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Biomedical subjects

Z Zhao

Publications and source records attributed to Z Zhao.

At least 325 records · Page 18Linked to original sources
PubMed1994

Effects of selenium and alpha-tocopherol on liver damage induced by feeding grains from an endemic area of Keshan disease in rats.

Previous studies have shown the pathogenic effects of grains cultivated in the endemic areas of Keshan disease and selenium is effective in the prevention of this disease. In this study, liver damages induced by feeding grains from an endemic area (endemic diet), and the effects of selenium and alpha-tocopherol supplement were examined. After 3 months on the endemic diet, the amounts of serum enzymes were significantly increased when compared to controls (animals receiving diet from a non-endemic area). Liver enzymes (alkaline phosphatase and choline esterase) were also found to be altered in the serum, further suggesting liver damages in animals on an endemic diet. Supplement of the endemic diet with selenium or alpha-tocopherol reversed the changes in serum enzymes. Increase in lipid peroxidation in the liver of animals on the endemic diet was observed when compared to that in control animals. Selenium and alpha-tocopherol supplements prevented the increase in lipid peroxidation in the liver by the endemic diet. Semi-quantitative histochemical analysis of glutamate dehydrogenase and succinate dehydrogenase in liver tissue showed that the livers of animals on an endemic diet were more sensitive to ischemic damages in vitro. Supplementation of the endemic diet with either selenium or alpha-tocopherol reduced the sensitivity to ischemic damages. The results suggest that increased lipid peroxidation in the liver of rats on an endemic diet may be responsible for liver damages and elevation of serum enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Purification and characterization of PTP2C, a widely distributed protein tyrosine phosphatase containing two SH2 domains.

PTP2C, a widely distributed protein tyrosine phosphatase (PTP) containing two SH2 domains, was expressed as a recombinant enzyme in Escherichia coli and purified to near homogeneity. The purified enzyme and a truncated form lacking the SH2 domains (delta SH2-PTP2C) have been characterized with four commonly used substrates. Both forms showed pH optima of around neutrality for protein substrates but below 5.5 for a peptide substrate and para-nitrophenylphosphate. The dependence of the enzymes on ionic strength varied with the nature of the substrates involved. Like its analog PTP1C, PTP2C displayed a specific activity of less than 0.1% of that observed with other known PTPs toward protein substrates. Deletion of the SH2 domains increased its activity by 12-45-fold, depending on the substrates used. Limited trypsinolysis which cleaved about 4 kDa from the carboxyl terminus resulted in a 2-5-fold activation of the full-length enzyme but was essentially without effect on the truncated enzyme. Both forms showed similar responses to effectors including activators (e.g. anionic phospholipids) or inhibitors (e.g. vanadate, molybdate, or Zn2+). PTP2C and delta SH2-PTP2C were phosphorylated in vitro by mitogen-activated protein kinase, protein kinase C, and various protein tyrosine kinases; in the latter case, they underwent autodephosphorylation. No significant effect of the phosphorylation reactions on enzyme activity could be observed in vitro.

Amino Acid Sequence↗
PubMed1994

Molecular entrapment of small molecules within the interior of horse spleen ferritin.

A procedure for trapping small molecules inside the interior of horse spleen ferritin (HoSF) and methods for characterizing HoSF and its small entrapped molecules are described. HoSF is first dissociated into subunits by adjustment to pH 2 in the presence of the small molecules to be trapped. The pH of the dissociated HoSF is then increased to 7 at which time the dissociated subunits reassemble reforming the 24-mer HoSF, thereby trapping solvent within its interior. HoSF is then separated from unbound molecules by dialysis, ultrafiltration, and/or ammonium sulfate precipitation. Sephadex G-25 and DEAE chromatographic methods were also used to separate HoSF from unbound small molecules. Capillary electrophoresis (CE) was used to demonstrate the association of small molecules with HoSF after the pH-induced unfolding-refolding process. The pH indicator neutral red was clearly associated with HoSF and presumed trapped within the ferritin interior. Acid/base titrations suggested that the trapped indicator had a different pKa than the free indicator, a result which indicates that the ferritin interior is different than the external solution. The utility of using trapped molecules for gaining information on ferritin function is proposed and discussed.

Ammonium Sulfate↗
PubMed1994

Regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase gene expression by sterols and nonsterols in rat liver.

The mechanisms by which sterols and nonsterols regulate hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase gene expression was investigated by measuring mRNA, protein, and enzyme activity in rats fed cholesterol or given drugs that deplete both endogenous sterols and nonsterols or that selectively deplete sterols. It was found that while dietary cholesterol had little effect on HMG-CoA reductase mRNA levels; immunoreactive protein was reduced to barely detectable levels, as was enzyme activity. Any possible effect on catalytic efficiency is thus ruled out. When rats were fed diets containing Lovastatin, a potent HMG-CoA reductase inhibitor which blocks synthesis of both nonsterols and sterols, similar 15- to 20-fold increases were observed for both HMG-CoA reductase mRNA and activity. However, HMG-CoA reductase immunoreactive protein was increased more than 200-fold. When endogenous sterols were selectively depleted by inhibiting squalene synthase with Zargozic acid A, the increase observed in reductase mRNA was similar to that seen in immunoreactive protein and enzyme activity. This is consistent with the concept that endogenous sterols exert their effects at the level of transcription while endogenous nonsterols act at the level of translation. The results suggest that in whole animals, sterols likely act at the level of mRNA while nonsterols exert their regulatory effects at the level of HMG-CoA reductase protein.

Animals↗
PubMed1994

Effect of squalene synthase inhibition on the expression of hepatic cholesterol biosynthetic enzymes, LDL receptor, and cholesterol 7 alpha hydroxylase.

Squalene synthase catalyzes the committed step in the biosynthesis of sterols. Treating rats with zaragozic acid A, a potent inhibitor of squalene synthase, caused marked increases in hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase, HMG-CoA reductase, squalene synthase, and LDL receptor mRNA levels. The increase in HMG-CoA reductase mRNA fully accounted for the increases seen in enzyme protein and activity. Farnesyl pyrophosphate synthase mRNA and activity were only slightly increased by zaragozic acid A, while cholesterol 7 alpha hydroxylase mRNA levels were decreased substantially. When rats were pretreated with zaragozic acid A, there was no change in mRNA levels for the cholesterol biosynthetic enzymes or cholesterol 7 alpha hydroxylase upon subsequent treatment with mevalonolactone. Under these same conditions, the enzymatic activity of HMG-CoA reductase was also unaffected. Mevalonolactone treatment reduced the zaragozic acid A-mediated increase in hepatic LDL receptor mRNA levels. Feeding cholesterol eliminated the zaragozic acid A-induced increase in HMG-CoA reductase mRNA levels. These results suggest that inhibition of squalene synthase decreases the level of a squalene-derived regulatory product, resulting in altered amounts of several mRNAs and coordinate increases in HMG-CoA reductase mRNA, protein, and activity. The increase in HMG-CoA reductase gene expression was closely related to the degree of inhibition of cholesterol synthesis caused by zaragozic acid A.

Animals↗
PubMed1994

A capillary electrophoresis method for studying apo, holo, recombinant, and subunit dissociated ferritins.

A capillary electrophoresis (CE) method is described for detecting and quantitating apo and holo ferritins from horse spleen (HoSF), rat liver (RLF), recombinant human light chain (rLF), recombinant human heavy chain (rHF), site-directed variants of human light chain, and Azotobacter vinelandii bacterial ferritin (AVBF). This procedure is carried out at pH 8.2, where the ferritin molecules are associated into their 24-mers. Protein mobilities as expressed as elution times were clearly resolved and could be used to distinguish one ferritin type from another, providing a means for detecting and quantitating various ferritin species in purified or partially purified states. Measurements of these and other ferritins were also conducted at pH 2.0, where dissociation into their respective subunits occurs. For HoSF and RLF, the individual L and H subunits were resolved and their relative concentrations were determined by integrating the areas of the elution peaks. HoSF gave 89.8% L and 10.2% H and RLF gave 70.7% L and 29.3% H, while rLF, rHF, and AVBF gave only a single subunit, all in agreement with reported values obtained by polyacrylamide gel electrophoresis. CE of HoSF, containing increasing amounts of iron in the interior, in general, showed that protein mobilities increased, reached a plateau, and then slowly decreased with increasing core size, although buffer effects altered this CE behavior to some extent. Such results indicate that species formed early during core formation have individual iron atoms present and differ from those formed later in which the oligomeric iron core has formed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Capillary electrophoresis of nucleotides on ucon-coated fused silica columns.

Ucon-coated columns have been used to isolate nucleotides, such as ribonucleotides, deoxyribonucleotides, and pyridine nucleotides, by capillary zone electrophoresis. This neutral, hydrophilic column coating (Ucon) significantly reduced macromolecule adsorption and electroosmotic flow, which provides the maximum resolution of the nucleotides separated under moderate buffer conditions (pH about 5-6). The relative standard deviations of the nucleotides were less than 1%. Low minimum detectable concentrations (about 2-8 microM) and quantities (about 70-360 fmol) of the ribonucleotides were obtained. A qualitative and quantitative analysis of the ribonucleotides in hybridoma cell extracts shows the applicability of the developed methodology for the determination of intracellular nucleotide pools under the desirable buffer conditions.

Cells, Cultured↗
PubMed1994

Effects of stimulated growth hormone secretion on age-related changes in plasma cholesterol and hepatic low density lipoprotein messenger RNA concentrations.

Growth hormone (GH) secretion declines during aging. Since GH alters plasma cholesterol (PC) concentrations, it was of interest to determine how GH secretagogues affect age-related hypercholesterolemia. Fischer 344 rats (3 and 14 months old) were co-administered (s.c.) GH releasing hormone (3 micrograms/kg; GHRH) and GH releasing hexapeptide (100 micrograms/kg; GHRP) for 120 consecutive days. Aging was associated with a progressive increase in PC, which was reduced in rats administered GHRH and GHRP compared to those administered vehicle, i.e. changes in PC during the study were 26.5 +/- 1.2 mg/dl vs. 40.1 +/- 0.9 mg/dl (P < 0.05) in the younger rats and 17.6 +/- 2.3 mg/dl vs. 31.6 +/- 5.3 mg/dl (P < 0.05) in the older rats, respectively. The lower concentrations of PC in GH secretagogue-treated older rats were associated with higher mean concentrations of hepatic LDL receptor mRNA (1.27 +/- 0.4 vs. 0.4 +/- 0.1; P < 0.05) but not cholesterol 7-alpha hydroxylase mRNA. Although GH secretagogue treatment was also associated with lower plasma cholesterol in the younger rats, it was not accompanied by quantitative changes in mean group concentrations of hepatic LDL receptor mRNA. Instead, daily administration of GHRH and GHRP in the younger rats correlated with a significant reciprocal relationship (P < 0.05) between PC and hepatic LDL receptor mRNA for individual group members. The results of this study suggest that reduced GH secretion during aging contributes, at least in part, to a progressive increase in plasma cholesterol that can be partially prevented with GH secretagogues. Furthermore, the effects on PC may result from GH-mediated, qualitative and quantitative changes in hepatic LDL receptor mRNA that increase receptor-mediated cholesterol clearance.

Aging↗
PubMed1994

Hyperacute xenograft rejection in the swine-to-human donor-recipient combination. In vitro analysis of complement activation.

Complement activation is central to the rejection of discordant xenografts. In order to assess the respective roles of direct and alternative pathways, an in vitro model of hyperacute rejection in the swine-to-human donor-recipient combination was designed, using a complement-dependent cytotoxicity test with swine endothelial cells in culture as targets, and fresh human serum as the source of xenogeneic antibodies and complement. The cytotoxic activity of the sera was evaluated by a colorimetric assay using (3-[4,5-dimethyldiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT). Pure human serum lysed 58 +/- 5% of swine endothelial cells. Selective inhibition of the direct pathway by adding EGTA to the serum reduced cytolysis to 51 +/- 2% (P < 0.01 versus normal serum). Similarly, when using C1q-deficient human sera, only 37 +/- 7% of swine endothelial cells were killed (P < 0.001 versus normal serum). When the alternative pathway was selectively inhibited by heating for 20 min at 50 degrees C, the lytic activity of human serum dropped to 42 +/- 5% (P < 0.001 versus normal serum). Factor B-deficient human serum could only lyse 42 +/- 10% of porcine endothelial cells (P < 0.001 versus normal serum). Syngeneic normal swine serum and heat-inactivated serum were not cytotoxic. Mixing serum with deficient direct pathway and serum with deficient alternative pathway restored the cytotoxicity to normal levels. Similarly, the cytotoxic activity of deficient serum supplemented with purified C1q or factor B at physiological concentrations reached that of normal human serum. In this model of in vitro hyperacute rejection, both pathways of complement activation are involved, suggesting that regimens designed to inhibit hyperacute rejection of swine xenografts into humans should take into account the dual activation of complement in this donor-recipient combination.

Acute Disease↗
PubMed1994

Identification and characterization of the terminators of the lys and P transcripts of bacteriophage Mu.

Transcription during the lytic cycle of phage Mu occurs in three phases: early, middle, and late. Late transcription requires the Mu C protein and initiates at four promoters: Plys, PI, PP, and Pmom. Northern blot analysis of total RNA isolated 30 min after heat induction of Mu cts lysogens demonstrated that the full-length lys and P transcripts were approximately 7.6 and 6.3 kb long, respectively. The 3' ends of the lys and P transcripts were further localized by S1 nuclease mapping to intergenic regions between G and I and between U and U' in both the G(+) and G(-) orientations of the invertible G segment, respectively. As expected, when DNA fragments containing these termination regions were cloned into plasmids between Pgal and the galK gene, they showed efficient termination activity, even in a Rho-deficient background. Deletion analysis indicated that efficient termination required the presence of potential RNA stem-loop structures immediately preceding the RNA 3' ends. For the P transcript from phage with the G(-) orientation, full termination activity required both the region containing the stem-loop structure and upstream sequences. Taken together, these results suggest that the transcription termination sites of the lys and P transcripts are Rho-independent terminators.

Amino Acid Sequence↗
PubMed1994

Signalling effect of elevated potassium concentrations and monoamines on brain energy metabolism at the cellular level.

The effects of elevated K+ concentrations and monoamine transmitters on different cell types in the CNS and on different subcellular structures in these cells are reviewed. Pronounced differences exist in the metabolic processes that are stimulated by excess K+ and by adrenergic agonists, e.g., noradrenaline. An elevation in the extracellular K+ concentration appears to enhance neuronal-astrocytic interaction by stimulating metabolic processes involved in (1) the promotion of supply of precursors for transmitter glutamate, and (2) reestablishment of resting ion distribution following neuronal excitation. The monoamine transmitters stimulate energy production and Na+,K(+)-ATPase activity in astrocytes in a complex manner and, in so doing, facilitate their role in ion regulation. However, in contrast to excess K+, they do not enhance the production of astrocytic precursors for neuronal glutamate production. Emphasis is placed on possible profound differences in metabolic effects on excitatory and inhibitory neurotransmission and on the importance of stimulation of glycolytic metabolism in astrocytes versus oxidative metabolism in neurons.

Animals↗
PubMed1994

Altered pulmonary microvascular reactivity to norepinephrine in canine pacing-induced heart failure.

Pulmonary hypertension in congestive heart failure causes medial hypertrophy in pulmonary vessels and thickening of the endothelial basement membrane. In this study, the functional consequences of such pulmonary vascular adaptations were evaluated. Heart failure was induced in dogs by rapid ventricular pacing (240 beats per minute) for 28 days, at which time left ventricular shortening fraction was decreased by 57% compared with that at baseline. Lung lobes from paced (n = 56) and control dogs (n = 68) were isolated and perfused with autologous blood. Total, arterial (Ra), and venous (Rv) vascular resistances were significantly increased and vascular capacitance decreased in lobes from paced animals compared with controls. Increments in Ra and Rv after intra-arterial boluses of norepinephrine were measured before and after sequential addition of the alpha 1- and alpha 2-receptor antagonists prazosin (16 mumol/L) and yohimbine (0.1 mumol/L) in the presence or absence of propranolol (5 mumol/L). Norepinephrine (1 to 40 micrograms) had little effect on Ra in the absence of propranolol, a pattern that persisted in control lobes after propranolol. However, when lobes from paced animals were pretreated with propranolol, norepinephrine increased Ra, Rv was increased after norepinephrine in control lobes, an effect that was enhanced in the paced group. In both groups, the increment in Rv was greater after propranolol. Irrespective of propranolol pretreatment, prazosin significantly attenuated, if not abolished, the response to norepinephrine. The enhancement in venous vascular reactivity in lobes from paced animals remained when venous pressure was elevated to 20 cm H2O. In control lobes under conditions of elevated tone or when endothelium-dependent relaxing factor was blocked, responses to norepinephrine did not mimic those observed in the paced group. Microvascular permeability, as measured by the capillary filtration coefficient, was not altered in the paced group. We conclude that the pulmonary adaptations to 4 weeks of rapid ventricular pacing include functional changes in pulmonary hemodynamics and vascular reactivity but not in microvascular permeability.

Adrenergic beta-Antagonists↗
PubMed1994

[A study on serologic markers for screening before hepatitis B vaccination].

Three serologic markers for screening before hepatitis B vaccination were HBsAg, anti-HBs and anti-HBc. The data of HB virus infection in eight cities were analysed in order to save test cost and to achieve similar immune effect. For routine screening, anti-HBc is the only one marker needed to be used. The neonates and children aged 0-3 years can be vaccinated directly without screening.

Adolescent↗
PubMed1993

Solute adsorption on polymer-coated fused-silica capillary electrophoresis columns using selected protein and peptide standards.

Three series of basic proteins and peptides were selected for use in studying the adsorption behavior of fused-silica capillary electrophoresis columns. A comparative study of untreated and treated fused-silica columns was done. The polymers used as coating materials ranged from very hydrophobic to very hydrophilic. The average efficiency of weakly hydrophilic Ucon-coated capillaries for basic proteins was over 1 million theoretical plates at a buffer pH of 4.8. For this coating, it was found that the maximum column efficiency was obtained at a film thickness of approximately 100 nm. It was easily seen that both ionic and hydrophobic interaction forces can play important roles in protein adsorption onto the capillary walls. Furthermore, strongly hydrophilic polymer coatings may possibly lead to hydrogen-bonding interactions, which decrease column efficiency. Studies have been conducted using two series of polypeptides with varying chain lengths. One series was used to study the effect of polypeptide chain length on retention behavior. Efficient separations of bioactive peptide drugs on Ucon-coated columns were achieved. The results indicate that high efficiency and resolution of basic peptides tested can be realized on columns modified with weakly hydrophilic polymers at a pH value of about 5.

Adsorption↗