Type 2 diabetes: principles of pathogenesis and therapy

Insulin resistance and impaired beta cell function in rheumatoid arthritis

OBJECTIVE

To identify factors that regulate glucose metabolism in rheumatoid arthritis (RA).

METHODS

We evaluated the homeostatic model assessment of insulin resistance (HOMA-IR) and beta cell function (HOMA-B) in 94 RA patients. We investigated the relationship between characteristics known to affect glucose metabolism in the general population (age, abdominal obesity [waist circumference], hypertension, antihypertensive therapy) as well as characteristics of RA (disease activity, glucocorticoid therapy) and insulin resistance and beta cell function.

RESULTS

Patients with high-grade inflammation (high-sensitivity C-reactive protein value >1.92 mg/liter) (n = 81) were more insulin resistant than patients with low-grade inflammation (n = 13), whereas beta cell function was similar in both groups. Insulin resistance and beta cell function were similar in both groups after adjustment for waist circumference. All recorded characteristics except for age were associated with HOMA-IR or/and HOMA-B in univariate analyses. In mixed regression models, abdominal obesity and patient's assessment of disease activity (by visual analog scale) were predictors of insulin resistance. The Disease Activity Score assessed using 28-joint counts for swelling and tenderness, tender joint count, and patient's assessment of disease activity were associated with reduced beta cell function, and the cumulative dose of glucocorticoids was associated with enhanced beta cell function. The cumulative glucocorticoid dose in all study patients was a mean of only 536 mg (95% confidence interval 239-1,173). In patients with high-grade inflammation, age was further associated with impaired beta cell function, whereas use of angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor blockers was associated with enhanced beta cell function.

CONCLUSION

The modifiable factors of abdominal obesity, antihypertensive therapy, disease activity, and use of glucocorticoids appear to affect glucose metabolism in RA.

Dodecanedioic acid overcomes metabolic inflexibility in type 2 diabetic subjects

Metabolically healthy skeletal muscle possesses the ability to switch easily between glucose and fat oxidation in response to homeostatic signals. In type 2 diabetes mellitus and obesity, the skeletal muscle shows a great reduction in this metabolic flexibility. A substrate like dodecanedioic acid (C-12), able to increase skeletal muscle glycogen stores via succinyl-CoA formation, might both postpone the fatigue and increase fatty acid utilization, since it does not affect insulin secretion. In healthy volunteers and in type 2 diabetic subjects, the effect of an oral C-12 load was compared with a glucose or water load during prolonged, moderate-intensity, physical exercise. C-12 metabolism was analyzed by a mathematical model. After C-12, diabetics were able to complete the 2 h of exercise. Nonesterified fatty acids increased both during and after the exercise in the C-12 session. C-12 oxidation provided 14% of total energy expenditure, and the sum of C-12 plus lipids oxidized after the C-12 meal was significantly greater than lipids oxidized after the glucose meal (P < 0.025). The fraction of C-12 that entered the central compartment was 47% of that ingested. During the first phase of the exercise ( approximately 60 min), the mean C-12 clearance from the central compartment toward tissues was 2.57 and 1.30 l/min during the second phase of the exercise. In conclusion, C-12 seems to be a suitable energy substrate during exercise, since it reduces muscle fatigue, is rapidly oxidized, and does not stimulate insulin secretion, which implies that lipolysis is not inhibited as reported after glucose ingestion.

Ca2+ microdomains and the control of insulin secretion

Nutrient-induced increases in intracellular free Ca(2+) concentrations are the key trigger for insulin release from pancreatic islet beta-cells. These Ca(2+) changes are tightly regulated temporally, occurring as Ca(2+) influx-dependent baseline oscillations. We explore here the concept that locally high [Ca(2+)] concentrations (i.e. Ca(2+) microdomains) may control exocytosis via the recruitment of key effector proteins to sites of exocytosis. Importantly, recent advances in the development of organelle- and membrane-targeted green fluorescent protein (GFP-) or aequorin-based Ca(2+) indicators, as well as in rapid imaging techniques, are providing new insights into the potential role of these Ca(2+) microdomains in beta-cells. We summarise here some of the evidence indicating that Ca(2+) microdomains beneath the plasma membrane and at the surface of large dense core vesicles may be important in the normal regulation of insulin secretion, and may conceivably contribute to "ATP-sensitive K(+)-channel independent" effects of glucose. We also discuss evidence that, in contrast to certain non-excitable cells, direct transfer of Ca(2+) from the ER to mitochondria via localised physical contacts between these organelles is relatively less important for efficient mitochondrial Ca(2+) uptake in beta-cells. Finally, we discuss evidence from single cell imaging that increases in cytosolic Ca(2+) are not required for the upstroke of oscillations in mitochondrial redox state, but may underlie the reoxidation process.

Does breastfeeding influence risk of type 2 diabetes in later life? A quantitative analysis of published evidence

BACKGROUND

Observational evidence suggests that having been breastfed in infancy may reduce the prevalence of type 2 diabetes in later life.

OBJECTIVE

The objective was to examine the influence of initial breastfeeding on type 2 diabetes and blood glucose and insulin concentrations.

DESIGN

A systematic review of published studies identified 1010 reports; 23 examined the relation between infant feeding and type 2 diabetes in later life or risk factors for diabetes. Risk factors in infants were examined separately from those in children and adults. All estimates were pooled by using fixed-effect models; differences <0 and ratios <1 imply a beneficial effect of breastfeeding.

RESULTS

Subjects who were breastfed had a lower risk of type 2 diabetes in later life than did those who were formula fed (7 studies; 76 744 subjects; odds ratio: 0.61; 95% CI: 0.44, 0.85; P = 0.003). Children and adults without diabetes who had been breastfed had marginally lower fasting insulin concentrations than did those who were formula fed (6 studies; 4800 subjects; percentage difference: -3%; 95% CI: -8%, 1%; P = 0.13); no significant difference in fasting glucose concentrations was observed. Breastfed infants had lower mean preprandial blood glucose (12 studies; 560 subjects; mean difference: -0.17 mmol/L; 95% CI: -0.28, -0.05 mmol/L; P = 0.005) and insulin (7 studies; 291 subjects; mean difference: -2.86 pmol/L; 95% CI: -5.76, 0.04 pmol/L; P = 0.054) concentrations than did those who were formula fed.

CONCLUSION

Breastfeeding in infancy is associated with a reduced risk of type 2 diabetes, with marginally lower insulin concentrations in later life, and with lower blood glucose and serum insulin concentrations in infancy.

Saturated fatty acids inhibit induction of insulin gene transcription by JNK-mediated phosphorylation of insulin-receptor substrates

JNKs are attractive targets for treatment of obesity and type-2 diabetes. A sustained increase in JNK activity was observed in dietary and genetic models of obesity in mice, whereas JNK deficiency prevented obesity-induced insulin resistance. A similar insulin-sensitizing effect was seen upon treatment of obese mice with JNK inhibitors. We now demonstrate that treatment with the saturated fatty acid palmitic acid results in sustained JNK activation and insulin resistance in primary mouse hepatocytes and pancreatic beta-cells. In the latter, palmitic acid treatment inhibits glucose-induced insulin gene transcription, in part, by interfering with autocrine insulin signaling through phosphorylation of insulin-receptor substrates 1 and 2 at sites that interfere with binding to activated insulin receptors. This mechanism may account for the induction of central insulin resistance by free fatty acids.

Hormonal disturbances associated with obesity in dogs

Obesity is associated with multiple endocrine alterations and changes in the concentration of circulating hormones. However, few studies have explored such alterations in dogs with naturally acquired excess weight. In the present study, we investigated the effect of naturally acquired obesity on cortisol, insulin-like growth factor (IGF)-1 and prolactin secretion in dogs. Thirty-one overweight dogs were enrolled in the trial. Blood samples were collected before and after adrenocorticotrophic hormone (ACTH) injection. Free thyroxine (fT4), cortisol, thyroid-stimulating hormone (TSH), IGF-1, prolactin and fructosamine were assayed. Body weight excess increased significantly with age and neutered dogs were more obese than entire ones. The ACTH stimulation test was within the normal range for 26 of 31 dogs. Prolactinaemia was increased in seven dogs and IGF-1 in six dogs. Twenty dogs had a fructosamine concentration >340 microm. Interestingly, 18 of 31 dogs showed disturbances of thyroid function based on high TSH and/or low fT4 baseline concentration, with 11 dogs showing both. According to these parameters only six of 31 dogs were free of hormonal disturbances. These results revealed the high incidence of such disturbances, especially thyroid dysfunction, in obese, but otherwise apparently healthy dogs. They demonstrate the importance of examining endocrine function during the initial evaluation of obese dogs to avoid failure of any nutritional treatment.

Diabetes and hyperglycemia: strict glycemic control

OBJECTIVE

To critically review recent evidence on pathophysiology, diagnosis, and control of acute and chronic hyperglycemia in medical and surgical intensive care unit (ICU) patients.

DATA SOURCE AND STUDY SELECTION

A MEDLINE/PubMed search (1966 through February 2006) with manual cross-referencing was conducted, including all relevant articles published on blood glucose control in intensive care patients. An emphasis was placed on more recent clinical trials investigating the effects of tight glycemic control in ICU patients and on basic science studies investigating the pathophysiology and systemic effects of transient hyperglycemia in nondiabetic patients.

DATA EXTRACTION AND SYNTHESIS

Original articles, selected reviews, letters to the editor, and chapters of selected textbooks were extracted. The reviewed information was then analyzed with respect to the prevalence of hyperglycemia in ICU patients, the pathophysiology of hyperglycemia in nondiabetics, and evidence on glycemic control in various subgroups of ICU patients. The risk of iatrogenic hypoglycemia in the ICU and potential future research directions are discussed at the end of the review.

CONCLUSIONS

Recent evidence shows direct improvements in patient mortality and in-hospital morbidity with strict control of even short-term elevations of glucose levels in certain subgroups of ICU patients. However, precisely defined target glucose levels, subgroup analyses of different patient populations and treatment interventions, and the avoidance of hypoglycemic episodes during insulin therapy remain incompletely resolved and warrant future investigation.

Molecular activation of PPARγ by angiotensin II type 1-receptor antagonists

OBJECTIVE AND DESIGN

Elevated blood pressure and insulin resistance are strongly associated in patients. We explored the potential for the anti-hypertensive angiotensin II type 1-receptor (ATR(1)) antagonists to improve insulin sensitivity through modulation of the nuclear receptor PPARgamma, in vitro and in vivo compared to the potent insulin sensitizer, rosiglitazone.

METHODS

PPARgamma modulation by ATR(1) antagonists was measured first by direct recruitment of PGC-1, followed by trans-activation reporter assays in cells, and promotion of adipogenesis in fibroblast and pre-adipocyte cell lines. Improvement of insulin sensitivity was measured as changes in levels of glucose, insulin, and adiponectin in ob/ob mice.

RESULTS

Telmisartan, candesartan, irbesartan, and losartan (but not valsartan or olmesartan) each served as bona fide PPARgamma ligands in vitro, with EC(50) values between 3 and 5 micro mol/l. However, only telmisartan, and to a lesser extent candesartan, resulted in significant PPARgamma agonism in cells. In vivo, although rosiglitazone significantly lowered both glucose (33%, p<0.01) and insulin (61%, p<0.01) levels and increased expression of adiponectin (74%, p<0.001), sartan treatment had no effect.

CONCLUSIONS

Many members of the sartan family of ATR(1) antagonists are PPARgamma ligands in cell-free assays but their modulation of PPARgamma in cells is relatively weak. Furthermore, none appear to improve insulin sensitivity in a rodent model under conditions where other insulin sensitizers, including rosiglitazone, do. These results question whether reported effects of sartans on insulin sensitivity may be through other means, and should guide further efforts to develop dual agents to treat hypertension and insulin resistance.

Can the Glycemic Index (GI) be used as a tool in the prevention and management of Type 2 diabetes?

The large increase in type 2 diabetes (T2DM), the considerable lifetime risk of diabetes and the loss of lifetime call for concerted action to prevent T2DM and its complications. Since diabetes is characterized by abnormal glucose metabolism, the question arises of whether a high intake of carbohydrates that are rapidly absorbed as glucose may increase the risk and worsen the course of T2DM. To quantify the impact of carbohydrates on blood glucose the glycemic index (GI) and the glycemic load (GL) have been applied. The GI of a food is a method of ranking carbohydrate rich foods according to their glycemic responses. GI is defined as the incremental area under the blood glucose curve of 50g carbohydrate of a test food expressed as a percentage of the area of the response to an equivalent amount of a reference food (glucose or white bread). In relation to GI/GL and prevention of T2DM there is insufficient information from observational studies to determine whether a positive association exists or not. Only randomized controlled clinical intervention studies will be able to provide the final answer. From meta-analyses of randomised controlled clinical trials comparing low and high GI diets in the treatment of diabetes it has been found that low GI diets improve the glycemic control. Labeling of foods with GI would be helpful for persons with diabetes, but the usefulness for healthy subjects remains to be clarified. At present it seems premature to introduce GI labeling for the entire population.

Clinically confirmed type 2 diabetes mellitus and colorectal cancer risk: a population-based, retrospective cohort study

OBJECTIVES

Patients with type 2 diabetes mellitus (DM) may be at increased colorectal cancer (CRC) risk. However, existing data are inconsistent. We investigated CRC risks, overall and by anatomic subsite, within a population-based inception cohort of clinically confirmed type 2 DM subjects.

METHODS

All residents of Rochester, Minnesota who first met standardized criteria for type 2 DM from 1970 to 1994 (997 men and 978 women) were identified and followed forward in time until emigration, death, or December 31, 1999. Incident CRC cases were identified by review of inpatient and outpatient medical records. Standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) were estimated to compare CRC incidence within the type 2 DM inception cohort with previously published rates for the Rochester general population.

RESULTS

Over 19,158 person-years of follow-up, 51 incident CRC cases were identified within the type 2 DM cohort, while only 36.8 cases were expected (SIR = 1.39, 95% CI 1.03-1.82). Among men, type 2 DM was associated with increased overall (SIR = 1.67, 95% CI 1.16-2.33) and proximal (SIR = 1.96, 95% CI 1.16-3.10) CRC risks; distal CRC risk was also increased, but the point estimate was not statistically significant (SIR = 1.43, 95% CI 0.82-2.32). Among women, type 2 DM was not a risk factor for overall, proximal, or distal CRC (SIR = 1.03, 95% CI 0.60-1.66; SIR = 1.17, 95% CI 0.58-2.09; and SIR = 0.74, 95% CI 0.24-1.72, respectively). Within the type 2 DM cohort, current and former cigarette smokers were at higher CRC risk (SIR = 1.77, 95% CI 1.24-2.47) than never smokers (SIR = 0.99, 95% CI 0.57-1.61) and the interaction between type 2 DM and cigarette smoking status was statistically significant (p= 0.05).

CONCLUSIONS

In this population-based, retrospective cohort study, clinically confirmed type 2 DM was associated with increased CRC risk, predominantly among men. Cigarette smoking appeared to positively modify DM-associated CRC risk, which to our knowledge has not been previously reported. These data suggest that further investigation of potential interactions between endogenous and exogenous factors involved in colorectal carcinogenesis may help to clarify the magnitude and extent of CRC risk experienced by persons with type 2 DM.

Selective PPAR agonists for the treatment of type 2 diabetes

Type 2 diabetes is a metabolic disease characterized by increased plasma glucose and insulin as well as dyslipidemia. If left untreated, chronic diseases will develop that are associated with neuropathic damage and higher mortality risk. Using a rational drug design, novel compounds have been developed that selectively activate the human PPAR receptors, leading to lessening of hyperglycemia and hyperinsulinemia as well as reduction of lipid levels in conjunction with an increase of the beneficial HDL-cholesterol. These PPAR agonists showed increased potency and efficacy compared to previously marketed insulin sensitizers. Lead compounds with desirable pharmacokinetic properties were chosen for further testing in several animal models. The in vivo activity of some synthetic ligands, capable of activating two or all three members of peroxisome proliferator-activated receptors (PPAR) family of receptors, suggested that they may have improved efficacy in type 2 diabetes therapy. Here, we briefly summarize the development of some novel PPAR agonists identified by our group in recent years.

Closing the gap between clinical research and clinical practice: can outcome studies with thiazolidinediones improve our understanding of type 2 diabetes?

Recent clinical research has provided a wealth of information to support optimal management strategies in type 2 diabetes mellitus (T2DM). In particular, outcome studies appropriately have had an increasingly important impact on clinical decision-making. Additional, new data are required, however, to close the current gaps in clinical knowledge and improve patient outcomes in T2DM. These outcome studies are particularly important in assessing the long-term benefit of newer agents for which data are available for short-term glycaemic control, effects on lipids and some data on non-traditional cardiovascular risk markers, but outcome data for harder end points relevant to the natural history of T2DM, particularly beta-cell function, are lacking. Outcome studies such as ADOPT and DREAM are investigating the impact of thiazolidinediones (TZDs) on beta-cell function and disease progression in T2DM and impaired glucose tolerance, respectively, the results of which are eagerly anticipated. The primary focus of this article is on TZD outcome studies evaluating beta-cell function and disease progression.

Type 2 diabetes increases the risk for uric acid stones

An increased prevalence of nephrolithiasis has been reported in patients with diabetes. Because insulin resistance, characteristic of the metabolic syndrome and type 2 diabetes, results in lower urine pH through impaired kidney ammoniagenesis and because a low urine pH is the main factor of uric acid (UA) stone formation, it was hypothesized that type 2 diabetes should favor the formation of UA stones. Therefore, the distribution of the main stone components was analyzed in a series of 2464 calculi from 272 (11%) patients with type 2 diabetes and 2192 without type 2 diabetes. The proportion of UA stones was 35.7% in patients with type 2 diabetes and 11.3% in patients without type 2 diabetes (P < 0.0001). Reciprocally, the proportion of patients with type 2 diabetes was significantly higher among UA than among calcium stone formers (27.8 versus 6.9%; P < 0.0001). Stepwise regression analysis identified type 2 diabetes as the strongest factor that was independently associated with the risk for UA stones (odds ratio 6.9; 95% confidence interval 5.5 to 8.8). The proper influence of type 2 diabetes was the most apparent in women and in patients in the lowest age and body mass index classes. In conclusion, in view of the strong association between type 2 diabetes and UA stone formation, it is proposed that UA nephrolithiasis may be added to the conditions that potentially are associated with insulin resistance. Accordingly, it is suggested that patients with UA stones, especially if overweight, should be screened for the presence of type 2 diabetes or components of the metabolic syndrome.

Computational disease gene identification: a concert of methods prioritizes type 2 diabetes and obesity candidate genes

Genome-wide experimental methods to identify disease genes, such as linkage analysis and association studies, generate increasingly large candidate gene sets for which comprehensive empirical analysis is impractical. Computational methods employ data from a variety of sources to identify the most likely candidate disease genes from these gene sets. Here, we review seven independent computational disease gene prioritization methods, and then apply them in concert to the analysis of 9556 positional candidate genes for type 2 diabetes (T2D) and the related trait obesity. We generate and analyse a list of nine primary candidate genes for T2D genes and five for obesity. Two genes, LPL and BCKDHA, are common to these two sets. We also present a set of secondary candidates for T2D (94 genes) and for obesity (116 genes) with 58 genes in common to both diseases.

The PPARalpha/gamma dual agonist chiglitazar improves insulin resistance and dyslipidemia in MSG obese rats

1. The aim of this study was to investigate the capacity of chiglitazar to improve insulin resistance and dyslipidemia in monosodium L-glutamate (MSG) obese rats and to determine whether its lipid-lowering effect is mediated through its activation of PPARalpha. 2. Chiglitazar is a PPARalpha/gamma dual agonist. 3. The compound improved impaired insulin and glucose tolerance; decreased plasma insulin level and increased the insulin sensitivity index and decreased HOMA index. Euglycemic hyperinsulinemic clamp studies showed chiglitazar increased the glucose infusion rate in MSG obese rats. 4. Chiglitazar inhibited alanine gluconeogenesis, lowered the hepatic glycogen level in MSG obese rats. Like rosiglitazone, chiglitazar promoted the differentiation of adipocytes and decreased the maximal diameter of adipocytes. In addition, chiglitazar decreased the fibrosis and lipid accumulation in the islets and increased the size of islets. 5. Chiglitazar reduced plasma triglyceride, total cholesterol (TCHO), nonesterified fatty acids (NEFA) and low density lipoprotein-cholesterol levels; lowered hepatic triglyceride and TCHO contents; decreased muscular NEFA level. Unlike rosiglitazone, chiglitazar showed significant increase of mRNA expression of PPARalpha, CPT1, BIFEZ, ACO and CYP4A10 in the liver of MSG obese rats. 6. These data suggest that PPARalpha/gamma coagonist, such as chiglitazar, affect lipid homeostasis with different mechanisms from rosiglitazone, chiglitazar may have better effects on lipid homeostasis in diabetic patients than selective PPARgamma agonists.

The diabetic surgical patient

PURPOSE OF REVIEW

This review summarizes the current progress in disease classification, pathophysiology and management of diabetes mellitus with a special focus on treatment modalities and recommendations for the practicing anesthesiologist.

RECENT FINDINGS

The revised classification of diabetes mellitus emphasizes disease cause and eliminates any reference to age-of-onset and insulin therapy. Hyperglycemia has emerged as an important marker of outcome in the operating room. Intensive insulin therapy promises to reduce health risk in the surgical and critical care setting. Perioperative beta-blocker and statin therapy are likely to reduce cardiac morbidity and mortality in diabetic patients. Promotility therapy (with metoclopromide) intended to reduce the aspiration risk of diabetic gastroparesis is likely over-utilized and may only be indicated for diabetics with poor glucose control and high hemoglobin A1c levels.

SUMMARY

According to World Health Organization projections, anesthesiologists can expect to care for more diabetic patients than ever before. Diabetes and its associated complications present unique challenges to the perioperative physician. As biomedical research continues to unravel the genetic, cellular and molecular mechanisms of this complex metabolic disease, our specialty must be prominently involved in the design and testing of innovative treatments to protect the diabetic patient from the risks of surgery and anesthesia.

Periodontitis deteriorates metabolic control in type 2 diabetic Goto-Kakizaki rats

BACKGROUND

Epidemiologic and clinical studies have indicated that periodontal disease (PD) may cause disturbances in general health and even affect diabetes. The aim of this study was to gain knowledge on the effect of PD on diabetes metabolic control in a new model for type 2 diabetes-associated PD (i.e., the Goto-Kakizaki [GK] rat).

METHODS

GK rats represented the type 2 diabetes group and were allocated into two groups: diabetes or diabetes+PD group; Wistar rats represented the non-diabetes group and were divided into non-diabetes+PD and non-diabetes groups. PD was induced by placing ligatures around second maxillary molars, and the animals were followed for 6 weeks. Serum insulin, glucose, and free fatty acid levels were evaluated; interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha were measured in adipose tissue supernatant; glucose tolerance and insulin resistance were calculated. Further, alveolar bone destruction was estimated morphometrically and radiographically.

RESULTS

Rats with diabetes+PD became almost 30% more glucose intolerant (P<0.01) and presented a 25% increase in IL-1beta in adipose tissue (P<0.05) compared to rats from the diabetes group. Moreover, PD associated with diabetes resulted in more alveolar bone destruction in comparison to PD in the absence of diabetes (P<0.01).

CONCLUSIONS

Our results indicated that PD deteriorates metabolic control in diabetes, which emphasizes that PD may play a significant role for the course of diabetes. The GK rat can represent a suitable model for further studies on the association between PD and diabetes.

Transcriptional regulation of metabolism

Our understanding of metabolism is undergoing a dramatic shift. Indeed, the efforts made towards elucidating the mechanisms controlling the major regulatory pathways are now being rewarded. At the molecular level, the crucial role of transcription factors is particularly well-illustrated by the link between alterations of their functions and the occurrence of major metabolic diseases. In addition, the possibility of manipulating the ligand-dependent activity of some of these transcription factors makes them attractive as therapeutic targets. The aim of this review is to summarize recent knowledge on the transcriptional control of metabolic homeostasis. We first review data on the transcriptional regulation of the intermediary metabolism, i.e., glucose, amino acid, lipid, and cholesterol metabolism. Then, we analyze how transcription factors integrate signals from various pathways to ensure homeostasis. One example of this coordination is the daily adaptation to the circadian fasting and feeding rhythm. This section also discusses the dysregulations causing the metabolic syndrome, which reveals the intricate nature of glucose and lipid metabolism and the role of the transcription factor PPARgamma in orchestrating this association. Finally, we discuss the molecular mechanisms underlying metabolic regulations, which provide new opportunities for treating complex metabolic disorders.

Adipose triglyceride lipase-mediated lipolysis of cellular fat stores is activated by CGI-58 and defective in Chanarin-Dorfman Syndrome

Adipose triglyceride lipase (ATGL) was recently identified as an important triacylglycerol (TG) hydrolase promoting the catabolism of stored fat in adipose and nonadipose tissues. We now demonstrate that efficient ATGL enzyme activity requires activation by CGI-58. Mutations in the human CGI-58 gene are associated with Chanarin-Dorfman Syndrome (CDS), a rare genetic disease where TG accumulates excessively in multiple tissues. CGI-58 interacts with ATGL, stimulating its TG hydrolase activity up to 20-fold. Alleles of CGI-58 carrying point mutations associated with CDS fail to activate ATGL. Moreover, CGI-58/ATGL coexpression attenuates lipid accumulation in COS-7 cells. Antisense RNA-mediated reduction of CGI-58 expression in 3T3-L1 adipocytes inhibits TG mobilization. Finally, expression of functional CGI-58 in CDS fibroblasts restores lipolysis and reverses the abnormal TG accumulation typical for CDS. These data establish an important biochemical function for CGI-58 in the lipolytic degradation of fat, implicating this lipolysis activator in the pathogenesis of CDS.

The Genetic Basis of Type 2 Diabetes

Type 2 Diabetes results from a complex physiologic process that includes the pancreatic beta cells, peripheral glucose uptake in muscle, the secretion of multiple cytokines and hormone-like molecules from adipocytes, hepatic glucose production, and likely the central nervous system. Consistent with the complex web of physiologic defects, the emerging picture of the genetics will involve a large number of risk susceptibility genes, each individually with relatively small effect (odds ratios below 1.2 in most cases). The challenge for the future will include cataloging and confirming the genetic risk factors, and understanding how these risk factors interact with each other and with the known environmental and lifestyle risk factors that increase the propensity to type 2 diabetes.

Pharmacological interventions that directly stimulate or modulate insulin secretion from pancreatic beta-cell: implications for the treatment of type 2 diabetes

Blood glucose concentration is controlled by a number of hormone and neurotransmitter signals, either increasing or reducing glucose levels in the case of hypoglycemia or hyperglycemia, respectively. The pancreatic beta-cell responds to an increase in circulating glucose levels by a cascade of metabolic and electrophysiological events leading to the secretion of insulin. Type 2 diabetes is a metabolic disorder characterized by chronic hyperglycemia; the progressive pancreatic beta-cell dysfunction, with altered insulin production and secretion, is a major pathophysiological determinant of the disease together with the resistance of insulin-sensitive tissues to the action of the hormone. Hence, drugs which stimulate or enhance insulin secretion will reduce plasma glucose concentrations; this lowering of hyperglycemia will, in turn, reduce the occurrence of long-term complications. K(ATP) channels play a critical role in insulin secretion and can be considered as transducers of glucose-induced metabolic changes into biophysical events leading to the exocytosis of insulin granules. All currently marketed insulin secretagogues, sulfonylureas and glinides, target the beta-cell K(ATP) channels and reduce their opening probability. They induce insulin release regardless of the plasma glucose concentration, thus favoring the occurrence of hypoglycemia in the fasting state. Despite the intensive use of current drugs, many patients suffering from type 2 diabetes still exhibit poor glycemic control, others fail to respond to the treatment, and some develop serious complications. Therefore, there is a real need for innovative compounds, either enhancing insulin secretion from the pancreas or improving insulin action on the hormone-sensitive tissues. Here, we overview the existing and novel approaches targeting the beta-cell to enhance the release of insulin, with special emphasis on new ways of amplifying insulin secretion in a glucose-dependent manner.

Increase of adiponectin receptor gene expression by physical exercise in soleus muscle of obese Zucker rats

Aerobic exercise, including treadmill running has been widely used to treat insulin resistance and type 2 diabetes. We studied the effects of endurance training on gene expression of adiponectin receptor 1 (AdipoR1) in skeletal muscle of obese Zucker rats: the 8-week moderate exercise program consisted of treadmill running at 20 m/min and 0 degrees gradient for 1 h/day, 7 days/week. After 8 weeks, insulin action on glucose disposal rate was measured by glucose-insulin index, the product of the areas under the curve of glucose and insulin during intraperitoneal glucose tolerance testing. In contrast to results for sedentary obese rats, exercise training decreased plasma levels of insulin and glucose as well as the glucose-insulin index in obese rats, indicating the merit of regular moderate exercise for improvement of insulin sensitivity in this insulin-resistant animal model. Also, diabetes-related reductions in mRNA and protein content of AdipoR1 in soleus muscle were observed in obese rats at baseline; they were markedly reversed after the 8-week exercise program. However, such exercise training did not alter plasma levels of insulin and glucose in lean Zucker rats. Also, AdipoR1 gene expression in soleus muscle was not changed by exercise in lean Zucker rats compared with the sedentary, lean littermates. These results suggest that long-term exercise training may reverse reduced AdipoR1 gene expression in soleus muscle and improve insulin sensitivity in the obese Zucker rats. Thus, an endurance exercise training is probably helpful clinically for obese individuals with insulin resistance.

Psychobiologic correlates of the metabolic syndrome and associated sexual dysfunction

OBJECTIVES

The association of low testosterone level and erectile dysfunction (ED) with metabolic syndrome (MS) is receiving increasing attention. The present study determined the psychobiologic characteristics of sexual dysfunction (SD) associated with MS (as defined by the National Cholesterol Education Program's Adult Treatment Panel III criteria) in a series of 803 consecutive male outpatients.

METHODS

Several hormonal, biochemical, and instrumental (penile Doppler ultrasound [PDU]) parameters were studied, along with general psychopathology scores (Middlesex Hospital Questionnaire modified [MHQ]). The Structured Interview on Erectile Dysfunction (SIEDY) was also applied.

RESULTS

Among the 236 patients (29.4%) diagnosed as having a MS, 96.5% reported ED, 39.6% hypoactive sexual desire (HSD), 22.7% premature ejaculation, and 4.8% delayed ejaculation. Patients with MS were characterised by greater subjective (as assessed by SIEDY) and objective (as assessed by PDU) ED and by greater somatised anxiety than the rest of the sample. The prevalence of overt hypogonadism (total testosterone <8 nM) was significantly higher in patients with MS. Among MS components, waist circumference and hyperglycaemia were the best predictors of hypogonadism. Hypogonadal patients with MS showed higher gonadotropin and lower free testosterone levels, suggesting a primary hypogonadism. Among patients with MS, hypogonadism was present in 11.9% and 3.8% in the rest of the sample (p<0.0001) and was associated with typical hypogonadism-related symptoms, such as hypoactive sexual desire, low frequency of sexual intercourse, and depressive symptoms.

CONCLUSIONS

Our data suggest that MS is associated with a more severe ED and induces somatisation. Furthermore, MS is associated with a higher prevalence of hypogonadism in patients with SD. The presence of hypogonadism can further exacerbate the MS-associated sexual dysfunction, adding the typical hypogonadism-related symptoms (including HSD, 66.7%). Recognising MS associated with hypogonadism is important for both sexual and general health and its serious potential associated risks.

Type 1 diabetes

Type 1 diabetes accounts for only about 5-10% of all cases of diabetes; however, its incidence continues to increase worldwide and it has serious short-term and long-term implications. The disorder has a strong genetic component, inherited mainly through the HLA complex, but the factors that trigger onset of clinical disease remain largely unknown. Management of type 1 diabetes is best undertaken in the context of a multidisciplinary health team and requires continuing attention to many aspects, including insulin administration, blood glucose monitoring, meal planning, and screening for comorbid conditions and diabetes-related complications. These complications consist of microvascular and macrovascular disease, which account for the major morbidity and mortality associated with type 1 diabetes. Newer treatment approaches have facilitated improved outcomes in terms of both glycaemic control and reduced risks for development of complications. Nonetheless, major challenges remain in the development of approaches to the prevention and management of type 1 diabetes and its complications.

Molecular aspects of insulin therapy in critically ill patients

PURPOSE OF REVIEW

This review provides an overview of molecular mechanisms involved in beneficial effects of insulin in insulin resistant critically ill patients.

RECENT FINDINGS

Intense insulin therapy reduced morbidity in critically ill patients. Insulin acts by two major molecular pathways: reduction of the inflammation process induced by free fatty acid excess in tissues and decrease of reactive oxygen species production induced by hyperglycemia. By these actions, insulin preserves mitochondrial function, enhances adiponectin secretion and probably modulates AMP-activated protein kinase activity, which in turn depletes lipid depots in tissues and restores glucose uptake and oxidation. Furthermore, it was recently established that insulin prevents microcirculation alteration and subsequent cellular hypoxia by reducing inducible nitric oxide synthase expression and activity in the endothelium. So, insulin beneficial effects in critically ill patients are dependent on metabolic and non-metabolic molecular pathways.

SUMMARY

Critically ill patients requiring intensive care for more than a few days have a high risk of death. A tight control of glucose levels by intense insulin therapy reduced morbidity in critically ill patients. Unraveling the molecular mechanisms of insulin will provide new insights into the pathogenesis of multiple organ failure and will allow novel therapeutic strategies to manage patients needing intensive care.

Role of islet amyloid in type 2 diabetes mellitus

Diabetes mellitus is one of the most common metabolic diseases worldwide and its prevalence is rapidly increasing. Due to its chronic nature (diabetes mellitus can be treated but as yet not cured) and its serious complications, it is one of the most expensive diseases with regard to total health care costs per patient. The elevated blood glucose levels in diabetes mellitus are caused by a defect in production and/or secretion of the polypeptide hormone insulin, which normally promotes glucose-uptake in cells. Insulin is produced by the pancreatic 'beta-cells' in the 'islets of Langerhans', which lie distributed within the exocrine pancreatic tissue. In type 2 diabetes mellitus, the initial defect in the pathogenesis of the disease in most of the patients is believed to be 'insulin resistance'. Hyperglycemia (clinically overt diabetes mellitus) will not develop as long as the body is able to produce enough insulin to compensate for the reduced insulin action. When this compensation fails ('beta-cell failure') blood glucose levels will become too high. In this review, we discuss one of the mechanisms that have been implicated in the development of beta-cell failure, i.e. amyloid formation in the pancreatic islets. This islet amyloid is a characteristic histopathological feature of type 2 diabetes mellitus and both in vitro and in vivo studies have revealed that its formation causes death of islet beta-cells. Being a common pathogenic factor in an otherwise heterogeneous disease, islet amyloidosis is an attractive novel target for therapeutic intervention in type 2 diabetes mellitus.

Non-alcoholic fatty liver disease is associated with carotid artery wall thickness in diet-controlled type 2 diabetic patients

Non-alcoholic fatty liver disease (NAFLD) is closely associated with several metabolic syndrome (MetS) features. We assessed whether NAFLD is significantly associated with carotid artery intima-media thickness (IMT), as a marker of subclinical atherosclerosis, and whether such association is independent of classical cardiovascular risk factors and MetS features. We studied 100 diet-controlled Type 2 diabetic patients with ultrasonographically diagnosed NAFLD and 100 diabetic patients without NAFLD who were comparable for age and sex. Main outcome measures were carotid IMT (by ultrasonography), classical risk factors, insulin resistance [as estimated by homeostasis model assessment (HOMA)-IR] and MetS (as defined by the Adult Treatment Panel III criteria). NAFLD patients had a markedly greater carotid IMT (1.24 +/- 0.13 vs 0.95 +/- 0.11 mm; p < 0.001) than those without the condition. The MetS and all its clinical traits were more highly prevalent in those with NAFLD (p < 0.001). Adjustment for age, sex, smoking history, diabetes duration, glycosylated hemoglobin, LDL cholesterol, liver enzymes and microalbuminuria did not really affect the significant differences in carotid IMT that were observed between the groups. Further adjustment for the MetS also had little impact, but additional adjustment for HOMA-IR score consistently attenuated any statistical significance (p = 0.28). In multivariate regression analysis, HOMA-IR score along with age and MetS (principally raised blood pressure values) were independently related to carotid IMT, whereas NAFLD was not. In conclusion, these results suggest that among diet-controlled Type 2 diabetic individuals the significant increase of carotid IMT in the presence of NAFLD is largely explained by HOMA-estimated insulin resistance.

Mechanisms of Disease: pathway-selective insulin resistance and microvascular complications of diabetes

Resistance to the actions of insulin is strongly associated with the microvascular complications of diabetes. To the extent that insulin resistance leads to hyperglycemia, dyslipidemia and hypertension, this association is not surprising. It is now clear that insulin also has direct actions in the microvasculature that influence the development and progression of microvascular disease. In the healthy state, insulin appears to have only minor effects on vascular function, because of the activation of opposing mediators such as nitric oxide and endothelin-1. Diabetes and obesity, however, are associated with selective insulin resistance in the phosphatidylinositol-3-kinase signaling pathway, which leads to reduced synthesis of nitric oxide, impaired metabolic control and compensatory hyperinsulinemia. By contrast, insulin signaling via extracellular signal-regulated kinase dependent pathways is relatively unaffected in diabetes, tipping the balance of insulin's actions so that they favor abnormal vasoreactivity, angiogenesis, and other pathways implicated in microvascular complications and hypertension. In addition, preferential impairment of nonoxidative glucose metabolism leads to increased intracellular formation of advanced glycation end products, oxidative stress and activation of other pathogenic mediators. Despite a strong temporal association, a causal link between pathway-selective insulin resistance and microvascular damage remains to be established. It is possible that this association reflects a common genotype or phenotype. Nonetheless, insulin resistance remains an important marker of risk and a key target for intervention, because those patients who achieve a greater improvement of insulin sensitivity achieve better microvascular outcomes.

Type 2 diabetes mellitus in youth: the complete picture to date

Type 2 diabetes mellitus is a heterogeneous condition in which the clinical manifestation of hyperglycemia is a reflection of the impaired balance between insulin sensitivity and insulin secretion. Clinical experience and research in youth type 2 diabetes mellitus are in an early stage because of the relative novelty of the condition in pediatrics. This article discusses the amassed information in type 2 diabetes mellitus of youth to date with respect to the epidemiology, pathophysiology, risk factors, clinical presentation, screening, and management strategies.

Link between obesity and type 2 diabetes

The relationship between obesity and diabetes is of such interdependence that the term 'diabesity' has been coined. The passage from obesity to diabetes is made by a progressive defect in insulin secretion coupled with a progressive rise in insulin resistance. Both insulin resistance and defective insulin secretion appear very prematurely in obese patients, and both worsen similarly towards diabetes. Thus, the classic 'hyperbolic relationship' between insulin resistance and insulin secretion and the 'glucose allostasis concept' remain prevailing concepts in this particular field of knowledge. An increase in overall fatness, preferentially of visceral as well as ectopic fat depots, is specifically associated with insulin resistance. The accumulation of intramyocellular lipids may be due to reduced lipid oxidation capacity. The ability to lose weight is related to the capacity to oxidize fat. Thus, a relative defect in fat oxidation capacity is responsible for energy economy and hampered weight loss.

Fatty acids and insulin resistance in muscle and liver

Free fatty acids (FFAs) circulate round the body and represent important nutrients and the key oxidative fuel for the heart and resting skeletal muscle. In addition, FFAs are thought to be potent signalling molecules. Growing evidence indicates that FFAs may be involved in type 2 diabetes mellitus and obesity by mediating insulin resistance. In 1963, it was postulated that accumulated glucose-6-phosphate as a result of increased FFA oxidation leads to decreased glucose uptake. An alternative hypothesis is that increased concentrations of plasma FFA induce insulin resistance in humans through inhibition of glucose transport activity, which appears to be a consequence of decreased insulin receptor substrate-1-associated phosphatidyl inositol 3 kinase activity. Moreover, FFAs can arise locally, and increased intramyocellular and hepatocellular lipids have been shown to be associated with insulin resistance. This paper reviews the main aspects of FFA metabolism in the development of insulin resistance in skeletal muscle and liver, as well as the role of ectopic lipid deposits as a local source of FFAs. Finally, the role of thiazolidinediones as modulators of FFA-induced insulin resistance will be discussed.

Exendin-4 uses Irs2 signaling to mediate pancreatic beta cell growth and function

The insulin receptor substrate 2 (Irs2) branch of the insulin/insulin-like growth factor-signaling cascade prevents diabetes in mice because it promotes beta cell replication, function, and survival, especially during metabolic stress. Because exendin-4 (Ex4), a long acting glucagon-like peptide 1 receptor agonist, has similar effects upon beta cells in rodents and humans, we investigated whether Irs2 signaling was required for Ex4 action in isolated beta cells and in Irs2(-/-) mice. Ex4 increased cAMP levels in human islets and Min6 cells, which promoted Irs2 expression and stimulated Akt phosphorylation. In wild type mice Ex4 administered continuously for 28 days increased beta cell mass 2-fold. By contrast, Ex4 failed to arrest the progressive beta cell loss in Irs2(-/-) mice, which culminated in fatal diabetes; however, Ex4 delayed the progression of diabetes by 3 weeks by promoting insulin secretion from the remaining islets. We conclude that some short term therapeutic effects of glucagon-like peptide 1 receptor agonists can be independent of Irs2, but its long term effects upon beta cell growth and survival are mediated by the Irs2 branch of the insulin/insulin-like growth factor signaling cascade.

Lipids for psychiatrists - an overview

Serum cholesterol is a major risk factor for cardiovascular disease. Total cholesterol, LDL cholesterol and triglycerides are positively related to cardiovascular disease, while HDL cholesterol has an inverse relationship. Measurement of lipids is essential in individuals with established cardiovascular disease or type 2 diabetes, and may also be carried out in healthy individuals as part of cardiovascular risk assessment. Lifestyle measures are important in cardiovascular disease prevention, but the mainstay of lipid lowering therapy is appropriate use of lipid lowering drugs. Total and LDL cholesterol are the primary targets for treatment, but consideration should also be given to raising HDL cholesterol and lowering triglycerides where appropriate. Statins are the most frequently used lipid lowering agents, but there is an important place for other drugs, including ezetimibe, fibrates and nicotinic acid.

Death-associated Protein Kinase as a Sensor of Mitochondrial Membrane Potential

We have investigated here the mechanism of dephosphorylation and activation of death-associated protein kinase (DAPK) and the role of lysosome in neuroblastoma cells (SH-SY5Y) treated with mitochondrial toxins, such as MPP(+) and rotenone. Mitochondrial respiratory chain inhibitors and uncouplers decreased mitochondrial membrane potential leading to DAPK dephosphorylation and activation. The class III phosphoinositide 3-kinase inhibitors attenuated DAPK dephosphorylation induced by mitochondrial toxins. Complex I inhibition by mitochondrial toxins (e.g. MPP(+)) resulted in mitochondrial swelling and lysosome reduction. Inhibition of class III phosphoinositide 3-kinase attenuated MPP(+)-induced lysosome reduction and cell death. The role of DAPK as a sensor of mitochondrial membrane potential in mitochondrial diseases was addressed.