It is proposed that the bond between nitric oxide (NO) and the Hb thiol Cys- 93 (SNOHb) is favored when hemoglobin (Hb) is in the relaxed (R, oxygenated) conformation, and that deoxygenation to tense (T) state destabilizes the SNOHb bond, allowing transfer of NO from Hb to form other (vasoactive) S-nitrosothiols (SNOs). However, it has not previously been possible to measure SNOHb without extensive Hb preparation, altering its allostery and SNO distribution. Here, we have validated an assay for SNOHb that uses carbon monoxide (CO) and cuprous chloride (CuCl)-saturated Cys. This assay is specific for SNOs and sensitive to 2-5 pmol. Uniquely, it measures the total SNO content of unmodified erythrocytes (RBCs) (SNORBC), preserving Hb allostery. In room air, the ratio of SNORBC to Hb in intact RBCs is stable over time, but there is a logarithmic loss of SNORBC with oxyHb desaturation (slope, 0.043). This decay is accelerated by extraerythrocytic thiol (slope, 0.089; P < 0.001). SNORBC stability is uncoupled from O2 tension when Hb is locked in the R state by CO pretreatment. Also, SNORBC is increased Ϸ20-fold in human septic shock (P ؍ 0.002) and the O2-dependent vasoactivity of RBCs is affected profoundly by SNO content in a murine lung bioassay. These data demonstrate that SNO content and O2 saturation are tightly coupled in intact RBCs and that this coupling is likely to be of pathophysiological significance.sepsis ͉ nitric oxide ͉ vascular physiology E vidence has accumulated for an S-nitrosothiol (SNO)-based vascular signaling system in which hemoglobin (Hb) reactions with nitric oxide (NO) transduce redox gradients into bioactivities (1-6). There is agreement that human Hb undergoes Snitrosylation at Cys- 93 (3,(7)(8)(9)(10)(11). Erythrocytes are proposed to couple O 2 tension to the distribution of NO activities (such as control of blood flow) by linking the allosteric transition of Hb (12, 13) to conformation-dependent changes in the redox activity of this Cys- 93 (13-18) and the stereochemistry of this SNO bond at Cys- 93 (6, 7). Indeed, Cys- 93 SNO in human Hb (SNOHb) can be crystallized only with the Hb tetramer in the relaxed (R, oxygenated) conformation; the SNO bond is unstable with Hb in the tense (T, deoxygenated) conformation (7). These observations support a paradigm in which NO binding to Cys- 93 is favored in the R state and NO binding to Fe(II) (and͞or transnitrosation to an alternate thiol) is favored in the T state (19-21). Thus, the change in stability of Cys- 93 SNO during Hb transition between R and T states may serve to couple regional O 2 gradients to the deployment or quenching of NO bioactivities in the microcirculation (2, 6, 22).However, assaying SNOHb has been problematic. First, detection of the SNO bond has required dilution and͞or pretreatment of Hb to (i) control for artifactual identification of nitrite and Fenitrosyl species and (ii) prevent autocapture of NO on Fe during analysis (8,19,(23)(24)(25). As a result, attempts to quantify Cys- 93 SNO density can be biased ...
NO transfer reactions between protein and peptide cysteines have been proposed to represent regulated signaling processes. We used the pharmaceutical antioxidant N-acetylcysteine (NAC) as a bait reactant to measure NO transfer reactions in blood and to study the vascular effects of these reactions in vivo. NAC was converted to S-nitroso-N-acetylcysteine (SNOAC), decreasing erythrocytic S-nitrosothiol content, both during wholeblood deoxygenation ex vivo and during a 3-week protocol in which mice received high-dose NAC in vivo. Strikingly, the NAC-treated mice developed pulmonary arterial hypertension (PAH) that mimicked the effects of chronic hypoxia. Moreover, systemic SNOAC administration recapitulated effects of both NAC and hypoxia. eNOS-deficient mice were protected from the effects of NAC but not SNOAC, suggesting that conversion of NAC to SNOAC was necessary for the development of PAH. These data reveal an unanticipated adverse effect of chronic NAC administration and introduce a new animal model of PAH. Moreover, evidence that conversion of NAC to SNOAC during blood deoxygenation is necessary for the development of PAH in this model challenges conventional views of oxygen sensing and of NO signaling.Introduction NO transfer reactions between protein and peptide cysteines have been proposed to represent regulated signaling processes (1, 2). For example, NO transfer from deoxygenated erythrocytes to glutathione ex vivo forms S-nitrosoglutathione (GSNO) (3). GSNO can signal acute vascular and central ventilatory effects characteristic of oxyhemoglobin desaturation (3-4) that are regulated by γ-glutamyl transpeptidase (GGT), GSNO reductase (GSNOR), and other enzymes (1, 3-6). However, direct measurement of S-nitrosothiol signaling in vivo has proven challenging because of the metabolism and tissue-specific localization of endogenous S-nitrosothiol species (1, 3, 4, 6). We have addressed these challenges by using N-acetylcysteine (NAC) as a bait reactant, allowing the stable NO transfer product, S-nitroso-N-acetylcysteine (SNOAC), to be distinguished by mass spectrometry (MS) from endogenous S-nitrosothiols. We report that NAC is converted to SNOAC in mice in vivo. Furthermore, chronic, systemic administration of either NAC or SNOAC to mice causes hypoxia-mimetic pulmonary arterial hypertension (PAH). These data reveal a previously unappreciated vascular toxicity of NAC and of S-nitrosothiols. Moreover, they suggest that S-nitrosothiol transfer reactions can signal hypoxia in vivo.PAH is characterized by increased pressure in the pulmonary arteries (PAs), increased RV weight, and thickening and remodeling of small PAs. Untreated human PAH can progress to right
Objectives: With decreasing mortality in PICUs, a growing number of survivors experience long-lasting physical impairments. Early physical rehabilitation and mobilization during critical illness are safe and feasible, but little is known about the prevalence in PICUs. We aimed to evaluate the prevalence of rehabilitation for critically ill children and associated barriers. Design: National 2-day point prevalence study. Setting: Eighty-two PICUs in 65 hospitals across the United States. Patients: All patients admitted to a participating PICU for greater than or equal to 72 hours on each point prevalence day. Interventions: None. Measurements and Main Results: The primary outcome was prevalence of physical therapy– or occupational therapy–provided mobility on the study days. PICUs also prospectively collected timing of initial rehabilitation team consultation, clinical and patient mobility data, potential mobility–associated safety events, and barriers to mobility. The point prevalence of physical therapy– or occupational therapy–provided mobility during 1,769 patient-days was 35% and associated with older age (adjusted odds ratio for 13–17 vs < 3 yr, 2.1; 95% CI, 1.5–3.1) and male gender (adjusted odds ratio for females, 0.76; 95% CI, 0.61–0.95). Patients with higher baseline function (Pediatric Cerebral Performance Category, ≤ 2 vs > 2) less often had rehabilitation consultation within the first 72 hours (27% vs 38%; p < 0.001). Patients were completely immobile on 19% of patient-days. A potential safety event occurred in only 4% of 4,700 mobility sessions, most commonly a transient change in vital signs. Out-of-bed mobility was negatively associated with the presence of an endotracheal tube (adjusted odds ratio, 0.13; 95% CI, 0.1–0.2) and urinary catheter (adjusted odds ratio, 0.28; 95% CI, 0.1–0.6). Positive associations included family presence in children less than 3 years old (adjusted odds ratio, 4.55; 95% CI, 3.1–6.6). Conclusions: Younger children, females, and patients with higher baseline function less commonly receive rehabilitation in U.S. PICUs, and early rehabilitation consultation is infrequent. These findings highlight the need for systematic design of rehabilitation interventions for all critically ill children at risk of functional impairments.
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