Biomedical subjects
Publications and source records attributed to D Ma.
The condensation of enantiopure beta-amino esters with beta-ketoesters followed by cyclization and decarboxylation afforded 2,3-dihydro-4-pyridones 3, which were selectively hydrogenated to provide 2,6-disubstituted 4-hydroxypiperdines.
Treatment of the enolates of 4 generated from the asymmetric Strecker reaction products with alkyl halides or aldehydes provided the corresponding functionalized products with high diastereoselectivity. Deprotection of these products afforded the corresponding enantiopure alpha,alpha-dialkyl amino acids.
Syringomycin E is an antifungal cyclic lipodepsinonapeptide produced by Pseudomonas syringae pv. syringae. To understand the mechanism of action of syringomycin E, a novel resistant Saccharomyces cerevisiae strain, BW7, was isolated and characterized. Lipid analyses revealed that BW7 contained only the hydrophobic subspecies of sphingolipids that are normally minor components in wild type strains. This aberrant sphingolipid composition was the result of lack of alpha-hydroxylation of the amide-linked very long chain fatty acids, suggesting a defective sphingolipid alpha-hydroxylase encoded by the FAH1 gene. A yeast strain that lacks the FAH1 gene was resistant to syringomycin E, and failed to complement BW7. These results demonstrate that BW7 carries a mutation in the FAH1 gene, and that the lack of alpha-hydroxylated very long chain fatty acids in yeast sphingolipids confers resistance to syringomycin E.
We isolated the mouse zfh-4 cDNA which is 12 kb long and capable of encoding a 3,550-amino acid protein containing four homeodomains and 22 zinc fingers including two pseudo zinc finger motifs. The mouse ZFH-4 is 51% homologous to the mouse ATBF1 and 23% to the Drosophila ZFH-2. The homeodomain and zinc finger regions are highly conserved between ZFH-4 and ATBF1 except that one zinc finger is missing in ZFH-4. Analysis of partial genomic sequences showed that the mouse zfh-4 and ATBF1 genes are similar in exon-intron organization. RT-PCR analysis of zfh-4 transcripts in adult mouse tissues showed that zfh-4 expression was low but reproducibly detectable in brain, heart, lung and muscle. In these mouse tissues, ATBF1 transcripts were poorly amplified by PCR under the conditions where zfh-4 transcripts were amplified, suggesting that the expression of zfh-4 mRNA is higher than that of ATBF1 mRNA. Other comparative analysis suggests functional similarities and dissimilarities between ZFH-4 and ATBF1.
We present evidence that Rb forms a repressor containing histone deacetylase (HDAC) and the hSWI/SNF nucleosome remodeling complex, which inhibits transcription of genes for cyclins E and A and arrests cells in the G1 phase of the cell cycle. Phosphorylation of Rb by cyclin D/cdk4 disrupts association with HDAC, relieving repression of the cyclin E gene and G1 arrest. However, the Rb-hSWI/SNF complex persists and is sufficient to maintain repression of the cyclin A and cdc2 genes, inhibiting exit from S phase. HDAC-Rb-hSWI/SNF and Rb-hSWI/SNF then appear to maintain the order of cyclin E and A expression during the cell cycle, which in turn regulates exit from G1 and from S phase, respectively.
Cytoskeletal proteins are axonally transported with slow components a and b (SCa and SCb). In peripheral nerves, the transport velocity of SCa, which includes neurofilaments and tubulin, is 1-2 mm/d, whereas SCb, which includes actin, tubulin, and numerous soluble proteins, moves as a heterogeneous wave at 2-4 mm/d. We have shown that two isoforms of microtubule-associated protein 1B (MAP1B), which can be separated on SDS polyacrylamide gels on the basis of differences in their phosphorylation states (band I and band II), were transported at two different rates. All of band I MAP1B moved as a coherent wave at a velocity of 7-9 mm/d, distinct from slow axonal transport components SCa and SCb. Several other proteins were detected within the component that moved at the velocity of 7-9 mm/d, including the leading wave of tubulin and actin. The properties of this component define a distinct fraction of the slow axonal transport that we suggest to term slow component c (SCc). The relatively fast transport of the phosphorylated MAP1B isoform at 7-9 mm/d may account for the high concentration of phosphorylated MAP1B in the distal end of growing axons. In contrast to band I MAP1B, the transport profile of band II was complex and contained components moving with SCa and SCb and a leading edge at SCc. Thus, MAP1B isoforms in different phosphorylation states move with distinct components of slow axonal transport, possibly because of differences in their abilities to associate with other proteins.
LPG2 (a gene involved in lipophosphoglycan assembly) encodes the Golgi GDP-Man transporter of the protozoan parasite Leishmania and is a defining member of a new family of eukaryotic nucleotide-sugar transporters (NSTs). Although NST activities are widespread, mammalian cells lack a GDP-Man NST, thereby providing an ideal heterologous system for probing the LPG2 structure and activity. LPG2 expression constructs introduced into either mammalian cells or a Leishmania lpg2(-) mutant conferred GDP-Man, GDP-Ara, and GDP-Fuc (in Leishmania only) uptake in isolated microsomes. LPG2 is the first NST to be associated with multiple substrate specificities. Uptake activity showed latency, exhibited an antiport mechanism of transport with GMP, and was susceptible to the anion transport inhibitor DIDS. The apparent K(m) for GDP-Man uptake was similar in transfected mammalian cells (12.2 microM) or Leishmania (6.9 microM). Given the evolutionary distance between protozoans and vertebrates, these data suggest that LPG2 functions autonomously to provide transporter activity. Using epitope-tagged LPG2 proteins, we showed the existence of hexameric LPG2 complexes by immunoprecipitation experiments, glycerol gradient centrifugation, pore-limited native gel electrophoresis, and cross-linking experiments. This provides strong biochemical evidence for a multimeric complex of NSTs, a finding with important implications to the structure and specificity of NSTs in both Leishmania and other organisms. Inhibition of essential GDP-Man uptake in fungal and protozoan systems offers an attractive target for potential chemotherapy.
The resistance of the human parasite Brugia malayi to the antiparasitic activity of cyclosporin A (CsA) may arise from the presence of cyclophilins with relatively low affinity for the drug. The structure of the complex of B. malayi cyclophilin (BmCYP-1) and CsA, with eight independent copies in the asymmetric unit, has been determined at a resolution of 2.7 A. The low affinity of BmCYP-1 for CsA arises from incomplete preorganization of the binding site so that the formation of a hydrogen bond between His132 of BmCYP-1 and N-methylleucine 9 of CsA is associated with a shift in the backbone of approximately 1 A in this region.
This study examined associations of life events and locus of control with behavioral problems among 1,365 Chinese adolescents by using the Youth Self-Report (YSR), Adolescent Self-Rating Life Events Checklist (ASLEC), and the Nowicki-Strickland Locus of Control Scale for Children. Results indicated that the overall prevalence of behavioral and emotional problems was 10.7% (95% CI = 9.9-11.5%). Logistic-regression analyses showed that a total of 13 negative life events mainly coming from academic domain and interpersonal relationships, high life-stress score, and high external locus score significantly increased the risk for behavioral problems. Life stress and locus of control significantly interacted with behavioral problems. These findings support the linkage between stressful life events and psychopathology in a general population of adolescents from mainland China, and demonstrate the stress-moderating effects of locus of control on psychopathology as well.
To investigate the best first-line chemotherapy regimen for the treatment of advanced epithelial ovarian cancer (AEOC), the efficacy of three chemotherapy regimens for treatment of the patients with AEOC in our hospital during Jan. 1992-Jan. 1999 was retrospectively analyzed. The therapeutic effects were compared with the supplement of Melphalan + Hexamethylme (PAM + HMM), cisplatin + adriamycin + cyclophosphamide or isofamide (PAC) or cisplatin + cyclophosphamide or isofamide (PC), Taxol + cisplatin (TP) combined chemotherapy after cytoreductive surgery. The results showed that the overall effective rate of TP was significantly higher than that of PAM + HMM (P < 0.05); The complete remission rate of TP was significantly higher than that of PAM + HMM and PAC or PC (all P < 0.05); The 2-year survival rate free of tumor of TP was obviously higher than that of PAM + HMM and PAC or PC (all P < 0.05). It was concluded that the therapeutic effect of TP regimen in the treatment of AEOC was better than PAM + HMM and PAC or PC and TP regimen could be recommended currently as the preferred first-line one for the treatment of AEOC.
Microtubule-associated protein 1B is a major constituent of the neuronal cytoskeleton during the early stages of development. This protein and its phosphorylated isoform, microtubule-associated protein 1B-P, defined by the monoclonal antibody 1B-P [Boyne L. J. et al. (1995) J. Neurosci. Res. 40, 439-450], are present in growing axons and concentrated in the distal end near the growth cone. In most regions of the central nervous system, microtubule-associated protein 1B and microtubule-associated protein 1B-P are developmentally down-regulated. They remain, however, at relatively high levels in the adult peripheral nervous system, where microtubule-associated protein 1B-P is localized exclusively in axons. The aim of this study was to examine the levels of microtubule-associated protein 1B and its phosphorylated isoform during regenerative growth of peripheral axons. Following transection and re-apposition of the sciatic nerve at midthigh, the levels of total microtubule-associated protein 1B, microtubule-associated protein 1B-P and microtubule-associated protein 1B messenger RNA were analysed in dorsal root ganglion neurons and sciatic nerve axons using western blots and RNase protection assays. After the lesion, there was a small decrease in the levels of microtubule-associated protein 1B and its messenger RNA in dorsal root ganglion neurons. The proximal axonal stump showed a similar decrease in the levels of microtubule-associated protein 1B 30days after lesion and returned to normal 60-90days post-lesion. In the distal stump of the sciatic nerve, the levels of microtubule-associated protein 1B increased dramatically and rapidly between three and 14days, but the protein was localized mainly in activated Schwann cells and myelin-like structures, and not in axons [Ma D. et al. (1999) Brain Res. 823, 141-153]. With the regeneration of axons into the distal stump, an intense expression of microtubule-associated protein 1B was observed in these axons. Microtubule-associated protein 1B-P, however, disappeared from the degenerated distal axonal stump as early as three days post-operation, and was absent in the regenerating axons and in Schwann cells between three and 14days. The levels of microtubule-associated protein 1B-P recovered slowly and did not reach the normal levels even after 90days post-operation. In contrast to the response following transection, the levels of microtubule-associated protein 1B and microtubule-associated protein 1B-P were much less affected after nerve crush. We propose that the relatively high levels of microtubule-associated protein 1B and its messenger RNA in adult dorsal root ganglions support peripheral neuron regeneration. The presence of microtubule-associated protein 1B in the regenerating axons suggests that microtubule-associated protein 1B is involved in axonal growth during peripheral nerve regeneration. However, the phosphorylated microtubule-associated protein 1B-P isoform, associated with growing axons during development, is not present in the regenerating axons after transection, presumably because of changes in the activities of kinases and phosphatases associated with the injury. These observations underscore the difference between axonal development and regeneration and the importance of injury-related effects that occur locally.
Horseradish peroxidase-mediated polymerization of styrene at ambient temperature is reported. Molecular weight and yield of polystyrene were influenced by solvent, concentration of hydrogen peroxide, and initiator (beta-diketones, coumarin). THF:H2O (v/v) and hydrogen peroxide (0.082 mol/L) provided maximum yield of polymer (21.2% weight conversion of styrene to polystyrene) with 2,4-pentanedione as initiator. 1,3-Cyclopentanedione and dibenzoylmethane as initiators resulted in higher yield of polymer (approximately 60%) and a higher molecular weight (Mn = 96,504, polydispersity = 2.16), respectively. This enzymatic strategy was also used for the synthesis of polymers from styrene derivatives, 4-methylstyrene and 2-vinylnaphthalene, the latter resulting in a > 90% yield of polymer. The presence of the initiators in the polymer chains is reported.
We have developed a noninvasive transesophageal signal averaging technique for direct recording of sinus node electrogram. In this study, sinus node electrograms were recorded from 106 of 138 patients (77%), comparable to that (46%) recorded by conventional transesophageal technique, 59 were male and 47 were female ranging in age from 10-74 years (mean 44.2+/-12.4 years). The signals from lead I, surface averaged lead and esophagus averaged lead were amplified (up to 100 microV/cm), filtered (0.1-50 Hz), AD converted to 16-bit accuracy at a sampling rate of 2 KHz and averaged by using the three channel low-noise amplifier. The signal averaged esophageal sinus node potentials are deflections of low-amplitude and low-frequency preceding the P wave. Two morphologies, the domed wave (64 of 106 patients, 60%) and the smooth upstroke slope (42 of 106 patients, 40%), can be seen. The directly recorded sinoatrial conduction time was 82.3 +/-18.6 msec (mean+/-2 SD), ranged from 23-112 msec, amplitude was 3.8-27.7 microV and dv/dt was 0.42-1.92 mV/sec. The sinoatrial conduction time recorded by the transesophageal catheter technique was comparable to that (80.4+/-18. 1 msec) recorded by the transvenous catheter method perfectly. We think that signal averaged sinus node electrogram could be recorded in sinus rhythm in most patients with normal sinus node function and proper filter settings, high amplification and anti-drift technique are important in recording signal averaged esophageal sinus node electrogram.
The effects of propofol on mean arterial pressure, heart rate and Adelta and C somatosympathetic reflexes, recorded in renal nerves, evoked by repeated individual supramaximal electrical stimuli applied to radial nerves, were observed in anaesthetized, paralysed and artificially ventilated dogs. Propofol was infused at rates from 0.4 to 2.0 mg kg-1 min-1. Mean C and Adelta reflexes were abolished at plasma concentrations (mean, SEM) of 24.3 (3.3) and 29.2 (2.6) microg mL-1 (P < 0.05), respectively, when mean arterial pressure and mean heart rate were reduced by approximately 55% (P < 0.01) and 26% (P > 0.05), respectively. Recovery of Adelta and C reflexes occurred at plasma concentrations of 13.1 (2.3) and 9.9 (1.3) microg mL-1 (P > 0.05), respectively. There was a log- arithmically linearly related fall in mean arterial pressure by 70% up to a plasma concentration approximately 97 microg mL-1 (r 2=0.7) with a 28% reduction in heart rate which was uncorrelated with the plasma concentrations (r 2=0.12). In conclusion, propofol abolished Adelta and C responses at comparable plasma concentrations and caused a major reduction in both mean arterial pressure and heart rate which is consistent with resetting of the baroreflexes. The reduction in mean arterial pressure was logarithmically, linearly correlated with a progressive increase in plasma concentrations without evidence of a ceiling effect.
Glial cell line-derived neurotrophic factor (GDNF) shows potent and relatively specific protective effects on dopaminergic neurons. However, the size of the GDNF protein (MW 32-42 kDa) precludes the clinical use of GDNF via parenteral administration. It would thus be useful to have a cell line that stably secretes GDNF with full biological activities. The present study shows that NIH 3T3 cells express a considerable amount of GDNF. After co-culturing with primary E14-E16 midbrain neurons, such cells protected primary rat midbrain TH-immunopositive neurons from degeneration and MPP+ toxicity. In order to enhance endogenous GDNF expression, NIH 3T3 cells were stably transfected with GDNF cDNA with the Kozak sequence. The clones with the highest GDNF expression level were selected. The protective effects of engineered cells increased as the GDNF expression level increased. These cell lines may merit clinical investigation.
Visceromotor responses and vasopressin release before and after colonic visceral distension were compared between male (n=5 (n=4 for vasopressin)) and female rats and between females during the oestrous cycle (proestrus n=6, oestrus n=5, metestrus n=5, diestrus n=6) at a controlled depth of anaesthesia. Pre-stimulation vasopressin and blood pressures demonstrated oestrous cycle variability. The mean (SEM) colonic balloon pressure triggering visceromotor responses was significantly higher in males (64 (4) mm Hg) than females (41 (1) mm Hg), P=0.002 and within females, proestrus rats had the lowest thresholds, (29 (1) mm Hg, P<0.01). Post-stimulation, vasopressin concentrations increased significantly in all groups (males 1.34 (0.39) to 2.24 (0.74) pmol litre(-1); females 1.54 (0.24) to 2.88 (0.58) pmol litre(-1); P=0.002). Within groups statistically significant differences were measured in proestrus 2.06 (0.56) to 3.42 (1.12) and oestrus 1.16 (0.38) to 2.76 (0.60) pmol litre(-1) (P<0.05). High vasopressin concentrations coupled with low-pressure stimulation during proestrus shows sex-hormone dependent integration of the neuroendocrine response to noxious visceral stimulation.
The effects of desflurane on renal sympathetic nerve activity (RSNA) were studied in intact or vagotomized anaesthetized rabbits with initial concentrations of 4.5-18%, subsequently equilibrated to end-tidal concentrations from 3%, 6%, 9% and 12% each for 20 min allowing sympathetic activity to stabilize. In intact animals, immediate transient increases in mean sympathetic activity from 27% to 63% were closely related to initial concentrations from 4.5% to 18%. During subsequent equilibration this remained elevated by 25-30% up to 6%, returned to control at 9% and fell by 33% at 12%. Bilateral vagotomy abolished sympathoexcitation apart from small increases in sympathetic activity, for example 14% at 4.5% (P < 0.05). We conclude that increases in inspired desflurane concentrations evoked rapid transient vagally mediated reflex sympathoexcitation with a small extra-vagal contribution. Central depression of sympathetic activity started at 6% and was 33% below baseline at 12%.
The role of the dendrites of magnocellular neurones in the release of neurosecretory peptides and the synthesis of many proteins locally is reviewed. Oxytocin and vasopressin contained in dense-cored neurosecretory vesicles are released from magnocellular dendrites not only by excitatory transmitters such as glutamate acting through well-established receptors, but also by a rapid action of oestradiol acting by a mechanism which appears to involve NMDA receptors. Magnocellular dendrites also contain substantial amounts of the synthetic machinery which could synthesise proteins for local use. The presence in dendrites of polysomes and of mRNAs encoding microtubule-associated protein 2, calcium calmodulin kinase II, alpha-synapsin-associated protein, and components of the GABA(A) and NMDA receptors strongly suggests that these proteins can be translated in the dendrites, close to the sites at which they function. Mechanism(s) which control the translation of these dendritic mRNAs and the insertion into the dendritic membranes of proteins translated by dendritic ribosomes remain to be determined. However, an overall picture emerges of magnocellular dendrites as active secretory and synthetic components of the neurosecretory neurones.