Laquinimod ameliorates secondary brain inflammation.

Accumulating evidence suggests that a degenerative processes within the brain can trigger the formation of new, focal inflammatory lesions in Multiple Sclerosis (MS). Here, we used a novel pre-clinical MS animal model to test whether the amelioration of degenerative brain events reduces the secondary recruitment of peripheral immune cells and, in consequence, inflammatory lesion development. Neural degeneration was induced by a 3 weeks cuprizone intoxication period. To mitigate the cuprizone-induced pathology, animals were treated with Laquinimod (25 mg/kg) during the cuprizone-intoxication period. At the beginning of week 6, encephalitogenic T cell development in peripheral lymphoid organs was induced by the immunization with myelin oligodendrocyte glycoprotein 35-55 peptide (i.e., Cup/EAE). Demyelination, axonal injury and reactive gliosis were determined by immunohistochemistry. Positron emission tomography (PET) imaging was performed to analyze glia activation in vivo. Vehicle-treated cuprizone mice displayed extensive callosal demyelination, glia activation and enhanced TSPO-ligand binding. This cuprizone-induced pathology was profoundly ameliorated in mice treated with Laquinimod. In vehicle-treated Cup/EAE mice, the cuprizone-induced pathology triggered massive peripheral immune cell recruitment into the forebrain, evidenced by multifocal perivascular inflammation, glia activation and neuro-axonal injury. While anti myelin oligodendrocyte glycoprotein 35-55 peptide immune responses were comparable in vehicle- and Laquinimod-treated Cup/EAE mice, the cuprizone-triggered immune cell recruitment was ameliorated by the Laquinimod treatment. This study clearly illustrates that amelioration of a primary brain-intrinsic degenerative process secondary halts peripheral immune cell recruitment and, in consequence, inflammatory lesion development. These findings have important consequences for the interpretation of the results of clinical studies.

Visualization of the Breakdown of the Axonal Transport Machinery: a Comparative Ultrastructural and Immunohistochemical Approach.

Axonal damage is a major factor contributing to disease progression in multiple sclerosis (MS) patients. On the histological level, acute axonal injury is most frequently analyzed by anti-amyloid precursor protein immunohistochemistry. To what extent this method truly detects axonal injury, and whether other proteins and organelles are as well subjected to axonal transport deficits in demyelinated tissues is not known. The aim of this study was to correlate ultrastructural morphology with the immunohistochemical appearance of acute axonal injury in a model of toxin-induced oligodendrocyte degeneration. C57BL/6J mice were intoxicated with 0.25% cuprizone to induce demyelination. The corpus callosum was investigated by serial block-face scanning electron microscopy (i.e., 3D EM), immunohistochemistry, and immunofluorescence microscopy. Brain tissues of progressive MS patients were included to test the relevance of our findings in mice for MS. Volumes of axonal swellings, determined by 3D EM, were comparable to volumes of axonal spheroids, determined by anti-APP immunofluorescence stains. Axonal swellings were present at myelinated and non-myelinated axonal internodes. Densities of amyloid precursor protein (APP)+ spheroids were highest during active demyelination. Besides APP, vesicular glutamate transporter 1 and mitochondrial proteins accumulated at sites of axonal spheroids. Such accumulations were found as well in lesions of progressive MS patients. In this correlative ultrastructural-immunohistochemical study, we provide strong evidence that breakdown of the axonal transport machinery results in focal accumulations of mitochondria and different synaptic proteins. We provide new marker proteins to visualize acute axonal injury, which helps to further understand the complex nature of axonal damage in progressive MS.