Carboxylate isosteres for caspase inhibitors: the acylsulfonamide case revisited.

As part of an ongoing effort to discover inhibitors of caspase-1 with an optimized selectivity and biopharmaceutical profile, acylsulfonamides were explored as carboxylate isosteres for caspase inhibitors. Acylsulfonamide analogues of the clinically investigated caspase-1 inhibitor VRT-043198 and of the pan-caspase inhibitor Z-VAD-CHO were synthesized. The isostere-containing analogues with an aldehyde warhead had inhibitory potencies comparable to the carboxylate references. In addition, the conformational and tautomeric characteristics of these molecules were determined using 1H- and 13C-based NMR. The propensity of acylsulfonamides with an aldehyde warhead to occur in a ring-closed conformation at physiological pH significantly increases the sensitivity to hydrolysis of the acylsulfonamide moiety, yielding the parent carboxylate containing inhibitors. These results indicate that the acylsulfonamide analogues of the aldehyde-based inhibitor VRT-043198 might have potential as a novel type of prodrug for the latter. Finally, inhibition of caspase 1 and 11 mediated inflammation in mouse macrophages was found to correlate with the potencies of the compounds in enzymatic assays.

Neuropeptide Y receptors activation protects rat retinal neural cells against necrotic and apoptotic cell death induced by glutamate.

It has been claimed that glutamate excitotoxicity might have a role in the pathogenesis of several retinal degenerative diseases, including glaucoma and diabetic retinopathy. Neuropeptide Y (NPY) has neuroprotective properties against excitotoxicity in the hippocampus, through the activation of Y1, Y2 and/or Y5 receptors. The principal objective of this study is to investigate the potential protective role of NPY against glutamate-induced toxicity in rat retinal cells (in vitro and in an animal model), unraveling the NPY receptors and intracellular mechanisms involved. Rat retinal neural cell cultures were prepared from newborn Wistar rats (P3-P5) and exposed to glutamate (500 µM) for 24 h. Necrotic cell death was evaluated by propidium iodide (PI) assay and apoptotic cell death using TUNEL and caspase-3 assays. The cell types present in culture were identified by immunocytochemistry. The involvement of NPY receptors was assessed using selective agonists and antagonists. Pre-treatment of cells with NPY (100 nM) inhibited both necrotic cell death (PI-positive cells) and apoptotic cell death (TUNEL-positive cells and caspase 3-positive cells) triggered by glutamate, with the neurons being the cells most strongly affected. The activation of NPY Y2, Y4 and Y5 receptors inhibited necrotic cell death, while apoptotic cell death was only prevented by the activation of NPY Y5 receptor. Moreover, NPY neuroprotective effect was mediated by the activation of PKA and p38K. In the animal model, NPY (2.35 nmol) was intravitreally injected 2 h before glutamate (500 nmol) injection into the vitreous. The protective role of NPY was assessed 24 h after glutamate (or saline) injection by TUNEL assay and Brn3a (marker of ganglion cells) immunohistochemistry. NPY inhibited the increase in the number of TUNEL-positive cells and the decrease in the number of Brn3a-positive cells induced by glutamate. In conclusion, NPY and NPY receptors can be considered potential targets to treat retinal degenerative diseases, such as glaucoma and diabetic retinopathy.