Effect of initial combination therapy with sitagliptin, a dipeptidyl peptidase-4 inhibitor, and pioglitazone on glycemic control and measures of ß-cell function in patients with type 2 diabetes.

AIM/HYPOTHESIS: To assess the safety and efficacy of initial combination therapy with sitagliptin and pioglitazone compared with pioglitazone monotherapy in drug-naïve patients with type 2 diabetes. METHODS: A total of 520 patients were randomised to initial combination therapy with sitagliptin 100 mg q.d. and pioglitazone 30 mg q.d. or pioglitazone 30 mg q.d. monotherapy for 24 weeks. RESULTS: Initial combination therapy with sitagliptin and pioglitazone led to a mean reduction from baseline in A1C of -2.4% compared with -1.5% for pioglitazone monotherapy (p<0.001). Mean reductions from baseline were greater in patients with a baseline A1C≥10% (-3.0% with combination therapy vs. -2.1% with pioglitazone monotherapy) compared with patients with a baseline A1C<10% (-2.0% with combination therapy vs. -1.1% with pioglitazone monotherapy). Sixty percent of patients in the combination therapy group vs. 28% in the pioglitazone monotherapy group had an A1C of <7% at week 24 (p<0.001). Fasting plasma glucose decreased by -63.0 mg/dl (-3.5 mmol/l) in the combination therapy group compared with -40.2 mg/dl (-2.2 mmol/l) for pioglitazone monotherapy (p<0.001), and 2-h post meal glucose decreased by -113.6 mg/dl (-6.3 mmol/l) with combination therapy compared with -68.9 mg/dl (-3.8 mmol/l) for pioglitazone monotherapy (p<0.001). Measures related to ß-cell function also improved significantly with combination therapy compared with pioglitazone monotherapy. Combination therapy was generally well-tolerated compared with pioglitazone monotherapy, with similar incidences of hypoglycemia (1.1% and 0.8%, respectively), gastrointestinal adverse events (5.7% and 6.9%, respectively), and oedema (2.7% and 3.5%, respectively). CONCLUSION/INTERPRETATION: Initial combination therapy with sitagliptin and pioglitazone substantially improved glycemic control and was generally well-tolerated compared with pioglitazone monotherapy.

A clinical trial assessing the safety and efficacy of the CB1R inverse agonist taranabant in obese and overweight patients: low-dose study.

OBJECTIVE: To evaluate the weight loss efficacy, safety and tolerability of taranabant, a CB1R inverse agonist, in obese and overweight patients. DESIGN: Multicenter, double-blind, randomized, placebo-controlled study. SUBJECTS: Patients >or=18 years old, BMI 27-43 kg m(-2), were randomized to placebo (n=209) or taranabant 0.5 mg (n=207), 1 mg (n=208) or 2 mg given orally once daily (n=417) for 52 weeks. MEASUREMENTS: Key efficacy measurements included body weight (BW), waist circumference (WC), lipid endpoints and glycemic endpoints. RESULTS: Based on a last observation carried forward analysis of the all-patients-treated population, mean change in BW for taranabant 0.5, 1, and 2 mg and placebo was -5.4, -5.3, -6.7 and -1.7 kg, respectively (P<0.001 for all doses vs placebo). The proportions of patients who lost at least 5 and 10% of their baseline BW at week 52 were significantly higher for all taranabant doses vs placebo (P<0.001 for all doses). Reductions in WC, percentage of body fat, and triglycerides were significant for taranabant 2 mg and in triglycerides for taranabant 1 mg vs placebo. There was no effect of taranabant vs placebo on other lipid or glucose-related endpoints. Incidences of adverse experiences classified in the gastrointestinal (diarrhea and nausea), nervous system (dizziness/dizziness postural), psychiatric-related (irritability and anger/aggression) and vascular (flushing/hot flush) organ systems were higher and statistically significant in the taranabant 2-mg group compared with the placebo group. Irritability was higher and statistically significant in all taranabant groups compared with the placebo group. CONCLUSION: All three doses of taranabant-induced clinically meaningful and statistically significant weight loss. Incidences of adverse experiences in organ systems known to express CB1R were higher in taranabant groups.

A clinical trial assessing the safety and efficacy of taranabant, a CB1R inverse agonist, in obese and overweight patients: a high-dose study.

OBJECTIVE: To evaluate the efficacy, safety and tolerability of taranabant in obese and overweight patients. DESIGN: Double-blind, randomized, placebo-controlled study. SUBJECTS: Patients were >or=18 years old, with body mass index of 27-43 kg m(-2), and 51% with metabolic syndrome (MS) randomized to placebo (N=417) or taranabant 2 mg (N=414), 4 mg (N=415) or 6 mg (N=1256) for 104 weeks. MEASUREMENTS: Key efficacy measurements included body weight, waist circumference (WC), lipid and glycemic end points. RESULTS: On the basis of risk/benefit assessments, the 6-mg dose was discontinued during year 1 (patients on 6 mg were down-dosed to 2 mg or placebo) and the 4-mg dose was discontinued during year 2 (patients on 4 mg were down-dosed to 2 mg). Changes from baseline in body weight at week 52 (all-patients-treated population, last observation carried forward analysis) were -2.6, -6.6 and -8.1 kg, respectively, for placebo and taranabant 2 and 4 mg (both doses P<0.001 vs placebo). For patients who completed year 1, changes from baseline in body weight at week 104 were -1.4, -6.4 and -7.6 kg for placebo and taranabant 2 and 4 mg, respectively (both doses P<0.001 vs placebo). The proportions of patients at weeks 52 and 104 who lost at least 5 and 10% of their baseline body weight were significantly higher and the proportions of patients who met criteria for MS were significantly lower for taranabant 2 and 4 mg vs placebo. The incidence of adverse experiences classified in the gastrointestinal, nervous, psychiatric, cutaneous and vascular organ systems were generally observed to be dose related with taranabant vs placebo. CONCLUSION: Taranabant at the 2- and 4-mg dose was effective in achieving clinically significant weight loss over 2 years and was associated with dose-related increases in adverse experiences. On the basis of these and other data, an assessment was made that the overall safety and efficacy profile of taranabant did not support its further development for the treatment of obesity.

Efficacy and safety of sitagliptin monotherapy compared with voglibose in Japanese patients with type 2 diabetes: a randomized, double-blind trial.

OBJECTIVE: To compare the efficacy and safety of sitagliptin (a dipeptidyl peptidase-4 inhibitor) and voglibose (an alpha-glucosidase inhibitor) monotherapy in Japanese patients with type 2 diabetes who have inadequate glycaemic control (HbA1c > or =6.5% and <10.0%) on diet and exercise. METHODS: In a multi-center, randomized, double-blind, parallel-group study, 319 patients were randomized (1:1) to 12-week treatment with sitagliptin 50 mg once daily or voglibose 0.2 mg thrice daily before meals. The primary analysis assessed whether sitagliptin was non-inferior to voglibose in lowering HbA1c. RESULTS: After 12 weeks, sitagliptin was non-inferior to voglibose for HbA1c-lowering efficacy. Furthermore, sitagliptin was superior to voglibose, providing significantly greater reductions in HbA1c from baseline [least squares mean changes in HbA1c [95% confidence intervals (CI)] = -0.7% (-0.8 to -0.6) and -0.3% (-0.4 to -0.2), respectively; between-group difference = -0.4% (-0.5 to -0.3), p < 0.001]. Sitagliptin was also superior to voglibose on other key efficacy endpoints, including change from baseline in 2-h postmeal glucose (-2.8 mmol/l vs. -1.8 mmol/l, p < 0.001) and fasting plasma glucose (-1.1 mmol/l vs. -0.5 mmol/l, p < 0.001). After 12 weeks, the incidences of clinical adverse experiences (AEs), drug-related AEs and gastrointestinal AEs in the sitagliptin group (48.5, 10.4 and 18.4%, respectively) were significantly (p < 0.05) lower than those in the voglibose group (64.7, 26.3 and 34.6%, respectively). The incidences of hypoglycaemia, serious AEs and discontinuations due to AEs were low and similar in both groups. CONCLUSIONS: In Japanese patients with type 2 diabetes, once-daily sitagliptin monotherapy showed greater efficacy and better tolerability than thrice-daily voglibose over 12 weeks.

Efficacy and safety of sitagliptin and metformin as initial combination therapy and as monotherapy over 2 years in patients with type 2 diabetes.

AIM: To assess the 104-week efficacy and safety of sitagliptin and metformin as initial combination therapy and as monotherapy in patients with type 2 diabetes and inadequate glycaemic control (HbA(1c) 7.5-11%) on diet and exercise. METHODS: This study was a 50-week, double-blind extension of a 54-week, randomized, double-blind, factorial study of the initial combination of sitagliptin and metformin, metformin monotherapy and sitagliptin monotherapy (104 weeks total duration). Patients assigned to active therapy in the 54-week base study remained on those treatments in the extension study: sitagliptin 50 mg b.i.d. + metformin 1000 mg b.i.d. (higher dose combination), sitagliptin 50 mg b.i.d. + metformin 500 mg b.i.d. (lower dose combination), metformin 1000 mg b.i.d. (higher dose), metformin 500 mg b.i.d. (lower dose) and sitagliptin 100 mg q.d. Patients randomized to receive the sequence of placebo/metformin were switched, in a blinded manner, from placebo to metformin monotherapy uptitrated to 1000 mg b.i.d. beginning at week 24 and remained on higher dose metformin through the extension. RESULTS: Amongst patients who entered the extension study without having initiated glycaemic rescue therapy, least-squares mean changes in HbA(1c) from baseline at week 104 were -1.7% (higher dose combination), -1.4% (lower dose combination), -1.3% (higher dose), -1.1% (lower dose) and -1.2% (sitagliptin). The proportions of patients with an HbA(1c) <7% at week 104 were 60% (higher dose combination), 45% (lower dose combination), 45% (higher dose), 28% (lower dose) and 32% (sitagliptin). Fasting and postmeal measures of glycaemic control and beta-cell function improved in all groups, with glycaemic responses generally maintained over the 104-week treatment period. The incidence of hypoglycaemia was low across all groups. The incidences of gastrointestinal adverse experiences were generally lower in the sitagliptin group and similar between the metformin monotherapy and combination groups. CONCLUSIONS: Initial combination therapy with sitagliptin and metformin and monotherapy with either drug alone provided substantial and sustained glycaemic improvements and were well tolerated over 104 weeks in patients with type 2 diabetes.

Efficacy and safety of sitagliptin when added to insulin therapy in patients with type 2 diabetes.

OBJECTIVE: To evaluate the efficacy and tolerability of sitagliptin when added to insulin therapy alone or in combination with metformin in patients with type 2 diabetes. METHODS: After a 2 week placebo run-in period, eligible patients inadequately controlled on long-acting, intermediate-acting or premixed insulin (HbA1c > or = 7.5% and < or = 11%), were randomised 1:1 to the addition of once-daily sitagliptin 100 mg or matching placebo over a 24-week study period. The study capped the proportion of randomised patients on insulin plus metformin at 75%. Further, the study capped the proportion of randomised patients on premixed insulin at 25%. The metformin dose and the insulin dose were to remain stable throughout the study. The primary endpoint was HbA1c change from baseline at week 24. RESULTS: Mean baseline characteristics were similar between the sitagliptin (n = 322) and placebo (n = 319) groups, including HbA1c (8.7 vs. 8.6%), diabetes duration (13 vs. 12 years), body mass index (31.4 vs. 31.4 kg/m(2)), and total daily insulin dose (51 vs. 52 IU), respectively. At 24 weeks, the addition of sitagliptin significantly (p < 0.001) reduced HbA1c by 0.6% compared with placebo (0.0%). A greater proportion of patients achieved an HbA1c level < 7% while randomised to sitagliptin as compared with placebo (13 vs. 5% respectively; p < 0.001). Similar HbA1c reductions were observed in the patient strata defined by insulin type (long-acting and intermediate-acting insulins or premixed insulins) and by baseline metformin treatment. The addition of sitagliptin significantly (p < 0.001) reduced fasting plasma glucose by 15.0 mg/dl (0.8 mmol/l) and 2-h postmeal glucose by 36.1 mg/dl (2.0 mmol/l) relative to placebo. A higher incidence of adverse experiences was reported with sitagliptin (52%) compared with placebo (43%), due mainly to the increased incidence of hypoglycaemia (sitagliptin, 16% vs. placebo, 8%). The number of hypoglycaemic events meeting the protocol-specified criteria for severity was low with sitagliptin (n = 2) and placebo (n = 1). No significant change from baseline in body weight was observed in either group. CONCLUSION: In this 24-week study, the addition of sitagliptin to ongoing, stable-dose insulin therapy with or without concomitant metformin improved glycaemic control and was generally well tolerated in patients with type 2 diabetes.

A one-year study to assess the safety and efficacy of the CB1R inverse agonist taranabant in overweight and obese patients with type 2 diabetes.

AIM: To evaluate the efficacy and safety of taranabant in overweight and obese patients with type 2 diabetes mellitus (T2DM). METHODS: This was a multicenter, double-blind, randomized, placebo-controlled study in overweight and obese patients with T2DM (ages > or = 18 and < or = 75 years) with a BMI > or = 27 kg/m(2) and < or = 43 kg/m(2) and HbA1c > or =7.0 and < or = 10.0%, who were either not on an antihyperglycaemic agent or on a stable dose of metformin (> or = 1500 mg/day). After a 2-week placebo run-in, patients were randomized to placebo (N = 156) or taranabant 0.5-mg (N = 155), 1-mg (N = 157), or 2-mg (N = 155) once daily for 52 weeks. Primary efficacy endpoints were changes from baseline in body weight (BW) and HbA1c at Week 36, with results at Week 52 being key secondary endpoints. RESULTS: In the all-patients-treated population, using a last-observation-carried-forward analysis, reductions in BW were -2.5, -3.7, -4.5 and -5.1 kg at Week 36 and -2.4, -4.0, -4.6 and -5.3 kg at Week 52 in the placebo, 0.5-, 1- and 2-mg groups, respectively (all doses significant vs. placebo at both time points). The proportion of patients who lost > or = 5 and > or = 10% of their baseline BW was significantly greater in the 1- and 2-mg groups vs. placebo at Week 36 and all taranabant groups vs. placebo at Week 52. Reductions in HbA1c were -0.40, -0.47, -0.68 and -0.71% at Week 36 and -0.30, -0.43, -0.65 and -0.64% at Week 52, in the placebo, 0.5-, 1- and 2-mg groups, respectively (1- and 2-mg doses significant vs. placebo at both time points). After 52 weeks, the incidences of adverse experiences classified in the gastrointestinal (diarrhoea, nausea, vomiting), nervous system-related (dizziness, sensory-related), and psychiatric (irritability, depression-related) organ systems were numerically higher or statistically significantly higher in all taranabant groups compared with the placebo group. CONCLUSIONS: After 36 and 52 weeks, treatment with taranabant at the 1- and 2-mg doses led to clinically significant weight loss and improvement in glycaemic parameters in overweight and obese patients with T2DM that was associated with dose-related increases in adverse experiences. Based on these data and data from other Phase III clinical studies, it was determined that the overall safety and efficacy profile of taranabant did not support further development for the treatment of obesity.

Safety and efficacy of treatment with sitagliptin or glipizide in patients with type 2 diabetes inadequately controlled on metformin: a 2-year study.

OBJECTIVES: To evaluate the 2-year safety and efficacy of adding sitagliptin or glipizide to ongoing metformin in patients with type 2 diabetes. METHODS: Patients who were on a stable dose of metformin (> or = 1500 mg/day) for at least 8 weeks were randomised in a double-blind manner to receive either sitagliptin 100 mg q.d. (N = 588) or glipizide 5 mg/day (up-titrated up to 20 mg/day based upon prespecified glycaemic criteria) (N = 584). The efficacy analysis assessed the change in HbA(1c) from baseline using the per-protocol (PP) population. RESULTS: For the PP cohort, mean baseline HbA(1c) was 7.3% in both groups. After 2 years, the least squares (LS) mean change in HbA(1c) from baseline [95% confidence interval (CI)] was -0.54% (-0.64, -0.45) with sitagliptin (n = 248) and -0.51% (-0.60, -0.42) with glipizide (n = 256). The rise in HbA(1c) from week 24 to week 104 [i.e. coefficient of durability (COD)] was smaller with sitagliptin [COD (95% CI) 0.16%/year (0.10, 0.21)] compared with glipizide [0.26%/year (0.21, 0.31)]. The proportion of patients with an HbA(1c)< 7% was 63% and 59% with sitagliptin and glipizide, respectively. The beta-cell responsiveness to a meal challenge was maintained with sitagliptin and decreased with glipizide. The proportion of patients who reported hypoglycaemia was 5% with sitagliptin and 34% with glipizide [difference in proportions (95% CI) = -29% (-33, -25)]. Relative to baseline, sitagliptin was associated with weight loss (-1.6 kg) compared with weight gain (+0.7 kg) with glipizide. CONCLUSION: In patients with type 2 diabetes, adding sitagliptin to metformin monotherapy improved glycaemic control over 2 years, similar to the glucose-lowering efficacy observed with adding glipizide, but with greater durability and generally better maintenance of beta-cell function. Sitagliptin was generally well tolerated with a lower risk of hypoglycaemia and weight loss compared with weight gain observed with glipizide.

Insulin receptors in hepatocytes: postreceptor events mediate down regulation.

Down regulation of the insulin receptor of primary cultures of rat hepatocytes occurs in the presence of insulin and several agents with insulin-like activity, which act through or distal to the insulin receptor. These findings indicate that the interaction of insulin with its specific binding site is not in itself sufficient to down-regulate this receptor and that one or more steps subsequent to this interaction are necessary. Thus, down regulation may be a complex biological response to insulin, and if a cell were resistant to this effect of insulin, our data may explain how target cells from a patient or animal can have a normal number of receptors in the presence of increased concentrations of circulating insulin.

Insulin receptor: role in the resistance of human obesity to insulin.

Large adipocytes from obese subjects have similar receptor numbers and affinities for insulin as small adipocytes from subjects of normal weight. These results indicate that the insulin insensitivity of large fat cells from obese humans occurs after the insulin-receptor interaction and might be explained by either a dilution of receptors over the cell surface or by alterations in intracellular metabolism.

Effects of once-daily sitagliptin on 24-h glucose control following 4 weeks of treatment in Japanese patients with type 2 diabetes mellitus.

The aim of the study was to assess the efficacy/safety of once- (100 mg q.d.) or twice-daily (50 mg b.i.d.) sitagliptin 100 mg/day in Japanese patients with type 2 diabetes (T2DM). In this randomized, double-blind study, 80 patients with inadequate glycemic control (HbA1c=6.5-10%; FPG

Safety and efficacy of sitagliptin in patients with type 2 diabetes and chronic renal insufficiency.

OBJECTIVE: To assess the safety of sitagliptin in patients with type 2 diabetes and moderate [creatinine clearance (CrCl) > or =30 to <50 ml/min] or severe renal insufficiency [CrCl <30 ml/min including patients with end-stage renal disease (ESRD) on dialysis]. The efficacy of sitagliptin in this patient population was also assessed. METHODS: In a 54-week, randomized, double-blind, parallel-group study, patients with baseline glycosylated haemoglobin A(1c) (HbA(1c)) values of 6.5-10% were allocated (2:1) to sitagliptin (for 54 weeks) or the sequence of placebo (for 12 weeks) followed by active treatment with glipizide (for 42 weeks). To achieve plasma concentrations similar to those observed in patients with normal renal function treated with 100 mg sitagliptin once daily, patients with moderate renal insufficiency were allocated to receive sitagliptin 50 mg once daily and patients with severe renal insufficiency to receive 25 mg once daily. Glipizide treatment was initiated at 2.5 or 5 mg/day and uptitrated to a maximum of 20 mg/day. RESULTS: Patients (N = 91) with a mean baseline HbA(1c) value of 7.7% (range: 6.2-10.3%) were randomized to sitagliptin (n = 65) or placebo (n = 26). After 12 weeks, the mean change [95% confidence interval (CI)] from baseline in HbA(1c) was -0.6% (-0.8, -0.4) in the sitagliptin group compared with -0.2% (-0.4, 0.1) in the placebo group [between-group difference (95% CI) = -0.4% (-0.7, -0.1)]. At 54 weeks, patients continuously treated with sitagliptin had a mean change (95% CI) from baseline in HbA(1c) of -0.7% (-0.9, -0.4). The overall incidence of adverse experiences was generally similar between groups. Between-group differences in incidences of specific clinical adverse experiences were generally small; however, the proportion of patients for whom hypoglycaemia was reported was lower in the sitagliptin group (4.6%) compared with the placebo/glipizide group (23.1%). Consistent with the high mortality risk in this patient population, there were six deaths during this 54-week study [5 of 65 patients (7.7%) in the sitagliptin group and 1 of 26 patients (3.8%) in the placebo/glipizide group]; no death was considered by the investigator to be drug related. The overall incidences of drug-related and serious adverse experiences and discontinuations because of adverse experiences were generally similar between groups. CONCLUSIONS: In this study, sitagliptin was generally well tolerated and provided effective glycaemic control in patients with type 2 diabetes and moderate to severe renal insufficiency, including patients with ESRD on dialysis.

Glucocorticoid-induced insulin resistance: the importance of postbinding events in the regulation of insulin binding, action, and degradation in freshly isolated and primary cultures of rat hepatocytes.

We have recently proposed that "down regulation" of the insulin receptor may be one of the many biological responses of a cell to insulin. In an attempt to further explore this hypothesis we have studied insulin action, binding, and degradation in freshly isolated hepatocytes from rats rendered insulin resistant by the administration of dexamethasone, 1.0 mg/kg every other day, for 1 and 4 wk, and in dexamethasone-treated (0.1 muM for 24 h) primary cultures of hepatocytes from normal rats. Dexamethasone treatment for 1 and 4 wk resulted in significant hyperinsulinemia and euglycemia when compared with age- and weight-matched control animals. Freshly isolated hepatocytes from rats treated with dexamethasone for 1 wk bound less insulin than cells from control animals. This decrease in insulin binding was reflected in a decrease in the total number of cellular insulin receptors upon solubilization of the cells. Insulin action was evaluated by the ability of insulin to stimulate the uptake of alpha-aminoisobutyric acid. The basal rate of aminoisobutyrate uptake in freshly isolated hepatocytes was enhanced by 1 wk of dexamethasone treatment, and although there was an apparent shift to the right in the dose-response curve for insulin-stimulated aminoisobutyrate uptake, at no insulin concentration was there a significant difference in the uptake by hepatocytes from control and dexamethasone-treated animals. This was true whether expressed as a percentage or absolute increment above basal. Insulin degradation was enhanced in hepatocytes from animals treated with dexamethasone for 1 wk but could not account for the observed changes in insulin binding. Hepatocytes from animals treated with dexamethasone for 4 wk were resistant to insulin with regard to aminoisobutyrate uptake, yet both insulin binding and insulin degradation returned to the levels observed in hepatocytes from control animals. Primary cultures of hepatocytes from normal rats exposed to dexamethasone, 0.1 muM, in vitro for 24 h were similar to hepatocytes from rats treated with dexamethasone for 4 wk in that they were insulin resistant with regard to aminoisobutyrate uptake and had normal to increased insulin binding. Insulin degradation was also similar. These cells were resistant to the ability of insulin, 0.1 muM, to down regulate its receptor whereas parallel cultures treated with insulin in the absence of dexamethasone had a 52% decrease in insulin binding. These data indicate that hepatocytes that are insulin responsive respond to in vivo hyperinsulinemia by a decrease in the number of insulin receptors and by increased insulin degradation. Hepatocytes rendered resistant to insulin both in vivo and in vitro are resistant to these effects of insulin. These studies emphasize the importance of postbinding events in the modulation of insulin binding, action, and degradation, and support the hypothesis that down regulation of the hepatocyte insulin receptor is one of the many biological actions of insulin. They also help explain how a cell can be insulin resistant and have a normal number of insulin binding sites in the presence of hyperinsulinemia.

Total and resting energy expenditure in obese women reduced to ideal body weight.

Obesity could be due to excess energy intake or decreased energy expenditure (EE). To evaluate this, we studied 18 obese females (148 +/- 8% of ideal body weight [IBW], mean +/- SD) before and after achieving and stabilizing at IBW for at least 2 mo and a control group of 14 never obese females (< 110% of IBW or < 30% fat). In the obese, reduced obese, and never obese groups, the percent of body fat was 41 +/- 4%, 27 +/- 4%, and 25 +/- 3%; total energy expenditure (TEE) was 2704 +/- 449, 2473 +/- 495, and 2259 +/- 192 kcal/24 h; while resting metabolic rate was 1496 +/- 169, 1317 +/- 159, and 1341 +/- 103 kcal/24 h, respectively. 15 obese subjects who withdrew from the study had a mean initial body composition and EE similar to the subjects who were successful in achieving IBW. In 10 subjects followed for at least one year after stabilizing at IBW there was no significant relationship between the deviation from predicted TEE at IBW and weight regain. These studies indicate that, in a genetically heterogeneous female population, neither the propensity to become obese nor to maintain the obese state are due to an inherent metabolic abnormality characterized by a low EE.

Overexpression of Glut4 protein in muscle increases basal and insulin-stimulated whole body glucose disposal in conscious mice.

The effect of increased Glut4 protein expression in muscle and fat on the whole body glucose metabolism has been evaluated by the euglycemic hyperinsulinemic clamp technique in conscious mice. Fed and fasting plasma glucose concentrations were 172 +/- 7 and 78 +/- 7 mg/dl, respectively, in transgenic mice, and were significantly lower than that of nontransgenic littermates (208 +/- 5 mg/dl in fed; 102 +/- 5 mg/dl in fasting state). Plasma lactate concentrations were higher in transgenic mice, (6.5 +/- 0.7 mM in the fed and 5.8 +/- 1.0 mM in fasting state) compared with that of non-transgenic littermates (4.7 +/- 0.3 mM in the fed and 4.2 +/- 0.5 mM in fasting state). In the fed state, the rate of whole body glucose disposal was 70% higher in transgenic mice in the basal state, 81 and 54% higher during submaximal and maximal insulin stimulation. In the fasting state, insulin-stimulated whole body glucose disposal was also higher in the transgenic mice. Hepatic glucose production after an overnight fast was 24.8 +/- 0.7 mg/kg per min in transgenic mice, and 25.4 +/- 2.7 mg/kg per min in nontransgenic mice. Our data demonstrate that overexpression of Glut4 protein in muscle increases basal as well as insulin-stimulated whole body glucose disposal. These results suggest that skeletal muscle glucose transport is rate-limiting for whole body glucose disposal and that the Glut4 protein is a potential target for pharmacological or genetic manipulation for treatment of patients with non-insulin-dependent diabetes mellitus.

Insulin regulates apolipoprotein B turnover and phosphorylation in rat hepatocytes.

Our laboratory has previously shown that insulin inhibits the secretion of newly-synthesized and immunoreactive apo B from rat hepatocytes. We have also shown that apo B is secreted as a phosphoprotein and that phosphorylation is increased in hypoinsulinemic nonketotic diabetes. The present studies were conducted to determine whether the ability of insulin to inhibit apo B secretion is related to alterations in apo B turnover and whether insulin itself affects apo B phosphorylation. Pulse-chase studies with [35S]methionine in primary cultures of hepatocytes from normal rats in the absence and presence of insulin show that the secretion of apo B100 and apo B48 are inhibited by insulin and that this inhibition may be due in part to enhanced intracellular degradation. In addition, there is a second intracellular apo B48 pool which is not insulin regulated or degraded. In experiments in which hepatocytes were incubated with [32P]orthophosphate, insulin decreased 32P incorporation into apo B100 (42%) with only small effects on apo B48 (11%). The small insulin effect on apo B48 may relate to an insulin-insensitive apo B48 intracellular pool. These studies show that insulin can affect the intracellular turnover, secretion, degradation, and phosphorylation of apo B and emphasize the differential regulation of apo B100 and apo B48 with regard to these parameters in rat liver.

Effects of nonketotic streptozotocin diabetes on apolipoprotein B synthesis and secretion by primary cultures of rat hepatocytes.

The effects of hypoinsulinemic nonketotic streptozotocin diabetes on hepatic apo B synthesis and secretion was studied in primary cultures of rat hepatocytes. Diabetic rats were characterized by their significantly elevated serum glucose, apo B, and triglyceride levels, while serum insulin levels were less than a third of normal. Serum transminase activities of diabetic rats were significantly elevated when compared with control rats, which was attributed to an increase in liver transaminase activity in diabetic rats. The pattern of enzyme activities of hepatocytes reflected that observed in livers of donor rats and the pattern was retained by primary cultures of hepatocytes over the culture period. Hepatocytes from diabetic rats secreted only one third of the apo B secreted by hepatocytes from control rats, which was determined by monoclonal immunoassay of rat total apo B. Decreases in secretion were confirmed by measurement of secretory [35S]methionine-labeled lipoprotein apo B radioactivity. The decreased apo B content of media of hepatocytes from diabetic rats was not due to increased apo B catabolism since hepatocytes from diabetic rats were shown to degrade less lipoprotein-apo B than hepatocytes from normal rats in control experiments. In addition, the apo B content of detergent-solubilized hepatocytes from diabetic rats was significantly less than that of hepatocytes from control rats. These results suggest that insulin is necessary for normal hepatic apo B synthesis and secretion and that the hyperlipidemia associated with hypoinsulinemia in vivo is primarily of intestinal origin.

The hepatic glucocorticoid domain: evidence for early and late hormone-mediated changes in the synthesis of individual protein gene products.

Studies were conducted to determine the extent of rapidly evolving effects of glucocorticoids on the transcriptional activity of individual hepatocyte genes through comparisons of the relative rates of synthesis of the more than 3000 protein gene products that are resolved in giant two-dimensional separatory gels. During the first 20 h in primary culture normal hepatocytes displayed substantial spontaneous changes in over 80 proteins. One effect of an added glucocorticoid, dexamethasone, was to retard or reverse the progression of roughly half of these. However, such long-term hormone treatment also caused 27 inductions and 26 repressions, many of which occurred in proteins that do not change spontaneously. Some of these coincide with the previously reported glucocorticoid domain of hepatoma cells. In contrast to such long-term changes, short-term (4 h) incubation with dexamethasone induced 10 proteins and repressed 6 others. Five of these early hormone inductions and all of the early repressions were maintained or enhanced by 20 h. However, the remaining five early glucocorticoid inductions appeared to be transient, since by 16-20 h the effects were either markedly reduced or absent. These results show the existence of an early glucocorticoid domain, qualitatively different from that seen at later times, which may be more representative of the primary steroid hormone responses.

Potentiation of insulin action by a sulfonylurea in primary cultures of hepatocytes from normal and diabetic rats.

Although sulfonylureas have been used extensively in the treatment of non-insulin-dependent (type II) diabetes, controversy exists as to whether these agents act primarily by increasing insulin secretion or by enhancing insulin action. To determine whether sulfonylureas potentiate insulin action in the liver, we evaluated the ability of the sulfonylurea tolazamide to affect insulin-sensitive lipogenesis utilizing primary cultures of hepatocytes prepared from both normal and nonketotic streptozotocin-diabetic rats. Hepatocytes were cultured for 16 h in serum-free media with no additions, tolazamide alone (0.3 mg/ml), or insulin (10(-10) to 10(-7)M) in the absence and presence of tolazamide. Following culture, lipogenesis and specific insulin binding were assessed. Dose-dependent increases in lipogenesis were found in hepatocytes from both normal and diabetic rats after the chronic exposure to insulin. In hepatocytes from diabetic rats, the basal and the maximal insulin-stimulated rates of lipogenesis were only 27% and 13% of normal, respectively, establishing this as a model of hepatic insulin resistance. In the presence of tolazamide, significant potentiation of insulin action was found in hepatocytes from normal and diabetic rats although hepatocytes from diabetic animals remained relatively resistant to insulin when compared with those from nondiabetic animals. While exposure to tolazamide increased insulin responsiveness in both groups of cells, no changes in insulin sensitivity (ED50) were observed. Tolazamide significantly increased insulin binding (12%) in hepatocytes from normal rats cultured in the absence of insulin, but no alterations in insulin binding were found under incubation conditions in which tolazamide potentiated insulin action. These results give the first direct evidence for an insulin-dependent action of a sulfonylurea on the liver from both normal and diabetic rats and indicate that the enhancement of insulin responsiveness occurs through postbinding mechanisms.

Insulin-induced alterations in insulin binding and insulin action in primary cultures of rat hepatocytes.

The exposure of primary cultures of hepatocytes to insulin. 10(-8) M, for 16 h results in a decrease in high affinity insulin binding with no alterations in lower affinity binding. This is reflected in a decrease in the sensitivity, but normal responsiveness, of cultured hepatocytes to the acute effect of insulin on the uptake of aminoisobutyric acid. The shift in sensitivity, however, can only be partially explained by the decrease in insulin binding. With regard to lipid synthesis, hepatocytes cultured in the presence of insulin, 10(-8) M, are normally sensitive and hyperresponsive to the acute effects of insulin. These data indicate that the insensitivity or resistance of a given tissue to insulin may be specific for the biologic response being evaluated, that postbinding events may be more important than alterations in insulin binding in determining both the sensitivity and responsiveness of a tissue to insulin, and that generalizations concerning the sensitivity or responsiveness of a tissue to insulin based on binding data alone may be unwarranted.