Human salivary carbonic anhydrase isoenzyme VI : physiology and association with the experience of dental caries
1University of Oulu, Faculty of Medicine, Department of Anatomy and Cell Biology
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|Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in the Auditorium of the Department of Anatomy and Cell Biology, on February 26th, 1999,
at 12 noon.
Doctor Silvia Pastoreková
Professor Jorma Tenovuo
The carbonic anhydrases (CAs) participate in the maintenance of pH homeostasis in various tissues of the human body by catalyzing the reversible reaction CO2 + H2O ⇔ HCO3- + H+. Carbonic anhydrase isoenzyme VI (CA VI) is secreted into the human saliva by the serous acinar cells of the parotid and submandibular glands. The present work was undertaken in order to gain an understanding of the physiological role of CA VI in the oral cavity.
CA VI concentrations were compared with other salivary characteristics and with the clinical dental status of the subjects. Saliva samples were collected under strictly controlled conditions from 209 young, healthy men and their CA VI concentrations determined by means of a specific time-resolved immunofluorometric assay. Salivary secretion rate, pH, buffering capacity, α-amylase activity level and counts of lactobacilli and mutans streptococci were also determined. Salivary CA VI concentrations showed positive correlations with salivary secretion rate (r = 0.20, p = 0.003) and amylase activity level (r = 0.46, p < 0.001), but not with pH, buffering capacity, or counts of mutans streptococci or lactobacilli. Salivary CA VI concentration, pH and buffering capacity correlated negatively with the number of decayed, missing or filled teeth (DMFT index). The correlation between salivary CA VI concentration and DMFT index was closest in the subjects with poor oral hygiene. No correlation was found between salivary secretion rate or amylase activity and the DMFT index.
The location of CA VI in the enamel pellicle, a thin layer of proteins on dental surfaces providing a protective interface between the tooth surface and the external environment, was demonstrated in samples of extracted teeth using immunostaining with anti-CA VI antibody. Immunostaining for salivary α-amylase, which was used as a positive control, produced virtually the same staining patterns. The presence of CA VI in the natural enamel pellicle was confirmed by Western blotting of pellicle proteins. Histochemical staining of enamel pellicle formed in vitro showed that the bound enzyme retains its CA activity.
To determine whether CA VI is transferred into the circulation, blood and saliva samples were collected from four healthy male volunteers at 3-h intervals throughout a 24-h period and assayed for CA VI concentration. CA VI was present in all the serum samples, although its concentration was about 22 times lower than in the saliva. The presence of CA VI in serum was confirmed using a sensitive Western blotting method. Western blotting also showed that serum CA VI is associated with IgG, which may protect the enzyme from proteolytic degradation or target it to sites that do not contain CA VI.
The present results suggest that salivary CA VI is not involved in regulation of the actual pH or buffering capacity of the saliva, but it does seem to have a specific role in the oral cavity. High salivary concentrations of CA VI appear to be associated with low caries experience. Since active CA VI is located in the enamel pellicle, it may function locally in the microenvironment of the dental surfaces and accelerate the neutralization of the acid metabolic products of bacterial plaque.
Acta Universitatis Ouluensis. D, Medica
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