Permselectivity of angiogenic microvessels following alteration of the endothelial fiber matrix by oligosaccharides

Accessing and Assessing the Cell-Surface Glycocalyx Using DNA Origami

The cell-surface glycocalyx serves as a physiological barrier regulating cellular accessibility to macromolecules and other cells. Conventional glycocalyx characterization has largely been morphological rather than functional. Here, we demonstrated direct glycocalyx anchoring of DNA origami nanotiles and performed a comprehensive comparison with traditional origami targeting to the phospholipid bilayer (PLB) using cholesterol. While DNA nanotiles effectively accessed single-stranded DNA initiators anchored on the glycocalyx, their accessibility to the underlying PLB was only permitted by extended nanotile-to-initiator spacing or by enzymatic glycocalyx degradation using trypsin or pathogenic neuraminidase. Thus, the DNA nanotiles, being expelled by the physiologic glycocalyx, provide an effective functional measure of the glycocalyx barrier integrity and faithfully predict cell-to-cell accessibility during DNA-guided multicellular assembly. Lastly, the glycocalyx-anchoring mechanism enabled enhanced cell-surface stability and cellular uptake of nanotiles compared to PLB anchoring. This research lays the foundation for future development of DNA nanodevices to access the cell surface.

Hydroxyethyl starches in equine medicine

OBJECTIVE

To review and discuss the use of hydroxyethyl starches (HES) in equine veterinary medicine, and to provide recommendations for its use.

DATA SOURCES

Veterinary and human peer-reviewed medical literature including scientific reviews, meta-analyses, and original research articles.

HUMAN DATA SYNTHESIS

Increasing evidences on adverse effects after HES use and decreasing support for beneficial effects with regards to volume expansion and colloid osmotic pressure (COP) support in critically ill subjects have led to a recent guideline to limit the use of HES in critically ill people.

EQUINE VETERINARY DATA SYNTHESIS

The rationale for HES use in horses is mainly extrapolated from human medicine, and very limited studies in horses are available. There is limited evidence suggesting a superiority of volume expansion effects of HES over crystalloids. The potential for HES to increase and maintain COP is well supported, but there is no evidence that maintaining or increasing plasma COP influences outcome, tissue edema formation, or rates of complications that potentially relate to edema formation. HES induce dose-dependent changes in coagulopathic parameters, but there is no evidence that HES causes clinical coagulopathies. Insufficient data are available on other adverse effects such as acute kidney injury, or mortality in horses. The use of HES should be restricted in septic patients, but may still have some use in cases of hemorrhagic shock resuscitation, hypoalbuminemia, or perioperative fluid replacement.

CONCLUSION

The evidence supporting the use of HES in horses is weak due to lack of species-specific investigations. Acknowledging species differences, the use of HES should be judicious, yet with some recognition of its benefits in particular cases. More research is necessary to improve knowledge on use of HES in horses and to establish better future recommendations.

Endothelial Glycocalyx as a Shield Against Diabetic Vascular Complications: Involvement of Hyaluronan and Hyaluronidases

The endothelial glycocalyx (EG), which covers the apical surface of the endothelial cells and floats into the lumen of the vessels, is a key player in vascular integrity and cardiovascular homeostasis. The EG is composed of PGs (proteoglycans), glycoproteins, glycolipids, and glycosaminoglycans, in particular hyaluronan (HA). HA seems to be implicated in most of the functions described for EG such as creating a space between blood and the endothelium, controlling vessel permeability, restricting leukocyte and platelet adhesion, and allowing an appropriate endothelial response to flow variation through mechanosensing. The amount of HA in the EG may be regulated by HYAL (hyaluronidase) 1, the most active somatic hyaluronidase. HYAL1 seems enriched in endothelial cells through endocytosis from the bloodstream. The role of the other main somatic hyaluronidase, HYAL2, in the EG is uncertain. Damage to the EG, accompanied by shedding of one or more of its components, is an early sign of various pathologies including diabetes mellitus. Shedding increases the blood or plasma concentration of several EG components, such as HA, heparan sulfate, and syndecan. The plasma levels of these molecules can then be used as sensitive markers of EG degradation. This has been shown in type 1 and type 2 diabetic patients. Recent experimental studies suggest that preserving the size and amount of EG HA in the face of diabetic insults could be a useful novel therapeutic strategy to slow diabetic complications. One way to achieve this goal, as suggested by a murine model of HYAL1 deficiency, may be to inhibit the function of HYAL1. The same approach may succeed in other pathological situations involving endothelial dysfunction and EG damage.

Controversies in the use of hydroxyethyl starch solutions in small animal emergency and critical care

OBJECTIVES

To (1) review the development and medical applications of hydroxyethyl starch (HES) solutions with particular emphasis on its physiochemical properties; (2) critically appraise the available evidence in human and veterinary medicine, and (3) evaluate the potential risks and benefits associated with their use in critically ill small animals.

DATA SOURCES

Human and veterinary original research articles, scientific reviews, and textbook sources from 1950 to the present.

HUMAN DATA SYNTHESIS

HES solutions have been used extensively in people for over 30 years and ever since its introduction there has been a great deal of debate over its safety and efficacy. Recently, results of seminal trials and meta-analyses showing increased risks related to kidney dysfunction and mortality in septic and critically ill patients, have led to the restriction of HES use in these patient populations by European regulatory authorities. Although the initial ban on the use of HES in Europe has been eased, proof regarding the benefits and safety profile of HES in trauma and surgical patient populations has been requested by these same European regulatory authorities.

VETERINARY DATA SYNTHESIS

The veterinary literature is limited mostly to experimental studies and clinical investigations with small populations of patients with short-term end points and there is insufficient evidence to generate recommendations.

CONCLUSIONS

Currently, there are no consensus recommendations regarding the use of HES in veterinary medicine. Veterinarians and institutions affected by the HES restrictions have had to critically reassess the risks and benefits related to HES usage based on the available information and sometimes adapt their procedures and policies based on their reassessment. Meanwhile, large, prospective, randomized veterinary studies evaluating HES use are needed to achieve relevant levels of evidence to enable formulation of specific veterinary guidelines.

Restrictive endothelial barrier function during normal angiogenesis in vivo: partial dependence on tyrosine dephosphorylation of beta-catenin

Differentiation of a restrictive endothelial barrier in the chick chorioallantoic membrane (CAM) occurs between Day 4.5 and Day 5.0 of the normal 21-day gestation. Whether molecular changes in the endothelial cell-cell junctional protein complex contribute to the ontogeny of barrier function represents the principal focus of this study. VE-cadherin has been shown to contribute to the regulation of endothelial cell monolayer permeability in vitro. Accordingly, VE-cadherin is complexed to the cytosolic catenins, and changes in monolayer permeability have been linked to alterations of the cadherin/catenin complex. Currently, a CAM endothelial VE-cadherin/beta-catenin complex was identified, and phosphotyrosine labeling of beta-catenin was decreased concurrently with the abrupt increase in CAM endothelial selectivity between Day 4.5 and Day 5.0. Further, inhibition of protein tyrosine phosphatases impeded regular tyrosine dephosphorylation of beta-catenin at Day 5.0 and this served to partially restore macromolecular extravasation to elevated levels normally present at Day 4.5. Thus, differentiation of selective barrier function in the angiogenic CAM endothelium in vivo is dependent, in part, on tyrosine dephosphorylation of beta-catenin.

Increased expression of VE-cadherin correlates temporally with differentiation of a restrictive endothelial barrier during normal angiogenesis in vivo

The purpose of this study was to evaluate temporal expression of VE- and N-cadherins within the angiogenic chick chorioallantoic membrane (CAM). Whether their relative patterns of expression changed in conjunction with abrupt differentiation of the restrictive CAM endothelial barrier between days 4.5 and 5.0 of the 21 days gestation was evaluated. Immunoblots against VE-cadherin depicted an increase of VE-cadherin expression between days 4.5 and 5.0, but no change in expression was detected between days 5.0 and 6.0. N-cadherin expression, on the other hand, remained uniform from day 4.5 to day 6.0. Immunogold-labeled anti-VE-cadherin was found exclusively on the CAM endothelium, and principally along the lateral inter-endothelial junctions. Hence, VE-cadherin expression by the angiogenic endothelium was similar to that of adult endothelium. That VE-cadherin expression by the CAM endothelium was increased between days 4.5 and 5.0 serves to suggest a temporal correlation with the ontogeny of restrictive barrier function in angiogenic endothelium in vivo.

Modulation of angiogenic endothelial permselectivity by the cAMP pathway

The chorioallantoic membrane (CAM) of the chick embryo provides an accessible model of normal angiogenesis in vivo. Previously, we reported a rapid reduction in CAM microvascular permeability to macromolecules between Days 4.5 and 5.0 of the normal 21-day gestation (V. Rizzo et al., 1995, Microvasc. Res. 49, 49-63). Here, we tested the hypothesis that activation of the cAMP signaling pathway at Day 4.5 would acutely increase permselectivity prior to normal differentiation of CAM endothelial barrier properties at Day 5.0. Changes in interstitial optical intensities due to extravasation of a graded series of FITC-dextrans (20, 40, and 70 kDa) were evaluated by computer-assisted image analysis, and endothelial ultrastructure was monitored by transmission electron microscopy. The cAMP analogue 8-bromo-cAMP (10(-4) and 10(-3) M) and forskolin (10(-5) and 10(-4) M), an adenylyl cyclase activator, acutely decreased permeability of the graded FITC-dextran series in a dose-dependent fashion. In addition, the nonspecific phosphodiesterase inhibitor IBMX (10(-4) M) served to increase basal restriction of the 20- and 40-kDa tracers. Further, Rp-cAMPS (10(-4) M), a cAMP antagonist for cAMP-dependent protein kinase, abolished the effects of both 8-bromo-cAMP (10(-3) M) and forskolin (10(-4) M) on FITC-Dextran 40 restriction. In all cases, ultrastructural presentation of both the endothelial cell junctions and the vesicles remained unchanged. The present results are consistent with the concept that exogenous cAMP activation decreased permeability of the angiogenic CAM endothelium at Day 4.5 without concomitant ultrastructural changes in the transendothelial macromolecular exchange pathways. Whether endogenous activity of cAMP contributes to normal differentiation of CAM endothelial barrier properties between Days 4.5 and 5.0 remains to be tested.