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Biomedical subjects

B Zhang

Publications and source records attributed to B Zhang.

At least 379 records · Page 21Linked to original sources
PubMed1998

Peptidyl-transferase ribozymes: trans reactions, structural characterization and ribosomal RNA-like features.

BACKGROUND: One of the most significant questions in understanding the origin of life concerns the order of appearance of DNA, RNA and protein during early biological evolution. If an 'RNA world' was a precursor to extant life, RNA must be able not only to catalyze RNA replication but also to direct peptide synthesis. Iterative RNA selection previously identified catalytic RNAs (ribozymes) that form amide bonds between RNA and an amino acid or between two amino acids. RESULTS: We characterized peptidyl-transferase reactions catalyzed by two different families of ribozymes that use substrates that mimic A site and P site tRNAs. The family II ribozyme secondary structure was modeled using chemical modification, enzymatic digestion and mutational analysis. Two regions resemble the peptidyl-transferase region of 23S ribosomal RNA in sequence and structural context; these regions are important for peptide-bond formation. A shortened form of this ribozyme was engineered to catalyze intermolecular ('trans') peptide-bond formation, with the two amino-acid substrates binding through an attached AMP or oligonucleotide moiety. CONCLUSIONS: An in vitro-selected ribozyme can catalyze the same type of peptide-bond formation as a ribosome; the ribozyme resembles the ribosome because a very specific RNA structure is required for substrate binding and catalysis, and both amino acids are attached to nucleotides. It is intriguing that, although there are many different possible peptidyl-transferase ribozymes, the sequence and secondary structure of one is strikingly similar to the 'helical wheel' portion of 23S rRNA implicated in ribosomal peptidyl-transferase activity.

Adenosine Monophosphate↗
PubMed1998

Fold and function predictions for Mycoplasma genitalium proteins.

BACKGROUND: Uncharacterized proteins from newly sequenced genomes provide perfect targets for fold and function prediction. RESULTS: For 38% of the entire genome of Mycoplasma genitalium, sequence similarity to a protein with a known structure can be recognized using a new sequence alignment algorithm. When comparing genomes of M. genitalium and Escherichia coli, > 80% of M. genitalium proteins have a significant sequence similarity to a protein in E. coli and there are > 40 examples that have not been recognized before. For all cases of proteins with significant profile similarities, there are strong analogies in their functions, if the functions of both proteins are known. The results presented here and other recent results strongly support the argument that such proteins are actually homologous. Assuming this homology allows one to make tentative functional assignments for > 50 previously uncharacterized proteins, including such intriguing cases as the putative beta-lactam antibiotic resistance protein in M. gentalium. CONCLUSIONS: Using a new profile-to-profile alignment algorithm, the three-dimensional fold can be predicted for almost 40% of proteins from a genome of the small bacterium M. genitalium, and tentative function can be assigned to almost 80% of the entire genome. Some predictions lead to new insights about known functions or point to hitherto unexpected features of M. genitalium.

Bacterial Proteins↗
PubMed1998

skittles, a Drosophila phosphatidylinositol 4-phosphate 5-kinase, is required for cell viability, germline development and bristle morphology, but not for neurotransmitter release.

The phosphatidylinositol pathway is implicated in the regulation of numerous cellular functions and responses to extracellular signals. An important branching point in the pathway is the phosphorylation of phosphatidylinositol 4-phosphate by the phosphatidylinositol 4-phosphate 5-kinase (PIP5K) to generate the second messenger phosphatidylinositol 4,5-bis-phosphate (PIP2). PIP5K and PIP2 have been implicated in signal transduction, cytoskeletal regulation, DNA synthesis, and vesicular trafficking. We have cloned and generated mutations in a Drosophila PIP5K type I (skittles). Our analysis indicates that skittles is required for cell viability, germline development, and the proper structural development of sensory bristles. Surprisingly, we found no evidence for PIP5KI involvement in neural secretion.

Animals↗
PubMed1998

Epidermal growth factor protects neuronal cells in vivo and in vitro against transient forebrain ischemia- and free radical-induced injuries.

Epidermal growth factor (EGF) has been considered to be a candidate for neurotrophic factors on the basis of the results of several in vitro studies. However, the in vivo effect of EGF on ischemic neurons as well as its mechanism of action have not been fully understood. In the present in vivo study using a gerbil ischemia-model, we examined the effects of EGF on ischemia-induced learning disability and hippocampal CA1 neuron damage. Cerebroventricular infusion of EGF (24 or 120 ng/d) for 7 days to gerbils starting 2 hours before or immediately after transient forebrain ischemia caused a significant prolongation of response latency time in a passive avoidance task in comparison with the response latency of vehicle-treated ischemic animals. Subsequent histologic examinations showed that EGF effectively prevented delayed neuronal death of CA1 neurons in the stratum pyramidale and preserved synapses intact within the strata moleculare, radiatum, and oriens of the hippocampal CA1 region. In situ detection of DNA fragmentation (TUNEL staining) revealed that ischemic animals infused with EGF contained fewer TUNEL-positive neurons in the hippocampal CA1 field than those infused with vehicle alone at the seventh day after ischemia. In primary hippocampal cultures, EGF (0.048 to 6.0 ng/mL) extended the survival of cultured neurons, facilitated neurite outgrowth, and prevented neuronal damage caused by the hydroxyl radical-producing agent FeSO4 and by the peroxynitrite-producing agent 3-morpholinosydnonimine in a dose-dependent manner. Moreover, EGF significantly attenuated FeSO4-induced lipid peroxidation of cultured neurons. These findings suggest that EGF has a neuroprotective effect on ischemic hippocampal neurons in vivo possibly through inhibition of free radical neurotoxicity and lipid peroxidation.

Animals↗
PubMed1998

The prosequence of pro-sigmaK promotes membrane association and inhibits RNA polymerase core binding.

Pro-sigmaK is the inactive precursor of sigmaK, a mother cell-specific sigma factor responsible for the transcription of late sporulation genes of Bacillus subtilis. Upon subcellular fractionation, the majority of the pro-sigmaK was present in the membrane fraction. The rest of the pro-sigmaK was in a large complex that did not contain RNA polymerase core subunits. In contrast, the majority of the sigmaK was associated with core RNA polymerase. Virtually identical fractionation properties were observed when pro-sigmaE was analyzed. Pro-sigmaK was completely solubilized from the membrane fraction and the large complex by Triton X-100 and was partially solubilized from the membrane fraction by NaCl and KSCN. The membrane association of pro-sigmaK did not require spoIVF gene products, which appear to be located in the mother cell membrane that surrounds the forespore, and govern pro-sigmaK processing in the mother cell. Furthermore, pro-sigmaK associated with the membrane when overproduced in vegetative cells. Overproduction of pro-sigmaK in sporulating cells resulted in more pro-sigmaK in the membrane fraction. In agreement with the results of cell fractionation experiments, immunofluorescence microscopy showed that pro-sigmaK was localized to the mother cell membranes that surround the mother cell and the forespore in sporulating wild-type cells and mutant cells that do not process pro-sigmaK. Treatment of extracts with 0.6 M KCl appeared to free most of the pro-sigmaK and sigmaK from other cell constituents. After salt removal, sigmaK, but not pro-sigmaK, reassociated with exogenous core RNA polymerase to form holoenzyme. These results suggest that the prosequence inhibits RNA polymerase core binding and targets pro-sigmaK to the membrane, where it may interact with the processing machinery.

Bacillus subtilis↗
PubMed1998

Role of CD4+ and CD8+ T cells in regulating the chronic development of liver injury induced by delayed-type hypersensitivity to picryl chloride.

In this study we first investigated the cellular immune responses in mice with chronic liver injury induced by delayed-type hypersensitivity to picryl chloride (PCl). A continuous reduction, after week 3 of liver injury, was observed in the level of PCl-induced contact sensitivity but not in sheep red blood cell-induced footpad reaction, suggesting the presence of PCl-specific suppression. When spleen cells from mice whose liver had been injured for 1 week were systemically transferred into syngeneic recipients with the liver injury, the elevation in serum lactic dehydrogenase and the decrease in alkaline phosphatase and albumin levels in recipient mice were significantly exacerbated. However, when the liver damage in the donor mouse was allowed to proceed for 3, 5 or 7 weeks, biochemical changes in recipients were reduced to near normal levels. A flow-cytometric assay demonstrated that the number of CD4+ T cells in both spleen cells and liver nonparenchymal cells decreased dramatically during the late phase of liver injury, while CD8+ counts did not. These findings suggest that CD4+ and CD8+ T lymphocytes may contribute to the positive and negative regulation, respectively, of the early and late phases in the chronic development of liver injury.

Animals↗
PubMed1998

Role of skeletal muscle in thiazolidinedione insulin sensitizer (PPARgamma agonist) action.

Thiazolidinedione (TZD) insulin sensitizers are specific agonists of peroxisome proliferator activated receptor (PPAR)gamma. However, their mechanism of action and the in vivo target tissue(s) that mediate insulin sensitization remain poorly defined. Although PPARgamma messenger RNA expression has been reported in skeletal muscle, the expression of PPARgamma within myocytes in intact muscle tissue has not been examined. An antipeptide PPARgamma antibody was generated; immunohistochemistry was then used to demonstrate that PPARgamma is present within nuclei of myocytes [in both skeletal (white and red fibers) and cardiac tissue (rodent and human)]. The effect of insulin sensitizer treatment on muscle insulin action was studied using ob/ob mice after 4 days dosing with a potent (6 nM PPARgamma Kd) TZD (10 mg/kg x day). 2-deoxyglucose (2-DOG) uptake was then assessed in freshly isolated soleus muscles from lean vs. ob/ob vs. TZD-treated ob/ob mice. In lean mouse muscles, 2-DOG uptake was stimulated by 82%, 95%, 165% (with 25, 100, 2000 microU/ml insulin); muscles from ob/ob were severely insulin resistant (<80% stimulation with 2000 microU/ml insulin). Muscles from TZD-treated ob/ob displayed a normal insulin response with 100 (71%) or 2000 (158%) microU/ml insulin. Additional studies were performed using ZDF rats treated with/without TZD for 7 days. In vivo 2-DOG glucose uptake into soleus, gastrocnemius, and diaphragm muscles was measured during euglycemic-hyperinsulinemic clamp. Compared with lean rats, muscle 2-DOG uptake in ZDF was reduced by 52% (soleus) or 71% (diaphragm). Partial (40-60%) normalization of the reduced 2-DOG uptake was evident in TZD-treated ZDF rats. In contrast to the effect of in vivo treatment on muscle insulin action, preincubation of isolated soleus muscles from naive lean or ob/ob mice for 5 h with 100 nM TZD did not affect insulin-stimulated 2-DOG uptake. We conclude: 1) PPARgamma is expressed in myocytes within skeletal and cardiac muscle. 2) In vivo activation of PPARgamma by treatment of insulin-resistant mice/rats with a potent TZD corrects impaired muscle insulin action. 3) The lack of a direct effect on muscle after 5 h in vitro TZD incubation suggests that changes in insulin action may require a longer duration of PPARgamma activation or that improved muscle insulin sensitivity may result from an indirect in vivo effect of PPARgamma activation (e.g. changes in systemic lipid metabolism).

Animals↗
PubMed1998

Urinary ovarian and gonadotropin hormone levels in premenopausal women with low bone mass.

We hypothesized that lower ovarian and gonadotropin hormone concentrations would be associated with lower levels of peak bone mineral density (BMD) in apparently normally menstruating women who did not exercise intensively and did not report anorexia or bulimia. This hypothesis was evaluated using a case-with-control study design (n = 65) which was nested within a population-based longitudinal study of peak bone mass (Michigan Bone Health Study) with annual assessment in women aged 25-45 years (n = 582). Cases were 31 premenopausal women with BMD of the lumbar spine, femoral neck, and total body less than the 10th percentile of the distribution, where controls were 34 premenopausal women with BMD between the 50th and 75th percentile. BMD was measured by dual-energy X-ray absorptiometry. In addition to their annual measurement, these 65 participants collected first-voided morning urine specimens daily through two consecutive menstrual cycles. The urine from alternating days of this collection was analyzed for estrone-3-glucuronide (E1G), pregnanediol glucuronide (PdG), testosterone, and follicle-stimulating hormone by radioimmunoassay and these values adjusted for daily creatinine excretion levels. Additionally, analyses of daily urine specimens for luteinizing hormone (uLH) was undertaken to better characterize the possible uLH surge. Cases had significantly lower amounts of E1G (p = 0.009) and PdG (p = 0.002) than did controls, whether amounts were characterized by a mean value, the highest value, or the area under the curve, and after statistically controlling for body size. Further, when B-splines were used to fit lines to the E1G and PdG data across the menstrual cycle, the 95% confidence intervals (CIs) about the line for the controls consistently excluded and excluded and exceeded the 95% confidence bands for the cases in the time frame associated with the luteal phase in ovulatory cycles. Likewise, 95% CIs for the LH surge in controls exceeded the fitted line for cases around the time associates with the LH surge. The cases and controls were not different according to dietary intake (energy, protein, calcium), family history of osteoporosis, reproductive characteristics (parity, age at menarche, age of first pregnancy), follicular phase serum hormone levels, calciotropic hormone levels, or by evidence of perimenopause. We conclude that these healthy, menstruating women with BMD at the lowest 10th percentile from a population-based study had significantly lower urinary sex steroid hormone levels during the luteal phase of menstrual cycles as compared with hormone levels in premenopausal women with BMD between the 50th and 75th percentile of the same population-based study, even after considering the role of body size. These data suggest that subclinical decreases in circulating gonadal steroids may impair the attainment and/or maintenance of bone mass in otherwise reproductively normal women.

Absorptiometry, Photon↗
PubMed1998

Absence of mycoplasmal gene in malignant mammalian cells transformed by chronic persistent infection of mycoplasmas.

Chronic persistent infections by mycoplasmas induced malignant transformation of C3H mouse embryo cells that normally had never been reported to undergo spontaneous transformation. This mycoplasma-mediated oncogenic process had a long latency (more than 7 weeks of continuous mycoplasmal infection) and showed a multistage progression characterized by reversibility (at least up to 11 weeks of mycoplasmal infection) and irreversibility of malignant properties upon removal of the mycoplasma from culture. Further prolonged infections (18 weeks) by Mycoplasma fermentans or M. penetrans resulted in permanent transformation of these C3H cells that no longer required the continued presence of the transformation-inducing mycoplasmas in cultures to retain their malignant properties. Previous studies of viral oncogenesis revealed that virus-transformed cells always had viral gene(s) present. Integration of viral gene(s) apparently played an important role in the process of oncogenesis. In this study, we examined if the continued presence of any mycoplasmal gene(s) in mammalian cells, in whatever form, was also crucial in causing malignant cell transformation. Representational difference analysis (RDA) was a recently developed powerful technique to compare differences between two complex genomes. In the RDA system, subtractive and kinetic enrichment was used to purify and isolate restriction endonuclease gene fragment(s) of mycoplasmal origin, presumably present only in mycoplasma-transformed C3H cells, but not in nonmycoplasma-exposed control C3H cells. After three rounds of subtractive hybridization following PCR enrichment for each of three different restriction enzymes DNA digests, no gene fragment of mycoplasmal origin was amplified or identified in the permanently transformed C3H cells. Differing from tumorigenesis in animal cells induced by most oncogenic viruses or in plant cells induced by Agrobacteria, mycoplasmas evidently did not cause malignant transformation by integrating their gene(s) into the mammalian cell genome.

Animals↗
PubMed1998

[Clinical applyeation of neural stump buried into muscle for the prevention and treatment of neuroma].

In order to verify the effectiveness of neural stump buried into the muscle in the prevention and treatment of neuroma, 17 cases were reported, in which 8 cases having 19 painful neuromas and 9 cases having 13 amputated meural stumps, buried into muscle. They wese followed up for 6 months to 40 months, It was shown that good and excellent results were obtained and no evidence of neuroma was observed in all cases except in one which had painful neuroma occurred from the failure of embedment of the neural stump into the muscle. The conclusion was that the neural stump buried into muscle was an effective method for the prevention and treatment of neuroma.

Adult↗
PubMed1998

[Microsurgical repair of defects of soft tissue and infected wounds of extremities].

A study was carried out to observe the application of microsurgical technique in the repair defects of soft tissue and infected wounds of extremities. Eighty-three patients with soft tissue defects and infected wounds of extremities were treated by either transferring of vascularized cutaneous flap or transplantation of myocutaneous flap with vascular anastomosis. The result showed that eighty-three patients had gained success after a follow-up of 6 months to 4 years. It was concluded that soft tissue defects and infected wounds of extremities should be repaired as early as possible. Selecting the donor flap near the recipient site was of first choice. The method used for repair should be simple and easily applicable rather these very complicated one. The success depended on the correct treatment of local conditions, resonable design of donor flap and close monitoring after operation.

Adolescent↗
PubMed1998

Influence of percentage of osseointegration on stress distribution around dental implants.

OBJECTIVE: Stress around implants may lead to bone resorption and loss of the implant. The present study examined the influence of percentage of osseointegration at the implant-bone interface on the transmission of occlusal forces for endosseous dental implants. METHODS: The three-dimensional finite element method used in the study was built from data obtained from slices of dental computed tomography scans. The study modeled a 3.75 x 10-mm cylindric implant placed in an edentulous mandible. Varying the elastic parameters assigned to the implant-bone interface, a load of 35 N was applied at the occlusal surface of the restoration at the vertical axis of the implant. Maximum principal stress, minimum principal stress and Von Mises stress were calculated. RESULTS AND CONCLUSIONS: The most extreme stresses in the bone were always located around the neck of the implant. Those stresses in the implant-tissue interface decreased in inverse proportion to the increase in percentage of osseointegration. These results indicate the value of osseointegration in the aspect of mechanics.

Alveolar Process↗
PubMed1998

[Effect of fluoride on proliferation and differentiation in rat and mouse embryo bud cell in vitro].

The effect of fluoride on differentiation and proliferation of rat and mouse embryo limb bud cell were studied with micromass cultures in vitro. Embryo limb bud cells of rat (13-day) and mouse (12-day) were subjected to culture for 5 days. The results showed that fluoride could inhibit differentiation of cells without affecting cells proliferation. The concentrations of 50% inhibition of cell differentiation (ID50) were 6.8 micrograms/ml(rat) and 7.3 micrograms/ml(mouse). The concentrations of 50% inhibitions of cell proliferation (IP50) were 44.1 micrograms/ml (rat) and 63.6 micrograms/ml (mouse). The IP/ID50 values 6.4(rat) and 8.7 (mouse) were both greater than 5. According to the assessment criteria of Flint and Cheng Wanrong, the fluoride may be an embryo limb bud cells specific inhibitor. It could have potent teratogenicity.

Animals↗
PubMed1998

[Preoperative radiotherapy reduces cervical metastasis of supraglottic carcinoma: a prospective randomized trial in 201 patients].

OBJECTIVE: To evaluate the effectiveness of preoperative radiotherapy in the control of overall cervical lymph node metastasis from supraglottic carcinoma. METHODS: A prospective randomized study on 210 patients with supraglottic carcinoma was performed. Nine patients were lost from follow-up and therefore excluded. The analysis was based on the remained 201 patients including fifteen who did not complete the treatment protocol. Surgery alone(S) was carried out in 102 patients and radiotherapy(40 Gy) followed by surgery (R + S) in 99 patients. All the patients were followed up for more than three years. RESULTS: No statistically significant difference in survival rates between S and R + S groups was found by using the Kaplan-Meier analysis. However, relative risk of overall cervical recurrence had a trend of reduction for patients in R + S group, versus patients in S group. There was a statistically significant reduction of lymph node metastasis in R + S group compared to S group in stage I-III(P = 0.0198) while in stage IV no such difference was observed. Patients with stage I-III disease who did not receive preoperative radiation were 1.766 times more likely to develop neck recurrence compared to patients who did. Among all the factors, only TNM stage and histological nodal status were found to be independent risk factors for regional control. Contralateral neck failure occurred more frequently in patients with advanced lesion(P = 0.020) and in patients without preoperative radiation(P = 0.018). CONCLUSION: There may be a trend towards improved control of cervical lymph node metastasis with preoperative radiation of 40 Gy dose in patients with supraglottic cancer in stage I-III of the disease.

Combined Modality Therapy↗
PubMed1998

[Effects of selective induceble nitric oxide synthase inhibitor on immunological hepatic injury in rat].

OBJECTIVE: To investigate the role and induced regulation of nitric oxide (NO) in rat immunological hepatic injury, and the effect of selective inhibitor on induceble nitric oxide synthase (iNOS). METHODS: The intracellular NOS gene expression in the immune damaged hepatocytes was determined by in situ PCR technique, and NO concentration and lactate dehydrogenase (LDH) activity in culture supernatant were measured. RESULTS: Administration of bacille calmette guerin (BCG, 15, 30, 50 mg/rat, i.v.) alone or BCG with the inflammatory cytokines mixture (CM), including IL-1 beta, IFN-gamma, TNF-alpha and lipopolysacchride (LPS) significantly increased NO production and LDH release in culture medium(P < 0.05). NO production was enhanced with hepatic injury degree in direct proportion, and with BCG dose in inverse proportion. Under immunological stimuli condition, hepatocytes NOS mRNA mainly expressed an induceble and soluble isoform (iNOS) in cytoplasm. Aminoguanidine (AG), a selective iNOS inhibitor, inhibited NO production and LDH release (83.4% and 36.0%, P < 0.05), but the transcription inhibitor actinomycin D enhanced LDH level in the medium (25.5%, P < 0.05). CONCLUSION: NO produced by immunological stimuli participates in rat hepatic injury mechanism.

Animals↗
PubMed1998

[Research reports in Chinese medical journals].

OBJECTIVE: To assess research designs employed in Chinese medical journals over the last decade. METHOD: The types of study design used in all original articles published in five leading journals (sponsored by the Chinese Medical Association) in 1985 (n = 640) and 1995 (n = 954) were evaluated. RESULTS: Of 1,594 articles, over 50% were case reports and cross-sectional studies, and one third were longitudinal studies. Compared with 1985, the proportion of clinical trials increased from 5.6% to 11.3%, especially that of RCT increased from 1.3% to 4.2%. The proportion of prospective studies also increased from 3.9% to 6.0% and that of retrospective studies decreased from 25.0% to 13.9%, particularly, that of case series decreased from 17.3% to 5.9%. The inappropriate use of research design was frequent, the proportion of this problem was 38.0% and 36.8% for 1985 and 1995 respectively. The longitudinal studies were most liable to have this problem. The five commonly problems were the lack or inappropriateness of control, non-representativeness of sample, unbelievable conclusion, no randomization, and no consideration of confounders. They accounted for 66.9%. CONCLUSION: The quality of research designs used in Chinese medical research is gradually improving in the last decade, but the lack or inappropriate use remains a serious problem.

China↗