(Co-)Encapsulation and vitamin-phytochemical interaction modulate bioaccessibility, absorption and bioefficacy of fat-soluble vitamins in vitro

Fat-soluble vitamins are generally characterized by their low bioavailability, therefore supplementation is advised for groups with special metabolic demands, such as elderly individuals or growing children. Here, we evaluated the impact of micellization and the joint addition of certain natural plant extracts on the bioaccessibility, intestinal absorption and bioefficacy of fat soluble vitamins.
Vitamin D3 (cholecalciferol), D2 (ergocalciferol), E (alpha tocopheryl acetate), and K2 (menaquionone-7) were tested in intestinal Caco-2 or buccal TR146 cells in combination with curcuma (Curcuma longa), black pepper (Piper nigrum), or ginger (Zingiber officinale) plant extracts. Bioaccessibility of Vitamin D2 was evaluated by static in vitro simulated digestion according to the INFOGEST protocol, while vitamin uptake was quantified by HPLC-MS and bioefficacy was determined via gene expression analyses.
Micellization had a beneficial impact on in vitro intestinal absorption of all tested vitamins. Buccal absorption of Vitamin E acetate was not affected by micellization, while micellated vitamins D2/D3 and K2 showed increased uptake characteristics in the buccal model. Plant extracts divergently interacted with vitamin absorption and metabolization. Curcuma extract increased uptake of vitamin D2 and D3, but adversely affected their bioefficacy, measured by expression of genes involved in calcium transport. Black pepper and ginger extracts increased the uptake of Vitamin E acetate, with the former influencing its conversion to free alpha tocopherol. Finally, ginger extracts increased both absorption and bioefficacy of Vitamin K2, measured in cellular NO production.
Our data substantiate the positive effects of micellization on fat-soluble vitamin bioaccessibility, absorption and bioefficacy in vitro. Co-encapsulation and co-administration with phytochemicals and plant extracts has the potential to further improve vitamin bioavailability, but further studies are warranted to elucidate vitamin-specific effects.