Nanoceria-Chondroitin Sulfate a: a Robust Synthetic Agglutinin in Saliva

Objectives: Whole human saliva (WHS) provides a natural defense against microbial colonization via salivary agglutinins. In hyposalivation patients, this protection is compromised resulting in dental caries development. Our laboratory develops nanoceria (cerium oxide nanoparticles, CeO₂-NP) as non-toxic, synthetic agglutinins for the sedimentation of non-adherent aggregates of Streptococcus mutans, a key pathogen in caries development. Our lead formulation is a nanoceria aggregate formulated with chondroitin sulfate A (CSA) that is bioactive in animal models. This is a study of the chemical and bioactivity of CeO₂-NP-CSA in WHS.
Methods: Fresh WHS was collected from adult volunteers, processed via known methods and diluted with buffer for the below experiments. A series of nanoceria formulations were screened via dynamic light scattering (DLS) and zeta potential (ZP) measurements in low ionic strength buffers with/without WHS. The hydrodynamic diameter, polydispersity index (PDI) and surface charge were recorded as a function of time. Sedimentation assays known in the literature were used to quantify the agglutination activity of each nanoceria formulation toward S. mutans in the above media.
Results: Nanoceria formulations exhibited a range of hydrodynamic diameters and ZP dependent on the buffer type and pH. Upon incubation in 12.5% WHS, both the hydrodynamic diameter (nm) and PDI of nanoceria formulations increased variably while the absolute ZP value dropped significantly, indicating differential agglomeration. Notably, CeO₂-NP-CSA formulations are anionic yet exhibited rapid and extensive agglomeration in WHS as identified by the hydrodynamic diameter and PDI, and also exhibited rapid sedimentation of S. mutans over the largest range of WHS conditions of nanoceria tested.
Conclusions: CeO₂-NP-CSA formulations have a negative surface charge and rapidly/extensively agglomerate in WHS, correlated with high bioactivity as an agglutinin toward S. mutans. Further studies are necessary to identify key role(s) of CSA in promoting agglutination activity in WHS.