Homocysteine Associated Health Effects and Diseases
🧬 What Is Homocysteine?
- Derived from the essential amino acid methionine
- Normally present in very small amounts in the blood
- Can be:
- Remethylated back to methionine
- Transsulfurated into cysteine
Enzymes and vitamins involved: Methionine synthase, cystathionine β-synthase, vitamin B6, B12, folate
⚙️ Physiological Roles of Homocysteine (Indirect Functions)
1. 🧪 Intermediate in Methionine Cycle
- Homocysteine is a key junction between:
- The methionine cycle (remethylation)
- The transsulfuration pathway (cysteine production)
- Maintains proper amino acid and methylation balance
2. 🧬 Involved in Methylation Reactions
- Homocysteine → Methionine → S-adenosylmethionine (SAM)
SAM is the universal methyl donor in the body.
🧠 Used in methylation of:
- DNA
- RNA
- Neurotransmitters (serotonin, dopamine)
- Phospholipids
- Proteins
Homocysteine levels affect the body’s ability to methylate — essential for gene regulation, detoxification, and neurotransmitter synthesis.
3. 🌱 Cysteine and Glutathione Production
- Through the transsulfuration pathway, homocysteine is converted to cysteine.
- Cysteine is a building block of glutathione, a powerful antioxidant.
⚖️ Why Homocysteine Matters Clinically
- Normally low levels are essential.
- Elevated homocysteine (hyperhomocysteinemia) is a risk factor for:
- Cardiovascular disease
- Stroke
- Dementia
- Neural tube defects in pregnancy
📊 Summary Table
| Role | Function |
| Methionine metabolism | Intermediate in methylation cycles |
| Methylation support | Affects SAM levels, gene expression |
| Transsulfuration | Produces cysteine and glutathione |
| Clinical marker | Elevated levels signal metabolic or vitamin deficiencies |