Cellular uptake of nanoparticles by membrane penetration: a study combining confocal microscopy with FTIR spectroelectrochemistry

It is well-known that nanomaterials are capable of entering living cells, often by utilizing the cells' endocytic mechanisms. Passive penetration of the lipid bilayer may, however, occur as an alternative process. Here we have focused on the passive transport of small nanoparticles across the plasma membranes of red blood cells, which are incapable of endocytosis. By using fluorescence microscopy, we have observed that zwitterionic quantum dots penetrate through the cell membranes so that they can be found inside the cells. The penetration-induced structural changes of the lipid bilayer were explored by surface-enhanced infrared absorption spectroscopy and electrochemistry studies of model membranes prepared on solid supports with lipid compositions identical to those of red blood cell membranes. A detailed analysis of the infrared spectra revealed a markedly enhanced flexibility of the lipid bilayers in the presence of nanoparticles. The electrochemistry data showed that the overall membrane structure remained intact; however, no persistent holes were formed in the bilayers.

Endo- and exocytosis of zwitterionic quantum dot nanoparticles by live HeLa cells

Uptake and intracellular transport of D-penicillamine coated quantum dots (DPA-QDs) of 4 nm radius by live HeLa cells have been investigated systematically by spinning disk and 4Pi confocal microscopies. Unlike larger nanoparticles, these small DPA-QDs were observed to accumulate at the plasma membrane prior to internalization, and the uptake efficiency scaled nonlinearly with the nanoparticle concentration. Both observations indicate that a critical threshold density has to be exceeded for triggering the internalization process. By using specific inhibitors, we showed that DPA-QDs were predominantly internalized by clathrin-mediated endocytosis and to a smaller extent by macropinocytosis. Clusters of DPA-QDs were found in endosomes, which were actively transported along microtubules toward the perinuclear region. Later on, a significant fraction of endocytosed DPA-QDs were found in lysosomes, while others were actively transported to the cell periphery and exocytosed with a half-life of 21 min.

Characterization of sulfur-centered radical intermediates formed during the oxidation of thiols and sulfite by peroxynitrite. ESR-spin trapping and oxygen uptake studies

Using a novel phosphorylated spin trap, 5-diethoxy-phosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), an analog of the commonly used trap 5,5'-dimethyl-1-pyrroline N-oxide (DMPO), we have investigated the reactions of sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite. The predominant species trapped in all cases are the corresponding sulfur-centered radicals, i.e. glutathionyl radical (GS) from glutathione (GSH), N-acetyl-DL-penicillamine thiyl radical (S-NAP) from N-acetyl-DL-penicillamine (NAP) and sulfate anion radical (SO3-) from sulfite. These radicals consume molecular oxygen forming either peroxyl or superoxide anion radicals. GS, S-NAP, and (SO3-)-derived radicals react with ammonium formate to form the carbon dioxide anion radical (CO2-). Further support of spin adduct assignments and radical reactions are obtained from photolysis of S-nitrosoglutathione and S-nitroso-N-acetyl-DL-penicillamine. We conclude that the direct reaction of peroxynitrite with thiols and sulfate forms thiyl and sulfate anion radicals, respectively, by a hydroxyl radical-independent mechanism. Pathological implications of thiyl radical formation and subsequent oxyradical-mediated chain reactions are discussed. Oxygen activation by thiyl radicals formed during peroxynitrite-mediated oxidation of glutathione may limit the effectiveness of GSH against peroxynitrite-mediated toxicity in cellular systems.

Solution stability of linear vs. cyclic RGD peptides

Arg-Gly-Asp (RGD) peptides contain an aspartic acid residue that is highly susceptible to chemical degradation and leads to the loss of biological activity. Our hypothesis is that cyclization of RGD peptides via disulphide bond linkage can induce structural rigidity, thereby preventing degradation mediated by the aspartic acid residue. In this paper, we compared the solution stability of a linear peptide (Arg-Gly-Asp-Phe-OH; 1) and a cyclic peptide (cyclo-(1, 6)-Ac-Cys-Arg-Gly-Asp-Phe-Pen-NH2; 2) as a function of pH and buffer concentration. The decomposition of both peptides was studied in buffers ranging from pH 2-12 at 50 degrees C. Reversed-phase HPLC was used as the main tool in determining the degradation rates and pathways of both peptides. Fast atom bombardment mass spectrometry (FAB-MS), electrospray ionization mass spectrometry (ESI-MS), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry, liquid chromatography-mass spectrometry (LC-MS), and one- and two-dimensional nuclear magnetic resonance spectroscopy (NMR) were used to characterize peptides 1 and 2 and their degradation products. In addition, co-elution with authentic samples was used to identify degradation products. Both peptides displayed pseudo-first-order kinetics at all pH values studied. The cyclic peptide 2 appeared to be 30-fold more stable than the linear peptide 1 at pH 7. The degradation mechanisms of linear (1) and cyclic (2) peptides primarily involved the aspartic acid residue. However, above pH 8 the stability of the cyclic peptide decreased dramatically due to disulphide bond degradation. Both peptides also exhibited a change in degradation mechanism upon an increase in pH. The increase in stability of cyclic peptide 2 compared to linear peptide 1, especially at neutral pH, may be due to decreased structural flexibility imposed by the ring. This rigidity would prevent the Asp side chain carboxylic acid from orientating itself in the appropriate position for attack on the peptide backbone.

Zwitterionic biocompatible quantum dots for wide pH stability and weak nonspecific binding to cells

Applications of water-soluble quantum dots (QDs) in the life sciences are limited by their poor colloidal stability in physiological media and nonspecific interaction with biomatter, particularly cell membranes. We have studied colloidal stability and nonspecific interactions with living cells for zwitterionic d-penicillamine-coated QDs (DPA-QDs) and the traditionally used carboxylated 11-mercaptoundecanoic acid-coated QDs (MUA-QDs) and found clear advantages of DPA-QDs. In single molecule fluorescence experiments, DPA-QDs showed no aggregation over the physiologically relevant pH range of 5-9, whereas MUA-QDs showed significant aggregation below pH 9. Upon exposure to living Mono Mac 6 cells, DPA-QDs, which possess overall charge-neutral surfaces, exhibited weak interactions with the cell membrane and were easily removed by flushing with buffer. By contrast, the highly charged MUA-QDs strongly associated with the cells and could not be removed even by extensive rinsing with buffer solution. DPA-QDs exhibit a high chemical stability even in strongly oxidizing conditions, in contrast to cysteine-coated QDs reported earlier. This beneficial property may arise from reduced interactions between DPA ligands due to steric effects of the methyl groups on their beta-carbon atoms.

Kinetics and equilibria of S-nitrosothiol-thiol exchange between glutathione, cysteine, penicillamines and serum albumin

The kinetics and equilibria of S-nitrosothiol-thiol (SNO-SH) exchange reactions were determined using differential optical absorption. At pH 7.4 and 37 degrees C, k2 values ranged from 0.9 M-1.s-1 for the reaction between S-nitroso-glutathione (GSNO) and N-acetyl-penicillamine, and up to 279 M-1.s-1 for the exchange between S-nitroso-penicillamine (penSNO) and GSH. SNO-SH exchange involving GSH/GSNO and cysteine/cySNO was relatively rapid, k2 approx. 80 M-1.s-1 with an equilibrium constant slightly in favour of GSNO. GSNO was strongly favoured in equilibrium with penSNO, keq 0.0039. In the case of SNO-SH exchange between S-nitroso human serum albumin (albSNO) and GSH or cysteine k2 values were 3.2 and 9.1 M-1.s-1, respectively. The results show that the initial rate of SNO-SH exchange between physiological albSNO (7 microM) and venous plasma levels of GSH and cysteine is very slow, < 1%/min. On the other hand, if a nitrosothiol such as cySNO were to enter a cell, it would be rapidly converted to GSNO (43%/s).

Biochemical characterization of human S-nitrosohemoglobin. Effects on oxygen binding and transnitrosation

S-Nitrosation of cysteine beta93 in hemoglobin (S-nitrosohemoglobin (SNO-Hb)) occurs in vivo, and transnitrosation reactions of deoxygenated SNO-Hb are proposed as a mechanism leading to release of NO and control of blood flow. However, little is known of the oxygen binding properties of SNO-Hb or the effects of oxygen on transnitrosation between SNO-Hb and the dominant low molecular weight thiol in the red blood cell, GSH. These data are important as they would provide a biochemical framework to assess the physiological function of SNO-Hb. Our results demonstrate that SNO-Hb has a higher affinity for oxygen than native Hb. This implies that NO transfer from SNO-Hb in vivo would be limited to regions of extremely low oxygen tension if this were to occur from deoxygenated SNO-Hb. Furthermore, the kinetics of the transnitrosation reactions between GSH and SNO-Hb are relatively slow, making transfer of NO+ from SNO-Hb to GSH less likely as a mechanism to elicit vessel relaxation under conditions of low oxygen tension and over the circulatory lifetime of a given red blood cell. These data suggest that the reported oxygen-dependent promotion of S-nitrosation from SNO-Hb involves biochemical mechanisms that are not intrinsic to the Hb molecule.

S-nitrosothiol-modified dendrimers as nitric oxide delivery vehicles

The synthesis and characterization of two generation-4 polyamidoamine (PAMAM) dendrimers with S-nitrosothiol exteriors are reported. The hyperbranched macromolecules were modified with either N-acetyl-D, L-penicillamine (NAP) or N-acetyl-L-cysteine (NACys) and analyzed via 1H and 13C NMR, UV absorption spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography. Treatment of the dendritic thiols with nitrite solutions yielded the corresponding S-nitrosothiol nitric oxide (NO) donors (G4-SNAP, G4-NACysNO). Chemiluminescent NO detection demonstrated that the dendrimers were capable of storing approximately 2 micromol NO x mg (-1) when exposed to triggers of S-nitrosothiol decomposition (e.g., light and copper). The kinetics of NO release were found to be highly dependent on the structure of the nitrosothiol (i.e., tertiary vs primary) and exhibited similar NO release characteristics to classical small molecule nitrosothiols reported in the literature. As a demonstration of utility, the ability of G4-SNAP to inhibit thrombin-mediated platelet aggregation was assayed. At equivalent nitrosothiol concentrations (25 microM), the G4-SNAP dendrimer resulted in a 62% inhibition of platelet aggregation, compared to only 17% for the small molecule NO donor. The multivalent NO storage, the dendritic effects exerted on nitrosothiol stability and reactivity, and the utility of dendrimers as drug delivery vehicles highlight the potential of these constructs as clinically useful S-nitrosothiol-based therapeutics.

Seleno compounds and glutathione peroxidase catalyzed decomposition of S-nitrosothiols

Seleno compounds such as selenocystamine and seleno-D, L-cystine were found to catalyze the decomposition of S-nitrosothiols (e.g. S-nitroso-glutathione and S-nitroso-N-acetyl-D, L-penicillamine) in the presence of different thiols (e.g. glutathione, N-acetyl-D-penicillamine and 2-mercaptoethanol), and liberate nitric oxide. It was also found that glutathione peroxidase itself can catalyze the decomposition of S-nitrosoglutathione without the presence of any thiol or H2O2.

Enantiomeric analysis of pharmaceutical compounds by ion/molecule reactions

Protonated complexes involving cyclodextrin hosts and guest compounds that are pharmacologically important are produced in the gas phase and reacted with a gaseous amine. The guest is exchanged to produce a new protonated complex with the amine. The reaction is enantioselective and is used to develop a method for determining enantiomeric excess using only mass spectrometry. The pharmaceutical compounds include DOPA, amphetamine, ephedrine, and penicillamine. The presence of more than one reacting species is observed with DOPA and penicillamine. Molecular dynamics calculations are used to understand the nature of the interactions and the possible source of the variations in the reactivities.

Size dependence of chiroptical activity in colloidal quantum dots

The synthesis of chiral penicillamine-capped CdS and CdSe quantum dots (QDs) was adjusted to control the size of the nanoparticles. This, together with size separation, allowed for simultaneous tuning of absorption, circular dichroism (CD), and fluorescence on a wide wavelength range. Band edge transitions were accompanied by circular dichroism peaks which red-shifted together with the increase in particle size. The clear correlation between absorption and CD bands as well as between absorption bands and size in semiconductor QDs was used to derive an experimental scaling law for optical activity. The decrease in the intensity of circular dichroism-to-absorption ratio (dissymmetry) with the increase in particle size was stronger than linear, probably exponential. In addition, strong material type dependence was observed. The CD line shape appeared to be sensitive to the nature of the transition and may thus serve as a tool for sorting out the electronic states of the QDs. Fluorescence-detected circular dichroism (FDCD) was introduced as a new probe of optically active fluorescent nanoparticles. The analysis of the size and material dependence of the chiroptical induction effect leads to the conclusion that it is primarily an electronic interaction effect between the adsorbed chiral molecules and the electron-hole states.

Reduction-oxidation (redox) state regulation of matrix metalloproteinase activity in human fetal membranes

OBJECTIVE

The mechanisms underlying membrane rupture at term and preterm are obscure. Collagenolytic activity of matrix metalloproteinases in amniochorionic membranes increases during spontaneous term and preterm labor associated with intra-amniotic infection. We sought to test the hypothesis that reduction-oxidation homeostasis, which is altered in inflammatory states, directly regulates amniochorionic matrix metalloproteinases.

STUDY DESIGN

Membranes were collected from 7 patients undergoing elective cesarean delivery at term, rinsed thoroughly, and immediately incubated in phosphate-buffered sodium chloride solution at 37 degrees C for 24 hours. Matrix metalloproteinase activity in the culture medium was assayed by substrate-gel electrophoresis and normalized against the dry weight of the tissue incubated. Superoxide anions were generated in the presence of membranes by a xanthine (2 mmol/L) and xanthine oxidase (20 mU/mL) mixture and monitored by reduction of ferri-cytochrome c to ferro-cytochrome c. Incubations were performed in the presence of xanthine alone, a xanthine-xanthine oxidase mixture, superoxide dismutase (500 U/mL), a xanthine-xanthine oxidase-superoxide dismutase mixture, nitro-L-arginine (a nitric oxide synthase inhibitor, 1 mmol/L), xanthine-xanthine oxidase-nitro-L-arginine, S-nitroso-N -acetylpenicillamine (a nitric oxide donor, 10 mmol/L), xanthine-xanthine oxidase-S-nitroso-N -acetylpenicillamine, N -acetylcysteine (a thiol-containing antioxidant, 0.1, 1, or 10 mmol/L), lipopolysaccharide (100 ng/mL), or lipopolysaccharide-N -acetylcysteine. Intracellular generation of superoxide anions was monitored by the reduction of nitroblue tetrazolium to formazan.

RESULTS

Basal matrix metalloproteinase 9 and matrix metalloproteinase 2 levels were detected in all samples. Superoxide anions significantly increased matrix metalloproteinase 9 activity but did not increase matrix metalloproteinase 2 activity, which effect was reversed by the addition of superoxide dismutase. N-acetylcysteine reduced basal activity of both matrix metalloproteinase 9 and matrix metalloproteinase 2 to 20%. Importantly, N-acetylcysteine completely inhibited intracellular formazan formation in cultured membranes both in the absence and in the presence of lipopolysaccharide. Neither nitric oxide synthase inhibition nor the nitric oxide donor S-nitroso-N -acetylpenicillamine had any effect on fetal membrane matrix metalloproteinase activity.

CONCLUSION

Matrix metalloproteinase activity in human fetal membranes is reduction-oxidation (redox)-regulated. Matrix metalloproteinase 9 activity in human fetal membranes is directly increased by superoxide anion, a byproduct of macrophages and neutrophils. Neither nitric oxide donors nor nitric oxide synthase inhibitors significantly affect matrix metalloproteinase activity in human fetal membranes. The glutathione precursor N-acetylcysteine dramatically inhibits amniochorionic matrix metalloproteinase activity in addition to inhibiting intrinsic superoxide generation within the tissue. Thus thiol-reducing agents, such as N-acetylcysteine, may be beneficial in preventing preterm premature rupture of the membranes.

Nitric oxide stimulates the activity of a 72-kDa neutral matrix metalloproteinase in cultured rat mesangial cells

We recently demonstrated that stimulation of inducible nitric oxide synthase (iNOS) activity reduced the accumulation of collagen and fibronectin in cultured rat mesangial cells. Therefore, we examined whether nitric oxide (NO) influenced the activity of a 72 kDa neutral matrix metalloproteinase by these cells in vitro. Enzyme activity was assessed in a biotin-avidin ELISA and by zymography. Exposure of mesangial cells to the cytokines, interferon (IFN)-gamma and lipopolysaccharide (LPS), increased gelatinolytic activity by 325 +/- 60% (P < 0.025). Co-incubation with 20 mM L-arginine caused a further increase in matrix metalloproteinase levels. Addition of L-NAME, an inhibitor of iNOS, reversed the IFN-gamma/LPS-induced rise in gelatinolytic activity. Incubation with the exogenous NO donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP), resulted in a dose dependent increase in metalloproteinase activity (P < 0.01). The NO-induced changes in metalloproteinase activity were also demonstrable by zymography. These data indicate that NO modulates the activity of a 72 kDa neutral matrix metalloproteinase and suggest that altered NO production may contribute to the development of glomerulosclerosis and tubulointerstitial fibrosis in chronic renal disease states.

Liquid-infused nitric oxide-releasing (LINORel) silicone for decreased fouling, thrombosis, and infection of medical devices

Recent reports on liquid-infused materials have shown promise in creating ultra-low fouling surfaces, but are limited in their ability to prevent bacterial proliferation and prevent platelet activation in blood-contacting applications. In this work, a liquid-infused nitric oxide-releasing (LINORel) material is created by incorporating the nitric oxide (NO) donor S-nitroso-acetylpenicillamine (SNAP) and silicone oil in commercial medical grade silicone rubber tubing through a solvent swelling process. This combination provides several key advantages over previous NO-releasing materials, including decreased leaching of NO donor, controlled release of NO, and maintenance of ultra-low fouling property of liquid-infused materials. The LINORel tubing reduces protein adhesion as observed using fluorescence imaging, and platelet adhesion (81.7 ± 2.5%) in vitro over a 2 h period. The LINORel combination greatly reduces bacterial adhesion and biofilm formation of two most common pathogens responsible for hospital acquired infections: gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa (99.3 ± 1.9% and 88.5 ± 3.3% respectively) over a 7-day period in a CDC bioreactor environment. Overall, the LINORel approach provides a synergistic combination of active and passive non-fouling approaches to increase biocompatibility and reduce infection associated with medical devices.

Identification of alpha-dicarbonyl scavengers for cellular protection against carbonyl stress

Tissue deterioration and aging have long been associated with the accumulation of chemically induced protein and DNA damage. Reactive oxygen species (ROS) and reactive carbonyl species (RCS), especially alpha-dicarbonyl compounds, are key mediators of damage caused by oxidative stress, glycation, and UV-irradiation. The toxic effects of ROS are counteracted in vivo by antioxidants and antioxidant enzymes, and the deleterious effects of one RCS, methylglyoxal, are counteracted by a ubiquitous glyoxalase system. Carbonyl stress as a result of toxic effects of various mono-dicarbonyls (e.g. 4-hydroxynonenal) and alpha-dicarbonyls (e.g. glyoxal and deoxyosones) cannot be directly antagonized by antioxidants, and only a small number of biological carbonyl scavengers like glutathione (GSH) have been identified to date. We have developed a new screening method for the identification of carbonyl scavengers using a rapid glycation system that proceeds independent of oxygen and therefore, excludes identification of inhibitory compounds acting as antioxidants. Using this screening assay adapted to 96-well microtiter plates, we have identified the cysteine derivative 3,3-dimethyl-D-cysteine as a potent inhibitor of non-oxidative advanced glycation. Comparative kinetic analyses demonstrated the superior alpha-oxoaldehyde-scavenging activity of D-penicillamine over that of aminoguanidine. D-Penicillamine traps alpha-oxoaldehydes by forming a 2-acylthiazolidine derivative as shown by structure elucidation of reaction products between D-penicillamine and methylglyoxal or phenylglyoxal. We demonstrated that upon co-incubation, D-penicillamine protects human skin keratinocytes and fibroblasts (CF3 cells) against glyoxal- and methylglyoxal-induced carbonyl toxicity. Our research qualifies alpha-amino-beta-mercapto-beta,beta-dimethyl-ethane as a promising pharmacophore for the development of related alpha-dicarbonyl scavengers as therapeutic agents to protect cells against carbonyl stress.

Modulation of white adipose tissue lipolysis by nitric oxide

In isolated adipocytes, the nitrosothiols S-nitroso-N-acetyl-penicillamine (SNAP) and S-nitrosoglutathione stimulate basal lipolysis, whereas the nitric oxide (NO.) donor 1-propamine, 3-(2-hydroxy-2-nitroso-1-propylhydrazine) (PAPA-NONOate) or NO gas have no effect. The increase in basal lipolysis due to nitrosothiols was prevented by dithiothreitol but not by a guanylate cyclase inhibitor. In addition the cyclic GMP-inhibited low Km, cyclic AMP phosphodiesterase activity was inhibited by SNAP suggesting that SNAP acting as NO+ donor increases basal lipolysis through a S-nitrosylation mediated inhibition of phosphodiesterase. Contrasting with these findings, SNAP reduced both isoproterenol-stimulated lipolysis and cyclic AMP production, whereas it failed to modify forskolin-, dibutyryl cyclic AMP-, or isobutylmethylxanthine-stimulated lipolysis, suggesting that SNAP interferes with the beta-adrenergic signal transduction pathway upstream the adenylate cyclase. In contrast with SNAP, PAPA-NONOate or NO gas inhibited stimulated lipolysis whatever the stimulating agents used without altering cyclic AMP production. Moreover PAPA-NONOate slightly reduces (30%) the hormone-sensitive lipase (HSL) activity indicating that stimulated lipolysis inhibition by NO. is linked to both inhibition of the HSL activity and the cyclic AMP-dependent activation of HSL. These data suggest that NO. or related redox species like NO+/NO- are potential regulators of lipolysis through distinct mechanisms.

Chemical mechanisms underlying the vasodilator and platelet anti-aggregating properties of S-nitroso-N-acetyl-DL-penicillamine and S-nitrosoglutathione

The chemistries of S-nitroso-DL-penicillamine (SNAP) and S-nitrosoglutathione (GSNO) in relation to their ability to relax vascular smooth muscle and prevent platelet aggregation have been investigated. Metal ion catalysis greatly accelerates the decomposition of SNAP, but has little effect on GSNO. Instead, NO release from GSNO is effected either by NO transfer to a free thiol (e.g. cysteine), or by enzymatic cleavage of the glutamyl-cystyl peptide bond. In both cases the resulting nitrosothiol (i.e. S-nitrosocysteine and S-nitrosocystylglycine, respectively) is susceptible to metal ion catalysed NO release. We conclude that transnitrosation or enzymatic cleavage are obligatory steps in the mechanism of NO release from GSNO, whereas SNAP needs only the presence of metal ions to effect this process. The different modes of NO production may go some way towards explaining the different physiological effectiveness of these S-nitrosothiols as vasodilators and inhibitors of platelet aggregation.

Tuning the interactions between chiral plasmonic films and living cells

Designing chiral materials to manipulate the biological activities of cells has been an important area not only in chemistry and material science, but also in cell biology and biomedicine. Here, we introduce monolayer plasmonic chiral Au nanoparticle (NP) films modified with L- or D-penicillamine (Pen) to be developed for cell growth, differentiation, and retrieval. The monolayer films display high chiroptical activity, with circular dichroism values of 3.5 mdeg at 550 nm and 26.8 mdeg at 775 nm. The L-Pen-NP films accelerate cell proliferation, whereas the D -Pen-NP films have the opposite effect. Remote irradiation with light is chosen to noninvasively collect the cells. The results demonstrate that left circularly polarized light improves the efficiency of cell detachment up to 91.2% for L-Pen-NP films. These findings will facilitate the development of cell culture in biomedical application and help to understand natural homochirality.

The kinetics of S-transnitrosation--a reversible second-order reaction

Transnitrosation between thiols and S-nitrosothiols has been suggested to be a mechanism of signal transduction. This kinetics of such reactions fit well to a reversible second-order model. Parameters derived from this model give both the forward and reverse rate constants and the equilibrium position at physiological temperature and pH. In addition, methods are shown for calculating the equilibrium distribution of the nitrosyl function group in mixtures of up to three thiols.

Radical releasing properties of nitric oxide donors GEA 3162, SIN-1 and S-nitroso-N-acetylpenicillamine

The nitric oxide (NO)-, superoxide anion (O2.-)- and peroxynitrite (ONOO-)-releasing properties of 1,2,3,4-oxatriazolium,5-amino-3-(3,4-dichlorophenyl)-chloride (GEA 3162) were characterized and compared with the known NO-donors 3-morpholino-sydnonimine (SIN-1) and S-nitroso-N-acetylpenicillamine. All the three compounds released NO in aqueous solutions in a dose-dependent manner as measured by ozone-chemiluminescence. GEA 3162 produced more NO than SIN-1, but less than S-nitroso-N-acetylpenicillamine during a 45 min incubation time. SIN-1 reduced nitro blue tetrazolium and the effect was inhibitable by superoxide dismutase. Reduction of nitro blue tetrazolium was not detected in the solutions of GEA 3162 and S-nitroso-N-acetylpenicillamine suggesting that SIN-1 but not GEA 3162 and S-nitroso-N-acetylpenicillamine release O2.- in their decomposition process. Formation of ONOO- in solutions of GEA 3162, SIN-1 and S-nitroso-N-acetylpenicillamine was estimated indirectly by measuring the formation of nitrotyrosine. The data indicate that ONOO- was produced in the presence of SIN-1 but not in solutions of GEA 3162 and S-nitroso-N-acetylpenicillamine. The results suggest that GEA 3162 produces negligible amounts of O2.- and ONOO- as compared to SIN-1. This adds the value of GEA 3162 as an useful tool in NO research and could well explain the earlier findings on the superior NO-like biological activity of oxatriazole derivatives as compared to SIN-1.

Chirality in antirheumatic drugs

Use of chiral molecules in clinical practice may cause problems because different chiral forms of a drug (enantiomers) may have different biological activities--yet clinicians have little awareness of these risks. After discussion of the chemical conventions used to describe chirality, examples of the influence of chirality on the efficacy and toxicity of antirheumatic drugs are given. It is recommended that single enantiomers should be used in biological experiments and clinical trials.

Nitrogen monoxide activates iron regulatory protein 1 RNA-binding activity by two possible mechanisms: effect on the [4Fe-4S] cluster and iron mobilization from cells

The iron-regulatory protein 1 (IRP1) regulates the expression of several molecules involved in iron (Fe) metabolism by reversibly binding to iron-responsive elements (IREs) in the untranslated regions (UTR) of particular mRNA transcripts. Several studies have indicated that nitrogen monoxide (NO) may influence IRP1 RNA-binding activity by a direct effect on the [4Fe-4S] cluster of the protein. It has also been suggested that NO may act indirectly on IRP1 by affecting the intracellular Fe pools that regulate the function of this protein [Pantopoulous et al. (1996) Mol. Cell. Biol. 16, 3781-3788]. There is also the possibility that NO may S-nitrosate sulfhydryl groups that are crucial for mRNA binding and decrease IRP1 activity by this mechanism. We have examined the effect of a variety of NO donors [e.g., S-nitroso-N-acetylpenicillamine (SNAP), spermine-NONOate (SperNO), and S-nitrosoglutathione (GSNO)] on IRP1 RNA-binding activity in both LMTK(-) fibroblast lysates and whole cells. In cell lysates, the effects of NO at increasing RNA-binding activity were only observed when cells were made Fe-replete. Under these circumstances, IRP1 contains an [4Fe-4S] cluster that was susceptible to NO. In contrast, when lysates were prepared from cells treated with the Fe chelator desferrioxamine (DFO), NO had no effect on the RNA-binding activity of IRP1. The lack of effect of NO under these conditions was probably because this protein does not have an [4Fe-4S] cluster. In contrast to the NO generators above, sodium nitroprusside (SNP) decreased IRP1 RNA binding when cells were incubated with this compound. However, SNP had no effect on IRP1 RNA-binding activity in lysates, suggesting that the decrease after incubation of cells with SNP was not due to S-nitrosation of critical sulfhydryl groups. Apart from the direct effect of NO on IRP1 in Fe-replete cells, we have shown that NO generated by SNAP, SperNO, and GSNO could also mobilize Fe from cells. When NO generation was induced in RAW 264.7 macrophages, an increase in IRP1 RNA-binding activity occurred but there was only a small increase in Fe release. Our results suggest that NO could activate IRP1 RNA-binding by two possible mechanisms: (1) its direct effect on the [4Fe-4S] cluster and (2) mobilization of (59)Fe from cells resulting in Fe depletion, which then increases IRP1 RNA-binding activity.

Silver(I) complex formation with cysteine, penicillamine, and glutathione

The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen), and glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and (109)Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol dm(-3) Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10-11) a mean Ag-S bond distance of 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and (109)Ag NMR spectra of a concentrated Ag(I)-cysteine solution (C(Ag(I)) = 0.8 mol dm(-3), L/Ag = 2.2) showed a mean Ag-S bond distance of 2.47 ± 0.02 Å and δ((109)Ag) 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (C(Ag(I)) = 0.5 mol dm(-3), L/Ag = 2.0) the mean Ag-S bond distance of 2.40 ± 0.02 Å and δ((109)Ag) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C(Ag(I)) = 0.01 mol dm(-3), pH ∼11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ∼10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N), and AgS3 coordination environments was used, together with a survey of (109)Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution.

Modification of creatine kinase by S-nitrosothiols: S-nitrosation vs. S-thiolation

Creatine kinase is reversibly inhibited by incubation with S-nitrosothiols. Loss of enzyme activity is associated with the depletion of 5,5'-dithiobis (2-nitrobenzoic acid)-accessible thiol groups, and is not due to nitric oxide release from RSNO. Full enzymatic activity and protein thiol content are restored by incubation of the S-nitrosothiol-modified protein with glutathione. S-nitroso-N-acetylpenicillamine, which contains a more sterically hindered S-nitroso group than S-nitrosoglutathione, predominantly modifies the protein thiol to an S-nitrosothiol via a transnitrosation reaction. In contrast, S-nitrosoglutathione modifies creatine kinase predominantly by S-thiolation. Both S-nitroso-N-acetylpenicillamine and S-nitrosoglutathione modify bovine serum albumin to an S-nitroso derivative. This indicates that S-thiolation and S-nitrosation are both relevant reactions for S-nitrosothiols, and the relative importance of these reactions in biological systems depends on both the environment of the protein thiol and on the chemical nature of the S-nitrosothiol.