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Biomedical subjects

K Tsuzuki

Publications and source records attributed to K Tsuzuki.

At least 91 records · Page 5Linked to original sources
PubMed1993

Influence of o-phenanthroline on DNA single-strand breaks, alkali-labile sites, glutathione reductase, and formation of chromium(V) in Chinese hamster V-79 cells treated with sodium chromate (VI).

The effect of the cell-permeable metal chelator o-phenanthroline (OP) on the formation of chromium(V), DNA breaks, alkali-labile sites, and enzyme inhibition of chromium(VI) was studied using Chinese hamster V-79 cells. Alkaline elution assays demonstrated that treatment with OP (100-500 microM) resulted in a dose-dependent decrease in cellular levels of either alkali-labile sites or the combination of alkali-labile sites plus DNA single-strand breaks caused by Na2CrO4. Cellular treatment with OP also attenuated the inhibition of glutathione reductase attributed to Na2CrO4. Under the same experimental conditions, the cellular uptake of chromate was not affected by OP. ESR studies revealed that cellular treatment with OP (100-500 microM) resulted in a concentration-dependent decrease in the level of chromium(V) intermediate in cells treated with Na2CrO4. Furthermore, OP inhibited the chromium(V) complex that formed during the reaction of Na2CrO4 with glutathione in vitro, resulting in the decrease of chromium(V)-mediated hydroxyl radical formation while neither the reduction of chromium(VI) nor the formation of the chromium(VI)-glutathione complex was affected, indicating that OP may react with chromium(V) but not with chromium(VI). These results suggest that the metal chelator OP decreases chromate-induced alkali-labile sites or the combination of alkali-labile sites plus DNA strand breaks, as well as chromium inhibition of glutathione reductase, possibly through its ability to directly decrease chromium(V) complex in cells.

Animals↗
PubMed1993

DNA single-strand breaks and cytotoxicity induced by sodium chromate(VI) in hydrogen peroxide-resistant cell lines.

Hydrogen peroxide-resistant Chinese hamster ovary (CHOR) cells were developed by exposing parental (CHO(P)) cells to sequential increases in H2O2 concentration. Cytotoxicity as well as DNA single-strand breaks induced by Na2CrO4 were then compared in CHOR and CHO(P) cell lines. Using the colony-forming assay, it was found that the cytotoxicity caused by Na2CrO4 did not differ in the parent and resistant cells. However, alkaline elution studies showed that the production of DNA single-strand breaks in CHOR cells treated with Na2CrO4 was reduced by about 50% as compared with that in CHO(P) cells. Similarly, electron spin resonance (ESR) studies revealed that the level of chromium(V) in CHOR cells during treatment with Na2CrO4 was about 50% that in CHO(P) cells. CHOR cells were also found to be cross-resistant to the cytotoxicity and DNA breaks caused by other toxic metals such as CdCl2 and HgCl2. Catalase activity in resistant cells was 2-fold and the cellular content of glutathione was 3-fold that in parental cells. However, no obvious differences were seen in superoxide dismutase and glutathione reductase activity, although the contents of ascorbic acid or alpha-tocopherol were slightly decreased in CHOR cells, suggesting that the resistance in CHOR cells may be associated with the increase in both catalase activity and glutathione contents in cells. These results indicate that chromate-induced DNA breaks appear to be mediated by a different mechanism than that for the cytotoxicity of this metal, and also suggest that the formation of active oxygen species and/or chromium(V) during reduction of chromium(VI) inside cells might be associated with the induction of the DNA strand breaks caused by the metal.

Animals↗
PubMed1993

The complete nucleotide sequence of the gene encoding the nontoxic component of Clostridium botulinum type E progenitor toxin.

We have analysed the genes borne on a 6.0 kb HindIII fragment cloned from the chromosome of Clostridium botulinum type E strain Mashike. This fragment, cloned within plasmid pU9EMH, contains part of the structural gene for botulinum toxin type E neurotoxin as well as the entire structural gene for a nontoxic component of botulinum type E progenitor neurotoxin gene, ent-120. ent-120 is transcribed in the same direction as the neurotoxin gene and consists of one open reading frame encoding 1162 amino acid residues. Western blotting with anti-nontoxic component sera demonstrates that ent-120 encodes a protein of 120 kDa which forms part of the nontoxic component. ent-120 is homologous to an analogous gene found in botulinum type C strains (69.3% identity at the nucleotide level and 56.1% at the amino acid level). Two stretches of amino acids at the N-terminus of the ent-120 protein are highly homologous to amino acid sequences within the type E neurotoxin. The stop codon of the ent-120 gene is situated 27 nucleotides upstream from the start codon of the neurotoxin gene.

Amino Acid Sequence↗
PubMed1993

Selective block of transient Ca channel current in mouse neuroblastoma cells by U-88779E.

Antioxidants and T-type Ca channel antagonists are neuroprotective during ischemia or other central nervous system traumas. U-88779E (1-[(4-chlorophenyl-phenyl)-methyl]-4-[(7-methoxy-5-isopropyl- 2,4,6-cycloheptatrien-1-one)-2-methyl]piperazine) has been shown to have both antioxidant activity and the ability to block Ca fluxes in cardiac microsomes. In this study, we examined the effect of U-88779E on Ca, Na and K channels in a neuronal cell line, N1E-115 cells. The drug blocked transient barium current (IBa) through low-threshold Ca channels (T-type) with little effect on other noninactivating IBa including the nifedipine-sensitive one. The drug at 20 microM reduced transient IBa at a constant rate, -7.2% of the control per min, and abolished the current within 15 min. This implies a continuous accumulation of the drug in cell membranes probably because of its high lipophilicity (log P = 7.003). U-88779E also blocked Na and K currents but at a rate about 8 times slower than that observed with transient IBa. Further studies on interactions of the drug with T-channels revealed that the drug had no effect on the shape of current-voltage curve, activation and inactivation kinetics, and steady-state activation curve. The drug, however, induced a hyperpolarizing shift in steady-state inactivation curve and became more potent under conditions where the channels in inactivated states prevail. These observations are consistent with the view that U-88779E has a higher affinity to T-type channels in inactivated states than in resting or open states.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The complete nucleotide sequence of the gene coding for the nontoxic-nonhemagglutinin component of Clostridium botulinum type C progenitor toxin.

The structural gene for a nontoxic-nonhemagglutinin component of Clostridium botulinum type C progenitor toxin was found to exist on a 7.8 kb DNA fragment obtained from a type C phage DNA. The gene existed between the neurotoxin and hemagglutinin genes, and consisted of an 3588 bp open reading frame (1196 amino acid residues). It was speculated that this gene and the neurotoxin gene were transcribed by the same mRNA (polycistronic transcription) in C. botulinum organisms.

Amino Acid Sequence↗
PubMed1992

Inhibition of norepinephrine secretion from digitonin permeabilized PC12 cells by botulinum type D toxin.

Botulinum type D neurotoxin inhibited Ca(2+)-evoked norepinephrine secretion in digitonin permeabilized PC12 cells. Inhibition by the toxin required prior incubation with dithiothreitol (DTT). The inhibition was dependent on both concentration and incubation times of the toxin, and was affected by Ca2+ concentration. With less than 0.7 microM Ca2+ almost complete inhibition was observed; however, above 0.7 microM, Ca2+ stimulated additional norepinephrine release in a dose-dependent manner.

Animals↗
PubMed1992

A zinc-protease specific domain in botulinum and tetanus neurotoxins.

Neurotoxins produced by Clostridium botulinum are classified into groups (A to G) based on their serological nature. They consist of two subunits, heavy and light chains, linked by one or more disulphide bridges. The light chain is responsible for the blocking of acetylcholine release. Amino acid sequences of light chains have already been reported for botulinum toxins types A, C, D and E. Five highly homologous regions are found between these four toxins. One of these homologous regions, sequence HELIHSL, shows strong similarity with the active site of zinc-proteases. We suggest that inhibition of acetylcholine release might be associated with this protease activity.

Acetylcholine↗
PubMed1992

Potentiation of sodium chromate(VI)-induced chromosomal aberrations and mutation by vitamin B2 in Chinese hamster V79 cells.

The effect of vitamin B2, which is capable of reducing chromium(VI) to chromium(V), on chromosomal aberrations and mutation caused by Na2CrO4 was investigated in Chinese hamster V79 cells. Pretreatment with 200 microM vitamin B2 (riboflavin) for 24 h prior to exposure to Na2CrO4 (2.5-5 microM) resulted in an increase of metal-induced chromosomal aberrations and mutation at the HGPRT locus. These and other previous studies suggest that vitamin B2 enhances the clastogenic and mutagenic action of chromate compounds, through its ability to directly reduce chromium(VI) in cells.

Animals↗
PubMed1992

Agonist- and subunit-dependent potentiation of glutamate receptors by a nootropic drug aniracetam.

GluR1 and GluR2 cDNAs encoding non-NMDA subtypes of glutamate receptor were isolated from a rat brain cDNA library by Boulter et al. (Science, 249 (1990) 1033-1037). Functional receptors activated by kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and glutamate were expressed in Xenopus oocytes injected with GluR1, GluR2 or a mixture of GluR1 and GluR2 RNAs. In GluR1-expressed oocytes, 1 mM aniracetam potentiated AMPA-induced currents by 99 +/- 10% (mean +/- S.E.M., n = 5) and glutamate-induced currents by 140 +/- 8% (n = 4), but little affected kainate-induced currents. Aniracetam was effective from a concentration of 0.1 mM, and it exhibited more conspicuous effects with the increase of the dose. In oocytes injected with GluR1 plus GluR2 RNAs, aniracetam more markedly potentiated current responses to AMPA and glutamate than those in oocytes injected with GluR1 RNA alone. For example, 1 mM aniracetam potentiated AMPA-induced currents by 396 +/- 76% (n = 4) and glutamate-induced currents by 970 +/- 65% (n = 5) in oocytes injected with 10% GluR1 and 90% GluR2 RNAs. In these oocytes, however, the potentiation of kainate-induced currents by 1 mM aniracetam was only 8 +/- 5% (n = 4). Thus, we conclude that the potentiation of the AMPA/kainate receptor by aniracetam depends on both species of agonists and subunit composition of the receptor.

Animals↗
PubMed1992

Transinterosseous transfer of a peroneal island flap for reconstruction of prepatellar skin defect: report of two patients.

We describe the use of a peroneal vascular transinterosseous island flap for the resurfacing of a prepatellar skin defect in 2 patients. Being a fasciocutaneous flap, the peroneal flap is thin, and the location of perforators is easily and safely detected with a Doppler flowmeter. When used as a vascular island flap, either a distal pedicle or a proximal pedicle can be used. The peroneal flap can be used as either a free flap or a vascularized fibular and fasciocutaneous flap. It may, therefore, be applied to compound skin, subcutaneous tissue, and bone defects in the lower extremities. A peroneal vascular transinterosseous island flap can reach a prepatellar skin defect, whereas the peroneal island flap with conventional proximal pedicle cannot.

Adult↗
PubMed1992

A prospective study of human herpesvirus-6 infection in renal transplantation.

Sixty-five kidney transplant recipients and their (22 living related and 43 cadaveric) donors were studied prospectively to determine the relationship between kidney transplantation and human herpesvirus-6 (HHV-6) infection. The virus isolation from peripheral blood and other tissues and sequential determination of neutralizing antibodies to HHV-6 were performed during 3 months following the transplantation. All of the donors and their recipients examined had neutralizing antibodies to HHV-6 at the time of renal transplantation and the virus was not isolated from them. HHV-6 was isolated from 3 renal tissues (2 living related and 1 cadaveric) obtained during transplant surgery, but not from their blood at that time. HHV-6 viremia occurred in 9 (14%) of the 65 recipients around 2 to 4 weeks after the transplantation. An additional 27 recipients showed a significant rise in the antibody titer. Thus, the infection with HHV-6 was confirmed in 36 (55%) of the 65. These results indicate that the virus is activated in many cases in the early posttransplant period and that HHV-6 establishes in vivo latency in the kidney tissue. There was no correlation between HHV-6 infection and acute rejection or the antirejection prophylaxis.

Adolescent↗
PubMed1992

Cloning and whole nucleotide sequence of the gene for the light chain component of botulinum type E toxin from Clostridium butyricum strain BL6340 and Clostridium botulinum type E strain Mashike.

Chromosomal DNAs were extracted from Clostridium butyricum strain BL6340 and Clostridium botulinum type E strain Mashike. The 6.0 Kbp fragment coding for the entire light chain (L) component and the N-terminus of heavy chain (H) component of botulinum type E toxin was obtained from each extracted DNAs after digestion with HindIII. The entire nucleotide sequences for the light chain components of these cloned genes were determined, and the derived amino acid sequences were compared to each other, and with those of botulinum type A, C1, D, and tetanus toxins reported previously. The cleavage site of L and H components of type E toxin was presumed to be Arg-422. In a total of 422 amino acid residues of L component, 17 residues were different between butyricum and type E toxins, and all these differences were found within 200 residues of N-terminus of L component. On the contrary, five regions showing highly homologous sequences were found in L components among these six toxins, and one more region between botulinum type E and tetanus toxins.

Amino Acid Sequence↗
PubMed1992

Effect of vitamin E on cytotoxicity, DNA single strand breaks, chromosomal aberrations, and mutation in Chinese hamster V-79 cells exposed to ultraviolet-B light.

The effect of pretreatment with vitamin E on cytotoxicity, DNA single strand breaks, and chromosomal aberrations as well as on mutation induced by ultraviolet-B light (UV-B) was investigated in Chinese hamster V-79 cells. Cellular pretreatment with non-toxic levels of 25 microM alpha-tocopherol succinate (vitamin E) for 24 h prior to exposure resulted in a 10-fold increase in cellular levels of alpha-tocopherol. Using a colony-forming assay, this pretreatment decreased the cytotoxicity of UV-B light. However, alkaline elution assays demonstrated that pretreatment with vitamin E did not affect the number of DNA single strand breaks caused by UV-B light. In addition, UV-B exposure produced a dose-dependent induction of chromosomal aberrations and mutations at the HGPRT locus, and neither of these actions of UV-B was influenced by pretreatment with the vitamin. These results suggest that vitamin E protects cells from UV-B-induced cytotoxicity, possibly through its ability to scavenge free radicals. The results also suggest that the extent of genotoxicity induced by UV-B light may not correlate directly with the cytotoxic action of this wavelength region in sunlight.

Animals↗
PubMed1992

Synthesis of 1233A analogs and their inhibitory activity against hydroxymethylglutaryl coenzyme A synthase.

Simple and efficient syntheses of 1233A analogs were developed and the inhibitory activity of the analogs against hydroxymethylglutaryl coenzyme A (HMG-CoA) synthase was determined. Study of the structure-activity relationships revealed that not only the geometry in beta-lactone moiety but also the length of the carbon side chain is important for inhibitory activity against HMG-CoA synthase.

Animals↗
PubMed1991

Effect of ascorbic acid on DNA damage, cytotoxicity, glutathione reductase, and formation of paramagnetic chromium in Chinese hamster V-79 cells treated with sodium chromate(VI).

The effect of pretreatment with ascorbic acid (vitamin C) on chromate-induced DNA damage, cytotoxicity, and enzyme inhibition as well as on the cellular reduction of chromium(VI) was investigated using Chinese hamster V-79 cells. Cellular pretreatment with nontoxic levels of 1 mM ascorbic acid for 24 h prior to exposure resulted in a significant increase (1.7-fold) in cellular levels of this vitamin. Alkaline elution assays demonstrated that this pretreatment decreased cellular levels of Na2CrO4-induced alkali-labile sites while the numbers of DNA-protein crosslinks produced by chromate increased. In colony-forming assays, pretreatment with ascorbic acid enhanced the cytotoxicity of chromate. However, the inhibition of glutathione reductase attributed to Na2CrO4 was attenuated by this pretreatment. Under the same experimental condition, the uptake of chromate in pretreated cells was found to increase. ESR studies revealed that cellular pretreatment with ascorbic acid reduced the level of chromium(V) intermediate and increased the level of chromium(III) complex, indicating that cellular reduction of chromium(VI) to chromium(III) was accelerated by this vitamin. These results suggest that ascorbic acid decreases chromate-induced alkali-labile sites and chromium inhibition of glutathione reductase, but it enhances DNA-protein cross-links and cytotoxicity caused by this metal through its ability to directly reduce chromium(VI).

Animals↗
PubMed1991

Reduction of chromium(VI) in Chinese hamster V-79 cells.

The cellular reduction of chromate(VI) was studied by electron spin resonance spectrometry. Incubation of Chinese hamster V-79 cells with Na2CrO4 resulted in the formation of both chromium(V) and chromium(III) complex in a manner dependent on time (30 min-2 h) and concentration (50-500 microM). Following removal of extracellular chromate, the level of chromium(V) complex decreased quickly during the first hour but more slowly for the next hour, whereas the level of chromium(III) remained unchanged, indicating that chromium(III) is the ultimate ion of this metal in cells. Alkaline elution studies demonstrated that treatment of cells with Na2CrO4 induced DNA single-strand breaks that decreased quickly and DNA-protein crosslinks that persisted for 2 h after removal of this metal. These results suggest that the cellular levels of chromium(V) and chromium(III) may be associated with the formation of DNA damage induced by chromium (VI).

Animals↗