A sensitive pH fluorescent probe based on triethylenetetramine bearing double dansyl groups in aqueous solutions and its application in cells

pH fluorescent probes possess many advantages, including intracellular detection, rapid response time and nondestructive testing. In this paper, a highly selective and sensitive fluorescent pH probe based on triethylenetetramine bearing double dansyl groups (1) was synthesized. This probe offers fluorescent measurement of pH value in the range of 5.81-7.21 in aqueous solution, with an 8.64-fold enhancement of fluorescent emission intensity over the unmodified probe. Probe 1 shows a fluorescent color change from a pale yellow to bright green when the pH is increased from 5.81 to 7.21. In addition, probe 1 shows good potential as a fluorescent visualizing sensor for pH values in living GS cells of epinepheluscoioides. The mechanism of the fluorescent response of probe 1 to solution pHs was further clarified by NMR, fluorescent spectra, and UV-vis absorption spectra. The results indicate that the fluorescent emission will shift with an increase in solution pHs, due to increasing deprotonation of the nitrogen atom on the sulfonamides. Deprotonation of the sulfonamide group will inhibits the intramolecular charge transfer process between the imino group and the naphthalene ring, resulting in the recognition phenomenon of blue shift and enhancement of fluorescent emission intensity.

Biotransformation of magnetic nanoparticles as a function of coating in a rat model

Long-term in vivo studies in murine models have shown that DMSA-coated nanoparticles accumulate in spleen, liver and lung tissues during extended periods of time (at least up to 3 months) without any significant signs of toxicity detected. During that time, nanoparticles undergo a process of biotransformation either by reducing the size or the particle aggregation or both. Using a rat model, we have evaluated the transformations of magnetic nanoparticles injected at low doses. Particles with two different coatings, dimercaptosuccinic acid (NP-DMSA) and polyethylene glycol (NP-PEG-(NH2)2) have been administered to animals, to evaluate the role of coating in the degradation of the particles. We have found that low doses of magnetic nanoparticles are quickly metabolized by the animals. In fact, using a nanoparticle dose four times lower than in previous experiments, NP-DMSA were not observed 24 h after the administration either in the liver or in the lungs. Interestingly, an increased amount of ferritin, the iron storage protein, was observed in liver tissues from rats that were treated with the low dose of NP-DMSA in comparison with the control ones, suggesting a rapid metabolization of the particles into ferritin iron. On the other side we have found that, NP-PEG-(NH2)2 are still detectable in several organs 24 h after their administration at low doses. Probably, due to the longer circulation times of the NP-PEG-(NH2)2, there is a delay in the arrival of the particles to the tissue and this is the reason why we are able to see the particles 24 h post-administration. PEG coating could also be protecting the nanoparticles from rapid degradation of the reticuloendothelial system. Knowledge on the biodistribution, circulation time and degradation processes is required to gain a better understanding of the safety evaluation of this kind of nanomaterial for biomedical applications.

Monodansylpentane as a blue-fluorescent lipid-droplet marker for multi-color live-cell imaging

Lipid droplets (LDs) are dynamic cellular organelles responsible for the storage of neutral lipids, and are associated with a multitude of metabolic syndromes. Here we report monodansylpentane (MDH) as a high contrast blue-fluorescent marker for LDs. The unique spectral properties make MDH easily combinable with other green and red fluorescent reporters for multicolor fluorescence imaging. MDH staining does not apparently affect LD trafficking, and the dye is extraordinarily photo-stable. Taken together MDH represents a reliable tool to use for the investigation of dynamic LD regulation within living cells using fluorescence microscopy.

VMY-1-103, a dansylated analog of purvalanol B, induces caspase-3-dependent apoptosis in LNCaP prostate cancer cells

The 2,6,9-trisubstituted purine group of cyclin dependent kinase inhibitors have the potential to be clinically relevant inhibitors of cancer cell proliferation. We have recently designed and synthesized a novel dansylated analog of purvalanol B, termed VMY-1-103, that inhibited cell cycle progression in breast cancer cell lines more effectively than did purvalanol B and allowed for uptake analyses by fluorescence microscopy. ErbB-2 plays an important role in the regulation of signal transduction cascades in a number of epithelial tumors, including prostate cancer (PCa). Our previous studies demonstrated that transgenic expression of activated ErbB-2 in the mouse prostate initiated PCa and either the overexpression of ErbB-2 or the addition of the ErbB-2/ErbB-3 ligand, heregulin (HRG), induced cell cycle progression in the androgen-responsive prostate cancer cell line, LNCaP. In the present study, we tested the efficacy of VMY-1-103 in inhibiting HRG-induced cell proliferation in LNCaP prostate cancer cells. At concentrations as low as 1 μM, VMY-1-103 increased both the proportion of cells in G(1) and p21(CIP1) protein levels. At higher concentrations (5 μM or 10 μM), VMY-1-103 induced apoptosis via decreased mitochondrial membrane polarity and induction of p53 phosphorylation, caspase-3 activity and PARP cleavage. Treatment with 10 μM Purvalanol B failed to either influence proliferation or induce apoptosis. Our results demonstrate that VMY-1-103 was more effective in inducing apoptosis in PCa cells than its parent compound, purvalanol B, and support the testing of VMY-1-103 as a potential small molecule inhibitor of prostate cancer in vivo.

[Kinetic study on inhibition effects of dansyl-L-phenylalanine and L-phenylalanine on calf intestinal alkaline phosphatase]

To evaluate the inhibition effect of dansyl-L-phenylalanine on calf intestinal alkaline phosphatase (CIAP), UV-Vis spectrophotometric method was employed. It was found that dansyl-L-phenylalanine can selectively inhibit CIAP. The kinetic inhibition processes of dansyl-L-phenylalanine and L-phenylalanine were comparatively studied. The authors' finding elucidates that at the optimized alkaline pH of alkaline phosphatase (pH 10.4) and 37 degrees C, dansyl-L-phenylalanine can inhibit alkaline phosphatase activity of CIAP efficiently and specifically, similar as L-phenylalanine. Both inhibition types were uncompetitive inhibition resulting from the double reciprocal curve fitting of upsilon versus substrate concentrations, and the inhibition constants Ki of both inhibitors were determined to be 2.3 and 1.1 mmol L(-1) respectively, both of which were at millimolar level. The investigation of the inhibition effect of dansyl modified L-phenylalanine on calf intestinal alkaline phosphatase not only helped get insight into the detailed inhibition mechanism of L-phenylalanine on tissue specific alkaline phosphatase, such as in the case of intestinal alkaline phosphatase, but also provided the possibility to employ fluorescence spectroscopy by labeling the specific inhibitors of alkaline phosphatase with chromophoric groups.

Endothelin A receptor blockade influences apoptosis and cellular proliferation in the developing rat kidney

Endothelin systems are believed to play important roles in the emergence and maintenance of functions of various organs during perinatal development, including the kidney. The present study was designed to investigate the roles of endothelin systems on physiologic renal growth and development. Newborn rat pups were treated with either Bristol-Myers Squibb-182874 (30 mg/kg/day), a selective endothelin A receptor (ET(A)R) antagonist, or vehicle for 7 days. To identify cellular changes, kidneys were examined for apoptotic cells by terminal deoxynucleotide transferase-mediated nick-end labeling stain and proliferating cell nuclear antigen (PCNA) by immunohistochemical (IHC) stain. To clarify the molecular control of these processes, immunoblots and reverse transcriptase-polymerase chain reaction for Clusterin, Bcl-2, Bcl-X(L), Bax, and p53 were performed. ETAR antagonist treatment resulted in reduced kidney weights, decreased PCNA-positive proliferating cells, and increased apoptotic cells. The protein expressions of renal Bcl-X(L) and Bax in the ETAR antagonist-treated group were significantly decreased, whereas the mRNA expressions of these genes were not changed. There were no significant differences in the expressions of Clusterin, Bcl-2, and p53. In conclusion, inhibition of endogenous endothelins impairs renal growth, in which decreased cellular proliferation, increased apoptosis and decreased expressions of renal Bcl-X(L) and Bax are possibly implicated.

Chemical study of the topography of porcine lutropin (LH) using dinitrofluorobenzene and dansyl chloride

Treatment of porcine lutropin beta-subunit by increasing amounts of dansyl chloride shows that only one fluorescent group can be bound to the free subunit, namely on tyrosine beta-37. This modification prevents reassociation with native chi-subunit. In contrast to dansyl chloride, dinitrofluorobenzene reacts preferentially with tyrosine beta-59. This substitution does not interfere with the reassociation with the native chi-subunit. By using equimolar ratio of dansyl chloride and porcine lutropin chi-subunit it is possible to modify this subunit on a single site, which is found to be a tyrosine residue. The monodansylated X-subunit is still able to recombine with native B-subunit but its fluorescence is found to be markedly quenched upon binding. In addition, the O-dansyl-tyrosyl fluorescence quenching by potassium iodide is more effective on the recombined dimer than on the free chi-subunit. Both reconstituted dimers (native xhi chi dinitrophenylated beta and dansylated chi chi native beta) are without biological activity. It is not clear whether the substituted phenolic groups are essential or whether the added groups prevent the chi beta dimer from taking the active conformation. This alternative is discussed in the light of recent data from this laboratory and others.

A novel combination of opiates and endothelin antagonists to manage pain without any tolerance development

Several neurotransmitter mechanisms have been proposed as playing a role in the development of morphine tolerance. We provide evidence for the first time that endothelin antagonists can restore morphine analgesia in morphine-tolerant rats and prevent the development of tolerance to morphine. Studies were carried out in rats and mice treated with implanted placebo or implanted morphine pellet. The maximal tail-flick latency in morphine pellet + vehicle-treated rats (7.54 seconds) was significantly lower when compared with placebo pellet + vehicle-treated rats (10 seconds), indicating that tolerance developed to the analgesic effect of morphine. BQ123 potentiated tail-flick latency by 30.0% in placebo-tolerant rats and 94.5% in morphine-tolerant rats compared with respective controls. BMS182874 potentiated tail-flick latency by 30.2% in placebo-tolerant rats and 66.7% in morphine-tolerant rats. The enhanced analgesic effect of morphine after treatment with endothelin antagonists could be blocked by naloxone, indicating an opiate-mediated effect; but naloxone binding to brain membranes was not affected by BQ123. Guanosine triphosphate binding was stimulated by morphine and endothelin-1 in non-tolerant mice and not in morphine-tolerant mice; however, guanosine triphosphate binding was stimulated by BQ123 in morphine-tolerant mice and was unaffected in non-tolerant mice. These results suggest that uncoupling of G-protein occurs in morphine tolerance and endothelin antagonist restores the coupling of G-protein to its receptors. A combination use of endothelin antagonist and opiates could provide a novel approach in improving analgesia and eliminating tolerance.

Isolation, purification, characterization and glycan-binding profile of a d-galactoside specific lectin from the marine sponge, Halichondria okadai

A lectin recognizing both Galbeta1-3GlcNAc and Galbeta1-4GlcNAc was purified from the demosponge Halichondria okadai by lactosyl-agarose affinity chromatography. The molecular mass of the lectin was determined to be 30 kDa by SDS-PAGE under reducing and non-reducing conditions and 60 kDa by gel permeation chromatography. The pI value of the lectin was 6.7. It was found to agglutinate trypsinized and glutaraldehyde-fixed rabbit and human erythrocytes in the presence and absence of divalent cations. The hemagglutinating activity by the lectin was inhibited by d-galactose, methyl-d-galactopyranoside, N-acetyl-d-galactosamine, methyl-N-acetyl-d-galactosaminide, lactose, melibiose, and asialofetuin. The K(d) of the lectin against p-nitrophenyl-beta-lactoside was determined to be 2.76x10(-5) M and its glycan-binding profile given by frontal affinity chromatography was shown to be similar to many other known galectins. Partial primary structure analysis of 7 peptides by cleavage with lysyl endopeptidase indicated that one of the peptides showed significant similarity with galectin purified from the sponge Geodia cydonium.

Effects of endothelin-1 on fibroblasts from type 2 diabetic patients: Possible role in wound healing and tissue repair

Endothelin-1 (ET-1) promotes the contractile ability of fibroblasts, essential for wound closure and reconstitution of the dermis. Wound healing is impaired in type 2 diabetic patients (D). We compared the effect of ET-1 on proliferative transforming growth factor (TGFbeta(1)) expression, fibronectin and laminin release), differentiative [alpha-smooth muscle actin (alpha-SMA) expression] and inflammatory [monocyte chemo-attractant protein (MCP-1) and interleukin-6 (IL-6) expression] responses in skin fibroblasts of healthy subjects (C) and D, testing the relative role of ET(A) and ET(B) receptors in mediating these responses. ET-1 did not influence TGFbeta(1), fibronectin or laminin production. alpha-SMA was more abundant and more stimulated in D, as well as MCP-1 and IL-6 expression and release. These effects were prevented by BMS-182874, selective antagonist of ET(A), more abundant than ET(B) in both cell strains and whose expression rose more in D than C upon stimulation with ET-1. This peculiar pattern of responses to ET-1, presumably acquired during the chronic in vivo exposure to hyperglycemia along the natural history of the disease, may partially explain the increased susceptibility of D to chronic ulcerations.

Pharmacological effects of the dansylated neuropeptide FF analogues on body temperature and morphine analgesia

In our previous work, the two putative agonists (dansyl-GSRFamide and dansyl-PQRFamide) and the two putative antagonists (dansyl-GSRamide and dansyl-PQRamide) on neuropeptide FF (NPFF) receptors were synthesized to evaluate the importance of Phe(8) of NPFF. In the present study, these putative NPFF agonists/antagonists containing different N-terminal sequences were further examined for their pharmacological profiles in thermoregulatory and nociceptive tests. The results indicated that the two dansylated agonists potently possessed similar thermoregulation (rank order of potencies: dansyl-GSRFamide>>NPFF>dansyl-PQRFamide) and different modulation of opioid-induced analgesia; in contrast, both of the two putative antagonists exhibited marked hypothermia (rank order of potencies: dansyl-PQRamide>dansyl-GSRamide) and facilitation of morphine analgesia (rank order of potencies: dansyl-PQRamide > dansyl-GSRamide). These data reveal that the difference of the N-terminal residues of the two putative agonists causes their dissociation of pharmacological pro- and anti-opioid effects. In addition, their N-terminal part is important to determine the potency of the dansylated agonists/antagonists. Our work might be helpful to develop a highly potent and fluorescent NPFF ligand.

Design and cellular kinetics of dansyl-labeled CADA derivatives with anti-HIV and CD4 receptor down-modulating activity

A new class of anti-retrovirals, cyclotriazadisulfonamide (CADA) and its derivatives, specifically down-regulate CD4, the main receptor of HIV, and prevent HIV infection in vitro. In this work, several CADA derivatives, chemically labeled with a fluorescent dansyl group, were evaluated for their biological features and cellular uptake kinetics. We identified a derivative KKD-016 with antiviral and CD4 down-modulating capabilities similar to those of the parental compound CADA. By using flow cytometry, we demonstrated that the dose-dependent cellular uptake of this derivative correlated with CD4 down-modulation. The uptake and activity of the dansyl-labeled compounds were not dependent on the level of expression of CD4 at the cell surface. Removal of the CADA compounds from the cell culture medium resulted in their release from the cells followed by a complete restoration of CD4 expression. The inability of several fluorescent CADA derivatives to down-modulate CD4 was not associated with their lower cellular uptake and was not reversed by facilitating their cell penetration by a surfactant. These results prove the successful integration of the dansyl fluorophore into the chemical structure of a CD4 down-modulating anti-HIV compound, and show the feasibility of tracking a receptor and its down-modulator simultaneously. These fluorescent CADA analogs with reversible CD4 down-regulating potency can now be applied in further studies on receptor modulation, and in the exploration of their potentials as preventive and therapeutic anti-HIV drugs.

Involvement of endothelin in morphine tolerance in neuroblastoma (SH-SY5Y) cells

Long-term use of morphine in pain management leads to adverse effects, such as development of antinociceptive tolerance. We have previously shown the involvement of central endothelin (ET) mechanisms in morphine analgesia and development of tolerance in vivo. The present study was conducted to investigate the in vitro mechanism of interaction of the ET(A) receptor antagonist, BMS182874, and morphine during acute and chronic morphine tolerance in SH-SY5Y cells. SH-SY5Y cells were exposed to acute and chronic treatment with vehicle, morphine, ET-1, BMS182874, or morphine plus BMS182874. Activation of G-protein-coupled receptors in SH-SY5Y cells was determined using [35S]GTPgammaS binding assays. Acute morphine treatment produced a concentration-dependent increase in GTP binding. Median effective concentration (EC50) values were significantly decreased after acute morphine treament, suggesting sensitization of opioid receptors. Chronic morphine treatment produced a lower maximal response of GTP binding compared with both control (vehicle treated) and acute morphine treatment, indicating uncoupling of G-proteins. Acute and chronic exposure of cells to ET-1 did not affect changes in ET-1-induced GTP binding. BMS182874 treatment alone (acute or chronic) did not produce G-protein activation. However, in cells chronically cotreated with 10 microM morphine and 1 microM BMS182874, morphine-induced GTP stimulation was significantly higher than control (vehicle treated). The EC50 value after control treatment was 414 nM, and was significantly increased in chronically morphine-treated cells (>1000 nM ). However, the EC50 value in cells receiving a chronic treatment of BMS182874 and 63 nM morphine was significantly reduced compared with control (vehicle treated) and chronic morphine treatment. ET(A) antagonists significantly enhance the coupling of G-protein to opioid receptors. Therefore, we propose that restoration of morphine antinociception by ET(A) antagonists in morphine-tolerant animals is likely via a G-protein mediated mechanism.

Involvement of central endothelin receptors in neonatal morphine withdrawal

The involvement of central endothelin (ET) receptors in neonatal morphine tolerance has been demonstrated. The present study investigates the role of central ET receptors in morphine withdrawal in neonatal rats. The aim was to determine whether activation of G-proteins coupled to opioid and ET receptors by morphine and various ET receptor modulators is affected during morphine withdrawal in neonatal rats. Pregnant female rats were rendered tolerant to morphine by chronic exposure to morphine pellets during 7 days. On Day 8, pellets were removed and rats were allowed to undergo withdrawal for 24 hrs. Rat pups were delivered by cesarean section. G-protein stimulation induced by morphine; ET-1; the ET(A) receptor antagonist, BMS182874; and the ET(B) receptor agonist, IRL1620, were determined in the brain of neonatal rats undergoing morphine withdrawal by [35S]GTPgammaS binding assay. Morphine produced higher (P < 0.05) maximal stimulation of G-protein in the morphine-withdrawal group (83.60%) compared with the placebo group (66.81%). ET-1-induced G-protein stimulation was also altered, and the median effective concentration (EC50) during morphine withdrawal (170.60 nM) was significantly higher than placebo (62.5 nM; P< 0.05). The maximal stimulation induced by the ET(A) receptor antagonist, BMS182874, in the morphine-withdrawal group (86.07%; EC50 = 31.25 nM) was significantly higher than in the placebo group (EC50 > 1000 nM). The ET(B) agonist, IRL1620, induced G-protein stimulation was similar in placebo (73.43%, EC50 = 13.26 nM) and morphine-withdrawal groups (75.08%, EC(50) = 11.70 nM), respectively. To our knowledge, this is the first report indicating involvement of central ET(A) receptors in neonatal morphine withdrawal.

Endothelin ETA receptor blockade potentiates morphine analgesia but does not affect gastrointestinal transit in mice

Development of analgesic tolerance and constipation remain a major clinical concern during long-term administration of morphine in pain management. Central endothelin mechanisms are involved in morphine analgesia and tolerance. The present study was conducted to investigate the effect of intracerebroventricular (i.c.v.) and peripheral administration of endothelin ET(A) receptor antagonist, BMS182874, and endothelin ET(B) receptor agonist, IRL1620, on morphine analgesia and changes in gastrointestinal transit in male Swiss Webster mice. Results indicate that morphine (6 mg/kg, s.c.) produced a significant increase in tail flick latency compared to control group. Pretreatment with BMS182874 (50 microg, i.c.v.) significantly enhanced morphine-induced analgesia, while IRL1620 (30 microg, i.c.v.) pretreatment did not affect tail-flick latency values. Changes in gastrointestinal transit were measured by percent of distance traveled by charcoal in the small intestine of gastrointestinal tract. Percent distance traveled in morphine (6 mg/kg, s.c.) treated mice (48.45+/-5.65%) was significantly lower (P<0.05) compared to control group (85.07+/-1.82%). Administration of BMS182874 centrally (50 mug, i.c.v.) or peripherally (10 mg/kg, i.p.) did not affect morphine-induced inhibition of gastrointestinal transit. Pretreatment with IRL1620 (30 microg, i.c.v., or 10 mg/kg, i.v.) also did not affect morphine-induced inhibition of gastrointestinal transit. This study demonstrates that endothelin ET(A) receptor antagonists delivered to the CNS enhance morphine analgesia without affecting gastrointestinal transit.

meso-Dihydroguaiaretic acid attenuates the neurotoxic effect of staurosporine in primary rat cortical cultures

The effect of meso-dihydroguaiaretic acid (MDGA) on the staurosporine-induced neuronal apoptosis and its potential mechanism were investigated using primary cultures of rat cortical cells as an assay system. Treatment of MDGA at the concentrations of 0.1, 1.0 and 10 microM significantly protected neuronal cells against Staurosporine-induced apoptosis. The neuroprotective activity of MDGA was the most potent at the concentration of 1.0 microM and was not increased at higher concentration. MDGA reduced apoptotic characteristics induced by STS; MDGA reduced the condensed nuclei in staurosporine-injured rat cortical cells. MDGA diminished the calcium influx that accompanies the staurosporine-induced apoptosis, and inhibited the subsequent overproduction of reactive oxygen species and peroxide to the level of control cells. It also preserved cellular activity of superoxide dismutase, an antioxidative enzyme reduced by staurosporine insult. In addition, MDGA significantly inhibited caspase-3/7 activation and cytochrome c release. Taken together, these results suggested that MDGA protected neuronal cells against staurosporine-induced apoptosis through the inhibition of Ca(2+) influx, cellular oxidation, cytochrome c release and caspase-3/7 activation.

Pharmacological characterization of endothelin receptors-mediated contraction in the mouse isolated proximal and distal colon

The study investigated the role of endothelin (ET) and the ET receptor subtypes ET(A) and ET(B) in mediating longitudinal contraction in the mouse proximal and distal colon. Cumulative concentration-response curves to a range of ET agonists (ET-1, ET-2, ET-3, (Ala(1,3,11,13)) ET and IRL 1620) were established by administering concentrations ranging from 0.01 nM to 0.3 microM. Concentration-response curves to ET-1, which exhibits a high affinity for both ET(A) and ET(B) receptor subtypes, were also established in the presence of the ET(A) antagonist BMS 182874 and the ET(B) antagonist IRL1038. The addition of the selective ET(A) receptor antagonist BMS 182874 caused a rightward shift of the concentration-response curve to ET-1 in both sections of the colon. The ET(B) receptor antagonist IRL1038 (0.3-1 microM) did not significantly effect the response to ET-1 in the proximal colon but caused a significant decrease in response towards higher concentrations ranges (>or=3 nM) in the distal colon. A comparison of the concentration-response curves to ET-1, ET-2 and ET-3 showed a rank order of potency ET-1>or=ET-2>>ET-3 in the proximal colon and ET-1>or=ET-2>or=ET-3 in the distal colon. The selective ET(B) receptor agonists, (Ala(1,3,11,13)) ET and IRL 1620 did not produce any response in the proximal sections of the colon but produced a smaller contraction in the distal segments. The data indicate that ET can contract the proximal tissues of the mouse colon predominantly via ET(A) receptors and in the distal tissues via ET(A) and ET(B) receptors.

Effect of spermine and N1-dansyl-spermine on epileptiform activity in mouse cortical slices

N(1)-dansyl-spermine is a novel polyamine analogue, which has been demonstrated to have an antagonist action at the stimulatory polyamine site on the N-methyl-D-aspartate (NMDA) receptor macrocomplex. Cortical wedges from genetically epilepsy-prone DBA/2 mice demonstrate spontaneous epileptiform activity when perfused with Mg(2+)-free artificial cerebrospinal fluid (aCSF). This epileptiform activity has been demonstrated to be primarily mediated through the NMDA receptor. N(1)-dansyl-spermine reduced the spontaneous epileptiform activity at a high dose (100 microM) but had no effect at a lower dose (50 microM). The polyamine, spermine (300 microM) caused an increase in the rate of the spontaneous epileptiform discharges. This effect of spermine was antagonised by administration of the low dose of N(1)-dansyl-spermine (50 microM). This further demonstrates the role of the NMDA receptor in the production of spontaneous epileptiform discharges in the cortical wedge preparation and clearly illustrates both the facilitatory action of spermine and the polyamine antagonist action of N(1)-dansyl-spermine at the stimulatory polyamine site on the NMDA receptor.

Development of a rapid and sensitive LC–ESI/MS/MS assay for the quantification of propofol using a simple off-line dansyl chloride derivatization reaction to enhance signal intensity

A rapid, selective and sensitive method was developed for the determination of propofol concentration using an off-line dansyl chloride derivatization step to enhance signal intensity. The method consisted of a protein precipitation extraction followed by derivatization with dansyl chloride and analysis by liquid chromatography ionspray tandem mass spectrometry (LC-ESI/MS/MS). The separation was achieved using a 100 mm x 2 mm C8 analytical column combined with an isocratic mobile phase composed of 80:20 acetonitrile: 0.5% formic acid in water. Signal intensity of the propofol-dansyl chloride derivative was increased up to 200-fold as compared to the underivatized propofol in positive electrospray mode. An analytical range of 20-20,000 ng/mL was used in the calibration curve of plasma and blood samples. The novel method met all requirements of specificity, sensitivity, linearity, precision, accuracy and stability. A pharmacokinetic study was performed in rats and the novel analytical method was used as a routine analysis to provide enhanced measurements of plasma and blood concentrations of propofol. Blood and plasma pharmacokinetic results show that a very important fraction of propofol distributes into red blood cells. In conclusion, a rapid and sensitive LC-ESI/MS/MS method using a derivatization agent was developed to enhance signal intensity of propofol. Routine analysis with the novel method provided accurate results and enhanced the detection levels of plasma and blood concentrations of propofol to better characterize the in vivo biodisposition of propofol.

Fluorimetric study of the artificial chaperone-assisted renaturation of carbonic anhydrase: A kinetic analysis

It is now well accepted that ionic detergents along with alpha- or beta-cyclodextrins can enhance protein refolding yields. In this report, we evaluated the effect of detergent's tail length on the kinetics of denatured carbonic anhydrase refolding along with determining the rate-limiting step of the whole refolding process. A sensitive fluorimetric technique was also developed to follow up the second-by-second fate of the denatured protein while undergoing refolding. In this technique, inclusion complexes are formed between the correctly refolded CA and the fluorescent active site probe, 5-dimethylaminonaphtalene-1-sulfonamide. By this specific technique, it became evident that the rate of detergent stripping from the CA-detergent mixed micelles that also appeared to be the rate-limiting step depends on the beta-CD-detergent association constants which are under the influence of detergent's tail length. Based on these findings, appropriate refolding conditions could be designed to kinetically diminish the rate of off-pathway aggregation.

Endothelin-1 contributes to the sexual differences in renal damage in DOCA-salt rats

We investigated whether gender differences in renal damage in DOCA-salt hypertension are associated with effects of ovarian hormones and/or endothelin-1 (ET-1). Renal injuries and renal pre-pro-ET-1 mRNA expression were enhanced in male and female ovariectomized (OVX) DOCA rats versus female DOCA rats. Treatment with estrogen plus progesterone or progesterone, but not estrogen alone, attenuated renal damage and pre-pro-ET-1 mRNA expression in OVX DOCA rats. The ETA antagonist BMS182874 greatly ameliorated renal damage in male and OVX DOCA rats. In conclusion, the ovarian hormones have a protective role on the renal structural alterations in female DOCA rats by modulating effects of ET-1, via ETA receptors.

The endothelin receptor antagonist decreases ischemia/reperfusion-induced tumor necrosis factor production in isolated rat hearts

Previous studies have shown that endothelin-1 (ET-1) may play a pathophysiological role in myocardial ischemia/reperfusion injury. In the present study, BMS-182874 significantly improved the recovery of cardiac function and reduced the release of CK during reperfusion after ischemia and the content of tumor necrosis factor (TNF-alpha) in myocardial tissues. BMS-182874 also reduced myocardial injury and the increased level of TNF-alpha by exogenous ET-1. These results suggest that the cardioprotective effects of the ET receptor antagonist may be related to inhibition of TNF-alpha production.

The pre-ischaemic neuroprotective effect of a novel polyamine antagonist, N1-dansyl-spermine in a permanent focal cerebral ischaemia model in mice

The polyamine sites on the NMDA receptor complex offer a therapeutic target for focal ischaemia, potentially devoid of most side effects associated with NMDA antagonists. In this study, we investigated the effect of a novel polyamine antagonist, N(1)-dansyl-spermine (0.5-10 mg kg(-1)) in a permanent focal cerebral ischaemia model in mice, and compared its effect to that of MK-801 (0.3-3 mg kg(-1)) following administration 30 min prior to ischaemia. A battery of histological and behavioural tests was employed following permanent middle cerebral artery occlusion to assess any neuroprotective effect. Following middle cerebral artery occlusion, N(1)-dansyl-spermine (1-5 mg kg(-1)) and MK-801 (1 or 3 mg kg(-1)) caused a comparable and significant reduction in the percentage hemisphere lesion volume. Similarly, both drugs significantly reduced oedema and neurological deficit score to a similar extent. Locomotor activity in MCAO mice was not significantly improved by MK-801 or N(1)-dansyl-spermine, although N(1)-dansyl-spermine induced a trend towards significant improvement. Significant improvement in rotarod performance was observed at neuroprotective doses with both drugs. Upon comparison of the profile of effects, N(1)-dansyl-spermine at least matched the effectiveness of MK-801 as a neuroprotective agent in this model. In addition, in sham-operated control mice, N(1)-dansyl-spermine was well tolerated, in contrast to the pronounced adverse effects of MK-801 on locomotor activity and rotarod performance. In conclusion, this study has shown that N(1)-dansyl-spermine is as effective a neuroprotective drug as MK-801 in this model. Moreover, in contrast to MK-801, N(1)-dansyl-spermine could be a promising therapeutic candidate for stroke as it is well tolerated at neuroprotective doses in sham-operated animals.

Chemical modification of transducin with dansyl chloride hinders its binding to light-activated rhodopsin

Transducin (T), the heterotrimeric guanine nucleotide binding protein in rod outer segments, serves as an intermediary between the receptor protein, rhodopsin, and the effector protein, cGMP phosphodiesterase. Labeling of T with dansyl chloride (DnsCl) inhibited its light-dependent guanine nucleotide binding activity. Conversely, DnsCl had no effect on the functionality of rhodopsin. Approximately 2-3 mol of DnsCl were incorporated per mole of T. Since fluoroaluminate was capable of activating DnsCl-modified T, this lysine-specific labeling compound did not affect the guanine nucleotide-binding pocket of T. However, the labeling of T with DnsCl hindered its binding to photoexcited rhodopsin, as shown by sedimentation experiments. Additionally, rhodopsin completely protected against the DnsCl inactivation of T. These results demonstrated the existence of functional lysines on T that are located in the proximity of the interaction site with the photoreceptor protein.

Evidence that morphine tolerance may be regulated by endothelin in the neonatal rat

BACKGROUND

Opioids are widely used in the neonatal intensive care units for analgesia and sedation. Management of tolerance and withdrawal symptoms in neonates remains a major challenge.

OBJECTIVES

The present study investigates the involvement of a central endothelin (ET) mechanism in the development of tolerance to morphine in neonatal rats.

METHODS

Pregnant female rats were rendered tolerant to morphine and rat pups were delivered at term by cesarean section. The affinity (Kd) and density (Bmax) of ET receptors was determined by [125I]ET-1 binding in the brains of neonatal rats. Changes in G-protein stimulation were determined in placebo and morphine-tolerant neonatal rats by [35S]-guanosine-5'-o-(3-thio)triphosphate ([35S]GTPgammaS)-binding assay.

RESULTS

Morphine tolerance did not affect the characteristics (affinity and density) of the ET receptors in the neonatal rat brains. Morphine as well as ET-1 produced significantly lower (p < 0.05) maximal stimulation of [35S]GTPgammaS binding in morphine-tolerant neonatal rats compared to the placebo group. The ETA receptor antagonist, BMS182874, produced significantly higher stimulation of G proteins in the morphine-tolerant compared to the placebo group. The ETB receptor agonist, IRL1620, produced a similar effect in both placebo and morphine-tolerant rats.

CONCLUSIONS

This is the first report indicating the involvement of the G-protein-coupled ETA receptor in neonatal morphine tolerance.

N1-Dansyl-spermine: a potent polyamine antagonist

The potential polyamine antagonist action of N1-dansyl-spermine (a potent NMDA antagonist) was assessed in two in vivo mouse models of polyamine action. Co-administration of N1-dansyl-spermine (2-10 microg, i.c.v.) with spermine (100 microg, i.c.v.) resulted in a dose-dependent antagonism of the spermine-induced CNS excitation (body tremor and fatal tonic convulsions). In addition, the same dose of N1-dansyl-spermine antagonised spermine's enhancement of NMDA-induced convulsions. These results suggest that N1-dansyl-spermine is in vivo a potent antagonist of the CNS effects of spermine and of its action at the positive polyamine modulatory site on the NMDA receptor.

The neuroprotective effects of N1-dansyl-spermine in the gerbil model of cerebral ischaemia

The effects of N1-dansyl-spermine, a polyamine antagonist, and ifenprodil, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, were investigated in the gerbil model of global cerebral ischaemia. Transient forebrain ischaemia was induced by 5-min bilateral occlusion of the common carotid arteries. N1-dansyl-spermine (2, 5 and 10 mg/kg) and ifenprodil (30 mg/kg) were administered intraperitoneally 30 min after bilateral carotid artery occlusion. On histological examination, 4 days (96 h) after ischaemia, there was a significant decrease in neuronal density of the hippocampal CA1 subfield. This reduction in neuronal density was attenuated in those animals treated with the 5 or 10 mg/kg dose of N1-dansyl-spermine and those treated with 30 mg/kg ifenprodil. However, unlike ifenprodil, N1-dansyl-spermine failed to attenuate the ischaemia-induced increase in locomotor activity. This demonstrates that polyamines play a significant role in the neuronal damage produced after cerebral ischaemia, while casting doubt on the suggestion that increased locomotor activity correlates with CA1 pyramidal cell damage.

Endothelin-like action of Pausinystalia yohimbe aqueous extract on vascular and renal regional hemodynamics in Sprague Dawley rats

The bark of the African tree Pausinystalia yohimbe has been used as a food additive with aphrodisiac and penile erection enhancing properties. The effect of an aqueous extract of P. yohimbe (CCD-X) on renal circulation was assessed in order to test the hypothesis that it possesses additional effects on nitric oxide production and/or endothelin-1 (ET-1)-like actions. In vivo studies with CCD-X in Sprague Dawley rats demonstrated a dose-dependent (1-1000 ng/kg) increase in mean blood pressure (p < 0.001) and an increase in medullary blood flow (MBF) (p < 0.001). Both the pressor action and renal medullary vasodilation were blocked by endothelinA (ETA) receptor antagonist BMS182874 and endothelinB (ETB) receptor antagonist BQ788 in combination. L-Nomega-nitro-l-arginine methyl ester (L-NAME; 10 mg/kg) also inhibited the increase in MBF induced by CCD-X. In vitro studies in isolated perfused kidney and in pressurized renal microvessels confirmed the dose-dependent vasoconstrictor action of this extract. ETA receptor antagonist BQ610 and ETB receptor antagonist BQ788 separately and significantly attenuated the renal vasoconstrictor actions of the extract (p < 0.001 ANOVA). These preliminary observations indicate that, in addition to the alpha-adrenergic antagonist actions that characterize yohimbine, CCD-X possesses endothelin-like actions and affects nitric oxide (NO) production in renal circulation. These findings suggest a strong possibility of post-receptor cross-talk between alpha2-adrenoceptors and endothelin, as well as a direct effect of alpha2-adrenoceptors on renal NO production.

Fluorescence detection-based functional assay for high-throughput screening for MraY

We have developed a novel assay specific to MraY, which catalyzes the first membrane step in the biosynthesis of bacterial cell wall peptidoglycan. This was accomplished by using UDP-MurNAc-N(epsilon)-dansylpentapeptide, a fluorescent derivative of the MraY nucleotide substrate, and a partially purified preparation of MraY solubilized from membranes of an Escherichia coli overproducing strain. Two versions of the assay were developed, one consisting of the high-pressure liquid chromatography separation of the substrate and product (dansylated lipid I) and the other, without separation and adapted to the high-throughput format, taking advantage of the different fluorescence properties of the nucleotide and lipid I in the reaction medium. The latter assay was validated with a set of natural and synthetic MraY inhibitors.

Endothelin ETA receptor antagonist did not affect development of tolerance to glyceryl trinitrate in rat

Glyceryl trinitrate (GTN), extensively used for the treatment of cardiovascular disorders, is associated with rapid development of tolerance. The exact mechanism responsible for tolerance development to GTN is still not known. Recently, it has been demonstrated that GTN tolerance is associated with increased expression of endothelin (ET). This study was carried out to determine the effect of ET(A) receptor antagonist, BMS182874, on the development of tolerance to GTN in urethane-anaesthetized rats. Diastolic blood pressure (DBP), systolic blood pressure (SBP) and heart rate (HR) were continuously recorded in vehicle- and BMS182874 (3 mg kg(-1), i.v.)-treated rats. GTN was infused at the rate of 10 microg min(-1), intravenously for 4 h. Tolerance to GTN was determined using challenge doses of GTN (10, 30 and 90 microg, i.v.). GTN produced a fall in DBP, SBP and an increase in HR. In vehicle-treated rats, the fall in SBP before induction of GTN tolerance was 28 +/- 2, 43 +/- 4 and 52 +/- 4 mmHg with 10, 30 and 90 microg GTN, respectively. However, following GTN infusion (10 microg min(-1), i.v. for 4 h) a rapid development of tolerance was observed and the fall in SBP was 1 +/- 1, 9 +/- 4 and 15 +/- 4 mmHg with 10, 30 and 90 microg GTN, respectively. Similarly, in BMS182874-treated rats the fall in SBP in non-tolerant rats was 28 +/- 4, 42 +/- 4 and 48 +/- 5 mmHg with 10, 30 and 90 microg GTN, respectively. In BMS182874-treated rats following GTN infusion (10 microg min(-1), i.v. for 4 h) a rapid development of tolerance was observed and the fall in SBP was 4 +/- 3, 10 +/- 2 and 13 +/- 4 mmHg with 10, 30 and 90 microg GTN, respectively. The decrease in DBP and SBP in vehicle- and BMS182874-treated GTN-tolerant rats was statistically similar. These results suggest that ET(A) receptor antagonist BMS182874 did not affect development of tolerance to GTN in rats.

ETA receptor mediates altered leukocyte-endothelial cell interaction and adhesion molecules expression in DOCA-salt rats

Leukocyte adhesion to endothelial cells plays a key role in inflammatory processes associated with end-organ injury. Endothelin-1 (ET-1), which stimulates inflammatory processes, contributes to cardiovascular damage in deoxycorticosterone (DOCA)-salt hypertension. We investigated whether ETA receptor blockade modulates in vivo leukocyte-endothelial cell interactions and expression of cell adhesion molecules (CAM) involved in these processes. DOCA-salt and control uninephrectomized rats were treated with the ETA antagonist BMS182874 (40 mg/kg per day) or vehicle. Analysis of CAMs expression by reverse transcription-polymerase chain reaction and immunohistochemistry showed increased cardiac platelet selectin (P-selectin), detected mainly in endothelial cells, and vascular cell adhesion molecule-1 (VCAM-1), but not intercellular adhesion molecule-1 (ICAM-1), in DOCA-salt rats. Cardiac expression of endothelial selectin (E-selectin) was decreased, whereas immunoreactivity to ED-1 and myeloperoxidase (MPO) activity, markers of macrophage and leukocyte infiltration, respectively, were increased in DOCA-salt. Leukocyte-endothelial cell interaction, functionally assessed in venules of internal spermatic fascia by intravital microscopy, was significantly altered in DOCA-salt rats as evidenced by increased leukocyte adhesion and decreased rolling. BMS182874 treatment normalized leukocyte-endothelium interactions, decreased cardiac VCAM-1 expression in DOCA and control groups, and had no effects on ICAM-1 expression. BMS182874 also increased E-selectin and abolished P-selectin expression in DOCA-salt, but not in control rats. The ETA antagonist reduced cardiac ED-1 content and MPO activity and prevented cardiac damage in DOCA-salt rats. These data indicate that ET-1 participates, via activation of ETA receptors, in altered leukocyte-endothelial cell interactions in DOCA-salt rats, possibly by modulating expression of CAMs, and that the inflammatory status is associated with cardiac damage in mineralocorticoid hypertension.

Dansylated analogues of the opioid peptide [Dmt1]DALDA: in vitro activity profiles and fluorescence parameters

Dansylated analogues of the potent and selective micro opioid peptide agonist [Dmt(1)]DALDA (H-Dmt-D-Arg-Phe-Lys-NH(2); Dmt = 2',6'-dimethyltyrosine) were prepared either by substitution of N(beta)-dansyl-alpha,beta-diaminopropionic acid or N(epsilon)-dansyllysine for Lys(4), or by attachment of a dansyl group to the C-terminal carboxamide function via a linker. All three analogues displayed high micro agonist potency in vitro and the C-terminally dansylated one retained significant micro receptor selectivity. The three analogues showed interesting differences in their fluorescence emission maxima and quantum yields, indicating that the dansyl group in two of them was engaged in intramolecular hydrophobic interactions. These dansylated [Dmt(1)]DALDA analogues represent valuable tools for binding studies, cellular uptake and intracellular distribution studies, and tissue distribution studies.

ETA receptor blockade decreases vascular superoxide generation in DOCA-salt hypertension

Development and progression of end-organ damage in hypertension have been associated with increased oxidative stress. Superoxide anion accumulation has been reported in deoxycorticosterone acetate (DOCA)-salt hypertension, in which endothelin-1 plays an important role in cardiovascular damage. We hypothesized that blockade of ETA receptors in DOCA-salt rats would decrease oxidative stress. Both systolic blood pressure (SBP, 210+/-9 mm Hg; P<0.05) and vascular superoxide generation in vivo were increased in DOCA-salt (44.9+/-10.3% of ethidium bromide-positive nuclei; P<0.05) versus control uninephrectomized (UniNx) rats (118+/-3 mm Hg; 18.5+/-3%, respectively). In DOCA-salt rats, the ETA antagonist BMS 182874 (40 mg/kg per day PO) lowered SBP (170+/-4 versus UniNx, 120+/-3 mm Hg) and normalized superoxide production (21.7+/-6 versus UniNx, 11.9+/-7%). Vitamin E (200 mg/kg per day PO) decreased superoxide formation in DOCA-salt rats (18.8+/-7%) but did not alter SBP. Oxidative stress in nonstimulated circulating polymorphonuclear cells (PMNs) or in PMNs treated with zymosan, an inducer of superoxide release, was similar in DOCA-salt and UniNx groups. Superoxide formation by PMNs was unaffected by treatment with BMS 182874. Western blot analysis showed increased nitrotyrosine-containing proteins in mesenteric vessels from DOCA-salt compared with UniNX. Treatment with either BMS 182874 or vitamin E abolished the differences in vascular nitrotyrosine-containing proteins between DOCA-salt and UniNX. Maximal relaxation to acetylcholine was decreased in DOCA-salt aortas (75.8+/-4.2% versus UniNx, 95.4+/-1.9%, P<0.05). BMS 182874 treatment increased acetylcholine-induced relaxation in DOCA-salt aortas to 93.5+/-4.5%. These in vivo findings indicate that increased vascular superoxide production is associated with activation of the endothelin system through ETA receptors in DOCA-salt hypertension, in apparently blood pressure-independent fashion.

Aggregation of human platelets in plasma by porcine blood cells in vitro is probably mediated by thrombin generation

The infusion of pig progenitor cells into baboons is associated with a thrombotic microangiopathy probably related to the interaction of these cells with the baboon endothelial cells and platelets. We have shown previously that pig peripheral blood mononuclear cells (p-PBMC), are able to activate the human coagulation cascade as they are able to generate thrombin when added to defibrinated plasma. In this work, we have tested the interaction of p-PBMC with human platelets to assess the capacity of p-PBMC to cause platelet aggregation and the possible role of complement activation in this aggregation. Human platelet aggregation assays, using collagen (1 or 2 microg/ml), were performed with platelets in platelet-rich plasma (PRP) or platelets washed by filtration. PRP or washed platelets were also incubated with p-PBMC or human PBMC (h-PBMC) at several concentrations and aggregation was measured. The effect of Dansylarginine N-(3-ethyl-1,5-pentanediyl)amide (DAPA), an inhibitor of thrombin, was studied on platelet aggregation caused by the pig cells. Complement activation was measured by deposition of fragment c derived from C3 splitting (C3c) on pig cells incubated with citrated platelet poor plasma (PPP). When human PRP was incubated with p-PBMC, aggregation was a consistent event quantitatively similar to that induced by collagen. No aggregation of washed platelets was observed when these were incubated with p-PBMC or h-PBMC. Aggregation of human platelets in PRP, induced by p-PBMC, was inhibited when DAPA (100 microm) was added to the incubation mixture (23%), indicating that the thrombin inhibitor blocked the capacity of p-PBMC to aggregate human platelets. No deposition of C3c fragments on p-PBMC was detected when the porcine cells were incubated for up to 20 min with citrated PPP. The fact is that p-PBMC induces human platelet aggregation in plasma being thrombin generation a likely explanation for this observation. Our data suggest that, in the system assayed, complement activation is not a cause of platelet aggregation. These findings are relevant for the clarification of the reported thrombotic microangiopathy complicating the intravenous infusion of pig cells in primates in attempts to induce pig tolerance in baboons.

Endothelin antagonism on aldosterone-induced oxidative stress and vascular remodeling

Endothelin A (ETA) receptor blockade has prevented vascular remodeling in aldosterone and salt-induced hypertension. To evaluate effects of the ETA receptor antagonist, BMS 182874, compared with the aldosterone antagonist, spironolactone, on vascular remodeling in aldosterone-infused rats not exposed to a high salt diet, Sprague-Dawley rats were infused subcutaneously with aldosterone (0.75 microg/h) and treated with BMS 182874 (40 mg. kg-1. d-1), spironolactone, or hydralazine (both 25 mg. kg-1. d-1) while receiving a normal salt diet for 6 weeks. Aldosterone increased systolic BP (P<0.01), plasma endothelin (3.33+/-0.32 versus 1.85+/-0.40 pmol/L in control, P<0.05), systemic oxidative stress as shown by plasma thiobarbituric acid-reacting substances and vascular nicotinamide adenine dinucleotide phosphate (NADPH) activity. Aldosterone increased small artery media thickness (17.7+/-0.9 versus 13.6+/-0.8 microm in control, P<0.05) and media/lumen ratio (7.6+/-0.4 versus 5.5+/-0.4% in control, P<0.05), with growth index of 21% indicating hypertrophic remodeling. Laser confocal microscopy showed increased collagen and fibronectin deposition and intercellular adhesion molecule-1 (ICAM-1) content in the vessel wall of aldosterone-infused rats. The 3 treatments lowered BP, although hydralazine was slightly less effective. BMS 182874 and spironolactone decreased oxidative stress, normalized the hypertrophic remodeling, decreased collagen and fibronectin deposition, and reduced ICAM-1 abundance in the vascular wall of aldosterone-infused rats, whereas hydralazine only reduced NADPH activity in aorta but did not affect the remaining parameters. Vascular remodeling of small arteries occurs in aldosterone-infused rats exposed to a normal salt diet and may be mediated in part by ET-1 via stimulation of ETA receptors. Endothelin blockade may exert beneficial effects on vascular remodeling, fibrosis, oxidative stress, and adhesion molecule expression in aldosterone-induced hypertension.

Endothelin receptor antagonists restore morphine analgesia in morphine tolerant rats

Several neurotransmitter mechanisms have been proposed to play a role in the development of morphine tolerance. The present study provides evidence for the first time that endothelin (ET) antagonists can restore morphine analgesia in morphine tolerant rats. Tolerance to morphine was induced by subcutaneous implantation of six morphine pellets during a 7-day period. The degree of tolerance to morphine was measured by determining analgesic response (tail-flick latency) and hyperthermic response to morphine sulfate (8 mg/kg, subcutaneously (s.c.)) in placebo and morphine pellet implanted rats. The maximal tail-flick latency in morphine pellet-vehicle treated rats (7.54 s) was significantly lower (P<0.05) when compared to placebo pellet-vehicle treated rats (10s), indicating that tolerance developed to the analgesic effect of morphine. In separate sets of experiments, ET antagonists, BQ123 (10 microg, intracerebroventricularly (i.c.v.)) and BMS182874 (50 microg, i.c.v.) were administered in placebo and morphine tolerant rats. BQ123 was injected twice daily for 7 days and once on day 8. BMS182874 was administered only on day 8. Morphine (8 mg/kg, s.c.) was administered 30min after BQ123 or BMS182874 administration. It was found that both BQ123 and BMS182874 potentiated morphine analgesia in placebo and morphine tolerant rats. BQ123 potentiated tail-flick latency by 30.0% in placebo tolerant rats and 94.5% in morphine tolerant rats compared to respective controls. BMS182874 potentiated tail-flick latency by 30.2% in placebo tolerant rats and 66.7% in morphine tolerant rats. Morphine-induced hyperthermic effect was also potentiated by BQ123 and BMS182874. The duration of analgesic action was also prolonged by BQ123 and BMS182874. The effect of BMS182874 was less as compared to BQ123. BQ123 and BMS182874 are selective ET(A) receptor antagonists. Therefore, it is concluded that ET(A) receptor antagonists restore morphine analgesia in morphine tolerant rats.

Cardiac fibrosis occurs early and involves endothelin and AT-1 receptors in hypertension due to endogenous angiotensin II

OBJECTIVES

We investigated if endothelin (ET)-1 and the renin-angiotensin-aldosterone system play a role in cardiac fibrosis.

BACKGROUND

Angiotensin II (Ang II) can induce cardiac fibrosis, but the underlying mechanisms are incompletely understood.

METHODS

Four-week-old transgenic (mRen2)27 rat (TGRen2) received for four weeks a placebo, the mixed ET(A)/ET(B) endothelin receptor antagonist bosentan, the angiotensin II type I receptor (AT-1) antagonist irbesartan, the ET(A) endothelin receptor antagonist BMS-182874, and a combined treatment with irbesartan plus BMS-182874. We measured collagen density on Sirius red-stained serial sections of the left ventricle (LV) with a photomicroscope equipped with specific software and assessed the gene expression of procollagen alpha1(I), atrial natriuretic peptide (ANP), transforming growth factor-beta 1 (TGFbeta1), endothelin converting enzyme, and ET(B) receptor.

RESULTS

In the placebo group, hypertension was associated with LV hypertrophy and cardiac fibrosis (LV weight: 4.0 +/- 0.3 mg/g body weight; collagen density: 2.21 +/- 0.16%), which were all prevented with irbesartan (2.3 +/- 0.1, 1.30 +/- 0.13, p < 0.001), but not with BMS-182874 (4.0 +/- 0.2, 2.41 +/- 0.22). Bosentan also prevented fibrosis (1.39 +/- 0.18) but not hypertension and LV hypertrophy (3.38 +/- 0.27). Combined irbesartan and BMS-182874 treatment prevented LV hypertrophy (2.9 +/- 0.1) but not fibrosis (2.52 +/- 0.16). Collagen density correlated (r = 0.414, p < 0.05) with plasma aldosterone levels. In TGRen2 with LV hypertrophy, the gene expression of ANP and ET(B) but not that of TGFbeta1 and procollagen alpha1(I) was increased.

CONCLUSIONS

In Ang II-dependent hypertension, cardiac fibrosis was associated with LV hypertrophy and was hindered by both mixed ET(A)/ET(B) blockade and AT-1 blockade. Only the latter treatment prevented both hypertension and LV hypertrophy. Thus, there is a dissociation between the mechanisms of cardiac fibrosis and hypertension, which do and do not entail ET-1, respectively.

Endothelin-1-induced vasospasms of spiral modiolar artery are mediated by rho-kinase-induced Ca(2+) sensitization of contractile apparatus and reversed by calcitonin gene-related Peptide

BACKGROUND AND PURPOSE

Vasospasms of the spiral modiolar artery may cause an ischemic stroke of the inner ear that manifests itself by a sudden hearing loss. Previously we have shown that endothelin-1 (ET-1) induces vasospasms of the spiral modiolar artery. Here we tested the hypotheses that ET-1-induced vasospasms are (1) reversible by ET(A) receptor antagonists; (2) mediated by a Ca(2+) sensitization of the contractile apparatus via a Rho-kinase-induced inhibition of myosin light chain phosphatase; and (3) reversible by the vasodilator calcitonin gene-related peptide (CGRP).

METHODS

The Ca(2+) sensitivity of the contractile apparatus was evaluated by correlation between the smooth muscle cell Ca(2+) concentration and the vascular diameter, which were measured by microfluorometry with the fluorescent dye fluo-4 and videomicroscopy, respectively.

RESULTS

ET-1-induced vasospasms were prevented but not reversed by the ET(A) receptor antagonists BQ-123 and BMS-182874. The Ca(2+) sensitivity of the contractile apparatus was increased by ET-1 and by inhibition of myosin light chain phosphatase with calyculin A and was decreased by CGRP. ET-1-induced vasospasms and Ca(2+) sensitization were prevented and reversed by the Rho-kinase antagonist Y-27632 and by CGRP.

CONCLUSIONS

ET-1 induces vasospasms of the spiral modiolar artery via ET(A) receptor-mediated activation of Rho-kinase, inhibition of myosin light chain phosphatase, and an increase in Ca(2+) sensitivity, which is reversed by CGRP. The observation that vasospasms were reversed by Y-27632 but not by BQ-123 or BMS-182874 suggests that Rho-kinase, rather than the ET(A) receptor, is the most promising pharmacological target for the treatment of ET-1-induced vasospasms, ischemic strokes, and sudden hearing loss.

Fluorescence changes on contractile activation in TnC(DANZ) labeled skinned rabbit psoas fibers

The increase in fluorescence of dansylaziridine (DANZ) labeled troponin C (TnC(DANZ) substituted into skinned rabbit psoas fibers was determined as a function of the pCa. The fluorescence data are expressed as the ratio of two wavelength bands, one that sees the fluorescence of TnC(DANZ), and one that sees background fluorescence and scatter. The percent TnC replaced with TnC(DANZ) was varied between 10 and 50% and, the fibers were randomly stretched, at the start of each experiment, between 10 and 50%. A large ratio increase accompanies increase in [Ca2+]. The pCa/force data are best fit by the Hill equation but the pCa/ratio data are best fit by a model in which Ca2+ binds in two phases. The position of the force curve on the pCa axis varies little between fibers, in contrast to that of the ratio or A-fluorescence curve. In accord with previous reports the delta-fluorescence can be left of the force on the pCa axis (type I) or superimpose in part on the force (type II). Not described previously, we find curves in which the second phase of the ratio cross-over the pCa/force curve. This type III relationship is found only in fibers less than 3 weeks postmuscle harvest. We propose that the first, relatively invariant, phase of the biphasic pCa/ratio curve accompanies Ca2+ binding to either of the two low affinity sites on TnC(DANZ) as it does for TnC in solution. The second, highly cooperative, phase of the ratio curve that accompanies muscle contraction and enhanced Ca2+ binding is initiated when sufficient Ca2+ is bound to overcome inhibitory systems. Loose coupling between the initial Ca2+ binding and the cooperative switch point may account for much of the variation in the shape and position of the pCa/ratio curve. There is evidence that, in the overlap zone, weakly attached myosin cross-bridges enhance cooperation between the regulatory units of the thin filaments.

Contribution of endothelin-1 to renal activator protein-1 activation and macrophage infiltration in aldosterone-induced hypertension

Aldosterone-induced hypertension is associated with renal damage that may be mediated by endothelin-1 (ET-1). We evaluated whether inflammatory cell infiltration and DNA-binding activity of the transcription factors nuclear factor kappa B (NF-kappa B) and activator protein-1 (AP-1) were increased in kidneys from aldosterone-infused rats. The role of ET-1 in these processes was evaluated by treating rats with the ET(A)-receptor blocker, BMS 182874. Rats were infused with aldosterone (0.75 microg/h) via a mini-osmotic pump and were given 1% NaCl in the drinking water in the absence and presence of BMS 182874 or of the aldosterone receptor blocker, spironolactone. Renal sections were used to assess inflammatory cell infiltration, which was identified immunocytochemically using monoclonal antibodies against macrophages (ED1+). Electrophoretic mobility shift assays evaluated the DNA-binding activity of NF-kappa B and AP-1 in renal tissue. Systolic blood pressure (BP) was increased in the aldosterone-infused group compared with controls (123+/-6 versus 110+/-10 mmHg, P<0.05). BMS 182874 and spironolactone significantly decreased BP (P<0.05). Macrophage infiltration was increased in the kidneys of aldosterone-infused rats compared with controls. Renal binding activity (arbitrary units) of AP-1, in contrast with that of NF-kappa B, increased in aldosterone-infused rats compared with control rats (AP-1, 4.2+/-0.3 versus 1.0+/-0.1, P<0.05; NF-kappa B, 1.6+/-0.5 versus 1.2+/-0.5). BMS 182874 and spironolactone decreased macrophage infiltration (by 70% and 50% respectively) and AP-1 binding activity (1.0+/-0.3 and 0.8+/-0.3 respectively). In conclusion, kidneys from aldosterone-infused rats exhibited macrophage infiltration and increased AP-1 DNA-binding activity. These processes were attenuated by BMS 182874. Our findings suggest that renal damage in aldosterone-dependent hypertension is associated with inflammatory processes that are mediated in part via ET-1.

Elevated mean arterial pressure in the ovariectomized rat was normalized by ET(A) receptor antagonist therapy: absence of cardiac hypertrophy and fibrosis

1. The influence of menopause on ventricular function and remodelling remains undefined. The following study examined the effect of ovariectomy on ventricular contractility, cardiac hypertrophy and extracellular matrix protein expression. 2. Elevated circulating levels of the vasoconstrictor endothelin-1 have been reported in post-menopausal women. Moreover, endothelin-1 has been shown to influence blood pressure, ventricular function and cardiac remodelling. In this regard, the potential pathophysiological role of endothelin-1 in the ovariectomized rat was assessed via the administration of the selective endothelin(A) receptor (ET(A)) antagonist BMS-182874. 3. In 3 and 6 week ovariectomized female Sprague - Dawley rats, uterus atrophy was associated with a significant increase in mean arterial pressure, and left ventricular systolic pressure, as compared to sham. By contrast, right ventricular contractile indices were normal in the ovariectomized rat. Despite increased systolic load, left ventricular hypertrophy was not evident, prepro-atrial natriuretic peptide (prepro-ANP) mRNA levels and collagen protein content were similar to sham. 4. The treatment of ovariectomized rats with BMS-182874 (60 mg kg(-1) per day) did not reverse uterus atrophy. However, BMS-182874 normalized mean arterial pressure, and left ventricular systolic pressure in the ovariectomized rat. 5. Thus, despite elevated blood pressure, ovariectomized rats were not associated with either cardiac hypertrophy or fibrosis. Lastly, endothelin-1, acting via the stimulation of the ET(A) receptor represents an integral mechanism implicated in the increase of mean arterial pressure following ovariectomy.

Aortic smooth muscle cell phenotypic modulation and fibrillar collagen deposition in angiotensin II-dependent hypertension

BACKGROUND

We investigated the effect of nifedipine, AT-1 and ET-1 receptor blockade on arterial smooth muscle cell phenotypes and collagen deposition in TGRen2 transgenic rat (TGR).

METHODS

Four-week-old TGR were blood pressure (BP)-matched and allocated to receive a placebo (n=8), the calcium antagonist nifedipine (n=6), the AT-1 specific receptor antagonist irbesartan (n=6), the ET(A)/ET(B) antagonist bosentan (n=6) or the ET(A)-selective antagonist BMS-182874 (n=5). Sprague-Dawley normotensive rats served as controls (n=6). After 4 weeks of treatment animals were euthanized and the left ventricle (LV) and the structural changes in intracardiac arterioles and aorta were assessed histomorphometrically. Smooth muscle cell phenotypes and fibrillar collagen content of the aortic wall were evaluated by immunostaining, using differentiation markers-specific antibodies and Syrius red staining, respectively. The changes in ET(A) and ET(B) receptor density were also assessed with quantitative autoradiography.

RESULTS

Compared to placebo, only irbesartan lowered BP (P<0.001) and prevented LV and small resistance artery hypertrophy. The aorta of placebo-treated TGR showed an increase in foetal-type smooth muscle cell content and fibrillar collagen staining, compared to controls. These changes were blunted by irbesartan, which increased ET(A) receptors in the arterial wall, enhanced by BMS-182874 and unaffected by bosentan. Nifedipine also blunted both the VSMC and collagen changes despite having no effect on BP and ET(A) receptors.

CONCLUSIONS

In TGRen2, vascular hypertrophy entails both smooth muscle cell phenotypic modulation and collagen deposition. These alterations do not follow closely the BP changes and seem to imply the dihydropyridine-sensitive calcium channels.

Cardiac and vascular fibrosis and hypertrophy in aldosterone-infused rats: role of endothelin-1

Increased endothelin-1 (ET-1) or aldosterone may be associated with promotion of cardiovascular hypertrophy and fibrosis. We evaluated whether the selective ETA receptor-antagonist BMS 182874 (BMS) prevents cardiac and vascular collagen deposition and hypertrophy in aldosterone-infused rats. Rats received subcutaneous aldosterone (0.75 microg/h) and 1% sodium chloride in drinking water +/- BMS (40 mg/kg per day in food) for 6 weeks. Heart and aorta were cross-sectioned and stained with Sirius red. Heart weight did not change with either aldosterone infusion or BMS treatment. Cardiac and aortic interstitial and perivascular collagen were quantified with videomorphometry. Aortic collagen and media cross-sectional area were significantly increased 3.5-fold (P < .01) and 1.13-fold (P < .05), respectively, with aldosterone infusion and decreased in BMS-treated rats (P < .05, P < .001, respectively). Aldosterone infusion increased interstitial and perivascular collagen in the left (1.6- and 2.7-fold, P < .05 and P < .01, respectively) and right ventricle (1.5- and 1.7-fold, P > .05 and P < .05, respectively). BMS prevented collagen deposition except for interstitial collagen in the right ventricle. Cardiac and aortic fibrosis were significantly increased in aldosterone-infused hypertensive rats. The ETA receptor antagonist prevented cardiac and aortic collagen deposition and aortic hypertrophy. This suggests a role for ET-1 in fibrosis of heart and large vessels in conditions associated with mineralocorticoid excess.

Recombinant tissue factor pathway inhibitor prevents lipopolysaccharide-induced systemic hypotension in rats by inhibiting excessive production of nitric oxide

Excessive production of nitric oxide (NO) by the inducible form of NO synthase (iNOS) plays a key role in the development of endotoxin shock. Tumor necrosis factor-alpha (TNF-alpha) induces iNOS, thereby contributing to the development of shock. We recently reported that recombinant tissue factor pathway inhibitor (r-TFPI), an important inhibitor of the extrinsic pathway of the coagulation system, inhibits TNF-alpha production by monocytes. In this study, we investigated whether r-TFPI could ameliorate hypotension by inhibiting excessive production of NO in rats given lipopolysaccharide (LPS). Pretreatment of animals with r-TFPI prevented LPS-induced hypotension. Recombinant TFPI significantly inhibited the increases in both the plasma levels of NO2-/NO3- and lung iNOS activity 3 h after LPS administration. Expression of iNOS mRNA in the lung was also inhibited by intravenous administration of r-TFPI. However, neither DX-9065a, a selective inhibitor of factor Xa, nor an inactive derivative of factor VIIa (DEGR-F.Vlla) that selectively inhibits factor VIIa activity, had any effect on LPS-induced hypotension despite their potent anticoagulant effects. Moreover, neither the plasma levels of NO2-/NO3- nor lung iNOS activity were affected by administration of DX-9065a and DEGR-F.VIIa. These results suggested that r-TFPI ameliorates LPS-induced hypotension by reducing excessive production of NO in rats given LPS and this effect was not attributable to its anticoagulant effects, but to the inhibition of TNF-alpha production.

Predicting and harnessing protein flexibility in the design of species-specific inhibitors of thymidylate synthase

BACKGROUND

Protein plasticity in response to ligand binding abrogates the notion of a rigid receptor site. Thus, computational docking alone misses important prospective drug design leads. Bacterial-specific inhibitors of an essential enzyme, thymidylate synthase (TS), were developed using a combination of computer-based screening followed by in-parallel synthetic elaboration and enzyme assay [Tondi et al. (1999) Chem. Biol. 6, 319-331]. Specificity was achieved through protein plasticity and despite the very high sequence conservation of the enzyme between species.

RESULTS

The most potent of the inhibitors synthesized, N,O-didansyl-L-tyrosine (DDT), binds to Lactobacillus casei TS (LcTS) with 35-fold higher affinity and to Escherichia coli TS (EcTS) with 24-fold higher affinity than to human TS (hTS). To reveal the molecular basis for this specificity, we have determined the crystal structure of EcTS complexed with DDT and 2'-deoxyuridine-5'-monophosphate (dUMP). The 2.0 A structure shows that DDT binds to EcTS in a conformation not predicted by molecular docking studies and substantially differently than other TS inhibitors. Binding of DDT is accompanied by large rearrangements of the protein both near and distal to the enzyme's active site with movement of C alpha carbons up to 6 A relative to other ternary complexes. This protein plasticity results in novel interactions with DDT including the formation of hydrogen bonds and van der Waals interactions to residues conserved in bacterial TS but not hTS and which are hypothesized to account for DDT's specificity. The conformation DDT adopts when bound to EcTS explains the activity of several other LcTS inhibitors synthesized in-parallel with DDT suggesting that DDT binds to the two enzymes in similar orientations.

CONCLUSIONS

Dramatic protein rearrangements involving both main and side chain atoms play an important role in the recognition of DDT by EcTS and highlight the importance of incorporating protein plasticity in drug design. The crystal structure of the EcTS/dUMP/DDT complex is a model system to develop more selective TS inhibitors aimed at pathogenic bacterial species. The crystal structure also suggests a general formula for identifying regions of TS and other enzymes that may be treated as flexible to aid in computational methods of drug discovery.

Studies toward the site specific incorporation of sugars into proteins: synthesis of glycosylated aminoacyl-tRNAs

A series of glycosylated serine derivatives was synthesized from peracetylated sugars and Fmoc-protected serine; these were chemically esterified with the tris-(tetrabutylammonium) salt of pdCpA. The fully protected and deprotected glycosylated aminoacyl pdCpAs were ligated enzymatically to an abbreviated tRNA (tRNA-C(OH)) to provide the title compounds that are key intermediates in the elaboration of glycoproteins using readthrough of a nonsense codon.

Role of NO and cytochrome P-450-derived eicosanoids in ET-1-induced changes in intrarenal hemodynamics in rats

Endothelin-1 (ET-1) produces potent renal effects that we have previously shown to be dependent on cytochrome P-450 (CYP450) metabolites of aracidonic acid (24) This study evaluated the role of these metabolites in the effects produced by ET-1 on renal blood flow (RBF), cortical blood flow (CBF), medullary blood flow (MBF), and mean arterial blood pressure (MBP). ET-1 (20-200 pmol/kg) increased MBP, renal vascular resistance (RVR), and MBF but reduced CBF and RBF in a dose-dependent manner. The decreases in CBF and RBF, and increases in MBP and RVR were blunted by BMS-182874, an ET(A) receptor antagonist or BQ-788, an ET(B) receptor antagonist. Similarly, indomethacin, an inhibitor of cyclooxygenase activity, or 12,12-dibromododecenoic acid (DBDD), a CYP450-dependent inhibitor of production of 20-hydroxyeicosatetraenoic acid (20-HETE), blunted these effects. ET-3 elicited dose-related reduction in CBF and increase in MBF. Indomethacin accentuated the reduction in CBF and attenuated the increase in MBF, as did DBDD. ET-1-induced increase in MBF was attenuated by BQ-788, N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, indomethacin, or DBDD. DBDD inhibited the hemodynamic effects of L-NAME. Miconazole, the inhibitor of CYP450-dependent epoxygenase activity, was without effect. These results indicate that hemodynamic changes produced by ET-1 are mediated by vasoconstrictor prostanoids and/or prostanoid-like substances, possibly, 20-HETE via activation of ET(A) and ET(B) receptors. However, the increase in MBF is mediated by vasodilator prostanoids or by NO via ET(B) receptor activation.

Recombinant tissue factor pathway inhibitor reduces lipopolysaccharide-induced pulmonary vascular injury by inhibiting leukocyte activation

Tissue factor pathway inhibitor (TFPI) is an important physiologic inhibitor of the extrinsic pathway of the coagulation system. We investigated whether recombinant TFPI (rTFPI) could reduce pulmonary vascular injury by inhibiting leukocyte activation in rats given lipopolysaccharide (LPS). Pre- or posttreatment of animals with rTFPI significantly inhibited LPS-induced pulmonary vascular injury, as well as coagulation abnormalities. rTFPI significantly inhibited increases in lung tissue levels of tumor necrosis factor (TNF)-alpha, cytokine-induced neutrophil chemoattractant, and myeloperoxidase. Expression of TNF-alpha messenger RNA in the lung after LPS administration was significantly reduced by rTFPI administration. However, neither DX-9065a, a selective inhibitor of Factor Xa, nor recombinant Factor VIIa treated with dansyl-glutamylglycylarginyl-chloromethyl ketone, a selective inhibitor of Factor VIIa, had any effects on LPS-induced pulmonary vascular injury despite their potent anticoagulant effects. rTFPI significantly inhibited TNF-alpha production by LPS-stimulated monocytes in vitro. rTFPI also significantly inhibited several formyl-Met-Leu-Phe-induced neutrophil functions, as well as increases in the expression of CD11b and CD18 on the neutrophil cell surface in vitro. Additionally, rTFPI inhibited increases in levels of intracellular calcium, a second messenger of neutrophil activation, in formyl-Met-Leu-Phe-stimulated neutrophils in vitro. These results strongly suggested that rTFPI reduces pulmonary vascular injury by inhibiting leukocyte activation, as well as coagulation abnormalities in rats given LPS.