Fig. 5. Effect of the CoQ₁₀-associated ferroptosis suppression pathways on VKD carboxylation.

a Scheme of the FSP1-CoQ₁₀-NADH and DHODH-CoQ₁₀-DHO pathways for ferroptosis suppression. CoQ₁₀ can be reduced to CoQ₁₀H₂ by either FSP1 or DHODH using the reducing equivalent from NADH or DHO, respectively. Reduced CoQ₁₀ traps lipophilic radicals to suppress ferroptosis. NADH reduced nicotinamide adenine dinucleotide, NAD+ oxidized nicotinamide adenine dinucleotide, DHO dihydroorotate, OA orotic acid, PLOOH phospholipid hydroperoxides, PLOO· phospholipid peroxyl radical. b Cell-based VKR activity of FSP1 and DHODH. FSP1 and DHODH were transiently expressed in TKO reporter cells for 24 h for carboxylation activity assay. Wild-type FSP1 activity was normalized to 100%. c Effect of FSP1 inhibitors on VKD carboxylation. Increasing concentrations of FSP1 inhibitors, HQNO or iFSP1, with 11 µM vitamin K were incubated with DKO reporter cells for 24 h for VKD carboxylation activity assay. Carboxylation activity of cells incubated with 11 µM vitamin K without inhibitor was normalized as 100%. d Effect DHODH inhibitors on VKD carboxylation. Increasing concentrations of DHODH inhibitors, BRQ and LFM, with 11 µM vitamin K were incubated with DKO reporter cells for 24 h for VKD carboxylation activity assay. Carboxylation activity of cells incubated with 11 µM vitamin K without inhibitor was normalized as 100%. e Lineweaver–Burk plot of VKR activity in DKO cells as a function of vitamin K concentration in the absence and presence of HQNO. DKO reporter cells were cultured with increasing concentrations of vitamin K containing 0, 0.625, 1.25, 2.5, 5.0, and 10 μM HQNO for the activity assay. Data were plotted using Graphpad software. Data are presented as mean ± SD of three independent experiments (n = 3) in Fig. 5b–d.