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Biomedical subjects

Z Hu

Publications and source records attributed to Z Hu.

At least 307 records · Page 17Linked to original sources
PubMed1995

Characterization of baculovirus insecticides expressing tailored Bacillus thuringiensis CryIA(b) crystal proteins.

Full-length, truncated, and mature forms of the CryIA(b) insecticidal crystal protein gene of Bacillus thuringiensis were engineered into the p10 locus of Autographa californica nuclear polyhdrosis virus (AcNPV). A signal sequence of Heliothis virescens juvenile hormone esterase was introduced at the N-terminus of these constructs to induce secretion. All recombinants, except those containing the mature toxin, produced high levels of CryIA(b) ICPs in insect cells. Thirty percent of the intracellular protoxin was N-glycosylated, suggesting that the protoxin was translocated across the ER membrane. Secretion into the medium, however, was limited. The production of the mature toxin was poor as a result of its cytotoxicity to insect cells. In a bioassay against second instar Spodoptera exigua larvae, using a recombinant expressing the Androctonus australis scorpion toxin gene in the same p10 locus as a positive control, the median survival time of AcNPV recombinants expressing the various B. thuringiensis CryIA(b) ICP constructs was not significant different from that of wild-type AcNPV. This suggests that production and/or secretion of B. thuringiensis (pro)toxins by AcNPV p10 recombinant viruses does not increase insecticidal activity since (i) the protoxins produced are inactive and not likely to be activated in vivo; (ii) secretion of the B. thuringiensis protoxins is poor; and (iii) production of the mature toxins results in cytotoxicity.

Animals↗
PubMed1995

MIG1-dependent and MIG1-independent glucose regulation of MAL gene expression in Saccharomyces cerevisiae.

Glucose repression is a global regulatory system in Saccharomyces cerevisiae controlling carbon-source utilization, mitochondrial biogenesis, gluconeogenesis and other metabolic pathways. Mig1p, a zinc-finger class of DNA-binding protein, is a transcriptional repressor regulating GAL and SUC gene expression in response to glucose. This report demonstrates that Mig1 protein represses transcription of the MAL61 and MAL62 structural genes and also the MAL63 gene, which encodes the Mal-activator. Mig1p DNA-binding sites were identified upstream of all three MAL genes. Both of the Mig1p-binding sites found in the bidirectional MAL61-MAL62 promoter were shown to function in the Mig1p-dependent glucose repression. Studies using constitutive Mal-activator alleles suggest that glucose regulation of inducer availability is a second major contributing factor in glucose repression of MAL gene expression and is even stronger than the Mig1p-dependent component of repression. Moreover, our results also suggest the contribution of other minor mechanisms in glucose regulation of MAL gene expression.

Base Sequence↗
PubMed1995

Topical delivery of growth hormone releasing peptide using liposomal systems: an in vitro study using hairless mouse skin.

The results of this study clearly demonstrates the utility of novel non-ionic liposomal systems in facilitating transfer of GHRP-6 into and across deeper strata of skin following topical application. These findings indicate that it may be possible to deliver therapeutic doses of a wide variety of peptides to local skin tissue via topical application. The results also suggest the possibility of controlled enhancement of skin penetration or metered polypeptide deposition through appropriate choice of liposomal lipid components. The pronounced enhancement of GHRP-6 and mannitol transport from emulsions containing the nonionic lipids suggests a promising delivery system for hydrophilic drugs in general.

Administration, Cutaneous↗
PubMed1995

Effect of dietary fat or tamoxifen on the expansion of cells harboring Ha-ras oncogenes in mammary glands from methylnitrosourea-treated rats.

Diets containing high levels of fat enhance the formation of methylnitrosourea (MNU)-induced mammary gland adenocarcinomas in rats, while administration of the antiestrogen tamoxifen decreases the incidence of these tumors. It is not known, however, at what stage during tumor development the fat or tamoxifen exert their effects. Here we have used a PCR/liquid hybridization and gel retardation assay to determine the effects of dietary fat and tamoxifen on the growth rate of cells harboring an Ha-ras oncogene in the mammary glands of rats at various times following MNU administration. Glands from animals on a high-fat diet had significantly higher mutant cell fractions than those on a low-fat diet at both 30 and 75 days following MNU treatment. In contrast, there was no difference between the mutant cell fractions of tamoxifen-treated animals and controls at either 30 or 70 days. These results suggest that dietary fat promotes tumor formation early in carcinogenesis by stimulating the growth of cells harboring Ha-ras mutations, while tamoxifen delays the appearance of tumors either by acting as a tumoristatic or tumoricidal agent, or by acting to eliminate or retard the growth of preneoplastic cells just prior to the emergence of tumors.

Animals↗
PubMed1995

Influence of exercise induced myocardial ischemia on right ventricular dP/dt: potential implications for rate responsive pacing.

BACKGROUND: Right ventricular (RV) dP/dtmax has been used as a simple parameter for rate responsive pacing to simulate the normal sinus node function. However, the effect of acute myocardial ischemia on RV dP/dtmax has not yet been evaluated. METHODS: RV high fidelity pressure was measured in 21 patients at rest and during supine bicycle exercise. Nine patients (Group 1 = controls) had no or only minimal alterations of the coronary arteries and 12 (Group 2 = CAD) had significant coronary artery disease with exercise induced left ventricular (LV) wall-motion abnormalities (n = 10) and/or angina pectoris (n = 6). RV pressure and its first derivative (RV dP/dt) were determined by an 8 French micromanometer catheter. The time constant of RV pressure decay (Tau) was calculated from the negative reciprocal of RV pressure versus negative dP/dt during isovolumic relaxation. RV volumes and ejection fraction were calculated from RV biplane angiograms (multiple slice method) at rest and during exercise. RESULTS: Heart rate (HR), RV dP/dtmax and dP/dtmin increased significantly during exercise, whereas Tau decreased. There were no significant differences between the two groups, although RV ejection fraction increased from 67% to 72% in the control group but decreased from 63% to 51% in the CAD group (P < 0.05). An exponential relationship was found between HR and dP/dtmax with a correlation coefficient of 0.82 (P < 0.01; SEE = 7% of the mean value). CONCLUSIONS: Acute exercise induced myocardial ischemia does not significantly influence RV dP/dtmax during sinus rhythm. Consequently, this index of RV contractility may be used in patients with coronary artery disease as a simple parameter for rate responsive pacing.

Adult↗
PubMed1995

Elevated concentrations of plasma lipids and apolipoproteins B, C-III, and E are associated with the progression of coronary artery disease in familial hypercholesterolemic swine.

We reported earlier that a complex familial hypercholesterolemia (c-FHC) phenotype characterized by elevated levels of total plasma cholesterol (TC) and apoB and reduced levels of HDL cholesterol (HDL-C) and apoA-I is associated with the development of spontaneous atherosclerotic lesions in swine. In this study, we investigated concentrations of plasma lipids and apolipoproteins B, C-III, and E in six parental animals of two cholesterol concentration phenotypes and their 32 offspring, which segregated into high, intermediate, and normal cholesterol phenotypes. Subsequently, we compared the extent of atherosclerotic lesion development in coronary arteries to the concentrations of plasma lipids and apolipoproteins in the parents and two offspring per family. Mean concentrations for the high (n = 23), intermediate (n = 13), and normal (n = 2) cholesterol level phenotypes at 4 months of age were TC, 316 +/- 62.2, 159 +/- 17.1, and 105 +/- 12 mg/dL; LDL cholesterol, 275 +/- 63.1, 113 +/- 16.4, and 67 +/- 18.4 mg/dL; HDL-C, 35 +/- 6.1, 41 +/- 5.7, and 33 +/- 6.4 mg/dL; triglycerides, 48 +/- 10.8, 39 +/- 8.0, and 29 +/- 5.7 mg/dL; apoB, 152 +/- 32.5, 80 +/- 7.2, and 48 +/- 5.7 mg/dL; apoC-III, 10 +/- 4.2, 8 +/- 1.7, and 3 +/- 0.1 mg/dL; and apoE, 17 +/- 3.4, 7 +/- 1.7, and 5 +/- 0.7 mg/dL, respectively. Histological analysis of the major coronary arteries from members of the three families showed considerable variation in the severity of lesions, ranging from foci of adaptive intimal thickening consisting of two to six layers of smooth muscle cells to advanced lesions containing necrotic cores, cholesterol clefts, calcification, and hemorrhage (type V). The most extensive lesions occurred only in animals of the high cholesterol phenotype (ie, c-FHC), in which the concentration of TC and apoB progressively increased after 4 months of age, apoC-III, apoE, and triglycerides increased or remained elevated, and HDL-C decreased, except for one animal. Data presented here show that the plasma cholesterol phenotypes in FHC animals are associated with levels of apolipoproteins B, C-III, and E and indicate that the increases in the studied parameters after 4 months of age correlate with the progression of coronary artery disease.

Animals↗
PubMed1995

Effect of vitamin A deficiency on the integrity of hepatocytes after partial hepatectomy.

The effect of vitamin A deficiency on hepatic regeneration in male and female rats was studied after partial hepatectomy. A fourfold increase in the number of positive dUTP end-labeled nuclei was observed in the deficient animals as early as 30 minutes after partial hepatectomy and their number reached a peak by 8 hours after the operation. The bile duct cells were both morphologically and biochemically intact at all time points. Administration of retinyl palmitate 1 hour before partial hepatectomy significantly reduced the number of positive nuclei, and treatment with retinyl palmitate 24 or 48 hours before the operation reduced the number of positive cells to the level observed in control vitamin A-supplemented rats. The level of transcripts for c-jun, c-fos, c-myc, and transforming growth factor-beta 1 were increased for an extended period of time in livers of deficient animals, whereas the expression of both p53 and max were unchanged. Immunocytochemistry demonstrated the presence of latent transforming growth factor-beta 1 in cells showing evident apoptotic or necrotic changes in their nuclei. This study demonstrates the importance of vitamin A for the survival of hepatocytes both in intact vitamin A-deficient liver and after partial hepatectomy, whereas the ductal cells appear to be less sensitive to vitamin A deficiency.

Animals↗
PubMed1995

Expression of fibroblast growth factor receptors flg and bek during hepatic ontogenesis and regeneration in the rat.

Fibroblast growth factors (FGFs) mediate their cellular responses through specific cell surface receptors. Previous studies have indicated that acidic FGF is involved in liver regeneration and hepatic differentiation via the stem cell compartment, as well as in liver development (Marsden et al., Lab. Invest. 67:427-433, 1992). To further define the role of acidic FGF and its receptor systems in the liver, we examined the expression and cellular localization of FGF receptor-1 (flg) and FGF receptor-2 (bek) in the liver by Northern blot analysis and in situ hybridization techniques during liver regeneration, hepatic differentiation, and ontogenesis. In the normal adult liver, flg is absent in hepatocytes, whereas a low level of bek can be detected. The transcripts for bek increased, while flg exhibited little change during liver regeneration after partial hepatectomy. Both flg and bek were expressed at high levels in the developing liver. flg was expressed at a high level in embryonic liver and further increased after birth, whereas a significant increase of bek occurred at the postnatal stage of liver development. In the 2-acetylaminofluorene/partial hepatectomy model, both flg and bek are expressed at high levels during the period of active proliferation and differentiation of oval cells. In situ hybridization showed that flg was mainly localized in oval cells, whereas bek was highly expressed in both oval and Ito cells. The data suggest that bek is involved in the proliferation of mature hepatocyte proliferation during liver regeneration, while flg is characteristic of primitive hepatic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

[Analysis of causes of accidental deaths in several districts of Sichuan province].

The causes of accidental deaths from 1981 to 1988, including drowning, traffic accident, poisonning, child asphyxia, hitting, electric shock, fire and explosion in two cities and six districts of Sichuan Province were analysed. The average mortality from accidental death was 35. 58/10(5). Drowning and traffic death stood first and constituted 65.55% of the accidental deaths. Drowning, traffic death, poisoning and hitting death were more frequent in the male (P < 0.05). The mortality from traffic accident in the city was higher than that in the countryside. The mortality from drowning, child asphyxia and hitting in the city was lower than that in the countryside (P < 0.05).

Accidents↗
PubMed1995

Absence of somatic changes in p21 gene in non-Hodgkin's lymphoma and chronic myelogenous leukemia.

p21 is induced by and mediates the effects of p53 in response to DNA damage arresting the cell in G1 or G2, by inhibiting multiple cyclin-cyclin-dependent kinases (CDK) or binding to proliferating-cell nuclear antigen (PCNA), respectively. To determine whether p21 mutants occur in tumors we examined DNA from 188 primary non-Hodgkin's B-cell lymphoma (NHL) tumors and 84 chronic myelogenous leukemia samples for mutational changes in the coding region of p21 by single-strand conformation polymorphism (SSCP) analysis and direct sequencing of polymerase chain reaction (PCR)-amplified DNA. We did not find mutations in the coding region in these two tumor types. We identified a polymorphic nucleotide change in codon 31 in which a transversion from C to A substituted amino acid arginine for serine. Three of 188 NHL tumors were homozygous for this change, but they were not identified in 84 CMLs or in 97 normal controls. On the other hand, in one CML case a transition from G to A in codon 64 substituted amino acid threonine for alanine. These data do not indicate that derangements in the coding region of p21 contribute to the initiation and/or progression of these tumors.

Base Sequence↗
PubMed1994

Mössbauer and EPR studies of Azotobacter vinelandii ferredoxin I.

Azotobacter vinelandii ferredoxin I (FdI) is a small protein that contains one Fe4S4 cluster and one Fe3S4 cluster. Previous studies of FdI have shown that the redox potential of the Fe3S4 cluster and the MCD and CD spectra of the reduced Fe3S4 cluster are pH-dependent. Using Mössbauer and EPR spectroscopy, we have studied FdI in different oxidation states and at different pH values. Here, we report the spin Hamiltonian parameters of the oxidized (S = 1/2) Fe3S4 cluster at pH 7.4 and the reduced (S = 2) Fe3S4 cluster at pH 6.0 and 8.5. The pH dependence observed by MCD is also evident in the Mössbauer spectra which show a change of the magnetic hyperfine tensor for one Fe site of the valence-delocalized pair. The Fe4S4 cluster is ligated by cysteines 20, 39, 42, and 45, but not by the adjacent cysteine 24. Treatment of FdI with 3 equiv of ferricyanide alters the Fe4S4 cluster, yielding a new species, [Fe4S4]'. The S = 1/2 EPR signal of [Fe4S4]' has previously been attributed to the formation of a cysteine disulfide radical from Cys24 and cluster sulfide. Here we show that the EPR signal is broadened by 57Fe, indicating that the electronic spin is significantly coupled to the cluster iron. Consistent with this, substantial magnetic hyperfine interactions are observed by Mössbauer spectroscopy. In addition, the average isomer shift of the four Fe sites is smaller for [Fe4S4]' than for [Fe4S4]2+, indicating that the oxidation is iron-based to at least some extent. Incubation of FdI with excess ferricyanide destroys the Fe4S4 cluster but leaves the Fe3S4 cluster intact. Our studies of (3Fe)FdI show that the S = 1/2 spin of the Fe3S4 cluster interacts with another paramagnet, presumably a radical generated at the site left vacant by the removal of the Fe4S4 cluster.

Azotobacter vinelandii↗
PubMed1994

Structures of heat-stable and unstable homologues of the sweet protein mabinlin. The difference in the heat stability is due to replacement of a single amino acid residue.

There are several analogues of the sweet protein mabinlin. In previous studies, we purified the heat-stable analogue, mabinlin II, from the seeds of Capparis masaikai Lévl. and determined its amino acid sequence [Liu, X., Maeda, S., Hu, Z., Aiuchi, T., Nakaya, K. & Kurihara, Y. (1993) Eur. J. Biochem. 211, 281-287] and the disulfide structure [Nirasawa, S., Liu, X., Nishino, T. & Kurihara, Y. (1993) Biochim. Biophys. Acta 1202, 277-280]. We have now purified four additional homologues of mabinlin. The sweet activities of mabinlin III and mabinlin IV were unchanged by incubation for 1 h at 80 degrees C, as was found previously for mabinlin II, while the sweet activity of mabinlin I-1 was completely abolished by a 1-h incubation at 80 degrees C. The circular dichroic spectrum showed that alpha-helical structures of mabinlins II-IV were unchanged by the 1-h incubation at 80 degrees C, while the alpha-helical structures of mabinlin I-1 were completely destroyed by the 1-h incubation in parallel with the decrease of the sweet activity. To compare the structures of the heat-stable and unstable homologues, we determined their amino acid sequences and the disulfide array. The positions of four disulfide bridges of mabinlin I-1 were the same as those of mabinlin II, suggesting that the disulfide bridges do not contribute to the difference in the heat stability among the homologues. There was a high similarity among amino acid sequences of the homologoues. Only three amino acid residues (A-chain residues at positions 22 and 32 and B-chain residue at position 47) were different between mabinlin I-1 and mabinlin III. A-chain residue at position 32 was lacking in mabinlin IV and the A-chain residue at position 22 was identical in both mabinlin I-1 and mabinlin II. The B-chain residue at position 47 was the only residue present in all three heat-stable homologues (mabinlins II-IV) and is not present in the unstable homologue (mabinlin I-1). This suggests that the difference in the heat stability of mabinlin is due to the difference in a B-chain residue at position 47; the difference in the heat-stable homologues is due to the presence of an arginine residue and the difference of the unstable homologue is due to the presence of glutamine.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Intestinal clearance of H2-antagonists.

Jejunal perfusion of cimetidine resulted in the appearance of lumenal cimetidine sulfoxide in both rats and humans. In the rat, ileal perfusion yielded negligible sulfoxide metabolite as compared with that of the jejunum. Jejunal co-perfusion of an anionic-exchange inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, blocked the appearance of drug sulfoxide, and methionine co-perfusion yielded concentration-dependent inhibition of lumenal cimetidine sulfoxide. Intravenous injection of high concentrations of cimetidine sulfoxide did not produce detectable lumenal metabolite levels during jejunal perfusion of drug-free buffer, providing in situ evidence that lumenal metabolite is generated by the small intestine. The extent of the appearance of lumenal sulfoxide was significantly greater for cimetidine than for the other three marketed H2-antagonists in rat jejunum. Variable intestinal clearance of this extensively prescribed class of therapeutic agents may contribute to their absorption variability.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Substrate activation of brewers' yeast pyruvate decarboxylase is abolished by mutation of cysteine 221 to serine.

Brewers' yeast pyruvate decarboxylase (EC 4.1.1.1), a thiamin diphosphate and Mg(II)-dependent enzyme, isolated from Saccharomyces cerevisiae possesses four cysteines/subunit at positions 69, 152, 221, and 222. Earlier studies conducted on a variant of the enzyme with a single Cys at position 221 (derived from a gene that was the product of spontaneous fusion) showed that this enzyme is still subject to substrate activation [Zeng, X., Farrenkopf, B., Hohmann, S., Jordan, F., Dyda, F., & Furey, W. (1993) Biochemistry 32, 2704-2709], indicating that if Cys was responsible for this activation, it had to be C221. To further test the hypothesis, the C221S and C222S single and the C221S-C222S double mutants were constructed. It is clearly shown that the mutation at C221, but not at C222, leads to abolished substrate activation according to a number of kinetic criteria, both steady state and pre steady state. On the basis of the three-dimensional structure of the enzyme [Dyda, F., Furey, W., Swaminathan, S., Sax, M., Farrenkopf, B., Jordan, F. (1993) Biochemistry 32, 6165-6170], it is obvious that while C221 is located on the beta domain, whereas thiamin diphosphate is wedged at the interface of the alpha and gamma domains, addition of pyruvate or pyruvamide as a hemiketal adduct to the sulfur of C221 can easily bridge the gap between the beta and alpha domains. In fact, residues in one or both domains must be dislocated by this adduct formation. It is very likely that regulation as expressed in substrate activation is transmitted via this direct contact made between the two domains in the presence of the activator.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

[Prinzmetal's variant angina: a case report].

Prinzmetal's angina is a variant of the classic exertion dependent angina pectoris. Typical is the appearance of the symptoms at rest during early morning hours. It is due to spasms in the coronary arteries. Various provocation tests may be used to trigger spasms, among others hyperventilation which leads to vasoconstriction of coronary arteries. The case of a 53-year-old patient with Prinzmetal's angina is described in whom spasms of the right coronary artery could be evoked by hyperventilation. The following pathogenetic mechanisms may be possible in Prinzmetal's angina: disturbed endothelial permeability, endothelial dysfunction, or secretion of vasoconstrictive substances as well as local hypersensitivity of segments disturbed by atherosclerotic lesions to circulating vasoconstrictors.

Angina Pectoris, Variant↗
PubMed1994

A covalently trapped folding intermediate of subtilisin E: spontaneous dimerization of a prosubtilisin E Ser49Cys mutant in vivo and its autoprocessing in vitro.

The propeptide of subtilisin E (the N-terminal 77 amino acid extension) is required for the proper folding of the nascent mature protein and is also a potent and specific inhibitor of the active enzyme. Previous studies have demonstrated that the propeptide can renature denatured mature sequence either in cis or in trans and can be considered an intramolecular chaperone, since it is not required for activity of the mature enzyme. In this paper it is shown that a prosubtilisin-S49C mutant can be expressed in Escherichia coli either as a monomer or as a disulfide-linked dimer, (prosubtilisin-S49C)2, depending on the vector selected. Interconversion between (prosubtilisin-S49C)2 and prosubtilisin-S49C could be readily achieved by reduction and oxidation in denaturing solutions, such as guanidine hydrochloride or urea. While the monomer can undergo autoprocessing in vitro under refolding conditions, the dimer is trapped in an intermediate state which could not be processed into active enzyme. Remarkably, the autoprocessing of this trapped intermediate could be induced readily upon reduction by dithiothreitol. This disulfide-linked (prosubtilisin-S49C)2 is fairly stable, but does tend to aggregate when the ionic strength of the solution is reduced below 0.1 M. The disulfide-linked (prosubtilisin-S49C)2 has far- and near-UV CD spectra revealing the presence of both secondary and tertiary structures, respectively, similar to those of the active mature monomer. Hence this autoprocessing-competent state appears to be a "late" folding intermediate, arising after the "molten globule" state formed in the absence of the prosequence, that has no discernible tertiary structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

Modulation of keratin 14 and alpha-fetoprotein expression during hepatic oval cell proliferation and liver regeneration.

Keratin 14 (K14) expression has recently been demonstrated in cell lines of non-parenchymal hepatic origin (Bisgaard et al., 1993, Mol. Carcinog., 7:60-66; Bisgaard et al., 1991, J. Cell. Physiol., 147:333-343). These cell lines are thought to represent a progeny of a dormant stem cell compartment present in the adult rat liver, which may participate in the restoration of the liver mass after experimental liver injury. Utilizing a combination of 2-acetylaminofluorene (2-AAF) administration and partial hepatectomy to activate liver regeneration by proliferation of oval cells, we examined the modulation of K14 as well as alpha-fetoprotein (AFP) expression in proliferating oval cells and lineages hypothesized to be derived herefrom. We showed by Northern blot and in situ hybridization analyses that K14 and AFP transcripts were initially accumulating in epithelial cells located in subsets of ductal structures in the portal areas. As oval cells infiltrated the liver parenchyma, K14 transcripts were detected in oval cells, in foci of small basophilic hepatocytes, and in structures resembling glandular intestinal-type epithelium. AFP was expressed in oval cells, and at low but detectable levels in foci of basophilic hepatocytes, but not in glandular intestinal-type epithelium. Neither K14 nor AFP transcripts were detected in bile ducts or mature hepatocytes at any time during oval cell proliferation and reconstitution of the liver mass. To further study the modulation of K14 and AFP expression we utilized an in vitro model in which spontaneous transformation of rat liver epithelial (RLE) cells appeared to mimic the process of early differentiation along the hepatic lineage in vivo. We demonstrated that undifferentiated RLE cells at a late passage expressed K14 and vimentin, whereas transformation and differentiation to hepatoblast-like progeny resulted in an abrogation of K14 and vimentin expression and an induction of K18 and AFP. We propose that K14 and AFP are sequentially modulated in subpopulations of oval cells involved in the ongoing reconstitution of the liver mass.

2-Acetylaminofluorene↗