Antidepressants interact with an LPA3 receptor binding site: functional and docking studies

The action of the antidepressants imipramine, amitriptyline, and paroxetine on LPA3 receptors was studied in cellulo, using receptor-transfected HEK 293 Flp-In TREx cells, and in silico, through docking simulations. These drugs showed a low affinity for LPA3 receptors with lesser efficacy than LPA (paroxetine {approx} 60% and imipramine and amitriptyline {approx} 30%). When LPA-treated cells (with the agonist present) were challenged with the antidepressants, paroxetine triggered a robust increase in intracellular calcium, whereas imipramine and amitriptyline decreased the calcium concentration below baseline values. For ERK 1/2 phosphorylation, imipramine induced a rapid and potent increase, whereas amitriptyline and paroxetine reduced ERK 1/2 phosphorylation below baseline. Similarly, imipramine produced rapid and robust ERK phosphorylation in LPA-stimulated cells, but amitriptyline decreased ERK 1/2 phosphorylation. Activation with the antidepressants leads to LPA3 internalization; dramatic morphological changes accompany these actions. Docking simulations showed these drugs interact with an LPA3 receptor pocket, denominated Upper Cavity. Although the agonist binding cavity was the same, the amino acids interacting with the various ligands were distinct due to their different chemical structure. The manuscript advances knowledge on the mechanisms of antidepressant effects on LPA3 receptors, which might have potential therapeutic implications.