Takayuki Masaki

Adiponectin protects LPS‐induced liver injury through modulation of TNF‐α in KK‐Ay obese mice

Adiponectin, an adipocytokine, has been identified in adipose tissue, and its receptors are widely distributed in many tissues, including the liver. The present study was performed to clarify the role of adiponectin in lipopolysaccharide (LPS)‐induced liver injury using KK‐Ay obese mice. We analyzed the effects of adiponectin pretreatment on liver injury induced by D‐galactosamine/LPS (GalN/LPS) in KK‐Ay obese mice. GalN/LPS treatment induced significant increases in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in the blood, apoptotic and necrotic changes in hepatocytes, and/or showed a high degree of lethality. The GalN/LPS‐induced liver injury was more pronounced in KK‐Ay obese mice than in lean controls. Pretreatment with adiponectin ameliorated the GalN/LPS‐induced elevation of serum AST and ALT levels and the apoptotic and necrotic changes in hepatocytes, resulting in a reduction in lethality. In addition, pretreatment with adiponectin attenuated the GalN/LPS‐induced increases in serum and hepatic tumor necrosis factor α (TNF‐α) levels and increased peroxisome proliferator‐activated receptor (PPAR) α messenger RNA expression in the liver. Furthermore, abdominal macrophages from KK‐Ay obese mice pretreated with adiponectin in vitro exhibited decreased LPS‐induced TNF‐α production compared with controls. Finally, adiponectin pretreatment also ameliorated TNF‐α‐induced liver injury. In conclusion, these findings suggest that adiponectin prevents LPS‐induced hepatic injury by inhibiting the synthesis and/or release of TNF‐α of KK‐Ay obese mice. (HEPATOLOGY 2004;40:177–184.)

TNF-α induces hepatic steatosis in mice by enhancing gene expression of sterol regulatory element binding protein-1c (SREBP-1C)

We investigated the effect of tumor necrosis factor-α (TNF-α), a member of the proinflammatory cytokine family, on steatosis of the mouse liver by analyzing morphological changes and hepatic triglyceride content in response to TNF-α. We also examined expression of the sterol regulatory element binding protein-1c gene. Intraperitoneal injection of TNF-α acutely and dramatically accelerated the accumulation of fat in the liver, as evidenced by histological analysis and hepatic triglyceride content. This treatment increased liver weight, increased serum levels of free fatty acids, and increased fatty acid synthase and sterol regulatory element binding protein-1c mRNA expression. Furthermore, intraperitoneal injection of lipopolysaccaride (LPS) to induce TNF-α expression also accelerated hepatic fat accumulation. Pretreatment with anti-TNF-α antibody attenuated the development of LPS-induced fatty change in the liver. Antibody pretreatment not only decreased sterol regulatory element binding protein-1c expression in LPS-treated mice but also attenuated the expression of suppressors of cytokine signaling-3 mRNA. This study suggests that TNF-α, acting downstream of LPS, increases intrahepatic fat deposition by affecting hepatic lipogenetic metabolism involving sterol regulatory element binding protein-1c.

Orexin-A Regulates Body Temperature in Coordination with Arousal Status:

Orexins, hypothalamic neuropeptides, are involved in modulation of food intake and arousal status. To further examine their physiological roles in brain function, the effect of centrally administered orexin-A on body temperature was investigated in rats. Assessed by a telemetry sensor system implanted into the abdominal cavity, infusion of orexin-A into the third cerebroventricle (i3vt) increased body temperature in a dose-responsive manner. Expression of uncoupling protein 1 (UCP1) mRNA in brown adipose tissue (BAT), as a marker for peripheral thermogenesis, failed to increase after the infusion. Expression of UCP3 mRNA in skeletal muscle was up-regulated, whereas UCP2 in white adipose tissue was unchanged after the infusion. The resulting information indicates that orexin neurons regulate body temperature in coordination with arousal status independently of peripheral thermogenesis, which is regulated by BAT UCP1.

Centrally administered ghrelin suppresses sympathetic nerve activity in brown adipose tissue of rats

To clarify the functional roles of ghrelin in regulating energy balance, we investigated the effects of a central infusion of ghrelin on food intake and the activity of the sympathetic nerve innervating brown adipose tissue (BAT), the site regulating energy expenditure in rodents. A bolus infusion of ghrelin at a dose of 1 nmol/rat into the third cerebral ventricle (i3vt) increased the 4 h cumulative food intake. I3vt infusion of ghrelin (1 nmol/rat) suppressed BAT sympathetic nerve activity, followed by a gradual recovery. In contrast, i3vt infusion of growth hormone (GH) at a dose of 0.5 nmol/rat induced a gradual increase in sympathetic nerve activity. The ghrelin infusion decreased BAT temperature, which recovered gradually, but did not affect rectal temperature. In conclusion, the central administration of ghrelin suppresses energy expenditure and thermogenesis in BAT via its inhibitory effect on BAT sympathetic nerve activity. Simultaneous GH secretion induced by ghrelin treatment may modulate the temporal course of the sympathetic nerve response to ghrelin. The stimulatory and inhibitory effects of ghrelin on energy intake and expenditure, respectively, may induce a positive energy balance, which, in turn, affects adiposity and body weight.

Telmisartan Prevents Obesity and Increases the Expression of Uncoupling Protein 1 in Diet-Induced Obese Mice

The aim of the present study was to clarify the effect of telmisartan, an angiotensin II receptor blocker, on the development of obesity and related metabolic disorders in diet-induced obese mice. Treatment with telmisartan dissolved in drinking water at a dosage of 5 mg/kg per day for 14 days attenuated the diet-induced weight gain without affecting food intake in diet-induced obese mice compared with controls using nontreated water. Telmisartan treatment decreased the weight of visceral adipose tissue and the triglyceride content in the liver and skeletal muscle. In addition, hyperglycemia, hyperinsulinemia, and hypertriglyceridemia in diet-induced obese mice all improved with telmisartan treatment. Furthermore, telmisartan treatment increased adiponectin mRNA in visceral white adipose tissue and was associated with a concomitant change in the serum adiponectin level. In contrast, the treatment reduced the serum level of resistin. Finally, telmisartan treatment increased the mRNA expression of uncoupling protein 1 in brown adipose tissue and was accompanied by an increase in oxygen consumption. In conclusion, telmisartan treatment might prevent the development of obesity and related metabolic disorders by altering the levels of adiponectin, resistin, and uncoupling protein 1 in diet-induced obese mice. Our results indicate that telmisartan can be used as a therapeutic tool for metabolic syndrome, including visceral obesity.

ENHANCED EXPRESSION OF UNCOUPLING PROTEIN 2 GENE IN RAT WHITE ADIPOSE TISSUE AND SKELETAL MUSCLE FOLLOWING CHRONIC TREATMENT WITH THYROID HORMONE

Evidence is rapidly emerging which suggests that uncoupling protein 2 (UCP2), by virtue of its ubiquitous expression, may be important for determining basal metabolic rate. To assess the functional modulation of UCP2 gene expression in relation to body weight control, we examined the effects of hyperthyroid state induced by chronic treatment with triiodothyronine (T3) on UCP2 mRNA expression in male rats. Daily subcutaneous injection of T3 (37 pmol/100 g body weight) for 7 days increased UCP2 mRNA expression in brown adipose tissue (BAT), white adipose tissue (WAT) and the soleus muscle 1.6‐, 1.6‐ and 1.7‐fold compared to the controls, respectively, and increased UCP1 mRNA expression in BAT 1.2‐fold. In contrast, the same treatment with T3 decreased both ob mRNA expression in WAT and plasma leptin level 0.5‐fold for each. The present results suggest that T3 may directly increase UCP2 expression independently of leptin action.

Ghrelin regulates adiposity in white adipose tissue and UCP1 mRNA expression in brown adipose tissue in mice.

To examine the involvement of ghrelin in obesity, we investigated the effects of treatment with peripherally administered ghrelin on food intake, adiposity, and expression of uncoupling protein (UCP) mRNA in brown (BAT) and white (WAT) adipose tissue in mice. Acute bolus administration of ghrelin at a dose of 120 nmol/kg increased cumulative food intake over 4 and 24 h as compared to controls (p<0.05 for each), whereas 12 nmol/kg/day ghrelin showed no remarkable effect (p>0.1). Chronic repeated treatment with 12 nmol/kg/day ghrelin for 7 days increased body weight and adiposity assessed by the weight of adipose tissue, triglyceride content in WAT (p<0.05 for each versus control). In addition, the same treatment decreased and increased mRNA expression of BAT UCP1 and WAT UCP2, respectively (p<0.05 for each). In conclusion, ghrelin can regulate body weight, adiposity and UCPs mRNA expression in mice. The present results provide evidence for a new regulatory loop involving ghrelin and UCP, and add novel insights into the regulatory mechanisms of obesity.

Anti-Obesity Actions of Mastication Driven by Histamine Neurons in Rats:

Implications of mastication in energy intake and expenditure regulated by histamine (HA) neurons were Investigated in rats. Depletion of neuronal HA from the mesencephalic trigeminal sensory nucleus (Me5) reduced eating speed, but that from a satiety center of the ventromedial hypothalamus (VMH) increased both meal size and its duration leaving eating speed unaffected. Turnover of neuronal HA in the Me5 was elevated at the early phase of feeding and that in the VMH was at the later phase. This elevated turnover was abolished by gastric intubations of an isocaloric liquid diet or an equivolume of water. Mastication-induced activation of HA neurons suppressed physiological food intake through H1-receptor in the hypothalamic paraventricular nucleus (PVN) and the VMH. On the other hand, the HA neurons activation accelerated lipolysis particularly in the visceral adipose tissues and up-regulated mRNA expression of uncoupling protein family through sympathetic efferent nerve. Mastication thus plays an important role as a potent input signal to activate HA neurons. Our recent findings have evidently shown how tightly and elegantly HA neurons are concordant with leptin signaling system through a negative feedback loop.

Hypothalamic Melanocortin System Regulates Sympathetic Nerve Activity in Brown Adipose Tissue

To clarify the neuronal mechanism of the hypothalamic melanocortin system in regulating energy metabolism, we investigated the effects of centrally administered α-melanocyte-stimulating hormone (α-MSH) and agouti-related protein (AGRP), an agonist and an antagonist for the melanocortin 4 receptor (MC4-R), respectively, on the activity of sympathetic nerves innervating brown adipose tissue (BAT) and on BAT temperature. A bolus infusion of α-MSH (1 nmol) into the third cerebral ventricle (i3vt) significantly increased sympathetic nerve activity and elevated BAT temperature (P < 0.05). The i3vt infusion of AGRP (1 nmol) gradually suppressed BAT sympathetic nerve activity and was accompanied by a significant reduction in BAT temperature (P < 0.05). In conclusion, the hypothalamic melanocortin system may regulate peripheral energy expenditure, as well as thermogenesis, through its influence on BAT sympathetic nerve activity.

Hypothalamic neuronal histamine regulates sympathetic nerve activity and expression of uncoupling protein 1 mRNA in brown adipose tissue in rats

To clarify how hypothalamic neuronal histamine regulates peripheral energy expenditure, we investigated the effect of infusion of histamine into the third cerebral ventricle or discrete hypothalamic regions on sympathetic nerve activity and expression of uncoupling protein 1 (UCP1) mRNA in brown adipose tissue (BAT). Infusion of histamine (200 nmol) into the third cerebral ventricle of anesthetized rats significantly increased the electrophysiological activity of sympathetic nerves (P<0.01) and UCP1 mRNA expression in the BAT (P<0.05). Microinjection of histamine (10 nmol) into the paraventricular nucleus (PVN) and preoptic area (POA) produced similar significant increases in BAT sympathetic nerve activity (P<0.01 for each). By contrast, injection of histamine into the ventromedial hypothalamic nucleus or lateral hypothalamic area had no effect. We conclude that hypothalamic neuronal histamine may regulate energy expenditure in BAT through the activation of sympathetic nerves. The PVN and/or POA appear to be the principal hypothalamic sites that mediate the stimulatory effect of histamine on this efferent pathway.