Effects of Probiotics on Androgenic Neurosteroids Levels and Cognitive Impairment in AlCl3-Induced Mouse Model of Alzheimer’s Disease

Abstract

Alzheimer disease (AD) accounts for the 80% of dementia worldwide in the elderly people, with clinical features represented by the beta-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs). Aβ aggregation facilitates a cascade of cytotoxic processes such as synaptic loss, neuronal death, glial activation, disruption of microRNA profiles and impaired mitochondrial function that collectively contribute to cognitive decline and dementia. In addition, hippocampal neurons overexpressing either amyloid precursor protein (APP) or Tau diminish the neurosteroid levels which are mainly involved in clearance of Aβ plaques. The present study investigated the changes in androgen steroidogenic enzymes expression both in brain and testicles, in an AlCl3-induced-AD mouse model. A combined treatment of four potential probiotics Lactobacillus rhamnosus LRa05, Lactobacillus acidophilus LRa85, Bifidobacterium lactis BLa80, Bifidobacterium bifidum BBi32 was used to assess their potential ameliorative effect in both brain and testicles. Donepezil, an acetylcholinesterase inhibitor was used as a positive control. Balb/c mice (male) were randomly divided into six groups (n=6 each). Three groups were given AlCl3 (300 mg/kg) in drinking water, followed by treatment with probiotics (2x108 CFU) and Donepezil (15 mg/kg) while the other three groups received probiotics, donepezil, and distil water, only. The treatment effects were assessed on anxiety, aggression, social exploration and cognition through elevated plus maze (EPM) test, the resident intruder test and Morris water maze (MWM) test. The findings indicated that probiotics significantly lowered anxiety like behavior after being exposed to AlCl3. Similarly, significant improvement was also observed in spatial memory with probiotics treatment (p < 0.0001). A substantial decrease in aggression and improved social exploration time was also observed with probiotics treatment post AlCl3 exposure. Histopathological assessment performed through Congo red staining showed significant decrease in amyloid plaque burden within the mice hippocampus observed in the group treated with LA85, LRa05, BLa80, & BBi32 post AlCl3 exposure. Treatment with LA85, LRa05, BLa80, & BBi32 lead to significant restoration of the neuronal density (p<0.0001) as seen by the cell count in the H&E-stained sections. Higher expression levels of APP770 were recorded in AlCl3-treated group which were significantly decreased in LA85, LRa05, BLa80, & BBi32 – treated groups, post AlCl3 exposure (p < 0.0001). The AlCl3 treatment reduced the expression of androgenic steroid enzymes (StAR, CYP11A1, 3β-HSD) in the brain and testicles. Interestingly, treatment with probiotics lead to substantial restoration of steroid levels in both organs. In conclusion, these findings indicate the combined ameliorative potential of probiotics for the dysregulated androgenic neurosteroids and behavioral and cognitive deficits through modulation of gene expression and reduction in plaque burden. Further investigations are required to elucidate the underlying molecular mechanism(s) and to confirm the clinical significance of present findings.