Reaction mass of glycerol 1,3-di(acetate) and glycerol acetate and triacetin

Endpoint summary

Additional information

Basic toxicokinetics

There are no studies available in which the toxicokinetic behaviour of "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" has been investigated.

Therefore, in accordance with Annex VIII, Column 1, Item 8.8.1, of Regulation (EC) No 1907/2006 and with Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2008), assessment of the toxicokinetic behaviour of the substance "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

has been conducted to the extent that can be derived from the relevant available information. This comprises a qualitative assessment of the available substance specific data on physico-chemical and toxicological properties according to Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2008) and taking into account further available information on the breakdown products of ester hydrolysis.

The substance "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

contains acetic acid bound to glycerol in form of short-chain diglycerides (30-60% Diacetin), triglycerides (5-40% Triacetin) and monoglycerides (10-40% Monoacetin) and additional free glycerol (0-15%).

"Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" is a clear colourless organic liquid at

20°C and has a molecular weight of 134.13 - 218.20 g/mol and a water solubility > 2000 g/L (Auty, 2012). The log Pow is calculated to be -1.24 - 0.36 (Müller, 2011) and the vapour pressure is calculated to be 0.0696 - 1.09 Pa at 20°C (Nagel, 2011).

Absorption

Absorption is a function of the potential for a substance to diffuse across biological membranes. The most useful parameters providing information on this potential are the molecular weight, the octanol/water partition coefficient (log Pow) value and the water solubility. The log Pow value provides information on the relative solubility of the substance in water and lipids (ECHA, 2008).

Oral

The smaller the molecule, the more easily it will be taken up. In general, molecular weights below 500 are favorable for oral absorption (ECHA, 2008). As the molecular weight of "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

ranges between 134.13 and 218.20 g/mol, absorption of the intact molecules in the gastrointestinal (GI) tract can be anticipated. Absorption after oral administration is also expected when the “Lipinski Rule of Five” (Lipinski, 2001), refined by Ghose (1999)) is applied to the substance

"Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin".

However, when assessing the potential of "Recation mixture of glycerol-1,3 -di(acetate), glycerol acetate and triacetin"to be absorbed in the GI tract, it has to be considered that fatty acid esters will undergo to a high extent hydrolysis by ubiquitous expressed GI enzymes (Long, 1958; Lehninger, 1970; Mattson and Volpenhein, 1972). Thus, due to the hydrolysis the predictions based upon the physico-chemical characteristics of the intact parent substance alone may no longer apply but also the physico-chemical characteristics of the breakdown products of the ester (ECHA, 2008).

After oral ingestion, "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

will undergo stepwise chemical changes in the GI fluids as a result of enzymatic hydrolysis. The cleavage products of ester hydrolysis are glycerol and acetic acid which are anticipated to be easily absorbed in the GI tract based on their low molecular weight.

The anticipation of hydrolysis of the ester "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

is supported by experiments with Monoacetin, Diacetin and Triacetin incubated in sacs of everted intestine from rats. It was shown that the glyceride esters entered the epithelial cells and were completely hydrolysed to free glycerol and acetic acid. The released acetate appeared in higher concentrations on the serosal side and the acetate release increased with the number of acetic acid residues in the glyceride (Barry, 1966).

No studies investigating the acute oral toxicity of "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

are available however a study with the structurally related analogue substance Triacetin (CAS 102-76-1) is available. The study from Triacetin after oral administration to rats showed no signs of systemic toxicity in an acute oral toxicity test resulting in a LD50 value greater than 2000 mg/kg bw (Reijnders, 1988). Furthermore, available data on the subacute oral toxicity of Triacetin showed no adverse systemic effects in animals resulting in a NOAEL of 1000 mg/kg bw/day (JECDB, 1998). The lack of short- and long-term systemic toxicity of the analogue substance cannot be equated with a lack of absorption or with absorption but rather with a low toxic potential of the test substance and the breakdown products themselves. Thus, systemic bioavailability of

"Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

and/or the respective cleavage products in humans is considered likely after oral uptake of the substance.

Dermal

The smaller the molecule, the more easily it may be taken up. In general, a molecular weight below 100 favours dermal absorption, above 500 the molecule may be too large (ECHA, 2008). As the molecular weight of "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" ranges between

134.13 and 218.20 g/mol and "Reaction mixture of glycerol-1,3 -di(acetate), glycerol acetate and triacetin"is highly water soluble (> 2000 g/L), a dermal absorption of the substance cannot be excluded. However, for substances with log Pow values < 0, poor lipophilicity will limit penetration into the stratum corneum and hence dermal absorption. Values < -1 suggest that a substance is not likely to be sufficiently lipophilic to cross the stratum corneum, therefore dermal absorption is likely to be low (ECHA, 2008). Regarding the log Pow value of "Reaction mixture of glycerol-1,3 -di(acetate), glycerol acetate and triacetin" of -1.24 - 0.36 in combination with the very high water solubility, dermal absorption is anticipated to be low.

If a substance shows skin irritating or corrosive properties, damage to the skin surface may enhance penetration (ECHA, 2008). As there are no studies available for "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin",

read-across from the structurally related analogue substance Triacetin (CAS 102-76-1) was conducted. Triacetin showed no skin irritating properties (Kästner, 1988) and thus no enhanced penetration of the substance due to local skin damage is expected.

Furthermore, QSAR dermal absorption values of 0.0083 mg/cm²/event (low) for Triacetin, 0.085 mg/cm²/event (moderate) for Diacetin and 0.068 mg/cm²/event (moderate) for monoacetin were calculated (Danish EPA 2010). Based on these values, the substances have a low to moderate potential for dermal absorption.

Overall, the calculated low to moderate dermal absorption potential, the high water solubility, the moderate molecular weight (< 500), the low log Pow values imply that dermal uptake of "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

in humans is considered to be possible but not to be higher than oral absorption.

Inhalation

The substance "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" has a low vapour pressure of

0.0696 – 1.09 Pa at 20 °C thus being of low volatility (Nagel, 2011). Therefore, under normal use and handling conditions, inhalation exposure and thus availability for respiratory absorption of the substance in the form ofvapours, gases, or mists is not expected to be significant. However, the substance may be available for respiratory absorption in the lung after inhalation of aerosols, if the substance is sprayed. In humans, particles with aerodynamic diameters below 100 μm have the potential to be inhaled. Particles with aerodynamic diameters below 50 μm may reach the thoracic region and those below 15 μm the alveolar region of the respiratory tract (ECHA, 2008).

Substances with a moderate log Pow values (between -1 and 4) arefavourablefor absorption directly across the respiratory tract epithelium by passive diffusion (ECHA, 2008). As the log Pow value for the substance "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" ranges from -1.24 to 0.36, absorption vis passive diffusion is possible.

The acute inhalation study with the structurally related analogue substance Triacetin (CAS 102-76-1) in rats did not show any mortality or systemic toxicity after inhalative exposure (Pauluhn, 1985). This lack of acute systemic toxicity of the analogue substance cannot be equated with a lack of absorption or with absorption but rather with a low toxic potential of the test substance itself.

Overall, a systemic bioavailability of "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

in humans is considered likely after inhalation of aerosols with aerodynamic diameters below 15 µm.

Distribution and Accumulation

Distribution of a compound within the body depends on the physicochemical properties of the substance; especially the molecular weight, the lipophilic character and the water solubility. In general, the smaller the molecule, the wider is the distribution. If the molecule is lipophilic, it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration, particularly in fatty tissues (ECHA, 2008).

Depending on the route of exposure,

"Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" will mainly be absorbed in the form of the

hydrolysis products and/or the parent substance. The fraction of substance absorbed unchanged will undergo enzymatic hydrolysis by ubiquitous esterases, primarily in the liver (Barry et al., 1966). Consequently, glycerol and acetic acid are the most relevant components to assess. These hydrolysis products are, due to their size and water solubility (glycerol: 1000000 mg/L, 92.09 g/mol; acetic acid: 602.9 g/L, 60.05 g/mol) expected to be distributed widely in the body (Riddick, 1986; Yalkowsky, 2003). This is supported by experimental data of Triacetin (CAS 102-76-1) intravenously administered to mongrel dogs. In the experiment, the majority of infused Triacetin undergoes intravascular hydrolysis and systemic acetate turnover accounted for ~ 70% of Triacetin-derived acetate, assuming complete hydrolysis of the triglyceride (Bleiberg, 1993). Therefore, the intact parent substance

"Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" is not assumed to be accumulated to a significant

amount as hydrolysis is anticipated to take place either before absorption or thereafter.

In summary, the available information on "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin"

indicates that no significant bioaccumulation of the parent substance is expected. The breakdown products of hydrolysis, glycerol and acetic acid will feed into metabolic and physiological pathways and are therefore widely distributed in the organism.

Metabolism and Excretion

The substance "Reaction mixture of glycerol-1,3-di(acetate), glycerol acetate and triacetin" is expected to be hydrolysed

to glycerol and acetic acid by ubiquitous esterases (Barry, 1966). Depending on the route of exposure, esterase-catalysed hydrolysis takes place at different places in the organism. After oral ingestion, "Reaction mixture of glycerol-1,3 -di(acetate), glycerol acetate and triacetin" will undergo chemical changes already in the GI fluids as a result of enzymatic hydrolysis. In contrast, substances that are absorbed through the pulmonary alveolar membrane or through the skin enter the systemic circulation directly before entering the liver where hydrolysis will basically take place. Bleiberg et al. (1993) showed that during intravenous administration in dogs, the majority of infused Triacetin undergoes intravascular hydrolysis, and the majority of the resulting acetate will be oxidised. Systemic acetate turnover accounted for approximately 70% of Triacetin-derived acetate, assuming complete hydrolysis of the triglyceride. It is apparent that the majority (85%) of acetate entering the system is directly oxidised. This is consistent with the generally accepted view that short- and medium-chain fatty acids undergo near quantitative oxidation rather than being re-esterified or elongated to longer fatty acid chain (Groot and Hulsmann, 1973). The second cleavage product, Glycerol, is considered a primordial biomolecule found in all species of living organisms. It is a building block for lipid synthesis and one of the end products of lipid metabolism. It can be re-esterified to form endogenous glycerides or be metabolised to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, which can be incorporated in the standard metabolic pathways of glycolysis and gluconeogenesis. Glycerol is phosphorylated to alpha-glycerolphosphate by glycerol kinase predominantly in the liver (80-90%) and kidneys (10-20%) and incorporated in the standard metabolic pathways to form glucose and glycogen (Tao, 1983; Lin, 1977). Glycerol kinase is also found in intestinal mucosa, brown adipose tissue, lymphatic tissue, lung and pancreas. Glycerol may also be combined with free fatty acids in the liver to form triglycerides (lipogenesis) which are distributed to the adipose tissues. The turnover rate is directly proportional to plasma glycerol levels (Bortz, 1972). Being a polar molecule, glycerol can also be readily excreted in the urine.

 

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within CSR.