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X Ruan

Publications and source records attributed to X Ruan.

33 records · Page 2Linked to original sources
PubMed1999

Effects of candesartan on angiotensin II-induced renal vasoconstriction in rats and mice.

This study determined the inhibitory effect of the angiotensin II (AngII) type I (AT1) receptor blocker candesartan on renal vascular reactivity in vivo. Reactivity to AngII before and during candesartan administration was assessed by measuring (by electromagnetic or ultrasonic flowmetry) renal blood flow responses to AngII in rats and mice. AngII produced greater renal vasoconstriction in 7-wk-old, spontaneously hypertensive rats than in Wistar-Kyoto rats. After indomethacin treatment, AngII (2 ng) produced 40% reductions in renal blood flow in both rat strains, without affecting systemic arterial pressure. Coadministration of candesartan blocked AngII effects in a dose-dependent manner, with similar levels of inhibition in spontaneously hypertensive rats and Wistar-Kyoto rats; maximal inhibition was 80%. In rats that had been pretreated (for 30 min) with intravenous candesartan, AngII-induced renal vasoconstriction was inhibited dose dependently up to 98%. To evaluate receptor subtype mediation, responses were compared in mice with or without the AT1A receptor (deleted by gene targeting). Intrarenal AngII (1 ng) caused a 32% reduction of renal blood flow in wild-type mice and an 8% reduction of renal blood flow in AT1A receptor-knockout mice. Ten nanograms of AngII were required to elicit 20% renal vasoconstriction in these mutant mice. Concurrent injection of candesartan caused dose-dependent inhibition of AngII up to 80%. The candesartan IC50 values for percentage changes in renal blood flow did not differ in the two groups of mice. These studies establish that candesartan is an effective, highly selective, AT1 receptor blocker, inhibiting renal vasoconstriction in rodents in a concentration- and time-dependent manner. Candesartan effectively blocks AT1A and AT1B receptors in renal resistance vessels of rodents, with similar efficacies in rats and mice.

Angiotensin II↗
PubMed1997

A second type-I PKS gene cluster isolated from Streptomyces hygroscopicus ATCC 29253, a rapamycin-producing strain.

Analysis of a 32.8-kb segment of DNA from the rapamycin (Rp) producer, Streptomyces hygroscopicus ATCC 29253, revealed a new type-I polyketide synthase (PKS) cluster consisting of four open reading frames (ORF 1-4), each encoding a single PKS module. The four ORFs are transcribed in the same direction and are flanked by several smaller ORFs (ORF 5-9), which may be related to the PKS cluster. The first PKS-containing ORF has a ligase domain at the N-terminus of the polypeptide. This domain has 55% aa identity to the CoA ligase domain of the Rp PKS (Schwecke et al., 1995. Proc. Natl. Acad. Sci. 92, 7839-7843) which is also encoded in this strain (Lowden et al., 1996. Angew. Chem. Int. Ed. Engl. 35, 2249-2251). ORF5 (340 aa) and ORF6 (924 aa) were found to be homologous to RapK (41% aa identity) and RapH (35% aa identity), which are hypothesized to be a pteridine-dependent dioxygenase and a regulatory protein, respectively (Molnar et al., 1996. Gene 169, 1-7). In addition, ORF7 (391 aa) was found to have up to 42% aa identity to a number of plant 3-deoxy-D-arabino-heptulosonate-7-phosphate synthases (DAHPS) and 47% aa identity to PhzF, a bacterial DAHPS involved in phenazine antibiotic synthesis. The proximity of the DAHPS-encoding gene to the PKS cluster containing a Rp-like ligase domain suggests that a derivative of shikimate may be used as the PKS starter. ORF8 (283 aa) was found to have homology (32% aa identity) to a Synechocystis sp. gene of unknown function. The N-terminal portion of ORF9 was found to be similar to a tetracycline 6-hydroxylase (34% aa identity) from Streptomyces aureofaciens.

3-Oxoacyl-(Acyl-Carrier-Protein) Synthase↗
PubMed1997

Regulation of angiotensin II receptor AT1 subtypes in renal afferent arterioles during chronic changes in sodium diet.

Studies determined the effects of chronic changes in sodium diet on the expression, regulation, and function of different angiotensin II (ANG II) receptor subtypes in renal resistance vessels. Rats were fed low- or high-sodium diets for 3 wk before study. Receptor function was assessed in vivo by measuring transient renal blood flow responses to bolus injections of ANG II (2 ng) into the renal artery. ANG II produced less pronounced renal vasoconstriction in rats fed a low- compared with high-sodium diet (16% vs. 56% decrease in renal blood flow, P < 0.001). After acute blockade of ANG II formation by iv enalaprilat injection in sodium-restricted animals, ANG II produced a 40% decrease in renal blood flow, a level between untreated dietary groups and less than high salt diet. Intrarenal administration of angiotensin II receptor type 1 (AT1) receptor antagonists losartan or EXP-3174 simultaneously with ANG II caused dose-dependent inhibition of ANG II responses. Based on maximum vasoconstriction normalized to 100% ANG II effect in each group, AT1 receptor antagonists produced the same degree of blockade in all groups, with an apparent maximum of 80-90%. In contrast, similar doses of the angiotensin II receptor type 2 (AT2) receptor ligand CGP-42112 had only a weak inhibitory effect. In vitro equilibrium-saturation 125I-ANG II binding studies on freshly isolated afferent arterioles indicated that ANG II receptor density was lower in the low- vs. high-sodium animals (157 vs. 298 fmol/mg, P < 0.04); affinity was similar (0.65 nM). Losartan and EXP-3174 displaced up to 80-90% of the ANG II binding; fractional displacement was similar in both diet groups. In contrast, the AT2 receptor analogues PD-123319 and CGP-42112 at concentrations < 10(-6) M had no effect on ANG II binding. RT-PCR assays revealed the expression of both angiotensin II receptor type 1A (AT(1A)) and angiotensin II receptor type 1B (AT(1B)) subtypes in freshly isolated afferent arterioles, while there was very little AT2 receptor expression. Total AT1 receptor mRNA expression was suppressed by low sodium intake to 66% of control levels, whereas it was increased to 132% of control by high-sodium diet, as indicated by ribonuclease protection assay. Receptor regulation was associated with parallel changes in AT(1A) and AT(1B) expression; the AT(1A)/AT(1B) ratio was stable at 3.7. We conclude that AT1 receptors are the predominant ANG II receptor type in renal resistance vessels of 7-wk-old rats. Chronic changes in sodium intake caused parallel regulation of expression and amount of receptor protein of the two AT1 receptor genes that modulate receptor function and altered reactivity of renal vessels to ANG II.

Actins↗
PubMed1997

Acyltransferase domain substitutions in erythromycin polyketide synthase yield novel erythromycin derivatives.

The methylmalonyl coenzyme A (methylmalonyl-CoA)-specific acyltransferase (AT) domains of modules 1 and 2 of the 6-deoxyerythronolide B synthase (DEBS1) of Saccharopolyspora erythraea ER720 were replaced with three heterologous AT domains that are believed, based on sequence comparisons, to be specific for malonyl-CoA. The three substituted AT domains were "Hyg" AT2 from module 2 of a type I polyketide synthase (PKS)-like gene cluster isolated from the rapamycin producer Streptomyces hygroscopicus ATCC 29253, "Ven" AT isolated from a PKS-like gene cluster of the pikromycin producer Streptomyces venezuelae ATCC 15439, and RAPS AT14 from module 14 of the rapamycin PKS gene cluster of S. hygroscopicus ATCC 29253. These changes led to the production of novel erythromycin derivatives by the engineered strains of S. erythraea ER720. Specifically, 12-desmethyl-12-deoxyerythromycin A, which lacks the methyl group at C-12 of the macrolactone ring, was produced by the strains in which the resident AT1 domain was replaced, and 10-desmethylerythromycin A and 10-desmethyl-12-deoxyerythromycin A, both of which lack the methyl group at C-10 of the macrolactone ring, were produced by the recombinant strains in which the resident AT2 domain was replaced. All of the novel erythromycin derivatives exhibited antibiotic activity against Staphylococcus aureus. The production of the erythromycin derivatives through AT replacements confirms the computer predicted substrate specificities of "Hyg" AT2 and "Ven" AT and the substrate specificity of RAPS AT14 deduced from the structure of rapamycin. Moreover, these experiments demonstrate that at least some AT domains of the complete 6-deoxyerythronolide B synthase of S. erythraea can be replaced by functionally related domains from different organisms to make novel, bioactive compounds.

Acyl Coenzyme A↗
PubMed1997

Silica-induced apoptosis in alveolar and granulomatous cells in vivo.

Silica is a toxicant that can stimulate cells to produce various cellular products such as free radicals, cytokines, and growth factors. Silica and its induced substances may induce apoptosis to regulate the evolution of silica-induced inflammation and fibrosis. To examine this hypothesis, groups of Wistar male rats were intratracheally instilled with different doses of Min-U-Sil 5 silica (Silica, Berkeley Springs, WV). Ten days after the instillation, we obtained cells by bronchoalveolar lavage and placed them on slides by cytospin preparation. The slides were stained with Diff-Quik (Lab Aids, Sydney, NSW, Australia) and examined under oil immersion. A substantial number of cells with apoptotic features were identified in all silica-instilled rats and the apoptosis was confirmed by agarose gel electrophoresis. The number of apoptotic cells was clearly related to silica dosage. Engulfment of apoptotic cells by macrophages was also noted. Neutrophil influx in silica-instilled rats could be saturated with the increase of silica dosage and the number of macrophages in different dose groups changed in parallel with the proportion of apoptotic cells. Fifty-six days after instillation, morphologically apoptotic cells could be identified in granulomatous cells of lung tissue from silica-instilled rats. We conclude that intratracheal instillation of silica could induce apoptosis in both alveolar and granulomatous cells, and the apoptotic change and subsequent engulfment by macrophages might play a role in the evolution of silica-induced effects.

Administration, Inhalation↗
PubMed1997

[Alterations of substance P-immune reaction positive neurons of cerebral tissues in epileptic rats].

Employing the immunocytochemical analysis, we observed the alterations of Substance P-Immune Reaction (SP-IR) positive neurons of the cerebral cortex, hippocampus and amygdala in rats suffering from epilepsy induced by Penicillin (PEN). The result showed that the number of neurons of epileptic group was higher than that of the control group and no significant change in the rumber of neurons was observed in the group in which PEN was given after injection of Nimodine. It indicates that SP and Ca2+ participate in the process of epileptogenesis.

Amygdala↗
PubMed1997

[Antiepileptic effects of nimodipine on penicillin-induced seizures in rats].

Injecting penicillin (PNC) intraperitoneally in Wistar rats, we observed their epileptic behaviour and electroencephalographys. The results showed that nimodipine (NIM), a calcium antagonist, could inhibit the seizures and epileptic discharges significantly. No epileptic action was noted while NIM was injected before PNC. It supports our consideration of NIM as a new sort of nonsedative anticonvulsant in clinical practice.

Animals↗
PubMed1996

Calcium entry and mobilization signaling pathways in ANG II-induced renal vasoconstriction in vivo.

The purpose of this study was to determine the relative importance of calcium signaling pathways in angiotensin II (ANG II)-induced renal vasoconstriction in vivo. Nifedipine was used to antagonize dihydropyridine-sensitive voltage-dependent calcium channels; BAY K 8644 was employed to activate these calcium channels. Intracellular calcium mobilization was evaluated using TMB-8 or heparin to inhibit calcium release from sarcoplasmic reticulum. Renal blood flow was measured by electromagnetic flowmetry in anesthetized euvolemic Wistar-Kyoto rats. The animals were pretreated with indomethacin to avoid interactions with prostaglandins. ANG II (2 ng) or BAY K 8644 (1 microgram) was injected into the renal artery to produce a transient 30-50% decrease in renal blood flow without affecting arterial pressure. Coadministration of nifedipine with BAY K 8644 produced dose-dependent inhibition of the maximum renal vasoconstriction elicited by BAY K 8644. The calcium-channel antagonist had similar effects on ANG II-induced renal vasoconstriction. Nifedipine exerted maximum inhibition by blocking 50% of the peak ANG II response. To evaluate intracellular calcium mobilization, TMB-8 or heparin was coadministered with ANG II. Each agent produced dose-dependent inhibition of up to 50% of the maximum renal vasoconstriction produced by ANG II. The inhibitory effects of nifedipine and TMB-8 were additive; neither agent had an effect when ANG II AT1 receptors were antagonized with losartan. These observations indicate that one-half of the ANG II-induced constriction of renal resistance vessels is mediated by voltage-dependent L-type calcium channels responsive to the dihydropyridine nifedipine. The remaining 50% of the renal vasoconstriction elicited by ANG II is mediated by inositol 1,4,5-trisphosphate-mediated calcium mobilization from intracellular sources. The additive nature of the inhibitory effects indicates distinct mechanisms involving calcium mobilization and calcium entry signaling pathways that are of equal importance in ANG II activation of AT1 receptors to trigger constriction of renal resistance vessels under basal conditions.

Angiotensin II↗
PubMed1996

Role of protein kinase C in angiotensin II-induced renal vasoconstriction in genetically hypertensive rats.

The renal vasculature of young spontaneously hypertensive rats (SHR) responds to angiotensin II (ANG II) with exaggerated vasoconstriction, due in part to defective buffering by the adenosine 3',5'-cyclic monophosphate (cAMP) pathway. In vitro studies suggest greater activation of phospholipase C and protein kinase C (PKC) in cultured mesangial cells and vascular smooth muscle cells. The present studies evaluated the role of PKC activation in renal vascular responses to ANG II receptor activation and the relative contributions in SHR vs. Wistar-Kyoto control rats (WKY). Renal blood flow was measured in 8-wk-old anesthetized SHR and WKY pretreated with indomethacin. ANG II (2 ng) injection into the renal artery produced a transient 45-50% maximum reduction of renal blood flow in both rat strains. Intrarenal infusion of either staurosporine or chelerythrine into the renal artery effectively attenuated the vasoconstriction elicited by ANG II in a dose-dependent manner, with maximum inhibition of 60-70%. The PKC inhibitory effects were significant and independent of strain. Coadministration of the PKC inhibitors produced maximal inhibition similar to that observed with one agent, suggesting action via a common pathway. In other studies, the linkage of the PKC pathway to the AT1 receptor was evaluated using sub and maximal doses of losartan to antagonize 50-80% of ANG II-induced vasoconstriction. The same degree of inhibition was observed when a PKC inhibitor was coadministered with losartan. These findings support the views that the PKC system is a major intracellular signaling pathway coupled to the AT1 receptor in renal resistance vessels and that PKC activation is involved to similar degrees in the renal vasoconstriction elicited by ANG II in young WKY and SHR. Exaggerated vascular reactivity to vasoconstrictor agents in genetically hypertensive animals is probably due to a defect in cAMP generation in the presence of a normally operating PKC pathway.

Alkaloids↗
PubMed1995

Defective G protein activation of the cAMP pathway in rat kidney during genetic hypertension.

The development of hypertension in the spontaneously hypertensive rat (SHR) is associated with renal dysfunction and vasoconstriction. The kidneys of young SHRs exhibit exaggerated reactivity to angiotensin II (Ang-II) and attenuated responses to vasodilators that normally activate the cAMP signal to buffer hormone-induced vasoconstriction. The present study investigates the mechanism(s) responsible for this abnormality in activation of the cAMP second-messenger pathway in hypertensive animals. Renal vascular reactivity was assessed in 7-week-old anesthetized SHRs and normotensive Wistar-Kyoto rats. The animals were pretreated with indomethacin to block prostanoid production throughout an experiment. Ang-II was injected into the renal artery either alone or mixed with the vasodilator fenoldopam, a dopamine-receptor agonist. These two opposing vasoactive agents were administered before and during intrarenal infusion of NaF or cholera toxin, two activators of G proteins that stimulate cAMP production. The results show that Ang-II reduced renal blood flow by 45% in both strains. In Wistar-Kyoto rats, fenoldopam reduced the Ang-II-induced decrease in renal blood flow from -45% to -30%. This protective effect of fenoldopam was increased further during infusion of NaF or cholera toxin (-18% or -19% decrease in renal blood flow). In SHRs, fenoldopam failed to attenuate Ang II-mediated vasoconstriction (-45% vs. -44%). In contrast, fenoldopam effectively blunted the Ang-II-induced vasoconstriction when it was given concurrently with NaF or cholera toxin (-27 or -31% decrease in renal blood flow). These findings provide evidence for defective interaction between receptor coupling and activation of guanine nucleotide stimulatory factor proteins in the renal microcirculation of 7-week-old SHRs. Such a deficiency could play an important role in renal dysfunction associated with the development of genetic hypertension.

Angiotensin II↗
PubMed1993

Bradyrhizobium japonicum rhizobitoxine genes and putative enzyme functions: expression requires a translational frameshift.

Some strains of Bradyrhizobium japonicum produce rhizobitoxine, a phytotoxin that causes foliar chlorosis on susceptible host plants. We have previously obtained Tn5-induced rhizobitoxine null mutants of B. japonicum. DNA sequence analysis of the region surrounding two Tn5 insertions identifies two overlapping open reading frames. The first open reading frame (rtxA) predicts a 54-kDa protein for which the N-terminal 280 residues have sequence similarity to serine: pyruvate aminotransferase. The sequence homology to aminotransferase is consistent with the involvement of this gene in serinol production, a likely intermediate in rhizobitoxine biosynthesis. Previously, a mutant in this open reading frame was shown not to make serinol. The predicted amino acid sequence of the second open reading frame (rtxB) has similarity to yeast O-acetylhomoserine sulfhydrolase. This enzyme function is similar to that required for dihydrorhizobitoxine synthase. The DNA sequence shows that the rtxB open reading frame overlaps rtxA, suggesting that expression of rtxB requires a -1 translational frameshift. Protein expression experiments demonstrate production of an RtxAB fusion protein. The ability of the overlapping rtxA and rtxB sequences to promote a translational frameshift was confirmed in a heterologous expression system. In Escherichia coli, this frameshift appears to be unusually efficient, occurring at a frequency of 80-90%.

Amino Acid Sequence↗
PubMed1993

Interactions of cAMP-mediated vasodilators with angiotensin II in rat kidney during hypertension.

In previous studies [C. Chatziantoniou and W.J. Arendshorst. Am. J. Physiol. 263 (Renal Fluid Electrolyte Physiol. 32): F573-F580, 1992], we reported that vasodilator prostaglandins (PGs) are defective in buffering the angiotensin II (ANG II)-induced vasoconstriction in the renal vasculature of spontaneously hypertensive rats (SHR). The purpose of the present study was to determine whether this defect in SHR kidneys is specific to PGs or generalized to the action of vasodilators and to gain insight into which intracellular signal(s) mediates this abnormality. Renal blood flow (RBF; electromagnetic flowmetry) was measured in 7 wk-old anesthetized, euvolemic SHR and normotensive Wistar-Kyoto (WKY) rats pretreated with indomethacin to avoid interactions with endogenous PGs. ANG II (2 ng) was injected into the renal artery before and during continuous intrarenal infusion of fenoldopam [DA1 receptor agonist and G protein-dependent stimulator of adenosine 3',5'-cyclic monophosphate (cAMP)], forskolin (G protein-independent stimulator of cAMP), dibutyryl-cAMP (soluble cAMP), and acetylcholine (cGMP stimulator). Each vasodilator was infused at a low dose that did not affect baseline arterial pressure or RBF. In the control period, ANG II reduced RBF by 50% in both strains. Infusion of fenoldopam significantly blunted the ANG II-induced vasoconstriction in WKY, but not in SHR. In contrast, forskolin, dibutyryl-cAMP, and acetylcholine effectively buffered the vasoconstriction due to ANG II in both SHR and WKY. These results suggest that renal vasodilators acting through receptor binding to stimulate the cAMP signaling pathway are ineffective in counteracting the ANG II-induced vasoconstriction in SHR kidneys. (ABSTRACT TRUNCATED AT 250 WORDS)

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1992

Isolation and characterization of rhizobitoxine mutants of Bradyrhizobium japonicum.

To explore the role of rhizobitoxine in Bradyrhizobium-legume symbiosis, 11 rhizobitoxine mutants of B. japonicum USDA61 were isolated on the basis of their inability to synthesize the toxin in culture. Each mutant is prototrophic and symbiotically effective on soybean, cowpea, siratro, and Glycine soja. The rhizobitoxine mutants differ in their chlorosis phenotypes and rhizobitoxine production in planta. As expected, one group of mutant fail to make toxin in planta, resulting in the absence of chlorosis. Another group of mutants causes severe chlorosis on all cultivars of soybean tested. Surprisingly, this group of mutants makes more rhizobitoxine in soybean nodules than the wild-type strain does. This phenotype is only observed on soybean and not on other hosts such as cowpea, siratro, or G. soja. The remaining mutants all produce rhizobitoxine in planta but vary in the amount of toxin they produce and the severity of chlorosis they induce in soybean plants. Biochemical analysis of mutants demonstrates that one mutant is unable to synthesize serinol, a molecule hypothesized to be an intermediate in rhizobitoxine biosynthesis. By using these mutants, it was found that rhizobitoxine plays no apparent role in the nodulation of rj1 soybeans. Recently, it was found that inhibition of ethylene biosynthesis allows Rhizobium meliloti to overcome nitrate inhibition of nodule formation on alfalfa. Because rhizobitoxine also inhibits ethylene biosynthesis, we tested the ability of mutants which accumulate high levels of toxin in planta to overcome nitrate inhibition of nodule formation on soybean plants and found that the nodule formation induced by the wild type and that induced by mutant strains were equally suppressed in the presence of nitrate.

DNA Transposable Elements↗
PubMed1991

Rapid and sensitive assay for the phytotoxin rhizobitoxine.

Rhizobitoxine is a phytotoxin synthesized by some strains of the legume symbiont genus Bradyrhizobium and the plant pathogen Pseudomonas andropogonis. We demonstrate here a new enzymatic assay which is 100-fold more sensitive than previous assays and can detect as little as 1.0 pmol of rhizobitoxine. The assay is based on the inhibition of Salmonella typhimurium beta-cystathionase by rhizobitoxine. Interestingly, beta-cystathionase from Bradyrhizobium japonicum is insensitive to rhizobitoxine at concentrations lower than 75 microM.

Lyases↗