The D-SPARK (D-Serine for Modifying PD Progression) trial is a Phase 2 clinical study evaluating the disease-modifying potential of D-serine in Parkinson's disease. This trial represents a novel approach to Parkinson's disease therapy by targeting N-methyl-D-aspartate receptor (NMDAR) signaling to potentially slow or halt disease progression rather than merely providing symptomatic relief[@mothet2000][@wolosker2021].
D-serine is an endogenous amino acid that acts as the primary co-agonist for NMDARs in the forebrain, making it a critical regulator of glutamatergic signaling. Unlike conventional dopamine replacement therapies (levodopa, dopamine agonists) that address motor symptoms, D-serine aims to modify the underlying neurodegenerative process.
| Attribute |
Value |
| Phase |
Phase 2 |
| NCT Number |
NCT07312110 |
| Status |
Active/Recruiting |
| Sponsor |
Haukeland University Hospital |
| Intervention |
D-serine (oral) |
| Study Design |
Randomized, double-blind, placebo-controlled |
| Indication |
Parkinson's disease (early to mid-stage) |
| Enrollment |
~80 participants (estimated) |
| Duration |
52 weeks treatment, 52 weeks follow-up |
- Parkinson's Disease (PD)
- Early to mid-stage disease (Hoehn & Yahr 1-3)
- Disease duration 1-10 years
Parkinson's disease is the second most common neurodegenerative disorder, affecting approximately 10 million people worldwide. The disease is characterized by:
1. Motor Features
- Bradykinesia (slowness of movement)
- Resting tremor
- Rigidity (muscle stiffness)
- Postural instability
2. Non-Motor Features
- Cognitive impairment/dementia
- Depression and anxiety
- Sleep disorders (REM behavior disorder)
- Autonomic dysfunction
- Hyposmia (loss of smell)
3. Neuropathology
- Loss of dopaminergic neurons in substantia nigra pars compacta
- Presence of Lewy bodies (alpha-synuclein inclusions)
- Neuroinflammation and mitochondrial dysfunction
¶ D-Serine and NMDAR Signaling
D-serine's role as an NMDAR co-agonist was discovered only in 2000, overturning the long-held assumption that glycine was the sole endogenous NMDAR modulator[@mothet2000]:
Key Discoveries:
- D-serine is more abundant than glycine in the forebrain
- Serine racemase (SR) synthesizes D-serine from L-serine
- D-serine has higher affinity for the NMDAR glycine site than glycine
- D-serine release is activity-dependent, like classical neurotransmitters
NMDAR Structure and Function
NMDARs are ionotropic glutamate receptors composed of:
- GluN1 subunit (mandatory)
- GluN2A-D subunits (determines properties)
- Sometimes GluN3 subunits
The glycine/D-serine binding site is on the GluN1 subunit - occupancy is required for channel opening upon glutamate binding.
Growing evidence indicates NMDAR signaling is altered in Parkinson's disease[@nmda2024]:
1. Altered NMDAR Expression
- Increased GluN2B subunit expression in PD models
- Shift toward GluN2B-containing receptors
- Altered subunit phosphorylation states
2. D-Serine Deficiency
- Reduced D-serine levels in PD patient brains
- Decreased serine racemase activity
- Impaired D-serine release mechanisms
3. Excitotoxic Vulnerability
- Dopaminergic neurons are particularly vulnerable to NMDAR overactivation
- Loss of dopaminergic input leads to NMDAR compensatory changes
- Creates a self-amplifying cycle of dysfunction[nmdargd2023]
NMDAR activation supports proper synaptic transmission in the striatum and substantia nigra[@nmda2024]:
- Maintains corticostriatal signaling integrity
- Supports burst firing patterns of dopaminergic neurons
- Preserves long-term potentiation (LTP) mechanisms
NMDAR signaling promotes brain-derived neurotrophic factor (BDNF) expression[@bdgf2024]:
- BDNF supports dopaminergic neuron survival
- Enhances synaptic plasticity
- Promotes neurogenesis in adult brain
NMDAR activity influences mitochondrial biogenesis and function:
- Proper NMDAR signaling supports mitochondrial health
- Prevents mitochondrial permeability transition
- Reduces oxidative stress
D-serine helps maintain glutamate homeostasis[@glu2023]:
- Prevents excessive NMDAR activation (paradoxically)
- Supports proper glutamate reuptake
- Reduces excitotoxic damage
The therapeutic rationale for D-serine in PD includes addressing:
- D-Serine Deficiency: Reduced endogenous D-serine availability
- NMDAR Dysfunction: Altered receptor composition and signaling
- Excitotoxic Vulnerability: Secondary to dopaminergic loss
- Neurotrophic Decline: Reduced BDNF signaling
By restoring D-serine levels, the trial aims to normalize NMDAR function and provide neuroprotection against progressive dopaminergic degeneration.
This is a Phase 2, randomized, double-blind, placebo-controlled clinical trial:
¶ Randomization
- 2:1 randomization (active:placebo)
- Stratified by disease severity and duration
- Computer-generated randomization schedule
- Double-blind design
- Matching placebo capsules
- Identical packaging and labeling
| Arm |
Intervention |
Dose |
Duration |
| Active |
D-serine oral |
TBD based on dose-finding |
52 weeks |
| Placebo |
Matching capsule |
N/A |
52 weeks |
-
Safety and Tolerability
- Assess adverse events
- Monitor vital signs and labs
- Evaluate discontinuation rates
-
Disease-Modifying Effects
- Measure motor and non-motor symptom progression
- Compare to natural history data
-
Clinical Outcomes
- Motor symptom progression (UPDRS)
- Non-motor symptom assessments
- Quality of life measures
-
Biomarker Outcomes
- Neuroimaging biomarkers
- CSF biomarker analysis
- Peripheral biomarkers
- Age: 40-75 years
- Diagnosis: Idiopathic Parkinson's disease (UK Brain Bank criteria)
- Disease Duration: 1-10 years
- Hoehn & Yahr Stage: 1-3
- Motor Status: Stable dopaminergic therapy for ≥4 weeks
- Cognitive Status: MMSE ≥24 (no significant impairment)
- Ability to provide informed consent
-
Neurological
- Previous neurosurgical intervention (DBS, etc.)
- Significant neurological disease other than PD
- History of stroke or traumatic brain injury
-
Psychiatric
- Active major depression
- Psychosis (unless well-controlled)
- Severe anxiety disorder
-
Medical
- Severe medical conditions
- Renal or hepatic impairment
- Seizure disorder
-
Prior Treatment
- Prior D-serine therapy
- NMDA receptor modulators within 3 months
- Investigational therapy within 30 days
Unified Parkinson's Disease Rating Scale (UPDRS) Parts I-III
- Part I: Mentation, behavior, mood
- Part II: Activities of daily living
- Part III: Motor examination
Primary analysis: Change from baseline to Week 52 in total UPDRS score (Parts I-III)
-
Motor Subscores
- UPDRS Part III (Motor Examination) alone
- Tremor, bradykinesia, rigidity subscores
-
Non-Motor Assessments
- Parkinson's Disease Questionnaire (PDQ-39)
- Montreal Cognitive Assessment (MoCA)
- Beck Depression Inventory (BDI)
- Epworth Sleepiness Scale
-
Functional Measures
- Timed Up and Go (TUG) test
- 6-minute walk distance
- Hand grip strength
-
Imaging Biomarkers
- DaTscan (dopamine transporter SPECT)
- MRI brain volume measurements
- Diffusion tensor imaging (DTI)
-
CSF Biomarkers
- Alpha-synuclein species
- Total tau and phosphorylated tau
- Neurofilament light chain (NfL)
- Inflammatory markers
-
Blood Biomarkers
- Peripheral inflammatory markers
- Oxidative stress markers
- Growth factors (BDNF)
D-SPARK represents a shift from symptomatic to disease-modifying approaches in PD:
Current Treatment Paradigm
- Levodopa: Dopamine replacement
- Dopamine agonists: Direct receptor activation
- MAO-B inhibitors: Prevent dopamine breakdown
- COMT inhibitors: Extend levodopa effect
- All address symptoms, not progression
Novel Approach
- Targets NMDAR signaling pathway
- Aims to protect remaining neurons
- May slow disease progression
- Different mechanism from all approved therapies
This trial directly tests whether NMDAR modulation can provide neuroprotection:
If positive, would validate:
- NMDAR dysfunction as therapeutic target
- D-serine as a neuroprotective agent
- Importance of co-agonist site modulation
If negative, would inform:
- Complexity of PD pathogenesis
- Need for combination approaches
- Limitations of single-target strategies
Success with D-serine could lead to:
- Combination with dopaminergic therapies
- Synergy with other disease-modifying approaches
- Personalized treatment based on biomarker profiles
flowchart TD
A["Dopaminergic Degeneration"] --> B["Glutamate Dysregulation"]
B --> C["Excessive NMDAR Activation / Dysfunction"]
C --> D["Calcium Overload"]
D --> E["Mitochondrial Dysfunction"]
E --> F["Oxidative Stress"]
F --> G["Neuronal Death"]
H["D-Serine Supplementation"] --> I["Normalized NMDAR Signaling"]
I --> J["Calcium Homeostasis"]
J --> K["Mitochondrial Protection"]
K --> L["Neuroprotection"]
L --> M["Slowed Disease Progression"]
style G fill:#ffcdd2,stroke:#333
style M fill:#c8e6c9,stroke:#333
D-serine has been studied in other clinical contexts:
Known Safety Data:
- Previously studied in schizophrenia (higher doses)
- Generally well-tolerated
- Main concern: potential for NMDAR overstimulation at high doses
Expected Adverse Events:
- Headache (most common)
- Nausea
- Fatigue
- Insomnia
- Dizziness
- Regular neurological examinations
- Cognitive assessments (to detect overstimulation)
- Laboratory monitoring
- Adverse event tracking
Potential interactions with:
- NMDA receptor modulators (amantadine, ketamine)
- Antipsychotic medications
- CNS depressants
The trial is conducted at specialized movement disorder centers:
- Haukeland University Hospital, Norway (lead site)
- Additional sites in Scandinavia and Europe
- MRI and imaging facilities
- Specialized movement disorder units
- Clinical trial infrastructure
¶ Current Status and Outlook
The D-SPARK trial represents an important step in developing disease-modifying therapies for Parkinson's disease. By targeting NMDAR signaling with D-serine, this approach differs from conventional dopamine replacement therapies and may address the underlying neurodegenerative process.
Positive results from this Phase 2 trial would support advancement to larger Phase 3 studies and potentially establish D-serine as a novel neuroprotective therapy for Parkinson's disease.
Future Directions:
- Biomarker development to identify responders
- Combination studies with standard therapies
- Extension to prodromal Parkinson's disease
- Genetic subpopulation analysis
- Mothet JP, Parent AT, Wolosker H, et al. D-Serine is an endogenous neurotransmitter for NMDA receptor activity in the brain. Proceedings of the National Academy of Sciences. 2000;97(9):4926-4931
- Wolosker H, Balu DT, Coyle JT. The regulation of serine racemase and the D-serine modulation of NMDA receptor signaling. Advances in Pharmacology. 2021;90:85-100
- Foltynie T, Athauda D. Repurposing diabetes drugs for neuroprotection in Parkinson's disease. Journal of Parkinson's Disease. 2020;10(s1):S53-S64
- Unknown, D-Serine in neuropsychiatric disorders (2019)
- Unknown, NMDA receptor dysfunction in Parkinson's disease (2024)
- Unknown, NURR1 in dopaminergic neuron development and Parkinson's disease (2023)
- Unknown, Brain-derived neurotrophic factor in Parkinson's disease (2024)
- Unknown, Glutamate dysregulation in Parkinson's disease (2023)
- Unknown, Serine racemase: structure, function, and therapeutic potential (2022)
- Unknown, NMDA receptor-dependent excitotoxicity in neurodegeneration (2023)