Development of fish liver PLHC-1 spheroids and its applicability to investigate the toxicity of plastic additives

Comparative analysis of 3D and 2D in vitro models of the permanent fish liver cell line RTL-W1: Metabolic capabilities and responses to xenobiotics

In vitro models based on permanent fish liver cell lines have proven to be versatile tools for examining chemical biotransformation and toxicity. However, their in vivo relevance remains uncertain due to their potentially de-differentiated phenotype. Here, we investigate whether a 3D cell culture environment can restore hepatocyte-like properties of the Rainbow trout liver cell line RTL-W1. Utilizing ultralow attachment (ULA) microwell plates, we achieved controlled sizing and extended culture (3 weeks) of spheroidal aggregate cultures (spheroids). RTL-W1 cells within the spheroids remained viable and metabolically active, as confirmed by the CellTiter-Glo 3D assay. Transmission electron microscopy revealed that spheroids exhibit tissue-like arrangements, such as interdigitations, cell-cell junctions, and endo- or exocytic activity at the cell-cell interface. They also displayed ultrastructural characteristics typical of metabolically active cells/hepatocytes, including abundant endoplasmic reticulum (ER), Golgi apparatus, and mitochondria. RT-qPCR analysis showed upregulation of genes involved in xenobiotic and endogenous (lipid) metabolism in 3D cultures over time. Notably, for several genes, especially cyp1a, expression levels were significantly higher in spheroids than in monolayers cultured for the same duration. This was corroborated at the enzyme level by increased Cyp1a-dependent catalytic activity (EROD). Interestingly, increased Cyp1a expression did not lead to heightened susceptibility to benzo[a]pyrene toxicity, which requires bioactivation. However, RTL-W1 3D and 2D cell cultures exhibited differential susceptibility to toxicity from other model chemicals, such as the surfactant SDS and the metal copper (Cu). These findings support the hypothesis that RTL-W1 cells can re-differentiate to a hepatocyte-like phenotype when cultured in a 3D configuration and may exhibit distinct biological responses upon exposure to xenobiotics. Overall, this study advances our understanding of the potential of cell line-derived 3D in vitro models for research and providing more physiologically relevant data for regulatory contexts.

Fish Cell Spheroids, a Promising In Vitro Model to Mimic In Vivo Research: A Review

In vitro cell culture systems serve as instrumental platforms for probing biological phenomena and elucidating intricate cellular mechanisms. These systems afford researchers the opportunity to scrutinize cellular responses within a regulated environment, thereby circumventing the ethical and logistical challenges associated with in vivo experimentation. Three-dimensional (3D) cell cultures have emerged as a viable alternative to mimic in vivo environments. Within this context, spheroids are recognized as one of the most straightforward and efficacious models, presenting a promising substitute for conventional monolayer cultures. The application of 3D cultures of fish cells remains limited, focusing mainly on physiological and morphological characterization studies. However, given the capacity of spheroids to emulate in vivo conditions, researchers are exploring diverse applications of these 3D cultures. These include eco-toxicology, immunology, drug screening, endocrinology, and metabolism studies, employing a variety of cell types such as fibroblasts, hepatocytes, embryonic cells, gonadal cells, gastrointestinal cells, and pituitary cells. This review provides a succinct overview, concentrating on the most frequently employed methods for generating fish cell spheroids and their applications to date. The aim is to compile and highlight the significant contributions of these methods to the field and their potential for future research.

Estrogenic Responsiveness of Brown Trout Primary Hepatocyte Spheroids to Environmental Levels of 17α-Ethinylestradiol

Three-dimensional (3D) fish hepatocyte cultures are promising alternative models for replicating in vivo data. Few studies have attempted to characterise the structure and function of fish 3D liver models and illustrate their applicability. This study aimed to further characterise a previously established spheroid model obtained from juvenile brown trout (Salmo trutta) primary hepatocytes under estrogenic stimulation. The spheroids were exposed for six days to environmentally relevant concentrations of 17α-ethinylestradiol-EE2 (1-100 ng/L). The mRNA levels of peroxisome (catalase-Cat and urate oxidase-Uox), lipid metabolism (acyl-CoA long chain synthetase 1-Acsl1, apolipoprotein AI-ApoAI, and fatty acid binding protein 1-Fabp1), and estrogen-related (estrogen receptor α-ERα, estrogen receptor β-ERβ, vitellogenin A-VtgA, zona pellucida glycoprotein 2.5-ZP2.5, and zona pellucida glycoprotein 3a.2-ZP3a.2) target genes were evaluated by quantitative real-time polymerase chain reaction. Immunohistochemistry was used to assess Vtg and ZP protein expressions. At the highest EE2 concentration, VtgA and ZP2.5 genes were significantly upregulated. The remaining target genes were not significantly altered by EE2. Vtg and ZP immunostaining was consistently increased in spheroids exposed to 50 and 100 ng/L of EE2, whereas lower EE2 levels resulted in a weaker signal. EE2 did not induce significant changes in the spheroids' viability and morphological parameters. This study identified EE2 effects at environmentally relevant doses in trout liver spheroids, indicating its usefulness as a proxy for in vivo impacts of xenoestrogens.

Protective role of fetal bovine serum on PLHC-1 spheroids exposed to a mixture of plastic additives: A lipidomic perspective

The use of fetal bovine serum (FBS) in cell culture is being questioned for scientific and ethical reasons, prompting the exploration of alternative approaches. Nevertheless, the influence of FBS on cell functioning, especially in fish cells, has not been comprehensively examined. This study aims to evaluate the impact of FBS on the lipidome of PLHC-1 spheroids and investigate cellular and molecular responses to plastic additives in the presence/absence of FBS. Lipidomic analyses were conducted on PLHC-1 cell spheroids using liquid chromatography coupled with a high-resolution quadrupole time-of-flight mass spectrometer (HRMS-QToF). The removal of FBS from the culture medium for 24 h significantly changed the lipid profile of spheroids, resulting in a depletion of cholesterol esters (CEs), phosphatidylcholines (PCs) and lyso-phosphatidylcholines (LPCs), while ceramides and certain glycerophospholipids slightly increased. Additionally, the exclusion of FBS from the medium led to increased cytotoxicity caused by a mixture of plastic additives and increased lipidomic alterations, including an elevation of ceramides. This study emphasizes the protective role of serum components in fish liver spheroids against a mixture of plastic additives and underscores the importance of considering exposure conditions when studying metabolomic and lipidomic responses to toxicants.