Advances in Ex Situ Tissue Optical Clearing

Abstract

Examination of whole organs with subcellular resolution in health, disease, and during development is necessary to decipher their biological complexity. However, until recently, this has been virtually impossible due to the natural opacity of organ tissue. Recent progress in tissue optical clearing (TOC) has overcome this limitation by turning organs into transparent, light-permitting specimens. At least 20 original TOC methods have been developed in less than a decade, which were followed by hundreds of attempts that were aimed at their optimization and practical application. The majority of proof-of-concept studies have focused on the brain. However, it is apparent that TOC might be equally valuable when applied to peripheral organs or even the whole body. The progress in TOC for peripheral organs is delineated in an organ-by-organ fashion and whole-body clearing approaches are discussed. Additionally, physical and optical approaches for TOC affecting the optical properties of the samples and image quality are discussed to explore their advantages, limitations, and future possibilities.

Biomedical Applications of Tissue Clearing and Three-Dimensional Imaging in Health and Disease

“…In the case of the placenta, it allowed a better evaluation of the morphology and transport capacities of placental blood barriers ( Carrillo et al., 2018 ), whereas in the case of myocardial tissue it has been used to evaluate the organization of collagen in healthy hearts and in heart failure tissue ( Perbellini et al., 2017 ). Optical clearing has also been presented as a powerful 3D histopathology tool for pancreatic lesions diagnosis ( Hong et al., 2019 ), in order to detect and visualize endocrine and exocrine pathologies and to evaluate the 3D architecture of neoplasia lesions and adenocarcinomas ( Matryba et al., 2019 ). In fact, cellular resolution is fundamental for early diagnosis, as several diseases arise as a direct consequence of changes in cellular structure and behavior ( Antonacci and Braakman, 2016 ) even before they are fully noticed.…”

Mesoscopic 3D imaging of pancreatic cancer and Langerhans islets based on tissue autofluorescence

“…Since the imaging technology required to perform the described analyses is either commercially available (LSFM) or built to a relatively low cost [32][33][34] (see also www.mesos pim.org), it should be possible to establish the www.nature.com/scientificreports/ proposed analysis schemes as a complement to routine procedures in most pathology laboratories. Given the dramatic development in tissue clearing procedures during the past decade (for review see Matryba et al 35 ), it is possible that these procedures can be further refined, facilitating studies of larger tissue samples with even shorter processing times and increased quality. Finally, the described protocols could be directly translated to study other organs and tissues, depending on their AF properties.…”

Multidimensional Imaging of Mammary Gland Development: A Window Into Breast Form and Function

“…These methods seek to increase tissue imaging depths by minimizing light scattering caused by mismatches in refractive indices (RIs) between heterogeneous cellular components. Broadly, optical clearing methods rely on organic solvent-based (e.g., 3DISCO; Erturk et al, 2012) or aqueous reagent-based clearing agents (e.g., Scale, Hama et al, 2015;SeeDB, Ke et al, 2013;CUBIC, Susaki et al, 2014;FRUIT, Hou et al, 2015; C e 3D, Li et al, 2017;UbasM, Chen et al, 2017) to equilibrate RIs within a tissue ( Table 1 and recently reviewed in Matryba et al, 2019). Samples may also be hydrogel-embedded prior to clearing to preserve cellular structures (e.g., "active" and "passive" CLARITY methods; Chung and Deisseroth, 2013;Yang et al, 2014).…”