Nicolas Renault

Minireview: Toward the Establishment of a Link between Melatonin and Glucose Homeostasis: Association of Melatonin MT2 Receptor Variants with Type 2 Diabetes

The existence of interindividual variations in G protein-coupled receptor sequences has been recognized early on. Recent advances in large-scale exon sequencing techniques are expected to dramatically increase the number of variants identified in G protein-coupled receptors, giving rise to new challenges regarding their functional characterization. The current minireview will illustrate these challenges based on the MTNR1B gene, which encodes the melatonin MT2 receptor, for which exon sequencing revealed 40 rare nonsynonymous variants in the general population and in type 2 diabetes (T2D) cohorts. Functional characterization of these MT2 mutants revealed 14 mutants with loss of Gi protein activation that associate with increased risk of T2D development. This repertoire of disease-associated mutants is a rich source for structure-activity studies and will help to define the still poorly understood role of melatonin in glucose homeostasis and T2D development in humans. Defining the functional defects in carriers of rare MT2 mutations will help to provide personalized therapies to these patients in the future.

Structural Insight into PPARγ Ligands Binding

Peroxisome Proliferator Activated Receptors (PPARs) are a family of three related nuclear receptors first cloned in 1990. Their involvement in glucidic and lipidic homeostasis quickly made them an attractive target for the treatment of metabolic syndrome, the most prevalent mortality factor in developed countries. They therefore attracted much synthetical efforts, more particularly PPARγ. Supported by a large number of crystallographic studies, data derived from these compounds lead to a fairly clear view of the agonist binding mode into the Ligand Binding Domain (LBD). Nearly all the compounds conform to a three-module structure, with a binder group involved in a series of hydrogen bonds in front of the ligand-dependent Activation Function (AF2), a linker mostly arranged around a phenoxyethyl and an effector end occupying the large cavity of the binding site. Following the marketing of the glitazones and the observation of the hepatotoxicity of troglitazone, variations in the binder led to the glitazars, and then pharmacomodulations have been undertaken on the two other modules, leading to a large family of highly related chemical structures. Some compounds, while still adhering to the three-module structure, diverge from the mainstream, such as the phthalates. Curiously, these plasticizers were known to elicit biological effects that led to the discovery of PPARs but were not actively studied as PPARs agonists. As the biological effects of PPARs became clearer, new compounds were also found to exert at least a part of their actions by the activation of PPARγ.

Switching invariant natural killer T (iNKT) cell response from anticancerous to anti-inflammatory effect: molecular bases.

Since the discovery in 1995 of α-galactosylceramide 1 (α-GalCer), also known as KRN7000,1 hundreds of compounds have been synthesized in order to activate invariant natural killer T (iNKT) cells. Such keen interest for this lymphocyte cell type is due to its ability to produce different cytokines that bias the immune response toward a Th1 or Th2 profile. Thus, an understanding of the immune polarization mechanism via iNKT activation may pave the way toward new therapeutics in various domains including cancer and infectious and autoimmune diseases. In this review, we propose an up-to-date analysis of iNKT activators associated with a structure-activity relationship (SAR) study aimed at complementing available reviews by highlighting molecular bases for a selective immune response.

3-Carboxamido-5-aryl-isoxazoles as new CB2 agonists for the treatment of colitis.

Recent investigations showed that anandamide, the main endogenous ligand of CB1 and CB2 cannabinoid receptors, possesses analgesic, antidepressant and anti-inflammatory effects. In the perspective to treat inflammatory bowel disease (IBD), our approach was to develop new selective CB2 receptor agonists without psychotropic side effects associated to CB1 receptors. In this purpose, a new series of 3-carboxamido-5-aryl-isoxazoles, never described previously as CB2 receptor agonists, was designed, synthesized and evaluated for their biological activity. The pharmacological results have identified great selective CB2 agonists with in vivo anti-inflammatory activity in a DSS-induced acute colitis mouse model.

New FAAH inhibitors based on 3-carboxamido-5-aryl-isoxazole scaffold that protect against experimental colitis

Growing evidence suggests a role for the endocannabinoid (EC) system, in intestinal inflammation and compounds inhibiting anandamide degradation offer a promising therapeutic option for the treatment of inflammatory bowel diseases. In this paper, we report the first series of carboxamides derivatives possessing FAAH inhibitory activities. Among them, compound 39 displayed significant inhibitory FAAH activity (IC(50)=0.088 μM) and reduced colitis induced by intrarectal administration of TNBS.

4-Oxo-1,4-dihydropyridines as Selective CB2 Cannabinoid Receptor Ligands: Structural Insights into the Design of a Novel Inverse Agonist Series

Growing evidence shows that CB(2) receptor is an attractive therapeutic target. Starting from a series of 4-oxo-1,4-dihydroquinoline-3-carboxamide as selective CB(2) agonists, we describe here the medicinal chemistry approach leading to the development of CB(2) receptor inverse agonists with a 4-oxo-1,4-dihydropyridine scaffold. The compounds reported here show high affinity and potency at the CB(2) receptor while showing only modest affinity for the centrally expressed CB(1) cannabinoid receptor. Further, we found that the functionality of this series is controlled by its C-6 substituent because agonists bear a methyl or a tert-butyl group and inverse agonists, a phenyl or 4-chlorophenyl group, respectively. Finally, in silico studies suggest that the C-6 substituent could modulate the conformation of W6.48 known to be critical in GPCR activation.

Homology Modeling of MT1 and MT2 Receptors

Melatonin is a neurohormone synthesized and secreted mainly during the dark period of the circadian cycle by the pineal gland. It has already been proved to be involved in a number of chronobiological processes, most of them being mediated by its membranar receptors MT1 and MT2. Both are members of the GPCR class and, despite the interest they elicit, their 3D structure is still to be described. Models for both human MT1 and MT2 receptors have been constructed by homology modeling, using the X-ray structure of bovine rhodopsin as template. These models have been evaluated in terms of hydrophobic properties of the helices and refined to take into account the rearrangement of GPCRs necessary for their activation, thus leading to a putative activated model for each subtype.

Molecular modelling of phthalates – PPARs interactions

Di(2-ethylhexyl) phthalate (DEHP) is the most widely plasticizer for polyvinyl chloride (PVC) that is used in plastic tubes, in medical and paramedical devices as well as in food storage packaging. The toxicological profile of DEHP has been evaluated in a number of experimental animal models and has been extensively documented. Its toxicity is in part linked to the activation of the peroxisome proliferator-activated receptor α (PPARα). As a response, an intensive research for a new, biologically inert plasticizer has been initiated. Among the alternative studied, tri(2-ethylhexyl) trimellitate (TEHTM) or trioctyl trimellitate (TOTM) has attracted increasing interest. However, very little information is available on their biological effects. We proceeded to dock TOTM, DEHP and its metabolites in order to identify compounds that are likely to interact with PPARα and PPARγ binding sites. The results obtained hint that TOTM is not able to bind to PPARs and should therefore be safer than DEHP.

Virtual screening of CB(2) receptor agonists from bayesian network and high-throughput docking: structural insights into agonist-modulated GPCR features.

The relevance of CB2‐mediated therapeutics is well established in the treatment of pain, neurodegenerative and gastrointestinal tract disorders. Recent works such as the crystallization of class‐A G‐protein‐coupled receptors in a range of active states and the identification of specific anchoring sites for CB2 agonists challenged us to design a reliable agonist‐bound homology model of CB2 receptor. Docking‐scoring enrichment tests of a high‐throughput virtual screening of 140 compounds led to 13 hits within the micromolar affinity range. Most of these hits behaved as CB2 agonists, among which two novel full agonists emerged. Although the main challenge was a high‐throughput docking run targeting an agonist‐bound state of a CB2 model, a prior 2D ligand‐based Bayesian network was computed to enrich the input commercial library for 3D screening. The exclusive discovery of agonists illustrates the reliability of this agonist‐bound state model for the identification of polar and aromatic amino acids as new agonist‐modulated CB2 features to be integrated in the wide activation pathway of G‐protein‐coupled receptors.

Genetic polymorphism of CYP4A11 and CYP4A22 genes and in silico insights from comparative 3D modelling in a French population

The CYP4A subfamily is known to ω-hydroxylate the endogenous arachidonic acid into 20-hydroxyeicosatetranoic acid, which has renovascular and tubular functions. The aim of this work was to report a comprehensive investigation of the CYP4A11 and CYP4A22 genetic polymorphisms in a French population. Using PCR-SSCP and sequencing strategies, a total of 26 sequence variations were identified comprising 3 missense mutations for CYP4A11 (Ser404Phe, Phe434Ser and Arg505His) and 7 missense mutations for CYP4A22 (Arg126Trp, Gly130Ser, Asn152Tyr, Val185Phe, Cys231Arg, Leu428Pro and Leu509Phe). In comparison with SNPs reported in the database (dbSNP) of the National Center for Biotechnology information (NCBI), 6 and 3 novel polymorphisms were identified in CYP4A11 and CYP4A22, respectively. The potential impact of the amino acid substitutions on the structure and/or catalytic activity of the enzymes has been estimated by the construction and validation of the CYP4A 3D models. These results could be helpful for further investigations of the potential role of CYP4A variants in the genetic susceptibility to cardiovascular diseases in humans such as arterial hypertension.