Inhibitory effect of hyperglycemia on insulin-induced Akt/protein kinase B activation in skeletal muscle.

To determine the molecular mechanism underlying hyperglycemia-induced insulin resistance in skeletal muscles, postreceptor insulin-signaling events were assessed in skeletal muscles of neonatally streptozotocin-treated diabetic rats. In isolated soleus muscle of the diabetic rats, insulin-stimulated 2-deoxyglucose uptake, glucose oxidation, and lactate release were all significantly decreased compared with normal rats. Similarly, insulin-induced phosphorylation and activation of Akt/protein kinase B (PKB) and GLUT-4 translocation were severely impaired. However, the upstream signal, including phosphorylation of the insulin receptor (IR) and insulin receptor substrate (IRS)-1 and -2 and activity of phosphatidylinositol (PI) 3-kinase associated with IRS-1/2, was enhanced. The amelioration of hyperglycemia by T-1095, a Na(+)-glucose transporter inhibitor, normalized the reduced insulin sensitivity in the soleus muscle and the impaired insulin-stimulated Akt/PKB phosphorylation and activity. In addition, the enhanced PI 3-kinase activation and phosphorylation of IR and IRS-1 and -2 were reduced to normal levels. These results suggest that sustained hyperglycemia impairs the insulin-signaling steps between PI 3-kinase and Akt/PKB, and that impaired Akt/PKB activity underlies hyperglycemia-induced insulin resistance in skeletal muscle.

Improved diabetic syndrome in C57BL/KsJ-db/db mice by oral administration of the Na(+)-glucose cotransporter inhibitor T-1095.

1. The therapeutic effects of an orally active inhibitor of Na(+)-glucose cotransporter (SGLT), T-1095 (a derivative of phlorizin; 3-(benzo[b]furan-5-yl)-2',6'-dihydroxy-4'-methylpropiophenone 2'-O-(6-O-methoxycarbonyl-beta-D-glycopyranoside)) were examined in C57BL/KsJ-db/db (db/db) mice, a genetic animal model of obese type 2 diabetes. 2. The higher renal SGLT activity in db/db mice than normoglycaemic C57BL/KsJ-db/+m (db/+m) mice may support the rationale for using an SGLT inhibitor in the treatment regimen for type 2 diabetes. Both T-1095 and its metabolite, T-1095A, which had approximately 10 times more potency, effectively inhibited renal SGLT activity of these mice in vitro. 3. Single oral administration of T-1095 (10, 30, 100 mg kg(-1), p.o.) to db/db mice caused a dose-dependent reduction in blood glucose levels and a concomitant increase in glucose excretion into urine. In contrast, T-1095 only slightly affected blood glucose levels in db/+m mice. 4. Chronic administration of T-1095 (0.1% w w(-1) pellet chow, for 12 weeks) decreased blood glucose and haemoglobin A(1C) levels, and improved glucose intolerance in db/db mice. The age-related decrease in plasma insulin levels was markedly inhibited and there was a 2.5 fold increase of insulin content in the pancreas of T-1095-treated db/db mice. Food consumption was not changed, while impaired body weight gain was ameliorated by T-1095 treatment. 5. Both the development of albuminuria and the expansion of glomerular mesangial area in db/db mice were significantly suppressed by chronic T-1095 treatment, indicating the prevention of the progression of diabetic nephropathy. 6. These results demonstrate that the SGLT inhibitor T-1095 is able to improve the metabolic abnormalities and inhibit the development of diabetic complications in db/db mice. Thus, T-1095 can be used for therapy of type 2 diabetic patients.

Amiloride-sensitive pressure-induced myogenic contraction in rat cerebral artery.

The inhibitory action of amiloride on the pressure-induced contraction was assessed in isolated rat cerebral artery. The artery was mounted in an arteriograph, and the change in intracellular Ca2+ concentration ([Ca2+]i) and vessel diameter were simultaneously measured. The contractile response elicited by intraluminal pressurization was independent of endothelium, i.e. myogenic in nature, and abolished by nicardipine, a Ca2+ antagonist or by removal of extracellular Ca2+, and was potentiated by 25 mM KCl. Cyclopiazonic acid and thapsigargin, inhibitors of the Ca2+-ATPase pump of the sarcoplasmic reticulum, and a protein kinase C inhibitor calphostin C did not suppress the pressure-induced contraction. Amiloride, a putative stretch-activated cation channel blocker, attenuated with an IC50 (50% inhibitory concentration) of about 3 microM the increase in [Ca2+]i and contractile activity in response to pressure, whereas the drug showed no apparent effect on the contraction produced by high KCl or 9,11-dideoxy-11alpha,9alpha-epoxymethano prostaglandin F2alpha (U46619). Furthermore, amiloride (100 microM) did not significantly affect intracellular pH in the artery. In spite of its multiple pharmacological actions, it seems possible that amiloride is a useful alternative tool at the cellular or tissue level to study the mechanotransduction mechanisms involved in the pressure-induced contraction in rat cerebral artery.

T-1095, a renal Na+-glucose transporter inhibitor, improves hyperglycemia in streptozotocin-induced diabetic rats.

The effect of T-1095, an inhibitor of renal glucose reabsorption, on hyperglycemia and the expression of Na+-glucose cotransporters (SGLTs) and facilitative glucose transporter 2 (GLUT2) in streptozotocin (STZ)-induced diabetic rats was examined. There was an elevation of blood glucose, hemoglobin A1c (HbA1c), kidney weight, and urinary excretion of both glucose and albumin in STZ rats. Administration of 0.03% and 0.1% (wt/wt diet) T-1095 to STZ rats for 4 weeks improved the hyperglycemia and dose-dependently decreased HbA1c. Moreover, treatment with 0.1% (wt/wt diet) T-1095 in STZ rats for 8 weeks not only reduced blood glucose and HbA1c, levels but also prevented the elevation of urinary albumin levels and kidney weight and the development of epithelial vacuolation. The expression of renal SGLT2, a major glucose transporter in the kidney, was not different in normal, STZ, and T-1095-treated STZ rats. In contrast, the elevated renal GLUT2 level in STZ rats was suppressed by T-1095. These data suggest that T-1095 improves hyperglycemia by suppressing the renal reabsorption of glucose, which results in a suppression of the development of functional and histological changes and abnormal expression of GLUT2 in the kidney.

Hyperglycemia contributes insulin resistance in hepatic and adipose tissue but not skeletal muscle of ZDF rats.

To determine the contribution of hyperglycemia to the insulin resistance in various insulin-sensitive tissues of Zucker diabetic fatty (ZDF) rats, T-1095, an oral sodium-dependent glucose transporter (SGLT) inhibitor, was administered by being mixed into food. Long-term treatment with T-1095 lowered both fed and fasting blood glucose levels to near normal ranges. A hyperinsulinemic euglycemic clamp study that was performed after 4 wk of T-1095 treatment demonstrated partial recovery of the reduced glucose infusion rate (GIR) in the T-1095-treated group. In the livers of T-1095-treated ZDF rats, hepatic glucose production rate (HGP) and glucose utilization rate (GUR) showed marked recovery, with almost complete normalization of reduced glucokinase/glucose-6-phosphatase (G-6-Pase) activities ratio. In adipose tissues, decreased GUR was also shown to be significantly improved with a normalization of insulin-induced GLUT-4 translocation. In contrast, in skeletal muscles, the reduced GUR was not significantly improved in response to amelioration of hyperglycemia by T-1095 treatment. These results suggest that the contribution of hyperglycemia to insulin resistance in ZDF rats is very high in the liver and considerably elevated in adipose tissues, although it is very low in skeletal muscle.

Antidiabetic effect of T-1095, an inhibitor of Na(+)-glucose cotransporter, in neonatally streptozotocin-treated rats.

3-(Benzo[b]furan-5-yl)-2', 6'-dihydroxy-4'-methylpropiophenone-2'-O-(6-O-methoxycarbonyl)-bet a-D -glucopyranoside (T-1095) is a derivative of phlorizin, a potent inhibitor of Na(+)-glucose cotransporters. We determined the antidiabetic effect of T-1095 in neonatally streptozotocin-treated diabetic rats. Orally administered T-1095 is metabolized to an active form, 3-(benzo[b]furan-5-yl)-2', 6'-dihydroxy-4'-methylpropiophenone-2'-O-beta-D-glucopyranoside (T-1095A), which inhibits renal Na(+)-glucose cotransporters as potently as phlorizin in vitro. A single oral administration of T-1095 (30 and 100 mg/kg, p.o.) markedly lowered blood glucose levels with a concomitant increase in urinary glucose excretion; whereas the effect on blood glucose levels in non-diabetic rats was minimal. Continuous administration of T-1095 to diabetic rats for 6 weeks (0.1% in diet) improved not only hyperglycemia, but also the elevation of plasma free fatty acid and plasma ketone body levels. In addition, oral glucose tolerance testing clearly illustrated the improvement of glucose tolerance and insulin secretion with T-1095. In fact, amelioration of impaired insulin sensitivity in diabetic rats was demonstrated by the increase of whole-body and skeletal-muscle insulin-mediated glucose utilization with normalization of muscle glucose transporter (GLUT)4 content, and decrease of the hepatic glucose production rate. Consequently, polyuria and glucosuria were also improved in the T-1095-treated group. Therefore, T-1095 has a therapeutic potential as a means of ameliorating abnormal glucose metabolism via diminished glucose toxicity.

Antihyperglycemic effect of T-1095 via inhibition of renal Na+-glucose cotransporters in streptozotocin-induced diabetic rats.

T-1095, a derivative of phlorizin, is an orally active inhibitor of Na+-glucose cotransporter (SGLT). We investigated the acute antihyperglycemic effect of T-1095 in streptozotocin-induced diabetic rats (STZ rats). T-1095 and its metabolite T-1095A inhibited the SGLT activity in brush border membranes prepared from kidneys of both normal and STZ rats, but the latter agent was approximately 10 times more potent than the former. Single oral administration of T-1095 (30-100 mg/kg) dose-dependently induced glycosuria in normal rats. The fed glucose levels in STZ rats were dose-dependently suppressed by single oral administration of T-1095 (3-100 mg/kg), whereas there was only marginal hypoglycemic effect in normal rats. Since there was no effect on blood glucose in nephrectomized STZ rats, inhibition of renal glucose reabsorption rather than intestinal glucose absorption mainly contributes to the antihyperglycemic effect of T-1095. In conclusion, T-1095 is the first orally active agent which has an acute antihyperglycemic action in the absence of endogenous insulin secretion with a low risk of hypoglycemia and has therapeutic potential for treatment of diabetes mellitus.

Correction of hyperglycemia and insulin sensitivity by T-1095, an inhibitor of renal Na+-glucose cotransporters, in streptozotocin-induced diabetic rats.

We investigated the effects of T-1095 (3-(benzo[b]furan-5-yl)-2',6'-dihydroxy-4'-methylpropiophenone 2'-O-(6-O-methoxycarbonyl)-beta-D-glucopyranoside), an orally active inhibitor of Na+-glucose cotransporter, on hyperglycemia and insulin resistance in skeletal muscle of streptozotocin (STZ)-induced diabetic rats. Chronic (4 weeks) administration of T-1095 as food admixture (0.01 -0.1% wt/wt) suppressed the blood glucose level without affecting the food intake and body weight. In addition, the reduced 2-deoxyglucose uptake and lactate release in the soleus muscle of STZ rat was ameliorated by chronic treatment of T-1095. These data suggest that T-1095 improves insulin sensitivity in skeletal muscle through correction of hyperglycemia and has novel therapeutic potential for treatment of diabetes mellitus through removing glucose toxicity.

Hyperglycemia impairs the insulin signaling step between PI 3-kinase and Akt/PKB activations in ZDF rat liver.

Akt/PKB activation is reportedly essential for insulin-induced glucose metabolism in the liver. During the hypoinsulinemic and hyperglycemic phase in the Zucker diabetic fatty (ZDF) rat liver, insulin-induced phosphorylations of the insulin receptor (IR) and insulin receptor substrate (IRS)-1/2 were significantly enhanced. Similarly, phosphatidylinositol (PI) 3-kinase activities associated with IRS-1/2 were markedly increased in ZDF rat liver compared with those in the control lean rat liver. However, interestingly, insulin-induced phosphorylation and kinase activation of Akt/PKB were severely suppressed. The restoration of normoglycemia by sodium-dependent glucose transporter (SGLT) inhibitor to ZDF rats normalized elevated PI 3-kinase activation and phosphorylation of IR and IRS-1/2 to lean control rat levels. In addition, impaired insulin-induced Akt/PKB activation was also normalized. These results suggest that chronic hyperglycemia reduces the efficiency of the activation step from PI 3-kinase to Akt/PKB kinase and that this impairment is the molecular mechanism underlying hyperglycemia-induced insulin resistance in the liver.

T-1095, an inhibitor of renal Na+-glucose cotransporters, may provide a novel approach to treating diabetes.

T-1095A and T-1095 are synthetic agents derived from phlorizin, a specific inhibitor of Na+-glucose cotransporters (SGLTs). Unlike phlorizin, T-1095 is absorbed into the circulation via oral administration, is metabolized to the active form, T-1095A, and suppresses the activity of SGLTs in the kidney. Orally administered T-1095 increases urinary glucose excretion in diabetic animals, thereby decreasing blood glucose levels. Indeed, the postprandial hyperglycemia after a meal load was shown to be suppressed by this compound in streptozotocin (STZ)-induced diabetic rats. With long-term T-1095 treatment, both blood glucose and HbA1c levels were reduced in STZ-induced diabetic rats and yellow KK mice. In addition, there was amelioration of abnormal carbohydrate metabolism, i.e., hyperinsulinemia and hypertriglyceridemia, and of the development of microalbuminuria, in yellow KK mice. Thus, T-1095 may be a useful antidiabetic drug, providing a novel therapeutic approach for diabetes.

Na(+)-glucose cotransporter (SGLT) inhibitors as antidiabetic agents. 4. Synthesis and pharmacological properties of 4'-dehydroxyphlorizin derivatives substituted on the B ring.

In our studies of Na(+)-glucose cotransporter (SGLT) inhibitors as antidiabetic agents, a series of novel 4'-dehydroxyphlorizin derivatives substituted on the B ring was prepared and their effects on urinary glucose excretion were evaluated in rats. Introduction of only a small alkyl group at the 4'-position increased the activity, and 3-(benzo¿bfuran-5-yl)-2',6'-dihydroxy-4'-methylpropiophenone 2'-O-beta-D-glucopyranoside (4) showed the most potent effect. To overcome hydrolysis of compound 4 by beta-glucosidase in the digestive tract, the OH groups on the glucose moiety of compound 4 were modified. Three prodrugs (5, 42, and 55) were more potent than the parent compound 4 by oral administration, and finally 3-(benzo¿bfuran-5-yl)-2',6'-dihydroxy-4'-methylpropiophenone 2'-O-(6-O-methoxycarbonyl-beta-D-glucopyranoside) (5) was selected as a new promising candidate. Compound 5 was metabolized mainly by liver esterase to the active form (4), which was about 10 times more potent than 5 in inhibiting SGLT. In oral glucose tolerance test in db/db mice, compound 5 dose-dependently suppressed the elevation of glucose levels. Single administration of 5 reduced hyperglycemia concurrently with increase of glucose excretion into urine in diabetic KK-A(y) mice. Furthermore, compound 5 suppressed the elevation of blood glucose levels but did not lower it below the normal level even in fasted conditions in KK-A(y) mice. Additionally, long-term treatment with 5 dose-dependently reduced hyperglycemia and HbA1c in KK-A(y) mice. These pharmacological data strongly suggest that compound 5 has a therapeutic potential in the treatment of NIDDM.

Stretch-induced contraction of rabbit isolated pulmonary artery and the involvement of endothelium-derived thromboxane A2.

1. The mechanism of stretch-induced contraction of the intrapulmonary artery of rabbit was studied with special regard to the endothelium-dependence and production of prostanoids. 2. Isolated intrapulmonary artery of rabbits in ring form produced contraction when stretched slowly up to 180% of its initial muscle length (= 100%) at a rate of 0.44 mm s-1, with a stimulus period of 5 min. 3. The stretch-induced contraction was attenuated by the mechanical removal of the endothelium, inhibitors of cyclo-oxygenase such as aspirin and indomethacin, [1S-[1 alpha,2 alpha (Z),3 alpha,4 alpha]]-7-[3-[[2-[(phenylamino)carbonyl] hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-y1]-5-heptenoic acid (SQ 29,548), which is a thromboxane A2/prostaglandin H2 receptor antagonist, or by ozagrel, an inhibitor of thromboxane A2 synthase. 4. Biochemical assay indicated that the production of thromboxane B2, a stable metabolite of thromboxane A2, was increased 17 times in response to stretch only when the endothelium was intact. The production of thromboxane B2 was also inhibited by aspirin or ozagrel. 5. The production of 6-keto prostaglandin F1 alpha, a stable metabolite of prostacyclin, was also increased in response to stretch in the preparation with intact endothelium. However, ozagrel showed no apparent effect on the production of 6-keto prostaglandin F1 alpha. 6. These results suggest that a mechanical stimulus like stretch can act on endothelial cells of rabbit pulmonary artery to cause contraction by activation of arachidonic acid metabolism via the cyclooxygenase pathway and subsequent release of thromboxane A2 and/or an increase in the ratio of thromboxane A2/prostacyclin.

[Practical use of mortality statistics and mass examination results by health workers in the local authority of the community].

In Kochi prefecture, the prefectural health service bureau tabulates both mortality statistics and mass examination results for each community and the tabulated report is sent annually to public health services staff in each local authority. While recognizing its limitations, methods of how to use the annual report are demonstrated. For example comparison of the mortality statistics and the mass examination results of the male population of A town, which is administered by Susaki Health Center, to that of the combined male population of all the towns administered by the health center shows that although the mortality rate for cerebrovascular disease for the A town-male population had been much higher than that of the combined male population in the early 1980's, the difference disappeared in the late 1980's. On the other hand, prevalence of systolic hypertension in the A town-male population continued to be higher than that for the combined male population in the late 1980's. Therefore hypertension prevention programs appears to still have significance in the A town-male population. Certain weaknesses exist in this annual report. In the comparison of mass examination results among different populations, the presence of selection bias of those receiving examinations should be considered. Standardization of mass examination procedures and quality controls of the examinations should also be considered. To get health workers to utilize the annual report further, the reported items should be improved. Particularly useful would be tabulation by residential subdivision and occupation.

[Bilateral fenestrations of the vertebrobasilar artery with trigeminal neuralgia. Case report].

Fenestration of cerebral vessels is congenital and usually of no clinical significance. A 58-year-old female presented with left trigeminal neuralgia associated with double fenestrations of the vertebrobasilar artery. Vertebral angiography showed bilateral fenestrations in the intracranial segment. The left fenestrated artery originated at the distal portion of the vertebral artery and terminated at the middle portion of the basilar artery, compressing the left Vth cranial nerve root. The neuralgia improved after microvascular decompression. Fenestration of cerebral vessels is usually single. Five of eight reported cases with double fenestrations had bilateral extracranial fenestrations at the atlantoaxial portion of the vertebral artery. Bilateral fenestrations of the vertebrobasilar artery with trigeminal neuralgia have not been previously reported.