Comparative clinical evaluation of different epinephrine concentrations in 4% articaine for dental local infiltration anesthesia.

OBJECTIVES: The aims of this study were to compare and evaluate the clinical anesthetic efficacy of five 4% articaine solutions with and without epinephrine in pulpal anesthesia after infiltration. MATERIALS AND METHODS: In a randomized, double-blinded, crossover study, ten volunteers received local anesthesia infiltration in the maxillary right central incisor with five different solutions (4% articaine + epinephrine 1:100,000, + epinephrine 1:200,000, + epinephrine 1:300,000, + epinephrine 1:400,000, without epinephrine). Electronic pulp tester was used to calculate the onset, utilization time, time to recede, and the surface integral under the time-effect curve. Additionally, cardiovascular parameters and post-experimental soft tissue anesthesia were examined. RESULTS: Onset as well as time to recede was not influenced by the epinephrine concentration. When using the epinephrine-free agent, time to recede was significantly shorter. Upon decreasing epinephrine concentration, duration of pulpal anesthesia and total anesthetic efficacy declined. The shortest time of anesthesia and lowest anesthetic efficacy were seen for the solution without epinephrine. No association was found between the local anesthetic drug and cardiovascular parameters. Soft tissue anesthesia was significantly shorter without epinephrine. CONCLUSIONS: This study shows the substantial benefits of vasoconstrictors in dental infiltration anesthesia. These findings were reflected by means of prolonged and deeper therapeutic effect in a dose-dependent manner. CLINICAL RELEVANCE: Even when utilizing agents with reduced amount of epinephrine, a safe anesthesia is possible. The epinephrine-free solutions resulted in a distinct limitation of utilization time and efficacy.

Protein phosphatase 2A and its B56 regulatory subunit inhibit Wnt signaling in Xenopus.

Wnt signaling increases beta-catenin abundance and transcription of Wnt-responsive genes. Our previous work suggested that the B56 regulatory subunit of protein phosphatase 2A (PP2A) inhibits Wnt signaling. Okadaic acid (a phosphatase inhibitor) increases, while B56 expression reduces, beta-catenin abundance; B56 also reduces transcription of Wnt-responsive genes. Okadaic acid is a tumor promoter, and the structural A subunit of PP2A is mutated in multiple cancers. Taken together, the evidence suggests that PP2A is a tumor suppressor. However, other studies suggest that PP2A activates Wnt signaling. We now show that the B56, A and catalytic C subunits of PP2A each have ventralizing activity in Xenopus embryos. B56 was epistatically positioned downstream of GSK3beta and axin but upstream of beta-catenin, and axin co-immunoprecipitated B56, A and C subunits, suggesting that PP2A:B56 is in the beta-catenin degradation complex. PP2A appears to be essential for beta-catenin degradation, since beta-catenin degradation was reconstituted in phosphatase-depleted Xenopus egg extracts by PP2A, but not PP1. These results support the hypothesis that PP2A:B56 directly inhibits Wnt signaling and plays a role in development and carcinogenesis.

Regulation of beta-catenin signaling by the B56 subunit of protein phosphatase 2A.

Dysregulation of Wnt-beta-catenin signaling disrupts axis formation in vertebrate embryos and underlies multiple human malignancies. The adenomatous polyposis coli (APC) protein, axin, and glycogen synthase kinase 3beta form a Wnt-regulated signaling complex that mediates the phosphorylation-dependent degradation of beta-catenin. A protein phosphatase 2A (PP2A) regulatory subunit, B56, interacted with APC in the yeast two-hybrid system. Expression of B56 reduced the abundance of beta-catenin and inhibited transcription of beta-catenin target genes in mammalian cells and Xenopus embryo explants. The B56-dependent decrease in beta-catenin was blocked by oncogenic mutations in beta-catenin or APC, and by proteasome inhibitors. B56 may direct PP2A to dephosphorylate specific components of the APC-dependent signaling complex and thereby inhibit Wnt signaling.

Characterization of Saccharomyces cerevisiae strains expressing ira1 mutant alleles modeled after disease-causing mutations in NF1.

The 2818 amino acids of neurofibromin, the product of the human NF1 gene, include a 230 amino acid Ras-GAP related domain (GRD). Functions which may be associated with the rest of the protein remain unknown. However, many NF1 mutations in neurofibromatosis 1 patients are found downstream of the GRD, suggesting that the C-terminal region of the protein is also functionally important. Since the C-terminal region of neurofibromin encompassing these mutations is homologous with the corresponding regions in the two Saccharomyces cerevisiae Ras-GAPs, Ira1p and Ira2p, we chose yeast as a model system for functional exploration of this region (Ira-C region). Three missense mutations that affect the Ira-C region of NF1 were used as a model for the mutagenesis of IRA1. The yeast phenotypes of heat shock sensitivity, iodine staining, sporulation efficiency, pseudohyphae formation, and GAP activity were scored. Even though none of the mutations directly affected the Ira1p-GRD, mutations at two of the three sites resulted in a decrease in the GAP activity present in ira1 cells. The third mutation appeared to disassociate the phenotypes of sporulation ability and GAP activity. This and other evidence suggest an effector function for Ira1p.