Understanding the molecular mechanism of blood-brain barrier damage in an experimental model of Japanese encephalitis: correlation with minocycline administration as a therapeutic agent.

The blood-brain barrier (BBB) serves to protect the central nervous system (CNS) from damage by exogenous molecules. Japanese encephalitis (JE), caused by a neurotropic flavivirus, leads to inflammation in the CNS, neuronal death and also compromises the structural and functional integrity of the BBB. Minocycline, a semisynthetic tetracycline, has been found to be broadly protective in neurological disease models featuring inflammation and cell death and at present, is being evaluated in clinical trials. In the present study, we propose that the neuroprotective role of minocycline in experimental models of JE extends also to the protection of the BBB. Damage to the BBB was assessed by Evan's blue dye exclusion test after minocycline treatment following Japanese encephalitis virus (JEV) infection. A breakdown of the BBB occurred in mice inoculated intravenously with JEV. This resulted in leakage of protein-bound Evan's blue dye into the brain tissue. Semi-quantitative RT-PCR revealed an up-regulation of chemokine receptors and adhesion molecules following JEV infection. Immunostaining showed leukocyte and neutrophil infiltration following JEV infection. Intraperitoneal injection of minocycline, beginning 24h post-JEV infection, abrogated the effects by reducing BBB damage, decreasing expression of iNOS, Cox-2, VEGF and also by reducing the elevated level of transcript of chemokine receptors and adhesion molecules in the brain. Matrix metalloproteinases (MMPs) are known to disrupt the BBB and minocycline was found to significantly decrease the activity of MMP-9 in brain tissue homogenates. Thus, minocycline, administered at a clinically relevant time, appears to maintain blood-brain barrier integrity following JEV infection.