Oxidative stress, insulin signaling, and diabetes

Oxidative stress has been implicated as a contributor to both the onset and the progression of diabetes and its associated complications. Some of the consequences of an oxidative environment are the development of insulin resistance, β-cell dysfunction, impaired glucose tolerance, and mitochondrial dysfunction, which can lead ultimately to the diabetic disease state. Experimental and clinical data suggest an inverse association between insulin sensitivity and ROS levels. Oxidative stress can arise from a number of different sources, whether disease state or lifestyle, including episodes of ketosis, sleep restriction, and excessive nutrient intake. Oxidative stress activates a series of stress pathways involving a family of serine/threonine kinases, which in turn have a negative effect on insulin signaling. More experimental evidence is needed to pinpoint the mechanisms contributing to insulin resistance in both type 1 diabetics and nondiabetic individuals. Oxidative stress can be reduced by controlling hyperglycemia and calorie intake. Overall, this review outlines various mechanisms that lead to the development of oxidative stress. Intervention and therapy that alter or disrupt these mechanisms may serve to reduce the risk of insulin resistance and the development of diabetes.     

Genetic susceptibility to non-insulin dependent diabetes mellitus and glucose intolerance are located in HLA region.

OBJECTIVES--To test the hypothesis that the genetic susceptibility to non-insulin dependent diabetes mellitus is the same as that to insulin dependent disease and to see whether glucose intolerance is associated with specific HLA haplotypes. DESIGN--Population based study of men in 1989 first tested for glucose tolerance in 1984. HLA haplotypes, including HLA-A, C, B, DR, and DQ, were defined serologically. HLA haplotype data from a population based Finnish study of childhood diabetes were used for predicting non-insulin dependent diabetes and impaired glucose tolerance. SETTING--Two communities in Finland. SUBJECTS--Representative cohort of Finnish men aged 70-89, comprising 98 men with non-insulin dependent diabetes mellitus and a randomly selected group of 74 men, who served as controls, who were tested for glucose tolerance twice within five years. MAIN OUTCOME MEASURES--Non-insulin dependent diabetes, impaired glucose tolerance, blood glucose concentration. RESULTS--Diabetes associated HLA haplotypes were present in 94% (85/90) of diabetic subjects, 79% (27/34) of subjects with impaired glucose tolerance, and only 13% (3/23) of non-diabetic subjects. In this group of elderly men sensitivity of the diabetes associated HLA haplotypes for non-insulin dependent diabetes and impaired glucose tolerance was 90%, specificity 87%, and predictive power 97%. Mean fasting blood glucose concentration was only just significantly higher in men with diabetes associated haplotypes than in men with no such haplotypes, but there was a substantial difference in blood glucose values two hours after glucose loading (10.4 and 6.4 mmol/l in men with diabetes associated HLA haplotypes and men with no such haplotypes, respectively (p < 0.0001)). CONCLUSIONS--These findings support the hypothesis that specific HLA haplotypes exhibit a common genetic determinant for insulin dependent and non-insulin dependent diabetes. Furthermore, HLA is a major genetic determinant of glucose intolerance in elderly Finnish men. The belief that the HLA predisposition to diabetes is specific for insulin dependent diabetes mellitus is largely incorrect.     

Prevention of type 2 diabetes

Changes in the human environment and in human behavior and lifestyle, in conjunction with genetic susceptibility, have resulted in a dramatic increase in the incidence and prevalence of diabetes in the world. The rapid escalation of the number of people with type 2 diabetes (T2DM) and diabetes-related cardiovascular disease demands urgent action on prevention. The Finnish Diabetes Prevention Study and The Diabetes Prevention Program showed that the prevention (or delaying) of T2DM is feasible and effective. Both of these trials led to a reduction of 58% in the conversion to diabetes in subjects with impaired glucose tolerance. Compared to lifestyle changes, drug treatment in the prevention of diabetes in people at high risk for T2DM has been less beneficial. Metformin (31%) or acarbose (25%) treatment obtained only about a half of the reduction in the conversion to diabetes compared to lifestyle changes. These drugs require monitoring, and have significant side-effects. Also the effect of orlistat (37%) did not reach the effect of lifestyle modification. Results of the Troglitazone in Prevention of Diabetes study are suggestive for the prevention, but the trial was too small, and included only one ethnic group (Hispanic) and one gender (women). On the basis of the evidence available, we do not have a definite proof that T2DM is prevented in any of these trials. However, we can safely conclude that the current evidence strongly favors the notion that lifestyle changes are the primary means to tackle the epidemic of T2DM.     

Regulating insulin signaling and beta-cell function through IRS proteins

Diabetes mellitus is a complex disorder that arises from various causes, including dysregulated glucose sensing and impaired insulin secretion (maturity onset diabetes of youth, MODY), autoimmune-mediated beta-cell destruction (type 1), or insufficient compensation for peripheral insulin resistance (type 2). Type 2 diabetes is the most prevalent form that usually occurs at middle age; it afflicts more than 30 million people over the age of 65, but is appearing with greater frequency in children and adolescents. Dysregulated insulin signaling exacerbated by chronic hyperglycemia promotes a cohort of systemic disorders--including dyslipidemia, hypertension, cardiovascular disease, and female infertility. Understanding the molecular basis of insulin resistance can prevent these disorders and their inevitable progression to type 2 diabetes.     

Unaltered Prion Pathogenesis in a Mouse Model of High-Fat Diet-Induced Insulin Resistance

Epidemiological, clinical, and experimental animal studies suggest a strong correlation between insulin resistance and Alzheimer’s disease. In fact, type-2 diabetes is considered an important risk factor of developing Alzheimer’s disease. In addition, impaired insulin signaling in the Alzheimer’s disease brain may promote Aβ production, impair Aβ clearance and induce tau hyperphosphorylation, thereby leading to deterioration of the disease. The pathological prion protein, PrP^Sc, deposits in the form of extracellular aggregates and leads to dementia, raising the question as to whether prion pathogenesis may also be affected by insulin resistance. We therefore established high-fat diet-induced insulin resistance in tga20 mice, which overexpress the prion protein. We then inoculated the insulin-resistant mice with prions. We found that insulin resistance in tga20 mice did not affect prion disease progression, PrP^Sc deposition, astrogliosis or microglial activation, and had no effect on survival. Our study demonstrates that in a mouse model, insulin resistance does not significantly contribute to prion pathogenesis.     

Role of microRNAs in diabetes

Diabetes is one of the most common chronic diseases in the world. Multiple and complex factors including various genetic and physiological changes can lead to type 1 and type 2 diabetes. However, the major mechanisms underlying the pathogenesis of diabetes remain obscure. With the recent discovery of microRNAs (miRNAs), these small ribonucleotides have been implicated as new players in the pathogenesis of diabetes and diabetes-associated complications. MiRNAs have been shown to regulate insulin production, insulin secretion, and insulin action. This review summarizes the recent progress in the cutting-edge research of miRNAs involved in diabetes and diabetes related complications.     

Molecular genetics of the transcription factor GLIS3 identifies its dual function in beta cells and neurons

The GLIS family zinc finger 3 isoform (GLIS3) is a risk gene for Type 1 and Type 2 diabetes, glaucoma and Alzheimer's disease endophenotype. We identified GLIS3 binding sites in insulin secreting cells (INS1) (FDR q < 0.05; enrichment range 1.40–9.11 fold) sharing the motif wrGTTCCCArTAGs, which were enriched in genes involved in neuronal function and autophagy and in risk genes for metabolic and neuro-behavioural diseases. We confirmed experimentally Glis3-mediated regulation of the expression of genes involved in autophagy and neuron function in INS1 and neuronal PC12 cells. Naturally-occurring coding polymorphisms in Glis3 in the Goto-Kakizaki rat model of type 2 diabetes were associated with increased insulin production in vitro and in vivo, suggestive alteration of autophagy in PC12 and INS1 and abnormal neurogenesis in hippocampus neurons. Our results support biological pleiotropy of GLIS3 in pathologies affecting β-cells and neurons and underline the existence of trans?nosology pathways in diabetes and its co-morbidities.     

Diabetes mellitus and the β cell: the last ten years

Diabetes is a major global problem. During the past decade, the genetic basis of various monogenic forms of the disease, and their underlying molecular mechanisms, have been elucidated. Many genes that increase type 2 diabetes (T2DM) risk have also been identified, but how they do so remains enigmatic. Nevertheless, defective insulin secretion emerges as the main culprit in both monogenic and polygenic diabetes, with environmental and lifestyle factors, via obesity, accounting for the current dramatic increase in T2DM. There also have been significant advances in therapy, particularly for some monogenic disorders. We review here what ails the β cell and how its function may be restored.     

Appropriate,timely, and rational treatment of type 2 diabetes mellitus: Meeting the challenges of primary care

Diabetes now affects >24 million people in the United States. As the prevalence of diabetes continues to increase, long-term complications of diabetes have emerged as major health care issues. Although much focus has been placed on diabetes, it is important to note that prediabetes, the intermediate state of type 2 diabetes mellitus (DM), is not benign. The progression to type 2 DM for patients with impaired glucose tolerance (IGT) is 6% to 10% per year; for persons with both impaired fasting glucose and IGT, the cumulative incidence of diabetes in 6 years may be as high as 60%. Given the significant clinical and financial impact of both conditions, it is vital that clinicians initiate treatment of diabetes and prediabetes early and aggressively. Despite advances in diabetes treatment, many health care providers do not initiate or intensify therapy appropriately during patient visits, which contributes to poor diabetes control. Although management of blood pressure and lipid levels can be complex, glycemic control is often problematic for patients and their clinicians. Thus, clinicians must learn to use the various pharmacologic and nonpharmacologic strategies effectively to achieve glucose targets in their patients with type 2 DM. Patients with prediabetes should be managed with a combination of lifestyle intervention and appropriately timed pharmacotherapy. Pancreatic β-cell preservation should be a primary metabolic target.     

Weight Gain and Management Concerns in Patients on Insulin Therapy

Background: The benefits of tight glycemic control in preventing the onset and progression of microvascular complications in patients with type 2 diabetes mellitus (DM) are unarguable. The majority of patients with type 2 DM will eventually require insulin to achieve adequate glycemic control. Using insulin earlier rather than later in the course of type 2 DM may diminish the deleterious effects of hyperglycemia on β-cell function and therefore help prolong good glycemic control and prevent the occurrence of microvascular complications. However, weight gain is a potential adverse effect of insulin therapy.Objective: The goal of this article was to describe the benefit of insulin therapy early in the course of type 2 DM, review the association of weight gain with insulin therapy, and examine potential detrimental effects that insulin-associated weight gain could have in patients with type 2 DM.Methods: Materials used for this article were identified through a search of MEDLINE (1966–2006). English-language articles were chosen using the search terms diabetes mellitus type 2, insulin, and obesity.Results: Intensive insulin therapy is often associated with weight gain. Although there is concern that weight gain in patients with type 2 DM may have adverse effects on risk factors for cardiovascular disease, unfavorable changes in blood pressure and lipid levels have not been consistently observed in clinical trials. Furthermore, clinical evidence, including data from the United Kingdom Prospective Diabetes Study, supports the view that intensive insulin therapy does not increase the risk for cardiovascular disease.Conclusions: Early insulin therapy in patients with type 2 DM may be a strategy that will help patients achieve and maintain good glycemic control, thereby reducing the risk of developing microvascular complications. Although weight gain is commonly associated with insulin therapy, it does not appear to put these patients at greater risk for cardiovascular disease.     

Development of Type 2 Diabetes Mellitus in the Obese Adolescent:A Growing Challenge

ObjectiveTo describe the metabolic phenotype of type 2 diabetes mellitus in youth and possible metabolic defects leading to its development with particular emphasis on fatty liver.MethodsWe present data gathered from studies performed in obese adolescents across the spectrum of glucose tolerance to assess both alterations in insulin sensitivity and secretion. Discussion regarding treatment options is presented using the data from the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study.ResultsAs the number of children with obesity continues to grow, the health implications of the condition are becoming increasingly evident. An unprecedented phenomenon rarely seen before has emerged: type 2 diabetes mellitus. At the time of diabetes diagnosis, cardiovascular disease may already be present, even in young adults. The progression from normal glucose tolerance to type 2 diabetes in adults occurs through an intermediate phase of altered glucose metabolism known as impaired glucose tolerance or prediabetes. Previous studies from our group and others reported a high prevalence of impaired glucose tolerance among children and adolescents with marked obesity. Cross-sectional studies demonstrate that impaired glucose tolerance in obese youth is associated with severe insulin resistance, β-cell dysfunction, and altered abdominal and muscle fat partitioning. We end briefly by discussing the current data available on treatment of this condition from the TODAY study, the largest clinical trial ever performed in youth with type 2 diabetes.ConclusionThe observed rapid progression of the glucose homeostasis alterations in adolescents underlines the importance of focusing attention on the earliest stages of the disease before the onset of any alterations in glucose tolerance. (Endocr Pract. 2012;18:791-795)     

Mitochondrial dysfunction and complications associated with diabetes

Background

Diabetes is a metabolic syndrome that results in chronically increased blood glucose (hyperglycaemia) due to defects either in insulin secretion consequent to the loss of beta cells in the pancreas (type 1) or to loss of insulin sensitivity in target organs in the presence of normal insulin secretion (type 2). Long term hyperglycaemia can lead to a number of serious health-threatening pathologies, or complications, especially in the kidney, heart, retina and peripheral nervous system.

Scope of review

Here we summarise the current literature on the role of the mitochondria in complications associated with diabetes, and the limitations and potential of rodent models to explore new modalities to limit complication severity.

Major conclusions

Prolonged hyperglycaemia results in perturbation of catabolic pathways and in an over-production of ROS by the mitochondria, which in turn may play a role in the development of diabetic complications. Furthermore, current models don't offer a comprehensive recapitulation of these complications.

General significance

The onset of complications associated with type 1 diabetes can be varied, even with tightly controlled blood glucose levels. The potential role of inherited, mild mitochondrial dysfunction in accelerating diabetic complications, both in type 1 and 2 diabetes, remains unexplored. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.     

Shift work and diabetes – A systematic review

Diabetes mellitus is a chronic disease, which has an increasing trend all over the world. Type 2 diabetes constitutes 90% of all diabetes. It is associated with weight gain and insulin resistance. Research during recent years has suggested that shift work could be a risk factor of type 2 diabetes. Since shift work is becoming more common, it could contribute to the increasing trend of diabetes. In this systematic review, we have studied the potential association between shift work and type 2 diabetes. We have also reviewed studies on control of diabetes in relation to shift work.     

Demographic and Lifestyle Characteristics,but Not Apolipoprotein E Genotype,Are Associated with Intelligence among Young Chinese College Students

Background

Intelligence is an important human feature that strongly affects many life outcomes, including health, life-span, income, educational and occupational attainments. People at all ages differ in their intelligence but the origins of these differences are much debated. A variety of environmental and genetic factors have been reported to be associated with individual intelligence, yet their nature and contribution to intelligence differences have been controversial.

Objective

To investigate the contribution of apolipoprotein E (APOE) genotype, which is associated with the risk for Alzheimer’s disease, as well as demographic and lifestyle characteristics, to the variation in intelligence.

Methods

A total of 607 Chinese college students aged 18 to 25 years old were included in this prospective observational study. The Chinese revision of Wechsler Adult Intelligence Scale (the fourth edition, short version) was used to determine the intelligence level of participants. Demographic and lifestyle characteristics data were obtained from self-administered questionnaires.

Results

No significant association was found between APOE polymorphic alleles and different intelligence quotient (IQ) measures. Interestingly, a portion of demographic and lifestyle characteristics, including age, smoking and sleep quality were significantly associated with different IQ measures.

Conclusions

Our findings indicate that demographic features and lifestyle characteristics, but not APOE genotype, are associated with intelligence measures among young Chinese college students. Thus, although APOE ε4 allele is a strong genetic risk factor for Alzheimer’s disease, it does not seem to impact intelligence at young ages.