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Abstracts

Life Extension Magazine October 2013
Abstracts

Diabetes

The worldwide epidemiology of type II diabetes mellitus--present and future perspectives.

Over the past three decades, the number of people with diabetes mellitus has more than doubled globally, making it one of the most important public health challenges to all nations. Type II diabetes mellitus (T2DM) and prediabetes are increasingly observed among children, adolescents and younger adults. The causes of the epidemic of T2DM are embedded in a very complex group of genetic and epigenetic systems interacting within an equally complex societal framework that determines behavior and environmental influences. This complexity is reflected in the diverse topics discussed in this Review. In the past few years considerable emphasis has been placed on the effect of the intrauterine environment in the epidemic of T2DM, particularly in the early onset of T2DM and obesity. Prevention of T2DM is a ‘whole-of-life’ task and requires an integrated approach operating from the origin of the disease. Future research is necessary to better understand the potential role of remaining factors, such as genetic predisposition and maternal environment, to help shape prevention programs. The potential effect on global diabetes surveillance of using HbA(1c) rather than glucose values in the diagnosis of T2DM is also discussed.

Nat Rev Endocrinol. 2011 Nov 8;8(4):228-36

Role of autophagy in diabetes and endoplasmic reticulum stress of pancreatic b -cells.

Type II diabetes mellitus is characterized by insulin resistance and failure of pancreatic b-cells producing insulin. Autophagy plays a crucial role in cellular homeostasis through degradation and recycling of organelles such as mitochondria or endoplasmic reticulum (ER). Here we discussed the role of b-cell autophagy in development of diabetes, based on our own studies using mice with b-cell-specific deletion of Atg7 (autophagy-related 7 ), an important autophagy gene, and studies by others. b-cell-specific Atg7-null mice showed reduction in b-cell mass and pancreatic insulin content. Insulin secretory function ex vivo was also impaired, which might be related to organelle dysfunction associated with autophagy deficiency. As a result, b-cell-specific Atg7-null mice showed hypoinsulinemia and hyperglycemia. However, diabetes never developed in those mice. Obesity and/or lipid are physiological ER stresses that can precipitate b-cell dysfunction. Our recent studies showed that b-cellspecific Atg7-null mice, when bred with ob/ob mice, indeed become diabetic. Thus, autophagy deficiency in b-cells could be a precipitating factor in the progression from obesity to diabetes due to inappropriate response to obesity-induced ER stress.

Exp Mol Med. 2012 Feb 29;44(2):81-8

Reversal of muscle insulin resistance by weight reduction in young, lean, insulin-resistant offspring of parents with type II diabetes.

To examine the role of intramyocellular lipid (IMCL) accumulation as well as circulating cytokines, branched-chain amino acids and acylcarnitines in the pathogenesis of muscle insulin resistance in healthy, young, lean insulin-resistant offspring of parents with type II diabetes (IR offspring), we measured these factors in plasma and used (1)H magnetic resonance spectroscopy to assess IMCL content and hyperinsulinemic-euglycemic clamps using [6,6-(2)H(2)] glucose to assess rates of insulin-stimulated peripheral glucose metabolism before and after weight reduction. Seven lean (body mass index < 25 kg/m(2)), young, sedentary IR offspring were studied before and after weight stabilization following a hypocaloric (1,200 Kcal) diet for ∼9 wks. This diet resulted in an average weight loss of 4.1 ± 0.6 kg (P < 0.0005), which was associated with an ∼30% reduction of IMCL from 1.1 ± 0.2% to 0.8 ± 0.1% (P = 0.045) and an ∼30% improvement in insulin-stimulated muscle glucose uptake [3.7 ± 0.3 vs. 4.8 ± 0.1 mg/(kg-min), P = 0.01]. This marked improvement in insulin-stimulated peripheral insulin responsiveness occurred independently of changes in plasma concentrations of TNF-a, IL-6, total adiponectin, C-reactive protein, acylcarnitines, and branched-chain amino acids. In conclusion, these data support the hypothesis that IMCL accumulation plays an important role in causing muscle insulin resistance in young, lean IR offspring, and that both are reversible with modest weight loss.

Proc Natl Acad Sci U S A. 2012 May 22;109(21):8236-40

Adipose tissue foam cells are present in human obesity.

CONTEXT: Adipose tissue macrophages (ATMs) are thought to engulf the remains of dead adipocytes in obesity, potentially resulting in increased intracellular neutral lipid content. Lipid-laden macrophages (foam cells [FCs]) have been described in atherosclerotic lesions and have been proposed to contribute to vascular pathophysiology, which is enhanced in obesity. OBJECTIVE: The objective of this study was to determine whether a subclass of lipid-laden ATMs (adipose FCs) develop in obesity and to assess whether they may uniquely contribute to obesity-associated morbidity. SETTING AND PATIENTS: Patients undergoing elective abdominal surgery from the Beer-Sheva (N = 94) and the Leipzig (N = 40) complementary cohorts were recruited. Paired abdominal subcutaneous (SC) and omental (Om) fat biopsy samples were collected and analyzed by histological and flow cytometry-based methods. Functional studies in mice included coculture of ATMs or FCs with adipose tissue. RESULTS: ATM lipid content was increased 3-fold in Om compared with SC fat, particularly in obese persons. FCs could be identified in some patients and were most abundant in Om fat of obese persons, particularly those with intra-abdominal fat distribution. Stepwise multivariate models demonstrated depot differential associations: fasting glucose with SC FCs (b = 0.667, P < .001) and fasting insulin (b = 0.413, P = .006) and total ATM count (b = 0.310, P = .034) with Om FCs in models including age, body mass index, high-density lipoprotein cholesterol, and high-sensitivity C-reactive protein. When cocultured with adipose explants from lean mice, FCs induced attenuated insulin responsiveness compared with adipose explants cocultured with control ATMs with low lipid content. CONCLUSIONS: FCs can be identified as an ATM subclass in human SC and Om adipose tissues in 2 independent cohorts, with distinct depot-related associations with clinical parameters. Once formed, they may engage in local cross-talk with adipocytes, contributing to adipose insulin resistance.

J Clin Endocrinol Metab. 2013 Mar;98(3):1173-81

Curcumin and obesity.

Turmeric has been long recognized for its anti-inflammatory and health-promoting properties. Curcumin is one of the principal anti-inflammatory and healthful components of turmeric comprising 2-8% of most turmeric preparations. Experimental evidence supports the activity of curcumin in promoting weight loss and reducing the incidence of obesity-related diseases. With the discovery that obesity is characterized by chronic low-grade metabolic inflammation, phytochemicals like curcumin which have anti-inflammatory activity are being intensely investigated. Recent scientific research reveals that curcumin directly interacts with white adipose tissue to suppress chronic inflammation. In adipose tissue, curcumin inhibits macrophage infiltration and nuclear factor kB (NF-kB) activation induced by inflammatory agents. Curcumin reduces the expression of the potent proinflammatory adipokines tumor necrosis factor-α (TNFa), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator inhibitor type-1 (PAI-1), and it induces the expression of adiponectin, the principal anti-inflammatory agent secreted by adipocytes. Curcumin also has effects to inhibit adipocyte differentiation and to promote antioxidant activities. Through these diverse mechanisms curcumin reduces obesity and curtails the adverse health effects of obesity.

Biofactors. 2013 Jan-Feb;39(1):78-87

Metabolism and the circadian clock converge.

Circadian rhythms occur in almost all species and control vital aspects of our physiology, from sleeping and waking to neurotransmitter secretion and cellular metabolism. Epidemiological studies from recent decades have supported a unique role for circadian rhythm in metabolism. As evidenced by individuals working night or rotating shifts, but also by rodent models of circadian arrhythmia, disruption of the circadian cycle is strongly associated with metabolic imbalance. Some genetically engineered mouse models of circadian rhythmicity are obese and show hallmark signs of the metabolic syndrome. Whether these phenotypes are due to the loss of distinct circadian clock genes within a specific tissue versus the disruption of rhythmic physiological activities (such as eating and sleeping) remains a cynosure within the fields of chronobiology and metabolism. Becoming more apparent is that from metabolites to transcription factors, the circadian clock interfaces with metabolism in numerous ways that are essential for maintaining metabolic homeostasis.

Physiol Rev. 2013 Jan;93(1):107-35

A systems biology approach identifies inflammatory abnormalities between mouse strains prior to development of metabolic disease.

OBJECTIVE: Type II diabetes and obesity are increasingly affecting human populations around the world. Our goal was to identify early molecular signatures predicting genetic risk to these metabolic diseases using two strains of mice that differ greatly in disease susceptibility. RESEARCH DESIGN AND METHODS: We integrated metabolic characterization, gene expression, protein-protein interaction networks, RT-PCR, and flow cytometry analyses of adipose, skeletal muscle, and liver tissue of diabetes-prone C57BL/6NTac (B6) mice and diabetes-resistant 129S6/SvEvTac (129) mice at 6 weeks and 6 months of age. RESULTS: At 6 weeks of age, B6 mice were metabolically indistinguishable from 129 mice, however, adipose tissue showed a consistent gene expression signature that differentiated between the strains. In particular, immune system gene networks and inflammatory biomarkers were upregulated in adipose tissue of B6 mice, despite a low normal fat mass. This was accompanied by increased T-cell and macrophage infiltration. The expression of the same networks and biomarkers, particularly those related to T-cells, further increased in adipose tissue of B6 mice, but only minimally in 129 mice, in response to weight gain promoted by age or high-fat diet, further exacerbating the differences between strains. CONCLUSIONS: Insulin resistance in mice with differential susceptibility to diabetes and metabolic syndrome is preceded by differences in the inflammatory response of adipose tissue. This phenomenon may serve as an early indicator of disease and contribute to disease susceptibility and progression.

Diabetes. 2010 Nov;59(11):2960-71

Lipotoxicity and decreased islet graft survival.

OBJECTIVE: To evaluate if baseline serum lipids are associated with islet graft survival in type 1 diabetes islet transplant (ITx) recipients. RESEARCH DESIGN AND METHODS: Baseline fasting lipid profile was collected from 44 ITx recipients. Comparisons were performed between subjects below and above the median values of each lipid fraction. Differences in outcomes were compared by Kaplan-Meier curves and Cox regression analysis. RESULTS: Subjects with baseline fasting plasma triglycerides and VLDL cholesterol above the median had shorter islet graft survival (triglycerides: 39.7 +/- 6.1 vs. 61.3 +/- 6.6 months, P = 0.029, and VLDL: 41.5 +/- 5.7 vs. 62.8 +/- 7.3 months, P = 0.032). Total, LDL, and HDL cholesterol did not influence islet function. Triglycerides (odds ratio 2.97 [95% CI 1.03-8.52], P = 0.044) maintained its association with graft failure after adjustments for confounders. CONCLUSIONS: Higher baseline triglycerides are associated with earlier decline in islet graft function. Prospective clinical trials should address whether it is directly caused by lipotoxicity and if strategies focusing on lowering serum lipids may prolong islet graft survival.

Diabetes Care. 2010 Mar;33(3):658-60

Fat tissue, aging, and cellular senescence.

Fat tissue, frequently the largest organ in humans, is at the nexus of mechanisms involved in longevity and age-related metabolic dysfunction. Fat distribution and function change dramatically throughout life. Obesity is associated with accelerated onset of diseases common in old age, while fat ablation and certain mutations affecting fat increase life span. Fat cells turn over throughout the life span. Fat cell progenitors, preadipocytes, are abundant, closely related to macrophages, and dysdifferentiate in old age, switching into a pro-inflammatory, tissue-remodeling, senescent-like state. Other mesenchymal progenitors also can acquire a pro-inflammatory, adipocyte-like phenotype with aging. We propose a hypothetical model in which cellular stress and preadipocyte overutilization with aging induce cellular senescence, leading to impaired adipogenesis, failure to sequester lipotoxic fatty acids, inflammatory cytokine and chemokine generation, and innate and adaptive immune response activation. These pro-inflammatory processes may amplify each other and have systemic consequences. This model is consistent with recent concepts about cellular senescence as a stress-responsive, adaptive phenotype that develops through multiple stages, including major metabolic and secretory readjustments, which can spread from cell to cell and can occur at any point during life. Senescence could be an alternative cell fate that develops in response to injury or metabolic dysfunction and might occur in nondividing as well as dividing cells. Consistent with this, a senescent-like state can develop in preadipocytes and fat cells from young obese individuals. Senescent, pro-inflammatory cells in fat could have profound clinical consequences because of the large size of the fat organ and its central metabolic role.

Aging Cell. 2010 Oct;9(5):667-84

Binge drinking induces whole-body insulin resistance by impairing hypothalamic insulin action.

Individuals with a history of binge drinking have an increased risk of developing the metabolic syndrome and type II diabetes. Whether binge drinking impairs glucose homeostasis and insulin action is unknown. To test this, we treated Sprague-Dawley rats daily with alcohol (3 g/kg) for three consecutive days to simulate human binge drinking and found that these rats developed and exhibited insulin resistance even after blood alcohol concentrations had become undetectable. The animals were resistant to insulin for up to 54 hours after the last dose of ethanol, chiefly a result of impaired hepatic and adipose tissue insulin action. Because insulin regulates hepatic glucose production and white adipose tissue lipolysis, in part through signaling in the central nervous system, we tested whether binge drinking impaired brain control of nutrient partitioning. Rats that had consumed alcohol exhibited impaired hypothalamic insulin action, defined as the ability of insulin infused into the mediobasal hypothalamus to suppress hepatic glucose production and white adipose tissue lipolysis. Insulin signaling in the hypothalamus, as assessed by insulin receptor and AKT phosphorylation, decreased after binge drinking. Quantitative polymerase chain reaction showed increased hypothalamic inflammation and expression of protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signaling. Intracerebroventricular infusion of CPT-157633, a small-molecule inhibitor of PTP1B, prevented binge drinking-induced glucose intolerance. These results show that, in rats, binge drinking induces systemic insulin resistance by impairing hypothalamic insulin action and that this effect can be prevented by inhibition of brain PTP1B.

Sci Transl Med. 2013 Jan 30;5(170):170ra14