| BackgroundSeptic acute respiratory distress syndrome (ARDS) is often encountered as a complication of various diseases, such as pneumonia, pancreatitis, trauma, burn injury, cardiovascular and gastrointestinal operations, or as a part of multiple system organ failure. Pathogenesis of acute lung injury (ALI) and ARDS in septic patients is related to intrapulmonary neutrophil accumulation and inflammatory damage of lungs, especially in alveoli. Such changes lead to impairment of lung mechanics and gas exchange, surfactant dysfunction and deficiency, pulmonary hypertension secondary to hypoxic intrapulmonary vasoconstriction, and increased vascular-to-alveolar permeability.Inhaled nitric oxide (iNO) was introduced primarily as a selective pulmonary vasodilator to alter ventilation-perfusion mismatching in ALI/ARDS. It may also act to prevent development of ARDS from pulmonary infection and septic lung injury, Although in patients with ARDS, iNO significantly reduces the pulmonary hypertension and the intrapulmonary shunt, it has not yet proved to be effective in reducing mortality.It has been speculated that iNO may cause secondary surfactant damage by formation of nitrotyrosine in its protein moiety due to production of peroxynitrite under hyperoxic condition. iNO is usually used in combination with high oxygen supply in critical conditions. Whether iNO alone or iNO together with hyperoxia would have any adverse effects on surfactant phosphatidylcholine (PC) de novo synthesis in inflammatory injury in the lungs remains an unanswered question, and of clinical importance in terms of new indication of iNO.Recent studies showed that iNO attenuates lung inflammatory injury. Whether iNO alone or iNO plus hyperoxia would affect the course of lung inflammation is not clear. In ARDS patients, elevated levels of TNF-α may be primarily responsible for inhibition of surfactant phospholipid synthesis. In sepsis, bacterial lipopolysaccharide (LPS) triggers the release of TNF-α from alveolar macrophages and alveolar epithelial cells and subsequently initiates an inflammatory cascade leading to diffusive lung injury. TNF-α inhibits PC synthesis via decreasing activity of cytidine triphosphorylate: phosphocholine cytidylyltransferase (CCT), a key rate-limiting enzyme in synthesis of PC. Our aim is to find out the mechanisms by which iNO alone or iNO plus hyperoxia affect PC de novo synthesis and its relation to the lung inflammatory injury.Objectives1. To explore safety and efficacy of iNO and/or hyperoxia in mature lungs with inflammatory injury in association with de novo synthesis and secretion of phosphatidylcholine (PC).2. To determine function and expression of cytidine triphosphorylate: phosphocholine cytidylyltransferase (CCT), a key rate-limiting enzyme in synthesis of PC, and influence of iNO and hyperoxia on CCT.3. Interaction between iNO and/or hyperoxia and lung inflammation in association with synthesis of PC.MethodsAdult male SD rats (clean conventional rats, 180~200 g) were used to induce lung inflammatory injury with bolus LPS (2 mg/kg, i.v) 24 hours prior to experiment. A saline control group was used with identical manner for comparison. LPS-treated (LPS) and control (C) rats were randomly allocated to subgroups exposed to: air, 95% oxygen (O), 20 ppm iNO (NO), 95% oxygen and 20 ppm iNO (ONO).PC de novo synthesis and secretion was determined by measurement of incorporated [3H]-choline chloride into PC. Each rat was injected intravenously with 15 μCi [3H]-choline chloride followed by exposure to various gases. They were sacrificed at 10 min, 4, 8, 12 and 24 hours after the exposure (n = 6~8). The radioactivity of 3H incorporated into total phospholipid (TPL) and disaturated phosphatidylcholine (DSPC) was measured in bronchoalveolar lavage fluid (BALF) and lung tissue (LT, after lavage) Pool size of PC was also measured in both BALF and LT.In a separate cohort study, rats were exposed for 4 and 24 hours in the same protocol of gas exposure. Eight or six rats in each subgroup we... |
PDF Full Text Request