The pathophysiological role of the blood brain barrier in the oxaliplatin-induced neuropathy

Oxaliplatin has become part of the world-wide standard of care for the adjuvant and the palliative treatment of the metastatic colon cancer. However, its efficacy is hampered by dose-limiting neurotoxicity, which leads to painful sensory neuropathy. Neurotoxicity can be manifested with two distinct syndromes: an acute one that onsets shortly after infusion, and a dose-limiting, cumulative sensory neuropathy. Paucity of information regarding the molecular basis of oxaliplatin-induced neuropathy makes difficult to find new therapeutic opportunities. Although alterations have been found in both peripheral and central nervous system, the latter is particularly distressed by antineoplastic treatment. Neurons and glial cells, in particular astrocytes, strongly react to oxaliplatin with a maladaptive response occurring in spinal and supra-spinal areas facilitating the chronicization of pain. To note, the relationship between neuropathic pain disorders and blood brain barrier (BBB) homeostasis alterations has been found. Interestingly, studies on non-human primates and rats revealed scarce capacity of the antineoplastic compound to cross the BBB after a single injection. The little amount found in the cerebrospinal fluid (CSF) could be enough to trigger acute pain sensitization as well as increased concentration could be reached after repeated administrations. The aim of this study was to evaluate the interference of oxaliplatin with the BBB system in a rat model of oxaliplatin-induced neuropathy and in a rat brain endothelial cell line (RBE4). As first, the immunofluorescent staining detected IgG extravasation and reactive astrocytes in the lumbar blood spinal cord barrier (BSCB) of rats daily treated with oxaliplatin (2.4 mg kg-1, i.p) for 14 days. Moreover, the i.v. injection of 10 kDa dextran texas red revealed enhanced permeability of the BBB/BSCB in specific brain and spinal cord areas crucially involved in the oxaliplatin-induced neuropathic pain sensitization (prefrontal cortex, somatosensory area S1 and lumbar spinal cord) after 7 days of chemotherapy treatment. Further, aimed to deeply explore the altered machinery of the endothelial compartment of the NVU, RBE4 cells were used to set up an in vitro model, which reproduced the vascular wall of the BBB. The vitality assay allowed choosing concentrations of oxaliplatin (10-30 μM) that slightly affected the RBE4 viability in 8-24 h period of 5 treatment, in order to mimic a damage that does not irreversibly alter the endothelial compartment of the NVU. Results showed that sub-lethal concentrations were able to alter levels of GRP- 78 (78 kDa glucose-regulated protein) as well as the cytoplasmic calcium concentration ([Ca2+]i), thus allowing the hypothesis of endoplasmic reticulum impairment. Furthermore, the sub-lethal concentrations of the antineoplastic agent activated caspase-3 after 8, 16 and 24 h treatment leaving unchanged expression of the pro-apoptotic factor Bax up to 16 h. Extracellular ATP concentration was also increased. Finally, the immunofluorescent staining revealed derangement of cytoskeleton protein F-actin and relocation of the tight junction protein ZO-1. In conclusion, our data revealed the involvement of BBB's endothelial compartment in the pathophysiology of oxaliplatin-induced neuropathy.