Neuromodulatory effect of vardenafil on aluminium chloride/D-galactose induced Alzheimer's disease in rats: emphasis on amyloid-beta, p-tau, PI3K/Akt/p53 pathway, endoplasmic reticulum stress, and cellular senescence

Abstract

Dysregulation of protein homeostasis, proteostasis, is a distinctive hallmark of many neurodegenerative disorders and aging. Deleteriously, the accumulation of aberrant proteins in Alzheimer's disease (AD) is accompanied with a marked collapse in proteostasis network. The current study explored the potential therapeutic effect of vardenafil (VAR), a phosphodiesterase-5 inhibitor, in AlCl₃/D-galactose (D-gal)-induced AD in rats and its possible underlying mechanisms. The impact of VAR treatment on neurobehavioral function, hippocampal tissue architecture, and the activity of the cholinergic system main enzymes were assessed utilizing VAR at doses of 0.3 mg/kg and 1 mg/kg. Additionally, the expression level of amyloid-beta and phosphorylated tau proteins in the hippocampus were figured out. Accordingly, VAR higher dose was selected to contemplate the possible underlying mechanisms. Intriguingly, VAR elevated the cyclic guanosine monophosphate level in the hippocampus and averted the repressed proteasome activity by AlCl₃/D-gal; hence, VAR might alleviate the burden of toxic protein aggregates in AD. In addition, a substantial reduction in the activating transcription factor 6-mediated endoplasmic reticulum stress was demonstrated with VAR treatment. Notably, VAR counteracted the AlCl₃/D-gal-induced depletion of nuclear factor erythroid 2-related factor 2 level. Moreover, the anti-senescence activity of VAR was demonstrated via its ability to restore the balance of the redox circuit. The modulation of phosphatidylinositol-3-kinase/protein kinase B/p53 pathway and the reduction of nuclear factor kappa B level, the key regulator of senescence-associated secretory phenotype mediators release, with VAR treatment were also elucidated. Altogether, these findings insinuate the possible therapeutic benefits of VAR in AD management.

Keywords: Alzheimer’s; Endoplasmic reticulum stress; PI3K/Akt/p53; Proteasome activation; Senescence; Vardenafil.

Fig. 1

Effect of vardenafil treatment on locomotor activity test (A), probe trial testing (B), step-through passive avoidance training (C), step-through passive avoidance testing (D), total arm entries (E), and spontaneous alternations (F) against AlCl₃/d-galactose-induced Alzheimer’s disease in rats. Data are presented as mean ± SD (n = 6) where: a; statistically significant from control group and b; statistically significant from AlCl₃/d-galactose-treated group, at P < 0.05 using one-way ANOVA followed by Tukey as a post-hoc test (A, B, E, and F) and Kruskal–Wallis test followed by Dunn’ post hoc test (C and D)

Fig. 2

Effects of vardenafil treatment on AlCl₃/d-galactose-induced histological alterations of rat hippocampal CA1, CA2, CA3, and DG regions. Photomicrographs of haematoxylin and eosin-stained sections from control group (group 1); AlCl₃/d-galactose-treated group (200 mg/kg, oral) and (60 mg/kg, ip), respectively, (group 2); donepezil-treated group (1 mg/kg) (group 3); vardenafil-treated group (0.3 mg/kg) (group 4); vardenafil-treated group (1 mg/kg) (group 5); vardenafil alone treated group (1 mg/kg) (group 6); with × 100 and × 200 magnification power

Fig. 3

Effect of treatment with vardenafil on hippocampal AChE (A) and BuChE activity (B) in an experimental model of Alzheimer’s disease induced by AlCl₃/d-galactose. Data are presented as mean ± SD (n = 6) where: a, b, c, and d; statistically significant from control group, AlCl₃/d-galactose-treated group, donepezil-treated group, and vardenafil (0.3 mg/kg)-treated group, respectively, at P < 0.05 using one-way analysis of variance (ANOVA) followed by Tukey as a post-hoc test

Fig. 4

Expression of the hippocampus amyloid-β and p-tau by immunohistochemical staining (× 100). A Photomicrographs of histological sections for control group (group I), B AlCl₃/d-galactose-treated group (200 mg/kg) and (60 mg/kg), respectively (group II), C donepezil-treated group (1 mg/kg) (group III), D vardenafil-treated group (0.3 mg/kg) (group IV), E vardenafil-treated group (1 mg/kg) (group V), and F vardenafil alone-treated group (1 mg/kg) (group V). Brown color (positive) indicates specific immunostaining of amyloid-β/p-tau and blue color (negative) indicates hematoxyline staining (n = 3)

Fig. 5

Effect of treatment with vardenafil on hippocampal cGMP level (A) and 20S proteasome chymotrypsin-like activity (B) in an experimental model of Alzheimer’s disease induced by AlCl₃/d-galactose. Data are presented as mean ± SD (n = 6) where: a, b, and c; statistically significant from control group, AlCl₃/d-galactose-treated group, and donepezil-treated group, respectively, at P < 0.05 using one-way analysis of variance (ANOVA) followed by Tukey as a post-hoc test

Fig. 6

Effect of treatment with vardenafil treatment on hippocampal GRP78 (A), ATF6 (B), CHOP (C), and Nrf2 (D) in an experimental model of Alzheimer’s disease induced by AlCl₃/d-galactose. Data are presented as mean ± SD (n = 6) where: a and b; statistically significant from control group and AlCl₃/d-galactose-treated group, respectively, at P < 0.05 using one-way analysis of variance (ANOVA) followed by Tukey as a post-hoc test

Fig. 7

Effect of treatment with vardenafil on hippocampal PI3K (A), pAkt (B), and p53 (C) in an experimental model of Alzheimer’s disease induced by AlCl₃/d-galactose. Data are presented as mean ± SD (n = 6) where: a and b; statistically significant from control group and AlCl₃/d-galactose-treated group, respectively, at P < 0.05 using one-way analysis of variance (ANOVA) followed by Tukey as a post-hoc test

Fig. 8

Effect of treatment with vardenafil on hippocampal catalase (A), reduced glutathione (B), superoxide dismutase activity (C), malondialdehyde (D), hydrogen peroxide (E), and p105 subunit of NF-κB (F) in an experimental model of Alzheimer’s disease induced by AlCl₃/d-galactose. Data are presented as mean ± SD (n = 6) where: a, b, and c; statistically significant from control, AlCl₃/d-galactose-treated group, and donepezil-treated group, respectively, at P < 0.05 using one-way analysis of variance (ANOVA) followed by Tukey as a post-hoc test