Variety And Clinical Significance Of Serum 2-oxoglutarate In Chronic Heart Failure

BackgroundChronic heart failure (CHF) is a complicated clinical syndrome causing by abnormality of the structure and/or function of heart. It has high morbidity and mortality. Though great progress has been made in the recognition of pathogenesis and treatment of chronic heart failure, the prognosis of CHF is still poor. Identified severe heart failure patients as early as possible and treated them in time can improve the prognosis of CHF significantly. Currently some indicators can be used to assess the severity of heart failure, but no one is easier and more objective. New York Heart Association (NYHA) classification, six-minutes walk test, cardiopulmonary exercise test (CEPT) and A-D cardiac function stage can offer a rough assessment of the severity of CHF. However, due to diagnostic providers’ subjective awareness or the complicated operation, these methods are limited to widespread application in clinical practice. N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a good indicator in reflecting the severity of acute heart failure but not appropriate to assess the severity of chronic heart failure. Investigation into new biomarker of CHF is promising. Metabolomics suggested that some metabolites in the serum change a lot in patients with CHF, and some clinical studies showed that the levels of some metabolites were associated with cardiac function. A prior report showed that 2-oxoglutarate was significant increased in CHF patients than healthy controls. But whether 2-oxoglutarate can reflect the severity and prognosis of CHF remains poorly understood.Failing heart had metabolic dysfunction and suffered from energy hungry. Myocardial energy expenditure (MEE) was an effective parameter of myocardial bioenergetics and significantly correlated with cardiac function in patients with CHF. Many studies including ours identified that MEE was significantly associated with the severity of CHF, particularly with reduced LVEF. The current methods for monitoring myocardial metabolism are imaging methods such as MRI, PET and echocardiography etc, but these methods are either difficult to implement in clinical settings due to their complexity and high cost or subjective to the doctors who act. Searching for some biomarkers of assessing MEE is a promising approach to study heart failure.Failing heart characterized as mitochondrial dysfunction, abnormal metabolism and metabolic remodeling. Peroxisome proliferator-activated receptorycoactivator-1 alpha (PGC-la) is the key regulator of energy metabolism, which also can control mitochondrial biogenesis. It has been reported that mitochondrial dysfunction and the decrease of catabolism of free fatty acid in CHF was due to the down-regulation of PGC-la. Maybe the down-regulation of PGC-la can alter the concentration of some intermediate metabolite of the tricarboxylic acid cycle.Up to now, whether the elevation of serum 2-oxoglutarate is related to decreased PGC-la is not clear. So the purpose of this study was to evaluate the relationship between 2-oxoglutarate and MEE in CHF patients. Our goals were:1) to test the hypotheses that whether the serum concentration of 2-oxoglutarate is associated with MEE levels and can reflect the severity of CHF; 2) to assess the predictive value of 2-oxoglutarate to the prognosis of CHF; and 3) to investigate whether the elevation of 2-oxoglutarate is associated with the decrease of serum PGC-1α.Chapter Ⅰ Association between serum 2-oxoglutarate and severity and short-term prognosis of heart failureIn our study the levels of serum 2-oxoglutarate in different groups classified by NT-proBNP and NYHA classification were assayed and compared. We want to know whether serum 2-oxoglutarate can reflect the clinical severity and short-term outcome of CHF. Materials and methods: 219 patients with CHF were consecutively enrolled after obtaining informed consent with the average age of 66.00 years.127 were males and 92 were females. Sixty-six age-matched control subjects with normal cardiac function were recruited from the health management center and outpatient with the average age of 63.50 years. CHF patients underwent oral glucose tolerance test (OGTT) with 75 g of oral anhydrous glucose. All participants were required to fast eight hours prior to blood sample collection, and to be free of diet pills and other drugs affecting metabolism. Antecubital venous blood was drawn into pryogen-free tubes with or without EDTA as anticoagulant respectively. After centrifuged at 3000 g at 4℃ for 10 min, serum or platelet-poor plasma were obtained. All samples were stored at -80℃. Serum 2-oxoglutarate was assayed with Agilent 6460 LC/MS/MS. Free thyroxine(FT4), free triiodothyronine(FT3), thyroid stimulating hormone (TSH), N-terminal pro-B-type natriuretic peptide (NT-proBNP), aspartate aminotransferase, alanine aminotransferase and blood lipid profile were measured. eGFR (estimated glomerular filtration rate) was calculated based on MDRD formula. Left ventricular ejection fraction (LVEF) was measured with ultrasound imaging. CHF patients were classified into 4 groups based on the levels of NT-proBNP and NYHA classification respectively and 2 groups according to LVEF. Follow-up events, including all-cause mortality and recurrent hospital admission due to CHF, were ascertained via hospital database, medical records and contact with patients and patients’ family members.Results: 1. Serum 2-oxoglutarate was higher in CHF patients compared with controls (median,13.72μg/ml [IQR 6.14 to 27.81] versus median,10.58μg/ml [IQR 7.69 to 13.42] p<0.01).2. Serum 2-oxoglutarate levels were lower in the group NYHA 1 than those in the group NYHA 3 and 4. Compared with the group NYHA 3 and 4, the similar results were found in the group NYHA 2. However, there were no significant differences between the group NYHA 1 and 2, neither the group NYHA 3 and 4.3. Compared with the group NT-proBNP 1 and 2,2-oxoglutarate levels were higher in the group NT-proBNP 3, the similar results were found in the group NT-proBNP 4.4. High LVEF group possessed lower levels of 2-oxoglutarate.5. Under the circumstance of NYHA Ⅰ and Ⅱ belonging to moderate CHF and NYHA Ⅲ and Ⅳ belonging to severe CHF, according to receiver operator characteristic curve analysis, the optimal cut-off value of 2-oxoglutarate to predict severity of CHF was over 19.732μg/ml, with 49.20% sensitivity and 80.20% specificity (area under the curve 0.679,95% CI; 0.608 to 0.750).6. Patients belonging to NYHA Ⅱ and Ⅱ class accounted for 52.90% of total in moderate CHF group and 22.22% in serious CHF group. Compared with moderate CHF group, the levels of NT-proBNP were higher in serious CHF group.7. According to the above mentioned ROC analysis, Kaplan-Meier survival curves for CHF with low (<19.732μg/ml) or high (≥19.732μg/ml) 2-oxoglutarate levels, showing an association between high 2-oxoglutarate levels and increased short adverse outcomes in CHF. Conclusions:1. Serum 2-oxoglutarate was higher in CHF patients compared with controls; 2. The levels of serum 2-oxoglutarate can reflect the clinical severity of CHF. The higher the levels of 2-oxoglutarate were, the worse the prognosis of CHF was.3. Patients with low LVEF had high levels of 2-oxoglutarate.4. Serum 2-oxoglutarate also can reflect the short-term outcome of CHF.Chapter II Relationship between serum 2-oxoglutarate and myocardial energy expenditureIn the first chapter we have demonstrated that serum 2-oxoglutarate can reflect the clinical severity and prognosis of CHF, but the relationship between serum 2-oxoglutarate and myocardial energy expenditure is still unclear. In this chapter we intend to know whether 2-oxoglutarate can be used as the marker of MEE. Materials and methods: The subjects and assay methods of biochemical indicator including 2-oxoglutarate were the same as those described in the first chapter. Some echocardiography parameters were measured by echocardiography ultrasound method and MEE, LVEF (left ventricular ejection fraction), LVMI (left ventricular mass index) were calculated according to appropriate formula. CHF patients were divided into 4 groups according to interquartile range of MEE. Results:1. Patients belonging to NYHA class Ⅲ and Ⅳ had significantly higher MEE values than class Ⅰ and Ⅱ patients. NYHA classes were higher with greater MEE. Serum 2-oxoglutarate levels were lower in the group MEE 1 than those in the group MEE 3 and 4 (P=0.004 and 0.001). Compared with the group MEE 3 and 4, the similar results were found in the group MEE 2 (P=0.032 and 0.005).2. Compared with low 2-oxoglutarate group divided by cut-off value of 2-oxoglutarate in ROC curve, MEE, N-terminal pro-B-type natriuretic peptide (NT-proBNP) and Tei index were higher in high 2-oxoglutarate group.3. In order to assess the association between 2-oxoglutarate and other clinical parameters, multiple linear correlation analysis was performed. Pearson correlation showed that Log 2-oxoglutarate was significantly correlated with Log NT-proBNP (Pearson’s r= 0.283, P<0.01), eGFR (Pearson’s r= 0.142, P= 0.036), NYHA classification (Pearson’s r= 0.284, P< 0.01) and Log MEE (Pearson’s r= 0.307, P<0.01), inversely correlated with age (Pearson’s r=-0.269, P<0.01) and Log LVEF (Pearson’s r= -0.192, P<0.01).4. Logistic regression analysis showed that age(OR=1.509,95%CI=1.077 to 2.116, P=0.017), LogNT-proBNP (OR=3.751, 95%CI=1.463 to 9.619, P=0.006), LVEF(OR=6.961,95%CI=2.992 to 16.195, P <0.001) and 2-oxoglutarate (OR=3.108,95%CI=1.334 to 7.241, P=0.009) were associated with increased MEE. Conclusions:1. The severity of heart failure was higher with greater MEE; 2. Patients with high MEE had elevated levels of 2-oxoglutarate; 3. Serum 2-oxoglutarate is associated with MEE levels, which can be used as potential biomarkers for MEE.Chapter Ⅲ Variety of serum peroxisome proliferator-activated receptor y coactivator-la and the correlation to 2-oxoglutarate in chronic heart failurePeroxisome proliferator-activated receptor y coactivator-1a (PGC-1a) is the key regulator of cardiac development and energy metabolism which also can control mitochondrial biogenesis. In chapter Ⅱ, we have showed that in failing heart MEE increased accomplished with elevated 2-oxoglutarate. Whether the elevation of serum 2-oxoglutarate is related to decreased PGC-la is not clear. In this chapter we investigate the correlation between 2-oxoglutarate and serum PGC-la in CHF patients to identify the effect of PGC-la on the levels of 2-oxoglutarate. Materials and methods: The subjects and assay methods of biochemical indicator including 2-oxoglutarate were the same as those described in the first chapter. The levels of serum PGC-la were measured by enzyme-linked immunosorbent assay. Myocardial energy expenditure (MEE), LVEF (left ventricular ejection fraction), LVMI (left ventricular mass index) were calculated according to appropriate formula as described in the second chapter. Patients were divided into 4 groups and 2 groups according to interquartile range of MEE and median of PGC-la respectively.Results:1. Difference existed in 4 different MEE groups. Serum PGC-1a levels were higher in the group MEE1 than those in the group MEE3 and 4 (P<0.001 and 0.004, respectively).2. There were more NYHA Ⅳ patients and less NYHA Ⅰ patients in low PGC-la group than those in high PGC-la group (P=0.022 and 0.041, respectively). Compared with high PGC-la group, LVMI, MEE and N-terminal pro-B-type natriuretic peptide (NT-proBNP) were higher in low PGC-la group. However, no difference of serum PGC-la was observed between low and high PGC-la group (P =0.129).3. Pearson correlation showed that PGC-1a was significantly positively correlated with Log LVEF (Pearson’s r= 0.166, P=0.014) and inversely correlated with Log NT-proBNP (Pearson’s r=-0.177, P<0.01), Log 2-oxoglutarate (Pearson’s r=-0.208, P<0.01) and Log MEE (Pearson’s r=-0.270, P<0.01).4. Logistic regression analysis showed that age(OR=0.649,95%CI=0.472 to 0.893, P=0.008), NYHA (OR=1.947,95%CI=1.245 to 3.043, P=0.003), PBG (OR=0.484, 95%CI=0.237 to 0.989, P=0.047) and MEE (OR=3.441,95%CI= 1.526 to 7.762, P =0.003) were associated with 2-oxoglutarate. PGC-1a (OR=0.885,95%CI= 0.448 to 1.748, P=0.725)was not associated with 2-oxoglutarate. Conclusions:1. The levels of serum PGC-la decreased in patients with chronic heart failure; 2. There was no relationship between serum PGC-la and 2-oxoglutarate, and the decrease of PGC-la could not lead to the elevation of 2-oxoglutarate.