Multisite study of a second generation whole blood rapid assay for cardiac troponin T.

We evaluated a second generation, qualitative, whole blood rapid assay for cardiac troponin T (cTnT), which employs a more cardio-specific troponin T mouse monoclonal capture antibody. Using quantitative cTnT enzyme-linked immunosorbent assay (ELISA) results as the benchmark for accuracy, we compared the performance of the second generation and the original whole blood rapid assays in 445 samples from patients with the following diagnoses, determined by medical record review: myocardial infarction, coronary bypass surgery, ischaemic heart disease, musculoskeletal disease, renal failure or other noncardiac conditions. Overall, concordance between the second generation cTnT Rapid Assay and the quantitative cTnT ELISA, compared using the McNemar test and a cut-off concentration of 0.1 microgram/L, was in the range 76-94% for each patient group. Using a receiver operating characteristic plot, the cut-off for the second generation cTnT Rapid Assay was in the range 0.06-0.08 microgram/L. We conclude that the second generation cTnT whole blood assay has a 2.5-fold lower analytical cut-off than the original rapid assay (0.2 microgram/L) and may represent a more sensitive clinical tool for the rapid triage and risk stratification of cardiac patients.

Absorption of therapeutic drugs by barrier gels in serum separator blood collection tubes. Volume- and time-dependent reduction in total and free drug concentrations.

The stability of seven commonly monitored therapeutic drugs in serum was examined following storage in Vacutainer SST and Corvac serum separator blood collection tubes. Significant decreases (ranging from 5.9% to 64.5%) in the measured concentrations of phenytoin, phenobarbital, lidocaine, quinidine, and carbamazepine were observed, as a function of both time and sample volume, when serum was stored in Vacutainer SST serum separator blood collection tubes. In contrast, measured concentrations of theophylline and salicylate did not change under identical specimen storage conditions. No significant changes in the concentrations of phenytoin, phenobarbital, carbamazepine, theophylline, quinidine, and salicylate were observed when serum was stored in Corvac serum separator blood collection tubes. Only serum lidocaine concentrations decreased (ranging from 31.5% to 72.6%, depending on sample volume) after storage in Corvac tubes for 24 hours. The apparent decreases in serum concentrations of therapeutic drugs in both Vacutainer SST and Corvac tubes were most pronounced when small volumes (200-500 microL) of serum remained in contact with the barrier gels for prolonged periods of time (> 2-6 hours). These decreases were due to absorption of drugs by the barrier gels, as demonstrated by the recovery of drugs following chemical extraction of the barrier gels with methanol. For phenytoin and phenobarbital, the reduction in total drug concentrations also resulted in a proportional decrease in free drug concentrations and was dependent on the extent of protein binding by the drug. None of the therapeutic drugs used in this study were adversely affected by prolonged storage in standard red top Vacutainer blood collection tubes without barrier gels. The data suggest that serum separator blood collection tubes should be used with extreme caution for therapeutic drug monitoring, particularly when reduced sample volumes or prolonged specimen storage may be required.

Pseudomembranous tracheobronchitis caused by Aspergillus.

Four immunosuppressed patients with a rapidly evolving, febrile, respiratory distress syndrome were found at autopsy to have Aspergillus pseudomembranes of their lower tracheobronchial tree. Steroids, neutropenia, broad spectrum antibiotic use, and alcoholism appear to be predisposing risk factors. Bronchoscopy may reveal the pathology but antemortem diagnosis is difficult because of the low yield of sputum cultures and fulminant nature of the disease.

Prediction of free phenytoin levels based on [total phenytoin]/[albumin] ratios. Potential errors with hypoalbuminemia.

Therapeutic monitoring of the pharmacologically active (free drug) fraction of protein-bound medications (e.g., phenytoin) represents a major diagnostic challenge in clinical and laboratory medicine. While free drug levels may be beneficial in many clinical situations, current methods for predicting free phenytoin concentrations are unreliable and not recommended for general use. The authors have demonstrated a linear relationship (r2 = 0.98) between serum levels of total and bound phenytoin in 56 patients with seizure disorders. No significant correlations were observed when total phenytoin and albumin levels were compared independently to measured concentrations of free phenytoin or percent free phenytoin. A good correlation (r2 = 0.89) existed between free phenytoin levels and [total phenytoin]/[albumin] ratios in patients with normal or elevated albumin levels, but significantly weaker correlations were found in patients with hypoalbuminemia. Thus, [total phenytoin]/[albumin] ratios may have clinical value in predicting free phenytoin levels in uncomplicated patients without hypoalbuminemia.

Displacement of phenytoin from serum protein carriers by antibiotics: studies with ceftriaxone, nafcillin, and sulfamethoxazole.

Increased concentrations of free phenytoin in serum, attributable to the displacement of this anticonvulsant by other drugs, e.g., valproic acid and salicylic acid, have been reported. We observed in vitro and in vivo displacement of phenytoin by the antibiotics ceftriaxone, nafcillin, and sulfamethoxazole. In vitro studies demonstrated statistically significant (P less than 0.05) increases in free phenytoin after the addition of specific antibiotics to patients' sera and to phenytoin-supplemented sera from controls. Concentrations of free phenytoin in vivo, predicted by an equation we have found to be accurate for albumin concentrations greater than or equal to 32 g/L, were consistently underestimated in patients receiving concomitant therapy with the antibiotics studied. The concentrations of free phenytoin decreased towards the predicted values when the antibiotic therapy was discontinued. We conclude that ceftriaxone, nafcillin, and sulfamethoxazole can displace phenytoin from the usual protein carriers found in serum, in vitro and in vivo.

Ethanol-induced alterations in human erythrocyte shape and surface properties: modulatory role of prostaglandin E1.

Exposure of human erythrocytes to ethanol (1 to 20% by vol) in Ca2+ and Mg2+-free phosphate-buffered saline, pH 7.4, transformed biconcave discs into spiculated echinocytes within 3 min at 25 degrees C. The effects of ethanol were concentration-and time-dependent, but reversible by washing in the incubation buffer system within 60 min of initial exposure to ethanol. After prolonged ethanol exposure (180 min), washing of cells resulted in the formation of stomatocytes (cup-forms). Ethanol-induced echinocytosis was also accompanied by a 30% enhancement in the agglutinability of erythrocytes by ligands with high affinity for negative surface charge (poly-L-lysine and wheat germ agglutinin, 20 microliters/ml) without any alterations in surface charge topography. Concomitant exposure of erythrocytes to prostaglandin E1 (100 nM) selectively prevented the enhancement of ligand-mediated agglutinability, but did not modify cell shape. These data indicate that certain erythrocyte surface properties may not be directly influenced by cell shape and suggest a unique modulatory action of prostaglandin E1 on shape-transformed cells.

Differential regulation of multiple neuroreceptors in a somatic cell hybrid by inhibitors of glycoprotein processing.

Specific binding of [3H][D-Ala2,D-Leu5]enkephalin, [3H]ethylketocyclazocine, 5-[3H]hydroxytryptamine, and [3H]spiperone was examined in neuroblastoma-brain hybrid cell line NCB-20 following exposure to inhibitors of N-linked protein glycosylation (tunicamycin, TM) and oligosaccharide processing (swainsonine, SW). TM treatment reduced ligand binding at delta- and sigma-opiate receptors and neuroleptic binding sites (20 to 50% of control), with no discernible effect on the binding properties of 5HT1-serotonin receptors. In contrast, exposure to SW resulted in a three-fold increase in binding capacity of sigma-receptors, while decreasing receptor affinity for ligand. SW treatment did not alter ligand interactions with either sigma-receptors or neuroleptic binding sites, but did reduce specific binding of serotonin to 5HT1-receptors. The effects of TM and SW on distinct receptor subpopulations were further demonstrated by attenuation of opiate and serotonin-mediated regulation of intracellular cyclic AMP.

Glycosylation-dependent regulation of opiate (enkephalin) receptors in neurotumor cells.

Electron inactivation analysis revealed that the opiate (enkephalin) binding site in neurotumor cell lines NG108-15 and NCB-20 had an apparent target size of 200,000 daltons. Expression of functional opiate receptors in neurotumor cells appeared to require glycosylation, as treatment of such cells with tunicamycin (TM; under conditions where de novo glycosylation of asparagine residues in protein was reduced by 80%, but overall protein and DNA synthesis were inhibited by less than 10%) resulted in the loss of 50% of the opiate binding sites. The loss of binding sites could not be prevented by addition of protease inhibitors to cell cultures, but binding sites were partially restored 48-60 h after removal of the TM. In addition, the number of enkephalin binding sites in TM-treated cells was also restored to near-normal levels by addition of physiological concentrations (1-10 mM) of manganese ions to the in vitro receptor binding incubation mixture. TM treatment resulted in receptor supersensitivity to manganese ions for both opiate agonists and antagonists, no change in the sodium effect for either agonists or antagonists, and subsensitivity to GTP for both agonists and antagonists. However, opiate binding to cell membranes was not substantially inhibited by either neuraminidase treatment or short-term incubation with lectins such as wheat germ agglutinin, ricin, or concanavalin A. Thus, the data suggest that oligosaccharide units are not directly involved in opiate receptor-ligand interactions, but protein glycosylation is required for functional expression of receptors.

[3H]ethylketocyclazocine binding to NCB-20 hybrid neurotumor cells.

Ethylketocyclazocine (EKC) binds to two sites on NCB-20 neuroblastoma X Chinese hamster brain hybrid cells (KDH = 2 nM, Bmax = 21,000 sites/cell; KDL = 27 nM, Bmax = 140,000 sites/cell. The high-affinity site has been characterized as a delta opiate receptor. The low-affinity site is relatively benzomorphan-specific; opioid peptides, morphine, etorphine, and naloxone do not compete at it. Rank order of potency among benzomorphans is (+)-EKC greater than Mr 2267 greater than (+)-ketocyclazocine greater than (+)-SKF 10047 greater than bremazocine greater than cyclazocine. Among other drugs of interest that inhibit [3H]EKC binding are phencyclidine and its analogues, Ki values for which are 0.2-40 microM. Stereoselectivity is the reverse of other opioid receptors: (+)-EKC much much greater than (-)-EKC, Mr 2267 greater than Mr 2266, (+)-SKF 10047 greater than (-)-SKF 10047. The site is sensitive to trypsin, but not to N-ethylmaleimide. Binding is insensitive to nucleotides, slightly sensitive to physiological concentrations of sodium, magnesium, and manganese ions and to EDTA but not EGTA.

Molecular size of opiate (enkephalin) receptors in neuroblastoma-glioma hybrid cells as determined by radiation inactivation analysis.

Opiate receptor binding decayed exponentially in mouse neuroblastoma-rat glioma (NG108-15) hybrid cell preparations following exposure to increasing doses of ionizing radiation (0.2 to 7.0 Mrads; 2.0 Mrads/min). Target size analysis revealed that [3H][D-Ala2, D-Leu5]enkephalin (agonist) and [3H]naloxone (antagonist) bound specifically to a component with an apparent molecular size of 200,000 +/- 20,000. Lyophilization of cells for the irradiation procedure did not significantly alter receptor affinity or binding capacity for these ligands. Furthermore, the loss of opiate receptor binding in irradiated cell samples could not be attributed to reduced receptor affinity since increasing concentrations of radiolabeled ligand failed to reverse the inhibition; nonspecific binding decreased only slightly under identical experimental conditions. The value of determining molecular size by radiation inactivation analysis was confirmed by showing that apparent target sizes for two representative lysosomal enzymes (beta-galactosidase and alpha-mannosidase) were consistent with results obtained previously using conventional methods. Thus, the data suggest that the ligand binding component of delta-opiate (enkephalin) receptors in NG108-15 cells has a minimum functional size of approximately 200,000.

Distinct high-affinity binding sites for benzomorphan drugs and enkephalin in a neuroblastoma--brain hybrid cell line.

The high-affinity binding of benzomorphan drugs (ethylketocyclazocine and N-allylnorcyclazocine) and [DAla2,DLeu5] enkephalin was examined in a mouse neuroblastoma--Chinese hamster brain clonal hybrid cell line (NCB-20). Scatchard analysis of saturation binding isotherms indicated the presence of a single binding site for 3H-labeled [DAla2,DLeu5]enkephalin (Kd = 3 nM) and multiple binding sites for [3H]ethylketocyclazocine (Kd = 4 and 20 nM) and N-[3H]allylnorcyclazocine (Kd = 0.5 and 15 nM). Both ethylketocyclazocine and N-allylnorcyclazocine competed (Ki = 10 and 30 nM, respectively) with [3H][DAla2,DLeu5]enkephalin binding in NCB-20 cells but neither [DAla2,DLeu5]enkephalin nor morphine could completely inhibit the specific binding of [3H]ethylketocyclazocine (7 nM) or N-[3H]allylnorcyclazocine (3 nM). Furthermore, not all benzomorphan drugs (e.g., ethylketocyclazocine) were totally efficacious in displacing 3 nM N-[3H]allylnorcyclazocine binding in the presence or absence of high concentrations of [DAla2,DLeu5]enkephalin. The data presented suggest that benzomorphan drugs interact with three distinct high-affinity binding sites: (i) a site that binds enkephalin and morphine in addition to ethylketocyclazocine and N-allylnorcyclazocine; (ii) a site that binds both ethylketocyclazocine and N-allylnorcyclazocine but not enkephalin and morphine; and (iii) a site that binds N-allylnorcyclazocine but not enkephalin, morphine, or ethylketocyclazocine. The first of these sites was comparable to the delta opiate receptor expressed in NG108-15 and N4TG1 cell lines based on the potency series obtained for various opiates and benzomorphan drugs in competition studies with [3H][DAla2,DLeu5]-enkephalin. However, the specific high-affinity benzomorphan binding sites thus far are unique and may represent biochemical correlates of kappa and sigma opiate receptors which have been proposed to exist on the basis of physiological studies.

Possible role of cyclic AMP in the receptor-mediated regulation of glycosyltransferase activities in neurotumor cell lines.

Exposure of mouse neuroblastoma cell line N4TGl to opiates or [D-Ala2,D-Leu5] enkephalin produced a naloxone-reversible inhibition of cyclic AMP synthesis and prevented, in a concentration-dependent manner, the formation of both ganglioside GM2 (GalNAc-[NeuNAc]-Gal-Glc-ceramide) from GM3 (NeuNAc-Gal-Glc-ceramide) and ganglioside GM1 (Gal-GalNAc-[NeuNAc]-Gal-Glc-ceramide) from GM2 in cell-free extracts. In contrast, the receptor-mediated elevation of intracellular cyclic AMP levels by agents such as prostaglandin E1 (in the presence of isobutylmethylxanthine) or the addition of the cyclic AMP derivatives (dibutyryl cyclic AMP) markedly stimulated the activities of UDP-GalNAc:GM3,N-acetylgalactosaminyltransferase and UDP-Gal:GM2,galactosyltransferase. An overall increase in the synthesis of gangliosides more complex than GM3 was also observed in the mouse neuroblastoma x hamster brain explant hybrid cell line NCB-20 following elevation of cyclic AMP levels by treatment with serotonin and pargyline. The data presented support the hypothesis that cyclic AMP may have a role in the regulation of sialoglycosphingolipid biosynthesis.