Pharmacokinetic/Pharmacodynamic Modeling of the PDE4 Inhibitor TAK-648 in Type 2 Diabetes: Early Translational Approaches for Human Dose Prediction

A Review of Antidiabetic Medicinal Plants as a Novel Source of Phosphodiesterase Inhibitors: Future Perspective of New Challenges Against Diabetes Mellitus

Intracellular glucose concentration plays a crucial role in initiating the molecular secretory process of pancreatic β-cells through multiple messengers and signaling pathways. Cyclic nucleotides are key physiological regulators that modulate pathway interactions in β -cells. An increase of cyclic nucleotides is controled by hydrolysed phosphodiesterases (PDEs), which degrades cyclic nucleotides into inactive metabolites. Despite the undeniable therapeutic potential of PDE inhibitors, they are associated with several side effects. The treatment strategy for diabetes based on PDE inhibitors has been proposed for a long time. Hence, the world of natural antidiabetic medicinal plants represents an ideal source of phosphodiesterase inhibitors as a new strategy for developing novel agents to treat diabetes mellitus. This review highlights medicinal plants traditionally used in the treatment of diabetes mellitus that have been proven to have inhibitory effects on PDE activity. The contents of this review were sourced from electronic databases, including Science Direct, PubMed, Springer Link, Web of Science, Scopus, Wiley Online, Scifinder and Google Scholar. These databases were consulted to collect information without any limitation date. After comprehensive literature screening, this paper identified 27 medicinal plants that have been reported to exhibit anti-phosphodiesterase activities. The selection of these plants was based on their traditional uses in the treatment of diabetes mellitus. The review emphasizes the antiphosphodiesterase properties of 31 bioactive components derived from these plant extracts. Many phenolic compounds have been identified as PDE inhibitors: Brazilin, mesozygin, artonin I, chalcomaracin, norartocarpetin, moracin L, moracin M, moracin C, curcumin, gallic acid, caffeic acid, rutin, quercitrin, quercetin, catechin, kaempferol, chlorogenic acid, and ellagic acid. Moreover, smome lignans have reported as PDE inhibitors: (+)-Medioresinol di-O-β-d-glucopyranoside, (+)- Pinoresinol di-O-β-d-glucopyranoside, (+)-Pinoresinol-4-O-β-d-glucopyranosyl (1→6)-β-dglucopyranoside, Liriodendrin, (+)-Pinoresinol 4'-O-β-d-glucopyranoside, and forsythin. This review provides a promising starting point of medicinal plants, which could be further studied for the development of natural phosphodiesterase inhibitors to treat diabetes mellitus. Therefore, it is important to consider clinical studies for the identification of new targets for the treatment of diabetes.

The Complexity and Multiplicity of the Specific cAMP Phosphodiesterase Family: PDE4, Open New Adapted Therapeutic Approaches

Cyclic nucleotides (cAMP, cGMP) play a major role in normal and pathologic signaling. Beyond receptors, cyclic nucleotide phosphodiesterases; (PDEs) rapidly convert the cyclic nucleotide in its respective 5′-nucleotide to control intracellular cAMP and/or cGMP levels to maintain a normal physiological state. However, in many pathologies, dysregulations of various PDEs (PDE1-PDE11) contribute mainly to organs and tissue failures related to uncontrolled phosphorylation cascade. Among these, PDE4 represents the greatest family, since it is constituted by 4 genes with multiple variants differently distributed at tissue, cellular and subcellular levels, allowing different fine-tuned regulations. Since the 1980s, pharmaceutical companies have developed PDE4 inhibitors (PDE4-I) to overcome cardiovascular diseases. Since, they have encountered many undesired problems, (emesis), they focused their research on other PDEs. Today, increases in the knowledge of complex PDE4 regulations in various tissues and pathologies, and the evolution in drug design, resulted in a renewal of PDE4-I development. The present review describes the recent PDE4-I development targeting cardiovascular diseases, obesity, diabetes, ulcerative colitis, and Crohn’s disease, malignancies, fatty liver disease, osteoporosis, depression, as well as COVID-19. Today, the direct therapeutic approach of PDE4 is extended by developing allosteric inhibitors and protein/protein interactions allowing to act on the PDE interactome.

Overexpression of PDE4D in mouse liver is sufficient to trigger NAFLD and hypertension in a CD36-TGF-β1 pathway: therapeutic role of roflumilast

Emerging evidence has shown that nonalcoholic fatty liver disease (NAFLD) may be both a consequence and a cause of hypertension. Recent studies have demonstrated that phosphodiesterase 4 (PDE4)-cAMP signaling represents a pathway relevant to the pathophysiology of metabolic disorders. This study aims to investigate the impact and the underlying mechanism of PDE4 in the pathogenesis of NAFLD and its associated hypertension. Here we demonstrated that high-fat-diet (HFD) fed mice developed NAFLD and hypertension, with an associated increase in hepatic PDE4D expression, which can be prevented and even reversed by PDE4 inhibitor roflumilast. Furthermore, we demonstrated that hepatic overexpression of PDE4D drove significant hepatic steatosis and elevation of blood pressure. Mechanistically, PDE4D activated fatty acid translocase CD36 signaling which facilitates hepatic lipid deposition, resulting in TGF-β1 production by hepatocytes and excessive TGF-β1 signaling in vessels and consequent hypertension. Specific silencing of TGF-β1 in hepatocytes by siRNA using poly (β-amino ester) nanoparticles significantly normalized hepatic PDE4D overexpression-activated TGF-β1 signaling in vessels and hypertension. Together, the conclusions indicated that PDE4D plays an important role in the pathogenesis of NAFLD and associated hypertension via activation of CD36-TGF-β1 signaling in the liver. PDE4 inhibitor such as roflumilast, which is clinically approved for chronic obstructive pulmonary disease (COPD) treatment, has the potential to be used as a preventive or therapeutic drug against NAFLD and associated hypertension in the future.

Phosphodiesterase 4 inhibitors in diabetic nephropathy

Phosphodiesterase subtype 4 (PDE4) hydrolyzes cyclic AMP, a secondary messenger that mediates intracellular signaling, and plays key roles in inflammatory and fibrotic responses. Based on these significant anti-inflammatory effects, oral administration of PDE4 inhibitor is approved for the treatment of chronic obstructive pulmonary disease, atopic dermatitis, and psoriasis. However, PDE4 inhibition also has adverse effects, such as diarrhea, vomiting, dyspepsia, and headache. Therefore, the application of PDE4 inhibitors for chronic diseases, such as diabetes and its complications, has not yet been approved. Recent studies have reported the clinical benefits of pentoxifylline, a non-selective PDE inhibitor, in patients with kidney disease. The PDE4 inhibitor, roflumilast, also clearly ameliorates the symptoms of diabetes mellitus by improving hyperglycemia and insulin resistance. However, the beneficial effects of PDE4 inhibition on diabetic nephropathy have not yet been evaluated, and its potential mechanisms of action remain unknown. In this review, we discuss the beneficial effects of PDE4 inhibitors and their mechanisms of action using diabetes and DN models.

Translational and pharmacokinetic-pharmacodynamic application for the clinical development of GDC-0334, a novel TRPA1 inhibitor

GDC‐0334 is a novel small molecule inhibitor of transient receptor potential cation channel member A1 (TRPA1), a promising therapeutic target for many nervous system and respiratory diseases. The pharmacokinetic (PK) profile and pharmacodynamic (PD) effects of GDC‐0334 were evaluated in this first‐in‐human (FIH) study. A starting single dose of 25 mg was selected based on integrated preclinical PK, PD, and toxicology data following oral administration of GDC‐0334 in guinea pigs, rats, dogs, and monkeys. Human PK and PK‐PD of GDC‐0334 were characterized after single and multiple oral dosing using a population modeling approach. The ability of GDC‐0334 to inhibit dermal blood flow (DBF) induced by topical administration of allyl isothiocyanate (AITC) was evaluated as a target‐engagement biomarker. Quantitative models were developed iteratively to refine the parameter estimates of the dose‐concentration‐effect relationships through stepwise estimation and extrapolation. Human PK analyses revealed that bioavailability, absorption rate constant, and lag time increase when GDC‐0334 was administered with food. The inhibitory effect of GDC‐0334 on the AITC‐induced DBF biomarker exhibited a clear sigmoid‐Emax relationship with GDC‐0334 plasma concentrations in humans. This study leveraged emerging preclinical and clinical data to enable iterative refinement of GDC‐0334 mathematical models throughout the FIH study for dose selection in subsequent cohorts throughout the study.

Role of Phosphodiesterase in the Biology and Pathology of Diabetes

Glucose metabolism is the initiator of a large number of molecular secretory processes in β cells. Cyclic nucleotides as a second messenger are the main physiological regulators of these processes and are functionally divided into compartments in pancreatic cells. Their intracellular concentration is limited by hydrolysis led by one or more phosphodiesterase (PDE) isoenzymes. Literature data confirmed multiple expressions of PDEs subtypes, but the specific roles of each in pancreatic β-cell function, particularly in humans, are still unclear. Isoforms present in the pancreas are also found in various tissues of the body. Normoglycemia and its strict control are supported by the appropriate release of insulin from the pancreas and the action of insulin in peripheral tissues, including processes related to homeostasis, the regulation of which is based on the PDE- cyclic AMP (cAMP) signaling pathway. The challenge in developing a therapeutic solution based on GSIS (glucose-stimulated insulin secretion) enhancers targeted at PDEs is the selective inhibition of their activity only within β cells. Undeniably, PDEs inhibitors have therapeutic potential, but some of them are burdened with certain adverse effects. Therefore, the chance to use knowledge in this field for diabetes treatment has been postulated for a long time.

Phosphodiesterase-4 enzyme as a therapeutic target in neurological disorders

Phosphodiesterases (PDE) are a diverse family of enzymes (11 isoforms so far identified) responsible for the degradation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which are involved in several cellular and biochemical functions. Phosphodiesterase 4 (PDE4) is the major isoform within this group and is highly expressed in the mammalian brain. An inverse association between PDE4 and cAMP levels is the key mechanism in various pathophysiological conditions like airway inflammatory diseases-chronic obstruction pulmonary disease (COPD), asthma, psoriasis, rheumatoid arthritis, and neurological disorders etc. In 2011, roflumilast, a PDE4 inhibitor (PDE4I) was approved for the treatment of COPD. Subsequently, other PDE4 inhibitors (PDE4Is) like apremilast and crisaborole were approved by the Food and Drug Administration (FDA) for psoriasis, atopic dermatitis etc. Due to the adverse effects like unbearable nausea and vomiting, dose intolerance and diarrhoea, PDE4 inhibitors have very less clinical compliance. Efforts are being made to develop allosteric modulation with high specificity to PDE4 isoforms having better efficacy and lesser adverse effects. Interestingly, repositioning PDE4Is towards neurological disorders including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS) and sleep disorders, is gaining attention. This review is an attempt to summarize the data on the effects of PDE4 overexpression in neurological disorders and the use of PDE4Is and newer allosteric modulators as therapeutic options. We have also compiled a list of on-going clinical trials on PDE4 inhibitors in neurological disorders.

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.

Placental DNA Methylation Adaptation to Maternal Glycemic Response in Pregnancy

Maternal hyperglycemia during pregnancy is associated with excess fetal growth and adverse perinatal and developmental outcomes. Placental epigenetic maladaptation may underlie these associations. We performed an epigenome-wide association study (>850,000 CpG sites) of term placentas and prenatal maternal glycemic response 2-h post oral glucose challenge at 24-30 weeks of gestation among 448 mother-infant pairs. Maternal 2-h glycemia postload was strongly associated with lower DNA methylation of four CpG sites (false discovery rate [FDR] q <0.05) within the phosphodiesterase 4B gene (PDE4B). Additionally, three other individual CpG sites were differentially methylated relative to maternal glucose response within the TNFRSF1B, LDLR, and BLM genes (FDR q <0.05). DNA methylation correlated with expression of its respective genes in placental tissue at three out of four independent identified loci: PDE4B (r = 0.31, P < 0.01), TNFRSF1B (r = -0.24, P = 0.013), and LDLR (r = 0.32, P < 0.001). In an independent replication cohort (N = 65-108 samples), results were consistent in direction but not significantly replicated among tested CpG sites in PDE4B and TNFRSF1B Our study provides evidence that maternal glycemic response during pregnancy is associated with placental DNA methylation of key inflammatory genes whose expression levels are partially under epigenetic control.