Dental biofilm is a dynamic and diverse microbial community enmeshed in an equally complex polysaccharide matrix. The extracellular polysaccharides (EPS) are synthesized by microorganisms (Streptococcus mutans, a key contributor) and promote biochemical and structural changes in the matrix enhancing the cariogenicity of the biofilm. Dental caries occurs as a result of persistent low pH environment within biofilms containing elevated amounts of extracellular polysaccharides. The development of novel chemotherapeutic approaches, other than microbiocides, that affect the development of EPS matrix and acidogenicity are promising routes to prevent or reduce oral diseases related to dental biofilm. Recently, we have identified a novel strategy to reduce the development and virulence of dental biofilms and caries by combining two naturally occurring anti- caries/anti-plaque agents (apigenin and tt-farnesol) with fluoride. The putative pathways by which these compounds attenuate the cariogenicity of S. mutans within biofilms involve, at least, three routes: (1) by inhibiting the activity and expression of glucosyltransferases, which are associated with the formation of the polysaccharide matrix in biofilms, (2) by affecting acid production by disrupting S. mutans membrane integrity, and (3) by reducing the synthesis and/or accumulation of IPS. These biological activities influenced the composition of the polysaccharide matrix and acidogenicity of S. mutans biofilms in vitro, which resulted in enhanced cariostatic properties of fluoride without affecting the viability of oral flora population in vivo. Although significant amount of data were generated from our previous USPHS/NIH supported studies, further analyses are required to elucidate the molecular and physiological mechanisms of action of these agents, and to evaluate their effectiveness in vivo. Therefore, we propose a multi-disciplinary, step-wise research project to investigate their influence on: 1) the expression of specific genes associated with the formation of the extracellular polysaccharide matrix using real-time PCR, 2) structure of the polysaccharides matrix in the biofilm using GC-MS, MALDI-TOF-MS and NMR;3) metabolic pathway of S. mutans by specific biochemical assays on PTS system and glycolytic enzymes. Furthermore, we will identify the most effective dosage of our therapeutic approach in vivo, which may also reduce fluoride exposure. By integrating biochemical and molecular techniques with an in vivo model of dental caries, we expect to enhance our understanding of how these compounds modulate the pathogenesis of S. mutans biofilm development, and expand their potential usefulness as a novel chemotherapeutic approach to prevention of biofilm-related diseases, which could be evaluated in future clinical trials. Project Narrative: This project proposes a novel therapeutic approach to prevent dental caries, the single most prevalent and costly oral infectious diseases in the United States. Our approach uses natural compounds, is highly effective without suppressing the resident oral flora (non-microbiocidal) and may decrease exposure to fluoride.
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