Deletion of phosphodiesterase 4D in mice shortens α2-adrenoceptor–mediated anesthesia, a behavioral correlate of emesis

Abstract

IntroductionCyclic nucleotides cAMP and cGMP are degraded by at least 11 families of phosphodiesterases (PDEs 1-11) classified according to their gene sequence, substrate specificity, biochemical regulation, and sensitivity to inhibitors (1, 2). The cAMP-specific PDE4 has attracted considerable attention for the treatment of airway inflammatory diseases, since its inhibition results in attenuated inflammatory responses (1,3,4). However, the therapeutic potential of PDE4 inhibitors has been limited by the side effects of nausea and emesis, observed both in humans and in various animal species following the administration of structurally diverse compounds (5-9). A major challenge in the development of new generations of PDE4 inhibitors is the improvement of the therapeutic index of this class of compounds.PDE4 enzymes use a common binuclear ion center as the core catalytic machinery (10). The reversible binding of the cation cofactors (e.g., Mg 2+ ) results in the presence of two coexisting conformers that bind inhibitors differently: the holoenzyme (enzyme bound with Mg 2+ ) and the apoenzyme (free enzyme) (11,12). In the past, it was observed that the potency of some inhibitors (e.g., rolipram) on PDE activity deviated from their affinity at the high-affinity rolipram binding site (HARBS); this led to the proposal that inhibitors with a reduced potency on the HARBS may have an improved therapeutic index over that of firstgeneration compounds (13-15). It has now been clarified that the HARBS corresponds to the holoenzyme conformer responsible for PDE4 catalysis (11,12).The PDE4 family is composed of four subtypes (PDE4A-D) and multiple splice variants (16). If it were possible to identify the subtype(s) responsible for the beneficial and the side effects associated with PDE4 inhibition, then subtype-selective inhibitors devoid of the tendency to induce nausea and vomiting could be developed. The mechanism of the emetic response associated with PDE4 inhibitors is thought to be a consequence of the inhibition of PDE4 in nontarget tissues (9, 13). It is believed that PDE4 inhibitors produce a pharmacologi- A combination of pharmacological and genetic approaches was used to determine the role of type 4 cAMP-specific cyclic nucleotide phosphodiesterase 4 (PDE4) in reversing α 2 -adrenoceptor-mediated anesthesia, a behavioral correlate of emesis in non-vomiting species. Among the family-specific PDE inhibitors, PDE4 inhibitors reduced the duration of xylazine/ketamine-induced anesthesia in mice, with no effect on pentobarbital-induced anesthesia. The rank order of the PDE4 inhibitors tested was 6-(4- -2450). The specific roles of PDE4B and PDE4D in this model were studied using mice deficient in either subtype. PDE4D-deficient mice, but not PDE4B-deficient mice, had a shorter sleeping time than their wild-type littermates under xylazine/ketamine-induced anesthesia, but not under that induced with pentobarbital. Concomitantly, rolipram-sensitive PDE activity in the brain stem was decreased only in PDE4D-deficient mice c...

Aging-related hyperinflammation in endotoxemia is mediated by the α2A-adrenoceptor and CD14/TLR4 pathways

“…Interestingly enough, while PDE4 has been shown to be critical in the inflammatory response, the isoform PDE4B specifically has been shown to be critical for LPS-activation of TNF-α. In the same study, PDE4D knockout mice were shown not affect the TNF-α levels (Robichaud et al 2002). However, the specific role of PDE4D and its effects on outcomes in the septic response has yet to be fully elucidated.…”

“…In human circulating monocytes, inhibition of PDE4 by rolipram markedly suppresses TNF-α synthesis and release in response to LPS (Torphy 1998). Inhibition of the PDE4 enzyme has been shown to correlate with decreased TNF-α release from LPS-stimulated whole blood, a cellular marker of nonselective PDE4 inhibition (Muise et al 2002; Robichaud et al 2002). …”

Comparison of the Pharmacological Profiles of Selective PDE4B and PDE4D Inhibitors in the Central Nervous System

“…Based on the work of Robichaud et al ., PDE4D has been viewed as the emetic target of PDE4 inhibitors30. Therefore much effort has been made by medicinal chemists to develop allosteric inhibitors that are able to target specific subtypes which differ in their amino acid sequences in the regulatory domains.…”

“…D159687 targets the dimeric form of PDE4D and is sensitive to the PKA phosphorylation activation state of the enzyme through which it appears to achieve improved tolerability22. A-33 targets the monomeric form of PDE4B and achieves improved tolerability by sparing inhibition of PDE4D as PDE4D is thought to be the emetogenic target162330.…”

Distinct Roles of PDE4 and PDE10A in the Regulation of cAMP/PKA Signaling in the Striatum

“…Among PDE4 subtypes, PDE4B is a possible target for rolipram, because the inhibition of conditioned avoidance responding by rolipram was attenuated in PDE4B knock-out mice (Siuciak et al, 2007, 2008). Because the nonselective PDE4 inhibitors including rolipram are known to induce the side effect of nausea and vomiting possibly via inhibition of PDE4D (Robichaud et al, 2002), the development of a PDE4B-selective inhibitor may be necessary for clinical trials in the treatment of psychiatric disorders.…”