Liver cancer, predominantly hepatocellular carcinoma (HCC), is the third leading cause of cancer-related deaths worldwide. Emerging data highlight the importance of gut homeostasis in the pathogenesis of HCC. Clinical and translational studies revealed the patterns of dysbiosis in HCC patients and their potential role for HCC diagnosis. Research on underlying mechanisms of dysbiosis in HCC development pointed out the direction for improving the treatment and prevention. Despite missing clinical studies, animal models showed that modulation of the gut microbiota by probiotics may become a new way to treat or prevent HCC development.
1. Introduction
Liver cancer, predominantly hepatocellular carcinoma (HCC), is a substantial health burden worldwide. In 2017, with an estimation of 803,400 (753,100 to 856,700) cases, the age-standardized years lived with disability (YLDs) rate increased by 8.1% when compared with that in 2007
. With a new death of 830,180 cases in 2020, liver cancer represents the third (8.3%) leading cause of cancer-related deaths worldwide
. Due to the low screening rate in high-risk populations and inadequate sensitivity of the present diagnostic technology (imaging and serum alpha-fetoprotein [AFP] quantification), HCC is usually diagnosed at the late stages, leading to low accessibility of curative therapy and high mortality. Early diagnosis and better prevention and treatment are the goals pursued by doctors and patients together. In terms of diagnostic technology, sensitive and specific biomarkers for early diagnosis of HCC are still lacking. As for prevention and treatment of HCC, apart from etiological treatment of HCC, such as anti-hepatitis B virus (HBV) in HBV-HCC, extra measures are in great need.
Approximately 4 × 10
13
microbial cells spanning ~3 × 10
3
species inhabit the human body. The vast majority (97%) of them are bacteria in the colon, and the remaining include extracolonic bacteria and Archaea and eukaryotes such as fungi
. Gut and liver are closely related, not only anatomically but also functionally. The liver receives blood from the gut through the portal vein, while the gut receives bile from the liver through the bile duct. Blood from the gut brings nutrition, microbial metabolite, and microbe-associated molecular patterns (MAMPs). MAMPs may elicit inflammatory responses by activating pattern recognition receptors (PRRs) in the liver, contributing to the progression of liver diseases and development of HCC. Bile acids, important components in bile, are synthesized from cholesterol in the liver, then metabolized by gut bacteria. They can shape the composition and function of the intestinal microbiota. Mutual interplay of bile acids and gut microbiota regulates many physiological processes
. Emerging data highlight the importance of gut homeostasis in the pathogenesis of HCC. Clinical and translational studies revealed the patterns of dysbiosis in HCC patients, indicating the diagnostic value of the dysbiosis in early diagnosis of HCC. Mechanism research demonstrates that gut microbiota plays an important role in liver tumorigenesis, which suggests the possibility of preventing and treating HCC by modulating gut microbiota.
Although the relationship between gut bacterial microbiota and fibrosis/liver cirrhosis is of importance to understand between gut bacterial microbiota and HCC, previous reviews have discussed this topic in detail
[7][8]. Therefore, in the present review, we only focus on the alteration of gut bacterial microbiota in HCC patients and the underlying mechanisms of dysbiosis in HCC development. Meanwhile, diagnostic value of gut dysbiosis and therapeutic potential by targeting gut dysbiosis in HCC were discussed. . Therefore, in the present review, we only focus on the alteration of gut bacterial microbiota in HCC patients and the underlying mechanisms of dysbiosis in HCC development. Meanwhile, diagnostic value of gut dysbiosis and therapeutic potential by targeting gut dysbiosis in HCC were discussed.
2. Gut Microbiota Changes in HCC Patients
Gut bacteria dysbiosis in HCC patients has been reported in many countries and regions recently (
Table 1
). Both stool and blood samples possess the value of diagnosing and assessing dysbiosis in HCC patients.
Gut bacteria dysbiosis in HCC patients.
Patients/Control |
Increased Microbiota |
Decreased Microbiota |
Reference |
cirrhotic HCC/cirrhosis |
Escherichia coli. |
|
[9] |
HCC/NC |
Escherichia coli., Enterococcus |
Bifidobacterium, Lactobacillus |
[10] |
HCC/cirrhosis HCC/cirrhosis HCC/control |
Actinobacteria Gemmiger, Parabacteroides, Paraprevotella, Clostridium_XVIII Klebsiella and Haemophilus |
Ruminococcus, Oscillibacter, Faecalibacterium, Clostridium IV, and Coprococcus |
[11] |
4. Microbial Dysbiosis in HCC Diagnosis
Microbiota | 1 |
Patients/Control |
AUC |
95% CI |
Sensitivity |
Specificity |
Reference |
Escherichia coli |
HCC/cirrhosis |
0.742 |
0.564–0.920 |
66.7% |
73.3% |
[9] |
30 OTUs markers |
HCC/non-HCC |
0.806 |
0.745–0.868 |
- |
- |
[11] |
Enterococcus |
Cirrhotic HCC/cirrhosis |
0.868 |
-NA |
95.8% |
69.2% |
[34] |
HCC/NC NBNC-HCC/NC HBV-HCC/NC NBNC-HCC/NC HBV-HCC/NC |
Lactobacillus, Bifidobacterium Proteobacteria Escherichia-Shigella, Enterococcus Faecalibacterium, Ruminococcus, Ruminoclostridium |
Firmicutes Proteobacteria Faecalibacterium, Ruminococcus |
Enterococcus | , | Ruminoclostridium |
[12] |
Non-cirrhotic HCC/cirrhosis |
0.899 |
NA |
100% |
78.3% |
HCC/NC |
Proteobacteria (Enterobacte, Haemophilus) |
|
[13] |
Limnobacter |
Non-cirrhotic HCC/cirrhosis |
0.858 |
NA |
62.5% |
91.3% |
NAFLD-HCC/NAFLD-cirrhosis |
Bacteroides, Ruminococcaceae |
Bifidobacterium |
[14] |
Phyllobacterium |
Non-cirrhotic HCC/cirrhosis |
0.868 |
NA |
75.0% |
91.3% |
cirrhotic HCC/cirrhosis |
Erysipelotrichaceae Odoribacter, Butyricimonas |
Leuconostocaceae Fusobacterium, Lachnospiraceae |
[ |
5 OTUs markers (serum) |
HCC/control | 15 |
0.879 | ] |
NA |
72.9% |
85.0% |
NAFLD-HCC/NAFLD-cirrhosis |
Enterobacteriaceae Bacteroides caecimuris, Veillonella parvula, Clostridium bolteae, and Ruminococcus gnavus |
Eubacteriaceae |
[16] |
HCC/NC |
Proteobacteria Staphylococcus, Acinetobacter, Klebsiella, Trabulsiella |
Pseudomonas |
[17] |
3. Mechanism Linking Gut Dysbiosis to HCC
3.1. Mechanisms Other Than Bile Acids Dysregulation
More than a decade ago, a mouse model tested the hypothesis that specific intestinal bacteria promote liver cancer in a chemical and viral transgenic mouse model Figure 1.[ |
17 |
] |
Phe-Trp + GCA (serum) |
HCC/cirrhosis |
0.807 |
0.753–0.861 |
92.1% |
52.8% |
[ | 28 | ] |
Phe-Trp + GCA +AFP (serum) |
HCC/cirrhosis |
0.826 |
0.774–0.877 |
77.9% |
76.4% |
CDCA + LPC 20:5 + succinyladenosine + uridine (serum) |
HCC/cirrhosis |
0.938 |
- |
93.3% |
86.7% |
[29] |
1 feces sample is used if not specified. AFP, alpha-fetoprotein; AUC, area under the curve; CDCA, chenodeoxycholic acid; CI, confidence interval; GCA; glycocholate; HCC, hepatocellular carcinoma; LPC, lysophosphatidylcholine; NA, not available; OTU, operational taxonomic unit; Phe-Trp, phenylalanyl-tryptophan. -NA: failed to find out the 95%CI from the paper.
5. Targeting Microbial Dysbiosis in HCC Treatment and Prevention
[44].
Together, targeting microbial dysbiosis to treat and prevent HCC seems promising. However, there is no clinical data in this regard currently.