In vivo and in vitro evaluation of the effect of 2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate on inflammation-sensitized hyperoxia-induced developing brain injury.

Supraphysiological oxygen concentrations are toxic to the developing brain. Inflammatory processes increase the risk for brain injury. Sigma-1 receptor agonists are potent suppressors of inflammation-related events and are powerful immunomodulatory and antioxidative agents. Neuroprotective effects of sigma-1 receptor agonists have been described previously for neonatal and adult models of brain injury. The aim of this study was to assess the selective sigma-1 receptor agonist 2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate (PRE-084) in models of inflammation-sensitized hyperoxia-induced developing brain injury. For in vivo studies, rat pups were randomly presensitized with 1) lipopolysaccharide or 2) vehicle on postnatal day 3. On day 6, pups received either 1) PRE-084 or 2) vehicle and were subsequently exposed to hyperoxic conditions for 6, 12, or 24 hr. At the end of exposure, animals were sacrificed and brains were processed for caspase-3 analysis using immunohistochemistry and Western blotting. For in vitro studies, oligodendroglial cells were subjected to hyperoxic conditions in the presence or absence of proinflammatory cytokines and PRE-084. Cell membrane integrity and cell viability were assessed by means of lactate dehydrogenase and 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assays. Inflammatory presensitization significantly increased hyperoxia-induced injury both in vivo and in vitro. PRE-084 administration did not attenuate damage. Sigma-1 receptor agonists have been described as a promising therapeutic strategy for brain injury. We were not able to confirm this in the present model. The exact mechanisms of action of sigma-1 receptor agonists as well as the pathophysiologic pathways involved in hyperoxia-induced injury in the developing brain remain to be elucidated.