The protein kinase Akt/protein kinase B (PKB) is implicated in insulin signaling in mammals and functions in a pathway that regulates longevity and stress resistance in Caenorhabditis elegans. We screened for long-lived mutants in nondividing yeast Saccharomyces cerevisiae and identified mutations in adenylate cyclase and SCH9, which is homologous to Akt/PKB, that increase resistance to oxidants and extend life-span by up to threefold. Stress-resistance transcription factors Msn2/Msn4 and protein kinase Rim15 were required for this life-span extension. These results indicate that longevity is associated with increased investment in maintenance and show that highly conserved genes play similar roles in life-span regulation in S. cerevisiae and higher eukaryotes.

Fibroblast growth factor 21 (FGF21) is a metabolic regulator that provides efficient and durable glycemic and lipid control in various animal models. However, its potential to treat obesity, a major health concern affecting over 30% of the population, has not been fully explored. Here we report that systemic administration of FGF21 for 2 wk in diet-induced obese and ob/ob mice lowered their mean body weight by 20% predominantly via a reduction in adiposity. Although no decrease in total caloric intake or effect on physical activity was observed, FGF21-treated animals exhibited increased energy expenditure, fat utilization, and lipid excretion, reduced hepatosteatosis, and ameliorated glycemia. Transcriptional and blood cytokine profiling studies revealed effects consistent with the ability of FGF21 to ameliorate insulin and leptin resistance, enhance fat oxidation and suppress de novo lipogenesis in liver as well as to activate futile cycling in adipose. Overall, these data suggest that FGF21 exhibits the therapeutic characteristics necessary for an effective treatment of obesity and fatty liver disease and provides novel insights into the metabolic determinants of these activities.

OBJECTIVE

To examine the effects of intranasal insulin administration on cognition, function, cerebral glucose metabolism, and cerebrospinal fluid biomarkers in adults with amnestic mild cognitive impairment or Alzheimer disease (AD).

METHODS

Randomized, double-blind, placebo-controlled trial.

METHODS

Clinical research unit of a Veterans Affairs medical center.

METHODS

The intent-to-treat sample consisted of 104 adults with amnestic mild cognitive impairment (n = 64) or mild to moderate AD (n = 40). Intervention Participants received placebo (n = 30), 20 IU of insulin (n = 36), or 40 IU of insulin (n = 38) for 4 months, administered with a nasal drug delivery device (Kurve Technology, Bothell, Washington).

METHODS

Primary measures consisted of delayed story recall score and the Dementia Severity Rating Scale score, and secondary measures included the Alzheimer Disease's Assessment Scale-cognitive subscale (ADAS-cog) score and the Alzheimer's Disease Cooperative Study-activities of daily living (ADCS-ADL) scale. A subset of participants underwent lumbar puncture (n = 23) and positron emission tomography with fludeoxyglucose F 18 (n = 40) before and after treatment.

RESULTS

Outcome measures were analyzed using repeated-measures analysis of covariance. Treatment with 20 IU of insulin improved delayed memory (P < .05), and both doses of insulin (20 and 40 IU) preserved caregiver-rated functional ability (P < .01). Both insulin doses also preserved general cognition as assessed by the ADAS-cog score for younger participants and functional abilities as assessed by the ADCS-ADL scale for adults with AD (P < .05). Cerebrospinal fluid biomarkers did not change for insulin-treated participants as a group, but, in exploratory analyses, changes in memory and function were associated with changes in the Aβ42 level and in the tau protein-to-Aβ42 ratio in cerebrospinal fluid. Placebo-assigned participants showed decreased fludeoxyglucose F 18 uptake in the parietotemporal, frontal, precuneus, and cuneus regions and insulin-minimized progression. No treatment-related severe adverse events occurred.

CONCLUSIONS

These results support longer trials of intranasal insulin therapy for patients with amnestic mild cognitive impairment and patients with AD. Trial Registration clinicaltrials.gov Identifier: NCT00438568.

Type 1 diabetes is an autoimmune disorder afflicting millions of people worldwide. Once diagnosed, patients require lifelong insulin treatment and can experience numerous disease-associated complications. The last decade has seen tremendous advances in elucidating the causes and treatment of the disease based on extensive research both in rodent models of spontaneous diabetes and in humans. Integrating these advances has led to the recognition that the balance between regulatory and effector T cells determines disease risk, timing of disease activation, and disease tempo. Here we describe current progress, the challenges ahead and the new interventions that are being tested to address the unmet need for preventative or curative therapies.

Since the discovery of insulin nearly 70 years ago, there has been no problem more fundamental to diabetes research than understanding how insulin works at the cellular level. Insulin binds to the alpha subunit of the insulin receptor which activates the tyrosine kinase in the beta subunit, but the molecular events linking the receptor kinase to insulin-sensitive enzymes and transport processes are unknown. Our discovery that insulin stimulates tyrosine phosphorylation of a protein of relative molecular mass between 165,000 and 185,000, collectively called pp185, showed that the insulin receptor kinase has specific cellular substrates. The pp185 is a minor cytoplasmic phosphoprotein found in most cells and tissues; its phosphorylation is decreased in cells expressing mutant receptors defective in signalling. We have now cloned IRS-1, which encodes a component of the pp185 band. IRS-1 contains over ten potential tyrosine phosphorylation sites, six of which are in Tyr-Met-X-Met motifs. During insulin stimulation, the IRS-1 protein undergoes tyrosine phosphorylation and binds phosphatidylinositol 3-kinase, suggesting that IRS-1 acts as a multisite 'docking' protein to bind signal-transducing molecules containing Src-homology 2 and Src-homology-3 domains. Thus IRS-1 may link the insulin receptor kinase and enzymes regulating cellular growth and metabolism.

There is mounting evidence that inflammation plays a role in the development of coronary heart disease (CHD). Observations have been made linking the presence of infections in the vessel wall with atherosclerosis, and epidemiological data also implicate infection in remote sites in the aetiology of CHD. In this article we propose a key role for the proinflammatory cytokine interleukin-6 (IL-6) in several mechanisms that contribute to the development of CHD. IL-6 is a powerful inducer of the hepatic acute phase response. Elevated concentrations of acute phase reactants, such as C-reactive protein (CRP), are found in patients with acute coronary syndromes, and predict future risk in apparently healthy subjects. The acute phase reaction is associated with elevated levels of fibrinogen, a strong risk factor for CHD, with autocrine and paracrine activation of monocytes by IL-6 in the vessel wall contributing to the deposition of fibrinogen. The acute phase response is associated with increased blood viscosity, platelet number and activity. Furthermore, raised serum amyloid A lowers HDL-cholesterol levels. IL-6 decreases lipoprotein lipase (LPL) activity and monomeric LPL levels in plasma, which increases macrophage uptake of lipids. In fatty streaks and in the atheromatous 'cap' and 'shoulder' regions, macrophage foam cells and smooth muscle cells (SMC) express IL-6, suggesting a role for this cytokine along with interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha), in the progression of atherosclerosis. Both these cytokines induce the release of IL-6 from several cell types, including SMC. During vascular injury SMC are exposed to platelets or their products, and cytokine production by SMC further contributes to vascular damage. Furthermore, circulating IL-6 stimulates the hypothalamic-pituitary-adrenal (HPA) axis, activation of which is associated with central obesity, hypertension and insulin resistance. Thus we propose a role for IL-6 in the pathogenesis of CHD through a combination of autocrine, paracrine and endocrine mechanisms. This hypothesis lends itself to testing using interventions to influence IL-6 secretion and actions.

Increasing numbers of reports concerning diabetes, ketoacidosis, hyperglycaemia and lipid dysregulation in patients treated with second-generation (or atypical) antipsychotics have raised concerns about a possible association between these metabolic effects and treatment with these medications. This comprehensive literature review considers the evidence for and against an association between glucose or lipid dysregulation and eight separate second-generation antipsychotics currently available in the US and/or Europe, specifically clozapine, olanzapine, risperidone, quetiapine, zotepine, amisulpride, ziprasidone and aripiprazole. This review also includes an assessment of the potential contributory role of treatment-induced weight gain in conferring risk for hyperglycaemia and dyslipidaemia during treatment with different antipsychotic medications. Substantial evidence from a variety of human populations, including some recent confirmatory evidence in treated psychiatric patients, indicates that increased adiposity is associated with a variety of adverse physiological effects, including decreases in insulin sensitivity and changes in plasma glucose and lipid levels. Comparison of mean weight changes and relative percentages of patients experiencing specific levels of weight increase from controlled, randomised clinical trials indicates that weight gain liability varies significantly across the different second generation antipsychotic agents. Clozapine and olanzapine treatment are associated with the greatest risk of clinically significant weight gain, with other agents producing relatively lower levels of risk. Risperidone, quetiapine, amisulpride and zotepine generally show low to moderate levels of mean weight gain and a modest risk of clinically significant increases in weight. Ziprasidone and aripiprazole treatment are generally associated with minimal mean weight gain and the lowest risk of more significant increases. Published studies including uncontrolled observations, large retrospective database analyses and controlled experimental studies, including randomised clinical trials, indicate that the different second-generation antipsychotics are associated with differing effects on glucose and lipid metabolism. These studies offer generally consistent evidence that clozapine and olanzapine treatment are associated with an increased risk of diabetes mellitus and dyslipidaemia. Inconsistent results, and a generally smaller effect in studies where an effect is reported, suggest limited if any increased risk for treatment-induced diabetes mellitus and dyslipidaemia during risperidone treatment, despite a comparable volume of published data. A similarly smaller and inconsistent signal suggests limited if any increased risk of diabetes or dyslipidaemia during quetiapine treatment, but this is based on less published data than is available for risperidone. The absence of retrospective database studies, and little or no relevant published data from clinical trials, makes it difficult to draw conclusions concerning risk for zotepine or amisulpride, although amisulpride appears to have less risk of treatment-emergent dyslipidaemia in comparison to olanzapine. With increasing data from clinical trials but little or no currently published data from large retrospective database analyses, there is no evidence at this time to suggest that ziprasidone and aripiprazole treatment are associated with an increase in risk for diabetes, dyslipidaemia or other adverse effects on glucose or lipid metabolism. In general, the rank order of risk observed for the second-generation antipsychotic medications suggests that the differing weight gain liability of atypical agents contributes to the differing relative risk of insulin resistance, dyslipidaemia and hyperglycaemia. This would be consistent with effects observed in nonpsychiatric samples, where risk for adverse metabolic changes tends to increase with increasing adiposity. From this perspective, a possible increase in risk would be predicted to occur in association with any treatment that produces increases in weight and adiposity. However, case reports tentatively suggest that substantial weight gain or obesity may not be a factor in up to one-quarter of cases of new-onset diabetes that occur during treatment. Pending further testing from preclinical and clinical studies, limited controlled studies support the hypothesis that clozapine and olanzapine may have a direct effect on glucose regulation independent of adiposity. The results of studies in this area are relevant to primary and secondary prevention efforts that aim to address the multiple factors that contribute to increased prevalence of type 2 diabetes mellitus and cardiovascular disease in populations that are often treated with second-generation antipsychotic medications.

The target of rapamycin (TOR) pathway is a major nutrient-sensing pathway that, when genetically downregulated, increases life span in evolutionarily diverse organisms including mammals. The central component of this pathway, TOR kinase, is the target of the inhibitory drug rapamycin, a highly specific and well-described drug approved for human use. We show here that feeding rapamycin to adult Drosophila produces the life span extension seen in some TOR mutants. Increase in life span by rapamycin was associated with increased resistance to both starvation and paraquat. Analysis of the underlying mechanisms revealed that rapamycin increased longevity specifically through the TORC1 branch of the TOR pathway, through alterations to both autophagy and translation. Rapamycin could increase life span of weak insulin/Igf signaling (IIS) pathway mutants and of flies with life span maximized by dietary restriction, indicating additional mechanisms.

BACKGROUND

Despite the popularity of the low-carbohydrate, high-protein, high-fat (Atkins) diet, no randomized, controlled trials have evaluated its efficacy.

METHODS

We conducted a one-year, multicenter, controlled trial involving 63 obese men and women who were randomly assigned to either a low-carbohydrate, high-protein, high-fat diet or a low-calorie, high-carbohydrate, low-fat (conventional) diet. Professional contact was minimal to replicate the approach used by most dieters.

RESULTS

Subjects on the low-carbohydrate diet had lost more weight than subjects on the conventional diet at 3 months (mean [+/-SD], -6.8+/-5.0 vs. -2.7+/-3.7 percent of body weight; P=0.001) and 6 months (-7.0+/-6.5 vs. -3.2+/-5.6 percent of body weight, P=0.02), but the difference at 12 months was not significant (-4.4+/-6.7 vs. -2.5+/-6.3 percent of body weight, P=0.26). After three months, no significant differences were found between the groups in total or low-density lipoprotein cholesterol concentrations. The increase in high-density lipoprotein cholesterol concentrations and the decrease in triglyceride concentrations were greater among subjects on the low-carbohydrate diet than among those on the conventional diet throughout most of the study. Both diets significantly decreased diastolic blood pressure and the insulin response to an oral glucose load.

CONCLUSIONS

The low-carbohydrate diet produced a greater weight loss (absolute difference, approximately 4 percent) than did the conventional diet for the first six months, but the differences were not significant at one year. The low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease. Adherence was poor and attrition was high in both groups. Longer and larger studies are required to determine the long-term safety and efficacy of low-carbohydrate, high-protein, high-fat diets.

The overnight urinary albumin excretion rate (AER) of 87 patients with insulin-dependent diabetes mellitus was measured in 1966-67, 14 years later information was obtained on 63 of the original cohort; those alive were restudied, and for those who had died relevant clinical information and case of death were recorded. The development of clinical diabetic nephropathy ('Albustix'positive proteinuria) was related to the 1966-67 AER values. Clinical proteinuria developed in only 2 of 55 patients with AER below 30 microgram/min but in 7 of 8 with AER between 30 and 140 microgram/min. The risk of clinical diabetic nephropathy in the latter group was twenty-four time higher than inthe former. 9.1% of patients with AER below 30 microgram/min had died, compared with 37.5% with higher AER. The two groups did not differ significantly in age, sex composition, and initial blood pressure. Mean duration of diabetes was longer, but not significantly so, in those with AER above 30 microgram/min. Thus, elevated levels of microalbuminuria strongly predict the development of clinical diabetic nephropathy. These levels of AER are potentially reversible, and their detection and treatment may prevent diabetic renal disease.

A cloned approximately 5 kb cDNA (human placenta) contains the coding sequences for the insulin receptor. The nucleotide sequence predicts a 1382 amino acid precursor. The alpha subunit comprises the N-terminal portion of the precursor and contains a striking cysteine-rich "cross-linking" domain. The beta-subunit (the C-terminal portion of the precursor) contains a transmembrane domain and, in the intracellular region, the elements of a tyrosine phosphokinase: an ATP-binding site and a possible tyrosine autophosphorylation site or sites. The overall structure is reminiscent of the EGF receptor; the cross-linking domain of the alpha subunit and several regions of the beta subunit exhibit sequence homology with the EGF receptor. The phosphokinase domain also exhibits homology with some oncogenic proteins that have tyrosine phosphokinase activity, in particular, a striking homology with v-ros. Southern blotting experiments suggest that the coding region spans more than 45 kb. The insulin receptor gene is located on chromosome 19.

Insulin stimulates the autophosphorylation of tyrosine residues of the beta subunit of the insulin receptor (IR); this modified insulin-independent kinase has increased activity toward exogenous substrates in vitro. We show here that replacement of one or both of the twin tyrosines (residues 1162 and 1163) with phenylalanine results in a dramatic reduction in or loss of insulin-activated autophosphorylation and kinase activity in vitro. In vivo, these mutations not only result in a substantial decrease in insulin-stimulated IR autophosphorylation but also in a parallel decrease in the insulin-activated uptake of 2-deoxyglucose. Furthermore, a truncated IR protein (lacking the last 112 amino acids) has an unstable beta subunit; this mutant has no kinase activity in vitro or in vivo and does not mediate insulin-stimulated uptake of 2-deoxyglucose. IR autophosphorylation is thus implicated in the regulation of IR activities, with tyrosines 1162 and 1163 as major sites of this regulation.

BACKGROUND

The gut hormone fragment peptide YY3-36 (PYY) reduces appetite and food intake when infused into subjects of normal weight. In common with the adipocyte hormone leptin, PYY reduces food intake by modulating appetite circuits in the hypothalamus. However, in obesity there is a marked resistance to the action of leptin, which greatly limits its therapeutic effectiveness. We investigated whether obese subjects were also resistant to the anorectic effects of PYY.

METHODS

We compared the effects of PYY infusion on appetite and food intake in 12 obese and 12 lean subjects in a double-blind, placebo-controlled, crossover study. The plasma levels of PYY, ghrelin, leptin, and insulin were also determined.

RESULTS

Caloric intake during a buffet lunch offered two hours after the infusion of PYY was decreased by 30 percent in the obese subjects (P<0.001) and 31 percent in the lean subjects (P<0.001). PYY infusion also caused a significant decrease in the cumulative 24-hour caloric intake in both obese and lean subjects. PYY infusion reduced plasma levels of the appetite-stimulatory hormone ghrelin. Endogenous fasting and postprandial levels of PYY were significantly lower in obese subjects (the mean [+/-SE] fasting PYY levels were 10.2+/-0.7 pmol per liter in the obese group and 16.9+/-0.8 pmol per liter in the lean group, P<0.001). Furthermore, the fasting PYY levels correlated negatively with the body-mass index (r = -0.84, P<0.001).

CONCLUSIONS

We found that obese subjects were not resistant to the anorectic effects of PYY. Endogenous PYY levels were low in the obese subjects, suggesting that PYY deficiency may contribute to the pathogenesis of obesity.

Recent studies have revealed that vascular cells can produce reactive oxygen species (ROS) through NAD(P)H oxidase, which may be involved in vascular injury. However, the pathological role of vascular NAD(P)H oxidase in diabetes or in the insulin-resistant state remains unknown. In this study, we examined the effect of high glucose level and free fatty acid (FFA) (palmitate) on ROS production in cultured aortic smooth muscle cells (SMCs) and endothelial cells (ECs) using electron spin resonance spectroscopy. Exposure of cultured SMCs or ECs to a high glucose level (400 mg/dl) for 72 h significantly increased the free radical production compared with low glucose level exposure (100 mg/dl). Treatment of the cells for 3 h with phorbol myristic acid (PMA), a protein kinase C (PKC) activator, also increased free radical production. This increase was restored to the control value by diphenylene iodonium, a NAD(P)H oxidase inhibitor, suggesting ROS production through PKC-dependent activation of NAD(P)H oxidase. The increase in free radical production by high glucose level exposure was completely restored by both diphenylene iodonium and GF109203X, a PKC-specific inhibitor. Exposure to palmitate (200 micromol/l) also increased free radical production, which was concomitant with increases in diacylglycerol level and PKC activity. Again, this increase was restored to the control value by both diphenylene iodonium and GF109203X. The present results suggest that both high glucose level and palmitate may stimulate ROS production through PKC-dependent activation of NAD(P)H oxidase in both vascular SMCs and ECs. This finding may be involved in the excessive acceleration of atherosclerosis in patients with diabetes and insulin resistance syndrome.

BACKGROUND

The immunopathogenesis of type 1 diabetes mellitus is associated with T-lymphocyte autoimmunity. However, there is growing evidence that B lymphocytes play a role in many T-lymphocyte-mediated diseases. It is possible to achieve selective depletion of B lymphocytes with rituximab, an anti-CD20 monoclonal antibody. This phase 2 study evaluated the role of B-lymphocyte depletion in patients with type 1 diabetes.

METHODS

We conducted a randomized, double-blind study in which 87 patients between 8 and 40 years of age who had newly diagnosed type 1 diabetes were assigned to receive infusions of rituximab or placebo on days 1, 8, 15, and 22 of the study. The primary outcome, assessed 1 year after the first infusion, was the geometric mean area under the curve (AUC) for the serum C-peptide level during the first 2 hours of a mixed-meal tolerance test. Secondary outcomes included safety and changes in the glycated hemoglobin level and insulin dose.

RESULTS

At 1 year, the mean AUC for the level of C peptide was significantly higher in the rituximab group than in the placebo group. The rituximab group also had significantly lower levels of glycated hemoglobin and required less insulin. Between 3 months and 12 months, the rate of decline in C-peptide levels in the rituximab group was significantly less than that in the placebo group. CD19+ B lymphocytes were depleted in patients in the rituximab group, but levels increased to 69% of baseline values at 12 months. More patients in the rituximab group than in the placebo group had adverse events, mostly grade 1 or grade 2, after the first infusion. The reactions appeared to be minimal with subsequent infusions. There was no increase in infections or neutropenia with rituximab.

CONCLUSIONS

A four-dose course of rituximab partially preserved beta-cell function over a period of 1 year in patients with type 1 diabetes. The finding that B lymphocytes contribute to the pathogenesis of type 1 diabetes may open a new pathway for exploration in the treatment of patients with this condition. (ClinicalTrials.gov number, NCT00279305.)

Calorie restriction (CR) is the only experimental manipulation that is known to extend the lifespan of a number of organisms including yeast, worms, flies, rodents and perhaps non-human primates. In addition, CR has been shown to reduce the incidence of age-related disorders (for example, diabetes, cancer and cardiovascular disorders) in mammals. The mechanisms through which this occurs have been unclear. CR induces metabolic changes, improves insulin sensitivity and alters neuroendocrine function in animals. In this review, we summarize recent findings that are beginning to clarify the mechanisms by which CR results in longevity and robust health, which might open new avenues of therapy for diseases of ageing.

The earliest defect in developing type 2 diabetes is insulin resistance, characterized by decreased glucose transport and metabolism in muscle and adipocytes. The glucose transporter GLUT4 mediates insulin-stimulated glucose uptake in adipocytes and muscle by rapidly moving from intracellular storage sites to the plasma membrane. In insulin-resistant states such as obesity and type 2 diabetes, GLUT4 expression is decreased in adipose tissue but preserved in muscle. Because skeletal muscle is the main site of insulin-stimulated glucose uptake, the role of adipose tissue GLUT4 downregulation in the pathogenesis of insulin resistance and diabetes is unclear. To determine the role of adipose GLUT4 in glucose homeostasis, we used Cre/loxP DNA recombination to generate mice with adipose-selective reduction of GLUT4 (G4A-/-). Here we show that these mice have normal growth and adipose mass despite markedly impaired insulin-stimulated glucose uptake in adipocytes. Although GLUT4 expression is preserved in muscle, these mice develop insulin resistance in muscle and liver, manifested by decreased biological responses and impaired activation of phosphoinositide-3-OH kinase. G4A-/- mice develop glucose intolerance and hyperinsulinaemia. Thus, downregulation of GLUT4 and glucose transport selectively in adipose tissue can cause insulin resistance and thereby increase the risk of developing diabetes.

A hallmark of Parkinson's disease (PD) is the preferential loss of substantia nigra dopamine neurons. Here, we identify a new parkin interacting substrate, PARIS (ZNF746), whose levels are regulated by the ubiquitin proteasome system via binding to and ubiquitination by the E3 ubiquitin ligase, parkin. PARIS is a KRAB and zinc finger protein that accumulates in models of parkin inactivation and in human PD brain. PARIS represses the expression of the transcriptional coactivator, PGC-1α and the PGC-1α target gene, NRF-1 by binding to insulin response sequences in the PGC-1α promoter. Conditional knockout of parkin in adult animals leads to progressive loss of dopamine (DA) neurons in a PARIS-dependent manner. Moreover, overexpression of PARIS leads to the selective loss of DA neurons in the substantia nigra, and this is reversed by either parkin or PGC-1α coexpression. The identification of PARIS provides a molecular mechanism for neurodegeneration due to parkin inactivation.

Glucotoxicity, lipotoxicity, and glucolipotoxicity are secondary phenomena that are proposed to play a role in all forms of type 2 diabetes. The underlying concept is that once the primary pathogenesis of diabetes is established, probably involving both genetic and environmental forces, hyperglycemia and very commonly hyperlipidemia ensue and thereafter exert additional damaging or toxic effects on the beta-cell. In addition to their contribution to the deterioration of beta-cell function after the onset of the disease, elevations of plasma fatty acid levels that often accompany insulin resistance may, as glucose levels begin to rise outside of the normal range, also play a pathogenic role in the early stages of the disease. Because hyperglycemia is a prerequisite for lipotoxicity to occur, the term glucolipotoxicity, rather than lipotoxicity, is more appropriate to describe deleterious effects of lipids on beta-cell function. In vitro and in vivo evidence supporting the concept of glucotoxicity is presented first, as well as a description of the underlying mechanisms with an emphasis on the role of oxidative stress. Second, we discuss the functional manifestations of glucolipotoxicity on insulin secretion, insulin gene expression, and beta-cell death, and the role of glucose in the mechanisms of glucolipotoxicity. Finally, we attempt to define the role of these phenomena in the natural history of beta-cell compensation, decompensation, and failure during the course of type 2 diabetes.

Evolutionary models of aging propose that a trade-off exists between the resources an organism devotes to reproduction and growth and those devoted to cellular maintenance and repair, such that an optimal life history always entails an imperfect ability to resist stress. Yet, since environmental stressors, such as caloric restriction or exposure to mild stress, can increase stress resistance and life span, it is possible that a common genetic mechanism could regulate the allocation of resources in response to a changing environment (for overview, see ). Consistent with predictions of evolutionary trade-off models, we show that nematodes carrying an integrated DAF-16::GFP transgene grow and reproduce more slowly yet are more stress resistant and longer lived than controls carrying the integration marker alone. We also show that the nuclear localization of the DAF-16::GFP fusion protein responds to environmental inputs as well as genetic. Environmental stresses, such as starvation, heat, and oxidative stress, cause rapid nuclear localization of DAF-16. In conditions rich in food, we find that DAF-16::GFP is inhibited from entry into the nucleus by daf-2 and akt-1/akt-2, both components of insulin-like signaling in nematodes. We suggest that changes in the subcellular localization of DAF-16 by environmental cues allows for rapid reallocation of resources in response to a changing environment at all stages of life.

Obesity is an epidemic disease that threatens to inundate health care resources by increasing the incidence of diabetes, heart disease, hypertension, and cancer. These effects of obesity result from two factors: the increased mass of adipose tissue and the increased secretion of pathogenetic products from enlarged fat cells. This concept of the pathogenesis of obesity as a disease allows an easy division of disadvantages of obesity into those produced by the mass of fat and those produced by the metabolic effects of fat cells. In the former category are the social disabilities resulting from the stigma associated with obesity, sleep apnea that results in part from increased parapharyngeal fat deposits, and osteoarthritis resulting from the wear and tear on joints from carrying an increased mass of fat. The second category includes the metabolic factors associated with distant effects of products released from enlarged fat cells. The insulin-resistant state that is so common in obesity probably reflects the effects of increased release of fatty acids from fat cells that are then stored in the liver or muscle. When the secretory capacity of the pancreas is overwhelmed by battling insulin resistance, diabetes develops. The strong association of increased fat, especially visceral fat, with diabetes makes this consequence particularly ominous for health care costs. The release of cytokines, particularly IL-6, from the fat cell may stimulate the proinflammatory state that characterizes obesity. The increased secretion of prothrombin activator inhibitor-1 from fat cells may play a role in the procoagulant state of obesity and, along with changes in endothelial function, may be responsible for the increased risk of cardiovascular disease and hypertension. For cancer, the production of estrogens by the enlarged stromal mass plays a role in the risk for breast cancer. Increased cytokine release may play a role in other forms of proliferative growth. The combined effect of these pathogenetic consequences of increased fat stores is an increased risk of shortened life expectancy.

The VFA, also known as short-chain fatty acids, are produced in the gastrointestinal tract by microbial fermentation of carbohydrates and endogenous substrates, such as mucus. This can be of great advantage to the animal, since no digestive enzymes exist for breaking down cellulose or other complex carbohydrates. The VFA are produced in the largest amounts in herbivorous animal species and especially in the forestomach of ruminants. The VFA, however, also are produced in the lower digestive tract of humans and all animal species, and intestinal fermentation resembles that occurring in the rumen. The principal VFA in either the rumen or large intestine are acetate, propionate, and butyrate and are produced in a ratio varying from approximately 75:15:10 to 40:40:20. Absorption of VFA at their site of production is rapid, and large quantities are metabolized by the ruminal or large intestinal epithelium before reaching the portal blood. Most of the butyrate is converted to ketone bodies or CO2 by the epithelial cells, and nearly all of the remainder is removed by the liver. Propionate is similarly removed by the liver but is largely converted to glucose. Although species differences exist, acetate is used principally by peripheral tissues, especially fat and muscle. Considerable energy is obtained from VFA in herbivorous species, and far more research has been conducted on ruminants than on other species. Significant VFA, however, are now known to be produced in omnivorous species, such as pigs and humans. Current estimates are that VFA contribute approximately 70% to the caloric requirements of ruminants, such as sheep and cattle, approximately 10% for humans, and approximately 20-30% for several other omnivorous or herbivorous animals. The amount of fiber in the diet undoubtedly affects the amount of VFA produced, and thus the contribution of VFA to the energy needs of the body could become considerably greater as the dietary fiber increases. Pigs and some species of monkey most closely resemble humans, and current research should be directed toward examining the fermentation processes and VFA metabolism in those species. In addition to the energetic or nutritional contributions of VFA to the body, the VFA may indirectly influence cholesterol synthesis and even help regulate insulin or glucagon secretion. In addition, VFA production and absorption have a very significant effect on epithelial cell growth, blood flow, and the normal secretory and absorptive functions of the large intestine, cecum, and rumen. The absorption of VFA and sodium, for example, seem to be interdependent, and release of bicarbonate usually occurs during VFA absorption.(ABSTRACT TRUNCATED AT 400 WORDS)

The objective of the present study was to develop a rat model that replicates the natural history and metabolic characteristics of human type 2 diabetes and is also suitable for pharmacological screening. Male Sprague-Dawley rats (160-180 g) were divided into two groups and fed with commercially available normal pellet diet (NPD) (12% calories as fat) or in-house prepared high-fat diet (HFD) (58% calories as fat), respectively, for a period of 2 weeks. The HFD-fed rats exhibited significant increase in body weight, basal plasma glucose (PGL), insulin (PI), triglycerides (PTG) and total cholesterol (PTC) levels as compared to NPD-fed control rats. Besides, the HFD rats showed significant reduction in glucose disappearance rate (K-value) on intravenous insulin glucose tolerance test (IVIGTT). Hyperinsulinemia together with reduced glucose disappearance rate (K-value) suggested that the feeding of HFD-induced insulin resistance in rats. After 2 weeks of dietary manipulation, a subset of the rats from both groups was injected intraperitoneally with low dose of streptozotocin (STZ) (35 mg kg(-1)). Insulin-resistant HFD-fed rats developed frank hyperglycemia upon STZ injection that, however, caused only mild elevation in PGL in NPD-fed rats. Though there was significant reduction in PI level after STZ injection in HFD rats, the reduction observed was only to a level that was comparable with NPD-fed control rats. In addition, the levels of PTG and PTC were further accentuated after STZ treatment in HFD-fed rats. In contrast, STZ (35 mg kg(-1), i.p.) failed to significantly alter PI, PTG and PTC levels in NPD-fed rats. Thus, these fat-fed/STZ-treated rats simulate natural disease progression and metabolic characteristics typical of individuals at increased risk of developing type 2 diabetes because of insulin resistance and obesity. Further, the fat-fed/STZ-treated rats were found to be sensitive for glucose lowering effects of insulin sensitizing (pioglitazone) as well as insulinotropic (glipizide) agents. Besides, the effect of pioglitazone and glipizide on the plasma lipid parameters (PTG and PTC) was shown in these diabetic rats. The present study represents that the combination of HFD-fed and low-dose STZ-treated rat serves as an alternative animal model for type 2 diabetes simulating the human syndrome that is also suitable for testing anti-diabetic agents for the treatment of type 2 diabetes.