title: Neurotoxicity of the steroidal alkaloids tomatine and tomatidine is RIP1 kinase- and caspase-independent and involves the eIF2α branch of the endoplasmic reticulum.
abstract: Steroidal alkaloids are a class of natural products that occur in several species of the Solanaceae family. In the case of the tomato plant (Lycopersicon esculentum Mill.), tomatine and its aglycone, tomatidine, are the most representative molecules. These steroidal alkaloids have already shown several potentially useful biological activities, from anticancer to anti-inflammatory or antibacterial. In this work, the toxicity of these molecules in neuronal cells, namely in the neuroblastoma cell line SH-SY5Y, was assessed, emphasis being given to the cellular mechanisms underlying the effects observed. The results show that tomatine/tomatidine-induced cell death is caspase- and RIP1 kinase-independent, as cell death is not prevented by the pan-caspase inhibitor Z-VAD.fmk or by RIP1 inhibitor necrostatin-1. Analysis of Ca2+levels using the fluorescent probe Fura-2/AM indicates that both tomatine and tomatidine have a marked effect upon Ca2+homeostasis by increasing cytosolic Ca2+, an event that might be associated with their effect upon the endoplasmic reticulum. We show that the toxicity of these molecules require the PERK/eIF2α branch of the unfolded protein response, but not the IRE1α branch. Given the role of the endoplasmic reticulum in proteostasis, the ability of these molecules to inhibit the proteasome was also evaluated. Tomatine was able to inhibit the chymotrypsin-like catalytic core of purified human 20S proteasome, as shown by its ability to prevent degradation of the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-AMC, thus suggesting that interference with proteostasis can be responsible for the toxicity of these steroidal alkaloids. This study is relevant as it sheds a light regarding the toxicity of molecules present in one of the most consumed plants worldwide.
authors.affiliation: REQUIMTE/LAQV, Laboratório de Farmacognosia, Departamento de Química, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, N° 228, 4050-213 Porto, Portugal.
authors.forename: Daniela Correia
authors.initials: DC
authors.lastname: da Silva
authors.affiliation: REQUIMTE/LAQV, Laboratório de Farmacognosia, Departamento de Química, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, N° 228, 4050-213 Porto, Portugal.
authors.forename: Paula B
authors.initials: PB
authors.lastname: Andrade
authors.affiliation: REQUIMTE/LAQV, Laboratório de Farmacognosia, Departamento de Química, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, N° 228, 4050-213 Porto, Portugal.
authors.forename: Patrícia
authors.initials: P
authors.lastname: Valentão
authors.affiliation: REQUIMTE/LAQV, Laboratório de Farmacognosia, Departamento de Química, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, N° 228, 4050-213 Porto, Portugal. Electronic address: dpereira@ff.up.pt.
authors.forename: David M
authors.initials: DM
authors.lastname: Pereira
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D020013:Calcium Signaling / Q000187:drug effects; D061945:Caspase Inhibitors / Q000494:pharmacology; D020169:Caspases / Q000737:chemistry / Q000378:metabolism; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism; D053145:Cell Nucleus Size / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D015852:Eukaryotic Initiation Factor-2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D018551:Solanum lycopersicum / Q000737:chemistry; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000633:toxicity*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014053:Tomatine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000633:toxicity*; D056811:Unfolded Protein Response / Q000187:drug effects*
chemical_list: D061945:Caspase Inhibitors; D015852:Eukaryotic Initiation Factor-2; D061988:Proteasome Inhibitors; D047428:Protein Kinase Inhibitors; C003677:tomatidine; D014053:Tomatine; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D020169:Caspases
keywords: Calcium; Cell death mechanisms; Neurotoxicity: unfolded protein response; Steroidal alkaloids