Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the two most prevalent neurodegenerative disorders, characterized by progressive cognitive and motor decline, respectively. Their complex pathophysiology involves multiple molecular mechanisms, including oxidative stress and metal dysregulation, which are increasingly recognized as central players in disease progression. Oxidative stress results from an imbalance between reactive oxygen species (ROS) production and the antioxidant defenses, leading to cellular damage and neuronal dysfunction [1]. In AD, oxidative stress has been linked to amyloid-beta plaque formation and tau hyperphosphorylation, while in PD, it contributes to dopaminergic neuron degeneration in the substantia nigra [2]. Trace metals such as iron, copper, and manganese are essential for neuronal function but can become toxic when dysregulated. In both AD and PD, abnormal metal accumulation has been shown to exacerbate oxidative damage, furthering neurodegeneration [3][4]. Recent studies suggest that biomarkers associated with oxidative stress and metal imbalance may provide valuable diagnostic and prognostic information, enabling early detection and intervention. Specifically, malondialdehyde (MDA) and glutathione (GSH) have emerged as promising oxidative stress markers, while metal concentrations such as iron and copper show strong associations with disease severity [5]. This study aims to explore the potential of these biomarkers as tools for early diagnosis and disease monitoring in AD and PD, highlighting their clinical relevance and therapeutic implications.

Study Design

This study adopts a case-control observational design to evaluate peripheral biomarkers, focusing on oxidative stress markers and trace metal concentrations in patients diagnosed with Alzheimer's disease (AD) and Parkinson's disease (PD). The design facilitates cross-sectional comparisons between clinically confirmed cases and age-matched controls, allowing for the identification of disease-specific biochemical alterations.

Study Setting

The study will be conducted at the Index Medical College, Hospital, and Research Center, located in Indore, Madhya Pradesh, India. The center has well-established facilities for clinical diagnosis and biochemical analysis, making it an ideal location for this research. The hospital's neurology department will provide access to AD and PD patients, while the research center will be responsible for laboratory testing and biomarker analysis.

Participant Selection

The study will include three groups:

1. Group A – Alzheimer's Disease (AD) Patients: Patients diagnosed with AD, confirmed through clinical evaluation using the Mini-Mental State Examination (MMSE).
2. Group B – Parkinson’s Disease (PD) Patients: Patients diagnosed with PD, confirmed through clinical assessment using the Unified Parkinson’s Disease Rating Scale (UPDRS).
3. Group C – Healthy Controls: Age-matched individuals without any history of neurodegenerative diseases or neurological impairments.

Inclusion Criteria

Participants aged ≥55 years, diagnosed with either AD or PD, and willing to provide written informed consent. Control subjects will be cognitively healthy adults, free from neurological or psychiatric disorders.

Exclusion Criteria

Participants with co-morbid conditions affecting oxidative stress or metal metabolism (e.g., chronic liver or kidney diseases), or those on antioxidant supplements or metal chelation therapy, will be excluded from the study.

Ethics Approval

The study protocol will be reviewed and approved by the Institutional Ethics Committee (IEC) of the Index Medical College, Hospital, and Research Center. All procedures will adhere to the Declaration of Helsinki and ICMR National Ethical Guidelines for Biomedical and Health Research Involving Human Participants.

Data Collection

Blood samples will be collected from all participants for the assessment of oxidative stress markers (MDA, GSH, SOD, catalase) and trace metals (iron, copper, manganese, zinc) using established biochemical assays, including Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for metal analysis and spectrophotometric methods for oxidative stress markers.

Statistical Analysis

Descriptive statistics will be used to summarize demographic and clinical data, and inferential statistics (ANOVA or Kruskal-Wallis tests) will be performed to compare biomarker levels across groups. Correlations between biomarkers and clinical scores will be analyzed using Pearson or Spearman correlation coefficients. A p-value of <0.05 will be considered statistically significant.

Demographic and Clinical Characteristics of Participants

A total of 192 participants were enrolled in the study, including 64 individuals each in the Alzheimer’s disease (AD), Parkinson’s disease (PD), and healthy control groups. The demographic characteristics of the study participants, including age, gender, and clinical scores, are summarized in Table 1.

Table 1: Demographic and Clinical Characteristics of Participants

Age Distribution

The mean age of the AD group was 72.1 ± 4.9 years, the PD group had a mean age of 71.6 ± 5.2 years, and the control group had a mean age of 68.1 ± 5.4 years. ANOVA testing revealed a statistically significant difference in age between the three groups (p < 0.05), with the control group being younger on average (Figure 1).

Figure 1: Age Distribution Across Groups

The boxplot shown in Figure 1 illustrates the distribution of age across the three study groups, with the AD group showing the highest mean age, followed by the PD group, and the control group having the youngest mean age.

Oxidative Stress Markers

The levels of oxidative stress markers, including malondialdehyde (MDA) and glutathione (GSH), were significantly altered in both AD and PD patients compared to healthy controls. MDA levels were markedly higher in both AD (p < 0.001) and PD (p < 0.01) groups compared to controls. GSH levels were significantly lower in both disease groups, with AD patients showing the most significant reduction (p < 0.001) (Figure 2).

Figure 2: Oxidative Stress Markers (MDA and GSH) in AD, PD, and Control Groups

(Figure 2 shows the mean MDA and GSH concentrations in µmol/mL for AD, PD, and control groups. Data indicate significantly higher MDA and lower GSH in both AD and PD compared to controls).

Trace Metal Concentrations

Trace metal analysis revealed significant dysregulation of metal ions in both AD and PD groups compared to controls. Iron and copper levels were significantly higher in both AD and PD groups, while manganese levels were significantly increased in the PD group (p < 0.05). Zinc levels did not show significant differences between the groups (Figure 3).

Figure 3: Trace Metal Concentrations in AD, PD, and Control Groups

(Figure 3 shows the concentrations of iron, copper, manganese, and zinc in serum. PD patients had higher manganese levels, while both AD and PD groups had elevated iron and copper levels compared to controls).

Correlation Between Biomarkers and Clinical Scores

Correlations were performed between oxidative stress markers, trace metal concentrations, and clinical scores (MMSE for AD and UPDRS for PD). The results showed a significant negative correlation between MDA levels and MMSE scores (r = -0.65, p < 0.01) in AD patients, indicating that higher oxidative stress is associated with more severe cognitive impairment. In PD patients, a significant positive correlation was found between UPDRS scores and manganese levels (r = 0.58, p < 0.05), suggesting that elevated manganese levels are linked to more severe motor dysfunction.

Table 2: Correlation Between Biomarkers and Clinical Scores

• p < 0.05, ** p < 0.01

Clinical Implications of Biomarkers

The correlation between oxidative stress markers and disease severity in both AD and PD highlights the potential of these biomarkers for early diagnosis and monitoring of disease progression. Elevated MDA levels and reduced GSH concentrations in peripheral blood reflect ongoing neurodegenerative processes and could be utilized as non-invasive markers in clinical practice. Additionally, the dysregulation of trace metals such as iron and copper, along with manganese in PD, suggests that these biomarkers could also serve as targets for novel therapeutic interventions aimed at modulating metal homeostasis and oxidative stress in these diseases.

The results from this study indicate that oxidative stress markers and trace metal concentrations are significantly altered in AD and PD, and these biomarkers are strongly correlated with disease severity. These findings underscore the potential of oxidative stress and metal dysregulation as diagnostic and prognostic biomarkers, which could facilitate early detection and therapeutic intervention in neurodegenerative diseases. Further research is needed to validate these biomarkers in larger, longitudinal cohorts and to explore their clinical applicability in routine practice.

The findings from this study suggest that oxidative stress and metal dysregulation play a critical role in the pathophysiology of Alzheimer’s disease (AD) and Parkinson’s disease (PD). The significantly elevated levels of oxidative stress markers, such as malondialdehyde (MDA), and the decreased levels of glutathione (GSH) observed in both AD and PD patients, support the hypothesis that oxidative damage is a central mechanism in these diseases. Our study also found significant alterations in trace metal concentrations, with iron and copper levels elevated in both AD and PD, and manganese levels notably increased in PD. These results align with previous studies that highlight the importance of oxidative stress and metal imbalances in neurodegeneration.

Oxidative Stress in AD and PD

Oxidative stress, characterized by an imbalance between reactive oxygen species (ROS) and antioxidant defense systems, has been implicated in the pathogenesis of both AD and PD. The elevated MDA levels in AD and PD patients observed in our study confirm the findings of several other studies that have reported increased lipid peroxidation in the brains and blood of individuals with neurodegenerative diseases [1][2]. Elevated MDA levels are considered a hallmark of oxidative damage and have been shown to correlate with the severity of cognitive decline in AD patients [3]. Similarly, the significant reduction in GSH, an important antioxidant, observed in our study, is consistent with previous research indicating that a depletion of GSH levels occurs in the brains of PD and AD patients, reflecting a compromised antioxidant defense system [4][5].

Role of Trace Metals in Neurodegeneration

The dysregulation of metal ions is another significant finding of this study. Both iron and copper are essential for normal brain function, but their accumulation has been associated with neurodegenerative diseases, primarily due to their role in generating ROS through redox cycling [6]. The elevated levels of iron and copper found in both AD and PD patients in this study are consistent with previous reports that show abnormal metal deposition in brain regions affected by these diseases [7]. Specifically, excess iron in the substantia nigra in PD has been implicated in the degeneration of dopaminergic neurons, while copper has been shown to exacerbate amyloid-beta aggregation in AD [8][9]. Furthermore, the increase in manganese levels observed in the PD group supports earlier findings linking manganese accumulation to motor dysfunction and the pathophysiology of PD, particularly in the basal ganglia [10].

Correlations with Clinical Scores

The correlations between biomarkers and clinical scores further support the potential of oxidative stress and metal dysregulation as diagnostic and prognostic tools in AD and PD. The negative correlation between MDA levels and Mini-Mental State Examination (MMSE) scores in AD patients is consistent with the idea that increased oxidative stress correlates with cognitive decline [3]. Additionally, the positive correlation between manganese levels and Unified Parkinson's Disease Rating Scale (UPDRS) scores in PD patients suggests that manganese may be a useful marker for monitoring motor dysfunction in PD, as higher manganese concentrations are associated with more severe motor impairment [11]. These findings align with studies that have suggested the utility of oxidative stress markers and trace metals as biomarkers for disease severity and progression in both AD and PD [12].

Potential for Early Diagnosis and Monitoring

One of the key implications of these findings is the potential for using oxidative stress markers and trace metal concentrations as non-invasive biomarkers for early diagnosis and disease monitoring in AD and PD. The ability to measure these biomarkers in peripheral blood is particularly advantageous, as cerebrospinal fluid (CSF) and neuroimaging techniques, while highly accurate, are invasive and resource-intensive [13]. Previous studies have shown that oxidative stress markers like MDA and GSH, as well as metal concentrations such as iron and copper, can be detected in blood and are reflective of central nervous system changes, making them promising candidates for routine clinical use [14][15]. The accessibility of blood-based biomarkers could enable broader population screening, especially in regions with limited access to advanced diagnostic facilities.

Therapeutic Implications

The alterations in oxidative stress and metal dysregulation observed in this study also have therapeutic implications. Several studies have suggested that targeting oxidative stress with antioxidant therapies could help mitigate neurodegeneration in AD and PD [16]. Our findings, particularly the elevated MDA and decreased GSH levels, highlight the potential of antioxidant treatments, such as coenzyme Q10 and N-acetylcysteine, which have been investigated for their neuroprotective properties in clinical trials [17][18]. Additionally, metal chelation therapies targeting iron and copper, such as deferiprone and clioquinol, are being explored as potential treatments for AD and PD due to their ability to reduce metal-induced oxidative damage [19][20].

Limitations and Future Directions

While this study provides important insights into the role of oxidative stress and metal dysregulation in AD and PD, there are several limitations. The cross-sectional design of the study limits the ability to draw conclusions about causality or track disease progression over time. Longitudinal studies are needed to confirm the potential of oxidative stress markers and trace metals as prognostic indicators. Additionally, while the sample size in this study was adequate, larger, multi-center studies are necessary to validate the findings and ensure their generalizability across diverse populations.

In conclusion, this study reinforces the critical role of oxidative stress and metal dysregulation in the pathophysiology of Alzheimer’s and Parkinson’s diseases. The findings suggest that biomarkers related to oxidative damage and trace metal imbalance could serve as useful tools for early diagnosis and monitoring of disease progression. Further research is needed to validate these biomarkers in larger cohorts and explore their clinical applicability in routine practice.

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