Biomedical subjects

Nobuhiko Takahashi

Publications and source records attributed to Nobuhiko Takahashi.

11 recordsLinked to original sources

PubMed2005

Increased expression of PPARgamma in high fat diet-induced liver steatosis in mice.

The present study was performed to examine a hypothesis that peroxisome proliferator-activated receptor gamma (PPARgamma) is implicated in high fat diet-induced liver steatosis. Mice were fed with control or high fat diet containing approximately 10% or 80% cholesterol, respectively. Macroscopic and microscopic findings demonstrated that lipid accumulation in the liver was observed as early as 2 weeks after high fat diet and that high fat diet for 12 weeks developed a fatty liver phenotype, establishing a novel model of diet-induced liver steatosis. Gene profiling with microarray and real-time PCR studies demonstrated that among genes involved in lipid metabolism, adipogenesis-related genes, PPARgamma and its targeted gene, CD36 mRNA expression was specifically up-regulated in the liver by high fat diet for 2 weeks. Immunohistochemical study revealed that PPARgamma protein expression is increased in the nuclei of hepatocytes by high fat diet. It was also shown that protein expression of cAMP response element-binding protein (CREB), an upstream molecule of PPARgamma, in the liver was drastically suppressed by high fat diet. All these results suggest for the first time that the CREB-PPARgamma signaling pathway may be involved in the high fat diet-induced liver steatosis.

Animals↗

PubMed2005

Involvement of MEK-ERK signaling pathway in the inhibition of cell growth by troglitazone in human pancreatic cancer cells.

In the present study, we examined a role of mitogen-activated protein kinases (MAPKs), extracellular signal-related kinase (ERK), c-Jun N-terminal protein kinase, and p38 MAPK in troglitazone-induced inhibition of cell growth in human pancreatic cancer cells. Among the three kinases, troglitazone specifically inhibited the phosphorylation of ERK1/2 in a dose- and time-dependent manner. Troglitazone also down-regulated the protein expression of mitogen-activated protein kinase kinase (MEK)1/2, an upstream molecule that regulates ERK phosphorylation. Treatment of human pancreatic cancer cells with specific MEK inhibitor, PD98059 or U0126, inhibited ERK1/2 phosphorylation and cell growth. These results suggest for the first time that the inhibition of the MEK1/2-ERK1/2 signaling pathway may be implicated in the growth inhibitory effect by troglitazone in human pancreatic cancer cells.

Antineoplastic Agents↗

PubMed2005

A selective orexin-1 receptor antagonist, SB334867, blocks 2-DG-induced gastric acid secretion in rats.

We have previously demonstrated that intracisternal orexin-A potently stimulated gastric acid secretion through the vagus nerve. Considering its stimulatory action on feeding, we hypothesized that orexin-A is a candidate mediator of cephalic phase gastric secretion. It has also been suggested that the stimulation of acid by central orexin-A may be mediated by orexin 1 receptor (OX1R) in the brain. In the present study, we tried to clarify whether endogenously released orexin-A in the brain indeed plays a physiological role in gastric secretion. To address the question, the effects of OX1R antagonist on gastric acid secretion was examined in rats. Intraperitoneal administration of SB334867, a specific OX1R antagonist, by itself did not change gastric acid secretion in pylorus-ligated conscious rats. Pretreatment with SB334867 in a dose of 10 mg/kg completely blocked the stimulated acid output by intracisternal orexin-A but not thyrotropin-releasing hormone, suggesting that SB334867 specifically blocked the action of orexin-A in the brain. 2-Deoxy-D-glucose (2-DG)-induced stimulation of gastric acid output was significantly blocked by pretreatment with intraperitoneal administration of SB334867. These results suggest that endogenously released orexin-A in the brain plays a vital role in central regulation of gastric secretion. Since 2-DG induces central glucoprivation as a hunger state, the present study furthermore supports the speculation that orexin-A may be an important molecule that triggers the cephalic phase gastric acid secretion.

Animals↗

PubMed2004

Adiponectin acts in the brain to decrease body weight.

Adiponectin (ADP) is an adipocyte hormone involved in glucose and lipid metabolism. We detected a rise in ADP in cerebrospinal fluid after intravenous (i.v.) injection, consistent with brain transport. In contrast to leptin, intracerebroventricular (i.c.v.) administration of ADP decreased body weight mainly by stimulating energy expenditure. Full-length ADP, mutant ADP with Cys39 replaced with serine, and globular ADP were effective, whereas the collagenous tail fragment was not. Lep(ob/ob) mice were especially sensitive to i.c.v. and systemic ADP, which resulted in increased thermogenesis, weight loss and reduction in serum glucose and lipid levels. ADP also potentiated the effect of leptin on thermogenesis and lipid levels. While both hormones increased expression of hypothalamic corticotropin-releasing hormone (CRH), ADP had no substantial effect on other neuropeptide targets of leptin. In addition, ADP induced distinct Fos immunoreactivity. Agouti (A(y)/a) mice did not respond to ADP or leptin, indicating the melanocortin pathway may be a common target. These results show that ADP has unique central effects on energy homeostasis.

Adiponectin↗

PubMed2004

Growth arrest by troglitazone is mediated by p27Kip1 accumulation, which results from dual inhibition of proteasome activity and Skp2 expression in human hepatocellular carcinoma cells.

In our study, we examined whether human hepatocellular carcinoma (HCC) expresses peroxisome proliferator-activated receptor gamma (PPARgamma) and the effects of PPAR gamma activation by its selective ligands on cell growth and cell invasion in HCC cells. RT-PCR and Western blot analysis revealed that HCC-derived cell lines, HepG2 and HLF, express PPARgamma mRNA and protein. Luciferase assay in HLF cells showed that troglitazone, a selective ligand for PPAR gamma, transactivated the transcription of a peroxisome proliferator response element-driven promoter in a dose-dependent manner, suggesting that the expressed PPARgamma functions as a transcriptional factor. Not only troglitazone but pioglitazone dose-dependently inhibited cell growth in HepG2 and HLF cells. Invasion assay using a transwell chamber demonstrated that troglitazone also inhibited cell invasion in HCC cells. To examine the mechanism of the troglitazone-induced growth inhibition, we determined p27(Kip1), a cyclin dependent kinase inhibitor, expression by Western blot analysis in troglitazone-treated HLF cells. Troglitazone increased p27(Kip1) in time- and dose-dependent manners, suggesting that p27(Kip1) may be involved in the growth inhibition by troglitazone in HLF cells. To further examine the mechanism of the troglitazone-induced p27(Kip1) protein accumulation, 2 major systems for regulation of p27(Kip1) protein, proteasome activity and Skp2, an F-box protein that targets p27(Kip1) for degradation, were evaluated. Troglitazone potently inhibited proteasome activity and decreased Skp2 protein levels. All these results suggest that human HCC cells express functional PPAR gamma and PPARgamma activation resulted in growth inhibition. The growth inhibition was mediated by p27(Kip1) accumulation, which is induced by both inhibition of ubiquitylation of p27(Kip1) and reduction of degradation activity of p27Kip1 by proteasome.

Adenosine Triphosphatases↗

PubMed2004

Inhibition of cell invasion and morphological change by troglitazone in human pancreatic cancer cells.

BACKGROUND: We have recently demonstrated that peroxisome proliferator activated receptor (PPAR) gamma activation by its selective ligand, troglitazone, potently inhibited cell proliferation in human pancreatic cancer cells. The present study was performed to clarify the role of PPARgamma in cell invasion/motility in human pancreatic cancer cells. METHODS: Cell invasive activity was assessed by an in vitro invasion assay, using a Transwell chamber, and by a wound-healing assay, in the human pancreatic cancer cell lines, PK-1 and PK-9. Cell morphology and actin structure were evaluated by phase-contrast and fluorescence microscopy. RESULTS: PPARgamma activation by troglitazone inhibited cell invasion and cell migration in PK-1 and PK-9 cells. We also examined the effect of troglitazone on cell morphology and actin structure because of its effect on cell motility. The size of PK-1 and PK-9 cells that had been incubated with troglitazone became smaller, and the in shape changed from flat to spindle, followed by round. The troglitazone-induced cell rounding was reversible by replacement with troglitazone-free medium. Rhodamine-phalloidin staining revealed a decreased number of actin filaments in PK-1 cells treated with troglitazone. In cells treated with mycalolide B, an actin depolymerizing agent, troglitazone failed to induce cell rounding. CONCLUSIONS: These results suggest that PPARgamma activation by troglitazone inhibited cell motility and changed cell morphology through modulating actin organization.

Actins↗

PubMed2004

A novel aminosterol reverses diabetes and fatty liver disease in obese mice.

BACKGROUND/AIMS: Non-alcoholic fatty liver disease (NAFLD) is common in obesity. However, weight reduction alone does not prevent the development or progression of NAFLD. Since NAFLD is associated with insulin resistance and diabetes, we hypothesized that improvement of these factors would reverse obesity-related NAFLD. METHODS: We examined the effects of an aminosterol, 1436, on glucose, lipids and liver metabolism in Lep(ob/ob) mice, a model of obesity, severe insulin resistance, diabetes, hyperlipidemia and hepatic steatosis. RESULTS: 1436 decreased body weight, specifically fat content, by inhibiting food intake and increasing energy expenditure. In contrast to weight loss from food restriction, this aminosterol specifically lowered circulating lipids, reversed hepatic steatosis and normalized alanine aminotransferase level. 1436 decreased glucose, increased adiponectin and enhanced insulin action in liver. These changes culminated in inhibition of hepatic triglyceride synthesis and increased fatty acid oxidation. Gene expression studies confirmed a reduction in lipogenic enzymes in liver, and elevation of enzymes involved in lipid catabolism. CONCLUSIONS: These results demonstrate that 1436 is an effective treatment for insulin resistance and hepatic steatosis in Lep(ob/ob) mice, by decreasing hepatic lipid synthesis and stimulating lipolysis. In contrast, weight loss from food restriction has no substantial effect on insulin resistance, lipids and hepatic steatosis.

Animals↗

PubMed2004

Regulation of resistin expression and circulating levels in obesity, diabetes, and fasting.

Resistin was originally reported as an adipose tissue-specific hormone that provided a link between obesity and diabetes. Resistin protein level was elevated in obese mice and decreased by insulin-sensitizing thiazolidinediones. Immunoneutralization of resistin improved insulin sensitivity in diet-induced obese mice, while the administration of exogenous resistin induced insulin resistance. More recently, we have shown that ablation of the resistin gene in mice decreased fasting glucose through impairment of gluconeogenesis, while resistin treatment in these knockout mice increased hepatic glucose production. However, the link between resistin and glucose homeostasis has been questioned by studies demonstrating reduced, rather than increased, resistin mRNA expression in obese and diabetic mice. To better understand the regulation of resistin, we developed a sensitive and specific RIA resistin that could accurately measure serum resistin levels in several mouse models. We show that while resistin mRNA is indeed suppressed in obese mice, the circulating resistin level is significantly elevated and positively correlated with insulin, glucose, and lipids. Both resistin mRNA expression and protein levels in Lep(ob/ob) mice are suppressed by leptin treatment in parallel with reductions in glucose and insulin. In wild-type mice, serum resistin increases after nocturnal feeding, concordant with rising levels of insulin. Resistin mRNA and protein levels decline in parallel with glucose and insulin during fasting and are restored after refeeding. We performed clamp studies to determine whether resistin is causally related to insulin and glucose. Adipose resistin expression and serum resistin increased in response to hyperinsulinemia and further in response to hyperglycemia. Taken together, these findings suggest that the nutritional regulation of resistin and changes in resistin gene expression and circulating levels in obesity are mediated, at least in part, through insulin and glucose.

Adipose Tissue↗

PubMed2003

PPAR gamma ligand-induced apoptosis through a p53-dependent mechanism in human gastric cancer cells.

We have recently demonstrated that the PPAR gamma ligand troglitazone induced cell growth arrest and evoked apoptosis in a gastric cancer cell line, MKN-45. Since in general, p53 plays an important role in the induction of apoptosis and growth inhibition, we tried to clarify whether or not p53 mediates troglitazone-induced apoptosis and growth arrest in gastric cancer cells. Troglitazone increased the number of apoptoic cells in MKN-28, MKN-45 and MKN-74, but not in KATO-III cells. The troglitazone-induced apoptotic change was significantly reduced by coincubation with bisphenol A digycidyl ether (BADGE), a synthetic PPAR gamma antagonist, in MKN-74 cells, suggesting that PPAR gamma mediates the apoptotic effect of troglitazone. Since KATO-III lacks the p53 gene, we speculated that p53 might be implicated in the PPAR gamma ligand-induced apoptosis. Western blot analysis revealed that p53 expression was increased by troglitazone in a time-dependent manner in MKN-74 cells, further suggesting that p53 may mediate the apoptotic process induced by troglitazone. We next established a dominant-negative p53 mutant by stable transfection of p53 mutant into MKN-74 cells. In the dominant-negative p53 mutant cells, troglitazone failed to induce apoptosis, strongly supporting the hypothesis that p53 indeed mediates the process of the troglitazone-induced apoptosis. In the dominant-negative p53 mutant cells, troglitazone significantly induced cell growth arrest and increased expression of p27(Kip1) protein, which is thought to be the key molecule to evoke growth arrest, suggesting that p53 is not involved in the growth inhibition by troglitazone. All these results suggest that p53 mediates the PPAR gamma ligand-induced apoptosis, but not the cell growth inhibition.

Antineoplastic Agents↗

PubMed2002

Troglitazone induces G1 arrest by p27(Kip1) induction that is mediated by inhibition of proteasome in human gastric cancer cells.

We examined in the present study whether human gastric cancer cells express peroxisome proliferator-activated receptor gamma (PPARgamma), the effect of PPARgamma activation by troglitazone, a selective ligand, on cellular growth, and the mechanism of the growth arrest by troglitazone in gastric cancer cells. RT-PCR, northern blot and western blot analysis demonstrated that all four tested human gastric cancer cell lines, MKN-28, MKN-45, MKN-74 and KATO-III, expressed PPARgamma mRNA and protein. WST-1 assay and flow cytometric analysis revealed that troglitazone inhibited the growth and induced G1 arrest in all four gastric cancer cell lines. To examine the role of p27(Kip1), a cyclin-dependent kinase inhibitor, in the G1 arrest by troglitazone, we determined p27(Kip1) protein expression by western blot analysis in gastric cancer cells that had been treated with troglitazone. Troglitazone increased p27(Kip1) in all four gastric cancer cell lines. Since it has been reported that the ubiquitin-proteasome system plays a vital role in the degradation of p27(Kip1) protein, we evaluated the hypothesis that inhibition of proteasome mediates the troglitazone-induced p27(Kip1) accumulation. Lactacystin, a proteasome inhibitor, inhibited cell growth and increased p27(Kip1) expression in MKN-74 cells. It was further demonstrated that troglitazone inhibited proteasome activity in a dose-dependent manner in MKN-74 cells. All these results suggest that troglitazone inhibited proteasome activity, followed by induction of p27(Kip1), which arrests cells at the G1 phase of the cell cycle in gastric cancer cells. The troglitazone-mediated inhibition of the proteasome suggests a novel mechanism for the anti-proliferative effect of this agent in cancer cells.

Antineoplastic Agents↗

PubMed2002

Appetite suppression and weight reduction by a centrally active aminosterol.

The rise in obesity and its complications has generated enormous interest in the regulation of feeding and body weight. We show that a spermine metabolite of cholesterol (MSI-1436) decreases body weight, specifically fat, by suppressing feeding and preventing the reduction in energy expenditure, hormonal changes, and patterns of neuropeptide expression normally associated with weight loss. MSI-1436 enters the brain after peripheral injection and is more potent when injected into the cerebral ventricle (intracerebroventricular [ICV]). Systemic or ICV MSI-1436 administration induced similar patterns of Fos immunoreactivity in the brain, especially the paraventricular hypothalamic nucleus (PVN). This brain region integrates neural signals from hypothalamic and brain stem nuclei and regulates feeding behavior, autonomic function, and neuroendocrine function. Microinjection of MSI-1436 into the PVN potently suppressed feeding and reduced body weight for several days. Unlike caloric restriction, MSI-1436 decreased mRNA levels of agouti-related peptide and neuropeptide Y in the hypothalamus. These findings indicate that MSI-1436 acts in the brain to regulate food intake and energy expenditure, likely through suppression of orexigenic hypothalamic pathways.

Animals↗