The phosphodiesterases (PDEs) are responsible for the hydrolysis of intracellular cyclic adenosine and guanosine monophosphate (cAMP and cGMP, respectively). They are classified into 11 major families (PDE1-11) and the type 4 phosphodiesterase (PDE4) is a cAMP-specific enzyme localized in airway smooth muscle cells as well as in immune and inflammatory cells. The PDE4 activity is associated with a wide variety of diseases some of which have been related to an inflammatory state, (e.g. asthma, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis (RA)) while others have recently been connected to autoimmune pathology. Therefore, an intense effort toward the development of PDE4 inhibitors has been generated for the last decade. Unfortunately, the effects of prototype PDE4 inhibitors have been compromised by side effects such as nausea and emesis and the clinical use of those compounds is still limited. Several companies have focused on the design of a new generation of PDE4 inhibitors dissociating beneficial activity and adverse effects. This review highlights the recent data of the most advanced clinical candidates, the design and structure activity relationships of the recent structural series reported in the literature over the last two years, as well as recent advances in the multiple therapeutic indications of PDE4 inhibitors (a review with 375 references).

PGs play key regulatory roles in inflammation and immunity. PGD2, released from mast cells and Th2 cells during allergic responses, has recently been shown to target a novel receptor, chemoattractant receptor-homologous molecule expressed TH2 cells (CRTH2), in addition to the classic PGD (DP) receptor. CRTH2 is expressed on Th2 cells and eosinophils and mediates chemotaxis of these cells to PGD2. Thus, CRTH2 is thought to be a key receptor mediating eosinophil and Th2 cell recruitment during allergic responses. To examine the role of CRTH2 in this context in vivo, we generated CRTH2 knockout mice. Surprisingly, in an allergic inflammatory model of asthma, CRTH2 knockout mice showed enhanced eosinophil recruitment into the lung compared with wild-type littermate mice. This is consistent with our observation that CRTH2 knockout cells produce significantly higher amounts of IL-5 and IL-3 in vitro. These results suggest a nonredundant role of CRTH2 in restricting eosinophilia and allergic response in vivo.

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The increase in adiponectin levels in obese patients with untreated dyslipidemia and its mRNA expression in adipose tissue of obese animals are one of the most interesting consequences of rimonabant treatment. Thus, part of rimonabant's metabolic effects could be related to an enhancement of adiponectin secretion and its consequence on the modulation of insulin action, as well as energy homeostasis. The present study investigated the effects of rimonabant in adiponectin knockout mice (Ad(-/-)) exposed to diet-induced obesity conditions. Six-week-old Ad(-/-) male mice and their wild-type littermate controls (Ad(+/+)) were fed a high-fat diet for 7 mo. During the last month, animals were administered daily either with vehicle or rimonabant by mouth (10 mg/kg). High-fat feeding induced weight gain by about 130% in both wild-type and Ad(-/-) mice. Obesity was associated with hyperinsulinemia and insulin resistance. Treatment with rimonabant led to a significant and similar decrease in body weight in both Ad(+/+) and Ad(-/-) mice compared with vehicle-treated animals. In addition, rimonabant significantly improved insulin sensitivity in Ad(+/+) mice compared with Ad(+/+) vehicle-treated mice by decreasing hepatic glucose production and increasing glucose utilization index in both visceral and subcutaneous adipose tissue. In contrast, rimonabant failed to improve insulin sensitivity in Ad(-/-) mice, despite the loss in body weight. Rimonabant's effect on body weight appeared independent of the adiponectin pathway, whereas adiponectin seems required to mediate rimonabant-induced improvement of insulin sensitivity in rodents.