Erythro-9-(2-hydroxy-3-nonyl)adenine inhibits cyclic-3',5'-guanosine monophosphate-stimulated phosphodiesterase to reverse hypoxic pulmonary vasoconstriction in the perfused rat lung

Erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) was shown to reverse the hypoxic pressor response (HPR) in the isolated, blood-perfused rat lung model. EHNA, an adenosine deaminase inhibitor, showed reversal of the HPR in a dose-dependent manner (EC50 = 129 +/- 30 microM). We found that the reversal of HPR by EHNA was not mediated by the adenosine receptors because the EHNA effect was not blocked by the adenosine receptor antagonist, 8-p-sulfophenyl-theophylline (67 microM; n = 6). Pretreatment with a cy-clic-3',5'-adenosine monophosphate (cAMP)-dependent protein kinase inhibitor, Rp-adenosine-3',5'-cyclic monophosphorothioate (0.5 mM; n = 4), blocked EHNA reversal of the HPR. As an alternative mechanism of action, EHNA inhibition of cyclic nucleotide phosphodiesterase(s) isozymes was studied in endothelium intact and denuded pulmonary arteries. Using anion-exchange chromatography the cyclic nucleotide phosphodiesterase (PDE) separated into predominantly PDE families 2 and a mixture of 3 and 4. DEAE fractions showing cAMP hydrolysis activated by 5 microM cyclic-3',5'-guanosine monophosphate (cGMP) had a Km for cAMP of 6.3 microM and an apparent Kact for cGMP of 1.4 microM. EHNA was shown to inhibit PDE2 competitively. In intact vessels, the IC50 for EHNA was 3.3 microM using 0.03 microM [3H]-cAMP substrate assayed in the presence of 2 microM cGMP and in denuded vessels 3.7 microM at 0.03 microM [3H]-cAMP substrate in the presence of 5 microM cGMP. Fractions in which cAMP hydrolysis was inhibited or not affected by 5 microM cGMP (PDE3 and 4, respectively) showed an IC50 of > 200 microM for EHNA. We conclude that reversal of the hypoxic pressor response by EHNA in the isolated, perfused rat lung model occurs with a mechanism involving in part inhibition of smooth muscle PDE2.

Schwann cell apoptosis at developing neuromuscular junctions is regulated by glial growth factor

Denervated adult mammalian muscle fibres are reinnervated by regenerating axons and, in the case of partially denervated muscles, by sprouts extended from remaining, intact axons. Recent experiments suggest that Schwann cells (SCs) regulate these events, inducing and guiding axonal outgrowth through the processes they extend. In contrast to adults, reinnervation o denervated neonatal muscles is deficient and axonal sprouting is absent. In light of the proposed roles for SCs in these processes, we examined whether SCs in neonatal muscles exhibit altered responses to denervation. We report here that neonatal denervation leads to the rapid, apoptotic death of SCs at rat neuro-muscular junctions. Injection of glial growth factor, a member of the neuregulin family of trophic factors present in developing sensory and motor neurons, prevents this apoptosis in vivo. These results provide further evidence for the importance of SCs in regulating nerve growth and suggest that axon-Schwann cell trophic interactions play a role in the normal development of the neuromuscular system.

Rolipram and isoproterenol reverse platelet activating factor-induced increases in pulmonary microvascular permeability and vascular resistance

Platelet activating factor (PAF) is an important mediator of pulmonary microvascular endothelial cell (PMVEC) injury in sepsis. Membrane receptors for PAF have been identified on PMVECs and mediate its actions at least in part by protein kinase C activation. Since rolipram, a family IV cyclic AMP phosphodiesterase inhibitor, and isoproterenol, an adenylate cyclase activator, both reverse ischemia-reperfusion-induced lung permeability, we studied the effects of these agents on PAF-induced pulmonary microvascular permeability. The isolated rat lung model was used in which lungs were ventilated and buffer perfused at constant flow while suspended from a force transducer to monitor lung weight along with arterial (P(a)) and venous (Pv) pressures. Control lungs (n = 6) were infused with PAF (40 nmole/kg) via an arterial port and the capillary permeability coefficient (Kf,c) was determined at 0, 15, and 60 min. The remaining lungs were randomized for infusion with either rolipram (n = 4, 20 mumole/kg) or isoproterenol (n = 4, 5 mumole/kg) via an arterial port 30 min after injury with PAF. In the rolipram- and isoproterenol-treated groups, the Kf,c was determined 15 and 60 min postinfusion with these agents. The control group showed significant elevation in the Kf,c and total pulmonary resistance (Rt). At 15 and 60 min, rolipram and isoproterenol reversed PAF injury as shown by the significant improvement in the Kf,c and Rt. These findings support the concept that increased cyclic AMP is an important mediator in the reversal of PAF-increased PMVEC permeability and pulmonary resistance.

TNF modulates endothelial properties by decreasing cAMP

Tumor necrosis factor-alpha (TNF-alpha), a monokine that contributes to vascular dysfunction accompanying the host response to gram-negative sepsis, has been shown to increase vascular permeability in vivo and to diminish the barrier function of cultured endothelial cell (EC) monolayers. The studies reported here indicate that a mechanism through which TNF alters EC barrier function involves a reduction in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) content, due in part to increased cyclic nucleotide phosphodiesterase (CNPDE) activities. TNF increased the diffusional transit of [3H]sorbitol, [3H]inulin, and 125I-labeled albumin across confluent bovine aortic EC monolayers. This effect of TNF was both time and dose dependent and occurred in parallel with a fall in EC cAMP. cAMP analogues, such as dibutyryl cAMP (DBcAMP), prevented TNF-induced perturbation of EC barrier function. TNF also mediated another important alteration in the EC phenotype, in that both mRNA and activity of the anticoagulant cofactor thrombomodulin were reduced after exposure of EC to TNF and were normalized by the addition of DBcAMP. EC monolayers exposed to TNF-alpha showed increased cAMP levels when exposed to 3-isobutyl-1-methylxanthine, a nonspecific CNPDE inhibitor. Ion exchange chromatography of cytosol derived from TNF-treated EC consistently showed an approximately 245% increase in phosphodiesterase (PDE) IV (high-affinity, cAMP-specific PDE) activity as identified by rolipram inhibition. PDE II activity was increased by 150% after TNF-alpha treatment of early passage EC, which was identified by cGMP-activated hydrolysis of cAMP. Western and Northern analyses, as well as activity studies, revealed that TNF treatment did not change the amount of PDE IV protein or mRNA but rather increased the specific activity of the isozyme, suggesting that a posttranslational modification had occurred. These data indicate that activation of EC CNPDE activity and decreased intracellular cAMP may represent a mechanism by which TNF increases EC permeability and promotes a procoagulant EC phenotype.

Adenosine-induced vasodilation: receptor characterization in pulmonary circulation

Adenosine mediates vascular smooth muscle relaxation in the pulmonary circulation. The A2 receptor has been suggested to mediate adenosine-induced vasodilation (AIV). In this study, the effect(s) of selective adenosine agonist and antagonist on the hypoxic pressor response (HPR) was assessed in the isolated blood-perfused rat lung. Adenosine (0.075-7.5 mM) infusion (0.125 ml/min) into the pulmonary artery dose dependently attenuated the HPR. AIV was mimicked by 10 microM 5'-(N-ethylcarboxamido)adenosine (NECA), a nonselective adenosine agonist. Adenosine- and NECA-induced vasodilation were attenuated by 67 microM 8-(p-sulfophenyl)theophylline. In contrast, NECA-induced vasodilation was not attenuated by the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (1 microM). At 10 microM, a minimal vasodilatory effect was seen with the nonselective adenosine agonists CV-1808 and N6-(2-phenylisopropyl)adenosine (R-PIA) compared with NECA. The highly selective A2a agonist 2-[p-(2-carboxyethyl)phenyl amino]-5'-N-ethyl carboxamido adenosine (CGS-21680C, 10 microM) and A1 agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 10 microM) had no vasodilatory effect. Neither the K+ channel blockers tetraethylammonium chloride (10 mM) and glibenclamide (100 microM) nor the NO synthase inhibitor N omega-nitro-L-arginine methyl ester attenuated NECA-induced vasodilation. These findings suggest that AIV is mediated via the A2b receptor and that AIV occurs via an NO-independent mechanism.

Metabolism of L-689,502 by rat liver slices to potent HIV-1 protease inhibitors

L-689,502, N-[2(R)-hydroxy-1(S)-indanyl]-5(S)-(1,1-dimethylethoxy- carbonyl-amino)-4(S)-hydroxy-6-phenyl-2(R)-(4-[2(R)-(4-morpholinyl) ethoxy]phenyl)methylhexamide, is a potent and specific inhibitor of human immunodeficiency virus-type 1 (HIV-1) protease in vitro. Metabolism of this compound in rat liver slices produced four major and several minor metabolites. The major metabolites were identified as morpholin-2-one, 3'(S)-hydroxyindan and 4'-hydroxyindan analogs, and a 4-O-glucuronic acid conjugate of the parent compound. The metabolites were characterized by Heteronuclear Multiple Quantum Coherence and Nuclear Overhauser Effect techniques in NMR spectroscopy, by MS, and/or comparison with authentic standards. Two of the minor metabolites were similarly characterized as a 2(R)-[4-(2-carboxymethoxy)phenyl]methyl analog and a product with a degraded morpholino ring. The hydroxyindan metabolites were lower in activity than L-689,502, whereas the morpholin-2-one and carboxymethoxyphenyl analogs were approximately 6- and 11-fold more potent as inhibitors of HIV-1 protease, respectively.

A priori prediction of activity for HIV-1 protease inhibitors employing energy minimization in the active site

We have observed a high correlation between the intermolecular interaction energy (Einter) calculated for HIV-1 protease inhibitor complexes and the observed in vitro enzyme inhibition. A training set of 33 inhibitors containing modifications in the P1' and P2' positions was used to develop a regression equation which relates Einter and pIC50. This correlation was subsequently employed to successfully predict the activity of proposed HIV-1 protease inhibitors in advance of synthesis in a structure-based design program. This included a precursor, 47, to the current phase II clinical candidate, L-735,524 (51). The development of the correlation, its applications, and its limitations are discussed, and the force field (MM2X) and host molecular mechanics program (OPTIMOL) used in this work are described.

Schwann cell processes guide regeneration of peripheral axons

Terminal Schwann cells overlying the neuromuscular junction sprout elaborate processes upon muscle denervation. We show here that motor axons use these processes as guides/substrates during regeneration; in so doing, they escape the confines of endplates and grow between endplates to generate polyneuronal innervation. We also show that Schwann cells in the nerve provide similar guidance. Axons extend from the cut end of a nerve in association with Schwann cell processes and appear to navigate along them. The processes extend from axotomized nerves at the same rate and in the same manner as they do from axon-containing nerves. The rate of process extension limits the rate at which axons regenerate. Thus, Schwann cell processes lead and guide peripheral regeneration.

Nerve sprouting in muscle is induced and guided by processes extended by Schwann cells

Partial denervation or paralysis with botulinum toxin, manipulations that induce sprouting of nerve terminals in muscle, also induced terminal Schwann cells to extend processes. These processes were associated with every nerve sprout and in some cases were longer than the sprouts that appeared to be growing along them. Following partial denervation, more than 70% of the nerve sprouts that grew to innervate nearby denervated endplates were associated with Schwann cell processes that had extended from the denervated endplates, i.e., in the direction opposite to nerve growth. Implantation of Schwann cells into an innervated muscle induced sprouting upon contact of an axon or nerve terminal by Schwann cell processes. These observations show that Schwann cells induce and guide axonal sprouting in muscle.

A novel cyclic GMP stimulated phosphodiesterase from rat brain

A cDNA clone for cyclic GMP Stimulated Phosphodiesterase (cGSPDE; PDE2) was isolated from a rat brain cDNA library. The cDNA has an open reading frame which encodes a protein of 928 amino acids of which 829 are identical with the reported bovine adrenal gland cGSPDE cDNA (Sonnenburg, W.K., Mullaney, P.J., and Beavo, J.A. (1991) J. Biol. Chem. 266, 17655-17661). Although the overall homology of these two cDNAs is high, they are distinctly different in their 5' ends, with the N-terminal 37 amino acids of the rat brain protein showing no homology with the N-terminal end of the bovine adrenal protein. Hydrophilicity plots show that in contrast to the bovine adrenal cGSPDE, the N-terminal end of the rat brain cGSPDE is highly hydrophobic. Isolation and analysis of a genomic clone for cGSPDE from a rat genomic library shows the presence of an exon/intron junction at the Gln39 codon. The cGSPDE cDNA we have isolated and that of Sonnenburg et al. represent alternatively spliced mRNA products from the same gene, with the brain isoform designed to be targeted to membranes.

Reversal of pulmonary capillary ischemia-reperfusion injury by rolipram, a cAMP phosphodiesterase inhibitor

Isoproterenol (ISO) and forskolin, agents that increase adenosine 3',5'-cyclic monophosphate (cAMP) via adenylyl cyclase activation, reverse lung injury associated with increased microvascular permeability. We studied the role of rolipram, a relatively isozyme-selective cAMP phosphodiesterase (PDE) inhibitor, in reversing increased capillary permeability due to ischemia-reperfusion (I/R), a form of oxidant injury in the lung, by using the isolated perfused rat lung model. Rolipram (2 microM) administered after 45 min of ischemia and 45 min of reperfusion reduced I/R-increased permeability as measured by the capillary filtration coefficient to control lung values. Computer image analysis of air space edema and perivascular cuffing, as well as wet-to-dry weight ratios, confirms the permeability reversal by rolipram administration. Rolipram inhibition of cAMP PDE in the lung was assessed by using [3H]adenine prelabeling adapted for the whole lung and perfusate [3H]cAMP accumulation. Rolipram failed to increase perfusate cAMP alone but dramatically increased perfusate cAMP above ISO alone. Dose-response relationships of ISO or rolipram show a close correlation of the half-maximal effective dose (ED50) for injury reversal and perfusate cAMP production. The combination of rolipram and ISO produced synergistic reversal of I/R injury. We conclude that reversal of I/R-induced increased microvascular permeability can be achieved with rolipram and that the mechanism of action of rolipram is probably through PDE isozyme-selective inhibition. The similarity of the ED50 values for cAMP efflux and reversal of permeability increases also supports a close coupling between cAMP accumulation and endothelial cell permeability.

Differential neural regulation of a neuromuscular junction-associated antigen in muscle fibers and Schwann cells

Monoclonal antibodies 3G2 and 4E2 recognize a postsynaptic component of rat neuromuscular junctions. In contrast to many other postsynaptic junctional antigens, expression of this antigen is nerve-dependent: immunoreactivity disappears from junctions following denervation and returns upon reinnervation (Astrow et al., 1992 J. Neurosci. 12:1602-1615). Here we show that the epitope is also expressed by Schwann cells and that this expression is also neurally regulated. Weak mAb 3G2/4E2 immunoreactivity was found in myelinating Schwann cells but was not detected in either nonmyelinating Schwann cells or in terminal Schwann cells at the neuromuscular junction. Following axotomy, immunoreactivity increased in myelinating Schwann cells, and nonmyelinating and terminal Schwann cells became immunopositive. Moreover, the immunoreactivity in terminal Schwann cells revealed their extensive sprouting in response to denervation (Reynolds and Woolf, 1992, J. Neurocytol. 21: 50-66). After nerve regeneration, mAb 3G2/4E2 immunoreactivity in all Schwann cells returned towards normal: it disappeared from terminal Schwann cells, returned to low levels in myelinating Schwann cells, and decreased in nonmyelinating Schwann cells. Immunoblots of axotomized nerve and cultured muscle fibers revealed the same set of immunoreactive bands. Therefore, Schwann cells and muscle fibers share the expression of an epitope that is under neural control, but is regulated differently at each site. In Schwann cells, the presence of the nerve suppresses expression of the epitope, whereas in muscle fibers, the nerve terminal promotes this expression. The differential regulation of mAb 3G2/4E2 immunoreactivity in terminal Schwann cells and muscle fibers suggests that the epitope may be involved in interactions between nerve terminals and these cells.

Cyclic GMP-dependent protein kinase activity in rat pulmonary microvascular endothelial cells

Cyclic GMP-dependent protein kinase (cGPK) activity was determined in rat pulmonary microvascular endothelial cells (RPMVEC) using cGMP-stimulated phosphorylation of BPDEtide and histone F2B substrates in the presence of PKI [peptide inhibitor of cAMP-dependent protein kinase (cAPK)]. RPMVEC cGPK activity was localized to the 100,000 x g cytosolic fraction. The EC50 for cGMP activation in the presence of PKI was 0.16 microM and H-89 inhibition under similar conditions showed an IC50 value of 0.16 microM. Anion-exchange chromatography of RPMVEC and rat lung cytosolic fractions showed separation of the cGMP-dependent from the cGMP-independent protein kinase activity and similar elution conductivities. Further, Western blots of RPMVEC active DEAE-Trisacryl fractions showed immunoreactivity using bovine Type I cGPK antiserum. Preliminary studies reveal six potential substrates phosphorylated by cGPK in RPMVEC. These studies describe an endothelial cell (EC) cGMP-receptor, cGPK, in addition to cGMP-activated (Type II) phosphodiesterase (PDE).

The development of cyclic sulfolanes as novel and high-affinity P2 ligands for HIV-1 protease inhibitors

Design and synthesis of a novel series of protease inhibitors incorporating conformationally constrained cyclic ligands for the S2-substrate binding site of HIV-1 protease is described. We recently reported urethanes of 3-tetrahydrofuranyl as P2 ligands for HIV-1 protease inhibitors. Subsequently, we have found that the urethane of 3(S)-hydroxysulfolane further increased the in vitro potency of these inhibitors. Furthermore, introduction of a small 2-alkyl group cis to the 3-hydroxyl group of either heterocyclic system further enhanced enzyme affinity. The cis-2-isopropyl group thus far offered optimum enhancement of the inhibitory properties. This led to the discovery of inhibitor 43 (IC50 3.5 nM, CIC95 50 +/- 14 nM) of comparable in vitro antiviral potency to the current clinical candidate 1 (Ro 31-8959) but of reduced molecular weight due to the exclusion of the P3 quinoline ligand. Also, it has been demonstrated that the octahydropyrindene derivative 34 is an effective replacement of the P1' decahydroisoquinoline derivative.

Contractile properties and myosin phenotype of single motor units from neonatal rats

The unloaded shortening velocity (Vus), twitch time to peak force (TTP), and myosin heavy chain (MHC) composition of motor units from soleus muscles of neonatal rats (7-8 and 16-18 days) were compared. The Vus range was from 2.2 to 7.1 fiber lengths (fl).s-1 and was unchanged from 7-8 to 16-18 days. TTP shifted from 7-8 (range, 66-120) to 16-18 days (range, 41-95). MHC-specific antibody staining of motor units revealed a correlation between MHC and Vus of individual motor units. Slowest motor units contained type I MHC. Intermediate Vus motor units contained both embryonic, neonatal, and/or type IIa MHCs. Fastest motor units contained neonatal and/or type IIa MHCs. These findings demonstrate that an individual motor unit of a neonatal muscle contains a nonrandom distribution of fiber types. The range of myosins present within the motor units of the soleus translates into a range of possible Vus.

Measurement of insulin wastage in five Ontario hospitals

This study was designed to determine the extent of insulin wastage and the extrapolated cost of wastage for Ontario hospitals. The five hospitals in the study were chosen to include differences in patient mix and drug distribution systems. Beginning and ending inventories of all insulin types were taken spanning a six-week period. The quantity of insulin dispensed and wasted during this time period was recorded. Partial vials were measured using a calibrated scale. Wastage was calculated as insulin discarded divided by the amount of insulin used in the time period. Insulin wastage averaged 34.1%. This was equivalent to up to $8,000 a year for the largest hospital surveyed and translates to an estimated cost of $360,000 a year in all Ontario hospitals. Therefore, hospitals should estimate their insulin wastage and seek ways to reduce it. The pharmaceutical industry should be encouraged to develop cost-effective insulin delivery systems.

Potent HIV protease inhibitors: the development of tetrahydrofuranylglycines as novel P2-ligands and pyrazine amides as P3-ligands

A series of protease inhibitors bearing constrained unnatural amino acids at the P2-position and novel heterocycles at the P3-position of compound 1 (Ro 31-8959) were synthesized, and their in vitro enzyme inhibitory and antiviral activities were evaluated. Replacement of P2-asparagine of compound 1 with (2S,3'R)-tetrahydrofuranylglycine resulted in improvement in enzyme inhibitory as well as antiviral potencies (compound 23). Interestingly, incorporation of (2S,3'S)-tetrahydrofuranylglycine at the P2-position proved to be less effective. The resulting compound 24 was 100-fold less potent than the 2S,3R-isomer (compound 23). This stereochemical preference indicated a hydrogen-bonding interaction between the tetrahydrofuranyl oxygen and the residues of the S2-region of the enzyme active site. Furthermore, replacement of P3-quinolinoyl ligand of 1 with various novel heterocycles resulted in potent inhibitors of HIV proteases. Of particular interest, compound 2 with (2S,3'R)-tetrahydrofuranylglycine at P2 and pyrazine derivative at P3 is one of the most potent inhibitors of HIV-1 (IC50 value 0.07 nM) and HIV-2 (IC50 value 0.18 nM) proteases. Another important result in this series is the identification of compound 27 in which the P2-P3-amide carbonyl has been removed. The resulting compound 27 has exhibited improvement in antiviral potency while retaining the enzyme inhibitory potency similar to compound 1.

Discrete and integral fourier transforms: analytical examples

Analytical examples of the discrete Fourier transform (DFT) help in understanding relations between the DFT and the Fourier integral transform (FIT). Such examples enable one to estimate the errors involved when one transform is approximated by the other, and they suggest how such approximation errors might be reduced. We present mathematical and numerical analyses of the time-to-frequency DFT of the complex exponential function and of the frequency-to-time inverse DFT of the relaxation function. The FITs of these functions are exact inverses, and so they serve to clarify the effects of aliasing and truncation on the DFT.

Sulfonylmethanesulfonamide inhibitors of carbonic anhydrase

A series of sulfonylmethanesulfonamide derivatives is described, which are inhibitors of carbonic anhydrase (CA). The most potent of these is the racemic fluoro sulfone 9, which inhibits carbon dioxide hydration catalyzed by human CA II (CA-II) with an IC50 of 3 nM. Binding competition studies versus dansylamide indicate that the enantiomers of 9 have different affinities for CA-II, with equilibrium dissociation constants of 3.6 and 0.6 nM. QSAR analysis suggests that the key factors involved in achieving high affinity in this series are sulfonamide acidity, hydrophobicity, and minimization of steric demands at the carbon atom adjacent to the sulfonamide group.

Effect of nitric oxide and cyclooxygenase products on vascular resistance in dog and rat lungs

Pulmonary vascular resistance decreases with increased cardiac output. Because nitric oxide (NO) and prostacyclin are potent vasodilators that are released with increased shear stress, their roles in the control of pulmonary vascular pressure were evaluated using isolated blood-perfused rat and dog lungs. Lungs were perfused with an initial arteriovenous pressure gradient (Ppa-Ppv) of 15 cmH2O; Ppa and Ppv were increased by the same amount, and the flow was measured. In rat lung (n = 6), the NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) decreased pulmonary blood flow by approximately 50% at the same pressure (P < 0.05), whereas the cyclooxygenase inhibitor indomethacin (n = 6) had no effect. In dog lungs (n = 6), indomethacin decreased pulmonary blood flow by approximately 50% at the same pressure gradient (P < 0.05), whereas L-NAME (n = 6) had no effect. Furthermore, the flow increase that occurs as venous and arterial pressures are elevated together (so that Ppa-Ppv is constant) was inhibited by L-NAME in rat lungs and by indomethacin in dog lungs (P < 0.05 for each). Plasma guanosine 3',5'-cyclic monophosphate (cGMP) rose with increased absolute pressure in rat lung [from 71 +/- 17 to 274 +/- 104 pM (P < 0.05)], and this increase was blocked by L-NAME. Plasma cGMP was unchanged in dog lung, but the ratio of prostacyclin to thromboxane tended to be higher.(ABSTRACT TRUNCATED AT 250 WORDS)