Inducibility of cytochromes P-450 by dioxin in liver and extrahepatic tissues of the marmoset monkey (Callithrix jacchus)

Immunoanalysis methods for the detection of dioxins and related chemicals

With the development of biotechnology, approaches based on antibodies, such as enzyme-linked immunosorbent assay (ELISA), active aryl hydrocarbon immunoassay (Ah-I) and other multi-analyte immunoassays, have been utilized as alternatives to the conventional techniques based on gas chromatography and mass spectroscopy for the analysis of dioxin and dioxin-like compounds in environmental and biological samples. These screening methods have been verified as rapid, simple and cost-effective. This paper provides an overview on the development and application of antibody-based approaches, such as ELISA, Ah-I, and multi-analyte immunoassays, covering the sample extraction and cleanup, antigen design, antibody preparation and immunoanalysis. However, in order to meet the requirements for on-site fast detection and relative quantification of dioxins in the environment, further optimization is needed to make these immuno-analytical methods more sensitive and easy to use.

In vitro exposure of precision-cut lung slices to 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole lysylamide dihydrochloride (NSC 710305, Phortress) increases inflammatory cytokine content and tissue damage

The anticancer drug (2-[4-amino-3-methylphenyl]-5-fluorobenzothiazole lysylamide dihydrochloride) (NSC 710305, Phortress) is a metabolically activated prodrug that causes DNA adduct formation and subsequent toxicity. Preclinically, it was found that hepatic, bone marrow, and pulmonary toxicity presented challenges to developing this drug. An ex vivo precision-cut lung slice (PCLS) model was used to search for concentration dependent effects of NSC 710305 (10, 25, 50, and 100 µM) on cytokine content, protein content, and immuno/histological endpoints. Preparation and culture of PCLS caused an initial spike in proinflammatory cytokine expression and therefore treatment with NSC 710305 was delayed until 48 h after initiating the slice cultures to avoid confounding the response to slicing with any drug response. PCLSs were evaluated after 24, 48, and 72 h exposures to NSC 710305. Reversibility of toxicity due to the 72-h treatment was evaluated after a 24-h recovery period. NSC 710305 caused a concentration-dependent cytokine response, and only the toxicity caused by a 72-h exposure to 25 µM reversed during the 24-h recovery period. Immuno/histological examination and quantitation of tissue protein levels indicated that tissue destruction, ED-1 (activated macrophage) staining, and protein levels were associated with the levels of proinflammatory cytokines in the tissue. In conclusion, the concentration- and time-dependent inflammatory response of PCLS to NSC 710305 preceded relevant tissue damage by a few days. The no-observable adverse effect level (NOAEL) for 24, 48, and 72 h exposures was established as 10 µM NSC 710305.

Debrisoquine metabolism and CYP2D expression in marmoset liver microsomes

The objective of this study was to define CYP2D enzymes in marmoset (Callithrix jacchus) liver microsomes, both at the activity level using debrisoquine as the model substrate and at the protein level using antibodies raised to human CYP2D6. Marmoset liver microsomes were incubated with [(14)C]debrisoquine, and the structure of the generated metabolites was determined using liquid chromatography-tandem mass spectrometry and NMR. Marmoset liver microsomes were very effective in hydroxylating debrisoquine at various positions. Although 4-hydroxydebrisoquine was formed, in contrast to rat and human it was only a minor metabolite. Debrisoquine was more extensively hydroxylated in the 7, 5, 6, and 8 positions. In addition to the monohydroxylated metabolites, a dihydroxy metabolite, namely 6,7-dihydroxydebrisoquine, was identified. Finally, metabolites that had undergone ring opening were also detected but were not investigated further. Antibodies to CYP2D6 immunoreacted with protein in marmoset and human but not rat hepatic microsomes. In conclusion, we demonstrate that marmoset liver microsomes are effective in hydroxylating debrisoquine at various positions and that they contain a protein that is immunorelated to human CYP2D6.

EROD and MROD as Markers of Cytochrome P450 1A Activities in Hepatic Microsomes from Entire and Castrated Male Pigs

In the present study, we characterized the kinetic parameters of 7-ethoxy-resorufin O-deethylation (EROD) and 7-methoxyresorufin O-demethylation (MROD) in hepatic microsomes from entire and castrated male pigs. Validation parameters of an HPLC-based method to analyse EROD and MROD activities are also described. Eadie-Hofstee plot analysis demonstrated a biphasic kinetic of EROD, indicating that at least two forms of cytochrome P450 are involved in this reaction. MROD followed monophasic kinetic, suggesting that a single enzyme, or enzymes with similar affinities, is responsible for the reaction. Inhibitory effects of α-naphthoflavone (ANF), ellipticine and furafylline were studied using microsomes from entire and castrated male pigs. ANF is a known inhibitor of both cytochrome P₄₅₀ 1A1 and 1A2 (CYP1A1 and CYP1A2); the presence of ANF in the incubations resulted in the inhibition of both EROD and MROD activities in porcine liver microsomes. EROD activities in porcine liver microsomes were also inhibited by selective CYP1A1 inhibitor ellipticine, but not by CYP1A2 inhibitor furafylline. MROD activities were strongly inhibited by ellipticine and to a much lesser extent by furafylline. Further studies are needed to evaluate substrate specificities of porcine CYP1A1 and CYP1A2.

Perinatal dioxin exposure, cytochrome P-450 activity, liver functions and thyroid hormones at follow-up after 7-12 years

OBJECTIVES

Prenatal and lactational exposure to Dutch "background" dioxin levels may cause health effects spanning many years. In addition, perinatal studies have shown a relationship between dioxin exposure and thyroid disturbance. To assess the later health effects of prenatal and lactational dioxin exposure on liver function we measured plasma ALAT and ASAT levels amongst our longitudinal cohort, as was done perinatally and at 2(1/2) years. The children underwent a caffeine loading test to determine CYP1A2 activity. To assess the later effects on thyroid function we measured plasma TSH and FT4.

STUDY DESIGN

A longitudinal cohort of 37 healthy children (age 7-12, mean 8.2 years), with documented prenatal and lactational dioxin exposure, ingested 3mg caffeine/kg BW 6h prior to blood withdrawal. Paraxanthine/caffeine molar ratio, ALAT, ASAT, TSH and FT4 were determined in venous blood.

RESULTS

Linear regression of ASAT and ALAT revealed no relation with prenatal and lactational dioxin exposure. No correlation was found between the paraxanthine/caffeine molar ratio and prenatal and lactational dioxin exposure. Linear regression of TSH and FT4 revealed no relation with prenatal and lactational dioxin exposure.

CONCLUSION

This follow-up has shown a normalisation of previously abnormal ALAT and ASAT levels, indicating a transient effect. CYP1A2 activity, measured by means of a caffeine-loading test, revealed no correlation with the prenatal and lactational exposures. A normalisation of previously abnormal thyroid hormone homeostasis was seen, also possibly indicating a transient effect. This study provides new data on long-term follow-up after perinatal dioxin exposure to background levels of dioxins.

Cloning of a cDNA encoding a novel marmoset CYP2C enzyme, expression in yeast cells and characterization of its enzymatic functions

We cloned a cDNA encoding a novel CYP2C enzyme, called P450 M-2C, from a marmoset liver. The deduced amino acid sequence showed high identities to those of human CYP2C8 (87%), CYP2C9 (78%) and CYP2C19 (77%). The P450 M-2C enzyme expressed in yeast cells catalyzed p-methylhydroxylation of only tolbutamide among four substrates tested, paclitaxel as a CYP2C8 substrate, diclofenac and tolbutamide as CYP2C9 substrates and S-mephenytoin as a CYP2C19 substrate. p-Methylhydroxylation of tolbutamide by marmoset liver microsomes showed monophasic kinetics, and the apparent K(m) value (1.2 mM) for the substrate was similar to that of the recombinant P450 M-2C (1.8 mM). Although all of the recombinant human CYP2C8, CYP2C9 and CYP2C19 expressed in yeast cells catalyzed tolbutamide p-methylhydroxylation, the kinetic profile of CYP2C8 was most similar to that of P450 M-2C. Tolbutamide oxidation by the marmoset liver microsomes and the recombinant P450 M-2C was inhibited most effectively by quercetin, a CYP2C8 inhibitor, followed by omeprazole, a CYP2C19 inhibitor, whereas sulfaphenazole, a CYP2C9 inhibitor, was less potent under the conditions used. These results indicate that P450 M-2C is the major tolbutamide p-methylhydroxylase in the marmoset liver.

Localization of cytochrome P450 1A1 in a specific region of hydronephrotic kidney of rat neonates lactationally exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Hydronephrosis is typically observed in terata caused by in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), via the arylhydrocarbon receptor, but the molecular mechanism underlying its pathogenesis is largely unknown. In the present study, pregnant Holtzman rats were treated once by gavage with TCDD (1.0 microg/kg bw) or corn oil on gestation day 15. All dams were allowed to litter, and standardized litters in terms of litter size were then reciprocally cross-fostered on postnatal day (PND) 1. On PND1, pups were divided into four experimental groups: pups exposed only in utero, pups exposed only lactationally, pups not exposed via either route (vehicle control), and pups exposed via both routes. Pups were euthanized on PND21 for further analyses. The TCDD dose used was not overtly toxic to the dams or neonates. The incidence and severity of hydronephrosis were markedly high in pups exposed to TCDD lactationally, but not those exposed in utero. On PND21, cytochrome P450 (CYP) 1A1 was detected predominantly in the outer zone of the medulla of the kidney from all the pups lactationally exposed to TCDD, regardless of the occurrence of hydronephrosis. Interestingly, TCDD concentrations in the cortex, the outer zone of the medulla and the inner zone of the medulla were similar. When adult Holtzman rats were administered TCDD, the induction of CYP1A1 was immunohistochemically detected in the liver but not in the kidney 7 days postadministration. The present findings suggest that TCDD-inducible genes via an AhR-dependent mechanism may be associated with the etiology of hydronephrosis in a particular region of the kidney.

Molecular cloning and functional analysis of cytochrome P450 1A2 from Japanese monkey liver: comparison with marmoset cytochrome P450 1A2

A cDNA encoding a novel cytochrome P450 1A2 (CYP1A2) was cloned from the liver of an adult female Japanese monkey. The CYP1A2 protein was expressed in yeast cells and its enzymatic properties were compared with those of marmoset CYP1A2 using ethoxyresorufin (ER) and phenacetin (PN) as substrates. The nucleotide sequence of Japanese monkey CYP1A2 revealed 94.7, 99.5 and 93.5% identities to those of human, cynomolgus monkey and marmoset monkey CYP1A2, respectively. Multiple amino acid sequence alignment of Japanese monkey CYP1A2 with CYP1A2 of humans, cynomolgus monkeys and marmosets showed that Japanese monkey CYP1A2 had 92.4, 99.0 and 91.9% identities to the human, cynomolgus monkey and marmoset enzymes, respectively. Kinetic studies demonstrated that the enzymatic properties as ER and PN O-deethylases were considerably different between the Japanese monkey and the marmoset CYP1A2. Furthermore, both of these reactions in liver microsomal fractions from the Japanese monkey and marmoset showed biphasic kinetics. On the basis of the kinetic parameters, it is suggested that Japanese monkey CYP1A2 is a high-K(m) enzyme in both ER and PN O-deethylations, whereas marmoset CYP1A2 is a high-K(m) and low-K(m) enzyme in ER and PN O-deethylations, respectively. alpha-Naphthoflavone, an inhibitor of human CYP1A1 and CYP1A2, did not completely inhibit the liver microsomal oxidations of ER and PN even at the highest concentration (50muM), supporting the notion that CYP1A2 enzymes are not the sole ER or PN O-deethylase in Japanese monkey and marmoset liver microsomes. Inhibitory effects of furafylline, an inhibitor of human CYP1A2, on ER O-deethylation by recombinant CYP1A2 enzymes were much lower than those of alpha-naphthoflavone, but marmoset CYP1A2 was more sensitive to furafylline than Japanese monkey CYP1A2. These results indicate that the properties of Japanese monkey CYP1A2 are considerably different from those of marmoset CYP1A2.

Nafenopin-, ciprofibroyl-, and palmitoyl-CoA conjugation in vitro: kinetic and molecular characterization of marmoset liver microsomes and expressed MLCL1

Acyl-CoA conjugation of xenobiotic carboxylic acids is catalyzed by hepatic microsomal long-chain fatty acid CoA ligases (LCL, EC 6.2.1.3). Marmosets (Callithrix jacchus) are considered genetically closer to humans than rodents and are used in pharmacological and toxicological studies. We have demonstrated that marmoset liver microsomes catalyze nafenopin-, ciprofibroyl-, and palmitoyl-CoA conjugation and that only palmitoyl-CoA conjugation is significantly upregulated (1.7-fold, P < 0.02) by a high fat diet. Additionally, the apparent C(50) values for nafenopin-, ciprofibroyl-, and palmitoyl-CoA conjugation of 149.7, 413.4, and 3.4 microM were comparable to those reported for human liver microsomes viz, 213.7, 379.8, and 3.4 microM, respectively. Comparison with human data was enabled by the cloning of a full-length marmoset cDNA (MLCL1) that encoded a 698-amino-acid protein sharing 83% similarity with rat liver acyl-CoA synthetase (ACS1) and 93 and 90% similarity with human liver LCL1 and LCL2, respectively. MLCL1 transiently expressed in COS-7 cells activated nafenopin (C(50) 192.9 microM), ciprofibrate (C(50) 168.7 microM), and palmitic acid (C(50) 4.5 microM) to their respective CoA conjugates. This study also demonstrated that the sigmoidal kinetics observed for nafenopin- and ciprofibroyl-CoA conjugation were not unique to human liver microsomes but were also characteristic of marmoset liver microsomes and recombinant MLCL1. More extensive characterization of the substrate specificity of marmoset LCL isoforms will aid in determining further the suitability of marmosets as a model for human xenobiotic metabolism via acyl-CoA conjugation.

Distribution of cytochrome P4501A (CYP1A) in the tissues of Baltic ringed and grey seals

Information about the expression of CYP1A in wildlife species is essential for understanding the impact of organochlorine exposure on the health status of an exposed population. Therefore, we aimed at characterising a putative CYP1A enzyme expression in both hepatic and extrahepatic tissues of ringed and grey seals from the Baltic Sea and from less polluted waters. The cellular localisation of CYP1A was identified using a monoclonal antibody against scup P4501A1 (MAb 1-12-3). Immunohistochemical staining showed the highest level of CYP1A expression in liver hepatocytes, and the second highest level in the endothelial cells of capillaries and larger blood vessels in the liver and other organs. The most frequent and strongest staining was found in Baltic ringed seals. Although CYP1A-positive staining was observed in only a few tissues in the other seal populations, it was more intense in Baltic grey seals than in Canadian grey seals. The CYP1A enzyme activity, expressed as ethoxyresorufin O-deethylation (EROD), followed a similar tissue distribution and geographical pattern as the immunohistochemistry with clearly elevated EROD activities in most tissues of both Baltic seal populations. Immunochemical characterisation by immunoblotting confirmed the presence and elevation pattern of a putative CYP1A protein in ringed and grey seals, supporting our findings using other methods. The evenly distributed elevation of CYP1A expression among most of the tissues examined indicates that Baltic seals are exposed to CYP1A inducing agents affecting the whole body. This may result in an increased or decreased toxic potential of foreign substances, which may ultimately determine the biological effects of the contaminants.

Assessment of P450 induction in the marmoset monkey using targeted anti-peptide antibodies

The identity and expression of hepatic P450 enzymes in marmosets was investigated using a panel of anti-peptide antibodies originally targeted against human P450 enzymes. In immunoblotting, of 12 antibodies examined, 10 bound specifically to bands in marmoset liver microsomal fraction corresponding to P450 enzymes. It is proposed that these represent marmoset CYP1A1, CYP1A2, CYP2A, CYP2B, CYP2C forms (CYP2C-1 and CYP2C-2), CYP2D19, CYP3A21 and another CYP3A form (CYP3A-m). The antibodies, together with an anti-marmoset CYP2E1 antibody, were used to investigate the expression of 10 P450 enzymes in marmosets treated with P450-inducing chemicals. Treatment with phenobarbitone caused CYP2B, CYP2C-2 and CYP3A21 levels to increase, rifampicin caused increases in CYP2B and CYP2C-1 and a decrease in CYP3A21 levels, whereas dioxin caused CYP1A1 and CYP1A2 levels to increase and CYP2E1 levels to decrease. Clofibric acid did not induce any P450. P450 enzyme activities were assessed using 8 different substrates and increases were found after treatment with phenobarbitone, rifampicin, and dioxin. However, due to species differences in substrate selectivity, it proved difficult to ascribe these changes to individual P450 enzymes. Thus, the use of anti-peptide antibodies provides a more informative way of assessing the levels of specific P450 enzymes than enzyme activity measurements.

Developmental toxicity of the HIV-protease inhibitor indinavir in rats

BACKGROUND

Indinavir is an antiviral agent used for the treatment of HIV infection. We studied its developmental toxicity in rats.

METHODS

Pregnant animals were treated orally with 500 mg indinavir/kg body weight (bw) from day 6 to 15 of gestation (once daily) or from day 9 to 11 (twice daily). Fetuses were evaluated for external and skeletal anomalies on day 21 of gestation. In addition, 19 rats were treated from day 9 of gestation to day 24 postnatally with 500 mg indinavir/kg bw once daily; a control group of 17 rats was treated with the vehicle accordingly. Developmental landmarks were recorded. Sixteen offspring each were studied on postnatal days 7, 14, 21, and 35 for hepatic enzyme activity. Liver tissue was examined by electron microscopy.

RESULTS

Fetal examination on day 21 of pregnancy showed no treatment-related effects on number, weight, and viability of the fetuses; however, an increased incidence was noted in the supernumerary ribs and variations of the vertebral ossification centers in both indinavir-treated groups. Postnatal evaluation showed delayed fur development, eye opening, and descensus testis. The most striking finding was unilateral anophthalmia, observed in 7 pups (3%) from 2 out of 19 litters exposed to indinavir, but not in controls. Only minor changes in hepatic monooxygenase activities occurred in dams. Electron microscopy of liver samples showed hepatocellular inclusions of lipids and myelin figure-like structures in maternal livers and infiltration with granulocytes in offspring livers.

CONCLUSIONS

Further studies on reproductive toxicity, including combinations of three or more antiretroviral agents as used therapeutically, are needed to determine the hazards of such a treatment.

Molecular approaches to evaluate pollutants

Many organisms are in use to test pollutants and their extensive variability clearly emerges from reviews since researchers in the world are involved in continuous effort to set up new assays and to improve those already in use. In the present paper we focus the attention on the mixed function oxidase system and the DNA adduct formation which are two biomarkers widely used and extensively studied in mammals and fish by different Authors. We compare their results with the ones we obtained in amphibians, which result to be a good model. Moreover we present some significative results obtained by the use of cultured cell lines to test the herbicide MCPA. The results obtained demonstrate that the amphibian Xenopus is a suitable indicator for induction of cytochrome P-450 by B[a]P as well as for production of DNA adducts. Cultured cells evidenced that cytoskeletal array and thiol proteins are molecular targets of the herbicide used, demonstrating that risk assessment can be properly analysed in in vitro systems.

Identification of CYP2E1 in marmoset monkey

CYP2E1 is the main enzyme responsible for chlorzoxazone 6-hydroxylase activity in human liver. Here, it is shown that marmoset monkey liver microsomal fraction catalyses this reaction at a similar rate and with a similar Km to human liver and that the activity is increased 4-fold in marmosets treated with isoniazid, a known inducer of CYP2E1. This indicates that CYP2E1 is present in marmoset liver. However conversely, an anti-peptide antibody targeted against the C-terminus of human and cynomolgus monkey CYP2E1 (Val-Ile-Pro-Arg-Ser) failed to bind to marmoset monkey hepatic microsomal fraction. To investigate if there is a difference in the C-terminus of CYP2E1 in these species, this region of marmoset CYP2E1 was sequenced following amplification of marmoset liver cDNA with primers selected according to conserved regions identified in human and cynomolgus monkey CYP2E1. It was found that the deduced amino acid sequence of marmoset CYP2E1 in this region is very similar to human CYP2E1, but due to two base differences in the marmoset nucleic acid sequence, the C-terminus of marmoset CYP2E1 is extended by 2 amino acids, i.e. Val-Ile-Pro-Arg-Ser-Ser-Val. This difference is sufficient to prevent the binding of an antibody raised against the C-terminus of human CYP2E1. The expression of CYP2E1 in the marmoset was confirmed by raising an antibody against the deduced C-terminus of marmoset CYP2E1 (Pro-Arg-Ser-Ser-Val). In immunoblotting, this antibody bound to a single protein of 54 kDa in marmoset liver microsomal fraction. The intensity of the band was increased in isoniazid-treated marmosets, consistent with induction of CYP2E1. The antibody did not recognise human or cynomolgus monkey CYP2E1. This was expected since the immunising peptide sequence does not occur in these enzymes. The results demonstrate the presence of CYP2E1 in marmoset liver and illustrate the importance of the C-terminus for the production of specific antibodies against P450 enzymes.