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Biomedical subjects

P Hu

Publications and source records attributed to P Hu.

At least 145 records · Page 8Linked to original sources
PubMed1997

Phosphatidylinositol 3-kinase mediates epidermal growth factor-induced activation of the c-Jun N-terminal kinase signaling pathway.

The signaling events which mediate activation of c-Jun N-terminal kinase (JNK) are not yet well characterized. To broaden our understanding of upstream mediators which link extracellular signals to the JNK pathway, we investigated the role of phosphatidylinositol (PI) 3-kinase in epidermal growth factor (EGF)-mediated JNK activation. In this report we demonstrate that a dominant negative form of PI 3-kinase as well as the inhibitor wortmannin blocks EGF-induced JNK activation dramatically. However, wortmannin does not have an effect on JNK activation induced by UV irradiation or osmotic shock. In addition, a membrane-targeted, constitutively active PI 3-kinase (p110beta) was shown to produce in vivo products and to activate JNK, while a kinase-mutated form of this protein showed no activation. On the basis of these experiments, we propose that PI 3-kinase activity plays a role in EGF-induced JNK activation in these cells.

Androstadienes↗
PubMed1997

Effect of simulated weightlessness on TNF-alpha production and the response of bone marrow cells to GM-CSF in rats.

The purpose of this experiment was to investigate the effect of 15 and 30 d simulated weightlessness (SWL) on tumor necrosis factor-alpha(TNF-alpha) production secreted by macrophage stimulated with lipopolysaccharide(LPS) and the ability of bone marrow cells to respond to granulocyte/monocyte colony-stimulating factor(GM-CSF) in tail-suspension rats. The TNF-alpha production was assessed by radioimmunoassay. The ability of bone marrow cells to respond to GM-CSF was measured by 3H-TdR incorporation method. The results showed that after 15 d SWL, TNF-alpha production showed a tendency to decrease; and that after 30 d SWL, the decrease became significant (P < 0.05). The results also demonstrated that the ability of bone marrow cells to respond to GM-CSF decreased significantly after 15 d SWL (P < 0.01); and there was no significant change after 30 d SWL. It suggested that SWL could depress immune function, and that reduction of TNF-alpha production might be related to bone marrow cell proliferation function.

Animals↗
PubMed1997

[Identification of semen Cuscutae by HPCE].

A method for identification of semen Cuscutae, a traditional Chinese herb, was developed. The proteins in semen Cuscutae were extracted under acid or basic conditions and separated by high performance capillary electrophoresis. The electrophoretograms of acidic or basic extractants from Cuscuta chinensis Lam., Cuscuta australis R. Br. and Cuscuta japonica Choisy showed significant differences, which can be used to identify the three different semen Cuscutae. The results of the identification for 13 pharmacognosical samples agreed well with those of scanning electronic microscopy and tissue microanalysis.

Drug Contamination↗
PubMed1997

[Selection of TLC solvent system for separating substituted ferrocyclopentadienyl borane using orthogonal array method].

A series of substituted ferro-cyclopentadienyl borane compounds were separated by using thin-layer chromatographic technique. The optimum mobile phase was acetone-cyclohexane-tetraethyl ammonium halide (0.59:8.24:1.18). The orthogonal array method was used to get the optimum chromatographic condition. The types and the concentrations of different kinds of ion-pair reagents, the contents of acetone and cyclohexane were considered as factors which affected the results of separation. The operating conditions for each experiment was adopted based on the L9 (3(4)) design. A statistical method of variance analysis was used to evaluate the overall degree of separation (D(S)), a criterion which reflects the degree of optimization. As a result, we found the most important factors that affected the separation and the optimum chromatographic condition for 8 compounds of this sort.

English Abstract↗
PubMed1997

Studies on the metabolic activation of disulfiram in rat. Evidence for electrophilic S-oxygenated metabolites as inhibitors of aldehyde dehydrogenase and precursors of urinary N-acetylcysteine conjugates.

Recent studies on the mechanism by which disulfiram inhibits aldehyde dehydrogenase have provided evidence for the formation of reactive intermediates that are thought to carbamoylate, and thereby inactivate the enzyme. In our study, rats were dosed with either disulfiram (0.25 mmol kg-1 i.p.) or its reduced metabolite diethyldithiocarbamate (DDTC; 0.5 mmol kg-1 i.p.) and urine was collected for the analysis of metabolites derived from putative reactive intermediates. By means of ionspray LC-MS/MS, two novel N-acetylcysteine (NAC) conjugates, i.e., N-acetyl-S-(N, N-diethylcarbamoyl)cysteine and N-acetyl-S-(N, N-diethylthiocarbamoyl)cysteine, were identified in urine specimens. Quantitative analyses indicated that, over the 0- to 24-hr period after drug administration, urinary excretion of N-acetyl-S-(N, N-diethylcarbamoyl)cysteine accounted for 7.5 +/- 4.0 and 6.2 +/- 1.0%, respectively, of the dose of disulfiram and diethyldithiocarbamate, while the corresponding thiocarbamoyl conjugate, N-acetyl-S-(N, N-diethylthiocarbamoyl)cysteine, accounted for a further 0.5 +/- 0.3 and 0.3 +/- 0.1%, respectively, of the dose. These conjugates are believed to derive from reactive sulfoxide and sulfone metabolites of disulfiram, namely S-methyl-N, N-diethylthiocarbamate sulfoxide (DETC-MeSO), S-methyl-N, N-diethylthiocarbamate sulfone (DETC-MeSO2), S-methyl-N, N-diethyldithiocarbamate sulfoxide (DDTC-MeSO) and S-methyl-N, N-diethyldithiocarbamate sulfone (DDTC-MeSO2), which were found to carbamoylate N-acetylcysteine in vitro with the following rank order of reactivity: DDTC-MeSO2 > DETC-MeSO2 > DDTC-MeSO > DETC-MeSO. In vitro experiments with aldehyde dehydrogenase showed that all four S-oxygenated metabolites inhibited the enzyme effectively. Furthermore, inclusion of NAC in incubation media attenuated significantly the inhibition by DDTC-MeSO2, DETC-MeSO2 and DDTC-MeSO, but had little effect on that by DETC-MeSO. Our results are consistent with the hypothesis that disulfiram and diethyldithiocarbamate undergo activation by a sequence of metabolic reactions leading to the formation of electrophilic S-methyl sulfoxides and sulfones that carbamoylate, and thereby inhibit, aldehyde dehydrogenase and possibly other enzymes.

Acetylcysteine↗
PubMed1997

[Screening of thermophilic superoxide dismatase producing strain and some properties of the enzyme].

A thermophilic SOD producing strain was obtained from the bacteria preserved in our lab. Its content of SOD was 8774u/g fresh cells. The strain can tolerate 0.4% H2O2 and 70 degrees C, and it has outstanding culture characteristics. It was identified as Bacillus stearothermophilus, called B.S 211-15. Crude SOD was extracted from B.S 211-15, the recovery of total activity was 69.5%, the specific activity was 1793u/mg protein. The enzyme showed fine heat stability, pH stability and good proteinase resistance. The SOD activity didn't decrease after being kept in room temperature for 2 months. The results of inhibition reactions indicated that this enzyme was Fe-SOD.

Geobacillus stearothermophilus↗
PubMed1996

A chimeric Lym-1/interleukin 2 fusion protein for increasing tumor vascular permeability and enhancing antibody uptake.

A murine antihuman B-cell monoclonal antibody, Lym-1, has shown considerable promise for the treatment of human malignant lymphomas. To enhance its clinical potential, a genetically engineered fusion protein consisting of a chimeric Lym-1 (chLym-1) and interleukin 2 (IL-2) was tested for mediating cytotoxicity, increasing vasopermeability, and enhancing antibody uptake in human malignant lymphomas. The chLym-1/IL-2 fusion protein, which was expressed initially in a baculovirus system and more recently in the glutamine synthetase gene amplification system, was shown to be processed and assembled into a normal immunoglobulin monomer with two IL-2 molecules per antibody. It was found to be equivalent to the chLym-1 antibody in antigen-binding specificity and relative affinity. In addition, it maintains IL-2 cytokine activity as demonstrated by support of T-cell proliferation. Moreover, in antibody-dependent cellular cytotoxicity assays against Raji target cells, chLym-1/IL-2 had approximately 2-fold and 4-fold higher cytotoxicity than chLym-1 and murine Lym-1, respectively. Used as a pretreatment, chLym-1/IL-2 enhances the uptake of chLym-1 at the tumor site by altering the permeability of tumor vessels producing tumor:normal organ ratios of 420:1 for blood and 1708:1 for muscle at 3 days. The in vitro and in vivo activities of chLym-1/IL-2, therefore, suggest that this genetically engineered antibody fusion protein may represent a new immunotherapeutic reagent for the treatment of human malignant lymphomas.

Animals↗
PubMed1996

Salbutamol changes the molecular and mechanical properties of canine skeletal muscle.

1. Salbutamol, a beta 2-agonist, increased the weight of the canine latissimus dorsi muscle. It also increased fusion frequency, and decreased time-to-peak tension, half-relaxation time, and total contraction time. These changes in twitch times and fusion frequency were associated with changes in the levels of proteins expressed in slow- and fast-twitch fibres. Salbutamol decreased the levels of the slow-twitch cardiac isoform of sarco-/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) and phospholamban proteins, and increased the level of the fast-twitch isoform of sarco-/endoplasmic reticulum Ca(2+)-ATPase (SERCA1a). 2. Changes in the levels of SERCA proteins, particularly SERCA1a, could account for most of the increases in calcium uptake rate observed in homogenates of muscles from the salbutamol-treated animals and could partially account for the changes in half-relaxation rates and other twitch times. 3. Changes in the levels of SERCA1a, SERCA2a and phospholamban protein did not always follow changes in the levels of their corresponding mRNAs. Divergence depended upon the SERCA isoform and muscle. The muscles studied were latissimus dorsi and vastus intermedius. 4. Salbutamol did not change the level of myosin heavy chain (HC)-I isoforms in either muscle, suggesting that it did not increase the proportion of slow-twitch fibres in these muscles. It did increase the level of HC-IIx and decrease the level of HC-IIa isoforms in the latissimus dorsi. Salbutamol did not produce these effects in the vastus intermedius. It is of particular interest that salbutamol changed the relative levels of SERCA proteins in the latissimus dorsi muscle without producing significant change in the level of HC-I isoform.

Adrenergic beta-2 Receptor Agonists↗
PubMed1996

Salbutamol and chronic low-frequency stimulation of canine skeletal muscle.

1. The effect of simultaneous application of chronic muscle stimulation and salbutamol on the expression of mRNAs and proteins normally expressed by fast- or slow-twitch fibres was followed and the effects of changes in protein expression on mechanical performance were evaluated. Chronic low-frequency stimulation increased the myosin heavy chain (HC)-I level in the canine latissimus dorsi muscle and simultaneous administration of salbutamol partially blocked this change. Associated with the increase in HC-I level was a decrease in the velocity of shortening at zero load, VMAX. The change in VMAX was partially blocked by salbutamol. 2. Chronic low-frequency stimulation increased the levels of slow-twitch cardiac isoform sarco-/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) and phospholamban mRNA, and SERCA2a and phospholamban protein expression. These changes were associated with an increase in time-to-peak tension and a decrease in fusion frequency. Simultaneous administration of salbutamol blocked these changes in protein expression and muscle mechanics. Chronic stimulation of latissimus dorsi decreased the levels of the fast-twitch isoform of sarco-/endoplasmic reticulum Ca(2+)-ATPase (SERCA1a) and increased SERCA2a protein expression and decreased calcium uptake rate by muscle homogenates. These changes were blocked by salbutamol. 3. The loss of latissimus dorsi muscle weight by chronic stimulation was partially blocked by salbutamol.

Adrenergic beta-Agonists↗
PubMed1996

Automated system for detailed measurement of respiratory mechanics.

OBJECTIVE: The mechanical properties of the respiratory system (i.e., elastance and resistance) depend on the frequency, tidal volume, and shape of the flow waveform used for forcing. We developed a system to facilitate accurate measurements of elastance and resistance in laboratory and clinical settings at the frequencies and tidal volumes in the physiologic range of breathing. METHODS: A personal computer (PC) is used to drive a common clinically used ventilator while simultaneously collecting measurements of airway flow, airway pressure, and esophageal pressure from the experimental subject or animal at different frequencies and tidal volumes. Analysis analogous to discrete Fourier transform at the fundamental frequency (i.e., ventilator setting) is used to calculate elastances and resistances of the total respiratory system and its components, the lungs and the chest wall. We have shown that this analysis is independent of the high-frequency harmonics that are present in the waveform from clinical ventilators. RESULTS: The system has been used successfully to make measurements in anesthetized/paralyzed dogs and awake or anesthetized human volunteers in the laboratory, and in anesthetized human volunteers in the laboratory, and in anesthetized humans in the operating room and intensive care unit. Elastances and resistances obtained with this approach are the same as those obtained during more controlled conditions, e.g., sinusoidal forcing. CONCLUSIONS: Accurate, standardized measurements of lung and chest wall properties can be obtained in many settings with relative ease with the system described. These properties, and their frequency and tidal volume dependences in the physiologic range, provide important information to aid in the understanding of changes in respiratory function caused by day-to-day conditions, clinical intervention and pathologies.

Airway Resistance↗
PubMed1996

Cigarette smoking and semen quality.

OBJECTIVE: To determine whether cotinine levels provide stronger evidence for an association between smoking and semen quality than the number of cigarettes smoked per day or years smoked controlling for potential confounders and effect modifiers. DESIGN: Cross-sectional study. SETTING: Male volunteers at the Reproductive Endocrinology-Fertility Laboratory. PARTICIPANTS: Eighty-eight men (ages 18 to 35 years) provided a semen, urine, and blood specimen and completed a self-administered questionnaire concerning smoking and demographic information as well as caffeine and alcohol consumption. Urine, blood, and semen cotinine levels were analyzed via RIA. MAIN OUTCOME MEASURE: Standard clinical semen analysis. RESULTS: Number of cigarettes smoked per day, years smoked, and log-transformed cotinine levels were associated negatively with semen quality (density, total count, and motility). The association was evident among men age > or = 22 years. For example, the correlation coefficient for the overall association between logged urine cotinine and logged sperm density was -0.23; those stratified by age were 0. 13 (age < 22 years) and - 0. 39 (age > or = 22 years). Potential confounders included in regression models did not diminish the associations. CONCLUSIONS: Smoking is associated with lowered semen quality.

Adolescent↗
PubMed1996

Determination intestinal metabolism and permeability for several compounds in rats. Implications on regional bioavailability in humans.

PURPOSE: To investigate the regional differences in small intestinal (SI) metabolism and permeability for several compounds and to ascertain the potential significance of these differences on the reported reductions in regional bioavailability in humans. METHODS: The regional SI metabolism and permeability of captopril, didanosine (ddI), mannitol, ofloxacin and zidovudine (ZDV) were investigated in rats using a Single Pass Perfusion (SPIP) procedure or intestinal homogenates. RESULTS: ddI was metabolized to a greater extent in the upper SI whereas captopril was metabolized to a greater extent in the lower SI. Relatively low homogenate concentrations resulted in significant degradation of captopril in the upper and lower SI. All other compounds were stable and changes in the buffer system or the initial concentration did not affect the results. The SI permeabilities of all compounds, with the exception of mannitol, decreased linearly with respect to SI location and the slopes of the corresponding normalized regression lines were not significantly different. CONCLUSIONS: It has been reported that captopril and ddI demonstrate regional intestinal bioavailability in several species including humans. The current results suggest that the reported reduction in the lower SI bioavailability of captopril may be a result of a reduction in permeability and an increase in intestinal metabolism whereas for ddI, the reduction in the lower SI bioavailability appears to be attributable to a reduction in intestinal permeability. Other factors such as luminal metabolism may also significantly effect regional differences in the intestinal bioavailability of ddI or captopril. Based on these results, a strong possibility exists that ofloxacin and ZDV may also demonstrate regional differences in intestinal bioavailability.

Animals↗
PubMed1996

[Characteristics and treatment of Staphylococcus aureus endocarditis].

In order to evaluate whether there were changes of the clinical features of Staphylococcus (Staph.) aureus endocarditis in recent years, the data of 21 cases of Staph. aureus endocarditis diagnosed from 1977 to 1994 were analyzed and compared with those of 11 cases of Staph. aureus endocarditis from 1957 to 1977. The results showed the following changes in recent years. The incidence of Staph. aureus endocarditis cases has been increasing. Cases of right-sided endocarditis increased in the recent two decades and this increase was related to intravenous drug abuse and increased use of vascular intervention. Right-sided endocarditis was different from left-sided endocarditis in their risk factors, underlying heart diseases, clinical manifestations and prognosis. The clinical manifestations of ventricular-wall endocarditis were atypical and it could be definitely diagnosed only with echocardiogram. Complications of Staph. aureus endocarditis became more common and serious, in recent decades but hospital mortality decreased markedly due to effective antibiotic management. The authors believe that sound knowledge of Staph. aureus endocarditis is essential for the proper diagnosis and treatment of Staph. aureus endocarditis.

Adolescent↗
PubMed1995

Transcriptional regulation of phospholamban gene and translational regulation of SERCA2 gene produces coordinate expression of these two sarcoplasmic reticulum proteins during skeletal muscle phenotype switching.

Chronic 1 Hz stimulation of the canine latissimus dorsi muscle produced a time-dependent switch from the fast-twitch to the slow-twitch phenotype. This included changes in the proteins of the sarcoplasmic reticulum. After 3 days of muscle stimulation, there was down-regulation of fast-twitch Ca-ATPase (SERCA1a) mRNA and induction of slow-twitch Ca-ATPase (SERCA2a) mRNA; most changes in both mRNAs were nearly complete after 14 days of stimulation. Although the induction of phospholamban mRNA began after 3 days of muscle stimulation, its up-regulation was not completed until the muscle had been stimulated for 42 days. The time course of expression of SERCA2a protein was very different from that of SERCA2a mRNA, suggesting that SERCA2 gene expression is regulated at the translational as well as the transcriptional level. The time course of expression of phospholamban protein closely followed that of phospholamban mRNA, suggesting that this gene is under transcriptional control. Thus coordinated expression of SERCA2a and phospholamban proteins is achieved via translational control of the SERCA2 gene and transcriptional control of the phospholamban gene.

Adenosine Triphosphatases↗
PubMed1995

Evidence for substrate stabilization in regulation of the degradation of Bacillus subtilis aspartate transcarbamylase in vivo.

Aspartate transcarbamylase (ATCase) is rapidly degraded in Bacillus subtilis cells that are starved for a carbon or nitrogen source or a required amino acid. The hypothesis that ATCase degradation may be regulated in vivo by protection of the enzyme by substrate binding was tested by studies of a mutant ATCase (Arg99 to Ala, R99A), which binds substrate so poorly that it fails to support pyrimidine-independent growth in a pyrB strain, but still has 10% of normal activity when saturated with substrates. Unlike normal ATCase, R99A ATCase was degraded rapidly in exponentially growing cells. Degradation of the mutant enzyme was two-fold slower in a relA strain, as was degradation of the normal ATCase. The stability of purified R99A ATCase to denaturation by heat or guanidine hydrochloride was identical to that of wild-type ATCase, as was its circular dichroic spectrum. The wild-type and R99A ATCase were degraded identically in vitro by subtilisin, except that the mutant enzyme was much less effectively protected against cleavage by carbamyl phosphate, as expected. The carbamyl phosphate pool in glucose-limited B. subtilis cells was only one-third of the pool in exponentially growing cells. These results indicate that protection of ATCase by carbamyl phosphate binding could be one of the elements that regulate ATCase stability in vivo. However, carbamyl phosphate pools were the same in cells grown with ammonium ions and with a mixture of 20 common amino acids, conditions under which ATCase stability in vivo differs. Thus, other means of regulating ATCase degradation must also exist.

Aspartate Carbamoyltransferase↗
PubMed1995

Oral absorption of anti-AIDS nucleoside analogues. 1. Intestinal transport of didanosine in rat and rabbit preparations.

The intestinal transport of didanosine (ddl), a nucleoside analog used in the treatment of human immunodeficiency virus (HIV) infection, was characterized using in situ and in vitro techniques. The zero-trans uptake of ddl in rat intestinal brush border membrane vesicles (BBMV) was linear over the range of 1 microM to 50 mM, ruling out a significant carrier-mediated absorption component. The lack of carrier-mediated transport was confirmed in a second species (rabbit). In order to quantitate the convective (Pconv) and diffusive (Pdiff) components of ddl intestinal permeability, the steady state wall permeability (P*w) was determined using an established perfusion technique in rats. Even though baseline P*w (pH 6.5, 290 mosm/kg, no modulator) and fluid absorption results were similar to those of furosemide, the ratios (ddl:furosemide) of Pdiff and phi, the sieving coefficient, were 0.31:1 and 1.70:1, respectively, demonstrating that ddl's Pdiff is low and Pconv is high relative to furosemide's, suggesting significant paracellular absorption of ddl. The apparent diffusive absorptive clearances (P'app) of ddl and furosemide were determined in BBMV, which lack functional tight junctions, and the ratios (ddl:furosemide) of P'app in rat and rabbit were 0.23:1 and 0.24:1, respectively. The BBMV results demonstrate that the majority of ddl intestinal transport does not occur by passive membrane diffusion, confirming the single pass intestinal perfusion (SPIP) findings. The results of these studies suggest that ddl is transported by nonfacilitated membrane and paracellular diffusion with paracellular transport being responsible for the majority of ddl absorption from the intestine.

Animals↗