Exploring new scaffolds for angiotensin II receptor antagonism

Nowadays, AT₁ receptor (AT₁R) antagonists (ARBs) constitute the one of the most prevalent classes of antihypertensive drugs that modulate the renin-angiotensin system (RAS). Their main uses include also treatment of diabetic nephropathy (kidney damage due to diabetes) and congestive heart failure. Towards this direction, our study has been focused on the discovery of novel agents bearing different scaffolds which may evolve as a new class of AT₁ receptor antagonists. To fulfill this aim, a combination of computational approaches and biological assays were implemented. Particularly, a pharmacophore model was established and served as a 3D search query to screen the ChEMBL15 database. The reliability and accuracy of virtual screening results were improved by using molecular docking studies. In total, 4 compounds with completely diverse chemical scaffolds from potential ARBs, were picked and tested for their binding affinity to AT₁ receptor. Results revealed high nanomolar to micromolar affinity (IC₅₀) for all the compounds. Especially, compound 4 exhibited a binding affinity of 199 nM. Molecular dynamics simulations were utilized in an effort to provide a molecular basis of their binding to AT₁R in accordance to their biological activities.     

Modulation of Coordinated Activity across Cortical Layers by Plasticity of Inhibitory Synapses

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Melanocortin‐1 receptor structure and functional regulation

The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light.     

The effect of phenformin and other adenosine triphosphate (ATP)-lowering agents on insulin binding to IM-9 human cultured lymphocytes

In the present study, we investigated the mechanism by which the antidiabetic drug phenformin increases insulin binding to its receptors in IM-9 human cultured lymphocytes. After a 24-hr preincubation, phenformin induced a twofold increase in specific 125I-insulin binding, and removal of phenformin was followed 6 hr later by a return in binding to control levels. This effect of phenformin on insulin binding was not a consequence of either inhibition of cell growth, changes in cellular cyclic adenosine monophosphate (AMP) levels, or changes in guanosine triphosphate (GTP) content. Since phenformin is known to inhibit various aspects of cellular energy metabolism, the relationship between 125I-insulin binding and energy metabolism in IM-9 cells was investigated. The phenformin-induced increase in insulin binding to IM-9 cells was related to a time- and dose-dependent decrease in ATP levels. Other agents that lowered ATP levels, including antimycin, dinitrophenol, and 2-deoxyglucose, also raised insulin binding. These studies indicated, therefore, that phenformin enhances insulin binding to receptors on IM-9 cells and that this effect on insulin receptors may be related to alterations in metabolic functions that are reflected by a lowering of ATP levels.     

Stimulation of tissue plasminogen activator production from epithelial cell lines

The aim of this study was to investigate the possibility of enhancing the yield of tissue plasminogen activator (tPA) from two epithelial cell lines of normal (non-malignant) derivation grown in tissue culture. The three agents used in this investigation were chosen because of their proven enhancing effect on analogous cells or products. The anabolic hormone stanozolol was found to have no significant stimulatory effect on these cell lines. A phorbol acetate (12-O-tetradecanoylphorbol 13-acetate) caused a twofold enhancement in tPA yield but the most significant results were obtained with 5-azacytidine. This agent increased the yield by up to fourfold in small stationary cultures and threefold in large-scale microcarrier cultures. A combination of azacytidine and phorbol acetate did not have an additive effect on total yield but did alter the kinetics of tPA expression with time. Indications were that the maximum yield with these types of potentiating agents was achieved as it could not be increased by using a combination of two different agents.     

Pulmonary neuroendocrine cells sense succinate to stimulate myoepithelial cell contraction

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Vitamin K epoxidase activity of rough and smooth microsomes from rat liver

The distribution of vitamin K epoxidase activity in rough and smooth microsomes has been studied and compared to the prothrombin precursor and vitamin K-dependent carboxylase activity. All three activities were high in rough microsomes as compared to the low levels found in smooth microsomes. The results are in agreement with the suggestion that there might be a linkage between the vitamin K-dependent carboxylation and epoxidation reaction in vivo.