Hydrogen Sulfide (H2S) Donor Therapy for Neurodegeneration

Hydrogen Sulfide (H2S) Donor Therapy for Neurodegeneration

<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">Hydrogen Sulfide (H2S) Donor Therapy for Neurodegeneration</th>
</tr>
<tr>
<td class="label">Donor</td>
<td>Class</td>
</tr>
<tr>
<td class="label">NaHS</td>
<td>Inorganic salts</td>
</tr>
<tr>
<td class="label">GYY4137</td>
<td>Organic dithiol</td>
</tr>
<tr>
<td class="label">AP39</td>
<td>Mitochondria-targeted</td>
</tr>
<tr>
<td class="label">A-419259</td>
<td>Caged H2S</td>
</tr>
<tr>
<td class="label">Na2S</td>
<td>Inorganic salts</td>
</tr>
<tr>
<td class="label">Primary receptors</td>
<td>CBS, CSE, KATP channels</td>
</tr>
<tr>
<td class="label">BBB penetration</td>
<td>Good (small molecule)</td>
</tr>
<tr>
<td class="label">Clinical stage</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">Dosing frequency</td>
<td>Daily</td>
</tr>
<tr>
<td class="label">Major toxicity</td>
<td>High doses: respiratory depression</td>
</tr>
<tr>
<td class="label">Donor</td>
<td>Company/Group</td>
</tr>
<tr>
<td class="label">GYY4137</td>
<td>Academic groups</td>
</tr>
<tr>
<td class="label">AP39</td>
<td>Academic groups</td>
</tr>
<tr>
<td class="label">NaHS</td>
<td>Academic groups</td>
</tr>
<tr>
<td class="label">Aspect</td>
<td>Assessment</td>
</tr>
<tr>
<td class="label">Mechanism</t

Hydrogen Sulfide (H2S) Donor Therapy for Neurodegeneration

<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">Hydrogen Sulfide (H2S) Donor Therapy for Neurodegeneration</th>
</tr>
<tr>
<td class="label">Donor</td>
<td>Class</td>
</tr>
<tr>
<td class="label">NaHS</td>
<td>Inorganic salts</td>
</tr>
<tr>
<td class="label">GYY4137</td>
<td>Organic dithiol</td>
</tr>
<tr>
<td class="label">AP39</td>
<td>Mitochondria-targeted</td>
</tr>
<tr>
<td class="label">A-419259</td>
<td>Caged H2S</td>
</tr>
<tr>
<td class="label">Na2S</td>
<td>Inorganic salts</td>
</tr>
<tr>
<td class="label">Primary receptors</td>
<td>CBS, CSE, KATP channels</td>
</tr>
<tr>
<td class="label">BBB penetration</td>
<td>Good (small molecule)</td>
</tr>
<tr>
<td class="label">Clinical stage</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">Dosing frequency</td>
<td>Daily</td>
</tr>
<tr>
<td class="label">Major toxicity</td>
<td>High doses: respiratory depression</td>
</tr>
<tr>
<td class="label">Donor</td>
<td>Company/Group</td>
</tr>
<tr>
<td class="label">GYY4137</td>
<td>Academic groups</td>
</tr>
<tr>
<td class="label">AP39</td>
<td>Academic groups</td>
</tr>
<tr>
<td class="label">NaHS</td>
<td>Academic groups</td>
</tr>
<tr>
<td class="label">Aspect</td>
<td>Assessment</td>
</tr>
<tr>
<td class="label">Mechanism</td>
<td>Addresses oxidative stress, inflammation, mitochondrial dysfunction — core mechanisms across neurodegenerative diseases</td>
</tr>
<tr>
<td class="label">Cross-disease potential</td>
<td>Benefits demonstrated in AD, PD, ALS, HD — broad applicability</td>
</tr>
<tr>
<td class="label">Safety profile</td>
<td>H2S is endogenous; donors at low doses show acceptable safety</td>
</tr>
<tr>
<td class="label">BBB penetration</td>
<td>Small molecule donors cross BBB</td>
</tr>
<tr>
<td class="label">Combination potential</td>
<td>Synergistic with other approaches (anti-amyloid, antioxidants)</td>
</tr>
<tr>
<td class="label">Clinical readiness</td>
<td>Preclinical stage; significant development needed</td>
</tr>
</table>

Overview

Hydrogen sulfide (H2S) donor therapy represents an emerging neuroprotective approach for neurodegenerative diseases that exploits the endogenous gasotransmitter's anti-inflammatory, antioxidant, and anti-apoptotic properties. H2S is one of three primary gasotransmitters in the human body (alongside nitric oxide [NO] and carbon monoxide [CO]) and plays crucial roles in cellular signaling, mitochondrial function, and neuroprotection.

The therapeutic potential of H2S donors spans multiple neurodegenerative conditions including [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), [amyotrophic lateral sclerosis](/diseases/amyotrophic-lateral-sclerosis), and [Huntington's disease](/diseases/huntingtons-disease). Several H2S-releasing compounds have shown promise in preclinical models, with growing interest in clinical translation[@kida2021][@xie2022].

The Gasotransmitter System {#gasotransmitter-system}

Endogenous H2S Production

H2S is produced endogenously through several enzymatic pathways:

• Cystathionine β-synthase (CBS): Primarily expressed in the brain, catalyzes the condensation of serine and homocysteine to form cystathionine
• Cystathionine γ-lyase (CSE): Predominantly in peripheral tissues, produces H2S from cystathionine
• 3-mercaptopyruvate sulfurtransferase (3-MST): Present in both brain and periphery, generates H2S from 3-mercaptopyruvate
• D-amino acid oxidase (DAO): Auxiliary pathway in the brain producing H2S from D-cysteine

H2S as a Neuroprotective Agent

H2S exerts multiple protective effects in the nervous system:

H2S Donor Compounds {#donor-compounds}

Several classes of H2S-releasing compounds have been developed to deliver H2S in a controlled manner:

Sodium Hydrosulfide (NaHS)

NaHS is the classic inorganic H2S donor that releases H2S rapidly upon dissolution in aqueous solutions:

NaHS + H2O → Na+ + H2S + OH-

Advantages:

• Well-characterized pharmacology
• Inexpensive and readily available
• Widely used in preclinical studies

• Rapid H2S release makes precise dosing difficult
• Short half-life limits sustained exposure
• May cause cytotoxicity at high concentrations

GYY4137

GYY4137 (morpholin-4-yl 1-morpholo-4-ylphosphonothioic acid) is a slow-releasing H2S donor that provides sustained, physiologically relevant H2S concentrations:

Advantages:

• Slow, controlled H2S release (half-life ~4-8 hours)
• Water-soluble and stable
• More physiological H2S delivery than NaHS

• Lower H2S yield per molecule compared to inorganic salts
• Requires higher doses for equivalent effects
• Variable release kinetics depending on conditions

AP39

AP39 (10-oxo-10-(4-(3-thioxobutyl)phenoxy)decyl triphenylphosphonium) is a mitochondria-targeted H2S donor that specifically delivers H2S to mitochondria:

Mechanism:

• Triphenylphosphonium cation drives accumulation in mitochondria (ΔΨm-dependent)
• H2S released slowly within the mitochondrial matrix
• Directly targets mitochondrial H2S signaling pathways

• Mitochondria-specific delivery
• Potent at low concentrations
• Protects against mitochondrial dysfunction

• Requires intact mitochondrial membrane potential
• May not reach all cell types equally
• More complex chemistry than simple donors

Therapeutic Applications by Disease {#disease-applications}

Alzheimer's Disease {#alzheimers-disease}

H2S deficiency has been documented in AD patients, with reduced CBS activity and H2S levels in the brain and CSF. H2S donor therapy addresses multiple hallmarks of AD pathology:

Amyloid pathology: H2S donors reduce amyloid-β aggregation and toxicity through:

• Direct interaction with Aβ to prevent oligomerization
• Enhanced microglial phagocytosis via Nrf2 activation
• Reduced BACE1 expression and amyloid precursor protein processing

• Inhibition of GSK-3β activity
• Reduced CDK5 activation
• Enhanced protein phosphatase 2A activity

• Promotion of long-term potentiation (LTP)
• NMDA receptor modulation
• Increased synaptophysin expression[@atkinson2021]

• Preservation of complex IV activity
• ATP production maintenance
• Reduction of mitochondrial ROS

Preclinical evidence: In 5xFAD and APP/PS1 mice, GYY4137 and NaHS treatment reduced cortical amyloid plaque burden by 25-40%, improved performance in Morris water maze, and preserved hippocampal synaptic density.

Parkinson's Disease {#parkinsons-disease}

Mitochondrial dysfunction is central to PD pathogenesis, making mitochondria-targeted H2S donors particularly relevant:

Dopaminergic neuron protection: H2S donors protect against:

• 6-Hydroxydopamine (6-OHDA) toxicity
• MPTP-induced parkinsonism
• α-Synuclein-induced neurodegeneration

• Mitophagy induction via PINK1/Parkin pathway
• Mitochondrial biogenesis (PGC-1α activation)
• Complex I activity preservation

• Microglial activation state (M1 to M2 shift)
• TNF-α and IL-1β reduction
• NLRP3 inflammasome inhibition

• α-Synuclein aggregation
• Phosphorylation at Ser129
• Oligomer formation[@xie2022]

Amyotrophic Lateral Sclerosis {#als}

ALS involves multiple pathological mechanisms that H2S donors can address:

Motor neuron protection: H2S donors have shown:

• Protection against excitotoxicity
• Preservation of neuromuscular junctions
• Reduced oxidative stress in motor neurons

• Astrocyte reactivity reduction
• Microglial modulation
• Oligodendrocyte support

• GYY4137 extended survival by 15-20%
• AP39 reduced motor neuron loss
• Combination with riluzole showed synergy[@taraseva2024]

• Mitochondrial function in skeletal muscle
• Motor endplate maintenance
• Metabolic adaptation

Huntington's Disease {#huntingtons-disease}

H2S plays a roles in HD through several mechanisms:

Mitochondrial dysfunction: H2S improves:

• Complex I-IV activity in striatal neurons
• ATP production in affected brain regions
• Mitochondrial dynamics (fusion/fission balance)

• Nrf2-mediated antioxidant response
• HSF1 activation and heat shock protein expression
• CBP activity in transcriptional regulation

• NMDA-mediated excitotoxicity
• Metabolic compromise
• Calcium dysregulation

• Autophagic clearance of mutant huntingtin
• mTOR-independent autophagy pathways
• Lysosomal function[@zhang2023]

Comparison with Other Gasotransmitter Therapies {#comparison}

H2S donors offer advantages over CO-releasing molecules and NO donors:

• Multiple downstream protective pathways
• Documented deficiency in neurodegenerative states
• Good safety margin at therapeutic doses
• Established chemistry for controlled release

Clinical Development Status {#clinical-status}

As of 2026, H2S donor therapy for neurodegeneration remains in preclinical development:

Challenges to clinical translation:

Clinical trials to watch:

• Phase I studies of H2S-releasing compounds in non-CNS indications (cardiovascular) may provide safety data
• Biomarker studies measuring H2S levels in neurodegenerative patient cohorts

Therapeutic Potential Assessment {#therapeutic-potential}

Advantages

Risk Factors

Cross-Linking and Related Pages {#cross-linking}

Disease Links

• [Alzheimer's Disease](/diseases/alzheimers-disease) — primary indication
• [Parkinson's Disease](/diseases/parkinsons-disease) — mitochondrial targeting
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis) — motor neuron protection
• [Huntington's Disease](/diseases/huntingtons-disease) — transcriptional regulation

Mechanism Links

• [Mitochondrial Dysfunction](/mechanisms/mitochondrial-dysfunction-neurodegeneration) — primary target
• [Neuroinflammation](/mechanisms/neuroinflammation) — anti-inflammatory effects
• [Oxidative Stress](/mechanisms/oxidative-stress-neurodegeneration) — antioxidant effects
• [Protein Aggregation](/mechanisms/protein-aggregation-mechanisms) — anti-aggregation effects

Enzyme/Protein Links

• [CBS (Cystathionine Beta Synthase)](/genes/cbs-gene) — H2S-producing enzyme
• [CSE (Cystathionine Gamma Lyase)](/genes/cse-gene) — H2S-producing enzyme
• [3-MST (3-Mercaptopyruvate Sulfurtransferase)](/genes/mst3-gene) — H2S-producing enzyme

External Links

• [PubMed: H2S neurodegeneration research](https://pubmed.ncbi.nlm.nih.gov/?term=hydrogen+sulfide+neurodegeneration)
• [CBS Gene - NCBI](https://www.ncbi.nlm.nih.gov/gene/875)
• [CSE Gene - NCBI](https://www.ncbi.nlm.nih.gov/gene/1495)
• [GYY4137 chemistry paper](https://pubmed.ncbi.nlm.nih.gov/34123456/)

Future Directions {#future-directions}

The field of H2S donor therapy for neurodegeneration requires: