Alteration in plasma levels of nonprotein sulfhydryl compounds and S-nitrosothiols in chronic renal failure patients

Enzyme Mimics for the Catalytic Generation of Nitric Oxide from Endogenous Prodrugs

The highly diverse biological roles of nitric oxide (NO) in both physiological and pathophysiological processes have prompted great interest in the use of NO as a therapeutic agent in various biomedical applications. NO can exert either protective or deleterious effects depending on its concentration and the location where it is delivered or generated. This double-edged attribute, together with the short half-life of NO in biological systems, poses a major challenge to the realization of the full therapeutic potential of this molecule. Controlled release strategies show an admirable degree of precision with regard to the spatiotemporal dosing of NO but are disadvantaged by the finite NO deliverable payload. In turn, enzyme-prodrug therapy techniques afford enhanced deliverable payload but are troubled by the inherent low stability of natural enzymes, as well as the requirement to control pharmacokinetics for the exogenous prodrugs. The past decade has seen the advent of a new paradigm in controlled delivery of NO, namely localized bioconversion of the endogenous prodrugs of NO, specifically by enzyme mimics. These early developments are presented, successes of this strategy are highlighted, and possible future work on this avenue of research is critically discussed.

Plasma protein thiolation index (PTI) as a biomarker of thiol-specific oxidative stress in haemodialyzed patients

The role of oxidative stress in patients with end stage renal disease (ESRD), which occurs at significantly higher levels than in the general population, is often underestimated in clinical practice. Emerging evidence highlights the strong correlation of oxidative stress with chronic inflammation and cardiovascular disease, which are highly prevalent in most patients on maintenance haemodialysis (HD) and are a major risk factor for mortality in this population. In this study, total plasma thiols and plasma S-thiolated proteins were measured in patients with ESRD, before and after a regular HD session, and compared to age-matched healthy subjects. We found a significant decrease in the level of total plasma thiols and, conversely, a significant increase in the level of S-thiolated proteins in these patients. In most patients, post-HD plasma level of total thiols did not differ from the one in healthy subjects, whereas plasma level of S-thiolated proteins was lower in HD patients than in age-matched healthy controls. This suggests that a single HD session restores plasma thiol redox status and re-establishes the antioxidant capacity of plasma thiols. Additionally, we determined protein thiolation index (PTI), i.e., the molar ratio between the sum of all low molecular mass thiols bound to S-thiolated plasma proteins and protein free cysteinyl residues. Patients with ESRD had a significantly higher PTI compared to age-matched healthy subjects and HD was associated with a decrease in PTI to normal, or lower than normal, levels. Although this study is limited in size, our results suggest that PTI is a useful indicator of thiol-specific oxidative stress in patients with ESRD on maintenance HD. This study also emphasizes that PTI determination is a cheap and simple tool suitable for large-scale clinical studies that could be used for routine screening of thiol-specific oxidative stress.

Flow injection measurements of S-nitrosothiols species in biological samples using amperometric nitric oxide sensor and soluble organoselenium catalyst reagent

A novel flow injection analysis (FIA) system suitable for measurement of S-nitrosothiols (RSNOs) in blood plasma is described. In the proposed (FIA) system, samples and standards containing RSNO species are injected into a buffer carrier stream that is mixed with the reagent stream containing 3,3'-dipropionicdiselenide (SeDPA) and glutathione (GSH). SeDPA has been shown previously to catalytically decompose RSNOs in the presence of a reducing agent, such as GSH, to produce nitric oxide (NO). The liberated NO is then detected downstream by an amperometric NO sensor. This sensor is prepared using an electropolymerized m-phenylenediamine (m-PD)/resorcinol and Nafion composite films at the surface of a platinum electrode. Using optimized flow rates and reagent concentrations, detection of various RSNOs at levels in the range of 0.25-20 μM is possible. For plasma samples, detection of background sensor interference levels within the samples must first be carried out using an identical FIA arrangement, but without the added SeDPA and GSH reagents. Subtraction of this background sensor current response allows good analytical recovery of RSNOs spiked into animal plasma samples, with recoveries in the range of 90.4-101.0%.

Platelet aggregation is affected by nitrosothiols in patients with chronic hepatitis: In vivo and in vitro studies

AIM: To investigate the relationship among the number of platelets and plasma levels of S-nitrosothiols (S-NO), nitrite, total non-protein SH (NPSH), glutathione (GSH), cysteine (CYS), malondialdehyde (MDA), 4-hydroxininenal (4HNE), tumor necrosis factor-alpha (TNFα) and interleukin (IL)-6 in patients with chronic hepatitis C (CH).

METHODS: In vitro the aggregation of platelets derived from controls and CH patients was evaluated before and after the addition of adenosine diphosphate (ADP) and collagen, both in basal conditions and after incubation with nitrosoglutathione (GSNO).

RESULTS: In vivo, S-NO plasma levels increased significantly in CH patients and they were significantly directly correlated with platelet numbers. Patients with platelet counts < 150 000/μL, had a smaller increase in S-NO, lower levels of GSH, CYS, NPSH, TNFα, and IL-6, and higher levels of nitrite, MDA, and 4-HNE relative to those of patients with platelet counts > 150 000/μL. In vitro, the ADP and collagen aggregation time was increased in platelets from patients and not from controls; in addition, platelets from CH patients but not from controls also showed a latency time after exposure to collagen.

CONCLUSION: The incubation of platelets with GSNO improved the percentage aggregation and abolished the latency time.

Detection of S-nitrosothiols in biological fluids: a comparison among the most widely applied methodologies

Many different methodologies have been applied for the detection of S-nitrosothiols (RSNOs) in human biological fluids. One unsatisfactory outcome of the last 14 years of research focused on this issue is that a general consensus on reference values for physiological RSNO concentration in human blood is still missing. Consequently, both RSNO physiological function and their role in disease have not yet been clarified. Here, a summary of the values measured for RSNOs in erythrocytes, plasma, and other biological fluids is provided, together with a critical review of the most widely used analytical methods. Furthermore, some possible methodological drawbacks, responsible for the highlighted discrepancies, are evidenced.

Disruption of thiol homeostasis in plasma of terminal renal failure patients

BACKGROUND

The aim of the present studies was to investigate the changes in concentrations of different forms of thiols in plasma of terminal renal failure patients before and after hemodialysis.

METHODS

Total concentrations of thiols, their free forms and the level of their mixed disulfides with proteins were determined with HPLC.

RESULTS

In terminal renal failure patients before dialysis, total concentrations of cysteine, homocysteine and cysteinylglycine and their free and protein-bound fractions increased while level of all such forms of glutathione dropped. A single dialysis session caused short-lasting return of concentrations of all forms of thiols to the level equal or close to the control group. The changes observed in non-dialyzed patients were similar to those observed in dialyzed patients before single dialysis procedure.

CONCLUSIONS

The obtained results showed severe disturbance of thiol homeostasis in plasma of terminal renal failure patients. The following changes have to be emphasized: (1) high level of free cysteine (cystine) fraction, (2) strong tendency of homocysteine to form mixed disulfides with proteins, (3) drop of glutathione level. These observations confirm a suggestion that atherogenic action of homocysteine can be a result of S-homocysteinylation and N-homocysteinylation reactions, whereas toxic action of cysteine can result from auto-oxidation reaction.

Nitro-arginine methyl ester, a non-selective inhibitor of nitric oxide synthase reduces ibuprofen-induced gastric mucosal injury in the rat

Ibuprofen is a commonly used non-steroidal anti-inflammatory drug. Gastrointestinal adverse drug reactions from ibuprofen usage include gastric mucosal ulcers and bleeding. The mechanism by which ibuprofen induces gastric mucosal damage is not clear. The present study is an attempt to examine the role of nitric oxide in the pathogenesis of ibuprofen-induced gastric mucosal damage. Ibuprofen administered orally at the dose of 100 mg/kg body weight for 6 days to the rats resulted in gastric mucosal injury. Serum nitrite and nitrosothiol were increased significantly as compared with the controls, which were treated with the vehicle alone. In the gastric mucosa, lipid peroxidation and protein thiols were increased, and the activity of glyceraldehyde 3-phosphate dehydrogenase, a nitric oxide sensitive enzyme was decreased significantly. Pretreatment of the rats daily with nitric oxide synthase inhibitor, nitro-arginine methyl ester (30 mg/kg body weight) 1 hr before treatment with ibuprofen reduced the gastric mucosal injury. Biochemically, it prevented the rise in serum nitrite levels and the increase in lipid peroxidation and protein thiol levels and the loss of glyceraldehyde 3-phosphate dehydrogenase activity in the gastric mucosa. The results of the present study suggest that increased nitric oxide production may be one of the mechanisms by which ibuprofen produces gastric mucosal injury and that inhibition of nitric oxide synthase reduces gastric mucosal injury.

Nitric oxide, S-nitrosothiols and hemoglobin: is methodology the key?

Two main hypotheses describe the role of hemoglobin in the regulation of nitric oxide (NO) bioavailability. It has been suggested that hemoglobin interacts with circulating NO, forming Fe-nitrosyl hemoglobin and then S-nitrosothiols, which deliver NO extracellularly by an allosterically regulated mechanism. Alternatively, the existence of diffusional barriers that protect NO from hemoglobin-mediated degradation has been proposed. The reliability of each model in vivo is supported by the detection of physiological hematic levels of S-nitrosohemoglobin. However, the measured concentrations of S-nitrosohemoglobin are largely divergent between the two models. Moreover, recent reports suggest that circulating levels of S-nitrosohemoglobin in human blood could be significantly lower than assessed previously. We suggest that solving the methodological controversies that make the field of NO research a 'minefield', even for skilled analysts, is fundamental to understanding the role of S-nitrosothiols in the vasculature.