Abstract 119: Protective Effects of Chloroquine on Ischemic and Nutrient Depleted Muscle are Mediated by HMGB1 and Caspase-1

Abstract

Introduction: Millions of Americans are at risk for amputation from severe peripheral arterial disease (PAD) when surgery is not possible. Pro-regenerative and angiogenic agents may improve outcome in that setting. Chloroquine (CQ) promotes wound healing in scleroderma but has not been tested in PAD. CQ promotes healing of ischemic muscle, increases muscle high mobility group box 1 (HMGB1), an inflammatory, pro-angiogenic protein, and activates caspase-1 in myoblasts. We hypothesize that HMGB1 mediates protective effects of CQ and is regulated by caspase-1 in muscle. Controlled rather than indiscriminate release of HMGB1 from damaged muscle may be protective during ischemia. Methods: C2C12 myoblasts in low serum were treated with CQ (0-50μM) ± Ac-YVAD-cmk (10 μg/ml), a caspase-1 inhibitor. HMGB1 release in supernatants was measured using ELISA. Cytotoxicity was assessed by comparing spontaneous lactate dehydrogenase (LDH) activity in culture media from control, treated and maximally lysed cells. CQ (50μg/ml) or placebo treated wild-type and inducible HMGB1 knockout (iHMGB1KO) mice underwent unilateral femoral artery ligation (FAL). Laser Doppler perfusion imaging (LDPI) before and 1,7,14 and 21d after FAL was reported as % improvement over time. ANOVA was used to assess statistical significance among groups. Results: CQ (5-10uM) attenuated spontaneous LDH leak after 12h from serum-depleted myoblasts (p <0.01, N=3), and modestly increased HMGB1 release (p <0.001, N=3). Ac-YVAD-cmk reversed the cytoprotective effects of CQ, significantly raising both LDH activity to 55% of maximal activity and HMGB1 in the supernatant. Compared to d1 post FAL, CQ improved perfusion recovery in WT mice by 300-800% over 21 days (p<0.03, N=7/group), but not in iHMGB1KO mice. Conclusion: We present the novel finding that in nutrient-depleted myoblasts, caspase-1 mediates the survival benefits of CQ and regulates HMGB1 release. In turn, HMGB1 is critical for CQ’s beneficial effects on perfusion after FAL, another stress condition. Regulated HMGB1 release may be immunomodulatory, regenerative and modifiable with drugs like CQ. Altering survival and inflammatory pathways through CQ may present a novel therapeutic strategy in PAD.