Phosphodiesterase 4 (PDE4) enzymes catalyze cyclic adenosine monophosphate (cAMP) hydrolysis and are involved in a variety of physiological processes, including brain function, monocyte and macrophage activation, and neutrophil infiltration. Among different PDE4 isoforms, Phosphodiesterases 4D (PDE4Ds) play a fundamental role in cognitive, learning and memory consolidation processes and cancer development. Selective PDE4D inhibitors (PDE4Dis) could represent an innovative and valid therapeutic strategy for the treatment of various neurodegenerative diseases, such as Alzheimer\'s, Parkinson\'s, Huntington\'s, and Lou Gehrig\'s diseases, but also for stroke, traumatic brain and spinal cord injury, mild cognitive impairment, and all demyelinating diseases such as multiple sclerosis. In addition, small molecules able to block PDE4D isoforms have been recently studied for the treatment of specific cancer types, particularly hepatocellular carcinoma and breast cancer. This review overviews the PDE4DIsso far identified and provides useful information, from a medicinal chemistry point of view, for the development of a novel series of compounds with improved pharmacological properties.

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Difamilast, a phosphodiesterase 4 (PDE4) inhibitor, has been shown to be effective in the treatment of atopic dermatitis (AD), although the mechanism involved remains unclear. Since IL-33 plays an important role in the pathogenesis of AD, we investigated the effect of difamilast on IL-33 activity. Since an in vitro model of cultured normal human epidermal keratinocytes (NHEKs) has been utilized to evaluate the pharmacological potential of adjunctive treatment of AD, we treated NHEKs with difamilast and analyzed the expression of the suppression of tumorigenicity 2 protein (ST2), an IL-33 receptor with transmembrane (ST2L) and soluble (sST2) isoforms. Difamilast treatment increased mRNA and protein levels of sST2, a decoy receptor suppressing IL-33 signal transduction, without affecting ST2L expression. Furthermore, supernatants from difamilast-treated NHEKs inhibited IL-33-induced upregulation of TNF-α, IL-5, and IL-13 in KU812 cells, a basophil cell line sensitive to IL-33. We also found that difamilast activated the aryl hydrocarbon receptor (AHR)-nuclear factor erythroid 2-related factor 2 (NRF2) axis. Additionally, the knockdown of AHR or NRF2 abolished the difamilast-induced sST2 production. These results indicate that difamilast treatment produces sST2 via the AHR-NRF2 axis, contributing to improving AD symptoms by inhibiting IL-33 activity.

Folliculitis decalvans (FD) is a rare primary neutrophilic cicatricial alopecia that commonly displays resistance to traditional therapies and remains challenging to treat. Currently, data are lacking with recommendations for therapy-recalcitrant FD. A systematic review was conducted to analyze biologics, small molecule inhibitors, tumor necrosis factor (TNF) inhibitors, Janus kinase (JAK) inhibitors, phosphodiesterase 4 (PDE4) inhibitors, and monoclonal antibodies utilized in the treatment of recalcitrant FD.

UNASSIGNED: Inflammatory Bowel Disease (IBD) poses a persistent challenge in the realm of gastroenterology, necessitating continual exploration of innovative treatment strategies. The limited efficacy and potential side effects associated with existing therapeutic modalities underscore the urgent need for novel approaches in IBD management. This study aims to examine potential therapeutic targets and recent advancements in understanding the disease\'s intricate pathogenesis, with a spotlight on the gut microbiome, immune dysregulation, and genetic predispositions.
UNASSIGNED: A comprehensive review was conducted to delve into the pressing demand for new avenues in IBD treatment. The study examined potential therapeutic targets such as phosphodiesterase 4 (PDE4) inhibitors, immune system modulators, Tyrosine kinase receptors (TYK), Toll-like receptors (TLRs), modulation of the gut microbiota, stem cell therapy, fibrosis management, interleukins (ILs) regulation, and oxidative stress mitigation. Additionally, advances in precision medicine, biologics, small molecule inhibitors, and microbiome modulation techniques were explored.
UNASSIGNED: The investigation unveiled promising therapeutic targets and provided insights into recent breakthroughs that herald a transformative era in the therapeutic landscape for IBD. Advances in precision medicine, biologics, small molecule inhibitors, and the exploration of microbiome modulation techniques stood out as pivotal milestones in the field of gastroenterology.
UNASSIGNED: The findings offer renewed hope for enhanced efficacy, reduced side effects, and improved patient outcomes in the treatment of IBD. These innovative approaches necessitate continual exploration and underscore the urgent need for novel strategies in IBD management, potentially revolutionizing the realm of gastroenterology.

UNASSIGNED: The pathophysiology of keloid formation is poorly understood, and current treatments, including intralesional corticosteroids, cryotherapy, and surgery, are often associated with high resistance to treatment and recurrence. The multifactorial pathogenesis of keloid formation suggests that aberrant inflammatory cytokine signaling associated with keratinocyte dysregulation may contribute to keloid-associated pruritus.
UNASSIGNED: In this paper, we report 2 cases of keloid-associated pruritus that were successfully treated with topical crisaborole 2% ointment, a phosphodiesterase 4 (PDE4) inhibitor. Both patients had previously undergone multiple unsuccessful treatments before being treated with crisaborole 2% ointment. In both cases, the patients experienced complete relief of pruritus with no significant change in keloid size, thickness, or appearance.
UNASSIGNED: We propose that PDE4 inhibitors, such as crisaborole, may be an effective therapy for keloid- associated pruritus.

UNASSIGNED: Although the treatment for pemphigus vulgaris (PV) has been revolutionized by the use of rituximab combined with corticosteroids, new effective therapies with a better safety profile are needed.
UNASSIGNED: A 67-year-old woman was diagnosed with severe mucosal PV, which was initially misdiagnosed as atypical Behçet\'s disease. Following an unsuccessful colchicine treatment, significant improvement was observed upon the introduction of apremilast: reduced pain, fewer lesions, and a stabilized weight. The discontinuation of apremilast led to a rapid relapse. Retrospective analysis through anti-Dsg3 ELISA indicated a gradual decrease in antibody levels during the apremilast treatment.
UNASSIGNED: Apremilast, a phosphodiesterase 4 inhibitor approved for psoriasis and Behçet\'s disease\'s related oral ulcers treatment, demonstrated its efficacy in this PV case. This is the second case report highlighting the effectiveness of apremilast for PV treatment. Apremilast\'s ability to upregulate cyclic adenosine monophosphate (cAMP) levels appears to contribute to the stabilization of keratinocyte adhesion.
UNASSIGNED: Apremilast may be a promising therapeutic option for the treatment of pemphigus, with an innovative mechanism of action, no induced immunosuppression, and good tolerance. It could be a good alternative to steroids, in the treatment regimen of steroids combined with rituximab.

Four new p-terphenyl derivatives, talaroterphenyls A-D (1-4), together with three biosynthetically related known ones (5-7), were obtained from the mangrove sediment-derived Talaromyces sp. SCSIO 41412. Compounds 1-3 are rare p-terphenyls, which are completely substituted on the central benzene ring by oxygen atoms; this is the first report of their isolation from natural sources. Their structures were elucidated through NMR spectroscopy, HRESIMS, and X-ray diffraction. Genome sequence analysis revealed that 1-7 were biosynthesized from tyrosine and phenylalanine, involving four key biosynthetic genes (ttpB-ttpE). These p-terphenyls (1-7) and 36 marine-derived terphenyl analogues (8-43) were screened for phosphodiesterase 4 (PDE4) inhibitory activities, and 1-5, 14, 17, 23, and 26 showed notable activities with IC50 values of 0.40-16 μM. The binding pattern of p-terphenyl inhibitors 1-3 with PDE4 were explored by molecular docking analysis. Talaroterphenyl A (1), with a low cytotoxicity, showed obvious anti-inflammatory activity in LPS-stimulated RAW264.7 cells. Furthermore, in the TGF-β1-induced medical research council cell strain-5 (MRC-5) pulmonary fibrosis model, 1 could down-regulate the expression levels of FN1, COL1, and α-SMA significantly at concentrations of 5-20 μM. This study suggests that the oxidized p-terphenyl 1, as a marine-derived PDE4 inhibitor, could be used as a promising antifibrotic agent.

UNASSIGNED: Atopic dermatitis (AD), a chronic inflammatory, pruritic skin disorder, is seen primarily in the pediatric population but can be found among all age groups. The symptoms of AD can cause embarrassment in patients and can interrupt daily activities and productivity, potentially resulting in avoidance of social situations. In addition to nonpharmacologic management, mainstay pharmacologic treatments for AD are topical medications including corticosteroids, calcineurin inhibitors, phosphodiesterase-4 inhibitors, and topical Janus kinase (JAK) inhibitors. Promising new drugs-oral JAK inhibitors and monoclonal antibodies-have emerged as new treatment options for moderate-to-severe AD.

Microglia activity can drive excessive synaptic loss during the prodromal phase of Alzheimer\'s disease (AD) and is associated with lowered cyclic adenosine monophosphate (cAMP) due to cAMP phosphodiesterase 4B (PDE4B). This study aimed to investigate whether long-term inhibition of PDE4B by A33 (3 mg/kg/day) can prevent synapse loss and its associated cognitive decline in APPswe/PS1dE9 mice. This model is characterized by a chimeric mouse/human APP with the Swedish mutation and human PSEN1 lacking exon 9 (dE9), both under the control of the mouse prion protein promoter. The effects on cognitive function of prolonged A33 treatment from 20 days to 4 months of age, was assessed at 7-8 months. PDE4B inhibition significantly improved both the working and spatial memory of APPswe/PSdE9 mice after treatment ended. At the cellular level, in vitro inhibition of PDE4B induced microglial filopodia formation, suggesting that regulation of PDE4B activity can counteract microglia activation. Further research is needed to investigate if this could prevent microglia from adopting their \'disease-associated microglia (DAM)\' phenotype in vivo. These findings support the possibility that PDE4B is a potential target in combating AD pathology and that early intervention using A33 may be a promising treatment strategy for AD.