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Biomedical subjects

Chen Chen

Publications and source records attributed to Chen Chen.

At least 55 records · Page 3Linked to original sources
PubMed2006

Differential regulation of GHRH-receptor and GHS-receptor expression by long-term in vitro treatment of ovine pituitary cells with GHRP-2 and GHRH.

GH secretion is regulated by GHRH and somatostatin via actions on their specific receptors in pituitary somatotropes. Ghrelin and synthetic analogs, GHRPs, also stimulate GH release via GHS-receptors (GHS-R). To examine the long-term effect of GHRH and/or GHRP on somatotropes, primary cultured ovine somatotropes were treated with GHRH (10(-9) and 10(-8) M) and GHRP-2 (10(-8) and 10(-7) M) for up to 2 d. After treatment, culture medium was collected for GH assay, and total RNA was extracted for RT-PCR analysis. To evaluate cell cultures used in this report, somatotrope-enriched pituitary cells were challenged by 6 h GHRH and dexamethasone (DEX) treatment. As expected, GHRH significantly decreased, whereas DEX increased, the levels of GHRHR mRNA. Combined low doses of GHRH (10(-9) M) and GHRP-2 (10(-8) M) treatment for 24 h increased accumulated GH secretion, significantly more than that induced by high doses of GHRH (10(-8) M) and GHRP-2 (10(-7) M). While levels of GHRH-R mRNA increased, GHS-R mRNA levels were decreased by low doses of GHRH and GHRP-2 for 24 h. High doses of GHRH and/or GHRP-2 for 2 d did not increase GH secretion in the second day of treatment and reduced the level of GHRH-R mRNA. High doses of GHRP-2 treatment decreased the levels of both GHRH-R and GHS-R mRNA. Low doses of GHRH and/or GHRP-2 for 2 d increased the level of GHS-R mRNA without changing GHRH-R mRNA levels. Such treatment also increased ghrelin- (10(-9) M) or ghrelin/GHRH (10(-9) M)-induced GH secretion. These results suggest that low doses of GHRP-2 and GHRH prime somatotropes for stimulation by GHRH and ghrelin.

Animals↗
PubMed2006

Study on the binding of procaine hydrochloride to DNA/DNA bases and the effect of CdS nanoparticles on the binding behavior.

The interaction between procaine hydrochloride and DNA/DNA bases in the absence and presence of cadmium sulfide (CdS) nanoparticles has been explored in this study by using differential pulse voltammetry, atomic force microscopy (AFM) and so on, which illustrates the different binding behaviors of procaine hydrochloride with different DNA bases. The results clearly indicate that the binding of purines to procaine hydrochloride is stronger than that of pyrimidines and the binding affinity is in the order of G > A > T > C. In addition, it was observed that the presence of CdS nanoparticles could remarkably enhance the probing sensitivity for the interaction between procaine hydrochloride and DNA/DNA bases. Furthermore, AFM study illustrates that procaine hydrochloride can bind to some specific sites of DNA chains, which indicates that procaine hydrochloride may interact with some special sequences of DNA.

Binding Sites↗
PubMed2006

[Application of distortion product otoacoustic emissions in detection of pseudohypacusis and exaggerated hearing loss].

OBJECTIVE: To explore the role of differential diagnosis of distortion product otoacoustic emissions (DPOAE) in pseudohypacusis and exaggerated hearing loss. METHOD: Detection and analysis of DPOAE were made by ILO96 Otodynamics Analyzer in the patients complaining of post-traumatic hearing loss and in cooperative in pure tone threshold (PTT) examination. RESULT: The detective results of DPOAE in 102 patients (121 ears) in cooperative in PTT examination revealed that pseudohypacusis was 66.12% (80/121 ears), exaggerated hearing loss was 33.88% (41/121 ears). The reactive threshold value determined by auditory brainstem response (ABR) in these patients confirmed that the results of DPOAE were objective and reliable. CONCLUSION: DPOAE can be used as a routine examination method in differential diagnosis of the post-traumatic hearing loss. It gives an objective and reliable diagnosis and differential diagnosis for the pseudohypacusis and exaggerated hearing loss.

Adolescent↗
PubMed2006

[Mechanism of myocardial cell apoptosis during delayed preconditioning induced by Sini decoction].

OBJECTIVE: The present study was designed to determine the mechanism of myocardial cell apoptosis during delayed preconditioning induced by Sini decoction (SND). METHODS: Sprage-Dawleytrats were divide into four groups: control, sham, I/R and SND groups. Left anterior descending coronary artery (LAD) of the rats in I/R group were occluded for h and reperfused for h. SND group rates were pretreated with Sini decoction (5 g x kg(-1) x d(-1)) for three days and the last treatment was pretreated 24h before the index occlusion. Cell apoptosis was measured by flow cytometry, mRNA level of bcl-xl/bcl-xs was detected by RT-PCR and apoptosis inducing factor (AIF) was detected by western blotting. RESULTS: SND pretreatment for 24 hours could decrease cell apoptosis, increase bcl-xl-bcl-xs mRNA ratio and decrease release of AIF from mitochondria. CONCLUSION: The delayed preconditioning induced by SND can decrease myocardial cell apoptosis. The mechanism is related to mitochondria protection.

Animals↗
PubMed2006

[Effect of delayed preconditioning induced by Sini decoction on myocardial cell apoptosis and its mitochondrial mechanism].

OBJECTIVE: To investigate the mechanism of myocardial cell apoptosis during delayed preconditioning induced by Sini decoction (SND). METHOD: SD rats were divide into four groups: control, sham, I/R and SND groups. The rats in I/R group, left anterior descending coronary artery (LAD) was occluded for 1h and reperfused for 1 h. The rats in SND group were pretreated with Sini decoction (5 g x kg(-1) x d(-1)) for three days, the last treatment was pretreated 24 h before the index occlusion. Cell apoptosis was measured by flow cytometry, cytochrome C and bcl-xl were detected by Western blotting and the activity of caspase-3 was detected by assay kit. RESULT: As compared with I/R group, apoptosis rate of myocardial cell, the release of cytochrome C from mitochondria and the activity of caspase-3 were significantly decreased, and the expression of bcl-xl protein was elevated in SND group. CONCLUSION: The delayed preconditioning induced by Sini decoction decreased myocardial cell apoptosis. The mechanism may be related to the inhibition of mitochondria signal pathway of apoptosis.

Aconitum↗
PubMed2006

[New option for gene-targeting vector construction Red/ET recombination].

The study of human new gene's function has become an increasingly active academic field basically relying on the gene knockout (KO) mouse. The construction of targeting vector economically and efficiently has turned into the key step to acquire a KO mouse because of the low efficiency of recombination with traditional constructed targeting vector. For study of the function of new gene-Resp18, we brought in a new DNA engineering platform-Red/ET recombination to construct Resp18 targeting vector. Red/ET recombineering differs from the conventional ways of vector construction (e.g., PCR, restriction enzyme digestion and ligation) and achieves genetic modification by acquisition, insertion, fusion or replacement of the target gene through small fragments mediated homologous recombination. Now Resp18 targeting vectors of three strategies were yielded successfully through two homologous recombination processes of retrieve and neo-targeting. Red/ET recombination has the advantage of getting longer homology regions without mutation, which makes it a new and reliable alternative to the construction of a targeting vector today.

Bacteriophage lambda↗
PubMed2005

Contribution of adipocyte-derived factors to beta-cell dysfunction in diabetes.

In addition to serving as an energy reservoir, the adipocyte has been characterized as an endocrine cell, secreting many bioactive factors which influence energy homeostasis. Being overweight, with excessive adipose tissue, is considered to be part of the pathogenesis of type 2 diabetes. Insulin resistance and beta-cell dysfunction are two major pathophysiological changes seen in type 2 diabetes. In addition to inducing insulin resistance in insulin-responsive tissues, adipocyte-derived factors play an important role in the pathogenesis of beta-cell dysfunction. Leptin, free fatty acids, adiponectin, tumor necrosis factor-alpha and interleukin-6 are all produced and secreted by adipocytes, and may directly influence aspects of beta-cell function, including insulin synthesis and secretion, insulin cell survival and apoptosis. During the progression from normal weight to obesity and on to overt diabetes, the adipocyte-derived factors contribute to the occurrence and development of beta-cell dysfunction and type 2 diabetes.

Adipocytes↗
PubMed2005

Effects of ghrelin and synthetic GH secretagogues on the cardiovascular system.

Ghrelin, a newly discovered endogenous hormone that is produced by the stomach, and synthetic peptides have been identified recently as potent growth-hormone secretagogues. This effect is exerted through interaction with a specific G-protein-coupled receptor, GHS-R1a, which is expressed mainly in the hypothalamus-pituitary complex. A study of the peripheral distribution of GHS receptors has shown that it is also present in cardiovascular tissue, which has led to the exploration of the cardiovascular functions of ghrelin and synthetic, growth-hormone-releasing peptides. These ligands have several cardiovascular activities, including a cardioprotective effect against myocardial ischemia, and vasoactive and cardiotropic effects in both experimental models and humans. These effects are mediated by the interaction of these ligands with binding sites, including GHS-1Ra, for which the signalling pathways are not documented fully. Identification of the cardiac and vascular binding sites for ghrelin and synthetic, growth-hormone-releasing peptides will provide new perspectives for treating cardiovascular diseases with these ligands.

Animals↗
PubMed2005

Molecular interactions of nonpeptide agonists and antagonists with the melanocortin-4 receptor.

The melanocortin-4 (MC4) receptor is a potential therapeutic target for obesity and cachexia, for which nonpeptide agonists and antagonists are being developed, respectively. The aim of this study was to identify molecular interactions between the MC4 receptor and nonpeptide ligands, and to compare the mechanism of binding between agonist and antagonist ligands. Nonpeptide ligand interaction was affected by mutations that reduce peptide ligand binding (D122A, D126A, S190A, M200A, F261A, and F284A), confirming overlapping binding determinants for peptide and nonpeptide ligands. The common halogenated phenyl group of nonpeptide ligands was a determinant of F261A and F284A mutations' affinity-reducing effect, implying this group interacts with the aromatic side chains of these residues. All affected compounds contain this group, the mutations reduced binding of 2,4-dichloro-substituted compounds more than 4-chloro-substituted-compounds, and F284A mutation eliminated the affinity-enhancing effect of 2-chloro-substitution. F261A and F284A mutations reduced the affinity of antagonists more than agonists, suggesting that the stronger ligand interaction with these residues, the lower the ligand efficacy. Supporting this hypothesis, F261A mutation increased the efficacy of nonpeptide antagonist and partial agonist ligands. D122A and D126A mutations reduced nonpeptide ligand interaction. Removing the ligands' derivatized amide group eliminated the effect of the mutations. Interaction of agonists, which bear a common amine within this group, was strongly reduced by D126A mutation (550-3300-fold), suggesting an electrostatic interaction between the amine and the acidic group of D126. These postulated interactions with aromatic and acidic regions of the MC4 receptor are consistent with a molecular model of the receptor. Furthermore, the strength of interaction with the aromatic pocket, and potentially the acidic pocket, controls the signaling efficacy of the ligand.

Amino Acid Sequence↗
PubMed2005

Practical asymmetric synthesis of alpha-branched 2-piperazinylbenzylamines by 1,2-additions of organometallic reagents to N-tert-butanesulfinyl imines.

[reaction: see text] 2-[4-(tert-Butoxycarbonyl)piperazinyl]benzylidene-tert-butanesulfinamides underwent nucleophilic 1,2-addition with different organometallic reagents to give highly diastereomerically enriched adducts. X-ray crystallography of the resulting alpha-branched N-Boc-2-piperazinylbenzyl-tert-butanesulfinamides confirms different mechanisms depending on the organometallic reagent used. Differential deprotection of the N-Boc and the tert-butanesulfinamides was investigated, and the dehydration byproducts have been identified and characterized. To avoid the formation of byproducts in the acidic deprotection step, the N-tert-butanesulfinamide group was converted to the corresponding N-tert-butanesulfonamide (Bus), which allowed for clean orthogonal deprotection. The efficient synthesis and deprotection of the N-Boc-2-piperazinylbenzyl-tert-butanesulfinamides herein described constitutes an attractive method for extensive structure-activity studies in the search for novel ligands of the human melanocortin 4 receptor.

Aldehydes↗
PubMed2005

Reduction in voltage-gated K+ currents in primary cultured rat pancreatic beta-cells by linoleic acids.

Free fatty acids (FFAs), in addition to glucose, have been shown to stimulate insulin release through the G protein-coupled receptor (GPCR)40 receptor in pancreatic beta-cells. Intracellular free calcium concentration ([Ca(2+)](i)) in beta-cells is elevated by FFAs, although the mechanism underlying the [Ca(2+)](i) increase is still unknown. In this study, we investigated the action of linoleic acid on voltage-gated K(+) currents. Nystatin-perforated recordings were performed on identified rat beta-cells. In the presence of nifedipine, tetrodotoxin, and tolbutamide, voltage-gated K(+) currents were observed. The transient current represents less than 5%, whereas the delayed rectifier current comprises more than 95%, of the total K(+) currents. A long-chain unsaturated FFA, linoleic acid (10 microm), reversibly decreased the amplitude of K(+) currents (to less than 10%). This reduction was abolished by the cAMP/protein kinase A system inhibitors H89 (1 microm) and Rp-cAMP (10 microm) but was not affected by protein kinase C inhibitor. In addition, forskolin and 8'-bromo-cAMP induced a similar reduction in the K(+) current as that evoked by linoleic acid. Insulin secretion and cAMP accumulation in beta-cells were also increased by linoleic acid. Methyl linoleate, which has a similar structure to linoleic acid but no binding affinity to GPR40, did not change K(+) currents. Treatment of cultured cells with GPR40-specific small interfering RNA significantly reduced the decrease in K(+) current induced by linoleic acid, whereas the cAMP-induced reduction of K(+) current was not affected. We conclude that linoleic acid reduces the voltage-gated K(+) current in rat beta-cells through GPR40 and the cAMP-protein kinase A system, leading to an increase in [Ca(2+)](i) and insulin secretion.

Animals↗
PubMed2005

Optimization of piperazinebenzylamines with a N-(1-methoxy-2-propyl) side chain as potent and selective antagonists of the human melanocortin-4 receptor.

Piperazinebenzylamines bearing a small N-(1-methoxy-2-propyl) side chain were found to be potent and selective antagonists of the human melanocortin-4 (MC4) receptor. Compound 7b, having K(i) values of 6.9 and 2800 nM at the human MC4 and MC3 receptors, respectively, has moderate oral bioavailability in mice, which is improved relative to the arylethyl analogues.

Administration, Oral↗
PubMed2005

Potent and orally active non-peptide antagonists of the human melanocortin-4 receptor based on a series of trans-2-disubstituted cyclohexylpiperazines.

The melanocortin-4 receptor (MC4R) plays an important role in the regulation of energy homeostasis. Recent studies have shown that blockade of the MC4R reverses tumor-induced weight loss in mice. Herein, we describe the synthesis and identification of potent and selective non-peptide antagonists of the human MC4R from a series of 2-ethoxycarbonylcyclohexyl-piperazines. Compound 12i was found to possess low nanomolar affinity for the MC4R, and exhibit oral bioavailability in rats. More importantly, when administered orally to mice (10 mg/kg), it led to statistically significant increases in food intake over a 24-h period.

Administration, Oral↗
PubMed2005

Cyclin D3 interacts with vitamin D receptor and regulates its transcription activity.

D-type cyclins are essential for the progression through the G1 phase of the cell cycle. Besides serving as cell cycle regulators, D-type cyclins were recently reported to have transcription regulation functions. Here, we report that cyclin D3 is a new interacting partner of vitamin D receptor (VDR), a member of the superfamily of nuclear receptors for steroid hormones, thyroid hormone, and the fat-soluble vitamins A and D. The interaction was confirmed with methods of yeast two-hybrid system, in vitro binding analysis and in vivo co-immunoprecipitation. Cyclin D3 interacted with VDR in a ligand-independent manner, but treatment of the ligand, 1,25-dihydroxyvitamin D3, strengthened the interaction. Confocal microscopy analysis showed that ligand-activated VDR led to an accumulation of cyclin D3 in the nuclear region. Cyclin D3 up-regulated transcriptional activity of VDR and this effect was counteracted by overexpression of CDK4 and CDK6. These findings provide us a new clue to understand the transcription regulation functions of D-type cyclins.

Animals↗