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Biomedical subjects

Y F Chen

Publications and source records attributed to Y F Chen.

At least 19 recordsLinked to original sources
PubMed1999

An aqueous concentration model for riverine spills.

A numerical model is developed to predict the aqueous concentrations of sparingly soluble compounds resulting from oil, fuel, or chemical spills onto rivers. The model computes the concentration of compounds both in the slick phase and in the aqueous phase by simulating the processes that affect the fate of the spilled compound. Processes simulated by the model include spreading and drifting of the surface slick, evaporation from the slick, dissolution from the slick into the water, volatilization from the water, and longitudinal dispersion in the river. The model is used to simulate a hypothetical spill of jet fuel, demonstrating that the concentration of a compound in the aqueous phase is strongly linked to its concentration in the slick phase. The most soluble and most volatile compounds exhibit the highest aqueous concentrations in the early stages of the spill, but ultimately the less soluble and less volatile compounds reach the highest aqueous concentrations. Streamwise concentration gradients in the slick due to the rapid evaporation of the more volatile compounds are shown to have an effect on the aqueous concentration.

Aircraft↗
PubMed1999

RFLAT-1: a new zinc finger transcription factor that activates RANTES gene expression in T lymphocytes.

RANTES (Regulated upon Activation, Normal T cell Expressed and Secreted) is a chemoattractant cytokine (chemokine) important in the generation of inflammatory infiltrate and human immunodeficiency virus entry into immune cells. RANTES is expressed late (3-5 days) after activation in T lymphocytes. Using expression cloning, we identified the first "late" T lymphocyte associated transcription factor and named it "RANTES Factor of Late Activated T Lymphocytes-1" (RFLAT-1). RFLAT-1 is a novel, phosphorylated, zinc finger transcription factor that is expressed in T cells 3 days after activation, coincident with RANTES expression. While Rel proteins play the dominant role in RANTES gene expression in fibroblasts, RFLAT-1 is a strong transactivator for RANTES in T cells.

Adult↗
PubMed1999

Renal cell carcinoma: unusual pediatric renal tumors.

Renal cell carcinoma (RCC), the most common renal tumor in adults, is rare in childhood, with an incidence much lower than that of Wilms' tumor. It is initially asymptomatic, but clinically overt symptoms such as an abdominal mass or hematuria may indicate late-stage disease and a poor prognosis. In this report, we describe the imaging features of pediatric RCC and emphasize the value of early diagnosis offered by ultrasonographic screening. From 1989 through 1997, we encountered five children (aged 7-15 yr) with RCC. Of these, two presented with symptoms, while the other three were asymptomatic and were identified in a large, school-based urologic ultrasonographic survey, in which more than 800,000 children were screened by our team. Reviewing the imaging features, we found that four tumors exhibited a heterogeneous nature. One patient had bilateral well-defined homogeneous tumors, which proved to be bilateral low-grade RCC. The three asymptomatic patients had smaller tumors than the other two patients. These three were treated with nephrectomy and were well after at least 15 months of follow-up. The two patients who presented with symptoms eventually died of tumor recurrence and pulmonary metastasis, respectively. The findings in these five cases of pediatric RCC add knowledge regarding the imaging features of this disease and highlight the value of ultrasonographic screening for early diagnosis.

Adolescent↗
PubMed1998

mu Opioid receptor knockout in mice: effects on ligand-induced analgesia and morphine lethality.

The mu opioid receptor gene (MOR) was mutated in mice by a gene targeting procedure. In these MOR-knockout mice, the analgesic effects of morphine, its major metabolites, morphine-6-glucuronide (M-6-G) and morphine-6-ethereal sulfate (M-6-S), and endomorphin-2, as well as morphine-induced lethality, were drastically reduced, whereas the effects of DPDPE and U50488 remained unchanged. It is concluded that analgesic effects of mu-specific opioid ligands and acute morphine lethality are mediated by the mu receptor.

Analgesics, Opioid↗
PubMed1998

Monte Carlo validation of a multireader method for receiver operating characteristic discrete rating data: factorial experimental design.

RATIONALE AND OBJECTIVES: The authors conducted a series of null-case Monte Carlo simulations to evaluate the Dorfman-Berbaum-Metz (DBM) method for comparing modalities with multireader receiver operating characteristic (ROC) discrete rating data. MATERIALS AND METHODS: Monte Carlo simulations were performed by using discrete ratings on fully crossed factorial designs with two modalities and three, five, and 10 hypothetical readers. The null hypothesis was true for all simulations. The population ROC areas, latent variable structures, case sample sizes, and normal/abnormal case sample ratios used in another study were used in these simulations. RESULTS: For equal allocation ratios and small (Az = 0.702) and moderate (Az = 0.855) ROC areas, the empirical type I error rate closely matched the nominal alpha level. For very large ROC areas (Az = 0.961), however, the empirical type I error rate was somewhat smaller than the nominal alpha level. This conservatism increased with decreasing case sample size and asymmetric normal/abnormal case allocation ratio. The empirical type I error rate was sometimes slightly larger than the nominal alpha level with many cases and few readers, where there was large residual, relatively small treatment-by-case interaction and relatively large treatment-by-reader interaction. CONCLUSION: The results suggest that the DBM method provides trustworthy alpha levels with discrete ratings when the ROC area is not too large and case and reader sample sizes are not too small. In other situations, the test tends to be somewhat conservative or slightly liberal.

Diagnostic Imaging↗
PubMed1998

Extraction of sp18 family membrane proteins on posterior head of bull sperm and the effect of anti-sp18 IgG on sperm motility and murine in vitro fertilization.

Bovine sperm heads were separated via ultrasonic treatment and centrifugation. Anti-bull sperm IgG was produced by immunizing rabbits with acrosome-reacted bull sperm heads. SDS PAGE patterns revealed that the main membrane proteins on acrosome-reacted bull sperm head were sp18 family, including 18, 16, and 14 kD, which represented about 64% of the total membrane proteins in bull sperm. Indirect immunofluorescence shown sp18 antigens primarily distributed in postacrosomal and proximal tail regions. Western blot analysis revealed that the anti-bull sperm IgG reacted with sp18 antigens in acrosome-reacted bull sperm head and bull seminal plasma. Anti-bull sperm IgG also reacted with 14, 16, 18, 42, 57 and 60 kD proteins in fresh bull, mouse and rabbit sperm. Anti-sp18 IgG caused agglutination of bull and rabbit sperm, but had no effect on murine sperm. In murine in vitro fertilization trials, preincubating capacitated sperm with 0.364 mg/ml of anti-sp18 IgG resulted in a decrease in the fertilization rate from 75.6% in the controls to 50.8% in the experimental groups (p < 0.001).

Acrosome↗
PubMed1998

Garlic prevents hypoxic pulmonary hypertension in rats.

Hypoxic pulmonary vasoconstriction underlies the development of high-altitude pulmonary edema. Anecdotal observations suggest a beneficial effect of garlic in preventing high-altitude symptoms. To determine whether garlic influences pulmonary vasoconstriction, we assessed the effect of garlic on pulmonary pressures in rats subjected to alveolar hypoxia and on vasoconstriction in isolated pulmonary arterial rings. Garlic gavage (100 mg/kg body wt) for 5 days resulted in complete inhibition of acute hypoxic pulmonary vasoconstriction compared with the control group. No difference in mean arterial pressure or heart rate response to hypoxia was seen between the groups. Garlic solution resulted in a significant dose-dependent vasorelaxation in both endothelium-intact and mechanically endothelium-disrupted pulmonary arterial rings. The administration of NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) inhibited the vasodilatory effect of garlic by 80%. These studies document that garlic blocks hypoxic pulmonary hypertension in vivo and demonstrate a combination of endothelium-dependent and -independent mechanisms for the effect in pulmonary arterial rings.

Acetylcholine↗
PubMed1998

A case of severe hyperammonemia and unconsciousness following sodium valproate intoxication.

Although valproic acid has gradually gained its popularity in the treatment of various seizure disorders, overdose of valproate is not common. An 18-y-old man with a history of epilepsy controlled by sodium valproate and clonazepam attempted suicide with an ingestion of 45 g sodium valproate. He presented to our service with drowsiness and irritability. Extremely high serum ammonia (623 ug/dL) and elevated serum valproate concentration (575 ug/mL) were found on admission. Several metabolic abnormalities, including hypernatremia, hypocalcemia and metabolic acidosis, as well as, increased serum transaminase levels were also recorded. With supportive measures, he became clear 24 h later and was discharged 6 d after ingestion. Serial follow-up of his serum valproate and ammonia levels disclosed a close relationship between these 2 measurables. After acute overdose of valproic acid, patients usually present with mild and generally reversible depression of the central nervous system. However, impairment of liver function, hyperammonemia, fluid-electrolyte disturbances, coma, seizures, hypotension and even death may occur following valproate overdose. Symptomatic and supportive measures are the mainstay in the treatment of valproic acid overdose. With prompt diagnosis and early institution of treatment, a complete recovery should be anticipated.

Adolescent↗
PubMed1997

Estrogen restores endothelial cell function in an experimental model of vascular injury.

BACKGROUND: It has been suggested that reendothelialization of damaged blood vessels protects against the vascular injury response. The goal of the present study was to determine whether estrogen restores endothelial cell function in balloon-injured rat carotid arteries. METHODS AND RESULTS: Ten-week-old male and female Sprague-Dawley rats with intact gonads underwent balloon injury to the right common carotid artery. Female rats were randomized to receive either daily subcutaneous injections of 17beta-estradiol (17betaE[2]; 20 microg x kg[-1] x d[-1]) or vehicle over the course of the study. Vessel morphology was assessed 2 weeks after injury. Significant neointima formation was observed in vehicle-treated males. This response was blunted in vehicle-treated and 17beta-E(2)-supplemented females. Intima-to-media ratios were 1.28+/-0.23 (males), 0.72+/-0.07 (vehicle-treated females), and 0.49+/-0.07 (17beta-E[2]supplemented females). To test whether reductions in neointimal lesion formation were related to the functional reendothelialization of the damaged vessel, endothelium-dependent relaxation was tested in isolated ring segments from the three experimental groups. Vessels were precontracted with phenylephrine followed by cumulative administration of acetylcholine, an endothelium-dependent vasodilator. Maximum relaxation to acetylcholine was 8.13+/-1.70% (males), 22.06+/-4.36% (vehicle-treated females), and 46.47+/-3.48% (17beta-E[2]-supplemented females). The enhanced endothelium-dependent relaxation of rings from 17betaE(2)-supplemented females correlated with reduced neointimal proliferation in this group. The concentration of nitric oxide metabolites in plasma correlated positively with plasma 17beta-E(2) concentration. CONCLUSIONS: These results suggest that estrogen protects against neointimal injury in the balloon-injured rat, at least in part, by facilitating the reendothelialization of the damaged vessel.

Acetylcholine↗
PubMed1997

T helper 2-dominant antilymphoma immune response is associated with fatal outcome.

The precise role of the endogenous immune system in modulating cancer development remains unclear. Tumor cells are generally thought to be nonimmunogenic because they are of 'self' origin. However, tumor-reactive lymphocytes can be isolated from patients with many types of cancer. It is unclear what role these lymphocytes play and why they fail to protect the host. Using a murine B-cell leukemia/lymphoma (BCL1) model, we showed the development of a vigorous antitumor T-cell response in the tumor-susceptible host. Specific T-cell responses against BCL1 developed as early as day 4. However, the nature of this nonprotective response is different from the protective response produced in a major histocompatibility complex-matched tumor-resistant host. Susceptible hosts developed a T helper 2 (Th2)-dominant response, whereas resistant hosts developed a Th1-dominant response to BCL1. Cytolytic activity against BCL1 developed in both resistant and susceptible hosts, but in the susceptible host, this response was weaker and delayed compared with that in the resistant host. Thus, tumor susceptibility does not necessarily mean the absence of an antitumor immune response. Rather, the nature of the antitumor immune response is critical in determining clinical outcome.

Animals↗
PubMed1997

DNA-melting at the Bacillus subtilis flagellin promoter nucleates near -10 and expands unidirectionally.

A central step in promoter activation by RNA polymerase (RNAP) is the localized separation of the DNA strands to form the transcription bubble. We have used potassium permanganate footprinting to monitor DNA strand-separation by the Bacillus subtilis sigmaD RNAP at the strong promoter, Phag, directing transcription of flagellin. The susceptibility of individual thymine bases to permanganate oxidation is influenced by temperature, Mg2+, nucleotides, and the RNAP delta subunit. In the absence of delta, sigmaD RNAP establishes a partially opened complex even at 0 degrees C with permanganate reactivity localized between -11 and -4 (RP(-4)). The region of strand separation expands to near -1 at 20 degrees C (RP(-1)) and to +3 at 40 degrees C (RP(+3)). The delta subunit inhibits the downstream propagation of the transcription bubble and thereby increases the concentration of early intermediates in the melting pathway. Indeed, E delta sigmaD forms a distinct nucleated complex (RPn) at 0 degrees C with a structural distortion localized to an AT base step within the -10 element. We propose a model for promoter melting in which strand separation nucleates within the conserved -10 consensus and subsequently propagates downstream. Mg2+ and nucleoside triphosphates (NTPs) favor the downstream propagation of the transcription bubble and strongly stimulate the RP(-1) to RP(+3) conversion. The NTP effects are apparently mediated by binding of substrate to the initiating NTP site: purines are more effective than pyrimidines and GMP alone can greatly increase the level of DNA-melting. The binding of substrates, but not Mg2+ alone, can effectively overcome the anti-melting effect of delta.

Bacillus subtilis↗
PubMed1997

Sexually dimorphic response of the balloon-injured rat carotid artery to hormone treatment.

BACKGROUND: Estrogen blunts the neointimal response to vascular injury in gonadectomized rats of both sexes; addition of a progestin blocks the estrogen effect. This study tested, in intact rats of both sexes, whether (1) exogenous estrogen has a vasoprotective effect in injured carotid arteries, (2) progestin (medroxyprogesterone acetate, MPA) blocks the vasoprotective effect of estrogen, and (3) any observed sexual dimorphism in the responses to estrogen and/or MPA can be accounted for by differences in serum 17 beta-estradiol levels. METHODS AND RESULTS: Intact male and female Sprague-Dawley rats were randomly divided into four subgroups treated with either (1) 17 beta-estradiol, (2) MPA, (3) 17 beta-estradiol + MPA, or (4) vehicle and were subjected to balloon injury of the right common carotid artery. Two weeks later, rats were killed by an overdose of pentobarbital, and the carotid arteries were evaluated for myointimal thickening. Neither estradiol nor MPA altered the neointimal response in males. In females, estradiol reduced and MPA enhanced the response, whereas addition of MPA to estradiol blocked the vasoprotective effects of estrogen. CONCLUSIONS: Intact male rats but not intact females are resistant to the vasoprotective effects of exogenous estrogen, despite attainment of physiological (for females) serum 17 beta-estradiol levels. MPA enhances the neointimal response in intact females, presumably by blocking the production and thus the vasoprotective effect of endogenous estrogen.

Angioplasty, Balloon↗
PubMed1997

A novel A/T-rich element mediates ANF gene expression during cardiac myocyte hypertrophy.

The induction of the atrial natriuretic factor (ANF) gene during alpha 1-adrenergic stimulation of neonatal rat ventricular myocytes has served as a model for gene expression during cardiac muscle cell hypertrophy. This study describes and identifies a single regulatory element that mediates expression of the ANF gene. Deletional mutations were generated in a 639-bp fragment of the ANF promoter that confers alpha 1-adrenergic inducibility to a luciferase reporter gene in transient transfection assays in ventricular myocytes. The results of gel mobility shift and diethylpyrocarbonate (DEPC) interference studies with nuclear cardiac cell extracts identified the nucleotide contract points for a novel A/T-rich element (ANF-AT) at positions -582/-575 that partially mediates alpha 1-adrenergic inducibility. Mutations in the ANF-AT element reduced alpha-adrenergic inducibility of an ANF-TK-luciferase fusion gene in cardiac cells by 35% but had no effect on expression in other muscle and non-muscle cells tested. Gel mobility supershift assays with antibodies directed against the MEF-2 protein, the homeobox protein MHox, or the zinc finger protein HF-1b, document that these factors are not major components of the endogenous ANF-AT binding activity in cardiac muscle cells. The current study provides evidence for a role for a novel A/T-rich element in the regulation of ANF gene expression in cardiac ventricular myocytes.

Animals↗
PubMed1997

Double mycotic aneurysms of the ascending aorta.

Infection in the vascular tree has been proved to be one of the greatest challenges for cardiovascular surgeons. Of these, mycotic aneurysms of the ascending aorta were considered to be almost always lethal until recently. A thorough survey of the literature indicates that only 42 cases of mycotic aneurysm of the ascending aorta have been reported. All the reported cases of mycotic aneurysm of the ascending aorta were a single lesion in the ascending aorta except a case reported in 1993. This report describes an additional case of double mycotic aneurysms of the ascending aorta caused by Pseudomonas infection.

Adult↗
PubMed1997

The interactions of paeoniflorin and veratrine on isolated rat atria.

In this study, we attempted to identify the interactions and mechanisms between veratrine and paeoniflorin on isolated rat atria. Paeoniflorin alone showed no effect on the rat atria. Veratrine increased the atrial contraction and induced arrhythmia at 1 x 10(-5) g/ml. Veratrine could directly induce contraction and elicit tetanic contraction at 1 x 10(-4) g/ml in the left atria with or without electric stimulation. Paeoniflorin (4.8 x 10(-6) to 4.8 x 10(-3) g/ml), verapamil (2.2 x 10(-6) g/ml), tetrodotoxin (TTX) (3.2 x 10(-8) g/ml) and quinidine (7.5 x 10(-6) g/ml) inhibited the increase of contraction and delayed the onset of contraction induced by veratrine (1 x 10(-5) g/ml). The inhibitory effect of paeoniflorin combined with verapamil on the contraction induced by veratrine was more potent than that of paeoniflorin or verapamil alone. However, the inhibitory effect of paeoniflorin was not potentiated by TTX or quinidine. From the above results, the contraction evoked by veratrine in the rat atria may be concluded to be caused by the stimulation of Na(+)- and Ca(2+)-ion channels. The inhibition of paeoniflorin on the contraction induced by veratrine may primarily be related to the blockade of Ca2+ channels.

Animals↗
PubMed1997

The dual role of mRNA half-lives in the expression of the yeast ALG7 gene.

The yeast ALG7 gene functions by initiating the synthesis of the dolichol-linked oligosaccharide precursor and plays an important role in the control of protein N-glycosylation. The levels of ALG7 multiple transcripts are modulated by the physiological status of the cell and environmental cues, and deregulation of their abundance is deleterious to several cellular functions. Since ALG7 mRNAs are unstable, we investigated the role of these transcripts' half-lives in determining their steady-state levels. Using a temperature-sensitive RNA polymerase II mutant, we demonstrate that increased stability was the primary determinant of higher ALG7 mRNA abundance in response to glucose limitation or treatment with tunicamycin. In contrast, at the G1/G0 transition point, changes in the decay rates were inversely related to ALG7 transcript accumulation: the decreased abundance of ALG7 mRNAs following exit from the mitotic cycle was associated with lengthening of the decay rates, while their increased accumulation after growth stimulation correlated with decreased stability. This suggests that, depending on the circumstance, mRNA half-lives can either directly determine the level of ALG7 transcript accumulation or oppose regulatory changes at other control levels.

Antifungal Agents↗