Limettin and PD98059 Mitigated Alzheimer's Disease Like Pathology Induced by Streptozotocin in Mouse Model: Role of p-ERK1/2/p-GSK-3β/p-CREB/BDNF Pathway.

Sporadic Alzheimer's disease (SAD) represents one of the major memory deficits that is characterized by tau hyperphosphorylation and amyloid beta (Aβ) deposition in the brain. Both are considered AD hallmarks which are mediated through neuroinflammation, oxidative stress, and cholinergic circuit interruption. This study aimed to show how limettin and PD98059 exert a neuroprotective effect against SAD and the possible role of the extracellular regulated kinase (p-ERK1/2) and glycogen synthase kinase-3 beta (p-GSK-3β) (Ser9)/cAMP-response element binding protein (p-CREB) (Ser133)/brain derived neurotrophic factor (BDNF) pathway. Control animals (Group I) received the vehicles, group II received PD98059 (10 mg/kg/i.p), while group III was administered limettin (15 mg/kg/i.p). Additionally, the other three groups received a single dose of streptozotocin (STZ; 3 mg/kg/ICV), where group IV served as the SAD group, while groups V and VI received PD98059 and limettin daily for 3 weeks, respectively. The SAD animals receiving PD98059 and limettin increased the number of arm entries, % alternations in Y-maze, with reduction in mean escape latency, increase in time spent in target quadrant and platform crossing in Morris Water Maze, compared to the SAD group. Additionally, PD98059 and limettin administration to the STZ group downregulated persistent activation of p-ERK1/2 which in turn increased p-GSK-3β (Ser9), leading to enhanced p-CREB (Ser133) and BDNF expressions, as well as reducing inflammatory markers viz., nuclear factor-kappa B and interleukin-6, leading to decreased Aβ deposition. Both treatments reduced immunohistochemical p-tau expression, brain edema, and increased intact neuron cells remarkably. Thus, based on these findings, PD98059 and limettin may have promising effects in protecting against SAD. Using blockers/inhibitory molecules are recommended to confirm effect through the corresponding pathway.