Astaxanthin Ameliorated Parvalbumin-Positive Neuron Deficits and Alzheimer’s Disease-Related Pathological Progression in the Hippocampus of AppNL-G-F/NL-G-F Mice

Abstract

Growing evidence suggests that oxidative stress due to amyloid b (Ab) accumulation is involved in Alzheimer's disease (AD) through the formation of amyloid plaque, which leads to hyperphosphorylation of tau, microglial activation, and cognitive deficits. The dysfunction or phenotypic loss of parvalbumin (PV)-positive neurons has been implicated in cognitive deficits. Astaxanthin is one of carotenoids and known as a highly potent antioxidant. We hypothesized that astaxanthin's antioxidant effects may prevent the onset of cognitive deficits in AD by preventing AD pathological processes associated with oxidative stress. In the present study, we investigated the effects of astaxanthin intake on the cognitive and pathological progression of AD in a mouse model of AD. The App NL-G-F/NL-G-F mice were fed with or without astaxanthin from 5-to-6 weeks old, and cognitive functions were evaluated using a Barnes maze test at 6 months old. PV-positive neurons were investigated in the hippocampus. Ab42 deposits, accumulation of microglia, and phosphorylated tau (pTau) were immunohistochemically analyzed in the hippocampus. The hippocampal anti-oxidant status was also investigated. The Barnes maze test indicated that astaxanthin significantly ameliorated memory deficits. Astaxanthin reduced Ab42 deposition and pTau-positive areal fraction, while it increased PVpositive neuron density and microglial accumulation per unit fraction of Ab42 deposition in the hippocampus. Furthermore, astaxanthin increased total glutathione (GSH) levels, although 4-hydroxy-2,3-trans-nonenal (4-HNE) protein adduct levels (oxidative stress marker) remained high in the astaxanthin supplemented mice. The results indicated that astaxanthin ameliorated memory deficits and significantly reversed AD pathological processes (Ab42 deposition, pTau formation, GSH decrease, and PV-positive neuronal

Molecular Mechanisms of Astaxanthin as a Potential Neurotherapeutic Agent

“…These changes were accompanied by a significant elevation in the level of superoxide dismutase (SOD) and a significant decline in the nitric oxide (NO) and nitric oxide synthase (NOS) levels. Interestingly, it was reported that ASX might induce a significant suppression of p-Tau expression; however, it did not affect the regulation of p-GSK-3β expression [ 58 ]. ASX possesses a powerful anti-inflammatory activity that abolishes the expression of inflammatory mediators, including TNF-α, PGE2, and IL-1β, and inhibits the development of nitric oxide (NO) as well as the NF-κB-dependent signaling pathway [ 36 , 59 ].…”

“…Hongo et al [ 58 ] used a new AD model, the App NL-G-F mice model, which is associated with mild memory decline, microglial formation, increased level of p-Tau, and accumulation of Aβ 42 in the hippocampus. Their findings indicated that ASX significantly reduced the Aβ 42 deposition, p-Tau, and Iba1 fraction.…”

Involvement of Parvalbumin-Positive Neurons in the Development of Hyperalgesia in a Mouse Model of Fibromyalgia

“…PV-positive neurons were immunostained based on the same protocol used in our previous studies (40)(41)(42)(43)(44). After the hotplate test was performed 3 days after the first injection, the mice were sacrificed under deep anesthesia with mixed anesthetics (5.0 mg/kg butorphanol, 4.0 mg/kg midazolam, and 0.75 mg/kg medetomidine, i.p.…”

“…Then, the brains were cut into 40 µm sections, collected in 0.01 M PBS, and stored in an antifreeze solution (25% glycerin, 25% ethylene glycol, and 50% 0.1 M PB) at −20 • C. Two stains were used on serial sections every 40 µm, one for PV immunocytochemistry, and the other for Cresyl violet (Nissl staining). In PV immunostaining, the sections were processed with mouse monoclonal anti-PV antibodies according to our previous protocol (40)(41)(42)(43)(44). Briefly, the sections were washed 3 times with 0.01 PBS for 5 min, blocked with 3% normal horse serum for 30 min, then mouse monoclonal anti-parvalbumin antibody (1: 10 000 dilution in 1% horse serum PBS, Sigma, St. Louis, MO, USA) was incubated overnight at 4 • C. These sections were washed 3 times with 0.01 PBS for 5 min and incubated with biotinylated horse antimouse IgG (1:200 dilution, Vector, Burlingame, USA) for 50 min at room temperature.…”

“…PV-positive neurons were counted based on our previous protocols (42)(43)(44). Section images were captured and digitized using a microscope system (BZ-9000, Keyence Corporation, Osaka, Japan).…”