What is SAA?

SAA as an ancient protein

Serum amyloid A (SAA) is an apolipoprotein associated with HDL, and the molecular weight is 11.4 kDa. The protein has been evolutionarily conserved among a wide range of vertebrate species [*1]. And more anciently, SAA has been identified in an echinoderm, sea cucumber [*2].

 

SAA as an inflammation marker

Data of horse SAA.
Created based upon data from: Jacobsen, S., Vinther, A.M., Kjelgaard-Hansen, M. et al. Validation of an equine serum amyloid A assay with an unusually broad working range. BMC Vet Res 15, 462 (2019).

SAA is also known as one of the acute phase proteins (APP) in serum and plasma.

Tissue damage, such as trauma, infection, stress, neoplasia and inflammation, triggers acute phase response (APR) as a part of the early-defense or innate immune system [*3]. APP are synthesized from liver and certain extrahepatic tissues during APR [*3, 4].

In some species, SAA is classified as a major APP (the concentrations increase more than 10-fold when inflammation occurs). For example, equine, feline, bovine, canine, goat, mouse, porcine, rabbit, sheep, cheetah, and elephant seal are found to have SAA as a major APP [*3, 5, 6] . The concentration of equine SAA increase from 10 to often 1000 times [*4].

 

SAA possibility for prognosis

Also, the change of SAA concentrations can provide important prognostic value. For equine SAA, the response time is 6-12 hours and the peak is 48 hours after inflammation starts [*4, 7]. For other species, generally SAA starts increase at 8-12 hours after inflammation occurs, and it reaches maximal levels in 24-48 hours [*8]. As inflammation is resolved, SAA concentration declines in a short term. Since the half-life period of SAA is estimated that 24-48 hours, the concentration returns to an undetectable level after synthesis ceases [*4, 9].

References

  1. Uhlar CM, Burgess CJ, Sharp PM, et al. Evolution of the serum amyloid A (SAA) protein superfamily. Genomics 1994;19:228–35.
  2. Santiago‐Cardona PG, Berrios CA, Ramirez F, et al. Lipopolysaccharides induce intestinal serum amyloid A expression in the sea cucumber Holothuria glaberrima. Dev Comp Immunol 2003; 27: 105– 10
  3. Cray C, Zaias J, Altman NH. Acute phase response in animals: a review. Comp Med 2009; 59:517–26.
  4. Jacobsen S and Andersen PH. The acute phase protein serum amyloid A (SAA) as a marker of inflammation in horses. EqVet Educ 2007;19:38–46.
  5. Depauw S, Delanghe J, Whitehouse-Tedd K, et al. Serum protein capillary electrophoresis and measurement of acute phase proteins in a captive cheetah (Acinonyx jubatus) population. J Zoo Wildlife Med. 2014;45:497–506.
  6. Sheldon JD, Johnson SP, Hernandez JA, et al. Acute-phase Responses in Healthy, Malnourished, and Otostrongylus-infected Juvenile Northern Elephant Seals (Mirounga Angustirostris). Journal of Zoo and Wildlife Medicine. 2017;48(3), 767-775.
  7. Jacobsen S, Vinther AM, Kjelgaard-Hansen M, et al. Validation of an equine serum amyloid A assay with an unusually broad working range. BMC Vet Res. 2019;19;15(1):462.
  8. Christensen M, Langhorn R, Goddard A, et al. Comparison of serum amyloid A and C-reactive protein as diagnostic markers of systemic inflammation in dog. Can Vet J, 55. 2014; 161-168
  9. Haltmayer E, Schwendenwein I, Licka TF. Course of serum amyloid A (SAA) plasma concentrations in horses undergoing surgery for injuries penetrating synovial structures, an observational clinical study. BMC Vet Res 2017;13, 137.

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