Inflammatory leukocytes infiltrate the CNS parenchyma in neuroinflammation. This involves cellular migration across various structures associated with the blood-brain barrier: the vascular endothelium, the glia limitans, and the perivascular space between them. Leukocytes accumulate spontaneously in the perivascular space in brains of transgenic (Tg) mice that overexpress CCL2 under control of a CNS-specific promoter. The Tg mice show no clinical symptoms, even though leukocytes have crossed the endothelial basement membrane. Pertussis toxin (PTx) given i.p. induced encephalopathy and weight loss in Tg mice. We used flow cytometry, ultra-small superparamagnetic iron oxide-enhanced magnetic resonance imaging, and immunofluorescent staining to show that encephalopathy involved leukocyte migration across the glia limitans into the brain parenchyma, identifying this as the critical step in inducing clinical symptoms. Metalloproteinase (MPs) enzymes are implicated in leukocyte infiltration in neuroinflammation. Unmanipulated Tg mice had elevated expression of tissue inhibitor of metalloproteinase-1, matrix metalloproteinase (MMP)-10, and -12 mRNA in the brain. PTx further induced expression of tissue inhibitor of metalloproteinase-1, metalloproteinase disintegrins-12, MMP-8, and -10 in brains of Tg mice. Levels of the microglial-associated MP MMP-15 were not affected in control or PTx-treated Tg mice. PTx also up-regulated expression of proinflammatory cytokines IL-1β and TNF-α mRNA in Tg CNS. Weight loss and parenchymal infiltration, but not perivascular accumulation, were significantly inhibited by the broad-spectrum MP inhibitor BB-94/Batimastat. Our finding that MPs mediate PTx-induced parenchymal infiltration to the chemokine-overexpressing CNS has relevance for the pathogenesis of human diseases involving CNS inflammation, such as multiple sclerosis.

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system (CNS). Anxiety and depression are the most common psychiatric comorbidities of MS, which seriously affect patients’ quality of life, treatment compliance, and prognosis. However, current treatments for anxiety and depression in MS show low therapeutic efficacy and significant side effects. In the present study, we explored the therapeutic effects of a novel low-toxic anti-inflammatory drug, nanoparticulate magnesium hydride (MgH2), on mood disorders of MS. We observed that anxiety/depression-like behaviors in experimental autoimmune encephalomyelitis (EAE) mice were alleviated by MgH2 treatment. In addition, disease severity and inflammatory demyelination were also diminished. Furthermore, we confirmed the suppressive effect of MgH2 on depression in the acute restraint stress model. Mechanistically, MgH2 may play a therapeutic role by promoting microglial M2 polarization, inhibiting microglial M1 polarization, and reducing oxidative stress and mitochondrial damage. Therefore, nanoparticulate MgH2 may be a promising therapeutic drug for psychiatric comorbidities of MS.