The effect of propranolol on salivary gland function and dental caries development in young and aged rats

Functional profiling in Streptococcus mutans: construction and examination of a genomic collection of gene deletion mutants

A collection of tagged deletion mutant strains was created in Streptococcus mutans UA159 to facilitate investigation of the aciduric capability of this oral pathogen. Gene-specific barcoded deletions were attempted in 1432 open reading frames (representing 73% of the genome), and resulted in the isolation of 1112 strains (56% coverage) carrying deletions in distinct non-essential genes. As S. mutans virulence is predicated upon the ability of the organism to survive an acidic pH environment, form biofilms on tooth surfaces, and out-compete other oral microflora, we assayed individual mutant strains for the relative fitness of the deletion strain, compared with the parent strain, under acidic and oxidative stress conditions, as well as for their ability to form biofilms in glucose- or sucrose-containing medium. Our studies revealed a total of 51 deletion strains with defects in both aciduricity and biofilm formation. We have also identified 49 strains whose gene deletion confers sensitivity to oxidative damage and deficiencies in biofilm formation. We demonstrate the ability to examine competitive fitness of mutant organisms using the barcode tags incorporated into each deletion strain to examine the representation of a particular strain in a population. Co-cultures of deletion strains were grown either in vitro in a chemostat to steady-state values of pH 7 and pH 5 or in vivo in an animal model for oral infection. Taken together, these data represent a mechanism for assessing the virulence capacity of this pathogenic microorganism and a resource for identifying future targets for drug intervention to promote healthy oral microflora.

Rodent model in caries research

The rodent model of dental caries has made fundamental contributions to the understanding of the etiology, pathogenesis, and prevention of this disease. In conducting animal-based investigations, important details considered essential for successful outcome are occasionally overlooked. Adequate number of animals of appropriate age should always be included to ensure sufficient statistical power to draw valid conclusions. Attention should be paid to litter source as it is clear that litter origin may have a profound effect on the outcome. Inclusion of additive in diet may also affect eating pattern. A range of special techniques are available which can expand the role of animals in exploring the pathogenesis of dental caries. The arrival of genetically altered microorganisms along with availability of knock-out rodents offers exciting challenges to further explore the pathogenesis of this still too common disease.

Dental caries as a side effect of infantile hemangioma treatment with propranolol solution

We report the case of an 18-month-old boy who presented with caries in the upper central incisors associated with the use of propranolol solution for the treatment of an infantile hemangioma. This side effect of propranolol solution has not been reported before, and it may result from a sucrose-based excipient of the solution, or decreased salivation caused by beta-adrenergic antagonist effect of propranolol.

Role of unsaturated fatty acid biosynthesis in virulence of Streptococcus mutans

An insertionally inactivated fabM strain of Streptococcus mutans does not produce unsaturated membrane fatty acids and is acid sensitive (E. M. Fozo and R. G. Quivey, Jr., J. Bacteriol. 186:4152-4158, 2004). In this study, the strain was shown to be poorly transmissible from host to host. Animals directly infected with the fabM strain exhibited fewer and less severe carious lesions than those observed in the wild-type strain.

Is medication a risk factor for dental caries among older people?

OBJECTIVES

This study examined the association between chronic medication exposure and 5-year dental caries increment among older people, using a theoretical model whereby xerogenic medication is thought to lead to increased caries by either (i) chronically lowering salivary flow, thus reducing salivary buffering of plaque acids, or (ii) producing the symptoms of dry mouth, leading to symptomatic relief through the use of cariogenic drinks and foodstuffs.

METHODS

Data were obtained from participants remaining at the 5-year follow-up phase of a cohort study of community-dwelling South Australians aged 60 +. Medication information was available at baseline and at 5 years, enabling only those medications taken on both occasions to be included in the analyses. Dental examinations were conducted at baseline and 5 years, and a reversal-adjusted 5-year caries increment was computed. Multivariate modelling was used to control the effects of potential confounders.

RESULTS

Of the original sample, 528 (62.3%) remained after 5 years, with those remaining tending to be younger, healthier and less medicated than those lost to follow-up. Five-year coronal caries incidence was 66.9%. The adjusted coronal caries increment (AdjCI) was higher among males and among those taking a beta-blocker or an antiasthma drug for the previous 5 years. The 5-year incidence of root surface caries was 59.3%. A lower root surface AdjCI was associated with taking daily aspirin. Of the medications shown in earlier analyses to predict dry mouth, only the antiasthma drugs were associated with higher caries experience, and they had predicted more severe xerostomia symptoms.

CONCLUSIONS

This study offers no strong evidence for a medication-caries relationship, as only one of the observed medication-caries associations was explicable in terms of the theoretical model. However, it should be acknowledged that older people taking antiasthma drugs may be at higher risk of coronal caries, possibly through measures taken for the symptomatic relief of dry mouth.

Role of nitric oxide and beta-adrenoceptors of the central nervous system on the salivary flow induced by pilocarpine injection into the lateral ventricle

Our studies have focused on the effect of L-NG-nitroarginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), and L-arginine, the substrate of NOS, on salivary secretion induced by the administration of pilocarpine into the lateral cerebral ventricle (LV) of rats. The present study has also investigated the role of the beta-adrenergic agonists and antagonist injected into LV on the salivary secretion elicited by the injection of pilocarpine into LV. Male Holtzman rats with a stainless-steel cannula implanted into the LV were used. The amount of salivary secretion was studied over a 7-min period after injection of pilocarpine, isoproterenol, propranolol, salbutamol, salmeterol, L-NAME and L-arginine. The injection of pilocarpine (10, 20, 40, 80 and 160 microg/microl) into LV produced a dose-dependent increase in salivary secretion. The injection of L-NAME (40 microg/microl) into LV alone produced an increase in salivary secretion. The injection of L-NAME into LV previous to the injection of pilocarpine produced an increase in salivary secretion. L-Arginine (30 microg/microl) injected alone into LV produced no change in salivary secretion. L-Arginine injected into LV attenuated pilocarpine-induced salivary secretion. The isoproterenol (40 nmol/microl) injected into LV increased the salivary secretion. When injected previous to pilocarpine at a dose of 20 and 40 microg/microl, isoproterenol produced an additive effect on pilocarpine-induced salivary secretion. The 40-nmol/microl dose of propranolol injected alone or previous to pilocarpine into LV attenuated the pilocarpine-induced salivary secretion. The injection of salbutamol (40 nmol/microl), a specific beta-2 agonist, injected alone into LV produced no change in salivary secretion and when injected previous to pilocarpine produced an increase in salivary secretion. The 40-nmol/microl dose of salmeterol, a long-acting beta-2 agonist, injected into LV alone or previous to pilocarpine produced no change in salivary secretion. The results have shown that central injections of L-NAME and L-arginine interfere with the salivary secretion, which implies that might participate in pilocarpine-induced salivary secretion. The interaction between cholinergic and beta-adrenergic receptors of the central nervous system (CNS) for the control of salivary secretion can also be postulated.

An analysis of parotid salivary gland function with desipramine and age in female NIA Fischer 344 rats

Cyclic antidepressants are still a dominating group of psychotherapeutic drugs used in the treatment of depression. Dry mouth is one of their major side effects. In this study we analyzed the effects of the long-term administration of the tricyclic antidepressant desipramine and the reversibility of this treatment following a 15-day washout period on different parameters in parotid gland function in aging rats. We hypothesized that glandular function would be decreased, and recovery delayed with age. Drug treatment affected body weight, glandular weight, DNA synthesis, and the concentration of soluble and structural membrane proteins. Surprisingly, parotid flow rate was increased with desipramine in all ages. While the concentration of secreted proteins was generally decreased with treatment, total proteins secreted were quite stable. SDS/PAGE analysis revealed prominent changes with desipramine. Amylase activity was depressed with treatment, but only low residual cellular enzyme activity was detected in the glandular supernatant. Therefore, a secretory impairment with desipramine was excluded. The content of the antimicrobial proteins peroxidase and lysozyme was increased with desipramine in all age groups. Most parameters measured revealed delayed recovery with age. These data indicate that the tricyclic antidepressant desipramine has profound effects on parotid gland function, accented with age.

High-resolution electrophoretic analysis of rat parotid salivary proteins

Silver staining and high-resolution electrophoretic methods have been used to compare the protein composition of rat parotid saliva evoked in response to (i) parasympathetic stimulation (including the nonadrenergic, noncholinergic, atropine-associated secretion), (ii) sympathetic stimulation, or (iii) the infusion of neuropeptides with secretagogue activity (substance P, calcitonin gene-related peptide, neuropeptide Y, or vasoactive intestinal peptide). The different stimuli influenced the protein concentration and flow rate of the evoked secretion but had little effect upon the protein composition of the saliva. In contrast to earlier studies using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie blue staining, the combination of silver staining and two-dimensional electrophoresis (2-DE) revealed many newly detected proteins. The results indicate that the protein composition of rat parotid saliva is more complex than previously reported but is unaffected by the mode of stimulation.

Are current models for preventive programs sufficient for the needs of tomorrow?

We can be proud of our accomplishment in the prevention of dental caries. Many children in developed countries are now caries-free; however, by age 50, fewer than 5% of the population is caries-free. The drop in the prevalence of caries among specific age groups is undoubtedly due to widespread exposure to fluorides. However, caries protection by fluorides is not absolute; if caries attack continues throughout life, the prevalence of caries will increase. All available evidence strongly suggests that ambient levels of fluoride in the mouth play a critical role in protection against caries. It is clear that novel methods of delivery, such as sustained-release technology, will be developed to enhance the protective effect of fluoride, utilizing amounts of fluoride significantly less than those currently in use. The problems of preventing dental caries in developing countries are much more severe than those facing Western countries. The prevalence of caries appears to be increasing in no small measure due to the introduction of Western diets. Administration of fluoride through conventional routes is either impractical or inordinately expensive. It appears sensible, therefore, to direct preventive measures through dietary constituents associated with caries. Fluoridation of sugars appears to be highly practical and safe way to reduce the prevalence of caries in such communities. Fluoride and iodide are currently added to salt in many parts of the world. If we are to reduce the prevalence of caries effectively in all countries and in all age groups, current methods of prevention will have to be greatly enhanced, and/or effective additional approaches will need to be developed.