Abstract
In vertebrates, vitamin K is a cofactor for the gamma-glutamyl carboxylase (GGCX) involved in the carboxylation of glutamic acid residues. During the vitamin K cycle, vitamin K is oxidised by GGCX, and then reduced by vitamin K epoxide reductase (VKOR), which is inhibited by the synthetic coumarin warfarin. GGCX and VKOR are present in Drosophila melanogaster, but the existence of a vitamin K cycle remains unproven. Semi-lethal concentrations (LC50) of K3, menadione sodium bisulfite (MSB), and warfarin to neutralise the negative effect of MSB were selected for the Drosophila cultivation medium. LC-MS analysis was used for vitamin K measurement in flies' extracts. The EPR method and RT-PCR were used for ROS level measurement and gene transcription assessment, respectively. The LC50 of MSB in the medium resulted in a more than 20-fold increase in endogenous K2 in flies, demonstrating the mechanism of K3-to-K2 conversion. Administration of 1 mM warfarin in the medium with MSB completely neutralised its negative effect on viability. Developed flies had decreased K2 level, confirming the existence of a vitamin K cycle, and both reduced ROS level and hsp22 gene transcription. The biochemical pathways affected by elevated K2 concentrations involves both elements of the vitamin K cycle and the adaptive mitochondrial antioxidant system.
