Electrophoretic, spectral, catalytic and immunochemical properties of highly purified cytochrome P-450 from sheep lung

Evaluation of bioreductive activation of anticancer drugs idarubicin and mitomycin C by NADH-cytochrome b5 reductase and cytochrome P450 2B4

This study attempted to investigate the ability of microsomal NADH-cytochrome b5 reductase and cytochrome P450 2B4 to reductively activate idarubicin and mitomycin C. In vitro plasmid DNA damage experiments and assays using purified hepatic enzymes were employed to examine their respective roles in the metabolic activation of anticancer drugs. Mitomycin C was found to be not a good substrate for microsomal b5 reductase unlike P450 reductase. It produced low amounts of strand breaks in DNA when incubated with b5 reductase and its one-electron reduction by purified enzyme was found as negligible. Our findings revealed that P450 reductase-mediated metabolism of idarubicin resulted in a large increase in single-strand DNA breaks, whereas, b5 reductase neither catalyzed the reduction of idarubicin nor mediated the formation of DNA damage in the presence of idarubicin. The reconstitution studies, on the other hand, have identified rabbit liver CYP2B4 isozyme as being a potential candidate enzyme for reductive bioactivation of idarubicin and mitomycin C. Thus, the present novel findings strongly suggest that while b5 reductase could not play a key role in the cytotoxic and/or antitumor effects of idarubicin and mitomycin C, CYP2B4 could potentiate their activity in combination with P450 reductase.

Assessment of pollution in the West Black Sea Coast of Turkey using biomarker responses in fish

Aim of this study was to determine the extent of pollution in the West Black Sea Coast of Turkey by measuring CYP1A associated EROD activity, phase II enzyme, glutathione S-transferase and antioxidant enzymes, catalase and glutathione reductase activities and immunochemical detection of CYP1A protein level in the liver of mullet. The fish samples were caught from six locations having a varying degree of pollution in the West Black Sea Region of Turkey in August 2005, 2006 and 2007. Mullets caught from Zonguldak Harbour, Ereğli Harbour and Gülüç Stream's Mouth displayed 6-9-fold higher EROD, 2-4-fold higher glutathione S-transferase and 2-3-fold higher catalase activities than the reference site, Amasra. Total polyaromatic hydrocarbon levels in mullets caught from these locations were also significantly higher (2-4-fold) than Amasra. The results of this study indicate that Zonguldak Harbour, Ereğli Harbour and Gülüç Stream are highly polluted by polycyclic aromatic hydrocarbons and related contaminants.

Purification of CYP2B-like protein from feral leaping mullet (Liza saliens) liver microsomes and its biocatalytic, molecular, and immunological characterization

In this study, CYP2B-immunoreactive protein was purified to electrophoretic homogeneity from the liver microsomes of leaping mullet. The purified cytochrome P450 (CYP) gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis having a M(r) of 49,300 Da. Absolute absorption spectrum of the purified CYP showed a maximum at 417 nm and CO-difference spectrum of dithionite-reduced cytochrome P450 gave a peak at 450 nm. The purified CYP was found to be active in N-demethylation of benzphetamine, erythromycin, and ethylmorphine, and O-dealkylation of pentoxyresorufin in the reconstituted system. However, it was unable to catalyze O-dealkylation of ethoxyresorufin, methoxyresorufin, benzyloxyresorufin, and hydroxylation of lauric acid and aniline. The purified CYP showed strong cross-reactivity with anti-sheep lung CYP2B, a homologue of CYP2B4. N-terminal amino acid sequence of the mullet P450 had the highest degree of homology with CYP2Bs among the known CYPs. Spectral, electrophoretic, immunochemical, N-terminal amino acid sequence, and biocatalytic properties of the purified CYP are most similar to those of mammalian cytochrome P4502B. All these data indicate that the purified CYP is certainly 2B-like. In this study, we not only purified biocatalytically active CYP2B-like protein from fish, but also demonstrated detailed functional properties of CYP2B-like protein for the first time.

Effects of diabetes on rabbit kidney and lung CYP2E1 and CYP2B4 expression and drug metabolism and potentiation of carcinogenic activity of N-nitrosodimethylamine in kidney and lung

There are limited number of studies regarding the influence of diabetes on the regulation of cytochrome P450s and associated drug metabolizing enzyme activities especially in extrahepatic tissues such as kidney. However, there is almost no such study in lung. Alloxan-induced diabetes did not change CYP2B4 expression as measured with immunoblot analysis and associated enzyme, benzphetamine N-demethylase, activity in rabbit kidney and lung. Induction of cytochrome P4502E1 by diabetes was identified by immunochemical detection on Western blots in the lung and kidney microsomes of rabbits. In parallel to CYP2E1 induction, aniline 4-hydroxylase and p-nitrophenol hydroxylase activities were markedly increased in diabetic rabbit lung and kidney. CYP2B4 and CYP2E1 dependent drug metabolism did not show any tissue variation in diabetic rabbit. These findings are in contrast to those of rats, mice and hamster. The results of the present work, in combination with those of the previous work [Arinç, E., Arslan, S., Adali, O., 2005. Differential effects of diabetes on CYP2E1 and CYP2B4 proteins and associated drug metabolizing enzyme activities in rabbit liver. Arch. Toxicol. 79, 427-433], indicate the existence of species-dependent response of CYP-dependent drug metabolizing enzymes to diabetes. A procarcinogen and food contaminant, N-nitrosodimethylamine (NDMA), is converted to its carcinogenic form after it is activated with NDMA N-demethylase. In the current study, a statistically significant increase of liver, kidney and lung NDMA N-demethylase activity associated with CYP2E1 was shown in diabetic rabbit. Thus, it is expected that, the risk of nitrosamine induced carcinogenesis will be greater in liver, kidney and lung of the diabetic subjects.

Biochemical characteristics of purified beef liver NADPH-cytochrome P450 reductase

NADPH-cytochrome P450 reductase, an obligatory component of the cytochrome P450 dependent monooxygenase system, was purified to electrophoretic homogeneity from beef liver microsomes. The purification procedure involved the ion exchange chromatography of the detergent-solubilized microsomes on first and second DEAE-cellulose columns, followed by 2',5'-ADP Sepharose affinity chromatography. Further concentration of the enzyme and removal of Emulgen 913 and 2'-AMP were accomplished on the final hydroxylapatite column. The enzyme was purified 239-fold and the yield was 13.5%. Monomer molecular weight of the enzyme was estimated to be 76000 +/- 3000 (N = 5) by SDS-PAGE. The absolute absorption spectrum of beef reductase showed two peaks at 455 and 378 nm, with a shoulder at 478 nm, characteristics of flavoproteins. The effects of cytochrome c concentration, pH, and ionic strength on enzyme activity were studied. Reduction of cytochrome c with the enzyme followed Michaelis-Menten kinetics, and the apparent K(m) of the purified enzyme was found to be 47.7 microM for cytochrome c when the enzyme activity was measured in 0.3 M potassium phosphate buffer (pH 7.7). Stability of cytochrome c reductase activity was examined at 25 and 37 degrees C in the presence and absence of 20% glycerol. The presence of glycerol enhanced the stability of cytochrome c reductase activity at both temperatures. Sheep lung microsomal cytochrome P4502B and NADPH-cytochrome P450 reductase were also purified by the already existing methods developed in our laboratory. Both beef liver and sheep lung reductases were found to be effective in supporting benzphetamine and cocaine N-demethylation reactions in the reconstituted systems containing purified sheep lung cytochrome P4502B and synthetic lipid, phosphatidylcholine dilauroyl.

Differential effects of phenobarbital on the constitutive and inducible expression of P450 2B and 3A subfamilies in sheep tissues

The activity and expression of cytochromes P450 were determined in liver, kidneys, lungs, duodenum, jejunum, ileum, and caecum of adult Lacaune sheep. High expression of total P450, benzphetamine and erythromycin demethylase activities, and P450 2B isoforms, as two distinct proteins that were detected and called P4502 Bm and P4502 Bx, was found in the lungs (in addition to liver). By contrast, the P450 3A subfamily was only expressed in liver and duodenal mucosa of untreated sheep. Phenobarbital (PB) treatment led to significant increases in all measured hepatic parameters and in total P450 of each investigated organ with the exception of ileum and caecum. Benzphetamine demethylase activity increased in liver and kidneys, correlating with the expression of the two P450 2B proteins, which were also induced in duodenum and ileum. By contrast, benzphetamine demethylase activity and expression of the P450 2B isoforms in lungs were unchanged by PB treatment. Erythromycin demethylation activity and P450 3A subfamily expression was increased only in liver of PB-treated sheep.Key words: phenobarbital, sheep, cytochromes P450, inducibility, tissue distribution.

Biotransformation Enzymes as Determinants of Xenobiotic Toxicity in Domestic Animals

After coming in contact with living organisms, the majority of foreign compounds undergo a number of chemical reactions known as biotransformations. These are performed by hepatic and extra-hepatic enzyme systems and usually yield more polar derivatives, referred to as 'metabolites', which may leave the body via the urinary and biliary routes or be excreted in animal products such as milk and eggs. Biotransformation does not always imply detoxification because in certain instances metabolites will be produced that are capable of reacting with tissue macromolecules or acquiring toxic properties different to or greater than those of the parent molecule. In this review, which is focused on domestic animals, the role played by oxidative, reductive, hydrolytic and conjugative biotransformation enzymes in the activation/detoxification of xenobiotics is examined. The relationship between extra-hepatic metabolism and target organ toxicity as well as the action of rumen microflora on feed additives, phytotoxins, and pesticides are then discussed. Some of the most important metabolic-based species-related susceptibilities to different poisons, and the influence of enzyme inducers or inhibitors on xenobiotic toxicity and drug safety are also reviewed.

Simultaneous purification and characterization of cytochrome b5 reductase and cytochrome b5 from sheep liver

Cytochrome b5 was purified from detergent solubilized sheep liver microsomes by using three successive DEAE-cellulose, and Sephadex G-100 column chromatographies. It was purified 54-fold and the yield was 23.5% with respect to microsomes. The apparent Mr of cytochrome b5 was estimated to be 16,200 +/- 500 by SDS-PAGE. Absolute absorption spectrum of the purified cytochrome b5 showed maximal absorption at 412 nm and dithionite-reduced cytochrome b5 gave peaks at 557, 526.5 and 423 nm. The ability of the purified sheep liver cytochrome b5 to transfer electrons from NADH-cytochrome b5 reductase to cytochrome c was investigated. The K(m) and Vmax values were calculated to be 0.088 microM cytochrome b5 and 315.8 microM cytochrome c reduced/min/mg enzyme, respectively. Also the reduction of cytochrome b5 by reductase was studied and K(m) and Vmax values were determined to be 5 microM cytochrome b5 and 5200 nmol cytochrome b5 reduced/min/mg enzyme, respectively. The K(m) and Vmax values for the cofactor NADH in the presence of saturating concentration of cytochrome b5 were found to be 0.0017 mM NADH and 6944 nmol cytochrome b5 reduced/min/mg enzyme, respectively. NADH-cytochrome b5 reductase was also partially purified from the same source, detergent solubilized sheep liver microsomes, by using two successive DEAE-cellulose, and 5'-ADP-agarose affinity column chromatographies. It was purified 144-fold and the yield was 7% with respect to microsomes. The apparent monomer Mr of reductase was estimated to be 34,000 by SDS-PAGE. When ferricyanide was used as an electron acceptor, reductase showed maximum activity between 6.8 and 7.5. The K(m) and Vmax values of the enzyme for ferricyanide were calculated as 0.024 mM ferricyanide and 673 mumol ferricyanide reduced/min/mg enzyme, respectively. The K(m) and Vmax values for the cofactor NADH in the presence of saturating amounts of ferricyanide were found to be 0.020 mM NADH and 699 mumol ferricyanide reduced/min/mg enzyme, respectively.

Immunochemical and sub-structural characterization of sheep lung cytochrome P450LgM2

Sheep lung cytochrome P450LgM2 belonging to gene subfamily 2B, was obtained in highly purified form and antibodies against sheep lung cytochrome P450LgM2 were produced in rabbits by using the previously developed methods in our laboratory. Immunological and enzymatic studies showed that antibodies against lung cytochrome P450LgM2 inhibited benzphetamine N-demethylation, ethylmorphine N-demethylation and aniline 4-hydroxylation reactions in sheep lung microsomes about 99, 80 and 62%, respectively. Benzphetamine N-demethylation reaction in sheep lung microsomes was only catalyzed by cytochrome P450LgM2 isozyme while the other isozymes of P450 as well as P450LgM2 are also involved in the metabolism of ethylmorphine and aniline. Similar to lung microsomes, benzphetamine N-demethylase activity of the reconstituted systems containing purified sheep lung cytochrome P450LgM2 or phenobarbital (PB)-treated rabbit liver cytochrome P450LM2(2B4) was also inhibited by P450LgM2 antibodies about 95 and 82%, respectively. A 50% inhibitory effect of sheep P450LgM2 antibodies was also observed in ethylmorphine N-demethylase activity of the reconstituted system containing purified sheep lung cytochrome P450LgM2. SDS-PAGE peptide maps obtained following the partial proteolysis of purified sheep lung cytochrome P450LgM2 and PB-rabbit liver P450LM2(2B4) isozymes, using chymotrypsin and papain, were similar in general. However they showed some differences both qualitatively and quantitatively, suggesting that some differences exist among the amino acid sequences of sheep lung cytochrome P450LgM2 and rabbit liver cytochrome P4502B4.

Different influences of two fractions of lung cytochrome b5 on reconstituted lung benzphetamine N-demethylase system

Chromatography of lung microsomal cytochrome b5 obtained from DEAE-cellulose columns, yielded two distinct cytochrome b5 fractions. These cytochrome b5 fractions were further purified by Sephadex G-100 gel filtration chromatography. The specific cytochrome b5 content of fraction 1 and fraction 2 was found to be 16.5 and 16.4 nmol/mg protein respectively. Both fractions were free of cytochrome P-450, NADPH-cytochrome P-450 reductase and NADH-cytochrome b5 reductase activities. The effects of lung cytochrome b5 (fraction 1 and fraction 2) and liver cytochrome b5 on benzphetamine N-demethylase activity were examined. Four different reconstitution systems were used. Lung cytochrome b5 fraction 2 and liver cytochrome b5 stimulated N-demethylase activity in all four systems when b5:P-450 molar ratio was low, i.e. 0.25 or 0.5. Both cytochrome b5 samples inhibited N-demethylase activity when b5:P-450 ratio exceeded 1:1 molar ratio. In contrast lung cytochrome b5 fraction 1 stimulated N-demethylase activity in all four systems. Maximal enhancement of the activity was obtained when b5:P-450 ratio was 0.5. The greatest increase in N-demethylation activity was observed in the reconstitution system with the lowest concentration of cytochrome P-450 reductase, conditions which most closely resemble intact microsomes.

Stimulatory effects of lung cytochrome b5 on benzphetamine N-demethylation in a reconstituted system containing lung cytochrome P450LgM2

Cytochrome b5 was partially purified from sheep lung microsomes in the presence of detergents Emulgen 913 and cholate by three consecutive DEAE-cellulose and Sephadex G-100 gel filtration chromatographies. The specific content of cytochrome b5 was 16.5 nmol/mg protein and purified cytochrome b5 fractions were free of cytochrome P450, NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase activities. The influences of increasing concentrations of lung cytochrome b5 on benzphetamine N-demethylation reactions were examined in four different reconstitution systems containing lung cytochrome P450LgM2, lung cytochrome P450 reductase and lipid. In each system concentration of reductase was doubled with respect to former system. In all systems cytochrome b5 stimulated benzphetamine N-demethylase activity especially when cytochrome b5 was present at 0.5:1 molar ratio with respect to cytochrome P450LgM2. Besides, the greatest fold of increase in benzphetamine N-demethylation activity due to addition of cytochrome b5 was observed in System 1 with the lowest concentration of reductase.

Hepatic cytochrome P450 induction in goats. Effects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA probe, rather than with a rat 3A1 probe. BNF selectively induced EROD, whereas TST hydroxylation and ETM dealkylation were inhibited. With BNF-treated animals, increased concentrations of a protein cross-reactive with anti-rat P450 1A1/1A2 and of an mRNA that showed homology with a human 1A1 cDNA probe, but not with a mouse 1A1/1A2 probe, were observed.

Ontogenic development of liver progesterone metabolism in female sheep. Contribution of cytochrome P4502B and P4503A subfamilies

Age-related changes in progesterone hepatic metabolism were measured in Lacaune ewes in the foetal, neonatal (1 and 4 weeks), growing (7 months), pregnant (11 months) and adult (6 years) stages. 6 beta-Hydroxylation and 20 alpha-reduction were found to be the most efficient metabolic process in ovine microsomes. These activities were detected in 3-month-old foetuses and they increased rapidly during the first month of life, in a similar manner to the developmental expression of the cytochrome P4503A subfamily. 16 alpha- and 21-hydroxylation of progesterone were characterized by low, constant turn over in sheep liver microsomes during development. The hepatic ovine P4502B isozyme was purified to electrophoretic homogeneity by means of successive DEAE cellulose, hydroxylapatite and CM cellulose chromatographic separations. This hemoprotein had an apparent molecular weight of 51 kDa and was characterized by spectral data, NH2-terminal amino-acid sequence, immunological and catalytic properties. The relative contribution of this form and of the previously purified ovine P4503A subfamily was investigated in liver progesterone metabolism by immunoinhibition studies using polyclonal antibodies raised in rabbits and from the existence of induction and of significant correlations between microsomal activity and specific P450 content. In sheep liver microsomes, it would appear that cytochrome P4502B is involved in progesterone 21-hydroxylation whereas P4503A participates in the 6 beta- and 16 alpha-hydroxylation and possibly in the reductive conversion of progesterone in its 20 alpha-hydroxy derivative.

Purification and characterization of two forms of soluble NADH cytochrome b5 reductases from human erythrocytes

1. Two forms of soluble NADH cytochrome b5 reductase were purified from human erythrocytes. Two distinct fractions both having the NADH cytochrome b5 reductase activity eluted from the second DEAE-cellulose column were further purified by ultrafiltration and 5'-ADP-agarose affinity chromatography. 2. The final preparations were purified 9070- and 4808-fold, respectively, over hemolysate. Both reductases exhibited identical electrophoretic patterns when subjected to SDS-PAGE and apparent monomer Mr of each reductase was determined to be 32,000 +/- 1300. 3. Vmax values of reductase II for the various electron acceptors, namely, 2,6-dichlorophenolindophenol, ferricyanide and cytochrome c through cytochrome b5 were found to be 1.9, 1.8 and 2 times higher than those of reductase I. 4. Some differences were noted for reductase I and reductase II fractions. Their elution profiles from a second DEAE-cellulose column were quite different and that suggested that reductase II is more acidic than reductase I. Reductase II was found to be more sensitive to heat treatment than reductase I.

Lung microsomal p-nitrophenol hydroxylase -- characterization and reconstitution of its activity

1. Formation of catechols from benzene and nitrobenzene have been implicated in the carcinogenic activity of these chemicals. In liver, p-nitrophenol, an intermediate of p-nitrobenzene is enzymatically converted to 4-nitrocatechol. 2. For the first time in this study, the presence of a highly active enzyme catalyzing the formation of 4-nitrocatechol from p-nitrophenol was detected in lung microsomes. The average specific activity of lung p-nitrophenol hydroxylase was found to be 0.494 nmol 4-nitrocatechol formed mg prot-1 min-1. 3. The optimum conditions for sheep lung microsomal p-nitrophenol hydroxylase were established. The maximal activity was noted at pH 6.8. The rate of p-nitrophenol hydroxylation was linear up to 2 mg prot/ml of incubation mixture. The maximal rate of 4-nitrocatechol formation was observed with 0.25 mM p-nitrophenol. 4. The Lineweaver-Burk and Eadie-Hofstee plots were found to be curve-linear. Two different Km values were calculated as 11.6 and 71.4 microM from the Lineweaver-Burk plot and as 10.7 and 74.5 microM from the Eadie-Hofstee plot. This suggested that there were either two forms of enzyme or two different enzymes participating in ortho hydroxylation of p-nitrophenol in lung microsomes. 5. Lung microsomal p-nitrophenol hydroxylase activity of sheep was reconstituted in the presence of purified lung microsomal cytochrome P-450, NADPH dependent cytochrome P-450 reductase and synthetic lipid, phosphatidylcholine dilauroyl.