Glucose transporters in human renal proximal tubular cells isolated from the urine of patients with non-insulin-dependent diabetes

The bulk of glucose that is filtered by the renal glomerulus is reabsorbed by the glucose transporters of the proximal convoluted tubular epithelium. However, it has been difficult to investigate this in diseases such as type 2 diabetes because of the inability to isolate primary renal cells from patients without a renal biopsy. We report here a method for the immunomagnetic isolation and novel primary culture of human exfoliated proximal tubular epithelial cells (HEPTECs) from fresh urine. The primary isolates are highly enriched and differentiated and express characteristic proximal tubular phenotypic markers. They continue to express the proximal tubular markers CD13/aminopeptidase-N, sodium glucose cotransporter (SGLT) 2, and alkaline phosphatase through up to six subsequent subcultures in a similar way to human proximal cells isolated from renal biopsies. In a hyperglycemic environment, HEPTECs isolated from patients with type 2 diabetes expressed significantly more SGLT2 and the facilitative glucose transporter GLUT2 than cells from healthy individuals. We also demonstrated a markedly increased renal glucose uptake in HEPTECs isolated from patients with type 2 diabetes compared with healthy control subjects. Our findings indicate for the first time in a human cellular model that increased renal glucose transporter expression and activity is associated with type 2 diabetes.     

Effect of kidney disease on glucose handling (including genetic defects)

Reabsorption of glucose in the proximal renal tubule involves the Na(+)-coupled glucose cotransporter (SGLT) and the facilitative glucose transport (GLUT) multigene glucose transport families. Mutations in SLC5A2, the SGLT2 coding gene, are responsible for familial renal glucosuria (FRG), a genetic disorder characterized by glucosuria in the absence of both hyperglycemia and generalized proximal tubular dysfunction. In this paper we focus on FRG and describe other inherited and acquired clinical conditions associated with glucosuria. In addition, a brief review on the regulation of renal glucose transport in diabetes is provided.     

Glucose handling by the kidney

The kidney contributes to glucose homeostasis through processes of gluconeogenesis, glucose filtration, glucose reabsorption, and glucose consumption. Each of these processes can be altered in patients with type-2 diabetes (T2DM), providing potential targets for novel therapies. Recent studies have indicated that the kidney is responsible for up to 20% of all glucose production via gluconeogenesis. In patients with T2DM, overall glucose production increases by as much as 300%, with equal contributions from hepatic and renal sources. This increased production contributes not only to increased fasting glucose in T2DM patients but also to raised postprandial glucose because, in contrast to the liver, glucose ingestion increases renal gluconeogenesis. Under normal circumstances, up to 180 g/day of glucose is filtered by the renal glomerulus and virtually all of it is subsequently reabsorbed in the proximal convoluted tubule. This reabsorption is effected by two sodium-dependent glucose cotransporter (SGLT) proteins. SGLT2, situated in the S1 segment, is a low-affinity high-capacity transporter reabsorbing up to 90% of filtered glucose. SGLT1, situated in the S3 segment, is a high-affinity low-capacity transporter reabsorbing the remaining 10%. In patients with T2DM, renal reabsorptive capacity maladaptively increases from a normal level of 19.5 to 23.3 mmol/l/min. Once glucose has been reabsorbed into the tubular epithelial cells, it diffuses into the interstitium across specific facilitative glucose transporters (GLUTs). GLUT1 and GLUT2 are associated with SGLT1 and SGLT2, respectively.     

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.     

Regulatory mechanisms of Na(+)/glucose cotransporters in renal proximal tubule cells

Glucose is a key fuel and an important metabolic substrate in mammals. Renal proximal tubular cells (PTCs) not only reabsorb filtered glucose but are also believed to play a role in the glucotoxicity associated with renal pathogenesis, such as in diabetes. The proximal tubule environment is where 90% of the filtered glucose is reabsorbed by the low-affinity/high-capacity Na(+)/glucose cotransporter 2 (SGLT2) and facilitated diffusion glucose transporter 2 (GLUT2). Both active and facilitative glucose transporters have distinct distribution profiles along the proximal tubule related to their particular kinetic characteristics. A number of mechanisms contribute to the changes in the cellular functions, which occur in response to exposure to various endogenous factors. Hyperglycemia was reported to regulate the renal SGLT activities through the reactive oxygen species-nuclear factor-kappaB pathways, which suggests that the transcellular glucose uptake within the PTCs contribute to the development of diabetic-like nephropathy. Angiotensin II (ANG II) plays an important role in its development through epidermal growth factor receptor (EGFR) transactivation. Therefore, a combination of high glucose, ANG II, and EGF are involved in diabetic-like nephropathy by regulating the SGLT activity. In addition, endogenously enhanced SGLTs have a cytoprotective function. The renal proximal tubules play a major role in regulating the plasma glucose levels, and there is increasing interest in the renal glucose transporters on account of their potential implications in the treatment of various conditions including diabetes mellitus.     

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.     

Effect of long-term type 1 diabetes on renal sodium and water transporters in rats

The effects of long-term diabetes in the presence of established nephropathy on tubular function remains poorly understood. We evaluated the levels of the main sodium and water transport proteins expressed in the kidney after long-term (8 weeks) of streptozotocin (STZ)-induced type 1 diabetes mellitus (DM) in untreated (D) and insulin (4 U/s.c./day)-treated (D+I) rats. D animals presented upregulation ( approximately 4.5-fold) of Na/glucose cotransporter (SGLT1), whereas the alpha-subunit of the epithelial sodium channel (alpha-ENaC) and aquaporin 1 (AQP1) were downregulated ( approximately 20 and 30% respectively) with no change in the Na/H exchanger (NHE3), Na/Cl cotransporter (TSC) and AQP2. Insulin replacement partially prevented these alterations and caused increases in the expression of alpha-ENaC and AQP2. These effects suggest an action of insulin in the tubular transport properties. The upregulation of SGLT1 may constitute a mechanism to prevent greater glucose losses in the urine but it may result in glucotoxicity to the proximal epithelial cells contributing to the diabetic nephropathy. The decrease of alpha-ENaC in D animals may compensate for the increased sodium reabsorption via SGLT1 resulting in discrete natriuresis. DM-induced polyuria was not due to changes in AQP2 expression.     

Molecular analysis of the SGLT2 gene in patients with renal glucosuria

The role of SGLT2 (the gene for a renal sodium-dependent glucose transporter) in renal glucosuria was evaluated. Therefore, its genomic sequence and its intron-exon organization were determined, and 23 families with index cases were analyzed for mutations. In 21 families, 21 different SGLT2 mutations were detected. Most of them were private; only a splice mutation was found in 5 families of different ethnic backgrounds, and a 12-bp deletion was found in two German families. Fourteen individuals (including the original patient with 'renal glucosuria type 0') were homozygous or compound heterozygous for an SGLT2 mutation resulting in glucosuria in the range of 14.6 to 202 g/1.73 m(2)/d (81 - 1120 mmol/1.73 m(2)/d). Some, but not all, of their heterozygous family members had an increased glucose excretion of up to 4.4 g/1.73 m(2)/d (24 mmol/1.73 m(2)/d). Likewise, in index cases with glucosuria below 10 g/1.73 m(2)/d (55 mmol/1.73 m(2)/d) an SGLT2 mutation, if present, was always detected in the heterozygous state. We conclude that SGLT2 plays an important role in renal tubular glucose reabsorption. Inheritance of renal glucosuria shows characteristics of a codominant trait with variable penetrance.     

SGLT2 deletion improves glucose homeostasis and preserves pancreatic beta-cell function

OBJECTIVE

Inhibition of the Na⁺-glucose cotransporter type 2 (SGLT2) is currently being pursued as an insulin-independent treatment for diabetes; however, the behavioral and metabolic consequences of SGLT2 deletion are unknown. Here, we used a SGLT2 knockout mouse to investigate the effect of increased renal glucose excretion on glucose homeostasis, insulin sensitivity, and pancreatic β-cell function.

RESEARCH DESIGN AND METHODS

SGLT2 knockout mice were fed regular chow or a high-fat diet (HFD) for 4 weeks, or backcrossed onto the db/db background. The analysis used metabolic cages, glucose tolerance tests, euglycemic and hyperglycemic clamps, as well as isolated islet and perifusion studies.

RESULTS

SGLT2 deletion resulted in a threefold increase in urine output and a 500-fold increase in glucosuria, as well as compensatory increases in feeding, drinking, and activity. SGLT2 knockout mice were protected from HFD-induced hyperglycemia and glucose intolerance and had reduced plasma insulin concentrations compared with controls. On the db/db background, SGLT2 deletion prevented fasting hyperglycemia, and plasma insulin levels were also dramatically improved. Strikingly, prevention of hyperglycemia by SGLT2 knockout in db/db mice preserved pancreatic β-cell function in vivo, which was associated with a 60% increase in β-cell mass and reduced incidence of β-cell death.

CONCLUSIONS

Prevention of renal glucose reabsorption by SGLT2 deletion reduced HFD- and obesity-associated hyperglycemia, improved glucose intolerance, and increased glucose-stimulated insulin secretion in vivo. Taken together, these data support SGLT2 inhibition as a viable insulin-independent treatment of type 2 diabetes.Treatments of type 2 diabetes must balance the prevention of microvascular complications with the minimization of clinically significant hypoglycemia. The difficulty in safely achieving these goals, combined with epidemic increases in diabetes worldwide, has spurred the search for novel therapeutic strategies. Among these, inhibition of the Na⁺-glucose cotransporter type 2 (SGLT2) has emerged as a promising therapy (1,2). SGLT2 is a member of the SLC5 gene family and transports glucose across cells using the Na⁺ gradient established by Na⁺-K⁺-ATPases (3). SGLT2 is a low-affinity, high-capacity transporter expressed predominantly in the early proximal tubule of the kidney and accounts for about 90% of renal glucose reabsorption (4–6). Given that the kidney filters approximately 180 g of glucose daily, SGLT2 inhibition may not just reduce hyperglycemia but may also promote negative energy balance and weight loss.Type 2 diabetes is characterized by fasting hyperglycemia as a result of insulin resistance, but is often preceded by hyperinsulinemia and normal blood glucose levels, a state that is maintained by compensatory insulin secretion by the pancreatic β-cell (7). The ability of the β-cell to counteract an increased glucose load is short-lived, however, and eventually pancreatic islets fail, giving rise to hyperglycemia. Rodent and human studies have both shown that glucose toxicity is implicated in β-cell failure by increasing the rate of β-cell death by the induction of proapoptotic genes (8–10). Inhibition of SGLT2 therefore has the potential to not only acutely lower hyperglycemia but to also improve glucose homeostasis by reducing glucose toxicity and preventing islet failure.Despite recent interest in SGLT2 as a potential target for diabetes treatment, relatively few long-term models of SGLT2 deficiency have been characterized. Previously, nonselective inhibition of both SGLT1 and SGLT2 for 4 weeks in partially pancreatomized diabetic rats by injection of phlorizin led to increases in insulin sensitivity and insulin secretion (11,12). More recently, improvements in glucose homeostasis were demonstrated in diabetic rodent models after treatment with SGLT2-specific inhibitors for periods of 2 to 9 weeks (13–16). As many as seven different SGLT2 inhibitors designed for use in humans have been characterized in cell culture and animal studies, and many of these have moved on to clinical trials (2,17–22). Here, we describe the first in vivo characterization of glucose homeostasis in a SGLT2 knockout mouse model. We investigated the behavioral and metabolic consequences of SGLT2 deletion, and furthermore, we determined the effect of renal glucose excretion on glucose homeostasis, insulin sensitivity, and β-cell function in the context of both high-fat feeding and genetically determined obesity (db/db) and diabetes.     

Na(+)-D-glucose cotransporter SGLT1 is pivotal for intestinal glucose absorption and glucose-dependent incretin secretion

To clarify the physiological role of Na(+)-D-glucose cotransporter SGLT1 in small intestine and kidney, Sglt1(-/-) mice were generated and characterized phenotypically. After gavage of d-glucose, small intestinal glucose absorption across the brush-border membrane (BBM) via SGLT1 and GLUT2 were analyzed. Glucose-induced secretion of insulinotropic hormone (GIP) and glucagon-like peptide 1 (GLP-1) in wild-type and Sglt1(-/-) mice were compared. The impact of SGLT1 on renal glucose handling was investigated by micropuncture studies. It was observed that Sglt1(-/-) mice developed a glucose-galactose malabsorption syndrome but thrive normally when fed a glucose-galactose-free diet. In wild-type mice, passage of D-glucose across the intestinal BBM was predominantly mediated by SGLT1, independent the glucose load. High glucose concentrations increased the amounts of SGLT1 and GLUT2 in the BBM, and SGLT1 was required for upregulation of GLUT2. SGLT1 was located in luminal membranes of cells immunopositive for GIP and GLP-1, and Sglt1(-/-) mice exhibited reduced glucose-triggered GIP and GLP-1 levels. In the kidney, SGLT1 reabsorbed ～3% of the filtered glucose under normoglycemic conditions. The data indicate that SGLT1 is 1) pivotal for intestinal mass absorption of d-glucose, 2) triggers the glucose-induced secretion of GIP and GLP-1, and 3) triggers the upregulation of GLUT2.     

Place of sodium-glucose co-transporter type 2 inhibitors for treatment of type 2 diabetes

Inhibitors of sodium-glucose co-transporter type 2 (SGLT2), such as canagliflozin and dapagliflozin, are recently approved for treatment of type 2 diabetes. These agents lower blood glucose mainly by increasing urinary glucose excretion. Compared with placebo, SGLT2 inhibitors reduce hemoglobin A1c (HbA1c) levels by an average of 0.5%-0.8% when used as monotherapy or add-on therapy. Advantages of this drug class include modest weight loss of approximately 2 kg, low risk of hypoglycemia, and decrease blood pressure of approximately 4 mmHg systolic and 2 mmHg diastolic. These characteristics make these agents potential add-on therapy in patients with HbA1c levels close to 7%-8.0%, particularly if these patients are obese, hypertensive, and/or prone for hypoglycemia. Meanwhile, these drugs are limited by high frequency of genital mycotic infections. Less common adverse effects include urinary tract infections, hypotension, dizziness, and worsening renal function. SGLT2 inhibitors should be used with caution in the elderly because of increased adverse effects, and should not be used in chronic kidney disease due to decreased or lack of efficacy and nephrotoxicity. Overall, SGLT2 inhibitors are useful addition for treatment of select groups of patients with type 2 diabetes, but their efficacy and safety need to be established in long-term clinical trials.     

Effect of Empagliflozin on Tacrolimus‐Induced Pancreas Islet Dysfunction and Renal Injury

An inhibitor of sodium glucose co‐transporter type 2 (SGLT‐2) is recommended in type 2 diabetes mellitus (DM) but its use is still undetermined in tacrolimus (TAC)‐induced DM. We evaluated the effect of empagliflozin (Em) on TAC‐induced pancreatic islet dysfunction and renal injury in an experimental model of TAC‐induced DM and in vitro. TAC induced a twofold increase in SGLT‐2 expression, while Em decreased SGLT‐2 expression and further increased urinary glucose excretion compared to the TAC group. Em reduced hyperglycemia and increased plasma insulin level, pancreatic islet size, and glucose‐stimulated insulin secretion compared to the TAC group. In kidney, Em alleviated TAC‐induced renal dysfunction and decreased albumin excretion and histological injury compared with the TAC group. Increased oxidative stress and apoptotic cell death by TAC was remarkably decreased with Em in serum and pancreatic and renal tissues. In in vitro study, TAC decreased cell viability and increased reactive oxygen species (ROS) production in both insulin‐secreting beta‐cell derived (INS‐1) and human kidney‐2 (HK‐2) cell lines. Addition of Em increased cell viability and decreased ROS production in HK‐2 but not in INS‐1 cell lines. This suggests that Em is effective in controlling TAC‐induced hyperglycemia and has direct protective effect on TAC‐induced renal injury.     

Ipragliflozin: A novel sodium-glucose cotransporter 2 inhibitor developed in Japan

Sodium-glucose cotransporter 2(SGLT2) inhibition induces glucosuria and decreases blood glucose levels in diabetic patients and lowers hypoglycemic risk. SGLT1 is expressed in the kidney and intestine; SGLT1 inhibition causes abdominal symptoms such as diarrhea and reduces incretin secretion. Therefore, SGLT2 selectivity is important. Ipragliflozin is highly selective for SGLT2. In type 2 diabetes mellitus(T2DM), urinaryglucose excretion increased to 90 g/24 h after 28 d of treatment with ipragliflozin 300 mg/d. Twelve weeks of ipragliflozin 50 mg/d vs placebo reduced glycated hemoglobin and body weight by 0.65% and 0.66 kg, respectively, in Western T2 DM patients, and by 1.3% and 1.89 kg, respectively, in Japanese patients. Ipragliflozin(highly selective SGLT2 inhibitor) improves glycemic control and reduces body weight and lowers hypoglycemic risk and abdominal symptoms. Ipragliflozin can be a novel anti-diabetic and antiobesity agent.     

Apical GLUT2: a major pathway of intestinal sugar absorption

Understanding the mechanisms that determine postprandial fluctuations in blood glucose concentration is central for effective glycemic control in the management of diabetes. Intestinal sugar absorption is one such mechanism, and studies on its increase in experimental diabetes led us to propose a new model of sugar absorption. In the apical GLUT2 model, the glucose transported by the Na(+)/glucose cotransporter SGLT1 promotes insertion of GLUT2 into the apical membrane within minutes, so that the mechanism operates during assimilation of a meal containing high-glycemic index carbohydrate to provide a facilitated component of absorption up to three times greater than by SGLT1. Here we review the evidence for the apical GLUT2 model and describe how apical GLUT2 is a target for multiple short-term nutrient-sensing mechanisms by dietary sugars, local and endocrine hormones, cellular energy status, stress, and diabetes. These mechanisms suggest that apical GLUT2 is a potential therapeutic target for novel dietary or pharmacological approaches to control intestinal sugar delivery and thereby improve glycemic control.     

Overexpression of angiotensinogen increases tubular apoptosis in diabetes

The intrarenal renin-angiotensin system (RAS) plays an important role in the progression of diabetic nephropathy. We have previously reported that mice overexpressing angiotensinogen in renal proximal tubular cells (RPTC) develop hypertension, albuminuria, and renal injury. Here, we investigated whether activation of the intrarenal RAS contributes to apoptosis of RPTC in diabetes. Induction of diabetes with streptozotocin in these transgenic mice led to significant increases in BP, albuminuria, RPTC apoptosis, and proapoptotic gene expression compared with diabetic nontransgenic littermates. Insulin and/or RAS blockers markedly attenuated these changes. Hydralazine prevented hypertension but not albuminuria, RPTC apoptosis, or proapoptotic gene expression. In vitro, high-glucose medium significantly increased apoptosis and caspase-3 activity in rat immortalized RPTC overexpressing angiotensinogen compared with control cells, and these changes were prevented by insulin and/or RAS blockers. In conclusion, intrarenal RAS activation and high glucose may act in concert to increase tubular apoptosis in diabetes, independent of systemic hypertension.     

Glucose dynamics and mechanistic implications of SGLT2 inhibitors in animals and humans

Glucose is freely filtered in the glomeruli before being almost entirely reabsorbed into circulation from the proximal renal tubules. The sodium-glucose cotransporter 2 (SGLT2), present in the S1 segment of the proximal tubule, is responsible for the majority of glucose reabsorption. SGLT2 inhibitors reduce glucose reabsorption and increase urinary glucose excretion. In animal models and humans with type 2 diabetes, this effect is associated with reduced fasting and postprandial blood glucose levels, and reduced hemoglobin A1c. Animal studies suggest that reduction of hyperglycemia with SGLT2 inhibitors may also improve insulin sensitivity and preserve β-cell function. Urinary excretion of excess calories with SGLT2 inhibitors is also associated with reduction in body weight. Modest reductions in blood pressure have been noted with SGLT2 inhibitors, consistent with a mild diuretic action. Some C-glucoside SGLT2 inhibitors, such as dapagliflozin, have pharmacokinetic properties that make them amenable to once-daily dosing.     

Islet transplantation to the renal subcapsular space improves late complications in streptozotocin-diabetic rats

Transplantation of isolated islets is a promising approach in the treatment of diabetes. We have examined the long-term effects on the late complications of islet transplantation in an experimental diabetes model in the rat. Diabetes was induced by streptozotocin (70 mg/kg i.v.) and the rats were treated with either insulin (daily injection of 40 U) or transplantation of 1,000 freshly isolated, hand-picked, islets into the left renal subcapsular space. Both islet transplantation and insulin treatment completely normalized the increased levels of blood glucose, urine volume and water intake that were observed in the diabetic rats. The decreased growth rate of the diabetic rats was almost normalized by both treatment protocols. As for late complications, after 3 months, all untreated diabetic rats had cataract. They also had swelling and vacuolation of renal tubular cells, and, consistent with this, very high levels of urinary beta 2-microglobulin excretion. Both islet transplantation and insulin treatment completely prevented these late complications. Thus, islet transplantation to the renal subcapsular space is in this experimental model as good as insulin treatment in treating the clinical signs of diabetes and in preventing diabetic complications in the eye and kidney.     

Ubiquitination and endoplasmic reticulum stress of renal intrinsic cells in hyperglycemia

Objective To investigate the effects of hyperglycemia on ubiquitination and endoplasmic reticulum stress in renal intrinsic cells (podocytes and proximal tubular epithelial cells) and its role in pathogenesis of diabetic nephropathy. Methods Diabetic mice were induced by streptozotocin injection. After 16 weeks of hyperglycemia, immunofluorescence was used to detect the expressions of ubiquitination and glucose-regulating protein 94 (GRP94) in renal cortex and medulla area of kidney sections. Primary mouse podocyte and proximal tubular epithelial cells were isolated by flow cytometry, and exposed to 30 mmol/L glucose for indicated time (1 d, 3 d and 7 d). Their ubiquitination and GRP94 expressions were evaluated by Western blotting. Results Diabetic mice presented microalbuminuria and slightly widened mesangium was found in glomerular area. Ubiquitinated proteins, mainly localized in podocytes and tubular epithelial cells, exhibited an apparently higher expression in diabetic mice than control mice (all P＜0.05). Hyperglycemia promoted the ubiquitination in a time-dependent manner. Compared with their normal cells, primary mouse podocyte and primary tubular epithilial cells treated with high glucose for 3 d and 7 d showed increased ubiquitinated protein (all P＜0.05). GRP94 was interspersed in podocytes and proximal tubular epithelial cells. Expression of GRP94 was significantly increased in glomerular area of diabetic mice and podocyte with 3 and 7 day-high glucose as compared with those in their control groups (all P＜0.05). GRP94 expression had no significant change in tubular area and tubular epithilial cells treated with high glucose. Conclusions Hyperglycemia may lead to accumulation of ubiquitinated proteins in intrinsic kidney cells. The imbalance of protein homeostasis in podocyte may contribute to podocyte injury during the onset of diabetic nephropathy.     

The generalized aminoaciduria seen in patients with hepatocyte nuclear factor-1alpha mutations is a feature of all patients with diabetes and is associated with glucosuria

Hepatocyte nuclear factor-1alpha (HNF-1alpha) mutations are the most common cause of maturity-onset diabetes of the young. HNF-1alpha homozygous knockout mice exhibit a renal Fanconi syndrome with glucosuria and generalized aminoaciduria in addition to diabetes. We investigated glucosuria and aminoaciduria in patients with HNF-1alpha mutations. Sixteen amino acids were measured in urine samples from patients with HNF-1alpha mutations, age-matched nondiabetic control subjects, and age-matched type 1 diabetic patients, type 2 diabetic patients, and patients with diabetes and chronic renal failure. The HNF-1alpha patients had glucosuria at lower glycemic control (as shown by HbA1c) than type 1 and type 2 diabetic patients, consistent with a lower renal glucose threshold. The HNF-1alpha patients had a generalized aminoaciduria with elevated levels of 14 of 16 amino acids and an increased mean Z score for all amino acids compared with control subjects (0.66 vs. 0.00; P < 0.0005). Generalized aminoaciduria was also present in type 1 diabetic (Z score, 0.80; P < 0.0001), type 2 diabetic (Z score, 0.71; P < 0.0002), and chronic renal failure (Z score, 0.65; P < 0.01) patients. Aminoaciduria was not associated with microalbuminuria or proteinuria but was associated with glucosuria (1.00 glucosuria vs. 0.19 no glucosuria; P = 0.002). In type 1 diabetic patients, urine samples taken on the same day showed significantly more aminoaciduria when glucosuria was present compared with when it was absent (P < 0.01). In conclusion, HNF-1alpha mutation carriers have a mutation-specific defect of proximal tubular glucose transport, resulting in increased glucosuria. In contrast, the generalized aminoaciduria seen in patients with HNF-1alpha mutations is a general feature of patients with diabetes and glucosuria. Glucose may depolarize and dissipate the electrical gradient of the sodium-dependent amino acid transporters in the proximal renal tubule, causing a reduction in amino acid resorption.