Jack T. Saari

Cardiac Metallothionein Induction Plays the Major Role in the Prevention of Diabetic Cardiomyopathy by Zinc Supplementation

Background— Our previous studies showed that transgenic mice that overexpress cardiac-specific metallothionein (MT) are highly resistant to diabetes-induced cardiomyopathy. Zinc is the major metal that binds to MT under physiological conditions and is a potent inducer of MT. The present study therefore explored whether zinc supplementation can protect against diabetic cardiomyopathy through cardiac MT induction. Methods and Results— Diabetes was induced in mice (C57BL/6J strain) by a single injection of streptozotocin. Half were supplemented intraperitoneally with zinc sulfate (5 mg/kg) every other day for 3 months. After zinc supplementation, mice were maintained for 3 more months and then examined for cardiomyopathy by functional and morphological analysis. Significant increases in cardiac morphological impairment, fibrosis, and dysfunction were observed in diabetic mice but not in diabetic mice supplemented with zinc. Zinc supplementation also induced a significant increase in cardiac MT expression. The role of MT in cardiac protection by zinc supplementation was examined in cultured cardiac cells that were directly exposed to high levels of glucose (HG) and free fatty acid (FFA) (palmitate), treatment that mimics diabetic conditions. Cell survival rate was significantly decreased for cells exposed to HG/FFA but did not change for cells exposed to HG/FFA and pretreated with zinc or low-dose cadmium, each of which induces significant MT synthesis. When MT expression was silenced with the use of MT small-interfering RNA, the preventive effect of pretreatment with zinc or low-dose cadmium was abolished. Conclusions— These results suggest that the prevention of diabetic cardiomyopathy by zinc supplementation is predominantly mediated by an increase in cardiac MT.

Zinc supplementation prevents alcoholic liver injury in mice through attenuation of oxidative stress

Alcoholic liver disease is associated with zinc decrease in the liver. Therefore, we examined whether dietary zinc supplementation could provide protection from alcoholic liver injury. Metallothionein-knockout and wild-type 129/Sv mice were pair-fed an ethanol-containing liquid diet for 12 weeks, and the effects of zinc supplementation on ethanol-induced liver injury were analyzed. Zinc supplementation attenuated ethanol-induced hepatic zinc depletion and liver injury as measured by histopathological and ultrastructural changes, serum alanine transferase activity, and hepatic tumor necrosis factor-alpha in both metallothionein-knockout and wild-type mice, indicating a metallothionein-independent zinc protection. Zinc supplementation inhibited accumulation of reactive oxygen species, as indicated by dihydroethidium fluorescence, and the consequent oxidative damage, as assessed by immunohistochemical detection of 4-hydroxynonenal and nitrotyrosine and quantitative analysis of malondialdehyde and protein carbonyl in the liver. Zinc supplementation suppressed ethanol-elevated cytochrome P450 2E1 activity but increased the activity of alcohol dehydrogenase in the liver, without affecting the rate of blood ethanol elimination. Zinc supplementation also prevented ethanol-induced decreases in glutathione concentration and glutathione peroxidase activity and increased glutathione reductase activity in the liver. In conclusion, zinc supplementation prevents alcoholic liver injury in an metallothionein-independent manner by inhibiting the generation of reactive oxygen species (P450 2E1) and enhancing the activity of antioxidant pathways.

High-fat diet-induced juvenile obesity leads to cardiomyocyte dysfunction and upregulation of Foxo3a transcription factor independent of lipotoxicity and apoptosis.

Background Obesity is associated with dyslipidemia, which leads to elevated triglyceride and ceramide levels, apoptosis and compromised cardiac function. Methods To determine the role of high-fat diet-induced obesity on cardiomyocyte function, weanling male Sprague–Dawley rats were fed diets incorporating 10% of kcal or 45% of kcal from fat. Mechanical function of ventricular myocytes was evaluated including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening and relengthening (± dl/dt). Intracellular Ca2+ properties were assessed using fluorescent microscopy. Results High-fat diet induced hyperinsulinemic insulin-resistant obesity with depressed PS, ± dl/dt, prolonged TPS/TR90 reduced intracellular Ca2+ release and Ca2+ clearing rate in the absence of hypertension, diabetes, lipotoxicity and apoptosis. Myocyte responsiveness to increased stimulus frequency and extracellular Ca2+ was compromised. SERCA2a and phospholamban levels were increased, whereas phosphorylated phospholamban and potassium channel (Kv1,2) were reduced in high-fat diet group. High-fat diet upregulated the forkhead transcription factor Foxo3a, and suppressed mitochondrial aconitase activity without affecting expression of the caloric sensitive gene silent information regulator 2 (Sir2), protein nitrotyrosine formation, lipid peroxidation and apoptosis. Levels of endothelial nitric oxide synthase (NOS), inducible NOS, triglycerides and ceramide were similar between the two groups. Conclusions Collectively, our data show that high-fat diet-induced obesity resulted in impaired cardiomyocyte function, upregulated Foxo3a transcription factor and mitochondrial damage without overt lipotoxicity or apoptosis.

Dietary copper supplementation reverses hypertrophic cardiomyopathy induced by chronic pressure overload in mice

Sustained pressure overload causes cardiac hypertrophy and the transition to heart failure. We show here that dietary supplementation with physiologically relevant levels of copper (Cu) reverses preestablished hypertrophic cardiomyopathy caused by pressure overload induced by ascending aortic constriction in a mouse model. The reversal occurs in the continued presence of pressure overload. Sustained pressure overload leads to decreases in cardiac Cu and vascular endothelial growth factor (VEGF) levels along with suppression of myocardial angiogenesis. Cu supplementation replenishes cardiac Cu, increases VEGF, and promotes angiogenesis. Systemic administration of anti-VEGF antibody blunts Cu regression of hypertrophic cardiomyopathy. In cultured human cardiomyocytes, Cu chelation blocks insulin-like growth factor (IGF)-1– or Cu-stimulated VEGF expression, which is relieved by addition of excess Cu. Both IGF-1 and Cu activate hypoxia-inducible factor (HIF)-1α and HIF-1α gene silencing blocks IGF-1– or Cu-stimulated VEGF expression. HIF-1α coimmunoprecipitates with a Cu chaperone for superoxide dismutase-1 (CCS), and gene silencing of CCS, but not superoxide dismutase-1, prevents IGF-1– or Cu-induced HIF-1α activation and VEGF expression. Therefore, dietary Cu supplementation improves the condition of hypertrophic cardiomyopathy at least in part through CCS-mediated HIF-1α activation of VEGF expression and angiogenesis.

Weak antioxidant defenses make the heart a target for damage in copper-deficient rats

Copper deficiency causes more salient pathologic changes in the heart than in the liver of rats. Although oxidative stress has been implicated in copper deficiency-induced pathogenesis, little is known about the selective toxicity to the heart. Therefore, we examined the relationship between the severity of copper deficiency-induced oxidative damage and the capacity of antioxidant defense in heart and liver to investigate a possible mechanism for the selective cardiotoxicity. Weanling rats were fed a purified diet deficient in copper (0.4 microgram/g diet) or one containing adequate copper (6.0 microgram/g diet) for 4 weeks. Copper deficiency induced a 2-fold increase in lipid peroxidation in the heart (thiobarbituric assay) but did not alter peroxidation in the liver. The antioxidant enzymatic activities of superoxide dismutase, catalase, and glutathione peroxidase were, respectively, 3-, 50- and 1.5-fold lower in the heart than in the liver, although these enzymatic activities were depressed in both organs by copper deficiency. In addition, the activity of glutathione reductase was 4 times lower in the heart than in the liver. The data suggest that a weak antioxidant defense system in the heart is responsible for the relatively high degree of oxidative damage in copper-deficient hearts.

Abrogation of Nuclear Factor-κB Activation Is Involved in Zinc Inhibition of Lipopolysaccharide-Induced Tumor Necrosis Factor-α Production and Liver Injury

Endotoxin (lipopolysaccharide, LPS)-induced tumor necrosis factor-α (TNF-α) release from Kupffer cells is critically involved in the pathogenesis of alcohol-induced liver injury. We recently reported that inhibition of alcohol-induced plasma endotoxin elevation contributes to the protective action of zinc against alcoholic hepatotoxicity. The present study was undertaken to determine whether zinc interferes with the endotoxin-TNF-α signaling pathway, and possible mechanism(s) by which zinc modulates the endotoxin-TNF-α signaling. Administration of LPS to metallothionein (MT)-knockout (MT-KO) mice and 129/Sv wild-type (WT) controls at 4 mg/kg induced hepatic TNF-α elevation at 1.5 hours, followed by liver injury at 3 hours. Zinc pretreatment (two doses at 5 mg/kg) attenuated TNF-α production and liver injury in both MT-KO and WT mice, indicating a MT-independent action of zinc. Immunohistochemical detection of the phosphorylation of I-κB and nuclear factor (NF)-κB in the liver of MT-KO mice demonstrated that zinc pretreatment abrogated LPS-induced NF-κB activation in the Kupffer cells. Fluorescent microscopy of superoxide by dihydroethidine and of zinc ions by Zinquin in the liver of MT-KO mice showed that zinc pretreatment increased the intracellular labile zinc ions and inhibited LPS-induced superoxide generation. These results demonstrate that zinc inhibits LPS-induced hepatic TNF-α production through abrogation of oxidative stress-sensitive NF-κB pathway, and the action of zinc is independent of MT. Thus, zinc may be beneficial in the treatment of LPS-induced liver injuries, such as sepsis and alcoholism.

Cardiac Metallothionein Synthesis in Streptozotocin-Induced Diabetic Mice, and Its Protection against Diabetes-Induced Cardiac Injury

Oxidative stress is involved in the pathogenesis of diabetes and its cardiovascular complications. Metallothionein (MT), a stress-response protein, is significantly increased in the liver and kidney of diabetic animals. We examined whether diabetes also induces cardiac MT synthesis through oxidative damage and whether MT overexpression protects the heart from injury. Diabetes was induced in mice by single injection of streptozotocin (STZ), and cardiac MT mRNA and protein levels were measured 2 weeks and 2 months after STZ treatment. Diabetes significantly increased cardiac MT synthesis 2 weeks and 2 months after STZ treatment, with no change in cardiac metals including zinc, copper, and iron. Serum and cardiac vasopeptide endothelin and inflammatory cytokine tumor necrosis factor-alpha were also significantly increased in diabetic hearts, as were the ratio of oxidized to reduced glutathione and the immunohistochemical staining of 3-nitrotyrosine and 4-hydroxynonenal. To explore the biological importance of increased MT synthesis in the heart, MT-overexpressing transgenic mice were treated with STZ and then examined 2 months later. A loss of inotropic reserve, uncovered during beta-adrenergic stimulation, and the presence of cardiac fibrosis, shown by increased Sirius red staining of collagen, were evident in the wild-type diabetic mice but not in the MT-overexpressing transgenic diabetic mice. These results suggest that diabetes-induced cardiac MT expression likely associates with systemic increases in endothelin-1 and tumor necrosis factor-alpha and the resulting cardiac oxidative stress. Overexpressing cardiac MT significantly protects the heart from diabetes-induced injury.

Cardiac Overexpression of Alcohol Dehydrogenase Exacerbates Cardiac Contractile Dysfunction, Lipid Peroxidation, and Protein Damage After Chronic Ethanol Ingestion

BACKGROUND Alcoholic cardiomyopathy is manifested as ventricular dysfunction, although its specific toxic mechanism remains obscure. This study was designed to examine the impact of enhanced acetaldehyde exposure on cardiac function via cardiac-specific overexpression of alcohol dehydrogenase (ADH) after alcohol intake. METHODS ADH transgenic and wild-type FVB mice were placed on a 4% alcohol or control diet for 8 weeks. Mechanical and intracellular Ca2+ properties were evaluated in cardiac myocytes. Levels of acetaldehyde, lipid peroxidation, and protein carbonyl formation were determined. RESULTS FVB and ADH mice consuming ethanol exhibited elevated blood ethanol/acetaldehyde, cardiac acetaldehyde, and cardiac hypertrophy compared with non-ethanol-consuming mice. However, the levels of cardiac acetaldehyde and hypertrophy were significantly greater in ADH ethanol-fed mice than FVB ethanol-fed mice. ADH transgene itself did not affect mechanical and intracellular Ca2+ properties with the exception of reduced resting intracellular Ca2+ and Ca2+ re-sequestration at low pace frequency. Myocytes from ethanol-fed mice showed significantly depressed peak shortening, velocity of shortening/relengthening, rise of intracellular Ca2+ transients, and sarco(endo)plasmic reticulum Ca2+ load associated with similar duration of shortening/relengthening compared with myocytes from control mice. Strikingly, the ethanol-induced mechanical and intracellular Ca2+ defects were exacerbated in ADH myocytes compared with the FVB group except velocity of shortening/relengthening. The lipid peroxidation end products malondialdehyde and protein carbonyl formation were significantly elevated in both livers and hearts after chronic ethanol consumption, with the cardiac lipid and protein damage being exaggerated by ADH transgene. CONCLUSION These data suggest that increased cardiac acetaldehyde exposure due to ADH transgene may play an important role in cardiac contractile dysfunctions associated with lipid and protein damage after alcohol intake.

Congestive Heart Failure in Copper-Deficient Mice

Copper Deficiency (CuD) leads to hypertrophic cardiomyopathy in various experimental models. The morphological, electrophysiological, and molecular aspects of this hypertrophy have been under investigation for a long time. However the transition from compensated hypertrophy to decompensated heart failure has not been investigated in the study of CuD. We set out to investigate the contractile and hemodynamic parameters of the CuD mouse heart and to determine whether heart failure follows hypertrophy in the CuD heart. Dams of FVB mice were fed CuD or copper-adequate (CuA) diet starting from the third day post delivery and the weanling pups were fed the same diet for a total period of 5 weeks (pre- and postweanling). At week 4, the functional parameters of the heart were analyzed using a surgical technique for catheterizing the left ventricle. A significant decrease in left ventricle systolic pressure was observed with no significant change in heart rate, and more importantly contractility as measured by the maximal rate of left ventricular pressure rise (+dP/dt) and decline (−dP/dt) were significantly depressed in the CuD mice. However, left ventricle end diastolic pressure was elevated, and relaxation was impaired in the CuD animals; the duration of relaxation was prolonged. In addition to significant changes in the basal level of cardiac function, CuD hearts had a blunted response to the stimulation of the β-adrenergic agonist isoproterenol. Furthermore, morphological analysis revealed increased collagen accumulation in the CuD hearts along with lipid deposition. This study shows that CuD leads to systolic and diastolic dysfunction in association with histopathological changes, which are indices commonly used to diagnose congestive heart failure.

Metallothionein inhibits ischemia-reperfusion injury in mouse heart.

Oxidative stress is believed to play a major role in ischemia-reperfusion injury to the heart. Metallothionein (MT), a potential free radical scavenger, may function in cardiac protection against ischemia-reperfusion damage. To test this hypothesis, a specific cardiac MT-overexpressing transgenic mouse model was used. The hearts isolated from these animals were subjected to 50 min of warm (37 degrees C) zero-flow ischemia followed by 60- or 90-min reflow. Compared with the nontransgenic controls, the transgenic mouse hearts with MT concentrations approximately 10-fold higher than normal showed significantly improved recovery of contractile force postischemia (69.2 +/- 4.2 vs. 26.0 +/- 6.0% at the end of 60-min reperfusion, P < 0.01). Efflux of creatine kinase from these transgenic hearts was reduced by more than 50% (P < 0.01). In addition, the zone of infarction induced by ischemia-reperfusion at the end of 90-min reperfusion was suppressed by approximately 40% (P < 0.01) in the transgenic hearts. The results strongly indicate that MT provides protection against ischemia-reperfusion-induced heart injury.Oxidative stress is believed to play a major role in ischemia-reperfusion injury to the heart. Metallothionein (MT), a potential free radical scavenger, may function in cardiac protection against ischemia-reperfusion damage. To test this hypothesis, a specific cardiac MT-overexpressing transgenic mouse model was used. The hearts isolated from these animals were subjected to 50 min of warm (37°C) zero-flow ischemia followed by 60- or 90-min reflow. Compared with the nontransgenic controls, the transgenic mouse hearts with MT concentrations ∼10-fold higher than normal showed significantly improved recovery of contractile force postischemia (69.2 ± 4.2 vs. 26.0 ± 6.0% at the end of 60-min reperfusion, P < 0.01). Efflux of creatine kinase from these transgenic hearts was reduced by more than 50% ( P < 0.01). In addition, the zone of infarction induced by ischemia-reperfusion at the end of 90-min reperfusion was suppressed by ∼40% ( P < 0.01) in the transgenic hearts. The results strongly indicate that MT provides protection against ischemia-reperfusion-induced heart injury.