A temporal profile of myocardial zinc changes after isoproterenol induced cardiac necrosis

Sleep fragmentation exacerbates myocardial ischemia‒reperfusion injury by promoting copper overload in cardiomyocytes

Sleep disorders increase the risk and mortality of heart disease, but the brain-heart interaction has not yet been fully elucidated. Cuproptosis is a copper-dependent type of cell death activated by the excessive accumulation of intracellular copper. Here, we showed that 16 weeks of sleep fragmentation (SF) resulted in elevated copper levels in the male mouse heart and exacerbated myocardial ischemia-reperfusion injury with increased myocardial cuproptosis and apoptosis. Mechanistically, we found that SF promotes sympathetic overactivity, increases the germination of myocardial sympathetic nerve terminals, and increases the level of norepinephrine in cardiac tissue, thereby inhibits VPS35 expression and leads to impaired ATP7A related copper transport and copper overload in cardiomyocytes. Copper overload further leads to exacerbated cuproptosis and apoptosis, and these effects can be rescued by excision of the sympathetic nerve or administration of copper chelating agent. Our study elucidates one of the molecular mechanisms by which sleep disorders aggravate myocardial injury and suggests possible targets for intervention.

Calcium and zinc dyshomeostasis during isoproterenol-induced acute stressor state

Acute hyperadrenergic stressor states are accompanied by cation dyshomeostasis, together with the release of cardiac troponins predictive of necrosis. The signal-transducer-effector pathway accounting for this pathophysiological scenario remains unclear. We hypothesized that a dyshomeostasis of extra- and intracellular Ca2+ and Zn2+ occurs in rats in response to isoproterenol (Isop) including excessive intracellular Ca2+ accumulation (EICA) and mitochondrial [Ca2+]m-induced oxidative stress. Contemporaneously, the selective translocation of Ca2+ and Zn2+ to tissues contributes to their fallen plasma levels. Rats received a single subcutaneous injection of Isop (1 mg/kg body wt). Other groups of rats received pretreatment for 10 days with either carvedilol (C), a β-adrenergic receptor antagonist with mitochondrial Ca2+ uniporter-inhibiting properties, or quercetin (Q), a flavonoid with mitochondrial-targeted antioxidant properties, before Isop. We monitored temporal responses in the following: [Ca2+] and [Zn2+] in plasma, left ventricular (LV) apex, equator and base, skeletal muscle, liver, spleen, and peripheral blood mononuclear cells (PBMC), indices of oxidative stress and antioxidant defenses, mitochondrial permeability transition pore (mPTP) opening, and myocardial fibrosis. We found ionized hypocalcemia and hypozincemia attributable to their tissue translocation and also a heterogeneous distribution of these cations among tissues with a preferential Ca2+ accumulation in the LV apex, muscle, and PBMC, whereas Zn2+ declined except in liver, where it increased corresponding with upregulation of metallothionein, a Zn2+-binding protein. EICA was associated with a simultaneous increase in tissue 8-isoprostane and increased [Ca2+]m accompanied by a rise in H2O2 generation, mPTP opening, and scarring, each of which were prevented by either C or Q. Thus excessive [Ca2+]m, coupled with the induction of oxidative stress and increased mPTP opening, suggests that this signal-transducer-effector pathway is responsible for Isop-induced cardiomyocyte necrosis at the LV apex.

Excessive intracellular zinc accumulation in cardiac and skeletal muscles of dystrophic hamsters

Zinc has been reported to be important in protein synthesis, collagen crosslinking, membrane structure and function, cellular necrosis, muscle glycolysis, and cardiac dysfunction. As all these processes are affected by muscular dystrophy, we studied the Zn concentrations in the cardiac and skeletal muscles of 7-month-old male dystrophic hamsters with advanced hypertrophic cardiomyopathy. Age- and sex-matched normal hamsters served as controls. Calcium, magnesium, and copper concentrations were also measured in the dystrophic and normal tissues. Flame atomic absorption spectrophotometry was used for mineral quantitation of the nitric acid tissue extracts. Zn concentrations in the myocardium (P less than 0.002), diaphragm (P less than 0.005), and rectus femoris muscles (P less than 0.001) were significantly elevated with concomitant elevations of Ca in dystrophic compared with normal hamsters. Although no appreciable changes in Cu or Mg concentrations were noted in the myocardium, slight depletions of Cu in the dystrophic diaphragm (P less than 0.025) and Mg in the dystrophic rectus femoris (P less than 0.05) were present. The intracellular Zn and Ca accumulations in the cardiac and skeletal muscles of dystrophic hamsters correlated with other dystrophic features such as increased rates of protein synthesis, significant myocardial enlargement, characteristic electrocardiographic and mechanophysiologic abnormalities, and classical histopathologic changes. We hypothesize that Zn2+ may be cotransported with Ca2+ across the cellular membrane or substituted for Ca2+ in certain pathways. These mechanisms may be affected by the high-energy ATP-pump and/or the sodium-potassium exchange system at the cellular level. Our observations suggest a possible pathogenetic involvement of Zn in muscular dystrophy which may be associated with an accelerated effort by the cellular system to repair the damaged cardiac and skeletal muscles.