Evaluation of a rapid, quantitative cardiac troponin I immunoassay

We evaluated a rapid, quantitative immunoassay for the detection of cardiac troponin I. Coefficient of variation is between 1.29 and 13.63% for intra-assay and between 3.88 and 10.15% for inter-assay imprecision. Linearity is given up to 35 micrograms/l. Possible interfering substances (haemoglobin, bilirubin, triacylglycerol and rheuma factors) do not disturb the assay. The analyte is stable under normal storage conditions (+20 degrees C/48 h and +4 degrees C/l week) with decrease up to 30% after 3 months at -20 degrees C. Reference value for apparently healthy individuals is < 0.1 microgram/l. In plasma cardiac troponin I is measured up to 30% depressed compared to serum. Comparison with another cardiac troponin I assay (y = 0.92x + 2.42, r = 0.940) and cardiac troponin T is good with y = 6.61x - 1.94, r = 0.91 for the first generation cardiac troponin T assay and y = 5.59x - 0.68, r = 0.87 for the second generation cardiac troponin T assay. In summary, the evaluated assay is fast, easy to perform, and can be used not only in a specialized laboratory, but is also suitable for emergency laboratory or smaller laboratory units.

Multiplexing of Y chromosome specific STRs and performance for mixed samples

A combination of four Y-specific polymorphic STR loci was amplified simultaneously using fluorescently labeled primers. Multiplex conditions required optimization to eliminate constant bands and amplification products for female DNA. A series of experiments was carried out for mixtures of DNA from two males, and from male and female individuals for the Y-specific STRs and an autosomal locus. For the male/male mixtures amplified with the Y specific system, and amplified for an autosomal locus, the minor component in the mixture could only be identified up to a ratio of 1:10, 1:50 respectively. In male/female DNA mixtures the Y STR alleles could be identified for the highest ratio tested, 400 pg male in DNA in 800 ng female DNA which amounts to a ratio of 1:2000.

Effects of short-term recombinant human insulin-like growth factor I administration on bone turnover in osteopenic women with anorexia nervosa

Significant osteoporosis affects over half of all women with anorexia nervosa (AN). The mechanisms of bone loss in this condition are not known, and estrogen administration alone has not been shown to prevent bone loss. Insulin-like growth factor I (IGF-I), a nutritionally dependent bone trophic hormone, is know to stimulate osteoblast function and collagen synthesis in vivo and in vitro. We hypothesized that short term administration of recombinant human IGF-I (rhIGF-I) would increase bone turnover in young women with AN. We studied 23 women, aged 18-29 yr (mean +/- SD, 23 +/- 4 yr) with AN. Spinal bone density was significantly reduced compared to that in age-matched controls (0.85 +/- 0.11 vs. 1.19 +/- 0.12 g/cm2 by dual energy x-ray absorptiometry; P < 0.001) and was below the normal mean in 54% of the women. Patients were randomized to receive rhIGF-I (100 or 30 micrograms/kg) or placebo sc twice a day for 6 days. Bone turnover was assessed at baseline and after 3 and 6 days of treatment using two markers of bone formation [osteocalcin (OC) and type I procollagen carboxyl-terminal propeptide (PICP)] and three specific markers of bone resorption [pyridinoline (PYRX), deoxypyridinoline (DPYRX), and N-telopeptide (NTX)]. Serum OC was reduced significantly (P < 0.001) in women with AN compared to normal premenopausal women (5.4 +/- 3.8 vs. 8.6 +/- 4.5 ng/mL) and correlated with percent fat mass (r = 0.60;P < 0.01) and body mass index (r = 0.50;P < 0.05). Markers of bone resorption were elevated significantly compared to normal levels [DPYRX, 18.2 +/- 7.0 vs. 11.4 +/- 5.2 nmol/mmol creatinine, (P < 0.001); NTX, 53.5 +/- 22.5 vs. 36.5 +/- 14.6 nmol BCE/mmol creatinine (P < 0.01)]. IGF-I levels were relatively low at baseline compared to those in age-matched controls (203 +/- 93 vs. 262 +/- 84 ng/mL;P < 0.01) and increased to 673 +/- 268 ng/mL [P < 0.05; 100 micrograms/kg twice daily (BID)] and 545 +/- 255 ng/mL (P < 0.05; 30 micrograms/kg BID). During short term administration of rhIGF-I at a dose of 100 micrograms/kg BID, there was a significant (P < 0.05) increase in markers of bone formation, as assessed by both PICP (147 +/- 33 to 303 +/- 187 ng/mL) and OC (5.3 +/- 3.8 to 10.9 +/- 7.4 ng/mL). There was also a significant (P < 0.05) increase in markers of bone resorption as assessed by PYRX (51.0 +/- 16.6 to 87.1 +/- 8.2 nmol/mmol creatinine) and DPYRX (17.3 +/- 4.5 to 26.3 +/- 3.7 nmol/mmol creatinine). The group randomized to receive short term administration of rhIGF-I at a dose of 30 micrograms/kg BID demonstrated a significant (P < 0.05) increase in PICP (110.9 +/- 47.0 to 134.8 +/- 43.2 ng/mL) and an insignificant increase in OC levels (4.5 +/- 3.2 to 6.8 +/- 5.9 ng/mL). However, markers of bone resorption were unchanged during rhIGF-I administration at this dose. Serum PTH and serum and urinary calcium were unchanged in both treatment groups compared to placebo levels. These data demonstrate that young women with anorexia nervosa have decreased markers of bone formation and increased bone resorption. This is the first demonstration that short term rhIGF-I administration increases markers of bone turnover in severely osteopenic women with AN. The effects of short term rhIGF-I on bone turnover are dose dependent. At a dose of 100 micrograms BID, rhIGF-I administration significantly stimulated both markers of bone formation and bone resorption. At a dose of rhIGF-I of 30 micrograms BID, there was an increase in one marker of bone formation, PICP, without a change in markers of bone resorption. Further studies are required to determine whether chronic administration of rhIGF-I can affect bone mass in young women with profound osteopenia due to anorexia nervosa.

Resolution of apolipoprotein B repeat unit position variants on agarose, denaturing, and native polyacrylamide gels

Utilizing three different electrophoresis systems for the separation of variable number of tandem repeats (VNTR) alleles of the high variable region 3' from the apolipoprotein B (Apo B) locus, it could be shown that apparent allele subtypes on native polyacrylamide gels comigrated with the regular ladder alleles on agarose and denaturing polyacrylamide gels. Two subtypes, one with a shift towards the cathode and one shifted towards the anode, and the corresponding ladder alleles were sequenced in order to determine the molecular basis for this aberrant electrophoretical mobility. Subtype and ladder alleles displayed the same number of repeat units but differed in the number and order of different types of repeats. Depending on the variation in the region of pure AT repeat units, the potential secondary structures of hairpin loop formation differed for subtypes and ladder alleles, which is thought to explain the shift in electrophoretic mobility on native polyacrylamide gel electrophoresis.

Molecular mimicry in the MHC: hidden clues to autoimmunity?

The term 'molecular mimicry' has been used to describe a spectrum of antigenic crossreactivities thought to underlie autoimmune disease. For T-cell crossreactivities to occur, appropriate T-cell clones must be available. Here, Harold Baum, Huw Davies and Mark Peakman speculate that an important source of self-peptides that govern thymic selection of such clones are MHC molecules themselves.

Mitochondrial antigens, molecular mimicry and autoimmune disease

The immune system is normally tolerant to mitochondrial self-antigens, but responsive against bacteria. Low-titre anti-mitochondrial antibodies (AMA) might be involved in this discrimination. Tolerance is broken in diseases characterised by high titre AMA. Some of these AMA, against cardiolipin, cross-react with DNA. The best studied AMA are those characterising primary biliary cirrhosis (PBC). These are directed against E2 subunits of the oxo-acid dehydrogenase complexes, and also against subunits E1 alpha, E1 beta and X of the pyruvate dehydrogenase complex. AMA of PBC patients also react with bacterial E2s. Reactivities are primarily peptide-specific but with cross-reactivity between mitochondrial and microbial antigens and between E2s of respective complexes. Immunodominant epitopes, for anti E2 AMA, include the conserved sequence flanking the site of lipoyl attachment. It is proposed that the initial stimulus for antibody production is chronic urinary tract infection. AMA themselves are not pathogenic, but CD4+ T-cells would be primed, recognising the lipoyl domain epitope in association with class II HLA. Inappropriate expression of class II antigens on bile duct epithelia, (as found in PBC), might lead to presentation of a particular fragment of HLA-DR alpha, known to be a major MHC presented self-peptide in the mouse. That sequence strongly mimics the lipoyl domain and might be recognised by primed T-cells, initiating the autoimmune cascade. In the mouse, a peptide of ND1 of Complex I is presented in association with class I MHC. Cells exhibiting somatic mutation of such a peptide might thus be subject to attack by CD8+ T-cells. If such peptides were presented by class II HLA, autoimmune diseases might arise, related to mimicry between such peptides and microbial sequences and/or self-antigens. These considerations might apply in Leber's disease and in age-related pathology.

Detection of M2 antibodies in patients with recurrent urinary tract infection using an ELISA and purified PBC specific antigens. Evidence for a molecular mimicry mechanism in the pathogenesis of primary biliary cirrhosis?

Primary Biliary Cirrhosis (PBC) is a chronic liver disease of unknown aetiology. The main characteristic feature of the disease is the presence of circulating antimitochondrial antibodies (AMA) to components (collectively named M2) of the mitochondrial 2-oxo-acid multienzyme complexes; pyruvate, oxoglutarate and branched chain oxo-acid dehydrogenase complexes. As these enzymes are phylogenetically conserved, AMA also exhibit reactivity against a range of microorganisms. PBC patients have an increased incidence of recurrent urinary tract infection (UTI) compared to other chronic liver disease controls. Interestingly, we have recently detected low titre AMA in patients with a history of recurrent UTI but normal liver function using crude bovine heart mitochondrial preparations and immunoblotting techniques. Here we confirm these findings using purified M2 antigens and ELISA. We found that 52% of "normal" subjects with a history of recurrent UTI had AMA specifically to M2 antigens. The percentage was significantly higher than that found for chronic liver disease (19%, p < 0.01) and normal controls (4%, p < 0.001). These results support our hypothesis for molecular mimicry in PBC. We propose that a bacterial trigger, possibly resulting from recurrent UTIs, is responsible for initiating an autoimmune response in a predisposed host because of a cross-reactivity between mitochondrial and bacterial antigens.

A rapid assay for the quantification of myoglobin: evaluation and diagnostic relevance in the diagnosis of acute myocardial infarction

We evaluated a new, fast, quantitative, turbidimetric assay (TurbiTimeSystem, Behringwerke AG, Marburg, Germany) for the determination of myoglobin concentration in serum. Within-run imprecision (n = 10) was < 3.7% in controls ranging from 81.1 to 621.4 micrograms/l and between-day imprecision (n = 50) was < 6% in controls ranging from 69.5 to 623.4 micrograms/l. The assay is linear over the measuring range and interfering substances such as bilirubin, haemoglobin or haptoglobin do not interfere but triacylglycerol-rich samples are only measurable after brief ultracentrifugation. EDTA- or citrate-treated samples display depressed myoglobin concentration when compared with serum samples. The upper reference limit for apparently healthy individuals (n = 100, 50 female and 50 male) is 61.5 micrograms/l. Comparison with nephelometry revealed a good correlation (r = 0.982) between the two methods with the regression equation: turbidimetric assay = 5.53 + 1.02x nephelometric assay. Serial determination of myoglobin concentration and creatine kinase in 18 patients with proven acute myocardial infarction showed in general an equal diagnostic significance for both analytes. In the first 4 hours after onset of chest pain, the determination of myoglobin can have an advantage, since it is released into the blood stream at an earlier stage, but thereafter myoglobin can lead to false negative diagnosis. Therefore, determination of creatine kinase and its isoenzyme MB is still the diagnostic strategy of choice in the diagnosis of acute myocardial infarction.

Plasma coenzyme Q (ubiquinone) concentrations in patients treated with simvastatin

Plasma coenzyme Q (CoQ) was measured in 20 hyperlipidaemic patients treated with diet and simvastatin (an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase); 22 hyperlipidaemic patients treated with diet with alone; and 20 normal controls. Patients treated with simvastatin had a significantly lower plasma CoQ and CoQ: cholesterol ratio than either patients receiving diet alone or normal controls. Use of simvastatin was inversely and independently correlated with both CoQ (p < 0.0001) and CoQ: cholesterol ratio (p < 0.01). There was a significant inverse association between CoQ and dose of simvastatin (p < 0.001). It is concluded that simvastatin may lower the plasma CoQ concentration and this may be greater than the reduction in cholesterol. The possible adverse effect of simvastatin on the metabolism of CoQ may be clinically important and requires further study.

Autoimmune disease and molecular mimicry: an hypothesis

Helper T lymphocytes are normally only stimulated to initiate an immune reaction through the recognition of peptides bound to class II major histocompatibility complex (MHC) molecules. Class II MHC molecules are constitutively expressed on antigen-presenting cells which play a critical role in the initiation of immune responses. In disease states, however, other cells often express class II MHC molecules inappropriately. This article suggests an hypothesis for the pathogenesis of autoimmune diseases based on molecular mimicry. The mimicry described is between microbial or viral peptides presented by antigen-presenting cells and self peptides presented inappropriately on a target tissue. This leads to helper T cells, stimulated by peptides derived from infectious organisms, initiating an autoimmune attack on the target tissue.

M2 mitochondrial antibodies and urinary rough mutant bacteria in patients with primary biliary cirrhosis and in patients with recurrent bacteriuria

Primary biliary cirrhosis (PBC) patients have a higher incidence of recurrent urinary tract infection and an increased prevalence of rough forms (mutants) of E. coli in their stool samples than other chronic liver disease patients. PBC patients exhibit autoantibody reactivity against mitochondria, the most common antigen (M2) being a family of antigens with the major components having approximate molecular weights of 74, 56, 52 and 48 kD. Cross-reactivity between M2 antigen components and corresponding antigenic bands of bacteria has been demonstrated with PBC sera. Patients with recurrent urinary tract infections, all of whom had normal liver function and were taking prophylactic antibiotic treatment, had weak anti-mitochondrial antibody (AMA) reactivity (69%), with reactivity against the 74-kD antigen alone being the most common. When antibody to the 74-kD band was eluted, it was found to cross-react with bacterial membrane fractions. In the controls, 12/77 chronic liver disease patients and 2/24 normals possessed AMA. Rough forms of bacteria were found in the urine of patients with significant bacteriuria: 39% PBC, 5.3% chronic liver disease and 41% of the recurrent urinary tract infection group. M2 antibodies may be induced by urinary organisms in 'normal' women with recurrent bacteriuria and in females with PBC.

Serum catalase as the protective agent against inactivation of alpha 1-proteinase inhibitor by hydrogen peroxide; comparison between normal and rheumatoid sera

Human serum contains catalase activity, which can protect alpha 1-proteinase inhibitor from inactivation by H2O2. The primary source of serum catalase is probably erythrocytic. The enzyme activity correlates with haemoglobin concentration in sera from control subjects but not in sera from patients with rheumatoid arthritis. Catalase is inactivated by oxidants, such as H2O2 and hypochlorous acid and it is suggested that the decrease in catalase/haemoglobin ratio observed in rheumatoid serum is due to oxidant stress associated with inflammation.