Structural shifts of fecal microbial communities in rats with acute rejection after liver transplantation

Gut Microbiota and Liver Regeneration: A Synthesis of Evidence on Structural Changes and Physiological Mechanisms

Liver regeneration (LR) is a unique biological process with the ability to restore up to 70% of the organ. This allows for the preservation of liver resections for various liver tumors and for living donor liver transplantation (LDLT). However, in some cases, LR is insufficient and interventions that can improve LR are urgently needed. Gut microbiota (GM) is one of the factors influencing LR, as the liver and intestine are intimately connected through the gut-liver axis. Thus, healthy GM facilitates normal LR, whereas dysbiosis leads to impaired LR due to imbalance of bile acids, inflammatory cytokines, microbial metabolites, signaling pathways, etc. Therefore, GM can be considered as a new possible therapeutic target to improve LR. In this review, we critically observe the current knowledge about the influence of gut microbiota (GM) on liver regeneration (LR) and the possibility to improve this process, which may reduce complication and mortality rates after liver surgery. Although much research has been done on this topic, more clinical trials and systemic reviews are urgently needed to move this type of intervention from the experimental phase to the clinical field.

Gut microbiota biotransformation of drug glucuronides leading to gastrointestinal toxicity: Therapeutic potential of bacterial β-glucuronidase inhibition in mycophenolate-induced enteropathy

AIMS

Drug-induced enteropathy is often associated with the therapeutic use of certain glucuronidated drugs. One such drug is mycophenolic acid (MPA), a well-established immunosuppressant of which gastrointestinal adverse effects are a major concern. The role of bacterial β-glucuronidase (β-G) from the gut microbiota in MPA-induced enteropathy has recently been discovered. Bacterial β-G hydrolyzes MPAG, the glucuronide metabolite of MPA excreted in the bile, leading to the digestive accumulation of MPA that would favor in turn these adverse events. We therefore hypothesized that taming bacterial β-G activity might reduce MPA digestive exposure and prevent its toxicity.

MAIN METHODS

By using a multiscale approach, we evaluated the effect of increasing concentrations of MPA on intestinal epithelial cells (Caco-2 cell line) viability, proliferation, and migration. Then, we investigated the inhibitory properties of amoxapine, a previously described bacterial β-G inhibitor, by using molecular dynamics simulations, and evaluated its efficiency in blocking MPAG hydrolysis in an Escherichia coli-based β-G activity assay. The pharmacological effect of amoxapine was evaluated in a mouse model.

KEY FINDINGS

We observed that MPA impairs intestinal epithelial cell homeostasis. Amoxapine efficiently blocks the hydrolysis of MPAG to MPA and significantly reduces digestive exposure to MPA in mice. As a result, administration of amoxapine in MPA-treated mice significantly attenuated gastrointestinal lesions.

SIGNIFICANCE

Collectively, these results suggest that the digestive accumulation of MPA is involved in the pathophysiology of MPA-gastrointestinal adverse effects. This study provides a proof-of-concept of the therapeutic potential of bacterial β-G inhibitors in glucuronidated drug-induced enteropathy.

Impact of gut microbiota on liver transplantation

The gut microbiota has been gaining attention due to its interactions with the human body and its role in pathophysiological processes. One of the main interactions is the "gut-liver axis," in which disruption of the gut mucosal barrier seen in portal hypertension and liver disease can influence liver allograft function over time. For example, in patients who are undergoing liver transplantation, preexisting dysbiosis, perioperative antibiotic use, surgical stress, and immunosuppressive use have each been associated with alterations in gut microbiota, potentially impacting overall morbidity and mortality. In this review, studies exploring gut microbiota changes in patients undergoing liver transplantation are reviewed, including both human and experimental animal studies. Common themes include an increase in Enterobacteriaceae and Enterococcaceae species and a decrease in Faecalibacterium prausnitzii and Bacteriodes, while a decrease in the overall diversity of gut microbiota after liver transplantation.

Cognitive Impairment in Liver Transplant Recipients With a History of Cirrhosis: A Systematic Review

Cognitive impairment is common among patients with cirrhosis and may persist post-transplantation. This systematic review seeks to (1) describe the prevalence of cognitive impairment in liver transplant (LT) recipients with a history of cirrhosis, (2) describe risk factors for this population, and (3) describe associations between post-transplant cognitive impairment and quality outcome measures.

Methods

Studies in PubMed, Embase, Scopus, PsychINFO, and the Cochrane Database of Controlled Trials were included through May 2022. Inclusion criteria included (1) population - LT recipient, age ≥18 y, (2) exposure - history of cirrhosis before transplant, and (3) outcome - cognitive impairment after transplant (per validated cognitive testing). Exclusion criteria included (1) wrong study type, (2) abstract-only publication, (3) full-text unavailable, (4) wrong population, (5) wrong exposure, and (6) wrong outcome. The risk of bias was assessed using the Newcastle-Ottawa Scale and the Appraisal tool for Cross-Sectional Studies. The Grading of Recommendations, Assessment, Development, and Evaluations system was used to assess evidence certainty. Data from individual tests were categorized into six cognitive domains: attention, executive function, working memory, long-term memory, visuospatial, and language.

Results

Twenty-four studies were included covering 847 patients. Follow-up ranged from 1 mo to 1.8 y after LT. Studies had a median of 30 (interquartile range 21.5-50.5) patients. The prevalence of cognitive impairment after LT ranged from 0% to 36%. Forty-three unique cognitive tests were used, the most common being the Psychometric Hepatic Encephalopathy Score. The most frequently assessed cognitive domains were attention (10 studies) and executive function (10 studies).

Conclusions

The prevalence of cognitive impairment after LT varied across studies depending on cognitive tests utilized and follow-up duration. Attention and executive function were most impacted. Generalizability is limited due to small sample size and heterogeneous methodology. Further studies are needed to examine differences in the prevalence of post-LT cognitive impairment by etiology, risk factors, and ideal cognitive measures.

Dysbiosis and Depletion of Fecal Organic Acids Correlate With the Severity of Rejection After Rat Liver Transplantation

The impact of T cell-mediated rejection (TCMR) after liver transplantation (LT) on the alterations in the gut microbiota (GM) and associated intestinal environment represented by fecal organic acids (OAs) require further elucidation. A rat allogeneic LT model was prepared without immunosuppressants or antibiotics, and a syngeneic model was used as a control. Qualitative and quantitative analyses of fecal samples at fixed time points were performed. Correlation analyses were also performed between liver function and GMs and OA levels. In the allogeneic TCMR group, the number of predominant obligate anaerobes decreased as liver function declined. Clostridioides difficile, Enterobacteriaceae, Enterococcus, Streptococcus, and Staphylococcus were significantly increased. Regarding fecal OA concentration, short-chain fatty acid (SCFA) concentrations were depleted as liver function declined. In contrast, in the syngeneic group, GM and OAs exhibited only slight, transient, and reversible disturbances. In addition, alanine aminotransferase and total bilirubin were positively correlated with the number of Enterobacteriaceae and Enterococcus, and negatively correlated with the fecal concentration of SCFAs. The allogeneic TCMR model demonstrated distinct dysbiosis and depletion of fecal OAs as TCMR progressed after LT. The degree of graft injury was closely related to the number of specific bacterial strains and the concentrations of fecal SCFAs.

A decrease in functional microbiomes represented as Faecalibacterium affects immune homeostasis in long-term stable liver transplant patients

LT, liver transplantation; HCC, hepatocellular carcinoma; IS, immunosuppressants; DC, dendritic cells; Treg, regulatory T; Th17, T helper 17; AST, aspartate transaminase; ALT, alanine transaminase; OUT, operational taxonomic unit; LEfSe, linear discriminant analysis effect size; LDA, linear discriminant analysis; IL, interleukin; TGF, transforming growth factor; GM-CSF, granulocyte-macrophage colony-stimulating factor; IFN, interferon; TNF-α, tumor necrosis factor-α; MIP-1α, macrophage inflammatory protein-1α; IP-10, interferon γ-induced protein; MCP-1, monocyte chemoattractant protein-1; ACR, acute cellular rejection; NF-κB, nuclear factor κB; PT INR, prothrombin time; QC, quality check; PBMC, peripheral blood mononuclear cells; PBS, phosphate-buffered saline; ELISA, enzyme-linked immunosorbent assay.

The role of bacterial translocation in sepsis: a new target for therapy

Sepsis is a leading cause of death in critically ill patients, primarily due to multiple organ failures. It is associated with a systemic inflammatory response that plays a role in the pathogenesis of the disease. Intestinal barrier dysfunction and bacterial translocation (BT) play pivotal roles in the pathogenesis of sepsis and associated organ failure. In this review, we describe recent advances in understanding the mechanisms by which the gut microbiome and BT contribute to the pathogenesis of sepsis. We also discuss several potential treatment modalities that target the microbiome as therapeutic tools for patients with sepsis.

Biliary Diseases from the Microbiome Perspective: How Microorganisms Could Change the Approach to Benign and Malignant Diseases

Recent evidence regarding microbiota is modifying the cornerstones on pathogenesis and the approaches to several gastrointestinal diseases, including biliary diseases. The burden of biliary diseases, indeed, is progressively increasing, considering that gallstone disease affects up to 20% of the European population. At the same time, neoplasms of the biliary system have an increasing incidence and poor prognosis. Framing the specific state of biliary eubiosis or dysbiosis is made difficult by the use of heterogeneous techniques and the sometimes unwarranted invasive sampling in healthy subjects. The influence of the microbial balance on the health status of the biliary tract could also account for some of the complications surrounding the post-liver-transplant phase. The aim of this extensive narrative review is to summarize the current evidence on this topic, to highlight gaps in the available evidence in order to guide further clinical research in these settings, and, eventually, to provide new tools to treat biliary lithiasis, biliopancreatic cancers, and even cholestatic disease.

Interactions between human microbiome, liver diseases, and immunosuppression after liver transplant

In liver transplant patients, solid tumors and post-transplant lymphoproliferative disorders have emerged as significant long-term mortality causes. In addition, it is assumed that de novo malignancy after liver transplantation (LT) is the second-leading cause of death after cardiovascular complications. Well-established risk factors for post-transplant lymphoproliferative disorders and solid tumors are calcineurin inhibitors, tacrolimus, and cyclosporine, the cornerstones of all immunosuppressive therapies used after LT. The loss of immunocompetence facilitated by the host immune system due to prolonged immunosuppressive therapy leads to cancer development, including LT patients. Furthermore, various mechanisms such as bacterial dysbiosis, activation through microbe-associated molecular patterns, leaky gut, and bacterial metabolites can drive cancer-promoting liver inflammation, fibrosis, and genotoxicity. Therefore, changes in human microbiota composition may contribute further to de novo carcinogenesis associated with the severe immunosuppression after LT.

Impact of gut microbiota on kidney transplantation

Kidney transplantation is recognized as one of the most effective treatments for patients who suffer from end-stage renal disease. The major potential outcomes following kidney transplantation include engraftment, rejection, and associated complications. The outcomes are dependent on a variety of factors in those who underwent renal grafts or kidney transplant recipients. Those factors include the administration of immunosuppressive drugs and prophylactic antimicrobial agents to recipients. Recent studies have shown that gut microbiota play an important role in the outcome of subjects with kidney transplantation. An imbalance of the components/diversity of gut microbiota, known as gut dysbiosis, has been shown to have a big impact on the immune system of the host and the modification of host inflammatory cytokines. Although gut dysbiosis is affected by variation in diet and medication, a substantial amount of evidence showing a link between alteration in human gut microbiota and outcomes of kidney transplantation has recently been reported. Therefore, the objective of this review is to comprehensively summarize and discuss the major findings from in vivo and clinical data pertaining to the impact of gut microbiota on kidney transplantation. Any controversial findings are compiled to enable a clear overview of the role of gut microbiota and the outcome of kidney transplantation.

Gut microbiota alterations associated with antibody-mediated rejection after kidney transplantation

Antibody-mediated rejection (AMR) has become the major challenge for kidney transplantation, and the efficacy of existing therapies was limited to prevent AMR. Increasing evidences have demonstrated the link between gut microbiota alterations and allograft outcome. However, there has been no comprehensive analysis to profile the gut microbiota associated with AMR after kidney transplantation. We performed this study to characterize the gut microbiota possibly associated with AMR. Fecal specimens were collected from 24 kidney transplantation recipients with AMR and 29 controls. DNA extracted from the specimens was processed for 16S rRNA gene sequencing using Illumina MiSeq. Gut microbial community of recipients with AMR was significantly different from that of controls based on unweighted (P = 0.001) and weighted (P = 0.02) UniFrac distances, and the bacterial richness (observed species: P = 0.0448; Chao1 index: P = 0.0450; ACE index: P = 0.0331) significantly decreased in the AMR group. LEfSe showed that 1 phylum, 5 classes, 7 families, and 10 genera were increased, whereas 1 class, 2 order, 3 families, and 4 genera were decreased in the AMR group. Specific taxa such as Clostridiales could be potentially used as biomarkers to distinguish the recipients with AMR from the controls (AUC = 0.77). PICRUSt analysis illustrated that 16 functional pathways were with significantly different abundances in the AMR and control groups. Our findings provide a foundation for further investigation on the role of gut microbiota in AMR after kidney transplantation, and potentially support novel diagnostic biomarkers and therapeutic options for AMR. KEY POINTS: • Gut microbial community of kidney recipients with AMR was different from that of controls. • Clostridiales is a potential marker to distinguish recipients with AMR from controls.

Focus on the Gut-Kidney Axis in Health and Disease

The recent new developments in technology with culture-independent techniques including genome sequencing methodologies shed light on the identification of microbiota bacterial species and their role in health and disease. Microbiome is actually reported as an important predictive tool for evaluating characteristic shifts in case of disease. Our present review states the development of different renal diseases and pathologies linked to the intestinal dysbiosis, which impacts on host homeostasis. The gastrointestinal–kidney dialogue provides intriguing features in the pathogenesis of several renal diseases. Without any doubt, investigation of this interconnection consists one of the most cutting-edge areas of research with potential implications on our health.

Effects of Gut Metabolites and Microbiota in Healthy and Marginal Livers Submitted to Surgery

Microbiota is defined as the collection of microorganisms within the gastrointestinal ecosystem. These microbes are strongly implicated in the stimulation of immune responses. An unbalanced microbiota, termed dysbiosis, is related to the development of several liver diseases. The bidirectional relationship between the gut, its microbiota and the liver is referred to as the gut–liver axis. The translocation of bacterial products from the intestine to the liver induces inflammation in different cell types such as Kupffer cells, and a fibrotic response in hepatic stellate cells, resulting in deleterious effects on hepatocytes. Moreover, ischemia-reperfusion injury, a consequence of liver surgery, alters the microbiota profile, affecting inflammation, the immune response and even liver regeneration. Microbiota also seems to play an important role in post-operative outcomes (i.e., liver transplantation or liver resection). Nonetheless, studies to determine changes in the gut microbial populations produced during and after surgery, and affecting liver function and regeneration are scarce. In the present review we analyze and discuss the preclinical and clinical studies reported in the literature focused on the evaluation of alterations in microbiota and its products as well as their effects on post-operative outcomes in hepatic surgery.

Pretreatment with a Phosphodiesterase-3 Inhibitor, Milrinone, Reduces Hepatic Ischemia-Reperfusion Injury, Minimizing Pericentral Zone-Based Liver and Small Intestinal Injury in Rats

BACKGROUND Severe pericentral zone (zone 3)-based liver injury (LI) may become intractable, with allograft dysfunction after liver transplantation. The phosphodiesterase-3 inhibitor, milrinone, has been reported to attenuate hepatic ischemia-reperfusion injury (IRI). This study clarified how hepatic IRI involved zone 3-based LI, in which zone milrinone was effective, and whether milrinone could improve small intestinal injury (SII) with hepatic IRI. MATERIAL AND METHODS Rats were divided into sham, ischemia-reperfusion (IR), or IR+milrinone groups (n=13 per group). Milrinone was administered intraportally via intrasplenic injection, and whole hepatic ischemia was induced for 30 min. Five hours after reperfusion, serum chemistry and histopathological findings were compared. Expression of CD34 for the detection of altered sinusoidal endothelium as sinusoidal capillarization and cleaved caspase-3 as an apoptosis marker were analyzed via immunohistochemistry. Survival rates were examined after 45 min of whole hepatic ischemia. RESULTS Serum aspartate aminotransferase and direct bilirubin levels were significantly decreased in the IR+milrinone group compared with those of the IR group. The degree of LI, sinusoidal capillarization and apoptosis at zone 3 in the IR group was significantly increased compared with those at the periportal zone (zone 1). These findings at zone 3 in the IR group were improved in the IR+milrinone group. SII with villus congestion and apoptosis in the IR group was significantly attenuated in the IR+milrinone group. The 7-day survival rate was significantly elevated in the IR+milrinone group as compared with that of the IR group. CONCLUSIONS A hepatic IRI model caused zone 3-based LI and SII, which were attenuated by intraportal administration of milrinone.

The histological assessment of liver fibrosis in grafts from extended criteria donors predicts the outcome after liver transplantation: A retrospective study

BACKGROUND

The use of extended criteria donors (ECD) in liver transplantation is increasing due to the organ shortage. Histological evaluation of the liver graft in the context of procurement is an important tool for extending the donor pool without affecting the quality of the transplanted organs. Macrovesicular steatosis is widely accepted as predictor of early allograft dysfunction (EAD), while other features, such as portal fibrosis, are poorly studied.

AIM

To identify morphological features, other than macrovesicular steatosis, that may affect recipients' outcome.

METHODS

Between 2014 and 2016, 132 donors with extended criteria underwent pre-transplant liver biopsy during procurement. Histological variables of the graft, donors'/recipients' clinical data, EAD and patient/graft survival were registered.

RESULTS

The recipients who received a graft with histological-proven portal fibrosis had a significant lower patient and graft survival in comparison to patients without fibrosis (P = 0.044 and P = 0.039, respectively). Donors' dyslipidemia was significantly associated with the occurrence of EAD (P = 0.021). When dyslipidemia was combined with histological liver fibrosis a 54.5% incidence of EAD was observed (P = 0.012).

CONCLUSIONS

The histological assessment of liver fibrosis in pre-transplant biopsy of ECD grafts, together with donor's clinical data, provides important information on recipients' outcome.

Role of Gut Dysbiosis in Liver Diseases: What Have We Learned So Far?

Accumulating evidence supports that gut dysbiosis may relate to various liver diseases. Alcoholics with high intestinal permeability had a decrease in the abundance of Ruminnococcus. Intestinal dysmotility, increased gastric pH, and altered immune responses in addition to environmental and genetic factors are likely to cause alcohol-associated gut microbial changes. Alcohol-induced dysbiosis may be associated with gut barrier dysfunction, as microbiota and their products modulate barrier function by affecting epithelial pro-inflammatory responses and mucosal repair functions. High levels of plasma endotoxin are detected in alcoholics, in moderate fatty liver to advanced cirrhosis. Decreased abundance of Faecalibacterium prausnitzii, an anti-inflammatory commensal, stimulating IL-10 secretion and inhibiting IL-12 and interferon-γ expression. Proteobacteria, Enterobacteriaceae, and Escherichia were reported to be increased in NAFLD (nonalcoholic fatty liver disease) patients. Increased abundance of fecal Escherichia to elevated blood alcohol levels in these patients and gut microbiota enriched in alcohol-producing bacteria produce more alcohol (alcohol hypothesis). Some undetermined pathological sequences related to gut dysbiosis may facilitate energy-producing and proinflammatory conditions for the progression of NAFLD. A shortage of autochthonous non-pathogenic bacteria and an overgrowth of potentially pathogenic bacteria are common findings in cirrhotic patients. The ratio of the amounts of beneficial autochthonous taxa (Lachnospiraceae + Ruminococaceae + Veillonellaceae + Clostridiales Incertae Sedis XIV) to those of potentially pathogenic taxa (Enterobacteriaceae + Bacteroidaceae) was low in those with early death and organ failure. Cirrhotic patients with decreased microbial diversity before liver transplantation were more likely to develop post-transplant infections and cognitive impairment related to residual dysbiosis. Patients with PSC had marked reduction of bacterial diversity. Enterococcus and Lactobacillus were increased in PSC patients (without liver cirrhosis.) Treatment-naive PBC patients were associated with altered composition and function of gut microbiota, as well as a lower level of diversity. As serum anti-gp210 antibody has been considered as an index of disease progression, relatively lower species richness and lower abundance of Faecalibacterium spp. in gp210-positive patients are interesting. The dysbiosis-induced altered bacterial metabolites such as a hepatocarcinogenesis promotor DCA, together with a leaky gut and bacterial translocation. Gut protective Akkermansia and butyrate-producing genera were decreased, while genera producing-lipopolysaccharide were increased in early hepatocellular carcinoma (HCC) patients.

Functional Microbiomics in Liver Transplantation: Identifying Novel Targets for Improving Allograft Outcomes

Gut dysbiosis, defined as a maladaptive gut microbial imbalance, has been demonstrated in patients with end-stage liver disease, defined as a contributor to disease progression, and associated clinically with severity of disease and liver-related morbidity and mortality. Despite this well-recognized phenomena in patients with end-stage liver disease, the impact of gut dysbiosis and its rate of recovery following liver transplantation (LT) remains incompletely understood. The mechanisms by which alterations in the gut microbiota impact allograft metabolism and immunity, both directly and indirectly, are multifactorial and reflect the complexity of the gut-liver axis. Importantly, while research has largely focused on quantitative and qualitative changes in gut microbial composition, changes in microbial functionality (in the presence or absence of compositional changes) are of critical importance. Therefore, to translate functional microbiomics into clinical practice, one must understand not only the compositional but also the functional changes associated with gut dysbiosis and its resolution post-LT. In this review, we will summarize critical advances in functional microbiomics in LT recipients as they apply to immune-mediated allograft injury, posttransplant complications, and disease recurrence, while highlighting potential areas for microbial-based therapeutics in LT recipients.

The vaginal microbiome in uterine transplantation

Women with congenital absolute uterine factor infertility (AUFI) often need vaginal restoration to optimise sexual function. Given their lack of procreative ability, little consideration has previously been given to the resultant vaginal microbiome (VM). Uterine transplantation (UTx) now offers the opportunity to restore these women's reproductive potential. The structure of the VM is associated with clinical and reproductive implications that are intricately intertwined with the process of UTx. Consideration of how vaginal restoration methods impact VM is now warranted and assessment of the VM in future UTx procedures is essential to understand the interrelation of the VM and clinical and reproductive outcomes. TWEETABLE ABSTRACT: The vaginal microbiome has numerous implications for clinical and reproductive outcomes in the context of uterine transplantation.

Structural shifts in the intestinal microbiota of rats treated with cyclosporine A after orthotropic liver transplantation

Understanding the effect of immunosuppressive agents on intestinal microbiota is important to reduce the mortality and morbidity from orthotopic liver transplantation (OLT). We investigated the relationship between the commonly used immunosuppressive agent cyclosporine A (CSA) and the intestinal microbial variation in an OLT model. The rat samples were divided as follows: (1) N group (normal control); (2) I group (isograft LT, Brown Norway [BN] rat to BN); (3) R group (allograft LT, Lewis to BN rat); and (4) CSA group (R group treated with CSA). The intestinal microbiota was assayed by denaturing gradient gel electrophoresis profiles and by using real-time polymerase chain reaction. The liver histopathology and the alanine/aspartate aminotransferase ratio after LT were both ameliorated by CSA. In the CSA group, the numbers of rDNA gene copies of Clostridium cluster I, Clostridium cluster XIV, and Enterobacteriaceae decreased, whereas those of Faecalibacterium prausnitzii increased compared with the R group. Cluster analysis indicated that the samples from the N, I, and CSA groups were clustered, whereas the other clusters contained the samples from the R group. Hence, CSA ameliorates hepatic graft injury and partially restores gut microbiota following LT, and these may benefit hepatic graft rejection.

Optimal immunosuppressor induces stable gut microbiota after liver transplantation

AIM

To study the influence of different doses of tacrolimus (FK506) on gut microbiota after liver transplantation (LT) in rats.

METHODS

Specific pathogen-free Brown Norway (BN) rats and Lewis rats were separated into five groups: (1) Tolerance group (BN-BN LT, n = 8); (2) rejection group (Lewis-BN LT, n = 8); (3) high dosage FK506 (FK506-H) group (Lewis-BN LT, n = 8); (4) middle dosage FK506 (FK506-M) group (Lewis-BN LT, n = 8); and (5) low dosage FK506 (FK506-L) group (Lewis-BN LT, n = 8). FK506 was administered to recipients at a dose of 1.0 mg/kg, 0.5 mg/kg, and 0.1 mg/kg body weight for 29 d after LT to the FK506-H, FK506-M, and FK506-L groups, respectively. On the 30^th day after LT, all rats were sampled and euthanized. Blood samples were harvested for liver function and plasma endotoxin testing. Hepatic graft and ileocecal tissues were collected for histopathology observation. Ileocecal contents were used for DNA extraction, Real-time quantitative polymerase chain reaction (RT-PCR) and digital processing of denaturing gradient gel electrophoresis (DGGE) profiles and analysis.

RESULTS

Compared to the FK506-H and FK506-L groups, FK506-M was optimal for maintaining immunosuppression and inducing normal graft function; the FK506-M maintained gut barrier integrity and low plasma endotoxin levels; furthermore, DGGE results showed that FK506-M induced stable gut microbiota. Diversity analysis indicated that FK506-M increased species richness and rare species abundance, and cluster analysis confirmed the stable gut microbiota induced by FK506-M. Phylogenetic tree analysis identified crucial bacteria associated with FK506-M; seven of the nine bacteria that were decreased corresponded to Bacteroidetes, while increased bacteria were of the Bifidobacterium species. FK506-M increased Faecalibacterium prausnitzii and Bifidobacterium spp. and decreased Bacteroides-Prevotella and Enterobacteriaceae, as assessed by RT-PCR, which confirmed the crucial bacterial alterations identified through DGGE.

CONCLUSION

Compared to the low or high dosage of FK506, an optimal dosage of FK506 induced immunosuppression, normal graft function and stable gut microbiota following LT in rats. The stable gut microbiota presented increased probiotics and decreased potential pathogenic endotoxin-producing bacteria. These findings provide a novel strategy based on gut microbiota for immunosuppressive dosage assessment for recipients following LT.

Characteristics of fecal microbial communities in patients with non-anastomotic biliary strictures after liver transplantation

AIM

To explore the possible relationship between fecal microbial communities and non-anastomotic stricture (NAS) after liver transplantation (LT).

METHODS

A total of 30 subjects including 10 patients with NAS, 10 patients with no complications after LT, and 10 non-LT healthy individuals were enrolled. Fecal microbial communities were assessed by the 16S rRNA gene sequencing technology.

RESULTS

Different from the uncomplicated and healthy groups, unbalanced fecal bacterium ratio existed in patients with NAS after LT. The results showed that NAS patients were associated with a decrease of Firmicutes and Bacteroidetes and an increase of Proteobacteria at the phylum level, with the proportion-ratio imbalance between potential pathogenic families including Enterococcaceae, Streptococcaceae, Enterobacteriaceae, Pseudomonadaceae and dominant families including Bacteroidaceae.

CONCLUSION

The compositional shifts of the increase of potential pathogenic bacteria as well as the decrease of dominant bacteria might contribute to the incidence of NAS.

Gut microbial balance and liver transplantation: alteration, management, and prediction

Liver transplantation is a conventional treatment for terminal stage liver diseases. However, several complications still hinder the survival rate. Intestinal barrier destruction is widely observed among patients receiving liver transplant and suffering from ischemia-reperfusion or rejection injuries because of the relationship between the intestine and the liver, both in anatomy and function. Importantly, the resulting alteration of gut microbiota aggravates graft dysfunctions during the process. This article reviews the research progress for gut microbial alterations and liver transplantation. Especially, this work also evaluates research on the management of gut microbial alteration and the prediction of possible injuries utilizing microbial alteration during liver transplantation. In addition, we propose possible directions for research on gut microbial alteration during liver transplantation and offer a hypothesis on the utilization of microbial alteration in liver transplantation. The aim is not only to predict perioperative injuries but also to function as a method of treatment or even inhibit the rejection of liver transplantation.

Liver transplant modulates gut microbial dysbiosis and cognitive function in cirrhosis

Liver transplantation (LT) improves daily function and cognition in patients with cirrhosis, but a subset of patients can remain impaired. Unfavorable microbiota or dysbiosis is observed in patients with cirrhosis, but the effect of LT on microbial composition, especially with poor post-LT cognition, is unclear. The aims were to determine the effect of LT on gut microbiota and to determine whether gut microbiota are associated with cognitive dysfunction after LT. We enrolled outpatient patients with cirrhosis on the LT list and followed them until 6 months after LT. Cognition (Psychometric Hepatic Encephalopathy score [PHES]), health-related quality of life (HRQOL), and stool microbiota (multitagged sequencing for diversity and taxa) tests were performed at both visits. Persistent cognitive impairment was defined as a stable/worsening PHES. Both pre-/post-LT data were compared with age-matched healthy controls. We enrolled 45 patients (56 ± 7 years, Model for End-Stage Liver Disease score 26 ± 8). They received LT 6 ± 3 months after enrollment and were re-evaluated 7 ± 2 months after LT with a stable course. A significantly improved HRQOL, PHES, with increase in microbial diversity, increase in autochthonous, and decrease in potentially pathogenic taxa were seen after LT compared with baseline. However, there was continued dysbiosis and HRQOL/cognitive impairment after LT compared with controls in 29% who did not improve PHES after LT. In these, Proteobacteria relative abundance was significantly higher and Firmicutes were lower after LT, whereas the reverse occurred in the group that improved. Delta PHES was negatively correlated with delta Proteobacteria and positively with delta Firmicutes. In conclusion, LT improves gut microbiota diversity and dysbiosis compared with pre-LT baseline but residual dysbiosis remains compared with controls. There is cognitive and HRQOL enhancement in general after LT, but a higher Proteobacteria relative abundance change is associated with posttransplant cognitive impairment. Liver Transplantation 23 907-914 2017 AASLD.

Impact of environmental factors on alloimmunity and transplant fate

Although gene-environment interactions have been investigated for many years to understand people's susceptibility to autoimmune diseases or cancer, a role for environmental factors in modulating alloimmune responses and transplant outcomes is only now beginning to emerge. New data suggest that diet, hyperlipidemia, pollutants, commensal microbes, and pathogenic infections can all affect T cell activation, differentiation, and the kinetics of graft rejection. These observations reveal opportunities for novel therapeutic interventions to improve graft outcomes as well as for noninvasive biomarker discovery to predict or diagnose graft deterioration before it becomes irreversible. In this Review, we will focus on the impact of these environmental factors on immune function and, when known, on alloimmune function, as well as on transplant fate.

The digestive tract as the origin of systemic inflammation

Failure of gut homeostasis is an important factor in the pathogenesis and progression of systemic inflammation, which can culminate in multiple organ failure and fatality. Pathogenic events in critically ill patients include mesenteric hypoperfusion, dysregulation of gut motility, and failure of the gut barrier with resultant translocation of luminal substrates. This is followed by the exacerbation of local and systemic immune responses. All these events can contribute to pathogenic crosstalk between the gut, circulating cells, and other organs like the liver, pancreas, and lungs. Here we review recent insights into the identity of the cellular and biochemical players from the gut that have key roles in the pathogenic turn of events in these organ systems that derange the systemic inflammatory homeostasis. In particular, we discuss the dangers from within the gastrointestinal tract, including metabolic products from the liver (bile acids), digestive enzymes produced by the pancreas, and inflammatory components of the mesenteric lymph.

The Intestinal Microbiome and the Liver Transplant Recipient: What We Know and What We Need to Know

The intestinal microbiome and immune system are in close symbiotic relationship in health. Gut microbiota plays a role in many chronic liver diseases and cirrhosis. However, alterations in the gut microbiome after liver transplantation and the implications for liver transplant recipients are not well understood and rely mainly on experimental animal studies. Recent advances in molecular techniques have identified that increased intestinal permeability, decreased beneficial bacteria, and increased pathogenic species may play important roles in the early posttransplant period. The associations between microbiota perturbation and postliver transplant infections and acute rejection are evolving. The link with metabolic syndrome, obesity, and cardiac disease in the general population require translation into the transplant recipient. This review focuses on our current knowledge of the known and potential interaction of the microbiome in the liver transplant recipient. Future human studies focused on microbiota changes in liver transplant patients are warranted and expected.

Induction of heme oxygenase-1 by hemin protects lung against orthotopic autologous liver transplantation-induced acute lung injury in rats

BACKGROUND

Post-liver transplantation acute lung injury (ALI) severely affects patients' survival, whereas the mechanism is unclear and effective therapy is lacking. The authors postulated that reperfusion-induced increased oxidative stress plays a critical role in mediating post-liver transplantation ALI and that induction of heme oxgenase-1 (HO-1), an enzyme with anti-oxidative stress properties, can confer effective protection of lung against ALI.

METHODS

Male Sprague-Dawley rats underwent autologous orthotopic liver transplantation (OALT) in the absence or presence of treatments with the selective HO-1 inducer (Hemin) or HO-1 inhibitor (ZnPP). Lung tissues were collected at 8 h after OALT, pathological scores and lung water content were evaluated; survival rate of rats was analyzed; protein expression of HO-1 was determined by western blotting, and nuclear translocation of Nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor(NF)-κB p65 were detected by Immunofluorescence staining. The inflammatory cytokines and oxidative indexes of lung tissue were determined.

RESULTS

In lungs harvested at the early stage i.e. 8 h after OALT, Hemin treatment significantly increased superoxide dismutase activities, and reduced malondialdehyde, hydrogen peroxide, interleukin-6, myeloperoxidase, and tumor necrosis factor-α production,which were associated with increased HO-1 protein expression and lower pathological scores and increased survival rate of rats. The underline mechanisms might associate with activation of Nrf2 and inhibition of NF-κB p65 nuclear translocation. However, these changes were aggravated by ZnPP.

CONCLUSIONS

Hemin pretreatment, by enhancing HO-1 induction, increased lung antioxidant capacity and reduced inflammatory stress,protected the lung from OALT-induced ALI at early stage of reperfusion.

Gut microbiota and allogeneic transplantation

The latest high-throughput sequencing technologies show that there are more than 1000 types of microbiota in the human gut. These microbes are not only important to maintain human health, but also closely related to the occurrence and development of various diseases. With the development of transplantation technologies, allogeneic transplantation has become an effective therapy for a variety of end-stage diseases. However, complications after transplantation still restrict its further development. Post-transplantation complications are closely associated with a host's immune system. There is also an interaction between a person's gut microbiota and immune system. Recently, animal and human studies have shown that gut microbial populations and diversity are altered after allogeneic transplantations, such as liver transplantation (LT), small bowel transplantation (SBT), kidney transplantation (KT) and hematopoietic stem cell transplantation (HTCT). Moreover, when complications, such as infection, rejection and graft versus host disease (GVHD) occur, gut microbial populations and diversity present a significant dysbiosis. Several animal and clinical studies have demonstrated that taking probiotics and prebiotics can effectively regulate gut microbiota and reduce the incidence of complications after transplantation. However, the role of intestinal decontamination in allogeneic transplantation is controversial. This paper reviews gut microbial status after transplantation and its relationship with complications. The role of intervention methods, including antibiotics, probiotics and prebiotics, in complications after transplantation are also discussed. Further research in this new field needs to determine the definite relationship between gut microbial dysbiosis and complications after transplantation. Additionally, further research examining gut microbial intervention methods to ameliorate complications after transplantation is warranted. A better understanding of the relationship between gut microbiota and complications after allogeneic transplantation may make gut microbiota as a therapeutic target in the future.

Intestinal microbial variation may predict early acute rejection after liver transplantation in rats

Background

Acute rejection (AR) remains a life-threatening complication after orthotopic liver transplantation (OLT) and there are few available diagnostic biomarkers clinically for AR. This study aims to identify intestinal microbial profile and explore potential application of microbial profile as a biomarker for AR after OLT.

Methods

The OLT models in rats were established. Hepatic graft histology, ultrastructure, function, and intestinal barrier function were tested. Ileocecal contents were collected for intestinal microbial analysis.

Results

Hepatic graft suffered from the ischemia-reperfusion (I/R) injury on day 1, initial AR on day 3, and severe AR on day 7 after OLT. Real-time quantitative polymerase chain reaction results showed that genus Faecalibacterium prausnitzii and Lactobacillus were decreased, whereas Clostridium bolteae was increased during AR. Notably, cluster analysis of denaturing gradient gel electrophoresis (DGGE) profiles showed the 7AR and 3AR groups clustered together with 73.4% similarity, suggesting that intestinal microbiota was more sensitive than hepatic function in responding to AR. Microbial diversity and species richness were decreased during AR. Phylogenetic tree analysis showed that most of the decreased key bacteria belonged to phylum Firmicutes, whereas increased key bacteria belonged to phylum Bacteroidetes. Moreover, intestinal microvilli loss and tight junction damage were noted, and intestinal barrier dysfunction during AR presented a decrease of fecal secretory immunoglobulin A (sIgA) and increase of blood bacteremia, endotoxin, and tumor necrosis factor-α.

Conclusion

We dynamically detail intestinal microbial characterization and find a high sensitivity of microbial change during AR after OLT, suggesting that intestinal microbial variation may predict AR in early phase and become an assistant therapeutic target to improve rejection after OLT.

Supplemental digital content is available in the text.

The lung microbiome after lung transplantation

Lung transplantation survival remains significantly impacted by infections and the development of chronic rejection manifesting as bronchiolitis obliterans syndrome (BOS). Traditional microbiologic data has provided insight into the role of infections in BOS. Now, new non-culture-based techniques have been developed to characterize the entire population of microbes resident on the surfaces of the body, also known as the human microbiome. Early studies have identified that lung transplant patients have a different lung microbiome and have demonstrated the important finding that the transplant lung microbiome changes over time. Furthermore, both unique bacterial populations and longitudinal changes in the lung microbiome have now been suggested to play a role in the development of BOS. In the future, this technology will need to be combined with functional assays and assessment of the immune responses in the lung to help further explain the microbiome's role in the failing lung allograft.

Interactions in the microbiome: communities of organisms and communities of genes

A central challenge in microbial community ecology is the delineation of appropriate units of biodiversity, which can be taxonomic, phylogenetic, or functional in nature. The term 'community' is applied ambiguously; in some cases, the term refers simply to a set of observed entities, while in other cases, it requires that these entities interact with one another. Microorganisms can rapidly gain and lose genes, potentially decoupling community roles from taxonomic and phylogenetic groupings. Trait-based approaches offer a useful alternative, but many traits can be defined based on gene functions, metabolic modules, and genomic properties, and the optimal set of traits to choose is often not obvious. An analysis that considers taxon assignment and traits in concert may be ideal, with the strengths of each approach offsetting the weaknesses of the other. Individual genes also merit consideration as entities in an ecological analysis, with characteristics such as diversity, turnover, and interactions modeled using genes rather than organisms as entities. We identify some promising avenues of research that are likely to yield a deeper understanding of microbial communities that shift from observation-based questions of 'Who is there?' and 'What are they doing?' to the mechanistically driven question of 'How will they respond?'

Microbiota-liver axis in hepatic disease

Accumulating evidence indicates that the gut microbiota, long appreciated to be a key determinant of intestinal inflammation, is also playing a key role in chronic inflammatory disease of the liver. Such studies have yielded a general central hypothesis whereby microbiota products activate the innate immune system to drive proinflammatory gene expression, thus promoting chronic inflammatory disease of the liver. This article reviews the background supporting this hypothesis, outlines how it can potentially explain classic and newly emerging epidemiological chronic inflammatory liver disease, and discusses potential therapeutic means to manipulate the microbiota so as to prevent and/or treat liver disease.

Molecular analysis of intestinal bacterial microbiota of broiler chickens fed diets containing fermented cottonseed meal

The study was conducted to investigate the effects of dietary inclusion of fermented cottonseed meal (FCM) on the ileal and cecal bacterial microbiota of broiler chickens. A total of 300 newborn yellow-feathered broiler chickens were randomly divided into 2 treatments with 3 replicates each (50 birds per replicate): control and 80 g/kg of FCM group. The feeding trial lasted for 42 d. Ileal and cecal digesta samples were collected from 8 chicks per replicate at 21 and 42 d of age to determine the composition of bacterial microbiota using denaturing gradient gel electrophoresis, cloning, sequencing, and real-time quantitative PCR analysis. The results demonstrated that the microbial composition in the ileum and cecum were considerably affected by the diet. The similarity dendrogram of banding profiles showed a more rapid stabilization of intestinal bacterial microbiota in broilers fed diets supplemented with FCM, compared with that of the birds fed the control diet. No significant difference was observed in total number of bands and Shannon-Weaver index, indicating that FCM had no effects on bacterial diversity. However, enumeration of bacteria in the ileal and cecal contents by quantitative PCR showed an increased (P < 0.05) population of lactobacilli, as well as a decreased (P < 0.05) Escherichia coli number by the dietary inclusion of FCM. In summary, dietary inclusion of FCM did not affect the intestinal microbial diversity but shifted intestinal microbiota, with a more homogenous population and an increased colonization of lactobacilli. The results also support the concept that dietary FCM inclusion could promote the beneficial bacteria in the intestinal tract.