Functional interactions between the gut microbiota and host metabolism

Ketone body metabolism and cardiovascular disease

Ketone bodies are metabolized through evolutionarily conserved pathways that support bioenergetic homeostasis, particularly in brain, heart, and skeletal muscle when carbohydrates are in short supply. The metabolism of ketone bodies interfaces with the tricarboxylic acid cycle, β-oxidation of fatty acids, de novo lipogenesis, sterol biosynthesis, glucose metabolism, the mitochondrial electron transport chain, hormonal signaling, intracellular signal transduction pathways, and the microbiome. Here we review the mechanisms through which ketone bodies are metabolized and how their signals are transmitted. We focus on the roles this metabolic pathway may play in cardiovascular disease states, the bioenergetic benefits of myocardial ketone body oxidation, and prospective interactions among ketone body metabolism, obesity, metabolic syndrome, and atherosclerosis. Ketone body metabolism is noninvasively quantifiable in humans and is responsive to nutritional interventions. Therefore, further investigation of this pathway in disease models and in humans may ultimately yield tailored diagnostic strategies and therapies for specific pathological states.

The NLRP3 inflammasome is up-regulated in cardiac fibroblasts and mediates myocardial ischaemia-reperfusion injury

AIMS

Nucleotide-binding oligomerization domain-Like Receptor with a Pyrin domain 3 (NLRP3) is considered necessary for initiating a profound sterile inflammatory response. NLRP3 forms multi-protein complexes with Apoptosis-associated Speck-like protein containing a Caspase recruitment domain (ASC) and Caspase-1, which activate pro-interleukin-1β (IL-1β) and pro-IL-18. The role of NLRP3 in cardiac cells is not known. Thus, we investigated the expression and function of NLRP3 during myocardial ischaemia.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in adult C57BL/6 mice and Wistar rats by ligation of the coronary artery. A marked increase in NLRP3, IL-1β, and IL-18 mRNA expression was found in the left ventricle after MI, primarily located to myocardial fibroblasts. In vitro studies in cells from adult mice showed that myocardial fibroblasts released IL-1β and IL-18 when primed with lipopolysaccharide and subsequently exposed to the danger signal adenosine triphosphate, a molecule released after tissue damage during MI. When hearts were isolated from NLRP3-deficient mice, perfused and subjected to global ischaemia and reperfusion, a marked improvement of cardiac function and reduction of hypoxic damage was found compared with wild-type hearts. This was not observed in ASC-deficient hearts, potentially reflecting a protective role of other ASC-dependent inflammasomes or inflammasome-independent effects of NLRP3.

CONCLUSION

This study shows that the NLRP3 inflammasome is up-regulated in myocardial fibroblasts post-MI, and may be a significant contributor to infarct size development during ischaemia-reperfusion.

Microbial 'Old Friends', immunoregulation and stress resilience

Chronic inflammatory diseases (autoimmunity, allergy and inflammatory bowel diseases) are increasing in prevalence in urban communities in high-income countries. One important factor is reduced exposure to immunoregulation-inducing macro- and microorganisms and microbiota that accompanied mammalian evolution (the hygiene hypothesis or 'Old Friends' mechanism). Reduced exposure to these organisms predisposes to poor regulation of inflammation. But inflammation is equally relevant to psychiatric disorders. Inflammatory mediators modulate brain development, cognition and mood, and accompany low socioeconomic status and some cases of depression in developed countries. The risk of all these conditions (chronic inflammatory and psychiatric) is increased in urban versus rural communities, and increased in immigrants, particularly if they move from a low- to a high-income country during infancy, and often the prevalence increases further in second generation immigrants, suggesting that critical exposures modulating disease risk occur during pregnancy and infancy. Diminished exposure to immunoregulation-inducing Old Friends in the perinatal period may enhance the consequences of psychosocial stressors, which induce increased levels of inflammatory mediators, modulate the microbiota and increase the risk for developing all known psychiatric conditions. In later life, the detrimental effects of psychosocial stressors may be exaggerated when the stress occurs against a background of reduced immunoregulation, so that more inflammation (and therefore more psychiatric symptoms) result from any given level of psychosocial stress. This interaction between immunoregulatory deficits and psychosocial stressors may lead to reduced stress resilience in modern urban communities. This concept suggests novel interpretations of recent epidemiology, and novel approaches to the increasing burden of psychiatric disease.

Bacterial bioluminescence regulates expression of a host cryptochrome gene in the squid-Vibrio symbiosis

The symbiosis between the squid Euprymna scolopes and its luminous symbiont, Vibrio fischeri, is characterized by daily transcriptional rhythms in both partners and daily fluctuations in symbiont luminescence. In this study, we sought to determine whether symbionts affect host transcriptional rhythms. We identified two transcripts in host tissues (E. scolopes cry1 [escry1] and escry2) that encode cryptochromes, proteins that influence circadian rhythms in other systems. Both genes cycled daily in the head of the squid, with a pattern similar to that of other animals, in which expression of certain cry genes is entrained by environmental light. In contrast, escry1 expression cycled in the symbiont-colonized light organ with 8-fold upregulation coincident with the rhythms of bacterial luminescence, which are offset from the day/night light regime. Colonization of the juvenile light organ by symbionts was required for induction of escry1 cycling. Further, analysis with a mutant strain defective in light production showed that symbiont luminescence is essential for cycling of escry1; this defect could be complemented by presentation of exogenous blue light. However, blue-light exposure alone did not induce cycling in nonsymbiotic animals, but addition of molecules of the symbiont cell envelope to light-exposed animals did recover significant cycling activity, showing that light acts in synergy with other symbiont features to induce cycling. While symbiont luminescence may be a character specific to rhythms of the squid-vibrio association, resident microbial partners could similarly influence well-documented daily rhythms in other systems, such as the mammalian gut.

In mammals, biological rhythms of the intestinal epithelium and the associated mucosal immune system regulate such diverse processes as lipid trafficking and the immune response to pathogens. While these same processes are affected by the diverse resident microbiota, the extent to which these microbial communities control or are controlled by these rhythms has not been addressed. This study provides evidence that the presentation of three bacterial products (lipid A, peptidoglycan monomer, and blue light) is required for cyclic expression of a cryptochrome gene in the symbiotic organ. The finding that bacteria can directly influence the transcription of a gene encoding a protein implicated in the entrainment of circadian rhythms provides the first evidence for the role of bacterial symbionts in influencing, and perhaps driving, peripheral circadian oscillators in the host.

Exploring host-microbiota interactions in animal models and humans

The animal and bacterial kingdoms have coevolved and coadapted in response to environmental selective pressures over hundreds of millions of years. The meta'omics revolution in both sequencing and its analytic pipelines is fostering an explosion of interest in how the gut microbiome impacts physiology and propensity to disease. Gut microbiome studies are inherently interdisciplinary, drawing on approaches and technical skill sets from the biomedical sciences, ecology, and computational biology. Central to unraveling the complex biology of environment, genetics, and microbiome interaction in human health and disease is a deeper understanding of the symbiosis between animals and bacteria. Experimental model systems, including mice, fish, insects, and the Hawaiian bobtail squid, continue to provide critical insight into how host-microbiota homeostasis is constructed and maintained. Here we consider how model systems are influencing current understanding of host-microbiota interactions and explore recent human microbiome studies.

Gut microbiota and metabolic syndrome

Symbiosis is the result of the relationship between gut microbiota and human surfaces; in fact, it regulates many functions such as metabolic and protective ones. It is widely known that any changes in the microbes in gut microbiota (dysbiosis) and the regulation of mucosal and systemic host's immunity have been linked to different diseases such as metabolic syndromes and associated disorders. Recent studies report an aberrant gut microbiota and an alteration of gut microbial metabolic activities in obese subjects, with an important influence of a number of human physiological functions. Most studies suggest that diet, especially the high-fat low-fiber western-style diet, dramatically impacts on gut microbiota composition and functions in those patients with metabolic syndrome. A deeper knowledge of a specific microbiota profile associated with increased risk of metabolic disease and its subsequent modification induced by prebiotics, probiotics or targeted antibiotics will be necessary for the development of new therapeutic approaches in the treatment of metabolic disease.

Lack of invariant natural killer T cells affects lipid metabolism in adipose tissue of diet-induced obese mice

OBJECTIVE

Obesity promotes a chronic inflammatory condition in adipose tissue (AT). Impairment of insulin sensitivity coincides with infiltration of T cells into AT in early stages of obesity, when macrophages are not yet present. Here, we examine the role of invariant natural killer T (iNKT) cells, a subtype of T cells activated by lipid antigens, on glucose and lipid metabolism in obesity.

APPROACH AND RESULTS

Jα18(-/-) mice, specifically lacking iNKT cells, and wild-type mice consumed a chow or high-fat diet for 10 weeks. One third of all T lymphocytes in the liver of wild-type mice were iNKT cells, whereas few were detected in AT. Diet-induced obesity increased blood glucose in both genotypes of mice, whereas glucose tolerance test revealed similar kinetics of glucose clearance in Jα18(-/-) and wild-type mice. Under obese conditions, expression of inflammatory cytokines in AT did not differ between the groups, although the number of T cells and macrophages was lower in Jα18(-/-) mice. Nonetheless, AT homeostasis in Jα18(-/-) mice was altered evidenced by lower AT weight, smaller adipocytes, accelerated lipogenesis, increased expression of hormone-sensitive lipase, and accelerated basal lipolysis.

CONCLUSIONS

iNKT cells do not affect glucose clearance but rather modulate lipid metabolism in both liver and AT. Only few iNKT cells are found in AT under lean and obese conditions, suggesting that their effects on lipid metabolism are mainly mediated in the liver, their primary host organ.

The role of gut microbiota on insulin resistance

The development of obesity and insulin resistance has been extensively studied in the last decades, but the mechanisms underlying these alterations are still not completely understood. The gut microbiota has been identified as a potential contributor to metabolic diseases. It has been shown that obese individuals present different proportions of bacterial phyla compared with lean individuals, with an increase in Firmicutes and Actinobacteria and a decrease in Bacteroidetes. This alteration seems to interfere with intestinal permeability, increasing the absorption of lipopolysaccharide (LPS), which reaches circulation and initiates activation of Toll-like receptor (TLR) 4 and 2 and LPS receptor CD14, leading to increased activation of inflammatory pathways. With these activations, an impairment of the insulin signaling is observed, with decreased phosphorylation of the insulin receptor, insulin receptor substrate (IRS) and Akt, as well as increased inhibitory serine phosphorylation of IRS-1. Altered proportions of bacterial phyla have also been demonstrated to interfere with host’s biochemical pathways, increasing energy extraction and depot in adipose tissue. Therefore, understanding the mechanisms by which the alteration in the gut microbiota produces different signaling activations and phenotype changes may offer an interesting opportunity for the treatment of obesity and type 2 diabetes.

Biosynthetic assembly of the Bacteroides fragilis capsular polysaccharide A precursor bactoprenyl diphosphate-linked acetamido-4-amino-6-deoxygalactopyranose

The sugar capsule capsular polysaccharide A (CPSA), which coats the surface of the mammalian symbiont Bacteroides fragilis, is a key mediator of mammalian immune system development. In addition, this sugar polymer has shown therapeutic potential in animal models of multiple sclerosis and other autoimmune disorders. The structure of the CPSA polymer includes a rare stereoconfiguration sugar acetamido-4-amino-6-deoxygalactopyranose (AADGal) that we propose is the first sugar linked to a bactoprenyl diphosphate scaffold in the production of CPSA. In this report, we have utilized a heterologous system to reconstitute bactoprenyl diphosphate-linked AADGal production. Construction of this system included a previously reported Campylobacter jejuni dehydratase, PglF, coupled to a B. fragilis-encoded aminotransferase (WcfR) and initiating hexose-1-phosphate transferase (WcfS). The function of the aminotransferase was confirmed by capillary electrophoresis and a novel high-performance liquid chromatography (HPLC) method. Production of the rare uridine diphosphate (UDP)-AADGal was confirmed through a series of one- and two-dimensional nuclear magnetic resonance experiments and high-resolution mass spectrometry. A spectroscopically unique analogue of bactoprenyl phosphate was utilized to characterize the transfer reaction catalyzed by WcfS and allowed HPLC-based isolation of the isoprenoid-linked sugar product. Importantly, the entire heterologous system was utilized in a single-pot reaction to biosynthesize the bactoprenyl-linked sugar. This work provides the first critical step in the in vitro reconstitution of CPSA biosynthesis.

The colon: an overlooked site for therapeutics in dialysis patients

Morbidity and mortality related to chronic kidney disease remain unacceptably high, despite tremendous progress in its prevention and treatment. In an ongoing quest to improve outcome in chronic kidney disease patients, the colon might be an appealing, but largely underexplored, therapeutic target. A clear bi-directional functional relationship exists between the colon and kidney, also referred as to the colo-renal axis. Uremia has an important impact on the colonic microbiome. The microbiome, in turn, is an important source of uremic toxins, with p-cresyl sulfate and indoxyl sulfate as important prototypes. These co-metabolites accumulate in the face of a falling kidney function, and may accelerate the progression of renal and cardiovascular disease. Several therapeutic interventions, including prebiotics and adsorbants, specifically target these colon-derived uremic toxins originating from bacterial metabolism. As kidney function declines, the colon also gains importance in the homeostasis and disposal of potassium and oxalate. Their colonic secretion may be increased by drugs increasing the expression of cAMP and by probiotics (e.g., Oxalobacter formigenes).

Regulation of intestinal homeostasis and immunity with probiotic lactobacilli

The gut microbiota provide important stimuli to the human innate and adaptive immune system and co-mediate metabolic and immune homeostasis. Probiotic bacteria can be regarded as part of the natural human microbiota, and have been associated with improving homeostasis, albeit with different levels of success. Composition of microbiota, probiotic strain identity, and host genetic differences may account for differential modulation of immune responses by probiotics. Here, we review the mechanisms of immunomodulating capacities of specific probiotic strains, the responses they can induce in the host, and how microbiota and genetic differences between individuals may co-influence host responses and immune homeostasis.

Associations between the human intestinal microbiota, Lactobacillus rhamnosus GG and serum lipids indicated by integrated analysis of high-throughput profiling data

Accumulating evidence indicates that the intestinal microbiota regulates our physiology and metabolism. Bacteria marketed as probiotics confer health benefits that may arise from their ability to affect the microbiota. Here high-throughput screening of the intestinal microbiota was carried out and integrated with serum lipidomic profiling data to study the impact of probiotic intervention on the intestinal ecosystem, and to explore the associations between the intestinal bacteria and serum lipids. We performed a comprehensive intestinal microbiota analysis using a phylogenetic microarray before and after Lactobacillus rhamnosus GG intervention. While a specific increase in the L. rhamnosus-related bacteria was observed during the intervention, no other changes in the composition or stability of the microbiota were detected. After the intervention, lactobacilli returned to their initial levels. As previously reported, also the serum lipid profiles remained unaltered during the intervention. Based on a high-resolution microbiota analysis, intake of L. rhamnosus GG did not modify the composition of the intestinal ecosystem in healthy adults, indicating that probiotics confer their health effects by other mechanisms. The most prevailing association between the gut microbiota and lipid profiles was a strong positive correlation between uncultured phylotypes of Ruminococcus gnavus-group and polyunsaturated serum triglycerides of dietary origin. Moreover, a positive correlation was detected between serum cholesterol and Collinsella (Coriobacteriaceae). These associations identified with the spectrometric lipidome profiling were corroborated by enzymatically determined cholesterol and triglyceride levels. Actinomycetaceae correlated negatively with triglycerides of highly unsaturated fatty acids while a set of Proteobacteria showed negative correlation with ether phosphatidylcholines. Our results suggest that several members of the Firmicutes, Actinobacteria and Proteobacteria may be involved in the metabolism of dietary and endogenous lipids, and provide a scientific rationale for further human studies to explore the role of intestinal microbes in host lipid metabolism.

Animals in a bacterial world, a new imperative for the life sciences

In the last two decades, the widespread application of genetic and genomic approaches has revealed a bacterial world astonishing in its ubiquity and diversity. This review examines how a growing knowledge of the vast range of animal-bacterial interactions, whether in shared ecosystems or intimate symbioses, is fundamentally altering our understanding of animal biology. Specifically, we highlight recent technological and intellectual advances that have changed our thinking about five questions: how have bacteria facilitated the origin and evolution of animals; how do animals and bacteria affect each other's genomes; how does normal animal development depend on bacterial partners; how is homeostasis maintained between animals and their symbionts; and how can ecological approaches deepen our understanding of the multiple levels of animal-bacterial interaction. As answers to these fundamental questions emerge, all biologists will be challenged to broaden their appreciation of these interactions and to include investigations of the relationships between and among bacteria and their animal partners as we seek a better understanding of the natural world.

Increased adiposity, dysregulated glucose metabolism and systemic inflammation in Galectin-3 KO mice

Obesity and type 2 diabetes are associated with increased production of Galectin-3 (Gal-3), a protein that modulates inflammation and clearance of glucose adducts. We used Lean and Diet-induced Obese (DIO) WT and Gal-3 KO mice to investigate the role of Gal-3 in modulation of adiposity, glucose metabolism and inflammation. Deficiency of Gal-3 lead to age-dependent development of excess adiposity and systemic inflammation, as indicated by elevated production of acute-phase proteins, number of circulating pro-inflammatory Ly6C^high monocytes and development of neutrophilia, microcytic anemia and thrombocytosis in 20-week-old Lean and DIO male Gal-3 KO mice. This was associated with impaired fasting glucose, heightened response to a glucose tolerance test and reduced adipose tissue expression of adiponectin, Gal-12, ATGL and PPARγ, in the presence of maintained insulin sensitivity and hepatic expression of gluconeogenic enzymes in 20-week-old Gal-3 KO mice compared to their diet-matched WT controls. Expression of PGC-1α and FGF-21 in the liver of Lean Gal-3 KO mice was comparable to that observed in DIO animals. Impaired fasting glucose and altered responsiveness to a glucose load preceded development of excess adiposity and systemic inflammation, as demonstrated in 12-week-old Gal-3 KO mice. Finally, a role for the microflora in mediating the fasting hyperglycemia, but not the excessive response to a glucose load, of 12-week-old Gal-3 KO mice was demonstrated by administration of antibiotics. In conclusion, Gal-3 is an important modulator of glucose metabolism, adiposity and inflammation.

Bridging the transgenerational gap with epigenetic memory

It is textbook knowledge that inheritance of traits is governed by genetics, and that the epigenetic modifications an organism acquires are largely reset between generations. Recently, however, transgenerational epigenetic inheritance has emerged as a rapidly growing field, providing evidence suggesting that some epigenetic changes result in persistent phenotypes across generations. Here, we survey some of the most recent examples of transgenerational epigenetic inheritance in animals, ranging from Caenorhabditis elegans to humans, and describe approaches and limitations to studying this phenomenon. We also review the current body of evidence implicating chromatin modifications and RNA molecules in mechanisms underlying this unconventional mode of inheritance and discuss its evolutionary implications.

Rattusin, an intestinal α-defensin-related peptide in rats with a unique cysteine spacing pattern and salt-insensitive antibacterial activities

Cationic antimicrobial peptides are essential components of the innate immune system. As a major family of mammalian antimicrobial peptides, defensins are expressed mainly by mucosal epithelial cells and promyelocytes. Despite the capacity to kill a broad spectrum of bacteria through physical disruption of membranes, most defensins show substantially reduced antibacterial activities in the presence of monovalent and divalent cations, thereby limiting their therapeutic potential, particularly for the treatment of systemic infections. Genome-wide computational screening of the rat genome led to the identification of the gene for a novel α-defensin-related peptide that we termed rattusin. Rattusin shares a highly conserved signal and prosequence with mammalian α-defensins, but instead of the canonical α-defensin six-cysteine motif, rattusin consists of five cysteines with a distinctive spacing pattern. Furthermore, rattusin is preferentially expressed in Paneth cells of the distal small intestine with potent antibacterial activity against a broad range of Gram-negative and Gram-positive bacteria, including antibiotic-resistant strains. The MICs were mostly in the range of 2 to 4 μM, with no appreciable toxicity to mammalian cells at up to 100 μM. In contrast to classical α- and β-defensins, rattusin retained its activity in the presence of physiological concentrations of NaCl and Mg(2+), making it an attractive antimicrobial candidate for both topical and systemic applications.

Understanding the microbiota in the midst of Renaissance architecture and olive groves

Leading scientists working on the microbiome gathered in an October 2012 meeting in Baeza, Spain, to discuss recent advances in the understanding of the role of the microbiota in immunity, pathogen colonization, metabolism and disease.

Pleiotropic actions of insulin resistance and inflammation in metabolic homeostasis

Metabolism and immunity are inextricably linked both to each other and to organism-wide function, allowing mammals to adapt to changes in their internal and external environments. In the modern context of obesogenic diets and lifestyles, however, these adaptive responses can have deleterious consequences. In this Review, we discuss the pleiotropic actions of inflammation and insulin resistance in metabolic homeostasis and disease. An appreciation of the adaptive context in which these responses arose is useful for understanding their pathogenic actions in disease.

Nickel and human health

This review focuses on the impact of nickel on human health. In particular, the dual nature of nickel as an essential as well as toxic element in nature is described, and the main forms of nickel that can come in contact with living systems from natural sources and anthropogenic activities are discussed. Concomitantly, the main routes of nickel uptake and transport in humans are covered, and the potential dangers that nickel exposure can represent for health are described. In particular, the insurgence of nickel-derived allergies, nickel-induced carcinogenesis as well as infectious diseases caused by human pathogens that rely on nickel-based enzymes to colonize the host are reviewed at different levels, from their macroscopic aspects on human health to the molecular mechanisms underlying these points. Finally, the importance of nickel as a beneficial element for human health, especially being essential for microorganisms that colonize the human guts, is examined.

The intestinal microbiota in chronic liver disease

Recent evidence indicates that the intestinal microflora plays a critical role in physiological and pathological processes; in particular, it is now considered a key determinant of immune pathologies and metabolic syndrome. Receiving the majority of its blood supply from the portal vein, the liver represents the first line of defense against food antigens, toxins, microbial-derived products, and microorganisms. Moreover, the liver is critically positioned to integrate metabolic outcomes with nutrient intake. To accomplish this function, the liver is equipped with a broad array of immune networks. It is now evident that, during pathological processes associated with obesity, alcohol-intake, or autoimmunity, the interaction between these immune cell populations and the intestinal microbiota promotes chronic liver disease progression and therefore they represent a novel therapeutic target. Herein, we highlight recent studies that have shed new light on the relationship between the microbiome, the innate immune system, and chronic liver disease progression.

Metabolomics in the studies of islet autoimmunity and type 1 diabetes

The metabolome is sensitive to genetic and environmental factors contributing to complex diseases such as type 1 diabetes (T1D). Metabolomics is the study of biochemical and physiological processes involving metabolites. It is therefore one of the key platforms for the discovery and study of pathophysiological phenomena leading to T1D and the development of T1D-associated complications. Although the application of metabolomics in T1D research is still rare, metabolomic research has already advanced across the full spectrum, from disease progression to the development of diabetic complications. Metabolomic studies in T1D have contributed to an improved etiopathogenic understanding and demonstrated their potential in the clinic. For example, metabolomic data from recent T1D studies suggest that a specific metabolic profile, or metabotype, precedes islet autoimmunity and the development of overt T1D. These early metabolic changes are attributed to many biochemical pathways, thus suggesting a systemic change in metabolism which may be inborn. Based on this evidence, the role of the metabolome in the progression to T1D is therefore to facilitate specific biochemical processes associated with T1D, and to contribute to the development of a vulnerable state in which disease is more likely to be triggered. This may have important implications for the understanding of T1D pathophysiology and early disease detection and prevention.

Ulcerative colitis-induced hepatic damage in mice: studies on inflammation, fibrosis, oxidative DNA damage and GST-P expression

There exists a close relationship between ulcerative colitis and various hepatic disorders. The present study was aimed to evaluate the hepatocellular damage in experimental colitis model. Ulcerative colitis was induced in Swiss mice by cyclic treatment with 3% w/v dextran sulfate sodium in drinking water. The severity of colitis was assessed on the basis of disease activity index and colon histology. The effect of ulcerative colitis on the liver was assessed using various biochemical parameters, histological evaluation, sirius red staining, immunohistochemical staining with peroxisome proliferator-activated receptor γ, 8-oxo-7,8-dihydro-2'-deoxyguanosine and placental glutathione S-transferase, comet assay (alkaline and modified), Terminal Deoxynucleotidyl Transferase-mediated dUTP Nick End Labeling assay and western blot analysis to detect the protein expression of nuclear factor kappa B, cyclooxygenase-2, nuclear erythroid 2-related factor 2 and NADPH: quinone oxidoreductase-1. Dextran sulfate sodium induced severe colitis in mice as evident from an elevated disease activity index and histological abnormalities. Ulcerative colitis increased the permeability of colon as apparent from a significant reduction in the expression of tight junction protein, occludin. Further, the bacterial translocation assay as well as the analysis of lipopolysaccharide level revealed the existence of various bacterial species in the liver of ulcerative colitis-induced mice. There was a significant increase in the plasma alanine and aspartate transaminases and liver triglyceride levels, expression of peroxisome proliferator-activated receptor γ, inflammatory markers, oxidative stress, fibrosis, oxidative DNA damage and apoptosis in the liver of mice. Moreover, there was an increase in the expression of nuclear factor kappa B and cyclooxygenase-2 and a reduction in the expression of nuclear erythroid 2-related factor 2 and NADPH: quinone oxidoreductase-1 in the liver of severe ulcerative colitis-induced mice. The results of the present study provide evidence that ulcerative colitis is accompanied with hepatic damage in mice.

Diet-induced alterations of host cholesterol metabolism are likely to affect the gut microbiota composition in hamsters

The gastrointestinal microbiota affects the metabolism of the mammalian host and has consequences for health. However, the complexity of gut microbial communities and host metabolic pathways make functional connections difficult to unravel, especially in terms of causation. In this study, we have characterized the fecal microbiota of hamsters whose cholesterol metabolism was extensively modulated by the dietary addition of plant sterol esters (PSE). PSE intake induced dramatic shifts in the fecal microbiota, reducing several bacterial taxa within the families Coriobacteriaceae and Erysipelotrichaceae. The abundance of these taxa displayed remarkably high correlations with host cholesterol metabolites. Most importantly, the associations between several bacterial taxa with fecal and biliary cholesterol excretion showed an almost perfect fit to a sigmoidal nonlinear model of bacterial inhibition, suggesting that host cholesterol excretion can shape microbiota structure through the antibacterial action of cholesterol. In vitro experiments suggested a modest antibacterial effect of cholesterol, and especially of cholesteryl-linoleate, but not plant sterols when included in model bile micelles. The findings obtained in this study are relevant to our understanding of gut microbiota-host lipid metabolism interactions, as they provide the first evidence for a role of cholesterol excreted with the bile as a relevant host factor that modulates the gut microbiota. The findings further suggest that the connections between Coriobacteriaceae and Erysipelotrichaceae and host lipid metabolism, which have been observed in several studies, could be caused by a metabolic phenotype of the host (cholesterol excretion) affecting the gut microbiota.

Multiple NSAID-induced hits injure the small intestine: underlying mechanisms and novel strategies

Nonsteroidal anti-inflammatory drugs (NSAIDs) can cause serious gastrointestinal (GI) injury including jejunal/ileal mucosal ulceration, bleeding, and even perforation in susceptible patients. The underlying mechanisms are largely unknown, but they are distinct from those related to gastric injury. Based on recent insights from experimental models, including genetics and pharmacology in rodents typically exposed to diclofenac, indomethacin, or naproxen, we propose a multiple-hit pathogenesis of NSAID enteropathy. The multiple hits start with an initial pharmacokinetic determinant caused by vectorial hepatobiliary excretion and delivery of glucuronidated NSAID or oxidative metabolite conjugates to the distal small intestinal lumen, where bacterial β-glucuronidase produces critical aglycones. The released aglycones are then taken up by enterocytes and further metabolized by intestinal cytochrome P450s to potentially reactive intermediates. The "first hit" is caused by the NSAID and/or oxidative metabolites that induce severe endoplasmic reticulum stress or mitochondrial stress and lead to cell death. The "second hit" is created by the significant subsequent inflammatory response that would follow such a first-hit injury. Based on these putative mechanisms, strategies have been developed to protect the enterocytes from being exposed to the parent NSAID and/or oxidative metabolites. Among these, a novel strategy already demonstrated in a murine model is the selective disruption of bacteria-specific β-glucuronidases with a novel small molecule inhibitor that does not harm the bacteria and that alleviates NSAID-induced enteropathy. Such mechanism-based strategies require further investigation but provide potential avenues for the alleviation of the GI toxicity caused by multiple NSAID hits.