Myocardial inflammation is associated with impaired mitochondrial oxidative capacity in ischaemic cardiomyopathy

Abstract

Aims: Myocardial inflammation and impaired mitochondrial oxidative capacity are hallmarks of heart failure (HF) pathophysiology. The extent of myocardial inflammation in patients suffering from ischaemic cardiomyopathy (ICM) or dilated cardiomyopathy (DCM) and its association with mitochondrial energy metabolism are unknown. We aimed at establishing a relevant role of cardiac inflammation in the impairment of mitochondrial energy production in advanced ischaemic and non-ischaemic HF.

Methods: We included 81 patients with stage D HF (ICM, n = 44; DCM, n = 37) undergoing left ventricular assist device implantation (n = 59) or heart transplantation (n = 22) and obtained left ventricular tissue samples during open heart surgery. We quantified mitochondrial oxidative capacity, citrate synthase activity (CSA) and fibrosis and lymphocytic infiltration. We considered infiltration of >14 CD3⁺ cells/mm² relevant inflammation.

Results: Patients with ICM or DCM did not differ regarding age (61.5 ± 5.7 vs. 56.5 ± 12.7 years, P = 0.164), sex (86% vs. 84% male, P = 0.725), type 2 diabetes mellitus (34% vs. 18%, P = 0.126) or chronic kidney disease (8% vs. 11%, P = 0.994). ICM exhibited oxidative capacity reduced by 23% compared to DCM (108.6 ± 41.4 vs. 141.9 ± 59.9 pmol/(s*mg), P = 0.006). Maximum production of reactive oxygen species was not significantly different between ICM and DCM (0.59 ± 0.28 vs. 0.69 ± 0.36 pmol/(s*ml), P = 0.196). Mitochondrial content, detected by CSA, was lower in ICM (359.6 ± 164.1 vs. 503.0 ± 198.5 nmol/min/mg protein, P = 0.002). Notably, relevant inflammation was more common in ICM (27% vs. 6%, P = 0.024), and the absolute number of infiltrating leucocytes correlated with lower oxidative capacity (r = -0.296, P = 0.019). Fibrosis was more prevalent in ICM (20.9 ± 21.2 vs. 7.2 ± 5.6% of area, P = 0.002), but not associated with oxidative capacity (r = -0.13, P = 0.327).

Conclusions: More than every fourth ICM patient with advanced HF displays myocardial inflammation in the range of inflammatory cardiomyopathy associated with reduced mitochondrial oxidative capacity. Future studies may evaluate inflammation in ICM at earlier stages in standardised fashion to explore the therapeutic potential of immunosuppression to influence trajectories of HF in ICM.

Keywords: Heart failure; Inflammation; Mitochondria; Reactive oxygen species.

Figure 1

Myocardial inflammation was more common in patients with ICM compared to DCM. Patients with inflammation differed in some parameters of myocardial function. (A–C) Patients with relevant myocardial inflammation showed lower OXPHOS capacity than those without inflammation. The difference in ETS capacity did not reach statistical significance. ROS production did not differ. (D) T‐lymphocytic infiltration was associated with lower OXPHOS. (E) No differences in specification for CD4⁺ T‐helper cells, CD8⁺ cytotoxic lymphocytes, CD45R0⁺ T‐memory cells or CD68⁺ macrophages were found between patients with ICM or DCM and more than 7 CD3⁺ lymphocytes per mm². (A) Chi square test. (A–C) Unpaired t‐tests. (D) Spearman correlation. (E) Mann–Whitney U tests. n (ICM) = 33, n (DCM) = 32, n (inflammation) = 11, n (no inflammation) = 51. CD, cluster of differentiation; DCM, dilated cardiomyopathy; ETS, electron transfer system; ICM, ischaemic cardiomyopathy; ROS, reactive oxygen species.

Figure 2

ICM myocardium showed larger fibrotic areas. Myocardial samples from ICM patients had larger fibrotic areas as determined by Azan staining with quantification. n (ICM) = 30, n (DCM) = 30. Mann–Whitney U test. DCM, dilated cardiomyopathy; ICM, ischaemic cardiomyopathy.

Figure 3

Lower mitochondrial respiration and mitochondrial content, comparable ROS production in patients with ICM or DCM. (A) OXPHOS capacity as well as electron transfer capacity on fatty acids were significantly reduced in patients with ICM compared to DCM. n (ICM) = 40 vs. n (DCM) = 34. (B) Protein content measured via bicinchoninic acid assay was comparable between the groups. n (ICM) = 35 vs. n (DCM) = 32. (C) Citrate synthase activity was significantly reduced in ICM patients compared to DCM. n (ICM) = 35 vs. n (DCM) = 32. (D) No significant difference in mitochondrial respiration after normalisation to citrate synthase activity (CSA) as a marker of mitochondrial content. n (ICM) = 35 vs. n (DCM) = 30. (E) OXPHOS capacity as well as electron transfer capacity were significantly reduced in patients with ICM compared to DCM. n (ICM) = 20 vs. n (DCM) = 13, respectively. (F) No significant difference in ROS production in ICM compared to DCM. n (ICM) = 37 vs. n (DCM) = 30. (A–D) Unpaired t‐tests and (F) two‐way ANOVA with Sidak's post hoc test. *P < 0.05, **P < 0.01, ***P < 0.001. Am, antimycin A; CETF, capacity of the electron‐transferring flavoprotein; CI/CII, Complex I/II; CSA, citrate synthase activity; DCM, dilated cardiomyopathy; ETC, electron transfer capacity; ETS, electron transfer system; ICM, ischaemic cardiomyopathy; LEAK = leak respiration (state 4_O); ROS, reactive oxygen species; ROX, residual oxygen consumption; suc, succinate.