Cisplatin Causes Mitochondrially Mediated Hippocampal Damage

Objectives: Chemotherapy-related cognitive deficits are a major neurological problem. Cisplatin (CDDP) is a commonly used cancer drug, which achieves high concentrations in the brain. We previously reported that CDDP causes neural stem/progenitor cells (NSCs) death. Since the disruption of dendritic spines is associated with cognitive impairments, we tested the hypothesis that CDDP also alters spine integrity in hippocampal neurons (HN) by a mitochondrial- mediated mechanism. Methods: Cultured rat HN and NSCs were treated with CDDP (0.1µM and 1µM). CDDP effects on dendritic spine integrity were studied by quantification of post-synaptic density protein (PSD95) puncta and GFP expressing neurons.  BDNF mRNA levels were quantified by qRT-PCR. For in-vivo studies, rats were treated with 10mg/kg CDDP intraperitoneally daily for 2 days.  Dendritic branching and spines were quantified by Golgi staining. TUNEL assay and Annexin V ICC was performed to detect apoptosis. Hippocampi of rats treated with 6mg/kg cumulative CDDP were harvested and imaged by electron microscopy (EM) 6, 15, and 28 days following exposure.  Mitochondrial respiration was measured using the Seahorse Bioscience Extracellular Flux Analyzer XF24. Results: CDDP induced non-reversible damage to dendritic spines and branches in HN. Exposure to 1µM CDDP caused HN apoptosis, and severe mitochondrial deficits in the surviving HN. In-vivo treatment with CDDP caused a reduction of dendritic branches and decreased spine density in CA1 and CA3 HN. An acute increase in cell death was measured in these regions, as well as in NSCs located in the dentate gyrus. EM revealed mitochondrial vacuolization and degradation in the hippocampi 15 days after exposure with more extensive damage at 28 days. CDDP treatment caused a significant decrease in BDNF mRNA after exposure to 0.1 µM or 1 µM CDDP at two and 24hr. A 25% mitochondrial respiration deficit was observed following cultured NSC exposure to 2µM Cisplatin following 48hr after treatment. Discussion: At clinically relevant CDDP doses, dendritic damage and HN and NSCs death occur in-vivo. At doses lower than those found in chemotherapy patients, CDDP can potentially induce both severe synaptic damage and neuronal cell loss, and mitochondrial damage.  This damage may be responsible for the cognitive impairment observed after chemotherapy treatment, and might be partially reversible using clinically available treatments (ampakines).