Asparagine

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
Based on Annex XI, 1.1(2) of Regulation (EC) No 1907/2006 (REACH) a toxicity to reproduction study is scientifically not justified as explained in detail below:

Background:
L-Asparagine is a ubiquitous occurring molecule, known to be readily metabolised by the intermediary metabolism. It is a substrate for the synthesis of L-aspartic acid and therefore participates as a precursor in the generation of neurotransmitter, i.e. glutamate and aspartate. Furthermore, once aspartic acid is synthesised, it plays a key role in the urea cycle and is involved in transamination reactions e.g. with oxaloacetate, thereby acting as carbon source to form ATP (see also general biochemistry textbooks). The metabolism of L-asparagine is not restricted to mammalian species, also algae and bacteria are capable of using asparagine as a carbon source for energy supply (Oda et al. 1982, Alpert et al. 2009). Furthermore, it was shown that L-asparagine administered in a rat model of sepsis was able to improve muscle wasting and reduce weight loss naturally occurring with the condition of sepsis (Breuille et al. 2006). In another study, it was reported that endotoxin administration inhibited gluconeogenesis rising from L-asparagine as a source (Perchellet et al. 1983). The results presented in this study indicate that L-asparagine plays a pivotal role in intermediary metabolism and its inhibition may be deleterious. The demand for amino acids increases during age and is also varying between different populations (Tan and Gajra, 2006).
It is also known that the amino acid requirements for human differ significantly dependent on health status or pregnancy and also life style. For parenteral nutrition mostly 5% (w/w) asparagine is used (B.Braun, Melsungen). It was published that uptake of even 1g in a single dose only caused a slight pulse reduction which was fully reversible within 5h.
The recommended uptake of amino acids is mainly restricted to indispensable amino acids. L-asparagine belongs to the dispensable amino acids, due to its metabolism to aspartic acid. However, Jauniax et al. reported that the concentration of asparagine significantly increased in the coelomic fluid during the first trimester. These findings indicate that the requirements for asparagine are higher in the developing embryo than in maternal serum.
Moreover, Newburg and Fillios (1980) showed in a study conducted with rats which were fed a diet containing up to 800 mg/100g diet asparagine, that a requirement for asparagine during pregnancy is indicated, and its omission from the diet during periods of rapid fetal brain growth may impair neurological development in the fetus.
In conclusion, testing of toxicity to reproduction is scientifically not justified with respect to animal welfare because there is adequate information available indicating that asparagine exhibits a low toxicity; even during pregnancy. It was shown from a 90-days repeated dose toxicity study conducted according to OECD guideline 408 that no adverse effect occurred up to a dose of 1650 mg/kg bw/d, which is above the limit dose of current OECD guideline studies. Thus, it can be concluded that L-asparagine is metabolised up to this dose level. Furthermore, it was shown that asparagine is required for a proper intermediary metabolism and that this requirement of asparagine is higher in the developing embryo than in maternal animals. Hence, L-asparagine administered in a screening reproduction/developmental toxicity study is not expected to mediate a toxic effect up to the limit dose recommended in the current OECD guideline studies.







References
Oda, Yuji, Yoshihisa Nakano, and Shozaburo Kitaoka. "Utilization and toxicity of exogenous amino acids in Euglena gracilis." Microbiology 128.4 (1982): 853-858.

Alpert, Carl, et al. "Adaptation of protein expression by Escherichia coli in the gastrointestinal tract of gnotobiotic mice." Environmental microbiology 11.4 (2009): 751-761.

Perchellet, Jean-Pierre, Elizabeth A. Conrad, and R. K. Boutwell. "Effects of amino acid treatments on 12-O-tetradecanoylphorbol-13-acetate-induced ornithine decarboxylase activity in mouse epidermis in vivo and in vitro." Journal of investigative dermatology 81.6 (1983): 560-566.

Breuillé, Denis, et al. "Beneficial effect of amino acid supplementation, especially cysteine, on body nitrogen economy in septic rats." Clinical Nutrition 25.4 (2006): 634-642.

Tan, I., and Bani Gajra. "Plasma and urine amino acid profiles in a healthy adult population of Singapore." Annals-Academy of Medicine Singapore 35.7 (2006): 468.

Jauniaux, Eric, Beatrice Gulbis, and Erik Gerloo. "Free amino acids in human fetal liver and fluids at 12–17 weeks of gestation." Human Reproduction 14.6 (1999): 1638-1641.

Newburg, David S., and Louis C. Fillios. "A requirement for dietary asparagine in pregnant rats." The Journal of nutrition 109.12 (1979): 2190-2197.