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Biomedical subjects

A Chow

Publications and source records attributed to A Chow.

At least 55 records · Page 3Linked to original sources
PubMed1994

A faster-acting and more potent form of tissue plasminogen activator.

Current treatment with tissue plasminogen activator (tPA) requires an intravenous infusion (1.5-3 h) because the clearance of tPA from the circulation is rapid (t 1/2 approximately 6 min). We have developed a tPA variant, T103N,N117Q, KHRR(296-299)AAAA (TNK-tPA) that has substantially slower in vivo clearance (1.9 vs. 16.1 ml per min per kg for tPA in rabbits) and near-normal fibrin binding and plasma clot lysis activity (87% and 82% compared with wild-type tPA). TNK-tPA exhibits 80-fold higher resistance to plasminogen activator inhibitor 1 than tPA and 14-fold enhanced relative fibrin specificity. In vitro, TNK-tPA is 10-fold more effective at conserving fibrinogen in plasma compared to tPA. Arterial venous shunt models of fibrinolysis in rabbits indicate that TNK-tPA (by bolus) induces 50% lysis in one-third the time required by tPA (by infusion). TNK-tPA is 8- and 13-fold more potent in rabbits than tPA toward whole blood clots and platelet-enriched clots, respectively. TNK-tPA conserves fibrinogen and, because of its slower clearance and normal clot lysis activity, is effective as a thrombolytic agent when given as a bolus at a relatively low dose.

Animals↗
PubMed1993

B cells are anergic in transgenic mice that express IgM anti-DNA antibodies.

B lymphocytes in individuals with systemic lupus erythematosus (SLE) secrete pathogenic autoantibodies to DNA which cause clinical nephritis. (NZB X NZW) F1 (BW) female mice also secrete pathogenic anti-DNA autoantibodies, and therefore are considered to be an animal model of SLE. The rearranged immunoglobulin (Ig) genes that encode an anti-DNA antibody from a diseased BW mouse have been cloned, and transgenic (Tg) mice have been created by microinjection of these constructs into fertilized eggs from normal mice. As we reported previously, when the construct contains the C gamma 2a heavy chain constant (CH) region, the mice spontaneously secrete anti-DNA IgG and they develop mild nephritis. This demonstrated that the Ig encoded by the transgene is pathogenic. In contrast, here we report that when the construct contains the same anti-DNA Ig variable (V) regions used previously, along with the C mu region, the autoreactive B cells are rendered tolerant. Most B cells in the Tg mice express the mu transgene product on their surface, and rearrangement of endogenous light chain genes is partially suppressed. Furthermore, most hybridomas made from Tg B cells secrete IgM anti-DNA. Despite this, the Tg mice have reduced levels of total serum Ig and they do not secrete anti-DNA IgM either spontaneously or following immunization with DNA. We conclude that most B cells in the Tg mice have been rendered anergic. Anergy is however reversible in vitro; lipopolysaccharide stimulation of Tg B cells leads to the production of a significant amount of IgM anti-DNA antibody. The studies demonstrate that in this line of Tg mice on a normal mouse genetic background potentially pathogenic B cells that express a high-affinity Ig specific for a natural autoantigen are subject to tolerance by induction of anergy.

Animals↗
PubMed1992

cDNA cloning and localization of a band 3-related protein from ileum.

A Cl(-)-HCO3- exchanger in the brush-border membrane mediates active Cl- absorption and regulates intracellular pH in rabbit ileum. The molecular identity of the ileal Cl(-)-HCO3- exchanger has not been established. The best-characterized plasma membrane Cl(-)-HCO3- exchanger is erythroid band 3. Structurally related proteins in nonerythroid tissues comprise an anion exchanger (AE) family. We used the polymerase chain reaction to amplify and clone a cDNA encoding an ileal band 3-related protein (B3RP) from rabbit ileal enterocytes. The composite sequence is 3,909 bp and is predicted to encode a protein of 136 kDa. The deduced amino acid sequence is 95% identical to murine renal AE2, indicating that ileal B3RP is rabbit AE2. Antisera generated against a cytoplasmic fragment of ileal B3RP recognized a 160- to 170-kDa polypeptide in the brush-border membrane, but not the basolateral membrane, of ileal crypt and villus enterocytes. This correlates with previous studies indicating that a Cl(-)-HCO3- exchange is present in brush-border but not basolateral membrane vesicles from rabbit ileal enterocytes. We conclude that ileal B3RP is a product of the AE gene family, and is present in the brush-border of ileal enterocytes, where it may mediate Cl(-)-HCO3- exchange.

Amino Acid Sequence↗
PubMed1991

Metabolism of bradykinin agonists and antagonists by plasma aminopeptidase P.

In addition to angiotensin I converting enzyme (ACE; EC 3.4.15.1) and carboxypeptidase N (CPN; EC 3.4.17.3), other peptidases contribute to bradykinin (BK) degradation in plasma. Rat plasma degraded BK by hydrolysis of the N-terminal Arg1-Pro2 bond, and the characteristics of hydrolysis are consistent with identification of aminopeptidase P (APP; EC 3.4.11.9) as the responsible enzyme. BK and BK[1-5] N-terminal hydrolysis was optimal at neutral pH, was inhibited by 2-mercaptoethanol, dithiothreitol, o-phenanthroline and EDTA, but was unaffected by the aminopeptidase inhibitors amastatin, puromycin and diprotin A, the endopeptidase-24.11 inhibitors phosphoramidon and ZINCOV, and the ACE and CPN inhibitors captopril and D,L-mercapto-methyl-3-guanidinoethylthiopropanoic acid (MERGETPA), respectively. Although kallidin (Lys-BK) was not metabolized directly by APP, conversion to BK by plasma aminopeptidase M (EC 3.4.11.2) resulted in subsequent degradation by APP. BK analogs containing N-terminal Arg1-Pro2 bonds, including [Tyr8-(OMe)] BK and [Phe8 psi(CH2NH)Arg9]BK (B2 agonists), des-Arg9-BK and [D-Phe8]des-Arg9-BK (B1 agonists), and [Leu8]des-Arg9-BK (B1 antagonist), were degraded by APP with Km and Vmax values comparable to those found for BK (Km = 19.7 +/- 2.6 microM; Vmax = 12.1 +/- 1.2 nmol/min/mL). In contrast, B2 antagonists containing D-Arg0 N-termini, including D-Arg[Hyp3,Thi5.8,D-Phe7]BK and D-Arg[Hyp3,D-Phe7,Phe8 psi(CH2NH)Arg9]BK, were resistant to APP-mediated hydrolysis. These data support a role for plasma aminopeptidase P in the degradation of circulating kinins, and a variety of B2 and B1 kinin agonists and antagonists. However, APP does not participate in the degradation of D-Arg0-containing antagonists.

3-Mercaptopropionic Acid↗
PubMed1990

Effects of retrograde flow on measured blood volume, Disse space, intracellular water space and drug extraction in the perfused rat liver: characterization by the multiple indicator dilution technique.

Previous rat liver perfusion studies had shown a preferential derecruitment of downstream (phenacetin O-de-ethylation) in relation to upstream (acetaminophen sulfation) hepatocyte activities with reductions in prograde (normal) flow, with substrates entering from the portal vein and exiting the hepatic vein. The reduction in metabolic activities was found associated with a reduction in accessible intracellular water space (Pang et al., J. Pharmacokinet. Biopharm. 16: 595, 1988). In the present studies, we investigated the changes in metabolic activities of the liver and its accessible spaces during retrograde flow (substrates entering from the hepatic vein and exiting the portal vein), an approach used to probe zonal heterogeneity in the liver. The multiple indicator dilution technique was used to gain information concerning the accessible sinusoidal blood volume, Disse space, and the intracellular water space; once-through perfusion with tracer [3H]acetaminophen and [14C]phenacetin was performed simultaneously within the same liver, to estimate metabolic activities at the periportal and perihepatic venous regions of the liver, respectively, at the designated flows. The estimated sinusoidal blood volume, total albumin and sucrose distribution spaces, the Disse space and the accessible albumin and sucrose Disse spaces showed weak but positive correlations with retrograde perfusate flow rate. The values were substantially greater than those for rat livers perfused with normal (prograde) flows, suggesting an increase in the vascular space and accessible Disse space of the liver during retrograde flow. The total water and accessible intracellular water spaces also showed weak but positive correlations with retrograde perfusate flow, and the average intracellular water space (which is also accessed by the substrates) at both retrograde flows of 8 and 12 ml/min was 0.52 +/- 0.08 and 0.55 +/- 0.08 ml/g liver, respectively, values that were not statistically different. When the intracellular water space was plotted vs. water flow rate (ml water/g liver), a weakly positive correlation was again found, suggesting that over the flow range, the accessible intracellular water space decreased in a very gradual and linear fashion with a reduction in water flow rate. When the estimated intracellular water space for retrograde flow was compared with values obtained for the same flow rate in a prograde fashion, slightly lower values were obtained. After consideration of the effect of the distended vascular and interstitial spaces on the weights of the liver, the values obtained for retrograde and prograde flow rates were closely similar. In both cases, it appeared that with reduction in flow, the accessible intracellular water spaces were reduced, regardless of the flow direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetaminophen↗
PubMed1989

Hepatocellular carcinoma in Wilson's disease. Case report and review of the literature.

A 33-year-old man with Wilson's disease developed hemoptysis and radiographic evidence of nodular pulmonary infiltrates. A premortem diagnosis of hepatocellular carcinoma was made on the basis of alpha-naphthylannidase stains of pulmonary tissue obtained by open lung biopsy. We review all previous cases of Wilson's disease with this unusual complication and discuss the role of copper in hepatic oncogenesis as well as the alpha-naphthylannidase stain for the diagnosis of hepatocellular carcinoma.

Adult↗
PubMed1986

Tracheal carbohydrate antigens identified by monoclonal antibodies.

In a previous study we described a family of monoclonal antibodies directed against tracheal antigens having a variety of cellular and subcellular distributions. In the present study, we have extended our findings on four representative antibodies to determine the periodate sensitivity, glycosidase sensitivity, and apparent molecular weight of the corresponding antigens. Since mild periodate oxidation selectively cleaves carbohydrate moiety leaving amino acids intact, loss of antigenicity following this treatment suggests the involvement of sugar residues in the antigenic determinant. This can be confirmed by testing the sensitivity of the antigens to specific glycosidases. By enzyme-linked immunosorbent assay (ELISA), all four antibodies were found to have highest affinity for void volume components isolated by Bio-Gel A15m chromatography of the total tracheal secretion. Further analysis of this void volume material by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions followed by immunoblot analysis revealed that all antigens were carried by high-molecular-weight species (greater than 200,000) which were periodate-Schiff positive but reacted poorly with Coomassie blue. In parallel experiments using immunofluorescence and ELISA, antibody binding was compared under control conditions and following periodate treatment of antigens under varying intensities (10 mM IO4-, 10 min, 4 degrees C; 50 mM IO4-, 1 h, 4 degrees C; 100 mM IO4-, 12 h, 20 degrees C). Similar results were obtained with the two methods, indicating a partial loss of antigenicity for one of the four antigens following the mildest periodate treatment, and total loss of antigenicity for all four antigens following each of the two prolonged treatments. All four antigens showed marked sensitivity to digestion with mixed exoglycosidases and three antigens were also susceptible to endo-beta-galactosidase digestion. Antigenicity was not decreased during incubation with chondroitinase ABC, heparitinase, or heparinase. Immunofluorescence analysis of tracheal tissue sections showed that the four antibodies recognized determinants in different locations, including gland and goblet cell cytoplasmic granules and the apical epithelial membrane. The characteristic immunofluorescence patterns of all antibodies were abolished by periodate incubation of the tracheal sections. Thus, the four antibodies appear to recognize carbohydrate antigens carried by high-molecular-weight glycoproteins, each with different cellular origins.

Animals↗
PubMed1985

A multicenter comparative trial of tobramycin and ticarcillin vs moxalactam and ticarcillin in febrile neutropenic patients.

During a multicenter prospective randomized trial in febrile neutropenic patients (neutrophil count, less than 1,000/cu mm), 103 episodes were treated with tobramycin sulfate plus ticarcillin disodium (TT) while 117 were treated with moxalactam plus ticarcillin disodium (MT). The majority of patients had an underlying diagnosis of leukemia (60%) and most (62.8%) had granulocyte counts of less than 100/cu mm at the start of therapy. The response rates for clinically or microbiologically documented episodes were 38 of 60 (55.1%) for TT and 38 of 64 (59.4%) for MT. The MT regimen appeared to be more effective for gram-positive infections (56% vs 33%) while TT appeared more effective for gram-negative infections (64% vs 40%). Nephrotoxicity attributable to study drugs occurred in only 2.3% of cases (one on each treatment arm). Prolongation of the prothrombin time was observed in only six of 78 (7.7%) in the TT arm as compared with 39 of 103 (38%) in the MT arm. Neither regimen was adequate for the unusually high frequency of gram-positive pathogens seen during this study.

Adolescent↗
PubMed1983

Characteristics of the post-somatostatin rebound in growth hormone secretion from perifused somatotrophs.

Dispersed rat somatotrophs were perifused with repeated step SRIF signals of 10 or 60 min (100 ng/ml) separated by 45-min control periods. Effluent was assayed for rat GH (RIA). Maximum suppression of GH secretion (on signal) or complete recovery (off signal) occurred within 1 min. Repeated signals evoked identical normalized responses. GH release fell to 67 +/- (SE) 2% of control with 10-min SRIF signals and 59 +/- 4% of control with 60-min SRIF signals. After SRIF removal, major overshoots of GH secretion were observed, lasting 21 +/- 2 min (after 10-min or 60-min SRIF steps). Peak secretion rates and total secretion due to the overshoot were greater after longer SRIF signals, despite the constant duration of the overshoot. However, the extra secretion during overshoots after 60-min SRIF exposure contained only 23 +/- 3% of the secretion suppressed by SRIF, whereas the extra secretion after 10-min SRIF exposure contained 79 +/- 12% of the amount suppressed by the SRIF exposure, suggesting an intracellular feedback which slows accumulation of readily releasable GH after a period of SRIF exposure. During overshoot, peak secretion rates of twice the control rate (and 3.5 times the SRIF-inhibited rate) were observed. Similarities between these overshoots and in vivo bursts of GH secretion are noted.

Animals↗
PubMed1978

Hypertriglyceridemia associated with deficiency of apolipoprotein C-II.

A 59-year-old man with severe hypertriglyceridemia and no post-heparin lipolytic activity was studied because of a marked fall in plasma triglyceride concentrations after a blood transfusion. An apolipoprotein activator (apolipoprotein C-II) for lipoprotein lipase could not be detected by polyacrylamide-gel electrophoresis of apoproteins, immunodiffusion of the plasma against anti-apolipoprotein CII or activation assays for lipoprotein lipase. Furthermore, the patient's triglyceride-rich lipoproteins would not serve as substrate for lipoprotein lipase. The patient had latent post-heparin lipolytic activity, which appeared after the addition of apolipoprotein CII to the post-heparin plasma. After a transfusion of 1 unit of plasma from a normal subject the patient's plasma triglycerides fell, within one day, from 1000 to 250 mg per deciliter and remained below preinfusion concentrations for six days. We conclude that this patient's hyperlipoproteinemia resulted from a deficiency of apolipoprotein C-II.

Animals↗
PubMed1978

Multi-laboratory comparison of three heparin-Mn2+ precipitation procedures for estimating cholesterol in high-density lipoprotein.

Plasma high-density lipoprotein is commonly estimated by measuring the cholesterol remaining in plasma supernatant solutions after other lipoproteins, which contain apolipoprotein B, are precipitated with heparin and Mn2+. The method (method I) now in use by the Lipid Research Clinics, in which Mn2+ is at 46 mmol/liter final concentration, is reasonably accurate, but precipitation and sedimentation of lipoproteins other than high-density lipoproteins is often incomplete. We evaluated two modifications of method I. In method II, the Mn2+ concentration was doubled; the second modification (method III) included the increased Mn2+ concentration in a combined heparin Mn2+ reagent, decreased sample volume (2 ml), and a shorter incubation time (10 min at room temperature). The percentages of samples with turbid supernates (i.e., incomplete sedimentation) by methods I, II, and III were 9, 3, and 2%, respectively. Among non-turbid supernates, the percentages of samples containing measurable apolipoprotein B (incomplete precipitation) were 79, 19, and 16%, respectively. We conclude that method III is the most convenient and accurate of the three procedures.

Chemical Precipitation↗
PubMed1972

Susceptibility of herpesviruses to cytosine arabinoside: standardization of susceptibility test procedure and relative resistance of herpes simplex type 2 strains.

Susceptibility testing of herpes simplex type 1 (HSV-1) and type 2 (HSV-2) viruses to cytosine arabinoside (Ara-C) has been standardized under conditions of optimal reproducibility, susceptibility, and simplicity. Standard conditions were defined as virus inoculum of 10(1.5) to 10(2.5) TCID(50), WI-38 strain of lung fibroblasts, 2-day incubation, and observation of virus cytopathic effect after staining by the May-Greenwald-Giemsa method. The variability of minimum inhibitory concentration (MIC) of cytopathic effect was fourfold within each test and sixfold in successive assays. MIC values of all seven tested HSV-1 strains were in the range of 0.25 to 0.75 mug per ml, whereas four of nine HSV-2 strains had MIC values of 0.9 mug per ml and greater. A similar method can be used for assay of virus inhibitory titers of body fluids.

Cells, Cultured↗