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Biomedical subjects

A Shih

Publications and source records attributed to A Shih.

At least 37 records · Page 2Linked to original sources
PubMed1997

AL-1-induced growth cone collapse of rat cortical neurons is correlated with REK7 expression and rearrangement of the actin cytoskeleton.

Previous experiments identified AL-1 as a glycosylphosphatidylinositol (GPI)-linked ligand for the Eph-related receptor, REK7, and showed that a REK7-IgG fusion protein blocks axon bundling in co-cultures of cortical neurons on astrocytes, suggesting a role for REK7 and AL-1 in axon fasciculation. Subsequent identification of RAGS, the chick homologue of AL-1, as a repellent axon guidance molecule in the developing chick visual system led to speculation that AL-1, expressed on astrocytes, provides a repellent stimulus for cortical axons, inducing them to bundle as an avoidance mechanism. Using a growth cone collapse assay to test this hypothesis, we show that a soluble AL-1-IgG fusion protein is a potent collapsing factor for embryonic rat cortical neurons. The response is strongly correlated with REK7 expression, implicating REK7 as a receptor mediating AL-1-induced collapse. Morphological collapse is preceded by an AL-1-IgG-induced reorganization of the actin cytoskeleton that resembles the effects of cytochalasin D. This suggests a pathway whereby REK7 activation by AL-1 leads to perturbation of the actin cytoskeleton, possibly by an effect on actin polymerization, followed by growth cone collapse. We further show that AL-1-IgG causes collapse of rat hippocampal neurons and rat retinal ganglion cells. These data suggest a role for REK7 and AL-1 in the patterning of axonal connections in the developing cortex, hippocampus and visual system.

Actins↗
PubMed1996

Prenatal diagnosis in a Chinese family with type Ia glycogen storage disease by PCR-based genetic analysis.

Type Ia glycogen storage disease (GSD), an autosomal recessive metabolic disorder, is caused by a deficiency in glucose-6-phosphatase (G6Pase). We had previously identified the nature of the causative mutations in a Chinese family whose first two children were affected with type Ia GSD. Two different point mutations in the G6Pase gene, a guanine to adenine substitution at base position 327 in exon 2 and a thymine to adenine substitution at base position 1101 in exon 5, change the restriction sites for the enzymes Fok I and Hinc II. Family study revealed that both parents were heterozygous carriers: the father with a mutant G6Pase allele at exon 2 and the mother with another mutant G6Pase allele at exon 5. This paper deals with a prenatal diagnosis on the fetus of this family who is at risk of type Ia GSD. Genomic DNA was extracted from a chorionic villus biopsy sampled at the tenth week of gestation. Exons 2 and 5 of the G6Pase gene were amplified by the polymerase chain reaction (PCR) followed by restriction enzyme digestion and direct sequence analysis. DNA analysis indicated that the fetus was a heterozygous carrier of type Ia GSD with a mutant G6Pase allele at exon 2 and a normal G6Pase allele at exon 5. The diagnosis was further confirmed by the same method with cultured amniocytes and with a blood sample after the baby was born. This is the first report of prenatal carrier detection of type Ia GSD at the gene level.

Chorionic Villi Sampling↗
PubMed1996

Effect of acute ketoacidosis on the myocardium in diabetes.

Abnormalities of left ventricular function are often present in patients with diabetes who are in a stable metabolic state. To determine whether acute metabolic abnormalities may contribute to pathogenesis, patients with diabetes and ketoacidosis (Group 1) or hyperglycemia without ketosis (Group 2) were studied. They were assessed noninvasively for evidence of acute injury or dysfunction of the myocardium. Left ventricular function was assessed on admission and after clinical recovery. Myocardial enzyme release was examined during the acute phase. In Group 1, plasma glucose averaged 32 mM/L and carbon dioxide content 12.4 mEq/L. On echocardiography, the initial circumferential shortening velocity of 1.85 + 0.07 circumferences per second was significantly higher than the final circumferential shortening velocity of 1.31 + 01 (P < 0.005). The systolic time interval ratio, pre-ejection period/left ventricular ejection time, was significantly lower on the initial day compared with the second study. These data are consistent with enhanced ventricular performance. In group 2, plasma glucose averaged 29 mM/L, and carbon dioxide content was normal. The initial circumferential shortening velocity of 1. 1 circumferences per second and pre-ejection period/left ventricular ejection time ratio of 0.38 were normal and remained unchanged. There was no significant alteration of heart rate or arterial pressure in either group. In both groups, total serum lactate dehydrogenase and creatinine phosphokinase levels, as well as their cardiac isoenzymes, were within normal limits. Therefore, the initial increase of myocardial performance and subsequent restoration to normal, as well as the lack of cardiac enzyme increase in plasma, support the view that shortterm ketoacidosis does not contribute to the abnormalities of ventricular function in diabetes.

Acute Disease↗
PubMed1996

Gastrin regulates growth of human pancreatic cancer in a tonic and autocrine fashion.

The gastrointestinal peptides gastrin and cholecystokinin (CCK) stimulate growth of human pancreatic cancer through a CCK-B/gastrin- like receptor. In the present study we evaluated whether growth of human pancreatic cancer is endogenously regulated by gastrin. Immunohistomical examination of BxPC-3 cells and tumor xenografts revealed specifc gastrin immunoreactivity. Gastrin was detected by radioimmunoassay in pancreatic cancer cell extracts and in pancreatic cancer cell extracts and in the growth media. With use of reverse-transcriptase polymerase chain reaction gastrin gene expression was detected in both cultured BxPC-3 cancer cells and transplanted tumors, as well as seven addition human pancreatic cancer cell lines. Growth of BxPC-3 human pancreatic cancer cell in serum-free medium was inhibited by the addition of the CCK-B/gastrin receptor antagonist L-365,260, and gastrin treatment reversed the inhibitory effect of the antagonist. A selective gastrin antibody (Ab repressed growth of BxPC-3 cells. Gastrin immunoreactivity was detected in fresh human pancreatic cancer specimens but not in normal human pancreatic tissue. These data provide the first evidence that growth of a human pancreatic cancer is tonically stimulated by the autocrine production of gastrin. Evidence for the ubiquity of this system was provided by the detection of gastrin gene expression in multiple human pancreatic cancer cell lines and detection of gastrin in cell lines and fresh pancreatic tumors.

Animals↗
PubMed1996

Exogenous Fibronectin to Prevent Neointimal Hyperplasia after Balloon Angioplasty.

This study examined the effect of fibronectin to prevent restenosis in a microswine model after balloon angioplasty of the right iliac artery. Immediately following angioplasty, fourteen hypercholesterolemic microswines were randomized to receive fibronectin (223.5 mg, n = 8) or saline containing albumin (75.6 mg, n = 6). At 60-days post-angioplasty, the angioplasty-injured and intact contralateral arteries were examined with angiography and histopathology. With angiography, there was no significant difference in the luminal diameters of angioplasty arteries compared with the intact contralateral vessels. Histological examination of angioplasty-injured vessels showed neointimal hyperplasia. The intimal areas of angioplasty-injured vessels, in the placebo and fibronectin groups, were much larger than the areas of their contralateral vessels (fibronectin 287 +/- 160 vs. 138 +/- 88 µm2, p = 0.018; and the placebo (1,245 +/- 1,567 vs. 248 +/- 219 µm2, p = 0.041). Mean total cholesterol levels of both groups were maintained at levels > 400 mg/dl throughout the study period. CONCLUSION: At sixty days after balloon angioplasty injury: 1) fibronectin did not only not prevent neointimal hyperplasia, in some animals, it increased neointimal growth; and 2) angiographic results were not sensitive enough to quantify changes observed in histologic findings.

Journal Article↗
PubMed1995

Overexpression or mutation of the p53 tumor suppressor gene does not occur in malignant ovarian germ cell tumors.

BACKGROUND: The p53 tumor suppressor gene has been well studied in epithelial ovarian cancers. However, little is known of the expression of this gene in ovarian germ cell tumors. The authors attempted to investigate whether p53 alterations occurred in this group of tumors. METHODS: Twenty-two patients with malignant ovarian germ cell tumors were included in this study. Immunohistochemical staining for p53 was performed on paraffin embedded tissue of each case. Single-strand conformation polymorphism analysis of exons 4-9 of the p53 gene was performed on 9 of the 22 tumors where genomic DNAs were obtained from the frozen tissue samples. Three tumors that revealed focal p53 positivity by immunostaining were studied further with direct DNA sequencing. RESULTS: Overexpression of p53 was not observed in all of the 22 ovarian germ cell tumors; only 3 were found to have nuclear staining in a small fraction of the malignant cells (< 5% in 1 immature teratoma, 5-10% in 2 yolk-sac tumors). Among the nine frozen tumors subjected to single-strand conformation polymorphism analysis, none revealed p53 mutation in exons 4-9. There was no p53 mutation detected by DNA sequencing of the three tumors with focal immunoreactivity. CONCLUSIONS: Alterations of the p53 tumor suppressor gene may not be associated with the pathogenesis of ovarian germ cell tumors. Instead, genetic changes such as inactivation of other tumor suppressor genes and/or activation of some protooncogenes need to be studied to determine the genetic mechanisms of the tumor development.

Adolescent↗
PubMed1995

Cloning of AL-1, a ligand for an Eph-related tyrosine kinase receptor involved in axon bundle formation.

REK7 is an Eph-related tyrosine kinase receptor expressed exclusively in the nervous system, predominantly in hippocampus and cortex. A soluble REK7-IgG fusion protein, produced to analyze the biological role of REK7, prevents axon bundling in cocultures of cortical neurons with astrocytes, a model of late stage nervous system development and differentiation. Using REK7-IgG as an affinity reagent, we purified and cloned a novel REK7 ligand called AL-1, a GPI-linked protein homologous to other members of an emerging ligand family. Membrane attachment of AL-1 appears necessary for receptor activation, since REK7 on cortical neurons is efficiently activated by transfected cells expressing GPI-linked AL-1, but not by soluble AL-1. Consistent with this, soluble AL-1 blocks axon bundling. Our findings, together with the observation that both molecules are expressed in the brain, suggest a role in the formation of neuronal pathways, a crucial feature of nervous system development and regeneration.

Amino Acid Sequence↗
PubMed1995

Separate domains of the Ran GTPase interact with different factors to regulate nuclear protein import and RNA processing.

The small Ras-related GTP binding and hydrolyzing protein Ran has been implicated in a variety of processes, including cell cycle progression, DNA synthesis, RNA processing, and nuclear-cytosolic trafficking of both RNA and proteins. Like other small GTPases, Ran appears to function as a switch: Ran-GTP and Ran-GDP levels are regulated both by guanine nucleotide exchange factors and GTPase activating proteins, and Ran-GTP and Ran-GDP interact differentially with one or more effectors. One such putative effector, Ran-binding protein 1 (RanBP1), interacts selectively with Ran-GTP. Ran proteins contain a diagnostic short, acidic, carboxyl-terminal domain, DEDDDL, which, at least in the case of human Ran, is required for its role in cell cycle regulation. We show here that this domain is required for the interaction between Ran and RanBP1 but not for the interaction between Ran and a Ran guanine nucleotide exchange factor or between Ran and a Ran GTPase activating protein. In addition, Ran lacking this carboxyl-terminal domain functions normally in an in vitro nuclear protein import assay. We also show that RanBP1 interacts with the mammalian homolog of yeast protein RNA1, a protein involved in RNA transport and processing. These results are consistent with the hypothesis that Ran functions directly in at least two pathways, one, dependent on RanBP1, that affects cell cycle progression and RNA export, and another, independent of RanBP1, that affects nuclear protein import.

Amino Acid Sequence↗
PubMed1994

Mutagenesis identifies amino-terminal residues of nerve growth factor necessary for Trk receptor binding and biological activity.

Limited proteolysis and site-directed mutagenesis of human nerve growth factor (hNGF) was utilized to determine the role of the NH2 terminus in p140TrkA (TrkA) receptor function. Purified (6-118)hNGF, representing deletion of the first 5 NH2-terminal residues, is 9-fold less potent than (1-118)hNGF in displacing 125I-hNGF from TrkA. The deletion of a further 4 residues to form (10-118)hNGF is nearly 300-fold less potent. (6-118)hNGF is only 2-4-fold less potent than (1-118)hNGF in eliciting TrkA autophosphorylation and PC12 cell neurite outgrowth, suggesting that the first 5 residues of the NH2 terminus are necessary for full TrkA binding activity but may be less critical for potent receptor activation and intracellular signaling. In contrast, purified mutant H4D results in a nearly 1000-fold loss in TrkA binding at 4 degrees C relative to (1-118)hNGF, at least 10-fold less potency of TrkA autophosphorylation, and 30-fold loss of potency in PC12 cell differentiation. NH2-terminal hBDNF/hNGF and hNT3/hNGF chimeric mutants further affected these activities suggesting that the NH2-terminal sequence specificity of hNGF contributes to structural interactions necessary for TrkA receptor binding and ligand-induced signaling. The potency of binding of all hNGF variants to the low affinity NGF receptor p75 was largely unaffected indicating distinct structural contributions of the NH2-terminal region of hNGF to the binding to TrkA versus p75.

Amino Acid Sequence↗
PubMed1994

Clinical and angiographic variables affecting the progression of coronary artery disease as determined by quantitative angiography.

To assess by serial quantitative angiography, the significance of clinical and angiographic variables that affect the progression of coronary artery disease (CAD). Progression of disease by sequential angiography is unpredictable and the role of clinical risk factors controversial. Various intervention trials have demonstrated less progression and even regression in hyperlipidemic patients. Correlates of progression have included a younger age, unstable angina, and greater involvement of the coronary arteries, with few studies looking at angiographic features of individual lesions. Serial angiograms on 74 patients were analyzed by computer assisted quantitative angiography using absolute measurements. A total of 99 diseased segments were analyzed for progression defined as an absolute reduction of 20% in luminal cross-sectional area. A preliminary correlation coefficient was calculated for each of the clinical and angiographic variables to detect any association with progression, and the odds ratio determined. The presence of any of the clinical risk factors-diabetes, hypertension, serum cholesterol, smoking, and a family history of coronary disease could not predict progression. The use of beta blockers was three times less likely to be associated with progression (odds ratio 0.33). While the presence of distal disease was associated with progression of a more proximal lesion (odds ratio 2.4), eccentricity, branch point location, lesion length, calcification, thrombus, or the presence of collaterals did not influence progression of disease in an individual segment. In conclusion, the presence of any of the clinical risk factors could not predict progression of disease in an individual coronary segment as determined by serial quantitative angiography, and the use of beta blockers and the absence of coexistent distal disease was associated with less progression of disease in an individual coronary segment. This may be related to changes in wall stress, reduced platelet interactions, and the integrity and permeability of the vascular endothelium to lipids.

Adrenergic beta-Antagonists↗
PubMed1993

Is the left main angulated, stenosed, or "bent" by the guiding catheter?

Exact angiographic and identification of significant stenosis of the left main coronary artery is imperative prior to performing elective percutaneous transluminal coronary angioplasty. A patient is presented with an apparent angiographically significant, but physiologically insignificant, left main stenosis. Both angiographic and physiological methods of detecting "false positive and negative" left main stenoses are discussed.

Aged↗
PubMed1993

A prospective randomized trial of Novoste right versus Judkins catheters for engagement of the right coronary artery during diagnostic catheterization.

There has been little technical advancement in catheter shape for diagnostic cardiac catheterization since the early reports of Sones and colleagues during the development of the procedure. In order to determine the utility of a new catheter that directly, without torque or rotation, engages the right coronary artery (RCA), one hundred patients were randomized between 6Fr standard RCA Judkins (6Fr R4) (Cordis Corporation, Miami, FL, USA) or 6Fr Novoste RCA catheters (Novoste Corporation, Aguadilla, Puerto Rico). Endpoints included the duration of the various aspects of the procedure and a qualitative and quantitative assessment of angiographic quality. The Novoste RCA catheters were associated with statistically decreased times of catheter insertion (42 +/- 37 vs 90 +/- 119 secs), and engagement (31 +/- 35 vs 77 +/- 117 secs), of the right coronary artery as compared to Judkins catheters. Judkins RCA catheters had a significantly higher primary success rate (96%) than the Novoste group (84%, P = 0.045). There was no difference in angiographic quality in either group and no complications occurred during the study. While taller patients (mean 68 in) had increased success with the Novoste catheter, no other clinical, demographic, or anatomical characteristics of the RCA orifice predicted successful engagement and angiography. The direct engagement Novoste RCA catheter is associated with a more expeditious procedure than Judkins catheters when they can engage the RCA orifice. However, Novoste catheters were less successful and required more frequent exchanges to complete the procedure.

Adult↗
PubMed1992

Human seminal relaxin is a product of the same gene as human luteal relaxin.

Unlike that of other species, which have only one gene encoding relaxin, the human genome contains two nonallelic genes for relaxin, designated H1 and H2, which encode markedly different relaxin peptides. Whereas human relaxin gene H2 is selectively expressed in the ovary, no ovarian expression of gene H1 has been detected. Since relaxin is actively produced in the human male, it is possible to postulate divergent gene expression of relaxin in the male and female. We examined this question directly through the structural determination of human seminal relaxin and its comparison with the structure of human luteal relaxin. Partially purified relaxin, prepared from pooled human seminal plasma which had been delipidated by extraction with acid acetone and hexane, subjected to two cycles of HPLC and an additional purification step by ion-exchange chromatography, was further purified by immunoaffinity chromatography, using a monoclonal antibody to the H2 relaxin A chain which cross-reacts with synthetic H1 relaxin, followed by an additional HPLC step performed on a C4 reverse-phase column. The recovered, purified relaxin was then analyzed by N-terminal gas-phase sequencing and fast atom bombardment mass spectroscopy for determination of the amino acid sequence and molecular ions of the A and B chains, respectively. The results demonstrate that the structure of the predominant relaxin in human semen plasma is derived from the product of the H2 gene, consisting of a N-terminal pyroglutamic acid A-24 A chain and a mixture of B-26 and B-27 B chains. With the exception of degradation of the seminal relaxin B chain C-terminus, this structure is identical to the structure of human luteal relaxin. Therefore, both human seminal and luteal relaxin are products of the H2 gene.

Amino Acid Sequence↗