A new vitamin E analogue more active than alpha-tocopherol in the rat curative myopathy bioassay

Design of the Functional Dialysis Membrane with a Catalase Pseudoactive Center on the Surface

Here, we have designed a functional dialysis membrane with a catalase pseudoactive center on the surface. To make the catalase pseudoactive center, we have modified the regenerated cellulose dialysis membrane with methylated or octylated poly(1-vinylimidazole) (PVIm-Me or PVIm-Oc), followed by manganese or iron tetrakis(4-carboxyphenyl)porphyrin (Mn- or Fe-TCPP), using the layer-by-layer (LbL) method. As a result of the optimization, the dialysis membrane modified with 25 mol % methylated poly(1-vinylimidazole) [PVIm-Me(25)] and Mn-TCPP produced the highest amount of oxygen (O2) from hydrogen peroxide (H2O2) without the decomposition of Mn-TCPP. Conversely, Mn- and Fe-TCPP were decomposed under other experimental conditions in the presence of H2O2. These results suggest the conversion of H2O2 to O2 by catalase catalytic activity on the surface coated with PVIm-Me(25) and Mn-TCPP.

A Review on Vitamin E Natural Analogues and on the Design of Synthetic Vitamin E Derivatives as Cytoprotective Agents

Vitamin E, essential for human health, is widely used worldwide for therapeutic or dietary reasons. The differences in the metabolism and excretion of the multiple vitamin E forms are presented in this review. The important steps that influence the kinetics of each form and the distribution and processing of vitamin E forms by the liver are considered. The antioxidant as well as non-antioxidant properties of vitamin E forms are discussed. Finally, synthetic tocopherol and trolox derivatives, based on the design of multitarget directed compounds, are reviewed. It is demonstrated that selected derivatization of vitamin E or trolox structures can produce improved antioxidants, agents against cancer, cardiovascular and neurodegenerative disorders.

Synthesis, DFT Calculations, and In Vitro Antioxidant Study on Novel Carba-Analogs of Vitamin E

Vitamin E is the most active natural lipophilic antioxidant with a broad spectrum of biological activity. α-Tocopherol (α-T), the main representative of the vitamin E family, is a strong inhibitor of lipid peroxidation as a chain-breaking antioxidant. Antioxidant and antiradical properties of vitamin E result from the presence of a phenolic hydroxyl group at the C-6 position. Due to stereoelectronic effects in the dihydropyranyl ring, the dissociation enthalpy for phenolic O–H bond (BDE_OH) is reduced. The high chain-breaking reactivity of α-T is mainly attributed to orbital overlapping of the 2p-type lone pair on the oxygen atom (O1) in para position to the phenolic group, and the aromatic π-electron system. The influence of the O1 atom on the antioxidant activity of vitamin E was estimated quantitatively. The all-rac-1-carba-α-tocopherol was synthesized for the first time. Along with model compounds, 1-carba-analog of Trolox and its methyl ester were screened for their in vitro antioxidant activity by inhibition of styrene oxidation, and for the radical-reducing properties by means of 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH) scavenging assay. To study the antioxidant activity, density functional theory (DFT) was also applied. Reaction enthalpies related to HAT (hydrogen atom transfer), SET–PT (sequential electron transfer—proton transfer), and SPLET (sequential proton loss—electron transfer) mechanisms were calculated.

A review on antioxidant potential of bioactive heterocycle benzofuran: Natural and synthetic derivatives

The majority of heterocycle compounds and typically common heterocycle fragments present in most pharmaceuticals currently marketed, alongside with their intrinsic versatility and unique physicochemical properties, have poised them as true cornerstones of medicinal chemistry. In this context, oxygen heterocycles exhibit diverse biological and pharmacological activities due in part to the similarities with many natural and synthetic molecules with known biological activity. Among oxygen containing heterocycles, benzofuran (synthetic and natural isolated) and its derivatives have attracted medicinal chemists and pharmacologists due to their pronounced biological activities and their potential applications as pharmacological agents such as antioxidant, antitumor, antiplatelet, antimalarial, antiinflammatory, antidepressant and anticonvulsant properties. There are also an amazing number of approved benzofuran-containing drugs in the market as well as compounds currently going through different clinical phases or registration statuses. Due to the wide range of biological activities of benzofurans, their structure activity relationships have generated interest among medicinal chemists, and this has culminated in the discovery of several lead molecules in numerous disease conditions. Recently, this scaffold has emerged as a pharmacophore of choice for designing antioxidant drug development as their derivatives have shown excellent results through different mechanism of action. This review focused on the recent development of benzofuran derivatives as antioxidant agents (including natural products) and their antioxidant activities; summarize the structure property, hoping to inspire new and even more creative approaches. Also, this study systematically provides a comprehensive report on current developments in benzofuran-based compounds as antioxidant agents and is also helpful for the researchers working on a substitution pattern around the nucleus, with an aim to help medicinal chemists to develop structure activity relationships (SAR) on these derivatives as antioxidant drugs.

In vitro antioxidant activity of tocopherols and tocotrienols and comparison of vitamin E concentration and lipophilic antioxidant capacity in human plasma

A comparative study investigated four tocopherols, four tocotrienols, and alpha-tocopheryl acetate on their antioxidative activities in five different popular assays, which were adapted to non-polar antioxidants. alpha-Tocopherol, used as calibration standard, showed the highest ferric reducing antioxidant power. Greater ring methyl substitution not only led to an increase of scavenging activity against the stable 2,2-diphenyl-1-picrylhydrazyl radical, but also to a decrease in oxygen radical absorbance capacity. Regarding alpha-tocopherol equivalent antioxidant capacity no significant differences in the antioxidant activity of all vitamin E isoforms were found. In contrast, a significantly lower peroxyl radical-scavenging activity of alpha-tocochromanols was determined in a chemiluminescence assay. Except oxygen radical absorbance capacity, no significant differences of the antioxidant activity related to the side chain could be detected. The data show that the reducing ability and radical chain-breaking activity of the several vitamin E forms depends on the circumstances under which the assays are performed. In our opinion, the used lipophilic methods can be useful for estimating the antioxidant activity of strong non-polar antioxidants, e.g. carotenoids, too. Furthermore, we could show a significant correlation between the total tocopherol content in human plasma and the lipophilic antioxidant capacity measured by alpha-tocopherol equivalent antioxidant capacity and 2,2-diphenyl-1-picrylhydrazyl.

Design, synthesis, and action of antiatherogenic antioxidants

Ample evidence supports the critical role of oxidized low-density lipoprotein (ox-LDL) in initiation and progression of atherosclerosis. Oxidation of LDL is a complex process involving several steps (processes) of reactions such as initiation and propagation. Both proteins and lipids in LDL undergo free radical-mediated oxidations leading to the formation of ox-LDL that plays a pivotal role in atherosclerosis. Antioxidants of various types (both aqueous and lipophilic) either arrest or retard the oxidation of LDL at various steps of the oxidation process (e.g., initiation or propagation). Certain lipophilic antioxidants act as the chain-terminating antioxidants leading to the inhibition of LDL oxidation. The current chapter describes the designing and efficacy of two novel lipophilic antioxidants (benzofuranol, BO-653 and aniline, BO-313) in inhibiting the LDL oxidation and atherogenesis in experimental animal model. Furthermore, the characteristics of an effective antioxidant to inhibit LDL oxidation and atherogenesis which dictates the designing of the antioxidant drug and its mechanism(s) of antiatherogenic action are discussed.

α‐Tocopherol: A Multifaceted Molecule in Plants

alpha-Tocopherol, which belongs to the vitamin E group of compounds, is a lipophilic antioxidant that has a number of functions in plants. Synthesized from homogentisic acid and isopentenyl diphosphate in the chloroplast envelope, alpha-tocopherol is essential to maintain the integrity of photosynthetic membranes and plays a major role in photo- and antioxidant protection. alpha-Tocopherol scavenges lipid peroxy radicals, thereby preventing the propagation of lipid peroxidation, and protects lipids and other membrane components by physically quenching and reacting chemically with singlet oxygen. Moreover, given that alpha-tocopherol increases membrane rigidity, its concentration, together with that of the other membrane components, may be regulated to afford adequate fluidity for membrane function. Furthermore, recent studies on tocopherol-deficient plants indicate that alpha-tocopherol may affect cellular signaling in plants. Evidence thus far indicates that the effects of this compound in plant cellular signaling may be linked to the control of redox homeostasis. alpha-Tocopherol may influence cellular signaling by controlling the propagation of lipid peroxidation in chloroplasts, therefore modulating the formation of oxylipins such as the phytohormone jasmonic acid.

Effect of Temperature, Cholesterol Content, and Antioxidant Structure on the Mobility of Vitamin E Constituents in Biomembrane Models Studied by Laterally Diffusion-Controlled Fluorescence Quenching

Kinetic parameters relevant for the antioxidant activity of the vitamin E constituents (alpha, beta, gamma, and delta homologues of tocopherols and tocotrienols) and of an amphiphilic vitamin C derivative, l-ascorbyl 6-palmitate, were determined. Fluorescence quenching experiments of 2,3-diazabicyclo[2.2.2]oct-2-ene in homogeneous acetonitrile-water mixtures afforded reactivity trends in terms of intermolecular quenching rate constants, while the quenching of Fluorazophore-L in liposomes provided the lateral diffusion coefficients relevant for understanding their biological activity in membranes. The reactivity in homogeneous solution was not influenced by the nature of the isoprenoid tail (tocopherol versus tocotrienol), but was dependent on the methylation pattern. The resulting order (alpha > beta = gamma > delta) was found to be in line with their reactivities toward peroxyl radicals as well as the phenolic O-H bond dissociation energies. The mutual lateral diffusion coefficient in POPC liposomes was the same, within error, for different tocopherols and tocotrienols (D(L) = (1.6 +/- 0.2) x 10(-7) cm(2) s(-1)). l-Ascorbyl 6-palmitate exhibited a reactivity similar to that of delta-tocopherol in homogeneous solution, but displayed a 1 order of magnitude lower fluorescence quenching efficiency in liposomes than the vitamin E constituents. Temperature effects on the laterally diffusion-controlled fluorescence quenching were large, with activation energies of 44 +/- 6 kJ mol(-1). The addition of cholesterol (0-30%) to POPC liposomes resulted only in slightly reduced diffusion coefficients. The combined results demonstrate that Fluorazophore-L can provide important physicochemical parameters for the understanding of antioxidant activity in biological environments.

Design and synthesis of 4,6-di-tert-butyl-2,3-dihydro-5-benzofuranols as a novel series of antiatherogenic antioxidants

Antioxidants have been considered as potential antiatherogenic agents by inhibiting oxidation of low-density lipoprotein (LDL), albeit vitamin E, a natural antioxidant, has failed to show reduction on atherosclerosis in clinical trials. We have rationally designed and synthesized a novel series of antioxidants, 4,6-di-tert-butyl-2,3-dihydro-5-benzofuranols, to overcome the clinical limitation of vitamin E. In vitro, the compounds showed a potent inhibitory effect on lipid peroxidation detected as 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (MCLA)-dependent chemiluminescence in linoleic acid autoxidation. They also inhibited the LDL oxidation induced by Cu(2+), and the inhibition is more potent than that of vitamin E and probucol. In vivo, 4,6-di-tert-butyl-2,3-dihydro-2,2-dipentyl-5-benzofuranol (BO-653, 1f), an optimal compound, showed the highest concentration in plasma and LDL fraction in Watanabe heritable hyperlipidemic rabbits, due to its high affinity to LDL. The isolated LDL samples from the 1f-treated rabbits showed potent resistibility to LDL oxidation. Compound 1f has been taken into clinical trials.

Hydrogen bonding between phenols and fatty acid esters: (1)H NMR study and ab initio calculations

[structure: see text] (1)H NMR measurements and ab initio calculations were used to study the interactions between hindered/nonhindered phenols and carboxylic acid esters. The dihedral angle (phi) between the OH group and a plane of the aromatic ring is close to 0 degrees in the hydrogen-bonded nonhindered phenols, whereas for 2,6-di-tert-butyl-4-methylphenol the OH group is completely twisted out of the aromatic plane (phi approximately 90 degrees ).

Protection of low density lipoprotein oxidation by the antioxidant agent IRFI005, a new synthetic hydrophilic vitamin E analogue

The oxidative modification of low density lipoprotein (LDL) is thought to be an important factor in the initiation and development of atherosclerosis. Antioxidants have been shown to protect LDL from oxidation and to inhibit atherosclerosis development in animals. Potent synthetic antioxidants are currently being tested, but they are not necessarily safe for human use. We here characterize the antioxidant activity of IRFI005, the active metabolite of Raxofelast (IRFI0016) that is a novel synthetic analog of vitamin E under clinical development, and demonstrate that it prevents oxidative modification of LDL. IFI005 inhibited the oxidative modification of LDL, measured through the generation of MDA, electrophoretic mobility and apo B100 fluorescence. During the oxidation process IRF1005 was consumed with the formation of the benzoquinone oxidation product. The powerful antioxidant activity of IRFI005 is at least in part mediated by a chain breaking mechanism as it is an efficient peroxyl radical scavenger with a rate constant k(IRFI005 + LOO(o)) of 1.8 X 10(6) M(-1)s(-1). 4. IRFI005 substantially preserved LDL-associated antioxidants, alpha-tocopherol and carotenoids, and when co-incubated with physiologic levels of ascorbate provoked a synergistic inhibition of LDL oxidation. Also the co-incubation of IRFI005 with Trolox caused a synergistic effect, and a lag phase in the formation of the trolox-benzoquinone oxidation product. A synergistic inhibition of lipid peroxidation was also demonstrated by co-incubating IRFI005 and alpha-tocopherol incorporated in linoleic acid micelles. These data strongly suggest that IRFI005 can operate by a recycling mechanism similar to the vitamin E/ascorbate sysem.

Antiatherogenic effects of the antioxidant BO-653 in three different animal models

Antioxidants have been proposed to have antiatherogenic potential by their inhibition of low density lipoprotein (LDL) oxidation. Here, we report an antioxidant, BO-653 (2,3-dihydro-5-hydroxy-2, 2-dipentyl-4,6-di-tert-butylbenzofuran), designed to exhibit antioxidative potency comparable to that of alpha-tocopherol, but yet possess a high degree of lipophilicity comparable to that of probucol. BO-653 exhibits a high affinity for LDL and is well distributed in aortic vessels in vivo. In atherosclerosis models of rabbits and mice, BO-653 has been shown to be able to suppress the formation of atherosclerotic lesions without untoward side effects. Specifically, there was no reduction of high density lipoprotein levels. This antioxidant provides additional evidence in support of the oxidized-LDL hypothesis, and itself is a promising candidate antioxidant for clinical use.

5-aminocoumarans: dual inhibitors of lipid peroxidation and dopamine release with protective effects against central nervous system trauma and ischemia

A series of 2,3-dihydro-5-benzofuranamines (5-aminocoumarans) were developed for the treatment of traumatic and ischemic central nervous system (CNS) injury. Compounds within this class were extremely effective inhibitors of lipid peroxidation in vitro and antagonized excitatory behavior coupled with peroxidative injury induced by spinal intrathecal injection of FeCl2 (mouse-FeCl2-it assay) in vivo. Selected compounds were tested for antagonistic activity on methamphetamine (MAP)-induced hypermotility resulting from dopamine release in the mouse brain. Among the compounds synthesized, compound 26n (2,3-dihydro-2,4,6,7-tetramethyl-2-[(4-phenyl-1-piperidinyl) methyl]-5-benzofuranamine) exhibited potent effects in these assays (inhibition of lipid peroxidation, IC50 = 0.07 microM; mouse-FeCl2-it assay, ID50 = 10.4 mg/ kg, po; MAP-induced hypermotility, 98% inhibition, 10 mg/kg, ip). The S-(+)-form of compound 26n dihydrochloride (TAK-218), which has 30 times more potent antagonistic activity on MAP-induced hypermotility than the R-(-)-form, improved more significantly the survival rate in the cerebral ischemia model (rat, 1-3 mg/kg, ip) during the period of 1-14 days after ischemia and decreased functional disorders in the traumatic brain injury model (rat, 0.1-1 mg/kg, ip) 3-14 days after injury. These results imply a role for dopamine in deterioration of CNS function after ischemic and traumatic injury. TAK-218 is a promising compound for the treatment of stroke and CNS trauma and is now under clinical investigation.

The chemistry and antioxidant properties of tocopherols and tocotrienols

This article is a review of the fundamental chemistry of the tocopherols and tocotrienols relevant to their antioxidant action. Despite the general agreement that alpha-tocopherol is the most efficient antioxidant and vitamin E homologue in vivo, there was always a considerable discrepancy in its "absolute" and "relative" antioxidant effectiveness in vitro, especially when compared to gamma-tocopherol. Many chemical, physical, biochemical, physicochemical, and other factors seem responsible for the observed discrepancy between the relative antioxidant potencies of the tocopherols in vivo and in vitro. This paper aims at highlighting some possible reasons for the observed differences between the tocopherols (alpha-, beta-, gamma-, and delta-) in relation to their interactions with the important chemical species involved in lipid peroxidation, specifically trace metal ions, singlet oxygen, nitrogen oxides, and antioxidant synergists. Although literature reports related to the chemistry of the tocotrienols are quite meager, they also were included in the discussion in virtue of their structural and functional resemblance to the tocopherols.

Efficacy of lipid soluble, membrane-protective agents against hydrogen peroxide cytotoxicity in cardiac myocytes

We examined the efficacy of a group of drugs that stabilize the cell membrane and can potentially prevent cytotoxicity in cultured fetal chick cardiac myocytes exposed to hydrogen peroxide (H2O2). The effects of various membrane-protective agents were determined by analysis of the kinetics of lactic dehydrogenase (LDH) release. The kinetic parameters calculated from the data include a rate constant for release of LDH (kb) and the fraction of total LDH that is released from the cells (CIIMax). The CIIMaxs derived from a range of H2O2 concentrations reveal that the mean toxic concentration of H2O2 is 1.1 mM and that the pattern of toxicity is consistent with the damage being directly proportional to the concentration of the free radicals generated from the H2O2. Maximum nontoxic concentrations of three amphiphilic membrane protective agents had no effect upon cytotoxicity from H2O2. The slightly polar lipophilic agent, Trolox C, a vitamin E derivative, was also without protective effect at a maximum nontoxic concentration. The highly lipophilic agent, probucol, had a small protective effect at 50 microM, the maximum concentration we succeeded in solubilizing in the culture medium. However, the lipophilic 21-aminosteroid U74500, delivered to the cells in an emulsion, markedly reduced cytotoxicity from H2O2. The CII Max was significantly reduced and the protection was concentration dependent over a range of concentrations from 50-400 nmol/ml. Furthermore, the inhibition by U74500 was fully consistent with a mechanism of scavenging of free radicals formed during lipid peroxidation. In support of this hypothesis, a dose of 400 nmoles/ml completely prevented an increase in lipid peroxides due to H2O2 exposure, whereas there was a sixfold increase during exposure to H2O2 in untreated myocytes. Thus, a lipid soluble 21-aminosteroid prevented lipid peroxidation and reduced cardiac myocyte injury during exposure to H2O2, probably by scavenging of free radicals formed during lipid peroxidation in the cell membrane, whereas amphiphilic agents, which probably altered the physicochemical structure of the cell membrane but did not scavenge free radicals, were not protective.

Comparative QSAR: radical toxicity and scavenging. Two different sides of the same coin

From an analysis of the toxicity of phenols to rat embryos and anilines to embryo fibroblast cells a new type of toxicity is postulated for these classes of compounds. Substituents which increase the electron density on the aromatic ring as estimated by sigma + or epsilon HOMO increase potency. It is postulated that it is the radical form of the phenols and the anilines that accounts for their toxicity. The results are compared with QSAR for radical scavengers and oxidoreductases acting on phenols, anilines and carbazoles.

Inhibition of free radical generation by biotin

To assess the inhibitory effect of biotin on free radical generation, we used a spectrophotometric assay of cytochrome c reduction and determined the 2-methyl-6-phenyl-3,7-dihydroimidazo[1,3-a]-pyrazin-3-one (CLA)-dependent chemiluminescence response of human neutrophils or a hypoxanthine-xanthine oxidase (XOD) system. In the spectrophotometric assay of cytochrome c reduction, superoxide (O2-) generation by neutrophils stimulated with N-formyl-methionyl-leucyl-phenylalanine (f-MLP) was reduced significantly when biotin was added. In the CLA-dependent chemiluminescence test of neutrophils stimulated by f-MLP, biotin significantly reduced the generation of free radical species, including O2-, in a concentration-dependent manner, the concentration corresponding to 50% inhibition (IC50) of biotin for free radical generation was 1.12 x 10(-7) mol. However, biotin did not exert an inhibitory effect on oxidative metabolism by directly scavenging superoxide anion, as shown by the study using the hypoxanthine-XOD system.

Molecular pharmacology of vitamin E: structural aspects of antioxidant activity

In this review, the involvement of vitamin E in free radical physiology and antioxidant mechanisms is discussed. Moreover, structure-activity relationship (SAR) studies on vitamin E analogues are presented. A molecular explanation for the antioxidant activity often is based on molecular parameters, such as Hammett sigma and Brown sigma +. These parameters correlate with the activity. Using semiempirical calculations, we have found other molecular parameters related to electron distribution and structure (such as the difference in heat of formation between the compound and its radical or the energy of the highest occupied molecular orbital, HOMO) which correlate with the antioxidant action of vitamin E and its derivatives.

The effect of vitamin E analogues and long hydrocarbon chain compounds on calcium-induced muscle damage. A novel role for alpha-tocopherol?

Previous studies have demonstrated that supplemental alpha-tocopherol inhibited calcium-induced cytosolic enzyme efflux from normal rat skeletal muscles incubated in vitro and suggested that the protective action was mediated by the phytyl chain of alpha-tocopherol [1]. In order to investigate this further a number of hydrocarbon chain analogues of tocopherol (7,8-dimethyl tocol, 5,7-dimethyl tocol, tocol, alpha-tocotrienol, alpha-tocopherol [10], vitamin K1, vitamin K1 [10], vitamin K1 diacetate, vitamin K2 [20], phytyl ubiquinone and retinol) were tested for any ability to inhibit calcium ionophore, A23187, induced creatine kinase (CK) enzyme efflux. Some compounds were found to be very effective inhibitors and comparison of their structures and ability to inhibit TBARS production in muscle homogenates revealed that the effects did not appear related to antioxidant capacity or chromanol methyl groups, but rather the length and structure of the hydrocarbon chain was the important mediator of the effects seen.

Drug antioxidant effects. A basis for drug selection?

A free radical is any species capable of independent existence that contains one or more unpaired electrons. Free radical reactions have been implicated in the pathology of more than 50 human diseases. Radicals and other reactive oxygen species are formed constantly in the human body, both by deliberate synthesis (e.g. by activated phagocytes) and by chemical side-reactions. They are removed by enzymic and nonenzymic antioxidant defence systems. Oxidative stress, occurring when antioxidant defences are inadequate, can damage lipids, proteins, carbohydrates and DNA. A few clinical conditions are caused by oxidative stress, but more often the stress results from the disease. Sometimes it then makes a significant contribution to the disease pathology, and sometimes it does not. Several antioxidants are available for therapeutic use. They include molecules naturally present in the body [superoxide dismutase (SOD), alpha-tocopherol, glutathione and its precursors, ascorbic acid, adenosine, lactoferrin and carotenoids] as well as synthetic antioxidants [such as thiols, ebselen (PZ51), xanthine oxidase inhibitors, inhibitors of phagocyte function, iron ion chelators and probucol]. The therapeutic efficacy of SOD, alpha-tocopherol and ascorbic acid in the treatment of human disease is generally unimpressive to date although dietary deficiencies of the last two molecules should certainly be avoided. Xanthine oxidase inhibitors may be of limited relevance as antioxidants for human use. Exciting preliminary results with probucol (antiatherosclerosis), ebselen (anti-inflammatory), and iron ion chelators (in thalassaemia, leukaemia, malaria, stroke, traumatic brain injury and haemorrhagic shock) need to be confirmed by controlled clinical trials. Clinical testing of N-acetylcysteine in HIV-1-positive subjects may also be merited. A few drugs already in clinical use may have some antioxidant properties, but this ability is not widespread and drug-derived radicals may occasionally cause significant damage.

Reactive oxygen species in living systems: source, biochemistry, and role in human disease

Reactive oxygen species are constantly formed in the human body and removed by antioxidant defenses. An antioxidant is a substance that, when present at low concentrations compared to that of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Antioxidants can act by scavenging biologically important reactive oxygen species (O2-., H2O2.OH, HOCl, ferryl, peroxyl, and alkyl), by preventing their formation, or by repairing the damage that they do. One problem with scavenging-type antioxidants is that secondary radicals derived from them can often themselves do biologic damage. These various principles will be illustrated by considering several thiol compounds.

Novel 6-hydroxychroman-2-carbonitrile inhibitors of membrane peroxidative injury

Novel 6-hydroxychroman-2-carbonitrile compounds have been synthesized, and their antiperoxidant activity against superoxide-dependent, iron-promoted mycocardial phospholipid peroxidation has been evaluated quantitatively. With few exceptions, these compounds afforded significant, concentration-dependent antiperoxidant protection to myocardial-membrane phospholipid at sub- to low-micromolar concentrations. Structure-activity correlation demonstrated that R1-, R2-, and R3-methyl groups in the aromatic ring enhanced antiperoxidant activity, whereas hydrophobic groups at either R4 or R5 of the pyran ring compromised antiperoxidant efficacy. The most efficacious antiperoxidant synthesized contained a catechol moiety at R4 and was some 10-fold more potent than alpha-tocopherol. None of the 6-hydroxychroman-2-carbonitrile antiperoxidants scavenged superoxide or inhibited the enzymatic superoxide generator, xanthine oxidase, at effective antiperoxidant concentrations. The ability of these compounds to interrupt the propagatory phase of an on-going peroxidation reaction indicated that they acted as antiperoxidants by trapping chain-carrying lipid peroxyl radicals. Since a number of the 6-hydroxychroman-2-carbonitriles were most potent antiperoxidants than a variety of known chain-breaking compounds, this new class of phenolic antioxidants may represent a novel approach to the design of therapeutics against diseases in which lipid peroxidation is a causative factor or in which lipid peroxidases serve as mediators.

Further studies of a new vitamin E analogue more active than alpha-tocopherol in the rat curative myopathy bioassay

The bioactivities of the acetates of 2R,4'R,8'R- and 2S,4'R,8'R-2,4,6,7-tetramethyl-2-(4',8',12'-trimethyltridecyl)-5-h ydroxy-3,4- dihydrobenzofuran (RRR- and SRR-1-Ac) have been measured in the rat curative myopathy bioassay and compared with the RRR and SRR stereoisomers of alpha-tocopheryl acetate (RRR- and SRR-2-Ac). Each stereoisomer of 1 is only slightly more active than the corresponding stereoisomer of 2(RRR-1-Ac/RRR-2-Ac = 1.10; SRR-1-Ac/SRR-2-Ac = 1.16). This finding contrasts with our earlier finding [(1986) FEBS Lett. 205, 117-120], confirmed in the present study, that all-rac-1-Ac is 1.5-1.9 as active as all-rac-2-Ac. We suggest that the stereochemistry (S vs R) at the 4' and 8' tail carbons is of less biological importance in 1 than in 2.

Is methyl-branching in alpha-tocopherol's "tail" important for its in vivo activity? Rat curative myopathy bioassay measurements of the vitamin E activity of three 2RS-n-alkyl-2,5,7,8-tetramethyl-6-hydroxychromans

The vitamin E activity of the acetates of three 2RS-n-alkyl-2,5,7,8-tetramethyl-6-hydroxychroman analogs of alpha-tocopherol have been measured and compared directly with all-rac-alpha-tocopheryl acetate, or indirectly via 2R,4'R,8'R-alpha-tocopheryl acetate, using the rat curative myopathy, plasma pyruvate kinase assay. The analogs with alkyl chain lengths of 11 and 13 carbons have activities which not only do not differ significantly (p greater than 0.05) from each other but also do not differ from that of all-rac-alpha-tocopheryl acetate. This finding indicates that methyl branching in the phytyl tail at the 4', 8', and 12' positions has little if any influence upon vitamin E activity. Thus physical interactions involving the methyl branches of the phytyl tail and the polyunsaturated moieties of membrane phospholipids are unimportant in vivo, insofar as this bioassay is concerned. However, the length of the hydrocarbon tail is important. This is indicated by the result obtained with the acetate of the analog with an alkyl chain length of 15 carbon atoms which had only 15% of the activity of 2R,4'R,8'R-alpha-tocopheryl acetate, i.e., 22% of the activity of all-rac-alpha-tocopheryl acetate since this form is 1.47 times less active than 2R,4'R,8'R-alpha-tocopheryl acetate in the curative myopathy bioassay (Weiser, Vecchi, & Schlachter, Internat. J. Vit. Nutr. Res. 55:149-158, 1985).

Vitamin E activity of 1-thio-alpha-tocopherol as measured by the rat curative myopathy bioassay

The bioactivity of the acetate of the all-racemic, 1-thio analog of alpha-tocopherol (all-rac-1-thio-alpha-tocopheryl acetate) has been determined by measuring its ability to decrease plasma levels of pyruvate kinase in vitamin E deficient rats using the curative myopathy bioassay. The thio analog is only 0.22 times as active as RRR-alpha-tocopheryl acetate and is therefore approximately 0.33 times as active as all-rac-alpha-tocopheryl acetate, since the latter has been shown to be 1.47 times less active than RRR-alpha-tocopheryl acetate in the same bioassay (H. Weiser, M. Vecchi and M. Schlachter, Internat. J. Vit. Nutr. Res., 55, 149-158 (1985)). The 0.33:1.0 ratio is similar to the ratio of 0.41:1.0 measured for the in vitro antioxidant activities of the corresponding free phenols. This finding lends further support to our view that the vitamin E activity in the curative myopathy bioassay of close structural analogs of alpha-tocopherol is determined primarily by the in vitro antioxidant activity of the analog relative to alpha-tocopherol, consistent with the belief that vitamin E functions primarily as a general purpose, lipid-soluble antioxidant in mammals.

Vitamin E as an in vitro and in vivo antioxidant

alpha-Tocopherol has near optimal activity as a chain-breaking antioxidant. Inherent antioxidant activity plays an important part in determining overall biological activity but the phytyl tail also exerts a very important influence. The new deuterated alpha-tocopherol/GC-MS technique is providing unprecedented insight into the importance of the stereochemistry of the phytyl tail in determining bioavailability, as well as helping to discover how rapidly and effectively absorption, transport, uptake, and loss occur. Measurements of rate of turnover in tissues indicate that differences exist between different types of animals. It is possible that these tissue differences may explain the diverse range of vitamin E deficiency symptoms observed across a wide variety of animals. It is not known what is responsible for the differences in biokinetic behavior.

Antioxidants in relation to lipid peroxidation

The role of antioxidants in lipid peroxidation is reviewed. Specifically, the rate and mechanism of inhibition of lipid peroxidation by water-soluble and lipid-soluble, chain-breaking antioxidants have been discussed.

Free radicals in iron-containing systems

All oxidative damage in biological systems arises ultimately from molecular oxygen. Molecular oxygen can scavenge carbon-centered free radicals to form organic peroxyl radicals and hence organic hydroperoxides. Molecular oxygen can also be reduced in two one-electron steps to hydrogen peroxide in which case superoxide anion is an intermediate; or it can be reduced enzymatically so that no superoxide is released. Organic hydroperoxides or hydrogen peroxide can diffuse through membranes whereas hydroxyl radicals or superoxide anion cannot. Chain reactions, initiated by chelated iron and peroxides, can cause tremendous damage. Chain carriers are chelated ferrous ion; hydroxyl radical .OH, or alkoxyl radical .OR, and superoxide anion O2-. or organic peroxyl radical RO2.. Of these free radicals .OH and RO2. appear to be most harmful. All of the biological molecules containing iron are potential donors of iron as a chain initiator and propagator. An attacking role for superoxide dismutase is proposed in the phagocytic process in which it may serve as an intermediate enzyme between NADPH oxidase and myeloperoxidase. The sequence of reactants is O2----O2-.----H2O2----HOCl.