(P03-067-23) Deuterium-Labeled Spinach as a Plant Model for Studying Food Matrix Interactions on Vitamin E Bioavailability in Humans

Objectives: The bioavailability of plant-based fat-soluble antioxidants, such as vitamin E (α-tocopherol; α-T), is expected to be poor because insufficient lipids are present to facilitate absorption. Food pairing with lipid-containing foods, such as eggs, could help to enhance the bioavailability of plant-based fat-soluble antioxidants. While others have examined this paradigm, intrinsically labeled α-T within a plant matrix was not used to accurately assess α-T bioavailability in response to eggs. The objective was to establish deuterium-labeled spinach, which is α-T-rich, as a tool to examine the food matrix interactions on α-T bioavailability in humans.

Methods: Spinach was grown hydroponically in 30% deuterium oxide. In a pilot study, healthy adults completed a 4-arm crossover study in which they ingested: 1) deuterium-labeled spinach (5 mg α-T; SPIN); 2) spinach + 2 whole eggs (SPIN+EGG; 3) spinach + 2 egg whites (SPIN+EW); 4) spinach + vegetable oil (SPIN+VO) at 9.6 g, which is equivalent to fat in 2 whole eggs. Plasma was collected prior to and after test meal ingestion at timed intervals for 72 h to determine pharmacokinetic parameters following LC-MS analysis.

Results: Spinach α-T was 100% intrinsically labeled at 6-wk of harvesting. d₅- to d₁₁-α-T (d_x-α-T) represented ~80% of all labeled isotopomers (d₁- to d₁₅-α-T), and these were selected for monitoring in the human pharmacokinetic study. Participants had adequate plasma α-T status (29.9 ± 5.1 μM) at study enrollment. For all trials, plasma d_x-α-T C_max was 220-580 nmol/L and occurred at a T_max of 8-12 h. Plasma d_x-α-T AUC_{0-72 h} in SPIN showed the highest inter-individual coefficient of variation (85%) compared with other study arms (28%).

Conclusions: These findings demonstrate that spinach grown with 30% deuterium oxide is deuterium-labeled in a manner suitable for clinical studies examining food matrix interactions on α-T bioavailability. Data have informed the planning and design of our underway large-scale clinical trial that will determine how eggs and other lipid sources influence plant-based α-T bioavailability.

Funding Sources: Egg Nutrition Center and OSU Center for Applied Plant Sciences