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Biomedical subjects

S Imaoka

Publications and source records attributed to S Imaoka.

At least 55 records · Page 3Linked to original sources
PubMed2000

Expression of N-acetylglucosaminyltransferase V in colorectal cancer correlates with metastasis and poor prognosis.

N-Acetylglucosaminyltransferase V (GnT-V) is an enzyme that catalyzes beta 1-6 branching of N-acetylglucosamine on asparagine-linked oligosaccharides of cell proteins. Metastatic potential of various cancer cells has been shown to correlate with increase of GnT-V activity and concomitant beta 1-6 branching of N-acetylglucosamine. However, protein expression of GnT-V in human cancer tissue and its clinical significance have not yet been demonstrated. To clarify the possible relationship between metastasis and GnT-V in human colorectal cancer, protein expression of GnT-V was studied using surgically resected specimens. We established a monoclonal antibody against GnT-V and performed immunohistochemical analysis of 103 human colorectal cancer cases. Of 103 cases, 26 cases (25.2 %) showed specific expression of GnT-V in colorectal cancer tissues. The expression of GnT-V was significantly correlated with distant metastasis (P < 0.05, chi2 test). Overall 5-year survival rate was 52.8% for GnT-V-positive patients and 81.7% for GnT-V-negative patients (P < 0.01, Log-rank test). We showed direct evidence for the relationship between GnT-V and metastasis in human colorectal cancer. Screening of GnT-V expression in colorectal cancer may provide useful information for prognosis of postoperative patients.

Aged↗
PubMed1999

Inhibition of liver glutathione S-transferase placental form-positive foci development in the rat hepatocarcinogenesis by Porphyra tenera (Asakusa-nori).

The effects of Asakusa-nori, Porphyra tenera (PT), a popular edible seaweed in Japan, on the development of putative preneoplastic lesions, glutathione S-transferase placental form (GST-P)-positive foci, in the male F344 rat liver were examined using a medium-term bioassay system. PT significantly decreased both the number and area of GST-P-positive foci in rat livers initiated with diethylnitrosamine (DEN). To investigate possible mechanisms of inhibition, effects of PT on 5-bromo-2'-deoxyuridine (BrdU) labeling in GST-P-positive foci and the surrounding area of hepatocytes were studied. The ratio of the GST-P-positive foci to surrounding tissue labeling indices was decreased in the PT-treated group as compared with the DEN alone group. Ornithine decarboxylase activity in the liver was slightly increased and spermidine/spermine N'-acetyltransferase activity was slightly decreased in the PT-treated animals. These results suggest that PT possesses chemopreventive effects against DEN-induced hepatocarcinogenesis.

Acetyltransferases↗
PubMed1999

Isoforms of cytochrome P450 on organic nitrate-derived nitric oxide release in human heart vessels.

Glutathione S-transferases and the cytochrome P450 system have been proposed for the vascular biotransformation systems in the metabolic activation of organic nitrates. The present study was designed to elucidate the role of human cytochrome P450 isoforms on nitric oxide formation from organic nitrates using lymphoblast microsomes transfected with human CYP isoforms cDNA. CYP3A4-transfected microsomes had the most effective potential of nitric oxide formation from isosorbide dinitrate. Anti-CYP3A2 antibody (which cross-reacts with CYP3A4) or ketoconazole (an inhibitor of the CYP3A superfamily) inhibited nitric oxide formation from isosorbide dinitrate in rat heart microsomes. Immunohistochemistry of human heart also showed intense bindings of CYP3A4 antibody in the endothelium of the endocardium and coronary vessels. These results suggest that the CYP3A4-NADPH-cytochrome P450 reductase system specifically participates in nitric oxide formation from isosorbide dinitrate.

Animals↗
PubMed1999

Phase II study of limited surgery for early gastric cancer: segmental gastric resection.

BACKGROUND: Endoscopic resection for treatment of early gastric cancer (EGC) is widely performed. Recently, however, surgeons began performing a limited operation for EGC when endoscopic resection was not indicated. This report discusses the surgical technique and the results of the limited operation, which is generally referred to as "segmental resection" (SR). METHODS: Since 1990, a total of 50 patients with intramucosal invasive EGC of the middle stomach underwent SR. The procedure included a limited gastrectomy, limited lymph node dissection, and preservation of the vagal nerve. We examined the surgical risk, postoperative complications, and patient survival rates and compared the results for the SR-treated patients (group A) with results for patients with EGC who underwent subtotal gastrectomy and systemic lymph node dissection (group B). RESULTS: Blood loss was less in group A (239 +/- 180 ml) than in group B (342 +/- 176 ml) (P < .05). The incidence of postoperative complications was also lower in group A (2.0%) than in group B (14.0%) (P < .05). The incidence of postoperative cholelithiasis was lower in group A (4.0%) than in group B (18.0%) (P < .05). All patients in both groups are alive without recurrence. CONCLUSIONS: Compared with distal gastrectomy, SR for EGC of the middle stomach decreased the surgical risk and postoperative complications without increasing the recurrence rate.

Female↗
PubMed1999

Evaluation of preoperative and intraoperative arterial stimulation and venous sampling for diagnosis and surgical resection of insulinoma.

BACKGROUND: The precise intraoperative localization of insulinoma is essential for successful surgical treatment. In addition to various imaging modalities developed recently, arterial stimulation and venous sampling (ASVS) has also been used for tumor localization. METHODS: Preoperative and intraoperative ASVS procedures were performed in 6 patients with insulinoma. Intraoperative ASVS was performed before and after tumor resection. Immunoreactive insulin (IRI) concentrations and the IRI ratio (IRI concentration at each time interval after calcium injection/baseline IRI concentration) were determined by the conventional or a quick IRI method. RESULTS: The site of the tumor was identified preoperatively in all patients. The peak of the IRI ratio varied widely, but setting the cutoff value at 3.0 clearly differentiated peak IRA ratios in feeding arteries from those of nonfeeding arteries. Intraoperative ASVS showed a similar elevation of IRI levels, but the elevation disappeared after tumor resection in all but 1 patient. In 2 patients, resection of the tumor was confirmed during surgery by measuring IRI levels by the quick IRI method. CONCLUSIONS: A combination of ASVS and conventional imaging modalities is useful for precise localization of insulinoma. Resection of the tumor can be confirmed intraoperatively by comparing IRI levels associated with preoperative and postresective ASVS.

Adult↗
PubMed1999

Hepatic cytochrome P450 is directly inactivated by nitric oxide, not by inflammatory cytokines, in the early phase of endotoxemia.

BACKGROUND/AIMS: Although the activity of the liver in metabolizing and eliminating various drugs decreases in endotoxemia, the mechanism remains to be elucidated. The generation of nitric oxide by the inducible type of nitric oxide synthase increases in endotoxemia. Nitric oxide readily reacts with heme proteins such as cytochrome P450 that metabolize various compounds, including steroids and eicosanoids. The purpose of this study was to determine the effect of nitric oxide on the function of hepatic cytochrome P450 in endotoxemic rats. METHODS: To determine the dynamic aspects of nitric oxide metabolism, hepatic levels of the inducible type of nitric oxide synthase and heme-iron nitrosyl complexes, and plasma levels of nitrite and nitrate were determined in rats before and after intravenous administration of lipopolysaccharide. Changes in the levels of P450 isoforms and testosterone hydroxylation activity in hepatic microsomes were also determined. To evaluate in vivo CYP3A2 activity, midazolam sleep time was measured. RESULTS: When lipopolysaccharide increased the hepatic inducible type of nitric oxide synthase and plasma levels of nitric oxide metabolites, the intensity of low-spin signal of electron spin resonance responsible for the ferric form of P450 decreased with a concomitant increase in heme-iron nitrosyl complexes in the liver. Lipopolysaccharide-related nitric oxide generation is followed by an early decrease in the levels of cytochrome P450 and of testosterone hydroxylation activity in liver microsomes. Midazolam sleep time was prolonged by lipopolysaccharide. All these early changes were prevented by the inhibitor of nitric oxide synthase, N(G)-iminoethyl-L-ornithine. Moreover, lipopolysaccharide suppressed the gene expression of CYP2C11 and CYP3A2. Decreases in levels of cytochrome P450 and their mRNAs were more pronounced at 24 h after LPS administration, but apparently they are NO-independent. CONCLUSIONS: These results suggest that lipopolysaccharide-induced modulation of cytochrome P450 may occur via the interplay of two different mechanisms and that, especially in the early phase, nitric oxide-dependent inhibition is more important.

Animals↗
PubMed1999

Phosphodiesterase type III inhibitor, cilostazol, inhibits colon cancer cell motility.

Metastasis of cancer cells is initiated by the cellular migration into extracellular matrix and surrounding vessels. We previously showed that elevation of cAMP levels in cancer cells suppressed trans-cellular migration in vitro. Drugs that can elevate cAMP levels in cancer cells effectively may be applied to prevent metastasis in cancer patients. Cilostazol, an oral anti-platelet drug, is a specific cAMP phosphodiesterase type III inhibitor and has been clinically used to treat thrombosis patients. In chemotaxis assay, cellular migration of human colon cancer cells, DLD- 1, was induced by 10 microg/ml of soluble fibronectin or 10% of fetal bovine serum (FBS). Treatment with cilostazol (50 microM) suppressed 92.3% or 84.6% of the migration in control cells, respectively. When DLD-1 cells were stimulated by soluble fibronectin in phagokinetic assay, migration assessed by the area of gold particle phagocytosis track was induced and cilostazol also decreased 67.3% of the cellular migration in control cells. Furthermore, in the trans-cellular migration assay, cilostazol suppressed cancer cell invasion induced by FBS. Thus, cilostazol can suppress colon cancer cell motility and might be effective as an anti-metastasis drug for cancer patients.

Animals↗
PubMed1999

Involvement of CYP3A-derived arachidonic acid metabolite(s) in responses to endothelium-derived K+ channel opening substance in monkey lingual artery.

1. In monkey lingual artery strips partially contracted with prostaglandin F2alpha, acetylcholine-induced, concentration-related relaxations were abolished by removal of the endothelium. The response was not significantly influenced by indomethacin but attenuated by NG-nitro-L-arginine (L-NOARG); the effect of the nitric oxide (NO) synthase inhibitor was reversed by L-arginine. 2. The response to acetylcholine resistant to L-NOARG was suppressed in the strips exposed to high K+ media. Charybdotoxin partially inhibited the relaxation, and the remaining relaxation was abolished by additional treatment with apamin, whereas glibenclamide, iberiotoxin or apamin alone was without effect. Relaxations induced by sodium nitroprusside were not influenced by charybdotoxin. 3. The L-NOARG-resistant acetylcholine-induced relaxation was inhibited by metyrapone, proadifen and 17-octadecynoic acid, non-selective cytochrome P450 mono-oxygenase (CYP) inhibitors, and progesterone and ketoconazole, inhibitors selective to CYP3A. The inhibitors did not affect the nitroprusside-induced relaxation. Selective inhibitors of other CYP isoforms, such as debrisoquine and lauric acid, did not reduce the response to acetylcholine. 4. Reaction mixture containing human liver microsome rich in CYPs, arachidonic acid and NADPH incubated at 37 degrees C and filtrated relaxed endothelium-denuded monkey lingual artery strips, used as bioassay tissues. This response was abolished in the strips exposed to high K+ media. The response was also suppressed by combined treatment of the assay tissue with charybdotoxin plus apamin, but was not affected by treatment with iberiotoxin. The reaction mixture co-incubated with ketoconazole failed to relax the strips. 5. It is concluded that the monkey lingual arterial relaxation dependent on the endothelium is mediated by NO and also by a charybdotoxin plus apamin-sensitive but iberiotoxin-insensitive Ca2+-activated K+ channel opening substance(s) that may be a CYP3A-derived arachidonic acid metabolite(s).

Animals↗
PubMed1999

Cytochrome P450 isoforms responsible for the N-deethylation and cyclohexane-hydroxylation of NS-21.

1. Cytochrome P450 (P450) isoforms responsible for the N-deethylation and cyclohexane-hydroxylation of (+/-)-4-diethylamino-1,1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate (NS-21) have been identified in rat and man. 2. Anti-CYP2C11 antibody inhibited the N-deethylation of S- and R-NS-21 in rat hepatic microsomes by 84 and 66% respectively, indicating that CYP2C11 is mainly responsible for these activities in male rats. 3. Of several human recombinant P450 isoforms, CYP3A4 had the activities for the N-deethylation of S- and R-NS-21. In addition, triacetyloleandomycin (TAO), an inhibitor of the CYP3A subfamily, significantly inhibited the N-deethylation of S- and R-NS-21 in human hepatic microsomes by 67 and 69%, respectively. CYP3A4 therefore contributes to it in man. 4. Quinine, an inhibitor of the rat CYP2D subfamily, significantly inhibited the cyclohexane-4-cis-hydroxylation of S-NS-21 by 48% in rat hepatic microsomes. In contrast, this inhibitor had little effect on the cyclohexane-4-trans-hydroxylation of S-NS-21, and the cyclohexane-4-cis- and trans-hydroxylation of R-NS-21. 5. Human recombinant CYP3A4 catalysed the cyclohexane-4-trans-hydroxylation of S-NS-21, and CYP2D6 supported the cyclohexane-4-cis- and trans-hydroxylation of S-NS-21. Quinidine, an inhibitor of human CYP2D6, had little effect on these latter activities in human hepatic microsomes. TAO significantly inhibited the cyclohexane-4-trans-hydroxylation of S-NS-21 by 75%, indicating that CYP3A4 catalyses this reaction.

Animals↗
PubMed1999

Frameshift mutation of the STK11 gene in a sporadic gastrointestinal cancer with microsatellite instability.

Germline mutations of the STK11 gene lead to emergence of hamartomas in the gastrointestinal tract of patients with Peutz-Jeghers syndrome, who bear an increased risk of malignancies of the gastrointestinal tract, genital tract, and other organs. We analyzed 80 sporadic colorectal cancers, six small-intestinal cancers, and 40 gastric cancers for somatic mutations of STK11 by SSCP methods. Among them only one colorectal cancer, which showed a phenotype of microsatellite instability, was found to possess a deleterious mutation in this gene, a frameshift involving deletion of one base at codons 279-281. This region of the gene contains a mononucleotide-repeat sequence, CCCCCC. The other allele of STK11 had been lost in this tumor. If the STK11 gene is one of the mutational targets of microsatellite instability, its inactivation may be associated with tumor development in a small proportion of colorectal cancers.

AMP-Activated Protein Kinase Kinases↗
PubMed1999

Extended pancreatectomy and liver perfusion chemotherapy for resectable adenocarcinoma of the pancreas.

In order to increase the long-term survival after resection of pancreatic adenocarcinoma, it is essential to eradicate both locoregional recurrence and hepatic metastasis. We have added a wide range of lymphatic and connective tissue clearance to conventional pancreatectomy (extended pancreatectomy) and succeeded in improving the 5-year survival rate from 8 to 25% via decreasing the incidence of local failure. Among many procedures which together compose an extended pancreatectomy, connective tissue clearance seems to have played a more important role on patients' prognosis rather than wide range lymphadenectomy. Concomitant resection of the portal vein is recommended for selected patients, and it is important not to overlook a minute invasion even though it appears macroscopically intact. With regard to adjuvant therapy in combination with our extended pancreatectomy, the addition of preoperative irradiation failed to further improve the long-term survival rate because the cause of cancer deaths shifted from local recurrence to hepatic metastasis. When liver perfusion chemotherapy was added to this operation (without radiation), the 5-year survival rate was improved to 39% by decreasing the incidence of hepatic metastasis. In the future, a combination of extended pancreatectomy with chemoradiation plus liver perfusion chemotherapy is one of the promising approaches for this cancer.

Adenocarcinoma↗
PubMed1999

Isoform-selective metabolism of mianserin by cytochrome P-450 2D.

The involvement of cytochrome P-450 (CYP) 2D isoforms in the metabolism of mianserin and the stereoselectivity of their catalytic activities were investigated by using five CYP2D isoforms (CYP2D1, 2D2, 2D3, 2D4, and 2D6). Using RS-mianserin as a substrate, we found that five CYP2D isoforms had similar levels of 8-hydroxylation activity. However, N-demethylation activity differed among the isoforms; CYP2D3 and 2D4 efficiently demethylated RS-mianserin compared with the other three isoforms. N-Oxidation activity was specific to CYP2D1 although its level was relatively low. Another metabolite, assigned as 8-hydroxy-N-desmethylmianserin by liquid chromatography/mass spectrometry analysis, was formed by CYP2D4 and 2D6. The metabolism exhibited stereoselectivity. CYP2D1 and 2D4 selectively 8-hydroxylated the R(-)-enantiomer, and CYP2D6 predominately N-demethylated R(-)-enantiomer. N-Oxidation by CYP2D1 was specific to R(-)-enantiomer. In conclusion, CYP2D isoforms are involved in several metabolic pathways of mianserin acting in an isoform-specific manner. Stereoselectivity of the catalytic activities was clearly observed in the reactions of CYP2D1, 2D4, and 2D6.

Alcohol Oxidoreductases↗
PubMed1999

Developmental changes in the catalytic activity and expression of CYP2D isoforms in the rat liver.

Developmental changes in bufuralol 1'-hydroxylation activity, which is known as a typical activity of cytochrome P-450 (CYP)2D isoforms, in the liver of rats were investigated. The catalytic activities of hepatic microsomes increased with development especially from 3 to 7 weeks. Eadie-Hofstee plots of bufuralol 1'-hydroxylation were obtained for monophasic kinetics (Km: 0.037 microM) at 1 week and for biphasic kinetics (Km: 0.051 and 6.4 microM) at 7 weeks of age. Quinine completely inhibited bufuralol 1'-hydroxylation activity of hepatic microsomes of 1- and 7-week-old rats. These results indicated that at least two kinds of CYP2D isoforms, which differ markedly in their affinity for bufuralol, were present at 7 weeks of age and that the CYP2D isoform that had low affinity for bufuralol was expressed with development. To assess the affinity of CYP2D isoforms for bufuralol, the kinetic properties of CYP2D1, 2D2, 2D3, and 2D4 expressed in yeast cells were investigated. The Km value of CYP2D2, 0.044 microM, was extremely small compared with that of the other rat CYP2D isoforms. We further investigated developmental changes of CYP2D isoform mRNA by reverse transcription-polymerase chain reaction. CYP2D3 mRNA increased with development although CYP2D1 and 2D2 mRNA were not changed. The CYP2D4 mRNA was not detected. These findings indicated that CYP2D2, which had high affinity for bufuralol, was expressed in immature and mature rats, but CYP2D3, which had low affinity for bufuralol, was expressed only in mature rats.

Animals↗
PubMed1998

Dopamine formation from tyramine by CYP2D6.

Dopamine is formed form L-tyrosine by tyrosine hydroxylase and aromatic L-amino acid decarboxylase. In addition to this pathway, however, the formation of catecholamines, including dopamine, from trace amines such as tyramine by hepatic microsomes has been demonstrated. In this study, we investigated the formation of dopamine from trace amines, using human hepatic microsomes and human cytochrome P450 (CYP) isoforms expressed in yeast. Among the 11 isoforms of human CYP expressed in yeast, CYP2D6 was the only isoform exhibiting strong ability to convert p-tyramine and m-tyramine to dopamine. In studies with human hepatic microsomes, the hydroxylation of tyramine to dopamine was inhibited by bufuralol, a typical substrate for CYP2D isoforms, and anti-CYP2D1 antiserum. This is the first report showing that CYP2D is capable of converting tyramine to dopamine. The Km values of CYP2D6, expressed in yeast, for p-tyramine and m-tyramine were 190.1 +/- 19.5 microM and 58.2 +/- 13.8 microM, respectively. Tyramine is an endogenous compound which exists in the brain as a trace amine but is also an exogenous compound which is found in foods such as cheese and wine. Our results suggest that dopamine is formed from endogenous and/or exogenous tyramine by this CYP2D isoform.

Animals↗
PubMed1998

Activation of the beta-catenin gene in primary hepatocellular carcinomas by somatic alterations involving exon 3.

We screened 75 primary hepatocellular carcinomas for somatic mutations in the entire coding region of the beta-catenin gene. We detected somatic mutations in 14 tumors; 12 were considered to cause amino acid substitutions and 2 were interstitial deletions of 51 or 195 nucleotides of genomic DNA, corresponding to exon 3. Among the 12 point mutations, 6 occurred at potential serine/threonine phosphorylation residues of codons 33, 41, or 45. The remaining six tumors contained a mutation at codon 32 (aspartic acid) or 34 (glycine), flanking to the serine residue at codon 33. By Western blot analysis, we confirmed accumulation of beta-catenin in five tumors for which frozen tissues were available; the five included tumors in which amino acid alterations had occurred at codons 32, 34, or 45, and one with a 17-amino acid deletion. Our results suggested that accumulation of beta-catenin due to amino acid substitutions at potential serine/threonine phosphorylation residues or at their neighboring codons or interstitial deletions involving exon 3 could contribute to hepatocellular carcinogenesis.

Carcinoma, Hepatocellular↗
PubMed1998

P450 isoforms in a murine macrophage cell line, RAW264.7, and changes in the levels of P450 isoforms by treatment of cells with lipopolysaccharide and interferon-gamma.

The presence of P450 in a murine macrophage cell line, RAW264.7, was investigated to clarify the biological role and regulation of P450. Microsomes of RAW264.7 cells were isolated and subjected to immunoblotting with anti-rat CYP2A1, 2B1, and 4A2 antibodies. The microsomes gave staining bands with all these antibodies, suggesting the presence of mouse Cyp2a, 2b, and 4a isoforms in RAW264.7. RAW264. 7 cells were treated with typical inducers of P450 (phenobarbital, clofibrate, beta-naphthoflavone and 3-methylcholanthrene). None of these chemicals induced these P450s. Stimulation of RAW264.7 cells with lipopolysaccharide (LPS) and interferon-gamma (INF-gamma) which increase inducible nitric oxide synthase (iNOS) and cytokines in cells decreased Cyp4a protein but not Cyp2a and 2b proteins. To identify P450 isoforms in RAW264.7, we used polymerase chain reaction (PCR) primers for mouse Cyp2a4, 2a12, 2b9/10, 4a10, and 4a12. Total RNA was isolated from these cells and converted to cDNA by reverse transcriptase. PCR was done with these primers and the amplified nucleotides were analyzed by a DNA sequencer. Only Cyp2b9/10 and 4a12 primers gave clear bands, although all primers gave clear bands from liver total RNA. Nucleotide sequences of these products amplified by PCR were identical with Cyp2b9 and 4a12. These findings indicate that Cyp2b9 and 4a12 were present in a macrophage cell line, RAW264.7, and the regulation of P450 by inducers and cytokine differed from that in liver.

Animals↗
PubMed1998

Cloning and characterization of the CYP2D1-binding protein, retinol dehydrogenase.

A CYP2D1-binding protein, 29 k-protein (p29), has been isolated and its N-terminal amino acid sequence has been reported (Ohishi et al. (1993) Biochim. Biophys. Acta 1158, 227-236). In this study, p29 cDNA was isolated by PCR with oligonucleotide probes designed from the N-terminal amino acid sequence and p29 was found to be a microsomal retinol dehydrogenase, a member of the short-chain alcohol dehydrogenase family which metabolize hydroxysteroids and prostaglandins. CYP2D1 and p29 were expressed in Saccharomyces cerevisiae to characterize these proteins. CYP2D1 had an absorption maximum at 448 nm in a CO-reduced form. Expressed p29 in yeast cells was detected with anti-p29 antibody. Solubilized CYP2D1 and p29 from yeast microsomes were mixed and applied to an anti-CYP2D1 antibody-binding column. Both proteins were retained in the column and eluted with glycine buffer (pH 2.8). However, when applied alone, p29 was not retained in the column. The findings indicated that CYP2D1 bound tightly with p29. Catalytic activities of p29 expressed in yeast were investigated. p29 had retinal reductase activity in the presence of NADPH. Addition of CYP2D1 and NADPH-P450 reductase increased the retinal reductase activity of p29. These findings suggest that the complex of CYP2D1, p29, and NADPH-P450 reductase has an important role in the metabolism of retinoids.

Alcohol Oxidoreductases↗