Asparagine (Plasma)

Asparagine is converted to aspartic acid, then to glutamic acid.

- Asparagine is a nontoxic carrier of residual ammonia. A byproduct of asparagine metabolism is oxaloacetate.

- Higher levels of asparagine were associated with lower rates of diabetes, insulin, and HOMA.

- Plasma asparagine and the tyrosine/phenylalanine ratio were found to be protective against depression.

- Higher asparagine, aspartic acid, and citrulline were associated with higher rates of physical frailty and sarcopenia.

- Plasma glutamine, cysteine, and asparagine were significantly downregulated in psoriasis patients.

Asparagine is a non-essential protein amino acid that is present in many fruits and vegetables including asparagus, from which it gets its name. Other dietary sources include meat, potatoes, eggs, nuts, and dairy. It can also be formed from aspartic acid and glutamine using the enzyme asparagine synthetase.

In addition to being a structural component of many proteins, asparagine is also useful to the urea cycle. It acts as a nontoxic carrier of residual ammonia to be eliminated from the body. Asparagine is rapidly converted to aspartic acid by the enzyme asparaginase. Interestingly, L-asparaginase has been successfully used as a chemotherapeutic agent for decades.

It causes extracellular depletion of asparagine which seems to play a critical role in cellular adaptations to glutamine and apoptosis.

References:

- Medicine Io. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press; 2005.

- Garg U, Smith LD. Biomarkers Inborn Errors of Metabolism: Clinical Aspects and Laboratory Determination. Elsevier; 2017.

- Lea PJ, Sodek L, Parry MA, Shewry PR, Halford NG. Asparagine in plants. Ann Applied Biol. 2007;150(1):1-26.

- Chiu M, Taurino G, Bianchi MG, Kilberg MS, Bussolati O. Asparagine Synthetase in Cancer: Beyond Acute Lymphoblastic Leukemia. Front Oncol. 2019;9:1480.

- Zhang J, Fan J, Venneti S, et al. Asparagine plays a critical role in regulating cellular adaptation to glutamine depletion. Molec Cell. 2014;56(2):205-218.

- Heitink-Polle KMJ, Prinsen BHCMT, de Koning TJ, van Hasselt PM, Bierings MB. High incidence of symptomatic hyperammonemia in children with acute lymphoblastic leukemia receiving pegylated asparaginase. JIMD Repo. 2013;7:103-108.

- Ruzzo EK, Capo-Chichi JM, Ben-Zeev B, et al. Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy. Neuron. 2013;80(2):429-441.