Phosphodiesterase 4B2 gene is an effector of Toll-like receptor signaling in astrocytes

Differential effects of two phosphodiesterase 4 inhibitors against lipopolysaccharide-induced neuroinflammation in mice

BACKGROUND

Several phosphodiesterase 4 (PDE4) inhibitors have emerged as potential therapeutics for central nervous system (CNS) diseases. This study investigated the pharmacological effects of two selective PDE4 inhibitors, roflumilast and zatolmilast, against lipopolysaccharide-induced neuroinflammation.

RESULTS

In BV-2 cells, the PDE4 inhibitor roflumilast reduced the production of nitric oxide and tumor necrosis factor-α (TNF-α) by inhibiting NF-κB phosphorylation. Moreover, mice administered roflumilast had significantly reduced TNF-α, interleukin-1β (IL-1β), and IL-6 levels in plasma and brain tissues. By contrast, zatolmilast, a PDE4D inhibitor, showed no anti-neuroinflammatory effects in vitro or in vivo. Next, in vitro and in vivo pharmacokinetic studies of these compounds in the brain were performed. The apparent permeability coefficients of 3 µM roflumilast and zatolmilast were high (> 23 × 10^-6 cm/s) and moderate (3.72-7.18 × 10^-6 cm/s), respectively, and increased in a concentration-dependent manner in the MDR1-MDCK monolayer. The efflux ratios were < 1.92, suggesting that these compounds are not P-glycoprotein substrates. Following oral administration, both roflumilast and zatolmilast were slowly absorbed and eliminated, with time-to-peak drug concentrations of 2-2.3 h and terminal half-lives of 7-20 h. Assessment of their brain dispositions revealed the unbound brain-to-plasma partition coefficients of roflumilast and zatolmilast to be 0.17 and 0.18, respectively.

CONCLUSIONS

These findings suggest that roflumilast, but not zatolmilast, has the potential for use as a therapeutic agent against neuroinflammatory diseases.

Phosphodiesterase 4B: Master Regulator of Brain Signaling

Phosphodiesterases (PDEs) are the only superfamily of enzymes that have the ability to break down cyclic nucleotides and, as such, they have a pivotal role in neurological disease and brain development. PDEs have a modular structure that allows targeting of individual isoforms to discrete brain locations and it is often the location of a PDE that shapes its cellular function. Many of the eleven different families of PDEs have been associated with specific diseases. However, we evaluate the evidence, which suggests the activity from a sub-family of the PDE4 family, namely PDE4B, underpins a range of important functions in the brain that positions the PDE4B enzymes as a therapeutic target for a diverse collection of indications, such as, schizophrenia, neuroinflammation, and cognitive function.

Targeting Phosphodiesterases-Towards a Tailor-Made Approach in Multiple Sclerosis Treatment

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS) characterized by heterogeneous clinical symptoms including gradual muscle weakness, fatigue, and cognitive impairment. The disease course of MS can be classified into a relapsing-remitting (RR) phase defined by periods of neurological disabilities, and a progressive phase where neurological decline is persistent. Pathologically, MS is defined by a destructive immunological and neuro-degenerative interplay. Current treatments largely target the inflammatory processes and slow disease progression at best. Therefore, there is an urgent need to develop next-generation therapeutic strategies that target both neuroinflammatory and degenerative processes. It has been shown that elevating second messengers (cAMP and cGMP) is important for controlling inflammatory damage and inducing CNS repair. Phosphodiesterases (PDEs) have been studied extensively in a wide range of disorders as they breakdown these second messengers, rendering them crucial regulators. In this review, we provide an overview of the role of PDE inhibition in limiting pathological inflammation and stimulating regenerative processes in MS.

Cross-talk between PKA-Cβ and p65 mediates synergistic induction of PDE4B by roflumilast and NTHi

Phosphodiesterase 4B (PDE4B) plays a key role in regulating inflammation. Roflumilast, a phosphodiesterase (PDE)4-selective inhibitor, has recently been approved for treating severe chronic obstructive pulmonary disease (COPD) patients with exacerbation. However, there is also clinical evidence suggesting the development of tachyphylaxis or tolerance on repeated dosing of roflumilast and the possible contribution of PDE4B up-regulation, which could be counterproductive for suppressing inflammation. Thus, understanding how PDE4B is up-regulated in the context of the complex pathogenesis and medications of COPD may help improve the efficacy and possibly ameliorate the tolerance of roflumilast. Here we show that roflumilast synergizes with nontypeable Haemophilus influenzae (NTHi), a major bacterial cause of COPD exacerbation, to up-regulate PDE4B2 expression in human airway epithelial cells in vitro and in vivo. Up-regulated PDE4B2 contributes to the induction of certain important chemokines in both enzymatic activity-dependent and activity-independent manners. We also found that protein kinase A catalytic subunit β (PKA-Cβ) and nuclear factor-κB (NF-κB) p65 subunit were required for the synergistic induction of PDE4B2. PKA-Cβ phosphorylates p65 in a cAMP-dependent manner. Moreover, Ser276 of p65 is critical for mediating the PKA-Cβ-induced p65 phosphorylation and the synergistic induction of PDE4B2. Collectively, our data unveil a previously unidentified mechanism underlying synergistic up-regulation of PDE4B2 via a cross-talk between PKA-Cβ and p65 and may help develop new therapeutic strategies to improve the efficacy of PDE4 inhibitor.

Combined anti-inflammatory effects of β2-adrenergic agonists and PDE4 inhibitors on astrocytes by upregulation of intracellular cAMP

Inflammation is an important hallmark of all neurodegenerative diseases and activation of different glial populations may be involved in the progression of some of these disorders. Especially, the activation of astroglia can lead to long-term detrimental morphological changes, such as scar formation. Therefore, improved strategies to modulate inflammation in these cells are currently being investigated. We investigated the interaction of phosphodiesterase (PDE) 4 inhibitors, such as rolipram, with other agents raising cellular cAMP levels. When used alone, none of the PDE4 inhibitors increased cAMP levels. The adenylate cyclase activator forskolin, the β(2)-adrenergic agonist clenbuterol and the mixed β(1)/β(2)-adrenergic agonist isoproterenol increased intracellular cAMP levels of cortical murine astrocytes. This increase was synergistically elevated by rolipram or the PDE4 inhibitor RO-201724, but not by inhibition of PDE3. Inflammatory stimulation of the cells with the cytokines TNF-α, IL-1β and IFN-γ strongly induced PDE4B and augmented overall PDE4 activity, while PDE3 activity was low. Clenbuterol and forskolin caused downregulation of cytokines and chemokines such as IL-6 and MCP-1. This effect was further enhanced by rolipram, but not by the PDE3 inhibitor milrinone. The cAMP-raising drug combinations attenuated the upregulation of TNF-α and IL-6 mRNA and the secretion of IL-6, but did not affect initial NF-κB signalling triggered by the stimulating cytokines. These results indicate that PDE4 may be a valuable anti-inflammatory target in brain diseases, especially under conditions associated with stimulation of cAMP-augmenting astrocyte receptors as is observed by clenbuterol treatment.