Allicin ameliorates aluminium- and copper-induced cognitive dysfunction in Wistar rats: relevance to neuro-inflammation, neurotransmitters and Aβ(1-42) analysis

Abstract

Alzheimer's disease (AD) is a multifactorial neurological disorder associated with neuropathological and neurobehavioral changes, like cognition and memory loss. Pathological hallmarks of AD comprise oxidative stress, formation of insoluble β-amyloid (Aβ) plaques, intracellular neurofibrillary tangles constituted by hyperphosphorylated tau protein (P-tau), neurotransmitters dysbalanced (DA, NE, 5-HT, GABA and Glutamate) and metal deposition. Chronic exposure to metals like aluminium and copper causes accumulation of Aβ plaques, promotes oxidative stress, neuro-inflammation, and degeneration of cholinergic neurons results in AD-like symptoms. In the present study, rats were administered with aluminium chloride (200 mg/kg p.o) and copper sulfate (0.5 mg/kg p.o) alone and in combination for 28 days. Allicin (10 and 20 mg/kg i.p) was administered from day 7 to day 28. Spatial and recognition memory impairment analysis was performed using Morris water maze, Probe trial, and Novel Object Recognition test. Animals were sacrificed on day 29, brain tissue was isolated, and its homogenate was used for biochemical (lipid peroxidation, nitrite, and glutathione), neuro-inflammatory (IL-1β, IL-6 and TNF- α), neurotransmitters (DA, NE, 5-HT, GABA and Glutamate), Aβ_(1-42) level, Al concentration estimation, and Na⁺/K⁺-ATPase activity. In the present study, aluminium chloride and copper sulfate administration increased oxidative stress, inflammatory cytokines release, imbalanced neurotransmitters' concentration, and promoted β-amyloid accumulation and Na⁺/K⁺-ATPase activity. Treatment with allicin dose-dependently attenuated these pathological events via restoration of antioxidants, neurotransmitters concentration, and inhibiting cytokine release and β-amyloid accumulation. Moreover, allicin exhibited the neuroprotective effect through antioxidant, anti-inflammatory, neurotransmitters restoration, attenuation of neuro-inflammation and β-amyloid-induced neurotoxicity.

Keywords: Aluminium chloride; Alzheimer’s disease; Copper sulfate; Excitotoxicity; Neuro-inflammatory markers; Neurotransmitters.