Cysteine
| Evidence Level: L4 | Predicted Indications: 10 |
Table of Contents
Cysteine: From Respiratory and Mucolytic Uses to Dry Eye Syndrome
One-Sentence Summary
Cysteine is an amino acid and antioxidant precursor, originally linked to bronchitis, paracetamol poisoning, cystic fibrosis, bronchiectasis and amyloidosis. The TxGNN model predicts it may be useful for dry eye syndrome, but the data compiled for this report contain no clinical trials and only preclinical or formulation-type publications, none of which test cysteine itself as a treatment.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Bronchitis, paracetamol poisoning, cystic fibrosis, bronchiectasis, amyloidosis (no approved indication text is available from Singapore licences) |
| Predicted New Indication | Dry eye syndrome |
| TxGNN Prediction Score | 99.98% |
| Evidence Level | L4 |
| Singapore Market Status | ✓ Marketed |
| Number of Registrations | 4 |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Detailed mechanism of action data are not currently available. Cysteine is a thiol-containing amino acid and a precursor of glutathione, a major cellular antioxidant. Its established uses (respiratory conditions, paracetamol poisoning) are consistent with antioxidant and mucus-modifying properties.
Excess reactive oxygen species (ROS) are thought to drive the inflammatory cycle in dry eye disease. Thiol groups also bind to mucus glycoproteins, which is why cysteine-modified materials show strong mucoadhesion. This gives a plausible rationale based on oxidative stress and ocular surface adhesion.
However, the retrieved publications involve cysteine-derived materials (e.g. cysteine-modified chitosan, hyaluronic acid-cysteine ethyl ester, a persulfide prodrug), not cysteine given as a drug. The link is therefore indirect.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
No randomised trials or clinical studies were found. The most relevant publications are preclinical or formulation studies:
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 40123221 | 2025 | Preclinical | Advanced Materials | Catalase combined with cysteine-modified chitosan as an eye-drop nanoformulation to reduce ROS in dry eye |
| 41485487 | 2026 | Preclinical | J Control Release | Superoxide-responsive persulfide prodrug to scavenge ROS in dry eye |
| 36581034 | 2023 | Preclinical | Int J Biol Macromol | Chondroitin sulfate–L-cysteine conjugate on nanocarriers improved corneal retention and permeation |
| 26606856 | 2015 | Preclinical | Therapeutic Delivery | Hyaluronic acid–cysteine ethyl ester evaluated as a mucoadhesive lubricant |
| 24993428 | 2014 | Review | J Control Release | Review of thiolated polymers (thiomers) and their mucoadhesive properties |
| 31028759 | 2019 | Review | Adv Drug Deliv Rev | Review of thiolated polymers and disulfide bonding with mucus and tissue proteins |
| 24836981 | 2014 | Preclinical | Exp Eye Res | ROS-activated NLRP3 inflammasomes prime inflammation in murine dry eye |
| 25701684 | 2015 | Preclinical/observational | Exp Eye Res | ROS-activated NLRP3 inflammasomes in hyperosmolar corneal cells and dry eye patients |
Singapore Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| SIN06299P | Nephrosteril for Intravenous Infusion | Injection | Not stated |
| SIN08352P | Aminoplasmal-15% Infusion | Injection | Not stated |
| SIN07846P | Trophamine Injection 10% | Injection | Not stated |
| SIN07428P | Vaminolact Intravenous Solution | Injection | Not stated |
All four registrations are valid, single-ingredient injectable amino acid products. No ophthalmic (eye-drop) cysteine product is registered, so the injectable forms do not match the route a dry eye treatment would need.
Safety Considerations
- Contraindication-related disease associations (from the drug-disease knowledge graph, not label text): peptic ulcer disease (including active), hypotensive disorder, respiratory failure, asthma, bronchial disease, esophageal varices, phenylketonuria, and disorders of phenylalanine metabolism.
- Drug Interactions: no interactions were found in the queried data.
Please refer to the package insert for full warnings and contraindications.
Conclusion and Next Steps
Decision: Hold
Rationale: The TxGNN score is very high, but support is limited to preclinical and formulation studies involving cysteine-derived materials, with no clinical trials. The registered Singapore products are intravenous nutrition solutions, not ocular formulations, so the prediction remains a research question.
To proceed, the following is needed:
- Mechanism of action data for cysteine (DrugBank)
- Package insert warnings and contraindications from the HSA website
- Direct preclinical evidence testing cysteine itself (not derivatives or conjugates) in dry eye models
- Assessment of a suitable ophthalmic formulation and route, plus ocular safety and tolerability data
- Evidence-based comparison against established dry eye therapies before any clinical study is designed
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.