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Biomedical subjects

X Huang

Publications and source records attributed to X Huang.

At least 595 records · Page 33Linked to original sources
PubMed1995

[Non-radioactive detection of dinucleotide repeat polymorphisms and its application to genetic diagnosis].

We have developed a rapid and non-radioactive procedure for detecting dinucleotide repeat polymorphisms. Specific primers flanking the repeats were used in the polymerase chain reaction (PCR). The generated allelic fragments were resolved by thin-layer denaturing polyacrylamide gel electrophoresis and visualized by improved silver staining. This method is simple, fast and without labelling of PCR products. Resolution of 1 bp can be easily obtained. It can also be used in multiplex PCR analysis of (CA)n loci. This method will be a valuable tool for linkage analysis and DNA diagnosis as demonstrated by its successful application to the CA dinucleotide repeat haplotying of a DMD family.

Base Sequence↗
PubMed1994

Altered oxidative stress responses in nickel-resistant mammalian cells.

BALB 3T3 cells exposed to NiCl2 acquired resistance to concentrations as high as 200 microM and retain resistance for many generations in the absence of nickel. This resistance was not due to alterations in uptake or to metallothionein overexpression. The nickel-resistant B200 cell line was found to also exhibit cross-resistance to hydrogen peroxide and menadione. These nickel-resistant cells had 1.8 times higher basal levels of glutathione compared to wild-type cells. Studies with the glutathione synthesis inhibitor buthionine sulfoximine showed that while glutathione turnover was more rapid in the nickel-resistant cells, its depletion following NiCl2 treatment of the parental BALB 3T3 cell line was greater than in the nickel-resistant B200 cells. The reduced level of binding of NFkB and AP-1 transcription factors to their DNA consensus sequences in B200 cells compared to wild-type cells, and their more reactive response following treatment of resistant cells with H2O2 or buthionine sulfoximine, strengthens the hypothesis that nickel resistance is closely allied to oxidative stress responses.

3T3 Cells↗
PubMed1994

1-(2,5-Dimethoxy-4-(trifluoromethyl)phenyl)-2-aminopropane: a potent serotonin 5-HT2A/2C agonist.

A method was found to synthesize 1-(2,5-dimethoxy-4-(trifluoromethyl) phenyl)-2-aminopropane, 5, and its des-alpha-methyl congener 2-(2,5-dimethoxy-4-(trifluoromethyl)phenyl)aminoethane, 6, the trifluoromethyl analogs of substituted hallucinogenic phenethylamine derivatives such as 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (3, DOI) that are potent 5-HT2A/2C agonists. In our hands, 5 and 6 have proven to have affinity for [3H]ketanserin or [125I]-3-labeled 5-HT2A/2C sites in rat cortex comparable to or higher than the analogous bromo or iodo analogs. Similarly, 5 and 6 had potency comparable to or slightly greater than that of their bromo or iodo congeners in the two-lever drug discrimination assay in rats trained to discriminate saline from LSD tartrate. The agonist properties of 5 and 6 were evaluated by measuring the accumulation of [3H]inositol monophosphate in cultured cells selectively expressing either 5-HT2A or 5-HT2C receptors. In comparison to serotonin (5-HT), compounds 3 (DOI), 5, and 6 were equally efficacious and full agonists at the 5-HT2C receptor. Similarly, 3 and 5 produced equivalent responses at the 5-HT2A receptor as compared to 5-HT. In contrast, 6, the alpha-desmethyl analog of 5, was only half as potent at stimulating inositol monophosphate accumulation at the 5-HT2A receptor. In conclusion, the title compound 5 and its alpha-desmethyl congener 6 appear to be the most potent of the so-called hallucinogenic amphetamine 5-HT agonists reported to date. Further, the reduced efficacy of 6 at the 5-HT2A receptor may offer at least a partial explanation for the observed higher in vivo potencies of alpha-methyl-substituted compounds in this series.

3T3 Cells↗
PubMed1994

Androgen receptor immunoreactivity in somatostatin neurons of the periventricular nucleus but not in the bed nucleus of the stria terminalis in male rats.

Somatostatin (SS) is a neuropeptide responsible for the inhibition of growth hormone (GH) release from the anterior pituitary. The existence of sexual dimorphism in the pattern of GH secretion in several mammalian species strongly suggests a role of sex steroids in the regulation of GH release. It has been recently demonstrated that SS mRNA levels are decreased by gonadectomy in male rats while administration of testosterone reversed the postgonadectomy decrease in hypothalamic SS mRNA levels. The mechanism(s) by which androgens regulate somatostatin neurons are unknown at this time. Both direct and indirect pathways have been suggested. In this study, double-labeling immunocytochemistry was used to address the question of whether SS neurons have androgen receptors in adult male rats. About 70-75% of SS-immunoreactive (-ir) neurons in the periventricular hypothalamic nucleus possess androgen receptors and this co-localization persists throughout the rostrocaudal extent of this nucleus. In the bed nucleus of the stria terminalis, no SS-ir neurons were shown to have androgen receptors. These results suggest that androgens may directly exert their effect upon SS neurons in the periventricular nucleus.

Animals↗
PubMed1994

Molecular mechanisms of nickel carcinogenesis.

Nickel treatment of intact cultured cells oxidized dichlorofluorescin to a fluorescent product indicating that nickel elevated the level of oxidants in cells. Nickel also caused an increase in crosslinking of amino acids to DNA and these complexes did not appear to involve the direct participation of Ni2+. Histidine, cysteine and tyrosine were prominent among the amino acids crosslinked to DNA. Nickel selectively damaged heterochromatin and this resulted in deletions of heterochromatic regions during nickel carcinogenesis. Thrombospondin was one of the genes expressed in normal cells that was not expressed in nickel-transformed cells. Other aspects of the molecular mechanism of nickel carcinogenesis are discussed.

Amino Acids↗
PubMed1994

Aromatic stacking and bending of the DNA helix by the individual repeat units of the carboxy-terminal domain of RNA polymerase II.

The carboxy-terminal domain (CTD) of RNA polymerase II consists of multiple repeats of the unique heptad sequence -(Ser-Pro-Thr-Ser-Pro-Ser-Tyr)- which may interact with DNA through the intercalation of adjacent tyrosine aromatic rings. We have examined details of the interaction of this motif with calf thymus DNA through analysis of peptide analogues that contain (1) an amino-terminal tyrosine which mimics the presence of an adjacent heptad repeat and (2) positively-charged lysine residues which facilitate the initial contact between peptide and DNA. Results of fluorescence experiments, NMR titrations, and viscometric analyses indicate that these peptides bind to the DNA helix through a non-classical intercalation mode involving partial aromatic stacking of the tyrosine rings with the Watson-Crick base pairs.

Amino Acid Sequence↗
PubMed1994

Protein oxidation and amino acid-DNA crosslinking by nickel compounds in intact cultured cells.

Oxidative damage induced by NiCl2 to protein has been investigated. We found that nickel induced a dose-dependent increase in the oxidation of bovine serum albumin (BSA) as detected by carbonyl formation in the presence of H2O2 in vitro, as well as producing carbonyl of proteins in intact cultured Chinese hamster ovary (CHO) cells. Other metals capable of producing oxidative damage to BSA in the presence of H2O2 included Cu, Co, Fe, and chromate. However, Cd2+, Hg2+, and Pb2+ were not active even in the presence of H2O2. As an indicator of nickel-induced genotoxic damage, the crosslinking of amino acids to DNA was also examined. Cysteine, histidine, and tyrosine were increased in their association with DNA based upon their persistent binding to DNA following washes with EDTA or SDS. The results suggest that DNA-protein or DNA-amino acids crosslinks induced by nickel may result from interaction of the nickel-oxidized carbonyl group of protein, peptides, and free amino acids.

Amino Acids↗
PubMed1994

Attenuation of 3,4-methylenedioxymethamphetamine (MDMA) induced neurotoxicity with the serotonin precursors tryptophan and 5-hydroxytryptophan.

Treatment of rats with serotonin (5-HT) precursors tryptophan (TRP, 400 mg/kg) and 5-hydroxytryptophan (5-HTP, 50 mg/kg) was shown to attenuate MDMA (20 mg/kg) induced serotonergic neurotoxicity as measured by [3H]-paroxetine binding in the striatum, hippocampus, and frontal cortex of the rat brain. Hippocampal 5-HT and 5-HIAA levels were also indicative of the protective effects of TRP and 5-HTP. These results suggest that depletion of 5-HT stores is important for MDMA-induced neurotoxicity. The possible significance of this 5-HT depletion in MDMA-induced serotonergic terminal degeneration is also discussed.

5-Hydroxytryptophan↗
PubMed1994

Drug discrimination and receptor binding studies of N-isopropyl lysergamide derivatives.

Isopropyl (IPLA), N-methyl-N-isopropyl (MIPLA), N-ethyl-N-isopropyl (EIPLA), and N,N-diisopropyl (DIPLA) lysergamides were evaluated for lysergic acid diethylamide (LSD)-like activity. In rats trained to discriminate 0.08 mg/kg LSD tartrate from saline, each of the subject compounds completely substituted, with an ED50 two to three times larger than that of LSD except for DIPLA, which had an ED50 about eightfold greater. Similarly, all the compounds displaced [125I](R)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane ([125I]DOI) from rat cortical homogenates and displaced [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) from rat hippocampal homogenates with KI values similar to those of LSD, again with the exception of DIPLA, which had about nine- and fourfold lower affinities, respectively. Interestingly, all the compounds had four- to fivefold lower affinities than LSD in displacing [3H]ketanserin from 5-HT2 binding sites. Molecular modeling studies found that all the compounds had low energy conformations similar to LSD. No correlation between the activity of the compounds and the preferred conformation of the amide substituents was apparent. In summary, N-alkyl-N-isopropyl analogs of LSD retain LSD-like activity in drug discrimination and 5-HT1A and 5-HT2 agonist binding assays only until the N-alkyl substitution is as large as ethyl; LSD-like activity dramatically drops when the second alkyl substituent is N-isopropyl.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1994

Age changes in mastication in the pig.

A comparative study of chewing in miniature pigs at three stages of dental development was carried out using electromyography and movement analysis. The mastication of the youngest pigs was characterized by longer burst durations of jaw muscles, particularly closing muscles, and greater relative jaw opening. Chewing side alternated irregularly and burst durations were variable. Between the intermediate and oldest ages, the parameters remained almost unchanged. Because the amount of dental development that occurred between the second two stages was just as extensive as that between the first two, progressive eruption cannot account for the age changes observed in mastication.

Age Factors↗
PubMed1994

Islet expression of interferon-alpha precedes diabetes in both the BB rat and streptozotocin-treated mice.

The mechanism(s) leading to beta cell dysfunction in type I diabetes has not been defined. We have investigated whether islet expression of IFN alpha could be a cause of the lesions that are hallmarks of type I diabetes. Streptozotocin induces the expression of interferon-alpha by pancreatic islets prior to the diabetes induced by streptozotocin. Increased IFN alpha, induced by poly I/C or expressed from a transgene will exacerbate the diabetogenic effects of streptozotocin. In another rodent model of type I diabetes (the BB rat), islet expression of IFN alpha precedes lymphocytic infiltration and diabetes. As in the streptozotocin model, in the BB rats poly I/C will induce islet expression of IFN alpha and accelerate the onset of diabetes. These results are consistent with the hypothesis that islet expression of IFN alpha participates in causing type I diabetes.

Animals↗
PubMed1994

Discovery of new ligand binding pathways in myoglobin by random mutagenesis.

A random library of single amino acid mutants of myoglobin was generated using a highly efficient, single-base-misincorporation random mutagenesis method to discover new ligand-binding pathways in myoglobin. A surprisingly large fraction of the library exhibits ligand-binding kinetics that are substantially different from the wild-type protein. In addition to residues 45, 64 and 68, which comprise the best studied ligand-binding pathway single mutations of several other clusters of residues far away from that pathway are discovered which profoundly affect the ligand-binding kinetics. These results provide a new approach to explore the relationship between the fluctuations in protein structure and function.

Amino Acid Sequence↗
PubMed1994

An algorithm for identifying regions of a DNA sequence that satisfy a content requirement.

We present a dynamic programming algorithm for identifying regions of a DNA sequence that meet a user-specified compositional requirement. Applications of the algorithm include finding C + G-rich regions, locating TA + CG-deficient regions, identifying CpG islands, and finding regions rich in periodical three-base patterns. The algorithm has an advantage over the simple window method in that the algorithm shows the exact location of each identified region. The algorithm has been implemented as a portable C program called LCP (Local Content Program). LCP is extremely efficient in computer time and memory; it instantly locates all regions of a long DNA sequence meeting a given requirement. The LCP program was used to analyze the rabbit alpha-like globin gene cluster sequence.

Algorithms↗
PubMed1994

On global sequence alignment.

We present a dynamic programming algorithm for computing a best global alignment of two sequences. The proposed algorithm is robust in identifying any of several global relationships between two sequences. The algorithm delivers a best alignment of two sequences in linear space and quadratic time. We also describe a multiple alignment algorithm based on the pairwise algorithm. Both algorithms have been implemented as portable C programs. Experimental results indicate that for a commonly used set of gap penalties, the new programs produce more satisfactory alignments on sequences of various lengths than some existing pairwise and multiple programs based on the dynamic programming algorithm of Needleman and Wunsch.

Algorithms↗
PubMed1994

Crystalline Ni3S2 specifically enhances the formation of oxidants in the nuclei of CHO cells as detected by dichlorofluorescein.

Dichlorofluorescein (DCF) was used as a fluorescent probe to detect oxidants formed in cultured CHO cells during nickel treatment. Crystalline Ni3S2 specifically enhanced the formation of oxidants in the nuclei of these living cells, but Ni3S2 particles did not enhance DCF fluorescence as much when added in vitro to isolated nuclei. Our results add to the emerging concept that oxidants mediated by nickel compounds may play an important role in nickel-induced genotoxicity.

Animals↗
PubMed1994

Molecular and phenotypic mapping of the short arm of chromosome 5: sublocalization of the critical region for the cri-du-chat syndrome.

Forty-nine individuals have been identified with deletions or translocations involving the short arm of chromosome 5. While most display the classical phenotype of the cri-du-chat syndrome, several of the patients do not have the syndrome or have only a subset of the clinical features. Somatic cell hybrids containing the deleted chromosome 5 were derived from each patient. Each somatic cell hybrid was analyzed at the DNA level using 136 chromosome 5p-specific DNA fragments. It was possible to unambiguously order most of the chromosomal breakpoints present in the somatic cell hybrids based on the hybridization patterns of Southern blots. Further comparisons between the deletions present in the patients and their clinical features identified several chromosomal regions that were involved in specific clinical features. A critical chromosomal region involved the high-pitched cry mapped to 5p15.3, while the chromosomal region involved in the remaining features of the cri-du-chat syndrome mapped to a small region within 5p15.2. Deletions that did not include these two chromosomal regions presented varying clinical phenotypes from severe mental retardation and microcephaly to a clinically normal phenotype. These results demonstrate the need for careful characterization of a 5p deletion in prenatal cases before clinical predictions are made.

Animals↗
PubMed1994

Effect of unilateral bite splint on mastication in the miniature pig.

Unilateral premature occlusal contacts are known to alter masticatory activity levels during clenching, but whether natural chewing is similarly affected is not known. The purpose of this study was to analyse the effects of a unilateral bite splint on mastication. Eleven experiments were carried out using three miniature pigs. Electromyography of the masticatory muscles and movements of the jaw were recorded during natural chewing before and after inserting a bite splint on the second and third deciduous premolars. In contrast to human clenching, the integrated activities of the jaw-closing muscles increased, especially on the contralateral side. The increases were mainly due to the prolongation of the burst durations. Jaw opening activity was increased as well. The frequency of mastication fell slightly and the animal preferred to chew food on the bite splint side. These results demonstrate the importance within the particular experimental conditions of the occlusal condition in regulating chewing behaviour.

Animals↗