Visualization of immune cell (lymphocyte) proliferation in the mesenteric lymph nodes, under the influence of a microbiota modulated by a high-fat diet. © Soraya Taleb/PARCC

Although a high-fat, low-fiber diet is recognized as promoting cardiovascular diseases such as atherosclerosis, the mechanisms involved have not yet been fully identified. Researchers from Inserm and Université Paris Cité have studied the role of the gut microbiota in the development of atherosclerosis. Their work in mice reveals that the low fiber content of the high-fat diet leads to an imbalance in the gut microbiota, which itself causes systemic inflammation, worsening the development of atherosclerotic plaques in the arteries. These findings, published in Cell Reports, provide further evidence of the importance of fiber in the diet, both for good bowel function and for preventing the onset of cardiovascular diseases.

Cardiovascular diseases constitute one of the leading causes of death worldwide. Among them, atherosclerosis is characterized by the formation of an atherosclerotic plaque (atheroma), composed mainly of lipids, on the walls of the arteries. Over time, these plaques can cause damage to the arterial wall, obstruct the vessel, or rupture – often with serious consequences. Among the major risk factors for atherosclerosis is obesity, particularly when caused by a diet that is too high in fat and low in fiber. As such, it is not just diet but also its impact on the gut microbiota that are now avenues of interest for research into cardiovascular diseases.

A team led by Soraya Taleb, Inserm research director at the Paris-Center for Cardiovascular Research (Inserm/Université Paris Cité), looked at the influence of a high-fat, low-fiber diet on the gut microbiota of mice and how this could contribute to the development of atherosclerosis.

The researchers used a mouse model of diet-induced atherosclerosis to compare the effects of several diets on the metabolism, microbiota and development of atherosclerosis.

Unsurprisingly, in the mice fed a high-fat, low-fiber diet, their findings show an increase in metabolic risk factors linked to cardiovascular diseases (significant weight gain, hyperglycemia, insulin resistance, increased weight of the liver and its triglyceride content, etc.).

However, these are not the only effects observed of this diet, which also appears to be associated with an overall imbalance in the microbiota – in its composition and immune response –, reflected in the altered production of metabolic derivatives by its component bacteria. In particular, short-chain fatty acids, derived from the fermentation of fiber and recognized for their positive impact on health, are produced in smaller quantities.

However, this imbalance itself appears to be associated not only with metabolic risk factors but also with a worsening of the manifestations of atherosclerosis at vascular level, with an increase in atheromatous plaque size in the aorta as well as a systemic inflammatory phenomenon which results in an increase in the number of immune cells in these plaques. However, supplementation with fiber made it possible to counteract these effects.

“These findings show, in mice fed a high-fat diet, that a pathological gut microbiota accelerates the development of atherosclerosis,” comments Taleb. Our observations also show that, more than its high fat content, it is the small amount of fiber in this diet that causes the microbiotal imbalance and as such the worsening of the atherosclerosis. This further supports the idea of the essential role of fiber in structuring a healthy microbiota and in preventing systemic inflammatory diseases such as cardiovascular diseases”, she continues.

But how can we explain the surprising link that appears between the composition of the microbiota and the accumulation of immune cells in atheromatous plaques? In mice grafted with a gut microbiota initially modulated by a high-fat diet, the research team observed an increased proliferation of immune cells in the mesenteric lymph nodes[1], the site of their activation in the gastrointestinal tract.

Techniques used to track migration of the immune cells confirmed that it was indeed cells from the mesenteric lymph nodes that, after passing from the gut into the bloodstream, accumulated in atheromatous plaques, thereby contributing to the development of atherosclerosis.

“The fact that we have seen that immune cells are capable of migrating from the gut to the periphery and thereby generate systemic inflammation that worsens the atheromatous plaques adds a new dimension to our understanding of the link between diet, gut, microbiota and atherosclerosis,” explains Taleb. Additional work is needed in order to identify which of the bacteria in the microbiota are involved in this mechanism, in order to envisage targeted therapeutic approaches and study these mechanisms in humans”, concludes the researcher.

 

[1] The mesenteric lymph nodes are located in the mesentery, a fold of the peritoneum (the membrane lining the abdominal cavity and covering the abdominal organs) that suspends the small intestine from the posterior abdominal wall.

The gelada (Theropithecus gelada) is one of the primate species without an appendix referenced in this research. ©Vallée des singes

Although the cecal appendix is no longer considered a vestige of evolution with no particular role, its exact function remains to be discovered and several hypotheses are currently being explored. A research team from Inserm, CNRS, the French National Museum of Natural History (MNHN), Université de Rennes, Sorbonne Université and the Eugène Marquis Center looked at how the presence of an appendix affects the onset and severity of infectious diarrhea in primates, an animal order that is particularly affected by these diseases. Its research shows that the primate species with an appendix are less affected by infectious diarrhea and that it is less severe than in those without an appendix. They are also better protected against these infections during the first part of their lives, a period that is more vulnerable to severe diarrhea and crucial for reproduction. These findings, published in Scientific Reports provide new evidence supporting the advantageous role of the appendix in evolution.

The cecal appendix (more commonly referred to as the “appendix”) is a small blind-ended tube located in the lower part of the cecum, the first part of the large intestine. It is found in some mammals and particularly in some primate species, including humans. While it has long been considered an unnecessary vestige of evolution, research over the past decade has challenged this paradigm with scientists now tending to view it as a potential evolutionary advantage, although its function remains poorly understood.

One hypothesis concerning the role of the appendix is based on its composition of microorganisms. Different from that of the rest of the gut microbiota, it could constitute a reservoir of healthy flora safeguarded from the fecal flow, likely to recolonize the gut after a gut infection and enable faster remission. And it just so happens that primates are an animal order particularly affected by infectious diarrhea. In humans, mortality related to these infections was identified in 2015 as being the second leading cause of mortality in children between 1 month and 5 years of age. More specifically, in patients who have had their appendix removed (appendectomy), there has been an increased risk of the occurrence and/or severity of certain forms of infectious diarrhea, although no direct link has been demonstrated at this time.

A research team led by Éric Ogier-Denis, Inserm research director at the Oncogenesis Stress Signaling unit Inserm/Université de Rennes/Eugène Marquis Center), and Michel Laurin, CNRS research director at the Center for Research on Paleontology – Paris (CNRS/MNHN/Sorbonne Université), had shown in previous research that the mammalian species with an appendix had longer longevity than those without one[1]. As a continuation of this research, the team looked at how the presence of a cecal appendix could affect the frequency and severity of diarrhea in primates and thus be a determining factor in the life span of each species.

To do this, the researchers examined the veterinary records of 1 251 primates of 45 different species – 13 with an appendix, 32 without – living in semi-liberty in “La Vallée des Singes” zoological park in Romagne, France. They listed the frequency and severity of the diarrhea episodes that occurred between 1998 and 2018 in these animals.

The gorilla (Gorilla gorilla gorilla) is one of the species of primates with an appendix referenced in this research. ©Vallée des singes

Half of the primates had experienced at least one episode of diarrhea during the 20-year follow-up period, with 13% of the episodes qualifying as “severe”.

In the primates with an appendix, the frequency of diarrhea episodes was very much lower (by around 85%) than in those without one. The cases of severe diarrhea were also much less frequent, particularly during the first quarter of life when the risk is highest (but then gradually decreases throughout life).

In addition, in the species with an appendix, the median age of onset of diarrhea, whether severe or not, was significantly higher.

“These findings support the hypothesis of a protective role of the cecal appendix against infectious diarrhea in primates, comments Jérémie Bardin, co-first author of the study. The observation of a particularly high protective effect in the first part of life, the period most vulnerable to severe diarrhea, but also the most optimal in terms of reproductive capacity, argues in favor of a selective advantage role in evolution”, adds Ogier-Denis.

The research should therefore be continued in order to gain deeper insights into the cecal appendix and a better understanding of the role of its specific flora. One of the next steps could be to compare the composition of the appendix microbiota between primate species in order to highlight possible similarities.

Finally, the last interesting observation in this study was that none of the primates with an appendix had been diagnosed with acute appendicitis over the 20-year period.

“Although this is more common in humans than in other primate species, if the protection associated with the presence of the appendix in humans is of the same level as that observed in primates, it would very much counterbalance the risk related to fatal appendicitis“, concludes Maxime Collard, co-first author of the study.

[1]See our August 3, 2021 press release: https://presse.inserm.fr/en/the-appendix-is-not-an-unnecessary-organ-but-is-in-fact-correlated-with-a-longer-lifespan/60347/

Cirrhosis is the final stage of fibrosis associated with chronic liver diseases. It affects 200,000 to 500,000 individuals in France and is responsible for 170,000 deaths per year in Europe. © Adobe Stock

Chronic liver diseases are characterized by persistent inflammation that contributes to their progression to more severe stages. They may progress to fibrosis and cirrhosis, and then require liver transplantation. Therefore, limiting the progression of fibrosis and bringing about its regression is a major therapeutic challenge. Several studies have recently suggested that one interesting approach could be to target the inflammatory response. In new research, scientists from Inserm and Université Paris-Cité at the Inflammation Research Center (CRI), in collaboration with teams from the Paris Public Hospitals Group (AP-HP)[1], have shown that blocking the activation of a particular population of T cells, the Mucosal-Associated Invariant T (MAIT) cells, could halt the progression of fibrosis and even bring about its regression. Targeting the MAIT cells involved in the inflammation seen in fibrosis and cirrhosis would therefore open up new avenues for better therapeutic care. This study has been published in Nature Communications.

Mainly alcoholic, viral, or metabolic in origin, cirrhosis is the last stage of fibrosis associated with chronic liver diseases. Cirrhosis affects between 200 000 and 500 000 people in France and is responsible for 170 000 deaths per year in Europe. Ultimately, it leads to liver failure for which the only cure is transplantation.

One characteristic of chronic liver diseases is persistent inflammation that contributes to their progression to more severe stages, particularly fibrosis and its final stage, cirrhosis. A better understanding of how to regulate this inflammatory response therefore constitutes a major challenge in developing new strategies to treat these diseases.

In 2018, the team of Inserm researcher Sophie Lotersztajn had shown that a population of T cells called MAIT promoted the progression of liver fibrosis. These immune cells are particularly abundant in the human liver and are involved in the inflammatory processes associated with fibrosis.

In their new study, the scientist and her colleagues worked on the basis of liver samples from cirrhotic patients as well as from mouse models of the disease.

They showed that the administration of a pharmacological agent to inhibit the activation of MAIT cells can limit liver inflammation and not only halt the progression of fibrosis, but also regress it.

It is now well known that other immune cells, such as the macrophages, play a central role in the progression and regression of fibrosis. Here, analysis of the mechanisms involved showed that blocking the activation of MAIT cells interrupts their dialog with profibrogenic macrophages, i.e. accelerators of fibrosis, and promotes the emergence of fibrosis-resolutive macrophages.

In the first image, the MAIT cells (in red, shown using arrows) are located near fibrogenic cells (in green) in the liver of cirrhotic patients. In the second image, the MAIT cells (in red) are activated (activation marker in green) in the liver of cirrhotic patients. This activation is blocked in the presence of a MAIT cell inhibitor. Credits: Sophie Lotersztajn

“Cirrhosis is a major public health problem. Even though the only treatment is liver transplantation, our research opens up other therapeutic avenues for targeting inflammation and halting or even regressing fibrosis. The research now needs to be continued, particularly in order to develop drug candidates that target and inhibit the MAIT cells,” concludes Lotersztajn.

[1] This research is the result of a collaboration between the team of Drs. Sophie Lotersztajn and Hélène Gilgenkrantz (Inflammation Research Center (CRI) Inserm-Université Paris Cité), the team of Dr. Valérie Paradis at the CRI (also Department of Pathology, Beaujon Hospital), Department of Anesthesiology and Critical Care (Prof. Emmanuel Weiss), the teams of Institut Curie (Dr. Olivier Lantz), Institut St Louis (Dr. Michèle Goodhardt) and Génosplice (Dr. Pierre de la Grange)

Liver cells invaded by lipid droplets (in white) from an animal on a diet rich in sugars and fats. © University Institute of Pathology of the University of Lausanne.

People with liver disease caused by eating too much sugar and fat could be at increased risk of developing serious neurological conditions like depression or dementia. In a study examining the link between non-alcoholic fatty liver disease (NAFLD) and brain dysfunction, scientists at the Roger Williams Institute of Hepatology, affiliated to King’s College London and the University of Lausanne, found an accumulation of fat in the liver causes a decrease in oxygen to the brain and inflammation to brain tissue – both of which have been proven to lead to the onset of severe brain diseases.

NAFLD affects approximately 25% of the population and more than 80% of morbidly obese people. Several studies have reported the negative effects of an unhealthy diet and obesity can have on brain function however this is believed to be the first study that clearly links NAFLD with brain deterioration and identifies a potential therapeutic target.

The research, conducted in collaboration with Inserm (the French National Institute of Health and Medical Research) and the University of Poitiers in France , involved feeding two different diets to mice. Half of the mice consumed a diet with no more than 10% fat in their calorie intake, while the other half’s calorie intake contained 55% fat; intended to resemble a diet of processed foods and sugary drinks.

After 16 weeks researchers conducted a series of tests to compare the effects of these diets on the body and more specifically, on the liver and the brain.

They found that all mice consuming the higher levels of fat were considered obese, and developed NAFLD, insulin resistance and brain dysfunction.

The study which was funded by the University of Lausanne and Foundation for Liver Research, published today in The Journal of Hepatology, also showed that the brain of mice with NAFLD suffered from lower oxygen levels. This is because the disease affects the number and thickness of the brain blood vessels, which deliver less oxygen to the tissue, but also due to specific cells consuming more oxygen while the brain is becoming inflamed. These mice were also more anxious and showed signs of depression.

By comparison, the mice consuming the healthy diet did not develop NAFLD or insulin resistance, they behaved normally, and their brain was completely healthy.

“It is very concerning to see the effect that fat accumulation in the liver can have on the brain, especially because it often starts off mild and can exist silently for many years without people knowing they have it,” said lead author Dr Anna Hadjihambi, sub-team lead in the Liver-Brain Axis group at the Roger Williams Institute of Hepatology and honorary lecturer at King’s College London.

To try and combat the dangerous effect that NAFLD has on the brain, the scientists bred mice with lower levels of a whole-body protein known as Monocarboxylate Transporter 1 (MCT1) – a protein specialised in the transport of energy substrates used by various cells for their normal function.

When these mice were fed the same unhealthy fat- and sugar-rich diet as those in the initial experiment, they had no fat accumulation in the liver and exhibited no sign of brain dysfunction – they were protected from both ailments.

“Identifying MCT1 as a key element in the development of both NAFLD and its associated brain dysfunction opens interesting perspectives,” said Professor Luc Pellerin, director of the Inserm U1313 research unit at the University of Poitiers in France and senior researcher in the study. “It highlights potential mechanisms at play within the liver-brain axis and points to a possible therapeutic target.”

Dr Hadjihambi added: “This research emphasises that cutting down the amount of sugar and fat in our diets is not only important for tackling obesity, but also for protecting the liver to maintain brain health and minimise the risk of developing conditions like depression and dementia during ageing, when our brain becomes even more fragile.“

The full paper is available to view online in The Journal of Hepatology.

Co-labeling of mouse skin expressing a PIK3CA gene mutation. © Marina Firpion/Guillaume Canaud – Inserm unit 1151

Disharmonious overgrowth syndromes are rare genetic diseases associated with a PIK3CA gene mutation. Since 2016, a team of researchers from Inserm, Paris Public Hospitals Group (AP-HP), Université de Paris, the Disharmonious Overgrowth and Vascular Abnormalities Unit of Institut Necker-Enfants Malades and the clinical departments of Hospices Civils of Lyon has demonstrated the therapeutic efficacy of alpelisib, a molecule used to fight certain cancers, in treating a group of children and adults with severe forms of these diseases. In a new publication, the team reports clinical, biological, and imaging improvements in two infants with severe forms of disharmonious overgrowth syndromes treated with alpelisib. These are the first data obtained on the use of this molecule in severe neonatal forms of the disease. The results of this one-year follow-up have been published in Journal of Experimental Medicine (JEM).

Disharmonious overgrowth syndromes are rare genetic diseases characterized by an increase in both the size and number of cells in the body. They manifest by an asymmetry that can affect any body part or tissue (fat, vessels, muscles, bones, etc.), including the brain. In 95% of cases, the disease is linked to a mutation, occurring during embryonic development, of the PIK3CA gene that regulates cell growth and proliferation.

When PIK3CA is overactivated, the parts of the body affected by the mutation grow excessively, leading to physical deformities that are more or less debilitating depending on the number of tissues affected. While some symptoms can be alleviated by surgery and other supportive care, there is currently no approved drug treatment for the disease.

In previous research, the drug alpelisib, a PIK3CA inhibitor recently approved for the treatment of certain forms of breast cancer1, had shown promising results – first in animal models of overgrowth syndrome, and then in a small number of adults and children. The drug is currently undergoing a series of larger-scale clinical trials, but until now there had been no data on its efficacy in infants.

In this new study, a team of researchers from Inserm, Paris Public Hospitals Group (AP-HP) and Université de Paris, coordinated by Professor Guillaume Canaud, reports encouraging results with alpelisib administered for one year to two infants – one girl and one boy aged 8 months and 9 months, respectively, at the start of treatment – presenting with a variety of severe symptoms caused by PIK3CA gene mutations. These symptoms included extreme blood vessel malformations, anemia, excessive asymmetric growth of the limbs and fingers and, in the boy, excessive growth of one of the brain hemispheres (hemimegaloencephaly) associated with epileptic seizures2. Before the start of treatment, the girl’s condition was life-threatening and the boy had a serious neurological prognosis, which did not respond to conventional epilepsy drugs.

Good tolerability

In both infants, daily oral doses of 25 mg alpelisib led to rapid and significant clinical improvement in the symptoms. Twelve months of treatment stopped the boy’s epileptic spasms and reduced the girl’s number of vascular malformations. The considerable decrease in the volume of her right leg has enabled her to remain upright and walk, with assistance. The anemia resolved in both children following initiation of the treatment.

The infants’ length and weight that initially were outside the norm for their age corrected themselves following the introduction of alpelisib. It is important to note that they had no side effects related to the treatment. Further analyses revealed that with a dose of 25 mg per day, their blood levels of alpelisib were much lower than those safely tolerated by adults3.

“The results of the alpelisib treatment in these two infants are encouraging because they show an improvement across all parameters, whether clinical, biological, or radiological. The high level of efficacy observed may be because alpelisib was started early. The patients had no history of surgery, which is relevant because we know that the remodeling caused by it can affect how well alpelisib is absorbed by the tissues. Furthermore, it is very likely that the plasticity of the tissues at this age enables the treatment to work better, explains Professor Canaud, coordinator of the study. These results should however be interpreted with caution and be confirmed over time and with further monitoring,” he says.

This use of alpelisib in overgrowth syndromes continues to be the subject of clinical trials in a population of consisting not just of adults but also of children from 6 years of age. These encouraging results make it possible to envisage extending the drug’s approval to include the clinical treatment of severe neonatal forms.

The treatment of these infants with alpelisib is provided as part of a compassionate use program, in which the French medicines agency (ANSM) issues exceptional approval to treat patients suffering from diseases with a severe prognosis and with no appropriate treatment available, in a given therapeutic indication.

1 The PIK3CA gene is frequently mutated in a certain number of cancers. This mutation is believed to occur in approximately 40% of breast cancers.

2 The boy had West syndrome, also known as infantile spasms, a rare form of epilepsy in infants.

3 When treating cancer, the daily dose of alpelisib administered to an adult (between 300 and 350 mg) is approximately 15 times higher.