• Astaxanthin's antioxidant properties as a quencher of singlet oxygen and a scavenger of free radicals, and its ability to protect lipids from peroxidation, have been largely demonstrated. Studies indicate astaxanthin antioxidant properties to be superior by up to 10-fold, when compared to other carotenoids, and by more than 100-fold, when compared to vitamin E.

• Astaxanthin's antioxidant properties are believed to be at the source of most its potential benefits in human health. Unlike beta-carotene, astaxanthin has no pro-vitamin A activity in mammals.

• Possible roles of astaxanthin in the immune response, health of the eye and nervous system, photo-protection, and against cancer, inflammation, infections, or artheriosclerosis, are discussed.

1. Astaxanthin as a general biological antioxidant

• Astaxanthin has been shown to be a powerful quencher of singlet oxygen activity in in vitro studies, with up to 80- (DiMascio et al. 1990) to 550-fold (Shimidzu et al. 1996) higher quenching rate constants than vitamin E .

• Astaxanthin is also a strong scavenger of oxygen free radicals, up to ten times stronger than beta-carotene (Miki 1991).

• In vitro experiments with red blood cells and mitochondria from rats have shown that astaxanthin could be 100 to 500 times more effective at inhibiting lipid peroxidation than is vitamin E (Kurashige et al. 1990).

• Astaxanthin's excellent ability to prevent lipid peroxidation was confirmed in vivo with rats given dietary supplements of astaxanthin and subjected to oxidizing agents (Miki 1991).

• The antioxidative properties of astaxanthin have been demonstrated in a number of different biological membranes (Kurashige et al. 1990; Palozza and Krinsky 1992; Oshima et al. 1993; Nakagawa et al. 1997).

• This antioxidant activity is believed to be at the origin of some of astaxanthin's most important potential beneficial properties in health.

2. Astaxanthin as an anti-cancer agent

Studies of the cancer-preventative properties of Astaxanthin have been carried out on rats and mice by Takuji Tanaka and colleagues at the Gifu University School of Medicine. Dietary administration of astaxanthin proved to significantly inhibit carcinogenesis in the mouse urinary bladder (Tanaka et al. 1994), rat oral cavity (Tanaka et al. 1995a), and rat colon (Tanaka et al. 1995b).

In addition, astaxanthin has been shown to induce xenobiotic-metabolizing enzymes in rat liver, a process which may help prevent carcinogenesis (Gradelet et al. 1996).

3. Astaxanthin for support of the immune system

Astaxanthin has been shown to significantly influence immune function in a number of in vitro and in vivo assays using animal models. The majority of this work has been carried out by Harumi Jyonouchi and colleagues at the University of Minnesota.

• Astaxanthin enhances in vitro antibody production by mouse spleen cells stimulated with sheep red blood cells (Jyonouchi et al. 1991), at least in part by exerting actions on T-cells, especially T-helper cells (Jyonouchi et al. 1993).

• Astaxanthin can also partially restore decreased humoral immune responses in old mice (Jyonouchi et al. 1994). These immuno-modulating properties are not related to provitamin-A activity, because astaxanthin, unlike beta-carotene, does not have such activity (Jyonouchi et al. 1991).

• Studies on human blood cells in vitro have demonstrated enhancement by astaxanthin of immunoglobulin production in response to T-dependent stimuli (Jyonouchi et al. 1995a).

• Other supporting data on astaxanthin and immune function, including studies on the mechanisms of action involved, may be found in Jyonouchi et al. (1995b), Jyonouchi et al. (1996), Okai & Higashi-Okai (1996), and Tomita et al. (1993).

4. Astaxanthin for health of the eye and central nervous system

The possible role of antioxidants in alleviating oxidation stress and other oxidative damages to the eye and the nervous system has been extensively reviewed by Trevithick and Mitton (1999).

• As one of nature's most effective antioxidants with the ability to cross the blood-brain barrier (Tso and Lam, 1996), astaxanthin's potential benefits for the health of the eye and the nervous system are very promising.

• The eye is potentially one of the organs which is the most exposed to oxidation, because it is exposed to air and UV-light as well as being fed by a very large number of small capillaries capable of bringing many of the metabolic oxidative residues through the blood.

• The eye also contains high levels of polyunsaturated fatty acids and pigments that are sensitive to oxidation (Starostin 1988, Donstov et al. 1999). Recently, a research group demonstrated increased superoxide and peroxide formation following UV irradiation of a lens protein (Linetsky et al. 1996). Photoxidation of the lens proteins have been associated to the development of cataract (Taylor, 1993).

• Lutein, and zeaxanthin, the carotenoids naturally found in the human retina, are closely related to astaxanthin. There is abundant evidence that certain carotenoids can help protect the retina from oxidative damage (Snodderly 1995).

• Investigations of the antioxidant effectiveness of astaxanthin in the eye are just beginning but are already very promising. A recent study with rats indicates that astaxanthin can be effective at ameliorating retinal injury, and that it is also effective at protecting photoreceptors from degeneration (Tso and Lam 1996).

• The conclusions of this study were that astaxanthin could be useful for prevention and treatment of neuronal damage associated with age-related macular degeneration, and that it may also be effective at treating ischemic reperfusion injury, Alzheimer's disease, Parkinson's disease, spinal cord injuries, and other types of central nervous system injuries (Tso and Lam 1996). In this study, astaxanthin was found to easily cross the blood-brain barrier (unlike beta-carotene), and did not form crystals in the eye (unlike canthaxanthin) (Tso and Lam 1996).

• These conclusions concur with those of Sokol & Papas (1999) who report encouraging results in the possible use of antioxidants to treat or prevent neurodegenerative diseases such as Alzheimer's disease.

5. Astaxanthin as a photo-protectant

Light, especially UV light, can trigger photoxidation mechanisms and produce active oxygen species such as singlet oxygen (Noguchi and Niki, 1999, McVean et al. 1999). Lipids (Dontsov et al. 1999, Guillen-Sans & Guzman-Chozas, 1998), pigments (Ostrovskii, 1987, Starostin et al. 1988), DNA (Dunford et al. 1997), proteins (Taylor 1993) have been reported to be sensitive to photoxidation.

Oxidative damage to the eye and skin by UV light has been widely documented (Trevithick and Mitton, 1999, McVean et al,. 1999). The strong antioxidative activities of astaxanthin suggest its potential as a photoprotectant, as indicated by the recent study by Tso and Lam (1996), cited above, indicating lower damage by UV light to the eye of animals fed astaxanthin, although the effects of astaxanthin on mice exposed to UV irradiation have not been conclusive (Savouré et al. 1995; Black 1998). Nevertheless, astaxanthin-containing preparations for prevention of light aging of skin have been developed (Suzuki et al. 1996a, 1996b).

6. Astaxanthin and infections

A recent study suggested that astaxanthin may be effective as a prophylactic and/or therapeutic treatment of Helicobacter infections of the mammalian gastrointestinal tract, and an oral preparation has been developed for this purpose (Alejung and Wadstroem 1998).

7. Astaxanthin for prevention of arteriosclerosis and related diseases

Astaxanthin has been shown in both in vitro experiments and in a study with human subjects to be effective for the prevention of the oxidation of low-density lipoprotein (Miki et al., 1998).

This suggests that it could be used as a preventative for arteriosclerosis, coronary artery disease, and ischemic brain damage; a number of astaxanthin-containing health products are under development based on these findings (Miki et al. 1998).

8. Astaxanthin in anti-inflammatory preparations

According to recent studies, astaxanthin diesters appear to exert a synergistic effect on anti-inflammatory agents, increasing the effectiveness of aspirin when the two are administered together (Yamashita 1995).

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