Production of oxygen free radicals and of hemolysis by cyclosporine

Antioxidant activity and free radical scavenging reactions of gentisic acid: in-vitro and pulse radiolysis studies

Abstract Antioxidant activity of gentisic acid has been studied using fast chemical kinetics and two in vitro models, namely the isolated rat liver mitochondria (RLM) and the human erythrocytes. The presence of gentisic acid (GA) during irradiation significantly reduced the levels of gamma radiation induced damages to lipids and proteins in RLM. Further, GA imparted protection to the human erythrocytes against exposure to gamma radiation. Molecular mechanism of free radical scavenging reactions has been evaluated with the help of rate constants and transients obtained from gentisic acid using pulse radiolysis technique. GA efficiently scavenged hydroxyl radical (k = 1.1 × 10(10) dm(3)mol(-1)s(-1)) to produce reducing adduct radical (~76%) and oxidizing phenoxyl radical (~24%). GA has also scavenged organohaloperoxyl radical (k = 9.3 × 10(7) dm(3) mol(-1)s(-1)). Ascorbate has been found to repair phenoxyl radical of GA (k = 1.0 × 10(7) dm(3)mol(-1)s(-1)). Redox potential value of GA(•)/GA couple (0.774 V vs NHE) obtained by cyclic voltammetry is less than those of physiologically important oxidants, which supports the observed antioxidant capacity of GA. We, therefore, propose that the antioxidant and radioprotective properties of GA are exerted by its phenoxyl group.

Anti-hemolytic and peroxyl radical scavenging activity of organoselenium compounds: an in vitro study

Selenium-containing amino acids, selenocystine (CysSeSeCys), methylselenocysteine (MeSeCys), and selenomethionine (SeMet) have been examined for anti-hemolytic and peroxyl radical scavenging ability. Effect of these compounds on membrane lipid peroxidation, release of hemoglobin, and loss of intracellular K(+) ion as a consequence of peroxyl radicals-induced oxidation of human red blood cells were used to evaluate their anti-hemolytic ability. The peroxyl radicals were generated from thermal degradation of 2,2'-azobis(2-methylpropionamidine) dihydrochloride. Significant delay (t(eff)) was observed in oxidative damage in the presence of the selenium compounds. From the IC(50) values for the inhibition of hemolysis, lipid peroxidation, and K(+) ion leakage, the relative anti-hemolytic ability of the compounds were found to be in the order of CysSeSeCys > MeSeCys > SeMet. The anti-hemolytic abilities of the compounds, when compared with sodium selenite (Na(2)SeO(3)) under identical experimental conditions, were found to be better than Na(2)SeO(3). Relative rate constants estimated for the reaction of MeSeCys and SeMet with peroxyl radicals by competition kinetics using ABTS(2-) as a reference confirmed that all the compounds are efficient peroxyl radical scavengers. Comparison of the GPx-like activity of these compounds, by NADPH-GSH reductase coupled assay, indicated that CysSeSeCys exhibits the highest activity. Based on these results, it is concluded that among the compounds examined, CysSeSeCys, possessing the ability to reduce peroxyl radicals and hydroperoxides showed efficient anti-hemolytic activity.

Matrix metalloproteinases in health and disease: regulation by melatonin

Matrix metalloproteinases (MMPs) are part of a superfamily of metal-requiring proteases that play important roles in tissue remodeling by breaking down proteins in the extracellular matrix that provides structural support for cells. The intricate balance in protease/anti-protease stoichiometry is a contributing factor in a number of diseases. Melatonin possesses multifunctional bioactivities including antioxidative, anti-inflammatory, endocrinologic and behavioral effects. As melatonin affects the redox status of tissues, the association of reactive oxygen species (ROS) with tissue injury under different circumstances may be mitigated by melatonin. Redox signaling is expanding into all areas of basic and clinical sciences, and this timely review focuses on the topic of regulation of MMP activities by melatonin. This is a rapidly growing field. Accumulating evidence indicates that oxidative stress plays an important role in regulating the activities of MMPs that are involved in various cellular processes such as cellular proliferation, angiogenesis, apoptosis, invasion and metastasis. This review offers sections on MMPs, melatonin, major physiological and pathophysiological conditions in the context to MMPs, followed by redox signaling mechanisms that are known to influence the cellular processes. Finally, we discuss the emerging molecular mechanisms relevant to regulatory actions of melatonin on the activities of MMPs. The possibility that melatonin might have therapeutic significance via regulation of MMPs may be a novel approach in the treatment of some diseases.

Concentration dependent antioxidant/pro-oxidant activity of curcumin studies from AAPH induced hemolysis of RBCs

The antioxidant properties of curcumin have been studied by evaluating its ability to protect RBCs from AAPH (2,2'-azobis (2-amidinopropane) hydrochloride) induced oxidative damage. RBCs are susceptible to oxidative damage, resulting in peroxidation of the membrane lipids, release of hemoglobin (hemolysis), release of intracellular K(+) ions and depletion of glutathione (GSH). In this paper, lipid peroxidation, hemolysis and K(+) ion loss in RBCs were assessed respectively by formation of thiobarbituric acid reactive substances (TBARS), absorbance of hemoglobin at 532nm and flame photometry. The treatment of RBCs with curcumin showed concentration dependant decrease in level of TBARS and hemolysis. The IC(50) values for inhibition of lipid peroxidation and hemolysis were estimated to be 23.2+/-2.5 and 43+/-5microM respectively. However in contrast to the above mentioned effects, curcumin in similar concentration range, did not prevent release of intracellular K(+) ions during the process of hemolysis, rather curcumin induced its release even in the absence of hemolysis. The ability of curcumin to prevent oxidation of intracellular GSH due to hemolysis showed mixed results. At low concentrations of curcumin (<10microM) it prevented GSH depletion and at higher concentrations, the GSH levels decreased gradually. Curcumin scavenges the peroxyl radical generated from AAPH. Based on these results, it is concluded that curcumin exhibits both antioxidant/pro-oxidant activity, in a concentration dependent manner.

3,3′-Diselenodipropionic Acid, an Efficient Peroxyl Radical Scavenger and a GPx Mimic, Protects Erythrocytes (RBCs) from AAPH-Induced Hemolysis

3,3'-diselenodipropionic acid (DSePA), a derivative of selenocystine, has been synthesized and examined for antioxidant activity, glutathione peroxidase (GPx) activity, and cytotoxicity. The effect of DSePA on membrane lipid peroxidation, release of hemoglobin, and intracellular K+ ion as a consequence of erythrocyte (red blood cells or RBCs) oxidation by free radicals generated by 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH) were used to evaluate the antioxidant ability. Lipid peroxidation, hemolysis, and K+ ion loss in RBCs were assessed, respectively, by formation of thiobarbituric acid reactive substances (TBARS), absorbance of hemoglobin at 532 nm and flame photometry. The IC50 values for lipid peroxidation, hemolysis, and K+ ion leakage were 45+/-5, 20+/-2, and 75+/-8 microM, respectively. DSePA treatment prevented the depletion of glutathione (GSH) levels in RBCs from free-radical-induced stress. DSePA is a good peroxyl radical scavenger and the bimolecular rate constant for the reaction of DSePA with a model peroxyl radical, trichloromethyl peroxyl radical (CCl 3O2*), was determined to be 2.7x10(8) M(-1) s(-1) using a pulse radiolysis technique. DSePA shows GPx activity with higher substrate specificity towards peroxides than thiols. The cytotoxicity of DSePA was studied in lymphocytes and EL4 tumor cells and the results showed that DSePA is nontoxic to these cells at the concentrations employed. These results when compared with two well-known selenium compounds, sodium selenite and ebselen, indicated that DSePA, although it shows lesser GPx activity, has higher free radical scavenging ability and lesser toxicity.

Effects of epigallocatechin gallate on the hemolysis induced by cyclosporine

INTRODUCTION

Hemolysis is one of the side effects of cyclosporine (CsA) therapy, in part due to, increased production of free radical species by CsA. Epigallocatechin gallate (EGCG), which acts as a highly efficient free radical scavenger, may have a protective effect on CsA-induced hemolysis. In this study, we measured the degree of hemolysis of as well as the amounts of hydrogen peroxide level and malondialdehyde produced by normal human erythrocytes (RBCs) incubated with CsA and with EGCG.

METHODS

Human RBCs were incubated as follows. In group 1, 4.2 x 10(6)/mL RBCs were incubated with Cremophore EL. In group 2, the RBCs were incubated with only 167 microg/mL EGCG. In group 3, the RBCs were incubated with 1.67 mg/mL CsA. In group 4, the RBCs were incubated with CsA plus EGCG.

RESULTS

The degree of hemolysis in group 2 (53.8 +/- 3.8) was significantly higher than that in group 1 (7.0 +/- 1.0). The degree of hemolysis in group 3 (86.2 +/- 2.2) was significantly higher than that in group 1 and group 2. The degree of hemolysis in group 4 (74.9 +/- 2.9) was significantly higher than in group 1 and in group 2, but lower than that in group 3. The hydrogen peroxide and malondialdehyde levels paralleled the degree of hemolysis.

CONCLUSIONS

These results suggest that CsA can induce free radical-mediated hemolysis, which can be partially prevented with EGCG.

Melatonin mitigates mitochondrial malfunction

Melatonin, or N-acetyl-5-methoxytryptamine, is a compound derived from tryptophan that is found in all organisms from unicells to vertebrates. This indoleamine may act as a protective agent in disease conditions such as Parkinson's, Alzheimer's, aging, sepsis and other disorders including ischemia/reperfusion. In addition, melatonin has been proposed as a drug for the treatment of cancer. These disorders have in common a dysfunction of the apoptotic program. Thus, while defects which reduce apoptotic processes can exaggerate cancer, neurodegenerative disorders and ischemic conditions are made worse by enhanced apoptosis. The mechanism by which melatonin controls cell death is not entirely known. Recently, mitochondria, which are implicated in the intrinsic pathway of apoptosis, have been identified as a target for melatonin actions. It is known that melatonin scavenges oxygen and nitrogen-based reactants generated in mitochondria. This limits the loss of the intramitochondrial glutathione and lowers mitochondrial protein damage, improving electron transport chain (ETC) activity and reducing mtDNA damage. Melatonin also increases the activity of the complex I and complex IV of the ETC, thereby improving mitochondrial respiration and increasing ATP synthesis under normal and stressful conditions. These effects reflect the ability of melatonin to reduce the harmful reduction in the mitochondrial membrane potential that may trigger mitochondrial transition pore (MTP) opening and the apoptotic cascade. In addition, a reported direct action of melatonin in the control of currents through the MTP opens a new perspective in the understanding of the regulation of apoptotic cell death by the indoleamine.

Melatonin and mitochondrial function

Melatonin is a natural occurring compound with well-known antioxidant properties. In the last decade a new effect of melatonin on mitochondrial homeostasis has been discovered and, although the exact molecular mechanism for this effect remains unknown, it may explain, at least in part, the protective properties found for the indoleamine in degenerative conditions such as aging as well as Parkinson's disease, Alzheimer's disease, epilepsy, sepsis and other injuries such as ischemia-reperfusion. A common feature in these diseases is the existence of mitochondrial damage due to oxidative stress, which may lead to a decrease in the activities of mitochondrial complexes and ATP production, and, as a consequence, a further increase in free radical generation. A vicious cycle thus results under these conditions of oxidative stress with the final consequence being cell death by necrosis or apoptosis. Melatonin is able of directly scavenging a variety of toxic oxygen and nitrogen-based reactants, stimulates antioxidative enzymes, increases the efficiency of the electron transport chain thereby limiting electron leakage and free radical generation, and promotes ATP synthesis. Via these actions, melatonin preserves the integrity of the mitochondria and helps to maintain cell functions and survival.