Chlorhexidine, ethanol, lipopolysaccharide and nicotine do not enhance the cytotoxicity of a calcium hydroxide pulp capping material.

AIM: To determine whether cells pre-stressed by known cytotoxic or inflammatory agents are more susceptible to the deleterious effects of a calcium hydroxide formulation used in pulp capping. METHODOLOGY: Adult human dermal fibroblasts were treated for 48 h with 0.001% chlorhexidine, 0.2% ethanol, 5 µg mL(-1) Escherichia coli lipopolysaccharide (LPS) or 0.05 mmol L(-1) nicotine. Cells were subsequently treated with the soluble materials extracted from Dycal pellets for an additional 24 h. Controls included cells cultured in medium only and cells exposed to Dycal only. Cytotoxicity was measured using colorimetric MTT, WST and secreted lactate dehydrogenase assays. In addition, mitotic activity was evaluated using a colorimetric histone H3 phosphorylation assay. Data were statistically analysed using anova with Tukey's multiple comparison post-test and significance at P ≤ 0.05. RESULTS: For all assays, measured values for cells treated with chlorhexidine, ethanol, LPS or nicotine plus the soluble materials extracted from Dycal pellets were significantly lower compared to control (P < 0.05) for all comparisons between experimental conditions. However, between treatments and for comparisons of treatments with Dycal, there were no differences observed for any assay. CONCLUSIONS: Calcium hydroxide in a formulation used in dental clinical procedures is highly cytotoxic to cultured cells, as evidenced by several cellular assays. However, other known toxic agents, including chlorhexidine, ethanol, bacterial LPS and nicotine, do not appear to function synergistically to increase the deleterious cellular effects of the calcium hydroxide in an in vitro model of cytotoxicity.

Retinopatía del prematuro / Retinopathy of Prematurity

La retinopatía del prematuro (RDP) es una complicación frecuente en los egresados de las UCIN y una causa importante de ceguera. Su prevención primaria depende de una tención reacional que respete límites de saturación en la oxigenoterapia. Su prevención secundaria requiere controles oftalmológicos oportunos y reiterados hasta completarse la vascularización de la retina. Estudios epidemiológcios realizados en el 2002 encontraron una situación alarmante por la frecuente afectación de pacientes de bajo riesgo (PN > 1500 g) y controles oftalmológicos tardíos. A partir del 2003 se conformó un grupo colaborativo multicéntrico para revertir esta situación. Objetivo: analizar las modificaciones de las características de los RN derivados por RDP al hospital JP Garrahan durante los períodos 1996-1999, 2000-2003 y 2004-2007. Métodos: diseño retrospectivo. Las variables analizadas fueron: PN, edad gestacional (EG), tiempo de tratamiento con 02 y ARM, edad de consulta, severidad de RDP, lugar dederivación (> o < a 70 Km). Resultados: el nº de consultas fue de 190, 613 y 489 respectivamente. La proporción de pacientes derivados de > 70 Km disminuyó del 50 al 35 por ciento. Los pacientes del último período han tenido > tiempo de ARM (P 0.04) y oxigenoterapia (p 0.001) pero no varió significativamente su PN ni EG. La proporción de pacientes con RDP severa aumentó del 56 por ciento al 67 por ciento. conclusión: ha disminuido la frecuentcia de derivaciones y las mismas coresponden a pacientes más graves. Continúa siendo la inaceptable la proporción de pacientes de bajo riesgo y la severidad de la RDP al momento de consulta.

A lipopolysaccharide-specific enhancer complex involving Ets, Elk-1, Sp1, and CREB binding protein and p300 is recruited to the tumor necrosis factor alpha promoter in vivo.

The tumor necrosis factor alpha (TNF-alpha) gene is rapidly activated by lipopolysaccharide (LPS). Here, we show that extracellular signal-regulated kinase (ERK) kinase activity but not calcineurin phosphatase activity is required for LPS-stimulated TNF-alpha gene expression. In LPS-stimulated macrophages, the ERK substrates Ets and Elk-1 bind to the TNF-alpha promoter in vivo. Strikingly, Ets and Elk-1 bind to two TNF-alpha nuclear factor of activated T cells (NFAT)-binding sites, which are required for calcineurin and NFAT-dependent TNF-alpha gene expression in lymphocytes. The transcription factors ATF-2, c-jun, Egr-1, and Sp1 are also inducibly recruited to the TNF-alpha promoter in vivo, and the binding sites for each of these activators are required for LPS-stimulated TNF-alpha gene expression. Furthermore, assembly of the LPS-stimulated TNF-alpha enhancer complex is dependent upon the coactivator proteins CREB binding protein and p300. The finding that a distinct set of transcription factors associates with a fixed set of binding sites on the TNF-alpha promoter in response to LPS stimulation lends new insights into the mechanisms by which complex patterns of gene regulation are achieved.

Assembly of a functional beta interferon enhanceosome is dependent on ATF-2-c-jun heterodimer orientation.

Heterodimeric transcription factors, including the basic region-leucine zipper (bZIP) protein ATF-2-c-jun, are well-characterized components of an enhanceosome that mediates virus induction of the human beta interferon (IFN-beta) gene. Here we report that within the IFN-beta enhanceosome the ATF-2-c-jun heterodimer binds in a specific orientation, which is required for assembly of a complex between ATF-2-c-jun and interferon regulatory factor 3 (IRF-3). We demonstrate that correct orientation of the ATF-2-c-jun binding site is required for virus induction of the IFN-beta gene and for IRF-3-dependent activation of a composite ATF-2- c-jun-IRF site in the IFN-beta promoter. We also show that in vitro the DNA-bound ATF-2-c-jun heterodimer adopts a fixed orientation upon the binding of IRF-3 at an adjacent site in the IFN-beta enhancer and that the DNA-binding domain of IRF-3 is sufficient to mediate this effect. In addition, we show that the DNA-binding domain of ATF-2 is necessary and sufficient for selective protein-protein interactions with IRF-3. Strikingly, in vivo chromatin immunoprecipitation experiments with IFN-beta reporter constructs reveal that recruitment of IRF-3 to the IFN-beta promoter upon virus infection is dependent on the orientation of the ATF-2-c-jun heterodimer binding site. These observations demonstrate functional and physical cooperativity between the bZIP and IRF transcription factor families and illustrate the critical role of heterodimeric transcription factors in formation of the IFN-beta enhanceosome.

A stimulus-specific role for CREB-binding protein (CBP) in T cell receptor-activated tumor necrosis factor alpha gene expression.

The cAMP response element binding protein (CREB)-binding protein (CBP)/p300 family of coactivator proteins regulates gene transcription through the integration of multiple signal transduction pathways. Here, we show that induction of tumor necrosis factor alpha (TNF-alpha) gene expression in T cells stimulated by engagement of the T cell receptor (TCR) or by virus infection requires CBP/p300. Strikingly, in mice lacking one copy of the CBP gene, TNF-alpha gene induction by TCR activation is inhibited, whereas virus induction of the TNF-alpha gene is not affected. Consistent with these findings, the transcriptional activity of CBP is strongly potentiated by TCR activation but not by virus infection of T cells. Thus, CBP gene dosage and transcriptional activity are critical in TCR-dependent TNF-alpha gene expression, demonstrating a stimulus-specific requirement for CBP in the regulation of a specific gene.

Stimulus-specific assembly of enhancer complexes on the tumor necrosis factor alpha gene promoter.

The human tumor necrosis factor alpha (TNF-alpha) gene is rapidly activated in response to multiple signals of stress and inflammation. We have identified transcription factors present in the TNF-alpha enhancer complex in vivo following ionophore stimulation (ATF-2/Jun and NFAT) and virus infection (ATF-2/Jun, NFAT, and Sp1), demonstrating a novel role for NFAT and Sp1 in virus induction of gene expression. We show that virus infection results in calcium flux and calcineurin-dependent NFAT dephosphorylation; however, relatively lower levels of NFAT are present in the nucleus following virus infection as compared to ionophore stimulation. Strikingly, Sp1 functionally synergizes with NFAT and ATF-2/c-jun in the activation of TNF-alpha gene transcription and selectively associates with the TNF-alpha promoter upon virus infection but not upon ionophore stimulation in vivo. We conclude that the specificity of TNF-alpha transcriptional activation is achieved through the assembly of stimulus-specific enhancer complexes and through synergistic interactions among the distinct activators within these enhancer complexes.

Assignments and structure determination of the catalytic domain of human fibroblast collagenase using 3D double and triple resonance NMR spectroscopy.

We report here the backbone 1HN, 15N, 13C alpha, 13CO, and 1H alpha NMR assignments for the catalytic domain of human fibroblast collagenase (HFC). Three independent assignment pathways (matching 1H, 13C alpha, and 13CO resonances) were used to establish sequential connections. The connections using 13C alpha resonances were obtained from HNCOCA and HNCA experiments; 13CO connections were obtained from HNCO and HNCACO experiments. The sequential proton assignment pathway was established from a 3D (1H/15N) NOESY-HSQC experiment. Amino acid typing was accomplished using 13C and 15N chemical shifts, specific labeling of 15N-Leu, and spin pattern recognition from DQF-COSY. The secondary structure was determined by analyzing the 3D (1H/15N) NOESY-HSQC. A preliminary NMR structure calculation of HFC was found to be in agreement with recent X-ray structures of human fibroblast collagenase and human neutrophil collagenase as well as similar to recent NMR structures of a highly homologous protein, stromelysin. All three helices were located; a five-stranded beta-sheet (four parallel strands, one antiparallel strand) was also determined. beta-Sheet regions were identified by cross-strand d alpha N and d NN connections and by strong intraresidue d alpha N correlations, and were corroborated by observing slow amide proton exchange. Chemical shift changes in a selectively 15N-labeled sample suggest that substantial structural changes occur in the active site cleft on the binding of an inhibitor.

Reversal of intrinsic DNA bends in the IFN beta gene enhancer by transcription factors and the architectural protein HMG I(Y).

In this paper, we investigate DNA bending induced by proteins required for virus induction of the human interferon-beta (IFN beta) gene. We show that NF-kappa B-DNA complexes that are functionally distinct in the context of the IFN beta enhancer are also conformationally distinct and that two sites in the enhancer contain in-phase bends that are counteracted or reversed by the binding of NF-kappa B, ATF-2/c-Jun, and HMG I(Y). Strikingly, this modulation of intrinsic enhancer architecture results in an orientation that favors predicted protein-protein interactions in a functional nucleoprotein complex, the enhanceosome. Furthermore, the subtle modulation of DNA structure by HMG I(Y) in this process distinguishes it from other architectural factors.

Examination of recombinant truncated mature human fibroblast collagenase by mass spectrometry: identification of differences with the published sequence and determination of stable isotope incorporation.

Human fibroblast collagenase belongs to a family of matrix metalloproteinases which have been implicated in a number of connective tissue disorders ranging from rheumatoid arthritis to tumor invasion. To examine the active site of this enzyme by biophysical studies, a 19 kDa recombinant truncated mature collagenase (mCL-t) was prepared. Electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry have been utilized for the characterization of mCL-t. The molecular weights measured by these techniques identified the presence of two closely related protein components separated by approximately 100 Da. Edman sequence analysis demonstrated that the two protein components differ from each other by an amino terminal valine, consistent with the mass spectrometric data. In addition, the molecular weight of mCL-t determined by mass spectrometry did not agree with that calculated from the reported sequence. To identify the origin of this discrepancy, the DNA sequence of the mCL-t clone was examined. Several differences were noted between the DNA sequence of mCL-t and the published collagenase gene sequence. When these differences were taken into account, the measured molecular weights were found to be in good agreement with that calculated for the modified sequence. In separate experiments, both ESI and MALDI mass spectrometry have been used to determine molecular weights of mCL-t samples enriched with stable isotopes 15N and (15N + 13C). The measured molecular weights demonstrated a 97% (15N) and 99% (15N + 13C) incorporation of labeled isotopes in the two samples.

Gene expression, purification and characterization of recombinant human neutrophil collagenase.

Human neutrophil collagenase (HNC) is a member of a family of matrix metalloproteinases (MMP). HNC is capable of cleaving all three alpha-chains of types I, II and III collagens. In rheumatoid and osteo-arthritis, MMP members have been implicated in the pathology associated with these diseases due to the accelerated breakdown of the extracellular matrix of articular cartilage. A cDNA coding for the HNC catalytic domain (lacking both the propeptide and C-terminal fragments) was sub-cloned into the pETlla prokaryotic expression vector. The cloned fragment encodes a protein that extends from amino acids (aa) Met100 through Gly262 of the full-length proenzyme, which as a result, would not require proteolytic or chemical activation. The HNC construct was expressed in Escherichia coli and recombinant mature, truncated neutrophil collagenase (re-mNC-t) was produced at high levels (approx. 30% of total bacterial protein). The re-mNC-t protein was extracted from inclusion bodies by solubilization in 6 M urea, followed by ion-exchange chromatography. The protein was refolded to an active conformation in the presence of Ca2+ and Zn2+. A final purification step on size-exclusion chromatography yielded 30 mg per liter of active re-mNC-t with minor autodegradative products. Alternatively, hydroxamate affinity chromatography was used to obtain pure, non-degraded re-mNC-t (20-25 mg per liter). The catalytic activity of re-mNC-t was abolished by known MMP inhibitors and the Ki measurement against actinonin was similar to that of HNC prepared from human blood.

The spontaneously hypertensive rat Y chromosome produces an early testosterone rise in normotensive rats.

OBJECTIVE: To investigate the relationship between testosterone and blood pressure during the rapid development phase of blood pressure rise in four strains of rats: Wistar-Kyoto (WKY) rats; spontaneously hypertensive rats (SHR); SHR/y, a substrain with an SHR Y chromosome and WKY rat autosomes and X chromosomes; and SHR/a, a substrain with SHR autosomes and X chromosomes and the WKY rat Y chromosome. METHODS: Blood pressure was measured every 2 weeks by the tail-cuff method, and was verified in selected rats at 23 weeks by aortic telemetry. Serum testosterone was measured, by radioimmunoassay, every 2 weeks from 5 to 23 weeks of age. RESULTS: During the rapid phase of blood pressure rise, between 5 and 9 weeks of age, there was a significantly larger rise in serum testosterone in SHR and SHR/y than in WKY rats and SHR/a groups. The hypertensive Y chromosome in the SHR and SHR/y accelerated peak testosterone approximately 4 weeks earlier, and blood pressure was increased in these two groups compared with the SHR/a and WKY rat groups, respectively. A gene on the SHR Y chromosome (Tty) affecting the timing of testosterone in development is proposed. At approximately 15 weeks of age testosterone levels decreased sharply towards prepubertal levels in WKY rats and at 23 weeks in SHR/y, whereas testosterone levels were maintained in SHR and SHR/a, which suggests an autosomal component. CONCLUSION: The SHR Y chromosome may accelerate the start of puberty and a cascade of molecular and neuroendocrine events that raise blood pressure.

1.56 A structure of mature truncated human fibroblast collagenase.

The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 A resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded beta-sheet and three alpha-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase.

Automated closed-vessel system for in vitro diagnostics based on polymerase chain reaction.

An automated system for polymerase chain reaction (PCR) amplification and detection combats false-positive results caused by "PCR product carryover." The system uses a single vessel for both PCR amplification and the subsequent detection of PCR products, eliminating the need to handle PCR products in an open environment and risk product carryover. The sample and PCR reagents are introduced into one compartment within the vessel, and amplification occurs as they are thermally cycled. Other compartments contain the reagents for detection of PCR products. Pressure from a roller provides for sequential delivery of the contents of the compartments to a detection area. The PCR products are biotinylated at their 5' ends during amplification through the use of biotinylated primers. After delivery to the detection area, they are specifically captured by hybridization with immobilized oligonucleotide probes. Subsequent reaction with streptavidin-horseradish peroxidase conjugate forms a complex that catalyzes dye formation from dye precursor. Wash steps minimize nonspecific background. This format is amenable to multiplexing, permitting internal controls, speciation of bacteria, typing of viruses, and panel testing. An HIV assay performed with this system demonstrated 100% sensitivity and 95% specificity for 64 patients' samples relative to a conventional PCR assay based on 32P solution hybridization. Similarly, an automated closed-vessel assay of cytomegalovirus exhibited 97.5% sensitivity and 100% specificity.

Effects of surface amino acid replacements in cytochrome c peroxidase on complex formation with cytochrome c.

Site-directed mutagenesis was employed to examine the role played by specific surface residues in the activity of cytochrome c peroxidase. The double charge, aspartic acid to lysine, point mutations were constructed at positions 37, 79, and 217 on the surface of cytochrome c peroxidase, sites purported to be within or proximal to the recognition site for cytochrome c in an electron-transfer productive complex formed by the two proteins. The resulting mutant peroxidases were examined for catalytic activity by steady-state measurements and binding affinity by two methods, fluorescence binding titration and cytochrome c affinity chromatography. The cloned peroxidases exhibit similar UV-visible spectra to the wild-type yeast protein, indicating that there are no major structural differences between the cloned peroxidases and the wild-type enzyme. The aspartic acid to lysine mutations at positions 79 and 217 exhibited similar turnover numbers and binding affinities to that seen for the "wild type-like" cloned peroxidase. The same change at position 37 caused more than a 10-fold decrease in both turnover of and binding affinity for cytochrome c. This empirical finding localizes a primary recognition region critical to the dynamic complex. Models from the literature proposing structures for the complex between peroxidase and cytochrome c are discussed in light of these findings.