Hyperinsulinemia and Insulin Receptor Gene Mutation in Nonobese Healthy Subjects in Japan.

CONTEXT: Hyperinsulinemia is often observed in obese people, owing to their insulin resistance accompanied by visceral fat accumulation, but the frequency of hyperinsulinemia in nonobese people is not well known. Mutations in the insulin receptor gene are known to cause insulin resistance and hyperinsulinemia in type A insulin resistance syndrome, Rabson-Mendenhall syndrome, and Donohue syndrome. However, insulin receptor gene abnormalities have not been investigated in asymptomatic hyperinsulinemic subjects. PURPOSE: The aim of the current study was to investigate the prevalence of hyperinsulinemia in nonobese Japanese subjects and to examine the involvement of insulin receptor gene mutations. METHODS: We enrolled 11,046 subjects who received health checkups. From these, we extracted nonobese subjects (body mass index <25 kg/m2) who exhibited hyperinsulinemia (serum fasting immunoreactive insulin ≥15 µU/mL). Genetic analysis was performed for the insulin receptor gene in 11 nonobese subjects with hyperinsulinemia. RESULTS: The prevalence of hyperinsulinemia without apparent diabetes in nonobese subjects was 0.4% (33/8630). In the 11 analyzed subjects, two novel heterozygous nonsense mutations were detected [c.2106 T>G (p.Y702X) and c.2779-2780 GC>A]. The prevalence of insulin receptor gene mutations was 18.2% (2/11). CONCLUSIONS: To our knowledge, this is the first report of the prevalence of hyperinsulinemia in nonobese healthy subjects. We identified two novel mutations in the insulin receptor gene. These findings indicate that mutations in the insulin receptor gene may be related to fasting hyperinsulinemia, and insulin receptor gene screening may be useful for determining the cause of unexplained hyperinsulinemia.

A Novel Mutation in the type Iα Regulatory Subunit of Protein Kinase A (PRKAR1A) in a Cushing's Syndrome Patient with Primary Pigmented Nodular Adrenocortical Disease.

A 40-year-old man presented with Cushing's syndrome due to bilateral adrenal hyperplasia with multiple nodules. Computed tomography scan results were atypical demonstrating an enlargement of the bilateral adrenal glands harboring multiple small nodules, but the lesion was clinically diagnosed to be primary pigmented nodular adrenocortical disease (PPNAD) based on both endocrinological test results and his family history. We performed bilateral adrenalectomy and confirmed the diagnosis histologically. An analysis of the patient and his mother's genomic DNA identified a novel mutation in the type Iα regulatory subunit of protein kinase A (PRKAR1A) gene; p.E17X (c.49G>T). This confirmed the diagnosis of PPNAD which is associated with Carney Complex.

Hyperinsulinemic hypoglycemia syndrome associated with mutations in the human insulin receptor gene: report of two cases.

Insulinoma and insulin or insulin receptor (IR) autoantibodies are the main causes of hyperinsulinemic hypoglycemia in adults, but the exact cause in other cases remains obscure. This study is to determine the genetic basis of hyperinsulinemic hypoglycemia in two cases without the above abnormalities. Sequence analysis of IR gene in two patients with adult-onset hyperinsulinemic hypoglycemia and their relatives were performed, and the mutant gene observed in one case was analyzed. Both cases had normal levels of fasting plasma glucose (FPG), fasting hyperinsulinemia, low insulin sensitivity, and hypoglycemia with excessive insulin secretion during oral glucose tolerance test (OGTT). Both reported adult-onset postprandial hypoglycemic symptoms. In one patient, a missense mutation (Arg256Cys) was detected in both alleles of the IR gene, and his parents had the same mutation in only one allele but no hypoglycemia. The other had a novel nonsense mutation (Trp1273X) followed by a mutation (Gln1274Lys) in one allele, and his 9-year old son had the same mutation in one allele, together with hyperinsulinemic hypoglycemia during OGTT. Overexpression experiments of the mutant gene found in Case 1 in mammalian cells showed abnormal processing of the IR protein and demonstrated reduced function of Akt/Erk phosphorylation by insulin in the cells. In two cases of hyperinsulinemic hypoglycemia in adults, we found novel mutations in IR gene considered to be linked to hypoglycemia. We propose a disease entity of adult-onset hyperinsulinemic hypoglycemia syndrome associated with mutations in IR gene.

Interferon stimulated gene 15 has an anti-apoptotic effect on MIN6 cells.

Type 1 diabetes, one of two major forms of diabetes, results from the complete destruction of pancreatic beta cells. Viral infection has been suggested to be a trigger of beta cell destruction, the pathogenesis of type 1 diabetes. The aim of this study was to clarify the role of the protein encoded by intherferon stimulated gene (ISG) 15, an antiviral effector, in the development of this clinical entity. We used the mouse beta cell line MIN6 to investigate the role of ISG15 and paid special attention to apoptosis. Although not detected in native MIN6 cells, free ISG15 and ISG15 conjugated proteins were both present in dose-dependently increased amounts following stimulation with interferon alpha. As assessed both by caspase 3/7 activity and an annexin V assay, the percentage of apoptotic MIN6 cells (after exposure to the inflammatory cytokines of interleukin-1beta plus interferon gamma or tumor necrosis factor alpha) was decreased by pretreatment with adenovirus-expressing ISG15 and increased by expressing a short hairpin RNA directed against ISG15. In conclusion, ISG15 has an anti-apoptotic effect on MIN6 cells. Thus, promoting ISG15 expression in the pancreatic beta cells could be a potential therapeutic approach for patients with type 1 diabetes.

Carotid intima-media thickness, but not visceral fat area or adiponectin, correlates with intracoronary stenosis detected by multislice computed tomography in people with type 2 diabetes and hypertension.

We investigated the relationship between intracoronary stenosis detected by multislice computed tomography and various clinical parameters in type 2 diabetic patients with hypertension treated with candesartan (n=42). The results showed that carotid intima-media thickness, but not visceral fat area or adiponectin, correlated significantly with intracoronary stenosis (p<0.05).

Reciprocal regulation of natriuretic peptide receptors by insulin in adipose cells.

Atrial- and brain-type natriuretic peptides (ANP and BNP, respectively) have been shown to exert potent lipolytic action in adipocytes. A family of natriuretic peptide receptors (NPRs), NPR-1, NPR-2, and NPR-3, mediates their physiologic effects. NPR-1 and NPR-2 are receptor guanylyl cyclases, while NPR-3 lacks enzymatic activity and functions primarily as a clearance receptor for natriuretic peptides. ANP has a high affinity for NPR-1 and NPR-3 than other natriuretic peptides. There is a possibility that ANP may exhibit its lipolytic effect through the balance of NPR-1 and NPR-3 expressions in adipocytes. However, the regulation of adipose NPRs has not been fully elucidated. We here examined the regulation of mouse adipose NPRs by insulin, an anti-lipolytic hormone. Among the insulin target organs, NPR-1 mRNA levels were higher in white adipose tissue (WAT) than in liver and skeletal muscle. NPR-3 mRNA was expressed most abundantly in WAT. Fasting condition induced NPR-1 mRNA level while suppressed NPR-3 mRNA level in WAT. Administration of streptozotocin resulted in the increase of NPR-1 mRNA level while the decrease of NPR-3 mRNA level in WAT. In ob/ob mice, hyperinsulinemic model, NPR-1 mRNA level was lower whereas NPR-3 mRNA level was higher compared to lean control mice. In 3T3-L1 adipocytes, insulin significantly reduced NPR-1 mRNA level while increased NPR-3 mRNA levels both through phosphatidylinositol 3-kinase (PI3-kinase) pathway. In summary, NPR-1 and NPR-3 were highly expressed in WAT and adipose NPR-1 and NPR-3 were reciprocally regulated by insulin. This study suggests that insulin may efficiently promote lipogenesis partly by reducing the lipolytic action of ANP through the opposite regulation of NPR-1 and NPR-3.

URB is abundantly expressed in adipose tissue and dysregulated in obesity.

Dysregulated production of adipocytokines in obesity is involved in the development of metabolic syndrome. URB/DRO1 contains N-terminal signal sequence and is thought to play a role in apoptosis of tumor cells. In the present study, we investigated the expression pattern of URB mRNA in adipose tissue and secretion from cultured adipocytes. In human and mouse, URB mRNA was predominantly expressed in adipose tissue and was downregulated in obese mouse models, such as ob/ob, KKAy, and diet-induced obese mice. In 3T3L1 adipocytes, insulin, TNF-alpha, H(2)O(2) and hypoxia decreased URB mRNA level. This regulation was similar to that for adiponectin and opposite to MCP-1. URB protein was secreted in media of URB cDNA-stably transfected cells and endogenous URB was detected in media of cultured human adipocytes. In conclusion, the expression pattern of URB suggests its role in obesity and the results suggest that URB is secreted, at least in part, from adipocytes.

Clinical significance of high-molecular weight form of adiponectin in male patients with coronary artery disease.

BACKGROUND: It has been reported previously that the measurement of plasma total adiponectin level is clinically useful to estimate the risk of coronary artery disease (CAD). Here, the relevance of high molecular weight (HMW) adiponectin with risk factors for atherosclerosis is investigated METHODS AND RESULTS: A total of 186 consecutive male CAD patients participated in the study and were categorized into quartiles based on their total adiponectin level. The interquartile cut-off points were 4.0, 5.5 and 7.0 microg/ml. The HMW adiponectin levels were significantly lower in the quartile of lower total adiponectin levels both in non-diabetic and diabetic patients. In contrast, low molecular weight adiponectin levels (which were calculated as the Total - HMW) were constant. In univariate analysis, total adiponectin correlated negatively with body mass index and hemoglobin (Hb) A1c, and HMW adiponectin correlated negatively with HbA1c in non-diabetic patients. On the other hand, total and HMW adiponectin correlated positively with high-density lipoprotein-cholesterol (HDL-C) in diabetic patients. Multiple regression analysis revealed that HMW adiponectin correlated negatively with HbA1c in non-diabetic patients, and total and HMW adiponectin correlated positively with HDL-C in diabetic patients. CONCLUSIONS: Change in the HMW isoform reflects a change in total adiponectin level. Measurement of total and HMW adiponectin were equally useful in assessing metabolic risk in CAD patients.