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Biomedical subjects

J Tang

Publications and source records attributed to J Tang.

At least 451 records · Page 25Linked to original sources
PubMed1993

[Molecular epidemiologic investigation on HSV infection among married women at childbearing age].

By PCR and ELISA, an investigation on HSV infection of cervix was carried out among 120 married women. The results indicated that the total infection rate was 23.3% (28/120). In HSV infection of cervix, HSV-2 constituted 89.3%. The positive rate of HSV in the cervicitis group and normal control group was 28.9% (26/90) and 6.7% (2/30), respectively, showing a marked difference: the positive rate in the group from 21 to 30 years old was 16.7% (7/43), from 31 to 40 was 34.6% (9/26); the positive rate in the group from rural areas was 30.8% (16/52), in the group from city was 17.6% (2/18).

Adult↗
PubMed1993

Guillain-Barre syndrome and Campylobacter jejuni infection. A study on the etiological characteristics of Guillain-Barre syndrome in China.

Fecal culture for Campylobacter jejuni with the method of Skirrow and serum class specific antibodies (IgG, IgM, IgA) against Campylobacter jejuni using a solid phase enzyme linked immunosorbent assay were performed in 17 cases of Guillain-Barre Syndrome, 17 other neurological disease controls, and 33 normal controls. The results revealed: 1. the incidence of Campylobacter jejuni infection, especially the recent one in Guillain-Barre Syndrome was much higher than in the other two groups; 2. the recent incidence of infection in those below 30 years old and those within the period of summer and autumn was higher than that above 30 years old and that in the other seasons. The results suggested that Campylobacter jejuni infection might be one of the important precipitating factors of Guillain-Barre syndrome and might play an important role in the epidemiological pattern of Guillain-Barre Syndrome in China.

Adolescent↗
PubMed1993

Gene expression of Na+/Ca2+ exchanger in brain ischemia.

It is known that intracellular Ca2+ is overloaded during ischemia as a result of the altered activity of the Na+/Ca2+ exchanger, one of the major pathways of Ca2+ efflux. But the molecular mechanism of the alteration is still unknown. We cloned a -500bp cDNA fragment of rat cerebellar Na+/Ca2+ exchanger gene. Using this cDNA fragment as the probe, we found that the Na+/Ca2+ exchanger mRNA is widely distributed in rat central and peripheral nervous system such as in cerebra, heart, lung and kidney. Using focal cerebral ischemic model, we detected the gene expression of Na+/Ca2+ exchanger in ischemic brain by Northern bolt and in situ hybridization, and found that in ischemic tissues, the mRNA level of Na+/Ca2+ exchanger is lowered.

Animals↗
PubMed1993

Expression of a fusion protein containing calf prochymosin B(1-161) and human proinsulin.

The plasmid pJG202 containing Tac promoter, calf prochymosin B(1-161) gene and human proinsulin gene was constructed and transformed into E. coli JM105. The expression of the fusion protein consisting of 249 amino acids was controlled by IPTG and temperature, and the expressed protein was estimated to be 20-35% of the total cellular proteins by scanning of the SDS-PAGE gel stained with Coomassie brilliant blue R250. After CNBr cleavage, sulfitolysis, partial separation of the S-sulfonated human proinsulin and recombination of the disulfide bonds, human proinsulin with native properties, as evidenced by amino acid composition analysis, receptor binding and radioimmunoassays, could be obtained.

Animals↗
PubMed1993

Possibility of targeting treatment for ischemic heart disease with liposome (II).

Studies on the isolated rat heart perfusion model have proved that perfusion with high Ca2+ (4.5 mmol/L), high K+ (8.7 mmol/L) or free radical generating system (FRGS) significantly increases myocardial uptake of liposomes. Intravenous injection of liposomes covalently combined with antibody of rat myocardial cells obviously elevates the target action of liposomes to myocardium. Liposome-carried SOD for treatment of rat myocardial ischemia-reperfusion injury is much more effective than simple SOD. The results evidence that the liposome as drug carrier for treatment of ischemic heart diseases shows a broad prospect for its clinical use.

Animals↗
PubMed1993

Effect of endothelin, angiotensin II and ANP on proliferation of vascular smooth muscle cells and cardiomyocytes.

By means of cell culture, 3H-thymidine (3H-TdR) incorporation and c-fos oncogene dot plotting technique, it was found that endothelin (ET) and angiotensin (ANG II) could promote proliferation and DNA synthesis of cultured vascular smooth muscle cells (VSMCs) and myocardial cells, and stimulate expression of c-fos oncogene of VSMCs. However, atrial natriuretic peptide (ANP) antagonizes the above effects of ET and ANG II.

Angiotensin II↗
PubMed1993

Human breast milk contains procathepsin D--detection by specific antibodies.

The presence of the zymogen of cathepsin D in human milk was detected using antibodies specific for the proenzyme and by the proteolytic activity at low pH. The antibodies were raised against a synthetic propeptide of human cathepsin D and were tested using immunoprecipitations and western blots of samples from different breast cancer cell lines as well as cytosol fractions of human breast cancer tissues. In all experiments these antibodies recognized specifically procathepsin D. Procathepsin D from human milk was partially activated at low pH. The activity was monitored using hemoglobin 14C proteolytic assay, and it was abolished by pepstatin A--a specific inhibitor of aspartic proteinases. Western blots did not reveal presence of cathepsin B or cathepsin H. These data indicate specific secretion of cathepsin D in human breast milk.

Antibodies↗
PubMed1993

[Five cases of Campylobacter jejuni enteritis accompanied with Guillain-Barré syndrome].

17 cases of Guillain-Barré syndrome (GBS) were admitted to The First Hospital of Beijing Medical University and Baoding Hospital from July, 1991 to October, 1992. Five patients had diarrhea before the onset of GBS and showed positive reaction for serum IgM antibodies to Campylobacter jejuni. They were considered to have Campylobacter jejuni enteritis as well. This incidence of Campylobacter jejuni enteritis in GBS patients was higher than in those with other neurological diseases and in normal controls. These five patients were all from countryside and had their onset in the summer and autumn. Moreover, four of them were below twenty-four years old. The epidemiological pattern was quite similar to that of Campylobacter jejuni enteritis in China. Our data showed the close association between GBS and Campylobacter jejuni enteritis and the possible mechanism was discussed.

Adolescent↗
PubMed1993

Plasma endothelin levels in cirrhotic patients and their correlation with atrial natriuretic peptide.

Plasma levels of endothelin (ET) were determined by radioimmunoassay in 11 healthy volunteers and 34 patients with liver cirrhosis. The results revealed that mean ET plasma level was significantly lower in 34 cirrhotic patients than in normal subjects (40.21 +/- 4.38 ng/L vs 84.55 +/- 7.88 ng/L, P < 0.01). Plasma ET was 32.17 +/- 3.98 ng/L in 23 cirrhosis patients with ascites compared with 57.0 +/- 9.0 ng/L in patients without ascites (P < 0.01). Moreover, it is apparent that plasma levels of ET decreased with the increase of ascites volume, and increased after the disappearance of ascites. But plasma levels of atrial natriuretic peptide (ANP) in cirrhotic patients were markedly higher than those in the controls (830.12 +/- 72.18 ng/L vs 439.45 +/- 50.18 ng/L, P < 0.01). In patients with ascites, ET plasma levels were inversely correlated to ANP. The results suggest that deficiency of circulating ET might be one of the important factors involved in sodium and water retention in cirrhosis.

Adult↗
PubMed1993

Reduction of intramuscular nerve branching and synaptogenesis is correlated with decreased motoneuron survival.

Blockade of neuromuscular activity during the period of naturally occurring cell death increases intramuscular nerve branching, synaptogenesis, and survival of embryonic chicken motoneurons. These results suggested that the enhanced motoneuron survival observed might result not from increased production of a trophic factor by the target, as often suggested, but rather from the enhanced ability of motoneurons to take up this factor via additional branches and/or synapses. Since removal of polysialic acid (PSA) by PSA-specific endoneuraminidase (endo N) during the period of nerve ingrowth and motoneuron cell death had been shown to reduce intramuscular nerve branching by altering adhesive interactions between axons and myotubes, we wished to determine, first, if this resulted in a reduction of synapse formation, and second, if this was correlated with decreased motoneuron survival. When PSA was removed from embryonic day 6 (E6) to E9 by injecting endo N into the limb, the number of synapses in the posterior iliotibialis muscle was greatly reduced both at E6.5, the onset of the cell death period, and at E7.5-E8, the middle of the cell death period. Total motoneuron counts at both E7.5-E8 and E10 (close to the end of cell death period) were significantly decreased compared to controls. These results indicate that a treatment that reduces intramuscular nerve branching and synapse formation also affects motoneuron survival. Furthermore, since removal of PSA in ovo via endo N altered neither the spontaneous embryonic motility nor the activation pattern of motoneurons or muscles, these experiments avoid the complication of activity blockade that may alter motoneuron survival by affecting events other than, or in addition to, intramuscular nerve branching.

Activity Cycles↗
PubMed1993

[Expression of left ventricular ANF-gene in rat with cardiac hypertrophy].

Plasma concentration of ANF and expression of left ventricular ANF-gene in rats with cardiac hypertrophy induced by abdominal aortic partial ligation were analyzed by RIA and Northern blot respectively. Results showed that plasma concentration of ANF and level of left ventricular ANF-mRNA in cardiac hypertrophic rats increased markedly, indicating that the cardiac load may induce transcription and expression of left ventricular ANF-gene. This effect could be potentiated by intracellular calcium modulator taurine and inhibited by vasodilator hydralazine.

Animals↗
PubMed1993

Possibility of targeting treatment for ischemic heart disease with liposome (I).

This paper reports the basic research on the possibility of using targeting treatment for ischemic heart disease with liposome as drug carrier. Studies have been performed on isolated rat cardiomyocytes, or isolated perfused rat and rabbit hearts. Results show that cardiomyocytes may interact with liposome through fusion, endocytosis, adsorption and molecular exchange of phospholipid. Forms of cellular uptake of liposome depend chiefly on the physicochemical properties of liposomes. Anoxia changes the pattern of liposome uptake by cardiomyocytes and increases uptake of liposomes. Uptake of liposomes, especially of positively charged liposomes by ischemic myocardium is significantly increased. The quantity of increase of liposome uptake is in the following order: ischemia-reperfusion area > peripheral area of the infarct > non-ischemic area > infarcted area. The above results indicate that liposome as drug carrier might promote the delivery of drug into ischemic myocardium and cardiomyocytes.

Animals↗
PubMed1992

Lengths of truncated forms of apolipoprotein B (apoB) determine their intestinal production.

Most truncations of apoB associated with hypobetalipoproteinemia (HBL) result from frame shift mutations of the apoB gene that give rise to premature stop codons and truncations of C-terminal sequences. The "natural" truncation, apoB-48, arises from a stop codon by cotranscriptional editing of intestinal apoB-100 mRNA. We hypothesized that mutant apoB mRNA would be normally edited and that only those apoB truncations shorter than apoB-48 would be expressed in enterocytes, because translation of mRNAs giving rise to longer truncations would be interrupted by the apoB-48 stop codon. Duodenal mucosal biopsies from HBL and normolipidemic subjects were incubated with [35S]methionine, apoB was immunoprecipitated and bands were visualized by autoradiography. Biopsies of three subjects heterozygous for apoB-54.8 or apoB-89 synthesized virtually only apoB-48. By contrast, the biopsy of a subject heterozygous for apoB-40 synthesized both apoB-48 and apoB-40. Thus, enterocytes in HBL edit the mutant mRNAs similarly to the apoB mRNA of normal enterocytes and the small intestine of heterozygotes with truncations longer than apoB-48 produce only apoB-48, as the apoB-48 stop codon terminates translation proximal to the mutant stop codon. By contrast, intestines of heterozygotes with truncations shorter than apoB-48 produce the truncated apoB because the mutant stop codon stops translation before the apoB-48 stop codon. In conclusion, only the liver secretes apoB truncations larger than apoB-48, whereas shorter truncations are secreted by both liver and intestine.

Apolipoproteins B↗
PubMed1992

Hormonal and nutritional stimuli modulate apolipoprotein B mRNA editing in mouse liver.

Human livers produce apoB-100, a major protein of VLDL, while intestines produce apoB-48, the major protein of chylomicrons. ApoB-48 is translated from apoB-100 mRNAs that are post-transcriptionally edited at codon 2153, converting CAA (glutamine) to TAA, a stop codon. In contrast to humans, mouse and rat livers contain the apoB-100 mRNA editing mechanism. Because hormones and nutrients affect the metabolism of apoB containing lipoproteins, we studied the effects of sex hormones and diets on apoB mRNA editing. Groups of male and female C3H/HeJ mice were castrated and treated with 17 beta-estradiol at 0.16 (E2L) or at 5 micrograms (E2H), or with testosterone propionate at 1 microgram/g body weight/day for 14 days. Plasma apoB levels and ratios of apoB-100/apoB-48 both increased 2-fold, but only in the E2H group. To determine if the increased apoB-100/apoB-48 ratios were associated with altered levels of apoB-100 and apoB-48 mRNA, both forms of apoB mRNA were quantified. We found that indeed ApoB-100 mRNA increased 1.8-fold (p < 0.025) compared to apoB-48 mRNA only in the E2H group. Next, we studied the individual effects of dietary fatty acids and dietary cholesterol on the relative abundance of apoB-100 and apoB-48 mRNA. Contrary to the estrogen effect, the high fat-combination diet increased apoB-48 mRNA relative to apoB-100 mRNA. Total plasma apoB as well as apoB-48 synthesis in liver also increased. Our studies demonstrate that estrogens and high fat diet both modulate apoB editing in mouse liver, but that estrogens and fat diet affected apoB mRNA editing in opposite directions.

Animals↗
PubMed1992

pH dependence of kinetic parameters of pepsin, rhizopuspepsin, and their active-site hydrogen bond mutants.

The pH dependence of the kinetic parameters of pepsin, rhizopuspepsin, and their active-site hydrogen bond mutants has been determined. These data have permitted the calculation of two active-site ionization constants in the free enzymes (pKe1 and pK32) and in the enzyme-substrate complexes (pKes1 and pKes2). The pKe1 of rhizopuspepsin (2.8) is near that of a normal carboxyl group and near the pKe1 of human immunodeficiency virus type 1 (HIV-1) protease (3.32) (Ido, E., Han, H. P., Kezdy, F. J., and Tang, J. (1991) J. Biol. Chem. 266, 24359-24366). The pKe1 of pepsin (1.57) is thus abnormally low. The pKe2 of rhizopuspepsin (4.44) is lower than that of pepsin (5.02) and HIV protease (6.80). The binding of substrate to rhizopuspepsin causes the lowering of pKes1 to 1.8 and the elevating of pKes2 to above 6. The pK alpha shifts due to substrate binding are much less pronounced in pepsin. Thus, the two enzyme-substrate complexes have similar pK alpha values. For both pepsin and rhizopuspepsin, the removal of hydrogen bonds to the active-site carboxyls by mutagenesis results in negligible changes in the four pK alpha values. The major alteration caused by these mutations is the decrease in kcat values, while there is little change in Km. These observations suggest that these hydrogen bonds to the active-site aspartyls contribute little to the pH-activity relationships of the aspartic proteases. The role of the active-site hydrogen bonds may well be to preserve the conformational rigidity of the catalytic apparatus.

Aspartic Acid Endopeptidases↗
PubMed1992

Enzymic activities of two-chain pepsinogen, two-chain pepsin, and the amino-terminal lobe of pepsinogen.

In order to study the relationships of aspartic proteases, we have modified pepsin, a single-chain eukaryotic enzyme, to a two-chain heterodimer, which resembles aspartic proteases from retrovirus, including human immunodeficiency virus. Two fragments of pepsinogen, residues 1P-172 and 173-326, were expressed separately in Escherichia coli. Mixtures of chains were refolded from urea solutions to generate an active two-chain pepsinogen, which was converted to two-chain pepsin in acid solutions. The intramolecular and bimolecular activation constants (k1 and k2) of two-chain pepsinogen are about 1.5-fold and one-sixth, respectively, of those for pepsinogen. Structural evidence suggests that the faster k1 of two-chain pepsinogen is due to decreased interaction of the propeptide with the pepsin moiety, implying that the rate-limiting step in the intramolecular activation of pepsinogen is the "conformational dissociation" of its propeptide. Two-chain pepsin has the same Km but only one-sixth of the kcat of pepsin. Both pepsinogen chains are capable of independent refolding. The refolding of the NH2-terminal chain, which contains the propeptide and the NH2-terminal lobe, generated a small amount of proteolytic activity which is likely derived from the homodimer of the NH2-terminal lobe. It has been postulated that mammalian aspartic proteases, which contain two structurally homologous lobes, are derived in evolution from a homodimer enzyme by gene duplication and fusion (Tang, J., James, M. N. G., Hsu, I.-N., Jenkins, J. A., and Blundell, T. L. (1978) Nature 271, 618-621). The observation of the homodimer activity of the NH2-terminal lobe of pepsinogen suggests that the interface of the lobes is conservative in evolution.

Base Sequence↗
PubMed1992

Dietary fatty acids and dietary cholesterol differ in their effect on the in vivo regulation of apolipoprotein A-I and A-II gene expression in inbred strains of mice.

Dietary cholesterol and dietary saturated fatty acids affected the plasma concentrations of various HDL components and the hepatic and intestinal expression of the apolipoprotein (apo) A-I gene and the hepatic expression of the A-II gene differently in three inbred strains of female mice. Thus, the HC diet (0.5% cholesterol, no added fatty acids) decreased HDL-cholesterol in C57BL and SWR strains but not in the C3H strain; plasma apo A-I and apo A-II concentrations decreased in all three strains. HDL-C/apo A-I and apo A-I/apo A-II mass ratios increased, suggesting that the HC diet altered both the concentrations and the compositions of HDL particles. In contrast, the HF diet (20% hydrogenated coconut oil, no added cholesterol) increased HDL cholesterol and apo A-I concentrations. The combination diet (HF/C, 20% coconut oil plus 0.5% cholesterol) increased HDL cholesterol and decreased triacylglycerols. Apo A-I concentrations were unaltered except for a significant increase in SWR mice. Apo A-II concentrations decreased in all strains. To examine molecular events that could lead to the changes in plasma apo A-I and apo A-II, we measured transcription rates in hepatic nuclei and steady state mRNA concentrations in liver and intestine and apo A-I synthetic rates in liver. Dietary cholesterol and fatty acids produced differing effects at transcriptional as well as post-transcriptional loci and the changes differed according to mouse strain. The most pronounced strain-related differences for both apo A-I and apo A-II occurred at post-transcriptional loci of apoprotein production. These could represent altered rates of translation in, or secretion from liver and/or intestine, or altered rates of clearance from plasma. In conclusion, the regulation of apo A-I and apo A-II gene expression by diet occurs at several steps of their production and perhaps also in catabolic pathways. This study identifies potential loci of regulation and forms the basis for future studies investigating specific genetic and molecular regulatory mechanisms.

Animals↗