Treatment with FGFR2-IIIc monoclonal antibody suppresses weight gain and adiposity in KKAy mice.

Expression of ß-Kotho, fibroblast growth factor receptor (FGFR)-1c and 2c, which bind FGF21, is decreased in the white adipose tissue of obese mice. The aim of the present study was to determine the role of FGFR2c in the development of obesity and diabetes in KKAy mice. Treatment with mouse monoclonal FGFR2-IIIc antibody (0.5 mg kg-1) significantly suppressed body weight gain and epididymal white adipose tissue weight in individually housed KKAy mice while having no effect on daily food intake. In addition, treatment with FGFR2-IIIc antibody significantly increased plasma-free fatty acid levels while having no effect on blood glucose or plasma FGF21 levels. Moreover, treatment with FGFR2-IIIc antibody had no significant effect on the expression of uncoupling protein-1, uncoupling protein-2 or peroxisome proliferator-activated receptor-γ coactivator 1α in the epididymal white adipose tissue. The treatment with FGFR2-IIIc antibody had no significant effects on daily food intake and body weight gain in individually housed KK mice. These findings suggest that FGFR2-IIIc upregulates the adiposity induced by social isolation in KKAy mice, and that decreased expression and/or function of FGFR2c might be a compensatory response to enhanced adiposity. Inhibition of FGFR2-IIIc function might be a novel therapeutic approach for obesity.

Pharmacological stimulation of serotonin 5-HT1B receptors enhances increases in plasma active glucagon-like peptide-1 levels induced by dipeptidyl peptidase-4 inhibition independently of feeding in mice.

AIM: Glucagon-like peptide-1 (GLP-1), an incretin hormone, is released from intestinal L cells in response to nutrient ingestion. Dipeptidyl peptidase-4 (DPP-4) rapidly degrades the active form of GLP-1 to an inactive form in the bloodstream. The present study aimed to investigate the role of serotonin (5-HT)1B receptors in the regulation of plasma active GLP-1 levels and glucose tolerance under DPP-4 inhibition. METHODS: C57BL6J mice treated with or without alogliptin, a highly selective DPP-4 inhibitor, for 4 days were intraperitoneally injected with either saline, the 5-HT1B/2C receptor agonist meta-chlorophenylpiperazine (mCPP) at 2.5mg/kg and 5mg/kg or the selective 5-HT1B receptor agonist CP94253 at 2.5mg/kg and 5mg/kg, and food-deprived after treatment. An hour later, plasma active GLP-1 levels were determined. Also, a glucose tolerance test was done by injecting D-glucose (2g/kg) following the injection of saline or CP94253 (5mg/kg) in mice treated with alogliptin. RESULTS: Intraperitoneal injection of mCPP (2.5 and 5mg/kg) or CP94253 (2.5 and 5mg/kg) in mice treated with alogliptin for 4 days significantly increased plasma active GLP-1 levels compared with saline controls in mice that were food-deprived after the injections. While intraperitoneal injection of either mCPP or CP94253 alone had no significant effect on plasma active GLP-1 levels, the injection of CP94253 improved glucose tolerance in mice treated with alogliptin compared with saline. CONCLUSION: These findings suggest that pharmacological stimulation of 5-HT1B receptors enhances the increases in plasma active GLP-1 induced by DPP-4 inhibition independently of feeding and also improves glucose tolerance in mice.

Up-regulation of peroxisome proliferator-activated receptors (PPAR-alpha) and PPAR-gamma messenger ribonucleic acid expression in the liver in murine obesity: troglitazone induces expression of PPAR-gamma-responsive adipose tissue-specific genes in the liver of obese diabetic mice.

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that play an important role in the regulation of genes involved in lipid utilization and storage, lipoprotein metabolism, adipocyte differentiation, and insulin action. The three isoforms of the PPAR family, i.e. alpha, delta, and gamma, have distinct tissue distribution patterns. PPAR-alpha is predominantly present in the liver, and PPAR-gamma in adipose tissue, whereas PPAR-delta is ubiquitously expressed. A recent study reported increased PPAR-gamma messenger RNA (mRNA) expression in the liver in ob/ob mice; however, it is not known whether increased PPAR-gamma expression in the liver has any functional consequences. The expression of PPAR-alpha and -delta in the liver in obesity has not been determined. We have now examined the mRNA levels of PPAR-alpha, -delta, and -gamma in three murine models of obesity, namely, ob/ob (leptin-deficient), db/db (leptin-receptor deficient), and serotonin 5-HT2c receptor (5-HT2cR) mutant mice. 5-HT2cR mutant mice develop a late-onset obesity that is associated with higher plasma leptin levels. Our results show that PPAR-alpha mRNA levels in the liver are increased by 2- to 3-fold in all three obese models, whereas hepatic PPAR-gamma mRNA levels are increased by 7- to 9-fold in ob/ob and db/db mice and by 2-fold in obese 5-HT2cR mutant mice. PPAR-delta mRNA expression is not altered in ob/ob or db/db mice. To determine whether increased PPAR-gamma expression in the liver has any functional consequences, we examined the effect of troglitazone treatment on the hepatic mRNA levels of several PPAR-gamma-responsive adipose tissue-specific genes that have either no detectable or very low basal expression in the liver. The treatment of lean control mice with troglitazone significantly increased the expression of adipocyte fatty acid-binding protein (aP2) and fatty acid translocase (FAT/CD36) in the liver. This troglitazone-induced increase in the expression of aP2 and FAT/CD36 was markedly enhanced in the liver in ob/ob mice. Troglitazone also induced a pronounced increase in the expression of uncoupling protein-2 in the liver in ob/ob mice. In contrast to the liver, troglitazone did not increase the expression of aP2, FAT/CD36, and uncoupling protein-2 in adipose tissue in lean or ob/ob mice. Taken together, our results suggest that the effects of PPAR-gamma activators on lipid metabolism and energy homeostasis in obesity and type 2 diabetes may be partly mediated through their effects on PPAR-gamma in the liver.

New insights into sympathetic regulation of glucose and fat metabolism.

The autonomic nervous system modulates glucose and fat metabolism through both direct neural effects and hormonal effects. This review presents recent concepts on the sympathetic regulation of glucose and fat metabolism. Focally released norepinephrine from sympathetic nerves is likely to increase glucose uptake in skeletal muscle and adipose tissues independent of insulin but norepinephrine does not contribute so much as epinephrine to hepatic glucose production. Epinephrine increases hepatic glucose production and inhibits insulin secretion and the glucose uptake by tissues that is induced by insulin. Additionally, catecholamines can increase thermogenesis and lipolysis, leading to increased energy expenditure and decreased fat stores. It is likely that beta-(beta3)-adrenergic receptors mediate these responses. Alterations of central neurotransmission and environmental factors can change the relative contribution of sympathetic outflow to the pancreas, liver, adrenal medulla and adipose tissues, leading to the modulation of glucose and fat metabolism. Recent studies have proposed that leptin, an adipocyte hormone, affects the central nervous system to increase sympathetic outflow independent of feeding. The effects of leptin on glucose and fat metabolism could be in part mediated by the sympathetic nervous system. Studies using mice with a genetic disruption of serotonin 5-HT2c receptor indicate that central neural mechanisms in the regulation of sympathetic outflow and satiety could be dissociated. Abnormalities of sympathetic effects, including disturbances of leptin and beta3-adrenergic receptor signalling, are likely to cause obesity and impaired glucose tolerance in rodents and humans. These findings indicate that dysfunction of the sympathetic nervous system could predispose to obesity and Type II (non-insulin-dependent) diabetes mellitus.

Leptin-independent hyperphagia and type 2 diabetes in mice with a mutated serotonin 5-HT2C receptor gene.

Brain serotonin and leptin signaling contribute substantially to the regulation of feeding and energy expenditure. Here we show that young adult mice with a targeted mutation of the serotonin 5-HT2C receptor gene consume more food despite normal responses to exogenous leptin administration. Chronic hyperphagia leads to a 'middle-aged'-onset obesity associated with a partial leptin resistance of late onset. In addition, older mice develop insulin resistance and impaired glucose tolerance. Mutant mice also responded more to high-fat feeding, leading to hyperglycemia without hyperlipidemia. These findings demonstrate a dissociation of serotonin and leptin signaling in the regulation of feeding and indicate that a perturbation of brain serotonin systems can predispose to type 2 diabetes.

Stress, acute hyperglycemia, and hyperlipidemia role of the autonomic nervous system and cytokines.

Stress is accompanied by metabolic alterations that could contribute to the etiology of diabetes mellitus, arteriosclerosis, and cardiovascular diseases; however, the mechanisms by which stress affects glucose and lipid metabolism remain to be resolved. Stress-induced effects on neurotransmission and interleukin-1 (IL-1) signaling rapidly produce hyperglycemia by increasing sympathetic outflow. Activation of the sympathetic nervous system can also rapidly stimulate lipolysis and hepatic triglyceride secretion. Furthermore, stress increases serum interleukin-6 (IL-6) and nerve growth factor (NGF) levels by activating neuroendocrine systems. IL-6 and NGF can rapidly increase lipolysis and hepatic triglyceride secretion without inducing hyperglycemia. The sympathetic nervous system does not mediate cytokine-induced hypertriglyceridemia. Thus, the central nervous system plays an important role in regulation of hepatic glucose and lipid metabolism via the sympathetic nervous system and cytokines. (Trends Endocrinol Metab 1997;8:192-197). (c) 1997, Elsevier Science Inc.

Role of central neural mechanisms in the regulation of hepatic glucose metabolism.

Central monoamine neurotransmitters affect blood glucose homeostasis. Activation of central cholinergic, noradrenergic histaminergic, and serotonergic neurons rapidly increase hepatic glucose output via the sympathetic nervous system. Acute hyperglycemia is mediated by three distinct pathways: the action of epinephrine on the liver, the action of glucagon on the liver, and the direct innervation of the liver. The relative contribution of these factors to hyperglycemia can be altered by diet and the kinds of neurotransmitters evoked in the central nervous system, but the magnitude of epinephrine secretion is closely related to the magnitude of hyperglycemia. On the other hand, neuropharmacological stimulation of central cholinergic muscarinic receptors, histaminergic H1 receptors, and serotonergic 5-HT2 receptors increases hypothalamic noradrenergic neuronal activity, which is associated with hyperglycemia. In contrast, central GABAA receptors play an inhibitory role in the regulation of hepatic glucose metabolism. Thus, central monoaminergic neurons could be linked together, and play a homeostatic role in the regulation of hepatic glucose metabolism.

LIF and CNTF, which share the gp130 transduction system, stimulate hepatic lipid metabolism in rats.

We determined the effects of leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) on lipid metabolism in intact rats. Administration of LIF and CNTF increased serum triglycerides in a dose-dependent manner with peak values at 2 h. The effects of LIF and CNTF on serum cholesterol were very small, and serum glucose was unaffected. Both LIF and CNTF stimulated hepatic triglyceride secretion, hepatic de novo fatty acid synthesis, and lipolysis. Pretreatment with phenylisopropyl adenosine, which inhibits lipolysis, partially inhibited LIF- and CNTF-induced hypertriglyceridemia. Interleukin-4, which inhibits cytokine-induced hepatic fatty acid synthesis, also partially inhibited LIF- and CNTF-induced hypertriglyceridemia. These results indicate that both lipolysis and de novo fatty acid synthesis play a role in providing fatty acids for the increase in hepatic triglyceride secretion. Neither indomethacin nor adrenergic receptor antagonists affected the hypertriglyceridemia. The combination of LIF plus CNTF showed no additive effects consistent with the action of both cytokines through the gp130 transduction system. Thus LIF and CNTF have similar effects on lipid metabolism; they join a growing list of cytokines that stimulate hepatic triglyceride secretion and may mediate the changes in lipid metabolism that accompany the acute phase response.

Beta-nerve growth factor as a mediator of the acute phase response in vivo.

Nerve growth factor (NGF) is increased during inflammation and stress. Stress-induced increases in specific serum proteins, such as serum amyloid A (SAA) and serum triglyceride (TG) levels, are part of the acute phase response which is mediated by cytokines. We now report the effect of systemic administration of beta-NGF on levels of serum lipids and SAA. Beta-NGF induced a rapid and sustained increase in serum TG and free fatty acid (FFA) in a dose dependent manner, while decreasing serum cholesterol levels in rats. Additionally, beta-NGF increased hepatic mRNA levels and serum concentrations of SAA at 16 hours in mice. Thus, beta-NGF joins the list of cytokines and growth factors that can mediate the acute phase response.

Increase in insulin release from rat pancreatic islets by quinolone antibiotics.

1. The present study was undertaken to elucidate the mechanism(s) of hypoglycaemia caused by quinolone antibiotics. We investigated the effects of various quinolone antibiotics on insulin release in rat pancreatic islets. 2. At a non-stimulatory concentration of 3 mM glucose, lomefloxacin (LFLX) or sparfloxacin at 1 mM and pipemidic acid (0.1-1 mM) induced slight insulin release but tosufloxacin or enoxacin up to 100 microM did not. 3. At the stimulatory concentration of 10 mM glucose, all quinolones augmented insulin release in a dose-dependent manner. LFLX (100 microM) shifted the dose-response curve of glucose-induced insulin release to the left without altering the maximal response. 4. At 10 mM glucose, LFLX (100 microM) increased insulin release augmented by forskolin (5 microM) or 12-O-tetradecanoyl phorbol-13-acetate (100 nM) but not by raising the K+ concentration from 6 to 25 mM. 5. Verapamil (50 microM) or diazoxide (50-400 microM) antagonized the insulinotropic effect of LFLX. 6. These data suggest that quinolone antibiotics may cause hypoglycaemia by increasing insulin release via blockade of ATP-sensitive K+ channels.

Keratinocyte growth factor increases fatty acid mobilization and hepatic triglyceride secretion in rats.

Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor family that was originally identified as a keratinocyte mitogen after isolation from a lung fibroblast cell line. In this study, we demonstrate that administration of KGF to mice and rats elevates serum lipid levels. In rats, 1 h after KGF administration, serum triglyceride and FFA levels were increased, with peak values at 2 h (1.9-fold increase). The increase in serum triglyceride levels was sustained for at least 16 h. Serum cholesterol levels were also increased, but the effect was delayed beginning at 4 h, with peak values at 16 h (1.27-fold increase). KGF did not decrease the clearance of triglyceride-rich lipoproteins, but increased hepatic triglyceride secretion. KGF stimulated lipolysis, but not hepatic de novo fatty acid synthesis, and the increased delivery of FFA to the liver plays a crucial role in the KGF-induced hypertriglyceridemia. Neither alpha- nor beta-adrenergic receptor antagonists affected the hypertriglyceridemia induced by KGF, indicating that endogenous catecholamines are not involved in mediating KGF-induced hypertriglyceridemia. These results demonstrate that KGF induces hypertriglyceridemia by increasing hepatic triglyceride secretion, with the fatty acids provided by lipolysis making a major contribution. Thus, KGF could modulate lipid metabolism in vivo.

Lipoteichoic acid stimulates lipolysis and hepatic triglyceride secretion in rats in vivo.

The host response to infection is frequently accompanied by changes in lipid metabolism. Previous studies have shown that endotoxin (LPS), a component of the cell wall of gram-negative bacteria, increases serum lipid levels. In this study, we demonstrate that lipoteichoic acid (LTA), a component of the cell membrane of gram-positive bacteria, also increases serum lipid levels in rats in a dose-dependent manner (0.1-300 micrograms/200 g body weight). Serum triglyceride levels increased within 2 h after LTA administration with peak values at 4 h (2-fold increase). Serum cholesterol levels also increased but the effect was delayed occurring at 16 h and was relatively small (1.2-fold increase). LTA (10 micrograms/200 g BW) did not decrease adipose tissue lipoprotein lipase activity or the clearance of triglyceride-rich lipoproteins. Rather, the LTA-induced hypertriglyceridemia is due to an increase in hepatic triglyceride secretion. LTA stimulates both hepatic de novo fatty acid synthesis and lipolysis. The increased delivery of free fatty acids to the liver plays a major role in the LTA-induced hypertriglyceridemia. Pretreatment with phentolamine, an alpha-adrenergic receptor antagonist, and alprenolol, a beta-adrenergic receptor antagonist, or phentolamine alone significantly suppressed the hypertriglyceridemia induced by LTA. These adrenergic inhibitors had no significant effect on the increase in lipolysis. These results indicate that catecholamines are involved in mediating the LTA-induced increase in hepatic triglyceride secretion via alpha-adrenergic receptors. These changes in lipid metabolism may play an important role in the organism's response to gram-positive infection.

Neuropeptide Y inhibits in vivo specific antibody production in rats.

The sympathetic neurotransmitter neuropeptide-Y (NPY) is hypothesized to play a role in the in vivo modulation of immune responses. This study examined the effects of intraperitoneal administration of NPY on specific antibody responses to keyhole limpet hemocyanin (KLH) in rats. Antibody levels were repeatedly measured by enzyme-linked immunosorbent assay before and after intraperitoneal immunization with KLH. NPY induced a dose-dependent inhibition of IgM and IgG antibody responses following immunization with either physiologic or supraphysiologic doses of antigen. These in vivo results suggests that NPY may be involved in endogenous modulation of immune responses.

Interleukin-6 stimulates hepatic triglyceride secretion in rats.

Interleukin-6 (IL-6) not only regulates a variety of immune functions, but also is the most potent cytokine in inducing the hepatic acute phase proteins. We determined the effect of IL-6 on serum lipid levels and the mechanism of IL-6-induced hypertriglyceridemia in rats. Intravenous administration of IL-6 (0.1-10 micrograms/200 g BW) increased serum triglyceride levels in a dose-dependent manner. One hour after IL-6 administration, serum triglyceride levels were increased, with peak values at 2 h (2.2-fold increase). Serum cholesterol levels also increased, but the effect was delayed, first occurring at 4 h and peaking at 8 h (1.24-fold increase). IL-6 treatment increased hepatic triglyceride secretion without decreasing the clearance of triglyceride-rich lipoproteins, indicating that the hypertriglyceridemia was due to increased secretion by the liver. Furthermore, IL-6 stimulates lipolysis, and the increased delivery of FFA to the liver significantly contributed to the IL-6-induced hypertriglyceridemia. Neither alpha 1- nor beta-adrenergic receptor antagonists affected the hypertriglyceridemia induced by IL-6, whereas previous studies have shown that endotoxin-induced hypertriglyceridemia was blocked by alpha-adrenergic receptor antagonists. These results demonstrate that IL-6 induces hypertriglyceridemia by stimulating hepatic triglyceride secretion independent of endogenous catecholamines. Thus, changes in hepatic triglyceride metabolism are another acute phase response that can be induced by IL-6.

Alpha-adrenergic receptors mediate the hypertriglyceridemia induced by endotoxin, but not tumor necrosis factor, in rats.

We assessed the role of catecholamines in mediating the hypertriglyceridemia induced by lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF alpha) in rats by employing specific adrenoreceptor antagonists. Pretreatment with phentolamine, an alpha-antagonist, but not propranolol, a beta-antagonist, suppressed the hypertriglyceridemia induced by either low dose LPS (100 ng/100 g BW) or high dose LPS (50 micrograms/100 g BW). Prazosin, an alpha 1-selective antagonist, significantly suppressed the low dose LPS-induced hypertriglyceridemia by inhibiting hepatic triglyceride secretion, but did not affect the increase in lipolysis. In contrast, yohimbine, an alpha 2-selective antagonist, partially suppressed the high dose LPS-induced hypertriglyceridemia by inhibiting the decrease in postheparin lipoprotein lipase activity. Treatment with phentolamine and propranolol did not affect the hypertriglyceridemia induced by TNF alpha. In summary, these findings suggest that catecholamines via alpha-adrenergic, but not beta-adrenergic, receptors are mediators of the hypertriglyceridemia induced by either low or high dose LPS in rats. alpha 1-Adrenergic receptors are involved in mediating the increased hepatic triglyceride secretion induced by low dose LPS, whereas alpha 2-adrenergic receptors are involved in mediating the decrease in lipoprotein lipase activity induced by high dose LPS. The hypertriglyceridemia induced by either low or high dose LPS may be regulated by a mechanism unrelated to TNF alpha in rats.

Effects of adrenoceptor antagonists on the hyperthermia and hyperglycemia induced by prostaglandin F2 alpha in rats.

We investigated the effects of intraperitoneal administration of adrenoceptor antagonists to the hyperthermia and hyperglycemia induced by prostaglandin F2 alpha (50 micrograms) injected into the third cerebral ventricle in anesthetized rats. Phentolamine inhibited the hyperthermia and hyperglycemia induced by prostaglandin F2 alpha. Prazosin inhibited the hyperthermia induced by prostaglandin F2 alpha, while enhancing the hyperglycemia. Yohimbine inhibited the prostaglandin F2 alpha-induced hyperglycemia without an effect on the hyperthermia. Propranolol had no effect on either prostaglandin F2 alpha-induced hyperglycemia or hyperthermia. These observations suggest that the hyperglycemia induced by prostaglandin F2 alpha is regulated by alpha 2-adrenoceptor systems while the hyperthermia is regulated by alpha 1-adrenoceptor systems in rats.

Bicuculline methiodide influences the central nervous system to produce hyperglycemia in rats.

The influence of bicuculline methiodide (BMI), a gamma-aminobutyric acid (GABA) receptor antagonist, on central nervous system regulation of blood glucose homeostasis was studied in fed rats. Injection of BMI (1-10 nmol) into the third ventricle was found to produce hepatic venous hyperglycemia in a dose-dependent manner. This change was associated with increased secretion of epinephrine and glucagon. The role of epinephrine in hyperglycemia was then studied in bilaterally adrenalectomized (ADX) rats injected with BMI. Plasma glucose concentration was found to increase in ADX rats although the level was approximately half that for intact rats and significantly higher than for controls. The increase in epinephrine and glucagon secretion seen in intact rats, but not in ADX rats, suggests BMI induced epinephrine release is responsible for the glucagon secretion. Three possible mechanisms are suggested to account for the rise in plasma glucose in the hepatic vein after injection of BMI: 1) that epinephrine is secreted by the adrenal medulla, 2) that epinephrine secretion stimulates glucagon secretion or 3) that there may be some direct innervation of the liver in rats.

Effects of central GABA receptors activation on catecholamine secretion in rats.

We investigated the effects of muscimol, the GABAA receptor agonist, and baclofen, the GABAB receptor agonist, injected into the third cerebral ventricle on plasma epinephrine (E) and norepinephrine (NE) levels in anesthetized rats. Baclofen (0.4-5 nmol) increased plasma NE levels in a dose dependent manner but did not affect plasma E levels. Muscimol (2.5 nmol) affected neither plasma E nor NE levels. Concomitant injection of muscimol (2.5 nmol) with baclofen (5 nmol) attenuated the baclofen (5 nmol)-induced NE secretion. These findings suggest that activation of GABAB receptors in the central nervous system (CNS) stimulates the sympathetic nervous system but not the adrenal medullary response. In contrast, activation of GABAA receptors in the CNS affects neither the sympathetic nervous system nor the adrenal medullary response, but inhibits the sympathetic neural activity induced by activation of GABAB receptors in anesthetized rats.

Activation of central GABAA receptors suppresses the alteration of plasma catecholamine levels induced by neostigmine or histamine in rats.

We investigated the effects of intraventricular injection of muscimol, the GABAA receptor agonist, on the alteration of plasma epinephrine (E) and norepinephrine (NE) levels induced by neostigmine or histamine in anesthetized rats. Injection of neostigmine (10 nmol) into the third cerebral ventricle increased plasma levels of E more than NE, while histamine (500 nmol) increased plasma levels of NE more than E. Concomitant injection of muscimol (2.5 nmol) with neostigmine or histamine significantly suppressed the alteration of E and NE levels induced by neostigmine or histamine. These findings suggest that activation of central cholinergic neuron stimulates the adrenal medullary response more than the sympathetic nervous system, while activation of central histaminergic neuron stimulates the sympathetic nervous system more than the adrenal medullary response in anesthetized rats. Activation of GABAA receptors in the CNS suppresses these effects.