Endocrine Disruption: In Vitro Determination of Deiodinase 1 Inhibition using Human Liver Microsomes: Mn Metal Powder and MnCl2

This study investigated the potential of two Mn-containing materials, manganese chloride (MnCl₂) and high-purity electrolytic manganese powder ((HPEMP) also known as Mn metal), to inhibit deiodinase I (DIO1) enzyme activity using reverse triiodothyronine as substrate and isolated human liver microsomes as the enzyme source.

A single valid DIO1 inhibition experiment was performed in which both materials were tested at eight concentrations in triplicate. Milli-Q water served as vehicle, and dimethyl sulfoxide was added to maintain a constant final concentration not exceeding 1% (v/v).

Solubility assessments defined top concentrations of 1 mM for MnCl₂ and nominally 9 mM for Mn metal, noting that actual Mn exposure from Mn metal was lower due to very low water solubility.

For both materials, DIO1-mediated iodide release activity remained above 80% of vehicle control activity at all concentrations. Consequently, MnCl₂ did not inhibit DIO1-catalyzed deiodination up to 1 mM, and Mn metal was likewise considered negative within the tested concentration range in this valid in vitro study.