Decreased thyroid peroxidase expression in cultured thyrocytes after external gamma irradiation

Impairment of thyroid function has been described in up to 50% of the patie nts after external irradiation of the neck region as well as after mantle i rradiation. In order to assess radiation-induced alterations in cultured th yroid cells, the occurrence of apoptosis and necrosis as well as the expres sion of thyroid peroxidase (TPO) and of two members of the 70 kD heat shock family. HSP-73 and HSP-72. were analysed following gamma irradiation. Huma n thyroid epithelial cells (TEC) were purified from surgical tissue specime ns. were cultured and irradiated with a single dose of 5 Gy or 50 Gy using Co-60 as radioactive source. Analysis was performed 1, 3 and 5 day(s) after irradiation. Apoptosis and necrosis were assessed by DNA staining with pro pidium iodide and FAGS analysis, TPO and HSP expression by SDS-PAGE and Wes tern blotting. The cell viability of TEC was not affected by irradiation an d there was no induction of HSP-72, a sensitive indicator of acute cellular stress. Interestingly, the expression of TPO. a key enzyme of thyroid horm one synthesis, decreased significantly in irradiated TEC, while HSP-73 expr ession remained unchanged; Decreased expression of TPO with a resulting sup pression of thyroid hormone synthesis could contribute to an early developm ent of thyroid dysfunction following irradiation. Thus. analysis of thyroid function. even early after external radiation therapy of the neck or after total body irradiation, seems to be indicated.