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United States Department of Agriculture

Agricultural Research Service

Senior Scientist Biographies
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Earl Harrison, Research Leader

My laboratory studies enzymes that hydrolyze lipid esters, with a focus on their role in regulating cellular accumulation and turnover of lipids. Some of these enzymes function as retinyl ester hydrolases (REHs) and are important in both the uptake of dietary vitamin A by the liver and in the mobilization of stored vitamin A from the liver. Although a number of liver enzymes can catalyze the hydrolysis of vitamin A esters the molecular identity and physiological role of these enzymes is unclear. Our research attempts to fill these gaps in knowledge by isolationg these proteins and studying their structure and function using techniques of biochemistry and molecular biology. Recent work focuses on the identification and characterization of carboxylesterases ES2 and ES10 as the neutral and acid REHs involved in the uptake of chylomicron retinyl esters in liver.

We also study the intestinal absorption, transport, metabolism and function of dietary carotenoids using cell culture models and investigations in human subjects. We are particularly interested in defining the proteins involved in the uptake and metabolism of dietary carotenoids in the intestine. Recent accomplishments include the demonstration of the facilitated uptake of carotenoids in CaCo2 cells in culture and the cloning of the enzyme that cleaves beta-carotene to vitamin A. We are also pursuing the role of carotenoids in LDL oxidation and vascular cell function, with the goal of elucidating the mechanisms by which dietary carotenoids may decrease the risk of atherosclerosis.

A new area of investigation involves the use of proteomic profiling of plasma, using surface-enhanced laser desorption and ionization (SELDI)--time-of-flight (ToF) mass spectrometry, to define new biomarkers of nutritional status in experimental animal models and in humans.

Research Projects: Metabolism of Vitamin A and Carotenoids

Hydrolysis of Vitamin A Esters in Liver

Dietary Vitamin A, Carotenoids and Cancer


Steve Britz, Plant Physiologist

Investigates the influence of environment on phytonutrient composition and variability in crops; develops methods for the isotopic labeling of crops for use in feeding studies to determine bioavailability and metabolism of phytonutrients.

Research Projects: Phytochemical Responses to the Environment: Implications of Global Change in Human Nutrition

Bioavailability and Metabolism of Phytochemicals and Micronutrients


Charles Caldwell, Plant Physiologist

Research Project: Phytochemical Responses to the Environment: Implications of Global Change in Human Nutrition


Jae Park, Research Chemist

Investigates the transport mechanisms of phytonutrients, and determines bioavailability from foods, in humans. Assesses the physiological role of phytonutrients and the molecular mechanisms of phytonutrients in human cells.

Research Project: Molecular Basis of Absorption, Interaction, and Functions of Flavonoids in Human Cells.


Thomas Wang, Research Chemist

Pursues a mechanism based cancer prevention approach. His projects focus on understanding the mechanism(s) by which phytochemicals alter the development of cancer. Both cell culture and whole animal model are employed and specific pathway that related to apoptosis, xenobiotic metabolism and hormone/cytokines actions examined using molecular and biochemical techniques.

Research Project: Molecular Basis of Absorption, Interaction, and Functions of Flavonoids in Human Cells.


Last Modified: 4/8/2005
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