Study on the protective effect of oxalic acid from rat tail on MPTP induced dopamine neuron damage
With the acceleration of aging process at home and abroad, the incidence rate of Parkinson’s disease (PD) is increasing, becoming the second largest neurodegenerative disease after Alzheimer’s disease (AD). The per capita economic burden of Parkinson’s disease patients accounts for 57.0% of the per capita annual income and 24.2% of the household annual income, bringing a heavy burden to families and society. In June 2018, Parkinson’s disease was included in the “First Batch of Rare Disease Catalogue” jointly released by the National Health Commission, Ministry of Science and Technology, Ministry of Industry and Information Technology, State Administration for Market Regulation, and State Administration of Traditional Chinese Medicine. The etiology and pathological mechanism of Parkinson’s disease are complex. Current research suggests that the pathogenesis of Parkinson’s disease may be related to multiple factors such as genetics, environment, and immunity, but it is not yet fully understood. Oxidative stress induces lipid peroxidation, destroys nucleic acids and proteins, damages ribonucleic acid (RNA) and nuclear deoxyribonucleic acid (DNA), especially causing damage to mitochondrial DNA. Mitochondrial dysfunction and abnormal energy metabolism are considered the main driving factors of neuronal damage. Although the molecular mechanism of PD has not been fully elucidated, numerous pieces of evidence suggest that oxidative stress leading to neuronal death and dysfunction is one of the important pathological mechanisms of PD. Protecting neurons from oxidative damage is crucial for the prevention and treatment of PD, and high-quality antioxidants are potential therapeutic drugs for PD.

Oxalic acid is the main component of the plant Rosmarinus officinalis L. (English name: Rosemary) in the family Lamiaceae. It is a highly effective natural antioxidant with antioxidant and anti-aging effects, which can inhibit A β aggregation and protect hippocampal neurons from A β – induced damage. However, there is still a lack of in-depth research on whether oxalic acid from rat tail can protect against MPTP induced neuronal damage and develop candidate drugs for the prevention and treatment of PD. Therefore, this study cultured dopamine neurons in vitro and induced neuronal damage with MPTP to investigate the protective effect of oxalic acid on MPTP induced dopamine neuronal damage and its possible mechanism.

The clinical treatment drugs for Parkinson’s disease include dopamine receptor agonists, monoamine oxidase B (MAO-B) inhibitors, anticholinergic drugs, compound levodopa preparations, amantadine, and neuroprotective agents. Although there are many types of drugs used to treat Parkinson’s disease, there is still no drug that can completely cure Parkinson’s disease. Excessive reactive oxygen species in the brain can cause reactions such as nucleic acid breakdown and lipid peroxidation, leading to mitochondrial dysfunction and neuronal loss. Mitochondrial dysfunction promotes oxidative stress response, aging, and neurodegenerative changes, directly participating in the pathological processes of various neurodegenerative diseases such as PD. High quality antioxidants may be potential therapeutic drugs.

Oxalic acid is one of the main polyphenolic components of rosemary, which has good antioxidant effects and has long been used as an antioxidant in food and daily chemical products. Previous studies have shown that oxalic acid and rosemary extracts mainly composed of oxalic acid have good central nervous system protection effects. However, whether they can protect dopaminergic neurons from oxidative damage and develop into drugs for the prevention and treatment of PD has not been confirmed by research. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that metabolizes 1-methyl-4-phenylpyridine ion (MPP+) in the body. MPP+enters the mitochondria and inhibits the activity of oxidative respiratory chain complex I, causing oxidative stress damage to dopaminergic neurons and leading to symptoms similar to Parkinson’s disease in mammals. It is widely recognized as the gold standard for constructing PD models. In this study, we treated dopamine neurons cultured in vitro with MPTP (10 μ mol/L) and found that MPTP treatment resulted in neuronal atrophy, axonal rupture, reduced dendrites, decreased neuronal activity, significant increase in caspase-3 mRNA and protein expression, significant increase in MDA content and LDH leakage from the culture medium, and significant decrease in neuronal SOD activity. After pretreatment with oxalic acid, MPTP induced neuronal morphological atrophy and decreased vitality can be reversed; Simultaneously, it can reverse the abnormal elevation of caspase-3 mRNA and protein induced by MPTP in neurons; Reduce the content of MDA and the leakage of LDH; Enhance the activity of SOD in neurons. This indicates that oxalic acid has a protective effect on MPTP induced dopaminergic neurons. As oxalic acid can reduce the content of MDA and leakage of LDH in MPTP induced dopaminergic neurons, and enhance the activity of SOD in neurons, we speculate that oxalic acid’s protective effect on Parkinson’s disease may be related to antioxidant damage. Luteolin is a natural substance that exists in various plants and has various pharmacological activities, such as anti-tumor, antibacterial, antiviral, anti-inflammatory, expectorant, uric acid lowering, anti allergic, and immune enhancing effects. Research reports that the combination of luteolin and rutin can alleviate 6-OHDA induced cell damage, inhibit tremor behavior in PD model rats, reduce DA neuron damage and the generation and release of inflammatory factors; It can improve the motor coordination ability of MPTP induced Parkinson’s disease mice, regulate neurotransmitter levels in the brain, inhibit inflammatory reactions, and reduce neuronal damage. Therefore, in this experiment, luteolin was selected as the positive control drug.

The results of this study showed that oxalic acid has a protective effect on MPTP induced dopamine neuron damage, and its mechanism of action may be related to its antioxidant, neuronal oxidative damage, and reversal of caspase-3 abnormal activation. However, more rigorous experiments are needed to confirm this (such as designing different doses of CA to improve MPTP induced neuronal damage after MPTP injury, adding antagonists, and detecting other related mitochondrial proteins). This study can provide assistance for the in-depth development and utilization of rosemary, as well as reference for the research and development of PD prevention and treatment drugs.