Abstract
To characterize the salivary microbiota in patients at different progressive histological stages of gastric carcinogenesis and identify microbial markers for detecting gastric cancer, two hundred and ninety-three patients were grouped into superficial gastritis (SG; n = 101), atrophic gastritis (AG; n = 93), and gastric cancer (GC; n = 99) according to their histology. 16S rRNA gene sequencing was used to access the salivary microbiota profile. A random forest model was constructed to classify gastric histological types based on the salivary microbiota compositions. A distinct salivary microbiota was observed in patients with GC when comparing with SG and AG, which was featured by an enrichment of putative proinflammatory taxa including Corynebacterium and Streptococcus. Among the significantly decreased oral bacteria in GC patients including Haemophilus, Neisseria, Parvimonas, Peptostreptococcus, Porphyromonas, and Prevotella, Haemophilus, and Neisseria are known to reduce nitrite, which may consequently result in an accumulation of carcinogenic N-nitroso compounds. We found that GC can be distinguished accurately from patients with AG and SG (AUC = 0.91) by the random forest model based on the salivary microbiota profiles, and taxa belonging to unclassified Streptophyta and Streptococcus have potential as diagnostic biomarkers for GC. Remarkable changes in the salivary microbiota functions were also detected across three histological types, and the upregulation in the isoleucine and valine is in line with a higher level of these amino acids in the gastric tumor tissues that reported by other independent studies. Conclusively, bacteria in the oral cavity may contribute gastric cancer and become new diagnostic biomarkers for GC, but further evaluation against independent clinical cohorts is required. The potential mechanisms of salivary microbiota in participating the pathogenesis of GC may include an accumulation of proinflammatory bacteria and a decline in those reducing carcinogenic N-nitroso compounds.
Highlights
Gastric cancer (GC) constitutes the third highest cause of cancer mortality worldwide (Bray et al, 2018), and the 5-year survival rates are 27.4 and 32% in China and the USA, respectively
There were no significant differences in body mass index (BMI), socioeconomic, medical history, or lifestyle characteristics among the four groups (Table 1)
We demonstrated that the salivary microbiota could identify gastric cancer (GC) among patients with non-malignant gastric diseases including superficial gastritis (SG) and atrophic gastritis (AG), yielding a high accuracy (AUC of 91%)
Summary
Gastric cancer (GC) constitutes the third highest cause of cancer mortality worldwide (Bray et al, 2018), and the 5-year survival rates are 27.4 and 32% in China and the USA, respectively. The occurrence and development of gastric carcinogenesis is a complex pathogenic process involving multiple factors, multistage changes and polygenic alterations (Massarrat and Stolte, 2014; Goral, 2016). Only about 3% of those infected with H. pylori will eventually develop into gastric cancer, and the eradication of H. pylori does not completely prevent the occurrence of GC (Peek and Crabtree, 2006). These lines of evidence suggest that non-H. pylori microorganisms colonizing the stomach may represent an additional modifier of gastric cancer risk (Sung et al, 2020). Our recent study suggested that a reduction of nitrite-oxidizing Nitrospirae taxa in the gastric mucosa may contribute to gastric neoplastic progression via nitrate accumulation (Wang et al, 2020)
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