Vitamin D₃ and Dimethyl Fumarate Partially Restore Neurotrophic Signaling Without Altering Mitochondrial Integrity in...

Alzheimer's disease (AD) is characterized by impaired neurotrophic support, oxidative stress, and metabolic dysfunction. Using the intracerebroventricular streptozotocin (ICV-STZ) rat model of sporadic AD, we investigated whether vitamin D₃ (VitD₃) and dimethyl fumarate (DMF), administered alone or in combination, modulate hippocampal neurotrophin-related signaling and redox balance. Animals were assigned to SHAM, STZ, VITD, DMF, and COMBO groups, representing control, ICV-STZ, VitD₃-treated ICV-STZ, DMF-treated ICV-STZ, and combined VitD₃ + DMF-treated ICV-STZ animals, respectively. Hippocampal neurotrophin processing (proBDNF and mature BDNF), downstream signaling (Akt and pAkt), IGF-1 content, mitochondrial oxoglutarate dehydrogenase (OGDH) content, citrate synthase (CS) activity, and glutathione peroxidase (GPx) activity were assessed. STZ administration showed a trend toward reduced mature BDNF content compared with the SHAM group (p = 0.07), whereas combined VitD₃ and DMF treatment significantly increased mature BDNF content compared with the STZ group. The mature BDNF/proBDNF ratio was reduced in the STZ group compared with the SHAM group and tended to be higher in the COMBO group compared with the STZ group (p = 0.09). proBDNF content remained unchanged. IGF-1, pTrkB, total Akt, and pAkt content did not differ significantly between groups. The pAkt/Akt ratio showed a trend toward reduction in the STZ group compared with SHAM group (p = 0.09). GPx activity increased in the STZ group, while CS activity and OGDH content were not significantly altered. These findings indicate that STZ-induced neurodegeneration is characterized by redox-associated uncoupling of neurotrophic signaling rather than mitochondrial disruption. Combined VitD₃ and DMF treatment partially modulated neurotrophic signaling, supporting a limited but measurable neuroprotective effect.