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S Chen

Publications and source records attributed to S Chen.

At least 1,351 records · Page 75Linked to original sources
PubMed1990

Positive ion fast atom bombardment mass spectrometric analysis of the molecular species of glycerophosphatidylserine.

The structure of 1,2-dipalmitoyl-sn-glycero-3-phosphoserine was analyzed by positive ion fast atom bombardment mass spectrometry and collisional activation mass-analyzed ion kinetic energy spectroscopy. The molecular weight, the polar-head group, and the fatty acid composition of this species were identified by the appearance of protonated and solvated protonated species ions, diglyceride and monoglyceride fragment ions. After purification of glycerophosphatidylserine from bovine brain and rat kidney by normal phase high-performance liquid chromatography, molecular species were identified by either positive or negative ion fast atom bombardment mass spectrometry. The study suggests that negative ion fast atom bombardment ionization is a more powerful tool for the identification of the molecular species of glycerophosphatidylserine from biological samples. Positive ion fast atom bombardment represents a useful alternative for analysis of major molecular species in natural glycerophosphatidylserine.

Animals↗
PubMed1990

Delayed wallerian degeneration in sciatic nerves of C57BL/Ola mice is associated with impaired regeneration of sensory axons.

Wallerian degeneration is delayed following sciatic nerve crush in C57BL/Ola mice. Compared to C57BL/6J mice, regeneration of sensory axons is significantly slowed in the Ola mice, but reinnervation does eventually occur. We conclude that Wallerian degeneration is a prerequisite for normal sensory axon regeneration following a crush injury to peripheral nerve.

Animals↗
PubMed1990

Regulation of serine protease activity by an engineered metal switch.

A recombinant trypsin was designed whose catalytic activity can be regulated by varying the concentration of Cu2+ in solution. Substitution of Arg-96 with a His in rat trypsin (trypsin R96H) places a new imidazole group on the surface of the enzyme near the essential active-site His-57. The unique spatial orientation of these His side chains results in the formation of a stable, metal-binding site that chelates divalent first-row transition-metal ions. Occupancy of this site by a metal ion prevents the imidazole group of His-57 from participating as a general base in catalysis. As a consequence, the primary effect of the transition metal ion is to inhibit the esterase and amidase activities of trypsin R96H. The apparent Ki for this inhibition is in the micromolar range for copper, nickel, and zinc, the tightest binding being to Cu2+ at 21 microM. Trypsin R96H activity can be fully restored by removing the bound Cu2+ ion with EDTA. Multiple cycles of inhibition by Cu2+ ions and reactivation by EDTA demonstrate that reversible regulatory control has been introduced into the enzyme. These results describe a novel mode of inhibition of serine protease activity that may also prove applicable to other proteins.

Amino Acid Sequence↗
PubMed1990

Afferent connections of the thalamic paraventricular and parataenial nuclei in the rat--a retrograde tracing study with iontophoretic application of Fluoro-Gold.

The origin of the afferents of the thalamic anterior paraventricular and parataenial nuclei (PVA-PT) in the rat was studied with fluorescent retrograde tracing method. After iontophoretic application of Fluoro-Gold into PVA-PT, many labeled cells were found in the medial frontal cortex, ventral subiculum, claustrum, septum, ventral pallidum, thalamic reticular nuc., zona incerta, hypothalamus, central gray, dorsal raphe nuc., parabrachial nuc., and the laterodorsal tegmental nuc. A few cells were labeled in the medial amygdaloid nuc., amygdalohippocampal area, median raphe nuc., and the locus coeruleus. Occasional neurons were labeled in the ventral lateral geniculate nuc., pretectal area, and in the solitary nuc. and the lateral reticular nuc. in the medulla.

Animals↗
PubMed1990

Robust synaptic plasticity of striatal cells following partial deafferentation.

Partial ablation of the cerebral cortical input to the neostriatum generates a rapid lasting effect on the size of remaining synaptic sites. The neocortex was lesioned in adult rats and the neostriatum was analyzed for effects on remaining spines of principal cells during the period from 2 to 40 days. There was an increase in the size of spine heads, boutons and synaptic contact sites. The spine heads became very complex and a corresponding bouton enlargement was accompanied by an increase in the number of synaptic vesicles. By two days, the average profile length of postsynaptic membrane densities (PSDs) had increased by 25% representing an equivalent 50% increase in synaptic contact area. The number of synaptic sites was reduced on each principal neuron of the lesioned group. Comparison of the number of sites per unit volume to their average contact area revealed a reciprocal relationship indicating a conservation in the total synaptic contact area on each neuron. This effect was consistent for all postsurgical days. The lack of a significant return of synaptic number by 40 days indicates that axonal sprouting is not a major factor in neuronal plasticity in the adult striatum. The rapid increase in the size of spines, boutons and synaptic sites at remaining connections suggests that dendrites are the first to initiate the plasticity response in adult neurons through postsynaptic attachments and their corresponding receptor structure. The underlying mechanism of this plasticity may be through a conservation of macromolecules forming postsynaptic membrane specializations on target neurons. Remaining axons appear to follow the dendritic response with a plasticity generating presynaptic appositional specializations to match the contact area of the postsynaptic site.

Animals↗
PubMed1990

Murine monoclonal antibodies raised against human non-small cell carcinoma of the lung: specificity and tumor targeting.

The tumor targeting properties of murine monoclonal antibodies (MAbs) generated in our laboratory against non-small cell carcinoma of the lung have been investigated in nude mouse xenograft models. The MAbs selected for evaluation, RS5-4H6, RS7-3G11, and R511-51, have pancarcinoma reactivity, as shown by immunoperoxidase staining of the majority of tumors from the lung as well as breast, colon, kidney, and ovary. The localization of the three MAbs which bind to distinct antigens, and exhibit different levels of cross-reactivity with normal human epithelial tissues, are compared. The MAbs are of the IgG1 isotype. Since these MAbs were reactive with Calu-3, a human adenocarcinoma of the lung cell line grown as xenografts in nude mice, this system was selected as our initial tumor target. The MAbs were found to localize preferentially to the heterotransplanted tumors, with from 6.6 to 8.6% of the injected dose per gram accreting in the tumor at 7 days. Tumor/nontumor ratios of up to 9.7 were seen with one MAb at day 14. The targeting of MAb RS11-51 and F(ab')2 fragments of RS11-51 in GW-39, a human colon cancer grown in nude mice, was also studied. Accretion of intact RS11-51 and F(ab')2 fragments into GW-39 was greatly increased compared to Calu-3. In view of the high frequency of antigen expression on a wide variety of tumors, and the ability to target in vivo, these new MAbs may have potential use in the imaging and therapy of cancer.

Animals↗
PubMed1990

N-arylazido-beta-alanyl-NAD+, a new NAD+ photoaffinity analogue. Synthesis and labeling of mitochondrial NADH dehydrogenase.

N-Arylazido-beta-alanyl-NAD+ [N3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl)NAD+] has been prepared by alkaline phosphatase treatment of arylazido-beta-alanyl-NADP+ [N3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl)NADP+]. This NAD+ analogue was found to be a potent competitive inhibitor (Ki = 1.45 microM) with respect to NADH for the purified bovine heart mitochondrial NADH dehydrogenase (EC 1.6.99.3). The enzyme was irreversibly inhibited as well as covalently labeled by this analogue upon photoirradiation. A stoichiometry of 1.15 mol of N-arylazido-beta-alanyl-NAD+ bound/mol of enzyme, at 100% inactivation, was determined from incorporation studies using tritium-labeled analogue. Among the three subunits, 0.85 mol of the analogue was bound to the Mr = 51,000 subunit, and each of the two smaller subunits contained 0.15 mol of the analogue when the dehydrogenase was completely inhibited upon photolysis. Both the irreversible inactivation and the covalent incorporation could be prevented by the presence of NADH during photolysis. These results indicate that N-arylazido-beta-alanyl-NAD+ is an active-site-directed photoaffinity label for the mitochondrial NADH dehydrogenase, and are further evidence that the Mr = 51,000 subunit contains the NADH binding site. Previous studies using A-arylazido-beta-alanyl-NAD+ [A3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl)NAD+] demonstrated that the NADH binding site is on the Mr = 51,000 subunit [Chen, S., & Guillory, R. J. (1981) J. Biol. Chem. 256, 8318-8323]. Results are also presented to show that N-arylazido-beta-alanyl-NAD+ binds the dehydrogenase in a more effective manner than A-arylazido-beta-alanyl-NAD+.

Affinity Labels↗
PubMed1990

Effects of MK-801 on glutamate-induced swelling of astrocytes in primary cell culture.

The effects of glutamate and its agonists and antagonists on the swelling of primary astrocytes were studied. Glutamate (Glu), aspartate (Asp), homocysteate (HCA), and quisqualate (Quis) at 1 mM concentration caused a significant increase in astrocytic swelling as measured by the 3-0-methyl-[14C]-glucose, whereas kainate (KA), N-methyl-D-aspartate (NMDA), and receptor antagonists 2-amino-5-phosphonovaleric acid (APV), 2-amino-7-phosphonohepatanoic acid (APH), and kynurenic acid (Kynu) were not effective. This glial swelling was time-dependent since 1-hr or greater incubations with Glu or its agonists were needed to produce such an effect. Preincubation of glutamate or NMDA receptor anatogonists including Kynu, APH, and APV failed to ameliorate the Glu effects. However, MK-801, a noncompetitive NMDA antagonist, when added to the Glu-incubated astrocytes significantly reduced Glu-induced astrocytic swelling. MK-801 was also effective in reducing the astrocytic swelling induced by agonists including Asp, Quis, and HCA, suggesting that those agonists may share similar mechanisms of Glu in inducing astrocytic swelling. Since the cultured astrocytes lack the NMDA receptors, our data suggest that the observed beneficial effects of MK-801 on excitotoxin-induced swelling of astrocytes may be mediated by mechanisms other than NMDA receptors.

Animals↗
PubMed1990

Analysis of arachidonic-acid-containing molecular species in glycerophospholipid classes from rat kidney by fast-atom bombardment mass spectrometry.

The qualitative analysis of the molecular species of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine from a rat kidney, by fast-atom bombardment mass spectrometry after separation and purification by liquid chromatography is described. The present results indicate that a high content of arachidonic-acid-containing molecular species within major glycerophospholipid classes is present in this biological sample.

Animals↗
PubMed1990

Role of macrophages in the immune response to hepatocytes.

The purpose of this study was to determine the role of host macrophages in the development of allospecific cytolytic T cells (allo-CTLs) in response to purified allogeneic MHC Class I+, Class II- hepatocytes in vivo in hepatocyte sponge matrix allografts (HC-SMA). Depletion of antigen-presenting cells (APCs) from responder splenocytes in mixed lymphocyte hepatocyte culture (MLHC) inhibits the development of allo-CTLs in response to purified hepatocytes. First the ability of sponge macrophages to function as accessory cells in indirect presentation of hepatocyte Class I antigen was tested in MLHC. We found that addition of irradiated sponge cells (a source of sponge macrophages) restored the development of allo-CTLs in MLHC depleted of responder APCs. Therefore, radioresistant sponge macrophages can function as accessory cells in MLHC. We next employed silica as an immunotherapy targeted against host macrophages and assessed the effect on development of allo-CTLs in HC-SMA. We found that local (intrasponge) silica treatment completely inhibited the development of allo-CTLs in HC-SMA. Combined local and systemic silica treatment resulted in inhibition of allocytotoxicity comparable to local silica treatment alone in the doses tested. We conclude that host macrophages which infiltrate HC-SMA can function as accessory cells in vitro in MLHC and that both infiltrating host macrophages and lymphocytes participate in the development of an alloimmune response to purified hepatocytes in vivo. This interaction may involve indirect antigen presentation of hepatocyte Class I antigen by macrophages to host lymphocytes which accumulate in HC-SMA.

Animals↗
PubMed1990

Effect of increased dietary calcium on the development of reduced renal mass saline hypertension in rats.

A diet fortified with calcium carbonate has been reported to reduce blood pressure in low-renin and salt-sensitive hypertensive patients. We have therefore examined the effect of increased dietary calcium on the development of reduced renal mass-saline hypertension in rats, a classical, low-renin, volume, and sodium-dependent model of hypertension. Rats with 70-75% reduction in renal mass were divided into experimental and control groups. The experimental rats were fed a sodium-free diet supplemented with calcium carbonate (2.0% calcium) and drank 1% saline for 5 weeks. Control rats consumed the salt-free diet and drank 1% saline for the same period. In control rats, as previously observed, blood pressure progressive increased from a control value of 120.0 +/- 1.2 to 174.2 +/- 1.2 mm Hg by the fifth week. In contrast, in the calcium-supplemented rats the development of hypertension was significantly attenuated; the blood pressure only increased from 117.0 +/- 1.2 to 134.0 +/- 3.8 mm Hg by the fifth week. This was associated with a 30% decrease in saline intake by the fifth week, with proportionate decreases in urine volume and sodium excretion but not potassium excretion. Urinary magnesium excretion increased. No such changes were seen in control rats. At the end of the treatment period, plasma levels of sodium, potassium, calcium, creatinine, BUN, and protein were not different, but plasma chloride and magnesium were lower in experimental rats; vascular smooth muscle cell membrane potentials were also not different. These data show that dietary calcium carbonate can attenuate the development of reduced renal mass-saline hypertension in the rat, possibly in part by altering sodium and water intake.

Animals↗
PubMed1990

Emergency free flaps to the type IIIC tibial fracture.

Type IIIC tibial fractures are complex injuries involving extensive bone and soft-tissue devascularization that result in a high percentage of complications and ultimate amputation. An emergency free flap transfer not only may salvage the limb but also may improve the aesthetic and functional results of reconstruction by placing the injured structures in a well-vascularized bed. Two cases of type IIIC tibial fracture were treated in this manner, and we present our experience with a 30-month follow-up of one patient and a 6-month follow-up of another patient.

Adult↗
PubMed1990

Comparison of in vivo and in vitro immune response to purified hepatocytes.

We have previously reported that freshly isolated percoll-purified hepatocytes are MHC class I+, Class II- and stimulate allospecific cytotoxicity in mixed lymphocyte hepatocyte culture. In this report we determined the immunogenicity of purified hepatocytes in vivo using a modification of the sponge matrix allograft model. We found that hepatocytes were immunogenic in vivo because they stimulated the development of cytolytic effectors in allogeneic but not syngeneic hepatocyte sponge matrix allografts. These cytolytic effectors were not macrophages (because cytotoxicity was intact after nylon wool depletion of the bulk sponge effectors) but rather were Ly2+, L3T4- T cells. Cytolytic effectors in both MLHC and hepatocyte sponge matrix allografts demonstrated marked specificity for allogeneic MHC class I antigen of stimulator and donor hepatocytes, respectively. Allospecific cytolytic T cells developed in both MLHC and hepatocyte sponge matrix allografts across an isolated MHC class I genetic disparity but not across an isolated class II genetic disparity. Finally, sequential phenotypic analysis of host cells infiltrating allogeneic hepatocyte sponge matrix allografts demonstrated the presence of macrophages, Ly2+, L3T4- and Ly2-, L3T4+ T cells.

Animals↗
PubMed1990

Identification of a region of simian virus 40 large T antigen required for cell transformation.

A series of replication-competent simian virus 40 (SV40) large T antigens with point and deletion mutations in the amino acid sequence between residues 105 and 115 were examined for the ability to immortalize primary cultures of mouse and rat cells. The results show that certain mutants, including one that deletes the entire region, are able to immortalize. However, consistent with previous data, the immortalized cells are not fully transformed, as judged by doubling time, sensitivity to concentrations of serum, and anchorage-independent growth. The region from 106 to 114 has structural features in common with a region involved in transformation by adenovirus E1a protein (J. Figge, T. Webster, T.F. Smith, and E. Paucha, J. Virol. 62:1814-1818, 1988) and influences the binding of the retinoblastoma gene product to large T (J.A. DeCaprio, J.W. Ludlow, J. Figge, J.-Y. Shew, C.-M. Huang, W.-H. Lee, E. Marsilio, E. Paucha, and D.M. Livingston, Cell 54:275-283, 1988). Together, these results imply that the sequence from 106 to 114 forms part of a domain that is essential for transformation of established cells, is dispensable for immortalization, and is not required for SV40 replication. The results also indicate that the ability of SV40 large T to immortalize primary cells is independent of its ability to bind to the retinoblastoma gene product.

Amino Acid Sequence↗