Body Fluid Proteome Research Articles

HBFP: a new repository for human body fluid proteome.

Body fluid proteome has been intensively studied as a primary source for disease biomarker discovery. Using advanced proteomics technologies, early research success has resulted in increasingly accumulated proteins detected in different body fluids, among which many are promising biomarkers. However, despite a handful of small-scale and specific data resources, current research is clearly lacking effort compiling published body fluid proteins into a centralized and sustainable repository that can provide users with systematic analytic tools. In this study, we developed a new database of human body fluid proteome (HBFP) that focuses on experimentally validated proteome in 17 types of human body fluids. The current database archives 11 827 unique proteins reported by 164 scientific publications, with a maximal false discovery rate of 0.01 on both the peptide and protein levels since 2001, and enables users to query, analyze and download protein entries with respect to each body fluid. Three unique features of this new system include the following: (i) the protein annotation page includes detailed abundance information based on relative qualitative measures of peptides reported in the original references, (ii) a new score is calculated on each reported protein to indicate the discovery confidence and (iii) HBFP catalogs 7354 proteins with at least two non-nested uniquely mapping peptides of nine amino acids according to the Human Proteome Project Data Interpretation Guidelines, while the remaining 4473 proteins have more than two unique peptides without given sequence information. As an important resource for human protein secretome, we anticipate that this new HBFP database can be a powerful tool that facilitates research in clinical proteomics and biomarker discovery.Database URL: https://bmbl.bmi.osumc.edu/HBFP/

Integrative analysis of cell state changes in lung fibrosis with peripheral protein biomarkers

The correspondence of cell state changes in diseased organs to peripheral protein signatures is currently unknown. Here, we generated and integrated single‐cell transcriptomic and proteomic data from multiple large pulmonary fibrosis patient cohorts. Integration of 233,638 single‐cell transcriptomes (n = 61) across three independent cohorts enabled us to derive shifts in cell type proportions and a robust core set of genes altered in lung fibrosis for 45 cell types. Mass spectrometry analysis of lung lavage fluid (n = 124) and plasma (n = 141) proteomes identified distinct protein signatures correlated with diagnosis, lung function, and injury status. A novel SSTR2+ pericyte state correlated with disease severity and was reflected in lavage fluid by increased levels of the complement regulatory factor CFHR1. We further discovered CRTAC1 as a biomarker of alveolar type‐2 epithelial cell health status in lavage fluid and plasma. Using cross‐modal analysis and machine learning, we identified the cellular source of biomarkers and demonstrated that information transfer between modalities correctly predicts disease status, suggesting feasibility of clinical cell state monitoring through longitudinal sampling of body fluid proteomes.

Ampholine immobilized polymer microspheres for increasing coverage of human urinary proteome

Urinary proteome, as an important component of body fluid proteome, could reflect kidney, urogenital tract function and pathological changes of human organs. This study reports a convenient strategy for urine proteome analysis through ampholine immobilized polymer microsphere (ampholine@PM) fractionation strategy. After ampholine@PM treatment, 16,543 unique peptides corresponding to 2173 non-redundant urinary proteins were identified, while only 856 proteins, corresponding to 3524 peptides were identified in the crude urine sample. The number of proteins and peptides was increased by 1.54 and 3.69 times, respectively. 31 urinary candidate biomarkers have also been identified (17 candidate biomarkers of glomerular injury and 14 candidate biomarkers of tubular injury), showing the potential of our strategy in urinary biomarker discovery study. In additional to the urine proteome, N-glycoproteome analysis was also performed after ampholine@PM fractionation followed by the N-glycopeptides enrichment. The number was increased from 144 to 281 for N-glycoproteins, 261 to 709 for N-glycopeptides, and 226 to 493 for N-glycosylation sites, after ampholine@PM treatment. Based on the significant increase on the identified N-glycoprotein number, ampholine@PM fractionation strategy also offered a beneficial tool for the post translational modification analysis of urine proteome.

Integrated Single Cell Analysis of Human Lung Fibrosis Resolves Cellular Origins of Predictive Protein Signatures in Body Fluids

Single cell genomics enables characterization of disease specific cell states, while improvements in mass spectrometry bring the clinical use of body fluid proteomics within reach. The correspondence of cell state changes in diseased organs to peripheral protein signatures is currently unknown. Here, we leverage single-cell RNA-seq and proteomic analysis of large pulmonary fibrosis patient cohorts to identify disease specific changes on the cellular level and their corresponding reflection in body fluid proteomes. We discovered and validated transcriptional changes in 45 cell types across three patient cohorts that translated into distinct changes in bronchoalveolar lavage fluid and plasma proteomes. These protein signatures correlated with diagnosis, lung function, smoking and injury status. Specifically, the altered expression of a novel marker of lung health, CRTAC1, in alveolar epithelium is robustly reflected in patient plasma. Our findings have direct implications for future non-invasive prediction and monitoring of pathological cell state changes in patient organs.

Comparative Glycoproteomic Profiling of Human Body Fluid between Healthy Controls and Patients with Papillary Thyroid Carcinoma.

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer among women worldwide. It is confirmed mainly by fine-needle aspiration biopsy (FNAB), an invasive diagnostic method. The key proteins responsible for thyroid hormone biosynthesis are glycosylated. Hence, changes in site-specific glycosylation are associated with thyroid cancer. Integrated quantitative proteomic and glycoproteomic analyses of body fluids from patients with PTC may identify potential noninvasive biomarkers, improve diagnostic accuracy, and elucidate the basic mechanisms of tumor development. In the present study, we demonstrate an integrated, highly reproducible, rapid method involving body fluid proteome and glycoproteome analysis. Moreover, this method may quantitatively profile protein glycosylation. Intact N-glycopeptides from the urine and plasma of healthy controls (HC), PTC, and PTC with Hashimoto's thyroiditis (PHT) were enriched by hydrophilic interaction liquid chromatography. Sialic acid was removed from the N-glycopeptides with trifluoroacetic acid and heat. The desialo-N-glycopeptides were analyzed by HCD-MS/MS using stepped collision energies and several search engines for quantitative profiling. Ninety-two altered proteins and 134 intact N-glycopeptides were isolated from the plasma and urine samples of the three groups (90 samples from 15 subjects). To the best of our knowledge, this study is the first to compare the plasma and urinary proteomes and glycoproteomes of HC, PTC, and PHT. Moreover, we reveal a novel indicator (ratio of fucosylated to nonfucosylated N-glycopeptide or F/NF) through desialo-N-glycopeptide analysis. These differently expressed glycoproteins and F/NF may serve as biomarkers contributing to clinical cancer diagnostics and could be used to improve diagnostic accuracy noninvasively.

Proteomics in Chronic Arthritis-Will We Finally Have Useful Biomarkers?

Current technical advances enable the assessment of the complex changes in body fluid proteomes and thus allow for the discovery of biomarker signatures rather than just following differences of a single marker. In this review, we aim to summarize current approaches to discover and evaluate multi-biomarker panels for improved monitoring of chronic arthritis disease activity. Mass spectrometry and affinity proteomic methodologies have been used to identify biomarker panels in synovial fluid, serum, plasma, or urine of pediatric and adult chronic arthritis patients. Notably, despite the numerous efforts to develop new and better biomarker panels, very few have undergone extensive analytical and clinical validation and been adopted into routine use for patient benefit. There remains a significant gap between discovery of chronic arthritis biomarker signatures and their validation for clinical use.

Bovine Milk Comparative Proteome Analysis from Early, Mid, and Late Lactation in the Cattle Breed, Malnad Gidda (Bos indicus).

Bovine milk is important for both veterinary medicine and human nutrition. Understanding the bovine milk proteome at different stages of lactation has therefore broad significance for integrative biology and clinical medicine as well. Indeed, different lactation stages have marked influence on the milk yield, milk constituents, and nourishment of the neonates. We performed a comparative proteome analysis of the bovine milk obtained at different stages of lactation from the Indian indigenous cattle Malnad Gidda (Bos indicus), a widely available breed. The milk differential proteome during the lactation stages in B. indicus has not been investigated to date. Using high-resolution mass spectrometry-based quantitative proteomics of the bovine whey proteins at early, mid, and late lactation stages, we identified a total of 564 proteins, out of which 403 proteins were found to be differentially abundant at different lactation stages. As is expected of any body fluid proteome, 51% of the proteins identified in the milk were found to have signal peptides. Gene ontology analyses were carried out to categorize proteins altered across different lactation stages based on biological process and molecular function, which enabled us to correlate their significance in each lactation stage. We also investigated the potential pathways enriched in different lactation stages using bioinformatics pathway analysis tools. To the best of our knowledge, this study represents the first and largest inventory of milk proteins identified to date for an Indian cattle breed. We believe that the current study broadly informs both veterinary omics research and the emerging field of nutriproteomics during lactation stages.

Body Fluid Degradomics and Characterization of Basic N-Terminome.

Rapid improvements in instrumentation and data analysis make mass spectrometry-based proteomics the method of choice for global characterization of proteomes and discovery of protein-based biomarkers. On the contrary to tissue biopsies, body fluids-e.g., blood, wound fluid, urine, and saliva-are noninvasive and easy to collect and process. However, they are very complex and present high dynamic ranges of protein concentrations, rendering direct shotgun proteomics analysis as inefficient for identification of low-abundance proteins in these specimens. Sample prefractionation, immunoaffinity depletion of highly abundant proteins, and enrichment of posttranslational modifications (PTM) are common strategies for proteome simplification of body fluids. Combinatorial peptide ligand libraries (CPLL) relatively deplete high-abundance proteins by binding equimolar amounts of protein species in the sample and provide an elegant species-independent alternative to immunoaffinity-based approaches. By cleaving target proteins, proteases catalyze an irreversible PTM, whereby uncontrolled proteolysis is associated with many diseases. Thus, proteolytic events represent powerful indicators for disease progression and their specific identification in body fluids holds great promises for establishment of novel biomarkers. Quantitative N-terminal enrichment strategies, such as terminal amine isotopic labeling of substrates (TAILS) detect protease-generated neo-N-termini with high specificity and increase coverage of low-abundance proteins by inherent proteome simplification. In this chapter, we describe a protocol that combines the CPLL technology with iTRAQ-based TAILS to systematically characterize the basic N-terminome of body fluid proteomes and its alterations in disease conditions that we have successfully applied to explore the wound fluid degradome at multiple time points after skin injury.

Biomarkers discovery by peptide and protein profiling in biological fluids based on functionalized magnetic beads purification and mass spectrometry.

Biomarkers discovery by peptide and protein profiling in biological fluids based on functionalized magnetic beads purification and mass spectrometry.

Biological sample collection for clinical proteomics: existing SOPs.

Proteomic study of clinical samples aims at the better understanding of physiological and pathological conditions, as well as the discovery of diagnostic and prognostic markers for the latter. Quantitative and/or qualitative variations of body fluid proteome may reflect health- or disease-associated events connected to the adjacent or distant body regions of the fluid production/secretion/excretion and/or systemic reactions to the presence of disease. Sample collection and preparation is a critical step in order to obtain useful and valid information in clinical proteomics analysis. In this chapter, we present the current protocols and guidelines for human body fluid collection and storage, prior to proteomic analysis. A variety of body fluids that are currently being used in proteomic analysis and have potential interest in clinical practice are presented including blood plasma and serum, urine, cerebrospinal fluid, cerumen, nasal secretions, saliva, tears, breast milk, bronchoalveolar fluid, nipple aspirate fluid, amniotic fluid, bile, cervico-vaginal fluid, and seminal plasma. With no doubt these body fluids differ in the extent of their application in clinical proteomics investigations, hence in some cases the presented SOPs are established following more extensive testing (e.g., plasma, serum, urine, CSF) than others (nasal secretions, saliva, tears, breast milk, bronchoalveolar fluid, nipple aspirate fluid, amniotic fluid, bile, cervico-vaginal fluid, and seminal plasma). However, even in these latter cases, the presented protocols were reported by at least two independent groups according to the literature. We hope they can thus serve as a reliable guide for sample collection based on our current knowledge in the field and excellent starting points for proteomics investigators. It should also be pointed that variations to these protocols exist and their further refinement in the future is foreseen following the evolution of the proteomics technologies.

Identification of Autoantigens in Body Fluids by Combining Pull-Downs and Organic Precipitations of Intact Immune Complexes with Quantitative Label-Free Mass Spectrometry

Most autoimmune diseases are multifactorial diseases and are caused by the immunological reaction against a number of autoantigens. Key for understanding autoimmune pathologies is the knowledge of the targeted autoantigens, both initially and during disease progression. We present an approach for autoantigen identification based on isolation of intact autoantibody-antigen complexes from body fluids. After organic precipitation of high molecular weight proteins and free immunoglobulins, released autoantigens were identified by quantitative label-free liquid chromatography mass spectrometry. We confirmed feasibility of target enrichment and identification from highly complex body fluid proteomes by spiking of a predefined antibody-antigen complex at low level of abundance. As a proof of principle, we studied the blinding disease autoimmune uveitis, which is caused by autoreactive T-cells attacking the inner eye and is accompanied by autoantibodies. We identified three novel autoantigens in the spontaneous animal model equine recurrent uveitis (secreted acidic phosphoprotein osteopontin, extracellular matrix protein 1, and metalloproteinase inhibitor 2) and confirmed the presence of the corresponding autoantibodies in 15-25% of patient samples by enzyme-linked immunosorbent assay. Thus, this workflow led to the identification of novel autoantigens in autoimmune uveitis and may provide a versatile and useful tool to identify autoantigens in other autoimmune diseases in the future.

The Application of SILAC Mouse in Human Body Fluid Proteomics Analysis Reveals Protein Patterns Associated with IgA Nephropathy

Body fluid proteome is the most informative proteome from a medical viewpoint. But the lack of accurate quantitation method for complicated body fluid limited its application in disease research and biomarker discovery. To address this problem, we introduced a novel strategy, in which SILAC-labeled mouse serum was used as internal standard for human serum and urine proteome analysis. The SILAC-labeled mouse serum was mixed with human serum and urine, and multidimensional separation coupled with tandem mass spectrometry (IEF-LC-MS/MS) analysis was performed. The shared peptides between two species were quantified by their SILAC pairs, and the human-only peptides were quantified by mouse peptides with coelution. The comparison for the results from two replicate experiments indicated the high repeatability of our strategy. Then the urine from Immunoglobulin A nephropathy patients treated and untreated was compared by this quantitation strategy. Fifty-three peptides were found to be significantly changed between two groups, including both known diagnostic markers for IgAN and novel candidates, such as Complement C3, Albumin, VDBP, ApoA,1 and IGFBP7. In conclusion, we have developed a practical and accurate quantitation strategy for comparison of complicated human body fluid proteome. The results from such strategy could provide potential disease-related biomarkers for evaluation of treatment.

An Overview of Endogenous Catechol-Isoquinolines and Their Related Enzymes: Possible Biomarkers for Parkinson’s Disease

For the most common neurodegenerative disorders, there is no simple, obvious, and effective biomarker for disease identification. Plasma biomarkers of neurodegenerative disorders should play an important role in early detection and diagnosis of diseases. The catechol isoquinoline compounds are considered as possible neurotoxins involved in the pathogenesis of Parkinson’s disease (PD). These catechol isoquinolines and enzymes involved in their biosynthesis and metabolism may be endogenous factors in the pathogenesis of PD. As we know, there exists a salsolinol N-methyltransferase (SNMT) in human brain and lymphocyte. In normal postmortem human brain regions, frontal cortex, caudate, putamen, and thalamus, the SNMT activity was significantly higher than the control, and was well relevant to PD. In parkinsonian lymphocytes, the SNMT activity was much higher than in control patients. In addition, there was significant positive correlation between the SNMT activity in the lymphocyte and the level of N-methylsalsolinol in cerebrospinal fluid from the same untreated PD patients. Mass spectrometry–based biomarker discovery, undoubtedly, is still in its early stage of infancy. However, in light of the potential of this technology to provide deep coverage of the body fluid proteomes, it will certainly consolidate its role in development molecular medicine into clinical practice.

Comprehensive proteomic analysis of human bile

Bile serves diverse functions from metabolism to transport. In addition to acids and salts, bile is composed of proteins secreted or shed by the hepatobiliary system. Although there have been previous efforts to catalog biliary proteins, an in-depth analysis of the bile proteome has not yet been reported. We carried out fractionation of non-cancerous bile samples using a multipronged approach (SDS-PAGE, SCX and OFFGEL) followed by MS analysis on an LTQ-Orbitrap Velos mass spectrometer using high resolution at both MS and MS/MS levels. We identified 2552 proteins - the largest number of proteins reported in human bile till date. To our knowledge, there are no previous studies employing high-resolution MS reporting a more detailed catalog of any body fluid proteome in a single study. We propose that extensive fractionation coupled to high-resolution MS can be used as a standard methodology for in-depth characterization of any body fluid. This catalog should serve as a baseline for the future studies aimed at discovering biomarkers from bile in gallbladder, hepatic, and biliary cancers.

Naturally Occurring Human Urinary Peptides for Use in Diagnosis of Chronic Kidney Disease

Because of its availability, ease of collection, and correlation with physiology and pathology, urine is an attractive source for clinical proteomics/peptidomics. However, the lack of comparable data sets from large cohorts has greatly hindered the development of clinical proteomics. Here, we report the establishment of a reproducible, high resolution method for peptidome analysis of naturally occurring human urinary peptides and proteins, ranging from 800 to 17,000 Da, using samples from 3,600 individuals analyzed by capillary electrophoresis coupled to MS. All processed data were deposited in an Structured Query Language (SQL) database. This database currently contains 5,010 relevant unique urinary peptides that serve as a pool of potential classifiers for diagnosis and monitoring of various diseases. As an example, by using this source of information, we were able to define urinary peptide biomarkers for chronic kidney diseases, allowing diagnosis of these diseases with high accuracy. Application of the chronic kidney disease-specific biomarker set to an independent test cohort in the subsequent replication phase resulted in 85.5% sensitivity and 100% specificity. These results indicate the potential usefulness of capillary electrophoresis coupled to MS for clinical applications in the analysis of naturally occurring urinary peptides.

Stable Isotope Metabolic Labeling with a Novel 15N-Enriched Bacteria Diet for Improved Proteomic Analyses of Mouse Models for Psychopathologies

The identification of differentially regulated proteins in animal models of psychiatric diseases is essential for a comprehensive analysis of associated psychopathological processes. Mass spectrometry is the most relevant method for analyzing differences in protein expression of tissue and body fluid proteomes. However, standardization of sample handling and sample-to-sample variability are problematic. Stable isotope metabolic labeling of a proteome represents the gold standard for quantitative mass spectrometry analysis. The simultaneous processing of a mixture of labeled and unlabeled samples allows a sensitive and accurate comparative analysis between the respective proteomes. Here, we describe a cost-effective feeding protocol based on a newly developed 15N bacteria diet based on Ralstonia eutropha protein, which was applied to a mouse model for trait anxiety. Tissue from 15N-labeled vs. 14N-unlabeled mice was examined by mass spectrometry and differences in the expression of glyoxalase-1 (GLO1) and histidine triad nucleotide binding protein 2 (Hint2) proteins were correlated with the animals' psychopathological behaviors for methodological validation and proof of concept, respectively. Additionally, phenotyping unraveled an antidepressant-like effect of the incorporation of the stable isotope 15N into the proteome of highly anxious mice. This novel phenomenon is of considerable relevance to the metabolic labeling method and could provide an opportunity for the discovery of candidate proteins involved in depression-like behavior. The newly developed 15N bacteria diet provides researchers a novel tool to discover disease-relevant protein expression differences in mouse models using quantitative mass spectrometry.

Proteomic analysis of lymphoid and haematopoietic neoplasms: There's more than biomarker discovery

Lymphoid and haematopoietic neoplasms comprise a broad spectrum of different tumours, classified by the World Health Organization (WHO) on the basis of a combination of morphology, immunophenotypic, genetic and clinical features. Up to date for many of these neoplasms no single feature is regarded as a diagnostic gold standard. The application of proteomics to the study of neoplastic haematological diseases could help in the search for new diagnostic and prognostic markers, as well as in the development of new therapeutic strategies. In this review, we focus on the actual role of proteomics technologies in the study of neoplastic haematology. In particular, we analyse the results obtained in the field of body fluid, cell lines, and tissues proteomics, and discuss the improvement allowed by the new developed proteomic strategies, such as nanofluidic systems, analysis of formalin-fixed tissues, and quantitative high throughput techniques (SILAC, ICAT, iTRAQ).

Approaching clinical proteomics: Current state and future fields of application in cellular proteomics

Recent developments in proteomics technology offer new opportunities for clinical applications in hospital or specialized laboratories including the identification of novel biomarkers, monitoring of disease, detecting adverse effects of drugs, and environmental hazards. Advanced spectrometry technologies and the development of new protein array formats have brought these analyses to a standard, which now has the potential to be used in clinical diagnostics. Besides standardization of methodologies and distribution of proteomic data into public databases, the nature of the human body fluid proteome with its high dynamic range in protein concentrations, its quantitation problems, and its extreme complexity present enormous challenges. Molecular cell biology (cytomics) with its link to proteomics is a new fast moving scientific field, which addresses functional cell analysis and bioinformatic approaches to search for novel cellular proteomic biomarkers or their release products into body fluids that provide better insight into the enormous biocomplexity of disease processes and are suitable for patient stratification, therapeutic monitoring, and prediction of prognosis. Experience from studies of in vitro diagnostics and especially in clinical chemistry showed that the majority of errors occurs in the preanalytical phase and the setup of the diagnostic strategy. This is also true for clinical proteomics where similar preanalytical variables such as inter- and intra-assay variability due to biological variations or proteolytical activities in the sample will most likely also influence the results of proteomics studies. However, before complex proteomic analysis can be introduced at a broader level into the clinic, standardization of the preanalytical phase including patient preparation, sample collection, sample preparation, sample storage, measurement, and data analysis is another issue which has to be improved. In this report, we discuss the recent advances and applications that fulfill the criteria for clinical proteomics with the focus on cellular proteomics (cytoproteomics) as related to preanalytical and analytical standardization and to quality control measures required for effective implementation of these technologies and analytes into routine laboratory testing to generate novel actionable health information. It will then be crucial to design and carry out clinical studies that can eventually identify novel clinical diagnostic strategies based on these techniques and validate their impact on clinical decision making.

Use of narrow‐range peptide IEF to improve detection of lung adenocarcinoma markers in plasma and pleural effusion

In this study we applied narrow-range peptide IEF to plasma or pleural effusion prior to LC/MS/MS. Two methods for narrow-range IEF were run; IPG strips and free-flow electrophoresis. Data from this study was compared with cell line data to evaluate the method performance in body fluids. To test the methods potential in quantitative biomarker discovery studies, plasma and pleural effusion from patients with lung adenocarcinoma (n=3) were compared with inflammatory pleuritis (n=3) using iTRAQ quantification. Using narrow-range IEF on the peptide level we were able to identify and quantify 282 proteins in plasma and 300 proteins in pleural effusion. These body fluid proteomes demonstrated high degree of overlap; however, more proteins significantly differently altered levels related to adenenocarcinoma were found in pleural effusion compared with plasma, suggesting enrichment of lung tissue-related proteins in pleural effusion. Nine proteins were chosen for initial validation with Western blot, and one protein (NPC2) was chosen for further validation using imunohistochemistry. Overall, the quantitative results from IEF/LC/MS/MS showed good correlation with the results from Western blot and imunohistochemistry, showing the potential of this methodology in quantitative biomarker discovery studies.

Approaching clinical proteomics: current state and future fields of application in fluid proteomics

The field of clinical proteomics offers opportunities to identify new disease biomarkers in body fluids, cells and tissues. These biomarkers can be used in clinical applications for diagnosis, stratification of patients for specific treatment, or therapy monitoring. New protein array formats and improved spectrometry technologies have brought these analyses to a level with potential for use in clinical diagnostics. The nature of the human body fluid proteome with its large dynamic range of protein concentrations presents problems with quantitation. The extreme complexity of the proteome in body fluids presents enormous challenges and requires the establishment of standard operating procedures for handling of specimens, increasing sensitivity for detection and bioinformatical tools for distribution of proteomic data into the public domain. From studies of in vitro diagnostics, especially in clinical chemistry, it is evident that most errors occur in the preanalytical phase and during implementation of the diagnostic strategy. This is also true for clinical proteomics, and especially for fluid proteomics because of the multiple pretreatment processes. These processes include depletion of high-abundance proteins from plasma or enrichment processes for urine where biological variation or differences in proteolytic activities in the sample along with preanalytical variables such as inter- and intra-assay variability will likely influence the results of proteomics studies. However, before proteomic analysis can be introduced at a broader level into the clinical setting, standardization of the preanalytical phase including patient preparation, sample collection, sample preparation, sample storage, measurement and data analysis needs to be improved. In this review, we discuss the recent technological advances and applications that fulfil the criteria for clinical proteomics, with the focus on fluid proteomics. These advances relate to preanalytical factors, analytical standardization and quality-control measures required for effective implementation into routine laboratory testing in order to generate clinically useful information. With new disease biomarker candidates, it will be crucial to design and perform clinical studies that can identify novel diagnostic strategies based on these techniques, and to validate their impact on clinical decision-making.