Search PubMed⌕ Search

Biomedical subjects

P Ma

Publications and source records attributed to P Ma.

At least 37 records · Page 2Linked to original sources
PubMed2000

[Local chemotherapy by fibrobronchoscopy for advanced bronchogenic carcinoma].

OBJECTIVE: To observe the effectiveness of treatment in the patients with advanced bronchogenic carcinoma of local chemotherapy with fibrobronchoscopy, combined with systematic chemotherapy. METHODS: 40 patients with advanced bronchogenic carcinoma were divided into the tested group (20 patients) and the control group (20 patients) randomly. By fibrobronchoscopy with its matched injecting needle, carboplatin 300 mg were injected into the centre of the tumor and the surroundings, combined with the routine carboplatin and etoposide (CE) regimen. While the control group was treated only by intravenous chemotherapy with the routine CE regimen. RESULTS: In the 20 patients with local chemotherapy by fibrobronchoscopy combined with intravenous chemotherapy, 7 cases (35%) were completely cured and 11 cases (55%) showed partial recovery, other 2 cases without change. The 90% effective rate was significantly higher than 55% of the control group (P < 0.05). CONCLUSIONS: The local chemotherapy by fibrobronchoscopy can remarkably reduce the size of tumor, and relieve symptom of dyspnea. Intravenous chemotherapy alleviated the obstruction caused by tracheal or bronchial neoplasms. The combined therapies led to much better therapeutic effect and symptomatic relief than those by the routine CE regimen.

Aged↗
PubMed1999

Evolution of the X-specific block embedded in the human Xq21.3/Yp11.1 homology region.

The region Xq21.3/Yp11.1 represents the largest segment of homology between the sex chromosomes in humans, though no recombination occurs in male meiosis. It presumably arose as a transposition from the X to the Y chromosome; the present-day organization in the latter chromosome indicates a paracentric inversion that disrupted its continuity. Moreover, an X-specific block (defined by the marker DXS214) is embedded in the region. Previously, no hypotheses about the length, origin, or evolution of this X-specific segment have been proposed. Here we report on the refinement of the size and the sequence of the distal boundary of the X-specific block. Furthermore, we have tracked by FISH experiments the evolution of this region in primates. This further clarifies the multistep mechanism of origin for the XY homology region, by demonstrating that the X-specific block was deleted from the Y chromosome after the initial transfer from the X chromosome.

Animals↗
PubMed1999

Deletion of SFI1, a novel suppressor of partial Ras-cAMP pathway deficiency in the yeast Saccharomyces cerevisiae, causes G(2) arrest.

When glucose is added to Saccharomyces cerevisiae cells grown into stationary phase or on non-fermentable carbon sources a rapid loss of heat stress resistance occurs. Mutants that retain high stress resistance after addition of glucose are called 'fil', for deficient in fermentation induced loss of stress resistance. Transformation of the fil1 mutant, which harbours a point mutation in adenylate cyclase, with a yeast gene library on a single copy plasmid resulted in transformants that were again stress-sensitive. One of the genes isolated in this way was a gene of previously unknown function. We have called it SFI1, for suppressor of fil1. SFI1 is an essential gene. Combination of Sfi1 and cAMP pathway mutations indicates that Sfi1 itself is not involved in the cAMP pathway. Conditional sfi1 mutants did not show enhanced heat resistance under the restrictive condition, whereas overexpression of SFI1 rendered cells heat-sensitive. Sfi1 may be a downstream target of the protein kinase A pathway, but its precise relationship with heat resistance remains unclear. Further analysis showed that Sfi1 is required for cell cycle progression, more specifically for progression through G(2)-M transition. Cells expressing SFI1 under the control of a galactose-inducible promoter arrest after addition of glucose as doublets of undivided mother and daughter cells. These doublets contain a single nucleus and lack mitotic spindles. Sfi1 shares homology with Xenopus laevis XCAP-C, a protein required for chromosome assembly. The conserved residues between these two proteins show a strong bias for charged amino acids. Hence, Sfi1 might be required for correct mitotic spindle assembly and its precise role might be in chromosome condensation. In conclusion, we have identified an essential function in the G(2)-M transition of the cell cycle for a yeast gene of previously unknown function.

Base Sequence↗
PubMed1999

Polymorph determination for the GP IIb/IIIa antagonist, roxifiban, using a combination of electron diffraction and synchrotron X-ray powder diffraction techniques.

Unit cell parameters of two polymorphs of roxifiban have been determined by a combination of transmission electron microscopy (TEM) single-crystal and synchrotron X-ray powder diffraction techniques. While it was difficult to differentiate the two forms by their standard X-ray diffraction patterns, the high-resolution synchrotron patterns clearly showed striking differences. Unit cells for the two forms required the use of cell parameters derived from TEM diffraction patterns. The two unit cells are, not surprisingly, very similar except for a doubling of one of the axes for form II. The combined use of TEM and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large unit cell) polymorphs.

Amidines↗
PubMed1999

A Saccharomyces cerevisiae G-protein coupled receptor, Gpr1, is specifically required for glucose activation of the cAMP pathway during the transition to growth on glucose.

In the yeast Saccharomyces cerevisiae the accumulation of cAMP is controlled by an elaborate pathway. Only two triggers of the Ras adenylate cyclase pathway are known. Intracellular acidification induces a Ras-mediated long-lasting cAMP increase. Addition of glucose to cells grown on a non-fermentable carbon source or to stationary-phase cells triggers a transient burst in the intracellular cAMP level. This glucose-induced cAMP signal is dependent on the G alpha-protein Gpa2. We show that the G-protein coupled receptor (GPCR) Gpr1 interacts with Gpa2 and is required for stimulation of cAMP synthesis by glucose. Gpr1 displays sequence homology to GPCRs of higher organisms. The absence of Gpr1 is rescued by the constitutively activated Gpa2Val-132 allele. In addition, we isolated a mutant allele of GPR1, named fil2, in a screen for mutants deficient in glucose-induced loss of heat resistance, which is consistent with its lack of glucose-induced cAMP activation. Apparently, Gpr1 together with Gpa2 constitute a glucose-sensing system for activation of the cAMP pathway. Deletion of Gpr1 and/or Gpa2 affected cAPK-controlled features (levels of trehalose, glycogen, heat resistance, expression of STRE-controlled genes and ribosomal protein genes) specifically during the transition to growth on glucose. Hence, an alternative glucose-sensing system must signal glucose availability for the Sch9-dependent pathway during growth on glucose. This appears to be the first example of a GPCR system activated by a nutrient in eukaryotic cells. Hence, a subfamily of GPCRs might be involved in nutrient sensing.

Amino Acid Sequence↗
PubMed1999

A mutation in Saccharomyces cerevisiae adenylate cyclase, Cyr1K1876M, specifically affects glucose- and acidification-induced cAMP signalling and not the basal cAMP level.

In the yeast Saccharomyces cerevisiae, the addition of glucose to derepressed cells and intracellular acidification trigger a rapid increase in the cAMP level within 1 min. We have identified a mutation in the genetic background of several related 'wild-type' laboratory yeast strains (e.g. ENY.cat80-7A, CEN.PK2-1C) that largely prevents both cAMP responses, and we have called it lcr1 (for lack of cAMP responses). Subsequent analysis showed that lcr1 was allelic to CYR1/CDC35, encoding adenylate cyclase, and that it contained an A to T substitution at position 5627. This corresponds to a K1876M substitution near the end of the catalytic domain in adenylate cyclase. Introduction of the A5627T mutation into the CYR1 gene of a W303-1A wild-type strain largely eliminated glucose- and acidification-induced cAMP signalling and also the transient cAMP increase that occurs in the lag phase of growth. Hence, lysine1876 of adenylate cyclase is essential for cAMP responses in vivo. Lysine1876 is conserved in Schizosaccharomyces pombe adenylate cyclase. Mn2+-dependent adenylate cyclase activity in isolated plasma membranes of the cyr1met1876 (lcr1) strain was similar to that in the isogenic wild-type strain, but GTP/Mg2+-dependent activity was strongly reduced, consistent with the absence of signalling through adenylate cyclase in vivo. Glucose-induced activation of trehalase was reduced and mobilization of trehalose and glycogen and loss of stress resistance were delayed in the cyr1met1876 (lcr1) mutant. During exponential growth on glucose, there was little effect on these protein kinase A (PKA) targets, indicating that the importance of glucose-induced cAMP signalling is restricted to the transition from gluconeogenic/respiratory to fermentative growth. Inhibition of growth by weak acids was reduced, consistent with prevention of the intracellular acidification effect on cAMP by the cyr1met1876 (lcr1) mutation. The mutation partially suppressed the effect of RAS2val19 and GPA2val132 on several PKA targets. These results demonstrate the usefulness of the cyr1met1876 (lcr1) mutation for epistasis studies on the signalling function of the cAMP pathway.

Adenylyl Cyclases↗
PubMed1999

The PDE1-encoded low-affinity phosphodiesterase in the yeast Saccharomyces cerevisiae has a specific function in controlling agonist-induced cAMP signaling.

The yeast Saccharomyces cerevisiae contains two genes, PDE1 and PDE2, which respectively encode a low-affinity and a high-affinity cAMP phosphodiesterase. The physiological function of the low-affinity enzyme Pde1 is unclear. We show that deletion of PDE1, but not PDE2, results in a much higher cAMP accumulation upon addition of glucose or upon intracellular acidification. Overexpression of PDE1, but not PDE2, abolished the agonist-induced cAMP increases. These results indicate a specific role for Pde1 in controlling glucose and intracellular acidification-induced cAMP signaling. Elimination of a putative protein kinase A (PKA) phosphorylation site by mutagenesis of serine252 into alanine resulted in a Pde1(ala252) allele that apparently had reduced activity in vivo. Its presence in a wild-type strain partially enhanced the agonist-induced cAMP increases compared with pde1Delta. The difference between the Pde1(ala252) allele and wild-type Pde1 was strongly dependent on PKA activity. In a RAS2(val19) pde2Delta background, the Pde1(ala252) allele caused nearly the same hyperaccumulation of cAMP as pde1Delta, while its expression in a PKA-attenuated strain caused the same reduction in cAMP hyperaccumulation as wild-type Pde1. These results suggest that serine252 might be the first target site for feedback inhibition of cAMP accumulation by PKA. We show that Pde1 is rapidly phosphorylated in vivo upon addition of glucose to glycerol-grown cells, and this activation is absent in the Pde1(ala252) mutant. Pde1 belongs to a separate class of phosphodiesterases and is the first member shown to be phosphorylated. However, in vitro the Pde1(ala252) enzyme had the same catalytic activity as wild-type Pde1, both in crude extracts and after extensive purification. This indicates that the effects of the S252A mutation are not caused by simple inactivation of the enzyme. In vitro phosphorylation of Pde1 resulted in a modest and variable increase in activity, but only in crude extracts. This was absent in Pde1(ala252), and phosphate incorporation was strongly reduced. Apparently, phosphorylation of Pde1 does not change its intrinsic activity or affinity for cAMP but appears to be important in vivo for protein-protein interaction or for targeting Pde1 to a specific subcellular location. The PKA recognition site is conserved in the corresponding region of the Schizosaccharomyces pombe and Candida albicans Pde1 homologues, possibly indicating a similar control by phosphorylation.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1999

[Combined use of rhBMP2/BCB and free periosteum in repairing segmental defects in radii of rabbits].

OBJECTIVE: To study the efficacy of combined use of rhBMP2/BCBand free periosteal graft in repairing segmental bony defects. METHODS: A new grafting material (rhBMP2/BCB) was made by combining recombinant human BMP2 (rhBMP2) and an antigen-free bovine cancellous bone (BCB) as a carrier. rhBMP2/BCB was used alone in conjunction with free periosteal graft to repair a 1.5 cm defect in the radius of the rabbit. The defect-repairing capability for each of the treatment modalities was assessed radiographically, biomechanically, and by densitometry and histological studies. RESULTS: rhBMP2/BCB used alone was capable of healing the defect in large by 16 weeks, with a similar repair process and mechanism seen with RBX. Combined use of rhBMP2/BCB and free periosteal graft was superior in terms of increased amount and quality of the new bone formed at the early stage of the repair process (within 12 weeks) to rhBMP2/BCB used in isolation, with the defect basically healed by 12 weeks. CONCLUSIONS: Both methods are effective in repairing segmental bony defects, with rhBMP2/BCB used in conjunction with free periosteal graft being most preferred, considering the satisfactory osteogenesis, osteoconduction and osteoinduction.

Animals↗
PubMed1999

[Allograft-prosthesis combination in limb salvage surgery].

OBJECTIVE: To study allograft-prosthesis combination in limb salvage and the rational of composite prosthesis. METHODS: Of 16 patients with bone tumors age from 19 to 60 years, 6 women 12 men, osteosarcoma was found in 4 patients, chondrosarcoma in 2, malignant giant cell tumor in 3, fibrosarcoma in 3, and other malignant bone tumor in 4. Allograft-prosthesis combination in included allograft proximal femurs with total hip arthroplasty (3 patients), allografts bipolar femoral head replacement (8), allografts with total knee arthroplasty prosthetic replacements (7). All patients received adjuvant therapy for tumor control. RESULTS: The length of follow-up ranged from 18 months to 5 years during which time 1 patients died, 3 survived as tumor-carriers, and 12 were disease free. All patients obtained better functional result in their extremities and had good quality of life. CONCLUSIONS: Both prosthetic replacement and allograft advantages, the use of large bone allografts with metallic prosthesis for the treatment of bone tumors near or involving joints can be applied with good results in selected patients having limb salvage surgery.

Adult↗
PubMed1998

Pharmaceutical development and specification of stereoisomers.

The pharmaceutical development of chiral drugs requires the activities of many different research and development groups. Guidelines which help to coordinate the activities of these groups and assist in the successful development of compounds with either single or multiple chiral centers are outlined and discussed.

Clinical Trials as Topic↗
PubMed1998

Involvement of distinct G-proteins, Gpa2 and Ras, in glucose- and intracellular acidification-induced cAMP signalling in the yeast Saccharomyces cerevisiae.

Adenylate cyclase activity in Saccharomyces cerevisiae is dependent on Ras proteins. Both addition of glucose to glucose-deprived (derepressed) cells and intracellular acidification trigger an increase in the cAMP level in vivo. We show that intracellular acidification, but not glucose, causes an increase in the GTP/GDP ratio on the Ras proteins independent of Cdc25 and Sdc25. Deletion of the GTPase-activating proteins Ira1 and Ira2, or expression of the RAS2(val19) allele, causes an enhanced GTP/GDP basal ratio and abolishes the intracellular acidification-induced increase. In the ira1Delta ira2Delta strain, intracellular acidification still triggers a cAMP increase. Glucose also did not cause an increase in the GTP/GDP ratio in a strain with reduced feedback inhibition of cAMP synthesis. Further investigation indicated that feedback inhibition by cAPK on cAMP synthesis acts independently of changes in the GTP/GDP ratio on Ras. Stimulation by glucose was dependent on the Galpha-protein Gpa2, whose deletion confers the typical phenotype associated with a reduced cAMP level: higher heat resistance, a higher level of trehalose and glycogen and elevated expression of STRE-controlled genes. However, the typical fluctuation in these characteristics during diauxic growth on glucose was still present. Overexpression of Ras2(val19) inhibited both the acidification- and glucose-induced cAMP increase even in a protein kinase A-attenuated strain. Our results suggest that intracellular acidification stimulates cAMP synthesis in vivo at least through activation of the Ras proteins, while glucose acts through the Gpa2 protein. Interaction of Ras2(val19) with adenylate cyclase apparently prevents its activation by both agonists.

Adenylyl Cyclases↗
PubMed1998

Saccharides as osmotic agents in peritoneal dialysate: determination of molecular weight essential for more efficient fluid removal.

Glucose has widely been used as an osmotic agent in continuous ambulatory peritoneal dialysis (CAPD) but owing to its low molecular weight (MW), ultrafiltration (UF) in a 6-hour dialysate exchange does not appear sufficient. Thus, in the present study, a search was made to find saccharides that would ensure optimal UF, exceeding that obtained with glucose in a 6-hour dwell period. Rats were intraperitoneally infused with peritoneal dialysate (20 mL/body) containing the same molar concentrations (75.5 mM, 126 mM, or 204 mM) of various osmotic agents including glucose (monosaccharide, MW = 180.16) at concentrations of 1.36%, 2.27%, and 3.86%; maltose (disaccharide, MW = 342.30) at concentrations of 2.58% and 4.32%; maltotriose (trisaccharide, MW = 504.44), at concentrations of 3.81% and 6.36%; and maltopentaose (pentasaccharide, MW = 828.72) at concentrations of 6.26% and 10.4%. Intraperitoneal-fluid volume was measured at 1, 2, 3, 4, and 6 hours. With glucose as the osmotic agent, maximal UF was noted at 2 to 4 hours. UF was more efficient at 6 hours with maltotriose or maltopentaose as the osmotic agent. Even with a trisaccharide or pentasaccharide (molecular weights of 500 to 830), UF at 6 hours was found more efficient, as evidenced by the delay in peritoneal absorption. Fluid removal in 6 hours should be greater when using a dialysate containing oligosaccharides such as maltotriose or maltopentaose in place of glucose.

Animals↗
PubMed1997

Glucose exerts opposite effects on mRNA versus protein and activity levels of Pde1, the low-affinity cAMP phosphodiesterase from budding yeast, Saccharomyces cerevisiae.

In budding yeast (Saccharomyces cerevisiae), a low-affinity phosphodiesterase, Pde1, and a high-affinity phosphodiesterase, Pde2, are responsible for the degradation of cAMP. Addition of glucose to glycerol-grown yeast cells is known to cause a transient increase in the cAMP level and recent work has indicated a specific involvement of Pde1 in this response. In this work we show that glucose addition induces the accumulation to high levels of mRNA encoding Pde1. This increase continues for at least 8 hours and is due to enhanced transcription of the PDE1 gene, since glucose addition does not change the stability of the Pde1 mRNA. Surprisingly, using an assay method specific for Pde1, we observed that the activity of Pde1 remains constant and finally decreases several-fold during the same period. In addition, this activity profile closely follows the Pde1 protein level as judged from Western blotting with antibodies directed against Pde1. Experiments using cycloheximide, a general inhibitor of translation, allow to exclude the possibility of a futile cycle of Pde1 synthesis and degradation. Hence, glucose addition appears to trigger an increase in PDE1 gene transcription together with a specific inhibition of the translation of Pde1 mRNA.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1997

Discovery of potent isoxazoline glycoprotein IIb/IIIa receptor antagonists.

Using the isoxazoline as a common structural feature, three series of glycoprotein IIb/IIIa receptor antagonists were evaluated, culminating in the discovery of XR299 (30). In an in vitro assay of platelet inhibition, XR299 had an IC50 of 0.24 microM and was a potent antiplatelet agent when dosed intravenously in a canine model. It was shown through X-ray studies of the cinchonidine salt 49 that the receptor required the 5(R)-stereochemistry for high potency. The ethyl ester prodrug of XR299, XR300 (29), was orally active in the dog.

Animals↗
PubMed1997

Convective mass transfer at the carotid bifurcation.

The convective conditions in regions of hemodynamic separation may produce uneven local mass transfer at the arterial wall which may lead to an atherogenic response. This study estimates the potential variation in local mass transfer of oxygen at the human carotid bifurcation under steady flow conditions. The three-dimensional separated flow at the bifurcation was studied using a computational analysis of the basic conservation equations of mass, momentum, and species. Mass transfer between the blood and the wall was estimated throughout the sinus region for a condition where the concentration at the wall was constant. Flow separation at the carotid bifurcation created a complex concentration field. The mass transfer was five times lower along the outer wall of the carotid sinus than the artery wall immediately upstream or downstream of the sinus. The region of low mass transfer was similar to the region of low shear stress but not identical. This distribution of low mass transfer correlated strongly with intimal thickening as measured previously from human specimens. Quantitative differences in mass transfer at the arterial wall should not be discarded as an important mechanism by which hemodynamics influences atherogenesis at this site of clinical disease.

Biomechanical Phenomena↗
PubMed1997

[Studies on the essential oil constituents of the stem bark of Magnolia obovata].

For the extensive studies of the chemical constituents of Magnollis obovata, the essential oil from Magnolia obovata was obtained by steam distillation. The chemical components of the oil were examined by means of capillary gas chromatography and gas chromatography-mass spectrometry. 29 of the 75 separated constituents were identified. The content of each component identified was determined by area normalization method, which showed the content of 9 compounds was higher than 1%.

Gas Chromatography-Mass Spectrometry↗
PubMed1997

Effects of osmotic agents on hyaluronan synthesis in human peritoneal mesothelial cells and fibroblasts.

Hyaluronan (HA) plays an important role in peritoneal tissue remodeling and the inflammatory process. In this study, attention was directed to the effects of various osmotic agents on HA synthesis in human peritoneal mesothelial cells (HMCs) and fibroblasts (HFBs). Following incubation with growth arrest media for 48 hours, the cells (4 x 10(4)/mL) were incubated for 72 hours in media at various concentrations (50, 100 mmol/L for crystalloid agents and 3.5%, 7% for oncotic agents) of glucose, mannitol, glycerol, sucrose, raffinose, NaCl, combined amino acids, maltodextrin, dextran 70, and hydroxyethylstarch 20. HA synthesis for 72 hours was measured by sandwich-binding protein assay. HMCs synthesized approximately 0.15 ng/cell/72 hours and HFBs 0.09 ng. All crystalloid osmotic agents significantly suppressed HA synthesis by HMCs and HFBs in a concentration-dependent manner. There was no such suppression by any oncotic osmotic agent, which, to the contrary, enhanced the synthesis by 6%-63% in HMCs. In conclusion, HMCs and HFBs may be considered sources of HA in the peritoneal dialysis effluent. Crystalloid osmotic agents suppressed HA synthesis in these cells. Oncotic osmotic agents seem to be less toxic in this regard.

Amino Acids, Essential↗