PubMed Health⌕ Search

Biomedical subjects

J T Lin

Publications and source records attributed to J T Lin.

At least 181 records · Page 10Linked to original sources
PubMed1992

Isozymes of cyclic-3',5'-nucleotide phosphodiesterases in renal epithelial LLC-PK1 cells.

Metabolism of cAMP and cGMP by the major types (families) of cyclic-3',5'-nucleotide phosphodiesterases (PDE) was studied in confluent renal epithelial LLC-PK1 cells grown in vitro. LLC-PK1 cells mainly contain the cAMP-specific rolipram-sensitive PDE type-IV (PDE-IV), the Ca(2+)-calmodulin dependent PDE type-I and cGMP-specific PDE type-V; all these PDEs are mainly localized in cytosol. Analysis of PDE activities in soluble extract of LLC-PK1 cell homogenate by FPLC ionex chromatography on Mono-Q column also disclosed the presence of low activities of cGMP-stimulated PDE-II and PDE-III. Moreover, activity of PDE-IV was resolved into four distinct chromatographic peaks. The increase of cAMP level in response to incubation of intact LLC-PK1 cells with vasopressin (AVP) was markedly enhanced in the presence of rolipram, but not in the presence of other PDE isozyme-specific inhibitors. Incubation with AVP and atriopeptin (ANP) together resulted in increase in cGMP and a small decrease of cAMP accumulation in LLC-PK1 cells. Results of these studies first show that the LLC-PK1 cells contain all five major types of PDE isozymes where PDE-IV, PDE-I and PDE-V are quantitatively predominant. The rolipram-sensitive PDE-IV, present in several chromatographically distinct forms, appears to be the key PDE isozyme involved in control of cAMP generated in response to stimulation by AVP in LLC-PK1 cells.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1992

Detection of replicative form of hepatitis C virus RNA in peripheral blood mononuclear cells.

Paired samples of plasma and peripheral blood mononuclear cells (PBMC) from 7 patients with posttransfusion hepatitis C were collected and studied for the presence of replicative forms of hepatitis C virus (HCV). RNA was extracted and tested for both positive and negative strands of HCV RNA by polymerase chain reaction. Positive-strand RNA of HCV was found in both plasma and PBMC of all 7 patients. However, negative-strand RNA was found in PBMC of 3 patients while none was found in the plasma. Levels of negative-strand RNA were about 10-100 times less than those of positive-strand RNA by semiquantification with serial dilution of viral cDNA. The results suggest that active infection and replication of HCV in PBMC is present in patients with posttransfusion hepatitis C and implicate the extrahepatic infection of HCV.

Adult↗
PubMed1992

Improved serodiagnosis of posttransfusion hepatitis C virus infection by a second-generation immunoassay based on multiple recombinant antigens.

Serial serum samples from 35 patients with posttransfusion non-A, non-B hepatitis in a prospective study were tested for antibody to hepatitis C virus (HCV) by a multiple recombinant antigen based immunoassay [anti-HCV (2nd); Abbott]. Of them, 23 were positive for anti-C100, and 27 were positive for HCV RNA by polymerase chain reaction. By anti-HCV (2nd), 28 patients were positive, and all except 1 of the 28 patients were positive for HCV RNA. A total of 24 patients, who became HCV RNA positive at the acute stage and who were negative for both anti-C100 and anti-HCV (2nd) before transfusion, were considered to have posttransfusion hepatitis C. The mean time to seroconversion for anti-HCV (2nd) was 7.5 or 12.1 weeks after the onset of hepatitis or the date of transfusion, respectively, and was generally 6 weeks earlier than that detected by anti-C100. However, seroconversion was delayed in 2 hepatitis B surface antigen carriers as compared with anti-C100. The anti-C100 assay detected 20 (83%) and the anti-HCV (2nd) all 24 patients with documented posttransfusion hepatitis C. The second-generation test is, therefore, better than conventional anti-C100 for the early diagnosis of HCV infection.

Adult↗
PubMed1992

Effects of anticoagulants and storage of blood samples on efficacy of the polymerase chain reaction assay for hepatitis C virus.

Blood samples from 11 patients with posttransfusion hepatitis C virus infection were collected. Each sample was divided into three fractions to obtain sera, sodium-citrated plasma, and heparinized plasma and then tested for HCV RNA by a nested polymerase chain reaction (PCR). Of them, eight sodium-citrated plasma samples, seven serum samples, and no heparinized plasma samples were PCR positive. Eight PCR-positive sodium-citrated plasma samples were exposed to different physical conditions and semiquantified for HCV RNA after serial dilutions. Samples stored at -70 degrees C showed the best preservation of HCV RNA, and storage at the other conditions resulted in only minimal loss of the PCR signal. Therefore, serum or sodium-citrated plasma specimens are satisfactory for detecting HCV RNA by PCR, but heparinized blood specimens are not.

Anticoagulants↗
PubMed1992

Endoscopic approaches in the diagnosis of obstructive jaundice--with special reference to endoscopic retrograde cholangiopancreatography.

Duodenofiberscopy with endoscopic retrograde cholangiopancreatography (ERCP) was performed in 102 patients with obstructive jaundice. Peritoneoscopy and peritoneoscopic cholecystocholangiography were done in patients whose ERCP was inconclusive. The causes of obstructive jaundice were carcinoma of the pancreas in 14 cases, carcinoma of the papilla of Vater in 12 cases, choledocholithiasis in 37 cases, carcinoma of the common bile duct in seven cases, hepatocellular carcinoma (HCC) in seven cases, intrahepatic cholestasis in three cases and miscellaneous causes in eight cases. No final diagnosis was made in 14 patients. The duodenofiberscopic examination with biopsy revealed the cause of obstructive jaundice directly in eight cases, when carcinoma of the pancreas or papilla of Vater extended to the duodenal mucosal surface. In 34 of the 37 patients with choledocholithiasis, ERCP alone was successful in making the diagnosis. Percutaneous transhepatic cholangiography and ERCP were used together to reach a diagnosis in the remaining three patients. We propose a classification for HCC on ERCP which may be useful for the study of icteric type HCC.

Ampulla of Vater↗
PubMed1992

Systematic development of bombesin/gastrin-releasing peptide antagonists.

Several families of very potent bombesin (Bn) receptor antagonist analogues have recently been developed and their biological potencies evaluated in a number of in vitro systems including guinea pig and rat pancreatic acini and Swiss 3T3 cells. These studies showed that analogues can exhibit diverse properties ranging from full antagonists, partial agonists, or full agonists depending on the assay system and animal species employed. We have developed two classes of more potent, shorter chain antagonists based on [psi CH2NH(13-14)]Bn(6-14) and desMet14Bn(6-13)NH2 structures. [D-Phe6 psi Leu13-Leu14] Bn(6-14)NH2 was a potent antagonist (Ki 6nM) in Swiss 3T3 cells and guinea pig acini but exhibited 10% partial agonist activity and lower binding affinity (Ki 60 nM) in rat acini. The partial agonism could be eliminated by using p-Cl-Phe or D-Phe at the C-terminus and partially eliminated using D-4-Cl-Phe in position 6. With the antagonist [D-Phe6]Bn(6-13)NH2 (Ki 96 nM), alkyl substituents on the amide group increased affinity 25-fold with the propylamide being the most potent peptide (Ki 4 nM) in 3T3 cells or guinea pig acini. It did, however, have high 40% partial agonist activity in rat acini. Alkyl esters or hydrazide derivatives were, in contrast, pure antagonists in all systems tested with [D-Phe6]Bn(6-13)OMe having the highest affinity in all systems and also excellent in vivo properties. All of the potent antagonists examined had little affinity for neuromedin B--preferring bombesin receptors, which had entirely new ligand structure-activity relationships.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1991

Prediction of antifolate efficacy in a rat sarcoma model.

A methylcholanthrene-induced rat sarcoma propagated both in vitro and in vivo was used to examine the usefulness of a rapid biochemical in situ assay that measures thymidylate synthase (TS) activity in whole cells to predict sensitivity and resistance to the folate antagonists methotrexate (MTX), 10-ethyl-10-deazaaminopterin (10-EDAM) and trimetrexate (TMTX). There was an excellent correlation between the effects of these drugs on inhibiting TS and cytotoxicity as measured by a clonogenic assay, when the exposure time was 4 hr and those when the rat sarcoma cell line was employed (p less than 0.001). When tumor-cell suspensions were prepared from the rat sarcoma propagated in vivo, they were less sensitive to these antifolates, but the relative effectiveness of the 3 antifolates was similar: TMTX much greater than 10-EDAM greater than MTX. As expected, continuous exposure (10 to 12 days) produced cytotoxicity at a much lower dose of these drugs. When the 3 drugs were tested for anti-tumor effectiveness in rats bearing this tumor, the tumor regression measured was best with TMTX; 10-EDAM was intermediate in effectiveness as compared with MTX. These results indicate that the in situ TS assay and clonogenic assay may be used to predict anti-tumor efficacy of antifolates in vivo in this rat sarcoma.

Aminopterin↗
PubMed1991

Covalently cyclized agonist and antagonist analogues of bombesin and related peptides.

During a search for possible cyclization points in shortened, potent bombesin agonists and antagonists, it was found that the joining of amino acid residues in positions 6 and 14 by various means resulted in retention of significant binding affinity for rat pancreatic acini and murine Swiss 3T3 cells. In one series of analogues, Cys residues in these positions were used for bridging via a disulfide bond. (D)-C-Q-W-A-V-G-H-L-C-NH2 retained significant binding affinity for rat pancreatic acini cells and was a full amylase releasing agonist (EC50 187 nM). Potency was markedly increased by substituting D-Ala for Gly (EC50 67 nM compared to 10 nM for its linear counterpart) and was decreased by substituting L-Cys for D-Cys in this analogue (EC50 214 nM), thus strongly suggesting stabilization of peptide folding by the D residues. Elimination of the COOH-terminal amino acid produces competitive antagonists in the linear analogues; however, (D)-C-Q-W-A-V-G-H-C-NH2 was devoid of activity. Likewise, cyclization to position 13 with the 14 amino acids intact to give (D)-C-Q-W-A-V-G-H-C-L-NH2 resulted in an almost inactive peptide. On the other hand, as in the linear series, the reduced peptide bond analogue, (D)-C-Q-W-A-V-(D)-A-H-L-psi (CH2NH)-C-NH2, was a receptor antagonist (IC50 5.7 mM), albeit much weaker than the corresponding linear analogues, but with no residual agonist activity. Direct head-to-tail cyclization was also tried. Both cyclo[(D)-F-Q-W-A-V-G-H-L-L] (EC50 346 nM) and the shorter cyclo [Q-W-A-V-G-H-L-L] (EC50 1236 nM) were full agonists. Elimination of the COOH-terminal residue in cyclo[(D)-p-Cl-F-Q-W-A-V-(D)-A-H-L] produced an agonist (EC50 716 nM) rather than an antagonist. These results provide support for the proposal that both bombesin agonists and antagonists adopt a folded conformation at their receptor(s). Furthermore, the retention of appreciable potencies using several cyclization strategies and chain lengths suggests that further optimization of these structures both in terms of potency and ring size is possible. Since these peptides have increased conformational restriction, they should begin to serve as useful substrates for NMR and molecular modeling studies aimed at comparing the obviously subtle differences between agonist and antagonist structures.

Amino Acid Sequence↗
PubMed1991

Quantitation of the Na(+)-Pi cotransporter in renal cortical brush border membranes. [14C]phosphonoformic acid as a useful probe to determine the density and its change in response to parathyroid hormone.

To determine the density of Na(+)-Pi symporters in brush border membranes (BBM) from rat renal cortex, [14C] phosphonoformic acid [( 14C] PFA), a competitive inhibitor of Na(+)-Pi cotransport, was employed as a probe. The [14C]PFA binding was measured in BBM vesicles (BBMV) under equilibrated conditions (extra-vesicular Na+, K+, and H+ = intravesicular Na+, K+, and H+) to avoid modulatory effects of these solutes. BBMV were preincubated in media without or with addition of molar excess of Pi (greater than 20 times) to determine the Pi-protectable PFA-binding sites, and then [14C] PFA binding was determined. Only the [14C]PFA binding in the presence of Na+ displaceable by an excess of Pi was saturated and was independent of intravesicular volume of BBMV. This value denoted as "Pi-protectable Na(+)-[14C]PFA binding," was analyzed by Scatchard plot showing BmaxPFA = 375 +/- 129 pmol of PFA/mg protein, KDPFA = 158 +/- 18 microM; the Hill coefficient was congruent to 1. For Na(+)-dependent binding of [3H]phlorizin, in the same BBMV, Bmax = 310 +/- 37 pmol/mg protein and KD V 2.2 +/- 0.5 microM. BBMV prepared from cortex of thyroparathyroidectomized rats infused with phosphaturic doses of parathyroid hormone (PTH) were compared with vehicle-infused controls. Administration of PTH resulted in decrease of BmaxPFA (-38%) and of Na(+)-gradient-dependent uptake of 32Pi (-35%), but KDPFA was not changed. Neither BmaxPhl and KDPhl for Na(+)-phlorizin binding, nor the Na(+)-gradient-dependent uptake of [3H]D-glucose differed between PTH-treated and control rats. We conclude: (a) measurement of Pi-protectable Na(+)-[14C]PFA binding determines numbers and affinity of Na(+)-Pi symporters in renal BBMV; (b) the affinity of PFA for Na(+)-Pi symporter is similar to apparent affinity for Pi (KmPi), as determined from measurements of Na(+)-gradient-dependent 32Pi uptake by BBMV; (c) both Na(+)-Pi symporter and [Na+]D-glucose symporters are present within renal BBM in a similar range of density; (d) PTH decreases the number of Na(+)-Pi cotransporters in BBMV commensurate with the parallel decrease of Na(+)-gradient-dependent Pi transport, whereas the affinity of Na(+)-Pi symporters for Pi is not changed. These observations support the hypothesis that PTH decreases capacity for Na(+)-dependent Pi reabsorption by internalization of Na(+)-Pi symporters in BBM of renal proximal tubules.

Animals↗
PubMed1991

Role of folylpolyglutamates in biochemical modulation of fluoropyrimidines by leucovorin.

The growth-inhibitory effect of fluoropyrimidines combined with a short-term exposure to leucovorin and the pattern of polyglutamylation of folates were compared between parental CCRF-CEM cells and a cell line with impaired ability to form polyglutamates (CCRF-CEM/P). The combination of leucovorin with 5-fluorouracil or 5-fluorodeoxyuridine increased the growth inhibition of CCRF-CEM cells compared to the fluoropyrimidine alone in the parent cell line but not in CCRF-CEM/P cells. In addition, leucovorin produced a significant increase in the inhibition of intracellular thymidylate synthase activity caused by 5-fluorouracil or 5-fluorodeoxyuridine as compared to these drugs alone in CCRF-CEM cells, but no increase in inhibition over that produced by the single drugs alone was observed in CCRF-CEM/P cells. Although levels of 5,10-methylene tetrahydrofolate after leucovorin administration were similar in both cell lines, polyglutamylation of this coenzyme was decreased in the CCRF-CEM/P cell line. The inability of CCRF-CEM/P cells to form significant levels of polyglutamates of N5,N10-methylenete-trahydrofolate, may be responsible for the lack of enhanced cell kill observed when a short exposure to leucovorin is used with fluoropyrimidines.

Cell Division↗
PubMed1991

Recombinant immunoblot assay for hepatitis C antibody in patients with posttransfusion non-A, non-B hepatitis.

In a prospective study of 287 patients who received blood transfusion, 26 who were found positive for hepatitis C antibody (anti-HCV) by an enzyme-linked immunosorbent assay (ELISA) were studied by a recombinant immunoblot assay (RIBA). Nineteen of the 26 patients had posttransfusion non-A, non-B (NANB) hepatitis. Sixteen (84.2%) of the 19 patients with hepatitis had positive results by RIBA, 2 had indeterminate results, and 1 was negative. By contrast, five of the 7 recipients without hepatitis were negative, 1 indeterminate, and 1 positive by RIBA. Those with negative RIBA results had significantly lower optical density (OD) readings by ELISA than those with positive RIBA tests. Therefore, patients without hepatitis or lower OD value have a higher false-positive rate in anti-HCV ELISA than did those with a high OD value or with evidence of hepatitis.

Adult↗
PubMed1991

Solid state ultraviolet laser (213 nm) ablation of the cornea and synthetic collagen lenticules.

We used a Q-switched Nd:YAG laser with non-linear optical crystals to produce the 5th (213 nm) and the 4th (266 nm) harmonic frequencies. Using these two wavelengths, we ablated fresh porcine corneas and type I collagen synthetic epikeratoplasty lenticules. For the 213-nm ablation, radiant exposure was 1.3 J/cm2. The ablation rate was 0.23 micron per pulse for the epikeratoplasty lenticules. We examined all tissues with light microscopy, transmission electron microscopy, and scanning electron microscopy. Histology for the 213-nm ablation showed a clean ablation crater with minimal collagen lamellae disruption and a damage zone less than 1 micron. In comparison, the 266 nm radiation showed more charring at the edges with a damage zone approximately 25 microns deep with disruption of the stromal lamella. Our results show that this solid state UV laser is a potential alternative to the excimer laser for cornea surgery.

Aluminum Silicates↗
PubMed1991

Basis for natural resistance to methotrexate in human acute non-lymphocytic leukemia.

The basis of intrinsic resistance of blasts from patients with acute non-lymphocytic leukemia (ANLL) to methotrexate was studied. MTX polyglutamate formation was measured in blast cells from 19 patients with ANLL and in 7 pediatric patients with acute lymphocytic leukemia (ALL), after in vitro incubation for 24 h with 3H-methotrexate. There was no significant differences seen in the total amount of MTX plus polyglutamates measured between ANLL and ALL blasts, indicating that transport defects do not account for intrinsic MTX resistance in ANLL. However, there were significant differences between the amounts of long chain MTX polyglutamates found in ANLL cells as compared to ALL cells. Most, but not all, ANLL blasts were unable to form long chain polyglutamates. In as much as the level of MTX polyglutamates found in blast cells after MTX administration allows for retention of this drug, this property may explain, at least in part, the refractoriness of most patients with ANLL to methotrexate.

Adolescent↗
PubMed1991

A prospective study of posttransfusion hepatitis in Taiwan.

In a follow-up study of 6 months or more of two hundred and ninety-six patients who had received blood transfusion, 37 (12.5%) developed acute posttransfusion hepatitis. Patients with posttransfusion hepatitis had significantly higher donor numbers and transfusion amounts than patients without hepatitis. Frequency was not related to the age, sex or hepatitis B carriage of recipients. There were no cases of fulminant hepatitis. Of 37 patients with hepatitis, 36 were diagnosed as non-A, non-B hepatitis and one as hepatitis B. Twenty-two (59.5%) of the 36 patients with non-A, non-B hepatitis seroconverted to hepatitis C antibody. Two of these were positive for hepatitis C antibody before transfusion and 12 were negative for hepatitis C antibody. Thirty-three of the 36 patients were followed-up for more than 6 months after the onset of hepatitis. While 13 of the 33 patients recovered, the remaining 20 (60.6%) patients still had persistent liver test abnormalities 6 months after the onset of hepatitis. Seventeen (85%) of the 20 patients who developed chronic hepatitis were hepatitis C antibody positive. In contrast, only four (30%) of the 13 patients who recovered after acute hepatitis were positive for the hepatitis C antibody. Chronicity rate was not related to the patient's sex, age, transfusion amount or donor number. Our results suggest a high frequency of posttransfusion hepatitis C in Taiwan and that the infection has a high risk of chronicity.

Adolescent↗
PubMed1991

Detection of hepatitis B virus DNA by polymerase chain reaction in plasma of volunteer blood donors negative for hepatitis B surface antigen.

Plasma samples from 206 volunteer blood donors were tested for hepatitis B virus (HBV) DNA by dot blot hybridization and polymerase chain reaction (PCR). All donors were negative for hepatitis B surface antigen (HBsAg) and had normal serum alanine aminotransferase levels. None of the 206 plasma samples was positive for HBV DNA by dot blot hybridization assay. However, nine samples were positive for HBV DNA by PCR using two primer pairs specific for surface and core regions. Nine persons received the HBV-DNA-positive plasma, and one developed posttransfusion non-A, non-B hepatitis; the others remained well 6 months later. Therefore, approximately 4% of blood donors in Taiwan have low titers of HBV DNA, and a more sensitive method to screen donors may be needed in the future, although the current serologic test remains the most practical at present.

Autoradiography↗
PubMed1991

Genetic evidence that genes fdhD and fdhE do not control synthesis of formate dehydrogenase-N in Escherichia coli K-12.

Enterobacteria synthesize two formate dehydrogenases, formate dehydrogenase-N (encoded by fdnGHI) and formate dehydrogenase H (encoded by fdhF). Previous work has identified two rha-linked Salmonella typhimurium genes, fdnB and fdnC, which are required primarily for formate dehydrogenase-N activity. Analogous mutants, termed fdhD and fdhE, have been isolated in Escherichia coli. We used gene fusions between fdnG, the structural gene for the large subunit of formate dehydrogenase-N, and lacZ, the structural gene for beta-galactosidase, to examine E. coli fdnGHI operon expression in fdhD and fdhE insertion mutants. Expression of the phi (fdnG-lacZ) gene fusions was little affected by these insertions, suggesting that fdhD and fdhE do not control transcription or UGA decoding of the formate dehydrogenase-N structural genes. Our complementation tests, with cloned E. coli fdhD and fdhE genes, indicate that the S. typhimurium fdnC and fdnB genes are functionally homologous to the E. coli fdhD and fdhE genes, respectively.

Cloning, Molecular↗