Effect of Antithyroid Agents 6-Propyl-2-Thiouracil and l-Methyl-2-Mercaptoimidazole on Human Thyroid Iodide Peroxidase

The mechanism of inhibition of human thyroid iodide peroxidase by 6-propyl-2-thiouracil and l-methyl-2-mercaptoimidazole used in the therapy of hyperthyroid patients was studied in vitro

AKIO NAGASAKA; HIROYOSHI HIDAKA

2009

Scholarcy highlights

  • The mechanism of inhibition of human thyroid iodide peroxidase by 6-propyl-2-thiouracil and l-methyl-2-mercaptoimidazole used in the therapy of hyperthyroid patients was studied in vitro
  • The inhibition of TPO by MMI was not restored either by dialysis or by dilution, but the inhibition by PTU was restored by both treatments
  • The concentrations of PTU and MMI producing 50% inhibition of TPO were 2 × 10−6M and 8 × 10−7M, respectively. 2-Mercaptoimidazole inhibited TPO reversibly but 1-methylimidazole and imidazole did not. Both the methyl and mercaptoresidues in MMI moiety are thought to be essential to its irreversible inhibition of TPO
  • TPO activity in the PTUtreated thyroid homogenate was significantly lower than that in the control before dialysis, but the activity was restored to the control value after dialysis
  • TPO activity in the MMI treated thyroid homogenate was significantly lower than that in the control and was not affected by dialysis. These data may explain why MMI is a more potent inhibitor of iodination than PTU and may fit the clinical results observed when hyperthyroid patients are treated with these agents
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