Neuroprotective potential of vitamin D3 against glucocorticoid-induced neurotoxicity: Focus on calcium-binding proteins and neuroinflammation in a rat model

Prolonged glucocorticoid (GC) therapy is frequently complicated by secondary vitamin D 3 deficiency, which acts as a potential pathogenetic modulator of GC-induced neurotoxicity. This study investigated the role of disturbed calcium homeostasis and neuroinflammation in GC-induced brain damage and evaluated the protective potential of vitamin D 3 (VD 3 , cholecalciferol). Female Wistar rats (n=54) were divided into control, GC-treated (prednisolone, 5mg/kg/day, 30 days, per os), and VD 3 -correction (1000 IU/kg/day, concurrent with GC) groups. Analysis of calcium-binding protein levels (calbindin-D28K, S100B, osteocalcin) and neurospecific markers (NF-L, MBP, GFAP) was performed using ELISA, Western blot, and confocal microscopy. Prolonged prednisolone administration caused significant systemic and local 25(OH)D 3 deficiency, accompanied by a twofold reduction in osteocalcin protein content and elevated calbindin-D28K levels. Reactive astrogliosis, characterized by increased GFAP + cell counts and S100B content, occurred alongside decline in NG2 + oligodendrocyte precursors. Significant neuroinflammation was recorded: TNF-α levels rose 1.62-fold in the cortex and 1.65-fold in the hippocampus, while IL-1β increased 2.66-fold and 2.40-fold, respectively. Furthermore, markedly increased serum levels of NF-L, S100B, GFAP, and MBP indicated alterations consistent with blood-brain barrier dysfunction and neuro-glial disintegration. VD 3 therapy effectively restored serum markers (osteocalcin, S100B, MBP), suppressed astrocyte reactivity, and normalized cortical cytokine levels while partially replenishing NG2 + cell pool. Although its impact on hippocampal inflammation was limited, these findings demonstrate that maintaining adequate VD 3 levels is paramount for preserving CNS integrity by stabilizing calcium buffering and suppressing neuroinflammation. Our results emphasize clinical importance of monitoring VD 3 status to mitigate risk of glucocorticoid-induced neurotoxicity and associated neurological complications.