Chick chorioallantoic membrane as an in vivo model to study vasoreactivity: characterization of development-dependent hyperemia induced by epoxyeicosatrienoic acids (EETs)

The angiogenic potential of pH-neutral borophosphate bioactive glasses

Borate bioactive glasses have gained attention in recent years due to their therapeutic and regenerative effects in vivo. However, borate bioactive glasses release alkaline ions, increasing the local pH and creating a toxic environment for cell culture studies. A partial compositional substitution of phosphate for borate can create a pH-neutral glass that does not significantly affect the local pH while still releasing therapeutic ions. In the present study, a series of Na-Ca-borophosphate bioactive glasses with different borate-to-phosphate ratios was evaluated in vitro and in vivo for cytotoxicity and angiogenic effects. Compared to more basic borate glasses, the pH-neutral glasses supported endothelial cell migration and stimulated greater blood vessel formation in a chick chorioallantoic membrane model. The results from this study indicate that these pH-neutral glasses are promising angiogenic biomaterials for use in tissue engineering and regenerative medicine.

Supplemental calcium increases hatch rate but not hatchling mass of chick embryos in shell-less culture

A method is described for culturing 64-70 h-old chicken embryos and egg contents outside of the eggshell through to hatching. Cultured egg contents were suspended in polymethylpentene kitchen wrap (F.O.R. wrap; Riken Fabro) supported in polyvinyl chloride tripods. Tripods were incubated in Plexiglas environmental chambers which were rocked automatically through an angle of ±20°. The concentration of CO₂ was maintained at 2% throughout incubation, while that of O₂ was increased from ambient to 50%, and relative humidity was decreased from 90%-92% to 83%-84% at incubation Day 9. Cultured embryos not supplemented with calcium did not hatch. The Hatch rate increased when supplemental calcium L-lactate hydrate was increased between 250 and 350 mg. A maximal hatch rate of 54.8% was achieved when cultures were supplemented with 350 mg of calcium L-lactate hydrate and 3.5 ml of sterile water. Adding 400 or 450 mg of calcium L-lactate hydrate did not increase the hatch rate further. The mass of cultured hatchlings (including the retracted yolk) and yolk-free carcass wet and dry mass and length of the right third toe were significantly less than the corresponding parameters observed in hatchlings in ovo. No statistically significant differences in hatchling mass, yolk-free carcass wet or dry mass, or length of the right third toe were noted among cultured hatchlings supplemented with 250-450 mg of calcium L-lactate hydrate. Failure to completely absorb albumen was the most common abnormality observed in cultures which failed to hatch. The present technique allows a unique approach to study the physiology of the developing chicken embryo.

Translational Studies on the Potential of a VEGF Nanoparticle-Loaded Hyaluronic Acid Hydrogel

Heart failure has a five-year mortality rate approaching 50%. Inducing angiogenesis following a myocardial infarction is hypothesized to reduce cardiomyocyte death and tissue damage, thereby preventing heart failure. Herein, a novel nano-in-gel delivery system for vascular endothelial growth factor (VEGF), composed of star-shaped polyglutamic acid-VEGF nanoparticles in a tyramine-modified hyaluronic acid hydrogel (nano-VEGF-HA-TA), is investigated. The ability of the nano-VEGF-HA-TA system to induce angiogenesis is assessed in vivo using a chick chorioallantoic membrane model (CAM). The formulation is then integrated with a custom-made, clinically relevant catheter suitable for minimally invasive endocardial delivery and the effect of injection on hydrogel properties is examined. Nano-VEGF-HA-TA is biocompatible on a CAM assay and significantly improves blood vessel branching (p < 0.05) and number (p < 0.05) compared to a HA-TA hydrogel without VEGF. Nano-VEGF-HA-TA is successfully injected through a 1.2 m catheter, without blocking or breaking the catheter and releases VEGF for 42 days following injection in vitro. The released VEGF retains its bioactivity, significantly improving total tubule length on a Matrigel^® assay and human umbilical vein endothelial cell migration on a Transwell^® migration assay. This VEGF-nano in a HA-TA hydrogel delivery system is successfully integrated with an appropriate device for clinical use, demonstrates promising angiogenic properties in vivo and is suitable for further clinical translation.

An angiogenesis platform using a cubic artificial eggshell with patterned blood vessels on chicken chorioallantoic membrane

The chorioallantoic membrane (CAM) containing tiny blood vessels is an alternative to large animals for studies involving angiogenesis and tissue engineering. However, there is no technique to design the direction of growing blood vessels on the CAM at the microscale level for tissue engineering experiments. Here, a methodology is provided to direct blood vessel formation on the surface of a three-dimensional egg yolk using a cubic artificial eggshell with six functionalized membranes. A structure on the lateral side of the eggshell containing a straight channel and an interlinked chamber was designed, and the direction and formation area of blood vessels with blood flow was artfully defined by channels with widths of 70-2000 μm, without sharply reducing embryo viability. The relationship between the size of interlinked chamber and the induction of blood vessels was investigated to establish a theory of design. Role of negative and positive pressure in the induction of CAM with blood vessels was investigated, and air pressure change in the culture chamber was measured to demonstrate the mechanism for blood vessel induction. Histological evaluation showed that components of CAM including chorionic membrane and blood vessels were induced into the channels. Based on our design theory, blood vessels were induced into arrayed channels, and channel-specific injection and screening were realized, which demonstrated proposed applications. The platform with position- and space-controlled blood vessels is therefore a powerful tool for biomedical research, which may afford exciting applications in studies involved in local stimulation of blood vessel networks and those necessary to establish a living system with blood flow from a beating heart.

Identification of potent inhibitors of the chicken soluble epoxide hydrolase

In vertebrates, soluble epoxide hydrolase (sEH) hydrolyzes natural epoxy-fatty acids (EpFAs), which are chemical mediators modulating inflammation, pain, and angiogenesis. Chick embryos are used to study angiogenesis, particularly its role in cardiovascular biology and pathology. To find potent and bio-stable inhibitors of the chicken sEH (chxEH) a library of human sEH inhibitors was screened. Derivatives of 1(adamantan-1-yl)-3-(trans-4-phenoxycyclohexyl) urea were found to be very potent tight binding inhibitors (KI <150pM) of chxEH while being relatively stable in chicken liver microsomes, suggesting their usefulness to study the role of EpFAs in chickens.

Acute effects of prostaglandin E1 and E2 on vascular reactivity and blood flow in situ in the chick chorioallantoic membrane

The chick chorioallantoic membrane (CAM) subserves gas exchange in the developing embryo and shell-less culture affords a unique opportunity for direct observations over time of individual blood vessels to pharmacologic interventions. We tested a number of lipids including prostaglandins PGE(1&2) for vascular effects and signaling in the CAM. Application of PGE(1&2) induced a decrease in the diameter of large blood vessels and a concentration-dependent, localized, reversible loss of blood flow through small vessels. The loss of flow was also mimicked by misoprostol, an agonist for 3 of 4 known PGE receptors, EP(2-4), and by U46619, a thromboxane mimetic. Selective receptor antagonists for EP(3) and thromboxane each partially blocked the response. This is a first report of the effects of prostaglandins on vasoreactivity in the CAM. Our model allows the unique ability to examine simultaneous responses of large and small vessels in real time and in vivo.

An investigation of the chick chorioallantoic membrane as an alternative model to various biological tissues for permeation studies

OBJECTIVES

The chick chorioallantoic membrane (CAM) was explored as a biological membrane for use in the study of drug permeation with a Franz diffusion cell.

METHODS

The CAM was removed from fertilized chicken eggs of embryo age 9-18 days. The permeation profiles of nicotine through the fresh CAM were first obtained with a Franz diffusion cell. The permeation profiles of nicotine through frozen CAM, snake skin, pig skin, pig retina and pig buccal mucosa were also determined and compared with those of the fresh CAM.

KEY FINDINGS

The permeability coefficient of the CAM varied with its age. The CAM at embryo age 13 was the most robust, showing the lowest standard error in permeability. It was thus chosen for comparative studies with snake skin, pig skin, retina and buccal mucosa. The CAM was found to be most similar to the buccal mucosa in terms of permeation profile and permeability coefficient values. Frozen CAM was also found to have a higher permeability coefficient than fresh CAM. The enhanced permeability was attributed to freezing, which affected the integrity of the CAM structure.

CONCLUSIONS

From the findings, CAM shows potential as an alternative to the pig buccal mucosa as an in-vitro buccal model. The robustness of the CAM for drug permeation studies is affected by its age.

Nitric oxide influences red blood cell velocity independently of changes in the vascular tone

Nitric oxide (NO) plays a key role in regulation of vascular tone and blood flow. In the microcirculation blood flow is strongly dependent on red blood cells (RBC) deformability. In vitro NO increases RBC deformability. This study hypothesized that NO increases RBC velocity in vivo not only by regulating vascular tone, but also by modifying RBC deformability. The effects of NO on RBC velocity were analysed by intra-vital microscopy in the microcirculation of the chorioallantoic membrane (CAM) of the avian embryo at day 7 post-fertilization, when all vessels lack smooth muscle cells and vascular tone is not affected by NO. It was found that inhibition of enzymatic NO synthesis and NO scavenging decreased intracellular NO levels and avian RBC deformability in vitro. Injection of a NO synthase-inhibitor or a NO scavenger into the microcirculation of the CAM decreased capillary RBC velocity and deformation, while the diameter of the vessels remained constant. The results indicate that scavenging of NO and inhibition of NO synthesis decrease RBC velocity not only by regulating vascular tone but also by decreasing RBC deformability.

Cytochrome P450-derived eicosanoids: the neglected pathway in cancer

Endogenously produced lipid autacoids are locally acting small molecule mediators that play a central role in the regulation of inflammation and tissue homeostasis. A well-studied group of autacoids are the products of arachidonic acid metabolism, among which the prostaglandins and leukotrienes are the best known. They are generated by two pathways controlled by the enzyme systems cyclooxygenase and lipoxygenase, respectively. However, arachidonic acid is also substrate for a third enzymatic pathway, the cytochrome P450 (CYP) system. This third eicosanoid pathway consists of two main branches: ω-hydroxylases convert arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) and epoxygenases convert it to epoxyeicosatrienoic acids (EETs). This third CYP pathway was originally studied in conjunction with inflammatory and cardiovascular disease. Arachidonic acid and its metabolites have recently stimulated great interest in cancer biology; but, unlike prostaglandins and leukotrienes the link between cytochome P450 metabolites and cancer has received little attention. In this review, the emerging role in cancer of cytochrome P450 metabolites, notably 20-HETE and EETs, are discussed.

Role of JNK in network formation of human lung microvascular endothelial cells

The signaling mechanisms in vasculogenesis and/or angiogenesis remain poorly understood, limiting the ability to regulate growth of new blood vessels in vitro and in vivo. Cultured human lung microvascular endothelial cells align into tubular networks in the three-dimensional matrix, Matrigel. Overexpression of MAPK phosphatase-1 (MKP-1), an enzyme that inactivates the ERK, JNK, and p38 pathways, inhibited network formation of these cells. Adenoviral-mediated overexpression of recombinant MKP-3 (a dual specificity phosphatase that specifically inactivates the ERK pathway) and dominant negative or constitutively active MEK did not attenuate network formation in Matrigel compared with negative controls. This result suggested that the ERK pathway may not be essential for tube assembly, a conclusion which was supported by the action of specific MEK inhibitor PD 184352, which also did not alter network formation. Inhibition of the JNK pathway using SP-600125 or l-stereoisomer (l-JNKI-1) blocked network formation, whereas the p38 MAPK blocker SB-203580 slightly enhanced it. Inhibition of JNK also attenuated the number of small vessel branches in the developing chick chorioallantoic membrane. Our results demonstrate a specific role for the JNK pathway in network formation of human lung endothelial cells in vitro while confirming that it is essential for the formation of new vessels in vivo.

Emerging mechanisms for growth and protection of the vasculature by cytochrome P450-derived products of arachidonic acid and other eicosanoids

Arachidonic acid (AA) is an essential fatty acid that is metabolized by cyclooxygenase (COX), lipoxygenase (LOX) or cytochrome P450 (CYP) enzymes to generate eicosanoids which in turn mediate a number of biological activities including regulation of angiogenesis. While much information on the effects of COX and LOX products is known, the physiological relevance of the CYP-derived products of AA are less well understood. CYP enzymes are highly expressed in the liver and kidney, but have also been detected at lower levels in the brain, heart and vasculature. A number of these enzymes, including members of the CYP 4 family, predominantly catalyze conversion of AA to 20-hydroxyeicosatetraenoic acid (20-HETE) while the CYP epoxygenases generate mainly epoxyeicosatrienoic acids (EETs). This review will focus on the emerging roles of inhibitors of eicosanoid production with emphasis on the CYP pathways, in the regulation of angiogenesis and tumor growth. We also discuss current observations describing the protective effects of EETs for survival of the endothelium.