Developmental delay associated with normal thyroidal function and long-term amiodarone therapy during fetal and neonatal life

Amiodarone Alters Cholesterol Biosynthesis through Tissue-Dependent Inhibition of Emopamil Binding Protein and Dehydrocholesterol Reductase 24

Amiodarone is prescribed for the treatment and prevention of irregular heartbeats. Although effective in clinical practice, the long-term use of amiodarone has many unwanted side effects, including cardiac, pulmonary, hepatic, and neurological toxicities. Our objective was to elucidate effects of amiodarone exposure on the cholesterol metabolism in cultured neuronal and non-neuronal cells and in individuals taking amiodarone. We observed that amiodarone increases distinct cholesterol precursors in different cell types in a dose-dependent manner. In liver and kidney cell lines, amiodarone causes increase in desmosterol levels, and in primary cortical neurons and astrocytes, amiodarone increases zymosterol, zymostenol, and 8-dehydrocholesterol (8-DHC). We conclude that amiodarone inhibits two enzymes in the pathway, emopamil binding protein (EBP) and dehydrocholesterol reductase 24 (DHCR24). Cortical neurons and astrocytes are more sensitive to amiodarone than liver and kidney cell lines. We confirmed the inhibition of EBP enzyme by analyzing the sterol intermediates in EBP-deficient Neuro2a cells versus amiodarone-treated control Neuro2a cells. To determine if the cell culture experiments have clinical relevance, we analyzed serum samples from amiodarone users. We found that in patient serum samples containing detectable amount of amiodarone there are elevated levels of the sterol precursors zymosterol, 8-DHC, and desmosterol. This study illustrates the need for close monitoring of blood biochemistry during prolonged amiodarone use to minimize the risk of side effects.

Towards in vitro DT/DNT testing: Assaying chemical susceptibility in early differentiating NT2 cells

Human pluripotent embryonal carcinoma (NT2) cells are increasingly considered as a suitable model for in vitro toxicity testing, e.g. developmental toxicity and neurotoxicity (DT/DNT) studies, as they undergo neuronal differentiation upon stimulation with retinoic acid (RA) and permit toxicity testing at different stages of maturation. NT2 cells have recently been reported to show specific changes in dielectric resistance profiles during differentiation which can be observed as early as 24h upon RA-stimulation. These observations suggest altered susceptibility to chemicals at an early stage of differentiation. However, chemical susceptibility of early differentiating NT cells has not yet been studied. To address this question, we have established a cell fitness screening assay based on the analysis of intracellular ATP levels and we applied the assay in a large-scale drug screening experiment in NT2 stem cells and early differentiating NT2 cells. Subsequent analysis of ranked fitness phenotypes revealed 19 chemicals with differential toxicity profile in early differentiating NT2 cells. To evaluate whether any of the identified drugs have previously been associated with DT/DNT, we conducted a literature search on the identified molecules and quantified the fraction of chemicals assigned to the FDA (Food and Drug Administration) pregnancy risk categories (PRC) N, A, B, C, D, and X in the hit list and the small molecule library. While the fractions of the categories N and B were decreased (0.81 and 0.35-fold), the classes C, D and X were increased (1.35, 1.47 and 3.27-fold) in the hit list compared to the chemical library. From these data as well as from the literature review, identifying large fractions of chemicals being directly (∼42%) and indirectly associated with DT/DNT (∼32%), we conclude that our method may be beneficial to systematic in vitro-based primary screening for developmental toxicants and neurotoxicants and we propose cell fitness screening in early differentiating NT2 cells as a strategy for evaluating chemical susceptibility at different stages of differentiation to reduce animal testing in the context of the 3Rs.