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Biomedical subjects

A H Wu

Publications and source records attributed to A H Wu.

At least 19 recordsLinked to original sources
PubMed1992

Mechanism of differential inhibition of lactate dehydrogenase isoenzymes in the BMC LD-1 assay.

The mechanism of inhibition of lactate dehydrogenase (LD) isoenzymes by guanidinium thiocyanate (GSCN) used in the LD-1 assay developed by Boehringer Mannheim Corporation (BMC) was investigated. Michaelis-Menten inhibition kinetics for the individual isoenzymes revealed that GSCN competitively inhibited LD-1 in the presence of lactate and NAD+, but is a noncompetitive inhibitor of LD-5. LD-2 and LD-3 exhibited mixed inhibition kinetics. The inhibition constants were two- to threefold smaller for LD-5 than for LD-1. Time-dependent studies also showed that the isoenzymes underwent a different rate of inactivation by GSCN. LD-5, LD-3, and LD-2 were rapidly inactivated within 1 min under the BMC assay conditions, whereas LD-1 lost only about 20% of activity after 10 min. The presence of lactate further protects LD-1, but not other isoenzymes. Under this condition, LD-1 was not inactivated during the initial 6 min of reaction. Separate experiments demonstrated that both guanidinium and thiocyanate ions are responsible for the inactivation process that was found to be irreversible. We speculate that GSCN selectively denatures the M subunit of LD. The H subunit is less susceptible to denaturation and is further stabilized by lactate.

Guanidines↗
PubMed1992

Clinical applications of muscle enzymes and proteins.

Total creatine kinase measurement in serum has remained the best overall marker for detection and monitoring of skeletal muscle diseases, despite that different human tissues exhibit varying distributions of cytoplasmic and mitochondrial isoenzymes of creatine kinase. Acute myocardial infarction aside, increases in total serum creatine kinase, as reflected by the MM isoenzyme, are most commonly caused by injury or diseases to striated muscle. Enzyme markers of skeletal muscle injury that have been previously used (eg, aldolase, enolase, aspartate aminotransferase, and lactate dehydrogenase isoenzyme 5) are not as specific as creatine kinase and have limited clinical utility. However, new enzyme and protein markers are currently being investigated, eg, troponin and carbonic anhydrase III, which are more specific than creatine kinase toward particular tissues. Moreover, measurement of creatine kinase isoforms may provide information about whether muscle turnover is acute or chronic.

Biomarkers↗
PubMed1992

Creatine kinase MB isoforms in patients with skeletal muscle injury: ramifications for early detection of acute myocardial infarction.

We measured total creatine kinase (CK), CK-MB isoenzyme, and the MB isoforms in 202 serum and plasma samples from nine groups of patients and normal individuals: 39 with acute myocardial infarction (MI), divided according to time between the onset of chest pain and blood collection (1-6 h, 7-12 h, and 13-48 h); 26 with chest pain for whom an MI was ruled out, sampled at admission; 17 undergoing bypass surgery or cardiac catheterization, sampled within 6 h after either procedure; 17 with acute skeletal muscle injury, sampled within 8 h after injury; 30 marathon runners immediately after a race; 17 runners and other athletes > 12 h after training or a race; 12 with cerebral injury or seizures, sampled at admission; 8 with closed head injury, sampled at admission; and 38 normal subjects. CK-MB (relative index) and MB isoforms (MB2/MB1) were respectively increased in 15% and 75% of MI patients 1-6 h after onset, 94% and 94% after 7-12 h, and 88% and 8% after 12 h, and in 87% and 82% of cardiac surgery patients. MB isoforms were increased in most patients with acute skeletal muscle trauma and in subjects examined after exercise, but were within normal limits in patients for whom MI was ruled out, patients with cerebral trauma, and normal individuals. The relative index of MB/total CK was normal in essentially all individuals in the last groups, including those with acute skeletal muscle trauma. We concluded that the CK-MB isoform ratio is increased in both acute skeletal muscle injury and MI. The isoform ratio is most useful for distinguishing recent from old (> 12 h) injury.

Adolescent↗
PubMed1992

Therapeutic drug monitoring for the 1990s: meeting the laboratory needs of a changing environment.

The need for monitoring serum and plasma concentrations for therapeutic drugs given to hospitalized and outpatients will continue to growth during the next few years, both in terms of the number of tests ordered each year and the number of different drugs that are monitored. The clinical laboratory will play an important role in implementing and maintaining accurate, cost-effective drug monitoring and treatment programs. To meet changing needs, further development and evaluation of automated analytical assays will be necessary.

Digoxin↗
PubMed1991

Luminal non-specific cationic channels in cultured strial marginal cells of guinea pig and gerbil as determined by patch clamp technique.

Using primary cultures of marginal cells of stria vascularis from guinea pig and gerbil, ionic channels located on the luminal membrane were investigated by means of patch clamp technique. Recordings were performed in cell-attached and inside-out configurations. In cell-attached configuration, single channel activity was identified with a conductance of about 25 pS. I-V curve was linear. The probability of opening was increased upon depolarization. Up to 7 channels could be present in the same patch, indicating a rather high density. In inside-out configuration, the reversal potential was 0 mV, suggesting a non-specific cationic channel. These luminal non-specific cationic channels would allow the passive K+ efflux and Na+ influx across the apical membrane of marginal cells. This finding is consistent with the "one-pump" model of strial activity. The present study suggests that culture of strial marginal cells may be a suitable model for in-depth investigation of endolymph physiology.

Animals↗
PubMed1990

Screening antisera for subtype specificity based on immunoblotting of lectin-affinity electrophoresis: application toward alpha-fetoprotein subfractions.

We adapted a method for evaluating monoclonal antibody specificity toward isoforms and examined 29 alpha-fetoprotein (AFP) antibodies from Hybritech. These antibodies were separated by affinity electrophoresis on agarose-containing erythroagglutinating phytohemagglutinin (PHA-E) followed by immunoblotting onto nitrocellulose. Under these conditions, AFP separates into four subfractions: NR (nonreactive with PHA-E), WR (reactive weakly), RS2 (strongly reactive), and RS1 (very strongly reactive). When polyclonal goat anti-AFP control was used as the test antibody, the distribution of amniotic fluid AFP was approximately 50%, 31%, 12%, and 7% for NR, WR, RS2, and RS1, respectively. The distribution for these same bands from the serum of a patient with hepatocellular carcinoma was 39%, 31%, 30%, and 0%; from the serum of a patient with embryonal carcinoma, it was 29%, 38%, 0%, and 33%, respectively. Twenty-six monoclonal antibodies, including the two used in the Hybritech Tandem-E assay for AFP, showed similar distribution, while the remaining three antibodies showed no reactivity to any of the AFP antigens in this system. Although we were not able to demonstrate any specificity of these antisera toward any single AFP isoform, use of this affinity electrophoresis system provides a model for studying isoform specificity of other AFP antibodies and other antibody-antigen systems.

Amniotic Fluid↗
PubMed1990

Rectal methohexital: concentration and length of the rectal catheters.

In the study, the authors evaluated the concentration of rectal methohexital (1% vs 10%) and the length of the rectal catheter (3.8 vs 12.7 cm), on sleep-success rate, administration-sleep time, methohexital plasma concentrations, and recovery time in 85 healthy children scheduled for elective ophthalmic or ear, nose, or throat operations lasting approximately 1 h. At a dose of 25 mg/kg, the 1% solution of rectal methohexital was associated with a significant (P less than 0.05) higher sleep-success rate (95% vs 70%), shorter administration-sleep time (5.7 +/- 1.9 vs 7.0 +/- 2.0 min), higher methohexital plasma concentrations at 20 min (6.5 vs 4.7 ng/mL) and at 30 min (5.3 vs 3.7 ng/mL), and prolonged recovery time (53.2 +/- 31.1 vs 32.4 +/- 18.5 min). The length of the rectal catheters did not significantly affect sleep-success rate, administration-sleep time, methohexital plasma concentrations, or recovery time. The use of 25 mg/kg of 1% rectal methohexital solution to induce anesthesia in children is superior to the use of 25 mg/kg of 10% methohexital solution for induction of anesthesia in children, particularly in operations 1 h or longer in duration.

Anesthesia Recovery Period↗
PubMed1990

Markers for hepatocellular carcinoma.

Markers for hepatocellular cancer include the best and worst of cancer detection. Although hepatocellular cancer is relatively infrequent compared to other cancers in the western world, HCC has a very high incidence in parts of Asia and Africa. It is estimated to be one of the most common cancer worldwide. High risk factors for HCC include previous hepatitis B infection, heavy alcohol consumption, cirrhosis, and aflatoxin exposure. Alpha fetoprotein may be the best human cancer marker that appears in the serum, but levels of this marker are often not elevated until the tumor is beyond surgical treatment. No other serum or tissue marker is particularly useful. Screening of high-risk populations in China has detected previously undiagnosed HCC in 1,000 of 5 million individuals tested and has led to an increase in survival from 5.5 to 61.6% with surgical resection over those who are later diagnosed with HCC without screening. Elevations of AFP due to yolk sac tumors may be differentiated from those due to HCC on the basis of Concanavalin A reactivity. Immunodetection using radiolabeled anti-AFP and immunoscintigraphy have given inconsistent results that are not as sensitive as ultrasonography in detecting HCC in the liver. Various enzymes, isoenzymes, and other markers may be useful as adjuncts to diagnosis in selected cases, but are not generally as good as AFP alone. If a patient has an AFP-producing tumor, the serum levels of AFP provide an excellent means of monitoring its progression. If the serum AFP levels drop to normal and stay there, cure is almost certain. If, however, the serum AFP level does not fall at the normal catabolic rate after therapy, or subsequently rises, regrowth of metastases are indicated. Immunotherapy using anti-AFP has not been shown to induce remission, but experimental studies indicate that drug-conjugated anti-AFP is effective in inhibiting growth of AFP-producing tumors. Clinical trials using drug-conjugated anti-AFP are now underway. Monoclonal antibodies have not yet identified the "antigens" useful for the diagnosis or treatment of HCC, but epitopes identified by monoclonal antibodies have been studied experimentally in rats which indicate multiple cellular lineages to HCC in cases of experimental chemically induced hepatocarcinoma.

Antigens, Neoplasm↗
PubMed1990

Clinical evaluation of an automated chemical inhibition assay for lactate dehydrogenase isoenzyme 1.

We evaluated an automated assay for lactate dehydrogenase (LD; EC 1.1.1.27) isoenzymes, supplied by Boehringer Mannheim Diagnostics (BMD) and based on selective chemical inhibition of non-LD-1 isoenzymes by guanidine thiocyanate. Results were compared with the Roche Isomune LD-1 method. The Hitachi 717 analyzer was used to measure enzyme activity for both procedures in 229 serum samples. One hundred specimens were also analyzed by the Helena rapid electrophoresis (REP) method. We determined the limit of linearity of the BMD method to be about 1200 U of LD-1 per liter. The analytical correlation of BMD (y) with Isomune (x) yielded y = 1.0x + 0.5 U/L, r = 0.997, Sy/x = 16.9 (range 20-1397 U/L). The regression equation for BMD vs REP was y = 1.1x + 7.2% (r = 0.800, Sy/x = 7.4, range 14-83%). Average values for within-run precision for low (38 U/L), medium (180 U/L), and high (865 U/L) controls were 4.1%, 1.0%, and 0.5%, respectively (16 trials of six each). The average values for run-to-run precision were 4.1%, 1.7%, and 1.1%, respectively, for these controls (n = 16). We used receiver-operating characteristic curves to determine optimum decision limits. Using an LD-1 cutoff of 40% of total LD, we obtained a clinical sensitivity of 97-100% and a specificity of 95% when blood was collected during the optimum interval, 24-48 h after the onset of chest pain. We conclude that the BMD LD-1 assay is equivalent to the immunochemical and electrophoretic assays for measuring the LD-1 isoenzyme.

Autoanalysis↗
PubMed1990

Candidate reference method for determining creatinine in serum: method development and interlaboratory validation.

We describe a "high-performance" liquid chromatographic (HPLC) method for accurately determining creatinine in serum. After prechromatographic precipitation of protein, we performed isocratic ion-exchange chromatography with ultraviolet detection (234 nm). Analytical results showed linearity up to 1770 mumol/L, a detection limit of 22 mumol/L, an average analytical recovery of 101%, and a CV ranging from 3% to 11%. We used certified human serum (National Institute of Standards and Technology), and additional lyophilized serum pools also assayed by definitive isotope-dilution mass spectrometry, to validate the accuracy of the HPLC method. In addition, the isocratic HPLC results showed close agreement with those obtained with a step-gradient HPLC method. We also compared the isocratic HPLC method with alkaline picrate and enzymatic methods. Our findings with samples from nonuremic, uremic, and diabetic ketoacidotic patients confirmed the positive bias previously reported with the alkaline picrate method. Interlaboratory transferability of the method was demonstrated with various commercial instruments and analytical columns. We evaluated column stability and possible interference from endogenous or exogenous compounds. On the basis of our analytical findings, we recommend the isocratic HPLC method as a candidate Reference Method for determining creatinine in serum.

Chemistry, Clinical↗
PubMed1989

Pharmacokinetic monitoring of nephrotoxic antibiotics in surgical intensive care patients.

An assessment of the dosage regimens prescribed for potentially nephrotoxic antibiotics (amikacin, gentamicin, tobramycin, and vancomycin) was undertaken on surgical intensive care unit patients. In 166 patients, 224 series of blood antibiotic level determinations were obtained. Using individualized pharmacokinetic determinations, the regimens were revised as necessary to provide optimal blood levels. Because of variable volumes of distribution and elimination rates, dosing according to standard clinical guidelines produced significantly lower peaks than did pharmacokinetically determined regimens for gentamicin (p less than 0.005), tobramycin (p less than 0.0001), and vancomycin (p less than 0.05). Importantly, fewer patients achieved therapeutic levels with the original regimens than with the revised regimens for gentamicin (9% vs. 91%, p less than 0.0005), tobramycin (27% vs. 92%, p less than 0.0001), and vancomycin (30% vs. 69%, p less than 0.0001). Individualized pharmacokinetic analysis of potentially nephrotoxic antibiotics in critically ill patients is essential if therapeutic, non-toxic levels are to be maintained.

Amikacin↗
PubMed1989

Creatine kinase isoforms in ischemic heart disease.

The MM and MB isoenzymes of creatine kinase exist in serum as a collection of at least three major MM and two major MB isoforms. Each of these are derived from single tissue MM and MB isoforms, which are converted to these other forms by carboxypeptidase N after their release from necrotic skeletal and myocardial tissue. Measurement of the MM isoforms in ischemic heart disease is useful for early diagnosis of acute myocardial infarction and for the noninvasive determination of coronary artery reperfusion for infarction patients receiving thrombolytic therapy. Because MM is also released in acute skeletal-muscle disease, MB isoform measurements may have the highest clinical sensitivity. These determinations are important for providing objective information to cardiologists who need to make critical decisions concerning the management of these patients. I review the procedures for treating patients with myocardial infarction, the potential role of CK isoforms, and the methods currently available for isoform analysis, including high-resolution electrophoresis, isoelectric and chromatofocusing, and liquid chromatography. Rapid and highly sensitive methods are needed for implementation of CK-MM and MB isoforms for prospective emergency determinations for patients with acute myocardial infarction.

Animals↗
PubMed1989

Role of rapid immunoassays for urgent ("stat") determinations of creatine kinase isoenyme MB.

We compared the analytical performance of three immunoassays used to rapidly determine creatine kinase (EC 2.7.3.2; CK) isoenzyme MB in serum: Dade's "Stratus," Corning's "Magic Lite," and Hybritech's "Icon QSR CK-MB." Performance criteria included precision, analytical sensitivity, sample stability, and analytical and clinical correlation of results for serum samples taken from healthy individuals, patients with suspected and confirmed acute myocardial infarction, and patients after coronary artery bypass surgery. We also examined 31 samples taken from patients in the emergency room suspected of myocardial infarction, to evaluate the potential of these assays for early diagnosis. Although these assays differ in the manner in which CK-MB is measured, and therefore have different procedural requirements, we conclude that they are equivalent in overall assay performance. None of these assays, however, is sufficiently sensitive for early diagnosis of myocardial infarction; therefore, results cannot be used by cardiologists in deciding whether acute thrombolytic therapy should be given. Other management decisions, such as the optimal utilization of intensive-care bed space, may justify using these assays on a "stat" basis.

Adult↗
PubMed1988

Personal and family history of lung disease as risk factors for adenocarcinoma of the lung.

To identify risk factors for adenocarcinoma of the lung, a population-based case-control study of 336 female cancers of this cell type and an equal number of neighborhood controls was conducted between 1983 and 1986. After adjusting for personal smoking, personal and family histories of lung disease emerged as additional risk factors. A personal history of any lung disease was associated with a 40% increase in risk [smoking adjusted relative risk (SARR) = 1.4, 95% confidence interval (CI) = 1.0, 2.0] with a more marked increase in risk for lung diseases occurring during childhood (SARR = 1.9, 95% CI = 1.2, 3.2) and for tuberculosis (SARR = 10.0, 95% CI = 1.1, 90.1). Family histories of tuberculosis (SARR = 2.0, 95% CI = 1.1, 3.6) and of lung cancer (SARR = 3.9, 95% CI = 2.0, 7.6) were also risk factors for adenocarcinoma of the lung. Increasing risk was observed with decreasing intake of dietary beta-carotene. After adjusting for personal smoking, women in the lowest quartile of intake showed a two-fold increased risk relative to those in the highest quartile of intake (P = 0.003). There were also some suggestive differences between cases and controls in their reproductive history and hormone use.

Adenocarcinoma↗
PubMed1988

An unusual case of toluene-induced metabolic acidosis.

We used gas chromatography-mass spectrometry to analyze serum specimens from a patient whose metabolic ketoacidosis resulted from sniffing a toluene-containing substance; we also analyzed a sample of the abused substance itself and a serum specimen from a normal subject. The blood samples from the patient showed abnormally high concentrations of acetoacetic, azelaic, benzoic, and 3-hydroxybutyric acids, and a smaller amount of hippuric acid than in the control serum. The ketone bodies and benzoic acid appeared to be factors contributing to her acidosis and ketosis. Analysis for volatile solvents in the patient's serum revealed a low concentration of methyl acetate, in contrast to the high concentrations of toluene and bis(2-ethylhexyl) phthalate and the trace concentration of xylene in the abused substance. We consider this case unusual because the presence and concentration of specific ketoacids was unexpected in light of what was known about the patient.

Acidosis↗
PubMed1987

Platelet dysfunction associated with Wilms tumor and hyaluronic acid.

Acquired von Willebrand disease (AVWD) has been described in two cases of nephroblastoma. We studied a patient with nephroblastoma who presented with a coagulopathy suggestive of AVWD. The subject had undetectable levels of F.VIIIR:Ag, diminished F.VIIIR:WF (16.3%), F.VIII:C activity (37%), and lack of platelet aggregation to ADP, epinephrine, collagen, and arachidonic acid. These results were associated with abnormally high serum levels (850 mg/dl) of hyaluronic acid (HA), which made the patient's serum hyperviscous. Examination of the neoplasm revealed HA in the tumor matrix. All abnormalities of coagulation resolved after chemotherapy and extirpation of the neoplasm, which produced normal serum HA levels. To study the effects of HA on platelet function, we added HA to normal platelet-poor plasma (NPP), which rendered F.VIIIR:Ag undetectable; treatment of HA with hyaluronidase eliminated F.VIIIR:Ag assay interference caused by HA. F.VIII:C activity decreased in vitro when HA was mixed with normal platelet-poor plasma (NPP). HA reduced the initial slope of normal platelet aggregation. Partial correction of platelet aggregation occurred after hyaluronidase treatment of HA-spiked PRP. Experiments in rabbits exposed to HA (serum level 400 mg/dl) demonstrated abnormalities similar to those noted in the patient. Shear rate studies of whole blood containing HA (500 mg/dl) yielded high shear stress, 27-136 dynes/cm2 over shear rates of 10-216 sec-1. We conclude that the coagulopathy demonstrated in this case is secondary to hyperviscosity produced by elevated levels of HA, which interferes with the assay for F.VIIIR:Ag. Thus the acquired coagulopathy associated with other cases of nephroblastoma may present as spurious von Willebrand disease.

Animals↗