Rationale and design of the EMPYREAN study

Aims

A sodium glucose cotransporter 2 (SGLT2) inhibitor was recently found to reduce heart failure hospitalization in the EMPA‐REG OUTCOME trial. We have hypothesized that autonomic nerve activity may be modulated by SGLT2 inhibition. The current study aims to investigate the impact of empagliflozin on sympathetic and parasympathetic nerve activity in patients with type 2 diabetes mellitus.

Methods and results

This ongoing study is a prospective, randomized, open‐label, multicentre investigation of 134 patients with type 2 diabetes mellitus. The patients are randomly allocated to receive either empagliflozin or sitagliptin with the treatment goal of the Japan Diabetes Society guidelines. Ambulatory electrocardiographic monitoring is performed at the baseline and at 12 and 24 weeks of treatment. Analyses of heart rate variability are conducted using the MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non‐linear least squares method for square analysis. The primary endpoint is the change in the low‐frequency (0.04–0.15 Hz)/high‐frequency (0.15–0.4 Hz) ratio from baseline to 24 weeks.

Conclusions

This investigation on the effect of EMPagliflozin on cardiac sYmpathetic and parasympathetic neRve activity in JapanEse pAtieNts with type 2 diabetes (EMPYREAN study) offers an important opportunity to understand the impact of SGLT2 inhibition on autonomic nerve activity in patients with type 2 diabetes.

A Novel p.L145Q Mutation in the HNF1B Gene in a Case of Maturity-onset Diabetes of the Young Type 5 (MODY5)

Maturity-onset diabetes of the young (MODY) is an autosomal dominant form of early onset diabetes. The hepatocyte nuclear factor-1-beta (HNF1B) gene is responsible for MODY type 5 (MODY5) with distinctive clinical features, including pancreatic atrophy and renal disease. We herein report a Japanese case of young-onset diabetes with typical phenotypes of MODY5 and a novel heterozygous missense mutation (p.L145Q) in the HNF1B gene. The mutation was located in the Pit-Oct-Unc (POU)-specific domain, and the amino acid residue L145 was highly conserved among species. It is strongly suggested that this mutation explains the phenotypes of MODY5.

Early Onset of Diabetes Mellitus Accelerates Cognitive Decline in Japanese Patients with Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-Like Episodes

Approximately 80% of patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) carry the A3243G mutation in the mitochondrial tRNALeu (UUR) gene. Conversely, this mutation has also been identified as one of the most prevalent genetic abnormalities in patients with diabetes mellitus. Mitochondrial diabetes mellitus complicated with MELAS is relatively common, and 12.5% of patients with the A3243G mutation develop MELAS after being diagnosed with diabetes mellitus. However, the clinical impact of diabetes mellitus in MELAS patients remains unclear. Therefore, we retrospectively studied 14 Japanese MELAS patients with the A3243G mutation: three men and eleven women, with the mean age of 48.0 (± 15.4) years. Eight patients had been diagnosed with diabetes mellitus prior to the diagnosis of mitochondrial disease, and all of them were treated with insulin. The other six included four patients with concurrent diagnosis of diabetes and mitochondrial disease, one patient diagnosed with diabetes after the diagnosis of mitochondrial disease, and one patient without developing diabetes currently. We thus compared the patients' characteristics between those with and without early onset of diabetes mellitus. Cognitive decline (75.0% vs. 0%; p = 0.03) and poor glycemic control with severe hypoglycemic events (75.0% vs. 16.7%; p = 0.05) were more common in MELAS patients with a prior diagnosis of diabetes than in those without the prior diagnosis of diabetes. Our data suggest that the latent progress of cognitive decline is accelerated because of early onset of diabetes mellitus in MELAS patients.

Successful Glycemic Control Decreases the Elevated Serum FGF21 Level without Affecting Normal Serum GDF15 Levels in a Patient with Mitochondrial Diabetes

Mitochondrial diabetes mellitus is a subtype of diabetes linked to mutations in mitochondrial DNA. In patients with mitochondrial diabetes mellitus, the effect of glycemic control on the serum concentrations of fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) has not been evaluated. FGF21 and GDF15 have been reported to be useful biomarkers for the diagnosis and severity assessment of mitochondrial diseases like mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Recent studies have shown FGF21 acts in an endocrine fashion to regulate glucose and lipid metabolism in type 2 diabetes mellitus, while the exact biological functions of GDF15 remain unknown. Although mitochondrial diabetes mellitus is commonly found in cases with mitochondrial diseases, the comparison of FGF21 and GDF15 levels between those with and without diabetes has not been performed. Here, we report a 24-year-old woman with mitochondrial diabetes mellitus, who showed a high level of serum FGF21, but not serum GDF15, at diagnosis. In our case, liraglutide, a glucagon-like peptide-1 receptor agonist, added to insulin glargine was effective for her glycemic control and showed no adverse effects, including gastrointestinal symptoms and hypoglycemia, during a 14-week observation. The successful glycemic control caused a decrease in the FGF21 level, without affecting the GDF15 level. Thus, we should consider patients' glycemic control levels in using FGF21 values for the diagnosis of mitochondrial diseases. In addition, sustained GDF15 levels during glycemic treatment in our case suggest the usefulness of GDF15 as a marker for clinical severity of muscle-manifested mitochondrial diseases.

Syndrome of Inappropriate Antidiuretic Hormone Secretion Associated with Amyotrophic Lateral Sclerosis in a Patient Developing Carbon Dioxide Narcosis

We report a rare case of syndrome of inappropriate antidiuretic hormone secretion (SIADH) associated with amyotrophic lateral sclerosis (ALS). A 69-year-old man was admitted to our hospital with sustained hyponatremia. Hyposmolality with elevated urinary osmolality and sodium excretion was observed, which indicated SIADH. The treatment for SIADH was challenging; the patient developed carbon dioxide narcosis, which led to the diagnosis of ALS. After the initiation of noninvasive positive-pressure ventilation, the patient's serum sodium concentration normalized and became stable. Thus, ALS should be recognized as a possible cause of SIADH in the clinical setting.

Challenging Differential Diagnosis of Hypergastremia and Hyperglucagonemia with Chronic Renal Failure: Report of a Case with Multiple Endocrine Neoplasia Type 1

A 53-year-old woman developed end-stage renal failure during a 15-year clinical course of primary hyperparathyroidism and was referred to our hospital for evaluation of suspected multiple endocrine neoplasia type 1 (MEN1). Genetic testing revealed a novel deletion mutation at codon 467 in exon 10 of the MEN1 gene. Systemic and selective arterial calcium injection (SACI) testing revealed hyperglucagonemia and hypergastrinemia with positive gastrin responses. A pathological examination revealed glucagonoma and a lymph node gastrinoma. The findings in this case indicate the importance of early diagnosis of MEN1 and demonstrate the utility of systemic and SACI testing in renal failure cases.

Add-on treatment with mitiglinide improves residual postprandial hyperglycemia in type 2 diabetic patients receiving the combination therapy with insulin glargine and sitagliptin

The combination of a dipeptidyl peptidase-4 (DPP-4) inhibitor and a long-acting insulin analogue is widely used in clinical practice. However, some patients fail to achieve lower postprandial hyperglycemia. Mitiglinide, a short-acting insulinotropic sulfonylurea receptor ligand, is effective for postprandial hyperglycemia. Recently, it has been reported that the combination therapy of mitiglinide with a DPP-4 inhibitor could improve glycemic control. However, the efficacy of those under long-acting insulin analogue therapy remains to be investigated. Thus, we conducted a prospective single-center study of eight Japanese patients with type 2 diabetes mellitus receiving mitiglinide added to the combination therapy of sitagliptin and insulin glargine, and evaluated its efficacy and safety by continuous glucose monitoring (CGM). Participants' (four men and four women) mean age was 70.3 ± 10.6 years. Their mean body mass index, HbA1c level, and urinary C-peptide level were 22.0 ± 2.8 kg/m(2), 9.2 ± 1.2%, and 50.0 ± 31.4 μg/day, respectively. CGM showed that as compared with the combination of only sitagliptin and insulin glargine, mitiglinide in combination with sitagliptin and insulin glargine significantly reduced glycemic fluctuation indices, total area for the range of 24-h glycemic fluctuations (p = 0.04), mean amplitude of glycemic excursions (p = 0.03), and the proportion of time in hyperglycemia (p = 0.02) without significant difference in the proportion of time in hypoglycemia (p = 0.18). Hence, we have demonstrated the efficacy and safety of the add-on treatment with mitiglinide in type 2 diabetic patients, receiving the combination therapy of sitagliptin and insulin glargine.

A Novel Missense Mutation of the MEN1 Gene in a Patient with Multiple Endocrine Neoplasia Type 1 with Glucagonoma and Obesity

A 35-year-old obese diabetic man presented with recurrent primary hyperparathyroidism during a three-year outpatient follow-up. He was clinically diagnosed with multiple endocrine neoplasia type 1 (MEN1) due to the presence of a pituitary adenoma and multiple glucagonomas. The glucagonomas may have affected his glycemic control. However, he did not demonstrate weight loss, suggesting that the patient's obesity could have obscured the early diagnosis of a glucagonoma. Genetic testing revealed a novel missense mutation at codon 561 in exon 10, resulting in an amino acid substitution from methionine to arginine (M561R) in the MEN1 gene. This mutation appeared to be responsible for the MEN1 pathogenicity.

Diffuse thyroid enlargement following metastasis of lung adenocarcinoma

A 55-year-old man presented with a rapidly enlarging thyroid. He had been diagnosed with lung adenocarcinoma nine months earlier. Computed tomography (CT) and ultrasound (US) detected reticular cord-like structures, but no nodules, in the thyroid. A fine-needle aspiration biopsy (FNAB) of the thyroid revealed thyroglobulin-negative adenocarcinoma cells, thus establishing the diagnosis of diffuse thyroid metastases of lung cancer. Moreover, the fluid demonstrated milky chyliform effusion. This case suggests that the presence of reticular cord-like structures on US and CT may be a key imaging finding for the clinical diagnosis of diffuse thyroid metastases and that chyliform effusion may contribute to rapid goiter formation.

Pseudohypoparathyroidism type II in a woman with a history of thyroid surgery

We herein describe the case of a woman with pseudohypoparathyroidism (PHP) type II. She had a history of subtotal thyroidectomy against Graves' disease without levothyroxine supplementation and presented with stiffness, numbness and muscle cramps. Her surgical history suggested the possibility of secondary hypoparathyroidism; however, the serum intact parathyroid hormone level and results of a Ellsworth-Howard test led to the diagnosis of PHP type II. In the present case, making the differential diagnosis was challenging because two distinct disorders, such as PHP and secondary hypoparathyroidism, may exist simultaneously. This case demonstrates the need to consider the possibility of PHP type II in patients exhibiting hypocalcemia.

Desmopressin orally disintegrating tablet in Japanese patients with central diabetes insipidus: a retrospective study of switching from intranasal desmopressin

Central diabetes insipidus (CDI) is a rare disease characterized by polyuria and polydipsia. Patients with CDI have been successfully treated with desmopressin administered either by intranasal instillation or oral tablets. Recently, a desmopressin orally disintegrating tablet (ODT) was approved as the first oral desmopressin tablet for CDI treatment in Japan. We conducted a retrospective single-center study of 15 Japanese CDI patients treated with desmopressin ODT therapy, which aimed to evaluate the efficacy and safety of switching to desmopressin ODT and to analyze the clinical factors that affect the desmopressin ODT dose in Japanese patients. The daily mean dose of desmopressin ODT was 104 ± 46.30 μg and the mean ratio of oral to nasal desmopressin dose was 17.0 ± 7.6, both of which are considerably smaller than those of previous dose-titration study. Moreover, the nasal spray group needed significantly smaller ratios of nasal to oral desmopressin than the nasal drop group (11.7 ± 6.5 vs 21.0 ± 5.5, p = 0.02). The ratio of oral to nasal desmopressin dose had a significant inverse correlation with the required nasal desmopressin dose. Multiple regression analysis demonstrated the ratios of nasal to oral desmopressin dose depended on intranasal formulations. In conclusion, desmopressin ODT was safe and effective in the treatment of Japanese adult CDI patients. When switching to ODT, we should care about the possibility that patients require smaller ODT doses than what was initially expected based on previously published data and also nasal formulations in terms of their differences of expected switching ratio.

Prolonged disturbance of consciousness caused by severe hypophosphatemia: a report of two cases

We herein describe two patients with a prolonged disturbance of consciousness due to severe hypophosphatemia. Case one presented with pneumococcal infection and acute exacerbation of chronic obstructive pulmonary disease and asthma. Case two presented with diabetic foot infections and diabetic ketoacidosis. Both patients responded to initial therapy for their primary diseases, but consciousness became worse in both cases. Their test results for impaired consciousness revealed severe hypophosphatemia; therefore, phosphate replacement therapy was administered, thus resulting in complete alertness. These cases demonstrate that we should consider the possibility of hypophosphatemia in critically ill patients with an altered consciousness.

cAMP-responsive element-binding protein (CREB)-regulated transcription coactivator 2 (CRTC2) promotes glucagon clearance and hepatic amino acid catabolism to regulate glucose homeostasis

cAMP-responsive element-binding protein (CREB)-regulated transcription coactivator 2 (CRTC2) regulates transcription of gluconeogenic genes by specifying targets for the transcription factor CREB in response to glucagon. We used an antisense oligonucleotide directed against CRTC2 in both normal rodents and in rodent models of increased gluconeogenesis to better understand the role of CRTC2 in metabolic disease. In the context of severe hyperglycemia and elevated hepatic glucose production, CTRC2 knockdown (KD) improved glucose homeostasis by reducing endogenous glucose production. Interestingly, despite the known role of CRTC2 in coordinating gluconeogenic gene expression, CRTC2 KD in a rodent model of type 2 diabetes resulted in surprisingly little alteration of glucose production. However, CRTC2 KD animals had elevated circulating concentrations of glucagon and a ∼80% reduction in glucagon clearance. When this phenomenon was prevented with somatostatin or a glucagon-neutralizing antibody, endogenous glucose production was reduced by CRTC2 KD. Additionally, CRTC2 inhibition resulted in reduced expression of several glucagon-induced pyridoxal 5'-phosphate-dependent enzymes that convert amino acids to gluconeogenic intermediates, suggesting that it may control substrate availability as well as gluconeogenic gene expression. CRTC2 is an important regulator of gluconeogenesis with tremendous impact in models of elevated hepatic glucose production. Surprisingly, it is also part of a previously unidentified negative feedback loop that degrades glucagon and regulates amino acid metabolism to coordinately control glucose homeostasis in vivo.

The role of the carbohydrate response element-binding protein in male fructose-fed rats

By 2030, nearly half of Americans will have nonalcoholic fatty liver disease. In part, this epidemic is fueled by the increasing consumption of caloric sweeteners coupled with an innate capacity to convert sugar into fat via hepatic de novo lipogenesis. In addition to serving as substrates, monosaccharides also increase the expression of key enzymes involved in de novo lipogenesis via the carbohydrate response element-binding protein (ChREBP). To determine whether ChREBP is a potential therapeutic target, we decreased hepatic expression of ChREBP with a specific antisense oligonucleotide (ASO) in male Sprague-Dawley rats fed either a high-fructose or high-fat diet. ChREBP ASO treatment decreased plasma triglyceride concentrations compared with control ASO treatment in both diet groups. The reduction was more pronounced in the fructose-fed group and attributed to decreased hepatic expression of ACC2, FAS, SCD1, and MTTP and a decrease in the rate of hepatic triglyceride secretion. This was associated with an increase in insulin-stimulated peripheral glucose uptake, as assessed by the hyperinsulinemic-euglycemic clamp. In contrast, ChREBP ASO did not alter hepatic lipid content or hepatic insulin sensitivity. Interestingly, fructose-fed rats treated with ChREBP ASO had increased plasma uric acid, alanine transaminase, and aspartate aminotransferase concentrations. This was associated with decreased expression of fructose aldolase and fructokinase, reminiscent of inherited disorders of fructose metabolism. In summary, these studies suggest that targeting ChREBP may prevent fructose-induced hypertriglyceridemia but without the improvements in hepatic steatosis and hepatic insulin responsiveness.

Evaluation of the effects of exenatide administration in patients with type 2 diabetes with worsened glycemic control caused by glucocorticoid therapy

Glucocorticoid-induced hyperglycemia is common in patients with or without known diabetes mellitus. Exenatide, a glucagon-like peptide-1 receptor agonist, improves glycemic control without causing weight gain or hypoglycemia and is currently widely used in patients with type 2 diabetes mellitus. We herein report four cases of patients with type 2 diabetes with worsened glycemic control due to glucocorticoids who were successfully treated with exenatide administration.

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.

Diabetic ketoacidosis accompanied by hypothermia: a case report

Diabetic ketoacidosis (DKA) is an acute, life-threatening complication of diabetes mellitus and is caused by insulin insufficiency. Hypothermia is defined as a core temperature of less than 35°C and is sometimes accompanied by DKA. We report two patients with diabetes who were admitted for DKA accompanied by hypothermia.

Distal renal tubular acidosis that became exacerbated by proton pump inhibitor use

Acid-base imbalances and electrolyte disorders induced by proton pump inhibitors (PPIs) are extremely rare. However, under certain conditions, PPIs may cause metabolic acidosis or hypokalemia, probably due to an inhibitory action on the proton pump that contributes to H(+) and K(+) homeostasis in the kidney. We herein present a case of marked hypokalemia accompanied by distal renal tubular acidosis in which a PPI appeared to contribute to the pathophysiology of metabolic acidosis.

SirT1 regulates adipose tissue inflammation

OBJECTIVE

Macrophage recruitment to adipose tissue is a reproducible feature of obesity. However, the events that result in chemokine production and macrophage recruitment to adipose tissue during states of energetic excess are not clear. Sirtuin 1 (SirT1) is an essential nutrient-sensing histone deacetylase, which is increased by caloric restriction and reduced by overfeeding. We discovered that SirT1 depletion causes anorexia by stimulating production of inflammatory factors in white adipose tissue and thus posit that decreases in SirT1 link overnutrition and adipose tissue inflammation.

RESEARCH DESIGN AND METHODS

We used antisense oligonucleotides to reduce SirT1 to levels similar to those seen during overnutrition and studied SirT1-overexpressing transgenic mice and fat-specific SirT1 knockout animals. Finally, we analyzed subcutaneous adipose tissue biopsies from two independent cohorts of human subjects.

RESULTS

We found that inducible or genetic reduction of SirT1 in vivo causes macrophage recruitment to adipose tissue, whereas overexpression of SirT1 prevents adipose tissue macrophage accumulation caused by chronic high-fat feeding. We also found that SirT1 expression in human subcutaneous fat is inversely related to adipose tissue macrophage infiltration.

CONCLUSIONS

Reduction of adipose tissue SirT1 expression, which leads to histone hyperacetylation and ectopic inflammatory gene expression, is identified as a key regulatory component of macrophage influx into adipose tissue during overnutrition in rodents and humans. Our results suggest that SirT1 regulates adipose tissue inflammation by controlling the gain of proinflammatory transcription in response to inducers such as fatty acids, hypoxia, and endoplasmic reticulum stress.

Hyperglucagonemia precedes a decline in insulin secretion and causes hyperglycemia in chronically glucose-infused rats

Islet damage from glucose toxicity is implicated in the pathogenesis of type 2 diabetes, but the sequence of events leading to islet cell dysfunction and hyperglycemia remains unclear. To examine the early stages of islet pathology resulting from increased basal glucose loads, normal awake rats were infused with glucose continuously for 10 days. Plasma glucose and markers of islet and liver function were monitored throughout the infusion. After initial hyperglycemia, rats adapted to the infusion and maintained euglycemia for approximately 4 days. Continued infusion led to worsening hyperglycemia in just 5% of rats after 6 days, but 69% after 8 days and 89% after 10 days, despite unchanged basal and stimulated plasma insulin and C-peptide concentrations. In contrast, plasma glucagon concentrations increased fivefold. Endogenous glucose production (EGP) was appropriately suppressed after 4 days (2.8 ± 0.7 vs. 6.1 ± 0.4 mg·kg(-1)·min(-1) on day 0, P < 0.001) but tripled between days 4 and 8 (9.9 ± 1.7 mg·kg(-1)·min(-1), P < 0.01). Surprisingly, the increase in EGP was accompanied by increased mitochondrial phosphoenolpyruvate carboxykinase expression with appropriate suppression of the cytosolic isoform. Infusion of anti-glucagon antibodies normalized plasma glucose to levels identical to those on day 4 and ∼300 mg/dl lower than controls. This improved glycemia was associated with a 60% reduction in EGP. These data support the novel concept that glucose toxicity may first manifest as α-cell dysfunction prior to any measurable deficit in insulin secretion. Such hyperglucagonemia could lead to excessive glucose production overwhelming the capacity of the β-cell to maintain glucose homeostasis.

The role of peroxisome proliferator-activated receptor gamma coactivator-1 beta in the pathogenesis of fructose-induced insulin resistance

Peroxisome proliferator-activated receptor gamma coactivator-1 beta (PGC-1beta) is known to be a transcriptional coactivator for SREBP-1, the master regulator of hepatic lipogenesis. Here, we evaluated the role of PGC-1beta in the pathogenesis of fructose-induced insulin resistance by using an antisense oligonucletoide (ASO) to knockdown PGC-1beta in liver and adipose tissue. PGC-1beta ASO improved the metabolic phenotype induced by fructose feeding by reducing expression of SREBP-1 and downstream lipogenic genes in liver. PGC-1beta ASO also reversed hepatic insulin resistance induced by fructose in both basal and insulin-stimulated states. Furthermore, PGC-1beta ASO increased insulin-stimulated whole-body glucose disposal due to a threefold increase in glucose uptake in white adipose tissue. These data support an important role for PGC-1beta in the pathogenesis of fructose-induced insulin resistance and suggest that PGC-1beta inhibition may be a therapeutic target for treatment of NAFLD, hypertriglyceridemia, and insulin resistance associated with increased de novo lipogenesis.

Increased hypothalamic-pituitary-adrenal axis activity and hepatic insulin resistance in low-birth-weight rats

Individuals born with a low birth weight (LBW) have an increased prevalence of type 2 diabetes, but the mechanisms responsible for this association are unknown. Given the important role of insulin resistance in the pathogenesis of type 2 diabetes, we examined insulin sensitivity in a rat model of LBW due to intrauterine fetal stress. During the last 7 days of gestation, rat dams were treated with dexamethasone and insulin sensitivity was assessed in the LBW offspring by a hyperinsulinemic euglycemic clamp. The LBW group had liver-specific insulin resistance associated with increased levels of PEPCK expression. These changes were associated with pituitary hyperplasia of the ACTH-secreting cells, increased morning plasma ACTH concentrations, elevated corticosterone secretion during restraint stress, and an approximately 70% increase in 24-h urine corticosterone excretion. These data support the hypothesis that prenatal stress can result in chronic hyperactivity of the hypothalamic-pituitary-adrenal axis, resulting in increased plasma corticosterone concentrations, upregulation of hepatic gluconeogenesis, and hepatic insulin resistance.

The role of skeletal muscle insulin resistance in the pathogenesis of the metabolic syndrome

We examined the hypothesis that insulin resistance in skeletal muscle promotes the development of atherogenic dyslipidemia, associated with the metabolic syndrome, by altering the distribution pattern of postprandial energy storage. Following ingestion of two high carbohydrate mixed meals, net muscle glycogen synthesis was reduced by approximately 60% in young, lean, insulin-resistant subjects compared with a similar cohort of age-weight-body mass index-activity-matched, insulin-sensitive, control subjects. In contrast, hepatic de novo lipogenesis and hepatic triglyceride synthesis were both increased by >2-fold in the insulin-resistant subjects. These changes were associated with a 60% increase in plasma triglyceride concentrations and an approximately 20% reduction in plasma high-density lipoprotein concentrations but no differences in plasma concentrations of TNF-alpha, IL-6, adiponectin, resistin, retinol binding protein-4, or intraabdominal fat volume. These data demonstrate that insulin resistance in skeletal muscle, due to decreased muscle glycogen synthesis, can promote atherogenic dyslipidemia by changing the pattern of ingested carbohydrate away from skeletal muscle glycogen synthesis into hepatic de novo lipogenesis, resulting in an increase in plasma triglyceride concentrations and a reduction in plasma high-density lipoprotein concentrations. Furthermore, insulin resistance in these subjects was independent of changes in the plasma concentrations of TNF-alpha, IL-6, high-molecular-weight adiponectin, resistin, retinol binding protein-4, or intraabdominal obesity, suggesting that these factors do not play a primary role in causing insulin resistance in the early stages of the metabolic syndrome.

Effect of acute activation of 5'-AMP-activated protein kinase on glycogen regulation in isolated rat skeletal muscle

5'-AMP-activated protein kinase (AMPK) has been implicated in glycogen metabolism in skeletal muscle. However, the physiological relevance of increased AMPK activity during exercise has not been fully clarified. This study was performed to determine the direct effects of acute AMPK activation on muscle glycogen regulation. For this purpose, we used an isolated rat muscle preparation and pharmacologically activated AMPK with 5-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR). Tetanic contraction in vitro markedly activated the alpha(1)- and alpha(2)-isoforms of AMPK, with a corresponding increase in the rate of 3-O-methylglucose uptake. Incubation with AICAR elicited similar enhancement of AMPK activity and 3-O-methylglucose uptake in rat epitrochlearis muscle. In contrast, whereas contraction stimulated glycogen synthase (GS), AICAR treatment decreased GS activity. Insulin-stimulated GS activity also decreased after AICAR treatment. Whereas contraction activated glycogen phosphorylase (GP), AICAR did not alter GP activity. The muscle glycogen content decreased in response to contraction but was unchanged by AICAR. Lactate release was markedly increased when muscles were stimulated with AICAR in buffer containing glucose, indicating that the glucose taken up into the muscle was catabolized via glycolysis. Our results suggest that AMPK does not mediate contraction-stimulated glycogen synthesis or glycogenolysis in skeletal muscle and also that acute AMPK activation leads to an increased glycolytic flux by antagonizing contraction-stimulated glycogen synthesis.

α2 isoform-specific activation of 5'adenosine monophosphate-activated protein kinase by 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside at a physiological level activates glucose transport and increases glucose transporter 4 in mouse skeletal muscle

5'Adenosine monophosphate-activated protein kinase (AMPK) has been implicated in exercise-induced stimulation of glucose metabolism in skeletal muscle. Although skeletal muscle expresses both the alpha1 and alpha2 isoforms of AMPK, the alpha2 isoform is activated predominantly in response to moderate-intensity endurance exercise in human and animal muscles. The purpose of this study was to determine whether activation of alpha2 AMPK plays a role in increasing the rate of glucose transport, promoting glucose transporter 4 (GLUT4) expression, and enhancing insulin sensitivity in skeletal muscle. To selectively activate the alpha2 isoform, we used 5-aminoimidazole-4-carboxamide-1-beta-d-ribonucleoside (AICAR), which is metabolized in muscle cells and preferentially stimulates the alpha2 isoform. Subcutaneous administration of 250 mg/kg AICAR activated the alpha2 isoform for 90 minutes, but not the alpha1 isoform in hind limb muscles of the C57/B6J mouse. The maximal activation of the alpha2 isoform was observed 30 to 60 minutes after administration of AICAR and was similar to the activation induced by a 30-minute swim in a current pool. The increase in alpha2 activity paralleled the phosphorylation of Thr(172), the essential residue for full kinase activation, and the activity of acetyl-coenzyme A carboxylase beta, a known substrate of AMPK in skeletal muscle. Subcutaneous injection of AICAR rapidly increased, by 30%, the rate of 2-deoxyglucose (2DG) transport into soleus muscle; 2DG transport increased within 30 minutes and remained elevated for 4 hours after administration of AICAR. Repeated intraperitoneal injection of AICAR, 3 times a day for 4 to 7 days, increased soleus GLUT4 protein by 30% concomitant with a significant 20% increase in insulin-stimulated 2DG transport. These data suggest that moderate endurance exercise promotes glucose transport, GLUT4 expression, and insulin sensitivity in skeletal muscle at least partially via activation of the alpha2 isoform of AMPK.

Possible involvement of the alpha1 isoform of 5'AMP-activated protein kinase in oxidative stress-stimulated glucose transport in skeletal muscle

Recent studies have suggested that 5'AMP-activated protein kinase (AMPK) is activated in response to metabolic stresses, such as contraction, hypoxia, and the inhibition of oxidative phosphorylation, which leads to insulin-independent glucose transport in skeletal muscle. In the present study, we hypothesized that acute oxidative stress increases the rate of glucose transport via an AMPK-mediated mechanism. When rat epitrochlearis muscles were isolated and incubated in vitro in Krebs buffer containing the oxidative agent H(2)O(2), AMPKalpha1 activity increased in a time- and dose-dependent manner, whereas AMPKalpha2 activity remained unchanged. The activation of AMPKalpha1 was associated with phosphorylation of AMPK Thr(172), suggesting that an upstream kinase is involved in the activation process. H(2)O(2)-induced AMPKalpha1 activation was blocked in the presence of the antioxidant N-acetyl-l-cysteine (NAC), and H(2)O(2) significantly increased the ratio of oxidized glutathione to glutathione (GSSG/GSH) concentrations, a sensitive marker of oxidative stress. H(2)O(2) did not cause an increase in the conventional parameters of AMPK activation, such as AMP and AMP/ATP. H(2)O(2) increased 3-O-methyl-d-glucose transport, and this increase was partially, but significantly, blocked in the presence of NAC. Results were similar when the muscles were incubated in a superoxide-generating system using hypoxanthine and xanthine oxidase. Taken together, our data suggest that acute oxidative stress activates AMPKalpha1 in skeletal muscle via an AMP-independent mechanism and leads to an increase in the rate of glucose transport, at least in part, via an AMPKalpha1-mediated mechanism.

Up-regulation of uncoupling protein 3 gene expression by fatty acids and agonists for PPARs in L6 myotubes

Uncoupling protein 3 (UCP3), which uncouples electron transport from ATP synthesis, is expressed at high levels in the skeletal muscle, an important organ in glucose and lipid metabolism. Because several reports proposed that fatty acids induced UCP3 gene expression in skeletal muscle in vivo, in the present study we examined the regulation of UCP3 gene expression by various fatty acids using L6 myotubes. UCP3 gene expression was increased in L6 myotubes by various fatty acids or by alpha-bromopalmitate, a nonmetabolized derivative of palmitic acid. Because fatty acids are also known as agonists for PPARs, we examined the involvement of PPARs in the regulation of the UCP3 gene expression. L-165041, a PPAR delta agonist, increased UCP3 gene expression in L6 myotubes, whereas neither Wy 14,643, a PPAR alpha agonist, nor Pioglitazone, a PPAR gamma agonist, increased it. Therefore, we conclude that UCP3 gene expression is increased by the activation of PPAR delta in L6 myotubes and postulate that PPAR delta mediates at least some part of the increased UCP3 gene expression by fatty acids in skeletal muscle in vivo.

Troglitazone not only increases GLUT4 but also induces its translocation in rat adipocytes

Thiazolidinediones, insulin-sensitizing agents, have been reported to increase glucose uptake along with the expression of glucose transporters in adipocytes and cardiomyocytes. Recently, we have further suggested that the translocation of GLUT4 is stimulated by thiazolidinediones in L6 myocytes. However, the direct effects of thiazolidinediones on translocation of glucose transporters have not yet been determined. In this study, using hemagglutinin epitope-tagged GLUT4 (GLUT4-HA), we provide direct evidence of the effect of troglitazone on the translocation of GLUT4 in rat epididymal adipocytes. Primary cultures of rat adipocytes were transiently transfected with GLUT4-HA and overexpressed eightfold compared with endogenous GLUT4 in transfected cells. A total of 24 h of treatment with troglitazone (10(-4) mol/l) increased the cell surface level of GLUT4-HA by 1.5 +/- 0.03-fold (P < 0.01) without changing the total amount of GLUT4-HA, whereas it increased the protein level of endogenous GLUT4 (1.4-fold) without changing that of GLUT1. Thus, the direct effect on the translocation can be detected apart from the increase in endogenous GLUT4 content using GLUT4-HA. Troglitazone not only increased the translocation of GLUT4-HA on the cell surface in the basal state but also caused a leftward shift in the dose-response relations between GLUT4-HA translocation and insulin concentration in the medium (ED(50): from approximately 0.1 to 0.03 nmol/l). These effects may partly contribute to the antidiabetic activity of troglitazone in patients with obesity and type 2 diabetes.

Troglitazone induces GLUT4 translocation in L6 myotubes

A number of studies have demonstrated that insulin resistance in the skeletal muscle plays a pivotal role in the insulin resistance associated with obesity and type 2 diabetes. A decrease in GLUT4 translocation from the intracellular pool to the plasma membranes in skeletal muscles has been implicated as a possible cause of insulin resistance. Herein, we examined the effects of an insulin-sensitizing drug, troglitazone (TGZ), on glucose uptake and the translocation of GLUT4 in L6 myotubes. The prolonged exposure (24 h) of L6 myotubes to TGZ (10(-5) mol/l) caused a substantial increase in the 2-deoxy-[3H]D-glucose (2-DG) uptake without changing the total amount of the glucose transporters GLUT4, GLUT1, and GLUT3. The TGZ-induced 2-DG uptake was completely abolished by cytochalasin-B (10 micromol/l). The ability of TGZ to translocate GLUT4 from light microsomes to the crude plasma membranes was greater than that of insulin. Both cycloheximide treatment (3.5 x 10(-6) mol/l) and the removal of TGZ by washing reversed the 2-DG uptake to the basal level. Moreover, insulin did not enhance the TGZ-induced 2-DG uptake additively. The TGZ-induced 2-DG uptake was only partially reversed by wortmannin to 80%, and TGZ did not change the expression and the phosphorylation of protein kinase B; the expression of protein kinase C (PKC)-lambda, PKC-beta2, and PKC-zeta; or 5'AMP-activated protein kinase activity. a-Tocopherol, which has a molecular structure similar to that of TGZ, did not increase 2-DG uptake. We conclude that the glucose transport in L6 myotubes exposed to TGZ for 24 h is the result of an increased translocation of GLUT4. The present results imply that the effects of troglitazone on GLUT4 translocation may include a new mechanism for improving glucose transport in skeletal muscle.

Downregulation of leptin by free fatty acids in rat adipocytes: effects of triacsin C, palmitate, and 2-bromopalmitate

Free fatty acid (FFA) has been reported to decrease leptin mRNA levels in 3T3-L1 adipocytes. When using this cell line, it is difficult to determine the protein levels because a very small amount of leptin is secreted into the medium. The effect of FFA on leptin secretion from adipocytes has not yet been determined. In addition, in vivo studies have failed to demonstrate a FFA-induced decrease in plasma leptin levels. To clarify the effect of FFA on leptin production, we investigated the leptin protein level in the medium and the mRNA level in primary cultured rat adipocytes treated with triacsin C, which is a potent inhibitor of acyl-coenzyme A (CoA) synthetase, palmitate, and 2-bromopalmitate. Triacsin C (0 to 5 x 10(-5) mol/L) decreased leptin concentrations in the culture medium in a dose-dependent manner. Leptin mRNA levels were decreased to 10% of the control in the presence of triacsin C. The concentration of triacsin C needed to suppress leptin production was similar to the Ki value (approximately 10(-5) mol/L) for inhibition of acyl-CoA synthetase. Both palmitate and 2-bromopalmitate decreased leptin concentra-tions but did not affect the triacsin C-induced decrease in leptin additively. In conclusion, both protein and mRNA levels of leptin were decreased by triacsin C and FFA in primary cultured rat adipocytes. Our findings suggest that FFA is involved in the regulation of leptin production in adipocytes.

Thyrotropin decreases leptin production in rat adipocytes

Leptin, which is secreted from adipocytes, has a role in the regulation of appetite and energy expenditure. The thyrotropin receptor (TSH-R) was recently found in adipocytes. We examined the effects of TSH on leptin production and lipolysis in rat epididymal adipocytes. TSH decreased the concentration of leptin in the medium time (approximately 24 hours)- and dose (approximately 10(-7) mol/L)-dependently (half-maximal inhibition [IC50] approximately 10(-9) mol/L). TSH also decreased the ob mRNA level approximately 55% in adipocytes. We confirmed the presence of TSH-R mRNA in the adipocytes by reverse transcription-polymerase chain reaction (RT-PCR). TSH stimulated glycerol release dose-dependently (IC50 approximately 10(-8) mol/L) in adipocytes. This TSH-induced glycerol release was further enhanced by adenosine deaminase (ADA). In summary, TSH reduced leptin production and stimulated lipolysis in rat epididymal adipocytes. Although the pathophysiological relevance of the regulation of leptin production and lipolysis by TSH is unknown, we speculate that TSH may affect the regulation of appetite and energy expenditure in pathophysiological states.

Spontaneous remission of primary hyperparathyroidism due to hemorrhagic infarction in the parathyroid adenoma

A 59-year-old man visited Kyoto University Hospital because of general malaise, polyuria, and polydipsia. The diagnosis of primary hyperparathyroidism was made based on hypercalcemia and an elevated circulating PTH level. A nodule was palpable in the left anterior neck. Two weeks later, the serum calcium level was normalized and his symptoms subsided. A temporary expansion, followed by reduction of the tumor size was observed by serial ultrasonography. Histology of the resected tumor showed central necrotic tissue, with some peripherally remaining glandular tissue. We report here a rare case of primary hyperparathyroidism with spontaneous remission due to hemorrhagic infarction in the adenoma.