Quantitative spectrophotometric methods for determination of sodium hypochlorite in aqueous solutions

A ratiometric fluorescent probe combined with smartphone technology based on cellulose for the detection of hypochlorous acid

Hypochloric acid (HClO) is a reactive oxygen species (ROS). ROS is an important component that has antibacterial effects on the biological immune defense system. Therefore, the detection of HClO has become an unavoidable issue. This paper reports a cellulose-based fluorescent probe. Naphthalimide serves as the fluorescent group, and the methylthio group serves as the recognition site. The principle is that HClO can oxidise the methyl sulphide group to a sulphoxide. Under a 365 nm UV lamp, this ratiometric fluorescent probe emits a bright yellow green fluorescence, which turns blue after adding HClO. This probe uses more environmentally friendly and sustainable biomass resources, and has significant fluorescence characteristics compared to most reported probes. Its detection limit (LOD) is as low as 4.34 μM. The equilibrium constant K = 3.54 × 102 M-1 for the probe plus HClO. The response time is 30 s, and it has good specificity recognition and anti-interference ability. In addition, the probe has been successfully prepared into a fluorescent film, providing potential applications for the convenient detection of HClO. Finally, the probe will be combined with smartphone technology as a portable signal processing device to further achieve visual detection of HClO.

Development of a new sterilization method for microalgae media using calcium hypochlorite as the sterilant

Calcium hypochlorite (Ca(ClO)2), which can be stably stored in powder form for a long period, is widely used as a disinfectant in various fields. A new sterilization process was developed in the present study, where a microalgal medium was sterilized using 0.02% Ca(ClO)2, followed by complete neutralization of the Ca(ClO)2 within 8 h through catalytic reaction of an MnCl2-Na2EDTA complex and a synergistic effect of glucose. When comparing the growth of Chlorella vulgaris in the autoclaved medium, a 2.65 times greater maximum cell growth was observed in cells grown in the medium prepared by treatment of Ca(ClO)2. This result indicates that denaturation of the medium by heat can hinder the growth of some microorganisms. In the case of cultivation of Euglena gracilis, successful culture growth was achieved without growth inhibition or contamination on a medium prepared in the same manner.

A simple spectrophotometric determination of hydrogen peroxide solution via spectral delta from redox reaction with sodium hypochlorite

Hydrogen peroxide (H₂O₂) is widely used in the synthesis of organic chemicals, bleaching of paper pulp, and the treatment of wastewater and as a food additive, important mediator of redox processes in natural water, and a disinfectant. However, H₂O₂ stock solution is unstable and slowly decomposes when exposed to, for example, light, elevated temperatures, or metal compounds. Therefore, the ability to measure the exact concentration of H₂O₂ stock solution is important for its proper use in diverse applications. This work proposes a simple method for the spectrophotometric determination of H₂O₂ solution via chemical reaction with sodium hypochlorite that is inexpensive and easy to acquire. The proposed method is based on the stoichiometric spectral change of hypochlorite ion at 292.5 nm following a redox reaction with a sample solution of H₂O₂. Due to high relationship between the spectral delta value and the applied H₂O₂ concentration (0.00188-0.03000%), H₂O₂ stock solution can be easily quantified.

Pencil graphite as electrode platform for free chlorine sensors and energy storage devices

Multifunctional and low-cost electrode materials are desirable for the next-generation sensors and energy storage applications. This paper reports the use of pencil graphite as an electrode for dual applications that include the detection of free residual chlorine using electro-oxidation process and as an electrochemical energy storage cathode. The pencil graphite is transferred to cellulose paper by drawing ten times and applied for the detection of free residual chlorine, which shows a sensitivity of 27 μA mM^-1 cm^-2 with a limit of detection of 88.9 μM and linearity up to 7 mM. The sample matrix effect study for the commonly interfering ions such as NO₃^-, SO₄^2-, CO₃^2-, Cl^-, HCO₃^- shows minimal impact on free residual chlorine detection. Pencil graphite then used after cyclic voltammogram treatment as a cathode in the aqueous Zn/Al-ion battery, showing an average discharge potential plateau of ~1.1 V, with a specific cathode capacity of ~54.1 mAh g^-1 at a current of 55 mA g^-1. It maintains ~95.8% of its initial efficiency after 100 cycles. Results obtained from the density functional theory calculation is consistent with the electro-oxidation process involved in the detection of free residual chlorine, as well as intercalation and de-intercalation behavior of Al³⁺ into the graphite layers of Zn/Al-ion battery. Therefore, pencil graphite due to its excellent electro-oxidation and conducting properties, can be successfully implemented as low cost, disposable and green material for both sensor and energy-storage applications.

Highly efficient separation of ruthenium from alkaline radioactive feeds using an anion exchange resin

Ruthenium recovery from the alkaline media was attempted using solid phase extraction. UV-Vis and X-ray absorption studies were performed to understand the ruthenium speciation under different conditions relevant to its extraction from alkaline medium. Since Ru forms anionic complex in the alkaline solution, an anion exchange resin (Dowex 1x8) was selected for its recovery from alkaline media. The precipitation of black RuO2 at the resin surface hinders its back exaction. Experimental conditions were optimized for the quantitative uptake of Ru from alkaline feed and its subsequent back extraction by a series of batch studies. About 90 % of the Ruthenium was back extracted from the resin using alkaline hypochlorite solution and nitric acid solution at different stages in the Ru back extraction cycle. The column studies were done under the optimized condition and showed ~80 % Ru recovery with 5 mL of the eluent (8 M HNO3) and ~90 % recovery in 10 mL including the tailing. The mechanism for the ruthenium extraction from alkaline medium and its back extraction from the resin was proposed.

Investigation of sp2-Carbon Pattern Geometry in Boron-Doped Diamond Electrodes for the Electrochemical Quantification of Hypochlorite at High Concentrations

An electrochemical sensor that contains patterned regions of sp²-carbon in a boron-doped diamond (BDD) matrix is presented for the quantitative detection of hypochlorite (OCl^-) at high concentrations in the alkaline, chemically oxidizing environment associated with bleach. As BDD itself is unresponsive to OCl^- reduction within the solvent window, by using a laser micromachining process, it is possible to write robust electrochemically active regions of sp²-carbon into the electrochemically inert sp³-BDD electrode. In this work, four different laser patterned BDD electrodes are examined, and their response compared across a range of OCl^- concentrations (0.02-1.50 M). A single macrospot (0.37 mm diameter disk) electrode and a closely spaced microspot (46 μm diameter disk) hexagonal array electrode, containing the same surface area of sp²-carbon, are shown to provide the most linear response toward OCl^- reduction. Finite element modeling (FEM) is employed to better understand the electrochemical system, due to the complexity of the electrode geometry, as well as the need to include contributions from migration and Ohmic drop at these high concentrations. FEM data suggest that only a small percentage (∼1 × 10^-3%) of the total laser-machined sp² area is active toward the OCl^- reduction process and that this process is kinetically very sluggish (∼k_eff = 1 × 10^-12 cm s^-1). The sensitivity at the array electrode (-0.127 ± 0.004 mA M^-1; R² = 0.992) is higher than that at the single-spot electrode (-0.075 ± 0.002 mA M^-1; R² = 0.996) due to the enhanced effect of transport to the edges of the microspots, shown via simulation. The electrodes returned a relatively stable response over a greater than 3 month period of use in the OCl^- solutions, demonstrating these hybrid sp²-BDD electrodes show promise for long-term monitoring applications in the harsh environments associated with bleaching applications.

Predominant N-Haloacetamide and Haloacetonitrile Formation in Drinking Water via the Aldehyde Reaction Pathway

In drinking water disinfection, switching from free chlorine to alternative chemical disinfectants such as monochloramine may result in the formation of different classes of toxic disinfection byproducts (DBPs). Haloacetonitriles (HANs) and haloacetamides (HAMs) are two currently unregulated nitrogen-containing DBP (N-DBP) groups commonly found in water disinfected with monochloramine that have been shown to be more cyto- and genotoxic than regulated DBPs. For the first time, this study confirms the formation of HAN and HAM dominant species found in disinfected water, dichloroacetonitrile and dichloroacetamide, from the reaction between monochloramine and dichloroacetaldehyde via the aldehyde reaction pathway. Results from experiments with natural water treated with labeled ¹⁵ N-monochloramine confirmed the relevance of the aldehyde pathway. Monochloramine reacted quickly with dichloroacetaldehyde reaching equilibrium with the carbinolamine 2,2-dichloro-1-(chloroamino)ethanol ( K₁ = 1.87 × 10⁴ M^-1 s^-1). Then, 2,2-dichloro-1-(chloroamino)ethanol underwent two parallel reactions where, (1) it slowly dehydrated to 1,1-dichloro-2-(chloroimino)ethane ( k₂ = 1.09 × 10^-5 s^-1) and further decomposed to dichloroacetonitrile, and (2) it was oxidized by monochloramine ( k₃ = 4.87 × 10^-2 M^-1 s^-1) to form a recently reported N-DBP, the N-haloacetamide N,2,2-trichloroacetamide. At high pH, dichloroacetonitrile hydrolyzed to dichloroacetamide ( k₄⁰ = 3.12 × 10^-7 s^-1, k₄^OH = 3.54 M^-1 s^-1). Additionally, trichloroacetaldehyde was also produced from the reaction of dichloracetaldehyde and monochloramine ( k₅ = 2.12 × 10^-2 M^-1 s^-1) under the presence of monochlorammonium ion, a product of monochloramine protonation. Within the N-haloacetamide family, N,2,2-trichloroacetamide (LC₅₀ = 3.90 × 10^-4 M) was found to be more cytotoxic than N-chloroacetamide but slightly less potent than N,2-dichloroacetamide.

The impact of disinfection Ct values on cytotoxicity of agricultural wastewaters: Ozonation vs. chlorination

Toxicity arising from toxic disinfection byproducts is an unintended result of disinfection during water reclamation. To ensure safe water reclamation treatment, it is important to develop a disinfection strategy with minimal formation of overall toxicity in the reclaimed water. The cumulative disinfectant concentration over time (Ct) is a useful concept for pathogen control during reuse water disinfection. We evaluated the toxicity impact of Ct values and different methods to achieve identical Ct values by ozonation or chlorination of wastewaters from four agricultural sources on mammalian cells. N-acetylcysteine (NAC) reactivity of the wastewater organic extracts was determined to reveal their impact on the thiol-specific biological detoxification mechanism. The results demonstrated that for two sources and for both ozonation and chlorination, higher Ct values enhanced cytotoxicity. The ozonated waters were at least 10% less toxic and as much as 22.4 times less toxic than either the non-disinfected controls or the chlorinated waters. Chlorination consistently induced higher cytotoxicity than ozonation by between 2.2 and 22.4 fold, respectively, and induced similar or higher cytotoxicity than the non-disinfected controls, by at most 4.4 fold. Given the same Ct values, the combination of high disinfectant concentration and short contact time produced finished wastewaters with higher toxicity, than the combination of low disinfectant concentration and long contact time. NAC thiol reactivity was positively and significantly correlated with mammalian cell cytotoxicity, and agreed with 80% of the cytotoxicity rank order. This suggests that the induction of cytotoxicity involved reactions with agents that acted as thiol pool quenchers. The overall results indicate that the cytotoxicity of wastewaters may increase when higher Ct values are applied to inactivate recalcitrant pathogens. To counteract the potential increase in cytotoxicity at high Ct values, for both ozonation and chlorination, lower disinfectant dose and longer contact time may be adopted.

Comparative Mammalian Cell Cytotoxicity of Wastewaters for Agricultural Reuse after Ozonation

Reusing wastewater in agriculture is becoming increasingly common, which necessitates disinfection to ensure reuse safety. However, disinfectants can react with wastewater constituents to form disinfection byproducts (DBPs), many of which are toxic and restrict the goal of safe reuse. Our objective was to benchmark the induction of mammalian cell cytotoxicity after ozonation against chlorination for three types of real wastewaters: municipal secondary effluent and two sources of minimally treated swine farm wastewaters. A new method to evaluate samples of suspected high cytotoxicity was devised. For the secondary effluent, ozonation reduced the cytotoxicity by as much as 10 times; chlorination lowered the cytotoxicity only when followed by dechlorination. The swine farm wastewaters were up to 2000 times more cytotoxic than the secondary effluent, and the highest reduction in cytotoxicity was 17 times as achieved by ozonation. These results indicate that secondary effluent is preferred over swine wastewaters for agricultural reuse regardless of the tested disinfectants. Ozonation consistently reduced the cytotoxicity of both the full strength and the organic extracts of all tested wastewaters more than chlorination. The only significant correlation was observed in the secondary wastewater between total haloacetonitriles and cytotoxicity. While the association of reduced toxicity with the modification or reduction of specific compound(s) is unclear, regulated DBPs may not be the primary forcing agents.

Simultaneous Measurement of 3-Chlorotyrosine and 3,5-Dichlorotyrosine in Whole Blood, Serum and Plasma by Isotope Dilution HPLC-MS-MS

Chlorine is a public health concern and potential threat due to its high reactivity, ease and scale of production, widespread industrial use, bulk transportation, massive stockpiles and history as a chemical weapon. This work describes a new, sensitive and rapid stable isotope dilution method for the retrospective detection and quantitation of two chlorine adducts. The biomarkers 3-chlorotyrosine (Cl-Tyr) and 3,5-dichlorotyrosine (Cl2-Tyr) were isolated from the pronase digest of chlorine exposed whole blood, serum or plasma by solid-phase extraction (SPE), separated by reversed-phase HPLC and detected by tandem mass spectrometry (MS-MS). The calibration range is 2.50-1,000 ng/mL (R2 ≥ 0.998) with a lowest reportable limit (LRL) of 2.50 ng/mL for both analytes, an accuracy of ≥93% and an LOD of 0.443 ng/mL for Cl-Tyr and 0.396 ng/mL for Cl2-Tyr. Inter- and intra-day precision of quality control samples had coefficients of variation of ≤10% and ≤7.0%, respectively. Blood and serum samples from 200 healthy individuals and 175 individuals with chronic inflammatory disease were analyzed using this method to assess background levels of chlorinated tyrosine adducts. Results from patients with no known inflammatory disease history (healthy) showed baseline levels of <LRL-4.26 ng/mL Cl-Tyr and <LRL Cl2-Tyr. Patients with inflammatory disease had baseline levels of <LRL-15.4 ng/mL Cl-Tyr and <LRL-5.22 ng/mL Cl2-Tyr. Blood exposed to 2.02 ppm chlorine gas for 15 min produced 941 ng/mL Cl-Tyr and 223 ng/mL Cl2-Tyr. This high-throughput method has been developed and analytically validated for the diagnosis of human exposure to chlorine.

Assessing PreCR™ repair enzymes for restoration of STR profiles from artificially degraded DNA for human identification

Forensic scientists have used several approaches to obtain short tandem repeat (STR) profiles from compromised DNA samples, including supplementing the polymerase chain reaction (PCR) with enhancers and using procedures yielding reduced-length amplicons. For degraded DNA, the peak intensities of the alleles separated by electrophoresis generally decrease as the length of the allele increases. When the intensities of the alleles decrease below an established threshold, they are described as drop-outs, thus contributing to a partial STR profile. This work assesses the use of repair enzymes to improve the STR profiles from artificially degraded DNA. The commercial PreCR™ repair kit of DNA repair enzymes was tested on both purified DNA and native DNA in body fluids exposed to oxidizing agents, hydrolytic conditions, ultraviolet (UV) and ionizing radiation, and desiccation. The strategy was to restrict the level of DNA damage to that which yields partial STR profiles in order to test for allele restoration as opposed to simple allele enhancement. Two protocols were investigated for allele restoration: a sequential protocol using the manufacturer's repair procedure and a modified protocol reportedly designed for optimal STR analysis of forensic samples. Allele restoration was obtained with both protocols, but the peak height appeared to be higher for the modified protocol (determined by Mann-Kendall Trend Test). The success of the approach using the PreCR™ repair enzymes was sporadic; it led to allele restoration as well as allele drop-out. Additionally, allele restoration with the PreCR™ enzymes was compared with restoration by alternative, but commonly implemented approaches using Restorase™, PCRBoost™, bovine serum albumin (BSA) and the Minifiler™ STR system. The alternative methods were also successful in improving the STR profile, but their success also depended on the quality of the template encountered. Our results indicate the PreCR™ repair kit may be useful for restoring STR profiles from damaged DNA, but further work is required to develop a generalized approach.

Sporicidal efficacy of pH-adjusted bleach for control of bioburden on production facility surfaces

pH-adjusted bleach was one of the agents used to disinfect contaminated public buildings in the USA following the 2001 bioterrorist attack with Bacillus anthracis spores. A USEPA fact sheet describes the preparation of pH-adjusted bleach by combining diluted sodium hypochlorite (NaOCl) with a controlled amount of 5 % acetic acid. This paper reports a modification of this procedure to qualify the use of pH-adjusted bleach for routine disinfection of cleanroom surfaces in pharmaceutical manufacturing facilities whenever a short contact time is desirable or there is a need for enhanced germicidal or sporicidal activity. Adjustment of pH was obtained reproducibly with either acetic acid or HCl, confirming the feasibility of developing standard procedures for the controlled addition of acid to diluted NaOCl solutions without compromising operator safety and convenience. Efficacy testing using spores from an in-house isolate of Bacillus pumilus confirmed that NaOCl solutions in the pH 5–8 range have much greater sporicidal activity on surfaces than do unadjusted alkaline solutions (pH &gt; 11). With a contact time of 0.5 min, the log10 reduction in spore viable counts was &gt;5.4 for the five representative surfaces tested relative to untreated controls. Solutions of pH-adjusted NaOCl are known to be less stable than unadjusted alkaline solutions. Stability studies were performed by monitoring sporicidal efficacy, level of free available chlorine (FAC), and pH. Testing included several NaOCl concentrations and adjustment to different starting pHs. The efficacy of pH-adjusted solutions persisted in open containers for at least 12 h even though some FAC degradation occurred. In addition, solutions of 0.29 or 0.50 % NaOCl stored at room temperature protected from light retained efficacy for at least 4 weeks, indicating that short-term storage of solutions is possible following pH adjustment. The inorganic chemical degradation of pH-adjusted NaOCl solutions generates chlorate ion, an undesirable by-product. A comparison of chemical stability for 0.12, 0.25, and 0.50 % NaOCl solutions adjusted to different initial pHs indicated that the least chlorate formation occurred with 0.12 % NaOCl.

Chemical inactivation of protein toxins on food contact surfaces

We compared the kinetics and efficacies of sodium hypochlorite, peracetic acid, phosphoric acid-based detergent, chlorinated alkaline detergent, quaternary ammonium-based sanitizer, and peracetic acid-based sanitizer for inactivating the potential bioterrorism agents ricin and abrin in simple buffers, food slurries (infant formula, peanut butter, and pancake mix), and in dried food residues on stainless steel. The intrinsic fluorescence and cytotoxicity of purified ricin and abrin in buffers decreased rapidly in a pH- and temperature-dependent manner when treated with sodium hypochlorite but more slowly when treated with peracetic acid. Cytotoxicity assays showed rapid and complete inactivation of ricin and crude abrin in food slurries and dried food residues treated 0-5 min with sodium hypochlorite. Toxin epitopes recognized by ELISA decayed more gradually under these conditions. Higher concentrations of peracetic acid were required to achieve comparable results. Chlorinated alkaline detergent was the most effective industrial agent tested for inactivating ricin in dried food residues.

Extraction methods determine the antioxidant capacity and induction of quinone reductase by soy products in vitro

Gastrointestinal (GI) mimic and organic solvent extracts of whole soybean powder (WSP), soy protein concentrate (SPC), and soy protein isolate (SPI) as well as soy isoflavone concentrate (SIC) were analyzed for total phenols; quinone reductase (QR) induction in hepa1c1c7 cells; antioxidant scavenging of DPPH, HOCl, ONOO(-), and O(2) (-.); and total antioxidant capacity via FRAP and ORAC assays. GI extracts of all the soy products had higher concentrations of total phenols than from acidified methanol (MeOH) but lower antioxidant potency. The MeOH extract of SPC was most potent in quenching HOCl and ONOO(-) and increasing FRAP and ORAC, but did not induce QR. Despite weak antioxidant activity, hexane (HX) extracts induced QR more than GI and MeOH extracts with WSP > SPC > SPI > IC. Soy extracts were ineffective scavengers of DPPH and O(2) (-.). Thus, extraction methods markedly affect the antioxidant profile and QR induction capacity of soy products.

Bioactivation of minocycline to reactive intermediates by myeloperoxidase, horseradish peroxidase, and hepatic microsomes: implications for minocycline-induced lupus and hepatitis

Of the tetracyclines, minocycline is unique in causing a significant incidence of a lupus-like syndrome and autoimmune hepatitis. It is also unique among the tetracyclines in having a para-N,N-dimethylaminophenol ring. Many drugs that cause autoimmune reactions are oxidized to reactive metabolites by the myeloperoxidase (MPO) system of macrophages. In this study, we showed that minocycline is oxidized to reactive intermediates by MPO/H(2)O(2)/Cl(-), HOCl, horseradish peroxidase/H(2)O(2), or hepatic microsomes. When trapped with N-acetylcysteine (NAC), two adducts with protonated molecular ions at m/z 619 were isolated and analyzed by NMR. One represents attack of the aromatic D ring by NAC meta to the N,N-dimethylamino group, which implies that the reactive intermediate was a quinone iminium ion. The NMR of the other adduct, which was not observed when minocycline was oxidized by hepatic microsomes, indicates that the NAC is attached at the junction of the B and C rings. In the oxidation by HOCl, we found an intermediate with a protonated molecular ion of m/z 510 that represents the addition of HOCl to minocycline. The HOCl presumably adds across the double bond of the B ring, and reaction of this intermediate with NAC led to the second NAC adduct. We were surprised to find that the same NAC adduct was not observed after oxidation of tetracycline with HOCl, even though this part of the tetracycline structure is the same as for minocycline. We propose that one or more of these reactive metabolites are responsible for the idiosyncratic drug reactions that are specific to this tetracycline.

In vitro activity of almond skin polyphenols for scavenging free radicals and inducing quinone reductase

Observational studies and clinical trials suggest nut intake, including almonds, is associated with an enhancement in antioxidant defense and a reduction in the risk of cancer and cardiovascular disease. Almond skins are rich in polyphenols (ASP) that may contribute to these putative benefits. To assess their potential mechanisms of action, we tested the in vitro effect of ASP extracted with methanol (M) or a gastrointestinal juice mimic (GI) alone or in combination with vitamins C (VC) or E (VE) (1-10 micromol/L) on scavenging free radicals and inducing quinone reductase (QR). Flavonoid profiles from ASP-M and -GI extracts were different from one another. ASP-GI was more potent in scavenging HOCl and ONOO (-) radicals than ASP-M. In contrast, ASP-M increased and ASP-GI decreased QR activity in Hepa1c1c7 cells. Adding VC or VE to ASP produced a combination- and dose-dependent action on radical scavenging and QR induction. In comparison to their independent actions, ASP-M plus VC were less potent in scavenging DPPH, HOCl, ONOO (-), and O 2 (-) (*). However, the interaction between ASP-GI plus VC promoted their radical scavenging activity. Combining ASP-M plus VC resulted in a synergistic interaction, inducing QR activity, but ASP-GI plus VC had an antagonistic effect. On the basis of their total phenolic content, the measures of total antioxidant activity of ASP-M and -GI were comparable. Thus, in vitro, ASP act as antioxidants and induce QR activity, but these actions are dependent upon their dose, method of extraction, and interaction with antioxidant vitamins.

Possible Bioactivation Pathways of Lamotrigine

The anticonvulsant lamotrigine is associated with idiosyncratic drug reactions, especially skin rashes. Most idiosyncratic reactions are believed to be caused by reactive metabolites. Previous studies have found evidence that an arene oxide is formed in rats; however, when we incubated radiolabeled lamotrigine with rat liver microsomes virtually no covalent binding was detected, and the expected downstream phenolic metabolites are not observed in humans. Rare cases of agranulocytosis have been associated with lamotrigine therapy, and we found that lamotrigine is oxidized to two different N-chloro products by HOCl. The more reactive N-chloro metabolite forms an adduct with N-acetylhistidine, and covalent binding was observed when radiolabeled lamotrigine was incubated with myeloperoxidase/H(2)O(2)/Cl(-). Another lamotrigine metabolite is an N-oxide. If this N-oxide were sulfated, it might be sufficiently reactive to bind to protein. The synthetic N-sulfate reacted with N-acetylserine; however, no covalent binding was detected when the radiolabeled N-oxide was incubated with sulfotransferase. We also investigated the possibility that lamotrigine might be oxidized to a free radical by other peroxidases or oxidized by other enzymes such as prostaglandin H synthase or tyrosinase, but no evidence of oxidation was found, and lamotrigine did not cause any detectable increase in lipid peroxidation in vivo. In view of the virtual lack of covalent binding to hepatic microsomes and the lack of any other likely pathway leading to metabolic activation in the skin, it is possible that the parent drug rather than a reactive metabolite causes lamotrigine-induced skin rashes.

Oxidized α2-Macroglobulin (α2M) Differentially Regulates Receptor Binding by Cytokines/Growth Factors: Implications for Tissue Injury and Repair Mechanisms in Inflammation

α2M binds specifically to TNF-α, IL-1β, IL-2, IL-6, IL-8, basic fibroblast growth factor (bFGF), β-nerve growth factor (β-NGF), platelet-derived growth factor (PDGF), and TGF-β. Since many of these cytokines are released along with neutrophil-derived oxidants during acute inflammation, we hypothesize that oxidation alters the ability of α2M to bind to these cytokines, resulting in differentially regulated cytokine functions. Using hypochlorite, a neutrophil-derived oxidant, we show that oxidized α2M exhibits increased binding to TNF-α, IL-2, and IL-6 and decreased binding to β-NGF, PDGF-BB, TGF-β1, and TGF-β2. Hypochlorite oxidation of methylamine-treated α2M (α2M*), an analogue of the proteinase/α2M complex, also results in decreased binding to bFGF, β-NGF, PDGF-BB, TGF-β1, and TGF-β2. Concomitantly, we observed decreased ability to inhibit TGF-β binding and regulation of cells by oxidized α2M and α2M*. We then isolated α2M from human rheumatoid arthritis synovial fluid and showed that the protein is extensively oxidized and has significantly decreased ability to bind to TGF-β compared with α2M derived from plasma and osteoarthritis synovial fluid. We, therefore, propose that oxidation serves as a switch mechanism that down-regulates the progression of acute inflammation by sequestering TNF-α, IL-2, and IL-6, while up-regulating the development of tissue repair processes by releasing bFGF, β-NGF, PDGF, and TGF-β from binding to α2M.

The binding of receptor-recognized alpha2-macroglobulin to the low density lipoprotein receptor-related protein and the alpha2M signaling receptor is decoupled by oxidation

Receptor-recognized forms of alpha2-macroglobulin (alpha2M*) bind to two classes of cellular receptors, a high affinity site comprising approximately 1500 sites/cell and a lower affinity site comprising about 60,000 sites/cell. The latter class has been identified as the so-called low density lipoprotein receptor-related protein (LRP). Ligation of receptors distinct from LRP activates cell signaling pathways. Strong circumstantial evidence suggests that the high affinity binding sites are responsible for cell signaling induced by alpha2M*. Using sodium hypochlorite, a powerful oxidant produced by the H2O2-myeloperoxidase-Cl- system, we now demonstrate that binding to the high affinity sites correlates directly with activation of the signaling cascade. Oxidation of alpha2M* using 200 microM hypochlorite completely abolishes its binding to LRP without affecting its ability to activate the macrophage signaling cascade. Scatchard analysis shows binding to a single class of high affinity sites (Kd - 71 +/- 12 pM). Surprisingly, oxidation of native alpha2-macroglobulin (alpha2M) with 125 microM hypochlorite results in the exposure of its receptor-binding site to LRP, but the ligand is unable to induce cell signaling. Scatchard analysis shows binding to a single class of lower affinity sites (Kd - 0.7 +/- 0.15 nM). Oxidation of a cloned and expressed carboxyl-terminal 20-kDa fragment of alpha2M (RBF), which is capable of binding to both LRP and the signaling receptor, results in no significant change in its binding Kd, supporting our earlier finding that the oxidation-sensitive site is predominantly outside of RBF. Attempts to understand the mechanism responsible for the selective exposure of LRP-binding sites in oxidized native alpha2M suggest that partial protein unfolding may be the most likely mechanism. These studies provide strong evidence that the high affinity sites (Kd - 71 pM) are the alpha2M* signaling receptor.

Oxidation of diclofenac to reactive intermediates by neutrophils, myeloperoxidase, and hypochlorous acid

Diclofenac is associated with a low, but significant, incidence of hepatotoxicity and bone marrow toxicity. It has been suggested that this could be due to a reactive acyl glucuronide. An alternative hypothesis is that an oxidative reactive metabolite could be responsible for such reactions and such metabolites formed by the enzymes present in neutrophils could be responsible for bone marrow toxicity. Others had reported the formation of 2,2'-dihydroxyazobenzene during the oxidation of diclofenac by myeloperoxidase/hydrogen peroxide. In contrast, in similar experiments we did not find evidence for the formation of 2,2'-dihydroxyazobenzene, but we did find several products, including a reactive iminoquinone. The same iminoquinone was formed by the oxidation of 5-hydroxydiclofenac. This iminoquinone was also formed by oxidation of diclofenac by HOCl or by activated neutrophils. It reacted with glutathione to form a conjugate. 5-Hydroxydiclofenac is also a major hepatic metabolite of diclofenac, and we found that rat hepatic microsomes oxidized 5-hydroxydiclofenac to the iminoquinone which was trapped with glutathione. This reactive metabolite represents another possible cause of the idiosyncratic reactions associated with the use of diclofenac.

Kinetics and mechanism of decomposition of N-chloroamino acids. II: conformationally restricted models

The kinetics of decomposition of the following conformationally restricted N-chloro-alpha-amino acids were studied: 1-amino-1-cyclopentanecarboxylic acid (2), 1-amino-1-cyclohexanecarboxylic acid (4), 2-amino-2-norbornanecarboxylic acid (6), and 2-amino-2-benzonorbornanecarboxylic acid (8). The first-order rate constants obtained were 0.520, 5.197, 0.198, and 0.078, respectively, which correlated with the ring strain in the structurally related cyclic ketones cyclopentanone, cyclohexanone, norborane-2-one, and benzonorbornane-2-one. The data are supportive of a concerted mechanism for the decomposition reaction involving an imine-like transition state.