Relaxant effect of YM976, a novel phosphodiesterase 4 inhibitor, on bovine tracheal smooth muscle

Non-Selective PDE4 Inhibition Induces a Rapid and Transient Decrease of Serum Potassium in Mice

Simple Summary

Inhibitors of phosphodiesterase 4 (PDE4), a group of isoenzymes that hydrolyze and inactivate the second messenger cAMP, produce promising therapeutic benefits, including anti-inflammatory and memory-enhancing effects. Here, we report that, unexpectedly, PDE4 inhibitors also reduce serum potassium levels in mice. As both the total potassium content of the body, as well as the distribution of potassium between intra- and extracellular compartments, are critical for normal cellular functions, we further explored this observation. Several structurally distinct PDE4 inhibitors reduce serum potassium levels in mice, suggesting it is a class effect of these drugs. Serum potassium levels decrease within 15 min of drug injection, suggesting that PDE4 inhibition lowers serum potassium levels by promoting a transcellular shift of potassium from the blood into cells. This shift is a characteristically fast process, compared to a loss of total-body potassium via the kidneys or digestive tract (e.g., diarrhea). Indeed, stimulating cAMP synthesis with β-adrenoceptor agonists is known to rapidly shift potassium into cells, and PDE4 inhibitors appear to mimic this process by preventing PDE4-mediated cAMP degradation. Our findings reveal that the various acute physiologic effects of PDE4 inhibitors are paralleled and/or may be affected by reduced serum potassium levels.

Abstract

The analysis of blood samples from mice treated with the PDE4 inhibitor Roflumilast revealed an unexpected reduction in serum potassium levels, while sodium and chloride levels were unaffected. Treatment with several structurally distinct PAN-PDE4 inhibitors, including Roflumilast, Rolipram, RS25344, and YM976 dose-dependently reduced serum potassium levels, indicating the effect is a class-characteristic property. PDE4 inhibition also induces hypothermia and hypokinesia in mice. However, while general anesthesia abrogates these effects of PDE4 inhibitors, potassium levels decrease to similar extents in both awake as well as in fully anesthetized mice. This suggests that the hypokalemic effects of PDE4 inhibitors occur independently of hypothermia and hypokinesia. PDE4 inhibition reduces serum potassium within 15 min of treatment, consistent with a rapid transcellular shift of potassium. Catecholamines promote the uptake of potassium into the cell via increased cAMP signaling. PDE4 appears to modulate these adrenoceptor-mediated effects, as PDE4 inhibition has no additional effects on serum potassium in the presence of saturating doses of the β-adrenoceptor agonist Isoprenaline or the α₂-blocker Yohimbine, and is partially blocked by pre-treatment with the β-blocker Propranolol. Together, these data suggest that PDE4 inhibitors reduce serum potassium levels by modulating the adrenergic regulation of cellular potassium uptake.

Inhibitors of phosphodiesterases in the treatment of cough

A group of 11 enzyme families of metalophosphohydrolases called phosphodiesterases (PDEs) is responsible for a hydrolysis of intracellular cAMP and cGMP. Xanthine derivatives (methylxanthines) inhibit PDEs without selective action on their single isoforms and lead to many pharmacological effects, e.g. bronchodilation, anti-inflammatory and immunomodulating effects, and thus they can modulate the cough reflex. Contrary, selective PDE inhibitors have been developed to inhibit PDE isoforms with different pharmacological effects based on their tissue expression. In this paper, effects of non-selective PDE inhibitors (e.g. theophylline) are discussed, with a description of other putative mechanisms in their effects on cough. Antitussive effects of selective inhibitors of several PDE isoforms are reviewed, focusing on PDE1, PDE3, PDE4, PDE5 and PDE7. The inhibition of PDEs suggests participation of bronchodilation, suppression of TRPV channels and anti-inflammatory action in cough suppression. Selective PDE3, PDE4 and PDE5 inhibitors have demonstrated the most significant cough suppressive effects, confirming their benefits in chronic inflammatory airway diseases associated with bronchoconstriction and cough.

Inhibitory mechanism of papaverine on carbachol-induced contraction in bovine trachea

We have demonstrated that the relaxing mechanism of papaverine in phasic muscles such as ileum, urinary bladder, and uterus is different from tonic muscles such as aorta. In this study, we examined the inhibitory mechanism of papaverine on carbachol (CCh)-induced contraction in the bovine trachea. Papaverine inhibited muscle contraction and increase in [Ca(2+)](i) level induced by CCh. Papaverine increased cAMP content but not cGMP content. Papaverine did not affect CCh-induced oxidized flavoproteins fluorescence or reduced pyridine nucleotides fluorescence. Papaverine (30 microM) remarkably inhibited muscle tension, but slightly decreased creatine phosphate and ATP contents. Iberiotoxin restored the inhibitions of muscle contraction and [Ca(2+)](i) level induced by papaverine or dibutyryl-cAMP. These results suggested that the relaxing mechanism of papaverine in the bovine trachea is mainly due to increases of cAMP content by inhibiting phosphodiesterase and the mechanism is partially involved in the activation of BK channel by cAMP.

Simultaneous determination of YM-64227, a phosphodiesterase type 4 inhibitor, and its ?ve metabolites in dog plasma by high-performance liquid chromatography with ?uorescence detection

We developed and validated a reversed-phase high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of YM-64227 [4-cyclohexyl-1-ethyl-7-methylpyrido(2,3-d)pyrimidin-2-(1H)-one], a novel and selective phosphodiesterase type 4 inhibitor, and its fi ve hydroxylated metabolites in dog plasma. The plasma samples were extracted with tert-butyl methyl ether under alkali conditions. The analytes were well separated on a phenyl ethyl column (5 microm, 250 x 4.6 mm i.d.), opreating at 40 degrees C and using an acetonitrile-acetic acid gradient at a fl ow rate of 1.0 mL/min. The fluorescence signal was monitored at an excitation and emission wavelength of 330 and 400 nm, respectively. No interfering peak was observed at the retention time of YM-64227, its metabolites or the internal standard. The validated quantitation range of the method was 0.4-200 ng/mL for all analytes using 0.5 mL of the plasma sample. The recovery of analytes in the extraction process was more than 65.5%. The intra- and inter-assay precision was less than 5.1 and 12.6%, respectively, and the intra- and inter-assay accuracy ranged from -8.1 to 11.8% and -8.0 to 9.9%, respectively. Using this assay, the plasma concentration of YM-64227 and metabolites can be determined after the oral administration of YM-64227 to beagle dogs.