Oral Bioavailability of Glycine
The oral bioavailability of glycine is relatively high, with estimates ranging from approximately 60-90% in healthy individuals, though it can be reduced in certain conditions such as renal insufficiency.
Factors Affecting Glycine Bioavailability
Glycine is the smallest non-essential amino acid with several important physiological functions. Its bioavailability is influenced by multiple factors:
Absorption mechanism: Glycine is primarily absorbed in the small intestine through specific amino acid transporters and dipeptide transporters 1
Physiological factors:
- Normal serum levels of glycine are approximately 300 μM
- Increasing glycine intake can lead to blood levels exceeding 900 μM without harmful side effects 1
- Absorption can be affected by intestinal health and function
Pathological conditions:
- In chronic renal insufficiency, glycine absorption is significantly reduced compared to healthy individuals 2
- Studies show that patients with chronic renal failure have lower plasma alpha-amino nitrogen levels after glycine administration compared to after glycyl-glycine administration, indicating reduced absorption of the free amino acid 2
Comparative Absorption
Dipeptide vs. free amino acid: Research indicates that in both healthy individuals and those with renal insufficiency, glycine may be better absorbed when administered as part of a dipeptide (glycyl-glycine) rather than as a free amino acid 2
Formulation considerations: The bioavailability of glycine can be affected by the formulation and administration route, similar to other amino acids and medications 3
Clinical Implications
Supplementation considerations: When glycine supplementation is indicated, the form of administration may need to be considered, particularly in patients with compromised renal function
Dosing: Due to its relatively high bioavailability in healthy individuals, oral glycine supplementation can effectively increase plasma glycine levels 4
Therapeutic applications: Glycine has shown potential benefits in:
Special Populations
Renal insufficiency: Patients with chronic renal failure show reduced glycine absorption, which may necessitate alternative administration methods or higher dosing 2
Conditional essentiality: Glycine is considered conditionally essential in certain states including late gestation, diabetes, insulin resistance, and malnutrition 6
Co-administration with L-serine: Due to the close metabolic relationship between glycine and L-serine, co-administration may be more appropriate in glycine-deficient conditions 6
Monitoring Considerations
For patients requiring glycine supplementation, monitoring plasma levels may be beneficial, particularly in those with conditions that might affect absorption
In patients with renal insufficiency, alternative forms of glycine (such as dipeptides) might provide better bioavailability 2
The bioavailability of glycine remains an important consideration when prescribing supplementation, particularly in patients with conditions that might affect absorption or in therapeutic applications requiring specific plasma concentrations.