PubMed Health⌕ Search

Biomedical subjects

C Y Zhang

Publications and source records attributed to C Y Zhang.

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

Energy metabolism in uncoupling protein 3 gene knockout mice.

Uncoupling protein 3 (UCP3) is a member of the mitochondrial anion carrier superfamily. Based upon its high homology with UCP1 and its restricted tissue distribution to skeletal muscle and brown adipose tissue, UCP3 has been suggested to play important roles in regulating energy expenditure, body weight, and thermoregulation. Other postulated roles for UCP3 include regulation of fatty acid metabolism, adaptive responses to acute exercise and starvation, and prevention of reactive oxygen species (ROS) formation. To address these questions, we have generated mice lacking UCP3 (UCP3 knockout (KO) mice). Here, we provide evidence that skeletal muscle mitochondria lacking UCP3 are more coupled (i.e. increased state 3/state 4 ratio), indicating that UCP3 has uncoupling activity. In addition, production of ROS is increased in mitochondria lacking UCP3. This study demonstrates that UCP3 has uncoupling activity and that its absence may lead to increased production of ROS. Despite these effects on mitochondrial function, UCP3 does not seem to be required for body weight regulation, exercise tolerance, fatty acid oxidation, or cold-induced thermogenesis. The absence of such phenotypes in UCP3 KO mice could not be attributed to up-regulation of other UCP mRNAs. However, alternative compensatory mechanisms cannot be excluded. The consequence of increased mitochondrial coupling in UCP3 KO mice on metabolism and the possible role of yet unidentified compensatory mechanisms, remains to be determined.

Animals↗
PubMed2000

Uncoupling proteins 1 and 3 are regulated differently.

Using a heterologous yeast expression system, we have previously found a marked discordance between the effects of uncoupling protein (UCP) 1 and UCP3L on basal O(2) consumption in whole yeast versus isolated mitochondria. In whole yeast, UCP3L produces a greater stimulation of basal O(2) consumption, while in isolated mitochondria, UCP1 produces a much greater effect. As shown previously and in this report, UCP3L, in contrast to UCP1, is not inhibited by purine nucleotides. In the present study, we addressed two hypothetical mechanisms that could account for the observed discordance: (i) in whole yeast, purine nucleotides inhibit UCP1 but not UCP3L and (ii) preparations of isolated mitochondria lack an activator of UCP3L that is normally present in vivo. By use of a mutant of UCP1 that lacks purine nucleotide inhibition, it is demonstrated that cytosolic concentrations of purine nucleotides present in yeast effectively inhibit UCP1 activity. This suggests that the lower activity of UCP1 compared to UCP3L in whole yeast is due to purine nucleotide inhibition of UCP1 but not UCP3L. As potential activators of UCP3L we tested free fatty acids in whole yeast and isolated mitochondria. While UCP1 was strongly activated by free fatty acids, no stimulatory effect on UCP3L was observed. In summary, this study indicates that UCP1 and UCP3L differ in their regulation by purine nucleotides and free fatty acids. This different regulation may be related to different physiological functions of the two proteins.

Animals↗
PubMed2000

Expression and cellular localization of the protein encoded by the 1C7 gene: a recently described component of the MHC.

The major histocompatibility complex (MHC) is located on human Chromosome 6 and includes clusters of class I, class II, and class III genes. Centromeric to the class I region is a cluster of genes designated as MHC class IV encoding genes involved in immunity and inflammation, including the 1C7 gene. The human 1C7 gene has several alternatively spliced forms and potentially codes for proteins with at least three unique carboxy termini. 1C7 mRNA in human (h1C7) is present in spleen, tonsil, B and NK cell lines, and with a different splicing pattern in liver. The 1C7 RNA and protein are present at highest levels in the germinal center of the lymphoid follicles in tonsil. The protein is expressed in NKL cells, tonsil, and unexpectedly in brain. In contrast, the mouse 1C7 gene is transcribed in liver but is predicted to be a pseudogene. However, the 1C7 homologue expressed in rat is predicted to have long stretches of amino acids essentially identical to the human protein.

Amino Acid Sequence↗
PubMed2000

Photoelectric measurements of s-BLM/nucleoli: a new technique for studying apoptosis.

A new method based on photoelectric measurement for analyzing apoptosis of cell-free MCF-7 nucleoli is reported. Supported bilayer lipid membrane (s-BLM) was used to enclose nucleoli in biological environment. The s-BLM was self-assembled on the wall of a super-thin cell. During the apoptosis induced by Taxol, the photoelectric current of the self-assembled s-BLM/nucleoli was found decreasing with time, suggesting the degradation of nucleus DNA. Electron transfer along the DNA double helix and along nuclear skeleton is assumed in the interpretation. This novel photoelectric analytical method may provide a rapid and sensitive technique to evaluate apoptosis.

Apoptosis↗
PubMed2000

Trichosanthin induced calcium-dependent generation of reactive oxygen species in human choriocarcinoma cells.

The type-I ribosome-inactivating protein trichosanthin (TCS) has a broad spectrum of biological and pharmacological activities, including abortifacient, anti-tumor and anti-HIV. We found for the first time that TCS induced the generation of reactive oxygen species (ROS) in human choriocarcinoma cells (JAR cells) at the level of the single cell by using the fluorescent probe 2',7'-dichlorofluorescein diacetate with confocal laser scanning microscopy. TCS-induced ROS formation was shown to be dependent on the presence of extracellular Ca2+ and was further reduced when cytosolic Ca2+ was chelated by BAPTA-AM. The production of ROS increased rapidly after the application of TCS, which paralleled TCS-induced increase in intracellular calcium monitored using fluo 3-AM. Simultaneous observation of the nuclear morphological changes via two-photon laser scanning microscopy and production of ROS via confocal laser scanning microscopy revealed that ROS were involved in the apoptosis of JAR cells. The contribution of ROS was confirmed by experiments in which the antioxidant alpha-tocopherol prevented TCS-induced ROS formation and cell death. The finding that TCS induced calcium-dependent generation of ROS in JAR cells and that ROS were involved in the apoptosis of JAR cells might provide new insight into the anti-tumor and anti-HIV mechanism of TCS.

Antineoplastic Agents, Phytogenic↗
PubMed1999

Role of the beta(3)-adrenergic receptor and/or a putative beta(4)-adrenergic receptor on the expression of uncoupling proteins and peroxisome proliferator-activated receptor-gamma coactivator-1.

Administration of beta-adrenergic receptor (beta-AR) agonists, especially beta(3)-AR agonists, is well known to increase thermogenesis in rodents and humans. In this work we studied the role of the beta(3)-AR in regulating mRNA expression of genes involved in thermogenesis, i.e., mitochondrial uncoupling proteins UCP2 and UCP3, and peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1), in mouse skeletal muscle. For this purpose, different beta(3)-AR agonists were administered acutely to both wild type mice and mice whose beta(3)-AR gene has been disrupted (beta(3)-AR KO mice). CL 316243 increased the expression of UCP2, UCP3 and PGC-1 in wild type mice only. By contrast, BRL 37344 and CGP 12177 increased the expression of UCP2 and UCP3 in both wild type and beta(3)-AR KO mice, whereas they increased the expression of PGC-1 in wild type mice only. Finally, acute (3 h) cold exposure increased the expression of UCP2 and UCP3, but not PGC-1, in skeletal muscle of both wild type and beta(3)-AR KO mice. These results show that selective stimulation of the beta(3)-AR affects the expression of UCP2, UCP3 and PGC-1 in skeletal muscle. This effect is probably indirect, as muscle does not seem to express beta(3)-AR. In addition, our data suggest that BRL 37344 and CGP 12177 act, in part, through an as yet unidentified receptor, possibly a beta(4)-AR.

Adrenergic beta-Agonists↗
PubMed1999

Assessment of uncoupling activity of the human uncoupling protein 3 short form and three mutants of the uncoupling protein gene using a yeast heterologous expression system.

The human uncoupling protein 3 gene generates two mRNA transcripts, uncoupling protein 3L and uncoupling protein 3S, which are predicted to encode long and short forms of the uncoupling protein 3 protein, respectively. While uncoupling protein 3L is similar in length to the other known uncoupling proteins, uncoupling protein 3S lacks the last 37 C-terminal residues. A splice site mutation in the human uncoupling protein 3 gene, resulting in the exclusive expression of uncoupling protein 3S, and a number of point mutations in the uncoupling protein 3 gene have been described. This study compares the biochemical activity of uncoupling protein 3S as well as three mutants of the uncoupling protein 3 gene (V9M, V102I, R282C) with that of uncoupling protein 3L utilizing a yeast expression system. All proteins were expressed at similar levels and had qualitatively similar effects on parameters related to the uncoupling function. Both uncoupling protein 3S and uncoupling protein 3L decreased the yeast growth rate by 35 and 52%, increased the whole yeast basal O2 consumption by 26 and 48%, respectively, and decreased the mitochondrial membrane potential as measured in whole yeast by uptake of the fluorescent potential-sensitive dye 3'3-dihexyloxacarbocyanine iodide. In isolated mitochondria, uncoupling protein 3S and uncoupling protein 3L caused a similar (33 and 35%, respectively) increase in state 4 respiration, which was relatively small compared to uncoupling protein 1 (102% increase). A truncated version of uncoupling protein 3S, lacking the last three C-terminal residues, Tyr, Lys and Gly, that are part of a carrier motif that is highly conserved among all mitochondrial carriers, had a greatly reduced uncoupling activity. The two naturally occurring uncoupling protein 3 mutants, V9M and V102I, were similar to uncoupling protein 3L with respect to effects on the yeast growth and whole yeast O2 consumption. The R282C mutant had a reduced effect compared to uncoupling protein 3L. In summary, uncoupling protein 3S and the three mutants of uncoupling protein 3 appear to be functional proteins with biochemical activities similar to uncoupling protein 3L, although uncoupling protein 3S and the R282C mutant have a modestly reduced function.

Carrier Proteins↗
PubMed1999

Assessment of uncoupling activity of uncoupling protein 3 using a yeast heterologous expression system.

Uncoupling protein 3L, uncoupling protein 1 and the mitochondrial oxoglutarate carrier were expressed in Saccharomyces cerevisae. Effects on different parameters related to the energy expenditure were studied. Both uncoupling protein 3L and uncoupling protein 1 reduced the growth rate by 49% and 32% and increased the whole yeast O2 consumption by 31% and 19%, respectively. In isolated mitochondria, uncoupling protein 1 increased the state 4 respiration by 1.8-fold, while uncoupling protein 3L increased the state 4 respiration by 1.2-fold. Interestingly, mutant uncoupling protein 1 carrying the H145Q and H147N mutations, previously shown to markedly decrease the H+ transport activity of uncoupling protein 1 when assessed using a proteoliposome system (Bienengraeber et al. (1998) Biochem. 37, 3-8), uncoupled the mitochondrial respiration to almost the same degree as wild-type uncoupling protein 1. Thus, absence of this histidine pair in uncoupling protein 2 and uncoupling protein 3 does not by itself rule out the possibility that these carriers have an uncoupling function. The oxoglutarate carrier had no effect on any of the studied parameters. In summary, a discordance exists between the magnitude of effects of uncoupling protein 3L and uncoupling protein 1 in whole yeast versus isolated mitochondria, with uncoupling protein 3L having greater effects in whole yeast and a smaller effect on the state 4 respiration in isolated mitochondria. These findings suggest that uncoupling protein 3L, like uncoupling protein 1, has an uncoupling activity. However, the mechanism of action and/or regulation of the activity of uncoupling protein 3L is likely to be different.

Animals↗
PubMed1999

Effects of 14-deoxyandrographolide and 14-deoxy-11,12-didehydroandrographolide on nitric oxide production in cultured human endothelial cells.

14-deoxyandrographolide (DA) and 14-deoxy-11,12-didehydroandrographolide (DDA) are two diterpenoids isolated from A. paniculata, a popular folk medicine used as an antihypertensive drug in Malaysia. We have previously reported that DDA exhibited a greater hypotensive effect in anaesthetized rats and a vasorelaxant activity in isolated rat aorta, compared with DA. Their vasorelaxant activities were mediated through the activation of the enzymes, nitric oxide synthase (NOS) and guanylyl cyclase. The present study demonstrated that both DA and DDA stimulated nitric oxide (NO) release from human endothelial cells. DDA compared with DA caused a greater production of NO; this is in line with the finding of the earlier study that the vasorelaxant effect of DDA was more dependent on endothelium than DA.

Antihypertensive Agents↗
PubMed1998

Vasorelaxation of rat thoracic aorta caused by 14-deoxyandrographolide.

1. The pharmacological effects of 14-deoxyandrographolide on rat isolated thoracic aorta were examined. 2. 14-Deoxyandrographolide (2.5-120 mumol/L) inhibited contractions induced by phenylephrine (PE; 0.1 mumol/L) and high K+ (80 mmol/L) in a concentration-dependent manner in endothelium-intact aorta. The effect was attenuated in endothelium-denuded aorta without modifying the maximal response. Like verapamil, 14-deoxyandrographolide produced a much greater vasorelaxant effect in aorta precontracted by KCl than by PE. 14-Deoxyandrographolide (20-60 mumol/L) also inhibited responses of the rat aorta to PE. 3. In Ca(2+)-free medium (KCl 55 mmol/L), 14-deoxyandrographolide (20-80 mumol/L) antagonized Ca(2+)-induced vasocontraction in a concentration-dependent manner and transient contractions induced by both caffeine (10 mmol/L) and nor-adrenaline (1 mumol/L) were suppressed or almost abolished by 14-deoxyandrographolide. 4. The vasorelaxant effect of 14-deoxyandrographolide was partially antagonized by NG-nitro-L-arginine methyl ester (25 mumol/L), a specific and competitive nitric oxide synthase (NOS) inhibitor, and methylene blue (10 mumol/L), a soluble guanylate cyclase inhibitor, but was not affected by indomethacin (20 mumol/L), a cyclo-oxygenase inhibitor, or glibenclamide (10 mumol/L), an ATP-sensitive K(+)-channel blocker. 5. These results suggest that the vasorelaxant activity of 14-deoxyandrographolide may be mediated via the activation of NOS and guanylate cyclase, as well as the blockade of Ca2+ influx through both voltage- and receptor-operated Ca2+ channels.

Animals↗
PubMed1998

Further characterization of thyroid hormone response elements in the human type 1 iodothyronine deiodinase gene.

The increased type 1 iodothyronine deiodinase expression in hyperthyroid patients increases the fraction of plasma T3 generated from T4 by the propylthiouracil-sensitive pathway. In this study, we extend our analysis of the thyroid hormone response elements (TREs) in the 5' flanking region of the human dio1 gene. The 5' TRE (TRE2), a direct repeat separated by 4 bp (DR+4) at -660 bp, arises from an A to G substitution in an Alu sequence, the first example of this phenomenon. An SP1 binding site immediately 5' to TRE2 increases basal expression of a 430-bp dio1 promoter-chloramphenicol acetyltransferase construct in the presence of unliganded thyroid hormone receptor, thus decreasing T3 responsiveness, but does not do so when this complex is placed in its more 5' wild-type location. The two octameric binding sites of TRE1, a retinoid X-receptor independent DR+10 structure at -90, can be exchanged or inverted without loss of T3 response potency, despite significant changes in thyroid hormone receptor binding, as assessed by gel shift assays. However, the retinoic acid response of the 716-bp dio1 5' flanking region is unaffected by elimination of TRE2 but is lost with mutations in TRE1. These findings indicate the importance of functional analyses of potential ligand-responsive transcription factors, as well as the influence of position, on TRE function and interaction with basal transcription factors. The unusual features of these TREs emphasize the need to consider alternatives to canonical half-site arrangements of receptor binding sites and contexts in the evaluation of T3- and retinoic acid-responsive genes.

Base Sequence↗
PubMed1997

Pharmacological activity of the interdomain segment between metalloproteinase and disintegrin domains.

Metalloproteinases (haemorrhagic or non-haemorrhagic), disintegrins and most probably C-type lectin-related proteins are derived by the proteolysis of a common precursor protein. There is a short interdomain segment between the metalloproteinase and disintegrin domains which will be released into the venom. To determine whether this region of the molecule contributes to the biological role of the precursors or the products derived by the proteolysis of the precursors, we synthesized a peptide based on this short segment and examined its toxicity and biological activity. The synthetic peptide did not show any lethal toxicity, anticoagulant and antiplatelet effects. However, the peptide appeared to lower the blood pressure or normotensive rats upon infusion, but did not affect the blood levels of triglyceride, total cholesterol, high-density lipoproteins or low-density lipoproteins. The peptide, however, failed to exhibit any effect on spontaneously hypertensive rats and hence may not have a potential as an antihypertensive agent. Based on these results, we conclude that this interdomain segment may not contribute significantly to the biological activity of precursor proteins.

Animals↗
PubMed1997

Mechanisms of cardiovascular activity of Andrographis paniculata in the anaesthetized rat.

The cardiovascular activities of crude water extract (WE) of Andrographis paniculata (Burm. f.) Nees (Acanthaceae), its three semi-purified ethyl acetate (FA), n-butanol (FB) and aqueous (FC) fractions, as well as andrographolide, a major plant constituent, were elucidated in anaesthetized Sprague-Dawley (SD) rats for the very first time. FA and andrographolide, which possesses multiple pharmacological activities, elicited no drop in mean arterial blood pressure (MAP), while WE, FB and FC produced a significant fall in MAP in a dose-dependent manner without significant decrease in heart rate. The ED50 values for WE, FB and FC were 11.4, 5.0 and 8.6 mg/kg-respectively. These suggested that the hypotensive substance(s) of the crude water extract was concentrated in FB. Pharmacological antagonist studies were consequently only tested in FB (5 mg/kg). The hypotensive action of FB was not mediated through effects on the beta-adrenoceptor, muscarinic cholinergic receptor and angiotensin-converting enzyme, for it was not affected by propranolol, atropine and captapril, respectively. However, it seems to work via alpha-adrenoceptors, autonomic ganglion and histaminergic receptors, since the hypotensive effect of FB was negated or attenuated in the presence of phentolamine, hexamethonium as well as pyrilamine and cimetidine.

1-Butanol↗
PubMed1997

In vitro sensitivity of Plasmodium falciparum to eight antimalarials in China-Myanmar and China-Lao PDR border areas.

In 1991-1995 by using the Rieckmann in vitro micro-method, susceptibilities of Plasmodium falciparum to eight antimalarials in the China-Lao PDR and China-Myanmar border areas were tested. The resistant rates of P. falciparum to chloroquinine were 95.0%-100%; IC50 114-240nmol/l. P. falciparum resistant rates to amodiaquine resistance accounted for 83.5%-100%, IC50 52-72nmol/l. All cases were sensitive to quinine, IC50 470-608nmol/l. P. falciparum isolates from the Lao PDR frontier were highly sensitive to artesunate, dihydroartemisinin, and arteether. Resistant rates from other areas were 0-11%. P. falciparum from China-Myanmar and Lao PDR border areas were also sensitive to mefloquine, IC50 68-88nmol/l. A longitudinal survey of the sensitivity of P. falciparum in vivo on the China-Lao PDR border showed that the average defervescent time of falciparum malaria was treated by pyronaridine increased from 32.7 +/- 16.0 hours during 1984-85 to 56.2 +/- 27.4 hours in 1995; the recrudescence rate rose up from 15.2% to 37.5%. The results monitored in vitro showed that all cases assessed in 1988 for response to pyronaridine were sensitive, but 36.4% of cases had emerging resistance, IC50 increased from 13nmol/l to 40 nmol/l. The above results suggested that P. falciparum in these areas has expressed resistance to chloroquine and amodiaquine. However, the parasites are still sensitive to artemisinin, pyronaridine, mefloquine, quinine, but with a declining sensitivities.

Amodiaquine↗
PubMed1996

Tissue-specific molecular heterogeneity of human growth hormone-releasing hormone receptor protein.

A site-directed anti-peptide antibody (anti-hGHRHRc18) was generated against the cytoplasmic tail of human GHRH receptor. The dissociation constant (Kd) and the antibody binding site (AbT) of anti-hGHRHRc18 were 2.5 nmol/l and 0.54 nmol/l, respectively. In an immunoblotting experiment, affinity-purified anti-hGHRHRc18 specifically recognized a single 50-kDa protein in human pituitary. In a screening of the expression of GHRH receptor protein in extra-pituitary tissues, only human kidney showed a single 52-kDa protein. Our results suggest that the GHRH receptor protein exhibits tissue-specific molecular heterogeneity.

Amino Acid Sequence↗
PubMed1996

Hypotensive activity of aqueous extract of Andrographis paniculata in rats.

1. The hypotensive activity of an aqueous extract of Andrographis paniculata was studied using chronic intraperitoneal (i.p.) infusions by osmotic pumps. The extract exhibited a dose-dependent hypotensive effect on the systolic blood pressure (SBP) of spontaneously hypertensive rats (SHR). 2. The optimum hypotensive dose determined was repeated in a study in SHR and their normotensive controls, Wistar-Kyoto (WKY) rats, to demonstrate its comparative effects on the SBP, plasma and lung angiotensin-converting enzyme (ACE) activities, as well as on lipid peroxidation in the kidneys, as measured by the thiobarbituric acid (TBA) assay. 3. The extract significantly lowered the SBP of both SHR and WKY rats. 4. Plasma, but not lung, ACE activity and kidney TBA level were significantly lower in extract-treated SHR when compared with vehicle-treated SHR controls. 5. Plasma and lung ACE activities as well as kidney TBA levels were not significantly different between extract- and vehicle-treated WKY rats. 6. This study indicates that the aqueous extract of A. paniculata lowers SBP in the SHR possibly by reducing circulating ACE in the plasma as well as by reducing free radical levels in the kidneys. The mechanism(s) of hypotensive action seems to be different in WKY rats.

Analysis of Variance↗
PubMed1996

Enhancement of thyroid hormone receptor isoform specificity by insertion of a distant half-site into a thyroid hormone response element.

The two isoforms of thyroid hormone receptor (TR), alpha and beta, are highly homologous, except in the amino-terminal domain. Specific physiological roles for the receptor isoforms have not yet been defined. In transient transfection assays, TRalpha is twice as potent a thyroid hormone (T3)-dependent transactivator as TRbeta on a number of thyroid hormone response elements (TREs). Using chimeras of TRalpha and -beta, we have determined that the higher transactivation by TRalpha requires the entire ligand-binding domain. The amino-terminal and DNA-binding domains of the two isoforms are interchangeable. These studies were facilitated by the use of a synthetic TRE composed of a direct repeat separated by 4 bp which also included a third half-site 19 bp 3' to this on the opposite strand. In the presence of T3, this TRE confers a 5-fold higher response to TRalpha than to TRbeta, but there is no difference in expression without T3. Functional studies indicate that all three half-sites are needed for the increased responsiveness to TRalpha, but gel shift analyses show no striking differences in the ratios of TRalpha to TRbeta binding compared to other wild-type TREs. These results suggest that important functional differences are present in the ligand-binding domain of TRalpha and -beta despite their high homology.

Animals↗