Free radical formation and erythrocyte membrane alterations during MetHb formation induced by the BHA metabolite, tert-butylhydroquinone

Synthesis and toxicity of monothiooxalamides against human red blood cells, brine shrimp (Artemia salina), and fruit fly (Drosophila melanogaster)

A new family of monothiooxalamides derived from 2-aminobenzimidazole was synthesized, and their structures were confirmed by 1H and 13C one-dimensional and 2D NMR experiments (COSY, HSQC, and HMBC). The antioxidant capacity was evaluated by free radical scavenging assays: 1,1-diphenyl-2-picrylhydrazyl (DPPH•), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS•+), ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), and the Fe(II) chelating ability. Our work group has previously reported the synthesis and antioxidant activity of monothiooxalamides derived from 2-aminopyridine (I). In this study, the in vitro hemolytic activity of compounds from the 2-aminopyridine (I) and 2-aminobenzimidazole (II) families was evaluated against human red blood cells (RBCs). The concentration at which monothiooxalamides showed no hemolytic activity was chosen to assess their ability to inhibit free radical-induced membrane damage in human RBCs, acute toxicity in brine shrimp, and in vivo toxicity against Drosophila melanogaster. Compounds with morpholine fragments (1g, 1h, 2g, and 2h) showed time- and concentration-dependent protective effects against radical-induced oxidative hemolysis. Moreover, they had the lowest acute toxicity in the brine shrimp lethality assay and a significant increase in chelating activity compared with the other molecules. In particular, monothiooxalamide 2g showed lower toxicity and can be considered for further biological screening and application trials.

Protection of Erythrocytes and Microvascular Endothelial Cells against Oxidative Damage by Fragaria vesca L. and Rubus idaeus L. Leaves Extracts-The Mechanism of Action

The aim of this work is to determine the biological activity of ellagitannins rich extracts from leaves of raspberry (Rubus idaeus L.) and wild strawberry (Fragaria vesca L.) in relation to cells and cell membranes. Detailed qualitative and quantitative analysis of phenolic compounds of the extract was made using chromatographic methods. Cytotoxic and antioxidant activities of tested extracts in relation to erythrocytes and human vascular endothelial cells (HMEC-1) were determined by using fluorimetric and spectrophotometric methods. In order to establish the influence of the extracts on the physical properties of the membrane, such as osmotic resistance and erythrocytes shapes, mobility and/or hydration of polar heads and fluidity of hydrocarbon chains of membrane lipids, microscopic and spectroscopic methods were used. The results showed that the extracts are non-toxic for erythrocytes and HMEC-1 cells (up to concentration of 50 µg/mL), but they effectively protect cells and their membranes against oxidative damage. The increase in osmotic resistance of erythrocytes, formation of echinocytes and changes only in the polar part of the membrane caused by the extracts demonstrate their location mainly in the hydrophilic part of the membrane. The results indicate that tested extracts have high biological activities and may be potentially used in delaying the ageing process of organisms and prevention of many diseases, especially those associated with oxidative stress.

Induction of lipid peroxidation in biomembranes by dietary oil components

Prooxidant formation and resulting lipid peroxidation are supposed to be involved in the pathogenesis of various diseases including cancer. Cancer risk is possibly influenced by the composition of diet with high intake of fat and red meat being harmful and high consumption of fruits and vegetables being protective. Since dietary oils may contain potential prooxidants, the aim of the present study was to prove (i) whether oxidative stress in biomembranes may be induced by dietary oils and if, (ii) which impact it has on the viability and proliferation of cultured colon (carcinoma) cells. Lipid hydroperoxide content in dietary oils increased after heating. Linoleic acid hydroperoxide (LOOH) and/or oils with different hydroperoxide contents induced lipid peroxidation in liposomes, erythrocyte ghosts and colon cells. Upon incubation with liposomes, both LOOH and heated oil induced lipid peroxidation only in the presence of iron and ascorbate. LOOH was sufficient to start lipid peroxidation of erythrocyte ghosts. LOOH incorporates into the lipid bilayer decreasing membrane fluidity and initiating lipid peroxidation in the lipid phase. When cultured cells (IEC18 intestinal epithelial cells, SW480 and HT29/HI1 colon carcinoma cells) were exposed to LOOH, they responded by cell death both via apoptosis and necrosis. Cells with higher degree of membrane unsaturation were more susceptible and antioxidants (vitamin E and selenite) were protective indicating the involvement of oxidative stress. Thus, peroxidation of biomembranes can be initiated by lipid hydroperoxides from heated oils. Dietary consumption of heated oils may lead to oxidative damage and to cell death in the colon. This may contribute to the enhanced risk of colon cancer due to regenerative cell proliferation.

Mutagenicity of tocopheryl quinones: evolutionary advantage of selective accumulation of dietary alpha-tocopherol

We have shown that phenolic antioxidant tocopherols are oxidized to nonarylating alpha-tocopheryl quinone (alpha-TQ) and arylating gamma- and delta-TQ electrophiles. The arylating quinones stimulate apoptosis and are highly cytotoxic in mammalian cells. Some xenobiotic phenolic antioxidants are mutagens, and it has been suggested that their arylating quinone metabolites are the active agents in mutagenesis related to carcinogenesis. We found that neither alpha- nor gamma-TQ was directly genotoxic in supercoiled-to-nicked circular DNA conversions, but these agents interacted with the cytomegalovirus reporter-driven plasmid and enhanced luciferase transfection, with gamma-TQ > alpha-TQ. The Ames test, using gamma-TQ and a number of Salmonella strains, showed no evidence of bacterial mutagenesis. gamma-TQ was highly cytotoxic and alpha-TQ slightly cytotoxic in eukaryocyte AS52 cells. A guanosine phosphoribosyltransferase gene assay showed that gamma-TQ was highly mutagenic and alpha-TQ slightly mutagenic in AS52 cells. A review of the literature identified associations where a decrease in dietary gamma-tocopherol (gamma-T) diminishes and an increase in dietary gamma-T and its quinone enhances carcinogenicity. Humans and other omnivores selectively accumulate alpha-tocopherol, even though gamma-T is their principal dietary tocopherol. We suggest that this selectivity confers an evolutionary advantage by limiting tissue gamma-T, a putative precursor of the mutagen gamma-TQ.

Electron spin resonance investigation of semiquinone radicals formed from the reaction of ubiquinone 0 with human oxyhemoglobin

The redox properties and thiol reactivity of quinones play critical roles in their therapeutic and toxicological properties. The present study was undertaken to investigate the binding activity of ubiquinone 0 (UQ(0)) to human oxyhemoglobin (HbO(2)) using electron spin resonance (ESR). Addition of UQ(0) to HbO(2) resulted in the immediate detection of a five-line ESR spectrum characteristic of the semiquinone radical of UQ(0) (UQ(0)). With time the HbO(2) adduct with UQ(0), which was characterized by a broad immobilized ESR spectrum, was gradually formed. Matrix-assisted laser desorption/ionization time-of-flight mass spectra analysis showed that UQ(0) bound to the beta-chain of HbO(2). Superoxide dismutase dose-dependently suppressed the intensity of the broad spectrum and accelerated its formation. However, N-ethylmaleimide, a thiol-blocking agent, completely eliminated its formation. The nonspecific protease mixture pronase also prevented its formation and resulted in the gradual appearance of a 4-line spectrum from the 5-line spectrum of UQ(0). The structure of the species responsible for the 4-line spectrum was confirmed and identified by the reaction of UQ(0) with reduced glutathione. In human red blood cells, UQ(0) rapidly bound to glutathione but more slowly to HbO(2). These results suggest that UQ(0) reacted with both ferrous heme and the reactive beta-93 cysteinyl residue of HbO(2) to generate its corresponding semiquinone radical. Subsequently UQ(0) bound to the beta-93 cysteinyl residue of HbO(2) to form a covalent-binding adduct responsible for the broad spectrum.