Severe hypoglycaemia is a major predictor of incident diabetic retinopathy in Japanese patients with type 2 diabetes.

AIM: Hypoglycaemia is a common complication in diabetes patients. However, its relationship with retinopathy has not been well documented in patients with type 2 diabetes (T2D). This study aimed to investigate the associations between hypoglycaemia and the incidence and progression of diabetic retinopathy (DR). METHODS: In this longitudinal cohort study, which was part of the Japan Diabetes Complications Study (JDCS), adult patients with T2D were recruited at 59 diabetes clinics across Japan. Their history of hypoglycaemia was assessed by standardized self-reported questionnaires. Severe hypoglycaemia was defined as having at least one episode with coma requiring an outpatients visit or hospitalization. Adjusted hazard ratios (HRs) for incidence and progression of DR over 8 years of follow-up were determined. RESULTS: Of 1221 patients without DR, 127 (10.4%) had experienced non-severe hypoglycaemia within the previous year, whereas 10 (0.8%) reported severe hypoglycaemia episodes. During the 8-year follow-up involving 8492 person-years, 329 patients developed DR. In 410 patients with prevalent DR, the adjusted HRs for incident DR were 4.35 (95% CI: 1.98-9.56; P<0.01) and, for progression of DR, 2.29 (95% CI: 0.45-11.78; P=0.32) with severe hypoglycaemia. CONCLUSION: Having a history of severe hypoglycaemia was one of the strongest predictors of incident DR in patients with T2D, with a fourfold increased risk. Identifying patients with greater risks of DR based on their history of hypoglycaemia may help to personalize risk evaluation in patients with diabetes.

Leisure-time physical activity is a significant predictor of stroke and total mortality in Japanese patients with type 2 diabetes: analysis from the Japan Diabetes Complications Study (JDCS).

AIMS/HYPOTHESIS: Our aim was to clarify the association between leisure-time physical activity (LTPA) and cardiovascular events and total mortality in a nationwide cohort of Japanese diabetic patients. METHODS: Eligible patients (1,702) with type 2 diabetes (mean age, 58.5 years; 47% women) from 59 institutes were followed for a median of 8.05 years. A comprehensive lifestyle survey including LTPA and occupation was performed using standardised questionnaires. Outcome was occurrence of coronary heart disease (CHD), stroke and total mortality. The adjusted HR and 95% CI were calculated by Cox regression analysis. RESULTS: A significant reduction in HR in patients in the top (≥ 15.4 metabolic equivalents [MET] h/week) vs the bottom tertile (≤ 3.7 MET h/week) of LTPA, adjusted by age, sex and diabetes duration, was observed in stroke (HR 0.55, 95% CI 0.32, 0.94) and total mortality (HR 0.49, 95% CI 0.26, 0.91) but not in CHD (HR 0.77, 95% CI 0.48, 1.25). The HR for stroke became borderline significant or nonsignificant after adjustment for lifestyle or clinical variables including diet or serum lipids. The significantly reduced total mortality by LTPA was independent of these variables and seemed not to be, at least mainly, attributed to reduced cardiovascular disease. CONCLUSIONS/INTERPRETATION: In Japanese persons with type 2 diabetes, LTPA of 15.4 MET h/week or more was associated with a significantly lower risk of stroke partly through ameliorating combinations of cardiovascular risk factors. It was also associated with significantly reduced total mortality but independently of cardiovascular risk factors or events. These findings, implying differences from Western diabetic populations, should be considered in the clinical management of East Asians with diabetes.

Incidence and progression of diabetic retinopathy in Japanese adults with type 2 diabetes: 8 year follow-up study of the Japan Diabetes Complications Study (JDCS).

AIMS/HYPOTHESIS: The aim of this study was to determine the incidence and progression rates of diabetic retinopathy and their associations in Japanese individuals with type 2 diabetes. METHODS: This is a part of the Japan Diabetic Complications Study (JDCS), a multi-centred randomised trial of type 2 diabetes patients aged 40-70 years with an 8 year follow-up. There were 1,221 patients without diabetic retinopathy at baseline; incidence of diabetic retinopathy was defined as the development of any diabetic retinopathy. There were 410 patients with mild non-proliferative diabetic retinopathy at baseline; progression of diabetic retinopathy was defined as the development of severe non-proliferative diabetic retinopathy or proliferative diabetic retinopathy. We used multivariate proportional Cox hazard models, and generalised additive models were also applied to identify potential threshold effect. RESULTS: The incidence and progression rate of diabetic retinopathy was 38.3/1,000 person-years and 21.1/1,000 person-years, respectively. Higher HbA(1c) (adjusted HR [aHR] per 1% [10.9 mmol/mol] 1.36 [95% CI 1.28-1.45]), longer duration of diabetes (aHR per 5 year period 1.26 [95% CI 1.17-1.35]), higher systolic blood pressure (aHR per +10 mmHg 1.01 [95% CI 1.00-1.02]) and higher body mass index (aHR per 1 kg/m(2) 1.05 [95% CI 1.00-1.09]) were associated with incident diabetic retinopathy. The association between HbA(1c) and incident diabetic retinopathy was linear; the association with duration of diabetes increased rapidly between 5 and 10 years. Higher HbA(1c) was also associated with progression of diabetic retinopathy (aHR per 1% [10.9 mmol/mol] 1.66 [95% CI 1.41-1.96]). CONCLUSIONS: Observed incidence and progression rates of diabetic retinopathy seemed lower than that in western populations. HbA(1c) was the only factor associated with both incidence and progression of diabetic retinopathy. The strength of the association between duration of diabetes and incidence of diabetic retinopathy increased rapidly during a period of 5 to 10 years duration of diabetes. TRIAL REGISTRATION: C000000222 ( www.umin.ac.jp ) FUNDING: This study is supported by the Ministry of Health, Labour and Welfare, Japan.

Low transition rate from normo- and low microalbuminuria to proteinuria in Japanese type 2 diabetic individuals: the Japan Diabetes Complications Study (JDCS).

AIMS/HYPOTHESIS: The aim of the study was to determine the transition rate and factors associated with the progression of normo- and low microalbuminuria to diabetic nephropathy (overt proteinuria). METHODS: For 8 years we prospectively observed 1,558 Japanese patients with type 2 diabetes mellitus whose basal urinary albumin:creatinine ratio (UACR) had been measured as <17.0 mg/mmol at entry. The incidence of nephropathy (UACR >33.9 mg/mmol) was determined by measuring UACR twice a year. RESULTS: Progression to nephropathy occurred in 74 patients. The annual transition rate was 0.67%, and was substantially higher for the low-microalbuminuric group than for the normoalbuminuric group (1.85% and 0.23%, respectively; hazard ratio for the low-microalbuminuric group 8.45, p < 0.01). The hazard ratio for an HbA(1c) of 7-9% or ≥9% was 2.72 (p < 0.01) or 5.81 (p < 0.01) relative to HbA(1c) <7.0%, respectively. In comparison with individuals with a systolic blood pressure (SBP) of <120 mmHg, the hazard ratios for patients with an SBP of 120-140 mmHg or ≥140 mmHg were 2.31 (p = 0.06) and 3.54 (p < 0.01), respectively. Smoking also affected progression to proteinuria (hazard ratio 1.99, p < 0.01). In contrast, 30.3% of the low-microalbuminuric group returned to normoalbuminuria (i.e. were in remission). CONCLUSIONS/INTERPRETATION: These results suggest that if patients with type 2 diabetes mellitus are receiving treatment from diabetologists for hyperglycaemia and hypertension when they are in the early stages of nephropathy (i.e. normo- or low microalbuminuria), their rate of transition to proteinuria is considerably lowered, and that differentiating patients with low microalbuminuria from those with high microalbuminuria might be clinically useful. TRIAL REGISTRATION: UMIN Clinical Trials Registry C000000222.

Long-term lifestyle intervention lowers the incidence of stroke in Japanese patients with type 2 diabetes: a nationwide multicentre randomised controlled trial (the Japan Diabetes Complications Study).

AIMS/HYPOTHESIS: The aim of the study was to clarify whether a therapeutic intervention focused on lifestyle modification affected the incidence of vascular complications in patients with established diabetes. METHODS: A total of 2,033 eligible Japanese men and women aged 40-70 years with type 2 diabetes from 59 institutes were randomised to a conventional treatment group (CON), which continued to receive the usual care, and a lifestyle intervention group (INT), which received education on lifestyle modification regarding dietary habits, physical activities and adherence to treatment by telephone counselling and at each outpatient clinic visit, in addition to the usual care. Randomisation and open-label allocation were done by a central computer system. Primary analysis regarding measurements of control status and occurrence of macro- and microvascular complications was based on 1,304 participants followed for an 8 year period. RESULTS: Although status of control of most classic cardiovascular risk factors, including body weight, glycaemia, serum lipids and BP, did not differ between groups during the study period, the incidence of stroke in the INT group (5.48/1,000 patient-years) was significantly lower than in the CON group (9.52/1,000 patient-years) by Kaplan- Meier analysis (p=0.02 by logrank test) and by multivariate Cox analysis (HR 0.62, 95% CI 0.39-0.98, p=0.04). The incidence of CHD, retinopathy and nephropathy did not differ significantly between groups. Lipoprotein(a) was another significant independent risk factor for stroke. CONCLUSIONS/INTERPRETATION: These findings suggest that lifestyle modification had limited effects on most typical control variables, but did have a significant effect on stroke incidence in patients with established type 2 diabetes. CLINICAL TRIAL REGISTRATION: UMIN-CTR C000000222 FUNDING: The Ministry of Health, Labour and Welfare, Japan

Effects of lifestyle modifications on patients with type 2 diabetes: the Japan Diabetes Complications Study (JDCS) study design, baseline analysis and three year-interim report.

BACKGROUND: Lifestyle modifications may affect the development of diabetes and prevent complications. However, there is no direct evidence to show that lifestyle intervention is beneficial for patients with established type 2 diabetes. OBJECTIVE: The ultimate goal is to determine whether long-term lifestyle intervention can improve glycemic control and prevent complications in patients with type 2 diabetes. This initial report on a multi-year study describes protocols and the analysis of baseline data and three-year interim results. DESIGN: The study was a randomized, controlled, multi-centre, prospective intervention trial. The trial included patients from 59 Japanese institutes specializing in diabetes care. PATIENTS: The study enrolled 2 205 patients with previously diagnosed type 2 diabetes. INTERVENTION: The lifestyle modification program included intensive lifestyle management at each outpatient clinic visit and frequent telephone counseling. The intervention group received educational materials concerning the importance of lifestyle and behavioural changes, a diary to record progress of laboratory and other data, and a pedometer. MEASUREMENTS: Parameters and indices related to glycemic control, diabetic complications, dyslipidemia, hypertension, obesity, and atherosclerosis were measured several times a year. RESULTS: Small but significant differences in HbA1c levels between the intervention (INT) and conventional (CON) therapy groups appeared as early as two years after the start of intervention and were maintained in the third year (CON group, 7.78 +/- 1.27 % vs. INT group, 7.62 +/- 1.20 %, the initial HbA1c level was 7.80 +/- 1.42 % for the CON group and 7.68 +/- 1.28 % for the INT group). Data on differences in occurrence of micro- or macrovascular complications are not yet available. CONCLUSIONS: The effect of lifestyle modification on improving the glycemic control of patients with established type 2 diabetes mellitus was small but significant three years after initiation of the intervention.

Adiponectin stimulates glucose utilization and fatty-acid oxidation by activating AMP-activated protein kinase.

Adiponectin (Ad) is a hormone secreted by adipocytes that regulates energy homeostasis and glucose and lipid metabolism. However, the signaling pathways that mediate the metabolic effects of Ad remain poorly identified. Here we show that phosphorylation and activation of the 5'-AMP-activated protein kinase (AMPK) are stimulated with globular and full-length Ad in skeletal muscle and only with full-length Ad in the liver. In parallel with its activation of AMPK, Ad stimulates phosphorylation of acetyl coenzyme A carboxylase (ACC), fatty-acid oxidation, glucose uptake and lactate production in myocytes, phosphorylation of ACC and reduction of molecules involved in gluconeogenesis in the liver, and reduction of glucose levels in vivo. Blocking AMPK activation by dominant-negative mutant inhibits each of these effects, indicating that stimulation of glucose utilization and fatty-acid oxidation by Ad occurs through activation of AMPK. Our data may provide a novel paradigm that an adipocyte-derived antidiabetic hormone, Ad, activates AMPK, thereby directly regulating glucose metabolism and insulin sensitivity in vitro and in vivo.

A genetic variation in the PGC-1 gene could confer insulin resistance and susceptibility to Type II diabetes.

AIMS/HYPOTHESIS: Peroxisome proliferator activated receptor gamma coactivator-1 (PGC-1), a transcriptional coactivator of the nuclear receptor PPARgamma, plays a role in adaptive thermogenesis and insulin sensitivity. Plasma fasting insulin has been linked to the chromosomal region where the PGC-1 gene is located. Thus, PGC-1 can be viewed as a functional and positional candidate for the susceptibility gene for Type II (non-insulin-dependent) diabetes mellitus. METHODS: After screening the PGC-1 gene for single nucleotide polymorphisms (SNPs), we performed an association study using the newly detected SNPs in 537 Type II diabetic patients and 417 non-diabetic subjects. RESULTS: We found three relatively frequent SNPs in the PGC-1 gene (IVS4-11T > C, Thr394Thr and Gly482Ser). There were significant differences in fasting insulin (Gly/Gly; 37.7 +/- 1.43, Gly/Ser; 40.2 +/- 1.21, Ser/Ser; 44.3 +/- 1.82 pmol/l, p = 0.018) and insulin resistance index (Gly/Gly; 1.48 +/- 0.06, Gly/Ser; 1.56 +/- 0.05, Ser/Ser; 1.75 +/- 0.08, p = 0.027) according to the genotype of the Gly482Ser polymorphism. The Thr394Thr - Gly482Ser haplotype was associated with Type II diabetes (p = 0.00003). CONCLUSION/INTERPRETATION. The results of this study suggested that the PGC-1 gene might be implicated in the pathogenesis of Type II diabetes.

A double-blind trial on the effects of atorvastatin on glycemic control in Japanese diabetic patients with hypercholesterolemia.

A double-blind, placebo-controlled, parallel-group study was performed to determine whether atorvastatin, a new HMG-CoA reductase inhibitor, could effectively and safely reduce plasma LDL-cholesterol concentrations in Japanese patients with type-2 diabetes without influencing glycemic control. The subjects were patients with hypercholesterolemia (serum cholesterol concentration > or =5.7 mmol/l (220 mg/dl)) and stable glycemic control. The fasting concentrations of hemoglobin A(1C) (HbA(1C)), fructosamine, and 1,5-anhydroglucitol (1,5-AG) were measured as indices of glycemic control. Plasma lipid concentrations and the safety of the drug were also examined. Forty eligible patients in two groups of 20 each were administered atorvastatin (10 mg/day) or placebo. Neither atorvastatin nor placebo caused a significant change in HbA(1C), fructosamine, or 1,5-AG concentrations. Atorvastatin significantly reduced total cholesterol and LDL-cholesterol concentrations from baseline by 29.7% (p<0.0001) and 41.6% (p<0.0001), respectively. The incidence of clinical adverse events and that of abnormal changes in laboratory test values did not differ between the two groups. In this trial, atorvastatin effectively and safely reduced LDL-cholesterol concentrations in diabetic patients with hypercholesterolemia without influencing glycemic control. These findings are clinically important because there are many diabetic patients with hypercholesterolemia and such patients have a high risk of developing arteriosclerotic disease.

Inhibition of RXR and PPARgamma ameliorates diet-induced obesity and type 2 diabetes.

PPARgamma is a ligand-activated transcription factor and functions as a heterodimer with a retinoid X receptor (RXR). Supraphysiological activation of PPARgamma by thiazolidinediones can reduce insulin resistance and hyperglycemia in type 2 diabetes, but these drugs can also cause weight gain. Quite unexpectedly, a moderate reduction of PPARgamma activity observed in heterozygous PPARgamma-deficient mice or the Pro12Ala polymorphism in human PPARgamma, has been shown to prevent insulin resistance and obesity induced by a high-fat diet. In this study, we investigated whether functional antagonism toward PPARgamma/RXR could be used to treat obesity and type 2 diabetes. We show herein that an RXR antagonist and a PPARgamma antagonist decrease triglyceride (TG) content in white adipose tissue, skeletal muscle, and liver. These inhibitors potentiated leptin's effects and increased fatty acid combustion and energy dissipation, thereby ameliorating HF diet-induced obesity and insulin resistance. Paradoxically, treatment of heterozygous PPARgamma-deficient mice with an RXR antagonist or a PPARgamma antagonist depletes white adipose tissue and markedly decreases leptin levels and energy dissipation, which increases TG content in skeletal muscle and the liver, thereby leading to the re-emergence of insulin resistance. Our data suggested that appropriate functional antagonism of PPARgamma/RXR may be a logical approach to protection against obesity and related diseases such as type 2 diabetes.

Increased expression of the sterol regulatory element-binding protein-1 gene in insulin receptor substrate-2(-/-) mouse liver.

Insulin receptor substrate (IRS)-2(-/-) mice develop diabetes because of insulin resistance in the liver and failure to undergo beta-cell hyperplasia. Here we show by DNA chip microarray analysis that expression of the sterol regulatory element-binding protein (SREBP)-1 gene, a downstream target of insulin, was paradoxically increased in 16-week-old IRS-2(-/-) mouse liver, where insulin-mediated intracellular signaling events were substantially attenuated. The expression of SREBP-1 downstream genes, such as the spot 14, ATP citrate-lyase, and fatty acid synthase genes, was also increased. Increased liver triglyceride content in IRS-2(-/-) mice assures the physiological importance of SREBP-1 gene induction. IRS-2(-/-) mice showed leptin resistance; low dose leptin administration, enough to reduce food intake and body weight in wild-type mice, failed to do so in IRS-2(-/-) mice. Interestingly, high dose leptin administration reduced SREBP-1 expression in IRS-2(-/-) mouse liver. Thus, IRS-2 gene disruption results in leptin resistance, causing an SREBP-1 gene induction, obesity, fatty liver, and diabetes.

A questionnaire for neurological symptoms in patients with diabetes--cross-sectional multicenter study in Saitama Prefecture, Japan.

This study was designed to investigate the prevalence of neurological symptoms in diabetic patients living in Saitama Prefecture, Japan using 13-item questionnaire. A total of 6472 outpatients with diabetes (3417 men and 3055 women) were recruited from 100 centers. Mean age and mean disease duration were 60.9-year old and 10.4 years, respectively. The questionnaire for monitoring of neurological symptoms was completed at the clinic or hospital visited, and Achilles' tendon reflex, ophthalmologic, blood and urinary examinations were also performed. Of the 6472 patients, 84.8% suffered from a mean of 3.3+/-2.2 neurological symptoms. However, half of these symptoms were not considered to be those of diabetic neuropathy by attending physicians. "Feeling as if a piece of paper is attached to the sole of the foot," "stinging and prickling sensations in feet," and "pain in feet" were the most common symptoms of diabetic neuropathy. The prevalence of diabetic neuropathy as determined by attending physician increased with disease duration and worse control of diabetes. This study found that the majority of diabetics were suffered from neurological symptoms, although half of such symptoms were not considered to be those of diabetic neuropathy by physicians. Furthermore, it is important for diabetics to be diagnosed and treated earlier to prevent progression to severe neuropathic complications by means of optimal glycemic control and use of some chemicals such as aldose reductase inhibitor, and to develop this study to evaluate the efficacy of treatments.

The mechanisms by which both heterozygous peroxisome proliferator-activated receptor gamma (PPARgamma) deficiency and PPARgamma agonist improve insulin resistance.

Peroxisome proliferator-activated receptor (PPAR) gamma is a ligand-activated transcription factor and a member of the nuclear hormone receptor superfamily that is thought to be the master regulator of fat storage; however, the relationship between PPARgamma and insulin sensitivity is highly controversial. We show here that supraphysiological activation of PPARgamma by PPARgamma agonist thiazolidinediones (TZD) markedly increases triglyceride (TG) content of white adipose tissue (WAT), thereby decreasing TG content of liver and muscle, leading to amelioration of insulin resistance at the expense of obesity. Moderate reduction of PPARgamma activity by heterozygous PPARgamma deficiency decreases TG content of WAT, skeletal muscle, and liver due to increased leptin expression and increase in fatty acid combustion and decrease in lipogenesis, thereby ameliorating high fat diet-induced obesity and insulin resistance. Moreover, although heterozygous PPARgamma deficiency and TZD have opposite effects on total WAT mass, heterozygous PPARgamma deficiency decreases lipogenesis in WAT, whereas TZD stimulate adipocyte differentiation and apoptosis, thereby both preventing adipocyte hypertrophy, which is associated with alleviation of insulin resistance presumably due to decreases in free fatty acids, and tumor necrosis factor alpha, and up-regulation of adiponectin, at least in part. We conclude that, although by different mechanisms, both heterozygous PPARgamma deficiency and PPARgamma agonist improve insulin resistance, which is associated with decreased TG content of muscle/liver and prevention of adipocyte hypertrophy.

Insulin-independent and wortmannin-resistant targeting of IRS-3 to the plasma membrane via its pleckstrin homology domain mediates a different interaction with the insulin receptor from that of IRS-1.

AIMS/HYPOTHESIS: In primary adipocytes, although IRS-1 and IRS-3 are expressed in comparable amounts, these proteins manifest distinct distribution and significance in insulin signalling. We investigated the molecular basis of the difference between these two proteins. METHODS: In Cos-1 cells transiently expressing rat IRS-1, IRS-3, or chimeric proteins of these two proteins we examined the tyrosine phosphorylation via the wild-type or mutant insulin receptors and evaluated their targeting to the plasma membrane by immunostaining the membrane ghost. RESULTS: In contrast to IRS-1, IRS-3 was tyrosine-phosphorylated by the insulin receptor altering Tyr960 to Phe (Y960F), which disrupts the binding site of the PTB domain of IRSs, to an extent comparable to the wild-type receptor. The tyrosine phosphorylation of IRS-3 with the PH domain replacement via the Y960F insulin receptor markedly decreased, whereas that of IRS-3 with the PTB domain alteration was mildly impaired. Insulin-stimulated translocation of IRS-1 to the plasma membrane, as well as that of IRS-3 with the PH domain replacement, was wortmannin-sensitive, although that of IRS-3 was insulin-independent and wortmannin-resistant. CONCLUSIONS/INTERPRETATION: The affinity of the PH domain for the phospholipids in the plasma membrane seems to influence the receptor-substrate interaction required for IRS tyrosine phosphorylation, indicating that the PH domain and the PTB domain of IRSs cooperatively function in insulin-stimulated tyrosine phosphorylation of these proteins.

The fat-derived hormone adiponectin reverses insulin resistance associated with both lipoatrophy and obesity.

Adiponectin is an adipocyte-derived hormone. Recent genome-wide scans have mapped a susceptibility locus for type 2 diabetes and metabolic syndrome to chromosome 3q27, where the gene encoding adiponectin is located. Here we show that decreased expression of adiponectin correlates with insulin resistance in mouse models of altered insulin sensitivity. Adiponectin decreases insulin resistance by decreasing triglyceride content in muscle and liver in obese mice. This effect results from increased expression of molecules involved in both fatty-acid combustion and energy dissipation in muscle. Moreover, insulin resistance in lipoatrophic mice was completely reversed by the combination of physiological doses of adiponectin and leptin, but only partially by either adiponectin or leptin alone. We conclude that decreased adiponectin is implicated in the development of insulin resistance in mouse models of both obesity and lipoatrophy. These data also indicate that the replenishment of adiponectin might provide a novel treatment modality for insulin resistance and type 2 diabetes.

Importance of standardization of hemoglobin A1c in the analysis of factors that predict hemoglobin A1c levels in non-diabetic residents of three distinct areas of Japan.

We performed a statistical analysis to elucidate effects of standardized measurement of hemoglobin A1c (HbA1c) on analysis of factors that affect HbA1c values. Subjects were participants in the Japan Public Health Center-based Prospective Study on Cancer and Cardiovascular Diseases, and a total of 1789 men and 3150 women in three distinct areas who did not have overt diabetes (HbA1c> or =6.1% or prior diagnosis) were analyzed. A different method of HbA1c assay was used in each area: high-performance liquid chromatography in one area and a different immunochemical method in each of the other two areas. Then, calibration of HbA1c was performed using two HbA1c standards (5.5 and 10.5%) provided by the Japan Diabetes Society. Analysis of co-variance was performed separately in men and women. When raw HbA1c data were used as the outcome, 'area', which represents differences in assay systems, lifestyles, etc. had a significant effect on HbA1c levels. When calibrated HbA1c data were used, however, 'area' was no longer a significant factor. In the latter analysis, age and BMI were the principal contributors to HbA1c, and parental history of diabetes had a weak effect in women. Thus, standardization of HbA1c reduced the difference between assay systems, and uncovered two common factors to determine HbA1c levels.

Subcellular localization of insulin receptor substrate family proteins associated with phosphatidylinositol 3-kinase activity and alterations in lipolysis in primary mouse adipocytes from IRS-1 null mice.

To clarify the roles of insulin receptor substrate (IRS) family proteins in phosphatidylinositol (PI) 3-kinase activation and insulin actions in adipocytes, we investigated the intracellular localization of IRS family proteins and PI 3-kinase activation in response to insulin by fractionation of mouse adipocytes from wild-type and IRS-1 null mice. In adipocytes from wild-type mice, tyrosine-phosphorylated IRS-1 and IRS-2, which were found to associate with PI 3-kinase in response to insulin, were detected in the plasma membrane (PM) and low-density microsome (LDM) fractions. By contrast, tyrosine-phosphorylated IRS-3 (pp60), which was found to associate with PI 3-kinase, was predominantly localized in the PM fraction. In adipocytes from IRS-1-null mice, insulin-stimulated PI 3-kinase activity in anti-phosphotyrosine (alphaPY) immunoprecipitates in the LDM fraction was almost exclusively mediated via IRS-2 and was reduced to 25%; however, insulin-stimulated PI 3-kinase activity in the PM fraction was primarily mediated via IRS-3 and was reduced to 60%. To determine the potential functional impact of the distinct subcellular localization of IRSs and associating PI 3-kinase activity on adipocyte-specific metabolic actions, we examined lipolysis in IRS-1 null mice. The level of isoproterenol-induced lipolysis was increased 5.1-fold in adipocytes from IRS-1 null mice as compared with wild-type mice. Moreover, hormone-sensitive lipase (HSL) protein was increased 4.3-fold in adipocytes from IRS-1-null mice compared with wild-type mice, and HSL mRNA expression was also increased. The antilipolytic effect of insulin in IRS-1 null adipocytes, however, was comparable to that in wild-type mice. Thus, discordance between these two insulin actions as well as the transcriptional and translational effect (HSL mRNA and protein regulation) and the PM effect (antilipolysis) of insulin may be explained by distinct roles of both PI 3-kinase activity associated with IRS-1/IRS-2 and PI 3-kinase activity associated with IRS-3 in insulin actions related to their subcellular localization.

Risk factors for the development of diabetic retinopathy in Japanese type 2 diabetic patients.

This study investigated the risk factors for development of diabetic retinopathy (DR) in 787 type 2 diabetic patients with no retinopathy at the first visit. The subjects were followed up for at least 3 years (mean, 6.7 years). Among the baseline factors, significant correlations were observed between the development of DR and HbA1c (P < 0.0001), the method of therapy (P < 0.005), the duration of diabetes at the first visit (P < 0.005) and the past maximal body mass index (BMI) (P < 0.01). No significant correlation was found with the blood pressure, age, gender, TC or BMI. Among the follow-up variables, the mean HbA1c (P < 0.0001) and duration of diabetes (P < 0.001) correlated significantly with DR development, whereas the blood pressure and age did not. We found that a 1% decrease in HbA1c led to a 35% reduction in the risk of development of DR during the follow-up. The patients whose HbA1c at the first visit was higher than the median value of 8.2% showed a higher probability of development of DR during the next 3 years even when the same blood glucose control was maintained during the follow-up. In conclusion, our study demonstrated that the most important risk factor influencing the development of DR was the blood glucose control. Moreover, we found that the glycemic level at the first visit also influenced the development of DR.

Essential role of insulin receptor substrate 1 (IRS-1) and IRS-2 in adipocyte differentiation.

To investigate the role of insulin receptor substrate 1 (IRS-1) and IRS-2, the two ubiquitously expressed IRS proteins, in adipocyte differentiation, we established embryonic fibroblast cells with four different genotypes, i.e., wild-type, IRS-1 deficient (IRS-1(-/-)), IRS-2 deficient (IRS-2(-/-)), and IRS-1 IRS-2 double deficient (IRS-1(-/-) IRS-2(-/-)), from mouse embryos of the corresponding genotypes. The abilities of IRS-1(-/-) cells and IRS-2(-/-) cells to differentiate into adipocytes are approximately 60 and 15%, respectively, lower than that of wild-type cells, at day 8 after induction and, surprisingly, IRS-1(-/-) IRS-2(-/-) cells have no ability to differentiate into adipocytes. The expression of CCAAT/enhancer binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma) is severely decreased in IRS-1(-/-) IRS-2(-/-) cells at both the mRNA and the protein level, and the mRNAs of lipoprotein lipase and adipocyte fatty acid binding protein are severely decreased in IRS-1(-/-) IRS-2(-/-) cells. Phosphatidylinositol 3-kinase (PI 3-kinase) activity that increases during adipocyte differentiation is almost completely abolished in IRS-1(-/-) IRS-2(-/-) cells. Treatment of wild-type cells with a PI 3-kinase inhibitor, LY294002, markedly decreases the expression of C/EBPalpha and PPARgamma, a result which is associated with a complete block of adipocyte differentiation. Moreover, histologic analysis of IRS-1(-/-) IRS-2(-/-) double-knockout mice 8 h after birth reveals severe reduction in white adipose tissue mass. Our results suggest that IRS-1 and IRS-2 play a crucial role in the upregulation of the C/EBPalpha and PPARgamma expression and adipocyte differentiation.