On the relationship between glucose absorption and glucose-stimulated secretion of GLP-1, neurotensin, and PYY from different intestinal segments in the rat

Ingested glucose powerfully stimulates the secretion of appetite‐ and metabolism‐regulating peptide hormones from the gut – including glucagon‐like peptide‐1 (GLP‐1), neurotensin (NT), and polypeptide YY (PYY). However, the regional origin of these secretions after glucose stimulation is not well characterized, and it remains uncertain how their secretion is related to glucose absorption. We isolated and perfused either the upper (USI) or the lower (LSI) small intestine or the colon from rats and investigated concomitant glucose absorption and secretory profiles of GLP‐1, NT, and PYY. In the USI and LSI luminal glucose (20%, w/v) increased GLP‐1 and NT secretion five to eightfold compared to basal secretion. Compared to the USI, basal and stimulated GLP‐1 secretion from the colon was 8–10 times lower and no NT secretion was detected. Luminal glucose stimulated secretion of PYY four to fivefold from the LSI and from the USI and colon, but the responses in the USI and colon were 5‐ to 15‐fold lower than in the LSI. Glucose was absorbed to a comparable extent in the USI and LSI by mechanisms that partly depended on both SGLT1 and GLUT2 activity, whereas the absorption in the colon was 80–90% lower. The absorption rates were, however, similar when adjusted for segmental length. Glucose absorption rates and NT, PYY and in particular GLP‐1 secretion were strongly correlated (P < 0.05). Our results indicate that the rate of secretion of GLP‐1, NT, and PYY in response to glucose, regardless of the involved molecular machinery, is predominantly regulated by the rate of glucose absorption.

Glucagon-like peptide-1 acutely affects renal blood flow and urinary flow rate in spontaneously hypertensive rats despite significantly reduced renal expression of GLP-1 receptors

Glucagon‐like peptide‐1 (GLP‐1) is an incretin hormone increasing postprandial insulin release. GLP‐1 also induces diuresis and natriuresis in humans and rodents. The GLP‐1 receptor is extensively expressed in the renal vascular tree in normotensive rats where acute GLP‐1 treatment leads to increased mean arterial pressure (MAP) and increased renal blood flow (RBF). In hypertensive animal models, GLP‐1 has been reported both to increase and decrease MAP. The aim of this study was to examine expression of renal GLP‐1 receptors in spontaneously hypertensive rats (SHR) and to assess the effect of acute intrarenal infusion of GLP‐1. We hypothesized that GLP‐1 would increase diuresis and natriuresis and reduce MAP in SHR. Immunohistochemical staining and in situ hybridization for the GLP‐1 receptor were used to localize GLP‐1 receptors in the kidney. Sevoflurane‐anesthetized normotensive Sprague–Dawley rats and SHR received a 20 min intrarenal infusion of GLP‐1 and changes in MAP, RBF, heart rate, dieresis, and natriuresis were measured. The vasodilatory effect of GLP‐1 was assessed in isolated interlobar arteries from normo‐ and hypertensive rats. We found no expression of GLP‐1 receptors in the kidney from SHR. However, acute intrarenal infusion of GLP‐1 increased MAP, RBF, dieresis, and natriuresis without affecting heart rate in both rat strains. These results suggest that the acute renal effects of GLP‐1 in SHR are caused either by extrarenal GLP‐1 receptors activating other mechanisms (e.g., insulin) to induce the renal changes observed or possibly by an alternative renal GLP‐1 receptor.

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.

Is GLP-1 a hormone: Whether and When?

Glucagon‐like peptide‐1 (GLP‐1) is a product of proglucagon cleavage synthesized in L cells in the intestinal mucosa, α‐cells in the pancreatic islet, and neurons in the nucleus of the solitary tract. GLP‐1 is essential for normal glucose tolerance and acts through a specific GLP‐1 receptor that is expressed by islet β‐cells as well as other cell types. Because plasma concentrations of GLP‐1 increase following meal ingestion it has been generally presumed that GLP‐1 acts as a hormone, communicating information from the intestine to the endocrine pancreas through the circulation. However, there are a number of problems with this model including low circulating concentrations of GLP‐1 in plasma, limited changes after meal ingestion and rapid metabolism in the plasma. Moreover, antagonism of systemic GLP‐1 action impairs insulin secretion in the fasting state, suggesting that the GLP‐1r is active even when plasma GLP‐1 levels are low and unchanging. Consistent with these observations, deletion of the GLP‐1r from islet β‐cells causes intolerance after IP or IV glucose, challenges that do not induce GLP‐1 secretion. Taken together, these data support a model whereby GLP‐1 acts through neural or paracrine mechanisms to regulate physiologic insulin secretion. In contrast, bariatric surgery seems to be a condition in which circulating GLP‐1 could have an endocrine effect. Both gastric bypass and sleeve gastrectomy are associated with substantial increases in postprandial GLP‐1 release and in these conditions interference with GLP‐1r signaling has a significant impact on glucose regulation after eating. Thus, with either bariatric surgery or treatment with long‐acting GLP‐1r agonists, circulating peptide mediates insulinotropic activity. Overall, a case can be made that physiologic actions of GLP‐1 are not hormonal, but that an endocrine mechanism of GLP‐1r activation can be co‐opted for therapeutics.

Mechanisms underlying glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 secretion

The incretin hormones, glucose‐dependent insulinotropic peptide and glucagon‐like peptide‐1, are secreted from intestinal K‐ and L cells, respectively, with the former being most abundant in the proximal small intestine, whereas the latter increase in number towards the distal gut. Although an overlap between K‐ and L cells can be observed immunohistochemically or in murine models expressing fluorescent markers under the control of the two hormone promoters, the majority (>80%) of labeled cells seems to produce only one of these hormones. Transcriptomic analysis showed a close relationship between small intestinal K‐ and L cells, and glucose sensing mechanisms appear similar in both cell types with a predominant role of electrogenic glucose uptake through sodium‐coupled glucose transporter 1. Similarly, both cell types produce the long‐chain fatty acid sensing G‐protein‐coupled receptors, FFAR1 (GPR40) and FFAR4 (GPR120), but differ in the expression/functionality of other lipid sensing receptors. GPR119 and FFAR2/3, for example, have clearly documented roles in glucagon‐like peptide‐1 secretion, whereas agonists for the endocannabinoid receptor type 1 have been found to show largely selective inhibition of glucose‐dependent insulinotropic peptide secretion. In conclusion, although K‐ and L cell populations overlap and share key molecular nutrient‐sensing mechanisms, subtle differences between the responsiveness of the different cell types might be exploited to differentially modulate glucose‐dependent insulinotropic peptide or glucagon‐like peptide‐1 secretion.

Carbohydrate-induced secretion of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1

Glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are the incretin hormones secreted from enteroendocrine K‐cells and L‐cells, respectively, by oral ingestion of various nutrients including glucose. K‐cells, L‐cells and pancreatic β‐cells are glucose‐responsive cells with similar glucose‐sensing machinery including glucokinase and an adenosine triphosphate‐sensitive K⁺ channel comprising KIR6.2 and sulfonylurea receptor 1. However, the physiological role of the adenosine triphosphate‐sensitive K⁺ channel in GIP secretion in K‐cells and GLP‐1 secretion in L‐cells is not elucidated. Recently, it was reported that GIP and GLP‐1‐producing cells are present also in pancreatic islets, and islet‐derived GIP and GLP‐1 contribute to glucose‐induced insulin secretion from pancreatic β‐cells. In this short review, we focus on GIP and GLP‐1 secretion by monosaccharides, such as glucose or fructose, and the role of the adenosine triphosphate‐sensitive K⁺ channel in GIP and GLP‐1 secretion.

Glucagon-like peptide-1 and cholecystokinin production and signaling in the pancreatic islet as an adaptive response to obesity

Precise control of blood glucose is dependent on adequate β‐cell mass and function. Thus, reductions in β‐cell mass and function lead to insufficient insulin production to meet demand, and result in diabetes. Recent evidence suggests that paracrine signaling in the islet might be important in obesity, and disruption of this signaling could play a role in the pathogenesis of diabetes. For example, we recently discovered a novel islet incretin axis where glucagon‐like peptide‐1 regulates β‐cell production of another classic gut hormone, cholecystokinin. This axis is stimulated by obesity, and plays a role in enhancing β‐cell survival. In the present review, we place our observations in the wider context of the literature on incretin regulation in the islet, and discuss the potential for therapeutic targeting of these pathways.

Phenotyping of type 2 diabetes mellitus at onset on the basis of fasting incretin tone: Results of a two-step cluster analysis

Aims/Introduction

According to some authors, in type 2 diabetes there is a reduced postprandial action of glucagon‐like peptide‐1 (GLP‐1) and glucose‐dependent insulinotropic polypeptide (GIP). However, little is known about the role of fasting incretins in glucose homeostasis. Our aim was to evaluate, through a two‐step cluster analysis, the possibility of phenotyping patients with type 2 diabetes at onset on the basis of fasting GLP‐1, GIP and ghrelin.

Materials and Methods

A total of 96 patients with type 2 diabetes within 6 months of onset (mean age 62.40 ± 6.36 years) were cross‐sectionally studied. Clinical, anthropometric and metabolic parameters were evaluated. At fasting the following were carried out: assay of GLP‐1, GIP, ghrelin, insulin, C‐peptide, glucagon and a panel of adipocytokines (visfatin, resistin, leptin, soluble leptin receptor and adiponectin).

Results

The analysis resulted in two clusters: cluster 1 (63 patients) had significantly lower levels of GLP‐1 (4.93 ± 0.98 vs 7.81 ± 1.98 pmol/L; P < 0.001), GIP (12.73 ± 9.44 vs 23.88 ± 28.56 pmol/L; P < 0.001) and ghrelin (26.54 ± 2.94 vs 39.47 ± 9.84 pmol/L; P < 0.001) compared with cluster 2 (33 patients). Between the two clusters, no differences in age, duration of disease, sex, clinical‐anthropometric parameters, insulin sensitivity and adipocytokines were highlighted. However, cluster 1 was associated with significantly higher levels of glycated hemoglobin (7.4 ± 0.61 vs 6.68 ± 0.57%, P = 0.007), glucagon (232.02 ± 37.27 vs 183.33 ± 97.29 ng/L; P = 0.001), fasting glucose (7.85 ± 1.60 vs 6.93 ± 1.01 mmol/L; P = 0.003) and significantly lower levels of C‐peptide (0.12 ± 0.11 vs 0.20 ± 0.20 nmol/L; P = 0.017).

Conclusions

The present study suggests that fasting incretins play an important role in the pathophysiology of type 2 diabetes, which requires to further investigation.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1: Incretin actions beyond the pancreas

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine on ingestion of various nutrients to stimulate insulin secretion from pancreatic β-cells glucose-dependently. GIP and GLP-1 undergo degradation by dipeptidyl peptidase-4 (DPP-4), and rapidly lose their biological activities. The actions of GIP and GLP-1 are mediated by their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which are expressed in pancreatic β-cells, as well as in various tissues and organs. A series of investigations using mice lacking GIPR and/or GLP-1R, as well as mice lacking DPP-4, showed involvement of GIP and GLP-1 in divergent biological activities, some of which could have implications for preventing diabetes-related microvascular complications (e.g., retinopathy, nephropathy and neuropathy) and macrovascular complications (e.g., coronary artery disease, peripheral artery disease and cerebrovascular disease), as well as diabetes-related comorbidity (e.g., obesity, non-alcoholic fatty liver disease, bone fracture and cognitive dysfunction). Furthermore, recent studies using incretin-based drugs, such as GLP-1 receptor agonists, which stably activate GLP-1R signaling, and DPP-4 inhibitors, which enhance both GLP-1R and GIPR signaling, showed that GLP-1 and GIP exert effects possibly linked to prevention or treatment of diabetes-related complications and comorbidities independently of hyperglycemia. We review recent findings on the extrapancreatic effects of GIP and GLP-1 on the heart, brain, kidney, eye and nerves, as well as in the liver, fat and several organs from the perspective of diabetes-related complications and comorbidities.

Dipeptidyl-peptidase IV inhibitor is effective in patients with type 2 diabetes with high serum eicosapentaenoic acid concentrations

Aims/Introduction:  Eicosapentaenoic acid (EPA) stimulates glucagon-like peptide-1 (GLP-1) secretion in mice. We investigated the relationship between serum EPA concentrations and the efficacy of dipeptidyl-peptidase IV (DPP-4) inhibitor in patients with type 2 diabetes.

MATERIALS AND METHODS

  Serum EPA concentrations were measured in 62 consecutive patients with type 2 diabetes who were newly given DPP-4 inhibitor as a monotherapy or as an add-on therapy to oral hypoglycemic agents. The dosage of oral hypoglycemic agents was maintained during the observation period. After 24 weeks of treatment with DPP-4 inhibitor, we evaluated the relationships between a decrease in hemoglobin A1c from baseline and serum EPA concentrations, as well as age, sex, body mass index (BMI), hemoglobin A1c at baseline and usage of antidiabetic concomitant drugs.

RESULTS

  Hemoglobin A1c was significantly decreased from 8.1 ± 1.1% to 7.2 ± 1.0% by DPP-4 inhibitor. A decrease in hemoglobin A1c correlated with BMI (r = -0.396, P = 0.0013), age (r = 0.275, P = 0.0032), hemoglobin A1c at baseline (r = 0.490, P < 0.0001) and log EPA (r = 0.285, P = 0.0246). Multiple regression analysis showed that BMI (β = -0.419, P = 0.0002), hemoglobin A1c at baseline (β = 0.579, P < 0.0001) and log EPA (β = 0.220, P = 0.0228) were independent determinants of decrease in hemoglobin A1c.

CONCLUSIONS

  DPP-4 inhibitor is effective in patients with type 2 diabetes with high serum EPA concentrations. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00220.x , 2012).

Liraglutide is effective in type 2 diabetic patients with sustained endogenous insulin-secreting capacity

Aims/Introduction:  Recently, glucagon-like peptide-1 (GLP-1) receptor agonists of liraglutide have become available in Japan. It has not yet been clarified what clinical parameters could discriminate liraglutide-effective patients from liraglutide-ineffective patients.

MATERIALS AND METHODS

  We reviewed 23 consecutive patients with type 2 diabetes admitted to Osaka University Hospital for glycemic control. All of the patients were treated with diet plus insulin (or plus oral antidiabetic drugs) to improve fasting plasma glucose (FPG) and postprandial glucose below 150 and 200 mg/dL, respectively. After insulin secretion and insulin resistance were evaluated, insulin was replaced by liraglutide. The efficacy of liraglutide was determined according to whether glycemic control was maintained at the target levels.

RESULTS

  Liraglutide was effective in 13 of 23 patients. There were significant differences in the parameters of insulin secretion, including fasting C-peptide (F-CPR), C-peptide index (CPI), insulinogenic index (I.I.) and urine C-peptide (U-CPR), between liraglutide-effective and -ineffective patients. The duration of diabetes was significantly shorter in liraglutide-effective patients than in liraglutide-ineffective patients. In receiver operating characteristic analyses, the cut-off value for predicting the efficacy of liraglutide was 0.14 for I.I., 1.1 for CPI, 1.5 ng/mL for F-CPR, 33.3 μg/day for U-CPR and 19.5 years for duration of type 2 diabetes.

CONCLUSIONS

  Insulin secretion evaluated by F-CPR, CPI, I.I., U-CPR and the duration of type 2 diabetes were useful parameters for predicting the efficacy of liraglutide in patients with type 2 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00168.x, 2011).

Synergistic effect of α-glucosidase inhibitors and dipeptidyl peptidase 4 inhibitor treatment

Monotherapy of α‐glucosidase inhibitor (α‐GI) or dipeptidyl peptidase 4 (DPP4) inhibitor does not sufficiently minimize glucose fluctuations in the diabetic state. In the present study, we evaluated the combined effects of various of α‐GI inhibitors (acarbose, voglibose or miglitol) and sitagliptin, a DPP4 inhibitor, on blood glucose fluctuation, insulin and active glucagon‐like peptide‐1 (GLP‐1) levels after nutriment loading in mice. Miglitol and sitagliptin elicited a 47% reduction (P < 0.05) of the area under the curve of blood glucose levels for up to 2 h after maltose‐loading, a 60% reduction (P < 0.05) in the range of blood glucose fluctuation, and a 32% decrease in plasma insulin compared with the control group. All three of the combinations elicited a 2.5–4.9‐fold synergistic increase in active GLP‐1 (P < 0.05 vs control). Thus, combined treatment with the α‐GI miglitol, which more strongly inhibits the early phase of postprandial hyperglycemia, and DPP4 inhibitor yields both complementary and synergistic effects, and might represent a superior anti‐hyperglycemic therapy. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00081.x, 2011)

Plasma gastric inhibitory polypeptide and glucagon-like peptide-1 levels after glucose loading are associated with different factors in Japanese subjects

Aims/Introduction:  Gastric inhibitory polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are major incretins that potentiate insulin secretion from pancreatic β‐cells. The factors responsible for incretin secretion have been reported in Caucasian subjects, but have not been thoroughly evaluated in Japanese subjects. We evaluated the factors associated with incretin secretion during oral glucose tolerance test (OGTT) in Japanese subjects with normal glucose tolerance (NGT).

Materials and Methods:  We measured plasma GIP and GLP‐1 levels during OGTT in 17 Japanese NGT subjects and evaluated the factors associated with GIP and GLP‐1 secretion using simple and multiple regression analyses.

Results:  GIP secretion (AUC‐GIP) was positively associated with body mass index (P < 0.05), and area under the curve (AUC) of C‐peptide (P < 0.05) and glucagon (P < 0.01), whereas GLP‐1 secretion (AUC‐GLP‐1) was negatively associated with AUC of plasma glucose (P < 0.05). The insulinogenic index was most strongly associated with GIP secretion (P < 0.05); homeostasis model assessment β‐cell was the most the strongly associated factor in GLP‐1 secretion (P < 0.05) among the four indices of insulin secretion and insulin sensitivity.

Conclusions:  Several distinct factors might be associated with GIP and GLP‐1 secretion during OGTT in Japanese subjects. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00078.x, 2011)

Ingestion of a moderate high-sucrose diet results in glucose intolerance with reduced liver glucokinase activity and impaired glucagon-like peptide-1 secretion

Aims/Introduction:  Excessive intake of sucrose can cause severe health issues, such as diabetes mellitus. In animal studies, consumption of a high‐sucrose diet (SUC) has been shown to cause obesity, insulin resistance and glucose intolerance. However, several in vivo experiments have been carried out using diets with much higher sucrose contents (50–70% of the total calories) than are typically ingested by humans. In the present study, we examined the effects of a moderate SUC on glucose metabolism and the underlying mechanism.

Materials and Methods:  C57BL/6J mice received a SUC (38.5% sucrose), a high‐starch diet (ST) or a control diet for 5 weeks. We assessed glucose tolerance, incretin secretion and liver glucose metabolism.

Results:  An oral glucose tolerance test (OGTT) showed that plasma glucose levels in the early phase were significantly higher in SUC‐fed mice than in ST‐fed or control mice, with no change in plasma insulin levels at any stage. SUC‐fed mice showed a significant improvement in insulin sensitivity. Glucagon‐like peptide‐1 (GLP‐1) secretion 15 min after oral glucose administration was significantly lower in SUC‐fed mice than in ST‐fed or control mice. Hepatic glucokinase (GCK) activity was significantly reduced in SUC‐fed mice. During the OGTT, the accumulation of glycogen in the liver was suppressed in SUC‐fed mice in a time‐dependent manner.

Conclusions:  These results indicate that mice that consume a moderate SUC show glucose intolerance with a reduction in hepatic GCK activity and impairment in GLP‐1 secretion. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00208.x, 2012)

GLP-1 receptor agonist attenuates endoplasmic reticulum stress-mediated β-cell damage in Akita mice

Aims/Introduction:  Endoplasmic reticulum (ER) stress is one of the contributing factors in the development of type 2 diabetes. To investigate the cytoprotective effect of glucagon‐like peptide 1 receptor (GLP‐1R) signaling in vivo, we examined the action of exendin‐4 (Ex‐4), a potent GLP‐1R agonist, on β‐cell apoptosis in Akita mice, an animal model of ER stress‐mediated diabetes.

Materials and Methods:  Ex‐4, phosphate‐buffered saline (PBS) or phlorizin were injected intraperitoneally twice a day from 3 to 5 weeks‐of‐age. We evaluated the changes in blood glucose levels, bodyweights, and pancreatic insulin‐positive area and number of islets. The effect of Ex‐4 on the numbers of C/EBP‐homologous protein (CHOP)‐, TdT‐mediated dUTP‐biotin nick‐end labeling (TUNEL)‐ or proliferating cell nuclear antigen‐positive β‐cells were also evaluated.

Results:  Ex‐4 significantly reduced blood glucose levels and increased both the insulin‐positive area and the number of islets compared with PBS‐treated mice. In contrast, there was no significant difference in the insulin‐positive area between PBS‐treated mice and phlorizin‐treated mice, in which blood glucose levels were controlled similarly to those in Ex‐4‐treated mice. Furthermore, treatment of Akita mice with Ex‐4 resulted in a significant decrease in the number of CHOP‐positive β‐cells and TUNEL‐positive β‐cells, and in CHOP mRNA levels in β‐cells, but there was no significant difference between the PBS‐treated group and the phlorizin‐treated group. Proliferating cell nuclear antigen staining showed no significant difference among the three groups in proliferation of β‐cells.

Conclusions:  These data suggest that Ex‐4 treatment can attenuate ER stress‐mediated β‐cell damage, mainly through a reduction of apoptotic cell death that is independent of lowered blood glucose levels. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00075.x, 2010)

Liraglutide administration in type 2 diabetic patients who either received no previous treatment or were treated with an oral hypoglycemic agent showed greater efficacy than that in patients switching from insulin

Aims/Introduction

Liraglutide, a glucagon‐like peptide‐1 receptor agonist, is expected to provide a new treatment option for diabetes. However, the suitable timing of liraglutide administration in type 2 diabetic patients has not yet been clarified.

Materials and Methods

We reviewed type 2 diabetic patients (n = 155) who visited the Osaka Red Cross Hospital for glycemic control, with administration of liraglutide at a dose of 0.6 mg (average glycated hemoglobin [HbA_1c] level, 8.7 ± 0.1%). The effect of liraglutide based on the pretreatment status was compared. We also analyzed the background factors of both a successful and failed group of patients who switched to liraglutide from insulin.

Results

An improvement in blood glucose levels was confirmed in 122 of 155 patients. During the 4‐month observation period, the improvement in HbA_1c levels was significantly greater in the group of drug‐naïve/previous oral hypoglycemic agent (9.1 ± 0.2 to 7.2 ± 0.2%) than that in the group switching from insulin (8.6 ± 0.2 to 7.8 ± 0.2%). In addition, C‐peptide immunoreactivity levels (fasting > 2.2 ng/mL; delta >1.6 ng/mL; urine > 70 μg/day), younger age and a smaller number of insulin units used per day were considered important when deciding on switching to liraglutide from insulin.

Conclusions

Liraglutide was more effective in patients who had not been treated previously or received oral hypoglycemic agents than in patients switching from insulin. With respect to switching to liraglutide from insulin, the most important factors to be considered were C‐peptide immunoreactivity levels, age, and the number of insulin units used per day.

Glucagon-like peptide-1 secretion by direct stimulation of L cells with luminal sugar vs non-nutritive sweetener

Aims/Introduction:  Oral ingestion of carbohydrate triggers secretion of glucagon-like peptide (GLP)-1, which inhibits the postprandial rise in blood glucose levels. However, the mechanism of carbohydrate-induced GLP-1 secretion from enteroendocrine L cells remains unclear. In the present study, GLP-1 secretion was examined by meal tolerance tests of healthy Japanese volunteers.

MATERIALS AND METHODS

  Twenty-one healthy Japanese men participated in the study. The meal tolerance test was performed with modified nutrient compositions, with or without pretreatment with the α-glucosidase inhibitor acarbose, or with substitution of sucrose with an equivalent dose of sweeteners in the meal. Blood concentrations of glucose, insulin, GLP-1, and apolipoprotein (Apo) B-48 were measured.

RESULTS

  GLP-1 secretion started concomitant with the increase in blood glucose levels 10 min after meal ingestion. Insulin secretion started at 5 min, before the increase in blood glucose levels, reflecting the contribution of direct nutrient stimulation on the former parameter and neural regulation in the latter. Carbohydrate retention in the gut lumen induced by acarbose pretreatment extended postprandial GLP-1 secretion and negated the increase in serum ApoB-48 levels. GLP-1 secretion was markedly decreased by a reduction in the amount of sucrose in the meal and was not restored by an equivalent dose of sweeteners used to compensate for the sweet taste.

CONCLUSIONS

  The results indicate that direct stimulation of L cells with sugar, but not sweetener, is required for carbohydrate-induced GLP-1 secretion. In addition, inhibition of digestion of dietary carbohydrate by α-glucosidase inhibitors may prevent postprandial hyperglycemia by increasing GLP-1 secretion and by inhibiting glucose absorption. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00163.x, 2011).

Comparison of efficacy of concomitant administration of mitiglinide with voglibose and double dose of mitiglinide in patients with type 2 diabetes mellitus

Aims/Introduction:  When monotherapy with an oral hypoglycemic agent (OHA) is not sufficiently effective for blood glucose control, combination therapy with OHA having different mechanisms of action might be indicated.

MATERIALS AND METHODS

  In the present study, we compared the efficacy of two options in type 2 diabetes mellitus patients whose blood glucose had not been well controlled with mitiglinide (30 mg/day) alone. A total of 20 patients were included in the study and divided into two groups: group A, in which mitiglinide was given concomitantly with the α-glucosidase inhibitor voglibose (0.6 mg/day); and group B, in which a double dose of mitiglinide was given (60 mg/day). Twelve weeks after changing the medication, HbA1c, glycoalbumin and 1,5-anhydroglucitol (1,5-AG) were measured. In addition, at weeks 0 and 12, a meal tolerance test was carried out, and plasma glucose, insulin, glucagon, active glucagon-like peptide-1 (GLP-1) and total glucose-dependent insulinotropic polypeptide levels were measured.

RESULTS

  The plasma level of 1,5-AG improved in both groups at week 12. In group A, the plasma insulin level significantly decreased and the plasma active GLP-1 level significantly increased during the meal tolerance test at week 12; thus, bodyweight significantly decreased only in group A.

CONCLUSIONS

  Our findings suggested that concomitant administration of mitiglinide with voglibose could achieve better glycemic control, particularly in the postprandial period, without bodyweight gain and might have beneficial effects in type 2 diabetic patients at risk of macrovascular complications. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.0082.x, 2011).