Pro-Resolving Mediator Resolvin E1 Restores Alveolar Fluid Clearance in Acute Respiratory Distress Syndrome.

ABSTRACT: Acute respiratory distress syndrome (ARDS) is a life-threatening condition characterized by increased permeability of the alveolar-capillary barrier and impaired alveolar fluid clearance. Resolvin E1 (RvE1) is a specialized pro-resolving mediator derived endogenously from omega-3-polyunsaturated fatty acids. RvE1 (10 µg/kg i.v.) was injected to rats 6 h post-lipopolysaccharide (LPS) (14 mg/kg) induction. After another 3 h, alveolar fluid clearance was measured in live rats (n = 8-9). The primary Type II alveolar epithelial cell was isolated and treated by LPS (1 µg/mL) with or without RvE1 (250 nM). The expression of epithelial sodium channel (ENaC), Na+/K+-ATPase (NKA), AKT, serum- and glucocorticoid-induced kinase 1 (SGK1), and Nedd4-2 were detected. RvE1 improved survival rate (30% vs. 70%, P = 0.048), increased the clearance of alveolar fluid (13.34% vs. 18.73%, P  < 0.001), reduced lung wet-dry weight ratio (5.01 vs. 4.63, P  < 0.001), mitigated lung injury scores (13.38 vs. 7.0, P  < 0.05) and inflammation in LPS-induced ARDS in rats. RvE1 upregulated alveolar ENaC and NKA expression in vivo and in vitro. In addition, RvE1 significantly increased the expression of phosphorylated AKT, SGK1, and phosphorylated Nedd4-2 in LPS-stimulated primary alveolar type II cells. The effects of RvE1 were abrogated by blocking phosphatidylinositide3'-kinase (PI3K) and SGK1 with LY294002 and GSK650394, respectively. In summary, RvE1 upregulated ENaC and NKA expression by activating PI3K/AKT/SGK1 pathway to promote alveolar fluid clearance, suggesting that RvE1 may be a potentially effective drug for ARDS treatment.

Effects of ouabain on human bronchial muscle in vitro.

The effects of ouabain, an inhibitor of the plasmalemmal Na(+)/K(+)-ATPase activity, were examined in human isolated bronchus. Ouabain produced concentration-dependent contraction with -logEC(50)=7.16+/-0.11 and maximal effect of 67+/-4% of the response to acetylcholine (1 mM). Ouabain (10 microM)-induced contraction was epithelium-independent and was not depressed by inhibitors of cyclooxygenase and lipoxygenase, antagonists of muscarinic, histamine H(1)-receptors and alpha-adrenoceptors, or neuronal Na(+) channel blockade. The inhibition of ouabain contraction in tissues bathed in K(+)-free medium, and the inhibition by ouabain of the K(+)-induced relaxation confirm that the contractile action of ouabain is mediated by inhibition of Na(+)/K(+)-ATPase. Furthermore, depolarization (16.4+/-0.9 mV) was observed in human isolated bronchus by intracellular microelectrode recording. Ouabain (10 microM)-induced contractions were abolished by a Ca(2+)-free solution but not by blockers of L-type Ca(2+) channels. In human cultured bronchial smooth muscle cells, ouabain (10 microM) produced a sustained increase in [Ca(2+)](i) (116+/-26 nM) abolished in Ca(2+)-free medium. Incubation with a Na(+)-free medium or amiloride (0.1 mM) markedly inhibited the spasmogenic effect of ouabain thus suggesting the role of Na(+)/Ca(2+) exchange in ouabain contraction while selective inhibitors of Na(+)/H(+)-antiport, Na(+)/K(+)/Cl(-)-antiport, or protein kinase C had no effect. Ouabain (10 microM) failed to increase inositol phosphate accumulation in human bronchus. Ouabain (10 microM) did not alter bronchial responsiveness to acetylcholine or histamine but inhibited the relaxant effects of isoprenaline, forskolin, levcromakalim, or sodium nitroprusside. These results indicate that ouabain acts directly to produce contraction of human airway smooth muscle that depends on extracellular Ca(2+) entry unrelated to L-type channels and involving the Na(+)/Ca(2+)-antiporter.

Na+, K(+)-ATPase inhibition and intracellular electrolyte content in essential and secondary hypertension.

A crucial role of humoral factors in the pathogenesis of primary hypertension is discussed. In 1982 Hamlyn et al demonstrated the presence of a Na+, K(+)-ATPase inhibitor in the plasma of essential hypertensives and showed a significant correlation of the Na+, K(+)-ATPase inhibition with the blood pressure. In this study we examined whether an Na+, K(+)-ATPase inhibitor could be found in the blood of essential hypertensives as compared to patients with secondary hypertension (renal hypertension, renal artery stenosis, pheochromocytoma). Second, the possible correlation between an inhibition of Na+, K(+)-ATPase and the intracellular electrolyte composition was examined. The results demonstrate a similar reduction of Na+, K(+)-ATPase inhibition in both essential hypertensives and secondary hypertensives as compared to normotensive controls. Further, the intracellular electrolyte composition (Na+, Na; K+, Ca) does not show a significant correlation to the degree of Na+, K(+)-ATPase inhibition, whereas a significant correlation between the degree of Na+, K(+)-ATPase inhibition and intracellular Cl- concentration could be demonstrated. The present study shows that an endogenous Na+, K(+)-ATPase inhibitor is also present in secondary forms of hypertension, thus implying that a specific role in the pathogenesis of primary hypertension for an Na+, K(+)-inhibitor is unlikely.