Intravital microscopy as a tool to study drug delivery in preclinical studies

The triggering pathway, the metabolic amplifying pathway, and cellular transduction in regulation of glucose-dependent biphasic insulin secretion

INTRODUCTION

Insulin secretion is a highly regulated process critical for maintaining glucose homeostasis. This abstract explores the intricate interplay between three essential pathways: The Triggering Pathway, The Metabolic Amplifying Pathway, and Cellular Transduction, in orchestrating glucose-dependent biphasic insulin secretion.

MECHANISM

During the triggering pathway, glucose metabolism in pancreatic beta-cells leads to ATP production, closing ATP-sensitive potassium channels and initiating insulin exocytosis. The metabolic amplifying pathway enhances insulin secretion via key metabolites like NADH and glutamate, enhancing calcium influx and insulin granule exocytosis. Additionally, the cellular transduction pathway involves G-protein coupled receptors and cyclic AMP, modulating insulin secretion.

RESULT AND CONCLUSION

These interconnected pathways ensure a dynamic insulin response to fluctuating glucose levels, with the initial rapid phase and the subsequent sustained phase. Understanding these pathways' complexities provides crucial insights into insulin dysregulation in diabetes and highlights potential therapeutic targets to restore glucose-dependent insulin secretion.

Real-Time Multiphoton Intravital Microscopy of Drug Extravasation in Tumours during Acoustic Cluster Therapy

Optimising drug delivery to tumours remains an obstacle to effective cancer treatment. A prerequisite for successful chemotherapy is that the drugs reach all tumour cells. The vascular network of tumours, extravasation across the capillary wall and penetration throughout the extracellular matrix limit the delivery of drugs. Ultrasound combined with microbubbles has been shown to improve the therapeutic response in preclinical and clinical studies. Most studies apply microbubbles designed as ultrasound contrast agents. Acoustic Cluster Therapy (ACT®) is a novel approach based on ultrasound-activated microbubbles, which have a diameter 5-10 times larger than regular contrast agent microbubbles. An advantage of using such large microbubbles is that they are in contact with a larger part of the capillary wall, and the oscillating microbubbles exert more effective biomechanical effects on the vessel wall. In accordance with this, ACT® has shown promising therapeutic results in combination with various drugs and drug-loaded nanoparticles. Knowledge of the mechanism and behaviour of drugs and microbubbles is needed to optimise ACT®. Real-time intravital microscopy (IVM) is a useful tool for such studies. This paper presents the experimental setup design for visualising ACT® microbubbles within the vasculature of tumours implanted in dorsal window (DW) chambers. It presents ultrasound setups, the integration and alignment of the ultrasound field with the optical system in live animal experiments, and the methodologies for visualisation and analysing the recordings. Dextran was used as a fluorescent marker to visualise the blood vessels and to trace drug extravasation and penetration into the extracellular matrix. The results reveal that the experimental setup successfully recorded the kinetics of extravasation and penetration distances into the extracellular matrix, offering a deeper understanding of ACT's mechanisms and potential in localised drug delivery.

Three-Photon Infrared Stimulation of Endogenous Neuroreceptors in Vivo

To interrogate neural circuits and crack their codes, in vivo brain activity imaging must be combined with spatiotemporally precise stimulation in three dimensions using genetic or pharmacological specificity. This challenge requires deep penetration and focusing as provided by infrared light and multiphoton excitation, and has promoted two-photon photopharmacology and optogenetics. However, three-photon brain stimulation in vivo remains to be demonstrated. We report the regulation of neuronal activity in zebrafish larvae by three-photon excitation of a photoswitchable muscarinic agonist at 50 pM, a billion-fold lower concentration than used for uncaging, and with mid-infrared light of 1560 nm, the longest reported photoswitch wavelength. Robust, physiologically relevant photoresponses allow modulating brain activity in wild-type animals with spatiotemporal and pharmacological precision. Computational calculations predict that azobenzene-based ligands have high three-photon absorption cross-section and can be used directly with pulsed infrared light. The expansion of three-photon pharmacology will deeply impact basic neurobiology and neuromodulation phototherapies.

Endocytosis in cancer and cancer therapy

Endocytosis is a complex process whereby cell surface proteins, lipids and fluid from the extracellular environment are packaged, sorted and internalized into cells. Endocytosis is also a mechanism of drug internalization into cells. There are multiple routes of endocytosis that determine the fate of molecules, from degradation in the lysosomes to recycling back to the plasma membrane. The overall rates of endocytosis and temporal regulation of molecules transiting through endocytic pathways are also intricately linked with signalling outcomes. This process relies on an array of factors, such as intrinsic amino acid motifs and post-translational modifications. Endocytosis is frequently disrupted in cancer. These disruptions lead to inappropriate retention of receptor tyrosine kinases on the tumour cell membrane, changes in the recycling of oncogenic molecules, defective signalling feedback loops and loss of cell polarity. In the past decade, endocytosis has emerged as a pivotal regulator of nutrient scavenging, response to and regulation of immune surveillance and tumour immune evasion, tumour metastasis and therapeutic drug delivery. This Review summarizes and integrates these advances into the understanding of endocytosis in cancer. The potential to regulate these pathways in the clinic to improve cancer therapy is also discussed.

Photoacoustic Tomography Opening New Paradigms in Biomedical Imaging

After the emergence of the ultrasound, X-ray CT, PET, and MRI, photoacoustic tomography (PAT) is now in the phase of its exponential growth, with its expected full maturation being another form of mainstream clinical imaging modality. By combining the high contrast benefit of optical imaging and the high-resolution deep imaging capability of ultrasound, PAT can provide unprecedented anatomical image contrasts at clinically relevant depths as well as enable the use of a variety of functional and molecular imaging information, which is not possible with conventional imaging modalities. With these strengths, PAT has achieved numerous breakthroughs in various biomedical applications and also provided new technical platforms that may be able to resolve unmet issues in clinics. In this chapter, we provide an overview of the development of PAT technology for several major biomedical applications and provide an approximate projection of the future of PAT.

Label-Free Visualization and Tracking of Gold Nanoparticles in Vasculature Using Multiphoton Luminescence

Gold nanoparticles continue to generate interest for use in several biomedical applications. Recently, researchers have been focusing on exploiting their dual diagnostic/therapeutic theranostic capabilities. Before clinical translation can occur, regulatory agencies will require a greater understanding of their biodistribution and safety profiles post administration. Previously, the real-time identification and tracking of gold nanoparticles in free-flowing vasculature had not been possible without extrinsic labels such as fluorophores. Here, we present a label-free imaging approach to examine gold nanoparticle (AuNP) activity within the vasculature by utilizing multiphoton intravital microscopy. This method employs a commercially available multiphoton microscopy system to visualize the intrinsic luminescent signal produced by a multiphoton absorption-induced luminescence effect observed in single gold nanoparticles at frame rates necessary for capturing real-time blood flow. This is the first demonstration of visualizing unlabeled gold nanoparticles in an unperturbed vascular environment with frame rates fast enough to achieve particle tracking. Nanoparticle blood concentration curves were also evaluated by the tracking of gold nanoparticle flow in vasculature and verified against known pre-injection concentrations. Half-lives of these gold nanoparticle injections ranged between 67 and 140 s. This label-free imaging approach could provide important structural and functional information in real time to aid in the development and effective analysis of new metallic nanoparticles for various clinical applications in an unperturbed environment, while providing further insight into their complex uptake and clearance pathways.

Understanding the in vivo Fate of Advanced Materials by Imaging

Engineered materials are ubiquitous in biomedical applications ranging from systemic drug delivery systems to orthopedic implants, and their actions unfold across multiple time- and length-scales. The efficacy and safety of biologics, nanomaterials, and macroscopic implants are all dictated by the same general principles of pharmacology as apply to small molecule drugs, comprising how the body affects materials (pharmacokinetics, PK) and conversely how materials affect the body (pharmacodynamics, PD). Imaging technologies play an increasingly insightful role in monitoring both of these processes, often simultaneously: translational macroscopic imaging modalities such as MRI and PET/CT offer whole-body quantitation of biodistribution and structural or molecular response, while ex vivo approaches and optical imaging via in vivo (intravital) microscopy reveal behaviors at subcellular resolution. In this review, the authors survey developments in imaging the in situ behavior of systemically and locally administered materials, with a particular focus on using microscopy to understand transport, target engagement, and downstream host responses at a single-cell level. The themes of microenvironmental influence, controlled drug release, on-target molecular action, and immune response, especially as mediated by macrophages and other myeloid cells are examined. Finally, the future directions of how new imaging technologies may propel efficient clinical translation of next-generation therapeutics and medical devices are proposed.

Spatial heterogeneity of nanomedicine investigated by multiscale imaging of the drug, the nanoparticle and the tumour environment

Genetic and phenotypic tumour heterogeneity is an important cause of therapy resistance. Moreover, non-uniform spatial drug distribution in cancer treatment may cause pseudo-resistance, meaning that a treatment is ineffective because the drug does not reach its target at sufficient concentrations. Together with tumour heterogeneity, non-uniform drug distribution causes “therapy heterogeneity”: a spatially heterogeneous treatment effect. Spatial heterogeneity in drug distribution occurs on all scales ranging from interpatient differences to intratumour differences on tissue or cellular scale. Nanomedicine aims to improve the balance between efficacy and safety of drugs by targeting drug-loaded nanoparticles specifically to tumours. Spatial heterogeneity in nanoparticle and payload distribution could be an important factor that limits their efficacy in patients. Therefore, imaging spatial nanoparticle distribution and imaging the tumour environment giving rise to this distribution could help understand (lack of) clinical success of nanomedicine. Imaging the nanoparticle, drug and tumour environment can lead to improvements of new nanotherapies, increase understanding of underlying mechanisms of heterogeneous distribution, facilitate patient selection for nanotherapies and help assess the effect of treatments that aim to reduce heterogeneity in nanoparticle distribution.

In this review, we discuss three groups of imaging modalities applied in nanomedicine research: non-invasive clinical imaging methods (nuclear imaging, MRI, CT, ultrasound), optical imaging and mass spectrometry imaging. Because each imaging modality provides information at a different scale and has its own strengths and weaknesses, choosing wisely and combining modalities will lead to a wealth of information that will help bring nanomedicine forward.

Applications of near infrared and surface enhanced Raman scattering techniques in tumor imaging: A short review

Imaging technologies play a vital role in clinical oncology and have undergone massive growth over the past few decades. Research in the field of tumor imaging and biomedical diagnostics requires early detection of physiological alterations so as to provide curative treatment in real time. The objective of this review is to provide an insight about near infrared fluorescence (NIRF) and surface enhanced Raman scattering (SERS) imaging techniques that can be used to expand their capabilities for the early detection and diagnosis of cancer cells. Basic setup, principle and working of the instruments has been provided and common NIRF imaging agents as well as SERS tags are also discussed besides the analytical advantages/disadvantages of these techniques. This review can help researchers working in the field of molecular imaging to design cost effective fluorophores and SERS tags to overcome the limitations of both NIRF as well as SERS imaging technologies.

Fluorescence anisotropy imaging in drug discovery

Non-invasive measurement of drug-target engagement can provide critical insights in the molecular pharmacology of small molecule drugs. Fluorescence polarization/fluorescence anisotropy measurements are commonly employed in protein/cell screening assays. However, the expansion of such measurements to the in vivo setting has proven difficult until recently. With the advent of high-resolution fluorescence anisotropy microscopy it is now possible to perform kinetic measurements of intracellular drug distribution and target engagement in commonly used mouse models. In this review we discuss the background, current advances and future perspectives in intravital fluorescence anisotropy measurements to derive pharmacokinetic and pharmacodynamic measurements in single cells and whole organs.

Seeing Better and Going Deeper in Cancer Nanotheranostics

Biomedical imaging modalities in clinical practice have revolutionized oncology for several decades. State-of-the-art biomedical techniques allow visualizing both normal physiological and pathological architectures of the human body. The use of nanoparticles (NP) as contrast agents enabled visualization of refined contrast images with superior resolution, which assists clinicians in more accurate diagnoses and in planning appropriate therapy. These desirable features are due to the ability of NPs to carry high payloads (contrast agents or drugs), increased in vivo half-life, and disease-specific accumulation. We review the various NP-based interventions for treatments of deep-seated tumors, involving "seeing better" to precisely visualize early diagnosis and "going deeper" to activate selective therapeutics in situ.

Application of nanoparticles in cancer detection by Raman scattering based techniques

In vitro detection technique Raman spectroscopy (Rs), in one number times another Rs  based expert ways of art and so on, are useful instruments for cancer  discovery. top gave greater value to Raman spectroscopy  sers is a relatively new careful way for in vitro  and in vivo discovery that takes away bad points of simple Raman spectroscopy (Rs). Raman spectroscopy (RS) and in particular, multiple RS-based techniques are useful for cancer detection. Surface enhanced Raman spectroscopy (SERS) is a relatively new method for both in vitro and in vivo detection, which eliminates the drawbacks of simple RS. Using nanoparticles has elevated the sensitivity and specificity of SERS. SERS has the potential to increase sensitivity, specificity and spatial resolution in cancer detection, especially in cooperation with other diagnostic imaging tools such as magnetic resonance imaging (MRI) and PET-scan polyethylene terephthalate. Developing a hand held instrument for detecting cancer or other illnesses may also be feasible by using SERS. Frequently, novel nanoparticles are used in SERS. With a focus on nanoparticle utilization, we review the benefits of RS in cancer detection and related biomarkers. With a focus on nanoparticles utilizations, the benefits of RS in cancer detection and related biomarkers were reviewed. In addition, Raman applications to detect some of prevalent were discussed. Also more investigated cancers such as breast and colorectal cancer, multiple nanostructures and their possible special biomarkers, especially as SERS nano-tag have been reviewed. The main purpose of this article is introducing of most popular nanotechnological approaches in cancer detection by using Raman techniques. Moreover, have been caught up on detection and reviewed some of the most prevalent and also more investigated cancers such as breast, colorectal cancer, multiple intriguing nanostructures, especially as SERS nano-tag, special cancer biomarkers and related approaches. The main purpose of this article is to introduce the most popular nanotechnological approaches in cancer detection by using Raman techniques.

A RhoA-FRET Biosensor Mouse for Intravital Imaging in Normal Tissue Homeostasis and Disease Contexts

The small GTPase RhoA is involved in a variety of fundamental processes in normal tissue. Spatiotemporal control of RhoA is thought to govern mechanosensing, growth, and motility of cells, while its deregulation is associated with disease development. Here, we describe the generation of a RhoA-fluorescence resonance energy transfer (FRET) biosensor mouse and its utility for monitoring real-time activity of RhoA in a variety of native tissues in vivo. We assess changes in RhoA activity during mechanosensing of osteocytes within the bone and during neutrophil migration. We also demonstrate spatiotemporal order of RhoA activity within crypt cells of the small intestine and during different stages of mammary gestation. Subsequently, we reveal co-option of RhoA activity in both invasive breast and pancreatic cancers, and we assess drug targeting in these disease settings, illustrating the potential for utilizing this mouse to study RhoA activity in vivo in real time.

Non-invasive intravital imaging of head and neck squamous cell carcinomas in live mice

Head and neck squamous cell carcinoma is one of the most common cancers with a 50% 5-year survival rate. Understanding the mechanisms that control development, progression, and spreading of the tumor to distal sites is of paramount importance to develop effective therapies. Here, we describe a minimally invasive procedure, which enables performing intravital microscopy of the mouse tongue in models for oral cancer and provides structural and dynamic information of the tumors at cellular and subcellular level.

An intravital microscopy model to study early pancreatic inflammation in type 1 diabetes in NOD mice

Intravital microscopy (IVM) of the pancreas has been proven to be an invaluable tool in pancreatitis, transplantation and ischemia/reperfusion research. Also in type 1 diabetes (T1D) pancreatic IVM offers unique advantages for the elucidation of the disease process. Female non-obese diabetic (NOD) mice develop T1D spontaneously by 40 weeks of age. Our goal was to establish an IVM-based method to study early pancreatic inflammation in NOD mice, which can be used to screen novel medications to prevent or delay T1D in future studies. This included evaluation of leukocyte-endothelial interactions as well as disturbances of capillary perfusion in the pancreatic microcirculation.

Hybrid optical and acoustic resolution optoacoustic endoscopy

We propose the implementation of hybrid optical and acoustic resolution optoacoustic endoscopy. Laser light is transmitted to tissue by two types of illumination for achieving optical and acoustic resolution imaging. A 20 MHz ultrasound detector is used for recording optoacoustic signals. The endoscopy probe attains a 3.6 mm diameter and is fully encapsulated into a catheter system. We validate the imaging performance of the hybrid endoscope on phantoms and ex vivo, and discuss the necessity for the extended resolution and depth range of endoscopy achieved.

Intravital Microscopy Imaging Approaches for Image-Guided Drug Delivery Systems

Rapid technical advances in the field of non-linear microscopy have made intravital microscopy a vital pre-clinical tool for research and development of imaging-guided drug delivery systems. The ability to dynamically monitor the fate of macromolecules in live animals provides invaluable information regarding properties of drug carriers (size, charge, and surface coating), physiological, and pathological processes that exist between point-of-injection and the projected of site of delivery, all of which influence delivery and effectiveness of drug delivery systems. In this Review, we highlight how integrating intravital microscopy imaging with experimental designs (in vitro analyses and mathematical modeling) can provide unique information critical in the design of novel disease-relevant drug delivery platforms with improved diagnostic and therapeutic indexes. The Review will provide the reader an overview of the various applications for which intravital microscopy has been used to monitor the delivery of diagnostic and therapeutic agents and discuss some of their potential clinical applications.

Recent Developments in Active Tumor Targeted Multifunctional Nanoparticles for Combination Chemotherapy in Cancer Treatment and Imaging

Nanotechnology and combination therapy are two major fields that show great promise in the treatment of cancer. The delivery of drugs via nanoparticles helps to improve drug's therapeutic effectiveness while reducing adverse side effects associated wifh high dosage by improving their pharmacokinetics. Taking advantage of molecular markers over-expressing on tumor tissues compared to normal cells, an "active" molecular marker targeted approach would be-beneficial for cancer therapy. These actively targeted nanoparticles would increase drug concentration at the tumor site, improving efficacy while further reducing chemo-resistance. The multidisciplinary approach may help to improve the overall efficacy in cancer therapy. This review article summarizes recent developments of targeted multifunctional nanoparticles in the delivery, of various drugs for a combinational chemotherapy approach to cancer treatment and imaging.

Optical-resolution photoacoustic endomicroscopy in vivo

Optical-resolution photoacoustic microscopy (OR-PAM) has become a major experimental tool of photoacoustic tomography, with unique imaging capabilities for various biological applications. However, conventional imaging systems are all table-top embodiments, which preclude their use in internal organs. In this study, by applying the OR-PAM concept to our recently developed endoscopic technique, called photoacoustic endoscopy (PAE), we created an optical-resolution photoacoustic endomicroscopy (OR-PAEM) system, which enables internal organ imaging with a much finer resolution than conventional acoustic-resolution PAE systems. OR-PAEM has potential preclinical and clinical applications using either endogenous or exogenous contrast agents.

Simultaneous multi-parametric analysis of Leishmania and of its hosting mammal cells: A high content imaging-based method enabling sound drug discovery process

Leishmaniasis is a vector-borne disease for which only limited therapeutic options are available. The disease is ranked among the six most important tropical infectious diseases and represents the second-largest parasitic killer in the world. The development of new therapies has been hampered by the lack of technologies and methodologies that can be integrated into the complex physiological environment of a cell or organism and adapted to suitable in vitro and in vivo Leishmania models. Recent advances in microscopy imaging offer the possibility to assess the efficacy of potential drug candidates against Leishmania within host cells. This technology allows the simultaneous visualization of relevant phenotypes in parasite and host cells and the quantification of a variety of cellular events. In this review, we present the powerful cellular imaging methodologies that have been developed for drug screening in a biologically relevant context, addressing both high-content and high-throughput needs. Furthermore, we discuss the potential of intra-vital microscopy imaging in the context of the anti-leishmanial drug discovery process.

Homeostasis of the apical plasma membrane during regulated exocytosis in the salivary glands of live rodents

In exocrine organs such as the salivary glands, fluids and proteins are secreted into ductal structures by distinct mechanisms that are tightly coupled. In the acinar cells, the major secretory units of the salivary glands, fluids are secreted into the acinar canaliculi through paracellular and intracellular transport, whereas proteins are stored in large granules that undergo exocytosis and fuse with the apical plasma membranes releasing their content into the canaliculi. Both secretory processes elicit a remodeling of the apical plasma membrane that has not been fully addressed in in vitro or ex vivo models. Recently, we have studied regulated exocytosis in the salivary glands of live rodents, focusing on the role that actin and myosin plays in this process. We observed that during exocytosis both secretory granules and canaliculi are subjected to the hydrostatic pressure generated by fluid secretion. Furthermore, the absorption of the membranes of the secretory granules contributes to the expansion and deformation of the canaliculi. Here we suggest that the homeostasis of the apical plasma membranes during exocytosis is maintained by various strategies that include: (1) membrane retrieval via compensatory endocytosis, (2) increase of the surface area via membrane folds and (3) recruitment of a functional actomyosin complex. Our observations underscore the important relationship between tissue architecture and cellular response, and highlight the potential of investigating biological processes in vivo by using intravital microscopy.

Fluorescence resonance energy transfer between ZnSe ZnS quantum dots and bovine serum albumin in bioaffinity assays of anticancer drugs

In the current work, using ZnSe ZnS quantum dots (QDs) as representative nanoparticles, the affinities of seven anticancer drugs for bovine serum albumin (BSA) were studied using fluorescence resonance energy transfer (FRET). The FRET efficiency of BSA-QD conjugates can reach as high as 24.87% by electrostatic interaction. The higher binding constant (3.63×10(7)Lmol(-1)) and number of binding sites (1.75) between ZnSe ZnS QDs and BSA demonstrated that the QDs could easily associate to plasma proteins and enhance the transport efficacy of drugs. The magnitude of binding constants (10(3)-10(6)Lmol(-1)), in the presence of QDs, was between drugs-BSA and drugs-QDs in agreement with common affinities of drugs for serum albumins (10(4)-10(6)Lmol(-1)) in vivo. ZnSe ZnS QDs significantly increased the affinities for BSA of Vorinostat (SAHA), Docetaxel (DOC), Carmustine (BCNU), Doxorubicin (Dox) and 10-Hydroxycamptothecin (HCPT). However, they slightly reduced the affinities of Vincristine (VCR) and Methotrexate (MTX) for BSA. The recent work will not only provide useful information for appropriately understanding the binding affinity and binding mechanism at the molecular level, but also illustrate the ZnSe ZnS QDs are perfect candidates for nanoscal drug delivery system (DDS).

Mechanisms of cooperation in cancer nanomedicine: towards systems nanotechnology

Nanoparticles are designed to deliver therapeutics and diagnostics selectively to tumors. Their size, shape, charge, material, coating, and cargo determine their individual functionalities. A systems approach could help predict the behavior of trillions of nanoparticles interacting in complex tumor environments. Engineering these nanosystems may lead to biomimetic strategies where interactions between nanoparticles and their environment give rise to cooperative behaviors typically seen in natural self-organized systems. Examples include nanoparticles that communicate the location of a tumor to amplify tumor homing or self-assemble and disassemble to optimize nanoparticle transport. The challenge is to discover which nanoparticle designs lead to a desired system behavior. To this end, novel nanomaterials, deep understanding of biology, and computational tools are emerging as the next frontier.

A method for noninvasive longitudinal measurements of [Ca2+] in arterioles of hypertensive optical biosensor mice

We used two-photon (2-p) Förster resonance energy transfer (FRET) microscopy to provide serial, noninvasive measurements of [Ca(2+)] in arterioles of living "biosensor" mice. These express a genetically encoded Ca(2+) indicator (GECI), either FRET-based exMLCK or intensity-based GCaMP2. The FRET ratios, Rmin and Rmax, required for in vivo Ca(2+) calibration of exMLCK were obtained in isolated arteries. For in vivo experiments, mice were anesthetized (1.5% isoflurane), and arterioles within a depilated ear were visualized through the intact skin (i.e., noninvasively), by 2-p excitation of exMLCK (at 820 nm) or GCaMP2 (at 920 nm). Spontaneous or agonist-evoked [Ca(2+)] transients in arteriolar smooth muscle cells were imaged (at 2 Hz) with both exMLCK and GCaMP2. To examine changes in arteriolar [Ca(2+)] that might accompany hypertension, five exMLCK mice were implanted with telemetric blood pressure transducers and osmotic minipumps containing ANG II (350 ng·kg(-1)·min(-1)) and fed a high (6%)-salt diet for 9 days. [Ca(2+)] was measured every other day in five smooth muscle cells of two to three arterioles in each animal. Prior to ANG II/salt, [Ca(2+)] was 246 ± 42 nM. [Ca(2+)] increased transiently to 599 nM on day 2 after beginning ANG II/salt, then remained elevated at 331 ± 42 nM for 4 more days, before returning to 265 ± 47 nM 6 days after removal of ANG II/salt. In summary, two-photon excitation of exMLCK and GCaMP2 provides a method for noninvasive, longitudinal quantification of [Ca(2+)] dynamics and vascular structure in individual arterioles of a particular animal over an extended period of time, a capability that should enhance future studies of hypertension and vascular function.

Imaging the dynamics of endocytosis in live mammalian tissues

In mammalian cells, endocytosis plays a pivotal role in regulating several basic cellular functions. Up to now, the dynamics and the organization of the endocytic pathways have been primarily investigated in reductionist model systems such as cell and organ cultures. Although these experimental models have been fully successful in unraveling the endocytic machinery at a molecular level, our understanding of the regulation and the role of endocytosis in vivo has been limited. Recently, advancements in intravital microscopy have made it possible to extend imaging in live animals to subcellular structures, thus revealing new aspects of the molecular machineries regulating membrane trafficking that were not previously appreciated in vitro. Here, we focus on the use of intravital microscopy to study endocytosis in vivo, and discuss how this approach will allow addressing two fundamental questions: (1) how endocytic processes are organized in mammalian tissues, and (2) how they contribute to organ physiopathology.

Accumulating advantages, reducing limitations: multimodal nonlinear imaging in biomedical sciences - the synergy of multiple contrast mechanisms

Multimodal nonlinear microscopy has matured during the past decades to one of the key imaging modalities in life science and biomedicine due to its unique capabilities of label-free visualization of tissue structure and chemical composition, high depth penetration, intrinsic 3D sectioning, diffraction limited resolution and low phototoxicity. This review briefly summarizes first recent advances in the field regarding the methodology, e.g., contrast mechanisms and signal characteristics used for contrast generation as well as novel image processing approaches. The second part deals with technologic developments emphasizing improvements in penetration depth, imaging speed, spatial resolution and nonlinear labeling strategies. The third part focuses on recent applications in life science fundamental research and biomedical diagnostics as well as future clinical applications.

Imaging cell biology in live animals: ready for prime time

Time-lapse fluorescence microscopy is one of the main tools used to image subcellular structures in living cells. Yet for decades it has been applied primarily to in vitro model systems. Thanks to the most recent advancements in intravital microscopy, this approach has finally been extended to live rodents. This represents a major breakthrough that will provide unprecedented new opportunities to study mammalian cell biology in vivo and has already provided new insight in the fields of neurobiology, immunology, and cancer biology.

Visualizing leukocyte trafficking in the living brain with 2-photon intravital microscopy

Intravital imaging of the superficial brain tissue in mice represents a powerful tool for the dissection of the cellular and molecular cues underlying inflammatory and infectious central nervous system (CNS) diseases. We present here a step-by-step protocol that will enable a non-specialist to set up a two-photon brain-imaging model. The protocol offers a two-part approach that is specifically optimized for imaging leukocytes but can be easily adapted to answer varied CNS-related biological questions. The protocol enables simultaneous visualization of fluorescently labeled immune cells, the pial microvasculature and extracellular structures such as collagen fibers at high spatial and temporal resolution. Intracranial structures are exposed through a cranial window, and physiologic conditions are maintained during extended imaging sessions via continuous superfusion of the brain surface with artificial cerebrospinal fluid (aCSF). Experiments typically require 1-2 h of preparation, which is followed by variable periods of immune cell tracking. Our methodology converges the experience of two laboratories over the past 10 years in diseased animal models such as cerebral ischemia, lupus, cerebral malaria, and toxoplasmosis. We exemplify the utility of this protocol by tracking leukocytes in transgenic mice in the pial vessels under steady-state conditions.

Intravital Microscopy Reveals Differences in the Kinetics of Endocytic Pathways between Cell Cultures and Live Animals

Intravital microscopy has enabled imaging of the dynamics of subcellular structures in live animals, thus opening the door to investigating membrane trafficking under physiological conditions. Here, we sought to determine whether the architecture and the environment of a fully developed tissue influences the dynamics of endocytic processes. To this aim, we imaged endocytosis in the stromal cells of rat salivary glands both in situ and after they were isolated and cultured on a solid surface. We found that the internalization of transferrin and dextran, two molecules that traffic via distinct mechanisms, is substantially altered in cultured cells, supporting the idea that the three dimensional organization of the tissue and the cues generated by the surrounding environment strongly affect membrane trafficking events.

Real-time in vivo imaging of fungal migration to the central nervous system

Recent technical advances have afforded valuable new insights into the pathogenesis of fungal infections in the central nervous system (CNS), which continue to cause devastating complications, particularly in immunocompromised individuals. To cause CNS mycosis, organisms such as Cryptococcus neoformans become blood borne and progress through a series of pathogenic checkpoints that culminate in fungal replication in the brain. Critical steps include fungal arrest in the vasculature of the brain, interaction and signalling of the fungal and endothelial cells leading to transmigration with subsequent parenchymal invasion and fungal replication in the CNS. Previous studies that made use of in vitro and ex vivo approaches contributed greatly to our understanding of brain invasion by fungi. However, the knowledge gained from previous studies relied on in vitro models that did not account for vascular haemodynamics. For this reason, more refined approaches that model blood flow and vascular anatomy are required, andultimately studying fungal invasion and dissemination in vivo. Indeed, in vivo imaging (also known as intravital imaging) has emerged as a valuable technique to probe host-pathogen interactions. In this review, with a focus on C. neoformans, we will provide an overview of the applications of the prior techniques and recent advances, their strengths and limitations in characterizing the migration of fungi into the brain, and unanswered questions that may provide new directions for research.

Tumor-targeting multi-functional nanoparticles for theragnosis: new paradigm for cancer therapy

Theragnostic nanoparticles (NPs) contain diagnostic and therapeutic functions in one integrated system, enabling diagnosis, therapy, and monitoring of therapeutic response at the same time. For diagnostic function, theragnostic NPs require the inclusion of noninvasive imaging modalities. Among them, optical imaging has various advantages including sensitivity, real-time and convenient use, and non-ionization safety, which make it the leading technique for theragnostic NPs. For therapeutic function, theragnostic NPs have been applied to chemotherapy, photodynamic therapy, siRNA therapy and photothermal therapy. In this review, we present a recent progress reported in the development and applications of theragnostic NPs for cancer therapy. More specifically, we will focus on theragnostic NPs related with optical imaging, highlighting promising strategies based on optical imaging techniques.

Intravital microscopy: new insights into cellular interactions

Inflammation is the body's way of combating invading pathogens or noxious stimuli. Under normal conditions, the complex host response of rubor, dolor, calor, tumor, and functio laesa is essential for survival and the return to homeostasis. However, unregulated inflammation is all too often observed in diseases such as rheumatoid arthritis, stroke, and cancer. The host inflammatory response is governed by a number of tightly regulated processes that enable cellular trafficking to occur at the sites of damage to ultimately ensure the resolution of inflammation. Intravital microscopy (IVM) provides quantitative, qualitative, and dynamic insights into cell biology and these cellular interactions. This review highlights the pros and cons of this specialized technique and how it has evolved to help understand the physiology and pathophysiology of inflammatory events in a number of different disease states, leading to a number of potential therapeutic targets for drug discovery.

Intravital microscopy: a practical guide on imaging intracellular structures in live animals

Intravital microscopy is an extremely powerful tool that enables imaging several biological processes in live animals. Recently, the ability to image subcellular structures in several organs combined with the development of sophisticated genetic tools has made possible extending this approach to investigate several aspects of cell biology. Here we provide a general overview of intravital microscopy with the goal of highlighting its potential and challenges. Specifically, this review is geared toward researchers that are new to intravital microscopy and focuses on practical aspects of carrying out imaging in live animals. Here we share the know-how that comes from first-hand experience, including topics such as choosing the right imaging platform and modality, surgery and stabilization techniques, anesthesia and temperature control. Moreover, we highlight some of the approaches that facilitate subcellular imaging in live animals by providing numerous examples of imaging selected organelles and the actin cytoskeleton in multiple organs.

Nanoscale drug delivery systems for enhanced drug penetration into solid tumors: current progress and opportunities

Poor penetration of anticancer drags into solid tumors significantly limits their efficacy. This phenomenon has long been observed for small-molecule chemotherapeutics, and it can be even more pronounced for nanoscale therapies. Nanoparticles have enormous potential for the treatment of cancer due to their wide applicability as drug delivery and imaging vehicles and their size-dependent accumulation into solid tumors by the enhanced permeability and retention (EPR) effect. Further, synthetic nanoparticles can be engineered to overcome barriers to drag delivery. Despite their promise for the treatment of cancer, relatively little work has been done to study and improve their ability to diffuse into solid tumors following passive accumulation in the tumor vasculature. In this review, we present the complex issues governing efficient penetration of nanoscale therapies into solid tumors. The current methods available to researchers to study nanoparticle penetration into malignant tumors are described, and the most recent works studying the penetration of nanoscale materials into solid tumors are summarized. We conclude with an overview of the important nanoparticle design parameters governing their tumor penetration, as well as by highlighting critical directions in this field.

Regulated exocytosis: novel insights from intravital microscopy

Regulated exocytosis is a fundamental process that every secretory cell uses to deliver molecules to the cell surface and the extracellular space by virtue of membranous carriers. This process has been extensively studied using various approaches such as biochemistry, electrophysiology and electron microscopy. However, recent developments in time-lapse light microscopy have made possible imaging individual exocytic events, hence, advancing our understanding of this process at a molecular level. In this review, we focus on intravital microscopy (IVM), a light microscopy-based approach that enables imaging subcellular structures in live animals, and discuss its recent application to study regulated exocytosis. IVM has revealed differences in regulation and modality of regulated exocytosis between in vitro and in vivo model systems, unraveled novel aspects of this process that can be appreciated only in in vivo settings and provided valuable and novel information on its molecular machinery. In conclusion, we make the case for IVM being a mature technique that can be used to investigate the molecular machinery of several intracellular events under physiological conditions.

Intravital multiphoton imaging of immune responses in the mouse ear skin

Multiphoton (MP) microscopy enables the direct in vivo visualization, with high spatial and temporal resolution, of fluorescently tagged immune cells, extracellular matrix and vasculature in tissues. This approach, therefore, represents a powerful alternative to traditional methods of assessing immune cell function in the skin, which are mainly based on flow cytometry and histology. Here we provide a step-by-step protocol describing experimental procedures for intravital MP imaging of the mouse ear skin, which can be easily adapted to address many specific skin-related biological questions. We demonstrate the use of this procedure by characterizing the response of neutrophils during cutaneous inflammation, which can be used to perform in-depth analysis of neutrophil behavior in the context of the skin microanatomy, including the epidermis, dermis and blood vessels. Such experiments are typically completed within 1 d, but as the procedures are minimally invasive, it is possible to perform longitudinal studies through repeated imaging.

Intravital microscopy to image membrane trafficking in live rats

Intravital microscopy is a powerful tool that enables imaging various biological processes in live animals. Here, we describe a series of procedures designed to image subcellular structures, such as endosomes and secretory vesicles in the salivary glands (SGs) of live rats. To this aim, we used fluorescently labeled molecules and/or fluorescently tagged proteins that were transiently transfected in the live animal.

Two-photon imaging within the murine thorax without respiratory and cardiac motion artifact

Intravital microscopy has been recognized for its ability to make physiological measurements at cellular and subcellular levels while maintaining the complex natural microenvironment. Two-photon microscopy (TPM), using longer wavelengths than single-photon excitation, has extended intravital imaging deeper into tissues, with minimal phototoxicity. However, due to a relatively slow acquisition rate, TPM is especially sensitive to motion artifact, which presents a challenge when imaging tissues subject to respiratory and cardiac movement. Thoracoabdominal organs that cannot be exteriorized or immobilized during TPM have generally required the use of isolated, pump-perfused preparations. However, this approach entails significant alteration of normal physiology, such as a lack of neural inputs, increased vascular resistance, and leukocyte activation. We adapted techniques of intravital microscopy that permitted TPM of organs maintained within the thoracoabdominal cavity of living, breathing rats or mice. We obtained extended intravital TPM imaging of the intact lung, arguably the organ most susceptible to both respiratory and cardiac motion. Intravital TPM detected the development of lung microvascular endothelial activation manifested as increased leukocyte adhesion and plasma extravasation in response to oxidative stress inducers PMA or soluble cigarette smoke extract. The pulmonary microvasculature and alveoli in the intact animal were imaged with comparable detail and fidelity to those in pump-perfused animals, opening the possibility for TPM of other thoracoabdominal organs under physiological and pathophysiological conditions.