Egg-Mediated Bioavailability of Plant-Derived Vitamins E and K in Humans: Development of Deuterium-Labeled Spinach

OBJECTIVES: While plant-centric diets are recommended for health, they often lack accessible fat to facilitate absorption of the shortfall nutrients vitamin E (α-tocopherol; α-T) and vitamin K (phylloquinone, PK). Because effective pairing of plants with lipid-containing foods, such as eggs, could help achieve α-T and PK nutriture, our objective was to establish a deuterium-labeled spinach model to study the bioavailability of plant-derived α-T and PK in humans. METHODS: Spinach was grown hydroponically with 30% deuterium oxide prior to harvesting twice at 6- and 10-weeks post-germination. Harvested leaves were washed, chopped, cooked, portioned, vacuum-sealed, and stored at −20°C until consumed. HPLC-ECD and LC-MS analyses were performed to assess nutrient concentration and isotopomer profile. In a pilot study focusing on α-T, a healthy female co-ingested cooked deuterium-labeled spinach (containing 3 mg α-T) with 0, 1, 2, and 3 eggs prior to timed blood collections over 72-h to assess dose-dependent effect of eggs on α-T bioavailability. Eucaloric diets controlled for α-T and PK were provided for 3 days prior to and during the initial 24 h of each 72-h trial. Deuterium-labeled α-T from plasma collected at each time point were analyzed by LC-MS. RESULTS: Cooked deuterium-labeled spinach contained 7.2 ± 0.4 mg α-T/100 g. Isotopomer profiling of spinach indicated that 100% of α-T and PK were deuterium-labeled, with 63–66% as hexa- (d(6)-) to deca- (d(10))-deuterium-labeled α-T and PK. Plasma isotopomer profiles of nutrients did not differ from spinach profiles. Pharmacokinetic profiling showed that α-T reached T(max) at 12 h regardless of the quantity of eggs co-ingested. Greater plasma α-T bioavailability was observed following co-ingestion of spinach with 2 or 3 eggs compared with 0 or 1 egg. CONCLUSIONS: These data demonstrate feasibility of deuterium-labeled spinach for use in human bioavailability studies. Proof-of-concept findings support a large-scale clinical bioavailability study, which is actively underway with a goal of establishing an effective food pairing-based dietary strategy to mitigate vitamins E and K inadequacy. FUNDING SOURCES: Egg Nutrition Center and OSU Center for Applied Plant Sciences.