Apolipoprotein C-III O-glycoform profiling of 500 serum samples by matrix-assisted laser desorption/ionization mass spectrometry for diagnosis of congenital disorders of glycosylation.

Congenital disorders of glycosylation (CDG) are caused by defects in various genes governing glycoconjugate biosynthesis. Several responsible genes have been identified in the protein N-glycosylation process. Analyses of mucin-type core-1 O-glycoform of apolipoprotein C-III (apoCIII) have recently revealed combined N- and O-glycosylation defects. We applied matrix-assisted laser desorption/ionization mass spectrometry profiling of apoCIII glycoforms to 500 serum samples for CDG screening, and reference values were determined. The content of unglycosylated apoCIII was low in early infancy, indicating that the O-glycan occupancy should be assessed based on age-matched reference values. The samples from patients with mutations in the ALG1, ATP6V0A2, B4GALT1, COG2, GCS1, PGM1, SLC35A2, and TRAPPC11 genes were analyzed. B4GALT1- and TRAPPC11-CDG were accompanied by under-sialylation of O-glycans and are now recognized as combined N- and O-glycosylation disorders.

Apolipoprotein C-III Strongly Correlates with Activated Factor VII-Anti-Thrombin Complex: An Additional Link between Plasma Lipids and Coagulation.

Activated factor VII-anti-thrombin (FVIIa-AT) complex is a potential biomarker of pro-thrombotic diathesis reflecting FVIIa-tissue factor (TF) interaction and has been associated with mortality in patients with coronary artery disease (CAD). Previous data indicated plasma lipids as predictors of FVIIa-AT variability, and plasma lipoproteins as potential stimulators of the coagulation cascade. Our aim was to evaluate the relationships between FVIIa-AT plasma concentration and a broad apolipoprotein profile (including ApoA-I, ApoB, ApoC-III and ApoE). Within the framework of the observational Verona Heart Study, we selected 666 subjects (131 CAD-free and 535 CAD, 75.4% males, mean age: 61.1 ± 10.9 years) not taking anticoagulant drugs and for whom plasma samples were available for both FVIIa-AT assay and a complete lipid profile. Plasma concentration of FVIIa-AT levels significantly and directly correlated with total and high-density lipoprotein cholesterol, triglycerides, ApoA-I, ApoC-III and ApoE levels. ApoC-III showed the strongest correlation (R = 0.235, p = 7.7 × 10-10), confirmed in all the sub-group analyses (males/females and CAD/CAD-free). Only ApoC-III remained associated with FVIIa-AT plasma concentration, even after adjustment for sex, age, CAD diagnosis, body mass index, renal function, smoking status, lipid-lowering therapies and FVIIa levels. The APOC3 gene locus-tagging polymorphism rs964184, previously linked with cardiovascular risk and plasma lipids by genome-wide association studies, was associated with both ApoC-III and FVIIa-AT plasma concentration. Our results indicate a strong association between ApoC-III and FVIIa-AT levels, thereby suggesting that an increased ApoC-III concentration may identify subjects with a pro-thrombotic diathesis characterized by an enhanced TF-FVIIa interaction and activity.

Targeted Measurements of O- and N-Glycopeptides Show That Proteins in High Density Lipoprotein Particles Are Enriched with Specific Glycosylation Compared to Plasma.

High density lipoprotein (HDL) particles are believed to be protective due to their inverse correlation with the prevalence of cardiovascular diseases. However, recent studies show that in some conditions such as heart disease and diabetes, HDL particles can become dysfunctional. Great attention has been directed toward HDL particle composition because the relative abundances of HDL constituents determine HDL's functional properties. A key factor to consider when studying the structure and composition of plasma particles is the protein glycosylation. Here, we profile the O- and N-linked glycosylation of HDL associated-proteins including the truncated form of Apo CIII and their glycan heterogeneity in a site-specific manner. Apolipoprotein CIII, fetuin A, and alpha 1 antitrypsin are glycoproteins associated with lipoproteins and are implicated in many cardiovascular and other disease conditions. A targeted method (UHPLC-QQQ) was used to measure the glycoprotein concentrations and site-specific glycovariations of the proteins in human plasma and compared with HDL particles isolated from the same plasma samples. The proteins found in the plasma are differentially glycosylated compared to those isolated in HDL. The results of this study suggest that glycosylation may play a role in protein partitioning in the blood, with possible functional implications.

Lycopene amends LPS induced oxidative stress and hypertriglyceridemia via modulating PCSK-9 expression and Apo-CIII mediated lipoprotein lipase activity.

This study was undertaken to uncover the regulatory role of lycopene in targeting lipopolysaccharide (LPS) induced oxidative stress and inflammatory cascades and subsequent regulation of proprotein convertase subtilisin/kexin type-9 (PCSK-9) expression via sterol regulatory element binding protein-2 (SREBP-2) and hepatocyte nuclear factor-1α (HNF-1α). Further, protein-protein interaction (PPI) studies for Lycopene-Apo-CIII complex against lipoprotein lipase (LPL) were also performed to assess its regulatory role behind the enhanced circulatory TG/TRLs clearance. Lycopene treatment down-regulated hepatocyte PCSK-9 expression via down-regulation of HNF-1α, whereas, LDL-receptor (LDL-R) was up-regulated by subsequent up-regulation of SREBP-2. PPI studies showed that lycopene diminishes the affinity of Apo-CIII to complex with LPL (ΔG: -917.1 Kcal/mol) resulting in increased LPL functionality and TRLs clearance. Moreover, lycopene also ameliorated LPS stimulated oxidative-stress via enhanced total antioxidant and HDL associated PON-1 activity in addition to down-regulate the expression and plasma level of inflammatory mediators. Based on above findings, we concluded that lycopene exhibits dual role in targeting LPS induced oxidative stress and hypertriglyceridemia via down-regulation of PCSK-9, making greater no. of surface LDL-R available for LPS processing and clearance, as well as increased LPL activity through inhibition of Apo-CIII.

Characterization of Apolipoprotein C3 (Apo C3) LNA/DNA Impurities and Degradation Products by LC-MS/MS.

Apolipoprotein C3 (Apo C3) LNA/DNA gapmer was evaluated under various stress and formulation conditions for the purpose of its development as a potential biotherapeutic for low density lipoprotein (LDL) lowering. Using ion-pairing (IP) reversed-phase (RP) liquid chromatography ultra-high resolution (UHR) tandem mass spectrometry (IP-RPLC-MS/MS), a combination of accurate mass measurements and collision-induced dissociation enabled in-depth characterization of Apo C3 LNA/DNA oligonucleotide, in particular the inherent impurities following synthesis and degradation products after exposure to stress conditions. In this study, oligonucleotide samples were stressed under different pH and UV exposure conditions. The primary impurities in Apo C3 LNA/DNA were losses of nucleotide moieties from both the 5'- and 3'-terminus leading to n-1, n-2, etc. species. Desulfurization and depurination were observed in Apo C3 LNA/DNA after a week under UV light stress conditions at low pH. Guanine oxidation and dimerization were the primary degradation products detected under UV light exposure for 1 week at high pH. The effect of antioxidants on the levels of these degradation products was evaluated under neutral pH conditions. In the presence of all antioxidants, levels of guanine oxidation and desulfurization under tested conditions were the same as those in the unstressed sample, except for sodium ascorbate. The thorough understanding of the Apo C3 LNA/DNA oligonucleotide structure, its impurities, and degradation products laid the foundation for the successful formulation development of this novel biotherapeutic modality.

Amyloid fibril proteins and amyloidosis: chemical identification and clinical classification International Society of Amyloidosis 2016 Nomenclature Guidelines.

The Nomenclature Committee of the International Society of Amyloidosis (ISA) met during the XVth Symposium of the Society, 3 July-7 July 2016, Uppsala, Sweden, to assess and formulate recommendations for nomenclature for amyloid fibril proteins and the clinical classification of the amyloidoses. An amyloid fibril must exhibit affinity for Congo red and with green, yellow or orange birefringence when the Congo red-stained deposits are viewed with polarized light. While congophilia and birefringence remain the gold standard for demonstration of amyloid deposits, new staining and imaging techniques are proving useful. To be included in the nomenclature list, in addition to congophilia and birefringence, the chemical identity of the protein must be unambiguously characterized by protein sequence analysis when possible. In general, it is insufficient to identify a mutation in the gene of a candidate amyloid protein without confirming the variant changes in the amyloid fibril protein. Each distinct form of amyloidosis is uniquely characterized by the chemical identity of the amyloid fibril protein that deposits in the extracellular spaces of tissues and organs and gives rise to the disease syndrome. The fibril proteins are designated as protein A followed by a suffix that is an abbreviation of the parent or precursor protein name. To date, there are 36 known extracellular fibril proteins in humans, 2 of which are iatrogenic in nature and 9 of which have also been identified in animals. Two newly recognized fibril proteins, AApoCII derived from apolipoprotein CII and AApoCIII derived from apolipoprotein CIII, have been added. AApoCII amyloidosis and AApoCIII amyloidosis are hereditary systemic amyloidoses. Intracellular protein inclusions displaying some of the properties of amyloid, "intracellular amyloid" have been reported. Two proteins which were previously characterized as intracellular inclusions, tau and α-synuclein, are now recognized to form extracellular deposits upon cell death and thus have been included in Table 1 as ATau and AαSyn.

Apolipoprotein C-III Nanodiscs Studied by Site-Specific Tryptophan Fluorescence.

Apolipoprotein C-III (ApoC-III) is found on high-density lipoproteins (HDLs) and remodels 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles into HDL-like particles known as nanodiscs. Using single-Trp-containing ApoC-III mutants, we have studied local side chain environments and interactions in nanodiscs at positions W42, W54, and W65. Using transmission electron microscopy and circular dichroism spectroscopy, nanodiscs were characterized at the ultrastructural and secondary conformational levels, respectively. Nearly identical particles (15 ± 2 nm) were produced from all proteins containing approximately 25 ± 4 proteins per particle with an average helicity of 45-51% per protein. Distinct residue-specific fluorescence properties were observed with W54 residing in the most hydrophobic environment followed by W42 and W65. Interestingly, time-resolved anisotropy measurements revealed that Trp side chain mobility is uncorrelated to the polarity of its surroundings. W54 is the most mobile compared to W65 and W42, which are more immobile in a nanodisc-bound state. On the basis of Trp spectral comparisons of ApoC-III in micellar and vesicle environments, ApoC-III binding within nanodiscs more closely resembles a bilayer-bound state. Despite the nanodiscs being structurally similar, we found marked differences during nanodisc formation by the Trp variants as a function of temperature, with W42 behaving the most like the wild-type protein. Our data suggest that despite the modest mutations of Trp to Phe at two of the three native sites, the interfacial location of W42 is important for lipid binding and nanodisc assembly, which may be biologically meaningful as of the three Trp residues, only W42 is invariant among mammals.

Mass spectrometry of transferrin and apolipoprotein C-III for diagnosis and screening of congenital disorder of glycosylation.

Congenital disorder of glycosylation (CDG), formerly representing a group of diseases due to defects in the biosynthetic pathway of protein N-glycosylation, currently covers a wide range of disorders affecting glycoconjugates. Since its first application to serum transferrin from a CDG patient with phosphomannomutase-2 deficiency in 1992, mass spectrometry (MS) has been playing a key role in identification and characterization of glycosylation defects affecting glycoproteins. MS of native transferrin detects a lack of glycans characteristic to the classical CDG-I type of molecular abnormality. Electrospray ionization MS of native transferrin, especially, allows glycoforms to be analyzed precisely but requires basic knowledge regarding deconvolution of multiply-charged ions which may generate ghost signals upon transformation into a singly-charged form. MS of glycopeptides from tryptic digestion of transferrin delineates site-specific glycoforms and reveals a delicate balance of donor/acceptor substrates or the conformational effect of nascent proteins in cells. Matrix-assisted laser desorption ionization MS of apolipoprotein C-III is a simple method of elucidating the profiles of mucin-type core 1 O-glycans including site occupancy and glycoforms. In this technological review, the principle and pitfalls of MS for CDG are discussed and mass spectra of various types of CDG are presented.

D25V apolipoprotein C-III variant causes dominant hereditary systemic amyloidosis and confers cardiovascular protective lipoprotein profile.

Apolipoprotein C-III deficiency provides cardiovascular protection, but apolipoprotein C-III is not known to be associated with human amyloidosis. Here we report a form of amyloidosis characterized by renal insufficiency caused by a new apolipoprotein C-III variant, D25V. Despite their uremic state, the D25V-carriers exhibit low triglyceride (TG) and apolipoprotein C-III levels, and low very-low-density lipoprotein (VLDL)/high high-density lipoprotein (HDL) profile. Amyloid fibrils comprise the D25V-variant only, showing that wild-type apolipoprotein C-III does not contribute to amyloid deposition in vivo. The mutation profoundly impacts helical structure stability of D25V-variant, which is remarkably fibrillogenic under physiological conditions in vitro producing typical amyloid fibrils in its lipid-free form. D25V apolipoprotein C-III is a new human amyloidogenic protein and the first conferring cardioprotection even in the unfavourable context of renal failure, extending the evidence for an important cardiovascular protective role of apolipoprotein C-III deficiency. Thus, fibrate therapy, which reduces hepatic APOC3 transcription, may delay amyloid deposition in affected patients.

Zeolite Nanoparticles for Selective Sorption of Plasma Proteins.

The affinity of zeolite nanoparticles (diameter of 8-12 nm) possessing high surface area and high pore volume towards human plasma proteins has been investigated. The protein composition (corona) of zeolite nanoparticles has been shown to be more dependent on the plasma protein concentrations and the type of zeolites than zeolite nanoparticles concentration. The number of proteins present in the corona of zeolite nanoparticles at 100% plasma (in vivo state) is less than with 10% plasma exposure. This could be due to a competition between the proteins to occupy the corona of the zeolite nanoparticles. Moreover, a high selective adsorption for apolipoprotein C-III (APOC-III) and fibrinogen on the zeolite nanoparticles at high plasma concentration (100%) was observed. While the zeolite nanoparticles exposed to low plasma concentration (10%) exhibited a high selective adsorption for immunoglobulin gamma (i.e. IGHG1, IGHG2 and IGHG4) proteins. The zeolite nanoparticles can potentially be used for selectively capture of APOC-III in order to reduce the activation of lipoprotein lipase inhibition during hypertriglyceridemia treatment. The zeolite nanoparticles can be adapted to hemophilic patients (hemophilia A (F-VIII deficient) and hemophilia B (F-IX deficient)) with a risk of bleeding, and thus might be potentially used in combination with the existing therapy.

Tryptophan probes reveal residue-specific phospholipid interactions of apolipoprotein C-III.

Apolipoproteins are essential human proteins for lipid metabolism. Together with phospholipids, they constitute lipoproteins, nm to µm sized particles responsible for transporting cholesterol and triglycerides throughout the body. To investigate specific protein-lipid interactions, we produced and characterized three single-Trp containing apolipoprotein C-III (ApoCIII) variants (W42 (W54F/W65F), W54 (W42F/W65F), W65 (W42F/W54F)). Upon binding to phospholipid vesicles, wild-type ApoCIII adopts an α-helical conformation (50% helicity) as determined by circular dichroism spectroscopy with an approximate apparent partition constant of 3×10(4) M(-1). Steady-state and time-resolved fluorescence measurements reveal distinct residue-specific behaviors with W54 experiencing the most hydrophobic environment followed by W42 and W65. Interestingly, time-resolved anisotropy measurements show a converse trend for relative Trp mobility with position 54 being the least immobile. To determine the relative insertion depths of W42, W54, and W65 in the bilayer, fluorescence quenching experiments were performed using three different brominated lipids. W65 had a clear preference for residing near the headgroup while W54 and W42 sample the range of depths ~8-11 Å from the bilayer center. On average, W54 is slightly more embedded than W42. Based on Trp spectral differences between ApoCIII binding to phospholipid vesicles and sodium dodecyl sulfate micelles, we suggest that ApoCIII adopts an alternate helical conformation on the bilayer which could have functional implications.

Protein corona of nanoparticles: distinct proteins regulate the cellular uptake.

Understanding nanoparticle-protein interactions is a crucial issue in the development of targeted nanomaterial delivery. Besides unraveling the composition of the nanoparticle's protein coronas, distinct proteins thereof could control nanoparticle uptake into specific cell types. Here we differentially analyzed the protein corona composition on four polymeric differently functionalized nanoparticles by label-free quantitative mass spectrometry. Next, we correlated the relative abundance of identified proteins in the corona with enhanced or decreased cellular uptake of nanoparticles into human cancer and bone marrow stem cells to identify key candidates. Finally, we verified these candidate proteins by artificially decorating nanoparticles with individual proteins showing that nanoparticles precoated with the apolipoproteins ApoA4 or ApoC3 significantly decreased the cellular uptake, whereas precoating with ApoH increased the cellular uptake.

Amyloid triangles, squares, and loops of apolipoprotein C-III.

While a significant component of atherosclerotic plaques has been characterized as amyloid, the specific proteins remain to be fully identified. Probable amyloidogenic proteins are apolipoproteins (Apos), which are vital for the formation and function of lipoproteins. ApoCIII is an abundant protein implicated in atherosclerosis, and we show it forms a ribbonlike looped amyloid, strikingly similar to that previously reported for ApoAI and ApoCII. Triangles and squares with a width of ~50 nm were also observed, which may be a novel form of amyloid or related to previously reported amyloid rings.

Apolipoproteins C-I and C-III inhibit lipoprotein lipase activity by displacement of the enzyme from lipid droplets.

Apolipoproteins (apo) C-I and C-III are known to inhibit lipoprotein lipase (LPL) activity, but the molecular mechanisms for this remain obscure. We present evidence that either apoC-I or apoC-III, when bound to triglyceride-rich lipoproteins, prevent binding of LPL to the lipid/water interface. This results in decreased lipolytic activity of the enzyme. Site-directed mutagenesis revealed that hydrophobic amino acid residues centrally located in the apoC-III molecule are critical for attachment to lipid emulsion particles and consequently inhibition of LPL activity. Triglyceride-rich lipoproteins stabilize LPL and protect the enzyme from inactivating factors such as angiopoietin-like protein 4 (angptl4). The addition of either apoC-I or apoC-III to triglyceride-rich particles severely diminished their protective effect on LPL and rendered the enzyme more susceptible to inactivation by angptl4. These observations were seen using chylomicrons as well as the synthetic lipid emulsion Intralipid. In the presence of the LPL activator protein apoC-II, more of apoC-I or apoC-III was needed for displacement of LPL from the lipid/water interface. In conclusion, we show that apoC-I and apoC-III inhibit lipolysis by displacing LPL from lipid emulsion particles. We also propose a role for these apolipoproteins in the irreversible inactivation of LPL by factors such as angptl4.

Identification of new apolipoprotein-CIII glycoforms with ultrahigh resolution MALDI-FTICR mass spectrometry of human sera.

Apolipoprotein-CIII (apoCIII) is an abundant blood glycoprotein associated with lipoprotein particles. Three different glycoforms have been described, all containing a mucin-type core-1 O-glycosylation with either zero, one or two sialic acids. Changes in the relative abundance of these glycoforms have been observed in a variety of different pathologies. In this study, ultrahigh resolution 15T MALDI Fourier transform ion cyclotron resonance (FTICR) MS was used to analyze apoCIII isoforms in serum protein profiles. For this purpose, serum proteins were purified using both a fully automated RPC18-based magnetic bead method and an RPC4 cartridge-based solid phase extraction method. Six new apoCIII isoforms were identified with low-ppm mass measurement errors and ultrahigh precision. These were characterized by more complex glycan moieties that are fucosylated instead of sialylated. To confirm the glycan moiety and localize the glycosylation site, top-down ESI-FTICR-MS/MS and bottom-up LC-ion trap MS/MS were used. A large variation in the presence and abundance of the fucosylated isoforms was found in a set of 96 serum samples. These findings of fucosylated apolipoprotein-CIII isoforms warrant further research to elucidate the implications these glycoforms may have for the plethora of studies where alterations in apoCIII have been linked to the development of many different pathologies.

Mapping O-glycosylation of apolipoprotein C-III in MALDI-FT-ICR protein profiles.

Ultrahigh resolution MALDI-FT-ICR profiles were obtained from human serum samples that were processed using a fully automated RPC18-based magnetic bead method. Proteins were profiled from m/z value 6630 with a resolving power of 73 000 up to m/z value 12 600 with a resolving power of 37 000. In this study, a detailed evaluation was performed of the isoforms of apolipoprotein C-III, i.e. the different mucin-type core 1 O-glycans with the addition of one or two sialic acid residues. The MALDI-FT-ICR profiles are discussed with regard to reproducibility of the signal intensities as well as the accurate mass measurements. ESI-FT-ICR-MS/MS analyses of the same serum samples were performed to confirm the identity of apolipoprotein C-III glycoforms.

Glycoproteins and glycosylation: apolipoprotein c3 glycoforms by top-down maldi-tof mass spectrometry.

Apolipoprotein C3 (ApoC3) is synthesized in liver so that levels or isoform distributions may constitute indicators of liver pathogenesis. The glycoforms of intact protein ApoC3 in serum or plasma can be readily analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry after a one-step extraction using a C4 reverse-phase ZipTip. Glycoform distributions were sensitive to severe systemic diseases such as sepsis or liver diseases such as chronic hepatitis C and alcoholic liver cirrhosis. Glycoisoform distributions were also altered in persons with elevated body mass index and were corrected to normal distribution by metformin, a common drug used for diabetes therapy. This simple method may offer an approach to analysis of health and the mechanism of drug therapies.

Identification of proteomic biomarkers in maternal plasma in the early second trimester that predict the subsequent development of gestational diabetes.

INTRODUCTION: This study is designed to identify proteomic biomarkers that predict the subsequent development of gestational diabetes mellitus (GDM). METHODS: Maternal blood was obtained prospectively from healthy pregnant women in the early second trimester (16-20 weeks). Twelve women subsequently diagnosed with GDM at 24 to 28 weeks were selected as cases; an equal number of normoglycemic women as controls. Proteomic analysis of the previously stored plasma was performed by surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry. RESULTS: Three peaks (9122 Da, 9412 Da, and 9701 Da) that were increased in cases were characterized as isoforms of apolipoprotein CIII. Another discriminatory peak (17 105 Da) that was decreased in cases was matched to apolipoprotein AII. Enzyme-linked immunosorbent assay (ELISA) confirmed that women who subsequently developed GDM had significantly higher levels of apolipoprotein CIII than controls did. Levels of apolipoprotein AII failed to reach statistical significance. CONCLUSION: Our data suggest that there already exist biomarkers in the maternal circulation at 16 to 20 weeks in women who subsequently develop GDM.

Mass spectrometric measurements of the apolipoproteins of bovine (Bos taurus) HDL.

As is the case in most mammals, high density lipoproteins (HDL) also comprise the major group of lipid carriers that circulate in bovine (Bos taurus) blood. As a continuation of our proteogenomic studies of mammalian apolipoproteins, we have obtained molecular masses for several of the apolipoproteins associated with bovine HDL. The major apolipoprotein on the HDL surface is apoA-I, but other apolipoproteins were also detected. Using electrospray-ionization mass spectrometry (ESI-MS), we report on values for apolipoproteins, A-I, proA-I and A-II, as well as post-translationally modified apoA-I. Analyses of tryptic fragments did reveal the presence of apoA-IV and apoC-III. However, in contrast to our previous studies of other mammalian HDL, we did not detect apoC-I. Interestingly, examination of the current assembly for the bovine genome does not show any evidence for an apoC-I gene.