Probing Bio-Nano Interactions between Blood Proteins and Monolayer-Stabilized Graphene Sheets

Meeting proteins is regarded as the starting event for nanostructures to enter biological systems. Understanding their interactions is thus essential for a newly emerging field, nanomedicine. Chemically converted graphene (CCG) is a wonderful two-dimensional (2D) material for nanomedicine, but its stability in biological environments is limited. Systematic probing on the binding of proteins to CCG is currently lacking. Herein, we report a comprehensive study on the interactions between blood proteins and stabilized CCG (sCCG). CCG nanosheets are functionalized by monolayers of perylene leading to significant improvement in their resistance to electrolyte salts and long-term stability, but retain their core structural characteristics. Five types of model human blood proteins including human fibrinogen, γ-globulin, bovine serum albumin (BSA), insulin, and histone are tested. The main driving forces for blood protein binding involve the π-π interacations between the π-plane of sCCG and surface aromatic amonic acid (sAA) residues of proteins. Several key binding parameters including the binding amount, Hill coefficient, and binding constant are determined. Through a detailed analysis of key controlling factors, we conclude that the protein binding to sCCG is determined mainly by the protein size, the number, and the density of the sAA.

Dynamics of statistically confident particle sizes and concentrations in blood plasma obtained by the dynamic light scattering method

The work is devoted to the study of sizes and concentrations of proteins, and their aggregates in blood plasma samples, using static and dynamic light scattering methods. A new approach is proposed based on multiple repetition of measurements of intensity size distribution and on counting the number of registrations of different sizes, which made it possible to obtain statistically confident particle sizes and concentrations in the blood plasma. It was revealed that statistically confident particle sizes in the blood plasma were stable during 30 h of observations, whereas the concentrations of particles of different sizes varied as a result of redistribution of material between them owing to the protein degradation processes.

Ex situ evaluation of the composition of protein corona of intravenously injected superparamagnetic nanoparticles in rats

It is now well recognized that the surfaces of nanoparticles (NPs) are coated with biomolecules (e.g., proteins) in a biological medium. Although extensive reports have been published on the protein corona at the surface of NPs in vitro, there are very few on the in vivo protein corona. The main reason for having very poor information regarding the protein corona in vivo is that separation of NPs from the in vivo environment has not been possible by using available techniques. Knowledge of the in vivo protein corona could lead to better understanding and prediction of the fate of NPs in vivo. Here, by using the unique magnetic properties of superparamagnetic iron oxide NPs (SPIONs), NPs were extracted from rat sera after in vivo interaction with the rat's physiological system. More specifically, the in vivo protein coronas of polyvinyl-alcohol-coated SPIONs with various surface charges are defined. The compositions of the corona at the surface of various SPIONs and their effects on the biodistribution of SPIONs were examined and compared with the corona composition of particles incubated for the same time in rat serum.

Atomic force microscopy and analytical ultracentrifugation for probing nanomaterial protein interactions

Upon contact with the human body, nanomaterials are known to interact with the physiological surroundings, especially with proteins. In this context, we explored analytical methods to provide biologically relevant information, in particular for manufactured nanomaterials as produced by the chemical industry. For this purpose, we selected two batches of SiO(2) nanoparticles as well as four batches of CeO(2) nanoparticles, each of comparably high chemical purity and similar physicochemical properties. Adsorption of serum proteins and bovine serum albumin (BSA) was quantified by SDS-PAGE in combination with densitometry and further investigated by atomic force microscopy (AFM) and analytical ultracentrifugation (AUC). The protein adsorption to SiO(2) nanoparticles was below the limit of detection, regardless of adjusting pH or osmolality to physiological conditions. In contrast, the four CeO(2) nanomaterials could be classified in two groups according to half-maximal protein adsorption. Measuring the work of adhesion and indention by AFM for the BSA-binding CeO(2) nanomaterials revealed the same classification, pointing to alterations in shape of the adsorbed protein. The same trend was also reflected in the agglomeration behavior/dispersibility of the four CeO(2) nanomaterials as revealed by AUC. We conclude that even small differences in physicochemical particle properties may nevertheless lead to differences in protein adsorption, possibly implicating a different disposition and other biological responses in the human body. Advanced analytical methods such as AFM and AUC may provide valuable additional information in this context.

Differential plasma protein binding to metal oxide nanoparticles

Nanoparticles rapidly interact with the proteins present in biological fluids, such as blood. The proteins that are adsorbed onto the surface potentially dictate the biokinetics of the nanomaterials and their fate in vivo. Using nanoparticles with different sizes and surface characteristics, studies have reported the effects of physicochemical properties on the composition of adsorbed plasma proteins. However, to date, few studies have been conducted focusing on the nanoparticles that are commonly exposed to the general public, such as the metal oxides. Using previously established ultracentrifugation approaches, two-dimensional gel electrophoresis and mass spectrometry, the current study investigated the binding of human plasma proteins to commercially available titanium dioxide, silicon dioxide and zinc oxide nanoparticles. We found that, despite these particles having similar surface charges in buffer, they bound different plasma proteins. For TiO2, the shape of the nanoparticles was also an important determinant of protein binding. Agglomeration in water was observed for all of the nanoparticles and both TiO2 and ZnO further agglomerated in biological media. This led to an increase in the amount and number of different proteins bound to these nanoparticles. Proteins with important biological functions were identified, including immunoglobulins, lipoproteins, acute-phase proteins and proteins involved in complement pathways and coagulation. These results provide important insights into which human plasma proteins bind to particular metal oxide nanoparticles. Because protein absorption to nanoparticles may determine their interaction with cells and tissues in vivo, understanding how and why plasma proteins are adsorbed to these particles may be important for understanding their biological responses.

Characterization of granulations of calcium and apatite in serum as pleomorphic mineralo-protein complexes and as precursors of putative nanobacteria

Calcium and apatite granulations are demonstrated here to form in both human and fetal bovine serum in response to the simple addition of either calcium or phosphate, or a combination of both. These granulations are shown to represent precipitating complexes of protein and hydroxyapatite (HAP) that display marked pleomorphism, appearing as round, laminated particles, spindles, and films. These same complexes can be found in normal untreated serum, albeit at much lower amounts, and appear to result from the progressive binding of serum proteins with apatite until reaching saturation, upon which the mineralo-protein complexes precipitate. Chemically and morphologically, these complexes are virtually identical to the so-called nanobacteria (NB) implicated in numerous diseases and considered unusual for their small size, pleomorphism, and the presence of HAP. Like NB, serum granulations can seed particles upon transfer to serum-free medium, and their main protein constituents include albumin, complement components 3 and 4A, fetuin-A, and apolipoproteins A1 and B100, as well as other calcium and apatite binding proteins found in the serum. However, these serum mineralo-protein complexes are formed from the direct chemical binding of inorganic and organic phases, bypassing the need for any biological processes, including the long cultivation in cell culture conditions deemed necessary for the demonstration of NB. Thus, these serum granulations may result from physiologically inherent processes that become amplified with calcium phosphate loading or when subjected to culturing in medium. They may be viewed as simple mineralo-protein complexes formed from the deployment of calcification-inhibitory pathways used by the body to cope with excess calcium phosphate so as to prevent unwarranted calcification. Rather than representing novel pathophysiological mechanisms or exotic lifeforms, these results indicate that the entities described earlier as NB most likely originate from calcium and apatite binding factors in the serum, presumably calcification inhibitors, that upon saturation, form seeds for HAP deposition and growth. These calcium granulations are similar to those found in organisms throughout nature and may represent the products of more general calcium regulation pathways involved in the control of calcium storage, retrieval, tissue deposition, and disposal.

PVA-DNA cryogel membranes: characterization, swelling, and transport studies

Double-stranded (ds) DNA from salmon testes has been incorporated into PVA hydrogels obtained by a technique of repeated freezing and thawing. The cryogels obtained are free of potential toxic species like chemical cross-linkers, and consequently, they can be used in pharmaceutical or medical applications. These cryogels show a good mechanical resistance and a white and opaque appearance caused by a heterogeneous porous structure. Encapsulated DNA molecules can be in a compacted or an extended conformation in the PVA matrix and can be controlled by tailoring the degree of crystallinity of the PVA network; this is supported by fluorescence microscopy and UV and FTIR spectroscopic studies. The two forms of encapsulated DNA were observed for different types of matrixes: an extended one in a more crystalline network and a globular one in a more amorphous one. Different associations of base pairs have also been observed. PVA cryogel crystallinity could be tailored by the cryogel contact with different salt solutions. Cryogel surface (scanning electron microscopy) and bulk morphology (porosimetry), swelling, DNA retention, and delivery kinetics have also been studied. All these investigations clearly show strong interactions between PVA and DNA.

Early stages of human plasma proteins adsorption probed by Atomic Force Microscope

Atomic Force Microscope (AFM) as a surface characterization technique has offered a great impulse in the advance of biocompatible materials. In this study AFM was implemented for the investigation of the early stages of adsorption of two human plasma proteins on titanium and hydrogenated carbon biocompatible thin films. The plasma proteins that were used were Human Serum Albumin and Fibrinogen, two of the most important proteins in human plasma. The concentration of the protein solutions was the same as that in human plasma. As the examined samples were soft, non-contact AFM mode was used to avoid their destruction. In order for the early stages of protein adsorption to be assessed, small incubation times were applied. AFM measurements in liquid buffer were also carried out, allowing the observation of the protein behaviour in an environment much closer to their native one. In addition, there was an assessment of the adsorption mechanism of the proteins on the above-mentioned biomaterials.

Rhizopus oryzae fungus cells producing L(+)-lactic acid: kinetic and metabolic parameters of free and PVA-cryogel-entrapped mycelium

Spores of the filamentous fungus Rhizopus oryzae were entrapped in macroporous poly(vinyl alcohol) cryogel (PVA-cryogel). To prepare immobilised biocatalyst capable of producing L(+)-lactic acid (LA), the fungus cells were cultivated inside the carrier beads. The growth parameters and metabolic activity of the suspended (free) and immobilised cells producing LA in a batch process were comparatively investigated. The immobilised cells possessed increased resistance to high concentrations of accumulated product and gave much higher yields of LA in the iterative working cycle than the free cells did. Detailed kinetic analysis of the changes in the intracellular adenosine triphosphate concentration, specific rate of growth, substrate consumption and LA production showed that the fungus cells entrapped in PVA-cryogel are more attractive for biotechnological applications compared to the free cells.

Binding mitochondria to cryogel monoliths allows detection of proteins specifically released following permeability transition

Following proapoptotic signals such as calcium-induced mitochondrial permeability transition or translocation of proapoptotic proteins, mitochondria induce cell death through release of apoptogenic proteins. The mechanism of release and the identity of the released proteins are currently debated. Earlier attempts at identification of the apoptogenic proteins have been hampered by a high nonspecific background. Our aim was to develop a novel method where background release was eliminated, allowing proteins specifically released from mitochondria following proapoptotic stimulation to be identified. Liver mitochondria were immobilized and washed on cryogel monoliths prior to induction of protein release (calcium or Bid/Bax). Immobilized mitochondria exhibited normal morphology and swelling response and retained respiratory activity. The released proteins were collected, concentrated, separated on polyacrylamide gels which were cut into pieces, trypsin-digested, and analyzed using liquid chromatography-tandem mass spectrometry. Control samples contained no protein, and stimulation with calcium and Bid/Bax resulted in identification of 68 and 82 proteins, respectively. We conclude that, in combination with the robust proteomic approach, immobilization on cryogel monoliths is a fruitful approach for studying specific protein release from isolated mitochondria. We propose that this method is a powerful tool to further characterize the role of mitochondria in cell death induction.

Preparation and characterization of novel biocompatible cryogels of poly (vinyl alcohol) and egg-albumin and their water sorption study

Polyvinyl alcohol (PVA) and egg albumin are water-soluble, biocompatible and biodegradable polymers and have been widely employed in biomedical fields. In this paper, novel physically cross-linked hydrogels composed of poly (vinyl alcohol) and egg albumin were prepared by cyclic freezing/thawing processes of aqueous solutions containing PVA and egg albumin. The FTIR analysis of prepared cryogels indicated that egg albumin was successfully introduced into the formed hydrogel possibly via hydrogen bonds among hydroxyl groups, amide groups and amino groups present in PVA and egg albumin. The gels were also characterized thermally and morphologically by DSC and SEM-techniques, respectively. The prepared so called 'cryogels' were evaluated for their water uptake potential and influence of various factors such as chemical architecture of the spongy hydrogels, pH and temperature of the swelling bath were investigated on the degree of water sorption by the cryogels. The effect of salt solution and various simulated biological fluids on the swelling of cryogel was also studied. The in vitro biocompatibility of the prepared cryogel was also judged by methods such as protein (BSA) adsorption, blood clot formation and percentage hemolysis measurements.

The 17Å structure of the 420kDa lobster clottable protein by single particle reconstruction from cryoelectron micrographs

Crustaceans form clots by the rapid crosslinking of a hemolymph clottable protein (CP) to form long, branched polymers. Clotting limits hemolymph loss from wounds as well as playing a part in the innate immune response. CP is a 420 kDa homodimer with a large quantity of associated lipid, primarily the carotenoid pigment astaxanthin. The three-dimensional structure of CP from the lobster Panulirus interruptus has been determined to 17 A resolution by single particle reconstruction from electron micrographs of the protein embedded in vitreous ice. The most prominent feature of this structure is a large cavity spanning the length of the molecule, which is the likely lipid binding pocket. The EM structure has been used in a low resolution molecular replacement search with data from orthorhombic CP crystals, and a solution is presented which describes the crystal packing.

Biostability and biocompatibility of a surface-grafted phospholipid monolayer on a solid substrate

We have previously demonstrated phosphorylcholine monolayer chemically grafted onto a methacryloyl-terminated solid substrate by in situ polymerization. The in situ polymerization was carried out at the interface between a pre-assembled acrylated phospholipid monolayer produced by vesicle fusion and a methacryloyl-terminated substrate using a water-soluble initiator, 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPD). Herein, we examined the biostability and biocompatibility of a surface-grafted phospholipid monolayer (poly-PC) on a methacryloyl-terminated substrate using a "wash off' test, in vitro protein adsorption and in vivo cage implantation for time intervals of 4, 7, 14 and 21 days, respectively. In order to compare the biostability and biocompatibility of phospholipid surfaces on solid substrates, we used two types of phospholipid surfaces: a physically adsorbed phospholipid monolayer (PC) and a poly-PC. Atomic force microscopy and water contact angle measurements indicated that the poly-PC surface was more stable in PBS, Triton X-100 and to EO gas sterilization than the PC surface. The adsorption of proteins such as albumin, fibrinogen, IgG and human plasma proteins on the poly-PC surfaces were significantly reduced, in vitro. Moreover, the poly-PC surface greatly reduced macrophage adhesion and the formation of foreign body giant cells, in vivo.

Competitive plasma protein adsorption onto fluorinated polyimide surfaces

A series of fluorinated polyimides cured at different temperatures was prepared, and plasma protein adsorption and platelet adhesion onto the polyimide films were evaluated in vitro using scanning electron microscopy, a micro-bicinchoninic acid protein assay, and a gold-colloid-labeled immunoassay. In particular, we focused on competitive plasma protein adsorption onto polyimide film because elucidation of the competitive adsorption mechanism is needed for a good understanding of in vivo biocompatibility of polyimide. Interestingly, the trend of IgG adsorption onto the polyimide surface measured in human plasma was completely contrary to that observed with IgG dissolved in PBS, and the adsorption increased with an increase in the curing temperature. We propose that the human plasma F(c) region in IgG might selectively adsorb onto polyimide film cured at high temperatures because of competitive plasma protein adsorption to the surface.

Isolation and characterization of haemoporin, an abundant haemolymph protein from Aplysia californica

In the present study, we show the isolation and characterization of the protein haemoporin, which constitutes the second most abundant protein fraction in the haemolymph of the marine gastropod Aplysia californica. Although Aplysia is commonly used to investigate the molecular basis of learning, not much is known about the proteins in its haemolymph, which is in contact with the neurons owing to the open circulatory system of molluscs. In the native state, haemoporin is a macromolecular complex forming a cylinder with a central solvent-filled pore. The native complex most probably is a homopentamer made up from 70 kDa subunits with a molecular mass of 360 kDa and a sedimentation coefficient of 11.7 S. Prediction of the secondary structure by CD spectroscopy revealed that haemoporin contains 36% alpha-helices and 19% beta-strands. An absorption band in the 300-400 nm region indicates that haemoporin probably contains a bound substance. Haemoporin also contains a below average amount of tryptophan as evident from absorption and fluorescence spectra. The specific absorption coefficient at 280 nm (a (280 nm, 1 mg/ml)) varies between 0.42 and 0.59 l x g(-1) x cm(-1) depending on the method. The function of the protein is not yet known, but there are structural parallels between haemoporin and a pore protein reported previously in the haemolymph of another marine gastropod Megathura crenulata. The alanine-rich N-terminal sequence (AAVPEAAAEATAEAAPVSEF) is unique among protein sequences and indicates an alpha-helical structure. Whereas one side of the helix is hydrophobic and faces the interior of the protein, the other side contains a glutamic cluster, which may form the channel of the pore in the quaternary structure. Thus both proteins might belong to a new class of haemolymph proteins present in the haemolymph of marine gastropods.

Molecular basis of non-self recognition by the horseshoe crab tachylectins

The self/non-self discrimination by innate immunity through simple ligands universally expressed both on pathogens and hosts, such as monosaccharides and acetyl group, depends on the density or clustering patterns of the ligands. The specific recognition by the horseshoe crab tachylectins with a propeller-like fold or a propeller-like oligomeric arrangement is reinforced by the short distance between the individual binding sites that interact with pathogen-associated molecular patterns (PAMPs). There is virtually no conformational change in the main or side chains of tachylectins upon binding with the ligands. This low structural flexibility of the propeller structures must be very important for specific interaction with PAMPs. Mammalian lectins, such as mannose-binding lectin and ficolins, trigger complement activation through the lectin pathway in the form of opsonins. However, tachylectins have no effector collagenous domains and no lectin-associated serine proteases found in the mammalian lectins. Furthermore, no complement-like proteins have been found in horseshoe crabs, except for alpha(2)-macroglobulin. The mystery of the molecular mechanism of the scavenging pathway of pathogens in horseshoe crabs remains to be solved.

Structural conversion between open and closed forms of radixin: low-angle shadowing electron microscopy

The function of ERM (ezrin/radixin/moesin) proteins as general cross-linkers between actin filaments and plasma membranes is regulated downstream of Rho, through the transition between active and inactive forms. To directly examine the conformational change between the active and inactive forms of ERM proteins, we applied low-angle rotary-shadowing electron microscopy to the radixin molecules, wild-type, T564A-non-phosphorylated-type, and T564E-phosphorylated-type, since most of the active forms are reportedly stabilized in cells by the C-terminal threonine phosphorylation. As a result, the T564A- and wild-type radixin molecules yielded the globular closed forms, approximately 8-14 nm in diameter, with some striations on their surfaces. In contrast, the T564E-radixin molecules tended to take elongated open forms, in which two globular structures measuring approximately 8 nm and approximately 5 nm in diameter were associated with both ends of the filamentous structures. The filamentous structure took either a approximately 20-25 nm-long straight course or a folded course. Taken together with the biochemical and the crystal structural results obtained to date, the closed and open forms represent the inactive and active forms of radixin as cross-linkers between actin filaments and plasma membranes.

Internal defenses of the snail Biomphalaria glabrata

Injection of foreign particles (zymosan, latex beads, living bacteria) and substances (ferritine, horseradish peroxidase) in Biomphalaria glabrata induces the rapid appearance of tubular double-helical filaments in the hemolymph. This rapid induction may be due to the polymerization of precursor proteins of the hemolymph. Tubular helical filaments are also observed in normal snails, especially in the hemal spaces of the proximal kidney; they seem to belong to the extracellular matrix and form bundles of a few parallel units associated with fine fibrils. Hemocytes adhere to these bundles by means of the filopodia tip or by small areas of the cell surface; consequently, they may become temporarily sedentary in the hemal spaces. The deposition of helical filaments seems increased in ageing snails and in snails parasitized by Echinostoma caproni.

Defensin promotes the binding of lipoprotein(a) to vascular matrix

Retention of lipoproteins within the vasculature is a central event in the pathogenesis of atherosclerosis. However, the signals that mediate this process are only partially understood. Prompted by putative links between inflammation and atherosclerosis, we previously reported that alpha-defensins released by neutrophils are present in human atherosclerotic lesions and promote the binding of lipoprotein(a) [Lp(a)] to vascular cells without a concomitant increase in degradation. We have now tested the hypothesis that this accumulation results from the propensity of defensin to form stable complexes with Lp(a) that divert the lipoprotein from its normal cellular degradative pathways to the extracellular matrix (ECM). In accord with this hypothesis, defensin stimulated the binding of Lp(a) to vascular matrices approximately 40-fold and binding of the reactants to the matrix was essentially irreversible. Defensin formed stable, multivalent complexes with Lp(a) and with its components, apoprotein (a) and low-density lipoprotein (LDL), as assessed by optical biosensor analysis, gel filtration, and immunoelectron microscopy. Binding of defensin/Lp(a) complexes to matrix was inhibited (>90%) by heparin and by antibodies to fibronectin (>70%), but not by antibodies to vitronectin or thrombospondin. Defensin increased the binding of Lp(a) (10 nmol/L) to purified fibronectin more than 30-fold. Whereas defensin and Lp(a) readily traversed the endothelial cell membranes individually, defensin/Lp(a) complexes lodged on the cell surface. These studies demonstrate that alpha-defensins released from activated or senescent neutrophils stimulate the binding of an atherogenic lipoprotein to the ECM of endothelial cells, a process that may contribute to lipoprotein accumulation in atherosclerotic lesions.

The three-dimensional structure of aquaporin-1

The entry and exit of water from cells is a fundamental process of life. Recognition of the high water permeability of red blood cells led to the proposal that specialized water pores exist in the plasma membrane. Expression in Xenopus oocytes and functional studies of an erythrocyte integral membrane protein of relative molecular mass 28,000, identified it as the mercury-sensitive water channel, aquaporin-1 (AQP1). Many related proteins, all belonging to the major intrinsic protein (MIP) family, are found throughout nature. AQP1 is a homotetramer containing four independent aqueous channels. When reconstituted into lipid bilayers, the protein forms two-dimensional lattices with a unit cell containing two tetramers in opposite orientation. Here we present the three-dimensional structure of AQP1 determined at 6A resolution by cryo-electron microscopy. Each AQP1 monomer has six tilted, bilayer-spanning alpha-helices which form a right-handed bundle surrounding a central density. These results, together with functional studies, provide a model that identifies the aqueous pore in the AQP1 molecule and indicates the organization of the tetrameric complex in the membrane.

cDNA cloning, tissue distribution, and subcellular localization of horseshoe crab big defensin

A full-length cDNA for horseshoe crab big defensin with a strong antimicrobial activity was obtained from a hemocyte cDNA library. The open reading frame of the cDNA coded for an NH2-terminal signal sequence followed by a propeptide and the mature big defensin. The propeptide is linked to the mature protein through an -Arg-X-Lys/Arg-Arg- motif, the processing site for Kex2-like proteases. Northern blot analysis revealed that big defensin is expressed in all the tissues tested, suggesting that big defensin plays an important role not only in hemocytes but also in other tissues for host defense. The subcellular localization, determined by immunocytochemistry at ultrastructural level, confirmed the previous findings obtained by biochemical analysis that big defensin locates in both small and large granules in hemocytes. Big defensin is the first example to demonstrate the existence of broad tissue distribution in horseshoe crab.

Effect of increasing concentrations of nonionic detergent Triton X-100 on solubilization and structure of rat liver and adipose plasma membranes

The extent of solubilization and the structure of rat liver and adipose plasma membranes after treatment with nonionic detergent Triton X-100 were studied. The concentration of Triton X-100 varied from 0.005 to 0.050% (0.26-2.6 mg/mg membrane protein). The excimerization of the pyrene fluorescent probe and the relative vibronic band intensities in the pyrene monomer fluorescence spectrum were measured to evaluate the membrane lipid bilayer fluidity and polarity. The data on the aqueous pyrene fluorescence in the presence of Triton X-100 showed that formation of micellar aggregates occurred at detergent concentrations of over 0.015%. This value is a crucial factor in the detergent action on the membrane structure: both intensive extraction of plasma membrane proteins and fluidization of the lipid bilayer were observed only at Triton X-100 concentration over 0.015%. However, Triton X-100 did not exert any action on the polarity of the membrane hydrophobic regions.

Extracellular matrix in tooth cementum and mantle dentin: localization of osteopontin and other noncollagenous proteins, plasma proteins, and glycoconjugates by electron microscopy

BACKGROUND

Noncollagenous proteins (NCPs) are considered to have multiple functions related to the formation, turnover, and repair of the collagen-based mineralized tissues. Collectively, they comprise a class of generally acidic, mineral-binding proteins showing extensive posttranslational modifications, including glycosylation, phosphorylation, and sulfation. METHODS. We have used colloidal-gold immunocytochemistry and lectin-gold cytochemistry, together with transmission electron microscopy, to examine the organic matrix composition of tooth cementum and the subjacent mantle dentin in rodent molar teeth. Molars were processed for immunocytochemistry using antibodies against osteopontin (OPN), osteocalcin (OC), bone sialoprotein (BSP), bone acidic glycoprotein-75 (BAG-75), albumin (ALB), and alpha 2HS-glycoprotein (alpha 2HS-GP), or for glycoconjugate cytochemistry using lectin-gold complexes.

RESULTS

Ultrastructurally, at the advancing root edge in developing molars, OPN and BSP initially were associated with small calcification foci in the mantle dentin. With progressing mineralization, OC and alpha 2HS-GP appeared diffusely distributed throughout the calcified mantle dentin, and diminished as a gradient toward the circumpulpal dentin. Immediately following disruption of Hertwig's epithelial root sheath, cementum deposition commenced at the root surface occasionally with the appearance of a cement line rich in OPN. Cementum matrix proper contained abundant OPN, BSP, OC, and alpha 2HS-GP, but no or little BAG-75 or ALB. Protein immunolabeling, as well as lectin labeling for beta-D-galactose and N-acetyl-neuraminic acid and/or N-glycolyl-neuraminic acid, both being prominent sugars of certain NCPs, was primarily concentrated between, and at the surface of, collagen fibrils in acellular extrinsic fiber cementum. OPN, BSP, OC, and alpha 2HS-GP were also prominent components of cellular cementum and of Sharpey's fibers. In cellular cementum, laminae limitantes sometimes present delimiting cementocyte lacunae and cell process-containing canaliculi were also rich in OPN. Along the root surface, occasional cementoblasts exhibited intracellular labeling for OPN over the Golgi apparatus and secretory granules.

CONCLUSIONS

We have identified OPN, BSP, OC, and alpha 2HS-GP as being prominent organic constituents of both mantle dentin and acellular and cellular cementum, and, have elucidated the details of their distribution at the ultrastructural level. The temporal appearance and spatial distribution of these organic moieties in the teeth root are similar to those seen during bone formation and are consistent with proposals that certain NCPs may be involved in regulating calcification and/or participating in cell-matrix and matrix-matrix/mineral adhesion events.

Stratifin, a keratinocyte specific 14–3-3 protein, harbors a pleckstrin homology (PH) domain and enhances protein kinase C activity

The intrinsic signal(s) responsible for the onset of human keratinocyte terminal differentiation is not yet fully understood. Evidence has been recently accumulated linking the phospholipase-mediated activation of protein kinase C to the coordinate changes in gene expression occurring during keratinocyte terminal differentiation. Here we report the purification of a keratinocyte-derived protein enhancing protein kinase C enzymatic activity. The stimulator eluted as a peak with estimated molecular mass of approximately 70 kDa, while analysis by SDS-PAGE showed a 30 kDa protein migrating as a distinct doublet, suggesting the formation of a 30 kDa homodimer. The amino acid sequence analysis allowed the unambigous identification of the protein kinase C stimulator as a mixture of the highly homologous sigma (stratifin) and zeta isoforms of 14–3-3 proteins, which are homodimers of identical 30 kDa subunits. Mono Q anion exchange chromatography and immunoblot analysis further confirmed that stratifin enhances protein kinase C activity. Stratifin was originally sequenced from a human keratinocyte protein database, but its function was unknown. The pleckstrin homology domain has been recently related to protein translocation to the cell membrane as well as to functional interactions of intracellular proteins involved in signal transduction. We show here that stratifin (and 14–3-3 zeta) harbors a pleckstrin homology domain, and the consequent functional implications will be discussed.

Scanning electron microscopic investigations of surface treated large-bore catheters used for extracorporeal detoxification methods

Typical complications caused by surface properties of synthetic catheter implants are infection, thrombosis, and stenosis. New methods for surface modification with the aim of reducing such complications are ion beam-based technologies. In our study 109 large-bore catheters without (n = 42) and with treated surfaces with silver (n = 39) or silicone (n = 28) were inserted into the interna jugular and the subclavian veins and were used for extracorporeal detoxification methods. After removal, the catheters were investigated with scanning electron microscopy (SEM) and for bacterial colonization. In 42 large-bore catheters without surface treatment deposits of fibrin, protein and blood cells were seen on the inner and outer surface. Bacterial colonization was observed in 38.1%. In contrast, the catheters with treated outer surfaces showed a very low thrombogenicity and a low contamination rate of 8.9%. The ion beam-based technologies reduce the thrombogenicity and infection rates of the catheter surfaces. In comparison to catheters without treated surfaces, catheters with surface treatment are good alternatives in blood contacting applications ranging from hemodialysis to oncology.

Multiple isoforms of the human pentraxin serum amyloid P component

Human serum amyloid P component (SAP) isolated from 20 healthy individuals was analyzed by anion exchange chromatography and isoelectric focusing (IEF) in order to investigate the existence of multiple forms of SAP and interindividual structural differences. Anion exchange chromatography showed one major and several minor subpopulations of SAP. IEF of all SAP isolates showed a previously unreported degree of heterogeneity with six isoelectric forms (pKi range 5.5-6.1) and with minor interindividual differences in respect of isoelectric points. Total enzymatic deglycosylation of SAP reduced the number of bands in IEF to two indicating the existence of two types of polypeptide chains.

Vascular changes and blood-brain barrier damage in the pathogenesis of polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (membranous lipodystrophy)

The histopathological, immunohistochemical and electron microscopic findings in eight patients with polycystic lipomembranous osteodysplasia and sclerosing leukoencephalopathy (PLO-SL) are described. This autosomally recessively inherited disease is first manifested by multiple bone cysts, which are later followed around the age of 30 by severe neuropsychiatric syndrome. The pathogenesis of PLO-SL has not been established, and the search for the most suspected error in lipid metabolism has been unsuccessful. The typical macroscopic features were marked hydrocephalus ex vacuo due to severe destruction of the white matter (WM) with extensive secondary astrocytic gliosis, and with relatively better preserved gray matter (GM). The basement membranes of blood vessels with plump endothelium were thickened and often multiplied, most prominently in the WM. Extravasation of plasma constituents was demonstrated immunohistochemically. On the basis of the vascular changes, also present in bone lesions, it is proposed that severe chronic vasogenic brain edema is the main pathogenetic mechanism of the severe leukoencephalopathy in this disease entity.

Red cell membrane protein band 4.2: phenotypic, genetic and electron microscopic aspects

The present status of band 4.2 has been reviewed from the standpoint of protein chemistry, gene analysis and clinical hematology. Band 4.2 plays an important role in various cellular functions. In 142 GCT-->ACT band 4.2 deficiency, abnormalities of the cytoskeletal network were clearly observed by electron microscopy and by ektacytometry, although the cytoskeletal proteins themselves were essentially normal in these red cells. The physiological states of band 3 in situ in the membranes were also affected in band 4.2 deficiency, as detected by electron microscopy, although again the biochemical properties of band 3 itself were essentially normal in these red cells. Other disorders of band 4.2 deficiency in the absence of the 142 GCT-->ACT mutation appear to be most interesting in the pathogenesis of hemolysis. In some of the band 4.2 anomalies, other membrane proteins including band 3 would appear to be most pathognomonic for the disease states. These conditions require elucidation by protein chemistry and gene analysis. The control mechanism of the gene expression should also be clarified to understand the important role of band 4.2 in health and disease.

A role for band 4.2 in human erythrocyte band 3 mediated anion transport

Human erythrocyte band 3 was purified essentially free of peripheral proteins, in particular band 4.2, using affinity chromatography. Band 3 protein was then reconstituted into liposomes of lipid type and ratio approximating that of erythrocyte membranes. Stilbenedisulfonate inhibition of band 3 mediated efflux of radiolabeled sulfate from preloaded liposomes was used to test the functionality and correct orientation of the protein. When sulfate efflux, mediated by purified band 3, was compared with partially purified band 3, which contained detectable amounts of bands 4.1 and 4.2, a clear difference in efflux was measured. Sulfate efflux was approximately 30% faster from liposomes containing purified band 3 compared with those containing partially purified protein. In order to investigate further any specific effect of band 4.2 protein on band 3 mediated anion transport, band 4.2 was purified. Increasing amounts of band 4.2 were complexed with purified band 3 and then reconstituted into liposomes. Increasing amounts of band 4.2 complexed with band 3 caused a decrease in band 3 mediated anion transport. The effect of band 4.2 on band 3 mediated anion transport appears to be specific since increasing concentrations of band 4.2 added exogenously to band 3 in reconstituted vesicles (rather than complexed with band 3 before reconstitution) produced no significant changes in sulfate efflux. Further, when increasing amounts of band 4.2 were added to the functionally active transmembrane domain of band 3 and then reconstituted into vesicles, there was also no significant change in sulfate efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

The fluid dynamic effect on protein adsorption in left ventricular assist devices

Plasma protein adsorption onto an artificial surface is strongly influenced by not only the surface characteristics of materials, but also by the fluid dynamics inside the blood pump, and it would influence subsequent platelet adhesion or activation, which plays a major role in the initiation of thrombus formation at the blood-material interface in vivo. In vitro flow visualization of an electrohydraulic LVAD was performed by a video camera (CCD, Hitachi) and an image processor (PC VISION PLUS) with an IBM PC. The electrohydraulic LVADs were implanted in mongrel dogs of approximately 20 kg. The authors sectioned the blood contacted ventricle after animal death according to the level of shear rate. Because analysis of adsorbed protein might be influenced by the size of the ventricle segment, the number of segments was limited to eight per ventricle. Platelet adhesion and its morphology were observed by scanning electron microscopy (SEM). Adsorbed plasma proteins (fibrinogen, albumin, and IgG) on each segment were quantified by enzyme linked immunosorbent assay (ELISA). The specimens were soaked in 2% (wt/vol) SDS/PBS for 2 days and the released protein concentration assessed. A well developed large vortex was observed at the center of the artificial ventricle. Polyurethane blood pumps displayed different degrees of protein adsorption and subsequent platelet adhesion on each segment.

Electron microscopic localization of silver binding proteins in the cytoplasmic granules of guinea pig eosinophil

A new electron optic configuration is described in the specific granules of eosinophil leukocytes. Application of the ammonium silver nitrate impregnation after treatment of intact cells with formaldehyde-OsO4 solution reveals regular deposits of 50 A-electron-opaque particles which are localized in the axial region of the central core. They contain acid-extractable proteins that seem to include the eosinophil basic proteins which participate to the local immune response of the host.

Hapten-tagged plasma proteins as immunocytochemical probes for the study of vascular permeability

Bovine serum albumin and transferrin were covalently coupled with fluorescein isothiocyanate and digoxigenin, respectively, and intravenously co-injected in equal amounts in mouse. The derivation of the two proteins induces minor alterations of their physicochemical properties as well as of their physiological functions. The two tracers were revealed within vascular and extravascular compartments of diaphragm by quantitative postembedding immunocytochemistry, using antibodies against each of the haptens in conjunction with the protein AG-gold complexes. The influence of different fixatives and embedding protocols on the immunodetectability of the hapten-tagged proteins was assessed. Both resist reasonably well to osmication and embedding in Epon. None of the haptens reacted with the heterologous antibody. At 30 minutes after injection, the tracers were detected in blood plasma, interstitium, and endothelial plasmalemmal vesicles. The presence of both proteins within the interendothelial clefts was inconspicuous. The ratios between the labeling densities found over endothelium, interstitial space, and vascular lumen were similar for both tracers. This suggests that the endothelium of mouse diaphragm capillaries might exhibit comparable permeabilities towards serum albumin and transferrin which are similar in size and charge. The study shows that hapten-tagged polypeptides are close to the corresponding native macromolecules, and represent interesting tools for the morphological study of dynamic processes such as transcytosis.

Solvent/detergent-treated plasma: a virus-inactivated substitute for fresh frozen plasma

Fresh frozen plasma (FFP) is prepared in blood banks world-wide as a by-product of red blood cell concentrate preparation. Appropriate clinical use is for coagulation factor disorders where appropriate concentrates are unavailable and when multiple coagulation factor deficits occur such as in surgery. Viral safety depends on donor selection and screening; thus, there continues to be a small but defined risk of viral transmission comparable with that exhibited by whole blood. We have prepared a virus sterilized FFP (S/D-FFP) by treatment of FFP with 1% tri(n-butyl)phosphate (TNBP) and 1% Triton X-100 at 30 degrees C for 4 hours. Added reagents are removed by extraction with soybean oil and chromatography on insolubilized C18 resin. Treatment results in the rapid and complete inactivation of greater than or equal to 10(7.5) infectious doses (ID50) of vesicular stomatitis virus (VSV) and greater than or equal to 10(6.9) ID50 of sindbis virus (used as marker viruses), greater than or equal to 10(6.2) ID50 of human immunodeficiency virus (HIV), greater than or equal to 10(6) chimp infectious doses (CID50) of hepatitis B virus (HBV), and greater than or equal to 10(5) CID50 of hepatitis C virus (HCV). Immunization of rabbits with S/D-FFP and subsequent adsorption of elicited antibodies with untreated FFP confirmed the absence of neoimmungen formation. Coagulation factor content was comparable with that found in FFP. Based on these laboratory and animal studies, together with the extensive history of the successful use of S/D-treated coagulation factor concentrates, we conclude that replacement of FFP with S/D-FFP, prepared in a manufacturing facility, will result in improved virus safety and product uniformity with no loss of efficacy.

Refined structure of charybdotoxin: common motifs in scorpion toxins and insect defensins

Conflicting three-dimensional structures of charybdotoxin (Chtx), a blocker of K+ channels, have been previously reported. A high-resolution model depicting the tertiary structure of Chtx has been obtained by DIANA and X-PLOR calculations from new proton nuclear magnetic resonance (NMR) data. The protein possesses a small triple-stranded antiparallel beta sheet linked to a short helix by two disulfides and to an extended fragment by one disulfide, respectively. This motif also exists in all known structures of scorpion toxins, irrespective of their size, sequence, and function. Strikingly, antibacterial insect defensins also adopt this folding pattern.

Crystal structure of defensin HNP-3, an amphiphilic dimer: mechanisms of membrane permeabilization

Defensins (molecular weight 3500 to 4000) act in the mammalian immune response by permeabilizing the plasma membranes of a broad spectrum of target organisms, including bacteria, fungi, and enveloped viruses. The high-resolution crystal structure of defensin HNP-3 (1.9 angstrom resolution, R factor 0.19) reveals a dimeric beta sheet that has an architecture very different from other lytic peptides. The dimeric assembly suggests mechanisms by which defensins might bind to and permeabilize the lipid bilayer.

[Serum factors regulating macrophage migration in chronic cicatricial stenosis of larynx and trachea in children]

Many children with chronic cicatricial stenosis of the larynx and trachea showed a high activity of the factor stimulating macrophage migration in vitro (MSF). The high MSF level is typical of patients with large scars in tissues rich in cellular elements. The MSF predominance was to a certain extent correlated with abnormal responses to surgical intervention. This was indicated by poor results of surgical treatment if the MSF was low before and immediately after it. With normal MSF the treatment was effective in at least 50% of cases. The therapeutic effectiveness was correlated with MSF variations at an early postoperative stage.

Morphologic characteristics of adsorbed human plasma proteins on vascular grafts and biomaterials

Protein adsorption on the surfaces of clinically significant prosthetic vascular graft materials from human whole blood was independent of plasma concentration as determined morphologically by use of immunogold labels. Some proteins, such as fibrinogen, adsorbed in a multilayer pattern on expanded polytetrafluoroethylene and had a preference for particular surface features of the polymer. Other proteins, such as Hageman factor (factor XII), showed diffuse adsorption patterns. Physiologically significant proteins that have not been well studied, such as immunoglobulin G and factor VIII, adsorbed readily to the surface of expanded polytetrafluoroethylene. This finding may be significant since adsorbed proteins may activate coagulation mechanisms and immunologic responses, including platelet and monocyte adhesion and activation. Any human blood protein for which an antibody has been developed can be studied by use of this technique.

In vivo protein adsorption onto polymers: a transmission electron microscopic study

This paper reports in vivo protein adsorption onto polymers, including Biomer, PEO grafted Biomer (B-PEO-4K), heparin immobilized Biomer with PEO spacers (B-PEO-4K-HEP), and HEMA-Styrene block copolymer (H-S). Vascular grafts (6 mm ID, 7 cm in length) were fabricated with Biomer, coated on their luminal surfaces with test polymers, and implanted into the abdominal aorta of dogs. After 3 weeks-1 month, the grafts were retrieved and processed for TEM and SEM. TEM measured the thickness of adsorbed protein layers stained with a OsO4 solution, and the distribution pattern of adsorbed proteins (albumin, IgG and fibrinogen) using the immunoperoxidase technique. Retrieved grafts of Biomer and B-PEO-4K showed mural thrombi along the graft length, while thrombus formation on B-PEO-4K-HEP and H-S grafts was limited to the anastomotic sites. SEM pictures of B-PEO-4-HEP and H-S surfaces demonstrated clear morphology, with minimal platelet adhesion and activation, and microthrombi. Biomer and B-PEO-4K demonstrated a thick proteinaceous layer (1000-2000 A), whereas B-PEO-4K-HEP and H-S showed what can be described as a monolayer protein thickness (200-300 A). B-PEO-4K-HEP and H-S showed a monolayer-like adsorbed protein pattern, with high concentrations of albumin and IgG, and less fibrinogen, while Biomer and B-PEO-4K showed multilayered patterns with relatively high concentrations of fibrinogen, and less albumin. These results suggest that the surface properties of polymer may control protein adsorption pattern, and the composition of adsorbed protein is essential to in vivo long-term blood compatibility.

Determination of the disulfide array in the human defensin HNP-2. A covalently cyclized peptide

HNP-2 is a 29-residue peptide present in human neutrophils and is a member of the defensin family of antimicrobial peptides. All defensins contain an invariant disulfide infrastructure comprised of 6 half-cystine residues. The disulfide structure of HNP-2 was determined using a novel method to identify the cross-links involving the amino- and carboxyl-terminal cysteine residues. A derivative of HNP-2 was synthesized by covalent modification of the terminal cysteine residues. This derivative was purified, characterized, and subjected to exhaustive proteolytic digestion. Characterization of purified proteolytic fragments by amino acid analysis and/or sequence analysis identified an oligopeptide containing all 6 cystine residues. This oligopeptide was subjected to a single cycle of Edman degradation to cleave the peptide bond linking 2 adjacent cysteines. Purification and characterization of the Edman reaction products allowed for assignment of the disulfide array in HNP-2, revealing a cystine motif unique to the defensin peptide family. Further, the covalent structure of HNP-2 was found to be cyclic as one disulfide links the amino- and carboxyl-terminal cysteine residues. HNP-2 is the only polypeptide known to possess such a configuration.