Chronic liver disease is reaching epidemic proportions with the increasing prevalence of obesity, nonalcoholic liver disease, and alcohol overuse worldwide. Most patients are not candidates for liver transplantation even if they have end-stage liver disease. There is growing evidence of a gut microbial basis for many liver diseases, therefore, better diagnostic, prognostic, and therapeutic approaches based on knowledge of gut microbiota are needed. We review the questions that need to be answered to successfully translate our knowledge of the intestinal microbiome and the changes associated with liver disease into practice.

Changes in the intestinal microbiome have been associated with obesity and type 2 diabetes, in epidemiological studies and studies of the effects of fecal transfer in germ-free mice. We review the mechanisms by which alterations in the intestinal microbiome contribute to development of metabolic diseases, and recent advances, such as the effects of the microbiome on lipid metabolism. Strategies have been developed to modify the intestinal microbiome and reverse metabolic alterations, which might be used as therapies. We discuss approaches that have shown effects in mouse models of obesity and metabolic disorders, and how these might be translated to humans to improve metabolic health.

The commensal microbiota has been implicated in the regulation of a diverse array of physiological processes, both within the gastrointestinal tract and at distant tissue sites. Cancer is no exception, and distinct aspects of the microbiota have been reported to have either pro- or anti-tumor effects. The functional role of the microbiota in regulating not only mucosal but also systemic immune responses has led to investigations into the impact on cancer immunotherapies, particularly with agents targeting the immunologic checkpoints PD-1 and CTLA-4. Microbial sequencing and reconstitution of germ-free mice have indicated both positive and negative regulatory bacteria likely exist, which either promote or interfere with immunotherapy efficacy. These collective findings have led to the development of clinical trials pursuing microbiome-based therapeutic interventions, with the hope of expanding immunotherapy efficacy. This review summarizes recent knowledge about the relationship between the host microbiota and cancer and anti-tumor immune response, with implications for cancer therapy.

Use of microbiome-based biomarkers in diagnosis, prognosis, risk profiling, and precision therapy requires definition of a healthy microbiome in different populations. To determine features of the intestinal microbiota associated with health, however, we need improved microbiome profiling technologies, with strain-level resolution. We must also learn more about how the microbiome varies among apparently healthy people, how it changes with age, and the effects of diet, medications, ethnicity, geography, and lifestyle. Furthermore, many intestinal microbes, including viruses, phage, fungi, and archaea, have not been characterized, and little is known about their contributions to health and disease.Whether a healthy microbiome can be defined is an important and seemingly simple question, but with a complex answer in continual need of refinement.

Inflammatory bowel diseases (IBD) develop via convergence of environmental, microbial, immunological, and genetic factors. Alterations in the gut microbiota have been associated with development and progression of IBD, but it is not clear which populations of microbes are involved or how they might contribute to IBD. We review the genetic and environmental factors affecting the gut microbiota, the roles of gut microbes and their bioproducts in the development and clinical course of IBD, and strategies by which microbiome-based therapies can be used to prevent, manage, and eventually cure IBD. We discuss research findings that help bridge the gap between the basic sciences and clinical application.

Pregnant women with inflammatory bowel disease (IBD) may require biologic or thiopurine therapy to control disease activity. Lack of safety data has led to therapy discontinuation during pregnancy, with health repercussions to mother and child.

Hepatic encephalopathy (HE) is a serious neurologic complication in patients with liver cirrhosis. Very little is known about the role of the meningeal lymphatic system in HE. We tested our hypothesis that enhancement of meningeal lymphatic drainage could decrease neuroinflammation and ameliorate HE.

The comparative effectiveness of sigmoidoscopy and fecal immunochemical testing (FIT) for colorectal cancer (CRC) screening is unknown.

Although Clostridioides difficile infection (CDI) is known to involve the disruption of the gut microbiota, little is understood regarding how mucus-associated microbes interact with C difficile. We hypothesized that select mucus-associated bacteria would promote C difficile colonization and biofilm formation.

Drug induced liver injury (DILI) is a necro-inflammatory liver disease caused by several drugs commonly used in clinical practice, herbs and dietary supplements prescribed for medical purposes. Despite its rarity, it represents the major cause of acute liver failure (ALF) requiring liver transplantation in USA and its frequency is increasing in Europe too. Two types of drug induced liver injury have been recognized: intrinsic and idiosyncratic. Predisposing factors may be classified in environmental, drugs- and individual- related risk factors, with the latter further distinguished in genetics and non-genetics. The liver injury can present with a hepatocellular, cholestatic or mixed pattern of disease. A definitive diagnosis of DILI is, nowadays, one of the main challenging issue in the management of these patients. Diagnosis often is based on suspicion derived from clinical history, biochemical exams and eventually on histological examination from liver biopsy. Score system may be helpful in these setting and new markers are gaining more prominence. Evaluation for liver transplantation is indicated when spontaneous resolution does not occur or in cases of ALF. Overall, the 1-year survival rate following liver transplantation is lower than that seen in patients who have been transplanted for chronic liver failure; however long-term survival is higher compared to other indications.

Hepatitis B virus (HBV) is a major health problem worldwide, with approximatively 240 million people living with a chronic HBV infection. HBV chronic infection remains the major cause of hepatocellular carcinoma worldwide, with more than half of HCC patients being chronic HBV carriers, even if underlying mechanisms of tumorigenesis are not totally understood. HBV-related HCC can be prevented by reducing the exposure to HBV by vaccination or by treatment of CHB infection. Current treatment of CHB are Peg-IFN alpha and oral NUCs. Treating HBV infection, either with IFN or NUCs, substantially reduces the risk of HCC development, even if antiviral therapy fails to completely eliminate HCC risk. Among treated patients, cirrhosis, HBeAg negative at baseline and failure to remain in virological remission were associated with an increased risk of HCC. The reduction of the risk of developing HCC during antiviral therapy is largely dependent upon the maintenance of virological remission, since viral load is found to be the most important factor leading to cirrhosis and its complications, including liver cancer development. The question whether Peg-IFN-alpha is superior to NUCs and whether there is a superior agent among NUCs is still controversial. Several studies demonstrated that antiviral therapy with NUCs could reduce the risk of HCC recurrence after curative treatment of HBV-related HCC.

Alcohol-related liver disease (ALD) was estimated to have a prevalence of 2% among the USA population. Since severe fibrosis in compensated patients is the main predictor of long-term survival, it is of utmost importance to early detect patients with severe fibrosis before decompensation occurs. Liver elastography has been used to stage liver fibrosis. However, there is a widespread lack in guidelines for the correct use of liver stiffness (LS) in ALD.

Hepatocellular carcinoma (HCC) represents the sixth most commonly diagnosed cancer and the fourth leading cause of cancer-related death worldwide. HCC occurs predominantly in patients with underlying chronic liver disease and cirrhosis, and it presents a poor prognosis in advanced stage. Since its approval, for the following 10 years, sorafenib remained the only systemic agent with proven clinical efficacy for patients with advanced HCC. Recently, more drugs have been studied and several advances in first‑line and second‑line treatment options should yield significant improvements in survival. Lenvatinib, another tyrosine‑kinase inhibitor, was found to be non-inferior to sorafenib in terms of overall survival (OS), with significantly better progression-free survival and objective response rate (ORR). The tyrosinekinase inhibitors, regorafenib and cabozantinib, were shown to significantly improve survival in the second‑line setting after sorafenib failure. Ramucirumab, a VEGF inhibitor, can also improve survival in the second‑line setting among patients with AFP≥400 ng/dL. Moreover, good efficacy was seen in phase I/II trials of immune checkpoint inhibitors as monotherapy. Ongoing trials are evaluating combination immune checkpoint inhibitor and tyrosine‑kinase inhibitors or VEGF inhibitors for increasing overall survival in this patient population with advanced HCC.