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

Pathophysiological Basis for Nutraceutical Supplementation in Heart Failure: A Comprehensive Review

There is evidence demonstrating that heart failure (HF) occurs in 1–2% of the global population and is often accompanied by comorbidities which contribute to increasing the prevalence of the disease, the rate of hospitalization and the mortality. Although recent advances in both pharmacological and non-pharmacological approaches have led to a significant improvement in clinical outcomes in patients affected by HF, residual unmet needs remain, mostly related to the occurrence of poorly defined strategies in the early stages of myocardial dysfunction. Nutritional support in patients developing HF and nutraceutical supplementation have recently been shown to possibly contribute to protection of the failing myocardium, although their place in the treatment of HF requires further assessment, in order to find better therapeutic solutions. In this context, the Optimal Nutraceutical Supplementation in Heart Failure (ONUS-HF) working group aimed to assess the optimal nutraceutical approach to HF in the early phases of the disease, in order to counteract selected pathways that are imbalanced in the failing myocardium. In particular, we reviewed several of the most relevant pathophysiological and molecular changes occurring during the early stages of myocardial dysfunction. These include mitochondrial and sarcoplasmic reticulum stress, insufficient nitric oxide (NO) release, impaired cardiac stem cell mobilization and an imbalanced regulation of metalloproteinases. Moreover, we reviewed the potential of the nutraceutical supplementation of several natural products, such as coenzyme Q10 (CoQ10), a grape seed extract, Olea Europea L.-related antioxidants, a sodium–glucose cotransporter (SGLT2) inhibitor-rich apple extract and a bergamot polyphenolic fraction, in addition to their support in cardiomyocyte protection, in HF. Such an approach should contribute to optimising the use of nutraceuticals in HF, and the effect needs to be confirmed by means of more targeted clinical trials exploring the efficacy and safety of these compounds.

Antidiabetic Effect of Schisandrae Chinensis Fructus Involves Inhibition of the Sodium Glucose Cotransporter

Preclinical Research Schisandrae Chinensis Fructus (SCF), the fruit of Schisandra chinensis (Turcz.) Baill. (family Schisandraceae) is traditionally used as a tonic and antidiabetic agent in Asia. In this study, SCF was investigated for its effects on sodium glucose cotransporters 1 and 2 (SGLT 1 and 2) expressed in a COS-7 cell line for its specificity in inhibiting SGLT2, which is a novel mechanism to screen for potential antidiabetic agents. Using a bioassay-guided fractionation, we then tried to isolate and identify the active fraction(s)/component(s). The ethanol extract of SCF at a concentration of 1 mg/mL significantly inhibited 89% of SGLT1 and 73% of SGLT2 activities in a [¹⁴ C]-α-methyl-d-glucopyranoside ([¹⁴ C]-AMG) uptake assay. Fractionation of the ethanol extract yielded nine fractions, of which F8, at a concentration of 1 mg/mL, was specific in inhibiting SGLT 2 (42% inhibition, P < 0.001), without inhibiting SGLT 1. Using LC/MS-MS, three compounds, deoxyschisandrin, schisandrin B (γ-schisandrin) and schisandrin were identified in F8 and their amounts quantified. However, subsequent evaluation in the [¹⁴ C]-AMG uptake assay showed that these three compounds failed to inhibit SGLT 2 activity indicating that the SGLT active component(s) from SCF have yet to be identified. Drug Dev Res 76 : 1-8, 2015.

Renal sodium glucose cotransporter 2 inhibitors as a novel therapeutic approach to treatment of type 2 diabetes: Clinical data and mechanism of action

Type 2 diabetes is characterized by impaired insulin secretion from pancreatic β-cells and/or reduced response of target tissues to insulin. Good glycemic control delays the development and slows the progression of micro- and macrovascular complications. Although there are numerous glucose-lowering agents in clinical use, only approximately half of type 2 diabetic patients achieve glycemic control, and undesirable side-effects often hamper treatment in those treated with the medications. There is a need for novel treatment options that can help overcome these difficulties. Sodium glucose cotransporter 2 (SGLT2) inhibitors have recently been developed as a novel potential therapeutic option for the treatment of type 2 diabetes. These drugs lower the plasma glucose concentration through inhibition of glucose reuptake in the kidney, independent of insulin secretion and insulin action, with a consequent lower risk of hypoglycemia. The data of clinical trials with monotherapy as well as combination therapy show that SGLT2 inhibitors have a blood glucose-lowering effect and also reduce bodyweight. A follow-up study shows long-term efficacy and the durability of these effects. SGLT2 inhibitors have the potential to reverse glucose toxicity, and to improve insulin resistance, blood pressure and lipid profile. The available data suggest a good tolerability profile. However, clinicians should carefully prescribe these drugs in light of already reported and/or unexpected side-effects. Further studies in larger numbers and longer-term clinical use data are required to place these agents in standard treatment of type 2 diabetes.

SGLT2 inhibition: a novel prospective strategy in treatment of diabetes mellitus

The role of the kidney in glucose homeostasis and the potential of the kidney as a therapeutic target in type 2 diabetes is little appreciated. Hyperglycemia is an important pathogenic component in the development of microvascular and macrovascular complications in type 2 diabetes mellitus. Inhibition of renal tubular glucose re-absorption that leads to glycosuria has been proposed as a new mechanism to attain normoglycemia and thus prevent and diminish these complications, thus representing an innovative therapeutic strategy for the treatment of hyperglycemia and/or obesity in patients with type 1 or type 2 diabetes by enhancing glucose and energy loss through the urine. Sodium glucose co-transporter 2 (SGLT2) has a key role in re-absorption of glucose in kidney. Competitive inhibitors of SGLT2 have been discovered and a few of them have also been advanced in clinical trials for the treatment of diabetes.

Role of sodium-glucose cotransporter 2 (SGLT 2) inhibitors in the treatment of type 2 diabetes

Hyperglycemia plays an important role in the pathogenesis of type 2 diabetes mellitus, i.e., glucotoxicity, and it also is the major risk factor for microvascular complications. Thus, effective glycemic control will not only reduce the incidence of microvascular complications but also correct some of the metabolic abnormalities that contribute to the progression of the disease. Achieving durable tight glycemic control is challenging because of progressive β-cell failure and is hampered by increased frequency of side effects, e.g., hypoglycemia and weight gain. Most recently, inhibitors of the renal sodium-glucose cotransporter have been developed to produce glucosuria and reduce the plasma glucose concentration. These oral antidiabetic agents have the potential to improve glycemic control while avoiding hypoglycemia, to correct the glucotoxicity, and to promote weight loss. In this review, we will summarize the available data concerning the mechanism of action, efficacy, and safety of this novel antidiabetic therapeutic approach.

SGLT2 inhibitors: molecular design and potential differences in effect

The physiological and pathological handling of glucose via sodium-glucose cotransporter-2 (SGLT2) in the kidneys has been evolving, and SGLT2 inhibitors have been focused upon as a novel drug for treating diabetes. SGLT2 inhibitors enhance renal glucose excretion by inhibiting renal glucose reabsorption. Consequently, SGLT2 inhibitors reduce plasma glucose insulin independently and improve insulin resistance in diabetes. To date, various SGLT2 inhibitors have been developed and evaluated in clinical studies. The potency and positioning of SGLT2 inhibitors as an antidiabetic drug are dependent on their characteristic profile, which induces selectivity, efficacy, pharmacokinetics, and safety. This profile decides which SGLT2 inhibitors can be expected for application of the theoretical concept of reducing renal glucose reabsorption for the treatment of diabetes. I review the structure and advancing profile of various SGLT2 inhibitors, comparing their similarities and differences, and discuss the expected SGLT2 inhibitors for an emerging category of antidiabetic drugs.

SGLT inhibitors as new therapeutic tools in the treatment of diabetes

Recently, the idea has been developed to lower blood glucose blood glucose levels in diabetes by inhibiting sugar reabsorption sugar reabsorption in the kidney kidney . The main target is thereby the early proximal tubule proximal tubule where secondary active transport secondary active transport of the sugar is mediated by the sodium-D: -glucose D-glucose cotransporter SGLT2 SGLT2 . A model substance for the inhibitors inhibitors is the O-glucoside O-glucoside phlorizin phlorizin which inhibits transport transport competitively. Its binding to the transporter involves at least two different domains: an aglucone binding aglucone binding site at the transporter surface, involving extramembranous loops extramembraneous loops , and the sugar binding sugar binding /translocation site buried in a hydrophilic pocket of the transporter. The properties of these binding sites differ between SGLT2 and SGLT1 SGLT1 , which mediates sugar absorption sugar absorption in the intestine intestine . Various O-, C-, N- and S-glucosides have been synthesized with high affinity affinity and high specificity specificity for SGLT2 SGLT2 . Some of these glucosides are in clinical trials clinical trials and have been proven to successfully increase urinary glucose excretion urinary glucose excretion and to decrease blood sugar blood sugar levels without the danger of hypoglycaemia hypoglycaemia during fasting fasting in type 2 diabetes type 2 diabetes .

The novel sodium glucose transporter 2 inhibitor dapagliflozin sustains pancreatic function and preserves islet morphology in obese, diabetic rats

AIMS

To investigate whether glucose lowering with the selective sodium glucose transporter 2 (SGLT2) inhibitor dapagliflozin would prevent or reduce the decline of pancreatic function and disruption of normal islet morphology.

METHODS

Female Zucker diabetic fatty (ZDF) rats, 7-8 weeks old, were placed on high-fat diet. Dapagliflozin (1 mg/kg/day, p.o.) was administered for ∼33 days either from initiation of high-fat diet or when rats were moderately hyperglycaemic. Insulin sensitivity and pancreatic function were evaluated using a hyperglycaemic clamp in anaesthetized animals (n = 5-6); β-cell function was quantified using the disposition index (DI) to account for insulin resistance compensation. Pancreata from a matched subgroup (n = 7-8) were fixed and β-cell mass and islet morphology investigated using immunohistochemical methods.

RESULTS

Dapagliflozin, administered from initiation of high-fat feeding, reduced the development of hyperglycaemia; after 24 days, blood glucose was 8.6 ± 0.5 vs. 13.3 ± 1.3 mmol/l (p < 0.005 vs. vehicle) and glycated haemoglobin 3.6 ± 0.1 vs. 4.8 ± 0.26% (p < 0.003 vs. vehicle). Dapagliflozin improved insulin sensitivity index: 0.08 ± 0.01 vs. 0.02 ± 0.01 in obese controls (p < 0.03). DI was improved to the level of lean control rats (dapagliflozin 0.29 ± 0.04; obese control 0.15 ± 0.01; lean 0.28 ± 0.01). In dapagliflozin-treated rats, β-cell mass was less variable and significant improvement in islet morphology was observed compared to vehicle-treated rats, although there was no change in mean β-cell mass with dapagliflozin. Results were similar when dapagliflozin treatment was initiated when animals were already moderately hyperglycaemic.

CONCLUSION

Sustained glucose lowering with dapagliflozin in this model of type 2 diabetes prevented the continued decline in functional adaptation of pancreatic β-cells.

Inhibition of renal glucose reabsorption: a novel strategy for achieving glucose control in type 2 diabetes mellitus

OBJECTIVE

To review the renal handling of glucose and the role of inhibition of a sodium-glucose transporter (SGLT2) in the treatment of type 2 diabetes mellitus (T2DM).

METHODS

We review the published data about (1) the filtration and reabsorption of glucose by the kidneys in normal subjects and patients with diabetes; (2) the deleterious effects of long-term elevation of plasma glucose levels on muscle and hepatic insulin sensitivity and beta cell function (that is, glucotoxicity); (3) the effect of inhibiting the SGLT2 transporter on the induction of glycosuria, glycemic control, insulin resistance, and beta cell dysfunction in animals and humans with diabetes; and (4) the safety of SGLT2 inhibition as a therapeutic modality to treat human T2DM.

RESULTS

Studies in animal models of diabetes document the efficacy of the SGLT2 inhibitors in inducing glycosuria, decreasing both fasting and postprandial glucose levels, augmenting beta cell function, and enhancing hepatic and muscle insulin sensitivity. In human T2DM, short-term studies with dapagliflozin (12 weeks) and sergliflozin (2 weeks) have confirmed the efficacy of these agents in improving glycemic control. Excessive urinary electrolyte or water loss, plasma electrolyte disturbances, and hypoglycemia were not observed.

CONCLUSION

SGLT2 inhibitors represent a promising approach to the treatment of T2DM. They have the potential to be used as monotherapy, as well as in combination with all approved antidiabetic agents. Because their mechanism of action is independent of the severity of beta cell dysfunction or insulin resistance, efficacy should not decline with progressive beta cell failure or in the presence of severe insulin resistance.

Glucose control by the kidney: an emerging target in diabetes

The full significance of the kidney's role in glucose homeostasis is now well recognized. For example, it is now known that renal gluconeogenesis contributes substantially to total-body glucose release in the postabsorptive state. The kidney contributes to glucose homeostasis by filtering and reabsorbing glucose. Under normal circumstances, glucose filtered by glomeruli is completely reabsorbed, but glucosuria may occur under conditions of hyperglycemia or reduced reabsorptive capacity. The sodium-glucose cotransporter SGLT2 (encoded by the SLC5A2 gene), which is expressed almost exclusively in proximal tubules, mediates approximately 90% of active renal glucose reabsorption. This transporter can be blocked by SGLT2 inhibitors, a class of compound that may prove effective in managing type 2 diabetes. The glucosuria induced by these compounds has a naturally occurring parallel in familial renal glucosuria (FRG), a condition in which SGLT2 mutations reduce renal reabsorptive capacity. Interestingly, the chronic glucosuria of patients with FRG does not appear to be associated with other pathological changes, and patients with FRG are mostly asymptomatic. This suggests that glucosuria is not intrinsically detrimental. Selective SGLT2 inhibitors are currently in clinical trials.

Does garlic have a role as an antidiabetic agent?

Diabetes affects a large segment of the population worldwide, and the prevalence of this disease is rapidly increasing. Despite the availability of medication for diabetes, traditional remedies are desirable and are currently being investigated. Garlic (Allium sativum), which is a common cooking spice and has a long history as a folk remedy, has been reported to have antidiabetic activity. However, there is no general agreement on the use of garlic for antidiabetic purposes, primarily because of a lack of scientific evidence from human studies and inconsistent data from animal studies. The validity of data from previous studies of the hypoglycemic effect of garlic in diabetic animals and the preventive effects of garlic on diabetes complications are discussed in this review. The role of garlic as both an insulin secretagogue and as an insulin sensitizer is reviewed. Evidence suggests that garlic's antioxidative, antiinflammatory, and antiglycative properties are responsible for garlic's role in preventing diabetes progression and the development of diabetes-related complications. Large-scale clinical studies with diabetic patients are warranted to confirm the usefulness of garlic in the treatment and prevention of diabetes.

Nonobese, insulin-deficient Ins2Akita mice develop type 2 diabetes phenotypes including insulin resistance and cardiac remodeling

Although insulin resistance has been traditionally associated with type 2 diabetes, recent evidence in humans and animal models indicates that insulin resistance may also develop in type 1 diabetes. A point mutation of insulin 2 gene in Ins2(Akita) mice leads to pancreatic beta-cell apoptosis and hyperglycemia, and these mice are commonly used to investigate type 1 diabetes and complications. Since insulin resistance plays an important role in diabetic complications, we performed hyperinsulinemic-euglycemic clamps in awake Ins2(Akita) and wild-type mice to measure insulin action and glucose metabolism in vivo. Nonobese Ins2(Akita) mice developed insulin resistance, as indicated by an approximately 80% reduction in glucose infusion rate during clamps. Insulin resistance was due to approximately 50% decreases in glucose uptake in skeletal muscle and brown adipose tissue as well as hepatic insulin action. Skeletal muscle insulin resistance was associated with a 40% reduction in total GLUT4 and a threefold increase in PKCepsilon levels in Ins2(Akita) mice. Chronic phloridzin treatment lowered systemic glucose levels and normalized muscle insulin action, GLUT4 and PKCepsilon levels in Ins2(Akita) mice, indicating that hyperglycemia plays a role in insulin resistance. Echocardiography showed significant cardiac remodeling with ventricular hypertrophy that was ameliorated following chronic phloridzin treatment in Ins2(Akita) mice. Overall, we report for the first time that nonobese, insulin-deficient Ins2(Akita) mice develop type 2 diabetes phenotypes including peripheral and hepatic insulin resistance and cardiac remodeling. Our findings provide important insights into the pathogenesis of metabolic abnormalities and complications affecting type 1 diabetes and lean type 2 diabetes subjects.

Thioglycosides as inhibitors of hSGLT1 and hSGLT2: potential therapeutic agents for the control of hyperglycemia in diabetes

The treatment of diabetes has been mainly focused on maintaining normal blood glucose concentrations. Insulin and hypoglycemic agents have been used as standard therapeutic strategies. However, these are characterized by limited efficacy and adverse side effects, making the development of new therapeutic alternatives mandatory. Inhibition of glucose reabsorption in the kidney, mediated by SGLT1 or SGLT2, represents a promising therapeutic approach. Therefore, the aim of the present study was to evaluate the effect of thioglycosides on human SGLT1 and SGLT2. For this purpose, stably transfected Chinese hamster ovary (CHO) cells expressing human SGLT1 and SGLT2 were used. The inhibitory effect of thioglycosides was assessed in transport studies and membrane potential measurements, using alpha-methyl-glucoside uptake and fluorescence resonance energy transfer, respectively. We found that some thioglycosides inhibited hSGLT more strongly than phlorizin. Specifically, thioglycoside I (phenyl-1'-thio-beta-D-glucopyranoside) inhibited hSGLT2 stronger than hSGLT1 and to a larger extent than phlorizin. Thioglycoside VII (2-hydroxymethyl-phenyl-1'-thio-beta-D-galacto-pyranoside) had a pronounced inhibitory effect on hSGLT1 but not on hSGLT2. Kinetic studies confirmed the inhibitory effect of these thioglycosides on hSGLT1 or hSGLT2, demonstrating competitive inhibition as the mechanism of action. Therefore, these thioglycosides represent promising therapeutic agents for the control of hyperglycemia in patients with diabetes.

Insulin sensitivity in streptozotocin-induced diabetic rats treated with different doses of 17beta-oestradiol or progesterone

It has been reported that in streptozotocin (STZ)-induced diabetes, hyperglycaemia leads to progressive insulin resistance of the peripheral tissues. In this study, we tried to elucidate the effects of hyperglycaemia on insulin sensitivity and insulin signalling in ovariectomized (STZ)-induced diabetic rats. In addition, we attempted to demonstrate the role of 17beta-oestradiol and progesterone on insulin sensitivity, focusing on their effects on key proteins of skeletal muscle, insulin receptor (IR) and glucose transporter-4 (Glut-4). Our results show that hyperglycaemia could modulate insulin signalling, at the IR and Glut-4 level, in different ways depending on exposure time. 17beta-Oestradiol and progesterone have different effects on insulin signalling. 17beta-Oestradiol treatment improves insulin sensitivity, but its action is dependent on the exposure time and its plasma level. During the early period of treatment (days 6-11), this hormone counteracts the effects of hyperglycaemia downstream of the IR, whereas during the later period of treatment (days 11-16), it may counteract the effects of hyperglycaemia by modulating IR relative tyrosine phosphorylation. By contrast, progesterone only improves insulin sensitivity during the early period of treatment (days 6-11), and this effect is not associated with changes in IR and Glut-4 content. Both hormones have a protective role in skeletal muscle against the effects of glucose toxicity, but their effects begin at different stages of treatment. These new findings improve our understanding of insulin resistance in type 1 diabetes mellitus and of the risk/benefit ratio when 17beta-oestradiol and progesterone are used in oral contraceptives or hormone replacement therapy taken by menopausal women with controlled type 1 diabetes mellitus.

Reduction of Renal Transport Maximum for Glucose by Inhibition of Na+-Glucose Cotransporter Suppresses Blood Glucose Elevation in Dogs

T-1095, an orally active inhibitor of Na(+)-glucose cotransporter (SGLT), excretes excess plasma glucose into urine, lowers blood glucose levels, and thus has therapeutic potential for treatment of diabetes mellitus. To elucidate the correlation between threshold for renal glucose reabsorption and blood glucose levels, we evaluated the effects of T-1095 on transport maximum for glucose (TmG) in dogs. Intravenous infusion of T-1095A (0.25-2.0 microg/kg/min), an active metabolite of T-1095, dose-dependently increased fractional glucose excretion induced by a hyper-amount of glucose infusion in anesthetized dogs. Calculated TmG was decreased by T-1095A in a dose dependent manner, and plasma concentration of T-1095A correlated well with the reduction of TmG (R2=0.704). Then, oral glucose tolerance tests (OGTT) were carried out in dogs. T-1095 at a dose of 3 mg/kg (p.o.) slightly increased urinary glucose excretion without affecting blood glucose levels. Ten mg/kg (p.o.) of T-1095 suppressed the elevation of blood glucose levels by excreting a large quantity urinary glucose. The estimated TmG reduction by 3 and 10 mg/kg of T-1095 was about 50% and more than 80%, respectively. In conclusion, this study clarified that more than 80% reduction of TmG by inhibition of SGLT was necessary for suppressing postprandial hyperglycemia in normoglycemic dogs.

Effects of garlic oil and diallyl trisulfide on glycemic control in diabetic rats

We investigated the effects of garlic oil and diallyl trisulfide on glycemic control in rats with streptozotocin-induced diabetes. Diabetic rats received by gavage garlic oil (100 mg/kg body weight), diallyl trisulfide (40 mg/kg body weight), or corn oil every other day for 3 weeks. Control rats received corn oil only. Both garlic compounds significantly raised the basal insulin concentration. The insulin resistance index as assessed by homeostasis model assessment and the first-order rate constant for glucose disappearance were significantly improved by both garlic compounds (P<0.05). Oral glucose tolerance was also improved by both garlic compounds and was accompanied by a significantly increased rate of insulin secretion (P<0.05). Glycogen formation (but not that of lactate or carbon dioxide) from glucose by the soleus muscle in the presence of 10 or 100 microU/ml of insulin was significantly better after treatment with both garlic compounds. Both garlic oil and diallyl trisulfide improve glycemic control in diabetic rats through increased insulin secretion and increased insulin sensitivity.

Long-term treatment with the Na+-glucose cotransporter inhibitor T-1095 causes sustained improvement in hyperglycemia and prevents diabetic neuropathy in Goto-Kakizaki Rats

We examined the effects of T-1095, an orally active inhibitor of Na(+)-glucose cotransporter (SGLT), on the development and severity of diabetes in Goto-Kakizaki (GK) rat, a spontaneous, non-obese model of type 2 diabetes. T-1095 was administered as dietary admixture (0.1% w/w) beginning at 7 weeks of age for 32 weeks. Untreated male GK rats were hyperglycemic compared with Wistar rats. Throughout the study, T-1095 treatment significantly decreased both blood glucose and hemoglobin A(1C) levels in the GK rats. The concomitant increase of urinary glucose excretion indicated that the hypoglycemic action of T-1095 is derived from the enhancement of urinary glucose disposal. Although food intake was not changed in the T-1095-treated rats, the body weight gain was retarded. T-1095 treatment partially ameliorated oral glucose tolerance but not the impaired glucose-induced insulin secretion. Homeostasis model assessment (HOMA) indicated the existence of insulin resistance in GK rats and a significant restoration by T-1095-treatment. There was a reduction of the thermal response in tail-flick testing following long-term hyperglycemia (diabetic neuropathy). Treatment of T-1095 significantly prevented the development of diabetic neuropathy in male GK rats. Sustained improvement of hyperglycemia and prevention of diabetic neuropathy by the T-1095-treatment provide further support the use of SGLT inhibitors for the treatment of diabetes.