The brain diseases account for 30% of all known diseases. Pharmacological treatment is hampered by the blood–brain barrier, limiting drug delivery to the central nervous system (CNS). Transcranial photobiomodulation (tPBM) is a promising technology for treating brain diseases, due to its effectiveness, non-invasiveness, and affordability. tPBM has been widely used in pre-clinical experiments and clinical trials for treating brain diseases, such as stroke and Alzheimer’s disease. This review provides a comprehensive overview of tPBM. We summarize emerging trends and new discoveries in tPBM based on over one hundred references published in the past 20 years. We discuss the advantages and disadvantages of tPBM and highlight successful experimental and clinical protocols for treating various brain diseases. A better understanding of tPBM mechanisms, the development of guidelines for clinical practice, and the study of dose-dependent and personal effects hold great promise for progress in treating brain diseases.
SignificanceSkin is the largest organ and also the first barrier of body. Skin diseases are common, and cutaneous microcirculation is relative to various diseases. Researchers attempt to develop novel imaging techniques to obtain the complex structure, components, and functions of skin. Modern optical techniques provide a powerful tool with non-invasiveness, but the imaging performance suffers from the turbid character of skin. In vivo skin optical clearing technique has been proposed to reduce tissue scattering and enhance penetration depth of light and became a hot topic of research.AimThe aim of this review is to provide a comprehensive overview of recent development of in vivo skin optical clearing methods, how in vivo skin optical clearing enhances imaging performance, and its applications in study and light therapy of various diseases.ApproachBased on the references published over the last decade, the important milestones on the mechanism, methods, and its fundamental and clinical applications of in vivo skin optical clearing technique are provided.ResultsWith the deepening understanding of skin optical clearing mechanisms, efficient in vivo skin optical clearing methods were constantly screened out. These methods have been combined with various optical imaging techniques to improve imaging performances and acquire deeper and finer skin-related information. In addition, in vivo skin optical clearing technique has been widely applied in assisting study of diseases as well as achieving safe, high-efficiency light-induced therapy.ConclusionsIn the last decade, in vivo skin optical clearing technique has developed rapidly and played an important role in skin-related studies.
SignificanceVisualization of intact vasculatures is crucial to understanding the pathogeneses of different neurological and vascular diseases. Although various fluorescent vessel labeling methods have been used in combination with tissue clearing for three-dimensional (3D) visualization of different vascular networks, little has been done to quantify the labeling effect of each vessel labeling routine, as well as their applicability alongside various clearing protocols, making it difficult to select an optimal combination for finely constructing different vasculatures. Therefore, it is necessary to systematically assess the overall performance of these common vessel labeling methods combined with different tissue-clearing protocols.AimA comprehensive evaluation of the labeling quality of various vessel labeling routines in different organs, as well as their applicability alongside various clearing protocols, were performed to find the optimal combinations for 3D reconstruction of vascular networks with high quality.ApproachFour commonly-used vessel labeling techniques and six typical tissue optical clearing approaches were selected as candidates for the systematic evaluation.ResultsThe vessel labeling efficiency, vessel labeling patterns, and compatibility of each vessel labeling method with different tissue-clearing protocols were quantitatively evaluated and compared. Based on the comprehensive evaluation results, the optimal combinations were selected for 3D reconstructions of vascular networks in several organs, including mouse brain, liver, and kidney.ConclusionsThis study provides valuable insight on selecting the proper pipelines for 3D visualization of vascular networks, which may facilitate understanding of the underlying mechanisms of various neurovascular diseases.
Significance: Photothrombotic stroke is an important and widely used model for ischemic stroke research. However, the significant scattering of the skull during the procedure limits the light’s ability to penetrate and focus on its target. Targeted photothrombosis uses surgery-based skull windows to obtain optical access to the brain, but it renders the brain’s environment unnatural even before a stroke is established.
Aim: To establish a targeted, controllable ischemic stroke model in mice through an intact skull.
Approach: The in vivo skull optical clearing technique provides a craniotomy-free “optical window” that allows light to penetrate. Alongside the local photodynamic effect, we have established targeted photothrombosis without skull removal, effectively controlling the degree of thrombotic occlusion by changing the light dose.
Results:Ex vivo and in vivo results demonstrated that skull optical clearing treatment significantly enhanced light’s ability to penetrate the skull and focus on its target, contributing to thrombotic occlusion. The skull optical clearing window was also used for continuous blood flow mapping, and the relationship between light dose and injury degree was evaluated over 14 days of monitoring. Per our findings, increasing the light dose was accompanied by more severe infarction, indicating that the model was easily controllable.
Conclusions: Herein, a targeted, controllable ischemic stroke model was established by combinedly running an in vivo skull optical clearing technique and a photothrombotic procedure, avoiding unnecessary damage or environmental changes to the brain caused by surgery on the skull. Our established model should offer significant value to research on ischemic stroke.
Diabetes can not only disrupt the blood brain barrier and the homeostasis of brain microenvironment, but also affect the function of immune cells. Since diabetes is a chronic disease, it is of great value to investigate the changes of various physiological indicators with the development of diabetes, while there are few relevant studies. In this work, the changes of blood brain barrier and microglial function in mice with the development of diabetes was in vivo monitored, using recently arisen skull optical clearing window with a variety of optical imaging techniques. The results showed that with the development of diabetes mellitus, the permeability of the blood brain barrier in the cortex of mice increased gradually, which further induced the morphological and functional changes of microglia. This study is expected to provide a reference for the study of diabetic complications, as well as interventional treatment and efficacy evaluation of diabetes mellitus.
Stimulated emission depletion (STED) nanoscopy is a typical super-resolution imaging technique that has become a powerful tool for visualizing intracellular structures on the nanometer scale. Aggregation-induced emission luminogens (AIEgens) are ideal fluorescent agents for bioimaging and have been widely used for organelle targeting, cellular mapping and tracing. Since AIEgens generally have a large Stokes’ shift, which is beneficial for restraining the fluorescence background induced by the STED light, as well as high photobleaching resistance in their nanoaggregate states, which provides the potential for long-term imaging under a STED beam with high power density, they are ideal fluorescent agents for STED nanoscopy. The STED efficiency of aggregated TPA-T-CyP could reach more than 80%, and the dynamic mitochondrial visualization was achieved on the nanometer scale. Their moving, fission and fussion of mitochondria was clearly observed with a lateral spatial resolution of 74 nm.
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