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Biomedical subjects

C Shih

Publications and source records attributed to C Shih.

At least 73 records · Page 4Linked to original sources
PubMed1996

MR imaging of articular cartilage in the ankle: comparison of available imaging sequences and methods of measurement in cadavers.

OBJECTIVE: To assess hyaline cartilage of cadaveric ankles using different magnetic resonance (MR) imaging techniques and various methods of measurement. DESIGN AND PATIENTS: Cartilage thicknesses of the talus and tibia were measured in ten cadaveric ankles by naked eye and by digitized image analysis from MR images of fat-suppressed T1-weighted gradient recalled (FS-SPGR), sequences and pulsed transfer saturation sequences with (FS-STS) and without fat-suppression (STS); these measurements were compared with those derived from direct inspection of cadaveric sections. The accuracy and precision errors were evaluated statistically for each imaging technique as well as measuring method. Contrast-to-noise ratios of cartilage versus joint fluid and marrow were compared for each of the imaging sequences. RESULTS: Statistically, measurements from FS-SPGR images were associated with the smallest estimation error. Precision error of measurements derived from digitized image analysis was found to be smaller than that derived from naked eye measurements. Cartilage thickness measurements in images from STS and FS-STS sequences revealed larger errors in both accuracy and precision. Inter-observer variance was larger in naked eye assessment of the cartilage. Contrast-to-noise ratio of cartilage versus joint fluid and marrow was higher with FS-SPGR than with FS-STS or STS sequences. CONCLUSION: Of the sequences and measurement techniques studied, the FS-SPGR sequence combined with the use of digitized image analysis provides the most accurate method for the assessment of ankle hyaline cartilage.

Aged↗
PubMed1996

The role of dietary folate in modulation of folate receptor expression, folylpolyglutamate synthetase activity and the efficacy and toxicity of lometrexol.

We have studied the molecular effects of a LFD in a murine model in order to better define the biochemical changes associated with folate deficiency. In addition, we have demonstrated the effect of a LFD on the pharmacokinetic profile and therapeutic activity and toxicity of lometrexol. These studies showed increased density of FR in tumors implanted in LFD mice and a decrease in the affinity of these receptors for folic acid. The results suggest that tumors can compensate for low folate bioavailability by up-regulation of a second FR with slightly lower affinity for folic acid. The higher density of this FR would provide greater capacity for garnering serum folate. FPGS activity increased in several tumors and liver and kidney of LFD mice. The increase in this enzyme activity would result in enhanced polyglutamation of folates and classical antifolates and thus increased cellular retention. Consistent with these changes in liver FPGS, mice injected i.v. with a single dose of lometrexol accumulated significantly more drug in liver and tumors of LFD animals compared to SD mice. Also, higher liver concentrations of lometrexol persisted longer in LFD mice. Polyglutamate analysis showed that longer polyglutamate forms appeared earlier in liver of LFD mice. After 7 days, longer polyglutamyl forms were recovered from liver of LFD mice (octa- and hepta-glutamyl lometrexol) compared to those on SD. A comparison of the efficacy and toxicity of lometrexol in C3H mammary tumor-bearing mice showed that in mice on LFD, lometrexol treatment produced a delayed toxicity with an LD50 of 0.1-0.3 mg/kg, a 3000-fold increase in lethality compared to SD mice. Supplementation of mice with folic acid restored anti-tumor activity and increased the therapeutic dose-range over which efficacy could be assessed. These studies support the use of folic acid supplementation for cancer patients treated with antifolate therapy in order to prevent the biochemical changes in FR and FPGS associated with folate deficiency, prevent delayed toxicity to GARFT inhibitors and enhance the therapeutic potential of this class of drugs.

Acyltransferases↗
PubMed1996

Effects of phenol feeding pattern on microbial community structure and cometabolism of trichloroethylene.

Cometabolism of trichloroethylene (TCE) by phenol-fed enrichments was evaluated in four reactors with distinct phenol feeding patterns. The reactors were inoculated from the same source, operated at the same average dilution rate, and received the same mass of phenol over time. Only the timing of phenol addition differed. Reactor C received phenol continuously; reactor SC5 received phenol semicontinuously--alternating between 5 h of feed and 3 h without feed; reactor SC2 alternated between 2 h of feed and 6 h without feed; and reactor P received a single pulse every 24 h. The structure of the enrichments and their capacity for TCE transformation were analyzed. In long-term operation, reactors C and SC5 were dominated by fungi, had higher levels of predators, were more susceptible to biomass fluctuations, and exhibited reduced capacity for TCE transformation. Reactors P and SC2 were characterized by lower levels of fungi, higher bacterial biomass, higher concentrations of TCE-degrading organisms, and higher rates of TCE transformation. After 200 days of operation, rates of TCE transformation increased 10-fold in reactor P, resulting in TCE transformation rates that were 20 to 100 times higher than the rates of the other reactor communities. The cause of this shift is unknown. Isolates capable of the highest rates of TCE transformation were obtained from reactor P. We conclude that cometabolic activity depends upon microbial community structure and that the community structure can be manipulated by altering the growth substrate feeding pattern.

Journal Article↗
PubMed1996

Interleukin-1 alpha stimulates osteoclast formation from peripheral blood monocytes and increases osteoclastic activity.

BACKGROUND: Interleukin-1 (IL-1) is produced by monocytes and marrow stromal cells and can stimulate bone resorption in tissue culture. In addition, IL-1 can induce osteoclast-like cell formation in long-term bone marrow culture. However, whether IL-1 can increase osteoclast formation by stimulating fusion of peripheral blood monocytes is not clear. In addition, the precise effect of IL-1 on osteoclastic activity is still not well known. METHODS: Using the bioassay of osteoclast formation, osteoclast-free fetal calvariae were harvested from 14-day timed-pregnant Sprague-Dawley rats and cultured in BGJb medium for 10 days. On the 10th day, mononuclear cells were obtained from peripheral blood of 8-week-old female Sprague-Dawley rats through cardiac puncture and Ficoll-Paque density gradient separation method and co-cultured with osteoclast-free developing bone explant. On the same day, various concentrations of IL-1 alpha (1,10 or 100 U/ml) were added daily in the experimental dishes while only BGJb medium was added in the controls. In addition, 45Ca release assay and quantitation of nuclei per osteoclast were performed to evaluate the effect of IL-1 alpha on osteoclastic activity. RESULTS: Ten days after adding monocytes, there were 14.25 osteoclasts in the control, without IL-1 alpha; with 1 U of IL-1 alpha, there were 14.75 osteoclasts; with 10 U of IL-1 alpha, there were 18.00 osteoclasts; with 100 U of IL-1 alpha, there were 20.75 osteoclasts. In addition, IL-1 alpha stimulated the release of 45Ca and increased the number of average nuclei per osteoclast dose-dependently, indicating a significant increase in bone resorption. CONCLUSIONS: IL-1 alpha could increase osteoclast formation by stimulating the fusion of peripheral blood monocytes. In addition, IL-1 alpha is a potent stimulator of osteoclastic activity.

Animals↗
PubMed1996

Characterization of folate receptor from normal and neoplastic murine tissue: influence of dietary folate on folate receptor expression.

Membrane-associated folate receptors (FRs) have been detected in many mammalian species, and multiple isoforms have been identified. The pharmacological properties of FRs from murine kidney, liver, and six murine tumors were characterized. Murine kidney expressed primarily folate-binding protein 1, analogous to human FR-alpha, whereas murine liver expressed predominantly folate-binding protein 2, analogous to human FR-beta. Five of six murine tumors expressed high-affinity FRs with pharmacological properties consistent with folate-binding protein 1 isoform expression. Restriction of dietary folate resulted in significant changes in the FR expression in most murine tissues. Kidney and tumor FRs showed a decreased affinity for folic acid, suggesting a change in isoform expression in response to a low folate diet. Density of the FR in the kidney decreased, and, in contrast, density of the FR in all tumors increased. The response of the liver to a low folate diet was unique in that there were no detectable changes in affinity or density of liver FR. Changes in dietary folate that modulate FR isoform expression may have relevance for cancer patients treated with antifolates.

Animals↗
PubMed1995

Core antigen mutations of human hepatitis B virus in hepatomas accumulate in MHC class II-restricted T cell epitopes.

Despite the extensive molecular information on serum-derived human hepatitis B viruses (HBV), liver-derived replicative HBV genomes have remained largely uninvestigated. We have examined the sequences of the entire core antigen (nucleocapsid) of liver-derived HBVs in 15 different hepatoma patients. Bona fide mutations, rather than subtype polymorphism, have been identified based on the high-frequency occurrence of structural differences from wild type at the highly evolutionarily conserved positions, instead of at the positions known to contain genetic heterogeneity among different isolates from different geographic locations. The distribution of these naturally occurring mutations of HBV core gene appears to be nonrandom and is found predominantly within three major (I, IV, and V) and four minor domains (II, III, VI, and VII). In general, domain IV mutations correlate with domain V mutations. The replicative HBV DNAs tend to accumulate a higher number of mutated core domains than the integrated HBV DNAs. At the domain level, there is no significant difference in HBV core mutation frequencies between the liver tumors and the adjacent nontumorous livers. Strikingly, domains I, III, and V coincide with three major known T cell epitopes within the core protein in acute and chronic hepatitis B patients. Furthermore, these domains coincide with HLA class II-restricted T cell epitopes, rather than with the conventional HLA class I-restricted epitopes of cytotoxic T lymphocytes. Our results support the hypothesis that HBV core antigen variants can accomplish immunoevasion via accumulated escape mutations. In addition, they also provide a potential molecular explanation for the maintenance of persistent infection of human hepatitis B virus in chronic carriers.

Adult↗
PubMed1995

The mechanism of natural occurrence of two closely linked HBV precore predominant mutations.

Two precore predominant mutations of human hepatitis B virus (HBV) at either nucleotide (nt) 1896 or nt 1899 often occur in combination. At nt 1896, a G to A mutation creates a TAG stop codon at codon 28 of precore protein. At nt 1899, a G to A mutation changes glycine at codon 29 to aspartic acid. To assess the effect of each individual mutation as well as any interaction between these two mutations, HBV derivatives bearing one or both precore predominant mutations have been constructed. HBV e-Ag-negative mutants bearing a TAG stop codon mutation at codon 28 uniformly replicate at least 20-fold better than mutants bearing a TGA stop codon at the same amino acid position, irrespective of the sequence context at nt 1899. A single mutation at nt 1899, changing the wild-type G to a pyrimidine (T or C) is deleterious to viral RNA encapsidation and DNA replication. Our results explain in part why only a purine (G or A) at nt 1899, never a pyrimidine, is observed in natural HBV genomes. The effects caused by these two closely linked mutations on viral replication are not independent of each other. The stringent selection for a highly efficient RNA encapsidation element may play a crucial role in the natural occurrence of these two closely linked precore mutations. The putative 27-amino-acid peptide resulting from the truncation of precore by the nt 1896 mutation has no apparent effect on viral replication. The preferential occurrence of the G to A mutation at nt 1896 and 1899, instead of at other nonpredominant positions, is likely to be a combined consequence of both selection and higher intrinsic mutation frequency at these positions.

Amino Acid Sequence↗
PubMed1995

Localization, interaction, and RNA binding properties of the V(D)J recombination-activating proteins RAG1 and RAG2.

The RAG1 and RAG2 gene products are indispensable for activating somatic rearrangement of antigen receptor gene segments. The two proteins form a stable complex in primary thymocytes as well as when expressed in adherent cells. In both cell types, most cells localize RAG proteins at the periphery of the nucleus. However, when overexpressed in fibroblast cells, RAG1 is found largely in the nucleolus. Nucleolar localization of RAG1 is mediated by several domains containing stretches of basic amino acids, indicating that RAG1 has affinity for RNA or ssDNA. The RAG1 interacting proteins SRP1 and Rch1 directly bind to the nuclear localization signals of RAG1, which mediate the nuclear and nucleolar translocation of the protein. RAG1 appears to have a binary structure, each half containing multiple regions that can act as NLSs, binding sites for the SRP1/Rch1 family, and RNA binding domains.

3T3 Cells↗
PubMed1995

Calculation of hydrolytic rate constants of poly(ortho ester)s from molecular weights determined by gel permeation chromatography.

PURPOSE: To obtained rate constants from weight-averaged (Mw) or z-averaged (Mz) molecular weights for polymers of Schule-Flory distribution and undergoing random scission. These constants were compared with those obtained by parallel 1HNMR studies. METHODS: The hydrolysis of two poly(ortho ester)s were followed by 1HNMR and gel permeation chromatography (GPC). RESULTS: Equations to convert number-averaged (Mn), Mw and Mz into fraction of backbone remaining (fc) were derived. First-order hydrolytic rate constants of two poly(ortho ester)s; DETOSU-HD and DETOSU-CDM were calculated using these relationships. The rate constants calculated from 1HNMR, Mz and Mw were 0.215, 0.21 and 0.182 hr-1, respectively, for DETOSU-CDM and 0.152, 0.086 and 0.038 hr-1 for DETOSU-HD. The large discrepancy in the rates determined by 1HNMR and GPC in the latter case was attributed to that the detector response (refractive index) of the monomers was lower than that of the high molecular weight polymer. The difference is small in the case of DETOSU-CDM, and the rates calculated from GPC data were comparable or nearly identical to that obtained from 1HNMR data. CONCLUSIONS: Although GPC can yield rapid and valuable kinetic data for the degradation of biodegradable polymers, the system, however, must be carefully calibrated to account for the variations in Mark-Houwink coefficients and in the response of the mass detector between the high and low MW polymers.

Chromatography, Gel↗
PubMed1995

A graphical method for the determination of the mode of hydrolysis of biodegradable polymers.

PURPOSE: To develop a qualitative method for the determination of the mode of scission in the hydrolysis of biodegradable polymers. METHODS: The method requires determination of the molar fraction of monomer (m1) by 1HNMR or HPLC, and the degree of polymer degradation (alpha) determined by 1HNMR. RESULTS: If the scission of the backbone bonds is completely random, the molar fraction of the monomer must equal the square of the degree of degradation as predicted by Kuhn (1). If the degradation follows an exclusive chain-end "unzipping" mechanism then, m1 = alpha. Experimental data falling on the theoretical curves (m1 vs. alpha) confirm the corresponding mode of scission. If the data fall between the two curves, it suggests a faster chain-end scission than random scission. When data fall below both of these curves, it suggests the chain-end bonds are less reactive than the internal bonds. CONCLUSIONS: The acid catalyzed hydrolysis of a poly(ortho ester) and the base catalyzed hydrolysis of poly(D,L-lactide) (PLA) were by a random scission mechanism, while acid catalyzed hydrolysis of PLA demonstrated faster chain-end scission.

Dichloroacetic Acid↗
PubMed1995

Chronically stressed wrists in adolescent gymnasts: MR imaging appearance.

PURPOSE: To investigate the magnetic resonance (MR) imaging appearance of a chronically stressed wrist and to assess the utility of MR imaging for evaluation of injuries to the growth plate. MATERIALS AND METHODS: Coronal T1-weighted spin-echo and gradient-echo MR images were obtained of 93 wrists in 47 high-risk gymnasts of a Chinese opera school. MR imaging and radiographic findings were correlated in 93 wrists. RESULTS: The major MR imaging abnormalities of 47 radii with abnormal radiographic findings were horizontal fractures (n = 23), physeal cartilage extension to metaphysis (n = 17), and physeal widening (n = 17). The major MR abnormalities of 46 radii with normal radiographs included physeal cartilage extension (n = 12), metaphyseal bone bruise (n = 8), and vertical fractures (n = 4). CONCLUSION: Physeal cartilage extension into the metaphysis represents a healing sign in chronically stressed adolescent wrists. MR imaging findings including horizontal fracture and physeal cartilage extension to the metaphysis suggest that physeal widening occurred secondary to metaphyseal injury.

Adolescent↗
PubMed1995

Wrist injuries in adolescent gymnasts of a Chinese opera school: radiographic survey.

PURPOSE: To determine the prevalence of chronic wrist injuries among adolescent gymnasts and the consequences of repetitive stress. MATERIALS AND METHODS: Students of a Chinese opera school underwent radiography of both wrists and answered a questionnaire. They were separated into study (n = 261) and control (n = 63) groups according to participation in or abstinence from exercise training, respectively. They were further separated into fused and unfused physis subgroups. The ulnar variance was measured on posteroanterior radiographs. Abnormalities of distal radii were investigated. RESULTS: An increase in both mean ulnar variance and frequency of ulnar-plus variance was noted in the study subgroups. Fourteen (8.2%) of 170 wrists of the fused physis study subgroup had an exceedingly large ulnar-plus variance. Sixty-one (17.3%) of 352 wrists had abnormal morphology of the distal radii in the unfused physis study subgroup. Widening of the physis was the most common finding. CONCLUSION: Chronic, repetitive stress in the wrists of adolescent gymnasts results in a localized growth disturbance of the distal radius with resultant ulnar-plus variance. Stress injuries of the physis may lead to permanent sequelae, even in asymptomatic individuals.

Adolescent↗
PubMed1995

Role of membrane-associated folate binding protein in the cytotoxicity of antifolates in KB, IGROV1, and L1210A cells.

Based on differential levels of membrane-associated folate binding protein (mFBP) expression, murine L1210 leukemia, human KB epidermoid carcinoma, and human IGROV1 ovarian carcinoma cells maintained under low (physiological) folate conditions (2 nM folinic acid) were used as model systems to investigate the potential role of mFBP in antifolate transport. In addition, L1210 parental cells were compared to a subline, L1210A, expressing high levels of mFBP and defective reduced folate carrier. Antifolates for which KB-derived mFBP has high affinity (5, 10-dideazatetrahydrofolic acid [DDATHF] and homo-DDATHF [0.24 and 0.78 respectively relative to folic acid]) and low affinity (methotrexate [0.002]) were chosen for this study. Protection against DDATHF/homo-DDATHF induced cytotoxicity was achieved preferentially by folic acid compared to folinic acid in IGROV1 and L1210A cells. In IGROV1 cells, cytotoxicity IC50s were increased 18- and 5.5-fold for DDATHF and homo-DDATHF respectively by 20 nM folic acid. Moreover, greater protection was observed in L1210A cells, where IC50s were increased 354- and 80-fold for these same compounds by 20 nM folic acid. Similar protection was not observed in KB cells, suggesting that KB mFBP was not functional in DDATHF transport. Although mFBP expression may be an important determinant in the cytotoxicity of antifolates for certain tumor cells, our data demonstrate a lack of correlation between levels of mFBP and function of mFBP for DDATHF transport in the models studied.

Animals↗
PubMed1995

Substrate specificity of mammalian folylpolyglutamate synthetase for 5,10-dideazatetrahydrofolate analogs.

The metabolism of 5,10-dideazatetrahydrofolate (DDATHF [lometrexol]) to polyglutamate derivatives by folylpoly-gamma-glutamate synthetase (FPGS) plays a central role in the activity of this compound as an antineoplastic agent. The availability of a series of DDATHF derivatives differing in structure throughout the molecule has allowed a study of the structural requirements for substrate activity with mouse liver and hog liver FPGS. Kinetics of the polyglutamation reaction in vitro have been related to the potency of these compounds as inhibitors of the growth of human CEM leukemic cells. The structure-activity relationships for enzyme from both sources were nearly identical. FPGS from both species showed a broad acceptance for structural changes in the pyridopyrimidine ring, in the phenyl group, and in the intermediate bridge region, with structural changes in these regions being reflected in changes in Km for FPGS but much more modest alterations in Vmax. The data suggested that the phenyl ring was not contributing to any pi-pi hydrophobic interactions. It appeared to function primarily in maintaining a favorable distance between the pyridopyrimidine ring and the glutamate side chain. The lowest Km values were found for DDATHF analogs in which there were small alterations at the 10 position, e.g., 5-deazatetrahydrofolate, 10-methyl-DDATHF, and 10-formyl-5-deazatetrahydrofolate; the first-order rate constants for these substrates were the highest in this series, an indication of the efficiency of polyglutamation at low substrate concentrations. After correction for the intrinsic inhibitory activity of the parent DDATHF analog as an inhibitor of the target enzyme, the first-order rate constants for FPGS were found to be predictive of the potency of tumor cell growth inhibition for most of the compounds in this structural series.

Acyltransferases↗
PubMed1994

A novel class of monoglutamated antifolates exhibits tight-binding inhibition of human glycinamide ribonucleotide formyltransferase and potent activity against solid tumors.

Tight-binding inhibition of recombinant human monofunctional glycinamide ribonucleotide formyltransferase by Lometrexol (6R-5,10-dideazatetrahydrofolate) requires polyglutamation. LY254155 and LY222306 differ from 5,10-dideazatetrahydrofolate in the replacement of the 1',4'- phenylene moiety by a 2',5'-thiophene and a 2',5'-furan, respectively. Compared to Lometrexol, the thiophene and furan analogues had 25- and 75-fold greater inhibitory potencies against human monofunctional glycinamides ribonucleotide formyltransferase (Ki = 2.1 and 0.77 nM, respectively). The binding affinities of the thiophene and furan analogues for membrane folate-binding protein from human KB cells were 6- and 350-fold weaker than Lometrexol, respectively. Both the thiophene analogue and 5,10-dideazatetrahydrofolate inhibited the in vivo growth of murine 6C3HED lymphosarcoma, murine C3H mammary carcinoma, and human xenograft HXGC3, HC1, and VRC5 colon carcinomas by 95-100%. The thiophene analogue was efficacious against human xenograft PANC-1, a pancreatic carcinoma which was completely resistant to 5,10- dideazatetrahydrofolate. These novel antifolates represent the first monoglutamated tight-binding inhibitors of glycinamide ribonucleotide formyltransferase. By eliminating the need for polyglutamation, this class of antifolates may have clinical activity in the treatment of solid tumors expressing low levels of folylpolyglutamate synthetase or tumors resistant to antifolate therapy due to increased gamma-glutamyl hydrolase activity.

Acyltransferases↗
PubMed1994

The transcription factor HNF1 acts with C/EBP alpha to synergistically activate the human albumin promoter through a novel domain.

HNF1 and C/EBP alpha are transcription factors that bind to and trans-activate the human albumin gene proximal promoter. Various 5' deletions of the human albumin promoter were coupled to a luciferase reporter gene (alb-luc constructs) and co-electroporated with HNF1 and/or C/EBP alpha expression vectors into HeLa cells. Luciferase activities from co-electroporation of the HNF1 and C/EBP alpha expression vectors with the alb-luc constructs were approximately 10-fold greater than the sum of the activities achieved with HNF1 and C/EBP alpha alone. Analysis of COOH-terminal or internal deletions of the HNF1 expression vector revealed that the domain important for collaborative interaction with C/EBP alpha could be localized to a 157 amino acid region not previously described. This domain is proline and glutamine-rich and is highly homologous (66%) to a portion of vHNF1, an evolutionarily related gene first identified in dedifferentiated hepatoma cells. A construct linking the negatively charged activation domain of herpes simplex virus protein VP16 to the DNA-binding domain of HNF1 showed that it could also synergize with C/EBP alpha to trans-activate the human albumin gene promoter. Our studies delineate a domain in HNF1 important for synergistic activation with C/EBP alpha.

Albumins↗
PubMed1994

Trinucleotide repeat length and progression of illness in Huntington's disease.

The genetic defect causing Huntington's disease (HD) has been identified as an unstable expansion of a trinucleotide (CAG) repeat sequence within the coding region of the IT15 gene on chromosome 4. In 50 patients with manifest HD who were evaluated prospectively and uniformly, we examined the relationship between the extent of the DNA expansion and the rate of illness progression. Although the length of CAG repeats showed a strong inverse correlation with the age at onset of HD, there was no such relationship between the number of CAG repeats and the rate of clinical decline. These findings suggest that the CAG repeat length may influence or trigger the onset of HD, but other genetic, neurobiological, or environmental factors contribute to the progression of illness and the underlying pace of neuronal degeneration.

Adolescent↗