Faculty Bibliography

PURPOSE: To determine both the efficacy and safety of the topical application of 50 mg penicillin G potassium troches (Cankercillin) in the treatment of minor recurrent aphthous stomatitis (RAS). STUDY DESIGN: The investigation used a phase 2 double-blind, randomized placebo-controlled trial with a no-treatment arm. Subjects with minor aphthous ulcers of duration <48 hours were followed for 1 week. The primary endpoint for efficacy was time (days) to complete ulcer resolution, and the secondary endpoint was time (days) to complete pain relief. RESULTS: Thirty-one, 33, and 36 subjects were randomized to the active treatment, placebo, and no-treatment arms, respectively. Baseline findings were heterogeneous across arms. Subjects who received penicillin G treatment had complete ulcer healing and pain relief significantly earlier than those in the placebo and no-treatment arms. No allergic reactions were observed. CONCLUSIONS: Topical penicillin G, by mechanisms which remain unclear, reduces the time of healing and pain relief of minor aphthous ulcers with minimal safety concerns. Larger phase 3 studies are necessary to confirm these findings

The sweeteners saccharin, D-tryptophan, and neohesperidin dihydrochalcone (NHD) and the bitter tastant cyclo(Leu-Trp) stimulated concentration-dependent pigment aggregation in a Xenopus laevis melanophore cell line similar to melatonin. Like melatonin, these tastants inhibited (by 45-92%) cAMP formation in melanophores; pertussis toxin pretreatment almost completely abolished the tastant-induced cAMP inhibition, suggesting the involvement of the inhibitory pathway (Gi) of adenylyl cyclase. The presence of luzindole (melatonin receptor antagonist) almost completely abolished the inhibition of cAMP formation induced by saccharin, D-tryptophan, and cyclo(Leu-Trp) but only slightly affected the inhibitory effect of NHD. In contrast, the presence of an alpha2-adrenergic receptor antagonist, yohimbine, almost completely abolished the inhibition of cAMP formation induced by NHD but had only a minor effect on that induced by the other tastants. Thus saccharin, D-tryptophan, and cyclo(Leu-Trp) are melatonin receptor agonists whereas NHD is an alpha2-adrenergic receptor agonist, but both pathways lead to the same transduction output and cellular response. Formation of D-myo-inositol 1,4,5-trisphosphate (IP3) in melanophores was reduced (15-58%, no concentration dependence) by saccharin, D-tryptophan, and cyclo(Leu-Trp) stimulation but increased by NHD stimulation. Tastant stimulation did not affect cGMP. Although some of the above tastants were found to be membrane permeant, their direct activation of downstream transduction components in this experimental system is questionable. MT1 and MT2 melatonin receptor mRNAs were identified in rat circumvallate papilla taste buds and nonsensory epithelium, suggesting the occurrence of MT1 and MT2 receptors in these tissues. Melatonin stimulation reduced the cellular content of cAMP in taste cells, which may or may not be related to taste sensation

Human submandibular/sublingual saliva contains a protein that promotes adhesion of Streptococcus mutans JBP serotype-c to spheroidal hydroxyapatite in vitro. A high molecular-weight (250,000-300,000 Da) adhesion-promoting protein (APP) was purified by Trisacryl 2000 M gel-filtration chromatography and gel electroelution before it was partially characterized. Lectin blotting identified that the terminal carbohydrates include N-acetyl glucosamine-beta 1-4-N-acetylglucosamine, galactose and galactose-beta 1-3-N-acetyl galactosamine. Antibodies to APP demonstrated no difference in the immunoreactive pattern of APP from saliva of caries-active or caries-resistant individuals belonging to four different ethnic groups: Asian, African-American, Hispanic or Caucasian. No immunological similarities to salivary mucins or parotid agglutinins were detected by Western blotting using immuno-cross-reactivity as a criterion. APP appears to be a unique protein found in submandibular/sublingual saliva. Understanding such a protein could help prevent S. mutans attachment to the enamel surface

Signal messengers such as cAMP, IP3 and cGMP in taste cells following bitter and sweet taste stimulation can be monitored in real time, in the subsecond range. However, many amphipathic sweeteners and bitter tastants are slow in taste onset and linger, and the molecular basis for these temporal properties is ill-defined. The bitter tastants quinine and cyclo(Leu-Trp), and the non-sugar sweetener saccharin, permeate rapidly through liposomes and taste cells. Furthermore, amphipathic bitter tastants appear to interact with and/or permeate phospholipid-based bitter taste inhibitors. Thus, bitter taste is masked by preventing access of these tastants to taste cells. Such tastants can stimulate responses in cells that are not related to taste cells, and are therefore unlikely to contain taste receptors. It is hypothesized that due to their rapid permeation into taste cells, these tastants may activate the downstream transduction components directly, in addition to their action on G-protein-coupled receptors. The delayed temporal properties produced by many bitter tastants and non-sugar sweeteners may be related to this phenomenon

The formation of chemical cellular signals in response to taste stimulation may be initiated in sub-second time range. We are using a Quench Flow Module (QFM) and a Fast Pippeting System (FPS) to monitor cellular signals in rat taste tissue homogenates and intact cells in response to bitter taste stimulants that are important to the acceptance of agricultural food products. Stimulation by grape-derived catechin and the citrus-derived naringin increased the formation of the IP3 signal with parallel decline of cAMP. Under similar experimental conditions, the citrus-derived limonin reduced cAMP whereas casein-derived cyclo(Leu-Trp) bitter dipeptide produced a rapid and transient increase of cAMP. cGMP was not affected by any of the four stimuli. These results further emphasize the presence of multiple transduction pathways and modulation of two parallel second messengers in bitter taste sensation of some bitter compounds

Current evidence points to the existence of multiple processes for bitter taste transduction. Previous work demonstrated involvement of the polyphosphoinositide system and an alpha-gustducin (Galpha(gust))-mediated stimulation of phosphodiesterase in bitter taste transduction. Additionally, a taste-enriched G protein gamma-subunit, Ggamma(13), colocalizes with Galpha(gust) and mediates the denatonium-stimulated production of inositol 1,4,5-trisphosphate (IP(3)). Using quench-flow techniques, we show here that the bitter stimuli, denatonium and strychnine, induce rapid (50-100 ms) and transient reductions in cAMP and cGMP and increases in IP(3) in murine taste tissue. This decrease of cyclic nucleotides is inhibited by Galpha(gust) antibodies, whereas the increase in IP(3) is not affected by antibodies to Galpha(gust). IP(3) production is inhibited by antibodies specific to phospholipase C-beta(2) (PLC-beta(2)), a PLC isoform known to be activated by Gbetagamma-subunits. Antibodies to PLC-beta(3) or to PLC-beta(4) were without effect. These data suggest a transduction mechanism for bitter taste involving the rapid and transient metabolism of dual second messenger systems, both mediated through a taste cell G protein, likely composed of Galpha(gust)/beta/gamma(13), with both systems being simultaneously activated in the same bitter-sensitive taste receptor cell

Gustducin is a transducin-like G protein selectively expressed in taste receptor cells. The alpha subunit of gustducin (alpha-gustducin) is critical for transduction of responses to bitter or sweet compounds. We identified a G-protein gamma subunit (Ggamma13) that colocalized with alpha-gustducin in taste receptor cells. Of 19 alpha-gustducin/Ggamma13-positive taste receptor cells profiled, all expressed the G protein beta3 subunit (Gbeta3); approximately 80% also expressed Gbeta1. Gustducin heterotrimers (alpha-gustducin/Gbeta1/Ggamma13) were activated by taste cell membranes plus bitter denatonium. Antibodies against Ggamma13 blocked the denatonium-induced increase of inositol trisphosphate (IP3) in taste tissue. We conclude that gustducin heterotrimers transduce responses to bitter and sweet compounds via alpha-gustducin's regulation of phosphodiesterase (PDE) and Gbetagamma's activation of phospholipase C (PLC)