Congratulations to this year’s Dr. Dolittle Travel Award winner, Alex Mohr from Arizona State University! Alex is presenting his research at the annual Experimental Biology conference in Orlando, FL (Mohr AE, Girard M, Rowe M, McGraw KJ, Sweazea KL. Varied Effects of Dietary Carotenoid Supplementation on Oxidative Damage in Tissues of Two Waterfowl Species).
Here is his award-winning blog entry describing his research on carotenoids in ducks:
In relation to tissue and DNA damage, oxidative stress is of great physiological interest and is thought to contribute to the process of aging. Oxidative stress occurs when reactive oxygen species cannot be fully detoxified by antioxidants, thus, cellular structures can become damaged (Nusse y et al., 2009).
In comparison to humans (and mammals in general), birds offer a unique model to study oxidative stress. Common causes of oxidative stress in mammals, such as high blood sugar, are normally present in birds at substantially higher levels. Yet birds are generally resistant to the development of oxidative stress and resultant tissue damage. For instance, glucose levels in birds normally exceed those of mammals of similar body mass by 1.5-2 times (Braun & Sweazea, 2008)!
Animals that maintain high glucose levels, resulting in elevated oxidative stress, would be expected to age at a faster rate than animals with lower glucose. Based on this assumption, birds would be expected to be shorter-lived than mammals of similar body mass. However, when comparing birds and mammals of equal body mass, the longevity of birds exceeds that of mammals (Holmes & Ottinger, 2003).
It is possible that birds are very good at handling oxidative stress or even just have lower production of oxidative stress (Jimenez, 2018). Birds use multiple antioxidant systems, including those produced inside the body and those from the environment, such as dietary vitamin E and carotenoids (Surai, 2002). Dietary carotenoids are yellow, orange and red pigments synthesized by plants. For humans, diets high in carotenoid-rich fruit and vegetables have been associated with reduced risks of cardiovascular disease and
some cancers (Wang et al., 2014; Gallicchio et al., 2008).
However, compared to humans, birds have carotenoid concentrations several times greater. For example, carotenoid concentration in plasma is approximately 1 µg/mL in humans (Kabat et al., 2009) compared to 16 μg/g in mallard ducks (Butler & McGraw, 2010). Maybe carotenoids are largely responsible for their apparent protection against oxidative stress?
Carotenoids are already well-known to be a cornerstone of a bird’s vitality, playing important roles in coloration, sexual selection, development, immunity, behavior and oxidative stress (Simons et al, 2012). Indeed, carotenoid metabolism in birds is far more extensive than what is found in mammals.
A more recent analysis of close to 90 species of birds reported that carotenoid levels were significantly positively related to antioxidant capacity, but not significantly related to oxidative damage (Simons et al., 2012). Currently, the role of carotenoids in oxidative balance is controversial in birds and it remains unclear whether carotenoids play a specific antioxidant role in various tissues and at different dosages.
Our lab recently investigated the effects of three levels of carotenoid supplementation on plasma, liver, fat, heart and muscle tissue oxidative damage in ducks. After a 6-week carotenoid depletion period, adult Northern pintail and mallard ducks of both sexes were fed either a carotenoid-depleted diet, a normal carotenoid-supplemented diet, or an unnaturally high carotenoid-rich diet for 17 weeks. We hypothesized that these different carotenoid dosages would differently affect oxidative damage, between species and sexes and among the tissues examined.
To our surprise, we found no significant effect of carotenoid dose on oxidative damage in males and females from both species. Moreover, for only two tissues (plasma and heart) did we find sex or species differences in oxidative damage. No other significant differences in tissue oxidative damage were observed. These findings align with the notion that carotenoids play a minor role in oxidative balance in birds. Our study suggests that carotenoids do not seem to play an important role in oxidative stress… at
least in adult ducks.
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2. Butler MW, McGraw KJ. Relationships between dietary carotenoids, body tissue carotenoids, parasite burden, and health state in wild mallard (Anas platyrhynchos) ducklings. Arch Biochem Biophys. 2010 Dec 1;504(1):154-60.
3. Gallicchio L, Boyd K, Matanoski G et al. Carotenoids and the risk of developing lung cancer: a systematic review. Am J Clin Nutr. 2008 Aug;88(2):372-83.
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9. Wang Y, Chung SJ, McCullough ML et al. Dietary carotenoids are associated with cardiovascular disease risk biomarkers mediated by serum carotenoid concentrations. J Nutr. 2014 Jul;144(7):1067-74.