A research team from Toulouse has just elucidated the mechanisms behind the differences in iron absorption between men and women. The team used mice to demonstrate how the action of testosterone can be “countered” with a drug already used in the treatment of some bronchial cancers.  The results are published this month in the Hepatology review.

The regulation of the iron metabolism differs between men and women. As a consequence, chronic liver diseases associated with a reduced hepcidin production capacity – a hormone that inhibits iron absorption by the duodenum – are often more severe in men than in women.

This is the case for hepatitis C, alcoholic liver disease and hereditary hemochromatosis.

With a view to better understanding the underlying mechanisms of this sexual dimorphism, Marie-Paule Roth and her co-workers at the Centre for Physiopathology in Purpan (Mixed Inserm/CNRS/Université Paul Sabatier Research Unit, Toulouse) have taken advantage of the major differences in hepcidin expression and iron overload observed in male and female mice with iron metabolism disorders.

The researchers showed that testosterone robustly represses hepcidin transcription in these mice since it activates the growth factor receivers in the liver (EGF). Yet, when these EGF receivers are inhibited in male mice by a drug used in the treatment of some bronchial cancers, testosterone-induced repression ceases.   Hepcidin production is then significantly increased. Castrating male mice leads to an increase in hepcidin production, as well as a very strong reduction in iron overload in the heart and pancreas of these mice.

To conclude, Marie-Paule Rothe and her team emphasise: “These results indicate that the testosterone-induced repression of hepcidin may have clinical repercussions for patients who, for different reasons, are only capable of producing hepcidin in limited quantities. Inhibiting the activation of EGF receivers in these patients could help them to produce more hepcidin, thus limiting iron overload that worsens the prognosis of chronic liver disease” they explain.

Patrick Collombat, Inserm Research Director and head of the Avenir team at the Institut de Biologie Valrose in Nice, has published new results concerning Type I diabetes. Researchers show that, in mice, the pancreas contains cells capable of being converted into insulin-producing β cells, something that can be done at any age. They also demonstrate that all pancreatic β cells can be regenerated several times and that chemically-induced diabetes in mice can thus be “treated” repeatedly. The challenge for the researchers is now to show that these procedures can be applied to humans.

This work is published online in the Developmental Cell journal dated 27 June 2013.

Type I diabetes, characterised by the selective loss of pancreatic, insulin-producing β cells, is a condition that affects more than 30 million people worldwide. Despite current treatments, type I diabetic patients have a life expectancy that is reduced by five to eight years. It is in this context that the Avenir “Diabetes Genetics” team have been working to develop new approaches designed to regenerate these cells.

In 2009, researchers at the Valrose Biology Institute (Inserm/University Nice Sophia Antipolis) managed to convert glucagon-producing α cells into β cells in young mice. Today, thanks to the use of transgenic mice, they report the mechanisms resulting in this exchange of cell identity. Specifically, they show that pancreatic ductal cells can be continuously mobilised and literally transformed into α and subsequently into β cells, a process that works at any age. Such transformation is obtained through the forced activation of the Pax4 gene in the α cells of the pancreas. The resulting cascade of events causes the generation of brand-new β cells, thanks to the reactivation of development genes. Throughout this process, α cells are regenerated and gradually adopt the profile of β cells. This means that the pancreas has a virtually inexhaustible source of cells capable of replacing the β cells.

β cell regeneration in the pancreas

© Patrick Collombat / Inserm

By artificially inducing type I diabetes in mice, 

“we also show that all the pancreatic β cells can be regenerated at least three times using this mechanism. Diabetes, induced in this way, in the mouse, can be literally “treated” multiple times thanks to the new stock of functional, insulin-producing β cells”

These promising results obtained in the mouse suggest that the pancreas contains cells that can regenerate several times those β cells lost in type I diabetics.

“We are currently working on the possibility of inducing such regeneration by using pharmacological molecules. Thanks to this new data, we shall be concentrating in future years on determining whether these processes can also be made to work in humans, a real challenge in offering better treatments for type I diabetic patients”, he concludes.

Certain food contaminants are suspected of triggering metabolic disorders, or of worsening them, particularly when they accompany a high-fat diet. In order to get a better understanding of these effects, researchers from the Inserm cardiovascular, metabolism, diabetology and nutrition unit (U1060 « Laboratoire de recherche en cardiovasculaire, métabolisme, diabétologie et nutrition » Inserm/Inra/Université Lyon 1) introduced a “cocktail” of contaminants mixed with low doses of dioxin, PCB, bisphenol A and phtalates into the feeding of mice that had already been rendered obese by a high-fat diet. The results show that metabolic changes occur in these mice, but that the effects differ depending on the gender. Females appeared to be more affected. Their obesity-induced glucose intolerance worsened and their estrogen pathway was altered.

These works have been published in the review Faseb Journal.

crédit : ©Fotolia

Obesity is a major public health problem because it is a risk factor in the development of metabolic complications (diabetes, cardiovascular diseases, etc.). It is a multi-factorial disorder. In addition to genetic predispositions and a life style that combines overeating with lack of exercise, there is a great volume of proof to suggest that contaminants, particularly in the food we eat, are responsible for the obesity epidemic and the resulting metabolic changes.

Researchers have put forward the hypothesis that contaminants in food could worsen certain metabolic problems already caused by eating an over-rich or a high-fat diet.

In this study, the researchers fed mice a high-fat diet (already a health risk), to which low doses of contaminants had been added. They were given this diet throughout their lives. Their mother had been nourished with this diet prior to their birth and during the gestation and lactation periods. Therefore, they suffered chronic exposure to this diet.

Two environmentally persistent contaminants[1] (dioxin and PCB) and two non-persistent contaminants[2] (phtalate and bisphenol A) were added to the high-fat (obesogenic) diet of the mice. The doses given were low, normally considered not to have any health impacts.  These products were chosen because they are present in human food and because they are known to trigger endocrine disruption. In parallel, a control group of mice was fed with the same obesogenic diet, but without added contaminants.

The researchers then ran glucose tolerance and insulin sensitivity tests. They measured the livers for lipid accumulation and the expression of certain genes that play key roles in the metabolism of the adult mice.

The results show that the effects are highly dependent on the gender of the animal.

Male and female: different effects

In the females fed with a high-fat diet, the addition of contaminants worsened the glucose intolerance and altered the estrogen pathway. In males, it altered the cholesterol and lipid metabolism. There was no change in weight between the exposed mice and the unexposed mice.

The researchers pursued the hypothesis that there was a connection between the observed glucose intolerance and the alteration in the estrogen signaling in exposed females. It is well known that estrogens protect against metabolic disorders. In other words, these works suggest that in obese females, exposure to food contaminants could lower the protection level that estrogens provide against metabolic disorders.

“With this study, we have succeeded in providing proof-of-concept that low doses of contaminants, even at levels normally considered to be without health impacts in humans, do in fact affect humans when subjected to chronic exposure, and when the contaminants are combined with a high-calorie diet” points out Brigitte Le Magueresse Battistoni.

This study was carried out as part of research programmes supported by the Institut Benjamin Delessert (2010), the ANSES (EST-2010/2/2007) and the EFSD (programme 2011) and by Brigitte Le Magueresse-Battistoni and Danielle Naville, 2 researchers who work for team 1 of the CarMeN Unit run by Hubert Vidal.

Are teeth the latest victims of bisphenol A? Yes, according to the conclusions of work carried out by the research team led by Ariane Berdal of the Université Paris-Diderot and Sylvie Babajko, Research Director at Inserm Unit 872 “Centre des Cordeliers”. The researchers have shown that the teeth of rats treated with low daily doses of BPA could be damaged by this. Analysis of the damage shows numerous characteristics that are common with a recently identified pathology of tooth enamel that affects roughly 18% of children between the ages of 6 and 8.

These results have been published in the American Journal of Pathology. 

Bisphenol A (BPA) is a chemical compound used in the composition of plastics and resins. It is used for example to manufacture food containers such as bottles or babies’ bottles. It is also used for the protective films inside drinks cans and food tins, or as developers on sales receipts. Significant amounts of BPA have also been found in human blood, urine, amniotic liquid and placentas. Recent studies have shown that this industrial compound has adverse effects on the reproduction, development and metabolism of laboratory animals. It is strongly suspected of having the same effects on humans.

As a precautionary measure, the manufacture and commercialisation of babies’ bottles containing bisphenol A were prohibited in Europe in January 2011. The prohibition will be extended to all food containers in France as from July 2015.

So this study shows that teeth are the latest in an already long list of victims of BPA.

The Inserm researchers have shown that the incisors of rats treated with low daily doses of BPA (5 microgrammes/kg/day) could be damaged by this.

Analysis of these teeth showed numerous characteristics that are common with a tooth enamel pathology known as MIH (Molar Incisor Hypomineralisation) that selectively affects first molars and permanent incisors. This enamel pathology is found in roughly 18% of children between the ages of 6 and 8. Children affected by this pathology present with teeth that are hypersensitive to pain and liable to cavities. It is interesting to note that the period during which these teeth are formed (the first years of life) correspond to the period during which humans are most sensitive to bisphenol A.

Amongst the earliest observations made was the appearance of “white marks” on the incisors of rats treated with endocrine disruptors, one of which was bisphenol A (BPA). The researchers decided to define the characteristics of incisors of rats treated with low doses of BPA and to compare these with the characteristics of teeth in humans suffering from MIH

Macroscopic observation of marks on both series of teeth showed similarities, in particular fragile and brittle enamel.

Microscope observation of the enamel showed a significant reduction of the Ca/P and the Ca/C ratios in affected teeth.  This leads to mineral depletion, making the teeth more fragile and more liable to cavities.

Finally, analysis of the proteins present in the tooth matrix of rats showed an increased quantity of enamelin, a key protein for enamel formation, and a buildup of albumin leading to hypomineralisation. Analysis of the expression of key enamel genes highlighted two BPA target genes: enamelin and kallicrein 4.

According to Sylvie Babajko, the latest author of this article, “Insofar as BPA has the same mechanism of action in rats as in men, it could also be a causal agent of MIH. Therefore, teeth could be used as early markers of exposure to endocrine disruptors acting in the same way as BPA and so could help in early detection of serious pathologies that would otherwise have occurred several years later”.

credit : ©Fotolia

Discovery in the rat reduces bleeding complications by 90% in the only treatment available for embolic stroke

Research performed by the Neurology Department and Stroke Reception and Treatment Unit at the Bichat Hospital (AP-HP/ Paris University Diderot) and the associated INSERM Unit 698 (Prof. Amarenco, Dr Olivier Meilhac) has highlighted the benefits of good cholesterol in reducing bleeding complications in the only treatment available for embolic stroke. The results of this experiment, performed on the rat, have just been published in Stroke .

As the third cause of death in France and throughout the world and the leading cause of disability acquired in adulthood, stroke currently affects 10 million people annually, 150,000 of them in France.

To date, the treatment of reference for stroke caused by occlusion of a cerebral artery that is recognised by the ANSM consists in performing an intravenous injection (in the crook of the elbow) of a medication known as Actilyse® (alteplase) the purpose of which is to dissolve the clot. This makes it possible to cure the patient in 40% of cases, but only if the injection is started within four and a half hours of the first stroke symptoms. An unfortunate complication of the intravenous injection of this medication, however, is a brain haemorrhage with neurological deterioration that leads to death in 6% of cases, though without visible neurological deterioration in 20% of cases.

Researchers have discovered a new treatment that may reduce the risk of the bleeding complication caused by alteplase by as much as 90%. The treatment consists of high-density lipoproteins  (HDL or “good cholesterol”), isolated from human plasma. HDLs are the particles whose job it is to evacuate the bad cholesterol from inside the arteries and send it to the liver, where it is eliminated. They have other favourable actions, in that they are anti-inflammatory, anti-oxidant and anti-protease, preventing the infiltration of white blood cells into the affected area.

The team has produced a hypothesis that, through the protective effect of the blood-brain barrier[1]¹, HDL can protect against the bleeding complications caused by alteplase. The team injected rats with alteplase three hours after blocking a brain artery using a filament or a clot. Bleeding occurred in 62% of the rats after the filament was withdrawn and in 46% of rats in which the brain artery was blocked by a clot. In both cases, when alteplase was injected jointly with HDLs, less than 90% fewer bleeding complications were observed. Both these models (occlusion using a filament or the creation of a clot) were used to check the effect of the treatment. The fact that the same type of result was obtained reinforces the evidence of the effect of HDLs.

“This discovery, if confirmed in humans through the clinical trial we intend to perform, could revolutionise stroke treatment and offer new opportunities for improving the cure for embolic stroke victims. It is even imaginable that in future, HDL-like particles could be produced through genetic engineering”, states Professor Amarenco, Head of the Neurology Department, Stroke Reception and Treatment Unit at theBichatHospital (AP-HP/University ofParis Diderot) and co-director with Professor Steg of the “Clinical Research into Atherothrombosis” Research Team at the Mixed INSERM-University of Paris Diderot Unit 698.

These studies were partly financed by the INSERM Unit 698 and partly by the Association SOS-Attaque Cerebrale, a stroke charity.

Photo : ©Fotolia

Liver and skeletal muscle resistance to the action of insulin is an early sign of the development of Type 2 Diabetes. The INSERM team at the “Obesity Research Laboratory ” in the Institut des Maladies Métaboliques and Cardiovasculaires (INSERM / Université Toulouse III – Paul Sabatier), headed by Dominique Langin, has shown through results published this week, that there is an association between lipolysis (mobilisation of fat in response to the body’s need for energy) and insulin sensitivity in humans. Researchers also showed that a reduction in lipolysis in mice, through genetic modification or pharmacological treatment, improved the action of insulin on glucose metabolism in the liver and the muscles. Lipolysis inhibition could be used in treating insulin resistance in the obese.

The results are accessible on the website of the Plos Biology journal for 19 February 2013.

Insulin is the hormone that controls the blood glucose level, inhibiting its production by the liver and stimulating its use in the muscles. When the body needs energy, during fasting or due to physical exercise, the triglycerides stored in the adipose tissue are released in the form of fatty acids through the action of adipocyte lipolysis. When this happens, the fatty acids have a favourable action because they are supplying energy.

These fatty acids may also have a deleterious action, however. When they are present in excessive quantities, as in the case of obesity, they are deposited in the peripheral organs and interfere with the action of insulin. Other lipids and proteins produced by an excess of adipose tissue are also involved in the development of insulin resistance. (Figure 1 opposite)

Figure 1 : Excess of fat mass and insulin resistance

© INSERM / Dominique Langin

Professeur Langin’s team at the Institut des Maladies Métaboliques and Cardiovasculaires (I2MC, Toulouse), (INSERM, Université Toulouse III – Paul Sabatier, Hôpitaux de Toulouse), in collaboration with other I2MC teams and researchers in Sweden at the Karolinska Institutet in Stockholm and Lund University, are seeking ways to treat insulin resistance, using a treatment strategy that avoids the onset of diabetes in the obese.

In this study, they showed that a reduction in adipocyte lipolysis through genetic modification or pharmacological treatment improves insulin sensitivity. An exploration of the mechanisms involved showed that the reduction in lipolysis causes a reduction in the flow of fatty acids within the organism and is accompanied by an improvement in insulin action on glucose metabolism in the liver and muscles.

“We discovered the effects of lipolysis reduction in humans through analysing data from cohorts of obese people in whom we reported that a reduction in lipolysis was associated with an improvement in insulin sensitivity. These results are all the more interesting in that they introduce a treatment strategy in which lipolysis inhibition does not involve any change to body weight”, explains Dominique Langin.

This study also showed quite unexpectedly that when lipolysis was reduced in mice, a special metabolic pathway, known as de novo lipogenesis, was activated enabling the synthesis of fatty acids directly from glucose (Figure 2 below). In Spring, 2012, a team from Harvard University, United States, suggested that the activation of de novo lipogenesis in adipose cells reduced resistance to the action of insulin. A clinical trial performed by Professor Langin’s team at the Centre d’Investigation Clinique INSERM-CHU de Toulouse also shows that chronic treatment with an anti-lipolytic molecule induced an increase in the expression of de novo lipogenesis genes in the adipocyte.

Figure 2 : Inhibition of the mobilisation of fat (lipolysis)  through the adipose cell reduces insulin resistance by increasing lipogenesis de novo.

© INSERM / Dominique Langin

Researchers are now attempting to identify the mediators produced by the adipose cell participating in the improvement of insulin action, as well as demonstrating the important of this treatment strategy in pre-diabetic obese patients.