Differential regulation of adipocytokine mRNAs by rosiglitazone in db/db mice.

The precise mechanism by which PPARgamma activation by thiazolidinediones (TZDs) improves insulin sensitivity is still unclear. Recent studies have focused on the role of adipocytokines in metabolic control and their regulation by TZDs. In this study, we compared the chronic effects of antihyperglycemic doses of the TZD rosiglitazone, the beta3-adrenoceptor agonist BRL-35135, and the PPARalpha agonist Wy-14,643 on the mRNA expression of adipocytokines in WAT of db/db mice. Rosiglitazone treatment decreased adiponectin and resistin mRNA levels by 57 and 72%, respectively (P < 0.001), with no effect on the level of TNFalpha or RELMalpha transcripts. In comparison, Wy-14,643 reduced adiponectin transcript levels by 31% (P = 0.015) while BRL-35135 increased RELMalpha mRNA expression by 245% (P < 0.001) without effect on the other transcripts. Our results indicate that although a reduction in adiponectin and resistin mRNA levels in WAT by rosiglitazone treatment of diabetic mice may contribute to the antidiabetic effects, an alteration in TNFalpha, adiponectin, resistin, or RELMalpha mRNA expression is not absolutely required for the regulation of blood glucose concentration in the db/db mouse.

Hypoglycemia activates orexin neurons and selectively increases hypothalamic orexin-B levels: responses inhibited by feeding and possibly mediated by the nucleus of the solitary tract.

Orexins are novel appetite-stimulating peptides expressed in the lateral hypothalamic area (LHA), and their expression is stimulated by hypoglycemia in fasted rats. We investigated activation of orexin and other neurons during insulin-induced hypoglycemia using the immediate early gene product Fos. Insulin (50 U/kg) lowered plasma glucose by >50% after 5 h and stimulated feeding sixfold compared with saline-injected controls. Hypoglycemic rats allowed to feed and normoglycemic controls both showed sparse Fos-positive (Fos+) neurons in the LHA and the paraventricular nucleus (PVN) and arcuate nucleus (ARC) and showed none in the nucleus of the solitary tract (NTS), which relays visceral feeding signals to the LHA. In the LHA, total numbers of Fos+ neurons were comparable in fed hypoglycemic and control groups (60 +/- 6 vs. 52 +/- 4 cells/mm2, P > 0.05), as were Fos+ neurons immunoreactive for orexin (1.4 +/- 0.4 vs. 0.6 +/- 0.4 cells/mm2, P > 0.05). By contrast, hypoglycemic rats that were fasted showed significantly more Fos+ nuclei in the LHA (96 +/- 10 cells/mm2, P < 0.05, vs. both other groups) and Fos+ orexin neurons (8.4 +/- 3.3 cells/mm2, P < 0.001, vs. both other groups). They also showed two- to threefold more Fos+ nuclei (P < 0.001) in the PVN and ARC than both fed hypoglycemic rats and controls and showed strikingly abundant Fos+ neurons in the NTS and dorsal motor nucleus of the vagus. In parallel studies, whole hypothalamic orexin-A levels were not changed in hypoglycemic rats, whether fasted or freely fed, whereas orexin-B levels were 10-fold higher in hypoglycemic fasted rats than in control and hypoglycemic fed groups. These data support our hypothesis that orexin neurons are stimulated by falling glucose levels but are readily inhibited by signals related to nutrient ingestion and suggest that they may functionally link with neuronal activity in the NTS. Orexin-A and -B may play specific roles in behavioral or neuroendocrine responses to hypoglycemia.

v- and t-SNARE protein expression in models of insulin resistance: normalization of glycemia by rosiglitazone treatment corrects overexpression of cellubrevin, vesicle-associated membrane protein-2, and syntaxin 4 in skeletal muscle of Zucker diabetic fatty rats.

Insulin stimulation of adipose and muscle cells results in the translocation of GLUT4 from an intracellular location to the plasma membrane; this translocation is defective in insulin resistance. Studies have suggested an important role for synaptobrevin and syntaxin homologues in this event, particularly the v-soluble N-ethylmaleimide attachment protein receptors (SNAREs) cellubrevin and vesicle-associated membrane protein-2 (VAMP-2) and the t-SNARE syntaxin 4, but the expression of these proteins has not been studied in insulin-resistant tissues. Therefore, we examined SNARE protein content in skeletal muscle from Zucker diabetic fatty (ZDF) rats compared with lean controls and determined the effect of the thiazolidinedione insulin sensitizer rosiglitazone on these proteins. GLUT4 levels in skeletal muscle from ZDF rats were similar to those in lean control animals. In contrast, cellubrevin, VAMP-2, and syntaxin 4 protein levels were elevated (2.8-fold, P = 0.02; 3.7-fold, P = 0.01; and 2.2-fold, P < 0.05, respectively) in skeletal muscle from ZDF rats compared with lean controls. Restoration of normoglycemia and normoinsulinemia in ZDF rats with rosiglitazone (30 micromol/kg) normalized cellubrevin, VAMP-2, and syntaxin 4 protein to levels approaching those observed in lean control animals. These data show that elevated v- and t-SNARE protein levels are associated with insulin resistance in skeletal muscle and that these increases may be reversed by rosiglitazone treatment concomitant with a restoration of glycemic control. Such increases in SNARE protein levels were not observed in streptozotocin-induced diabetic rats, which suggests that hyperinsulinemia rather than hyperglycemia may be more important in modulating SNARE protein expression in rodent models of insulin resistance. Consistent with this hypothesis, elevated levels of SNARE proteins were also observed in 3T3-L1 adipocytes chronically treated with insulin (500 nmol/l for 24 h). These data argue that SNARE protein levels may be altered in insulin-resistant states and that the levels of these proteins are modulated by agents that increase insulin sensitivity. Moreover, these data demonstrate for the first time altered expression of proteins known to regulate GLUT4 translocation in a model of diabetes.

Down-regulation of orexin gene expression by severe obesity in the rats: studies in Zucker fatty and zucker diabetic fatty rats and effects of rosiglitazone.

Orexins (hypocretins) are lateral hypothalamic neuropeptides implicated in regulating feeding and the sleep-wake cycle. To study their possible relevance to obesity and diabetes, we measured hypothalamic prepro-orexin mRNA levels in obese, normoglycemic Zucker fatty (fa/fa) and in hyperglycemic, non-obese Zucker diabetic fatty (ZDF) rats. Hypothalamic prepro-orexin mRNA concentrations in Zucker fatty rats were 31% lower than those in lean controls (0. 69+/-0.06 vs. 1.00+/-0.10 arbitrary units, P<0.05), but did not differ between ZDF diabetic rats and non-diabetic controls. Treatment of ZDF diabetic rats with rosiglitazone (1 or 3 mg/kg body weight daily for 13 weeks) normalized plasma glucose and significantly reduced plasma insulin, while leptin levels were 67% higher than in untreated ZDF rats (20.2+/-0.5 vs. 12.1+/-2.5, P<0. 001). Rosiglitazone treatment markedly enhanced weight gain compared with untreated ZDF rats (final weight 732+/-13 g vs. 409+/-13 g, P<0. 001) even though they were restricted to the same food intake. Rosiglitazone-treated ZDF rats had significantly lower hypothalamic prepro-orexin mRNA levels (0.68+/-0.07 arbitrary units) than both non-diabetic lean controls (1.00+/-0.10, P=0.02) and untreated diabetics (1.03+/-0.14, P=0.03). Our data suggest that prepro-orexin gene expression may be suppressed by substantial weight gain. Obesity-related signals that might mediate this effect have not been identified, but plasma leptin, insulin and glucose are not obviously involved.

Rosiglitazone prevents the onset of hyperglycaemia and proteinuria in the Zucker diabetic fatty rat.

AIM: To investigate the potential of rosiglitazone, a highly potent agonist at the nuclear peroxisome proliferator activated receptor-gamma (PPAR-gamma), to prevent the development of diabetes in the Zucker diabetic fatty (ZDF) rat or to ameliorate the condition at a later stage of the disease. METHODS: Rosiglitazone (10 micromol/kg body weight daily) was given via the diet to ZDF rats from aged 6 weeks, before the onset of hyperglycaemia (Prevention group), or from aged 21 weeks after hyperglycaemia and proteinuria were established (Intervention group). Untreated ZDF rats and age-matched Zucker lean rats (ZL) served as controls and the experiment was terminated when the animals were aged 28 weeks. RESULTS: Whilst the combined ZDF control and Intervention groups were already hyperglycaemic (14.6 +/- 1.6 vs. ZL 5.7 +/- 0.1 mmol/l, mean +/- s.e.m.; p < 0.05), glycosuric and polydipsic at aged 11 weeks, and thereafter had a declining plasma insulin concentration, rosiglitazone Prevention treatment maintained normoglycaemia even at aged 27 weeks (3.7 +/- 0.3 mmol/l vs. ZL 3.0 +/- 0.3 mmol/l; NS). Intervention treatment at aged 21 weeks, however, failed to ameliorate the diabetes. These functional data were supported by determinations of pancreatic insulin content (microg/mg tissue as follows: ZL, 43.1 +/- 3.9; ZDF control (28 weeks) + ZDF Intervention control (21 weeks), 6.0 +/- 0.8; Prevention, 63.6 +/- 15.8; Intervention, 6.2 +/- 0.9) and by morphological, immunohistochemical and electron microscopical examination of pancreata at the end of the study. Thus, islets from rosiglitazone Prevention rats were similar to ZL rats, whereas ZDF controls and Intervention rats exhibited islets depleted of insulin, with a disorganized architecture and an ultrastructure indicative of work hypertrophy. ZDF control rats and Intervention rats, though not rosiglitazone Prevention rats, also exhibited marked proteinuria, indicative of renal glomerular damage. CONCLUSIONS: Our results demonstrate that in ZDF rats, rosiglitazone prevents the progression from insulin resistance to overt diabetes. These data provide a rationale for investigating whether treatment with rosiglitazone of patients with early signs of perturbed glucose metabolism (e.g. impaired fasting glucose (IGT)) may prevent the progression to type 2 diabetes and its associated complications.

Leptin treatment increases suppressors of cytokine signaling in central and peripheral tissues.

Leptin concentrations are elevated in the majority of obese individuals raising the possibility that leptin resistance contributes to their obesity. Peripheral leptin administration for 48 h caused a several-fold increase in mRNA encoding the suppressors of cytokine signaling SOCS-3 and CIS in hypothalamus and peripheral tissues. Paradoxically, CIS and SOCS-3 mRNAs are also elevated in the leptin-deficient ob/ob mouse. Forced expression of CIS in insulinoma cells prevented transactivation mediated by leptin. Thus tissues continuously exposed to leptin and/or other factors associated with obesity accumulate excessive amounts of SOCS-3 and CIS which could provide a potential mechanism for leptin resistance.

Non-thiazolidinedione antihyperglycaemic agents. Part 3: The effects of stereochemistry on the potency of alpha-methoxy-beta-phenylpropanoic acids.

Rhizopus delemar lipase catalysed ester hydrolysis of the alpha-methoxy-beta-phenylpropanoate 1 affords the (R)-(+) and (S)-(-) isomers in > 84% enantiomeric excess. Absolute stereochemistry was determined by a single crystal X-ray analysis of a related synthetic analogue. The activity of these two enantiomers on glucose transport in vitro and as anti-diabetic agents in vivo is reported and their unexpected equivalence attributed to an enzyme-mediated stereospecific isomerisation of the (R)-(+) isomer. Binding studies using recombinant human PPARgamma (peroxisomal proliferator activated receptor gamma), now established as a molecular target for this compound class, indicate a 20-fold higher binding affinity for the (S) antipode relative to the (R) antipode.

Antidiabetic efficacy of BRL 49653, a potent orally active insulin sensitizing agent, assessed in the C57BL/KsJ db/db diabetic mouse by non-invasive 1H NMR studies of urine.

High resolution 1H nuclear magnetic resonance (NMR) spectroscopic analysis of biofluids is a recently established tool for evaluating inherited and acquired errors in metabolic control. In the present study 1H NMR analysis of urine was used to monitor efficacy of BRL 49653, a potent and selective antihyperglycaemic agent, following oral administration for up to 36 weeks to the genetically diabetic C57BL/KsJ db/db mouse. The effects of BRL 49653 on carbohydrate and fatty acid metabolism were monitored by determination of changes in concentrations of low molecular weight urinary metabolites. A qualitative comparison of the NMR spectra of urine from untreated diabetic mice with those of lean littermates and literature examples revealed several abnormalities, the majority of which could be explained in terms of the non-insulin dependent diabetes syndrome exhibited by these animals. Quantitatively the most prominent was the extreme glycosuria of both young (8-12 weeks; 0.9 g glucose kg-1 h-1) and older (42 weeks; 2 g glucose kg-1 h-1) diabetic mice. This was accompanied by the excretion of a number of unassigned sugar derivatives and by ketone bodies. Administration of BRL 49653 (3 mumol kg-1) to db/db mice for 24 days reduced blood glucose concentrations to values comparable with non-diabetic lean littermates and reduced glycosuria by > 90%. BRL 49653 significantly reduced excretion of unassigned sugars, acetate, lactate, and the ketone bodies, acetoacetate, 3-D-hydroxybutyrate and acetone. The anti-diabetic efficacy of BRL 49653, assessed from the pattern of urinary metabolites, was maintained over a 36-week treatment period. These results demonstrate the value of 1H NMR to evaluate non-invasively the efficacy of novel therapeutic agents.

Repeat treatment of obese mice with BRL 49653, a new potent insulin sensitizer, enhances insulin action in white adipocytes. Association with increased insulin binding and cell-surface GLUT4 as measured by photoaffinity labeling.

(+/-)-5-([4-[2-Methyl-2(pyridylamino)ethoxy]phenyl]methyl) 2,4-thiazolidinedione (BRL 49653) is a new potent antidiabetic agent that improves insulin sensitivity in animal models of NIDDM. In C57BL/6 obese (ob/ob) mice, BRL 49653, included in the diet for 8 days, improved glucose tolerance. The half-maximal effective dose was 3 mumol/kg diet, which is equivalent to approximately 0.1 mg/kg body wt. Improvements in glucose tolerance were accompanied by significant reductions in circulating triacylglycerol, nonesterified fatty acids, and insulin. The insulin receptor number of epididymal white adipocytes prepared from obese mice treated with BRL 49653 (30 mumol/kg diet) for 14 days was increased twofold. The affinity of the receptor for insulin was unchanged. In the absence of added insulin, the rates of glucose transport in adipocytes from untreated and BRL 49653-treated obese mice were similar. Insulin (73 nmol/l) produced only a 1.5-fold increase in glucose transport in adipocytes from control obese mice, whereas after BRL 49653 treatment, insulin stimulated glucose transport 2.8-fold. BRL 49653 did not alter the sensitivity of glucose transport to insulin. The increase in insulin responsiveness was accompanied by a 2.5-fold increase in the total tissue content of the glucose transporter GLUT4. Glucose transport in adipocytes from lean littermates was not altered by BRL 49653. To establish the contribution of changes in glucose transporter trafficking to the BRL 49653-mediated increase in insulin action, the cell-impermeant bis-mannose photolabel 2-N-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]-1,3-bis-(D-mannos++ +-4-yloxy) -2-[2-3H]-propylamine was used to measure adipocyte cell-surface-associated glucose transporters.(ABSTRACT TRUNCATED AT 250 WORDS)

[[omega-(Heterocyclylamino)alkoxy]benzyl]-2,4-thiazolidinediones as potent antihyperglycemic agents.

A series of [(ureidoethoxy)benzyl]-2,4-thiazolidinediones and [[(heterocyclylamino)alkoxy]-benzyl]-2,4-thiazolidinediones was synthesized from the corresponding aldehydes. Compounds from the urea series, exemplified by 16, showed antihyperglycemic potency comparable with known agents of the type such as pioglitazone and troglitazone (CS-045). The benzoxazole 49, a cyclic analogue of 16, was a very potent enhancer of insulin sensitivity, and by modification of the aromatic heterocycle, an aminopyridine, 37, was identified as a lead compound from SAR studies. Evaluation of antihyperglycemic activity together with effects on blood hemoglobin content, to determine the therapeutic index, was performed in 8-day repeat administration studies in genetically obese C57 Bl/6 ob/ob mice. From these studies, BRL 49653 (37) has been selected, on the basis of antihyperglycemic potency combined with enhanced selectivity against reductions in blood hemoglobin content, for further evaluation.

Improved glycemic control in C57Bl/KsJ (db/db) mice after treatment with the thermogenic beta-adrenoceptor agonist, BRL 26830.

BRL 26830, (R*,R*)-(+/-)-methyl-4-(2-[(2-hydroxy-2-phenylethyl)amino]propyl)-benzoa te, is a new type of beta-adrenoceptor receptor agonist that combines antihyperglycemic and thermogenic properties. In C57Bl/KsJ db/db mice, treatment with BRL 26830 (50 mg of the hemifumarate salt/kg diet) decreased blood glucose concentration and normalized water intake. As judged by the normalization of polydipsia, BRL 26830 was effective within 2 days and the effect was maintained throughout a treatment period of up to 11 wk. Treatment of db/db mice with BRL 26830 resulted in an increase in both plasma and pancreatic insulin concentrations and a partial restoration of first-phase insulin secretion by the isolated, perfused pancreas in response to a high (16.7 mM) glucose pulse. Given acutely, BRL 26830 increased energy expenditure in both fed and fasted db/db mice. When given chronically, BRL 26830 increased significantly the dietary and thermoregulatory component of metabolic rate. It is suggested that the antidiabetic and thermogenic properties of BRL 26830 are linked and that blood glucose acts either directly or indirectly as a substrate for thermogenesis.

Effects of novel beta-adrenoceptor agonists on carbohydrate metabolism: relevance for the treatment of non-insulin-dependent diabetes.

BRL 26830A, (R*, R*)-(+/-)-methyl 4-[2-[(2-hydroxy-2-phenylethyl) amino] propyl]-benzoate, (E)-2-butenedioate (2:1) salt, is a new antihyperglycemic agent orally active in obese-hyperglycemic animal models. In C57Bl/6 ob/ob mice, BRL 26830A (1 mg/kg) given daily for periods of 14 d-6 weeks produced a marked improvement in glucose tolerance and a reduction in the fasting plasma insulin concentration. Adipocytes prepared from treated mice showed improved insulin responsiveness. In Zucker fa/fa rats, treatment with BRL 26830A (2.9 mg/kg/d for 23 d) produced improvements in both glucose tolerance and whole animal insulin sensitivity, as assessed by rate of fall of blood glucose in response to an intravenous dose of insulin. In C57Bl/KSJ db/db mice, BRL 26830A (admixed with food at 50 mg/kg diet) decreased blood glucose to values similar to those in lean mice. At the end of a 10-week treatment, BRL 26830A-treated mice had a higher plasma and pancreatic insulin content than the untreated db/db mice. In normoglycaemic rats and mice, BRL 26830A increases the plasma insulin concentration and increases glucose disposal. However, in most circumstances, there is a counteracting increase in endogenous glucose synthesis and, therefore, no change in blood glucose occurs. Improvements in glucose tolerance occur in 24-h fasted rats and mice. BRL 26830A has thermogenic activity and it is suggested that this might be linked to increased glucose utilization. Brown adipose tissue (BAT) of C57Bl/KSJ db/db mice has a reduced maximum glycolytic capacity relative to lean littermates. Treatment with BRL 26830A increased the glycolytic capacity 10-fold.