Cardiotoxicity in light chain amyloidosis: Insights from the first murine model with intramyocardial injection of patient-derived amyloidogenic light chains

Abstract Background Light chain amyloidosis (AL) is a plasma cell dyscrasia in which cardiac involvement determines the prognosis. Cardiotoxicity of light chains (LCs) complicates the management of heart failure in AL and has not been addressed in the clinical praxis. We have previously genetically identified and biotechnologically produced full-length LCs from patients with AL and cardiac involvement and isotype LCs (WT) from healthy volunteers. We characterized the LCs’ toxicity on primary adult ventricular murine cardiomyocytes (CMs) and our investigation led to the selection of three cardiotoxic and amyloidogenic patient-derived LCs (one from the kappa and two from the lambda family) for further characterization. Purpose We aimed to 1) generate a murine model that recapitulates LCs’ cardiotoxicity in vivo, 2) characterize the mechanism of cardiotoxicity and 3) identify cardioprotective therapies. Methods C57BL6 mice were randomized into 6 groups as follows: 1) PBS (vehicle), 2) WT_kappa, 3) AL_kappa, 4) WT_lambda, 5) AL_lambda1 and 6) AL_lambda2. The animals received the LCs (1 mg/mouse) or vehicle via intramyocardial injection (IMI). Echocardiography evaluation and blood sampling was performed weekly. The animals were sacrificed on the 4th week post IMI for histology, electron microscopy and investigation of the cardiotoxicity mechanism. Results On the 4th week, the AL-lambda LCs significantly reduced the fractional shortening and ejection fraction compared to the vehicle and isotype control groups. The AL_lambda2 also increased mortality of the mice. The AL-kappa did not alter the systolic function of the mice. The circulating lactate dehydrogenase was significantly increased on the 2nd and 4th week in the AL-LCs treated mice indicative of the LCs’ toxicity. The IMI of AL_kappa led to signs of apoptosis including the shrinkage of cardiomyocytes and increased condensation of nuclear chromatin to the nuclear membranes. The IMI of AL_lambda LCs led to increased cardiomyocyte size indicative of hypertrophy, interstitial fibrosis, and increased number of autophagosomes. None of the animals bared amyloid deposits in the heart. The AL-LCs induced different molecular responses in vivo and confirmed the histology findings. The AL-kappa increased apoptosis via the CHOP-Bax pathway, and the ΑL-lambda increased Beclin-1 mediated autophagy without inducing apoptosis. We identified that the common upstream mediator of AL-LCs cardiotoxicity in vivo is the overexpression of the endoplasmic reticulum stress (ERS) markers, IRE-1a and Bip. In vitro, we confirmed that the AL-LCs induce cell death in CMs through ERS. Treatment with the IRE-1a inhibitor STF-083010 and the molecular chaperone tauroursodeoxycholic acid restored the LCs’ induced cardiotoxicity. Conclusions The IMI of AL-LCs stands as a method for the investigation of the LCs cardiotoxicity in vivo in the absence of amyloid deposits via which we identified ERS as a target to alleviate AL-LCs toxicity.