Arginine Metabolism in Supragingival Oral Biofilms as a Potential Predictor of Caries Risk

Introduction:Ammonia production via the arginine deiminase system (ADS) of oral bacteria can function to reduce the cariogenicity of oral biofilms by neutralizing glycolytic acids that cause tooth demineralization.Objectives:This cohort study investigated the relationship between ADS activity and bacterial profile changes of supragingival biofilms with caries experience among children over time.Methods:A total of 79 children aged 2 to 7 y at baseline were assessed every 6 mo for a period of 18 mo. Children were grouped as caries free (CF), caries active with enamel lesions (CAE), or caries active with dentin lesions (CA). Supragingival plaque samples were collected from caries-free surfaces (PF) and from enamel (PE) and dentin (PD) lesions. Plaque ADS activity was measured by monitoring citrulline production from arginine and compared with ribosomal 16S rRNA–derived taxonomic profiles for the same samples.Results:At baseline, 37% of the children were CF, 34% CAE, and 29% CA. At 18 mo, 26% were CF, 41% CAE, 23% CA, and 10% were caries experienced (new restorations but no caries activity). Throughout the study period, ADS activity was significantly higher in the CF group than the CA group (P \u3c 0.0001), and ADS activity in the PF samples was significantly higher than in the PE and PD samples (P \u3c 0.0001). Distance-based redundancy analysis showed that the bacterial communities could be differentiated when plaque samples are grouped into levels of high and low ADS activity.Conclusions:There is a positive correlation between caries activity and low arginolytic capacity of the supragingival oral biofilms of children and tooth surfaces over time. Measurements of arginine metabolism via ADS may be useful to differentiate the caries risk of individuals and tooth surfaces.Knowledge Transfer Statement:Findings from this study support the development of new strategies for caries risk assessment and prevention based on modulation of the virulence of the oral microbiome through arginine metabolism in supragingival biofilms

Supplementary Material for: Diversity in Antagonistic Interactions between Commensal Oral Streptococci and Streptococcus mutans

<p>Arginine metabolism via the arginine deiminase system (ADS) of oral bacteria generates ammonia, which can increase the pH of oral biofilms and decrease the risk for dental caries. Antagonistic interactions between ADS-positive and cariogenic bacteria in oral biofilms may be an important ecological determinant of caries. This study investigated the antagonistic potential and mechanisms of clinical isolates of arginolytic streptococci on and by <i>Streptococcus mutans </i>UA159, a well-characterized cariogenic human isolate. Low-passage isolates of <i>Streptococcus gordonii</i>, <i>Streptococcus sanguinis</i>, <i>Streptococcus parasanguinis, Streptococcus australis</i>, and <i>Streptococcus cristatus</i> inhibited the growth of <i>S. mutans </i>to various degrees when they were inoculated on growth media first or simultaneously with <i>S. mutans</i>. The antagonistic effects of arginolytic strains against <i>S. mutans </i>and the production of H₂O₂ by these strains were enhanced during growth in a less-rich medium or when galactose was substituted for glucose as the primary carbohydrate source. Pyruvate oxidase was the dominant pathway for H₂O₂ production by arginolytic strains, but lactate oxidase activity was also detected in some strains of <i>S. gordonii</i> and<i> S. cristatus. </i>UA159 inhibited the growth of all tested arginolytic strains when inoculated first, especially in aerobic conditions. However, the antagonistic effects of <i>S. mutans </i>on certain strains of <i>S. gordonii</i> and<i> S. australis</i> were not observed during anaerobic growth in the presence of arginine. Thus, arginolytic commensal streptococci may have a synergistically positive impact on the ecology of oral biofilms by moderating biofilm pH while antagonizing the growth and virulence of caries pathogens.</p

Metabolic Profile of Supragingival Plaque Exposed to Arginine and Fluoride

Caries lesions develop when acid production from bacterial metabolism of dietary carbohydrates outweighs the various mechanisms that promote pH homeostasis, including bacterial alkali production. Therapies that provide arginine as a substrate for alkali production in supragingival oral biofilms have strong anticaries potential. The objective of this study was to investigate the metabolic profile of site-specific supragingival plaque in response to the use of arginine (Arg: 1.5% arginine, fluoride-free) or fluoride (F: 1,100 ppm F/NaF) toothpastes. Eighty-three adults of different caries status were recruited and assigned to treatment with Arg or F for 12 wk. Caries lesions were diagnosed using International Caries Detection and Assessment System II, and plaque samples were collected from caries-free and carious tooth surfaces. Taxonomic profiles were obtained by HOMINGS (Human Oral Microbe Identification using Next Generation Sequencing), and plaque metabolism was assessed by the levels of arginine catabolism via the arginine deiminase pathway (ADS), acidogenicity, and global metabolomics. Principal component analysis (PCA), partial least squares–discriminant analysis, analysis of variance, and random forest tests were used to distinguish metabolic profiles. Of the 509 active lesions diagnosed at baseline, 70 (14%) were inactive after 12 wk. Generalized linear model showed that enamel lesions were significantly more likely to become inactive compared to dentin lesions (P \u3c 0.0001), but no difference was found when treatment with Arg was compared to F (P = 0.46). Arg significantly increased plaque ADS activity (P = 0.031) and plaque pH values after incubation with glucose (P = 0.001). F reduced plaque lactate production from endogenous sources (P = 0.02). PCA revealed differences between the metabolic profiles of plaque treated with Arg or F. Arg significantly affected the concentrations of 16 metabolites, including phenethylamine, agmatine, and glucosamine-6-phosphate (P \u3c 0.05), while F affected the concentrations of 9 metabolites, including phenethylamine, N-methyl-glutamate, and agmatine (P \u3c 0.05). The anticaries mechanisms of action of arginine and fluoride are distinct. Arginine metabolism promotes biofilm pH homeostasis, whereas fluoride is thought to enhance resistance of tooth minerals to low pH and reduce acid production by supragingival oral biofilms

Investigating cortical features of Sotos syndrome using mice heterozygous for Nsd1

Sotos syndrome is a developmental disorder characterized by a suite of clinical features. In children, the three cardinal features of Sotos syndrome are a characteristic facial appearance, learning disability and overgrowth (height and/or head circumference > 2 SDs above average). These features are also evident in adults with this syndrome. Over 90% of Sotos syndrome patients are haploinsufficient for the gene encoding nuclear receptor-binding Su(var)3-9, Enhancer-of-zesteand Trithorax domain-containing protein 1 (NSD1). NSD1 is a histone methyltransferase that catalyzes the methylation of lysine residue 36 on histone H3. However, although the symptomology of Sotos syndrome is well established, many aspects of NSD1 biology remain unknown. Here, we assessed the expression of Nsd1 within the mouse brain, and showed a predominantly neuronal pattern of expression for this histone-modifying factor. We also generated a mouse strain lacking one allele of Nsd1 and analyzed morphological and behavioral characteristics in these mice, showing behavioral characteristics reminiscent of some of the deficits seen in Sotos syndrome patients.Sabrina Oishi, Oressia Zalucki, Michelle S. Vega, Danyon Harkins, Tracey J. Harvey, Maria Kasherman, Raul A. Davila, Lauren Hale, Melissa White, Sandra Piltz, Paul Thomas, Thomas H. J. Burne, Lachlan Harris, Michael Pipe