Afamin is a novel human vitamin E-binding glycoprotein characterization and in vitro expression

Afamin--A pleiotropic glycoprotein involved in various disease states

The human glycoprotein afamin was discovered as the fourth member of the albumin gene family. Despite intense research over the last 20 years, our knowledge of afamin's physiological or pathophysiological functions is still very limited. Circulating afamin is primarily of hepatic origin and abundant concentrations are found in plasma, cerebrospinal, ovarian follicular and seminal fluids. In vitro binding studies revealed specific binding properties for vitamin E. A previously performed analytical characterization and clinical evaluation study of an enzyme-linked immunosorbent assay for quantitative measurement of afamin in human plasma demonstrated that the afamin assay meets the quality specifications for laboratory medicine. Comparative proteomics has identified afamin as a potential biomarker for ovarian cancer and these findings were confirmed by quantitative immunoassay of afamin and validated in independent cohorts of patients with ovarian cancer. Afamin has also been investigated in other types of carcinoma. Most of these studies await further evaluation with validated quantitative afamin assays and require validation in larger patient cohorts. Transgenic mice overexpressing the human afamin gene revealed increased body weight and increased blood concentrations of lipids and glucose. These transgenic mouse data were in line with three large human population-based studies showing that afamin is strongly associated with the prevalence and development of the metabolic syndrome. This review summarizes and discusses the molecular, biochemical and analytical characterization of afamin as well as possible clinical applications of afamin measurement.

Albuminoid genes: evolving at the interface of dispensability and selection

The albuminoid gene family comprises vitamin D-binding protein (GC), alpha-fetoprotein (AFP), afamin (AFM), and albumin (ALB). Albumin is the most abundant human serum protein, and, as the other family members, acts as a transporter of endogenous and exogenous substances including thyroxine, fatty acids, and drugs. Instead, the major cargo of GC is 25-hydroxyvitamin D. We performed an evolutionary study of albuminoid genes and we show that ALB evolved adaptively in mammals. Most positively selected sites are located within albumin-binding sites for fatty acids and thyroxine, as well as at the contact surface with neonatal Fc receptor. Positive selection was also detected for residues forming the prostaglandin-binding pocket. Adaptation to hibernation/torpor might explain the signatures of episodic positive selection we detected for few mammalian lineages. Application of a population genetics-phylogenetics approach showed that purifying selection represented a major force acting on albuminoid genes in both humans and chimpanzees, with the strongest constraint observed for human GC. Population genetic analysis revealed that GC was also the target of locally exerted selective pressure, which drove the frequency increase of different haplotypes in distinct human populations. A search for known variants that modulate GC and 25-hydroxyvitamin D concentrations revealed linkage disequilibrium with positively selected variants, although European and Asian major GC haplotypes carry alleles with reported opposite effect on GC concentration. Data herein indicate that albumin, an extremely abundant housekeeping protein, was the target of pervasive and episodic selection in mammals, whereas GC represented a selection target during the recent evolution of human populations.

Afamin serum concentrations are associated with insulin resistance and metabolic syndrome in polycystic ovary syndrome

BACKGROUND

High plasma concentrations of the vitamin E-binding protein afamin have been previously shown to be associated with insulin resistance and metabolic syndrome. We set out to determine whether the concentration of afamin in the serum of women with polycystic ovarian syndrome (PCOS) is elevated in relation to the presence and severity of insulin resistance (IR).

METHODS

This cross-sectional study looked at 53 patients with PCOS and 49 non-PCOS patients. IR was diagnosed as a HOMA Index >2.4 and confirmed with a three-hour glucose tolerance test. Serum concentrations of afamin were determined using enzyme-linked immunosorbent assay (ELISA). Clinical characteristics, hormone and metabolic parameters were correlated to afamin concentrations.

RESULTS

Serum concentrations of afamin did not differ between women with PCOS and controls. When separated according to the presence of IR a significant difference in median afamin levels was seen between PCOS with IR and PCOS without IR (73.06+/-27.36 mg/L and 64.25+/-17.41 mg/L, p = 0.033). No difference in afamin levels was detected when comparing the few controls with IR and the controls without IR (76.20+/-27.96 mg/L and 60.44+/-21.03 mg/L, p = 0.235). On univariate analyses, afamin serum concentrations significantly correlated with BMI, triglycerides, HOMA Index, and AUC-Insulin. On multivariate linear regression analysis, only triglyceride concentration was seen to be an independent predictor of afamin. Subjects with metabolic syndrome had higher median afamin concentrations than did those without metabolic syndrome (77.43+/-28.60 mg/L and 65.08+/-18.03 mg/L, p = 0.010).

CONCLUSIONS

Elevated afamin concentrations are associated with the presence of metabolic syndrome in young women and may potentially serve as an independent predictor for the development of metabolic syndrome in at-risk women, especially those with IR.

Serum concentrations of afamin are elevated in patients with polycystic ovary syndrome

Oxidative stress seems to be present in patients with polycystic ovary syndrome (PCOS). The aim of this study was to evaluate the correlation between characteristics of PCOS and serum concentrations of afamin, a novel binding protein for the antioxidant vitamin E. A total of 85 patients with PCOS and 76 control subjects were investigated in a pilot cross-sectional study design between 2009 and 2013 in the University Hospital of Essen, Germany. Patients with PCOS were diagnosed according to the Rotterdam ESHRE/ASRM-sponsored PCOS Consensus Workshop Group. Afamin and diagnostic parameters of PCOS were determined at early follicular phase. Afamin concentrations were significantly higher in patients with PCOS than in controls (odds ratio (OR) for a 10 mg/ml increase in afamin=1.3, 95% CI=1.08-1.58). This difference vanished in a model adjusting for age, BMI, free testosterone index (FTI), and sex hormone-binding globulin (SHBG) (OR=1.05, 95% CI=0.80-1.38). In patients with PCOS, afamin correlated significantly with homeostatic model assessment-insulin resistance (HOMA-IR), fasting glucose, BMI, FTI, and SHBG (P<0.001), but in a multivariate linear model, only HOMA-IR remained significantly associated with afamin (P=0.001). No correlation was observed between afamin and androgens, LH, FSH, LH/FSH ratio, antral follicle count, ovarian volume, or anti-Müllerian hormone. In conclusion, elevated afamin values may indicate a state of oxidative stress and inflammation, strongly associated with IR and offering an indicator of impaired glucose tolerance in patients with PCOS irrespective of obesity.

Plasma concentrations of afamin are associated with the prevalence and development of metabolic syndrome

BACKGROUND

Afamin is a human plasma vitamin E-binding glycoprotein primarily expressed in the liver and secreted into the bloodstream. Because little is known about (patho)-physiological functions of afamin, we decided to identify phenotypes associated with afamin by investigating transgenic mice overexpressing the human afamin gene and performing large-scale human epidemiological studies.

METHODS AND RESULTS

Transgenic mice overexpressing afamin revealed increased body weight and serum concentrations of lipids and glucose. We applied a random-effects meta-analysis using age- and sex-adjusted baseline and follow-up investigations in the population-based Bruneck (n=826), Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR; n=1499), and KOoperative Gesundheitsforschung in der Region Augsburg (KORA) F4 studies (n=3060). Mean afamin concentrations were 62.5±15.3, 66.2±14.3, and 70.6±17.2 mg/L in Bruneck, SAPHIR, and KORA F4, respectively. Per 10 mg/L increment in afamin measured at baseline, the number of metabolic syndrome components increased by 19% (incidence rate ratio=1.19; 95% confidence interval [CI], 1.16-1.21; P=5.62×10(-64)). With the same afamin increment used at baseline, we observed an 8% gain in metabolic syndrome components between baseline and follow-up (incidence rate ratio=1.08; 95% CI, 1.06-1.10; P=8.87×10(-16)). Afamin concentrations at baseline were highly significantly related to all individual metabolic syndrome components at baseline and at follow-up. This observation was most pronounced for elevated waist circumference (odds ratio, 1.79; 95% CI, 1.54-2.09; P=4.15×10(-14) at baseline and odds ratio, 1.46; 95% CI, 1.31-1.63; P=2.84×10(-11) for change during follow-up) and for elevated fasting glucose concentrations (odds ratio, 1.46; 95% CI, 1.40-1.52; P=1.87×10(-69) and odds ratio, 1.46; 95% CI, 1.24-1.71; P=5.13×10(-6), respectively).

CONCLUSIONS

This study in transgenic mice and >5000 participants in epidemiological studies shows that afamin is strongly associated with the prevalence and development of metabolic syndrome and all its components.

The vitamin E-binding protein afamin increases in maternal serum during pregnancy

Background

Afamin is a liver-derived plasma glycoprotein with vitamin E-binding properties and a putative function in fertility. This study evaluated serum afamin concentrations during and postpartum to uncomplicated pregnancies and investigated a potential association between afamin concentrations and pregnancy outcome.

Methods

Afamin serum concentrations were measured in women with uncomplicated pregnancies in a retrospective cohort (n = 466) at different gestational ages and a prospective observational study (n = 76) in the first, second and third trimester. Furthermore, afamin was determined in the first trimester in a cross-sectional pilot study including women with preeclampsia (PE), pregnancy-induced hypertension (PIH) and women without pregnancy complications (n = 13 each). Finally, expression of afamin was investigated in human placental tissue by RT-PCR and immunohistochemistry.

Results

Afamin concentrations increased linearly almost two-fold during pregnancy in both retrospective and prospective studies in women without pregnancy complications with median afamin serum concentrations of 61.9 mg/l, 79.6 mg/l, and 98.6 mg/l in the first, second, and third trimester, respectively. After delivery, median afamin concentrations decreased to baseline values of 54.6 mg/l. In the pilot study with pregnancy complications, women with PE displayed significantly higher median afamin concentrations than did women with uncomplicated pregnancy (70.0 mg/l vs. 55.4 mg/l, P = 0.007). Expression analyses revealed no placental afamin expression at either mRNA or protein level in uncomplicated pregnancy.

Conclusion

A linear increase in the maternally expressed glycoprotein afamin during pregnancy may serve as basic reference for subsequent investigations of afamin in pregnancy-related disorders.

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Serum afamin concentrations during and postpartum to uncomplicated pregnancies were evaluated.

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Analysis of afamin in cross-sectional pilot study in patients with pregnancy complications.

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Afamin linearly increased two-fold in women with uncomplicated pregnancies.

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First trimester serum values of afamin were significantly higher in women with pregnancy complications.

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Lacking placental afamin expression suggests maternal origin of circulating afamin.

Proteomic analysis of human osteoarthritis synovial fluid

Background

Osteoarthritis is a chronic musculoskeletal disorder characterized mainly by progressive degradation of the hyaline cartilage. Patients with osteoarthritis often postpone seeking medical help, which results in the diagnosis being made at an advanced stage of cartilage destruction. Sustained efforts are needed to identify specific markers that might help in early diagnosis, monitoring disease progression and in improving therapeutic outcomes. We employed a multipronged proteomic approach, which included multiple fractionation strategies followed by high resolution mass spectrometry analysis to explore the proteome of synovial fluid obtained from osteoarthritis patients. In addition to the total proteome, we also enriched glycoproteins from synovial fluid using lectin affinity chromatography.

Results

We identified 677 proteins from synovial fluid of patients with osteoarthritis of which 545 proteins have not been previously reported. These novel proteins included ADAM-like decysin 1 (ADAMDEC1), alanyl (membrane) aminopeptidase (ANPEP), CD84, fibulin 1 (FBLN1), matrix remodelling associated 5 (MXRA5), secreted phosphoprotein 2 (SPP2) and spondin 2 (SPON2). We identified 300 proteins using lectin affinity chromatography, including the glycoproteins afamin (AFM), attractin (ATRN), fibrillin 1 (FBN1), transferrin (TF), tissue inhibitor of metalloproteinase 1 (TIMP1) and vasorin (VSN). Gene ontology analysis confirmed that a majority of the identified proteins were extracellular and are mostly involved in cell communication and signaling. We also confirmed the expression of ANPEP, dickkopf WNT signaling pathway inhibitor 3 (DKK3) and osteoglycin (OGN) by multiple reaction monitoring (MRM) analysis of osteoarthritis synovial fluid samples.

Conclusions

We present an in-depth analysis of the synovial fluid proteome from patients with osteoarthritis. We believe that the catalog of proteins generated in this study will further enhance our knowledge regarding the pathophysiology of osteoarthritis and should assist in identifying better biomarkers for early diagnosis.

Plasma protein profiling of Mild Cognitive Impairment and Alzheimer's disease using iTRAQ quantitative proteomics

BACKGROUND

With the promise of disease modifying treatments, there is a need for more specific diagnosis and prognosis of Alzheimer's disease (AD) and mild cognitive impairment (MCI). Plasma biomarkers are likely to be utilised to increase diagnostic accuracy and specificity of AD and cognitive decline.

METHODS

Isobaric tags (iTRAQ) and proteomic methods were used to identify potential plasma biomarkers of MCI and AD. Relative protein expression level changes were quantified in plasma of 411 cognitively normal subjects, 19 AD patients and 261 MCI patients. Plasma was pooled into 4 groups including normal control, AD, amnestic single and multiple domain MCI (aMCI), and nonamnestic single and multiple domain MCI (nMCI). Western-blotting was used to validate iTRAQ data. Integrated function and protein interactions were explored using WEB based bioinformatics tools (DAVID v6.7 and STRING v9.0).

RESULTS

In at least two iTRAQ replicate experiments, 30 proteins were significantly dysregulated in MCI and AD plasma, relative to controls. These proteins included ApoA1, ApoB100, complement C3, C4b-binding protein, afamin, vitamin D-binding protein precursor, isoform 1 of Gelsolin actin regulator, Ig mμ chain C region (IGHM), histidine-rich glycoprotein and fibrinogen β and γ chains. Western-blotting confirmed that afamin was decreased and IGHM was increased in MCI and AD groups. Bioinformatics results indicated that these dysregulated proteins represented a diversity of biological processes, including acute inflammatory response, cholesterol transport and blood coagulation.

CONCLUSION

These findings demonstrate that expression level changes in multiple proteins are observed in MCI and AD plasma. Some of these, such as afamin and IGHM, may be candidate biomarkers for AD and the predementia condition of MCI.

Lysine and arginine content of proteins: computational analysis suggests a new tool for solubility design

Prediction and engineering of protein solubility is an important but imprecise area. While some features are routinely used, such as the avoidance of extensive non-polar surface area, scope remains for benchmarking of sequence and structural features with experimental data. We study properties in the context of experimental solubilities, protein gene expression levels, and families of abundant proteins (serum albumin and myoglobin) and their less abundant paralogues. A common feature that emerges for proteins with elevated solubility and at higher expression and abundance levels is an increased ratio of lysine content to arginine content. We suggest that the same properties of arginine that give rise to its recorded propensity for specific interaction surfaces also lead to favorable interactions at nonspecific contacts, and thus lysine is favored for proteins at relatively high concentration. A survey of protein therapeutics shows that a significant subset possesses a relatively low lysine to arginine ratio, and therefore may not be favored for high protein concentration. We conclude that modulation of lysine and arginine content could prove a useful and relatively simple addition to the toolkit available for engineering protein solubility in biotechnological applications.

Afamin stimulates osteoclastogenesis and bone resorption via Gi-coupled receptor and Ca2+/calmodulin-dependent protein kinase (CaMK) pathways

BACKGROUND

Afamin was recently identified as a novel osteoclast-derived coupling factor that can stimulate the in vitro and in vivo migration of preosteoblasts.

AIM

In order to understand in more detail the biological roles of afamin in bone metabolism, we investigated its effects on osteoclastic differentiation and bone resorption.

METHODS

Osteoclasts were differentiated from mouse bone marrow cells. Tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells were considered as osteoclasts, and the resorption area was determined by incubating the cells on dentine discs. The intracellular cAMP level was determined using a direct enzyme immunoassay. Signaling pathways were investigated using western blot and RT-PCR. Recombinant afamin was administered exogenously to bone cell cultures.

RESULTS

Afamin stimulated both osteoclastogenesis and in vitro bone resorption. Consistently, the expressions of osteoclast differentiation markers were significantly increased by afamin. Although afamin mainly affected the late-differentiation stages of osteoclastogenesis, the expression levels of receptor activator of nuclear factor-κB ligand (RANKL)-dependent signals were not changed. Afamin markedly decreased the levels of intracellular cAMP with reversal by pretreatment with pertussis toxin (PTX), a specific inhibitor of Gi-coupled receptor signaling. In addition, PTX almost completely blocked afamin-stimulated osteoclastogenesis. Furthermore, pretreatment with KN93 and STO609 - Ca2+/cal - mo dulin-dependent protein kinase (CaMK) and CaMK kinase inhibitors, respectively - significantly prevented decreases in the intracellular cAMP level by afamin while attenuating afamin-stimulated osteoclastogenesis.

CONCLUSION

Afamin enhances osteoclastogenesis by decreasing intracellular cAMP levels via Gi-coupled receptor and CaMK pathways.

Analytical characterization and clinical evaluation of an enzyme-linked immunosorbent assay for measurement of afamin in human plasma

Background

Comparative proteomics has recently identified afamin, the newest member of the albumin gene family, as a potential biomarker for ovarian cancer. The aim of this study was the analytical and clinical evaluation of a sandwich enzyme-linked immunosorbent assay for the determination of afamin in human plasma.

Methods

We evaluated precision, linearity, and detection limit of the assay, analyte stability and biological variability, determined reference values and quantified afamin concentrations in various diseases.

Results

Within-run and total coefficients of variation were < 10%. The method was linear across the tested measurement range. Detection limit was 7 mg/L for the assay. The analyte was stable for 24 h at room temperature, for 48 h at 4 °C, and for at least one year at − 20 °C and − 80 °C. The reference change value for healthy individuals was 24%. Age- and sex-independent reference values in healthy blood donors were 45–99 mg/L (median 68 mg/L). In the clinical assay evaluation afamin plasma concentrations were modestly decreased in patients with heart failure. Patients with pneumonia or sepsis exhibited markedly decreased afamin plasma concentrations. However, patients with chronic renal disease or chronic obstructive pulmonary disease showed no difference in afamin plasma concentrations as compared to healthy individuals. Correlation analyses revealed an inverse association between afamin and inflammatory biomarkers.

Conclusions

The afamin assay meets quality specifications for laboratory medicine. The results of the clinical assay evaluation revealed novel insights with respect to afamin as a potential negative acute phase protein and should encourage further studies.

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The aim of this study was the analytical and clinical evaluation of a human afamin ELISA.

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The afamin assay meets the needs of quality specifications of laboratory medicine.

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Afamin exerts a good in vitro stability which is important of preanalytical issues.

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The RCV was 24% and reference values in healthy blood donors were 45–99 mg/L.

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We revealed novel insights with respect to afamin as a potential negative acute phase protein.

α-Tocopherol binding to human serum albumin

Given the ability of human serum albumin (HSA) to bind hydrophobic ligands, the binding mode of α-tocopherol, the most representative member of the vitamin E family, is reported. α-Tocopherol binds to HSA with Kd0 = (7.0 ± 3.0) × 10(-6) M (pH 7.2, 25.0°C). Competitive and allosteric modulation of α-tocopherol binding to full-length and truncated (Asp1-Glu382) HSA by endogenous and exogenous ligands suggests that it accommodates preferentially in the FA3-FA4 site. As HSA is taken up into cells, colocalizes with the α-tocopherol transfer protein, and contributes to ligand secretion via ABCA1, it might participate in the distribution of α-tocopherol between plasma, cells, and tissues.

Plasma concentrations of the vitamin E-binding protein afamin are associated with overall and progression-free survival and platinum sensitivity in serous ovarian cancer--a study by the OVCAD consortium

OBJECTIVE

Comparative proteomics identified the plasma protein afamin as potential biomarker for ovarian cancer (OC). Significantly decreased afamin plasma concentrations in pre-therapeutic OC patients reconstituted to control values after successful tumor surgery. This study evaluates the association of afamin with survival and response to therapy in serous OC patients within the OVCAD consortium project.

METHODS

We measured afamin in 215 pre-therapeutic plasma samples, 246 tumor lysates and 109 plasma samples taken 6months after finishing platinum-based chemotherapy. Differences in afamin plasma concentrations among FIGO stages were tested by Kruskal-Wallis test; association of afamin concentrations with overall and progression-free survival was evaluated using Kaplan-Meier survival plots and multivariate adjusted COX regression analysis.

RESULTS

Pre-therapeutic afamin correlated significantly with FIGO stages (p=0.012) and was lower in the presence of metastases (p=0.013) and poorly differentiated OC in patients responding to therapy (p=0.016). Afamin ≥48.0mg/L was also associated with a lower hazard ratio for recurrent disease as compared to afamin <48.0mg/L (p=0.007). Post-therapeutic afamin ≥48mg/L was positively correlated with overall (p<0.001) and progression-free (p=0.012) survival and was lower in non-responders than in responders (p=0.048). Thus, afamin returned post-therapeutically to values of healthy controls in responders (p<0.001) but not in non-responders (p=0.114). Afamin in tumor lysates was lower in poorly differentiated OC than in G 1+2 tumors (p=0.041). Higher afamin concentrations in tumor lysates were associated with increased overall survival (p=0.003).

CONCLUSION

These data indicate that afamin is associated with therapy response and survival rate in advanced OC patients.

Afamin secreted from nonresorbing osteoclasts acts as a chemokine for preosteoblasts via the Akt-signaling pathway

Although it is well known that osteoclastic bone resorption is followed by osteoblastic bone formation, questions remain as to when coupling factors are produced during bone resorption and which stages of bone formation are affected by these factors. To clarify these mechanisms, we established an in vitro system to investigate the coupling phenomenon. We obtained conditioned media (CM) from osteoclasts in the early and late stages of differentiation and from bone resorption stages. The collected CM was used to treat primary mouse calvarial osteoblasts and preosteoblastic MC3T3-E1 cells and to evaluate its influence on the migration, viability, proliferation, and differentiation of osteoblasts. We found that CM from osteoclasts in the early stage of differentiation predominantly stimulated the migration of osteoblastic lineages. By further performing fractional analyses of the CM with liquid chromatography-tandem mass spectrometry, we identified afamin, which has binding activity with vitamin E, as a possible coupling factor. The CM collected from afamin siRNA-transfected osteoclasts significantly suppressed preosteoblast migration. Afamin activated Akt in preosteoblasts, and pretreatment with Akt inhibitor significantly blocked afamin-stimulated preosteoblast migration. In conclusion, these results indicate that osteoclasts themselves play a central role in the coupling of bone resorption and formation by stimulating preosteoblast migration. In addition, we identified afamin as one of osteoclast-derived chemokines that affect preosteoblasts through the activation of the Akt-signaling pathway.

The HDL proteome in acute coronary syndromes shifts to an inflammatory profile

Inflammation is a major factor underlying acute coronary syndromes (ACS). HDL particles may be remodeled, becoming functionally defective, under the inflammatory conditions seen in ACS. Shotgun proteomics was used to monitor changes in the HDL proteome between male age-matched control, stable CAD, and ACS subjects (n=10/group). HDL was isolated by ultracentrifugation and separated by 1D-gel followed by LC-MS/MS. We identified 67 HDL-associated proteins, 20 of which validated recently identified proteins including vitronectin and complement C4B, and 5 of which were novel. Using gene ontology analysis, we found that the HDL-proteome consisted of proteins involved in cholesterol homeostasis (~50%), with significant contributions by proteins involved in lipid binding, antioxidant, acute-phase response, immune response, and endopeptidase/protease inhibition. Importantly, levels of apoA-IV were significantly reduced in ACS patients, whereas levels of serum amyloid A (SAA) and complement C3 (C3) were significantly increased (spectral counting; t-test p≤0.05), as confirmed by immunoblot or ELISA. Despite differences in protein composition, ABCA1, ABCG1, and SR-BI mediated cholesterol efflux assays did not indicate that HDL from ACS patients is functionally deficient as compared to controls, when corrected for apoA-I mass. Our results support that the HDL proteome differs between control, CAD and ACS patients. Increased abundance of SAA, C3, and other inflammatory proteins in HDL from ACS patients suggests that HDL reflects a shift to an inflammatory profile which, in turn, might alter the protective effects of HDL on the atherosclerotic plaque. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

The vitamin E-binding protein afamin is altered significantly in the peritoneal fluid of women with endometriosis

The objective of this case-control study of 242 reproductive-age women was to determine the concentration of afamin in the serum and peritoneal fluid of women with and without endometriosis and to test afamin as a diagnostic marker of endometriosis. Afamin levels were altered significantly in the peritoneal fluid of women with endometriosis compared with disease-free controls, correlated with vitamin E levels, and are consistent with increased oxidative stress in the peritoneal cavity of women with endometriosis.

Proteomic signatures in plasma during early acute renal allograft rejection

Acute graft rejection is an important clinical problem in renal transplantation and an adverse predictor for long term graft survival. Plasma biomarkers may offer an important option for post-transplant monitoring and permit timely and effective therapeutic intervention to minimize graft damage. This case-control discovery study (n = 32) used isobaric tagging for relative and absolute protein quantification (iTRAQ) technology to quantitate plasma protein relative concentrations in precise cohorts of patients with and without biopsy-confirmed acute rejection (BCAR). Plasma samples were depleted of the 14 most abundant plasma proteins to enhance detection sensitivity. A total of 18 plasma proteins that encompassed processes related to inflammation, complement activation, blood coagulation, and wound repair exhibited significantly different relative concentrations between patient cohorts with and without BCAR (p value <0.05). Twelve proteins with a fold-change >or=1.15 were selected for diagnostic purposes: seven were increased (titin, lipopolysaccharide-binding protein, peptidase inhibitor 16, complement factor D, mannose-binding lectin, protein Z-dependent protease and beta(2)-microglobulin) and five were decreased (kininogen-1, afamin, serine protease inhibitor, phosphatidylcholine-sterol acyltransferase, and sex hormone-binding globulin) in patients with BCAR. The first three principal components of these proteins showed clear separation of cohorts with and without BCAR. Performance improved with the inclusion of sequential proteins, reaching a primary asymptote after the first three (titin, kininogen-1, and lipopolysaccharide-binding protein). Longitudinal monitoring over the first 3 months post-transplant based on ratios of these three proteins showed clear discrimination between the two patient cohorts at time of rejection. The score then declined to baseline following treatment and resolution of the rejection episode and remained comparable between cases and controls throughout the period of quiescent follow-up. Results were validated using ELISA where possible, and initial cross-validation estimated a sensitivity of 80% and specificity of 90% for classification of BCAR based on a four-protein ELISA classifier. This study provides evidence that protein concentrations in plasma may provide a relevant measure for the occurrence of BCAR and offers a potential tool for immunologic monitoring.

Quantitative plasma proteomic profiling identifies the vitamin E binding protein afamin as a potential pathogenic factor in SIV induced CNS disease

Investigating, predicting, diagnosing, and treating HIV-1-associated neurocognitive disorder (HAND) has been hindered by the lack of disease-related molecular markers. In this study, plasma from rhesus monkeys (n = 6), before and after infection with simian immunodeficiency virus (SIV), was profiled to obtain differential fingerprints in protein expression during SIV-induced central nervous system (CNS) disease. A quantitative proteomic analysis was performed by means of isobaric tag for relative and absolute quantification (iTRAQ) labeling, using multidimensional liquid chromatography tandem mass spectrometry (LC-MS/MS) run on a linear ion trap mass spectrometer in an integrated mode comprising pulsed-Q-dissociation (PQD) and CID. Among a panel of proteins showing differential expression following SIV infection, we identified afamin, a member of the albumin superfamily, to be significantly down regulated after infection. Validation by Western blot confirmed this observation and, given its potential implication in neuroprotection by transport of alpha-tocopherol (alphaTocH), provides new avenues into further understanding HIV induced CNS disease. iTRAQ-based LC-MS/MS provides a valuable platform for plasma protein profiling and has important implications in identifying molecular markers relevant for the pathogenesis of neurodegenerative diseases. Using such an approach, we show its successful application in identifying differential fingerprints in SIV/HIV induced CNS disease.

Proteomic and metabolomic strategies to investigate HIV-associated neurocognitive disorders

Diagnosing neurodegenerative diseases, monitoring their progression and assessing responses to treatments will all be aided by the identification of molecular markers of different stages of pathology. Protein biomarkers for HIV-associated neurocognitive disorders that have been discovered using proteomics include complement C3, soluble superoxide dismutase and a prostaglandin synthase. Metabolomics has not yet been widely used for biomarker discovery, but early work shows that it has great potential.

Afamin and apolipoprotein A-IV: novel protein markers for ovarian cancer

Comparative proteomics identified the vitamin E-binding plasma protein afamin as a potential novel tumor marker for ovarian cancer. In addition, we observed in a previous small study decreased plasma concentrations of apolipoprotein A-IV (apoA-IV) in preoperative patients with kidney cancer. The aim of this study was therefore to analyze afamin and apoA-IV in a large case-control study to evaluate the diagnostic utility of the two potential novel tumor markers in ovarian cancer patients. We measured plasma concentrations of afamin and apoA-IV by means of a specific sandwich-type ELISA using affinity-purified polyclonal and monoclonal antibodies in 181 ovarian cancer patients of various clinical stages, 399 patients with benign gynecologic diseases, including endometriosis, and 177 controls and compared results with those for the conventional ovarian cancer tumor marker cancer antigen 125 (CA125). Afamin concentrations decreased from a median of 70.7 mg/L (range, 34.6-116.1 mg/L) in healthy controls to 65.2 mg/L (range, 20.2-206.6 mg/L) in patients with benign gynecologic diseases to 56.0 mg/L (range, 4.7-96.0 mg/L) in ovarian cancer patients (P < 0.001 for all pairwise comparisons). Similar results were obtained with apoA-IV concentrations decreasing from 13.0 mg/dL (range, 5.5-34.0 mg/dL) in controls to 11.7 mg/dL (range, 2.0-32.3 mg/dL) in benign conditions to 9.4 mg/dL (range, 0.3-29.5 mg/dL) in ovarian cancer (all P < 0.001). Receiver operating characteristic analysis for differentiating ovarian cancer patients from healthy controls revealed for a specificity of 90% sensitivity values of 92.4%, 42.4%, and 40.8% for CA125, afamin, and apoA-IV, respectively. Afamin, but not apoA-IV, added independent diagnostic information to CA125 and age for differentiating ovarian cancer from benign and healthy samples; the odds ratio of ovarian cancer was reduced by 44% for each doubling of afamin (P = 0.032). The relatively low sensitivity, however, clearly indicates that afamin and apoA-IV alone are not sufficiently suitable as diagnostic markers for ovarian cancer. Afamin contributes, however, independent diagnostic information to CA125, thus establishing its potential as an adjunct marker to CA125.

Afamin is synthesized by cerebrovascular endothelial cells and mediates alpha-tocopherol transport across an in vitro model of the blood-brain barrier

Alpha-tocopherol (alphaTocH), a member of the vitamin E family, is essential for normal neurological function. Despite the importance of alphaTocH transport into the CNS, transfer mechanisms across the blood-brain barrier (BBB) are not entirely clear. We here investigate whether afamin, a known alphaTocH-binding protein, contributes to alphaTocH transport across an in vitro model of the BBB consisting of primary porcine brain capillary endothelial cells (BCEC) and basolaterally cultured astrocytoma cells. Exogenously added afamin had no adverse effects on BCEC viability or barrier function and was transported across BCEC Transwell cultures. Furthermore, alphaTocH transport across polarized BCEC cultures to astrocytoma cells is facilitated by afamin, though to a lesser extent than by high-density lipoprotein-mediated transport, an essential and in vivo operating alphaTocH import pathway at the cerebrovasculature. We also demonstrate that porcine BCEC endogenously synthesize afamin. In line with these in vitro findings, afamin was detected by immunohistochemistry in porcine, human postmortem, and mouse brain, where prominent staining was observed almost exclusively in the cerebrovasculature. The demonstration of afamin mRNA expression in isolated brain capillaries suggests that afamin might be a new family member of binding/transport proteins contributing to alphaTocH homeostasis at the BBB in vivo.

Sera proteomic biomarker profiling in HIV-1 infected subjects with cognitive impairment

HIV-1 infection of the brain commonly leads to cognitive impairments (CIs). In its most severe form, HIV-1 associated dementia (HAD) is associated with advanced immune suppression and debilitating loss of memory, behavioral, and motor functions. Despite significant research activities, diagnosis remains one of exclusion. Bioimaging, neuropsychological testing, and viral and immune biomarkers serve to support but not define a diagnosis of HIV-1 associated CI. This is timely and required as brain injury triggered by HIV-1 can be controlled, in part, by antiretroviral medicines. The recent development of proteomics has opened new ways to study viral-host interactions which may provide new insight into treatment and disease monitoring. To this end, we developed a proteomics platform for HIV-1 associated CI biomarker discovery and used it to perform a pilot study for sera-associated HAD proteins. A 2-DE map of a serum proteome was focused on differentially expressed proteins. Differential expression of two proteins was validated by Western blot tests identifying afamin and ceruloplasmin as a potential biomarkers for CI associated with advanced HIV-1 infection.

Plasma proteomic analysis of patients with squamous cell carcinoma of the uterine cervix

OBJECTIVE

To compare plasma protein expression between patients with squamous cell carcinoma (SCC) of the cervix and normal controls.

METHODS

Plasma samples from patients with benign gynecological disease (normal cervix, n=6) and cervical cancer (SCC, n=6) were subjected to plasma proteomic analysis using two dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization mass spectroscopy (MALDI-MS). Western blotting and immunoturbidimetric assay were performed to validate the results of 2-DE.

RESULTS

Eight proteins showed differential expression between controls and SCC patients; six (ceruloplasmin, complement C3, afamin precursor, alpha-1-B-glycoprotein, transferrin, alpha-fibrinogen precursor) were up-regulated, while two (chain A, crystal structure of antithrombin and apolipoprotein A-IV precursor) were down-regulated in the plasma of SCC patients. Western blotting analysis revealed significant elevation of ceruloplasmin, complement C3, afamin, and alpha-1-B-glycoprotein in the plasma of SCC patients in comparison to controls. Immunoturbidimetric assay of a larger group confirmed the results of 2-DE and Western blotting, and showed that ceruloplasmin and complement C3 were significantly elevated in the plasma of SCC patients in comparison with controls and patients with carcinoma in situ (CIS) of the uterine cervix.

CONCLUSION

Plasma protein expression determined using 2-DE and MALDI-MS will give a chance to identify tumor-specific biomarkers for SCC of the cervix.

Incorporation of vitamin E in poly(3hydroxybutyrate)/Bioglass composite films: effect on surface properties and cell attachment

This study investigated the possibility of incorporating alpha-tocopherol (vitamin E) into poly(3hydroxybutyrate) (P(3HB))/Bioglass composites, which are being developed for bone tissue engineering matrices. P(3HB) films with 20 wt% Bioglass and 10 wt% vitamin E were prepared using the solvent casting technique. Addition of vitamin E significantly improved the hydrophilicity of the composites along with increasing the total protein adsorption. The presence of protein adsorbed on the composite surface was further confirmed using X-ray photoelectron spectroscopy analysis. Preliminary cell culture studies using MG-63 human osteoblasts showed that the addition of vitamin E in the P(3HB)/20 wt% Bioglass films significantly increased cell proliferation. The results achieved in this study confirmed the possibility of incorporating vitamin E as a suitable additive in P(3HB)/Bioglass composites to engineer the surface of the composites by promoting higher protein adsorption and increasing the hydrophilicity.

Deletion of apolipoprotein E gene modifies the rate of depletion of alpha tocopherol (vitamin E) from mice brains

Our previous reports show that apolipoprotein E (apoE) influences the dynamics of alpha tocopherol (vitamin E) in brain. In this investigation, the patterns of depletion of alpha tocopherol from tissues of apoE deficient and wild type mice were compared after the animals were fed vitamin E deficient diets. Alpha tocopherol concentrations in specific regions of the brain and peripheral tissues at different times were determined by HPLC with electrochemical detection. ApoE deficiency significantly retarded the rate of depletion of alpha tocopherol from all regions of the brain. In addition, comparison of the rates of depletion of alpha tocopherol in both apoE deficient and wild type animals showed that cerebellum behaved differently from other areas such as cortex, hippocampus and striatum. This reinforces the uniqueness of cerebellum with regard to vitamin E biology. Patterns of depletion of tocopherol from peripheral tissues were different from brain. Serum tocopherol was higher in apoE deficient animals and remained higher than wild type during E deficiency. Depletion of liver tocopherol also tended to be unaffected by apoE deficiency. Our current and previous observations strongly suggest that apoE has an important role in modulating tocopherol concentrations in brain, probably acting in concert with other proteins as well.

Proteomic profiling identifies afamin as a potential biomarker for ovarian cancer

PURPOSE

To discover and validate serum glycoprotein biomarkers in ovarian cancer using proteomic-based approaches.

EXPERIMENTAL DESIGN

Serum samples from a "discovery set" of 20 patients with ovarian cancer or benign ovarian cysts or healthy volunteers were compared by fluorescence two-dimensional differential in-gel electrophoresis and parallel lectin-based two-dimensional profiling. Validation of a candidate biomarker was carried out with Western blotting and immunoassay (n = 424).

RESULTS

Twenty-six proteins that changed significantly were identified by mass spectrometric sequencing. One of these, confirmed by Western blotting, was afamin, a vitamin E binding protein, with two isoforms decreasing in patients with ovarian cancer. Validation using cross-sectional samples from 303 individuals (healthy controls and patients with benign, borderline, or malignant ovarian conditions and other cancers) assayed by ELISA showed significantly decreased total afamin concentrations in patients with ovarian cancer compared with healthy controls (P = 0.002) and patients with benign disease (P = 0.046). However, the receiver operating characteristic areas for total afamin for the comparison of ovarian cancer with healthy controls or benign controls were only 0.67 and 0.60, respectively, with comparable figures for CA-125 being 0.92 and 0.88 although corresponding figures for a subgroup of samples analyzed by isoelectric focusing for afamin isoform 2 were 0.85 and 0.79. Analysis of a further 121 samples collected prospectively from 9 patients pretreatment through to relapse indicated complementarity of afamin with CA-125, including two cases in whom CA-125 was noninformative.

CONCLUSIONS

Afamin shows potential complementarity with CA-125 in longitudinal monitoring of patients with ovarian cancer, justifying prospective larger-scale investigation. Changes in specific isoforms may provide further information.

Proteomic Profiling of Ovarian Cancer Plasma using Immunoaffinity Depleted Plasma and Two-Dimensional PAGE

Objective

The aim of this study was to evaluate a multiple immunoaffinity protein depletion (multiple affinity removal system, MARS) pre-treatment strategy with subsequent two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and peptide mass finger printing analysis for the detection of ovarian cancer-associated plasma proteins.

Materials and Methods

Following immunoaffinity depletion, total plasma protein content was reduced by 84.2 ± 1.8% (mean ± SE, n = 32). The number of proteins detected in the control and ovarian cancer groups was 349 and 357, respectively. This represented an increase in spot detection of almost twofold when compared to 2D PAGE displays of untreated plasma (174 spots). Of the proteins displayed, post-depletion, 300 (control) and 302 (ovarian cancer, OC) were common within each group. PDQuest analysis indicated that 109 protein spots were statistically different between the two groups and, of these, 59 exhibited greater than or equal to twofold difference in spot density (Student’s t test, p = 0.01). Thirty-nine of these proteins were successfully identified with reliable confidence.

Results and Discussion

The data obtained in this study demonstrates that immunodepletion of plasma before 2D PAGE profiling have generated identifiable plasma proteins that are differentially expressed in the high-grade ovarian cancer sample set compared to controls. This approach, therefore, may be useful in identifying candidate biomarkers for inclusion in multi-marker tests for ovarian cancer that may exhibit greater sensitivity and specificity than those currently available. It was evident, however, from the predominant identification of host response proteins that immunodepletion did not generate sufficient levels of enrichment of lower abundance tumor-specific proteins to facilitate detection.

High abundance synovial fluid proteome: distinct profiles in health and osteoarthritis

The development of increasingly high-throughput and sensitive mass spectroscopy-based proteomic techniques provides new opportunities to examine the physiology and pathophysiology of many biologic fluids and tissues. The purpose of this study was to determine protein expression profiles of high-abundance synovial fluid (SF) proteins in health and in the prevalent joint disease osteoarthritis (OA). A cross-sectional study of 62 patients with early OA (n = 21), patients with late OA (n = 21), and control individuals (n = 20) was conducted. SF proteins were separated by using one-dimensional PAGE, and the in-gel digested proteins were analyzed by electrospray ionization tandem mass spectrometry. A total of 362 spots were examined and 135 high-abundance SF proteins were identified as being expressed across all three study cohorts. A total of 135 SF proteins were identified. Eighteen proteins were found to be significantly differentially expressed between control individuals and OA patients. Two subsets of OA that are not dependent on disease duration were identified using unsupervised analysis of the data. Several novel SF proteins were also identified. Our analyses demonstrate no disease duration-dependent differences in abundant protein composition of SF in OA, and we clearly identified two previously unappreciated yet distinct subsets of protein profiles in this disease cohort. Additionally, our findings reveal novel abundant protein species in healthy SF whose functional contribution to SF physiology was not previously recognized. Finally, our studies identify candidate biomarkers for OA with potential for use as highly sensitive and specific tests for diagnostic purposes or for evaluating therapeutic response.

Peptide correlation: A means to identify high quality quantitative information in large-scale proteomic studies

A major challenge of proteomic studies is the accurate quantitation of proteins. LC-MS/MS-based methods are especially suited for profiling proteins in large sample sets. In this setup, the measurement of relative protein abundance relies on the correct quantitation of tryptic peptides. However, peptide intensities often do not unequivocally reflect the abundance of the native proteins in the sample. In this study, we show that peptides that accurately reflect relative protein abundances in large-scale sample sets can be selected based on the correlation to each other. This strategy was tested in a well-controlled experiment using a set of spiked serum samples as well as 55 clinical serum samples from schizophrenia patients and healthy volunteers. The peptide correlation analysis we present here provides an intuitive and simple procedure to obtain a high quality quantitative information from proteomics data.

Identification and Validation of Mannose 6-Phosphate Glycoproteins in Human Plasma Reveal a Wide Range of Lysosomal and Non-lysosomal Proteins

Acid hydrolase activities are normally confined within the cell to the lysosome, a membrane-delimited cytoplasmic organelle primarily responsible for the degradation of macromolecules. However, lysosomal proteins are also present in human plasma, and a proportion of these retain mannose 6-phosphate (Man-6-P), a modification on N-linked glycans that is recognized by Man-6-P receptors (MPRs) that normally direct the targeting of these proteins to the lysosome. In this study, we purified the Man-6-P glycoforms of proteins from human plasma by affinity chromatography on immobilized MPRs and characterized this subproteome by two-dimensional gel electrophoresis and by tandem mass spectrometry. As expected, we identified many known and potential candidate lysosomal proteins. In addition, we also identified a number of abundant classical plasma proteins that were retained even after two consecutive rounds of affinity purification. Given their abundance in plasma, we initially considered these proteins to be likely contaminants, but a mass spectrometric study of Man-6-phosphorylation sites using MPR-purified glycopeptides revealed that some proportion of these classical plasma proteins contained the Man-6-P modification. We propose that these glycoproteins are phosphorylated at low levels by the lysosomal enzyme phosphotransferase, but their high abundance results in detection of Man-6-P glycoforms in plasma. These results may provide useful insights into the molecular processes underlying Man-6-phosphorylation and highlight circumstances under which the presence of Man-6-P may not be indicative of lysosomal function. In addition, characterization of the plasma Man-6-P glycoproteome should facilitate development of mass spectrometry-based tools for the diagnosis of lysosomal storage diseases and for investigating the involvement of Man-6-P-containing glycoproteins in more widespread human diseases and their potential utility as biomarkers.

Proteome analysis of human follicular fluid

We used proteomic approach to analyze the protein profile of human follicular fluid (HFF) obtained from 25 normo-ovulatory women undergoing assisted reproduction techniques due to a male infertility factor. In all HFF samples analyzed we found 695 common spots distributed in the 3 to 10 pH range and in the 10-200 kDa range. Only 625 of these spots were also present in the plasma. We used MALDI-TOF-MS analysis to unequivocally assign 183 HFF/plasma matched spots and 27 HFF/plasma unmatched spots. A large number of acute-phase proteins, including transferrin, ceruloplasmin, afamin, hemopexin, haptoglobin and plasma amyloid protein, were identified in HFF in relatively high concentration supporting the hypothesis that mammalian ovulation can be compared to an inflammatory event. We also identified several important antioxidant enzymes; i.e., catalase, superoxide dismutase, glutathione transferase, paraoxonase, heat shock protein 27 and protein disulfide isomerase. This indicates that during maturation the human follicle is well protected against toxic injury due to oxidative stress.

Identification of N-linked glycoproteins in human saliva by glycoprotein capture and mass spectrometry

Glycoproteins make up a major and important part of the salivary proteome and play a vital role in maintaining the health of the oral cavity. Because changes in the physiological state of a person are reflected as changes in the glycoproteome composition, mapping the salivary glycoproteome will provide insights into various processes in the body. Salivary glycoproteins were identified by the hydrazide coupling and release method. In this approach, glycoproteins were coupled onto a hydrazide resin, the proteins were then digested and formerly N-glycosylated peptides were selectively released with the enzyme PNGase F and analyzed by LC-MS/MS. Employing this method, coupled with in-solution isoelectric focusing separation as an additional means for pre-fractionation, we identified 84 formerly N-glycosylated peptides from 45 unique N-glycoproteins. Of these, 16 glycoproteins have not been reported previously in saliva. In addition, we identified 44 new sites of N-linked glycosylation on the proteins.