Oxidative stress biomarkers in neurodegenerative disorders

Introduction

Neurodegenerative disorders affect over 50 million individuals globally, with prevalence projected to triple by 2050 as populations age [1] . Alzheimer's disease alone accounts for 60-70% of dementia cases, while Parkinson's disease represents the second most common neurodegenerative condition affecting approximately 1% of adults over age 60 [2] . Amyotrophic lateral sclerosis, though rarer, carries devastating prognosis with median survival of 2-4 years from diagnosis [3] . Despite distinct clinical presentations and affected neuronal populations, these disorders share oxidative stress as a convergent pathophysiological mechanism contributing to neuronal dysfunction and death. Oxidative stress occurs when production of reactive oxygen species exceeds cellular antioxidant defense capacity, resulting in oxidative damage to lipids, proteins, and nucleic acids [4] . The brain demonstrates particular vulnerability to oxidative damage owing to high oxygen consumption, abundant polyunsaturated fatty acids susceptible to peroxidation, relatively modest antioxidant defenses, and limited regenerative capacity [5] . Post-mortem studies consistently demonstrate elevated oxidative damage markers in affected brain regions across neurodegenerative disorders, establishing oxidative stress as a pathological hallmark rather than epiphenomenon [6] . Peripheral blood biomarkers offer accessible windows into central nervous system oxidative status, with several markers demonstrating correlations between plasma and cerebrospinal fluid concentrations [7] . Malondialdehyde, a secondary product of lipid peroxidation, represents the most widely studied oxidative stress biomarker with established elevation in multiple neurodegenerative conditions [8] . 8hydroxydeoxyguanosine reflects oxidative DNA damage, while protein carbonyl content indicates irreversible protein oxidation [9] . Antioxidant enzyme activities including superoxide dismutase, catalase, and glutathione peroxidase provide complementary assessment of defensive capacity.

Cross-sectional studies have established elevated oxidative stress markers in neurodegenerative disease patients compared to controls, yet longitudinal data characterizing biomarker trajectories over disease course remain sparse [10] .

Understanding temporal dynamics of oxidative stress markers carries implications for disease monitoring, prognostication, and evaluation of therapeutic interventions targeting oxidative pathways. Comparative analysis across different neurodegenerative conditions may reveal diseasespecific signatures informing diagnostic approaches and mechanistic understanding [11] . China faces rapidly increasing neurodegenerative disease burden as the world's most populous nation undergoes demographic transition. An estimated 15 million Chinese individuals currently live with dementia, projected to reach 45 million by 2050 [12] . Despite this substantial burden, longitudinal biomarker research in Chinese neurodegenerative disease populations remains limited, with most data derived from Western cohorts of different ethnic composition and environmental exposures. This prospective cohort research aimed to characterize longitudinal oxidative stress biomarker trajectories in Chinese patients with Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis compared to healthy controls. The specific objectives included comparing baseline oxidative stress profiles across neurodegenerative conditions, modeling biomarker trajectories over 36 months of follow-up, evaluating correlations between oxidative markers and cognitive function, and identifying biomarker predictors of disease progression rate. We hypothesized that oxidative stress marker trajectories would differ across conditions, reflecting disease-specific pathophysiology and progression rates.

Biomarker Selection Rationale

The oxidative stress biomarker panel was selected to comprehensively capture oxidative damage across major biomolecular targets while including antioxidant defense assessment. Malondialdehyde was chosen as the primary lipid peroxidation marker given extensive validation literature, established assay methodology, and demonstrated sensitivity to neurodegenerative disease states [13] . 8hydroxydeoxyguanosine provides assessment of oxidative DNA damage, a critical pathway in neuronal dysfunction given the post-mitotic nature of neurons limiting DNA repair capacity. Protein carbonyl measurement captures irreversible protein oxidation affecting enzyme function and structural proteins. The antioxidant enzyme panel comprising superoxide dismutase, catalase, and glutathione peroxidase represents the primary enzymatic defense system against reactive oxygen species, with each enzyme targeting specific reactive species in coordinated fashion. Reduced glutathione was included as the principal non-enzymatic antioxidant maintaining cellular redox balance. This comprehensive panel enables assessment of both oxidative damage burden and defensive capacity. Exclusion criteria common to all groups included active malignancy, chronic inflammatory conditions, recent infection within two weeks, antioxidant supplement use within three months, current smoking, excessive alcohol consumption, and chronic kidney or liver disease. Diseasespecific exclusions for neurodegenerative groups included atypical presentations suggesting alternative diagnoses and concurrent neurological conditions. Sample size calculations based on anticipated effect sizes from previous crosssectional research indicated requirement for 40-100 participants per group with 80% power.

Materials and Methods

Materials

Methods

Participants underwent standardized assessments at baseline and six-month intervals for 36 months. Fasting venous blood samples were collected between 8:00 and 10:00 AM to minimize circadian variation. Samples were processed within two hours of collection with plasma and serum aliquots stored at -80°C until batch analysis. Malondialdehyde was quantified using thiobarbituric acid reactive substances assay with spectrophotometric detection. 8-hydroxydeoxyguanosine was measured by competitive enzyme-linked immunosorbent assay (Jaica, Japan). Protein carbonyl content was determined by derivatization with 2,4-dinitrophenylhydrazine followed by spectrophotometric measurement. Superoxide dismutase activity was assessed using xanthine oxidase method, catalase activity by hydrogen peroxide decomposition rate, and glutathione peroxidase activity using cumene hydroperoxide as substrate. Reduced The research cohort comprised 305 participants followed for a median of 32 months (interquartile range 24-36 months). Retention rates were 92% for controls, 86% for Alzheimer's disease, 89% for Parkinson's disease, and 64% for amyotrophic lateral sclerosis, with losses primarily attributable to death in the ALS group and institutionalization in advanced dementia cases. Baseline oxidative damage markers were significantly elevated across all neurodegenerative groups compared to controls, while antioxidant enzyme activities demonstrated corresponding reductions. Longitudinal modeling revealed significantly accelerated oxidative stress marker increases across all neurodegenerative groups compared to the minimal changes observed in healthy controls. Amyotrophic lateral sclerosis demonstrated the most rapid progression, with malondialdehyde increasing at more than three times the rate observed in Alzheimer's disease. This accelerated trajectory reflects the aggressive clinical course characteristic of ALS and suggests oxidative damage as a dynamic process paralleling disease progression.

Discussion

This longitudinal cohort research demonstrates diseasespecific oxidative stress signatures across major neurodegenerative disorders, with trajectory analysis revealing accelerated oxidative damage accumulation that parallels clinical progression rates. The finding that amyotrophic lateral sclerosis exhibits the steepest biomarker trajectories aligns with its aggressive clinical course and supports oxidative stress as a mechanistically relevant pathological process rather than epiphenomenon of neurodegeneration [14] . The coordinated elevation of multiple oxidative damage markers alongside depletion of antioxidant defenses indicates systemic redox imbalance in neurodegenerative states. This pattern suggests that therapeutic approaches targeting single antioxidant pathways may prove insufficient, potentially explaining disappointing results from clinical trials of individual antioxidant compounds [15] . Comprehensive strategies addressing multiple oxidative pathways or upstream triggers of reactive oxygen species generation may offer superior therapeutic potential. The strong correlations between peripheral oxidative stress markers and cognitive function in Alzheimer's disease support the biological relevance of these accessible biomarkers. The predictive relationship between baseline malondialdehyde and subsequent cognitive decline rate suggests potential utility for prognostication and clinical trial enrichment strategies [16] . Identifying patients with elevated oxidative stress at disease presentation could enable targeted enrollment in antioxidant intervention trials or more aggressive management approaches. The differential trajectory patterns across neurodegenerative conditions may reflect underlying pathophysiological distinctions. Amyotrophic lateral sclerosis involves rapid motor neuron degeneration with substantial mitochondrial dysfunction and excitotoxicity, processes generating abundant reactive oxygen species [17] . Alzheimer's disease demonstrates more gradual progression with amyloid and tau pathology indirectly promoting oxidative damage through inflammatory activation and mitochondrial dysfunction [18] . These mechanistic differences manifest as quantifiable biomarker trajectory differences.

Conclusion

This prospective longitudinal cohort research establishes disease-specific oxidative stress biomarker signatures across major neurodegenerative disorders, demonstrating accelerated damage accumulation that parallels clinical progression trajectories. The findings support oxidative stress as a mechanistically relevant and dynamically evolving pathological process in neurodegeneration rather than static cross-sectional abnormality. Comparative analysis across Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis reveals quantifiable differences in oxidative burden and trajectory slopes reflecting underlying pathophysiological distinctions. The coordinated pattern of elevated oxidative damage markers alongside depleted antioxidant defenses indicates systemic redox failure rather than isolated pathway dysfunction. Malondialdehyde, 8-hydroxydeoxyguanosine, and protein carbonyls all demonstrated progressive increases across follow-up, while superoxide dismutase, catalase, and glutathione peroxidase activities showed corresponding declines. This comprehensive biomarker assessment captures the full scope of oxidative stress evolution in neurodegenerative states. Amyotrophic lateral sclerosis exhibited the most aggressive oxidative stress trajectory, with malondialdehyde accumulation proceeding at more than triple the rate observed in Alzheimer's disease. This accelerated pattern aligns with the rapid clinical course characteristic of motor neuron disease and suggests oxidative damage as particularly central to ALS pathophysiology. The distinct trajectory profiles across conditions may inform diseasespecific therapeutic development and prognostic assessment approaches. The strong negative correlation between oxidative markers and cognitive function in Alzheimer's disease supports the biological relevance of peripheral biomarker assessment. The independent predictive relationship between baseline malondialdehyde and subsequent cognitive decline rate demonstrates prognostic utility extending beyond crosssectional associations. These findings support potential clinical applications including risk stratification at diagnosis, monitoring disease progression, and identifying candidates for antioxidant intervention trials. This research conducted in a Chinese population addresses important representation gaps in the neurodegenerative biomarker literature. The similar biomarker patterns observed compared to Western cohort studies suggest oxidative stress represents a conserved pathological mechanism across ethnic groups, supporting generalizability of findings. However, population-specific reference ranges and prognostic thresholds warrant further investigation given potential genetic and environmental modifiers. Future research priorities include validation of prognostic biomarker thresholds in independent cohorts, evaluation of biomarker responses to disease-modifying therapies, and investigation of interventions targeting multiple oxidative pathways simultaneously. The dynamic nature of oxidative stress biomarker trajectories positions them as potential surrogate endpoints for clinical trials, enabling more efficient therapeutic development. Integration of oxidative stress assessment into neurodegenerative disease management protocols could facilitate personalized treatment approaches addressing this fundamental pathological mechanism.

Acknowledgement

Acknowledgements Funding SourcesThis research received support from the National Natural Science Foundation of China (Grant 81971028), the Beijing Municipal Natural Science Foundation (Grant 7192108), and the CAMS Innovation Fund for Medical Sciences (CIFMS 2021-I2M-1-003). The funding bodies had no involvement in research design, data analysis, or manuscript preparation. Institutional SupportThe authors acknowledge the Neurodegenerative Disease Center and Clinical Biochemistry Laboratory at Peking Union Medical College Hospital for providing essential research infrastructure.

References

1. GBD 2016 Dementia Collaborators. Global, regional, and national burden of Alzheimer's disease and other dementias, 1990-2016: a systematic analysis for the Global Burden of Disease Study 2016. The Lancet Neurology. 2019;18(1):88-106.
2. Poewe W, Seppi K, Tanner CM, et al. Parkinson disease. Nature Reviews Disease Primers. 2017;3:17013.
3. Hardiman O, Al-Chalabi A, Chio A, et al. Amyotrophic lateral sclerosis. Nature Reviews Disease Primers. 2017;3:17071.
4. Sies H, Berndt C, Jones DP. Oxidative stress. Annual Review of Biochemistry. 2017;86:715-748.
5. Cobley JN, Fiorello ML, Bailey DM. 13 reasons why the brain is susceptible to oxidative stress. Redox Biology. 2018;15:490-503.
6. Nunomura A, Perry G, Aliev G, et al. Oxidative damage is the earliest event in Alzheimer disease. Journal of Neuropathology and Experimental Neurology. 2001;60(8):759-767.
7. Praticò D. The neurobiology of isoprostanes and Alzheimer's disease. Biochimica et Biophysica Acta. 2010;1801(8):930-933.
8. Greilberger J, Koidl C, Greilberger M, et al. Malondialdehyde, carbonyl proteins and albumindisulphide as useful oxidative markers in mild cognitive impairment and Alzheimer's disease. Free Radical Research. 2008;42(7):633-638.
9. Dalle-Donne I, Rossi R, Giustarini D, et al. Protein carbonyl groups as biomarkers of oxidative stress. Clinica Chimica Acta. 2003;329(1-2):23-38.
10. Sharma A, Weber D, Raber J, et al. Systemic oxidative stress and neurodegeneration: the connection and impact on cognition. Frontiers in Physiology. 2020;11:611.
11. Kim GH, Kim JE, Rhie SJ, Yoon S. The role of oxidative stress in neurodegenerative diseases. Experimental Neurobiology. 2015;24(4):325-340.
12. Jia L, Quan M, Fu Y, et al. Dementia in China: epidemiology, clinical management, and research advances. The Lancet Neurology. 2020;19(1):81-92.
13. Ayala A, Muñoz MF, Argüelles S. Lipid peroxidation: production, metabolism, and signaling mechanisms of malondialdehyde and 4-hydroxy-2-nonenal. Oxidative Medicine and Cellular Longevity. 2014;2014:360438.
14. Barber SC, Mead RJ, Shaw PJ. Oxidative stress in ALS: a mechanism of neurodegeneration and a therapeutic target. Biochimica et Biophysica Acta. 2006;1762(11-12):1051-1067.
15. Galasko D, Montine TJ. Biomarkers of oxidative damage and inflammation in Alzheimer's disease. Biomarkers in Medicine. 2010;4(1):27-36.
16. H, Burnham SC. Blood-based molecular biomarkers for Alzheimer's disease. Molecular Brain. 2019;12(1):26.
17. Smith EF, Shaw PJ, De Vos KJ. The role of mitochondria in amyotrophic lateral sclerosis. Neuroscience Letters. 2019;710:132933.
18. Butterfield DA, Halliwell B. Oxidative stress, dysfunctional glucose metabolism and Alzheimer disease. Nature Reviews Neuroscience. 2019;20(3):148-160.
19. Tönnies E, Trushina E. Oxidative stress, synaptic dysfunction, and Alzheimer's disease. Journal of Alzheimer's Disease. 2017;57(4):1105-1121.