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United States Department of Agriculture

Agricultural Research Service

Research Project: Phytochemicals and Aging: Bioavailability, Metabolomics, and Bioactivity

Location: Human Nutrition Research Center on Aging

2011 Annual Report


1a.Objectives (from AD-416)
1. Identify and quantify the flavonoid content of: blueberries, cranberries, and grapes; almonds, pistachios, and walnuts; and cocoa-based foods and contribute to future updates of the USDA Database for the Flavonoid Content of Selected Foods. 2. Investigate the effect of age on quercetin bioavailability and metabolism due to changes in phase II enzyme activity. 3. Test whether exposure of rat dams to a “Western” diet during pregnancy and lactation will increase obese phenotypes in their pups and whether dietary flavonoids, particularly isoflavones, will decrease the obese phenotype.


1b.Approach (from AD-416)
Using advanced chromatographic methods, we will measure the flavonoid content and evaluate the total antioxidant capacity of selected plant foods and the influence of geographical regions, agricultural practices, and processing and storage. We will also investigate the bioavailability and chemopreventive properties of flavonoids, particularly anthocyanins, from berry fruit in a mouse model by examining their actions to reduce oxidative stress, modulate cell signaling pathways, decrease inflammation, and promote phase II detoxification. A rat model as well as microsomes from various rat tissues will be utilized to determine the effect of age on quercetin bioavailability and metabolism due to changes in phase II enzyme activity. We will explore the possible fetal origins of chronic disease by feeding obesigenic diets to rat dams during pregnancy and lactation and examine the change in obese phenotypes in their pups and test whether dietary flavonoids, particularly isoflavones, will decrease this phenotype. Using healthy older adults, we will determine the bioavailability and distribution of cranberry anthocyanins to blood, urine, and feces. Employing volunteers with coronary heart disease, we will test the effect of almond consumption on biomarkers of oxidative stress, inflammation, and vascular reactivity.


3.Progress Report

Tree nuts are sources of a wide variety of phytochemicals that are incompletely indexed in nutrient databanks, so we assessed nutrient databank values for tree nut phytochemicals and antioxidants. The content of flavonoids, isoflavones, proanthocyanidins, and total phenols in tree nuts are included in Phenol-Explorer (PE) and USDA databases. PE also reports ellagitannins, phenolic acids, naphthoquinones, and stilbenes. The USDA National Nutrient Database (SR-22) provides carotenoid and sterol content. The “antioxidant capacity” of tree nuts is indexed by the USDA ORAC and University of Oslo FRAP databases. The antioxidant content of tree nuts varies considerably by nut, especially when the pellicle or skin is included in analysis. Total phenols range from 58-1816 mg gallic acid equivalents/100 g. A wide range (in mg/100 g) of polyphenols is also found in oligomeric proanthocyanidins (2-491), flavonoids (0-34), isoflavones (0-4), phenolic acids (0-36), naphtoquinones (0-12), ellagitannins (0-29), and stillbenes (0-0.80). Tree nuts also have significant quantities of phytates (200-2542), sphingolipids (0-613), alkylphenols (0-144), and lignans (0-0.97) that are not presently indexed in databanks. This assessment reveals a need to include more phytochemical classes in nutrient databases and update all the values where such work has not been completed in several years.

We undertook a 12-week clinical trial with a crossover design to investigate the effects of almond consumption on inflammation and oxidative stress biomarkers in 20 Chinese patients with type 2 diabetes and mild hyperlipidemia. After a 2-week run-in period, subjects were randomly assigned to either a NCEP step 2 diet (control) or almond diet for 4 weeks with a 2-week washout period. Almonds were added to the control diet to replace 20% of total daily calories. As compared to the control diet, the almond diet decreased inflammatory biomarkers interleukin-6 and C-reactive protein as well as plasma protein carbonyls,a biomarker of protein oxidation. The almond diet increased the resistance of LDL-cholesterol to oxidation. These results suggest that incorporation of almonds into a healthy diet may decrease the risk of cardiovascular disease in people with diabetes.

We examined the effect of isoflavones on genes and proteins related to energy utilization in muscle. Rats were pair-fed with a control or isoflavone-supplemented diet for 6 weeks. Using real-time polymerase chain reactions, we measured gene expression in gastrocnemius muscle. Cpt1b, a gene that encodes the enzyme required for the transport of coenzymes involved in the metabolism of fatty acids from the cytoplasm into the mitochondria and beta-oxidation, and the activity of citrate synthase, marker of metabolic capacity, were increased as compared to the control diet. In the isoflavone-fed rats, total ACACA protein, which catalyzes the rate-limiting reaction in the biogenesis of long-chain fatty acids, was decreased. These results suggest that isoflavones may enhance metabolic capacity.


4.Accomplishments
1. Hibiscus tea lowers elevated blood pressure. High blood pressure is an established risk factor for heart disease and foods that contribute to reducing this condition present an important approach to this public health problem. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, investigated the antihypertensive effects of hibiscus tea (3 glasses daily) in a randomized, double-blind, placebo-controlled clinical trial of 65 pre- and mildly hypertensive adults not taking any blood pressure lowering medications. After 6 weeks, hibiscus tea significantly lowered systolic blood pressure compared to the placebo beverage. Diastolic blood pressure was also lowered, although this change did not differ statistically from the placebo. The change in mean arterial pressure was of borderline significance compared with placebo. Participants with a higher systolic blood pressure at baseline showed a greater response to hibiscus treatment. These results suggest daily consumption of hibiscus tea, in an amount readily incorporated into the diet, lowers blood pressure in pre- and mildly hypertensive adults and may prove an effective component of the dietary changes recommended for people with these conditions.

2. Cranberry anthocyanins are absorbed in older adults. Research suggests that anthocyanins from berry fruit may affect a variety of physiological responses, including vascular functions, but little information is available regarding the pharmacokinetics of these flavonoids in humans. Characterizing the pharmacokinetics of phytochemicals is an essential step for informing the design of future human studies of plant compounds. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, studied the pharmacokinetics of anthocyanins from cranberry juice in 15 older adults with coronary artery disease. Marked inter-individual differences in plasma anthocyanin pharmacokinetics were observed with maximum concentrations detected between 1 and 3 hours. Cranberry anthocyanins were bioavailable but with notable differences in their maximum concentration and total absorption between individuals. The pattern of anthocyanin glucosides observed in plasma and urine generally reflected the relative concentration determined in the juice. Total recovery of urinary anthocyanin was less than 1% of the dose delivered. These data can now inform the rational design of clinical trials on the putative health benefits of cranberry juice

3. The metabolism of flavonoids may change with age. Age-related changes in the metabolism of flavonoids and other phytochemicals have not been studied. This lack of information represents an important gap in our knowledge about flavonoids as their metabolites appear to be the principal bioactive form of these phytochemicals. Since flavonoids are metabolized extensively by the enzyme UDP-glucuronosyltransferases (UGT), ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, hypothesized that UGT flavonoid conjugating activity changes with age. The effect of age on flavonoid glucuronidation toward the flavonol quercetin and the isoflavone genistein was determined using liver microsomes from rats of different ages (4-, 18- and 28-months). Significant changes were observed in the hepatic metabolite profile produced for both flavonoids with greater changes for genistein than quercetin. The capacity for flavonoid glucuronidation by rat liver microsomes appears dependent on age, UGT isoenzymes and flavonoid structure. Future research in humans is warranted to determine whether the putative health benefits of flavonoids are different between young and older adults. This study is the first demonstration of age-related changes in flavonoid metabolism.


Last Modified: 4/20/2014
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