Extravascular transport of fluorescently labeled albumins in the rat mesentery

Microperfusion Technique to Investigate Regulation of Microvessel Permeability in Rat Mesentery

Experiments to measure the permeability properties of individually perfused microvessels provide a bridge between investigation of molecular and cellular mechanisms regulating vascular permeability in cultured endothelial cell monolayers and the functional exchange properties of whole microvascular beds. A method to cannulate and perfuse venular microvessels of rat mesentery and measure the hydraulic conductivity of the microvessel wall is described. The main equipment needed includes an intravital microscope with a large modified stage that supports micromanipulators to position three different microtools: (1) a beveled glass micropipette to cannulate and perfuse the microvessel; (2) a glass micro-occluder to transiently block perfusion and enable measurement of transvascular water flow movement at a measured hydrostatic pressure, and (3) a blunt glass rod to stabilize the mesenteric tissue at the site of cannulation. The modified Landis micro-occlusion technique uses red cells suspended in the artificial perfusate as markers of transvascular fluid movement, and also enables repeated measurements of these flows as experimental conditions are changed and hydrostatic and colloid osmotic pressure difference across the microvessels are carefully controlled. Measurements of hydraulic conductivity first using a control perfusate, then after re-cannulation of the same microvessel with the test perfusates enable paired comparisons of the microvessel response under these well-controlled conditions. Attempts to extend the method to microvessels in the mesentery of mice with genetic modifications expected to modify vascular permeability were severely limited because of the absence of long straight and unbranched microvessels in the mouse mesentery, but the recent availability of the rats with similar genetic modifications using the CRISPR/Cas9 technology is expected to open new areas of investigation where the methods described herein can be applied.

Ubiquinol decreases hemorrhagic shock/resuscitation-induced microvascular inflammation in rat mesenteric microcirculation

Hemorrhagic shock (HS) is a leading cause of death in traumatic injury. Ischemia and hypoxia in HS and fluid resuscitation (FR) creates a condition that facilitates excessive generation of reactive oxygen species (ROS). This is a major factor causing increased leukocyte-endothelial cell adhesive interactions and inflammation in the microcirculation resulting in reperfusion tissue injury. The aim of this study was to determine if ubiquinol (coenzyme Q10) decreases microvascular inflammation following HS and FR. Intravital microscopy was used to measure leukocyte-endothelial cell adhesive interactions in the rat mesentery following 1-h of HS and 2-h post FR with or without ubiquinol. Hemorrhagic shock was induced by removing ~ 40% of anesthetized Sprague Dawley rats' blood volume to maintain a mean arterial blood pressure <50 mmHg for 1 h. Ubiquinol (1 mg/100 g body weight) was infused intravascularly in the ubiquinol group immediately after 1-h HS. The FR protocol included replacement of the shed blood and Lactate Ringer's in both the control and ubiquinol groups. We found that leukocyte adherence (2.3 ± 2.0), mast cell degranulation (1.02 ± 0.01), and ROS levels (159 ± 35%) in the ubiquinol group were significantly reduced compared to the control group (10.8 ± 2.3, 1.36 ± 0.03, and 343 ± 47%, respectively). In addition, vascular permeability in the control group (0.54 ± 0.11) was significantly greater than the ubiquinol group (0.34 ± 0.04). In conclusion, ubiquinol attenuates HS and FR-induced microvascular inflammation. These results suggest that ubiquinol provides protection to mesenteric microcirculation through its antioxidant properties.

Vascular permeability modulation at the cell, microvessel, or whole organ level: towards closing gaps in our knowledge

Multiple processes modulate net blood-to-tissue exchange in a microvascular unit in normal and pathophysiological conditions. These include mechanisms that control the number and type of microvessels perfused, the balance of adhesion and contractile forces that determine the conductance of the spaces between endothelial cells to water and solutes, the pressure and chemical potential gradients determining the driving forces through these conductive pathways, and the organization of barriers to macromolecules in the endothelial glycocalyx. Powerful methods are available to investigate these mechanisms at the levels of cultured endothelial monolayers, isolated microvessels, and the microvascular units within intact organs. Here we focus on current problems that limit the integration of our knowledge of mechanisms investigated in detail at the cellular level into a more complete understanding of modulation of blood-to-tissue exchange in whole organs when the endothelial barrier is exposed to acute and more long-term inflammatory conditions. First, we review updated methods, applicable in mouse models of vascular permeability regulation, to investigate both acute and long-term changes in permeability. Methods to distinguish tracer accumulation due to change in perfusion from real increases in extravascular accumulation are emphasized. The second part of the review compares normal and increased permeability in individually perfused venular microvessels and endothelial cell monolayers. The heterogeneity of endothelial cell phenotypes in the baseline state and after exposure to injury and inflammatory conditions is emphasized. Lastly, we review new approaches to investigation of the glycocalyx barrier properties in cultured endothelial monolayers and in whole-body investigations.

Impact of fluorescent probes on albumin sorption profiles to ophthalmic biomaterials

Bovine serum albumin (BSA) was conjugated to three organic fluorescent probes, 5-(4,6-dichloro-s-triazin-2-ylamino)fluorescein hydrochloride (DTAF), Rhodamine B isothiocyanate (RITC), and Lucifer yellow VS (LY). The protein sorption profile to one pHEMA-based (etafilcon A) and three silicone hydrogel (SH) contact lens types (lotrafilcon B, balafilcon A and senofilcon A) was determined using confocal laser scanning microscopy. In addition, all lenses were incubated in dye solutions containing the fluorescent probe alone; and in a separate experiment BSA accumulation was quantified using radiolabeling. The different fluorescent conjugates showed similar sorption profiles for the pHEMA-based lens, but marked differences for all SH lenses. Lotrafilcon B accumulated more protein on the surface as compared to the matrix, independent of the fluorescent probe used for conjugation. Protein sorption varied for senofilcon A, with DTAF-BSA sorbing primarily to the surface region, while the other conjugates penetrated in equal amounts into the matrix. Balafilcon A exhibited smaller differences between conjugates, with LY-BSA allowing the protein to fully penetrate the matrix, while the other conjugates showed minor surface adsorption. Sorption curves of unbound dyes were often similar compared to the conjugated results. BSA profiles to pHEMA-based and silicone hydrogel lenses were highly dependent on the fluorescent probe used and none of the probes accurately reflected quantitative protein levels for the lens materials investigated.

Fluorescent derivatization of a protease antigen to track antigen uptake and processing in human cell lines

BACKGROUND

We have devised a simple and efficient fluorescence-based method to track antigen uptake and processing in human B lymphoblastoid cells (B-LCL). Fluorescein labelled subtilisin was used to optimize antigen uptake conditions and identify processed peptides from human cell lines.

RESULTS

Fluorescein labelled subtilisin conjugates had 0.06 to 2 moles of fluorescein per subtilisin molecule. High performance liquid chromatography and mass spectrometry (NanoESI-LC/MS/MS) analysis identified fluorescein conjugated to K141, K256, and the N terminus. Conjugates retained antigenic specificity to subtilisin specific antibodies and could be processed by whole cell extracts into low molecular weight fragments at pH 5.2. Maximal antigen uptake and processing occurred when PMSF (phenylmethylsulfonyl fluoride) inhibited subtilisin conjugate was incubated with cells at 100-200 microg/ml for 16 to 24 hr. Once optimal uptake conditions were established, processed subtilisin peptides were isolated and identified from human cell lines.

CONCLUSION

Our studies show that FITC-conjugation provides an efficient tool to track the uptake and processing of this protease antigen and to facilitate identification of processed antigenic peptides from human cell lines.