Ventricular endomyocardial mitochondrial impairment and inflammation accompany diastolic dysfunction in the type 2 diabetic human heart

 

Type 2 Diabetes Mellitus (T2DM) is a major risk factor for chronic heart failure, even independent of coronary artery disease. Various underlying mechanisms worsening ventricular function in T2DM have been postulated based on data from animal studies, including mitochondrial abnormalities, alterations of Nuclear factor kappa-B (NfκB) expression, increased oxidative stress and inflammation and cardiac fibrosis and diastolic impairment. However, evidence in humans for these mechanisms is currently lacking. Especially early T2DM-related alterations and the impact of T2DM in the absence of coronary artery disease remain unclear.

We hypothesize that T2DM (I) leads to distinct changes in diastolic cardiac function, (II) impairs mitochondrial function of the ventricular myocardium, and (III) increases ventricular myocardial NfκB expression.

Heart transplant recipients with T2DM (“T2DM”, n=17) and without (“Non-DM”, n=32) T2DM (as determined by oral glucose tolerance tests) were included, if they had received their heart from a donor without Diabetes Mellitus. Thus, diabetes-exposure of the transplanted hearts exactly corresponded to the time since transplantation. Magnetic resonance imaging was performed to assess left ventricular ejection fraction, global longitudinal strain (GLS), diastolic strain, and T2 relaxation times, a marker of myocardial edema. We assessed NfκB p105 subunit (NfκB1) mRNA expression using real-time PCR and myocardial mitochondrial respiration using high-resolution respirometry in ventricular endomyocardial biopsies.

All participants had normal left ventricular ejection fraction (LVEF) without angiographic signs of coronary artery disease post transplantation (average 2.9±2.4 years). Age, sex distribution and LVEF were comparable between T2DM and Non-DM participants (p=0.50, 0.40 and 0.36, respectively). While GLS was not different (p=0.34), T2DM exhibited lower diastolic strain (1.0±0.4 vs. 1.4±0.4s-1, p<0.01) and higher T2 relaxation times (67±3 vs. 64±3ms, p<0.05) than Non-DM, indicating impaired diastolic function and increased myocardial edema. In T2DM, myocardial mitochondrial respiration with fatty acids and glycolytic substrates was 22–27% lower and mitochondrial uncoupling was 19% higher, whereas ORP and TBARS were 17% and 34% higher than in Non-DM (all p<0.05). Myocardial oxidative capacity related negatively to fasting blood glucose (r=−0.35; p<0.01), and positively to insulin sensitivity (r=0.49; p<0.05) across all participants. Myocardial NfκB mRNA expression was 60% higher in T2DM (0.45 [0.29; 0.71] vs. 0.28 [0.21; 0.44] AU, p<0.05) and correlated inversely with complex I respiration (r=−0.33; p<0.05).

Exposure to T2DM diminishes mitochondrial function in ventricular myocardium, which relates to hyperglycemia, insulin resistance, oxidative stress, inflammation, and ventricular diastolic dysfunction and edema. These changes appear within short-term overt diabetes and might precede T2DM-related heart failure.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): This work was supported by funding from the German Research Council (SFB1116) and a grant provided by the research commission of the Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany.

Aetiology-dependent impairment of mitochondrial function in the failing human heart

Background

Alterations of mitochondrial function have been identified to play a role in Heart Failure (HF) pathophysiology. Oxidative phosphorylation (OXPHOS) capacity of the myocardium was shown to be reduced in the failing heart. Ineffective mitochondrial function promotes formation of reactive oxygen species (ROS) that may affect remodelling in ischemia. Thus far, human mitochondrial function comparing dilated cardiomyopathy (DCM) and ischemic cardiomyopathy (ICM) resembling the main aetiologies of heart failure with reduced ejection fraction (HFrEF) has not been investigated.

Purpose

We hypothesised that

1. ROS production is elevated in left ventricular myocardial tissue specimens of ICM patients compared to DCM.

2. Mitochondrial OXPHOS capacity is higher in left ventricular myocardial tissue specimens of DCM compared to ICM patients.

Methods

Myocardial tissue was obtained from the left ventricular apex from 63 patients (38 ICM, 25 DCM) with advanced HFrEF requiring implantation of a Left Ventricular Assist Device (LVAD). We performed high-resolution respirometry (HRR, OROBOROS Oxygraph-2k) in saponine-permeabilised myocardial fibres and measured ROS production fluoroscopically via the Amplex Red method. Statistical analysis was conducted using GraphPad Prism 7 and IBM SPSS v26.0.

Results

Groups were of comparable age (61.5±1.2 vs. 59.3±2.4 years, p=n.s.), sex (87% vs 85% male, p=n.s.), diabetic status (32% vs 38.4% type 2 diabetes mellitus, p=n.s.), and body mass index (28.1±0.8 vs. 26.3±1.1 kg/m2, p=n.s.). We detected reduced myocardial mitochondrial OXPHOS capacity in ICM under state 3 conditions by about 15% (68.7±34.0 vs. 80.9±30.5 pmol/(s*mg), p<0.05), after addition of Glutamate by 25% (78.9±38.7 vs. 104.8±41.2 pmol/(s*mg), p<0.01) as well as after Succinate (115.5±65.5 vs. 155±62.0 pmol/(s*mg), p<0.01), uncoupling agent FCCP (114.1±56.8 vs. 150.5±47.3 pmol/(s*mg), p<0.01), and by about 40% after addition of Complex I inhibitor Rotenone (55.5±25.9 vs. 96.9±28.0 pmol/(s*mg), p<0.001). We detected no difference in ROS production between ICM and DCM (0.6±0.05 vs. 0.76±0.08 pmol/(s*ml), p=n.s.).

Conclusion

This is the first human study deciphering distinct alterations in mitochondrial function (OXPHOS capacity) in ventricular myocardium of HFrEF patients. Future studies may address how distinct metabolic patterns at the time of implantation may relate to long-term outcome of HFrEF in terms of remodelling and recovery.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): DFG (German Research Foundation)

[Recommendations for extracorporeal cardiopulmonary resuscitation (eCPR) : Consensus statement of DGIIN, DGK, DGTHG, DGfK, DGNI, DGAI, DIVI and GRC]

Extracorporeal cardiopulmonary resuscitation (eCPR) may be considered as a rescue attempt for highly selected patients with refractory cardiac arrest and potentially reversible etiology. Currently there are no randomized, controlled studies on eCPR, and valid predictors of benefit and outcome which might guide the indication for eCPR are lacking. Currently selection criteria and procedures differ across hospitals and standardized algorithms are lacking. Based on expert opinion, the present consensus statement provides a proposal for a standardized treatment algorithm for eCPR.

P3476High-resolution respirometry reveals enhanced myocardial mitochondrial ketone oxidation after fasting and ventricular unloading

Background

Impairment of myocardial mitochondrial function is regarded as an established pathomechanism in heart failure. Enhanced oxidation of ketone bodies may potentially exert protective effects on myocardial function. High-resolution respirometry (HRR) resembles a gold-standard methodology to determine myocardial mitochondrial metabolism and oxidative function but has not been validated for ketone substrates yet.

Purpose

We hypothesized that (1) quantification of ketone body oxidative capacity (OC) in myocardium utilizing ex-vivo HRR is feasible and that (2) ketone-associated OC is elevated after fasting and under conditions of chronic mechanical ventricular unloading.

Methods

We established new HRR (Oxygraph-2k) protocols, measuring oxygen flux generated by oxidation of the ketone substrates beta-hydroxybutyrate (HBA) and acetoacetate (ACA). Ketone protocols were then applied to twelve C57BL/6 mice' (of which six were fasted for 16h) left ventricular and right liver lobe tissue, as well as to eleven terminal heart failure patients' left ventricular tissue, harvested at heart transplantation. Heart transplant recipients were subdivided into patients with left ventricular assist device prior to transplantation (LVAD group, n=6) or no unloading prior to transplantation (HTX group, n=5).

Results

In non-fasted rodent hearts, HBA yielded an OC of 25±4 pmol/(s*mg tissue) above basal respiration, when applied as sole substrate (21±11 pmol/(s*mg) in liver). ACA alone did not induce oxygen flux, but ACA+succinate yielded 229% higher oxygen flux than succinate alone in state III (146±32 vs 44±12 pmol/(s*mg); p=0.0003). When titrated after succinate, ACA increased OC by 93±25 pmol/(s*mg) (p=0.0003). In 16h-fasted rodent hearts, HBA-supported OC was 27% higher (41±3 vs 52±9 pmol/(s*mg); p=0.04), while OC with ACA+succinate was unchanged (p=0.60). In rodent liver, no oxygen flux was induced by ACA, reflecting absence of 3-oxoacid CoA-transferase. However, HBA-supported OC was 118% higher in fasted liver (37±13 vs 57±13 pmol/(s*mg); p=0.03). In humans, left ventricular unloading was not associated with altered myocardial OC for fatty acids and glycolytic substrates (standard protocol, p=0.13), but HBA-supported OC was 39% higher in the LVAD group compared to the HTX group (54±12 vs 39±9 pmol/(s*mg), p=0.04).

Conclusion

Quantification of ketone body OC with HRR is feasible in permeabilized myocardial fibers. Applying this novel method revealed increased HBA-supported myocardial mitochondrial respiration after fasting and chronic left ventricular unloading. These data support a concept of enhanced ketone oxidation following ventricular unloading in myocardial mitochondria. Our findings facilitate new studies on myocardial ketone turnover and the interaction of mitochondrial ketone metabolism with cardiac performance.

Acknowledgement/Funding

CRC 1116, Research commission of the University Hospital Düsseldorf