Metabolic alterations in a rat model of takotsubo syndrome.

AIMS: Cardiac energetic impairment is a major finding in takotsubo patients. We investigate specific metabolic adaptations to direct future therapies. METHODS AND RESULTS: An isoprenaline-injection female rat model (vs. sham) was studied at Day 3; recovery assessed at Day 7. Substrate uptake, metabolism, inflammation, and remodelling were investigated by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography, metabolomics, quantitative PCR, and western blot (WB). Isolated cardiomyocytes were patch-clamped during stress protocols for redox states of NAD(P)H/FAD or [Ca2+]c, [Ca2+]m, and sarcomere length. Mitochondrial respiration was assessed by seahorse/Clark electrode (glycolytic and ß-oxidation substrates). Cardiac 18F-FDG metabolic rate was increased in takotsubo (P = 0.006), as was the expression of GLUT4-RNA/GLUT1/HK2-RNA and HK activity (all P < 0.05), with concomitant accumulation of glucose- and fructose-6-phosphates (P > 0.0001). Both lactate and pyruvate were lower (P < 0.05) despite increases in LDH-RNA and PDH (P < 0.05 both). ß-Oxidation enzymes CPT1b-RNA and 3-ketoacyl-CoA thiolase were increased (P < 0.01) but malonyl-CoA (CPT-1 regulator) was upregulated (P = 0.01) with decreased fatty acids and acyl-carnitines levels (P = 0.0001-0.02). Krebs cycle intermediates α-ketoglutarate and succinyl-carnitine were reduced (P < 0.05) as was cellular ATP reporter dihydroorotate (P = 0.003). Mitochondrial Ca2+ uptake during high workload was impaired on Day 3 (P < 0.0001), inducing the oxidation of NAD(P)H and FAD (P = 0.03) but resolved by Day 7. There were no differences in mitochondrial respiratory function, sarcomere shortening, or [Ca2+] transients of isolated cardiomyocytes, implying preserved integrity of both mitochondria and cardiomyocyte. Inflammation and remodelling were upregulated-increased CD68-RNA, collagen RNA/protein, and skeletal actin RNA (all P < 0.05). CONCLUSION: Dysregulation of glucose and lipid metabolic pathways with decreases in final glycolytic and ß-oxidation metabolites and reduced availability of Krebs intermediates characterizes takotsubo myocardium. The energetic deficit accompanies defective Ca2+ handling, inflammation, and upregulation of remodelling pathways, with the preservation of sarcomeric and mitochondrial integrity.

Acute dietary zinc deficiency in rats exacerbates myocardial ischaemia-reperfusion injury through depletion of glutathione.

Zn plays an important role in maintaining the anti-oxidant status within the heart and helps to counter the acute redox stress that occurs during myocardial ischaemia and reperfusion. Individuals with low Zn levels are at greater risk of developing an acute myocardial infarction; however, the impact of this on the extent of myocardial injury is unknown. The present study aimed to compare the effects of dietary Zn depletion with in vitro removal of Zn (N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN)) on the outcome of acute myocardial infarction and vascular function. Male Sprague-Dawley rats were fed either a Zn-adequate (35 mg Zn/kg diet) or Zn-deficient (<1 mg Zn/kg diet) diet for 2 weeks before heart isolation. Perfused hearts were subjected to a 30 min ischaemia/2 h reperfusion (I/R) protocol, during which time ventricular arrhythmias were recorded and after which infarct size was measured, along with markers of anti-oxidant status. In separate experiments, hearts were challenged with the Zn chelator TPEN (10 µm) before ischaemia onset. Both dietary and TPEN-induced Zn depletion significantly extended infarct size; dietary Zn depletion was associated with reduced total cardiac glutathione (GSH) levels, while TPEN decreased cardiac superoxide dismutase 1 levels. TPEN, but not dietary Zn depletion, also suppressed ventricular arrhythmias and depressed vascular responses to nitric oxide. These findings demonstrate that both modes of Zn depletion worsen the outcome from I/R but through different mechanisms. Dietary Zn deficiency, resulting in reduced cardiac GSH, is the most appropriate model for determining the role of endogenous Zn in I/R injury.