Adsorption of low density lipoproteins onto selected biomedical polymers

Early-Stage Protein Adsorption Sequence on Blood-Contacting Surfaces: Answer to Vroman's Question

Plasma protein adsorption on blood-contacting surfaces is the initiating significant event and modulates the subsequent coagulation response. Despite decades of research in this area, Vroman's questions in 1986 "Who gets there first?" and "When does the next protein arrive?" remain unanswered due to the lack of detection techniques with sufficient temporal resolution. In this work, we develop a droplet microfluidic technology to detect protein adsorption sequences on six typical blood-contacting surfaces in milliseconds. Apolipoproteins (Apo) are found to be the first proteins to adsorb onto the surfaces in a plasma droplet, and the specific type of apolipoprotein depends on the surface. Apo CI is the first protein adsorbed on gold, platinum, graphene, stainless steel, and polyvinyl chloride with the adsorption time varying from 0.01 to 1 s, while Apo CIII preferentially reaches the titanium alloy surface within 1 s. Subsequent to the initial adsorption, Apo AI, AII, and other proteins continue to adsorb until albumin arrives. Thus, the adsorption sequence is revealed, and Vroman's questions are answered. Moreover, this finding demonstrates the influence of the initial protein adsorption on subsequent coagulation at the surface, and it offers new insights into the development of anticoagulant surfaces.

Biomembrane-mimetic hemoperfusion adsorbent for efficient removal of low-density lipoprotein from hyperlipemia blood

Lowering of low-density lipoprotein (LDL) levels in blood of patients with hyperlipidaemia can effectively prevent the progression of atherosclerosis and coronary heart disease. The present study demonstrated a facile synthesis strategy to prepare biomembrane-mimetic LDL adsorbent (PVA@COOH-PE) via directional immobilization of phospholipid onto macro-porous cross-linked poly(vinyl alcohol) spheres. The binding between the prepared adsorbent and LDL particles simulates the cytosolic lipid droplets to form a lipid-packing structure. The adsorbent possesses satisfactory removal efficiency for LDL and total cholesterol (TCH) in hyperlipemia serum, while remains high-density lipoprotein (HDL) concentration within the normal range. The adsorption capacities for LDL and TCH are about 1.13 and 1.74 mg/ml respectively, which are nearly three and four times higher than that of HDL (0.42 mg/ml). The adsorbent also possesses satisfactory anticoagulant properties, causes negligible effect on blood cells and produces low hemolysis ratios. The excellent blood compatibility plus LDL removal efficiency of PVA@COOH-PE indicates its good application prospect as hemoperfusion adsorbent in the treatment of hyperlipidaemia.

Amphiphilic shell nanomagnetic adsorbents for selective and highly efficient capture of low-density lipoprotein from hyperlipidaemia serum

Removal of low-density lipoprotein (LDL) from hyperlipemia patients’ blood represents an effective approach to prevent the progression of atherosclerotic cardiovascular disease. Based on the LDL structural characteristics and intermolecular interactions,...

Bio-inspired dual-functional phospholipid-poly(acrylic acid) brushes grafted porous poly(vinyl alcohol) beads for selective adsorption of low-density lipoprotein

Elevated levels of low-density lipoproteins (LDL) are recognized as a crucial indicator of hyperlipidemia (HLP) and lowering of LDL levels represents an effective clinical treatment strategy. Inspired by the conjugation of phospholipid monolayers and the lipid content of the LDL particle, the current study describes the preparation of an innovative hemoperfusion adsorbent. The adsorbent was prepared by attachment of phosphatidyl ethanolamine to poly(acrylic acid) modified poly(vinyl alcohol-co-triallyl isocyanurate) beads (PVA@PAA-PE). The interaction between LDL and adsorbent mimics the lipoprotein microemulsion present in the blood and thus promotes efficient binding with high affinity. In vitro adsorption using serum from patients with HLP revealed that the LDL adsorption of PVA@PAA-PE was 4.44 times higher than that of controls and the removal rate of LDL using PVA@PAA-PE was about twice as high as that of the anti-atherogenic high-density lipoprotein (HDL). In vivo whole blood perfusion demonstrated the superior affinity of PVA@PAA-PE for LDL since LDL concentration was significantly reduced from 10.71 ± 2.36 mmol L^-1 to 6.21 ± 1.45 mmol L^-1, while the HDL level was not severely reduced (from 0.98 ± 0.12 mmol L^-1 to 0.56 ± 0.15 mmol L^-1). Additionally, PVA@PAA-PE exhibited excellent hemocompatibility and low cytotoxicity. Therefore, PVA@PAA-PE is a potential adsorbent for whole blood perfusion to treat hyperlipidemia.

Interactions of Apolipoproteins AI, AII, B and HDL, LDL, VLDL with Polyurethane and Polyurethane-PEO Surfaces

The lipoproteins (HDL, LDL, VLDL) are important components of blood present in high concentration. Surprisingly, their role in blood-biomaterial interactions has been largely ignored. In previous work apolipoprotein AI (the main protein component of HDL) was identified as a major constituent of protein layers adsorbed from plasma to biomaterials having a wide range of surface properties, and quantitative data on the adsorption of apo AI to a biomedical grade polyurethane were reported. In the present communication quantitative data on the adsorption of apo AI, apo AII and apoB (the latter being a constituent of LDL and VLDL), as well as the lipoprotein particles themselves (HDL, LDL, VLDL), to a biomedical segmented polyurethane (PU) with and without an additive containing poly(ethylene oxide) (material referred to as PEO) are reported. Using radiolabeled apo AI, apo AII, and apoB, adsorption levels on PU from buffer at a protein concentration of 50 μg/mL were found to be 0.34, 0.40, and 0.14 μg/cm(2) (12, 23, and 0.25 nmol/cm(2)) respectively. Adsorption to the PEO surface was <0.02 μg/cm(2) for all three apolipoproteins demonstrating the strong protein resistance of this material. In contrast to the apolipoproteins, significant amounts of the lipoproteins were found to adsorb to the PEO as well as to the PU surface. X-ray photoelectron spectra, following exposure of the surfaces to the lipoproteins, showed a strong phosphorus signal, confirming that adsorption had occurred. It therefore appears that a PEO-containing surface that is resistant to apolipoproteins may be less resistant to the corresponding lipoproteins.

Physicochemical and formulation developability assessment for therapeutic peptide delivery--a primer

Peptides are an important class of endogenous ligands that regulate key biological cascades. As such, peptides represent a promising therapeutic class with the potential to alleviate many severe disease states. Despite their therapeutic potential, peptides frequently pose drug delivery challenges to scientists. This review introduces the physicochemical, biophysical, biopharmaceutical, and formulation developability aspects of peptides pertinent to the drug discovery-to-development interface. It introduces the relevance of these properties with respect to the delivery modalities available for peptide pharmaceuticals, with the parenteral route being the most prevalent route of administration. This review also presents characterization strategies for oral delivery of peptides with the aim of illuminating developability issues with the drug candidate. A brief overview of other routes of administration, including inhaled, transdermal, and intranasal routes, is provided as these routes are generally preferred by patients over injectables. Finally, this review presents formulation techniques to mitigate some of the developability obstacles associated with peptide delivery. The authors emphasize opportunities for the thoughtful application of pharmaceutical science to the development of peptide drugs and to the general advancement of this promising class of pharmaceuticals.

Blood compatible aspects of poly(2-methoxyethylacrylate) (PMEA)--relationship between protein adsorption and platelet adhesion on PMEA surface

Platelet adhesion and spreading is suppressed when a poly(2-methoxyethylacrylate) (PMEA) surface is used, compared with other polymer surfaces. To clarify the reason for this suppression, the relationship among the amount of the plasma protein adsorbed onto PMEA, its secondary structure and platelet adhesion was investigated. Poly(2-hydroxyethylmethacrylate) (PHEMA) and polyacrylate analogous were used as references. The amount of protein adsorbed onto PMEA was very low and similar to that absorbed onto PHEMA. Circular dichroism (CD) spectroscopy was applied to examine changes in the secondary structure of the proteins after adsorption onto the polymer surface. The conformation of the proteins adsorbed onto PHEMA changed considerably, but that of proteins adsorbed onto PMEA differed only a little from the native one. These results suggest that low platelet adhesion and spreading are closely related to the low degree of the denaturation of the protein adsorbed onto PMEA. PMEA could be developed as a promising material to produce a useful blood-contacting surface for medical devices.

Ellipsometry Studies of Lipoprotein Adsorption

The adsorption of a number of lipoproteins, i.e., low-density lipoprotein (LDL), oxidized LDL (oxLDL), high-density lipoprotein (HDL), and lipoprotein (a), at silica and methylated silica as well as at the latter surface modified through adsorption of proteoheparan sulfate, was investigated with in situ ellipsometry at close to physiological conditions. It was found that LDL, oxLDL, HDL, and lipoprotein (a) all adsorbed more extensively at silica than at methylated silica. Upon exposure of the methylated silica surface to proteoheparan sulfate, this proteoglycan adsorbs through its hydrophobic moiety, thereby forming a layer similar to that in the biological system, with the polysaccharide chains forming brushes oriented toward the aqueous solution. Analogous to the biological system, both lipoprotein (a) and LDL were found to deposit at such surfaces, the latter particularly in the simultaneous presence of Ca(2+). After HDL pre-exposure, however, no LDL deposition was observed, even at high LDL and Ca(2+) concentrations. These findings correlate well with those obtained from clinical investigations on risk factors for atherosclerosis. Copyright 2000 Academic Press.

Human low density lipoprotein and human serum albumin adsorption onto model surfaces studied by total internal reflection fluorescence and scanning force microscopy

The adsorption of low density lipoprotein (LDL) and human serum albumin (HSA) to model surfaces of different hydrophobicities has been studied using two, surface-sensitive, real-time, in situ techniques: total internal reflection fluorescence (TIRF) and scanning force microscopy (SFM). The model surfaces used were: (1) hydrophilic negatively charged silica (TIRF) and mica (SFM) surfaces, (2) hydrophobic octadecyldimethylsilyl-(ODS)-modified silica (TIRF) and ODS-modified oxidized silicon (SFM) surfaces and (3) amphiphilic ODS-silica gradient surfaces (TIRF). The kinetics of fluorescein isothiocyanate-LDL adsorption onto the ODS-silica gradient surface from FITC-LDL solution and from a solution mixture of LDL and HSA showed that a transport-limited process on the clean silica changed into an adsorption-limited process with increasing surface coverage of ODS chains. SFM analysis of the in situ adsorption of LDL on hydrophilic mica demonstrated a steady increase in surface coverage with time which was somewhat lower than determined by TIRF for FITC-LDL adsorption on silica. The adsorption behavior of a binary mixture of HSA and LDL suggested that lateral interactions between HSA and LDL affect the adsorption process. The diameter of LDL adsorbed on mica and ODS-modified silicon has been determined using SFM to be approximately 55 nm. Tetrameric LDL aggregates were observed on all of the surfaces in addition to some dimers and trimers. Imaging LDL and HSA adsorption on clean oxidized silicon surfaces using "contact mode' SFM techniques was hindered by probe manipulation of the proteins.

Protein adsorption onto poly(ether urethane ureas) containing Methacrol 2138F: a surface-active amphiphilic additive

Surface characterization and protein adsorption studies were carried out on a series of additive dispersed and additive coated poly(ether urethane ureas), PEUUs, to characterize early events in the blood compatibility of these materials. A hypothesis that is based on surface hydrophilicity, surface flexibility, and adsorption media has been developed to understand the modulated adsorption of plasma proteins by PEUU additives. Electron spectroscopy for chemical analysis (ESCA) and contact angle analysis were performed on two PEUU formulation as well as on PEUU formulations modified with Methacrol 2138F (co[diisopropylaminoethyl methacrylate (DIPAM)/decyl methacrylate (DM)][3/1]) or acrylate or methacrylate polymer or copolymer analogs of Methacrol 2138F. Methacrol 2138F is a commercially used amphiphilic copolymethacrylate. ESCA showed that the PEUUs loaded with Methacrol 2138F or with its hydrophilic component, homopoly (DIPAM) (h-(DIPAM)), had a higher percentage of nitrogen at their surfaces than did the base PEUUs. Contact angle analysis also showed that the air side of PEUU formulations loaded with Methacrol 2138F were more hydrophobic than was the air side of base PEUUs when films were cast from dimethylacetamide. However, during contact angle testing, the air side of PEUU films loaded with Methacrol 2138F rapidly became more hydrophilic than did the air side of the base PEUU films. A radioimmunoassay and whole or diluted human plasma were also used to characterize the presence of the proteins fibrinogen, immunoglobulin G, factor VIII/von Willebrand factor, Hageman factor (factor XII), and albumin, on the surface of the same PEUUs as analyzed by ESCA and contact angle. The protein adsorption assay showed that PEUU films loaded or coated with Methacrol 2138F, with a copolyacrylate analog of Methacrol 2138F (co(diisopropylaminoethyl acrylate [DIPAA]/decyl acrylate [DA]) [3/1]), or with the hydrophilic polyacrylate or polymethacrylate component analogs of Methacrol 2138F (h-DIPAM or h-DIPAA) adsorbed significantly lower amounts of the proteins than did either the base PEUU formulations or the homopoly(decyl methacrylate) (h-DM) or homopoly(decyl acrylate) (h-DA) coated or loaded PEUUs.

Protein adsorption from plasma onto poly(n-alkyl methacrylate) surfaces

Protein adsorption of human serum albumin (HSA), human fibrinogen (Fg), human immunoglobulin G (IgG), high density lipoprotein (HDL) and high molecular weight kininogen (HMWK) from plasma onto poly (n-alkyl methacrylate) (PAMA) surfaces was measured using a semi-quantitative enzyme-immunoassay. Adsorption was investigated for PAMA(n = 1) (n is the number of C-atoms in the n-alkyl side chain), PAMA(n = 8) and PAMA(n = 18). PAMA(n = 1) has a relatively hydrophilic surface as compared to the more hydrophobic PAMA(n = 8) surface. Both polymers have surface chains which do not reorient after contact with water. The PAMA(n = 18) surface is relatively hydrophobic but in this case polymer surface chains and segments are able to reorient after contact with water. Protein adsorption was measured both as a function of time and as a function of the plasma dilution. If adsorption from plasma was measured as a function of time no exchange of proteins could be observed. The amount of adsorbed protein was always larger in the case of the hydrophobic PAMA(n = 8) as compared to PAMAS(n = 1 and 18), probably due to hydrophobic interactions between the proteins and the PAMA(n = 8) surface. At high plasma concentration relatively large amounts of HDL adsorb onto PAMA(n = 8), indicating that this lipoprotein preferentially adsorbs onto this surface.

Determination of cholesterol and cortisone absorption in polyurethane. I. Methodology using size-exclusion chromatography and dual detection

A size-exclusion chromatographic method is described for measuring the absorption of the steroid-based lipids cholesterol and cortisone into Pellethane 2363, a polyurethane used in biomedical implants. The method uses refractometry and ultraviolet diode-array detection, with tetrahydrofuran as the mobile phase. Using an injection volume of 150 microliters, the lower limit of accurate measurement for cholesterol (refractive index detection) was 6 micrograms/ml with a lower limit of detection, based on a 2:1 signal-to-noise ratio, of 0.15 micrograms (1 microgram/ml). For cortisone (ultraviolet detection), the lower accurate limit was 0.6 micrograms/ml with a lower limit of 0.015 micrograms (0.1 micrograms/ml). The results show that after 44 h, 2037 micrograms/g cholesterol and 3131 micrograms/g cortisone were absorbed by the polyurethane. The method eliminates extensive sample manipulation and is sensitive to low levels of lipid in the presence of a high-molecular-mass synthetic polymer.

Compositional analysis of Biomer

Biomer, a segmented polyether polyurethane, has been analyzed via hydrolysis/gas chromatography to determine its composition. In addition to the previously reported 4,4'-methylene bis(phenyl isocyanate) (MDI), polytetramethylene glycol (PTMO), and ethylenediamine, we now report the presence of diethylamine, 1,3-diaminocyclohexane and poly(diisopropylaminoethyl methacrylate-co-decyl methacrylate), Biomer's cloudy insoluble phase. In addition, a method is presented to characterize the methacrylate additive by molecular weight based on GPC. Also found by chromatography were the antioxidants Santowhite Powder and BHT. XPS shows no Si (silicone) on the Biomer surface, and a total chloride analysis reports no chloride (less than 0.03%). Time-of-flight SIMS data suggest evidence for the methacrylate additive at the surface, and mass spectroscopy can be interpreted as evidence for a diaminocyclohexane.

Spectrometric and chromatographic methods for the analysis of polymeric explant materials

Several analytical pyrolysis methods, namely pyrolysis mass spectrometry (Py-MS), time-resolved pyrolysis mass spectrometry (TRPy-MS), and pyrolysis short column gas chromatography mass spectrometry (Py-GC/MS) were used to analyze polymers of clinical interest both before and after implantation. A sample of Biomer, a poly(ether urethane urea) used in the Utah artificial heart, was analyzed using these methods. Two poly(ether urethanes) (Tecoflex and Pellethane) and a poly(dimethylsilicone) (Silastic) sample were analyzed using Py-GC/MS. The direct Py-MS of Biomer identified the components used in the manufacture of Biomer. Py-GC/MS of Biomer, Tecoflex, Pellethane, and Silastic also identified the components used in their manufacture. The analysis of explanted Biomer detected the presence of adsorbed cholestadiene, the reaction of chloride ions with a stabilizer, and the presence of a siloxane contaminant. The cholestadiene was detected on the outside housing of an artificial heart which had been implanted for 297 days. The cholestadiene was detected at low levels and was identified by library search on the MS data system. The siloxane contaminant was also identified by the MS data system. All of the methods demonstrated required only short instrumental analysis times (10 min or less). Data analysis required much more time, but much of the data analysis can be automated.