Exisulind, a novel proapoptotic drug, inhibits rat urinary bladder tumorigenesis

Exisulind (Aptosyn) is a novel antineoplastic drug being developed for the prevention and treatment of precancerous and malignant diseases. In colon tumor cells, the drug induces apoptosis by a mechanism involving cyclic GMP (cGMP) phosphodiesterase inhibition, sustained elevation of cGMP, and protein kinase G activation. We studied the effect of exisulind on bladder tumorigenesis induced in rats by the carcinogen, N-butyl-N-(4-hydroxybutyl) nitrosamine. Exisulind at doses of 800, 1000, and 1200 mg/kg (diet) inhibited tumor multiplicity by 36, 47, and 64% and tumor incidence by 31, 38, and 61%, respectively. Experiments on the human bladder tumor cell line, HT1376, showed that exisulind inhibited growth with a GI(50) of 118 microM, suggesting that the antineoplastic activity of the drug in vivo involved a direct effect on neoplastic urothelium. Exisulind also induced apoptosis as determined by DNA fragmentation, caspase activation, and morphology. Analysis of phosphodiesterase (PDE) isozymes in HT1376 cells showed PDE5 and PDE4 isozymes that were inhibited by exisulind with IC(50)s of 112 and 116 microM, respectively. Inhibition of PDE5 appears to be pharmacologically relevant, because treatment of HT1376 cells increased cGMP and activated protein kinase G at doses that induce apoptosis, whereas cyclic AMP levels were not changed. Immunocytochemistry showed that PDE5 was localized in discrete perinuclear foci in HT1376 cells. Immunohistochemistry showed that PDE5 was overexpressed in human squamous and transitional cell carcinomas compared with normal urothelium. The data lead us to conclude that future clinical trials of exisulind for human bladder cancer treatment and/or prevention should be considered and suggest a mechanism of action involving cGMP-mediated apoptosis induction.

Protein kinase G activates the JNK1 pathway via phosphorylation of MEKK1

We recently obtained evidence that treatment of human colon cancer cells with exisulind (sulindac sulfone) and related compounds induces apoptosis by activation of protein kinase G (PKG) and c-Jun kinase (JNK1). The present study further explores this mechanism. We demonstrate that in NIH3T3 cells a constitutively active mutant of PKG causes a dose-dependent activation of JNK1 and thereby transactivates c-Jun and stimulates transcription from the AP-1 enhancer element. The activation of JNK1 and the transactivation of c-Jun by this mutant of PKG were inhibited by a dominant negative MEKK1. In vitro assays showed that a purified PKG directly phosphorylated the N-terminal domain of MEKK1. PKG also directly phosphorylated a full-length MEKK1, and this was associated with enhanced MEKK1 phosphorylation. Thus, it appears that PKG activates JNK1 through a novel PKG-MEKK1-SEK1-JNK1 pathway, by directly phosphorylating and activating MEKK1.

Cyclic GMP mediates apoptosis induced by sulindac derivatives via activation of c-Jun NH2-terminal kinase 1

Sulindac sulfone (Exisulind) induces apoptosis and exhibits cancer chemopreventive activity, but in contrast to sulindac, it does not inhibit cyclooxygenases 1 or 2. We found that sulindac sulfone and two potent derivatives, CP248 and CP461, inhibited the cyclic GMP (cGMP) phosphodiesterases (PDE) 2 and 5 in human colon cells, and these compounds caused rapid and sustained activation of the c-Jun NH2-terminal kinase 1 (JNK1). Rapid activation of stress-activated protein/ERK kinase 1 (SEK1) and mitogen-activated protein kinase kinase kinase (MEKK1), which are upstream of JNK1, was also observed. Other compounds that increase cellular levels of cGMP also activated JNK1, and an inhibitor of protein kinase G (PKG), Rp-8-pCPT-cGMPS, inhibited JNK1 activation by the sulindac sulfone derivatives. Expression of a dominant-negative JNK1 protein inhibited CP248-induced cleavage of poly(ADP-ribose) polymerase, a marker of apoptosis. Thus, it appears that sulindac sulfone and related compounds induce apoptosis, at least in part, through activation of PKG, which then activates the MEKK1-SEK1-JNK1 cascade. These studies also indicate a role for cGMP and PKG in the JNK pathway.

Functional identification of phosphodiesterase activity in human trabecular meshwork cells

The phosphodiesterases (PDE) activity in human trabecular meshwork cells (HTM-3) was investigated in this study in order to better understand the signal transduction pathways in the conventional outflow tract of the eye. Agonists (isoproterenol or nitroprusside) were used to stimulate adenylyl cyclase and guanylyl cyclase, respectively, in the absence and presence of nonselective IBMX or PDE5 specific inhibitors E4021 (1). The subcellular distribution of cAMP and cGMP PDEs was determined directly by PDE enzyme assays using HTM-3 cells. Levels of cyclic nucleotides were measured in the same cells by radioimmunoassay (RIA). Isoproterenol alone elevated cAMP levels, and this response was enhanced by IBMX. Nitroprusside alone caused no increase in basal cGMP levels but, in the presence of E4021, nitroprusside produced significant, dose-related elevation of cGMP levels. Subcellular distribution experiments indicated that the greatest activity for PDEs resided in the supernatant fraction. In conclusion, HTM-3 cells contain PDEs that degrade both cyclic nucleotides. The PDE activities reside predominantly in the supernatant, but the PDE activity for degrading cGMP is more pronounced. Moreover, results with E4021 suggest that PDE5 activity could play a critical role in modulating cGMP-related activity in the trabecular meshwork.

Exisulind induction of apoptosis involves guanosine 3',5'-cyclic monophosphate phosphodiesterase inhibition, protein kinase G activation, and attenuated beta-catenin

Sulindac sulfone (exisulind), although a nonsteroidal anti-inflammatory drug derivative, induces apoptosis in tumor cells by a mechanism that does not involve cyclooxygenase inhibition. SW480 colon tumor cells contain guanosine 3',5'-monophosphate (cGMP) phosphodiesterase (PDE) isoforms of the PDE5 and PDE2 gene families that are inhibited by exisulind and new synthetic analogues. The analogues maintain rank order of potency for PDE inhibition, apoptosis induction, and growth inhibition. A novel mechanism for exisulind to induce apoptosis is studied involving sustained increases in cGMP levels and cGMP-dependent protein kinase (PKG) induction not found with selective PDE5 or most other PDE inhibitors. Accumulated beta-catenin, shown to be a substrate for PKG, is decreased by exisulind, suggesting a mechanism to explain apoptosis induction in neoplastic cells harboring adenomatous polyposis coli gene mutations.

Glial cells promote muscle reinnervation by responding to activity-dependent postsynaptic signals

After nerve injury, denervated synaptic sites in skeletal muscle commonly become reinnervated by sprouts that grow from nerve terminals on nearby muscle fibers. These terminal sprouts grow along a glial cell guide or "bridge" formed by Schwann cell (SC) processes that extend from denervated synaptic sites. Data presented here show that most bridges connect innervated and denervated synaptic sites rather than pairs of denervated sites even when most sites in the muscle are denervated. Furthermore, bridges are inhibited by presynaptic or postsynaptic blockade of synaptic transmission, manipulations that do not alter the extent of SC growth. These results show that an activity-dependent postsynaptic signal promotes the formation and/or maintenance of glial bridges and thus muscle reinnervation.

Neonatal partial denervation results in nodal but not terminal sprouting and a decrease in efficacy of remaining neuromuscular junctions in rat soleus muscle

Mature motoneurons respond to partial denervation of their target muscle by sprouting to reinnervate denervated fibers, thus maintaining muscle strength in the face of motoneuronal loss caused by injury or disease. Neonatal motoneurons, however, do not expand to innervate more muscle fibers. The present work seeks to understand this developmental change in motoneuron response to partial denervation. It has been suggested that neonatal motor units cannot increase in size because they are already at their maximum size (approximately five times larger than in adulthood). We ruled out this explanation by showing that after partial denervation on postnatal day 14 (P14), when motor units have decreased to their adult size, motoneurons still did not sprout to reinnervate as many fibers as in adulthood. Instead, we found evidence supporting an alternative explanation involving terminal Schwann cells. After partial denervation of neonatal (but not adult) muscles, terminal Schwann cells at denervated endplates undergo apoptosis. We found that terminal (but not nodal) sprouting was absent in partially denervated neonatal muscles. This finding suggests that terminal Schwann cells, previously reported to guide terminal sprouts to denervated endplates in adult muscles, are necessary for the formation and growth of terminal sprouts. Moreover, partial denervation on P14 severely weakened the remaining, uninjured synapses, suggesting that neonatal motoneurons may withdraw terminals after the denervation of nearby fibers. These findings have implications for the interpretation of previous studies on synapse elimination and offer insight into the failure of young motor units to expand after partial denervation.

Control of cAMP in lung endothelial cell phenotypes. Implications for control of barrier function

Pulmonary microvascular endothelial cells (PMVECs) form a more restrictive barrier to macromolecular flux than pulmonary arterial endothelial cells (PAECs); however, the mechanisms responsible for this intrinsic feature of PMVECs are unknown. Because cAMP improves endothelial barrier function, we hypothesized that differences in enzyme regulation of cAMP synthesis and/or degradation uniquely establish an elevated content in PMVECs. PMVECs possessed 20% higher basal cAMP concentrations than did PAECs; however, increased content was accompanied by 93% lower ATP-to-cAMP conversion rates. In PMVECs, responsiveness to beta-adrenergic agonist (isoproterenol) or direct adenylyl cyclase (forskolin) activation was attenuated and responsiveness to phosphodiesterase inhibition (rolipram) was increased compared with those in PAECs. Although both types of endothelial cells express calcium-inhibited adenylyl cyclase, constitutive PMVEC cAMP accumulation was not inhibited by physiological rises in cytosolic calcium, whereas PAEC cAMP accumulation was inhibited 30% by calcium. Increasing either PMVEC calcium entry by maximal activation of store-operated calcium entry or ATP-to-cAMP conversion with rolipram unmasked calcium inhibition of adenylyl cyclase. These data indicate that suppressed calcium entry and low ATP-to-cAMP conversion intrinsically influence calcium sensitivity. Adenylyl cyclase-to-cAMP phosphodiesterase ratios regulate cAMP at elevated levels compared with PAECs, which likely contribute to enhanced microvascular barrier function.

Multiple cyclic nucleotide phosphodiesterases in human trabecular meshwork cells

PURPOSE

To characterize cyclic nucleotide phosphodiesterase isozyme activities in human trabecular meshwork cells and primary cultures of porcine trabecular meshwork cells.

METHODS

Radioimmunoassay of acetylated acid extracts was used to determine changes in cyclic adenosine monophosphate (cAMP) and cyclic quanosine monophosphate (cGMP) in human trabecular meshwork cells treated with phosphodiesterase isoform selective inhibitors. Cyclic nucleotide phosphodiesterase activities were measured using the two-step radioisotope procedure (Thompson). Enzyme activities in the supernatant of human cells were fractionated using anion-exchange chromatography. Additionally, human and porcine trabecular meshwork cell transcripts of phosphodiesterase family-specific isoforms were studied by reverse transcription-polymerase chain reaction and nucleotide sequencing.

RESULTS

In intact human cells, selective inhibitors for phosphodiesterase 4 (rolipram) and 5 (E4021) gene families were effective in augmenting cyclic nucleotide accumulation in response to isoproterenol or sodium nitroprusside, respectively. cAMP and cGMP hydrolytic activities, resolved using Trisacryl M anion-exchange chromatography, showed a cAMP phosphodiesterase peak that was minimally sensitivity to cGMP but modestly inhibited by rolipram and a cGMP phosphodiesterase peak that was sensitive to inhibition by E4021. Further evaluation of the cGMP phosphodiesterase demonstrated Michaelis-Menten kinetics and competitive inhibition by E4021. Messenger RNA transcripts for phosphodiesterase 4, 5, and 7 isozymes were isolated in human trabecular meshwork cells. However, in porcine trabecular meshwork cells only isozymes for phosphodiesterase 4 and 5 isozymes were detected.

CONCLUSIONS

Human trabecular meshwork cells express phosphodiesterase 4, 5, and 7 gene family isoforms and enzyme activities, suggesting that selective isoform inhibitors could be used to augment the actions of antiglaucoma drugs that use cyclic nucleotides as second messengers.

Schwann cells proliferate at rat neuromuscular junctions during development and regeneration

Terminal Schwann cells (TSCs) cover neuromuscular junctions and are important in the repair and maintenance of these synapses. We have examined how these cells are generated at developing junctions and how their number is regulated during repair of nerve injury. At birth, approximately half of the junctions in rat soleus and extensor digitorum longus muscles have one TSC soma. Somata are absent from the remainder, although Schwann cell (SC) processes arising from somata along the preterminal axon cover almost all of these synapses. By 2 months of age, junctions have gained an additional two to three TSCs. Most of this gain occurs during the first 2 postnatal weeks and largely precedes the expansion of endplate size. Although the initial addition is caused by cell migration, mitotic labeling shows extensive division of TSCs at junctions. A slower addition of TSCs occurs in adult muscles, and TSC number in the adult is correlated with endplate size. During repair of nerve injury, TSC number is regulated by a combination of signals from motor neurons and denervated tissue. As shown previously (Connor et al., 1987), denervation of adult muscles did not, in itself, cause TSC mitosis. However, TSCs became mitotic during reinnervation. Partial denervation induced division of TSCs at innervated but not denervated endplates. A disproportionate number of these mitotic cells were found at endplates contacted by TSC processes extended from nearby denervated endplates, contacts known to promote nerve sprouting. These results show an association between TSC mitotic activity and alterations in synaptic structure during development, sprouting, and reinnervation.

Cyclic GMP and cGMP-binding phosphodiesterase are required for interleukin-1-induced nitric oxide synthesis in human articular chondrocytes

This study addressed the role of guanylyl cyclase (GC) and phosphodiesterase (PDE) in interleukin (IL)-1 activation of human articular chondrocytes. The GC inhibitors LY83583 and methylene blue dose-dependently inhibited IL-1-induced nitric oxide (NO) production, inducible NO synthase (iNOS) protein, and mRNA expression. These effects of GC inhibition were consistent with the rapid induction of cGMP by IL-1, which reached maximal levels after 5 min. The effects of GC inhibitors were selective as they did not reduce IL-1-induced cyclooxygenase II protein and mRNA. An inhibitor specific for soluble GC did not affect IL-1-induced NO production, and activators of soluble GC did not induce NO. However, the expression of iNOS mRNA was induced by atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP), activators of particulate GC, indicating that particulate rather than soluble guanylyl cyclases were involved in iNOS induction. The expression of iNOS mRNA and the production of NO were induced by a slowly hydrolyzable analog of cGMP, 8-bromo-cGMP, but not by nonhydrolyzable analog, dibutyryl cGMP, suggesting that PDE rather than cGMP-dependent protein kinase mediates the cGMP effects. Chondrocytes contained extensive cGMP PDE activity. This had PDE5 biochemical features and an inhibitor profile consistent with PDE5. Furthermore, the nonisoformspecific PDE inhibitor IBMX and PDE5-specific inhibitors suppressed IL-1-induced NO release and iNOS mRNA expression. PDE5 mRNA was constitutively expressed in chondrocytes. In addition to increasing PDE5 activities, IL-1 treatment reduced the sensitivity of PDE5 to several pharmacological inhibitors by up to 50-fold. In summary, inhibitors of either GC or PDE5 prevented IL-1 induction of iNOS; IL-1 increased the rates of both cGMP generation and hydrolysis; and exogenous PDE hydrolyzable cGMP analog induced iNOS and NO. These results suggest that increased cGMP metabolic flux is sufficient to induce iNOS, and GC and PDE5 activities are required for IL-1 induction of iNOS expression via increases in coupled cGMP synthesis and hydrolysis.

Design and synthesis of N-alkylated saccharins as selective alpha-1a adrenergic receptor antagonists

Benign prostatic hyperplasia can be managed pharmacologically with alpha-1 adrenergic receptor antagonists. Agents that demonstrate selectivity for the alpha-1a receptor subtype may offer advantages in clinical applications with respect to hypotensive side effects. The N-alkylated saccharins reported here represent a new class of subtype selective alpha-1a adrenergic receptor antagonists which demonstrate potent effects on prostate function in vivo and are devoid of blood pressure side effects.

Pulmonary microvascular and macrovascular endothelial cells: differential regulation of Ca2+ and permeability

Cytosolic Ca2+ concentration ([Ca2+]i) plays an important role in control of pulmonary vascular endothelial cell (ECs) barrier function. In this study, we investigated whether thapsigargin- and ionomycin-induced changes in cytosolic Ca2+ induce permeability in rat pulmonary microvascular (RPMV) versus macrovascular (RPA) ECs. In Transwell cultures, RPMVECs formed a tighter, more restrictive barrier than RPAECs to 12,000-, 72,000-, and 150,000-molecular-weight FITC-labeled dextrans. Thapsigargin (1 microM) produced higher [Ca2+]i levels in RPAECs than in RPMVECs and increased permeability in RPAEC but not in RPMVEC monolayers. Due to the attenuated [Ca2+]i response in RPMVECs, we investigated whether reduced activation of store-operated Ca2+ entry was responsible for the insensitivity to thapsigargin. Addition of the drug in media containing 100 nM extracellular Ca2+ followed by readdition media with 2 mM extracellular Ca2+ increased RPMVEC [Ca2+]i to a level higher than that in RPAECs. Under these conditions, RPMVEC permeability was not increased, suggesting that [Ca2+]i in RPMVECs does not initiate barrier disruption. Also, ionomycin (1.4 microM) did not alter RPMVEC permeability, but the protein phosphatase inhibitor calyculin A (100 nM) induced permeability in RPMVECs. These data indicate that, whereas increased [Ca2+]i promotes permeability in RPAECs, it is not sufficient in RPMVECs, which show an apparent uncoupling of [Ca2+]i signaling pathways or dominant Ca(2+)-independent mechanisms from controlling cellular gap formation and permeability.

Altered expression of cyclic nucleotide phosphodiesterase isozymes during culture of aortic endothelial cells

Primary cultures of bovine aortic endothelial cells (BAEC) express cyclic nucleotide phosphodiesterase (CN PDE) isozymes of the PDE2, PDE4 and PDE5 gene families. We report here that the isozyme profiles of CN PDE and the amounts of each vary with the passage number of BAEC cultures. Characterization by anion-exchange chromatography and pharmacological criteria were used to study CN PDE in early (4-6), intermediate (6-10), and late (> 17) passages of purified BAEC. PDE2 and a minor fraction of PDE5 accounted for cyclic GMP hydrolysis in early passages, but both isozymes were lost with cell passage. Cyclic AMP was hydrolyzed by both PDE2 and PDE4 isozymes in early passage endothelial cells, but PDE4 was increased dramatically in higher passage cells. Also appearing in the higher passage cells were prominent PDE1 and minor PDE3 activities. The ratios of cytosolic to particulate activities were similar at all passages. BAEC PDE isoforms in intact cells assessed by [3H]-adenine prelabeling showed that atriopeptin II decreased isoproterenol-induced cyclic AMP accumulation in early but not later passage cells, consistent with the loss of PDE2 expression. Enhancement of isoproterenol-induced cyclic AMP accumulation by rolipram, a PDE4 inhibitor, was also greatly diminished during culture passages. Changes in CN PDE isoform expression and consequent cyclic AMP turnover validate the importance of considering cell passage number when cultures of BAEC are used to study the regulation of endothelial cell cyclic nucleotide metabolism and processes mediated by cyclic nucleotides in this model system.

Glial growth factor rescues Schwann cells of mechanoreceptors from denervation-induced apoptosis

Golgi tendon organs and Pacinian corpuscles are peripheral mechanoreceptors that disappear after denervation during a critical period in early postnatal development. Even if regeneration is allowed to occur, Golgi tendon organs do not reform, and the reformation of Pacinian corpuscles is greatly impaired. The sensory nerve terminals of both types of mechanoreceptors are closely associated with Schwann cells. Here we investigate the changes in the Schwann cells found in Golgi tendon organs and Pacinian corpuscles after nerve resection in the early neonatal period. We report that denervation induces the apoptotic death of these Schwann cells and that this apoptosis can be prevented by administration of a soluble form of neuregulin, glial growth factor 2. Schwann cells associated with these mechanoreceptors are immunoreactive for the neuregulin receptors erbB2, erbB3, and erbB4, and the sensory nerve terminals are immunoreactive for neuregulin. Our results suggest that Schwann cells in developing sensory end organs are trophically dependent on sensory axon terminals and that an axon-derived neuregulin mediates this trophic interaction. The denervation-induced death of mechanoreceptor Schwann cells is correlated with deficiencies in the re-establishment of these sensory end organs by regenerating axons.

Nerve terminal withdrawal from rat neuromuscular junctions induced by neuregulin and Schwann cells

Schwann cells (SCs) that cap neuromuscular junctions (nmjs) play roles in guiding nerve terminal growth in paralyzed and partially denervated muscles; however, the role of these cells in the day-to-day maintenance of this synapse is obscure. Neuregulins, alternatively spliced ligands for several erbB receptor tyrosine kinases, are thought to play important roles in cell-cell communication at the nmj, affecting synapse-specific gene expression in muscle fibers and the survival of terminal SCs during development. Here we show that application of a soluble neuregulin isoform, glial growth factor II (GGF2), to developing rat muscles alters terminal SCs, nerve terminals, and muscle fibers. SCs extend processes and migrate from the synapse. Nerve terminals retract from acetylcholine receptor-rich synaptic sites, and their axons grow, in association with SCs, to the ends of the muscle. These axons make effective synapses only after withdrawal of GGF2. These synaptic alterations appear to be induced by the actions of neuregulin on SCs, because SC transplants growing into contact with synaptic sites also caused withdrawal of nerve terminal branches. These results show that SCs can alter synaptic structure at the nmj and implicate these cells in the maintenance of this synapse.

Ca(2+)-inhibitable adenylyl cyclase and pulmonary microvascular permeability

Intracellular mechanisms responsible for endothelial cell disruption are unknown, although either elevated cytosolic Ca2+ ([Ca2+]i) or decreased adenosine 3',5'-cyclic monophosphate (cAMP) promotes permeability. Recent identification that Ca(2+)-inhibitable adenylyl cyclase establishes an inverse relationship between [Ca2+]i and cAMP in macrovascular endothelial cells provided a possible mechanism of development of permeability. However, these data utilized an in vitro model; lacking was evidence supporting 1) expression of Ca(2+)-inhibitable adenylyl cyclase in pulmonary microvascular endothelium and 2) Ca2+ inhibition of adenylyl cyclase and cAMP content as a paradigm for inflammatory mediator-induced permeability in the intact circulation. We therefore addressed these issues in microvascular endothelial cells derived from rat lung and in an isolated perfused rat lung preparation. Results demonstrate expression of a Ca(2+)-inhibitable adenylyl cyclase in microvascular endothelial cells. Furthermore, data suggest that Ca2+ inhibition of adenylyl cyclase is necessary for development of microvascular permeability in the intact circulation. We conclude Ca2+ inhibition of cAMP represents a critical step in genesis of microvascular permeability in the intact pulmonary circulation.

Vasoconstriction increases pulmonary nitric oxide synthesis and circulating cyclic GMP

Vascular shear stress increases when blood flow or blood viscosity increases or when vessel diameter decreases. In the systemic circulation, shear stress is a potent stimulus for endothelial nitric oxide synthesis. We studied isolated rat lungs to determine whether increasing shear stress increases nitric oxide synthesis in the pulmonary circulation. Lungs were given the vasoconstrictor, U46619 (a thromboxane analogue), and perfused at constant flow rates or at constant pressure, since constant pressure perfusion minimizes changes in shear stress with vasoconstriction. The subsequent effect of the NOS inhibitor, N omega-methyl-L-arginine (LMA), or the soluble guanylyl cyclase inhibitor, 6-anilino-5,8-quinolinodione (LY83583) was assessed. Changes in pulmonary vascular resistance (PVR), pulmonary vascular compliance, and perfusate cyclic GMP concentration were measured as indicators of nitric oxide synthesis. The effect of the cyclic GMP-specific (type V) phosphodiesterase inhibitor, zaprinast, on perfusate cyclic GMP concentrations was also examined. An infusion of U46619 consistently increased PVR and decreased compliance. LMA and LY83583 also increased PVR in U46619-treated lungs perfused at constant flow rates, primarily by increasing precapillary resistance. LMA had no effect in U46619-treated lungs perfused at constant pressure. Perfusate cyclic GMP concentrations increased significantly after U46619 in lungs perfused at constant flow rates, but cyclic GMP levels did not change after U46619 in lungs perfused at constant pressure. Zaprinast also increased perfusate cyclic GMP, demonstrating that increases in intracellular cyclic GMP are reflected in circulating cyclic GMP concentrations. We conclude that vasoconstriction with U46619 increases nitric oxide synthesis in isolated rat lungs. Lungs perfused at constant pressure respond differently to NOS inhibitors compared to those perfused at constant flow, suggesting that shear stress may increase nitric oxide synthesis in the lung. Perfusate concentrations of cyclic GMP reflect activation of soluble guanylyl cyclase in this model.

Inhibition of serine-threonine protein phosphatases decreases barrier function of rat pulmonary microvascular endothelial cells

The flux of multisized fluorescein-isothiocyanate-labeled hydroxy ethyl starch (FITC-HES) macromolecules was used to assess changes in barrier function of rat pulmonary microvascular endothelial cell (RPMVEC) monolayers exposed to protein phosphatase (PP) inhibitors or cGMP analogs and atriopeptin (ANF). Two potent PP inhibitors, calyculin A (CalA) and okadaic acid (OA), increased RPMVEC permeability in a dose- and time-dependent manner, and CalA had a higher intrinsic activity than OA. In contrast, ANF and potent cGMP analogs had no effect on basal RPMVEC permeability. The phosphohistone PP activity contained in RPMVEC sonicates was inhibited by OA with an inhibition profile that suggested at least two components were present, with PP2A accounting for approximately 70% of the OA-inhibitable phosphohistone phosphatase activity. Following separation with heparin-Sepharose chromatography, PP activity exhibited equipotent inhibition by CalA and differential inhibition by OA. Differential inhibition of PP1 and PP2A by OA suggested that PP1 is involved in regulating RPMVEC barrier function. Permeabilized RPMVEC showed increased phosphorylation of several proteins in the presence of phosphatase inhibitors. Treatment with KT 5926, a myosin light chain (MLC) kinase (MLCK) inhibitor, or rolipram, a phosphodiesterase inhibitor, decreased 32P incorporation into immunoprecipitated MLC by CalA and OA. However, this effect did not abolish either the CalA- or OA-induced decrease in the RPMVEC barrier function. Localization of filamentous (F) actin was at the periphery as well as in the cytoplasm and perinuclear region, whereas nonmuscle myosin was seen in the perinuclear region. Neither of these patterns was changed in the presence of CalA. Thus, cGMP does not alter RPMVEC permeability, but inhibition of PP activity results in loss of barrier function by a mechanism independent from MLC phosphorylation.

Cyclic GMP accumulation in pulmonary microvascular endothelial cells measured by intact cell prelabeling

Cyclic GMP accumulation in cultured rat pulmonary microvascular endothelial cells (RPMVEC) was studied with a new prelabeling method developed using intact platelets and smooth muscle cells (1). [3H]-hypoxanthine was used to radiolabel the cellular guanine nucleotide pool. Neutral alumina and Dowex-50 double column chromatography was used to purify and quantitate the levels of [3H]-cyclic GMP. Changes in cyclic GMP metabolism in short and long term RPMVEC cultures were studied using rat atrial naturetic factor 8-33 (ANF) and sodium nitroprusside (SNP) in the presence and absence of cyclic nucleotide (CN) phosphodiesterase (PDE) inhibitors. In RPMVEC exogenous hypoxanthine was incorporated into both low (65% uptake) and high (34% uptake) passage cells in a time-dependent manner reaching maximum incorporation near 8 hours. Basal cyclic GMP values in both groups were 0.003% of the total cellular tritium (9 x 10(6) and 4 x 10(6) cpm/10(6) cells, respectively). ANF treatment of prelabeled RPMVEC resulted in a 10- to 12-fold increase in [3H]-cyclic GMP in the absence of CN PDE inhibitors (EC50 = 5.4 nM). However, incubation with SNP showed no changes in cellular cyclic GMP accumulation. Several relatively selective CN PDE inhibitors had no effect on ANF or SNP induced cyclic GMP accumulation in RPMVEC. The ANF induced cGMP accumulation was verified by radioimmunoassay. These studies confirm the utility of the hypoxanthine prelabeling technique to monitor intact microvascular EC cyclic GMP accumulation. Cultured RPMVEC show little or no functional soluble guanylate cyclase or cyclic GMP PDE activity.

Our experience in combining mechanics

The use of more than one orthodontic technique in an orthodontic practice can significantly increase treatment capability. Being able to carry out the efficient and effective use of multiple techniques, however, requires that the appliance and the force systems are designed to do both tipping and translation in an optimal manner, either individually or in a variable combination. The application of this philosophy of combining treatment mechanics has been very favorable in our practice. The case reports and mechanics described were selected from our practice to show the diversity and potential that is possible with combination anchorage treatment mechanics. The key to success in a multiattachment straight wire system is to have the ability to use light tipping movements in combination with rigid translation and to be able to vary the location of either, at any time the need arises during treatment.

Comparison of indolidan analog binding sites of drug antibody and sarcoplasmic reticulum with inhibition of cyclic AMP phosphodiesterase

Dihydropyridazinone(DHP) derivatives such as indolidan are positive inotropic agents that show inhibition of cyclic AMP phosphodiesterase(PDE) activity. Indolidan inhibition is selective for PDE3 among the seven PDE gene families. DHP derivatives and related analogs have been used to define critical regions of the active site of PDE3 isoforms and radiolabeled analogs have been used to define indolidan sarcoplasmic reticulum (SR) receptor sites. We report here studies comparing the structure-activity relationships (SAR) for PDE3 inhibition with indolidan binding to two types of sites: canine SR and a monoclonal antibody derived against indolidan conjugated to a hemocyanin. SR and monoclonal antibody binding both fit singlesite, high affinity models (IC50 = 1.2 and 62 nM) that were near 52 and 360 times that of SR PDE3. Indolidan and thirteen analogs showed similar competition with either SR 3H-LY186126 binding or SR PDE3 inhibition. Antibody binding maintained selectivity but showed a different rank order potency for SR binding. Indole ring C3 methylation increased and DHP ring C4' methylation decreased indolidan monoclonal antibody binding while both substitutions increased SR binding. These studies support the hypothesis that SR PDE3 is a cardiotonic receptor site in myocardial membranes and indicate that models of the structural features of binding sites derived from inhibitor data alone could produce models with limited topography relative to the natural ligand.

Nonpeptidal P2 ligands for HIV protease inhibitors: structure-based design, synthesis, and biological evaluation

Design and synthesis of nonpeptidal bis-tetrahydrofuran ligands based upon the X-ray crystal structure of the HIV-1 protease-inhibitor complex 1 led to replacement of two amide bonds and a 10 pi-aromatic system of Ro 31-8959 class of HIV protease inhibitors. Detailed structure-activity studies have now established that the position of ring oxygens, ring size, and stereochemistry are all crucial to potency. Of particular interest, compound 49 with (3S,3aS,6aS)-bis-Thf is the most potent inhibitor (IC50 value 1.8 +/- 0.2 nM; CIC95 value 46 +/- 4 nM) in this series. The X-ray structure of protein-inhibitor complex 49 has provided insight into the ligand-binding site interactions. As it turned out, both oxygens in the bis-Thf ligands are involved in hydrogen-bonding interactions with Asp 29 and Asp 30 NH present in the S2 subsite of HIV-1 protease. Stereoselective routes have been developed to obtain these novel ligands in optically pure form.

Schwann cells induce and guide sprouting and reinnervation of neuromuscular junctions

The "terminal' Schwann cells that sit atop the neuromuscular junction sense neuromuscular transmission and respond to perturbations of this transmission by extending long processes. These processes have the ability to induce nerve growth and serve as substrates to guide this growth. These processes thus play major roles in muscle reinnervation and in sprouting. An absence of nerve sprouting is correlated with the apoptotic death of terminal Schwann cells at denervated endplates in neonatal muscles. Thus, Schwann cells appear to participate actively in the maintenance and repair of neuromuscular synapses.