"Chemistry is the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 25: Lipids.
People all over the world are in constant combat against those "evil forces" which cause aging. This article is on a particular study of how our environment lends to the adverse effects of aging on the eye in macular degeneration and focuses on the preventions that should be used to remedy this leading cause for legal blindness in the United States.
Age-related macular degeneration (AMD) is an irreversible disorder that causes a loss of central vision by damage to the macular region of the eye.
There are two types of deterioration that might occur. The less common dry form occurs when the macula becomes thin and speckled with small yellow spots called drusen. The type pertinent to our report is the wet form. In this case, capillaries proliferate under the retinal pigment epithelium and may grow into the subretinal space. These capillaries leak causing detachment of retinal epithelium which will bleed and result in scar tissue. The underlying cause of the latter type is oxidative damage to the delicate cells of the macula through exposure to free radicals in the environment by means of ultra-violet sunlight, tobacco smoke, and blue light. Antioxidants, which are molecules that can donate some of their electrons to stabilize free radicals without becoming free radicals themselves, are the best means of protection against macular degeneration. The carotenoids lutein and zeaxanthin are two antioxidants that specifically reside in the macula to absorb the blue light which is not filtered out by the lens and cornea with ultraviolet light.
Blue light induces photoxidative decay on the retina. Sufficient levels of lutein and zeaxanthin minimize photoxidation and inhibit lipid peroxidation of the retina. After oxidation of lutein, the carotenoid identified as 3-hydroxy-beta, epsilon-caroten-3’-one was found to be the most prevalent oxidative product. The presence of the direct oxidation product of lutein in the human retina suggests that lutein and zeaxanthin may act as antioxidants to protect the macula against short-wavelength visible light. The oxidative-reductive pathways for lutein and zeaxanthin in human retina, may therefore play an important role in prevention of age-related macular degeneration. In seeking prevention of this disease one must supplement their diet with the nutrients lutein and zeaxanthin, which are found in fruits and leafy green vegetables.
Thus lutein and zeaxanthin may protect the macular region from photodamage by inhibiting peroxidation of fatty acids in the retina, and may also preserve the blood vessels that supply the macular region.
Pertinent Text References
Chapter 25-6: Steroids.
Chapter 25-8: Terpenes.
Question 1: According to the article where do free radicals come from?
A: Ultraviolet sunlight, tobacco smoke, and blue light cause molecules in the eye to form free radicals making the eye the area of the body with the highest concentration of free radicals.
Question 2: Which carotenoid(s) is best for preventing macular degeneration?
A: Of the key carotenoids identified in the carotenoid link - alpha carotene, beta carotene, lycopene, lutein, and zeaxanthin - lutein and zeaxanthin have proved to be the carotenoids which reside in and protect the macular region the most. In experiments, altering the levels of the other carotenoids found in the body have not shown any significant differences with the prevention or promotion of AMD.
Question 3: What are the major causes of wet macular degeneration?
A: Free radical damage to tissues in the macula.
Question 4. What is the best way to prevent this disease?
A: Beyond the recommendation to eat lots of fruits and leafy green vegetables (to insure proper intake of lutein and zeaxanthin), other steps can be taken in prevention: wear sunglasses, do not smoke, limit alcohol intake (men six drinks a week and women three drinks per week), and get a daily supplement of zinc.
Question 5. How do lutein and zeaxanthin protect the macular region?
A: Lutein and zeaxanthin absorb free radicals by being oxidized by them. After lutein is oxidized it creates the oxidative product 3-hydroxy-beta, epsilon-caroten-3’-one. The oxidative pathways of lutein and zeaxanthin have been found by experimental and clinical investigation to thicken the macular pigment density and lens density, and in doing so, retard the deterioration of the macular region.