M. Veliky¹, I. Shymanskyi¹*, O. Lisakovska¹, A. Khomenko^1,
Yu. Parkhomenko¹, Ye. Kucheriavyi², V. Bilous³

¹Department of Biochemistry of Vitamins and Coenzymes, Palladin Institute
of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
²Department of Protein Structure and Function, Palladin Institute
of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
³Department of Enzyme Chemistry and Biochemistry, Palladin Institute
of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
*e-mail: ihorshym@gmail.com

Received: 11 January 2026; Revised: 19 February 2026;
Accepted: 03 April 2026; Available on-line: April 2026

The liver plays a central role in vitamin D metabolism, facilitating its primary activation and systemic transport. However, the molecular mechanisms of vitamin D hydroxylation and reception involving the auto-/paracrine vitamin D system in the liver remain insufficiently understood. The aim of the study was to evaluate cytochrome P450 (CYP) enzymes and vitamin D receptor (VDR) expression in the liver of rats with nutritional vitamin D₃ deficiency and after therapeutic treatment. Vitamin D deficiency was modeled by maintaining female Wistar rats on vitamin D-free diet for 60 days. The treatment was performed by cholecalciferol (1000 IU/kg bw) oral administration for 30 days. Serum 25(OH)D level was determined by ELISA, 25-hydroxylase activity in hepatocytes was evaluated using [³H]cholecalciferol as a substrate. The level of CYP2R1, CYP27A1, CYP27B1, CYP24A1 and VDR proteins in the liver was studied via Western blot analysis. A 60-day vitamin D-deficiency led to a critical decrease in 25(OH)D level in the serum, significant increase in 25-hydroxylase activity, CYP2R1 and VDR expression, against the background of reduced CYP24A1 level, in the liver. Vitamin D₃ administration ensured the restoration of serum 25(OH)D, as well as the level of the molecular markers­ of vitamin D transformation and reception in the liver, except for CYP27B1, which maintained mode­rately elevated expression. Thus, the metabolic adaptation under vitamin deficiency was manifested through compensatory enhancement in vitamin D synthesis and increased receptor sensitivity against the background of suppressed catabolic pathways. Nutritional correction effectively restored the balance in the auto-/paracrine vitamin D system, ensuring stable homeostasis.