The effect of isoenzyme-selective PDE inhibitors on methacholine-induced contraction of guinea-pig and rat ileum

Effects of Extracts and Flavonoids from Drosera rotundifolia L. on Ciliary Beat Frequency and Murine Airway Smooth Muscle

Extracts from Drosera rotundifolia are traditionally used to treat cough symptoms during a common cold. The present study aimed to investigate the impact of extracts from D. rotundifolia and active compounds on the respiratory tract. Tracheal slices of C57BL/6N mice were used ex vivo to examine effects on airway smooth muscle (ASM) and ciliary beat frequency (CBF). Phosphodiesterase (PDE) inhibition assays were carried out to test whether PDE1 or PDE4 are targeted by the active compounds. An ethanol–water extract, as well as an aqueous fraction of this extract, exerted antispasmodic properties against acetylcholine-induced contractions. In addition, contractions induced by 60 mM K⁺ were abrogated by the aqueous fraction. Effects on ASM could be attributed to the flavonoids quercetin, 2″-O-galloylhyperoside and hyperoside. Moreover, the Drosera extract and the aqueous fraction increased the CBF of murine tracheal slices. Quercetin and 2″-O-galloylhyperoside were identified as active compounds involved in the elevation of CBF. Both compounds inhibited PDE1A and PDE4D. The elevation of CBF was mimicked by the subtype-selective PDE inhibitor rolipram (PDE4) and by 8-methoxymethyl-IBMX. In summary, our study shows, for the first time, that a Drosera extract and its flavonoid compounds increase the CBF of murine airways while antispasmodic effects were transferred to ASM.

cAMP Catalyzing Phosphodiesterases Control Cholinergic Muscular Activity But Their Inhibition Does Not Enhance 5-HT4 Receptor-Mediated Facilitation of Cholinergic Contractions in the Murine Gastrointestinal Tract

Background: As the signal transduction of 5-HT₄ receptors on cholinergic neurons innervating smooth muscle is controlled by phosphodiesterase (PDE) 4 in porcine stomach and colon, and human large intestine, the in vivo gastroprokinetic effects of a 5-HT₄ receptor agonist might be enhanced by combination with a selective PDE4 inhibitor. The presence of 5-HT₄ receptors on cholinergic neurons towards murine gastrointestinal circular muscle was recently shown. If the control of this receptor pathway by PDE4 is also present in mice, this might be a good model for in vivo testing of the combination therapy. Therefore this study investigates the role of cAMP catalyzing PDEs in smooth muscle cell activity and in the intraneuronal signal transduction of the 5-HT₄ receptors in the gastrointestinal tract of C57Bl/6J mice.

Methods: In circular smooth muscle strips from murine fundus, jejunum, and colon, submaximal cholinergic contractions were induced by either electrical field stimulation (EFS) or by carbachol (muscarinic receptor agonist). The influence of the PDE inhibitors IBMX (non-selective), vinpocetine (PDE1), EHNA (PDE2), cilostamide (PDE3), and rolipram (PDE4) was tested on these contractions and on the facilitating effect of a submaximal concentration of prucalopride (5-HT₄ receptor agonist) on EFS-induced contractions.

Results: In the three gastrointestinal regions, IBMX and cilostamide concentration-dependently decreased carbachol- as well as EFS-induced contractions. Some inhibitory effect was also observed with rolipram. In the fundus a non-significant trend for an enhancement of the facilitating effect of prucalopride on EFS-induced contractions was observed with IBMX, but none of the selective PDE inhibitors enhanced the facilitating effect of prucalopride in fundus, jejunum or colon.

Conclusion: In analogy with the porcine gastrointestinal tract, in murine fundus, jejunum, and colon circular smooth muscle PDE3 is the main regulator of the cAMP turnover, with some contribution of PDE4. In contrast to the porcine gastrointestinal tract, the in vitro facilitation of electrically induced cholinergic contractions by 5-HT₄ receptor stimulation could not be enhanced by specific PDE inhibition. The C57Bl/6J murine model is thus not suitable for in vivo testing of a 5-HT₄ receptor agonist combined with a selective PDE4 inhibitor.

PDE4 and PDE5 regulate cyclic nucleotide contents and relaxing effects on carbachol-induced contraction in the bovine abomasum

The effects of various selective phosphodiesterase (PDE) inhibitors on carbachol (CCh)-induced contraction in the bovine abomasum were investigated. Various selective PDE inhibitors, vinpocetine (type 1), erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, type 2), milrinone (type 3), Ro20-1724 (type 4), vardenafil (type 5), BRL-50481 (type 7) and BAY73-6691 (type 9), inhibited CCh-induced contractions in a concentration-dependent manner. Among the PDE inhibitors, Ro20-1724 and vardenafil induced more relaxation than the other inhibitors based on the data for the IC₅₀ or maximum relaxation. In smooth muscle of the bovine abomasum, we showed the expression of PDE4B, 4C, 4D and 5 by RT-PCR analysis. In the presence of CCh, Ro20-1724 increased the cAMP content, but not the cGMP content. By contrast, vardenafil increased the cGMP content, but not the cAMP content. These results suggest that Ro20-1724-induced relaxation was correlated with cAMP and that vardenafil-induced relaxation was correlated with cGMP in the bovine abomasum. In conclusion, PDE4 and PDE5 are the enzymes involved in regulation of the relaxation associated with cAMP and cGMP, respectively, in the bovine abomasum.

The facilitating effect of prucalopride on cholinergic neurotransmission in pig gastric circular muscle is regulated by phosphodiesterase 4

The influence of the selective 5-HT(4) receptor agonist prucalopride on acetylcholine release from cholinergic nerve endings innervating pig gastric circular muscle and the possible regulation of this effect by phosphodiesterases (PDEs) was investigated, as PDEs have been shown to control the response to 5-HT(4) receptor activation in pig left atrium. Circular muscle strips were prepared from pig proximal stomach and either submaximal cholinergic contractions or tritium outflow after incubation with [(3)H]-choline, induced by electrical field stimulation, were studied. Prucalopride concentration-dependently increased the amplitude of submaximal cholinergic contractions and of acetylcholine release induced by electrical field stimulation. The effect of the highest concentration tested (0.3 μM) on cholinergic contractions was antagonized by the selective 5-HT(4) receptor antagonist GR113808 but not by granisetron or methysergide; the antagonism of prucalopride by GR113808 was confirmed in the release assay. The non-selective PDE-inhibitor 3-isobutyl-methyl-xanthine (IBMX) concentration-dependently reduced the amplitude of the cholinergic contractions; 3 μM IBMX reduced the cholinergic contractions maximally by 16% but it enhanced the facilitating effect of prucalopride from 51 to 83%. IBMX (10 μM) induced and enhanced the facilitating effect of prucalopride on electrically induced acetylcholine release. The selective inhibitors vinpocetine (PDE1), EHNA (PDE2) and cilostamide (PDE3) did not influence the effect of prucalopride on acetylcholine release but the PDE4-inhibitor rolipram (1 μM) enhanced the facilitating effect of prucalopride to the same extent as IBMX. These results demonstrate that 5-HT(4) receptors are present on the cholinergic nerves towards the pig gastric circular muscle, facilitating acetylcholine release; the intracellular transduction pathway of this facilitation is regulated by PDE4. Combination of a 5-HT(4) receptor agonist with selective inhibition of the PDE involved in this regulation of transmitter release might enhance the prokinetic effect of the 5-HT(4) receptor agonist.

Inhibitory effects of bromelain, a cysteine protease derived from pineapple stem (Ananas comosus), on intestinal motility in mice

BACKGROUND

Bromelain (BR) is a cysteine protease with inhibitory effects on intestinal secretion and inflammation. However, its effects on intestinal motility are largely unexplored. Thus, we investigated the effect of this plant-derived compound on intestinal contractility and transit in mice.

METHODS

Contractility in vitro was evaluated by stimulating the mouse isolated ileum, in an organ bath, with acetylcholine, barium chloride, or electrical field stimulation. Motility in vivo was measured by evaluating the distribution of an orally administered fluorescent marker along the small intestine. Transit was also evaluated in pathophysiologic states induced by the pro-inflammatory compound croton oil or by the diabetogenic agent streptozotocin.

KEY RESULTS

Bromelain inhibited the contractions induced by different spasmogenic compounds in the mouse ileum with similar potency. The antispasmodic effect was reduced or counteracted by the proteolytic enzyme inhibitor, gabexate (15 × 10(-6)  mol L(-1) ), protease-activated receptor-2 (PAR-2) antagonist, N(1) -3-methylbutyryl-N(4) -6-aminohexanoyl-piperazine (10(-4) mol L(-1) ), phospholipase C (PLC) inhibitor, neomycin (3 × 10(-3) mol L(-1) ), and phosphodiesterase 4 (PDE4) inhibitor, rolipram (10(-6)  mol L(-1) ). In vivo, BR preferentially inhibited motility in pathophysiologic states in a PAR-2-antagonist-sensitive manner.

CONCLUSIONS & INFERENCES

Our data suggest that BR inhibits intestinal motility - preferentially in pathophysiologic conditions - with a mechanism possibly involving membrane PAR-2 and PLC and PDE4 as intracellular signals. Bromelain could be a lead compound for the development of new drugs, able to normalize the intestinal motility in inflammation and diabetes.

Effects of various selective phosphodiesterase inhibitors on relaxation and cyclic nucleotide contents in porcine iris sphincter

The effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in porcine iris sphincter were investigated. Forskolin and sodium nitroprusside inhibited carbachol (CCh)-induced contraction in a concentration-dependent manner. Various selective PDE inhibitors, vinpocetine (type 1), erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20-1724 (type 4) and zaprinast (type 5), also inhibited CCh-induced contraction in a concentration-dependent manner. The rank order of potency of IC(50) was zaprinast > Ro20-1724 > EHNA >/= milrinone > vinpocetine. In the presence of CCh (0.3 muM), vinpocetine, milrinone and Ro20-1724 increased cAMP, but not cGMP, contents. In contrast, zaprinast and EHNA both increased cGMP, but not cAMP, contents. This indicates that vinpocetine-, milrinone- and Ro20-1724-induced relaxation is correlated with cAMP, while EHNA- and zaprinast- induced relaxation is correlated with cGMP in porcine iris sphincter.

Effect of Boswellia serrata on intestinal motility in rodents: inhibition of diarrhoea without constipation

Clinical studies suggest that the Ayurvedic plant Boswellia serrata may be effective in reducing diarrhoea in patients with inflammatory bowel disease. In the present study, we evaluated the effect of a Boswellia serrata gum resin extract (BSE) on intestinal motility and diarrhoea in rodents. BSE depressed electrically-, acetylcholine-, and barium chloride-induced contractions in the isolated guinea-pig ileum, being more potent in inhibiting the contractions induced by acetylcholine and barium chloride. The inhibitory effect of BSE on acetylcholine-induced contractions was reduced by the L-type Ca(2+) channel blockers verapamil and nifedipine, but not by the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid, by the phosphodiesterase type IV inhibitor rolipram or by the lipoxygenase inhibitor zileuton. 3-acetyl-11-keto-beta-boswellic acid, one of the main active ingredients of B. serrata, inhibited acetylcholine-induced contractions. BSE inhibited upper gastrointestinal transit in croton oil-treated mice as well as castor oil-induced diarrhoea. However, BSE did not affect intestinal motility in control mice, both in the small and in the large intestine. It is concluded that BSE directly inhibits intestinal motility with a mechanism involving L-type Ca(2+) channels. BSE prevents diarrhoea and normalizes intestinal motility in pathophysiological states without slowing the rate of transit in control animals. These results could explain, at least in part, the clinical efficacy of this Ayurvedic remedy in reducing diarrhoea in patients with inflammatory bowel disease.

Effects of various selective phosphodiesterase inhibitors on carbachol-induced contraction and cyclic nucleotide contents in the guinea pig gall bladder

The effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in the guinea pig gall bladder were investigated. Various selective PDE inhibitors, vinpocetine (type 1), erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20-1724 (type 4), and zaprinast (type 5), inhibited CCh-induced contractions in a concentration-dependent manner. The rank order of potency for the gall bladder was Ro20-1724 > vinpocetine > EHNA > milrinone > zaprinast, which was different from that of the trachea, taenia coli, and aorta. In the presence of CCh (0.3 muM), vinpocetine, milrinone, and Ro20-1724 each increased cAMP content, but not cGMP. By contrast, zaprinast increased cGMP content, but not cAMP, and EHNA increased both cAMP and cGMP contents. These results suggest that vinpocetine-, milrinone-, and Ro20-1724-induced relaxation was correlated with cAMP, zaprinast-induced relaxation was correlated with cGMP, and that EHNA-induced relaxation was correlated with cAMP and cGMP in the guinea pig gall bladder. In conclusion, the effect of PDE inhibitors in the guinea pig gall bladder was different from those in smooth muscles, such as the trachea, taenia coli, and aorta.

Effects of various selective phosphodiesterase inhibitors on carbachol-induced contraction and cyclic nucleotide contents in guinea pig taenia coli

Effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in guinea pig taenia coli were investigated. Forskolin and sodium nitroprusside inhibited carbachol (CCh)-induced contraction in a concentration-dependent manner. Various selective PDE inhibitors, vinpocetine (type 1), erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20-1724(type 4) and zaprinast (type 5) inhibited CCh-induced contraction in a concentration-dependent manner, but the inhibition of milrinone was noticeably smaller than that of the other PDE inhibitors. The rank order of potency was zaprinast > vinpocetine > EHNA > Ro20-1724 > milrinone. In the presence of CCh (0.3 microM), vinpocetine and Ro20-1724 both increased cAMP content, but not cGMP. By contrast, EHNA and zaprinast both increased cGMP content, but not cAMP. Pretreatment with ODQ (30 microM), a soluble guanylyl cyclase inhibitor, decreased the inhibition of CCh-induced contraction by EHNA or zaprinast. Pretreatment with SQ22536 (100 microM), an adenylyl cyclase inhibitor, decreased the inhibition of CCh-induced contraction by vinpocetine or Ro20-1724. In conclusion, it was indicated that vinpocetine- or Ro20-1724-induced relaxation was correlated with cAMP but EHNA- or zaprinast- induced relaxation was correlated with cGMP.

Relationship between phosphodiesterase inhibition induced by several Kampo medicines and smooth muscle relaxation of gastrointestinal tract tissues of rats

Given a lack of information, we assessed the effects of Kampo medicines: Dai-saiko-to, Tsu-do-san, San'o-shashin-to, and Sairei-to, which have been used for various gastrointestinal diseases, on the phosphodiesterase activity and smooth muscle tone of the gastrointestinal tract. Clinically relevant concentrations of each Kampo extract (0.1 - 1 mg/ml) decreased the phosphodiesterase activity as well as smooth muscle tone. The extent of phosphodiesterase inhibition as well as smooth muscle relaxation by these Kampo extracts was prominent for the lower gastrointestinal tract. Also, there was a good correlation between the extents of drug-induced phosphodiesterase inhibition and smooth muscle relaxation, indicating the presence of their causal link. These results may partially provide the basis for understanding the mechanism of the clinical utility of Kampo extracts in gastrointestinal tract diseases.

Lack of cyclic nucleotide regulation of MBCQ-induced relaxation of rat ileal smooth muscle

The effects of the type V phosphodiesterase (PDE V) inhibitors, MBCQ, zaprinast and dipyridamole, on the relationship between relaxation and cyclic nucleotide content were investigated in rat ileal smooth muscle. Each of MBCQ (0.01-10 microM), zaprinast (0.1-100 microM) and dipyridamole (0.1-100 microM) inhibited carbachol (CCh; 10 microM)-induced contractions in a concentration-dependent manner. When compared with the concentrations of these agents producing 50% relaxation (IC50) of CCh-induced contraction, MBCQ was 14-20 fold more potent than the other agents. The inhibitory potency of these agents against high K+ (65 mM KCl)-induced contractions were similar to that for CCh. MBCQ (1, 10 microM) did not significantly increase the cGMP content above control levels in the presence of CCh (10 microM). Both Zaprinast (1-100 microM) and dipyridamole (1-100 microM) increased the cGMP content of smooth muscle preparations in a concentration-dependent manner. There was a positive correlation between the inhibition of the CCh-induced contraction and the increase in cGMP content elicited by zaprinast and dipyridamole (zaprinast; r=0.72, P<0.05, dipyridamole; r=0.92, P<0.05). However, MBCQ at a concentration which induced a medium-sized relaxation did not significantly increase the cGMP content. Neither MBCQ, zaprinast nor dipyridamole significantly increased the cAMP content of the preparations above control. In summary, it is suggested that the inhibition of CCh-induced contractions by zaprinast and dipyridamole involves increases in cGMP content via inhibition of PDE V. However the inhibition of CCh-induced contraction by MBCQ may not involve cyclic nucleotides in rat ileal smooth muscle.

Vinpocetine selectively inhibits neurotransmitter release triggered by sodium channel activation

The effects of vinpocetine on internal Na+ (Na(i)), cAMP accumulation, internal Ca2+ (Ca(i)) and excitatory amino acid neurotransmitters release, under resting and under depolarized conditions, was investigated in rat striatum synaptosomes. Veratridine (20 microM) or high K+ (30 mM) were used as depolarizing agents. Results show that vinpocetine in the low microM range inhibits the elevation of Na(i), the elevation of Ca(i) and the release of glutamate and aspartate induced by veratridine depolarization. In contrast, vinpocetine fails to inhibit the rise of Ca(i) and the neurotransmitter release induced by high K+, which are both TTX insensitive responses. Results also show that the inhibition exerted by vinpocetine on all the above veratridine-induced responses is not reflected in PDE activity. Our interpretation of these results is that vinpocetine inhibits neurotransmitter release triggered by veratridine activation of voltage sensitive Na+ channels, but not that triggered by a direct activation of VSCC. Thus, the main mechanism involved in the neuroprotective action of vinpocetine in the CNS is unlikely to be due to a direct inhibition of Ca2+ channels or PDE enzymes, but rather the inhibition of presynaptic Na+ channel-activation unchained responses.

The role of cyclic nucleotides in guinea-pig bladder contractility

1. The effects of phosphodiesterase (PDE) inhibition and forskolin pretreatment on the contractile responses of guinea-pig urinary bladder strips to electrical field stimulation, carbachol, ATP and KCl were studied. 2. Inhibition of cyclic AMP-specific PDE4 isozymes by rolipram significantly reduced the contractile response of bladder strips to field stimulation. Rolipram also suppressed the contractile response to low concentrations of carbachol, but potentiated the response to high concentrations. The contractile response to ATP was significantly reduced by rolipram treatment, but that to KCl was unaltered. 3. Inhibition of cyclic GMP-specific PDE5 isozymes by zaprinast had no effects on the contractile response of bladder strips to field stimulation, ATP or KCl. Zaprinast suppressed the contractile responses to 1 microM carbachol and potentiated the response to high concentrations. 4. Contractile responses to field stimulation and to carbachol after pretreatment with the adenylyl cyclase activator, forskolin, were qualitatively similar to those caused by rolipram treatment. beta-Adrenoceptor blockade with propranolol partially reversed the inhibitory effects of rolipram on the response to field stimulation. 5. Rolipram significantly reduced the contractile response of bladder strips from sensitized guinea-pigs to ovalbumin challenge, but zaprinast was ineffective. PDE inhibition had similar effects on the responsiveness of control and of sensitized guinea-pig bladder strips to field stimulation, carbachol, ATP and KCl. 6. The data suggest that the contractile response of guinea-pig bladder strips can be modified by increases in cyclic AMP levels.