Immunolabeling efficiency of protein A-gold complexes

Extra-Small Gold Nanospheres Decorated With a Thiol Functionalized Biodegradable and Biocompatible Linear Polyamidoamine as Nanovectors of Anticancer Molecules

Gold nanoparticles are elective candidate for cancer therapy. Current efforts are devoted to developing innovative methods for their synthesis. Besides, understanding their interaction with cells have become increasingly important for their clinical application. This work aims to describe a simple approach for the synthesis of extra-small gold nanoparticles for breast cancer therapy. In brief, a biocompatible and biodegradable polyamidoamine (named AGMA1-SH), bearing 20%, on a molar basis, thiol-functionalized repeat units, is employed to stabilize and coat extra-small gold nanospheres of different sizes (2.5, 3.5, and 5 nm in gold core), and to generate a nanoplatform for the link with Trastuzumab monoclonal antibody for HER2-positive breast cancer targeting. Dynamic light scattering, transmission electron microscopy, ultraviolet visible spectroscopy, X-ray powder diffraction, circular dichroism, protein quantification assays are used for the characterization. The targeting properties of the nanosystems are explored to achieve enhanced and selective uptake of AGMA1-SH-gold nanoparticles by in vitro studies against HER-2 overexpressing cells, SKBR-3 and compared to HER-2 low expressing cells, MCF-7, and normal fibroblast cell line, NIH-3T3. In vitro physicochemical characterization demonstrates that gold nanoparticles modified with AGMA1-SH are more stable in aqueous solution than the unmodified ones. Additionally, the greater gold nanoparticles size (5-nm) is associated with a higher stability and conjugation efficiency with Trastuzumab, which retains its folding and anticancer activity after the conjugation. In particular, the larger Trastuzumab functionalized nanoparticles displays the highest efficacy (via the pro-apoptotic protein increase, anti-apoptotic components decrease, survival-proliferation pathways downregulation) and internalization (via the activation of the classical clathrin-mediated endocytosis) in HER-2 overexpressing SKBR-3 cells, without eliciting significant effects on the other cell lines. The use of biocompatible AGMA1-SH for producing covalently stabilized gold nanoparticles to achieve selective targeting, cytotoxicity and uptake is completely novel, offering an important advancement for developing new anticancer conjugated-gold nanoparticles.

Nanoparticle Therapy for Prostate Cancer: Overview and Perspectives

Traditional prostate cancer therapy and especially chemotherapy has faced many challenges. Low accumulation levels, rapid clearance or drug resistance at the tumor site have been central to why the effect of chemotherapy drugs has declined. Applications of nanotechnology to biomedicine have enabled the development of nanoparticle therapeutic carriers suited for the delivery of chemotherapeutics in cancer therapy. This review describes the current nature of nanoparticle therapeutic carriers for prostate cancer. It describes typical nanocarriers commonly used for the delivery of chemotherapy or for imaging examination. Targeting strategies and related influencing factors are investigated to find ways of enhancing treatment effects of nanoparticles. The overall purpose of this review is to further understanding and to offer recommendations on the design and development of therapeutic nanoparticles for prostate cancer.

Bioengineered cellular and cell membrane-derived vehicles for actively targeted drug delivery: So near and yet so far

Cellular carriers for drug delivery are attractive alternatives to synthetic nanoparticles owing to their innate homing/targeting abilities. Here, we review molecular interactions involved in the homing of Mesenchymal stem cells (MSCs) and other cell types to understand the process of designing and engineering highly efficient, actively targeting cellular vehicles. In addition, we comprehensively discuss various genetic and non-genetic strategies and propose futuristic approaches of engineering MSC homing using micro/nanotechnology and high throughput small molecule screening. Most of the targeting abilities of a cell come from its plasma membrane, thus, efforts to harness cell membranes as drug delivery vehicles are gaining importance and are highlighted here. We also recognize and report the lack of detailed characterization of cell membranes in terms of safety, structural integrity, targeting functionality, and drug transport. Finally, we provide insights on future development of bioengineered cellular and cell membrane-derived vesicles for successful clinical translation.

Influence of Physicochemical Properties and PEG Modification of Magnetic Liposomes on Their Interaction with Intestinal Epithelial Caco-2 Cells

The present study aimed to investigate the effect of particle size (100, 500 nm), surface charge (cationic, neutral and anionic) and polyethylene glycol (PEG) modification of magnetic liposomes on their interaction with the human intestinal epithelial cell line, Caco-2. The cellular associated amount of all the magnetic liposomes was significantly increased by the presence of a magnetic field. The highest association and internalization into Caco-2 cells was observed with magnetic cationic liposomes. Moreover, small magnetic liposomes were more efficiently associated and taken up into the cells, than large ones. In contrast, PEG modification significantly attenuated the enhancing effect of the magnetic field on the cellular association of magnetic liposomes. We also found that magnetic cationic liposomes had the highest retention properties to Caco-2 cells. Moreover, the retention of large magnetic liposomes to the cells was much longer than that of small ones. In addition, magnetic cationic and neutral liposomes had relatively high stability in Caco-2 cells, whereas magnetic anionic liposomes rapidly degraded. These results indicate that the physicochemical properties and PEG modification of magnetic liposomes greatly influences their intestinal epithelial transport.

Modeling Nanoparticle Targeting to a Vascular Surface in Shear Flow Through Diffusive Particle Dynamics

Nanoparticles are regarded as promising carriers for targeted drug delivery and imaging probes. A fundamental understanding of the dynamics of polymeric nanoparticle targeting to receptor-coated vascular surfaces is therefore of great importance to enhance the design of nanoparticles toward improving binding ability. Although the effects of particle size and shear flow on the binding of nanoparticles to a vessel wall have been studied at the particulate level, a computational model to investigate the details of the binding process at the molecular level has not been developed. In this research, dissipative particle dynamics simulations are used to study nanoparticles with diameters of several nanometers binding to receptors on vascular surfaces under shear flow. Interestingly, shear flow velocities ranging from 0 to 2000 s(-1) had no effect on the attachment process of nanoparticles very close to the capillary wall. Increased binding energy between the ligands and wall caused a corresponding linear increase in bonding ability. Our simulations also indicated that larger nanoparticles and those of rod shape with a higher aspect ratio have better binding ability than those of smaller size or rounder shape.

Development and application of a label-free fluorescence method for determining the composition of gold nanoparticle-protein conjugates

A method was developed for determining the composition of the conjugates between gold nanoparticles and proteins based on the intrinsic fluorescence of unbound protein molecules. The fluorescence was evaluated after separation of the conjugates from the reaction mixture by centrifugation. Gold nanoparticles obtained using the citrate technique (average diameter 24 nm) were conjugated at pH 5.4 with the following four proteins: human immunoglobulin G (IgG), bovine serum albumin (BSA), recombinant streptococcal protein G (protein G), and Kunitz-type soybean trypsin inhibitor (STI). The compositions of these conjugates were determined using the developed method. The conjugate compositions were dependent on the concentration of the added protein, and in all cases reached saturation. The equilibrium dissociation constants of the gold nanoparticle conjugates with IgG, BSA, protein G, STI in the initial section of the concentration dependence curve were 4, 6, 10, and 15 nM, respectively. Close to saturation, the corresponding values were 25, 76, 175, and 100 nM, respectively. The maximal binding capacities of a single gold nanoparticle for IgG, BSA, Protein G, and STI were 52, 90, 500, and 550, respectively, which agrees well with the hypothesis of monolayer immobilization.

Cancer nanotechnology: the impact of passive and active targeting in the era of modern cancer biology

Cancer nanotherapeutics are progressing at a steady rate; research and development in the field has experienced an exponential growth since early 2000's. The path to the commercialization of oncology drugs is long and carries significant risk; however, there is considerable excitement that nanoparticle technologies may contribute to the success of cancer drug development. The pace at which pharmaceutical companies have formed partnerships to use proprietary nanoparticle technologies has considerably accelerated. It is now recognized that by enhancing the efficacy and/or tolerability of new drug candidates, nanotechnology can meaningfully contribute to create differentiated products and improve clinical outcome. This review describes the lessons learned since the commercialization of the first-generation nanomedicines including DOXIL® and Abraxane®. It explores our current understanding of targeted and non-targeted nanoparticles that are under various stages of development, including BIND-014 and MM-398. It highlights the opportunities and challenges faced by nanomedicines in contemporary oncology, where personalized medicine is increasingly the mainstay of cancer therapy. We revisit the fundamental concepts of enhanced permeability and retention effect (EPR) and explore the mechanisms proposed to enhance preferential "retention" in the tumor, whether using active targeting of nanoparticles, binding of drugs to their tumoral targets or the presence of tumor associated macrophages. The overall objective of this review is to enhance our understanding in the design and development of therapeutic nanoparticles for treatment of cancers.

Ultrasensitive on-chip immunoassays with a nanoparticle-assembled photonic crystal

Electrophoretic particle entrapment system (EPES) is employed to generate 2D array of nanoparticles coated with biological molecules (i.e., antibodies). Phase matching of the excitation and the emission in the 2D arrays with particles produces a highly enhanced fluorescence signal that was shown to improve the limit of detection in immunoassays. The phase matching is achieved when the particle are in the sub-100 nm range. A comparison between different size particles shows that the sensitivity of an immunoassay is extended to a range that is difficult to achieve with standard technology (e.g., enzyme-linked immunosorbent assay-ELISA). The effectiveness of this novel configuration of particle-in-a-well was demonstrated with an assay for human epidermal growth factor receptor 2 (HER2; breast cancer biomarker), with a detection limit as low as 10 attomolar (aM) in less than 10 μL of serum-based sample. The limit of detection of HER2 indicated far superior assay performance compared to the corresponding standard 96-well plate-based ELISA. The particle-based photonic platform reduces the reagent volume and the time for performing an assay in comparison to competing methods. The simplicity of operation and the level of sensitivity demonstrated here can be used for rapid and early stage detection of biomarkers.

Circular, nanostructured and biofunctionalized hydrogel microchannels for dynamic cell adhesion studies

We report on a method to fabricate biofunctionalized polyethylene glycol hydrogel microchannels with adjustable circular cross-sections. The inner channel surfaces are decorated with Au-nanoparticle arrays of tunable density. These Au-nanoparticles are functionalized with biomolecules whereas the hydrogel material provides an inert and biocompatible background. This technology provides control over flow conditions, channel curvature and biomolecule density on the channel surface. It can be applied for biophysical studies of cell-surface interactions mimicking, for example, leukocyte interactions with the endothelial lining in small vessels.

Impact of the nanoparticle-protein corona on colloidal stability and protein structure

In biological fluids, proteins may associate with nanoparticles (NPs), leading to the formation of a so-called "protein corona" largely defining the biological identity of the particle. Here, we present a novel approach to assess apparent binding affinities for the adsorption/desorption of proteins to silver NPs based on the impact of the corona formation on the agglomeration kinetics of the colloid. Affinities derived from circular dichroism measurements complement these results, simultaneously elucidating structural changes in the adsorbed protein. Employing human serum albumin as a model, apparent affinities in the nanomolar regime resulted from both approaches. Collectively, our findings now allow discrimination between the formation of protein mono- and multilayers on NP surfaces.

Influence of particle size on the binding activity of proteins adsorbed onto gold nanoparticles

We used optical extinction spectroscopy to study the structure of proteins adsorbed onto gold nanoparticles of sizes 5-60 nm and their resulting biological binding activity. For these studies, proteins differing in size and shape, with well-characterized and specific interactions-rabbit immunoglobulin G (IgG), goat anti-rabbit IgG (anti-IgG), Staphylococcal protein A, streptavidin, and biotin-were used as model systems. Protein interaction with gold nanoparticles was probed by optical extinction measurements of localized surface plasmon resonance (LSPR) of the gold nanoparticles. Binding of the ligands in solution to protein molecules already immobilized on the surface of gold causes a small but detectable shift in the LSPR peak of the gold nanoparticles. This shift can be used to probe the binding activity of the adsorbed protein. Within the context of Mie theory calculations, the thickness of the adsorbed protein layer as well as its apparent refractive index is shown to depend on the size of the gold nanoparticle. The results suggest that proteins can adopt different orientations that depend on the size of the gold nanospheres. These different orientations, in turn, can result in different levels of biological activity. For example, we find that IgG adsorbed on spheres with diameter ≥20 nm does not bind to protein A. This study illustrates the principle that the size of nanoparticles can strongly influence the binding activity of adsorbed proteins. In addition to the importance of this in cases of direct exposure of proteins to nanoparticles, the results have implications for proteins adsorbed to materials with nanometer scale surface roughness.

Application of colloidal palladium nanoparticles for labeling in electron microscopy

The application of palladium nanoparticles as electron-dense markers for labeling in both transmission and scanning electron microscopy requires their conjugation to a specific protein. The conjugation protocol described here includes the dihydrolipoic acid (DHLA) capping of Pd nanoparticles (8 nm equivalent diameter) and their subsequent covalent attachment to functional protein molecules such as streptavidin, protein A, or avidin. The single-step reaction was mediated using the cross-linking agent ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The final Pd conjugates were fully functional, as demonstrated by labeling of ultrathin resin sections of either bovine serum albumin or secretory granules of the salivary gland isolated from the partially fed female Ixodes ricinus tick. The results of bovine serum labeling were quantified, statistically evaluated, and compared with results obtained using commercially available gold particle conjugates (10 nm diameter). The highest values of labeling density were achieved using both streptavidin-Pd (106 ± 7 particles/μm2) and protein A-Au conjugates (130 ± 18 particles/μm2) compared to a commercial streptavidin-Au (66 ± 16 particles/μm2) and protein A-Pd conjugates (70 ± 11 particles/μm2). The concentrations of both DHLA and EDC, pH during conjugation, and finally thorough washing away of unbound proteins crucially influenced conjugation.

Impact of pre-concentration to covalently biofunctionalize suspended nanoparticles

The effective biofunctionalization of nanoparticles is crucial for biomedical applications. In this study we investigated the covalent biofunctionalization of magnetic nanoparticles based on carbodiimide activation. An important aspect in the covalent biofunctionalization of nanoparticles has been neglected, namely pre-concentration. Exploiting the electrostatic attraction forces between a protein and the nanoparticle surface will favor the covalent immobilization. We showed that low ionic strength buffers with a pH slightly lower than the pI of the selected biomolecules is needed to increase the yield of covalent immobilization. Additionally, it is demonstrated that the covalently immobilized proteins are bioactive, relying on a sandwich assay using gold nanoparticles as reporter labels.

Dynamic light scattering as a powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies

Dynamic light scattering (DLS) is an analytical tool used routinely for measuring the hydrodynamic size of nanoparticles and colloids in a liquid environment. Gold nanoparticles (GNPs) are extraordinary light scatterers at or near their surface plasmon resonance wavelength. In this study, we demonstrate that DLS can be used as a very convenient and powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies. The conjugation process between protein A and gold nanoparticles under different experimental conditions and the quality as well as the stability of the prepared conjugates were monitored and characterized systematically by DLS. Furthermore, the specific interactions between protein A-conjugated gold nanoparticles and a target protein, human IgG, can be detected and monitored in situ by measuring the average particle size change of the assay solution. For the first time, we demonstrate that DLS is able to directly and quantitatively measure the binding stoichiometry between a protein-conjugated GNP probe and a target analyte protein in solution.

Nanoparticle-mediated cellular response is size-dependent

Nanostructures of different sizes, shapes and material properties have many applications in biomedical imaging, clinical diagnostics and therapeutics. In spite of what has been achieved so far, a complete understanding of how cells interact with nanostructures of well-defined sizes, at the molecular level, remains poorly understood. Here we show that gold and silver nanoparticles coated with antibodies can regulate the process of membrane receptor internalization. The binding and activation of membrane receptors and subsequent protein expression strongly depend on nanoparticle size. Although all nanoparticles within the 2-100 nm size range were found to alter signalling processes essential for basic cell functions (including cell death), 40- and 50-nm nanoparticles demonstrated the greatest effect. These results show that nanoparticles should no longer be viewed as simple carriers for biomedical applications, but can also play an active role in mediating biological effects. The findings presented here may assist in the design of nanoscale delivery and therapeutic systems and provide insights into nanotoxicity.

Internalization and transcytosis of pancreatic enzymes by the intestinal mucosa

As early as the beginning of the twentieth century some data indicated that macromolecules are able to cross the intestinal mucosa to reach the blood. Further evidence was added over the years; however, pathways for this transport still remain to be established. We report here the transfer of two pancreatic enzymes, amylase and lipase, from the intestinal lumen to the blood. Both are present in higher concentrations in the intestinal mucosa and in blood of fed rats. Upon cholinergic stimulation of pancreatic secretion, there was not only an increase in blood enzyme concentrations, but evidence for internalization by duodenal enterocytes was obtained. Following insertion of fluorochrome-tagged amylase and lipase into the duodenal lumen of fasting rats, blood and intestinal tissues were sampled at different time points. Serum activities for both enzymes clearly increased with time. Light microscopy established internalization of both proteins by duodenal enterocytes, and immunogold outlined the pathway taken by both proteins across the enterocytes. From the intestinal lumen, enzymes are channeled through the endosomal compartment to the Golgi apparatus and to the basolateral membrane reaching the interstitial space and blood circulation. Transcytosis through the intestinal mucosa thereby represents an access route for pancreatic enzymes to reach blood circulation.

Amplification methods for the immunolocalization of rare molecules in cells and tissues

The needs to precisely assign macromolecules to specific locations and domains within tissues and cells and to reveal antigens which are present in low or even in trace amounts, led to the elaboration of a wide spectrum of immunocytochemical amplification procedures. These arise from the successive improvements of tissue preparation techniques, of antigen retrieval procedures and of immunological or non-immunological detection systems. Improvement of detection systems may be the most active in the development of amplification techniques. Since the early work of Coons, in which by the introduction of the indirect technique has started amplifying the signal, different systems have succeeded in increasing the sensitivity of antigens detection. Indeed, amplification techniques such as the multiple antibody layers, the multiple bridges, the enzyme complexes, the avidin-biotin, the silver intensification, and the numerous variations and combinations among these have increased the sensitivity for the detection of scarce tissue antigens. However, as shown by the recent progress carried out with new approaches such as the catalyzed reporter deposition (CARD) and the enhanced polymer one-step staining (EPOS), more efficient methods are still needed. In electron microscopy, few techniques have reached the resolution afforded by the post-embedding immunogold approach. In spite of this and in order to further increase its sensitivity, new probes and novel approaches are allowing combination of the gold marker with the amplification capacity of enzymes afforded by the CARD technique. Immunogold amplification strategies, such as the multiple incubations with the primary antibody and the use of an anti-protein A antibody have also led to enhanced signals displaying the advantages in terms of resolution and possibilities of quantification inherent to the colloidal gold marker.

Alterations of the rat mesentery vasculature in experimental diabetes

The alteration induced by diabetes on vascular permeability to serum albumin was investigated in the mesentery of streptozotocin-induced hyperglycemic rats. Double-tagged ((125)I and dinitrophenol-haptenated) heterologous albumin was intravenously administered in normal and hyperglycemic animals, and the extravasation of the tracer was evaluated by radioactivity measurements and by morphometry at the ultrastructural level using quantitative protein A-colloidal gold immunocytochemistry. The results demonstrate that diabetes induces a significant increase in the permeability of the mesentery vessels to albumin. This increase is due to a more efficient transport of macromolecules by endothelial plasmalemmal vesicles and not to leakier interendothelial junctions. Passage across the endothelial basement membranes did not appear to be restricted in either the control or diabetic condition. However, in diabetes, the mesothelial basement membrane appeared to become modified and to restrain the passage of albumin toward the peritoneal cavity. After 3 months of diabetes, the rats presented a net increase in the average diameter of the blood vessels localized in the mesentery arcada (macrovascular hyperplasy) and a notable angiogenesis, manifested at the level of the microvasculature in the mesenteric windows.

Introduction of a novel HRP substrate-Nanogold probe for signal amplification in immunocytochemistry

Amplification of immunological signals with catalyzed reporter deposition (CARD) allows improved detection of scarce tissue antigens in light and electron microscopy. The technique takes advantage of the oxidation ability of horseradish peroxidase (HRP), in the presence of hydrogen peroxide, to yield the accumulation of one of its specific reporter-tagged substrates. This immunocytochemical approach continues to be improved by the introduction of new reporter molecules tagged to tyramine or to other HRP substrates. In this study we introduced a novel HRP substrate tagged to Nanogold particles. The amplification protocol is based on the application of a specific primary antibody, a biotinylated secondary antibody, streptavidin-HRP, and an HRP substrate coupled to Nanogold, followed by silver intensification. In addition to amplification of immunological signals of high resolution, direct accumulation of Nanogold particles at target sites by enzymatic activity of HRP improves the efficiency of the technique compared to other amplification protocols. Moreover, this approach combines the CARD amplification potentials with the ultrasmall gold probe and the silver intensification method. Immunolabeling obtained by light and electron microscopy, as well as immunodot assay using this new amplification strategy, appear to be highly sensitive, specific, and of enhanced intensity.

Enhanced labeling efficiency using ultrasmall immunogold probes: immunocytochemistry

Detection of antigen-antibody interactions in immunocytochemistry relies on a reporter system. The most commonly employed reporter systems used are fluorochromes, enzymes, and particulate probes. This article considers the advantages and disadvantages associated with ultrasmall immunogold particles as the reporter system in immunocytochemical applications.

Glycoprotein Ib is homogeneously distributed on external and internal membranes of resting platelets

Recent ultrastructural studies have suggested that Glycoprotein Ib (GPIb) has a different distribution on external (surface) versus internal (open canalicular system) membranes in resting discoid platelets. The differential distribution proposed for GPIb differs from that reported for the fibrinogen receptor, GPIIb-IIIa, and could have profound physiological significance when platelets are activated by surfaces. The present study explored the distribution of GPIb on external and internal membranes of resting platelets. Immunogold cytochemical techniques were applied to ultrathin cryosections of washed platelets. Polyclonal antibodies or mixtures of monoclonal antibodies (AP1 and 6D1) were used for labeling. To avoid the technical problem posed by limited accessibility of antigens located in very narrow portions of the open canalicular system (OCS) to antibodies, the same methods were applied to patients with giant platelets syndromes. The OCS of normal resting platelets was also dilated by exposure of platelets to hypertonic conditions or to cytochalasin-B, an agent that prevents assembly of actin, and, reportedly, movement of GPIb. Morphometric analysis revealed that rates of labeling on internal versus external membranes of giant platelets does not differ significantly (0.93 +/- 0.20), provided the OCS is sufficiently dilated. Platelets exposed to cytochalasin B (1.01 +/- 0.31) or to hypertonic conditions (0.96 +/- 0.20) revealed similar ratios for immunogold particles on external and internal membranes. Results of our study indicate that membranes of the exposed surface and lining OCS channels of resting platelets are continuous, identical structures and GPIb is homogeneously distributed on external and internal membranes.

Roles for alpha(2)p24 and COPI in endoplasmic reticulum cargo exit site formation

A two-step reconstitution system for the generation of ER cargo exit sites from starting ER-derived low density microsomes (LDMs; 1.17 g/cc) is described. The first step is mediated by the hydrolysis of Mg(2+)ATP and Mg(2+)GTP, leading to the formation of a transitional ER (tER) with the soluble cargo albumin, transferrin, and the ER-to-Golgi recycling membrane proteins alpha(2)p24 and p58 (ERGIC-53, ER-Golgi intermediate compartment protein) enriched therein. Upon further incubation (step two) with cytosol and mixed nucleotides, interconnecting smooth ER tubules within tER transforms into vesicular tubular clusters (VTCs). The cytosolic domain of alpha(2)p24 and cytosolic COPI coatomer affect VTC formation. This is deduced from the effect of antibodies to the COOH-terminal tail of alpha(2)p24, but not of antibodies to the COOH-terminal tail of calnexin on this reconstitution, as well as the demonstrated recruitment of COPI coatomer to VTCs, its augmentation by GTPgammaS, inhibition by Brefeldin A (BFA), or depletion of beta-COP from cytosol. Therefore, the p24 family member, alpha(2)p24, and its cytosolic coat ligand, COPI coatomer, play a role in the de novo formation of VTCs and the generation of ER cargo exit sites.

Epidermal growth factor and transforming growth factor alpha down-regulate human gastric lipase gene expression

BACKGROUND & AIMS

It was recently reported that human gastric lipase (HGL) activity is modulated by epidermal growth factor (EGF). The aims of this study were to establish the cellular localization of HGL, to assess the correlation between HGL messenger RNA (mRNA) and protein levels, and to establish the molecular mechanism of action of EGF and its homologue transforming growth factor alpha (TGF-alpha) on HGL expression.

METHODS

Cellular localization of HGL was determined by immunohistochemistry using a polyclonal antibody. Enzymic determinations, Western blotting, and Northern hybridization were used to analyze expression of HGL mRNA, protein, lipase activity, and the p42/p44(mapk) activation status.

RESULTS

HGL was localized in the secretory granules of gastric chief cells as early as 13 weeks. A close parallelism was found between the variations of mRNA, protein, and enzymic activity. EGF and/or TGF-alpha down-regulated HGL mRNA levels and decreased enzymic activity. The role of the mitogen-activated protein kinase cascade in the regulation of HGL expression was highlighted by the use of MAP kinase kinase-1/2 inhibitor PD98059, which blunted both the activation of p42/p44(mapk) and the down-regulation of HGL mRNA induced by EGF and/or TGF-alpha.

CONCLUSIONS

The expression of HGL is regulated at the mRNA level, and the down-regulatory action of EGF and/or TGF-alpha on HGL involves the stimulation of p42/p44(mapk) cascade.

The size of sites containing SR proteins in human nuclei. Problems associated with characterizing small structures by immunogold labeling

Some SR proteins are associated with eukaryotic transcripts as they move from synthetic sites (transcription "factories"), through downstream sites, to nuclear pores. Downstream sites can also be isolated as large nuclear ribonucleoprotein particles of approximately 200 S (diameter approximately 50 nm). In ultrathin sections of HeLa nuclei, indirect immunogold labeling with a specific antibody gives many small clusters of approximately 10 gold particles (diameter 50-80 nm). We gauged errors in estimating the diameter of underlying structures marked by immunogold probes (lengths approximately 20 nm). We examined systematically how probe dimensions affected cluster diameter. Probes contained one to three immunoglobulin molecules, sometimes a protein A molecule, and a gold particle of 5-15 nm. We found that (a) immunolabeling particles were tightly packed, (b) reducing particle size by 5 nm reduced cluster diameter by 10 nm, (c) reducing the number of immunoglobulins in the immunolabeling sandwich from three to two reduced cluster diameter by approximately 4 nm, (d) replacing the last immunoglobulin in a sandwich with protein A increased diameter by approximately 7 nm and led to a peripheral concentration of particles, and (e) increasing the number of layers in the sandwich increased sensitivity. Assuming that underlying structures had diameters of 50 nm, we find that errors ranged from -20% to +50%.

Ultrasmall immunogold particles: important probes for immunocytochemistry

In this article, we review the immunocytochemical literature with respect to a comparison between conventional colloidal gold and ultrasmall gold particles as immunoprobes. We discuss the relative advantages and disadvantages of each of these types of particles for immunocytochemical applications. We present results from our own laboratories, in which we compared these immunoprobes in selected experimental situations. In addition, we discuss our work on the use of a fluorescently labeled ultrasmall immunoprobe for correlative microscopy.

Preparation, use, and enlargement of ultrasmall gold particles in immunoelectron microscopy

The introduction of ultrasmall (approximately 1-3 nm) colloidal gold markers in immunoelectron microscopy (IEM) in 1989 has considerably improved the sensitivity of this marker system. Ultrasmall gold markers have opened the field of pre-embedding labeling studies to gold markers without the need of harsh permeabilizing steps. They are recommended for the detection of scarce antigens in ultrathin cryosections which may otherwise escape immunodetection. However, reports concerning the preparation of ultrasmall gold colloids, their conjugation to proteins, and their use in high-resolution studies (without an additional enlargement step) are very limited. Also, the available enlargement techniques necessary for the use of this marker in conventional electron microscopy require detailed discussion to clarify the large number of contradictory observations. The present review summarizes and discusses the findings accumulated within the last 10 years on the application of ultrasmall gold markers in IEM with regard to their merits, limitations, detection sensitivity, and suitability for different labeling techniques. It should provide practical hints for the use of ultrasmall gold colloids and discusses problems arising with enlargement techniques such as silver enhancement and gold toning procedures.

Efficient immunocytochemical labeling of leukocyte microtubules with FluoroNanogold: an important tool for correlative microscopy

We tested the immunoprobe FluoroNanogold (FNG) for its utility as an immunocytochemical labeling reagent. This immunoprobe consists of a 1.4-nm gold particle to which a specific Fab' fragment and a fluorochrome are conjugated. We employed the microtubules (MTs) of human phagocytic leukocytes as a model system for testing the usefulness of FNG as a secondary antibody for immunocytochemistry. We show that these fluorescently labeled ultrasmall immunogold particles are very efficient for labeling MTs in these cells. The signal from FNG can be detected directly by fluorescence microscopy or indirectly by other modes of optical microscopy and electron microscopy, after silver-enhancement of the gold. The spatial resolution of immunolabeled MTs obtained with FNG and silver enhancement was comparable to that of conventional immunofluorescence detection. Colloidal gold (5-nm and 10-nm in diameter), on the other hand, failed to label MTs in cells prepared in a similar manner. This difference in labeling was due in large part to greater penetration of 1.4-nm gold into aldehyde-fixed cells than either 5-nm or 10-nm gold particles. The fluorescent 1.4-nm immunoprobe was shown to be an important new tool for general use in correlative microscopy.

Prohormone convertase PC5 is a candidate processing enzyme for prorenin in the human adrenal cortex

We isolated a cDNA clone encoding the human prohormone convertase PC5 from human adrenal gland mRNA. The deduced protein sequence would encode a 915 amino acid preproPC5 that shares a very high degree of homology with previously cloned rat and mouse homologues. PC5 mRNA was detected in multiple human tissues, including the brain, adrenal and thyroid glands, heart, placenta, lung, and testes. PC5 mRNA was undetectable in the liver and was present at lower levels in skeletal muscle, kidney, pancreas, small intestine, and stomach. Co-transfection of human PC5 and human prorenin expression vectors in cultured GH4C1 cells led to secretion of active renin. The activation of human prorenin by PC5 depended on a pair of basic amino acids at positions 42 and 43 of the prorenin prosegment and occurred only in cells containing dense core secretory granules. Human PC5 was colocalized with renin by immunohistochemistry in the zona glomerulosa of the adrenal gland, suggesting that it could participate in the activation of a local renin-angiotensin system in the human adrenal cortex.

Transport of insulin and albumin by the microvascular endothelium of the rete mirabile

Vascular permeability for albumin and insulin in the continuous capillary network of the rete mirabile of the eel swimbladder was evaluated by ultrastructural immunocytochemistry and countercurrent perfusion experiments. Upon perfusion of the rete capillaries with a buffer solution containing albumin and insulin, these serum proteins were revealed at the electron microscope level, by the Protein A-gold immunocytochemical technique on a post-embedding step. For the simultaneous detection of both proteins, the double labeling technique with different sized gold particles was used. Furthermore, labeling was performed with the mixture of anti-albumin and anti-insulin anti-bodies. The labelings obtained were morphometrically evaluated and demonstrate that: (1) serum proteins such as albumin and insulin are transported by the endothelial cells through their plasmalemmal vesicular system; (2) insulin is transported preferentially to albumin; and (3) this transport involves different populations of plasmalemmal vesicles. Measurements of diffusion permeability coefficients have confirmed the preferential transport of insulin, its coefficient being higher than that of albumin. Conversely, when compared to that of insulin or sucrose, which are assumed to be markers of the paracellular diffusion, it was found to be much lower, indicating that transcytosis through the vesicular system is less efficient than diffusion along the intercellular junctions. These results indicate that transcytosis of insulin and albumin occurs via different sets of plasmalemmal vesicles, probably through receptor-mediated mechanisms, and that the overall rate of transport across the rete capillaries, with respect to paracellular diffusion, is higher for insulin than for albumin.

Improved immuno double labelling for cell and structural biology

Colloidal gold is the most widely used electron dense marker in biological electron microscopy. The development of procedures for making gold particles of very defined sizes has made double or even multiple labelling possible using gold of two or more different sizes. Lately a new type of electron dense marker has been developed consisting of ligand-stabilized metal atom clusters rather than colloidal particles. The differences between these two types of markers are highlighted and the advantages of using metal atom clusters for immuno labelling of certain biological specimens are discussed. Possible methods of distinguishing two such cluster labels in double labelling experiments are reviewed.

Alteration of Chlamydia trachomatis biologic behavior in synovial membranes. Suppression of surface antigen production in reactive arthritis and Reiter's syndrome

OBJECTIVE

To investigate the biologic state of Chlamydia and its surface antigen expression in the synovial membranes of patients with Chlamydia-associated reactive arthritis/Reiter's syndrome (ReA/RS).

METHODS

Expression of chlamydial lipopolysaccharide (LPS), major outer membrane protein (MOMP), and elementary body (EB) antigens was studied by gold labeling immunoelectron microscopy on 6 synovial membrane and 2 synovial fluid (SF) pellet samples from 6 patients with Chlamydia-associated arthritis. The study findings were compared with 24-hour cultures of HeLa cells infected with Chlamydia trachomatis EB.

RESULTS

Persistent C trachomatis infection was found in all 6 synovial membrane samples from patients who had either early or chronic arthritis. The infection persisted despite antibiotic treatment, including a 1-month course of doxycycline therapy. Most persistent organisms were atypical reticulate bodies (RBs) found in both fibroblasts and macrophages. Specific, but weak, immunogold staining for all 3 antibodies was found on both intracellular RBs and extracellular EBs. In the SF samples, Chlamydia surface antigens were detected only in phagosomes containing degraded electron-dense materials.

CONCLUSION

The synovial membrane biopsies conducted in this study of Chlamydia-associated ReA/RS revealed atypical RBs with diminished MOMP and LPS expression. Such altered organisms may escape immune surveillance and contribute to disease chronicity; moreover, these organisms may be difficult to detect and treat in some ReA/RS patients.

The determination of comparable labeling densities in quantitative immunoelectron microscopic double labeling studies

In quantitative ultrastructural studies using colloidal gold immunocytochemical techniques, labeling intensities vary according to the size of the probe used. Using postembedded indirect two-sided double labeling and single labeling protocols, the labeling characteristics of four antigens were studied using two probe sizes commonly used in double labeling studies. It was determined that the labeling intensity variation resulting from the use of different probe sizes was unpredictable after correcting for the increased probe size alone. It was possible, however, to obtain comparable labeling densities by first determining the labeling intensities for each probe size with its antigen in single label studies on serial sections and using the same procedure as the double labeling studies. A probe size correction factor for each antigen was calculated from these data. This factor was used to obtain comparable measurements of the relative abundance of each label.

Molecular chaperones in pancreatic tissue: the presence of cpn10, cpn60 and hsp70 in distinct compartments along the secretory pathway of the acinar cells

Three chaperones, the chaperonins cpn10 and cpn60, and the hsp70 protein, were revealed by immunochemistry and cytochemistry in pancreatic rat acinar cells. Western immunoblotting analysis of rat pancreas homogenates has shown that antibodies against cpn10, cpn60 and hsp70 protein recognize single protein bands of 25 kDa, 60 kDa and 70 kDa, respectively. Single bands for the cpn10 and cpn60 were also detected in pancreatic juice. Immunofluorescence studies on rat pancreatic tissue revealed a strong positive signal in the apical region of the acinar cells for cpn10 and cpn60, while an immunoreaction was detected at the juxtanuclear Golgi region with the anti-hsp70 antibody. Immunocytochemical gold labeling confirmed the presence of these three chaperones in distinct cell compartments of pancreatic acinar cells. Chaperonin 10 and cpn60 were located in the endoplasmic reticulum, Golgi apparatus, condensing vacuoles and secretory granules. Interestingly, the labeling for both cpn10 and cpn60 followed the increasing concentration gradient of secretory proteins along the RER-Golgi-granule secretory pathway. On the contrary, the labeling for hsp70 was mainly concentrated in the endoplasmic reticulum and the Golgi apparatus. In the latter, the hsp70 was found to be primary located in the trans-most cisternae and to colocalize with acid phosphatase in the trans-Golgi network. The three chaperones were also present in mitochondria. In view of the role played by the chaperones in the proper folding, sorting and aggregation of proteins, we postulate that hsp70 assists the adequate sorting and packaging of proteins from the ER to the trans-Golgi network while cpn10 and cpn60 play key roles in the proper packaging and aggregation of secretory proteins as well as, most probably, in the prevention of early enzyme activation in secretory granules.

Biochemical and morpho-cytochemical evidence for the intestinal absorption of insulin in control and diabetic rats. Comparison between the effectiveness of duodenal and colon mucosa

A combined biochemical and morpho-cytochemical investigation was carried out in order to assess insulin absorption by the duodenal and colon epithelium. Insulin was introduced in the lumen of the rat duodenum or colon in combination with sodium cholate and aprotinin. Blood analysis made at several time points has demonstrated a rapid increase in circulating levels of insulin followed by significant and consistent decreases in blood glucose. This indicates that biologically active insulin is absorbed by the intestinal mucosa and transferred to the circulation. Because of the initial high blood glucose levels, the lowering of the glycaemic values was more significant in diabetic animals. Also, levels of circulating insulin remained higher for longer time when the administration was performed in the colon. The integrity of the intestinal wall after insulin administration, evaluated morphologically, was retained. Application of protein A-gold immunocytochemistry has established the pathway for insulin absorption. In both duodenal and colon epithelial cells the labelling for insulin was detected in the endosomal compartment, in the Golgi apparatus and in association with the baso-lateral plasma membrane interdigitations. Some labelling was also present in the interstitial space and in capillary endothelial plasmalemmal vesicles. Insulin introduced in the lumen of the rat duodenum and colon appears thus to be rapidly internalized by the epithelial cells and transferred through a transcytotic pathway to the interstitial space from which it reaches the blood circulation. This exogenous insulin then induces significant decreases in plasma glucose levels which lasts for several hours. The results obtained support the possibility for the clinical development of an oral preparation of insulin.

Immunogold detection of chromogranin A in the neuroendocrine tumor

Immunogold ultrastructural localization of chromogranin A in secretory granules within tumor cells provides convincing evidence of endocrine or neuroendocrine differentiation. A modified immunogold method (designed for use on osmicated tissue) produced positive labeling of small granules not only in well-differentiated tumors but also in poorly differentiated small cell tumors primary in lung, cervix, and skin; only a proportion of granules in some of the tumor cells were positively labeled. Many non-small cell lung tumors often stain focally positive for chromogranin A at the light microscopy level, and such tumors may also contain sparse, small, dense granules. Because positive labeling could not be demonstrated over small granules in non-small cell lung tumors, the theory that such tumors are neuroendocrine in type may be erroneous.

The application of immunogold silver staining (IGSS) for the detection of transmissible gastroenteritis virus in fixed tissues

Protein A-gold (PAG) and a primary porcine antiserum were used in immunogold silver staining (IGSS) for the detection of transmissible gastroenteritis virus (TGEV) in formalin-fixed paraffin-embedded tissue sections of small intestine originating from infected pigs. Immunogold electron microscopy was used to evaluate the reactivity of the prepared PAG marker with the specific porcine TGEV antiserum. Gold particles were closely associated with single virions and immune aggregates of TGEV. When IGSS, using PAG as the marker, was applied to tissue sections, dark staining of TGEV-infected villous enterocytes was observed. Background was low, allowing good visualization by light microscopy of the distribution of viral antigen. Two other gold conjugates, protein A/G-gold (PA/GG) and protein G-gold (PGG), were tested in IGSS. The labeling with PA/GG was comparable to that obtained with PAG. However, no staining was observed when PGG was used. The use of IGSS and PAG offers advantages and may represent a useful technique for the detection of other viral pathogens.

Preparation and use of the poly-L-lysine-gold probe: a differential marker of glomerular anionic sites

The conditions required for the production of a polylysine-coated gold (PL-G) complex, which shows optimal sensitivity for the demonstration of tissue anionic sites, expressed under different conditions of pH have been investigated. Problems encountered with this complex have been compared with those found with other methods of conjugation of polylysine to colloidal gold. The performance of a bovine serum albumin (BSA)-stabilized PL-G complex was examined against other PL-G conjugates, including complexes that are commercially available, for the detection of heterogeneous glomerular anionic site populations, expressed at pH 2.5 and pH 7.0.

Transendothelial transport of serum albumin: a quantitative immunocytochemical study

The steady-state distribution of endogenous albumin in mouse diaphragm was determined by quantitative postembedding protein A-gold immunocytochemistry using a specific anti-mouse albumin antibody. Labeling density was recorded over vascular lumen, endothelium, junctions, and subendothelial space. At equilibrium, the volume density of interstitial albumin was 18% of that in circulation. Despite this large difference in albumin concentration between capillary lumen and interstitium, plasmalemmal vesicles labeling was uniformly distributed across the endothelial profile. 68% of the junctions displayed labeling for albumin, which was however low and confined to the luminal and abluminal sides. The scarce labeling of the endothelial cell surface did not confirm the fiber matrix theory. The kinetics of albumin transcytosis was evaluated by injecting radioiodinated and DNP-tagged BSA. At 3, 10, 30, and 60 min, and 3, 5, and 24 h circulation time, blood radioactivity was measured and diaphragms were fixed and embedded. Anti-DNP antibodies were used to map the tracer in aforementioned compartments. A linear relationship between blood radioactivity and vascular labeling density was found, with a detection sensitivity approaching 1 gold particle per DNP-BSA molecule. Tracer presence over endothelial vesicles reached rapidly (10 min) a saturation value; initially localized near the luminal front, it evolved towards a uniform distribution across endothelium during the first hour. An hour was also needed to reach the saturation limit within the subendothelial space. Labeling of the junctions increased slowly, out of phase with the inferred transendothelial albumin fluxes. This suggests that they play little, if any, role in albumin transcytosis, which rather seems to proceed through the vesicular way.