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Don't forget the vitamin A when working with its carrier protein
September 29, 2008Vitamin A is an essential nutrient involved in vision, growth, cellular differentiation, and immune function. Because vitamin A is fat-soluble, it is chaperoned through the body on carrier proteins. Researchers at the University of Wisconsin-Madison in a study funded by USDA and NIH, discovered that not only was one of the carrier proteins for vitamin A, retinol-binding protein (RBP), elevated in obese individuals compared to leaner controls, but some of it was not attached to retinol, the main circulating form of the vitamin. RBP that is not bound to vitamin A is called apo-RBP by vitamin A scientists. Their study will appear in the October 08 issue of Experimental Biology and Medicine.
The research team led by Sherry Tanumihardjo, an associate professor of Nutritional Sciences, originally was interested in determining the degree of hypervitaminosis A in the cohort for preliminary data on excessive liver storage of the vitamin. Her graduate student, Jordan Mills, was interested in determining the retinol-binding protein concentrations. While the degree of hypervitaminosis A was remarkable at 4% prevalence for the obese cohort, the relationship of retinol to RBP was a more interesting discovery. The retinol to RBP ratio (retinol:RBP) was significantly lower in the obese subjects than nonobese subjects. This was attributable to more RBP circulating in the serum not bound to vitamin A. RBP was strongly associated with vitamin A in both groups, but more so in the nonobese individuals.
"A series of studies in mice and humans revealed a strong relationship between serum RBP and obesity-induced insulin resistance. While some studies validated these original observations of elevated RBP in obesity and insulin resistance in humans, others have not. Often lacking in these publications are data for serum retinol, arguably RBP's most important physiological companion, representing a possible explanation for conflicting results," said Mills. Tanumihardjo added, "Our results further the understanding of the relationship of retinol, RBP, and BMI and suggest that apo-RBP should be evaluated. Retinol:RBP may add new insights and be a better clinical diagnostic for potential insulin resistance than RBP alone." The authors say, "This elevated serum apo-RBP may be adipose-derived and it is unknown whether it is a direct contributor to insulin resistance in obese individuals. Alternatively, apo-RBP from adipose may transport an unidentified ligand that is responsible for mediating insulin signaling." Further research is needed to determine whether apo-RBP is bound to some other compound in circulation. Dr. Steven R. Goodman, Editor-in-Chief of Experimental Biology and Medicine, said "this interesting study, led by Dr. Tanumihardjo, opens the door to the determination of the role of apo-RBP in insulin resistance in obese individuals. This will be an important issue for those working on type 2 diabetes".
Society for Experimental Biology and Medicine
Society for Experimental Biology and Medicine
Vitamin A Current Events and Vitamin A News RSSVitamin A pushes breast cancer to form blood vessel cells
Researchers at Georgetown University Medical Center have discovered that vitamin A, when applied to breast cancer cells, turns on genes that can push stem cells embedded in a tumor to morph into endothelial cells. These cells can then build blood vessels to link up to the body's blood supply, promoting further tumor growth.
Newborn vitamin A reduces infant mortality
A single, oral dose of vitamin A, given to infants shortly after birth in the developing world can reduce their risk of death by 15 percent, according to a study conducted by researchers at the Johns Hopkins Bloomberg School of Public Health. The study is published in the July 2008 edition of the journal Pediatrics.
Study suggests a little milk could go a long way for your heart
Grabbing as little as one glass of lowfat or fat free milk could help protect your heart, according to a new study published in the American Journal of Clinical Nutrition. Researchers found that adults who had at least one serving of lowfat milk or milk products each day had 37 percent lower odds of poor kidney function linked to heart disease compared to those who drank little or no lowfat milk.
Good news for a fast-wrinkling generation: Some anti-aging methods work
Fine wrinkles, deeper creases, saggy areas around the mouth and neck - the sights in the mirror that make baby boomers wince - are not inevitable. They result from a structural breakdown inside the skin that some existing treatments effectively counteract by stimulating the growth of new, youthful collagen, University of Michigan scientists say.
Antioxidant users don't live longer, analysis of studies concludes
The vitamin industry has long touted antioxidants as a way to improve health by filling in gaps in diet, but a new review of studies found no evidence that the nutrition supplements extend life.
New study shows children benefit from drinking chocolate/flavored milk
A new study released today in the Journal of the American Dietetic Association found that children who drink flavored or plain milk consume more nutrients and have a lower or comparable body mass index (BMI - a measure of body fatness) than children who don't drink milk.
Rutgers Researchers Unlock Mysteries of Vitamin A Metabolism During Embryonic Development
Researchers at Rutgers have unlocked some of the mysteries of how the developing embryo reacts to fluctuations in the amount of vitamin A present in the maternal blood stream. Their results are presented in the February 28 issue of the Journal of Biological Chemistry.
Drinking milk may help ease the pressure
Women who drank more fat free milk and had higher intakes of calcium and vitamin D from foods, and not supplements, tended to have a lower risk for developing hypertension or high blood pressure, according to a new study published in the American Heart Association journal, Hypertension.
Supplementary approach to malaria
Could a simple vitamin A and zinc supplement help protect young children from malaria" A randomized double blind trial reported in the open access publication, Nutrition Journal, would suggest the answer is yes.
Team finds an economical way to boost the vitamin A content of maize
A team of plant geneticists and crop scientists has pioneered an economical approach to the selective breeding of maize that can boost levels of provitamin A, the precursors that are converted to vitamin A upon consumption.
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