Insulin resistance: current concepts

A glucagon-like peptide-1 receptor antagonist reduces the insulin response to a glycemic meal in ponies

High plasma concentrations of insulin can cause acute laminitis. Ponies and horses with insulin dysregulation (ID) exhibit marked hyperinsulinemia in response to dietary hydrolyzable carbohydrates. Glucagon-like peptide-1 (GLP-1), an incretin hormone released from the gastrointestinal tract, enhances insulin release, and is increased postprandially in ponies with ID. The aim of this study was to determine whether blocking the GLP-1 receptor reduces the insulin response to a high glycemic meal. Five adult ponies were adapted to a cereal meal and then given two feed challenges 24 h apart of a meal containing 3 g/kg BW micronized maize. Using a randomized cross-over design all ponies received both treatments, where one of the feeds was preceded by the IV administration of a GLP-1 receptor blocking peptide, Exendin-3 (9-39) amide (80 µg/kg), and the other feed by a sham treatment of peptide diluent only. Blood samples were taken before feeding and peptide administration, and then at 30-min intervals via a jugular catheter for 6 h for the measurement of insulin, glucose, and active GLP-1. The peptide and meal challenge caused no adverse effects, and the change in plasma glucose in response to the meal was not affected (P = 0.36) by treatment: peak concentration 9.24 ± 1.22 and 9.14 ± 1.08 mmol/L without and with the antagonist, respectively. Similarly, there was no effect (P = 0.35) on plasma active GLP-1 concentrations: peak concentration 14.3 ± 1.36 pM and 13.7 ± 1.97 pM without and with the antagonist, respectively. However, the antagonist caused a significant decrease in the area under the curve for insulin (P = 0.04), and weak evidence (P = 0.06) of a reduction in peak insulin concentration (456 ± 147 μIU/mL and 370 ± 146 μIU/mL without and with the antagonist, respectively). The lower overall insulin response to the maize meal after treatment with the antagonist demonstrates that blocking the GLP-1 receptor partially reduced insulin production in response to a high starch, high glycemic index, diet. Using a different methodological approach to published studies, this study also confirmed that GLP-1 does contribute to the excessive insulin production in ponies with ID.

Unraveling Gut Microbiota Signatures Associated with PPARD and PARGC1A Genetic Polymorphisms in a Healthy Population

Recent studies have revealed the importance of the gut microbiota in the regulation of metabolic phenotypes of highly prevalent metabolic diseases such as obesity, type II diabetes mellitus (T2DM) and cardiovascular disease. Peroxisome proliferator-activated receptors (PPARs) are a family of ligand-activated nuclear receptors that interact with PPAR-γ co-activator-1α (PPARGC1A) to regulate lipid and glucose metabolism. Genetic polymorphisms in PPARD (rs 2267668; A/G) and PPARGC1A (rs 8192678; G/A) are linked to T2DM. We studied the association between the single-nucleotide polymorphisms (SNPs) rs 2267668 and rs 8192678 and microbiota signatures and their relation to predicted metagenome functions, with the aim of determining possible microbial markers in a healthy population. Body composition, physical exercise and diet were characterized as potential confounders. Microbiota analysis of subjects with PPARGC1A (rs 8192678) and PPARD (rs 2267668) SNPs revealed certain taxa associated with the development of insulin resistance and T2DM. Kyoto encyclopedia of gene and genomes analysis of metabolic pathways predicted from metagenomes highlighted an overrepresentation of ABC sugar transporters for the PPARGC1A (rs 8192678) SNP. Our findings suggest an association between sugar metabolism and the PPARGC1A rs 8192678 (G/A) genotype and support the notion of specific microbiota signatures as factors related to the onset of T2DM.

Relationship between insulin sensitivity and gene expression in human skeletal muscle

BACKGROUND

Insulin resistance (IR) in skeletal muscle is a key feature of the pre-diabetic state, hypertension, dyslipidemia, cardiovascular diseases and also predicts type 2 diabetes. However, the underlying molecular mechanisms are still poorly understood.

METHODS

To explore these mechanisms, we related global skeletal muscle gene expression profiling of 38 non-diabetic men to a surrogate measure of insulin sensitivity, i.e. homeostatic model assessment of insulin resistance (HOMA-IR).

RESULTS

We identified 70 genes positively and 110 genes inversely correlated with insulin sensitivity in human skeletal muscle, identifying autophagy-related genes as positively correlated with insulin sensitivity. Replication in an independent study of 9 non-diabetic men resulted in 10 overlapping genes that strongly correlated with insulin sensitivity, including SIRT2, involved in lipid metabolism, and FBXW5 that regulates mammalian target-of-rapamycin (mTOR) and autophagy. The expressions of SIRT2 and FBXW5 were also positively correlated with the expression of key genes promoting the phenotype of an insulin sensitive myocyte e.g. PPARGC1A.

CONCLUSIONS

The muscle expression of 180 genes were correlated with insulin sensitivity. These data suggest that activation of genes involved in lipid metabolism, e.g. SIRT2, and genes regulating autophagy and mTOR signaling, e.g. FBXW5, are associated with increased insulin sensitivity in human skeletal muscle, reflecting a highly flexible nutrient sensing.

Evaluation of Insulin Resistance Induced Brain Tissue Dysfunction in Obese Dams and their Neonates: Role of Ipriflavone Amelioration

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is associated with activation of liver fibrogenesis and predisposes to cirrhosis and associated morbi-mortality. A high fat high cholesterol diet (HFD) was provided to female albino rats to establish a NASH model. It is well known that the offspring of obese mothers have an increased risk of obesity and diabetes. The present study aimed at evaluating the ameliorative effects of ipriflavone (IP) as a natural food supplement on lipid metabolism, improving insulin sensitivity, reducing oxidative stress and inflammation, modifying metabolic risk factors and/or reduce brain damage, in both neonates and their dams.

MATERIALS AND METHODS

The present aim was achieved by evaluating the oxidative stress and antioxidant defense system biomarkers, as thiobarbituric acid reactive substances (TBARS) and reduced glutathione (GSH), catalase, and superoxide dismutase (SOD) activities. In addition, the neurotransmitter acetylcholine (Ach) and acetylcholine esterase (AchE) activities, as well as levels of the apolipoprotein E4 (APOE4); β-secretase, hyper phosphor-tau and β-amyloid 42; 3-hydroxy- 3-methyl glutaryl coenzyme A reductase (HMG CoA R)" and COX-II by immunoblotting assays in the brain tissue of neonates and their dams in all the studied groups.

RESULTS

A very significant amelioration in acetylcholine and acetylcholine esterase neurotransmitters, Alzheimer's makers (β-amyloid), antioxidants (reduced glutathione (GSH) contents, catalase (CAT) and superoxide dismutase (SOD); and inflammatory cytokines in NASH model is observed upon administrating ipriflavone (IP) as a natural food supplement. The multifunctional activities of ipriflavone as an antioxidant, anti-inflammatory and anti-insulin resistance drug were discussed and correlated with other investigations.

CONCLUSION

Regarding steatohepatitis, the present study confirmed the anti-inflammatory effects of the ipriflavone (IP). Therefore, future studies should focus on hepatic fatty acid uptake, hepatic lipogenesis, and fatty acid oxidation and the role of IP in regulating hepatic fat metabolism. In addition, natural products like IP could be combined with the highly used pharmaceutical drugs to reduce the side effects of nonalcoholic steatohepatitis, and minimize progression of dementia. Moreover, the present study supports further attempts to heal the neural dysfunction via antioxidant and anti-inflammatory cascade activities using ipriflavone (IP).

A review of recent developments in the pharmacological prevention and treatment of endocrinopathic laminitis

Despite the prevalence of endocrinopathic laminitis, the pharmacologic options for preventing and treating the disease are severely limited. The present review aims to discuss the spectrum of potential therapeutic agents for the condition, ranging from early experimental compounds to agents nearing registration. There are different pharmacologic targets for, and approaches to, managing laminitis. Reducing hyperinsulinaemia is central to diminishing endocrinopathic laminitis risk, and a detailed understanding of the pathophysiology of insulin dysregulation is necessary to identify pathways that can be targeted to minimise post-prandial insulin secretion and action. This area of research is advancing rapidly, with several exciting prospects, such as sodium-dependent glucose co-transporter-2 inhibitors, on the horizon for the treatment of equine metabolic dysfunction. Drugs that directly target the lamellae and aim to reduce the damage inflicted on the lamellae as part of this condition, are not yet available. Although progress in this area of laminitis therapy is slower, improved understanding of the events that lead to lamellar failure has enabled the investigation of novel drugs that aim to prevent laminitis at the site of the lesion. Finally, a brief review is included of the directions being taken in the management of the chronic and acute pain that accompanies laminitis. Medications for relieving the pain associated with laminitis are currently the most-prescribed drugs for the disease, and range from simple, affordable and thoroughly tested options, such as phenylbutazone, to newer, less-understood applications such as paracetamol and gabapentin. In the future, endocrinopathic laminitis management plans will likely take a multi-faceted approach that still hinge on effective dietary management and exercise, but also include drugs that address foot pathology, pain and underlying endocrine disturbances.

Effect of body mass index on diabetogenesis factors at a fixed fasting plasma glucose level

Aim

The present study evaluated the relative influence of body mass index (BMI) on insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) at a fixed fasting plasma glucose level in an older ethnic Chinese population.

Methods

In total, 265 individuals aged 60 years with a fasting plasma glucose level of 5.56 mmol/L were enrolled. Participants had BMIs of 20.0–34.2 kg/m². IR, FPIS, SPIS, and GE were estimated using our previously developed equations. Pearson correlation analysis was conducted to assess the correlations between the four diabetogenesis factors and BMI. A general linear model was used to determine the differences in the percentage of change among the four factor slopes against BMI.

Results

Significant correlations were observed between BMI and FPIS, SPIS, IR, and GE in both women and men, which were higher than those reported previously. In men, BMI had the most profound effect on SPIS, followed by IR, FPIS, and GE, whereas in women, the order was slightly different: IR, followed by FPIS, SPIS, and GE. Significant differences were observed among all these slopes, except for the slopes between FPIS and SPIS in women (p = 0.856) and IR and FPIS in men (p = 0.258).

Conclusions

The contribution of obesity to all diabetes factors, except GE, was higher than that reported previously. BMI had the most profound effect on insulin secretion in men and on IR in women in this 60-year-old cohort, suggesting that lifestyle modifications for obesity reduction in women remain the most important method for improving glucose metabolism and preventing future type 2 diabetes mellitus.

Hyperinsulinemia Down-Regulates TLR4 Expression in the Mammalian Heart

Toll-like receptors (TLR) are key regulators of innate immune and inflammatory responses and their activation is linked to impaired glucose metabolism during metabolic disease. Determination of whether TLR4 signaling can be activated in the heart by insulin may shed light on the pathogenesis of diabetic cardiomyopathy, a process that is often complicated by obesity and insulin resistance. The aim of the current study was to determine if supraphysiological insulin concentrations alter the expression of TLR4, markers of TLR4 signaling and glucose transporters (GLUTs) in the heart. Firstly, the effect of insulin on TLR4 protein expression was investigated in vitro in isolated rat cardiac myocytes. Secondly, protein expression of TLR4, the pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) suppressor of cytokine signaling 3 (SOCS3) and GLUTs (1, 4, 8, 12) were examined in the equine ventricular myocardium following a prolonged, euglycemic, hyperinsulinemic clamp. Down-regulation of TLR4 protein content in rat cardiac myocytes was observed after incubation with a supraphysiologic concentration of insulin as well as in the equine myocardium after prolonged insulin infusion. Further, cardiac TLR4 expression was negatively correlated with serum insulin concentration. Markers of cardiac TLR4 signaling and GLUT expression were not affected by hyperinsulinemia and concomitant TLR4 down-regulation. Since TLRs are major determinants of the inflammatory response, our findings suggest that insulin infusion exerts an anti-inflammatory effect in the hearts of non-obese individuals. Understanding the regulation of cardiac TLR4 signaling during metabolic dysfunction will facilitate improved management of cardiac sequela to metabolic syndrome and diabetes.

Obesity - should we revise indications for treatment with metformin?

Introduction

Treatment of obesity with life style modifications often fails; therefore pharmacological treatment has become a very popular approach. Metformin is one of the examined possibilities. The aim of this study was to verify indications for metformin use in obese women based on metabolic and anthropometric parameters assessed by dual-X-ray absorptiometry (DXA), to establish the degree of insulin resistance and its correlations.

Material and methods

Anthropometry, fat measurement by bioimpedance and metabolic profile, including lipids, and oral glucose tolerance test (OGTT) with insulin (0 and 120 min) were performed in 50 female patients diagnosed with simple obesity, aged 18-40 years. Homeostatic model assessment HOMA-R was calculated for insulin resistance, and area under the curve (AUC) for insulin response. Total, android and gynoid fat distribution, and their ratio (A/G), were measured by DXA.

Results

From 50 women who entered the study, 33 were classified as insulin resistant (IR subgroup) and 17 as non-insulin resistant (non-IR subgroup), according to their HOMA-R indices. IR women presented higher waist circumference and DXA A/G ratio. The IR subgroup demonstrated elevated fasting triglycerides and glucose (but in the normal range) and a higher insulin response in OGTT (4.1-fold vs 2.5-fold). From different insulin measurements HOMA index turned out to have the strongest correlations with the metabolic parameters triglycerides and glucose. We found significant positive correlations between android fat and insulin: waist circumference and HOMA-R, WHR and HOMA-R, android fat and HOMA-R, A/G ratio and insulin after OGTT, and A/G ratio and HOMA-R. We found a strong correlation between WHR and A/R ratio.

Conclusions

67% of premenopausal obese women were insulin resistant. Measures of DXA visceral fat determined by android fat percentage and android/gynoid ratio were the strongest determinants of insulin resistance. Waist-to-hip ratio might be a simple method for determining the indications for metformin treatment.

Hormonal profile in Indian men with premature androgenetic alopecia

Introduction:

Alopecia in male is considered as a genetically determined disorder characterized by increased level of local androgen metabolite and increase androgen receptor binding in balding areas. Frequent deviations of hormones from normal values have been reported in men diagnosed with premature androgenetic alopecia (AGA) especially for androgens, gonadotropins and sex hormone binding globulin (SHBG). Different studies in the past have inferred that premature baldness before the age of thirty in males could be considered equivalent to the polycystic ovary syndrome (PCOS) in female.

Materials and Methods:

Hormonal profile of 50 men with severe premature balding before 30 years of age were compared with same numbers of age matched controls. The serum concentrations of total testosterone, dehydroepiandrosterone sulfate, luteinizing hormone, follicle stimulating hormone, SHBG, insulin and fasting blood sugar were estimated. Statistical analysis was performed with paired Student's t-test for cases and controls.

Results:

Decreased levels of SHBG with high free androgen index were found in cases when compared with the controls.

Conclusion:

Though altered hormonal profile may coexist in some of men with premature AGA it can’t be considered as male equivalent to PCOS in female or the metabolic syndrome.

Androgenetic alopecia and insulin resistance: are they truly associated?

BACKGROUND

Controversies exist regarding the association of androgenetic alopecia (AGA) with insulin resistance. Are they truly associated, or is insulin resistance just related to aging, obesity, or to the presence of metabolic syndrome?

OBJECTIVE

To assess insulin resistance in young nonobese patients with AGA with and without metabolic syndrome.

METHODS

The study included four equally distributed groups of age-, sex-, and body mass index-matched young, nonobese subjects: 30 patients with AGA and metabolic syndrome (group 1); 30 patients with AGA and no metabolic syndrome (group 2); 30 patients with metabolic syndrome and no AGA (group 3); and 30 healthy controls (group 4). Insulin resistance based on fasting insulin levels and homeostasis model assessment of insulin resistance (HOMA-IR) was assessed in all groups.

RESULTS

Twenty-three patients in group 1, four patients in group 2, 25 patients in group 3, and three healthy controls had insulin resistance with statistically significant differences in fasting insulin and HOMA-IR levels between all groups, between groups 1 and 2, groups 1 and 4, groups 2 and 3, and groups 3 and 4. No significant differences existed between groups 2 and 4 or groups 1 and 3. Correlations between insulin resistance parameters, age of patients, disease duration, and stages of AGA in males and females revealed nonsignificant differences.

CONCLUSIONS

Patients with metabolic syndrome, with or without AGA, were significantly more insulin resistant compared with patients with AGA with no metabolic syndrome and with healthy subjects and, therefore, no true association exists between AGA and insulin resistance.

Elevated serum retinol-binding protein 4 is associated with insulin resistance in older women

Retinol-binding protein 4 (RBP4), a molecule secreted from adipocytes and hepatocytes, may contribute to insulin resistance and is a potential predictor for type 2 diabetes mellitus. We investigated the association between serum RBP4 concentrations and insulin resistance in perimenopausal women. In addition, we examined associations of serum RBP4 concentrations with age, risk factors of cardiovascular disease, and metabolic syndrome. A total of 73 healthy women were included in this study. Subjects' anthropometric measurements were taken, and body mass index and waist-hip ratio were calculated. Fasting glucose, fasting insulin, serum RBP4, and lipid parameters were examined. These various parameters were compared in subjects younger than and older than 50 years. Serum RBP4 concentrations in women at least 50 years of age were significantly higher than those in women younger than 50 years. In all subjects, serum RBP4 concentrations positively correlated with age, diastolic blood pressure, fasting glucose, and homeostatic assessment model of insulin resistance. After subgroup analysis, serum RBP4 concentrations positively correlated with age, fasting glucose, and homeostatic assessment model of insulin resistance in women at least 50 years of age. In women younger than 50 years, serum RBP4 concentrations positively correlated only with fasting glucose. Serum RBP4 appears to identify age-induced insulin resistance by physiologic changes due to aging or menopause and by increasing hepatic glucose production. However, the clinical implication of RBP4 for detecting cardiovascular disease and metabolic syndrome is not clear.

Measures of insulin sensitivity

Many approaches may be taken in the assessment of insulin sensitivity in humans. The euglycemic hyperinsulinemic glucose clamp and measurement of steady-state plasma glucose are direct but time- and resource-intensive approaches. Alternative approaches, including calculations based on fasting plasma insulin and glucose levels or analyses of glucose and insulin levels after intravenous or oral glucose administration, are useful but provide only modest correlation with the primary analyses. Surrogate measures of insulin sensitivity may be found in body mass index, waist circumference, or serum triglyceride or C-reactive peptide determination. New, innovative isotopic approaches now being developed offer the potential to characterize whole-body glucose metabolism in a fashion that may eventually allow routine clinical testing of insulin sensitivity.

Cardiovascular metabolic syndrome - an interplay of, obesity, inflammation, diabetes and coronary heart disease

Cardiovascular disease is currently one of the biggest causes of morbidity and mortality facing humanity. Such a paradigm shift of disease pattern over the last century has only worsened due to the alarming global prevalence of obesity and type 2 diabetes. In recent years there is increasing focus on inflammation as one of the key players in the patho-physiology of these disorders. In addition to these overt risk factors new research is unraveling the significance of a constellation of early metabolic abnormalities that include weight gain, insulin resistance, prehypertension and a specific pattern of dyslipidaemia. There exists a complex interrelationship of these various metabolic disorders and their effect on cardiovascular system. Simplified explanation can be that inflammation increases insulin resistance, which in turn leads to obesity while perpetuating diabetes, high blood pressure, prothrombotic state and dyslipidaemia. While inflammation and insulin resistance have direct adverse effects on cardiac muscle, these metabolic abnormalities as a whole cause causes cardiovascular complications; warranting a multi pronged therapeutic and preventive approach for the 'Cardiovascular Metabolic Syndrome' as an entity.

Pten (phosphatase and tensin homologue gene) haploinsufficiency promotes insulin hypersensitivity

AIMS/HYPOTHESIS

Insulin controls glucose metabolism via multiple signalling pathways, including the phosphatidylinositol 3-kinase (PI3K) pathway in muscle and adipose tissue. The protein/lipid phosphatase Pten (phosphatase and tensin homologue deleted on chromosome 10) attenuates PI3K signalling by dephosphorylating the phosphatidylinositol 3,4,5-trisphosphate generated by PI3K. The current study was aimed at investigating the effect of haploinsufficiency for Pten on insulin-stimulated glucose uptake.

MATERIALS AND METHODS

Insulin sensitivity in Pten heterozygous (Pten(+/-)) mice was investigated in i.p. insulin challenge and glucose tolerance tests. Glucose uptake was monitored in vitro in primary cultures of myocytes from Pten(+/-) mice, and in vivo by positron emission tomography. The phosphorylation status of protein kinase B (PKB/Akt), a downstream signalling protein in the PI3K pathway, and glycogen synthase kinase 3beta (GSK3beta), a substrate of PKB/Akt, was determined by western immunoblotting.

RESULTS

Following i.p. insulin challenge, blood glucose levels in Pten(+/-) mice remained depressed for up to 120 min, whereas glucose levels in wild-type mice began to recover after approximately 30 min. After glucose challenge, blood glucose returned to normal about twice as rapidly in Pten(+/-) mice. Enhanced glucose uptake was observed both in Pten(+/-) myocytes and in skeletal muscle of Pten(+/-) mice by PET. PKB and GSK3beta phosphorylation was enhanced and prolonged in Pten(+/-) myocytes.

CONCLUSIONS/INTERPRETATION

Pten is a key negative regulator of insulin-stimulated glucose uptake in vitro and in vivo. The partial reduction of Pten due to Pten haploinsufficiency is enough to elicit enhanced insulin sensitivity and glucose tolerance in Pten(+/-) mice.

Association between C-reactive protein and insulin resistance in a Japanese population: the Minoh Study

OBJECTIVE

To investigate the association between C-reactive protein (CRP) and insulin resistance.

MATERIALS AND METHODS

This study included 1,624 Japanese participants (652 men and 972 women) aged 40 to 69 years who were non-diabetics or did not have medication for hypertension or dyslipidemia, a history of cardiovascular disease or CRP levels >10 mg/l. Serum CRP level, fasting glucose level, and fasting insulin level were measured, and the degree of insulin resistance was assessed using the homeostasis model assessment of insulin resistance (HOMA-IR). Categories of CRP were defined by the following tertiles: <0.25 mg/l, 0.25-0.59 mg/l, and > or = 0.60 mg/l.

RESULTS

Elevated CRP levels were associated with increased fasting insulin levels, fasting glucose levels, and HOMA-IR in both men and women. Although the adjustment for body mass index in addition to age, cigarette smoking, and alcohol consumption attenuated the associations between CRP and fasting insulin, fasting glucose, and HOMA-IR, elevated CRP levels were associated with increased insulin levels and HOMA-IR in both sexes. Stratified analyses by CRP level and obesity showed that obesity status was associated with increased fasting insulin levels, fasting glucose levels, and HOMA-IR in both sexes and that fasting insulin levels, fasting glucose levels, and HOMA-IR were higher among obese individuals than among non-obese individuals at the same level of CRP.

CONCLUSION

These results suggest a possible role of subclinical inflammation in insulin resistance and glucose intolerance in Japanese, but it only partly explains the link between obesity and impaired glucose homeostasis.

Insulin sensitivity in growth hormone-deficient children: influence of replacement treatment

OBJECTIVE

In adults, excessive GH secretion may lead to secondary diabetes mellitus, while prolonged GH treatment may accelerate the onset of type 2 diabetes mellitus in predisposed children. The aim of the study was to evaluate insulin sensitivity (IS) and glucose tolerance (GT) in a group of GH-deficient children treated with GH for a period of 6 years.

PATIENTS AND DESIGN

One hundred and twenty-eight children (40 females, 88 males) were included in the study. At the beginning of treatment chronological age was 8.9 +/- 3.2 years, height standard deviation score (SDS) -2.43 +/- 0.90 and body mass index (BMI) SDS 0.18 +/- 1.60. At the end of the study chronological age was 13.0 +/- 2.9 years, height SDS -1.24 +/- 1.27 and BMI SDS 0.23 +/- 1.54. GH was administered at a mean weekly dosage of 0.3 mg/kg, injected subcutaneously over 6-7 days. GT was assessed according to the criteria of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. IS was evaluated with the quantitative insulin sensitivity check index (QUICKI).

RESULTS

No cases of impaired GT or diabetes were recorded during the follow-up period. IS, already lower than in controls before starting treatment with GH, decreased significantly during the first year of therapy (QUICKI: 0.346 +/- 0.033 vs. 0.355 +/- 0.044, P < 0.05), with no further decrease in the following years. No correlation was found between QUICKI, BMI, years of treatment and onset of puberty.

CONCLUSIONS

GH treatment in GH-deficient children does not lead to an impaired GT or type 2 diabetes mellitus, although it does significantly decrease IS.

Insulin resistance: from predisposing factor to therapeutic target in type 2 diabetes

BACKGROUND

Insulin resistance contributes to the pathogenesis of type 2 diabetes and is closely linked with cardiovascular risk factors and premature cardiovascular disease.

OBJECTIVE

The purpose of this paper was to review the importance of insulin resistance as a core defect in type 2 diabetes, a potential contributor to accelerated atherosclerosis, and a potential target for insulin-sensitizing agents.

METHODS

Articles considered for inclusion in this review were identified through a search of MEDLINE/PubMed for reports published from 1966 to April 2003. Search terms used were insulin resistance, diabetes, insulin sensitivity, obesity, cardiovascular disease, metformin, thiazolidinediones, pioglitazone, rosiglitazone, and troglitazone.

RESULTS

An overview of the epidemiology, natural history, and pathophysiology of type 2 diabetes is provided, with a focus on insulin resistance and a related discussion of the impact of current therapies used to treat insulin-resistant patients. In particular, information on insulin-sensitizing agents-metformin and the currently available thiazolidinediones (TZDs), pioglitazone and rosiglitazone-is presented. Although metformin has been shown to indirectly reduce insulin resistance, TZDs are the only available agents that have been shown to directly lower insulin resistance.

CONCLUSIONS

Recent evidence indicates that metformin, pioglitazone, and rosiglitazone may improve the dyslipidemic profile, reduce vascular inflammation, and improve endothelial dysfunction, all of which may be particularly important to physicians seeking treatment options to prevent or reduce cardiovascular complications in patients with type 2 diabetes.

Contributions of insulin-resistance and insulin-secretory defects to the pathogenesis of type 2 diabetes mellitus

Controlled clinical trials have shown that optimal glycemic control can prevent the microvascular complications of type 2 diabetes mellitus; considerable epidemiological data suggest that this may also be true for macrovascular complications. However, this is frequently not achieved. Consequently, research efforts have been undertaken to better understand the pathophysiology of this disorder. It is now well recognized that 2 factors are involved: impaired beta-cell function and insulin resistance. Prospective studies of high-risk populations have shown insulin-resistance and/ or insulin-secretory defects before the onset of impaired glucose tolerance. Thus, there has been a long-standing debate whether an alteration in insulin sensitivity or in insulin secretion is the primary genetic factor. Most of the available evidence favors the view that type 2 diabetes is a heterogeneous disorder in which the major genetic factor is impaired beta-cell function and insulin resistance is the major acquired factor. Superimposition of insulin resistance on a beta cell that cannot appropriately compensate leads to deterioration in glucose tolerance. Therefore, clinicians managing type 2 diabetes must reduce insulin resistance and augment and/or replace beta-cell function.

Type 2 diabetes, cardiovascular risk, and the link to insulin resistance

BACKGROUND

Patients with type 2 diabetes mellitus frequently have coexistent dyslipidemia, hypertension, and obesity, and are at risk for microvascular and macrovascular disease complications such as myocardial infarction, stroke, retinopathy, and microalbuminuria. To optimize cardiovascular health outcomes for patients with type 2 diabetes, strategies to reduce the risks of microvascular and macrovascular disease are needed in clinical practice.

OBJECTIVE

This article provides an overview of the cardiovascular risk profile of patients with type 2 diabetes and discusses the cardiovascular consequences of use of the thiazolidinediones (insulin-sensitizing agents) in the treatment of type 2 diabetes.

METHODS

A literature search of MEDLINE/PubMed was performed to identify relevant articles published from 1966 to April 2003. Search terms used were diabetes, cardiovascular disease, atherosclerosis, dyslipidemia, obesity, hypertension, blood pressure, hyperglycemia, inflammation, C-reactive protein, fibrinolysis, plasminogen activator inhibitor type-1, microalbuminuria, thiazolidinediones, safety, hepatotoxicity, and edema. Bibliographies within the identified articles were also evaluated for additional relevant articles and information.

RESULTS

Recommendations for cardiovascular risk reduction through preventive and therapeutic strategies that target the symptoms of insulin resistance may reduce the microvascular and macrovascular sequelae of diabetes and ameliorate the impact of other components of the metabolic syndrome, including hypertension, hyperglycemia, and obesity. In this regard, thiazolidinediones are promising therapies.

CONCLUSIONS

Early data suggest that, in addition to reducing hyperglycemia, pioglitazone and rosiglitazone effect changes in the dyslipidemic profile, hemodynamics, vascular inflammation, and endothelial functioning of patients with type 2 diabetes. Additional research is needed to further distinguish the cardiovascular benefits of these drugs.

Insulin resistance as the core defect in type 2 diabetes mellitus

Insulin resistance is a major contributor to the pathogenesis of type 2 diabetes and plays a key role in associated metabolic abnormalities, such as dyslipidemia and hypertension. Obesity, especially visceral adiposity, is negatively correlated with insulin sensitivity. The release of free fatty acids from adipocytes can block insulin-signaling pathways and lead to insulin resistance. In addition, recently identified adipocyte-specific chemical messengers, the adipocytokines, such as tumor necrosis factor-alpha, adiponectin, and resistin, appear to modulate the underlying insulin resistance. When insulin resistance is combined with beta-cell defects in glucose-stimulated insulin secretion, impaired glucose tolerance, hyperglycemia, or type 2 diabetes can result. The thiazolidinediones are potent peroxisome proliferator-activated receptor-gamma agonists and directly improve insulin resistance and glycemic control in patients with type 2 diabetes. Increasing evidence supports the early use of thiazolidinediones for preventing, delaying, or treating diabetes by improving insulin sensitivity and beta-cell insulin secretion.

Evaluation of liver function in type 2 diabetic patients during clinical trials: evidence that rosiglitazone does not cause hepatic dysfunction

OBJECTIVE

Troglitazone treatment has been associated with idiosyncratic hepatic reaction leading to hepatic failure and death in some patients. This raises questions regarding whether all thiazolidinediones or peroxisomal proliferator-activated receptor-gamma (PPAR-gamma) agonists are hepatotoxic and whether data from clinical trials are adequate to detect a signal of potentially serious drug-related hepatotoxicity. The purpose of this study was to assess whether the idiosyncratic liver toxicity reported with troglitazone is molecule-specific or a thiazolidinedione class effect, based on liver enzyme data collected prospectively during phase 2/3 clinical trials with rosiglitazone, a new, potent, and specific member of the thiazolidinedione class.

RESEARCH DESIGN AND METHODS

This is an analysis of liver function in type 2 diabetic patients at baseline and serially in 13 double-blind, 2 open-label active-controlled, and 7 open-label extension studies of rosiglitazone treatment conducted in outpatient centers throughout North America and Europe. The study comprised > 6,000 patients aged 30-80 years with type 2 diabetes. Patients underwent baseline liver function studies and were excluded from clinical trials if they had an alanine aminotransferase (ALT), aspartate aminotransferase (AST), or alkaline phosphatase value 2.5 times greater than the upper limit of the reference range. The main outcome measures were liver enzyme levels, which were assessed at screening, at baseline, and every 4 weeks for the first 3 months of treatment and at 6- to 12-week intervals thereafter. Patients with at least one on-therapy ALT value >3 times the upper limit of the reference range were identified, and their case records examined in detail.

RESULTS

At baseline, 5.6% of the patients with type 2 diabetes (mean HbA(1c) 8.5-9.0%) had serum ALT values between 1.0 and 2.5 times the upper limit of the reference range. On antidiabetic therapy, most of those patients ( approximately 83%) had a decrease in ALT values, many into the normal range. The percentages of all patients with an on-therapy ALT value >3 times the upper limit of the reference range during double-blind and open-label treatment were as follows: rosiglitazone-treated 0.32%, placebo-treated 0.17%, and sulfonylurea-, metformin-, or insulin-treated 0.40%. The respective rates of ALT values >3 times the upper limit of the reference range per 100 person-years of exposure were 0.29, 0.59, and 0.64.

CONCLUSIONS

No evidence of hepatotoxic effects was observed in studies that involved 5,006 patients taking rosiglitazone as monotherapy or combination therapy for 5,508 person-years. This is in keeping with hepatic data from clinical trials of another member of the class, pioglitazone, and in contrast to the clear evidence of hepatotoxic effects observed during the troglitazone clinical trial program. These findings suggest that the idiosyncratic liver toxicity observed with troglitazone is unlikely to be a thiazolidinedione or a PPAR-gamma agonist class effect. Poorly controlled patients with type 2 diabetes may have moderate elevations of serum ALT that will decrease with improved glycemic control during treatment with rosiglitazone or other antihyperglycemic agents.

A review of rosiglitazone in type 2 diabetes mellitus

The thiazolidinedione rosiglitazone maleate works primarily to improve insulin sensitivity in muscle and adipose tissue. It may have additional pharmacologic effects, however, as its main target is peroxisome proliferator-activated receptor-gamma. Data using the homeostasis model assessment and proinsulin:insulin ratio in patients with type 2 diabetes mellitus suggest that rosiglitazone may have the potential to sustain or improve beta-cell function. In these patients the drug reduces fasting plasma glucose, glycosylated hemoglobin, insulin, and C-peptide. In clinical trials, rosiglitazone monotherapy significantly reduced glycosylated hemoglobin by 1.5% compared with placebo and led to significant improvements in glycemic control when given in combination with metformin, sulfonylureas, or insulin. A dosage of 4 mg twice/day significantly reduced fasting plasma glucose levels and produced comparable reductions in glycosylated hemoglobin compared with glyburide. Rosiglitazone has a low risk of gastrointestinal side effects and hypoglycemia, reduced insulin demand, potential sparing effects on beta-cells, and favorable drug interaction profile. Adverse events of clinical significance are edema, anemia, and weight gain. Premarketing data indicate no significant difference in liver enzyme elevations for rosiglitazone, placebo, or active controls. Another drug in the thiazolidinedione class, troglitazone, was associated with idiosyncratic hepatotoxicity and was removed from the market. Therefore, until long-term data are available for rosiglitazone, liver enzyme monitoring is recommended.

Biomarkers in disease and health

Biomarkers have considerable potential in aiding the understanding of the relationship between diet and disease or health. However, to assess the role, relevance and importance of biomarkers on a case by case basis it is essential to understand and prioritise the principal diet and health issues. In the majority of cases, dietary compounds are only weakly biologically active in the short term, have multiple targets and can be both beneficial and deleterious. This poses particular problems in determining the net effect of types of foods on health. In principle, a biomarker should be able to contribute to this debate by allowing the measurement of exposure and by acting as an indicator either of a deleterious or of an enhanced health effect prior to the final outcome. In this review, the examples chosen - cancer (stomach, colon/rectal, breast); coronary heart disease and osteoporosis - reflect three major diet-related disease issues. In each case the onset of the disease has a genetic determinant which may be exacerbated or delayed by diet. Perhaps the most important factor is that in each case the disease, once manifest, is difficult to influence in a positive way by diet alone. This then suggests that the emphasis for biomarker studies should focus on predictive biomarkers which can be used to help in the development of dietary strategies which will minimise the risk and be of greater benefit.

Association between physical activity and markers of inflammation in a healthy elderly population

Higher levels of physical activity are associated with lower risk of cardiovascular disease. There is growing evidence that the development of the atherosclerotic plaque is associated with inflammation. In this study, the authors investigated the cross-sectional association between physical activity and markers of inflammation in a healthy elderly population. Data obtained in 1989-1990 and 1992-1993 from the Cardiovascular Health Study, a cohort of 5,888 men and women aged >/=65 years, were analyzed. Concentrations of the inflammation markers-C-reactive protein, fibrinogen, Factor VIII activity, white blood cells, and albumin-were compared cross-sectionally by quartile of self-reported physical activity. Compared with persons in the lowest quartile, those in the highest quartile of physical activity had 19%, 6%, 4%, and 3% lower concentrations of C-reactive protein, white blood cells, fibrinogen, and Factor VIII activity, respectively, after adjustment for gender, the presence of cardiovascular disease, age, race, smoking, body mass index, diabetes, and hypertension. Multivariate regression models suggested that the association of higher levels of physical activity with lower levels of inflammation markers may be mediated by body mass index and glucose. There was no association between physical activity and albumin. Higher levels of physical activity were associated with lower concentrations of four out of five inflammation markers in this elderly cohort. These data suggest that increased exercise is associated with reduced inflammation. Prospective studies will be required for verification of these findings.

Effects of troglitazone on insulin sensitivity in HIV-infected patients with protease inhibitor-associated diabetes mellitus

Antiretroviral therapy (ART) is frequently associated with metabolic alterations, including insulin resistance and diabetes mellitus. In this pilot study, we evaluated the effect of the PPARgamma activator troglitazone on ART-associated insulin resistance in HIV-infected patients with ART-associated diabetes mellitus. Six patients with protease inhibitor (PI)-associated diabetes mellitus, lipodystrophy and dyslipidemia were treated with troglitazone 400 mg q.d. for 3 months. Previous oral antidiabetics were discontinued prior to the study. At baseline and after 3 months, insulin sensitivity (intravenous insulin tolerance test), body composition (multifrequence bioelectrical impedance analysis) and fat distribution (CT scan quantification) were assessed. Glycaemic control (fasting and postprandial blood glucose, fructosamine, glycosylated haemoglobin) and serum lipid status were determined monthly. In four of the six patients, there was a clear improvement in insulin sensitivity, resulting in a reversal of insulin resistance in two of these patients. Overall, there was an increase in lean body mass and a decrease in total body fat. The volume of visceral adipose tissue decreased whilst the volume of subcutaneous adipose tissue increased. Total cholesterol, LDL and HDL cholesterol increased, and total triglycerides and VLDL-cholesterol decreased. No adverse effects such as hepatotoxicity were observed. Treatment with troglitazone 400 mg q.d. can ameliorate and in some cases even reverse ART-associated insulin resistance. Therefore, further studies including non-diabetic patients with ART-associated insulin resistance may be helpful in evaluating the long-term effects of thiazolidinediones on ART-associated insulin resistance and other metabolic complications, such as adipose maldistribution and dyslipidaemia.

The Pro115Gln and Pro12Ala PPAR gamma gene mutations in obesity and type 2 diabetes

OBJECTIVE

Peroxisome-proliferator-activated receptors gamma (PPAR gamma), is a key regulator of adipocyte differentiation and energy balance. Two naturally occurring mutations in the PPAR gamma gene, Pro115Gln and Pro12Ala, have recently been shown to impair the function of the PPAR gamma2 isoform of the receptor and to be associated with obesity or diabetes-related phenotypes in different populations.

SUBJECTS

We studied the occurrence and possible associations of the Pro115Gln and Pro12Ala in the PPAR gamma2 gene with several clinical and metabolic phenotypes in three independent large populations of non-obese non-diabetic, type 2 diabetic, and morbidly obese French Caucasians.

RESULTS

The Pro115Gln mutation was not found in any of the 1069 subjects screened including 626 obese patients. The frequency of the Pro12Ala mutation was similar in all groups (0.08, 0.11, 0.09) and was not associated with BMI or any of the clinical parameters tested.

CONCLUSIONS

We conclude that the Pro115Gln mutation is not a frequent cause of morbid obesity in Caucasians and that the Pro12Ala mutation is not associated with clinically significant changes in these populations.

Endothelial cell dysfunction and the pathogenesis of diabetic macroangiopathy

Type 2 diabetes mellitus (DM) represents a high risk condition for the development of atherosclerotic and thromboembolic macroangiopathy, which make major contributions to diabetic mortality and morbidity. While many cardiovascular risk factors are common to both atherosclerosis and Type 2 DM, the enhanced risk of diabetic macroangiopathy may be attributable to additional pro-atherogenic mediators associated with insulin resistance syndrome. Given the central pathogenic role of endotheliopathy in atherosclerosis, it is likely that this vascular monolayer is the ultimate target of injury in response to such mediators. Furthermore, a pro-oxidative, dysfunctional endothelium may actively contribute to the pro-atherogenic environment through an inappropriate regulation of vascular tone, permeability, coagulation, fibrinolysis, cell adhesion and proliferation. Such dysfunction may mediate hypertension, dyslipidaemia and altered haemostasis, in addition to aggravating in vivo insulin resistance.

Rosiglitazone

Rosiglitazone, a thiazolidinedione antidiabetic agent, improves insulin resistance, a key underlying metabolic abnormality in most patients with type 2 (non-insulin-dependent) diabetes mellitus. In animal models of insulin resistance, rosiglitazone decreased plasma glucose, insulin and triglyceride levels and also attenuated or prevented diabetic nephropathy and pancreatic islet cell degeneration. In contrast with troglitazone, rosiglitazone does not induce cytochrome P4503A4 metabolism. It does not interact significantly with nifedipine, oral contraceptives, metformin, digoxin, ranitidine or acarbose. In clinical trials in patients with type 2 diabetes mellitus, rosiglitazone 2 to 12 mg/day (as a single daily dose or 2 divided daily doses) improved glycaemic control, as shown by decreases in fasting plasma glucose and glycosylated haemoglobin (HbA1c). Addition of rosiglitazone 2 to 8 mg/day to existing sulphonylurea, metformin or insulin therapy achieved further reductions in fasting plasma glucose and HbA1c. Oral combinations improved insulin sensitivity and beta-cell function according to a homeostasis model assessment. Consistent with its mechanism of action, rosiglitazone appears to be associated with a low risk of hypoglycaemia (<2% of patients receiving monotherapy). There is no evidence to date that rosiglitazone shares the hepatotoxicity of troglitazone.