Mepolizumab for Eosinophil-Associated COPD: Analysis of METREX and METREO.

Background: A pre-specified meta-analysis of individual patient data from the 52-week METREX and METREO trials, which investigated mepolizumab for chronic obstructive pulmonary disease (COPD) in patients with blood eosinophil counts ≥150 cells/µL (screening) or ≥300 cells/µL (prior year) and frequent exacerbations, enables more robust characterization of mepolizumab efficacy in COPD and exploration of the relationship between blood eosinophil count and treatment responses. Methods: In METREX (117106/NCT02105948) and METREO (117113/NCT02105961), randomized patients received mepolizumab or placebo added to existing inhaled corticosteroid (ICS)-based triple maintenance therapy. The annual rate of moderate/severe exacerbations (primary endpoint) was compared between subcutaneous (SC) mepolizumab 100 mg versus placebo (primary comparison of interest) and all doses (100 mg and 300 mg SC) versus placebo in patients with blood eosinophil counts ≥150 cells/µL at screening or ≥300 cells/µL in the prior year. Secondary/other endpoints included time to first moderate/severe exacerbation, exacerbations leading to emergency department visit/hospitalization and health-related quality of life (HRQoL). A predictive model of the relationship between screening blood eosinophil counts and exacerbation rates included data from all randomized patients. Results: In total, 1510 patients were randomized in METREX and METREO and 1136 patients were included in the pre-specified meta-analysis. From the meta-analysis, mepolizumab 100 mg SC significantly reduced annual moderate/severe exacerbation rates versus placebo by 18% (rate ratio: 0.82; 95% confidence interval: 0.71, 0.95; p=0.006) and delayed time to first moderate/severe exacerbation (hazard ratio: 0.80 [0.68, 0.94]; p=0.006). Mepolizumab 100 mg SC versus placebo numerically reduced exacerbations leading to ED visits/hospitalization and improved HRQoL. A modelling approach demonstrated increasing efficacy for moderate/severe exacerbations with increasing screening blood eosinophil count; this relationship was more pronounced for exacerbations requiring oral corticosteroids (post hoc). The all-doses comparison had similar results. Conclusion: Mepolizumab reduces exacerbations in patients with eosinophil-associated COPD. Results suggest that blood eosinophil counts (≥150 cells/µL at screening or ≥300 cells/µL in the prior year) allow for identification of patients with COPD who experience exacerbations while treated with maximal ICS-based triple maintenance therapy who are likely to benefit from mepolizumab.

Validation of the Summit Lab Score in Predicting Exacerbations of Chronic Obstructive Pulmonary Disease Among Individuals with High Arterial Stiffness.

INTRODUCTION: The presence of cardiovascular (CV) risk factors and CV disease in patients with chronic obstructive pulmonary disease (COPD) leads to worse outcomes. A number of tools are currently available to stratify the risk of adverse outcomes in these patients with COPD. This post hoc analysis evaluated the Summit Lab Score for validation as a predictor of the first episode of moderate-to-severe acute exacerbation of chronic obstructive pulmonary disease (AECOPD) and other outcomes, in patients with COPD and high arterial pulse wave velocity (aPWV). METHODS: Data from a multicenter, randomized, placebo-controlled, double-blind study were retrospectively analyzed to evaluate treatment effects of once-daily fluticasone furoate/vilanterol 100/25 µg in patients with COPD and an elevated CV risk (aPWV≥11m/s) over 24 weeks. The previously derived Summit Lab Score and, secondarily, the Intermountain Risk Score (IMRS) were computed for each patient, with patients then stratified into tertiles for each score. Risk of moderate-to-severe AECOPD was analyzed across tertiles using Kaplan-Meier survival curve and Cox regression analyses. RESULTS: In 430 patients with COPD, Kaplan-Meier probabilities of no moderate-to-severe AECOPD for Summit Lab Score tertiles 1, 2, and 3 were 92.3%, 95.5%, and 85.1%, respectively (P trend = 0.015), over 24 weeks. Grouped by IMRS tertiles, the respective probabilities were 92.9%, 91.2%, and 88.3%, respectively (P trend = 0.141). Length of stay in the hospital (P = 0.034) and the hospital ward (P = 0.042) were also significantly different between Summit Lab Score tertiles but not for intensive care (P = 0.191). CONCLUSION: The Summit Lab Score was associated with the 24-week risk of moderate-to-severe AECOPD in COPD patients with elevated CV risk. Secondarily, IMRS showed a trend towards differences in the risk of AECOPD, which was not statistically significant.

Predictors of pneumonia on routine chest radiographs in patients with COPD: a post hoc analysis of two 1-year randomized controlled trials.

Background: Patients with COPD are at risk for life-threatening pneumonia. Although anatomical abnormalities in the thorax may predispose to pneumonia, those abnormalities identified on routine chest X-rays (CXRs) in patients with COPD have not been studied to better understand pneumonia risk. Methods: We conducted a post hoc exploratory analysis of data from two replicate year-long clinical trials assessing the impact of fluticasone furoate-vilanterol versus vilanterol alone on COPD exacerbations (GSK studies: HZC102871/NCT01009463 and HZC102970/NCT01017952). Abnormalities on baseline CXRs from 179 patients who developed pneumonia and 50 randomly selected patients who did not were identified by blinded consensus readings conducted by two radiologists. Positive and negative likelihood ratios and diagnostic odds ratios (ORs) were calculated to evaluate the markers for subsequent pneumonia development during the 1-year study period. Results: Baseline characteristics distinguishing the pneumonia and non-pneumonia groups included a lower body mass index (24.9 vs 27.5 kg/m2, P=0.008), more severe airflow obstruction (mean post-bronchodilator forced expiratory volume in 1 second [FEV1]/forced vital capacity ratio: 42.3% vs 47.6%, P=0.003), and prior pneumonia (36% vs 20%, P=0.030). Baseline CXR findings with the highest diagnostic ORs were: elevated hemi-diaphragm (OR: 6.87; 95% CI: 0.90, 52.26), thick tracheal-esophageal stripe (OR: 4.39 [0.25, 78.22]), narrow cardiac silhouette (OR: 2.91 [0.85, 9.99]), calcified pleural plaque/mid-chest pleural thickening (OR: 2.82 [0.15, 53.76]), and large/prominent pulmonary artery shadow (OR: 1.94 [0.95, 3.97]). The presence of a narrow cardiac silhouette at baseline was associated with a statistically significant lower mean pre-bronchodilator FEV1 (P=0.040). There was also a trend for a lower mean pre-bronchodilator FEV1 in patients with a large/prominent pulmonary artery shadow at baseline (P=0.095). Conclusion: Findings on routine CXR that relate to pathophysiological mechanisms of pneumonia could help determine pneumonia risk in patients with COPD.

Mepolizumab for Eosinophilic Chronic Obstructive Pulmonary Disease.

BACKGROUND: Patients with chronic obstructive pulmonary disease (COPD) with an eosinophilic phenotype may benefit from treatment with mepolizumab, a monoclonal antibody directed against interleukin-5. METHODS: We performed two phase 3, randomized, placebo-controlled, double-blind, parallel-group trials comparing mepolizumab (100 mg in METREX, 100 or 300 mg in METREO) with placebo, given as a subcutaneous injection every 4 weeks for 52 weeks in patients with COPD who had a history of moderate or severe exacerbations while taking inhaled glucocorticoid-based triple maintenance therapy. In METREX, unselected patients in the modified intention-to-treat population with an eosinophilic phenotype were stratified according to blood eosinophil count (≥150 per cubic millimeter at screening or ≥300 per cubic millimeter during the previous year). In METREO, all patients had a blood eosinophil count of at least 150 per cubic millimeter at screening or at least 300 per cubic millimeter during the previous year. The primary end point was the annual rate of moderate or severe exacerbations. Safety was also assessed. RESULTS: In METREX, the mean annual rate of moderate or severe exacerbations in the modified intention-to-treat population with an eosinophilic phenotype (462 patients) was 1.40 per year in the mepolizumab group versus 1.71 per year in the placebo group (rate ratio, 0.82; 95% confidence interval [CI], 0.68 to 0.98; adjusted P=0.04); no significant between-group differences were found in the overall modified intention-to-treat population (836 patients) (rate ratio, 0.98; 95% CI, 0.85 to 1.12; adjusted P>0.99). In METREO, the mean annual rate of moderate or severe exacerbations was 1.19 per year in the 100-mg mepolizumab group, 1.27 per year in the 300-mg mepolizumab group, and 1.49 per year in the placebo group. The rate ratios for exacerbations in the 100-mg and 300-mg mepolizumab groups versus the placebo group were 0.80 (95% CI, 0.65 to 0.98; adjusted P=0.07) and 0.86 (95% CI, 0.70 to 1.05; adjusted P=0.14), respectively. A greater effect of mepolizumab, as compared with placebo, on the annual rate of moderate or severe exacerbations was found among patients with higher blood eosinophil counts at screening. The safety profile of mepolizumab was similar to that of placebo. CONCLUSIONS: Mepolizumab at a dose of 100 mg was associated with a lower annual rate of moderate or severe exacerbations than placebo among patients with COPD and an eosinophilic phenotype. This finding suggests that eosinophilic airway inflammation contributes to COPD exacerbations. (Funded by GlaxoSmithKline; METREX and METREO ClinicalTrials.gov numbers, NCT02105948 and NCT02105961 .).

A randomized trial of once-daily fluticasone furoate/vilanterol or vilanterol versus placebo to determine effects on arterial stiffness in COPD.

INTRODUCTION: Chronic obstructive pulmonary disease (COPD) is associated with increased cardiovascular morbidity and mortality. Elevated arterial stiffness, measured by aortic pulse wave velocity (aPWV), is a cardiovascular risk surrogate and is potentially modifiable by inhaled corticosteroid/long-acting beta2-agonist combinations in patients with COPD. MATERIALS AND METHODS: The effects of once-daily inhaled fluticasone furoate/vilanterol (FF/VI) 100/25 µg, VI 25 µg, versus placebo on arterial stiffness in patients with COPD and baseline aPWV ≥11.0 m/s were investigated in a 24-week, multicenter, double-blind, randomized, stratified (by COPD exacerbation history), parallel-group, placebo-controlled trial. Eligible patients were ≥40 years old, with ≥10 pack-year smoking history, forced expiratory volume in 1 s (FEV1)/forced vital capacity ≤0.70, and post-bronchodilator FEV1 ≤70% of predicted. Patients with a major cardiovascular event in the previous 6 months/current severe heart failure/uncontrolled hypertension were excluded. Primary endpoint is change from baseline in aPWV after 24 weeks of treatment. Safety analyses included adverse events (AEs). RESULTS: The intent-to-treat population included 430 patients: FF/VI (n=135), VI (n=154), and placebo (n=141). Patients were predominantly male (79%) and Asian or White (each 48%), with a mean age of 68.5 years (standard deviation [SD] =7.9), percentage predicted post-bronchodilator FEV1 50.1% (SD =13.3), and aPWV 13.26 m/s (SD =2.22) at screening. At 24 weeks, mean (standard error [SE]) changes from baseline in aPWV were -1.75 m/s (SE =0.26, FF/VI), -1.95 m/s (SE =0.24, VI), and -1.97 m/s (SE =0.28, placebo). AEs occurred in 57% (FF/VI), 51% (VI), and 41% (placebo) of patients. CONCLUSION: No differences were observed in aPWV-adjusted mean change from baseline for FF/VI 100/25 µg, compared with placebo.

Inhaled ß-agonist does not modify sympathetic activity in patients with COPD.

BACKGROUND: Neurohumoral activation is present in COPD and might provide a link between pulmonary and systemic effects, especially cardiovascular disease. Because long acting inhaled ß-agonists reduce hyperinflation, they could reduce sympathoexcitation by improving the inflation reflex. We aimed to evaluate if inhaled therapy with salmeterol reduces muscle sympathetic nerve activity (MSNA) evaluated by microneurography. METHODS: MSNA, heart rate, blood pressure, and respiration were continually measured. After baseline recording of 20 minutes, placebo was administered; after further 45 minutes salmeterol (50 µg) was administered which was followed by a further 45 minutes of data recording. Additionally, lung function, plasma catecholamine levels, arterial pulse wave velocity, heart rate variability, and baroreflex sensitivity were evaluated. Following 4 weeks of treatment with salmeterol 50 µg twice daily, measurements were repeated without placebo administration. RESULTS: A total of 32 COPD patients were included. Valid MSNA signals were obtained from 18 patients. Change in MSNA (bursts/100 heart beats) following acute administration of salmeterol did not differ significantly from the change following placebo (-1.96 ± 9.81 vs. -0.65 ± 9.07; p = 0.51) although hyperinflation was significantly reduced. Likewise, no changes in MSNA or catecholamines were observed after 4 weeks. Heart rate increased significantly by 3.8 ± 4.2 (p < 0.01) acutely and 3.9 ± 4.3 bpm (p < 0.01) after 4 weeks. Salmeterol treatment was safe and well tolerated. CONCLUSIONS: By using microneurography as a gold standard to evaluate sympathetic activity we found no change in MSNA following salmeterol inhalation. Thus, despite an attenuation of hyperinflation, the long acting ß-agonist salmeterol does not appear to reduce nor incite sympathoexcitation. TRIAL REGISTRATION: This study was registered with the European Clinical Trials Database (EudraCT No. 2011-001581-18) and ClinicalTrials.gov ( NCT01536587 ).

Long-acting bronchodilators and arterial stiffness in patients with COPD: a comparison of fluticasone furoate/vilanterol with tiotropium.

BACKGROUND: Increased arterial stiffness as measured by aortic pulse wave velocity (aPWV) predicts cardiovascular events and mortality and is elevated in patients with COPD. Prior investigation suggests that a long-acting ß-agonist (LABA)/inhaled corticosteroid (ICS) lowers aPWV in patients with baseline aPWV ≥ 11 m/s. This study compared the effect of the ICS/LABA fluticasone furoate/vilanterol (FF/VI), 100/25 µg, delivered via the ELLIPTA dry powder inhaler, with tiotropium bromide (TIO), 18 µg, on aPWV. METHODS: This multicenter, randomized, blinded, double-dummy, parallel-group, 12-week study compared FF/VI and TIO, both administered once daily. The primary end point was aPWV change from baseline at 12 weeks. Safety end points included adverse events (AEs), vital signs, and clinical laboratory tests. RESULTS: Two hundred fifty-seven patients with COPD and aPWV ≥ 11 m/s were randomized; 87% had prior cardiovascular events and/or risk. The mean difference in aPWV between FF/VI and TIO at week 12 was not significant (P = .484). Because the study did not contain a placebo arm, a post hoc analysis was performed to show that both treatments lowered aPWV by an approximate difference of 1 m/s compared with baseline. The proportion of patients reporting AEs was similar with FF/VI (24%) and TIO (18%). There were no changes in clinical concern for vital signs or clinical laboratory tests. CONCLUSIONS: No differences on aPWV were observed between FF/VI and TIO. However, further studies with a placebo arm are required to establish definitively whether long-acting bronchodilators lower aPWV. Both treatments demonstrated an acceptable tolerability profile. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT01395888; URL: www.clinicaltrials.gov.

Risk of pneumonia with inhaled corticosteroid/long-acting ß2 agonist therapy in chronic obstructive pulmonary disease: a cluster analysis.

BACKGROUND: Pneumonia poses a significant risk in patients with moderate to severe chronic obstructive pulmonary disease but data are limited on the disease phenotypes most susceptible to pneumonia. METHODS: Cluster analysis using a data-driven recursive partitioning algorithm was employed using baseline data from two pooled one-year randomized exacerbation trials (n=3,255) of fluticasone furoate/vilanterol or vilanterol alone to identify distinct patient groups at greatest risk of pneumonia or serious (hospitalization or death) pneumonia. RESULTS: Five clusters were identified. Patients at greater risk of first pneumonia had more severe obstruction (forced expiratory volume in one second/forced vital capacity <46%) and either a body mass index <19 kg/m(2) (hazard ratio 7.8, 95% confidence interval 4.7-13.0; n=144) or a pneumonia history and greater comorbidities (hazard ratio 4.8, 95% confidence interval 3.0-7.7; n=374) relative to the cluster with the lowest pneumonia risk (reference; n=1310). Multiple comorbidities and use of psychoanaleptics also contributed to an increased risk of pneumonia in more obstructed patients. Independent of cluster, use of inhaled corticosteroids was associated with pneumonia (hazard ratio 1.89, 95% confidence interval 1.25-2.84) and serious pneumonia (hazard ratio 2.92, 95% confidence interval 1.40-6.01). CONCLUSION: Cluster analysis can identify patient populations at risk for serious safety outcomes and inform risk management strategies to optimize patient management. The greatest risk for pneumonia was in subjects with multiple pneumonia risk factors.

Which patients with chronic obstructive pulmonary disease benefit from the addition of an inhaled corticosteroid to their bronchodilator? A cluster analysis.

OBJECTIVE: To identify subsets of chronic obstructive pulmonary disease (COPD) patients who are more protected from exacerbations with the use of an inhaled corticosteroid/long-acting ß2 agonist (ICS/LABA) combination, compared with the use of LABA monotherapy. DESIGN: Post hoc cluster analysis of patients from two randomised clinical trials of salmeterol/fluticasone propionate (SFC) and salmeterol (SAL) that had primary endpoints of moderate/severe exacerbation rates. SETTING: Centres in North America. PARTICIPANTS: 1543 COPD patients were studied. INTERVENTIONS: SFC 50/250 µg or SAL 50 µg, twice daily. PRIMARY AND SECONDARY OUTCOME MEASURES: The analysis identified clusters of COPD patients more responsive to SFC versus SAL with respect to the annual rate of moderate/severe exacerbations and compared their baseline clinical characteristics. RESULTS: Overall, SFC significantly reduced the annual rate of moderate/severe exacerbations as compared with SAL alone (rate ratio (RR)=0.701, p<0.001). Three-patient clusters were identified: COPD patients receiving diuretics (RR=0.56, p<0.001); patients not receiving diuretics but with forced expiratory volume in 1 s (FEV1) reversibility ≥12% (RR=0.67, p<0.001) exhibited a substantial reduction in the annual rate of moderate/severe exacerbations relative to SAL. A third cluster, consisting of patients not receiving diuretics and without FEV1 reversibility, demonstrated no difference for SFC versus SAL. Patients receiving diuretics had a significantly higher prevalence of comorbid cardiovascular disease. CONCLUSIONS: COPD patients receiving diuretics and those not receiving diuretics but with FEV1 reversibility >12% at baseline were significantly more likely to experience a reduction in COPD-associated exacerbations with SFC versus SAL alone. TRIAL REGISTRATION: NCT00115492, NCT00144911.

Effect of fluticasone propionate/salmeterol on arterial stiffness in patients with COPD.

BACKGROUND: COPD is associated with increased arterial stiffness which may in part explain the cardiovascular morbidity observed in the disease. A causal relationship between arterial stiffness and cardiovascular events has not been established, though their strong association raises the possibility that therapies that reduce arterial stiffness may improve cardiovascular outcomes. Prior studies suggest that fluticasone propionate/salmeterol (FSC) may improve cardiovascular outcomes in COPD and we hypothesized that FSC would reduce arterial stiffness in these patients. METHODS: This multicenter, randomized, double-blind, placebo-controlled study compared the effects of FSC 250/50 µg twice-daily and placebo on aortic pulse wave velocity (aPWV) as determined by ECG-gated carotid and femoral artery waveforms. The primary endpoint was aPWV change from baseline at 12-weeks (last measure for each patient). RESULTS: 249 patients were randomized; the mean FEV(1) in each group was similar (55% predicted) and 60% of patients reported a cardiovascular disorder. At 12-weeks, aPWV between FSC and placebo was -0.42 m/s (95%CI -0.88, 0.03; p = 0.065). A statistically significant reduction in aPWV between FSC and placebo was observed in those who remained on study drug throughout the treatment period [-0.49 m/s (95%CI -0.98, -0.01; p = 0.045)]. A post hoc analysis suggested the effect of FSC was greater in patients with higher baseline aPWV. CONCLUSION: FSC does not reduce aPWV in all patients with moderate to severe COPD, but may have effects in those with elevated arterial stiffness. Additional studies are required to determine if aPWV could serve as a surrogate for cardiovascular events in COPD.

Circulating endothelial cell levels correlate with proinflammatory cytokine increase in the acute phase of thermal injury.

Circulating endothelial cells (CECs) are increased in sickle cell disease, myocardial infarction, and acute lung injury. The purpose of this study was to determine whether CECs are a prognosticating marker for the development of pneumonia in burn patients with/without inhalation injury in addition to their relationship to proinflammatory cytokines. There were 24 patients: 6 with inhalation injury, 5 with burn only,and 13 with burn plus inhalation injury. CECs were measured by anchored cytometry (Clarient ChromaVision, San Juan Capistrano, CA). In addition, plasma levels of tumor necrosis factor-alpha, interferon-gamma, and interleukins (IL)-10, IL-6, IL-4, and IL-2 were compared with CEC levels. Patients with inhalation injury had a significant (P < .001) paucity of CECs compared with the thermally injured with inhalation. There was a statistically significant increase in inteferon-gamma, tumor necrosis factor-alpha, and IL-6, IL-4, and IL-2 compared with control patients (P < .01), with a concomitant increase in the number of CECs. The numbers of CEC levels did not prognosticate which patients would develop pneumonia. Burn patients with/without inhalation injury had concurrent increase in CECs and proinflammatory cytokines during the acute phase of injury.

Positron emission tomography demonstrates radiation-induced changes to nonirradiated lungs in lung cancer patients treated with radiation and chemotherapy.

STUDY OBJECTIVES: To determine whether acute changes in shielded lungs can be detected by positron emission tomography (PET) after radiation therapy. DESIGN: Retrospective cohort study. SETTING: University-affiliated medical center. PATIENTS: Sixteen patients undergoing radiation therapy for lung cancer who had PET scans after receiving treatment. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: Thirteen of 16 patients (81.2%) showed increased (18)fluoro-2-deoxyglucose uptake in shielded nonirradiated lung in the following four distinct patterns: (1) contralateral peripheral pleural uptake in 5 of 16 patients (31.2%); (2) ipsilateral peripheral pleural uptake in 5 of 16 patients (31.2%); (3) bilateral peripheral pleural uptake in 1 of 16 patients (6.2%); and (4) bilateral diffuse background uptake in 1 of 16 patients (6.2%). This last patient developed clinically evident radiation pneumonitis. CONCLUSIONS: Increased lung metabolic activity can be demonstrated in the nonirradiated lung in patients who have undergone radiation therapy for lung cancer and can be detected by PET scanning. PET scanning of lungs in irradiated patients may provide an early demonstrable barometer of pulmonary toxicity. If verified, this imaging tool could prove to be useful in monitoring patients receiving radiation therapy for thoracic malignancies and may have predictive value for subsequent fibrosis. PET scanning may also be an important tool in future studies to further elucidate the pathogenetic mechanism of radiation-induced lung injury.

Properties of selected S-nitrosothiols compared to nitrosylated WR-1065.

WR-1065 ([N-mercaptoethyl]-1-3-diaminopropane), the active form of the aminothiol drug Ethyol/Amifostine, protects against toxicity caused by radiation, chemotherapy and endotoxin. Because WR-1065 and other thiols readily bind nitric oxide (NO), injurious conditions or therapies that induce the production or mobilization of NO could alter the effects of WR-1065. S-Nitrosothiols were prepared from various thiols by a standard method to compare properties and stability. Heteromolecular quantum correlation 2D nuclear magnetic resonance was used to characterize nitrosylated glutathione (GSH) and WR-1065; both S- and N-nitrosothiols were observed, depending on the experimental conditions. Three categories of S-nitrosothiol stability were observed: (1) highly stable, with t(1/2) > 8 h, N-acetyl-L-cysteine nitrosothiol (t(1/2) 15 h) > GSH nitrosothiol (t(1/2) 8 h); (2) intermediate stability, t(1/2) approximately 2 h, cysteamine nitrosothiol and WR-1065 nitrosothiol; and (3) low stability, t(1/2) < 1 h, cysteine nitrosothiol and Captopril nitrosothiol. Similar relative rates were observed for Hg(+2)-induced denitrosylation: WR-1065 reacted faster than GSH nitrosothiol, while GSH nitrosothiol reacted faster than N-acetyl-L-cysteine nitrosothiol. Mostly mediated by mixed-NPSH disulfide formation, the activity of the redox-sensitive cysteine protease, cathepsin H, was inhibited by the S-nitrosothiols, with WR-1065 nitrosothiol > cysteine nitrosothiol > N-acetyl-L-cysteine nitrosothiol and GSH nitrosothiol. These observations indicate that, relative to other nitrosylated non-protein thiols, the S-nitrosothiol of WR-1065 is an unstable non-protein S-nitrosothiols with a high reactive potential in the modification of protein thiols.