Threonine - Nutrition

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What is Threonine?

Threonine is an essential amino acid for dogs and cats. Threonine is characterised as a gluconeogenic amino acid and contains a hydroxyl side chain which is chemically reactive. Dietary threonine is absorbed by a neutral amino acid transporter in the small intestine (particularly the jejunum) and plasma threonine is actively reabsorbed in the proximal tubule of the kidney.

Why is it Important?

Threonine is a component of structural proteins. The hydroxyl group on the side chain of threonine often serves as the site for phosphorylation and de-phosphorylation reactions that control the activities of many proteins and enzymes[1].

Roles in the body

The phosphorylation/dephosphorylation of the threonine hydroxyl groups on proteins is by either serine/threonine kinase or serine/threonine phosphatase, respectively, and controls activity of normal physiologic function, such as insulin release[2] or cellular apoptosis[3].

Consequences of Threonine Deficiency

Dogs:

Puppies fed a threonine-deficient diet experienced decreased food intake and weight loss[4].

Cats:

Feeding of a threonine-deficient diet to kittens caused decreased food intake and weight loss[5], as well as cerebellar dysfunction resulting in ataxia, tremors, and incoordination that was reversible with threonine supplementation[6].

Toxicity

There are no studies on either acute or chronic toxicity related to feeding high doses of threonine to dogs and no reports of safe upper limits. Kittens fed purified diets containing threonine at 9x the requirement for growth showed no adverse effects[7]. There are no studies on acute or chronic toxicity of high dose threonine in adult cats.

Dietary Sources

Sufficient threonine is found in plant and animal protein sources, such as muscle meat, eggs, dairy protein (e.g. casein), cereal grains, and pulses (i.e. legumes).

Diagnosing Threonine Deficiency

Diagnosis of threonine deficiency is based on fasted plasma amino acids.

References

  1. National Research Council (NRC). Protein and Amino Acids. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p. 130-131.
  2. Ortsader H, et al. Protein phosphatase in pancreatic islets. J Endo 2014;221:R121-R144.
  3. Depaoli-Roach AA, et al. Serine/threonine protein phosphatases in the control of cell function. Adv Enz Regul 1994;34:199-224.
  4. Burns RA and Milner JA. Threonine, tryptophan and histidine requirements of immature beagle dogs. J Nutr 1982;112:447-452.
  5. Rogers QR and Morris JG. Essentiality of amino acids for the growing kitten. J Nutr 1979;109:718-723.
  6. Titchenal CA, et al. Threonine imbalance, deficiency, and neurological dysfunction in the kitten. J Nutr 1980;110:2444-2459.
  7. Taylor TP, et al. Optimizing the pattern of essential amino acids as the sole source of dietary nitrogen supports near maximal growth in kittens. J Nutr 1996;126:2243-2252.



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