Takehiro Sato

The protective roles of GLP-1R signaling in diabetic nephropathy: possible mechanism and therapeutic potential.

Glucagon-like peptide-1 (GLP-1) is a gut incretin hormone that has an antioxidative protective effect on various tissues. Here, we determined whether GLP-1 has a role in the pathogenesis of diabetic nephropathy using nephropathy-resistant C57BL/6-Akita and nephropathy-prone KK/Ta-Akita mice. By in situ hybridization, we found the GLP-1 receptor (GLP-1R) expressed in glomerular capillary and vascular walls, but not in tubuli, in the mouse kidney. Next, we generated C57BL/6-Akita Glp1r knockout mice. These mice exhibited higher urinary albumin levels and more advanced mesangial expansion than wild-type C57BL/6-Akita mice, despite comparable levels of hyperglycemia. Increased glomerular superoxide, upregulated renal NAD(P)H oxidase, and reduced renal cAMP and protein kinase A (PKA) activity were noted in the Glp1r knockout C57BL/6-Akita mice. Treatment with the GLP-1R agonist liraglutide suppressed the progression of nephropathy in KK/Ta-Akita mice, as demonstrated by reduced albuminuria and mesangial expansion, decreased levels of glomerular superoxide and renal NAD(P)H oxidase, and elevated renal cAMP and PKA activity. These effects were abolished by an adenylate cyclase inhibitor SQ22536 and a selective PKA inhibitor H-89. Thus, GLP-1 has a crucial role in protection against increased renal oxidative stress under chronic hyperglycemia, by inhibition of NAD(P)H oxidase, a major source of superoxide, and by cAMP-PKA pathway activation.

Comparisons of the effects of 12‐week administration of miglitol and voglibose on the responses of plasma incretins after a mixed meal in Japanese type 2 diabetic patients

To compare the effects of miglitol [an alpha‐glucosidase inhibitor (AGI) absorbed in the intestine] and voglibose (an AGI not absorbed) on plasma glucagon‐like peptide‐1 (GLP‐1) and gastric inhibitory polypeptide (GIP) levels, 26 and 24 Japanese type 2 diabetic patients were randomly assigned to receive miglitol or voglibose, respectively. After 12‐week administration of both drugs, during 2‐h meal tolerance test, plasma glucose, serum insulin and total GIP were significantly decreased and active GLP‐1 was significantly increased. Miglitol group showed a significantly lower total GIP level than voglibose group. Miglitol, but not voglibose, significantly reduced body weight (BW). In all participants, the relative change in BW was positively correlated with that of insulin significantly and of GIP with a weak tendency, but not of GLP‐1. In conclusion, both drugs can enhance postprandial GLP‐1 responses and reduce GIP responses. The significant BW reduction by miglitol might be attributable to its strong GIP‐reducing efficacy.

Miglitol induces prolonged and enhanced glucagon-like peptide-1 and reduced gastric inhibitory polypeptide responses after ingestion of a mixed meal in Japanese Type 2 diabetic patients.

At present, strategies of enhancing glucagon-like peptide-1 (GLP-1) action have received attention as new therapies in Type 2 diabetic patients (T2DM). In experimental studies in high-fat-fed animals, gastric inhibitory polypeptide (GIP) signals are reduced, obesity prevented and glycaemic control improved through reduction of insulin resistance [1]. Administration of α -glucosidase inhibitors (AGIs) simultaneously with nutrient intake leads to reduction of GIP responses and prolonged elevation of GLP-1 in healthy control subjects. These findings can be explained by the fact that AGIs move the absorption site of carbohydrates from the GIP-producing upper portions of intestine to the GLP-1 producing lower intestine. However, in T2DM, only a few studies in obese patients after a mixed meal have reported conflicting effects of AGIs on GLP-1 secretion [2–4] and a consistent finding of reduced GIP secretion [2,4]. Therefore, we measured plasma glucose (PG), insulin, GLP-1 (active and total forms) and GIP periodically for 3 h after ingestion of a mixed meal (56.5 g of carbohydrates, 18 g of protein, 18 g of fat) before and after administration of 50 mg miglitol three times per day for 14 days in nine Japanese T2DM subjects without severe obesity [glycated haemoglobin (HbA 1c ) 6.6 ± 0.16%; body mass index (BMI) 24.1 ± 1.0 kg/m 2 , (mean ± SE )] treated with diet therapy alone ( n = 5) or with oral glucose-lowering agents ( n = 4; glimepiride 1 or 2 mg/day in three cases; pioglitazone 30 mg/day in one case). Active forms of GLP-1 and total GIP levels, and total GLP-1 levels were measured with commercially available ELISA and RIA kits (Linco Research, St Charles, MO, USA), respectively. As seen in Fig. 1, in response to administration of miglitol, PG, insulin and GIP were unchanged at time 0 min, but during the early phase were significantly decreased. However, both active and total GLP-1 levels were significantly higher during the late phase. Our present study and that of Lee et al . [4] have demonstrated consistent enhancing effects of miglitol on GLP-1 responses to a mixed meal in T2DM. This is in contrast to results after treatment with acarbose, where the GLP-1 response to a mixed meal is unchanged [2,3]. Miglitol is absorbed in the upper portion of the intestine, where AGIs have their main effects [5]. In contrast, acarbose cannot be absorbed from the intestine. Accordingly, the relatively higher amount of carbohydrate absorption in the lower intestine with miglitol than with acarbose may explain the strong enhancement of GLP-1 secretion with miglitol treatment in T2DM subjects, although the percentages of miglitol and carbohydrates actually remaining in the lower part of the intestine are unknown. Additionally, the fact that our patients were not severely obese might partially explain the significant enhancement of GLP-1 response after miglitol; the GLP-1 response to carbohydrate is attenuated in obese individuals [6]. It is possible that the enhancement of postprandial active GLP-1 in response to miglitol might be as a result of dipeptidyl peptidase-4 (DPP-4) inhibition. However, enhancement of both active and total GLP-1 in our present study does not support this implication as DPP-4 inhibitors enhance active GLP-1 and reduce total GLP-1 levels [7]. In this 14-day study, we did not observe any change in body weight or determine directly a change in pancreatic B-cell function. A long-term follow-up study to examine the effects of miglitol on these parameters in relation to enhanced GLP-1 and reduced GIP secretion is warranted.

Stromal cell–derived factor-1 is upregulated by dipeptidyl peptidase-4 inhibition and has protective roles in progressive diabetic nephropathy

The role of stromal cell-derived factor-1 (SDF-1) in the pathogenesis of diabetic nephropathy and its modification by dipeptidyl peptidase-4 (DPP-4) inhibition are uncertain. Therefore, we studied this independent of glucagon-like peptide-1 receptor (GLP-1R) signaling using two Akita diabetic mouse models, the diabetic-resistant C57BL/6-Akita and diabetic-prone KK/Ta-Akita. Increased SDF-1 expression was found in glomerular podocytes and distal nephrons in the diabetic-prone mice, but not in kidneys from diabetic-resistant mice. The DPP-4 inhibitor linagliptin, but not the GLP-1R agonist liraglutide, further augmented renal SDF-1 expression in both Glp1r(+/+) and Glp1r(-/-) diabetic-prone mice. Along with upregulation of renal SDF-1 expression, the progression of albuminuria, glomerulosclerosis, periglomerular fibrosis, podocyte loss, and renal oxidative stress was suppressed in linagliptin-treated Glp1r(+/+) diabetic-prone mice. Linagliptin treatment increased urinary sodium excretion and attenuated the increase in glomerular filtration rate which reflects glomerular hypertension and hyperfiltration. In contrast, selective SDF-1 receptor blockade with AMD3100 reduced urinary sodium excretion and aggravated glomerular hypertension in the Glp1r(+/+) diabetic-prone mice. Thus, DPP-4 inhibition, independent of GLP-1R signaling, contributes to protection of the diabetic kidney through SDF-1-dependent antioxidative and antifibrotic effects and amelioration of adverse renal hemodynamics.

SOD1, but not SOD3, deficiency accelerates diabetic renal injury in C57BL/6-Ins2Akita diabetic mice

Superoxide dismutase (SOD) is a major defender against excessive superoxide generated under hyperglycemia. We have recently reported that renal SOD1 (cytosolic CuZn-SOD) and SOD3 (extracellular CuZn-SOD) isoenzymes are remarkably down-regulated in KK/Ta-Ins2(Akita) diabetic mice, which exhibit progressive diabetic nephropathy (DN), but not in DN-resistant C57BL/6- Ins2(Akita) (C57BL/6-Akita) diabetic mice. To determine the role of SOD1 and SOD3 in DN, we generated C57BL/6-Akita diabetic mice with deficiency of SOD1 and/or SOD3 and investigated their renal phenotype at the age of 20 weeks. Increased glomerular superoxide levels were observed in SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice but not in SOD1(+/+)SOD3(-/-) C57BL/6-Akita mice. The SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice exhibited higher glomerular filtration rate, increased urinary albumin levels, and advanced mesangial expansion as compared with SOD1(+/+)SOD3(+/+) C57BL/6-Akita mice, yet the severity of DN did not differ between the SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita groups. Increased renal mRNA expression of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF), reduced glomerular nitric oxide (NO), and increased renal prostaglandin E2 (PGE2) production were noted in the SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice. This finding indicates that such renal changes in fibrogenic cytokines, NO, and PGE2, possibly caused by superoxide excess, would contribute to the development of overt albuminuria by promoting mesangial expansion, endothelial dysfunction, and glomerular hyperfiltration. The present results demonstrate that deficiency of SOD1, but not SOD3, increases renal superoxide in the setting of diabetes and causes overt renal injury in nephropathy-resistant diabetic mice, and that SOD3 deficiency does not provide additive effects on the severity of DN in SOD1-deficient C57BL/6-Akita mice.

Novel extrapancreatic effects of incretin

The hormonal factors implicated as transmitters of signals from the gut to pancreatic β‐cells are referred to as incretins. Gastric inhibitory polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are incretins. In addition to the insulinotropic effects, we have shown, using the GIP receptor and GLP‐1 receptor‐deficient mice, that GIP and GLP‐1 have direct actions on adipocytes and the kidney, respectively. Because GIP receptors and GLP‐1 receptors are differentially expressed in a tissue‐specific manner, GIP and GLP‐1 have specific physiological activities, and further comprehensive characterization of the extrapancreatic actions of GIP and GLP‐1 is anticipated, as dipeptidyl peptidase IV inhibitors activate both GIP and GLP‐1 signaling.

A case of insulinoma following total gastrectomy--effects of an alpha-glucosidase inhibitor on suppressing GIP and GLP-1 elevations.

A 61-year-old woman with fasting hypoglycemia following total gastrectomy was diagnosed as insulinoma. GIP and GLP-1 levels after a mixed meal were extremely increased. Administration of miglitol, an alpha-glucosidase inhibitor, suppressed the GIP and GLP-1 elevations.

GLP-1 release and vagal afferent activation mediate the beneficial metabolic and chronotherapeutic effects of D -allulose

Overeating and arrhythmic feeding promote obesity and diabetes. Glucagon-like peptide-1 receptor (GLP-1R) agonists are effective anti-obesity drugs but their use is limited by side effects. Here we show that oral administration of the non-calorie sweetener, rare sugar d-allulose (d-psicose), induces GLP-1 release, activates vagal afferent signaling, reduces food intake and promotes glucose tolerance in healthy and obese-diabetic animal models. Subchronic d-allulose administered at the light period (LP) onset ameliorates LP-specific hyperphagia, visceral obesity, and glucose intolerance. These effects are blunted by vagotomy or pharmacological GLP-1R blockade, and by genetic inactivation of GLP-1R signaling in whole body or selectively in vagal afferents. Our results identify d-allulose as prominent GLP-1 releaser that acts via vagal afferents to restrict feeding and hyperglycemia. Furthermore, when administered in a time-specific manner, chronic d-allulose corrects arrhythmic overeating, obesity and diabetes, suggesting that chronotherapeutic modulation of vagal afferent GLP-1R signaling may aid in treating metabolic disorders.The sweetener D-allulose has beneficial metabolic effects in animal models, but its mechanism of action was unclear. Here the authors report that D-allulose triggers GLP-1 release in the gut and GLP-1R signaling on vagal afferents, counteracting arrhythmic overeating, obesity and diabetes.

Efficacy and safety of patient‐directed titration of once‐daily pre‐dinner premixed biphasic insulin aspart 70/30 injection in Japanese type 2 diabetic patients with oral antidiabetic drug failure: STEP‐AKITA study

Aims/Introduction:  To clarify clinical characteristics related to optimal glycemic control achieved after adding once‐daily pre‐dinner biphasic insulin aspart 70/30 (BIAsp 30) in Japanese type 2 diabetic (T2D) patients with oral antidiabetic drug (OAD) failure.

Effects of Long-Term Pravastatin Treatment on Serum and Urinary Monocyte Chemoattractant Protein-1 Levels and Renal Function in Type 2 Diabetic Patients with Normoalbuminuria

To explore the renoprotective and anti-inflammatory effects of pravastatin, we analyzed the changes in renal function and urinary monocyte chemoattractant protein-1 (MCP-1) level as a renal tubulointerstitial inflammatory biomarker and serum MCP-1 level as a systemic inflammatory biomarker following the introduction of treatment with 10 mg/day of pravastatin in 10 hyperlipidemic type 2 diabetic patients with normoalbuminuria. Twelve months of the pravastatin treatment did not affect urinary levels of albumin, transferrin, N-acetylglucosaminidase, or MCP-1 in the hyperlipidemic diabetic patients, whereas the treatment significantly reduced serum levels of MCP-1 in the patients. The pravastatin treatment effectively lowered low-density lipoprotein cholesterol (LDL-C) levels in the hyperlipidemic diabetic patients to levels nearly to those in 11 non-hyperlipidemic type 2 diabetic patients with normoalbuminuria. Interestingly, serum MCP-1 levels were significantly lower in the hyperlipidemic patients treated with pravastatin than in the non-hyperlipidemic patients. No significant correlation was observed between serum LDL-C and MCP-1 levels in all the data in the hyperlipidemic patients before and after the pravastatin treatment and in the non-hyperlipidemic patients. These results collectively indicate that pravastatin may ameliorate systemic vascular inflammation rather than local renal inflammation in hyperlipidemic type 2 diabetic patients with normoalbuminuria, independent of its cholesterol-lowering effects.