Synergistic effects of dopamine and Zn2+ on the induction of PC12 cell death and dopamine depletion in the striatum: possible implication in the pathogenesis of Parkinson's disease

Evaluating Manganese, Zinc, and Copper Metal Toxicity on SH-SY5Y Cells in Establishing an Idiopathic Parkinson's Disease Model

Parkinson's disease (PD) is a neurodegenerative condition marked by loss of motor coordination and cognitive impairment. According to global estimates, the worldwide prevalence of PD will likely exceed 12 million cases by 2040. PD is primarily associated with genetic factors, while clinically, cases are attributed to idiopathic factors such as environmental or occupational exposure. The heavy metals linked to PD and other neurodegenerative disorders include copper, manganese, and zinc. Chronic exposure to metals induces elevated oxidative stress and disrupts homeostasis, resulting in neuronal death. These metals are suggested to induce idiopathic PD in the literature. This study measures the effects of lethal concentration at 10% cell death (LC10) and lethal concentration at 50% cell death (LC50) concentrations of copper, manganese, and zinc chlorides on SH-SY5Y cells via markers for dopamine, reactive oxygen species (ROS) generation, DNA damage, and mitochondrial dysfunction after a 24 h exposure. These measurements were compared to a known neurotoxin to induce PD, 100 µM 6-hydroxydopamine (6-ODHA). Between the three metal chlorides, zinc was statistically different in all parameters from all other treatments and induced significant dopaminergic loss, DNA damage, and mitochondrial dysfunction. The LC50 of manganese and copper had the most similar response to 6-ODHA in all parameters, while LC10 of manganese and copper responded most like untreated cells. This study suggests that these metal chlorides respond differently from 6-ODHA and each other, suggesting that idiopathic PD utilizes a different mechanism from the classic PD model.

Synaptic Zinc: An Emerging Player in Parkinson's Disease

Alterations of zinc homeostasis have long been implicated in Parkinson's disease (PD). Zinc plays a complex role as both deficiency and excess of intracellular zinc levels have been incriminated in the pathophysiology of the disease. Besides its role in multiple cellular functions, Zn²⁺ also acts as a synaptic transmitter in the brain. In the forebrain, subset of glutamatergic neurons, namely cortical neurons projecting to the striatum, use Zn²⁺ as a messenger alongside glutamate. Overactivation of the cortico-striatal glutamatergic system is a key feature contributing to the development of PD symptoms and dopaminergic neurotoxicity. Here, we will cover recent evidence implicating synaptic Zn²⁺ in the pathophysiology of PD and discuss its potential mechanisms of actions. Emphasis will be placed on the functional interaction between Zn²⁺ and glutamatergic NMDA receptors, the most extensively studied synaptic target of Zn²⁺.

Postnatal zinc or paraquat administration increases paraquat or zinc-induced loss of dopaminergic neurons: insight into augmented neurodegeneration

Epidemiological evidences have shown an association of exposure to pesticides or heavy metals with increased incidences of Parkinson's disease (PD) in humans. Exposure to pesticides or metals during the decisive period of the brain development increases the susceptibility of dopaminergic neurons upon re-exposure in adult rodents. However, the effect of early life exposure to pesticide on the heavy metal-induced neurodegeneration or heavy metal on pesticide-induced neurodegeneration is not yet explored. The current study explored the effect of developmental exposure to zinc (Zn), a metal or paraquat (PQ), a pesticide on the nigrostriatal dopaminergic neurons of rats challenged to Zn or PQ during adulthood. Exposure of Zn or PQ during adulthood alone exhibited marked reduction in motor activities, striatal dopamine and metabolites, glutathione content and number of dopaminergic neurons. However, the levels of lipid peroxidation, protein carbonyls, superoxide dismutase activity, pro-inflammatory cytokines and 4-hydroxynonenal-protein adducts were increased. While the expression of vesicular monoamine transporter-2 and tyrosine hydroxylase were attenuated, dopamine transporter and microglial marker Iba-1 expression, activated microglia, nuclear factor-kappa B activation, mitochondrial cytochrome c release and caspase-3/9 activation were augmented following Zn or PQ exposure. Albeit postnatal alone exposure did not alter any of the studied parameters, the developmental administration of Zn/PQ in re-challenged adult rats produced more pronounced changes in the aforementioned variables as compared with adulthood Zn or PQ alone intoxicated animals. The results demonstrate that postnatal Zn/PQ intoxication dents the oxidative stress, inflammation, cell death and dopamine metabolism and storage regulating machineries, which speed up the toxicant-induced degeneration during adulthood.

Synaptic zinc contributes to motor and cognitive deficits in 6-hydroxydopamine mouse models of Parkinson's disease

Hyperactivity of glutamatergic corticostrial pathways is recognized as a key pathophysiological mechanism contributing to development of PD symptoms and dopaminergic neurotoxicity. Subset of corticostriatal projection neurons uses Zn²⁺ as a co-transmitter alongside glutamate, but the role of synaptically released Zn²⁺ in PD remains unexplored. We used genetically modified mice and pharmacological tools in combination with 6-hydroxydopamine (6-OHDA) lesion models of PD to investigate the contribution of synaptic zinc to disease associated behavioral deficits and neurodegeneration. Vesicular zinc transporter-3 (ZnT3) knockout mice lacking releasable Zn²⁺ were more resistant to locomotor deficit and memory impairment of nigrostriatal dopamine (DA) denervation compared to wildtype littermates. The loss of striatal dopaminergic fibers was comparable between genotypes, indicating that synaptically released Zn²⁺ contributes to behavioral deficits but not neurotoxic effects of 6-OHDA. To gain further insight into the mechanisms of Zn²⁺ actions, we used the extracellular Zn²⁺ chelator CaEDTA and knock-in mice lacking the high affinity Zn²⁺ inhibition of GluN2A-containing NMDA receptors (GluN2A-NMDARs). Acute chelation of extracellular Zn²⁺ in the striatum restored locomotor deficit of 6-OHDA lesion, confirming that synaptic Zn²⁺ suppresses locomotor behavior. Disruption of the Zn²⁺-GluN2A interaction had, on the other hand, no impact on locomotor deficit or neurotoxic effect of 6-OHDA. Collectively, these findings provide clear evidence for the implication of striatal synaptic Zn²⁺ in the pathophysiology of PD. They unveil that synaptic Zn²⁺ plays predominantly a detrimental role by promoting motor and cognitive deficits caused by nigrostriatal DA denervation, pointing towards new therapeutic interventions.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.

Phenotype-Dependent Interactions between N-acetyl-L-Aspartate and Acetyl-CoA in Septal SN56 Cholinergic Cells Exposed to an Excess of Zinc

Pyruvate dehydrogenase reaction utilizing glucose-derived pyruvate is an almost exclusive source of acetyl-CoA in different cell mitochondrial compartments of the brain. In neuronal mitochondria, the largest fraction of acetyl-CoA is utilized for energy production and the much smaller one for N-acetyl-L-aspartate (NAA) synthesis. Cholinergic neurons, unlike others, require additional amounts of acetyl-CoA for acetylcholine synthesis. Therefore, several neurotoxic signals, which inhibit pyruvate dehydrogenase, generate deeper shortages of acetyl-CoA and greater mortality of cholinergic neurons than noncholinergic ones. NAA is considered to be a marker of neuronal energy status in neuropathic brains. However, there is no data on putative differential fractional distribution of the acetyl-CoA pool between energy producing and NAA or acetylcholine synthesizing pathways in noncholinergic and cholinergic neurons, respectively. Therefore, the aim of this study was to investigate whether zinc-excess, a common excitotoxic signal, may evoke differential effects on the NAA metabolism in neuronal cells with low and high expression of the cholinergic phenotype. Differentiated SN56 neuronal cells, displaying a high activity of choline acetyltransferase and rates of acetylcholine synthesis, contained lower levels of acetyl-CoA and NAA, being more susceptible to ZnCl2 exposition that the nondifferentiated SN56 or differentiated dopaminergic SHSY5Y neuronal and astroglial C6 cells. Differentiated SN56 accumulated greater amounts of Zn2 + from extracellular space than the other ones, and displayed a stronger suppression of pyruvate dehydrogenase complex activity and acetyl-CoA, NAA, ATP, acetylcholine levels, and loss of viability. These data indicate that the acetyl-CoA synthesizing system in neurons constitutes functional unity with energy generating and NAA or acetylcholine pathways of its utilization, which are uniformly affected by neurotoxic conditions.

Cell death caused by the synergistic effects of zinc and dopamine is mediated by a stress sensor gene Gadd45b - implication in the pathogenesis of Parkinson's disease

The pathogenesis of Parkinson's disease (PD) is not completely understood, Zinc (Zn(2+) ) and dopamine (DA) have been shown to involve in the degeneration of dopaminergic cells. By microarray analysis, we identified Gadd45b as a candidate molecule that mediates Zn(2+) and DA-induced cell death; the mRNA and protein levels of Gadd45b are increased by Zn(2+) treatment and raised to an even higher level by Zn(2+) plus DA treatment. Zn(2+) plus DA treatment-induced PC12 cell death was enhanced when there was over-expression of Gadd45b and was decreased by knock down of Gadd45b. MAPK p38 and JNK signaling was able to cross-talk with Gadd45b during Zn(2+) and DA treatment. The synergistic effects of Zn(2+) and DA on PC12 cell death can be accounted for by an activation of the Gadd45b-induced cell death pathway and an inhibition of p38/JNK survival pathway. Furthermore, the in vivo results show that the levels of Gadd45b protein expression and phosphorylation of p38 were increased in the substantia nigra by the infusion of Zn(2+) /DA in the mouse brain and the level of Gadd45b mRNA is significantly higher in the substantia nigra of male PD patients than normal controls. The novel role of Gadd45b and its interactions with JNK and p38 will help our understanding of the pathogenesis of PD and help the development of future treatments for PD. Zinc and dopamine are implicated in the degeneration of dopaminergic neurons. We previously demonstrated that zinc and dopamine induced synergistic effects on PC12 cell death. Results from this study show that these synergistic effects can be accounted for by activation of the Gadd45b-induced cell death pathway and inhibition of the p38/JNK survival pathway. We provide in vitro and in vivo evidence to support a novel role for Gadd45b in the pathogenesis of Parkinson's disease.

Zn(2+)-Triggered Drug Release from Biocompatible Zirconium MOFs Equipped with Supramolecular Gates

A new theranostic nanoplatform, comprising of monodisperse zirconium metal-organic frameworks (MOFs) as drug carriers and carboxylatopillar[5]arene-based supramolecular switches as gating entities, is constructed, and controlled drug release triggered by bio-friendly Zn(2+) ions (abundant in synaptic vesicles) and auxiliary thermal stimulus is realized. This on-command drug delivery system exhibits large pore sizes for drug encapsulation, excellent biodegradability and biocompatibility, extremely low cytotoxicity and premature drug release, and superior dual-stimuli responsiveness, opening a new avenue in targeted drug delivery and controlled release of therapeutic agents, especially in the treatment of central nervous system diseases.

Dopamine- and zinc-induced autophagosome formation facilitates PC12 cell survival

Dopamine oxidation and divalent cations have been reported to induce neuronal cell death. Although autophagy is involved in neuronal cell death, it has also been suggested to facilitate cell survival. We sought to investigate the role of autophagy in PC12 cells and cultured neurons treated with dopamine and Zn2+. Cells expressing EGFP-LC3 were treated with high concentrations of dopamine and Zn2+, and the formation of EGFP-LC3 fluorescence aggregates was monitored. Our results showed a significant increase in the number of fluorescent puncta in the cytosol of PC12 cells treated with these chemicals. These treatments enhanced LC3 lipidation levels in PC12 cells. Decreasing the ATG7 protein level using specific small interference RNA (siRNA) and pretreating with phosphatidylinositol 3-phosphate kinase blockers, wortmannin and LY294002, inhibited puncta formation. Dopamine or Zn2+ treatment significantly elevated the intracellular Zn2+ concentration ([Zn2+] i ); however, inhibiting the [Zn2+] i elevation in dopamine-treated cells suppressed the puncta formation. LY294002 or siRNA-directed members of the autophagy pathway increased the fraction of phosphatidylserine present on the outer membrane leaflet in PC12 cells treated with dopamine or Zn2+, suggesting an increase in apoptosis. Primary embryonic midbrain neurons expressing EGFP-LC3 also displayed a significant increase in the number of fluorescent aggregates in cells upon treatment with dopamine or Zn2+. Dopamine or Zn2+ treatment significantly elevated the [Zn2+] i in neurons and caused neuronal death. Our results indicate that treating cells with dopamine and Zn2+ results in the activation of the autophagy pathway in an effort to enhance cell survival.

Elemental micro-imaging and quantification of human substantia nigra using synchrotron radiation based x-ray fluorescence--in relation to Parkinson's disease

Synchrotron radiation based x-ray fluorescence (SRXRF) was applied to the quantitative evaluation of elemental changes in substantia nigra pars compacta (SNc) in Parkinson's disease (PD) in the framework of a study on the role of chemical elements in the pathophysiology of PD. The analysis was carried out for dopaminergic nerve cells and extraneuronal spaces. The mass fractions of P, S, Cl, K, Ca, Fe, Cu, Zn, Br and Rb were determined. The application of standard samples developed especially for the determination of elemental mass fractions in thin tissue sections using the SRXRF technique is presented. Two-dimensional maps of elemental distribution show that the location of nerve cells in SNc sections is precisely visualized by the high levels of most elements. It was found that statistically significant differences between control and PD neurons are observed for S (p = 0.04), Cl (p = 0.02), Ca (p = 0.08), Fe (p = 0.04) and Zn (p = 0.04). The mass fractions of P (p = 0.08), S (p = 0.07), Cl (p = 0.04), Zn (p = 0.08) and Rb (p = 0.08) in areas outside the nerve cell bodies differed significantly between PD and control groups. A clear cluster separation between the PD nerve cells and neurons representing the control group was noticed. It was found that Cl, Fe, Ca and Zn are the most significant elements in the general discrimination between PD nerve cells and the control. The comparison between the extraneuronal spaces showed that Cl, Fe and Cu differentiate the PD and control group the most. The evident contribution of chemical elements to the pathophysiology of PD was shown.

Changes in plasma membrane surface potential of PC12 cells as measured by Kelvin probe force microscopy

The plasma membrane of a cell not only works as a physical barrier but also mediates the signal relay between the extracellular milieu and the cell interior. Various stimulants may cause the redistribution of molecules, like lipids, proteins, and polysaccharides, on the plasma membrane and change the surface potential (Φ_s). In this study, the Φ_ss of PC12 cell plasma membranes were measured by atomic force microscopy in Kelvin probe mode (KPFM). The skewness values of the Φ_ss distribution histogram were found to be mostly negative, and the incorporation of negatively charged phosphatidylserine shifted the average skewness values to positive. After being treated with H₂O₂, dopamine, or Zn²⁺, phosphatidylserine was found to be translocated to the membrane outer leaflet and the averaged skewness values were changed to positive values. These results demonstrated that KPFM can be used to monitor cell physiology status in response to various stimulants with high spatial resolution.

Effect of zinc and paraquat co-exposure on neurodegeneration: Modulation of oxidative stress and expression of metallothioneins, toxicant responsive and transporter genes in rats

Oxidative stress is implicated in Parkinson's disease (PD). Metallothioneins (MT), cytochrome P450 IIE1 (CYP2E1) and glutathione S-transferases alpha4-4 (GSTA4-4) are involved in oxidative stress-mediated damage. Altered dopamine transporter (DAT) and vesicular monoamine transporter-2 (VMAT-2) are also documented in PD. The present study was undertaken to investigate the effect of Zn and PQ co-exposure on neurodegeneration in rats. A significant reduction was observed in spontaneous locomotor activity (SLA), striatal dopamine (DA) levels, tyrosine hydroxylase (TH) immunoreactivity, glutathione reductase (GR) and catalase activity along with increased lipid peroxidation (LPO) and glutathione peroxidase (GPx) activity after Zn and/or PQ exposure. Zn and/or PQ exposure increased gene expression of DAT, CYP2E1, GSTA4-4, MT-I and MT-II, but reduced the expression of VMAT-2. Protein expression analysis of TH, VMAT-2 and DAT showed results similar to those obtained with gene expression study. Zn and PQ co-exposure caused a more pronounced effect than that of individual exposure. The results obtained in this study suggest that, similar to PQ, Zn induced neurodegeneration via alterations in oxidative stress and expression of the above-mentioned genes. However, the effect of Zn+PQ was only slightly higher than that of alone, indicating that probably Zn and PQ follow some different molecular events leading to neurodegeneration.

Development of advanced therapies based on viral vector-mediated overexpression of therapeutic molecules and knockdown of disease-related genes for Parkinson’s disease

The last decade witnessed the translation of several gene-based therapeutic approaches from experimental studies to early clinical trials. Studies targeting the treatment of Parkinson’s disease (PD) were among the forefront of trials in the CNS. In this article, we overview three major strategies for the treatment of PD: the enzyme-replacement strategies are based on well-defined principles of functional restoration and are well suited for treatment of patients with advanced disease who would typically experience complications due to side effects of pharmacotherapy. Neurotrophic factor delivery, on the other hand, aims to delay the disability and eventually modifiy disease progression. Finally, we present an outlook to a completely new way of interfering with the disease process, which is taking advantage of recently discovered RNAi mechanisms in cells. Gene therapy is now becoming a reality in the clinics and developments in the next decade will help uncover the true potential of this approach for not only the treatment of PD patients, but also many other neurological disorders.

Cytosolic labile zinc accumulation in degenerating dopaminergic neurons of mouse brain after MPTP treatment

High levels of labile zinc accumulate in degenerating neurons after brain injury, such as ischemic stroke, trauma, epilepsy, and hypoglycemia. Cytosolic zinc accumulation is also found in brain neurons undergoing apoptosis during development or after neuronal target ablation. Thus, staining with zinc-specific probes can be used to identify neuronal death in the brain. In this study, mice were intraperitoneally given four 20 mg/kg doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at 2-hour intervals, and dopaminergic neurons were then evaluated for zinc accumulation and apoptosis. In the substantia nigra pars compacta, zinc-specific fluorescent dyes revealed that all degenerating neurons, identified by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL), or acid fuchsin or Fluoro-Jade C staining, contained high levels of cytosolic labile zinc. Nuclear condensation/fragmentation was noted in dopaminergic neurons with cytosolic zinc accumulation, indicating apoptotic cell death. These findings support the supposition that cytosolic labile zinc accumulation is an indicator of degenerating dopaminergic neurons in animal models of Parkinson's disease.

Covalent arylation of metallothionein by oxidized dopamine products: a possible mechanism for zinc-mediated enhancement of dopaminergic neuron survival

Metallothioneins are a group of low molecular weight proteins which can be induced upon exposure to metal ions, including Zn(II). These cysteine-rich proteins are believed to have antioxidant-like properties due to their ability to scavenge free radicals with their multiple sulfhydryl groups. Dopamine is a neurotransmitter that can form toxic quinone and semi-quinone products in an oxidative environment. While Zn(II) is known to be toxic to some neuron subtypes, here we report a beneficial effect of Zn(II) on dopaminergic neurons and identify a mechanism through which metallothionein may scavenge toxic dopamine oxidation products. Cultured embryonic neurons were treated with Zn(II), and the number of dopaminergic neurons surviving after two or three weeks in culture was determined. We demonstrate that under these conditions metallothionein is upregulated and is able to form covalent arylation products with dopamine and 6-hydroxydopamine both in vitro and in culture. These experiments suggest that Zn(II) enhances the survival of dopaminergic neurons, and we propose that as a mechanism, upregulated metallothioneins form covalent adducts with both dopamine and 6-hydroxydopamine, resulting in the observed neuroprotective effect of Zn(II) on these cells. As Zn(II) homeostasis and modulation of metallothionein expression are hallmarks of neurodegeneration, these studies may have significant implications for understanding the underlying basis of degenerative diseases involving dopaminergic neurons, including Parkinson's disease.

Imunoreactivity of zinc transporter 7 (ZNT7) in mouse dorsal root ganglia

In the present study, we showed for the first time the localization of ZNT7 immunoreactivity in the mouse dorsal root ganglion (DRG) by means of immunohistochemistry and confocal laser scanning microscopy. Our results revealed that ZNT7 immunoreactivity was abundantly expressed in the nerve cells of the mouse DRG. Strong ZNT7 immunoreactivity was predominantly distributed in the perinuclear region of positive cells, while the nuclei were devoid of staining. Double immunofluorescence labeling of ZNT7 and TGN38 revealed a colocalization of the two antigens in the Golgi apparatus. In addition, the presence of labile zinc ions was detected with in vivo zinc selenium autometallography (AMG). AMG observations showed that the zinc staining pattern was also predominately located in the perinuclear Golgi area, like the ZNT7 immunostaining pattern in the DRG. These observations strongly suggest that ZNT7 may play an important role in facilitating zinc transport into the Golgi apparatus from the cytosol in the mouse DRG.

Effects of tri butyl tin acetate on dopamine biosynthesis and l-dopa-lnduced cytotoxicity in pc12 cells

The effects of tributyltin acetate (TBTA) on dopamine biosynthesis and L-3,4-dihydroxyphenylalanine (L-DOPA)-induced cytotoxicity in PC12 cells were examined. TBTA at concentrations of 0.1-0.2 microM inhibited dopamine biosynthesis by reducing tyrosine hydroxylase (TH) activity and TH gene expression in PC12 cells. TBTA at 0.1-0.4 microM also reduced L-DOPA (20-50 microM)-induced increases in dopamine content for 24 h in PC12 cells. TBTA at concentrations up to 0.3 microM did not affect cell viability. However, TBTA at concentrations higher than 0.4 microM caused apoptotic cytotoxicity. Exposure of PC12 cells to non-cytotoxic (0.1 and 0.2 microM) or cytotoxic (0.4 microM) concentrations of TBTA with L-DOPA (20, 50 and 100 microM) significantly increased the cell loss and the percentage of apoptotic cells after 24 or 48 h compared with TBTA or L-DOPA alone. These data suggest that TBTA inhibits dopamine biosynthesis and enhances L-DOPA-induced cytotoxicity in PC12 cells.

Zinc balance and medications commonly used in the management of heart failure

Heart failure (HF) is a prevalent syndrome resulting in a high mortality rate. HF may be associated with zinc deficiency through a reduction in dietary intake, decreased absorption due to gastrointestinal edema, impaired motility or intestinal zinc losses. Diseases concomitant with HF such as diabetes mellitus (DM) and hypertension may enhance zinc deficiency. Medications given for HF may affect zinc metabolism in different ways. It was shown that thiazides may cause zincuria and a decrease in tissue zinc concentration. There is conflicting evidence about furosemide, even though patients with chronic furosemide treatment showed low tissue zinc levels in autopsies. Treatment with angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) resulted in zincuria and zinc deficiency, but this outcome was not consistent in all studies. Beta-blockers did not alter plasma zinc concentration. Matrix metalloproteinases (MMPs) and ACE are zinc-containing enzymes, which play a role in the process of remodeling in HF. It was shown that ACE inhibitors may inhibit the activity of different MMPs. The exact interrelationship between HF, zinc-containing enzymes, zinc deficiency and the clinical manifestation of HF has to be investigated.