Chronic exposure to valproic acid promotes insulin release, reduces KATP channel current and does not affect Ca2+ signaling in mouse islets

Hyperinsulinemia is one of the reported side effects of valproic acid (VPA), a medicine used to treat epilepsy. However, its underlying mechanism remains unknown. The present study was designed to investigate a direct effect of VPA on insulin secretion by using mouse pancreactic islets and β-cells. VPA had no acute effect on insulin secretion from islets, or on cytosolic Ca²⁺ ([Ca²⁺]_i) in single β-cells. However, following long-term exposure to VPA (48 h), both basal and glucose-stimulated insulin secretion were markedly elevated (5-fold), while the insulin gene expression level was unaltered. Following long-term exposure to VPA, β-cells showed a decrease in whole cell K_ATP channel current. However, the increase in [Ca²⁺]_i in response to the sulfonylurea drug, tolbutamide was attenuated. The present study shows that VPA has no acute effects, but long-term treatment results in enhancement of both basal and glucose-stimulated insulin secretion. This long-term effect may mediate the K_ATP channel, while VPA can also attenuate the effect of the K_ATP channel blocker tolbutamide.     

Seasonal Variations of Severe Hypoglycemia in Patients With Type 1 Diabetes Mellitus,Type 2 Diabetes Mellitus,and Non-diabetes Mellitus: Clinical Analysis of 578 Hypoglycemia Cases

Blood glucose control in patients with diabetes mellitus (DM) is reportedly influenced by the seasons, with hemoglobin A1c (HbA1c) levels decreasing in the summer or warm season and increasing in the winter or cold season. In addition, several studies have shown that sepsis is also associated with the seasons. Although both blood glucose control and sepsis can strongly affect the occurrence of severe hypoglycemia, few studies have examined the seasonal variation of severe hypoglycemia. The aim of the present study is to examine the association between severe hypoglycemia and the seasons in patients with type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM), and non-diabetes mellitus (non-DM). We retrospectively reviewed all the patients with severe hypoglycemia at a national center in Japan between April 1, 2006 and March 31, 2012. A total of 57,132 consecutive cases that had visited the emergency room by ambulance were screened, and 578 eligible cases of severe hypoglycemia were enrolled in this study. The primary outcome was to assess the seasonality of severe hypoglycemia. In the T1DM group (n = 88), severe hypoglycemia occurred significantly more often in the summer than in the winter (35.2% in summer vs 18.2% in winter, P = 0.01), and the HbA1c levels were highest in the winter and lowest in the summer (9.1% [7.6%–10.1%] in winter vs 7.7% [7.1%–8.3%] in summer, P = 0.13). In the non-DM group (n = 173), severe hypoglycemia occurred significantly more often in the winter than in the summer (30.6% in winter vs 19.6% in summer, P = 0.01), and sepsis as a complication occurred significantly more often in winter than in summer (24.5% in winter vs 5.9% in summer, P = 0.02). In the T2DM group (n = 317), the occurrence of severe hypoglycemia and the HbA1c levels did not differ significantly among the seasons. The occurrence of severe hypoglycemia might be seasonal and might fluctuate with temperature changes. Patients should be treated more carefully during the season in which severe hypoglycemia is more common.     

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. Materials and Methods: Under this regimen, we evaluated changes in HbA_1c levels and daily self‐monitoring blood glucose (BG) profiles, as well as the incidences of hypoglycemia and retinopathy progression. The patients adjusted BIAsp 30 dosages themselves every 3–4 days according to a pre‐determined algorithm to achieve fasting BG levels of 101–120 mg/dL. HbA_1c levels were expressed as Japan Diabetes Society values. Results: Of 29 enrolled patients, 22 (HbA_1c levels, 8.5 ± 1.5% [mean ± SD]) and 20 patients completed the 16‐ and 24‐week follow‐up, respectively. At 16 weeks 68.2 and 45.5%, and at 24 weeks 80.0 and 35% of patients had achieved HbA_1c levels of <7.0 and <6.5%, respectively. The patients who had achieved optimal glycemic control, including daytime postprandial BG profiles after treatment, had lower post‐breakfast BG excursions at baseline, shorter diabetes durations and younger age. No severe hypoglycemic episodes were recorded. Progression of retinopathy was observed in 3 of the 29 enrolled patients. Conclusions: Lower post‐breakfast BG excursions, shorter diabetes duration and younger age in Japanese T2D patients with OAD failure might warrant optimal glycemic control with safety after adding once‐daily pre‐dinner BIAsp 30 initiating regimen. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00062.x, 2010)     

The Functional Role of the Cerebellum in Visually Guided Tracking Movement

We propose a new method to provide a functional interpretation of motor commands (i.e., muscle activities) and their relationship to movement kinematics. We evaluated our method by analyzing the motor commands of normal controls and patients with cerebellar disorders for visually guided tracking movement of the wrist joint. Six control subjects and six patients with cerebellar disorders participated in this study. We asked the subjects to perform visually guided smooth tracking movement of the wrist joint with a manipulandum, and recorded the movements of the wrist joint and activities of the four wrist prime movers with surface electrodes. We found a symmetric relationship between the second-order linear equation of motion for the wrist joint and the linear sum of activities of the four wrist prime movers. The symmetric relationship determined a set of parameters to characterize the muscle activities and their similarity to the components of movement kinematics of the wrist joint. We found that muscle activities of the normal controls encoded both the velocity and the position of the moving target, resulting in precise tracking of the target. In contrast, muscle activities of the cerebellar patients were characterized by a severer impairment for velocity control and more dependence on position control, resulting in poor tracking of the smoothly moving target with many step-like awkward movements. Our results suggest that the cerebellum plays an important role in the generation of motor commands for smooth velocity and position control.     

Ghrelin attenuates cAMP-PKA signaling to evoke insulinostatic cascade in islet β-cells

OBJECTIVE

Ghrelin reportedly restricts insulin release in islet β-cells via the Gα_i2 subtype of G-proteins and thereby regulates glucose homeostasis. This study explored whether ghrelin regulates cAMP signaling and whether this regulation induces insulinostatic cascade in islet β-cells.

RESEARCH DESIGN AND METHODS

Insulin release was measured in rat perfused pancreas and isolated islets and cAMP production in isolated islets. Cytosolic cAMP concentrations ([cAMP]_i) were monitored in mouse MIN6 cells using evanescent-wave fluorescence imaging. In rat single β-cells, cytosolic protein kinase-A activity ([PKA]_i) and Ca²⁺ concentration ([Ca²⁺]_i) were measured by DR-II and fura-2 microfluorometry, respectively, and whole cell currents by patch-clamp technique.

RESULTS

Ghrelin suppressed glucose (8.3 mmol/L)-induced insulin release in rat perfused pancreas and isolated islets, and these effects of ghrelin were blunted in the presence of cAMP analogs or adenylate cyclase inhibitor. Glucose-induced cAMP production in isolated islets was attenuated by ghrelin and enhanced by ghrelin receptor antagonist and anti-ghrelin antiserum, which counteract endogenous islet-derived ghrelin. Ghrelin inhibited the glucose-induced [cAMP]_i elevation and [PKA]_i activation in MIN6 and rat β-cells, respectively. Furthermore, ghrelin potentiated voltage-dependent K⁺ (Kv) channel currents without altering Ca²⁺ channel currents and attenuated glucose-induced [Ca²⁺]_i increases in rat β-cells in a PKA-dependent manner.

CONCLUSIONS

Ghrelin directly interacts with islet β-cells to attenuate glucose-induced cAMP production and PKA activation, which lead to activation of Kv channels and suppression of glucose-induced [Ca²⁺]_i increase and insulin release.Ghrelin, an acylated 28-amino acid peptide, is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R) (1,2). Ghrelin is produced predominantly in the stomach and stimulates growth hormone release and feeding and exhibits positive cardiovascular effects, suggesting its possible clinical application (3). Ghrelin and GHS-R are located in the pancreatic islets (4–6). Furthermore, ghrelin O-acyltransferase (GOAT), which has been identified as the enzyme that promotes the acylation of the third serine residue of ghrelin, is highly expressed in the pancreatic islets (7–9). Administration of ghrelin at 10⁻⁹–10⁻⁸ mol/L, the concentrations higher than the circulating levels of 10⁻¹⁰–10⁻⁹ mol/L, attenuates insulin release and deteriorates glucose tolerance in rodents and humans, whereas desacyl ghrelin has no effects (5,10,11). This effective concentration of ghrelin that is approximately one log order higher than the circulating level is considered physiological in the pancreatic islets for the following reasons: 1) ghrelin is produced in the pancreatic islets (5), and the ghrelin level in the pancreatic vein is one log order higher than that in the pancreatic artery (12), indicative of release of ghrelin from the pancreas; 2) ghrelin immunoneutralization and GHS-R antagonists augment glucose-induced insulin release from perfused pancreas and isolated islets (5,12); and 3) ghrelin knockout mice display enhanced glucose-induced insulin release from isolated islets without altering islet density and size, insulin content, or insulin mRNA levels, indicating increased secretory activity in the knockout mouse islets (12). Furthermore, glucose intolerance in high-fat diet–induced obese (DIO) mice is prevented in the ghrelin knockout mice as a result of enhanced insulin secretory response to glucose (12). These findings suggest that the islet-derived ghrelin regulates insulin release in a paracrine and/or autocrine manner and that manipulation of the ghrelin action could provide a novel tool to optimize insulin release (13,14).It is currently thought that GHS-R is coupled primarily to G₁₁-phospholipase C signaling (2). Intriguingly, our previous data indicated that the insulinostatic ghrelin signaling is produced via pertussis toxin (PTX)-sensitive G-protein Gα_i2 in β-cells; ghrelin PTX-sensitively activates voltage-dependent K⁺ (Kv) channels, attenuates membrane excitability, and suppresses glucose-induced Ca²⁺ concentration ([Ca²⁺]_i) increases in β-cells to attenuate insulin release (15). However, the mechanism that links GHS-R and Gα_i2 to these activities in β-cells remains to be clarified. It is known that PTX-sensitive G_i-proteins inhibit adenylate cyclase, which produces cyclic AMP in the cells. In pancreatic β-cells, intracellular cAMP signals are generated by nutrient secretagogues and play a critical role in regulating insulin secretion (16–18). However, implication of cAMP signaling in the insulinostatic function of ghrelin has been unclear. In this study, we aimed to clarify whether ghrelin regulates cAMP pathway in islet β-cells and whether this regulation leads to insulinostatic cascade in islet β-cells. We here show a novel signaling mechanism for ghrelin that operates in islet β-cells; GHS-R–mediated attenuation of cAMP and protein kinase-A (PKA) signaling leads to activation of Kv channels and suppression of glucose-induced [Ca²⁺]_i increase and insulin release.     

Impact of setup error and anatomical change on dose distribution during conventional radiation therapy

The purpose of this study was to evaluate the impact of setup error and anatomical change on dose distribution during conventional radiation therapy. We performed regional irradiation (Plan1) using opposing pair fields, and then we planned local irradiation (Plan2) with a computed tomography (CT) acquired at that time in 10 patients with advanced oral cancer. To consider the setup error, a minimum dose of gross tumor volume (GTV) and a maximum dose for the spinal cord were re-calculated with isocenter shifts of ±5 mm. We also evaluated an alteration of reference dose due to anatomical changes during radiation therapy. A minimum dose of GTV was decreased with isocenter shifts; the trend was stronger in Plan2 than Plan1 (-5.7% vs. -1.2%, p=0.02). Similarly, a maximum dose of spinal cord was increased with isocenter shifts, especially in Plan2 (12.2% vs. 0.5%, p<0.01). Anatomical changes during radiation therapy were observed in all patients, and the mean difference for depth was -4 mm in Plan1; the reference dose was increased in Plan1 and Plan2. Precise setup is necessary, especially for local irradiation in spite of anatomical changes during radiation therapy. Reimaging and replanning are recommended for patients with marked anatomical changes.     

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.