Spheroids and organoids as humanized 3D scaffold-free engineered tissues for SARS-CoV-2 viral infection and drug screening.

The new coronavirus (2019-nCoV) or the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was officially declared by the World Health Organization (WHO) as a pandemic in March 2020. To date, there are no specific antiviral drugs proven to be effective in treating SARS-CoV-2, requiring joint efforts from different research fronts to discover the best route of treatment. The first decisions in drug discovery are based on 2D cell culture using high-throughput screening. In this context, spheroids and organoids emerge as a reliable alternative. Both are scaffold-free 3D engineered constructs that recapitulate key cellular and molecular events of tissue physiology. Different studies have already shown their advantages as a model for different infectious diseases, including SARS-CoV-2 and for drug screening. The use of these 3D engineered tissues as an in vitro model can fill the gap between 2D cell culture and in vivo preclinical assays (animal models) as they could recapitulate the entire viral life cycle. The main objective of this review is to understand spheroid and organoid biology, highlighting their advantages and disadvantages, and how these scaffold-free engineered tissues can contribute to a better comprehension of viral infection by SARS-CoV-2 and to the development of in vitro high-throughput models for drug screening.

Reprogramming to a pluripotent state modifies mesenchymal stem cell resistance to oxidative stress.

Properties of induced pluripotent stem cells (iPSC) have been extensively studied since their first derivation in 2006. However, the modification in reactive oxygen species (ROS) production and detoxification caused by reprogramming still needs to be further elucidated. The objective of this study was to compare the response of iPSC generated from menstrual blood-derived mesenchymal stem cells (mb-iPSC), embryonic stem cells (H9) and adult menstrual blood-derived mesenchymal stem cells (mbMSC) to ROS exposure and investigate the effects of reprogramming on cellular oxidative stress (OS). mbMSC were extremely resistant to ROS exposure, however, mb-iPSC were 10-fold less resistant to H(2)O(2), which was very similar to embryonic stem cell sensitivity. Extracellular production of ROS was also similar in mb-iPSC and H9 and almost threefold lower than in mbMSC. Furthermore, intracellular amounts of ROS were higher in mb-iPSC and H9 when compared with mbMSC. As the ability to metabolize ROS is related to antioxidant enzymes, we analysed enzyme activities in these cell types. Catalase and superoxide dismutase activities were reduced in mb-iPSC and H9 when compared with mbMSC. Finally, cell adhesion under OS conditions was impaired in mb-iPSC when compared with mbMSC, albeit similar to H9. Thus, reprogramming leads to profound modifications in extracellular ROS production accompanied by loss of the ability to handle OS.