The influence of non-steroidal anti-inflammatory and antithyroid agents on myeloperoxidase-catalysed activities of human leucocytes
CITATION: Van Zyl, A. et al. 1979. The influence of non-steroidal anti-inflammatory and antithyroid agents on myeloperoxidase-catalysed activities of human leucocytes. South African Medical Journal, 55:1082-1087.
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Viable leucocytes obtained fresh from normal human subjects were shown to be able to catalyse the in vitro iodination of bovine serum albumin (BSA) in a H20 2-generating system. The rate and degree of iodination were greatly improved by sonication of the cells. A balanced salt solution was a more favourable medium than phosphate buffer for the myeloperoxidase (MPO)-catalysed iodination of whole cells and sonicated cells. Reactions known to be catalysed by other peroxidases (e.g_ thyroid peroxidase (TPO) and lactoperoxidase), such as inorganic iodide exchange for organic iodine in di-iodotyrosine (01T) and the de-iodination of thyroxine (T4)' were also catalysed by the sonicated leucocyte suspension in the system used. The non-steroidal anti-inflammatory drugs indomethacin, flufenamic acid and naproxen were far less effective inhibitors of MPO-catalysed BSA iodination of sonicated leucocytes at concentrations expected in blood with therapeutic dose levels than was observed earlier with TPO-catalysed in vitro iodination of BSA. The antithyroid drug ethylmercapto-imidazole (MM!) inhibited in vitro MPO-catalysed "'I delabelling of '''1·01l at all concentrations between 10·' and 10·'M, whereas "'I-T4 delabelling was markedly stimulated at the same drug concentrations. On the other hand, '251 incorporation into '''I-OIT was not affected by increased concentrations of MMI up to 10·'M. At higher drug concentrations the drug caused inhibition of MPO-catalysed exchange of inorganic iodide for organic iodine in Oil.