Xenon is an Inhibitor of Tissue-Plasminogen Activator: Adverse and Beneficial Effects in a Rat Model of Thromboembolic Stroke

Abstract

Preclinical evidence in rodents has proven that xenon may be a very promising neuroprotective agent for treating acute ischemic stroke. This has led to the general thinking that clinical trials with xenon could be initiated in acute stroke patients in a next future. However, an unappreciated physicochemical property of xenon has been that this gas also binds to the active site of a series of serine proteases. Because the active site of serine proteases is structurally conserved, we have hypothesized and investigated whether xenon may alter the catalytic efficiency of tissue-type plasminogen activator (tPA), a serine protease that is the only approved therapy for acute ischemic stroke today. Here, using molecular modeling and in vitro and in vivo studies, we show (1) xenon is a tPA inhibitor; (2) intraischemic xenon dose dependently inhibits tPA-induced thrombolysis and subsequent reduction of ischemic brain damage; (3) postischemic xenon virtually suppresses ischemic brain damage and tPA-induced brain hemorrhages and disruption of the blood-brain barrier. Taken together, these data indicate (1) xenon should not be administered before or together with tPA therapy; (2) xenon could be a golden standard for treating acute ischemic stroke if given after tPA-induced reperfusion, with both unique neuroprotective and antiproteolytic (anti-hemorrhaging) properties.

Human Recombinant Tissue-Plasminogen Activator (Alteplase): Why Not Use the ‘Human’ Dose for Stroke Studies in Rats?

“…Particularly, using 0.9 mg/kg rtPA could be of major importance for pharmacological considerations. For instance, in line with previous data that have demonstrated that the noble gas xenon binds within the catalytic site of a series of serine proteases (Schiltz et al, 1995), recent data from our laboratory have shown that xenon, which possesses neuroprotective properties (David et al, 2003(David et al, , 2008Homi et al, 2003), also inhibits the catalytic (enzymatic) and thrombolytic activity of rtPA (David et al, 2010). As medical gases such as xenon cannot be used at concentrations above 75 to 80 vol% (as at least 20 vol% oxygen is required to maintain normal body oxygenation), it appears of critical importance to use the clinical dose of 0.9 mg/kg rtPA to avoid the presence of rtPA molecules free of xenon as it would occur if rtPA would be given in excess at 10 mg/ kg.…”

Protein-Noble Gas Interactions Investigated by Crystallography on Three Enzymes - Implication on Anesthesia and Neuroprotection Mechanisms

“…Tissue-type plasminogen activator (tPA), the only approved treatment for thrombolysis after an ischemic stroke, is also a serine protease. As in the case of elastase, xenon inhibited tPA enzymatic activity (David et al, 2010). This inhibition is likely to be a direct inhibition with xenon binding directly in the S1 pocket in the active site of tPA.…”

“…However, xenon and nitrous oxide inhibit tPA-induced thrombolysis, preventing their use during the intra-ischemic period. When administrated after the reperfusion, xenon has beneficial effect by suppressing ischemic brain damage and tPA-induced brain hemorrhages Protein-Noble Gas Interactions Investigated by Crystallography on Three Enzymes -Implication on Anesthesia and Neuroprotection Mechanisms 287 (David et al, 2010) while nitrous oxide reduces ischemic brain damage but increases tPAinduced brain hemorrages (Haelewyn et al, 2011). Xenon is thus a very promising neuroprotective drug with few or no adverse side effects in models of acute ischemic stroke or perinatal hypoxia-ischemia (Homi et al, 2003;Ma et al, 2003;Abraini et al, 2005;David et al, 2008;Luo et al, 2008).…”

Interactions between Nitrous Oxide and Tissue Plasminogen Activator in a Rat Model of Thromboembolic Stroke

“…Each tube containing 0.4 M tPA or 10 M tPA substrate was saturated for 20 min at a flow rate of 60 -80 ml/min with nitrous oxide of 25-75 vol% or medical air composed of 25% oxygen and 75% nitrogen as described previously. 29 We assessed the catalytic efficiency of human and murine tPA (N ϭ 3, n ϭ 12, per concentration) in the presence of air or nitrous oxide by incubating 50 l tPA with 50 l substrate at 37°C using a spectrofluorometer microplate reader.…”

“…However, a recent study performed in a rat model of thromboembolic stroke has shown that xenon inhibits tPA by binding directly within its catalytic site, thereby producing adverse effects by reducing tPA-induced thrombolysis and, as a consequence, thrombolysis-induced reduction of brain damage when administered during the intraischemic period and beneficial effects by suppressing both ischemic brain damage and recombinant tPA-induced brain hemorrhages and disruption of the blood-brain barrier when given after reperfusion. 29 Because nitrous oxide shares pharmacologic and neuroprotective properties similar to that of xenon in excitotoxic-ischemic models, 14,[21][22][23] we hypothesized that nitrous oxide may modulate the catalytic efficiency of tPA and thereby alter the beneficial and/or adverse effects of recombinant tPA therapy in a rat model of thromboembolic ischemia.…”