Familial renal glucosuria: a clinicogenetic study of 23 additional cases

Adverse events and drug-drug interactions of sodium glucose co-transporter 2 inhibitors in patients treated for heart failure

INTRODUCTION

Sodium glucose co-transporter 2-inhibitors (SGLT2-I), antihyperglycemic agents, are increasingly prescribed in chronic heart failure (CHF). Their risk for drug-drug interactions (DDI) seems low. Safety-data derive mainly from diabetes-patients. This review aims to summarize adverse-events (AE) and DDI of the SGLT2-I dapagliflozin, empagliflozin and sotagliflozin in patients with CHF.

AREAS COVERED

Literature-search-terms in PubMed were 'adverse event/drug-drug interaction' and 'heart failure AND 'dapagliflozin' OR 'empagliflozin' OR 'sotagliflozin.'AEreported in randomized controlled trials (RCT) comprisegenitaland urinary-tract infections, hypotension, ketoacidosis, renal impairment, hypoglycemia, limb-amputations, Fournier's gangrene, bone-fractures, hepatopathy, pancreatitis, diarrhea, malignancy and venous thromboembolism. Their incidence is largely unknown, since they were not consistently evaluated in RCT of CHF. Further AE from meta-analyses, pharmacovigilance reports, case-series and case-reports include erythrocytosis, hypertriglyceridemia, myopathy, sarcopenia, skin problems, ventricular tachycardia, and urinary retention. The maximal observation period of RCT in CHF was 26 months.DDI were mainly studied in healthy volunteers for 3-8 days. In CHF or diabetes-patients, DDI were reported with interleukin-17-inhibitors, linezolid, lithium, tacrolimus, valproate, angiotensin-receptor-neprilysin-inhibitors and intravenous iron.

EXPERT OPINION

Guidelines recommend treatment with SGLT2-I for CHF but no data on AE during long-term therapy and only little information on DDI are available, which stresses the need for further research. Evidence-based recommendations for ketoacidosis-prevention are desirable.

Mouse Models with SGLT2 Mutations: Toward Understanding the Role of SGLT2 beyond Glucose Reabsorption

The sodium–glucose cotransporter 2 (SGLT2) mainly carries out glucose reabsorption in the kidney. Familial renal glycosuria, which is a mutation of SGLT2, is known to excrete glucose in the urine, but blood glucose levels are almost normal. Therefore, SGLT2 inhibitors are attracting attention as a new therapeutic drug for diabetes, which is increasing worldwide. In fact, SGLT2 inhibitors not only suppress hyperglycemia but also reduce renal, heart, and cardiovascular diseases. However, whether long-term SGLT2 inhibition is completely harmless requires further investigation. In this context, mice with mutations in SGLT2 have been generated and detailed studies are being conducted, e.g., the SGLT2−/− mouse, Sweet Pee mouse, Jimbee mouse, and SAMP10-ΔSglt2 mouse. Biological changes associated with SGLT2 mutations have been reported in these model mice, suggesting that SGLT2 is not only responsible for sugar reabsorption but is also related to other functions, such as bone metabolism, longevity, and cognitive functions. In this review, we present the characteristics of these mutant mice. Moreover, because the relationship between diabetes and Alzheimer’s disease has been discussed, we examined the relationship between changes in glucose homeostasis and the amyloid precursor protein in SGLT2 mutant mice.

Clinical features of pediatric renal glucosuria cases due to SLC5A2 gene variants

BACKGROUND

Familial renal glycosuria (FRG) is a rare renal tubular disorder characterized by a variable loss of glucose in the urine despite normal blood glucose levels, which is seen in a condition in which other tubular functions are preserved. In this study, the molecular and clinical characteristics of pediatric FRG cases due to SLC5A2 gene variants were defined.

METHODS

Demographic features, diagnostic tests, and molecular analyses of patients with a diagnosis of FRG cases due to SLC5A2 gene variants were retrospectively analyzed between 2016 and 2019.

RESULTS

The data of 16 patients who were clinically and genetically diagnosed with FRG in a 4-year period were analyzed. Seven (44%) of the cases were female and 9 (56%) were male. The median age at diagnosis was 6 years old (2 months old to 17 years old). Neuromotor development was found to be appropriate for the age in each case. Systemic blood pressure was evaluated as normal. A homozygous pathogenic variant in the SLC5A2 gene was detected in 14 patients in the genetic examination. A heterozygous variant was detected in one patient. In the other patient, two different heterozygous pathological variants were found in the SLC5A2 gene.

CONCLUSIONS

It was revealed that growth and development were normal in children with glucosuria due to variations in the SCL5A2 gene. Renal function tests and urinary amino acid excretion were also within normal values. In our case series, the most common genetic variation in the SCL5A2 gene was the A219T (c.655G>A) variant.

SLC5A2 mutations, including two novel mutations, responsible for renal glucosuria in Chinese families

Background

Familial renal glucosuria (FRG) is characterized by persistent glucosuria without other impairments of tubular function in the presence of normal serum glucose. SGLT2, which is almost exclusively expressed in the kidney, accounts for most of the glucose reabsorption. Recently, some studies have confirmed that SLC5A2 mutations are responsible for the pathogenesis of familial renal glucosuria, but FRG cases are still rare. Furthermore, there are a few reports about splice-site mutations in previous studies, but the effect of these variants at the mRNA level has hardly been verified.

Methods

Ten patients were recruited in our renal division because of persistent glucosuria, and clinical data of the patients and their family members were recorded as much as possible. The entire coding region and adjacent intronic segments of SLC5A2 were sequenced in FRG patients and their relatives. Permanent growing lymphoblastoid cell lines from FRG patients were established to better preserve genetic information.

Results

A total of nine different mutations were identified: IVS1-16C > A, c.305C > T/p.(A102V), c.395G > A/p.(R132H), c.736C > T/p.(P246S), c.886(−10_-31)delGCAAGCGGGCAGCTGAACGCCC, c.1152_1163delGGTCATGCTGGC/p.(Val385_Ala388del), c.1222G > T/p.(D408Y), c.1496G > A/p.(R499H) and c.1540C > T/p.(P514S); two novel mutations in SLC5A2, c.1222G > T/p.(D408Y) and c.1496G > A/p.(R499H), were identified in the Chinese FRG pedigrees. Ten individuals with heterozygous or compound heterozygous variants had glucosuria in the range of 3.1 to 37.6 g/d.

Conclusion

We screened ten additional Chinese FRG pedigrees for mutations in the SLC5A2 gene and found nine mutations, including two novel mutations. Most variants were private, but IVS1-16C > A and c.886(−10_-31) del may be high frequency splice-site mutations that could be preferentially screened when variants cannot be found in the SLC5A2 exon. Furthermore, we successfully established a permanent growing lymphoblastoid cell line from patients with FRG, which could facilitate further studies of the SLC5A2 gene. The current study provides a valuable clue for further research on the molecular mechanism of SGLT2.

Learning Physiology From Inherited Kidney Disorders

The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.

Renal glucosuria is associated with lower body weight and lower rates of elevated systolic blood pressure: results of a nationwide cross-sectional study of 2.5 million adolescents

BACKGROUND

Gene coding mutations found in sodium glucose co-transporters (SGLTs) are known to cause renal glucosuria. SGLT2 inhibitors have recently been shown to be effective hypoglycemic agents as well as possessing cardiovascular and renal protective properties. These beneficial effects have to some extent, been attributed to weight loss and reduced blood pressure. The aim of the current study was to evaluate the prevalence of renal glucosuria amongst a large cohort of Israeli adolescents and to investigate whether renal glucosuria is associated with lower body weight and lower blood pressure values.

METHODS

Medical and socio-demographic data were collected from the Israeli Defense Force's conscription center's database. A cross-sectional study to evaluate the association between conscripts diagnosed as overweight [BMI percentiles of ≥ 85 and < 95 and obesity (≥ 95 BMI percentile)] and afflicted with renal glucosuria was conducted. In addition, we assessed the association of renal glucosuria with elevated diastolic and systolic blood pressure. Multinomial regression models were used.

RESULTS

The final study cohort comprised 2,506,830 conscripts of whom 1108 (0.044%) were diagnosed with renal glucosuria, unrelated to diabetes mellitus, with males twice as affected compared to females. The adjusted odds ratio for overweight and obesity was 0.66 (95% CI 0.50-0.87) and 0.62 (95% CI 0.43-0.88), respectively. Adolescents afflicted with renal glucosuria were also less likely to have an elevated systolic blood pressure of 130-139 mmHg with an adjusted odds ratio of 0.74 (95% CI 0.60-0.90).

CONCLUSIONS

Renal glucosuria is associated with lower body weight and obesity as well as with lower rates of elevated systolic blood pressure.

Relevance of solute carrier family 5 transporter defects to inherited and acquired human disease

The solute carrier (SLC) group of membrane transport proteins is crucial for cells via their control of import and export of vital molecules across the cellular membrane. Defects in these transporters with narrow substrate specificities cause monogenic disorders, giving us essential clues of their precise roles in cellular functioning. The SLC5 family in particular has been linked to various human diseases, of mild and severe phenotype as well as high and low prevalence. In this review, we describe the effects on health of SLC5 dysfunction and dysregulation by summarizing findings in patients with transporter gene defects. Patients display a plethora of pathologies which include glucose/galactose malabsorption, familiar renal glycosuria, thyroid dyshormonogenesis, and distal hereditary motor neuronopathies. In addition, the therapeutic potential of intervening in transporter activities for treating common diseases such as diabetes and cancer is explored.

A novel compound heterozygous mutation in SLC5A2 contributes to familial renal glucosuria in a Chinese family, and a review of the relevant literature

Familial renal glucosuria (FRG) is a rare condition that involves isolated glucosuria despite normal blood glucose levels. Mutations in the solute carrier family 5 member 2 (SLC5A2) gene, which encodes sodium-glucose cotransporter 2 (SGLT2), have been reported to be responsible for the disease. Genetic testing of the SLC5A2 gene was conducted in a Chinese family with FRG. A number of online tools were used to predict the potential effect of the identified mutations on SGLT2 function. Additionally, the SLC5A2 mutations previously reported in PubMed were summarized. A novel compound heterozygous mutation (c.514T>C, p.W172R; c.1540C>T, p.P514S) of the SLC5A2 gene in a Chinese child with FRG was identified. In total, 86 mutations of the SLC5A2 gene have been reported to be associated with FRG. The novel compound heterozygous mutation (c.514T>C, p.W172R; c.1540C>T, p.P514S) of the SLC5A2 gene may be responsible for the onset of FRG. The present study provides a starting point for further investigation of the molecular pathogenesis of the SLC5A2 gene mutation in patients with FRG.

Identification of ten novel SLC5A2 mutations and determination of the renal threshold for glucose excretion in Chinese patients with familial renal glucosuria

BACKGROUND

Familial renal glucosuria (FRG) is a rare renal tubular disorder characterized by isolated persistent glucosuria without both abnormal glucose metabolism and any signs of proximal tubular dysfunction. SLC5A2 gene mutations are responsible for most FRG cases.

METHODS

Quantitative test for 24-hour urine glucose and RT_G were determined in 9 families (totaling 25 subjects). All coding regions, including intron-exon boundaries, were analyzed with PCR followed by direct sequence analysis.

RESULTS

Ten novel mutations were identified (c.331 T > C, p.W111R; c.374T>C, p.M125T; c.394C>T, p.R132C; c.612G>C, p.Q204H; c.829C>T, p.P277S; c.880G>A, p.D294N; c.1129G>A, p.G377S; c.1194C>A, p.F398L; c.1540C > T, p.P514S and c.1573C>T, p.H525Y). c.886(-10_-31)del that is specific to Chinese population was found in 5 out of 9 families, with a mutation rate of 28% (5/18). The compound heterozygotes presented with much lower RT_G values (1.28 ± 0.10 mmol/L), compared with the carriers of heterozygous variants (5.14 ± 0.77 mmol/L) (p<0.01); c.886(-10_-31)del heterozygotes had significant lower RT_G values than others (4.43 ± 0.37 vs 5.7 ± 0.51 mmol/L; p<0.01).

CONCLUSIONS

Ten novel SLC5A2 mutations are found and c.886(-10-31)del may be a hot spot mutation in Chinese population. Compound heterozygotes had much lower RT_G values than simple heterozygotes. Mixed-meal tolerance test is a simple method for determining RT_G in FRG patients.

Renal glucosuria is not associated with atherosclerotic cardiovascular disease outcome in a general Japanese community

BACKGROUND AND AIMS

Renal glucosuria is defined as the excretion of detectable amounts of glucose in the urine without diabetes or hyperglycemia. Few data exist regarding the prevalence of renal glucosuria and its clinical impact on atherosclerotic cardiovascular diseases.

METHODS

This study included 47,842 subjects (16,913 men, 35.4%) aged ≥40 years who underwent the Japanese specific health checkup in Kanazawa City during 2014. We defined renal glucosuria as fulfillment of all of the following three criteria: 1) detectable glucosuria; 2) the absence of diabetes; 3) normal blood glucose (<110 mg/dl fasting, and <140 mg/dl non-fasting). The presence of renal glucosuria and of factors associated with atherosclerotic cardiovascular diseases, including coronary artery disease and stroke, was assessed.

RESULTS

The criteria for renal glucosuria were met by 665 (1.4%) subjects. Significantly higher proportions of subjects with renal glucosuria exhibited coronary artery disease, stroke, or either outcome than those without (14.9% vs. 12.1%, p = 0.0305; 9.9% vs. 6.9%, p = 0.00255; 22.3% vs. 17.0%, p = 4.0 × 10^-4, respectively), but multivariate logistic regression analyses revealed that renal glucosuria was not associated with coronary artery disease (odds ratio [OR] = 0.940, 95% confidence interval [CI] = 0.748-1.171, not significant), stroke (OR = 1.122, 95% CI = 0.853-1.453, not significant), or atherosclerotic cardiovascular diseases (OR = 1.122, 95% CI = 0.853-1.453, not significant).

CONCLUSIONS

These results indicate that the prevalence of renal glucosuria in the Japanese general population was 1.4%, and that renal glucosuria was not associated with atherosclerotic cardiovascular diseases per se.

A recurrent deletion in the SLC5A2 gene including the intron 7 branch site responsible for familial renal glucosuria

Familial renal glycosuria (FRG) is caused by mutations in the SLC5A2 gene, which codes for Na⁺-glucose co-transporters 2 (SGLT2). The aim of this study was to analyze and identify the mutations in 16 patients from 8 families with FRG. All coding regions, including intron-exon boundaries, were analyzed using PCR followed by direct sequence analysis. Six mutations in SLC5A2 gene were identified, including five missense mutations (c.393G > C, p.K131N; c.1003A > G, p.S335G; c.1343A > G, p.Q448R; c.1420G > C, p.A474P; c.1739G > A, p.G580D) and a 22-bp deletion in intron 7 (c.886(-10_-31)del) removing the putative branch point sequence. By the minigene studies using the pSPL3 plasmids, we confirmed that the deletion c.886(-10_-31)del acts as a splicing mutation. Furthermore, we found that this deletion causes exclusion of exon 8 in the SCL5A2 transcript in patients. The mutation c.886(-10_-31)del was present in 5 (62.5%) of 8 families, and accounts for about 37.5% of the total alleles (6/16). In conclusion, six mutations resulting in FRG were found, and the c.886(-10_-31)del may be the high frequency mutation that can be screened in FRG patients with uniallelic or negative SLC5A2 mutations.

Novel SLC5A2 mutation contributes to familial renal glucosuria: Abnormal expression in renal tissues

Familial renal glucosuria (FRG) is characterized by persistent glucosuria in the presence of normal serum glucose concentrations, while other impairments of tubular function are absent. Mutations in the sodium-glucose co-transporter 2 (SLC5A2) gene have been found to be responsible for FRG. However, direct evidence for the presence of SLC5A2 mutant in renal tissues is very rare. In previous studies, a non-sense mutation (c.1320 G>A:p.W440X) that would cause premature termination of the protein was found. However, the effects in the renal tissues were not reported. In the current study, a patient with FRG and a urinary glucose excretion rate of 8.3 g/day is described, for whom a novel missense mutation (c.1319G>A:p.W440X) was revealed by sequencing. Furthermore, in the immunofluorescence examination of a renal biopsy specimen, SLC5A2 was detected in the apical side of the proximal convoluted tubule, discontinuously decreased in comparison with that in normal and disease controls. The results imply that both wild-type SLC5A2 and mutant SLC5A2 with abnormal distribution were expressed in the renal tissues, and that the reduction of SLC5A2 expression and function were due to the c.1319G>A:p.W440X mutation. The current study provides valuable clues regarding the SLC5A2 molecule from genotype to phenotype in families affected by FRG.

Influence of Familial Renal Glycosuria Due to Mutations in the SLC5A2 Gene on Changes in Glucose Tolerance over Time

Familial renal glycosuria is an inherited disorder resulting in glucose excretion in the urine despite normal blood glucose concentrations. It is most commonly due to mutations in the SLC5A2 gene coding for the glucose transporter SGLT2 in the proximal tubule. Several drugs have been introduced as means to lower glucose in patients with type 2 diabetes targeting SGLT2 resulting in renal glycosuria, but no studies have addressed the potential effects of decreased renal glucose reabsorption and chronic glycosuria on the prevention of glucose intolerance. Here we present data on a large pedigree with renal glycosuria due to two mutations (c.300-303+2del and p.A343V) in the SLC5A2 gene. The mutations, which in vitro affected glucose transport in a cell line model, and the ensuing glycosuria were not associated with better glycemic control during a follow-up period of more than 10 years. One individual, who was compound heterozygous for mutations in the SLC5A2 gene suffered from severe urogenital candida infections and postprandial hypoglycemia. In conclusion, in this family with familial glycosuria we did not find any evidence that chronic loss of glucose in the urine would protect from deterioration of the glucose tolerance over time.

A safety evaluation of canagliflozin : a first-in-class treatment for type 2 diabetes

INTRODUCTION

Numerous treatments are available for type 2 diabetes mellitus (T2DM), which can improve insulin sensitivity or stimulate its secretion. These are usually unable to halt progression. Inhibition of glucose reabsorption from the renal filtrate was proposed as a novel therapeutic target. Sodium/glucose co-transporter 2 (SGLT2) inhibitors were developed accordingly, with canagliflozin the first to launch in the US in 2013.

AREAS COVERED

The mechanism of action of canagliflozin, its pharmacokinetic data and its clinical applications and efficacy data from clinical studies of both subjects with T2DM controlled on diet and exercise, and those on glucose-lowering agents and insulin. The evaluation focuses primarily on the safety of canagliflozin in clinical trials conducted for initial registration due to limited post-marketing data, discusses safety in special populations, before comparing its safety with existing therapies.

EXPERT OPINION

Canagliflozin offers a novel therapeutic approach to T2DM; advantages include weight loss and blood pressure lowering with a low intrinsic risk of hypoglycaemia. The main adverse effects likely to be seen are a very small increase in risk of urinary tract infections and a modest risk of developing genital fungal infections. Studies suggest no increased risk of cardiovascular (CV) disease, but longer duration outcome studies are essential.

Novel SLC5A2 variants contribute to renal glucosuria in Chinese families: abnormal expression and dysfunction of variant SLC5A2

Familial renal glucosuria (FRG) is characterized by persistent glucosuria despite normal serum glucose and the absence of overt tubular dysfunction. Variants in solute carrier family 5 (sodium-glucose cotransporter), member 2 (SLC5A2) have been reported in FRG patients. However, the functional and expression-related consequences of such variants have been scarcely investigated. In the current study, we studied five FRG families and identified six missense mutations, including four novel variants (c.1051T>C/.(C351R), c.1400T>C/p.(V467A), c.1420G>C/p.(A474P), c.1691G>A/p.(R564Q); RNA not analyzed) and two variants that had been previously reported (c.294C>A/p.(F98L), c.736C>T/p.(P246S); RNA not analyzed). The probands were either heterozygous or compound heterozygous for SLC5A2 variants and had glucosuria of 5.9%-19.6 g/day. Human 293 cells were transfected with plasmid constructs to study the expression and function of SLC5A2 variants in vitro. Western blotting revealed that the expression levels of SLC5A2-351R-GFP, SLC5A2-467A-GFP, SLC5A2-474P-GFP, and SLC5A2-564Q-GFP were significantly decreased compared with wild-type SLC5A2-GFP (37%-55%). Confocal microscopy revealed that three variants (c.1400T>C, c.1420G>C, c.1691G>A) resulted in a loss of the punctate membrane pattern typical of wild-type SLC5A2. All variants had a significantly lower transport capacity in than the wild-type control. The current study provides a starting point to further investigate the molecular mechanism of SLC5A2 in FRG families and provides functional clues for antidiabetes drugs.

De novo expression of sodium-glucose cotransporter SGLT2 in Bowman's capsule coincides with replacement of parietal epithelial cell layer with proximal tubule-like epithelium

In kidney nephron, parietal epithelial cells line the Bowman's capsule and function as a permeability barrier for the glomerular filtrate. Bowman's capsule cells with proximal tubule epithelial morphology have been found. However, the effects of tubular metaplasia in Bowman's capsule on kidney function remain poorly understood. Sodium-glucose cotransporter 2 (SGLT2) plays a major role in reabsorption of glucose in the kidney and is expressed on brush border membrane (BBM) of epithelial cells in the early segment of the proximal tubule. We hypothesized that SGLT2 is expressed in tubularized Bowman's capsule and used our novel antibody to test this hypothesis. Immunohistochemical analysis was performed with our SGLT2 antibody on C57BL/6 mouse kidney prone to have tubularized Bowman's capsules. Cell membrane was examined with periodic acid-Schiff (PAS) stain. The results showed that SGLT2 was localized on BBM of the proximal tubules in young and adult mice. Bowman's capsules were lined mostly with normal brush border-less parietal epithelial cells in young mice, while they were almost completely covered with proximal tubule-like cells in adult mice. Regardless of age, SGLT2 was expressed on BBM of the tubularized Bowman's capsule but did not co-localize with nephrin in the glomerulus. SGLT2-expressing tubular cells expanded from the urinary pole toward the vascular pole of the Bowman's capsule. This study identified the localization of SGLT2 in the Bowman's capsule. Bowman's capsules with tubular metaplasia may acquire roles in reabsorption of filtered glucose and sodium.

Metabolic response to sodium-glucose cotransporter 2 inhibition in type 2 diabetic patients

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors lower glycemia by enhancing urinary glucose excretion. The physiologic response to pharmacologically induced acute or chronic glycosuria has not been investigated in human diabetes.

METHODS

We evaluated 66 patients with type 2 diabetes (62 ± 7 years, BMI = 31.6 ± 4.6 kg/m(2), HbA1c = 55 ± 8 mmol/mol, mean ± SD) at baseline, after a single dose, and following 4-week treatment with empagliflozin (25 mg). At each time point, patients received a mixed meal coupled with dual-tracer glucose administration and indirect calorimetry.

RESULTS

Both single-dose and chronic empagliflozin treatment caused glycosuria during fasting (median, 7.8 [interquartile range {IQR}, 4.4] g/3 hours and 9.2 [IQR, 5.2] g/3 hours) and after meal ingestion (median, 29.0 [IQR, 12.5] g/5 hours and 28.2 [IQR, 15.4] g/5 hours). After 3 hours of fasting, endogenous glucose production (EGP) was increased 25%, while glycemia was 0.9 ± 0.7 mmol/l lower (P < 0.0001 vs. baseline). After meal ingestion, glucose and insulin AUC decreased, whereas the glucagon response increased (all P < 0.001). While oral glucose appearance was unchanged, EGP was increased (median, 40 [IQR, 14] g and 37 [IQR, 11] g vs. 34 [IQR, 11] g, both P < 0.01). Tissue glucose disposal was reduced (median, 75 [IQR, 16] g and 70 [IQR, 21] g vs. 93 [IQR, 18] g, P < 0.0001), due to a decrease in both glucose oxidation and nonoxidative glucose disposal, with a concomitant rise in lipid oxidation after chronic administration (all P < 0.01). β Cell glucose sensitivity increased (median, 55 [IQR, 35] pmol • min(-1) • m(-2) • mM(-1) and 55 [IQR, 39] pmol • min(-1) • m(-2) • mM(-1) vs. 44 [IQR, 32] pmol • min(-1) • m(-2) • mM(-1), P < 0.0001), and insulin sensitivity was improved. Resting energy expenditure rates and those after meal ingestion were unchanged.

CONCLUSIONS

In patients with type 2 diabetes, empagliflozin-induced glycosuria improved β cell function and insulin sensitivity, despite the fall in insulin secretion and tissue glucose disposal and the rise in EGP after one dose, thereby lowering fasting and postprandial glycemia. Chronic dosing shifted substrate utilization from carbohydrate to lipid. Trial registration. ClinicalTrials.Gov NCT01248364 (EudraCT no. 2010-018708-99). Funding. This study was funded by Boehringer Ingelheim.

Sodium glucose cotransporter 2 and the diabetic kidney

PURPOSE OF REVIEW

Reabsorption of glucose in the proximal tubule occurs predominantly via the sodium glucose cotransporter 2 (SGLT2). There has been intense interest in this transporter as a number of SGLT2 inhibitors have entered clinical development. SGLT2 inhibitors act to lower plasma glucose by promoting glycosuria and this review aims to outline the effect on the diabetic kidney of this hypoglycaemic agent.

RECENT FINDINGS

This review provides an overview of recent findings in this area: the transcriptional control of SGLT2 expression in human proximal tubular cells implicates a number of cytokines in the alteration of SGLT2 expression; experimental data show that SGLT2 inhibition may correct early detrimental effects of diabetes by reducing proximal tubular sodium and glucose transport, suggesting a possible renoprotective effect independent of the glucose lowering effects of these agents; and the nonglycaemic effects of SGLT2 inhibitors may have an impact on renal outcomes.

SUMMARY

The available clinical evidence shows consistent reduction in glycaemic parameters and some evidence suggests additional effects including weight loss and mild blood pressure reduction. There are some side effects that warrant further investigation and establishing whether SGLT2 inhibition provides a renal benefit relies on future long-term studies with specific renal end-points.

A novel SGLT is expressed in the human kidney

Selective inhibitors of sodium-glucose cotransporter 2 (SGLT2)-mediated reabsorption of glucose in the proximal tubule of the kidney are being developed for the treatment of diabetes. SGLT2 shares high degree of homology with SGLT3; however, very little is known about the expression and functional role of SGLT3 in the human kidney. Indeed, the SGLT2 inhibitors that are currently in clinical trials might affect the expression and/or the activity of SGLT3. Therefore, the present study examined the expression of SGLT3 mRNA and protein in human kidney and in a human proximal tubule HK-2 cell line. The results indicated that human SGLT3 (hSGLT3) message and protein are expressed both in vivo and in vitro. We also studied the activity of hSGLT3 protein following its over-expression in mammalian kidney-derived COS-7 cells and in HK-2 cells treated with the imino sugar deoxynojirimycin (DNJ), a potent agonist of hSGLT3. Over-expression of hSGLT3 in COS-7 cells increased intracellular sodium concentration by 3-fold without affecting glucose transport. Activation of hSGLT3 with DNJ (50μM) increased sodium uptake in HK-2 cells by 5.5 fold and this effect could be completely blocked with SGLT inhibitor phlorizin (50μM). These results suggest that SGLT3 is expressed in human proximal tubular cells where it serves as a novel sodium transporter. Up-regulation of the expression of SGLT3 in the proximal tubule in diabetic patients may contribute to the elevated sodium transport in this segment of the nephron that has been postulated to promote hyperfiltration and renal injury.