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 D3 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 D3 (VD3, cholecalciferol). Female Wistar rats (n = 54) were divided into control, GC-treated (prednisolone, 5 mg/kg/day, 30 days, per os), and VD3-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)D3 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. VD3 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 VD3 levels is paramount for preserving CNS integrity by stabilizing calcium buffering and suppressing neuroinflammation. Our results emphasize clinical importance of monitoring VD3 status to mitigate risk of glucocorticoid-induced neurotoxicity and associated neurological complications.