Cardiac Cytochrome-c Oxidase Deficiency Occurs During Late Postnatal Development in Progeny of Copper-Deficient Rats

The possible association of mitochondrial fusion and fission in copper deficiency-induced oxidative damage and mitochondrial dysfunction of the heart

INTRODUCTION

As an essential trace element, Copper (Cu) participates in numerous physiological and biological reactions in the body. Cu is closely related to heart health, and an imbalance of Cu will cause cardiac dysfunction. The research aims to examine how Cu deficiency affects the heart, assess mitochondrial function in the hearts, and disclose possible mechanisms of its influence.

METHODS

Weaned mice were fed Cu-deficient diets and intraperitoneally given copper sulfate (CuSO4) to correct the Cu deficiency. The pathological change of the heart was assessed using histological inspection. Cardiac function and oxidative stress levels were evaluated by biochemical assay kits. ELISA and ATP detection kits were used to detect the levels of complexes I-IV in the mitochondrial respiratory chain (MRC) and ATP, respectively. Real time PCR was utilized to determine mRNA expressions, and Western blotting was adopted to determine protein expressions, of molecules related to mitochondrial fission and fusion.

RESULTS

Cu deficiency gave rise to elevated heart index, cardiac histological alterations and oxidation injury, increased serum levels of creatine kinase (CK), lactic dehydrogenase (LDH), and creatine kinase isoenzyme MB (CK-MB) together with increased malondialdehyde (MDA) production, decreased the glutathione (GSH), Superoxide Dismutase (SOD), and Catalase (CAT) activities or contents. Besides, Cu deficiency caused mitochondrial damage characterized by decreased contents of complexes I-IV in the MRC and ATP in the heart. In the meantime, Cu deficiency also reduced protein and mRNA expressions of factors associated with mitochondrial fusion, including Mfn1 and Mfn2, while significantly increased factors Drip1 and Fis1 related to mitochondrial fission. However, adding CuSO4 improved the above changes significantly.

CONCLUSION

According to research results, Cu deficiency can cause heart damage in mice, along with oxidative damage and mitochondrial dysfunction, which are closely related to mitochondrial fusion and fission disorders.

Redox homeostasis in cardiac fibrosis: Focus on metal ion metabolism

Cardiac fibrosis is a major public health problem worldwide, with high morbidity and mortality, affecting almost all patients with heart disease worldwide. It is characterized by fibroblast activation, abnormal proliferation, excessive deposition, and abnormal distribution of extracellular matrix (ECM) proteins. The maladaptive process of cardiac fibrosis is complex and often involves multiple mechanisms. With the increasing research on cardiac fibrosis, redox has been recognized as an important part of cardiac remodeling, and an imbalance in redox homeostasis can adversely affect the function and structure of the heart. The metabolism of metal ions is essential for life, and abnormal metabolism of metal ions in cells can impair a variety of biochemical processes, especially redox. However, current research on metal ion metabolism is still very limited. This review comprehensively examines the effects of metal ion (iron, copper, calcium, and zinc) metabolism-mediated redox homeostasis on cardiac fibrosis, outlines possible therapeutic interventions, and addresses ongoing challenges in this rapidly evolving field.

Exposure to essential and non-essential trace elements and risks of congenital heart defects: A narrative review

Congenital heart defects (CHDs) are congenital abnormalities involving the gross structures of the heart and large blood vessels. Environmental factors, genetic factors and their interactions may contribute to the pathogenesis of CHDs. Generally, trace elements can be classified into essential trace elements and non-essential trace elements. Essential trace elements such as copper (Cu), zinc (Zn), iron (Fe), selenium (Se), and manganese (Mn) play important roles in human biological functions such as metabolic function, oxidative stress regulation, and embryonic development. Non-essential trace elements such as cadmium (Cd), arsenic (As), lead (Pb), nickle (Ni), barium (Ba), chromium (Cr) and mercury (Hg) are harmful to health even at low concentrations. Recent studies have revealed the potential involvement of these trace elements in the pathogenesis of CHDs. In this review, we summarized current studies exploring exposure to essential and non-essential trace elements and risks of CHDs, in order to provide further insights for the pathogenesis and prevention of CHDs.

An Emerging Role of Defective Copper Metabolism in Heart Disease

Copper is an essential trace metal element that significantly affects human physiology and pathology by regulating various important biological processes, including mitochondrial oxidative phosphorylation, iron mobilization, connective tissue crosslinking, antioxidant defense, melanin synthesis, blood clotting, and neuron peptide maturation. Increasing lines of evidence obtained from studies of cell culture, animals, and human genetics have demonstrated that dysregulation of copper metabolism causes heart disease, which is the leading cause of mortality in the US. Defects of copper homeostasis caused by perturbed regulation of copper chaperones or copper transporters or by copper deficiency resulted in various types of heart disease, including cardiac hypertrophy, heart failure, ischemic heart disease, and diabetes mellitus cardiomyopathy. This review aims to provide a timely summary of the effects of defective copper homeostasis on heart disease and discuss potential underlying molecular mechanisms.

Evaluation of the Safety and Toxicity of the Original Copper Nanocomposite Based on Poly-N-vinylimidazole

A new original copper nanocomposite based on poly-N-vinylimidazole was synthesized and characterized by a complex of modern physicochemical and biological methods. The low cytotoxicity of the copper nanocomposite in relation to the cultured hepatocyte cells was found. The possibility to involve the copper from the nanocomposite in the functioning of the copper-dependent enzyme systems was evaluated during the incubation of the hepatocyte culture with this nanocomposite introduced to the nutrient medium. The synthesized new water-soluble copper-containing nanocomposite is promising for biotechnological and biomedical research as a new non-toxic hydrophilic preparation that is allowed to regulate the work of key enzymes involved in energy metabolism and antioxidant protection as well as potentially serving as an additional source of copper.

IHD from copper deficiency: a unified theory

The theory, in brief outline here, implicating deficiency of Cu in the aetiology and pathophysiology of IHD explains more attributes of the disease than any other theory. This theory satisfies several of Hill's criteria of a half-century ago for deducing association between an environmental feature and presence of an illness. Most important is the temporal association between the rise of IHD and the decrease in dietary Cu since the 1930s along with a parallel increase in the supplementation of pregnant women with Fe, a Cu antagonist. There are more than eighty anatomical, chemical and physiological similarities between animals deficient in Cu and individuals with IHD. Few of these similarities have been produced by other dietary manipulations because feeding cholesterol induces Cu deficiency in animals. The most recent of these to be identified is decreased serum dehydroepiandrosterone. Some concomitant aspects of Cu metabolism and utilisation have been identified in other theories about heart disease: fetal programming, homocysteine, and Fe overload.

Role of copper in regression of cardiac hypertrophy

Pressure overload causes an accumulation of homocysteine in the heart, which is accompanied by copper depletion through the formation of copper-homocysteine complexes and the excretion of the complexes. Copper supplementation recovers cytochrome c oxidase (CCO) activity and promotes myocardial angiogenesis, along with the regression of cardiac hypertrophy and the recovery of cardiac contractile function. Increased copper availability is responsible for the recovery of CCO activity. Copper promoted expression of angiogenesis factors including vascular endothelial growth factor (VEGF) in endothelial cells is responsible for angiogenesis. VEGF receptor-2 (VEGFR-2) is critical for hypertrophic growth of cardiomyocytes and VEGFR-1 is essential for the regression of cardiomyocyte hypertrophy. Copper, through promoting VEGF production and suppressing VEGFR-2, switches the VEGF signaling pathway from VEGFR-2-dependent to VEGFR-1-dependent, leading to the regression of cardiomyocyte hypertrophy. Copper is also required for hypoxia-inducible factor-1 (HIF-1) transcriptional activity, acting on the interaction between HIF-1 and the hypoxia responsible element and the formation of HIF-1 transcriptional complex by inhibiting the factor inhibiting HIF-1. Therefore, therapeutic targets for copper supplementation-induced regression of cardiac hypertrophy include: (1) the recovery of copper availability for CCO and other critical cellular events; (2) the activation of HIF-1 transcriptional complex leading to the promotion of angiogenesis in the endothelial cells by VEGF and other factors; (3) the activation of VEGFR-1-dependent regression signaling pathway in the cardiomyocytes; and (4) the inhibition of VEGFR-2 through post-translational regulation in the hypertrophic cardiomyocytes. Future studies should focus on target-specific delivery of copper for the development of clinical application.

Vascular endothelial growth factor recovers suppressed cytochrome c oxidase activity by restoring copper availability in hypertrophic cardiomyocytes

Cardiomyocyte hypertrophy induced by phenylepherine (PE) is accompanied by depression of cytochrome c oxidase (COX) activity. Vascular endothelial growth factor (VEGF) recovers the suppressed COX activity and reverses cardiomyocyte hypertrophy. Because PE causes intracellular copper (Cu) depletion and COX activity is Cu-dependent, the present study was undertaken to test the hypothesis that VEGF recovers suppressed COX activity by restoring Cu availability. Primary cultures of neonatal rat cardiomyocytes were treated with PE at a final concentration of 100 µmol/L in cultures for 48 h to induce cell hypertrophy. The hypertrophic cardiomyocytes were exposed to VEGF at a final concentration of 20 ng/mL in cultures for 24 h. Atomic absorption spectrometry analysis revealed that VEGF restored PE-depleted Cu concentrations in hypertrophic cardiomyocytes along with the recovery of COX activity. Western blot analysis showed that protein contents of COX subunit COX-IV and Cu chaperones for COX (COX17, COX11, and SCO2) were decreased in response to PE treatment, and recovered after VEGF treatment. In addition, VEGF treatment suppressed PE-induced accumulation of reactive oxygen species (ROS) and the relevant elevation of homocysteine, which has been shown to form complexes with Cu to restrict Cu availability. This study thus demonstrates that VEGF recovers PE-suppressed COX activity by restoring Cu availability and VEGF suppression of ROS accumulation and homocysteine elevation would contribute to the increased Cu availability.

Variable response of selected cuproproteins in rat choroid plexus and cerebellum following perinatal copper deficiency

Recent immunohistochemical characterization of the copper transport protein, Ctr1, reported enriched levels in mouse choroid plexus, and enhancement by copper deficiency. To extend and confirm this, experiments were conducted with Holtzman rats. Following perinatal copper deficiency there was an 80% reduction in brain copper of 24-27 day old copper-deficient (Cu-) rat pups compared to copper-adequate (Cu+) controls. Choroid plexus immunoblot analysis with rabbit anti-hCtr1 demonstrated a 50% higher Ctr1 protein expression in Cu-samples. However, levels of copper chaperone for superoxide dismutase (CCS) were unchanged, suggesting that Ctr1 buffers the choroid plexus against copper deficiency, since CCS normally is much higher in Cu-tissues. There were 13% lower levels of cytochrome c oxidase subunit IV (COX IV) detected in Cuchoroid plexus. In contrast, in cerebellum of Cu-rats CCS was 2-fold higher and COXIV 1.7-fold lower than Cu+ rats consistent with severe copper deficiency. Brain mitochondria from Cu-rats had severe reductions in COXIV content and CCO activity and modest but significant elevations in CCS and reductions in Cu, Zn-superoxide dismutase. COXIV may be a more sensitive marker for copper deficiency than CCS and may prove useful to assess copper status.

Cardiac cytochrome C oxidase activity and contents of subunits 1 and 4 are altered in offspring by low prenatal copper intake by rat dams

It has been reported previously that the offspring of rat dams consuming low dietary copper (Cu) during pregnancy and lactation experience a deficiency in cardiac cytochrome c oxidase (CCO) characterized by reduced catalytic activity and mitochondrial and nuclear subunit content after postnatal d 10. The present study was undertaken to determine whether the cardiac CCO deficiency was caused directly by low postnatal Cu intake or whether it was a prenatal effect of low Cu intake by the dams that became manifest postnatally. Dams were fed either a Cu-adequate diet (6 mg Cu/kg) or Cu-deficient diet (1 mg Cu/kg) beginning 3 wk before conception and throughout gestation and lactation. One day following parturition, several litters from Cu-adequate dams were cross fostered to Cu-deficient dams and several litters from Cu-deficient dams were cross fostered to Cu-adequate dams. Litters that remained with their birth dams served as controls. CCO activity, the content of the mitochondrial-encoded CCO subunit 1 (COX1), and the content of the nuclear-encoded subunit COX4 in cardiac mitochondria were reduced in the 21-d-old offspring of Cu-deficient dams. COX1 content was normal in the 21-d-old cross-fostered offspring of Cu-deficient dams, but CCO activity and COX4 were reduced. Cross fostering the offspring of Cu-adequate dams to Cu-deficient dams did not significantly affect CCO activity, COX1 content, or COX4 content in cardiac mitochondria of 21-d-old offspring. These data indicate that low prenatal Cu intake by dams was the determinant of CCO activity in cardiac mitochondria of the 21-d-old offspring and may have led to the assembly of a less-than-fully active holoenzyme.

Copper deficiency decreases complex IV but not complex I, II, III, or V in the mitochondrial respiratory chain in rat heart

It has been documented that dietary copper (Cu) deficiency impairs mitochondrial respiratory function, which is catalyzed by 5 membrane-bound multiple protein complexes. However, there are few reports on the simultaneous analysis of Cu effect on the subunit protein expression on all 5 protein complexes. The present study was undertaken to determine the effect of Cu deficiency on each mitochondrial respiratory complex's protein expression in rat heart tissue with western-blot analysis. Male Sprague-Dawley rats were fed diets that were either Cu adequate (6.0 microg Cu/g diet, n = 5) or Cu deficient (0.3 microg Cu/g diet, n = 5) for 5 wk. The monoclonal antibody-based western-blot analysis suggested that the protein levels of 39-kDa and 30-kDa subunits in complex I; 70-kDa and 30-kDa subunits in complex II; core I and core II subunits in complex III; and alpha and beta subunits of F1 complex in complex V in both high-salt buffer (HSB) and low-salt buffer (LSB) protein fractions from heart tissue of Cu-deficient rats did not differ from those of Cu-adequate rats. However, the protein level of cytochrome c oxidase (CCO) subunit (COX) I, COX Vb, and COX VIb subunits in complex IV (CCO) in both HSB and LSB protein fractions from heart tissue of Cu-deficient rats was lower than those of Cu-adequate rats. Collectively, these data demonstrate that Cu deficiency decreases each tested subunit protein expression of complex IV but not those of complex I, II, III, and V in mitochondrial respiratory complexes.