Determination of heparin on intraocular lens surfaces by ion chromatography

A polyadenosine-coralyne complex as a novel fluorescent probe for the sensitive and selective detection of heparin in plasma

This study presents the development of a simple, label-free, sensitive, and selective detection system for heparin based on the use of a complex of 20-repeat adenosine (A20) and coralyne. Coralyne emits relatively weak fluorescence in an aqueous solution. In the presence of A20, coralyne molecules complexed with A20 through A2-coralyne-A2 coordination. An increase in the fluorescence of coralyne was observed because coralyne remained separate from water in the hydrophobic environment of the folded A20. The presence of heparin and the formation of the coralyne-heparin complex caused coralyne to be removed from the A20-corlayne complex. Because heparin promoted coralyne dimerization, the fluorescence of coralyne decreased as a function of the concentration of added heparin. This detection method is effective because the electrostatic attraction between heparin and coralyne is substantially stronger than the coordination between A20 and coralyne in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer at pH 7.0. Under optimal conditions (5 μM coralyne, 1 μM poly A20, and 10mM HEPES), this probe exhibited high selectivity (>90-fold) toward heparin over hyaluronic acid and chondroitin sulfate. The probe׳s detection limit for heparin was determined to be 4 nM (75 ng/mL) at a signal-to-noise ratio of 3. This study validates the practicality of using the A20-corlayne complex to determine the concentration of heparin in plasma.

Study on the surface properties of surface modified silicone intraocular lenses

AIM

To prepare a new-type soft intraocular lens (IOL) that silicone intraocular lenses (IOLs) were modified by surface modification technique to assess IOLs biocompatibility.

METHODS

With the technique of ion beam combined with low temperature and low pressure plasma, the surface characteristics of the IOLs including physical and optical properties were determined by the instruments of IOLs resolution, UV/VIS scanning spectrophotometer, contact angle measurement system, electron spectroscopy for chemical analysis (ESCA) and scanning electron microscope (SEM).

RESULTS

The color of titanium (Ti) modified IOLs was light yellow and that of titanium nitride (TiN) modified IOLs was light brown. The absorptive degree of ultraviolet rays and the hydrophilicity of the surfaces of modified IOLs were increased, and appeared suitable chemical compositions. The resolution of unmodified and modified IOLs reached normal standard. The surfaces of unmodified and Ti-modified IOLs appeared uniform. The surfaces of TiN-modified IOLs presented fine porcelain structure.

CONCLUSION

The optical properties of all IOLs and the surface morphology of the modified IOLs were not affected by modification processes. The surface properties of the modified IOLs were improved.

Hyphenated techniques for the analysis of heparin and heparan sulfate

The elucidation of the structure of glycosaminoglycan has proven to be challenging for analytical chemists. Molecules of glycosaminoglycan have a high negative charge and are polydisperse and microheterogeneous, thus requiring the application of multiple analytical techniques and methods. Heparin and heparan sulfate are the most structurally complex of the glycosaminoglycans and are widely distributed in nature. They play critical roles in physiological and pathophysiological processes through their interaction with heparin-binding proteins. Moreover, heparin and low-molecular weight heparin are currently used as pharmaceutical drugs to control blood coagulation. In 2008, the health crisis resulting from the contamination of pharmaceutical heparin led to considerable attention regarding their analysis and structural characterization. Modern analytical techniques, including high-performance liquid chromatography, capillary electrophoresis, mass spectrometry, and nuclear magnetic resonance spectroscopy, played critical roles in this effort. A successful combination of separation and spectral techniques will clearly provide a critical advantage in the future analysis of heparin and heparan sulfate. This review focuses on recent efforts to develop hyphenated techniques for the analysis of heparin and heparan sulfate.

Heparin-immobilized microspheres for the capture of cytokines

The preparation and characterization of heparin-immobilized microspheres which were used to bind acidic fibroblast growth factor (aFGF), vascular endothelial growth factor (VEGF), monocyte chemoattractant protein 1 (MCP-1/CCL2), and regulation upon activation normal T cell express sequence (RANTES/CCL5) is described. These beads were used as trapping agents in microdialysis sampling experiments in a separate study. Both free heparin and a synthesized heparin-albumin conjugate were immobilized onto microspheres and compared for their effectiveness. The heparin-albumin conjugate microspheres exhibited significant nonspecific adsorption which appeared to be due to the albumin content. The prepared heparin-immobilized microspheres were stable for 3 months at 4 °C. A bead-based flow cytometric assay was developed to study the binding capacity and specificity of the heparin-immobilized microspheres to cytokines. These heparin-immobilized microspheres exhibited broad dynamic ranges for binding to the four cytokines (aFGF, 1.0-1,000 ng/mL; VEGF, 0.5-1,000 ng/mL; CCL2, 1.95-1,000 ng/mL; CCL5, 1.95-500 ng/mL). Fast binding kinetics of the cytokines to the heparin-immobilized beads suggests that these beads may be useful as affinity agents in microfluidic flow systems.

Affinity-based microdialysis sampling using heparin for in vitro collection of human cytokines

Microdialysis sampling is a widely used method to sample from complex biological matrices. Cytokines are important signaling proteins that are typically recovered with low relative recovery values during microdialysis sampling. Heparin was included in the microdialysis perfusion fluid as an affinity agent to increase in vitro recovery of different cytokines through polyethersulfone (PES) microdialysis membranes with 100 kDa molecular weight cutoff. No change in fluid volumes collected from the microdialysis probes occurred when heparin was included in the perfusion fluid up to concentrations of 10 microM. The loss of heparin (10 microM) across the dialysis membrane was minimal (2.7+/-0.9%, n=3). Additionally, heparin at these concentrations did not interfere with the cytokine immunoassays. The control and heparin-enhanced relative recoveries for five human cytokines using 0.1 microM heparin in the microdialysis perfusion fluid flowing at 0.5 microL min(-1) were (n=3): interleukin-4 (IL-4), 4.2+/-0.5% and 7.2+/-3.1%; interleukin-6 (IL-6), 1.4+/-0.8% and 3.6+/-1.3%; interleukin-7 (IL-7), 1.3+/-0.8% and 4.8+/-1.8%; monocyte chemoattractant protein-1 (MCP-1), 9.0+/-1.6% and 19.5+/-2.7%; and tumor necrosis factor-alpha (TNF-alpha), 7.4+/-1.3% and 16.9+/-1.6%, respectively. Heparin increased the microdialysis sampling relative recovery of several human cytokines in vitro.

Direct detection of the binding of avidin and lactoferrin fluorescent probes to heparinized surfaces

We describe the use of two heparin-binding proteins, avidin and lactoferrin, as probes for monitoring the amount of heparin immobilized to plastic surfaces. The proteins were derivatized with either fluorescent labels or europium chelates, enabling sensitive, fast, reproducible, and robust assays, and were used to measure the amount of protein bound to heparinized microplates, with particular attention to plates that have been coated with bovine serum albumin (BSA)-heparin conjugate. This direct method unequivocally shows that BSA-heparin affords an economical, convenient, and reliable method for coating both polystyrene microtiter plates and magnetic beads with heparin. We demonstrate that assays using directly labeled proteins overcome the problems of dissociation of the heparin-protein complex, which can occur during incubation and washing steps associated with antibody-based detection methods, and the loss in binding capacity caused by certain blocking regimes. We suggest that labeled avidin and lactoferrin are convenient probes for heparinized surfaces with the potential for much wider applicability than that presented here.

Development of a simple analytical methodology for determination of glucosamine release from modified release matrix tablets

A simple spectrophotometric method for determination of glucosamine release from sustained release (SR) hydrophilic matrix tablet based on reaction with ninhydrin is developed, optimized and validated. The purple color (Ruhemann purple) resulted from the reaction was stabilized and measured at 570 nm. The method optimization was essential as many procedural parameters influenced the accuracy of determination including the ninhydrin concentration, reaction time, pH, reaction temperature, purple color stability period, and glucosamine/ninhydrin ratio. Glucosamine tablets (600 mg) with different hydrophilic polymers were formulated and manufactured on a rotary press. Dissolution studies were conducted (USP 26) using deionized water at 37+/-0.2 degrees C with paddle rotation of 50 rpm, and samples were removed manually at appropriate time intervals. Under given optimized reaction conditions that appeared to be critical, glucosamine was quantitatively analyzed and the calibration curve in the range of 0.202-2.020 mg (r=0.9999) was constructed. The recovery rate of the developed method was 97.8-101.7% (n=6). Reproducible dissolution profiles were achieved from the dissolution studies performed on different glucosamine tablets. The developed method is easy to use, accurate and highly cost-effective for routine studies relative to HPLC and other techniques.

Evaluation of the physicochemical stability and skin permeation of glucosamine sulfate

Glucosamine sulfate (GS) is known to stop the degenerative process of osteoarthritis. Because most of the GS formulation on the market is in the oral form, an alternative formulation such as a transdermal delivery system (TDS) is necessary in order to increase patient compliance. As the initial step to develop a TDS of GS, the physicochemical stability and permeation study in rat skin were examined. Evaluation of the stability of GS at different pHs showed the compound to be most stable at pH 5.0. The degradation rate constant at 25 degrees C was estimated to be 5.93 x 10(-6) hr(-1) (t90 approximately 2.03 years) in a pH 5 buffer solution. Due to its hydrophilic characteristic, low skin permeability was expected of GS. However, the skin permeation rate was determined to be 13.27 microg/cm2/hr at 5% concentration. Results of this study suggest the possibility of developing GS into a transdermal delivery system.

Determination of glycosaminoglycan monosaccharides by capillary electrophoresis using laser-induced fluorescence detection

A newly developed capillary electrophoretic method using laser-induced fluorescence detection (CE-LIF) for the analysis of monosaccharides released from acid hydrolysis of glycosaminoglycans was studied. The method was compared with a previously published method using indirect LIF detection (CE-ILIF). For the CE-LIF method, electrophoretic conditions for the separation of the monosaccharides derivatised with 8-aminopyrene-1,3,6-trisulfonate (APTS) were optimised. The best separations were obtained using 100 mM acetate at pH 4.5 as running buffer. The influence of the injection vial volume on the precision and stability of the sample in different conditions was studied. The detection limits of the CE-LIF method were found to be 0.4-0.6 nM, while those obtained by CE-ILIF ranged from 11.4 to 14.3 microM. Other quality parameters of the method, such as run-to-run precision, day-to-day precision, and linearity were also determined. Finally, the new method was applied to the analysis of the acid hydrolysis products from a glucosaminoglycan (heparin) and a galactosaminoglycan (dermatan sulfate) and cross-contamination between the two solutions was determined. The high sensitivity of the new method allows the determination of dermatan sulfate contaminations in a heparin raw sample down to 0.04% (w/w) and broadens the practical applicability of CE-LIF for the quantitation of the endogenous levels of glycosaminoglycans in animal samples and for pharmacokinetic control after therapeutical heparin administration.