S-Nitroso-N-acetyl-L-cysteine ethyl ester (SNACET) and N-acetyl-L-cysteine ethyl ester (NACET)-Cysteine-based drug candidates with unique pharmacological profiles for oral use as NO, H2S and GSH suppliers and as antioxidants: Results and overview

Synergistic reductive catalytic effects of an organic and inorganic hybrid covalent organic framework for hydrogen fuel production

Electrocatalytic hydrogen generation in alkaline medium has become widely used in a variety of sectors. However, the possibility for additional performance improvement is hampered by slow kinetics. Because of this restriction, careful control over processes such as water dissociation, hydroxyl desorption and hydrogen recombination is required. Covalent organic frameworks (COFs) based on porphyrin and polyoxometalates (POMs) show encouraging electrocatalytic performance, offering a viable route for effective and sustainable hydrogen generation. Their specific architectures lead to increased electrocatalytic activity, which makes them excellent choices for developing water electrolysis as a clean energy conversion method in the alkaline medium. In this regard, TTris@ZnPor and Lindqvist POM were coordinated to create a new eco-friendly and highly active covalent organic framework (TP@VL-COF). In order to describe TP@VL-COF, extensive structural and morphological investigations were carried out through FTIR, 1H NMR, elemental analysis, SEM, fluorescence, UV-visible, PXRD, CV, N2-adsorption isotherm, TGA and DSC analyses. In an alkaline medium, the electrocatalytic capability of 20%C/Pt, TTris@ZnPor, Lindqvist POM and TP@VL-COF was explored and compared for the hydrogen evolution reaction (HER). The TP@VL-COF showed the best catalytic efficiency for HER in an alkaline electrolyte, requiring just a 75 mV overpotential to drive 10 mA cm-2 and outperforming 20%C/Pt, TTris@ZnPor, Lindqvist POM and other reported catalysts. The Tafel slope value also indicates faster kinetics for TP@VL-COF (114 mV dec-1) than for 20%C/Pt (182 mV dec-1) TTris@ZnPor (116 mV dec-1) and Lindqvist POM (125 mV dec-1).

Development of an eco-friendly fluorescent probe for mefenamic acid sensing in pharmaceuticals and biofluids

Mefenamic acid, renowned for its analgesic properties, stands as a reliable choice for alleviating mild to moderate pain. However, its versatility extends beyond pain relief, with ongoing research unveiling its promising therapeutic potential across diverse domains. A straightforward, environmentally friendly, and sensitive spectrofluorometric technique has been developed for the precise quantification of the analgesic medication, mefenamic acid. This method relies on the immediate reduction of fluorescence emitted by a probe upon interaction with varying concentrations of the drug. The fluorescent probe utilized, N-phenyl-1-naphthylamine (NPNA), was synthesized in a single step, and the fluorescence intensities were measured at 480 nm using synchronous fluorescence spectroscopy with a wavelength difference of 200 nm. Temperature variations and lifetime studies indicated that the quenching process was static. The calibration curve exhibited linearity within the concentration range of 0.50-9.00 μg/mL, with a detection limit of 60.00 ng/mL. Various experimental parameters affecting the quenching process were meticulously examined and optimized. The proposed technique was successfully applied to determine mefenamic acid in pharmaceutical formulations, plasma, and urine, yielding excellent recoveries ranging from 98% to 100.5%. The greenness of the developed method was evaluated using three metrics: the Analytical Eco-scale, AGREE, and the Green Analytical Procedure Index.

The Reducing Agent Dithiothreitol Modulates the Ventilatory Responses That Occur in Freely Moving Rats during and following a Hypoxic-Hypercapnic Challenge

The present study examined the hypothesis that changes in the oxidation-reduction state of thiol residues in functional proteins play a major role in the expression of the ventilatory responses in conscious rats that occur during a hypoxic-hypercapnic (HH) gas challenge and upon return to room air. A HH gas challenge in vehicle-treated rats elicited robust and sustained increases in minute volume (via increases in frequency of breathing and tidal volume), peak inspiratory and expiratory flows, and inspiratory and expiratory drives while minimally affecting the non-eupneic breathing index (NEBI). The HH-induced increases in these parameters, except for frequency of breathing, were substantially diminished in rats pre-treated with the potent and lipophilic disulfide-reducing agent, L,D-dithiothreitol (100 µmol/kg, IV). The ventilatory responses that occurred upon return to room air were also substantially different in dithiothreitol-treated rats. In contrast, pre-treatment with a substantially higher dose (500 µmol/kg, IV) of the lipophilic congener of the monosulfide, N-acetyl-L-cysteine methyl ester (L-NACme), only minimally affected the expression of the above-mentioned ventilatory responses that occurred during the HH gas challenge or upon return to room air. The effectiveness of dithiothreitol suggests that the oxidation of thiol residues occurs during exposure to a HH gas challenge and that this process plays an essential role in allowing for the expression of the post-HH excitatory phase in breathing. However, this interpretation is contradicted by the lack of effects of L-NACme. This apparent conundrum may be explained by the disulfide structure affording unique functional properties to dithiothreitol in comparison to monosulfides. More specifically, the disulfide structure may give dithiothreitol the ability to alter the conformational state of functional proteins while transferring electrons. It is also possible that dithiothreitol is simply a more efficient reducing agent following systemic injection, although one interpretation of the data is that the effects of dithiothreitol are not due to its reducing ability.

L-NAC and L-NAC methyl ester prevent and overcome physical dependence to fentanyl in male rats

N-acetyl-L-cysteine (L-NAC) is a proposed therapeutic for opioid use disorder. This study determined whether co-injections of L-NAC (500 μmol/kg, IV) or its highly cell-penetrant analogue, L-NAC methyl ester (L-NACme, 500 μmol/kg, IV), prevent acquisition of acute physical dependence induced by twice-daily injections of fentanyl (125 μg/kg, IV), and overcome acquired dependence to these injections in freely-moving male Sprague Dawley rats. The injection of the opioid receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IV), elicited a series of withdrawal phenomena (i.e. behavioral and cardiorespiratory responses, hypothermia and body weight loss) in rats that received 5 or 10 injections of fentanyl and similar numbers of vehicle co-injections. With respect to the development of dependence, the NLX-precipitated withdrawal phenomena were reduced in rats that received had co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme. In regard to overcoming established dependence, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) were reduced in rats that had received co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme beginning with injection 6 of fentanyl. This study provides compelling evidence that co-injections of L-NAC and L-NACme prevent the acquisition of physical dependence and overcome acquired dependence to fentanyl in male rats. The higher efficacy of L-NACme is likely due to its greater cell penetrability in brain regions mediating dependence to fentanyl and interaction with intracellular signaling cascades, including redox-dependent processes, responsible for the acquisition of physical dependence to fentanyl.

Lipophilic analogues of D-cysteine prevent and reverse physical dependence to fentanyl in male rats

We examined whether co-injections of the cell-permeant D-cysteine analogues, D-cysteine ethyl ester (D-CYSee) and D-cysteine ethyl amide (D-CYSea), prevent acquisition of physical dependence induced by twice-daily injections of fentanyl, and reverse acquired dependence to these injections in freely-moving male Sprague Dawley rats. Injection of the opioid receptor antagonist, naloxone HCl (NLX, 1.5 mg/kg, IV), elicited a series of withdrawal phenomena that included cardiorespiratory and behavioral responses, and falls in body weight and body temperature, in rats that received 5 or 10 injections of fentanyl (125 μg/kg, IV), and the same number of vehicle co-injections. Regarding the development of physical dependence, the NLX-precipitated withdrawal phenomena were markedly reduced in fentanyl-injected rats that had received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV). Regarding reversal of established dependence to fentanyl, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) was markedly reduced in rats that received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV), starting with injection 6 of fentanyl. This study provides evidence that co-injections of D-CYSee and D-CYSea prevent the acquisition of physical dependence, and reverse acquired dependence to fentanyl in male rats. The lack of effect of D-cysteine suggests that the enhanced cell-penetrability of D-CYSee and D-CYSea into cells, particularly within the brain, is key to their ability to interact with intracellular signaling events involved in acquisition to physical dependence to fentanyl.

S-nitrosothiols as nitrite alternatives: Effects on residual nitrite, lipid oxidation, volatile profile, and cured color of restructured cooked ham

This study evaluated the use of the S-nitrosothiols, S-nitroso-N-acetylcysteine (NAC-SNO) and S-nitroso-N-acetylcysteine ethyl ester (NACET-SNO), at different concentrations (25-300 mg nitrite equivalent - NEq/kg) as sodium nitrite substitutes in restructured cooked hams. The pH value and instrumental cured color were not affected by the type or amount of curing agent used. Products with 25 and 50 mg/kg ingoing nitrite had lower thiobarbituric acid-reactive substance values than those with equimolar amounts of S-nitrosothiols. Products with >150 mg NEq/kg of S-nitrosothiols had residual nitrite similar to 50 mg/kg nitrite, and this resulted in the same volatile compound profile as nitrite added in equimolar amounts. A 300 mg NEq/kg of S-nitrosothiols was required to obtain a similar and minimally stable cured pink color perception as sliced samples with 50-150 mg/kg added nitrite. The results obtained reinforce the great potential of both alternative curing agents in the complete replacement of nitrite by equimolar amounts in restructured cooked products; however, differences in cured color stability should be considered.

L-cysteine ethylester reverses the adverse effects of morphine on breathing and arterial blood-gas chemistry while minimally affecting antinociception in unanesthetized rats

L-cysteine ethylester (L-CYSee) is a membrane-permeable analogue of L-cysteine with a variety of pharmacological effects. The purpose of this study was to determine the effects of L-CYSee on morphine-induced changes in ventilation, arterial-blood gas (ABG) chemistry, Alveolar-arterial (A-a) gradient (i.e., a measure of the index of alveolar gas-exchange), antinociception and sedation in male Sprague Dawley rats. An injection of morphine (10 mg/kg, IV) produced adverse effects on breathing, including sustained decreases in minute ventilation. L-CYSee (500 μmol/kg, IV) given 15 min later immediately reversed the actions of morphine. Another injection of L-CYSee (500 μmol/kg, IV) after 15 min elicited more pronounced excitatory ventilatory responses. L-CYSee (250 or 500 μmol/kg, IV) elicited a rapid and prolonged reversal of the actions of morphine (10 mg/kg, IV) on ABG chemistry (pH, pCO2, pO2, sO2) and A-a gradient. L-serine ethylester (an oxygen atom replaces the sulfur; 500 μmol/kg, IV), was ineffective in all studies. L-CYSee (500 μmol/kg, IV) did not alter morphine (10 mg/kg, IV)-induced sedation, but slightly reduced the overall duration of morphine (5 or 10 mg/kg, IV)-induced analgesia. In summary, L-CYSee rapidly overcame the effects of morphine on breathing and alveolar gas-exchange, while not affecting morphine sedation or early-stage analgesia. The mechanisms by which L-CYSee modulates morphine depression of breathing are unknown, but appear to require thiol-dependent processes.

Determination of N-Acetyl-L-cysteine Ethyl Ester (NACET) by Sequential Injection Analysis

New sequential injection analysis (SIA) methods with optical sensing for the determination of N-acetyl-L-cysteine ethyl ester (NACET) have been developed and optimized. NACET is a potential drug and antioxidant with advantageous pharmacokinetics. The methods involve the reduction of Cu(II) in its complexes with neocuproine (NCN), bicinchoninic acid (BCA), and bathocuproine disulfonic acid (BCS) to the corresponding chromophoric Cu(I) complexes by the analyte. The absorbance of the Cu(I) complexes with NCN, BCA, and BCS was measured at their maximum absorbance wavelengths of 458, 562, and 483 nm, respectively. The sensing manifold parameters and experimental conditions were optimized for each of the Cu(II) complexes used. Under optimal conditions, the corresponding linear calibration ranges, limits of detection, and sampling rates were 8.0 × 10-6-2.0 × 10-4 mol L-1, 5.5 × 10-6 mol L-1, and 60 h-1 for NCN; 6.0 × 10-6-1.0 × 10-4 mol L-1, 5.2 × 10-6 mol L-1, and 60 h-1 for BCA; and 4.0 × 10-6-1.0 × 10-4 mol L-1, 2.6 × 10-6 mol L-1, and 78 h-1 for BCS. The Cu(II)-BCS complex was found to be best performing in terms of sensitivity and sampling rate. Usual excipients in pharmaceutical preparations did not interfere with NACET analysis.

UVC-Protective Activity of Lemongrass Among 12 Fat-soluble Herbal Extracts: Rapid Decay Due to Cytotoxicity

BACKGROUND/AIM

The COVID-19 pandemic led to the rapid spread of the use of ultraviolet C (UVC) sterilizers in many public facilities. Considering the harmful effects of prolonged exposure to UVC, manufacturing of safe skin care products is an important countermeasure. In continuation of our recent study of water-soluble herbal extracts, the present study aimed at searching for anti-UVC components from fat-soluble herbal extracts.

MATERIALS AND METHODS

Human dermal fibroblast and melanoma cells were exposed to UVC (1.193 W/m2) for 3 min. Viable cell number was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell-cycle analysis was performed using a cell sorter. UVC-protective activity was quantified by the selective index (SI), i.e., the ratio of the 50% cytotoxic concentration for unirradiated cells to the concentration that restored viability of UVC-treated cells by 50%.

RESULTS

Only lemongrass extract, among 12 fat-soluble herbal extracts, showed significant anti-UVC activity, comparable to that of lignified materials and tannins, but exceeding that of N-acetyl-L-cysteine and resveratrol. Lemongrass extract was highly cytotoxic, producing a subG1 cell population. During prolonged incubation in culture medium, the anti-UVC activity of lemongrass extract, sodium ascorbate and vanillic acid declined with an approximate half-life of <0.7, 5.4-21.6, and 27.8-87.0 h, respectively.

CONCLUSION

Removal of cytotoxic principle(s) from lemongrass extract is crucial to producing long-lasting UVC-protective effects.

Optimizing Excitation Light for Accurate Rapid Bacterial Species Identification with Autofluorescence

Rapid identification of bacterial species in patient samples is essential for the treatment of infectious diseases and the economics of health care. In this study, we investigated an algorithm to improve the accuracy of bacterial species identification with fluorescence spectroscopy based on autofluorescence from bacteria, and excitation wavelengths suitable for identification. The diagnostic accuracy of each algorithm for ten bacterial species was verified in a machine learning classifier algorithm. The three machine learning algorithms with the highest diagnostic accuracy, extra tree (ET), logistic regression (LR), and multilayer perceptron (MLP), were used to determine the number and wavelength of excitation wavelengths suitable for the diagnosis of bacterial species. The key excitation wavelengths for the diagnosis of bacterial species were 280 nm, 300 nm, 380 nm, and 480 nm, with 280 nm being the most important. The median diagnostic accuracy was equivalent to that of 200 excitation wavelengths when two excitation wavelengths were used for ET and LR, and three excitation wavelengths for MLP. These results demonstrate that there is an optimum wavelength range of excitation wavelengths required for spectroscopic measurement of bacterial autofluorescence for bacterial species identification, and that measurement of only a few wavelengths in this range is sufficient to achieve sufficient accuracy for diagnosis of bacterial species.

BINOL and triazole-containing Janus rings and 29-8-29-membered tricyclic ladder-type hybridized siloxane: application in the fluorescence sensing of anions

Tetrachloro- and tetraazide-substituted all-cis-tetraphenylcyclotetrasiloxanes (all-cis-T₄) 2 and 3 were synthesized in high yields and were fully characterized. Then the precursor 3 underwent CuAAC click reaction with monopropargyl BINOL 4 and dipropargyl BINOL 6 to give the novel BINOL and triazole-containing all-cis-T₄ cyclic siloxane 5 and the 29-8-29-membered-ring ladder-type hybrid siloxane 7. The sensing ability of compounds 5 and 7 towards anions was studied as well, and it was observed that 7 could selectively recognize iodides through synergistic C-H⋯I hydrogen bonding, resulting in an impressive fluorescence quenching with a K_sv of 8.10 × 10⁴ M^-1.

Coronary "Microvascular Dysfunction": Evolving Understanding of Pathophysiology, Clinical Implications, and Potential Therapeutics

Until recently, it has been generally held that stable angina pectoris (SAP) primarily reflects the presence of epicardial coronary artery stenoses due to atheromatous plaque(s), while acute myocardial infarction (AMI) results from thrombus formation on ruptured plaques. This concept is now challenged, especially by results of the ORBITA and ISCHEMIA trials, which showed that angioplasty/stenting does not substantially relieve SAP symptoms or prevent AMI or death in such patients. These disappointing outcomes serve to redirect attention towards anomalies of small coronary physiology. Recent studies suggest that coronary microvasculature is often both structurally and physiologically abnormal irrespective of the presence or absence of large coronary artery stenoses. Structural remodelling of the coronary microvasculature appears to be induced primarily by inflammation initiated by mast cell, platelet, and neutrophil activation, leading to erosion of the endothelial glycocalyx. This leads to the disruption of laminar flow and the facilitation of endothelial platelet interaction. Glycocalyx shedding has been implicated in the pathophysiology of coronary artery spasm, cardiovascular ageing, AMI, and viral vasculitis. Physiological dysfunction is closely linked to structural remodelling and occurs in most patients with myocardial ischemia, irrespective of the presence or absence of large-vessel stenoses. Dysfunction includes the impairment of platelet and vascular responsiveness to autocidal coronary vasodilators, such as nitric oxide, prostacyclin, and hydrogen sulphide, and predisposes both to coronary vasoconstriction and to a propensity for microthrombus formation. These findings emphasise the need for new directions in medical therapeutics for patients with SAP, as well as a wide range of other cardiovascular disorders.

Light induced diversity-oriented synthesis (DOS) library of annulated indolizine fluorophores for imaging non-lysosomal lipid droplets (LDs)

We report the design, synthesis, and biological evaluation of a novel class of annulated indolizines as fluorescent probes. The compounds were generated through an eco-friendly, blue LED-induced domino reaction in ethyl acetate. A library of 24 coloured compounds exhibited tuneable emissions. One of the compounds (which we call DASS-fluor) proved to be an excellent polarity sensing probe. It is biocompatible, photostable, and detects specific types of lipid droplets (LDs in response to oleic acid, stress, and drug-induced autophagy in lungs and hepatic carcinoma cells). In comparison to Nile Red (a commercial probe), DASS-fluor can differentiate non-lysosomal LDs from lysosomal LDs and offers an advantage in precisely mapping drug-induced lipidosis caused by increased non-lysosomal LDs in cancerous cells. This unique probe could be a potential fluorescent marker for specific types of lipidosis induced by drugs.

L-cysteine methyl ester overcomes the deleterious effects of morphine on ventilatory parameters and arterial blood-gas chemistry in unanesthetized rats

We are developing a series of thiolesters that produce an immediate and sustained reversal of the deleterious effects of opioids, such as morphine and fentanyl, on ventilation without diminishing the antinociceptive effects of these opioids. We report here the effects of systemic injections of L-cysteine methyl ester (L-CYSme) on morphine-induced changes in ventilatory parameters, arterial-blood gas (ABG) chemistry (pH, pCO₂, pO₂, sO₂), Alveolar-arterial (A-a) gradient (i.e., the index of alveolar gas-exchange within the lungs), and antinociception in unanesthetized Sprague Dawley rats. The administration of morphine (10 mg/kg, IV) produced a series of deleterious effects on ventilatory parameters, including sustained decreases in tidal volume, minute ventilation, inspiratory drive and peak inspiratory flow that were accompanied by a sustained increase in end inspiratory pause. A single injection of L-CYSme (500 μmol/kg, IV) produced a rapid and long-lasting reversal of the deleterious effects of morphine on ventilatory parameters, and a second injection of L-CYSme (500 μmol/kg, IV) elicited pronounced increases in ventilatory parameters, such as minute ventilation, to values well above pre-morphine levels. L-CYSme (250 or 500 μmol/kg, IV) also produced an immediate and sustained reversal of the deleterious effects of morphine (10 mg/kg, IV) on arterial blood pH, pCO₂, pO₂, sO₂ and A-a gradient, whereas L-cysteine (500 μmol/kg, IV) itself was inactive. L-CYSme (500 μmol/kg, IV) did not appear to modulate the sedative effects of morphine as measured by righting reflex times, but did diminish the duration, however, not the magnitude of the antinociceptive actions of morphine (5 or 10 mg/kg, IV) as determined in tail-flick latency and hindpaw-withdrawal latency assays. These findings provide evidence that L-CYSme can powerfully overcome the deleterious effects of morphine on breathing and gas-exchange in Sprague Dawley rats while not affecting the sedative or early stage antinociceptive effects of the opioid. The mechanisms by which L-CYSme interferes with the OR-induced signaling pathways that mediate the deleterious effects of morphine on ventilatory performance, and by which L-CYSme diminishes the late stage antinociceptive action of morphine remain to be determined.

N-Acetyl-L-cysteine in human rheumatoid arthritis and its effects on nitric oxide (NO) and malondialdehyde (MDA): analytical and clinical considerations

N-Acetyl-L-cysteine (NAC) is an endogenous cysteine metabolite. The drug is widely used in chronic obstructive pulmonary disease (COPD) and as antidote in acetaminophen (paracetamol) intoxication. Currently, the utility of NAC is investigated in rheumatoid arthritis (RA), which is generally considered associated with inflammation and oxidative stress. Besides clinical laboratory parameters, the effects of NAC are evaluated by measuring in plasma or serum nitrite, nitrate or their sum (NOx) as measures of nitric oxide (NO) synthesis. Malondialdehyde (MDA) and relatives such as 4-hydroxy-nonenal and 15(S)-8-iso-prostaglandin F_2α serve as measures of oxidative stress, notably lipid peroxidation. In this work, we review recent clinico-pharmacological studies on NAC in rheumatoid arthritis. We discuss analytical, pre-analytical and clinical issues and their potential impact on the studies outcome. Major issues include analytical inaccuracy due to interfering endogenous substances and artefactual formation of MDA and relatives during storage in long-term studies. Differences in the placebo and NAC groups at baseline with respect to these biomarkers are also a serious concern. Modern applied sciences are based on data generated using commercially available instrumental physico-chemical and immunological technologies and assays. The publication process of scientific work rarely undergoes rigorous peer review of the analytical approaches used in the study in terms of accuracy/trueness. There is pressing need of considering previously reported reference concentration ranges and intervals as well as specific critical issues such as artefactual formation of particular biomarkers during sample storage. The latter especially applies to surrogate biomarkers of oxidative stress, notably MDA and relatives. Reported data on NO, MDA and clinical parameters, including C-reactive protein, interleukins and tumour necrosis factor α, are contradictory in the literature. Furthermore, reported studies do not allow any valid conclusion about utility of NAC in RA. Administration of NAC patients with rheumatoid arthritis is not recommended in current European and American guidelines.

D-Cysteine Ethyl Ester Reverses the Deleterious Effects of Morphine on Breathing and Arterial Blood-Gas Chemistry in Freely-Moving Rats

Cell-penetrant thiol esters including the disulfides, D-cystine diethyl ester and D-cystine dimethyl ester, and the monosulfide, L-glutathione ethyl ester, prevent and/or reverse the deleterious effects of opioids, such as morphine and fentanyl, on breathing and gas exchange within the lungs of unanesthetized/unrestrained rats without diminishing the antinociceptive or sedative effects of opioids. We describe here the effects of the monosulfide thiol ester, D-cysteine ethyl ester (D-CYSee), on intravenous morphine-induced changes in ventilatory parameters, arterial blood-gas chemistry, alveolar-arterial (A-a) gradient (i.e., index of gas exchange in the lungs), and sedation and antinociception in freely-moving rats. The bolus injection of morphine (10 mg/kg, IV) elicited deleterious effects on breathing, including depression of tidal volume, minute ventilation, peak inspiratory flow, and inspiratory drive. Subsequent injections of D-CYSee (2 × 500 μmol/kg, IV, given 15 min apart) elicited an immediate and sustained reversal of these effects of morphine. Morphine (10 mg/kg, IV) also A-a gradient, which caused a mismatch in ventilation perfusion within the lungs, and elicited pronounced changes in arterial blood-gas chemistry, including pronounced decreases in arterial blood pH, pO2 and sO2, and equally pronounced increases in pCO2 (all responses indicative of decreased ventilatory drive). These deleterious effects of morphine were immediately reversed by the injection of a single dose of D-CYSee (500 μmol/kg, IV). Importantly, the sedation and antinociception elicited by morphine (10 mg/kg, IV) were minimally affected by D-CYSee (500 μmol/kg, IV). In contrast, none of the effects of morphine were affected by administration of the parent thiol, D-cysteine (1 or 2 doses of 500 μmol/kg, IV). Taken together, these data suggest that D-CYSee may exert its beneficial effects via entry into cells that mediate the deleterious effects of opioids on breathing and gas exchange. Whether D-CYSee acts as a respiratory stimulant or counteracts the inhibitory actions of µ-opioid receptor activation remains to be determined. In conclusion, D-CYSee and related thiol esters may have clinical potential for the reversal of the adverse effects of opioids on breathing and gas exchange, while largely sparing antinociception and sedation.

L-NAC reverses of the adverse effects of fentanyl infusion on ventilation and blood-gas chemistry

There is an urgent need for development of drugs that are able to reverse the adverse effects of opioids on breathing and arterial blood-gas (ABG) chemistry while preserving opioid analgesia. The present study describes the effects of bolus injections of N-acetyl-L-cysteine (L-NAC, 500 μmol/kg, IV) on ventilatory parameters, ABG chemistry, Alveolar-arterial (A-a) gradient, sedation (righting reflex) and analgesia status (tail-flick latency assay) in unanesthetized adult male Sprague Dawley rats receiving a continuous infusion of fentanyl (1 μg/kg/min, IV). Fentanyl infusion elicited pronounced disturbances in (1) ventilatory parameters (e.g., decreases in frequency of breathing, tidal volume and minute ventilation), (2) ABG chemistry (decreases in pH, pO₂, sO₂ with increases in pCO₂), (3) A-a gradient (increases that were consistent with reduced alveolar gas exchange), and (4) sedation and analgesia. Bolus injections of L-NAC given 60 and 90 min after start of fentanyl infusion elicited rapid and sustained reversal of the deleterious effects of fentanyl infusion on ventilatory parameters and ABG chemistry, whereas they did not affect the sedative or analgesic effects of fentanyl. Systemic L-NAC is approved for human use, and thus our findings raise the possibility that this biologically active thiol may be an effective compound to combat opioid-induced respiratory depression in human subjects.

Infrared Spectroscopy in Aqueous Solutions: Capabilities and Challenges

Fourier-transform infrared (FTIR) spectroscopy provides rapid, reliable, quantitative, and qualitative analysis of samples in different aggregation states, i.e., gases, thin films, solids, liquids, etc. However, when analyzing aqueous solutions, particular issues associated with the rather pronounced IR absorption characteristics of water appear to interfere with the solute determination. In this review, Fourier-transform infrared spectroscopic techniques and their analytical capabilities for analyzing aqueous solutions are reviewed, and highlight examples are discussed.

Determination of N-Acetyl-l-cysteine Ethyl Ester (NACET) by Flow Injection Analysis and Spectrophotometric Detection Using Different Thiol-Sensitive Ligands

A new flow injection spectrophotometric method for the determination of N-acetyl-l-cysteine ethyl ester (NACET) was developed and validated. The method is based on the reduction of Cu(II)-ligand complexes to chromophoric Cu(I)-ligand complexes with the analyte. The studied ligands were neocuproine (NCN), bicinchoninic acid (BCA) and bathocuproine disulfonic acid (BCS). The absorbance of the Cu(I)-ligand complex was measured at 458, 562 and 483 nm for the reactions of NACET with NCN, BCA and BCS, respectively. The method was validated in terms of linear dynamic range, limit of detection and quantitation, accuracy, selectivity, and precision. Experimental conditions were optimized by a univariate method, yielding linear calibration curves in a concentration range from 2.0 × 10⁻⁶ mol L⁻¹ to 2.0 × 10⁻⁴ mol L⁻¹ using NCN; 2.0 × 10⁻⁶ mol L⁻¹ to 1.0 × 10⁻⁴ mol L⁻¹ using BCA and 6.0 × 10⁻⁷ mol L⁻¹ to 1.2 × 10⁻⁴ mol L⁻¹ using BCS. The achieved analytical frequency was 90 h⁻¹ for all three ligands. The method was successfully employed for NACET determination in pharmaceutical preparations, indicating that this FIA method fulfilled all the essential demands for the determination of NACET in quality control laboratories, as it combined low instrument and reagent costs with a high sampling rate.

S-Nitroso-N-acetyl-l-cysteine Ethyl Ester (SNACET) Catheter Lock Solution to Reduce Catheter-Associated Infections

Antimicrobial-lock therapy is an economically viable strategy to prevent/reduce the catheter-related bloodstream infections (CRBSI) that are associated with central venous catheters (CVCs). Herein, we report the synthesis and characterization of the S-nitroso-N-acetyl-l-cysteine ethyl ester (SNACET), a nitric oxide (NO)-releasing molecule, and for the first time its application as a catheter lock solution to combat issues of bacterial infection associated with indwelling catheters. Nitric oxide is an endogenous gasotransmitter that exhibits a wide range of biological properties, including broad-spectrum antimicrobial activity. The storage stability of the SNACET and the NO release behavior of the prepared lock solution were analyzed. SNACET lock solutions with varying concentrations exhibited tuneable NO release at physiological levels for >18 h, as measured using chemiluminescence. The SNACET lock solutions were examined for their efficacy in reducing microbial adhesion after 18 h of exposure toStaphylococcus aureus (Gram-positive bacteria) andEscherichia coli (Gram-negative bacteria). SNACET lock solutions with 50 and 75 mM concentrations were found to reduce >99% (ca. 3-log) of the adhered S. aureus and E. coli adhesion to the catheter surface after 18 h. The SNACET lock solutions were evaluated in a more challenging in vitro model to evaluate the efficacy against an established microbial infection on catheter surfaces using the same bacteria strains. A >90% reduction in viable bacteria on the catheter surfaces was observed after instilling the 75 mM SNACET lock solution within the lumen of the infected catheter for only 2 h. These findings propound that SNACET lock solution is a promising biocidal agent and demonstrate the initiation of a new platform technology for NO-releasing lock solution therapy for the inhibition and treatment of catheter-related infections.

D-Cystine di(m)ethyl ester reverses the deleterious effects of morphine on ventilation and arterial blood gas chemistry while promoting antinociception

We have identified thiolesters that reverse the negative effects of opioids on breathing without compromising antinociception. Here we report the effects of D-cystine diethyl ester (D-cystine diEE) or D-cystine dimethyl ester (D-cystine diME) on morphine-induced changes in ventilation, arterial-blood gas chemistry, A-a gradient (index of gas-exchange in the lungs) and antinociception in freely moving rats. Injection of morphine (10 mg/kg, IV) elicited negative effects on breathing (e.g., depression of tidal volume, minute ventilation, peak inspiratory flow, and inspiratory drive). Subsequent injection of D-cystine diEE (500 μmol/kg, IV) elicited an immediate and sustained reversal of these effects of morphine. Injection of morphine (10 mg/kg, IV) also elicited pronounced decreases in arterial blood pH, pO2 and sO2 accompanied by pronounced increases in pCO2 (all indicative of a decrease in ventilatory drive) and A-a gradient (mismatch in ventilation-perfusion in the lungs). These effects of morphine were reversed in an immediate and sustained fashion by D-cystine diME (500 μmol/kg, IV). Finally, the duration of morphine (5 and 10 mg/kg, IV) antinociception was augmented by D-cystine diEE. D-cystine diEE and D-cystine diME may be clinically useful agents that can effectively reverse the negative effects of morphine on breathing and gas-exchange in the lungs while promoting antinociception. Our study suggests that the D-cystine thiolesters are able to differentially modulate the intracellular signaling cascades that mediate morphine-induced ventilatory depression as opposed to those that mediate morphine-induced antinociception and sedation.

Extra-platelet low-molecular-mass thiols mediate the inhibitory action of S-nitrosoalbumin on human platelet aggregation via S-transnitrosylation of the platelet surface

Nitrosylation of sulfhydryl (SH) groups of cysteine (Cys) moieties is an important post-translational modification (PTM), often on a par with phosphorylation. S-Nitrosoalbumin (ALB-Cys³⁴SNO; SNALB) in plasma and S-nitrosohemoglobin (Hb-Cys^β93SNO; HbSNO) in red blood cells are considered the most abundant high-molecular-mass pools of nitric oxide (NO) bioactivity in the human circulation. SNALB per se is not an NO donor. Yet, it acts as a vasodilator and an inhibitor of platelet aggregation. SNALB can be formed by nitrosation of the sole reduced Cys group of albumin (Cys³⁴) by nitrosating species such as nitrous acid (HONO) and nitrous anhydride (N₂O₃), two unstable intermediates of NO autoxidation. SNALB can also be formed by the transfer (S-transnitrosylation) of the nitrosyl group (NO⁺) of a low-molecular-mass (LMM) S-nitrosothiol (RSNO) to ALB-Cys³⁴SH. In the present study, the effects of LMM thiols on the inhibitory potential of ALB-Cys³⁴SNO on human washed platelets were investigated. ALB-Cys³⁴SNO was prepared by reacting n-butylnitrite with albumin after selective extraction from plasma of a healthy donor on HiTrapBlue Sepharose cartridges. ALB-Cys³⁴SNO was used in platelet aggregation measurements after extended purification on HiTrapBlue Sepharose and enrichment by ultrafiltration (cutoff, 20 kDa). All tested LMM cysteinyl thiols (R-CysSH) including L-cysteine and L-homocysteine (at 10 µM) were found to mediate the collagen-induced (1 µg/mL) aggregation of human washed platelets by SNALB (range, 0-10 µM) by cGMP-dependent and cGMP-independent mechanisms. The LMM thiols themselves did not affect platelet aggregation. It is assumed that the underlying mechanism involves S-transnitrosylation of SH groups of the platelet surface by LMM RSNO formed through the reaction of SNALB with the thiols: ALB-Cys³⁴SNO + R-CysSH ↔ ALB-Cys³⁴SH + R-CysSNO. Such S-transnitrosylation reactions may be accompanied by release of NO finally resulting in cGMP-dependent and cGMP-independent mechanisms.

GC-MS approach revealing hidden nitrite reactions in hemolysate using 18O-labelled nitrite and cysteine-based thiols

In erythrocytes, nitric oxide (NO) and its autoxidation product nitrite undergo multiple reactions with hemoglobin species to form nitrate, Fe-nitrosyl hemoglobin (HbFe^(II)NO), S-nitrosohemoglobin (HbCys^β93SNO), and other intermediates including nitrito-methemoblobin HbFe^(III)ONO, nitro-methemoblobin HbFe^(III)NO₂ and nitrous anhydride (N₂O₃). Here, we report a stable-isotope dilution GC-MS assay that allows studying reactions of nitrite in hemolysate. The method is based on the use of ¹⁸O-labelled nitrite in combination with l-cysteine or N-acetyl-l-cysteine ethyl ester and GC-MS measurement of unlabelled and labelled nitrite and nitrate species. This approach reveals reactions that are hidden at physiological nitrite concentrations.

Biotransformation of organic nitrates by glutathione S-transferases and other enzymes: An appraisal of the pioneering work by William B. Jakoby

Organic nitrates (R-ONO₂; R, organic residue) such as nitroglycerin are used as drugs in part for more than a century. Their pharmacological use is associated with clinically relevant tolerance which is reportedly known since 1888. The underlying mechanisms of both, the mechanisms of action and the main pharmacological effect, which is vasodilatation and reduction of blood pressure, and the development of tolerance, which means increasing need of drug amount in sustained long-term therapy, are still incompletely understood. William B. Jakoby and associates were the first to report the biotransformation of organic nitrates, notably including nitroglycerin (i.e., glycerol trinitrate; GTN), by glutathione S-transferase (GST)-catalyzed conjugation of glutathione (GSH) to the nitrogen atom of one of the three nitrate groups of GTN to generate glutathione sulfenyl nitrite (glutathione thionitrate, S-nitroglutathione; GSNO₂). Jakoby's group was also the first to suggest that GSNO₂ reacts with a second GSH molecule to produce inorganic nitrite (ONO^-) and glutathione disulfide (GSSG) without the catalytic involvement of GST. This mechanism has been adopted by others to the biotransformation of GTN by mitochondrial aldehyde dehydrogenase (mtALDH-(CysSH)₂) which does not require GSH as a substrate. The main difference between these reactions is that mtALDH forms an internal thionitrate (mtALDH-(CysSH)-CysSNO₂) which releases inorganic nitrite upon intra-molecular reaction to form mtALDH disulfide (mtALDH-(CysS)₂). Subsequently, ONO^- and GSNO₂ are reduced by several proteins and enzymes to nitric oxide (NO) which is a very potent activator of soluble guanylyl cyclase to finally relax the smooth muscles thus dilating the vasculature. GSNO₂ is considered to rearrange to GSONO which undergoes further reactions including GSNO and GSSG formation. The present article is an appraisal of the pioneering work of William B. Jakoby in the area of the biotransformation of organic nitrates by GST. The two above mentioned enzymatic reactions are discussed in the context of tolerance development to organic nitrates, still a clinically relevant pharmacological concern.

S-nitrosothiols and H2S donors: Potential chemo-therapeutic agents in cancer

Nitric Oxide (NO) and Hydrogen Sulfide (H2S) are components of an "interactome", which is defined as a redox system involving the interactions of RSS, RNS and ROS. Chemical interaction by these species is common and is characterized by one and two electron oxidation, nitrosylation, nitration and sulfuration/polysulfidation reactions. NO and H2S are gases that penetrate cell membranes, are synthesized by specific enzymes, are ubiquitous, regulate protein activities through post-translational modifications and participate in cell signaling. The two molecules at high concentrations compared to physiological concentrations may result in cellular damage particularly through their interaction with other reactive species. NO and H2S can interact with each other and form a variety of molecular species which may have constructive or destructive behavior depending on the cell type, the cellular environment (ex. oxygen tension, pH, redox state), where the products are produced and in what concentrations. Cross talk exists between NO and H2S, whereby they can influence the generation and signaling behavior of each other. Given the above mentioned properties of NO and H2S and studies in cancer cells and animal models employing NO and H2S donors that generate higher than physiological concentrations of NO and H2S and are effective in killing cancer cells but not normal cells, lend credence to the possibility of the utility of these donors in an approach to the treatment of cancer.

Pharmacological activation of dimethylarginine dimethylaminohydrolase (DDAH) activity by inorganic nitrate and DDAH inhibition by NG-hydroxy-L-arginine, Nω,Nω-dimethyl-L-citrulline and Nω,Nω-dimethyl-Nδ-hydroxy-L-citrulline: results and overview

Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are endogenous inhibitors of nitric oxide (NO) synthase. SDMA is excreted in the urine without major metabolization. About 10% of daily produced ADMA are excreted unchanged in the urine. The major elimination route of ADMA (about 90%) involves its hydrolysis to dimethylamine (DMA) and L-citrulline by dimethylarginine dimethylaminohydrolase (DDAH) and excretion of DMA in the urine. High circulating and low excretory concentrations of ADMA are considered risk factors. Experimentally, DDAH activity can be inhibited by SH-specific agents such as inorganic and organic mercury compounds, and by S-nitrosothiols which block the SH group of a particular cysteine moiety of DDAH that is essential for its hydrolytic activity. Alternatively, DDAH activity can be inhibited by organic compounds that compete with the substrate ADMA for DDAH. Arginine analogs that contain substituents on guanidine nitrogen atom(s) (N^G) represent a class of DDAH inhibitors. In the present study, we investigated the effects of physiological and natural amino acid derivatives of L-arginine and L-citrulline as well as of nitrate and nitrite, the major circulating and excretory metabolites of NO and NO donating drugs. Here, we report for the first time that the physiological N^G-hydroxy-L-arginine, an isolable intermediate in NO synthesis, inhibits recombinant DDAH-1 activity (IC₅₀ ≈ 100 µM). Two plant L-citrulline derivatives, i.e., N^ω,N^ω-dimethyl-L-citrulline and N^ω,N^ω-dimethyl-N^δ-hydroxy-L-citrulline (connatin), were found to inhibit almost completely hepatic DDAH activity in vitro in rat homogenate at a concentration of 100 µM each. At pharmacological concentrations (i.e., 1 mM), inorganic nitrate, but not inorganic nitrite, was found to increase rat liver DDAH activity. In urine of 18 patients with Becker's muscular dystrophy, nitrate was found to correlate closely with DMA (Spearman, r = 0.73, p = 0.002). In summary, N^G-hydroxy-L-arginine, N^ω,N^ω-dimethyl-L-citrulline and N^ω,N^ω-dimethyl-N^δ-hydroxy-L-citrulline are novel inhibitors of DDAH activity. This article provides an overview of amino acid-based DDAH inhibitors and discusses potential underlying inhibition mechanisms.