Extent of vitamin K absorption from the equine hindgut

Extent of vitamin K absorption from the equine hindgut

Vitamin K consists of a group of structurally related compounds: phylloquinone (K1), that is synthesized by plants; the menaquinones (MKs also known as K2) synthesized by bacteria and menadione (K3), a synthetic vitamer that does not have a sidechain. There is increasing evidence that vitamin K has a significant role in bone metabolism, energy metabolism, spermatogenesis, apoptosis and innate immunity, in addition to blood coagulation. The lack of a side chain restricts the activity of K3 to a role in blood clotting. The consensus is that animals meet their vitamin K requirements from plant and bacterial sources. Bacterial synthesis and subsequent absorption of K2 is generally considered to be an important source of vitamin K and yet there are no published reports of the extent and efficiency of these processes. The aim of this study was to determine if vitamin K is absorbed from the hindgut of the horse. Vitamin K1 was coated with calcium alginate to prevent absorption in the small intestine thus allowing it to pass into the hindgut. Four mature geldings were dosed with a 200 mg oral of either (1) KQ [QAQ, Quinaquanone a soluble form of K1 and K2 (10:1)]; (2) KQ coated with 1.5% calcium alginate; or (3) K1 oil. Blood sampling was undertaken for 12 h and plasma samples were analyzed by HPLC for K1, MK-4 and K3 concentrations. In vitro studies with enzymes (amylase, protease, lipase, and cellulase) showed minimal release of K1 and breakdown of the alginate capsule over a period of 10 h. In contrast, when incubated with a concentrated microbial fraction of horse feces, breakdown of the alginate capsule was complete within 30 min. Plasma K1 concentrations differed significantly between treatments (P < 0.05). Plasma K1 concentrations were 3-fold higher in the KQ treatment compared with K1 oil and K1 oil was higher than the encapsulated KQ; peak plasma values occurred for all 3 treatments at 4 h. The results of this study questions the absorption of vitamin K from the hindgut of the horse. It shows that the intestines are partly responsible for the breakdown of the capsule with encapsulated KQ reaching a Cmax of 1.5 ng/mL as opposed to 3.75 ng/mL for KQ at 4 h. There was no further uptake of K1 from the spheres in the hind gut, suggesting that the hind gut does not facilitate vitamin K absorption in the horse. Studies in rats and humans have also demonstrated extremely poor absorption of vitamin K from the hindgut suggesting that bacterially synthesized vitamin K does not contribute substantially to vitamin K status.

Abstract #59.