Effect of chrysotile asbestos on cytochrome P-450-dependent monooxygenase and glutathione-S-transferase activities in rat lung

The in vitro and in vivo effect of a carcinogenic variety of asbestos, chrysotile, both on xenobiotic metabolizing enzymes such as benzo[a]pyrene hydroxylase, epoxide hydrolase as well as glutathione-S-transferase activities and microsomal lipid peroxidation in rat lung were examined. The in vitro incubation of chrysotile with microsomes significantly adsorbed heme proteins, cytochrome P-450 and P-448 with the concomitant decrease in the dependent monooxygenase activities. The prolonged incubation of this mineral fibre with microsomes also resulted in the release of heme. It also led to the depletion in the activities of epoxide hydrolase and glutathione-S-transferase. However, it induced lipid peroxidation. When these in vitro effects were validated in vivo, the exposure to early stages produced similar alterations as observed in in vitro studies. However, reverse pattern in the alterations was observed after 90 days of exposure except in the case of lipid peroxidation which remained induced.     

Comparative FISH mapping of human cDNA clones to chromosomes of the musk shrew (Suncus murinus, Insectivora)

Forty-one cDNA clones of human functional genes were newly mapped to chromosomes of the musk shrew (Suncus murinus, Insectivora) by fluorescence in situ hybridization, and a comparative cytogenetic map of 51 genes, including 10 genes reported in our previous study, was constructed between human (HSA) and musk shrew (SMU) chromosomes. In this comparative map, the 51 genes localized to human autosomes, except HSA 8, 16, and 20, were mapped to 15 shrew autosomes, except SMU 4, 16, 17 and 18. Twelve conserved segments were identified between human and shrew chromosomes, and six segments among the musk shrew, human, and mouse. Our results defined the presence of at least one inversion and several interchromosomal rearrangements that occurred during evolution after the two species diverged from a common ancestor. Localization of three major histocompatibility complex (MHC) genes to shrew chromosome 3 suggested that the MHC genes of the musk shrew are located in a cluster on chromosome 3. The cytogenetic map constructed in this study is the first cytogenetic map with many functional genes in insectivore species. This approach provides clues for clarifying the chromosomal evolution in this order.     

The house musk shrew (Suncus murinus): a unique animal with extremely low level of expression of mRNAs for CYP3A and flavin-containing monooxygenase

Expression of drug-metabolizing enzymes including cytochrome P450 (CYP) and flavin-containing monooxygenase (FMO) in various tissues of Suncus murinus (Suncus) were examined. Northern blot analysis showed that mRNAs hybridizable with cDNAs for rat CYP1A2, human CYP2A6, rat CYP2B1, human CYP2C8, human CYP2D6, rat CYP2E1, human CYP3A4 and rat CYP4A1 were expressed in various tissues from Suncus. The mRNA level of CYP2A in the Suncus lung was very high. Furthermore, it was found that the level of CYP2A mRNA in the Suncus lung was higher compared to the Suncus liver. The expression level of mRNA hybridizable with cDNA for human CYP3A4 was very low. The presence of CYP3A gene in Suncus was proven by the induction of the CYP with dexamethasone. Very low expression levels of mRNAs hybridizable with cDNAs for rat FMO1, rat FMO2, rat FMO3 and rat FMO5 were also seen in Suncus liver. No apparent hybridization band appeared when human FMO4 cDNA was used as a probe. The hepatic expression of mRNAs hybridizable with cDNAs for UDP-glucuronosyltransferase 1*6, aryl sulfotransferase, glutathione S-transferase 1, carboxyesterase and microsomal epoxide hydrolase in the Suncus were observed. These results indicate that the Suncus is a unique animal species in that mRNAs for CYP3A and FMO are expressed at very low levels.     

Use of a microelectrode array to record extracellular pacemaker potentials from the gastrointestinal tracts of the ICR mouse and house musk shrew (Suncus murinus)

BackgroundThe rhythmic contraction and relaxation of smooth muscles in the gastrointestinal (GI) tract is governed by pacemaker electrical potentials, also termed slow waves, which are calcium currents generated by interstitial cells of Cajal (ICCs). Malfunction of pacemaker rhythms contributes to a number of clinically challenging gastrointestinal motility disorders.MethodA microelectrode array (MEA) was used to record slow waves in vitro from intact GI tissues freshly isolated from the ICR mouse and Suncus murinus. The effects of temperature, extracellular calcium and potassium concentrations on pacemaker potentials were quantified using spatiotemporal metrics.ResultsPacemaker frequency decreased from the duodenum to the ileum in the mouse, but this phenomenon was less significant in Suncus murinus. In both the mouse and Suncus murinus, the stomach had a much lower pacemaker frequency than the intestine. Propagation velocity and amplitude were highest in the proximal intestine. Temperature significantly increased pacemaker frequency in the intestinal tissues of both species. Removal of Ca²⁺ from the medium inhibited pacemaker potential and increasing the Ca²⁺ concentration increased pacemaker frequency in the mouse ileum. Increasing K⁺ concentration decreased pacemaker frequency in the absence of nifedipine.ConclusionsThe MEA allows efficient investigation of gut pacemaker frequency and propagation.     

Genomic analyses of the Formosan harvest mouse (Micromys minutus) and comparisons to the brown Norway rat (Rattus norvegicus) and the house mouse (Mus musculus)

The harvest mouse, Micromys minutus (MMIN), has a very wide range of distribution (from the British Isles across the Euroasian continent to Japan and Taiwan). We studied an isolated population of MMIN in Taiwan, which is at the southeastern margin of the species’ geographic distribution, and compared its genetic complement with those of the same species previously reported from other geographic locations and with two model rodent species, the house mouse (Mus musculus) and the brown Norway rat (Rattus norvegicus). The diploid number (2N) of MMIN was 68, consistent with that reported for other populations. However, variations were noted in the fundamental number (FN) and the shape and banding patterns of the individual chromosomes among populations. The FN of MMIN was estimated to be 72, including 2 bi-armed autosomes, 31 one-armed autosomes, and one pair of one-armed sex chromosomes. Here, we propose the first ideogram for MMIN. C-banding, Ag-NOR, and the locations of 18S rRNA gene sequences (MMIN chromosomes no. 10, 14, 19, 29, 31, 33, and X) mapped by fluorescence in situ hybridization (FISH) are also reported. Additionally, we compared the 18S rDNA sequences and performed cross-species X chromosome painting (FISH) for M. minutus, M. musculus, and R. norvegicus. The results indicate that both genetic elements are rather conserved across species. Thus, implications for the phylogenetic position of Micromys were limited.     

Evidence for the involvement of cytochrome P-450-dependent monooxygenase(s) in the formation of genotoxic metabolites from N-hydroxyurea

Hydroxyurea induces DNA repair replication in the cytochrome P-450-containing C2Rev7 rat hepatoma cell line. Repair is severalfold increased by pretreatment of the cells with dexamethasone, which induces cytochrome P-450-dependent monooxygenase activities in these cells. In the dedifferentiated hepatoma line H5, which strongly expresses cytochrome P-448 but no cytochrome P-450-dependent enzyme activities, hydroxyurea is not genotoxic. The results support the notion that the formation of genotoxic metabolites from hydroxyurea is mediated by a cytochrome P-450-dependent enzyme.     

Identification of lactotropes (PRL cells), somatotropes (GH cells), corticotropes (ACTH cells) and thyrotropes (TSH cells) in the pituitary gland of the musk shrew, Suncus murinus L. (Insectivora), by immunohistochemistry

By means of immunohistochemistry, lactotropes, somatotropes, corticotropes and thyrotropes in the pituitary of the male musk shrew, Suncus murinus L., were identified at the electron-microscopic level. Lactotropes were classified into three types: type I containing large (200-450 nm in diameter) round secretory granules, type II with medium-sized (150-250 nm in diameter) ones and type III with small (50-150 nm in diameter) ones. Somatotropes were also classified into type I somatotropes that contain large (450 nm in diameter) spherical secretory granules and type II somatotropes containing comparatively small (300 nm in diameter) round granules. Both type I and II somatotropes were small and sometimes contained rod-shaped granules. Corticotropes were round or oval cells with round secretory granules in various densities and sizes (150-500 nm in diameter) scattered all over the cytoplasm. Thyrotropes were angular or polyhedral cells containing electron-transparent round secretory granules (200-300 nm in diameter) and large irregularly shaped granules with a maximum diameter of about 1,500 nm. Each type of the cells may be distinguished by its respective ultrastructural characteristics alone without the aid of immunohistochemistry.     

Monoclonal antibodies to liver microsomal cytochrome P-450E of the marine fish Stenotomus chrysops (scup): cross reactivity with 3-methylcholanthrene induced rat cytochrome P-450

Hybridomas were prepared from myeloma cells and spleen cells of BALB/c female mice immunized with hepatic cytochrome P-450E purified from the marine fish, Stenotomus chrysops (scup). Nine independent hybrid clones produced MAbs, either IgG1, IgG2b, or IgM, that bound to purified cytochrome P-450E in radioimmunoassay. Antibodies from one clone MAb (1-12-3), also strongly recognized rat cytochrome P-450MC-B (P-450BNF-B; P-450c). The nine antibodies inhibited reconstituted aryl hydrocarbon hydroxylase (AHH) and ethoxycoumarin O-deethylase of scup cytochrome P-450E to varying degrees, and inhibited AHH activity of beta-naphthoflavone-induced scup liver microsomes in a pattern similar to that in reconstitutions, indicating that cytochrome P-450E is identical to the AHH catalyst induced in this fish by beta-naphthoflavone. MAb 1-12-3 also inhibited the reconstituted AHH activity of the major BNF-induced rat isozyme. Conversely, MAb 1-7-1 to rat cytochrome P-450MC-B had little effect on AHH activity of scup cytochrome P-450E, and did not recognize cytochrome P-450E in radioimmunoassay nor in an immunoblot. Scup cytochrome P-450E and rat cytochrome P-450MC-B thus have at least one common epitope recognized by MAb 1-12-3, but the epitope recognized by Mab 1-7-1 is absent or recognized with low affinity in cytochrome P-450E. The various assays indicate that the nine MAbs against cytochrome P-450E are directed to different epitopes of the molecule. These MAbs should be useful in determining phylogenetic relationships of the BNF- or MC-inducible isozymes and their regulation by other environmental factors.     

Differential permeability of pineal capillaries to lanthanum ion in the rat (Rattus norvegicus), gerbil (Meriones unguiculatus) and golden hamster (Mesocricetus auratus)

Summary Capillaries in the pineal gland of the rat (Rattus norvegicus), gerbil (Meriones unguiculatus) and golden hamster (Mesocricetus auratus) were investigated by means of electron-microscopical tracer studies using lanthanum. The tracer was administered together with the fixative solution by perfusion via the left cardiac ventricle. In the rat, endothelial junctions of fenestrated capillaries are permeable to lanthanum. In the gerbil the tracer does not leave the capillaries, which are of the non-fenestrated type throughout the organ. In the golden hamster the two portions of the pineal system have different types of capillaries. While in the superficial pineal fenestrated capillaries permeable to lanthanum predominate, the deep pineal possesses capillaries that are, without exception, devoid of fenestrations and impermeable to the tracer. It is suggested that differences in the structure of the capillaries are related to differences in the extent of a specialized contact of the pineal gland to the third ventricle.The authors dedicate this paper to Professor H. Rollhäuser, Münster, on the occasion of his 65th birthday     

Effect of flumecinol (Zixoryn) on the cytochrome P450 and cytochrome P448 dependent hepatic microsomal monooxygenase activities in male rats.

The effect of three-day oral administration of 50 mg/kg bw. and 100 mg/kg bw. flumecinol (Zixoryn, Gedeon Richter Chemical Works Ltd., Budapest, Hungary) and intraperitoneal administration of 50 mg/kg bw. phenobarbital as well as the single intraperitoneal administration of 20 mg/kg bw. 3-methylcholanthrene on various cytochrome P450 and P448 dependent hepatic microsomal enzyme activities was studied in male albino Wistar rats. 50 mg/kg bw. flumecinol had no significant effect. 100 mg/kg bw. flumecinol had an inducing effect comparable to the one of phenobarbital. The activity of the cytochrome P448 dependent 7-ethoxyresorufin O-deethylase was enhanced by all three substances, but flumecinol's effect was by far behind that of 3-methylcholanthrene, so the carcinogenic promoter effect of flumecinol can be questioned.     

Structural analysis and specific expression of microsomal cytochrome P-450(M-1) mRNA in male rat livers

cDNA clones for the P-450(M-1) mRNA, which exhibits a male-specific expression in rat livers, were isolated by using synthetic oligonucleotides as the probes. Sequence analysis of the cDNAs showed that P-450(M-1) mRNA contains 1,853 nucleotides in addition to a poly(A) chain, and a single open reading frame of 1,500 nucleotides encodes a polypeptide of 500 amino acids with a Mr = 57,187. The predicted NH2-terminal sequence of 30 amino acids agrees well with that of the purified protein determined by Edman degradation, and the predicted primary structure included all the partial sequences of six internal peptides of P-450(M-1) obtained by the proteolytic digestion and a conserved amino acid sequence containing a putative heme-binding cysteine, proximate to the COOH terminus of the molecules. P-450(M-1) showed relatively high sequence similarity with P-450b (Fujii-Kuriyama, Y., Mizukami, Y., Kawajiri, K., Sogawa, K., and Muramatsu, M. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 2793-2797) (52% similarity), P-450-3b (Ozols, J., Heinemann, F. S., and Johnson, E. F. (1985) J. Biol. Chem. 260, 5427-5434) (64%), P-450-1 (Tukey, R. H., Okino, S., Barnes, H., Griffin, K. J., and Johnson, E. F. (1985) J. Biol. Chem. 260, 13347-13354) (74%), P-450PBc1 (Leighton, J. K., DeBrunner-Vossbrinck, B. A., and Kemper, B. (1984) Biochemistry 23, 4598-4603) (71%), while its sequence similarity with 3-methylcholanthrene-inducible P-450c and P-450d is rather low. Consequently, P-450(M-1) could be structurally classified into the phenobarbital-inducible type of P-450 gene family. RNA blot analysis using a synthetic oligonucleotide specific for P-450(M-1) revealed that P-450(M-1) mRNA was expressed exclusively in the livers of mature male rats in a sex-specific manner, but not in other tissues so far examined.     

Purification and characterization of a new form (RLM2) of liver microsomal cytochrome P-450 from untreated rat

A new cytochrome P-450 isozyme (RLM2) has been purified to electrophoretic homogeneity from liver microsomes of the untreated rat. It has an apparent minimum molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 49,000. Absolute spectrum of the oxidized form indicates that this isozyme is essentially all in the low spin state. The maximum of the reduced CO complex is at 449 nm. Amino-terminal partial amino acid sequence and amino acid composition are different from those of RLM3 and RLM5, two other native forms of cytochrome P-450 previously reported from this laboratory as well as other forms reported in the literature. RLM2 is capable of oxidizing a variety of drug substrates, like benzphetamine and aminopyrine, and to a lesser extent ethoxycoumarin. With the steroid substrate multiple isomeric products are formed differentially. Progesterone is preferentially hydroxylated at the 15-position (15 beta-hydroxylation (34%) and 15 alpha-hydroxylation (13%) of the total) and at the 6 beta-position (21%). The major metabolite when testosterone was the substrate, 15 alpha-hydroxytestosterone, comprised 43% of the total, while a modest amount of 6 beta-hydroxytestosterone (12%) is formed. Another major metabolite (31%) has yet to be unequivocally identified, but is suggested to be 7 beta-hydroxytestosterone. Examination of the substrate dependence of major and minor isomeric metabolites provides evidence for a single substrate-binding site on RLM2. Regardless of the position hydroxylated, a common Km value was obtained. It is suggested that differences in formation of the isomeric and epimeric products relate to differences in distance from the active oxygen center and the position of attack.     

Comparative metabolism of phenothiazine in the rat (Rattus norvegicus), mouse (Mus musculus), hamster (Mesocricetus auratus) and gerbil (Gerbillus gerbillus)

1. The urinary metabolites of phenothiazine have been identified and quantitated for the rat, mouse, hamster and gerbil.2. All species excreted the majority of the compound in conjugated form.3. The rat, mouse and gerbil were similar in producing leucophenothiazone sulphate as their major metabolite, relying more on the C-oxidation pathways than the hamster which excreted large amounts of phenothiazine-N-glucuronide.4. In all species the 24 hr urinary recovery was low (18–44%).5. These results are discussed in comparison to previous metabolic studies on this compound in other species.     

Characterization of some monooxygenase activities and solubilization of hepatic cytochrome P-450 in two species of freshwater fish, the nase (Chondrostoma nasus) and the roach (Rutilus rutilus)

1. Hepatic monooxygenase activities were studied in microsomal fractions from two species of freshwater fish, the nase (Chondrostoma nasus) and the European roach (Rutilus rutilus). 2. These activities were determined by using four substrates, 7-ethoxycoumarin, 7-ethoxyresorufin, benzo(a)pyrene, and 2,5-diphenyloxazole and were characterized according to pH, temperature, cofactors, and the differential effects of two inhibitors, metyrapone and alpha-naphthoflavone. 3. Solubilization of microsomes was achieved by the use of detergents, with a good recovery of the cytochrome P-450.     

Responses to insulin by two forms of rat hepatic microsomal cytochrome P-450 that undergo major (RLM6) and minor (RLM5b) elevations in diabetes

Total cytochrome P-450 levels rise in diabetic rats. Two specific forms of cytochrome P-450 that are elevated have been isolated from liver microsomes of streptozotocin-induced idabetic male rats. One enzyme, termed RLM6, metabolizes aniline and acetol, but not testosterone, in a reconstituted system with NADPH-cytochrome P-450 reductase. RLM6 is isolated as a high spin cytochrome with a minimum molecular weight of 53,500. It has a unique amino-terminal amino acid sequence lacking methionine at the amino-terminal position. Polyclonal antibodies to RLM6 recognized most other forms of cytochrome P-450 in Western blots, but could be made monospecific by adsorption to cross-reacting proteins coupled to Sepharose 4B. Using the monospecific antibodies, RLM6 was estimated to be present in microsomes of untreated male rats at 0.04 nmol/mg protein (5% of total P-450). In chronically diabetic rats this level rose to 0.35 nmol/mg protein and 24% of the P-450 content. Immunoreactive protein of molecular weight identical to RLM6 was elevated in microsomes of non-diabetic rats treated with ethanol, acetone, or isoniazid as well as in rats starved for 48 h. Insulin treatment of diabetic rats for 1 week lowered the immunologically detectable levels of RLM6 to levels found in the untreated rat. The other form of cytochrome P-450, RLM5b, does not metabolize aniline and only poorly metabolizes acetol and testosterone. This 52.5-kDa protein is isolated as a predominantly (60%) high spin enzyme. It has a unique NH2-terminal amino acid sequence with methionine as the terminal residue, and is present in untreated male rat liver microsomes at 0.16 nmol/mg protein. It is elevated in diabetes, like RLM6, but treatment with insulin for 1 week does not completely restore the microsomal content to that of the non-diabetic rat.     

Induction of microsomal aryl hydrocarbon (3,4-benzo(alpha)pyrene) hydroxylase and cytochrome P-450K in rat kidney cortex. II. Interactions with the induced hemoprotein

Benzo(α)pyrene treatment resulted in stimulation of only cytochrome P-450_K and benzo(α)pyrene hydroxylase activity in rat kidney cortex microsomes. Spectral properties of cytochrome P-450_K showed that the 452 nm peak of the reduced hemoprotein CO-complex was not shifted in benzo(α)pyrene-treated rats. The off-balance absolute spectrum of oxidized cytochrome P-450_K displayed an absorption maximum at 414 nm, another band at 385 nm, and a distinct shoulder at 398 nm. Addition of benzo(α)pyrene to kidney microsomes resulted in a type I spectral change seen only in benzo(α)pyrene-treated rats. The addition of ethyl isocyanide to dithionitetreated microsomes from control rats gave rise to two Soret peaks, 432 nm and 458 nm. These peaks were proportionately increased in benzo(α)pyrene-treated rats; furthermore, the 458 nm peak was not shifted. The relative heights of the two peaks were in a pH-dependent equilibrium similar to that observed in liver; however, in contrast to liver, the pH, at which the ratio of the peak heights equals one, was the same for both benzo(α)pyrene-treated and control microsomes. These data indicate that the newly induced hemoprotein has spectral properties markedly different from those of the benzo(α)pyrene-induced liver hemoprotein, yet similar to those of the “noninduced” kidney hemoprotein. α-Naphthoflavone, an inhibitor of the aryl hydroxylase system, induced a type I spectral change, suggesting the mode of action of α-naphthoflavone to be its interaction with cytochrome P-450_K probably at or near the active site. Finally, the rate of reduction of cytochrome P-450_K was not affected by the presence of benzo(α)pyrene.     

Induction of mRNA coding for phenobarbital-inducible form of microsomal cytochrome P-450 in rat liver by administration of 1,1-Di(p-chlorophenyl)-2,2-dichloroethylene and phenobarbital

In the preceding paper (Yoshioka, H., et al. (1984) J. Biochem. 95, 937-947), we reported that 1,1-di(p-chlorophenyl)-2,2-dichloro-ethylene (DDE) induced the phenobarbital (PB)-inducible form of microsomal cytochrome P-450 (P-450(PB-1) in rat liver. In order to study more precisely the molecular events responsible for the induction of this particular form of cytochrome P-450 by the two chemical compounds, we determined the amounts of the mRNA coding for P-450(PB-1) in the liver of rats given a single dose of PB or DDE. RNA was extracted from the livers of the treated rats and the determination of the specific mRNA was carried out by using the rabbit reticulocyte lysate translation system and by a dot hybridization method using cloned P-450(PB-1) cDNA (Fujii-Kuriyama, Y., et al. (1982) Proc. Natl. Acad. Sci. U.S. 79, 2793-2797) as the probe. The amounts of P-450(PB-1) mRNA determined by these two methods at various time points of the induction process showed good agreement. These observations further confirmed the induction of an identical form of cytochrome P-450 by DDE and PB. The maximum level of P-450(PB-1) mRNA, which was about 8-fold higher than the control level, was attained at 20-30 h and at 48-72 h after the administration of PB and DDE, respectively. The mRNA level showed a rapid decrease after the peak in the liver of PB-treated rats, but the decrease was much slower with DDE-treated rats. We conclude that DDE had a more persistent inducing effect on the mRNA level than PB, although these two compounds induced an identical form of cytochrome P-450 in the liver microsomes of the animals.     

Comparative study of monomeric reconstituted and membrane microsomal monooxygenase systems of the rabbit liver. I. Properties of NADPH-cytochrome P450 reductase and cytochrome P450 LM2 (2B4) monomers.

Oligomers and monomers of NADPH-cytochrome P450 reductase and cytochrome P450 LM2 (2B4) isolated from the liver microsomes of phenobarbital-treated rabbits were examined for physicochemical properties and catalytic activities. As measured using laser correlation spectroscopy the particle sizes of NADPH-cytochrome P450 reductase and cytochrome P450 LM2 oligomers were 14.8 +/- 1.7 and 19.2 +/- 1.4 nm, respectively. Twenty-four-hour incubation with Emulgen 913 at 4 degrees C at a molar ratio of 1:100 led to the monomerization of NADPH-cytochrome P450 reductase and cytochrome P450 LM2 oligomers, the particle sizes diminishing to 6.1 +/- 1.3 and 5.2 +/- 0.4 nm, respectively. The thermal stability of NADPH-cytochrome P450 reductase monomers was the same as that of oligomers, whereas cytochrome P450 LM2 monomers were less thermostable than oligomers and cytochrome P450 in microsomes. Similar to cytochrome P450 LM2 oligomers and the microsomal hemoprotein, cytochrome P450 LM2 monomers formed complexes with type I and II substrates, but with Kd values higher than those of microsomes and cytochrome P450 LM2 oligomers. Kinetic parameters (Vmax and Km) of H2O2- and cumene hydroperoxide-dependent oxidation of benzphetamine and aniline in the presence of cytochrome P450 LM2 oligomers, monomers, and microsomes were determined. Peroxidase activities of the oligomers and monomers were the same, but were lower than those of microsomes. Thus the substitution of protein-protein interactions in cytochrome P450 LM2 oligomers with protein-detergent interactions in the monomers did not influence the catalytic properties of the hemoprotein.