Smouldering Inflammation in Multiple Sclerosis – A PET Imaging Study on Prediction of Disease Progression and Effects of Treatment

Background: Multiple sclerosis (MS) is the most common inflammatory and neurodegenerative autoimmune disease of the central nervous system in young adults, where the inflammatory reaction causes destruction of the myelin sheet surrounding the neurons in addition to irreversible damage to the neuronal axons. A large proportion of people with MS continue to experience disease accumulation throughout the years, despite proper disease modifying therapy (DMT). The DMTs presently available fail to effectively prevent the disease accrual in progressive forms of MS. According to neuropathological studies, the diffuse inflammation in the area surrounding the MS lesions and in the normal appearing white matter (NAWM) is related to activated microglial cells. Overactivation of microglial cells is known to correlate with disease severity. Microglial activation can be detected by using in vivo positron emission tomography (PET) imaging with radioligands that bind to the translocator protein (TSPO), a molecule upregulated mostly in activated microglia. Aims of the study: The main aims of this thesis were to evaluate the effect of DMTs (fingolimod and natalizumab) on the microglial activity in the MS brain and to evaluate the role of activated microglia in predicting future disease progression by using PET imaging with TSPO binding 11C-PK11195 radioligand. Results: Fingolimod- and natalizumab treatment decreased microglial activity in brain regions critical to MS disease progression. Higher microglial activation in the perilesional area and NAWM predicted later disease progression independent of relapse activity. Conclusions: The results demonstrate that TSPO-PET is a promising imaging method to identify the diffuse neuroinflammation in progressive MS, to predict future MS related disease progression independent of relapses and to evaluate the effect of DMTs.Kytevä inflammaatio MS-taudissa – PET-kuvantamistutkimus ennustamaan taudin etenemistä ja hoitovastetta Tausta: MS-tauti on yleisin nuorten aikuisten tulehduksellinen, keskushermostoa rappeuttava autoimmuunisairaus. Suurella osalla potilaista tauti etenee vuosien saatossa. Etenevän MS-taudin hoitoon ei toistaiseksi ole käytettävissä lääkitystä, joka estäisi tehokkaasti taudin etenemistä. Neuropatologisten tutkimusten mukaan MS-taudille tyypillisten tulehduspesäkkeitä ympäröivien alueiden sekä normaalilta näyttävän valkean aineen (NAWM) diffuusiin tulehdukseen liittyy mikrogliasolujen aktivoituminen, jonka voimakkuus korreloi taudin vaikeusasteeseen. Mikroglia-solujen aktiivisuutta voidaan mitata positroni-emissiotomografia (PET) -kuvauksella. Tavoitteet: Arvioida miten MS-taudin kulkuun vaikuttavat lääkitykset (fingolimodi ja natalitsumabi) muuttavat aivojen mikrogliasolujen aktiviteettia ja miten mikrogliasolujen aktiviteetti korreloi taudin etenemiseen tulevaisuudessa käyttäen aktivoituneisiin mikrogliasoluihin sitoutuvaa 11C-PK11195 -merkkiainetta. Tulokset: Fingolimodi- ja natalitsumabihoito vähensivät mikrogliasolujen aktiivisuutta MS-taudin etenemiselle kriittisillä aivoalueilla. Korkeampi mikroglia¬solujen aktivaatio NAWM:ssa ja tulehduspesäkkeitä ympäröivillä alueilla ennusti taudin myöhempää etenemistä pahenemisvaiheista riippumatta. Johtopäätökset: PET-kuvantaminen on lupaava menetelmä tunnistamaan aivojen laaja-alainen inflammaatio etenevässä MS-taudissa, ennustamaan taudin etenemistä pahenemisvaiheista riippumatta sekä arvioimaan taudin kulkuun vaikuttavien lääkitysten hoitovastetta

Association between microglial activation and serum kynurenine pathway metabolites in multiple sclerosis patients

Microglial activation associates with MS progression but it is unclear what drives their persistent pro-inflammatory state. Metabolites of the kynurenine pathway (KP), the main metabolism route of tryptophan, can influence the function of brain innate immune cells.To investigate whether tryptophan metabolites in blood associate with TSPO-PET measurable microglial activation in MS brain.Microglial activation was detected using PET imaging and the TSPO-binding radioligand [11C]PK11195. Distribution volume ratios (DVR) for specific [11C]PK11195-binding in the normal appearing white matter (NAWM), lesions, and thalamus were calculated. Ultrahigh performance liquid chromatography-tandem mass spectrometry was used to measure serum levels of tryptophan and kynurenine pathway metabolites.The study cohort consisted of 48 MS patients. Increased DVR in the NAWM and thalamus correlated with decreased serum 3-hydroxykynurenine level (R = -0.31, p = 0.031 and R = -0.32, p = 0.028). Increased EDSS correlated with decreased 3-hydroxykynurenine and xanthurenic acid (R = -0.36, p = 0.012 and R = -0.31, p = 0.034) and increased DVR in the NAWM and thalamus (R = 0.33, p = 0.023 and R = 0.34, p = 0.020, respectively).This clinical study demonstrates an association between low serum 3-hydroxykynurenine and high microglial activation in MS. Further investigations are warranted for elucidation of the biological mechanisms behind this association

Rituximab in the treatment of multiple sclerosis in the Hospital District of Southwest Finland

BackgroundThere are already numerous B-cell depleting monoclonal anti-CD20 antibodies which have been used to reduce the inflammatory burden associated with multiple sclerosis (MS). We describe here our experience of treating MS-patients with B-cell depleting rituximab.Patients and methodsAll MS-patients (n = 72) who had received rituximab treatment for at least six months by January 2019 were identified from the patient charts at the Turku University Hospital. Information about MS disease subtype, disease severity, MR-imaging outcomes and B-cell counts were collected from the charts.ResultsRituximab was well received and well tolerated by the patients. There were no serious infusion-related side effects. The most serious adverse event that led to treatment discontinuation was neutropenia. After rituximab initiation the annual number of relapses was decreased in the relapsing remitting and secondary progressive MS groups and the mean number of gadolinium-enhancing lesions was decreased in relapsing remitting MS. Our study confirms the usability of rituximab treatment for MS in the Finnish health care environment.ConclusionsOff-label rituximab-treatment can be successfully used to reduce MS disease burden for the benefit of MS patients.</div

Phenotyping of multiple sclerosis lesions according to innate immune cell activation using TSPO-PET

Abstract Chronic active lesions are promotors of neurodegeneration and disease progression in multiple sclerosis. They harbour a dense rim of activated innate immune cells at the lesion edge, which promote lesion growth and thereby induce damage. Conventional MRI is of limited help in identifying the chronic active lesions, so alternative imaging modalities are needed. Objectives were to develop a PET-based automated analysis method for phenotyping of chronic lesions based on lesion-associated innate immune cell activation and to comprehensively evaluate the prevalence of these lesions in the various clinical subtypes of multiple sclerosis, and their association with disability. In this work we use TSPO-PET-imaging for phenotyping chronic multiple sclerosis lesions at large scale. For this, we identified 1510 white matter T1-hypointense lesions from 91 multiple sclerosis patients [67 relapsing-remitting, 24 secondary progressive]. Innate immune cell activation at the lesion rim was measured using PET-imaging and the TSPO-binding radioligand 11C-PK11195. A T1-hypointense lesion was classified as rim-active if the distribution volume ratio of 11C-PK11195-binding was low in the plaque core and considerably higher at the plaque edge. If no significant ligand-binding was observed, the lesion was classified as inactive. Plaques that had considerable ligand-binding both in the core and at the rim were classified as overall-active. Conventional MRI and disability assessment using Expanded Disability Status Scale were performed at the time of PET-imaging. In the secondary progressive cohort, an average of 19% (median, interquartile range 11-26) of T1 lesions were rim-active in each individual patient, compared to 10% (interquartile range 0-20) among relapsing remitting patients (P = 0.009). Secondary progressive patients had a median of 3 (range 0-11) rim-active lesions, vs. 1 (range 0-18) among relapsing remitting patients (P = 0.029). Among those patients who had rim-active lesions (n = 63) the average number of active voxels at the rim was higher among secondary progressive compared to relapsing remitting patients (median 158 versus 74; P = 0.022). The number of active voxels at the rim correlated significantly with Expanded Disability Status Scale (R = 0.43, P <0.001), and the volume of the rim-active lesions similarly correlated with Expanded Disability Status Scale (R = 0.45, P < 0.001). Our study is the first to report in vivo phenotyping of chronic lesions at large scale, based on TSPO-PET. Patients with higher disability displayed a higher proportion of rim-active lesions. The in vivo lesion phenotyping methodology offers a new tool for individual assessment of smouldering (rim-active) lesion burden

Innate Immune Cell-Related Pathology in the Thalamus Signals a Risk for Disability Progression in Multiple Sclerosis

Background and Objectives Our aim was to investigate whether 18-kDa translocator protein (TSPO) radioligand binding in gray matter (GM) predicts later disability progression in multiple sclerosis (MS). Methods In this prospective imaging study, innate immune cells were investigated in the MS patient brain using PET imaging. The distribution volume ratio (DVR) of the TSPO-binding radioligand [C-11]PK11195 was determined in 5 GM regions: thalamus, caudate, putamen, pallidum, and cortical GM. Volumetric brain MRI parameters were obtained for comparison. The Expanded Disability Status Scale (EDSS) score was assessed at baseline and after follow-up of 3.0 +/- 0.3 (mean +/- SD) years. Disability progression was defined as an EDSS score increase of 1.0 point or 0.5 point if the baseline EDSS score was >= 6.0. A forward-type stepwise logistic regression model was constructed to compare multiple imaging and clinical variables in their ability to predict later disability progression. Results The cohort consisted of 66 patients with MS and 18 healthy controls. Patients with later disability progression (n = 17) had more advanced atrophy in the thalamus, caudate, and putamen at baseline compared with patients with no subsequent worsening. TSPO binding was significantly higher in the thalamus among the patients with later worsening. The thalamic DVR was the only measured imaging variable that remained a significant predictor of disability progression in the regression model. The final model predicted disability progression with 52.9% sensitivity and 93.9% specificity with an area under the curve value of 0.82 (receiver operating characteristic curve). Discussion Increased TSPO radioligand binding in the thalamus has potential in predicting short-term disability progression in MS and seems to be more sensitive for this than GM atrophy measures.</p

Increased serum glial fibrillary acidic protein associates with microstructural white matter damage in multiple sclerosis: GFAP and DTI

BackgroundAstrocytes and microglial cells are now recognized as active players in contributing to the diffuse neuroaxonal damage associated with disease progression of multiple sclerosis (MS). The serum level of glial fibrillary acidic protein (GFAP), a biomarker for astrocytic activation, is increased in MS and associates with disease progression and disability. Similarly, diffusion tensor imaging (DTI) parameters for microstructural changes in brain, including demyelination and axonal loss, associate with disability. The association between brain DTI parameters and serum GFAP has not been previously explored in MS. The objective of the study was to get insights into DTI-measurable pathological correlates of elevated serum GFAP in the normal appearing white matter (NAWM) of MS.MethodsA total of 62 MS patients with median age of 49.2 years were included in the study. Study patients underwent DTI-MRI and blood sampling for GFAP determination by single molecule array (Simoa). Mean fractional anisotropy (FA) and mean (MD), axial (AD) and radial (RD) diffusivities were calculated within the entire NAWM and six segmented NAWM regions. The associations between the DTI parameters and GFAP levels were analysed using Spearman correlation analysis and multiple regression model with sex and disease modifying treatment (no, 1st line or 2nd line) as adjustments.ResultsElevated serum GFAP levels correlated significantly with decreased FA values within the entire (ρ = -0.39, p = 0.03), frontal (ρ = -0.42, p = 0.02), temporal (ρ = -0.37; p = 0.04) and cingulate (ρ = -0.38, p = 0.034) NAWM, and increased MD and RD within the frontal NAWM (ρ = 0.36, p = 0.046 for both). Similarly, higher GFAP associated with lower FA in frontal and cingulate NAWM in the multiple regression model corrected for confounding variables (standardised regression coefficient β = -0.29, p = 0.045 and β = -0.33, p = 0.025).ConclusionsOur results give evidence that increased serum GFAP levels associate with DTI-measurable micro-damage in the NAWM in MS. Our work supports the use of serum GFAP as a biomarker for MS pathology-related astrocytopathy and related diffuse white matter damage.</p

High serum neurofilament associates with diffuse white matter damage in MS

Objective To evaluate to which extent serum neurofilament light chain (NfL) increase is related to diffusion tensor imaging-MRI measurable diffuse normal-appearing white matter (NAWM) damage in MS.Methods Seventy-nine patients with MS and 10 healthy controls underwent MRI including diffusion tensor sequences and serum NfL determination by single molecule array (Simoa). Fractional anisotropy and mean, axial, and radial diffusivities were calculated within the whole and segmented (frontal, parietal, temporal, occipital, cingulate, and deep) NAWM. Spearman correlations and multiple regression models were used to assess the associations between diffusion tensor imaging, volumetric MRI data, and NfL.Results Elevated NfL correlated with decreased fractional anisotropy and increased mean, axial, and radial diffusivities in the entire and segmented NAWM (for entire NAWM ρ = −0.49, p = 0.005; ρ = 0.49, p = 0.005; ρ = 0.43, p = 0.018; and ρ = 0.48, p = 0.006, respectively). A multiple regression model examining the effect of diffusion tensor indices on NfL showed significant associations when adjusted for sex, age, disease type, the expanded disability status scale, treatment, and presence of relapses. In the same model, T2 lesion volume was similarly associated with NfL.​​​​​​​Conclusions Our findings suggest that elevated serum NfL in MS results from neuroaxonal damage both within the NAWM and focal T2 lesions. This pathologic heterogeneity ought to be taken into account when interpreting NfL findings at the individual patient level.</p

Insights into disseminated MS brain pathology with multimodal diffusion tensor and PET imaging

Objective To evaluate in vivo the co-occurrence of microglial activation and microstructural white matter (WM) damage in the MS brain and to examine their association with clinical disability.Methods 18-kDa translocator protein (TSPO) brain PET imaging was performed for evaluation of microglial activation by using the radioligand [11C](R)-PK11195. TSPO binding was evaluated as the distribution volume ratio (DVR) from dynamic PET images. Diffusion tensor imaging (DTI) and conventional MRI (cMRI) were performed at the same time. Mean fractional anisotropy (FA) and mean (MD), axial, and radial (RD) diffusivities were calculated within the whole normal-appearing WM (NAWM) and segmented NAWM regions appearing normal in cMRI. Fifty-five patients with MS and 15 healthy controls (HCs) were examined.Results Microstructural damage was observed in the NAWM of the MS brain. DTI parameters of patients with MS were significantly altered in the NAWM compared with an age- and sex-matched HC group: mean FA was decreased, and MD and RD were increased. These structural abnormalities correlated with increased TSPO binding in the whole NAWM and in the temporal NAWM (p Conclusions Widespread structural disruption in the NAWM is linked to neuroinflammation, and both phenomena associate with clinical disability. Multimodal PET and DTI allow in vivo evaluation of widespread MS pathology not visible using cMRI.</div

Microglial activation, white matter tract damage and disability in multiple sclerosis

Abstract Objective: To investigate the relationship of in vivo microglial activation to clinical and MRI parameters in MS. Methods: Patients with secondary progressive MS (n = 10) or relapsing-remitting MS (n = 10) and age-matched healthy controls (n = 17) were studied. Microglial activation was measured using PET and radioligand [11C](R)-PK11195. Clinical assessment and structural and quantitative MRI including diffusion tensor imaging (DTI) were performed for comparison. Results: [11C](R)-PK11195 binding was significantly higher in the normal-appearing white matter (NAWM) of patients with secondary progressive vs relapsing MS and healthy controls, in the thalami of patients with secondary progressive MS vs controls, and in the perilesional area among the progressive compared with relapsing patients. Higher binding in the NAWM was associated with higher clinical disability and reduced white matter (WM) structural integrity, as shown by lower fractional anisotropy, higher mean diffusivity, and increased WM lesion load. Increasing age contributed to higher microglial activation in the NAWM among patients with MS but not in healthy controls. Conclusions: PET can be used to quantitate microglial activation, which associates with MS progression. This study demonstrates that increased microglial activity in the NAWM correlates closely with impaired WM structural integrity and thus offers one rational pathologic correlate to diffusion tensor imaging (DTI) parameters