2011 Annual Report
1a.Objectives (from AD-416)
Objective 1: Conduct a controlled, vitamin D supplementation trial in volunteers with vitamin D insufficiency (VDI) to determine if supplementation to achieve the proposed level of >75 nmol/L for maintenance of bone health is also appropriate for maintenance of immune function. Sub-objective 1A. Determine if supplements decrease the production of proinflammatory and increase the production of anti-inflammatory cytokines and chemokines by innate immune cells stimulated ex vivo. Objective 1B. Determine if supplements decrease serum markers of inflammation and autoimmune activity, and increase serum levels of defensive molecules. Objective 1C. Determine if supplements decrease blood levels of proinflammatory T-helper type 1 (Th1) and Th17 cells and increase levels of anti-inflammatory T-regulatory (Treg) and Th2 cells.
Objective 2: Determine the impact of plant polyphenols and polyphenol-rich foods on immune cell function using cell culture systems, mouse models, and human volunteers. Examine anti-inflammatory and anti-cancer activities of polyphenols in animal models, as well as inflammation and oxidative damage in studies with human volunteers, including overweight/obese individuals. Objective 2A. Analyze the effects of polyphenol-rich foods and individual plant polyphenols on immune cell function in vivo and ex vivo. Ojective 2B. Examine anti-inflammatory activities of polyphenol-rich foods, individual plant polyphenols and vitamin A in mice and humans who are at risk for developing inflammatory disease, such as autoimmune mice and obese humans. Objective 2C. Evaluate the anti-cancer activity of polyphenol-rich foods and individual plant polyphenols.
Objective 3: Examine the absorption of B-cryptoxanthin (CX) from supplements and foods, its contribution to vitamin A stores, and the impact of CX, other carotenoids and vitamin A on immune function. Objective 3A. Measure the absorption and metabolism of CX from Satsuma mandarin juice fed to healthy adult humans. Objective 3B. Estimate the impact of daily consumption of food sources of CX or B-carotene (BC) on plasma and breast milk concentrations of CX, BC and retinol in lactating women. Objective 3C. Determine the impact of CX on immune and bone marker status in the Mongolian gerbil.
Objective 4: Determine if high-level vitamin A intake is associated with higher Th2 and Treg responses and lower Th1 and Th17 responses relative to adequate and deficient intake. Objective 4A. Using dietary and targeted gene disruption approaches in mice, determine if vitamin A enhances Th2 and Treg responses by acting directly on T cells. Objective 4B. Using subjects recruited in the vitamin D supplementation trial described under Objective 1, determine if vitamin A status is associated with higher blood levels of NK, NK-T, Th2 and Treg cells, and lower levels of Th1 and Th17 cells.
Objective 5: Identify the role of dietary selenium and selenoproteins in regulating cellular responses to oxidative stress. Objective 5A. Identify the pro-inflammatory and anti-inflammatory proteins S-glutathionylated by selenoprotein W. Objective 5B. Determine the role of selenoprotein W in key inflammatory pathways.
1b.Approach (from AD-416)
The impact of selenium, vitamins A and D, and plant polyphenols, on immune function will be examined using cell culture systems, mouse models, and human intervention trials. The anti-cancer activities of polyphenols will be examined in animal models. Absorption of beta-cryptoxanthin will be examined in gerbils and humans. The effect of selenium on cell division and cell signaling will be examined in cell culture.
Objective 1: A pilot study of eight subjects to establish methods for measuring the production of cytokines by vaccine-specific T cells was completed. We began recruitment of subjects with vitamin D insufficiency for the main study. By the end of July, 188 subjects had been screened for enrollment by telephone, 21 had come for screening visits, ten had enrolled and six had completed the study. Enrollment is slower than planned and we have thus expanded recruitment from Davis to Sacramento and are now specifically recruiting African Americans due to their greater risk of vitamin D insufficiency.
Objective 2: (1) Analysis of data from our previously completed human trial showed that consuming strawberries increased the number of cytotoxic T cells and the production of the cytokine tumor necrosis factor, both being important for immune responses to bacteria and viruses. A second study is in progress to evaluate the effect of grapes on inflammation in people at risk for cardiovascular disease. (2) The High Bush Blueberry Council awarded a grant to determine if blueberries will decrease the inflammatory response to a fatty meal. Data analysis from earlier studies with a mouse model for diet-induced obesity and diabetes found that feeding strawberries reduced blood glucose and serum C-reactive protein. (3) Data analysis from earlier mouse studies found that feeding purified polyphenols at levels higher than found in foods did not kill leukemia cells. Thus the diet studies planned for this year with polyphenol-rich foods will not be pursued as this approach is likely to be ineffective.
Objective 3: (1) In vitro methods were developed to analyze carotenoid and retinoid absorption from foods, including sweet potatoes, cassava and mandarin oranges. The methods are being modified for use with an “artificial stomach” model to better predict absorption. (2) Enrollment for the beta-cryptoxanthin study is complete. Laboratory and data analysis is in progress. Baseline characteristics did not differ between groups, showing that randomization was effective. (3) New extraction and chromatography methods were developed for small amounts of tissues, and tissue samples are being analyzed from the gerbil study.
Objective 5: We developed a method to measure selenoprotein W1 in cell culture to determine if silencing its transcription also decreases protein levels, which was confirmed. We then explored how this silencing causes cell cycle arrest, a phenomenon that we reported previously in epithelial cells whose growth is stimulated by epidermal growth factor. Briefly, silencing promotes a cascade of events including activation of the enzyme p38 to add phosphate residues to the regulatory protein p53 on serine 33 and 46. This blocks p53 degradation and allows its accumulation in the nucleus where it induces p21 gene transcription. The protein p21 then induces arrest. We also found that selenoprotein W1 was associated with the epidermal growth factor receptor complex, and that cell cycle arrest was not due to loss of antioxidant activity or DNA damage.
Strawberries and type 2 diabetes. Loss of control of blood sugar (glucose), as occurs in type 2 diabetes, leads to adverse health consequences which might be ameliorated by improving diet quality. ARS scientists at the Western Human Nutrition Research Center in Davis, California, determined that feeding a diet containing strawberry powder (prepared from whole freeze-dried strawberries) reduced blood glucose levels in both lean and obese mice, and reduced C-reactive protein in lean mice. A mouse model for diet-induced obesity and diabetes was used for these studies to represent humans consuming high dietary fat. Eating strawberries may thus be beneficial for controlling blood sugar in obese humans with type 2 diabetes
Selenoprotein W1 and the cell cycle. Selenium deficiency causes immune deficiency and other adverse health outcomes but the role of specific selenoproteins in mediating such effects is largely undefined. ARS scientists at the Western Human Nutrition Research Center in Davis, California, have examined the role of selenoprotein W1 in a basic cellular process, signaling from a cell-surface receptor, the epidermal growth factor receptor, to regulate cellular proliferation. The scientists found that selenoprotein W1 is required for epidermal growth factor signaling and thus for cellular proliferation, and that selenoprotein W1 is associated with three proteins that are components of the activated epidermal growth factor receptor complex. Because selenoprotein W1 is decreased by low dietary intake of selenium this mechanism may explain, at least in part, the relationship between low dietary selenium intake and decreased immune function.
Methods to study the effect of diet on vaccine responses. Vaccine-specific T cells are rare in peripheral blood and it is thus difficult to measure the effect of nutritional interventions on aspects of T cell-mediated immunity that have been well-studied in animal model systems. To address this problem, ARS scientists at the Western Human Nutrition Research Center in Davis, California, have tested a method to expand and subsequently identify cytokine production from vaccine-specific T cells from peripheral blood, following one week of amplification in cell culture. Using this method in healthy adults the scientists found a broader than expected pattern of cytokine production by tetanus vaccine-specific T cells, including cytokines from the major groups of T-helper (Th) cells, including Th1, Th2, Th17 and Treg cells. These methods can now be used in nutritional intervention studies to characterize the effect of diet on immune function and resistance to infection or autoimmune disease.
Availability of vitamin A-forming carotenoids from foods. The amount of vitamin A that carotenoid containing foods provide depends not only on the amounts of the carotenoid in the food, but also on how well the carotenoids are absorbed. ARS scientists at the Western Human Nutrition Research Center in Davis, California, used in-vitro digestion methods to compare the apparent bioavailabilities of mandarin oranges and sweet potatoes, excellent dietary sources of the vitamin A-forming carotenoids beta-carotene, and beta-cryptoxanthin, respectively. Beta-cryptoxanthin from mandarin oranges was approximately 240% more bioavailable than beta-carotene from sweet potatoes. This result supports earlier research showing that eating comparable amounts of beta-cryptoxanthin and beta-carotene-rich foods resulted in much higher beta-cryptoxanthin concentrations in the blood. This suggests that beta-cryptoxanthin-rich foods, which include citrus fruit, might be better sources of vitamin A than has traditionally been expected based on their relatively low abundance in the diet.
Strawberries and resistance to infectious diseases. Understanding how specific foods promote good health will improve the quality of dietary recommendations. ARS scientists at the Western Human Nutrition Research Center in Davis, California, determined that feeding strawberries to obese individuals increased their cytotoxic T cell response and the production of tumor necrosis factor alpha by monocytes. Cytotoxic T cells and monocytes are important for preventing bacterial and viral infections. Obese individuals are at higher risk for infections than normal weight people. Eating strawberries may be a means of balancing important immune responses in individuals who are at risk for developing infections.
Burri, B.J., Chang, J., Neidlinger, T.R. 2011. Beta-Cryptoxanthin- and alpha-carotene-rich foods have greater apparent bioavailability than beta-carotene-rich foods in Western diets. British Journal of Nutrition. 105:212-219.
Burri, B.J. 2011. Evaluating the sweet potato as an intervention food to prevent vitamin A deficiency. Comprehensive Reviews in Food Science and Food Safety. 10:118-130.
Makhoul, Z., Kristal, A.R., Gulati, R., Luick, B., Bersamin, A., O'Brien, D., Hopkins, S.E., Stephensen, C.B., Stanhope, K.L., Havel, P.J., Boyer, B. 2011. Associations of obesity with triglycerides and C-reactive protein are attenuated in adults with high red blood cell eicosapentaenoic and docosahexaenoic acids. European Journal of Clinical Nutrition. 65(7):808-817. Available: http://www.nature.com/ejcn/journal/v65/n7/full/ejcn201139a.html
Stephensen, C.B., Armstrong, P., Newman, J.W., Pedersen, T.L., Legault, J., Schuster, G., Kelley, D.S., Vikman, S., Hartiala, J., Hooman, A. 2011. ALOX5 gene variants affect eicosanoid production and response to fish oil supplementation. Journal of Lipid Research. 52(5):991-1003.
Hartiala, J., Li, D., Conti, D.V., Vikman, S., Patel, Y., Tang, W., Brennan, M., Newman, J.W., Stephensen, C.B., Armstrong, P., Hazen, S.L., Allayee, H. 2011. Genetic contribution of the leukotriene pathway to coronary artery disease. Human Genetics. 129(6):617-627.
Sharkar, M., Jou, M., Hossain, M.B., Lonnerdal, B., Stephensen, C.B., Raquib, R. 2011. Prenatal zinc supplementation of zinc-adequate rats adversely affects immunity in offspring. Journal of Nutrition. 141(8):1559-1564.
Burri, B.J., Chang, J.S., Turner, T. 2011. Citrus can help prevent vitamin A deficiency in developing countries. California Agriculture. 65(3):130-135.