Sum activity of peripheral deiodinases

Sum activity of peripheral deiodinases
Medical diagnostics
Reference range 20–40 nmol/s
LOINC 82367-4

The sum activity of peripheral deiodinases (GD, also referred to as deiodination capacity, total deiodinase activity or SPINA-GD) is the maximum amount of triiodothyronine produced per time-unit under conditions of substrate saturation.[1] It is assumed to reflect the activity of deiodinases outside the central nervous system and other isolated compartments. GD is therefore expected to reflect predominantly the activity of type I deiodinase.

How to determine GD

GD can be determined experimentally by exposing a cell culture system to saturating concentrations of T4 and measuring the T3 production. Whole body deiodination activity can be assessed by measuring production of radioactive iodine after loading the organism with marked thyroxine.

However, both approaches are faced with draw-backs. Measuring deiodination in cell culture delivers little, if any, information on total deiodination activity. Using marked thyroxine exposes the body to thyrotoxicosis and radioactivity. Additionally, it is not possible to differentiate step-up reactions resulting in T3 production from the step-down reaction catalyzed by type 3 deiodination, which mediates production of reverse T3.

In vivo, it may therefore be beneficial to estimate GD from equilibrium levels of T4 and T3. It is obtained with

or

: Dilution factor for T3 (reciprocal of apparent volume of distribution, 0.026 l−1)
: Clearance exponent for T3 (8e-6 sec−1)
KM1: Dissociation constant of type-1-deiodinase (5e-7 mol/l)
K30: Dissociation constant T3-TBG (2e9 l/mol)[2]

Reference range

Lower limitUpper limitUnit
20[2]40[2]nmol/s

The equations and their parameters are calibrated for adult humans with a body mass of 70 kg and a plasma volume of ca. 2.5 l.[2]

Clinical significance

SPINA-GD correlates with resting energy expenditure[3], body mass index[2][4][5] and thyrotropin levels in humans,[6][7] and it is reduced in nonthyroidal illness with hypodeiodination.[4][8][9][10][11]

Recent research revealed total deiodinase activity to be higher in hypothyroid patients as long as thyroid tissue is still present,.[7] This effect may ensue from the existence of an effective TSH-deiodinase axis or TSH-T3 shunt. After total thyroidectomy or high-dose radioiodine therapy (e.g. in treated thyroid cancer) as well as after initiation of substitution therapy with levothyroxine the activity of step-up deiodinases decreases and the correlation of SPINA-GD to thyrotropin concentration is lost.[12] SPINA-GD is also reduced in certain chronic diseases, e.g. chronic fatigue syndrome.[13] In Graves's disease, initially elevated SPINA-GD decreaes with antithyroid treatment in parallel to declining TSH receptor autoantibody titres[3].

Deiodination capacity proved to be an inpedendent predictor of substitution dose in a trial with over 300 patients on replacement therapy with levothyroxine.[14]

See also

References

  1. ↑ Dietrich JW, Landgrafe-Mende G, Wiora E, Chatzitomaris A, Klein HH, Midgley JE, Hoermann R (9 June 2016). "Calculated Parameters of Thyroid Homeostasis: Emerging Tools for Differential Diagnosis and Clinical Research". Frontiers in Endocrinology. 7: 57. doi:10.3389/fendo.2016.00057. PMC 4899439. PMID 27375554.
  2. 1 2 3 4 5 Dietrich JW (2002). Der Hypophysen-Schilddrüsen-Regelkreis. Berlin, Germany: Logos-Verlag Berlin. ISBN 978-3-89722-850-4. OCLC 50451543.
  3. 1 2 Kim, Min Joo; Cho, Sun Wook; Choi, Sumin; Ju, Dal Lae; Park, Do Joon; Park, Young Joo (2018). "Changes in Body Compositions and Basal Metabolic Rates during Treatment of Graves' Disease". International Journal of Endocrinology. 2018: 1–8. doi:10.1155/2018/9863050.
  4. 1 2 Liu S, Ren J, Zhao Y, Han G, Hong Z, Yan D, Chen J, Gu G, Wang G, Wang X, Fan C, Li J (February 2013). "Nonthyroidal illness syndrome: is it far away from Crohn's disease?". Journal of Clinical Gastroenterology. 47 (2): 153–9. doi:10.1097/MCG.0b013e318254ea8a. PMID 22874844.
  5. ↑ Dietrich JW, Landgrafe G, Fotiadou EH (2012). "TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis". Journal of Thyroid Research. 2012: 351864. doi:10.1155/2012/351864. PMC 3544290. PMID 23365787.
  6. ↑ Hoermann R, Midgley JE, Larisch R, Dietrich JW (February 2013). "Is pituitary TSH an adequate measure of thyroid hormone-controlled homoeostasis during thyroxine treatment?". European Journal of Endocrinology. 168 (2): 271–80. doi:10.1530/EJE-12-0819. PMID 23184912.
  7. 1 2 Hoermann R, Midgley JE, Giacobino A, Eckl WA, Wahl HG, Dietrich JW, Larisch R (December 2014). "Homeostatic equilibria between free thyroid hormones and pituitary thyrotropin are modulated by various influences including age, body mass index and treatment". Clinical Endocrinology. 81 (6): 907–15. doi:10.1111/cen.12527. PMID 24953754.
  8. ↑ Rosolowska-Huszcz D, Kozlowska L, Rydzewski A (August 2005). "Influence of low protein diet on nonthyroidal illness syndrome in chronic renal failure". Endocrine. 27 (3): 283–8. doi:10.1385/ENDO:27:3:283. PMID 16230785.
  9. ↑ Han G, Ren J, Liu S, Gu G, Ren H, Yan D, Chen J, Wang G, Zhou B, Wu X, Yuan Y, Li J (September 2013). "Nonthyroidal illness syndrome in enterocutaneous fistulas". American Journal of Surgery. 206 (3): 386–92. doi:10.1016/j.amjsurg.2012.12.011. PMID 23809674.
  10. ↑ Dietrich JW, Müller P, Schiedat F, Schlömicher M, Strauch J, Chatzitomaris A, Klein HH, Mügge A, Köhrle J, Rijntjes E, Lehmphul I (June 2015). "Nonthyroidal Illness Syndrome in Cardiac Illness Involves Elevated Concentrations of 3,5-Diiodothyronine and Correlates with Atrial Remodeling". European Thyroid Journal. 4 (2): 129–37. doi:10.1159/000381543. PMC 4521060. PMID 26279999.
  11. ↑ Fan S, Ni X, Wang J, Zhang Y, Tao S, Chen M, Li Y, Li J (February 2016). "Low Triiodothyronine Syndrome in Patients With Radiation Enteritis: Risk Factors and Clinical Outcomes an Observational Study". Medicine. 95 (6): e2640. doi:10.1097/MD.0000000000002640. PMC 4753882. PMID 26871787.
  12. ↑ Hoermann R, Midgley JE, Larisch R, Dietrich JW (2017). "Advances in applied homeostatic modelling of the relationship between thyrotropin and free thyroxine". PLOS One. 12 (11): e0187232. doi:10.1371/journal.pone.0187232. PMC 5695809. PMID 29155897.
  13. ↑ Ruiz-Núñez, Begoña; Tarasse, Rabab; Vogelaar, Emar F.; Janneke Dijck-Brouwer, D. A.; Muskiet, Frits A. J. (20 March 2018). "Higher Prevalence of "Low T3 Syndrome" in Patients With Chronic Fatigue Syndrome: A Case–Control Study". Frontiers in Endocrinology. 9. doi:10.3389/fendo.2018.00097.
  14. ↑ Midgley JE, Larisch R, Dietrich JW, Hoermann R (December 2015). "Variation in the biochemical response to l-thyroxine therapy and relationship with peripheral thyroid hormone conversion efficiency". Endocrine Connections. 4 (4): 196–205. doi:10.1530/EC-15-0056. PMC 4557078. PMID 26335522.

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