatory Death

Hepatocyte transplantation is a promising treatment for liver failure and inborn metabolic liver diseases, but progress has been hampered by a scarcity of available organs. Here, hepatocytes isolated from livers procured for a neonatal hepatocyte donation program within a research setting were assessed for metabolic function and suitability for transplantation. Organ donation was considered for infants who died in neonatal intensive care in the Stockholm region during 2015–2021. Inclusion was assessed when a decision to discontinue life-sustaining treatment had been made and hepatectomy performed after declaration of death. Hepatocyte isolation was performed by three-step collagenase perfusion. Hepatocyte viability, yield, and function were assessed using fresh and cryopreserved cells. Engraftment and maturation of cryopreserved neonatal hepatocytes were assessed by transplantation into an immunodeficient mouse model and analysis of the gene expression of phase I, phase II, and liver-specific enzymes and proteins. Twelve livers were procured. Median warm ischemia time (WIT) was 190 [interquartile range (IQR): 80–210] minutes. Median viability was 86% (IQR: 71%–91%). Median yield was 6.9 (IQR: 3.4–12.8) x10⁶ viable hepatocytes/g. Transplantation into immunodeficient mice resulted in good engraftment and maturation of hepatocyte-specific proteins and enzymes. A neonatal organ donation program including preterm born infants was found to be feasible. Hepatocytes isolated from neonatal donors had good viability, function, and engraftment despite prolonged WIT. Therefore, neonatal livers should be considered as a donor source for clinical hepatocyte transplantation, even in cases with extended WIT.

A geroscience approach for Parkinson's disease: Conceptual framework and design of PROPAG-AGEING project

Advanced age is the major risk factor for idiopathic Parkinson's disease (PD), but to date the biological relationship between PD and ageing remains elusive. Here we describe the rationale and the design of the H2020 funded project "PROPAG-AGEING", whose aim is to characterize the contribution of the ageing process to PD development. We summarize current evidences that support the existence of a continuum between ageing and PD and justify the use of a Geroscience approach to study PD. We focus in particular on the role of inflammaging, the chronic, low-grade inflammation characteristic of elderly physiology, which can propagate and transmit both locally and systemically. We then describe PROPAG-AGEING design, which is based on the multi-omic characterization of peripheral samples from clinically characterized drug-naïve and advanced PD, PD discordant twins, healthy controls and "super-controls", i.e. centenarians, who never showed clinical signs of motor disability, and their offspring. Omic results are then validated in a large number of samples, including in vitro models of dopaminergic neurons and healthy siblings of PD patients, who are at higher risk of developing PD, with the final aim of identifying the molecular perturbations that can deviate the trajectories of healthy ageing towards PD development.

Molecular Aging of Human Liver: An Epigenetic/Transcriptomic Signature

The feasibility of liver transplantation from old healthy donors suggests that this organ is able to preserve its functionality during aging. To explore the biological basis of this phenomenon, we characterized the epigenetic profile of liver biopsies collected from 45 healthy liver donors ranging from 13 to 90 years old using the Infinium HumanMethylation450 BeadChip. The analysis indicates that a large remodeling in DNA methylation patterns occurs, with 8,823 age-associated differentially methylated CpG probes. Notably, these age-associated changes tended to level off after the age of 60, as confirmed by Horvath's clock. Using stringent selection criteria, we further identified a DNA methylation signature of aging liver including 75 genomic regions. We demonstrated that this signature is specific for liver compared to other tissues and that it is able to detect biological age-acceleration effects associated with obesity. Finally, we combined DNA methylation measurements with available expression data. Although the intersection between the two omic characterizations was low, both approaches suggested a previously unappreciated role of epithelial-mesenchymal transition and Wnt-signaling pathways in the aging of human liver.

Exogenous alpha 1-antitrypsin down-regulates SERPINA1 expression

The main goal of the therapy with purified human plasma alpha1-antitrypsin (A1AT) is to increase A1AT levels and to prevent lungs from elastolytic activity in patients with PiZZ (Glu342Lys) A1AT deficiency-related emphysema. Potential hepatic gains of this therapy are unknown. Herein, we investigated the effect of A1AT therapy on SERPINA1 (gene encoding A1AT) expression. The expression of SERPINA1 was determined in A1AT or A1AT plus Oncostatin M (OSM) treated primary human hepatocytes isolated from liver tissues from A1AT deficient patients and control liver tissues. In addition, SERPINA1 mRNA was assessed in lung tissues from PiZZ emphysema patients with and without A1AT therapy, and in adherent human peripheral blood mononuclear cells (PBMC) isolated from healthy PiMM donors. In a dose-dependent manner purified A1AT lowered SERPINA1 expression in hepatocytes. This latter effect was more prominent in hepatocytes stimulated with OSM. Although it did not reach statistical significance (P = 0.0539)-analysis of lung tissues showed lower SERPINA1 expression in PiZZ emphysema patients receiving augmentation therapy relative to those without therapy. Finally, exogenously added purified A1AT (1mg/ml) reduced SERPINA1 expression in naïve as well as in lipopolysaccharide (LPS)-stimulated human adherent PBMCs. Exogenous A1AT protein reduces its own endogenous expression. Hence, augmentation with native M-A1AT protein and a parallel reduction in expression of dysfunctional mutant Z-A1AT may be beneficial for PiZZ liver, and this motivates further studies.

De Novo Donor-Specific HLA Antibody Formation in Two Patients With Crigler-Najjar Syndrome Type I Following Human Hepatocyte Transplantation With Partial Hepatectomy Preconditioning

Clinical hepatocyte transplantation is hampered by low engraftment rates and gradual loss of function resulting in incomplete correction of the underlying disease. Preconditioning with partial hepatectomy improves engraftment in animal studies. Our aim was to study safety and efficacy of partial hepatectomy preconditioning in clinical hepatocyte transplantation. Two patients with Crigler-Najjar syndrome type I underwent liver resection followed by hepatocyte transplantation. A transient increase of hepatocyte growth factor was seen, suggesting that this procedure provides a regenerative stimulus. Serum bilirubin was decreased by 50%, and presence of bilirubin glucuronides in bile confirmed graft function in both cases; however, graft function was lost due to discontinuation of immunosuppressive therapy in one patient. In the other patient, serum bilirubin gradually increased to pretransplant concentrations after ≈600 days. In both cases, loss of graft function was temporally associated with emergence of human leukocyte antigen donor-specific antibodies (DSAs). In conclusion, partial hepatectomy in combination with hepatocyte transplantation was safe and induced a robust release of hepatocyte growth factor, but its efficacy on hepatocyte engraftment needs to be evaluated with additional studies. To our knowledge, this study provides the first description of de novo DSAs after hepatocyte transplantation associated with graft loss.

Incidence and prognostic impact of other cancers in a population of long-term survivors of chronic lymphocytic leukemia

BACKGROUND

Information on the impact of other cancers (OCs) in long-term survivors (LTSs) of chronic lymphocytic leukemia (CLL) is limited.

PATIENTS AND METHODS

Patients with CLL who survived >10 years were defined as LTSs of CLL. We calculated standardized incidence ratios (SIRs) to compare the incidence of OC in LTS of CLL versus the general population. A multivariable model was used to identify independent predictors of OC. Overall survival was analyzed as a function of the presence of OC.

RESULTS

Among 797 LTSs of CLL, the cumulative frequency of OC was 36%, similar between 570 patients (72%) who required treatment for CLL (TRT) and 227 (28%) who remained untreated (UT). The most common OC in both groups was non-melanoma skin cancer, followed by prostate cancer, breast cancer, melanoma, lung cancer, and leukemia in TRT patients, and by prostate cancer, breast cancer, melanoma, lung cancer, and gastrointestinal tumors in the UT group. The SIR for all OC was 1.2 (P = 0.034). It was higher in males (SIR 1.31; P = 0.013) and patients <60 years (SIR 1.27; P = 0.027). A higher SIR was shown for secondary leukemia, melanoma, and head-and-neck cancers, whereas a lower SIR was found for gastrointestinal and bladder cancers. Independent predictors of OC development were advanced age, male gender, and lower platelets. The survival of patients with OC was 16.2 months and that of patients without OC 22.9 years.

CONCLUSIONS

LTSs of CLL have an increased incidence of OC compared with the general population. CLL therapy is not a risk factor for OC in LTSs of CLL. The presence of an OC in these patients may be associated with shorter survival.

Current status of hepatocyte xenotransplantation

The treatment of acute liver failure, a condition with high mortality, comprises optimal clinical care, and in severe cases liver transplantation. However, there are limitations in availability of organ donors. Hepatocyte transplantation is a promising alternative that could fill the medical need, in particular as the bridge to liver transplantation. Encapsulated porcine hepatocytes represent an unlimited source that could function as a bioreactor requiring minimal immunosuppression. Besides patients with acute liver failure, patients with alcoholic hepatitis who are unresponsive to a short course of corticosteroids are a target for hepatocyte transplantation. In this review we present an overview of the innate immune barriers in hepatocyte xenotransplantation, including the role of complement and natural antibodies; the role of phagocytic cells and ligands like CD47 in the regulation of phagocytic cells; and the role of Natural Killer cells. We present also some illustrations of physiological species incompatibilities in hepatocyte xenotransplantation, such as incompatibilities in the coagulation system. An overview of the methodology for cell microencapsulation is presented, followed by proof-of-concept studies in rodent and nonhuman primate models of fulminant liver failure: these studies document the efficacy of microencapsulated porcine hepatocytes which warrants progress towards clinical application. Lastly, we present an outline of a provisional clinical trial, that upon completion of preclinical work could start within the upcoming 2-3 years.

Strategies for short-term storage of hepatocytes for repeated clinical infusions

Hepatocyte transplantation is an upcoming treatment for patients with metabolic liver diseases. Repeated cell infusions over 1-2 days improve clinical outcome. Isolated hepatocytes are usually cold stored in preservation solutions between repeated infusions. However, during cold storage isolated hepatocytes undergo cell death. We investigated if tissue preservation and repeated isolations are better than storage of isolated hepatocytes when cold preserving human hepatocytes. Liver tissue obtained from liver surgery or organ donors was divided into two pieces. Hepatocytes were isolated by collagenase digestion. Hepatocytes were analyzed directly after isolation (fresh) or after storage for 48 h at 4°C in University of Wisconsin solution (UW cells). Liver tissue from the same donor was stored at 4°C in UW and hepatocytes were isolated after 48 h (UW tissue cells). Hepatocyte viability and function was evaluated by trypan blue exclusion, plating efficiency, ammonia metabolism, CYP 1A1/2, 2C9, 3A7, and 3A4 activities, phase II conjugation, and apoptosis evaluation by TUNEL assay and caspase-3/7 activities. Hepatocytes stored in UW showed a significantly lower viability compared to fresh cells or hepatocytes isolated from tissue stored for 48 h (54% vs. 71% vs. 79%). Plating efficiency was significantly decreased for cells stored in UW (40%) compared to fresh and UW tissue cells (63% vs. 55%). No significant differences between UW cells and UW tissue cells could be shown for CYP activities or ammonia metabolism. Hepatocytes stored in UW showed a strong increase in TUNEL-positive cells, whereas TUNEL staining in cold-stored liver tissue and hepatocytes isolated after 48 h was unchanged. This observation was confirmed by increased caspase-3/7 activities in UW cells. Although preservation of isolated hepatocytes in UW maintains function, cold storage of liver tissue and repeated hepatocyte isolations is superior to cold storage of isolated hepatocytes in preserving hepatocyte viability and function.

Mice with human livers

Animal models are used to study many aspects of human disease and to test therapeutic interventions. However, some very important features of human biology cannot be replicated in animals, even in nonhuman primates or transgenic rodents engineered with human genes. Most human microbial pathogens do not infect animals and the metabolism of many xenobiotics is different between human beings and animals. The advent of transgenic immune-deficient mice has made it possible to generate chimeric animals harboring human tissues and cells, including hepatocytes. The liver plays a central role in many human-specific biological processes and mice with humanized livers can be used to model human metabolism, liver injury, gene regulation, drug toxicity, and hepatotropic infections.

Three-dimensional culture and cAMP signaling promote the maturation of human pluripotent stem cell-derived hepatocytes

Human pluripotent stem cells (hPSCs) represent a novel source of hepatocytes for drug metabolism studies and cell-based therapy for the treatment of liver diseases. These applications are, however, dependent on the ability to generate mature metabolically functional cells from the hPSCs. Reproducible and efficient generation of such cells has been challenging to date, owing to the fact that the regulatory pathways that control hepatocyte maturation are poorly understood. Here, we show that the combination of three-dimensional cell aggregation and cAMP signaling enhance the maturation of hPSC-derived hepatoblasts to a hepatocyte-like population that displays expression profiles and metabolic enzyme levels comparable to those of primary human hepatocytes. Importantly, we also demonstrate that generation of the hepatoblast population capable of responding to cAMP is dependent on appropriate activin/nodal signaling in the definitive endoderm at early stages of differentiation. Together, these findings provide new insights into the pathways that regulate maturation of hPSC-derived hepatocytes and in doing so provide a simple and reproducible approach for generating metabolically functional cell populations.

Comparison of culture media for bile Acid transport studies in primary human hepatocytes

BACKGROUND

Primary human hepatocytes are a useful in vitro model system to examine hepatic biochemical pathways, liver disorders and/or pharmacotherapies. This system can also be used for transport studies to investigate uptake and excretion of bile acids. Proper modeling of hepatic function requires careful attention to media components, and culture substrates and conditions.

OBJECTIVES

To examine the effects of different culture media and conditions on bile acid transport in cultured human hepatocytes.

METHODS AND RESULTS

Hepatocytes cultured in Williams' medium E showed an increase in both uptake and excretion of taurocholate compared to cells cultured in Dulbecco's Modified Eagle Medium (DMEM). Supplementation of DMEM with glutathione or ascorbic acid did not compensate for the lower transport. The difference can be explained by lower mRNA expression of the transporter proteins sodium taurocholate cotransporting polypeptide (NTCP) and bile salt export pump (BSEP; ABCB11) when cultured in DMEM. Hepatocytes cultured in DMEM also display fewer and smaller bile canaliculi. Following extended time in culture supplementation of Williams' medium E with dexamethasone increased the expression of NTCP and BSEP.

CONCLUSION

Williams' medium E is superior to DMEM for transport studies in primary human hepatocytes. Supplementation with dexamethasone increase mRNA levels of NTCP and BSEP.

FoxO6 integrates insulin signaling with gluconeogenesis in the liver

OBJECTIVE

Excessive endogenous glucose production contributes to fasting hyperglycemia in diabetes. This effect stems from inept insulin suppression of hepatic gluconeogenesis. To understand the underlying mechanisms, we studied the ability of forkhead box O6 (FoxO6) to mediate insulin action on hepatic gluconeogenesis and its contribution to glucose metabolism.

RESEARCH DESIGN AND METHODS

We characterized FoxO6 in glucose metabolism in cultured hepatocytes and in rodent models of dietary obesity, insulin resistance, or insulin-deficient diabetes. We determined the effect of FoxO6 on hepatic gluconeogenesis in genetically modified mice with FoxO6 gain- versus loss-of-function and in diabetic db/db mice with selective FoxO6 ablation in the liver.

RESULTS

FoxO6 integrates insulin signaling to hepatic gluconeogenesis. In mice, elevated FoxO6 activity in the liver augments gluconeogenesis, raising fasting blood glucose levels, and hepatic FoxO6 depletion suppresses gluconeogenesis, resulting in fasting hypoglycemia. FoxO6 stimulates gluconeogenesis, which is counteracted by insulin. Insulin inhibits FoxO6 activity via a distinct mechanism by inducing its phosphorylation and disabling its transcriptional activity, without altering its subcellular distribution in hepatocytes. FoxO6 becomes deregulated in the insulin-resistant liver, accounting for its unbridled activity in promoting gluconeogenesis and correlating with the pathogenesis of fasting hyperglycemia in diabetes. These metabolic abnormalities, along with fasting hyperglycemia, are reversible by selective inhibition of hepatic FoxO6 activity in diabetic mice.

CONCLUSIONS

Our data uncover a FoxO6-dependent pathway by which the liver orchestrates insulin regulation of gluconeogenesis, providing the proof-of-concept that selective FoxO6 inhibition is beneficial for curbing excessive hepatic glucose production and improving glycemic control in diabetes.

Targeted prostate cancer screening in men with mutations in BRCA1 and BRCA2 detects aggressive prostate cancer: preliminary analysis of the results of the IMPACT study

OBJECTIVE

To evaluate the role of targeted prostate cancer screening in men with BRCA1 or BRCA2 mutations, an international study, IMPACT (Identification of Men with a genetic predisposition to ProstAte Cancer: Targeted screening in BRCA1/2 mutation carriers and controls), was established. This is the first multicentre screening study targeted at men with a known genetic predisposition to prostate cancer. A preliminary analysis of the data is reported.

PATIENTS AND METHODS

Men aged 40-69 years from families with BRCA1 or BRCA2 mutations were offered annual prostate specific antigen (PSA) testing, and those with PSA > 3 ng/mL, were offered a prostate biopsy. Controls were men age-matched (± 5 years) who were negative for the familial mutation.

RESULTS

In total, 300 men were recruited (205 mutation carriers; 89 BRCA1, 116 BRCA2 and 95 controls) over 33 months. At the baseline screen (year 1), 7.0% (21/300) underwent a prostate biopsy. Prostate cancer was diagnosed in ten individuals, a prevalence of 3.3%. The positive predictive value of PSA screening in this cohort was 47·6% (10/21). One prostate cancer was diagnosed at year 2. Of the 11 prostate cancers diagnosed, nine were in mutation carriers, two in controls, and eight were clinically significant.

CONCLUSIONS

The present study shows that the positive predictive value of PSA screening in BRCA mutation carriers is high and that screening detects clinically significant prostate cancer. These results support the rationale for continued screening in such men.

Toward cell therapy using placenta-derived cells: disease mechanisms, cell biology, preclinical studies, and regulatory aspects at the round table

Among the many cell types that may prove useful to regenerative medicine, mounting evidence suggests that human term placenta-derived cells will join the list of significant contributors. In making new cell therapy-based strategies a clinical reality, it is fundamental that no a priori claims are made regarding which cell source is preferable for a particular therapeutic application. Rather, ongoing comparisons of the potentiality and characteristics of cells from different sources should be made to promote constant improvement in cell therapies, and such comparisons will likely show that individually tailored cells can address disease-specific clinical needs. The principle underlying such an approach is resistance to the notion that comprehensive characterization of any cell type has been achieved, neither in terms of phenotype nor risks-to-benefits ratio. Tailoring cell therapy approaches to specific conditions also requires an understanding of basic disease mechanisms and close collaboration between translational researchers and clinicians, to identify current needs and shortcomings in existing treatments. To this end, the international workshop entitled "Placenta-derived stem cells for treatment of inflammatory diseases: moving toward clinical application" was held in Brescia, Italy, in March 2009, and aimed to harness an understanding of basic inflammatory mechanisms inherent in human diseases with updated findings regarding biological and therapeutic properties of human placenta-derived cells, with particular emphasis on their potential for treating inflammatory diseases. Finally, steps required to allow their future clinical application according to regulatory aspects including good manufacturing practice (GMP) were also considered. In September 2009, the International Placenta Stem Cell Society (IPLASS) was founded to help strengthen the research network in this field.

A novel bile acid-activated vitamin D receptor signaling in human hepatocytes

Vitamin D receptor (VDR) is activated by natural ligands, 1alpha, 25-dihydroxy-vitamin D(3) [1alpha,25(OH)(2)-D(3)] and lithocholic acid (LCA). Our previous study shows that VDR is expressed in human hepatocytes, and VDR ligands inhibit bile acid synthesis and transcription of the gene encoding cholesterol 7alpha-hydroxylase (CYP7A1). Primary human hepatocytes were used to study LCA and 1alpha,25(OH)(2)-D(3) activation of VDR signaling. Confocal immunofluorescent microscopy imaging and immunoblot analysis showed that LCA and 1alpha, 25(OH)(2)-D(3) induced intracellular translocation of VDR from the cytosol to the nucleus and also plasma membrane where VDR colocalized with caveolin-1. VDR ligands induced tyrosine phosphorylation of c-Src and VDR and their interaction. Inhibition of c-Src abrogated VDR ligand-dependent inhibition of CYP7A1 mRNA expression. Kinase assays showed that VDR ligands specifically activated the c-Raf/MEK1/2/extracellular signal-regulated kinase (ERK) 1/2 pathway, which stimulates serine phosphorylation of VDR and hepatocyte nuclear factor-4alpha, and their interaction. Mammalian two-hybrid assays showed a VDR ligand-dependent interaction of nuclear receptor corepressor-1 and silencing mediator of retinoid and thyroid with VDR/retinoid X receptor-alpha (RXRalpha). Chromatin immunoprecipitation assays revealed that an ERK1/2 inhibitor reversed VDR ligand-induced recruitment of VDR, RXRalpha, and corepressors to human CYP7A1 promoter. In conclusion, VDR ligands activate membrane VDR signaling to activate the MEK1/2/ERK1/2 pathway, which stimulates nuclear VDR/RXRalpha recruitment of corepressors to inhibit CYP7A1 gene transcription in human hepatocytes. This membrane VDR-signaling pathway may be activated by bile acids to inhibit bile acid synthesis as a rapid response to protect hepatocytes from cholestatic liver injury.

Genetic predictors of interindividual variability in hepatic CYP3A4 expression

Variability in hepatic CYP3A4 cannot be explained by common CYP3A4 coding variants. We previously identified polymorphisms in pregnane X receptor (PXR) and ATP-binding cassette subfamily B member 1 (ABCB1) associated with CYP3A4 mRNA levels in small cohorts of human livers. However, the relative contributions of these genetic variations or of polymorphisms in other CYP3A4 regulators to variable CYP3A4 expression were not known. We phenotyped livers from white donors (n = 128) by quantitative real-time polymerase chain reaction for expression of CYP3A4, CYP3A5, and CYP3A7 and nine transcriptional regulators, coactivators, and corepressors. We resequenced hepatic nuclear factor-3-beta (HNF3beta, FoxA2), HNF4alpha, HNF3gamma (FoxA3), nuclear receptor corepressor 2 (NCoR2), and regions of the CYP3A4 promoter and genotyped informative single-nucleotide polymorphisms in PXR and ABCB1 in the same livers. CYP3A4 mRNA was positively correlated with PXR and FoxA2 and negatively correlated with NCoR2 mRNA. A common silent polymorphism and a polymorphic trinucleotide (CCT) repeat in FoxA2 were associated with CYP3A4 expression. The transcriptional activity of the FoxA2 polymorphic CCT repeat alleles (wild-type, n = 14 and variant, n = 13, 15, and 19) when assayed by luciferase reporter transactivation assays was greatest for the wild-type repeat, with deviations from this number having decreased transcriptional activity. This corresponded with higher expression of FoxA2 mRNA and its targets PXR and CYP3A4 in human livers with (CCT) n = 14 genotypes. Multiple linear regression analysis was used to quantify the contributions of selected genetic polymorphisms to variable CYP3A4 expression. This approach identified sex and polymorphisms in FoxA2, HNF4alpha, FoxA3, PXR, ABCB1, and the CYP3A4 promoter that together explained as much as 24.6% of the variation in hepatic CYP3A4 expression.

CYP2C9*1B promoter polymorphisms, in linkage with CYP2C19*2, affect phenytoin autoinduction of clearance and maintenance dose

The commonly prescribed antiepileptic drug phenytoin has a narrow therapeutic range and wide interindividual variability in clearance explained in part by CYP2C9 and CYP2C19 coding variants. After finding a paradoxically low urinary phenytoin metabolite (S)/(R) ratio in subjects receiving phenytoin maintenance therapy with a CYP2C9*1/*1 and CYP2C19*1/*2 genotype, we hypothesized that CYP2C9 regulatory polymorphisms (rPMs), G-3089A and -2663delTG, in linkage disequilibrium with CYP2C19*2 were responsible. These rPMs explained as much as 10% of the variation in phenytoin maintenance dose in epileptic patients, but were not correlated with other patients' warfarin dose requirements or with phenytoin metabolite ratio in human liver microsomes. We hypothesized the rPMs affected CYP2C9 induction by phenytoin, a pregnane X receptor (PXR), and constitutive androstane receptor (CAR) activator. Transfection studies showed that CYP2C9 reporters with wild-type versus variant alleles had similar basal activity but significantly greater phenytoin induction by cotransfected PXR, CAR, and Nrf2 and less Yin Yang 1 transcription factor repression. Phenytoin induction of CYP2C9 was greater in human hepatocytes with the CYP2C9 wild type versus variant haplotype. Therefore, CYP2C9 rPMs affect phenytoin-dependent induction of CYP2C9 and phenytoin metabolism in humans, with an effect size comparable with that for CYP2C9*2 and 2C9*3. These findings may also be relevant to the clinical use of other PXR, CAR, and Nrf2 activators.

ADME transcriptome in Hispanic versus White donor livers: Evidence of a globally enhanced NR1I3 (CAR, constitutive androstane receptor) gene signature in Hispanics

Previous studies have found that, compared with Whites, Hispanic donor livers had elevated expression of CYP2 enzymes, gene products regulated by the constitutive androstane receptor (CAR). The objectives of the current study were to determine (1) the CAR activation signature in human liver (2) whether other drug detoxification (absorption, distribution, metabolism and excretion (ADME)) genes were differentially expressed in Hispanic versus White livers, and (3) the extent of overlap in the CAR and Hispanic liver transcriptomes. The CAR transcriptome (ADME genes differentially expressed following phenobarbital versus vehicle treatment of human hepatocytes) and the Hispanic liver transcriptome (ADME genes differentially expressed in Hispanic versus White livers) were identified using Affymetrix oligonucleotide arrays. Quantitative real-time polymerase chain reaction (PCR) was used to verify candidate genes in a larger sample size. Comparison of the CAR and Hispanic liver ADME transcriptomes revealed a significant association between the gene changes. Sixty-four per cent of the ADME genes induced more than twofold by phenobarbital were also induced in Hispanics, and 14% of the ADME genes repressed more than twofold by phenobarbital were repressed in Hispanics. In conclusion, compared with Whites, Hispanic donor livers have increased expression of many genes that are transcriptionally regulated by CAR. This result has practical implications to the drug treatment of Hispanic patients.

Forkhead box transcription factor O1 inhibits cholesterol 7alpha-hydroxylase in human hepatocytes and in high fat diet-fed mice

The conversion of cholesterol to bile acids is the major pathway for cholesterol catabolism. Bile acids are metabolic regulators of triglycerides and glucose metabolism in the liver. This study investigated the roles of FoxO1 in the regulation of cholesterol 7alpha-hydroxylase (CYP7A1) gene expression in primary human hepatocytes. Adenovirus-mediated expression of a phosphorylation defective and constitutively active form of FoxO1 (FoxO1-ADA) inhibited CYP7A1 mRNA expression and bile acid synthesis, while siRNA knockdown of FoxO1 resulted in a approximately 6-fold induction of CYP7A1 mRNA in human hepatocytes. Insulin caused rapid exclusion of FoxO1 from the nucleus and resulted in the induction of CYP7A1 mRNA expression, which was blocked by FoxO1-ADA. In high fat diet-fed mice, CYP7A1 mRNA expression was repressed and inversely correlated to increase hepatic FoxO1 mRNA expression and FoxO1 nuclear retention. In conclusion, our current study provides direct evidence that FoxO1 is a strong repressor of CYP7A1 gene expression and bile acid synthesis. Impaired regulation of FoxO1 may cause down-regulation of CYP7A1 gene expression and contribute to dyslipidemia in insulin resistance.

Bile acids activate fibroblast growth factor 19 signaling in human hepatocytes to inhibit cholesterol 7alpha-hydroxylase gene expression

Mouse fibroblast growth factor 15 (FGF15) and human ortholog FGF19 have been identified as the bile acid-induced intestinal factors that mediate bile acid feedback inhibition of cholesterol 7alpha-hydroxylase gene (C YP7A1) transcription in mouse liver. The mechanism underlying FGF15/FGF19 inhibition of bile acid synthesis in hepatocytes remains unclear. Chenodeoxycholic acid (CDCA) and the farnesoid X receptor (FXR)-specific agonist GW4064 strongly induced FGF19 but inhibited CYP7A1 messenger RNA (mRNA) levels in primary human hepatocytes. FGF19 strongly and rapidly repressed CYP7A1 but not small heterodimer partner (SHP) mRNA levels. Kinase inhibition and phosphorylation assays revealed that the mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (MAPK/Erk1/2) pathway played a major role in mediating FGF19 inhibition of CYP7A1. However, small interfering RNA (siRNA) knockdown of SHP did not affect FGF19 inhibition of CYP7A1. Interestingly, CDCA stimulated tyrosine phosphorylation of the FGF receptor 4 (FGFR4) in hepatocytes. FGF19 antibody and siRNA specific to FGFR4 abrogated GW4064 inhibition of CYP7A1. These results suggest that bile acid-activated FXR is able to induce FGF19 in hepatocytes to inhibit CYP7A1 by an autocrine/paracrine mechanism.

CONCLUSION

The hepatic FGF19/FGFR4/Erk1/2 pathway may inhibit CYP7A1 independent of SHP. In addition to inducing FGF19 in the intestine, bile acids in hepatocytes may activate the liver FGF19/FGFR4 signaling pathway to inhibit bile acid synthesis and prevent accumulation of toxic bile acid in human livers.

Identification of enzymes involved in the metabolism of 17alpha-hydroxyprogesterone caproate: an effective agent for prevention of preterm birth

Preterm delivery, that is delivery before 37 completed weeks of gestation, is the major determinant of neonatal morbidity and mortality. Until recently, no effective therapies for prevention of preterm birth existed. In a recent multicentered trial, 17alpha-hydroxyprogesterone caproate (17-OHPC) reduced the rate of preterm birth by 33% in a group of high-risk women. Limited pharmacologic data exist for this drug. The recommended dose is empiric; the metabolic pathways are not well defined especially in pregnant women; and the fetal exposure has not been quantified. To define the metabolic pathways of 17-OHPC we used human liver microsomes (HLMs), fresh human hepatocytes (FHHs), and expressed enzymes. HLMs in the presence of NADPH generated three metabolites, whereas two major metabolites were observed with FHHs. Metabolism of 17-OHPC was significantly inhibited by the CYP3A4 inhibitors ketoconazole and troleandomycin in HLM and FHH. Metabolism of 17-OHPC was significantly greater in FHH treated with the CYP3A inducers, rifampin and phenobarbital. Furthermore, studies with expressed enzymes showed that 17-OHPC is metabolized exclusively by CYP3A4 and CYP3A5. The caproic acid ester was intact in the major metabolites generated, indicating that 17-OHPC is not converted to the primary progesterone metabolite, 17alpha-hydroxyprogesterone. In summary, this study shows that 17-OHPC is metabolized by CYP3A. Because CYP3A is involved in the oxidative metabolism of numerous commonly used drugs, 17-OHPC may be involved in clinically relevant metabolic drug interactions with coadministered CYP3A inhibitors or inducers.

A comprehensive in vitro and in silico analysis of antibiotics that activate pregnane X receptor and induce CYP3A4 in liver and intestine

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.

Association of breast cancer resistance protein/ABCG2 phenotypes and novel promoter and intron 1 single nucleotide polymorphisms

The hypothesis was tested that sequence diversity in breast cancer resistance protein (BCRP)'s cis-regulatory region is a significant determinant of BCRP expression. The BCRP promoter and intron 1 were resequenced in lymphoblast DNA from the polymorphism discovery resource (PDR) 44 subset. BCRP single nucleotide polymorphisms (SNPs) were genotyped in donor human livers, intestines, and lymphoblasts quantitatively phenotyped for BCRP mRNA expression. Carriers of the -15622C>T SNP had lower BCRP expression in multiple tissues. The intron 1 SNP 16702C>T was associated with high expression in livers; 1143G>A was associated with low expression in intestine; 12283T>C was associated with higher expression in the PDR44 and White livers. The -15994C>T promoter SNP was significantly associated with higher BCRP expression in multiple tissues. Patients with the -15994C>T genotype had substantially higher clearance of p.o. imatinib. We next determined whether BCRP expression was related to polymorphic alternative splicing or alternative promoter use. Liver polymorphically expressed an alternatively spliced mRNA [splice variant (SV) 1] skipping exon 2. Although SV1+ livers did not uniformly carry the exon 2 G34A allele, 90% of G34A livers expressed SV1 (versus 4% of 34GG livers). BCRP mRNA was significantly lower among Hispanic livers with the G34A variant genotype and may be due, in part, to polymorphic exon 2 splicing. Analysis of allele expression imbalance (AEI) showed that PDR44 samples with AEI had lower BCRP mRNA expression; however, no linked cis-polymorphisms were identified. BCRP used multiple promoters, and livers differentially using alternative exon 1b had lower BCRP. In conclusion, BCRP expression in lymphoblasts, liver, and intestine is associated with novel promoter and intron 1 SNPs.

Hepatocyte growth factor signaling pathway inhibits cholesterol 7alpha-hydroxylase and bile acid synthesis in human hepatocytes

Bile acid synthesis in the liver is regulated by the rate-limiting enzyme cholesterol 7alpha-hydroxylase (CYP7A1). Transcription of the CYP7A1 gene is inhibited by bile acids and cytokines. The rate of bile acid synthesis is reduced immediately after partial hepatectomy and during the early stage of liver regeneration. Hepatocyte growth factor (HGF) released from stellate cells activates a receptor tyrosine kinase c-Met, in hepatocytes and stimulates signaling pathways that regulate cell growth, proliferation, and apoptosis. This study demonstrated that HGF strongly and rapidly repressed CYP7A1 mRNA expression and the rate of bile acid synthesis in primary human hepatocytes. HGF rapidly induced c-Jun and small heterodimer partner mRNA and protein expression and increased phosphorylation of ERK1/2, JNK, and c-Jun. Specific inhibitors of protein kinase C, extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK) blocked HGF inhibition of CYP7A1 expression. Knockdown of c-Met by small interfering RNA resulted in a significant increase in CYP7A1 and blocked HGF inhibition of CYP7A1 mRNA expression. Chromatin immunoprecipitation assays showed that HGF induced recruitment of c-Jun and small heterodimer partner (SHP) but reduced recruitment of the coactivators peroxisome proliferators activated receptor rho coactivator 1alpha (PGC-1alpha) and cAMP response element binding protein (CREB)-binding protein (CBP) to chromatin.

CONCLUSION

This study demonstrated that HGF is a novel regulator of CYP7A1 and bile acid synthesis in human hepatocytes and may protect hepatocytes from accumulating toxic bile acids and developing intrahepatic cholestasis during the early stage of liver regeneration.

Ethanol stimulates bile acid formation in primary human hepatocytes

The conversion of cholesterol to bile acids is a key pathway for elimination of cholesterol from the body, thereby reducing the risk of arteriosclerosis. Moderate consumption of ethanol has been shown to have preventive effects on cardiovascular disease and decrease the risk of gallstone formation. In the present study primary human hepatocytes were used to investigate if ethanol affected bile acid synthesis. Hepatocytes were prepared from donor liver (n=11) and treated with ethanol, 7.7 or 50 mM, for 24 h. mRNA levels for enzymes in bile acid synthesis pathways were studied and bile acid synthesis was analyzed. Treatment with 7.7 mM ethanol increased cholic acid synthesis by 20% and treatment with 50 mM ethanol up-regulated cholic acid formation by 60%. The synthesis of cholic acid increased more than that of chenodeoxycholic acid, indicating that the classical pathway for bile acid synthesis was up-regulated. Increased bile acid levels in the cells treated with ethanol were seen after approximately 20 h. mRNA expression of CYP7A1, CYP27A1, and CYP8B1 in the hepatocytes was not affected by alcohol exposure.

Lack of Fas antagonism by Met in human fatty liver disease

Hepatocytes in fatty livers are hypersensitive to apoptosis and undergo escalated apoptotic activity via death receptor-mediated pathways, particularly that of Fas-FasL, causing hepatic injury that can eventually proceed to cirrhosis and end-stage liver disease. Here we report that the hepatocyte growth factor receptor, Met, plays an important part in preventing Fas-mediated apoptosis of hepatocytes by sequestering Fas. We also show that Fas antagonism by Met is abrogated in human fatty liver disease (FLD). Through structure-function studies, we found that a YLGA amino-acid motif located near the extracellular N terminus of the Met alpha-subunit is necessary and sufficient to specifically bind the extracellular portion of Fas and to act as a potent FasL antagonist and inhibitor of Fas trimerization. Using mouse models of FLD, we show that synthetic YLGA peptide tempers hepatocyte apoptosis and liver damage and therefore has therapeutic potential.

Robust expansion of human hepatocytes in Fah-/-/Rag2-/-/Il2rg-/- mice

Mice that could be highly repopulated with human hepatocytes would have many potential uses in drug development and research applications. The best available model of liver humanization, the uroplasminogen-activator transgenic model, has major practical limitations. To provide a broadly useful hepatic xenorepopulation system, we generated severely immunodeficient, fumarylacetoacetate hydrolase (Fah)-deficient mice. After pretreatment with a urokinase-expressing adenovirus, these animals could be highly engrafted (up to 90%) with human hepatocytes from multiple sources, including liver biopsies. Furthermore, human cells could be serially transplanted from primary donors and repopulate the liver for at least four sequential rounds. The expanded cells displayed typical human drug metabolism. This system provides a robust platform to produce high-quality human hepatocytes for tissue culture. It may also be useful for testing the toxicity of drug metabolites and for evaluating pathogens dependent on human liver cells for replication.

Physiological differences between human and rat primary hepatocytes in response to liver X receptor activation by 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy]phenylacetic acid hydrochloride (GW3965)

The liver is central to the maintenance of glucose and lipid homeostasis, and liver X receptors (LXRs) are key regulators of expression of the genes involved. So far, effects of activation of LXR in human hepatocytes have not been well characterized. Here we show that treatment of primary human hepatocytes with the synthetic LXR ligand 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy]phenylacetic acid hydrochloride (GW3965) results in reduced output of bile acids and very low density lipoprotein triglycerides and induced expression of adipose differentiation-related protein accompanied by increased lipid storage. Genome wide-expression profiling identified novel human LXR target genes in the glycolytic and lipogenic pathways and indicated that LXR activation reduced hepatic insulin sensitivity. Comparative experiments showed significant differences in the response to GW3965 between human and rat hepatocytes, raising the question as to how well rodent models reflect the human situation. In summary, the risk of hepatic steatosis upon pharmaceutical targeting of LXR may be a particularly serious consequence in humans.

Hyperglycemia and obesity in patients (pts) with acute lymphoblastic leukemia (ALL): Association with prevalence, response, and survival

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Increasing evidence suggests associations between obesity, diabetes and/or hyperglycemia (DM/HG) and solid tumors. Less is known about the relationship of these metabolic factors to the hematologic malignancies. To determine the prevalence of DM/HG and obesity in pts with ALL and whether these are predictors of response and survival, we conducted a retrospective chart review of 299 pts with newly diagnosed ALL, who were evaluated at our institution between November 1999 and May 2005 and received hyper-CVAD therapy: fractionated cyclophosphamide, vincristine, doxorubicin, dexamethasone alternating with methotrexate and high-dose cytarabine. Median age was 43 yrs (range 15–83). Sixty-one percent of pts were male, and 39% female. Seventy-four percent had a diagnosis (dx) of precursor B cell ALL (22% Ph+), 18% Burkitt's ALL, 6% lymphoblastic lymphoma, 2% other. Prior to therapy, the overall prevalence of DM/HG (diabetes based on reported dx prior to ALL-dx, and hyperglycemia based on baseline serum glucose ≥200 mg/dL) was 16%. Pts with DM/HG were significantly older than those without DM/HG (median age 57 yrs vs. 40 yrs, p<0.001). Complete remission (CR) rate and the CR duration (CRD) were similar in the DM/HG vs. non-DM/HG group. However, the mean CRD was 80 wks in the HG separately group and 121 wks in the non-HG group (p=0.04). The mean CRD was 102 wks in the obese pts and 124 wks in the non-obese pts (p=.04). In univariate analysis, DM/HG, obesity, and older age were associated with shorter overall survival (OS). Mean OS of pts with DM/HG was 134 vs. 194 wks for pts without DM/HG, (p=0.2). Mean OS of obese pts was 136 vs. 199 wks for non-obese pts, (p=0.01). In a multivariable Cox regression model, the only factors that remained significant for survival were age, obesity, and white blood cell count (WBC). There was no significant difference in OS by leukemia diagnosis. In conclusion, the prevalence data suggests that DM/HG may be involved in the development of ALL. However, DM/HG has no impact on survival, probably because of its strong correlation with age. The association of obesity with shorter OS warrants further investigation.

No significant financial relationships to disclose.

Adenoviral-mediated correction of methylmalonyl-CoA mutase deficiency in murine fibroblasts and human hepatocytes

BACKGROUND

Methylmalonic acidemia (MMA), a common organic aciduria, is caused by deficiency of the mitochondrial localized, 5'deoxyadenosylcobalamin dependent enzyme, methylmalonyl-CoA mutase (MUT). Liver transplantation in the absence of gross hepatic dysfunction provides supportive therapy and metabolic stability in severely affected patients, which invites the concept of using cell and gene delivery as future treatments for this condition.

METHODS

To assess the effectiveness of gene delivery to restore the defective metabolism in this disorder, adenoviral correction experiments were performed using murine Mut embryonic fibroblasts and primary human methylmalonyl-CoA mutase deficient hepatocytes derived from a patient who harbored two early truncating mutations, E224X and R228X, in the MUT gene. Enzymatic and expression studies were used to assess the extent of functional correction.

RESULTS

Primary hepatocytes, isolated from the native liver after removal subsequent to a combined liver-kidney transplantation procedure, or Mut murine fibroblasts were infected with a second generation recombinant adenoviral vector that expressed the murine methylmalonyl-CoA mutase as well as eGFP from distinct promoters. After transduction, [1-14C] propionate macromolecular incorporation studies and Western analysis demonstrated complete correction of the enzymatic defect in both cell types. Viral reconstitution of enzymatic expression in the human methylmalonyl-CoA mutase deficient hepatocytes exceeded that seen in fibroblasts or control hepatocytes.

CONCLUSION

These experiments provide proof of principle for viral correction in methylmalonic acidemia and suggest that hepatocyte-directed gene delivery will be an effective therapeutic treatment strategy in both murine models and in human patients. Primary hepatocytes from a liver that was unsuitable for transplantation provided an important resource for these studies.

An optimal culture condition maintains human hepatocyte phenotype after long-term culture

BACKGROUND

Long-term culture of primary hepatocytes from various species is impeded by a decrease of cell viability and a loss of hepatocyte-specific function. The aim of the present study was to investigate whether our optimal culture condition (OC) can maintain the phenotype of primary hepatocytes in long-term culture.

METHODS

Primary human hepatocytes were cultured in either hepatocyte maintenance medium (HM) or OC for 2-4 weeks. Expression of hepatocyte-specific genes was determined by real-time quantitative RT-PCR.

RESULTS

The level of albumin mRNA in human hepatocytes cultured in OC was 11-fold more than in HM and gene expression levels of alpha1-antitrypsin and transferrin were at approximately 40 and 11% of freshly isolated primary human hepatocytes. Electron microscopy revealed that cells in OC displayed hepatocyte properties (e.g. polarity, junctional complexes, bile canaliculi and glycogen particles). Cytochrome P4501A1/2 activity of hepatocytes cultured in OC was 15- and 17-fold higher than in HM at 2 and 4 weeks of culture, and DNA synthesis was higher.

CONCLUSIONS

Using our optimal culture condition, we were able to maintain the phenotype of primary human hepatocytes in long-term culture. They not only maintain better liver-specific function, but also retain higher proliferative potential.

Increased CYP3A4 copy number in TONG/HCC cells but not in DNA from other humans

Two recent screens for copy-number variations in the entire human genome found 12.4 gene copy number variations per person, including 2.5% of individuals with gains between 7q21.1 and 7q22.1, the chromosomal location of CYP3A4. CYP3A4 is involved in the metabolism of approximately 50% of all drugs, including many cancer chemotherapeutic agents. CYP3A4 gene copy was determined in DNA from 143 individuals: normal human livers, primary and secondary liver tumors, human hepatic cell lines, and immortalized cell lines representing eight ethnically diverse populations. CYP3A4 gene copy was normal in all but one sample, a primary human hepatocellular carcinoma cell line (TONG/HCC). Southern blots of TONG/HCC DNA revealed an approximate 10-fold increase in CYP3A and a corresponding increase in CYP3A mRNA expression and catalytic activity. Fluorescent in situ hybridization of TONG/HCC revealed specific amplification of the CYP3A4 gene on chromosome 7q21 but no amplification of the MDR1 gene that localizes 11.9 Mb upstream of CYP3A4. High resolution analysis of DNA copy number by comparative genomic hybridization confirmed amplification at 7q21.3-7q22. The amplicon spanned 1.7 Mb and contained 30 known genes, including the entire CYP3A locus. To determine whether CYP3A4 expression affected chemotherapeutic toxicity, LLC-PK1 cells were transduced with adenoviruses expressing CYP3A4 and P450 reductase. CYP3A4 conferred resistance to taxol, vinblastine and topotecan. These studies demonstrate that CYP3A4 copy number differences do not contribute to the normal variation in CYP3A4 expression. Tumors with increased CYP3A copy number (via amplification or increased chromosome 7q) would be expected to show reduced cytotoxicity to some chemotherapeutic drugs and potentially an increase in the outgrowth of drug resistant tumors.

MDR1 genotype is associated with hepatic cytochrome P450 3A4 basal and induction phenotype

OBJECTIVES

Variant cytochrome P450 (CYP) 3A4 alleles cannot explain human variation in CYP3A4 expression. This study investigated whether common single-nucleotide polymorphisms (SNPs) in multidrug resistance 1 (MDR1), encoding P-glycoprotein, or the pregnane X receptor (PXR) were associated with basal or inducible CYP3A4 expression.

METHODS

MDR1 G2677T and C3435T SNPs and a PXR 6-base pair (bp) deletion were genotyped in the deoxyribonucleic acid from 144 human livers in 3 cohorts each phenotyped for basal or rifampin (INN, rifampicin)-inducible hepatic CYP3A4 expression (or both) and in 57 human small bowel biopsy specimens from 3 cohorts each phenotyped for either basal or rifampin-induced CYP3A4 expression (or both).

RESULTS

Hepatic CYP3A4 expression/function was significantly higher in persons homozygous for the MDR1 2677T (Ser893) allele compared with persons homozygous for 2677G (Ala893) in all 3 hepatic cohorts. For example, homozygous MDR1 2677 TT livers had higher midazolam hydroxylase activity than homozygous 2677 GG livers (1831 +/- 1336 pmol x min(-1) x mg protein(-1) versus 1060 +/- 552 pmol x min(-1) x mg protein(-1), P = .03). In 2 of the 3 groups the association was observed in men but not in women. For example, homozygous MDR1 2677 TT male hepatocytes had significantly higher testosterone 6beta-hydroxylase activity compared with homozygous 2677 GG livers (0.120 +/- 0.06 pmol x min(-1) x mg protein(-1) versus 0.069 +/- 0.04 pmol x min(-1) x mg protein(-1), P = .0002). Conversely, rifampin induction of testosterone 6beta-hydroxylation in primary human hepatocytes was significantly higher in persons homozygous for 2677G (12.0 +/- 5.7-fold) compared with MDR1 homozygous TT carriers (7.3 +/- 4.6-fold) (P = .01). Suggestive evidence for higher CYP3A4 expression in MDR1 2677T carriers was also observed in human intestines. CYP3A4 expression was also related to a 6-bp deletion in PXR in 2 of the liver cohorts. Two-factor ANOVA analysis revealed a significant interaction between the MDR1 2677 SNP and the PXR 6-bp deletion influencing CYP3A4 expression (P = .007).

CONCLUSIONS

Individuals homozygous for the MDR1 2677T allele show enhanced constitutive CYP3A4 expression in the liver and intestine, as compared with those homozygous for the MDR1 2677G allele, particularly in men. Conversely, the magnitude of CYP3A4 induction by rifampin is greater in persons with the MDR1 2677G allele and is inversely related to baseline CYP3A4 expression. MDR1 likely influences basal CYP3A4 expression by limiting the intracellular concentration of an endogenous regulator. MDR1 genotype may be a useful predictor of basal CYP3A4 and the extent of some CYP3A4-mediated drug interactions in humans. Moreover, the influence of MDR1 genotype on CYP3A4 expression adds additional complexity to determining the relative contribution of the MDR1 alleles to the disposition of substrates shared by CYP3A4 and MDR1/P-glycoprotein.

In vitro and in vivo assessment of herb drug interactions

Herbal products contain several chemicals that are metabolized by phase 1 and phase 2 pathways and also serve as substrates for certain transporters. Due to their interaction with these enzymes and transporters there is a potential for alteration in the activity of drug metabolizing enzymes and transporters in presence of herbal components. Induction and inhibition of drug metabolizing enzymes and transporters by herbal component has been documented in several in vitro studies. While these studies offer a system to determine the potential for a herbal component to alter the pharmacokinetics of a drug, they cannot always be used to predict the magnitude of any potential effect in vivo. In vivo studies are the ultimate way to determine the clinical importance of herb drug interactions. However, lack of content uniformity and lack of documentation of the bioavailability of herbal components makes even in vivo human studies difficult to interpret as the effect may be product specific. It appears that St. John's wort extract is probably one of the most important herbal product that increases the metabolism and decreases the efficacy of several drugs. Milk thistle on the other hand appears to have minimal effect on phase 1 pathways and limited data exists for phase 2 pathways and transporter activity in vivo. Further systematic studies are necessary to assess the significance of herb drug interactions.