The protective effect of anthocyanins from the black fruit gland of the Chinese parasol tree on oxidative stress and apoptosis induced by A β 1-42 in SH-SY5Y cells through the Nrf2 mechanism
Alzheimer’s disease (AD), also known as senile dementia, is a progressive neurodegenerative disease that can lead to memory loss, cognitive impairment, behavioral disorders, social disorders, and is the most common cause of dementia. It is estimated that 24 million people worldwide suffer from dementia, with the majority suffering from Alzheimer’s disease. In addition, Alzheimer’s disease is a common age-related disease, most commonly found in people aged 65 or older. Therefore, Alzheimer’s disease remains one of the main health issues of an aging population, and the number of Alzheimer’s disease cases is destined to significantly increase in the coming decades. At present, there are several hypotheses that can explain the pathogenesis of Alzheimer’s disease, including beta amyloid (A β) peptide and tau protein hyperphosphorylation, which play a major role in the pathogenesis of Alzheimer’s disease. In addition, increasing evidence suggests that oxidative stress and cell apoptosis play critical roles in Alzheimer’s disease. Related studies have shown that oxidative stress in AD patients can lead to cell apoptosis. Meanwhile, oxidative stress can activate cellular protective mechanisms, including endogenous antioxidants and antioxidant enzyme systems. The main antioxidant enzymes involved in this protective effect are heme oxygenase-1 (HO-1), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (CSH Px). The transcriptional activation of antioxidant enzyme genes is mainly regulated by nuclear transcription related factors (Nrf2). Some phytochemicals can activate Nrf2/antioxidant response element (ARE) signaling, thereby upregulating the expression of antioxidant enzymes and enhancing neuronal resistance to oxidative stress. In the resting state, Nrf2 exists in the form of a complex. When the complex is disrupted, Nrf2 translocates to the nucleus and binds to the ARE sequence to promote the expression of antioxidant enzymes. It is known that extracellular deposition of A β can cause oxidative damage and apoptosis of neurons, and A β has also been shown to induce excessive production of ROS and hydrogen peroxide (H202), as well as reduce SOD and GSH Px levels, leading to oxidative stress.

At present, research progress has been made on the preventive and protective effects of anthocyanins on Alzheimer’s disease. Heo et al. investigated the neuroprotective activity of strawberry anthocyanins on Alzheimer’s disease cell models. Research has shown that strawberry anthocyanins can reduce the occurrence of oxidative stress and oxidative stress-induced cell apoptosis, thereby providing a protective effect on nerve cells. Badshah et al. investigated the neuroprotective effects of anthocyanins in black soybeans on A β 1-24-induced neurodegenerative cells and animal models. Research has shown that anthocyanins effectively reduce neuronal apoptosis by maintaining Ca2+homeostasis and have a protective effect on neuronal cells. Meng et al. investigated the protective effect of cyanidin-3-O-glucoside on Alzheimer’s disease cell models. The results indicate that cyanidin-3-O-glucoside can protect Alzheimer’s disease cells from A β 1-40-induced oxidative stress and apoptosis by regulating cellular antioxidant and apoptosis related genes. The above research indicates that anthocyanins may become potential candidate drugs for neurodegenerative diseases such as AD. In addition, recent research by Isaak et al. found that cranberry anthocyanins composed of cyanidin-3-O-galactoside, cyanidin-3-O-glucoside, and cyanidin-3-O-arabinoside can protect cardiomyocytes from oxidative stress and damage caused by cell apoptosis. Previous studies have shown that the content of anthocyanins in the black fruit gland ribbed elm tree is very high, with a simple structure mainly composed of cyanidin-3-O-galactoside, cyanidin-3-O-glucoside, cyanidin-3-O-arabinoside, and cyanidin-3-O-xyloside. High purity anthocyanins are relatively easier to isolate. Therefore, we chose high-purity anthocyanins from the black fruit gland of Eucommia ulmoides to investigate their preventive and protective effects on oxidative stress-related Alzheimer’s disease.

The ROS generated by oxidative stress directly or indirectly damages the physiological functions of intracellular and macromolecular substances such as proteins, lipids, and nucleic acids, and is the pathological and physiological basis for the occurrence of many diseases. The body forms a complex oxidative stress response system to cope with the damage caused by free radicals and toxic substances. When exposed to electrophilic agents or reactive oxygen species, the body can induce a series of protective proteins to alleviate the damage to cells. This coordinated response is regulated by the antioxidant responsive element (ARE) in the upstream regulatory region of protective protein DNA. Research has shown that nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the encoding of antioxidant proteins through its interaction with ARE, making it the most important endogenous antioxidant stress pathway discovered to date. Previous studies have shown that anthocyanins, due to their strong antioxidant capacity, can clear free radicals in the body, reduce oxidative stress levels, and protect the body from damage caused by oxidative stress. With further research, it has been shown that anthocyanins can upregulate the expression of related antioxidant enzymes through the Nrf2 signaling pathway, reduce oxidative stress levels, and protect Alzheimer’s disease cells or animal models from damage caused by oxidative stress.

In addition, apoptosis often occurs with oxidative stress, and apoptosis in mammalian cells occurs through both external and internal pathways. The external pathway involves the binding of extracellular signaling factors to death receptors in the plasma membrane. The intrinsic pathway is activated by intracellular stress and carried out through mitochondria. The mitochondrial apoptosis pathway is regulated by the Bcl-2 family, which includes anti apoptotic proteins such as Bcl-2 and Bcl xL, as well as pro apoptotic proteins such as Bax and Bak. In recent years, studies have shown that oxidative stress and cell apoptosis promote the development of Alzheimer’s disease. Therefore, exploring bioactive substances that can prevent neuronal oxidative damage and apoptosis is of great research significance for the prevention and control of Alzheimer’s disease.

As introduced in the preface, some studies have reported that anthocyanins can prevent and protect Alzheimer’s disease by reducing the occurrence of oxidative stress and oxidative stress-induced cell apoptosis. Therefore, this study used A β 1-42 induced SH-SY5Y cells to construct an Alzheimer’s disease cell model system. ROS, SOD, and H2O2 were selected as oxidative stress-related indicators, and the protective effect of anthocyanins on oxidative stress and cell apoptosis was studied through the Nrf2 signaling pathway to evaluate the cell protective effect of anthocyanins. The results showed that anthocyanins from the black fruit gland of the Chinese parasol tree can activate the Nrf2 metabolic pathway, upregulate the mRNA and protein expression of HO-1 and NQO1 genes, thereby upregulating the expression of related antioxidant enzymes such as HO-1, NQO1, SOD, and reducing intracellular oxidative stress levels. At the same time, anthocyanins from the black fruit gland of the Chinese parasol tree can upregulate the expression of Bcl-2 gene and protein, downregulate the expression of Bax gene and protein, thereby reducing cell apoptosis. Therefore, anthocyanins from Scutellaria lobata can effectively protect Alzheimer’s disease from oxidative stress and apoptosis induced by A β 1-42 in SH-SY5Y cells. Previous studies on the effects of anthocyanins on Alzheimer’s disease mostly used crude extracts or mixtures of anthocyanins. However, the anthocyanin mixture used in this study has a simple and clear structure, with a purity of over 93%, which further demonstrates the role of anthocyanins in Alzheimer’s disease. This is of great significance for the further development of anthocyanins and related products.