Differences in metabolite profile between blood plasma and serum

In metabolomic research, blood plasma and serum have been considered to possess similar compositions and properties. Their perceived equivalence has resulted in researchers choosing arbitrarily between serum and plasma for analysis. Here, routine serum and plasma were prepared and their low-molecular-weight compounds were determined using gas chromatography/time-of-flight mass spectrometry. Principal components analysis was applied to process the acquired data, and marked differences in metabolite profiles were observed between serum and plasma. Of the 72 identified compounds, 36 (50%) discriminate serum from plasma, with 29 and 7 metabolites showing a significantly higher abundance (t test, P < 0.05) in serum and plasma, respectively. Incubation of blood had distinct effects on the analyte peak areas, with the effects being more pronounced for plasma than for serum and more pronounced for a shorter incubation than for a longer incubation. These results highlight the importance in choosing serum or plasma as the analytical sample and in stipulating the incubation time. Because incubation affected the analyte peak areas less in serum than in plasma, we recommend serum as the sample of choice in metabolomic studies.     

Associations between thyroid hormones and serum metabolite profiles in an euthyroid population

Metabolomics - The aim was to characterise associations between circulating thyroid hormones—free thyroxine (FT4) and thyrotropin (TSH)—and the metabolite profiles in serum samples from...     

Differences in metabolite profiles between blood matrices,ages, and sexes among Caucasian individuals and their inter-individual variations

Endobiotic metabolites are associated with biological processes in the body and therefore may serve as biomarkers for disease states or therapeutic efficacy and toxicity. However, information is limited regarding how differences between blood matrices, patient backgrounds, and sample handling affect human metabolite profiles. Our objective was to obtain metabolite profiles from Caucasian individuals, based on different matrices (plasma and serum), subject backgrounds (male/female and young/old), and storage conditions (2 or 10 freeze–thaw cycles). In total, 297 metabolites were detected by LC/MS and GC/MS, and more than 75 % of them were highly represented in all sample groups. The multivariate discriminant analysis (OPLS-DA as a model) singled out the matrix type as the most important variable influencing global metabolic profiles; that is, more than 100 metabolites were significantly different based on the matrix type. The influence of subject backgrounds on global metabolic profiles was consistent between plasma and serum. Age-associated differences were more predominant in females than males, whereas gender-associated differences were more prevalent in young subjects than old individuals were. The relative standard deviation of metabolite levels in subjects with the same background ranked from 0.1 to 1.5. Moreover, the changes of metabolite levels caused by freeze–thaw cycles were limited, and the effect was more prominent in plasma than serum. These data demonstrate the impact of matrix, age, gender, and freeze–thaw cycles on the metabolite profiles and reveal metabolites affected by these factors. Thus, our results provide would useful fundamental information for exploring and qualifying biomarkers for clinical applications.     

Differences between human and rabbit transferrins

Rabbit reticulocyte incorporation of iron from rabbit transferrin was independent of transferrin iron saturation but uptake from human transferrin was saturation dependent. Unlike human transferrin, rabbit transferrin does not surrender its iron from any unique preferred iron-binding site and can be described as functionally homogeneic.The two proteins also differ in their acid-base iron-binding properties. One human transferrin iron binding site retains an ability to bind iron at somewhat acid pH but this property is not shared by rabbit transferrin.     

A comparison between the concentration of prostaglandin F in human plasma and serum

The concentration of prostaglandin F (PGF) has been measured in serum and plasma samples prepared under different conditions from the antecubital vein blood of 4 non-pregnant and 7 pregnant women. Prostaglandin F concentrations were less than 41 pg/ml in 19 samples of serum or plasma prepared by centrifugation within 30 minutes of collection. When the blood was allowed to clot at room temperature for 24 hours, highly variable, but usually markedly increased concentrations of PGF (<30 - 3020 pg/ml) were found in the serum. Plasma obtained from blood which stood at 23°C for 24 hours contained undetectable amounts of PGF in 4 out of 6 samples and less than 75 pg/ml in the 2 remaining samples. Plasma and serum obtained from blood which stood at 4°C for 24 hours contained less than 45 pg PGF/ml. These results show that (i) incubation of blood at room temperature may markedly elevate concentrations of PGF in serum, (ii) plasma samples rather than serum should be used for measurements of PGF concentrations.     

Aggregation of biopharmaceuticals in human plasma and human serum

Analytical methods based on light microscopy, 90° light-scattering and surface plasmon resonance (SPR) allowed the characterization of aggregation that can occur when antibodies are mixed with human plasma. Light microscopy showed that aggregates formed when human plasma was mixed with 5% dextrose solutions of Herceptin^® (trastuzumab) or Avastin^® (bevacizumab) but not Remicade^® (infliximab). The aggregates in the plasma-Herceptin^®-5% dextrose solution were globular, size range 0.5–9 μm, with a mean diameter of 4 μm. The aggregates in the plasma-Avastin^®-5% dextrose samples had a mean size of 2 μm. No aggregation was observed when 0.9% NaCl solutions of Herceptin^®, Avastin^® and Remicade^® were mixed with human plasma. 90° light-scattering measurements showed that aggregates were still present 2.5 h after mixing Herceptin^® or Avastin^® with 5% dextrose-plasma solution. A SPR method was utilized to qualitatively describe the extent of interactions of surface-bound antibodies with undiluted human serum. Increased binding was observed in the case of Erbitux^® (cetuximab), whereas no binding was measured for Humira^® (adalimumab). The binding of sera components to 13 monoclonal antibodies was measured and correlated with known serum binding properties of the antibodies. The data presented in this paper provide analytical methods to study the intrinsic and buffer-dependent aggregation tendencies of therapeutic proteins when mixed with human plasma and serum.     

Differences between human and rabbit transferrins.

Rabbit reticulocyte incorporation of iron from rabbit transferrin was independent of transferrin iron saturation but uptake from human transferrin was saturation dependent. Unlike human transferrin, rabbit transferrin does not surrender its iron from any unique preferred iron-binding site and can be described as functionally homogeneic. The two proteins also differ in their acid-base iron-binding properties. One human transferrin iron binding site retains an ability to bind iron at somewhat acid pH but this property is not shared by rabbit transferrin.     

Cancer-specific MALDI-TOF profiles of blood serum and plasma: Biological meaning and perspectives

MALDI-TOF mass-spectrometry has become a popular tool of cancer research during the last decade. High throughput and relative simplicity of this technology have made it attractive for biomarker discovery and validation across various platforms in blood serum/plasma. Many technical approaches have been developed for plasma/serum profiling including protein-chip based SELDI-TOF mass-spectrometry, purification of serum on magnetic beads, analysis of carrier-associated fraction and mass-spectrometric immunoassays. Extensive data about the identity of differential features detected on mass-spectra up to now makes it possible to draw conclusions about potency and perspectives of MALDI-TOF mass-spectrometry in this field. A great majority of identified differentially expressed proteins are either house-keeping or inflammatory proteins as well as their modifications or fragments. Discriminating ability of mass-spectra is likely to be based on differential modification and fragmentation patterns of abundant serum proteins reflecting activity of enzymes including proteases and their inhibitors.     

Differences in methylation profiles between HPV-positive and HPV-negative oropharynx squamous cell carcinoma

Oropharyngeal squamous cell carcinoma (OPSCC) is associated with human papillomavirus (HPV). HPV-positive OPSCC is considered a distinct molecular entity with a better prognosis than HPV-negative cases of OPSCC. However, the exact pathogenic mechanisms underlying the differences in clinical and molecular behavior between HPV-positive and HPV-negative OPSCC remain poorly understood. Epigenetic events play an important role in the development of cancer. Hypermethylation of DNA in promoter regions and global hypomethylation are 2 epigenetic changes that have been frequently observed in human cancers. It is suggested that heterogeneous epigenetic changes play a role in the clinical and biological differences between HPV-positive and HPV-negative tumors. Unraveling the differences in methylation profiles of HPV-associated OPSCC may provide for promising clinical applications and may pave the road for personalized cancer treatment. This systematic review aims to assess the current state of knowledge regarding differences in promoter hypermethylation and global methylation between HPV-positive and HPV-negative OPSCC.     

Pilot analysis of the plasma metabolite profiles associated with emphysematous Chronic Obstructive Pulmonary Disease phenotype

The current pilot study examined the hypothesis that cigarette smokers who developed an emphysematous phenotype of Chronic Obstructive Pulmonary Disease (COPD) were associated with distinctive patterns in their corresponding metabolomics profile as compared to those who did not. Peripheral blood plasma samples were collected from 38 subjects with different phenotypes of COPD. They were categorized into three groups: healthy non-smokers (n = 16), smokers without emphysema (n = 8), and smokers with emphysema (n = 14). Ultra High Performance Liquid Chromatography/quadrupole-Time-of-Flight Mass Spectrometry techniques were used to identify a large number of metabolite markers (3534). Unsupervised clustering analysis accurately separated the smokers with emphysema from others without emphysema and demonstrated potentials of this metabolomics data. Subsequently predictive models were created with a supervised learning set, and these predictive models were found to be highly accurate in identifying the subjects with the emphysematous phenotype of COPD with excellent sensitivity and specificity. Our methodology provides a preliminary model that differentiates an emphysematous COPD phenotype from other COPD phenotypes on the basis of the metabolomics profiles. These results also suggest that the metabolomics profiling could potentially guide the characterization of relevant metabolites that leads to an emphysematous COPD phenotype.     

High-Mr glycoprotein profiles in human milk serum and fat-globule membrane.

In the standard [3H]ouabain-binding assay for quantification of the Na,K-ATPase (Na+ + K+-dependent ATPase) concentration in rat skeletal muscles, samples are incubated for 2 X 60 min in 1 microM-[3H]ouabain at 37 degrees C followed by a wash-out for 4 X 30 min at 0 degree C. To obtain accurate determinations, values determined by this standard assay should be corrected for non-specific uptake and retention of [3H]ouabain (11% overestimation), loss of specifically bound [3H]ouabain during wash-out (21% underestimation), evaporation from muscle samples during weighing (4% overestimation), impurity of [3H]ouabain (5% underestimation) and incomplete saturation of [3H]ouabain binding sites (6% underestimation). Thus corrected the standard [3H]ouabain-binding assay determines the total Na,K-ATPase concentration. Hence, in the soleus muscle of 12-week-old rats the total [3H]ouabain-binding-site concentration is 278 +/- 20 pmol/g wet wt. This is at variance with the evaluation of the Na,K-ATPase concentration from Na,K-ATPase activity measurements in muscle membrane fractions, where the recovery of Na,K-ATPase is only 2-18%. Quantification of the total Na,K-ATPase concentration is of particular importance since it is a prerequisite for the discussion of quantitative aspects of the Na,K-ATPase.     

Calcification inhibitors in rat and human serum and plasma

Rat and human serum and plasma were shown to contain considerable amounts of calcium phosphate precipitation inhibitors. Two general classes of inhibiting molecules were observed for both species: high molecular weight (approx. 30 000-200 000) and low molecular weight (less than 1000). The high molecular weight components eluted from a Bio-Gel P-200 column in two peaks, one at approx. 158 000 and a broader peak at approx. 43 000. The identity of these inhibitors is unknown at present. Low molecular weight inhibitors include magnesium, pyrophosphate, and citrate ions and at least one unidentified component that coelutes with pyrophosphate and citrate on a Bio-Gel P-4 column. Quantitatively, most of the inhibitor activity resides in the high molecular weight components and it is possible that it is this activity which is responsible for maintaining the metastability of the circulating fluids. The role of the low molecular weight components may be to regulate calcification at sites inaccessible to high molecular weight molecules.     

Differences between human and mouse embryonic stem cells

We compared gene expression profiles of mouse and human ES cells by immunocytochemistry, RT-PCR, and membrane-based focused cDNA array analysis. Several markers that in concert could distinguish undifferentiated ES cells from their differentiated progeny were identified. These included known markers such as SSEA antigens, OCT3/4, SOX-2, REX-1 and TERT, as well as additional markers such as UTF-1, TRF1, TRF2, connexin43, and connexin45, FGFR-4, ABCG-2, and Glut-1. A set of negative markers that confirm the absence of differentiation was also developed. These include genes characteristic of trophoectoderm, markers of germ layers, and of more specialized progenitor cells. While the expression of many of the markers was similar in mouse and human cells, significant differences were found in the expression of vimentin, beta-III tubulin, alpha-fetoprotein, eomesodermin, HEB, ARNT, and FoxD3 as well as in the expression of the LIF receptor complex LIFR/IL6ST (gp130). Profound differences in cell cycle regulation, control of apoptosis, and cytokine expression were uncovered using focused microarrays. The profile of gene expression observed in H1 cells was similar to that of two other human ES cell lines tested (line I-6 and clonal line-H9.2) and to feeder-free subclones of H1, H7, and H9, indicating that the observed differences between human and mouse ES cells were species-specific rather than arising from differences in culture conditions.     

Isoelectric profiles of human erythropoietin are different in serum and urine

By adding a step of immunoaffinity to the method we had previously developed for analysing erythropoietin (EPO) in urine, we were able to study the isoelectric profiles of this hormone in human serum samples. This method was sensitive enough to investigate samples presenting physiological levels of this hormone. Comparison with the corresponding profiles in urine showed that natural EPO was systematically more acidic in urine. The acidification process, which was not patent in the non-human primate Cynomolgus macaque, clearly also affected recombinant EPO when injected into humans. This process was unrelated to any enzymatic activity in urine since the incubation of natural or recombinant EPO in urine induced no transformation of their isoelectric profiles. The nature and mechanism of the structural modifications occurring during the renal handling of this hormone remain to be investigated.     

Growth inhibitors in plasma derived human serum

Summary It was reported previously that plasma derived human serum (PDS) inhibited the growth of cells established from malignant human breast tissues and the MCF-7 cell line but did not inhibit the growth of cells from nonmalignant mammary tissues, including the HBL-100 cell line. Plasma derived human serum was fractionated in the current study by molecular sieve chromatography on Sephadex G-100 in an effort to characterize the factor(s) responsible for inhibition. Plasma derived human serum contained several growth inhibitory fractions, which were designated G-1, G-2, G-3, and G-4. The G-1 was associated with the lipoproteins and immunoglobulins of serum. The lipid portion of G-1 inhibited the growth of both MCF-7 and HBL-100 cells, whereas the protein fraction contained a low activity factor directed against MCF-7 cells only. The G-2 also inhibited MCF-7 cell growth at a low specific activity and was separated in the serum albumin fraction. The MCF-7 inhibitory activity in the G-3 fractions from individual donors fluctuated with the level of activity in the starting sera. The cell specific G-3 components were purified further by Sephadex G-100 superfine chromatography and gel electrophoresis. A tentative molecular weight of 50,000 was assigned to the G-3 inhibitor. The G-4 fraction consisted of small molecular weight materials migrating in advance of the column volume, which inhibited the growth of both cell lines. This investigation was supported by Grant PDT-140 from the American Cancer Society, Inc., and PHS Grant CA30284 awarded by the National Cancer Institute, Bethesda, Maryland.     

Simultaneous determination of intact cisplatin and its metabolite monohydrated cisplatin in human plasma

Cisplatin is a cytotoxic platinum compound, used in the treatment of several solid tumors. Cisplatin and to a greater extent its hydrolysis product monohydrated cisplatin are responsible for side-effects like nephrotoxicity. A sensitive, accurate and precise method was developed to simultaneously determine cisplatin and monohydrated cisplatin in plasma. The compounds were separated by high-performance liquid chromatography and quantified by off-line furnace atomic absorption spectrophotometry. The linear ranges for cisplatin and monohydrated cisplatin in deproteinized plasma were 60-600 and 87.5-700 nM, respectively. From plasma, the mean recovery of cisplatin was 83.2% and that of monohydrated cisplatin 79.1%. The lower limits of quantification of cisplatin and monohydrated cisplatin in deproteinized plasma were 60 and 87.5 nM, respectively. Over the whole calibration range, the within- and between-day accuracy of intact cisplatin ranged from 100.7 to 111.4 and 94.8-102.0%, respectively. The within- and between-day accuracy of monohydrated cisplatin ranged from 107.1 to 113.3 and 101.4-104.9%, respectively. The within-day and between-day precision of cisplatin ranged from 3.4 to 11.5 and 7.3-10.3%, respectively. For monohydrated cisplatin, the within-day and between-day precision ranged from 3.7 to 6.2 and 5.6-7.9%, respectively. Currently, the developed assay has been implemented in pharmacokinetic studies of patients treated with cisplatin alone or in combination with other drugs.     

Determination of esmolol and metabolite enantiomers within human plasma using chiral column chromatography

A high performance liquid chromatography–tandem mass spectrometry (LC–MS/MS) method has been developed for the simultaneous determination of each of esmolol's enantiomers at the 25–1000 ng/ml concentrations observed in human plasma upon intravenous administration of this rapidly metabolized beta-adrenergic receptor blocking agent. Alternatively, a high performance liquid chromatography (HPLC) UV detection method has been developed for the simultaneous determination of each of the enantiomers for esmolol's metabolite which, in turn, achieve 2.5–50 μg/ml concentrations in human plasma. Utilizing chiral columns, these methods do not require a precolumn asymmetric derivatization step. Linearity in all cases was >0.99. Precision and accuracy at all but the lowest concentrations were within ±6% for the esmolol enantiomers and within ±2.5% for the esmolol metabolite enantiomers. These values should be suitable for performing thorough pharmacokinetic studies for all of the stereoisomers of this prototypical soft drug and its corresponding metabolite.