Compositional and functional changes in the salivary microbiota related to oral leukoplakia and oral squamous cell carcinoma: a case control study

Abstract

Background: Oral squamous cell carcinoma (OSCC) is one of the most common malignant tumours with increasing incidence, and oral leukoplakia (OLK) has a strong tendency to undergo malignant transformation. The oral microbiota may influence oral cancer progression, but the salivary bacterial composition and functional changes in OSCC and OLK have not been comprehensively elucidated. Therefore, we compared salivary bacteria in OLK and OSCC patients with healthy controls (HC).

Methods: Metagenomic sequencing was used to compare the bacterial composition and functional changes of 18 OSCC patients, 21 OLK patients and 21 HC. Spearman correlation was used to identify possible associations between functions and bacteria.

Results: Gemella was the most differentially enriched genus in OSCC. At the species level, Streptococcus sp. NPS 308, Streptococcus agalactiae, Gemella haemolysans and Gemella morbillorum were slightly increased in OLK and OSCC. Kyoto Encyclopedia of Genes and Genomes (KEGG) results showed that OSCC was mainly associated with metabolism functions, including lipid metabolism, carbohydrate metabolism and glycan biosynthesis and metabolism. The synthesis and degradation of ketone bodies, cysteine and methionine metabolism and glycerolipid metabolism differed significantly among the three groups, and were highest in OSCC and lowest in HC. And G. haemolysans was significantly associated with these selected metabolic pathways.

Conclusions: Metagenomic analysis revealed significant differences in the salivary microbiota among OSCC, OLK and HC. Thus, salivary microbiota composition and functional changes may be associated with OSCC progression. Metabolism of nonessential amino acids such as cysteine and methionine in bacteria may play an important role in oral oncogenesis, and more studies of the mechanism between metabolisms of bacteria and oral oncogenesis are needed in the future.

Keywords: Gemella; Metagenomic sequencing; Oral leukoplakia; Oral microbiome; Oral squamous cell carcinoma; Saliva.

Fig. 1

(a) Venn diagram of the three groups at the species level. (b) Ace, Chao and Shannon indices of the three groups. Wilcox tests were used to compare the significance of differences. The p-value between HC and OLK was 0.048 according to Chao. The p-value between HC and OLK was 0.043 according to Ace. *p < 0.05; **p < 0.01; ***p < 0.001. (c) Principal coordinate analysis (PCoA) of the three groups (PERMANOVA, F = 2.829, R² = 0.09, p-value = 0.001). Axis 1 and Axis 2 explain 34.36% of the total variability among the three groups. Blue represents the healthy control group, red represents the OSCC group and orange represents the OLK group

Fig. 2

(a) Bacteria with significant differences in the three groups at the phylum level. (b) Bacteria with significant differences in the three groups at the genus level. (c) Bacteria with significant differences in the three groups at the species level. Blue represents the healthy control group, red represents the OSCC group and orange represents the OLK group. LDA Score > 2 was considered significant

Fig. 3

(a) Principal coordinate analysis (PCoA) among the three groups at the species level (PERMANOVA, F = 1.675, R² = 0.112, p = 0.013). (b) Bacteria with differences among groups at the genus level. (c) Bacteria with differences among groups at the species level. Yellow represents the hyperplasia/keratosis (HK) group, red represents the OSCC group and orange represents the epithelial dysplasia (ED) group. LDA Score > 2 was considered significant

Fig. 4

(a) Functional differences of bacteria among groups at KEGG level (1) (b) Functional differences of bacteria among groups at KEGG level (2) (c) Functional differences of bacteria among groups at KEGG level (3) Blue represents the healthy control group, red represents the OSCC group and orange represents the OLK group. LDA Score > 2 was considered significant

Fig. 5

Differences in metabolic functions of bacteria potentially related to OSCC. *p < 0.05; **p < 0.01; ***p < 0.001. All the above p values in this figure were adjusted. Blue represents the healthy control group, red represents the OSCC group and orange represents the OLK group

Fig. 6

Heatmap showing correlations between microbiomes and metabolic functions that may be associated with OSCC