Molecular Weight Fraction Of Serum Research Articles

Peptides in Low Molecular Weight Fraction of Serum Associated with Hepatocellular Carcinoma

The incidence of hepatocellular carcinoma (HCC) in the United States is increasing and the increase is projected to continue for several decades. The overall survival of HCC patients is poor and treatments are not effective in part because most of the diagnoses come at a late stage. The development of new markers for detection of HCC would significantly improve patient prognosis. This paper describes identification of candidate markers previously reported in our serologic study of an Egyptian population by quantitative comparison of matrix assisted laser desorption ionization time of flight (MALDI-TOF) mass spectra. To identify these marker candidates, we performed LC-MS/MS sequencing that identified nine native peptides associated with HCC, including two reported previously. Four truncations of N terminus of complement C3f and a fibrinopeptide increased in control sera; two complement C4α peptides, a zyxin peptide, and a coagulation factor XIII peptide increased in cancer patient sera. We have also identified increased biliverdin diglucuronide in the sera of cancer patients. These peptides could potentially serve as markers of HCC following additional validation studies; however, association of similar peptides with other diseases and cancers dictates a very cautious approach.

Peptides in low molecular weight fraction of serum associated with hepatocellular carcinoma.

The incidence of hepatocellular carcinoma (HCC) in the United States is increasing and the increase is projected to continue for several decades. The overall survival of HCC patients is poor and treatments are not effective in part because most of the diagnoses come at a late stage. The development of new markers for detection of HCC would significantly improve patient prognosis. This paper describes identification of candidate markers previously reported in our serologic study of an Egyptian population by quantitative comparison of matrix assisted laser desorption ionization time of flight (MALDI-TOF) mass spectra. To identify these marker candidates, we performed LC-MS/MS sequencing that identified nine native peptides associated with HCC, including two reported previously. Four truncations of N terminus of complement C3f and a fibrinopeptide increased in control sera; two complement C4α peptides, a zyxin peptide, and a coagulation factor XIII peptide increased in cancer patient sera. We have also identified increased biliverdin diglucuronide in the sera of cancer patients. These peptides could potentially serve as markers of HCC following additional validation studies; however, association of similar peptides with other diseases and cancers dictates a very cautious approach.

Elevated Levels of Phosphorylated Fibrinogen-α-Isoforms and Differential Expression of Other Post-Translationally Modified Proteins in the Plasma of Ovarian Cancer Patients

We evaluated the differentially expressed proteins in the plasma of ovarian cancer (OVC) patients using 2-D SDS-polyacrylamide gel electrophoresis (SDS-PAGE) with post-translational modification (PTM) specific stains after the removal of six high-abundance proteins. The pooled plasma from patients with stage III or IV OVC was compared to a pooled postmenopausal age-matched control. Several proteins were identified as differentially expressed in the plasma of OVC patients. Among them, the phosphorylated fibrinogen-alpha-chain isoform (containing fibrinopeptide-A) was found to be up-regulated. Previously in our laboratory, phosphorylated fibrinopeptide-A was found to be up-regulated in the low molecular weight fraction of serum derived from OVC patients. We examined the levels of phosphorylated fibrinogen-alpha-chain in each patient that constituted the pooled plasma using Western blot, mass spectrometry (MS), and PTM specific stains. Phosphoprotein bands containing fibrinogen-alpha-chain fragments showed up-regulation in all OVC patients.

Enrichment of low molecular weight fraction of serum for MS analysis of peptides associated with hepatocellular carcinoma

A challenging aspect of biomarker discovery in serum is the interference of abundant proteins with identification of disease-related proteins and peptides. This study describes enrichment of serum by denaturing ultrafiltration, which enables an efficient profiling and identification of peptides up to 5 kDa. We consistently detect several hundred peptide-peaks in MALDI-TOF and SELDI-TOF spectra of enriched serum. The sample preparation is fast and reproducible with an average CV for all 276 peaks in the MALDI-TOF spectrum of 11%. Compared to unenriched serum, the number of peaks in enriched spectra is 4 times higher at an S/N ratio of 5 and 20 times higher at an S/N ratio of 10. To demonstrate utility of the methods, we compared 20 enriched sera of patients with hepatocellular carcinoma (HCC) and 20 age-matched controls using MALDI-TOF. The comparison of 332 peaks at p < 0.001 identified 45 differentially abundant peaks that classified HCC with 90% accuracy in this small pilot study. Direct TOF/TOF sequencing of the most abundant peptide matches with high probability des-Ala-fibrinopeptide A. This study shows that enrichment of the low molecular weight fraction of serum facilitates an efficient discovery of peptides that could serve as biomarkers for detection of HCC as well as other diseases.

Analysis of the low molecular weight fraction of serum by LC-dual ESI-FT-ICR mass spectrometry: precision of retention time, mass, and ion abundance.

This study quantifies the experimental uncertainty for LC retention time, mass measurement precision, and ion abundance obtained from replicate nLC-dual ESI-FT-ICR analyses of the low molecular weight fraction of serum. We used ultrafiltration to enrich the < 10-kDa fraction of components from the high-abundance proteins in a pooled serum sample derived from ovarian cancer patients. The THRASH algorithm for isotope cluster detection was applied to five replicate nLC-dual ESI-FT-ICR chromatograms. A simple two-level grouping algorithm was applied to the more than 7000 isotope clusters found in each replicate and identified 497 molecular species that appeared in at least four of the replicates. In addition, a representative set of 231 isotope clusters, corresponding to 188 unique molecular species, were manually interpreted to verify the automated algorithm and to set its tolerances. For nLC retention time reproducibility, 95% of the 497 species had a 95% confidence interval of the mean of +/- 0.9 min or less without the use of chromatographic alignment procedures. Furthermore, 95% of the 497 species had a mass measurement precision of < or = 3.2 and < or = 6.3 ppm for internally and externally calibrated spectra, respectively. Moreover, 95% of replicate ion abundance measurements, covering an ion abundance range of approximately 3 orders of magnitude, had a coefficient of variation of less than 62% without using any normalization functions. The variability of ion abundance was independent of LC retention time, mass, and ion abundance quartile. These measures of analytical reproducibility establish a statistical rationale for differentiating healthy and disease patient populations for the elucidation of biomarkers in the low molecular fraction of serum.

Extrathymic signals regulate the onset of T cell repertoire selection.

The thymus is the principal site of T cell development, coordinating positive and negative selection of an immunocompetent repertoire. The ability of fetal thymi from C57BL/6 mice to support these selection events in culture is, however, critically dependent on the timing of their excision: whereas thymi from 16 day embryos generate mature CD4+8(-) and CD4(-)8+ thymocytes, 14 day thymi show a profound blockage in positive selection at the CD4+8+ stage. Here we show that this blockage is not due to intrinsic deficiencies in the ability of thymocytes to transduce positive selection signals, suggesting the defect to lie within the thymic microenvironment. Since vascularization of the thymus occurs at day 15 of gestation, we investigated whether the exclusion of plasma proteins from 14 day thymi was responsible. Accordingly, the addition of serum from 16 day embryos to organ cultures of 14 day thymi rescued mature CD4+8(-) and CD4(-)8+ subsets. Activity was found to reside in a low molecular weight fraction of serum, sensitive to proteolysis, which was present only transiently during ontogeny. Our data suggest that repertoire selection is initiated following "priming" of the thymic microenvironment by plasma proteins, thereby ensuring the onset of positive selection to be delayed until the entry of extrathymic proteins to which self tolerance must be established.

Species-specificity of growth-promoting effects of prolactin during rat embryogenesis.

In the early stages of embryonic development, many growth-promoting molecules must be provided by the maternal system. The molecules involved in growth processes may be either hormones or growth factors, or molecules that interact with such factors. The pregnancy related hormone, prolactin (PRL, MW 23 kDa) has been implicated in the control of embryonic growth. The growth-promoting potential of PRL and its species-specificity was investigated by culturing 9.5 d rat embryos in vitro for 48 h in depleted serum in the presence and absence of PRL from 3 different species. The growth-supporting capacity of the serum was reduced by removal of low molecular weight molecules by prolonged filtration of the serum using filters with a molecular weight exclusion of 30 kDa. This method provided a 'semidefined' medium (retenate) in which embryonic growth and development was significantly reduced, demonstrating that the low molecular weight fraction of serum may contain some growth-promoting factors. Addition of PRL (0.4-25.6 ng/ml) from different species (human, sheep and rat) to retenate significantly improved embryonic growth and development, suggesting that the developing embryo may utilise PRL. Amongst PRLs, rat PRL was found to be active at much lower concentrations than either of the other molecules, and human PRL had more effect in low concentrations than sheep PRL suggesting a species-specificity for this hormone. It may be that the PRL receptors of the rat embryos have greater affinity for the rat hormone as different responses for hormones from different species have been shown. These findings suggest that embryos may be able to utilise maternally derived PRL during organogenesis.

Anti-pig IgM antibodies in human serum react predominantly with Gal(alpha 1-3)Gal epitopes.

A major problem with pig-to-human-tissue xenograft studies is that humans have natural antibodies to pig cells; these antibodies would cause hyperacute rejection if pig tissues were xenografted to humans. Here we show that most of human IgM antibodies present in the serum of healthy donors and reactive with pig cells react with galactose in an (alpha 1-3) linkage with galactose--i.e., Gal(alpha 1-3)Gal. Absorption studies demonstrated that the antibodies detected the same or similar epitopes on the surface of pig erythrocytes, blood and splenic lymphocytes, and aortic endothelial cells (EC). The antibodies were sensitive to 2-mercaptoethanol (2ME) treatment, did not bind to protein A or G, and were present in the high molecular weight fraction of serum; they are clearly IgM antibodies. Further, the antibodies did not react with human ABO blood group substances and are not related to human blood group A or B, which carry a terminal galactose. The reaction of human serum with pig erythrocytes was specifically inhibited by mono- and disaccharides: D-galactose, melibiose, stachyose, methyl-alpha-D-galactopyranoside, and D-galactosamine but not by D-glucose or methyl-beta-D-galactopyranoside; demonstrating that the reaction is with galactose in an alpha and not a beta linkage. A cDNA clone encoding the murine alpha-1,3-galactosyltransferase (which transfers a terminal galactose residue with an (alpha 1-3) linkage to a subterminal galactose) was isolated by polymerase chain reaction (PCR), cloned, and transfected into COS cells, which are of Old World monkey origin and, like humans, do not express Gal(alpha 1-3)Gal. After transfection, COS cells became strongly reactive with human serum and with IB4 lectin [which reacts only with Gal(alpha 1-3)Gal]; this reactivity could be removed by absorption with pig erythrocytes. As most of the antibody reacting with pig cells can be removed by absorption with either melibiose or Gal(alpha 1-3)Gal+ COS cells, most of these react with Gal(alpha 1-3)Gal. These findings provide the basis for genetic manipulation of the pig alpha-1,3-galactosyltransferase for future transplantation studies.

Modulation of cholestatic factor production by serum components.

When lymph node cells from sensitized guinea pigs were stimulated in vitro with a specific antigen and their culture supernatant was injected into the mesenteric vein of rats, a marked decrease in bile flow was demonstrated. The treatment of activated lymphocytes with a higher molecular weight fraction of normal human serum Fr-1 and Fr-2 was shown to decrease the reduction of bile flow. Conversely, a lower molecular weight fraction of serum (Fr-3) was found to augment the reduction of bile flow. These findings suggest that the serum components may regulate the production of a factor (or factors) causing the decrease in bile flow from the activated lymphocytes.

Modulation of the macrophage hepatocytotoxicity and plasminogen activator activity of activated macrophages from guinea pigs by serum components from normal human and patients with liver diseases.

Activated macrophages (m phi) exhibited cytotoxic effects on isolated liver cells and produced plasminogen activator (PA) in vitro. A high molecular weight fraction of normal human serum (Fr-1) was shown to reduce the m phi-mediated hepatocytotoxicity and enhance the PA activity of activated m phi. Conversely, a lower molecular weight fraction of serum (Fr-3) was found to enhance the hepatotoxic potential and decrease the PA activity of activated m phi. Although similar effects were seen with serum fraction prepared from patients with acute hepatitis, somewhat different influences were observed with serum components from patients with chronic active hepatitis or liver cirrhosis: Fr-1 from patients with chronic active hepatitis was less active in reducing m phi-mediated hepatocytotoxicity, and and Fr-3 was more active in enhancing it, in comparison with fractions from individuals or patients with active hepatitis. Fr-3 from patients with liver cirrhosis was shown to be remarkably less active in enhancing m phi-mediated hepatocytotoxicity. Furthermore, Fr-1 from patients with liver cirrhosis reduced PA activity, Fr-3 was less active in decreasing such activity. These findings suggest that the serum components may regulate m phi-mediated hepatocytotoxicity as well as PA secretion of activated m phi. Our studies also suggested the possibility that relative doses of these serum components may differ in various pathological conditions of the liver.

Arrest of cell growth in the G1 phase of the cell cycle by serine deprivation

BHK21 cells cultured in minimal essential medium (Eagle) supplemented with 10% dialyzed fetal calf serum did not grow as they did in whole serum containing medium. Logarithmic growth was, however, initiated after a lag period, the length of which was dependent upon the cell density: medium volume ratio. The quiescent cells conditioned the medium during this lag period, and growth stimulation was apparently due to the release of serine into the medium. Cells cultured in 10% dialyzed serum plus the low molecular weight fraction of serum (serum dialysate), grew with kinetics similar to cells cultured in serum containing medium. When serum dialysate was chromatographed on Bio-gel P-2 the growth promoting activity eluted with the amino acids. Each of the non-essential amino acids was tested for its ability to stimulate the growth of cells in 10% dialyzed serum. Serine was capable of stimulating cell growth to the same extent as 10% serum dialysate and its concentration optimum was similar to its concentration in 10% serum dialysate. The remaining non-essential amino acids were either slightly stimulatory or had no effect on cell growth. Shifting a logarithmically growing population of cells to serine-free medium resulted in the accumulation of 95% of the cells in the G1 phase of the cell cycle within 24 h. Escape from the G1 block could occur if serine was added to the medium or if the cells were allowed to condition the medium. Entry of cells into S phase after the addition of 0.05 μmoles/ml of serine followed a 4–6 h lag and 80% of the cells were synthesizing DNA 12 h after shift-up.

Detection of a diffusible factor controlling the synthesis of a single hemoglobin chain in mice

The synthesis of hemoglobin alpha-chains was investigated in splenic colonies derived from syngenic colony-forming units injected in lethally irradiated C3H mice. Whereas normal adult mice of this strain synthesize two structurally distinct alpha-chains, the "alphaC57" and the "alpha NB", chains, it was found that erythrocytes from splenic colonies of irradiated recipient mice contained no alpha chain of the C57 type. Daily injection of serum from adult C3H mice into irradiated recipient mice of the same strain stimulates the synthesis of alphaC57 chain, whereas the injection of serum of lethally irradiated mice, drawn 8 days after irradiation, does not. It is concluded that the serum of adult C3H mice contains one or several factors that are responsible for the differential activation of the synthesis of the alphaC57 globin chain. This factor is shown to be associated exclusively with a high molecular weight fraction of serum.

A Humoral Inhibitor of Sodium Transport in Uremic Serum

A low molecular weight fraction of serum from uremic patients has been found to inhibit several different transport systems. These include the uptake of p-aminohippuric acid (PAH) by rabbit kidney cortical slices, the transepithelial transport of sodium by the isolated frog skin, and finally, sodium reabsorption by the rat kidney tubule. The following possibilities are considered: first, that the substance might be a naturally occurring humoral agent which serves in a homeostatic role to increase sodium excretion rate per nephron as the number of nephrons diminishes in advancing renal disease; and second, that in advanced renal disease, very high levels of this humoral agent could lead to inhibition of sodium transport in extrarenal organs and, thus, could contribute importantly to the symptoms and signs of the uremic state.