Toxicological safety evaluation of pasteurized Akkermansia muciniphila

Gut microorganisms are vital for many aspects of human health, and the commensal bacterium Akkermansia muciniphila has repeatedly been identified as a key component of intestinal microbiota. Reductions in A. muciniphila abundance are associated with increased prevalence of metabolic disorders such as obesity and type 2 diabetes. It was recently discovered that administration of A. muciniphila has beneficial effects and that these are not diminished, but rather enhanced after pasteurization. Pasteurized A. muciniphila is proposed for use as a food ingredient, and was therefore subjected to a nonclinical safety assessment, comprising genotoxicity assays (bacterial reverse mutation and in vitro mammalian cell micronucleus tests) and a 90-day toxicity study. For the latter, Han Wistar rats were administered with the vehicle or pasteurized A. muciniphila at doses of 75, 375 or 1500 mg/kg body weight/day (equivalent to 4.8 × 10⁹ , 2.4 × 10¹⁰ , or 9.6 × 10¹⁰ A. muciniphila cells/kg body weight/day) by oral gavage for 90 consecutive days. The study assessed potential effects on clinical observations (including detailed arena observations and a modified Irwin test), body weight, food and water consumption, clinical pathology, organ weights, and macroscopic and microscopic pathology. The results of both in vitro genotoxicity studies were negative. No test item-related adverse effects were observed in the 90-day study; therefore, 1500 mg/kg body weight/day (the highest dose tested, equivalent to 9.6 × 10¹⁰ A. muciniphila cells/kg body weight/day) was established as the no-observed-adverse-effect-level. These results support that pasteurized A. muciniphila is safe for use as a food ingredient.

Pasteurized Akkermansia muciniphila protects from fat mass gain but not from bone loss

Probiotic bacteria can protect from ovariectomy (ovx)-induced bone loss in mice. Akkermansia muciniphila is considered to have probiotic potential due to its beneficial effect on obesity and insulin resistance. The purpose of the present study was to determine if treatment with pasteurized Akkermansia muciniphila (pAkk) could prevent ovx-induced bone loss. Mice were treated with vehicle or pAkk for 4 wk, starting 3 days before ovx or sham surgery. Treatment with pAkk reduced fat mass accumulation confirming earlier findings. However, treatment with pAkk decreased trabecular and cortical bone mass in femur and vertebra of gonadal intact mice and did not protect from ovx-induced bone loss. Treatment with pAkk increased serum parathyroid hormone (PTH) levels and increased expression of the calcium transporter Trpv5 in kidney suggesting increased reabsorption of calcium in the kidneys. Serum amyloid A 3 (SAA3) can suppress bone formation and mediate the effects of PTH on bone resorption and bone loss in mice and treatment with pAkk increased serum levels of SAA3 and gene expression of Saa3 in colon. Moreover, regulatory T cells can be protective of bone and pAkk-treated mice had decreased number of regulatory T cells in mesenteric lymph nodes and bone marrow. In conclusion, treatment with pAkk protected from ovx-induced fat mass gain but not from bone loss and reduced bone mass in gonadal intact mice. Our findings with pAkk differ from some probiotics that have been shown to protect bone mass, demonstrating that not all prebiotic and probiotic factors have the same effect on bone.

Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study

Metabolic syndrome is characterized by a constellation of comorbidities that predispose individuals to an increased risk of developing cardiovascular pathologies as well as type 2 diabetes mellitus (T2DM)¹. The gut microbiota is considered as a new key contributor involved in the onset of obesity-related disorders². In humans, studies have provided evidence for a negative correlation between Akkermansia muciniphila abundance and overweight, obesity, untreated T2DM, or hypertension^3–8. As the administration of A.muciniphila has never been investigated in humans, we conducted a randomized double-blind placebo-controlled pilot study in overweight/obese insulin resistant volunteers, 40 were enroled and 32 completed the trial. The primary endpoints were on safety, tolerability and metabolic parameters (i.e., insulin resistance, circulating lipids, visceral adiposity, body mass). The secondary outcomes were the gut barrier function (i.e., plasma lipopolysacharrides (LPS) and gut microbiota composition. In this single-center study, we demonstrated that daily oral supplementation of 10¹⁰ bacteria either alive or pasteurized A.muciniphila for 3 months was safe and well tolerated. Compared to the Placebo, pasteurized A.muciniphila improved insulin sensitivity (+28.62±7.02%, P=0.002), reduced insulinemia (-34.08±7.12%, P=0.006) and plasma total cholesterol (-8.68±2.38%, P=0.02). Pasteurized A.muciniphila supplementation slightly decreased body weight (-2.27±0.92kg, P=0.091) as compared to the Placebo group, and fat mass (-1.37±0.82kg, P=0.092) and hip circumference (-2.63±1.14cm, P = 0.091) as compared to baseline. After 3 months of supplementation, A.muciniphila reduced the levels of relevant blood markers of liver dysfunction and inflammation while the overall gut microbiome structure was unaffected. In conclusion, this proof-of-concept study (NCT02637115) shows that the intervention was safe and well-tolerated and that the supplementation with A.muciniphila improves several metabolic paramaters.

Akkermansia muciniphila induces gut microbiota remodelling and controls islet autoimmunity in NOD mice

OBJECTIVE

Intestinal microbiota is implicated in the pathogenesis of autoimmune type 1 diabetes in humans and in non-obese diabetic (NOD) mice, but evidence on its causality and on the role of individual microbiota members is limited. We investigated if different diabetes incidence in two NOD colonies was due to microbiota differences and aimed to identify individual microbiota members with potential significance.

DESIGN

We profiled intestinal microbiota between two NOD mouse colonies showing high or low diabetes incidence by 16S ribosomal RNA gene sequencing and colonised the high-incidence colony with the microbiota of the low-incidence colony. Based on unaltered incidence, we identified a few taxa which were not effectively transferred and thereafter, transferred experimentally one of these to test its potential significance.

RESULTS

Although the high-incidence colony adopted most microbial taxa present in the low-incidence colony, diabetes incidence remained unaltered. Among the few taxa which were not transferred, Akkermansia muciniphila was identified. As A. muciniphila abundancy is inversely correlated to the risk of developing type 1 diabetes-related autoantibodies, we transferred A. muciniphila experimentally to the high-incidence colony. A. muciniphila transfer promoted mucus production and increased expression of antimicrobial peptide Reg3γ, outcompeted Ruminococcus torques from the microbiota, lowered serum endotoxin levels and islet toll-like receptor expression, promoted regulatory immunity and delayed diabetes development.

CONCLUSION

Transfer of the whole microbiota may not reduce diabetes incidence despite a major change in gut microbiota, but single symbionts such as A. muciniphila with beneficial metabolic and immune signalling effects may reduce diabetes incidence when administered as a probiotic.

The impact of human activities and lifestyles on the interlinked microbiota and health of humans and of ecosystems

Plants, animals and humans, are colonized by microorganisms (microbiota) and transiently exposed to countless others. The microbiota affects the development and function of essentially all organ systems, and contributes to adaptation and evolution, while protecting against pathogenic microorganisms and toxins. Genetics and lifestyle factors, including diet, antibiotics and other drugs, and exposure to the natural environment, affect the composition of the microbiota, which influences host health through modulation of interrelated physiological systems. These include immune system development and regulation, metabolic and endocrine pathways, brain function and epigenetic modification of the genome. Importantly, parental microbiotas have transgenerational impacts on the health of progeny. Humans, animals and plants share similar relationships with microbes. Research paradigms from humans and other mammals, amphibians, insects, planktonic crustaceans and plants demonstrate the influence of environmental microbial ecosystems on the microbiota and health of organisms, and indicate links between environmental and internal microbial diversity and good health. Therefore, overlapping compositions, and interconnected roles of microbes in human, animal and plant health should be considered within the broader context of terrestrial and aquatic microbial ecosystems that are challenged by the human lifestyle and by agricultural and industrial activities. Here, we propose research priorities and organizational, educational and administrative measures that will help to identify safe microbe-associated health-promoting modalities and practices. In the spirit of an expanding version of "One health" that includes environmental health and its relation to human cultures and habits (EcoHealth), we urge that the lifestyle-microbiota-human health nexus be taken into account in societal decision making.

Increased gut permeability in cancer cachexia: mechanisms and clinical relevance

Intestinal disorders often occur in cancer patients, in association with body weight loss, and this alteration is commonly attributed to the chemotherapy. Here, using a mouse model of cancer cachexia induced by ectopic transplantation of C26 cancer cells, we discovered a profound alteration in the gut functions (gut permeability, epithelial turnover, gut immunity, microbial dysbiosis) independently of any chemotherapy. These alterations occurred independently of anorexia and were driven by interleukin 6. Gut dysfunction was found to be resistant to treatments with an anti-inflammatory bacterium (Faecalibacterium prausnitzii) or with gut peptides involved in intestinal cell renewal (teduglutide, a glucagon-like peptide 2 analogue). The translational value of our findings was evaluated in 152 colorectal and lung cancer patients with or without cachexia. The serum level of the lipopolysaccharide-binding protein, often presented as a reflection of the bacterial antigen load, was not only increased in cachectic mice and cancer patients, but also strongly correlated with the serum IL-6 level and predictive of death and cachexia occurrence in these patients. Altogether, our data highlight profound alterations of the intestinal homeostasis in cancer cachexia occurring independently of any chemotherapy and food intake reduction, with potential relevance in humans. In addition, we point out the lipopolysaccharide-binding protein as a new biomarker of cancer cachexia related to gut dysbiosis.

Reduced obesity, diabetes, and steatosis upon cinnamon and grape pomace are associated with changes in gut microbiota and markers of gut barrier

Increasing evidence suggests that polyphenols have a significant potential in the prevention and treatment of risk factors associated with metabolic syndrome. The objective of this study was to assess the metabolic outcomes of two polyphenol-containing extracts from cinnamon bark (CBE) and grape pomace (GPE) on C57BL/6J mice fed a high-fat diet (HFD) for 8 wk. Both CBE and GPE were able to decrease fat mass gain and adipose tissue inflammation in mice fed a HFD without reducing food intake. This was associated with reduced liver steatosis and lower plasma nonesterified fatty acid levels. We also observed a beneficial effect on glucose homeostasis, as evidenced by an improved glucose tolerance and a lower insulin resistance index. These ameliorations of the overall metabolic profile were associated with a significant impact on the microbial composition, which was more profound for the GPE than for the CBE. At the genus level, Peptococcus were decreased in the CBE group. In the GPE-treated group, several key genera that have been previously found to be linked with HFD, metabolic effects, and gut barrier integrity were affected: we observed a decrease of Desulfovibrio, Lactococcus, whereas Allobaculum and Roseburia were increased. In addition, the expression of several antimicrobial peptides and tight junction proteins was increased in response to both CBE and GPE supplementation, indicating an improvement of the gut barrier function. Collectively, these data suggest that CBE and GPE can ameliorate the overall metabolic profile of mice on a high-fat diet, partly by acting on the gut microbiota.

Targeting the gut microbiota with inulin-type fructans: preclinical demonstration of a novel approach in the management of endothelial dysfunction

OBJECTIVE

To investigate the beneficial role of prebiotics on endothelial dysfunction, an early key marker of cardiovascular diseases, in an original mouse model linking steatosis and endothelial dysfunction.

DESIGN

We examined the contribution of the gut microbiota to vascular dysfunction observed in apolipoprotein E knockout (Apoe^-/-) mice fed an n-3 polyunsaturated fatty acid (PUFA)-depleted diet for 12 weeks with or without inulin-type fructans (ITFs) supplementation for the last 15 days. Mesenteric and carotid arteries were isolated to evaluate endothelium-dependent relaxation ex vivo. Caecal microbiota composition (Illumina Sequencing of the 16S rRNA gene) and key pathways/mediators involved in the control of vascular function, including bile acid (BA) profiling, gut and liver key gene expression, nitric oxide and gut hormones production were also assessed.

RESULTS

ITF supplementation totally reverses endothelial dysfunction in mesenteric and carotid arteries of n-3 PUFA-depleted Apoe^-/- mice via activation of the nitric oxide (NO) synthase/NO pathway. Gut microbiota changes induced by prebiotic treatment consist in increased NO-producing bacteria, replenishment of abundance in Akkermansia and decreased abundance in bacterial taxa involved in secondary BA synthesis. Changes in gut and liver gene expression also occur upon ITFs suggesting increased glucagon-like peptide 1 production and BA turnover as drivers of endothelium function preservation.

CONCLUSIONS

We demonstrate for the first time that ITF improve endothelial dysfunction, implicating a short-term adaptation of both gut microbiota and key gut peptides. If confirmed in humans, prebiotics could be proposed as a novel approach in the prevention of metabolic disorders-related cardiovascular diseases.

Erythritol Availability in Bovine, Murine and Human Models Highlights a Potential Role for the Host Aldose Reductase during Brucella Infection

Erythritol is the preferential carbon source for most brucellae, a group of facultative intracellular bacteria that cause a worldwide zoonosis. Since this polyol is abundant in genital organs of ruminants and swine, it is widely accepted that erythritol accounts at least in part for the characteristic genital tropism of brucellae. Nevertheless, proof of erythritol availability and essentiality during Brucella intracellular multiplication has remained elusive. To investigate this relationship, we compared ΔeryH (erythritol-sensitive and thus predicted to be attenuated if erythritol is present), ΔeryA (erythritol-tolerant but showing reduced growth if erythritol is a crucial nutrient) and wild type B. abortus in various infection models. This reporting system indicated that erythritol was available but not required for B. abortus multiplication in bovine trophoblasts. However, mice and humans have been considered to lack erythritol, and we found that it was available but not required for B. abortus multiplication in human and murine trophoblastic and macrophage-like cells, and in mouse spleen and conceptus (fetus, placenta and envelopes). Using this animal model, we found that B. abortus infected cells and tissues contained aldose reductase, an enzyme that can account for the production of erythritol from pentose cycle precursors.

Brucella central carbon metabolism: an update

The brucellae are facultative intracellular pathogens causing brucellosis, an important zoonosis. Here, we review the nutritional, genetic, proteomic and transcriptomic studies on Brucella carbon uptake and central metabolism, information that is needed for a better understanding of Brucella virulence. There is no uniform picture across species but the studies suggest primary and/or secondary transporters for unknown carbohydrates, lactate, glycerol phosphate, erythritol, xylose, ribose, glucose and glucose/galactose, and routes for their incorporation to central metabolism, including an erythritol pathway feeding the pentose phosphate cycle. Significantly, all brucellae lack phosphoenolpyruvate synthase and phosphofructokinase genes, which confirms previous evidence on glycolysis absence, but carry all Entner-Doudoroff (ED) pathway and Krebs cycle (and glyoxylate pathway) genes. However, glucose catabolism proceeds through the pentose phosphate cycle in the classical species, and the ED pathway operates in some rodent-associated brucellae, suggesting an ancestral character for this pathway in this group. Gluconeogenesis is functional but does not rely exclusively on classical fructose bisphosphatases. Evidence obtained using infection models is fragmentary but suggests the combined or sequential use of hexoses/pentoses, amino acids and gluconeogenic substrates. We also discuss the role of the phosphotransferase system, stringent reponse, quorum sensing, BvrR/S and sRNAs in metabolism control, an essential aspect of the life style of facultative intracellular parasites.

Hepatocyte MyD88 affects bile acids, gut microbiota and metabolome contributing to regulate glucose and lipid metabolism

OBJECTIVE

To examine the role of hepatocyte myeloid differentiation primary-response gene 88 (MyD88) on glucose and lipid metabolism.

DESIGN

To study the impact of the innate immune system at the level of the hepatocyte and metabolism, we generated mice harbouring hepatocyte-specific deletion of MyD88. We investigated the impact of the deletion on metabolism by feeding mice with a normal control diet or a high-fat diet for 8 weeks. We evaluated body weight, fat mass gain (using time-domain nuclear magnetic resonance), glucose metabolism and energy homeostasis (using metabolic chambers). We performed microarrays and quantitative PCRs in the liver. In addition, we investigated the gut microbiota composition, bile acid profile and both liver and plasma metabolome. We analysed the expression pattern of genes in the liver of obese humans developing non-alcoholic steatohepatitis (NASH).

RESULTS

Hepatocyte-specific deletion of MyD88 predisposes to glucose intolerance, inflammation and hepatic insulin resistance independently of body weight and adiposity. These phenotypic differences were partially attributed to differences in gene expression, transcriptional factor activity (ie, peroxisome proliferator activator receptor-α, farnesoid X receptor (FXR), liver X receptors and STAT3) and bile acid profiles involved in glucose, lipid metabolism and inflammation. In addition to these alterations, the genetic deletion of MyD88 in hepatocytes changes the gut microbiota composition and their metabolomes, resembling those observed during diet-induced obesity. Finally, obese humans with NASH displayed a decreased expression of different cytochromes P450 involved in bioactive lipid synthesis.

CONCLUSIONS

Our study identifies a new link between innate immunity and hepatic synthesis of bile acids and bioactive lipids. This dialogue appears to be involved in the susceptibility to alterations associated with obesity such as type 2 diabetes and NASH, both in mice and humans.

Enteroendocrine Cells: Metabolic Relays between Microbes and Their Host

Gut bacteria exert a variety of metabolic functions unavailable to the host and are increasingly seen as a virtual organ located inside our gastrointestinal tract. Scattered in our intestinal epithelium, enteroendocrine cells (EECs) regulate several aspects of the host's physiology and translate signals coming from the gut microbiota through their hormonal secretions. In this chapter, we will assess the interplay between the gut microbiota and EEC and its consequences for the physiology of the host. We will first describe alterations of different populations of EEC in germ-free animals. The role of mediators of this interaction, such as microbial metabolites and their receptors will also be discussed. Finally, different strategies harnessing host-microbe crosstalk for therapeutic purposes will be presented with an emphasis on obesity and related disorders.

Endocannabinoids--at the crossroads between the gut microbiota and host metabolism

Various metabolic disorders are associated with changes in inflammatory tone. Among the latest advances in the metabolism field, the discovery that gut microorganisms have a major role in host metabolism has revealed the possibility of a plethora of associations between gut bacteria and numerous diseases. However, to date, few mechanisms have been clearly established. Accumulating evidence indicates that the endocannabinoid system and related bioactive lipids strongly contribute to several physiological processes and are a characteristic of obesity, type 2 diabetes mellitus and inflammation. In this Review, we briefly define the gut microbiota as well as the endocannabinoid system and associated bioactive lipids. We discuss existing literature regarding interactions between gut microorganisms and the endocannabinoid system, focusing specifically on the triad of adipose tissue, gut bacteria and the endocannabinoid system in the context of obesity and the development of fat mass. We highlight gut-barrier function by discussing the role of specific factors considered to be putative 'gate keepers' or 'gate openers', and their role in the gut microbiota-endocannabinoid system axis. Finally, we briefly discuss data related to the different pharmacological strategies currently used to target the endocannabinoid system, in the context of cardiometabolic disorders and intestinal inflammation.

Adipose tissue NAPE-PLD controls fat mass development by altering the browning process and gut microbiota

Obesity is a pandemic disease associated with many metabolic alterations and involves several organs and systems. The endocannabinoid system (ECS) appears to be a key regulator of energy homeostasis and metabolism. Here we show that specific deletion of the ECS synthesizing enzyme, NAPE-PLD, in adipocytes induces obesity, glucose intolerance, adipose tissue inflammation and altered lipid metabolism. We report that Napepld-deleted mice present an altered browning programme and are less responsive to cold-induced browning, highlighting the essential role of NAPE-PLD in regulating energy homeostasis and metabolism in the physiological state. Our results indicate that these alterations are mediated by a shift in gut microbiota composition that can partially transfer the phenotype to germ-free mice. Together, our findings uncover a role of adipose tissue NAPE-PLD on whole-body metabolism and provide support for targeting NAPE-PLD-derived bioactive lipids to treat obesity and related metabolic disorders.

Endocannabinoids are bioactive lipid molecules produced in the body. Here, Geurts et al. create mice lacking the endocannabinoid-producing enzyme NAPE-PLD in adipocytes and report defects in adipose-induced browning, which are mediated by alterations in the gut microbiome.

Microbial modulation of energy availability in the colon regulates intestinal transit

Gut microbiota contribute to host metabolic efficiency by increasing energy availability through the fermentation of dietary fiber and production of short-chain fatty acids (SCFAs) in the colon. SCFAs are proposed to stimulate secretion of the proglucagon (Gcg)-derived incretin hormone GLP-1, which stimulates insulin secretion (incretin response) and inhibits gastric emptying. We find that germ-free (GF) and antibiotic-treated mice, which have severely reduced SCFA levels, have increased basal GLP-1 levels in the plasma and increased Gcg expression in the colon. Increasing energy supply, either through colonization with polysaccharide-fermenting bacteria or through diet, suppressed colonic Gcg expression in GF mice. Increased GLP-1 levels in GF mice did not improve the incretin response but instead slowed intestinal transit. Thus, microbiota regulate the basal levels of GLP-1, and increasing these levels may be an adaptive response to insufficient energy availability in the colon that slows intestinal transit and allows for greater nutrient absorption.

Glucose metabolism: focus on gut microbiota, the endocannabinoid system and beyond

The gut microbiota is now considered as a key factor in the regulation of numerous metabolic pathways. Growing evidence suggests that cross-talk between gut bacteria and host is achieved through specific metabolites (such as short-chain fatty acids) and molecular patterns of microbial membranes (lipopolysaccharides) that activate host cell receptors (such as toll-like receptors and G-protein-coupled receptors). The endocannabinoid (eCB) system is an important target in the context of obesity, type 2 diabetes (T2D) and inflammation. It has been demonstrated that eCB system activity is involved in the control of glucose and energy metabolism, and can be tuned up or down by specific gut microbes (for example, Akkermansia muciniphila). Numerous studies have also shown that the composition of the gut microbiota differs between obese and/or T2D individuals and those who are lean and non-diabetic. Although some shared taxa are often cited, there is still no clear consensus on the precise microbial composition that triggers metabolic disorders, and causality between specific microbes and the development of such diseases is yet to be proven in humans. Nevertheless, gastric bypass is most likely the most efficient procedure for reducing body weight and treating T2D. Interestingly, several reports have shown that the gut microbiota is profoundly affected by the procedure. It has been suggested that the consistent postoperative increase in certain bacterial groups such as Proteobacteria, Bacteroidetes and Verrucomicrobia (A. muciniphila) may explain its beneficial impact in gnotobiotic mice. Taken together, these data suggest that specific gut microbes modulate important host biological systems that contribute to the control of energy homoeostasis, glucose metabolism and inflammation in obesity and T2D.