Bactericidal activity of micromolar N-chlorotaurine: evidence for its antimicrobial function in the human defense system

Endogenous metabolite N-chlorotaurine attenuates antiviral responses by facilitating IRF3 oxidation

Cellular microenvironments critically control the activation of innate immune responses. N-chlorotaurine (Tau-Cl) is an endogenous metabolite that is markedly produced and secreted during pathogenic invasion. However, its effect on the antiviral innate immune responses remains unclear. Here, we demonstrate that viral infection upregulates cellular Tau-Cl level. Tau-Cl attenuates viral infection-induced expression of type I IFNs and facilitates viral replication both in vitro and in vivo. Mechanistically, Tau-Cl facilitates the oxidation of IRF3 at Cys222 and Cys371, a key transcription factor that governs the transcription of type I IFNs. Tau-Cl inhibits phosphorylation and nuclear translocation of IRF3, and blocks IRF3 binding to the IFN-β promoter region. Therefore, we identify Tau-Cl as an endogenous suppressor of IRF3-driven antiviral innate responses and uncover an immune escape mechanism of viruses by affecting host microenvironments.

Regulatory role of the Cpx ESR in bacterial behaviours

The envelope demarcates the boundary between bacterial cell and its environment, providing a place for bacteria to transport nutrients and excrete metabolic waste, while buffering external environmental stress. Envelope stress responses (ESRs) are important tools for bacteria to sense and repair envelope damage. In this review, we discussed evidence that indicates the important role of the Cpx ESR in pathogen-host interactions, including environmental stress sensing and responses, modulation of bacterial virulence, antimicrobial resistance, and inter-kingdom signaling.

Tolerability of N-chlorotaurine in comparison with routinely used antiseptics: an in vitro study on chondrocytes

BACKGROUND

Currently, povidone-iodine (PVP-I) and hydrogen peroxide (H2O2) are frequently used antiseptics in joint infections, but the cytotoxic effects of these solutions are already reported. N-chlorotaurine (NCT) shows a broad-spectrum bactericidal activity and is well tolerated in various tissues, but its effect on human chondrocytes is unknown. The purpose of this study was to assess the cytotoxic effect of NCT, PVP-I, and H2O2 on human chondrocytes compared to a control group in an in vitro setting to get first indications if NCT might be a promising antiseptic in the treatment of septic joint infections for the future.

MATERIAL AND METHODS

Chondrocytes extracted from human cartilage were incubated with various concentrations of NCT, PVP-I, and H2O2 for 5 and 30 min respectively. EZ4U cell viability kit was used according to the manufacturer's recommendations determining cell viability. To assess cell viability based on their nuclear morphology, cells were stained with acridine-orange and identified under the fluorescence microscope.

RESULTS

EZ4U kit showed after 5 and 30 min of incubation a significant decrease in cell viability at NCT 1%, NCT 0.1%, PVP-I, and H2O2, but not for NCT 0.001% and NCT 0.01%. Acridine-orange staining likewise presented a significant decrease in vital cells for all tested solutions except NCT 0.001% and NCT 0.01% after 5 and 30 min of incubation.

CONCLUSION

Our results demonstrate that NCT is well tolerated by chondrocytes in vitro at the tested lower NCT concentrations 0.01% and 0.001% in contrast to the higher NCT concentrations 1% and 0.1%, PVP-I (1.1%), and H2O2 (3%), for which a significant decrease in cell viability was detected. Considering that the in vivo tolerability is usually significantly higher, our findings could be an indication that cartilage tissue in vivo would tolerate the already clinically used 1% NCT solution. In combination with the broad-spectrum bactericidal activity, NCT may be a promising antiseptic for the treatment of septic joint infections.

Activity of N-Chlorotaurine against Periodontal Pathogens

Dental plaque bacteria play an important role in the pathogenicity of periodontitis and peri-implantitis. Therefore, antimicrobial agents are one means of treatment. N-chlorotaurine (NCT) as an endogenous well-tolerated topical antiseptic could be of advantage for this purpose. Accordingly, its microbicidal activity against some dental plaque bacteria was investigated at therapeutic concentrations in vitro. In quantitative killing assays, the activity of NCT against planktonic bacteria and against biofilms grown for 48 h on implantation screws was tested. Electron microscopy was used to demonstrate the formation of biofilm and its morphological changes. The killing of planktonic bacteria of all tested species, namely Streptococcus sanguinis, Streptococcus salivarius, Streptococcus oralis, Streptococcus cristatus, Rothia aeria, and Capnocytophaga ochracea, was shown within 10-20 min by 1% NCT in 0.01 M phosphate-buffered saline at 37 °C. Bacteria grown on screws for 24 h were inactivated by 1% NCT after 15-20 min as well, but the formation of biofilm on the screws was visible in electron microscopy not before 48 h. The killing of biofilms by 1% NCT was demonstrated after 30 min (streptococci) and 40 min (R. aeria). As expected, NCT has broad activity against dental plaque bacteria as well and should be further investigated on its clinical efficacy in periodontitis and peri-implantitis.

Comparative analysis reveals the trivial role of MsrP in defending oxidative stress and virulence of Salmonella Typhimurium in mice

Sulphur containing amino acids, methionine and cysteine are highly prone to oxidation. Reduction of oxidized methionine (Met-SO) residues to methionine (Met) by methionine sulfoxide reductases (Msrs) enhances the survival of bacterial pathogens under oxidative stress conditions. S. Typhimurium encodes two types (cytoplasmic and periplasmic) of Msrs. Periplasmic proteins, due to their location are highly vulnerable to host-generated oxidants. Therefore, the periplasmic Msr (MsrP) mediated repair (as compared to the cytoplasmic counterpart) might play a more imperative role in defending host-generated oxidants. Contrary to this, we show that in comparison to the ΔmsrP strain, the mutant strains in the cytoplasmic Msrs (ΔmsrA and ΔmsrAC strains) showed many folds more susceptibility to chloramine-T and neutrophils. Further ΔmsrA and ΔmsrAC strains accumulated higher levels of ROS and showed compromised fitness in mice spleen and liver. Our data suggest the pivotal role of cytoplasmic Msrs in oxidative stress survival of S. Typhimurium.

Salmonella Typhimurium uses the Cpx stress response to detect N-chlorotaurine and promote the repair of oxidized proteins

The cell envelope of gram-negative bacteria constitutes the first protective barrier between a cell and its environment. During host infection, the bacterial envelope is subjected to several stresses, including those induced by reactive oxygen species (ROS) and reactive chlorine species (RCS) produced by immune cells. Among RCS, N-chlorotaurine (N-ChT), which results from the reaction between hypochlorous acid and taurine, is a powerful and less diffusible oxidant. Here, using a genetic approach, we demonstrate that Salmonella Typhimurium uses the CpxRA two-component system to detect N-ChT oxidative stress. Moreover, we show that periplasmic methionine sulfoxide reductase (MsrP) is part of the Cpx regulon. Our findings demonstrate that MsrP is required to cope with N-ChT stress by repairing N-ChT-oxidized proteins in the bacterial envelope. By characterizing the molecular signal that induces Cpx when S. Typhimurium is exposed to N-ChT, we show that N-ChT triggers Cpx in an NlpE-dependent manner. Thus, our work establishes a direct link between N-ChT oxidative stress and the envelope stress response.

Nanomaterials: an intra-periodontal pocket drug-delivery system for periodontitis

Periodontitis is a microbiological condition that affects the tissues supporting the teeth. The fundamental to effective periodontal therapy is choosing the suitable antimicrobial and anti-inflammatory agent, together with the proper route of drug administration and delivery system. Intra-periodontal pocket approach with nano drug-delivery systems (NDDS) such as polymeric nanoparticles, gold nanoparticles, silica nanoparticles, magnetic nanoparticles, liposomes, polymersomes, exosomes, nano micelles, niosome, solid lipid nanoparticles, nano lipid carriers, nanocomposites, nanogels, nanofibers, scaffolds, dendrimers, quantum dots, etc., will be appropriate route of drug administration and delivery system. This NDDS delivers the drugs at the site of infection to inhibit growth and promote tissue regeneration. The present review focused on providing comprehensive information on the NDDS for periodontitis, which enhanced therapeutic outcomes via intra-periodontal pocket delivery.

Periplasmic methionine sulfoxide reductase (MsrP)-a secondary factor in stress survival and virulence of Salmonella Typhimurium

Among others, methionine residues are highly susceptible to host-generated oxidants. Repair of oxidized methionine (Met-SO) residues to methionine (Met) by methionine sulfoxide reductases (Msrs) play a chief role in stress survival of bacterial pathogens, including Salmonella Typhimurium. Periplasmic proteins, involved in many important cellular functions, are highly susceptible to host-generated oxidants. According to location in cell, two types of Msrs, cytoplasmic and periplasmic are present in S. Typhimurium. Owing to its localization, periplasmic Msr (MsrP) might play a crucial role in defending the host-generated oxidants. Here, we have assessed the role of MsrP in combating oxidative stress and colonization of S. Typhimurium. ΔmsrP (mutant strain) grew normally in in-vitro media. In comparison to S. Typhimurium (wild type), mutant strain showed mild hypersensitivity to HOCl and chloramine-T (ChT). Following exposure to HOCl, mutant strain showed almost similar protein carbonyl levels (a marker of protein oxidation) as compared to S. Typhimurium strain. Additionally, ΔmsrP strain showed higher susceptibility to neutrophils than the parent strain. Further, the mutant strain showed very mild defects in survival in mice spleen and liver as compared to wild-type strain. In a nutshell, our results indicate that MsrP plays only a secondary role in combating oxidative stress and colonization of S. Typhimurium.

Redox-Mediated Inactivation of the Transcriptional Repressor RcrR is Responsible for Uropathogenic Escherichia coli's Increased Resistance to Reactive Chlorine Species

The ability to overcome stressful environments is critical for pathogen survival in the host. One challenge for bacteria is the exposure to reactive chlorine species (RCS), which are generated by innate immune cells as a critical part of the oxidative burst. Hypochlorous acid (HOCl) is the most potent antimicrobial RCS and is associated with extensive macromolecular damage in the phagocytized pathogen. However, bacteria have evolved defense strategies to alleviate the effects of HOCl-mediated damage. Among these are RCS-sensing transcriptional regulators that control the expression of HOCl-protective genes under non-stress and HOCl stress. Uropathogenic Escherichia coli (UPEC), the major causative agent of urinary tract infections (UTIs), is particularly exposed to infiltrating neutrophils during pathogenesis; however, their responses to and defenses from HOCl are still completely unexplored. Here, we present evidence that UPEC strains tolerate higher levels of HOCl and are better protected from neutrophil-mediated killing compared with other E. coli. Transcriptomic analysis of HOCl-stressed UPEC revealed the upregulation of an operon consisting of three genes, one of which encodes the transcriptional regulator RcrR. We identified RcrR as a HOCl-responsive transcriptional repressor, which, under non-stress conditions, is bound to the operator and represses the expression of its target genes. During HOCl exposure, however, the repressor forms reversible intermolecular disulfide bonds and dissociates from the DNA resulting in the derepression of the operon. Deletion of one of the target genes renders UPEC significantly more susceptible to HOCl and phagocytosis indicating that the HOCl-mediated induction of the regulon plays a major role for UPEC’s HOCl resistance.

The Protective Effects of Lactobacillus plantarum KLDS 1.0344 on LPS-Induced Mastitis In Vitro and In Vivo

Cow mastitis, which significantly lowers milk quality, is mainly caused by pathogenic bacteria such as E. coli. Previous studies have suggested that lactic acid bacteria can have antagonistic effects on pathogenic bacteria that cause mastitis. In the current study, we evaluated the in vitro and in vivo alleviative effects of L. plantarum KLDS 1.0344 in mastitis treatment. In vitro antibacterial experiments were performed using bovine mammary epithelial cell (bMEC), followed by in vivo studies involving mastitis mouse models. In vitro results indicate that lactic acid was the primary substance inhibiting the E. coli pathogen. Meanwhile, treatment with L. plantarum KLDS 1.0344 can reduce cytokines' mRNA expression levels in the inflammatory response of bMEC induced by LPS. In vivo, the use of this strain reduced the secretion of inflammatory factors IL-6, IL-1β, and TNF-α, and decreased the activity of myeloperoxidase (MPO), and inhibited the secretion of p-p65 and p-IκBα. These results indicate that L. plantarum KLDS 1.0344 pretreatment can reduce the expression of inflammatory factors by inhibiting the activation of NF-κB signaling pathway, thus exerting prevent the occurrence of inflammation in vivo. Our findings show that L. plantarum KLDS 1.0344 has excellent properties as an alternative to antibiotics and can be developed into lactic acid bacteria preparation to prevent mastitis disease.

Taurine ameliorates thioacetamide induced liver fibrosis in rats via modulation of toll like receptor 4/nuclear factor kappa B signaling pathway

Liver fibrosis is a significant health problem that can cause serious illness and death. Unfortunately, a standard treatment for liver fibrosis has not been approved yet due to its complicated pathogenesis. The current study aimed at assessing the anti-fibrotic effect of taurine against thioacetamide induced liver fibrosis in rats through the modulation of toll like receptor 4/nuclear factor kappa B signaling pathway. Both concomitant and late taurine treatment (100 mg/kg, IP, daily) significantly reduced the rise in serum ALT and AST activities and significantly reversed the decrease in serum albumin and total protein. These results were confirmed by histopathological examinations and immunehistochemical inspection of α-SMA, caspase-3 and NF-κB. The antioxidant potential of taurine was verified by a marked increase of GSH content and a reduction of MDA level in liver tissue. The anti-fibrotic effects of taurine were evaluated by investigating the expression of TLR4, NF-κB. The protein levels of IL-6, LPS, MyD88, MD2, CD14, TGF-β1 and TNF-α were determined. Docking studies were carried out to understand how taurine interacts inside TLR4-MD2 complex and it showed good binding with the hydrophobic binding site of MD2. We concluded that the anti-fibrotic effect of taurine was attributable to the modulation of the TLR4/NF-κB signaling.

Roles of RcsA, an AhpD Family Protein, in Reactive Chlorine Stress Resistance and Virulence in Pseudomonas aeruginosa

Reactive chlorine species (RCS), particularly hypochlorous acid (HOCl), are powerful antimicrobial oxidants generated by biological pathways and chemical syntheses. Pseudomonas aeruginosa is an important opportunistic pathogen that has adapted mechanisms for protection and survival in harsh environments, including RCS exposure. Based on previous transcriptomic studies of HOCl exposure in P. aeruginosa, we found that the expression of PA0565, or rcsA, which encodes an alkyl hydroperoxidase D-like protein, exhibited the highest induction among the RCS-induced genes. In this study, rcsA expression was dominant under HOCl stress and greatly increased under HOCl-related stress conditions. Functional analysis of RcsA showed that the distinguishing core amino acid residues Cys60, Cys63, and His67 were required for the degradation of sodium hypochlorite (NaOCl), suggesting an extended motif in the AhpD family. After allelic exchange mutagenesis in the P. aeruginosa rcsA, the P. aeruginosa rcsA deletion mutant showed significantly decreased HOCl resistance. Ectopic expression of P. aeruginosa rcsA led to significantly increased NaOCl resistance in Escherichia coli Moreover, the pathogenicity of the rcsA mutant decreased dramatically in both Caenorhabditis elegans and Drosophila melanogaster host model systems compared to the wild type (WT). Finally, the Cys60, Cys63, and His67 variants of RcsA were unsuccessful at complementing phenotypes of the rcsA mutant. Overall, our data indicate the importance of P. aeruginosa RcsA in defense against HOCl stress under disinfections and during infections of hosts, which involves the catalytic Cys60, Cys63, and His67 residues.IMPORTANCE Pseudomonas aeruginosa is a common pathogen that is a major cause of serious infections in many hosts. Hypochlorous acid (HOCl) is a potent antimicrobial agent found in household bleach and is a widely used disinfectant. P. aeruginosa has evolved adaptive mechanisms for protection and survival during HOCl exposure. We identified P. aeruginosa rcsA as a HOCl-responsive gene encoding an antioxidant protein that may be involved in HOCl degradation. RcsA has a distinguishing core motif containing functional Cys60, Cys63, and His67 residues. P. aeruginosa rcsA plays an important role in bleach tolerance, with expression of P. aeruginosa rcsA in Escherichia coli also conferring HOCl resistance. Interestingly, RcsA is required for full virulence in worm and fruit fly infection models, indicating a correlation between mechanisms of bleach toxicity and host immunity during infection. This provides new insights into the mechanisms used by P. aeruginosa to persist in harsh environments such as hospitals.

The Anti-Inflammatory Effect of Taurine on Cardiovascular Disease

Taurine is a non-protein amino acid that is expressed in the majority of animal tissues. With its unique sulfonic acid makeup, taurine influences cellular functions, including osmoregulation, antioxidation, ion movement modulation, and conjugation of bile acids. Taurine exerts anti-inflammatory effects that improve diabetes and has shown benefits to the cardiovascular system, possibly by inhibition of the renin angiotensin system. The beneficial effects of taurine are reviewed.

Role of taurine, its haloamines and its lncRNA TUG1 in both inflammation and cancer progression. On the road to therapeutics? (Review)

For one century, taurine is considered as an end product of sulfur metabolism. In this review, we discuss the beneficial effect of taurine, its haloamines and taurine upregulated gene 1 (TUG1) long non‑coding RNA (lncRNA) in both cancer and inflammation. We outline how taurine or its haloamines (N‑Bromotaurine or N‑Chlorotaurine) can induce robust and efficient responses against inflammatory diseases, providing insight into their molecular mechanisms. We also provide information about the use of taurine as a therapeutic approach to cancer. Taurine can be combined with other chemotherapeutic drugs, not only mediating durable responses in various malignancies, but also circumventing the limitations met from chemotherapeutic drugs, thus improving the therapeutic outcome. Interestingly, the lncRNA TUG1 is regarded as a promising therapeutic approach, which can overcome acquired resistance of cancer cells to selected strategies. In this regard, we can translate basic knowledge about taurine and its TUG1 lncRNA into potential therapeutic options directed against specific oncogenic signaling targets, thereby bridging the gap between bench and bedside.

Bacterial Defense Systems against the Neutrophilic Oxidant Hypochlorous Acid

Neutrophils kill invading microbes and therefore represent the first line of defense of the innate immune response. Activated neutrophils assemble NADPH oxidase to convert substantial amounts of molecular oxygen into superoxide, which, after dismutation into peroxide, serves as the substrate for the generation of the potent antimicrobial hypochlorous acid (HOCl) in the phagosomal space. In this minireview, we explore the most recent insights into physiological consequences of HOCl stress. Not surprisingly, Gram-negative bacteria have evolved diverse posttranslational defense mechanisms to protect their proteins, the main targets of HOCl, from HOCl-mediated damage. We discuss the idea that oxidation of conserved cysteine residues and partial unfolding of its structure convert the heat shock protein Hsp33 into a highly active chaperone holdase that binds unfolded proteins and prevents their aggregation. We examine two novel members of the Escherichia coli chaperone holdase family, RidA and CnoX, whose thiol-independent activation mechanism differs from that of Hsp33 and requires N-chlorination of positively charged amino acids during HOCl exposure. Furthermore, we summarize the latest findings with respect to another bacterial defense strategy employed in response to HOCl stress, which involves the accumulation of the universally conserved biopolymer inorganic polyphosphate. We then discuss sophisticated adaptive strategies that bacteria have developed to enhance their survival during HOCl stress. Understanding bacterial defense and survival strategies against one of the most powerful neutrophilic oxidants may provide novel insights into treatment options that potentially compromise the ability of pathogens to resist HOCl stress and therefore may increase the efficacy of the innate immune response.

Microbicidal activity of N-chlorotaurine can be enhanced in the presence of lung epithelial cells

BACKGROUND

N-chlorotaurine (NCT) is an endogenous active chlorine compound that can be used as an antiseptic and anti-infective in different body regions. Recently, tolerability of inhaled NCT has been demonstrated in humans so that it is of interest for future treatment of cystic fibrosis. In the present study, we tested the bactericidal and fungicidal activity of NCT in different lung cell culture models.

METHODS

Bacteria (Staphylococcus aureus, Pseudomonas aeruginosa) and fungi (Candida albicans, Exophiala dermatitidis) were co-incubated with lung epithelial cell cultures, and after 4 h NCT was added. After different incubation times, aliquots were removed and quantitative cultures were performed.

RESULTS

NCT at the therapeutically applied concentration of 1% (55 mM) completely killed the test pathogens within 15 - 30 min at 20 °C and at 37 °C. Killing by 0.3% NCT lasted up to 4 h dependent on the pathogen at 20 °C and up to 1 h at 37 °C. 0.1% NCT was the threshold concentration for killing since this amount of oxidation capacity was consumed by reactions with the organic compounds of the medium within 3 h (20 °C) and 0.5 h (37 °C).

CONCLUSIONS

NCT in therapeutic concentration demonstrated its microbicidal activity in the presence of lung epithelial cells. Remarkably, particularly the fungicidal activity was higher under these conditions than in phosphate buffer. This can be explained by formation of the stronger microbicidal monochloramine in equilibrium by transchlorination. The results suggest the suitability of NCT as inhalation medication in the lung.

Neutrophils as Sentinel Cells of the Immune System: A Role of the MPO-halide-system in Innate and Adaptive Immunity

For decades, neutrophils were generally regarded as the cells of innate immunity with proinflammatory and phagocytic properties involved in a dual activity, beneficial (antimicrobial) and detrimental (tissue damage). Importantly, until the discovery of toll-like receptors (TLRs), a role of neutrophils in adaptive immunity was limited to the effector stage of humoral response and phagocytosis of opsonized antigens. Moreover, in common opinion, neutrophils, as well as the entire innate immune system, were not functionally associated with adaptive immunity. At the time we demonstrated protein chlorination by HOCl, the major product of neutrophil MPO-halide system enhances protein immunogenicity. Based on this discovery, we proposed, as the first, a new role for neutrophils as APC-accessory cells involved in the induction stage of adaptive immunity. Thereafter, we developed our theory concerning the role of neutrophils as the cells which link innate and adaptive immunity. We proposed that protein modification by HOCl may act as a neutrophildependent molecular tagging system, by which sentinel dendritic cells can faster recognise pathogen- derived antigens. Contemporaneously, it was demonstrated that taurine, the most abundant free amino acid in neutrophil cytosol and the major scavenger of HOCl, is a part of the oxidantantioxidant network and is responsible for the regulation and termination of acute inflammation. Moreover, it has been described, that taurine chloramine (TauCl), the physiological products of the reaction of HOCl with taurine, show anti-microbial and anti-inflammatory properties. In this review, the role of HOCl, taurine and TauCl in innate and adaptive immunity will be discussed.

Exposure to N-chlorotaurine induces oxidative stress responses in Aspergillus fumigatus

PURPOSE

The neutrophil-derived oxidant N-chlorotaurine (NCT) displays remarkable in vivo tolerability and efficacy against a range of pathogens. The aim of this study was to characterize the response of the pulmonary pathogen Aspergillus fumigatus to NCT.

METHODOLOGY

The effect of NCT on the growth and viability of A. fumigatus was characterized. NCT-induced alteration of amino acids and gliotoxin from A. fumigatus mycelium was assessed. Label-free shotgun quantitative proteomic analysis was performed on A. fumigatus exposed to NCT for 24 h.

RESULTS

Incubation of A. fumigatus with NCT at concentrations ranging from 6.8 to 55 mM decreased conidial growth and viability, and mycelium biomass relative to the controls. Exposure to NCT (13.77 mM) resulted in increased amino acids and gliotoxin levels from A. fumigatus mycelium. Exposure of A. fumigatus mycelium to NCT (6.8 mM) revealed an enrichment in proteins associated with the ribosome, transcription and translation and non-ribosomal peptide biosynthesis (e.g. Pes1, Pes3), which play an essential role in oxidative stress resistance in A. fumigatus. A decrease in the abundance of proteins associated with fumagillin and pseurotin biosynthesis highlighted the anti-virulence activity of NCT.

CONCLUSION

These results indicate that NCT induces an oxidative stress response in A. fumigatus as evidenced by alterations in the proteome and inhibits conidial and mycelial growth. Clinical investigations of topical application of NCT to treat Aspergillus infections are encouraged.

Comparative Analysis of Microbicidal and Anti-inflammatory Properties of Novel Taurine Bromamine Derivatives and Bromamine T

Taurine, the most abundant free amino acid in leukocyte cytosol traps hypohalous acids (HOCl and HOBr) to produce N-chlorotaurine (taurine chloramine, NCT and N-bromotaurine (taurine bromamine, Tau-NHBr,) respectively. Both haloamines show anti-inflammatory and antimicrobial properties. However, the therapeutic applicability of Tau-NHBr is limited due to its relatively poor stability. To overcome this disadvantage, we have synthesized the stable N-bromotaurine compounds N-monobromo-2,2-dimethyltaurine (Br-612) and N-dibromo-2,2-dimethyltaurine (Br-422). The aim of this study was to compare anti-inflammatory and microbicidal properties of Br-612 and Br-422 with that of Tau-NHBr and bromamine T (BAT). We have shown that all the tested compounds show similar anti-inflammatory properties. Importantly, the stable N-bromotaurine compounds exerted even stronger microbicidal activity than Tau-NHBr. Finally, for the purpose of topical application of these compounds we have developed a carbomer-based bioadhesive solid dosage form of BAT and Br-612, featuring sustained release of the active substance.

The endogenous antiseptic N-chlorotaurine irreversibly inactivates Chlamydia pneumoniae and Chlamydia trachomatis

PURPOSE

The antimicrobial activity of N-chlorotaurine (NCT), an endogenous long-lived oxidant applied topically, was tested against Chlamydiae in vitro.

METHODOLOGY

Elementary bodies of Chlamydia pneumoniae strain CV-6 and Chlamydia trachomatis serovars A and D were incubated in 0.01, 0.1 and 1 % (w/v) NCT solution at pH 7.1 and 37 °C. After different incubation times, aliquots were removed and grown in cell culture. The number of inclusion forming units was quantified by immunofluorescence and real-time qPCR.Results/Key findings.Chlamydia pneumoniae and Chlamydia trachomatis were inactivated by 1 and 0.1 % NCT within 1 min. Moreover, 0.025-0.1 % NCT significantly reduced the number of intracellularly growing C. pneumoniae within 30 min.

CONCLUSIONS

This is the first study demonstrating the antimicrobial activity of NCT against Chlamydiae. Clinical implications of these findings have to be investigated in further trials.

In Vitro Study on the Influence of N-Chlorotaurine on the Ciliary Beat Frequency of Nasal Mucosa

Background

The aim of this study was to investigate the in vitro effects of N-chlorotaurine (NCT), a new endogenous antimicrobial agent, on the nasal ciliary beat frequency (CBF) in nasal mucosa samples of 10 adult patients who underwent conchotomy.

Methods

CBF was measured by a photometric technique, combining a light microscope, a photometer, a photograph multiplier, and a computed analyzing unit.

Results

CBF decreased ∼10% after 20 minutes of incubation in aqueous 1% NCT solution compared with 3% in 0.9% saline, and 0.1 and 0.01% NCT had no effect. However, a solution of 7% cocaine, which is used routinely for shrinking the nasal mucosa before rhinoscopy lowered the CBF to 50% after the same incubation time.

Conclusion

These results confirm the very low toxic potential of NCT, and they are fundamental for clinical investigations regarding its topical application in the nasal and paranasal sinuses.

Role of heme oxygenase-1 in potentiation of phagocytic activity of macrophages by taurine chloramine: Implications for the resolution of zymosan A-induced murine peritonitis

Phagocytosis of pathogens by macrophages is crucial for the successful resolution of inflammation induced by microbial infection. Taurine chloramine (TauCl), an endogenous anti-inflammatory and antioxidative substance, is produced by reaction between taurine and hypochlorous acid by myeloperoxidase activity in neutrophils under inflammatory conditions. In the present study, we investigated the effect of TauCl on resolution of acute inflammation caused by fungal infection using a zymosan A-induced murine peritonitis model. TauCl administration reduced the number of the total peritoneal leukocytes, while it increased the number of peritoneal monocytes. Furthermore, TauCl promoted clearance of pathogens remaining in the inflammatory environment by macrophages. When the macrophages isolated from thioglycollate-treated mice were treated with TauCl, their phagocytic capability was enhanced. In the murine macrophage-like RAW264.7 cells treated with TauCl, the proportion of macrophages clearing the zymosan A particles was also increased. TauCl administration resulted in elevated expression of heme oxygenase-1 (HO-1) in the peritoneal macrophages. Pharmacologic inhibition of HO-1 activity or knockdown of HO-1 in the murine macrophage RAW264.7 cells abolished the TauCl-induced phagocytosis, whereas the overexpression of HO-1 augmented the phagocytic ability of macrophages. Moreover, peritoneal macrophages isolated from HO-1 null mice failed to mediate TauCl-induced phagocytosis. Our results suggest that TauCl potentiates phagocytic activity of macrophages through upregulation of HO-1 expression.

N-Chlorotaurine, a Promising Future Candidate for Topical Therapy of Fungal Infections

N-Chlorotaurine (NCT) is a mild long-lived oxidant that can be applied to sensitive body regions as an endogenous antiseptic. Enhancement of its microbicidal activity in the presence of proteinaceous material because of transchlorination, a postantibiotic/postantifungal effect and antitoxic activity renders it interesting for treatment of fungal infections, too. This is confirmed by first case applications in skin and mucous membranes of different body sites. Recent findings of good tolerability of inhaled NCT suggest further investigations of this substance for treatment of bronchopulmonary diseases, where microorganisms play a role, particularly multi-resistant ones. The availability of a well-tolerated and effective inhaled antiseptic with anti-inflammatory properties could be a significant progress, in particular for chronic pulmonary diseases, such as chronic obstructive pulmonary disease or cystic fibrosis.

The potential protective role of taurine against experimental allergic inflammation

AIMS

Taurine has been widely evaluated as a potential therapeutic agent in chronic inflammatory disorders and various infections. However, the potential role of taurine in regulating allergic inflammatory responses is currently unknown.

MATERIALS AND METHODS

The present study was designed to evaluate the in vitro effects of taurine on the levels of thymic stromal lymphopoietin (TSLP) and other pro-inflammatory cytokines and activation of caspase-1 and nuclear factor (NF)-κB as well as the phosphorylations of c-Jun N-terminal kinase (JNK) and p38 in phorbol 12-myristate 13-acetate and calcium ionophore A23187 (PMACI)-triggered human mast cell line, HMC-1 cells. Furthermore, we assessed the therapeutic effects of taurine on ovalbumin (OVA)-induced allergic rhinitis (AR) animal models.

KEY FINDINGS AND SIGNIFICANCE

Here, the obtained results showed that taurine dose-dependently inhibited the production and mRNA expression of TSLP and pro-inflammatory cytokines in HMC-1 cells exposed to PMACI. Taurine attenuated the phosphorylation of JNK and p38 in activated HMC-1 cells. Moreover, taurine brought a significant inhibition of the activities of NF-κB and caspase-1. In an OVA-induced AR animal model, the increased levels of nose rubbing, histamine, immunoglobulin E, TSLP, and interleukin IL-1β were dramatically reduced by the administration of taurine. In summary, taurine could serve as potential novel remedy of allergic inflammatory disorders.

Variant innate immune responses of mammary epithelial cells to challenge by Staphylococcus aureus, Escherichia coli and the regulating effect of taurine on these bioprocesses

Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are important pathogens causing subclinical and clinical bovine mastitis, respectively. Taurine, an organic acid found in animal tissues, has been used for the treatment of various superficial infections and chronic inflammations. We challenged a bovine mammary epithelial cell (MEC) line (MAC-T) or a mouse mammary epithelial cell line (EpH4-Ev) with either E. coli or S. aureus and compared the responses of MECs to these 2 pathogens. We also examined the regulatory effects of taurine on these responses. Receptor analyses showed that both TLR2 and TLR4 are upregulated upon exposure to either E. coli or S. aureus. Taurine pre-treatment dampened upregulation to some extent. E. coli and S. aureus stimulated comparable levels of ROS, which could be inhibited by taurine pre-treatment. E. coli infection elicited a dramatic change in iNOS expression. Taurine significantly decreased iNOS expression in the S. aureus challenged group. Protein microarray demonstrated that 32/40 and 8/40 inflammatory molecules/mediators were increased after E. coli or S. aureus challenge, respectively. The fold changes of most molecules were higher in the E. coli infection group than that in the S. aureus infection group. Taurine negatively regulated the inflammatory profile in both bacterial infections. Pro-inflammatory cytokines (such as TNF-α) connected with TLR activation were down-regulated by taurine pre-treatment. The influence of TAK-242 and OxPAPC on cytokine/molecule expression profiles to E. coli challenge are different than to S. aureus. Some important factors (MyD88, TNF-α, IL-1β, iNOS and IL-6) mediated by TLR activation were suppressed either in protein microarray or special assay (PCR/kits) or both. TAK-242 restrained ROS production and NAGase activity similar to the effect of taurine in E. coli challenge groups. The detection of 3 indices (T-AOC, SOD and MDA) reflecting oxidative stress in vivo, showed that taurine improved the antioxidant ability of cells. We conclude that taurine can regulate the inflammatory response during infection with E. coli and prevent cell damage by affecting the signaling pathways mediated by TLRs and by improving the antioxidant ability of cells. In S. aureus infections, taurine's antioxidant ability may be the primary means of resistance to inflammation. This study provides a better understanding of the inflammatory mechanisms of E. coli and S. aureus mastitis, and it provides a putative strategy for the prevention of this disease.

The role of Ca(2+) mediated signaling pathways on the effect of taurine against Streptococcus uberis infection

To provide insight into the mechanisms of taurine attenuation of pro-inflammatory response in mouse mammary epithelial cell line (EpH4-Ev, purchased by ATCC, USA) after Streptococcus uberis (S. uberis, 0140J) challenge, we infected MECs with S. uberis (2.5×10(7)cfumL(-1), MOI=10) for 3h and quantified changes in TLR-2 and calcium (Ca(2+)) mediated signaling pathways. The results indicate that S. uberis infection significantly increases the expression of TLR-2, intracellular Ca(2+) levels, PLC-γ1 and PKC-α, the activities of transcription factors NF-κB and NFAT, and related cytokines (TNF-α, IL-1β, IL-6, G-CSF, IL-2, KC, IL-15, FasL, MCP-1, and LIX) in culture supernatants. Taurine administration downregulated all these indices, the activities of NF-κB and NFAT. Cytokine secretions were similar using special PKC inhibitor Go 6983 and NFAT inhibitor VIVIT. Our data indicate that S. uberis infection induces pro-inflammatory response of MECs through a TLR-2 mediated signaling pathway. In addition, taurine can prevent MEC damage by affecting both PLC-γ1-Ca(2+)-PKC-α-NF-κB and PLC-γ1-Ca(2+)-NFATs signaling pathways. This is the first report to demonstrate the mechanisms of taurine attenuated pro-inflammatory response in MECs after S. uberis challenge.

Influence of dietary taurine and housing density on oviduct function in laying hens

Experiments were conducted to study the effects of dietary taurine and housing density on oviduct function in laying hens. Green-shell laying hens were randomly assigned to a free range group and two caged groups, one with low-density and the other with high-density housing. Each group was further divided into control (C) and taurine treatment (T) groups. All hens were fed the same basic diet except that the T groups' diet was supplemented with 0.1% taurine. The experiment lasted 15 d. Survival rates, laying rates, daily feed consumption, and daily weight gain were recorded. Histological changes, inflammatory mediator levels, and oxidation and anti-oxidation levels were determined. The results show that dietary taurine supplementation and reduced housing density significantly attenuated pathophysiological changes in the oviduct. Nuclear factor-κB (NF-κB) DNA binding activity increased significantly in the high-density housing group compared with the two other housing groups and was reduced by taurine supplementation. Tumor necrosis factor-α (TNF-α) mRNA expression in the high-density and low-density C and T groups increased significantly. In the free range and low-density groups, dietary taurine significantly reduced the expression of TNF-α mRNA. Supplementation with taurine decreased interferon-γ (IFN-γ) mRNA expression significantly in the low-density groups. Interleukin 4 (IL-4) mRNA expression was significantly higher in caged hens. IL-10 mRNA expression was higher in the high-density C group than in the free range and low-density C groups. Supplementation with taurine decreased IL-10 mRNA expression significantly in the high-density group and increased superoxide dismutase (SOD) activity in the free range hens. We conclude that taurine has important protective effects against oviduct damage. Reducing housing density also results in less oxidative stress, less inflammatory cell infiltration, and lower levels of inflammatory mediators in the oviduct. Therefore, both dietary taurine and reduced housing density can ameliorate oviduct injury, enhance oviduct health, and promote egg production in laying hens.

N-Chlorotaurine Exhibits Fungicidal Activity against Therapy-Refractory Scedosporium Species and Lomentospora prolificans

N-Chlorotaurine (NCT), a well-tolerated endogenous long-lived oxidant that can be applied topically as an antiseptic, was tested on its fungicidal activity against Scedosporium and Lomentospora, opportunistic fungi that cause severe infections with limited treatment options, mainly in immunocompromised patients. In quantitative killing assays, both hyphae and conidia of Scedosporium apiospermum, Scedosporium boydii, and Lomentospora prolificans (formerly Scedosporium prolificans) were killed by 55 mM (1.0%) NCT at pH 7.1 and 37°C, with a 1- to 4-log10 reduction in CFU after 4 h and a 4- to >6-log10 reduction after 24 h. The addition of ammonium chloride to NCT markedly increased this activity. LIVE/DEAD staining of conidia treated with 1.0% NCT for 0.5 to 3 h increased the permeability of the cell wall and membrane. Preincubation of the test fungi in 1.0% NCT for 10 to 60 min delayed the time to germination of conidia by 2 h to >12 h and reduced their germination rate by 10.0 to 100.0%. Larvae of Galleria mellonella infected with 1.0 × 10(7) conidia of S. apiospermum and S. boydii died at a rate of 90.0 to 100% after 8 to 12 days. The mortality rate was reduced to 20 to 50.0% if conidia were preincubated in 1.0% NCT for 0.5 h or if heat-inactivated conidia were used. Our study demonstrates the fungicidal activity of NCT against different Scedosporium and Lomentospora species. A postantifungal effect connected with a loss of virulence occurs after sublethal incubation times. The augmenting effect of ammonium chloride can be explained by the formation of monochloramine.

Taurine Chloramine Stimulates Efferocytosis Through Upregulation of Nrf2-Mediated Heme Oxygenase-1 Expression in Murine Macrophages: Possible Involvement of Carbon Monoxide

AIMS

To examine the pro-resolving effects of taurine chloramine (TauCl).

RESULTS

TauCl injected into the peritoneum of mice enhanced the resolution of zymosan A-induced peritonitis. Furthermore, when the macrophages obtained from peritoneal exudates were treated with TauCl, their efferocytic ability was elevated. In the murine macrophage-like RAW264.7 cells exposed to TauCl, the proportion of macrophages engulfing the apoptotic neutrophils was also increased. In these macrophages treated with TauCl, expression of heme oxygenase-1 (HO-1) was elevated along with increased nuclear translocation of the nuclear factor E2-related factor 2 (Nrf2). TauCl binds directly to Kelch-like ECH association protein 1 (Keap1), which appears to retard the Keap1-driven degradation of Nrf2. This results in stabilization and enhanced nuclear translocation of Nrf2 and upregulation of HO-1 expression. TauCl, when treated to peritoneal macrophages isolated from either Nrf2 or HO-1 wild-type mice, stimulated efferocytosis (phagocytic engulfment of apoptotic neutrophils by macrophages), but not in the macrophages from Nrf2 or HO-1 knockout mice. Furthermore, transcriptional expression of some scavenger receptors recognizing the phosphatidylserines exposed on the surface of apoptotic cells was increased in RAW264.7 cells treated with TauCl. Pharmacologic inhibition of HO-1 activity or knockdown of HO-1 gene in RAW264.7 cells abolished the TauCl-induced efferocytosis, whereas both overexpression of HO-1 and treatment with carbon monoxide (CO), the product of HO, potentiated the efferocytic activity of macrophages.

INNOVATION

This work provides the first evidence that TauCl stimulates efferocytosis by macrophages. The results of this study suggest the therapeutic potential of TauCl in the management of inflammatory disorders.

CONCLUSION

TauCl can facilitate resolution of inflammation by increasing the efferocytic activity of macrophages through Nrf2-mediated HO-1 upregulation and subsequent production of CO.

Cornus mas (Linnaeus) Novel Devised Medicinal Preparations: Bactericidal Effect against Staphylococcus aureus and Pseudomonas aeruginosa

The medicinal properties of Cornus mas L. (=Cornus mascula L.), Cornaceae, are well described in Hippocratian documents, and recent research provides experimental evidence for some of these properties. However, the chemical components of Cornus mas L. that may be of pharmaceutical importance are relatively unstable. In this respect a novel methodology for plant nutrient element extraction that provides favorable conditions for simultaneous stabilization of such fragile and unstable structures has been devised. Using this methodology, medicinal preparations derived from Cornus mas L. fresh fruits, proved to possess significant antimicrobial activity selective against S. aureus and P. aeruginosa. This effect became apparent with the addition of sodium bromide in the extraction procedure and varied with the ion availability during extraction. The identification of novel agents with potent antimicrobial activity against these species is of medical importance to overcome the problem of universal antibiotic resistance.

Protein quality control under oxidative stress conditions

Accumulation of reactive oxygen and chlorine species (RO/CS) is generally regarded to be a toxic and highly undesirable event, which serves as contributing factor in aging and many age-related diseases. However, it is also put to excellent use during host defense, when high levels of RO/CS are produced to kill invading microorganisms and regulate bacterial colonization. Biochemical and cell biological studies of how bacteria and other microorganisms deal with RO/CS have now provided important new insights into the physiological consequences of oxidative stress, the major targets that need protection, and the cellular strategies employed by organisms to mitigate the damage. This review examines the redox-regulated mechanisms by which cells maintain a functional proteome during oxidative stress. We will discuss the well-characterized redox-regulated chaperone Hsp33, and we will review recent discoveries demonstrating that oxidative stress-specific activation of chaperone function is a much more widespread phenomenon than previously anticipated. New members of this group include the cytosolic ATPase Get3 in yeast, the Escherichia coli protein RidA, and the mammalian protein α2-macroglobulin. We will conclude our review with recent evidence showing that inorganic polyphosphate (polyP), whose accumulation significantly increases bacterial oxidative stress resistance, works by a protein-like chaperone mechanism. Understanding the relationship between oxidative and proteotoxic stresses will improve our understanding of both host-microbe interactions and how mammalian cells combat the damaging side effects of uncontrolled RO/CS production, a hallmark of inflammation.

Activation of RidA chaperone function by N-chlorination

Escherichia coli RidA is a member of a structurally conserved, yet functionally highly diverse protein family involved in translation inhibition (human), Hsp90-like chaperone activity (fruit fly) and enamine/imine deamination (Salmonella enterica). Here, we show that E. coli RidA modified with HOCl acts as a highly effective chaperone. Although activation of RidA is reversed by treatment with DTT, ascorbic acid, the thioredoxin system and glutathione, it is independent of cysteine modification. Instead, treatment with HOCl or chloramines decreases the amino group content of RidA by reversibly N-chlorinating positively charged residues. N-chlorination increases hydrophobicity of RidA and promotes binding to a wide spectrum of unfolded cytosolic proteins. Deletion of ridA results in an HOCl-sensitive phenotype. HOCl-mediated N-chlorination thus is a cysteine-independent post-translational modification that reversibly turns RidA into an effective chaperone holdase, which plays a crucial role in the protection of cytosolic proteins during oxidative stress.

Hypochlorous acid generated by neutrophils acts as a potent antibacterial agent. Müller et al. now show that this oxidant directly activates a protective counter-response in E. coli by N-chlorinating the protein RidA and converting it into an effective protein chaperone.

Polyphosphate is a primordial chaperone

Composed of up to 1,000 phospho-anhydride bond-linked phosphate monomers, inorganic polyphosphate (polyP) is one of the most ancient, conserved, and enigmatic molecules in biology. Here we demonstrate that polyP functions as a hitherto unrecognized chaperone. We show that polyP stabilizes proteins in vivo, diminishes the need for other chaperone systems to survive proteotoxic stress conditions, and protects a wide variety of proteins against stress-induced unfolding and aggregation. In vitro studies reveal that polyP has protein-like chaperone qualities, binds to unfolding proteins with high affinity in an ATP-independent manner, and supports their productive refolding once nonstress conditions are restored. Our results uncover a universally important function for polyP and suggest that these long chains of inorganic phosphate may have served as one of nature's first chaperones, a role that continues to the present day.

The RclR protein is a reactive chlorine-specific transcription factor in Escherichia coli

Reactive chlorine species (RCS) such as hypochlorous acid are powerful antimicrobial oxidants. Used extensively for disinfection in household and industrial settings (i.e. as bleach), RCS are also naturally generated in high quantities during the innate immune response. Bacterial responses to RCS are complex and differ substantially from the well characterized responses to other physiologically relevant oxidants, like peroxide or superoxide. Several RCS-sensitive transcription factors have been identified in bacteria, but most of them respond to multiple stressors whose damaging effects overlap with those of RCS, including reactive oxygen species and electrophiles. We have now used in vivo genetic and in vitro biochemical methods to identify and demonstrate that Escherichia coli RclR (formerly YkgD) is a redox-regulated transcriptional activator of the AraC family, whose highly conserved cysteine residues are specifically sensitive to oxidation by RCS. Oxidation of these cysteines leads to strong, highly specific activation of expression of genes required for survival of RCS stress. These results demonstrate the existence of a widely conserved bacterial regulon devoted specifically to RCS resistance.

Taurine chloramine produced from taurine under inflammation provides anti-inflammatory and cytoprotective effects

Taurine is one of the most abundant non-essential amino acid in mammals and has many physiological functions in the nervous, cardiovascular, renal, endocrine, and immune systems. Upon inflammation, taurine undergoes halogenation in phagocytes and is converted to taurine chloramine (TauCl) and taurine bromamine. In the activated neutrophils, TauCl is produced by reaction with hypochlorite (HOCl) generated by the halide-dependent myeloperoxidase system. TauCl is released from activated neutrophils following their apoptosis and inhibits the production of inflammatory mediators such as, superoxide anion, nitric oxide, tumor necrosis factor-α, interleukins, and prostaglandins in inflammatory cells at inflammatory tissues. Furthermore, TauCl increases the expressions of antioxidant proteins, such as heme oxygenase 1, peroxiredoxin, thioredoxin, glutathione peroxidase, and catalase in macrophages. Thus, a central role of TauCl produced by activated neutrophils is to trigger the resolution of inflammation and protect macrophages and surrounding tissues from being damaged by cytotoxic reactive oxygen metabolites overproduced during inflammation. This is achieved by attenuating further production of proinflammatory cytokines and reactive oxygen metabolites and also by increasing the levels of antioxidant proteins that are able to scavenge and diminish the production of cytotoxic oxygen metabolites. These findings suggest that TauCl released from activated neutrophils may be involved in the recovery processes of cells affected by inflammatory oxidative stresses and thus TauCl could be used as a potential physiological agent to control pathogenic symptoms of chronic inflammatory diseases.

Bacterial responses to reactive chlorine species

Hypochlorous acid (HOCl), the active ingredient of household bleach, is the most common disinfectant in medical, industrial, and domestic use and plays an important role in microbial killing in the innate immune system. Given the critical importance of the antimicrobial properties of chlorine to public health, it is surprising how little is known about the ways in which bacteria sense and respond to reactive chlorine species (RCS). Although the literature on bacterial responses to reactive oxygen species (ROS) is enormous, work addressing bacterial responses to RCS has begun only recently. Transcriptomic and proteomic studies now provide new insights into how bacteria mount defenses against this important class of antimicrobial compounds. In this review, we summarize the current knowledge, emphasizing the overlaps between RCS stress responses and other more well-characterized bacterial defense systems, and identify outstanding questions that represent productive avenues for future research.

NemR is a bleach-sensing transcription factor

BACKGROUND

Little is known about how bacteria sense or respond to reactive chlorine species, such as bleach.

RESULTS

NemR is a redox-regulated transcription factor which senses bleach.

CONCLUSION

NemR controls expression of genes encoding electrophile detoxification enzymes, which increase bleach resistance.

SIGNIFICANCE

We demonstrate a bleach-sensing bacterial response system and a new mechanism contributing to bacterial bleach survival. Hypochlorous acid (HOCl), the active component of household bleach, also functions as a powerful antimicrobial during the innate immune response. Despite its widespread use, surprisingly little is known about how cells sense or respond to HOCl. We now demonstrate that Escherichia coli NemR is a redox-regulated transcriptional repressor, which uses the oxidation status of HOCl-sensitive cysteine residues to respond to bleach and related reactive chlorine species. NemR controls bleach-mediated expression of two enzymes required for detoxification of reactive electrophiles: glyoxalase I and N-ethylmaleimide reductase. Both enzymes contribute to bacterial bleach survival. These results provide evidence that bleach resistance relies on the capacity of organisms to specifically sense reactive chlorine species and respond with the up-regulation of enzymes dedicated to detoxification of methylglyoxal and other reactive electrophiles.

N-chloramines, a promising class of well-tolerated topical anti-infectives

Antibiotic resistance is a growing public health crisis. To address the development of bacterial resistance, the use of antibiotics has to be minimized for nonsystemic applications in humans, as well as in animals and plants. Possible substitutes with low potential for developing resistance are active chlorine compounds that have been in clinical use for over 180 years. These agents are characterized by pronounced differences in their chlorinating and/or oxidizing activity, with hypochlorous acid (HOCl) as the strongest and organic chloramines as the weakest members. Bacterial killing in clinical practice is often associated with unwanted side effects such as chlorine consumption, tissue irritation, and pain, increasing proportionally with the chlorinating/oxidizing potency. Since the chloramines are able to effectively kill pathogens (bacteria, fungi, viruses, protozoa), their application as anti-infectives is advisable, all the more so as they exhibit additional beneficial properties such as destruction of toxins, degradation of biofilms, and anticoagulative and anti-inflammatory activities. Within the ample field of chloramines, the stable N-chloro derivatives of β-aminosulfonic acids are most therapeutically advanced. Being available as sodium salts, they distinguish themselves by good solubility and absence of smell. Important representatives are N-chlorotaurine, a natural compound occurring in the human immune system, and novel mono- and dichloro derivatives of dimethyltaurine, which feature improved stability.

Influence of taurine haloamines (TauCl and TauBr) on the development of Pseudomonas aeruginosa biofilm: a preliminary study

Biofilms are consortia of microorganisms (sessile cells) that form on various surfaces including mucosal membranes or teeth. Bacterial biofilms cause many human infections such as chronic sinusitis, acne vulgaris, periodontal diseases, and chronic wounds. These infections are persistent as they show increased resistance to antibiotics and host defense system. Taurine chloramine (TauCl) and taurine bromamine (TauBr) are the physiological products of activated neutrophils, resulting from the reaction between taurine with hypochlorous acid (HOCl) and hypobromous acid (HOBr), respectively. It has been shown in vitro that taurine haloamines exert antimicrobial properties against various pathogenic bacteria. Moreover, clinical studies have shown that both haloamines are effective in the local treatment of skin and mucose infections, including biofilm-related infections. Nevertheless, it has been not tested yet whether they can kill bacteria hidden in biofilm or disrupt biofilm structure. In this study we have investigated the capacity of TauCl and TauBr to inhibit in vitro the formation of P. aeruginosa biofilm. We have also tested their ability to destroy the mature biofilm. Our results suggest that TauBr is able to inhibit in vitro the formation of P. aeruginosa biofilm but cannot destroy the mature biofilm and effectively killed hidden bacteria. In further studies, the combined effect of TauBr and DNase, one of suggested biofilm inhibitors, was tested. Together, we conclude that TauBr is a better than TauCl candidate for local therapy of biofilm-related infections. However, a combined therapy, an application of TauBr together with other anti-biofilm agents (e.g., DNase), seems to be more promising.

NVC-422 inactivates Staphylococcus aureus toxins

Bacterial pathogens have specific virulence factors (e.g., toxins) that contribute significantly to the virulence and infectivity of microorganisms within the human hosts. Virulence factors are molecules expressed by pathogens that enable colonization, immunoevasion, and immunosuppression, obtaining nutrients from the host or gaining entry into host cells. They can cause pathogenesis by inhibiting or stimulating certain host functions. For example, in systemic Staphylococcus aureus infections, virulence factors such as toxic shock syndrome toxin 1 (TSST-1), staphylococcal enterotoxin A (SEA), and staphylococcal enterotoxin B (SEB) cause sepsis or toxic shock by uncontrolled stimulation of T lymphocytes and by triggering a cytokine storm. In vitro, these superantigens stimulate the proliferation of human peripheral blood mononuclear cells (PBMC) and the release of many cytokines. NVC-422 (N,N-dichloro-2,2-dimethyltaurine) is a broad-spectrum, fast-acting topical anti-infective agent against microbial pathogens, including antibiotic-resistant microbes. Using mass spectrometry, we demonstrate here that NVC-422 oxidizes methionine residues of TSST-1, SEA, SEB, and exfoliative toxin A (ETA). Exposure of virulence factors to 0.1% NVC-422 for 1 h prevented TSST-1-, SEA-, SEB-, and ETA-induced cell proliferation and cytokine release. Moreover, NVC-422 also delayed and reduced the protein A- and clumping factor-associated agglutination of S. aureus cultures. These results show that, in addition to its well-described direct microbicidal activity, NVC-422 can inactivate S. aureus virulence factors through rapid oxidation of methionines.

N-chlorotaurine, a long-lived oxidant produced by human leukocytes, inactivates Shiga toxin of enterohemorrhagic Escherichia coli

N-chlorotaurine (NCT), the main representative of long-lived oxidants produced by granulocytes and monocytes, is known to exert broad-spectrum microbicidal activity. Here we show that NCT directly inactivates Shiga toxin 2 (Stx2), used as a model toxin secreted by enterohemorrhagic Escherichia coli (EHEC). Bacterial growth and Stx2 production were both inhibited by 2 mM NCT. The cytotoxic effect of Stx2 on Vero cells was removed by ≥5.5 mM NCT. Confocal microscopy and FACS analyses showed that the binding of Stx2 to human kidney glomerular endothelial cells was inhibited, and no NCT-treated Stx2 entered the cytosol. Mass spectrometry displayed oxidation of thio groups and aromatic amino acids of Stx2 by NCT. Therefore, long-lived oxidants may act as powerful tools of innate immunity against soluble virulence factors of pathogens. Moreover, inactivation of virulence factors may contribute to therapeutic success of NCT and novel analogs, which are in development as topical antiinfectives.