Metabolic Remodeling And Effect Of Carvedilol On Left Ventricular Hypertrophy Induced By Pressure Overload In Rats

Background and ObjectivesAll cellular processes are driven by ATP-dependent pathways. The heart has perpetually high energy demands related to the maintenance of specialized cellular processes,including ion transport,sarcomeric function,and intracellular Ca2+ homeostasis. The majority of experimental and clinical studies indicates that the hypertrophied and failing myocardium is characterized by changes in energy, including alterations in high-energy-phosphate content,mitochondrial function and an increased dependence on glucose as substrate,thus the notion of metabolic remodeling is proposed. These metabolic alterations could reflect either an increased energy demand of the cardiac muscle,or compromised capacity to generate sufficient amounts of ATP,or a combination of both. Although the cause-effect relationship between ventricular remodeling and metabolic remodeling is not clearly,it has attracted much attention.ATP is the direct source of energy for all energy-consuming reactions in the heart. Mitochondria provides 95 percent energy for cell activites by oxidative phosphorylation. Since mitochondria are the principal sites of ATP regeneration, limitations in oxygen delivery or intrinsic defects in mitochondrial function,may well be responsible for the observed energetic alterations. Mitochondrial energy production depends on the enzymatic of mitochondrial respiratory chain complexes. Reducing equivalent coming from fatty acidβ-oxidation and the oxidation of carbohydrates through the TCA cycle is transfered from respiratory-chain complexes I to IV, thereby creating a proton electrochemical gradient across the inner mitochondrial membrane. This gradient drives the mitochondrial ATP synthase(ATPase),which produces ATP by phosphorylating ADP. Then ATP is transferred by adenine nucleotide translocase (ANT) out of mitochondria for utilizing by myofibrils. ATPase and ANT represent major cardiac constitutive mitochondrial membrane protein,which combine mitochondrial energy-producing and cytosolic energy-consuming processes. The recent study pay more emphasis on change of substrate utilization during ventricular remodeling,but the key of energy synthesis-mitochondria,is paid less attention. Clinical trials have shown that carvedilol offers a high degree of cardiac protection in patients with congestive heat failure. But little is known about the role of carvedilol on cardiac energy metabolism as yet. The purpose of this paper is to investigate the alteration of metabolic remodeling and effect of carvedilol on left ventricular hypertrophy induced by pressure overload in rats.MethodsMale SD rats ( total number : 78 ) were randomized into 6 groups:coarctation of abdominal aorta group(A5w,A15w group),sham operation group(SH5w,SH15 wgroup) and carvedilol intervention group (B5w,B15w group, 2 mg·kg-1·d-1 ). Hemodynamics and ventriclar remodeling parameters were measured. Mitochondria were isolated by centrifugation. The size of adenine acid pool (ATP, ADP, AMP) and phosphocreatine (Pcr) in myocardium and mitochondria were measured by high performance liquid chromatography (HPLC). Mitochondrial respiratory function and myocardial respiratory chain enzyme activities were measured by Clark oxygen electrodes. The ANT activity was detected by the atractyloside-inhibitor stop technique. The mitochondrial membrane potential (MMP) was determined by Rhodamine-123. The synthesis and hydrolysis activity of ATPase was determined by oligomycin-inhibitor method. The mRNA copies of ANT1,ANT2 and ATPase-αsubunit,ATPase -6 subunit in ventricular myocardium were determined by RT-PCR. The protein content of ANT and F1-ATPase in mitochondria was detected by Western blot analysis.Results1. Compared with SH group, the ratio of left ventricular weight to body weight(LVW/BW),mean arterial pressure(MAP) and left ventricular end diastolic pressure(LVEDP) were increased in all A group, and LVW/BW in A15w group were significantly higher than A5w group. The±dp/dt max was decreased in A15w group. carvedilol can increase±dp/dt max and decrease LVW/BW, MAP and LVEDP. Right ventricular weight to body weight(RVW/BW) is no change in all groups.2. Compared with SH group, ATP and content of adenine acid pool decreased significantly in myocardium both in A5w group and A15w group as well as PCr decreased significantly in myocardium in A15w group. ATP and content of adenine acid pool in mitochondria decreased in A15w group. Carvedilol increased content of adenine acid pool and PCr in myocardium and mitochondria.3. Compared with SH5w group, mitochondrial state 3 respiration(ST3), mitochondrial state 4 respiration(ST4) and oxidative phosphorylation rate(OPR) all increased and respiratory control rate(RCR) decreased significantly in A5w group. Carvedilol increased RCR by decreasing ST4. Compared with SH15w group, ST3, OPR and RCR all decreased significantly in A15w group. Carvedilol increased RCR by increasing ST3 and restored to the control(SH15w group) level.4. Compared with SH5w group, the activity of cytochrome c oxidase(CCO) and reduced form of nicotinamide-adenine dinucleotid (NADH) oxidase were increased significantly in A5w group. Compared with SH15w group, the activity of CCO, succinate oxidase(SO) and NADH oxidase were decreased in A15w group.5. Mitochondrial membrane potention(MMP) was decreased in A5w group and A15w group.6. Compared with SH5w group, the synthesis activity of ATPase was decreased significantly and hydrolysis activity was increased in A5w group. Carvedilol can increase synthasis activity and decrease hydrolysis activity in B5w group. The synthasis and hydrolysis activity of ATPase were both decreased in A15w group . The synthasis activity can be increased by Carvedilol in B15w group, but was lower than SH15w group.7. Compared with SH5w group, The mRNA copies of ATPase-αsubunit,ATPase -6 subunit and The protein content of F1-ATPase were decreased in A15w group. Carvedilol can increase ATPase-6 subunit mRNA and protein content of F1-ATPase.8. The transport activity of ANT was decreased in all A groups. Carvedilol improved transport activity of ANT9. ANT1 mRNA was decreased in all A groups. ANT2 mRNA was decreased only in A15w groups. Carvedilol can increase ANT1 and ANT2 mRNA, restore ANT1 mRNA in A5w groups to SH group level. The protein content of ANT in A15w groups was decreased and improved by carvedilol.Conclusion1. The hypertrophic myocardium is characterized by metabolic remodeling during pressure overloaded: including content of adenine acid and Pcr decreased in myocardium and mitochondria; myocardial respiratory chain enzyme activities and mitochondrial respiratory function was changed; MMP decreased. These findings identify imbalance of energy generation and utilization may play a critical role in hypertrophy and disfunction of heart2. Carvedilol treatment protected mitochondrial respiratory function. Accordingly, high energy phosphates content in myocardium were increased which lead to improve myocardial metabolism. Meanwhile cardiac function was improved and left ventricular remodeling was reversed by administrating Carvedilol.3. In earlier period of hypertrophy, the synthasis activity of ATPase was decreased significantly and hydrolysis activity was increased. Carvedilol can increase synthasis activity and decrease hydrolysis activity. The synthasis and hydrolysis activity of ATPase were both decreased in later period of hypertrophy and the synthasis activity was increased by Carvedilol4. In later period of hypertrophy with cardiac disfunction, expression of F1-ATPase decreased parallel with shift of its activity. It is also suggested that quantitative control of F1-ATPase expression might be a way in the regulation of ATPase activity to some degree during later period of hypertrophy with cardiac disfunction.5. The transport activity of ANT was decreased in hypertrophic myocardium. The alteration in content of ATP and ADP of myocardium as well as mitochondria showed a parallel change with ANT activity, which suggested it might regulate mitochondrial oxidation respiratory.6. The change with ANT activity was correlated to ANT1 isoform expression in earlier period of hypertrophy, which suggested ANT1 might play a leading role in the ANT function. ANT activity decreased accompany reducing of ANT1,2 mRNA and ANT protein in later period of hypertrophy, which implied the worsen of ANT activity was closely associatied with gene expression of ANT.7. Carvedilol raised activity of ATPase and ANT by upregulating gene of ATPase,ANT1mRNA and total ANT protein, improved energy-producing and energy-transporting, which might be one of cardiac protective mechanisms of carvedilol.