Influence of phytostanol phosphoryl ascorbate (FM-VP4) on insulin resistance,hyperglycemia, plasma lipid levels,and gastrointestinal absorption of exogenous cholesterol in Zucker (fa/fa) fatty and lean rats

The purpose of this investigation was to determine the effects of Phytostanol Phosphoryl Ascorbate (FM-VP4) on insulin resistance, hyperglycemia, plasma lipid levels, body weight, and gastrointestinal absorption of exogenous cholesterol in Zucker (fa/fa) fatty and lean rats. A group of 12 age-matched male obese (n = 6) and lean (n = 6) Zucker rats were administered 250 mg/kg twice a day (as 2% FM-VP4 in drinking water) for 30 consecutive days. Fasted blood samples prior to and following treatment were taken from all rats for glucose, lipid, insulin, and leptin determination. An oral glucose tolerance test was also carried out at the end of the treatment protocol. In addition, male obese (n = 7) and lean (n = 8) Zucker rats were coadministered a single oral gavage of [(3)H]cholesterol plus cold cholesterol with or without FM-VP4 (20 mg/kg) dissolved in Intralipid and the plasma concentration of the radiolabel was determined 10 h following the dose. FM-VP4 30-day treatment did not alter body weight, morning glucose, insulin, lipids, and leptin concentrations. There was no alteration in glucose tolerance in the nondiabetic, normoglycemic lean group; however, there was a highly significant improvement in glucose tolerance in the fatty group following FM-VP4 treatment. In addition, the insulin response to oral glucose showed no significant change in nondiabetic lean rats, whereas there was a change in the insulin secretory profile in the fatty group following FM-VP4 treatment. Furthermore, following a single oral gavage of FM-VP4 resulted in a significant decrease in the percentage of radiolabeled cholesterol absorbed. These findings suggest that FM-VP4 treatment to fatty Zucker rats could result in increased glucose responsiveness of the insulin secreting pancreatic beta cells. Furthermore, our findings suggest that FM-VP4 may only be effective presystemically. Systemic administration of FM-VP4 is warranted to determine the therapeutic potential of this effect.     

TS-071 is a novel, potent and selective renal sodium-glucose cotransporter 2 (SGLT2) inhibitor with anti-hyperglycaemic activity

BACKGROUND AND PURPOSE

The renal sodium-glucose cotransporter 2 (SGLT2) plays an important role in the reuptake of filtered glucose in the proximal tubule and therefore may be an attractive target for the treatment of diabetes mellitus. This study characterizes the pharmacological profile of TS-071 ((1S)-1,5-anhydro-1-[5-(4-ethoxybenzyl)-2-methoxy-4-methylphenyl]-1-thio-d-glucitol hydrate), a novel SGLT2 inhibitor in vitro and in vivo.

EXPERIMENTAL APPROACH

Inhibition of glucose uptake by TS-071 was studied in CHO-K1 cells stably expressing either human SGLT1 or SGLT2. Single oral dosing studies were performed in rats, mice and dogs to assess the abilities of TS-071 to increase urinary glucose excretion and to lower plasma glucose levels.

KEY RESULTS

TS-071 inhibited SGLT2 activity in a concentration-dependent manner and was a potent and highly selective inhibitor of SGLT2. Orally administered TS-071 increased urinary glucose excretion in Zucker fatty rats and beagle dogs at doses of 0.3 and 0.03 mg·kg⁻¹ respectively. TS-071 improved glucose tolerance in Zucker fatty rats without stimulating insulin secretion and reduced hyperglycaemia in streptozotocin (STZ)-induced diabetic rats and db/db mice at a dose of 0.3 mg·kg⁻¹.

CONCLUSION AND IMPLICATIONS

These data indicate that TS-071 is a potent and selective SGLT2 inhibitor that improves glucose levels in rodent models of type 1 and 2 diabetes and may be useful for the treatment for diabetes mellitus.     

Hypoglycemic activity of 1-alpha-(3,4-dimethoxyphenethylaminomethyl) -2-hydroxybenzylalcohol 1/2 fumarate (TA-078) in the mouse, rat and dog

1-alpha-(3,4-Dimethoxyphenethylaminomethyl)-2-hydroxybenzylalcohol 1/2 fumarate (TA-078) is a new hypoglycemic agent structurally different from any existing hypoglycemic drug. It depresses the rise of blood glucose when it is orally administered to glucose-loaded mice, rats and beagle dogs at minimal doses of 1, 10 and 2.5 mg/kg, respectively. In contrast with tolbutamide, TA-078 hardly affected fasting blood glucose levels in rats and dogs and only weakly reduced fasting blood glucose levels in mice. Oral administration of TA-078 to KK mice also improved glucose tolerance, while no improvement was observed in streptozotocin-diabetic rats. TA-078 elevated plasma immunoreactive insulin (IRI) levels in mice and rats soon after its oral administration. In fasted rats, TA-078 caused only a transient increase in plasma IRI but did not affect plasma immunoreactive glucagon (IRG) levels in the early phase after its administration. On the other hand, tolbutamide induced a sustained increase in plasma IRI and a transient but marked decrease in plasma IRG. In perfused rat pancreas, TA-078 stimulated insulin secretion. The stimulation by 10 micrograms/ml TA-078 in the perfusion liquid required the presence of a normal concn (5.6 mM) of glucose, whereas the same concn of tolbutamide stimulated insulin release even at a low glucose concn (2.8 mM).     

Ameliorating effect of FK614, a novel nonthiazolidinedione peroxisome proliferator-activated receptor gamma agonist, on insulin resistance in Zucker fatty rat

Effect of 3-(2,4-dichlorobenzyl)-2-methyl-N-(pentylsulfonyl)-3H-benzimidazole-5-carboxamide (FK614), a novel nonthiazolidinedione peroxisome proliferator-activated receptor (PPAR) gamma agonist, on glucose tolerance and insulin resistance in peripheral tissues and in liver using Zucker fatty rats (genetically obese and insulin-resistant) was evaluated and compared to other insulin sensitizers. FK614 (0.32, 1 and 3.2 mg/kg), two thiazolidinedione PPAR gamma agonists, rosiglitazone (0.1, 0.32, 1 and 3.2 mg/kg) and pioglitazone (1, 3.2 and 10 mg/kg), and a biguanide, metformin (320 and 1000 mg/kg), were orally administered to Zucker fatty rats once a day for 14 days. Zucker fatty rats treated with FK614 and rosiglitazone were subjected to evaluation by oral glucose tolerance test. Ameliorating effect of each compound on peripheral and hepatic insulin resistance was evaluated using a euglycemic-hyperinsulineamic clamp procedure. FK614 and rosiglitazone dose-dependently improved impaired glucose tolerance in Zucker fatty rats. In addition, FK614 dose-dependently ameliorated peripheral and hepatic insulin resistance in Zucker fatty rats, with the degree of its effect in peripheral tissues almost equivalent to that in liver when compared at each dose tested. Similar data indicating ameliorating effects on insulin resistance was obtained for rosiglitazone and pioglitazone. Metformin showed less potent effects than other insulin sensitizers and its effect in liver tended to be greater than that in peripheral tissues. These findings suggest clinical potential for FK614 as a treatment of type 2 diabetes, acting by ameliorating insulin resistance both in peripheral tissues and liver.     

Effect of the new imidazoline derivative S-22068 (PMS 847) on insulin secretion in vitro and glucose turnover in vivo in rats.

We have investigated the possible mechanisms underlying the antihyperglycaemic effect of the imidazoline derivative S-22068. In vitro, in the presence of 5 mmol/l glucose, S-22068 (100 micromol/l) induced a significant and sustained increase in insulin secretion from isolated, perifused, rat islets and a marked sensitization to a subsequent glucose challenge (10 mmol/l). S-22068 (100 micromol/l was able to antagonize the stimulatory effect of diazoxide on 86Rb efflux from preloaded islets incubated in the presence of 20 mmol/l glucose. Experiments were also performed to investigate whether S-22068 can alter glucose turnover and peripheral insulin sensitivity in vivo in mildly diabetic rats and obese, insulin resistant, Zucker rats. Neither glucose production nor individual tissue glucose utilization was modified by S-22068 in either group of rats. Similar results were obtained whether the studies were performed under basal conditions or during euglycaemic/hyperinsulinemic clamps. The results suggest that S-22068 exerts part of its antihyperglycaemic effect by promoting insulin secretion without alteration of peripheral insulin sensitivity.     

Effects of (-)-(R)-1-(p-hydroxyphenyl)-2-[3,4-dimethoxyphenethyl)amino]ethanol (TA-064), a new cardiotonic agent, on circulating parameters of carbohydrate and lipid metabolism in the rat

Effects of the new cardiotonic and selective beta 1-adrenergic agonist TA-064, (-)-(R)-1-(p-hydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino] ethanol, on circulating concentrations of glucose, lactate, free fatty acids (FFA), glycerol, cyclic AMP and the pancreatic hormones insulin (IRI) and glucagon (IRG) were examined in rats. TA-064, administered orally or intraperitoneally at the dose of 10 mg/kg (ca. 50 times the therapeutic dose) or higher, caused a slight transient rise followed by a persistent lowering of blood glucose concentrations, but it did not affect blood lactate levels at all. The same treatment with TA-064 elevated the concentrations of blood FFA, glycerol and plasma IRI and IRG. These changes induced by TA-064 were inhibited by pretreatment with propranolol (a non-selective beta-adrenergic antagonist) and practolol (a selective beta 1-adrenergic antagonist). The non-selective beta-adrenergic agonist isoproterenol and the selective beta 2-adrenergic agonist terbutaline elevated both blood glucose and lactate when administered intraperitoneally. They also brought about sustained rises in blood glycerol and plasma IRI, but only transiently increased the plasma IRG level. The cardiotonic agent prenalterol, claimed to be a selective beta 1-agonist, elevated blood glucose, lactate, and glycerol only slightly, and plasma IRI significantly, but it had no effect on plasma IRG. The cardiotonic agents dobutamine and amrinone also elevated blood glucose. Thus, TA-064 is unique among the beta-adrenergic and other cardiotonic agents in that it produces sustained hypoglycemia while it has no lactacidemic effect. Since this hypoglycemic action of TA-064 was always preceded by a rise in plasma IRI and abolished in streptozotocin-diabetic rats, we conclude that increased secretion of pancreatic insulin and the lack of hyperglycemic action are responsible for the hypoglycemia by high doses of TA-064.     

Stimulation of insulin secretion and improvement of glucose tolerance in rat and dog by the P2y-purinoceptor agonist, adenosine-5'-O-(2-thiodiphosphate).

1. In vivo effect of a P2y-purinoceptor agonist, adenosine-5'-O-(2-thiodiphosphate) (ADP beta S), on insulin secretion and glycaemia were studied both in rats and dogs. 2. In anaesthetized rats, i.v. administered ADP beta S (0.2 mg kg-1) produced an insulin response dependent on the nutritional state of the animals, since we observed only a transient increase in overnight-fasted rats and a sustained insulin secretion followed by a reduction in plasma glucose levels in fed rats. During an i.v. glucose tolerance test, ADP beta S enhanced insulin release and thus increased the glucose disappearance rate. 3. In anaesthetized fasted dogs, i.v. administered ADP beta S (0.1 mg kg-1) increased pancreaticoduodenal insulin output and slightly decreased blood glucose levels. 4. In conscious fasted dogs, orally administered ADP beta S (0.1 mg kg-1) transiently increased insulinemia and punctually reduced glycaemia. Furthermore, during an oral glucose tolerance test, orally administered ADP beta S at the same dose markedly enhanced insulin secretion and consequently reduced the hyperglycaemia. 5. In conclusion, the P2y-agonist, ADP beta S, is a potent insulin secretagogue in vivo, improves glucose tolerance and is effective after oral administration. Thus, the P2y-purinoceptors of the beta cell may be a target for new antidiabetic drugs.     

DNA microarray analysis of white adipose tissue from obese (fa/fa) Zucker rats treated with a beta3-adrenoceptor agonist, KTO-7924.

We aimed to examine the effects of KTO-7924 (beta3-adrenoceptor agonist) on lipid metabolism and mRNA expressions in retroperitoneal white adipose tissue (RP WAT) in obese (fa/fa) Zucker rats using DNA microarray. Oral KTO-7924 for 28 days significantly decreased RP WAT weight, plasma triglyceride, free fatty acid, and insulin, and improved insulin resistance in oral glucose tolerance tests. In RP WAT of KTO-7924-treated rats, DNA microarray analysis revealed specifically enhanced mRNA expressions of uncoupling protein 1 (UCP1) and cytochrome c oxidase subunit VIII-H (COX8H), which are reportedly highly expressed in brown adipose tissue (BAT). Since these mRNA expression levels in RP WAT were significantly lower in obese (fa/fa) Zucker rats than in lean Zucker rats, these genes may be important in lipid metabolism. Our results imply that in obese (fa/fa) Zucker rats, continuous stimulation of beta3-adrenoceptors by KTO-7924 causes BAT-like adipocytes to appear in RP WAT, and improves lipid metabolism.     

Sulfonyliminoimidazolidines, a new class of oral hypoglycemic agents. 3. Hypoglycemic activity and mode of action of 1-[p-[2-(crotonylamino)-ethyl]-phenylsulfonyl]-3-cyclohexyl-2-imino- imidazolidine (CGP 11 112)

1-[p-[2-(Crotonylamino)-ethyl]-phenylsulfonyl]-3-cyclohexyl-2-imino- imidazolidine (CGP 11 112) is a representative of a new class of oral hypoglycemic agents. It lowers blood glucose in normal animals and in streptozocin (streptozotocin)-diabetic rats. In normal mice, rats and dogs the hypoglycemic effect is more potent (range 3-30 times) and has a shorter duration than that of tolbutamide. CGP 11 112 increases plasma insulin after oral administration in normal animals and stimulates release of insulin in perifused rat islets in vitro (sulfonylurea-like effect). In streptozocin-diabetic rats CGP 11 112 decreases blood glucose with a potency comparable to that of phenformin. In contrast to phenformin, CGP 11 112 does not increase blood lactate in diabetic rats or inhibit intestinal absorption of glucose. An effect of CGP 11 112 on gluconeogenesis and glycogenolysis could not be demonstrated. It is suggested that the hypoglycemic activity in streptozocin-diabetic rats may be due to stimulation of glucose efflux from the circulation. In vitro, CGP 11 112 inhibits glucose oxidation and lipolysis in isolated rat fat cells.     

Antidiabetic activity of white skinned sweet potato (Ipomoea batatas L.) in obese Zucker fatty rats

Antidiabetic effects of white skinned sweet potato (Ipomoea batatas L.) (WSSP) and troglitazone, an insulin sensitizer, were investigated. Hyperinsulinemia in Zucker fatty rats was reduced by 23%, 26%, 60% and 50%, respectively, 3, 4, 6 and 8 weeks after starting the oral administration of WSSP. Similar results were obtained with troglitazone. In the glucose tolerance test after 7 weeks of treatment, increases in blood glucose levels after glucose loading were inhibited by the administration of WSSP. Glucose tolerance was also improved. Blood triacylglyceride (TG) and free fatty acid (FFA) lactate levels were lowered by the oral administration of WSSP. Similar effects on blood insulin, lipid and lactate levels were observed after the administration of troglitazone. Body weight gain increased in the troglitazone group, but not in the WSSP group, compared to the control group. In histological examinations of the pancreas of Zucker fatty rats, remarkable regranulation of pancreatic islet B-cells was observed in the WSSP and troglitazone groups after 8 weeks of treatment. These results suggest that WSSP shows remarkable antidiabetic activity and improves the abnormality of glucose and lipid metabolism by reducing insulin resistance.     

Effects of BRL 26830, a novel beta-adrenoceptor agonist, on glucose tolerance, insulin sensitivity and glucose turnover in Zucker (fa/fa) rats

Zucker fa/fa rats exhibit glucose intolerance in comparison with lean Fa/? littermates. A single acute dose of BRL 26830 (2.9 mg/kg p.o.) improved glucose tolerance in Fa/? littermates but exacerbated glucose intolerance in the fa/fa rats. This latter effect occurred in spite of an increase in the plasma insulin concentration. Chronic treatment of Zucker fa/fa rats with BRL 26830 (2.9 mg/kg) for 24 days or more produced a significant reduction in the area under the glucose tolerance curve. In addition, the glucose decay rate (k%) following the administration of insulin intravenously was significantly increased in the BRL 26830-treated rats suggesting that tissue insulin sensitivity was increased. Glucose turnover measurements show that chronic treatment of Zucker fa/fa rats with BRL 26830 produced a significant increase in the rate of glucose utilization integrated over a 3 hr period, but this increase was, in part, off-set by an increase in the endogenous rate of glucose production. The ultimate fate of the extra glucose that is metabolized is not known but it is suggested that it might be used to support the thermogenic response that is also activated by BRL 26830.     

重组人胰高血糖素类多肽-1(7-36)对化学致糖尿病模型动物的降血糖作用

目的　本文研究了重组人胰高血糖素类多肽 1(7 36 )[rhGLP 1(7 36 ) ]对化学所致糖尿病模型动物的降血糖和促胰岛素分泌作用。方法　对四氧嘧啶型糖尿病小鼠及链脲霉素型糖尿病大鼠皮下注射不同剂量的rhGLP 1,分别于给药 4天后采血 ,收取血清 ,测定血糖及胰岛素值。结果　四氧嘧啶型糖尿病小鼠皮下注射 4 0、80 μg·kg-1rhGLP 1后 ,血糖值显著下降 (P <0 0 1) ,而 2 0 μg·kg-1剂量组则无显著性改变 ;链脲霉素型糖尿病大鼠皮下注射 2 8、5 6 μg·kg-1rhGLP 1后 ,血糖值显著下降 (P <0 0 5、P <0 0 1) ,而 14 μg·kg-1剂量组则无显著性改变。结论　rhGLP 1对实验动物部分 β细胞破坏的胰岛仍有促分泌胰岛素及降糖作用     

(2S,4S)-4-Fluoro-1-{[(2-hydroxy-1,1-dimethylethyl)amino]acetyl}-pyrrolidine-2-carbonitrile monobenzenesulfonate (TS-021) is a selective and reversible dipeptidyl peptidase IV inhibitor

The incretin hormone glucagon-like peptide-1 (GLP-1) has significant roles in the regulation of postprandial glucose metabolism, and the active form of GLP-1 is rapidly degraded by dipeptidyl peptidase (DPP)-IV. Therefore, DPP-IV inhibition is a promising approach for the treatment of type 2 diabetes. In the present study, we investigated the character of a DPP-IV inhibitor, TS-021, (2S, 4S)-4-fluoro-1-{[(2-hydroxy-1,1-dimethylethyl)amino]acetyl}-pyrrolidine-2-carbonitrile monobenzenesulfonate both in vitro and in vivo. TS-021 inhibits DPP-IV activity in human plasma with an IC(50) value of 5.34nM. In kinetics experiments, TS-021 had a relatively higher dissociation rate constant, with a k(off) value of 1.09×10(-3)s, despite exhibiting a potent human plasma DPP-IV inhibition activity with a K(i) value of 4.96nM. TS-021 exhibited significant inhibition selectivity against DPP-8 (>600 fold), DPP-9 (>1200 fold) and other peptidases examined (>15,000 fold). In normal rats, dogs and monkeys, a single oral dose of TS-021 exhibited favorable pharmacokinetic profiles. In Zucker fatty (fa/fa) rats, a rat model of obesity and impaired glucose tolerance, the oral administration of TS-021 resulted in the suppression of plasma DPP-IV activity and an increase in the active form of GLP-1. Furthermore, TS-021 exhibited a significant improvement in glucose tolerance by increasing the plasma insulin level during oral glucose tolerance tests at doses of 0.02-0.5mg/kg. These results suggest that TS-021 is a selective and reversible dipeptidyl peptidase IV inhibitor and has excellent characteristics as an oral anti-diabetic agent for postprandial hyperglycemia in patients with impaired glucose tolerance or type 2 diabetes.     

Effect of a series of novel sulphonylthioureas on glucose tolerance in the obese fa/fa Zucker rat

1. The recent development of a series of novel KATP channel modulators, namely sulphonylthioureas and sulphonylureas, is thought to make improvements in potency and tissue selectivity compared with current sulphonylureas, such as glibenclamide, which shares a similar structure to the novel compounds. 2. These novel compounds were first examined for their effect on hyperglycaemia and glucose tolerance during an oral glucose tolerance test following 5 days administration in the lean fa/- and obese fa/fa Zucker rat (a model of insulin resistance). Comparisons with present antidiabetic agents, metformin and glibenclamide were performed. 3. Several compounds showed improvements in glucose tolerance compared with control and the primary structural prerequisites for the maintenance of this activity were investigated. Of most interest was compound 3-15 ((N-[(4-methylphenylsulphonyl]-N'-(2-ethoxypyrid-4-yl)thiourea; 0.1 mg/kg per day), which significantly improved glucose tolerance following 5 days administration in the fa/fa Zucker rat. This paralleled the improvement seen in metformin (300 mg/kg per day)-treated fa/fa rats, but compound 3-15 was up to 3000-fold more potent than metformin. 4. Obese fa/fa Zucker rats were then treated with compound 3-15 for 28 days to determine whether glycaemic control could be maintained over the longer term. 5. Compound 3-15 showed a significant improvement in glucose clearance and reduction in insulin concentration following 28 days treatment during an intravenous glucose tolerance test compared with untreated rats, without any change in the rate of weight gain. 6. The novel sulphonylthiourea 3-15 appears to improve glucose clearance during acute and chronic treatment in the fa/fa Zucker rat with no effect on the rate of weight gain. It is thought that compound 3-15 may be eliciting its actions by improving insulin sensitivity, but its effects on insulin secretion are still to be elucidated.     

Effects of dual angiotensin-converting enzyme and neutral endopeptidase 24-11 chronic inhibition by mixanpril on insulin sensitivity in lean and obese Zucker rats

The aim of this study was to examine the effects of chronic (8-day) oral treatment with the dual angiotensin-converting enzyme (ACE) and neutral endopeptidase 24-11 (NEP) inhibitor mixanpril (25 mg/kg twice a day), compared with the ACE inhibitor captopril (25 mg/kg twice a day), on whole body insulin-mediated glucose disposal in young (10-week) and old (19-week) obese Zucker rats (ZOs). Moreover, the effects of chronic mixanpril administration on femoral blood flow at rest and during an insulin infusion were assessed. In the young ZOs, mixanpril decreased the glucose response during an IV glucose tolerance test more effectively than did captopril (-49 and -30%, respectively, p < 0.05). Incremental glucose area under the curve in mixanpril-treated ZOs was then no longer different from that observed in vehicle-treated lean rats (1,592 +/- 175 and 1, 470 +/- 104 mg/dl x min, respectively). The beneficial effects resulting from mixanpril or captopril administration were observed in ZOs but not in lean littermates. In the old ZOs, mixanpril induced higher glucose infusion rates to maintain euglycemia than did captopril during a hyperinsulinemic euglycemic clamp test (+92 and +35%, respectively, p < 0.001). However, the glucose infusion rates in mixanpril-treated ZOs remained much lower than that observed in vehicle-treated lean rats (9.4 +/- 0.7 mg/kg/min vs 28.6 +/- 1.0 mg/kg/min, p < 0.001). Mixanpril did not affect resting femoral vascular bed hemodynamics but restored the femoral blood flow response to insulin infusion. In conclusion, in ZOs, chronic dual ACE/NEP inhibition improves whole body insulin-mediated glucose disposal more effectively than does ACE inhibition alone. This beneficial effect seems to be restricted to conditions of insulin resistance and not directly linked to the improvement in the femoral blood flow response to insulin.     

Improved metabolic status and insulin sensitivity in obese fatty (fa/fa) Zucker rats and Zucker Diabetic Fatty (ZDF) rats treated with the thiazolidinedione,MCC-555

1. We examined the effect of chronic (21 days) oral treatment with the thiazolidinedione, MCC-555 ((±)-5-[{6-(2-fluorbenzyl)-oxy-2-naphy}methyl]-2,4-thiazolidinedione) on metabolic status and insulin sensitivity in obese (fa/fa) Zucker rats and Zucker Diabetic Fatty (ZDF) rats which display an impaired glucose tolerance (IGT) or overt diabetic symptoms, respectively.
2. MCC-555 treatment to obese Zucker rats (10 and 30 mg kg⁻¹) and diabetic ZDF rats (10 mg kg⁻¹) reduced non-esterified fatty acid concentrations in both rat strains and reduced plasma glucose and triglyceride concentrations in the obese Zucker rats. Liver glycogen concentrations were significantly increased by chronic MCC-555 treatment in both obese Zucker rats (30 mg kg⁻¹ day⁻¹) and diabetic ZDF rats (10 mg kg⁻¹ day⁻¹), as compared with vehicle-treated lean and obese rats and there was a significant increase in hepatic glycogen synthase activity in MCC-555-treated diabetic ZDF rats as compared to vehicle-treated controls.
3. During a euglycaemic hyperinsulinaemic clamp, MCC-555-treated obese Zucker rats and diabetic ZDF rats required significantly higher glucose infusion rates to maintain stable glucose concentrations (2.01±0.19 mg min⁻¹ and 6.42±1.03 mg min⁻¹, respectively) than vehicle-treated obese controls (0.71±0.17 mg min⁻¹ and 2.09±0.71 mg min⁻¹; P<0.05), demonstrating improved insulin sensitivity in both Zucker and ZDF rats. MCC-555 treatment also enhanced insulin-induced suppression of hepatic glucose production in ZDF rats as measured using infusions of [6-³H]-glucose under clamp conditions.
4. In conclusion, we have demonstrated that MCC-555 improves metabolic status and insulin sensitivity in obese Zucker and diabetic ZDF rats. MCC-555 may prove a useful compound for alleviating the metabolic disturbances and IGT associated with insulin resistance in man.

     

Effects of a glucosidase inhibitor (acarbose, BAY g 5421) on the development of obesity and food motivated behavior in Zucker (fafa) rats

BAY g 5421 (acarbose) inhibits carbohydrate digestion in the gut, thereby reducing the rate of glucose absorption. This experiment tested whether long term administration of acarbose to developing Zucker "fatty" (fafa) rats would, by reducing several lipogenic factors, attenuate lipid deposition and reduce the hyperphagia and increased food motivated behavior of these animals. From 7 to 20 weeks of life groups of fatty and lean (FaFa) control rats were fed 0, 20 or 40 mg acarbose/100 g maintenance diet (45% carbohydrate, 35% fat, 20% protein calories), while an additional fatty and lean group were pair-fed to respective 40 mg acarbose groups. Lean groups fed acarbose exhibited dose dependent reductions of body weight, insulin, triglycerides, retroperitoneal and epididymal pad weight, adipocyte size, LPL activity/cell (retroperitoneal pad only), and lipid deposition both in total grams of fat and as a percentage of carcass weight. Fatty groups fed acarbose exhibited dose dependent reductions of insulin, blood glucose, retroperitoneal pad weight, and, at one of the two doses used, significantly lowered body weight, (40 mg), triglycerides (20 mg) and cholesterol (20 mg). However, acarbose-fed fatty groups failed to show significant reductions of adipocyte size, number or LPL activity/cell in retroperitoneal and epididymal fat pads, and maintained their obese body composition, on a percentage basis, at levels not significantly different from that of the 0 mg fatty control group. Acarbose administration led to an initial dose dependent reduction of food intake in both genotypes, which persisted for the lean groups. Fatties fed the 20 mg dose showed a gradual tendency (ns) towards increased daily intake, lever pressed at elevated rates for food pellets, and refed at faster rates following fasting. Fatties fed the 40 mg dose maintained their daily intake at fatty control levels, did not lever press at elevated rates, and showed significantly reduced refeeding following fasting. The 40 mg fatty and both lean acarbose treated groups had decreased sucrose solution preference. Possible bases for these differing effects of the drug on feeding behavior by the groups are considered.     

Toxicological evaluation of 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-(methylaminocarbonyl)hydrazine (VNP40101M), a novel alkylating agent with potential antitumor activity, with intravenous administration in rats and dogs

These studies investigated the toxicological effects of 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-(methylaminocarbonyl) hydrazine, VNP40101M, a novel alkylating antitumor agent, in animals. Sprague-Dawley rats (2-10/sex/time point at each dose) and Beagle dogs (1-3/sex/time point at each dose) were treated with VNP40101M (0 [vehicle], 1, 3, 10, and 20 mg/kg in rats and 0, 0.3, 1, and 3 mg/kg in dogs), given intravenously (IV, bolus via the tail or slow push via the cephalic or saphenous vein, respectively) once daily for 5 consecutive days. Clinical signs, mortality, body weight, clinical pathology, gross necropsy, organ weights, and histopathology were evaluated for as long as 43 days in rats and 50 days in dogs. In rats, the toxic doses were found to be at 10 and 20 mg/kg, which induced mainly pulmonary toxicity and mortality. The pulmonary toxicity was reflected by an increase in lung weight; clear, pink or red fluid within the thoracic cavity observed at necropsy; and histopathological evidence of alveolar edema, vascular congestion, alveolar histiocytosis, and vascular thrombi. Although some of these effects were observed in rats treated with 3 mg/kg, the incidence was low (approximately 7%-30%) and may be reversible (based on the time-dependent reduction in the magnitude of lung weight increases). Therefore, the maximum tolerated dose (MTD, or the maximum dose that did not induce significant toxicity or induced reversible toxicity) was > or = 3 mg/kg. VNP40101M at 1 mg/kg did not induce any toxicity, other than low incidence of alveolar edema (2/30 rats), and increased incidences of capillary ectasis/congestion and alveolar histocytosis (2-6/30 rats vs. 1/30-36 in control rats). Therefore, the low effect level (LOEL) is considered to be 1 mg/kg in rats when given IV for 5 days. In dogs, LOEL, MTD, and toxic dose levels were comparable (based on a body weight/surface area conversion) to those in rats, except for some gastrointestinal (GI) effects (i.e., red lesion in the ileum) observed at 0.3 mg/kg (equivalent to 1 mg/kg, or similar to the LOEL in rats) and the associated effects (slight body weight loss and inappetence). For dogs treated with 1 mg/kg (equivalent to approximately 3 mg/kg, or MTD, in rats), VNP40101M induced the same GI effects seen in dogs treated with 0.3 mg/kg of VNP40101M. Additionally, a transient reduction in white blood cell counts was also observed. Three mg/kg (equivalent to approximately 10 mg/kg, or toxic dose level, in rats) was toxic to dogs, as reflected by the poor clinical condition of these dogs, which subsequently required euthanasia. In conclusion, VNP40101M, when given IV once daily for 5 consecutive days, has a LOEL of 1 mg/kg, a MTD of 3 mg/kg, and toxic doses at > or = 10 mg/kg in rats. The primary toxicity of VNP40101M was pulmonary toxicity and mortality. Based on an interspecies body weight/surface area conversion, VNP40101M had comparable LOEL (0.3 mg/kg), MTD (1 mg/kg), and toxic doses (> or = 3 mg/kg) in dogs, except that dogs appeared to be more sensitive to the GI effects of VNP40101M.     

Actions of Fenfluramine on Glucose Uptake in Vitro and in Vivo

Abstract Fenfluramine stimulates the glucose uptake of the isolated hemi-diaphragm from normal and streptozotocin diabetic rats in the presence of insulin. The drug does not cause an increased storage of glycogen. During hind leg perfusion of the dog fenfluramine stimulated peripheral glucose uptake. No increase in lactate or in free fatty acids release was observed during prolonged infusions of the drug. Fenfluramine caused an improvement of glucose tolerance in normal glucose-primed rats. A single dose of fenfluramine significantly lowered the blood glucose levels in streptozotocin diabetic rats and in diabetic dogs treated with insulin. Prolonged treatment with fenfluramine of streptozotocin diabetic rats had no significant effect on blood glucose levels. Additional treatment for one week of insulin dependent diabetic dogs with small non-anorexic doses of fenfluramine resulted in slightly decreased blood glucose levels. The dogs could not be maintained on fenfluramine alone (without insulin).     

Actions of fenfluramine on glucose uptake in vitro and in vivo.

Fenfluramine stimulates the glucose uptake of the isolated hemidiaphragm from normal and streptozotocin diabetic rats in the presence of insulin. The drug does not cause an increased storage of glycogen. During hind leg perfusion of the dog fenfluramine stimulated peripheral glucose uptake. No increase in lactate or in free fatty acids release was observed during prolonged infusions of the drug. Fenfluramine caused an improvement of glucose tolerance in normal glucose-primed rats. A single dose of fenfluramine significantly lowered the blood glucose levels in streptozotocin diabetic rats and in diabetic dogs treated with insulin. Prolonged treatment with fenfluramine of streptozotocin diabetic rats had no significant effect on blood glucose levels. Additional treatment for one week of insulin dependent diabetic dogs with small non-anorexic doses of fenfluramine resulted in slightly decreased blood glucose levels. The dogs could not be maintained on fenfluramine alone (without insulin).