‘Breakfast like a king, lunch like a prince, sup like a pauper’ is an old and well known proverb but a recently published study gives new insights into why following this advice might help to fight obesity and diabetes.

Researchers at ETH have suggested that eating snacks – even healthy ones – between meals leads to a vicious circle of physical inactivity and overeating, and could ultimately lead to diabetes. The team have identified a novel mechanism by which insulin regulates both metabolic and behavioural responses to food intake. Insulin produced by the pancreas as a result of feeding inhibits the forkhead box transcription factor, Foxa2. Foxa2 regulates fat metabolism in the liver but also influences neurons in the lateral hypothalamic area of the brain which is considered to be the classic ‘feeding centre’, controlling feeding, diurnal rhythm, sleep and sexual behaviour. In the fasted state, Foxa2 is active and promotes synthesis of melanin-concentrating hormone (MCH) and orexin, proteins with roles in controlling food intake and motivated behaviour. In obese mice, Foxa2 was found to be non-functional, regardless of whether the animals were fasted or fed. Genetically modified mice with permanently active Fox2a in their brains have more MCH and orexin, eat more and have increased insulin sensitivity. The levels of physical activity after feeding are also significantly higher, and more closely resemble those of fasted animals. Conditional activation of Foxa2 in the brains of obese mice also resulted in improved glucose homeostasis, decreased fat and increased lean body mass.

The authors suggest that periods of fasting are important to ensure correct body weight since each time food is consumed, Fox2a is suppressed which reduces the motivation for physical activity and, consequently, energy expenditure. Prevention of Foxa2 phosphorylation may lead to increased levels of physical activity and could be a potential pharmacological target for the treatment of obesity and diabetes.

The study is published in the journal Nature.

The link between diet and epigenetics in humans is notoriously difficult to study since people are, unsurprisingly, resistant to being fed a strictly controlled diet. Researchers at the Karolinska Institute have, however, shown that exposure to fatty acids can cause epigenetic modifications in muscle cells from healthy individuals that are the same as changes seen in people with type II diabetes.

Both hereditary and environmental factors are believed to play a role in the development of type II diabetes which is characterised by reduced sensitivity to insulin and a reduced ability to consume energy in the form of glucose. The team had previously shown that, in skeletal muscle cells from individuals with early-onset diabetes, the gene for PGC-1α (peroxisome proliferator-activated receptor-gamma coactivator 1α) is hypermethylated and shows reduced expression levels. PGC-1α is a promiscuous co-activator that plays a key role in regulating mitochondrial function and metabolism. In the present study, the team showed that DNA methylation occurs rapidly when cells from healthy individuals are exposed to factors linked to diabetes such as the fatty acid, palmitic acid, and the cytokine, TNF-α. It remains to be seen whether dietary factors substantially influence methylation of the gene for PGC-1α but the study suggests a mechanism whereby over-consumption of fatty foods could promote the development of type II diabetes. Since some epigenetic modifications are known to be inheritable, the study also raises the interesting question of whether the consequences of dietary excess can be visited on future generations.

The study is published in the journal Cell Metabolism.

The incretin, glucagon-like peptide-1 (GLP-1), is an intestinal hormone that stimulates production and release of insulin from pancreatic beta cells. Consequently there has been considerable interest in mimicking the activity of GLP-1 for treatment of metabolic disorders such as Type-II diabetes and obesity. There are currently two approved classes of drug that modulate GLP-1 activity: analogues of GLP-1 and inhibitors of dipeptidyl peptidase IV (DPPIV). Analogues of GLP-1, such as the 39-residue synthetic peptide, exenatide, activate the GLP-1 receptor but are resistant to proteolytic cleavage by DPPIV. The gliptins, such as sitagliptin, inhibit DPPIV, extending the half-life of the natural hormone.

Researchers at Ecole Polytechnique Fédérale de Lausanne, in collaboration with the University of Perugia and Intercept Pharmaceuticals, have now published data showing that stimulation of TGR5, a G-protein coupled receptor, leads to release of GLP-1 in obese mice. The same group had previously demonstrated that activation of TGR5 in brown adipose tissue and muscle by endogenous bile acids boosted energy expenditure and reversed diet-induced obesity in mice.

In the current work the researchers used a combination of genetic gain- and loss-of-function studies together with the TGR5 agonist, INT-777, to show the link between TGR5 signalling and GLP-1 secretion. In vitro experiments with INT-777 in enteroendocrine L-cells confirmed the induction of GLP-1 secretion and that this was linked to increased intracellular ATP/ADP ratio and a subsequent rise in intracellular calcium mobilization.

The study, published in the September 2^nd edition of Cell Metabolism, opens up a potential third route to modulation of GLP-1 activity and treatment of metabolic disorders.

The nuclear receptor, PPARγ, has hitherto been regarded as the master regulator of adipogenesis, without which new adipose tissue cannot be formed. Adipogenesis plays a key role in obesity and associated metabolic diseases such as type II diabetes and the thiazolidines, which target PPARγ are widely used to treat type II diabetes. Researchers at the University of Central Florida have now discovered, however, that monocyte chemotactic protein-1 (MCP-1)-induced protein (MCPIP), can trigger adipogenesis without involvement of PPARγ. The authors had previously shown that binding of MCP-1 to its receptor, CCR2, leads to induction of the Zn-finger protein, MCPIP. In the present study, MCP-1 was found to be produced, and MCPIP to be induced, before induction of PPARγ or other transcription factors in fibroblasts undergoing differentiation into adipocytes. Knockdown of MCPIP using siRNA was found to inhibit both gene induction and adipogenesis whereas treatment with MCP-1 or forced expression of MCPIP induced adipogenesis. Forced expression of MCPIP was also shown to induce adipogenesis in PPARγ-/- mouse embryonic fibroblasts, further demonstrating that MCPIP can act independently of PPARγ.

Obesity is well known to increase MCP-1 levels and the finding that MCPIP is able to induce adipogenesis without involvement of PPARγ provides new mechanistic evidence for the role of MCP-1/CCR2 in obesity and type II diabetes. Since there is experimental evidence that MCPIP promotes angiogenesis, MCP-1/CCR2 interaction could promote the formation of new blood vessels to supply blood to growing adipose tissue as well as promoting development of the adipocytes. A drug that could block the function of MCPIP may thus have the potential to treat obesity and type II diabetes.

The study is published in the online edition of Journal of Biological Chemistry.

The physiological role of aldose reductase (AR) is still incompletely understood, although it has long been associated with the pathogenesis of diabetes-associated diseases such as cataract and neuropathy. In the last twenty years a number of AR inhibitors have entered clinical trials for the potential treatment of diabetic neuropathy. Whilst the compounds have generally been well tolerated, efficacy has not been clearly established (although one compound, Epalrestat, is approved in Japan for treatment of subjective neuropathy symptoms associated with diabetic peripheral neuropathy).

The rationale for use of AR inhibitors in diabetic complications is based on the ability of AR to reduce glucose to sorbitol, levels of which are elevated in tissues of diabetic patients. Although glucose does not have high affinity for AR, the pathway is believed to be relevant in hyperglycaemia.

AR is also known to reduce lipid aldehydes and their glutathione conjugates in response to reactive oxygen species (ROS). The products of the AR-catalysed reduction mediate activation of NFκB and the subsequent generation of inflammatory proteins. This observation led researchers at University of Texas Medical Branch and Louisiana State University Health Sciences Center to hypothesise that AR inhibitors may be useful in inflammatory diseases such as asthma. In a study published in PLoSone, the scientists stimulated primary human small airway epithelial cells (SAEC) with ragweed pollen extract (RWE). In this in vitro experiment, AR inhibition prevented RWE-induced apoptosis and expression of inflammatory mediators. Further, AR inhibition prevented allergic airway inflammation in mice sensitised with endotoxin-free RWE.

The results encourage exploration of AR inhibitors in inflammatory diseases such as asthma.

Pancreatic cancer has one of the highest fatality rates of all cancers and is the fourth leading cause of cancer-related deaths in the United States; more than 35,000 people were estimated to have died from the disease in 2008. Patients diagnosed with pancreatic cancer typically have poor prognoses because the cancer is difficult to detect in its early stages – there are few symptoms and any that do present are vague and often go unnoticed. Although the exact causes of pancreatic cancer are not understood, the disease is more common in people with type 2 diabetes, although the reasons for this link are also unclear.

A recent study by researchers at the University of Texas M.D. Anderson Cancer Center has shown, however, that diabetics who have taken the anti-diabetic drug, metformin, alone or in combination with other drugs, have a 60% lower risk of developing pancreatic cancer compared with patients who have never taken it. Metformin is the most popular anti-diabetic drug in the United States and works primarily by suppressing glucose production by the liver and by increasing insulin sensitivity.

The study, which is published in the journal Gastroenterology, also suggested some increased risk of developing pancreatic cancer in patients who received insulin or insulin secretagogues, such as sulfonylureas and meglitinides. The study population was too small to determine the effects of another class of anti-diabetic drugs, the thiazolidinones.

The study evaluated prior use of antidiabetic drugs in just over 1800 people, 973 with pancreatic adenocarcinoma (including 259 diabetic patients) and 863 controls (including 109 diabetic patients). Use of metformin was found to be associated with a significantly decreased risk of pancreatic cancer compared with metformin non-use (adjusted odds ratio 0.38) whereas long-term insulin use was associated with a moderately higher risk of pancreatic cancer compared to insulin non-use (adjusted odds ratio 2.78). The association between pancreatic cancer and long term insulin use was, however, based on only 17 cases and 9 controls and needs to be investigated further in a larger study. The impact of insulin secretagogues on risk of pancreatic cancer likewise needs to be fully assessed in a larger study. Although it was not possible to gauge the effect of severity of diabetes or effectiveness of diabetes control on the results, the study does, however, show a robust protective effect of metformin, especially after long term use, against pancreatic cancer in people with type 2 diabetes.

In people with diabetes, damage to peripheral nerves and blood vessels means that wounds can initially go unnoticed, leading to infection, poor healing and, in extreme cases, the need for amputation. Globally, diabetes is one of the leading causes of lower limb amputation and foot problems are one of the most common reasons for hospitalisation of diabetic patients. One of the reasons for poor healing is that diabetic tissue fails to form new blood vessels to reconnect ischemic areas to a blood supply, and researchers at Stanford University School of Medicine and the Albert Einstein College of Medicine have been investigating the reasons for this.

They found that whereas normal fibroblasts – cells that play a critical role in wound healing – increase production of vascular endothelial growth factor (VEGF) in response to low oxygen levels, fibroblasts from diabetic patients did not increase production. They went on to grow healthy fibroblasts in either a low or high glucose environment for four weeks and then subjected the cells to low oxygen levels for 24 hours. The cells that had been growing in the high glucose environment increased VEGF production by only 20%, compared with 200% for the cells grown in the low glucose environment. Production of VEGF is triggered by hypoxia-inducible factor-1α (HIF-1α) acting in concert with the co-activator, p300, and the team further showed that HIF-1α- p300 binding was reduced by 50% in a high glucose environment. High glucose levels initiate a cascade of radical reactions leading to dysfunctional p300 and, since release of protein-bound iron is involved in this cascade, the team reasoned that treatment with an iron-chelating agent should interrupt the chain of reactions. They showed that deferoxamine was able to restore HIF-1α – p300 binding in cell culture experiments and, when they treated small wounds in diabetic mice with topical deferoxamine, the treated mice produced three times more VEGF than untreated animals and their wounds healed in 13 days compared with 23 days for the control group.

Deferoxamine is an iron chelating agent that is administered, usually intravenously, to treat acute iron poisoning, especially in small children. The researchers hope that they will soon be able to determine whether topical deferoxamine promotes healing of wounds in diabetic patients.

The report is published in the July 28^th early edition of PNAS.

Mast cells are best known for their role in allergic responses but a new study by researchers at Brigham and Women’s Hospital and colleagues has now shown a link with diet-induced obesity and type 2 diabetes. Writing in the July edition of Nature Medicine, they show that mast cells are far more abundant in white adipose tissue from obese humans and mice than in tissue from normal weight individuals.

In mice on a high calorie diet, treatment for two months with either of the allergy treatments, ketotifen fumarate or cromolyn, led to significant weight loss and improvement in diabetic markers compared with control animals. More dramatic improvements were seen if the animals were also switched to a reduced fat diet.

In further studies, the team showed that mice which lack mature mast cells neither became obese nor developed diabetes over a three month period, despite being fed a Western diet rich in sugars and fats. As a next step towards possible testing in humans, the researchers plan to study the effect of the compounds on obese and diabetic non-human primates.

Ketotifen fumarate and cromolyn are both used in anti-allergy eye drops, and to prevent asthma attacks. Although both stabilise mast cells, the exact mechanisms by which they achieve this are somewhat different.

During the development of type 2 diabetes, uptake of glucose from the blood by muscle and fat cells in response to insulin is reduced. The pathways involved in the insulin-stimulated uptake of glucose were believed to be similar in all mammals, but US scientists have now highlighted a key difference between mice and humans. Glucose is taken up by fat and muscle cells via the GLUT4 glucose transporter, thus removing glucose from the bloodstream. When blood glucose is low, the receptor is sequestered away from the cell surface and is released from the intracellular compartment in response to insulin stimulation when blood glucose rises. In type 2 diabetes, however, the GLUT4 compartment is abnormal and the transporter is not mobilised to the cell surface in response to insulin stimulation. The muscle isoform of clathrin heavy chain, CHC22, was found to be involved in formation of the intracellular GLUT 4 components in human muscle cells and adipocytes and was also found to be associated with the abnormal GLUT4 compartments in muscle cells from people with type 2 diabetes. Mice also have an insulin-responsive GLU4 compartment but lack the CHC22 protein – mice engineered to express CHC22 in fat and muscle tissue had defects in their GLUT4 transport pathway and showed features of diabetes, including high blood sugar and reduced responses to insulin. As well as suggesting that faulty vesicle trafficking, as well as problems with insulin signalling, may play a role in the development of type 2 diabetes, the study highlights the importance of being aware of differences between animals used in model studies and humans.

The study is published in the journal Science.

The increasing incidence of type I diabetes underlines the importance of securing affordable sources of insulin. The first insulins to be used therapeutically were extracted from the pancreases of pigs and cattle but, since the 1980s, most of the insulin used has the human sequence and is produced by genetically modified bacteria or yeasts. In December, SemBioSys Genetics Inc announced that it had begun a phase I//II clinical trial designed to demonstrate the bioequivalence of its SBS-1000 insulin and two commercially available insulins. The trial, involving up to 30 healthy volunteers and taking place in the UK, will compare both insulin concentrations and effects on blood glucose levels. SBS-1000 insulin is prepared from proinsulin produced by genetically modified safflower plants and has been shown to be physically, structurally and functionally indistinguishable from pharmaceutical-grade human insulin by analytical testing and in pre-clinical studies. The trial is the first in which insulin produced by plants has been administered to humans, and full results are expected to be available during the first half of 2009.

Some critics oppose the growing of genetically modified crops and believe that these pose a threat to livestock, wildlife and human health. If, however, the safflower-derived insulin is cheaper to purify – purification represents a significant proportion of the cost in manufacturing insulin by fermentation – the new technology could provide better access to insulin, especially for children in the developing world with type 1 diabetes.