Ghrelin attenuates kainic acid-induced neuronal cell death in the mouse hippocampus

Abstract

Ghrelin is an endogenous ligand for GH secretagogue receptor type 1a (GHSR1a), and is produced and released mainly from the stomach. It has been recently demonstrated that ghrelin can function as a neuroprotective factor by inhibiting apoptotic pathways. Kainic acid (KA), an excitatory amino acid L-glutamate analog, causes neuronal death in the hippocampus; previous studies suggest that activated microglia and astrocytes actively participate in the pathogenesis of KA-induced hippocampal neurodegeneration. However, it is unclear whether ghrelin has neuroprotective effect in KA-induced hippocampal neurodegeneration. I.p. injection of KA produced typical neuronal cell death in the CA1 and CA3 pyramidal layers of the hippocampus, and the systemic administration of ghrelin significantly attenuated KA-induced neuronal cell death in these regions through the activation of GHSR1a. Ghrelin prevents KA-induced activation of microglia and astrocytes, and the expression of proinflammatory mediators tumor necrosis factor a, interleukin-1b, and cyclooxygenase-2. The inhibitory effect of ghrelin on the activation of microglia and astrocytes appears to be associated with the inhibition of matrix metalloproteinase-3 expression in damaged hippocampal neurons. Our data suggest that ghrelin has a therapeutic potential for suppressing KA-induced pathogenesis in the brain.

Inactivation of the Constitutively Active Ghrelin Receptor Attenuates Limbic Seizure Activity in Rodents

“…Data from human studies in this area are conflicting, with some studies concluding either increased [15,16] or decreased [17][18][19][20][21][22] plasma levels of ghrelin in epileptic patients. Rodent studies are more consistent, with the majority of studies indicating that ghrelin shows an anticonvulsant action in different models [10,[23][24][25], but its mechanism of action is unknown.…”

“…The ghrelin mimetic capromorelin and the presumed GHSR antagonist A778193 (found in this study to be a GHSR inverse agonist) were generously provided by Dr. Luc Ver Donck and Dr. Dieder Moechars. The ghrelin fragments (1-5) amide, (1-7), (1-9), (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11), (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), and (23-28) were supplied by Phoenix Pharmaceuticals (Karlsruhe, Germany). All other chemicals were analytical reagent grade or better and were supplied by Merck (Darmstadt, Germany).…”

“…Cells were subcultured at 70 to 80 % confluency and re-suspended in 96-well plates at 60,000 cells per well. Concentrations of A778193 were added in quadruplicate to the cells and incubated for 90 minutes at 37°C in air/CO 2 (1-7), (1-9), (1-11), (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), and (23)(24)(25)(26)(27)(28) were tested next to the GHSR agonist capromorelin. A sigmoidal dose response curve was fitted using GraphPad Prism software, GraphPad Software, (La Jolla, USA), yielding a pEC 50 and curve maximum.…”

“…As previously described for activation, cells were first loaded with Fluo-4-acetoxymethyl ester and then pre-incubated for 3 minutes with ghrelin, capromorelin, ghrelin (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) or ghrelin (1-5) amide to induce desensitization. Three minutes later, a second stimulation with ghrelin was performed, and it consisted of a concentration response curve for ghrelin (range, 10 -6 -10 -10 M).…”

“…As for the hippocampus, peripheral ghrelin was shown to enter this brain region to bind to the GHSR, where it promoted spine synapse formation in the stratum radiatum of the CA1 subfield as well as facilitated long-term potentiation generation, which were paralleled by enhanced spatial learning and memory [2]. Since then, various reports have implicated ghrelin in hippocampal functions, and more recently in epilepsy mechanisms [7][8][9][10][11].…”