Phosphodiesterase type 4 (PDE4) (PDE4)

Phosphodiesterase type 4 (PDE4) is a family of enzymes, comprising four subtypes (PDE4A, PDE4B, PDE4C, and PDE4D), that specifically catalyze the hydrolysis of cyclic adenosine monophosphate (cAMP) [9, 18]. As cAMP is a critical second messenger in various signaling pathways, PDE4 plays a central role in regulating immune responses, neurotransmission, and smooth muscle tone [1, 8]. These enzymes are predominantly expressed in inflammatory and immune cells, as well as in the central nervous system and airway smooth muscle [1, 15]. Dysregulation of PDE4 activity is associated with chronic inflammatory diseases such as chronic obstructive pulmonary disease (COPD), asthma, psoriasis, and atopic dermatitis, as well as neurological conditions like depression and cognitive impairment [1, 4, 12]. Therapeutic targeting of PDE4 with small-molecule inhibitors, such as roflumilast and apremilast, increases intracellular cAMP levels to exert potent anti-inflammatory and bronchodilatory effects [3, 5]. However, the clinical utility of systemic PDE4 inhibitors is often limited by a narrow therapeutic window, primarily due to gastrointestinal side effects like nausea and emesis, which are thought to be mediated by the inhibition of specific PDE4 isoforms in the brain [4, 9, 17].

Other names

PDE4APDE4BPDE4CPDE4DcAMP-specific 3',5'-cyclic phosphodiesterase 4ROI-cAMP-PDERolipram-inhibited cAMP phosphodiesterase

PDE4 inhibitors prevent the hydrolysis of cyclic adenosine monophosphate (cAMP) into 5'-adenosine monophosphate (5'-AMP) by the PDE4 enzyme family [1, 3]. This inhibition leads to increased intracellular cAMP levels, which subsequently activate protein kinase A (PKA) and exchange protein activated by cAMP (Epac) [12]. These pathways modulate gene expression and protein activity to suppress the production of pro-inflammatory cytokines (e.g., TNF-α, IL-17, IL-23) and enhance the production of anti-inflammatory mediators (e.g., IL-10), resulting in reduced inflammatory cell activation and smooth muscle relaxation [3, 12, 15].