TO THE EDITOR
We have thoroughly reviewed the study by Feng et al[1] published in the World Journal of Gastroenterology and extend our sincere appreciation for the team's diligent work. Using an integrated metabolomics and microbiomics approach, through their analysis, the researchers investigated the crosstalk between host-microbial co-metabolism and systemic physiological changes in hepatocellular carcinoma (HCC). The findings provide a new biological rationale for developing early screening strategies. Building upon their findings, we wish to explore two pertinent issues: Variations in HCC gut microbiota across different studies, potentially influenced by multiple factors; the specific roles of chronic hepatitis B virus (HBV) infection and subsequent antiviral treatment regimens in shaping the gut microbial landscape in this patient population.
Variations in gut microbiota changes between HCC patients and healthy individuals across studies, potentially influenced by multiple factors
A growing body of research indicates that gut microbiota is associated with the occurrence of HCC and holds promise as a diagnostic biomarker. Feng et al[1] concluded that there were no significant fluctuations in the gut microbiota at the phylum level among the healthy control (HC), an early-stage HCC cohort (HCC12, inclusive of TNM stages I and II), and an advanced-stage HCC cohort (HCC34, inclusive of TNM stages III and IV), whereas significant differences were observed at the genus or species level. Among the three representative genera, Lachnospira, Streptococcus, and Veillonella, HCC was characterized by a decreased abundance of Lachnospira and an increased abundance of Streptococcus and Veillonella. These specific bacterial communities, along with their associated metabolites, could collectively represent a unique panel of biomarkers for the disease. Most studies also have indicated differences in the alpha or beta diversity of the gut microbiota between patients with HCC and HCs. However, when investigating the intestinal microflora of those suffering from HCC in further detail, specifically when delving into their classification at the genus or species stratum, these differences can vary.
In 2019, Zhang et al[2] studied the gut microbiota among healthy individuals, liver cirrhosis patients, and liver cancer patients, finding that HCC patients had decreased abundance of Firmicutes and a significant decrease in the Firmicutes/Bacteroidetes ratio, while Enterobacteriaceae and Escherichia-Shigellawere enriched. In 2023, Zhang et al[3] studied the characteristics of gut microbiota in elderly patients with HCC. At the family level, the HCC group had the lowest relative abundance of Lachnospiraceae; at the genus level, compared to the control group, the HCC group showed significantly reduced abundance of Blautia, Fusicatenibacter, Anaerotruncus, Lachnospiraceae ND3007 group, *CAG-56*, Eggerthella, and Lachnospiraceae FCS020 group, while Escherichia-Shigella had the highest relative abundance; a positive correlation was identified between the quantity of Streptococcus and the concentration of the tumor - related biomarker AFP. Additionally, this study also found a negative correlation between the age of the subjects and the abundance of Bifidobacterium. In 2024, Jinato et al[4] focused on analyzing patients with HCC with or without viral infection and found significant differences in the gut microbiota between the viral and HC groups. Their results indicated that, compared to healthy individuals, five genera, Bacteroides, Streptococcus, Ruminococcus, Veillonella, and Erysipelatoclostridium were more abundant in HCC patients. Furthermore, HCC gut microbiota differs under the influence of viral infection, with Bacteroides and Streptococcus being more abundant in the non-viral subgroup. Comparative analyses of HCC and control cohorts have highlighted three genera with altered abundances: While Streptococcus and Veillonella exhibit notably elevated levels in HCC patients, the relative abundance of Lachnospira demonstrates a marked reduction. The discrepancies across studies indicate that the intestinal microflora in individuals diagnosed with HCC may well be subject to the influence of multiple confounding factors, which have been linked to factors such as medication, alcohol intake, diet[5]. Moreover, a dietary pattern typical of the Western world, characterized by elevated levels of lipids, sterols, and saccharides, is capable of disturbing the equilibrium of the intestinal microbial community. This disruption subsequently results in a reduction in the abundance of beneficial commensal bacteria and facilitates the extensive multiplication of conditional pathogenic microorganisms[6]. For instance, the development of non-alcoholic fatty liver disease (NAFLD)-related HCC driven by dietary cholesterol is linked to intestinal dysbiosis, with the gut ecosystem undergoing dynamic restructuring during disease progression. Research reveals sequential proliferation of Muribaculaceae, Desulfovibrio, Anaerotruncus, and Desulfovibrionaceae throughout carcinogenesis. Experimental models using high-fat, high-cholesterol diets further demonstrate a corresponding decline in Bifidobacterium concurrent with Bacteroides enrichment - a microbial signature later corroborated in hypercholesterolemia patients[7]. Therefore, further validation of the unique biomarkers for HCC is required.
Distinguishing the independent effects of HBV infection and HCC, and incorporating data on antiviral drug use
HBV infection and antiviral therapy can alter the structure of the gut microbiota and metabolic pathways in patients with liver disease, thereby influencing its progression of liver disease. When studying changes in the intestinal microbial community and influencing factors on chronic liver conditions associated with HBV (HBV-CLD), Shen et al[8] found that disease progression and entecavir (ETV) antiviral therapy were key drivers of changes in the gut microbiota and metabolites in HBV-CLD patients. HBV-infected patients themselves possess a distinct microbial signature, and the administration of antiviral agents is capable of partially rectifying the dysregulation of the gut microbiota triggered by HBV, which is associated with the restoration of beneficial microbial genera and metabolites such as increased levels of deoxycholic acid and medium-chain fatty acids[8,9]. One interesting study demonstrated that probiotics possessing concurrent anti-HBV activity can ameliorate both the structure and function of the intestinal microbial community among individuals suffering from liver malignancy associated with HBV infection (HBV-HCC). This intervention facilitated the normalization of beneficial bacteria, such as Lactobacillus and Bifidobacterium, and increased the levels of short-chain fatty acids[10]. Furthermore, the antiviral drug entecavir not only suppresses HBV replication effectively, but has also been shown to reverse HBV-induced gut microbial dysbiosis in mouse models. Notably, it restored key beneficial bacteria, including the gut barrier-protecting genus Akkermansia, to levels comparable to those in healthy subjects[11]. The gut microbiota also exhibits distinct shifts as the liver disease progresses. Throughout the continuum from HBV infection to hepatitis and further to cirrhosis, dominant bacterial phyla and beneficial genera like Anaerostipes gradually diminish, while disease-specific microbial communities become progressively abundant[12]. HCC not driven by the hepatitis virus, such as NAFLD-HCC, also displays reduced alpha diversity. Its gut microbiota composition differs from that of both healthy individuals and patients with NAFLD-related cirrhosis at the phylum, family, and species levels. Specifically, species such as B. ceceimuris and V. parvula were found to be specifically enriched in NAFLD-HCC[13]. In a study by Liu et al[14] investigating gut microbiota alterations in both HBV-related and non-B non-C (NBNC) related HCC, distinct differences in richness and community structure of microbial species were observed between the two etiologies, with results also demonstrating opposite trends. Their findings indicated that HBV-related HCC was associated with greater species richness and a relatively higher abundance of anti-inflammatory bacteria, such as Prevotella. In contrast, NBNC-related HCC was characterized by a reduction in Faecalibacterium. In summary, we conclude that HBV infection exerts a significant modulatory effect on the gut microbiota in HCC. However, within the context of the natural progression of chronic liver disease, this influence likely manifests not in isolation, but rather as a superimposed effect upon the dysbiosis driven by the underlying liver pathology.
The impact of HBV on the gut microbiota in patients with liver disease is not a simple one-way cause-effect relationship, but rather a complex interplay. Specifically, HBV infection can hijack the sodium taurocholate co-transporting polypeptide on the surface of hepatocytes, competitively inhibiting the uptake of bile acids. This process disrupts the enterohepatic circulation of bile acids. Under normal physiological conditions, this circulation is highly efficient, maintaining serum bile acid concentrations at low levels that are non-detrimental to the liver. Concurrently, the gut microbiota contributes to the dynamic balance of the bile acid pool's composition and function by secreting key enzymes, such as bile salt hydrolase, which convert primary bile acids into secondary bile acids[15-17]. Furthermore, bile acids not only inhibit harmful bacteria but also regulate the composition of the gut microbiota[18]. In addition to the bile acid pathway, altered intestinal permeability and immune mechanisms are also crucial in the progression of HBV-related liver disease. HBV can trigger the host's innate immune response. Pattern recognition receptors, notably Toll-like receptors (TLRs) present on various hepatic immune cells, act as a bridge for recognizing the virus and activating the immune system. The subsequent activation of signaling pathways helps the body combat the viral infection; conversely, the downregulation of TLRs can facilitate HBV immune evasion, leading to persistent infection[19,20]. Dysbiosis in patients with liver disease can increase intestinal permeability, allowing gut microbial metabolites such as lipopolysaccharide to enter the portal vein and cause liver injury. This process is associated with the TLR4-NF-κB pathway. Meanwhile, persistent hepatic inflammation and immune activation can, in turn, feedback through the gut-liver axis to further compromise intestinal barrier function and alter the microbiota composition[21,22].
Therefore, we speculate that the presence or absence of HBV infection and the use of antiviral therapy may exert an impact on the dynamics of intestinal microbial communities and metabolites. In the study by Feng et al[1], the proportion of HBV infections within the HCC population was very high (78.95%). Based on previous research, conducting further subgroup analyses of HCC patients who were HBV(+) vs HBV(-), By documenting the administration of antiviral drugs and conducting a comprehensive assessment of their therapeutic outcomes, we can gain a more precise understanding of the specific correlations pertaining to HCC among differential metabolites, gut microbiota, and serum biomarkers.
CONCLUSION
The study by Feng et al[1], which stratified HCC, provided more detailed links between fecal metabolites, gut microbiota, and serum indicators. The imbalance in the gut microbial community exhibits a close association with the advancement of liver malignancy via the gut-liver axis. Changes in the gut microbiota differ across various stages from healthy individuals to viral hepatitis, cirrhosis, and liver cancer, while etiology, age, diet, and ethnicity can all exert an influence. HBV-related cirrhosis is the primary cause of HCC in Chinese patients. Therefore, to make the research findings more scientifically robust, a subgroup analysis based on the viral infection status or antiviral drug use is necessary. Elucidating the causal interplay among HBV infection, antiviral treatment, and the gut-liver axis will refine our understanding of HCC pathogenesis and improve diagnostic biomarker discovery.
