Novel Potential Treatment of Familial Hypertrophic Cardiomyopathy with Analogues of the Green Tea Polyphenol Epigallocatechin-3-Gallate

Mutations in thin filament regulatory proteins that cause hypertrophic cardiomyopathy (HCM) directly alter regulation of cardiac contractility. We have modelled HCM in isolated guinea pig cardiomyocytes by adenoviral expression of human thin filament proteins; in addition to altered contractility, expression of HCM mutants (cTnT R92Q, cTnI R145G and α-TM D175N) results in increased myofilament Ca2+-buffering, leading to altered Ca2+ handling and stimulation of Ca2+-dependent signalling pathways that contribute to HCM pathophysiology. A promising therapeutic approach for correcting these defects is direct desensitisation of myofilament Ca2+ affinity. The green tea catechin, epigallocatechin-3-gallate (EGCg), is known to reduce myofilament Ca2+ binding via interaction with troponin C. We have analysed the effect of EGCg and a panel of analogues on in vitro actomyosin ATPase regulation and myofilament Ca2+ affinity (measured using cTnC labelled with IAANS fluorophore at Cys 35), and on cardiomyocyte contractility and Ca2+ handling. We have found that the parent ECGg compound has poor potency, requiring 30-100 μM to desensitise the myofilament, and suffers from significant off-target effects at lower concentrations (<1 μM) when applied to isolated cardiomyocytes. We have screened several panels of novel compounds and identified at least three catechins with greater efficacy and specificity than the parent compound. They desensitise the myofilament to the same or greater extent than EGCg at 10-100 fold lower concentrations (between 10 and 1 μM). Similar concentrations applied to isolated cardiomyocytes expressing the HCM troponin T mutant R92Q were sufficient to restore normal Ca2+ handling and contractility. This indicates the novel analogues have improved specificity in restoring myofilament Ca2+ buffering compared with the parent compound. This could make them more appealing therapeutically for the treatment of HCM.