Caries-associated Oral Proteome and Microbiome in Head and Neck Cancer

Objectives: Head and neck cancer (HNC) patients undergoing radiation therapy (RT) frequently develop caries which can lead to tooth loss and osteoradionecrosis. Our objectives were to determine the salivary proteome composition at pre-RT baseline (T0), and the associated oral microbiome changes 6-months post-RT (T6) for patients who developed caries compared to those who did not.
Methods: Using nanoLC-MS/MS, salivary proteomic and peptidomic profiles were obtained at T0 from HNC patients (n=10) who had an increase in DMFS score at T6 (DMFS[+] group) and age- and gender-matched HNC patients (n=10) who had no increase in DMFS score (DMFS[-] group). Salivary protein and peptide abundances ratios of both groups were determined using an empirical Bayes method, which computes log₂-fold changes and moderated t-statistics. Microbiome profiles of oral samples from DMFS[+] patients (n=5) and DMFS[-] patients (n=5) from the same cohort were determined by next generation sequencing. PERMANOVA and non-metric multidimensional scaling were used to compare the microbiome profiles of DMFS[+] and DMFS[-] groups.
Results: We found abundance differences at T0 for 19 proteins and 52 peptides in the DMFS[+] vs. DMFS[-] groups (unadjusted p<0.05). More breakdown products of the salivary anti-microbial proteins, such as statherin and basic proline-rich proteins, were detected in the DMFS[+] group compared to the DMFS[-] group. Additionally, microbiome beta-diversity change from T0 to T6 differed significantly between the DMFS[+] and DMFS[-] groups (adjusted p<0.001). DMFS[+] group patients had a higher relative abundance of species often associated with development of caries including S. mutans, Veillonella spp., and Actinomyces spp. The relative abundance of the caries-associated species, S. mutans, increased over time in both patient groups, but increased significantly more in the DMFS[+] group.
Conclusions: Differences in baseline salivary proteome involving protective peptides, and associated microbiome changes affecting caries-associated species, may reflect different susceptibilities to caries for HNC patients undergoing RT.