Lodelaben (SC-39026)

SC-39026, a serine elastase inhibitor, prevents muscularization of peripheral arteries, suggesting a mechanism of monocrotaline-induced pulmonary hypertension in rats

In rats injected with the toxin monocrotaline, altered synthesis and distribution of pulmonary artery elastin suggest that increased elastase activity may be important in the development of vascular changes and progressive pulmonary hypertension. To test this hypothesis, male Sprague-Dawley rats (250-300 g) were given 40 mg/kg of the elastase inhibitor SC-39026 in a carboxymethylcellulose vehicle or vehicle only by gavage, 12 hours before and twice daily for 8 days after a single subcutaneous injection of either monocrotaline (60 mg/kg) or saline. Thirteen days after injection, indwelling cardiovascular catheters were inserted under pentobarbital anesthesia, and at 15 days after injection, pulmonary and systemic hemodynamic measurements were recorded with the animals awake. At post-mortem examination, the lungs were perfused and morphometric techniques applied for light and electron microscopic evaluation. Saline-injected rats given either SC-39026 or vehicle were similar in all features assessed. In contrast, monocrotaline-injected rats given SC-39026 had significantly lower mean pulmonary artery pressure than those given vehicle (21.0 +/- 1.6 vs. 27.5 +/- 0.8 mm Hg, p less than 0.05), and this correlated with a significant reduction in the number of abnormally muscularized arteries at alveolar wall level (r2 = 0.89, p less than 0.001). SC-39026 did not significantly reduce monocrotaline-induced medial hypertrophy of muscular arteries, endothelial injury, and associated subendothelial edema; nor was there a significant increase in the proportion of the medial elastin, although a trend was apparent. Additional groups of monocrotaline injected rats were followed 3 weeks after injection, but both SC-39026 and vehicle-treated rats were similar at this point. Our data suggest that increased serine elastase activity associated with endothelial injury may mediate early abnormal pulmonary vascular smooth muscle differentiation resulting in muscularization of normally nonmuscular peripheral arteries and pulmonary hypertension induced in rats by injection of the toxin monocrotaline. Lack of persistence of this protective effect suggests that there may be continued elastase activity in this model. Failure to inhibit medial hypertrophy with SC-39026 suggests that a different mechanism or a different elastase may be involved in this structural change.

SC-39026, a specific human neutrophil elastase inhibitor

SC-39026, (+/-) 2-chloro-4-(1-hydroxyoctadecyl)benzoic acid, inhibits human neutrophil elastase with an IC50 of 0.5 microM (KI of 1.5 microM). Its inhibition of elastase is reversible and noncompetitive at low concentrations (0.5-1.25 microM). Inhibition is "mixed" at higher inhibitor concentrations. SC-39026 is inactive against hog pancreatic elastase, bovine alpha-chymotrypsin and Pseudomonas aeruginosa elastase, but does inhibit human neutrophil cathepsin G with an IC50 of approximately 2.5 microM. Neutrophil elastases isolated from rat, hamster, rabbit and hog are also inhibited by SC-39026.

Neutrophil elastase inhibitors, SC-37698 and SC-39026, reduce endotoxin-induced lung dysfunction in awake sheep

Neutrophils have been implicated as important cellular mediators of the pulmonary dysfunction observed following endotoxemia in chronically instrumented awake sheep. Several areas of research suggest that neutrophil-derived proteases may be mediators of this dysfunction. We hypothesized that neutrophil elastase inhibitors would attenuate the effects of endotoxemia in sheep. To test this hypothesis, we studied the effects of two putative neutrophil elastase inhibitors, SC-37698 and SC-39026 (Searle, Skokie, IL), on endotoxin-induced lung dysfunction in awake sheep. Sheep were given intravenous neutrophil elastase inhibitor alone (20 mg/kg/h for 6 h), intravenous endotoxin (E. coli endotoxin, 0.5 microgram/kg over 20 min) 1 h after beginning the 6-h infusion of elastase inhibitor, or endotoxin 1 h after beginning a 6-h infusion of elastase inhibitor vehicle. SC-37698 attenuated the increase in lung lymph flow and lung lymph protein clearance, the alterations in lung mechanics, and the fall in white blood count. Qualitatively similar effects were seen with SC-39026. These data suggest the need for further research examining the role of protease-antiprotease interactions and the potential utility of neutrophil elastase inhibitors in acute lung injury like that observed in the adult respiratory distress syndrome (ARDS) in the human.

Chronic hypoxic pulmonary hypertension in rats and increased elastolytic activity

Previously in rats injected with the toxin monocrotaline and administered SC-39026, a serine elastase inhibitor, pulmonary hypertension was decreased in association with reduced muscularization of peripheral pulmonary arteries. To determine whether inhibition of elastolytic activity might prevent this vascular change in other conditions producing pulmonary hypertension, we administered SC-39026 to rats during a 10-day exposure to chronic hypobaric hypoxia. We also measured elastolytic activity in the central pulmonary arteries of rats using [3H]elastin substrate and determined whether there was an increase in activity either as early as 2 days or at completion of the hypoxic exposure, which could be inhibited by SC-39026. to further determine whether the mechanism of muscularization of peripheral arteries is modulated by degradation of elastin or other elastase-susceptible extracellular matrix proteins, we assessed desmosine excretion and ultrastructural alterations in elastin as well as in type IV collagen, fibronectin, and laminin. SC-39026 reduced the number of muscularized arteries and the level of pulmonary arterial pressure during exposure to chronic hypoxia. Elastolytic activity was fourfold higher in central pulmonary arteries 2 days after hypoxia when compared with values in control vessels, and the activity was inhibited by SC-39026. In small peripheral pulmonary arteries there were no significant changes with hypoxia reflected in desmosines or in the immunocytochemistry of elastase-susceptible glycoproteins, with the exception of decreased laminin. This feature was not inhibited by SC-39026. To further assess whether the protective effect of SC-39026 was related to its inhibition of elastase, an extended study was carried out using a different elastase inhibitor, alpha 1-proteinase inhibitor. An even greater reduction in hypoxia-induced pulmonary hypertension and vascular changes was observed with this elastase inhibitor and the latter included medial hypertrophy.

Monocrotaline-induced cardiopulmonary injury in rats. Modification by the neutrophil elastase inhibitor SC39026

Rats were killed after 6 weeks of continuous ingestion of the pneumotoxic alkaloid monocrotaline (2.2 mg/kg/day), the neutrophil elastase inhibitor SC39026 (60 mg/kg/day), or both. Pulmonary reactions were evaluated by light and electron microscopy. Lung endothelial function was monitored by angiotensin converting enzyme (ACE) activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. Lung hydroxyproline content was measured as an index of interstitial fibrosis. Cardiac right ventricular hypertrophy was determined by the right ventricle to the left ventricle plus septum weight ratio (RV/LV + S). Rats receiving SC39026 alone did not differ significantly from untreated control animals with respect to any of the quantitative endpoints, although rarefaction of Type I pneumocytes was observed in the electron micrographs of these animals. Monocrotaline-treated rats, in contrast, developed a significant increase in RV/LV + S, and exhibited pulmonary edema, inflammation, fibrosis, and muscularization and occlusive mural thickening of the pulmonary small arteries and arterioles. These monocrotaline-induced structural changes were accompanied by decreased lung ACE and PLA activities, and increased PGI2 and TXA2 production, and by an increase in lung hydroxyproline content. Cotreatment with SC39026 ameliorated the monocrotaline-induced pulmonary vascular wall thickening and the cardiac right ventricular hypertrophy. These data suggest that inappropriate neutrophil elastase activity contributes to monocrotaline pulmonary vasculopathy and hypertension. On the other hand, cotreatment with SC39026 had no significant effect on the severity of the monocrotaline-induced lung inflammatory reaction, the pulmonary endothelial dysfunction, or the increase in lung hydroxyproline content.