After prolonged exposure to ascorbate, collagen synthesis in cultured human skin fibroblasts increased approximately 8-fold with no significant change in synthesis ofnoncollagen protein. This effect of ascorbate appears to be unrelated to its cofactor function in collagen hydroxylation. The collagenous protein secreted in the absence of added ascorbate was normal in hydroxylysine but was mildly deficient in hydroxyproline. In parallel experiments, lysine hydroxylase (peptidyllysine, 2-oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) activity increased 3-fold in response to ascorbate administration whereas proline hydroxylase (prolyl-glycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.2) activity decreased considerably. These results suggest that collagen polypeptide synthesis, posttranslational hydroxylations, and activities of the two bydroxylases are independently regulated by ascorbate.Ascorbic acid is essential for normal collagen formation (1-3) by virtue ofthe fact that it is a required component in the synthesis of hydroxyproline and hydroxylysine in collagen (4). Hydroxyproline serves to stabilize the collagen triple helix (5, 6); its absence results in structurally unstable collagen (7, 8) which is not secreted from cells at a normal rate (9). Hydroxylysine is necessary for formation of the intermolecular crosslinks in collagen (10). In addition, specific carbohydrate residues are linked glycosidically to collagen through hydroxylysine, a process that may be important in the regulation of crosslink formation (11).It is generally believed that ascorbate modulates collagen production through its effect on prolyl hydroxylation (12). There have been indications, however, that ascorbate may have an additional role in collagen biosynthesis (13-16). Notable are the early studies by Jeffrey and Martin (13) who observed a substantial increase in the size of chicken long bones cultured in the presence of ascorbate, concomitant with an increase in the incorporation of proline into peptidyl hydroxyproline.In this study we have examined the long-term effect of ascorbate on collagen production by cultured human skin fibroblasts. The influence ofascorbate on prolyl hydroxylase (prolylglycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.2) and lysyl hydroxylase (peptidyllysine, 2 oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) levels was also examined simultaneously to understand better the interrelationship of collagen synthesis and posttranslational hydroxylation. The data indicate that ascorbate increases collagen synthesis by acting at a level other than hydroxylation. MATERIALS AND METHODSHuman skin fibroblasts from a normal 3-day-old boy (GM 970) were obtained from the Institute for Medical Research (Camden, NJ) and grown to confluent density in Dulbecco's modified Eagle's medium buffered with 24 mM sodium bicarbonate and 25 mM Hepes and supplemented with 20% fetal calf serum (GIBCO) which had been inactivated for 30 min at 560C. Cultures were growth arrested for 90 hr in ...

Teeth offer nonshedding surfaces on which a wide range of bacterial species accumulate as thick, cohesive plaques. Intergeneric coaggregation mediated by specific recognition between surface "cohesins" is thought to contribute to both the cohesiveness of plaque and the sequence in which bacteria colonize the tooth surface. There is some evidence that Gram-positive species, like the efficient tooth colonizer Actinomyces viscosus, enhance subsequent tooth colonization by the more virulent periodontal pathogen Bacteroides gingivalis. To study their mechanism of cohesion, we have developed an in vitro assay that measures the sequential binding of tritium-labeled B. gingivalis to A. viscosus adsorbed to saliva-coated hydroxyapatite beads, mimicking teeth (actinobeads). The assay yields equilibrium and kinetics data amenable to statistical analysis. The presence of A. viscosus significantly increased the number of B. gingivalis cells bound. Inhibition studies were conducted to test the sensitivity of binding to heat; to various saccharides and sugar amines; to proteolytic treatment of Bacteroides; and to incorporation of various chaotropic agents, increased KCl, and saliva in the suspension buffer. Heating the Bacteroides cells but not the actinobeads diminished Bacteroides adherence. Proteolysis and various saccharides had little, if any, effect. Among chaotropic agents, NaSCN and LiCl reduced numbers of cells bound by 40%, but tetramethylurea had no effect. Increasing the ionic concentration of KCl reduced binding by 50 to 60%. Diluted saliva showed a concentration-dependent inhibition of B. gingivalis adherence to actinobeads. To begin examining B. gingivalis surface molecules significant to these reactions, lipopolysaccharide was extracted by the phenol-water method and analyzed by biochemical assays and polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous reports have shown that Treponema denticolacauses rearrangement of filamentous actin (F-actin) in human gingival fibroblasts (HGF). The purpose of this investigation was to determine the effect of T. denticola on the generation of inositol phosphates (IPs) in relation to a time course for F-actin disruption in HGF. Cultured HGF were exposed to washed cells of T. denticola ATCC 35405 for 140 min. Changes in the fluorescence intensity of rhodamine-phalloidin-labeled F-actin in serial optical sections of single HGF were quantified by confocal microscopy image analysis. The percentage of cells with stress fiber disruption was also determined by fluorescence microscopy. Challenge with T. denticola caused a significant reduction in F-actin within the first hour, especially at the expense of F-actin in the ventral third of the cells, and a significant increase in the percentage of HGF with altered stress fiber patterns. Significant concentration-dependent disruption of stress fibers was also caused by HGF exposure to a Triton X-100 extract of T. denticola outer membrane (OM). IPs were measured by a radiotracer assay based on the incorporation ofmyo-[3H]inositol into IPs in HGF incubated with LiCl to inhibit endogenous phosphatases. HGF challenge with several strains of T. denticola and the OM extract ofT. denticola ATCC 35405 resulted in a diminished accumulation of radiolabeled IPs relative to both 15 and 1% fetal bovine serum, which served as strongly positive and background control agonists, respectively. The significantly diminished IP response toT. denticola ATCC 35405 occurred within 60 min, concomitant with significant reduction of total F-actin and disruption of stress fibers. Pretreatment with the proteinase inhibitor phenylmethylsulfonyl fluoride, which had previously been found to block T. denticola’s degradation of endogenous fibronectin and detachment of HGF from the extracellular matrix, had little effect on F-actin stress fiber disruption and the IP response. Therefore, in addition to its major surface chymotrypsin-like properties, T. denticola expresses cytopathogenic activities that diminish the generation of IPs during the time course associated with significant cytoskeletal disruption in fibroblasts.

Laboratory strains representing six numerical taxonomy clusters and fresh isolates of human Actinomyces viscosus and Actinomyces naeslundii were studied by standard flocculation slide tests for the ability to hemagglutinate erythrocytes (RBC) from various animal species. Human AB and horse RBC were agglutinated more frequently and rapidly than others; guinea pig RBC were agglutinated by only a few strains. Human AB RBC were selected for studies of hemagglutination mechanisms. Treatment of RBC with clostridial neuraminidase (NTRBC) greatly enhanced hemagglutination for almost all strains. In hapten inhibition experiments in which various concentrations of sugars were used, β-galactosides were the most effective inhibitors of hemagglutination for both RBC and NTRBC; inhibition of NTRBC agglutination required higher concentrations. Soybean lectin agglutinated both RBC and NTRBC but not Actinomyces cells. NTRBC agglutinated at a 125-fold-lower concentration. Hemagglutination was sensitive to ethylenediaminetetraacetate for one strain tested. Hemagglutination reactions were reversible by addition of β-galactosides. The ability of Actinomyces strains to “prime” RBC for hemagglutination by removing sialic acid to expose more penultimate β-galactoside sites was studied by recycling Actinomyces -agglutinated RBC which were dispersed with a lactose solution and washed free of bacteria (primed RBC). Priming in this manner augmented subsequent hemagglutination by indicator Actinomyces strains and made the RBC more sensitive to agglutination by soybean lectin. The priming ability of Actinomyces strains generally correlated with the amount of sialic acid removed from primed RBC. Strains representing the numerical taxonomy clusters differed in both their hemagglutinating and priming activities. Cluster 5 strains (typical A. naeslundii ) were good agglutinators of RBC, NTRBC, and primed RBC but were poor primers. Cluster 3 strains (atypical A. naeslundii ) were the weakest hemagglutinators but could prime RBC adequately for subsequent agglutination by other strains. Together, these data indicate that Actinomyces hemagglutination proceeds via a two-step mechanism: (i) neuraminidase removal of terminal sialic acid and (ii) lectin-like binding to exposed β-galactoside-associated sites on the RBC. Strains differ in the extent to which they can perform the two functions, and this specificity may relate to their taxonomic classification.

There is limited evidence, mostly indirect, to suggest that the adherence of Bacteroides gingivalis to teeth may be enhanced by the presence of gram-positive dental plaque bacteria like Actinomyces viscosus. The purpose of this study was to carry out direct quantitative assessments of the cohesion of B. gingivalis and A. viscosus by using an in vitro assay modeled on the natural sequence in which these two species colonize the teeth. The assay allowed comparisons to be made of the adherence of 3H-labeled B. gingivalis 2561 and 381 to saliva-coated hydroxyapatite beads (S-HA) and A. viscosus WVU627or T14V-coated S-HA (actinobeads) in equilibrium and kinetics binding studies. A series of preliminary binding studies with 3H-labeled A. viscosus and parallel studies by scanning electron microscopy with unlabeled A. viscosus were conducted to establish a protocol by which actinobeads suitable for subsequent Bacteroides adherence experiments could be prepared. By scanning electron microscopy, the actinobeads had only small gaps of exposed S-HA between essentially irreversibly bound A. viscosus cells. Furthermore, B. gingivalis cells appeared to bind preferentially to the Actinomyces cells instead of the exposed S-HA. B. gingivalis binding to both S-HA and actinobeads was saturable with at least 2 x 109 to 3 x 109 cells per ml, and equilibrium with saturating concentrations was reached within 10 to 20 min. B. gingivalis always bound in greater numbers to the actinobeads than to S-HA. These findings provide direct measurements supporting the concept that cohesion with dental plaque bacteria like A. viscosus may foster the establishment of B. gingivalis on teeth by enhancing its adherence.