Cysteine
| Evidence Level: L4 | Predicted Indications: 7 |
Table of Contents
- Cysteine
- Pharmacist Assessment Report
- Cysteine: From Respiratory and Amyloidosis-Related Indications to Dry Eye Syndrome
- One-Sentence Summary
- Quick Overview
- Why is This Prediction Reasonable?
- Clinical Trial Evidence
- Literature Evidence
- Canada Market Information
- Safety Considerations
- Conclusion and Next Steps
- Disclaimer
Cysteine: From Respiratory and Amyloidosis-Related Indications to Dry Eye Syndrome
One-Sentence Summary
Cysteine is an amino acid whose recorded uses include respiratory conditions (such as bronchitis and cystic fibrosis), paracetamol poisoning and amyloidosis. The TxGNN model predicts it may be useful for dry eye syndrome, with a very high score. Currently there are no registered clinical trials, and the 19 publications retrieved are almost entirely preclinical or formulation studies, so support remains at the research-question stage.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Bronchitis, paracetamol poisoning, cystic fibrosis, bronchiectasis, amyloidosis (the Canadian licence record lists no indication text) |
| Predicted New Indication | Dry eye syndrome |
| TxGNN Prediction Score | 0.9998 |
| Evidence Level | L4 |
| Canada Market Status | Marketed (marketed DINs: 1 of 1) |
| Number of DINs | 1 (marketed: 1) |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available. Based on known information, cysteine is a sulfur-containing amino acid with a reactive thiol group. It is a precursor of glutathione and of hydrogen sulfide/persulfide donors, and its derivative N-acetylcysteine is used as a mucolytic and antioxidant in respiratory disease.
Excess reactive oxygen species (ROS) are thought to drive a vicious cycle of inflammation in dry eye, including ROS/NLRP3 inflammasome activation in the lacrimal gland and ocular surface. An antioxidant, thiol-based mechanism could therefore plausibly be relevant. The thiol group is also the basis of thiolated polymers (thiomers, e.g., thiolated chitosan), which improve mucoadhesion and residence time on the ocular surface.
An important caveat: the retrieved evidence mainly concerns cysteine-modified delivery materials and ROS-scavenging prodrugs, not cysteine itself as a dry eye treatment. The very high model score has not been confirmed by human data.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
The 19 publications retrieved are mostly preclinical. The most relevant ones are listed below.
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 40123221 | 2025 | Preclinical | Advanced Materials | Eye-drop nanoparticles of catalase with cysteine-modified chitosan, designed to counter ROS in dry eye |
| 36581034 | 2023 | Preclinical | Int J Biol Macromol | Chondroitin sulfate–L-cysteine conjugate on lipid carriers improved corneal retention and permeation |
| 41485487 | 2026 | Preclinical | J Control Release | Superoxide-responsive persulfide prodrug designed to eliminate ROS in dry eye |
| 36626177 | 2023 | Preclinical | Invest Ophthalmol Vis Sci | Aquaporin5 deficiency worsens ROS/NLRP3-mediated pyroptosis in lacrimal glands |
| 25701684 | 2015 | Preclinical/Clinical samples | Exp Eye Res | ROS-activated NLRP3 inflammasomes initiate inflammation in corneal epithelial cells and dry eye patients |
| 24836981 | 2014 | Preclinical | Exp Eye Res | ROS-activated NLRP3 inflammasomes prime environment-induced murine dry eye |
| 24993428 | 2014 | Review | J Control Release | Thiomers: thiolated polymers with improved mucoadhesion, from bench to market |
| 31028759 | 2019 | Review | Adv Drug Deliv Rev | Thiolated polymers form disulfide bonds with mucus glycoproteins |
| 26606856 | 2015 | Preclinical | Ther Deliv | Hyaluronic acid–cysteine ethyl ester derivative as a mucoadhesive lubricant for dry eye |
| 41523131 | 2025 | Preclinical | Taiwan J Ophthalmol | Liquiritigenin reduced dry eye pathology through anti-inflammatory and antioxidant action (not cysteine) |
Canada Market Information
| DIN | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| 02236875 | PRIMENE 10% | Not specified | Not specified |
Safety Considerations
Contraindication associations drawn from the knowledge graph (not from label text) include: peptic ulcer disease, hypotensive disorder, respiratory failure, asthma, bronchial disease, esophageal varices, phenylketonuria and disorders of phenylalanine metabolism. These should be verified against the product label.
No drug interaction records were found.
Please refer to the package insert for further safety information.
Conclusion and Next Steps
Decision: Hold
Rationale: The prediction score is very high, but no clinical trials exist, and the literature shows cysteine only as a component of delivery materials or as a theoretical antioxidant source, not as a tested dry eye therapy. Health Canada label data and mechanism-of-action data are also missing, so the safety review cannot proceed.
To proceed, the following is needed:
- Health Canada package insert warnings and contraindications (a blocking gap)
- Mechanism of action data for cysteine
- Preclinical studies testing cysteine itself, or a defined ophthalmic formulation, in dry eye models
- A feasibility assessment of an ophthalmic route, since the marketed product (PRIMENE 10%) appears to be a parenteral amino acid solution and no ocular route is currently available
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.