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Biomedical subjects

T M Chen

Publications and source records attributed to T M Chen.

At least 91 records · Page 5Linked to original sources
PubMed1994

Correlation of uterine hemodynamics with chemotherapy response in gestational trophoblastic tumors.

OBJECTIVE: To assess the uterine hemodynamics in gestational trophoblastic tumors and to correlate them with response to chemotherapy. METHODS: Using transvaginal color Doppler ultrasound, we measured the peak systolic velocity and the resistance index (RI) of the uterine arteries in 23 women with gestational trophoblastic tumors before each course of chemotherapy. Fifty-five nonpregnant women and another 15 women who had uneventful molar evacuation were enrolled as controls. Two-tailed Student t test was used for statistical analysis. RESULTS: A hyperdynamic uterine circulation was noticed at diagnosis in all gestational trophoblastic tumors, manifested as higher peak systolic velocity (mean +/- standard deviation 57.5 +/- 20.4 cm/second) of the uterine arteries compared to nonpregnant (28.3 +/- 3.41 cm/second; P < .0001) and uneventful post-mole uteri (26.8 +/- 3.08 cm/second; P < .0001). The RI values of the uterine arteries in gestational trophoblastic tumors at diagnosis ranged from 0.21-0.80. However, the mean value (0.56 +/- 0.19) was lower than those of nonpregnant (0.80 +/- 0.05; P < .0001) and post-mole uteri (0.75 +/- 0.06; P < .0001). A higher pre-treatment uterine artery RI (mean 0.71 +/- 0.09) was noted in ten patients with gestational trophoblastic tumors requiring fewer than five courses of chemotherapy, compared with the mean in 13 patients requiring longer courses of treatment (0.47 +/- 0.14; P < .0001). There was a marked decrease of peak systolic velocity during the first three courses of treatment in the former group (54.2 to 23.6 cm/second; P < .001), in contrast to no change in the latter group (60.1 to 60.5 cm/second). CONCLUSION: Uterine hemodynamic characteristics assessed by color Doppler ultrasound might predict and monitor the response to chemotherapy in gestational trophoblastic tumors.

Adult↗
PubMed1994

Interplay of two functionally and structurally distinct domains of the c-fos AU-rich element specifies its mRNA-destabilizing function.

AU-rich elements (ARE) in the 3' untranslated region of many highly labile mRNAs for proto-oncogenes, lymphokines, and cytokines can act as an RNA-destabilizing element. The absence of a clear understanding of the key sequence and structural features of the ARE that are required for its destabilizing function has precluded the further elucidation of its mode of action and the basis of its specificity. Combining extensive mutagenesis of the c-fos ARE with in vivo analysis of mRNA stability, we were able to identify mutations that exhibited kinetic phenotypes consistent with the biphasic decay characteristic of a two-step mechanism: accelerated poly(A) shortening and subsequent decay of the transcribed portion of the mRNA. These mutations, which affected either an individual step or both steps, all changed the mRNA stability. Our experiments further revealed the existence of two structurally distinct and functionally interdependent domains that constitute the c-fos ARE. Domain I, which is located within the 5' 49-nucleotide segment of the ARE and contains the three AUUUA motifs, can function as an RNA destabilizer by itself. It forms the essential core unit necessary for the ARE-destabilizing function. Domain II is a 20-nucleotide U-rich sequence which is located within the 3' part of the c-fos ARE. Although it alone can not act as an RNA destabilizer, this domain serves two critical roles: (i) its presence enhances the destabilizing ability of domain I by accelerating the deadenylation step, and (ii) it has a novel capacity of buffering decay-impeding effects exerted by mutations introduced within domain I. A model is proposed to explain how these critical structural features may be involved in the c-fos ARE-directed mRNA decay pathway. These findings have important implications for furthering our understanding of the molecular basis of differential mRNA decay mediated by different AREs.

3T3 Cells↗
PubMed1994

Serum neuron-specific enolase levels in patients with small cell carcinoma of the uterine cervix.

Serum neuron-specific enolase (NSE) is a tumor marker for neuroendocrine tumors or tumors of neuroepithelial origin. While the clinical application of NSE in small cell lung cancer has been established, its role in small cell carcinoma of the uterine cervix is unknown. We examined serum NSE in six patients with cervical small cell carcinoma and 13 patients with cervical squamous cell carcinoma. Elevated serum NSE was noted in four of six patients (67%) with small cell carcinoma, but none of the 13 patients with squamous cell carcinoma. An extremely high NSE serum level (154.7 ng/mL) was found in one patient with recurrence of small cell carcinoma, suggesting its correlation with disease extension. Although further studies to evaluate its relevance to prognosis, treatment effect, and early detection of recurrence are in progress, this preliminary result seems promising.

Adult↗
PubMed1994

Factors contributing to the accuracy in diagnosing ovarian malignancy by color Doppler ultrasound.

OBJECTIVE: To determine whether resistance index values obtained by color Doppler ultrasound contribute to the accuracy in diagnosing ovarian malignancies. METHODS: Four hundred ten patients with ovarian neoplasms referred for color Doppler ultrasound evaluation were enrolled, excluding patients examined during the luteal phase. Resistance index of the intra-tumor arteries was measured by color Doppler ultrasound. The corresponding clinical and histopathologic information was recorded. For statistical determinations, we used the Yates corrected chi 2 analysis, Fisher exact test, Student t test, and linear regression analysis. RESULTS: Satisfactory intra-tumor artery waveforms were obtained in 96.1% (99 of 103) of ovarian malignancies. Resistance index values varied at 0.23-0.82. Regression analysis of resistance index values on tumor size and amount of ascites demonstrated a linear association (R = 0.498 and 0.362, respectively; P < .01 in both). If we regard a resistance index of 0.4 as a cutoff value, the overall sensitivity and specificity in detecting malignancy were 68.0 and 97.4%, respectively. Primary ovarian malignancies exhibited significantly more false negatives (30 of 79) than malignancies metastasized to the ovary (three of 24) (P = .018). Malignancies containing mainly cystic components exhibited more false negatives (20 of 41) than did tumors with primarily solid components (13 of 62) (P < .01). Significantly more false negatives were encountered in malignancies with larger diameters (greater than 10 cm) compared to smaller ones (27 of 63 versus six of 40; P < .01), and in malignancies accompanied by considerable ascites (greater than 1000 mL) (13 of 25 versus 20 of 78; P < .05). CONCLUSIONS: Tumor origin, size, component nature, and amount of ascites contributed to the accuracy in diagnosing ovarian malignancies using resistance index values obtained by color Doppler ultrasound.

Adolescent↗
PubMed1993

Genetic analysis of in vitro progression of human papillomavirus-transfected human cervical cells.

The authors have established an in vitro model system which demonstrates the progression of the transformed phenotypes of human cervical epithelial cells transfected with human papillomavirus (HPV) type 16 and 18 DNAs. Both viral DNAs exhibit immortalizing potential; however, only HPV 18-immortalized cell lines progress to exhibit anchorage-independent growth and, in a limited number of cases, tumorigenesis. In this paper, the authors have examined the genetic basis for this in vitro progression step by step, including immortalization, anchorage-independent growth, and tumorigenicity of the HPV-transfected human cervical epithelial cells by cell fusion. The results suggest that (a) all three transformed phenotypes, i.e., immortalization, anchorage-independent growth, and tumorigenesis, in this in vitro cervical carcinogenesis model are a result of recessive changes in genes or processes involved; (b) inactivation of p53 and retinoblastoma protein is not sufficient for immortalization of human cervical epithelial cells; (c) HPV expression per se does not account for immortalization of human cervical epithelial cells; (d) immortalization of human cervical epithelial cells initiated by HPV can occur through different processes, although one of them is the most preferred; and (e) probably only one group of recessive genes appears to be involved in the loss of anchorage-dependent growth for HPV-immortalized human cervical cells.

Base Sequence↗
PubMed1993

Lysine residues 2 and 104 of the human chorionic gonadotrophin beta subunit influence receptor binding.

Human chorionic gonadotrophin (hCG), like other members of the glycoprotein hormone family, contains a common alpha subunit and a hormone-specific beta subunit. The latter is a 145 amino acid residue polypeptide with six sites of glycosylation. Positions 2 and 104 are occupied by basic amino acid residues in the 12 known amino acid sequences of mammalian beta subunits from CG and LH, a related gonadotrophin that acts through the same receptor. Lysine residues are found in both these positions in hCG-beta. Using site-directed mutagenesis, each of these two lysines in hCG-beta was replaced with glutamic acid. The mutant and wild-type cDNAs were subcloned into a eukaryotic expression vector, which was then transiently transfected into Chinese hamster ovary cells containing a stably integrated gene for the bovine alpha subunit. Holoprotein formation occurred with each of the two heterologous gonadotrophin mutants, i.e. the bovine alpha subunit bound to hCG-beta (Glu2) and to hCG-beta (Glu104), as well as with the control, i.e. the bovine alpha subunit bound to the hCG-beta wild-type subunit. In two in-vitro assays, one a competitive binding assay with 125I-labelled hCG as bound ligand and the other based on stimulation of progesterone production in a transformed murine Leydig cell line, MA-10, both the heterodimers containing a mutant beta subunit exhibited bioactivity, but their potencies were lower than that of the bovine alpha subunit bound to the hCG-beta wild-type subunit. These results suggest that the basic amino acid residues at positions 2 and 104 in hCG-beta participate, either directly or indirectly, in receptor binding.

Amino Acid Sequence↗
PubMed1993

Intrahepatic distribution of hydrochlorothiazide and quinidine in rats: implications in pharmacokinetics.

The intrahepatic distributions of a nonmetabolized drug, hydrochlorothiazide (HCTZ) and a highly metabolized drug, quinidine (QD), were studied separately in five anesthetized rats during steady-state intravenous infusion. Liver samples (20-24) from various parts (0.1-0.2 g each) at the end of infusion were collected from each rat and analyzed for drug concentration by HPLC. The distribution of HCTZ in various macro regions appears quite "homogeneous," with a CV of drug concentration for each rat ranging from 2.6 to 4.7% (grand mean, 3.7 +/- 0.8%), whereas that of QD seems less "homogeneous," with a CV ranging from 8.5 to 28.3% (grand mean, 15.6 +/- 7.7%). The above results indicate that drugs that are not complicated by hepatic metabolism may tend to show more "homogeneous" distribution and those that are highly metabolized and/or known to strongly bind to hepatic tissue component(s) may show less "homogeneous" distribution. The results from the present QD study are in contrast with the general, much more heterogeneous distribution found in an isolated in situ perfusion study reported earlier. The implication of the present study in physiological pharmacokinetic and hepatic modeling is discussed.

Animals↗
PubMed1993

The state of p53 in primary human cervical carcinomas and its effects in human papillomavirus-immortalized human cervical cells.

Wild-type (wt) p53 acts as a tumor suppressor, while certain mutant type (mt) p53 may exhibit 'oncogenic' function. We have recently demonstrated that human papillomavirus type 18 (HPV-18) E6 can partially overcome the growth-suppressive effects of wt p53, but it remains unclear what role p53 plays in cervical carcinogenesis. In this report, we have examined nine HPV-immortalized human cervical epithelial cell lines and 13 HPV-positive and two HPV-negative primary cervical cancers for p53 mutations by polymerase chain reaction--single-strand conformation polymorphism (PCR-SSCP). None of them contained p53 mutations in exons 5-9 where most p53 mutations in human tumors have been found. The entire p53-coding region of the two HPV-negative cervical cancers was sequenced and no mutations were noted. In order to examine the effects of wt p53 and mt p53 on HPV-immortalized human cells, we transfected HPV-immortalized cell lines with wt p53 and a mt p53 (mtp53Val-135). The results indicate that HPV-immortalized cells cannot tolerate large amounts of exogenous wt p53, while mt p53Val-135 can enhance transformation of these cells. The results support the notion that inactivation of wt p53 by E6 may be important for HPV-associated transformation and also suggests that mt p53 can act as an oncogene in HPV-immoralized human cells.

Base Sequence↗
PubMed1992

Erythrocytes as a total barrier for renal excretion of hydrochlorothiazide: slow influx and efflux across erythrocyte membranes.

The potential barrier effect of erythrocytes (RBC) on renal excretion (mainly by tubular secretion) of hydrochlorothiazide (HCTZ) was evaluated in nine anesthetized rats during steady-state iv infusion. Drug concentrations in plasma and blood from the carotid artery and renal vein were assayed by a simple modified HPLC method. Renal extraction ratios were concentration-independent with a mean of 0.17 +/- 0.05 (SD). The renal excretion was found to occur primarily from the drug in plasma; the mean net fractional removal from plasma was 0.57 +/- 0.12, while that from RBC was less than 0.008 +/- 0.041. The virtual total unavailability of HCTZ from RBC (containing approximately 70% of drug in arterial blood) for renal excretion is attributed to relatively slow efflux of drug from RBC to plasma during each passage through the kidney compared with the blood transit time (in seconds). Preliminary in vitro influx and efflux kinetics of HCTZ across RBC membranes were studied using rat and human blood. The flux data could be adequately described by a linear, reversible, closed two-component system model, and the mean equilibration half-times (ET1/2) in rat and human blood were 10.9 and 20.5 min, respectively. The mean residence time of drug in blood circulation of rats was estimated to be 8.32 +/- 1.06 min, which is shorter than the ET1/2. This is consistent with data indicating that distribution equilibrium of HCTZ in arterial blood might not be reached in vivo even at steady state. Other implications of slow transport kinetics of drugs across RBC membranes are discussed.

Adult↗
PubMed1992

Metabolism of 11-deoxycorticosterone by hamster adrenal mitochondria.

Metabolism of 11-deoxycorticosterone (DOC) by hamster adrenal mitochondria gives 19-hydroxy-DOC and corticosterone (via 11-hydroxylation) in approximately equal yields. The ratio of 19- to 11-hydroxylation was invariant with changes in concentration of substrate or a competitive inhibitor. It is most likely, therefore, that a single 11,19-hydroxylase catalyzes both oxidations. Both primary products are further oxidized to the corresponding carbonyl analogs, 19-oxo-DOC and 11-dehydrocorticosterone, at rates that are approx. 20% of their rates of formation. The oxidation of 11-dehydrocorticosterone is catalyzed by a dehydrogenase utilizing either NAD or NADP while the oxidation of 19-hydroxy-DOC is catalyzed by an oxidase requiring NADPH. The 11-dehydrocorticosterone is stable in this enzyme preparation while 19-oxo-DOC is metabolized to two additional products, which are tentatively identified as 19-oic-DOC and 19-norcorticosterone. 19-nor-DOC was found to be hydroxylated at a rate that is 20% faster than the rate for DOC under the same conditions. It is therefore possible that 19-norcorticosterone can arise from 19-oic-DOC via decarboxylation to 19-nor-DOC and subsequent 11-hydroxylation, but the kinetics of its formation suggest that it may actually be formed directly from 19-oxo-DOC without free intermediates. 4-Androstene-3,17-dione and 17-hydroxy-DOC were also substrates for this 11,19-hydroxylase, but 18-hydroxy-DOC was not. Maintenance of hamsters on a low sodium diet had no effect on the metabolism of DOC by the isolated adrenal mitochondria.

Adrenal Glands↗
PubMed1992

Functional interaction of p53 with HPV18 E6, c-myc and H-ras in 3T3 cells.

Wild-type (wt) p53 has been suggested to be the product of a tumor-suppressor gene. Recently, it has been shown that the E6 oncoproteins of human papillomavirus (HPV) types 16 and 18, like the SV40 large T antigen, are physically associated with wt p53. We have investigated the functional interaction of wt p53 with the viral oncogene products of HPV16 and 18 and with cellular oncogenes by transfection of NIH3T3 cells with p53 wt alone or with several oncogene(s). We found that over-expression of HPV18 E6, c-myc or activated H-ras, like SV40 large T, can partially overcome the growth-inhibitory effect of wt p53 in NIH3T3 cells, while HPV16 E6 and E7, HPV18 E7, k-fgf, c-fos and mutant (mt) p53 do not. Further studies indicate that HPV18 E6 and c-myc can overcome the antiproliferative effect, but not the antitransforming effect, of wt p53, while activated H-ras can overcome both the antiproliferative and antitransforming effects of wt p53. These data show evidence of a functional interaction between HPV18 E6 and wt p53, and suggest that the cooperation of HPV E6 and cellular oncogenes c-myc and H-ras, which are activated in several cases of human cervical cancers, may be necessary to overcome completely the anti-oncogenic function of p53 in the development of these tumors.

3T3 Cells↗
PubMed1992

Large differences in the biological half-life and volume of distribution of hydrochlorothiazide in normal subjects from eleven studies. Correlation with their last blood sampling times.

In spite of more than three decades of wide use of hydrochlorothiazide as a diuretic, its mean biological half-life (t1/2) and apparent volume of distribution (Vdarea) in normal subjects were found to vary greatly among 11 studies reported between 1976 and 1986. For example, the mean t1/2 values ranged from 3.2 to 13.1 h and Vdarea values from 1.53 to 4.19 l/kg. Furthermore, a t1/2 of only 2.5 h and a Vdarea of only 0.83 l/kg were cited in a recent textbook. The present analyses show a positive correlation between the length of the last blood sampling time (tlast) employed and the t1/2 or Vdarea. The smaller t1/2 and Vdarea values reported were attributed to the insufficient length of time used in blood sampling for a drug exhibiting polyexponential disposition function. The kinetic and dynamic significance of the findings were briefly described.

Blood Volume↗
PubMed1991

Direct enantiomeric separation of terfenadine and its major acid metabolite by high-performance liquid chromatography, and the lack of stereoselective terfenadine enantiomer biotransformation in man.

Direct enantiomeric separation of terfenadine and its major acid metabolite was achieved by using two different chiral stationary phase columns with two different mobile phase systems. Further, the enantiomeric composition of the human urinary acid metabolite has been determined, indicating a non-stereoselective biotransformation in man.

Biotransformation↗
PubMed1991

Incorporation of tandem mass spectrometric detection to the analysis of peptide mixtures by continuous flow fast atom bombardment mass spectrometry.

The ability to acquire structurally informative daughter ion spectra for individual peptides undergoing separation and analysis by continuous flow fast atom bombardment (CF FAB) is demonstrated. To illustrate the potential of this methodology, tryptic and chymotryptic digests of the 29-residue peptide glucagon were analyzed by CF FAB using mass spectrometric and tandem mass spectrometric detection in consecutive analyses. Daughter ion spectra were recorded using B/E linked scans for the major hydrolysis products observed by liquid chromatography/mass spectrometry. The peptide mixtures were separated by gradient capillary high-performance liquid chromatography with the FAB matrix being added post-column using a coaxial flow interface between the column and flow probe. The entire effluent (3 microl min(-1)) was sampled by the mass spectrometer. Results obtained using less than 300 pmol of digested glucagon indicated several advantages to tandem mass spectrometric detection including the ability to confirm identities for products of enzymatic digestion and the potential use of this method for tandem sequence analysis of peptide mixtures.

Amino Acid Sequence↗
PubMed1991

Inhaled epinephrine and oral theophylline-ephedrine in the treatment of asthma.

Inhaled and oral over-the-counter bronchodilators are used for self-therapy by asthmatic patients. To evaluate their safety and efficacy, we compared epinephrine and theophylline combined with ephedrine with inhaled metaproterenol and the placebo. Twelve asthmatic patients were studied in a randomized, double-blind, placebo-controlled, crossover trial comparing forced expiratory volume in 1 second (FEV1) after two inhalations of epinephrine (0.2 mg/inh), 1 minute apart, followed in 15 minutes by theophylline (130 mg) with ephedrine (24 mg) versus two inhalations of metaproterenol (0.65 mg/inh), 1 minute apart, versus placebo inhaler and tablets. Onset of FEV1 greater than 15% above baseline values occurred within 15 seconds after inhalations for 100% of epinephrine-treated patients, 92% of metaproterenol-treated patients, and 33% of placebo-treated patients. FEV1 responses were significantly greater (P less than .05) for epinephrine at 0.66 to 1.66 minutes compared with the responses of metaproterenol, and epinephrine and theophylline that was combined with ephedrine compared with metaproterenol beginning at 2 hours. Mean duration of activity was 5.7 hours for the epinephrine- and theophylline with ephedrine-treated patients, 4.9 hours for metaproterenol-treated patients, and 2 hours for the placebo group. There were statistically significant differences for patients receiving epinephrine and theophylline with ephedrine versus the placebo group (P less than .001), metaproterenol patients versus the placebo group (P = .02), and patients receiving epinephrine and theophylline with ephedrine versus metaproterenol-treated patients (P less than .05). Compared with inhaled metaproterenol, inhaled epinephrine followed in 15 minutes by a theophylline-ephedrine tablet had a significantly earlier onset, longer duration of action, numerically greater peak effect, and patient preference.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1991

Comparison of steroidogenic potencies of homologous and heterologous gonadotropins in rat and mouse Leydig cells.

The in vitro steroidogenic potencies have been determined in rat and mouse Leydig cells for two homologous human gonadotropins, lutropin (hLH) and choriogonadotropin (hCG), and two heterologous gonadotropins, hCG beta wild-type and the product of an hCG beta clone containing a premature termination codon at position 122, each associated with a co-expressed bovine alpha subunit. hCG was found to be more potent than hLH in rat, but not mouse Leydig cells, and the heterologous gonadotropin containing the truncated hCG beta subunit was equipotent to that with hCG beta wild-type in both rat and mouse Leydig cells. Persistent steroidogenesis was determined by measuring testosterone production following pre-incubation with each of the above four gonadotropins and with ovine LH, subsequent washing of the cells, and re-incubation in the absence and presence of additional hormone. Interesting differences were found with the five gonadotropins in rat and mouse Leydig cells. The testosterone response to all gonadotropins in rat Leydig cells was essentially the same whether or not additional hormone was added after the initial cell incubation and washing. In contrast, only hLH and hCG yielded identical responses in mouse Leydig cells in the presence and absence of additional hormone, testosterone production being invariably lower with ovine LH and the two expressed heterologous gonadotropins unless they were present in the second incubation. In summary, the hCG beta C-terminal sequence from residues 122-145 makes no discernible contribution to the in vitro potency in rat or mouse Leydig cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Determination of the metabolites of terfenadine in human urine by thermospray liquid chromatography-mass spectrometry.

Thermospray liquid chromatography-mass spectrometry (TSP LC-MS) was used to determine human urinary metabolites of terfenadine after oral administration of terfenadine tablets. In addition to the two previously identified major metabolites, azacyclonol (MDL 4829) and the 'acid' metabolite (MDL 16,455), three additional metabolites were also detected. One of the additional metabolites was identified as the 'alcohol' metabolite (MDL 17,523) and the other two were proposed to be an 'aldehyde' and a 'ketone-acid' metabolites from their TSP mass spectra. The results of this study demonstrated that TSP LC-MS is a useful technique for the study of terfenadine biotransformation.

Chromatography, Liquid↗