Sodium dichloroacetate stimulates cardiac mitochondrial metabolism and improves cardiac conduction in the ovine fetus during labor

Abstract

Previous studies in our laboratory have suggested that the increase in stillbirth in pregnancies complicated by chronic maternal stress or hypercortisolemia is associated with cardiac dysfunction in late stages of labor and delivery. Transcriptomics analysis of the overly represented differentially expressed genes in the fetal heart of hypercortisolemic ewes indicated involvement of mitochondrial function. Sodium dichloroacetate (DCA) has been used to improve mitochondrial function in several disease states. We hypothesized that administration of DCA to laboring ewes would improve both cardiac mitochondrial activity and cardiac function in their fetuses. Four groups of ewes and their fetuses were studied: control, cortisol-infused (1 g/kg/day from 115 to term; CORT), DCA-treated (over 24 h), and DCA + CORT-treated; oxytocin was delivered starting 48 h before the DCA treatment. DCA significantly decreased cardiac lactate, alanine, and glucose/glucose-6-phosphate and increased acetylcarnitine/isobutyryl-carnitine. DCA increased mitochondrial activity, increasing oxidative phosphorylation (P_CI, P_{CI + II}) per tissue weight or per unit of citrate synthase. DCA also decreased the duration of the QRS, attenuating the prolongation of the QRS observed in CORT fetuses. The effect to reduce QRS duration with DCA treatment correlated with increased glycerophosphocholine and serine and decreased phosphorylcholine after DCA treatment. There were negative correlations of acetylcarnitine/isobutyryl-carnitine to both heart rate (HR) and mean arterial pressure (MAP). These results suggest that improvements in mitochondrial respiration with DCA produced changes in the cardiac lipid metabolism that favor improved conduction in the heart. DCA may therefore be an effective treatment of fetal cardiac metabolic disturbances in labor that can contribute to impairments of fetal cardiac conduction.

Keywords: ECG; cortisol; fetus; labor; stress.

Figure 1.

Summary of the experimental design depicting timing of treatments to the ewe. DCA, dichloroacetate; HR, heart rate.

Figure 2.

Maternal (left) and fetal (right) cortisol concentrations at 135 days gestation, and before (0 h) and after the start of oxytocin (at end of first pulse at 5 min, and after pulses at 24 h and 48 h). Circles represent data from control group; squares represent data from CORT group; hatched symbols are data collected before DCA infusion; open symbols at 48 and 72 h are from the groups not treated with DCA, closed symbols are from DCA-treated animals. All data are shown as means ± SE for 6 control fetuses (4 females, 2 males), 6 CORT (3 females, 3 males), 5 CORT + DCA (3 female and 2 male), and 6 control + DCA (4 males and 2 females; last time point n = 3 fetuses). CORT, cortisol-infused; DCA, dichloroacetate.

Figure 3.

Fetal mean aortic pressure (MAP), heart rate (HR), P width, ST interval (middle), and QRS duration (bottom) calculated from the fetal ECG during an oxytocin pulse administered at 48 h after start of oxytocin pulses (left); n = 7 control (4 males, 3 females), 7 CORT (3 males, 4 females) for ECG, 8 CORT for HR and MAP (3 males, 5 females). Data are also shown at ∼20 h after the start of DCA infusion (∼68 h after the start of oxytocin pulses; right); n = 3 control fetuses (2 males, 1 female), 4 CORT fetuses (2 males, 2 females), 4 control + DCA fetuses (3 males, 1 female), 4 CORT + DCA fetuses (1 male, 3 females). Circles represent data from control group; squares represent data from CORT group; cross-hatched symbols at 48 h represent pre-DCA infusion values, open symbols are from the groups not treated with DCA, and closed symbols are from DCA-treated animals. All data are shown as means ± SE. CORT, cortisol-infused; DCA, dichloroacetate; bpm, beats per minute.

Figure 4.

Variable influence on projection (VIP) from OSC-PLSDA of the top 15 metabolites identified by NMR metabolomics measurements (NOESYPR) in hearts (left and right ventricular free wall and septum) from fetuses treated with DCA as compared with non-DCA-treated fetuses (with and without maternal cortisol infusion). Inset shows the scores plot. Red symbols indicate metabolites with greater abundance in hearts of DCA-treated fetuses; green symbols indicate metabolites with reduced abundance in hearts of DCA-treated fetuses. For the DCA group, n = 48 tissue samples from 16 animals (control DCA and CORT + DCA), for non-DCA group, n = 39 tissue samples from 13 animals (control and CORT without DCA administration). UK indicates unknown. OL indicates overlap, OL1: phosphoethanolamine overlaps with serine, OL2: serine overlaps with glycerophosphocholine, OL3: pantothenate overlap with carnitine. CORT, cortisol-infused; DCA, dichloroacetate; NOESYPR, nuclear overhauser effect spectroscopy with water presaturation; OSC-PLSDA, orthogonal signal-corrected partial least squares discriminant analysis.

Figure 5.

Mitochondrial respiration of permeabilized muscle fibers from the cardiac septum of control fetuses, and fetuses in the CORT, DCA, and CORT + DCA groups. Oxygen consumption (O₂ flux) is reported as integrative mitochondrial function (per tissue weight, pmol·s⁻¹·mg wet wt⁻¹) and as intrinsic mitochondrial function (per mitochondrial unit, with weight-specific citrate synthase activity as a proxy for mitochondrial content; pmol·s⁻¹·U CS activity⁻¹) in the following respiratory states: LEAK respiration, activated respiration supported by complex I substrates (OXPHOS, P_CI), activated respiration supported by complex I and II substrates (OXPHOS, P_CI+II), maximal respiration (maximal ETS capacity, E_CI+II), ETS capacity with only complex II substrates (E_CII), and maximal electron transport capacity of complex IV (E_CIV; with TMPD as the electron donor in the presence of ascorbate; for concentrations of all substrates, inhibitors, and uncoupler, see text. Leak, P_CI, P_CI+II, E_CI+II, and E_CII are corrected for residual, nonmitochondrial oxygen consumption (ROX), whereas E_CIV is corrected for chemical background. Values are means ± SE; n = 7 control, 6 CORT, 6 control + DCA, and 5 CORT + DCA samples of septum. ^aMain effect of DCA treatment at P < 0.05. CORT, cortisol-infused; DCA, dichloroacetate; ETS, electron transport system; TMPS, N,N,N′,N′-tetramethyl-p-phenylenediamine.