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Biomedical subjects

E Lee

Publications and source records attributed to E Lee.

At least 325 records · Page 18Linked to original sources
PubMed1991

Stimulation of phagocytosis in rat polymorphonuclear leukocytes by A23187 is accompanied by activation of myeloperoxidase.

The incubation of polymorphonuclear leukocytes from rats with A23187 resulted in stimulation of phagocytosis with a concomitant increase in the activity of myeloperoxidase. Activation of the enzyme by A23187 reached the maximum at 2.5 min of incubation and preceded the maximum stimulation of phagocytosis. Propylthiouracil, an inhibitor of myeloperoxidase, and Ca2+ chelators prevented activation of myeloperoxidase and phagocytosis by A23187. These results indicate that A23187 increases intracellular Ca2+ level, followed by activation of myeloperoxidase involved in stimulation of phagocytosis.

Affinity Labels↗
PubMed1991

Migratory arrest of gonadotropin-releasing hormone neurons in transgenic mice.

Gonadotropin-releasing hormone (GnRH) is important in reproduction, although the mechanism of central hypogonadism in humans remains unclear. Because the GnRH neuron originates from the olfactory placode and migrates to the hypothalamus during development, central hypogonadism in humans could be caused by failure in normal migration of GnRH neurons to the hypothalamus. We report that in transgenic mice expression of the simian virus 40 T antigen, driven by the promoter of human GnRH gene, resulted in central hypogonadism due to an arrest in neuronal migration during development and tumor formation along the migratory pathway. This system appears to be an important animal model of hypogonadotropic hypogonadism in humans. Additionally, olfactory bulb tumors from these animals were dispersed, and a GnRH-secreting neuronal cell line (GN cell line) was established.

Animals↗
PubMed1991

Psoralen binding and inhibition of epidermal growth factor binding by psoralen/ultraviolet light (PUVA) in human epithelial cells.

The psoralen analogs 8-methoxypsoralen (8-MOP) and 4,5',8-trimethylpsoralen (TMP), in combination with ultraviolet light (UVA, 320-400 nm), are potent modulators of epidermal cell growth and differentiation and are commonly used in photochemotherapy of psoriasis and vitiligo. We have used KB cells, a human epithelial cell line, to examine the mechanism of action of these compounds. In KB cells, 8-MOP was found to bind to specific, saturable receptor sites. Binding of [3H]-8-MOP to its receptor was inhibited by TMP as well as psoralen. We found that binding of these analogs to the cells followed by UVA light treatment was associated with inhibition of epidermal growth factor (EGF) receptor binding. Inhibition of EGF binding was temperature dependent, occurred immediately following UVA light exposure, and appeared to be due to a decrease in the number of EGF receptors. In KB cells, 125I-labeled EGF surface receptor binding is followed by its rapid internalization and degradation. We found that photoactivated psoralens also inhibited internalization of 125I-EGF, but had no apparent effect on EGF metabolism. These data indicate that the cell surface membrane may be an important target for the photoactivated psoralens. In addition, since photoactivated psoralens regulate cell proliferation, the interaction of these compounds with EGF receptor function may underlie their biological activity.

Binding, Competitive↗
PubMed1991

Aluminum fluoride stimulates inositol phosphate metabolism and inhibits expression of differentiation markers in mouse keratinocytes.

Mouse keratinocytes are induced to differentiate in vitro by elevating the level of extracellular calcium from 0.05 mM, where keratinocytes express a basal cell phenotype, to greater than 0.10 mM, where they express the differentiated phenotype. This process has been associated with a rapid, sustained increase in inositol phosphate (InsP) turnover, which precedes the expression of differentiation-specific proteins. In 0.05 mM Ca2+ medium, aluminum and fluoride salts (AIF4-), which combine to activate nonspecifically heterotrimeric guanine nucleotide-binding (G) proteins, cause a concentration-dependent increase in InsP metabolism in keratinocytes, and generate elevated intracellular diacylglycerol levels. This is associated with an inhibition of cell growth. Treatment with both AIF4- and Ca2+ greater than 0.10 mM resulted in an additive increase in InsP turnover, implying the presence of at least two responsive InsP pools. AIF4- inhibited the expression of differentiation markers induced by Ca2+ greater than 0.10 mM and altered the morphology of keratinocytes from squamous to dendritic, which was reversible upon withdrawal of AIF4-. Neoplastic keratinocytes, in which basal levels of InsP metabolism are higher than in normal cells, do not differentiate in response to Ca2+. Neoplastic keratinocytes responded to AIF-4 treatment with an even greater rise in InsP metabolism. AIF-4 also inhibited cell growth and reversibly altered morphology in neoplastic keratinocytes. These data suggest that InsP metabolism in keratinocytes is at least partially regulated by a G protein mechanism. Furthermore, an increase in InsP metabolism is not sufficient to stimulate differentiation and may be inhibitory to differentiation if exceeding limited increases. However, these observations cannot exclude the possibility that other AIF-4 stimulated pathways involving G or non-G proteins can also influence keratinocyte biology.

Aluminum↗
PubMed1991

Use of the urokinase-type plasminogen activator gene as a general tool to monitor expression in transgenic animals: study of the tissue-specificity of the murine whey acidic protein (WAP) expression signals.

Urokinase-type plasminogen activator (uPA) is a proteolytic enzyme able to convert the zymogen plasminogen into the strong protease plasmin. The availability of very sensitive tests to measure the enzymatic activity of a plasminogen activator renders the corresponding gene an ideal candidate for the detection of promoter activity. In this paper we describe the utilization of the human uPA gene as detector of tissue-specificity of the murine whey acidic protein (WAP) expression signals in transgenic mice. The WAP promoter has been previously investigated for the production of foreign proteins in the milk of transgenic animals. In our genetic constructions, the human uPA cDNA was linked to the promoter region as well as to 3'-end distal sequences of the WAP gene. Five transgenic lines were obtained in which, however, expression levels of human uPA in the milk were still quite low. Surprisingly, four of these five positive transgenic mice show a consistent activity of the WAP promoter in brain extracts compared to other tissues.

Animals↗
PubMed1991

Selective release of glutathione transferase subunits from primary cultured rat hepatocytes by carbon tetrachloride and deoxycholic acid.

The change in the activity of glutathione (GSH) transferases by carbon tetrachloride or deoxycholic acid, which induced hepatotoxicity, was studied using primary cultured rat hepatocytes. The activity of GSH transferases in the hepatocytes was decreased after the treatment with carbon tetrachloride or deoxycholic acid in their concentration- and incubation time-dependent manners. On the other hand, these compounds elicited the release of the activity of GSH transferases into the medium. Glycyrrhizin, an antihepatotoxic agent, inhibited the release of both aspartate transaminase (AST) and GSH transferases induced by carbon tetrachloride or deoxycholic acid. All subunits comprised of GSH transferases could not be released by these compounds. The main subunits of GSH transferases released by hepatotoxicity were identified as 3 and 4. These results indicate that hepatotoxicity is accompanied by the selective release of GSH transferase isozymes (class mu) following the loss of the enzymes activity in the cells.

Animals↗
PubMed1991

Subunit selective alteration of hepatic glutathione transferases in spontaneously hypertensive rats.

1. The activities of glutathione (GSH) transferases in male, spontaneously hypertensive rats (SHR) and stroke-prone rats (SHR-SP) were different from those of normotensive male Wistar Kyoto rats (WKY). 2. These alterations of the enzyme activities were partly due to the changes in the levels of subunits 2 and 4. 3. Subunit selective alterations were observed in pathophysiological conditions, namely spontaneous hypertension. 4. The sex-related difference of GSH transferases in these animals was also discussed.

Animals↗
PubMed1991

The flail mitral valve: echocardiographic findings by precordial and transesophageal imaging and Doppler color flow mapping.

To determine the echocardiographic and Doppler characteristics of mitral regurgitation associated with a flail mitral valve, precordial and transesophageal echocardiography with pulsed wave and Doppler color flow mapping was performed in 17 patients with a flail mitral valve leaflet due to ruptured chordae tendineae (Group I) and 22 patients with moderate or severe mitral regurgitation due to other causes (Group II). Echocardiograms were performed before or during cardiac surgery; cardiac catheterization was also performed in 28 patients (72%). Mitral valve disease was confirmed at cardiac surgery in all patients. By echocardiography, the presence of a flail mitral valve leaflet was defined by the presence of abnormal mitral leaflet coaptation or ruptured chordae. Using these criteria, transesophageal imaging showed a trend toward greater sensitivity and specificity than precordial imaging in the diagnosis of flail mitral valve leaflet. By Doppler color flow mapping, a flail mitral valve leaflet was also characterized by an eccentric, peripheral, circular mitral regurgitant jet that closely adhered to the walls of the left atrium. The direction of flow of the eccentric jet in the left atrium distinguished a flail anterior from a flail posterior leaflet. By transesophageal echocardiography with Doppler color flow mapping, the ratio of mitral regurgitant jet arc length to radius of curvature was significantly higher in Group I than Group II patients (5.0 +/- 2.3 versus 0.7 +/- 0.6, p less than 0.001); all of the Group I patients and none of the Group II patients had a ratio greater than 2.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Chordae Tendineae↗
PubMed1991

Changes in inositol phosphate metabolism are associated with terminal differentiation and neoplasia in mouse keratinocytes.

Cultured murine keratinocytes respond to specific Ca2+ levels in medium (Ca0) by expressing markers of terminal differentiation. A Ca0 of 0.05 mM selects for a basal cell phenotype, whereas spinous cell characteristics occur in 0.12 mM Ca2+ and cornified envelopes develop in 1.0 mM Ca2+. An increase in inositol phosphate (InsP) metabolism is associated with higher Ca2+ in the medium. The magnitude of Ca(2+)-stimulated InsP turnover is Ca0-dependent, whereas Ca0 of 0.05, 0.12 or 1.4 mM resulted in a graded, sustained (greater than 24 h) increase in InsPs. Diacylglycerol (DAG) levels similarly increased in a graded manner. The major inositol trisphosphate (InsP3) to accumulate was Ins-1,3,4-P3 while Ins-1,4,5-P3 increased transiently. Neoplastic keratinocyte cell lines, 308 and SP-1, which produce benign tumors and have a mutated c-rasHa gene, do not express markers of differentiation in response to Ca2+. Basal InsP and DAG are 2- and 5-fold higher respectively in the neoplastic cells relative to normal keratinocytes. However, the metabolic profiles of InsPs were similar in normal and neoplastic cells. In neoplastic cells, InsP metabolism was stimulated even further following a Ca2+ increase, and this was graded to the Ca0. The unusual, sustained Ca(2+)-graded InsP response in normal cells is consistent with the turnover of InsP contributing to the signals controlling expression of markers of differentiation. Very high InsP turnover and DAG levels, as in neoplastic cells, may be inhibitory to marker expression.

Animals↗
PubMed1991

Intraoperative estimation of cardiac output by transesophageal pulsed Doppler echocardiography.

To determine whether transesophageal echocardiography could be used to estimate intraoperative cardiac output, the authors studied 35 consecutive patients undergoing cardiovascular surgery (coronary artery disease [n = 22], aortic valve disease [n = 5], mitral valve stenosis [n = 5], peripheral vascular disease [n = 3]). Two-dimensional echocardiographic and pulsed-wave Doppler signals of the pulmonary artery and mitral valve flow velocity were obtained simultaneously with thermodilution measurements of cardiac output. Cardiac output derived from pulsed Doppler imaging of pulmonary artery systolic flow velocity modestly correlated with the thermodilution-derived cardiac output (r = 0.65), but output determined from the mitral valve diastolic flow velocity did not (r = 0.24). Transesophageal echocardiography of pulmonary artery systolic flow satisfactorily detected intraoperative increases in cardiac output greater than 15% (sensitivity, 71%; specificity, 82%) but not decreases (sensitivity, 54%; specificity, 90%). Although this technique identifies increases in cardiac output greater than 15%, it does not detect decreases as accurately as those detected by thermodilution measurements. At this time, therefore, transesophageal Doppler echocardiography has significant limitations as an off-line monitor of cardiac output.

Adult↗
PubMed1991

Effects of methanol vapors on testosterone production and testis morphology in rats.

Potential toxic effects of methanol vapors on testicular production of testosterone and the morphology of testes were investigated using normal or methanol-sensitive folate-reduced rats. Methanol inhalation at the level of the current permissible exposure limit, 200 ppm, for up to six weeks (8 hours/day, 5 days/week), did not reduce serum testosterone levels in normal rats. Testes isolated from methanol-exposed (200 ppm) rats had the same capability as those from air-exposed rats in synthesizing testosterone whether testes were incubated in the absence or presence of hCG. The testes-to-body weight ratio of rats exposed up to 800 ppm methanol for up to 13 weeks (20 hours/day, 7 days/week) were not different from those of the air-exposed rats. Furthermore, methanol had no adverse effect on testicular morphology at the end of the 13 week exposure period at 800 ppm in either normal rats or folate-reduced methanol-sensitive rats when they were 10 months old at the time of examination. Thus, these data indicate that low level methanol may not cause an inhibitory effect on testosterone synthesis contrary to previous literature reports. However, a greater incidence of testicular degeneration was noticed in the 18 month old folate-reduced rats exposed to 800 ppm for 13 weeks (20 hours/day, 7 days/week), suggesting that methanol may have a potential to accelerate the age-related degeneration of the testes.

Administration, Inhalation↗
PubMed1991

Alterations in epidermal biochemistry as a consequence of stage-specific genetic changes in skin carcinogenesis.

The induction of cancer on mouse skin by initiation-promotion protocols occurs through stages in which a benign squamous papilloma is an obligate precursor of squamous cell carcinoma. Activation of the Ha-ras gene is sufficient to produce the papilloma phenotype, while additional genetic changes are required for malignant conversion. The introduction of Ha-ras into normal keratinocytes suppresses the expression of differentiation markers, keratin K1 and K10, and loricrin (a cornified envelope precursor) and, to a lesser extent, filaggrin, at the level of transcription. However, cells initiated by Ha-ras express a nonepidermal keratin, K8. The transcription of K8 in these cells is sensitive to the level of medium Ca2+, being abundant in 0.5 mM Ca2+ and not detected in 0.05 mM Ca2+. Epidermal differentiation is regulated by signalling, which involves changes in phosphatidylinositol turnover and intracellular Ca2+. Cells initiated by Ha-ras do not differ from normal keratinocytes in their intracellular Ca2+ response patterns, at least in response to changes in extracellular Ca2+ and serum factors. However, c-Ha-ra keratinocytes have a high basal level of phosphatidylinositol (PI) turnover, which is additive with several other inducers of this pathway, including Ca2+ and aluminum fluoride. Additional studies suggest that high turnover of the PI pathway is incompatible with differentiation-specific gene expression in keratinocytes. We suggest this negative relationship is mediated through elevated diacylglycerol production and chronic down-modulation of protein kinase C. Protein kinase C is known to be essential for expression of differentiation-related genes in keratinocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Seroprevalence of antibodies to the hepatitis C virus in Singapore.

The prevalence of antibodies to the hepatitis C virus (anti-HCV) in Singapore was assessed using a recombinant-based enzyme linked immunoassay system. 1004 serum samples were obtained from normal subjects (463), hemodialysis patients (112), hepatitis B virus (HBV) carriers (188), patients with hepatocellular carcinoma (HCC) (58) and patients with non-hepatitis B virus related liver diseases (183). Anti-HCV was found to be positive in 1.7% of healthy subjects, and in 20% of patients on regular hemodialysis. Three percent of HBV carriers were positive for anti-HCV. Twelve percent of patients with acute hepatitis with no known causes and 20% patients with chronic hepatitis with no known causes were positive for anti-HCV. Among patients with cirrhosis for which no known causes were found 33% were positive for anti-HCV. Thirty six percent of patients with HCC not associated with the presence of HBsAg were positive of anti-HCV. None of the patients with known causes of liver disease were positive for anti-HCV.

Adolescent↗
PubMed1990

Drosophila melanogaster contains a single calmodulin gene. Further structure and expression studies.

We have previously characterized a calmodulin gene from the organism Drosophila melanogaster. In the higher vertebrates a multi-gene system for encoding calmodulin is present and, in at least one invertebrate species, genes encoding highly related calmodulin isotypes exist. We have therefore searched for additional calmodulin genes within D. melanogaster. Although our searches were sensitive enough to detect a relatively divergent gene encoding a calmodulin family protein, we were unable to detect any additional genes for calmodulin per se. Further studies of the structure and expression of the single calmodulin gene of D. melanogaster have established that the gene contains a tiny additional 5' exon encoding only 50 residues of the 5' leader. Sequencing at the 3' terminus has established that the two transcript size classes derived from the gene are produced as a result of alternative polyadenylation site usage. The relative abundance of the two size classes of mRNAs differs throughout the life cycle, indicating developmental regulation of polyadenylation site usage.

Amino Acid Sequence↗
PubMed1990

Human and murine urokinase cDNAs linked to the murine alpha A-crystallin promoter exhibit lens and non-lens expression in transgenic mice.

cDNAs encoding either the human or the murine urokinase-type plasminogen activator (uPA) were fused downstream from the promoter-enhancer element of the murine gene encoding alpha A-crystallin, a protein found exclusively in the ocular lens. The DNAs were microinjected into fertilized mouse eggs as linear fragments free of bacterial sequences, and for each construct one line of transgenic mice was generated. In both lines transgenic uPA activity was detected in the ocular lens, in agreement with previous results reported on transgenic mice bearing genes fused to the same regulatory region. Unexpectedly however relatively high levels of this activity were found also in the retina, and furthermore, human uPA activity was found also in different parts of the brain and in the bone marrow, and to a lesser extent in the spleen, thymus and optic nerve. Transgenic uPA transcript was found in the lens, retina, brain and thymus of mice carrying the murine cDNA. Such a pattern of expression was different from that exhibited by the endogenous murine uPA gene and, excluding the lens, it appeared to be conferred by the cDNAs. The putative regulation by uPA cDNAs is suggested to be mediated through an internal enhancer-like element functioning in combination with the alpha A-crystallin promoter in a fashion independent of the specific nature of the promoter.

Animals↗