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H M Chen

Publications and source records attributed to H M Chen.

At least 145 records · Page 8Linked to original sources
PubMed1993

Fe(III)-EHPG and Fe(III)-5-Br-EHPG as contrast agents in MRI: an animal study.

The development of specific agents for hepatobiliary magnetic resonance imaging (MRI), iron (III) ethylenebis-(2-hydroxyphenylglycinate) [Fe(EHPG)-] and its derivative iron (III)-N, N' ethylenebis[5-bromo-2-hydroxyphenyl)-glycinate] [Fe(5-Br-EHPG)-] was investigated. Test procedures included method of synthesis, identification, and a test for purity, lipophilicity, toxicity, relaxivity, biodistribution and animal MRIs. Free EHPG and free Fe3+ were undetectable in the purity test. The partition coefficient for the lipophilicity of Fe(EHPG)- was 0.007 and for Fe(5-Br-EHPG)- it was 1.785. The acute toxicity test of Fe(EHPG)- in mice revealed that the LD50 dose of Fe(EHPG)- was 8 mmol/kg. Their relaxivity values were 1.167 and 0.780 s-1mM-1 in an agarose gel system and 1.313 and 0.725 s-1mM-1 in an aqueous solution, respectively. Biodistribution was performed with 59Fe(EHPG)- in anesthetized dogs. There was 1.097% to 1.19% contrast excretion through the opened common bile duct and 54.29% to 61.45% through the urinary tract in a six-hour period. After six hours, the residual contrast agent was only evident in the kidney and liver. The MRIs of dogs with intravenous contrast administration showed significant opacification of the common bile duct within a 10-minute period. Complete opacification of the biliary system could be identified within 1.5 hours. There was no significant difference in the enhancement effect between the inversion recovery sequence and T1-weighted spin echo sequence. The change in signal intensity of the hepatobiliary system on MRIs was similar between Fe(EHPG)- and Fe(5-Br-EHPG)-. The recommended administration dose was 0.083 mmol/kg for both contrast agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Kinetic evidence of microscopic states in protein folding.

Staphylococcal nuclease unfolds at acidic pHs and refolds at neutral pH. Previous kinetic analysis based on both the direct pH jump and the sequential pH jump, from a native condition (pH 7.0) to pHs beyond unfolding transition zones (pH 3.0 and pH 12), and vice versa, supports the mechanism, D3<-->D2<-->D1<-->N0, in which N0 is the native state and D's are the three substates of the denatured form [Chen, H.M., You, J.L., Markin, V.S., & Tsong, T.Y. (1990) J. Mol. Biol. 220, 771-778; Chen, H.M., Markin, V.S., & Tsong, T.Y. (1992) Biochemistry 31, 1483-1491]. Here we show that both the single- and the double-pH jump kinetics of folding and unfolding to the intermediate pHs (3.4-5.0, i.e., in the transition zone), in which both the native and the denatured states coexist, are not compatible with this simple sequential model. At 25 degrees C, log tau 1(-1) (for the D1<-->N0 step) and log tau 2(-1) (for the D2<-->D1 step) vs pH show a square root of-shaped dependence on the final pH, with minimal values (tau 1(-1) of 0.56 s-1 and tau 2(-1) of around pH 3.9. The third relaxation tau 3 (for the D3<-->D2 step, 35 s) was independent of pH in the range 3.4-8.5. The square root of-shaped dependence on pH of log tau 1(-1) and log tau 2(-1) cannot be reproduced by the above but can be accounted for if each of N0, D1, and D2 is composed of many microscopic states in rapid equilibrium.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrogen-Ion Concentration↗
PubMed1992

pH-induced folding/unfolding of staphylococcal nuclease: determination of kinetic parameters by the sequential-jump method.

On the basis of previous stopped-flow pH-jump experiments, we have proposed that the acid- and alkaline-induced folding/unfolding transition of staphylococcal nuclease, in the time range 2 ms to 300 s, follows the pathway N0 in equilibrium with D1 in equilibrium with D2 in equilibrium with D3, in which D1, D2, and D3 are three substates of the unfolded state and N0 is the native state. The stopped-flow "double-jump" technique has been employed to test this mechanism and to determine the rate constants which would not be accessible by the direct pH jump because of the lack of fluorescence signal, i.e., the rates for the conversion of D1 to D2 and of D2 to D3. In the forward jump, a protein solution kept at pH 7.0 was mixed with an acidic or alkaline solution to the final pH of 3.0 or 12.2, respectively. The mixed solution was kept for varying periods of time, called the delay time, tD. A second mixing (the back jump) was launched to bring the protein solution back to pH 7.0. The time course of the Trp-140 fluorescence signals recovered in the back jump was analyzed as a function of tD. Kinetics of the unfolding were found to be triphasic by the double-jump method, contrary to the monophasic kinetics observed by the direct pH jump. Complex kinetics of unfolding are expected with the proposed kinetic scheme.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme Stability↗
PubMed1992

A cryptopromoter is activated in the proliferating cell nuclear antigen gene of growth arrested cells.

We have examined the regulation of the proliferating cell nuclear antigen gene (PCNA) in a hamster fibroblast cell line (tk-ts13) which is temperature sensitive for growth. These tk-ts13 cells, at the restrictive temperature, are growth arrested in the G1 phase of the cell cycle. The cells were stably transfected with a full length human PCNA gene, and the resulting cell lines (K525 cells) were analyzed. We find that, in growth arrested K525 cells, a cryptopromoter is activated in the transfected human PCNA gene. The cryptopromoter resides in intron 4 which is necessary for proper regulation of the PCNA gene. Removal of this intron leads to increased expression of PCNA in cells which have entered the G0 state. An Alu sequence residing in intron 4 is implicated as the promoter element which is active during growth arrest.

Animals↗
PubMed1992

Production and characterisation of a monoclonal antibody (Cx-99) against cervical carcinoma.

An IgG1 monoclonal antibody (MAb Cx-99) has been established which recognises a surface antigen on epithelial cells, but not on fibroblastic or hematopoietic cells. Immunohistochemical studies showed that this antigen was present in all 37 squamous cell carcinomas (SCC) including 33 cervical SCC, and 30 of the 32 adenocarcinomas examined; most of the 33 cervical SCC were stained extensively. It was also detected in the culture medium of cervical cancer cell lines. In the normal cervix, this antigen was restricted to the undifferentiated basal cells. This observation suggests that the widespread expression of the antigen was triggered by oncogenesis. The MAb Cx-99 recognised an epitope on an asialyted glycoprotein which has an apparent molecular weight of 37 kilodaltons (kD) (and 2 minor proteins at 18 and 27 kD) and an isoelectric point (pI) of 5.3. It may have potential for studies on differentiation and oncogenesis and for diagnostic applications.

Animals↗
PubMed1991

Adhesion molecules in skin development: morphogenesis of feather and hair.

Figure 9 summarizes the morphogenetic process of feather and hair. Hair of feathers are formed from a layer of homogeneously distributed mesenchymal cells. The mesenchymal cells start to condense to form foci in response to some unidentified induction signal (Fig. 9B). Several adhesion molecules, including L-CAM, N-CAM, integrin, tenascin, as well as proteoglycan, are involved. These adhesion molecules appear to have different roles in this process, because perturbation with specific antibodies leads to different aborted patterns. Hair or feather follicles then form following cell proliferation and epithelial invagination (Fig. 9C). The dermal papilla is enriched with N-CAM and tenascin, whereas the feather collar (equivalent of hair matrix) is enriched with L-CAM and PDGF receptor. Epithelial cells in the feather collar receive a signal from the dermal papilla and are able to continue to divide. Several growth factors, such as PDGF and EGF, may be involved. As epithelial cells are pushed upwards, they differentiate and keratinize in a cylindrical structure into hair. In feather, another morphogenetic event takes place to form the branched structure. The epithelial cylinder of the feather shaft invaginates to form rows of cells that die to become space and create the secondary branch or barbs (Fig. 9D). N-CAM is enriched in the cells destined to die and appears to form the border of cell groups within which the "death signal" is transmitted. In some, but not all, feathers the same process is repeated, in a way analogous to fractal formation, to form the tertiary branches or the barbules (Fig. 9E). Thus, in each step of the morphogenesis of feather and hair, different adhesion molecules are expressed and are involved in different functions: induction, mesenchymal condensation, epithelial folding, and cell death, depending on different scenarios. We have just begun to elucidate these molecular events.

Animals↗
PubMed1991

Kinetic analysis of the acid and the alkaline unfolded states of staphylococcal nuclease.

Thermodynamic analysis by differential scanning calorimetry shows that the folding/unfolding transition of staphylococcal nuclease is consistent with the two-state process. Stopped-flow kinetic measurements, monitoring the Trp140 fluorescence and covering five decades in time (2 ms to 300 s), indicate that the unfolding from pH 7.0 to 3.1 is monophasic (time constant 1.15 s) and from pH 7.0 to 12.2 is biphasic (time constants: one less than 2 ms and the other 0.6 s). However, the folding, either from pH 3.1 to 7.0 or from pH 12.2 to 7.0, is triphasic (time constants 150 ms, 850 ms and 30 s from acid, 90 ms, 565 ms and 33 s from alkaline). A simple sequential model, which agrees with the above observations for acidic folding/unfolding is, D3 in equilibrium D2 in equilibrium D1 in equilibrium N. The three Ds denote three sub-states of the unfolded state and N denotes the native state. These sub-states of D have similar enthalpy and tryptophan fluorescence, and their equilibrium cannot be shifted by temperature changes. However, they are kinetically distinctive. Data do not favor alternative mechanisms assuming parallel transitions of the three Ds to N, or complexity of the N state, or parallel transitions of sub-states of N1, N2 and N3 to D. Other more complex, branched or cyclic, kinetics are not considered because of the lack of evidence, pH dependence of the unfolding kinetics suggests that the unfolding is triggered by protonation of 0.8(+/- 0.3) ionizable groups, with a pKa of 3.9 or by deprotonation of 1.6(+/- 0.4) ionizable groups with pKa values near 10.5. Circular dichroisms indicate that these three D states retain nonrandom chain conformation. Possible role of these "chain conformation" in the protein folding is discussed.

Calorimetry, Differential Scanning↗
PubMed1991

Interleukin-6 responsiveness and cell-specific expression of the rat kininogen gene.

The serum concentration of rat T1 kininogen increases 20-30-fold in response to acute inflammation, an induced hepatic synthesis regulated primarily at the transcriptional level. To analyze the cis-regulatory elements responsible for the induced transcription, we fused a 1.6-kilobase segment of the rat T1 kininogen promoter to a reporter gene, chloramphenicol acetyltransferase (CAT). The resultant chimeric DNA was transfected into cultured cells. In transient transfection assays, this 5'-flanking sequence was sufficient to confer cell-specific expression: CAT activity was readily detectable when the construct was transfected into liver-derived cells, but it was not detectable in nonliver cells. Furthermore, when liver cells (Hep3B) transfected with this construct were treated with conditioned medium prepared from activated mixed lymphocyte cultures or with recombinant interleukin-6 (IL-6), a 5-fold increase in CAT activity was detected. Addition of dexamethasone to the conditioned medium or to IL-6 showed synergistic effects and resulted in a 10-fold increase in CAT activity. In contrast, when IL-1 was used with IL-6, induction of CAT activity was inhibited. Deletion analyses revealed two regions important for tissue-specific and induced regulation of T1 kininogen: sequences proximal to base pair -73 conferred enhanced expression in liver-derived cells and a distal region that conferred responsiveness to conditioned medium, recombinant IL-6, and dexamethasone. This responsive element had properties of an inducible transcriptional enhancer, and it was functional in both liver and nonliver cells when placed immediately upstream of a thymidine kinase promoter.

Animals↗
PubMed1991

Immunological properties of the fibrinolytic enzyme (fibrolase) from southern copperhead (Agkistrodon contortrix contortrix) venom and its purification by immunoaffinity chromatography.

An antibody to the fibrinolytic enzyme in southern copperhead venom was produced by immunizing rabbits with chromatographically purified enzyme. The antibody was purified from rabbit blood by ammonium sulfate fractionation and protein-A affinity chromatography. The purified antibody reacted only with the fibrinolytic enzyme in southern copperhead venom as demonstrated by immunodiffusion and immunoelectrophoresis. Western immunoblotting revealed that several snake venoms, including Agkistrodon piscivorus conanti, Crotalus atrox, Crotalus basiliscus basiliscus, and Bothrops asper, cross-reacted with the antibody to varying degrees. However, Deinagkistrodon acutus showed no cross-reaction. Immobilized antibody has been used, in combination with molecular sieve chromatography, to purify the fibrinolytic enzyme from southern copperhead venom. In this two-step purification procedure, the enzyme was purified in good yield within two days. The specific activity of the enzyme purified by the immunoaffinity chromatography procedure is comparable with that of enzyme purified by a four-step chromatographic procedure. The mol. wt of the purified enzyme is approximately 23,000-24,000 as determined by SDS-PAGE. Interestingly, the enzyme purified by this two-step immunoaffinity chromatography procedure possesses virtually no hemorrhagic activity.

Animals↗
PubMed1991

Enhanced expression of neural cell adhesion molecules and tenascin (cytotactin) during wound healing.

Both neural cell adhesion molecules (N-CAM) and tenascin (cytotactin) are important in embryonic morphogenesis but their expression is reduced greatly in adults. This study examined whether they are induced during wound healing. The spatial and temporal expression patterns of these two and other adhesion molecules in the healing of skin, cartilage, and tendon were compared. Neural cell adhesion molecules, tenascin, and fibronectin are induced in the granulation tissue but the order of prevalence is fibronectin, tenascin, N-CAM. The order of appearance is N-CAM and fibronectin, and then tenascin. The order of disappearance is N-CAM, tenascin, fibronectin. Liver cell adhesion molecules are present in the epidermis undergoing re-epithelization. Explant cultures showed that N-CAM and tenascin are synthesized by wound fibroblasts. These results suggest that N-CAM and tenascin, widely used in embryonic morphogenesis, are induced in a variety of connective tissues during wound healing.

Animals↗
PubMed1990

Gradients of homeoproteins in developing feather buds.

Homeoproteins are functionally involved in pattern formation. Recently, homeoproteins have been shown to be distributed in a graded fashion in developing limb buds. Here we examine the expression of homeoproteins in chicken feather development by immunocytochemical localization. We find that XlHbox 1 antigen is present in cell nuclei and is distributed in a gradient in the mesoderm of developing feather buds, with strongest expression in the anterior-proximal region. The gradient is most obvious in feather buds from the mid-trunk level. Feather buds from the scapular level express very high levels of XlHbox 1 and feather buds from the caudal region express no XlHbox 1, suggesting that a broad gradient along the body axis is superimposed on a smaller gradient within each individual feather bud. Feather ectoderm also expresses XlHbox 1 antigen but without an obvious graded pattern. Another homeoprotein, Hox 5.2, is also expressed in developing feather buds in a graded way, and its distribution pattern is partially complementary to that of XlHbox 1. These observations suggest that homeoproteins may be involved in setting up the anteroposterior polarity of cell fields at different levels, first for the body axis, then for the limb axis and finally for the feather axis.

Animals↗
PubMed1990

Expression of serum IL-2, IL-2R, and CD8 levels during hyposensitization in house-dust-sensitive asthmatics.

In this study, we used the enzyme-linked immunosorbent assay (ELISA) to evaluate the changes of serum interleukin-2 (IL-2), interleukin-2 receptor (IL-2R), and suppressor/cytotoxicity factor (CD8) in house dust-sensitive asthmatic children during hyposensitization. Patients before immunotherapy presented significantly higher serum levels of IL-2 and IL-2R than normal subjects (p less than 0.001), but these levels became normal after three years of hyposensitization. No significant difference of serum CD8 level was noted between pretreated patients and normal controls. Although the serum CD8 level in treated patients also decreased after three years of immunotherapy, this decrease was not significant compared with the pretreated patients (p greater than 0.05). This study suggests that serum IL-2 and IL-2R markers might be helpful in analyzing allergic states associated with immune activation and in evaluating the therapeutic effects of hyposensitization.

Adolescent↗
PubMed1989

Stressors associated with pregnancy as perceived by pregnant women during three trimesters.

A Pregnancy Stress Rating Scale that rated the incidence and severity of stressors associated with pregnancy was administered to 65 pregnant women during their three trimesters. The scores obtained from this scale were analyzed by factor analysis to determine the relationships within categories of stressor, and were analyzed by MANOVA, ANOVA, and trend analysis to determine the variations among nulliparas and multiparas. Factor analysis of the quantitative data defined three categories of stressor experiences, which were labeled Factor I, Factor II and Factor III. It was found that the effects of parity and trimester, on Factor I and Factor II were not statistically significant. The findings also show that "stress from altering body structure and body function" (Factor III) continues to be an important factor throughout pregnancy. It gradually increases and maximizes during the third trimester. A statistically significant linear trend is revealed in three different trimesters. There is no significant difference, however, between nulliparous and multiparous women.

Analysis of Variance↗
PubMed1989

Preparation of fecal samples for assay of volatile fatty acids by gas-liquid chromatography and high-performance liquid chromatography.

We describe a procedure for preparing fecal samples for determination of volatile fatty acids (VFAs) by gas-liquid chromatography (GLC) and "high-performance" liquid chromatography (HPLC). The simple, one-step procedure involves only ultrafiltration through a membrane with a molecular-mass cutoff of 3000 Da. As revealed by the GLC chromatograms, ultrafiltration appears to be as effective as steam distillation in sample clean-up. It also enables higher, more reproducible analytical recoveries of long-chain VFAs. The VFA content of the filtrate can also be measured by HPLC. Use of the ion-exclusion mechanism completely resolves isobutyric acid and butyric acid on a cation-exchange column. The mean (+/- SD) percentage distribution values of VFAs (measured by GLC) from five healthy subjects were 56.0 +/- 3.5 (acetic acid), 17.0 +/- 5.3 (propionic acid), 2.9 +/- 1.5 (isobutyric acid), 18.8 +/- 5.8 (butyric acid), 2.3 +/- 1.2 (isovaleric acid), and 2.9 +/- 0.8 (valeric acid).

Acetates↗
PubMed1988

Suppression of the growth of human colorectal carcinoma cells (LS174T) by radiolabeled monoclonal antibody (131I-MAbC27) in tissue culture and nude mice.

A monoclonal antibody against carcinoembryonic antigen (CEA), MAbC27, and its F(ab')2 fragments were prepared and labeled with 131I. They effectively suppressed the growth of a human colorectal carcinoma cell line, LS174T, both in culture medium and in inoculated nude mice, whereas 131I-labeled normal mouse immunoglobulin or 131I itself did not have similar effects. Intravenous injection of 131I-MAbC27 or 131I-MAbF(ab')2 following inoculation of carcinoma cells suppressed their growth in vivo. The suppression effect was even more effective when intact antibody rather than its F(ab')2 fragments was used, especially when the treatment was repeated. This study indicates that radiolabeled MAbC27 may be used as a therapeutic agent in CEA-secreting human colorectal carcinomas.

Animals↗
PubMed1988

Correlation between serum IgE and specific IgE antibody titer to house dust mite in children with asthma.

Using the enzyme-linked immunosorbent assay (ELISA) for IgE specific to mites, we evaluated the relationship between total serum IgE levels and IgE antibodies specific to mite in 58 asthmatic children. Our results showed that there was a positive correlation between total serum IgE and IgE antibody specific to Dermatophagoides pteronyssinus (r = 0.57; p less than 0.001) and Dermatophagoides farinae (r = 0.59; p less than 0.001). There was also a significant correlation between D. pteronyssinus-specific IgE and D. farinae-specific IgE (r = 0.68; p less than 0.001). This suggests that there are common allergens between the two species. The close correlation between the ELISA assay and skin test suggests that the former will be useful for the diagnosis of mite allergy in asthma.

Adolescent↗
PubMed1988

Localization of human colorectal carcinoma xenografts in mice using radiolabeled monoclonal antibody to carcinoembryonic antigen.

A mouse IgG1 monoclonal antibody (MAbC27) with high affinity for human carcinoembryonic antigen (CEA) has been used in vitro and in vivo for study of human colorectal carcinoma (CRC). After introduction to tumor-bearing mice, the distribution of radiolabeled MAbC27 and its F(ab')2 fragments was analyzed by direct measurement of radioactivity in the tumor and in normal organs as well as by whole-body scanning. Radiolabeled MAbC27 and its F(ab')2 were used successfully in localizing tumor xenografts in mice 40 and 20 hr after inoculation, respectively. A tumor as small as 60 mg (4.2 mm in diameter) was visualized by labeled F(ab')2. Circulating CEA, up to 200 micrograms per mouse did not prevent successful tumor imaging. This study indicates that the MAbC27 is highly useful in detection and localization of CRC in mice.

Animals↗