P3829Antiarrhythmic effects of Sacubitrilat (LBQ657) on Ca2+ homeostasis in ventricular cardiomyocytes

Background and objectives

Simultaneous inhibition of neprilysin and angiotensin II receptors by sacubitril/valsartan was shown to significantly reduce morbidity and mortality in heart failure patients compared to sole interference with the renin angiotensin system. Beneficial effects of increased levels of natriuretic peptides following neprilysin inhibition have been suggested, whereas direct effects of sacubitrilat on myocardial Ca2+ cycling properties remain elusive.

Methods and results

Under basal conditions the combination of active neprilysin-inhibitior sacubitrilat (LBQ657) and angiotensin II receptor inhibitor valsartan did not influence diastolic Ca2+ spark frequency (CaSpF) nor arrhythmogenic SR Ca2+ leak in murine ventricular cardiomyocytes (confocal microscopy, n CMs/hearts=80/7 vs. 100/7, P=0.91/0.99). In contrast, sacubitrilat/valsartan treatment significanty reduced CaSpF by 35±9% and SR Ca2+ leak by 45±9% in CMs that had been put under catecholaminergic stress (isoproterenol 10nM, n=81/7 vs. 62/7, P<0.001 both). This effect could be clearly be attributed to the neprilysin inhibitor sacubitrilat as sole sacubitrilat treatment also reduced both parameters by similar degrees (reduction of CaSpF by 57±7% and SR Ca2+ leak by 76±5%; n=101/4 vs. 108/4, P<0.01 both) whereas sole valsartan treatment did not affect diastolic SR Ca2+ leak. Of note, systolic Ca2+ release, SR Ca2+ load and Ca2+ transient kinetics of murine CMs were not compromised upon treatment with sacubitrilat (epifluorescence microscopy, n=41/6 vs. 39/6). Importantly, sacubitrilat/valsartan in combination as well as sacubitrilat alone also reduced diastolic CaSpF and SR Ca2+ leak by 40–74% in human left-ventricular CMs from patients with end-stage heart failure (n=71/8 vs. 78/8, P<0.05).

Conclusion

This study demonstrates that neprilysin-inhibition directly exerts beneficial effects on Ca2+ homeostasis in human heart failure. We can show for the first time that neprilysin-inhibition by sacubitrilat yields a strong reduction of arrhythmogenic SR Ca2+ leak without affecting systolic Ca2+ release. These effects might contribute to the mortality benefit of sacubitril/valsartan treatment in the PARADIGM Study.

Acknowledgement/Funding

THF was funded by the Deutsche Forschungsgemeinschaft (DFG) through the SFB 1002 (A11). SS is supported by the Marga und Walter Boll-Stiftung.

Autoantibodies from patients with coeliac disease recognize distinct functional domains of the autoantigen tissue transglutaminase

The enzyme tissue transglutaminase (tTG) has been recently identified to represent a highly sensitive and specific target of autoantibodies in coeliac disease. To characterize autoantigenic epitopes, we generated novel tTG deletion mutants by polymerase chain reaction, produced radiolabelled fragments by in vitro transcription/translation, immunoprecipitated the mutants using sera from patients with coeliac disease, and related the binding data with putative structural and functional domains of human tTG. We show that tTG antibody positive sera display a heterogeneous autoantibody response covering distinct regions of the molecule. The N-terminal and C-terminal third of tTG, comprising amino acid (aa) 1-281 and aa 473-687, harbour the dominant epitopes (67.4% and 69.4% positive), whereas the catalytic region is of minor antigenicity (22.5% positive). Autoantibodies directed to one, two and three domains were observed in 36.7%, 28.6% and 22.4% of patients, respectively. Comparative analysis revealed the presence of strictly conformational epitopes which were dependent on the N-terminus (aa 1-12) or the intact beta-barrel domains in the C-terminus (aa 473-497, aa 649-687). In conclusion, we here demonstrate for the first time that the humoral autoimmunity is directed against distinct functional tTG domains. The spectrum of autoantibodies indicates that the native folded protein may be the target of autoantibodies.

Isolation and structural elucidation of urinary metabolites of ciprofloxacin

After oral administration of 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-piperazine-1-ylquinoline++ +-3-carboxylic acid (ciprofloxacin, Bay o 9867; designated trademark: Ciprobay) four metabolites M1-M4 were isolated from human urine by Craig counter current distribution and semipreparative high-performance liquid chromatography. Their molecular structures were elucidated by nuclear magnetic resonance and mass spectrometry and confirmed by comparing their spectra with those of authentic synthetic reference compounds.

Etofenamate fatty acid asters. An example of a new route of drug metabolism

Etofenamate [2-(2-hydroxyethoxy)ethyl-N-(alpha, alpha, alpha-trifluoro-m-tolyl)-anthranilate] was administered to dogs by the oral route. Minor amounts of etofenamate (Eto) and its glucuronide were found in urine and feces. The main portion of metabolites was eliminated as flufenamic acid (Flu) and hydroxy derivatives of Eto and Flu. Furthermore, a highly lipophilic fraction was isolated (extraction and TLC) and further separated into several compounds (HPLC, GLC). These metabolites were identified as Eto oleate, palmitate, linoleate, stearate, palmitoleate, myristate, and laurate by NMR and MS. The structures were confirmed by comparison with authentic material. The conjugation of etofenamate with fatty acids is an example of a new route of drug metabolism.