Reconstructed human intestinal comet assay, a possible alternative in vitro model for genotoxicity assessment.

The aim of the present study was to evaluate the compatibility of reconstructed 3D human small intestinal microtissues to perform the in vitro comet assay. The comet assay is a common follow-up genotoxicity test to confirm or supplement other genotoxicity data. Technically, it can be performed utilizing a range of in vitro and in vivo assay systems. Here, we have developed a new reconstructed human intestinal comet (RICom) assay protocol for the assessment of orally ingested materials. The human intestine is a major site of food digestion and adsorption, first-pass metabolism as well as an early site of toxicant first contact and thus is a key site for evaluation. Reconstructed intestinal tissues were dosed with eight test chemicals: ethyl methanesulfonate (EMS), ethyl nitrosourea (ENU), phenformin hydrochloride (Phen HCl), benzo[a]pyrene (BaP), 1,2-dimethylhydrazine hydrochloride (DMH), potassium bromate (KBr), glycidamide (GA), and etoposide (Etop) over a span of 48 h. The RICom assay correctly identified the genotoxicity of EMS, ENU, KBr, and GA. Phen HCl, a known non-genotoxin, did not induce DNA damage in the 3D reconstructed intestinal tissues whilst showing high cytotoxicity as assessed by the assay. The 3D reconstructed intestinal tissues possess sufficient metabolic competency for the successful detection of genotoxicity elicited by BaP, without the use of an exogenous metabolic system. In contrast, DMH, a chemical that requires liver metabolism to exert genotoxicity, did not induce detectable DNA damage in the 3D reconstructed intestinal tissue system. The genotoxicity of Etop, which is dependent on cellular proliferation, was also undetectable. These results suggest the RICom assay protocol is a promising tool for further investigation and safety assessment of novel ingested materials. We recommend that further work will broaden the scope of the 3D reconstructed intestinal tissue comet assay and facilitate broader analyses of genotoxic compounds having more varied modes of actions.

The Polyamine Regulator AMD1 Upregulates Spermine Levels to Drive Epidermal Differentiation.

Maintaining tissue homeostasis depends on a balance between cell proliferation, differentiation, and apoptosis. Within the epidermis, the levels of the polyamines putrescine, spermidine, and spermine are altered in many different skin conditions, yet their role in epidermal tissue homeostasis is poorly understood. We identify the polyamine regulator, Adenosylmethionine decarboxylase 1 (AMD1), as a crucial regulator of keratinocyte (KC) differentiation. AMD1 protein is upregulated on differentiation and is highly expressed in the suprabasal layers of the human epidermis. During KC differentiation, elevated AMD1 promotes decreased putrescine and increased spermine levels. Knockdown or inhibition of AMD1 results in reduced spermine levels and inhibition of KC differentiation. Supplementing AMD1-knockdown KCs with exogenous spermidine or spermine rescued aberrant differentiation. We show that the polyamine shift is critical for the regulation of key transcription factors and signaling proteins that drive KC differentiation, including KLF4 and ZNF750. These findings show that human KCs use controlled changes in polyamine levels to modulate gene expression to drive cellular behavior changes. Modulation of polyamine levels during epidermal differentiation could impact skin barrier formation or can be used in the treatment of hyperproliferative skin disorders.