High resolution imaging of vascular function in zebrafish

Role of berberine on angiogenesis and blood flow hemodynamics using zebrafish model

Angiogenesis and hemodynamic instability created by the irregular blood vessels causes hypoperfusion and angiogenesis-mediated diseases. Therefore, therapies focusing on controlling angiogenesis will be a valuable approach to treat a broad spectrum of diseases. In this study, we explored the anti-angiogenic potential of berberine (BBR) and also analyzed blood flow hemodynamics using zebrafish embryos. Zebrafish embryos treated with BBR (0.01-0.75 mM) at various doses at 1 hour post-fertilization (hpf) developed a variety of phenotypic variations including aberrant blood vessels, tail bending, edema, and hemorrhage. Survival rates were much lower at higher dosages, and hatching rates were almost 99%, whereas control group appeared normal. Heart rate is an essential measure that has a strong association with hemodynamics. We used ImageJ software to study the heart rate of embryos treated with BBR, preceded by video processing. The resultant graph shows a significant decrease in heart rate of embryos treated with BBR in dose-dependent manner. Also, RBC staining using o-Dianisidine confirms the anti-angiogenic potential of BBR by indicating the decrease in the intersegmental vessels at 0.5 and 0.75 mM treated embryos. Further, the gene expression study determined that the transcripts (vegf, vegfr2, nrp1a, hif-1α, nos2a, nos2b, cox-2a, and cox-2b) measured were found to be downregulated by BBR at 0.5 mM concentration, from which we conclude that enos/vegf signaling could play an important role in modulating angiogenesis. Our data imply that BBR may be an effective compound for suppressing angiogenesis in vivo, which might be helpful in the treatment of vascular disorders like cancer and diabetic retinopathy in future.

Optical transparency and label-free vessel imaging of zebrafish larvae in shortwave infrared range as a tool for prolonged studying of cardiovascular system development

Optical techniques are utilized for the non-invasive analysis of the zebrafish cardiovascular system at early developmental stages. Being based mainly on conventional optical microscopy components and image sensors, the wavelength range of the collected and analyzed light is not out of the scope of 400-900 nm. In this paper, we compared the non-invasive optical approaches utilizing visible and near infrared range (VISNIR) 400-1000 and the shortwave infrared range (SWIR) 900-1700 nm. The transmittance spectra of zebrafish tissues were measured in these wavelength ranges, then vessel maps, heart rates, and blood flow velocities were calculated from data in VISNIR and SWIR. An increased pigment pattern transparency was registered in SWIR, while the heart and vessel detection quality in this range is not inferior to VISNIR. Obtained results indicate an increased efficiency of SWIR imaging for monitoring heart function and hemodynamic analysis of zebrafish embryos and larvae and suggest a prolonged registration period in this range compared to other optical techniques that are limited by pigment pattern development.

OpenBloodFlow: A User-Friendly OpenCV-Based Software Package for Blood Flow Velocity and Blood Cell Count Measurement for Fish Embryos

The transparent appearance of fish embryos provides an excellent assessment feature for observing cardiovascular function in vivo. Previously, methods to conduct vascular function assessment were based on measuring blood-flow velocity using third-party software. In this study, we reported a simple software, free of costs and skills, called OpenBloodFlow, which can measure blood flow velocity and count blood cells in fish embryos for the first time. First, videos captured by high-speed CCD were processed for better image stabilization and contrast. Next, the optical flow of moving objects was extracted from the non-moving background in a frame-by-frame manner. Finally, blood flow velocity was calculated by the Gunner Farneback algorithm in Python. Data validation with zebrafish and medaka embryos in OpenBloodFlow was consistent with our previously published ImageJ-based method. We demonstrated consistent blood flow alterations by either OpenBloodFlow or ImageJ in the dorsal aorta of zebrafish embryos when exposed to either phenylhydrazine or ractopamine. In addition, we validated that OpenBloodFlow was able to conduct precise blood cell counting. In this study, we provide an easy and fully automatic programming for blood flow velocity calculation and blood cell counting that is useful for toxicology and pharmacology studies in fish.

High-Throughput Imaging of Blood Flow Reveals Developmental Changes in Distribution Patterns of Hemodynamic Quantities in Developing Zebrafish

Mechanical forces from blood flow and pressure (hemodynamic forces) contribute to the formation and shaping of the blood vascular network during embryonic development. Previous studies have demonstrated that hemodynamic forces regulate signaling and gene expression in endothelial cells that line the inner surface of vascular tubes, thereby modifying their cellular state and behavior. Given its important role in vascular development, we still know very little about the quantitative aspects of hemodynamics that endothelial cells experience due to the difficulty in measuring forces in vivo. In this study, we sought to determine the magnitude of wall shear stress (WSS) exerted on ECs by blood flow in different vessel types and how it evolves during development. Utilizing the zebrafish as a vertebrate model system, we have established a semi-automated high-throughput fluorescent imaging system to capture the flow of red blood cells in an entire zebrafish between 2- and 6-day post-fertilization (dpf). This system is capable of imaging up to 50 zebrafish at a time. A semi-automated analysis method was developed to calculate WSS in zebrafish trunk vessels. This was achieved by measuring red blood cell flow using particle tracking velocimetry analysis, generating a custom-made script to measure lumen diameter, and measuring local tube hematocrit levels to calculate the effective blood viscosity at each developmental stage. With this methodology, we were able to determine WSS magnitude in different vessels at different stages of embryonic and larvae growth and identified developmental changes in WSS, with absolute levels of peak WSS in all vessel types falling to levels below 0.3 Pa at 6 dpf. Additionally, we discovered that zebrafish display an anterior-to-posterior trend in WSS at each developmental stage.

Label-free quantitative measurement of cardiovascular dynamics in a zebrafish embryo using frequency-comb-referenced-quantitative phase imaging

SIGNIFICANCE

Real-time monitoring of the heart rate and blood flow is crucial for studying cardiovascular dysfunction, which leads to cardiovascular diseases.

AIM

This study aims at in-depth understanding of high-speed cardiovascular dynamics in a zebrafish embryo model for various biomedical applications via frequency-comb-referenced quantitative phase imaging (FCR-QPI).

APPROACH

Quantitative phase imaging (QPI) has emerged as a powerful technique in the field of biomedicine but has not been actively applied to the monitoring of circulatory/cardiovascular parameters, due to dynamic speckles and low frame rates. We demonstrate FCR-QPI to measure heart rate and blood flow in a zebrafish embryo. FCR-QPI utilizes a high-speed photodetector instead of a conventional camera, so it enables real-time monitoring of individual red blood cell (RBC) flow.

RESULTS

The average velocity of zebrafish's RBCs was measured from 192.5 to 608.8  μm  /  s at 24 to 28 hour-post-fertilization (hpf). In addition, the number of RBCs in a pulsatile blood flow was revealed to 16 cells/pulse at 48 hpf. The heart rates corresponded to 94 and 142 beats-per-minute at 24 and 48 hpf.

CONCLUSIONS

This approach will newly enable in-depth understanding of the cardiovascular dynamics in the zebrafish model and possible usage for drug discovery applications in biomedicine.

Haemodynamic dependence of mechano-genetic evolution of the cardiovascular system in Japanese medaka

The progression of cardiac gene expression-wall shear stress (WSS) interplay is critical to identifying developmental defects during cardiovascular morphogenesis. However, mechano-genetics from the embryonic to larval stages are poorly understood in vertebrates. We quantified peak WSS in the heart and tail vessels of Japanese medaka from 3 days post fertilization (dpf) to 14 dpf using in vivo micro-particle image velocimetry flow measurements, and in parallel analysed the expression of five cardiac genes (fgf8, hoxb6b, bmp4, nkx2.5, smyd1). Here, we report that WSS in the atrioventricular canal (AVC), ventricular outflow tract (OFT), and the caudal vessels in medaka peak with inflection points at 6 dpf and 10-11 dpf instead of a monotonic trend. Retrograde flows are captured at the AVC and OFT of the medaka heart for the first time. In addition, all genes were upregulated at 3 dpf and 7 dpf, indicating a possible correlation between the two, with the cardiac gene upregulation preceding WSS increase in order to facilitate cardiac wall remodelling.

In vivo brain ischemia-reperfusion model induced by hypoxia-reoxygenation using zebrafish larvae

Cerebral infarct is caused by cerebrovascular occlusion and results in brain damage. Although many rodent models of cerebral infarct exist, there is none based on zebrafish. In this study, we developed a novel ischemia-reperfusion model induced by hypoxic treatment using zebrafish. We first examined the changes in blood flow under hypoxic conditions. Hypoxic treatment interrupted the blood flow in 4 dpf (days post fertilization) zebrafish larvae. To quantify the trunk and cerebral blood flow, we selected the middle mesencephalic central artery (MMCtA) as a cerebral blood vessel and the dorsal aorta (DA) as a blood vessel of the trunk. Interestingly, the interruption of blood flow in MMCtA preceded that in DA. Considering these results, we hypothesized that reoxygenation immediately after hypoxia-induced cerebral ischemia leads to reperfusion. As a result, hypoxia-reoxygenation (H/R) treatment induced ischemia-reperfusion in cerebral vessels. Furthermore, brain cell death was increased 24 h after H/R treatment. Transgenic zebrafish (HuC:kaede), with neuronal cells expressing the kaede fluorescent protein, was used to investigate the effect of H/R on neuronal cells. The H/R treatment reduced the fluorescence intensity of kaede. Besides, glial fibrillary acidic protein immunoreactivity in H/R-treated larvae was significantly increased. In conclusion, H/R-treated zebrafish larvae may provide a novel ischemia-reperfusion model.

Blood Vessel Imaging at Pre-Larval Stages of Zebrafish Embryonic Development

The zebrafish (Danio rerio) is an increasingly popular animal model biological system. In cardiovascular research, it has been used to model specific cardiac phenomena as well as to identify novel therapies for human cardiovascular disease. While the zebrafish cardiovascular system functioning is well examined at larval stages, the mechanisms by which vessel activity is initiated remain a subject of intense investigation. In this research, we report on an in vivo stain-free blood vessel imaging technique at pre-larval stages of zebrafish embryonic development. We have developed the algorithm for the enhancement, alignment and spatiotemporal analysis of bright-field microscopy images of zebrafish embryos. It enables the detection, mapping and quantitative characterization of cardiac activity across the whole specimen. To validate the proposed approach, we have analyzed multiple data cubes, calculated vessel images and evaluated blood flow velocity and heart rate dynamics in the absence of any anesthesia. This non-invasive technique may shed light on the mechanism of vessel activity initiation and stabilization as well as the cardiovascular system’s susceptibility to environmental stressors at early developmental stages.

Imaging photoplethysmography and videocapillaroscopy enable noninvasive study of zebrafish cardiovascular system functioning

We report on the noninvasive method for in vivo study of fish's cardiovascular system, that is, the heart and the structure of vessels that carry blood throughout the body. The proposed approach is based on combined photoplethysmographic and videocapillaroscopic microscopic imaging and enables noncontact two-dimensional mapping of blood volume changes. We demonstrate that the obtained data allows precise measurements of heartbeat, blood flow velocity and other important parameters (see Videos S1 and S2). To validate the developed image processing technique, we have carried out multiple experiments on zebrafish-a well-proven informative model organism widely used to understand cardiac development. The proposed approach may be effective for the study of cardiovascular system formation and functioning as well as the impact of various influencing factors on them.

Functional optical coherence tomography and photoacoustic microscopy imaging for zebrafish larvae

We present a dual modality functional optical coherence tomography and photoacoustic microscopy (OCT-PAM) system. The photoacoustic modality employs an akinetic optical sensor with a large imaging window. This imaging window enables direct reflection mode operation, and a seamless integration of optical coherence tomography (OCT) as a second imaging modality. Functional extensions to the OCT-PAM system include Doppler OCT (DOCT) and spectroscopic PAM (sPAM). This functional and non-invasive imaging system is applied to image zebrafish larvae, demonstrating its capability to extract both morphological and hemodynamic parameters in vivo in small animals, which are essential and critical in preclinical imaging for physiological, pathophysiological and drug response studies.

Four-dimensional visualization of zebrafish cardiovascular and vessel dynamics by a structured illumination microscope with electrically tunable lens

We established a four-dimensional (4D) microscopy method using structured illumination for optical axial imaging with an electrically tunable lens. With its fast imaging capability, the dynamics of the cardiovascular system of the zebrafish and cerebral vessels were imaged based on the coverage of two stacks (25 layers) per second with lateral /axial resolutions of 0.6 µm and 1.8 µm, respectively. Time lapse imaging clearly shows the contractile-relaxation response of the beating heart at different cardiac phases and with different mobilities of blood vessels in different regions. This new 4D technique will facilitate in vivo imaging of organ function, generation, as well as drug responses in small-sized animals.

Development of a Simple ImageJ-Based Method for Dynamic Blood Flow Tracking in Zebrafish Embryos and Its Application in Drug Toxicity Evaluation

This study aimed to develop a simple and cost-effective method to measure blood flow in zebrafish by using an image-based approach. Three days post fertilization (dpf) zebrafish embryos were mounted with methylcellulose and subjected to video recording for tracking blood flow under an inverted microscope equipped with a high-speed CCD camera. In addition, Hoffman lens was used to enhance the blood cell contrast. The red blood cell movement was tracked by using the TrackMate plug-in in the ImageJ image processing program. Moreover, Stack Difference and Time Series Analyzer plug-in were used to detect dynamic pixel changes over time to calculate the blood flow rate. In addition to blood flow velocity and heart rate, the effect of drug treatments on other cardiovascular function parameters, such as stroke volume and cardiac output remains to be explored. Therefore, by using this method, the potential side effects on the cardiovascular performance of ethyl 3-aminobenzoate methanesulfonate (MS222) and 3-isobutyl-1-methylxanthine (IBMX) were evaluated. MS222 is a common anesthetic, while IBMX is a naturally occurring methylxanthine. Compared to normal embryos, MS222- and IBMX-treated embryos had a reduced blood flow velocity by approximately 72% and 58%, respectively. This study showed that MS222 significantly decreased the heart rate, whereas IBMX increased the heart rate. Moreover, it also demonstrated that MS222 treatment reduced 50% of the stroke volume and cardiac output. While IBMX decreased the stroke volume only. The results are in line with previous studies that used expensive instruments and complicated software analysis to assess cardiovascular function. In conclusion, a simple and low-cost method can be used to study blood flow in zebrafish embryos for compound screening. Furthermore, it could provide a precise measurement of clinically relevant cardiac functions, specifically heart rate, stroke volume, and cardiac output.

Tissue Architectural Cues Drive Organ Targeting of Tumor Cells in Zebrafish

Tumor cells encounter a myriad of physical cues upon arrest and extravasation in capillary beds. Here, we examined the role of physical factors in non-random organ colonization using a zebrafish xenograft model. We observed a two-step process by which mammalian mammary tumor cells showed non-random organ colonization. Initial homing was driven by vessel architecture, where greater numbers of cells became arrested in the topographically disordered blood vessels of the caudal vascular plexus (CVP) than in the linear vessels in the brain. Following arrest, bone-marrow- and brain-tropic clones exhibited organ-specific patterns of extravasation. Extravasation was mediated by β1 integrin, where knockdown of β1 integrin reduced extravasation in the CVP but did not affect extravasation of a brain-tropic clone in the brain. In contrast, silencing myosin 1B redirected early colonization from the brain to the CVP. Our results suggest that organ selectivity is driven by both vessel topography and cell-type-dependent extravasation.

Fluid forces shape the embryonic heart: Insights from zebrafish

Heart formation involves a complex series of tissue rearrangements, during which regions of the developing organ expand, bend, converge, and protrude in order to create the specific shapes of important cardiac components. Much of this morphogenesis takes place while cardiac function is underway, with blood flowing through the rapidly contracting chambers. Fluid forces are therefore likely to influence the regulation of cardiac morphogenesis, but it is not yet clear how these biomechanical cues direct specific cellular behaviors. In recent years, the optical accessibility and genetic amenability of zebrafish embryos have facilitated unique opportunities to integrate the analysis of flow parameters with the molecular and cellular dynamics underlying cardiogenesis. Consequently, we are making progress toward a comprehensive view of the biomechanical regulation of cardiac chamber emergence, atrioventricular canal differentiation, and ventricular trabeculation. In this review, we highlight a series of studies in zebrafish that have provided new insight into how cardiac function can shape cardiac morphology, with a particular focus on how hemodynamics can impact cardiac cell behavior. Over the long-term, this knowledge will undoubtedly guide our consideration of the potential causes of congenital heart disease.

High-speed extended-volume blood flow measurement using engineered point-spread function

Experimental characterization of blood flow in living organisms is crucial for understanding the development and function of cardiovascular systems, but there has been no technique reported for snapshot imaging of thick samples in large volumes with high precision. We have combined computational microscopy and the diffraction-free, self-bending property of Airy-beams to track fluorescent beads with sub-micron precision through an extended axial range (up to 600 μm) within the flowing blood of 3 days post-fertilization (dpf) zebrafish embryos. The spatial trajectories of the tracer beads within flowing blood were recorded during transit through both cardinal and intersegmental vessels, and the trajectories were found to be consistent with the segmentation of the vasculature recorded using selective-plane illumination microscopy (SPIM). This method provides sufficiently precise spatial and temporal measurement of 3D blood flow that has the potential for directly probing key biomechanical quantities such as wall shear stress, as well as exploring the fluidic repercussions of cardiovascular diseases. Although we demonstrate the technique for blood flow, the ten-fold better enhancement in the depth range offers improvements in a wide range of applications of high-speed precision measurement of fluid flow, from microfluidics through measurement of cell dynamics to macroscopic aerosol characterizations.

Nanoparticle localization in blood vessels: dependence on fluid shear stress, flow disturbances, and flow-induced changes in endothelial physiology

Nanoparticles in the bloodstream are subjected to complex fluid forces as they move through the curves and branches of healthy or tumor vasculature. While nanoparticles are known to preferentially accumulate in angiogenic vessels, little is known about the flow conditions in these vessels and how these conditions may influence localization. Here, we report a methodology which combines confocal imaging of nanoparticle-injected transgenic zebrafish embryos, 3D modeling of the vasculature, particle mapping, and computational fluid dynamics, to quantitatively assess the effects of fluid forces on nanoparticle distribution in vivo. Six-fold lower accumulation was found in zebrafish arteries compared to the lower velocity veins. Nanoparticle localization varied inversely with shear stress. Highest accumulation was present in regions of disturbed flow found at branch points and curvatures in the vasculature. To further investigate cell-particle association under flow, human endothelial cells were exposed to nanoparticles under hemodynamic conditions typically found in human vessels. Physiological adaptations of endothelial cells to 20 hours of flow enhanced nanoparticle accumulation in regions of disturbed flow. Overall our results suggest that fluid shear stress magnitude, flow disturbances, and flow-induced changes in endothelial physiology modulate nanoparticle localization in angiogenic vessels.

Live imaging molecular changes in junctional tension upon VE-cadherin in zebrafish

Forces play diverse roles in vascular development, homeostasis and disease. VE-cadherin at endothelial cell-cell junctions links the contractile acto-myosin cytoskeletons of adjacent cells, serving as a tension-transducer. To explore tensile changes across VE-cadherin in live zebrafish, we tailored an optical biosensor approach, originally established in vitro. We validate localization and function of a VE-cadherin tension sensor (TS) in vivo. Changes in tension across VE-cadherin observed using ratio-metric or lifetime FRET measurements reflect acto-myosin contractility within endothelial cells. Furthermore, we apply the TS to reveal biologically relevant changes in VE-cadherin tension that occur as the dorsal aorta matures and upon genetic and chemical perturbations during embryonic development.

Mechanical forces play a crucial role during morphogenesis, but how these are sensed and transduced in vivo is not fully understood. Here the authors apply a FRET tension sensor to live zebrafish and study changes in VE-cadherin tension at endothelial cell-cell junctions during arterial maturation.

Yap/Taz transcriptional activity is essential for vascular regression via Ctgf expression and actin polymerization

Vascular regression is essential to remove redundant vessels during the formation of an efficient vascular network that can transport oxygen and nutrient to every corner of the body. However, no mechanism is known to explain how major blood vessels regress during development. Here we use the dorsal part of the caudal vein plexus (dCVP) in Zebrafish to investigate the mechanism of regression and discover a new role of Yap/Taz in vascular regression. During regression, Yap/Taz is activated by blood circulation in the endothelial cells. This leads to induction of Ctgf and actin polymerization. Interference with Yap/Taz activation decreased Ctgf production, which decreased actin polymerization and vascular regression. These results implicate a novel role of Yap/Taz in vascular regression.

Blood circulation in the ascidian tunicate Corella inflata (Corellidae)

The body of the ascidian tunicate Corella inflata is relatively transparent. Thus, the circulatory system can be visualized by injecting high molecular weight fluorescein labeled dextran into the heart or the large vessels at the ends of the heart without surgery to remove the body wall. In addition, after staining with neutral red, the movement of blood cells can be easily followed to further characterize the circulatory system. The heart is two gently curved concentric tubes extending across the width of the animal. The inner myocardial tube has a partial constriction approximately in the middle. As in other tunicates, the heart is peristaltic and periodically reverses direction. During the branchial phase blood leaves the anterior end of the heart by two asymmetric vessels that connect to the two sides of the branchial basket. Blood then flows in both transverse directions through a complex system of ducts in the basket into large ventral and dorsal vessels which carry blood back to the visceral organs in the posterior of the animal. During the visceral phase blood leaves the posterior end of the heart in two vessels that repeatedly bifurcate and fan into the stomach and gonads. Blood velocity, determined by following individual cells in video frames, is high and pulsatory near the heart. A double peak in velocity at the maximum may be due to the constriction in the middle of the heart tube. Blood velocity progressively decreases with distance from the heart. In peripheral regions with vessels of small diameter blood cells frequently collide with vessel walls and cell motion is erratic. The estimated volume of blood flow during each directional phase is greater than the total volume of the animal. Circulating blood cells are confined to vessels or ducts in the visible parts of the animal and retention of high molecular weight dextran in the vessels is comparable to that seen in vertebrates. These are characteristics of a closed circulatory system.

Modeling the Behavior of Red Blood Cells within the Caudal Vein Plexus of Zebrafish

Due to the important biological role of red blood cells (RBCs) in vertebrates, the analysis of reshaping and dynamics of RBCs motion is a critical issue in physiology and biomechanics. In this paper the behavior of RBCs within the immature capillary plexus during embryonic development of zebrafish has been analyzed. Relying on the fact that zebrafish embryos are small and optically transparent, it is possible to image the blood flow. In this way the anatomy of blood vessels is monitored along with the circulation throughout their development. Numerical simulations were performed using a specific numerical model that combines fluid flow simulation, modeling of the interaction of individual RBCs immersed in blood plasma with the surrounding fluid and modeling the deformation of individual cells. The results of numerical simulations are in accordance with the in vivo observed region of interest within the caudal vein plexus of the zebrafish embryo. Good agreement of results demonstrates the capabilities of the developed numerical model to predict and analyze the motion and deformation of RBCs in complex geometries. The proposed model (methodology) will help to elucidate different rheological and hematological related pathologies and finally to design better treatment strategies.

Pharmacological Modulation of Hemodynamics in Adult Zebrafish In Vivo

Introduction

Hemodynamic parameters in zebrafish receive increasing attention because of their important role in cardiovascular processes such as atherosclerosis, hematopoiesis, sprouting and intussusceptive angiogenesis. To study underlying mechanisms, the precise modulation of parameters like blood flow velocity or shear stress is centrally important. Questions related to blood flow have been addressed in the past in either embryonic or ex vivo-zebrafish models but little information is available for adult animals. Here we describe a pharmacological approach to modulate cardiac and hemodynamic parameters in adult zebrafish in vivo.

Materials and Methods

Adult zebrafish were paralyzed and orally perfused with salt water. The drugs isoprenaline and sodium nitroprusside were directly applied with the perfusate, thus closely resembling the preferred method for drug delivery in zebrafish, namely within the water. Drug effects on the heart and on blood flow in the submental vein were studied using electrocardiograms, in vivo-microscopy and mathematical flow simulations.

Results

Under control conditions, heart rate, blood flow velocity and shear stress varied less than ± 5%. Maximal chronotropic effects of isoprenaline were achieved at a concentration of 50 μmol/L, where it increased the heart rate by 22.6 ± 1.3% (n = 4; p < 0.0001). Blood flow velocity and shear stress in the submental vein were not significantly increased. Sodium nitroprusside at 1 mmol/L did not alter the heart rate but increased blood flow velocity by 110.46 ± 19.64% (p = 0.01) and shear stress by 117.96 ± 23.65% (n = 9; p = 0.03).

Discussion

In this study, we demonstrate that cardiac and hemodynamic parameters in adult zebrafish can be efficiently modulated by isoprenaline and sodium nitroprusside. Together with the suitability of the zebrafish for in vivo-microscopy and genetic modifications, the methodology described permits studying biological processes that are dependent on hemodynamic alterations.

Association of Early Atherosclerosis with Vascular Wall Shear Stress in Hypercholesterolemic Zebrafish

Although atherosclerosis is a multifactorial disease, the role of hemodynamic information has become more important. Low and oscillating wall shear stress (WSS) that changes its direction is associated with the early stage of atherosclerosis. Several in vitro and in vivo models were proposed to reveal the relation between the WSS and the early atherosclerosis. However, these models possess technical limitations in mimicking real physiological conditions and monitoring the developmental course of the early atherosclerosis. In this study, a hypercholesterolaemic zebrafish model is proposed as a novel experimental model to resolve these limitations. Zebrafish larvae are optically transparent, which enables temporal observation of pathological variations under in vivo condition. WSS in blood vessels of 15 days post-fertilisation zebrafish was measured using a micro particle image velocimetry (PIV) technique, and spatial distribution of lipid deposition inside the model was quantitatively investigated after feeding high cholesterol diet for 10 days. Lipids were mainly deposited in blood vessel of low WSS. The oscillating WSS was not induced by the blood flows in zebrafish models. The present hypercholesterolaemic zebrafish would be used as a potentially useful model for in vivo study about the effects of low WSS in the early atherosclerosis.

Quantitative measurement of blood velocity in zebrafish with optical vector field tomography

Microscopy techniques can readily visualize the finest details of embryo vasculature, but still lack to provide a complete three-dimensional representation of blood flow parameters. We present an in-vivo 3D imaging technique, able to reconstruct the blood cell velocity vector over a large volume of zebrafish embryos. This low cost and relatively simple technique is exploited to quantitatively assess blood velocity in the zebrafish tail at different stages of development.

Impact of a combined high cholesterol diet and high glucose environment on vasculature

AIMS

Vascular complications are the leading cause of mortality and morbidity in patients with diabetes. However, proper animal models of diabetic vasculopathy that recapitulate the accelerated progression of vascular lesions in human are unavailable. In the present study, we developed a zebrafish model of diabetic vascular complications and the methodology for quantifying vascular lesion formation real-time in the living diabetic zebrafish.

METHODS AND RESULTS

Wild type zebrafish (AB) and transgenic zebrafish lines of fli1:EGFP, lyz:EGFP, gata1:dsRed, double transgenic zebrafish of gata1:dsRed/fli1:EGFP were exposed to high cholesterol diet and 3% glucose (HCD-HG) for 10 days. The zebrafish model with HCD-HG treatment was characterized by significantly increased tissue levels of insulin, glucagon, glucose, total triglyceride and cholesterol. Confocal microscopic analysis further revealed that the diabetic larvae developed clearly thickened endothelial layers, distinct perivascular lipid depositions, substantial accumulations of inflammatory cells in the injured vasculature, and a decreased velocity of blood flow. Moreover, the vascular abnormalities were improved by the treatment of pioglitazone and metformin.

CONCLUSION

A combination of high cholesterol diet and high glucose exposure induces a rapid onset of vascular complications in zebrafish similar to the early atherosclerotic vascular injuries in mammalian diabetic models, suggesting that zebrafish may be used as a novel animal model for diabetic vasculopathy.

A multi-endpoint in vivo larval zebrafish (Danio rerio) model for the assessment of integrated cardiovascular function

INTRODUCTION

Despite effective in vitro preclinical strategies to identify cardiovascular (CV) liabilities, there remains a need for early functional assessment prior to complex in vivo mammalian models. The larval zebrafish (Danio rerio, Zf) has been suggested for this role: previous data suggest that cardiac electrophysiology and vascular ultrastructure are comparable with mammals, and also indicate responsiveness of individual Zf CV system endpoints to some functional modulators. Little information is, however, available regarding integrated functional CV responses to drug treatment. Consequently, we developed a novel larval Zf model capable of simultaneous quantification of chronotropic, inotropic and arrhythmic effects, alongside measures of blood flow and vessel diameter.

METHODS

Non-invasive video analysis of the heart and dorsal aorta of anaesthetized and agarose-embedded larval ZF was used to measure multiple cardiovascular endpoints, simultaneously, following treatment with a range of functional modulators of CV physiology.

RESULTS

Changes in atrial and ventricular beat frequencies were detected in response to acute treatment with cardio-stimulants (adrenaline and theophylline), and negative chrono/inotropes (cisapride, haloperidol, terfenadine and verapamil). Arrhythmias were also observed including terfenadine-induced 2:1 atrial-ventricular (A-V) block, a previously proposed hERG surrogate measure. Significant increases in blood flow were detected in response to adrenaline and theophylline exposure; and decreases after cisapride, haloperidol, terfenadine, and verapamil treatment. Using dorsal aorta (DA) blood flow and ventricular beat rate, surrogate stoke volumes were also calculated for all compounds.

DISCUSSION

These data support the use of this approach for CV function studies. Moreover the throughput and compound requirements (approximately 3 compounds/person effort/week and <10 mg) make our approach potentially suitable for higher throughput drug safety and efficacy applications, pending further assessment of ZF-mammalian pharmacological comparability.

Cryopreservation Causes Genetic and Epigenetic Changes in Zebrafish Genital Ridges

Cryopreservation is an important tool routinely employed in Assisted Reproduction Technologies (ARTs) and germplasm banking. For several years, the assessment of global DNA fragmentation seemed to be enough to ensure the integrity of genetic material. However, cryopreservation can produce molecular alterations in key genes and transcripts undetectable by traditional assays, such modifications could interfere with normal embryo development. We used zebrafish as a model to study the effect of cryopreservation on key transcripts and genes. We employed an optimized cryopreservation protocol for genital ridges (GRs) containing primordial germ cells (PGCs) considered one of the best cell sources for gene banking. Our results indicated that cryopreservation produced a decrease in most of the zebrafish studied transcripts (cxcr4b, pou5f1, vasa and sox2) and upregulation of heat shock proteins (hsp70, hsp90). The observed downregulation could not always be explained by promoter hypermethylation (only the vasa promoter underwent clear hypermethylation). To corroborate this, we used human spermatozoa (transcriptionally inactive cells) obtaining a reduction in some transcripts (eIF2S1, and LHCGR). Our results also demonstrated that this effect was caused by freezing/thawing rather than exposure to cryoprotectants (CPAs). Finally, we employed real-time PCR (qPCR) technology to quantify the number of lesions produced by cryopreservation in the studied zebrafish genes, observing very different vulnerability to damage among them. All these data suggest that molecular alterations caused by cryopreservation should be studied in detail in order to ensure the total safety of the technique.