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Biomedical subjects

Y Inui

Publications and source records attributed to Y Inui.

At least 19 recordsLinked to original sources
PubMed1992

Cytochrome P450 2E1 and 2A6 enzymes as major catalysts for metabolic activation of N-nitrosodialkylamines and tobacco-related nitrosamines in human liver microsomes.

An acetyltransferase-overexpressing strain of Salmonella typhimurium (NM2009) has been used to investigate roles of human liver microsomal cytochrome P450 (P450) enzymes in the activation of carcinogenic nitrosamine derivatives, including N-nitrosodialkylamines and tobacco-smoke-related nitrosamines, to genotoxic products. Studies employing correlation of activities with several P450-dependent monooxygenase reactions in different human liver samples, inhibition of microsomal activities by antibodies raised against human P450 enzymes and by specific P450 inhibitors, and reconstitution of activities with purified P450 enzymes suggest that the tobacco-smoke-related nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and N-nitrosonornicotine (NNN) as well as N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) are oxidized to genotoxic products by different P450 enzymes, particularly P450 2E1 and 2A6. The activation of NDMA and NNN by liver microsomes was suggested to be catalyzed more actively by P450 2E1 than by other P450 enzymes because the activities were well correlated with NDMA N-demethylation and aniline p-hydroxylation in different human samples, and purified P450 2E1 had the highest activities in reconstituted monooxygenase systems. The relatively high contribution of P450 2A6 to the activation of NDEA and NNK was supported by the correlation seen with coumarin 7-hydroxylation in human liver microsomes, and antibodies raised against P450 2A6 inhibited both activities by approximately 50%. P450 3A4, 2D6 and 2C enzymes appear not to be extensively involved in the activation of these nitrosamines as judged by several criteria examined. Thus, this work indicates that several P450 enzymes, particularly P450 2E1 and 2A6, catalyze metabolic activation of nitrosamine derivatives including N-nitrosodialkylamines and tobacco-smoke-related nitrosamines in human liver microsomes.

Animals↗
PubMed1992

Participation of rat liver cytochrome P450 2E1 in the activation of N-nitrosodimethylamine and N-nitrosodiethylamine to products genotoxic in an acetyltransferase-overexpressing Salmonella typhimurium strain (NM2009).

The possible roles of cytochrome P450 (P450) enzymes in the metabolic activation of N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) by rat liver microsomes have been examined in a system containing the bacterial tester strain Salmonella typhimurium NM2009, a newly developed strain showing high O-acetyltransfer activities. The DNA-damaging activity could be determined by measuring expression of the umu gene in a plasmid containing the fused umuC-lacZ gene construct in the bacteria. The following lines of evidence support the view that both NDMA and NDEA are principally oxidized to reactive products by P450 2E1 in rat liver microsomes. First, NDMA and NDEA were activated by rat liver microsomes in a protein- and substrate-dependent manner and the former chemical was more active than the latter; both activities were induced in rats treated with P450 2E1 inducers such as ethanol, acetone and isoniazid and by starvation. Second, activation of NDMA and NDEA were both inhibited significantly by antibodies raised against rat P450 2E1 and by P450 2E1 inhibitors such as diethyldithiocarbamate and 4-methylpyrazole in rat liver microsomes. Finally, in reconstituted monooxygenase systems containing purified rat P450 enzymes, P450 2E1 gave the highest rates of the activation of both NDMA and NDEA; the addition of rabbit cytochrome b5 to the system caused about a 1.5-fold increase in both reactions. In separate experiments we also found that N-nitrosomethylacethoxymethylamine, a compound that reacts with DNA after ester cleavage, is more genotoxic in S.typhimurium NM2009 than in S.typhimurium NM2000, a strain that is defective in O-acetyltransferase activity. Part of the pathway involved in the activation of nitrosamines is suggested to be acetylation of alkyldiazohydroxides formed by P450 or acetylesterase, because the genotoxic activity of N-nitrosomethylacethoxymethylamine in S.typhimurium NM2009 could be inhibited by the O-acetyltransferase inhibitor pentachlorophenol. These results indicate that NDMA and NDEA are oxidized to gentoxoic products by rat liver microsomes and that a P450 2E1 enzyme plays a major role in the activation of these two potent carcinogens. The activation pathway of N-nitrosodialkylamines through acetylation by O-acetyltransferase has been proposed. This simple bacterial system for measuring genotoxicity should facilitate studies on the activation of N-nitroso alkylamines.

Acetyltransferases↗
PubMed1992

Effect of pravastatin, a potent 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, on survival of AH130 hepatoma-bearing rats.

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor is known to have an inhibitory effect on cell growth in addition to a cholesterol-lowering effect. This study examined the effect of pravastatin, a potent inhibitor of HMG-CoA reductase, on the survival of AH130 hepatoma-bearing rats. Pravastatin (1, 2, or 8 mg/kg body weight) was intraperitoneally injected once a day into tumor-bearing rats. The difference in the survival curves was significant between the controls and the rats treated with 8 mg/kg of pravastatin (P < 0.019 by logrank test) but not between the controls and the rats treated with 1 or 2 mg/kg of the inhibitor. The tumor volume was significantly decreased in the rats treated with 8 mg/kg of pravastatin (P < 0.05). These observations showed that intraperitoneal injection of pravastatin could improve the survival of AH130 hepatoma-bearing rats and had an inhibitory effect on the growth of the ascites form tumor.

Animals↗
PubMed1992

Apolipoprotein B messenger RNA editing in rat liver: developmental and hormonal modulation is divergent from apolipoprotein A-IV gene expression despite increased hepatic lipogenesis.

Rat hepatic apolipoprotein B (apoB) mRNA editing is regulated developmentally as well as by hormonal and nutritional modulation of hepatic lipogenesis, changes previously associated with coordinate modulation of hepatic apoA-IV gene expression. We have examined the effects of dexamethasone administration on apoB mRNA editing and the expression of other apolipoprotein genes in both neonatal and adult rats. Administration of dexamethasone increased hepatic triglyceride content in neonatal rats and increased hepatic but not intestinal apoA-IV mRNA abundance. However, neither the developmental profile nor the extent of hepatic apoB mRNA editing was changed after hormone administration. Dexamethasone produced a dose-dependent increase in adult hepatic triglyceride content and a coordinate fourfold increase in hepatic but not intestinal apoA-IV mRNA abundance, and hepatic and serum apoA-IV protein concentrations. Immunocytochemical localization revealed apoA-IV to be expressed in hepatocytes around the central vein while dexamethasone treatment produced a dose-dependent appearance of fat-filled hepatocytes throughout the lobule that were immunoreactive for apoA-IV. Despite these changes in hepatic triglyceride accumulation there was no change in the extent of hepatic apoB mRNA editing at any dose of dexamethasone. The data suggest that hormonal and metabolic modulation of hepatic apoB mRNA editing may be independent of factors that modulate apoA-IV gene expression despite alterations in hepatic triglyceride content.

Animals↗
PubMed1991

Modulation of cholesterol 7 alpha-hydroxylase activity by nonspecific lipid transfer protein in human liver--possibly altered regulation of its cytosolic level in patients with gallstones.

Nonspecific lipid transfer protein (nsLTP) partially purified from human liver stimulated human microsomal cholesterol 7 alpha-hydroxylase activity. Addition of the nsLTP preparation to the reaction mixture enhanced the activity two-fold. Treatment of the nsLTP preparation with anti-rat nsLTP antiserum, which cross-reacts with human nsLTP, reduced the 7 alpha-hydroxylase-stimulating ability. These observations suggested that nsLTP plays a role in regulating the 7 alpha-hydroxylase activity in the human liver. 7 alpha-Hydroxylase activity in eight patients with cholesterol gallstones (4.7 +/- 1.6 pmol/min per mg microsomal protein) was significantly lower than that in five controls (7.9 +/- 3.4) (P less than 0.05). The amount of nsLTP in the cytosolic fraction (105,000 X g supernatant) of human liver was determined by dot-blotting immunoquantitation with the antiserum. The cytosolic level of nsLTP in the liver of the patients (716 +/- 239 cpm/3 micrograms protein) was higher than that in the controls (438 +/- 184) although the difference between the two groups was not statistically significant. This suggested that control of the cytosolic level may be affected in patients with cholesterol gallstones.

Adult↗
PubMed1991

Animal model of systemic carnitine deficiency: analysis in C3H-H-2 degrees strain of mouse associated with juvenile visceral steatosis.

We analyzed carnitine profiles in C3H-H-2 degrees strain of mouse associated with fatty liver, hyperammonemia and hypoglycemia (Koizumi et al., 1988). Carnitine levels in serum, liver and muscle of mouse with fatty liver were markedly decreased in comparison with those of control mouse (littermates without fatty liver). This is a useful animal model to analyze the role of carnitine in lipid, amino acid and carbohydrate metabolism.

Aging↗
PubMed1991

Thyroid hormone regulates developmental changes in muscle during flounder metamorphosis.

Morphological and biochemical changes in the muscular tissue of metamorphosing flounder were studied in relation to the regulatory role of thyroid hormone. Premetamorphic larvae were reared in seawater alone or seawater containing either thyroxine (T4) or an antithyroid drug (thiourea, TU). Histological changes in the muscle were examined and biochemical changes in the muscle proteins were evaluated by SDS-PAGE and immunoblotting for troponin T (TNT). The muscle tissue of premetamorphic larvae was characterized by abundant vacuoles and basophilic sarcoplasm. In control fish, the larval muscle transformed into the adult type during metamorphic climax; the fibers were filled with abundant myofibrils and the vacuoles disappeared. Analysis by SDS-PAGE showed that the bands at 41.5, 35.5, 34.0, 33.5, 25.5, 23.0, 20.0, and 19.0 kDa clearly increased in density from the climax stage. Premetamorphic larvae possessed two immunoreactive TNT isoforms of 41.5 and 34.0 kDa, the former being predominant. At the climax stage an additional isoform appeared at 33.5 kDa, and the 34.0- and 33.5-kDa TNT became predominant. The administration of T4 precociously induced these histological and biochemical changes in the muscle tissue of flounder larvae. In contrast, TU treatment inhibited these developmental changes in the larval muscle. Our results suggest that the developmental changes in the muscular tissue of metamorphosing flounder are regulated by thyroid hormone.

Animals↗
PubMed1991

Changes in cortisol and thyroid hormone concentrations during early development and metamorphosis in the Japanese flounder, Paralichthys olivaceus.

Both cortisol and thyroid hormones were detected in newly fertilized eggs of the Japanese flounder, Paralichthys olivaceus. Mean cortisol levels ranged around 2.5 ng/g wet weight. Cortisol concentrations declined to about one-tenth of their initial levels by 2 days before hatching. The concentrations of triiodothyronine (T3; 7 ng/g) were greater than those of thyroxine (T4; 0.4 ng/g). The T3 levels decreased gradually in the eggs until the time of hatching and then decreased rapidly to undetectable levels within 2 days, whereas T4 remained at more or less constant levels during early development. The significance of the "selective" clearance of the three hormones from eggs remains unclear. Tissue concentrations of cortisol during premetamorphosis were about 4 ng/g and increased to a peak level of 11 ng/g at climax. After climax, cortisol declined by 50%. The changes in thyroid hormone levels were in parallel with the changes in cortisol. T4 remained below 1 ng/g during prematamorphosis but increased gradually during prometamorphosis, reaching peak levels (12 ng/g) during metamorphic climax, and then declined by approximately 50%. T3 remained at low levels through most of the metamorphosis. Histologically, the interrenal tissue was activated during the metamorphosis. The coincident increases in cortisol and thyroid hormones support previous results of a synergistic action of both hormones during metamorphosis in the flounder.

Aging↗
PubMed1991

Roles of different cytochrome P450 enzymes in bioactivation of the potent hepatocarcinogen 3-methoxy-4-aminoazobenzene by rat and human liver microsomes.

The potent hepatocarcinogen 3-methoxy-4-aminoazobenzene (3-MeO-AAB) has been reported to be bioactivated to mutagenic intermediates by rat liver microsomal cytochrome P450 (P450) and to be a selective inducer of rat P450IA2. In this study we have further investigated the roles of individual rat and human P450 enzymes in the bioactivation of this hepatocarcinogen in a Salmonella typhimurium TA1535/pSK1002 system where umu response is indicative of DNA damage. 3-MeO-AAB was found to be bioactivated by liver microsomal enzymes from rats and humans in this assay system. The liver microsomal activities are increased by pretreatment of rats with various P450 inducers such as phenobarbital (PB), beta-naphthoflavone (BNF), dexamethasone (DEX), acetone, ethanol, isoniazid (INH), diphenylhydantoin and valproic acid, and can be inhibited considerably by SKF-525A and metyrapone. alpha-Naphthoflavone (ANF) is also an inhibitor for the reaction catalyzed in BNF-treated rats, but stimulated the microsomal activity in DEX-treated rats. Evidence has also been obtained that specific antibodies raised against P450IIB1, P450IA1 or IA2, P450IIE1, and P450IIIA2 inhibited the activation in liver microsomes from rats pretreated with PB, BNF, INH and DEX respectively, suggesting the possible roles of several P450 enzymes in the bioactivation of 3-MeO-AAB. The results obtained with reconstituted monooxygenase systems containing various rat P450 enzymes are highly supportive of this conclusion. Human liver microsomal activation of 3-MeO-AAB was also inhibited to various extents by antibodies raised against P450IA2, P450MP, P450IIE1 and P450IIIA4. In a reconstituted system containing purified forms of human P450, P450IA2 was the most active in catalyzing 3-MeO-AAB, followed by P450IIIA4 and P450MP. ANF, a known activator of P450IIIA-catalyzed reactions, caused an increase in activation of 3-MeO-AAB in human liver microsomal and P450IIIA4- and P450MP-containing reconstituted systems. From these results it is concluded that multiple P450 enzymes in rat and human liver microsomes are involved in the bioactivation of 3-MeO-AAB, regardless of its selective induction of the rat P450IA2 gene.

Animals↗
PubMed1991

Selective increase in cytochrome P450 content in hepatic microsomes from rats with ventromedial hypothalamic lesions.

Changes in the components of hepatic microsomal electron transport systems and in drug hydroxylase activities were investigated in ventromedial hypothalamus (VMH) lesioned obese rats. Eight weeks after electrolysis of the bilateral VMH, the content of cytochrome P450 per mg microsomal protein (0.79 +/- 0.07 nmol/mg protein) was significantly higher (P less than 0.02) than that in the sham-operated rats (0.59 +/- 0.02). Cytochrome P450 per whole liver in the VMH-lesioned obese rats had also significantly increased (87 +/- 9 nmol vs 56 +/- 3, P less than 0.02). No significant differences were found in the cytochrome b5 contents, and the activities of NADPH- and NADH-cytochrome c reductases between the VMH-lesioned obese and sham-operated rats. The demethylation activities of aminopyrine (1.04 +/- 0.02 nmol/mg protein/min vs 0.94 +/- 0.02, P less than 0.05) and p-nitroanisole (0.96 +/- 0.02 vs 0.89 +/- 0.02 , p less than 0.02) and the aniline hydroxylase activity (0.22 +/- 0.01 vs 0.16 +/- 0.01, P less than 0.01) were enhanced, but 7-ethoxycoumarin O-deethylase activity was unchanged in the VMH-lesioned obese rats. These results indicate a selective increase in the content of cytochrome P450 among the components of the P450-dependent mixed function oxidase system in the liver of VMH-lesioned obese rats. Our observations suggest that drug metabolism may be enhanced in the hypothalamic obesity.

Animals↗
PubMed1990

Cortisol enhances the stimulating action of thyroid hormones on dorsal fin-ray resorption of flounder larvae in vitro.

Effects of thyroid hormones and cortisol on fin-ray resorption of the larval flounder were studied in vitro. Dorsal fin rays were dissected from the prometamorphic larvae of the Japanese flounder (Paralichthys olivaceus) and were cultured for 7-8 days in a medium supplemented with different concentrations of thyroxine (T4) or triiodothyronine (T3) or combinations of either thyroid hormone or cortisol (0.1 micrograms/ml). Both T4 and T3 induced shortening of the second fin ray. T3 was more potent than T4; doses of 0.1 and 1.0 micrograms/ml T4 significantly accelerated shortening of the fin rays, whereas T3 was effective at concentrations ranging from 0.001 to 1.0 micrograms/ml. Cortisol further enhanced the effects of both T4 and T3 but was ineffective in the absence of thyroid hormones. When the prometamorphic larvae were reared in water containing T4 (0.01 micrograms/ml), T4 + cortisol (0.10 micrograms/ml), or cortisol alone for 15 days, both the T4- and T4 + cortisol-treated groups showed an advancement of the morphological changes associated with metamorphosis relative to the control group without hormone treatment. However, no clear synergistic effect of cortisol was observed in the in vivo experiment; a sufficient quantity of cortisol may be produced by the larval interrenal.

Animals↗
PubMed1990

Effects of recombinant eel growth hormone on the uptake of [35S]sulfate by ceratobranchial cartilages of the Japanese eel, Anguilla japonica.

Effects of growth hormone (GH) on the synthesis of mucopolysaccharide by ceratobranchial cartilages of the Japanese eel, Anguilla japonica, were examined by monitoring the in vitro uptake of [35S]sulfate. The [35S]sulfate uptake decreased rapidly to one-third of the initial level during the first 3 days after hypophysectomy, and decreased gradually thereafter. When hypophysectomized eels were injected intramuscularly with recombinant eel GH (2 micrograms/g), the plasma GH concentrations increased maximally after 6 hr, and declined rapidly thereafter. On the other hand, the sulfate uptake increased significantly after 12 hr, and high levels were maintained until 48 hr. The stimulating effect of GH was dose dependent (0.02-2 micrograms/g). However, the addition of eel GH (0.05-5 micrograms/ml) to the culture medium did not affect the sulfate uptake by hypophysectomized eel cartilages, suggesting that the stimulative action of GH on the sulfate uptake by the cartilages is indirect.

Anguilla↗
PubMed1990

Evidences for the presence of a somatomedin-like plasma factor(s) in the Japanese eel, Anguilla japonica.

The indirect action of growth hormone (GH) through a somatomedin-like plasma factor(s) on the synthesis of mucopolysaccharides in the ceratobranchial cartilages of the Japanese eel, Anguilla japonica, was studied by monitoring the uptake of [35S]sulfate in vitro. Addition of plasma obtained from intact eels significantly stimulated the sulfate uptake by the cartilages of hypophysectomized eel, whereas plasma from hypophysectomized eels had no effect. On the other hand, the plasma from hypophysectomized eels which had been injected with eel GH significantly stimulated the uptake. The maximal stimulating activity was found in the plasma 24 hr after a single injection of eel GH (2 micrograms/g). This stimulatory activity was dependent on the dose of GH injected. These findings indicate that GH elicits its effect on the cartilages indirectly through a GH-dependent plasma factor(s). The system established in the present study can provide as a biological assay for the somatomedin-like plasma factor(s).

Anguilla↗
PubMed1990

Inhibitory effect of a new alpha-glucosidase inhibitor on fatty liver in Zucker fatty rats.

The livers of Zucker fatty (fa/fa) and lean (Fa/-) rats treated with standard rat chow diet containing 0, 10 or 50 ppm alpha-glucosidase inhibitor (AO-128) for 10 weeks were studied morphologically and biochemically. Light microscopic examination of livers from untreated Zucker fatty rats showed severe steatosis. The triglyceride content in the livers from Zucker fatty rats was significantly higher than that from lean rats (73 +/- 9 micrograms/mg protein for Zucker fatty rats vs. 30 +/- 10 for lean rats, p less than 0.01). Administration of the inhibitor caused a marked decrease in the number and size of lipid droplets in the hepatocytes from Zucker fatty rats and a decrease in the triglyceride content in the liver (73 +/- 9 micrograms/mg protein for untreated, 54 +/- 16 for 10-ppm-treated and 48 +/- 23 for 50-ppm-treated rats, p less than 0.05). This is the first report showing an inhibitory effect of an alpha-glucosidase inhibitor on steatosis in Zucker fatty rats.

Animals↗
PubMed1990

Laparoscopic findings of fatty liver using multiple regression analysis. "Spotty" and "diffuse" yellow color.

Laparoscopic features of fatty liver including the cases with fibrotic change were studied by multiple regression analysis. The coloration of the liver surface under laparoscopy was classified into three types: "spotty" yellow color (YC) type, "diffuse" YC type, and without YC type. The presence of YC on the liver surface depended on the amount of deposited lipid (standardized estimate = 0.606, p = 0.0001). However, the presence of YC and whether it appeared "spotty" or "diffuse" was independent of the intralobular distribution and size of the deposited lipid droplets. When YC was observed in cases without fibrotic change, 19 of the 23 with more than 30% lipid droplets in the biopsy specimens had "spotty" YC. When YC was found in cases with fibrotic change, all of the 14 cases with more than 30% lipid droplets were "diffuse" YC. A linear regression model showed that the yellow colored liver with fibrotic change had a "diffuse" appearance (yes = 1, no = 0) standardized estimate = 0.569, p = 0.0009). These data suggested that the amount of lipid deposited was responsible for the presence of YC on the liver surface both with and without fibrotic change, and that the co-existence of fibrotic change was a major factor for giving the yellow colored liver a "diffuse" appearance.

Biopsy↗
PubMed1989

Increased level of apolipoprotein B mRNA in the liver of ventromedial hypothalamus lesioned obese rats.

The mRNA level of apolipoprotein B (apoB), which is a principal protein component of nascent very low density lipoprotein (VLDL), was determined in parallel with the measurement of acetyl-coenzyme A (Ac-CoA) carboxylase activity in the liver of ventromedial hypothalamus (VMH) lesioned obese rats. Eight weeks after the electrolysis of the bilateral VMH, the level of apoB mRNA in the VMH-lesioned rats was about 1.5-fold higher than that in the sham-operated rats, indicating increased apoB synthesis in the liver of the VMH-lesioned obese rats. The activity of Ac-CoA carboxylase, which is a rate-limiting enzyme for the fatty acid biosynthesis, was about 1.8-fold higher in the VMH-lesioned rats. These observations indicated that VLDL synthesis is increased in the liver of VMH-lesioned obese rats.

Actins↗
PubMed1989

Effects of bovine TSH on the tissue thyroxine level and metamorphosis in prometamorphic flounder larvae.

Bovine thyroid-stimulating hormone (TSH) was microinjected (0.2 microliter/fish) into prometamorphic flounder larvae and the effects on metamorphosis as well as the tissue thyroxine (T4) and triiodothyronine (T3) levels were studied. After a single injection of TSH (5 mIU/g), the tissue T4 concentration increased markedly after 5 hr, reached a peak after 10 hr, and decreased subsequently. T4 concentration after 24 hr was still higher than in saline-injected fish but returned to the control level 48 hr after the injection. On the other hand, tissue T3 concentration was kept lower than the detectable level (0.2 ng/g) throughout the experimental period of 72 hr after a single injection of TSH (5 mIU/g). TSH treatment also accelerated the process of metamorphic climax, such as shortening of the second fin ray and eye migration. These results suggest that an increased secretion of TSH from the pituitary stimulates the thyroid, resulting in a surge of the tissue T4 concentration which induces the climax of the flounder larvae.

Aging↗