Increased cytokine production by monocytes from human subjects who consumed grape powder was not mediated by differences in dietary intake patterns

Authors: Zunino, Susan; Keim, Nancy; Kelley, Darshan; BONNEL, ELLEN - University Of California; SOUZA, ELAINE - University Of California; PEERSON, JAN - University Of California

Submitted to: Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2017
Publication Date: 3/3/2017
Citation: Zunino, S.J., Keim, N.L., Kelley, D.S., Bonnel, E.L., Souza, E.C., Peerson, J.M. 2017. Increased cytokine production by monocytes from human subjects who consumed grape powder was not mediated by differences in dietary intake patterns. Nutrition Research. 40:32-39.

Interpretive Summary: Obesity increases the risk of developing heart disease, diabetes, and also bacterial and viral infections compared to people with normal weight. In a 9 wk human study, twenty-four obese volunteers were fed a grape powder or a placebo powder to determine effects of dietary grapes on cells of the immune system. Monocytes are immune cells that are part of the first line of defense against invading pathogens. In our study with grape powder, we found that the production of monocyte proteins, interleukin-1' and interleukin-6, was increased in the activated monocytes from the group of human volunteers consuming grape compared to the placebo group. These data suggest that the grape powder increased the sensitivity of monocytes and this increased sensitivity may reduce the risk for developing infections in obese individuals. However, we needed to show that the food consumed by the volunteers during the course of the study was not responsible for our observations on monocyte function. We used dietary recalls that were conducted during our study to evaluate if there were changes in diets during our study. Dietary recalls consisted of telephoning the subjects three times when they were taking the grape powder and three more times when they were taking the placebo powder, and asking detailed questions about what the subject had eaten in the last 24 h period. Using these dietary recalls, we analyzed the responses and calculated the amounts of different foods that were consumed by each subject. We found that there were no differences in dietary intake that could account for the increased monocyte function observed when the volunteers consumed the grape powder. This information further supported our hypothesis that the components of grapes were responsible for the increased function of these immune cells and that fruits may contain compounds that can help monocytes fight infections in obese individuals.

Technical Abstract: Recently, in a randomized, double-blind cross-over study, we reported that consumption of grape powder by obese human subjects increased the production of the pro-inflammatory cytokines interleukin-1' and interleukin-6 by ex vivo-derived peripheral blood monocytes after exposure to bacterial lipopolysaccharide (LPS) compared to the placebo treatment. Using 24 h dietary recall data collected during this study, we determined if differences in dietary patterns by the subjects played a role in increased cytokine production. No significant differences in total energy, protein, carbohydrates, or fat intake in the diets were observed between the grape powder and placebo intervention periods. A decrease in butyric and capric acid intake was observed in the grape powder period compared to the placebo period (P < 0.05). There were no differences observed in consumption of meats and poultry, eggs, fish, vegetables, grains, total dairy, or nuts and seeds by the subjects between the two intervention periods. Path analysis showed that total energy, protein, carbohydrates, fat, and individual saturated, monounsaturated, or polyunsaturated fatty acids did not influence the production of pro-inflammatory cytokines by monocytes. However, positive associations between the intake of margaric acid which is found in dairy products, butter, total dairy, and whole grain and IL-6 production by monocytes were observed (P < 0.05). The path analysis suggests that increased cytokine production observed in LPS-treated monocytes from subjects consuming grape powder was not due to diet and supports a role for components of grapes in altering monocyte function.