Long-Term Stability and Efficacy of NCT Solutions.

To realize the potential for the use of N-chlorotaurine (NCT) in healthcare, a better understanding of the long-term stability of the compound in water is needed. An array of analytical procedures is required that can measure changes in NCT concentration over time and allow for the detection and identification of contaminants and likely degradation end products. We used UV-Vis and NMR spectroscopy, HPLC, and LCMS to establish the stability of NCT in solutions subjected to prolonged ambient and elevated temperatures. Stability proved to be dependent on concentration with half-lives of ~120 days and ~236 days for 1% and 0.5% solutions of NCT at ~20 °C. Regardless of initial pH, all solutions shifted toward and maintained a pH of ~8.3 at 20 °C and 40 °C. NCT at 500 µg/mL and 250 µg /mL inhibited biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus but did not disperse established biofilms. NCT exposure to the biofilms had profound effects on the viability of both bacteria, reducing live organisms by >90%. Exposure of Interleukin-6 (IL-6) to 11 µM NCT reduced the binding of IL-6 to an immobilized specific antibody by ~48%, which is 5× the amount required for HOCl to bring about the same effect in this test system. Our data demonstrate the potency of the compound as an antimicrobial agent with potential benefits in the management of infected chronic wounds and suggest that NCT may contribute to anti-inflammatory processes in vivo by direct modification of cytokine mediators.

Hypochlorous acid as a disinfectant for high-risk HPV: Insight into the mechanism of action.

Medical instruments that are not autoclavable but may become contaminated with high-risk human papillomaviruses (HPVs) during use must be thoroughly disinfected to avoid the possibility of iatrogenic transmission of infection. There is an expectation that prolonged soaking of instruments in the United States Food and Drug Administration-cleared chemical disinfectant solutions will result in high-level decontamination, but HPV16 and HPV18 are known to be resistant to commonly used formulations. However, they are susceptible to a variety of oxidative agents, including those based on chlorine. Here, we tested the efficacy of homogeneous hypochlorous acid (HOCl) solutions against mature infectious virions of HPV16 and HPV18 dried onto butadiene styrene coupons and ultrasonic probes. Both viruses were inactivated to >4 log reduction value (LRV) after 15 s on coupons and 5 min on ultrasonic probes. Morphologic changes became evident within those contact times by transmission electron microscopy when HPV16 virus-like particles were exposed to HOCl under identical conditions. Mass spectrometry analysis of trypsin-digested products of L1 capsid proteins exposed to HOCl showed that mostly conserved residues were modified by oxidation and that these changes rapidly lead to instability of the protein demonstrable on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Modifications to these residues may contribute to rapid virus inactivation. The use of homogeneous HOCl solutions for HPV decontamination provides a highly effective means of assuring the safety of nonautoclavable medical instruments.

Testing the efficacy of topical antimicrobial treatments using a two- and five-species chronic wound biofilm model.

AIMS: The effectiveness of commercially available wound dressings and a HOCl gel formulation was tested against two- and five-species biofilms in a dynamic in vitro chronic wound infection model. METHOD: Two-species biofilms (Pseudomonas aeruginosa and Staphylococcus aureus) were cultured using a biofilm flow device and treated with wound dressings containing silver, iodine, polyhexamethylene biguanide, crystal violet or HOCl gel at 5 h. Five-species biofilms (P. aeruginosa, S. aureus, Enterococcus faecalis, Streptococcus pyogenes and Escherichia coli) were similarly cultured and treated with HOCl gel at 5 and 24 h. Multidose experiments used two- and five-species biofilms with HOCl applied at 24, 48 and 72 h. RESULTS: None of the treatments completely disrupted the biofilms and, with the exception of silver, bacteria recovered in number post-treatment. HOCl was most effective when applied to 24 h established biofilms with most activity against P. aeruginosa. Recovery post-treatment was negligible with HOCl applied at 24 h and multiple doses indicated that bacteria were not becoming tolerant to treatment. CONCLUSIONS: Realistic models are necessary to test the effectiveness of antimicrobial wound treatments to ensure findings are clinically translatable. HOCl gel shows promise as a new topical antimicrobial for wounds, especially due to its ability to inhibit P. aeruginosa. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights a need for robust in vitro data to support development and use of wound treatments that can only be obtained from the refinement of realistic infection models. Furthermore, it indicates the potential use of HOCl gel for chronic wound management.

Mechanistic investigations of the hydrolysis of amides, oxoesters and thioesters via kinetic isotope effects and positional isotope exchange.

The hydrolysis of amides, oxoesters and thioesters is an important reaction in both organic chemistry and biochemistry. Kinetic isotope effects (KIEs) are one of the most important physical organic methods for determining the most likely transition state structure and rate-determining step of these reaction mechanisms. This method induces a very small change in reaction rates, which, in turn, results in a minimum disturbance of the natural mechanism. KIE studies were carried out on both the non-enzymatic and the enzyme-catalyzed reactions in an effort to compare both types of mechanisms. In these studies the amides and esters of formic acid were chosen because this molecular structure allowed development of methodology to determine heavy-atom solvent (nucleophile) KIEs. This type of isotope effect is difficult to measure, but is rich in mechanistic information. Results of these investigations point to transition states with varying degrees of tetrahedral character that fit a classical stepwise mechanism. This article is part of a special issue entitled: Enzyme Transition States from Theory and Experiment.

An investigation into the butyrylcholinesterase-catalyzed hydrolysis of formylthiocholine using heavy atom kinetic isotope effects.

Heavy atom kinetic isotope effects (KIEs) were determined for the butyrylcholinesterase-catalyzed hydrolysis of formylthiocholine (FTC). The leaving-S, carbonyl-C, and carbonyl-O KIEs are (34)k=0.994±0.004, (13)k=1.0148±0.0007, and (18)k=0.999±0.002, respectively. The observed KIEs support a mechanism for both acylation and deacylation where the steps up to and including the formation of the tetrahedral intermediate are at least partially rate determining. These results, in contrast to previous studies with acetylthiocholine, suggest that the decomposition of a tetrahedral intermediate is not rate-determining for FTC hydrolysis. Structural differences between the two substrates are likely responsible for the observed mechanism change with FTC.

A mechanistic study of thioester hydrolysis with heavy atom kinetic isotope effects.

The carbonyl-C, carbonyl-O, and leaving-S kinetic isotope effects (KIEs) were determined for the hydrolysis of formylthiocholine. Under acidic conditions, (13)k(obs) = 1.0312, (18)k(obs) = 0.997, and (34)k(obs) = 0.995; for neutral conditions, (13)k(obs) = 1.022, (18)k(obs) = 1.010, and (34)k(obs) = 0.996; and for alkaline conditions, (13)k(obs) = 1.0263, (18)k(obs) = 0.992, and (34)k(obs) = 1.000. The observed KIEs provided helpful insights into a qualitative description of the bond orders in the transition state structure.

Modification of Superabsorbent Polymer Granules and Fibers for Antimicrobial Efficacy and Malodor Control.

Superabsorbent polymer (SAP) granules, typically used in personal care devices such as diapers, incontinence devices, hygiene pads, and wound dressings, and granular particles of zeolite and bentonite were each subjected to modification by exposure to solutions of 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone (MC) in ethanol at room temperature. The air-dried granules showed newly acquired properties attributable to the presence of active chlorine (Cl+). The treated particles effectively oxidized the malodorant 3-mercapto-3-methylbutanol (3M3MB). MC-treated granules inactivated urease, a microbial exoenzyme commonly involved in ammonia production. Modified SAP granules and superabsorbent fibers (SAFs) showed powerful antibacterial activity in an in vitro chronic wound model. The results suggest that processing of SAP granules and SAFs by this simple method at an industrial scale could add value to their widespread use in a variety of personal hygiene devices and specifically to the improvement of chronic wound care.

A kinetic isotope effect and isotope exchange study of the nonenzymatic and the equine serum butyrylcholinesterase-catalyzed thioester hydrolysis.

Formylthiocholine (FTC) was synthesized and found to be a substrate for nonenzymatic and butyrylcholinesterase (BChE)-catalyzed hydrolysis. Solvent (D2O) and secondary formyl-H kinetic isotope effects (KIEs) were measured by an NMR spectroscopic method. The solvent (D2O) KIEs are (D2O)k = 0.20 in 200 mM HCl, (D2O)k = 0.81 in 50 mM HCl, and (D2O)k = 4.2 in pure water. The formyl-H KIEs are (D)k = 0.80 in 200 mM HCl, (D)k = 0.77 in 50 mM HCl, (D)k = 0.75 in pure water, (D)k = 0.88 in 50 mM NaOH, and (D)(V/K) = 0.89 in the BChE-catalyzed hydrolysis in MES buffer at pH 6.8. Positional isotope exchange experiments showed no detectable exchange of (18)O into the carbonyl oxygen of FTC or the product, formate, under any of the above conditions. Solvent nucleophile-O KIEs were determined to be (18)k = 0.9917 under neutral conditions, (18)k = 1.0290 (water nucleophile) or (18)k = 0.989 (hydroxide nucleophile) under alkaline conditions, and (18)(V/K) = 0.9925 for BChE catalysis. The acidic, neutral, and BChE-catalyzed reactions are explained in terms of a stepwise mechanism with tetrahedral intermediates. Evidence for a change to a direct displacement mechanism under alkaline conditions is presented.

A Synthetic Polymicrobial Community Biofilm Model Demonstrates Spatial Partitioning, Tolerance to Antimicrobial Treatment, Reduced Metabolism, and Small Colony Variants Typical of Chronic Wound Biofilms.

Understanding chronic wound infection is key for successful treatment and requires accurate laboratory models. We describe a modified biofilm flow device that effectively mimics the chronic wound environment, including simulated wound fluid, a collagen-based 3D biofilm matrix, and a five-species mixture of clinically relevant bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, and Citrobacter freundii). Mixed biofilms were cultured for between 3 and 14 days with consistent numbers of bacteria that exhibited reduced metabolic activity, which increased with a high dose of glucose. S. aureus was recovered from biofilms as a small colony variant, but as a normal colony variant if P. aeruginosa was excluded from the system. Bacteria within the biofilm did not co-aggregate but formed discrete, species-specific clusters. Biofilms demonstrated differential tolerance to the topical antimicrobials Neosporin and HOCl, consistent with protection due to the biofilm lifestyle. The characteristics exhibited within this model match those of real-world wound biofilms, reflecting the clinical scenario and yielding a powerful in vitro tool that is versatile, inexpensive, and pivotal for understanding chronic wound infection.

Control of felinine-derived malodor in cat litter.

OBJECTIVES: Malodors stemming from soiled cat litter are a major frustration for cat owners, despite the widespread use of absorbent litters with claims of odor control. Technologies for effective litter odor control have not been rigorously evaluated. Here, we report on the effectiveness of a novel litter formulation of 1-monochlorodimethylhydantoin (MCDMH)-modified clinoptilolite zeolite (MCDMH-Z) to control the odors of 3-mercapto-3-methylbutanol (3M3MB) and ammonia, the principal products generated by the enzymatic breakdown of felinine and urea, respectively. METHODS: The efficacy of MCDMH-Z for the odor control of 3M3MB was determined by solid-phase microextraction and gas chromatography mass spectrometry analysis, colorimetric analysis and a sensory panel. Enzyme inhibition was monitored by a colorimetric coupled assay for ammonia. The antimicrobial properties were measured by a reduction in colony-forming units (CFUs). RESULTS: 3M3MB proved highly susceptible to modification by MCDMH-Z granules. Headspace above litter exposed to MCDMH-Z showed no detectable 3M3MB; levels >59 ng were detected in commercially available products. Urease activity decreased by >97% after incubation with MCDMH-Z to 0.14 mg/ml. Cat litter F showed comparable inhibition (0.13 mg/ml); others showed less inhibition, producing up to 4.8 mg/ml of ammonia. MCDMH-Z reduced the CFUs of Proteus vulgaris by six log reduction values in 30 mins; in the same amount of time, no reduction was seen with commercial products tested. The odor control capability of the MCDMH-Z granules was further supported by a sensory panel scoring 3M3MB-spiked litters. CONCLUSIONS AND RELEVANCE: Samples of commercially available litter products showed an effect on malodor, or inhibition of urease, or contained antimicrobial activity; no samples were capable of accomplishing these concurrently. In contrast, MCDMH-Z granules were effective in all three test categories. Control of felinine-derived odors, in particular, has the potential to improve cat owner satisfaction, and may beneficially affect cat behaviors provoked by pheromonally active sulfurous metabolites deposited in the litter.

Modifications of IL-6 by Hypochlorous Acids: Effects on Receptor Binding.

Interleukin-6 (IL-6) has been implicated in the pathogenesis of inflammatory events including those seen with COVID-19 patients. Positive clinical responses to monoclonal antibodies directed against IL-6 receptors (IL-6Rs) suggest that interference with IL-6-dependent activation of pro-inflammatory pathways offers a useful approach to therapy. We exposed IL-6 to hypochlorous acid (HOCl) in vitro at concentrations reported to develop in vivo. After HOCl treatment, binding of IL-6 to IL-6R was reduced in a dose-dependent manner using a bioassay with human cells engineered to provide a luminescence response to signal transduction upon receptor activation. Similar results followed the exposure of IL-6 to N-chlorotaurine (NCT) and hypobromous acid (HOBr), two other reactive species produced in vivo. SDS-PAGE analysis of HOCl-treated IL-6 showed little to no fragmentation or aggregation up to 1.75 mM HOCl, suggesting that the modifications induced at concentrations below 1.75 mM took place on the intact protein. Mass spectrometry of trypsin-digested fragments identified oxidative changes to two amino acid residues, methionine 161 and tryptophan 157, both of which have been implicated in receptor binding of the cytokine. Our findings suggest that exogenous HOCl and NCT might bring about beneficial effects in the treatment of COVID-19. Further studies on how HOCl and HOBr and their halogenated amine derivatives interact with IL-6 and related cytokines in vivo may open up alternative therapeutic interventions with these compounds in COVID-19 and other hyperinflammatory diseases.

A kinetic and isotope effect investigation of the urease-catalyzed hydrolysis of hydroxyurea.

The urease-catalyzed hydrolysis of hydroxyurea is known to exhibit biphasic kinetics, showing a rapid burst phase followed by a slow plateau phase. Kinetic isotope effects for both phases of this reaction were measured at pH 6.0 and 25 °C. The observed nitrogen isotope effects for the ammonia leaving group [(15)(V/K)(NH(3))] were 1.0016 ± 0.0005 during the burst phase and 1.0019 ± 0.0007 during the plateau phase, while those for the hydroxylamine leaving group [(15)(V/K)(NH(2)OH)] were 1.0013 ± 0.0005 for the burst phase and 1.0022 ± 0.0003 for the plateau phase. These isotope effects are consistent with a rate-determining step that occurs prior to breaking either of the two possible C-N bonds. The observed carbonyl carbon isotope effects [(13)(V/K)] were 1.0135 ± 0.0003 during the burst phase and 1.0178 ± 0.0003 during the plateau phase. The similarity of the magnitude of the carbon isotope effects argues for formation of a common intermediate during both phases.

Modification of Major Contributors Responsible for Latrine Malodor on Exposure to Hypochlorous Acid: The Potential for Simultaneously Impacting Odor and Infection Hazards to Encourage Latrine Use.

Open defecation remains a common practice in developing countries and leads to high incidence and prevalence of acute gastroenteritis, which is most often caused by human noroviruses (human NoV). Encouraging the use of toilets and pit latrines is one method of improving sanitation; however, it is often hindered by not only cultural traditions but also from a reluctance to use latrines and toilets due to their odor and impression of uncleanliness. In an effort to establish new means to encourage toilet and latrine use, laboratory experiments tested the ability of hypochlorous acid (HOCl) to modify the malodorous compounds identified in the air in latrines in developing countries (indole, p-cresol, dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), and butyric acid) and inactivate MS2 bacteriophage, a surrogate for human NoV. After 5 minutes, > 94% of indole, p-cresol, DMDS, and DMTS was modified as determined by high-pressure liquid chromatography in the presence of 100 ppm HOCl. A log10 reduction value (LRV) greater than 6 was seen for MS2 bacteriophage after 5 minutes of exposure to 100 ppm HOCl in solution. Sensory studies indicated that there was a significant difference (P ≤ 0.05) between the untreated and HOCl-treated samples for all five malodorous compounds tested. The findings suggest that introduction of HOCl into the headspace air could encourage latrine and toilet use. Optimization of HOCl dosing in air to accomplish both odor control and reduction of infectious hazards is worthy of further study.

Structural basis for the sugar nucleotide and acyl-chain selectivity of Leptospira interrogans LpxA.

The first step of lipid A biosynthesis is catalyzed by LpxA in Escherichia coli (EcLpxA), an acyltransferase selective for UDP-GlcNAc and R-3-hydroxymyristoyl-acyl carrier protein (ACP). Leptospira interrogans LpxA (LiLpxA) is extremely selective for R-3-hydroxylauroyl-ACP and an analogue of UDP-GlcNAc, designated UDP-GlcNAc3N, in which NH(2) replaces the GlcNAc 3-OH group. EcLpxA does not discriminate between UDP-GlcNAc and UDP-GlcNAc3N; however, E. coli does not make UDP-GlcNAc3N. With LiLpxA, R-3-hydroxylauroyl-methylphosphopantetheine efficiently substitutes for R-3-hydroxylauroyl-ACP. We now present crystal structures of free LiLpxA and its complexes with its product UDP-3-N-(R-3-hydroxylauroyl)-GlcNAc3N and with its substrate R-3-hydroxylauroyl-methylphosphopantetheine. The positions of the acyl chains of the R-3-hydroxylauroyl-methylphosphopantetheine and the UDP-3-N-(R-3-hydroxylauroyl)-GlcNAc3N are almost identical and are similar to that of the acyl chain in the EcLpxA/UDP-3-O-(R-3-hydroxymyristoyl)-GlcNAc complex. The selectivity of LiLpxA for UDP-GlcNAc3N may be explained by the orientation of the backbone carbonyl group of Q68, which differs by approximately 82 degrees from the corresponding Q73 carbonyl group in EcLpxA. This arrangement provides an extra hydrogen-bond acceptor for the 3-NH(2) group of UDP-GlcNAc3N in LiLpxA. The R-3-hydroxylauroyl selectivity of LiLpxA is explained by the position of the K171 side chain, which limits the length of the acyl-chain-binding groove. Our results support the role of LiLpxA H120 (which corresponds to EcLpxA H125) as the catalytic base and provide the first structural information about the orientation of the phosphopantetheine moiety during LpxA catalysis.

Uridine-based inhibitors as new leads for antibiotics targeting Escherichia coli LpxC.

The UDP-3-O-(R-3-hydroxyacyl)-N-acetylglucosamine deacetylase LpxC catalyzes the committed reaction of lipid A (endotoxin) biosynthesis in Gram-negative bacteria and is a validated antibiotic target. Although several previously described compounds bind to the unique acyl chain binding passage of LpxC with high affinity, strategies to target the enzyme's UDP-binding site have not been reported. Here the identification of a series of uridine-based LpxC inhibitors is presented. The most potent examined, 1-68A, is a pH-dependent, two-step, covalent inhibitor of Escherichia coli LpxC that competes with UDP to bind the enzyme in the first step of inhibition. Compound 1-68A exhibits a K(I) of 54 muM and a maximal rate of inactivation (k(inact)) of 1.7 min(-1) at pH 7.4. Dithiothreitol, glutathione and the C207A mutant of E. coli LpxC prevent the formation of a covalent complex by 1-68A, suggesting a role for Cys-207 in inhibition. The inhibitory activity of 1-68A and a panel of synthetic analogues identified moieties necessary for inhibition. 1-68A and a 2-dehydroxy analogue, 1-68Aa, inhibit several purified LpxC orthologues. These compounds may provide new scaffolds for extension of existing LpxC-inhibiting antibiotics to target the UDP binding pocket.

4'-Methyl-4,5'-bithiazole-based correctors of defective delta F508-CFTR cellular processing.

The synthesis and Delta F508-CFTR corrector activity of a 148-member methylbithiazole-based library are reported. Synthetic routes were devised and optimized to generate methylbithiazole analogs in four steps. Corrector potency and efficacy were assayed using epithelial cells expressing human Delta F508-CFTR. These structure-activity data establish that the bithiazole substructure plays a critical function; eight novel methylbithiazole correctors were identified with low micromolar potencies.

1,3,5-triazine-based mass spectral tagging of one-bead one-compound libraries.

A triazine-based mass encoding strategy that accommodates cleavable linker, isotopic labeling, and diversity receptor moieties is reported. The resulting triazine-based tags, which are coupled to bifunctionalized TentaGel resin in a one-pot transformation, enable the construction of a 1-oxa-2,8-diazaspiro[4.5]dec-2-ene-7-carboxamide library and facilitate decoding by equalizing the ionization potential of the liberated tags in single bead MALDI-TOF experiments as well as balancing the reactivity of the starting tags in the resin coupling step. [reaction: see text].

Indirect DNA Sequence Recognition and Its Impact on Nuclease Cleavage Activity.

LAGLIDADG meganucleases are DNA cleaving enzymes used for genome engineering. While their cleavage specificity can be altered using several protein engineering and selection strategies, their overall targetability is limited by highly specific indirect recognition of the central four base pairs within their recognition sites. In order to examine the physical basis of indirect sequence recognition and to expand the number of such nucleases available for genome engineering, we have determined the target sites, DNA-bound structures, and central four cleavage fidelities of nine related enzymes. Subsequent crystallographic analyses of a meganuclease bound to two noncleavable target sites, each containing a single inactivating base pair substitution at its center, indicates that a localized slip of the mutated base pair causes a small change in the DNA backbone conformation that results in a loss of metal occupancy at one binding site, eliminating cleavage activity.

3-(Arylthiomethyl)isoxazole-4,5-dicarboxamides: chemoselective nucleophilic chemistry and insecticidal activity.

A collection of 91 3-(arylthiomethyl)isoxazole-4,5-dicarboxamides was prepared starting from dimethyl 3-(chloromethyl)isoxazole-4,5-dicarboxylate. The thioether moieties in these compounds were subsequently oxidized to give the corresponding 3-(arylsulfonylmethyl)isoxazole-4,5-dicarboxamides. By carefully controlling stoichiometry and reaction conditions, the C4 and C5 carbomethoxy groups could be differentially derivatized to carboxamides. A total of 182 trisubstituted isoxazoles are reported and deposited in the National Institutes of Health Molecular Repository; an 80 compound subset was evaluated for insecticidal activity.

A facile synthesis of new 5H-indazolo[3,2-b]benzo[d]-1,3-oxazines via one-pot intramolecular Bis-heterocyclizations.

The parent 5H-indazolo[3,2-b]benzo[d]-1,3-oxazine heterocycle as well as a series of novel analogues have been synthesized utilizing two subsequent intramolecular heterocyclizations in one pot. A variety of diversity groups were added to explore the scope of this reaction and to provide a number of new compounds for biological screening.