A rapid assay of human thyroid peroxidase activity

Impaired synthesis or action of thyroid hormones (THs) during critically sensitive periods of development can have long term adverse effects on health. Development of rapid assays to identify chemicals that impair THs physiology is an important goal for reducing risks from chemical use. Thyroid peroxidase (TPO) is a key enzyme regulating THs synthesis in thyroid gland and a vulnerable target for chemicals that disrupt THs synthesis. To develop a human-relevant, rapid assay for TPO inhibition, we have engineered two cell lines (CHO and LentiX-293) to express active human TPO (hTPO) enzyme and applied them in a recently-described assay using a stable fluorescent product (Amplex UltraRed). Assay performance was assessed by comparing activity of 19 reference chemicals with known strong, weak or no TPO inhibitory activity. The assay using hTPO from either cell line consistently identified the relative potency of strong to moderate inhibitors and chemicals known to be inactive. Results were less consistent for chemicals reported to be weak inhibitors of rodent TPO, possibly suggesting some species specificity. Our studies support the use of hTPO from stably transfected cell lines to substitute for animal-derived thyroid microsomes for rapid high throughput screening assays to identify and characterize TPO inhibitors.