The microbiota protects against ischemia/reperfusion-induced intestinal injury through nucleotide-binding oligomerization domain-containing protein 2 (NOD2) signaling

Gut Microbiota and Liver Transplantation: Immune Mechanisms behind the Rejection

Liver transplantation (LT) is the treatment of choice for patients with cirrhosis, decompensated disease, acute liver failure, and hepatocellular carcinoma (HCC). In 3-25% of cases, an alarming problem is acute and chronic cellular rejection after LT, and this event can lead to the need for new transplantation or the death of the patient. On the other hand, gut microbiota is involved in several mechanisms sustaining the model of the "gut-liver axis". These include modulation of the immune response, which is altered in case of gut dysbiosis, possibly resulting in acute graft rejection. Some studies have evaluated the composition of the gut microbiota in cirrhotic patients before and after LT, but few of them have assessed its impact on liver rejection. This review underlines the changes in gut microbiota composition before and after liver transplantation, hypothesizing possible immune mechanisms linking dysbiosis to transplantation rejection. Evaluation of changes in the gut microbiota composition in these patients is therefore essential in order to monitor the success of LT and eventually adopt appropriate preventive measures.

MSC Promotes the Secretion of Exosomal miR-34a-5p and Improve Intestinal Barrier Function Through METTL3-Mediated Pre-miR-34A m6A Modification

Intestinal ischemia/reperfusion (I/R) injury (IIRI) is associated with high prevalence and mortality rate. Recently, mesenchymal stem cell (MSC) therapy attracted more attentions. However, the function and regulatory mechanism of MSC-derived exosomal miRNAs during IIRI remain largely uninvestigated. The in vitro and in vivo IIRI models were established. MSC were characterized by immunofluorescent staining and flow cytometry. Purified exosomes were characterized by transmission electron microscopy (TEM), flow cytometry, and western blot. The expression of key molecules was detected by western blot and qRT-PCR. CCK-8, TUNEL, and transepithelial electrical resistance (TER) assays were employed to assess cell viability, apoptosis, and intestinal integrity, respectively. Pre-miR-34A m⁶ modification was evaluated by methylated RNA immunoprecipitation (MeRIP)-qPCR. RNA pull-down and RIP were used to validate the direct association between pre-miR-34A and IGF2BP3. MSC-derived exosomal miR-34a-5p alleviated OGD/R-induced injury. In addition, MSC ameliorated OGD/R-induced injury through METTL3 pathway. Mechanistic study revealed that miR-34a-5p was modulated by METTL3/IGF2BP3-mediated m⁶A modification in MSC. The in vitro and in vivo functional experiments revealed that MSC secreted exosomal miR-34a-5p and ameliorated IIRI through METTL3/IGF2BP3-mediated m⁶A modification of pre-miR-34A. MSC promoted the secretion of exosomal miR-34a-5p and improved intestinal barrier function through METTL3/IGF2BP3-mediated pre-miR-34A m⁶A modification.

Predictive and Prognostic Roles of Gut Microbial Variation in Liver Transplant

Patients undergoing liver transplant (LTX) typically confront a challenging postoperative journey. A dysbiotic gut microbiome is associated with the development of complications, including post-LTX allograft rejection, metabolic diseases and de novo or recurrent cancer. A major explanation of this are the bipartite interactions between the gut microbiota and host immunity, which modulates the alloimmune response towards the liver allograft. Furthermore, bacterial translocation from dysbiosis causes pathogenic changes in the concentrations of microbial metabolites like lipopolysaccharides, short-chain fatty acids (SCFAs) and Trimethylamine-N-Oxide, with links to cardiovascular disease development and diabetes mellitus. Gut dysbiosis also disrupts bile acid metabolism, with implications for various post-LTX metabolic diseases. Certain taxonomy of microbiota such as lactobacilli, F.prausnitzii and Bacteroides appear to be associated with these undesired outcomes. As such, an interesting but as yet unproven hypothesis exists as to whether induction of a “beneficial” composition of gut microbiota may improve prognosis in LTX patients. Additionally, there are roles of the microbiome as predictive and prognostic indicators for clinicians in improving patient care. Hence, the gut microbiome represents an exceptionally exciting avenue for developing novel prognostic, predictive and therapeutic applications.

Lactobacillus murinus alleviate intestinal ischemia/reperfusion injury through promoting the release of interleukin-10 from M2 macrophages via Toll-like receptor 2 signaling

BACKGROUND

Intestinal ischemia/reperfusion (I/R) injury has high morbidity and mortality rates. Gut microbiota is a potential key factor affecting intestinal I/R injury. Populations exhibit different sensitivities to intestinal I/R injury; however, whether this interpopulation difference is related to variation in gut microbiota is unclear. Here, to elucidate the interaction between the gut microbiome and intestinal I/R injury, we performed 16S DNA sequencing on the preoperative feces of C57BL/6 mice and fecal microbiota transplantation (FMT) experiments in germ-free mice. The transwell co-culture system of small intestinal organoids extracted from control mice and macrophages extracted from control mice or Toll-like receptor 2 (TLR2)-deficient mice or interleukin-10 (IL-10)-deficient mice were established separately to explore the potential mechanism of reducing intestinal I/R injury.

RESULTS

Intestinal I/R-sensitive (Sen) and intestinal I/R-resistant (Res) mice were first defined according to different survival outcomes of mice suffering from intestinal I/R. Fecal microbiota composition and diversity prior to intestinal ischemia differed between Sen and Res mice. The relative abundance of Lactobacillus murinus (L. murinus) at the species level was drastically higher in Res than that in Sen mice. Clinically, the abundance of L. murinus in preoperative feces of patients undergoing cardiopulmonary bypass surgery was closely related to the degree of intestinal I/R injury after surgery. Treatment with L. murinus significantly prevented intestinal I/R-induced intestinal injury and improved mouse survival, which depended on macrophages involvement. Further, in vitro experiments indicated that promoting the release of IL-10 from macrophages through TLR2 may be a potential mechanism for L. murinus to reduce intestinal I/R injury.

CONCLUSION

The gut microbiome is involved in the postoperative outcome of intestinal I/R. Lactobacillus murinus alleviates mice intestinal I/R injury through macrophages, and promoting the release of IL-10 from macrophages through TLR2 may be a potential mechanism for L. murinus to reduce intestinal I/R injury. This study revealed a novel mechanism of intestinal I/R injury and a new therapeutic strategy for clinical practice. Video Abstract.

Colonization with Altered Schaedler Flora Impacts Leukocyte Adhesion in Mesenteric Ischemia-Reperfusion Injury

The microbiota impacts mesenteric ischemia-reperfusion injury, aggravating the interaction of leukocytes with endothelial cells in mesenteric venules. The role of defined gut microbiomes in this life-threatening pathology is unknown. To investigate how a defined model microbiome affects the adhesion of leukocytes in mesenteric ischemia-reperfusion, we took advantage of gnotobiotic isolator technology and transferred altered Schaedler flora (ASF) from C3H/HeNTac to germ-free C57BL/6J mice. We were able to detect all eight bacterial taxa of ASF in fecal samples of colonized C57BL/6J mice by PCR. Applying qRT-PCR for quantification of species-specific 16S rDNA sequences of ASF bacteria, we found a major shift in the abundance of ASF 500, which was greater in C57BL/6J mice relative to the C3H/HeNTac founder breeding pair. Using high-speed epifluorescence intravital microscopy to visualize the venules of the small bowel mesentery, we found that gnotobiotic ASF-colonized mice showed reduced leukocyte adherence, both pre- and post-ischemia. Relative to germ-free mice, the counts of adhering leukocytes were increased pre-ischemia but did not significantly increase in ASF-colonized mice in the post-ischemic state. Collectively, our results suggest a protective role of the minimal microbial consortium ASF in mesenteric ischemia-reperfusion injury.

LncRNA Bmp1 promotes the healing of intestinal mucosal lesions via the miR-128-3p/PHF6/PI3K/AKT pathway

Intestinal mucosal injuries are directly or indirectly related to many common acute and chronic diseases. Long non-coding RNAs (lncRNAs) are expressed in many diseases, including intestinal mucosal injury. However, the relationship between lncRNAs and intestinal mucosal injury has not been determined. Here, we investigated the functions and mechanisms of action of lncRNA Bmp1 on damaged intestinal mucosa. We found that Bmp1 was increased in damaged intestinal mucosal tissue and Bmp1 overexpression was able to alleviate intestinal mucosal injury. Bmp1 overexpression was found to influence cell proliferation, colony formation, and migration in IEC-6 or HIEC-6 cells. Moreover, miR-128-3p was downregulated after Bmp1 overexpression, and upregulation of miR-128-3p reversed the effects of Bmp1 overexpression in IEC-6 cells. Phf6 was observed to be a target of miR-128-3p. Furthermore, PHF6 overexpression affected IEC-6 cells by activating PI3K/AKT signaling which was mediated by the miR-128-3p/PHF6 axis. In conclusion, Bmp1 was found to promote the expression of PHF6 through the sponge miR-128-3p, activating the PI3K/AKT signaling pathway to promote cell migration and proliferation.

Emerging roles of microRNAs in intestinal ischemia/reperfusion-induced injury: a review

Intestinal ischemia/reperfusion (II/R) injury is a serious pathological phenomenon in underlying hemorrhagic shock, trauma, strangulated intestinal obstruction, and acute mesenteric ischemia which associated with high morbidity and mortality. MicroRNAs (miRNAs, miRs) are endogenous non-coding RNAs that regulate post-transcriptionally target mRNA translation via degrading it and/or suppressing protein synthesis. This review discusses on the role of some miRNAs in underlying II/R injury. Some of these miRNAs can have protective action through agomiR or specific antagomiR, and others can have destructive effects in the basal level of II/R insult. Based on these literature reviews, II/R injury affects several miRNAs and their specific target genes. Some miRNAs upregulate under condition of II/R injury, and multiple miRNAs downregulate following II/R damage. Data of this review have been collected from the scientific articles published in databases such as Science Direct, Scopus, PubMed, Web of Science, and Scientific Information Database from 2000 to 2020. It is shown a correlation between changes in the expression of miRNAs and autophagy, inflammation, oxidative stress, apoptosis, and epithelial barrier function. Taken together, agomiR or antagomiR of some miRNAs can be considered as one new target for the research and development of innovative drugs to the prevention or treatment of II/R damage.

Autophagy Induction Ameliorates Inflammatory Responses in Intestinal Ischemia-Reperfusion Through Inhibiting NLRP3 Inflammasome Activation

Intestinal ischemia/reperfusion (I/R)-induced systemic inflammation leads to multiple organ dysfunction syndrome. Previous studies have indicated that the NOD-like receptor protein (NLRP)3 inflammasome modulates intestinal inflammation; however, the pathophysiological mechanisms remain unclear. Autophagy is a critical metabolic mechanism that promotes cellular survival following ischemic injury. Recently, basal autophagy has been implicated in the alleviation of extensive inflammation. However, the role of autophagy in NLRP3 inflammasome activation in intestinal I/R-induced inflammatory injury remains undefined. In the present study, we examined whether NLRP3 inflammasome activation is induced in mice subjected to intestinal I/R injury, which is measured as increased apoptosis-associated speck-like protein containing a CARD levels, caspase-1 activity, and interleukin-1β (IL-1β) secretion. Importantly, the in-vitro results showed that NLRP3 knockdown decreases proinflammatory cytokine production and increases resistance to hypoxia/reoxygenation (H/R)-triggered inflammation. Subsequently, we demonstrated a critical role for autophagy in suppressing intestinal I/R-induced NLRP3 inflammasome activation in vivo. Furthermore, we showed that the loss of autophagy activates inflammasome-mediated IL-1β secretion, which aggravates H/R injury, and NLRP3 knockdown reverses these effects. Collectively, these results directly implicated the homeostatic process of autophagy and NLRP3 inflammasome in ischemic bowel disease and identified a novel pathway for therapeutic intervention in intestinal I/R.

Gut Microbiota Restricts NETosis in Acute Mesenteric Ischemia-Reperfusion Injury

OBJECTIVE

Recruitment of neutrophils and formation of neutrophil extracellular traps (NETs) contribute to lethality in acute mesenteric infarction. To study the impact of the gut microbiota in acute mesenteric infarction, we used gnotobiotic mouse models to investigate whether gut commensals prime the reactivity of neutrophils towards formation of neutrophil extracellular traps (NETosis). Approach and Results: We applied a mesenteric ischemia-reperfusion (I/R) injury model to germ-free (GF) and colonized C57BL/6J mice. By intravital imaging, we quantified leukocyte adherence and NET formation in I/R-injured mesenteric venules. Colonization with gut microbiota or monocolonization with Escherichia coli augmented the adhesion of leukocytes, which was dependent on the TLR4 (Toll-like receptor-4)/TRIF (TIR-domain-containing adapter-inducing interferon-β) pathway. Although neutrophil accumulation was decreased in I/R-injured venules of GF mice, NETosis following I/R injury was significantly enhanced compared with conventionally raised mice or mice colonized with the minimal microbial consortium altered Schaedler flora. Also ex vivo, neutrophils from GF and antibiotic-treated mice showed increased LPS (lipopolysaccharide)-induced NETosis. Enhanced TLR4 signaling in GF neutrophils was due to elevated TLR4 expression and augmented IRF3 (interferon regulatory factor-3) phosphorylation. Likewise, neutrophils from antibiotic-treated conventionally raised mice had increased NET formation before and after ischemia. Increased NETosis in I/R injury was abolished in conventionally raised mice deficient in the TLR adaptor TRIF. In support of the desensitizing influence of enteric LPS, treatment of GF mice with LPS via drinking water diminished LPS-induced NETosis in vitro and in the mesenteric I/R injury model.

CONCLUSIONS

Collectively, our results identified that the gut microbiota suppresses NETing neutrophil hyperreactivity in mesenteric I/R injury, while ensuring immunovigilance by enhancing neutrophil recruitment.

Carbon Monoxide Inhibits the Expression of Proteins Associated with Intestinal Mucosal Pyroptosis in a Rat Model of Sepsis Induced by Cecal Ligation and Puncture

BACKGROUND Carbon monoxide (CO) has anti-inflammatory effects and protects the intestinal mucosal barrier in sepsis. Pyroptosis, or cell death associated with sepsis, is mediated by caspase-1 activation. This study aimed to investigate the role of CO on the expression of proteins associated with intestinal mucosal pyroptosis in a rat model of sepsis induced by cecal ligation and puncture (CLP). MATERIAL AND METHODS The rat model of sepsis was developed using CLP. Male Sprague-Dawley rats (n=120) were divided into six study groups: the sham group (n=20); the CLP group (n=20); the hemin group (treated with ferric chloride and heme) (n=20); the zinc protoporphyrin IX (ZnPPIX) group (n=20); the CO-releasing molecule 2 (CORM-2) group (n=20); and the inactive CORM-2 (iCORM-2) group (n=20). Hemin and CORM-2 were CO donors, and ZnPPIX was a CO inhibitor. In the six groups, the seven-day survival curves, the fluorescein isothiocyanate (FITC)-labeled dextran 4000 Da (FD-4) permeability assay, levels of intestinal pyroptosis proteins caspase-1, caspase-11, and gasdermin D (GSDMD) were measured by confocal fluorescence microscopy. Proinflammatory cytokines interleukin (IL)-18, IL-1ß, and high mobility group box protein 1 (HMGB1) were measured by Western blot and enzyme-linked immunosorbent assay (ELISA). RESULTS CO reduced the mortality rate in rats with sepsis and reduced intestinal mucosal permeability and mucosal damage. CO also reduced the expression levels of IL-18, IL-1ß, and HMGB1, and reduced pyroptosis by preventing the cleavage of caspase-1 and caspase-11. CONCLUSIONS In a rat model of sepsis induced by CLP, CO had a protective role by inhibiting intestinal mucosal pyroptosis.

Tle1 attenuates hepatic ischemia/reperfusion injury by suppressing NOD2/NF-κB signaling

Liver damage induced by ischemia/reperfusion (I/R) remains a primary issue in multiple hepatic surgeries. Innate immune-mediated inflammatory responses during the reperfusion stage aggravate the injury. Nevertheless, the detailed mechanism of hepatic I/R has not been fully clarified yet. Our research focuses on the role of Transducin-like enhancer of split-1 (Tle1) in the liver I/R injury and the relation between Tle1 and Nucleotide-binding oligomerization domain 2 (NOD2). To answer these questions, we constructed mouse models of I/R and cell models of hypoxia/reoxygenation (H/R). We found decreased Tle1 accompanied by increased NOD2 during reperfusion. Mice pro-injected with Tle1-siRNA emerged aggravated liver dysfunction. Repression of Tle1 had a significant impact on NOD2 and downstream NF-κB signaling in vitro. However, alteration of NOD2 failed to affect the expression of Tle1. To conclude, our study demonstrates that Tle1 shelters the liver from I/R injury through suppression of NOD2-dependent NF-κB activation and subsequent inflammatory responses.

MicroRNA-29b-3p reduces intestinal ischaemia/reperfusion injury via targeting of TNF receptor-associated factor 3

BACKGROUND AND PURPOSE

The microRNA miR-29b-3p shows important roles in regulating apoptosis and inflammation. However, its effects on intestinal ischaemia/reperfusion (II/R) injury have not been reported. Here we have investigated the functions of miR-29b-3p on II/R injury on order to find drug targets to treat the injury.

EXPERIMENTAL APPROACH

Two models - in vitro hypoxia/reoxygenation (H/R) of IEC-6 cells; in vivo, II/R injury in C57BL/6 mice were used. Western blotting and dual-luciferase reporter assays were used and mimic and siRNA transfection tests were applied to assess the effects of miR-29b-3p on II/R injury via targeting TNF receptor-associated factor 3 (TRAF3).

KEY RESULTS

The H/R procedure decreased cell viability and promoted inflammation and apoptosis in IEC-6 cells, and the II/R procedure also promoted intestinal inflammation and apoptosis in mice. Expression levels of miR-29b-3p were decreased in H/R-induced cells and II/R-induced intestinal tissues of mice compared with control group or sham group, which directly targeted TRAF3. Decreased miR-29b-3p level markedly increased TRAF3 expression via activating TGF-α-activated kinase 1 phosphorylation, increasing NF-κB (p65) levels to promote inflammation, up-regulating Bcl2-associated X expression, and down-regulating Bcl-2 expression to trigger apoptosis. In addition, the miR-29b-3p mimetic and TRAF3 siRNA in IEC-6 cells markedly suppressed apoptosis and inflammation to alleviate II/R injury via inhibiting TRAF3 signallimg.

CONCLUSIONS AND IMPLICATIONS

The miR-29b-3p played a critical role in II/R injury, via targeting TRAF3, which should be considered as a significant drug target to treat the disease.

Irritable Bowel Syndrome in Terms of Changes in the Microbiota

Aim:to review available data confirming the pathogenetic role of the intestinal microbiota in the formation of irritable bowel syndrome (IBS).

Key findings.Changes in the intestinal biotope cause the development of visceral hypersensitivity and impaired intestinal motor activity, as well as neuroimmune transmission. This article discusses the main aspects of the biological properties of probiotic bacteria in terms of their action within the “brain — intestine — microbiota” chain. The results of experimental and clinical studies elucidating the mechanisms of action of probiotic cultures have been generalized. The understanding of these mechanisms allows practitioners to make informed decisions in prescribing probiotics to IBS patients. Key concepts concerning fecal microbiota transplantation, as well as the prospects and difficulties of implementing this approach are considered.

Conclusions.The term “microbiota — intestine — brain” clearly demonstrates the correlation between the main functional components of IBS. Meta-analyses and systematic reviews confirm the efficacy of probiotics in IBS. However, further research into probiotic therapy options is needed to identify specific bacterial strains with proven clinical efficacy. The fecal microbiota transplantation method also requires further research, since many issues associated with this approach remain unclear.

Silencing of NOD2 protects against diabetic cardiomyopathy in a murine diabetes model

The aim of the present study was to investigate the role of the nucleotide‑binding oligomerization domain (NOD) 2 in high glucose (HG)‑induced myocardial apoptosis and fibrosis in mice. Mouse models of diabetes were induced by streptozotocin (STZ). NOD2 expression was knocked down by injection of lentivirus‑mediated short‑hairpin RNA. Alternatively, small interfering RNA‑NOD2 was transfected into cardiomyocytes and cardiac fibroblasts (CFs). A hemodynamic assay was used to assess the cardiac function in the mouse model. Hematoxylin and eosin, Masson and terminal deoxynucleotidyl transferase dUTP nick end labeling staining was performed to observe pathological changes and injury of myocardial tissue. The expression levels of NOD2, collagen I and III, and transforming growth factor‑β (TGF‑β) and apoptotic proteins were quantified by reverse transcription‑quantitative polymerase chain reaction and western blotting. NOD2 silencing ameliorated diabetes‑induced myocardial apoptosis and fibrosis in mice. NOD2, collagen I, collagen III, TGF‑β and pro‑apoptotic proteins were upregulated in the diabetic cardiomyopathy (DCM) model group, but interference of NOD2 suppressed these alterations in protein expression levels. NOD2 is upregulated in HG‑induced primary cardiomyocytes and CFs. Suppression of NOD2 attenuated HG‑induced cardiomyocyte apoptosis and proliferation of CFs. Overall, NOD2 silencing alleviated myocardial apoptosis and fibrosis in diabetic mice. The results of the present study demonstrated an understanding of the role of NOD2 in diabetes‑induced cardiomyopathy, which provides a novel target and therapies for the prevention and treatment of DCM.

Targeting the miR-665-3p-ATG4B-autophagy axis relieves inflammation and apoptosis in intestinal ischemia/reperfusion

Autophagy is an essential cytoprotective response against pathologic stresses that selectively degrades damaged cellular components. Impaired autophagy contributes to organ injury in multiple diseases, including ischemia/reperfusion (I/R), but the exact mechanism by which impaired autophagy is regulated remains unclear. Several researchers have demonstrated that microRNAs (miRNAs) negatively regulate autophagy by targeting autophagy-related genes (ATGs). Therefore, the effect of ATG-related miRNAs on I/R remains a promising research avenue. In our study, we found that autophagy flux is impaired during intestinal I/R. A miRNA microarray analysis showed that miR-665-3p was highly expressed in the I/R group, which was confirmed by qRT-PCR. Then, we predicted and proved that miR-665-3p negatively regulates ATG4B expression in Caco-2 and IEC-6 cells. In ileum biopsy samples from patients with intestinal infarction, there was an inverse correlation between miR-665-3p and ATG4B expression, which supports the in vitro findings. Moreover, based on miR-665-3p regulation of autophagy in response to hypoxia/reoxygenation in vitro, gain-of-function and loss-of-function approaches were used to investigate the therapeutic potential of miR-665-3p. Additionally, we provide evidence that ATG4B is indispensable for protection upon inhibition of miR-665-3p. Finally, we observed that locked nucleic acid-modified inhibition of miR-665-3p in vivo alleviates I/R-induced systemic inflammation and apoptosis via recovery of autophagic flux. Our study highlights miR-665-3p as a novel small molecule that regulates autophagy by targeting ATG4B, suggesting that miR-665-3p inhibition may be a potential therapeutic approach against inflammation and apoptosis for the clinical treatment of intestinal I/R.

From sensing to shaping microbiota: insights into the role of NOD2 in intestinal homeostasis and progression of Crohn's disease

NOD2 was the first susceptibility gene identified for Crohn's disease (CD), one of the major forms of inflammatory bowel disease (IBD). The field of NOD2 research has opened up many questions critical to understanding the complexities of microbiota-host interactions. In addition to sensing its specific bacterial components as a cytosolic pattern recognition receptor, NOD2 also appears to shape the colonization of intestinal microbiota. Activated NOD2 triggers downstream signaling cascades exampled by the NF-κB pathway to induce antimicrobial activities, however, defective or loss of NOD2 functions incur a similarly activated inflammatory response. Additional studies have identified the involvement of NOD2 in protection against non-microbiota-related intestinal damages as well as extraintestinal infections. We survey recent molecular and genetic studies of NOD2-mediated bacterial sensing and immunological modulation, and integrate evidence to suggest a highly reciprocal but still poorly understood cross talk between enteric microbiota and host cells.

Europium-Doped Cerium Oxide Nanoparticles Limit Reactive Oxygen Species Formation and Ameliorate Intestinal Ischemia-Reperfusion Injury

Accumulating evidence suggests that ischemia-reperfusion-induced injury is associated with the formation of reactive oxygen species (ROS). This study demonstrates the therapeutic effectiveness of novel europium-doped cerium oxide nanoparticles (Eu-doped Ceria NPs) as ROS scavengers in a mouse model of intestinal ischemia-reperfusion-induced injury. An increased production of superoxide radicals is detected in the intestine throughout the ischemia stage and again after initiating reperfusion. These changes in superoxide radical formation are associated with the induction of inflammatory cytokines in the intestine. This study further shows that Eu-Ceria NPs exhibit superoxide scavenging activity in vitro. Importantly, administration of Eu-Ceria NPs into the intestinal lumen during the onset of ischemia effectively blocks superoxide accumulation, reduces the expression of IL-1b, and ameliorates the intestinal pathology. These results suggest that early increased production of ROS during the ischemia-reperfusion promotes intestinal pathology and that mucosal delivery of Eu-Ceria NPs may be a potential therapeutic approach to block ROS accumulation and ameliorate the severity of intestinal disease.

Metabolomic profiling to characterize acute intestinal ischemia/reperfusion injury

Sepsis and septic shock are the leading causes of death in critically ill patients. Acute intestinal ischemia/reperfusion (AII/R) is an adaptive response to shock. The high mortality rate from AII/R is due to the severity of the disease and, more importantly, the failure of timely diagnosis. The objective of this investigation is to use nuclear magnetic resonance (NMR) analysis to characterize urine metabolomic profile of AII/R injury in a mouse model. Animals were exposed to sham, early (30 min) or late (60 min) acute intestinal ischemia by complete occlusion of the superior mesenteric artery, followed by 2 hrs of reperfusion. Urine was collected and analyzed by NMR spectroscopy. Urinary metabolite concentrations demonstrated that different profiles could be delineated based on the duration of the intestinal ischemia. Metabolites such as allantoin, creatinine, proline, and methylamine could be predictive of AII/R injury. Lactate, currently used for clinical diagnosis, was found not to significantly contribute to the classification model for either early or late ischemia. This study demonstrates that patterns of changes in urinary metabolites are effective at distinguishing AII/R progression in an animal model. This is a proof-of-concept study to further support examination of metabolites in the clinical diagnosis of intestinal ischemia reperfusion injury in patients. The discovery of a fingerprint metabolite profile of AII/R will be a major advancement in the diagnosis, treatment, and prevention of systemic injury in critically ill patients.

Cutaneous Nod2 Expression Regulates the Skin Microbiome and Wound Healing in a Murine Model

The skin microbiome exists in dynamic equilibrium with the host, but when the skin is compromised, bacteria can colonize the wound and impair wound healing. Thus, the interplay between normal skin microbial interactions versus pathogenic microbial interactions in wound repair is important. Bacteria are recognized by innate host pattern recognition receptors, and we previously showed an important role for the pattern recognition receptor NOD2 in skin wound repair. NOD2 is implicated in changes in the composition of the intestinal microbiota in Crohn’s disease, but its role on skin microbiota is unknown. Nod2-deficient (Nod2^–/–) mice had an inherently altered skin microbiome compared with wild-type controls. Furthermore, we found that Nod2^–/– skin microbiome dominated and caused impaired healing, shown in cross-fostering experiments of wild-type pups with Nod2^–/– pups, which then acquired altered cutaneous bacteria and delayed healing. High-throughput sequencing and quantitative real-time PCR showed a significant compositional shift, specifically in the genus Pseudomonas in Nod2^–/– mice. To confirm whether Pseudomonas species directly impair wound healing, wild-type mice were infected with Pseudomonas aeruginosa biofilms and, akin to Nod2^–/– mice, were found to exhibit a significant delay in wound repair. Collectively, these studies show the importance of the microbial communities in skin wound healing outcome.

Autophagy can alleviate severe burn-induced damage to the intestinal tract in mice

BACKGROUND

The present study was designed to examine the effect of autophagy and apoptosis on intestinal injury in mice after severe burns.

METHODS

Kunming mice were subjected to third degree burns over 30% of the total body surface area. Damage to the intestine was assessed by examining changes in intestinal mucosal morphology, enzyme-linked immunosorbent assay of serum d-lactate, diamine oxidase, lipopolysaccharide, interleukin-6, and tumor necrosis factor α (marker of intestinal damage), hematoxylin and eosin staining, and Western blotting under 4 experimental conditions: control group, burn only (burn group), burn and administration of rapamycin to stimulate intestinal autophagy (rapamycin group), or burn and administration of 3-methyladenine to inhibit intestinal autophagy (3-methyladenine group).

RESULTS

At day 1 postburn, the expression levels of light chain 3 II, beclin-1, and cleaved caspase-3 were significantly greater in all 3 groups of mice subjected to the burn injury than in the control group 1 day postburn; while the levels of light chain 3 II and beclin-1 were significantly greater and those of cleaved caspase-3 were significantly less in the rapamycin group than in the burn group. In contrast, light chain 3 II and beclin-1 levels were significantly less and those of cleaved caspase-3 significantly greater in the 3-methyladenine group. All 3 groups subjected to burn injury showed significantly increased levels of d-lactate, diamine oxidase, lipopolysaccharide, interleukin-6, and tumor necrosis factor α. Of the 3 groups, the rapamycin group exhibited the least observed levels, the 3-methyladenine group the greatest, and the burn group intermediate. Pathologic sections of the intestinal tissue showed that all 3 burn groups exhibited severe intestinal mucosal damage at 1 day postburn. The condition of the 3-methyladenine treatment group was worse than that of the rapamycin treatment group, but better than that of the burn group.

CONCLUSION

Intestinal autophagy is activated in response to intestinal apoptosis after severe burns and may alleviate burn-induced intestinal injury.

The gut microbiota and gastrointestinal surgery

Surgery involving the gastrointestinal tract continues to prove challenging because of the persistence of unpredictable complications such as anastomotic leakage and life-threatening infections. Removal of diseased intestinal segments results in substantial catabolic stress and might require complex reconstructive surgery to maintain the functional continuity of the intestinal tract. As gastrointestinal surgery necessarily involves a breach of an epithelial barrier colonized by microorganisms, preoperative intestinal antisepsis is used to reduce infection-related complications. The current approach to intestinal antisepsis varies widely across institutions and countries with little understanding of its mechanism of action, effect on the gut microbiota and overall efficacy. Many of the current approaches to intestinal antisepsis before gastrointestinal surgery run counter to emerging concepts of intestinal microbiota contributing to immune function and recovery from injury. Here, we review evidence outlining the role of gut microbiota in recovery from gastrointestinal surgery, particularly in the development of infections and anastomotic leak. To make surgery safer and further reduce complications, a molecular, genetic and functional understanding of the response of the gastrointestinal tract to alterations in its microbiota is needed. Methods can then be developed to preserve the health-promoting functions of the microbiota while at the same time suppressing their harmful effects.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Murine Model of Intestinal Ischemia-reperfusion Injury

Intestinal ischemia is a life-threatening condition associated with a broad range of clinical conditions including atherosclerosis, thrombosis, hypotension, necrotizing enterocolitis, bowel transplantation, trauma and chronic inflammation. Intestinal ischemia-reperfusion (IR) injury is a consequence of acute mesenteric ischemia, caused by inadequate blood flow through the mesenteric vessels, resulting in intestinal damage. Reperfusion following ischemia can further exacerbate damage of the intestine. The mechanisms of IR injury are complex and poorly understood. Therefore, experimental small animal models are critical for understanding the pathophysiology of IR injury and the development of novel therapies. Here we describe a mouse model of acute intestinal IR injury that provides reproducible injury of the small intestine without mortality. This is achieved by inducing ischemia in the region of the distal ileum by temporally occluding the peripheral and terminal collateral branches of the superior mesenteric artery for 60 min using microvascular clips. Reperfusion for 1 hr, or 2 hr after injury results in reproducible injury of the intestine examined by histological analysis. Proper position of the microvascular clips is critical for the procedure. Therefore the video clip provides a detailed visual step-by-step description of this technique. This model of intestinal IR injury can be utilized to study the cellular and molecular mechanisms of injury and regeneration.

Gut microbiota role in irritable bowel syndrome: New therapeutic strategies

In the last decade the impressive expansion of our knowledge of the vast microbial community that resides in the human intestine, the gut microbiota, has provided support to the concept that a disturbed intestinal ecology might promote development and maintenance of symptoms in irritable bowel syndrome (IBS). As a correlate, manipulation of gut microbiota represents a new strategy for the treatment of this multifactorial disease. A number of attempts have been made to modulate the gut bacterial composition, following the idea that expansion of bacterial species considered as beneficial (Lactobacilli and Bifidobacteria) associated with the reduction of those considered harmful (Clostridium, Escherichia coli, Salmonella, Shigella and Pseudomonas) should attenuate IBS symptoms. In this conceptual framework, probiotics appear an attractive option in terms of both efficacy and safety, while prebiotics, synbiotics and antibiotics still need confirmation. Fecal transplant is an old treatment translated from the cure of intestinal infective pathologies that has recently gained a new life as therapeutic option for those patients with a disturbed gut ecosystem, but data on IBS are scanty and randomized, placebo-controlled studies are required.

The potential of mesenchymal stem cells in the management of radiation enteropathy

Although radiotherapy is effective in managing abdominal and pelvic malignant tumors, radiation enteropathy is still unavoidable. This disease severely affects the quality of life of cancer patients due to some refractory lesions, such as intestinal ischemia, mucositis, ulcer, necrosis or even perforation. Current drugs or prevailing therapies are committed to alleviating the symptoms induced by above lesions. But the efficacies achieved by these interventions are still not satisfactory, because the milieus for tissue regeneration are not distinctly improved. In recent years, regenerative therapy for radiation enteropathy by using mesenchymal stem cells is of public interests. Relevant results of preclinical and clinical studies suggest that this regenerative therapy will become an attractive tool in managing radiation enteropathy, because mesenchymal stem cells exhibit their pro-regenerative potentials for healing the injuries in both epithelium and endothelium, minimizing inflammation and protecting irradiated intestine against fibrogenesis through activating intrinsic repair actions. In spite of these encouraging results, whether mesenchymal stem cells promote tumor growth is still an issue of debate. On this basis, we will discuss the advances in anticancer therapy by using mesenchymal stem cells in this review after analyzing the pathogenesis of radiation enteropathy, introducing the advances in managing radiation enteropathy using regenerative therapy and exploring the putative actions by which mesenchymal stem cells repair intestinal injuries. At last, insights gained from the potential risks of mesenchymal stem cell-based therapy for radiation enteropathy patients may provide clinicians with an improved awareness in carrying out their studies.