An enzyme-linked immunosorbent assay for lactose synthase (galactosyltransferase) in serum and its application as a tumor marker in ovarian carcinoma

This assay for lactose synthase (galactosyltransferase, EC 2.4.1.22) in serum involves two sequential incubations: serially diluted standard or sample antigen is reacted with a fixed amount of antibody; unbound antibody is then adsorbed to wells of antigen-coated microtiter plates and determined by a second antibody directed against the first antibody and coupled to phosphatase. The standard curve is linear for galactosyltransferase concentrations of 10 to 600 micrograms/L. The within-assay CV of a serum sample was 9.3% (SD 4.1%), the between-assay was 3.8% (SD 2.4%). Serum galactosyltransferase concentrations computed from three different dilutions yielded CVs of 6.5% (SD 5.7%, n = 14). We evaluated the method's accuracy by recovery analysis and by comparing enzyme activity in serum with that of purified galactosyltransferase from human milk. The normal reference interval, as estimated from data on 27 healthy blood donors, was 60-436 micrograms/L (mean 224, SD 101 micrograms/L). We applied the assay to samples of serum from ovarian carcinoma patients grouped according to tumor burden. We also determined galactosyltransferase in ascites fluid and found these values useful for diagnosis, whereas determinations in serum may serve mainly for patient monitoring.     

Placental alkaline phosphatase and cancer antigen 125 in sera of patients with benign and malignant diseases

Human placental alkaline phosphatase (hPLAP; EC 3.1.3.1), cancer antigen 125 (CA 125), and carcinoembryonic antigen (CEA) were determined in sera of patients with malignant and nonmalignant disorders. For CA 125 we used two different commercial assay systems, based on the same monoclonal antibody. hPLAP had the same sensitivity (20%) as CA 125 for detecting non-ovarian neoplasia, whereas that of CEA was 45%. For detecting ovarian cancer CA 125 (Cis kit) was slightly more sensitive (50%) than hPLAP (45%), much more than CEA (10%). hPLAP was increased in sera of 2% of patients with nonmalignant disorders, CA 125 in 23%, and CEA in 18%. hPLAP was increased in only one of 10 diabetic patients and two of 50 patients on chronic renal dialysis. CA 125 and CEA were respectively increased in 45% and 23% of all liver pathologies studied and in 12% and 17% of patients with renal insufficiency. The sensitivity of hPLAP for detecting ovarian cancer is slightly inferior to that of CA 125, but its specificity is much higher. We found the Abbott system for CA 125 to be more sensitive than the Cis system.     

Kinetic determination of serum sorbitol dehydrogenase activity with a centrifugal analyzer

We describe a mechanized method for centrifugal analyzer determination of sorbitol dehydrogenase in serum, based on conversion of D-fructose to sorbitol with simultaneous oxidation of NADH, in triethanolamine buffer at pH 7.4 and 30 degrees C. The standard curve for this assay is linear to 200 U of activity per liter of serum. The mean within-run precision (CV) of the assay is 0.8%. Results correlate well with those by a spectrophotometric method. In sera from 20 apparently healthy adult humans, sorbitol dehydrogenase activity averaged 1.7 (SD +/- 0.8; range, 1-3) U/L. The mean activity (U/L) for a group of 30 rats was 4.4 (SD, +/- 0.2; range, 3-6); for 20 dogs, 5.8 (SD, +/- 0.7; range 3-9); and for 30 mice, 26.8 (SD +/- 2.1; range, 22-34). To determine the utility of measuring this enzyme in the serum of rats for assessment of hepatotoxicity in drug-safety studies, we compared sorbitol dehydrogenase activity with that of alkaline phosphatase, aspartate aminotransferase, and alanine aminotranferase in the sera of rats treated with thioacetamide or in which the common bile duct has been ligated.     

Measurement of lipase activity by a differential pH technique

This is a new electrochemical method for determination of lipase activity in biological fluids, including serum, plasma, and duodenal juice. Advantages of turbidimetric methods--short reaction time, and small sample and reagent volumes--are combined with those of titrimetric methods: measurement of absolute activity (i.e., no standardization required), saturated substrate conditions, and direct measurement of reaction products. The proposed method is easy, inexpensive, and takes only 3 min. Precision is good: CV = 3.74% within day and 7.3% between days at the clinical-decision concentration, CV = 1.86% within day and 4.65% between days for above-normal lipase activities. The standard curve is linear up to 4500 U/L. Results (y) correlate well with those by turbidimetry (x): y = 0.9287x - 65.3 (r = 0.9719). Reference values are between 0 and 130 U/L.     

Measurement of free calcium ion in capillary blood and serum.

We describe a new calcium ion-selective electrode for measurement of the substance concentration of free calcium ion [Ca2+] in the plasma phase of whole blood and in serum at 37 degrees C. A sample volume of 50 microliter suffices to obtain simultaneous values of pH and [Ca2+]. We found the within-series analytical standard deviation for serum to be 0.013 mmol/litre (CV, 1.1%) and day-to-day precision to be 0.022 mmol/litre (CV, 1.7%). The reference interval for [Ca2+] (at pH 7.40) in serum was found to be 1.184 +/- 0.054 mmol/litre (2 SD) from measurements on sera from 121 healthy blood donors. Measurements on capillary blood from 29 healthy volunteers gave a mean (+/- 2 SD) value for [Ca2+] (at pH 7.40) of 1.22 +/- 0.072 mmol/litre.     

Determination of serum catalase activity on a centrifugal analyzer by an NADP/NADPH coupled enzyme reaction system.

We developed a simple, kinetic method for the determination of catalase activity in which i) the enzyme catalyzes the peroxidation of ethanol by hydrogen peroxide to acetaldehyde and water, and ii) the acetaldehyde so formed is rapidly oxidized to acetic acid and NADPH by the addition of an excess of NADP+ and aldehyde dehydrogenase. The rate of NADPH production was monitored at 340 nm in a COBAS centrifugal analyzer. The reaction was linear to 800 U/L or a delta A of 0.020/min. Using human serum pools containing 80 and 460 U/L of peroxidase activity, the within-run coefficients of variation (CV) were 1.9 and 1.3%, respectively. Between-run CV values were 5% for both pools. The reference range for sera from 72 males and 52 females was 23 to 158 U/L (mean + 2 SD) by log normal transformation. The activity in red cells was 600 U/g hemoglobin but did not change the reference range appreciably provided that serum without visible hemolysis was used. Preliminary observations on sera from nine patients with various pancreatic disorders showed a poor correlation between the activities of catalase (peroxidase) and amylase in serum. The reasons for this discrepancy are under investigation.     

Quantitative nephelometric assay for determining myoglobin evaluated

A recently introduced automated nephelometric immunoassay involving shell/core particles for determination of myoglobin (Behringwerke) was evaluated with the BNA Nephelometer. Method precision was good: the intra-assay CV varied between 1.5% and 6.1%; with daily calibration, the interassay CV ranged between 1.5% and 7.5%. For usual sample dilutions, the assay response varied linearly with myoglobin concentrations up to 23.1 nmol/L. After automatic dilution by the instrument, concentrations up to 2310 nmol/L could be measured without high-dose "hook" effect. Further manual dilution allowed measurement of myoglobin concentrations up to 26,000 nmol/L. Calibration was stable for at least seven days. We detected no significant interferences from hemoglobin, haptoglobin, bilirubin, iodine-containing contrast media, and rheumatoid factors. Treating lipemic samples with Lipoclean (Behringwerke) decreased test results. Simultaneously drawn serum and plasma samples from the same subject showed no consistent differences in myoglobin concentrations. The mean reference myoglobin concentration was 1.380 (SD 0.82) nmol/L for men and 0.878 (SD 0.45) nmol/L for women. In patients with renal insufficiency, serum creatinine values were moderately related to serum myoglobin values (r = 0.465). Although a commercial radioimmunoassay (Byk-Sangtec) and the nephelometric assay intercorrelated well (r = 0.929), values obtained by nephelometry were significantly lower (P less than 0.05). By both assays, results for heart and skeletal muscle tissue extracts showed no correlation, a finding that suggests the existence of multiple forms of myoglobin in human tissues. We conclude that immunonephelometry is a rapid, practical, and reliable method for measuring myoglobin in serum.     

Serum mitochondrial aspartate aminotransferase activity: not useful as a marker of excessive alcohol consumption in an unselected population

Using an immunochemical method, we measured the activity of the mitochondrial isoenzyme (mAST) of aspartate amino-transferase (EC 2.6.1.1, AST) in the serum of 687 subjects attending the Centre for Preventive Medicine for a health examination. The distributions of the activities were asymmetrical, with mean values of 1.8 U/L (SD 2.0) for men and 1.4 U/L (SD 1.6) for women. The average ratio of mitochondrial to total AST activity was 0.051 (range 0-0.42). In this unselected population we found no change in the mitochondrial activity or in the mitochondrial-to-total ratio attributable to alcohol consumption, even in subjects who consumed more than 88 g per day. Of 35 men with an alcohol consumption greater than 88 g/d, 19 had a serum gamma-glutamyltransferase activity of greater than or equal to 60 U/L, 17 had glutamate dehydrogenase values greater than or equal to 5 U/L, and only nine had an mAST activity greater than or equal to 3 U/L (values corresponding to the 80th percentiles of the total population). We conclude that the test is not particularly useful as a screening procedure in an unselected population under present-day conditions of measurement.     

24,25-dihydroxyvitamin D3 in serum: sample purification with Sep-Pak C-18 cartridges and liquid chromatography before protein-binding assay

We describe a precise, specific method for measuring 24,25-dihydroxyvitamin D3 in human serum. A 2-mL serum sample is extracted with acetonitrile and passed through a Sep-Pak C-18 cartridge. The sample is further purified by "high-performance" liquid chromatography under isocratic conditions on a normal-phase column (Radial-Pak silica-gel cartridge), then subjected to a protein-binding assay. The mean concentration of 24,25-dihydroxyvitamin D3 in serum from 22 normal adults (measured during the spring) was 2.9 micrograms/L (SD 1.9, range 6.3-0.42 microgram/L). The intra-assay CV was 7.7%, the interassay CV 11.2%. Purification of the sample with Sep-Pak C-18 and liquid chromatography on normal plus reversed-phase columns leads to a mean value of 3.4 micrograms/L (SD 1.6 micrograms/L, n = 12), not significantly different from results with our method.     

逆向两点校正测定血清亚铁氧化酶

目的探讨一种血清铜蓝蛋白亚铁氧化酶活性的新的测定方法,并使实验方法和步骤可用于自动化分析。方法用亚铁离子作底物,37℃pH5.80.45mol/L醋酸盐缓冲液条件下Fe2+被血清铜蓝蛋白亚铁氧化酶氧化成Fe3+,一定时间后,加入亚铁嗪显色,λ570nm下测定未被氧化的Fe2+离子的含量,依据反应前后底物浓度的变化,用逆向两点校正计算出被氧化的Fe2+所对应的亚铁氧化酶活性。结果亚铁嗪与Fe2+显色稳定,效果好。标本平均回收率105.2%,线性可达780U/L;精密度:批内CV:4.8%,批间:5.5%,标本存放4℃下稳定时间可达1周以上;脂血、溶血标本不影响亚铁氧化酶测定;EDTA能完全络合Fe2+离子。测定正常人标本30人份,平均值262.1U/L。SD:69.2U/L。结论运用逆向两点校正法,用EDTA作第二校准物取代铜蓝蛋白标准,克服了酶易失活的弱点,使校准更加可靠。可用于自动化分析,检测速度快、精密度较高,易于推广。     

Column chromatography and immunoassay compared for measuring the isoenzymes of aspartate aminotransferase in serum.

We compare a column-chromatographic method and a homogeneous immunoassay method for separately measuring the mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase. Analytical recovery for the two methods averaged 102% (SD, 2%) and 103% (SD, 4%), respectively, for 11 pools prepared by adding the purified isoenzymes to serum and 102% (SD 8.9%) and 89% (SD, 8.1%) for 26 unaltered specimens of human serum. In comparing the results of the immunoassay method (y) to the chromatographic method (x), our measurements agreed closely for the mitochondrial (y = 0.947 X + 7, r = 0.9991, standard error of estimate = 2.9 U/L) and cytoplasmic (y = 0.92x-6, r = 0.9995, standard error of estimate = 2.1 U/L) isoenzymes in pools prepared from the purified isoenzymes. Similar measurements of the 26 human serum specimens yielded the following results for least-squares evaluation; cytoplasmic isoenzyme y = 1.03x-11, r = 0.994, and standard error of estimate = 6.0 U/L; mitochondrial isoenzyme y = 0.75x+0, r = 0.927, and standard error of estimate = 3.9 U/L.     

Measurement of c-erbb-2 proteins in sera from patients with carcinomas and in breast tumor tissue cytosols: Correlation with serum tumor markers and membrane-bound oncoprotein

Using a commercial kit with antibodies against the ectodomain of c-erbB-2 protein, we detected c-erbB-2 immunoreactivity in human serum. We found that the percentages of patients with elevated serum c-erbB-2 immunoreactivities were 35, 21, and 9% in breast, prostate, and ovarian carcinoma, respectively. The majority of the elevated immunoreactivities were associated with sera containing highly elevated tumor markers with the highest in breast carcinoma (35%) and lowest in ovarian cancer (9%). Excellent correlations were also observed between the serum levels of c-erbB-2 immunoreactivity and the dominant tumor markers in serial specimens from individual cancer patients. We could also detect the c-erbB-2 immunoreactivity in the cytosols prepared from the breast tumor tissue for estrogen and progesterone receptor (ER&PgR) measurements using the same commercial kit for serum studies, and the intact c-erbB-2 oncoprotein (p 185) in the extracts of the tissue membrane fractions with a different kit designed for tissue extract. The level of c-erbB-2 immunoreactivity in the cytosol from 124 human breast tumor specimens had an excellent correlation with the cell membrane concentrations of p 185 (γ = 0.89). Most of the elevated cytosol c-erbB-2 immunoreactivities were also found to associate with breast tumor specimens containing low concentrations of ER&PgR. It appears that measuring the c-erbB-2 immunoreactivity potentially could be used as a prognostic marker without performing tissue biopsies and also as a serum tumor marker for managing cancer patients.©1995 wiley-Liss, inc.     

Interlaboratory study of the IFCC method for alanine aminotransferase performed with use of a partly purified reference material.

We present the results of a study on performance of a reference material for alanine aminotransferase (ALT, EC 2.6.1.2) and the corresponding IFCC-approved method in an interlaboratory trial involving 13 laboratories. The ALT material was partly purified from pig heart (specific activity, 150 kU/g) and was essentially free of six potentially contaminating enzyme activities, including aspartate aminotransferase (EC 2.6.1.1). The partly purified ALT was lyophilized in a triethanolamine-buffered matrix, pH 6.4, containing bovine serum albumin and saccharose. Under these conditions, the predicted yearly loss of activity was 0.02% at 4 degrees C and < 0.01% at -20 degrees C. The final blank-corrected results of the accepted set of data gave a mean (SD) of 128.5 (5.1) U/L. The among-laboratory SD was 4.6 U/L and the within-laboratory SD was 2.0 U/L. The certified ALT catalytic concentration in the reconstituted material was 129 U/L with a 0.95 confidence interval of +/- 4 U/L.     

Analytical and physiological characteristics of prostate-specific antigen and prostatic acid phosphatase in serum compared

We did a comparative analysis of the physiological and analytical properties of prostate-specific antigen (PSA), acid phosphatase (ACP; EC 3.1.32) activity, and acid phosphatase antigen (PAP) in serum. The PSA assay is sensitive to 0.2 microgram/L and demonstrates good linearity (y = 1.01x + 0.74). The CV was 3.9% at 40 micrograms/L, 8.0% at 3.1 micrograms/L. PSA and PAP are less stable at 4 degrees C than at -20 degrees C. Serum PAP and ACP concentrations showed large intra-individual fluctuations (average CVs of 22% and 24%, respectively), which were not observed with PSA measurements (average CV 6.2%). We saw significant correlation with the magnitude of physiological change when analytes were compared for serially collected split samples [y(PSA) = 0.14x(PAP) + 0.00, r = 0.767], which indicates that a common factor is influencing this variation. The excellent analytical performance, tissue specificity, and small degree of intra-individual variance are characteristics that favor the measurement of PSA in serum for monitoring patients with prostatic cancer.     

Effects of methylamine and heparin on a rapid chromogenic assay of C1-esterase inhibitor in plasma

We describe a rapid assay of C1-esterase inhibitor (C1-inh) activity in plasma. After adding purified C1s serine protease (EC 3.4.21.42) in excess to plasma, we determine the residual C1s activity towards a new chromogenic tripeptide, CH3CO-Lys(CbO)-Gly-Arg-pNA. Optimal conditions include the addition of methylamine (final concentration 0.12 mol/L) to reduce the potential inhibitory capacity of alpha 2-macroglobulin towards C1s and the addition of heparin (final concentration 3000 int. units/L) to enhance the reaction of C1s with C1-inh. The correlation with C1-inh antigen concentrations in plasma was excellent. The estimated interassay CV was 4.3%, whereas the intra-assay CV was 2.0% for activity concentrations within the range of normal individuals (means +/- 2 SD: 70-124%), 1.3% at lower concentrations. The method is more convenient, rapid, and precise than previous methods, and C1-inh activity in plasma can be assessed within 30 min. We found that concentrations of C1-inh in plasma were low during open-heart bypass surgery.     

Development of an immunofluorometric assay and quantification of human kallikrein 7 in tissue extracts and biological fluids

BACKGROUND: Human kallikrein 7 (hK7), also known as human stratum corneum chymotryptic enzyme, is a chymotrypsin-like serine protease first identified in human skin extracts and predicted to be a secreted protease. The aim of this study was to develop a sensitive and specific immunoassay for hK7 and to examine the distribution of hK7 in tissue extracts and biological fluids. METHODS: Recombinant hK7 was produced in human embryonic kidney cells (HEK293T) and purified by a three-step column chromatographic procedure. The purified hK7 was injected into mice for antibody generation. A sandwich-type immunoassay was developed with the anti-hK7 monoclonal antibodies. RESULTS: The assay had imprecision (CV) <10% through the dynamic range of 0.2-20 microg/L and had no detectable cross-reactivity from other members in the human kallikrein gene family. Highest concentrations were found in skin, esophagus, and kidney. hK7 was also found in amniotic fluid, ascites from ovarian cancer patients, breast milk, cerebrospinal fluid, saliva, seminal plasma, serum, sweat, synovial fluid, and urine. CONCLUSIONS: This study describes the first ELISA-type immunoassay for hK7 protein quantification. hK7 is found many human tissues and in various biological fluids.     

Enzymic determination of free fatty acids in serum

We describe the enzymic determination of free fatty acids in serum with use of acyl-CoA synthetase (EC l.2.1.3), acyl-CoA oxidase (no EC no. assigned) and peroxidase (EC 1.11.1.7). The free fatty acids are activated by acyl-CoA synthetase in the presence of ATP and coenzyme A. The acyl-CoA formed is oxidized by acyl-CoA oxidase to enoyl-CoA with simultaneous production of hydrogen peroxide, which is oxidatively coupled with 4-amino-antipyrine and 2,4-dibromphenol in the presence of peroxidase to yield a product that absorbs maximally at 505 nm. Standard curves prepared with various kinds of fatty acids are linear to at least 2.0 mmol/L and are practically congruent. Ascorbic acid or bilirubin interferes slightly. Results by the present method correlate well with those by the colorimetric method involving 2-(2-thiozolylazo)-p-cresol (r = 0.98). Replicate analyses of standard solution and of two kinds of control sera demonstrated the following between-assay precision: mean absorbance 0.224 (SD 0.002), CV 0.85%; mean concentration, 326 (SD 7.3) and 1076 (SD 22.7) mumol/L, CV 2.24 and 2.11%, respectively.     

Sensitive salivary estradiol assay for monitoring ovarian function

Measurement of steroids in saliva has excited interest because of the numerous potential clinical applications; noninvasive, convenient sampling; and apparently accurate reflection of the concentrations of physiologically active unbound steroid in the circulation. Although assays of saliva for several steroid hormones are available and widely used, assays for salivary estradiol are not, primarily because of methodological limitations. By modifying a commercially available kit for serum estradiol, our laboratory has developed a procedure that is sensitive, highly specific, and reliable for measuring salivary estradiol. Assay sensitivity is 0.5 fmol (0.14 pg; sample concentration 1.3 pmol/L) with a mean interassay CV of 10.8% at low concentrations. Clinical studies showed that values for serum and saliva are highly correlated (P less than 0.001), and demonstrated reliable detection of estradiol peaks during normal ovulatory cycles in serial samples from 15 women. Salivary estradiol peaked at 5.4 (SD 1.9) pmol/L on cycle day 14.4 (SD 3.2), 1.2 (SD 0.8) days before ovulation detected by ultrasound. This assay may be particularly helpful in investigating ovarian function and free estradiol in women at various stages of the reproductive cycle.     

血清过氧化氢酶活活性比色测定法

介绍一种简便、快速的血清过氧化氢酶活性的比色测定方法。探讨了其比色波长的选择、Ｈ２Ｏ２、钼酸铵试剂浓度与吸光度的关系，溶血、脂血、黄疸标本对测定结果的影响，以及标本与试剂的存放等因素。本法精密度试验批内变异系数（ｃｖ）为４．６％，批间ＣＶ为５．０％。对４７例新生儿脐血清标本的过氧化氢酶活性测定平均值是：１４７．７±５９．９ＫＵ／Ｌ（４２．０～２３６．４）．测定了９７７例健康人的血清过氧化氢酶活性为：５２．７±１７．０ＫＵ／Ｌ（１５．２～１１８．２）。试验结果表明：男性血清过氧化氢酶活性较女性１６．６％，其结果有随年龄增长而增高的趋势。