The pro-oxidant role of protein SH groups of hemoglobin in rat erythrocytes exposed to menadione

Distribution, adaptation and physiological meaning of thiols from vertebrate hemoglobins

In the present review, the sequences of hemoglobins (Hb) of 267 adult vertebrate species belonging to eight major vertebrate taxa are examined for the presence and location of cysteinyl residues in an attempt at correlation with their ecophysiology. Essentially, all vertebrates have surface cysteinyl residues in Hb molecules whereby their thiol groups may become highly reactive. Thiol-rich Hbs may display eight or more thiols per tetramer. In vertebrates so far examined, the cysteinyl residues occur in 44 different sequence positions in alpha chains and 41 positions in beta chains. Most of them are conservatively located and occur in only a few positions in Teleostei, Aves and Mammalia, whereas they are dispersed in Amphibia. The internal cysteinyl residue alpha104 is ubiquitous in vertebrates. Residue beta93 is highly conserved in reptiles, birds and mammals. The number of cysteine residues per tetramer with solvent access varies in vertebrates, mammalians and bony fish having the lowest number of external residues, whereas nearly all external cysteine residues in Aves and Lepidosauria are of the surface crevice type. In cartilaginous fish, amphibians, Crocodylidae and fresh water turtles, a substantial portion of the solvent accessible thiols are of the totally external type. Recent evidence shows that some Hb thiol groups are highly reactive and undergo extensive and reversible S-thiolation, and that they may be implicated in interorgan redox equilibrium processes. Participation of thiol groups in nitric oxide ((*)NO) metabolism has also been proved. The evidence argues for a new physiologically relevant role for Hb via involvement in free radical and antioxidant metabolism.

Metabolism of oxidants by blood from different mouse strains

Haemoglobins bearing reactive sulfhydryl groups have been shown to be able to interplay with glutathione in some detoxification processes. Blood from different mouse strains commonly used as experimental animal models, i.e., C57, DBA and ICR, was treated with oxidants with the aim of evaluating: (i) the involvement of protein SH groups in oxido-reductive reactions that are commonly carried out by glutathione and (ii) the impact of this phenomenon on blood-mediated metabolism of thiol reactants. All the main forms of glutathione (reduced, disulfide, and mixed disulfide with haemoglobin) were measured after oxidant treatment. Significant differences were found among the studied strains: DBA mice formed preferably mixed disulfides instead of glutathione disulfide, whereas the opposite behaviour was shown by C57 mice. Unexpectedly, the ICR strain resulted to be composed of three different subgroups (ICRa, ICRb, and ICRc), with the ICRa behaving similarly to the DBA strain, ICRc to the C57 strain, and ICRc showing an intermediate behaviour. These results are due to the different number of haemoglobin SH groups in the studied mouse strains. In particular, additional fast-reacting SH groups were found in haemoglobin from DBA, ICRa, and ICRb mice, but not in the C57 and ICRc strain. These differences were also reflected in the susceptibility of haemoglobin to dimerize and in its ability to react with S-nitrosocysteine. Because of the widely different reactivity of haemoglobin cysteinyl residues, the mouse strains examined are an interesting but complicated model in which to study the pharmacological and toxicological action of some drugs.

Influence of plasma total antioxidant ability on lipid and protein oxidation products in plasma and erythrocyte ghost obtained from developing and adult rats pretreated with two vitamin K formulations

Ferric reducing ability of plasma (FRAP), as an index of total antioxidant capacity of plasma was found to be enhanced significantly (p < 0.05) in suckling rats pretreated either with vitamin K1 (28, 56 or 84 mg/kg/3 days) or menadione (vitamin K3) at a dose of 15 mg/kg b.w./3 days. The effect of vitamin K1 on FRAP was dose-dependent and it was inversely related to the formation of lipid peroxidation products in plasma as judged by thiobarbituric acid reacting substances (TBARS). Lack of influence of the drugs on FRAP in adults was corroborated with elevation in the levels of plasma TBARS. Possible role of FRAP on the rate of lipid peroxidation and protein oxidation (protein carbonyls) on erythrocyte membrane was also investigated following isolation of erythrocyte ghost from control and treated rats. Vitamin K1 as well as menadione failed to change the levels of protein carbonyls in erythrocyte ghost obtained from both the age groups. Analysis of major erythrocyte membrane proteins, using SDS-polyacrylamide gel electrophoresis (SDS-PAGE) substantiated these results. In spite of higher antioxidant capacity of plasma and erythrocytes obtained from young rats, the rate of lipid peroxidation in erythrocyte ghost preparation was also high in this age group (p < 0.05). These results suggest that the drug-related induction in FRAP occurs only in immature animals as a part of protective mechanism against lipid peroxidation products generated in plasma.

Menadione causes endothelial barrier failure by a direct effect on intracellular thiols, independent of reactive oxidant production

Menadione (MQ), a quinone used with cancer chemotherapeutic agents, causes cytotoxicity to endothelial cells (EC). Previous studies have suggested that MQ induces an oxidative stress and dysfunction in EC by either increasing hydrogen peroxide (H(2)O(2)) production or depleting intracellular glutathione (GSH), the main intracellular antioxidant. Since a primary function of EC is to form a barrier to fluid movement into tissues, protecting organs from edema formation and dysfunction, our aim was to see if MQ would cause a barrier dysfunction and to ascertain the mechanism. Using diffusional permeability to fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) as a measure of barrier function, we found that 15 micro M MQ incubated with a bovine pulmonary artery EC (BPAEC) monolayer for 4 h produced a profound barrier failure ( approximately 7-fold increase in permeability) with a parallel fall in glutathione, almost to depletion. These two events were highly correlated. Immunofluorescent imaging showed formation of paracellular holes consistent with a loss or rearrangement of cell-cell and cell-matrix adhesion molecules. H(2)O(2) (100 micro M), a concentration which gave about the same increase in permeability as MQ, only slightly decreased GSH concentration. Antioxidants, such as catalase (CAT) and dimethylthiourea (DMTU), which were able to block the H(2)O(2)-induced changes, had no effect on the MQ-induced permeability and GSH changes, suggesting that H(2)O(2) was not involved in MQ-induced effects. MQ caused a severe EC cytotoxicity as judged by lactate dehydrogenase (LDH) leakage from the EC, whereas H(2)O(2) caused only a minor increase. Also, MQ profoundly inhibited the activities of glucose-6-phosphate dehydrogenase (G6PDH) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), key thiol enzymes involved in glutathione and ATP metabolism, whereas H(2)O(2) produced only a slight decrease in these activities. We conclude that the cytotoxicity of MQ and resulting barrier dysfunction correlate with GSH depletion and inactivation of key metabolic enzymes, compromising antioxidant defenses, rather than being consistent with H(2)O(2)-mediated oxidative stress.