Intestinal microecology in mice bearing diethylnitrosamine-induced primary hepatocellular carcinoma

To explore the characteristics of intestinal microecology in hepatocellular carcinoma (HCC) model mice.

C57BL/6 male mice aged 2 weeks were divided into normal control group and HCC model group. Mice in HCC model group were exposed to a single intraperitoneal injection of diethylnitrosamine (DEN) 2 weeks after birth; the surviving mice were intraperitoneally injected with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), once every 2 weeks for 8 times starting from the 4 ^th week after birth. Mice in each group were randomly selected and sacrificed at 10 ^th, 18 ^th and 32 ^nd weeks after birth, respectively, the liver tissue samples were obtained for histopathological examination. At the 32 ^nd week, all mice in both groups were sacrificed and the feces samples were collected under sterile conditions right before the sacrifice. The feces samples were sequenced for the V3-V4 hypervariable regions of the 16S rRNA gene, and the species abundance, flora diversity and phenotype, as well as flora correlation and functional prediction were analyzed.

Alpha diversity analysis showed that all Good's coverage reached the maximum value of 1.00, and the differences in the Observed features, Chao1 index, Shannon index and Simpson index of the intestinal flora of mice between normal control group and HCC model group were all statistically significant (all P<0.05). Beta diversity analysis showed that PCoA based on weighted or unweighted Unifrac distances all yielded R>0, confirming that the intra-group differences of the samples were less than the inter-group differences; the trend of separation between the two groups was significant ( P<0.05). Bacteroidetes, Firmicutes, Actinobacteria and Patescibacteria were the dominant taxa at the phylum level in both normal control group and HCC model group. However, compared with normal control group, the abundance of Bacteroidetes in HCC model group was significantly decreased ( P<0.01), while the abundance of Patescibacteria was significantly increased ( P<0.05). Moreover, the dominant taxa at the genus level in normal control group mainly included Muribaculaceae_unclassified, Paramuribaculum, Muribaculum, Lachnospiraceae_NK4A 136 group, Olsenella. The dominant taxa at the genus level in HCC model group mainly included Akkermansia, Dubosiella, Muribaculaceae_unclassified, Lachnospiraceae_NK4A 136 group, Coriobacteriaceae_UCG-002. There were 30 genera with statistically significant differences in relative abundance at the genus level between the two groups (all P<0.05). LEfSe analysis of the intestinal flora of mice in the two groups revealed a total of 14 multi-level differential taxa (all P<0.05, LDA score>4.0), which were mainly enriched in Bacteroidetes. The enrichment of 10 differential taxa including Bacteroidetes, Bacteroidia, Bacteroidales, Muribaculaceae, etc. were found in normal control group, and the enrichment of 4 differential taxa including Dubosiella, Peptostreptococus, etc. were found in HCC model group. There were both positive and negative correlations between the dominant intestinal genera in normal control group (|rho|>0.5, P<0.05), while the correlations of the dominant intestinal genera in HCC model group, being less complex than that in normal control group, were all positive. The relative abundance of gram positive and mobile element containing in the intestinal flora of mice in HCC model group was significantly up-regulated compared with normal control group (both P<0.05), while that of gram negative ( P<0.05) and pathogenic potential ( P<0.05) was significantly down-regulated. The metabolic pathways of the intestinal flora in the two groups were significantly different. For instance, 18 metabolic pathways were enriched in normal control group (all P<0.005), including those related to energy metabolism, cell division, nucleotide metabolism, etc., while 12 metabolic pathways were enriched in HCC model group (all P<0.005), including those related to energy metabolism, amino acid metabolism, carbohydrate metabolism, etc. Conclusions: The amount of intestinal flora in DEN-induced primary HCC model mice decreased, and the composition, correlation, phenotype and function of the intestinal flora in mice were significantly altered. Bacteroidetes at the phylum level, as well as several microbial taxa at the genus level such as Muribaculaceae_unclassified, Muribaculum, Peptostreptococus and Dubosiella could be closely associated with DEN-induced primary HCC in mice.