Astaxanthin the newest eye healthcare dietary supplement

Astaxanthin, the Newest Carotenoid Eye Healthcare Dietary Supplement Solution
Chances are good that in the last 24 hours you’ve eaten several different carotenoids. This class of naturally occurring isoprenoid based antioxidant molecules include over 600 unique compounds, however most people are only familiar with a few of the most important carotenoids. These include lycopene, the color of red tomatoes, zeaxanthin, the color of yellow corn, and beta-carotene, the color of orange carrots. In addition, Vitamin A, or retinol, is an essential vitamin for human eye health, which is available in many vegetables and can also be manufactured in vivo from dietary beta-carotene on an as needed basis. The vitamin in its oxidized form, as retinal, serves as a key component the functioning retina. Chronic Vitamin A deficiency leads to total blindness in man.

Carotenoids are divided into two distinct structural groups, namely carotenes which contain no oxygen atoms (typical examples are lycopene and beta-carotene) and the xanthophylls whose notable examples include lutein and zeaxanthin. Xanthophylls are all characterized by the fact that they contain oxygen atoms added to the structures of the simpler carotenes.

Interestingly, none of the carotenes tested to date, and most of the xanthophylls tested to date do not pass through the blood brain barrier with a few notable exceptions. These exceptions include lutein, zeaxanthin, canthaxanthin and astaxanthin.

Human serum typically contains about ten carotenoids. The major carotenoids in human serum include beta-carotene, alpha-carotene, cryptoxanthin, lycopene and lutein.  Small amounts of zeaxanthin, phytofluene and phytoene are also found in human organs. However, of all of these carotenoids, only zeaxanthin and lutein are found in the human retina. Indeed, the retina has the highest concentration of polyunsaturated fatty acids of any tissue in the human body.

It has been theorized that zeaxanthin and lutein are concentrated in the retina because of their ability to quench singlet oxygen and to scavenge free radicals, because they pass the blood and eye brain barriers and are required in the oxygen rich environment of the retina to prevent light mediated free radical damage to the retina.

In fact, zeaxanthin is the predominant carotenoid found in the central portion of the retina and more specifically is located in concentration in the retinal cones located in the central area of the retina (ie. the macula).Lutein, on the other hand, is located in the peripheral area of the retina in the rod cells. Therefore, the eye preferentially accumulates zeaxanthin over lutein in the critical central macular retinal area, (zeaxanthin interestingly, is a much more effective singlet oxygen scavenger than lutein), where the greatest level of light impinges.

Biochemists have determined the exact, yet complicated, mechanism for light sensory response in the eye. It involves a key protein called rhodopsin whose structure includes a bound polyunsaturated compound called retinal (retinal is structurally related to vitamin A). When light enters the eye, cis-retinal isomerizes to all its all-trans isomer, causing disassociation of itself from its protein carrier.The disassociation triggers a complicated cascade leading to nerve based transmission of electrons to the brain via the optic nerve. All of this "photochemistry" takes a mere 200 femtoseconds to occur making it one of the fastest biochemical to electron transformations known.

Chemists have learned that retinal is highly susceptible to polymerization by localized free radicals and highly reactive singlet oxygen. Because retinal is a strong absorber of light and because the retina is highly vascularized and thus rich in dissolved oxygen, nature has provided zeaxanthin as the key retinal carotenoid for protection of the retina from light induced damage at that point in the center of the retina where the most significant light impingement occurs. Clinical studies in man indicate that photic injury is a cause of age related macular degeneration because of the cumulative effect of repeated photic insult leading to the gradual loss of photoreceptor cells.

Other naturally occurring antioxidants such as ascorbate have been clearly shown to reduce the loss of rhodopsin in animal experiments after exposure to light thereby suggesting that ascorbate (Vitamin C) can protect against retinal injury due to excessive light energy. Indeed high levels of ascorbate are found in retinal tissue in humans.

Therefore, antioxidants which can cross the blood brain/eye barrier would be expected to provide enhanced protection of the retina particularly if the antioxidant can reach the central retinal macula.

One naturally occurring xanthphyll able to cross the blood brain/eye barrier is canthaxanthin, however, scientists have observed that chronic ingestion of canthaxanthin at high doses for extended periods of time leads to the deposition of canthoxanthin crystals in the inner layers of the retina. Therefore, the blood retinal pigment epithelium layer permits only particular carotenoids to enter the retina. Thus only zeaxanthin, lutein and natures most potent carotenoid, astaxanthin, appear to have favorable transport properties while lacking side effects and offering significant antioxidant protection.

There have been many clinical trials designed to support the supplementation of the diet with lutein, however, as of 2007, there appears to be no unequivocal evidence that lutein supplementation is necessary in eye healthcare despite its wide acceptance as a supplement (the current retail market for lutein eye healthcare supplements is approximately $160M). This may simply imply that supplementation with extra lutein is not necessary since it is a readily available xanthophyll in many vegetables. More recently zeaxanthin has also entered the marketplace as an eye healthcare supplement which indeed makes sense.  However, is there yet a better carotenoid meeting all the requirements associated with eye/blood/brain barrier transport, accumulation in the macula and capable of long term use? The answer is yes.

Dr. Mark Tso, at the Univ. of Ill, has clearly demonstrated that astaxanthin is one such naturally occurring antioxidant meeting all of these critical criteria. Astaxanthin is the carotenoid xanthophyll responsible for the red color in salmon, lobster, krill, crab, other shell fish and in the micro algae Haematoccous pluvialis. The latter source has made astaxanthin readily available worldwide for such uses. His work with astaxanthin resulted in the issuance of a US patent (and global equivalents) covering the use of astaxanthin in the prevention of macular degeneration, photic injury, ischemic diseases and inflammatory diseases of the eye and central nervous system.

In addition, astaxanthin turns out to be a much more powerful antioxidant than canthoaxanthin, beta-carotene, zeaxanthin, lutein and alpha-tocopherol. Shimidzu etal. discovered that astaxanthin is 550 times more potent than alpha-tocopherol, 27.5 times more potent than lutein and 11 times more potent that beta-carotene in quenching singlet oxygen. In addition, Bagchi discovered that natural astaxanthin is 14 times more potent than alpha-tocopherol, 54 times more potent that beta-carotene and 65 times more potent that ascorbic acid (Vitamin C) in scavenging oxygen free radicals. Thus, though there are dramatic differences in the potency of astaxanthin when comparing the quenching of singlet oxygen and the scavenging of oxygen free radicals, it is clear that astaxanthin compares very favorably to zeaxanthin and lutein, the two carotenoids that are found naturally in the retina.

There is one more aspect of carotenoids worth mentioning at this point, namely that some carotenoids can act as pro-oxidants. This is important since a carotenoid with pro-oxidant capability actually causes oxidation to occur in the body when high concentrations are present in tissue. Martin, etal., showed that beta-carotene, lycopene and zeaxanthin can become pro-oxidants under certain conditions, however because astaxanthin is the most potent of all carotenoids, Beutner etal. showed that astaxanthin can never be nor has it ever exhibited any pro-oxidant activity unlike the zeaxanthin found in the human eye. This would seem to rule out over-supplementation with zeaxanthin in eye helthcare.

Since humans already have an abundant source of lutein and zeaxanthin in their diets from many vegetable sources and are already present in the human eye, it appears that astaxanthin with its unique properties we have mentioned, unlike lutein or zeaxanthin, should be the eye healthcare supplement of choice. But why you might say?

Only naturally occurring astaxanthin can provide a new and much more powerful layer of antioxidant protection since it is not currently in most human diets unlike lutein and zeaxanthin (unless you eat salmon regularly).

With astaxanthin’s extraordinarily potent antioxidant properties, its ability to cross the blood brain/eye barrier and concentrate in the retinal macula, without the side effects seen with canthaxanthin, and in light of Tso’s contributions, astaxanthin, in a convenient dietary supplement presentation, is now emerging as the pre-eminent alternative to lutein or zeaxanthin eye healthcare supplementation for the management of eye related oxidative stress and thus the prevention and mitigation of degenerative diseases of the eye such as macular degeneration.

In addition, Tso found that light induced damage, photo-receptor cell damage, ganglion cell damage and damage to neurons of the inner retinal layers can be prevented or ameliorated by the use of astaxanthin including neuronal damage from ischemic, photic, inflammatory and degenerative insult.

Tso’s patent claims the use of astaxanthin across a wide range of eye diseases including age related macular degeneration, diabetic neuropathy, cystoid macular edema, central retinal arterial and veneous occlusion, glaucoma and inflammatory eye diseases such as retinitis, uveitis, iritis, keratitis and scleritis, all disease states common to eye insult by oxidative species such as free radicals.

Dr. John Minatelli
Sr. VP Business Development
Valensa International