Dissociation of Fatty Liver and Insulin Resistance in I148M PNPLA3 Carriers: Differences in Diacylglycerol (DAG) FA18:1 Lipid Species as a Possible Explanation.

Fatty liver is tightly associated with insulin resistance and the development of type 2 diabetes. I148M variant in patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene is associated with high liver fat but normal insulin sensitivity. The underlying mechanism of the disassociation between high liver fat but normal insulin sensitivity remains obscure. We investigated the effect of I148M variant on hepatic lipidome of subjects with or without fatty liver, using the Lipidyzer method. Liver samples of four groups of subjects consisting of normal liver fat with wild-type PNPLA3 allele (group 1); normal liver fat with variant PNPLA3 allele (group 2); high liver fat with wild-type PNPLA3 allele (group 3); high liver fat with variant PNPLA3 allele (group 4); were analyzed. When high liver fat to normal liver fat groups were compared, wild-type carriers (group 3 vs. group 1) showed similar lipid changes compared to I148M PNPLA3 carriers (group 4 vs. group 2). On the other hand, in wild-type carriers, increased liver fat significantly elevated the proportion of specific DAGs (diacylglycerols), mostly DAG (FA18:1) which, however, remained unchanged in I148M PNPLA3 carriers. Since DAG (FA18:1) has been implicated in hepatic insulin resistance, the unaltered proportion of DAG (FA18:1) in I148M PNPLA3 carriers with fatty liver may explain the normal insulin sensitivity in these subjects.

Detection and site localization of phosphorylcholine-modified peptides by NanoLC-ESI-MS/MS using precursor ion scanning and multiple reaction monitoring experiments.

Phosphorylcholine (PC)-modified biomolecules like lipopolysaccharides, glycosphingolipids, and (glyco)proteins are widespread, highly relevant antigens of parasites, since this small hapten shows potent immunomodulatory capacity, which allows the establishment of long-lasting infections of the host. Especially for PC-modified proteins, structural data is rare because of the zwitterionic nature of the PC substituent, resulting in low sensitivities and unusual but characteristic fragmentation patterns. We have developed a targeted mass spectrometric approach using hybrid triple quadrupole/linear ion trap (QTRAP) mass spectrometry coupled to nanoflow chromatography for the sensitive detection of PC-modified peptides from complex proteolytic digests, and the localization of the PC-modification within the peptide backbone. In a first step, proteolytic digests are screened using precursor ion scanning for the marker ions of choline (m/z 104.1) and phosphorylcholine (m/z 184.1) to establish the presence of PC-modified peptides. Potential PC-modified precursors are then subjected to a second analysis using multiple reaction monitoring (MRM)-triggered product ion spectra for the identification and site localization of the modified peptides. The approach was first established using synthetic PC-modified synthetic peptides and PC-modified model digests. Following the optimization of key parameters, we then successfully applied the method to the detection of PC-peptides in the background of a proteolytic digest of a whole proteome. This methodological invention will greatly facilitate the detection of PC-substituted biomolecules and their structural analysis.

MS binding assays-with MALDI toward high throughput.

A novel type of MS binding assay, a substitute for radioligand binding, in which the quantification of the MS marker is performed by MALDI-MS-MS (FlashQuant) has been established. Because conventional MS binding assays can only be carried out by LC-ESI-MS-MS, the use of the FlashQuant system substantially increases the throughput capacity of this method. The study was performed for mGAT1 as a model system. First, a method was developed to quantify NO 711 as a marker for mGAT1 in a range from 208 pM to 16.7 nM using [2H10]NO 711 as an internal standard. On this basis, MS binding assays for mGAT1 could be implemented. Affinity constants determined in both saturation and competition experiments were in excellent agreement with those obtained in MS binding assays based on LC-ESI-MS-MS quantification. As the MALDI-MS system takes only a few seconds for quantification per sample, and the whole assay procedure is executed in a 96-well format, this technique is amenable to high-throughput screening.

Prevalidation of potential protein biomarkers in toxicology using iTRAQ reagent technology.

Today, toxicoproteomics still relies mainly on 2-DE followed by MS for detection and identification of proteins, which might characterize a certain state of disease, indicate toxicity or even predict carcinogenicity. We utilized the classical 2-DE/MS approach for the evaluation of early protein biomarkers which are predictive for chemically induced hepatocarcinogenesis in rats. We were able to identify statistically significantly deregulated proteins in N-nitrosomorpholine exposed rat liver tissue. Based on literature data, biological relevance in the early molecular process of hepatocarcinogenicity could be suggested for most of these potential biomarkers. However, in order to ensure reliable results and to create the prerequisites necessary for integration in routine toxicology studies in the future, these protein expression patterns need to be prevalidated using independent technology platforms. In the current study, we evaluated the usefulness of iTRAQ reagent technology (Applied Biosystems, Framingham, USA), a recently introduced MS-based protein quantitation method, for verification of the 2-DE/MS biomarkers. In summary, the regulation of 26 2-DE/MS derived protein biomarkers could be verified. Proteins like HSP 90-beta, annexin A5, ketohexokinase, N-hydroxyarylamine sulfotransferase, ornithine aminotransferase, and adenosine kinase showed highly comparable fold changes using both proteomic quantitation strategies. In addition, iTRAQ analysis delivered further potential biomarkers with biological relevance to the processes of hepatocarcinogenicity: e.g. placental form of glutathione S-transferase (GST-P), carbonic anhydrase, and aflatoxin B1 aldehyde reductase. Our results show both the usefulness of iTRAQ reagent technology for biomarker prevalidation as well as for identification of further potential marker proteins, which are indicative for liver hepatocarcinogenicity.

Proteomic study of human bronchoalveolar lavage fluids from smokers with chronic obstructive pulmonary disease by combining surface-enhanced laser desorption/ionization-mass spectrometry profiling with mass spectrometric protein identification.

Bronchoalveolar lavage fluid (BALF) is an important diagnostic source to investigate cellular and molecular changes in the course of lung disorders. The pattern of soluble proteins in BALF obtained from patients at different stages of respiratory disorders may provide deeper insights in the molecular mechanisms of the disease. We used surface-enhanced laser desorption/ionization mass spectrometry (MS) for differential protein display combined with reversed-phase chromatography and subsequent matrix-assisted laser desorption/ionization-MS or nanoliquid chromatography MS/MS analysis for protein identification to compare the protein pattern of BALF samples obtained from ten smokers suffering from chronic obstructive pulmonary disease (COPD), eight clinically asymptomatic smokers, and eight nonsmokers without pulmonary disease. In this context, we were able to identify small proteins and peptides, either differentially expressed or secreted in the course of COPD or in a direct response to cigarette smoke. The concentrations of neutrophil defensins 1 and 2, S100A8 (calgranulin A), and S100A9 (calgranulin B) were elevated in BALFs of smokers with COPD when compared to asymptomatic smokers. Increased concentrations in S100A8 (Calgranulin A), salivary proline-rich peptide P-C, and lysozyme C were detected in BALFs of asymptomatic smokers when compared to nonsmokers, whereas salivary proline-rich peptide P-D and Clara cell phospholipid-binding protein (CC10) were reduced in their concentration. The identified proteins and peptides might be useful in the future as diagnostic markers for smoke-induced lung irritations and COPD.