Pharmacological Inhibition of Cathepsin S Suppresses Abdominal Aortic Aneurysm in Mice

Abstract

Evidence suggests that cathepsin S (CTSS), a potent mammalian elastase, participates in abdominal aortic aneurysm (AAA) formation. This study examines the hypothesis that pharmacological inhibition of CTSS with an α-ketoamide based compound 6r might suppress AAA in mice. Experimental study of the CaCl2 induced AAA model in B6 mice and angiotensin II (AngII) infused AAA model in ApoE-/- mice. The effects of intraperitoneal administration of 6r (25mg/kg) and vehicle every three days since one day after AAA induction were evaluated at 28 days using CaCl2 induced (n=12 per group) and AngII infused (n=8 per group) models. Additionally, the effects of post-treatment with 6r and vehicle from seven days or 14 days after AAA induction were evaluated at 28 days using the CaCl2 induced model (n=6 per group). Aortic samples were harvested for histological and biochemical analyses, including cathepsin levels, Verhoeff Van Gieson staining, TUNEL assay, and immunostaining for macrophages. In the CaCl2 induced model, treatment with 6r suppressed aortic dilatation observed in vehicle treated controls (median: 0.58 vs. 0.92mm; p<.001), along with reduced CTSS and cathepsin K (CTSK) levels (both p<.001), preserved elastin integrity (p<.001), fewer medial apoptotic cells (p=.012) and less macrophage infiltration (p=.041). In the AngII infused model, the aortic diameter was smaller in 6r treated mice than in vehicle treated controls (median: 0.95 vs. 1.84mm; p=.047). The levels of CTSS (p<.001) and CTSK (p=.033) and the numbers of elastin breaks (p<.001), medial apoptotic cells (p<.001) and infiltrating macrophages (p=.030) were attenuated under 6r treatment. Finally, post-treatment with 6r from seven days (p=.046) or 14 days (p=.012) after AAA induction limited CaCl2 induced AAA. Pharmacological inhibition of CTSS by 6r suppresses AAA formation in mice. Also, post-treatment with 6r retards mouse AAA progression. These findings provide proof of concept validation for CTSS as a potential therapeutic target in AAA.