Neuroprotective Potential of Edible Bird’s Nest and Thymoquinone in Parkinsonian Zebrafish

Technical Summary: Neuroprotective Potential of Edible Bird's Nest and Thymoquinone in Parkinsonian Zebrafish

Problem Statement
Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, leading to motor impairments such as bradykinesia and tremors. While the zebrafish (Danio rerio) is an established vertebrate model for PD research due to its genetic homology and complex motor behaviors, the evaluation of novel neuroprotective agents like Edible Bird's Nest (EBN) and Thymoquinone (TQ) is hindered by a lack of standardized, safe dosing protocols. Existing literature often lacks detailed methodological reporting regarding velocity thresholds and movement parameters in automated tracking, leading to inter-study variability. Furthermore, before assessing neuroprotective efficacy in toxin-induced models (e.g., MPTP), it is critical to establish dose ranges that are biologically relevant and behaviorally neutral, ensuring that observed locomotor changes result from therapeutic action rather than systemic toxicity or confounding pharmacological effects.

Methodology
This preliminary study utilized adult wild-type zebrafish (>5 months old) to optimize dosing parameters for EBN and TQ through a 14-day systematic assessment.

• Experimental Design: A total of 80 mixed-gender zebrafish were randomly allocated into eight groups (n=10 each): two untreated controls, two vehicle controls (Normal Saline for EBN; DMSO for TQ), and four treatment groups.
• Dosing Regimens: Agents were administered orally via micropipette.
  • EBN: Low-dose (LD: 60 mg/kg) and Mid-dose (MD: 90 mg/kg). High-dose (120 mg/kg) was tested but excluded due to toxicity.
  • TQ: Low-dose (LD: 20 mg/kg) and Mid-dose (MD: 110 mg/kg). High-dose (200 mg/kg) was excluded due to toxicity.
• Behavioral Assessment: Locomotor activity was evaluated using the Open Field Test (OFT) on Days 0 (baseline), 7, and 14.
• Tracking and Analysis: Movements were recorded via top-view cameras and analyzed using Noldus EthoVision XT software (v11.5). The study implemented a standardized protocol with specific velocity thresholds: start velocity at 1.5 cm/s and stop velocity at 0.8 cm/s to distinguish active swimming from non-movement (e.g., sliding, freezing). Additional parameters included total distance traveled, freezing bouts/duration, and exploratory patterns (time in inner vs. outer zones).
• Statistical Analysis: Due to non-normal data distribution (Shapiro-Wilk test), non-parametric Kruskal-Wallis tests followed by post-hoc pairwise comparisons were used.

Key Contributions

1. Standardization of Behavioral Protocols: The study validated and applied a specific behavioral analysis template (based on Razali et al., 2025) for adult zebrafish, defining precise start/stop velocity thresholds (1.5/0.8 cm/s) and mobility state classifications to enhance reproducibility in PD research.
2. Dose Optimization: The research successfully identified safe, behaviorally neutral, and biologically relevant dose ranges for EBN and TQ in adult zebrafish, distinguishing them from toxic thresholds.
3. Safety and Viability Data: The study provided critical viability data, demonstrating that high doses (120 mg/kg EBN; 200 mg/kg TQ) induce acute systemic toxicity and mortality, whereas lower doses are well-tolerated.
4. Differentiation of Pharmacological Effects: By monitoring anxiety markers (freezing behavior) alongside locomotor activity, the study ensured that observed motor enhancements were not artifacts of stress or anxiogenic responses.

Results

• Toxicity and Viability: High-dose exposure resulted in significant mortality and was excluded from further analysis. Control and LD groups maintained 100% survival. MD groups showed reduced survival (66.7% for EBN; 50.0% for TQ), indicating these doses represent the upper limit of safety.
• Locomotor Activity (EBN): EBN induced moderate, dose-dependent enhancements in locomotor activity. The MD-EBN group (90 mg/kg) showed the most rapid stimulatory effect on Day 1 (6.21 cm/s velocity) and sustained improvements by Day 14 (6.63 cm/s). LD-EBN (60 mg/kg) also improved activity but less pronouncedly.
• Locomotor Activity (TQ): TQ elicited a more potent and progressive stimulatory effect. The MD-TQ group (110 mg/kg) demonstrated significant increases in distance traveled (4543 cm on Day 1 vs. 675 cm in controls) and achieved the highest velocity by Day 14 (7.1 cm/s).
• Anxiety and Freezing: Neither agent induced consistent anxiogenic effects. Freezing durations remained relatively stable across groups, suggesting that the observed motor improvements were not driven by stress or anxiety-like behaviors.
• Comparative Outcomes: TQ demonstrated a stronger and more sustained boost to locomotor function compared to the moderate, stable improvements seen with EBN.

Significance and Claims
The authors claim that this study establishes a foundational framework for future neuroprotective investigations in zebrafish models of Parkinson's disease. By defining optimized doses—60–90 mg/kg for EBN and 20–110 mg/kg for TQ—the study ensures that subsequent efficacy trials against MPTP-induced neurodegeneration can be conducted under ethically responsible and scientifically rigorous conditions. The findings suggest that while both agents enhance motor function, TQ may act through more direct dopaminergic modulation, whereas EBN likely supports neuronal health via antioxidant and anti-inflammatory mechanisms. The study emphasizes that these optimized doses allow researchers to attribute behavioral changes to therapeutic mechanisms rather than confounding toxic or stress-related effects, thereby improving the translational validity of preclinical PD research.