Toxicity Assessment of 4 Azo Dyes in Zebrafish Embryos.

Azo dyes are used widely as color additives in food, drugs, and cosmetics; hence, there is an increasing concern about their safety and possible health hazards. In the present study, we chose 4 azo dyes tartrazine, Sunset Yellow, amaranth, and Allura red and evaluated their developmental toxicity on zebrafish embryos. At concentration levels of 5 to 50 mM, we found that azo dyes can induce hatching difficulty and developmental abnormalities such as cardiac edema, decreased heart rate, yolk sac edema, and spinal defects including spinal curvature and tail distortion. Exposure to 100 mM of each azo dye was completely embryolethal. The median lethal concentration (LC50), median effective concentration (EC50), and teratogenic index (TI) were calculated for each azo dye at 72 hours postfertilization. For tartrazine, the LC50 was 47.10 mM and EC50 value was at 42.66 mM with TI ratio of 1.10. For Sunset Yellow, the LC50 was 38.93 mM and EC50 value was at 29.81 mM with TI ratio of 1.31. For amaranth, the LC50 was 39.86 mM and EC50 value was at 31.94 mM with TI ratio of 1.25. For Allura red, the LC50 was 47.42 mM and EC50 value was 40.05 mM with TI ratio of 1.18. This study reports the developmental toxicity of azo dyes in zebrafish embryos at concentrations higher than the expected human exposures from consuming food and drugs containing azo dyes.

The mechanism of Jurkat cells apoptosis induced by Aggregatibacter actinomycetemcomitans cytolethal distending toxin.

Cytolethal distending toxin (CDT) which is produced by Aggregatibacter actinomycetemcomitans causes apoptosis in lymphocytes. But the specific mechanism is not clear. The aim of our research was to investigate the effect and mechanism during this process. The wild-type CdtA, CdtB, CdtC (CdtAW, CdtBW, CdtCW) and mutant CdtB (CdtBM) were expressed and purified respectively and the purity of each subunit was examined by BandScan software. And the type I deoxyribonuclease and PI-3,4,5-triphosphate (PI-3,4,5-P3, PIP3) phosphatase activity were detected by DNA agarose gel electrophoresis and enzyme-linked immunosorbent assay respectively. The cell apoptosis rates were analyzed by flow cytometry. The morphological changes of apoptosis cells were observed by confocal laser scanning microscopy. The protein expression of Bax and Bcl-2 was examined by western blot. Differentially expressed apoptosis-related proteins were identified based on isobaric tags for relative and absolute quantitation technology. In the present study we found that: (i) recombinant wild-type CdtA, CdtB and CdtC (CdtAW, CdtBW, CdtCW) and mutant CdtB (CdtBM) were correctly expressed and the purity of each protein was higher than 80%, (ii) the average apoptosis rate in wild-type CDT (CDTW) treated groups was 50.54%, which was significantly higher than the controls (4.71%) and mutant CDT (CDTM) treated groups (5.58%) (p < 0.05), (iii) morphological changes of apoptosis were observed in CDTW treated cells, (iv) the expression of Bax protein was significantly increased in CDTW treated cells, while Bcl-2 protein expression was significantly decreased, (v) 17 apoptosis-related proteins were expressed differentially, among which 10 proteins (SMNDC1, TNFRSF10B, UBE2I, ITM2A, CASP3, P53, EIF1, TCF3, HMGN5, CASP8) were up-regulated and 7 proteins (RRM2, TPX2, KIF11, NUCKS1, TOP2A, XRCC1, PTPLAD1, RRM2) were down-regulated, (vi) one possible apoptotic pathway [Ubc9 (UBE2I)/P53/DR5 (TNFRSF10B)/Caspase-8 (CASP8)/ Caspase-3 (CASP3)] was selected and partially proved.

A new functional site W115 in CdtA is critical for Aggregatibacter actinomycetemcomitans cytolethal distending toxin.

Aggregatibacter actinomycetemcomitans, a specific pathogen of localized aggressive periodontitis, produces a cytolethal distending toxin (CDT) that arrests eukaryotic cells irreversibly in G0/G1 or G2/M phase of the cell cycle. Although structural studies show that the aromatic patch region of CdtA plays an important role in its biological activity, the functional sites of CdtA have not been firmly established. In this study, site-specific mutagenesis strategy was employed for cdtA point mutations construction so as to examine the contributions of individual amino acids to receptor binding and the biological activity of holotoxin. The binding ability was reduced in CdtA(Y181A)BC holotoxin and the biological function of CDT was not weaken in CdtA(Y105A)BC, CdtA(Y125A)BC, CdtA(F109A)BC and CdtA(S106N)BC holotoxin suggesting that these sites were not critical to CDT. But the binding activity and cell cycle arrest ability of holotoxin complexes were inhibited in CdtA(W115G)BC. And this site did not affect the holotoxin assembly by size exclusion chromatography. Therefore, W115 might be a critical site of CdtA binding ability. These findings suggest that the functional sites of CdtA are not only in the aromatic patch region. W115, the new functional site is critical for receptor binding and cell cycle arrest, which provides potential targets for pharmacological disruption of CDT activity.

Effects of aging on endotoxin tolerance induced by lipopolysaccharides derived from Porphyromonas gingivalis and Escherichia coli.

BACKGROUND: Periodontitis is a bacterially induced chronic inflammatory disease. Exposure of the host to periodontal pathogens and their virulence factors induces a state of hyporesponsiveness to subsequent stimulations, termed endotoxin tolerance. Aging has a profound effect on immune response to bacteria challenge. The aim of this study was to explore the effects of aging on endotoxin tolerance induced by Porphyromonas gingivalis (P. gingivalis) lipopolysaccharide (LPS) and Escherichia coli (E. coli) LPS in murine peritoneal macrophages. METHODOLOGY/PRINCIPAL FINDINGS: We studied the cytokine production (TNF-α and IL-10) and Toll-like receptor 2, 4 (TLR2, 4) gene and protein expressions in peritoneal macrophages from young (2-month-old) and middle-aged (12-month-old) ICR mice following single or repeated P. gingivalis LPS or E. coli LPS stimulation. Pretreatment of peritoneal macrophages with P. gingivalis LPS or E. coli LPS resulted in a reduction in TNF-α production and an increase in IL-10 production upon secondary stimulation (p<0.05), and the markedly lower levels of TNF-α and higher levels of IL-10 were observed in macrophages from young mice compared with those from middle-aged mice (p<0.05). In addition, LPS restimulations also led to the significantly lower expression levels of TLR2, 4 mRNA and protein in macrophages from young mice (p<0.05). CONCLUSIONS/SIGNIFICANCE: Repeated LPS stimulations triggered endotoxin tolerance in peritoneal macrophages and the ability to develop tolerance in young mice was more excellent. The impaired ability to develop endotoxin tolerance resulted from aging might be related to TLR2, 4 and might lead to the incontrollable periodontal inflammation in older adults.

[Gene cloning of cdtB from Actinobacillus actinomycetemcomitans and bioactivity test of the recombinant protein CdtB in vitro].

OBJECTIVE: To construct the prokayotic expression vector pET-15b-cdtB containing the cdtB gene from Actinobacillus actinomycetemcomitans (Aa) and to test the bioactivity of this recombinant CdtB in vitro. METHODS: The toxic cytolethal distending toxin (CDT) subunit encoding gene cdtB was amplified by PCR. Through restriction endonuclease digestion, gene cdtB and vector pET-15b were ligated to form pET-15b-cdtB expression system which was transformed into competent cells Escherichia coli BL21 (DE3). Protein expression was induced by isopropyl-beta-D-thiogalactoside and examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Supercoiled plasmid pET-32a DNA was incubated with purified recombinant CdtB protein in vitro to view any changes in the electrophoretic mobility of the plasmid pET-32a DNA band. RESULTS: PCR testing results of pET-15b-cdtB transformed cells demonstrated that all strains contained cdtB gene. The DNA sequence was blast with cdtB gene from GenBank and 99% homology was obtained. Both of SDS-PAGE and Western blotting confirmed that recombinant CdtB was obtained. After incubated with the purified recombinant CdtB in vitro, the supercoiled plasmid pET-32a DNA was observed relaxing by 1% agarose gel electrophoresis test. CONCLUSIONS: The recombinant plasmid pET-15b-cdtB was successfully constructed and the recombinant CdtB protein which has the DNaseI-like activity was obtained.