Biomedical subjects

J Xiang

Publications and source records attributed to J Xiang.

At least 109 records · Page 6Linked to original sources

PubMed1997

Choroid plexus ion transporter expression and cerebrospinal fluid secretion.

The Cl-/HCO3- exchanger (AE2 isoform) and the Na+/K(+)-ATPase at the choroid plexus are both thought to be involved in CSF secretion. However, both transport mechanisms are also postulated to have a role in CSF ion homeostasis raising questions as to which parameters control the expression of these transporters? Northern blots have been used to assess AE2 mRNA levels in rats subjected to alterations in blood pH or blood osmolality (a factor affecting CSF secretion). Six hours of alkalosis induced a 40% increase in AE2 mRNA (p < 0.01), suggesting that alterations in the expression of this transporter play a role in CSF pH homeostasis. In contrast, changes in osmolality did not affect AE2 mRNA. Western blots of Na+/K(+)-ATPase subunits were also examined to determine whether hypo and hyperkalemia affect protein levels of this transporter. There was a positive correlation between the plasma K+ concentration and both alpha 1- and beta 1 subunit protein levels suggesting a role for this transporter in CSF K+ homeostasis. As changes in plasma K+ and pH affect choroid plexus ion transporters but do not appear to alter CSF production, these results suggest the presence of compensatory mechanisms. Understanding of such mechanisms may facilitate therapeutic control of CSF production.

Animals↗

PubMed1997

Somatosensory evoked magnetic fields and potentials following passive toe movement in humans.

The somatosensory evoked magnetic fields (SEFs) and evoked potentials (SEPs) following passive toe movement were studied in 10 normal subjects. Five main components were identified in SEFs recorded around the vertex around the foot area of the primary sensory cortex (SI). The first and second components, 1M and 2M, were identified at approximately 35 and 46 ms. Equivalent current dipoles (ECDs) of both 1M and 2M were estimated around SI in the hemisphere contralateral to the movement toe, and were probably generated in area 3a or area 2, which mainly receive inputs ascending through muscle and joint afferents. The large inter-individual difference of 1M and 2M in terms of ECD orientation was probably due to a large anatomical variance of the foot area of SI. The third and fourth components, 3M and 4M, were identified at approximately 62 ms and 87 ms, respectively. They appeared to be a single large long-duration component with two peaks. Since the 3M and 4M components were significantly larger than the 1M and 2M components in amplitude and their ECD location was significantly superior to that of 1M and 2M, we suspected that they were generated in different sites from those of 1M and 2M, probably area 3b or area 4. Four components, 1E, 2E, 3E and 4E, were identified in SEPs, which appeared to correspond to 1M, 2M, 3M and 4M, respectively. The variation observed in the scalp distribution of the primary component, 1E, could be accounted for by the variation of the orientation of ECD of the 1M component. There was a large difference in the waveform of the long-latency component (longer than 100 ms) between SEFs and SEPs. The 5E of SEPs was a large amplitude component, but the 5M of SEFs was small or absent. We speculate that this long-latency component was generated by multiple generators.

Adult↗

PubMed1997

Somatosensory evoked magnetic fields following passive finger movement.

The somatosensory evoked magnetic field (SEF) following passive finger movement and electrical stimulation of finger was studied in 10 normal subjects. Four main components were identified in SEFs recorded at the hemisphere contralateral to the moved finger: 1M(P), 2M(P), 3M(P) and 4M(P). The 1M(P) was clearly identified only in three subjects and was smaller than other components. The equivalent current dipoles (ECDs) of 1M(P) were located around the finger area of the primary sensorimotor cortex and oriented either posteriorly or anteriorly. We speculate that it was generated in areas 3a or 2 of the primary sensory cortex. The 2M(P) and 3M(P) were usually combined as one large deflection with two peaks. Because the ECDs of 2M(P) and 3M(P) were located around the finger area of the sensorimotor cortex and both oriented posteriorly, they were considered to be generated in area 4 and/or 3b, and their activities have temporal overlapping. The 4M(P) has large inter-individual difference in terms of amplitude and latency. The ECD of 4M(P) was also located around the finger area of the primary sensorimotor cortex, and oriented anteriorly. The 4M(PI), the main component recorded from the hemisphere ipsilateral to the moved finger, was located in the upper bank of the sylvian fissure, probably the second sensory cortex (SII). Five components, 1M(E), 2M(E), 3M(E), 4M(E) and 4M(EI), corresponding to 1M(P), 2M(P), 3M(P), 4M(P) and 4M(PI), were identified following electrical stimulation of the same finger. However, SEFs following passive movement were clearly different from SEFs following electrical stimulation, in terms of waveforms and source locations, probably due to differences of ascending fibers and receptive fields.

Adult↗

PubMed1997

Antitumor vaccination with gene-transduced tumor cells expressing a fusion protein RM4/IFN-tau.

Our previous studies showed that secretion of a fusion protein RM4/IFN-tau from a mouse myeloma cell line VKCK/RM4-IFN-tau curtailed its tumorigenicity. Inoculation of VKCK/RM4-IFN-tau tumor cells further induced a protective immunity against a secondary challenge of parental VKCK tumor cells, in which the predominant immune cellular components are CD8+ T cells. In this study, VKCK/RM4-IFN-tau cell line was again used to further characterize the protective immunity. We found that the reduced tumorigenicity of VKCK/RM4-IFN-tau was directly related to the amount of fusion protein secreted by tumor cells, and that CD8+ T cells derived from mice experienced with VKCK/RM4-IFN-tau tumor regression played an important role in the protective immunity in a chromium release assay in vitro and in an animal study in vivo by using T-cell subset depleted mice. Our animal studies also showed that not only the cytotoxic but also the memory T cells against the secondary challenge of parental VKCK cells could be adoptively transferred to normal BALB/c mice. In addition, our animal studies further showed that local vaccination of irradiated VKCK/RM4-IFN-tau cells was able to significantly inhibit established tumors in early stages in vivo. This study thus highlights the potential utility of this engineered VKCK/RM4-IFN-tau tumor cells secreting the fusion protein RM4/IFN-tau in cancer gene therapy.

Animals↗

PubMed1997

[Study on the relationship between the expression of adhesion molecules and the invasiveness of acute myeloid leukemia cells].

OBJECTIVE: To study the relationship between the expression of adhesion molecules CD49d (VLA-4) and CD11a (LFA-1) and the invasiveness of acute myeloid leukemia (AML) cells. METHODS: Peripheral blood and/or bone marrow samples from 50 AML patients were investigated by APAAP and Western blotting method. RESULTS: Extramedullary invasion developed in 32 of 50 patients (64%). The expression of CD49d and CD11a in the invasive group was much higher than that in the non-invasive group (P<0.005), while the difference between the leukemic cells from bone marrow and peripheral blood for CD49d/CD11a expression was not significant. CONCLUSION: AML cells might adhere to and get through vascular endothelium by CD49d/VCAM-1 and CD11a/ICAM-1 adhesion mechanism, and the expressions of CD49d and CD11a were not critically responsible for the release of leukemic cells from bone marrow.

Adolescent↗

PubMed1996

BAX-induced cell death may not require interleukin 1 beta-converting enzyme-like proteases.

Expression of BAX, without another death stimulus, proved sufficient to induce a common pathway of apoptosis. This included the activation of interleukin 1 beta-converting enzyme (ICE)-like proteases with cleavage of the endogenous substrates poly(ADP ribose) polymerase and D4-GDI (GDP dissociation inhibitor for the rho family), as well as the fluorogenic peptide acetyl-Asp-Glu-Val-Asp-aminotrifluoromethylcoumarin (DEVD-AFC). The inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD-fmk) successfully blocked this protease activity and prevented FAS-induced death but not BAX-induced death. Blocking ICE-like protease activity prevented the cleavage of nuclear and cytosolic substrates and the DNA degradation that followed BAX induction. However, the fall in mitochondrial membrane potential, production of reactive oxygen species, cytoplasmic vacuolation, and plasma membrane permeability that are downstream of BAX still occurred. Thus, BAX-induced alterations in mitochondrial function and subsequent cell death do not apparently require the known ICE-like proteases.

Apoptosis↗

PubMed1996

Fas-induced activation of the cell death-related protease CPP32 Is inhibited by Bcl-2 and by ICE family protease inhibitors.

The human proto-oncogene bcl-2 and its Caenorhabditis elegans homologue ced-9 inhibit programmed cell death. In contrast, members of the human interleukin-1beta converting enzyme (ICE) family of cysteine proteases and their C. elegans homologue CED-3 promote the death program. Genetic experiments in C. elegans have shown that ced-9 is formally a negative regulator of ced-3 function, but neither those studies nor others have determined whether CED-9 or Bcl-2 proteins act biochemically upstream or downstream of CED-3/ICE proteases. CPP32, like all known members of the CED-3/ICE family, is synthesized as a proenzyme that is subsequently processed into an active protease with specificity for cleavage at Asp-X peptide bonds. In this report, we demonstrate that the CPP32 proenzyme is proteolytically processed and activated in Jurkat cells induced to die by Fas ligation. CPP32 activation is blocked by cell-permeable inhibitors of aspartate-directed, cysteine proteases, suggesting that pro-CPP32 is cleaved by active CPP32 or by other ICE family members. Heterologous expression of Bcl-2 in Jurkat cells prevents Fas-induced cell death as well as proteolytic processing and activation of CPP32. Thus, Bcl-2 acts at or upstream of the CPP32 activation step to inhibit apoptosis induced by Fas stimulation.

Amino Acid Sequence↗

PubMed1996

Choroid plexus taurine transport.

The putative osmoregulatory agent, taurine, is lost from the brain during hypo-osmotic stress or ischemia, but the regulatory mechanisms involved in this loss have not been fully elucidated. In this study, we have examined taurine transport by the isolated rat choroid plexus, one element of the brain-blood interface, and examined how it may be regulated as part of brain volume regulation. Choroid plexus taurine uptake was Na- and Cl-dependent with a Vmax and Km of 6.5 +/- 0.3 pmol/mg/min and 232 +/- 33 microM. The latter is substantially greater than the normal CSF taurine concentration and this may be important in removing taurine released into the CSF during parenchymal cell swelling. Taurine uptake also appears calmodulin dependent as it was reduced by 84 and 91% in the presence of 25 microM trifluoperazine and 100 microM W-7, two calmodulin inhibitors. Taurine efflux from choroid plexus was stimulated by trifluoperazine, taurine, and hypo-osmotic stress. The latter two effects were reduced by niflumic acid, suggesting that taurine and hypo-osmotic stress act on the same pathway. The stimulation of efflux by hypo-osmotic stress decreased with time, whereas the effect of external taurine was sustained. If this efflux pathway is involved in the movement of taurine from choroid plexus to blood, these results suggest that changes in extracellular taurine may be more important than the direct effect of hypo-osmolality in the long-term loss of taurine from the brain.

Animals↗

PubMed1996

Selection of a peptide with affinity for the tumor-associated TAG72 antigen from a phage-displayed library.

A hexapeptide phage library was used to select peptides with affinity for the tumor-associated TAG72 antigen. Twenty-one phage clones were selected after the third round of biopanning. Three phage clones with the same DNA insert of ARTLRF were found to bind more strongly to the TAG72 antigen than other phage clones and the wild-type phage. A synthetic decapeptide GAARTLRFGA with two conjunctive amino acid residues of the phage coat protein III on each side of the selected peptide was found to bind more strongly to the TAG72 antigen than to other antigens such as the mouse metallothionein. Furthermore, immunohistochemical studies revealed that this peptide displayed preferential binding to colonic adenocarcinomatous cells expressing the TAG72 antigen. Therefore, this anti-TAG72 peptide may be useful in serving as the starting point with regard to further designing peptidomimetics as potential pharmaceuticals.

Adenocarcinoma↗

PubMed1996

Identification of a decapeptide with the binding reactivity for tumor-associated TAG72 antigen from a phage displayed library.

Peptide ligands for tumor-associated TAG72 antigen were identified by screening a large, diverse decapeptide library expressed on the surface of filamentous phages. Fifty-eight clones of phages were selected from the eluates after the third round of biopanning and their DNA inserts were sequenced. A dominant decapeptide HYVSIELPDH (14/58) was found with the binding reactivity for TAG72 antigen in the TAG72-binding ELISA and Western dot blotting. It also showed a preferential binding to colonic adenocarcinomatous cells expressing the TAG72 antigen in the histochemical study. Therefore, this anti-TAG72 decapeptide may be useful in serving as the starting point with regard to further designing peptidomimetics for potential pharmaceuticals.

Adenocarcinoma↗

PubMed1996

Radioimmunoscintigraphy of gastric adenocarcinomas with 99mTc-chimeric ccM4 antibody.

Fourteen patients with gastric lesions were studied for radioimmunoscintigraphy using the 99mTc-ccM4 chimeric antibody reactive with the human tumor-associated TAG72 antigen. These include 10 gastric adenocarcinomas, 3 gastric ulcers and 1 gastric lymphoma. Each patient received an infusion of 30-40 mCi 99mTc-ccM4 antibody. Gamma camera scans were performed at 12-h postadministration. All patients underwent operation after radioimmunoscintigraphy. All surgical specimens including gastric adenocarcinomas, lymphoma and ulcers were confirmed by histopathological studies. The 99mTc-ccM4 antibody was able to detect 6 out of 10 gastric adenocarcinomas (60%) by scans. Its accuracy was even 5 out of 6 (83%) in a group of patients with well/moderately-differentiated adenocarcinomas. In addition to the primary adenocarcinomatous lesions, the 99mTc-ccM4 antibody was also able to detect metastatic lesions in liver and lymph nodes. The smallest adenocarcinomatous lesion detected by scans was about 1 x 1 x 2 cm3. All four patients with gastric ulcers or lymphoma showed negative scan results. Therefore, the chimeric ccM4 antibody may be useful in radioimmunoscintigraphy of gastric adenocarcinomas, especially the well/moderately-differentiated adenocarcinomas.

Adenocarcinoma↗

PubMed1996

Establishment of a rat colonic carcinoma model for study of immunoreagents against the human tumor-associated TAG72 antigen.

TAG72 originally defined by the mouse B72.3 antibody is a mucin-like, human tumor-associated antigen present in more than 85% of human colonic adenocarcinomas. Establishment of a tumor model expressing the TAG72 antigen in immunocompetent animals would be of great benefit in evaluating the therapeutic efficacy and studying anti-tumor immune mechanisms of anti-TAG72 immunoreagents. In this study, we screened 6 animal tumor cell lines including 3 derived from mouse colonic adenocarcinomas (MCR-26, MCR-38-LD and CA-51), 1 from mouse ovarian adenocarcinoma (MOT), 1 from rat colonic adenocarcinoma LMCR, and 1 from rat mammalial adenocarcinoma (R3230AB) for TAG72 expression by using the B72.3 antibody. Immunohistochemistry disclosed significant amounts of TAG72-expression in the dimethylhydrazine-induced BDIX rat colonic adenocarcinoma LMCR. The rat TAG72 antigen purified from rat LMCR tumors showed strong immunoreactivity for the B72.3 antibody in ELISA analysis and displayed a smear band of high molecular weight in Western blotting, which is similar to the human TAG72 antigen purified from human LS174T colonic adenocarcinoma. In addition, the iodinated B72.3 antibody was able to localize LMCR tumor in BDIX rats. Therefore, this rat LMCR model should be useful in studying human colonic cancer, especially in evaluating the therapeutic efficacy of anti-TAG72 immunoreagents such as the recombinant fusion proteins possessing the anti-TAG72 antibody fragment and the cytokine moiety.

Animals↗

PubMed1996

Mouse myeloma cell line secreting bifunctional fusion protein RM4/IFN-gamma [corrected] elicits antitumor CD8 MHC class I-restricted T cells that are cytolytic in vitro and tumoricidal in vivo.

Mouse myeloma cell line VKCK/RM4-IFN-gamma secreting the bifunctional fusion protein RM4/IFN-gamma was used to study the relationship between IFN-gamma secretion of tumor cells and its tumorigenicity and to study the potential mechanism responsible for the immune response. IFN-gamma secretion of VKCK/RM4-IFN-gamma tumor cells was estimated at 90 U/ml using an antiviral assay. To evaluate tumorigenicity, 5 x 10(5) viable IFN-gamma-secreting VKCK/RM4-IFN-gamma and non-IFN-gamma-secreting VKCK tumor cells were injected s.c. into syngeneic BALB/c mice and VKCK/RM4-IFN-gamma-immunized or T cell subset-depleted BALB/c mice, respectively. Tumor progression or regression was evaluated 2 weeks after tumor inoculation. Our animal studies showed that RM4/IFN-gamma secretion by VKCK/RM4-IFN-gamma tumor cells curtailed its tumorigenicity in BALB/c mice and induced a persistant protective immune response against a subsequent graft of parental VKCK tumor. This protective immunity is long term and tumor specific as measured in a 51Cr-release assay. In addition, our animal studies in T cell subset-depleted BALB/c mice showed that CD8 CTL play a major role in the reduction of tumorigenicity. This study thus highlights the potential advantages of localized IFN-gamma in tumors to induce potent antitumor immunity and further suggests that the bifunctional fusion protein RM4/IFN-gamma may be useful in cancer immunotherapy because of its capacity of targeting IFN-gamma to human tumors expressing the human tumor-associated TAG72 antigen [corrected].

Animals↗

PubMed1996

Complementarity determining region residues aspartic acid at H55, serine at H95 and tyrosines at H97 and L96 play important roles in the B72.3 antibody-TAG72 antigen interaction.

Structural analysis derived from the crystallographic study of the chimeric B72.3 antibody illustrated some major atomic interactions between complementarity determining region (CDR) residues. For example, hydrogen bonds are formed between H35/H95, L50/H97, H53/H55 and H96/L96 respectively. These CDR residues may play important roles in the B72.3-TAG72 (antibody-antigen) interaction either by direct interaction with the TAG72 antigen or by maintaining a CDR loop conformation through atomic interactions between CDR residues. In order to confirm these assumptions, we altered these CDR residues by site-directed mutagenesis and determined binding affinities of these mutant chimeric antibodies for the TAG72 antigen in a solid-phase radioimmunoassay. We found that H55, H95, H97 and L96 are important CDR residues for the B72.3-TAG72 interaction. Single amino acid substitutions of aspartic acid and serine by alanine at H55 of CDR2 and at H95 of CDR3 respectively and of tyrosine by phenylalanine at H97 and L96 of CDR3, significantly reduced the binding affinity for the TAG72 antigen by 20-, 8-, 16- and 45-fold respectively. Therefore, this study reveals some of the requirements for maintaining the integrity of the B72.3 antibody combining sites.

Amino Acid Sequence↗

PubMed1996

Granulomatous appendicitis in acute myeloblastic leukemia: expanding the clinicopathologic spectrum of invasive candidiasis.

The incidence of systemic candidiasis appears to be on the rise, and unusual or hitherto undocumented clinicopathologic features of invasive candidiasis continue to be described. This report adds further to this spectrum by describing granulomatous appendicitis due to invasive candidiasis. The patient was a 23-year-old woman with acute promyelocytic leukemia. Her other risk factors included the use of aggressive chemotherapy, immunosuppressives, broadspectrum antibiotics, and invasive instrumentation. In view of the acquired immunodeficiency syndrome epidemic, as well as the improved survival of patients with prolonged neutropenia owing to better intensive care units, there is reason to believe that other as yet undocumented clinicopathologic manifestations of invasive candidiasis or other opportunistic infections may come to light.

Adult↗

PubMed1996

Targeting gamma interferon to tumor cells by a genetically engineered fusion protein secreted from myeloma cells.

The construction, synthesis and expression of a genetically engineered bifunctional antibody/cytokine fusion protein is described. To target IFN-tau to tumor cells, recombinant antibody techniques were used to construct a RM4/IFN-tau fusion protein containing the chimeric anti-tumor F(ab')2 (RM4) and the IFN-tau moiety. The recombinant cDNA of IFN-tau was linked to 3 prime end of the chimeric heavy-chain gene fragment (M4) containing the VH, the CH1 and the hinge region to form the fused heavy-chain gene fragment M4-IFN-tau. Transfection of the M4-IFN-tau gene fragment into a myeloma derived cell line VKCK which produced the chimeric light-chain of the same antibody, allowed the transfectant secreting the bifunctional fusion protein RM4/IFN-tau. The RM4/IFN-tau was purified by the affinity chromatography. Our data showed that the RM4/IFN-tau retained the TAG72 antigen-binding reactivity as well as the IFN-tau activity as measured in ELISA, FACS analysis of cell-surface TAG72 expression, immunohistochemical study, and up-regulation of cell-surface expression of CEA, HLA class I and class II antigens. Therefore, the bifunctional fusion protein RM4/IFN-tau may prove to be useful in targeting biological effects of the IFN-tau to tumor cells and in this way to stimulate the immune destruction of tumor cells.

Adenocarcinoma↗

PubMed1996

Characterization of anti-tumor immunity derived from the inoculation of myeloma cells secreting the fusion protein RM4/IFN-tau.

Our previous study showed that the injection of mouse myeloma VKCK/RM4-IFN-tau cells secreting the fusion protein RM4/IFN-tau to syngeneic BALB/c mice resulted in tumor regression in 70% of mice after tumor inoculation. In this study, the VKCK/RM4-IFN-tau cell line was used to characterize the protective immunity subsequent to tumor inoculation. Our histologic findings demonstrated that, in the primary response to VKCK/RM4-IFN-tau inoculation, tumor regression is associated with macrophage infiltration. This macrophage-dominated regression further leads to a protective immunity against the 2nd challenge of parental VKCK tumor cells. FACS analysis and chromium release assays showed that the majority of T lymphocytes that mediated this anti-tumor immunity were CD8+ cytotoxic T lymphocytes (CTLs). Our animal studies further showed that the VKCK/RM4-IFN-tau cells were able to grow as aggressively as the parental VKCK cells in T lymphocyte deficient nude mice. The protective immunity started 7 days, became complete 10 days following and lasted up to at least 12 months subsequent to the tumor inoculation. The adoptive transfer of T lymphocyte-enriched spleen cells or CTLs also conferred significant protection against tumor growth of parental VKCK cells (p < 0.01). These data thus support the notion that genetically engineered tumor cells secreting IFN-tau may have potential use as tumor vaccines in preventing the development of tumor recurrence and/or metastases following the surgical removal of the primary tumors.

Animals↗

PubMed1995

Framework residues 71 and 93 of the chimeric B72.3 antibody are major determinants of the conformation of heavy-chain hypervariable loops.

Structural analysis derived from the crystallographic study of the chimeric B72.3 antibody illustrated that some heavy-chain framework residues having atomic interactions with heavy-chain CDR residues may directly affect the conformation of CDR loops. For example, an alanine residue at H71 provides room for packing CDR2/CDR1 and lysine residues at H73 and H93 contribute a salt-bridge to aspartic acid at H55 in CDR2 and a hydrogen bond to the carbonyl group at H96 in CDR3, respectively. We have analysed the contribution of these framework residues to the TAG72-binding affinity. We altered these framework residues by site-directed mutagenesis, and determined the affinity of these mutant chimeric antibodies for the TAG72 antigen by solid phase radioimmunoassay. We found that a single amino acid substitution of alanine by phenylalanine at H71 or lysine by isoleucine at H93, significantly reduced the binding affinity for the TAG72 antigen by 12 and 20-fold, respectively, whereas the substitution of lysine by alanine at H73 reduced the binding affinity only two-fold. Our results indicate that heavy-chain framework residues alanine at H71 and lysine at H93 of the chimeric B72.3 antibody are the major determinants of the conformation of heavy-chain CDR2/CDR1 and CDR3 loops, whereas the salt-bridge between lysine at H73 and aspartic acid at H55 is less important. The hydrogen bond between two framework residues, glutamine at H5 and serine at H25 does not affect any CDR conformation. Our results will thus be of importance especially when the humanized B72.3 antibody is constructed by grafting the CDR loops to a human framework. The important framework region interactions must be maintained in the final humanized antibody.

Amino Acid Sequence↗