Salivary Aldehyde Dehydrogenases in Oral Toxicology: Biological Functions, Disease Associations, and Translational Perspective

Salivary aldehyde dehydrogenases (ALDHs), particularly ALDH3A1, are increasingly recognized as potential contributors to oral defense against aldehyde-associated stress at the oral–environment interface. Unlike freely secreted salivary enzymes, measurable salivary ALDH activity primarily reflects intracellular and vesicle-associated enzymes derived from salivary gland epithelial cells, oral mucosal cells, immune cells, and exfoliated cellular components. Within the oral exposome, ALDHs expressed in oral epithelial and salivary gland tissues participate in the detoxification of reactive aldehydes, while salivary ALDH activity may serve as an indicator of local aldehyde-detoxification capacity and tissue redox status. Beyond aldehyde metabolism, emerging evidence suggests that ALDH-associated pathways are linked to redox regulation, epithelial stress adaptation, inflammatory signaling, and tissue repair through NAD(P)+-dependent processes and stress-responsive networks such as Nrf2 and SIRT1. This review provides a saliva-focused synthesis of ALDH biology, emphasizing isoform-specific functions and the potential importance of ALDH3A1 in oral epithelial defense. Altered salivary ALDH activity has been reported in association with oral conditions including periodontitis, oral lichen planus, radiation-induced salivary dysfunction, and oral squamous cell carcinoma (OSCC). Genetic factors, particularly ALDH2 polymorphisms, together with environmental exposures and microbial dysbiosis, may further influence aldehyde burden and oral disease susceptibility. Although current evidence supports the biological relevance of salivary ALDHs, their utility as clinical biomarkers or therapeutic targets remains investigational and requires further mechanistic and clinical validation.