Host – Dan Keller
Hello, and welcome to Episode Forty-Seven of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m your host, Dan Keller.
This week’s podcast features the second part of a two-part interview with Dr. Hans Lassmann, who discusses oxidative stress as a mechanism of tissue injury in progressive MS. But first, here are some of the new items in the MS Discovery Forum.
According to our curated list of the latest scientific articles related to MS, 56 such articles were published last week. To see the list, go to msdiscovery.org and click on Papers. We selected two of those papers as Editors’ Picks. One of them includes revised guidelines from the Association of British Neurologists on prescribing disease-modifying treatments for MS. The other describes an international consensus on diagnostic criteria for neuromyelitis optica and related disorders.
Our Drug-Development Pipeline includes continually updated information on 44 investigational agents for MS. During the month of June, we added 10 new trials, we updated information on 6 other trials, and we’ve added 67 other pieces of information. The drugs with important additions and changes are alemtuzumab, cladribine, cyclophosphamide, daclizumab, dalfampridine, dimethyl fumarate, fingolimod, glatiramer acetate, idebenone, interferon beta-1a, interferon beta-1b, laquinimod, rituximab, natalizumab, and ocrelizumab. To find information on all 44 compounds, visit msdiscovery.org and click first on Research Resources and then on Drug-Development Pipeline.
Now to our interview with Dr. Hans Lassmann of the Medical University of Vienna in Austria. Last week we spoke about biomarkers, and this week we’ll discuss oxidative stress as a mechanism of tissue injury in progressive MS.
Interviewer – Dan Keller
What's interesting there at this point?
Interviewee – Hans Lassmann
The big problem in multiple sclerosis is that we have very good therapies for the early stage of multiple sclerosis, and they all interfere with the inflammation and the immune system. But when the patients have reached a progressive stage of the disease, then all these therapies are currently noneffective. So the key points were to define what are actually the mechanisms of inflammation and tissue injury in the progressive stage of multiple sclerosis, and there are still a lot of open questions. It is clear that even in the progressive stage there is an inflammatory process, and this inflammatory process is associated with active tissue damage. From that certainly we cannot definitely conclude that the inflammatory process drives the tissue damage; however, it's clearly associated.
Now, we were then very interested to see what are the mechanisms of tissue injury. And this involves, first of all, studies on the nature of the inflammatory process. And here what we found is that in the progressive stage of multiple sclerosis the inflammatory reaction is predominantly hidden within the central nervous system behind a repaired blood-brain barrier. So that means this inflammatory process is no longer really under control of the peripheral immune system. And also, the therapies which we have currently mainly interfere with immune functions in the periphery, and they have actually very little access to an inflammatory process which is taking place within the central nervous system.
So that means that new drugs have to be developed and tested which actually exert an antiinflammatory or some neuroprotective action directly within the central nervous system. And there are now a number of the large companies fully engaged in this process, and there are new candidates coming up, which will have to be tested in proper clinical trials in patients with progressive MS.
The second question, which we have mainly addressed during the last year, was the mechanisms how the tissue damage is induced. And in this regard, we concentrated on cortical lesions in multiple sclerosis, which are very, very specific for the disease. And we compared in gene expression studies these cortical lesions not only with normal controls but also with inflammatory controls. And we used here a disease which has very similar inflammatory infiltrates, as you see in multiple sclerosis brain, but doesn't lead to the MS typical demyelination, and this is tuberculous meningitis. And then we also used as a control for neurodegeneration Alzheimer's disease just to see what is a reaction in gene expression due to degeneration of neurons.
And when we did that, actually it was interesting to see that there were relatively few genes which were specifically changed in their expression in multiple sclerosis patients in comparison to these other disease controls. And these genes were, in part, associated with inflammatory processes. A large part of the genes were associated with a more or less single pathway of tissue injury, which includes oxidative injury leading to mitochondrial injury and its secondary consequences. And then, there were also some genes involved which were MS specifically related to tissue regenerative processes.
We have then looked in further detail, and it now turns out that this cascade of oxidative injury leading to mitochondrial dysfunction and with that to a state of energy deficiency is actually one of the major driving forces of neurodegeneration in the progressive stage of multiple sclerosis. So this oxidative injury is, in part, driven by the inflammatory process. But it is also augmented by factors which are related to age of the patients and to the accumulation of lesion burden due to the chronic disease.
So here the central portion is the activation of microglial cells which can, on the one hand, be activated in the inflammatory process, but they also get activated when tissue is damaged due to completely different causes. And they also get activated just simply in an aging process. And in this respect, then they get activated in a pro-oxidative form. And then, the tissue injury can further be propagated through additional age-related changes, including, for instance, the accumulation of iron in the central nervous system and also obviously the chronic microglia activation due to retrograded and anterograde degeneration when lesions already present within the central nervous system.
Are the microglia just overdoing what they normally would be expected to do? I mean macrophages use oxidative systems to get rid of pathogens.
Yeah, this is absolutely true. That is a key element of microphage and microglia function. And this is exaggerated in both the aging process, as well as in the chronic inflammatory state like multiple sclerosis. The question only remains what is really driving this massive microglia activation in MS, which is even more and more pronounced than even in very severe other inflammatory diseases of the central nervous system.
Can you identify or has anyone identified factors that disappear with aging or are increased with aging that may lead to this state?
That is also not really very clear now. I think one interesting aspect is that this massive microglia activation in the direction of oxidative stress you don't really see in rodents and even not in primate experimental models; you see it in humans. And the reason for that is not completely clear, but it may very well be that environmental factors actually play a major role. I think one of the major differences between humans and these experimental animals is that the experimental animals are genetically very homogenous; they are generally inbred strains. And the second is that they are kept under a very constant pathogen-free environment. And this is very different in a human situation, and these animals also have a very … standardized diet. Now this is completely different in human situations, and there are certainly many factors, including peripheral infections but also including diet changes, and many other factors can actually have an influence on microglia in the central nervous system.
And experimental animals also have optimized diets; people have figured out the nutrients they need I suppose. They're getting a good diet compared to people who knows how everybody is eating these days.
Yes, that's absolutely the case. They have a standardized diet, and they certainly are not exposed to very much of the fats, for instance, which we take into when we eat fat pork meat.
Do any of the antiinflammatory agents modify the course? Things like lipoxygenase inhibitors and things like that? Not necessarily NSAIDs but now that you bring up fats?
I think there is certainly an aspect behind that is that lifestyle control certainly has a beneficial effect. One can just see that in a way that environmental lifestyle factors, which actually also increase the risk for vascular injury or other things, will be certainly deleterious in a patient with progressive multiple sclerosis where the brain is already damaged due to the original disease process and where the functional reserve capacity of the brain is already partially exhausted. So in that case, even minor changes – which are related to lifestyle or aging – will have a more dramatic effect in such a brain than in a normal aging brain.
Finally, circling back to something you said at the beginning, in progressive MS I think you said that the immune system the cells have now entered the brain, but the blood-brain barrier has – once again – become a real barrier. So do you really have an immune response running autonomously in the brain no longer subject to any sort of peripheral control?
Yeah, this is certainly a very important open question. We know that the inflammatory cells are present within the central nervous system in the progressive stage and that they are associated with the degenerative processes and the demyelination. We know currently very little about the exact phenotype and functional activation of the inflammatory cells within the central nervous system. This is actually a large research project, which is running currently in my lab, to try to define exactly the functional polarization of the cells within the MS lesions and to determine their activation state, their proliferation rate, and so on.
What we can say from our preliminary data on that is that they are present, they are in part activated. They also express certain transcription factors, which would be associated with a proinflammatory state in the central nervous system. However, overall all these changes are relatively small in comparison to an acute, for instance, virus-induced inflammatory process in the brain. So it seems to be that there is a slow and low-grade activation state which, however, could be completely sufficient to drive the degenerative process in the patients. But that is not the final answer yet.
Thank you for listening to Episode Forty-seven of Multiple Sclerosis Discovery. This podcast was produced by the MS Discovery Forum, MSDF, the premier source of independent news and information on MS research. MSDF’s executive editor is Robert Finn. Msdiscovery.org is part of the non-profit Accelerated Cure Project for Multiple Sclerosis. Robert McBurney is our President and CEO, and Hollie Schmidt is vice president of scientific operations.
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