Search

Abstract: Recent cross-sectional studies suggest that reduced ability to generate alkali via the urease pathway in dental plaque may be an important caries risk factor, but it has not been assessed prospectively. Objective: To evaluate the effect of plaque and saliva urease activity on the risk for developing new caries over a three-year period in children. Methods: A panel of 80 children, three to six years of age at recruitment, was followed prospectively for three years. Plaque urease activity, saliva urease activity and dental caries were measured every six months. Survival analysis methodology was used to evaluate the effect of urease on caries development during the study period adjusted for gender, age, baseline caries levels, sugar consumption, amount of plaque, and mutans streptococci levels. Results: The risk for developing new caries increased in a dose-responsive manner with increasing levels of urease activity in saliva (adjusted HRQ4 vs. Q1: 4.98; 95% CI: 1.33, 18.69) and with decreasing urease activity in plaque (adjusted HRQ4 vs. Q1: 0.29; 95% CI: 0.11, 0.76). Multiple measurements of urease activity were conducted to overcome the variability of urease activity in this study. Baseline caries and mutans streptococci in saliva were also important predictors of caries risk. Conclusions: Increased urease activity in saliva can be an indicator of increased caries risk in children, whilst increased urease activity in plaque may be associated with reduced caries risk. The reproducibility of urease measurements must be improved before these findings can be further tested and clinically applied. [Copyright &y& Elsevier]

Abstract: Bacterial urease activity in dental plaque and in saliva generates ammonia, which can increase the plaque pH and can protect acid-sensitive oral bacteria. Recent cross-sectional studies suggest that reduced ability to generate ammonia from urea in dental plaque can be an important caries risk factor. In spite of this proposed important clinical role, there is currently no information available regarding important clinical aspects of oral ureolysis in children. Objective: The objective of this study was to evaluate the distribution and pattern of urease activity in the dental plaque and in the saliva of children during a three-year period, and to examine the relationship of urease with some important caries risk factors. Methods: A longitudinal study was conducted with repeated measures over a three-year period on a panel of 80 children, aged 3–6 years at recruitment. The dynamics of change in urease activity were described and associated with clinical, biological, and behavioural caries risk factors. Results: Urease activity in plaque showed a trend to remain stable during the study period and was negatively associated with sugar consumption (P <0.05). Urease activity in unstimulated saliva increased with age, and it was positively associated with the levels of mutans streptococci in saliva and with the educational level of the parents (P <0.05). Conclusions: The results of this study reveal interesting and complex interactions between oral urease activity and some important caries risk factors. Urease activity in saliva could be an indicator of mutans infection in children. [Copyright &y& Elsevier]

Abstract: T-514 (Peroxisomicine A1) from Karwinskia humboldtiana is a dimeric hydroxyanthracenone with a highly selective cytotoxic effect on tumor cells. We evaluated the metabolism of this compound in two in vitro systems (liver microsomes and hepatocytes) and assessed the cytotoxicity of its metabolites on normal and tumor cells. Microsomes (12.5, 125 and 250 μg of protein/ml) and hepatocytes (1×106 cells/ml) were incubated with the toxin (25 μM) for 0.5, 1, 3, 6, 9, 12 and 24 h and the samples were examined using chromatographic analysis and UV spectra. Two metabolites (M1 and M2) were detected in the rat microsomes and one (M1) in the monkey microsomes. The retention times and UV spectra of the peaks were very similar to those of the toxin T-514. M1 was isolated and identified as a mixture of two isomers. The cytotoxicity of the metabolites was evaluated in Chang liver and Hep G2 cells but they did not show the selective cytotoxic effect on tumor cells seen in the original compound. [Copyright &y& Elsevier]