Evaluation of thiol-based antioxidant therapeutics in cystic fibrosis sputum: Focus on myeloperoxidase.

Neutrophil-dependent reactions catalysed by myeloperoxidase (MPO) are thought to play important roles in the pulmonary pathobiology of cystic fibrosis (CF). Aerosolized thiol antioxidants such as glutathione (GSH) and N-acetylcysteine (NAC) are currently being utilized as therapeutics to modify CF respiratory tract oxidative processes. This study hypothesized that MPO in CF airway lining fluids may be a target of such therapeutics. MPO activity in sputum from 21 adult CF patients was found to be inversely associated with lung function (FEV(1)). In contrast, systemic inflammation (assessed by plasma C-reactive protein) was not correlated with lung function. Ex vivo studies revealed that GSH and NAC effectively scavenged N-chloramines in sputum and inhibited sputum MPO activity with potency exquisitely dependent upon MPO activity levels. Detailed kinetic analyses revealed that NAC and GSH inhibit MPO by distinct mechanisms. Activation of the key pro-inflammatory transcription factor NF-κB in cultured HBE1 cells was inhibited by GSH. The findings reveal that MPO activity and its reactive products represent useful predictors of the doses of inhaled thiol antioxidants required to ameliorate airway oxidative stress and inflammation in CF patients and provide mechanistic insight into the antioxidative/anti-inflammatory mechanisms of action of GSH and NAC when administered into the CF lung.

Bench-to-bedside review: the role of nitric oxide in sepsis.

Sepsis is a state of systemic inflammation directed at microbes or their toxins in blood or tissues. Nitric oxide (NO) is one of many vasoactive molecules released from a variety of cell types during sepsis. Almost two decades ago, NO emerged as a potential therapeutic target in sepsis. NO produced by the constitutive NO synthase (NOS) isoform (endothelial NOS and neuronal NOS) in the vascular endothelium and elsewhere acts as a nonadrenergic, noncholinergic neurotransmitter, an inhibitor of platelet aggregation and a vasodilator. During sepsis, activation of inducible NOS (iNOS) in the lung epithelium and other organs occurs, leading to NO overproduction. The result of excessive circulating NO is enhanced bacterial destruction, but also profound vasodilatation, activation of inflammatory cascades and depression of cardiac function. Trials of nonselective NOS inhibitors have shown increased mean arterial pressure, but also increased pulmonary artery pressure and reduced cardiac output. Small animal studies of iNOS selective inhibition have produced dichotomous results, but larger clinical studies assessing mortality are lacking. Inhaled NO has been touted as a therapeutic option to improve systemic oxygenation in the acute lung injury of sepsis (hypoxic pulmonary vasoconstriction and pulmonary hypertension); however, studies of inhaled NO in acute respiratory distress syndrome have not shown survival efficacy. Further investigation into the role of NO in human sepsis, and the development of methods to assess NO balance in patients with sepsis is essential in this field. In this review, we outline the effects of NO in sepsis, and summarize the therapeutic outcomes of NOS inhibitors, and inhaled NO in sepsis and acute respiratory distress syndrome.