Two-dimensional gels for toxicological drug discovery applications

Two-dimensional gel electrophoresis (2DGE) continues to be a useful approach to study protein expression. Although liquid chromatographic and mass spectrometric approaches that overcome some of the limitations and labour intensity of 2DGE are increasingly popular, this electrophoretic approach still has exceptional relevance in toxicology. Despite the technical challenges, pharmacologists/toxicologists continue to use gel-based proteomics to assess the biological and health effects of chemical treatment and exposure. This brief review addresses the use of 2DGE-based proteomics in drug development and toxicology, emphasising its unique strengths and weaknesses, and considers recent developments in this strategy that have evolved to directly confront the issues of dynamic range and reproducibility that have previously limited the overall use of 2D electrophoresis.     

Target identification and validation in drug discovery: the role of proteomics

Proteomics, the study of cellular protein expression, is an evolving technology platform that has the potential to identify novel proteins involved in key biological processes in the cell that may serve as potential drug targets. While proteomics has considerable theoretical promise, individual cells/tissues have the potential to generate many millions of proteins while the current analytical technologies that involve the use of time-consuming two dimensional gel electrophoresis (2DIGE) and various mass spectrometry (MS) techniques are unable to handle complex biological samples without multiple high-resolution purification steps to reduce their complexity. This can significantly limit the speed of data generation and replication and requires the use of bioinformatic algorithms to reconstitute the parent proteome, a process that does not always result in a reproducible outcome. In addition, membrane bound proteins, e.g., receptors and ion channels, that are the targets of many existing drugs, are not amenable to study due, in part, to limitations in current proteomic techniques and also to these being present in low abundance and thus disproportionally represented in proteome profiles. Subproteomes with reduced complexity have been used to generate data related to specific, hypothesis-driven questions regarding target identification, protein-interaction networks and signaling pathways. However progress to date, with the exception of diagnostic proteomics in the field of cancer, has been exceedingly slow with an inability to put such studies in the context of a larger proteome, limiting the value of the information. Additionally the pathway for target validation (which can be more accurately described at the preclinical level as target confidence building) remains unclear. It is important that the ability to measure and interrogate proteomes matches expectations, avoiding a repetition of the disappointment and subsequent skepticism that accompanied what proved to be unrealistic expectations for the rapid contribution of data based on the genome maps, to biomedical research.     

An Integrated Quantitative Proteomics and Systems Biology Approach to Explore Synaptic Protein Profile Changes During Morphine Exposure

Morphine is a classic analgesic for the treatment of chronic pain. However, its repeated use is known to produce tolerance, physical dependence, and addiction; these properties limit its long-term therapeutic use and this has led to a quest for therapeutics without these unwanted side effects. Understanding the molecular changes in response to long-term use of morphine is likely to aid in the development of novel therapeutics for the treatment of pain. Studies examining the effects of chronic morphine administration have reported alterations in gene expression, synapse morphology, and synaptic transmission implying changes in synaptic protein profile. To fully understand the changes in protein profiles, proteomic techniques have been used. Studies using two-dimensional gel electrophoresis of various brain regions combined with mass spectrometry have found alterations in the levels of a number of proteins. However, neither the changes in brain regions relevant to morphine effects nor changes in the abundance of synaptic proteins have been clearly delineated. Recent studies employing subcellular fractionation to isolate the striatal synapse, combined with quantitative proteomics and graph theory-inspired network analyses, have begun to quantify morphine-regulated changes in synaptic proteins and facilitate the generation of networks that could serve as targets for the development of novel therapeutics for the treatment of chronic pain. Thus, an integrated quantitative proteomics and systems biology approach can be useful to identify novel targets for the treatment of pain and other disorders of the brain.     

A review on proteomics analysis to reveal biological pathways and predictive proteins in sulfur mustard exposed patients: roles of inflammation and oxidative stress

Sulfur mustard (SM) is a mutagenic compound that targets various organs. Although it causes a wide range of abnormalities, cellular and molecular mechanisms of its action are not-well-understood. Oxidation of DNA, proteins, lipids, as well as depletion of cellular nicotinamide adenine dinucleotide (NAD), antioxidants and increase of intracellular calcium are the hypothesized mechanisms of its action at the acute phase of injury. In this review, the proteome analysis of SM toxicity has been considered. We selected articles that considered proteomics analysis of SM toxicity with two-dimensional gel electrophoresis (2DE) followed by mass spectrometry. Our search yielded nine related articles, four original in vitro and five human studies. The results of these studies have revealed a change in expression pattern of various proteins such as haptoglobin, amyloid A1, surfactant proteins, S100 proteins, apolipoprotein, Vit D binding protein, transferrin, alpha 1 antitrypsin, protein disulfide isomerase and antioxidant enzymes in patients who were exposed to SM about 30 years ago. Most of these proteins are up- or down-regulated in response to excessive production of reactive oxygen species (ROS) and oxidative stress (OS). There is a tight link between the expression pattern of these proteins with accumulation of leukocytes, inflammatory conditions, antioxidant depletion, mitochondrial deficiency, as well as increased expression or activity of several proteases such as caspases and matrix metalloproteinases (MMPs). Therefore, excessive production of ROS and OS along with chronic inflammatory may be the long-term toxic effects of SM following acute exposure.     

Tracking cell signaling protein expression and phosphorylation by innovative proteomic solutions

The most challenging and fruitful biomedical research endeavor of this decade will be the mapping of cell signaling systems and establishing their linkages to normal and disease-related processes. Amongst other things, the Human Genome Sequencing Project has greatly facilitated MALDI-TOF mass spectrometry identification of proteins that have been resolved by standard 2D gel electrophoresis. However, the low abundance of protein kinases and other signal transduction proteins has rendered their analyses particularly problematic without some means of purification and enrichment from cell and tissue lysates. Antibodies have been the most specific affinity probes for tracking target proteins, but their variable quality and high cost preclude their deployment in most discovery-based proteomics studies. Current multi-immunoblotting techniques can permit the probing of a single mini-SDS-PAGE gel with 50 or more antibodies at a time to monitor large changes in the expression and phosphorylation states of signaling proteins. The development of new affinity probes to replace antibodies is necessary to drive large scale proteomics studies. Such affinity probes could include short peptide antibody mimetics (PAM's) and oligonucleotide aptamers that when spotted in 2D array formats (e.g. membrane macroarrays, glass microarrays) or presented on specific beads (e.g. Luminex beads) can capture target proteins for their specific enrichment. The bound target proteins can then be detected using reporter antibodies or other specific probes for their quantitation by high throughput systems. These new proteomics methodologies will accelerate assessment of specific protein expression, post-translational modification, protein-protein interactions and protein-drug interactions to provide a more holistic view of cellular operations and how they might be manipulated under pathological circumstances.     

Search for breast cancer-related biomarker proteins for drug discovery

The identification of biomarkers is a promising approach for the diagnosis and effective therapy of cancer. In particular, disease proteomics is a potentially useful method for identifying such biomarkers. However, very few biomarker proteins for drug development have been discovered using this approach. The main difficulty is to efficiently select potential biomarkers from the many candidate proteins identified by the proteomics approach. To circumvent this problem, we have developed "antibody proteomics technology" that can screen for biomarker proteins by isolating antibodies against each candidate in a rapid and comprehensive manner. Here, we applied "antibody proteomics technology" to breast cancer-related biomarker discovery and evaluated the utility of this novel technology. Cell extracts derived from breast tumor cells (SKBR3) and normal cells (184A1) were analyzed by two-dimensional differential gel electrophoresis (2D-DIGE) to identify proteins over-expressed in the tumor cells. Candidate proteins were extracted from the gel pieces, immobilized onto a nitrocellulose membrane using a dot blot apparatus and then used as target antigens in scFv-phage enrichment and selection. Following this in vitro phage selection procedure, scFvs binding to 21 different over-expressed proteins in tumor cells were successfully isolated within several weeks. The expression profiles of the identified proteins were then determined by tissue microarray analysis using the scFv-phages. Consequently, we identified three breast tumor-specific proteins. Our data demonstrates the utility of an antibody proteomics system for discovering and validating tumor-related proteins in pharmaceutical proteomics. Currently, we are analyzing the functions of these proteins to use them as diagnostic markers or therapeutic targets.     

Proteomic analysis in cardiovascular diseases

1. Cardiovascular diseases are a major cause of morbidity and mortality in western countries. The molecular mechanisms responsible for heart dysfunction are still largely unknown, except in cases of genetic defects or alteration of genes and proteins. 2. The publication of genome sequences from humans and other species has demonstrated the complexity of biology, including the finding that one gene does not encode for only one protein but for several, due to mRNA splicing and post-translational modifications. 3. Proteomic analysis can provide an overall understanding of changes in the levels of protein expression. Differential proteomics is a powerful tool for improving our understanding of integrated biochemical responses. The main techniques used are two-dimensional electrophoresis (2D-gel) and Surface-Enhanced Laser Desorption/Ionization Time of Flight (SELDI-TOF) to separate proteins associated with mass spectrometry. Bioinformatic tools make it possible to compare protein profiles obtained from diverse biological samples. 4. The combination of these approaches has proved to be particularly interesting for studying cardiovascular diseases and thereby improving our understanding of the mechanisms involved and identifying new biochemical factors and biomarkers involved in these diseases.     

Capillary electrophoresis–mass spectrometry: Recent trends in clinical proteomics

The increasing attention now paid to the elucidation of human proteome strengthened the development of analytical instruments able to provide reliable proteins and peptides quantitation and characterization in biological fluids and tissues. Emerging from proteomics, clinical proteomics exclusively considers its biomedical applications. It evaluates, often by high-throughput comparative platforms, the protein and peptide variations in body fluids, cells and tissues under different physiological and pathological conditions with the aim of discovering disease biomarkers. Among the available analytical methodologies, mass spectrometry in coupling with liquid chromatography or capillary electrophoresis demonstrated to be the eligible technique for protein detection and identification. This review summarizes the most recent applications of capillary electrophoresis–mass spectrometry to clinical proteomics, focusing on capillary zone electrophoresis separation mode and ESI and MALDI ionizations, which are the most frequently applied capillary electrophoresis–mass spectrometry hyphenated techniques.     

Proteomics: recent applications and new technologies

Interest in proteomics as a tool for drug development and a myriad of other applications continues to expand at a rapid rate. Proteomic analyses have recently been conducted on tissues, biofluids, subcellular components and enzymatic pathways as well as various disease and toxicological states, in both animal models and man. In addition, several recent studies have attempted to integrate proteomics data with genomics and/or metabonomics data in a systems biology approach. The translation of proteomic technology and bioinformatics tools to clinical samples, such as in the areas of disease and toxicity biomarkers, represents one of the major opportunities and challenges facing this field. An ongoing challenge in proteomics continues to be the analysis of the serum proteome due to the vast number and complexity of proteins estimated to be present in this biofluid. Aside from the removal of the most abundant proteins, a number of interesting approaches have recently been suggested that may help reduce the overall complexity of serum analysis. In keeping with the increasing interest in applications of proteomics, the tools available for proteomic analyses continue to improve and expand. For example, enhanced tools (such as software and labeling procedures) continue to be developed for the analysis of 2D gels and protein quantification. In addition, activity-based probes are now being used to tag, enrich and isolate distinct sets of proteins based on enzymatic activity. One of the most active areas of development involves microarrays. Antibody-based microarrays have recently been released as commercial products while numerous additional capture agents (e.g. aptamers) and many additional types of microarrays are being explored.     

The use of proteomics to study infectious diseases

Technology surrounding genomics, or the study of an organism's genome and its gene use, has advanced rapidly resulting in an abundance of readily available genomic data. Although genomics is extremely valuable, proteins are ultimately responsible for controlling most aspects of cellular function. The field of proteomics, or the study of the full array of proteins produced by an organism, has become the premier arena for the identification and characterization of proteins. Yet the task of characterizing a proteomic profile is more complex, in part because many unique proteins can be produced by the same gene product and because proteins have more diverse chemical structures making sequencing and identification more difficult. Proteomic profiles of a particular organism, tissue or cell are influenced by a variety of environmental stimuli, including those brought on by infectious disease. The intent of this review is to highlight applications of proteomics used in the study of pathogenesis, etiology and pathology of infectious disorders. While many infectious agents have been the target of proteomic studies, this review will focus on those infectious diseases which rank among the highest in worldwide mortalities, such as HIV/AIDS, tuberculosis, malaria, measles, and hepatitis.     

Clinical proteomics in cancer research-promises and limitations of current two-dimensional gel electrophoresis

Cancer can be defined as a deviated protein network system toward dysregulated cellular proliferation. Alteration in the content and functional state of the proteins with many linkages may shift the equilibrium state of the protein signaling network to enhance a survival advantage of the affected cells. Searching for such hub proteins is the main purpose of the cancer proteomics. Although the progression in the vanguard proteomic technologies would largely contribute to cancer diagnosis and treatment in the future, the technology most frequently used for the analysis of clinical tissue samples is the two-dimensional gel electrophoresis (2DE) combined with matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). Accumulation of 2DE data has generated many candidate biomarkers with potential clinical value. The identified proteins are restricted to a subset of the predicted human proteome, and ubiquitously exist in all normal cells taking important roles in the basic biological functions. Although these proteins can be used as valuable prognostic markers, the low-abundance proteins which is tissue-specific and useful as diagnostic markers could not easily be found by the standard 2DE technology alone. None of the current proteomic technologies can identify the whole proteome by themselves. Adequate combinations of different approaches not only in proteomics but in immunological methods would be necessary for the tissue specific markers.     

The Critical Roles of Zinc: Beyond Impact on Myocardial Signaling

Zinc has been considered as a vital constituent of proteins, including enzymes. Mobile reactive zinc (Zn²⁺) is the key form of zinc involved in signal transductions, which are mainly driven by its binding to proteins or the release of zinc from proteins, possibly via a redox switch. There has been growing evidence of zinc''s critical role in cell signaling, due to its flexible coordination geometry and rapid shifts in protein conformation to perform biological reactions. The importance and complexity of Zn²⁺ activity has been presumed to parallel the degree of calcium''s participation in cellular processes. Whole body and cellular Zn²⁺ levels are largely regulated by metallothioneins (MTs), Zn²⁺ importers (ZIPs), and Zn²⁺ transporters (ZnTs). Numerous proteins involved in signaling pathways, mitochondrial metabolism, and ion channels that play a pivotal role in controlling cardiac contractility are common targets of Zn²⁺. However, these regulatory actions of Zn²⁺ are not limited to the function of the heart, but also extend to numerous other organ systems, such as the central nervous system, immune system, cardiovascular tissue, and secretory glands, such as the pancreas, prostate, and mammary glands. In this review, the regulation of cellular Zn²⁺ levels, Zn²⁺-mediated signal transduction, impacts of Zn²⁺ on ion channels and mitochondrial metabolism, and finally, the implications of Zn²⁺ in health and disease development were outlined to help widen the current understanding of the versatile and complex roles of Zn²⁺.     

Applying proteomics to drug discovery

Proteomics is a technology that has come to prominence over the last few years largely as a result of the advances that have been made in the equipment and software associated with the performance and analysis of two dimensional (2D) gel electrophoresis. With this technique it is now possible to resolve and identify proteins on 2D gels with a high degree of reproducibility and sensitivity. This facilitates the detection and quantification of thousands of proteins from complex biological samples in a single analysis and, more significantly, the comparison of these data accurately and reproducibly between samples. Thus, qualitative and quantitative assessments of changes are possible between the healthy and diseased state, in the presence and absence of drug, or between responders and non-responders. The added ability of carrying out such analysis at a high throughput opens up the possibilities for using proteomics to great effect throughout the drug discovery process. This review outlines the proteomic process and indicates areas where its potential has begun to be realised.     

Bacterial proteomics and vaccine development

Until recently, the development of vaccines for use in humans relied on the response to attenuated or whole-cell preparations, or empirically selected antigens. The post-genomic era holds the possibility of rational design of novel vaccines for important human pathogens. The discovery and development of these new vaccines is likely to be accomplished through integrated proteomic strategies. Although most proteomic studies are based on two-dimensional gel electrophoresis (2D-PAGE) as a separation technique, new methods have been developed within the past two years that provide complementary information concerning microbial protein expression. The 2D-PAGE technique in combination with Western blotting has been successfully applied in the discovery of antigens from Helicobacter pylori, Chlamydia trachomatis and Borrelia garinii. Two-dimensional semi-preparative electrophoresis has provided complementary information regarding membrane protein expression in a strain of H. pylori. Through two-dimensional liquid chromatography-tandem mass spectrometry, the most comprehensive information to date regarding protein expression in yeast was obtained. This technique may shortly become an important tool in vaccinology. This review of the current state of bacterial proteomics as applied in vaccinology presents analytical techniques for protein separation, proteomics without gels, reverse vaccinology, and functional approaches to the identification of virulence proteins in microbes.     

Redox proteomic analysis of mytilus edulis gills: effects of the pharmaceutical diclofenac on a non‐target organism

Veterinary and human pharmaceuticals are an emerging category of chemical pollutants with potential to cause serious toxicity to non‐target organisms. Filter‐feeding aquatic organisms such as mussels are especially threatened. In this study, the blue mussel, Mytilus edulis, was exposed to two doses (0.2 mg/L and 1 mg/L) of the anti‐inflammatory diclofenac. Effects on the gill, the principal feeding organ of mussels, were investigated. It was noted that, while no effect was evident on gill glutathione transferase or catalase activities, there was a tissue‐specific increase in glutathione reductase activity and reduction in total protein thiol groups. Two dimensional electrophoresis was performed and some affected proteins identified by in‐gel tryptic digestion and peptide mass fingerprinting. Of these, four unique proteins (caspase 3/7‐4, heat‐shock cognate protein 70, a predicted enolase‐like protein, arginine kinase) were found to be oxidized whilst eight unique proteins (β‐tubulin, actin, isocitrate dehydrogenase, arginine kinase, heavy metal‐binding HIP, cytosolic malate dehydrogenase, proteasome subunit alpha type 2, Mg: bb02e05 (glyceraldehyde‐3‐phosphate dehydrogenase) and superoxide dismutase) were found to have altered abundance. In addition, bioinformatic analysis suggested putative identities for six hypothetical proteins which either were oxidized or decreased in abundance. These were; 78 kDa glucose‐regulated protein precursor, α‐enolase, calreticulin, mitochondrial H + ‐ATPase, palmitoyl protein thioesterase 1 and initiation factor 5a. It is concluded that diclofenac causes significant oxidative stress to gills and that this affects key structural, metabolic and stress‐response proteins. Copyright © 2015 John Wiley & Sons, Ltd.     

Differentiating Two Closely Related Alexandrium Species Using Comparative Quantitative Proteomics

Alexandrium minutum and Alexandrium tamutum are two closely related harmful algal bloom (HAB)-causing species with different toxicity. Using isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics and two-dimensional differential gel electrophoresis (2D-DIGE), a comprehensive characterization of the proteomes of A. minutum and A. tamutum was performed to identify the cellular and molecular underpinnings for the dissimilarity between these two species. A total of 1436 proteins and 420 protein spots were identified using iTRAQ-based proteomics and 2D-DIGE, respectively. Both methods revealed little difference (10–12%) between the proteomes of A. minutum and A. tamutum, highlighting that these organisms follow similar cellular and biological processes at the exponential stage. Toxin biosynthetic enzymes were present in both organisms. However, the gonyautoxin-producing A. minutum showed higher levels of osmotic growth proteins, Zn-dependent alcohol dehydrogenase and type-I polyketide synthase compared to the non-toxic A. tamutum. Further, A. tamutum had increased S-adenosylmethionine transferase that may potentially have a negative feedback mechanism to toxin biosynthesis. The complementary proteomics approach provided insights into the biochemistry of these two closely related HAB-causing organisms. The identified proteins are potential biomarkers for organismal toxicity and could be explored for environmental monitoring.     

A new approach to pharmacogenomics

The medicine in the 21st century will be so called "evidence based medicine" or "personalized medicine," based on the principle of "right drug to right patient." Pharmacogenomics covers the entire spectrum of genes that determines drug behavior and sensitivity, and we anticipate it will bring major impact on the healthcare system as well as the drug discovery process in the near future. Three waves of genomic impact are predicted to arise as follows: The first wave will hit on existing drugs and late-phase development candidates within the next 2-3 years, aiming to minimize the risks in clinical trials (adverse events, resistance, etc.). The wave will then affect the candidate selection process in the early pre-development stage, and finally the disease gene finding to target discovery process. The driving force will be technologies such as SNPs database, differential gene expression (DGE) analysis, proteomics, serial analysis of gene expression (SAGE) and bioinformatics. This new approach of genomic discovery (so called "integrated approach") requires knowledge on how to implement and integrate new valuable technologies from an early stage of the discovery process. The implication of SNPs, high throughput proteomics and application of structural genomics will be the key issues in the pharmacogenomics era.