Inflammation and Microbiota Fingerprint: Delphi’s Oracle for Nonalcoholic Fatty Liver Disease–Related Hepatocellular Carcinoma?
Authors: Marco Cassano, Jean‐François Dufour
Journal: Hepatology (2018)

SEE ARTICLE ON PAGE 107. Dysfunctions of the gut bacterial flora have an important impact on liver diseases. Quantitative or qualitative ruptures of intestinal homeostasis, collectively termed "dysbiosis," constitute an increasingly recognized associated factor for chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD). The evidence that gut maladaptation is a common feature in NAFLD settings led Ponziani et al. to investigate whether specific variations of the flora and inflammatory cues are enriched in patients who have NAFLD and present with hepatocellular carcinoma (HCC).1 The authors included prospectively 21 patients with NAFLD‐related cirrhosis and HCC, 20 patients with NAFLD‐related cirrhosis without HCC, and 20 healthy controls. In addition to age, cohorts with cirrhosis were matched on severity of liver disease and portal hypertension. While observing similar dysfunctions of gut permeability in patients with cirrhosis, the authors reported an increased intestine‐derived permeability in subjects with cirrhosis and HCC, revealed by increases in lipopolysaccharides and zonulin‐1 plasma level compared to healthy controls. The pattern of cytokines further supports an inflammatory milieu specific to patients with cirrhosis with and without HCC. Myeloid‐derived suppressor cells (MDSCs), which are bone marrow–derived cells whose diagnostic and prognostic significance has been recently reported in HCC patients, are thought to promote tumor progression primarily by suppressing antitumor immunity and favoring tumor angiogenesis.2 Ponziani et al. found that proinflammatory mediators such as interleukin 8 (IL‐8), IL‐13, chemokine (C‐C motif) ligand 3 (CCL3), CCL4, and CCL5 were significantly increased in the presence of HCC and positively correlated with the levels of circulating activated monocytes and monocytic MDSCs (Fig. 1).Figure 1: The presence of HCC in patients with cirrhosis due to NAFLD is associated with changes in the gut and in the blood compartments. In the gut, the authors report an increased intestinal permeability, increased levels of fecal calprotectin, and modifications in the composition of the microbiome. In the blood, they found increased levels of proinflammatory mediators such as IL‐8, IL‐13, CCL3, CCL4, and CCL5. Abbreviations: DC, dendritic cell; MΦ, macrophage; NK, natural killer; PD‐1, programmed death 1; PD‐L1, PD‐1 ligand; TJ, tight junction.When Ponziani and colleagues performed the 16S RNA‐based metagenomic analysis of the gut microbial composition, they found that patients with cirrhosis had a lower gut microbial diversity compared to controls, independent of the presence of HCC. The authors suggest a framework where cirrhosis affects the gut microbial composition. According to their results, the dysbiotic fingerprint of the whole cohort with cirrhosis (with and without HCC) is characterized by alterations of specific bacterial families and genera, as defined by the relative abundance in Enterobacteriaceae, Streptococcus, Bacteroides, and Ruminococcus, among others, and the reduction in Bifidobacterium and Akkermansia. The authors proposed that the reduction of specific bacterial genera such as Akkermansia and Bifidobacterium sensitizes the inflammatory risks of patients with NAFLD and correlates with increased CCL5 and calprotectin levels. Importantly, Ponziani et al. have shown unappreciated taxonomic differences when comparing the microbiota of patients with cirrhosis with or without HCC, such as the increased abundance of Bacteroides and Ruminococcaceae, potentially spurring disease progression through protumorigenic cues. Studies point out that hepatometabolic disease risk involves multiple strains of bacteria, and because the gut flora composition can differ from person to person, single bacterial species might not explain the full responsibility of the disease. A promising strategy might be to promote the growth of healthy bacterial strains rather than target the bad ones. This is supported by some early clinical evidence that specially formulated probiotics (cocktails of "good" bacteria) can bump the microbiome back into balance.3 It is still early days for this research, but the premises are exciting because almost 30% of the metabolites in the blood are derived from intestinal bacteria. This study advances our knowledge of intestine‐derived inflammation and HCC. The authors define a specific set of inflammatory regulators such as CCL3, CCL4, and CCL5 associated with cirrhosis and HCC. They also highlight the clinical significance of correlating the cytokine/chemokine profile with the recruitment of cellular infiltrates, hastening tumor progression through immunosuppressive effects. Their findings corroborate previous studies defining the protumorigenic role of these cytokines in both animal models and clinical settings.5 These observations follow previous seminal studies performed with similarities and remarkable differences in terms of both study design and operational procedures. Exploiting a quantitative metagenomic‐based resource, Qin and colleagues compared the gut‐metagenomic signature of 98 Chinese patients with cirrhosis predominantly due to viral hepatitis and alcoholic cirrhosis with 83 healthy controls, finding an enrichment of taxonomical species of buccal origin, indicative of an invasion of the gut from the mouth in liver cirrhosis.9 Further, Bajaj and coworkers characterized the association of the gut microbiome with hepatic decompensation in 219 patients with cirrhosis, although 17% of patients presented with NAFLD‐related conditions and only 68% were of Caucasian origin, precluding comparison with the study of Ponziani et al.10 Loomba and colleagues integrated stool metagenomic profiling with the assessment of serum analytes through metabolomics in 86 patients with biopsy‐proven NAFLD to examine the diagnostic potential of the microbiome‐derived signature for the presence of advanced fibrosis.11 All of these studies recorded changes in the gut microbiota of patients with different states known to predispose to liver diseases. Additionally, dysbiosis seems to associate with an increase in the size of the population of bacteria that produce ethanol. So, although the name "NAFLD" contains the term "nonalcoholic," the reality of the condition is more complicated, and alcohol from bacteria may still play a part in its origins. An alluring and so far unexplored frame prompted by Ponziani et al. might come from the correlation of the phenotypic severity with the deregulation of the ethanol‐producing bacterial population. The generalizability of the results of Ponziani et al. is uncertain because this is a single‐center study with a relatively small cohort size. Their cohort selection followed tight criteria, ethnicity and diet among many others, aimed at minimizing the impact of these confounding factors, though such stringency may also limit the holistic interpretation of microbial composition shifts. Nevertheless, this work elegantly corroborates the compelling evidence of a link between inflammation, changes in the gut microbiota composition, and NAFLD‐related cirrhosis and HCC. The details and relative importance of the proposed mechanisms by which dysbiosis causes liver damage through inflammation are still unclear. Intestinal microbiota profiling has not yet provided a clear causative relationship between dysbiosis and HCC development. Still, the potential of microbiome‐based metagenomic signatures is enormous, and interventions to prevent this dreadful disease warrant further studies to pin down the importance of these associations. This work sets the stage for a new way of monitoring and preventing liver cirrhosis, indicating that stool‐based and plasma‐based tests may represent powerful diagnostic tools for disease detection, adjunctive to or more optimistically substitutive for current invasive approaches for staging liver diseases. It is plausible that the serum/plasma‐based tests, as the cytokine analysis performed by the authors, may be used in conjunction with the bacterial metagenomic signature to elevate the noninvasive screening potential of detecting advanced fibrosis, cirrhosis, and ultimately HCC risk. Potential conflict of interest Nothing to report.