Prevention of lipid peroxidation does not prevent oxidant-induced myocardial contractile dysfunction

Synthesis, Characterization, and Applications of Rare-Earth-Based Complexes with Antibacterial and Antialgal Properties

The pursuit of environmentally friendly and highly effective antifouling materials for marine applications is of paramount importance. In this study, we successfully synthesized novel rare earth-based complexes by coordinating cerium (Ce III), samarium (Sm III), and europium (Eu III) with pyrithione (1-hydroxy-2-pyridinethione; PT). Extensive characterizations were performed, including single-crystal X-ray analysis, which revealed the intriguing binuclear structure of these complexes. This structural motif comprises two rare-earth ions intricately double-bridged by two oxygen atoms from the PT ligand, resulting in a distinctive and intriguing geometry. Furthermore, the central rare earth ion is surrounded by three sulfur atoms and two additional oxygen atoms, forming a unique distorted bicapped trigonal prismatic configuration. Compared with conventional antifouling biocides such as sodium pyrithione (NaPT), copper pyrithione (CuPT), and zinc pyrithione (ZnPT), these newly synthesized rare-earth complexes exhibited a remarkable boost in their in vitro antibacterial efficacy against both Gram-positive and Gram-negative bacteria. Additionally, these complexes demonstrated significant potential as antialgal agents, displaying impressive activity against marine planktonic organisms. These findings underscore the promising application prospects of these rare-earth complexes in the field of marine antifouling.

Utilization of microbial iron assimilation processes for the development of new antibiotics and inspiration for the design of new anticancer agents

Pathogenic microbes rapidly develop resistance to antibiotics. To keep ahead in the "microbial war", extensive interdisciplinary research is needed. A primary cause of drug resistance is the overuse of antibiotics that can result in alteration of microbial permeability, alteration of drug target binding sites, induction of enzymes that destroy antibiotics (ie., beta-lactamase) and even induction of efflux mechanisms. A combination of chemical syntheses, microbiological and biochemical studies demonstrate that the known critical dependence of iron assimilation by microbes for growth and virulence can be exploited for the development of new approaches to antibiotic therapy. Iron recognition and active transport relies on the biosyntheses and use of microbe-selective iron-chelating compounds called siderophores. Our studies, and those of others, demonstrate that siderophores and analogs can be used for iron transport-mediated drug delivery ("Trojan Horse" antibiotics) and induction of iron limitation/starvation (Development of new agents to block iron assimilation). Recent extensions of the use of siderophores for the development of novel potent and selective anticancer agents are also described.

Prolonged administration of a dithiol antioxidant protects against ventricular remodeling due to ischemia-reperfusion in mice

The prolonged production of reactive oxygen species due to ischemia-reperfusion (I/R) is a potential cause of the pathological remodeling that frequently precedes heart failure. We tested the ability of a potent dithiol antioxidant, bucillamine, to protect against the long-term consequences of I/R injury in a murine model of myocardial infarction. After transiently occluding the left anterior descending coronary artery for 30 min, saline or bucillamine (10 microg/g body wt) was injected intravenously as a bolus within the first 5 min of reperfusion. The antioxidant treatment continued with daily subcutaneous injections for 4 wk. There were no differences in infarct sizes between bucillamine- and saline-treated animals. After 4 wk of reperfusion, cardiac hypertrophy was decreased by bucillamine treatment (ventricular weight-to-body weight ratios: I/R + saline, 4.5 +/- 0.2 mg/g vs. I/R + bucillamine, 4.2 +/- 0.1 mg/g; means +/- SE; P < 0.05). Additionally, the hearts of bucillamine-treated mice had improved contractile function (echocardiographic measurement of fractional shortening) relative to saline controls: I/R + saline, 32 +/- 3%, versus I/R + bucillamine, 41 +/- 4% (P < 0.05). Finally, I/R-induced injury in the saline-treated mice was accompanied by a fetal pattern of gene expression determined by ribonuclease protection assay that was consistent with pathological cardiac hypertrophy and remodeling [increased atrial natriuretic peptide, beta-myosin heavy chain (MHC), skeletal alpha-actin; decreased sarco(endo)plasmic reticulum Ca2+ ATPase 2a, and alpha-MHC-to-beta-MHC ratio]. These changes in gene expression were significantly attenuated by bucillamine. Therefore, treatment with a dithiol antioxidant for 4 wk after I/R preserved ventricular function and prevented the abnormal pattern of gene expression associated with pathological cardiac remodeling.

Post-exercise vitamin C supplementation and recovery from demanding exercise

The aim of this study was to investigate whether post-exercise vitamin C supplementation influences recovery from an unaccustomed bout of exercise. Sixteen male subjects were allocated to either a placebo (P; n=8) or vitamin C (VC) group ( n=8). Subjects performed a prolonged (90-min) intermittent shuttle-running test, and supplementation began after the cessation of exercise. Immediately after exercise the VC group consumed 200 mg of VC dissolved in a 500 ml drink, whereas the subjects in the P group consumed the drink alone. Later on the same day and then in the morning and evening of the following 2 days, subjects consumed additional identical drinks. Plasma VC concentrations in the VC group increased above those in the P group 1 h after exercise and remained above P values for the 3 days after exercise. Nevertheless, post-exercise VC supplementation was not associated with improved recovery. Post-exercise serum creatine kinase activities and myoglobin concentrations were unaffected by supplementation. Muscle soreness and the recovery of muscle function in the leg flexors and extensors were not different in VC and P groups. Furthermore, although plasma concentrations of interleukin-6 and malondialdehyde increased following exercise, there was no difference between VC and P groups. These results suggest that either free radicals are not involved in delaying the recovery process following a bout of unaccustomed exercise, or that the consumption of VC wholly after exercise is unable to deliver this antioxidant to the appropriate sites with sufficient expediency to improve recovery.

Distinct roles of peroxynitrite and hydroxyl radical in triggering stunned myocardium-like impairment of cardiac myocytes in vitro

Myocardial stunning is characterized by the impairment of excitation-contraction coupling via a decrease in myofilament Ca2+ responsiveness, thought to be triggered by hydroxyl radicals (*OH) generated upon reperfusion. Since peroxynitrite is also expected to be produced during reperfusion, we examined whether it can induce a stunned myocardium-like impairment of cardiac myocytes. Its effect on cultured cardiac myocytes was compared with that of hydrogen peroxide (H2O2), *OH source. Infusion of peroxynitrite (0.2 mM) induced a decrease in cell motion and a complete arrest in diastole at 2.9 +/- 0.3 min, which coincided with an elevation in [Ca2+]i. Arrest induced by infusion of H2O2 (10 mM) was not associated with an increase in [Ca2+]i. The ATP content was unaffected by peroxynitrite (control, 34.3 +/- 3.4: + peroxynitrite, 32.9 +/- 3.5 nmol/mg protein) and the cells remained viable. Sulfhydryl (SH) content was decreased by peroxynitrite, but not by H2O2. The membrane fluidity (a measure of peroxidation of the membrane lipids) was not affected by peroxynitrite, but was decreased by H2O2. Onset time of arrest was unaffected by deferoxamine (0.2 mM), but was delayed by DTT (10 mM) (from 2.9 +/- 0.3 to 19.2 +/- 1.6 min). Nitrotyrosine content was unchanged by peroxynitrite, and its augmentation with Fe3+/EDTA (1 mM) was not associated with a shortened onset time of arrest. The function of the Na+/Ca2+ exchanger was impaired by peroxynitrite, but not by H2O2. Peroxynitrite and H2O2 each induce arrest, but only the former increases [Ca2+]i. One of the mechanisms of the increase in [Ca2+]i is Na/Ca2+ exchanger dysfunction. The impairments were induced through SH oxidation by peroxynitrite, but through lipid peroxidation by H2O2. Myocardial stunning may be induced by both species in concert.

Na/K-ATPase under oxidative stress: molecular mechanisms of injury

1. The authors compare oxidative injury to brain and kidney Na/K-ATPase using in vitro and in vivo approaches. The substrate dependence of dog kidney Na/K-ATPase was examined both before and after partial hydrogen peroxide modification. A computer simulation model was used for calculating kinetic parameters. 2. The substrate dependence curve for the unmodified endogenous enzyme displayed a typical curve with an intermediate plateau, adequately described by the sum of hyperbolic and sigmoidal components. 3. The modified enzyme demonstrated a dependent curve that closely approximates normal hyperbola. The estimated ATP K(m) value for the endogenous enzyme was about 85 microM; the Kh was equal to 800 microM. The maximal number of protomers interacting was 8. Following oxidative modification, the enzyme substrate dependence curve did not show a significant change in the maximal protomer rate Vm, while the K(m) was increased slightly and interprotomer interaction was abolished. 4. Na/K-ATPase from an ischemic gerbil brain showed a 22% decrease in specific activity. The maximal rate of ATP hydrolysis by an enzyme protomer changed slightly. but the sigmoidal component, characterizing the enzyme's ability to form oligomers was abolished completely. The K(m) value was almost unchanged, but the Hill coefficient fell to 1. These data show that Na/K-ATPase molecules isolated from the ischemic brain have lost the ability to interact with one another. 5. We suggest that the most important consequence of oxidative modification is Na/K-ATPase oligomeric structure formation and subsequent hydrolysis rate suppression.

Oxidative resistance of Na/K-ATPase

1. Oxidative modification of Na/K-ATPase from brain and kidney has been studied. Brain enzyme has been found to be more sensitive than kidney enzyme to inhibition by both H2O2 and NaOCl. 2. The inhibition of Na/K-ATPase correlates well with the decrease in a number of SH groups, suggesting that the latter belong mainly to ATPase protein and are essential for the enzyme activity. We suggest that the differences in the number, location, and accessibility of SH groups in Na/K-ATPase isozymes predict their oxidative stability. 3. The hydrophilic natural antioxidant carnosine, the hydrophobic natural antioxidant alpha-tocopherol, and the synthetic antioxidant ionol as well as the ferrous ion chelating agent deferoxamine were found to protect Na/K-ATPase from oxidation by different concentrations of H2O2. The data suggest that these antioxidants are effective due to their ability to neutralize or to prevent formation of hydroxyl radicals.

Lipophilic siderophores of Mycobacterium tuberculosis prevent cardiac reperfusion injury

Reperfusion injury, which occurs upon the reintroduction of blood flow to an ischemic organ, is responsible for considerable damage in heart attacks and strokes. However, no treatment for reperfusion injury is currently available. A major cause of reperfusion injury is the iron-mediated generation of hydroxyl radical (.OH). In this study we have explored the capacity of novel iron chelators called "exochelins" to prevent reperfusion injury. Exochelins, siderophores of Mycobacterium tuberculosis, are unique iron chelators because they are lipid soluble, and hence able to enter cells rapidly. In the iron-free state, exochelins prevented .OH formation. Desferri-exochelins prevented oxidative injury to cultured cardiac myocytes, and did so more rapidly and effectively than the nonlipid soluble iron chelator deferoxamine. The capacity of various desferri-exochelins to protect myocytes from oxidative injury varied directly with their solubility in lipid. Infused into isolated rabbit hearts during reperfusion after a period of ischemia, desferri-exochelins dramatically improved systolic and diastolic left ventricular function, preserved coronary flow, reduced release of the cardiac enzyme lactic dehydrogenase, and reduced myocardial concentrations of .OH metabolites. Thus, highly diffusible desferri-exochelins block injury caused by .OH production and have potential for the treatment of reperfusion injury.