Sreenivas Koka

Human immunodeficiency virus type 1 (HIV-1) tat induces nitric-oxide synthase in human astroglia

Human immunodeficiency virus type 1 (HIV-1) infection is known to cause neuronal injury and dementia in a significant proportion of patients. However, the mechanism by which HIV-1 mediates its deleterious effects in the brain is poorly defined. The present study was undertaken to investigate the effect of the HIV-1tat gene on the expression of inducible nitric-oxide synthase (iNOS) in human U373MG astroglial cells and primary astroglia. Expression of the tat gene as RSV-tat but not that of the CAT gene as RSV-CAT in U373MG astroglial cells led to the induction of NO production and the expression of iNOS protein and mRNA. Induction of NO production by recombinant HIV-1 Tat protein and inhibition of RSV-tat-induced NO production by anti-Tat antibodies suggest that RSV-tat-induced production of NO is dependent on Tat and that Tat is secreted from RSV-tat-transfected astroglia. Similar to U373MG astroglial cells, RSV-tat also induced the production of NO in human primary astroglia. The induction of human iNOS promoter-derived luciferase activity by the expression of RSV-tat suggests that RSV-tat induces the transcription of iNOS. To understand the mechanism of induction of iNOS, we investigated the role of NF-κB and C/EBPβ, transcription factors responsible for the induction of iNOS. Activation of NF-κB as well as C/EBPβ by RSV-tat, stimulation of RSV-tat-induced production of NO by the wild type of p65 and C/EBPβ, and inhibition of RSV-tat-induced production of NO by Δp65, a dominant-negative mutant of p65, and ΔC/EBPβ, a dominant-negative mutant of C/EBPβ, suggest that RSV-tat induces iNOS through the activation of NF-κB and C/EBPβ. In addition, we show that extracellular signal-regulated kinase (ERK) but not that p38 mitogen-activated protein kinase (MAPK) is involved in RSV-tat induced production of NO. Interestingly, PD98059, an inhibitor of the ERK pathway, and ΔERK2, a dominant-negative mutant of ERK2, inhibited RSV-tat-induced production of NO through the inhibition of C/EBPβ but not that of NF-κB. This study illustrates a novel role for HIV-1 tat in inducing the expression of iNOS in human astrocytes that may participate in the pathogenesis of HIV-associated dementia.

Effects of abutment size and luting cement type on the uniaxial retention force of implant-supported crowns

STATEMENT OF PROBLEMnThe assumption that increasing the diameter of the abutment/crown components will provide greater resistance to crown loosening forces than standard-sized components has not been reported either with clinical trials or in the laboratory.nnnPURPOSEnThis study attempted to determine what effect abutment dimension and type of luting agent have on the retention of the prosthetic crown.nnnMETHODS AND MATERIALnTest specimens consisted of standard, wide, and experimental CeraOne titanium abutments and matching CeraOne gold cylinders cemented with a zinc phosphate permanent or a zinc oxide eugenol provisional cement. The mean uniaxial force (Newtons) and the load (MPa) required to dislodge the cylinder from the abutment was determined. Statistical analysis of the sample data was performed using a 2-way analysis of variance test (alpha=.05).nnnRESULTSnMean uniaxial resistance force (Newtons) was significantly greater for zinc phosphate cement than for zinc oxide cement (P <. 001). Abutment size was a significant factor when permanent luting cement is used (P <.001). Retention strength per unit area (MPa) of the wide abutments was lower than the standard size and experimental abutments.nnnCONCLUSIONnPermanent luting cement produced uniaxial retention forces approximately 3 times greater than provisional cement. The increase in surface area provided by a wide abutment did not result in an improvement in retention strength over the standard abutment.

The formin-homology-domain-containing protein FHOD1 enhances cell migration

Formin-homology-domain-containing proteins interact with Rho-family GTPases and regulate actin cytoskeleton organization and gene transcription. FHOD1 is a member of this family, interacts with Rac1 and induces transcription from the serum response element. In this study, we examined the effects of FHOD1 expression on cytoskeletal organization and function in mammalian cells. FHOD1 proteins were stably expressed in WM35 melanoma cells and NIH-3T3 fibroblasts. Cells expressing full-length FHOD1 demonstrated an elongated phenotype compared with vector-transfected cells and cells expressing a truncated FHOD1 (1-421) that lacks the conserved FH1 and FH2 domains. Full-length FHOD1 co-localized with filamentous actin at cell peripheries. Cells transiently expressing a C-terminal FHOD1 truncation mutant (ΔC, residues 1-1010), which lacks an autoinhibitory protein-protein interaction domain, displayed prominent stress fibers. FHOD1 (1-421) did not induce stress fibers but localized to membrane ruffles in a manner similar to the full-length protein, indicating that the FH1 and FH2 domains are required for stress fiber appearance. FHOD1 ΔC (1-1010)-dependent stress fibers were sensitive to dominant-negative RacN17 and the RhoA and ROCK inhibitors, C3 transferase and Y-27632. Stable overexpression of full-length FHOD1 enhanced the migration of WM35 and NIH-3T3 cells to type-I collagen and fibronectin, respectively. Cells expressing FHOD1 (1-421) migrated similar to control cells. Integrin expression and activation were not affected by FHOD1 expression. Moreover, FHOD1 overexpression did not alter integrin usage during adhesion or migration. These data demonstrate that FHOD1 interacts with and regulates the structure of the cytoskeleton and stimulates cell migration in an integrin-independent manner.

The effect of cementing agent and technique on the retention of a CeraOne gold cylinder: a pilot study.

Endosseous dental implants are routinely used for the replacement of missing teeth. The CeraOne system uses a gold cylinder that is luted to a metal abutment. This study evaluated two luting agents and two luting techniques on the retention of a CeraOne gold cylinder to a CeraOne titanium abutment. A mechanical testing instrument was used to provide an uniaxial tensile force on the gold cylinder, which was cemented with zinc phosphate or Tempbond NE. The access opening to the gold abutment screw was filled or unfilled. Filling the access opening resulted in significantly higher retentive values (P < 0.01) compared to leaving the access opening unfilled. The gold cylinder was significantly more retentive when cemented with zinc phosphate as compared with Tempbond NE (P < 0.01). A Tukey post hoc test demonstrated that all means were significantly different at the P=0.01 level. The results suggest that the choice of luting agent and luting technique may affect retention of a CeraOne gold cylinder. (Implant Dent 1995;4:32–35)

FACTORS INFLUENCING RETENTION OF A CeraOne GOLD CYLINDER

Missing single teeth may be replaced using an endosseous dental implant. The CeraOne system uses a gold alloy cylinder that is cemented to a titanium abutment. This study evaluated the effect of three variables on cement failure loads required to unseat a gold alloy cylinder from its abutment. Two chimney heights (commercially available 3.7 mm and custom fabricated 5.0mm), three luting agents (zinc phosphate, Tempbond NE, and Tempbond), and two luting volumes (0.01 mL and 0.02 mL) were tested. A mechanical testing instrument was used to exert a uniaxial tensile force on the gold cylinders 2 hours after cementation. An analysis of variance and Tukey post hoc test demonstrated that both the choice of luting agent and chimney height affected cement failure loads (P <0.0001). An interactive effect between luting agent and chimney height was observed, with the combination of zinc phosphate and a 5.0 mm abutment-gold alloy cylinder complex resulting in significantly greater retention (P<0.0001). The use of 0.01 mL or 0.02 mL of luting agent resulted in comparable retention values. The results indicate that both chimney height and choice of luting agent may affect retention of a CeraOne gold alloy cylinder. The use of 0.01 mL of luting agent is recommended to minimize expression of excess cement at the restoration-abutment interface.

Periodontal pathogen-related stimulation indicates unique phenotype of primary cultured human fibroblasts from gingiva and periodontal ligament: Implications for oral health disease

STATEMENT OF PROBLEMnThe fibroblast is considered an important cellular component in periodontitis because it is the predominant cell type in periodontal connective tissue.nnnPURPOSEnThe purpose of this study was to test whether gingival fibroblasts (GF) and periodontal ligament fibroblasts (PDLF) are heterogeneous in their production of inflammatory mediators associated with bone resorption in response to lipopolysaccharides from the gram-negative bacterium Porphyromonas gingivalis. To test this hypothesis, we (1) compared interleukin-6 production by cultured human PDLF and GF isolated from the same individual when exposed to P. gingivalis lipopolysaccharide; and (2) compared prostaglandin-E2 production by cultured human PDLF and GF isolated from the same individual when exposed to P. gingivalis lipopolysaccharide.nnnMATERIAL AND METHODSnHuman periodontal ligament and gingival fibroblasts were cultured from biopsies and exposed to P. gingivalis lipopolysaccharide. Levels of interleukin-6 and prostaglandin-E2 secreted into culture supernatant were measured by enzyme-linked immunosorbent assay and the data analyzed. Gingival fibroblasts secreted similar interleukin-6 and elevated prostaglandin-E2 levels compared with unstimulated cells. Periodontal ligament fibroblasts secreted elevated levels of both mediators compared with unstimulated cells. Secreted levels of interleukin-6 and prostaglandin-E2 by primary gingival and periodontal ligament fibroblast cultures appear to differ when stimulated with a periodontal pathogen-related virulence factor.nnnCONCLUSIONnThe fibroblast of the periodontal ligament and the fibroblast of the gingiva may represent different phenotypes that play unique roles in tissue responses to implants.

Identification of FHOD1-binding proteins and mechanisms of FHOD1-regulated actin dynamics

Formin homology‐2‐domain containing protein 1 (FHOD1) regulates gene transcription, actin‐cytoskeleton structure, and cell migration. To gain insight into the mechanisms by which FHOD1 mediates these diverse activities, a yeast‐two‐hybrid screen was performed to identify FHOD1‐binding proteins. Three proteins specifically interacted with the carboxy‐terminal two‐thirds of FHOD1, which includes the FH1, FH2, and diaphanous activating domains (DAD). The newly identified FHOD1‐binding proteins are protein kinase C binding protein 1 (PRKCBP1), cyclophilin B, and an isoform of WASP‐interacting SH3‐domain protein/diaphanous‐interacting protein 1 (WISH/DIP1), named WISH‐B. The proline‐rich FH1 domain of FHOD1 was sufficient to interact with the central portion of PRKCP1 and full‐length cyclophilin B. The FH1 domain also interacted with full‐length WISH‐B, but the extreme amino‐terminus was sufficient to associate with WISH‐B as well. WISH‐B altered the solubility of FHOD1 in vitro and a truncation mutant containing the amino‐terminal 227 residues of WISH‐B disrupted FHOD1‐induced stress fibers. WISH‐B did not affect FHOD1‐induced gene transcription through the serum response factor (SRF) recognition site on the skeletal α actin promoter (SkA). However, stabilization of F‐actin prevented FHOD1 dependent activation of this promoter in presence of high, but not low serum concentrations. Thus, the identification of a new FHOD1‐binding protein provides insight into the mechanisms by which FHOD1 regulates actin polymerization and transcription.

The effects of two air-powder abrasive prophylaxis systems on the surface of machined titanium: a pilot study.

This in vitro pilot project compared the effect of two air-abrasive prophylaxis systems on the surface of machined titanium. Single Brånemark titanium abutment cylinders were exposed to the Prophy-Jet and Microprophy systems for 90 seconds each. Both of the test cylinders were compared with an untreated control cylinder by scanning electron microscopy. Machining marks were completely removed by the Prophy-Jet and only partially removed by the Microprophy. Both of the resultant surfaces appeared to be smoother and thus may be more resistant to plaque formation. A rationale for the removal of machining marks is presented, although the reason for the difference in removal by the two systems is unclear. The prophylaxis cleaning powders were also examined by scanning electron microscopy and exhibited similar particle dimensions and morphology. A noncrystalline deposit was observed on the surface of the abutment cylinder exposed to the Microprophy. Energy dispersive spectroscopy analysis revealed that the deposit consisted almost entirely of sodium. Further investigation of the deposit is needed. (Implant Dent 1992;1:259–265)

Qualitative and quantitative determination of dental amalgam restoration volume.

STATEMENT OF PROBLEMnVolume of tooth structure replaced by an existing restoration, as assessed by visual and radiographic examination, is one diagnostic measure used by dental practitioners and dental insurance agencies to determine the relative need to restore a tooth with a full-coverage cast restoration. However, use of these methods has not been validated.nnnPURPOSEnThis study compared the volume of a range of dental amalgam restorations placed in typodont teeth, as estimated by dentists, dental students and laypersons, with the actual volume of each restoration.nnnMETHODS AND MATERIALnSixty subjects (20 dental school faculty, 20 dental students, and 20 clerical staff [laypersons]) participated. After reviewing photographic images of typodont teeth with mesial-occlusal-distal dental amalgam restorations, subjects estimated the volume of each restoration using various restorations on different teeth as a percentage of its tooths coronal volume. The actual volume of each dental amalgam restoration and that of the coronal portion of the prepared teeth was calculated with a volumetric displacement technique. The single sample 2-sided t test with a.05 level of significance was used to evaluate the null hypothesis (H0 ): The survey participants estimates of each restorations percentage volume are the same as the measured volume values versus the alternative hypothesis (H1 ): estimates differed from the measured volume values. One-way analysis of variance was used to determine the significance of any difference between the estimates of the 3 survey test groups.nnnRESULTSnAverage volumes reported by all 3 groups were significantly different than the measured volume values (P <.05). Experience and dental training did not significantly affect a participants ability to evaluate restoration volumes with greater accuracy. Results reported by dentists, dental students, and laypersons were not significantly different (P >.05).nnnCONCLUSIONSnThe volume of a restoration is inaccurately assessed by visual and radiographic examination.

Dermal Filler Presenting as Lobular Radiopacities in an Edentulous Patient: A Clinical Report: Dermal Filler Appearance on Panoramic Image

This clinical report describes the unusual appearance of radiopacities, lobular in nature, observed on a dental panoramic image of an edentulous patient. Upon questioning, the patient described a history of recently having hydroxylapatite-based dermal filler placed in her right and left cheeks to reduce wrinkles and enhance cosmetic appearance. The localization and shape of the radiopacities were consistent with the placement of the dermal filler.