Tetsuro Matsunaga

EFFECTS OF HYPERBARIC EXPOSURE WITH HIGH OXYGEN CONCENTRATION ON GLUCOSE AND INSULIN LEVELS AND SKELETAL MUSCLE-FIBER PROPERTIES IN DIABETIC RATS

The effects of hyperbaric exposure with high oxygen concentration on glucose and insulin levels and skeletal muscle‐fiber properties were investigated in type 2 diabetic Goto‐Kakizaki rats. Five‐week‐old rats were exposed to a hyperbaric environment (1.25 atmospheric pressure) with a high oxygen concentration (36%) for 6 h daily. Glucose and insulin levels and properties including fiber‐type distribution, cross‐sectional area, and oxidative enzyme activity in the soleus muscle were examined after hyperbaric exposure for 4 weeks. The growth‐related increase in glucose level was inhibited by hyperbaric exposure, and insulin also showed lower levels compared with control rats. The percentage of low‐oxidative type I fibers in the muscle decreased and high‐oxidative type IIA and type IIC fibers, which were not detected in the muscle of control rats, were observed after hyperbaric exposure. The oxidative enzyme activity of type I fibers in the muscle increased after hyperbaric exposure. Hyperbaric exposure with high oxygen concentration might therefore provide a new approach to improve the glucose tolerance, insulin resistance, and altered skeletal muscle metabolism that are caused by diabetes mellitus. Muscle Nerve, 2006

Fibre type distribution and gene expression levels of both succinate dehydrogenase and peroxisome proliferator‐activated receptor‐γ coactivator‐1α of fibres in the soleus muscle of Zucker diabetic fatty rats

We have reported that a change in muscle fibre type distribution is present in two strains of diabetic rats (Otsuka Long–Evans Tokushima Fatty and Goto‐Kakizaki rats). In this study, we determined whether the change in soleus muscle fibre type distribution was caused by diabetes, using obese, diabetic (Zucker diabetic fatty, ZDF), obese, non‐diabetic (Zucker fatty, ZF) and non‐diabetic, non‐obese rats (Zucker lean, ZL). Moreover, we investigated whether the gene expression levels of metabolic key molecules, namely the transcriptional factors of metabolic genes, exemplified by peroxisome proliferator‐activated receptor‐γ coactivator‐1α (PGC‐1α), and the oxidative enzymes in mitochondria, exemplified by succinate dehydrogenase (SDH), were changed in type I and II muscle fibres in each type of rat, using the new technique of laser capture microdissection (LCM). Both plasma glucose and glucosylated haemoglobin levels were significantly higher in ZDF than in ZL and ZF rats. A lower percentage of type IIA fibres was observed in the muscles of ZDF rats than in those of ZL and ZF rats. The mRNA expression levels of SDH in type II fibres and of PGC‐1α in type I fibres were significantly lower in ZDF than in ZL and ZF rats as assessed by LCM and real‐time PCR analysis. We have shown, for the first time, that a lower percentage of type IIA fibres was observed in ZDF rats. We have also discovered that the expression levels of the oxidative metabolism‐related genes, PGC‐1α and SDH, decreased in type I and type II fibres, respectively, of ZDF rats.

γ-tocotrienol attenuates TNF-α-induced changes in secretion and gene expression of MCP-1, IL-6 and adiponectin in 3T3-L1 adipocytes

Tocotrienols, members of the vitamin E family, have been shown to possess anti-inflammatory properties and display activity against a variety of chronic diseases, such as cancer, cardiovascular and neurological diseases. However, whether tocotrienols contribute to the prevention of inflammatory responses in adipose tissue remains to be elucidated. In this study, we examined the effects of γ-tocotrienol, the most common tocotrienol isomer, on tumor necrosis factor-α (TNF-α)-induced inflammatory responses by measuring the expression of the adipokines, monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6) and adiponectin in 3T3-L1 adipocytes. Exposure to TNF-α (10 ng/ml) for 24 h increased MCP-1 and IL-6 secretion, and decreased adiponectin secretion and peroxisome proliferator-activated receptor-γ (PPARγ) mRNA expression. γ-tocotrienol effectively improved the TNF-α-induced adverse changes in MCP-1, IL-6 and adiponectin secretion, and in MCP-1, IL-6, adiponectin and PPARγ mRNA expression. Furthermore, TNF-α-mediated IκB-α phosphorylation and nuclear factor-κB (NF-κB) activation were significantly suppressed by the γ-tocotrienol treatment. Our results suggest that γ-tocotrienol may improve obesity-related functional abnormalities in adipocytes by attenuating NF-κB activation and the expression of inflammatory adipokines.

Adrenergic receptor polymorphisms and autonomic nervous system function in human obesity

Adrenergic receptors (ARs) are cell-surface G-protein-coupled receptors for catecholamines. They are essential components of the sympathetic nervous system, organized within the autonomic nervous system (ANS), which controls various physiological functions, including energy homeostasis and metabolism of glucose and lipids. An impairment of ANS function in metabolism is considered to be one of the pathological states associated with human obesity and related metabolic diseases; thus, alterations in AR function might be implicated in the pathophysiology of these diseases. Several studies have suggested an association between obesity phenotypes and some AR polymorphisms. In vitro and human clinical studies indicate that some of these polymorphisms have functional and pathophysiological significance, including the linkage to ANS function. This review summarizes present knowledge of AR polymorphisms related to human obesity, and their association with ANS function.

Hyperbaric exposure with high oxygen concentration inhibits growth-associated increase in the glucose level of diabetic Goto-Kakizaki rats

We have specially designed a hyperbaric chamber for animal experiments, which is an oxygen tank with an oxygen concentrator and an air compressor [1]. This hyperbaric chamber is designed to automatically maintain the elevated atmospheric pressure and oxygen concentration. Increased atmospheric pressure enhances the partial pressure of oxygen and causes more oxygen to dissolve into the blood and plasma. We postulated that the increased availability of oxygen induced by hyperbaric exposure with high oxygen concentration might have a beneficial impact on glucose metabolism. Therefore, we tested this hypothesis by exposing type 2 diabetic Goto-Kakizaki (GK) rats to hyperbaric exposure with high oxygen concentration. GK rats are non-obesemodels of type 2 diabetesmellitus, developed by selective breeding of an outbred colony of Wistar rats with high glucose levels asmeasured by the oral glucose tolerance test [2]. Ten 5-week-old male GK rats were randomly assigned to the control (n 1⁄4 5) or hyperbaric (n 1⁄4 5) group. All rats were individually housed in cages of the same size. Rats in the hyperbaric group were exposed to an atmospheric pressure of 1.25 atm with an oxygen concentration of 35.0% automatically maintained by a computer-assisted system. The chamber was 180 cm long and 70 cm in diameter, making it large enough to house a number of rats (up to 20 cages) simultaneously. The rats in the hyperbaric group were exposed to the hyperbaric environment for 6 h (10 : 00–16 : 00) daily for 4weeks. Food andwater were provided ad libitum for both groups. All ratswere kept in a controlled environmentwith fixed 12 : 12 h light : dark cycles (lights off from 19 : 00 to 07 : 00) and room temperature maintained at 22 2 C. After the rats were anaesthetized with an intraperitoneal injection of sodium pentobarbital (50 mg/kg), blood was sampled. Plasma obtained by centrifugation was used for measurement of glucose level. Plasma glucose was determined by a glucose-oxidative method [3]. The glucose levels were significantly lower in the hyperbaric group at 7 and 9 weeks than in the control group (figure 1). Exercise is known to be effective for preventing and improving impaired glucose tolerance in type 2 diabetes mellitus. Previous studies demonstrated that voluntary running exercise is effective in preventing insulin resistance in streptozotocin-induceddiabetic (impaired insulin secretion model) [4] and Otsuka Long-Evans Tokushima Fatty (OLETF) (insulin resistant model) [5–7] rats. Previous studies observed that both non-obese GK [8] and obese OLETF [9] rats showed a growth-associated increase in the glucose level. Consistent with our hypothesis that the increased availability of oxygen induced by hyperbaric exposure with high oxygen concentration would have a beneficial impact on glucose metabolism, we observed that the growth-associated increase in the glucose level was completely inhibited by hyperbaric exposure with high oxygen concentration (figure 1). Hyperbaric exposure with high oxygen concentration might therefore provide a new approach to improve impaired glucose tolerance without exercise, food restriction, or drug, e.g. insulin treatment.

GLUCOSE REGULATION OF DIPEPTIDYL PEPTIDASE IV GENE EXPRESSION IS MEDIATED BY HEPATOCYTE NUCLEAR FACTOR-1α IN EPITHELIAL INTESTINAL CELLS

1 Dipeptidyl peptidase IV (DPP‐IV) is a new drug target in the treatment of Type 2 diabetes. Dipeptidyl peptidase IV enzyme activity is significantly altered in Type 2 diabetic patients with hyperglycaemia, but the underlying molecular mechanisms remain unclear. 2 The first aim of the present study was to clarify whether glucose regulates DPP‐IV enzyme activity. To address this, DPP‐IV gene expression and enzyme activity were measured in Caco2 cells cultured in the presence of low (2.5 mmol/L) or high (16.7 mmol/L) concentrations of glucose. We observed that high glucose inhibited DPP‐IV gene expression and enzyme activity. 3 The second aim of the present study was to investigate whether hepatocyte nuclear factor (HNF)‐1α contributes to glucose regulation of DPP‐IV gene expression. To explore this question, associations between the gene expression of DPP‐IV and HNF‐1α were examined in Caco‐2 cells cultured in the presence of low (2.5 mmol/L) or high (16.7 mmol/L) glucose. We found that the pattern of glucose‐regulated DPP‐IV gene expression is similar to that of HNF‐1α. Moreover, to elucidate whether glucose regulation of DPP‐IV gene expression is affected when HNF‐1α is inhibited, we produced two stable cell lines in which a dominant‐negative mutant HNF‐1αR271G or basic vectors were stably expressed. We found that glucose regulation of DPP‐IV gene expression was compromised in HNF‐1αR271G cells, but was well maintained in basic vector cells. 4 These results suggest that glucose regulation of DPP‐IV gene expression is mediated by HNF‐1α.

T393C polymorphism of GNAS1 associated with the autonomic nervous system in young, healthy Japanese subjects

1. T393C polymorphism of the gene encoding the Gs‐protein α‐subunit (GNAS1) has been reported recently to be associated with hypertension in which dysfunctions of the autonomic nervous system (ANS) are closely involved. In the present study, the association of this polymorphism with ANS activity was investigated in young, healthy Japanese males.

Association of UCP2 and UCP3 polymorphisms with heart rate variability in Japanese men.

Objectives The mitochondrial uncoupling proteins UCP2 and UCP3 are implicated in energy metabolism and regulation of reactive oxygen species, which are closely involved in autonomic nervous system function. Heart rate variability (HRV) reflects cardiac autonomic regulation and has been used to evaluate dysfunction of the autonomic nervous system in hypertension and cardiovascular diseases. We examined the association between polymorphisms in the UCP2 and UCP3 genes and HRV in healthy young Japanese men. Methods The 45 bp insertion/deletion polymorphism in exon8 of UCP2 and the −55C/T polymorphism in the UCP3 promoter region were genotyped (n = 255). Cardiac autonomic function was evaluated by power spectral analysis of HRV during supine rest and in a standing position. Low-frequency (<0.15 Hz) and high-frequency (>0.15 Hz) components of HRV were quantified by frequency domain analysis. Results The I/I genotype of the UCP2 45 bp insertion/deletion polymorphism was associated with relatively higher blood pressure and HRV sympathetic indices (low frequency percentage and low frequency:high frequency ratio) at supine rest. For the −55C/T polymorphism of UCP3, individuals carrying the −55T allele had significantly lower HRV sympathetic indices, but higher HRV parasympathetic indices (high frequency and high frequency percentage), than carriers of the C/C genotype at standing. Both UCP2 and UCP3 polymorphisms were significantly associated with a third-degree family history of hypertension, diabetes, and obesity. Additionally, carriers of the UCP2 45 bp I allele −UCP3 −55C/C combined genotype had the lowest HRV sympathetic and the highest HRV parasympathetic indices at standing among the combined genotypes. Conclusion UCP2 and UCP3 polymorphisms were associated with HRV in young and healthy states, suggesting a significant relationship between autonomic cardiovascular regulation and UCP2/UCP3 polymorphisms.

Enteral supplement enriched with glutamine, fiber, and oligosaccharide attenuates experimental colitis in mice.

OBJECTIVE Ulcerative colitis is a chronic recurrent disease characterized by acute inflammation of the colonic mucosa. In Japan, a dietary supplementation product enriched with glutamine, dietary fiber, and oligosaccharide (GFO) is widely applied for enteral nutrition support. These three components have been suggested to improve intestinal health. In this study, we investigated whether GFO has suppressive effects on mucosal damage in ulcerative colitis in an experimental mouse model. METHODS C57BL/6 mice received 2.5% dextran sulfate sodium in drinking water for 5 d to induce colitis. Then, they were given 0.25 mL of GFO or a 20% glucose solution twice daily for 10 d. Another set of mice receiving unaltered drinking water was used as the normal control group. RESULTS The body weight loss and disease activity index were significantly lower in the GFO-treated mice compared with the glucose-treated mice (P < 0.05). The decrease in colon length induced by dextran sulfate sodium was significantly alleviated in GFO-treated mice compared with glucose-treated mice (P < 0.01). In addition, the histologic findings showed that intestinal inflammation was significantly attenuated in mice treated with GFO. Furthermore, treatment with GFO significantly inhibited the dextran sulfate sodium-induced increase in the mRNA expression of interleukin-1β. CONCLUSION These results suggest that GFO has potential therapeutic value as an adjunct therapy for ulcerative colitis.

Alpha-adrenoceptor gene variants and autonomic nervous system function in a young healthy Japanese population.

Abstractα1A-adrenergic receptor (α1A-AR) regulates the cardiac and peripheral vascular system through sympathetic activation, and α2A-AR and α2C-AR subtypes are essential for presynaptic feedback regulation of catecholamine release from the central and peripheral sympathetic nerve. Genetic variations in each human α-AR subtype gene have been identified and have been implicated in hypertension and cardiovascular disease. It is not yet clear whether these genetic variations actually have an effect on sympatho-vagal modulation. The aim of the present study was to evaluate the relation between the five representative genetic polymorphisms of α-AR subtypes (Arg347Cys of α1A-AR; C-1291G, Asn251Lys, and DraI RFLP of α2A-AR; and Del322–325 of α2C-AR) and autonomic nervous system (ANS) function in young and healthy Japanese males. One hundred forty-nine subjects were genotyped for each α-AR polymorphism, and underwent evaluation of ANS function by power spectral analysis of heart rate variability (HRV) during supine rest and in a standing position. In a supine position, the α1A-AR 347Cys allele was significantly associated with lower HRV sympathetic index (normalized low frequency power [LF(%)] and LF:HF ratio) and higher HRV parasympathetic index [HF(%)]. Meanwhile, subjects with the α2C-AR Del322–325 allele had markedly higher LF(%) and LF:HF ratio and lower HF(%) than noncarriers. Thus, the α1A-AR and α2C-AR genetic variations influence sympatho-vagal balance even in young and healthy normotensive states, which could be postulated to constitute an intermediate phenotype for future pathological episodes of various ANS dysfunction-related diseases.