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Biomedical subjects

M Xu

Publications and source records attributed to M Xu.

At least 289 records · Page 16Linked to original sources
PubMed1996

Preclinical evaluation of fluorine-18-labeled androgen receptor ligands in baboons.

UNLABELLED: A noninvasive method for detecting and quantifying androgen receptors (AR) in metastatic prostate cancer may be helpful in choosing the method of treatment and in better understanding the pathophysiology of this disease. Nine previously synthesized fluorinated androgens exhibited high affinity binding to AR and showed AR-mediated uptake in the ventral and dorsal prostate of the rat. Further evaluation of these agents for PET imaging is needed since sex hormone binding globulin (SHBG), a glycoprotein which binds androgens with high affinity, is absent in rat blood but is present at high levels in the blood of primates. We chose to study three of the nine fluoro-androgens by PET in the baboon. METHODS: In this study, 16beta-[18F]fluoro-5 alpha-dihydrotestosterone (I), 16beta-[18F]fluoromibolerone (II) and 20-[18F]fluoromibolerone (III) were synthesized and studied in both a young and old male baboon using PET. Blood samples were withdrawn in three of the 10 studies and analyzed for total radioactivity and percent unmetabolized radioligand. Tissue radioactivity was evaluated semiquantitatively, using prostate absolute, standard and target to nontarget uptake values. RESULTS: Prostate uptake was observed with all three 18F-androgens. At 60 min postinjection, compound I gave the highest prostate to soft tissue ratios in both baboons and prostate uptake was shown to be AR-mediated by blocking uptake through the coadministration of testosterone. Compound I gave the highest level of unmetabolized radioligand present in blood up to 45 min postinjection, and gave a 37-fold greater prostate-to-bone ratio at 2 hr postinjection in baboons compared to rats. The favorable behavior of this compound in the baboon may be related to its high affinity for SHBG. CONCLUSION: All three compounds can be used to determine AR-positive tissue in primates. Compound I was selected for the evaluation of AR in men with prostate cancer using PET.

Animals↗
PubMed1996

[A novel nonsense point mutation in the arylsulfatase B gene with a severe type Maroteaux-Lamy syndrome].

Maroteaux-Lamy syndrome (MLS, also known as Mucopolysaccharidosis VI) is an inherited lysosomal disease due to a deficiency of the enzyme arylsulfatase B (ASB). Clinically, severe, intermediate and mild types are classified according to the symptoms and the age of onset. In recent years, several cases have been reported in which various mutations have been found by sequence analysis of ASB cDNA or genomic DNA. All of these mutations were reported occurred in single patients. Here I report a severe type MLS patient. A new point mutation was found on ASB gene which resulted in a stop codon at ASB peptide 421 (Glu). Due to this point mutation, a peptide fragment composed of 112 amino acids should have been deleted out. This point mutation was confirmed as a homoallele by direct sequence analysis of genomic DNA. Expression experiment on this point mutation revealed that the mutant produced neither mature ASB protein nor enzyme activity.

Adolescent↗
PubMed1996

Secretory expression of a single-chain insulin precursor in yeast and its conversion into human insulin.

A synthetic single-chain porcine insulin precursor (PIP) gene and an alpha-mating factor leader sequence (alpha MFL) gene obtained by the PCR method are inserted between the promoter and 3'-terminating sequence of the alcohol dehydrogenase gene ADH1 in plasmid pVT102-U to form plasmid pVT102-U/alpha MFL-PIP. The single-chain insulin precursor is expressed and secreted to the culture medium by Saccharomyces cerevisiae transformed by pVT102-U/alpha MFL-PIP. The precursor is purified and converted into human insulin by tryptic transpeptidation. The purified human insulin is fully active and can be crystallized. The overall yield of human insulin is 25 mg per liter of culture medium.

Base Sequence↗
PubMed1996

[Effect of Chinese herbs on the circadian rhythm of body temperature and heart rate in rabbits with hypothyroidism (yang deficiency)].

The rectal temperature (Tr) and heart rate (HR) of three groups of New Zealand white rabbits, i. e. thyroidectomized (G1), thyroidectomized and treated with Chinese herbs (a decoction composed of tonifying kidney-yang herbs) (G2) and pseudothyroidectomized for control (G3), were observed dynamically for 26 hours. The results indicated that the Tr and HR in G1 were decreased, and the circadian rhythms of the Tr and HR disordered significantly, while these changes in G2 were corrected obviously.

Animals↗
PubMed1996

[Effects of acetylcholine, glycine and their antagonist on spontaneous discharge of neurons in nucleus paragigantocellularis lateralis in rats].

The effects of iontophoretic application of acetylcholine (ACh), glycine (Gly) and their antagonist atropine, strychnine on the spontaneous discharge of the neurons in the caudal half of the nucleus paragigantocellularis lateralis (cPGCL) and the influence of atropine and strychnine on the effects of ACh and Gly respectively were observed on 17 anesthetized spontaneously breathing Sprague-Dawley rats. ACh could excite 79.6% of the tested nuerons. Gly could inhibit 91.5% of the tested nuerons. Atropine could excite 8% and inhibit 48% of the tested neurons. Strychnine could excite 21.9% and inhibite 6.3% of the tested nuerons. The excitatory effect of ACh and the inhibitory effect of Gly and atropine were dose-dependent. In most of the tested nuerons, the excitatory response to ACh (80.3%) and the inhibitory response to Gly (92.6%) could be blocked by their antagonists atropine and strychnine respectively. The results suggest that there exist endogenous ACh and Gly in the cPGCL and M receptors and Gly receptors on some of neurons cPGCL. These neurotransmitters and neuromodulators and receptors might be involved in the regulation of respiratory and cardiovascular function by cPGCL.

Acetylcholine↗
PubMed1996

[Patterns and distribution of the spontaneously discharges neurons in the nucleus paragigantocellularis lateralis of rats].

Using extracellular recording technique, we systematically explored the spontaneously discharging neruons in the caudal half of nucleus paragigantocellularis lateralis (cPGCL) in anesthetized and spontaneously breathing Sprague-Dawley rats. The discharge patterns of the neurons and the distribution of the respiratory related neurons (RRNs) in this PGCL area were analysed. A total of 237 neurons with spontaneous discharge were stably recorded in 14 rats. Among them 39 were RRNs and 198 non-RRNs (NRRNs). The discharge patterns of the 198 NRRNs were primarily tonic (n = 178). Of the 39 RRNs, 24 were inspiratory (INs), 12, expiratory (ENs), and 3, phase spanning (PSNs). The INs could be further classified into augmenting (n = 20) and constant or bellshaped (n = 4) INs, and the ENs, into decrementing (n = 7) and constant or bell-shaped (n = 5) ENs. The phase spanning neurons showed a constant or bell-shaped pattern of discharge, including inspiratory-exspiratory (IENs, n = 2) and expiratory-inspiratory (EIN, n = 1) phase spanning ones. Most of the RRNs were distributed in the dorsolateral portion of the cPGCL area and tended to concentrate in the more caudal part. These results suggest that PGCL is one of the important neural substrates responsible for the regulation of rhythimic respiration.

Animals↗
PubMed1995

Differential expression and co-assembly of NMDA zeta 1 and epsilon subunits in the mouse cerebellum during postnatal development.

The differential distribution of NMDA receptor subunit mRNAs in the developing mammalian cerebellum has been previously described. In this study, we investigated the temporal expression of NMDA receptor proteins in the postnatal murine cerebellum using antibodies specific for the NMDA zeta 1 and NMDA epsilon subunits. Our results showed a gradual increase during the first three weeks of life in the relative amount of NMDA zeta 1 and NMDA epsilon 1 proteins. In contrast, NMDA epsilon 2 increased transiently during this period, reaching a maximum around postnatal day 9 and decreasing thereafter to nearly undetectable levels by the end of the third week of life. The level of NMDA epsilon 3 increased dramatically between postnatal days 9 and 15 and thereafter remained constant. Immunoprecipitation of native proteins revealed that a large fraction of NMDA epsilon 2 was associated with NMDA zeta 1 and epsilon 1. At later developmental stages, NMDA epsilon 3 was predominantly assembled with NMDA zeta 1 but not with NMDA epsilon 1 or NMDA epsilon 2. These results demonstrate that NMDA receptor subtypes, formed by the assembly of different NMDA epsilon subunits with NMDA zeta 1, are sequentially expressed in the developing mouse cerebellum. The time course of their expression suggest, that these NMDA receptor subtypes may contribute to specific aspects of granule cell differentiation in the cerebellum.

Amino Acid Sequence↗
PubMed1995

Electroporation of influenza virus ribonucleoprotein complexes for rescue of the nucleoprotein and matrix genes.

Reverse genetics has been successfully used for the generation of recombinant influenza virus with altered biological properties. The standard method is based on DEAE-dextran transfection of in vitro reconstituted influenza virus ribonucleoprotein complex (RNP) into helper virus infected cells with subsequent selection of the recombinant viruses. Here we report the utilization of electroporation for reverse genetics of influenza virus as an improvement over the standard method. In a neuraminidase (NA) gene rescue system, we were able to demonstrate that electroporation of in vitro reconstituted NA RNP of influenza A/WSN/33 (H1N1) virus into WSN/HK virus infected cells allows the rescue of the transfectant WSN virus. The titer of transfectant virus obtained using electroporation is comparable to that generated using the DEAE-dextran transfection method. More significantly, the ratio of transfectant virus to helper virus is as much as 20-fold greater than that achieved using the DEAE-dextran system. We have also used electroporation to generate recombinant influenza virus carrying cDNA-derived matrix (M) gene or nucleoprotein (NP) gene of the WSN virus by using the temperature-sensitive (ts) mutants ts51 and ts56 as helper viruses. In the case of electroporation of M gene RNP, 88% of the viruses isolated after selection at 39 degrees C were transfectants. In contrast, the majority of viruses obtained using the DEAE-dextran transfection method were revertants of the helper virus. The NP-gene transfectant was only generated by the electroporation method. Our results suggest that electroporation of influenza virus RNP may be a useful method for generation of recombinant influenza viruses, especially in a system in which a ts mutant is used as helper virus.

Animals↗
PubMed1995

Interaction of picrotoxin with GABAA receptor channel-lining residues probed in cysteine mutants.

We used the substituted-cysteine-accessibility method to identify the channel-lining residues in a region (257-261) near the putative cytoplasmic end of the M2 membrane-spanning segment of the rat gamma-aminobutyric acid type A (GABAA) receptor alpha 1 subunit. The residues alpha 1Val257 and alpha 1Thr261 were accessible to charged, sulfhydryl-specific reagents applied extracellularly in both the open and closed states. The accessibility of alpha 1V257C and alpha 1T261C in the closed state implies that the gate must be at least as close to the cytoplasmic end of the channel as alpha 1Val257. Also, the positively charged reagent methanethiosulfonate ethylammonium penetrated from the extracellular end of the channel to alpha 1T261C, with which it reacted, indicating that the anion-selectivity filter is closer to the cytoplasmic end of the channel than this residue is. Co-application of picrotoxin prevented the sulfhydryl reagents from reacting with alpha 1V257C but did not prevent reaction with the more extracellular residue alpha 1T261C. Picrotoxin protection of alpha 1V257C may be due to steric block by picrotoxin bound in the channel at the level of alpha 1Val257; however, if this protection is allosteric, it is not due to the induction of the resting closed state in which alpha 1V257C was accessible to sulfhydryl reagent.

Amino Acid Sequence↗
PubMed1995

Differential recognition of microfilarial chitinase, a transmission-blocking vaccine candidate antigen, by sera from patients with Brugian and Bancroftian filariasis.

We examined the reactivity of human sera with recombinant microfilarial chitinase and with the antigenic determinant on the native parasite molecule identified by monoclonal antibody (MAb) MF1. In Brugian filariasis, the MF1 epitope is preferentially recognized by residents of endemic areas who remain amicrofilaremic and asymptomatic despite lifelong exposure to filarial worms. Reactivity with filarial chitinase and its MF1 epitope inversely correlates with microfilaremia levels in Bancroftian filariasis and is associated with a prolonged amicrofilaremic state following a single course of treatment with diethylcarbamazine. Chitinase does not appear to be a target of human antibodies that promote the adherence of cells to microfilariae, even though MAb MF1 itself promotes antibody-dependent, cell-mediated cytotoxic (ADCC) reactions that kill microfilariae in vitro. Such ADCC reactions are most often mediated by sera from amicrofilaremic patients with chronic elephantiasis that contain low or undetectable levels of IgG antibodies to chitinase. In contrast, antibodies to the MF1 epitope on this microfilarial stage-specific antigen are mostly present in amicrofilaremic donors without clinical lymphatic disease. These observations indicate that antibodies to the MF1 epitope of microfilarial chitinase reflect some degree of immune resistance to microfilaremia in a subgroup of patients with asymptomatic lymphatic filariasis. The amicrofilaremic state of individuals with chronic lymphatic disease appears to be mediated by reactivity to a different parasite antigen(s).

Adult↗
PubMed1995

[A preliminary study on metastasis-associated gene screened by monoclonal antibodies HIL].

The cDNA expression libraries derived from a highly metastatic cell subline Anip[973] and from the poorly metastatic, parental cell line, AGZY-83a were screened by monoclonal antibodies HIL. A positive clone (H4-D) from the Anip[973] cDNA library was isolated and its nucleotide sequence was determined. This clone contained 978 bp with an open reading frame of 318 bp encoding a polypeptide consisting of 106 amino acids. The H4-D cDNA sequence showed 85% homology with a human propionyl-CoA carboxylase alpha-chain. In western blotting analysis, the MoAb H4 recognized 2 bands (15KD and 27KD) of Anip[973] cell membrane proteins. The mRNA expression of H4-D was higher in Anip[973] cells than in AGZY-83a cells. The metastatic potential of Anip[973] cells was markedly decreased after being pretreated with MoAb H4. The above findings indicate that H4-D has a certain relationship with the metastatic phenotype of Anip[973] cells.

Adenocarcinoma↗