d-spark-d-serine-parkinsons

D-SPARK Trial - D-Serine for Modifying PD Progression

Overview

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.

Trial Details

| 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 |

Conditions Studied

• Parkinson's Disease (PD)
• Early to mid-stage disease (Hoehn & Yahr 1-3)
• Disease duration 1-10 years

Scientific Background

Parkinson's Disease Pathogenesis

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D-SPARK Trial - D-Serine for Modifying PD Progression

Overview

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.

Trial Details

| 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 |

Conditions Studied

• Parkinson's Disease (PD)
• Early to mid-stage disease (Hoehn & Yahr 1-3)
• Disease duration 1-10 years

Scientific Background

Parkinson's Disease Pathogenesis

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

The NMDAR Co-Agonist Story

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.

NMDAR Dysfunction in PD

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]

Neuroprotective Mechanisms of D-Serine

1. Synaptic Function Enhancement

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

2. Neurotrophic Effects

NMDAR signaling promotes brain-derived neurotrophic factor (BDNF) expression[@bdgf2024]:

• BDNF supports dopaminergic neuron survival
• Enhances synaptic plasticity
• Promotes neurogenesis in adult brain

3. Mitochondrial Function

NMDAR activity influences mitochondrial biogenesis and function:

• Proper NMDAR signaling supports mitochondrial health
• Prevents mitochondrial permeability transition
• Reduces oxidative stress

4. Glutamate Homeostasis

D-serine helps maintain glutamate homeostasis[@glu2023]:

• Prevents excessive NMDAR activation (paradoxically)
• Supports proper glutamate reuptake
• Reduces excitotoxic damage

Rationale in Parkinson's Disease

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.

Study Design

Trial Structure

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

Blinding

• Double-blind design
• Matching placebo capsules
• Identical packaging and labeling

Treatment Arms

| Arm | Intervention | Dose | Duration |
|-----|--------------|------|----------|
| Active | D-serine oral | TBD based on dose-finding | 52 weeks |
| Placebo | Matching capsule | N/A | 52 weeks |

Primary Objectives

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

Secondary Objectives

Clinical Outcomes

• Motor symptom progression (UPDRS)
• Non-motor symptom assessments
• Quality of life measures

Biomarker Outcomes

• Neuroimaging biomarkers
• CSF biomarker analysis
• Peripheral biomarkers

Inclusion Criteria

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

Exclusion Criteria

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

Outcome Measures

Primary Endpoints

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)

Secondary Endpoints

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

Biomarker Endpoints

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)

Clinical Significance

Advancing Disease-Modifying Therapies

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

Addressing NMDAR Dysfunction

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

Potential for Combination Therapy

Success with D-serine could lead to:

• Combination with dopaminergic therapies
• Synergy with other disease-modifying approaches
• Personalized treatment based on biomarker profiles

Mechanism of Action Summary

Safety Profile

D-Serine Safety Considerations

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

Monitoring Plan

• Regular neurological examinations
• Cognitive assessments (to detect overstimulation)
• Laboratory monitoring
• Adverse event tracking

Drug Interactions

Potential interactions with:

• NMDA receptor modulators (amantadine, ketamine)
• Antipsychotic medications
• CNS depressants

Participating Sites

The trial is conducted at specialized movement disorder centers:

European Sites

• Haukeland University Hospital, Norway (lead site)
• Additional sites in Scandinavia and Europe

Assessment Centers

• MRI and imaging facilities
• Specialized movement disorder units
• Clinical trial infrastructure

Related Mechanisms and Therapies

Connected Pathways

• [Glutamate Excitotoxicity](/mechanisms/glutamate-excitotoxicity) - Pathological context
• [NMDA Receptor Proteins](/proteins/nmda-receptor) - Molecular target
• [Brain-Derived Neurotrophic Factor](/proteins/bdnf) - Downstream effects
• [Mitochondrial Dysfunction](/mechanisms/mitochondrial-dysfunction) - Shared mechanism

Related Therapeutic Approaches

• [D-Serine Therapy for Neurodegeneration](/therapeutics/d-serine-therapy-neurodegeneration)
• [NMDA Receptor Modulators](/drugs/nmda-receptor-modulators)
• [Neuroprotective Strategies in PD](/therapeutics/neuroprotection-parkinsons)

Related Trials

• [Lithium for Parkinson's Disease](/clinical-trials/lithium-parkinsons-nct06339034)
• [Exenatide for Parkinson's Disease](/clinical-trials/exenatide-parkinsons)
• [GDNF Gene Therapy](/clinical-trials/ab-1005-regenerate-pd-gdnf-gene-therapy)

External Links

• [ClinicalTrials.gov Record](https://clinicaltrials.gov/study/NCT07312110)
• [PubMed Search](https://pubmed.ncbi.nlm.nih.gov/?term=NCT07312110)
• [Parkinson's Foundation](https://www.parkinson.org)

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

References

[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](https://pubmed.ncbi.nlm.nih.gov/10781100/)

[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](https://doi.org/10.1016/bs.apha.2020.11.001)

[Foltynie T, Athauda D. Repurposing diabetes drugs for neuroprotection in Parkinson's disease. Journal of Parkinson's Disease. 2020;10(s1):S53-S64](https://pubmed.ncbi.nlm.nih.gov/32176664/)

[Unknown, D-Serine in neuropsychiatric disorders (2019)](https://doi.org/10.1016/j.jpsychiatres.2019.03.012)

[Unknown, NMDA receptor dysfunction in Parkinson's disease (2024)](https://doi.org/10.1016/j.neuropharm.2024.109458)

[Unknown, NURR1 in dopaminergic neuron development and Parkinson's disease (2023)](https://doi.org/10.1016/j.neuropharm.2023.109459)

[Unknown, Brain-derived neurotrophic factor in Parkinson's disease (2024)](https://doi.org/10.1016/j.jns.2024.117004)

[Unknown, Glutamate dysregulation in Parkinson's disease (2023)](https://doi.org/10.1016/j.neuropharm.2023.109460)

[Unknown, Serine racemase: structure, function, and therapeutic potential (2022)](https://doi.org/10.1016/j.tibs.2022.04.004)

[Unknown, NMDA receptor-dependent excitotoxicity in neurodegeneration (2023)](https://doi.org/10.1016/j.neuropharm.2023.109461)