Adverse Outcomes in Obese Cardiac Surgery Patients Correlates With Altered Branched-Chain Amino Acid Catabolism in Adipose Tissue and Heart. Biswas D, Tozer K, Dao KT, Perez LJ, Mercer A, Brown A, Hossain I, Yip AM, Aguiar C, Motawea H, Brunt KR, Shea J, Legare JF, Hassan A, Kienesberger PC, Pulinilkunnil T. Front Endocrinol (Lausanne). 2020 Aug 7;11:534. doi: 10.3389/fendo.2020.00534. eCollection 2020.

Background: Predicting relapses of post-operative complications in obese patients who undergo cardiac surgery is significantly complicated by persistent metabolic maladaptation associated with obesity. Despite studies supporting the linkages of increased systemic branched-chain amino acids (BCAAs) driving the pathogenesis of obesity, metabolome wide studies have either supported or challenged association of circulating BCAAs with cardiovascular diseases (CVDs). Objective: We interrogated whether BCAA catabolic changes precipitated by obesity in the heart and adipose tissue can be reliable prognosticators of adverse outcomes following cardiac surgery. Our study specifically clarified the correlation between BCAA catabolizing enzymes, cellular BCAAs and branched-chain keto acids (BCKAs) with the severity of cardiometabolic outcomes in obese patients pre and post cardiac surgery. Methods: Male and female patients of ages between 44 and 75 were stratified across different body mass index (BMI) (non-obese = 17, pre-obese = 19, obese class I = 14, class II = 17, class III = 12) and blood, atrial appendage (AA), and subcutaneous adipose tissue (SAT) collected during cardiac surgery. Plasma and intracellular BCAAs and BC ketoacids (BCKAs), tissue mRNA and protein expression and activity of BCAA catabolizing enzymes were assessed and correlated with clinical parameters. Results: Intramyocellular, but not systemic, BCAAs increased with BMI in cardiac surgery patients. In SAT, from class III obese patients, mRNA and protein expression of BCAA catabolic enzymes and BCKA dehydrogenase (BCKDH) enzyme activity was decreased. Within AA, a concomitant increase in mRNA levels of BCAA metabolizing enzymes was observed, independent of changes in BCKDH protein expression or activity. BMI, indices of tissue dysfunction and duration of hospital stay following surgery correlated with BCAA metabolizing enzyme expression and metabolite levels in AA and SAT. Conclusion: This study proposes that in a setting of obesity, dysregulated BCAA catabolism could be an effective surrogate to determine cardiac surgery outcomes and plausibly predict premature re-hospitalization. Read here.

Branched-chain ketoacid overload inhibits insulin action in the muscle. Biswas D, Dao KT, Mercer A, Cowie AM, Duffley L, El Hiani Y, Kienesberger PC, Pulinilkunnil T. J Biol Chem. 2020 Nov 13; 295(46):15597-15621. doi: 10.1074/jbc.RA120.013121.

Branched-chain α-keto acids (BCKAs) are catabolites of branched-chain amino acids (BCAAs). Intracellular BCKAs is cleared by branched-chain ketoacid dehydrogenase (BCKDH), which is sensitive to inhibitory phosphorylation by BCKD kinase (BCKDK). Accumulation of BCKAs is an indicator of defective BCAA catabolism and has been correlated with glucose intolerance and cardiac dysfunction. However, it is unclear whether BCKAs directly alter insulin signaling and function in the skeletal and cardiac muscle cell. Furthermore, the role of excess fatty acids (FA) in perturbing BCAA catabolism and BCKA availability merits investigation. By using immunoblot and UPLC MS/MS to analyze the hearts of fasted mice, we observed decreased BCAA catabolizing enzyme expression and increased circulating BCKAs, but not BCAAs. In mice subjected to diet-induced obesity (DIO), we observed similar increases in circulating BCKAs with concomitant changes in BCAA catabolizing enzyme expression only in the skeletal muscle. Effects of DIO were recapitulated by simulating lipotoxicity in skeletal muscle cells treated with saturated FA, palmitate. Exposure of muscle cells to high concentrations of BCKAs resulted in inhibition of insulin-induced AKT phosphorylation, decreased glucose uptake and mitochondrial oxygen consumption. Altering intracellular clearance of BCKAs by genetic modulation of BCKDK and BCKDHA expression showed similar effects on AKT phosphorylation. BCKAs increased protein translation and mTORC1 activation. Pretreating cells with mTORC1 inhibitor rapamycin restored BCKAs effect on insulin-induced AKT phosphorylation. This study provides evidence for FA mediated regulation of BCAA catabolizing enzymes, BCKA content and highlights the biological role of BCKAs in regulating muscle insulin signaling and function. Read here.

Serum GDF15, a Promising Biomarker in Obese Patients Undergoing Heart Surgery. Sarkar S, Legere S, Haidl I, Marshall J, MacLeod JB, Aguiar C, Lutchmedial S, Hassan A, Brunt KR, Kienesberger P, Pulinilkunnil T, Légaré JF. Front Cardiovasc Med. 2020 Jun 24;7:103. doi: 10.3389/fcvm.2020.00103. eCollection 2020.

Background: Obesity is a risk factor that negatively impacts outcomes in patients undergoing heart surgery by mechanisms that are not well-defined nor predicated on BMI alone. This knowledge gap has fuelled a search for biomarkers associated with cardiovascular diseases that could provide clinical insight to surgeons. One such biomarker is growth differentiation factor15(GDF15), associated with inflammation, metabolism, and heart failure outcomes but not yet examined in the context of obesity and cardiac surgery outcomes. Methods: Patients undergoing open-heart surgery were consented and enrolled for blood and tissue (atria) sampling at the time of surgery. Biomarker analysis was carried out using ELISA and western blot/qPCR, respectively. Biomarker screening was classified by inflammation(NLR, GDF15, Galectin3, ST2, TNFR2), heart failure(HF)/remodeling(NT-proBNP) and metabolism(glycemia, lipid profile). Patients were categorized based on BMI: obese group (BMI ≥30.0) and non-obese group(BMI 20.0-29.9). Subsequent stratification of GDF15 high patients was conservatively set as being in the 75th percentile. Results: A total of 80 patients undergoing any open-heart surgical interventions were included in the study. Obese (mean BMI = 35.8, n = 38) and non-obese (mean BMI = 25.7, n = 42) groups had no significant differences in age, sex, or co-morbidities. Compared to other biomarkers, plasma GDF15 (mean 1,736 vs. 1,207 ng/l, p < 0.001) was significantly higher in obese patients compared to non-obese. Plasma GDF15 also displayed a significant linear correlation with BMI (R 2 = 0.097; p = 0.0049). Atria tissue was shown to be a significant source of GDF15 protein and tissue levels significantly correlated with plasma GDF15 (R 2 = 0.4, p = 0.0004). Obesity was not associated with early/late mortality at median follow-up >2years. However, patients with high GDF15 (>1,580 ng/l) had reduced survival (65%) compared to the remaining patients with lower GDF15 levels (95%) by Kaplan Meier Analysis (median >2 years; p = 0.007). Conclusions: Circulating GDF15 is a salient biomarker likely sourced from heart tissue that appears to predict higher risk obese patients for adverse outcomes. More importantly, elevated GDF15 accounted for more sensitive outcome association than BMI at 2 years post-cardiac surgery, suggesting it heralds links to pathogenicity and should be actively studied prospectively and dynamically in a post-operative follow-up. Trial number: NCT03248921. Read here.

Myocardial Ketones Metabolism in Heart Failure: Role of ketone in heart failure. Karwi QG, Biswas D, Pulinilkunnil T, Lopaschuk GD. J Card Fail. 2020 May 19:S1071-9164(20)30033-6. doi: 10.1016/j.cardfail.2020.04.005.

Ketone bodies can become a major source of adenosine triphosphate (ATP) production during stress to maintain bioenergetic homeostasis in the brain, heart and skeletal muscles. In the normal heart, ketone bodies contribute from 10 to 15% of the cardiac ATP production, while their contribution during pathological stress is still not well characterized and currently represents an exciting area of cardiovascular research. This review focuses on the mechanisms which regulate circulating ketone levels under physiological and pathological conditions and how this impacts cardiac ketone metabolism. We also review the current understanding of the role of augmented ketone metabolism as an adaptive response in different types and stages of heart failure. This includes the emerging experimental and clinical evidence of the potential favourable effects of boosting ketone metabolism in the failing heart and the possible mechanisms of action through which these interventions may mediate their cardioprotective effects. We also critically appraise the emerging data from animal and human studies which characterize the role of ketones in mediating the cardioprotection established by the new class of anti-diabetic drugs, namely sodium-glucose co-transporter inhibitors (SGLT2i). Read here