Alpha-tocopheryl hydroquinone is an efficient multifunctional inhibitor of radical-initiated oxidation of low density lipoprotein lipids

In defence of ferroptosis

Rampant phospholipid peroxidation initiated by iron causes ferroptosis unless this is restrained by cellular defences. Ferroptosis is increasingly implicated in a host of diseases, and unlike other cell death programs the physiological initiation of ferroptosis is conceived to occur not by an endogenous executioner, but by the withdrawal of cellular guardians that otherwise constantly oppose ferroptosis induction. Here, we profile key ferroptotic defence strategies including iron regulation, phospholipid modulation and enzymes and metabolite systems: glutathione reductase (GR), Ferroptosis suppressor protein 1 (FSP1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), Dihydrofolate reductase (DHFR), retinal reductases and retinal dehydrogenases (RDH) and thioredoxin reductases (TR). A common thread uniting all key enzymes and metabolites that combat lipid peroxidation during ferroptosis is a dependence on a key cellular reductant, nicotinamide adenine dinucleotide phosphate (NADPH). We will outline how cells control central carbon metabolism to produce NADPH and necessary precursors to defend against ferroptosis. Subsequently we will discuss evidence for ferroptosis and NADPH dysregulation in different disease contexts including glucose-6-phosphate dehydrogenase deficiency, cancer and neurodegeneration. Finally, we discuss several anti-ferroptosis therapeutic strategies spanning the use of radical trapping agents, iron modulation and glutathione dependent redox support and highlight the current landscape of clinical trials focusing on ferroptosis.

Complex I activity in hypoxia: implications for oncometabolism

Certain cancer cells within solid tumors experience hypoxia, rendering them incapable of oxidative phosphorylation (OXPHOS). Despite this oxygen deficiency, these cells exhibit biochemical pathway activity that relies on NAD+. This mini-review scrutinizes the persistent, residual Complex I activity that oxidizes NADH in the absence of oxygen as the electron acceptor. The resulting NAD+ assumes a pivotal role in fueling the α-ketoglutarate dehydrogenase complex, a critical component in the oxidative decarboxylation branch of glutaminolysis - a hallmark oncometabolic pathway. The proposition is that through glutamine catabolism, high-energy phosphate intermediates are produced via substrate-level phosphorylation in the mitochondrial matrix substantiated by succinyl-CoA ligase, partially compensating for an OXPHOS deficiency. These insights provide a rationale for exploring Complex I inhibitors in cancer treatment, even when OXPHOS functionality is already compromised.

Role of SEC14-like phosphatidylinositol transfer proteins in membrane identity and dynamics

Membrane identity and dynamic processes, that act at membrane sites, provide important cues for regulating transport, signal transduction and communication across membranes. There are still numerous open questions as to how membrane identity changes and the dynamic processes acting at the surface of membranes are regulated in diverse eukaryotes in particular plants and which roles are being played by protein interaction complexes composed of peripheral and integral membrane proteins. One class of peripheral membrane proteins conserved across eukaryotes comprises the SEC14-like phosphatidylinositol transfer proteins (SEC14L-PITPs). These proteins share a SEC14 domain that contributes to membrane identity and fulfills regulatory functions in membrane trafficking by its ability to sense, bind, transport and exchange lipophilic substances between membranes, such as phosphoinositides and diverse other lipophilic substances. SEC14L-PITPs can occur as single-domain SEC14-only proteins in all investigated organisms or with a modular domain structure as multi-domain proteins in animals and streptophytes (comprising charales and land plants). Here, we present an overview on the functional roles of SEC14L-PITPs, with a special focus on the multi-domain SEC14L-PITPs of the SEC14-nodulin and SEC14-GOLD group (PATELLINs, PATLs in plants). This indicates that SEC14L-PITPs play diverse roles from membrane trafficking to organism fitness in plants. We concentrate on the structure of SEC14L-PITPs, their ability to not only bind phospholipids but also other lipophilic ligands, and their ability to regulate complex cellular responses through interacting with proteins at membrane sites.

Malondialdehyde as an Important Key Factor of Molecular Mechanisms of Vascular Wall Damage under Heart Diseases Development

This mini review is devoted to a specific issue: the role of malondialdehyde (MDA)-a secondary product of free radical lipid peroxidation-in the molecular mechanisms of the formation of primary atherosclerotic vascular wall lesions. The principal difference between this review and the available literature is that it discusses in detail the important role in atherogenesis not of "oxidized" LDL (i.e., LDL particles containing lipohydroperoxides), but of LDL particles chemically modified by the natural low-molecular weight dicarbonyl MDA. To confirm this, we consider the data obtained by us earlier, indicating that "atherogenic" are not LDL oxidized as a result of free radical lipoperoxidation and containing lipohydroperoxy derivatives of phospholipids in the outer layer of particles, but LDL whose apoprotein B-100 has been modified due to the chemical reaction of terminal lysine residue amino groups of the apoB-100 with the aldehyde groups of the MDA (Maillard reaction). In addition, we present our original data proving that MDA injures endothelial glycocalyx that suppress the ability of the endothelium to control arterial tone according to changes in wall shear stress. In summary, this mini review for the first time exhaustively discloses the key role of MDA in atherogenesis.

Reactivity of Vitamin E as an Antioxidant in Red Meat and the Stomach Medium

The stomach is a bioreactor and an important intersection of biochemical reactions that affect human health. Lipid peroxidation of meat in the stomach medium generates malondialdehyde (MDA), which is absorbed from the gut into human plasma and modifies low-density lipoprotein (LDL) to MDA-LDL. We found in the stomach medium (pH 3.0) a high antioxidant activity of vitamin E against meat lipid peroxidation, almost 35-fold higher than at pH 6.3. In the stomach medium, the antioxidant activity of vitamin E on meat lipid peroxidation was 20-fold higher than that of catechin. Vitamin E, at pH 3.0, acts synergistically with metmyoglobin (MbFe⁺³), as a peroxidase/antioxidant couple. The synergistic effect of MbFe⁺³/vitamin E was almost 150-fold higher than the antioxidant effect achieved by MbFe⁺³/catechin. The meat antioxidant activity was maintained continuously by addition of a low concentration of vitamin E, catechin, and vitamin C, preventing the propagation of lipid oxidation, reactive aldehyde generation, and the loss of vitamin E.

Fluorescence-Amplified Detection of Redox Turnovers in Supported Lipid Bilayers Illuminates Redox Processes of α-Tocopherol

Electron-transfer processes in lipid membranes are key to biological functions, yet challenging to study because of the intrinsic heterogeneity of the systems. Here, we report spectro-electrochemical measurements on indium tin oxide-supported lipid bilayers toward the selective induction and sensing of redox processes in membranes. Working at neutral pH with a fluorogenic α-tocopherol analogue, the dynamics of the two-electron oxidation of the chromanol to a chromanone and the rapid thermal decay of the latter to a chromoquinone are recorded as a rapid surge and drop in intensity, respectively. Continuous voltage cycling reveals rapid chromoquinone two-electron, two-proton reduction to dihydrochromoquinone at negative bias, followed by slow regeneration of the former at positive bias. The kinetic parameters of these different transitions are readily obtained as a function of applied potentials. The sensitivity and selectivity afforded by the reported method enables monitoring signals equivalent to femtoampere currents with a high signal-to-background ratio. The study provides a new method to monitor membrane redox processes with high sensitivity and minimal concentrations and unravels key dynamic aspects of α-tocopherol redox chemistry.

Inhibition of Pro-Inflammatory Cytokine Secretion by Select Antioxidants in Human Coronary Artery Endothelial Cells

Abstract. Inflammatory and oxidative stress in endothelial cells are implicated in the pathogenesis of premature atherosclerosis in diabetes. To determine whether high-dextrose concentrations induce the expression of pro-inflammatory cytokines, human coronary artery endothelial cells (HCAEC) were exposed to either 5.5 or 27.5 mM dextrose for 24-hours and interleukin-1β (IL-1β), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor α (TNF α) levels were measured by enzyme immunoassays. To determine the effect of antioxidants on inflammatory cytokine secretion, cells were also treated with α-tocopherol, ascorbic acid, and the glutathione peroxidase mimetic ebselen. Only the concentration of IL-1β in culture media from cells exposed to 27.5 mM dextrose increased relative to cells maintained in 5.5 mM dextrose. Treatment with α-tocopherol (10, 100, and 1,000 μM) and ascorbic acid (15, 150, and 1,500 μM) at the same time that the dextrose was added reduced IL-1β, IL-6, and IL-8 levels in culture media from cells maintained at 5.5 mM dextrose but had no effect on IL-1β, IL-6, and IL-8 levels in cells exposed to 27.5 mM dextrose. However, ebselen treatment reduced IL-1β, IL-6, and IL-8 levels in cells maintained in either 5.5 or 27.5 mM dextrose. IL-2 and TNF α concentrations in culture media were below the limit of detection under all experimental conditions studied suggesting that these cells may not synthesize detectable quantities of these cytokines. These results suggest that dextrose at certain concentrations may increase IL-1β levels and that antioxidants have differential effects on suppressing the secretion of pro-inflammatory cytokines in HCAEC.

Vitamins C and E alone and in combination partly protect against chronic ethanol-induced toxicity in rat erythrocytes

Oxidative stress is part of the mechanisms involved in ethanol toxicity. We investigated effects of vitamins C (VC), E (VE) and the combination of VC+VE on chronic ethanol-induced toxicity in rat erythrocytes. The following groups were treated for 30 days: control (C), VC (200 mg/kg), VE (200 mg/kg), VC (200 mg/kg) + VE (200 mg/kg), ethanol 4 g/kg, ethanol + VC, ethanol + VE and ethanol + VC + VE. The doses of vitamins and ethanol were selected for per kilogram of animal's body weight. Blood samples collected at the end of treatments were analyzed for erythrocyte osmotic fragility and plasma scavenging activity. The washed erythrocytes were used to determine superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and malondialdeyde (MDA). Ethanol induced erythrocyte fragility (p < 0.001) and increased lipid peroxidation (p < 0.001) in rat erythrocytes. Furthermore, there were significant decreases in plasma scavenging (p < 0.001), SOD (p < 0.001), CAT (p < 0.01) and GPx (p < 0.001) activities in erythrocytes of ethanol-treated animals. Although VC or VE alone restored all of ethanol-induced disturbances to near normal (p > 0.05) but there were still significant differences compared to control animals. Combination therapy completely corrected ethanol-induced erythrocyte fragility, lipid peroxidation and prooxidant/antioxidant imbalance. We showed the beneficial effects of VC and VE combination in decreasing erythrocyte fragility and lipid peroxidation in both ethanol and control groups. Therefore this combination treatment may provide a new potential alternative for prevention of ethanol toxicity which deserves consideration and further examination.

Novel and rare prenyllipids - Occurrence and biological activity

The data presented indicate that there is a variety of unique prenyllipids, often of very limited taxonomic distribution, whose origin, biosynthesis, metabolism and biological function deserves to be elucidated. These compounds include tocoenols, tocochromanol esters, tocochromanol acids, plastoquinones and ubiquinones. Additionally, based on the available data, it can be assumed that there are still unrecognized prenyllipids, like prenylquinols fatty acid esters of the hydroquinone ring, including prenylquinol phosphates, and others, whose biological function might be of great importance. Our knowledge of these compounds is not only important from the scientific point of view, but may also be of practical significance to medicine, pharmacy or cosmetics.

Function of isoprenoid quinones and chromanols during oxidative stress in plants

Isoprenoid quinones and chromanols in plants fulfill both signaling and antioxidant functions under oxidative stress. The redox state of the plastoquinol pool (PQ-pool), which is modulated by interaction with reactive oxygen species (ROS) during oxidative stress, has a major regulatory function in both short- and long-term acclimatory responses. By contrast, the scavenging of ROS by prenyllipids affects signaling pathways where ROS play a role as signaling molecules. As the primary antioxidants, isoprenoid quinones and chromanols are synthesized under high-light stress in response to any increased production of ROS. During photo-oxidative stress, these prenyllipids are continuously synthesized and oxidized to other compounds. In turn, their oxidation products (hydroxy-plastochromanol, plastoquinol-C, plastoquinone-B) can still have an antioxidant function. The oxidation products of isoprenoid quinones and chromanols formed specifically in the face of singlet oxygen, can be indicators of singlet oxygen stress.

A panoramic overview of mitochondria and mitochondrial redox biology

Mitochondria dysfunction was first described in the 1960s. However, the extent and mechanisms of mitochondria dysfunction’s role in cellular physiology and pathology has only recently begun to be appreciated. To adequately evaluate mitochondria-mediated toxicity, it is not only necessary to understand mitochondria biology, but discerning mitochondrial redox biology is also essential. The latter is intricately tied to mitochondrial bioenergetics. Mitochondrial free radicals, antioxidants, and antioxidant enzymes are players in mitochondrial redox biology. This review will provide an across-the-board, albeit not in-depth, overview of mitochondria biology and mitochondrial redox biology. With accumulating knowledge on mitochondria biology and mitochondrial redox biology, we may devise experimental methods with adequate sensitivity and specificity to evaluate mitochondrial toxicity, especially in vivo in living organisms, in the near future.

Steroidal and α-tocopherylhydroquinone glycosides from two soft corals Cladiella hirsuta and Sinularia nanolobata

Cytotoxic and anti-inflammatory glycosides were isolated from two soft corals,Cladiella hirsutaandSinularia nanolobata. Compounds3and4represent the first example of tocopheryl xyloside derivatives.

High-fat diet-induced met-hemoglobin formation in rats prone (WOKW) or resistant (DA) to the metabolic syndrome: effect of CoQ10 supplementation

The aim of this study was to evaluate the effects of a high-fat diet (HFD) on oxidative indexes in WistarOttawaKarlsburg W (WOKW) rats used as a model of metabolic syndrome in comparison with Dark Agouti (DA) rats used as a control strain. This syndrome is defined by the occurrence of two or more risk factors including obesity, hypertension, dyslipidemia, and insulin resistance. Forty rats were used in the study and the effect of HFD was evaluated in terms of body weight and both hemoglobin and CoQ oxidative status. Moreover, 16 rats (8 of each strain) were supplemented with 3 mg/100 g b.w. of CoQ10 for 1 month in view of its beneficial properties in cardiovascular disease due to its antioxidant activity in the lipid environment. HFD promoted an increase in body weight, in particular in WOKW males, and in the methemoglobin (met-Hb) index in both strains. Moreover, HFD promoted endogenous CoQ10 oxidation. CoQ10 supplementation was able to efficiently counteract the HFD pro-oxidant effects, preventing met-Hb formation and CoQ oxidation.

Induction of phase 2 antioxidant enzymes by broccoli sulforaphane: perspectives in maintaining the antioxidant activity of vitamins a, C, and e

Consumption of fruits and vegetables is recognized as an important part of a healthy diet. Increased consumption of cruciferous vegetables in particular has been associated with a decreased risk of several degenerative and chronic diseases, including cardiovascular disease and certain cancers. Members of the cruciferous vegetable family, which includes broccoli, Brussels sprouts, cauliflower, and cabbage, accumulate significant concentrations of glucosinolates, which are metabolized in vivo to biologically active isothiocyanates (ITCs). The ITC sulforaphane, which is derived from glucoraphanin, has garnered particular interest as an indirect antioxidant due to its extraordinary ability to induce expression of several enzymes via the KEAP1/Nrf2/ARE pathway. Nrf2/ARE gene products are typically characterized as Phase II detoxification enzymes and/or antioxidant (AO) enzymes. Over the last decade, human clinical studies have begun to provide in vivo evidence of both Phase II and AO enzyme induction by SF. Many AO enzymes are redox cycling enzymes that maintain redox homeostasis and activity of free radical scavengers such as vitamins A, C, and E. In this review, we present the existing evidence for induction of PII and AO enzymes by SF, the interactions of SF-induced AO enzymes and proposed maintenance of the essential vitamins A, C, and E, and, finally, the current view of genotypic effects on ITC metabolism and AO enzyme induction and function.

Vitamins C and E: beneficial effects from a mechanistic perspective

The mechanistic properties of two dietary antioxidants that are required by humans, vitamins C and E, are discussed relative to their biological effects. Vitamin C (ascorbic acid) is an essential cofactor for α-ketoglutarate-dependent dioxygenases. Examples are prolyl hydroxylases, which play a role in the biosynthesis of collagen and in down-regulation of hypoxia-inducible factor (HIF)-1, a transcription factor that regulates many genes responsible for tumor growth, energy metabolism, and neutrophil function and apoptosis. Vitamin C-dependent inhibition of the HIF pathway may provide alternative or additional approaches for controlling tumor progression, infections, and inflammation. Vitamin E (α-tocopherol) functions as an essential lipid-soluble antioxidant, scavenging hydroperoxyl radicals in a lipid milieu. Human symptoms of vitamin E deficiency suggest that its antioxidant properties play a major role in protecting erythrocyte membranes and nervous tissues. As an antioxidant, vitamin C provides protection against oxidative stress-induced cellular damage by scavenging of reactive oxygen species, by vitamin E-dependent neutralization of lipid hydroperoxyl radicals, and by protecting proteins from alkylation by electrophilic lipid peroxidation products. These bioactivities bear relevance to inflammatory disorders. Vitamin C also plays a role in the function of endothelial nitric oxide synthase (eNOS) by recycling the eNOS cofactor, tetrahydrobiopterin, which is relevant to arterial elasticity and blood pressure regulation. Evidence from plants supports a role for vitamin C in the formation of covalent adducts with electrophilic secondary metabolites. Mechanism-based effects of vitamin C and E supplementation on biomarkers and on clinical outcomes from randomized, placebo-controlled trials are emphasized in this review.

The role of EPR spectroscopy in studies of the oxidative status of biological systems and the antioxidative properties of various compounds

In this era of intense study of free radicals and antioxidants, electron paramagnetic resonance (EPR) is arguably the best-suited technique for such research, particularly when considering biochemical and biological systems. No attempt was made to cover all the topics of EPR application but instead attention was restricted to two areas that are both novel and received less attention in previous reviews. In the first section, the application of EPR in assessing the oxidative status of various biological systems, using endogenous stabile paramagnetic species, such as the ascorbyl radical, semiquinone, melanin, and oxidized pigments, is addressed. The second section covers the use of EPR in the emerging field of antioxidant development, using EPR spin-trapping and spin-probing techniques. In both sections, in addition to giving an overview of the available literature, examples (mostly from the authors? recent work) are also presented in sufficient detail to illustrate how to explore the full potential of EPR. This review aims at encouraging biologists, chemists and pharmacologists interested in the redox metabolism of living systems, free radical chemistry or antioxidative properties of new drugs and natural products to take advantage of this technique for their investigations.

Tocopheryl quinones and mitochondria

In the past, the role of tocopherols and tocopheryl hydroquinones as antioxidants in mitochondria has been examined. However, structural properties of tocopherols and tocopheryl quinones (arrangement of polar/apolar moieties) have also been recognized as being crucial for the selective transport of RRR-alpha-congeners compared with other tocopherols in the cell, suggesting that these properties might be generally important for the binding of vitamin E-related compounds to proteins and enzymes in mitochondria. Therefore, direct modulation of mitochondrial activities, such as bioenergetics, production of reactive oxygen species and apoptosis, not exclusively related to the redox activity of these compounds is increasingly studied. This overview focuses on the influence of alpha-/gamma-tocopheryl quinones and their parent alpha-/gamma-tocopherols on mitochondrial functions, including formation of tocopheryl quinones, their analytical aspects, their potential as alternative substrates and their inhibitory activity for some mitochondrial functions. It is shown that the understanding of how tocopheryl quinones and tocopherols interfere with mitochondrial functions on the molecular level is still incomplete and that a better comprehension requires further research activities.

Occurrence, biosynthesis and function of isoprenoid quinones

Isoprenoid quinones are one of the most important groups of compounds occurring in membranes of living organisms. These compounds are composed of a hydrophilic head group and an apolar isoprenoid side chain, giving the molecules a lipid-soluble character. Isoprenoid quinones function mainly as electron and proton carriers in photosynthetic and respiratory electron transport chains and these compounds show also additional functions, such as antioxidant function. Most of naturally occurring isoprenoid quinones belong to naphthoquinones or evolutionary younger benzoquinones. Among benzoquinones, the most widespread and important are ubiquinones and plastoquinones. Menaquinones, belonging to naphthoquinones, function in respiratory and photosynthetic electron transport chains of bacteria. Phylloquinone K(1), a phytyl naphthoquinone, functions in the photosynthetic electron transport in photosystem I. Ubiquinones participate in respiratory chains of eukaryotic mitochondria and some bacteria. Plastoquinones are components of photosynthetic electron transport chains of cyanobacteria and plant chloroplasts. Biosynthetic pathway of isoprenoid quinones has been described, as well as their additional, recently recognized, diverse functions in bacterial, plant and animal metabolism.

Synthesis and theoretical study of molecularly imprinted nanospheres for recognition of tocopherols

Molecular imprinting is a technology that facilitates the production of artificial receptors toward compounds of interest. The molecularly imprinted polymers act as artificial antibodies, artificial receptors, or artificial enzymes with the added benefit over their biological counterparts of being highly durable. In this study, we prepared molecularly imprinted polymers for the purpose of binding specifically to tocopherol (vitamin E) and its derivative, tocopherol acetate. Binding of the imprinted polymers to the template was found to be two times greater than that of the control, non-imprinted polymers, when using only 10 mg of polymers. Optimization of the rebinding solvent indicated that ethanol-water at a molar ratio of 6:4 (v/v) was the best solvent system as it enhanced the rebinding performance of the imprinted polymers toward both tocopherol and tocopherol acetate with a binding capacity of approximately 2 mg/g of polymer. Furthermore, imprinted nanospheres against tocopherol was successfully prepared by precipitation polymerization with ethanol-water at a molar ratio of 8:2 (v/v) as the optimal rebinding solvent. Computer simulation was also performed to provide mechanistic insights on the binding mode of template-monomer complexes. Such polymers show high potential for industrial and medical applications, particularly for selective separation of tocopherol and derivatives.

Vitamin E in human health and disease

Vitamin E in nature is comprised of a family of tocopherols and tocotrienols. The most studied of these is alpha-tocopherol (alpha-TOH), because this form is retained within the body, and vitamin E deficiency is corrected with this supplement. alpha-TOH is a lipid-soluble antioxidant required for the preservation of cell membranes, and it potentially acts as a defense against oxidative stress. Many studies have investigated the metabolism, transport, and efficacy alpha-TOH in the prevention of sequelae associated with cardiovascular disease (CVD). Supplementation with vitamin E is considered to provide health benefits against CVD through its antioxidant activity, the prevention of lipoprotein oxidation, and the inhibition of platelet aggregation. However, the results from large prospective, randomized, placebo-controlled clinical trials with alpha-TOH have been largely negative. A recent meta-analysis suggests that alpha-TOH supplements may actually increase all-cause mortality; however, the mechanism for this increased risk is unknown. In vitro studies performed in human cell cultures and animal models suggest that vitamin E might increase the hepatic production of cytochrome P450s and MDR1. Induction of CYP3A4 or MDR1 by vitamin E could potentially lower the efficacy of any drug metabolized by CYP3A4 or MDR1. Other possibilities include an adverse effect of alpha-TOH on blood pressure in high-risk populations. Because of the wide popularity and use of vitamin E supplements, further research into potential adverse effects is clearly warranted.

Tocopherol quinone content of green algae and higher plants revised by a new high-sensitive fluorescence detection method using HPLC--effects of high light stress and senescence

A rapid, sensitive fluorescence method was applied here for detection of oxidized tocopherol quinones in total plant tissue extracts using HPLC, employing a post-column reduction of these compounds by a Zn column. Using this method, we were able to detect both alpha- and gamma-tocopherol quinones in Chlamydomonas reinhardii with a very high degree of sensitivity. The levels of both compounds increased under high light stress in the presence of pyrazolate in parallel to a decrease in the content of the corresponding tocopherols. The formation of tocopherol quinones from tocopherols was apparently due to their oxidation by singlet oxygen, which is formed in photosystem II under high light stress. alpha-Tocopherol quinone was also detected in a variety of higher plants of different age, and its level was found to increase during senescence in leaves grown under natural conditions. In contrast to alpha-tocopherol quinone, gamma-tocopherol quinone was not found in the higher plant species investigated with the exception of young runner bean leaves, where the levels of both compounds increased dramatically during cold and light stress. Taking advantage of native fluorescence of the reduced alpha-tocopherol quinone (alpha-tocopherol quinol), it can be detected in plant tissue extracts with a high sensitivity. In young runner bean leaves, alpha-tocopherol quinol was found at a level similar to alpha-tocopherol.

In vivo gamma-tocopherol supplementation decreases systemic oxidative stress and cytokine responses of human monocytes in normal and asthmatic subjects

We have recently reported that gamma-tocopherol (gammaT) reduces allergen- and zymosan-induced inflammation using rodent models. As an initial step in extending these observations to humans, we conducted an open-label, Phase I dosing study of two doses (one or two capsules daily for 1 week) of a gamma-tocopherol-rich preparation containing 623 mg of gamma-tocopherol, 61.1 mg of d-alpha-tocopherol, 11.1 mg of d-beta-tocopherol (11.1 mg), and 231 mg of d-sigma-tocopherol per capsule. Endpoints for this study include serum levels of 5-nitro-gamma-tocopherol, as a marker of oxidative stress, and changes in serum gamma-, alpha-, and delta-tocopherol and gamma-2'-carboxyethyl-6-hydroxychroman (CEHC) 6 and 24 h after the first dose and after 1 week of treatment. To assess the biological activity of this treatment, we obtained peripheral blood mononuclear cells at baseline and after 1 week of treatment with two capsules of a gamma-tocopherol-rich preparation/day and examined the inflammatory cytokine response of these cells in culture to ex vivo endotoxin/LPS (0.01 ng/ml) challenge. We also monitored a number of safety endpoints to examine how well this preparation is tolerated in eight normal volunteers (four allergic and four nonallergic) and eight allergic asthmatics. We further obtained human monocytes from a subset of these volunteers and treated them ex vivo with gammaT, alphaT, gamma-CEHC, and alpha-CEHC and assessed their actions on LPS-induced degradation of IkappaBalpha and JNK signaling and ROS generation. As detailed herein, this open-label study demonstrates that gamma-tocopherol-enriched supplementation decreased systemic oxidative stress, increased serum levels of gamma-tocopherol, and inhibited monocyte responses to LPS without any adverse health effects. Further, in vitro treatment of human monocytes with gamma-CEHC and alpha-CEHC inhibits ROS generation and LPS-induced degradation of IkappaB and JNK activation.

Copper-induced peroxidation of phosphatidylserine-containing liposomes is inhibited by nanomolar concentrations of specific antioxidants

Copper-induced peroxidation of liposomal palmitoyllinoleoyl-phosphatidylcholine (PLPC) is inhibited by alpha-tocopherol at micromolar concentrations. In our previous study we found that when the liposomes contain phosphatidylserine (PS), nanomolar concentrations of Toc were sufficient to inhibit peroxidation. In an attempt to gain understanding of the origin of this extreme antioxidative potency, we tested the antioxidative potency of 36 additional antioxidants and the dependence of their potency on the presence of PS in the liposomes. The results of these studies reveal that only 11 of the tested antioxidants possess similar antioxidative potency to that of Toc. These include trolox, butylated hydroxytoluene (BHT), curcumin, nordihydroguaiaretic acid (NDGA), diethylstilbestrol (DES), 2 of the 13 tested flavonoids (luteolin and 7,3',4'-trihydroxyflavone; T-414), alpha-naphthol, 1,5-, 1,6- and 1,7-dihydroxynaphthalenes (DHNs). Propyl gallate (PG), methyl syringate, rosmarinic acid, resveratrol, other flavonoids, as well as beta-naphthol, 1,2-, 1,3-, 1,4-, 2,3-, 2,6-, and 2,7-DHNs were either moderately antioxidative or pro-oxidative. For liposomes made of PLPC (250 microM) and PS (25 microM) the "lag" preceding copper-induced peroxidation (5 microM copper) was doubled upon addition of 30-130nM of the "super-active" antioxidants. We propose that the mechanism responsible for the extreme antioxidative potency against copper-induced peroxidation in PS-containing liposomes involves replenishment of the antioxidant in a ternary PS-copper-antioxidant complex. Based on structure-activity relationship of the 37 tested antioxidants, the "super-antioxidative potency" is attributed to the recycling of relatively stable semiquinone or semiquinone-like radicals.

Plastoquinol as a singlet oxygen scavenger in photosystem II

It has been found that in Chlamydomonas reinhardtii cells, under high-light stress, the level of reduced plastoquinone considerably increases while in the presence of pyrazolate, an inhibitor of plastoquinone and tocopherol biosynthesis, the content of reduced plastoquinone quickly decreases, similarly to alpha-tocopherol. In relation to chlorophyll, after 18 h of growth under low light with the inhibitor, the content of alpha-tocopherol was 22.2 mol/1000 mol chlorophyll and that of total plastoquinone (oxidized and reduced) was 19 mol/1000 mol chlorophyll, while after 2 h of high-light stress the corresponding amounts dropped to 6.4 and 6.2 mol/1000 mol chlorophyll for alpha-tocopherol and total plastoquinone, respectively. The degradation of both prenyllipids was partially reversed by diphenylamine, a singlet oxygen scavenger. It was concluded that plastoquinol, as well as alpha-tocopherol is decomposed under high-light stress as a result of a scavenging reaction of singlet oxygen generated in photosystem II. The levels of both alpha-tocopherol and of the reduced plastoquinone are not affected significantly in the absence of the inhibitor due to a high turnover rate of both prenyllipids, i.e., their degradation is compensated by fast biosynthesis. The calculated turnover rates under high-light conditions were twofold higher for total plastoquinone (0.23 nmol/h/ml of cell culture) than for alpha-tocopherol (0.11 nmol/h/ml). We have also found that the level of alpha-tocopherolquinone, an oxidation product of alpha-tocopherol, increases as the alpha-tocopherol is consumed. The same correlation was also observed for gamma-tocopherol and its quinone form. Moreover, in the presence of pyrazolate under low-light growth conditions, the synthesis of plastoquinone-C, a hydroxylated plastoquinone derivative, was stimulated in contrast to plastoquinone, indicating for the first time a functional role for plastoquinone-C. The presented data also suggest that the two plastoquinones may have different biosynthetic pathways in C. reinhardtii.

Vitamin E metabolism

The aim of this paper is to provide an overview of vitamin E metabolism. The topics covered include: major classes of vitamin E metabolites; their production pathways and route of excretion; possible biological activities of vitamin E metabolites; and use of vitamin E metabolites as markers of oxidant generation. Recent investigations into vitamin E metabolism have also highlighted important new areas of research, such as the potential for high dose vitamin E supplementation to interfere with drug metabolism, as well as alternative methods to alter vitamin E bioavailability in vivo. These issues will also be discussed in the review.

Oxidant Stress and Damage in Post-Ischemic Mouse Hearts: Effects of Adenosine

Despite the general understanding that ischemia-reperfusion (I/R) promotes oxidant stress, specific contributions of oxidant stress or damage to myocardial I/R injury remain poorly defined. Moreover, whether endogenous 'cardioprotectants' such as adenosine act via limiting this oxidant injury is unclear. Herein we characterized effects of 20 min ischemia and 45 min reperfusion on cardiovascular function, oxidative stress and damage in isolated perfused mouse hearts (with glucose or pyruvate as substrate), and examined whether 10 microM adenosine modified these processes. In glucose-perfused hearts post-ischemic contractile function was markedly impaired (< 50% of pre-ischemia), cell damage assessed by lactate dehydrogenase (LDH) release was increased (12 +/- 2 IU/g vs. 0.2 +/- 0.1 IU/g in normoxic hearts), endothelial-dependent dilation in response to ADP was impaired while endothelial-independent dilation in response to nitroprusside was unaltered. Myocardial oxidative stress increased significantly, based on decreased glutathione redox status ([GSSG]/[GSG + GSSH] = 7.8 +/- 0.3% vs. 1.3 +/- 0.1% in normoxic hearts). Tissue cholesterol, native cholesteryl esters (CE) and the lipid-soluble antioxidant alpha-tocopherol (alpha-TOH, the most biologically active form of vitamin E) were unaffected by I/R, whereas markers of primary lipid peroxidation (CE-derived lipid hydroperoxides and hydroxides; CE-O(O)H) increased significantly (14 +/- 2 vs. 2 +/- 1 pmol/mg in normoxic hearts). Myocardial alpha -tocopherylquinone (alpha-TQ; an oxidation product of alpha -TOH) also increased (10.3 +/- 1.0 vs. 1.7 +/- 0.2 pmol/mg in normoxic hearts). Adenosine treatment improved functional recovery and vascular function, and limited LDH efflux. These effects were associated with an anti-oxidant effect of adenosine, as judged by inhibition of I/R-mediated changes in glutathione redox status (by 60%), alpha-TQ (80%) and CE-O(O)H (100%). Provision of 10 mM pyruvate as sole substrate (to by-pass glycolysis) modestly reduced I/R injury and changes in glutathione redox status and alpha-TQ, but not CE-O(O)H. Adenosine exerted further protection and anti-oxidant actions in these hearts. Functional recoveries and LDH efflux correlated inversely with oxidative stress and alpha -TQ (but not CE-O(O)H) levels. Collectively, our data reveal selective oxidative events in post-ischemic murine hearts, which are effectively limited by adenosine (independent of substrate). Correlation of post-ischemic cardiovascular outcomes with specific oxidative events (glutathione redox state, alpha-TQ) supports an important anti-oxidant component to adenosinergic protection.

Influence of pulmonary arterial endothelial cells on quinone redox status: effect of hyperoxia-induced NAD(P)H:quinone oxidoreductase 1

The objective of this study was to examine the impact of chronic hyperoxic exposure (95% O2for 48 h) on intact bovine pulmonary arterial endothelial cell redox metabolism of 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ). DQ or durohydroquinone (DQH2) was added to normoxic or hyperoxia-exposed cells in air-saturated medium, and the medium DQ concentrations were measured over 30 min. DQ disappeared from the medium when DQ was added and appeared in the medium when DQH2was added, such that after ∼15 min, a steady-state DQ concentration was approached that was ∼4.5 times lower for the hyperoxia-exposed than the normoxic cells. The rate of DQ-mediated reduction of the cell membrane-impermeant redox indicator, potassium ferricyanide [Fe(CN)[Formula: see text]], was also approximately twofold faster for the hyperoxia-exposed cells. Inhibitor studies and mathematical modeling suggested that in both normoxic and hyperoxia-exposed cells, NAD(P)H:quinone oxidoreductase 1 (NQO1) was the dominant DQ reductase and mitochondrial electron transport complex III the dominant DQH2oxidase involved and that the difference between the net effects of the cells on DQ redox status could be attributed primarily to a twofold increase in the maximum NQO1-mediated DQ reduction rate in the hyperoxia-exposed cells. Accordingly, NQO1 protein and total activity were higher in hyperoxia-exposed than normoxic cell cytosolic fractions. One outcome for hyperoxia-exposed cells was enhanced protection from cell-mediated DQ redox cycling. This study demonstrates that exposure to chronic hyperoxia increases the capacity of pulmonary arterial endothelial cells to reduce DQ to DQH2via a hyperoxia-induced increase in NQO1 protein and total activity.

Inhibition of lipoprotein lipid oxidation

According to the oxidative modification hypothesis, antioxidants that inhibit the oxidation of low-density lipoprotein (LDL) are expected to attenuate atherosclerosis, yet not all antioxidants that inhibit LDL oxidation in vitro inhibit disease in animal models of atherosclerosis. As with animal studies, a benefit with dietary supplements of antioxidants in general and vitamin E in particular was anticipated in humans, yet the overall outcome of large, randomized controlled studies has been disappointing. However, in recent years it has become clear that the role of vitamin E in LDL oxidation and the relationship between in vitro and in vivo inhibition of LDL oxidation are more complex than previously appreciated, and that oxidative events in addition to LDL oxidation in the extracellular space need to be considered in the context of an antioxidant as a therapeutic drug against atherosclerosis. This review focuses on some of these complexities, proposes a novel method to assess in vitro 'oxidizability' of lipoprotein lipids, and summarizes the present situation of development of antioxidant compounds as drugs against atherosclerosis and related cardiovascular disorders.

Molecular Mechanisms of Vitamin E Transport

Vitamin E is the most important lipid-soluble antioxidant in humans. Specific tocopherol-binding proteins favor the retention of the most potent vitamin E homologue, RRR-alpha-tocopherol (RRR-alpha-T) in man. The crystal structures of both the ligand-charged and the apo-forms of human alpha-tocopherol transfer protein (alpha-TTP) and of human supernatant protein factor (SPF) have been solved. The renewed interest in the biological function of tocopherol binders is based on the discovery of ataxia with vitamin E deficiency, a neurological disorder that is caused by genetic defects of the alpha-TTP gene and/or vitamin E deficiency. The analysis of the crystal structure of alpha-TTP provides the molecular basis of vitamin E retention in man. SPF has been reported to enhance cholesterol biosynthesis by facilitating the conversion of squalene to lanosterol. Nevertheless, the physiological role of SPF as well as its ligand specificity is not known. Investigations on the substrate specificity of SPF have uncovered binding of RRR-alpha-tocopherylquinone (RRR-alpha-TQ). RRR-alpha-TQ represents the major physiological oxidation product of RRR-alpha-T. The three-dimensional overlay of the ligand-charged structures of SPF and alpha-TTP indicates that ligand specificity in both proteins is mostly modulated by side-chain variations rather than by the backbone. Recent reports point towards the in vivo reduction of RRR-alpha-TQ to RRR-alpha-TQH(2) and its protective role in low-density lipoprotein oxidation. On the basis of these reports, it is proposed that SPF may enhance cholesterol biosynthesis indirectly by mediating the transfer of RRR-alpha-TQ to low-density lipoprotein, thus reducing oxidation of low-density lipoprotein and its subsequent cellular uptake by scavenger receptors.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Redox-interaction of α-tocopheryl quinone with isolated mitochondrial cytochrome bc1 complex

The homogenous distribution of vitamin E in lipid membranes is a prerequisite for its universal function as lipophilic antioxidant. Its antioxidant activity leads to the irreversible formation of alpha-tocopheryl quinone (TQ) in those membranes. Very little is known about the interference of TQ with redox-cycling enzymes normally interacting with ubiquinone (UQ), which exerts important bioenergetic functions in the mitochondrial respiratory chain. One of the most complex redox reactions of the respiratory chain is the interaction of reduced UQ (UQH(2)) with the cytochrome bc(1) complex (ubiquinol:cytochrome c reductase, EC 1.10.2.2). The aim of this study was to elucidate the influence of TQ on the electron transfer from UQH(2) to cytochrome c via the isolated mitochondrial cytochrome bc(1) complex. Although TQ is present in substoichiometric amounts with respect to UQ in mitochondria and in our experiments with isolated bc(1) complex, we observed a decrease of the total electron transfer rate via the bc(1) complex with increasing amounts of TQ. Both reduced TQ (TQH(2)) and UQH(2) are able to reduce b-cytochromes in the bc(1) complex, however, they act in a completely different way. While reduction of b-cytochromes by UQH(2) can occur both via the Q(o) and the Q(i) pocket of the cytochrome bc(1) complex, TQH(2) can preferably reduce b-cytochromes via the Q(i) pocket. These differences are also reflected by the extremely low turnover numbers of the bc(1) activity for TQ/TQH(2) compared to UQ/UQH(2) suggesting that TQ/TQH(2) acts as a weak competitive inhibitor for binding sites of UQ/UQH(2). In contrast, the oxidation properties of TQ and UQ are similar. Furthermore, oxidized TQ was observed to decrease the O(2)(*)(-) release rate of UQH(2)-consuming cytochrome bc(1) complex. These findings suggest that the irreversible oxidation of vitamin E to TQ in mitochondrial membranes causes a downregulation of respiratory activities as well as a lower O(2)(*)(-) formation rate by the cytochrome bc(1) complex.

Alpha-tocopherol and alpha-tocopheryl quinone levels in cervical intraepithelial neoplasia and cervical cancer

OBJECTIVE

alpha-Tocopherol is a potent antioxidant that protects cell membranes against oxidative damage. Red blood cell alpha-tocopherol levels reflect membrane alpha-tocopherol concentrations, and altered levels may suggest membrane damage. The objective of this study was to determine the levels of alpha-tocopherol and alpha-tocopheryl quinone, the oxidized product of alpha-tocopherol, in plasma and red blood cells that were obtained from control subjects and patients with cervical intraepithelial neoplasia and cervical cancer.

STUDY DESIGN

In this cross-sectional study, 72 women, (32 African American and 40 Hispanic) were recruited. Among these subjects, 37 women had cervical intraepithelial neoplasia; 14 women had cervical cancer, and 21 women were considered control subjects, who had normal Papanicolaou test results. alpha-Tocopherol and alpha-tocopheryl quinone levels were determined in red blood cell and plasma by high-pressure liquid chromatography.

RESULTS

Plasma levels of alpha-tocopherol and alpha-tocopheryl quinone were decreased significantly (P=.012 and=.005, respectively, by Kruskal-Wallis test) in study groups compared with the control group; red blood cell levels of alpha-tocopherol and alpha-tocopheryl quinone were not altered significantly.

CONCLUSION

The lower alpha-tocopherol level that was observed in this study is consistent with our previous reports of decreased antioxidant concentrations and increased oxidative stress in women with cervical intraepithelial neoplasia. Unaltered red blood cell alpha-tocopherol and alpha-tocopheryl quinone levels suggest undamaged cell membrane. Further studies are needed to investigate the potential role of oxidative stress in cervical intraepithelial neoplasia.

Inhibition of peroxynitrite-mediated reactions by vanillin

Several neurodegenerative diseases such as Alzeimer's and Parkinson's as well as septic shock and inflammation involve formation of reactive oxygen and nitrogen species that include peroxynitrite (PON). PON can also react with endogenous antioxidants. Therefore, dietary supplementation with antioxidants may help in these diseases. An exogenous antioxidant, vanillin (4-hydroxy-3-methoxybenzaldehyde), used widely as a food flavoring agent, was evaluated for its ability to scavenge PON and inhibit PON-mediated reactions. Nitration of tyrosine by PON was assessed by high-performance liquid chromatography (HPLC). This reaction was inhibited by vanillin. The oxidation of dihydrorhodamine 123 to fluorescent rhodamine 123 was also inhibited by vanillin. The kinetics of reaction between PON and vanillin was studied by stopped-flow technique. The products of this reaction were analyzed by HPLC, and hydroxyvanillin was identified as one of the five products with absorption at 350 nm. These data demonstrate that vanillin effectively scavenges PON in cell-free systems.

INVITED REVIEW - Ecosystem Consequences of Enhanced Solar Ultraviolet Radiation: Secondary Plant Metabolites as Mediators of Multiple Trophic Interactions in Terrestrial Plant Communities¶

The potential role of ultraviolet-B (UV-B)-induced secondary plant metabolites as mediators of multiple trophic responses in terrestrial ecosystems is considered through review of the major classes of secondary metabolites, the pathways for their biosynthesis, interactions with primary and secondary consumers and known UV effects on their induction. Gross effects of UV-B radiation on plant growth and survival under realistic spectral balances in the field have been generally lacking, but subtle changes in carbon allocation and partitioning induced by UV-B, in particular production of secondary metabolites, can affect ecosystem-level processes. Secondary metabolites are important in plant-herbivore interactions and may affect pathogens. They act as feeding or oviposition deterrents to generalists and nonadapted specialists, but adapted specialists are stimulated to feed by these same compounds, which they detoxify and often sequester for use against their predators. This provides a route for tritrophic effects of enhanced UV-B radiation whereby herbivory may be increased while predation on the herbivore is simultaneously reduced. It is in this context that secondary metabolites may manifest their most important role. They can be the demonstrable mechanism establishing cause and effect at higher trophic levels because the consequences of their induction can be established at all trophic levels.

Supernatant protein factor in complex with RRR-alpha-tocopherylquinone: a link between oxidized Vitamin E and cholesterol biosynthesis

The vast majority of monomeric lipid transport in nature is performed by lipid-specific protein carriers. This class of proteins can enclose cognate lipid molecules in a hydrophobic cavity and transport them across the aqueous environment. Supernatant protein factor (SPF) is an enigmatic representative of monomeric lipid transporters belonging to the SEC14 family. SPF stimulates squalene epoxidation, a downstream step of the cholesterol biosynthetic pathway, by an unknown mechanism. Here, we present the three-dimensional crystal structure of human SPF in complex with RRR-alpha-tocopherylquinone, the major physiological oxidation product of RRR-alpha-tocopherol, at a resolution of 1.95A. The structure of the complex reveals how SPF sequesters RRR-alpha-tocopherylquinone (RRR-alpha-TQ) in its protein body and permits a comparison with the recently solved structure of human alpha-tocopherol transfer protein (alpha-TTP) in complex with RRR-alpha-tocopherol. Recent findings have shown that RRR-alpha-TQ is reduced in vivo to RRR-alpha-TQH(2), the latter has been suggested to protect low-density lipoprotein (LDL) particles from oxidation. Hence, the antioxidant function of the redox couple RRR-alpha-TQ/RRR-alpha-TQH(2) in blocking LDL oxidation may reduce cellular cholesterol uptake and thus explain how SPF upregulates cholesterol synthesis.

Mitotropic compounds for the treatment of age-related macular degeneration. The metabolic approach and a pilot study

Recent histopathologic studies have shown that mitochondria and peroxisomes of the retinal pigment epithelium may play a central role in the pathophysiology of age-related macular degeneration (AMD). We supposed that compounds which improve mitochondrial functions (mitotropic compounds) may show beneficial effects in preventing AMD. Fourteen patients affected by early AMD were treated with a mixture containing acetyl-L-carnitine (ALC), polyunsaturated fatty acids (PUFAs), coenzyme Q10 (CoQ10) and vitamin E, while an equal number of age- and sex-matched patients affected by early AMD were treated with vitamin E only. Recovery time after macular photostress, foveal sensitivity and mean defect in the visual field as well as blood lipid levels were recorded at the beginning and after 3, 6, 9, 12 and 24 months of follow-up. In the treated group, all the visual functions showed slight improvement which was evident after 3 months of treatment and remained nearly stationary by the end of 24 months. The same tests in the control group showed slow worsening. The divergence between treated and control groups became more marked with time, but the difference was not significant at any time of the follow-up. These findings suggest that the blend of ALC, PUFA, CoQ10 and vitamin E may improve retinal functions in early AMD.

The role of vitamin E in atherosclerosis

Epidemiological and biochemical studies infer that oxidative processes, including the oxidation of low-density lipoprotein (LDL), are involved in atherosclerosis. Vitamin E has been the focus of several large supplemental studies of cardiovascular disease, yet its potential to attenuate or even prevent atherosclerosis has not been realised. The scientific rationale for vitamin E supplements protecting against atherosclerosis is based primarily on the oxidation theory of atherosclerosis, the assumption that vitamin E becomes depleted as disease progresses, and the expectation that vitamin E prevents the oxidation of LDL in vivo and atherogenic events linked to such oxidation. However, it is increasingly clear that the balance between vitamin E and other antioxidants may be crucial for in vivo antioxidant protection, that vitamin E is only minimally oxidised and not deficient in atherosclerotic lesions, and that vitamin E is not effective against two-electron oxidants that are increasingly implicated in both early and later stages of the disease. It also remains unclear as to whether oxidation plays a bystander or a casual role in atherosclerosis. This lack of knowledge may explain the ambivalence of vitamin E and other antioxidant supplementation in atherosclerosis.

Gamma-tocopheryl quinone stimulates apoptosis in drug-sensitive and multidrug-resistant cancer cells

Chemotherapy-induced cell death is linked to apoptosis, and there is increasing evidence that multidrug-resistance in cancer cells may be the result of a decrease in the ability of a cell to initiate apoptosis in response to cytotoxic agents. In previous studies, we synthesized two classes of electrophilic tocopheryl quinones (TQ), nonarylating alpha-TQ and arylating gamma- and delta-TQ, and found that gamma- and delta-TQ, but not alpha-TQ, were highly cytotoxic in human acute lymphoblastic leukemia cells (CEM) and multidrug-resistant (MDR) CEM/VLB100. We have now extended these studies on tumor biology with CEM, HL60 and MDR HL60/MX2 human promyelocytic leukemia, U937 human monocytic leukemia, and ZR-75-1 breast adenocarcinoma cells. gamma-TQ, but not alpha-TQ or tocopherols, showed concentration and incubation time-dependent effects on loss of plasma membrane integrity, diminished viable cell number, and stimulation of apoptosis. Its cytotoxicity exceeded that of doxorubicin in HL60/MX2 cells, which express MRP, an MDR-associated protein. Apoptosis was confirmed by TEM, TUNEL, and DNA gel electrophoresis. Kinetic studies showed that an induction period was required to initiate an irreversible multiphase process. Gamma-TQ released mitochondrial cytochrome c to the cytosol, induced the cleavage of poly(ADP-ribose)polymerase, and depleted intracellular glutathione. Unlike xenobiotic electrophiles, gamma-TQ is a highly cytotoxic arylating electrophile that stimulates apoptosis in several cancer cell lines including cells that express MDR through both P-glycoprotein and MRP-associated proteins. The biological properties of arylating TQ electrophiles are closely associated with cytotoxicity and may contribute to other biological effects of these highly active agents.

Coenzyme Q blocks biochemical but not receptor-mediated apoptosis by increasing mitochondrial antioxidant protection

Generation of free radicals is often associated with the induction and progression of apoptosis. Therefore, antioxidants can prove anti-apoptotic, and can help to elucidate specific apoptotic pathways. Here we studied whether coenzyme Q, present in membranes in reduced (ubiquinol) or oxidised (ubiquinone) forms, can affect apoptosis induced by various stimuli. Exposure of Jurkat cells to alpha-tocopheryl succinate (alpha-TOS), hydrogen peroxide, anti-Fas IgM or TRAIL led to induction of apoptosis. Cell death due to the chemical agents was suppressed in cells enriched with the reduced form of coenzyme Q. However, coenzyme Q did not block cell death induced by the immunological agents. Ubiquinol-10 inhibited reactive oxygen species (ROS) generation in cells exposed to alpha-TOS, and a mitochondrially targeted coenzyme Q analogue also blocked apoptosis triggered by alpha-TOS or hydrogen peroxide. Therefore, it is plausible that ubiquinol-10 protects cells from chemically-induced apoptosis by acting as an antioxidant in mitochondria. Our results also indicate that generation of free radicals may not be a critical step in induction of apoptosis by immunological agents.

The role of vitamin E in atherogenesis: linking the chemical, biological and clinical aspects of the disease

Atherosclerosis is a disease involving both oxidative modifications and disbalance of the immune system. Vitamin E, an endogenous redox-active component of circulating lipoproteins and (sub)cellular membranes whose levels can be manipulated by supplementation, has been shown to play a role in the initiation and progression of the disease. Recent data reveal that the activities of vitamin E go beyond its redox function. Moreover, it has been shown that vitamin E can exacerbate certain processes associated with atherogenesis. In this essay we review the role of biology of atherosclerosis, and suggest that these two facets decide the clinical manifestation and outcome of the disease.