Location: Jean Mayer Human Nutrition Research Center On Aging
2021 Annual Report
Objectives
Objective 1: Determine the effect of nutritional intervention such as vitamin E on immune and inflammatory responses and resistance to infection using appropriate human and animal models.
Sub-objective 1A: Establish the effects of vitamin E supplementation on the incidence and severity of human rhinovirus infection in healthy community dwelling older adults.
Sub-objective 1B: Understand the mechanistic basis for vitamin E-mediated changes in incidence and severity of common cold.
Objective 2: Determine the life-long effect and underlying mechanisms of food components such as fruits and vegetables on life and health span through longitudinal intervention trials using appropriate animal models.
Sub-objective 2A: Determine the effect of long term fruit and vegetable consumption on key biological functions, pathologies, and median life span in lean and obese mice.
Sub-objective 2B: Determine the underlying mechanism of fruit and vegetable impact on life- and health-span in normal weight and obese mice.
Approach
Aging is associated with dysregulation of immune and inflammatory responses, which contribute to higher morbidity and mortality from several infectious and non-infectious chronic diseases associated with aging. Nutritional status, through maintaining healthy metabolic activity, and immune and inflammatory responses, is a key factor in enhancing health- and life-span. Our long-term goal is to determine the underlying mechanisms of age-related immune and inflammatory dysregulation in order to develop nutritional interventions to prevent/reduce these alterations. Objective 1 will determine the impact and underlying mechanisms of vitamin E on human rhinovirus (HRV)-induced infection (common cold) utilizing a double-blind, randomized, placebo-controlled trial in healthy community-dwelling older adults. Efficacy of vitamin E will be assessed following exposure to HRV by disease incidence and severity, viral shedding, anti-viral immune response, oxidative stress, and expression of signature genes. Objective 2 will determine effect of long-term consumption of fruits and vegetables on median life-span and key immune and metabolic functions at different life stages in an animal model (normal weight and obese mice). Both longitudinal and cross-sectional design will be used to gain insight into causaul relationship between increasing fruits and vegetable consumption and promotion of health- and life-span. Mechanistic investigation will focus on inflammation, oxidative stress, sphingolipid (particularly ceramide) metabolism, and gut microbiota. The results generated from these studies will help develop effective nutritional strategies to delay/mitigate age-related diseases leading to increased health- and life-span.
Progress Report
Previously we showed that supplementing a high-fat diet (HFD) with 15% fruits and vegetables (F&V) – composed of 24 F&V commonly consumed by Americans – prevented HFD-induced non-alcoholic fatty liver disease (NAFLD). Observational studies suggest the potential for higher consumption of fruits and vegetables (F&V) to prevent obesity, improve metabolic and immune health, and expand health- and lifespan. However, causal relation has not been demonstrated, and the mechanisms need to be determined. We are conducting studies to address both of these gaps. Pre-clinical animal studies, using both longitudinal (LG) and cross-sectional (CS) design, were conducted to allow us to determine the effect of F&V on health and median life span, gut microbiota, oxidative stress, ceramides, inflammatory cytokines and T cell profile, using the same groups of lean and obese mice.
Both LG and CS studies have four diet groups (low fat, high fat, without, and with F&V). The LG study (240 mice; 60 mice/group) was started at the beginning of September 2019, and the body weights and food intakes have been recorded at planned intervals without interruption. Based on the weight gain and body composition results thus far, the model works well, and F&V supplementation is effective, i.e., mice fed the high-fat diet had more weight gain and fat mass, which are reduced by F&V supplementation. F&V supplementation does not impact weight gain in mice fed the LF diet. We collected blood samples to perform FACS analysis and isolated plasma for later analysis of sphingolipids, cytokines, and oxidative stress markers. We found that mice fed the HF diet had a significantly lower percentage of total T lymphocytes and helper T cells (also known as CD4-positive cells) than those fed the LF diet. F&V supplementation restored total T lymphocytes and helper T cell population that were impaired by the HF diet. Next, at the 12-month time point, we performed a glucose tolerance test (GTT) on these mice.
Further, we performed a cognitive function test and found that mice fed the HF diet had significantly impaired cognitive function than those fed the LF diet. F&V supplementation prevented HF diet-induced cognitive dysfunction in these mice. At 21-months-old, the death rate in one group (HF diet group) reached 50%. Therefore, as specified in our plans, we terminated all mice in the LG study. Before termination, we infected half of the mice with an influenza virus to determine the response to influenza infection. We then collected blood, urine, and fecal samples as well as organ and tissues such as brain, liver, colon, muscle, etc., from both influenza-infected and uninfected mice for further analysis. We also collected spleen to isolate splenocytes from both influenza-infected and uninfected mice for assessment of ex vivo cytokine production and the ability of lymphocytes to proliferate.
The mice from the 16-month cross-sectional study have now been terminated, and blood and urine samples as well as organs and tissues such as brain, liver, colon, muscle, etc., have been collected for further analysis. We also collected spleens to isolate splenocytes for assessment of ex vivo cytokine production and lymphocyte proliferation.
The forms of iron (mainly ferrous sulfate) currently available have serious adverse effects that limit their use in addressing prevalent iron deficiency. We have been conducting a clinical trial to test whether two novel sources of iron, a nanoparticulate form (IHAT) and a fungal form (Aspiron), would be better choices (in terms of their effects on host susceptibility to malaria and bacterial proliferation, iron utilization, and other adverse effects). The Safe Iron Study is being conducted in two phases; all study-related activities for Phase I have been completed. For Phase II, we met 43 participant visits and sample collection, 7 participants were scheduled for second visits, and 10 were enrolled in the study.
Accomplishments
1. Fruits and vegetables reduce risk of atherosclerosis. The development of atherosclerotic plaque in coronary arteries, is the key pathogenic contributor to cardiovascular disease (CVD), a leading cause of death in the United States. Epidemiologic studies suggest that fruits and vegetable consumption is inversely associated with the incidence of CVD. However, evidence for causality is lacking, and the underlying mechanisms are not well understood. ARS-funded researchers in Boston, Massachusetts, used a mouse model of diet-induced atherosclerosis to determine the effect of high consumption (equivalent to 8 servings in humans) of a variety of fruits and vegetables commonly consumed by Americans to prevent atherosclerosis. They found that mice fed a high-fat and high-cholesterol atherogenic diet supplemented with fruits and vegetables had a 72 percent less atherosclerotic lesion area in their aorta than those fed the atherogenic diet alone. The fruits and vegetable diet's beneficial effect was mediated by normalizing blood lipid levels, reducing inflammation, and increasing the diversity of gut microbiota. These results show that consuming a large quantity and variety of fruits and vegetables causally attenuates diet-induced atherosclerosis and provides evidence-based support for the Dietary Guidelines for American's daily recommendation of 8-10 servings of fruits and vegetables.
Review Publications
Wang, J., Xinli, N., Wu, C., Wu, D. 2018. Naringenin modifies the development of lineage-specific effector CD4+ T cells. Frontiers in Immunology. 9:2267. https://doi.org/10.3389/fimmu.2018.02267.
Inomata, M., Xu, S., Chandra, P., Meydani, S.N., Takemura, G., Philips, J.A., Leong, J.M. 2020. Macrophage LC3-associated phagocytosis is an immune defense against Streptococcus pneumoniae that diminishes with host aging. Proceedings of the National Academy of Sciences (PNAS). 117(52):33561-33569. https://doi.org/10.1073/pnas.2015368117.
