The melatonin receptor antagonist luzindole induces the activation of cellular stress responses and decreases viability of rat pancreatic stellate cells

Abstract

In this study, we have examined the effects of luzindole, a melatonin receptor-antagonist, on cultured pancreatic stellate cells. Intracellular free-Ca 2+ concentration, production of reactive oxygen species (ROS), activation of mitogen-activated protein kinases (MAPK), endoplasmic reticulum stress and cell viability were analyzed. Stimulation of cells with the luzindole (1, 5, 10 and 50 μM) evoked a slow and progressive increase in intracellular free Ca 2+ ([Ca 2+ ] i) towards a plateau. The effect of the compound on Ca 2+ mobilization depended on the concentration used. Incubation of cells with the sarcoendoplasmic reticulum Ca 2+-ATPase inhibitor thapsigargin (1 μM), in the absence of Ca 2+ in the extracellular medium, induced a transient increase in [Ca 2 + ] i. In the presence of thapsigargin, the addition of luzindole to the cells failed to induce further mobilization of Ca 2+. Luzindole induced a concentration-dependent increase in ROS generation, both in the cytosol and in the mitochondria. This effect was smaller in the absence of extracellular Ca 2+. In the presence of luzindole the phosphorylation of p44/42 and p38 MAPKs was increased, whereas no changes in the phosphorylation of JNK could be noted. Moreover, the detection of the endoplasmic reticulum stress-sensor BiP was increased in the presence of luzindole. Finally, viability was decreased in cells treated with luzindole. Because cellular membrane receptors for melatonin have not been detected in pancreatic stellate cells, we conclude that luzindole could exert direct effects that are not mediated through its action on melatonin membrane receptors.

Melatonin alleviates myocardial dysfunction through inhibition of endothelial‐to‐mesenchymal transition via the NF‐κB pathway

“…Melatonin binds to its receptors on HUVECs, which are involved in antioxidant and anti‐inflammatory effects and regulate EC function 21 . Luzindole, an antagonist of the melatonin receptor located at the cell membrane, is used to study the signaling pathways through which melatonin acts in diverse cellular types 22 . The competitive antagonist of melatonin receptors was confirmed to interfere with the inhibition of melatonin‐induced EndMT progression by assessing endothelial and mesenchymal related proteins (Supporting Information data).…”

“…21 Luzindole, an antagonist of the melatonin receptor located at the cell membrane, is used to study the signaling pathways through which melatonin acts in diverse cellular types. 22 The competitive antagonist of melatonin receptors was confirmed to interfere with the inhibition of melatonin-induced EndMT progression by assessing endothelial and mesenchymal related proteins (Supporting Information data). The expression of melatonin receptors, MT1 and MT2, was confirmed with no changes in HUVECs treated with melatonin or melatonin and luzindole in presence of TGF-β2/IL-1β-induced EndMT.…”

Nocturnal melatonin increases glucose uptake via insulin-independent action in the goldfish brain

“…Luzindole is supposed to be an antagonist of melatonin; however, some reports have showed that it can exert paradoxical effects ( 47 ). It may also act as a partial agonist of the melatonin receptor subtype found in human kidney cells ( 48 ) and have similar effects in rats ( 49 , 50 ). Luzindole has also been found to act as a partial antagonist or a full agonist depending on the receptor subtype in medaka ( 51 ).…”

Pituitary Hormones mRNA Abundance in the Mediterranean Sea Bass Dicentrarchus labrax: Seasonal Rhythms, Effects of Melatonin and Water Salinity

“…However, paradoxical effects as the ones described in this study have been reported. In rats, luzindole may also act as a partial agonist at the MT2 receptor subtype ( Legros et al, 2020 ) or exert direct proper effects ( i.e ., not mediated through melatonin receptors) on plasma membrane K + currents ( Zhou et al, 2003 ) or [Ca 2+ ] i stores ( Estaras et al, 2020 ). In the medaka luzindole acted as a partial antagonist or a full agonist depending on the receptor subtype ( Sakai et al, 2019 ).…”