Post-translational modifications of FDA-approved plasma biomarkers in glioblastoma samples.

Liquid chromatography-tandem mass spectrometry was used to analyze plasma proteins of volunteers (control) and patients with glioblastoma multiform (GBM). A database search was pre-set with a variable post-translational modification (PTM): phosphorylation, acetylation or ubiquitination. There were no significant differences between the control and the GBM groups regarding the number of protein identifications, sequence coverage or number of PTMs. However, in GBM plasma, we unambiguously observed a decreased fraction in post-translationally modified peptides identified with high quality. The disease-specific PTM patterns were extracted and mapped to the set of FDA-approved plasma protein markers. Decreases of 46% and 24% in the number of acetylated and ubiquitinated peptides, respectively, were observed in the GBM samples. Significance of capturing disease-associated patterns of protein modifications was envisaged.

Plasma preparation to measure FDA-approved protein markers by selected reaction monitoring.

BACKGROUND: The development of commercially available panels for human blood plasma screening via selected reaction monitoring (SRM) offers reliable, cost-efficient and highly-standardized discovery and validation of protein biomarkers. However, protein detection by SRM can be hampered by interfering peptide fragment ions. To estimate the influence of interference on protein detection, we performed different types of sample preparation and implemented SRM measurements for well-characterized protein targets approved by the US Food and Drug Administration. METHODS: We used the PlasmaDeepDive™ SRM assay from BiognoSYS AG for absolute quantification of 18 proteins in 19 samples of human plasma using three different protocols for sample preparation. SRM measurements were performed using iRT standards for retention time normalization and isotopically-labeled reference peptides for absolute quantification. SpectroDive™ software was used for automated detection of reliable peak groups. RESULTS: Fourteen targeted proteins were quantitatively measured in more than half of the samples. Depletion of highly-abundant plasma proteins and peptide fraction clean-up on centrifuge plates resulted in detection of all 18 targeted proteins in femtomolar to picomolar concentrations. CONCLUSIONS: It was shown that commercially designed SRM kits are suitable for SRM detection of well-established plasma/serum biomarkers.

One-dimensional proteomic profiling of Danio rerio embryo vitellogenin to estimate quantum dot toxicity.

BACKGROUND: Vitellogenin (Vtg) is the major egg yolk protein (YP) in most oviparous species and may be useful as an indicator in ecotoxicological testing at the biochemical level. In this study, we obtained detailed information about the Vtgs of Danio rerio embryos by cutting SDS-PAGE gel lanes into thin slices, and analyzing them slice-by-slice with (MALDI-TOF) mass spectrometry. RESULTS: We conducted three proteomic analyses, comparing embryonic Danio rerio Vtg cleavage products after exposure for 48 h to CdSecore/ZnSshell quantum dots (QDs), after exposure to a mixture of the components used for quantum dot synthesis (MCS-QDs), and in untreated embryos. The Vtg mass spectrometric profiles of the QDs-treated embryos differed from those of the unexposed or MCS-QDs-treated embryos. CONCLUSION: This study demonstrates the possible utility of Vtg profiling in D. rerio embryos as a sensitive diagnostic tool to estimate nanoparticle toxicity.

Applying of hierarchical clustering to analysis of protein patterns in the human cancer-associated liver.

BACKGROUND: There are two ways that statistical methods can learn from biomedical data. One way is to learn classifiers to identify diseases and to predict outcomes using the training dataset with established diagnosis for each sample. When the training dataset is not available the task can be to mine for presence of meaningful groups (clusters) of samples and to explore underlying data structure (unsupervised learning). RESULTS: We investigated the proteomic profiles of the cytosolic fraction of human liver samples using two-dimensional electrophoresis (2DE). Samples were resected upon surgical treatment of hepatic metastases in colorectal cancer. Unsupervised hierarchical clustering of 2DE gel images (n = 18) revealed a pair of clusters, containing 11 and 7 samples. Previously we used the same specimens to measure biochemical profiles based on cytochrome P450-dependent enzymatic activities and also found that samples were clearly divided into two well-separated groups by cluster analysis. It turned out that groups by enzyme activity almost perfectly match to the groups identified from proteomic data. Of the 271 reproducible spots on our 2DE gels, we selected 15 to distinguish the human liver cytosolic clusters. Using MALDI-TOF peptide mass fingerprinting, we identified 12 proteins for the selected spots, including known cancer-associated species. CONCLUSIONS/SIGNIFICANCE: Our results highlight the importance of hierarchical cluster analysis of proteomic data, and showed concordance between results of biochemical and proteomic approaches. Grouping of the human liver samples and/or patients into differing clusters may provide insights into possible molecular mechanism of drug metabolism and creates a rationale for personalized treatment.

Producing a one-dimensional proteomic map for human liver cytochromes p450.

In this chapter we explore the inducible cytochrome P450 (CYP) forms as an example of membrane proteins analysis that relies on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) fractionation with subsequent mass spectrometric (MS) identification. The approach involves cutting an SDS-PAGE gel lane into thin slices and identifying proteins in each slice by MS with the aim of obtaining detailed information on proteins of interest. A one-dimensional proteomic map showing the distribution of selected CYP isoforms across 40 slices was constructed using mass spectra obtained from each slice. Our protocol proved to be efficient enough to obtain a comprehensive profile of drug-metabolizing enzymes in the human liver. In addition to human tissues, the approach described should be applicable to the characterization of membrane proteins in other eukaryotic species.

Computational approach to characterization of human liver drug-metabolizing enzymes.

Cytochromes P450 are the key enzymes for activating and inactivating many drugs; individual expression levels of CYPs may play a crucial role in drug safety and drug efficacy. Statistical comparison of biochemical profiles of 23 human liver microsomes have been used to characterize human liver samples. The profile included 12 parameters, namely activity of NADPH-cytochrome P450 reductase, cytochrome P450 content and cytochrome P450-dependent monooxygenase activities with marker substrates. Unsupervised statistical methods including cluster analysis and principal component analysis revealed with very high confidence the presence of two groups. Difference between the groups was explained by peculiarities of reductase activity and cytochrome P450 enzyme activities with 7-ethoxyresorufin, 7-methoxyresorufin, 7-methoxycoumarin, 7-benzyloxyresorufin and 7-benzyloxyquinoline. Results of biochemical assays coupled with multidimensional data analysis can be further used for targeted proteomic profiling of microsome oxidation mechanisms.

Application of slicing of one-dimensional gels with subsequent slice-by-slice mass spectrometry for the proteomic profiling of human liver cytochromes P450.

Sequential thin slicing of one-dimensional electrophoresis gels followed by slice-by-slice mass spectrometry to allow protein identification was used to produce a proteomic map for cytochromes P450. Parallel MALDI-TOF-MS and LC-MS/MS analyses were performed. Combination of the two MS methods increased the quality of protein identification. We have proposed an efficient approach to obtain a comprehensive profile of drug-metabolizing enzymes in the liver that can be used to differentiate between polymorphic variants of cytochromes P450.

Fluorescent assay for riboflavin binding to cytochrome P450 2B4.

The interactions between the hemoprotein cytochrome P450 2B4 (CYP 2B4) and riboflavin - a low molecular weight component of the flavoprotein NADPH-dependent cytochrome P450 reductase - were investigated by fluorescence spectroscopy. Riboflavin fluorescence quenching by cytochrome P450 2B4 was used to probe the ligand-enzyme binding (lambda(ex)=385 nm, lambda(em)=520 nm). Fluorescence titration experiments showed formation of a complex between cytochrome P450 2B4 and riboflavin with an apparent dissociation constant value, K(d)=8.8+/-1 microM. The fluorescence intensity of riboflavin was decreased with increasing the cytochrome P450 2B4 concentration, indicating the transfer of resonance excitation energy from riboflavin (energy donor) to the cytochrome P450 2B4 heme (energy acceptor). The data obtained are suggestive of the existence of riboflavin binding site(s) on the hemeprotein molecule.