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Biomedical subjects

K Xu

Publications and source records attributed to K Xu.

At least 199 records · Page 11Linked to original sources
PubMed1995

Alterations of alpha1-adrenoceptor subtypes in the hearts of thyroxine-treated rats.

Alterations in the cardiac alpha1-adrenoceptor and its subtypes in thyroxine-treated rats were studied by means of radioligand binding assays, measurement of contractile response and reverse transcription-polymerase chain reaction (RT-PCR). The results showed that in thyroxine-treated rats the cardiac alpha1-adrenoceptor density (Bmax) was reduced from 51.6 +/- 6.0 fmol/mg in control to 40.9 +/- 3.7 fmol/mg (P<0.01); and the percentage of high affinity sites for 5-methyl-urapidil decreased from 23.3 +/- 2.0% in control to 10.8 +/- 2.0% in thyroxine-treated rats (P<0.05). The data indicated that the high-affinity sites for 5-methyl-urapidil (alpha1A-adrenoceptor) were reduced (from 12.0 to 4.4 fmol/mg), but the low-affinity sites for 5-methyl-urapidil (alpha1B- plus alpha1D-adrenoceptor) were not changed (from 39.6 to 36.5 fmol/mg). RT-PCR showed that steady-state levels of mRNA for alpha1A- and alpha1B-adrenoceptors were decreased, while that for alpha1D-adrenoceptor was raised in thyroxine-treated rats. In the isolated electrically driven left atria the phenylephrine-induced maximal contractions were reduced from 258 +/- 17 mg in control to 188 +/- 24 mg in thyroxine-treated rats (P<0.05). The pA2 values of 5-methyl-urapidil were reduced from 8.89 +/- 0.36 in control to the hyperthyroidism of 7.87 +/- 0.43 in thyroxine-treated rats (P<0.05). Chlorethylclonidine preincubation shifted concentration-response curves for phenylephrine to the right and reduced the maximal response to a lesser extent in thyroxine-treated rats than in control rats. Thus we concluded that the total number of cardiac alpha1-adrenoceptors is reduced in thyroxine-treated rats. The change is subtype selective, with alpha1A- and alpha1B-adrenoceptors being reduced in number and alpha1D-adrenoceptor being increased.

Animals↗
PubMed1995

Selective inhibition of the slow K+ current at motor nerve ending by plasma from a myasthenia gravis patient.

The effect of plasma from a myasthenia gravis (MG) patient, containing anti-presynaptic membrane receptor (PsmR) antibody on the membrane currents of motor nerve ending was investigated in mouse intercostal nerve triangularis sterni preparations by perineurial recording. After inhibition of both the fast K+ current and Ca(2+)-dependent K+ current by 30 mM Tetraethyl-ammonium (TEA) unmasked the voltage dependent fast Ca2+ current and the "Ca plateau", which was contributed by the voltage-dependent slow Ca2+ current and slow K+ current. Application of the MG plasma caused further prolongation and increase of the Ca plateau, due to blockage of the slow K+ current. This effect was observed immediately after the application and could be partially reversed by washing, whereas no change was found by addition of the plasma from healthy persons. When K+ current was completely blocked by 30 mM TEA and 300 microM 3,4-diaminopyridine (3,4-DAP), the fast Ca2+ current and the slow Ca2+ current were revealed. Neither the fast nor the slow Ca2+ current could be affected by the MG plasma; It was also shown that the MG plasma was devoid of noticeable effect on the voltage dependent Na+ current, fast K+ current as well as the Ca(2+)-dependent K+ current. So the effect of the MG plasma with antibody to PsmR was concluded to inhibit the slow K+ current selectively. As we knew, the beta-bungarotoxin binding protein was a kind of K+ channel, these results further confirmed that the beta-bungarotoxin binding protein should be the target of the antibody to PsmR found in the plasma of some patients suffering from MG.

Adult↗
PubMed1995

Analysis of envelope glycoprotein-specific antibodies from SIV-infected and gp110-immunized monkeys in ACC and ADCC assays.

Sera collected from SIV-infected or recombinant glycoprotein-immunized monkeys were characterized for antibodies participating in antibody-complement-mediated cytolysis (ACC) and antibody-dependent cellular cytolysis (ADCC) in terms of their IgG subclass and epitope specificity. In a competitive inhibition ELISA, gp110-specific antibody reactivity with nondenatured rgp110 was blocked completely by soluble homologous rgp110 and partially inhibited by heterologous rgp110, suggesting cross-reactivity between viral strains. However, only partial inhibition was observed with denatured recombinant gp140 (rgp140) in selected monkeys, indicating that the majority of gp110-specific antibodies recognized conformational epitopes. ACC activity against recombinant vaccinia-infected, envelope-expressing targets was found in sera from both infected and immunized monkeys, whereas ADCC activity was observed only in sera from infected monkeys. ACC was blocked with denatured rgp140 as well as nondenatured rgp110, indicating that ACC-mediating antibodies recognized mainly linear epitopes. In contrast, rgp140 did not compete as effectively as rgp110 in the ADCC assay, indicating that the majority of ADCC antibodies recognized conformational epitopes. Competitive inhibition using three peptide fragments of gp110 indicated that epitopes recognized by ACC antibodies lie within amino acid residues 214-471, a region that spans V3, whereas ADCC-reactive epitopes lie between amino acid residues 52 and 214 at the N-terminal end of gp110. Column chromatography of rhesus IgG resulted in three subclass-enriched fractions, designated IgG-I, IgG-II, and IgG-III. IgG-I, but not IgG-II or IgG-III, from both infected and immunized monkeys mediated ACC, whereas IgG-I and IgG-II from infected monkeys mediated ADCC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Purification of human lung leukotriene C4 synthase and preparation of a polyclonal antibody.

Leukotriene (LT) C4 synthase is an integral membrane protein that catalyzes the conjugation of LTA4 to reduced glutathione to form LTC4. LTC4 synthase has been cloned and characterized from transformed cell lines, but the protein has not been defined from a tissue source. LTC4 synthase was purified to homogeneity from human lung tissue, utilizing S-hexyl glutathione chromatography followed by LTC4 affinity chromatography. A greater than 100,000-fold purification with a yield of 8 to 25% (n = 4) was achieved. The purified LTC4 synthase migrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as an 18-kD protein, and its 19 N-terminal amino acid sequence is identical to that of purified LTC4 synthase from KG-1 myeloid cells or from expression cloning of a KG-1 library in COS cells. Using a rabbit polyclonal IgG raised against purified LTC4 synthase, SDS-PAGE immunoblotting of LTC4 synthase from human lung tissue, eosinophils, KG-1 cells, and platelets showed an 18-kD protein. Immunofluorescence staining of alveolar macrophages in human lung sections with the anti-LTC4 synthase IgG revealed LTC4 synthase to be largely perinuclear in distribution. Thus, LTC4 synthase, the biosynthetic enzyme responsible for the formation of cysteinyl LTs, is present in lung tissue in a form apparently identical to that of hematopoietic cells.

Amino Acid Sequence↗
PubMed1995

Experimental leprosy in monkeys. I. Sooty mangabey monkeys: transmission, susceptibility, clinical and pathological findings.

A total of 31 sooty mangabey monkeys (SMM) (Cercocebus torquatus atys) inoculated by various routes with differing numbers of SMM-origin Mycobacterium leprae (ML) and 4 SMM inoculated with human-origin ML were observed for 4-12 years. SMM-origin ML was more pathogenic in SMM than human-origin ML. The spectrum of disease ranged from indeterminate to borderline and lepromatous in different animals. Some animals developed pure neural leprosy. Erythema nodosum leprosum (SNL) was also observed. Combined intravenous/intracutaneous (IV/IC) routes of inoculation more effectively induced advancing, disseminated lepromatous forms of leprosy; IV or IC routes alone were less effective at comparable doses. Total IV/IC doses of SMM-origin ML equal to or greater than 5 x 10(8), with morphologic indices (MIs) ranging from 5 to 10%, produced advancing, disseminated LL leprosy in 92% of SMM. Lower IV/IC doses and inoculations by a single IV or IC route produced fewer leprosy infections and more spontaneous regressions. As a species, captive SMM are highly susceptible to experimental leprosy and provide an excellent model for the longitudinal study of leprosy.

Animals↗
PubMed1995

Experimental leprosy in monkeys. II. Longitudinal serological observations in sooty mangabey monkeys.

In this study, 11 SMM were grouped and inoculated with differing doses of SMM-origin Mycobacterium leprae (ML) between 4.5 x 10(8) and 1 x 10(9) by either combined IV/IC routes or by IV or IC route alone. The combined route was the most effective in eliciting progressive, disseminated LL leprosy. In all, 6 of 7 SMM inoculated by the combined routes developed leprosy requiring treatment at some point. Only 1 of 4 inoculated by a single route developed persisting leprosy requiring chemotherapy. Either no disease or spontaneous regression of initial disease occurred in the other 3 animals inoculated by a single route. Doses in excess of 1 x 10(9) ML were more effective than lesser doses. An association was observed between the development of IgG anti-PGL-I ELISA OD values and resistance to leprosy and between IgM anti-PGL-I and leprosy progression or susceptibility. Serum PGL-I antigen levels, determined by dot ELISA, paralleled disease severity longitudinally. High positive OD values of anti-LAM IgG prior to ML inoculation were observed in the majority of leprosy-susceptible SMM in contrast to negative levels in more resistant animals. Anti-LAM IgG OD values exceeded the positive cut-off point after inoculation in 5 of 11 SMM; 3 of these 5 had concurrent detectable serum levels of PGL-I antigen.

Animals↗
PubMed1995

Purification and partial amino acid sequences of a new presynaptic toxin and a cytotoxin from venom of pit veper Agkistrodon blomhoffii brevicaudus.

The technique of the reverse-phase performance liquid chromatography (RP-HPLC) was employed to separate and purify the toxic proteins from the venom of Agkistrodon blomhoffii brevicaudus collected in China. 3 toxic proteins marked as AgTx-1, AgTx-2 and AgTx-3 consisting of about 122 amino acid residues were screened. The toxicities (LD50) of the AgTx-1, AgTx-2 and AgTx-3 were 0.075, 0.51 and 6.6 mg per kg weight of mice respectively. Toxicological experiment in the chick biventer cervicis nerve-muscle preparation showed that the acetylcholine (Ach) sensitivity of the preparation was unchanged after the total failure of the indirect contraction caused by AgTx-1 and AgTx-2, suggesting that they were presynaptic blockers, namely beta-type of snake toxins. However, the amplitude of indirect contraction of the preparation was gradually reduced due to its incomplete relaxation caused by AgTx-3, indicating that it should belong to the category of cytotoxins. The partial amino acid sequences of 3 toxins have been established. It was found in ref. [1] that the sequences of the first 32 N-terminal amino acid residues of AgTx-1 and AgTx-2, as well as beta-agkistrodotoxin (beta-AgTx) reported previously were identical (the residue at the position 30 of beta-AgTx should be Trp). In view of the similarity in toxicities, and the amounts in the venom and other properties, it was concluded that AgTx-1 should be beta-AgTx and consequently was renamed beta 1-AgTx. AgTx-2 should be the isoform of beta 1-AgTx, and correspondingly named beta 2-AgTx.

Agkistrodon↗
PubMed1995

HBV surface antigen proteins with deletions in the preS region.

Four pairs of HBV surface antigen genes, in which the preS region was partially deleted, were constructed by the polymerase chain reaction (PCR). The comparison of the levels of the expression in mammalian cells of these genes and the ones constructed before, and the properties of these gene products showed that the missing of a part of the preS region did not affect the overall spatial structure of the S region and the surface localization of the preS region. The removal of the preS1 retention sequence (a. a. 2-19) alleviated significantly the shelter of the major antigenic determinants in the S region by the preS sequence. It was found that the long preS region seriously impaired the secretion of the surface antigen proteins from mammalian cells. In addition to the previously reported preS1 retention sequence, the preS1 sequence (a.a. 48-65) may also inhibit the secretion of the surface antigen proteins, whereas the preS2 region exerts no major influence on the retention of the large surface antigen protein. One of the expressed surface antigen proteins, in which the preS1 sequence (a.a. 21-47) and the S region were directly fused, deserves further study and may be developed into a new HBV vaccine which contains the preS1 binding site for hepatocyte receptors due to its stability, fine secretability and strong preS1 antigenicity.

Animals↗
PubMed1995

[Significance of immunohistochemical study in the diagnosis and differential diagnosis of chordoma].

Seven cases of chordoma were studied immunohisto-chemically with antibodies directed to epithelium, nerve, mesenchyme, muscle and histiocyte. Six cases of chondrosarcoma and three cases of mucinous carcinoma of colon were studied as control. The results showed that the chordomas were positive for cyto-K 6/7, EMA 7/7, CEA 6/7, Vim 7/7, S-100 7/7, alpha-AT 7/7, Lyso 4/7, while negative for GFAP and Des in all 7 cases indicating that chordoma, just like notochord, had the potentiality of multidirectional differentiation. In contrast, none of the chondrosarcomas was positive for cyto-K, EMA or CEA, but positive for Vim and S-100 in 6 cases. Three cases of colon mucinous carcinoma were positive for epithelial antibodies, but none reacted with other antibodies. Thus, immunohistochemical studies are of help in the diagnosis and differential diagnosis of chordoma.

Adenocarcinoma, Mucinous↗
PubMed1994

Enhanced tumor cell growth suppression by an N-terminal truncated retinoblastoma protein.

The retinoblastoma (RB) gene encodes a nuclear phosphoprotein of 928 amino acids (pRB). Thus far, much effort in RB research has been focused on both the viral oncoprotein-binding domains and the C-terminal domain, whereas little is known about the N-terminal moiety of the protein. We report here that an N-terminal truncated RB protein of approximately 94 kDa (pRB94) exerts more potent cell growth suppression as compared to the full-length pRB protein in a diversity of tumor cell lines examined, including those having a normal endogenous RB gene. Tumor cells transfected with the pRB94-expressing plasmids displayed multiple morphological changes frequently associated with cellular senescence and/or apoptosis. They failed to enter S phase and rapidly died. The pRB94 expressed in recipient tumor cells had a longer half-life than the full-length pRB protein and tended to remain in an active un- or hypophosphorylated form. Since it has also been found that N-terminal truncated RB proteins often accumulated in growth-arrested and/or differentiated tumor cells, we suggest that N-terminal truncation of pRB may be one of the cellular mechanisms modulating the RB protein function in cell-cycle control.

Animals↗
PubMed1994

Further characterization of retinoblastoma gene-mediated cell growth and tumor suppression in human cancer cells.

We have transfected the osteosarcoma cell line Saos2 and the bladder carcinoma cell line 5637 with additional retinoblastoma (RB) expression plasmids. The RB-reconstituted Saos2 and 5637 cells showed only slightly lower ratios of cells undergoing DNA synthesis compared to their parental RB- tumor cells, and there were no noticeable changes in cell morphology. Furthermore, we have isolated long-term RB+ clones from Saos2, 5637, and the retinoblastoma cell line WERI-Rb27 after transfection/transduction with a RB expression plasmid or retrovirus. These clones were similar to their parental cell lines in terms of morphology and growth rates, and they all expressed functional RB protein (p110RB) as evidenced by its potential of phosphorylation, simian virus 40 large tumor antigen binding, and nuclear tethering. No mutation or deletion of the exogenous RB gene was detectable by PCR and single-strand conformation polymorphism analysis. In addition, either the individual or pooled RB+ clones did form malignant tumors in nude mice but usually with a longer latency period and lower frequency. Such tumors also retained normal RB expression, suggesting that at least a portion of the RB-reconstituted tumor cells were still tumorigenic. This phenomenon is referred to by us as tumor suppressor resistance (TSR).

Animals↗
PubMed1994

Alpha-spirocyclopentyl- and alpha-spirocyclopropyl-gamma-butyrolactones: conformationally constrained derivatives of anticonvulsant and convulsant alpha,alpha-disubstituted gamma-butyrolactones.

To further study the putative gamma-butyrolactone site of the GABAA/chloride channel complex, constrained derivatives of convulsant and anticonvulsant alpha,alpha-disubstituted gamma-butyrolactones (alpha-spirocyclopropyl- and alpha-spirocyclopentyl-gamma-butyrolactones) were synthesized and evaluated biologically. Most of the spirocyclopropyl agents were anticonvulsants when tested against pentylenetetrazole-induced seizures in mice. These agents effectively displaced 35[S]-tert-butylbicyclophosphorothionate (35[S]-TBPS), a ligand for the picrotoxin binding site of the GABAA/chloride channel, from rat neuronal membranes and affected the GABA-mediated current in hippocampal neurons. The monomethyl-substituted spirocyclopropyl agent with a methyl group cis to the carbonyl (15) potentiates GABA-induced current whereas the trans derivative (16) blocks the current. The only anticonvulsant in the spirocyclopentyl series was the unsubstituted spirocyclopentyl compound 2. All the other substituted spirocyclopentyl targets were inactive in vivo at the highest dose tested except for convulsant 9, which has a trans 2,5-dimethyl-substituted cyclopentyl ring. All the spirocyclopentyl derivatives displaced 35[S]-TBPS from rat neuronal membranes very effectively, and they also all potentiated GABA-induced chloride current except for convulsant 9 which blocked the current. From the data obtained in this investigation, it appears that when the volume occupied above and below the lactone ring is as large as that occupied by spirocyclopentyl agent 9, convulsant activity is observed. Groups with less volume in these areas either are inactive in the behavioral test or have anticonvulsant activity. When bound to the GABAA/chloride channel, the larger molecules may stabilize the closed state of the channel whereas the smaller molecules may stabilize the open state.

4-Butyrolactone↗
PubMed1994

Caffeine metabolism in cystic fibrosis: enhanced xanthine oxidase activity.

STUDY OBJECTIVE: To characterize the activities of the P450 mixed-function oxidase CYP1A2 as well as the cytosolic enzymes N-acetyltransferase and xanthine oxidase using caffeine as a probe in children with cystic fibrosis compared to age-matched healthy control subjects. METHODS: After administration of caffeine (cola beverage) to 12 children with cystic fibrosis (age range, 5 to 11 years) and 12 healthy control subjects (age range, 5 to 12 years), urine was collected for 4 hours. Caffeine metabolites were determined by HPLC, and urinary caffeine metabolite ratios were computed to determine liver enzyme activities. In addition, a blood sample was used to detect cystic fibrosis mutant alleles by polymerase chain reaction. RESULTS: The indexes for CYP1A2, N-acetyltransferase, and 8-hydroxylation were similar in both groups of subjects. In contrast, there was a significant difference in the frequency distribution of the xanthine oxidase activity between the two groups. Nine of 12 patients with cystic fibrosis but only one of 12 healthy volunteers had xanthine oxidase activities above 0.42 (Kolmogorov-Smirnov two-sample test, p < 0.01). CONCLUSIONS: Differences in xanthine oxidase may have clinical implications with regard to interindividual variation in xenobiotic biotransformation and the exposure to lung tissue-damaging oxygen radicals. Hepatic enzyme activities appear to be selectively altered in patients with cystic fibrosis.

Alleles↗
PubMed1994

Infection with human immunodeficiency virus type 1 (HIV-1) and human T cell lymphotropic viruses among leprosy patients and contacts: correlation between HIV-1 cross-reactivity and antibodies to lipoarabinomannan.

To determine the association between leprosy and human retroviral infections, 57 leprosy patients, 39 leprosy contacts, and 500 pregnant women were investigated serologically for antibodies to human immunodeficiency virus type 1 (HIV) and human T cell lymphotropic virus (HTLV) types I and II. Antibodies to Mycobacterium leprae phenolic glycolipid I (PGL-I), and lipoarabinomannan (LAM) were also analyzed. A low prevalence of HIV-1 infection was observed among leprosy patients (3.5%), leprosy contacts (0), and pregnant women (3.6%). Antibodies to HTLV-I but not -II were found more often in leprosy patients (8.7%) and contacts (12.8%) than in pregnant women (0). Sera from leprosy patients and leprosy contacts were often false-positive for HIV-1 by ELISA and were indeterminate by Western blot. LAM IgM and PGL-I IgM antibodies in sera from leprosy patients yielded significant cross-reactivities with HIV-1 pol and gag proteins. These data suggest that mycobacterial cell wall antigens may share common epitopes with HIV. Caution should be exercised when interpreting HIV-1 ELISA and Western blot data from regions where leprosy or other mycobacterial diseases are endemic.

Adult↗
PubMed1994

Cloning, DNA sequence, and complementation analysis of the Salmonella typhimurium hemN gene encoding a putative oxygen-independent coproporphyrinogen III oxidase.

Coproporphyrinogen oxidation is a last step in heme biosynthesis. The biochemically characterized eukaryotic coproporphyrinogen III oxidases have an obligate requirement for molecular oxygen, and a similar enzyme is encoded by the hemF gene in Salmonella typhimurium. Anaerobic heme synthesis requires an oxygen-independent coproporphyrinogen oxidase, which is probably encoded by the hemN gene in S. typhimurium. The hemN gene has been cloned from an insertion mutant. The nucleotide sequence was obtained and used for PCR amplification of the wild-type gene. A single open reading frame was identified as the hemN gene on the basis of its interruption by the insertion mutation and plasmid complementation studies of hemF hemN double mutants. The predicted HemN protein has 38% amino acid sequence identity to a putative anaerobic Rhodobacter sphaeroides coproporphyrinogen oxidase. The hemN RNA 5' end and the inferred transcription initiation site were mapped by primer extension. The 52.8-kDa HemN protein is expressed from the second ATG codon of the hemN open reading frame. An open reading frame with an unknown function directly upstream of hemN has a striking amino acid sequence, including 11 acidic residues in a row.

Amino Acid Sequence↗