Augusta Askari

Studies on the specificity of the effects of oxygen metabolites on cardiac sodium pump

Isolated myocytes of rat heart, and sealed sarcolemmal vesicles of bovine heart, were used to examine the selectivity of the effects of partially reduced oxygen species (generated by a mixture of xanthine and xanthine oxidase) on cardiac sodium pump and several other ion transporters of the plasma membrane. When myocytes were exposed to xanthine plus xanthine oxidase, there were time-dependent inhibitions of ouabain-sensitive 86Rb+ uptake and (Na+ + K+)-ATPase activity that could be prevented by allopurinol, or by catalase and superoxide dismutase; suggesting the involvements of H2O2 or oxygen free radicals in the inhibition of the pump. This inhibition preceded any significant decrease in cellular ATP or in the number of viable cells. While ouabain increased 45Ca2+ uptake by myocytes as expected, exposure to xanthine plus xanthine oxidase decreased 45Ca2+ uptake; suggesting that the Na+, Ca2(+)-exchanger of the intact myocytes is also inhibited by oxygen metabolites. Simultaneous inhibitions of the pump, the Na+, Ca2(+)-exchange, the Na+, H(+)-exchange, and the Na+, Pi-cotransport activities also occurred in sarcolemmal vesicles that were treated with xanthine plus xanthine oxidase. These findings indicate that inactivations of the sodium pump and other sarcolemmal ion carriers are early events in the oxidant-induced damage to the cardiomyocyte. In the rat heart myocytes, a fraction of (Na+ + K+)-ATPase that seems to be more sensitive to ouabain, was inactivated more rapidly upon exposure of myocytes to xanthine plus xanthine oxidase; raising the possibility of the existence of different pump populations with different sensitivities to extracellularly generated oxygen metabolites.

Differential regulation of superoxide dismutase in copper-deficient rat organs

The effects of dietary copper deprivation on the activities, immunoreactive protein concentrations, and mRNA abundance of copper/zinc- and manganese-superoxide dismutase (Cu/Zn- and Mn-SOD) were examined in liver, heart, and brain of weanling rats fed a Cu-deficient diet for 4 weeks. Hepatic Cu/Zn-SOD activity, enzyme content, and mRNA abundance were significantly reduced, and, conversely, the activity, protein, and mRNA levels of Mn-SOD were significantly elevated in Cu-deficient rats. In Cu-deficient heart, the activity and protein content for Cu/Zn-SOD were reduced, whereas those for Mn-SOD were increased; the levels of mRNAs for these two enzymes was unaffected. Dietary Cu deficiency was without effect on the activities, enzyme contents, and mRNA abundance of brain Cu/Zn- and Mn-SOD. These results indicate that SODs from liver, heart, and brain exhibit differential sensitivities to dietary Cu deprivation, and that different mechanisms (transcriptional, posttranscriptional, or posttranslational) may be involved in their regulation.

Effects of doxorubicin on cardiomyocytes with reduced level of superoxide dismutase

Our previous studies have shown that isolated adult rat cardiomyocytes with normal and reduced Cu/Zn SOD activities are equally susceptible to extracellularly generated oxidants (hydrogen peroxide, glucose oxidase/glucose and xanthine oxidase/xanthine systems). In the present study we exposed myocytes with reduced SOD activity to doxorubicin (adriamycin). Cardiotoxicity of doxorubicin has been attributed to the production of superoxide anion inside the cell. Cardiomyocytes with reduced SOD activity, but normal ATP content and viability, were obtained by the treatment of isolated cells with diethyldithiocarbamate (DDC). DDC-treated myocytes were significantly less resistant to doxorubicin than controls. Doxorubicin-stimulated superoxide anion formation, measured by the rate of SOD-inhibitable acetylated cytochrome C reduction, was significantly higher in the cytosolic fraction of DDC-treated cells compared to controls. These results indicate that for isolated cardiac myocytes an essential part of cytotoxicity of doxorubicin can be explained by the formation of superoxide anion and that the level of intracellular SOD activity should be considered as a significant factor for cell protection.

Expression of glutathione peroxidase and catalase in copper-deficient rat liver and heart

Oxidative stress resulting from dietary copper deficiency in rats differentially regulates the expression of copperl zinc- and manganese-superoxide dismutases in the liver and heart. It was hypothesized that the expression of catalase and glutathione peroxidase, the non-copper-containing antioxidant enzymes, in the rat heart and liver may also be regulated by dietary copper deprivation. The expression of the activities, protein concentrations, and mRNA levels for glutathione peroxidase and catalase were studied in the liver and heart of rats made copper-deficient for 4 weeks. The activities and mRNA levels for liver selenium (Se)-dependent glutathione peroxidase and catalase as well as the immunoreactive protein concentration for the catalase were reduced to a similar extent in copper-deficient animals, which suggests transcriptional regulation. The mRNA, activity, and protein concentration for the myocardial catalase were increased in copper-deficient rats. However, the increase was larger for the mRNA than for the activity and protein concentration; this indicates that its regulation probably involves both transcriptional and post-translational mechanisms. Se-dependent glutathione peroxidase was not changed in the heart of copper-deficient rats. These results demonstrate that dietary copper deficiency in rats differentially alters the expression of Se-dependent glutathione peroxidase and catalase in the liver and heart.

Altered expressions of cardiac Na/K-ATPase isoforms in copper deficient rats

OBJECTIVE The aim was to determine if copper deficiency affects the expression of Na/K-ATPase alpha isoforms in the rat heart. METHODS Copper deficiency was induced by placing weanling rats on a copper deficient diet for 4-5 weeks. Adult ventricular tissue, isolated ventricular myocytes, and brain stems of the control and deficient rats were compared for Cu, Zn-superoxide dismutase (CuZn-SOD) activity and for protein and mRNA contents of Na/K-ATPase alpha isoforms. RESULTS In brain stem, where copper deficiency did not alter CuZn-SOD activity, mRNA and protein levels of alpha isoforms also remained unchanged. In ventricular tissue and ventricular myocytes, copper deficiency reduced CuZn-SOD activity, mRNAs of alpha 1 and alpha 2 isoforms, and the alpha 2 isoform protein. The alpha 1 isoform protein of ventricular tissue and its myocytes was marginally reduced by copper deficiency. CONCLUSIONS In the rat ventricular tissue, oxidative stress resulting from copper deficiency (1) enhances the turnover of the more oxidant sensitive alpha 2 isoform to a greater extent than the turnover of the alpha 1 isoform; (2) regulates mRNA levels of alpha 1 and alpha 2 isoforms; and (3) contributes to the cardiomyopathy of copper deficiency.

Zinc, Copper, and Parenteral Nutrition in Cancer. A Review

Literature concerning zinc and/or copper investigations pertaining to cancer is surveyed; the interrelationships of zinc, copper, and parenteral nutrition (PN) in cancer are examined; and the advantages of adequate nutritional support for patients with malignancies are discussed. Zinc and copper are both essential trace elements and, therefore, are necessary nutrients for cancer patients. Zinc supports growth, including that of neoplasia; copper is a zinc competitor and antagonist; and cancer patients on PN are in danger of becoming both zinc- and copper-deficient. The addition of these trace elements as supplements to PN formulae is undertaken with knowledge of only the approximate concentrations of zinc and copper in total intake, but without knowledge of specific requirements for cancer patients for these trace elements, of all the possible interactions of zinc and copper with each other or different trace elements, or even of zinc and copper lower levels of toxicity in cancer patients; balance studies are needed to determine zinc and copper requirements in them. In the future, it is conceivable that manipulations of the host nutrients might be used to control tumors. This might be accomplished by adjusting total PN formulae so that required nutrients will be presented to a cancer patient in such amounts and in such ratios that a desired alteration may be effected in that patients metabolism.

Net metabolic changes of zinc, copper, nitrogen, and potassium balances in skeletal trauma patients

Zinc, copper, nitrogen, and potassium balances of 10 male skeletal trauma patients were determined over 5-6 days each. Nutrition consisted of electrolyte/glucose and/or blood/blood product infusions. Patients were started on balance studies within 24 hr following injury. Zinc and copper were analyzed by atomic absorption while nitrogen was measured by the microKjeldahl technique and potassium by flame photometry. The mean daily balances for these patients were -1563 micrograms zinc, -266 micrograms copper, -20.0 g nitrogen and -29 mEq potassium for 5 patients receiving electrolyte/glucose infusions and +1273 micrograms zinc, +322 micrograms copper, -12.9 g nitrogen, and -26 mEq potassium for 5 patients receiving blood/blood products in addition to electrolyte/glucose. Routine daily maintenance supplementation of 2 mg zinc and 2 mg copper is recommended for skeletal trauma patients on electrolyte/glucose and those on electrolyte/glucose with blood/blood products intravenous infusions. Further balance studies are necessary to ascertain the level of zinc and copper supplementation needed by skeletal trauma patients receiving different nutritional support.

Urinary Zinc, Copper, Nitrogen, and Potassium Losses in Response to Trauma

The urinary losses of zinc, copper, nitrogen and potassium were measured for 14 trauma patients for periods ranging from nine to 30 days and for nine normal subjects over four days each. The mean losses per day as well as peak losses by patients were compared to the mean normal losses. The mean peak losses of all elements were 2 to 10 times greater than normal. The ratios of the urinary concentrations of these catabolites in relation to each other were calculated. Since nutritional support was predominantly by routine intravenous solutions, the large amounts of urinary zinc, copper, nitrogen and potassium excreted represent a severe drain on the bodys reserves of these elements.

Effect of copper-deficient diet on metabolism in rat auditory structures

Copper is a trace element known to be critical for normal brain function, and abnormal copper metabolism has been associated with some disorders involving the auditory system. We examined effects of copper deficiency on metabolism in major structures of the auditory system. Homogenates of cochlea, cochlear nucleus and inferior colliculus of rats, as well as whole brain, were assayed for activities of enzymes of oxidative and glycolytic energy metabolism--malate and lactate dehydrogenase, enzymes of acetylcholine metabolism--choline acetyltransferase and acetylcholinesterase, and concentrations of amino acids. Whole brain was also assayed for activity of superoxide dismutase, a copper-containing enzyme, and concentrations of minerals. For these chemicals and tissues, the only significant differences between copper-deficient and copper-adequate rats were: (1) decreased copper and magnesium and increased potassium concentrations in whole brain of copper-deficient rats and (2) an elevation of glutamine concentration in inferior colliculus and whole brain of copper-deficient rats. The elevated glutamine could not be related to any change in activity of glutamine synthetase or glutaminase, major enzymes of glutamine metabolism. It is speculated that the increase in glutamine might result from a net increase in ammonia accumulation in the brains of copper-deficient rats.

The influence of ketosis on the metabolic response to skeletal trauma

Intravenous glucose and ketone body feeding were compared for their potential in altering urinary nitrogen losses by the traumatized rat. Eighteen male rats were traumatized by bilateral femoral fracture. The rats were fed totally by vein for 3 days prior and 3 days after injury and the infusion rate was held constant over the 6 days of infusion. Group GT rats were fed glucose as the source of nonprotein energy while group MT rats were fed a mixture of 72% monoacetoacetin (the monoglyceride of acetoacetate)-28% glucose for the nonprotein energy. Total urinary nitrogen excretion on a 24-hr basis was measured for each of the 6 days of intravenous feeding. On the third day post-trauma, each rat was evaluated for leucine kinetics using a continuous infusion of L-[1-14C]leucine and measurement of breath and plasma specific activities. Rats from group MT were hyperketonemic and normoglycemic and rats from group GT were normoketonemic and hyperglycemic. Urinary nitrogen losses, leucine oxidation, and leucine turnover were similar for the two groups. We conclude that ketone bodies are as good an intravenous source of energy as is glucose, and the ketone bodies do not cause hyperglycemia.