Hydrogen sulfide contributes to hypoxic inhibition of airway transepithelial sodium absorption

Abstract

In lung epithelial cells, hypoxia decreases the expression and activity of sodium-transporting molecules, thereby reducing the rate of transepithelial sodium absorption. The mechanisms underlying the sensing of hypoxia and subsequent coupling to sodium-transporting molecules remain unclear. Hydrogen sulfide (H2S) has recently been recognized as a cellular signaling molecule whose intracellular concentrations critically depend on oxygen levels. Therefore, it was questioned whether endogenously produced H2S contributes to hypoxic inhibition of sodium transport. In electrophysiological Ussing chamber experiments, hypoxia was established by decreasing oxygen concentrations in the chambers. Hypoxia concentration dependently and reversibly decreased amiloride-sensitive sodium absorption by cultured H441 monolayers and freshly dissected porcine tracheal epithelia due to inhibition of basolateral Na(+)/K(+)-ATPase. Exogenous application of H2S by the sulfur salt Na2S mimicked the effect of hypoxia and inhibited amiloride-sensitive sodium absorption by both tissues in an oxygen-dependent manner. Hypoxia increased intracellular concentrations of H2S and decreased the concentration of polysulfides. Pretreatment with the cystathionine-γ-lyase inhibitor d/l-propargylglycine (PAG) decreased hypoxic inhibition of sodium transport by H441 monolayers, whereas inhibition of cystathionine-β-synthase (with aminooxy-acetic acid; AOAA) or 3-mercaptopyruvate sulfurtransferase (with aspartate) had no effect. Inhibition of all of these H2S-generating enzymes with a combination of AOAA, PAG, and aspartate decreased the hypoxic inhibition of sodium transport by H441 cells and pig tracheae and decreased H2S production by tracheae. These data suggest that airway epithelial cells endogenously produce H2S during hypoxia, and this contributes to hypoxic inhibition of transepithelial sodium absorption.

International Union of Basic and Clinical Pharmacology. CII: Pharmacological Modulation of H2S Levels: H2S Donors and H2S Biosynthesis Inhibitors

“…The IC 50 for PAG using purified CSE and cysteine as a substrate in two different studies was reported to be 40 (Asimakopoulou et al, 2013) and 20 mΜ (Sun et al, 2009), whereas that of BCA was shown to be 14 mΜ (Asimakopoulou et al, 2013). However, these compounds are typically used at much higher concentrations (1-10 mM) to block H 2 S production in cell-based assays, suggesting that they poorly cross the cell membrane (Pan et al, 2006;Brancaleone et al, 2008;Bucci et al, 2009;Papapetropoulos et al, 2009;Schleifenbaum et al, 2010;Wang et al, 2013a,b;Lee et al, 2014a;Potenza et al, 2014;Martinez-Cutillas et al, 2015;Testai et al, 2015;Tsai et al, 2015a;Yang et al, 2015;Krause et al, 2016). A significant difference between the PAG and BCA is that the former has an irreversible mode of action, acting as a suicide inhibitor (Abeles and Walsh, 1973;Steegborn et al, 1999).…”

“…Taken together, although various screening efforts have identified many different CBS inhibitors, for most pharmacological studies (both in vitro and in vivo) AOAA remains the compound of choice; it has been used in a large number of publications over the last decade. The basic physiological papers include mechanistic studies investigating the role of endogenous H 2 S on various channels and cellular processes (e.g., Donovan et al, 2011;Gil et al, 2011;Roy et al, 2012;Martinez-Cutillas et al, 2015;Rios et al, 2015;Xiao et al, 2015;Krause et al, 2016;Liu et al, 2016d;Rios et al, 2016;Yan et al, 2016;Yetik-Anacak et al, 2016). Many of these reports are in the area of cancer, where they show the antiproliferative effects of this compound and as additive or synergistic antitumor effects in combination with various chemotherapeutic agents (Szabo et al, 2013;Bhattacharyya et al, 2013;Módis et al, 2014b;Szczesny et al, 2016).…”

Endogenous Hydrogen Sulfide Contributes to Tone Generation in Porcine Lower Esophageal Sphincter Via Na+/Ca2+ Exchanger

“… 34 , 38 It was reported that H 2 S inhibited the Na + /K + -ATPase function and increased [Na + ] i in lung epithelial cells and renal tubular epithelial cells. 39 , 40 Increasing the [Na + ] i inhibits the forward mode activity of NCX, resulting in an increase in the net Ca 2+ inflow. Therefore, endogenous H 2 S may inhibit Na + /K + -ATPase, thereby indirectly potentiating the reverse mode of NCX ( Figure 7 ).…”

Biological Effects of Thermal Water-Associated Hydrogen Sulfide on Human Airways and Associated Immune Cells: Implications for Respiratory Diseases

“…These findings corroborate the hypothesis that H 2 S may act as a cellular oxygen sensor (42). Indeed, the decrease in H 2 S oxidation under hypoxic conditions has been associated with the production of significant amounts of H 2 S by airway epithelial cells (AECs) (43), akin to production via reduction of preexisting sulfites in mitochondria (44). Fu et al suggested that this occurs as a result of CSE enzyme translocation to mitochondria, thereby allowing H 2 S synthesis even after a stress-inducing stimulus, such as hypoxia (45).…”

“…This leads to an increase in mucociliary clearance, and therefore the elimination of foreign microorganisms can be more effective (43). Krause et al also proposed that inhibition of transepithelial sodium absorption (via inhibition of Na + /K + -ATPase) is favored under acute hypoxia, in order to avoid H 2 S degradation, as well as exogenous H 2 S exposure (43).…”