Cardiac Energy Metabolism In Patients With Arrhythmogenic Right Ventricular Cardiomyopathy/dysplasia Compared To Those With Dilated Cardiomyopathy And Healthy Controls

BACKGROUND Arrhythmogenic right ventricular cardiomyopathy/dysplasia(ARVC/D)is characterized by fibrofatty replacement of the right ventricle.Arrhythmias and dysfunction of right ventricle are the prominent clinical manifestation.Compared to other cardiomyopathies,ARVC/D has a predilection for the right ventricle,with the left ventricle less affected.The pathogenesis of ARVC/D is associated with disorders in lipid metabolism.However,the myocardial glucose utilization,amino acid metabolism,TCA cycle,oxidative stress of ARVC/D,and the correlation between myocardial metabolic remodeling and right ventricle involvement of ARVC/D remain incompletely understood.OBJECTIVE The purpose of this study was to assess cardiac energy metabolism alterations in both ventricles of ARVC/D,and to analyse the pathogenesis of arrhythmias and dysfunction of right ventricle from metabolic point of view,which could provide new clues for the therapy of this cardiomyopathy.METHODS Myocardial fibrosis and myocyte volume were observed by Masson's trichrome staining and analyzed by using the software Image-Pro Plus(IPP).Myocardial lipid droplets deposition was observed by transmission electron microscopy.The mRNA level of brain natriuretic peptide(BNP)were detected by qPCR.Correlation analyses between echocardiography parameters(RVD,LVEDD,LVEF)and myocardial gene expression level of BNP were analyzed by Spearman correlation.Myocardial mRNA expression of candidate genes involved in fatty acid utilization,glucose utilization,glutamate metabolism,TCA cycle,and oxidative stress was performed in both ventricles of nonfailing(n = 7),dilated cardiomyopathy(DCM)(n = 8),and ARVC/D(n = 8)samples.Ultra-performance liquid chromatography tandem mass spectrometry(UPLC-MS)-based metabolomics was conducted in both ventricles of ARVC/D(n = 26)samples.Relative quantification of mtDNA copy numbers was determined by using a human mitochondrial DNA(mtDNA)monitoring kit.Myocyte apoptosis were detected according to a TUNEL Apoptosis Detection Kit.RESULTS Compared with DCM patients,ARVC/D patients had less severe left ventricular dilatation(49.50±11.30mm vs.65.50±14.50mm,ARVC/D vs.DCM,LVEDD,P<0.001)and left ventricular systolic dysfunction(43.50±19.90%vs.22.00±6.90%,ARVC/D vs.DCM,LVEF,P<0.001),but more severe right ventricular dilatation(43.50±13.00mm vs.27.00±4.30mm,ARVC/D vs.DCM,RVD,P<0.001).Histological examination found that RV of ARVC/D showed increased fibrosis,myofibrillar degeneration,and increased cardiomyocyte size.Lipid droplet deposition in cytoplasm of myocytes were observed in the RV of ARVC/D.The mRNA expression level of BNP in RV of ARVC/D was nearly thirteen-fold higher than that of DCM.There was a positive correlation between BNP expression in RV and RVD in the ARVC/D and DCM groups(r=0.692,P=0.003).The expression level of BNP in the LV showed no difference between ARVC/D and DCM(P=0.247).There was no significant correlation between BNP expression in LV and LVEDD(P=0.122)or LVEF(P=0.138)in the heart failure groups.Compared to healthy controls,the mRNA expression levels of most genes involved in the fatty acid metabolism(SLC27A1,SLC27A6,FABP3,CPT1B,ACADVL,ACADS,PPARA),triacylglycerol turnover(GPAT2,PNPLA2,PLIN5),glucose metabolism(SLC2A4,PFKM,PKM,PDHB),mitochondrial glutamate oxidation(SLC1A5,GLUD1),and TCA cycle(CS)were downregulated or showed a decreased trend in both ventricles of ARVC/D and DCM.Compared to RV of DCM,the mRNA expression levels of most genes involved in the fatty acid metabolism(SLC27A1,SLC27A6,FABP3,CPT1B,ACADVL,ACADS,PPARA),triacylglycerol turnover(GPAT2,PNPLA2,PLIN5),glucose metabolism(SLC2A4,PFKM,PKM,PDHB),and TCA cycle(CS)were downregulated or showed a decreased trend in RV of ARVC/D.Compared to LV of DCM,the mRNA expression levels of the above genes showed no significant difference in LV of ARVC/D.However,the downregulation of mRNA expression of genes involved in glutamine-glutamate metabolism(GLS,GLUL,CPS1)and glutathione reductase(GSR)was restricted to the right ventricle of ARVC/D and DCM.Moreover,the level of urea cycle metabolites(arginine,ornithine,citrulline)and glutathione(GSH)in RV of ARVC/D was lower than that of LV(P=0.0013),while the level of oxidized glutathione(GSSG)was higher in RV compared to LV(P=0.0039).Mitochondrial DNA(mtDNA)content in RV of ARVC/D was lower than that of healthy controls(P=0.0013).Apoptosis of residual cardiomyocytes in RV of ARVC/D was observed.CONCLUSION First,there is a global impairment in the utilization of energy substrates(fatty acid,glucose,glutamate)and a reduction in turnover rates of TCA cycle in both ventricles of ARVC/D and DCM.The energy metabolism disorder in RV of ARVC/D is more severe,which is associated with RV dysfunction.Second,dysregulation of glutamine-glutamate metabolism and glutathione metabolism only occur in the RV of ARVC/D,resulting in oxidative stress damage,which may be associated with arrhythmogenesis and myocardial apoptosis in RV of ARVC/D.