Poloxamer 188 Attenuates in vitro Traumatic Brain Injury-Induced Mitochondrial and Lysosomal Membrane Permeabilization Damage in Cultured Primary Neurons

Acute membrane damage due to traumatic brain injury (TBI) is a critical precipitating event. However, the subsequent effects of the mechanical trauma, including mitochondrial and lysosomal membrane permeability (MOMP and LMP) remain elusive. The main objective of the current study was to assess the role of a putative membrane-resealing agent poloxamer 188 (P188) in MOMP and LMP in response to a well-defined mechanical insult. Using an in vitro cell shearing device (VCSD), mechanical injury resulted in immediate disruption of membrane integrity in cultured primary neurons, and neurons were treated with P188 or a cathepsin B inhibitor (CBI) after VCSD 10 min. The protective effect of P188 on cultured primary neurons was first detected visually with a light microscope, and measured by MTT assay and LDH assay. The validity of monitoring changes in mitochondrial membrane potential (Delta Psi m) was measured by JC-1 staining, and Western blot for cytochrome c and truncated Bid (tBid) in purified mitochondria was also performed. In addition, lysosomal integrity was detected by blotting for cathepsin B and tBid in purified lysosomes. Our results showed post-injury P188 treatment moderated the dissipation of Delta Psi m in mitochondria, and inhibited VCSD-induced cytochrome c release from mitochondria as well as cathepsin B from lysosomes. Cathepsin B inhibition (CBI) could also increase cell viability, maintain mitochondrial membrane potential, and repress VCSD-induced release of cytochrome c from mitochondria to cytosol. Both P188 and CBI treatment decreased the cytosolic accumulation of tBid in supernatant of purified lysosomes, and the amount of mitochondrial localized tBid. These data indicate injured neurons have undergone mitochondrial and lysosomal membrane permeability damage, and the mechanism can be exploited with pharmacological interventions. P188's neuroprotection appears to involve a relationship between cathepsin B and tBid-mediated mitochondrial initiation of cell death.