Introduction
The heart is a blood-pumping organ with the highest energy demand in the body. In a normal heart, 60%–80% of energy-producing substances are free fatty acids (FFA), while 10%–20% are derived from glucose, acetone, lactic acid, and ketone bodies [
1]. Heart failure, the end stage of multiple cardiovascular diseases, is a development process with cardiac remodeling as the core, in which multiple factors such as hemodynamics, neurohormones, genetic factors, and energy metabolism participate jointly [
2]. Among these, abnormal energy metabolism is not only the direct manifestation of heart failure symptoms, but also one of their pathological bases. Normal myocardial energy metabolism comprises the following three steps [
3‐
5]: (1) the utilization of substrates, (2) the oxidative phosphorylation of mitochondrial respiratory chain, and (3) the transport and utilization of ATP. Problems arising in any of the three steps would cause disorders of myocardial energy metabolism.
Heart failure often manifests as energy deficiency and mitochondrial oxidative damage due to changes in energy substrates. Metabolites associated with glucose, lipid, and amino acid metabolism processes are abnormal in heart failure. In an early stage of the disease, fatty acid (FA) oxidation (FAO) appears to be normal or slightly higher. With progression of the disease, FAO is impaired, and glucose is then preferentially used as a substrate for energy metabolism, known as the “cardiac metabolic reprogramming” [
6]. In 2004, van Bilsen et al. put forward the concept of metabolic remodeling of the failing myocardium, which argued that when heart failure occurs, myocardial structure and cell metabolism are both disordered, causing cardiac dysfunction, and changes in cardiac energy metabolism give rise to severe heart failure [
7]. In addition, Guo et al. investigated the mechanisms of heart failure using a metabolomics technique based on ultra-performance liquid chromatograph quadrupole time-of-flight mass spectrometry (UPLC/TOF–MS). They identified 13 metabolites in the serum as potential biomarkers of heart failure, and these compounds were mainly associated with inflammation, energy metabolism disorders, and amino acid disorders [
8]. Li et al. established a rat model of chronic heart failure (CHF) and identified 23 metabolites related to CHF with non-targeted metabonomics. Their results showed that the metabolism of branched chain amino acids (BCAA) in the heart of rats with heart failure was significantly inhibited [
9]. Li et al. selected 27 healthy, 22 stage B1, 18 stage B2 pre clinical MMVD dogs with mucinous mitral valve disease and 17 MMVD dogs with congestive heart failure (CHF) history for metabonomic analysis. They found that there were 173 known metabolites of different concentrations among the four groups, of which 40% were amino acids and 30% were lipids, revealing changes in energy metabolism and amino acid metabolism during the occurrence and development of MMVD and CHF [
10]. Li et al. used the method of metabonomics and 16S rRNA sequencing to analyze the fecal metabolism profile and intestinal microbial composition of H-HF rats, and found that the intestinal microbial composition of H-HF rats had changed significantly, the mycelium/Bacteroid (F/B) ratio increased, and the number of bacteria in rhamnoideae, lactobacilliaceae, and lactobacilliaceae decreased. The levels of 17 genera and 35 metabolites changed significantly and were identified as potential biomarkers of H-HF. Correlation analysis showed that there was a strong correlation between specific altered genera and altered fecal metabolites. The reduction of short chain fatty acid (SCFA) producing bacteria and trimethylamine N-oxide (TMAO) may be a significant feature of H-HF [
11]. Furthermore, Juho Heliste et al. included Finnish patients with heart failure to screen out a new genetic variation related to heart failure, and identified a new variation for function through in vitro and in vivo studies. This study suggests the role of TRIM55 gene polymorphism in heart failure susceptibility [
12]. Vilela et al. [
13] found that uncoupling protein 2 (UCP2), a proton transporter located in the inner mitochondrial membrane, can transport H
+ from the outer side back to the inner side of the membrane. This reduces the electrochemical gradient of H
+ across the membrane formed during substrate oxidation, and decouples oxidative phosphorylation of the respiratory chain from ATP synthesis. As a result, the energy released from H
+ oxidation is converted into heat, and ATP production is diminished. If UCP2 expression is upregulated in smooth muscle tissue, it can further mediate a reduction in ATP production, increasing myocardial energy metabolism disorders and thereby aggravating heart failure. Therefore, UCP2 is considered to be a “ruler” of myocardial cell metabolism, which can sense changes in the metabolism–energy state. UCP2 influences multiple steps of substrate metabolism to modulate the process of glycolysis, glucose uptake, and energy production, regulate the efficiency of oxidative phosphorylation, and maintain the balance of energy supply and demand [
13]. Kim et al. and Fry et al. have all demonstrated that beta3 adrenoceptor (beta3-AR) agonists inhibit adipocyte differentiation by downregulating gene expression levels of peroxisome proliferator-activated receptor (PPAR) and adipocyte FA-binding protein (aP2), thereby causing the reversion of myocardial energy metabolism back towards fetal energy metabolism [
14,
15]. Other researchers have proposed that cardiac beta3-AR activates the extracellular signal-regulated kinase/mitogen-activated protein kinase (Erk-MAPK) pathway through phosphorylation, which downregulates PPAR-alpha expression or activity; subsequently, FAO is impaired and metabolic remodeling is induced. This may be another mechanism by which beta3-AR mediates negative inotropic effects through influencing myocardial cell metabolism, but it still needs to be verified. Perilipin 5 (Plin5) plays a role in bidirectional regulation of lipid metabolism balance during energy metabolism in myocardial cells. Plin5 binds to adipose triglyceride lipase (ATGL), thereby inhibiting lipid dissolution and facilitates FA storage. When stress or heart failure occurs, protein kinase A (PKA) phosphorylates and activates Plin5, promotes the release of ATGL from the complex, and triggers ATGL activity, thus accelerating FA degradation and participating in metabolic reprogramming of myocardial cells [
16].
Metabolomics is a scientific method emerging after genomics and proteomics in recent years, and it constitutes an essential part of systems biology. Metabonomic analysis can detect small-molecule metabolites (including lipids, carbohydrates, and amino acids), and these indicators are further analyzed using multivariate statistical methods, such as principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) [
17], and orthogonal partial least squares discriminant analysis (OPLS-DA) in order to determine the corresponding biomarkers and elaborate the mechanisms of disease pathogenesis and associated molecular pathways. Identification of novel biomarkers can predict disease progression and guide individualized treatment [
18]. Various physiological reactions catalyzed by gene encoding enzymes and their interaction systems can be reflected through metabolic networks [
19]. In the present study, an integrated analysis strategy based on non-targeted metabolomics and transcriptomics was used to analyze the metabolic profile of patients with heart failure, and patients without heart failure were included as a control group. The aim of the study was to explore systemic metabolic changes in heart failure and the involved pathways of metabolic disorders, and to search for novel markers and therapeutic targets for heart failure. The findings could provide new thoughts for clinical diagnosis and treatment of heart failure.
Discussion
Based on the integrated analysis of transcriptomics and complete-spectrum metabolomics, we found that purine metabolism may be a prominent metabolic change in cardiac pathological progression of patients with DCM. Purine metabolism is involved in the normal energy flow of the heart. Purines are often distributed in DNAs and RNAs, catalyzed by various oxidases to form hypoxanthine and xanthine, then oxidized by urate oxidase to realize uric acid metabolism. Evidence is accumulating that levels of purine degradation intermediates indicate the energy state of myocardial cells. In physiological conditions, if energy consumption of the heart increases, purine nucleotides and their metabolites also increase; conversely, a distinctive reduction in total purine release suggests that myocardial cells relatively conserve energy and maintain the energy state of the myocardium. In pathological conditions, when myocardial ischemia occurs, ATP is degraded into xanthine and accumulated in tissues, and massive xanthine in myocardial cells is then degraded into uric acid by xanthine oxidase, with simultaneous production of superoxide anions in a large number, causing pathological damage of the cells. In hypoxic conditions, the degradation products of adenosine and inosine are better energy sources than extracellular glucose, which further delay the accumulation of nicotinamide adenine dinucleotide (NADH) and display a certain protective effect on the cells. DCM patients with heart failure have abnormal energy metabolism, and this condition can further aggravate damage of myocardial cell structure and function, namely, “myocardial metabolic remodeling”, with the two factors mutually influencing each other.
The
IMPDH1 encoded the rate-limiting enzyme in the de novo synthesis of xanthine monophosphate (XMP) from inosine-5'-monophosphate (IMP). As reported,
IMPDH1 function as the catalyzes in the development of multiple organs and progression of cardiovascular disease. Kofler et al., found that the inosine monophosphate dehydrogenase (
IMPDH) activity may significantly correlated with the incidence of acute rejection episodes and transplant vasculopathy based on a prospective study [
41]. Ohmann et al., demonstrated that the haplotype of
IMPDH1, includes the SNPs of rs2288553, rs2288549, rs2278293, rs2278294, and rs2228075, may strongly associated with the gastrointestinal related side effects of immunosuppressive therapy after heart transplantation in pediatric patients [
42].Burckart and Amur reviewed that the polymorphisms of
IMPDH1 and
IMPDH2 were detected which’re significantly correlated with the static graft, survival rate, and the incidence of adverse drug effects in heart transplant patients [
43]. The
ENTPD2 is encoded type 2 enzyme of the family of ECTO-nucleoside triphosphate diphosphohydrolase (E-NTPDase), playing an important role in hydrolyze 5'-triphosphates and maintain the stability of cell membrane protein. During the normal systolic and diastolic physiological activities of mice, Rücker et al., via detects the functional state of mitochondria, pH value, ATP and ADP hydrolysis in heart tissue, and thus found that the cation-dependent enzymes of ATP and ADP hydrolysis optimum pH is 8.0, and AMP hydrolysis is 9.5. Additionally, the content of
ENTPD2 gene and protein was the highest expression in the left ventricle of mice [
44]. It is suggested that a play an important role in maintaining normal cardiac diastolic and systolic function. Bertoni et al., also found that the activity of ENTPD2 may play a significant role in regulate the extracellular ATP and adenosine levels during the pathological process of vascular smooth muscle cell plasticity [
45].
CANT1 is a subset of cell growth factor of apyrase family and functions as a calcium-dependent nucleotidase with a preference for urinary dihydrate (UDP); it plays a key role in the pathophysiological process involved in calcium ion binding and pyrophosphatase activity. Yang et al., found that the
CANT1 expression level is closely related with TP53-mutantation and poor prognosis of hepatocellular carcinoma [
46]. Based on whole-exome sequencing (WES) analysis of three patients from two unrelated families, Byrne et al. found that a variant of
CANT1 may contribute to the pathogenesis of pseudodiastrophic dysplasia related cardiac developmental defect [
47]. Jelin et al., also reported that the mutations in
CANT1 may significantly correlated with specific skeletal dysplasias in the neonatal dysplasia [
48].
AK2 and
AK9 are belong to the family proteins of adenylate kinases, that catalyze the production and breakdown of adenine nucleotide composition with the reversible transfer method. However,
AK2 and AK9 shown a tissue-specific and developmentally regulated in different physiological and pathological processes. Isozyme-2 of adenylate kinase is major localized in the mitochondrial intermembrane space and presenting an important role in regulation of catalase, oxidase cell apoptosis. Zhang et al., illustrated that the
AK2 deletion wound lead to fetal intrauterine death. And in adult mice, organ-specific ablation of
AK2 can lead to heart failure, which may be related to metabolic dysfunction involved in Krebs cycle and glycolytic metabolite buildup [
49]. As the key metabolic sensor of cell energy economy, the expression level of
AK2 play an important role in regulate metabolic signaling circuits, nuclear transport, and energetics of cell cycle involving in DNA synthesis and repair [
50]. Carrasco et al., found that the deletion of
AK2 may compromise the nucleotide exchange in the mitochondrial intermembrane space, and thus regulate the balance of mitochondria energetics with K(ATP) channels [
51]. The enzyme Adenylate Kinase 7 (
AK7) may function as the phosphotransferase, and plays a role in energy homeostasis. Romeo-Guitart et al., found that
AK7 may significantly correlated with intracellular endoplasmic reticulum (ER) stress and the activation of unfolded protein response [
52]. Lorès et al., shown that the homozygous missense mutation L673P leads to the deletion of Ak7 protein, and thus result in the injury of mitochondria respiratory function and dysfunction of assembly [
53].
The function of stem cell in the heart can be enhanced by biomaterials [
54], and it has good therapeutic effect on heart failure. Heart failure is caused by primary myocardial cell dysfunction (such as hereditary cardiomyopathy) or myocardial cell loss (such as after myocardial infarction). The current drug treatment has reduced the mortality and morbidity, but can not produce new myocardial cells [
55]. The natural materials commonly used in heart tissue engineering include collagen, elastin, gelatin, fibrin, chitosan and silk fibroin [
56], and they have proper biochemical characteristics of cell attachment and proliferation [
57]. Engineered heart tissue (EHT) based on novel biomaterials or nanomaterials is a promising method to treat heart failure. It is mainly to obtain mature EHT in drug screening or cell therapy, use natural biological materials or synthetic nanomaterials to provide mechanical support, and generate 2D or 3D myocardial cell slices with non-shrinking cells [
58]. Nevertheless, researchers are faced with many obstacles in translating the application of biomaterials into clinical practice [
59]. Finding an ideal biomaterial is still challenging. It should be close to the natural extracellular matrix cells to survive, strengthen the coupling between donor and host cells, and have no immune response after degradation. Using stem cells and bioengineering technology to develop EHT technology will provide mature myocardial cells to supplement lost myocardium, repair scar tissue, and bear local mechanical and hemodynamic loads imposed on them. In addition to manipulating EHT in vitro, researchers can also optimize the host substrate environment by targeting fibroblast activation pathways or modifying ECM to promote cell implantation and functional integration of newborn cardiomyocytes. Good biomaterials can be combined in stem cell therapy. These intervention methods need further research, combined with EHT technology, to ensure the efficacy of heart failure treatment.
Studies have shown that ventricular remodeling and myocardial energy metabolism remodeling are the basis of heart failure [
60]. Mitochondria are the main energy source of myocardial cells, accounting for about one-third of the volume of myocardial cells, and myocardial cells also have high metabolic activity [
61]. Therefore, new cardiovascular diseases can be developed for mitochondria. Heart failure is closely related to energy deficiency and mitochondrial dysfunction [
62]. The mitochondrial dysfunction of heart failure may provide a new method, which is not only conducive to hemodynamics, but also a supplement to the existing limited methods. However, up to now, mitochondrial targeted therapy has not successfully affected the progress of this disease [
63]. Compared with other organs, the heart needs a lot of energy. About a third of an adult cardiomyocyte is made up of mitochondria. Most of the energy consumed by the heart is provided by oxidative metabolism of mitochondria, and the key mechanism of cardiac systolic failure is the inability to produce and transfer energy. However, more and more people are realizing that mitochondria not only provide energy, but also play important biological and regulatory roles, such as cell growth and death, protein quality control, REDOX balance, ion homeostasis, biosynthesis, reactive oxygen species (Ros) signaling, etc. Researchers are beginning to realize that the pathogenic role of mitochondria in cardiovascular disease and heart failure is not only related to decreased ATP production, but also to general maladaptation of the functional spectrum [
64]. But the integration of mitochondrial bioenergetics into each behavior is poorly understood, and the contribution of each unique biological function of mitochondria to the development of heart failure remains unclear. In addition. Further elucidation of the linkages between the many other functions of mitochondria and the processes involved in oxidative metabolism may help to discover new therapeutic targets. The renin-angiotensin system (RAS) is involved in cardiovascular disease risk factors and is an enzymatic pathway that promotes cardiovascular disease (CVD) and the progression of cardiovascular disease. Renin mediates the conversion of angiotensinogen to the inactive polypeptide angiotensin I and then to the active hormone angiotensin II (Ang II) [
65]. As a pro-oxidant and fibroblast factor, angiotensin II (Ang II) is the main effector peptide of RAS [
66]. The increase of angiotensin ii and superoxide disproportionation in central and peripheral nervous system play a role in enhancing sympathetic vasomotor tension in heart failure. RAS activity and oxidative stress are gradually increased during the development of heart failure [
67]. Drugs that target various components of the systemic RAS, including angiotensin ii type 1 receptor blockers (ARBs), renin inhibitors, and angiotensin converting enzyme inhibitors, are used to treat heart failure [
68].
In this study, due to the complexity of collecting samples, not many samples were included. New samples should be collected in future work to further verify our findings. In addition, we should further verify the expression level of AK2, AK7, CANT1, ENTPD2, IMPHD1 and other marker genes in DCM patients, and screen important pathways for further in-depth research. In addition, in future research, we will collect external data to further verify our results, and conduct internal cross validation to further ensure the accuracy of our conclusions.
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