Active oxygen or free radical causes various troubles in a living body. Active oxygen or free radical is generated by bacteria invasion into the living body, in chitin-chitosan oxidase system, arachidonic cascade system, or a process of saccharification, and so forth.
Active oxygen is a generic name of super hydroxy radical (.O.sub.2.sup.-), singlet oxygen (.sup.1 O.sub.2) and hydroxy radical (.OH). Hydroxy radical is formed by taking an electron into the orbital of triplet oxygen in ground states. The singlet oxygen is defined as the oxygen wherein two unpaired electrons of an oxygen atom make a pair to enter orbital of the other oxygen atom, resulting the electron orbitals are empty.
Furthermore, perhydoxyradical (.OOH), which is a typical free radical, is generated when peroxide is decomposed by autoxidation via the following route. EQU RH+O.sub.2.fwdarw.ROOH.fwdarw.R.+.OOH
Perhydoxyradical looses a proton in alkaline solution to be converted to superoxide (.OO.sup.-). In the living body, free dihydroflavin non-enzymatically reacts with oxygen very quickly to generate perhydroxy radical.
Perhydroxyradical is converted to the above-mentioned superoxide, and then superoxide is catalyzed by superoxide dismutase (SOD) to generate an oxygen molecule and hydrogen peroxide. EQU 2.O.sub.2.sup.- +2H.sup.+.revreaction.O.sub.2 +H.sub.2 O.sub.2
In the bacteria invasion, free radicals including active oxygen are generated to exclude extraneous material for the living body; after bacteria invade to the living body, neutrophils phagocytose such materials and release activated oxygen from their membrane. In chitin-chitosan oxidase system, serious tissue lesion occurs; in ischemia, active oxygen is generated by increasing hypoxanthine and xanthine oxidase level in cells, and after ischemia a larger amount of active oxygen is generated by introducing a lot of oxygen into the cells. Such tissue lesion is referred to as ischemia-perfusion disorder. In an arachidonic acid cascade system, unsaturated fatty acid is peroxidized through autoxidation mechanism to generate peroxides and radicals.
Since thus generated free radicals cause various diseases such as inflammation, allergy, cerebral nerve disease and tissue lesions, it is required that the excessive generation of free radicals should be prevented or the generated free radicals should be scavenged. Target molecules and lesions caused by damaging them are shown in Table 1.
TABLE 1 In vivo target molecule for active oxygen and free radicals Target molecules Lesions Lipids Peroxidation and lesion of biomembrane Nucleic Acids Cell cycle change, mutation, DNA chain cleavage, base damage, carcinogenesis, and AIDS Amino Acids Denaturation of protein, polymerization, enzyme repression, and cross-linking denaturation Carbohydrate Change of cell surface receptor Hyaluronic acid Depolymerization Biological Factors Inactivation (.alpha.-antitrypsin, chemotactic factor, chemical mediator, neurotransmitter)
Among the substances, which are biosynthesized in vivo, any substance capable of scavenging .OH is not known. In vivo, .OH is generated by reduction of H.sub.2 O.sub.2 by using transition metal, decomposition of H.sub.2 O upon irradiation and reaction of NO with superoxide. This .OH is highly reactive and reacts with almost all the biosubstance in a rate-determining manner by nucleic acids. Therefore, the .OH often gives a living body a mortal wound. Accordingly, in order to prevent or terminate such wounds, it is required to provide a substance having antioxidation activity for .OH from outside of the living body.
As active oxygen inhibitors, which are presently known, there can be mentioned ceruloplasmin, metallothionein and vitamin C. Ceruloplasmin is a plasma protein of which molecular weight is about 16,000, including 6 to 7 copper ions per molecule, and it is known that it shows SOD activity against .O.sub.2.sup.-. This protein is rich in blood, and it seems to be a scavenger of active oxygen (.O.sub.2.sup.-) in blood vessel. Metallothionein is a metalloprotein of which molecular weight is about 60,000, and cysteine occupies 30% of its structure protein. It is known that this protein scavenges hydroxy radicals (.OH) and suppresses peroxidation of lipids. Vitamin C is known as a scavenger for .O.sub.2.sup.-, .OH, singlet oxygen (.sup.1 O.sub.2), hydrogen peroxide (H.sub.2 O.sub.2), and so forth. These substances are used as pharmaceuticals, but all of them are water-soluble and have a relatively high molecular weight. Furthermore, they are mainly administered per os or via injection. They act as the scavengers in extracellular fluid, but are not incorporated into the cells.
In general, drugs are transferred into blood and then delivered to target sites by blood flow. Since fat-soluble drugs pass through blood-brain barrier (BBB) to be transferred into brain, such drugs have a trouble from the viewpoint of side effects. Therefore, water-soluble drugs are selected, and such administration routes are used. However, it is difficult to deliver the drug to the target sites with effective dose by transferring the drug in blood. Particularly, it is almost impossible to deliver the drug at such dose when the target site is lymph tissue.
Such drugs are desired to have a low molecular weight rather than a high molecular weight from the viewpoint of formulation or administration, and to be compounds or compositions having antioxidizing activity. As mentioned above, free radicals cause various diseases or tissue lesions, particularly peroxidation of lipid, to generate peroxides and radicals to influence badly for living body. Considering these matters, lymptropic drugs or compositions are needed.
However, lymptropic drug or compositions having antioxidization activities are not known. Particularly, those capable of preventing lipid peroxidization have not found.
On the other hand, it is known that enzymes such as SOD, catalase and glutathione peroxidase scavenge free radicals. Furthermore, as examples of antioxidizing substances, which are defined as the substances having antioxidization activities, a singlet oxygen scavenger, a superoxide scavenger, a hydroxy radical scavenger, and an antioxidizing of which mechanism is not clarified are known. Specifically, as examples of the singlet oxygen scavenger, there can be mentioned .beta.-carotene, amines, tocopherols and histidines; as superoxide scavengers, tocopherols, phenols, thiols, ascorbic acid, and copper(II)-histidine complexes; as hydroxy radical scavengers, mannitol; and as the antioxidizing of which mechanism is not clarified, nucleic acid bases, fulavonoids, sterol, terpene, and polycarboxilic acid.
Accordingly, there are not effective means to scavenge free radicals at present, and only preventive means for free radical generation is used. In such preventive means, enzymes such as SOD, catalase and glutathione peroxidase, fat-soluble or water-soluble vitamins included in foods such as vitamin E, which is called tocopherol, vitamin A, vitamin D, vitamin C and vitamin Bs, and various coloring matters such as carotenoid which is fat-soluble coloring matters, and fulavonoid which is water-soluble coloring matters are taken parenterally or per os as antioxidizing substances.
Such compounds may be taken alone, or in combination; for example, several antioxidizing compounds such as tannin, flavonoid, carotenoid, vitamin C, caffeic acid derivatives, lignans and saponin which are included in Chinese orthodox crude drug used in Oriental medicine from ancient age.
In Chinese orthodox medicine, it is known that those antioxidizing compounds play great roles in action mechanism. However, since these compounds are water-soluble, there is a problem from the viewpoint of lymptropic activity.
When the above-mentioned antioxidizing enzymes or substances are taken per os, those enzymes are digested digestive tract or liver in absorption step to be metabolites, their bioavailability as drugs are not enhanced. Furthermore, if they are administrated parenterally, they are transferred into blood but not into lymph. Such tendency is also observed in the antioxidizing substance, vitamins described above.