Diltiazem prevents stress‐induced contractile deficits in cardiomyocytes, but does not reverse the cardiomyopathy phenotype in Mybpc3‐knock‐in mice

Abstract

Left ventricular hypertrophy, diastolic dysfunction and fibrosis are the main features of hypertrophic cardiomyopathy (HCM). Guidelines recommend β-adrenoceptor or Ca channel antagonists as pharmacological treatment. The Ca channel blocker diltiazem recently showed promising beneficial effects in pre-clinical HCM, particularly in patients carrying MYBPC3 mutations. In the present study we evaluated whether diltiazem could ameliorate or reverse the disease phenotype in cells and in vivo in an Mybpc3-targeted knock-in (KI) mouse model of HCM. Sarcomere shortening and Ca transients were measured in KI and wild-type (WT) cardiomyocytes in basal conditions (1-Hz pacing) and under stress conditions (30 nm isoprenaline, 5-Hz pacing) with or without pre-treatment with 1 μm diltiazem. KI cardiomyocytes exhibited lower diastolic sarcomere length (dSL) at baseline, a tendency to a stronger positive inotropic response to isoprenaline than WT, a marked reduction of dSL and a tendency towards arrhythmias under stress conditions. Pre-treatment of cardiomyocytes with 1 μm diltiazem reduced the drop in dSL and arrhythmia frequency in KI, and attenuated the positive inotropic effect of isoprenaline. Furthermore, diltiazem reduced the contraction amplitude at 5 Hz but did not affect diastolic Ca load and Ca transient amplitude. Six months of diltiazem treatment of KI mice did not reverse cardiac hypertrophy and dysfunction, activation of the fetal gene program or fibrosis. In conclusion, diltiazem blunted the response to isoprenaline in WT and KI cardiomyocytes and improved diastolic relaxation under stress conditions in KI cardiomyocytes. This beneficial effect of diltiazem in cells did not translate in therapeutic efficacy when applied chronically in KI mice.

Extracellular Matrix From Hypertrophic Myocardium Provokes Impaired Twitch Dynamics in Healthy Cardiomyocytes

“…When treatment was given after the emergence of detectable pathology, it failed to completely reverse the mechanical effects of disease, although signaling pathways leading to fibrosis were attenuated. This failure to reverse phenotype has also been shown in mouse models of HCM that feature mutations to MYBPC3 (30). In that study, treatment with the calcium-channel blocker diltiazem was performed on 2-month-old mice with a preexisting cardiac disease phenotype.…”

Nebivolol Desensitizes Myofilaments of a Hypertrophic Cardiomyopathy Mouse Model

“…The Mybpc3 KI cardiomyopathy mouse model was generated by the targeted insertion of a G>A transition on the last nucleotide of exon 6 (Vignier et al, 2009 ; Fraysse et al, 2012 ; Schlossarek et al, 2012 , 2014 ; Gedicke-Hornung et al, 2013 ; Mearini et al, 2013 , 2014 ; Stohr et al, 2013 ; Friedrich et al, 2014 ; Najafi et al, 2015 ; Thottakara et al, 2015 ; Flenner et al, 2016 , 2017 ). Mice were maintained on the C57 background.…”

Preventative therapeutic approaches for hypertrophic cardiomyopathy

“…With this, it has been proposed that diltiazem may reduce hypertrophic presentation by normalizing alterations in mitochondrial Ca 2+ concentration, thereby improving cardiac energetics (Semsarian et al 2002). In a recent study, diltiazem was assessed as an HCM therapeutic in homozygous Mybpc3-targeted knock-in (KI) mice carrying a c.772G>A transition on the last nucleotide of exon 6 (Mybpc3 KI (c.772G>A)) (Fraysse et al 2012;Flenner et al 2017). Mybpc3 KI (c.772G>A) mice exhibit increased systolic and diastolic dysfunction and myofilament Ca 2+ sensitivity followed by cardiac hypertrophy (Fraysse et al 2012;Flenner et al 2017).…”