Preparation and high-performance size-exclusion chromatographic (HPSEC) analysis of fluorescein isothiocyanate-hydroxyethyl starch: macromolecular probes of the blood-lymph barrier

Hydroxyethyl starch as an effective methotrexate carrier in anticancer therapy

At present, effective anticancer therapy remains one of the most challenging tasks facing the scientific community. A major limitation to most conventional low-molecular weight anticancer chemotherapeutics is their unfavourable uptake by healthy tissue, fast metabolism and lack of tumour cell selectivity. One way to solve this problem is the application of hybrid nanoparticles containing widely known therapeutic substances. This study was performed with the aim of investigating the potential of use hydroxyethyl starch (HES) as a high-molecular weight carrier for anticancer drug (methotrexate, MTX). HES-MTX conjugates were characterized in terms of MTX content, hydrodynamic size, zeta potential, and drug release kinetics. In vitro biological characteristics were determined using different cancer cell lines. The antitumor effect in vivo was tested in NOD/SCID mice subcutaneously inoculated with MV-4-11 human leukaemia cells and CDF1 mice intraperitoneally inoculated with P388 murine leukaemia cells. The in vivo experiments revealed the considerably higher antitumor efficacy of HES-MTX conjugates in comparison to unconjugated drug. The results presented in this article demonstrate that the application of HES as an anticancer drug carrier can improve the treatment efficacy and have significant implications for the future design and implementation of drug-carrier conjugates. The study should help create new opportunities in the design of HES-based innovative drug-carrier conjugates.

Hydroxyethyl Starch: The Effect of Molecular Weight and Degree of Substitution on Intravascular Retention In Vivo

BACKGROUND

Hydroxyethyl starch (HES) solution is characterized by its mean molecular weight (MW), concentration, and degree of substitution (DS). This character varies worldwide.

METHODS

After binding fluorescein-isothiocyanate (FITC-HES), we evaluated the retention rate of three types of 6% HES in the A2 and V2 blood vessels of rat cremaster muscles using intravital microscopy in a mild hemorrhage model (10% of total blood volume). After blood withdrawal, we infused three types of FITC-HES: HES-A (MW 150-200 kDa, DS 0.6-0.68), HES-B (MW 175-225 kDa, DS 0.45-0.55), or HES-C (MW 550-850 kDa, DS 0.7-0.8) before determining the FITC-HES retention rate in the intravital microscope.

RESULTS

For V2, the FITC-HES retention rates 120 min after the start of the infusion were 27% +/- 7.2% of baseline values (HES-A), 65% +/- 9.1% (HES-B), and 86% +/- 9.6% (HES-C); for A2 they were 27% +/- 6.6%, 73% +/- 10.2%, and 89% +/- 8.7%, respectively. HES-B and HES-C were retained in the vessels longer than HES-A (P = 0.028 for V2, P = 0.038 for A2 between HES-B and HES-A; P = 0.022 for V2, P = 0.037 for A2 between HES-C and HES-A). There was no difference in the rate of disappearance from the vessels between HES-B and HES-C.

CONCLUSIONS

HES-B and HES-C are equally retained in the blood vessels. Middle-sized HES-B with low DS and middle substitution pattern stayed in the blood vessels as long as the large-sized HES. HES solutions of varying characters should be examined to optimize HES infusion.

Endothelial contraction and monolayer hyperpermeability are regulated by Src kinase

Endothelial monolayer hyperpermeability is regulated by a myosin light chain phosphorylation (MLCP)-dependent contractile mechanism. In this study, we tested the role of Src-dependent tyrosine phosphorylation to modulate endothelial contraction and monolayer barrier function with the use of the myosin phosphatase inhibitor calyculin A (CalA) to directly elevate MLCP with the Src family tyrosine kinase inhibitor herbimycin A (HA) in bovine pulmonary artery endothelial cells (EC). CalA stimulated an increase in MLCP, Src kinase activity, an increase in the tyrosine phosphorylation of paxillin and focal adhesion (FA) kinase (p125(FAK)), and monolayer hyperpermeability. Microscopic examination of CalA-treated EC revealed a contractile morphology characterized by peripheral contractile bands of actomyosin filaments and stress fibers linked to phosphotyrosine-containing FAs. These CalA-dependent events were HA sensitive. HA alone stimulated an improvement in monolayer barrier formation by reducing the levels of MLCP and phosphotyrosine-containing proteins and the number of large paracellular holes. These data show that Src kinase plays an important role in regulating monolayer hyperpermeability through adjustments in tyrosine phosphorylation, MLCP, and EC contraction.

The rat glomerular filtration barrier does not show negative charge selectivity

OBJECTIVE

To characterize the effects of size, shape, and negative charge on the transport of macromolecules across the glomerular capillary wall by using the sieving curves (fractional clearance vs. solute molecular radii) of fluorescent polydispersed polysaccharide tracers.

METHODS

Glomerular fractional clearances (FC) were measured with fluorescent neutral [isoelectric point (pI) = 7.3 +/- 0.2] and negatively charged (pI = 3.5 +/- 0.4) dextrans (DEX) in comparison with negatively charged (pI = 4.8 +/- 0.3) hydroxy ethyl starch (HES) and (pI = 4.6 +/- 0.1) bovine serum albumin (BSA) in Sprague-Dawley and Fischer 344/Brown Norway rats. FCs (n = 53) were measured by using the urinary clearance of (14)C-inulin to determine the glomerular filtration rate. The relative uptake of each fluorescent probe by endothelial and renal proximal tubule epithelial (LLC-PK(1)) cells, in vitro, was measured microscopically by using a cooled (-25 degrees C) CCD camera.

RESULTS

The sieving curves for randomly coiled neutral and negatively charged DEX probes were identical. These FC values were 6-fold greater than those for HES and 200-fold above similarly sized fluorescent BSA. The polysaccharide probes did not show significant binding to serum proteins. The uptake of BSA by LLC-PK(1) cells was 20- to 100-fold greater than that for neutral or negatively charged macromolecules.

CONCLUSIONS

These findings indicate that the rat glomerular filtration barrier restricts the transport of polysaccharide macromolecules as a function of their size and configuration but not negative charge.

ROCK mediates thrombin's endothelial barrier dysfunction

Thrombin-induced endothelial monolayer hyperpermeability is thought to result from increased F-actin stress fiber-related contractile tension, a process regulated by the small GTP-binding protein Rho. We tested whether this process was dependent on the Rho-associated protein kinase, ROCK, using a specific ROCK inhibitor, Y-27632. The effects of Y-27632 on thrombin-induced myosin light chain phosphorylation (MLCP) and tyrosine phosphorylation of p125 focal adhesion kinase (p125(FAK)) and paxillin were measured by Western blotting. F-actin organization and content were analyzed by digital imaging, and endothelial monolayer permeability was measured in bovine pulmonary artery endothelial cell (EC) monolayers using a size-selective permeability assay. Y-27632 enhanced EC monolayer barrier function due to a decline in small-pore number that was associated with increased EC surface area, reduced F-actin content, and reorganization of F-actin to beta-catenin-containing cell-cell adherens junctions. Although Y-27632 prevented thrombin-induced MLCP, stress fiber formation, and the increased phosphotyrosine content of paxillin and p125(FAK), it attenuated but did not prevent the thrombin-induced formation of large paracellular holes. These data indicate that thrombin-induced stress fiber formation is ROCK dependent. In contrast, thrombin-induced paracellular hole formation occurs in a ROCK-independent manner, whereas thrombin-induced monolayer hyperpermeability appears to be partially ROCK dependent.

Conjugation of hydroxyethyl starch to desferrioxamine (DFO) modulates the dual role of DFO in Yersinia enterocolitica infection

The iron chelator desferrioxamine (DFO) B is widely used in the therapy of patients with iron overload. As a side effect, DFO may favor the occurrence of fulminant Yersinia infections. Previous work from our laboratory showed that this might be due to a dual role of DFO: growth promotion of the pathogen and immunosuppression of the host. In this study, we sought to determine whether conjugation of DFO to hydroxyethyl starch (HES-DFO) may prevent exacerbation of Yersinia infection in mice. We found HES-DFO to promote neither growth of Yersinia enterocolitica nor mitogen-induced T-cell proliferation and gamma interferon production by T cells in vitro. Nevertheless, in vivo HES-DFO promoted growth of Y. enterocolitica possibly due to cleavage of HES and release of DFO. The pretreatment of mice with DFO resulted in death of all mice 2 to 5 days after application of a normally sublethal inoculum of Y. enterocolitica, while none of the mice pretreated with HES-DFO died within the first 7 days postinfection. However, some of the HES-DFO-treated mice died 8 to 14 days postinfection. Thus, due to the delayed in vivo effect HES-DFO failed to trigger Yersinia-induced septic shock, which accounts for early mortality in DFO-associated septicemia. Moreover, our data suggest that DFO needs to be taken up by host cells in order to exert its immunosuppressive action. These results strongly suggest that HES-DFO might be a favorable drug with fewer side effects than DFO in terms of DFO-promoted fulminant infections.

RhoA inactivation enhances endothelial barrier function

The modulation of endothelial barrier function is thought to be a function of contractile tension mediated by the cell cytoskeleton, which consists of actomyosin stress fibers (SF) linked to focal adhesions (FA). We tested this hypothesis by dissociating SF/FA with Clostridium botulinum exoenzyme C3 transferase (C3), an inhibitor of the small GTP-binding protein RhoA. Bovine pulmonary artery endothelial cell (EC) monolayers given C3, C3 + thrombin, thrombin, or no treatment were examined using a size-selective permeability assay and quantitative digital imaging measurements of SF/FA. C3 treatment disassembled SF/FA, stimulated diffuse myosin II immunostaining, and reduced the phosphotyrosine (PY) content of paxillin and 130- to 140-kDa proteins that included p125(FAK). C3-treated monolayers displayed a 60-85% decline in F-actin content and a 170-300% increase in EC surface area with enhanced endothelial barrier function. This activity correlated with reorganization of F-actin and PY protein(s) to beta-catenin-containing cell-cell junctions. Because C3 prevented the thrombin-induced formation of myosin ribbons, SF/FA, and the increased PY content of proteins, these characteristics were Rho dependent. Our data show that C3 inhibition of Rho proteins leads to cAMP-like characteristics of reduced SF/FA and enhanced endothelial barrier function.

VEGF stimulates tyrosine phosphorylation of beta-catenin and small-pore endothelial barrier dysfunction

The purpose of this study was to test the hypothesis that tyrosine phosphorylation signaling events and protein kinase C (PKC) activation mediate vascular endothelial growth factor-A(165) (VEGF)-induced endothelial cell (EC) proliferation and barrier dysfunction in bovine pulmonary artery EC monolayers. A size-selective permeability assay showed that VEGF stimulated a delayed, prolonged (6-45 h), concentration-dependent (50-200 ng/ml, approximately 1-4 nM) increase in the number of predominantly small-"pore" transport pathways (<60 A) across EC monolayers. The tyrosine kinase inhibitor herbimycin A (HA) and the selective PKC inhibitor bisindolylmaleimide (BIM) prevented this phenomenon. After 6-24 h, VEGF-treated monolayers displayed an HA- and BIM-sensitive reorganization of beta-catenin adherens junctions with fingerlike projections and the loss of beta-catenin at sites of small paracellular hole formation. HA and BIM prevented the VEGF-induced increase in EC growth. HA blocked the VEGF-induced rapid and prolonged (10 min-45 h) increases in the phosphotyrosine (PY) contents of VEGF receptor 2, phospholipase C-gamma1, paxillin, and beta-catenin as well as approximately 140- and 128- to 117-kDa proteins, whereas BIM inhibited only the tyrosine phosphorylation of beta-catenin. These data suggest that VEGF initiates increased EC growth and chronic, small-pore endothelial barrier dysfunction by PY signaling through beta-catenin that depends on PKC.

The glomerular barrier fits a two-pore-and-fiber-matrix model: derivation and physiologic test

Failure of the glomerular barrier causing proteinuria has been modeled chiefly by Chang, Deen, and Brenner. They have refined models from an isoporous filter to a mostly isoporous membrane, which during proteinuric disease opens up nondiscriminating shunts. This report extends these concepts by measuring a larger distribution of macromolecular tracer sizes and bringing in a fiber matrix. By clearance methods, glomerular sieving curves of relatively neutral tetramethyl rhodamine aminodextran from radii of 15 to over 80 A were obtained and fitted to theory. Two pores filled with matrix fit all data without exception, and no other model did. Five parameters described the curve in control rats and in proteinuric rats made so by albumin injections. From highest to lowest degree of confidence, these were small and large pore radii ros = 42.7 +/- 0.9 SEM A and rol = 926 +/- 156 A; small to large pore density ns/nl = 3859 +/- 942; mean fiber radius rf = 20.3 +/- 1. 1 A; and fiber void volume ratio epsilon = 0.52 +/- 0.05. In proteinuria, ros rose 13% (P = 0.002), nl increased 150% (P = 0.04), and there was a compensatory rise in rf of 26% (P = 0.002). The consideration of basement membrane and glycocalyx remain to be incorporated into the model. Moreover, the closeness of rf to ros indicates that fiber matrix theory may need modification for a complete description.

H2O2 and genistein differentially modulate protein tyrosine phosphorylation, endothelial morphology, and monolayer barrier function

The effects of hydrogen peroxide (H2O2) and the protein tyrosine kinase (PTK) inhibitor, genistein, to modulate protein tyrosine phosphorylation (PTP) and endothelial barrier function were examined in bovine pulmonary artery endothelial cell (EC) monolayers. H2O2 stimulated a concentration (100-800 microM) and time-dependent increase in the phosphotyrosine (PY) content of multiple (56-72, 93-97, 113-142, and 161-183 kDa) EC proteins. A size-selected solute permeability assay of EC monolayer barrier function showed that (200 microM) H2O2 elevated EC monolayer permeability to large solutes. This effect was associated with paracellular hole formation and a loss of beta-catenin immunostaining at these sites. In contrast, genistein (100 microM, 1 h) reduced basal PY protein content and reorganized F-actin to beta-catenin containing cell-cell junctions, enhancing endothelial monolayer barrier function. In addition, genistein prevented the H2O2-induced increases in tyrosine phosphorylation, monolayer permeability, and paracellular hole formation. These data suggest that H2O2 and genistein differentially regulate PTP, endothelial morphology, and monolayer barrier function.

Human monocytes and keratinocytes in culture ingest hydroxyethylstarch

Severe itching for unknown reasons has been reported after administration of hydroxyethylstarch (HES) in haemodilution therapy of humans. In skin sections from patients who had received HES for otological reasons HES deposition was found by immunohistochemical methods in keratinocytes, epidermal dendritic cells, endothelial cells and macrophages. The aim of the present investigation was to study the interaction of cultured human monocytes and keratinocytes, normal (HNK) and malignant (KB, A431), with FITC-conjugated HES (200/0.5). Peripheral blood monocytes from healthy donors were isolated by Ficoll-Hypaque gradient centrifugation and adherence to plastic surfaces. Cells were incubated with HES-FITC (1 mg/ml) for 10, 20, 30, 60 and 120 min at 37 degrees C, washed several times to minimize cell-associated HES-FITC. The uptake of HES-FITC (200/0.5) was detected by fluorescence microscopy and flow cytometry. Monocytes and keratinocytes (HNK, KB, A431) acquired significant amounts of HES-FITC after 120 min. Endocytosis was blunted by the addition of unconjugated HES in ten-fold concentration. At 4 degrees C, a further inhibition was achieved, indicating an uptake of HES-FITC by monocytes and keratinocytes in vitro. These results indicate that a connection between the storage of HES by keratinocytes and monocytes and the observed itching in patients might be possible.

Convection of macromolecules is the dominant mode of transport across horizontal 0.4- and 3-microns filters in diffusion chambers: significance for biologic monolayer permeability assessment

The purpose of the present study was to evaluate the permeability characteristics of fluorescein-labeled hydroxyethyl starch (FITC-HES, 20 less than molecular radius, aE less than 111 A) across large pore (0.4- and 3-microns polycarbonate) filters used in endothelial cell monolayer diffusion studies. Although the apparent permeability (P) of the FITC-HES macromolecules across these filters declined as the molecular radius increased, this decline was less than that associated with each solute's free diffusion (D0). Thus, the P/D0 anomalously increased as aE increased, a pattern not seen for free diffusion (flat P/D0 with increased aE) or restricted diffusion (decline in P/D0 with increased aE). Substantial natural convection across the porous filters produced the anomalous P/D0 curve for the following reasons: (1) this effect was elevated with positive pressure and ameliorated by zero driving pressure, and (2) the effect was much greater across filters with large (3 microns) vs small (0.4 microns) pore sizes. In addition, we estimated that less than half of macromolecular transport above 50 A probe radius at zero transmural pressure arrives by diffusion. The findings suggest that the property of restricted diffusion of biologic layers on these filters will be artifactually exaggerated when the measured resistance of the filter is subtracted from that of the filter plus biologic monolayer. Remedies for this problem may include using smaller pore filters, filters layered with extracellular material, or structural methods to determine true filter permeability.

Heterogeneity of Echis venoms from different sources

The heterogeneity of separate Echis carinatus and Echis coloratus venom lots were evaluated by high performance size-exclusion chromatography, as well as by clotting and esterolytic activities. Each lot of E. carinatus and E. coloratus venoms appeared to be unique. The variation in E. carinatus venom activities from snakes within the same species could lead to contradictory biochemical and/or physiological test results.