Cytochrome P450 1A1 (CYP1A1) in blood lymphocytes evidence for catalytic activity and mRNA expression

The Novel Atypical Antipsychotic Lurasidone Affects Cytochrome P450 Expression in the Liver and Peripheral Blood Lymphocytes

Lurasidone is a novel atypical antipsychotic drug acting on dopaminergic, serotonergic and noradrenergic receptors; it is applied for the long-term treatment of schizophrenia and depression in patients with bipolar disorders. We aimed at performing a comparative study on the influence of chronic treatment with lurasidone on the expression of cytochrome P450 enzymes in the liver and in peripheral blood lymphocytes, and to evaluate the relationship between changes in the expression of CYP enzymes in the two experimental models. The obtained results show a fairly similar expression pattern of the main CYP enzymes in the rat livers and lymphocytes, and they indicate that in the liver, lurasidone exerts an inhibitory effect on the activity, protein and mRNA levels of CYP2B1/2 (not CYP2B2 mRNA), CYP2C11 and CYP2E1, while in the case of CYP3A1 and CYP3A2, it causes enzyme induction. At the same time, lurasidone decreases the expression of CYP2B, CYP2C11 (CYP2C11 protein only) and CYP2E1 but increases that of CYP3A2 (not CYP3A1) in lymphocyte cells. In conclusion, chronic treatment with lurasidone simultaneously and in the same way influences the expression and activity of CYP2B, CYP2C11, CYP2E1 and CYP3A2 in the liver and peripheral blood lymphocytes of rats. Thus, the lymphocyte cytochrome P450 profile may be utilized as an indicator of the hepatic cytochrome P450 profile in further clinical studies with lurasidone, and lymphocytes may serve as easily available surrogates for examining the impact of new drugs and chronic in vivo treatments on CYP enzyme expression, as well as to estimate drug-drug interactions and toxicity risk.

A transcriptome profile in gallbladder cancer based on annotation analysis of microarray studies

The purpose of the present study was to identify aberrantly expressed genes for gallbladder cancer based on the annotation analysis of microarray studies and to explore their potential functions. Differential gene expression was investigated in cholesterol polyps, gallbladder adenoma and gallbladder cancer using microarrays. Subsequently, microarray results were comprehensively analyzed. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to determine the affected biological processes or pathways. Differentially expressed genes (DEGs) of cholesterol polyps, gallbladder adenoma and gallbladder cancer were identified. Following comprehensive analysis, 14 genes were found to be differentially expressed in the gallbladder wall of both gallbladder cancer and gallbladder adenoma. The 20 most significantly upregulated genes were only upregulated in the gallbladder wall of gallbladder cancer, but not in the gallbladder wall of cholesterol polyps and gallbladder adenoma. In addition, 182 DEGs were upregulated in the gallbladder wall of gallbladder adenoma compared with the gallbladder wall of cholesterol polyps. A total of 20 most significant DEGs were found in both the tumor and gallbladder wall of gallbladder cancer. In addition, the most significant DEGs that were identified were only upregulated in the tumor of gallbladder cancer. GO and KEGG analysis indicated that the aforementioned DEGs could participate in numerous biological processes or pathways associated with the development of gallbladder cancer. The present findings will help improve the current understanding of tumorigenesis and the development of gallbladder cancer.

Identifying the role of ASPN and COMP genes in knee osteoarthritis development

Background

Osteoarthritis (OA) is a common cause of musculoskeletal disability among elders and is characterized by late-onset degeneration of articular cartilage. OA affects various joints, commonly hand, knee, and hip, with clinical features that are unique to each joint. This study was initiated to identify and evaluate the role of the ASPN and COMP genes in the development of knee OA.

Methods

A case–control study was carried out involving 500 cases with knee OA (diagnosed by the American College of Rheumatology) and an equal number of healthy controls. Blood was drawn for genomic DNA isolation. PCR-RFLP and TaqMan assay methods were used to identify the SNPs. mRNA and protein expression of genes were carried out in peripheral blood lymphocytes (PBLs) by RT-PCR and Western immunoblotting. The data obtained were analyzed for the statistical significance between control and case groups.

Results

The variant genotype of ASPN and COMP genes was found to be present at a relatively higher frequency in cases than controls. RT-PCR and immunochemical studies revealed increased mRNA and protein expression of such gene in PBLs isolated from cases of knee OA as compared to healthy control.

Conclusion

The allelic alteration in ASPN and COMP genes in knee OA cases points to the role of these genes in the development of knee OA. Further, increased mRNA and protein expression of ASPN and COMP in peripheral blood samples of patients with the disease suggest that expression profile of candidate gene could be used as a biomarker for predicting the development and progression of knee OA.

Expression of Genes and Their Polymorphism Influences the Risk of Knee Osteoarthritis

Introduction

Genetic factors including the level of expression of the fingerprint of genes involved in the development of bones and cartilage such as GDF-5 or ESR-α or CALM-1 are known to be strong determinants of the osteoarthritis (OA) in Caucasian and Oriental populations. Because of high prevalence of OA in Indian population and availability of limited genetic data, we determined whether similar genetic factors are involved in Indians as well.

Methods

A case control study was carried out involving 500 patients of knee OA and equal number of healthy controls. Genotyping analyses in whole blood, mRNA, and protein expressions in peripheral blood lymphocytes (PBLs) were performed using established protocols.

Results

Our results showed a significantly decreased level of mRNA and protein expressions for GDF-5, ESR-α, and CALM-1 genes in PBLs of OA cases when compared to healthy controls. The frequency of variant genotypes of these genes was also increased significantly in cases of OA compared to controls.

Conclusion

Our results demonstrated that the decrease in expression of GDF-5, ESR-α, and CALM-1 in PBLs and association of polymorphism in these genes may be important in predicting the severity and thereby the progression of OA in Indian population.

Gene expression profiling of candidate genes in peripheral blood mononuclear cells for predicting toxicity of diesel exhaust particles

To validate gene expression profiling of peripheral blood mononuclear cells (PBMCs) as a surrogate for monitoring tissue expression, this study using RT-PCR-based TaqMan low-density array (TLDA) was initiated to investigate similarities in the mRNA expression of target genes altered by exposure to diesel exhaust particles (DEPs) in freshly prepared PBMCs and in lungs. Adult Wistar rats were treated transtracheally with a single dose of 7.5 or 15 or 30mg/kg DEPs and sacrificed 24h later. Blood and lungs were immediately taken out and processed for RT-PCR. DEP treatment induced similar patterns of increase in the expression of polycyclic aromatic hydrocarbon-responsive cytochrome P450s, the phase II enzymes, and their associated transcription factors in both lungs and PBMCs, at all doses. Similar to that seen in lungs, a dose-dependent increase was observed in the expression of genes involved in inflammation, such as cytokines, chemokines, and adhesion molecules, in PBMCs. The expression of various genes involved in DNA repair and apoptosis was also increased in a dose-dependent manner in PBMCs and lungs. The present TLDA data indicating similarities in the responsiveness of candidate genes involved in the toxicity of DEPs between PBMCs and lungs after exposure to DEPs demonstrate that expression profiles of genes in PBMCs could be used as a surrogate for monitoring the acute toxicity of fine and ultrafine particulate matter present in vehicular emissions.

Expression profiling of selected genes of toxication and detoxication pathways in peripheral blood lymphocytes as a biomarker for predicting toxicity of environmental chemicals

To develop a rapid and sensitive tool for determining gene expression profiles of peripheral blood lymphocytes (PBL) as a surrogate for predicting toxicity associated with environmental exposures, studies were initiated using Taqman Low Density Array (TLDA), a medium throughput method for real time PCR (RT-PCR), for selected genes involved in toxication and detoxication processes. Total RNA was prepared from PBL and liver samples isolated from young rats treated with inducers of drug metabolizing enzymes, e.g. phenobarbital (PB, 80mg/kg i.p. X5 days) or methylcholanthrene (30mg/kg, i.p. X5 days) or ethanol (0.8ml/kg, i.p. X1 day). TLDA data showed that PBL expressed drug metabolizing enzymes (DMEs), though the level of expression was several folds lower when compared to liver. Treatment with different inducers of DMEs produced a similar pattern of an increase in the expression of various phase I and phase II DMEs and their respective transcription factors in liver and PBL. While treatment with MC increased the expression of MC inducible cytochrome P450 (CYP) 1A1, 1A2, 1B1, 2A2 & 3A1 and their associated transcription factors in PBL, an increase in the expression of CYP2B1, 2B2, 2C11 & 3A1 and their transcription factor was observed in PBL after PB treatment. Similarly, treatment of ethanol increased the expression of CYP2E1 and 3A1 along with transcription factors in PBL. These inducers were found to increase the expression of various phase II enzymes such as glutathione S-transferases, GSTs (GSTM1, GSTA1, GSTP1 and GSTK1), NQO1, Ephx1 and Sod1, genes involved in inflammation and apoptosis (p53, BCl2, Apaf1 and Caspase9) in both PBL and liver. The data suggests that the low-density array of selected genes in PBL has the potential to be developed as a rapid and sensitive tool for monitoring of individuals exposed to environmental chemicals as well as in clinical studies.

Cytochrome P450 2A isoenzymes in freshly prepared blood lymphocytes isolated from rats and validation as a biomarker for clinical studies in humans

1. The present study aimed to identify the expression of carcinogen metabolizing cytochrome P4502A (CYP2A) isoenzymes in freshly prepared rat peripheral blood lymphocytes (PBL) isolated from adult rats and investigate similarities in the regulation of lymphocyte CYP2A-isoenzymes with the tissue enzyme. 2. qRT-PCR studies demonstrated significant constitutive mRNA expression of CYP2A-isoenzymes in PBL isolated from male and female rats which further increases significantly after pretreatment with nicotine or 3-methylcholanthrene (MC) indicating responsiveness of CYP2A-isoenzymes in PBL. This increase in the CYP2A expression was associated with an increase in the protein expression and CYP2A3-dependent coumarin hydroxylase (COH) activity in PBL. 3. Clinical studies further demonstrated significant increase in the expression of CYP2A6 and associated enzyme activity in PBL isolated from lung cancer patients. Our data thus provided evidence for similarities in the regulation of carcinogen metabolizing CYP2A-isoenzymes in PBL with the tissue enzymes. Further, responsiveness of blood CYP2A6 in human blood lymphocytes isolated from lung cancer patients has led us to suggest that associating expression profiles of CYP2A6 and other polycyclic aromatic hydrocarbons (PAH)-responsive CYPs in PBL with the genotyping data could lead to the development of a possible screen to monitor and predict environment-induced diseases and toxicity in humans.

Similarities in diesel exhaust particles induced alterations in expression of cytochrome P-450 and glutathione S-transferases in rat lymphocytes and lungs

Freshly prepared peripheral blood lymphocytes (PBL) are known to express cytochrome P450s (CYPs) and glutathione S-transferases (GSTs) involved in the bioactivation and detoxification of organic components of diesel exhaust particles (DEPs). To validate that blood lymphocyte expression profiles could be used as a biomarker to predict exposure to vehicular emissions, similarities in the alterations in the mRNA expression of CYPs and GSTs were studied in PBL and lungs of rats exposed to DEPs. Adult male Wistar rats were treated transtracheally with different doses of DEPs (3.75- or 7.5- or 15- or 30-mg/kg b.wt.). The animals were anaesthetized after 24 h and blood was drawn and lungs were taken out and processed. DEP produced a similar pattern of increase in the mRNA expression of CYPs (CYP1A1, 1A2, 1B1, 2E1), associated arylhydrocarbon receptor (Ahr) and arylhydrocarbon nuclear translocator (Arnt) and GSTs (GSTPi, GSTM1 and GSTM2) at all the doses in lungs and PBL. The protein expression of CYP1A1/1A2 and 2E1 and catalytic activity of CYPs and GSTs also showed a similar pattern of increase in blood lymphocyte and in lungs isolated from DEP treated rats. Our data indicating similarities in the alterations in the expression of carcinogen metabolizing CYPs and GSTs in PBL with the lung enzymes suggests the suitability of using expression profiles of blood lymphocyte CYPs and GSTs as a biomarker to predict exposure to vehicular emissions.

Evidence for cytochrome P450 2B1/2B2 isoenzymes in freshly prepared peripheral blood lymphocytes

Cytochrome P450 2B1 and 2B2, the major hepatic drug metabolizing enzymes belonging to CYP2 family and associated constitutive androstane receptor (CAR) were found to be expressed in peripheral blood lymphocytes (PBL) isolated from rats. As observed in liver, pretreatment of phenobarbital (PB) or phenytoin were found to increase the expression of CYP2B1, CYP2B2 and associated enzyme activity in PBL. Like in liver, blood lymphocyte CYP2B1/2B2 catalyzed the activity of 7-pentoxyresorufin O-dealkylase (PROD). The present data, demonstrating similarities in the regulation of blood lymphocyte CYP2B-isoenzymes with the liver enzymes, suggests that blood lymphocyte CYP2B-isoenzymes could be used as a biomarker to monitor tissue levels.

Induction of blood lymphocyte cytochrome P450 2E1 in early stage alcoholic liver cirrhosis

To validate the induction of blood lymphocyte cytochrome P450 2E1 (CYP2E1) expression in alcoholic liver cirrhosis and mRNA and protein expression of CYP2E1 in freshly prepared blood lymphocytes of alcoholic liver cirrhotic (ACP), nonalcoholic cirrhotic patients (NACP), alcoholic controls (ACs), and nonalcoholic controls (NACs) were investigated. Registered ACP and NACP patients at Sanjay Gandhi Postgraduate Institute of Medical Science, Lucknow, India along with NACs and ACs were included in the study. Real time polymerase chain reaction, enzyme-linked immunosorbent assay, and CYP2E1-dependent enzyme activity were determined in blood lymphocytes isolated from cases and controls. Significant increases in CYP2E1 mRNA and protein expression were observed in freshly prepared blood lymphocytes isolated from ACs and ACP patients as compared with respective NACs or NACP patients. A concomitant increase in N-nitrosodimethyamine demethylase activity was evident in the blood lymphocytes of ACs and ACP patients. Interestingly, the comparative increase observed in CYP2E1 expression was of greater magnitude in the blood lymphocytes isolated from ACP patients, although they abstained from alcohol drinking. Findings suggest that significant increase in the CYP2E1 mRNA and protein expression in the blood lymphocytes, isolated from early stage ACP patients, can be used to predict alcohol-induced toxicity.

Identification of internal control genes for quantitative expression analysis by real-time PCR in bovine peripheral lymphocytes

Gene expression studies in blood cells, particularly lymphocytes, are useful for monitoring potential exposure to toxicants or environmental pollutants in humans and livestock species. Quantitative PCR is the method of choice for obtaining accurate quantification of mRNA transcripts although variations in the amount of starting material, enzymatic efficiency, and the presence of inhibitors can lead to evaluation errors. As a result, normalization of data is of crucial importance. The most common approach is the use of endogenous reference genes as an internal control, whose expression should ideally not vary among individuals and under different experimental conditions. The accurate selection of reference genes is therefore an important step in interpreting quantitative PCR studies. Since no systematic investigation in bovine lymphocytes has been performed, the aim of the present study was to assess the expression stability of seven candidate reference genes in circulating lymphocytes collected from 15 dairy cows. Following the characterization by flow cytometric analysis of the cell populations obtained from blood through a density gradient procedure, three popular softwares were used to evaluate the gene expression data. The results showed that two genes are sufficient for normalization of quantitative PCR studies in cattle lymphocytes and that YWAHZ, S24 and PPIA are the most stable genes.

Polycyclic aromatic hydrocarbon metabolizing cytochrome P450s in freshly prepared uncultured rat blood lymphocytes

In an attempt to develop blood lymphocyte cytochrome P450 expression profile as a surrogate to monitor tissue enzyme, the present study aimed to identify the expression and regulation of polycyclic aromatic hydrocarbons (PAHs) responsive CYPs in freshly prepared rat blood lymphocytes. Semi-quantitative and RT-PCR studies demonstrated constitutive and inducible mRNA expression of CYP1A1, 1A2, 1B1 isoenzymes and the associated transcription factors, aryl hydrocarbon receptor (AhR) and AhR translocator (ARNT) in blood lymphocytes. Absolute quantification using RT-PCR revealed several fold lower basal expression of CYP1A1, 1A2 and 1B1 in lymphocytes when compared to the liver. However, significant increase in the mRNA expression of these isoenzymes as well as AhR and ARNT in lymphocytes following pretreatment with 3-methylcholanthrene (MC) have demonstrated that responsiveness is retained in the blood lymphocytes, though the magnitude of increase is several fold lower when compared to liver. This increase in the mRNA expression was found to be associated with an increase in the protein expression of CYP1A1 and 1A2 in blood lymphocytes. Further, CYPs expressed in blood lymphocytes catalysed the O-dealkylation of 7-ethoxy- and 7-methoxyresorufins (ER or MR), though the reactivity was several fold lower in lymphocytes when compared to the liver enzyme. Our data providing quantitative evidence for similarities in the regulation of PAH-regulated CYP in uncultured and non-mitogen stimulated blood lymphocytes with the liver enzyme has led us to suggest that blood lymphocytes could be used as a surrogate to monitor tissue expression of CYPs.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Cellular metabolism of brevetoxin (PbTx-2) by a monocyte cell line (U-937)

Blooms of Karenia brevis produce brevetoxins which cause neurotoxic shellfish poisoning and respiratory symptoms in humans as well as harmful effects on sea life. To investigate potential effects of brevetoxins on immune system components, a monocyte cell line (U-937) was exposed in vitro to PbTx-2. U-937 cells metabolized PbTx-2 through cellular detoxification mechanisms, as evidenced by depletion of intracellular glutathione and formation of glutathione and cysteine conjugates. Total intracellular glutathione was significantly decreased in toxin-treated cells compared to control cells, as measured using an enzymatic recycling method. LC/MS was used to detect the following brevetoxin metabolites: a cysteine-PbTx-2 conjugate (m/z 1018) and two putative glutathione-PbTx-2 conjugates (m/z 1204 and 1222). During 3h incubation, glutathione conjugates were detectable as early as 1h and increased in concentration after 2 and 3h. A cysteine-PbTx-2 conjugate appeared after 2h and increased in concentration after 3h. Detectable levels of brevetoxin conjugates were present in response to toxin concentrations of 1muM. Depletion of intracellular glutathione and formation of brevetoxin metabolites, with changes in concentrations over time, suggest immune cells (U-937) have important cellular detoxification pathways for PbTx-2.

DNA damage and mutagenicity induced by endosulfan and its metabolites

Endosulfan is a widely used broad-spectrum organochlorine pesticide, which acts as a contact and stomach poison. Nontarget species, such as cattle, fish, birds, and even humans, are also affected. Studies on the genotoxicity and mutagenicity of endosulfan have been inconsistent and nothing is known about the genotoxicity of its metabolites. In the present study, endosulfan (as a commercial isomeric mixture and as the alpha- and beta-isomers), and metabolites of endosulfan (the sulfate, lactone, ether, hydroxyether, and diol derivatives) were assayed for their ability to induce DNA damage in Chinese hamster ovary (CHO) cells and human lymphocytes using the Comet assay and were assayed for their mutagenicity using the Salmonella reversion assay (Ames test with TA98, TA97a, TA102, TA104, and TA100, with and without S9 activation). The compounds produced statistically significant (P < 0.01), concentration-dependent (0.25-10 microM) increases in DNA damage in both CHO cells and human lymphocytes. Endosulfan lactone caused the most DNA damage in CHO cells, while the isomeric mixture of endosulfan produced the greatest response in lymphocytes. The test compounds also were mutagenic in Salmonella strains at concentrations of 1-20 mug/plate (P < 0.05), with TA98 being the most sensitive strain and the diol and hydroxyether metabolites producing the highest responses. The results indicate that exposure to sublethal doses of endosulfan and its metabolites induces DNA damage and mutation. The contribution of the metabolites to the genotoxicity of the parent compound in Salmonella and mammalian cells, however, is unclear, and the pathways leading to bacterial mutation and mammalian cell DNA damage appear to differ.

Evidence for cytochrome P450 3A expression and catalytic activity in rat blood lymphocytes

Freshly isolated peripheral blood lymphocytes from control rats were found to catalyze the N-demethylation of erythromycin, known to be mediated by cytochrome P450 3A (CYP3A) isoenzymes in rat liver. Pretreatment of rats with dexamethasone (100 mg/kgx3 days, i.p.), a CYP3A inducer, resulted in 3-4-fold increase in the activity of erythromycin demethylase (EMD) in freshly isolated peripheral blood lymphocytes. This increase in the enzyme activity was found to be associated with an increase in the rate of the reaction and affinity of the substrate towards the enzyme. Significant inhibition of the EMD activity on in vitro addition of ketoconazole, a specific CYP3A inhibitor in liver and polyclonal antibody raised against rat liver CYP3A have suggested that EMD activity in blood lymphocytes is catalyzed primarily by CYP3A isoenzymes. Further, immunoblot analysis with polyclonal antibody raised against rat liver CYP3A revealed significant immunoreactivity, co-migrating with the liver isoenzyme, indicating constitutive expression of CYP3A in blood lymphocytes. Pretreatment with dexamethasone was found to significantly increase the expression of CYP3A protein in freshly isolated rat blood lymphocytes, as observed with liver. Likewise, significant CYP3A mRNA detected in control rat blood lymphocytes has further demonstrated constitutive expression of CYP3A isoenzymes in blood lymphocytes. Furthermore, several fold increase in CYP3A mRNA expression following pretreatment with dexamethasone showed similarities in the regulation of CYP3A isoenzymes in rat blood lymphocytes with the liver enzyme. The data suggest that the blood lymphocytes can be used to monitor tissue expression of CYP3A isoenzymes and validate the suitability of lymphocytes as surrogates of CYP status in less accessible target tissues.

The possibility of cytochrome P450 1A1/1A2 induction in cells of distant lymph nodes of rats after enteral treatment with benzo[a]pyrene

The mesenteric, mediastinal, and popliteal lymph nodes of rats were studied by indirect immunoperoxidase method using monoclonal antibodies to cytochrome P450 1A1/1A2 after oral treatment with benzo[a]pyrene. These cytochrome forms were detected in monocytes, macrophages, reticular and littoral cells, cell detritus, and liquid contents of the paracortical and medullary sinuses of all studied lymph nodes. The results indicate that exo- and endogenous toxic substances are oxidized not only in the liver, but also in lymph nodes.

Human response to dioxin: aryl hydrocarbon receptor (AhR) molecular structure, function, and dose-response data for enzyme induction indicate an impaired human AhR

The aryl hydrocarbon receptor (AhR) mediates nearly all studied adverse effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and many related compounds. Binding of TCDD or related ligands to AhR is the key initiating event in downstream biochemical responses. The binding affinity of AhR for TCDD is specific to species and strain, and studies of human AhR demonstrate binding affinities approximately an order of magnitude or more lower than those observed in the most sensitive laboratory strains and species. Molecular genetic studies confirmed that human AhR shares key mutations with the DBA mouse strain that result in an "impaired" AhR (with respect to TCDD binding and responsiveness). Despite a number of polymorphisms in human AhR, the key "DBA-type" mutations appear to be a constant feature of the human AhR, and no polymorphisms have been identified that compensate for the impaired binding function conferred by these mutations. Consistent with the impaired binding status of the human AhR, human cells have consistently required approximately 10-fold higher concentrations of TCDD in vitro than rodent cells to respond with enzyme induction. Recent studies of in vivo enzyme induction-related endpoints in human populations with moderately and highly increased TCDD body burdens detected no relationship between these endpoints and TCDD body burdens at body-burden levels up to 250 ng TEQ/kg body weight, or approximately 25 times above the upper range of current general population background body burdens, while marked elevations in enzyme activity were observed in persons with body burdens above 750 ng TEQ/kg. In contrast, the more sensitive laboratory rodent strains and species exposed to TCDD exhibit significant enzyme induction at body burdens below 50 ng/kg. These interspecies data on the most sensitive and best understood response to binding of TCDD and related compounds to the AhR are consistent with the binding affinity and molecular structure data and support the hypothesis that the human AhR is less functional than the AhR of the more sensitive laboratory animals at a molecular level. Quantitative risk assessments involving interspecies extrapolation from sensitive laboratory species and strains should take these fundamental differences into account when margins of exposure and safety factors are considered.

Role of bioactivation in drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are a major problem in both clinical treatment and drug development. This review covers recent developments in our understanding of the pathogenic mechanisms involved, with special focus on the potential role of metabolism and bioactivation in generating a chemical signal for activation of the immune system. The possible role of haptenation and neoantigen formation is discussed, alongside recent findings that challenge this paradigm. Additionally, the essential role of costimulation is examined, as are the potential points whereby costimulation may be driven by reactive metabolites. The relevance of local generation of metabolites in determining the location and character of a reaction is also covered.

Evidence for cytochrome P450 2E1 catalytic activity and expression in rat blood lymphocytes

Studies initiated to characterize cytochrome P450 2E1(CYP2E1) in freshly isolated rat blood lymphocytes revealed significant mRNA of CYP2E1 in control blood lymphocytes. RT-PCR studies have shown that as observed in liver, acute treatment of ethanol (single oral dose of 0.8 ml/kg b.wt, i.p), resulted in increase in the mRNA expression of CYP2E1 in freshly isolated rat blood lymphocytes. Western blotting studies using polyclonal antibody raised against rat liver CYP2E1 demonstrated significant immunoreactivity, comigrating with the liver isoenzyme, in freshly isolated control rat blood lymphocytes. Similar to that seen in liver, pretreatment of ethanol was found to produce an increase in the CYP2E1 isoenzyme in the blood lymphocytes. Blood lymphocytes were also found to catalyze the CYP dependent N-demethylation of N-nitrosodimethylamine (NDMA), which like in liver increased 2-3 fold following pretreatment of rats with known CYP2E1 inducers. Kinetic studies have further shown significant increase in the apparent Vmax and the affinity towards the substrate in rat blood lymphocytes indicating that as observed in liver, the increase in mRNA and protein expression following exposure to CYP2E1 inducers is associated with the increased catalytic activity of CYP2E1 in freshly isolated rat blood lymphocytes. The data indicating similarities of the blood lymphocyte CYP2E1 with the liver enzyme suggest that lymphocyte CYP2E1 levels in freshly isolated rat blood lymphocytes could be used to monitor tissue enzyme levels.

Hematite (Fe2O3) acts by oxydative stress and potentiates benzo[a]pyrene genotoxicity

Since epidemiological studies have implicated the co-exposition of iron oxides and polycyclic aromatic hydrocarbons as potential etiological factors involved in the excess of mortality from lung cancer in miners, experimental studies have been performed to investigate the role of iron on benzo[a]pyrene (B[a]P)-induced lung pathogenesis. We demonstrated previously that in vivo damage was higher when B[a]P was coated onto hematite than when B[a]P was administered alone. In order to determine the role of (i) different cell types and (ii) adsorption of hematite in this potentiation, in vitro studies were developed. The Comet assay was first used to measure DNA damage in four isolated cell types from Sprague-Dawley rats at 1, 2, 4, 8 and 24h after in vitro treatment with hematite (Fe2O3) or B[a]P or B[a]P coated onto hematite. For the two treatments with B[a]P, no damage was observed in alveolar macrophages, but significant increases in damage were seen in lymphocytes, hepatocytes and lung cells (where the effects of B[a]P coated onto hematite were stronger than those of B[a]P alone). In a second part of the study, the Comet assay was conducted with lung cells to measure the in vitro effect of (i) the coating and (ii) the role of the physical properties of Fe2O3. A statistically significant increase in damage was observed for the coating of B[a]P onto Fe2O3 compared (i) with their simple addition and (ii) with the coating of B[a]P onto graphite used as an inert compound. This study showed that (i) Fe2O3/B[a]P acts essentially in lung cells, (ii) the coating is a primordial step and (iii) the physical properties of Fe2O3 play a very minor role, which suggests another mechanism of action to explain the higher toxicity. Hence, our data may contribute to explain the excess of mortality in epidemiological studies and overall why exposures to B[a]P coated onto Fe2O3 resulted in higher toxicity in rodents compared to exposure to B[a]P alone.

Only truncated, not complete cytochrome p450 2D6 RNA transcript and no detectable enzyme activity are expressed in human lymphocytes

Genotyping of the highly polymorphic cytochrome p450 2D6 (CYP2D6) permits a gross classification of individual phenotype (viz. ultra-rapid, extensive, and poor metabolizers). It does not, however, provide a precise prediction of CYP2D6 activity, particularly in an individual possessing at least one functional CYP2D6 allele. It has been suggested that the level of mRNA expression or enzyme activity in lymphocytes, isolated from blood, could potentially provide a better quantitative estimate of in vivo hepatic enzymatic activity in human subjects. Although short sequences of CYP2D6 mRNA have been detected in human lymphocytes by reverse transcriptase-polymerase chain reaction (RT-PCR) that suggests the potential use of lymphocyte RNA as a readily accessible biomarker, it is not known whether a functional enzyme is expressed in human lymphocytes. In this study, human lymphocyte activity was assessed with a CYP2D6-specific, high-turnover probe substrate that is severalfold more sensitive than traditional markers of CYP2D6 (e.g., dextromethorphan). CYP2D6 catalytic activity could not be detected in homogenates of human lymphocytes, even at high protein concentrations and with supplementation of enzyme cofactors. Further RT-PCR analysis of lymphocytes collected from eight human donors revealed the presence of only a fragment, but not the complete transcript, of CYP2D6 mRNA. Northern blot RNA transcript analysis also failed to indicate the presence of the full-length transcript in lymphocytes. Collectively, these data indicate that human lymphocytes express neither the full-length CYP2D6 mRNA transcript nor functional enzyme activity. Therefore, the utility of lymphocytes as a functional biomarker for CYP2D6 enzyme activity is not clear at present.

Hematite (Fe(2)O(3)) enhances benzo[a]pyrene genotoxicity in endotracheally treated rat, as determined by Comet Assay

Since epidemiological studies have firmly implied the co-exposition between iron oxides and polycyclic aromatic hydrocarbons (PAH) as potential etiological factor involved in the excess of mortality by lung cancer in miners, experimental studies have been performed to investigate the role of iron particles on benzo[a]pyrene (B[a]P)-induced lung pathogenesis. In the present study, the alkaline single-cell gel electrophoresis (SCGE; Comet Assay) was used to measure DNA single-strand breaks in four cell types (alveolar macrophages, lung cells, peripheral lymphocytes and hepatocytes) of OFA Sprague-Dawley rats 24h after endotracheal administration of a single dose of an iron oxide (hematite; Fe(2)O(3)) (0.75mg) or B[a]P (0.75mg) or B[a]P (0.75mg) coated onto hematite particles (0.75mg). No damage was observed in cell from the four investigated organs in rats treated with iron oxide alone, while a statistically significant increase in DNA damage was observed compared with control animals in all tested cell types of rats treated with B[a]P alone or in association with hematite. The highest levels of damage were observed in lung cells and peripheral lymphocytes; the levels of damage in alveolar macrophages and hepatocytes were increased, but to a lesser extent compared with the first two cell types. The main finding was to notice a statistically significant increase of the damage in all organs of rats treated with B[a]P coated onto hematite (approximately two-fold increases; P<0.001), versus B[a]P alone. The current study shows that iron particles increase the genotoxic properties of B[a]P in the respiratory tract of endotracheally treated OFA Sprague-Dawley rats. Hence, our data may contribute to explain the excess mortality by lung cancer in epidemiological studies and overall why exposures to B[a]P coated onto Fe(2)O(3) particles resulted in higher toxicity in rodents compared with exposure to B[a]P alone.

Functional activation of arylhydrocarbon receptor (AhR) in primary T cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exerts diverse adverse health effects by activating the transcription factor arylhydrocarbon receptor (AhR). The activated AhR induces the expression of various genes having xenobiotic responsive elements (XREs) in their enhancer regions, such as the gene for cytochrome P-450 1A1 (CYP1A1). The immune system is sensitively affected by TCDD, while the precise mechanism of how TCDD acts in each immune cell type remains to be determined. The results of previous studies on AhR activation in B cell lines, T cell clones, and thymocytes, which mainly consist of immature T cells, suggested that AhR in mature T cells is inactive, whereas that in B cells and immature T cells act functionally. In the present study, we investigated whether or not TCDD induces the CYP1A1 gene by functionally activating AhR in primary mature T cells in mice. When the splenocytes that contain mature T and B lymphocytes as their predominant cell types or the thymocytes were cultured in the presence of TCDD, each of them showed a similar magnitude of CYP1A1 induction with a peak induction at 4 h. Both mature T cells and B cells that had been separated from total splenocytes also showed CYP1A1 induction at the same magnitude with a peak induction at 4 h. Gene expression of CYP1A1 was observed at 0.1 nM or greater concentrations of TCDD in splenocytes and separated T cells. The induction of CYP1A1 in T cells was confirmed in mice exposed to TCDD. These results indicate that TCDD induces the functional activation of AhR in primary mature T cells in mice.

The inhibition of superoxide production in EL4 lymphoma cells overexpressing growth hormone

A substantial body of research exists to support the production of growth hormone by cells of the immune system. However, the function and mechanism of action of lymphocyte-derived growth hormone remain largely unelucidated. Since, it has been found that exogenous growth hormone (GH) primes neutrophils for the production of reactive oxygen intermediates (ROI) and in particular superoxide (O2-), we investigated the role of GH on the production of O2- in T cells. Furthermore, we examined whether endogenous and exogenous GH act similarly. Our studies show that overexpression of GH in EL4, a T-cell lymphoma cell line, results in a decrease in the production of O2- compared to control cells, as detected using the fluorescent dye, dihydroethidium. O2- production in control cells was not affected by treatment with inhibitors of xanthine oxidase or a non-specific NADPH-oxidase inhibitor. However, treatment with diallyl sulfide, an inhibitor of cytochrome P450 2E1 mimicked the reduction in O2- production seen in cells overexpressing GH. Although no significant change could be detected in CYP2E1 protein levels, CYP2E1 activity was found to be greater in control EL4 than in cells overexpressing GH. Both the decrease in O2- production and the lower CYP2E1 activity in GH overexpressing cells could be abrogated by treatment with N(G)-monomethyl-L-arginine, an inhibitor of nitric oxide synthase. The overexpression of GH protects cells from apoptosis induced by isoniazid, a CYP2E1 inducer, suggesting a role for nitric oxide as a mediator in the regulation of xenobiotic metabolism and apoptosis-protection by lymphocyte GH.

Assessment of genotoxic effect of benzo[a]pyrene in endotracheally treated rat using the comet assay

Although benzo[a]pyrene (B[a]P) is a well-known genotoxic agent, little is known about the extent of DNA effects induced by B[a]P in rat tissues after pulmonary exposure. The alkaline single-cell gel electrophoresis (comet assay) was used to measure DNA single-strand breaks in alveolar macrophages, lung cells, peripheral lymphocytes and hepatocytes of OFA Sprague-Dawley rats exposed to a single dose of B[a]P by endotracheal administration. Statistically significant damage was observed in all organs tested after 3, 24 and 48h of pulmonary exposure to 3mg of B[a]P per animal, with a time-dependent relationship. The maximum damage was observed in the four cell types 24h after exposure. The higher level of damage was observed both in lung cells and peripheral lymphocytes; in alveolar macrophages and hepatocytes the level of damage was increased, but at a lower level than in the two other cell types. Furthermore, B[a]P demonstrated a clear dose-related genotoxic activity in the lung cells when tested at doses of 0.75, 1.5 and 3mg. The current study shows that B[a]P caused DNA single-strand breaks in the respiratory tract of endotracheally treated OFA Sprague-Dawley rats. The study also suggests that pulmonary exposure to B[a]P can induce a high level of DNA damage in peripheral lymphocytes. The clear relationship between lung exposure to B[a]P and consequences observed in lymphocytes suggests that the comet assay in peripheral lymphocytes can be used as a sensitive marker in human monitoring studies.

Cytochrome P450 2E1 dependent catalytic activity and lipid peroxidation in rat blood lymphocytes

To investigate the similarities in the catalytic activity of blood lymphocyte P450 2E1 in blood lymphocyte with the liver isoenzyme, NADPH dependent lipid peroxidation and activity of N-nitrosodimethyamine demethylase (NDMA-d) was studied in rat blood lymphocytes. Blood lymphocytes were found to catalyse NADPH dependent (basal) lipid peroxidation and demethylation of N-nitrosodimethylamine (NDMA). Pretreatment with ethanol or pyrazole or acetone resulted in significant increase in the NADPH dependent lipid peroxidation and the activity of NDMA-d in blood lymphocytes and liver microsomes. In vitro addition of CCl(4) to the blood lymphocytes isolated from control or ethanol pretreated rats resulted in an increase in the NADPH dependent lipid peroxidation. Significant inhibition of the basal and CCl(4) supported NADPH dependent lipid peroxidation and NDMA-d activity in blood lymphocytes isolated from control or ethanol pretreated rats by dimethyl formamide or dimethyl sulfoxide or hexane, solvents known to inhibit P450 2E1 catalysed reactions in liver and anti- P450 2E1, have indicated the role of P450 2E1 in the NADPH dependent lipid peroxidation in rat blood lymphocytes. The data indicating similarities in the NADPH dependent lipid peroxidation and NDMA-d activity in blood lymphocyte with the liver microsome have provided evidence that blood lymphocyte P450 2E1 could be used as a surrogate to monitor and predict hepatic levels of the enzyme.