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T Chen

Publications and source records attributed to T Chen.

At least 289 records · Page 16Linked to original sources
PubMed1994

Ischemic tolerance can be induced repeatedly in the gerbil hippocampal neurons.

We investigated whether ischemic tolerance can be induced repeatedly in the gerbil hippocampal neurons. The gerbils were firstly treated with two episodes of 2-min forebrain ischemia 1 day apart, which procedure is known to induce ischemic tolerance. After 4 weeks of recirculation, the animals were subjected to a 2-min period of preconditioning ischemia again and then to a 3-min period of ischemia after 3 days. The hippocampal CA1 neurons were destroyed 7 days after 3-min ischemia without the second preconditioning but not in animals with the second preconditioning. Thus, ischemic tolerance can be induced repeatedly when the first ischemic tolerance has disappeared.

Animals↗
PubMed1994

Myeloblastin/proteinase 3 belongs to the set of negatively regulated primary response genes expressed during in vitro myeloid differentiation.

Regulation of myeloblastin expression was studied during myeloid differentiation of HL60 cells and compared with that of myeloperoxidase. Induction towards the monocytic pathway of differentiation caused a rapid, marked and parallel down-regulation of both transcripts which were insensitive to cycloheximide. Thus, myeloblastin is directly regulated and, similarly to myeloperoxidase, belongs to the set of primary response genes. Nuclear run-on experiments and RNA half-life determinations revealed that myeloblastin regulation was at both the transcriptional and posttranscriptional levels.

Base Sequence↗
PubMed1994

Temporal regulation of the IgE-dependent 1,2-diacylglycerol production by tyrosine kinase activation in a rat (RBL 2H3) mast-cell line.

We explored the possible role of tyrosine kinases in the IgE-dependent regulation of 1,2-diacylglycerol (DAG) production in RBL 2H3 cells. When triggered via their high-affinity IgE receptors (Fc epsilon RI), there was a rapid phosphorylation of tyrosine residues on a number of proteins. The phosphorylation of these proteins and ultimately histamine release were inhibited in a concentration-dependent manner by the tyrosine kinase inhibitor, tyrphostin. In cells labelled with [3H]myristic acid, we observed a characteristic biphasic increase in [3H]DAG production. In the presence of tyrosine kinase inhibitor, the initial increase in DAG was still observed, but the secondary increase, which was dependent on phosphatidylcholine-specific phospholipase D (PC-PLD) activation, was completely abolished. Tyrphostin significantly inhibited IgE-dependent activation of PC-PLD, suggesting that PC-PLD activation was regulated by tyrosine phosphorylation. Furthermore, when proteins from RBL 2H3 cells were immunoprecipitated with an anti-phosphotyrosine antibody, PC-PLD activity was recovered from the immunoprecipitated fraction. These results demonstrate that the secondary, but not the initial, phase of 1,2-DAG production in response to Fc epsilon RI aggregation is regulated by the initial activation of tyrosine kinases and that PC-PLD may be regulated directly by this mechanism.

Animals↗
PubMed1994

Screening for ferrochelatase mutations: molecular heterogeneity of erythropoietic protoporphyria.

The DNA of 21 patients from 19 unrelated families with erythropoietic protoporphyria (EPP) were screened for the 6 ferrochelatase point mutations so far described. The mutation previously described by us (A >> T transversion at position -3 of the donor site of intron 10, causing exon 10 skipping) was detected in two additional unrelated EPP patients: in these patients, cDNA lacking exon 10 was also detected. The mutation described by Nakahashi et al. as responsible for exon 2 skipping (C >> T transition at position -23 of the acceptor site of intron 1), although also observed in some normal individuals, was invariably observed in all EPP patients tested and may thus play some role in the pathogenesis of EPP. Thus, it does not appear that this mutation is the primary mechanism underlying exon 2 skipping. None of the other four previously described mutations were detected. These data demonstrate the heterogeneity of the ferrochelatase locus and of the genetic defect in EPP.

Base Sequence↗
PubMed1994

Interleukin-1 beta induces cytosolic phospholipase A2 and prostaglandin H synthase in rheumatoid synovial fibroblasts. Evidence for their roles in the production of prostaglandin E2.

OBJECTIVE: In order to investigate potential regulatory mechanisms for the increased production of prostaglandin E2 (PGE2) in interleukin-1 beta (IL-1 beta)-stimulated rheumatoid synovial fibroblasts (RSF), this study examined the induction of phospholipase A2 (PLA2) and prostaglandin H synthase (PGHS) enzymes and the correlation of these events with PGE2 production in IL-1 beta-stimulated RSF. METHODS: Protein and messenger RNA (mRNA) levels of cytosolic PLA2 (cPLA2) and PGHS-2 enzymes in IL-1 beta-stimulated RSF were measured by Western and Northern blotting, respectively, using specific antisera and complementary DNA probes. Enzymatic activity of cPLA2 was determined in cell-free reaction mixtures utilizing mixed micelles of 14C-phosphatidylcholine and Triton X-100 as the substrate. PGE2 levels were quantitated using a commercial enzyme immunoassay kit. RESULTS: Incubation of RSF with IL-1 beta increased the mRNA and protein levels for the high molecular weight cPLA2 as well as for the mitogen/growth factor-responsive PGHS (PGHS-2). The IL-1 receptor antagonist completely abolished the induction of these two enzymes and the stimulation of PGE2 production by IL-1 beta in RSF. In contrast, levels of the other known forms of these enzymes, i.e., the 14-kd secretory group II PLA2 (sPLA2) and the constitutive form of PGHS (PGHS-1), were unaffected by IL-1 beta treatment. CONCLUSION: These are the first data to demonstrate the coordinate induction by IL-1 of cPLA2 and PGHS-2 in RSF. The time-course for the induction of these enzymes suggests that their increase contributes to the increased production of PGE2 in IL-1-treated RSF, and may help explain the capacity of RSF to produce large amounts of PGE2.

Arthritis, Rheumatoid↗
PubMed1994

Experience with 500 prenatal diagnoses of sickle cell diseases: the effect of gestational age on affected pregnancy outcome.

Prenatal diagnosis of sickle cell diseases is obtained rapidly and precisely by polymerase chain reaction (PCR) with Ddel restriction analysis and dot-blotting with allele-specific oligonucleotides (ASO). Prenatal diagnosis of HgbSS and HgbSC was performed in 500 pregnancies, 196 by Southern blot and 304 by PCR. PCR drastically shortened the interval from sampling to reporting, allowing acceptance even of samples with unknown paternal phenotype, and resulted in an overall four-fold increase in diagnoses. In 108 pregnancies, the diagnosis was an affected fetus; 25 were HgbSC: 3 (12 per cent) were terminated; 83 were HgbSS: four ended in miscarriage; 40/79 (51 per cent) were terminated. The gestational age at the time of report to the mother appeared to be a major outcome determinant when the fetal diagnosis was HgbSS. The change-point in the maternal decision was found at 20 weeks of gestation. Before the 20th week, most mothers (64 per cent) chose termination; thereafter, the majority (72 per cent) chose continuation. The odds ratio of termination in earlier relative to later reporting was 4.7. In order to offer a choice to the mothers at risk of delivering a fetus affected by sickle cell disease, the diagnosis should be reported before the 20th week of gestation.

Amniocentesis↗
PubMed1994

Deficient ileal 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in sitosterolemia: sitosterol is not a feedback inhibitor of intestinal cholesterol biosynthesis.

We correlated the activity of the rate-limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, with the sterol content and composition of mucosal cells from the ileum of three homozygous sitosterolemic subjects and one control subject. In this inherited disease, whole-body cholesterol biosynthesis is decreased and increased amounts of sitosterol are absorbed from the intestine and deposited in tissues. For comparison, similar measurements were obtained in the ileal mucosa of sitosterol-fed rats where sitosterol accounted for 11% of enterocyte sterols. In the three sitosterolemic homozygotes, sitosterol represented 9% to 11% of the total microsomal sterols in the intestinal mucosa, although normal architecture for both crypts and villi is observed. The mean ileal microsomal HMG-CoA reductase activity in the three homozygotes was less than half of control values. In the ileum of sitosterol-fed rats with increased mucosal sitosterol concentrations, microsomal HMG-CoA reductase activity was not inhibited. These results show that in three sitosterolemic homozygotes, abnormally low HMG-CoA reductase activity was detected in the ileum, as previously demonstrated in mononuclear leukocytes and liver. The failure of the increased tissue sitosterol pool to inhibit HMG-CoA reductase in rat ileum suggests that deficient cholesterol biosynthesis in homozygous sitosterolemia is inherited and is not due to feedback inhibition by tissue sitosterol.

Adult↗
PubMed1994

Differential effects of serum on lipopolysaccharide receptor-directed macrophage activation for nitric oxide production.

In this manuscript, the effects of fetal bovine serum (FBS) on activation of mouse macrophages through the p73 lipopolysaccharide (LPS) receptor have been evaluated. In confirmation of earlier published studies, FBS will significantly potentiate the ability of LPS to activate macrophages to produce nitric oxide (NO). Evidence that this potentiating effect of FBS is mediated primarily by an interaction with LPS is provided by data showing that the stimulating effects of a hamster IgM monoclonal antibody to the p73 LPS receptor are significantly suppressed under identical conditions of FBS addition. The presence of FBS enhances both the kinetics of LPS-induced NO production and delays the induction of MAb5D3-induced NO production. The data establish that the ability of FBS to reduce MAb5D3-initiated NO production can only be manifest during the first 4-6 h following activation with antibody. Similarly, the ability of polymyxin B (which does not affect MAb5D3 activity) to inhibit LPS-dependent macrophage activation is also only effective during the first 4-6 h of stimulation, suggesting a parallel kinetic profile in the activation of the inducible NO synthase by these related activators. These studies provide data which suggest a dual role for serum factors in LPS-dependent macrophage activation, a direct effect of FBS on LPS which potentiates its immunostimulatory activity, and a secondary down-regulation effect which is manifest at the level of the macrophage.

Animals↗
PubMed1994

Simulation of integrin-cytoskeletal interactions in migrating fibroblasts.

Cell migration is a dynamic phenomenon requiring a physical interaction between the internal cell motile machinery and the external substratum in which adhesion receptors, such as integrins, serve as the transmembrane link. To analyze quantitatively this interaction, we apply a modified Brownian dynamics algorithm to simulate cytoskeleton-mediated transport of integrin on the dorsal surfaces of migrating fibroblasts. Previously, we experimentally demonstrated that integrin is transported in an intermittent fashion, with directed excursions interspersed by diffusive periods, preferentially toward the cell edge where the integrin is likely used in the formation of nascent adhesions. Integrins containing mutations in the cytoskeleton-binding region of the cytoplasmic domain display statistically different degrees of directed transport, indicating that this phenomenon is dependent on cytoskeletal associations. In the present work, we develop a computer algorithm generating simulated integrin transport trajectories, given estimates for the rate constants defining coupling (kc) and uncoupling (ku) of integrin with cytoskeletal components. Other parameters supplied to the program, the diffusion coefficient (D) for integrin in the membrane and the instantaneous velocity (vi) of the integrin/cytoskeleton complex, have been measured independently in our experimental system. By comparing the simulated trajectories with those obtained experimentally, we are able to estimate the coupling and uncoupling rate constants for the interaction of integrin with cytoskeletal elements in vivo. We find that integrin couples with cytoskeletal elements at a rate approximately 10 times slower than its rate of uncoupling (kc = 0.3 s-1, ku = 3 s-1). Comparison of these rate constants with an equivalent rate constant for diffusion, k+ = 0.4 s-1, indicates that the coupling interaction is likely a diffusion-limited process, as is typically expected for membrane processes. We further show by calculation that directed transport is necessary for integrin to traverse the length of an extending lamellipod to its leading edge; diffusion alone is not sufficiently fast to supply adhesion receptors to points of new cell/substratum contact.

Algorithms↗
PubMed1994

Elderly women in northern New England exhibit seasonal changes in bone mineral density and calciotropic hormones.

A seasonal component to bone loss has been reported in some postmenopausal women. We hypothesized that elderly women in northern New England would be at high risk for bone loss during winter because of their age, diet and lack of sunlight. Eighteen elderly but healthy women (mean age 77 years) started a 2-year observational study in a remote area of northwestern Maine (Greenville: 45.5 degrees N latitude). Fifteen women completed the study. Bone mineral density of the spine (L-BMD) and hip (F-BMD) and biochemical markers of bone turnover were measured biannually. In vitro photo-conversion of provitamin D3 to previtamin D3 was determined in the winter and spring. Initial calcium and vitamin D intake averaged 700 +/- 72 mg/day and 6.2 +/- 1.2 micrograms/day, respectively. During the first year L-BMD dropped 4.2% (P = 0.002) while F-BMD dropped 2.4% (P = 0.09), primarily because of steep declines during the fall and winter (August to February: L-BMD: 3.6%, P = 0.001; F-BMD: 3.0%, P = 0.04). In that 6-month period, serum 25 hydroxyvitamin D (25(OH)D) fell 13 +/- 6% (P = 0.06) and PTH rose 27 +/- 11% (P = 0.01). Additionally, there was no detectable in vitro conversion of provitamin D to previtamin D over 8 h of one sunny winter day. In the summer, PTH and 25(OH)D reverted to basal levels and significant in vitro photoconversion of provitamin D to previtamin D was detected. In the 2nd year of the study, vitamin D consumption increased (+2.0 +/- 1.2 micrograms/day, P = 0.03 vs. baseline), L-BMD increased slightly (+1.8%, P = 0.05) and F-BMD did not change (+0.5%, P = NS). Again, changes in BMD and vitamin D were seasonal: L-BMD and F-BMD were constant during fall and winter but both sites showed increases during summer (L-BMD: +1.7%, P = 0.04, F-BMD: +1.6%, P = 0.25). In the second winter, serum 25(OH)D fell nearly 20% and PTH rose 17%. Increased dietary consumption of vitamin D was positively correlated with changes in F-BMD at 18 months (r = 0.61, P = 0.02) and resulted in slightly greater serum 25(OH)D concentrations during the second winter than the first. The difference in serum 25(OH)D between the first and second winter was the strongest predictor of lumbar bone accretion during the second year of the study (r = 0.59, P = 0.04). In this 24-month observational study, significant seasonal changes in BMD, 25(OH)D and PTH were reported.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Intermittent microclimate cooling during rest increases work capacity and reduces heat stress.

Requirements for special protective equipment while working in hazardous environments can present a significantly increased thermal burden and early onset of physical fatigue. Ambulatory (backpack) or tethered personal cooling can accelerate metabolic heat removal, but is often not practical from an ergonomic standpoint. The efficacy of incorporating personal cooling during non-ambulatory rest periods was evaluated in subjects (n = 8) with varying levels of fitness. Treadmill work (approximately 475 W, 40% VO2 max) was alternately performed for 30 min followed by 30 min of rest. Subjects walked and rested under three separate experimental conditions: (1) control (C), in which light clothing was worn; (2) CPE, in which a chemical protective ensemble (CPE) was worn, and (3) CPE plus intermittent microclimate cooling (COOL). The WBGT condition for all trials was 31 degrees C. During the COOL trial the subjects additionally wore a personal cooling vest which allowed for the circulation of chilled liquid over the torso during rest. Under C conditions, relatively modest changes in rectal temperature (Tre) were observed, which stabilized over time. CPE wear resulted in a progressive rise in Tre and early fatigue. The addition of intermittent cooling during each rest cycle (COOL trial) significantly attenuated heat storage such that an oscillating, but equilibrated Tre was established and work capacity was at least doubled. Moreover, the perceived cooling effect was appreciable for all subjects. Therefore, intermittent personal cooling provided a useful means of enhancing work productivity and may have application for certain military and industrial personnel performing heavy work in hot environments. This approach should provide a practical alternative for reducing stress/fatigue when work/rest cycles are employed.

Body Temperature Regulation↗
PubMed1994

Enhancing effects of organosulfur compounds from garlic and onions on hepatocarcinogenesis in rats: association with increased cell proliferation and elevated ornithine decarboxylase activity.

Four organosulfur compounds from garlic and onions were examined for modifying effects on diethylnitrosamine (DEN)-induced neoplasia of the liver in male F344 rats using the medium-term bioassay system based on the two-step model of hepatocarcinogenesis. Carcinogenic potential was scored by comparing the numbers and areas per cm2 of induced glutathione S-transferase placental form-positive foci. Isothiocyanic acid isobutyl ester (IAIE), dipropyl trisulfide (DPT), and allyl mercapton (AM) exerted enhancing effects on their development, while dimethyl trisulfide also tended to increase them. To investigate possible mechanisms of the modifying influence, sequential changes in ornithine decarboxylase activity (ODC) over 24 h were measured in AM-treated liver tissue without prior DEN initiation. The activity started to increase by 4 h after AM-treatment, and reached maximum at 16 h, compared to controls. Spermidine/spermine N1-acetyltransferase activity was not significantly changed. An increase in proliferating cell nuclear antigen-positive cells followed the elevation of ODC activity. These results suggest that IAIE, DPT, and AM promote rat hepatocarcinogenesis and their promoting effect might be caused by increased cell proliferation with increased polyamine biosynthesis. In evaluating relationships between diet and cancer, it is thus appropriate to consider not only a possible protective role of garlic and onions, but also enhancing effects.

Acetyltransferases↗
PubMed1994

Effect of 5' non-coding region on expression of LT-B gene.

The different construction of mRNA 5' non-coding region may affect gene expression. To improve gene expression levels, we constructed recombinant plasmids with different nucleotide composition of the 5' non-coding region which direct the synthesis of human toxicogenic E. coli heat-labile enterotoxin B subunit coded by LT-B gene under the control of the PRPL tandem promoter of vector pBV220. These recombinants were expressed in E. coli HB101 and DH5 alpha, respectively. The results show that the expression levels of LT-B gene with two tandem SD sequences upstream from the initiation codon are lower than those with only one SD sequence and translation coupling can improve the expression levels; the different SD sequences can affect the expression of LT-B gene a little. The SD sequence of LT-B gene itself may be better for expression than that of the vector pBV220; the length of 5' non-coding region in the recombinants harboring only one SD sequence has no effect on the expression of LT-B gene; the expression of LT-B gene in HB101 is higher than that in DH5 alpha.

Bacterial Toxins↗