Hypoxia-like tissue injury as a component of multiple sclerosis lesions

A method for the analysis of the geometrical relationship between white matter pathology and the vascular architecture of the brain

A novel method for the visual and quantitative analysis of the geometrical relationship between the vascular architecture of the brain and white matter pathology is presented. The cerebro vascular system is implicated in the pathogenesis of many diseases of the cerebral white matter, for example, stroke, microcerebrovascular disease, and multiple sclerosis (MS). In our work, white matter lesions and vessels are depicted using magnetic resonance imaging (MRI) and extracted using image analysis techniques. We focus on measuring distance relationships between white matter lesions and vessels, and distribution of lesions with respect to vessel caliber. Vascular distance maps are generated by computing for each voxel the Euclidean distance to the closest vessel. Analogously, radius maps assign the radius of the closest vessel to each voxel in the image volume. The distance and radius maps are used to analyze the distribution of lesions with respect to the vessels' locations and their calibers. The method was applied to three MS patients to demonstrate its functionality and feasibility. Preliminary findings indicate that larger MS lesions tend to be farther from detected vessels and that the caliber of the vessels nearest to larger lesions tends to be smaller, suggesting a possible role of relative hypoperfusion or hypoxia in lesion formation.

Microvascular abnormality in relapsing-remitting multiple sclerosis: perfusion MR imaging findings in normal-appearing white matter

PURPOSE

To prospectively determine hemodynamic changes in the normal-appearing white matter (NAWM) of patients with relapsing-remitting multiple sclerosis (RR-MS) by using dynamic susceptibility contrast material-enhanced perfusion magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Conventional MR imaging (which included acquisition of pre- and postcontrast transverse T1-weighted, fluid-attenuated inversion recovery, and T2-weighted images) and dynamic susceptibility contrast-enhanced T2*-weighted MR imaging were performed in 17 patients with RR-MS (five men and 12 women; median age, 38.4 years; age range, 27.6-56.9 years) and 17 control patients (seven men and 10 women; median age, 42.0 years; age range, 18.7-62.5 years). Absolute cerebral blood volume (CBV), absolute cerebral blood flow (CBF), and mean transit time (MTT) (referenced to an arterial input function by using an automated method) were determined in periventricular, intermediate, and subcortical regions of NAWM at the level of the lateral ventricles. Least-squares regression analysis (controlled for age and sex) was used to compare perfusion measures in each region between patients with RR-MS and control patients. Repeated-measures analysis of variance and the Tukey honestly significant difference test were used to perform pairwise comparison of brain regions in terms of each perfusion measure.

RESULTS

Each region of NAWM in patients with RR-MS had significantly decreased CBF (P <.005) and prolonged MTT (P <.001) compared with the corresponding region in control patients. No significant differences in CBV were found between patients with RR-MS and control patients in any of the corresponding areas of NAWM examined. In control patients, periventricular NAWM regions had significantly higher CBF (P =.03) and CBV (P =.04) than did intermediate NAWM regions. No significant regional differences in CBF, CBV, or MTT were found in patients with RR-MS.

CONCLUSION

The NAWM of patients with RR-MS shows decreased perfusion compared with that of controls.

Relapsing and remitting multiple sclerosis: pathology of the newly forming lesion

The study describes the clinical and pathological findings in 12 patients with relapsing and remitting multiple sclerosis, who died during or shortly after the onset of a relapse. Pathological changes not previously associated with the formation of new symptomatic lesions were observed in seven cases, namely, extensive oligodendrocyte apoptosis and microglial activation in myelinated tissue containing few or no lymphocytes or myelin phagocytes. No current laboratory model of multiple sclerosis, in particular, experimental allergic encephalomyelitis, is known with these features, which raises the possibility of some novel process underlying new lesion formation in multiple sclerosis.

Fibrin depletion decreases inflammation and delays the onset of demyelination in a tumor necrosis factor transgenic mouse model for multiple sclerosis

In multiple sclerosis, in which brain tissue becomes permeable to blood proteins, extravascular fibrin deposition correlates with sites of inflammatory demyelination and axonal damage. To examine the role of fibrin in neuroinflammatory demyelination, we depleted fibrin in two tumor necrosis factor transgenic mouse models of multiple sclerosis, transgenic lines TgK21 and Tg6074. In a genetic analysis, we crossed TgK21 mice into a fibrin-deficient background. TgK21fib(-/-) mice had decreased inflammation and expression of major histocompatibility complex class I antigens, reduced demyelination, and a lengthened lifespan compared with TgK21 mice. In a pharmacologic analysis, fibrin depletion, by using the snake venom ancrod, in Tg6074 mice also delayed the onset of inflammatory demyelination. Overall, these results indicate that fibrin regulates the inflammatory response in neuroinflammatory diseases. Design of therapeutic strategies based on fibrin depletion could potentially benefit the clinical course of demyelinating diseases such as multiple sclerosis.

Expression of chemokine receptors CCR1 and CCR5 reflects differential activation of mononuclear phagocytes in pattern II and pattern III multiple sclerosis lesions

Multiple sclerosis (MS) is an inflammatory demyelinating disorder of the CNS. A recent study identified 4 patterns of demyelination in active MS lesions. The characteristics of pattern II lesions suggested a primary inflammatory mechanism of myelin injury, while pattern III lesions showed features consistent with dying-back oligodendrogliopathy. The recruitment, differentiation, and activation of mononuclear phagocytes are dependent on the expression of chemokine receptors. Using immunohistochemistry we quantified cellular expression of CCR1 and CCR5 in pattern II (n = 21) and pattern III (n = 17) lesion areas of differing demyelinating activity. Infiltrating monocytes in both lesion patterns co-expressed CCR1 and CCR5, suggesting conserved mechanisms of monocyte recruitment into the CNS. In pattern II lesions, the number of cells expressing CCR1 significantly decreased while CCR5 increased in late active compared with early active demyelinating regions. In striking contrast, numbers of cells expressing CCR1 and CCR5 were equal in all regions of pattern III lesions. As hypoxia-like mechanisms may play a role in pattern III lesions, we extended these studies to white matter infarcts (n = 7) in which the expression of CCR1 better resembled pattern III than pattern II lesions. As judged by mononuclear phagocyte chemokine receptor expression, there appear to be distinct tissue environments in pattern II and III MS lesions.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Angiogenesis in multiple sclerosis: is it good, bad or an epiphenomenon?

Characteristic pathological features of multiple sclerosis (MS) include inflammation, demyelination and axonal and oligodendrocyte loss. In addition, lesions can also have a significant vascular component. In this review, morphological, biochemical and radiological evidence is presented suggesting angiogenesis as a potential focus for investigation in MS. We hypothesize that angiogenesis plays a significant role in the MS lesion, perpetuating disease progression. Thus, treatment strategies that inhibit angiogenesis may decrease clinical and pathological signs of disease. Several approaches for testing this hypothesis are outlined.

Phenytoin protects spinal cord axons and preserves axonal conduction and neurological function in a model of neuroinflammation in vivo

Axonal degeneration within the spinal cord contributes substantially to neurological disability in multiple sclerosis (MS). Thus neuroprotective therapies that preserve axons, so that they maintain their integrity and continue to function, might be expected to result in improved neurological outcome. Sodium channels are known to provide a route for sodium influx that can drive calcium influx, via reverse operation of the Na+/Ca2+ exchanger, after injury to axons within the CNS, and sodium channel blockers have been shown to protect CNS axons from degeneration after experimental anoxic, traumatic, and nitric oxide (NO)-induced injury. In this study, we asked whether phenytoin, which is known to block sodium channels, can protect spinal cord axons from degeneration in mice with experimental allergic encephalomyelitis (EAE), which display substantial axonal degeneration and clinical paralysis. We demonstrate that the loss of dorsal corticospinal tract (63%) and dorsal column (cuneate fasciculus; 43%) axons in EAE is significantly ameliorated (corticospinal tract: 28%; cuneate fasciculus: 17%) by treatment with phenytoin. Spinal cord compound action potentials (CAP) were significantly attenuated in untreated EAE, whereas spinal cords from phenytoin-treated EAE had robust CAPs, similar to those from phenytoin-treated control mice. Clinical scores in phenytoin-treated EAE at 28 days were significantly improved (1.5, i.e., minor righting reflex abnormalities) compared with untreated EAE (3.8, i.e., near-complete hindlimb paralysis). Our results demonstrate that phenytoin has a protective effect in vivo on spinal cord axons, preventing their degeneration, maintaining their ability to conduct action potentials, and improving clinical status in a model of neuroinflammation.