Models of Disease

Three-Dimensional Cell Cultures: The Bridge between In Vitro and In Vivo Models

Although historically, the traditional bidimensional in vitro cell system has been widely used in research, providing much fundamental information regarding cellular functions and signaling pathways as well as nuclear activities, the simplicity of this system does not fully reflect the heterogeneity and complexity of the in vivo systems. From this arises the need to use animals for experimental research and in vivo testing. Nevertheless, animal use in experimentation presents various aspects of complexity, such as ethical issues, which led Russell and Burch in 1959 to formulate the 3R (Replacement, Reduction, and Refinement) principle, underlying the urgent need to introduce non-animal-based methods in research. Considering this, three-dimensional (3D) models emerged in the scientific community as a bridge between in vitro and in vivo models, allowing for the achievement of cell differentiation and complexity while avoiding the use of animals in experimental research. The purpose of this review is to provide a general overview of the most common methods to establish 3D cell culture and to discuss their promising applications. Three-dimensional cell cultures have been employed as models to study both organ physiology and diseases; moreover, they represent a valuable tool for studying many aspects of cancer. Finally, the possibility of using 3D models for drug screening and regenerative medicine paves the way for the development of new therapeutic opportunities for many diseases.

A Roadmap of In Vitro Models in Osteoarthritis: A Focus on Their Biological Relevance in Regenerative Medicine

Osteoarthritis (OA) is a multifaceted musculoskeletal disorder, with a high prevalence worldwide. Articular cartilage and synovial membrane are among the main biological targets in the OA microenvironment. Gaining more knowledge on the accuracy of preclinical in vitro OA models could open innovative avenues in regenerative medicine to bridge major gaps, especially in translation from animals to humans. Our methodological approach entailed searches on Scopus, the Web of Science Core Collection, and EMBASE databases to select the most relevant preclinical in vitro models for studying OA. Predicting the biological response of regenerative strategies requires developing relevant preclinical models able to mimic the OA milieu influencing tissue responses and organ complexity. In this light, standard 2D culture models lack critical properties beyond cell biology, while animal models suffer from several limitations due to species differences. In the literature, most of the in vitro models only recapitulate a tissue compartment, by providing fragmented results. Biotechnological advances may enable scientists to generate new in vitro models that combine easy manipulation and organ complexity. Here, we review the state-of-the-art of preclinical in vitro models in OA and outline how the different preclinical systems (inflammatory/biomechanical/microfluidic models) may be valid tools in regenerative medicine, describing their pros and cons. We then discuss the prospects of specific and combinatorial models to predict biological responses following regenerative approaches focusing on mesenchymal stromal cells (MSCs)-based therapies to reduce animal testing.

Current Models for Development of Disease-Modifying Osteoarthritis Drugs

Osteoarthritis (OA) is a painful and disabling disease that affects millions of people worldwide. Symptom-alleviating treatments exist, although none with long-term efficacy. Furthermore, there are currently no disease-modifying OA drugs (DMOADs) with demonstrated efficacy in OA patients, which is, in part, attributed to a lack of full understanding of the pathogenesis of OA. The inability to translate findings from basic research to clinical applications also highlights the deficiencies in the available OA models at simulating the clinically relevant pathologies and responses to treatments in humans. In this review, the current status in the development of DMOADs will be first presented, with special attention to those in Phase II-IV clinical trials. Next, current in vitro, ex vivo, and in vivo OA models are summarized and the respective advantages and disadvantages of each are highlighted. Of note, the development and application of microphysiological or tissue-on-a-chip systems for modeling OA in humans are presented and the issues that need to be addressed in the future are discussed. Microphysiological systems should be given serious consideration for their inclusion in the DMOAD development pipeline, both for their ability to predict drug safety and efficacy in human clinical trials at present, as well as for their potential to serve as a test platform for personalized medicine. Impact statement At present, no disease-modifying osteoarthritis (OA) drugs (DMOADs) have been approved for widespread clinical use by regulatory bodies. The failure of developing effective DMOADs is likely owing to multiple factors, not the least of which are the intrinsic differences between the intact human knee joint and the preclinical models. This work summarizes the current OA models for the development of DMOADs, discusses the advantages/disadvantages of each, and then proposes future model development to aid in the discovery of effective and personalized DMOADs. The review also highlights the microphysiological systems, which are emerging as a new platform for drug development.