Salivary AQP9 mRNA expression is associated with caries and periodontitis prevalence

Dental caries and periodontitis are the most frequently diagnosed dental diseases worldwide. Their occurrence is age-dependent and, due to their widespread prevalence, they represent a major public health challenge. Further research is essential to identify factors that can be used to develop more effective prevention strategies. Potential factors contributing to the development of caries and periodontitis may be identified at the molecular level. Aquaporins (AQPs) are interesting candidate molecules in this context. Among them, AQP9, known for its role as a permeable channel for water, glycerol and other small molecules, has attracted considerable scientific interest in recent years. In this study we examined if AQP9 could serve as a biomarker for caries and periodontitis. The OKAPI study, a prospective observational study, enrolled patients in a dental practice and an oral and maxillofacial plastic surgery clinic. Clinical data like PSI-index and DMFT-Index were recorded and documented. Saliva samples were collected and RNA was isolated from saliva. cDNA was synthesized from the samples and qRT-PCR was performed using specific primers for AQP9 and ACTB (n = 159; 40.9% male). 39.4% of probands had severe caries and 15.3% had periodontitis. AQP9 mRNA expression was increased in patients with severe caries compared to milder forms (p = 0.0120), and increased AQP9 expression was also detected in patients with periodontitis compared to unaffected individuals (p = 0.0364). An AQP9 cut-off value was calculated to discriminate patients with and without severe caries. The groups below and above the cut-off differed only in the variables presence of severe caries or periodontitis and age: a binary logistic regression model was used to identify risk factors for caries (p = 0.009) and periodontitis (p = 0.023) and led to the conclusion that the AQP9 cut-off was most relevant. AQP9 mRNA expression is associated with the prevalence of caries or periodontitis and could represent a novel biomarker.