(T0930-05-33) Direct Diffusion–Driven Salivary Gland Accumulation of Buprenorphine Following Sublingual Administration Promotes Dental Caries

Purpose: Buprenorphine (BUP) is the most recently approved and one of only three FDA-approved medications for treating substance use disorders. In January 2022, the FDA issued a warning linking sublingual BUP formulations to dental adverse effects, though the underlying mechanisms remain unknown. This study aims to elucidate the mechanisms responsible for salivary gland accumulation and release of BUP, which contribute to elevated oral fluid exposure and alterations in salivary composition—ultimately resulting in buprenorphine-induced dental adverse effects (BIDAE).

Methods: To investigate whether BUP directly diffuses from the oral mucosa into the salivary glands, we employed matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) to visualize the spatial and temporal distribution of BUP and its metabolites. Mice and rats (n=3 per time point) received either sublingual (s.l.) or intravenous (i.v.) BUP and were sacrificed at 0.5, 3, 6, or 24 hrs post-administration (single or multiple doses). Tissues including oral mucosa, tongue, connective tissue, salivary glands, brain, and 10 other organs were collected for imaging studies. Semi-quantitative MALDI-IMS results were further validated by absolute quantification using LC-MS. To probe accumulation mechanisms, lysosomal BUP levels were measured in salivary gland and lysosomal abundance RAW cell lines via LC-MS. Pilocarpine was used to stimulate salivation and assess its impact on BUP levels.

Results: The time-course MALDI-IMS imaging revealed that BUP directly penetrates from the oral mucosa through adjacent tissues into the salivary glands, establishing direct diffusion as the primary accumulation pathway, without major contribution from systemic circulation. This was strongly supported by the significantly higher glandular BUP intensity following sublingual administration compared to intravenous dosing, despite higher systemic exposure via i.v. administration. Furthermore, glandular BUP accumulation showed dose-dependent increases, with multiple doses resulting in significantly higher intensity than single doses. Notably, drug distribution varied across different salivary glands: the sublingual and parotid glands showed the highest levels of BUP accumulation, while the submandibular gland showed minimal uptake. Spatial analysis further indicated that the parent drug and its metabolites exhibited distinct distribution patterns within both the salivary glands and the tongue. These findings were further corroborated by LC-MS quantification of BUP and its metabolites in salivary glands. Mechanistically, lysosomal trapping likely contributes to the observed glandular accumulation. Importantly, pilocarpine-stimulated salivation significantly reduced BUP concentrations in both oral fluid (by ~40-fold) and salivary glands (by ~10-fold), without affecting systemic drug levels.

Conclusion: This is the first study to visualize and confirm the direct diffusion of BUP from oral mucosa to salivary glands following sublingual administration. These findings provide mechanistic insight into why BIDAE incidence is higher with sublingual delivery and suggest new strategies for mitigating local toxicity—such as saliva stimulation or formulation redesign. Additionally, this distribution route may have broader applications in the development of localized drug delivery systems for salivary gland or oral diseases.

References: Zheng Z, Chen J, Srinual S, Tumbas Šaponjac V, Yin T, Wang BY, Sun R, Hu M. Buprenorphine Salivary Gland Accumulation Sustaining High Oral Fluid Exposure and Increasing the Risk of Streptococcus mutans Biofilm Formation. J Addict Med. 2024 Dec 2:10.1097/ADM.0000000000001401. doi: 10.1097/ADM.0000000000001401. Epub ahead of print. PMID: 39621545; PMCID: PMC12127498.

Acknowledgements: Grant funding: This work was supported by the National Institutes of Health (R01 DE033321-01). Declaration of competing interest: The authors report no conflict of interests. Dr. Ming Hu is the co-founder of Sanarentero LLC. Sanarentero is not involved in deciding the research direction of this project.