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Description of key information

Ethyl-S-lactate, as all lactate esters, is rapidly hydrolysed in-vivo into lactic acid and ethanol.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Ethyl-S-lactate, as all lactate esters, is rapidly hydrolyzed in-vivo into lactic acid and ethanol (see 7.9.3.001). A summary of the data collected is presented below:

In a hydrolysis study of ethyl-S-lactate by rat nasal olfactory epithelium homogenate, lactic acid was formed by enzymic reaction of carboxylesterase; the kinetic parameters were: Km = 1.1 mM and Vmax = 170 nmol/min/mg protein. In general, the olfactory epithelium carboxylesterase showed increasing capacity (increasing Vmax) and afinity (decreasing Km) towards L-lactate esters with increasing molecular weight of the alkyl group. From a large discrepancy between the amount of lactic acid formed and the increase in proton concentration even in very poorly buffered systems it is suggested that a certain defence against acidification exists.

In another study, solutions of ethyl-L-lactate in water, solutions of ethanol and Li-L-lactate in water or water were administered intragastricaly to rats. The results revealed that ethyl-L-lactate is at least partially absorbed unhydrolysed from the gastro-intestinal tract of rats, but it hydrolysed rapidly after uptake.

Aqueous solutions of ethyl-L-lactate, containing 1 mg of ester/ml, were incubated in a 0.05 M phosphate buffer pH 7.5 with or without pancreatin or a porcine intestinal mucosa preparation at 37 °C. The degree of hydrolysis was determined after 1-2 h. The results of the study suggested that orally administered ethyl-L-lactate in concentrations below 1 mg/ml will be completely hydrolyzed in the intestinal tract.

In another study the rates of hydrolysis of ethyl-L-lactate to ethanol and L-lactic acid by homogenates of male rat liver, blood, skin, small intestinal mucosa and nasal olfactory epithelium and caecum content homogenates, was examined. All homogenates showed esterase activity to ethyl-L-lactate. Nasal olfactory epithelium, liver and skin were, in this order, the most efficient tissues with respect to the hydrolysis of ethyl-L-lactate. Enzymatic hydrolysis of ethyl-L-lactate in vivo would be much faster than chemical hydrolysis.

Lactic acid is a ubiquitous and essential biological molecule, in humans and other mammals, but also in most if not all vertebrate and invertebrate animals, as well as in many micro-organisms. As such the biokinetics, metabolism and distribution of lactic acid have to be considered in the context of its normal biochemistry; exogenous lactic acid will be indistinguishable from endogenous lactic acid and will follow the same biochemical pathways as endogenous lactic acid, at least up to a certain systemic level.

Additionally, the biochemistry of lactic acid has been reviewed and summarized in Sterenborg, 2007 (see section 7.9.3).

Ethanol is an alcohol that is metabolised by the normal alcohol metabolism pathways.