Are low ergothioneine levels a risk factor for age-related macular degeneration and other ocular disorders?

This study reveals that L-ergothioneine accumulates in ocular tissues to protect against oxidative damage and identifies significantly lower levels of this antioxidant in patients with neovascular age-related macular degeneration, suggesting a strong link between low ergothioneine and the disease.

The Gist

The Big Picture: The Eye's "Fire Extinguisher"

Imagine your eyes are like a high-performance sports car engine. They work incredibly hard, burning fuel (oxygen) at a massive rate to help you see. But just like a fast engine, this hard work creates a lot of heat and exhaust fumes. In the body, these "exhaust fumes" are called oxidative stress. Over time, if you don't clean them up, they rust the engine parts. This rusting is what causes Age-Related Macular Degeneration (AMD), a disease that slowly blinds older people by damaging the center of their vision.

To fight this rust, your body needs a "fire extinguisher" or a "rust remover." For a long time, we knew about some of these protectors (like vitamins C and E), but scientists have been hunting for a special, super-strong one called Ergothioneine (ET).

The main question of this study: Is this special "rust remover" missing in people who have AMD?

The Detective Work: What the Scientists Found

The researchers acted like detectives, looking for clues in two places: the blood (the body's main highway) and the fluid inside the eye (the local neighborhood).

1. The Blood Clues (The Highway)

They compared the blood of 100 people with AMD to 100 healthy people of the same age.

• The Finding: The people with AMD had significantly lower levels of the "rust remover" (ET) in their blood.
• The Smoking Gun: Not only was the good stuff low, but they found high levels of "trash" in the AMD patients' blood. This trash included broken-down pieces of the rust remover and other signs that the body was under heavy attack by rust (oxidative stress).
• The Analogy: Imagine a house on fire. In the healthy houses, you see plenty of fire extinguishers ready to go. In the houses with AMD, the fire extinguishers are empty, and you see a lot of smoke and burnt debris floating around.

2. The Eye Clues (The Neighborhood)

Since the blood showed a problem, they wanted to see if the eye itself was suffering. They looked at fluid taken from the front of the eye (Aqueous Humor) from AMD patients and cataract patients.

• The Finding: The trend was the same. The AMD eyes had lower levels of the "rust remover" and higher levels of the "trash" (broken-down ET), though the difference wasn't as huge as in the blood.
• The Caveat: The control group for the eye fluid was people with cataracts (cloudy lenses). We already know cataracts are a "rusty" condition. So, the AMD eyes were actually looking worse than eyes that were already known to be in bad shape.

3. The Map of the Eye (Where does the protector live?)

To understand how the eye protects itself, the scientists looked at donated human eyes (from people who passed away naturally, with no eye disease). They sliced the eye open and checked every part.

• The Finding: The eye is a hoarder of this special protector! It concentrates ET heavily in the most vulnerable spots: the lens (the clear window), the retina (the film that captures the image), and the RPE (the layer that feeds the retina).
• The Analogy: It's like a castle. The guards (ET) are stationed in the highest numbers right at the front gates and the most critical towers (the retina and lens) where the enemy (sunlight and oxygen) attacks hardest. The lens had the most of this protector—about 50 times more than the back of the eye!

What Does This Mean for You?

1. Low ET might be a warning sign.
The study suggests that if your levels of this special "rust remover" drop too low, you might be at higher risk for losing your vision as you age. It's like a low-battery warning light on your dashboard.

2. The body is under attack.
The fact that the "trash" (broken-down ET) is high in AMD patients means their eyes are under constant, heavy oxidative stress. They are using up their defenses faster than they can replace them.

3. Hope for the future.
Here is the exciting part: Ergothioneine is safe. It's found in foods like mushrooms and beans. The researchers found that because the eye loves to hoard this substance, giving people extra ET (through diet or supplements) might be a way to refill the fire extinguishers.

The Bottom Line

Think of your eyes as a garden that needs constant watering to stop the weeds (oxidative stress) from taking over. This study found that people with AMD have dry soil (low ET) and lots of weeds.

While this study doesn't prove that eating mushrooms will cure AMD, it strongly suggests that keeping your levels of this special "rust remover" high is crucial for keeping your eyes healthy. It opens the door for new treatments where doctors might prescribe ET supplements to help protect our vision as we get older.

---

Note: This is a preprint study, meaning it is new research that hasn't been fully peer-reviewed yet. It's a strong clue, but scientists will need to do more tests to confirm that taking ET supplements will actually prevent or slow down vision loss.

Technical Summary

1. Problem Statement

Age-related macular degeneration (AMD) is a leading cause of irreversible vision loss in aging populations, driven significantly by oxidative stress and mitochondrial dysfunction. While the dietary antioxidant L-ergothioneine (ET) is known to accumulate avidly in various tissues and has been linked to reduced risks of neurodegenerative and cardiovascular diseases, its specific relationship with AMD and its distribution within human ocular tissues remain uninvestigated. Existing treatments for AMD are limited to managing late-stage complications, and there is a need to identify modifiable risk factors or protective agents for earlier disease stages.

2. Methodology

The study employed a multi-cohort, cross-sectional design utilizing Liquid Chromatography-Mass Spectrometry (LC-MS/MS) to quantify ET and its metabolites.

• Cohort I (Serum Analysis):
  • Participants: 200 participants from Singapore (100 treatment-naïve neovascular AMD patients vs. 100 age-matched healthy controls).
  • Samples: Serum samples were collected and analyzed for ET, its metabolites (hercynine, ETSO₃), and allantoin (a biomarker of oxidative damage to urate).
• Cohort II (Aqueous Humour Analysis):
  • Participants: 141 patients from Japan (98 neovascular AMD patients vs. 43 controls undergoing cataract surgery without macular abnormalities).
  • Samples: Aqueous humour (AH) was collected prior to anti-VEGF injections (AMD) or cataract surgery (controls).
• Human Ocular Dissections:
  • Samples: 10 healthy cadaveric eye globes (no history of AMD, dementia, or neurodegenerative disease) were dissected into specific compartments: cornea, iris, lens, optic nerve, retina, retinal pigment epithelium (RPE)-choroid complex, sclera, aqueous humour, and vitreous humour.
  • Analysis: Tissues were homogenized and analyzed via LC-MS/MS to determine the spatial distribution of ET and its metabolites.
• Statistical Analysis:
  • Used Mann-Whitney U tests for group comparisons and Pearson's correlation for age associations. Significance was set at $p < 0.05$.

3. Key Contributions

• First Human Ocular Mapping: This is the first study to definitively map the distribution of ET and its metabolites across various human ocular tissues (lens, retina, RPE, choroid, etc.) using modern analytical methods.
• Systemic and Local Biomarkers: It establishes a strong association between low serum ET levels and neovascular AMD, while simultaneously identifying elevated oxidative stress markers (hercynine, ETSO₃, allantoin) in AMD patients.
• Mechanistic Insight: The study provides evidence that the eye concentrates ET in regions most vulnerable to oxidative injury, supporting a physiological protective role for ET in ocular health.

4. Key Results

A. Serum Findings (Cohort I)

• ET Levels: AMD patients had significantly lower serum ET levels compared to healthy controls ($617.4 \pm 50.58$ nM vs. $1169 \pm 80.88$ nM; $p < 0.0001$).
• Metabolites: AMD patients exhibited significantly elevated levels of ET metabolites:
  • Hercynine: $40.86 \pm 2.79$ nM (AMD) vs. $35.88 \pm 4.27$ nM (Control).
  • ETSO₃: $315.7 \pm 65.79$ nM (AMD) vs. $59.13 \pm 18.3$ nM (Control).
  • Interpretation: These metabolites are likely generated via oxidative breakdown of ET, suggesting higher oxidative stress in AMD patients.
• Oxidative Damage Marker: Serum allantoin (product of urate oxidation) was significantly higher in AMD patients ($37.08 \pm 2.12$ nM) than controls ($4.83 \pm 0.17$ nM), confirming elevated systemic oxidative stress.
• Age Correlation: A significant inverse correlation was found between age and serum ET levels in both healthy controls and AMD patients.

B. Aqueous Humour Findings (Cohort II)

• ET Levels: A decreasing trend in ET was observed in AMD patients compared to cataract controls, though it did not reach statistical significance.
• Metabolites: Hercynine levels were significantly higher in AMD AH ($p < 0.05$). ETSO₃ showed an increasing trend but was not statistically significant.
• Allantoin: No significant difference was found between groups, potentially because cataract controls already have elevated oxidative stress/allantoin levels.

C. Tissue Distribution (Cadaveric Eyes)

• Accumulation Pattern: ET was detected in all ocular compartments but showed highly differential accumulation:
  • Lens: Highest concentration ($408.70 \pm 126$ ng/mg wet weight), approximately 50 times higher than the RPE/choroid.
  • RPE & Choroid: Second highest ($12.47 \pm 2.98$ ng/mg).
  • Other Tissues: Cornea ($5.45$), Retina ($4.95$), and Iris ($1.20$) ng/mg.
• Metabolites: Hercynine and ETSO₃ followed similar distribution trends to ET (highest in lens).
• Allantoin: Unlike ET, allantoin was highest in the RPE & Choroid, suggesting localized oxidative damage in these posterior segments.

5. Significance and Implications

• Risk Factor Identification: The study identifies low ET levels as a potential risk factor for AMD. Given that low blood ET levels have been shown to precede other age-related diseases, this suggests ET deficiency may be a modifiable risk factor for AMD onset or progression.
• Therapeutic Potential: Since ET is a "Generally Recognized As Safe" (GRAS) compound that avidly accumulates in the eye and protects mitochondria (a key defect in AMD), the findings support further investigation into ET supplementation as a preventative or adjunctive therapy for AMD.
• Oxidative Stress Mechanism: The elevation of ET metabolites (hercynine, ETSO₃) and allantoin in AMD patients provides biochemical evidence that the disease state is characterized by heightened oxidative stress, which may deplete ET reserves.
• Future Directions: The authors call for longitudinal studies to determine causality and clinical trials to assess if ET supplementation can modify AMD risk or slow disease progression, potentially in combination with existing anti-VEGF therapies.