Discussion
We herein provided evidence that the CSF inflammatory profile and especially the levels of TNF and osteopontin are associated with disease activity in early RRMS patients treated with DMF. We also suggest that testing for such markers could help clinicians in a more accurate treatment personalization highlighting patients who will be possible responders to DMF.
Notably, an early and proper introduction of a DMT to prevent disease activity in the first years after a diagnosis of MS, and possibly reduce the long-term disability accumulation, is mandatory.
5,18 Although many treatments for RRMS, each with a different mechanism of action and target, have been developed,
19 a real personalized approach, based on individual biological characteristics, is still an unmet need.
20In this context, we recruited a cohort of treatment-naïve patients at the time of diagnosis, avoiding biases due to different drug exposure or disease duration, and we evaluated the disease activity early after the exposure to a commonly adopted typical first-line therapy.
Our results are in line with the idea that CSF inflammatory markers could reflect chronic intrathecal processes that occur since early disease phases,
14 and that an early assessment of inflammatory markers could contribute to a better stratification of patients at higher risk of disease activity in the short- and long-term follow-up.
6,7,21 Since included in the recent revision of diagnostic criteria and available for all patients, we decided to include the occurrence of new CLs in our definition of NEDA-3. This makes our percentage of cases that showed disease activity not easily comparable with the previously reported results
22,23 but possibly makes more accurate our identification of treatment responders.
Globally, the extent of intrathecal inflammation was significantly increased in patients with disease activity, with particular regard to TNF, osteopontin, IFN gamma, the B-cell chemoattractants CXCL12 and CXCL13, all molecules that have been previously associated with disease activity and early disability progression.
6,24 Due to complex relationships between CSF variables, with a high correlation between each other, we considered the RF as the most suitable approach in order to improve the data interpretability. In particular, by RF, we computed how much each variable contributes to the NEDA outcome using two different stable measures – that is, MD and times a root – which are based on the topology and the construction of the model.
The result of our RF approach is in line with several previous published data. Increasing evidence from
in vitro and
in vivo studies points to a crucial role of TNF signalling in mediating both WM and GM pathology.
25–28 CSF TNF levels in progressive MS patients have been linked to altered synaptic transmission, with exacerbation of glutamatergic transmission and neuronal damage when incubating CSF with corticostriatal slices.
29,30 Recently, persistent expression of CSF TNF along with IFN gamma has been described as a potent inducer of meningeal inflammation and subpial demyelination in the myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) model.
27 Nevertheless, so far, targeting TNF and its receptors did not provide satisfactory results in clinical trials. This is possibly due to the inadequate therapeutic levels of anti-TNF reaching the central nervous system (CNS) or to the dual intrinsic nature of TNF signalling that involves soluble and membrane-bound isoforms and two receptors, thus leading to both pro- and anti-inflammatory downstream signals.
30,31 In particular, a shift towards the TNF/TNFR1 and RIPK3-mediated signalling have been recently found associated with GM demyelination and neurodegeneration,
25 being involved in neuronal necroptosis in the cortex of post-mortem MS cases,
32 thus suggesting new possible pathogenetic mechanisms and targets related to the TNF-related downstream cascades. Notably, when adding to our model MRI measures of CLs and global CTh, the association of CSF TNF levels with the EDA status was confirmed, suggesting an additional
in vivo value of CSF assessment also when considering MRI measures related to focal and diffuse GM damage. Among others, TNF was the only marker exerting a prognostic effect when inserted in the multivariate model, including baseline features.
Along with TNF levels, osteopontin emerged after the RF approach as the most important protein linked to disease activity. Notably, osteopontin has been suggested to be locally produced by CNS residents and infiltrating cells, further underlying the crucial role of intrathecal processes in MS-related pathology. This involves the intrathecal release of the molecule by endothelial cells, microglial cells, macrophages and dendritic cells, and the survival of myelin-reactive T cell with subsequent relapses and early progression of disability.
33,34 Along with its strong association with disease activity, osteopontin has also been associated with progressive MS course from the onset,
24 further underlying its contribution to pathological processes that ultimately lead to MS-related disability accumulation.
Our work is limited by the low sample size and the absence of a validation cohort that prevent us from drawing conclusions, particularly regarding the application of these markers in predicting MS response to other treatments. Furthermore, we assessed the treatment response only through the NEDA-3 status. Although this is commonly adopted in clinical practice,
12 it is mainly weighted on neuroinflammation and focal demyelination parameters, thus reflecting only clinical and subclinical WM inflammatory activity, whose long-term prognostic value on disability accumulation remains debated.
35,36 This is why we decided to include our definition of disease activity also the appearance of new CLs; nevertheless, further MRI measures including brain and spinal cord atrophy or assessment of chronic lesion activity
37–41 as well as assessment of fluid markers of neurodegeneration
42 would provide additional prognostic information.
43However, whether evaluating inflammatory markers at the time of diagnosis will provide additional information on long-term disability remains to be fully elucidated. With the above limitations, our study confirms the importance of studying the CSF inflammatory profile at diagnosis to identify the most suitable patients for a tailored and proper approach with a first-line DMT such as DMF
Conflict of interest statement
The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: DM received honoraria for research or speaking and funds for travel from Biogen Idec, Roche, Sanofi-Genzyme and Novartis. AIP, GMS, VM, MCas, AT, FB, FC, SM, FBP and GKR: no disclosures relevant to the manuscript. MC received honoraria for research or speaking and funds for travel from Roche, Sanofi-Genzyme, Merck-Serono, Biogen Idec, Teva and Novartis.