Biomedical subjects

M Shintani

Publications and source records attributed to M Shintani.

At least 19 recordsLinked to original sources

PubMed2004

Cortical neuromagnetic fields preceding voluntary jaw movements.

Slow cortical potentials (readiness potentials, RPs) reflecting the central programming of voluntary jaw movements were reported to appear preceding the movements. However, the current source producing the RP has not yet been localized. This study aimed to determine the cortical regions involved in the central programming of bilaterally symmetrical voluntary jaw movements, by locating the current source of the neuromagnetic counterpart of the RP (readiness field, RF). The RFs were found in the fronto-lateral region bilaterally, starting around 860 and 600 ms prior to the onset of masseter and digastric electromyograms (EMGs), respectively, and gradually increasing in magnitude to the peak within 100 ms before the EMG onset. Thus, the RFs appeared long before the reported onset of the excitability increase of pyramidal tract neurons. The current sources producing the RFs were located in the precentral gyrus bilaterally, with no bilateral differences in strength. We conclude that the primary motor cortex is involved bilaterally in central programming as well as in execution of bilaterally symmetrical voluntary jaw movements.

Adult↗

PubMed2003

Divergence of mobile genetic elements involved in the distribution of xenobiotic-catabolic capacity.

Bacteria adapt rapidly to environmental stimuli, such as exposure to xenobiotics. Mobile genetic elements (MGEs) play a major role in such bacterial adaptation, via the dispersal of catabolic capacity; and, in fact, genes that encode the degradation enzymes for xenobiotics are often located on MGEs. The list of reported catabolic MGEs keeps growing as researchers continue to isolate and characterize xenobiotic degraders and the corresponding catabolic genes. Major catabolic MGEs include (conjugative) plasmids, transposons, and conjugative transposons. Catabolic transposons can be divided into class I elements (composite transposons) and class II elements (Tn 3 family transposons). This review includes a comprehensive list of naturally occurring discrete catabolic MGEs, together with a brief description for each. While MGEs are often rather large, genome-wide or large-scale sequence analyses have provided useful information on the whole genetic structure of MGEs, with clues to their function (transfer, maintenance, catabolism, etc.) and behavior in a complex natural environment. This review also gives an insight into MGE functions, based on the complete sequencing of several catabolic plasmids and two Pseudomonas genomes.

Adaptation, Biological↗

PubMed2001

Polymorphism in gene for islet autoantigen, IA-2, and type 1 diabetes in Japanese subjects.

Autoantibodies against IA-2 have been detected in up to 86% of newly diagnosed patients with type 1 diabetes and appear to identify a subgroup of prediabetic subjects who rapidly progress to type 1 diabetes. We examined the association of IA-2 gene polymorphism with type 1 diabetes in Japanese subjects. A total of 276 Japanese subjects were studied for disease association and, in addition, another 53 patients were studied for association with the autoantibody status to IA-2. A microsatellite marker D2S1753E, located in the intron of the IA-2 gene, was used as a genetic marker in this study. In Japanese, two alleles (161mu and 165mu) were more frequent, and the 163mu allele was less frequent than in Caucasians (p = 0.0001). There was no significant difference in frequencies of alleles between diabetic patients and control subjects. The frequency of IA-2 gene polymorphism was not significantly different between patients stratified by age-at-onset, or between patients with and without susceptible HLA, DRB1*0405, DRB1*0802 and DRB1*0901. There was no significant difference in allele frequency of the IA-2 gene polymorphism between patients with and without autoantibody to IA-2. In conclusion, IA-2 gene polymorphism is not associated with either susceptibility to, or heterogeneity in type 1 diabetes in Japanese subjects.

Alleles↗

PubMed2001

Genetic polymorphisms and functional characterization of the 5'-flanking region of the human CYP2C9 gene: in vitro and in vivo studies.

OBJECTIVE: Genetic polymorphisms were identified in the 5'-flanking region of the human CYP2C9 gene, and their effects on the phenotype were evaluated on the basis of the luciferase reporter gene assay and the in vivo pharmacokinetics of phenytoin. METHODS: Genetic polymorphisms were screened by polymerase chain reaction-single-strand conformational polymorphism analysis, following sequencing with DNA samples obtained from 50 healthy volunteers and 133 adult epileptic patients. HepG2 hepatoma cells were cotransfected with various sequence patterns of 5'-flanking region-luciferase reporter gene constructs. Pharmacokinetic parameters of phenytoin in relation to the corresponding sequence patterns were estimated by the Bayesian method, and the results were compared with in vitro activities. RESULTS: Genetic analysis revealed the existence of 7 single nucleotide polymorphisms (SNPs). Allele frequencies of T-->C transition at position -1912 (T-1912C), C-1886G, C-1566T, G-1538A, C-1189T, G-982A, and A-162G were 0.019, 0.019, 0.077, 0.019, 0.579, 0.019, and 0.003, respectively. Some mutations occurred simultaneously, and a total of 6 sequence patterns (patterns 1-6) were observed. The luciferase reporter gene assay indicated that the presence of mutation(s) resulted in a reduction in luciferase activity of 41.4% (pattern 2) to 86.8% (pattern 5) compared with the activity of the wild-type construct. The calculated intrinsic clearance of phenytoin was also lower (up to a 40% reduction for pattern 2) when a mutation(s) was present. CONCLUSION: In addition to the two major mutations in the coding region (CYP2C9*2 and CYP2C9*3 ), mutations in the 5'-flanking region of the human CYP2C9 gene appear to contribute to the large interindividual variability in drug metabolism activity.

Adult↗

PubMed2001

Sequence analysis of candidate genes for common susceptibility to type 1 and type 2 diabetes in mice.

Although type 1 and type 2 diabetes are regarded as clinically distinct diseases, several lines of evidence have suggested common genetic factors between the two types of diabetes. The non-obese diabetic (NOD) mouse, an animal model of type 1 diabetes, and the Nagoya-Shibata-Yasuda (NSY) mouse, a model of type 2 diabetes, are derived from the same outbred colony, Jcl:HCR, suggesting a shared susceptibility between the two types of diabetes in mice. Genetic as well as functional studies have supported the possibility that Tcf2, which encodes the transcription factor, hepatocyte nuclear factor 1beta (HNF-1beta), is a candidate gene for the common susceptibility between NSY and NOD mice. Txn, encoding thioredoxin which is a redox (reduction/oxidation)-active protein, is also a positional and functional candidate for a common susceptibility gene. To investigate whether either of these two genes is a common susceptibility gene, the coding nucleotide sequences of these two genes were compared among the NSY, NOD and control C3H strains. The coding sequence of Tcf2 of the NOD mouse was identical to that of the C3H mouse, but was different from that of the NSY mouse. The coding sequence of Txn was identical in the three strains. These data suggest that neither of the two genes is a common susceptiblity gene between type 1 and type 2 diabetes in mice.

Animals↗

PubMed2001

Troglitazone not only increases GLUT4 but also induces its translocation in rat adipocytes.

Thiazolidinediones, insulin-sensitizing agents, have been reported to increase glucose uptake along with the expression of glucose transporters in adipocytes and cardiomyocytes. Recently, we have further suggested that the translocation of GLUT4 is stimulated by thiazolidinediones in L6 myocytes. However, the direct effects of thiazolidinediones on translocation of glucose transporters have not yet been determined. In this study, using hemagglutinin epitope-tagged GLUT4 (GLUT4-HA), we provide direct evidence of the effect of troglitazone on the translocation of GLUT4 in rat epididymal adipocytes. Primary cultures of rat adipocytes were transiently transfected with GLUT4-HA and overexpressed eightfold compared with endogenous GLUT4 in transfected cells. A total of 24 h of treatment with troglitazone (10(-4) mol/l) increased the cell surface level of GLUT4-HA by 1.5 +/- 0.03-fold (P < 0.01) without changing the total amount of GLUT4-HA, whereas it increased the protein level of endogenous GLUT4 (1.4-fold) without changing that of GLUT1. Thus, the direct effect on the translocation can be detected apart from the increase in endogenous GLUT4 content using GLUT4-HA. Troglitazone not only increased the translocation of GLUT4-HA on the cell surface in the basal state but also caused a leftward shift in the dose-response relations between GLUT4-HA translocation and insulin concentration in the medium (ED(50): from approximately 0.1 to 0.03 nmol/l). These effects may partly contribute to the antidiabetic activity of troglitazone in patients with obesity and type 2 diabetes.

Adipocytes↗

PubMed2001

Ghrelin, an endogenous growth hormone secretagogue, is a novel orexigenic peptide that antagonizes leptin action through the activation of hypothalamic neuropeptide Y/Y1 receptor pathway.

Ghrelin, an endogenous ligand for growth hormone secretagogue (GHS) receptor originally isolated from the stomach, occurs in the hypothalamic arcuate nucleus and may play a role in energy homeostasis. Synthetic GHSs have activated the hypothalamic arcuate neurons containing neuropeptide Y (NPY), suggesting the involvement of NPY in some of ghrelin actions. This study was designed to elucidate the role of ghrelin in the regulation of food intake. A single intracerebroventricular (ICV) injection of ghrelin (5-5,000 ng/rat) caused a significant and dose-related increase in cumulative food intake in rats. Ghrelin (500 ng/rat) was also effective in growth hormone-deficient spontaneous dwarf rats. Hypothalamic NPY mRNA expression was increased in rats that received a single ICV injection of ghrelin (500 ng/rat) (approximately 160% of that in vehicle-treated groups, P < 0.05). The ghrelin's orexigenic effect was abolished dose-dependently by ICV co-injection of NPY Y1 receptor antagonist (10-30 microg/rat). The leptin-induced inhibition of food intake was reversed by ICV co-injection of ghrelin in a dose-dependent manner (5-500 ng/rat). Leptin reduced hypothalamic NPY mRNA expression by 35% (P < 0.05), which was abolished by ICV co-injection of ghrelin (500 ng/rat). This study provides evidence that ghrelin is an orexigenic peptide that antagonizes leptin action through the activation of hypothalamic NPY/Y1 receptor pathway.

Animals↗

PubMed2001

Troglitazone induces GLUT4 translocation in L6 myotubes.

A number of studies have demonstrated that insulin resistance in the skeletal muscle plays a pivotal role in the insulin resistance associated with obesity and type 2 diabetes. A decrease in GLUT4 translocation from the intracellular pool to the plasma membranes in skeletal muscles has been implicated as a possible cause of insulin resistance. Herein, we examined the effects of an insulin-sensitizing drug, troglitazone (TGZ), on glucose uptake and the translocation of GLUT4 in L6 myotubes. The prolonged exposure (24 h) of L6 myotubes to TGZ (10(-5) mol/l) caused a substantial increase in the 2-deoxy-[3H]D-glucose (2-DG) uptake without changing the total amount of the glucose transporters GLUT4, GLUT1, and GLUT3. The TGZ-induced 2-DG uptake was completely abolished by cytochalasin-B (10 micromol/l). The ability of TGZ to translocate GLUT4 from light microsomes to the crude plasma membranes was greater than that of insulin. Both cycloheximide treatment (3.5 x 10(-6) mol/l) and the removal of TGZ by washing reversed the 2-DG uptake to the basal level. Moreover, insulin did not enhance the TGZ-induced 2-DG uptake additively. The TGZ-induced 2-DG uptake was only partially reversed by wortmannin to 80%, and TGZ did not change the expression and the phosphorylation of protein kinase B; the expression of protein kinase C (PKC)-lambda, PKC-beta2, and PKC-zeta; or 5'AMP-activated protein kinase activity. a-Tocopherol, which has a molecular structure similar to that of TGZ, did not increase 2-DG uptake. We conclude that the glucose transport in L6 myotubes exposed to TGZ for 24 h is the result of an increased translocation of GLUT4. The present results imply that the effects of troglitazone on GLUT4 translocation may include a new mechanism for improving glucose transport in skeletal muscle.

Animals↗

PubMed2001

Transgenic overexpression of leptin rescues insulin resistance and diabetes in a mouse model of lipoatrophic diabetes.

Lipoatrophic diabetes is caused by a deficiency of adipose tissue and is characterized by severe insulin resistance, hypoleptinemia, and hyperphagia. The A-ZIP/F-1 mouse (A-ZIPTg/+) is a model of severe lipoatrophic diabetes and is insulin resistant, hypoleptinemic, hyperphagic, and shows severe hepatic steatosis. We have also produced transgenic "skinny" mice that have hepatic overexpression of leptin (LepTg/+) and no adipocyte triglyceride stores, and are hypophagic and show increased insulin sensitivity. To explore the pathophysiological and therapeutic roles of leptin in lipoatrophic diabetes, we crossed LepTg/+ and A-ZIPTg/+ mice, producing doubly transgenic mice (LepTg/+:A-ZIPTg/+) virtually lacking adipose tissue but having greatly elevated leptin levels. The LepTg/+:A-ZIPTg/+ mice were hypophagic and showed improved hepatic steatosis. Glucose and insulin tolerance tests revealed increased insulin sensitivity, comparable to LepTg/+ mice. These effects were stable over at least 6 months of age. Pair-feeding the A-ZIPTg/+ mice to the amount of food consumed by LepTg/+:A-ZIPTg/+ mice did not improve their insulin resistance, diabetes, or hepatic steatosis, demonstrating that the beneficial effects of leptin were not due to the decreased food intake. Continuous leptin administration that elevates plasma leptin concentrations to those of LepTg/+:A-ZIPTg/+ mice also effectively improved hepatic steatosis and the disorder of glucose and lipid metabolism in A-ZIP/F-1 mice. These data demonstrate that leptin can improve the insulin resistance and diabetes of a mouse model of severe lipoatrophic diabetes, suggesting that leptin may be therapeutically useful in the long-term treatment of lipoatrophic diabetes.

Animals↗

PubMed2001

[Pathology and significance of leptin resistance in obesity].

Leptin, the protein product of the ob gene, is predominantly secreted from white adipose tissue, and acts on the brain to regulate food intake, energy expenditure, and neuroendocrine function. Obese rodent and humans are mostly associated with high circulating leptin levels. These findings have led to the conclusion that obese individuals are relatively insensitive to endogenous leptin termed 'leptin resistance'. The potential sites for leptin resistance include the blood-brain-barrier transport system and the leptin signaling mechanism in leptin-responsive neurons in the hypothalamus. In this review, we describe leptin, leptin receptor, and potential hypothesis of leptin resistance.

Animals↗

PubMed2001

Lack of association between hepatocyte nuclear factor-1beta gene and common forms of type 2 diabetes in the Japanese population.

Mutations in the hepatocyte nuclear factor-1beta (HNF-1beta) gene have been shown to be a cause of maturity-onset diabetes of the young (MODY). We studied the contribution of the HNF-1beta gene to susceptibility to common forms of Type 2 diabetes in the genetically homogeneous Japanese population, by investigating the allelic association of Type 2 diabetes with two markers in the HNF-1beta region. The frequency of a nonsense mutation, R177X, which was previously reported in a Japanese family, was also studied by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method using a mismatch primer. A total of 200 subjects were studied. There was no significant difference in allele frequencies of either of the two polymorphisms studied between patients with Type 2 diabetes and control subjects, or between subgroups of patients subdivided by the presence of mild or severe diabetic nephropathy. None of the subjects studied had R177X mutation, giving a frequency of less than 1.1% in common forms of Type 2 diabetes in Japan. These results suggest that mutations in the HNF-1beta gene derived from a limited number of founders are not a major cause of common forms of Type 2 diabetes, even in the genetically homogeneous Japanese population.

Adult↗

PubMed2000

Downregulation of leptin by free fatty acids in rat adipocytes: effects of triacsin C, palmitate, and 2-bromopalmitate.

Free fatty acid (FFA) has been reported to decrease leptin mRNA levels in 3T3-L1 adipocytes. When using this cell line, it is difficult to determine the protein levels because a very small amount of leptin is secreted into the medium. The effect of FFA on leptin secretion from adipocytes has not yet been determined. In addition, in vivo studies have failed to demonstrate a FFA-induced decrease in plasma leptin levels. To clarify the effect of FFA on leptin production, we investigated the leptin protein level in the medium and the mRNA level in primary cultured rat adipocytes treated with triacsin C, which is a potent inhibitor of acyl-coenzyme A (CoA) synthetase, palmitate, and 2-bromopalmitate. Triacsin C (0 to 5 x 10(-5) mol/L) decreased leptin concentrations in the culture medium in a dose-dependent manner. Leptin mRNA levels were decreased to 10% of the control in the presence of triacsin C. The concentration of triacsin C needed to suppress leptin production was similar to the Ki value (approximately 10(-5) mol/L) for inhibition of acyl-CoA synthetase. Both palmitate and 2-bromopalmitate decreased leptin concentra-tions but did not affect the triacsin C-induced decrease in leptin additively. In conclusion, both protein and mRNA levels of leptin were decreased by triacsin C and FFA in primary cultured rat adipocytes. Our findings suggest that FFA is involved in the regulation of leptin production in adipocytes.

Adipocytes↗

PubMed2000

Age-related association of MHC class I chain-related gene A (MICA) with type 1 (insulin-dependent) diabetes mellitus.

To assess the contribution of the HLA class I region to susceptibility to and heterogeneity of type 1 diabetes, we investigated the association of polymorphism of MHC class I chain-related gene A (MICA) with age-at-onset as well as susceptibility to type 1 diabetes. One hundred one Japanese patients and 110 healthy control subjects were studied. The frequency of A4 allele was significantly higher and that of A6 allele was significantly lower in patients than in control subjects. The frequency of A5.1 allele was highest in early-onset patients (23.0%), intermediate in intermediate-onset patients (9.2%) and lowest in late-onset patients (7.7%) (trend chi-squared test, p = 0.0098). A5. 1 allele was strongly associated with HLA-B7 and Cw7, suggesting that MICA*A5.1-B7-Cw7 haplotype contains a gene responsible for age-at-onset. A4 allele was associated with a susceptible haplotype, DR4-DQB1*0401, and A6 allele was associated with a protective haplotype, DR2-DQB1*0601, suggesting that the association of MICA with type 1 diabetes susceptibility may be due to linkage disequilibrium with class II haplotypes. These data suggest that MICA gene is associated with age-at-onset and that a gene (or genes) responsible for age-at-onset of type 1 diabetes is located in the HLA class I region, probably near the region of MICA-B-C.

Adolescent↗

PubMed2000

Structure-activity relationship of orally potent tripeptide-based HIV protease inhibitors containing hydroxymethylcarbonyl isostere.

We designed and synthesized a new class of peptidomimetic human immunodeficiency virus protease inhibitors containing a unique unnatural amino acid, allophenylnorstatine [Apns; (2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid], with a hydroxymethylcarbonyl isostere as the active moiety. From a structure-activity relationship study of HIV-1 protease inhibition, enzyme selectivity for other aspartyl proteases, the antiviral activity and pharmacokinetics in rats, 24c (KNI-227) and 24d (KNI-272, our first clinical candidate) were found to be selective and orally potent HIV protease inhibitors. Moreover, an improvement of the pharmacokinetic features of KNI-272 provided two long-lasting and highly bioavailable compounds (24g: JE-2178, 24h: JE-2179).

Animals↗

PubMed2000

[Insulin resistance, role of leptin and leptin receptor].

Leptin, the obese gene product, is an adipocyte-derived satiety factor which is involved in the regulation of food intake and energy expenditure. Obesity often accompanies insulin resistance and high levels of leptin. In in vitro studies, leptin has been reported to increase fatty acid oxidation and decrease fatty acid synthesis in adipocytes and hepatocytes. The direct effects of leptin on glucose metabolism and insulin signaling have not been clarified yet. In in vivo studies, however, leptin has been reported to improve insulin sensitivity and glucose metabolism in normal and obese rodents acting mainly through hypothalamus. Moreover leptin has been reported to have antidiabetic effects in insulin-deficient diabetes rats and lipoatrophic diabetes mice. It is suggested that leptin modulates insulin sensitivity and glucose disposal and that leptin may have a pathophysiological and therapeutic implications in diabetes.

Adipocytes↗

PubMed2000

Comparative evaluation of conjugate vaccines in the Haemophilus influenzae infection model.

We used a murine model of Haemophilus influenzae type b (Hib) infection to analyze the immunologic response to two commercially available PRP conjugate vaccines (HbOC, PRP-T). The mortality rate in mice infected with a large dose of the bacteria after vaccination with HbOC or PRP-T at two and three doses was significantly lower than in non-vaccinated mice and mice vaccinated by one dose. Furthermore, for infections caused by a small bacterial dose, the mortality rate in mice vaccinated with one, two, or three doses was significantly lower than in non-vaccinated mice. The induction level of anti-PRP antibodies, especially IgG, in serum of mice vaccinated by two or three doses was higher than in those vaccinated with a single dose. Our results indicate that the dose of vaccine influences its efficacy in protecting against Hib infection. Our results also showed a lack of difference between two different PRP conjugate vaccines.

Animals↗

PubMed1999

Abnormal blinking of newscasters.

When compared with a control group, blink rates of Japanese TV newscasters were increased, suggesting a possible reaction to reading the news under stressful studio conditions. Frequent blinking may be distractive to the viewing audience.

Adult↗

PubMed1999

JE-2147: a dipeptide protease inhibitor (PI) that potently inhibits multi-PI-resistant HIV-1.

We designed, synthesized, and identified JE-2147, an allophenylnorstatine-containing dipeptide HIV protease inhibitor (PI), which is potent against a wide spectrum of HIV-1, HIV-2, simian immunodeficiency virus, and various clinical HIV-1 strains in vitro. Drug-resistant clinical HIV-1 strains, isolated from seven patients who had failed 9-11 different anti-HIV therapeutics after 32-83 months, had a variety of drug-resistance-related amino acid substitutions and were highly and invariably resistant to all of the currently available anti-HIV agents. JE-2147 was, however, extremely potent against all such drug-resistant strains, with IC(50) values ranging from 13-41 nM (<2-fold changes in IC(50) compared with that of wild-type HIV-1). The emergence of JE-2147-resistant HIV-1 variants in vitro was substantially delayed compared with that of HIV-1 resistant to another allophenylnorstatine-containing compound, KNI-272, and other related PIs. Structural analysis revealed that the presence of a flexible P2' moiety is important for the potency of JE-2147 toward wild-type and mutant viruses. These data suggest that the use of flexible components may open a new avenue for designing PIs that resist the emergence of PI-resistant HIV-1. Further development of JE-2147 for treating patients harboring multi-PI-resistant HIV-1 is warranted.

Adult↗