Replacement of Thr-303 of P450 2E1 with serine modifies the regioselectivity of its fatty acid hydroxylase activity

Threonine-303 of rabbit P450 2E1, which is putatively located at the distal heme surface, was replaced by serine and valine via site-directed mutagenesis. In the oxidized state, the Ser-mutated P450 exhibited a low- and high-spin mixed-type (low > high) absorption spectrum, whereas the Val-mutated P450, like the wild-type P450, exhibited a nearly high-spin type spectrum. The reduced CO complexes of the Ser- and Val-mutated P450s, as well as that of the wild-type P450, showed a Soret absorption maximum at 452 nm. Both mutated P450s were active in the hydroxylation of C10 to C18 fatty acids at somewhat lower rates than the wild-type P450. The Val-mutated P450 gave the same two products (the major one is probably the omega-1 hydroxy analog) as the wild-type P450, while additional products were formed on incubation with C11 to C17 fatty acids as substrates of the Ser-mutated P450; a total of four products was detected for each of the C12 to C15 fatty acids, and three for each of the C11, C16, and C17 homologues. The metabolites of laurate were determined by GC-MS analysis to be the omega-1, omega-2, omega-3, and omega-4 hydroxy counterparts. The Ser-mutated P450 hydroxylated drug substrates at almost the same rates as the wild-type P450, while the mutation to valine significantly lowered the drug hydroxylase activities.(ABSTRACT TRUNCATED AT 250 WORDS)

[Relationship between lymphocyte subsets of the peripheral blood and noise induced hearing loss]

Biochemical examination and two-color flow cytometric analysis of lymphocyte subsets of the peripheral blood were carried out in 107 healthy males working in high noise environments. The level of hearing disorder was compared with these results. By audiometry at six frequency levels, 51 of the 107 healthy males showed hearing loss. Their mean value of hearing ability was 30 dB and/or above. Among the peripheral lymphocyte subsets, helper T cells of CD4+CD45R- were significantly increased and the CD4/CD8 ratio tended to be elevated. CD20 that indicate B cells were reduced. These results suggested a relationship between susceptibility to acoustic trauma and cell-mediated immunity.

Molecular cloning of monkey liver cytochrome P-450 cDNAs: similarity of the primary sequences to human cytochromes P-450

Three cDNAs coding for monkey cytochrome P-450 (P450) 2C, 2E and 3A (MKmp13, MKj1 and MKnf2, respectively) were isolated from a lambda gt11 cDNA library of a liver from a 3-methylcholanthrene (3MC)-treated crab-eating monkey, using cDNA fragments for human P450 2C, 2E and 3A as respective probes. MKmp13 and MKnf2 were 1901 and 2032 bp long, containing entire coding regions for polypeptides of 490 and 503 residues, respectively. The deduced N-terminal amino acid sequences of MKmp13 and MKnf2 were identical with those of P450-MK1 and P450-MK2, which had been purified from liver microsomes of untreated and polychlorinated biphenyl (PCB)-treated crab-eating monkeys, respectively. MKj1 was 1508 bp long, encoding a polypeptide of 449 residues, which is presumed to lack N-terminal 45 residues as compared with the sequence for human P450 2E1. Northern blot analysis indicated that monkey P450 2C, 2E and 3A mRNAs were expressed constitutively in monkey livers. P450 2E and 3A mRNAs were induced by both 3MC and PCB, while P450 2C mRNA was induced only by PCB. The deduced amino acid sequences of four monkey cytochrome P-450 cDNAs, including P450 1A1 (MKah1) which we isolated previously, were more than 92% identical with those of corresponding human cytochrome P-450 cDNAs.

[A case report of a burn produced by the probe of a pulse oximeter]

We experienced a case of burn produced by the pulse oximeter probe at the finger of a patient. Patient was a 75-year old man scheduled to transurethral prostatectomy. The pulse oximeter probe made by Physio-Control Co. was attached at his finger and was connected to a pulse oximeter manufactured by Ohmeda Co. Soon after the start of Spo2 measurement the anesthetist became aware of abnormal heating of the probe and removed it immediately. But unfortunately a small thermal injury was formed at patient's finger. Abnormally excessive current went through the detector diode and heated the finger probe. Attention to correct connection between the pulse oximeter probe and the finger is necessary before use.

Human fetal liver cytochrome P-450: capacity to form genotoxic metabolites

Unlike most experimental animals, human fetal liver possesses forms of cytochrome P-450. Thus, the purpose of this study was to clarify the toxicological significance of these forms of cytochrome P-450 to understand possible roles of these cytochromes in producing genotoxic metabolites from promutagens. In fact, human fetal livers showed considerable capacity to activate aflatoxin B1 and IQ (2-amino-3-methylimidazo [4,5-f] quinoline). Three of four forms of cytochrome P-450, P-450HFLa-d, which we could purify from human fetal livers were capable of activating promutagens to mutagens. One of these three forms, namely P-450HFLa, catalyzed the metabolic activation of aflatoxin B1 and IQ. An expression plasmid containing HFL33 cDNA encoding P-450HFLa was constructed and the protein expressed in insect (Sf9) cells and in human cancer cells, MCF-7. Aflatoxin B1 was efficiently activated to a mutagen upon addition of the lysate of Sf9 cells to the incubation mixture for the assay. Transformants of MCF-7 cells expressing P-450IIIA7 (HFLa) showed higher sensitivity to aflatoxin B1 than the parental MCF-7 cells as detected by cytotoxicity.

Six-base deletion occurring in messages of human cytochrome P-450 in the CYP2C subfamily results in reduction of tolbutamide hydroxylase activity

We isolated and expressed a clone, hPA6, possibly corresponding to the CYP2C9 cDNA. Compared with the other CYP2C9 cDNA clones, hPA6 showed a 6-nucleotide deletion near its middle. From the same cDNA library, we could also isolate another cDNA clone, named hPA22, which retained the 6 bases. For clarification of the effect of the 2-amino acid deletion resulting from the 6-base deletion on enzymatic activities, both clones were expressed in yeast. The expressed enzymes showed tolbutamide hydroxylase activities, and these activities were inhibited by antibodies against P-450-HM2, a probable CYP2C9. The activity of the enzyme encoded by hPA6 was lower than that encoded by hPA22; thus the 2-amino acid deletion in the CYP2C9 reduced the enzymatic activity.

Toxicological significance of dog liver cytochrome P-450: examination with the enzyme expressed in Saccharomyces cerevisiae using recombinant expression plasmid

A complementary DNA (cDNA) coding for a form of beagle dog cytochrome P-450 (Dah1), which is the orthologue to the CYP1A1 cDNA of rat, mouse and human, was inserted between the alcohol dehydrogenase (ADH) promoter and terminator regions of the yeast expression vector pAAH5. On introduction of the resulting recombinant plasmid pDC-1, Saccharomyces cerevisiae strain AH22 cells synthesized up to 1.5 x 10(5) molecules per cell of cytochrome P-450 protein (P-450(Dah1)). The carbon monoxide-bound reduced form of P-450(Dah1) showed an absorption peak at 447 nm and specific content of P-450(Dah1) was about 0.1 nmole P-450 per mg of microsomal protein. P-450(Dah1) cross-reacted with antibodies to rat P-448-H (CYP1A2) and dog P-450-D2 (CYP1A2). P-450(Dah1) activated 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) most efficiently in the umu test and exhibited a high activity of aryl hydrocarbon hydroxylase toward benzo[a]pyrene.

Molecular cloning of monkey P450 1A1 cDNA and expression in yeast

Monkey P450 1A1 cDNA (MKah1) was isolated from the lambda gt11 cDNA library of a liver from a 3-methylcholanthrene (3MC)-treated crab-eating monkey using a dog P450 1A1 cDNA fragment as a probe. MKah1 was 2453 bp long and contained an entire coding region for a polypeptide of 512 residues. The nucleotide and deduced amino acid sequences of MKah1 displayed 95% and 94% identity with those of the human P450 1A1 gene, respectively. Even in the 3' noncoding region, MKah1 showed 94% homology with human P450 1A1, whereas it showed less than 69% homology with other mammalian P450 1A1. Monkey P450 1A1 mRNA was not detectable in untreated livers, but was induced by polychlorinated biphenyl and 3MC. The expression plasmid (designated as pMKC-1) was constructed by introduction of the coding region of MKah1 into a yeast expression vector (pAM82) containing the promoter of acid phosphatase (APase). Northern blot analysis revealed that monkey P450 1A1 mRNA was expressed in yeast under the control of the APase promoter. Microsomes from yeast transformed by pMKC-1 catalyzed 7-ethoxycoumarin O-deethylation, benzo(a)pyrene hydroxylation and the mutagenic activation of 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), 3-amino-1-methyl-5H-pyrido(4,3-b)-indole acetate (Trp-P-2) and 2-amino-6-methyldipyrido(1,2-a:3',2'-d)imidazole acetate (Glu-P-1).

Quantitative assessment of digitized portal images: effect of sampling frequency on observer performance

To investigate spatial resolution requirements for digitized portal images in radiation therapy, observer performance tests were performed. One hundred twenty portal images were digitized with sampling frequencies of 0.700, 0.350, and 0.175 mm for observation. Receiver operating characteristic analysis was used to determine the acceptable sampling frequency for clinical portal images. The detectability of setup errors was significantly better on the original images than on the digitized images with sampling frequencies of 0.700 mm (P = .005) and 0.350 (P = .046). Some clinical disadvantages might accrue with the use of a sampling frequency of 0.350 mm or larger.

Dynamic light scattering studies on hydrodynamic properties of fibrinogen-fibronectin complex

A high molecular weight 'cryogel' was obtained as insoluble complexes by cold incubation at near-freezing temperatures from heparinized plasma of patients with rheumatoid arthritis. After the cryogel was solubilized at 37 degrees C, 1:1 complex of fibrinogen and fibronectin was purified at room temperature by affinity chromatography on a gelatin-Sepharose 4B. Hydrodynamic properties of the complex were investigated as a function of temperature and NaCl concentration using a dynamic light scattering. The diffusion coefficients of the complex at 20 degrees C decreased with increasing of NaCl concentration as free fibronectin. The complex appears to be a more compact form at low ionic concentration, which is associated with conformational changes of fibronectin. The diffusion coefficient of the complex at 20 degrees C in 0.05 M TrisHCl(pII7.4) containing 0.5 M NaCl was estimated as 8.5 x 10(-8) cm2s-1. The complex did not dissociate over the temperature range from 20 to 37 degrees C. The diffusion coefficients of the complex decreased significantly at 12 degrees C and 40 degrees C. The thermal denaturation of fibrinogen molecule in the complex was observed at 40 degrees C. The CONTIN analysis of the light scattering data showed that the complex associated to form higher aggregates at 15 degrees C, but not at near-freezing temperature. The equilibrium between the complex and higher aggregates appeared reversible.

Stable expression of cytochrome P450IIIA7 cDNA in human breast cancer cell line MCF-7 and its application to cytotoxicity testing

A mammalian cell expression plasmid containing cytochrome P450IIIA7 complementary DNA was constructed. Breast cancer cells (MCF-7) were transfected with the plasmid and neomycin-resistant selection marker plasmid. We established three cell lines, termed M13, M21, and M27, which expressed the cytochrome P450IIIA7 as examined by RNA blot and immunoblot analyses. These cell lines showed 8- to 10-fold higher sensitivity against aflatoxin B1 compared to parental MCF-7 cells, suggesting that cytochromes P450IIIA7 expressed in the cells were responsible for the production of the cytotoxic metabolite of aflatoxin B1.

Nicorandil reduces the basal level of cytosolic free calcium in single guinea pig ventricular myocytes

Using fluorescent Ca2+ indicator fura-2 and whole-cell patch-clamp techniques, we examined the effect of 2-nicotinamidoethyl nitrate (nicorandil) on the intracellular free Ca2+ concentration ([Ca2+]i) and electrical properties in single guinea pig ventricular myocytes. Nicorandil (10 nM approximately 1 mM) reduced the resting level [Ca2+]i monitored as fura-2 fluorescence ratio in a concentration-dependent manner. Dibutyryl guanosine 3':5'-cyclic monophosphate (cyclic GMP), a membrane permeable cyclic GMP analogue, mimicked the nicorandil action. Neither application of caffeine (10 mM) nor deprivation of extracellular Na+ ions could prevent the nicorandil action on [Ca2+]i. In contrast, the nicorandil effect was virtually blocked by sodium orthovanadate (40 microM), a Ca2+ pumping ATPase inhibitor. During electrophysiological experiments, nicorandil shortened action potential durations (205 +/- 80 ms to 153 +/- 76 ms) by increasing a glibenclamide-sensitive outward K+ conductance. However, the drug produced little hyperpolarization (approximately 2 mV) because the resting potential of ventricular myocytes was close to the K+ equilibrium potential. The involvement of voltage-dependent Ca-channel current and Na-Ca exchanger was considered to be minimal under physiological conditions. It is thus concluded that nicorandil decreases basal [Ca2+]i via cyclic GMP-mediated activation of the plasma membrane Ca2+ pump in guinea pig ventricular myocytes.

Effect of protonation on the isomerization properties of n-butylamine Schiff base of isomeric retinal as revealed by direct HPLC analyses: selection of isomerization pathways by retinal proteins

Alumina adsorption chromatography and ion-pair reversed-phase chromatography were developed to analyze the isomers of unprotonated and protonated n-butylamine Schiff base of retinal (RSB and PRSB), respectively. Photoisomerization starting from the all-trans, 11-cis and 13-cis isomers was traced for RSB in n-hexane, acetonitrile, methanol and 1-butanol, and for PRSB in methanol, acetonitrile and 1-butanol. The quantum yields of photoisomerization for the all-trans, 9-cis, 11-cis and 13-cis isomers were determined for RSB and PRSB in the above solvents except 1-butanol. On the other hand, photoisomerization of isomeric retinal bound (through Schiff base linkage) to bovine serum albumin (RBSA) in aqueous solution (pH 3, 7 and 12) as well as thermal isomerization of RSB (in n-hexane), PRSB (in methanol) and RBSA (in aqueous solution, pH 7) were traced starting from the all-trans, 11-cis, and 13-cis isomers. Protonation of RSB drastically changes the pathway of photoisomerization and increases the quantum yields of isomeric RSB. The solvent polarity increases the quantum yields of RSB differently depending on the configuration. Protonation enhances thermal isomerization also. The results of the above model systems are compared with those of retinal proteins to rationalize their selection of the particular isomerization pathways.

Sulphate conjugation enhances reversible binding of drug to human serum albumin

Reversible binding of model compounds, their conjugated metabolites (sulphates and glucuronides), and also derivatives of the compounds, to human serum albumin (HSA) has been examined using an ultrafiltration method. p-Nitrophenol (p-NP), alpha-naphthol (alpha-NA) and beta-naphthol (beta-NA) were used as model compounds. Reversible binding of 500 microM p-NP sulphate to 4% HSA (96.6 +/- 0.35%, mean +/- s.d. n = 3) was significantly higher (P less than 0.001), whereas reversible binding of p-NP glucuronide to 4% HSA (33.3 +/- 9.82%) was much lower (P less than 0.001) than that of 500 microM p-NP (90.9 +/- 0.60%). Reversible binding of 500 microM p-NP glucopyranoside to 4% HSA (25.8 +/- 2.82%) was comparable with that of the glucuronide, with which it is structurally similar. In contrast, reversible binding of 500 microM p-NP phosphate, an anionic compound like p-NP sulphate, to 4% HSA (61.4 +/- 5.28%) was significantly lower than that of p-NP (P less than 0.001). Similar results were observed in reversible binding of sulphates of alpha-NA and beta-NA. Significant differences of dissociation constants for HSA binding were observed between the parent compound (alpha- or beta-NA) and its sulphate conjugate (P less than 0.005 for alpha-NA and alpha-NA sulphate, P less than 0.001 for beta-NA and beta-NA sulphate), but the number of binding sites was the same. These results indicated that sulphate conjugation enhances reversible binding of a parent compound to HSA by increasing the binding affinity of the parent compound to HSA. This enhancement appeared to be advantageous for preventing random distribution of this metabolite to organs in the body.

Two common RFLPs of the human CYP2E gene

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Molecular toxicology on cytochrome P-450 in human fetal livers

Among mammalian species, humans and monkeys are sole species which possess cytochrome P-450 in the liver in fetal life. Cytochrome P-450 catalyzes oxidations of a wide variety of compounds including steroids, drugs and toxicants. Thus, the purpose of this study was to examine the toxicological significance of human fetal cytochrome P-450. Firstly, we found that human fetal livers were capable of activating numbers of carcinogenic compounds. Secondly, the capacity of human fetal cytochrome P-450 to activate mutagens and carcinogens was confirmed using purified forms of cytochrome P-450. For this, we purified four forms of cytochrome P-450 from human fetal livers. Lastly, we could isolate a cDNA clone coding for P-450HFLa which is one of the major forms of cytochrome P-450 in human fetal livers. Utilizing synthesized cD-NAs as probes, we found that this form of cytochrome was expressed specifically in fetuses.

Isolation of cDNAs coding for three different forms of liver microsomal cytochrome P-450 from polychlorinated biphenyl-treated beagle dogs

Three different cDNA clones, namely DM1-1, Dah1, and Dah2, encoding hepatic cytochrome P-450, were isolated from a cDNA library in lambda gt11 constructed from liver RNA of polychlorinated biphenyl-treated beagle dogs. DM1-1 was 1857 base pairs (bp) long and encoded a polypeptide of 457 residues. Dah1 was 2394 bp long and contained an entire coding region for 524 amino acid residues. In addition, Dah2 was 1623 bp long and had an open reading frame consisting of 503 amino acid residues, although it lacked the translational initiation codon. Judging from the similarity of the nucleotide and amino acid sequences, forms of cytochrome P-450 encoded by DM1-1, Dah1, and Dah2 were judged to belong to the P450IIC, P450IA1, and P450IA2 subfamilies, respectively. Northern blot analysis of RNA from various tissues, using the specific 3' noncoding regions of Dah1 and Dah2 as probes, indicated that mRNAs for P-450(Dah1) and P-450(Dah2) were not detectable in tissues from untreated dogs, except for P-450(Dah2) in livers. Polychlorinated biphenyl induced both mRNAs in liver, kidney, and lung, especially in the kidney.

[Effect of ulinastatin on microcirculation under hemodilution and hypothermia]

Microcirculation during hemodilution and hypothermia under ether anesthesia treated with or without ulinastatin was studied by means of rabbit ear chamber. Sixteen rabbits were divided into 2 groups; 8 rabbits without ulinastatin treatment (C group) and 8 rabbits treated with ulinastatin (U group). Surface cooling to 20 degrees C and rewarming were performed. No significant differences between the groups were found in blood pressure and heart rate, but pulse pressure in U group was significantly larger (P less than 0.01) than that in C group. Pulmonary edema occurred in 3 rabbits in C group during rewarming. The results suggest that ulinastatin inhibited edema formation in U group. In C group, the blood flow velocity was very slow and the blood flow rate was very small at 20 degrees C in arterioles and venules. In U group the flow velocity and the flow rate were well maintained at 20 degrees C in arterioles and venules. It is concluded that ulinastatin is effective in maintaining microcirculation during hemodilution and hypothermia.

Fetus-specific expression of a form of cytochrome P-450 in human livers

The developmentally regulated expression of forms of cytochrome P-450, namely, those encoded by lambda HFL33 and NF25 or HLp cDNAs, which were isolated from respective fetal and adult human liver cDNA libraries, was investigated. When EcoRI fragments of cDNA clones of lambda HFL33 and NF25 were used as probes, these probes hybridized with RNA from both fetal and adult human livers. However, when oligonucleotides specific to the coding and 3'-noncoding region of lambda HFL33 (oli-HFL and oli-HFL3', respectively) were used as probes, these probes gave hybridizable bands with RNA from fetal but not adult livers. On the other hand, an oligonucleotide probe specific to the coding region of NF25 and HLp (oli-NF) gave positive bands with RNA only from adult livers. These results indicate that P-450(HFL33) is expressed specifically in fetal livers and that neither P-450NF nor HLp is expressed in fetal livers, but one or both are expressed in adult livers.

Decrease in a constitutive form of cytochrome P-450 by macrolide antibiotics

The effects of administration of macrolide antibiotics on cytochrome P-450 in liver microsomes of male rats were investigated. The macrolides tested were those with a 14-membered ring such as oleandomycin, troleandomycin, erythromycin and erythromycin estolate, and those with a 16-membered ring such as rokitamycin, leucomycin and josamycin. Cytochrome P-450-metabolite complex was detected with oleandomycin, troleandomycin, erythromycin and erythromycin estolate, whereas no such effect was observed with rokitamycin, leucomycin and josamycin. The content of uncomplexed cytochrome P-450 in liver microsomes remained unchanged with rokitamycin, leucomycin and josamycin, decreased with troleandomycin and oleandomycin, and increased with erythromycin and erythromycin estolate, indicating that oleandomycin, troleandomycin, erythromycin and erythromycin estolate also affect the amounts of other forms of cytochrome P-450. The administration of oleandomycin, troleandomycin, erythromycin and erythromycin estolate resulted in a dramatic decrease in the activities of testosterone 2 alpha- and 16 alpha-hydroxylases in liver microsomes. Supporting these results, a marked decrease (more than 75%) in the content of P-450-male, a major constitutive form of cytochrome P-450 in male rats, was noted with oleandomycin, troleandomycin, erythromycin and erythromycin estolate, while the decrease was rather small with rokitamycin and leucomycin. We conclude that the administration of the 14-membered ring macrolides may affect drug and steroid metabolism not only by formation of P-450-metabolite complex but also by decrease in the content of P-450-male.

Distributional variation of P-450 immunoreactive hepatocytes in human liver disorders

Implications of P-450 in human hepatic disorders were immunohistochemically examined. We first confirmed that an antibody against P-450-HM1, an isozyme of cytochrome P-450 which was purified from human livers at autopsy, detects only P-450 on immunoblots. In a study of 79 consecutive autopsied livers using the avidin-biotin-peroxidase complex method, the antibody reacted strongly with fetal hepatocytes, the reaction being more intense in the left lobe than in the right lobe. In normal livers, immunoreactivity was confined to centrilobular hepatocytes, decreasing in the periportal zone. Enhanced expression was occasionally found in scattered hepatocytes and in hepatocytes surrounding sublobular veins; this enhancement was related to longterm steroid therapy. No specific induction was observed in patients with toxic hepatitis. In patients with fibrosis, cirrhosis, or regenerative nodules, however, P-450-positive hepatocytes were observed in the periportal and middle zones as well as in the central zone. In contrast, hepatocellular carcinomas were devoid of P-450 immunoreactivity. These results suggest that P-450-HM1, which is abundant in the fetal liver, is reexpressed in regenerating hepatocytes but not in cancers.