Biomedical subjects

R Zhang

Publications and source records attributed to R Zhang.

At least 271 records · Page 15Linked to original sources

PubMed1998

Synergistic activation of p53 by inhibition of MDM2 expression and DNA damage.

The MDM2 oncogene encodes an inhibitor of the p53 tumor suppressor protein that regulates p53 in a negative feedback loop. MDM2 gene amplification and overexpression occur in several types of tumors and are often associated with poor prognosis. An MDM2 antisense phosphorothioate oligodeoxynucleotide has been identified that effectively inhibits MDM2 expression in tumor cells containing MDM2 gene amplifications. Antisense inhibition of MDM2 is associated with a decrease in MDM2-p53 complex formation, increase in p53-inducible gene expression, increase in p53 transcriptional activity, and apoptosis. Significantly, inhibition of MDM2 expression enhances the activation of p53 by a DNA-damaging cancer chemotherapy agent in a synergistic fashion. Therefore, the MDM2 negative feedback pathway is an important limiting factor in DNA damage-induced p53 activation. MDM2 antisense oligonucleotides may be useful as antitumor agents alone or as enhancers of other conventional DNA-damaging drugs.

Apoptosis↗

PubMed1998

Both hydroxylamine and nitroxide protect cardiomyocytes from oxidative stress.

The unique anti-oxidative activity of nitroxide radicals protecting against reactive oxygen-derived species (ROS) has been recently demonstrated in several model systems. The present study focuses on the activity of nitroxide and of its reduced form in cultured rat ventricular cardiomyocytes exposed to O2.- and H2O2 generated by hypoxanthine (HX) and xanthine oxidase (XO). To evaluate cell injury, spontaneous beating, leakage of lactate dehydrogenase (LDH), and depletion of cellular ATP were determined. The protective effect of 4-OH-2,2,6,6-tetramethyl-piperidine-N-oxyl (TPL) was compared with that of 4-OH-2,2,6,6-tetramethyl-1-hydroxypiperidine (TPL-H) and of several common anti-oxidants. A rapid exchange between TPL and TPL-H, is mediated by cellular metabolism and through reactions with ROS. In particular, TPL under O2.- flux is oxidized to oxo-ammonium cation (TPL+) which comproportionates with TPL-H yielding two nitroxide radicals. Because this exchange limits the distinction between the biological activities of TPL and TPL-H, NADH which can reduce TPL+ was included in order to maintain the nitroxide in its reduced form. The results demonstrate that both TPL and TPL-H protect cardiomyocytes against beating loss and LDH leakage. Conversely, cellular ATP depletion induced by HX/XO is inhibited by TPL-H, though not by TPL, suggesting that different mechanisms underlie their protective activities. Through a flip-flop between the two forms, which coexist in the system, the levels of TPL-H and TPL are continuously replenished. The conversion, upon reaction, of each antioxidant into the other one enables them, contrary to common antioxidants which operate in a stoichiometric mode, to act catalytically.

Animals↗

PubMed1998

Cloning oncogenic ras-regulated genes by differential display.

The coordinated regulation of gene expression is a key cellular function that specifies cell characteristics as well as controls normal physiological processes of the organism. Deregulation of this gene expression leads to a variety of abnormal conditions such as cancer. The ras oncogene is one of the most frequently found mutations in various types of human cancer. The mutated Ras protein constitutively elicits multiple mitogenic signals to the nucleus to alter gene expression of target genes that are involved in a broad range of normal cellular functions. Thus the identification of these genes may provide an important tool toward the understanding of these pathogenic processes. As a first step to reveal these processes at the molecular level and to dissect the key pathway employed by oncogenic Ras protein, we have looked for its target genes in rodent model cell lines using the differential display method. Our initial screening has isolated a number of genes either up- or downregulated by oncogenic ras activation. Although the functional analyses of these genes in terms of ras-mediated cell transformation will be the major challenge, differential display has come to be a very efficient tool that helped us move to the next step. In this short report, we focus primarily on the technical aspects of differential display and experimental designs used in this study.

Animals↗

PubMed1998

Preclinical pharmacology of the natural product anticancer agent 10-hydroxycamptothecin, an inhibitor of topoisomerase I.

PURPOSE: 10-Hydroxycamptothecin (HCPT) is an indole alkaloid isolated from a Chinese tree, Camptotheca acuminata, and has a wide spectrum of anticancer activity in vitro and in vivo mainly through inhibitory effects on topoisomerase I. HCPT has been shown to be more potent and less toxic than camptothecin and has recently undergone clinical trials. To determine how HCPT might be best used as an anticancer agent, preclinical studies of the pharmacokinetics, tissue distribution, metabolism and elimination of HCPT in rats were undertaken. METHODS: HCPT was administered to rats by i.v. bolus injection at doses of 1, 3, and 10 mg/kg body weight. HCPT (lactone and carboxylate) and its metabolites in plasma, urine, feces, and various tissues were quantitated by reversed-phase HPLC. Pharmacokinetic parameters were then estimated. RESULTS: Following i.v. administration at doses of 3 or 10 mg/kg, the plasma concentration-time profile for lactone HCPT could be best described by a three-compartment model, with terminal elimination half-lives of 140.4 and 428.6 min, respectively. A two-compartment model was used to fit the plasma concentration-time curve at 1 mg/kg, with a terminal elimination half-life of 30.5 min. Carboxylate HCPT had a longer half-life than the lactone form of HCPT. During the initial 6 h after dosing, urinary excretion was the major route of elimination, and fecal excretion became the major route of elimination thereafter. HCPT was widely distributed to various tissues including the enterohepatic system, kidney, and bone marrow. The lactone form of HCPT was detectable in various tissues examined up to 72 h after dosing at all the three test doses. HCPT glucuronides were present in plasma, urine, feces and various tissues. No significant toxicity was observed at doses of 1 or 3 mg/kg. Polyuria and hematuria were observed only during the initial 3 h after dosing at 10 mg/kg. CONCLUSIONS: Prolonged elimination of HCPT in vivo may have a significant impact on its therapeutic effects. HCPT is metabolized to its carboxylate form and glucuronides. Dose-dependent toxicity was observed with i.v. administration of HCPT. The results of this study should be useful in the design of future human trials with this anticancer drug.

Animals↗

PubMed1998

Membrane structure characterization using variable-period x-ray standing waves.

The variable-period x-ray standing wave (XSW) technique is emerging as a powerful tool for studying membrane structure. However, two significant problems arise when the method is used to characterize membranes of thickness dL < 100 A. First, the surface roughness, sigma(r), of the supporting reflecting mirror convolutes with the intrinsic half-width of the marker atom distribution in the membrane, sigma(in), and contributes to an apparent half-width, sigma, which is measured in the XSW experiment. Here we show how the latter terms are related quantitatively [sigma(in) = (sigma2 - sigma(r)2)(1/2)], such that rough mirrors give rise to larger marker atom distribution widths, sigma, and how the required quantity sigma(in) can be determined in the XSW measurement. Second, when the mean position of the marker atom layer, (z), is close to one or both boundaries of the membrane, its distribution function is truncated at the boundary. In such cases, we show why marker atom distribution should be expressed in terms of its first and second moments. We also demonstrate by numerical simulations of realistic samples how the physical parameters, sigma(r), sigma, (z), and dL, affect x-ray reflectivity and fluorescence yield profiles as an aid in their interpretation.

Biophysical Phenomena↗

PubMed1998

Toxic effects of Erycibe obtusifolia, a Chinese medicinal herb, in mice.

Extract of stem of Erycibe obtusifolia (EO) at doses of 10, 20 and 30 mg/kg was experimentally tested through oral and intraperitoneal administration. Toxic effects of EO were assessed through functional changes of the liver and kidneys. Mice died immediately following the i.p. injection at the dose of 10 mg/kg. However, no death occurred after the oral administration at the dose of 10, 20 or 30 mg/kg under close observations for at least 2 weeks. Changes of several functional parameters in both the liver and kidney appeared simultaneously after the oral administration. Although the higher dose increased the levels of serum glutamate-oxalate-transaminase (sGOT), serum glutamate-pyruvate-transaminase (sGPT), and blood urea nitrogen (BUN), and decreased the levels of hematocrit at 6 h after the treatment, no distinct dose-dependent relationship existed between the administered doses and the changes in functional parameters observed.

Alanine Transaminase↗

PubMed1998

Immunogenicity of live attenuated SA14-14-2 Japanese encephalitis vaccine--a comparison of 1- and 3-month immunization schedules.

Live attenuated SA14-14-2 Japanese encephalitis (JE) vaccine has been safe and effective in >100 million immunized children, but its current administration schedule of two doses given a year apart does not lend itself to inclusion in established Expanded Program of Immunization (EPI) schedules of childhood immunization. Immune responses to immunization at shorter intervals were compared in middle-school-aged children immunized with two doses separated by 1 month (n = 116) or 2.5 months (n = 115). Two vaccine lots were compared. Seroconversion to the vaccine was observed in 100% of vaccinees immunized in the 1-month schedule and in 94% (lot 2) and 100% (lot 1) of vaccinees immunized in the 2.5-month schedule. Geometric mean titers were almost 2-fold higher with the longer schedule. The routine administration of JE SA14-14-2 vaccine to infants in an EPI schedule should be possible using either interval.

Adolescent↗

PubMed1998

Genetic immunotherapy for medullary thyroid carcinoma: destruction of tumors in mice by in vivo delivery of adenoviral vector transducing the murine interleukin-2 gene.

A replication defective adenovirus harboring the interleukin-2 gene (AdCMVmIL2) was used for treatment of a mouse medullary thyroid carcinoma (mMTC). We evaluated the antitumor effect and immunological response in the animal model. In small tumors (< or = 30 mm3), intratumor injection of AdCMVmIL2 led to mMTC tumor regression in up to 69% of animals. With large tumors (>30 mm3), almost all treated tumors showed stabilization in size, but did not completely resolve. All mice cured by AdCMVmIL2 treatment failed to develop tumors after reinjection of wild-type mMTC cells, indicating that long-term antitumor immunity developed. Analysis of cytotoxicity indicates that the antitumor effect in cured mice was dependent on cytotoxic T lymphocyte (CTL) activity against the tumor. Histological and immunohistological studies of treated tumors revealed massive CD4+ and CD8+ cell infiltration in AdCMVmIL2 treated tumors, but not in untreated or control virus treated tumors. The data demonstrate the ability of interleukin 2 (IL-2) to elicit specific antitumor immunity and offer hope for this therapy in humans.

Adenoviridae↗

PubMed1998

A new criterion to classify globular proteins based on their secondary structure contents.

MOTIVATION: With the enlargement of protein structure databases, it is hoped that a method to classify proteins automatically will be developed. Although the classification criterion proposed by Nakashima et al. ( J. Biochem., 1986, 99, 153-162) was widely used in the literature, it leads to some inconsistencies with the classification databases currently available in the class assignment of protein structures. To improve their work, a new classification criterion is proposed relying on statistical analysis of the secondary structure contents of more than 200 proteins with well-known structural classes. The Fisher linear discriminant algorithm is used to derive the new classification criterion. RESULTS: Three cross-validation tests are performed to evaluate the new criterion. In the jackknife test, of the 210 proteins used to derive the criterion, 206 are correctly classified with an accuracy of 98.10%. Of the 16 proteins of purely intermediate structure (i.e. structures lying near borderlines between two classes) in the first test set, 15 are correctly classified with an accuracy of 93.75%. For the second test set which consists of 200 proteins selected randomly from SCOP, a testing accuracy of 94.00% is obtained. For comparison, the criterion of Nakashima et al. is also used to classify the 210, 16 and 200 proteins, respectively. Consequently, accuracies of 94.76%, 62.50% and 91.50% are obtained, respectively. On average, the accuracy of the new classification criterion is 4% higher than that of Nakashima et al. AVAILABILITY: The program is available on request from the first author. CONTACT: ctzhang@tju.edu.cn

Algorithms↗

PubMed1998

Glutamine reduces heat shock-induced cell death in rat intestinal epithelial cells.

Glutamine supplementation is beneficial for preventing intestinal atrophy and maintaining mucosal functions in metabolically stressed patients. The mechanisms by which glutamine prevents mucosal atrophy remain unclear. In particular, the role of glutamine in the survival of cells under stress is unknown. Intestinal epithelial cells (IEC-6) were cultured in media with or without supplementation of L-glutamine. A low concentration of L-glutamine (1.0 mmol/L) was sufficient to minimize the percentage of floating cells under basal conditions. Heat shock at 43 degrees C for 90 min decreased (P < 0. 001) the number of attached cells, while increasing (P < 0.001) the number of floating cells, which is a measurement of the extent of cell death in these cultures. Glutamine enhanced attached cell count and diminished heat shock-induced cell death in a dose-dependent manner. Of note, 2 mmol/L was suboptimal in both respects, thus indicating that heat-shocked cells require higher concentrations of glutamine for optimal cell survival. Maximal effect was achieved with 8 mmol/L glutamine, which increased (P < 0.001) cell growth (indicated by the number of attached cells) and diminished (P < 0. 001) cell death (indicated by the number of floating cells). Further increase of L-glutamine concentration to 12 or 20 mmol/L did not provide additional benefit in minimizing cell death. Heat shock protein 70 (hsp 70) mRNA was induced by heat shock only in cultures supplemented with L-glutamine, and the induction was more consistent and greater in cultures containing higher concentrations of glutamine. Thus, glutamine supplementation reduced heat shock-induced cell death. This effect, together with the maintenance of cell growth, may play a key role in the prevention of intestinal mucosal atrophy.

Animals↗

PubMed1998

Immunoreactive endothelin-1 and its receptors in human adrenal tissues.

To elucidate the pathophysiologic significance of endothelin-1 (ET-1) in adrenal and the mechanism for reduced responsiveness to exogenous ET-1 in aldosterone-producing adenoma (APA), we have investigated ET-1 receptors by radioligand binding assay (RBA) in human normal adrenal (NA), APA, idiopathic hyperaldosteronism (IHA), and pheochromocytoma (PHEO), immunoreactive (ir-) ET-1 content in NA, APA and PHEO by radioimmunoassay (RIA), and immunohistochemical staining of ET-1 with the peroxidase-anti-peroxidase (PAP) method in NA, APA, and PHEO. A single class of high-affinity binding sites for ET-1 was found in human NA and tumor tissues. Dissociation constant (Kd) values of ET-1 receptors were similar in NA, APA, and IHA, but maximal binding capacity (Bmax) of ET-1 receptors was lower in APA than in NA and IHA. Both Kd and Bmax in PHEO were higher than those in NA, APA, and IHA. Ir-ET-1 content in tumors of APA and PHEO were higher than in NA. Immunohistochemical staining was more intense in the tumor cells of APA and PHEO than in NA. These results suggest that the reduced response to exogenous ET-1 in APA could be related to downregulation of ET-1 receptors in the tumor. Increased ET-1 content and receptors may lead to hypersecretion of catecholamine in PHEO. ET-1 produced in normal and tumor adrenal tissues may regulate aldosterone and catecholamine secretion from adrenals in a paracrine/autocrine fashion.

Adrenal Gland Neoplasms↗

PubMed1998

Identification of rCop-1, a new member of the CCN protein family, as a negative regulator for cell transformation.

By using a model system for cell transformation mediated by the cooperation of the activated H-ras oncogene and the inactivated p53 tumor suppressor gene, rCop-1 was identified by mRNA differential display as a gene whose expression became lost after cell transformation. Homology analysis indicates that rCop-1 belongs to an emerging cysteine-rich growth regulator family called CCN, which includes connective-tissue growth factor, CYR61, CEF10 (v-src inducible), and the product of the nov proto-oncogene. Unlike the other members of the CCN gene family, rCop-1 is not an immediate-early gene, it lacks the conserved C-terminal domain which was shown to confer both growth-stimulating and heparin-binding activities, and its expression is lost in cells transformed by a variety of mechanisms. Ectopic expression of rCop-1 by retroviral gene transfers led to cell death in a transformation-specific manner. These results suggest that rCop-1 represents a new class of CCN family proteins that have functions opposing those of the previously identified members.

Aging↗

PubMed1998

Transfer function analysis of dynamic cerebral autoregulation in humans.

To test the hypothesis that spontaneous changes in cerebral blood flow are primarily induced by changes in arterial pressure and that cerebral autoregulation is a frequency-dependent phenomenon, we measured mean arterial pressure in the finger and mean blood flow velocity in the middle cerebral artery (VMCA) during supine rest and acute hypotension induced by thigh cuff deflation in 10 healthy subjects. Transfer function gain, phase, and coherence function between changes in arterial pressure and VMCA were estimated using the Welch method. The impulse response function, calculated as the inverse Fourier transform of this transfer function, enabled the calculation of transient changes in VMCA during acute hypotension, which was compared with the directly measured change in VMCA during thigh cuff deflation. Beat-to-beat changes in VMCA occurred simultaneously with changes in arterial pressure, and the autospectrum of VMCA showed characteristics similar to arterial pressure. Transfer gain increased substantially with increasing frequency from 0.07 to 0.20 Hz in association with a gradual decrease in phase. The coherence function was > 0.5 in the frequency range of 0.07-0.30 Hz and < 0.5 at < 0.07 Hz. Furthermore, the predicted change in VMCA was similar to the measured VMCA during thigh cuff deflation. These data suggest that spontaneous changes in VMCA that occur at the frequency range of 0.07-0.30 Hz are related strongly to changes in arterial pressure and, furthermore, that short-term regulation of cerebral blood flow in response to changes in arterial pressure can be modeled by a transfer function with the quality of a high-pass filter in the frequency range of 0.07-0.30 Hz.

Adult↗

PubMed1998

Deterioration of cerebral autoregulation during orthostatic stress: insights from the frequency domain.

To determine whether dynamic cerebral autoregulation is impaired during orthostatic stress, cerebral blood flow (CBF) velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (MAP; Finapres) were measured continuously in 12 healthy subjects during ramped maximal lower body negative pressure (LBNP) to presyncope. Velocity and pressure were averaged over 6-min periods of stable data at rest and during LBNP to examine steady-state cerebral hemodynamics. Beat-to-beat variability of velocity and pressure were quantified by a "variation index" (oscillatory amplitude/steady-state mean value) and by power spectral analysis. The dynamic relationship between changes in pressure and velocity was evaluated by the estimates of transfer and coherence function. The results of the study were as follows. Steady-state MAP remained relatively constant during LBNP, whereas CBF velocity decreased progressively by 6, 15, and 21% at -30, -40, and -50 mmHg LBNP, respectively (P < 0.05 compared with baseline). At the maximal level of LBNP (30 s before presyncope) MAP decreased by 9.4% in association with a prominent reduction in velocity by 24% (P < 0.05 compared with baseline). The variation index of pressure increased significantly from 3.8 +/- 0.3% at baseline to 4.5 +/- 0. 6% at -50 mmHg LBNP in association with an increase in the variation index of velocity from 6.0 +/- 0.6 to 8.4 +/- 0.7% (P < 0.05). Consistently, the low- (0.07-0.20 Hz) and high-frequency (0.20-0.30 Hz) power of variations in pressure and velocity increased significantly at high levels of LBNP (P < 0.05) in association with an increase in transfer function gain (24% at -50 mmHg, P < 0.05). We conclude that the damping effects of autoregulation on variations in CBF velocity are diminished during orthostatic stress in association with substantial falls in steady-state CBF velocity. We suggest that these changes may contribute in part to the development of presyncope.

Adult↗

PubMed1998

Aldosterone overproduction and CYP11B2 mRNA overexpression in vessels of spontaneously hypertensive rats.

Aldosterone is synthesized in extra-adrenal tissues such as blood vessels and brain. Damage to blood vessels could play a crucial role in perpetuating hypertension. In this study, we determined both aldosterone production and aldosterone synthase gene-CYP11B2 mRNA expression in vessels of spontaneously hypertensive rats (SHR). The results showed that aldosterone was overproduced in the vasculature of SHR, by means of ex vivo mesenteric artery perfusion, HPLC, and RIA, and that CYP11B2 mRNA expression was upregulated in aortas of SHR, confirmed by RT-PCR and Southern blot.

Aldosterone↗

PubMed1998

Immunotherapy for medullary thyroid carcinoma by a replication-defective adenovirus transducing murine interleukin-2.

We have evaluated the feasibility of gene transduction using replication-defective adenovirus vector as a novel therapy for medullary thyroid carcinoma (MTC), a thyroid C cell neoplasm. Replication-defective adenoviruses were constructed to express murine interleukin-2 (mIL-2) gene and Escherichia coli beta-galactosidase (beta-gal; lacZ) gene under the control of the human cytomegalovirus (CMV) promoter (AdCMVmIL2, AdCMVbeta-gal) by homologous recombination. The efficiency of transduction was evaluated using AdCMVbeta-gal at different conditions. The gene transduction efficiency was dependent on multiplicity of infection, duration of exposure to the virus, and viral concentration. The expression of functional mIL-2 in transduced tumor cells was verified both in vitro and in vivo. Two cell lines (rat MTC and mMTC) secreted large amounts of functional mIL-2 after transduction, as tested in cytotoxic T lymphocyte (CTL) L-2 cells. When AdCMVmIL2-infected mMTC cells were injected s.c. into their host animals, tumors developed in 2 of 10 animals, in contrast to 9 of 10 animals injected with AdCMVbeta-gal-infected mMTC cells and all 10 animals injected with parental mMTC cells. Moreover protected animals developed a long lasting immunity against mMTC tumor cells and their splenocytes, showing cytotoxicity to parental tumor cells, and active natural killer (NK) cell activity. BALB/c-SCID (severe combined immune deficiency) mice were also used to evaluate the function of NK cells in antitumor activities. No tumor developed in SCID mice injected with AdCMVmIL2-infected cells, whereas all animals injected with either AdCMVbeta-gal-infected or parental mMTC cells developed tumors. Our data indicate that IL-2 production by MTC cells leads to rejection in syngeneic animals and suggest that both cytotoxic T cells and NK cells may play an important role. In addition, transduction of adenoviral vectors into tumor cells produces some nonspecific antitumor effects.

Adenoviridae↗

PubMed1998

Effect of aspirin on protein binding and tissue disposition of oligonucleotide phosphorothioate in rats.

Pharmacokinetic studies of phosphorothioate oligodeoxynucleotides (PS-oligonucleotides) in animals show that following intravenous administration, PS-oligonucleotide clears out rapidly from the plasma and is distributed to majority of the organs. PS-oligonucleotides are bound to plasma proteins extensively. This study was aimed to determine the effect of aspirin, a commonly used drug, on pharmacokinetics of PS-oligonucleotides. In the present study, PS-oligonucleotide was administered to rats that had received aspirin by gavage. Pharmacokinetic study shows that if PS-oligonucleotide was administered following aspirin administration in rats, a) plasma pharmacokinetic parameters (t1/2alpha?, t1/2beta, AUC, etc.) had lower values, b) tissue disposition was different, and c) rate and route of elimination was affected in animals compared to rats receiving PS-oligonucleotide alone. This finding suggests that pharmacokinetics of PS-oligonucleotides can be affected with certain class of drugs, which may have direct impact on biological activity and safety.

Animals↗

PubMed1998

[Treatment of 129 patients with advanced and recurrent malignant ovarian germ cell tumor].

OBJECTIVE: To investigate the improved treatment for advanced malignant germ cell tumors of the ovary. METHODS: 129 patients with advanced and recurrent germ cell tumor of the ovary treated from 1958 to 1993 were retrospectively analyzed. The results of malignant nondysgerminomatous germ cell tumor of the ovary treated from 1958-1983 were compared with those treated with the supplement of VAC (Vincristine + ActinomycinD + Cyclophosphamide), PVB (Cisplatin + Vinblastine + Bleomycin) or BEP (Bleomycin + Etoposide + Cisplatin) combined chemotherapy from 1984-1993. RESULTS: The overall 5-year survival rate was 30% (39/129) of advanced and recurrent germ cell tumor of the ovary. The 5-year survival rates of dysgerminoma and nondysgerminomatous germ cell tumor of the ovary were 68% (19/28) and 20%(20/101), respectively. The 5-year survival rate of patients with malignant nondysgerminomatous germ cell tumor of the ovary was raised from 3% (1/40) to 42% (15/36) in the recent years. The institution of combination chemotherapy is critical for the improvement with BEP regimen as the best among the three. CONCLUSIONS: The endodermal sinus tumor of the ovary stands first in the incidence of malignant germ cell tumors of the ovary in China. To improve the prognosis of advanced malignant germ cell tumor of the ovary, BEP regimen is the most effective at present.

Adolescent↗