Quantitation of S-nitrosothiols in cells and biological fluids

High-Density Three-Dimensional Network of Covalently Linked Nitric Oxide Donors to Achieve Antibacterial and Antibiofilm Surfaces

Bacterial colonization on biomedical devices often leads to biofilms that are recalcitrant to antibiotic treatment and the leading cause of hospital-acquired infections. We have invented a novel pretreatment chemistry for device surfaces to produce a high-density three-dimensional (3-D) network of covalently linked S-nitrosothiol (RSNO), which is a nitric oxide (NO) donor. Poly(polyethylene glycol-hydroxyl-terminated) (i.e., PPEG-OH) brushes were grafted from an ozone-pretreated polyurethane (PU) surface. The high-density hydroxyl groups on the dangling PPEG-OH brushes then underwent condensation with a mercapto-silane (i.e., MPS, mercaptopropyl trimethoxysilane) followed by S-nitrosylation to produce a 3-D network of NO-releasing RSNO to form the PU/PPEG-OH-MPS-NO coating. This 3-D coating produces NO flux of up to 7 nmol/(cm² min), which is nearly 3 orders of magnitude higher than the picomole/(cm² min) levels of other NO-releasing biomedical implants previously reported. The covalent immobilization of RSNO avoids donor leaching and reduces the risks of cytotoxicity arising from leachable RSNO. Our coated PU surfaces display good biocompatibility and exhibit excellent antibiofilm formation activity in vitro (up to 99.99%) against a broad spectrum of Gram-positive and Gram-negative bacteria. Further, the high-density RSNO achieves nearly 99% and 99.9% in vivo reduction of Pseudomonas aeruginosa (P. aeruginosa) and methicillin-resistant Staphylococcus aureus (MRSA) in a murine subcutaneous implantation infection model. Our surface chemistry to create high NO payload without NO-donor leaching can be applied to many biomedical devices.

Evaluation of a novel vascular graft with a distal bifurcation designed to reduce the development of intimal hyperplasia. Experimental study in a porcine aorta model

OBJECTIVE

Abnormal haemodynamics is commonly agreed to be a major contributor to the development of distal anastomotic intimal hyperplasia. A new vascular graft design proposed by computational studies was used to demonstrate its surgical feasibility and to compare it with the conventional graft in a porcine model.

METHOD

The device was used in 12 eight-month-old pigs, six received the new graft and six had a conventional graft. The proximal graft end was implanted into the aorta, the distal graft end was implanted into the iliac artery. The host artery was ligated in order to simulate occlusion. At 20 weeks after surgery the pigs were killed and the device was excised for histological and morphometric analysis.

RESULTS

In five experimental grafts the reconstruction was occluded due to thrombosis; only one prosthesis was patent showing a minimum of neointimal hyperplasia. In the control group too only three of the six grafts were patent. A histological analysis revealed, as the cause of occlusion, fibrous tissue overgrowth corresponding in structure to neointimal hyperplasia. Differences in the number of obliterations and in occlusion rates between the profiles of the two groups were evaluated using the median test (P<0.05). The results were not statistically significant.

CONCLUSION

Although mathematical modelling had shown significant haemodynamic benefits of a naturally bifurcated graft, our study did not confirm its superiority over conventionally used prostheses.

Influence of glutathione and its derivatives on fibrin polymerization

A complex relationship exists between reduced, oxidized, and nitrosated glutathione (GSH, GSSG, and GSNO, respectively). Although previous studies have demonstrated S-nitrosoglutathione (GSNO) has potent antiplatelet efficacy, little work has examined the role of GSNO and related species on subsequent aspects of coagulation (e.g., fibrin polymerization). Herein, the effects of GSH, GSSG, and GSNO on the entire process of fibrin polymerization are described. Relative to normal fibrinogen, the addition of GSH, GSSG, or GSNO leads to prolonged lag times, slower rates of protofibril lateral aggregation and the formation of clots with lower final turbidities. Dose-dependent studies indicate the influence of GSH on fibrin formation is a function of both GSH and fibrinogen concentration. Studies with Aalpha251 recombinant fibrinogen (lacking alphaC regions) showed GSH had no influence on its polymerization, suggesting the glutathione species interact within the alphaC region of fibrinogen.

Nitric oxide: what a vascular surgeon needs to know

Atherosclerosis in the form of peripheral arterial disease results in significant morbidity and mortality. Surgical treatment options for peripheral arterial disease include angioplasty with and without stenting, endarterectomy, and bypass grafting. Unfortunately, all of these procedures injure the vascular endothelium, which impairs its ability to produce nitric oxide (NO) and ultimately leads to neointimal hyperplasia and restenosis. To improve on current patency rates after vascular procedures, investigators are engaged in research to improve the bioavailability of NO at the site of vascular injury in an attempt to reduce the risk of thrombosis and restenosis after successful revascularization. This article reviews some of the previous research that has aimed to improve NO bioavailability after vascular procedures whether through systemic or local delivery, as well as to describe some of the NO-releasing products that are currently undergoing study for use in clinical practice.

Modified prosthetic vascular conduits

Atherosclerosis in the form of peripheral arterial disease results in significant morbidity. Surgical treatment options for peripheral arterial disease include angioplasty, endarterectomy, and bypass grafting. For bypass grafting, vein remains the conduit of choice; however, poor quality and limited availability have led to the use of prosthetic materials. Unfortunately, because of a lack of endothelium and compliance mismatch, neointimal hyperplasia develops aggressively, resulting in high failure rates. To improve graft patency, investigators have developed surgical, chemical, and biological graft modifications. This review describes common prosthetic materials, as well as approaches currently in use and under investigation to modify and improve prosthetic conduits for bypass grafting in an effort to improve graft patency rates.

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.

Nitrosative stress inhibits the aminophospholipid translocase resulting in phosphatidylserine externalization and macrophage engulfment: implications for the resolution of inflammation

Macrophage recognition of apoptotic cells depends on externalization of phosphatidylserine (PS), which is normally maintained within the cytosolic leaflet of the plasma membrane by aminophospholipid translocase (APLT). APLT is sensitive to redox modifications of its -SH groups. Because activated macrophages produce reactive oxygen and nitrogen species, we hypothesized that macrophages can directly participate in apoptotic cell clearance by S-nitrosylation/oxidation and inhibition of APLT causing PS externalization. Here we report that exposure of target HL-60 cells to nitrosative stress inhibited APLT, induced PS externalization, and enhanced recognition and elimination of "nitrosatively" modified cells by RAW 264.7 macrophages. Using S-nitroso-L-cysteine-ethyl ester (SNCEE) and S-nitrosoglutathione (GSNO) that cause intracellular and extracellular trans-nitrosylation of proteins, respectively, we found that SNCEE (but not GSNO) caused significant S-nitrosylation/oxidation of thiols in HL-60 cells. SNCEE also strongly inhibited APLT, activated scramblase, and caused PS externalization. However, SNCEE did not induce caspase activation or nuclear condensation/fragmentation suggesting that PS externalization was dissociated from the common apoptotic pathway. Dithiothreitol reversed SNCEE-induced S-nitrosylation, APLT inhibition, and PS externalization. SNCEE but not GSNO stimulated phagocytosis of HL-60 cells. Moreover, phagocytosis of target cells by lipopolysaccharide-stimulated macrophages was significantly suppressed by an NO. scavenger, DAF-2. Thus, macrophage-induced nitrosylation/oxidation plays an important role in cell clearance, and hence in the resolution of inflammation.

Polymers incorporating nitric oxide releasing/generating substances for improved biocompatibility of blood-contacting medical devices

The current state-of-the-art with respect to the preparation, characterization and biomedical applications of novel nitric oxide (NO) releasing or generating polymeric materials is reviewed. Such materials show exceptional promise as coatings to prepare a new generation of medical devices with superior biocompatiblity. Nitric oxide is a well-known inhibitor of platelet adhesion and activation, as well as a potent inhibitor of smooth muscle cell proliferation. Hence, polymers that release or generate NO locally at their surface exhibit greatly enhanced thromboresistivity and have the potential to reduce neointimal hyperplasia caused by device damage to blood vessel walls. In this review, the use of diazeniumdiolates and nitrosothiols as NO donors within a variety polymeric matrixes are summarized. Such species can either be doped as discrete NO donors within polymeric films, or covalently linked to polymer backbones and/or inorganic polymeric filler particles that are often employed to enhance the strength of biomedical polymers (e.g., fumed silica or titanium dioxide). In addition, very recent efforts to create catalytic polymers possessing immobilized Cu(II) sites capable of generating NO from endogenous oxidized forms of NO already present in blood and other physiological fluids (nitrite and nitrosothiols) are discussed. Preliminary literature data illustrating the efficacy of the various NO release/generating polymers as coatings for intravascular sensors, extracorporeal blood loop circuits, and arteriovenous grafts/shunts are reviewed.

Synthesis, characterization, and controlled nitric oxide release from S-nitrosothiol-derivatized fumed silica polymer filler particles

A new type of nitric oxide (NO)-releasing material is described that utilizes S-nitrosothiols anchored to tiny fumed silica (FS) particles as the NO donor system. The synthetic procedures suitable for tethering three different thiol species (cysteine, N-acetylcysteine, and N-acetylpenicillamine) to the surface of FS polymer filler particles are detailed. The thiol-derivatized particles are converted to their corresponding S-nitrosothiols by reaction with t-butylnitrite. The total NO loading on the resulting particles range from 21-138 nmol/mg for the three different thiol-derivatized materials [S-nitrosocysteine-(NO-Cys)-FS, S-nitroso-N-acetylcysteine (SNAC)-FS, and S-nitroso-N-acetylpenicillamine (SNAP)-FS], with SNAP-FS yielding the highest NO loading. NO can be generated from these particles when suspended in solution via the addition of copper(II) ions, ascorbate, or irradiation with visible light. The SNAC-FS and SNAP-FS particles can be blended in polyurethane and silicone rubber matrixes to create films that release NO at controlled rates. Polyurethane films containing SNAC-FS submerged in phosphate-buffered saline (pH 7.4) generate NO surface fluxes approximately 0.1-0.7x10(-10) mol cm-2 min-1 and SNAP-FS films generate NO fluxes of approximately 0-7.5x10(-10) mol cm-2 min-1 upon addition of increasing amounts of copper ions. Silicone rubber films containing SNAC-FS or SNAP-FS do not liberate NO upon exposure to copper ions or ascorbate in phosphate-buffered saline solution. However, such films are shown to release NO at rates proportional to increasing intensities of visible light impinging on the films. Such photoinitiated NO release from these composite materials offers the first NO-releasing hydrophobic polymers with an external on/off trigger to control NO generation.

S-nitrosoalbumin-mediated relaxation is enhanced by ascorbate and copper: effects in pregnancy and preeclampsia plasma

S-nitrosoalbumin (SNO-Alb) is a major reservoir of releasable nitric oxide (NO) in plasma. In preeclampsia, a pregnancy-specific disorder associated with endothelial dysfunction, we previously found significant elevations in plasma SNO-Alb concentrations and decreased plasma ascorbate (Asc) levels. This increased SNO-Alb may result from low-plasma Asc if Asc, along with transition metals (eg, copper [Cu]) are necessary for release of NO from S-nitrosothiols. We propose that vasodilator effects of SNO-Alb, mediated by release of NO, are fully realized only when Asc/Cu availability is sufficient. Relaxation responses to SNO-Alb or the control reduced human serum albumin (SH-Alb), and responses to pooled plasma from normal or preeclamptic pregnancies were examined in isolated mouse arteries. Arteries preconstricted with phenylephrine were exposed to SNO-Alb or SH-Alb at physiologically relevant concentrations. When free Cu was added in excess (10 mumol/L), NO release was not dependent on Asc. However, when Cu was added at lower (physiological) levels, NO release was dependent on Asc. The addition of Asc and Cu to SNO-Alb stimulated vasodilatory responses in isolated arteries >90%, whereas no change in the SH-Alb (5%) response was observed. Preeclampsia plasma with higher levels of SNO-Alb caused arteries to relax 44.1+/-4.7%, whereas normal pregnancy plasma caused 11.9+/-4.2% relaxation (P=0.007). These data indicate that SNO-Alb alone or in plasma can act as a potent vasodilator, and that sufficient Asc/Cu promotes this action. We suggest that the higher circulating levels of SNO-Alb, in women with preeclampsia, reflect a deficiency in Asc/Cu-mediated release of NO from SNO-Alb.

Current concepts in the use of antioxidants for the treatment of preeclampsia

Preeclampsia is a leading cause of maternal and neonatal mortality and morbidity. It is a complex syndrome of undetermined etiologic origin, usually diagnosed during the second half of pregnancy, with clinical features of hypertension, proteinuria, and edema. No cure for preeclampsia exists, except premature delivery. There is increasing evidence that oxidative stress is an important contributing factor to the pathogenesis of preeclampsia. Oxidative stress is defined as an imbalance between reactive oxygen species (ROS), such as nitric oxide (NO*), superoxide anion (O2*-), and hydrogen peroxide (H2O2), and antioxidants, favouring an overabundance of ROS. The consequence of an overproduction of ROS can be observed as increased levels of markers of oxidative stress, such as lipid peroxides. Pregnant women affected by preeclampsia may have abnormal ROS production, particularly NO* and O2*-, abnormal levels of antioxidant defences, and increased placental lipid peroxidation. Several observations suggest that decreased bioavailability of endothelium-derived NO*, due to oxidative destruction of NO* by ROS, might contribute to the impaired endothelium-dependent vasodilatory responses and multisystemic pathology of preeclampsia, a phenomenon in which antioxidant vitamins may play a beneficial role. This review focuses on the rationale for vitamins C and E supplementation toward prevention of preeclampsia, with an emphasis on the limit of our scientific knowledge concerning the deleterious oxidative events taking place in this pathology.

Binding of fatty acids facilitates oxidation of cysteine-34 and converts copper-albumin complexes from antioxidants to prooxidants

As a transition metal capable of undergoing one-electron oxidation-reduction conversions, copper (Cu) is essential for life and fulfills important catalytic functions. Paradoxically, the same redox properties of copper can make it extremely dangerous because it can catalyze production of free radical intermediates from molecular oxygen. Factors involved in regulation of redox activity of albumin-bound copper have not been well characterized. In the present study, effects of modification of the albumin cysteine-34 (Cys-34) and binding of nonesterified fatty acids on the redox-cycling activity of the complex of copper with human serum albumin (Cu/HSA) were studied. Because ascorbate is the most abundant natural reductant/scavenger of free radicals in blood plasma, the electron paramagnetic resonance assay of ascorbate radical formation was used as a method to monitor Cu/HSA redox-cycling activity. At Cu/HSA ratios below 1:1, the bound Cu was virtually redox inactive, as long as Cys-34 was in reduced state (Cu/HSA-SH). Alkylation, nitrosylation, or oxidation of Cu/HSA resulted in the appearance of redox-cycling activity. Experiments with ultrafiltration of Cu/HSA alkylated with N-ethylmaleimide (Cu/HSA-NEM) showed that at Cu/HSA-NEM ratios below 1:1, the ascorbate radicals were produced by Cu tightly bound to HSA rather than by Cu released in solution. The rate of ascorbate radical production in HSA-NEM and S-nitrosylated HSA (HSA-NO) was, however, more than one order of magnitude lower than that in a solution containing equivalent concentration of free copper ions. While Cu/HSA-SH was redox inactive, binding of oleic or linoleic acids induced Cu-dependent redox-cycling with maximal activity reached at a fatty acid to protein molar ratio of 3:1 for oleic acid and 2:1 for linoleic acid. Binding of fatty acids caused profound conformational changes and facilitated oxidation of the Cys-34 SH-group at essentially the same ratios as those that caused redox-cycling activity of Cu/HSA. We conclude that fatty acids regulate anti-/prooxidant properties of Cu-albumin via controlling redox status of Cys-34.

Nitric oxide and S-nitrosothiols in human blood

The hypothesis that endothelial-derived relaxing factor (EDRF) is nitric oxide has stimulated a wealth of research into the significance of this novel intriguing molecule. Given its short life, many storage forms of NO as well as targets have been postulated. Among these, a pool of derivatives of NO (S-nitrosothiols, RSNOs) covalently bound to SH groups of proteins and low molecular weight thiols (e.g., glutathione) have been identified in various biological systems. The importance of RSNOs results from the very similar biological actions exhibited by both NO and RSNOs in vivo as well as in vitro. In particular, it has been observed that in the bloodstream, these molecules are able to provoke vasodilatation with a consequent fall in blood pressure and an antithrombotic effect by inhibition of platelet aggregation. Many hypotheses have been postulated about the biochemical species and the mechanisms involved in these processes, but many aspects have not yet been clarified. In addition, some RSNOs have been recently proposed to be clinical parameters, whose levels may vary under some pathological conditions. The therapeutic utility of RSNOs as an alternative to classic NO donors has also been suggested.Here, we provide a critical analysis of the main reports about the biochemical, physiological, pathological and therapeutic properties of RSNOs in the cardiovascular system. Particular attention is addressed to conflicting results and to discrepancies in the methodologies and models utilized. The numerous unanswered questions concerning the role of RSNOs in the control of vascular tone are discussed.

Increased S-nitrosothiols and S-nitrosoalbumin in cerebrospinal fluid after severe traumatic brain injury in infants and children: indirect association with intracranial pressure

Nitric oxide (NO) is implicated in both secondary damage and recovery after traumatic brain injury (TBI). Transfer of NO groups to cysteine sulfhydryls on proteins produces S-nitrosothiols (RSNO). S-nitrosothiols may be neuroprotective after TBI by nitrosylation of N-methyl-D-aspartate receptor and caspases. S-nitrosothiols release NO on decomposition for which endogenous reductants (i.e., ascorbate) are essential, and ascorbate is depleted in cerebrospinal fluid (CSF) after pediatric TBI. This study examined the presence and decomposition of RSNO in CSF and the association between CSF RSNO level and physiologic parameters after severe TBI. Cerebrospinal fluid samples (n = 72) were obtained from 18 infants and children on days 1 to 3 after severe TBI (Glasgow Coma Scale score < 8) and 18 controls. Cerebrospinal fluid RSNO levels assessed by fluorometric assay peaked on day 3 versus control (1.42 +/- 0.11 micromol/L vs. 0.86 +/- 0.04, P< 0.05). S-nitrosoalbumin levels were also higher after TBI (n = 8, 0.99 +/- 0.09 micromol/L on day 3 vs. n = 6, 0.42 +/- 0.02 in controls, P< 0.05). S-nitrosoalbumin decomposition was decreased after TBI. Multivariate analysis showed an inverse relation between CSF RSNO and intracranial pressure and a direct relation with barbiturate treatment. Using a novel assay, the presence of RSNO and S-nitrosoalbumin in human CSF, an approximately 1.7-fold increase after TBI, and an association with low intracranial pressure are reported, supporting a possible neuroprotective role for RSNO. The increase in RSNO may result from increased NO production and/or decreased RSNO decomposition.

Redox sensor function of metallothioneins

In summary, the redox conversions of MT cysteines are likely to be the principal mechanisms for regulation of metal binding and release by this protein. Oxidative and/or nitrosative challenges can serve to promote metal ion release from MT to render their delivery to specific target proteins. It is tempting to consider the potential roles of MTs as redox sensors because of their high sensitivity to cysteine modification, as well as their potential to amplify signals by releasing multiple metal ions. In other words, MTs may act early in a biological signaling cascade that triggers metal-dependent biochemical and cellular responses. Alternatively, uncontrolled release of metals by excessive oxidative stress may contribute to metal toxicity. Because oxidative and nitrosative signaling is ubiquitous within cells, the physiological function of MT demands that efficient recycling of modified cysteines be operative. Little is known regarding the potential mechanisms for the regeneration of MT after oxidative/nitrosative modification, but they may involve endogenous dithiols, such as thioredoxin, and pharmacologically relevant dithiols, such as dihydrolipoate.