What Is Ophthalmic Acid? Definition and What Research Reports
Ophthalmic acid, also called ophthalmate, is a naturally occurring tripeptide closely related to glutathione: it carries the same γ-glutamyl–X–glycine backbone, but 2-aminobutyrate replaces cysteine, so the molecule has no thiol group. It is made by the same two biosynthetic enzymes that build glutathione. Published work has mostly examined it as a metabolomic marker of hepatic glutathione consumption and oxidative stress, as an analytical target in mass-spectrometry methods, and, more recently, as a signalling molecule in its own right.
Definition
Ophthalmic acid (also written ophthalmate, and formally L-γ-glutamyl-L-2-aminobutyryl-glycine) is a naturally occurring tripeptide that is structurally almost identical to glutathione. Both molecules share the same γ-glutamyl–X–glycine architecture; in ophthalmic acid the central cysteine residue of glutathione is replaced by 2-aminobutyrate, which means the molecule lacks the sulfhydryl (–SH) group that gives glutathione its redox chemistry. Because it is assembled by the same enzymes that build glutathione but cannot perform thiol-based antioxidant reactions, ophthalmic acid has been studied principally as a read-out of glutathione metabolism rather than as an antioxidant itself. The name is historical and does not indicate a function restricted to the eye.
What Class of Molecule Is It?
Ophthalmic acid belongs to the small class of γ-glutamyl tripeptides — short peptides in which the first amino acid is linked through the side-chain carboxyl of glutamate rather than through a conventional α-peptide bond. This isopeptide linkage is the same one found in glutathione and is what makes both molecules resistant to ordinary aminopeptidases. In the literature, ophthalmic acid is usually described alongside glutathione as its non-thiol analogue.
| Feature | Ophthalmic acid (ophthalmate) | Glutathione (GSH) |
|---|---|---|
| Residues | γ-Glu – 2-aminobutyrate – Gly | γ-Glu – Cys – Gly |
| Thiol group | Absent | Present |
| Biosynthetic enzymes | Glutamate–cysteine ligase and glutathione synthetase | Glutamate–cysteine ligase and glutathione synthetase |
| Typical research framing | Biomarker and, more recently, signalling molecule | Principal intracellular antioxidant |
Where It Comes From
Ophthalmic acid is produced endogenously in animals when the enzymes of the glutathione pathway accept 2-aminobutyrate in place of cysteine — a substitution that becomes more likely when cysteine is scarce or when glutathione is being rapidly consumed. Its occurrence is not limited to mammals: researchers reported that ophthalmic acid functions as a marker of oxidative stress in plants in a manner comparable to animals, extending the molecule's relevance beyond mammalian physiology (PMID 29413907). It also appears in bacteria; one study described accumulation of ophthalmic acid in an Escherichia coli mutant lacking the conserved pyridoxal 5′-phosphate-binding protein YggS (PMID 27426274). Separately, researchers reported the production of ophthalmic acid using engineered Escherichia coli, describing a microbial route to the tripeptide (PMID 29352090).
Substrate supply matters as well. In a mouse study, researchers reported that increased ophthalmic acid production was supported by amino acid catabolism under fasting conditions, linking the tripeptide's abundance to nutritional state rather than to oxidative challenge alone (PMID 28757411).
Doing the math on a vial? The PeptideU app does reconstitution, units and dilution for you.
Try it freeHow the Term Is Used in Peptide Research
Within peptide and metabolomics literature, "ophthalmic acid" is most often used in three distinct senses:
- As a biomarker. The dominant usage: circulating or hepatic ophthalmic acid is measured as an indirect index of glutathione turnover and oxidative stress.
- As an analytical target. Method papers treat it as a small peptide that must be separated from glutathione and quantified reliably; one report described measurement of the tripeptides glutathione and ophthalmic acid by gas chromatography–mass spectrometry (PMID 32721386).
- As a candidate signalling molecule. A more recent framing in which the peptide is investigated for receptor-mediated activity rather than only as a passive read-out.
It is worth noting what the term does not mean in most published work: ophthalmic acid is generally discussed as an endogenous metabolite measured in tissue or plasma, not as an administered research peptide with an established exposure regimen. This page is for educational purposes only and is not medical advice; consult a licensed physician for questions about health, diagnosis or treatment.
What the Published Literature Reports
Origins as a glutathione-depletion marker
The biomarker concept came out of differential metabolomics. In that work, researchers reported that ophthalmic acid emerged as an oxidative stress biomarker indicating hepatic glutathione consumption (PMID 16608839). The rationale described in the paper is that when hepatic glutathione is consumed, feedback inhibition on glutamate–cysteine ligase is relieved and flux through the pathway rises; with cysteine limited, more of that flux is diverted into the 2-aminobutyrate-containing product.
Translation to human liver injury
Several studies extended the marker to human settings. One analysis reported that detection of ophthalmic acid in serum from acetaminophen-induced acute liver failure patients was more frequent in non-survivors than in survivors (PMID 26407170). Another examined ophthalmic acid as a read-out for hepatic glutathione metabolism in humans (PMID 30873484). A modelling study combined a kinetic model of glutathione metabolism with physiologically based pharmacokinetic models of paracetamol and of the potential glutathione-depletion biomarkers ophthalmic acid and 5-oxoproline in humans and rats, examining whether biomarker behaviour could be predicted from pathway kinetics (PMID 23632663).
Beyond biomarker status
More recent papers have asked whether the tripeptide does something rather than merely reflects something. A 2024 review-style article in The FEBS Journal described ophthalmic acid as a glutathione-regulating tripeptide, reframing it as a participant in glutathione homeostasis rather than an inert by-product (PMID 38245827). A 2024 paper in Brain reported that ophthalmate acts as a regulator of motor functions via the calcium-sensing receptor (CaSR), with the authors discussing implications for movement disorders (PMID 38537648). A 2024 preprint described ophthalmic acid as a bloodborne metabolite that contributes to age-induced cardiomyocyte hypertrophy (PMID 39211274); as a preprint, that report had not completed peer review at the time of posting.
Tracking research? Log entries with dates, lots and notes — records, never plans.
Get the appSafety and Adverse Events: What Studies Report
The verified literature summarised on this page is largely analytical, biomarker and mechanistic in character — metabolomic profiling, mass-spectrometry method development, microbial production and receptor-level pharmacology. Those papers did not report controlled human safety studies of administered ophthalmic acid, and no adverse-event profile for exogenous ophthalmic acid in people can be drawn from them. Where the peptide appears in human data, it does so as an endogenous analyte measured in serum, as in the acute liver failure cohort in which detection was reported more frequently among non-survivors (PMID 26407170) — an association with outcome, not evidence that the molecule caused harm.
Points of Confusion
- Ophthalmic acid is not an eye drug. Despite the name, the cited literature concerns hepatic glutathione metabolism, oxidative stress markers, motor-function signalling and cardiac ageing, not ophthalmology.
- It is not an antioxidant analogue of glutathione. Lacking a thiol, it cannot substitute for glutathione's redox chemistry; the reviewed framing is regulatory and diagnostic (PMID 38245827).
- Elevated levels are not automatically a stress signal. Fasting-associated amino acid catabolism was reported to support increased production in mice, so nutritional context can influence the measurement (PMID 28757411).
- "Ophthalmate" and "ophthalmic acid" refer to the same molecule, the former being the anionic form used in much of the signalling literature.
Want the full course? Every compound, evidence-graded and cited, inside PeptideU.
Start learning freeReferences
- Differential metabolomics reveals ophthalmic acid as an oxidative stress biomarker indicating hepatic glutathione consumption (The Journal of Biological Chemistry, 2006)
- Multiscale modelling approach combining a kinetic model of glutathione metabolism with PBPK models of paracetamol and the potential glutathione-depletion biomarkers ophthalmic acid and 5-oxoproline in humans and rats (Integrative Biology, 2013)
- Detection of Ophthalmic Acid in Serum from Acetaminophen-Induced Acute Liver Failure Patients Is More Frequent in Non-Survivors (PLoS One, 2015)
- Ophthalmic acid accumulation in an Escherichia coli mutant lacking the conserved pyridoxal 5'-phosphate-binding protein YggS (Journal of Bioscience and Bioengineering, 2016)
- Increased ophthalmic acid production is supported by amino acid catabolism under fasting conditions in mice (Biochemical and Biophysical Research Communications, 2017)
- Production of Ophthalmic Acid Using Engineered Escherichia coli (Applied and Environmental Microbiology, 2018)
- Ophthalmic acid is a marker of oxidative stress in plants as in animals (Biochimica et Biophysica Acta. General Subjects, 2018)
- Ophthalmic acid as a read-out for hepatic glutathione metabolism in humans (Journal of Clinical and Translational Research, 2018)
- Measurement of the tripeptides glutathione and ophthalmic acid by gas chromatography-mass spectrometry (Analytical Biochemistry, 2022)
- Ophthalmic acid is a glutathione regulating tripeptide (The FEBS Journal, 2024)
- Ophthalmate is a new regulator of motor functions via CaSR: implications for movement disorders (Brain, 2024)
- Ophthalmic acid is a bloodborne metabolite that contributes to age-induced cardiomyocyte hypertrophy (bioRxiv preprint, 2024)
Frequently asked questions
What exactly is ophthalmic acid?▾
It is a naturally occurring tripeptide, γ-glutamyl-2-aminobutyryl-glycine, also called ophthalmate. It shares glutathione's backbone but replaces cysteine with 2-aminobutyrate, so it has no thiol group. It is built by the same two enzymes that make glutathione, and a 2024 review described it as a glutathione-regulating tripeptide rather than an inert by-product (PMID 38245827).
Why is it used as a biomarker?▾
Differential metabolomics identified ophthalmic acid as an oxidative stress biomarker indicating hepatic glutathione consumption, because glutathione depletion increases pathway flux while limiting cysteine availability (PMID 16608839). Researchers later examined it as a read-out for hepatic glutathione metabolism in humans (PMID 30873484), and modelling work paired it with 5-oxoproline as a potential glutathione-depletion biomarker (PMID 23632663).
Does the name mean it relates to the eye?▾
No. The name is historical. The published work cited here concerns hepatic glutathione metabolism, oxidative stress markers in animals and plants (PMID 29413907), microbial production (PMID 29352090), and signalling roles such as regulation of motor functions via the calcium-sensing receptor (PMID 38537648) — not ophthalmology or eye disease.
How is ophthalmic acid measured?▾
It is quantified in biological samples by mass spectrometry. One method paper described measurement of the tripeptides glutathione and ophthalmic acid by gas chromatography–mass spectrometry (PMID 32721386). Because the two peptides differ by a single residue, analytical methods focus on separating and distinguishing them reliably within the same sample matrix.
Is it found outside humans and animals?▾
Yes. Researchers reported that ophthalmic acid serves as a marker of oxidative stress in plants as it does in animals (PMID 29413907). It also occurs in bacteria: one study described its accumulation in an Escherichia coli mutant lacking the pyridoxal 5'-phosphate-binding protein YggS (PMID 27426274), and another reported production using engineered E. coli (PMID 29352090).
What did human clinical data report about it?▾
In one cohort study, detection of ophthalmic acid in serum from acetaminophen-induced acute liver failure patients was more frequent among non-survivors than survivors (PMID 26407170). That is an observed association with outcome in a biomarker analysis, not evidence of causation. This information is educational only and is not medical advice.
Is ophthalmic acid studied as an administered peptide?▾
The verified literature summarised here treats it mainly as an endogenous metabolite and analytical target rather than an administered therapeutic. Newer mechanistic work has explored activity — for example receptor-mediated effects on motor function (PMID 38537648) and a preprint linking the circulating metabolite to age-induced cardiomyocyte hypertrophy (PMID 39211274) — without establishing human safety data.
Track it. Calculate it. Actually understand it.
References
This page summarises published research for education — it is not medical advice, and nothing here is a recommendation to use, purchase, or dose any substance. Study parameters described are what researchers reported, not instructions. Consult a qualified clinician before any health decision.