Impact of luteolin on the production of alpha-toxin by Staphylococcus aureus

AIMS

To investigate the influence of subinhibitory concentrations of luteolin on the production of α-toxin in Staphylococcus aureus.

METHODS AND RESULTS

The minimal inhibitory concentrations (MICs) were determined using a broth microdilution method, and the MICs of luteolin against the tested Staph. aureus strains ranged from 16 to 64 μg ml(-1). Haemolysis, Western blot and real-time reverse transcription (RT)-PCR assays were used to evaluate the effect of luteolin on Staph. aureusα-toxin secretion and on the level of gene expression, respectively. The data indicated that subinhibitory concentrations of luteolin dose dependently decreased the production of α-toxin in both meticillin-sensitive Staph. aureus (MSSA) and meticillin-resistant Staph. aureus (MRSA). Furthermore, the transcriptional levels of agr (accessory gene regulator) in Staph. aureus were also inhibited by luteolin.

CONCLUSIONS

Luteolin decreases the production and/or secretion of α-toxin in Staph. aureus; the reduced production may be dependent, in part, upon the luteolin-induced inhibition of the agr locus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings indicate that luteolin may be used as a basis for the development of antimicrobial agents aimed at bacterial virulence factors.

Regulation of NF-κB activity by competition between RelA acetylation and ubiquitination

The NF-κB transcription factor plays essential roles in inflammation and oncogenesis. Its ubiquitous RelA subunit is regulated by several post-translational modifications (PTMs) including phosphorylation, ubiquitination, and acetylation. Ubiquitination promotes the termination of RelA-dependent transcription, but its regulation is incompletely understood. Through mass spectrometry analysis of ubiquitinated RelA, we identified 7 lysines that were attached to degradative and non-degradative forms of polyubiquitin. Interestingly, lysines targeted for acetylation were among the residues identified as ubiquitin acceptor sites. Mutation of these particular sites resulted in decreased polyubiquitination. Acetylation and ubiquitination were found to inhibit each other consistent with their use of overlapping sites. Reconstitution of rela^−/− fibroblasts with wild-type and mutant forms of RelA revealed that modifications at these residues can play activating and inhibitory functions depending on the target gene context. Altogether, this study elucidates that ubiquitination and acetylation can modulate each other and regulate nuclear NF-κB function in a gene-specific manner.

Chicken adipocyte fatty acid-binding protein knockdown affects expression of peroxisome proliferator-activated receptor γ gene during oleate-induced adipocyte differentiation

Adipocyte fatty acid-binding protein (A-FABP) is expressed in both adipose cells and macrophages. As one of the downstream genes of peroxisome proliferator-activated receptor γ (PPAR-γ), A-FABP plays an important role in the lipid metabolism of adipocytes in mammal and poultry. However, studies in A-FABP null macrophages of mice showed that A-FABP was a critical regulator of PPAR-γ and could affect the expression of PPAR-γ. The current study was designed to investigate whether the same mechanism as that in macrophages exists in chicken adipocytes. After transfection with interference and overexpression plasmids of A-FABP in chicken adipocytes for 24 h, oleate was added to the medium. Then, lipid accumulation, nonesterified fatty acids (NEFA) in the medium, and expression of lipid metabolism-related genes were detected. The results showed that in the A-FABP knockdown adipocytes, lipid accumulation was decreased at 6 h and NEFA in the medium was higher at 1 and 6 h compared with that in the control group. Moreover, gene expression levels of lipoprotein lipase, perilipin, and PPAR-γ were higher than that of the control group (P < 0.05). In the A-FABP overexpression adipocytes, lipid accumulation and expression of lipid metabolism related genes were similar to that of the control group. However, NEFA in the medium was significantly lower in the A-FABP overexpression group 1 h after adding oleate (P < 0.05). The present study suggested that the A-FABP knockdown might lead to decreased lipid accumulation and upregulated expression of PPAR-γ in chicken adipocytes.

The influence of silver content on the tribological and antimicrobial properties of ZrN/Ag nanocomposite coatings

ZrN/Ag nanocomposite coatings with varying silver contents were produced by co-deposition in a dual pulsed magnetron sputtering system. The coatings were characterised using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scratch adhesion testing, thrust washer wear testing and nanoindentation. The hardness of the ZrN/Ag coatings and the friction coefficient running unlubricated against a steel counterface decreased with increasing silver content, whereas the coating-to-substrate adhesion increased for coatings with higher silver contents, compared to a 'pure' ZrN coating. The antimicrobial properties of the coatings were investigated using two well established microbiological assay techniques: zones of inhibition and a NBT (nitro-blue tetrazolium) redox dye. Zones of inhibition were used to determine the extent of silver ion release from the nanocomposite materials, and a NBT (nitro-blue tetrazolium) redox dye was used to determine the antimicrobial effectiveness of the surfaces following incubation. The microorganisms tested were Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Whilst no zones of inhibition were observed for S. aureus, on any of the surfaces, the diameter of the 'kill' zones generally increased with increasing silver content for the other microorganisms. For the NBT assays, after incubation, no P. aeruginosa colony forming units were observed on any surface and the number of viable cells of E. coli and S. aureus decreased with increasing silver content, compared to a 'pure' ZrN surface.

p,p'-DDE disturbs the homeostasis of thyroid hormones via thyroid hormone receptors, transthyretin, and hepatic enzymes

1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene (p, p'-dichlorodiphenyldichloroethylene, p, p'-DDE), the major metabolite of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT), is a known persistent organic pollutant and endocrine disrupting toxicant. In recent years, it has attracted many attentions on account of its disturbing effects on thyroid and thyroid hormones (THs). However, the mechanisms by which the p, p'-DDE exposure influences THs still remain uncertain. To elucidate the possible mechanisms, 20 male rats are administered with different doses of p, p'-DDE (0, 20, 60, 100 mg/kg body wt) every other day by intraperitoneal injection for 10 days. The results indicate that after the p, p'-DDE exposure, serum total thyroxine (TT4) and free thyroxine (FT4) are significantly reduced and other THs changed only little. Transthyretin (TTR) declines in serum and thyroid hormone receptors (TRα1 and TRβ1) mRNA expressions elevate in hypothalamus. The hepatic enzymes CYP1A1 (EROD), CYP2B1 (PROD), and UDPGTs are significantly upregulated, but CYP1A2 (MROD) does not show significant change. Taken together, the observed effects in the present study show that p, p'-DDE could disturb the homeostasis of THs via TRs increase, TTR decrease, and hepatic enzymes induction.