Registration Dossier
Registration Dossier
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EC number: 227-842-3 | CAS number: 6000-44-8
Endpoint summary
Administrative data
Link to relevant study record(s)
Description of key information
Key value for chemical safety assessment
Additional information
There were no experimental studies available investigating the toxicokinetic properties of sodium glycinate. However, TK data does exist for a close analog that is applied (see read across assessment for justification). Therefore, the TK assessment is based on the physiochemical properties and read across data for toxicology data (based on read across to glycine) according to the “Guidance on information and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2017)”.
Absorption
Glycine has a low pKa (2.35) meaning that in acidic pH, such as the stomach, the molecule will become ionized (the hydrogen will be given up by the molecule). Sodium glycinate, which is the sodium salt of glycine, is also expected to ionize in acidic pH. Therefore, it is expected that oral absorption of sodium glycinate will act in a similar manner to glycine. Glycine has been found to be rapidly absorbed after oral administration along the GI tract via special carrier systems (Elmadfa and Leitzmann, 1998); therefore, sodium glycinate is expected to be absorbed through the same systems following exposure in the gut.
Based on modeling, glycine is expected to have low dermal bioavailability. A Dermwin v2.0 QSAR modeling estimated a dermal permeability constant Kp of 4.37E‑006 cm/h. Similar to the approach taken by Kroes et al. (2007), the maximum flux Imax (Imax = Kp [cm/h] x water solubility [mg/cm³]) was calculated, resulting in dermal absorption of 1 µg glycine/cm²/h. The Danish QSAR Database predicted a low dermal bioavailability as well (0.002 mg/cm²/event). As noted in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7C: Endpoint Specific Guidance, June, 2017, if water solubility is above 10,000 mg/L and the log P value below 0 the substance may be too hydrophilic to cross the lipid rich environment of the stratum corneum and dermal uptake for these substances will be low. Dermal absorption of the notified substance is expected to be similar to glycine based on the physiochemial properites (water solubility) and chemical structure.
Inhalation as a vapor is not cosidered a relevant route of sodium glycinate due to the low vapor pressure of 0.012300 mm/Hg @ 25.00°C
Metabolism
Glycine is a non-essential amino acid and can be biosynthesized in the body from the amino acid serine. In most organs, the enzyme serine hydroxymethyltransferase catalyses this transformation using tetrahydrofolate (THF), leading to methylene THF and glycine. Glycine can be degraded via three pathways. The predominant way in mammals involves the glycine cleavage system. This leads to the degradation of glycine into ammonia and CO2. In the second pathway, glycine is degraded in two steps. The first step is the reverse of glycine biosynthesis from serine with serine hydroxymethyl transferase. Serine is then converted to pyruvate by serine dehydratase. In the third route to glycine degradation, the amino acid is converted to glyoxylate by D-amino acid oxidase. Glyoxylate is then oxidized by hepatic lactate dehydrogenase to oxalate in an NAD+-dependent reaction (Lehninger 2005, Salway 2004).
The OECD QSAR application toolbox was used for a qualitative prediction of metabolites formed in liver, skin and gastrointestinal tract. It predicted 3 hepatic, 2 gastrointestinal and 6 skin metabolites. Among these metabolites, pyruvate, glycolic and oxalic acid could be identified (REACH dossier for Glycine CAS 56-40-6). Metabolism of sodium glycinate is expected to occur through the same pathways based on physiochemical properties and the structure of the molecule.
Excretion
Glycine, that is not used for synthesis processes within the body will be excreted. Glycine and its metabolites are soluble in water and thus subjected to renal elimination. Significant fecal excretion of glycine is not expected (REACH dossier for Glycine CAS 56-40-6). Based on similar structure and physiochemical properties the same method of excretion is expected with sodium glycinate.
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