Astaxanthin Protects Hippocampal Neurons Against Memory Impairment Caused by Vascular Dementia in Rats

Background Introduction

Vascular Dementia (VAD) is a progressive cognitive disorder caused by cerebrovascular disease leading to cognitive decline. Current research shows that chronic cerebral hypoperfusion (CCH) and insufficient blood supply are the main causes of VAD, further leading to white matter damage and hippocampal neuron death. The hippocampus is a key brain region in learning and memory processes and is particularly sensitive to ischemic injury. VAD is usually accompanied by oxidative stress, inflammatory response, and neurovascular dysfunction, resulting in cognitive decline. Currently, effective treatments and specific drugs for VAD are still lacking.

In recent years, the natural carotenoid astaxanthin (AST) has attracted attention due to its potential therapeutic effects in neurodegenerative diseases. AST has strong antioxidant, anti-inflammatory, and neuroprotective properties and can penetrate the blood-brain barrier to act directly on the central nervous system. However, the protective mechanism of astaxanthin in VAD and its effects on hippocampal neuron death have not been fully elucidated.

Paper Source

This research paper was written by Na Wei, Luo-Man Zhang, Jing-Jing Xu, Sheng-Lei Li, Rui Xue, Sheng-Li Ma, Cai Li, and Miao-Miao Sun. The paper was published in the journal “Neuromolecular Medicine” in 2024 and was accepted on June 25, 2024.

Research Methods

The authors used bilateral common carotid artery occlusion (BCCAo) to establish a rat model of chronic cerebral hypoperfusion. Rats were given astaxanthin by gavage at a dose of 25 mg/kg/day for 4 weeks to explore its therapeutic effects. Y-maze and Morris water maze tests were used to assess memory impairment in rats. To further explore the protective mechanism of astaxanthin, the authors conducted biochemical analyses to evaluate hippocampal neuron death and apoptosis-related protein levels, as well as the effects on the PI3K/AKT/MTOR pathway and oxidative stress.

Experimental Steps

1. Animal Model Establishment and Group Assignment:

   • Adult male Sprague-Dawley rats were randomly divided into 4 groups: sham surgery group, CCH group, CCH+AST group, and high-dose AST alone group.
   • Rats in the CCH+AST and AST groups received astaxanthin treatment once daily for 4 weeks, starting 4 weeks before surgery.

2. Chronic Cerebral Hypoperfusion Surgery:

   • Bilateral common carotid artery ligation surgery was performed, and blood flow was measured using a laser Doppler flowmeter.
   • Rats in the sham surgery and AST groups underwent similar operations but without ligation.

3. Memory Function Assessment:

   • Y-maze and Morris water maze tests were used to assess working memory and spatial memory in rats.
   • Spontaneous alternation behavior in the Y-maze and escape latency, target quadrant dwelling time, and platform crossings in the water maze were recorded.

4. Hippocampal Tissue Morphology Study:

   • Nissl staining was performed on hippocampal tissue from selected rats to observe changes in neuron number and morphology.

5. Biochemical Analysis and Western Blot Experiments:

   • Rat hippocampal tissue was isolated for protein level detection, including apoptosis-related proteins Caspase-3, Bax, Bcl-2, etc.
   • Western Blot was used to assess the activity of the PI3K/AKT/MTOR signaling pathway.

6. Oxidative Stress Measurement:

   • Kits were used to detect oxidative stress indicators in hippocampal tissue, including changes in SOD, MDA, ROS, and GSH-PX activity.

Main Results

1. Memory Function Recovery:

   • Y-maze and Morris water maze test results showed that astaxanthin significantly improved working memory and spatial memory in VAD rats.
   • CCH group rats showed significant memory impairment, while astaxanthin-treated rats showed improvement trends.

2. Hippocampal Neuron Survival:

   • Nissl staining results showed a significant decrease in hippocampal neuron numbers in CCH rats, with cells showing atrophy and dense nuclei. Astaxanthin significantly alleviated these changes.
   • Western Blot results indicated increased expression of apoptosis-related proteins Caspase-3 and Bax, and decreased expression of Bcl-2 in CCH rat hippocampal tissue. Astaxanthin treatment significantly inhibited these changes.

3. PI3K/AKT/MTOR Signaling Pathway Regulation:

   • Western Blot results showed that astaxanthin could restore phosphorylated MTOR, AKT, and PI3K levels in the PI3K/AKT/MTOR signaling pathway in CCH rat hippocampal tissue, promoting neuron survival.

4. Oxidative Stress Alleviation:

   • Test results showed that astaxanthin significantly alleviated the increase in MDA levels, enhanced SOD and GSH-PX activity, and reduced ROS levels in CCH rat hippocampal tissue.

Conclusion and Significance

This study is the first to explore the mechanism by which astaxanthin improves VAD cognitive function by regulating the PI3K/AKT/MTOR signaling pathway to combat neuronal degeneration. Astaxanthin showed significant neuroprotective and cognitive improvement effects by reducing hippocampal neuron apoptosis and oxidative stress. The results provide new insights for VAD treatment and scientific evidence for astaxanthin as a potential drug for treating vascular dementia. However, the study did not use signaling pathway inhibitors for further verification, and the effectiveness of astaxanthin in clinical treatment still requires more research for validation.

This research reveals the potential of astaxanthin in protecting hippocampal neurons and alleviating VAD memory impairment, which is of significant value for developing new approaches to treating VAD. More research and clinical trials are needed in the future to fully understand the therapeutic potential and application of astaxanthin.