Location: Immunity and Disease Prevention ResearchTitle: Dietary supplementation with purified citrus limonin glucoside does not alter ex vivo functions of circulating T lymphocytes or monocytes in overweight/obese human adults
|FREYTAG, TAMMY - UNIVERSITY OF CALIFORNIA|
|BONNEL, ELLEN - UNIVERSITY OF CALIFORNIA|
Submitted to: Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2015
Publication Date: 1/1/2016
Citation: Zunino, S.J., Storms, D.H., Freytag, T.L., Adkins, Y.C., Bonnel, E.L., Woodhouse, L.R., Breksa III, A.P., Manners, G.D., Mackey, B.E., Kelley, D.S. 2016. Dietary supplementation with purified citrus limonin glucoside does not alter ex vivo functions of circulating T lymphocytes or monocytes in overweight/obese human adults. Nutrition Research. 36(1):24-30.
Interpretive Summary: Citrus fruits contain compounds called liminoids that have health benefits to humans and may be important for preventing the development of inflammatory diseases, such as cardiovascular disease. Overweight/obese people have a higher risk for developing many diseases and infections. In a human feeding study with 10 overweight/obese volunteers, we tested the effects of the liminoid limonin glucoside on immune functions. Several parameter of immune function were evaluated after a 56 day feeding of beverages containing limonin glucoside or placebo preparation. Blood was collected after the 56 day feeding periods and immune cells were isolated. T cells were activated with antibodies that bind to the cell surface and cause proliferation and secretion of molecules called cytokines that regulate immune responses. Monocytes, which are part of the first line of defense against bacteria and viruses, were isolated and activated with a component of bacterial cell wall (lipopolysaccharide). The production cytokines was measured to show the activation status of the T cells and monocytes. The cytokines interferon-', tumor necrosis factor-', interleukin-2, interleukin-4, and interleukin-10 were measured for the activated T cells. The cytokines tumor necrosis factor-', interleukin-1', and interleukin-6 were measured for the activated monocytes. The percent of CD14+CD36+ cells in whole blood was analyzed by flow cytometry. Also, the activated T cells were stained with a fluorescent dye to measure the number of cell divisions that occurred after activation. The cell divisions of the two subpopulations of T cells were measured using a fluorescence-activated cell sorter. The two subpopulations that were measured were helper T cells (CD4+) and cytotoxic T cells (CD8+) which help clear cancer cells and cells infected with viruses. No differences were observed for the production of T cell cytokines or monocyte cytokines between the periods when volunteers drank the placebo or limonin glucoside beverages. No differences in cell division were observed between the two treatments. These results suggest that limonin glucoside found in citrus fruits does not directly alter immune function, at least with the methods used in this study. However, limonin glucoside was reported in this study to decrease circulating levels of inflammatory proteins and liver enzymes, and this citrus product may be important for the prevention of several inflammatory or metabolic diseases.
Technical Abstract: Overweight/obesity is associated with chronic inflammation and impairs both innate and adaptive immune responses. Limonoids found in citrus fruits have shown health benefits in human and animal studies. In a double-blind, randomized, crossover study, 10 overweight/obese human subjects were fed purified limonin glucoside or a placebo as beverages for 56 days each to determine the changes in different parameters of immune function. The percent of CD14+CD36+ cells in whole blood was analyzed by flow cytometry. Peripheral blood mononuclear cells (PBMCs) were isolated and activated with CD3 plus CD28 antibodies (T lymphocyte activation) or lipopolysaccharide (LPS, monocyte activation). Interferon-' (IFN-'), TNF-', IL-2, IL-4, and IL-10 were measured in supernatants from activated T cells. Supernatants from activated monocytes were analyzed for the production of TNF-', IL-1', and IL-6. PBMCs were prestained with PKH dye and activated with CD3 plus CD28 antibodies to determine the proliferative responses of CD4+ and CD8+ T lymphocytes by flow cytometry. No differences were observed for CD14+CD36+ monocyte populations, T cell proliferation, or the production of T cell and monocyte cytokines between the two treatments. These data suggest that dietary supplementation with purified limonin glucoside does not directly affect circulating T cells or monocyte functions from overweight/obese individuals, even if it decreased several markers of hepatic inflammation as we have previously reported.