Renal Tubular Reabsorption Of Glucose Research Articles

Role of SGLT2 Inhibitors in Diabetes Management: Focus on HbA1c Levels, Weight Loss and Genetic Variation

Sodium Glucose Co-transporters-2 (SGLT2) inhibitors are the recent addition to treatment strategies for Type 2 Diabetes Mellitus (T2DM). It is a non-insulin dependent anti-diabetic therapeutic approach that eliminates plasma glucose by urination. The study was carried out with the aim of evaluating the effect of SGLT2 inhibitors on HbA1c levels and weight loss in responders and non-responders. In addition, the role of two significant variants, SLC5A2 (rs9934336) and UGT1A9 (rs72551330), affecting the inter-individual variation in response to SGLT2 inhibitors was evaluated in the study population. 200 confirmed T2DM patients on SGLT2 inhibitors were enrolled for the study. Patients with decreased HbA1c levels and body weight were categorized as responders, whereas the ones who did not show a significant decrease in these two parameters after treatment were categorised as non-responders. Association of HbA1c levels and weight loss before as well as after treatment with responders and non-responders was evaluated. Patients were screened for two significant variants, SLC5A2 (rs9934336) and UGT1A9 (rs72551330), affecting the inter-individual variation in response to SGLT2 inhibitors by Sanger Sequencing. A significant difference in HbA1c levels and weight was found in responders and non-responders before and after the treatment. However, both of the variants, SLC5A2 (rs9934336) and UGT1A9 (rs72551330), were not found to be significantly associated with the drug response. In conclusion, SGLT2 inhibitors reduced HbA1c levels and weight effectively in responders. However, the targeted gene variants need not to be involved in genetic testing before prescribing this class of drugs to T2DM patients from Malwa region of Punjab. Highlights: Treatment of Type 2 diabetes mellitus (T2DM) with Sodium Glucose co-transporter-2 (SGLT2) inhibitors is an insulin-independent method of reducing blood glucose levels by lowering renal tubular glucose reabsorption. Significant decrease in HbA1c levels and weight loss in responders was observed after the treatment with SGLT2 inhibitors. Pharmacogenetic analysis was carried out for two gene variants, SLC5A2 (rs9934336) and UGT1A9 (rs72551330), reported to be involved in inter-individual response to SGLT2 inhibitors. None of the tested variants were found to be significantly associated with inter-individual response to SGLT2 inhibitors. Pharmacogenetic testing for the two most commonly reported variants is not required for the T2DM patients on SGLT2 inhibitors from the Malwa region of Punjab.

Abstract #1316800: Acute Pancreatitis as a Rare Side Effect of Using Empagliflozin

Acute pancreatitis is a rapid onset inflammatory process of the pancreas. The most common causes are gallstones and alcohol use. Other causes include drug-induced, hypertriglyceridemia, trauma, infectious. Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a class of oral hypoglycemic agents which is approved by the FDA for treating diabetes and heart failure. SGLT2 inhibitors function through a novel mechanism of reducing renal tubular glucose reabsorption, producing a reduction in blood glucose without stimulating insulin release.

LBSUN289 Ketonuria — A Possible Early Indicator Of Impending Euglycemic DKA In Setting Of Recent SGLT-2 Inhibitor Use And Acute Stress

Abstract Introduction - Euglycemic DKA is a notorious entity; previously thought to be primarily afflicting type 1 diabetics and rarely type 2 diabetics in a state of relative insulin deficiency, it has now become a major cause of concern and lead to the issuance of FDA warning in 2015 with regards to its link with SGLT-2 inhibitors. Although DKA is characterized by hyperglycemia, metabolic acidosis and ketogenesis, euglycemic DKA poses a diagnostic challenge as it remains disguised under the cover of euglycemia. Moreover, in the setting of recent SGLT-2 inhibitor use, this definition becomes even more of a paradox as SGLT-2 inhibitors, by the virtue of their action, promote ketogenesis thereby further adding to this enigma. Case presentation - A 67 year old male with hypertension and diabetes mellitus type 2 (on Metformin and Empagliflozin) presented to the emergency room with dizziness. He woke up to go to the bathroom that day and felt weak, dizzy and like he was going to fall. He endorsed nausea and vomiting but denied headache, fever, chills, chest pain, shortness of breath, abdominal pain, and problems with urination/bowel movements. He was afebrile and hemodynamically stable. On examination, left sided dysmetria, loss of coordination, and axial imbalance were noted. No motor/sensory deficits. Labs were significant for WBC count 10 k/mm cu (4 - 11), Creatinine 0.78 mg/dL (0.7 - 1.3), Glucose 279 mg/dL (70 - 99), Bicarbonate 21 mmol/L (21 -31), Anion gap 19 mmol/L (6 - 14), and Lactate 3.2 mmol/L (0.7 - 2). Urinalysis showed glucosuria (glucose >500 mg/dL) and ketonuria (ketones 20 mg/dl). CT head was negative but MRI brain showed left inferior cerebellar peduncle acute ischemic infarct. Stroke protocol was initiated and he transferred to telemetry. The next day, labs showed Glucose 166, Bicarbonate 13, Anion gap 21, and Ketones 5.6 mmol/L (<0.6). Since blood glucose levels remained less than 250 mg/dl with concurrent anion gap metabolic acidosis in the setting of recent Empagliflozin use, he was transferred to ICU for insulin infusion for management of euglycemic diabetic ketoacidosis. Subsequently, he was transitioned to a basal-bolus insulin regimen and transferred to the floors. Discussion - SGLT-2 inhibitors reduce renal tubular glucose reabsorption, causing glycosuria, and promote ketonemia directly by enhancing ketogenesis via glucagon secretion from the pancreatic alpha cells and indirectly by decreasing the renal clearance of ketone bodies. In the setting of acute stress, such as stroke in our patient, and recent SGLT-2 inhibitor use, the presence of ketonuria should be recognized as an early ominous warning sign for euglycemic DKA. A targeted approach detailing diagnostic and therapeutic interventions should be designed to halt its progression in its track before it transforms into the dreaded euglycemic DKA. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

123-LB: Extended Fasting Reveals Effect of Canagliflozin to Mobilize Ketones in Canines

SGLT2 inhibitors (SGLT2i) improve glycemic control by inhibiting renal proximal tubular glucose reabsorption. SGLT2i may also elevate ketones. Fasting is expected to increase endogenous ketones, and SGLT2i may enhance ketosis. We asked if SGLT2i alters circulating ketones (β-hydroxybutyrate; BOHB) and disrupts glycemia during prolonged fasting. Dogs (n=7) were studied with a crossover design. Dogs received either canagliflozin (CANA; 300 mg) or placebo (PL) once/day for 7 d, after which a 48 h fast was performed while treatment was continued. To begin the fast, after morning feeding (9 am to noon) , remaining food was removed (“t=0”) . Blood was sampled at regular intervals over a 48 h period of total fasting (urine collected over final 3 h) . After the fast, dogs were fed over 3 h. Treatment was then discontinued for 2 wk washout, and dogs were then assigned to the alternate treatment (CANA or PL) for 7 d, after which fasting experiment was repeated. Glycemia was sustained in both treatment groups during initial 22 h of fasting, presumably due to reduction of insulin (↓50.7±13.1% and ↓49.5±21.5% for CANA and PL, respectively; p<0.035 for both) . But marked effects of CANA alone were revealed after 22 h of fasting, when glucose declined markedly in CANA (52.9±3.4 mg/dl at t=48 h) , but not PL (86.6±2.5 mg/dl at 48 h; p=0.0002 vs. CANA) , due to drug-induced glycosuria (13948±543 vs. 19.6±1.5 mg/dl; p<0.0001) . After 22 h of fasting, CANA induced ∼5-fold increase in FFA (p<0.03) and marked increase in plasma BOHB that persisted for duration of fast (CANA: 0.560±0.065 mM, PL: 0.048±0.006 mM; p<0.0001) . After refeeding, glucose and BOHB normalized, although BOHB remained higher in CANA (p<0.0007) . In conclusion, effect of SGLT2i on ketones is manifest after 24 h of total food restriction. CANA treatment induces glycosuria, after which reduction in carbohydrate stores switches animals to fat-based metabolism, characterized by increased FFA and ketosis. CANA appears to induce ketosis when carbohydrate stores are depleted. Disclosure M. Ader: None. R. Sedighi: None. M. Kabir: None. R. N. Bergman: Consultant; Fractyl Health, Inc., Novo Nordisk, Research Support; AstraZeneca, Janssen Research & Development, LLC. Funding Janssen Pharmaceutica, Inc.; NIH (DK29867, DK27619)

Sodium-glucose cotransporter-2 inhibitors: updated evidence on their efficacy and safety in patients with type-2 diabetes

Management of type-2 diabetes mellitus (T2DM) is challenging. The scope of existing therapies toward T2DM has transformed remarkably. These large assortments of therapies have produced evidence-based data. Sodium-glucose cotransporter-2 inhibitor (SGLT-2i) is the most recent class of oral anti-hyperglycemic agents. They are approved by Food and Drug Administration for the treatment of diabetes mellitus. SGLT-2i has a unique mechanism of action and that lower glucose independent of insulin. They reduce renal tubular glucose reabsorption, thereby lowering blood glucose without stimulating the release of insulin. Additional advantages involve suitable effects on blood pressure and weight. According to guidelines of the American Association of Clinical Endocrinologists/ the American College of Endocrinology 2016, SGLT-2i (in the form of canagliflozin, dapagliflozin, and empagliflozin) is one of the acceptable alternatives to metformin as initial therapy towards T2DM. Canagliflozin, dapagliflozin, and empagliflozin reduce the cardiovascular risk in comparison to placebo as the part of standard care. This review article focuses on the clinical trials published over the past year and specifically the metabolic aspect of SGLT-2i and the adverse effects related to SGLT-2 inhibitors.

Comparative Pharmacokinetics and Pharmacodynamics of a Novel Sodium-Glucose Cotransporter 2 Inhibitor, DWP16001, with Dapagliflozin and Ipragliflozin.

Since sodium-glucose cotransporter 2 (SGLT2) inhibitors reduced blood glucose level by inhibiting renal tubular glucose reabsorption mediated by SGLT2, we aimed to investigate the pharmacokinetics and kidney distribution of DWP16001, a novel SGLT2 inhibitor, and to compare these properties with those of dapagliflozin and ipragliflozin, representative SGLT2 inhibitors. The plasma exposure of DWP16001 was comparable with that of ipragliflozin but higher than that of dapagliflozin. DWP16001 showed the highest kidney distribution among three SGLT2 inhibitors when expressed as an area under curve (AUC) ratio of kidney to plasma (85.0 ± 16.1 for DWP16001, 64.6 ± 31.8 for dapagliflozin and 38.4 ± 5.3 for ipragliflozin). The organic anion transporter-mediated kidney uptake of DWP16001 could be partly attributed to the highest kidney uptake. Additionally, DWP16001 had the lowest half-maximal inhibitory concentration (IC50) to SGLT2, a target transporter (0.8 ± 0.3 nM for DWP16001, 1.6 ± 0.3 nM for dapagliflozin, and 8.9 ± 1.7 nM for ipragliflozin). The inhibition mode of DWP16001 on SGLT2 was reversible and competitive, but the recovery of the SGLT2 inhibition after the removal of SGLT2 inhibitors in CHO cells overexpressing SGLT2 was retained with DWP16001, which is not the case with dapagliflozin and ipragliflozin. In conclusion, selective and competitive SGLT2 inhibition of DWP16001 could potentiate the efficacy of DWP16001 in coordination with the higher kidney distribution and retained SGLT2 inhibition of DWP16001 relative to dapagliflozin and ipragliflozin.

SGLT2 inhibitors for the treatment of diabetes: a patent review (2013-2018)

ABSTRACTIntroduction: The sodium-glucose co-transporter 2 (SGLT2) is ascribed to target renal tubular glucose re-absorption, and its inhibition has been proved to induce glucosuria which improves the glycemic index. Accordingly, SGLT2 inhibitors have found to be the promising class of antidiabetic agents for the management of type 2 diabetes mellitus. A large number of SGLT2 inhibitors have developed through structural modification and investigated for their ability to selectivity inhibit SGLT2 transporters with better bioavailability.Areas covered: This review comprises a summary of patent applications (2013–2018) of SGLT2 inhibitors with focus on chemical structural advancement and therapeutic potentials in the management of diabetes and related disorders.Expert opinion: SGLT2 inhibitors exert multiple metabolic benefits, including reduced glycated hemoglobin (HbA1c), improved glycemic control (fasting and postprandial), reduced body weight, reduced systolic and diastolic blood pressure and improved HDL cholesterol. Due to the virtue of no interference with insulin action and secretion, their efficacy remains the same even in presence of progressive β cell failure in type 2 diabetes. Additionally, few members of this class have been reported to exhibit cardioprotective, renoprotective, and anticancer activity. However, more study on the long-term outcomes in patients taking SGLT2 inhibitors is warranted.

The renal effects of SGLT2 inhibitors and a mini-review of the literature.

Sodium-glucose linked transporter 2 (SGLT2) inhibitors are a new and promising class of antidiabetic agents which target renal tubular glucose reabsorption. Their action is based on the blockage of SGLT2 sodium-glucose cotransporters that are located at the luminal membrane of tubular cells of the proximal convoluted tubule, inducing glucosuria. It has been proven that they significantly reduce glycated hemoglobin (HbA1c), along with fasting and postprandial plasma glucose in patients with type 2 diabetes mellitus (T2DM). The glucosuria-induced caloric loss as well as the osmotic diuresis significantly decrease body weight and blood pressure, respectively. Given that SGLT2 inhibitors do not interfere with insulin action and secretion, their efficacy is sustained despite the progressive β-cell failure in T2DM. They are well tolerated, with a low risk of hypoglycemia. Their most frequent adverse events are minor: genital and urinal tract infections. Recently, it was demonstrated that empagliflozin presents a significant cardioprotective effect. Although the SGLT2 inhibitors' efficacy is affected by renal function, new data have been presented that some SGLT2 inhibitors, even in mild and moderate renal impairment, induce significant HbA1c reduction. Moreover, recent data indicate that SGLT2 inhibition has a beneficial renoprotective effect. The role of this review paper is to explore the current evidence on the renal effects of SGLT2 inhibitors.

Beat it early: putative renoprotective haemodynamic effects of oral hypoglycaemic agents.

Diabetic kidney disease represents a considerable burden; around one-third of patients with type 2 diabetes develop chronic kidney disease. In health, the kidneys play an important role in the regulation of glucose homeostasis via glucose utilization, gluconeogenesis and glucose reabsorption. In patients with diabetes, renal glucose homeostasis is significantly altered with an increase in both gluconeogenesis and renal tubular reabsorption of glucose. Environmental factors, both metabolic (hyperglycaemia, obesity and dyslipidaemia) and haemodynamic, together with a genetic susceptibility, lead to the activation of pro-oxidative, pro-inflammatory and pro-fibrotic pathways resulting in kidney damage. Hyperfiltration and its haemodynamic-driven insult to the kidney glomeruli is an important player in proteinuria and progression of kidney disease towards end-stage renal failure. Control of glycaemia and blood pressure are the mainstays to prevent kidney damage and slow its progression. There is emerging evidence that some hypoglycaemic agents may have renoprotective effects which are independent of their glucose-lowering effects. Sodium-glucose co-transporter-2 (SGLT-2) inhibitors may exert a renoprotective effect by a number of mechanisms including restoring the tubuloglomerular feedback mechanism and lowering glomerular hyperfiltration, reducing inflammatory and fibrotic markers induced by hyperglycaemia thus limiting renal damage. Simultaneous use of an SGLT-2 inhibitor and blockade of the renin-angiotensin-aldosterone system may be a strategy to slow progression of diabetic nephropathy more than either drug alone. The use of dipeptidyl peptidase-4 inhibitors and glucagon-like peptide 1 receptor agonists may exert a renoprotective effect by reducing inflammation, fibrosis and blood pressure. Given the burden of diabetic kidney disease, any additional renoprotective benefit with hypoglycaemic therapy is to be welcomed. Large randomized controlled trials are currently underway investigating if these new anti-diabetic agents can provide renoprotection in diabetes.

Mathematical Modeling of Renal Tubular Glucose Absorption after Glucose Load

A partial differential Progressive Tubular Reabsorption (PTR) model, describing renal tubular glucose reabsorption and urinary glucose excretion following a glucose load perturbation, is proposed and fitted to experimental data from five subjects. For each subject the Glomerular Filtration Rate was estimated and both blood and urine glucose were sampled following an Intra-Venous glucose bolus. The PTR model was compared with a model representing the conventional Renal Threshold Hypothesis (RTH). A delay bladder compartment was introduced in both formulations. For the RTH model, the average threshold for glycosuria varied between 9.90±4.50 mmol/L and 10.63±3.64 mmol/L (mean ± Standard Deviation) under different hypotheses; the corresponding average maximal transport rates varied between 0.48±0.45 mmol/min (86.29±81.22 mg/min) and 0.50±0.42 mmol/min (90.62±76.15 mg/min). For the PTR Model, the average maximal transports rates varied between 0.61±0.52 mmol/min (109.57±93.77 mg/min) and 0.83±0.95 mmol/min (150.13±171.85 mg/min). The time spent by glucose inside the tubules before entering the bladder compartment varied between 1.66±0.73 min and 2.45±1.01 min.The PTR model proved much better than RTH at fitting observations, by correctly reproducing the delay of variations of glycosuria with respect to the driving glycemia, and by predicting non-zero urinary glucose elimination at low glycemias. This model is useful when studying both transients and steady-state glucose elimination as well as in assessing drug-related changes in renal glucose excretion.

More Information on the Diabetes Drug Canagliflozin

For diabetes treatment, the newest kid on the block is canagliflozin (Invokana), which lowers blood glucose levels by decreasing renal tubular reabsorption of glucose and increasing urinary glucose excretion. In this double-blind, industry-sponsored trial, researchers randomized 756 patients with longstanding type 2 diabetes — all of whom …

Clinical and genetic analysis in a patient with primary renal glucosuria: Identification of a novel mutation in the SLC5A2 gene

Primary renal glucosuria (PRG; OMIM #233100) is characterized by persistent glucosuria due to a reduction in the renal tubular reabsorption of glucose in the presence of a normal concentration of serum glucose and the absence of any other impairment of tubular function. The SLC5A2 gene is the causative gene, which codes for the low-affinity sodium/glucose co-transporter SGLT2. In the present study, the case of a patient with PRG associated with a novel mutation of the SLC5A2 gene is reported. The patient visited hospital for the evaluation of glucosuria in the absence of hyperglycemia, a condition that had been present for >20 years. The patient showed a fasting blood sugar level of 104 mg/dl, a 2-h postprandial sugar level of 101 mg/dl, a sodium level of 144 mmol/l, a potassium level of 3.7 mmol/l and a chloride level of 106 mmol/l in serum. Urine chemistry revealed that the amount of glucose excreted was 10.8 g/1.73 m2/24 h; however, the levels of the other parameters were unremarkable. Polymerase chain reaction (PCR) sequencing analysis of the SLC5A2 gene from the patient revealed a novel 1 bp deletion mutation, which altered the coding sequence of exon 10 in the transmembrane domain (c.1162delG; Ala388ProfsX48), suggesting an autosomal dominant inheritance pattern. This study identified a novel mutation in the SLC5A2 gene related to a benign clinical characteristic and suggests that the molecular diagnosis of the SLC5A2 gene may be useful for diagnosing renal glucosuria in patients and for deciding intervention measures for their family members.

SGLT2 inhibitors: a promising new therapeutic option for treatment of type 2 diabetes mellitus

Hyperglycemia is an important pathogenic component in the development of microvascular and macrovascular complications in type 2 diabetes mellitus. Inhibition of renal tubular glucose reabsorption that leads to glycosuria has been proposed as a new mechanism to attain normoglycemia and thus prevent and diminish these complications. Sodium glucose cotransporter 2 (SGLT2) has a key role in reabsorption 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. To discuss the therapeutic potential of SGLT2 inhibitors currently in clinical development. A number of preclinical and clinical studies of SGLT2 inhibitors have demonstrated a good safety profile and beneficial effects in lowering plasma glucose levels, diminishing glucotoxicity, improving glycemic control and reducing weight in diabetes. Of all the SGLT2 inhibitors, dapagliflozin is a relatively advanced compound with regards to clinical development. SGLT2 inhibitors are emerging as a promising therapeutic option for the treatment of diabetes. Their unique mechanism of action offers them the potential to be used in combination with other oral anti-diabetic drugs as well as with insulin.

Inhibition of the sodium glucose co‐transporter‐2: its beneficial action and potential combination therapy for type 2 diabetes mellitus

Sodium glucose co-transporter-2 (SGLT2) inhibitors are an emerging class of glucose-lowering drugs in the management of type 2 diabetes mellitus (T2DM). In this context, SGLT2 is a low-affinity, high-capacity transporter that is expressed predominantly in the proximal renal tubules. The rationale for using SGLT2 inhibition as a drug for T2DM is derived from early evidence obtained from individuals with familial renal glycosuria, due to a SGLT2 mutation, which exhibits decreased renal tubular reabsorption of glucose in the absence of hyperglycaemia or any other signs of dysfunction. Thus, reduction of glucose reabsorption by SGLT2 inhibition represents a novel T2DM treatment approach. In light of the emerging role of SGLT2 inhibition in controlling glucose homeostasis, the current review provides a critical appraisal of the rationale, overviews of structural differences between SGLT2 inhibitors and summarizes recent preclinical and clinical studies. The physiological actions of SGLT2 inhibition in relation to insulin sensitivity, islet morphology, inflammation, body weight and blood pressure are reviewed. Finally, the safety and tolerability of SGLT2 inhibitors are also discussed in relation to their potential to provide insulin independence and enhance β-cell function, as well as their potential for synergistic/additive effects if used in combination with other antidiabetic drugs.

Teaching the renal tubular reabsorption of glucose using two classic papers by Shannon et al.

Most of the transport along the nephron uses membrane proteins and exhibits the three characteristics of mediated transport: saturation, specificity, and competition. Glucose reabsorption in the nephron is an excellent example of the consequences of saturation. Two classic papers by James A. Shannon and colleagues clearly show the ability of the kidney in transporting glucose and its saturation process, providing students with examples of the handling of glucose by the kidney. In addition, these articles demonstrate how stable and reproducible is the transport maximum of glucose in the proximal tubule under different experimental conditions. One key figure from each classic paper can be used to give students insight into how glucose transport becomes saturated, resulting in the excretion of glucose in urine, and will also give students a clear example of how careful experimentation and a clear interest in renal physiology led Shannon and colleagues to advance the field.

Akt/PKB‐sensitive proximal tubular glucose and phosphate transport

Akt/PKB stimulates the glucose carrier GLUT4. Here we explored whether Akt directly regulates Na+‐coupled transport of glucose (by SGLT1) or phosphate (by NaPiIIa). Immunohistochemistry showed that Akt2 is expressed in proximal renal tubules. According to dual electrode voltage clamp experiments the coexpression of Akt increased the glucose‐induced current in SGLT1‐expressing and the phosphate‐induced current in NapiIIa‐expressing Xenopus oocytes. Renal transport was further studied using Akt2 deficient (akt2−/−) and wild type mice (akt2+/+). akt2−/− mice suffered from glucosuria which was partially due to increased plasma glucose levels but was not observed in akt2+/+ mice made similarly hyperglycemic as akt2−/− mice by fructose feeding pointing to defective renal tubular glucose reabsorption. Glucose‐induced depolarization was significantly smaller in isolated perfused renal tubules from akt2−/− than from akt2+/+ mice. In addition, the phosphate clearance was higher in akt2−/− than in akt2+/+ mice despite a significantly decreased plasma PTH and enhanced 1,25‐dihydroxyvitamin D3 concentration and a tendency of lower plasma phosphate. Bone density was significantly reduced in akt2−/− mice. In conclusion, Akt plays a role in the regulation of renal glucose and phosphate transport contributing to the maintenance of phosphate balance and adequate mineralization of bone.

Regulation of renal tubular glucose reabsorption by Akt2/PKBβ

Akt/PKB is known to regulate the facilitative glucose carrier GLUT4. Nothing is known, however, of the role of Akt/PKB in the regulation of renal epithelial transport. To explore whether Akt2/PKBβ influences the Na(+)-coupled glucose cotransporter SGLT1, human SGLT1 was expressed in Xenopus laevis oocytes with or without Akt/PKB, and electrogenic glucose transport was determined by dual-electrode voltage clamp. The coexpression of Akt/PKB in SGLT1-expressing oocytes was followed by an increase in glucose-induced currents. To study the functional significance of Akt/PKB-sensitive renal glucose transport, further experiments were performed in gene-targeted mice lacking functional Akt2/PKBβ (akt2(-/-)) and in their wild-type littermates (akt2(+/+)). Plasma glucose concentration was significantly higher in akt2(-/-) mice than in akt2(+/+) mice but was virtually identical to the plasma glucose concentration in fructose-treated akt2(+/+) mice. Urinary glucose excretion was significantly higher in akt2(-/-) mice compared with akt2(+/+) mice with or without fructose treatment. Moreover, the glucose-induced depolarization of proximal tubular cells was significantly smaller in isolated, perfused renal tubules from akt2(-/-) mice than in those from akt2(+/+) mice. In conclusion, Akt2/PKBβ plays a role in the regulation of renal glucose transport.

Steviol effect, a glycoside of Stevia rebaudiana, on glucose clearances in rats

Stevia rebaudiana, a South American plant normally used as a natural herbal sweetener, has been suggested as exerting beneficial effects on human health, including as an antihypertensive and antihyperglycemic. The present experiment was undertaken to evaluate the renal excretion of steviol, the aglycone of several natural products extracted from the leaves of S. rebaudiana, and to clarify the actual participation of this compound on the renal excretion of glucose in rats, which has been previously suggested as the preferential action of steviol on the Na+-glucose renal tubular transport system. Steviol was obtained by enzymatic hydrolysis of stevioside with pectinase. Thirty normal male Wistar rats weighing 345 g were used. After a control period, steviol was infused iv at three doses (0.5, 1.0 and 3.0 mg.kg-1/h), according to classical clearance techniques. During all the experiments no significant changes in inulin clearance (Cin) and p-aminohipuric acid clearance (C PAH) were observed. Administration of steviol resulted in a statistically significant increase in the fractional sodium excretion (FeNa+), fractional potassium excretion (FeK+), urinary flow as percent of glomerular filtration rate (V/GFR) and glucose clearance (C G) when compared to controls, but these effects were absent with the dose of 0.5 mg.kg-1/h. The steviol clearance (C S) was higher than the Cin and lower than the C PAH at all the doses employed in this study. The data suggest that steviol is secreted by renal tubular epithelium, causing diuresis, natriuresis, kaliuresis and a fall in renal tubular reabsorption of glucose.

SGK1-sensitive renal tubular glucose reabsorption in diabetes

The hyperglycemia of diabetes mellitus increases the filtered glucose load beyond the maximal tubular transport rate and thus leads to glucosuria. Sustained hyperglycemia, however, may gradually increase the maximal renal tubular transport rate and thereby blunt the increase of urinary glucose excretion. The mechanisms accounting for the increase of renal tubular glucose transport have remained ill-defined. A candidate is the serum- and glucocorticoid-inducible kinase SGK1. The kinase has been shown to stimulate Na(+)-coupled glucose transport in vitro and mediate the stimulation of electrogenic intestinal glucose transport by glucocorticoids in vivo. SGK1 expression is confined to glomerula and distal nephron in intact kidneys but may extend to the proximal tubule in diabetic nephropathy. To explore whether SGK1 modifies glucose transport in diabetic kidneys, Akita mice (akita(+/-)), which develop spontaneous diabetes, have been crossbred with gene-targeted mice lacking SGK1 on one allele (sgk1(+/-)) to eventually generate either akita(+/-)/sgk1(-/-) or akita(+/-)/sgk1(+/+) mice. Both akita(+/-)/sgk1(-/-) and akita(+/-)/sgk1(+/+) mice developed profound hyperglycemia (>20 mM) within approximately 6 wk. Body weight and plasma glucose concentrations were not significantly different between these two genotypes. However, urinary excretion of glucose and urinary excretion of fluid, Na(+), and K(+), as well as plasma aldosterone concentrations, were significantly higher in akita(+/-)/sgk1(-/-) than in akita(+/-)/sgk1(+/+) mice. Studies in isolated perfused proximal tubules revealed that the electrogenic glucose transport was significantly lower in akita(+/-)/sgk1(-/-) than in akita(+/-)/sgk1(+/+) mice. The data provide the first evidence that SGK1 participates in the stimulation of renal tubular glucose transport in diabetic kidneys.

Sodium glucose co-transporter 2 inhibitors: blocking renal tubular reabsorption of glucose to improve glycaemic control in patients with diabetes

The kidney plays a central role in the regulation of plasma glucose levels, although until recently this has not been widely appreciated or considered a target for therapeutic intervention. The sodium glucose co-transporter type 2 (SGLT2) located in the plasma membrane of cells lining the proximal tubule mediates the majority of renal glucose reabsorption from the tubular fluid, which normally prevents the loss of glucose in the urine. Competitive inhibitors of SGLT2 that provoke the renal excretion of glucose have been discovered, thereby providing a unique mechanism to potentially lower the elevated blood glucose levels in patients with diabetes. To explore the physiology of SGLT2 action and discuss several SGLT2 inhibitors that have entered early clinical development. All publicly available data were identified by searching the internet for 'SGLT2' and 'SGLT2 inhibitor' through 1 November 2007. Published articles, press releases and abstracts presented at national and international meetings were considered. Sodium glucose co-transporter type 2 inhibition is a novel treatment option for diabetes, which has been studied in preclinical models and a few potent and selective SGLT2 inhibitors have been reported and are currently in clinical development. These agents appear to be safe and generally well tolerated, and will potentially be a beneficial addition to the growing battery of oral antihyperglycaemic agents.