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Biomedical subjects

A Chen

Publications and source records attributed to A Chen.

At least 19 recordsLinked to original sources
PubMed1996

Raf and mitogen-activated protein kinase regulate stellate cell collagen gene expression.

Hepatic stellate cells become activated into myofibroblast-like cells during the early stages of hepatic injury associated with fibrogenesis. The subsequent dysregulation of hepatic stellate cell collagen gene expression is a central pathogenetic step during the development of cirrhosis. The cytoplasmic Raf and mitogen-activated protein (MAPK) kinases were found to differentially regulate alpha I(I) collagen gene expression in activated stellate cells. This suggests an unappreciated branch point exists between Raf and MAPK. A MAPK-stimulatory signal was mapped to the most proximal NF-1 and Sp-1 binding domains of the 5'-untranslated region of the collagen gene. A Raf-inhibitory signal was mapped to a further upstream binding domain involving a novel 60-kDa DNA-binding protein (p60). The cell-specific expression and induction of p60 in stellate cells during the early stages of hepatic fibrogenesis in vivo suggest a central role for this pathway during liver injury and stellate cell activation.

Animals↗
PubMed1996

Identification of the gltX gene encoding glutamyl-tRNA synthetase from Methanobacterium thermoautotrophicum.

The gltX gene encoding glutamyl-tRNA synthetase from Methanobacterium thermoautotrophicum has been cloned, sequenced, and identified. The gene is located immediately downstream of idsA in an operon containing at least three additional ORFs. The deduced protein sequence from gltX contains conserved regions (HIGH and KMSKS) indicative of a class I aminoacyl-tRNA synthetase.

Amino Acid Sequence↗
PubMed1996

Flutamide-induced liver toxicity including fatal hepatic necrosis.

PURPOSE: To describe hepatic injuries in three patients who received flutamide prior to and during radiation treatment to make radiation oncologists aware of the need for careful monitoring of liver function during use of this drug. METHODS AND MATERIALS: The records of three patients who developed abnormal liver function tests while undergoing total androgen suppression (TAS), as well as the literature concerning flutamide toxicity were reviewed and summarized. RESULTS: Three of 34 patients treated with a TAS regimen incorporating flutamide developed significant hepatic abnormalities: elevated transaminases [2] and fatal hepatic necrosis [1]. Following the discontinuation of flutamide, two patients recovered fully. Unfortunately, the third patient's hepatic function continued to deteriorate, which culminated in his death. Transient elevations in serum transaminases, which do not exceed four times the upper limits of normal, are common and apparently without clinical significance. Unfortunately, idiosyncratic serious and/or fatal liver damage can occur. Significant liver toxicity may be obviated by monitoring of liver function tests (LFT) early in the course of flutamide therapy. CONCLUSION: The incidence of hepatic toxicity associated with flutamide may be higher than previously suggested. To prevent the development of serious hepatic dysfunction, all patients receiving flutamide should be monitored clinically for signs and symptoms referable to hepatic injury and with serial LFT. We recommend baseline LFT followed by serial LFT at weeks 2, 4, 6, and 8 from the start of treatment with flutamide. Flutamide should be stopped promptly if significant liver abnormalities are detected.

Adenocarcinoma↗
PubMed1996

Methylprednisolone administration improves axonal regeneration into Schwann cell grafts in transected adult rat thoracic spinal cord.

Schwann cell (SC) grafts support the regeneration of axons of numerous spinal cord neurons when placed into transected adult rat midthoracic spinal cord. Clinically, methylprednisolone (MP) has been shown to be neuroprotective if administered within 8 h after spinal cord injury. We investigated whether axonal regrowth into SC grafts is enhanced when MP is administered at the time of spinal cord transection and SC implantation. SCs from adult rat sciatic nerves were purified in culture, suspended in Matrigel, and drawn into semipermeable polymeric channels. MP (30 mg/kg) or vehicle (control) was administered intravenously at 5 min, 2 h, and 4 h to adult Fischer rats after transection at T8 and removal of the next three caudal segments. The rostral cord stump was inserted 1 mm into the channel; the distal end of the channel was capped. Thirty to forty-five days later, the SC/MP group showed large tissue cables in the channels and host cord tissue retained in the rostral end of the channels. Significantly more myelinated axons (1159 +/- 308) were present at the 5-mm level in SC/MP grafts (n = 6) than in SC/vehicle cables (355 +/- 108, n = 5). More unmyelinated than myelinated axons (approximately 4:1, n = 3) were resolved in the cables by electron microscopy. In the SC/MP group, unlike the SC/vehicle group, serotonergic and noradrenergic fibers were detected immunocytochemically 2.5 and 2.0 mm respectively, into the graft; astrocytes were also identified at similar distances from the interface. Fast Blue retrograde tracing (SC/MP, n = 4; SC/vehicle, n = 3) showed that more spinal cord neurons (1116 +/- 113 vs 284 +/- 88, respectively) and spinal cord neurons more distant from the graft (C8 vs C5) responded by extending axons into the graft in the presence of MP. Also, very significantly, supraspinal brain stem neurons extended axons into the graft only when MP was administered (mean 46 vs 0, n = 3). These results indicate that MP improves axonal regenerationn from both spinal cord and brain stem neurons into thoracic SC grafts, possibly by reducing secondary host tissue loss adjacent to the graft.

Animals↗
PubMed1996

Pharmacology of L-744,453, a novel nonpeptidyl endothelin antagonist.

L-744,453 ((+/-)3-[4-(1-carboxy-1-(3,4-methylenedioxyphenyl)methoxy)-3,5-diprop ylphenyl methyl]-3H-imidazo[4,5-c]pyridine) is an endothelin (ET) receptor antagonist from a new structural class, the dipropyl-alpha-phenoxyphenylacetic acid derivatives. L-744,453 competitively and reversibly inhibits [125I]-ET-1 binding to Chinese Hamster Ovary cells expressing cloned human ET receptors (K(i)s: hET(A)=4.3 nM; hET(B)=232 nM), and is selective for endothelin receptors compared to other peptide receptors. It is an antagonist of ET-1 stimulated phosphatidyl inositol hydrolysis in rat uterine slices (IC50=220 nM) and exhibits no agonist activity. This compound also inhibits ET-1 stimulated contraction of rat aortic rings with a K(b) value of 50 nM. L-744,453 protects against ET-1 induced lethality in mice after i.v. (AD50=13 mg/kg i.v.) or oral administration. This compound also antagonizes ET-1 induced increases in diastolic blood pressure in conscious normotensive rats (AD50=0.67 mg/kg i.v.) and anesthetized ferrets (AD50=1.6 mg/kg i.v.). L-744,453 is a potent, selective, orally active endothelin antagonist which may be useful in elucidating the role of endothelin in normal and pathophysiological states.

Animals↗
PubMed1996

Sialosyl-Tn antigen is prevalent and precedes dysplasia in ulcerative colitis: a retrospective case-control study.

BACKGROUND & AIMS: Expression of the carbohydrate-associated sialosyl-Tn (STn) antigen has been correlated with carcinogenesis in sporadic colon cancer. This retrospective study analyzed surveillance colonoscopy biopsy specimens to determine whether STn antigen could serve as a marker for neoplasia risk in patients with long-standing ulcerative colitis. METHODS: Eleven patients who developed dysplasia or cancer and who had undergone at least three surveillance colonoscopies were matched with 11 controls who had not developed neoplasia. Sections from 969 available surveillance biopsy specimens were stained immunohistochemically with monoclonal antibody TKH2 and were interpreted blindly. RESULTS: Compared with controls, patients expressed STn antigen more frequently in their biopsy specimens (44% patient biopsy specimens vs. 11% control biopsy specimens). Patients were also more likely to undergo colonoscopies with two or more colonic segments expressing STn antigen (73% vs. 22%), repeated STn antigen expression in two or more consecutive colonoscopies (91% vs. 27%), and STn antigen expression proximal to the hepatic flexure (64% vs. 0%). STn antigen appearance preceded the detection of neoplasia by 7 or fewer years, and its preferential expression in patients was not confounded by the degree of active inflammation. CONCLUSIONS: Repeated STn antigen expression in nondysplastic colonic mucosa may presage the development of neoplasia in long-standing ulcerative colitis and may be a useful adjunct to dysplasia during colonoscopic surveillance.

Adult↗
PubMed1996

Phase I and pharmacologic study of 9-aminocamptothecin given by 72-hour infusion in adult cancer patients.

PURPOSE: To conduct a phase I and pharmacologic study of the new topoisomerase I inhibitor, 9-aminocamptothecin (9-AC). PATIENTS AND MATERIALS: A 72-hour infusion of 9-AC was administered every 14 days to 48 solid-tumor patients at doses of 5 to 59 microg/m2/h without granulocyte colony-stimulating factor (G-CSF) and 47 to 74 microg/m2/h with G-CSF. RESULTS: Without G-CSF, two of eight patients who received 47 microg/m2/h had dose-limiting neutropenia in their initial cycle, as did both patients who received 59 microg/m2/h (with a platelet count < 25,000/microL in one). With G-CSF, zero of seven patients treated with 47 microg/m2/h had dose-limiting neutropenia in their first cycle, while dose-limiting neutropenia occurred in six of 14 patients (with platelet count < 25,000/microL in five) entered at 59 microg/m2/h. Among 39 patients entered at > or = 25 microg/m2/h 9-AC with or without G-CSF, fatigue, diarrhea, and nausea/vomiting of grade 2 severity ultimately occurred in 54%, 30%, and 38%, respectively, while grade 3 toxicities of each type occurred in 8% of patients. Steady-state 9-AC lactone concentration (Css) increased linearly from 0.89 to 10.6 nmol/L, and correlated strongly with leukopenia ( r = .85). CONCLUSION: The recommended phase II dose of 9-AC given by 72-hour infusion every 2 weeks is 35 microg/m2/h without G-CSF or 47 microg/m2/h with G-CSF support. Dose escalation in individual patients may be possible according to their tolerance.

Adult↗
PubMed1996

Monomeric immunoglobulin A protects glomerulus against polymeric immunoglobulin A immune complex in experimental immunoglobulin A nephropathy.

Polymeric (p) IgA constitutes 13% of total serum IgA, whereas monomeric (m) IgA represents the other 87%. pIgA tends to form complexes in the circulation that eventually localize in the glomerulus. mIgA is a nonprecipitable antibody. When complexed with an antigen in vivo, the circulating mIgA immune complex (IC) thus formed does not deposit in the glomerulus. The purpose of the present study was to evaluate the influence of mIgA on the formation of pIgA-lC and subsequent glomerular deposition of the IC in an experimental model of IgA nephropathy. The influence of mIgA anti-dinitrophenyl (DNP) on pIgA anti-DNP/DNP-conjugated BSA (BSA-DNP) IC formation was assessed by double diffusion test and competition PAGE in combination with autoradiography. Only the BSA-DNP, a model antigen of relatively low molecular mass, was radiolabeled and monitored throughout the latter experiment. An analysis of clearance kinetics (1 and 6 hours) of the antigen using 4-week-old female BALB/c mice, and a series of renal studies were performed after intravenous injection with a single dose of combined pIgA anti-DNP, BSA-DNP, and mIgA anti-DNP. As demonstrated by the double diffusion test, addition of mIgA anti-DNP resulted in suppression of the precipitating reaction of pIgA anti-DNP and BSA-DNP. This effect was confirmed by PAGE for size determination of the BSA-DNP which had been complexed with either pIgA anti-DNP or a mixture of pIgA anti-DNP and mIgA anti-DNP. The clearance kinetics studies showed that the elimination of BSA-DNP injected with pIgA anti-DNP was prolonged in the presence of mIgA anti-DNP in a partially dose-dependent manner. The experimental mice receiving pIgA anti-DNP, BSA-DNP, and mIgA anti-DNP showed less hematuria (p < 0.005) than mice receiving pIgA anti-DNP and BSA-DNP (positive control) when examined 1 hour after injection. Immunofluorescence study of the renal tissue of mice receiving pIgA anti-DNP, BSA-DNP, and mIgA anti-DNP showed a suppressed glomerular localization of IgA and third component of complement, as compared with those injected with pIgA anti-DNP and BSA-DNP alone. Similarly, a significant decrease of glomerular BSA-DNP deposits was observed in mice receiving pIgA anti-DNP, BSA-DNP, and mIgA anti-DNP compared with those receiving pIgA anti-DNP and BSA-DNP alone, as demonstrated by light microscopic autoradiography. These findings indicate that a high dose of specific mIgA was capable of modulating glomerular deposition of the pIgA-IC in this animal model of IgAN.

Animals↗
PubMed1996

[Cloning and sequencing of VH and VL genes of an anti-human lung adenocarcinoma monoclonal antibody].

By comparing the conserved regions at each end of the nucleotide sequences of murine germ-line genes encoding FR1 and FR4 regions of immunoglobulin heavy and light chain variable regions, we designed two sets of primer for amplification of VH and VL genes. Hybridoma cell WLA-2C4, secreting an antihuman lung adenocarcinoma McAb, was cultured and the genome DNA was extracted and used as template for PCR. After PCR the desired VH and VL fragments were amplified. The PCR products were then cloned into pUC19 vector. By screening and identification, several recombinants that had been inserted with the target fragments were obtained. Then they were sequenced with Sanger's method. It was confirmed by computer-assisted comparative sequence analysis that clones of full-length and potentially functional VH and VL genes from the hybridoma cell line WLA-2C4 were ob-tained.

Adenocarcinoma↗
PubMed1995

Phenotypic manifestations of branchio-oto-renal syndrome.

Branchiootorenal (BOR) syndrome is a variable, autosomal-dominant disorder of the first and second embryonic branchial arches, kidneys, and urinary tract. We describe the phenotype in 45 individuals, highlighting differences and similarities reported in other studies. Characteristic temporal bone findings include cochlear hypoplasia (4/5 of normal size with only 2 turns), dilation of the vestibular aqueduct, bulbous internal auditory canals, deep posterior fossae, and acutely-angled promontories.

Abnormalities, Multiple↗
PubMed1995

Structural requirements regulate endoproteolytic release of the L-selectin (CD62L) adhesion receptor from the cell surface of leukocytes.

L-selectin mediates leukocyte rolling on vascular endothelium at sites of inflammation and lymphocyte migration to peripheral lymph nodes. L-selectin is rapidly shed from the cell surface after leukocyte activation by a proteolytic mechanism that cleaves the receptor in a membrane proximal extracellular region. This process may allow rapid leukocyte detachment from the endothelial surface before entry into tissues. In this study, the structural requirements for regulation of human L-selectin endoproteolytic release were examined through analysis of chimeric selectin molecules and mutant L-selectin receptors. The use of chimeric selectins and a cytoplasmic tail truncation mutant demonstrated that the extracellular membrane-proximal 15-amino acid region of L-selectin is required for endoproteolytic release. The introduction of alanine-scanning mutations within this membrane-proximal region did not prevent endoproteolytic release, indicating that a specific amino acid motif was not an absolute requirement for cleavage. Furthermore, alterations within the putative primary cleavage site (K283-S284) resulted in either constitutive endoproteolytic release of the receptor or inhibition of cell activation-induced shedding to variable extents. The length of the membrane-proximal region was also critical since truncations of this region completely abolished endoproteolytic release. Thus, release of L-selectin is likely to be regulated by the generation of an appropriate tertiary conformation within the membrane-proximal region of the receptor which allows recognition by a membrane-bound endoprotease with relaxed sequence specificity that cleaves the receptor at a specific distance from the plasma membrane. These observations suggest a generalized protein-processing pathway involved in the endoproteolytic release of specific transmembrane proteins which harbor widely differing primary sequences at or neighboring their cleavage sites.

Amino Acid Sequence↗
PubMed1995

Validity of the three-column theory of thoracolumbar fractures. A biomechanic investigation.

STUDY DESIGN: This study validated the three-column theory of fractures by correlating the multidirectional instabilities and the vertebral injuries to each of the three columns, using a biomechanic trauma model. OBJECTIVES: The objective was to validate the three-column theory as applied to the thoracolumbar fractures. SUMMARY OF BACKGROUND DATA: The widely used three-column theory of fractures for classification and evaluation was based on retrospective analysis of radiographs. No biomechanic study, using realistic spinal fractures and multidirectional instability measurements, was available. METHODS: Using 16 fresh cadaveric thoracolumbar human spine specimens, two groups of burst fractures were produced by either simple axial compression or flexion-compression, using a high-speed trauma model. Multidirectional flexibility was measured before and after the trauma, thus quantifying the instability of the burst fracture. Computed tomography scans were taken after the fracture, and a newly developed injury scoring scheme quantified the injuries to the anterior, middle, and posterior columns. Statistical correlations were obtained between the flexibility parameters and injuries to each of the three columns. RESULTS: In the axial compression group, the middle column injury, compared with the other two columns, showed the highest correlations to eight of the nine flexibility parameters (average R2 = 0.77). In the flexion-compression group, again the middle column injury showed the highest correlations to eight of the nine flexibility parameters (average R2 = 0.85). CONCLUSIONS: The results of this study supported the three-column theory of the thoracolumbar fractures and bolstered the concept of the middle column being the primary determinant of mechanical stability of this region of the spine.

Adult↗
PubMed1995

Tumor-associated sialylated antigens are constitutively expressed in normal human colonic mucosa.

Immunohistochemical studies have indicated that sialylated carbohydrate antigens such as sialyl-Tn, sialyl-Le(a), and sialyl-Le(x) are expressed in a tumor-associated fashion in human colon. Since sialic acid residues are O-acetylated more extensively in normal colonic epithelium than in colon cancer cells, we examined whether deacetylation of colonic tissues might enable monoclonal antibodies to recognize these tumor-associated sialylated antigens. In normal colon, deacetylation turned most cases (82%) positive with anti-sialyl-Tn mAb TKH2; and in colon cancers, it increased the number of TKH2-positive cells. Sialyl-Le(a) and sialyl-Le(x) detection was also increased after deacetylation of normal and malignant colonic tissues so that the frequency of positive cases in normal tissues was similar to that in the cancers. However, in the stomach and pancreas, the same treatment rarely increased the detection of the sialylated epitopes in normal or cancerous tissues. Thus, the same sialylated epitopes can be expressed in a tumor-associated fashion by different mechanisms in different gastrointestinal organs; in the colon, these antigens are constitutively expressed and O-acetylated, whereas in the upper gastrointestinal tract, they are rarely O-acetylated, suggesting that other mechanisms such as differences in glycosylation account for the cancer-associated expression.

Adenocarcinoma↗
PubMed1995

Tyrosine 27 of the specificity polypeptide of EcoKI can be UV crosslinked to a bromodeoxyuridine-substituted DNA target sequence.

The specificity (S) subunit of the restriction enzyme EcoKI imparts specificity for the sequence AAC(N6)GTGC. Substitution of thymine with bromodeoxyuridine in a 25 bp DNA duplex containing this sequence stimulated UV light-induced covalent crosslinking to the S subunit. Crosslinking occurred only at the residue complementary to the first adenine in the AAC sequence, demonstrating a close contact between the major groove at this sequence and the S subunit. Peptide sequencing of a proteolytically-digested, crosslinked complex identified tyrosine 27 in the S subunit as the site of crosslinking. This is consistent with the role of the N-terminal domain of the S subunit in recognizing the AAC sequence. Tyrosine 27 is conserved in the S subunits of the three type I enzymes that share the sequence AA in the trinucleotide component of their target sequence. This suggests that tyrosine 27 may make a similar DNA contact in these other enzymes.

Amino Acid Sequence↗
PubMed1995

E2F-4 and E2F-5, two members of the E2F family, are expressed in the early phases of the cell cycle.

The E2F transcription factors play a role in regulating the expression of genes required for cell proliferation. Their activity appears to be regulated by association with the retinoblastoma protein (pRb) and the pRb-related proteins p107 and p130. In vivo, pRb is found in complex with a subset of E2F components--namely, E2F-1, E2F-2, and E2F-3. Here we describe the characterization of cDNAs encoding two unusual E2Fs, E2F-4 and E2F-5, each identified by the ability of their gene product to interact with p130 in a yeast two-hybrid system. E2F-4 and -5 share common sequences with E2F-1, E2F-2, and E2F-3 and, like these other E2Fs, the ability to heterodimerize with DP-1, thereby acquiring the ability to bind an E2F DNA recognition sequence with high affinity. However, in contrast to E2F-1, E2F-4 and E2F-5 fail to bind pRb in a two-hybrid assay. Moreover, they show a unique pattern of expression in synchronized human keratinocytes: E2F-4 and E2F-5 mRNA expression is maximal in mid-G1 phase before E2F-1 expression is detectable. These findings suggest that E2F-4 and E2F-5 may contribute to the regulation of early G1 events including the G0/G1 transition.

Amino Acid Sequence↗
PubMed1995

Activation of monocyte effector genes and STAT family transcription factors by inflammatory synovial fluid is independent of interferon gamma.

Activated monocytes play an important role in the pathogenesis of inflammatory arthritis. Blood monocytes which enter the inflamed joint become activated upon adherence to extracellular matrix and exposure to a complex inflammatory environment. We have analyzed the mechanism of monocyte activation by soluble factors present in inflammatory synovial fluid (SF). Greater than 75% of inflammatory SFs tested (a total of 22 fluids to date) increased cell surface expression and dramatically increased mRNA levels of monocyte activation markers Fc gamma RI, Fc gamma RIII, and HLA-DRA. This induction was not triggered by adherence, a known activating stimulus, and several lines of evidence showed that induction was not dependent upon interferon gamma (IFN-gamma). Induction was not prevented by neutralizing anti-IFN-gamma antibodies and IFN-gamma was not detected in the SFs using a sensitive enzyme-linked immunosorbent assay. The SFs also were not able to activate the IFN-gamma-activated transcription factor Stat1, thus providing further support for the absence of IFN-gamma. SFs did activate a related signal transducer and activator of transcription (STAT) family factor, termed Stat-SF, which bound specifically to the IFN-gamma response region (GRR), a well-characterized transcription element in the Fc gamma RI promoter. Based upon DNA-binding specificity and mobilities in gel shift assays, and reactivity with specific antisera, Stat-SF likely contains Stat3, or a closely related STAT family member. Neutralization of interleukin 6, a cytokine present in SFs which is known to activate Stat3, abolished the activation of Stat-SF and inhibited the induction of Fc gamma RI expression by SFs. These results demonstrate the activation of monocytes by inflammatory SF and suggest that monocyte activation at an inflammatory site may occur in the absence of IFN-gamma through the triggering of signal transduction pathways that activate STAT transcription factors.

Arthritis, Rheumatoid↗