Identification of endothelial cell-surface proteins as targets for diagnosis and treatment of disease

Multifunctional Nanoparticles in Precise Cancer Treatment: Considerations in Design and Functionalization of Nanocarriers

Nanotechnology has revolutionized cancer treatment in both diagnosis and therapy. Since the initial application of nanoparticles (NPs) in cancer treatment, the main objective of nanotechnology was developing effective nanosystems with high selectivity and specificity for cancer treatment and diagnosis. To achieve this, different encapsulation and conjugation strategies along with surface functionalization techniques have been developed to synthesize anticancer drugs loaded NPs with effective targeting to specific tumor cells. The unique physicochemical attributes of NPs make them promising candidates for targeted drug delivery, localized therapies, sensing, and targeting at cellular levels. However, a nanosystem for localized and targeted cancer managements should overcome several biological barriers and biomedical challenges such as endothelial barriers, blood brain barrier, reticuloendothelial system, selective targeting, biocompatibility, acute/chronic toxicity, tumor-targeting efficacy. The NPs for in vivo applications encounter barriers at system, organ, and the cellular level. To overcome these barriers, different strategies during the synthesis and functionalization of NPs should be adapted. Pharmacokinetics and cellular uptake of NPs are largely associated with physicochemical attributes of NPs, morphology, hydrodynamic size, charge, and other surface properties. These properties can be adjusted during different phases of synthesis and functionalization of the NPs. This study reviews the advances in targeted cancer treatment and the parameters influencing the efficacies of NPs as therapeutics. Different strategies for overcoming the biological barriers at cellular, organ and system levels and biomedical challenges are discussed. Moreover, the applications of NPs in preclinical and clinical practice are reviewed.

Rational design for multifunctional non-liposomal lipid-based nanocarriers for cancer management: theory to practice

Nanomedicines have gained more and more attention in cancer therapy thanks to their ability to enhance the tumour accumulation and the intracellular uptake of drugs while reducing their inactivation and toxicity. In parallel, nanocarriers have been successfully employed as diagnostic tools increasing imaging resolution holding great promises both in preclinical research and in clinical settings. Lipid-based nanocarriers are a class of biocompatible and biodegradable vehicles that provide advanced delivery of therapeutic and imaging agents, improving pharmacokinetic profile and safety. One of most promising engineering challenges is the design of innovative and versatile multifunctional targeted nanotechnologies for cancer treatment and diagnosis. This review aims to highlight rational approaches to design multifunctional non liposomal lipid-based nanocarriers providing an update of literature in this field.

Intracellular delivery of polymeric nanocarriers: a matter of size, shape, charge, elasticity and surface composition

Recent progress in drug discovery has enabled the targeting of specific intracellular molecules to achieve therapeutic effects. These next-generation therapeutics are often biologics that cannot enter cells by mere diffusion. Therefore, it is imperative that drug carriers are efficiently internalized by cells and reach specific target organelles before releasing their cargo. Nanoscale polymeric carriers are particularly suitable for such intracellular delivery. Although size and surface charge have been the most studied parameters for nanocarriers, it is now well appreciated that other properties, for example, particle shape, elasticity and surface composition, also play a critical role in their transport across physiological barriers. It is proposed that a multivariate design space that considers the interdependence of particle geometry with its mechanical and surface properties must be optimized to formulate drug nanocarriers for effective accumulation at target sites and efficient intracellular delivery.

Enrichment of plasma membrane proteins using nanoparticle pellicles: comparison between silica and higher density nanoparticles

Proteomic and other characterization of plasma membrane proteins is made difficult by their low abundance, hydrophobicity, frequent carboxylation, and dynamic population. We and others have proposed that underrepresentation in LC-MS/MS analysis can be partially compensated by enriching the plasma membrane and its proteins using cationic nanoparticle pellicles. The nanoparticles increase the density of plasma membrane sheets and thus enhance separation by centrifugation from other lysed cellular components. Herein, we test the hypothesis that the use of nanoparticles with increased densities can provide enhanced enrichment of plasma membrane proteins for proteomic analysis. Multiple myeloma cells were grown and coated in suspension with three different pellicles of three different densities and both pellicle coated and uncoated suspensions analyzed by high-throughput LC-MS/MS. Enrichment was evaluated by the total number and the spectral counts of identified plasma membrane proteins.

Peptides as targeting elements and tissue penetration devices for nanoparticles

The use of nanoparticles in medicine (nanomedicine) has recently become an intensely studied field. Nanoparticles carrying drugs and imaging agents have already reached the clinic, but they are essentially passive delivery vehicles, not what are referred to as "smart" nanoparticles. An important function to add to make nanoparticles smarter is active homing to the target tissue. It makes nanoparticles accumulate in the target tissue at higher concentrations than would be the case without this feature, increasing therapeutic efficacy and reducing side effects. This review discusses the recent developments in the nanoparticle targeting field with emphasis on peptides that home to vascular "zip codes" in target tissues and provide a tissue- and cell-penetrating function.

Recycling and LFA-1-dependent trafficking of ICAM-1 to the immunological synapse

Little is known about how adhesion molecules on APCs accumulate at immunological synapses. We show here that ICAM-1 on APCs is continuously internalized and rapidly recycled back to the interface after antigen-priming T-cell contact. The internalization rate is high in APCs, including Raji B cells and dendritic cells, but low in endothelial cells. Internalization is significantly reduced by inhibitors of Na(+)/H(+) exchangers (NHEs), suggesting that members of the NHE-family regulate this process. Once internalized, ICAM-1 is co-localized with MHC class II in the polarized recycling compartment. Surprisingly, not only ICAM-1, but also MHC class II, is targeted to the immunological synapse through LFA-1-dependent adhesion. Cytosolic ICAM-1 is highly mobile and forms a tubular structure. Inhibitors of microtubule or actin polymerization can reduce ICAM-1 mobility, and thereby block accumulation at immunological synapses. Membrane ICAM-1 also moves to the T-cell contact zone, presumably through an active, cytoskeleton-dependent mechanism. Collectively, these results demonstrate that ICAM-1 can be transported to the immunological synapse through the recycling compartment. Furthermore, the high-affinity state of LFA-1 on T cells is critical to induce targeted movements of both ICAM-1 and MHC class II to the immunological synapse on APCs.

Strategies in the design of nanoparticles for therapeutic applications

Engineered nanoparticles have the potential to revolutionize the diagnosis and treatment of many diseases; for example, by allowing the targeted delivery of a drug to particular subsets of cells. However, so far, such nanoparticles have not proved capable of surmounting all of the biological barriers required to achieve this goal. Nevertheless, advances in nanoparticle engineering, as well as advances in understanding the importance of nanoparticle characteristics such as size, shape and surface properties for biological interactions, are creating new opportunities for the development of nanoparticles for therapeutic applications. This Review focuses on recent progress important for the rational design of such nanoparticles and discusses the challenges to realizing the potential of nanoparticles.

Proteomics analysis of plasma membrane from liver sinusoidal endothelial cells after partial hepatectomy by an improved two-dimensional electrophoresis

Liver regeneration is an angiogenesis-associated phenomenon. To identify key plasma membrane (PM) proteins of endothelial cells involved in the initiation of angiogenesis during liver regeneration, the PM of liver sinusoidal endothelial cells (LSEC) at 72 h after partial hepatectomy was enriched by an established in vivo membrane density perturbation method. The differentially expressed membrane proteins compared to those from sham operation were quantified using an improved two-dimensional 16-BAC/SDS-PAGE and identified by LC-MS/MS. Several proteins were further confirmed by cICAT labeling quantitative strategy. A total of 47 proteins were identified including known and novel proteins involved in angiogenesis or liver regeneration, such as inducible nitric oxide synthase, type IV collagen, and integrin beta3. Our results indicated that the combination of the membrane density perturbation strategy and the improved two-dimensional electrophoresis (2-DE) method are useful for investigating the endothelial dysfunctions in vivo.

Overcoming key technological challenges in using mass spectrometry for mapping cell surfaces in tissues

Plasma membranes form a critical biological interface between the inside of every cell and its external environment. Their roles in multiple key cellular functions make them important drug targets. However the protein composition of plasma membranes in general is poorly defined as the inherent properties of lipid embedded proteins, such as their hydrophobicity, low abundance, poor solubility and resistance to digestion and extraction makes them difficult to isolate, solubilize, and identify on a large scale by traditional mass spectrometry methods. Here we describe some of the significant advances that have occurred over the past ten years to address these challenges including: i) the development of new and improved membrane isolation techniques via either subfractionation or direct labeling and isolation of plasma membranes from cells and tissues; ii) modification of mass spectrometry methods to adapt to the hydrophobic nature of membrane proteins and peptides; iii) improvements to digestion protocols to compensate for the shortage of trypsin cleavage sites in lipid-embedded proteins, particularly multi-spanning proteins, and iv) the development of numerous bioinformatics tools which allow not only the identification and quantification of proteins, but also the prediction of membrane protein topology, membrane post-translational modifications and subcellular localization. This review emphasis the importance and difficulty of defining cells in proper patho- and physiological context to maintain the in vivo reality. We focus on how key technological challenges associated with the isolation and identification of cell surface proteins in tissues using mass spectrometry are being addressed in order to identify and quantify a comprehensive plasma membrane for drug and target discovery efforts.

Targeting of drugs and nanoparticles to tumors

The various types of cells that comprise the tumor mass all carry molecular markers that are not expressed or are expressed at much lower levels in normal cells. These differentially expressed molecules can be used as docking sites to concentrate drug conjugates and nanoparticles at tumors. Specific markers in tumor vessels are particularly well suited for targeting because molecules at the surface of blood vessels are readily accessible to circulating compounds. The increased concentration of a drug in the site of disease made possible by targeted delivery can be used to increase efficacy, reduce side effects, or achieve some of both. We review the recent advances in this delivery approach with a focus on the use of molecular markers of tumor vasculature as the primary target and nanoparticles as the delivery vehicle.

Caveolae and cancer

All blood vessels are lined by a layer of endothelial cells that help to control vascular permeability. The luminal surface of vascular endothelial cells is studded with transport vesicles called caveolae that are directly in contact with the blood and can transport molecules into and across the endothelium. The vasculature within distinct tissue types expresses a unique array of proteins that can be used to target intravenously injected antibodies directly to that tissue. When the tissue-specific proteins are concentrated in caveolae, the antibodies can be rapidly pumped out of the blood and into the tissue. Tumors appear to be a distinct tissue type with their own unique marker proteins. Targeting accessible proteins at the surface of tumor vasculature with radiolabeled antibodies destroys tumors and drastically increases animal survival. One day, it may be possible to specifically pump targeted molecules into tumors. This could increase therapeutic efficacy and decrease side effects because most of the drug would accumulate specifically in the tumor. Thus, targeting caveolae may provide a universal portal to pump drugs, imaging agents, and gene vectors out of the blood and into underlying tissue.

Targeting and imaging signature caveolar molecules in lungs

A major goal of molecular medicine is to target imaging agents or therapeutic compounds to a single organ. Targeting imaging agents to a single organ could facilitate the high-resolution, in vivo imaging of molecular events. In addition, genetic and acquired diseases primary to a single organ, such as cystic fibrosis, tuberculosis, lung cancer, pulmonary fibrosis, pulmonary hypertension, and acute respiratory distress syndrome, could be specifically targeted in the lung. By targeting and concentrating imaging agents or therapeutics to the lungs, deleterious side effects can be avoided with greater efficacy at much lower dosages. Pathologic changes can be identified earlier and followed over time. In addition, therapeutics that have been abandoned due to toxicities may find renewed utility when coupled with specific targeting agents such as antibodies. To achieve these goals, distinct molecular signatures must be found for each organ or disease-state.

Purification of basolateral integral membrane proteins by cationic colloidal silica-based apical membrane subtraction

Epithelial cell polarity mediates many essential biological functions and perturbation of the apical/basolateral divide is a hallmark of epithelial to mesenchymal transition in carcinoma. Therefore, correct targeting of proteins to the apical and basolateral surfaces is essential to proper epithelial cell function. However, proteomic characterisation of apical/basolateral sorting has been largely ignored, due to ineffectual separation techniques and contamination of plasma-membrane preparations with housekeeping proteins. Here we describe a method that strips the apical membrane from the adherent cells and releases the intracellular contents, thereby leaving the basolateral membrane available for stringent washes and collection. Analysis of the basolateral membrane of an adherent colon adenocarcinoma cell line resulted in 66% of identified proteins being integral membrane proteins, which possessed either a transmembrane domain or lipid modification, including 35 CD antigens. Based on the abundance of peptides from basolateral marker proteins, this method efficiently captures basolateral integral membrane proteins, with minimal contamination from other membranes and basic proteins.

Proteomic identification of endothelial proteins isolated in situ from atherosclerotic aorta via systemic perfusion

The functional and structural alterations of vascular endothelium contribute to the initiation, progression, and complications of atherosclerotic plaque formation, but limited information is known about the molecular composition and pathways underlying pathological changes during atherosclerosis. We have developed an affinity proteomic strategy for in situ isolation and differential mapping of vascular endothelial proteins in normal and atherosclerotic aorta tissues. The selective labeling was carried out by perfusion of the blood vessels with an active biotin reagent for covalent modification of accessible vascular endothelial proteins. The biotinylated proteins were then enriched by streptavidin affinity chromatography, separated by SDS-PAGE, and subsequently characterized by LC-MS/MS. The described procedure led to the identification of 454 distinct proteins in normal and atherosclerotic aorta tissues. A majority of the proteins are plasma membrane associated and extracellular matrix proteins, and 81 showed altered expressions in atherosclerotic aorta tissue. The differentially expressed proteins are involved in immune and inflammatory responses, cell adhesion, and lipid metabolism. The method provides a new avenue for investigating the endothelial dysfunction and development of atherosclerosis.

Preparation of Tissue-Specific Monoclonal Antibodies Using Purified Endothelial Membrane Proteins from Biotinylated Pulmonary Vasculature of Rhesus Monkey

In the present study, we perfused the rhesus lung vascular bed in situ with sulfo-NHS-LC-Biotin to biotinylate its luminal surface membrane proteins. After homogenization, dialysis, and affinity chromatography, biotinylated endothelial membrane proteins were successfully isolated and characterized as enriched endothelial membrane proteins with no contamination of intracellular proteins. When they were used as immunogens to develop monoclonal antibodies (MAbs), three MAbs--TX111, TX112, and TX113--were obtained. Among them, TX111 was demonstrated to specifically bind to rhesus lung tissue by Western blotting and enzymelinked immunosorbent assay (ELISA)--that is, positively stained capillary endothelium of rhesus lung. The molecular weight of the corresponding antigen for TX111 was approximately 70 kDa under reducing conditions. TX111 also reacted with human lung homogenate, but not with rat lung homogenate. These results suggest that (1) the biotinylation method is applicable for isolating endothelial proteins in situ from large animals; (2) anti-human protein MAbs are likely to be obtained using monkey proteins; and (3) TX111 is potentially useful for pulmonary vascular targeting.

Biomedical aspects of targeted delivery of drugs to pulmonary endothelium

Drug targeting to selected subcellular compartments of the pulmonary endothelium may optimise treatment of many diseases. This paper describes endothelial determinants that are potentially useful for such targeting, including endothelial ectopeptidases, cell adhesion molecules and novel candidates identified by high-throughput methods, as well as the means to achieve optimal subcellular targeting of drugs in the endothelium that have been explored in cell culture and animal studies. Criteria for determining the applicability for targeting include accessibility, specificity, safety and subcellular precision. The effects of endothelial delivery of therapeutic agents, including the effects mediated by the intervention in the function of the target determinants, must be characterised in the context of given pathological conditions.

A novel method to isolate and map endothelial membrane proteins from pulmonary vasculature

Vascular endothelium has attracted extensive attention due to its important role in many physiological and pathological processes. Many methods have been developed to study the components and their functions in vascular endothelium. Here we report a novel approach to investigate vascular endothelium using normal rat lungs as the model. We perfused lung vascular beds with sulfosuccinimidyl-6-(biotinamido) hexanoate, a biotin analog, to label endothelial membrane proteins. The biotinylated proteins were isolated from lung homogenate with immobilized monomeric avidin and confirmed to be highly pure endothelial membrane proteins with little contamination of intracellular proteins. These biotinylated proteins were used as immunogens for development of monoclonal antibodies. Indeed, newly generated monoclonal antibodies have revealed different expression patterns of proteins across tissues. Some proteins were found highly specifically expressed to capillary vessels of pulmonary vasculature. This method has also been proven useful for investigating vasculature of other organs, as this study explored.

Molecular targeting of angiogenesis

The majority of pharmacological approaches for the treatment of solid tumors suffer from poor selectivity, thus limiting dose escalation (i.e., the doses of drug which are required to kill tumor cells cause unacceptable toxicities to normal tissues). The situation is made more dramatic by the fact that the majority of anticancer drugs accumulate preferentially in normal tissues rather than in neoplastic sites, due to the irregular vasculature and to the high interstitial pressure of solid tumors. One avenue towards the development of more efficacious and better tolerated anti-cancer drugs relies on the targeted delivery of therapeutic agents to the tumor environment, thus sparing normal tissues. Molecular markers which are selectively expressed in the stroma and in neo-vascular sites of aggressive solid tumors appear to be particularly suited for ligand-based tumor targeting strategies. Tumor blood vessels are accessible to agents coming from the bloodstream, and their occlusion may result in an avalanche of tumor cell death. Furthermore, endothelial cells and stromal cells are genetically more stable than tumor cells and can produce abundant markers, which are ideally suited for tumor targeting strategies. This review focuses on recent advances in the development of ligands for the selective targeting of tumor blood vessels and new blood vessels in other angiogenesis-related diseases.

A novel endocytic pathway induced by clustering endothelial ICAM-1 or PECAM-1

Antibody conjugates directed against intercellular adhesion molecule (ICAM-1) or platelet-endothelial cell adhesion molecule (PECAM-1) have formed the basis for drug delivery vehicles that are specifically recognized and internalized by endothelial cells. There is increasing evidence that ICAM-1 and PECAM-1 may also play a role in cell scavenger functions and pathogen entry. To define the mechanisms that regulate ICAM-1 and PECAM-1 internalization, we examined the uptake of anti-PECAM-1 and anti-ICAM-1 conjugates by endothelial cells. We found that the conjugates must be multimeric, because monomeric anti-ICAM-1 and anti-PECAM-1 are not internalized. Newly internalized anti-ICAM-1 and anti-PECAM-1 conjugates did not colocalize with either clathrin or caveolin, and immunoconjugate internalization was not reduced by inhibitors of clathrin-mediated or caveolar endocytosis, suggesting that this is a novel endocytic pathway. Amiloride and protein kinase C (PKC) inhibitors, agents known to inhibit macropinocytosis, reduced the internalization of clustered ICAM-1 and PECAM-1. However, expression of dominant-negative dynamin-2 constructs inhibited uptake of clustered ICAM-1. Binding of anti-ICAM-1 conjugates stimulated the formation of actin stress fibers by human umbilical vein endothelial cells (HUVEC). Latrunculin, radicicol and Y27632 also inhibited internalization of clustered ICAM-1, suggesting that actin rearrangements requiring Src kinase and Rho kinase (ROCK) were required for internalization. Interestingly, these kinases are part of the signal transduction pathways that are activated when circulating leukocytes engage endothelial cell adhesion molecules, suggesting the possibility that CAM-mediated endocytosis is regulated using comparable signaling pathways.

Proteomics: drug target discovery on an industrial scale

The discovery of targets that are sufficiently robust to yield marketable therapeutics is an enormous challenge. Through the years, several approaches have been used with varying degrees of success. These include target-independent screening of tumor-derived cell lines (disease-dependent), reductionist approaches to identifying crucial elements of disease-affected pathways, disease-independent screening of homologs of previously drugged targets, disease-dependent 'global' examination of gene transcript levels, and disease-dependent global examination of protein expression levels. These endeavors have been enabled by several major advancements in technology, most recently, the sequencing of the human genome. This review identifies the technical issues to be addressed for industrial-scale protein-based discovery in the identification of targets for therapeutic (or diagnostic) intervention. Such approaches aim to direct discovery in a way that increases the probability of robust target identification, and decreases the probability of failure owing to variable expression in this emerging field.

Drug targeting to specific vascular sites

The blood vessels of individual tissues are biochemically distinct, and pathological lesions put their own signature on the vasculature. In tumors, both blood and lymphatic vessels differ from normal vessels. New methods, such as in vivo screening of phage libraries, have provided peptides and antibodies that recognize these vascular signatures and can be used in targeted delivery of therapeutic agents. Targeting a therapy to the diseased tissue enhances the efficacy of the treatment while reducing the side effects in mouse experiments. Results from drug delivery to tumor vessels have been particularly encouraging.

Dermatological aspects of angiogenesis

Neovascularization is vital for the growth of tumours, providing a lifeline for sustenance and waste disposal. Tumour vessels can grow by sprouting, intussusception or by incorporating bone marrow-derived endothelial precursor cells into growing vessels. Recent advances in vascular biology have identified some key factors that control vascular growth, and have led to the hypothesis that in normal tissues vascular quiescence is maintained by the dominant influence of endogenous angiogenesis inhibitors over angiogenic stimuli. In contrast, increased secretion of angiogenic factors and the down-regulation of endogenous angiogenesis inhibitors induce tumour angiogenesis. Vascular quiescence in the skin seems to be primarily maintained by a balance between the endogenous angiogenesis inhibitors thrombospondin 1 and thrombospondin 2 and the potent proangiogenic factor vascular endothelial growth factor A. Inhibiting tumour growth by controlling angiogenesis is an intriguing approach with great potential for the treatment of vascular tumours such as haemangioma, Kaposi's sarcoma and solid cutaneous tumours such as squamous cell carcinoma, melanoma and basal cell carcinoma. In this review, the role of angiogenesis and more recent topics such as lymphangiogenesis in cutaneous tumour growth, invasion and metastasis will be discussed.

Vascular immunotargeting to endothelial surface in a specific macrodomain in alveolar capillaries

A novel 85 kD glycoprotein (gp85) is a marker of the avesicular zone, a thin part of pulmonary endothelial cells separating alveolar and vascular compartments and lacking vesicles. This report presents the first evaluation whether mAb 30B3, a monoclonal antibody to gp85, can be used for targeting of drugs to the surface of lung endothelium. 125I-mAb 30B3 accumulated in isolated perfused lungs (IPL) (22.8 +/- 1.1 versus 0.5 +/- 0.1 %ID/g for 125I-IgG) and accumulated preferentially in the lungs after intravenous or intraarterial injection (10.9 +/- 0.7 and 11.0 +/- 1.5 versus 0.9 +/- 0.2 %ID/g for 125I-IgG). 125I-mAb 30B3 uptake in IPL was rapid (T1/2 15 min), saturable (Bmax appr. 10(5) molecules/cell), specific (inhibited by nonlabeled mAb 30B3) and temperature independent (26.3 +/- 2.1 versus 22.8 +/- 1.1 %ID/g at 6 degrees C versus 37 degrees C). Biotinylated mAb 30B3 permitted subsequent accumulation of perfused avidin derivative in IPL. Because these data indicated that mAb 30B3 binds to an accessible, poorly internalizable antigen in the lung, we conjugated mAb 30B3 with a plasminogen activator, 125I-tPA. After intravenous injection in rats, lung-to-blood ratio was 8.4 +/- 0.9 for mAb 30B3/125I-tPA versus 0.4 +/- 0.1 for IgG/125I-tPA, indicating that mAb 30B3 may deliver drugs, which was supposed to exert therapeutic action in the vascular lumen (e.g., antithrombotic proteins), to the surface of pulmonary endothelium.

Insights into a plasma membrane signature

The plasma membrane (PM) is an organized biological system that serves as a structural barrier and communication interface with the extracellular environment. Many basic questions regarding the PM as a system remain unanswered. In particular, we do not understand the scope of similarity and differences in protein expression at the PM. This study takes an initial step toward addressing these questions by comparing the PM proteomes of fibroblasts and mammary carcinoma cells. Three sets of proteins were revealed by the study. The first set comprises between 9 and 23% of all proteins at the PM and appears to be common to both fibroblasts and mammary carcinoma. A second group of proteins, comprising approximately 40% of the proteins at the PM, is tightly linked to cell lineage. The third set of proteins is unique to each cell line and is independent of cell lineage. It is reasonable to hypothesize then, that this third group of proteins is responsible for unique aspects of cell behavior. In an effort to find proteins linked to the metastatic phenotype, we identified several proteins that are uniquely expressed at the PM of the metastatic MDA-MB-435 cells. These proteins have functions ranging from cell adhesion to the regulation of translation and the control of oxidant stress.

Aberrant T cell responses to myelin antigens during clinical exacerbation in patients with multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of presumed T cell autoimmunity against self myelin. We hypothesized that if myelin-reactive T cells are associated with the disease processes, they may undergo activation and expansion during acute exacerbation. In this study, we examined the precursor frequency, epitope recognition and cytokine profile of myelin-reactive T cells in 14 relapsing/remitting MS patients during exacerbation and remission. The study revealed that T cells recognizing the immunodominant peptides of candidate myelin antigens, including myelin basic protein (MBP), proteolipid protein and myelin oligodendrocyte glycoprotein, occurred at increased precursor frequency during acute exacerbation. The T cell responses to MBP focused on the immunodominant regions (residues 83-99 and 151-170) during exacerbation and shifted toward other epitopes of MBP at the time of remission. Furthermore, there was a marked increase in the production of T(h)1 cytokines among T cell lines obtained during exacerbation compared to those obtained during remission. The study demonstrated that myelin-reactive T cells underwent selective activation and expansion during acute MS exacerbation. In contrast, myelin-reactive T cells found during remission in the same patients generally resembled those identified in healthy controls with some discrepancies. The findings suggest potential association of aberrant myelin-reactive T cell responses with acute exacerbation in MS, which may reflect transient activation of myelin-reactive T cell populations of pathogenic potential.

An address system in the vasculature of normal tissues and tumors

The vasculature of individual tissues is highly specialized. The endothelium in lymphoid tissues expresses tissue-specific receptors for lymphocyte homing, and recent work utilizing phage homing has revealed an unprecedented degree of specialization in the vasculature of other normal tissues. In vivo screening of libraries of phage that displace random peptide sequences on their surfaces has yielded specific homing peptides for a large number of normal tissues. The tissue-specific endothelial molecules to which the phage peptides home may serve as receptors for metastasizing malignant cells. Probing of tumor vasculature has yielded peptides that home to endothelial receptors expressed selectively in angiogenic neovasculature. These receptors, and those specific for the vasculature of individual normal tissues, are likely to be useful in targeting therapies to specific sites.

Cationic colloidal silica membrane perturbation as a means of examining changes at the sinusoidal surface during liver regeneration

By employing the cationic colloidal silica membrane density perturbation technique, we examined growth factor receptor and extracellular matrix (ECM) changes at the sinusoidal surface during rat liver regeneration 72 hours after 70% partial hepatectomy (PHx). At this time after PHx, hepatocyte division has mostly subsided, while sinusoidal endothelial cell (SEC) proliferation is initiating, resulting in avascular hepatocyte islands. Because of the discontinuous nature of the surface of liver SEC, ECM proteins underlying the SEC, as well as SEC luminal membrane proteins, are available to absorption to the charged silica beads when the liver is perfused with the colloid. Subsequent liver homogenization and density centrifugation yield two separate fractions, enriched in SECs as well as hepatocyte basolateral membrane-specific proteins up to 50-fold over whole liver lysates. This technique facilitates examination of changes in protein composition that influence or occur as a result of SEC mitogenesis and migration during regeneration of the liver. When ECM and receptor proteins from SEC-enriched fractions were examined by Western immunoblotting, urokinase plasminogen activator receptor, fibronectin, and plasmin increased at the SEC surface 72 hours after PHx. Epidermal growth factor receptor, plasminogen, SPARC (secreted protein, acidic and rich in cysteine, also called osteonectin or BM40), and collagen IV decreased, and fibrinogen subunits and c-Met expression remained constant 72 hours after PHx when compared to control liver. These results display the usefulness of the cationic colloidal silica membrane isolation protocol. They also show considerable modulation of surface components that may regulate angiogenic processes at the end stage of liver regeneration during the reformation of sinusoids.

Opposite sorting and transcytosis of the polymeric immunoglobulin receptor in transfected endothelial and epithelial cells

We have transfected a polarised endothelial cell line, ECV 304, and an epithelial cell line, MDCK, with a well characterised epithelial protein, the rat polymeric immunoglobulin receptor (pIgR), in order to study the protein sorting and transcytosis in endothelial cells. The expressed protein was normally processed and the steady state distribution between apical and basolateral surfaces was similar in both cell types. MDCK cells, however, showed a marked polarity in the delivery of newly synthesised pIgR to the cell surface, and in the release of secretory component. 88% of newly synthesised pIgR in MDCK cells was first delivered to the basolateral surface and 99% of secretory component was released from the apical surface. In contrast the basolateral targeting signal of pIgR was only partially recognised in endothelial cells, with 63% of the newly synthesised pIgR being first delivered to the basolateral surface. At steady state only 43% of the pIgR was found on the basolateral membrane. The direction of dimeric IgA transcytosis in endothelial cells was from apical to basolateral surfaces, opposite to that in MDCK cells. These data suggest that endothelial cells poorly recognise the targeting signals of proteins from epithelial cells, and that the direction of transcytosis is linked to the biological role of the cells.

An integrated approach to proteome analysis: identification of proteins associated with cardiac hypertrophy

Hypertrophy of cardiac myocytes is a primary response of the heart to overload, and is an independent predictor of heart failure and death. Distinct cellular phenotypes are associated with hypertrophy resulting from different causes. These phenotypes have been described by others at the molecular level by analysis of gene transcription patterns. An alternative approach is the analysis of large-scale protein expression patterns (the proteome) by two-dimensional polyacrylamide gel electrophoresis. Realization of this goal requires the ability to rigorously analyze complex 2D gel images, efficiently digest individual gel isolated proteins (especially those expressed at low levels), and analyze the resulting peptides with high sensitivity for rapid database searches. We have undertaken to improve the technology and experimental approaches to these challenges in order to effectively study a cell culture model for cardiac hypertrophy. The 2D gel patterns for cell lysates from multiple samples of cardiac myocytes with or without phenylephrine-induced hypertrophy were analyzed and spots which changed in abundance with statistical significance were located. Eleven such spots were identified using improved procedures for in-gel digestion of silver-stained proteins and high-sensitivity mass spectrometry. The incorporation of low levels of sodium dodecyl sulfate into the digestion buffer improved peptide recovery. The combination of matrix-assisted laser desorption mass spectrometry for initial measurements and capillary liquid chromatography-ion trap mass spectrometry for peptide sequence determination yielded efficient protein identification. The integration of 2D gel image analysis and routine identification of proteins present in gels at the subpicomole level represents a general model for proteome studies relating genomic sequence with protein expression patterns.