Antioxidants for
ocular health How these nutrients are proving beneficial for genetic eye disease. by Dr. Carmen Colitz, DVM, DACVO, PhD and Dr. Terri McCalla, DVM, DACVO
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oday’s dogs seem far more predisposed to cancer and other immune-mediated diseases than dogs in decades past. Conditions like these result from an excess of oxidative stress that cannot be counteracted by the endogenous antioxidant systems of the cells, or by the typical diet. The causes are likely numerous but certainly the quest for the perfect dog in a specific breed has led to many of the genetic diseases we see in veterinary medicine – and ophthalmology. The hybrid or designer breeds now popular are not immune even though the intent was to diminish the genetic issues; unfortunately, this did not entirely happen.
The most common genetic diseases we see in veterinary ophthalmology practice include cataracts, retinal degenerations and glaucoma.1-3 Each breed or group of breeds likely have various mutation(s) that predispose that dog to one or more of these diseases. And unfortunately, you cannot change your genes. Thanks to the Dog Genome Project, the mutations for these diseases are already identified for some breeds, and many more will continue to be identified. The new disciplines of nutrigenomics and nutrigenetics have helped cement nutrients as ways in which to modulate health. Nutrigenomics refers to genetic variation and its dietary response.1 Nutrigenetics refers to the evolutionary aspects of diet and the role of nutrients in gene expression.1 While the impact of diet and nutritional supplementation may not appear to affect inherited ophthalmic diseases in dogs, we might learn that genes that become involved in any of these diseases may be affected by what a dog eats. Likewise, this same concept of genetic variation and genenutrient interaction is important in drug metabolism and adverse reactions to drugs.1 That said, an intake of certain nutrients may directly or indirectly modulate genes, including those that affect eye diseases.
Cataracts While inherited cataracts in dogs are unlikely to be prevented or inhibited by nutriceutical supplementation, antioxidants will improve the environment of the lens cells and possibly reduce secondary sequellae to the
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integrative veterinary care
ensuing oxidative stress caused by cataractogenesis. Some examples of nutrients shown to have aprotective effect on lens epithelial cells and/or cataract development include grapeseed extract, lutein/zeaxanthin, lycopene, zinc and coenzyme Q10. Proanthocyanidins are powerful antioxidants found in grapeseeds, tea, nuts, pine bark and other plant extracts. They have a variety of effects, including free radical scavenging and anti-inflammatory, anti-viral and antimicrobial activities. They also potentiate the function of vitamins C and E.5-7 A strain of rats (ICR/f) predisposed to hereditary cataracts due to lipid peroxidation were fed a diet containing grapeseed extract (GSE). Cataracts were slowed in progression and active glutathione (GSH) was higher in GSE-fed rats as compared to unsupplemented control rats.2 Selenite-induced cataracts, a form of toxininduced cataract, were also significantly slowed or prevented by GSE.3 In vitro studies on lens epithelial cells found that GSE reduced oxidative stress-induced reactive oxygen species production and attenuated stress-induced cell-signaling markers and NF-kB.4, 5 Lutein and its coexistent isomer, zeaxanthin, are oxycarotenoids with two hydroxyl groups on either side of the molecule. They protect ocular tissues against photooxidative stress, quench and scavenge ultraviolet radiation-induced reactive oxygen species, inhibit lipid peroxidation, and filter blue light.6 They are the only continued on page 24
