| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 04.04.00 |
| PATENT TITLE |
Synthetic catalytic free radical scavengers useful as antioxidants for prevention and therapy of disease |
| PATENT ABSTRACT |
The invention provides antioxidant salen-metal complexes, compositions of such antioxidant salen-metal complexes having superoxide activity, catalase activity, and/or peroxidase activity, compositions of salen-metal complexes in a form suitable for pharmaceutical administration to treat or prevent a disease associated with cell or tissue damage produced by free radicals such as superoxide, and cosmetic and free radical quenching formulations of salen metal compounds. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | March 11, 1998 |
| PATENT CT FILE DATE | June 6, 1996 |
| PATENT CT NUMBER | This data is not available for free |
| PATENT CT PUB NUMBER | This data is not available for free |
| PATENT CT PUB DATE | December 19, 1996 |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method for treating inflammation in a mammal, said method comprising administering to said mammal a therapeutically effective amount of a salen-metal complex of the formula: ##STR16## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 2. The method in accordance with claim 1, wherein said salen-metal complex is a member selected from the group consisting of ##STR17## 3. The method in accordance with claim 2, wherein said salen-metal complex is selected from the group consisting of: 4. The method in accordance with claim 1, wherein said salen-metal complex is 5. The method in accordance with claim 1, wherein said salen-metal complex is formulated in a pharmaceutically acceptable form with an excipient or carrier. 6. The method in accordance with claim 5, wherein said salen-metal complex is formulated a pharmaceutically acceptable topical carrier. 7. The method in accordance with claim 6, wherein said salen-metal complex is formulated in a dental linament for treating inflammation associated with a periodontal disease. 8. A method for treating inflammation in a mammal, said method comprising: topically administering to said mammal a therapeutically effective amount of a salen-metal complex of the formula: wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 9. A method for preventing or retarding the aging of skin, said method comprising: applying to said skin an effective amount of a salen-metal complex of the formula: ##STR18## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 10. The method in accordance with claim 9, wherein said salen-metal complex is formulated in a pharmaceutically acceptable topical carrier. 11. A method for preventing the deleterious effects of ultraviolet light exposure to skin, said method comprising: topically applying to said skin an effective amount of a salen-metal complex of the formula: ##STR19## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 12. The method in accordance with claim 11, wherein said salen-metal complex is topically applied to said skin prior to ultraviolet light exposure. 13. The method in accordance with claim 11, wherein said salen-metal complex is topically applied to said skin in conjunction with ultraviolet light exposure. 14. The method in accordance with claim 11, wherein said salen-metal complex is topically applied to said skin after ultraviolet light exposure. 15. A method for enhancing the recovery of skin of a mammal to a wound, said method comprising: applying to said skin an effective amount of a salen-metal complex of the formula: ##STR20## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 16. The method in accordance with claim 15, wherein said wound is a member selected from the group consisting of surgical incisions, burns, inflammation and irritations due to oxidative damage. 17. A method for protecting cells from the deleterious effects of ionizing radiation, said method comprising: contacting said cells with an effective amount of a salen-metal complex of the formula: ##STR21## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 18. The method in accordance with claim 17, wherein said ionizing radiation is ultraviolet radiation. 19. The method in accordance with claim 17, wherein said ionizing radiation is gamma(.gamma.)-radiation. 20. The method in accordance with claim 17, wherein said cells are human cells. 21. The method in accordance with claim 17, wherein said contacting is carried out by administering to a human said salen-metal complex. 22. A method for protecting cells from the deleterious effects of a chemotherapeutic agent, said method comprising: contacting said cells with an effective amount of a salen-metal complex of the formula: ##STR22## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. 23. The method in accordance with claim 22, wherein said cells are human cells. 24. A composition useful for topical application, said composition comprising a topical carrier and a salen-metal complex of the formula: ##STR23## wherein: M is selected from the group consisting of Mn, Co, Fe, V, Cr, and Ni; A is an anion; n is either 0, 1, or 2; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are independently selected from the group consisting of hydrogen, silyls, aryls, arylalkyls, primary alkyls, secondary alkyls, tertiary alkyls, alkoxys, aryloxys, aminos, quaternary amines, heteroatoms, and hydrogen; Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, and Y.sub.6 are independently selected from the group consisting of hydrogen, halides, alkyls, aryls, arylalkyls, silyl groups, aminos, alkyls or aryls bearing heteroatoms, alkoxys, and halide; and R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, aryl, fatty acid esters, substituted alkoxyaryls, heteroatom-bearing aromatic groups, arylalkyls, primary alkyls, secondary alkyls, and tertiary alkyls. |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The invention provides antioxidant compositions, including pharmaceutical compositions, of synthetic catalytic small molecule antioxidants and free radical scavengers for therapy and prophylaxis of disease and prevention of oxyradical-mediated oxidation, methods for using the small molecule antioxidants in prevention and treatment of pathological conditions, methods for using the small molecule antioxidants as preservatives and oxyradical quenching agents in hydrocarbons, methods for using the small molecule antioxidants for targeted protection of tissues and/or cell types during cancer chemotherapy, and methods for using the small molecule antioxidants to prevent toxicologic damage to individuals exposed to irritating oxidants or other sources of oxidative damage, particularly oxygen-derived oxidative species such as superoxide radical. The compositions and methods of the invention are also used for preventing oxidative damage in human transplant organs and for inhibiting reoxygenation injury following reperfusion of ischemic tissues. The compositions and methods of the invention are also useful for chemoprevention of chemical carcinogenesis and alteration of drug metabolism involving epoxide or free oxygen radical intermediates. BACKGROUND OF THE INVENTION Molecular oxygen is an essential nutrient for nonfacultative aerobic organisms, including, of course, humans. Oxygen is used in many important ways, namely, as the terminal electronic acceptor in oxidative phosphorylation, in many dioxygenase reactions, including the synthesis of prostaglandins and of vitamin A from carotenoids, in a host of hydroxylase reactions, including the formation and modification of steroid hormones, and in both the activation and the inactivation of xenobiotics, including carcinogens. The extensive P-450 system uses molecular oxygen in a host of important cellular reactions. In a similar vein, nature employs free radicals in a large variety of enzymic reactions. Excessive concentrations of various forms of oxygen and of free radicals can have serious adverse effects on living systems, including the peroxidation of membrane lipids, the hydroxylation of nucleic acid bases, and the oxidation of sulfhydryl groups and of other sensitive moieties in proteins. If uncontrolled, mutations and cellular death result. Biological antioxidants include well-defined enzymes, such as superoxide dismutase, catalase, selenium glutathione peroxidase, and phospholipid hydroperoxide glutathione peroxidase. Nonenzymatic biological antioxidants include tocopherols and tocotrienols, carotenoids, quinones, bilirubin, ascorbic acid, uric acid, and metal-binding proteins. various antioxidants, being both lipid and water soluble, are found in all parts of cells and tissues, although each specific antioxidant often shows a characteristic distribution pattern. The so-called ovothiols, which are mercaptohistidine derivatives, also decompose peroxides nonenzymatically. Free radicals, particularly free radicals derived from molecular oxygen, are believed to play a fundamental role in a wide variety of biological phenomena. In fact, it has been suggested that much of what is considered critical illness may involve oxygen radical ("oxyradical") pathophysiology (Zimmermen J J (1991) Chest 100: 189S). Oxyradical injury has been implicated in the pathogenesis of pulmonary oxygen toxicity, adult respiratory distress syndrome (ARDS), bronchopulmonary dysplasia, sepsis syndrome, and a variety of ischemia-reperfusion syndromes, including myocardial infarction, stroke, cardiopulmonary bypass, organ transplantation, necrotizing enterocolitis, acute renal tubular necrosis, and other disease. Oxyradical can react with proteins, nucleic acids, lipids, and other biological macromolecules producing damage to cells and tissues, particularly in the critically ill patient. Free radicals are atoms, ions, or molecules that contain an unpaired electron (Pryor, W A (1976) Free Radicals in Biol. 1: 1). Free radicals are usually unstable and exhibit short half-lives. Elemental oxygen is highly electronegative and readily accepts single electron transfers from cytochromes and other reduced cellular components; a portion of the O.sub.2 consumed by cells engaged in aerobic respiration is univalently reduced to superoxide radical (.O.sub.2.sup.-) (Cadenas E (1989) Ann. Rev. Biochem. 58: 79). Sequential univalent reduction of .O.sub.2.sup.- produces hydrogen peroxide (H.sub.2 O.sub.2), hydroxyl radical (.OH), and water. Free radicals can originate from many sources, including aerobic respiration, cytochrome P-450-catalyzed monooxygenation reactions of drugs and xenobiotics (e.g., trichloromethyl radicals, CCl.sub.3., formed from oxidation of carbon tetrachloride), and ionizing radiation. For example, when tissues are exposed to gamma radiation, most of the energy deposited in the cells is absorbed by water and results in scission of the oxygen-hydrogen covalent bonds in water, leaving a single electron on hydrogen and one on oxygen creating two radicals H. and .OH. The hydroxyl radical, .OH, is the most reactive radical known in chemistry. It reacts with biomolecules and sets off chain reactions and can interact with the purine or pyrimidine bases of nucleic acids. Indeed, radiation-induced carcinogenesis may be initiated by free radical damage (Breimer L H (1988) Brit. J. Cancer 57: 6). Also for example, the "oxidative burst" of activated neutrophils produces abundant superoxide radical, which is believed to be an essential factor in producing the cytotoxic effect of activated neutrophils. Reperfusion of ischemic tissues also produces large concentrations of Oxyradical, typically superoxide (Gutteridge J M C and Halliwell B (1990) Arch. Biochem. Biophys. 283: 223). Moreover, superoxide may be produced physiologically by endothelial cells for reaction with nitric oxide, a physiological regulator, forming peroxynitrite, ONOO.sup.- which may decay and give rise to hydroxyl radical, .OH (Marletta M A (1989) Trends Biochem. Sci. 14: 488; Moncada et al. (1989) Biochem. Pharmacol. 38: 1709; Saran et al. (1990) Free Rad. Res. Commun. 10: 221; Beckman et al. (1990) Proc. Natl. Acad. Sci. (U.S.A.) 87: 1620). Additional sources of oxyradical are "leakage" of electrons from disrupted mitochondrial or endoplasmic reticular electron transport chains, prostaglandin synthesis, oxidation of catecholamines, and platelet activation. Oxygen, though essential for aerobic metabolism, can be converted to poisonous metabolites, such as the superoxide anion and hydrogen peroxide, collectively known as reactive oxygen species (ROS). Increased ROS formation under pathological conditions is believed to cause cellular damage through the action of these highly reactive molecules on proteins, lipids, and DNA. During inflammation, ROS are generated by activated phagocytic leukocytes; for example, during the neutrophil "respiratory burst", superoxide anion is generated by the membrane-bound NADPH oxidase. ROS are also believed to accumulate when tissues are subjected to ischemia followed by reperfusion. Many free radical reactions are highly damaging to cellular components; they crosslink proteins, mutagenize DNA, and peroxidize lipids. Once formed, free radicals can Interact to produce other free radicals and non-radical oxidants such as singlet oxygen (.sup.1 O2) and peroxides. Degradation of some of the products of free radical reactions can also generate potentially damaging chemical species. For example, malondialdehyde is a reaction product of peroxidized lipids that reacts with virtually any amine-containing molecule. Oxygen free radicals also cause oxidative modification of proteins (Stadtman E R (1992) Science 257: 1220). Aerobic cells generally contain a number of defenses against the deleterious effects of oxyradicals and their reaction products. Superoxide dismutases (SODs) catalyze the reaction: 2.O.sub.2.sup.- +2H.sup.+ .fwdarw.O.sub.2 +H.sub.2 O.sub.2 which removes superoxide and forms hydrogen peroxide. H.sub.2 O.sub.2 is not a radical, but it is toxic to cells; it is removed by the enzymatic activities of catalase and glutathione peroxidase (GSH-Px). Catalase catalyzes the reaction: 2H.sub.2 O.sub.2 .fwdarw.2H.sub.2 O+O.sub.2 and GSH-Px removes hydrogen peroxide by using it to oxidize reduced glutathione (GSH) into oxidized glutathione (GSSG) according to the following reaction: 2GSH+H.sub.2 O.sub.2 .fwdarw.GSSG+2H.sub.2 O Other enzymes, such as phospholipid hydroperoxide glutathione peroxidase (PLOOH-GSH-Px), converts reactive phospholipid hydroperoxides, free fatty acid hydroperoxides, and cholesterol hydroperoxides to corresponding harmless fatty acid alcohols. Glutathione S-transferases also participate in detoxifying organic peroxides. In the absence of these enzymes and in presence of transition metals, such as iron or copper, superoxide and hydrogen peroxide can participate in the following reactions which generate the extremely reactive hydroxyl radical .cndot.OH.sup.- : .cndot.O.sub.2.sup.- +Fe.sup.3+ .fwdarw.O.sub.2 +Fe.sup.2+ H.sub.2 O.sub.2 +Fe.sup.2+ .fwdarw..OH+OH.sup.- +Fe.sup.3+ In addition to enzymatic detoxification of free radicals and oxidant species, a variety of low molecular weight antioxidants such as glutathione, ascorbate, tocopherol, ubiquinone, bilirubin, and uric acid serve as naturally-occurring physiological antioxidants (Krinsky N I (1992) Proc. Soc. Exp. Biol. Med. 200:248-54). Carotenoids are another class of small molecule antioxidants and have been implicated as protective agents against oxidative stress and chronic diseases. Canfield et al. (1992) Proc. Soc. Exp. Biol. Med. 200: 260 summarize reported relationships between carotenoids and various chronic diseases, including coronary heart disease, cataract, and cancer. Carotenoids dramatically reduce the incidence of certain premalignant conditions, such as leukoplakia, in some patients. In an effort to prevent the damaging effects of oxyradical formation during reoxygenation of ischemic tissues, a variety of antioxidants have been used. One strategy for preventing oxyradical-induced damage is to inhibit the formation of oxyradicals such as superoxide. Iron ion chelators, such as desferrioxamine (also called deferoxamine or Desferol) and others, inhibit iron ion-dependent .OH generation and thus act as inhibitors of free radical formation (Gutteridge et al. (1979) Biochem. J. 184: 469; Halliwell B. (1989) Free Radical Biol. Med. 7: 645; Van der Kraaij et al. (1989) Circulation 80: 158). Amino-steroid-based antioxidants such as the 21-aminosteroids termed "lazaroids" (e.g., U74006F) have also been proposed as inhibitors of oxyradical formation. Desferrioxamine, allopurinol, and other pyrazolopyrimidines such as oxypurinol, have also been tested for preventing oxyradical formation in a myocardial stunning model system (Bolli et al. (1989) Circ. Res. 65: 607) and following hemorrhagic and endotoxic shock (DeGaravilla et al. (1992) Drug Devel. Res. 25: 139). However, each of these compounds has notable drawbacks for therapeutic usage. For example, deferoxamine is not an ideal iron chelator and its cellular penetration is quite limited. Another strategy for preventing oxyradical-induced damage is to catalytically remove oxyradicals such as superoxide once they have been formed. Superoxide dismutase and catalase have been extensively explored, with some success, as protective agents when added to reperfusates in many types of experiments or when added pre-ischemia (reviewed in Gutteridge J M C and Halliwell B (1990) op. cit.). The availability of recombinant superoxide dismutase has allowed more extensive evaluation of the effect of administering SOD in the treatment or prevention of various medical conditions including reperfusion injury of the brain and spinal cord (Uyama et al. (1990) Free Radic. Biol. Med. 8: 265; Lim et al. (1986) Ann. Thorac. Surg. 42: 282), endotoxemia (Schneider et al. (1990) Circ. Shock 30: 97; Schneider et al. (1989) Prog. Clin. Biol. Res. 308: 913, and myocardial infarction (Patel et al. (1990) Am. J. Physiol. 258: H369; Mehta et al. (1989) Am. J. Physiol. 257: H1240; Nejima et al. (1989) Circulation 79: 143; Fincke et al. (1988) Arzneimittelforschung 38: 138; Ambrosio et al. (1987) Circulation 75: 282), and for osteoarthritis and intestinal ischemia (Vohra et al. (1989) J. Pediatr. Surg. 24: 893; Flohe L (1988) Mol. Cell. Biochem. 84: 123). Superoxide dismutase also has been reported to have positive effects in treating systemic lupus erythematosus, Crohn's disease, gastric ulcers, oxygen toxicity, burned patients, renal failure attendant to transplantation, and herpes simplex infection. An alternative strategy for preventing oxyradical-induced damage is to scavenge oxyradicals such as superoxide once these have been formed, typically by employing small molecule scavengers which act stoichiometrically rather than catalytically. Congeners of glutathione have been used in various animal models to attenuate oxyradical injury. For example, N-2-mercaptopropionylglycine has been found to confer protective effects in a canine model of myocardial ischemia and reperfusion (Mitsos et al. (1986) Circulation 73: 1077) and N-acetylcysteine ("Mucomyst") has been used to treat endotoxin toxicity in sheep (Bernard et al. (1984) J. Clin. Invest. 73: 1772). Dimethyl thiourea (DMTU) and butyl-.alpha.-phenylnitrone (BPN) are believed to scavenge the hydroxyl radical, .OH, and has been shown to reduce ischemia-reperfusion injury in rat myocardium and in rabbits (Vander Heide et al. (1987) J. Mol. Cell. Cardiol. 19: 615; Kennedy et al. (1987) J. Appl. Physiol. 63: 2426). Mannitol has also been used as a free radical scavenger to reduce organ injury during reoxygenation (Fox RB (1984) J. Clin. Invest. 74: 1456; Ouriel et al. (1985) Circulation 72: 254). In one report, a small molecule chelate was reported to have activity as a glutathione peroxidase mimic (Spector et al. (1993) Proc. Natl. Acad. Sci. (U.S.A.) 90: 7485). Thus, application of inhibitors of oxyradical formation and/or enzymes that remove superoxide and hydrogen peroxide and/or small molecule oxyradical scavengers have all shown promise for preventing reoxygenation damage present in a variety of ischemic pathological states and for treating or preventing various disease states associated with free radicals. However, each of these categories contains several drawbacks. For example, inhibitors of oxyradical formation typically chelate transition metals which are used in essential enzymatic processes in normal physiology and respiration; moreover, even at very high doses, these inhibitors do not completely prevent oxyradical formation. Superoxide dismutases and catalase are large polypeptides which are expensive to manufacture, do not penetrate cells or the blood-brain barrier, and generally require parenteral routes of administration. Free radical scavengers act stoichiometrically and are thus easily depleted and must be administered in high dosages to be effective. The complex formed between the chelator desferroxamine and manganese has SOD activity and has shown some activity in biological models but the instability of the metal ligand complex apparently precludes its pharmaceutical use. Porphyrin-manganese complexes have been shown to protect bacteria from paraquat toxicity and to promote the aerobic survival of SOD-deficient E. coli mutants. A class of manganese macrocyclic ligand complexes with SOD activity has also been recently described with one prototype reportedly showing protection in a model for myocardial ischemia-reperfusion injury (Black et al. (1994) J. Pharmacol. Exp. Ther. 270: 1208). Based on the foregoing, it is clear that a need exists for antioxidant agents which are efficient at removing dangerous oxyradicals, particularly superoxide and hydrogen peroxide, and which are inexpensive to manufacture, stable, and possess advantageous pharmacokinetic properties, such as the ability to cross the blood-brain barrier and penetrate tissues. Such versatile antioxidants would find use as pharmaceuticals, chemoprotectants, and possibly as dietary supplements. It is one object of the invention to provide a class of novel antioxidants which possess advantageous pharmacologic properties and which catalytically and/or stoichiometrically remove superoxide and/or hydrogen peroxide. It is another object of the invention to provide antioxidant compositions and methods for inhibiting undesirable polymerization, oxidation, and/or gum formation in hydrocarbons, including plastics, nitrile rubbers, chloroprene rubbers, silicone rubber, isoprene rubbers, other rubber analogs, oils and waxes, cosmetic bases, animal fats, petroleum and petrochemicals and distillates, polymerizable resins, dyes, photosensitive agents, flavor agents, adhesives, sealants, polymer precursors, and the like. Also encompassed in the invention are salen-metal antioxidants and methods for inhibiting oxyradical-mediated polymerization and/or oxyradical-mediated decomposition. The polymers are usually formed by reactions of unsaturated hydrocarbons, although any hydrocarbon can polymerize. Generally, olefins tend to polymerize more readily than aromatics, which in turn polymerize more readily than paraffins. Trace organic materials containing hetero atoms such as nitrogen, oxygen and sulfur also contribute to polymerization, as does molecular oxygen, oxyradicals (e.g., superoxide, peroxides, hydroxyl radical), and other free radicals. Polymers are generally formed by free radical chain reactions. These reactions, typically consist of two phases, an initiation phase and a propagation phase. Free radicals, which have an odd (unpaired) electron, can act as chain carriers and/or initiators. During chain propagation, additional free radicals are formed and the hydrocarbon molecules grow larger and larger, sometimes forming unwanted polymers which accumulate. Research indicates that even very small amounts of oxygen can cause or accelerate polymerization. Accordingly, antioxidant antifoulants have been developed to prevent oxygen from initiating polymerization, such as in petroleum refining apparatus. Antioxidants act as chain-stoppers by forming inert molecules with the oxidized free radical hydrocarbons. U.S. Pat. No. 4,466,905, Butler et al., teaches a polymer inhibiting composition and process for inhibiting the polymerization of vinyl aromatic compounds. U.S. Pat. No. 3,907,745, Bsharah et al., teaches a synergistic antioxidant system for use in polymer system susceptible to oxidation. This system comprises a combination of an antioxidant such as a phenylenediamine and a chelating agent or metal deactivator such as a polyamine. U.S. Pat. No. 4,720,566 Martin, teaches compositions and methods for inhibiting acrylonitrile polymerization in quench columns of acrylonitrile producing systems. U.S. Pat. No. 4,929,778, Roling, teaches compositions and methods for inhibiting the polymerization of vinyl aromatic monomers during the preparation of monomers and the storage and shipment of products containing such monomers. New antioxidants and antioxidant methods are needed in the art, particularly for use in aqueous or mixed aqueous/organic systems. The present invention fulfills these and other needs. The references discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention. All publications cited are incorporated herein by reference. SUMMARY OF THE INVENTION In accordance with the foregoing objects, in one aspect of the invention pharmaceutical compositions are provided which have potent antioxidant and/or free radical scavenging properties and function as in vivo antioxidants. The pharmaceutical compositions of the invention comprise an efficacious dosage of at least one species of salen-transition metal complex, typically a salen-manganese complex such as a salen-Mn(III) complex. In one embodiment, the pharmaceutical composition comprises a salen-Mn complex which is a chelate of Mn(III) with a diamine derivative, such as ethylenediamine linked to two substituted salicylaldehydes. These pharmaceutical compositions possess the activity of dismutating superoxide (i.e., superoxide dismutase activity) and, advantageously, also converting hydrogen peroxide to water (i.e., catalase activity). The pharmaceutical compositions are effective at reducing pathological damage related to formation of oxyradicals such as superoxide and peroxides and other free radical species. The invention also provides methods for treating and preventing pathological conditions by applying or administering compositions of salen-transition metal complexes in a therapeutic or prophylactic dosage. Salen-transition metal complexes used in the methods of the invention are typically salen-manganese complexes, such as Mn(III)-salen complexes. The invention provides methods for preventing or reducing ischemic/reperfusion damage to critical tissues such as the myocardium and central nervous system. The invention also provides methods for preventing or reducing cellular damage resulting from exposure to various chemical compounds which produce potentially damaging free radical species, comprising administering a therapeutically or prophylactically efficacious dosage of at least one species of salen-transition metal complex, preferably a salen-manganese complex having detectable SOD activity and preferably also having detectable catalase activity. The antioxidant salen-transition metal complexes of the invention are administered by a variety of routes, including parenterally, topically, and orally. In one aspect of the invention, a therapeutic or prophylactic dosage of a salen-transition metal complex of the present invention is administered alone or combined with (1) one or more antioxidant enzymes, such as a Mn-SOD, a Cu,Zn-SOD, or catalase, and/or (2) one or more free radical scavengers, such as tocopherol, ascorbate, glutathione, DMTU, N-acetylcysteine, or N-2-mercaptopropionylglycine and/or (3) one or more oxyradical inhibitors, such as desferrioxamine or allopurinol, and/or one or more biological modifier agents, such as calpain inhibitors. The formulations of these compositions is dependent upon the specific pathological condition sought to be treated or prevented, the route and form of administration, and the age, sex, and condition of the patient. These compositions are administered for various indications, including: (1) for preventing ischemic/reoxygenation injury in a patient, (2) for preserving organs for transplant in an anoxic, hypoxic, or hyperoxic state prior to transplant, (3) for protecting normal tissues from free radical-induced damage consequent to exposure to ionizing radiation and/or chemotherapy, as with bleomycin, (4) for protecting cells and tissues from free radical-induced injury consequent to exposure to xenobiotic compounds which form free radicals, either directly or as a consequence of monooxygenation through the cytochrome P-450 system, (5) for enhancing cryopreservation of cells, tissues, organs, and organisms by increasing viability of recovered specimens, and (6) for prophylactic administration to prevent: carcinogenesis, cellular senescence, cataract formation, formation of malondialdehyde adducts, HIV pathology and macromolecular crosslinking, such as collagen crosslinking. In one aspect of the invention, salen-transition metal complexes are formulated for administration by the oral route by forming a pharmaceutical dosage form comprising an excipient and not less than 1 .mu.g nor more than about 10 grams of at least one antioxidant salen-transition metal complex of the invention. Dietary formulations are administered for therapy of free radical-induced diseases and/or for the chemoprevention of neoplasia and/or oxidative damage associated with normal aerobic metabolism. In another aspect of the invention, buffered aqueous solutions comprising at least one antioxidant salen-transition metal complex of the invention at a concentration of at least 1 nM but not more than about 100 mM is formulated for administration, usually at a concentration of about 0.1 to 10 mM, typically by intravenous route, to a patient undergoing or expected to undergo: (1) an ischemic episode, such as a myocardial infarction, cerebral ischemic event, transplantation operation, open heart surgery, elective angioplasty, coronary artery bypass surgery, brain surgery, renal infarction, traumatic hemorrhage, tourniquet application, (2) antineoplastic or antihelminthic chemotherapy employing a chemotherapeutic agent which generates free radicals, (3) endotoxic shock or sepsis, (4) exposure to ionizing radiation, (5) exposure to exogenous chemical compounds which are free radicals or produce free radicals, (6) thermal or chemical burns or ulcerations, (7) hyperbaric oxygen, or (8) apoptosis of a predetermined cell population (e.g., lymphocyte apoptosis). The buffered aqueous solutions of the invention may also be used, typically in conjunction with other established methods, for organ culture, cell culture, transplant organ maintenance, and myocardial irrigation. Nonaqueous formulations, such as lipid-based formulations are also provided, including stabilized emulsions. The antioxidant salen-metal compositions are administered by various routes, including intravenous injection, intramuscular injection, subdermal injection, intrapericardial injection, surgical irrigation, topical application, ophthalmologic application, lavage, gavage, enema, intraperitoneal infusion, mist inhalation, oral rinse, and other routes, depending upon the specific medical or veterinary use intended. In another aspect of the invention, antioxidant salen-transition metal complexes of the invention are employed to modulate the expression of naturally-occurring genes or other polynucleotide sequences under the transcriptional control of an oxidative stress response element (e.g., an antioxidant responsive element, ARE), such as an antioxidant response element of a glutathione S-transferase gene or a NAD(P)H:quinone reductase gene. The antioxidant salen-metal complexes may be used to modulate the transcription of ARE- regulated polynucleotide sequences in cell cultures (e.g., ES cells) and in intact animals, particularly in transgenic animals wherein a transgene comprises one or more AREs as transcriptional regulatory sequences. The present invention also encompasses pharmaceutical compositions of antioxidant salen-manganese complexes, therapeutic uses of such antioxidant salen-manganese complexes, methods and compositions for using antioxidant salen-manganese complexes in diagnostic, therapeutic, and research applications in human and veterinary medicine. The invention also provides methods for preventing food spoilage and oxidation by applying to foodstuffs an effective amount of at least one antioxidant salen-metal complex species. The invention also provides compositions for preventing food spoilage comprising an effective amount of at least one species of antioxidant salen-metal complex, optionally in combination with at least one additional food preservative agent (e.g., butylated hydroxytoluene, butylated hydroxyanisole, sulfates, sodium nitrite, sodium nitrate). For example, an antioxidant salen-metal complex is incorporated into a foodstuff subject to rancidification (e.g., oxidation) to reduce the rate of oxidative decomposition of the foodstuff when exposed to molecular oxygen. In an aspect, the invention relates to antioxidant compositions and methods of use in inhibiting formation of undesired hydrocarbon polymers generated via free radical-mediated polymerization mechanisms, especially oxyradical-mediated polymerization and/or oxyradical-mediated rancidification or gum formation. The antioxidant salen-metal complexes of the invention can be applied to a variety of hybdrocarbons to reduce undesired oxidation and/or polymerization, or to quench a polymerization reaction at a desired state of polymer formation (e.g., at a desired average chain length). For example and not to limit the invention, examples of such saturated and unsaturated hydrocarbons include: petroleum distillates and petrochemicals, turpentine, paint, synthetic and natural rubber, vegetable oils and waxes, animal fats, polymerizable resins, polyolefin, and the like. The invention relates to antioxidant compositions and methods of use in hydrocarbon compositions to reduce and/or control the formation of undesired polymers which comtaminate such hydrocarbon compositions, including hydrocarbons present in aqueous systems, two-phase aqueous:organic systems, and organic solvent systems. This invention relates to a method and composition for controlling the formation of polymers in such systems which comprises an antioxidant composition comprising an antioxidant salen-metal compound, optionally in combination with an antioxidant or stabilizer other than a salen-metal compound (e.g., BHT, BHA, catechol, tocopherol, hydroquinone, etc.). More particularly, this invention relates to a method and composition for controlling the formation of polymers which comprises an antioxidant composition comprising an antioxidant salen-metal complex. The amount of the individual ingredients of the antioxidant composition will vary depending upon the severity of the undesirable polymer formation encountered due to free radical polymerization as well as the activity of the salen-metal compound utilized. In other embodiments the invention provides methods for enhancing the recovery of skin of a warm-blooded animal from wounds, such as surgical incisions, burns, inflammation or minor irritation due to oxidative damage, etc. The methods comprise administering to the skin wound or irritation a therapeutically or, in some cases a prophylactically effective amount of a composition which comprises an antioxidant salen-metal complex. The present invention also provides compounds having glutathione peroxidase activity and, therefore, capable of serving as effective glutathione peroxidase replacements. These compounds are useful as drugs for the prevention of many pathological conditions, including but not limited to neoplasia, apoptosis of somatic cells, skin aging, cataracts, and the like; and as anti-oxidants for scavenging H.sub.2 O.sub.2 and other peroxides. The present invention also provides methods and pharmaceutical compositions of these compounds. The present invention also concerns a method of reducing H.sub.2 O.sub.2 and/or other peroxides which comprises contacting H.sub.2 O.sub.2 and/or other peroxides with a suitable amount of any of the compounds of the invention effective to reduce H.sub.2 O.sub.2 and/or other peroxides. Additionally, the invention provides a method of treating a peroxide-induced condition in a subject which comprises administering to the subject an amount of any of the compounds of the invention effective to reduce peroxide in a subject and thereby treat the peroxide-induced condition. Further, the invention provides a pharmaceutical composition which comprises an amount of any of the compounds of the invention effective to reduce peroxide in a subject with a peroxide-induced condition and a pharmaceutically acceptable carrier. Further, the invention provides a method of treating a peroxide-induced condition in a subject, e.g. a human subject, which comprises administering, e.g. by topical, oral, intravenous, intraperitoneal, intramuscular, intradermal, or subcutaneous administration, to the subject an amount of an antioxidant salen-metal compound effective to reduce peroxide in the subject and thereby treat the peroxide-induced condition. It is worthy to point out at this time that the administration of the compound to the subject may be effected by means other than those listed herein. Further, the peroxide-induced condition may involve cataracts, inflammation of a tissue, ischemia, an allergic reaction, or pathology caused by oxidative stress. Where the peroxide-induced condition involves cataracts, administration is effected by, but is not limited to, topical contact to the surface of an eye. All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the general structure of salen deriviatives of the invention. FIG. 2 shows a salen derivative according to the structure shown in FIG. 1, wherein n is 0. FIG. 3 shows structures of preferred compounds of the invention. FIG. 4 shows schematically the effect of an ischemic/reoxygenation episode on synaptic transmission in isolated brain slices. FIG. 5 shows the effect of a salen-Mn complex on EPSP amplitude following an episode of ischemia/reoxygenation. FIG. 6 shows the effect of a salen-Mn complex on EPSP initial slope following an episode of ischemia/reoxygenation. FIG. 7 shows the effect of a salen-Mn complex on brain slice viability following repeated episodes of ischemia/reoxygenation. FIGS. 8A and 8B show the protective effect of a salen-Mn complex in an animals model of iatrogenic Parkinson's disease. FIG. 9 shows that C7 protects hippocampal slices from lactic acid-induced lipid peroxidation. FIG. 10 shows C7 protects dopaminergic neurons in mouse striatum from 6-OHDA-induced degeneration. FIGS. 11A and 11B shows C7 protects dopaminergic neurons in mouse striatum from MPTP-induced degeneration. FIG. 12 shows examples of structures of antioxidant salen-metal complexes. FIGS. 13A and 13B shows that C7 inhibits NBT reduction without affecting xanthine oxidase activity in an SOD assay. C7 was assayed for SOD activity as described under Experimental Procedures using NBT as acceptor. FIG. 13A: NBT reduction in the presence of (solid circle), 0; (open circle), 0.1 .mu.M; (solid triangle), 0.5 .mu.M; (open triangle), 1.5 .mu.M; (solid square), 3 .mu.M; and (open square), 6 .mu.M C7. FIG. 13B: xanthine oxidase activity, detected by the formation of urate in the presence of (solid circle), 0; (open circle), 6 .mu.M; and (solid triangle), 11 .mu.M C7. FIG. 14 shows that C7 exhibits catalase activity. C7 was assayed for catalase activity as described under Experimental Procedures. The concentration of C7 was 10 MM and the concentration of H.sub.2 O.sub.2 was as indicated: (solid circle), 0.6 my.; (open circle), 1.2 mM; (solid triangle), 2.3 mM; (open triangle), 4.6 mM; (solid diamond) 9.2 mM; (open diamond), 18.3 mM; (X) 36.6 mM. FIGS. 15A and 15B show that C7 exhibits peroxidase activity toward the substrate ABTS. C7 was assayed for peroxidase activity as described under Experimental Procedures. The concentration of C7 was 10 .mu.M and the concentration of H.sub.2 O.sub.2 and the pH of the sodium phosphate reaction buffers were as indicated. FIG. 15A: pH 8.1, H.sub.2 O.sub.2 concentration of: (solid circle), 0.1 mM; (open circle), 1 mM; (solid triangle), 10. mM; FIG. 15B: 10 mM H.sub.2 O.sub.2, pH was: (solid circle), 6.0; (open circle) 7.1; (solid triangle), 8.1. FIGS. 16A and 16B show inactivation of C7 in the presence of H.sub.2 O.sub.2. C7 was incubated with H.sub.2 O.sub.2 as described under Experimental procedures with aliquots removed and analyzed by HPLC. FIG. 16A: Time-dependent changes in levels of C7 (solid circle), salicylaldehyde (X), and an unidentified substance (open triangles) in incubation mixtures lacking ABTS. FIG. 16B. The percent of initial C7 remaining in incubations conducted in the absence (solid circle) and presence (open circle) of 1 mM ABTS. FIG. 17 shows a comparison of the catalase activities of C7 and C40. Catalase assays were performed as described for Table VII, using C7 (solid circle) or C40 (open circle). FIG. 18 shows protection against glucose and glucose-oxidase induced cytotoxicity by salen manganese complexes. Cytotoxicity studies were performed as described under Experimental procedures. Absorbance values, corrected by subtracting the blank signal of 0.17 OD units, are the means.+-.sd of triplicate samples. Control cells (open circle) received no glucose oxidase. Catalase-treated (solid circle) cells received glucose oxidase (0.019) units/ml) as well as bovine liver catalase (290 units/ml). Other samples received the same dose of glucose oxidase and the indicated concentrations of salen manganese complex. C40 (open triangle), C32 (solid triangle), C41 (open square), C38 (solid square), C7 (open diamond), and C35 (solid diamond). Several other compounds tested (C31, C33, C34, C36, and C37) were about equally as effective as C7 and have been omitted from the figure for clarity. FIG. 19A shows structures of salen-manganese complexes. FIG. 19B shows the catalase rate, catalase endpoint, peroxidase rate, and SOD activity of these compounds relative to C7. FIG. 20 Time-dependent generation of oxygen in the catalase assay. Catalase was assayed with a polarographic oxygen electrode as described in Example 2. Each compound was present at 10 .mu.M. Hydrogen peroxide was added at a final concentration of 10 mM at the indicated times (arrows). FIG. 21 Catalase and peroxidase activities of a series of compounds. Assay methods were as described for Table VII. Activities are expressed relative to C31. (mean.+-.sd for n=.sup.3). FIG. 22 Protection of human cells against toxicity by glucose and glucose oxidase. Cytotoxicity assays were performed using human dermal fibroblasts as for FIG. |
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