Paolo Giannetti

Increased PK11195 PET binding in the cortex of patients with MS correlates with disability

Objective: Activated microglia are thought to play a major role in cortical gray matter (GM) demyelination in multiple sclerosis (MS). Our objective was to evaluate microglial activation in cortical GM of patients with MS in vivo and to explore its relationship to measures of disability. Methods: Using PET and optimized modeling and segmentation procedures, we investigated cortical 11C-PK11195 (PK11195) binding in patients with relapsing-remitting MS (RRMS), patients with secondary progressive MS (SPMS), and healthy controls. Disability was assessed with the Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Impact Scale (MSIS-29). Results: Patients with MS showed increased cortical GM PK11195 binding relative to controls, which was multifocal and highest in the postcentral, middle frontal, anterior orbital, fusiform, and parahippocampal gyri. Patients with SPMS also showed additional increases in precentral, superior parietal, lingual and anterior superior, medial and inferior temporal gyri. Total cortical GM PK11195 binding correlated with EDSS scores, with a stronger correlation for the subgroup of patients with SPMS. In patients with SPMS, PK11195 binding also correlated with MSIS-29 scores. No correlation with disability measures was seen for PK11195 binding in white matter. Higher EDSS scores correlated with higher levels of GM PK11195 binding in the postcentral gyrus for patients with RRMS and in precentral gyrus for those with SPMS. Conclusions: Microglial activation in cortical GM of patients with MS can be assessed in vivo. The distribution is not uniform and shows a relationship to clinical disability. We speculate that the increased PK11195 binding corresponds to enhanced microglial activation described in postmortem SPMS cortical GM.

In Vivo Assessment of Brain White Matter Inflammation in Multiple Sclerosis with 18 F-PBR111 PET

PET radioligand binding to the 18-kD translocator protein (TSPO) in the brains of patients with multiple sclerosis (MS) primarily reflects activated microglia and macrophages. We previously developed genetic stratification for accurate quantitative estimation of TSPO using second-generation PET radioligands. In this study, we used 18F-PBR111 PET and MR imaging to measure relative binding in the lesional, perilesional, and surrounding normal-appearing white matter of MS patients, as an index of the innate immune response. Methods: 18F-PBR111 binding was quantified in 11 MS patients and 11 age-matched healthy volunteers, stratified according to the rs6971 TSPO gene polymorphism. Fluid-attenuated inversion recovery and magnetization transfer ratio (MTR) MR imaging were used to segment the white matter in MS patients as lesions, perilesional volumes, nonlesional white matter with reduced MTR, and nonlesional white matter with normal MTR. Results: 18F-PBR111 binding was higher in the white matter lesions and perilesional volumes of MS patients than in white matter of healthy controls (P < 0.05). Although there was substantial heterogeneity in binding between different lesions, a within-subject analysis showed higher 18F-PBR111 binding in MS lesions (P < 0.05) and in perilesional (P < 0.05) and nonlesional white matter with reduced MTR (P < 0.005) than in nonlesional white matter with a normal MTR. A positive correlation was observed between the mean 18F-PBR111 volume of distribution increase in lesions relative to nonlesional white matter with a normal MTR and the MS severity score (Spearman ρ = 0.62, P < 0.05). Conclusion: This study demonstrates that quantitative TSPO PET with a second-generation radioligand can be used to characterize innate immune responses in MS in vivo and provides further evidence supporting an association between the white matter TSPO PET signal in lesions and disease severity. Our approach is practical for extension to studies of the role of the innate immune response in MS for differentiation of antiinflammatory effects of new medicines and their longer term impact on clinical outcome.

Increased central microglial activation associated with peripheral cytokine levels in premanifest Huntington's disease gene carriers

Previous studies have shown activation of the immune system and altered immune response in Huntingtons disease (HD) gene carriers. Here, we hypothesized that peripheral and central immune responses could be concurrent pathophysiological events and represent a global innate immune response to the toxic effects of mutant huntingtin in HD gene carriers. We sought to investigate our hypothesis using [(11)C]PK11195 PET as a translocator protein (TSPO) marker of central microglial activation, together with assessment of peripheral plasma cytokine levels in a cohort of premanifest HD gene carriers who were more than a decade from predicted symptomatic conversion. Data were also compared to those from a group of healthy controls matched for age and gender. We found significantly increased peripheral plasma IL-1β levels in premanifest HD gene carriers compared to the group of normal controls (P=0.018). Premanifest HD gene carriers had increased TSPO levels in cortical, basal ganglia and thalamic brain regions (P<0.001). Increased microglial activation in somatosensory cortex correlated with higher plasma levels of IL-1β (rs=0.87, P=0.013), IL-6 (rs=0.85, P=0.013), IL-8 (rs=0.68, P=0.045) and TNF-α (rs=0.79; P=0.013). Our findings provide first in vivo evidence for an association between peripheral and central immune responses in premanifest HD gene carriers, and provide further supporting evidence for the role of immune dysfunction in the pathogenesis of HD.

Increased PK11195-PET binding in normal-appearing white matter in clinically isolated syndrome

The most accurate predictor of the subsequent development of multiple sclerosis in clinically isolated syndrome is the presence of lesions at magnetic resonance imaging. We used in vivo positron emission tomography with (11)C-(R)-PK11195, a biomarker of activated microglia, to investigate the normal-appearing white matter and grey matter of subjects with clinically isolated syndrome to explore its role in the development of multiple sclerosis. Eighteen clinically isolated syndrome and eight healthy control subjects were recruited. Baseline assessment included: history, neurological examination, expanded disability status scale, magnetic resonance imaging and PK11195-positron emission tomography scans. All assessments except the PK11195-positron emission tomography scan were repeated over 2 years. SUPERPK methodology was used to measure the binding potential relative to the non-specific volume, BPND. We show a global increase of normal-appearing white matter PK11195 BPND in clinically isolated syndrome subjects compared with healthy controls (P = 0.014). Clinically isolated syndrome subjects with T2 magnetic resonance imaging lesions had higher PK11195 BPND in normal-appearing white matter (P = 0.009) and their normal-appearing white matter PK11195 BPND correlated with the Expanded Disability Status Scale (P = 0.007; r = 0.672). At 2 years those who developed dissemination in space or multiple sclerosis, had higher PK11195 BPND in normal-appearing white matter at baseline (P = 0.007 and P = 0.048, respectively). Central grey matter PK11195 BPND was increased in subjects with clinically isolated syndrome compared to healthy controls but no difference was found in cortical grey matter PK11195 BPND. Microglial activation in clinically isolated syndrome normal-appearing white matter is diffusely increased compared with healthy control subjects and is further increased in those who have magnetic resonance imaging lesions. Furthermore microglial activation in clinically isolated syndrome normal-appearing white matter is also higher in those subjects who developed multiple sclerosis at 2 years. Our finding, if replicated in a larger study, could be of prognostic value and aid early treatment decisions in clinically isolated syndrome.

Hippocampal Neuroinflammation, Functional Connectivity, and Depressive Symptoms in Multiple Sclerosis

Background Depression, a condition commonly comorbid with multiple sclerosis (MS), is associated more generally with elevated inflammatory markers and hippocampal pathology. We hypothesized that neuroinflammation in the hippocampus is responsible for depression associated with MS. We characterized the relationship between depressive symptoms and hippocampal microglial activation in patients with MS using the 18-kDa translocator protein radioligand [18F]PBR111. To evaluate pathophysiologic mechanisms, we explored the relationships between hippocampal neuroinflammation, depressive symptoms, and hippocampal functional connectivities defined by resting-state functional magnetic resonance imaging. Methods The Beck Depression Inventory (BDI) was administered to 11 patients with MS and 22 healthy control subjects before scanning with positron emission tomography and functional magnetic resonance imaging. We tested for higher [18F]PBR111 uptake in the hippocampus of patients with MS relative to healthy control subjects and examined the correlations between [18F]PBR111 uptake, BDI scores, and hippocampal functional connectivities in the patients with MS. Results Patients with MS had an increased hippocampal [18F]PBR111 distribution volume ratio relative to healthy control subjects (p = .024), and the hippocampal distribution volume ratio was strongly correlated with the BDI score in patients with MS (r = .86, p = .006). Hippocampal functional connectivities to the subgenual cingulate and prefrontal and parietal regions correlated with BDI scores and [18F]PBR111 distribution volume ratio. Conclusions Our results provide evidence that hippocampal microglial activation in MS impairs the brain functional connectivities in regions contributing to maintenance of a normal affective state. Our results suggest a rationale for the responsiveness of depression in some patients with MS to effective control of brain neuroinflammation. Our findings also lend support to further investigation of the role of inflammatory processes in the pathogenesis of depression more generally.

Development of oral immunomodulatory agents in the management of multiple sclerosis.

The emergence of oral disease-modifying therapies in multiple sclerosis (MS) will have a significant impact on the evolving scenario of immunomodulatory treatments in MS where current therapies are all injectable. Reducing relapses in trials translates for individuals with MS into a therapeutic aim of stopping future events. Thus the possible absence of any perceived benefits to the individual together with the long disease course, variable outcome, and a younger age group affected in MS makes side effects the major issue. The use of disease-modifying therapies as a whole needs to be placed in the context of a widening therapeutic indication where the use of these therapies is being justified at an increasingly early stage and in pre-MS syndromes such as clinically isolated and radiologically isolated syndromes where no fixed disability is likely to have accumulated. The five oral therapies discussed (cladribine, fingolimod, laquinimod, BG-12, and teriflunomide) have just completed Phase III studies and some have just been licensed. New oral drugs for MS need to be placed within this evolving marketplace where ease of delivery together with efficacy and side effects needs to be balanced against the known issues but also the known long-term safety of standard injectables.

BG-12 and its potential for the prevention of relapse in multiple sclerosis

Multiple sclerosis (MS) arises from an immune attack on the central nervous system producing demyelination and axonal loss. Clinically the relapsing-remitting course is characterized by subacute onset of neurological symptoms usually with partial or complete recovery, while the progressive course, predominant in the later stages, is characterized by progressive disability in the absence of relapses. A number of disease-modifying treatments have been developed and are increasingly effective at targeting relapses. Early injectable therapies such as interferon and glatiramer acetate are only partially effective, but have a good safety record. Recently, natalizumab, an intravenous therapy, demonstrated increased effectiveness, but side effects complicate its use. The first oral therapy offering good efficacy and convenience, fingolimod, was approved in USA in 2010 and Europe in 2011. BG-12 is a potential novel oral therapy for MS, which has previously been used as a different formulation for psoriasis. It has anti-inflammatory and neuroprotective actions in vitro, which makes it a promising candidate for future therapies. Phase II studies showed that BG-12 reduced MRI inflammatory activity over placebo, which was confirmed in two Phase III studies indicating immune modulation may be its principal action rather than neuroprotection. In these studies, BG-12 reduced relapse rates consistently with variable effects on progression and few serious adverse events. With its favorable efficacy-tolerability profile, BG-12 could offer a substantial step forward for the care for subjects affected by relapsing MS.

Corrigendum to “Increased central microglial activation associated with peripheral cytokine levels in premanifest Huntington's disease gene carriers” [Neurobiol. Dis. 83 (2015) 115–121]

a Neurodegeneration Imaging Group, Department of Basic and Clinical Neuroscience, Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK b Division of Brain Sciences, Department of Medicine, Imperial College London, London, UK c Huntingtons Disease Research Group, Department of Neurodegenerative Disease, Institute of Neurology, University College London, London, UK d Department of Neuroimaging, Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK