Serum albumin cysteine trioxidation is a potential oxidative stress biomarker of type 2 diabetes mellitus

Metabolic disorders in T2DM generate multiple sources of free radicals and oxidative stress that accelerate nonenzymatic degenerative protein modifications (DPMs) such as protein oxidation, disrupt redox signaling and physiological function, and remain a major risk factor for clinical diabetic vascular complications. In order to identify potential oxidative biomarkers in the blood plasma of patients with T2DM, we used LC-MS/MS-based proteomics to profile plasma samples from patients with T2DM and healthy controls. The results showed that human serum albumin (HSA) is damaged by irreversible cysteine trioxidation, which can be a potential oxidative stress biomarker for the early diagnosis of T2DM. The quantitative detection of site-specific thiol trioxidation is technically challenging; thus, we developed a sensitive and selective LC-MS/MS workflow that has been used to discover and quantify three unique thiol-trioxidized HSA peptides, ALVLIAFAQYLQQC_(SO3H)PFEDHVK (m/z 1241.13), YIC_(SO3H)ENQDSISSK (m/z 717.80) and RPC_(SO3H)FSALEVDETYVPK (m/z 951.45), in 16 individual samples of healthy controls (n = 8) and individuals with diabetes (n = 8). Targeted quantitative analysis using multiple reaction monitoring mass spectrometry revealed impairment of the peptides with m/z 1241.13, m/z 717.80 and m/z 951.45, with significance (P < 0.02, P < 0.002 and P < 0.03), in individuals with diabetes. The results demonstrated that a set of three HSA thiol-trioxidized peptides, which are irreversibly oxidatively damaged in HSA in the plasma of patients with T2DM, can be important indicators and potential biomarkers of oxidative stress in T2DM.

Search for breast cancer biomarkers in fractionated serum samples by protein profiling with SELDI-TOF MS

BACKGROUND

Many high-abundant acute phase reactants have been previously detected as potential breast cancer biomar-kers. However, they are unlikely to be specific for breast cancer. Cancer-specific biomarkers are thought to be among the lower abundant proteins.

METHODS

We aimed to detect lower abundant discriminating proteins by performing serum fractionation by strong anion exchange chromatography preceding protein profiling with SELDI-TOF MS. In a pilot study, we tested the different fractions resulting from fractionation, on several array types. Fraction 3 on IMAC30 and Fraction 6 on Q10 yielded the most discriminative proteins and were used for serum protein profiling of 73 incident breast cancer cases and 73 matched controls.

RESULTS

Eight peaks showed statistically significantly different intensities between cases and controls (P⧁0.05), and had less than 10% chance to be a false-positive finding. Seven of these were tentatively identified as apolipoprotein C-II (m/z 8,909), oxidized apolipoprotein C-II (m/z 8,925), apolipoprotein C-III (m/z 8,746), fragment of coagulation factor XIIIa (m/z 3,959), heterodimer of apolipoprotein A-I and apolipoprotein A-II (m/z 45,435), hemoglobin B-chain (m/z 15,915), and post-translational modified hemoglobin (m/z 15,346).

CONCLUSION

By extensive serum fractionation, we detected many more proteins than in previous studies without fractionation. However, discriminating proteins were still high abundant. Results indicate that either lower abundant proteins are less distinctive, or more rigorous fractionation and selective protein depletion, or a more sensitive assay, are needed to detect lower abundant discriminative proteins.

Mass spectrometry-based proteomic quest for diabetes biomarkers

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia, which affects hundreds of millions of individuals worldwide. Early diagnosis and complication prevention of DM are helpful for disease treatment. However, currently available DM diagnostic markers fail to achieve the goals. Identification of new diabetic biomarkers assisted by mass spectrometry (MS)-based proteomics may offer solution for the clinical challenges. Here, we review the current status of biomarker discovery in DM, and describe the pressure cycling technology (PCT)-Sequential Window Acquisition of all Theoretical fragment-ion (SWATH) workflow for sample-processing, biomarker discovery and validation, which may accelerate the current quest for DM biomarkers. This article is part of a Special Issue entitled: Medical Proteomics.

Gender dimorphism in regulation of plasma proteins in streptozotocin-induced diabetic rats

In the present study, we examined differentially regulated plasma proteins between healthy control and streptozotocin (STZ)-induced male and female diabetic rats by 2DE-based proteomic analysis. Animal experiments revealed that significantly lower plasma insulin levels were observed in female diabetic rats, consequently resulting in higher blood glucose levels in female diabetic rats. Importantly, plasma levels of sex hormones were significantly altered in a gender-dependent manner before and after STZ treatment. Results of the animal experiment indicated the existence of sexual dimorphism in the regulation of plasma proteins between healthy control and diabetic rats. Plasma proteome analysis enabled us to identify a total of 38 proteins showing sexual dimorphic regulation patterns. In addition, for the first time, we identified several differentially regulated plasma proteins between healthy control and diabetic rats, including apolipoprotein E, fetuin B, α-1-acid glycoprotein, β-2-glycoprotein 1, 3-hydroxyanthranilate 3,4-dioxygenase, and serum amyloid P-component. To the best of our knowledge, this is the first proteomic approach to address sexual dimorphism in diabetic animals. These proteomic data on gender-dimorphic regulation of plasma proteins provide valuable information that can be used for evidence-based gender-specific clinical treatment of diabetes.

Human serum proteome analysis: new source of markers in metabolic disorders

The prevalence of metabolic disorders (MDs), especially diabetes, is rapidly increasing worldwide, leading to an increasing risk of cardiovascular and other socially relevant complications. To boost MD biomarker discovery, advanced proteomics can harmonize metabolomics. Indeed, the rapid development of mass spectrometry (MS) has designated proteomics as an emerging platform to interrogate the plasma/serum proteome for the discovery of next-generation biomarkers exploitable for risk assessment, early detection and prognosis of MDs. Preanalytical plasma/serum treatment, such as combinatorial peptide ligand libraries with nano-liquid chromatography coupled with tandem MS or selected reaction monitoring coupled to triple-quadrupole time-of-flight instruments, are proven clinical laboratory techniques for quantitative analyses. New strategies, such as SWATH™ MS, which allows us to systematically characterize and quantify query sample sets of 'any protein of interest' in complex biological samples, may dramatically improve next-generation MD biomarkers, especially considering the plethora of candidates coming from the 'bioreactor' gut microbiota affecting MD onset and progression.

Quantitative statistical analysis of standard and human blood proteins from liquid chromatography, electrospray ionization, and tandem mass spectrometry

It will be important to determine if the parent and fragment ion intensity results of liquid chromatography, electrospray ionization and tandem mass spectrometry (LC-ESI-MS/MS) experiments have been randomly and independently sampled from a normal population for the purpose of statistical analysis by general linear models and ANOVA. The tryptic parent peptide and fragment ion m/z and intensity data in the mascot generic files from LC-ESI-MS/MS of purified standard proteins, and human blood protein fractionated by partition chromatography, were parsed into a Structured Query Language (SQL) database and were matched with protein and peptide sequences provided by the X!TANDEM algorithm. The many parent and/or fragment ion intensity values were log transformed, tested for normality, and analyzed using the generic Statistical Analysis System (SAS). Transformation of both parent and fragment intensity values by logarithmic functions yielded intensity distributions that closely approximate the log-normal distribution. ANOVA models of the transformed parent and fragment intensity values showed significant effects of treatments, proteins, and peptides, as well as parent versus fragment ion types, with a low probability of false positive results. Transformed parent and fragment intensity values were compared over all sample treatments, proteins or peptides by the Tukey-Kramer Honestly Significant Difference (HSD) test. The approach provided a complete and quantitative statistical analysis of LC-ESI-MS/MS data from human blood.

Mass spectrometry of peptides and proteins from human blood

It is difficult to convey the accelerating rate and growing importance of mass spectrometry applications to human blood proteins and peptides. Mass spectrometry can rapidly detect and identify the ionizable peptides from the proteins in a simple mixture and reveal many of their post-translational modifications. However, blood is a complex mixture that may contain many proteins first expressed in cells and tissues. The complete analysis of blood proteins is a daunting task that will rely on a wide range of disciplines from physics, chemistry, biochemistry, genetics, electromagnetic instrumentation, mathematics and computation. Therefore the comprehensive discovery and analysis of blood proteins will rank among the great technical challenges and require the cumulative sum of many of mankind's scientific achievements together. A variety of methods have been used to fractionate, analyze and identify proteins from blood, each yielding a small piece of the whole and throwing the great size of the task into sharp relief. The approaches attempted to date clearly indicate that enumerating the proteins and peptides of blood can be accomplished. There is no doubt that the mass spectrometry of blood will be crucial to the discovery and analysis of proteins, enzyme activities, and post-translational processes that underlay the mechanisms of disease. At present both discovery and quantification of proteins from blood are commonly reaching sensitivities of ∼1 ng/mL.

Proteomic study of serum proteins in a type 2 diabetes mellitus rat model by Chinese traditional medicine Tianqi Jiangtang Capsule administration

Proteomics technology was for the first time applied to investigate the changes of serum proteins levels in type 2 diabetes mellitus (T2DM) rat model after treated by Chinese traditional medicine Tianqi Jiangtang Capsule (ten normal Wistar rats, ten with T2DM and ten with T2DM administrated by Tianqi Jiangtang Capsule). In addition to two-dimensional polyacrylamide gel electrophoresis (2-DE), serum protein profiling in the three groups was further performed using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF-TOF/MS). 11 visualized spots were differentially regulated and identified as diabetes-associated proteins. All the samples in three groups were then analyzed by ELISA and estimated the 7 proteins which were found to vary. The distinct effect of T2DM induction on the pattern of rat serum includes the down-regulation of Apolipoprotein E, Apolipoprotein A-I, Ig gamma-2A chain C region, and up-regulation of Transthyretin (TTR), Haptoglobin (Hp), Serum amyloid P-componen (SAP), Prothrombin. The majority of those protein levels were interestingly restored to those of healthy rats after Tianqi Jiangtang Capsule treatment.

Serum Proteome Pool Changes in Type 2 Diabetic Patients Treated with Anakinra

Introduction

High glucose concentrations induce the production of IL-1β in human pancreatic beta cells leading to impaired insulin secretion, decreased cell proliferation and apoptosis. Blockade of IL-1 signalling with the recombinant human IL-1 receptor antagonist anakinra reduces HbA1c in patients with type 2 diabetes. The aims of the present study were to identify: (1) candidate surrogates for improved glycemia in type 2 diabetic patients following treatment with anakinra, (2) proteins that change serum concentration because of anakinra treatment and (3) candidate biomarkers that may predict improved glycemia in type 2 diabetic subjects treated with anakinra.

Methods

Surface-enhanced laser desorption/ionisation time-of-flight mass spectrometry was used to analyse serum from 67 type 2 diabetic patients who had received either placebo or anakinra for 13 weeks. Immunodepletion with magnetic protein G bead-coupled antibodies were used to identify three proteins and Western blotting confirmed the biomarker concentration pattern of four proteins.

Results

Twelve proteins, including transthyretin (TTR) and transferrin (Tf), were identified as candidate surrogates for improved glycemia. Six proteins, including retinol-binding protein 4 (RPB4) and a protein tentatively identified as modified apolipoprotein-A1 (apo-AI), increased expression as a consequence of anakinra treatment and four proteins were candidate biomarkers that may predict improved glycemia following anakinra treatment. Furthermore, we found increased RBP4 to be associated with improved beta cell secretory function and increased TTR, RBP4 and modified apo-AI (peak at 28,601 Da) to be associated with decreased inflammation.

Conclusions

Anakinra-induced changes in the serum proteome pool associated with a decreased cardiovascular disease risk, reduced inflammation and improved beta cell secretory function.

Comparison of three methods for fractionation and enrichment of low molecular weight proteins for SELDI-TOF-MS differential analysis

In most diseases, the clinical need for serum/plasma markers has never been so crucial, not only for diagnosis, but also for the selection of the most efficient therapies, as well as exclusion of ineffective or toxic treatment. Due to the high sample complexity, prefractionation is essential for exploring the deep proteome and finding specific markers. In this study, three different sample preparation methods (i.e., highly abundant protein precipitation, restricted access materials (RAM) combined with IMAC chromatography and peptide ligand affinity beads) were investigated in order to select the best fractionation step for further differential proteomic experiments focusing on the LMW proteome (MW inferior to 40,000 Da). Indeed, the aim was not to cover the entire plasma/serum proteome, but to enrich potentially interesting tissue leakage proteins. These three methods were evaluated on their reproducibility, on the SELDI-TOF-MS peptide/protein peaks generated after fractionation and on the information supplied. The studied methods appeared to give complementary information and presented good reproducibility (below 20%). Peptide ligand affinity beads were found to provide efficient depletion of HMW proteins and peak enrichment in protein/peptide profiles.

Precipitation and selective extraction of human serum endogenous peptides with analysis by quadrupole time-of-flight mass spectrometry reveals posttranslational modifications and low-abundance peptides

The endogenous peptides of human serum may have regulatory functions, have been associated with physiological states, and their modifications may reveal some mechanisms of disease. In order to correlate levels of specific peptides with disease alongside internal standards, the polypeptides must first be reliably extracted and identified. Endogenous blood peptides can be effectively enriched by precipitation of the serum with organic solvents followed by selective extraction of peptides using aqueous solutions modified with organic solvents. Polypeptides on filter paper were assayed with Coomasie brilliant blue binding. The polypeptides were resolved by detergent tricine polyacrylamide electrophoresis and visualized by diamine silver staining. Peptides in the extracts were collected by C18 and analyzed by matrix-assisted laser desorption/ionization and liquid chromatography-electrospray ionization-tandem mass spectrometry (MS/MS) quadrupole time-of-flight MS/MS. Peptides were resolved as multiple isotopic peaks in MS mode with mass deviation of 0.1 Da or less and similar accuracy for fragments. The sensitivity of MS and MS/MS analysis was estimated to be in the picomolar range or less. The peptide composition of the extracts was dependent on solvent formulation. Multiple peptides from apolipoproteins, complement proteins, coagulation factors, and many others were identified by X!Tandem with high mass accuracy of peptide ions and fragments from collision-induced dissociation. Many previously unreported posttranslational modifications of peptides including phosphorylations, oxidations, glycosylations, and others were detected with high mass accuracy and may be of clinical importance. About 4,630 redundant peptides were identified with 99% confidence separately, and together some 1,251 distinct proteins were identified with 99% confidence or greater using the Paragon algorithm.

Serum retinol-binding protein 4 is associated with insulin secretion in Chinese people with normal glucose tolerance

BACKGROUND

Serum levels of retinol-binding protein 4 (RBP4) are associated with insulin resistance and type 2 diabetes mellitus (T2DM) and may impact on β-cell function. Thus, the present study investigated the relationship between serum RBP4 and insulin secretion in Chinese people with and without T2DM.

METHODS

A 75 g oral glucose tolerance test was administered to all 867 subjects and serum RBP4 concentrations were determined. Insulin secretion was assessed by ΔI/ΔG (increment in plasma insulin concentration/plasma glucose concentration 30 min after the oral administration of 75 g glucose) and the total area under the curve for insulin over 180 min (AUC-I). Magnetic resonance imaging was used to measure visceral fat area (VFA) at L4-L5; subjects with VFA ≥80 cm(2) were considered to have visceral obesity (VO).

RESULTS

Serum RBP4 concentrations were significantly higher in subjects with VO than without, regardless of the presence of T2DM. In addition, in the entire group with normal glucose tolerance (NGT), serum RBP4 was positively correlated with ΔI/ΔG (r = 0.152; P < 0.01) and AUC-I (r = 0.218; P < 0.01) after adjustment for gender. The correlation between RBP4 and ΔI/ΔG (r =  0.162; P < 0.05) and AUC-I (r = 0.195; P < 0.01) remained in NGT non-VO subjects. No correlation was found between serum RBP4 and ΔI/ΔG or AUC-I in T2DM patients. Stepwise multiple regression analysis showed that serum RBP4 is an independent factor that contributes to ΔI/ΔG (β = 0.176) and AUC-I (β = 0.204) in NGT non-VO subjects.

CONCLUSIONS

Serum RBP4 is correlated with glucose-stimulated insulin secretion in NGT non-VO subjects, but not in NGT VO subjects and T2DM patients.

Role of MAPK in apolipoprotein CIII-induced apoptosis in INS-1E cells

Background

Individuals with type 2 diabetes mellitus (T2DM) have elevated levels of circulating apolipoprotein CIII (apoCIII). ApoCIII plays an important role for plasma triglyceride levels and elevated levels of the apolipoprotein have been connected with dyslipidemia in T2DM subjects. In addition, apoCIII has been linked to enhanced β-cell apoptosis. The present study was undertaken to investigate apoptotic mechanisms induced by the apolipoprotein.

Results

ApoCIII (10 μg/ml) enhanced apoptosis 2-fold in insulin-producing INS-1E cells after 24 hours exposure to the apolipoprotein. At this time point phosphorylation of mitogen activated protein kinase (MAPK) p38 had doubled but ERK1/2 and JNK were not activated. Instead, ERK1/2 showed rapid and transient phosphorylation (2-fold after 0.5 hour). No JNK phosphorylation was observed. In support of a role of activation of not only p38 but also ERK1/2 in apoCIII-induced apoptosis, inclusion of p38 inhibitor SB203580 (10 μM) or ERK1/2 inhibitor PD98059 (100 μM) normalized apoptosis. Whereas influx of Ca²⁺ was linked to apoCIII-induced ERK1/2 activation, pro-apoptotic protein CHOP/GADD of the unfolded protein response (UPR) was not affected by apoCIII.

Conclusion

It is suggested that elevated circulating apoCIII levels may contribute to β-cell apoptosis via activation of p38 and ERK1/2 in individuals with T2DM. Therapies aiming at normalizing levels of apoCIII could be beneficial not only for the function of the β-cell but also for cardiovascular protection.