Imaging Alzheimer’s Disease Beta-amyloid Pathology in Transgenic Mouse Models Using Positron Emission Tomography

Accumulation of beta-amyloid (Aβ) in the brain is known to have an important role in the complex chain of pathological events leading to Alzheimer’s disease (AD). Based on current knowledge, Aβ is also seen as an interesting target for novel disease modifying therapies. Non-invasive and quantitative imaging of transgenic mouse models of AD by positron emission tomography (PET) would represent an ideal translational approach for evaluation of novel Aβ targeted therapeutics in vivo already during the preclinical phase of drug development. The aim of this thesis was to evaluate the suitability of Aβ targeted PET tracers, 11C-PIB and 18F-flutemetamol, for small animal PET imaging and for longitudinal follow-up of β-amyloidosis in three AD mouse models, i.e. transgenic APP23, Tg2576 and APPswe-PS1dE9 mice. In addition, the effect of novel functionalized Aβ targeted nanoliposomes, known as mApoE-PA-LIPs, were investigated in APP23 mice exploiting longitudinal 11C-PIB PET imaging. A temporal increase in tracer retention reflecting increased Aβ-deposition could be detected in vivo only in the APP23 mouse model. Both tracers specifically bound Aβ in mouse brain sections, however, the higher non-specific binding of [18F]flutemetamol to the white matter structures limited its sensitivity in comparison to 11C-PIB. In the APP23 model, the mApoE-PA-LIP treatment showed a trend to reduce the increase in the 11C-PIB binding ratios as compared to the saline-treated group; in addition, the binding ratios correlated well with the histologically-assessed amyloid load, further validating the method. In summary, these results demonstrate that 11C-PIB binding is a valid biomarker of Aβ deposition in the APP23 mouse – an animal model that expresses abundant, large and congophilic Aβ deposits. However, the sensitivity of the method is not sufficient for use in animal models with lower plaque loads and different plaque morphologies, nor does it seem capable of detecting early pathological changes in young AD mice.Siirretty Doriast

PET Agents in Dementia:An Overview

This article presents an overview of imaging agents for PET that have been applied for research and diagnostic purposes in patients affected by dementia. Classified by the target which the agents visualize, seven groups of tracers can be distinguished, namely radiopharmaceuticals for: (1) Misfolded proteins (beta-amyloid, tau, alpha-synuclein), (2) Neuroinflammation (overexpression of translocator protein), (3) Elements of the cholinergic system, (4) Elements of monoamine neurotransmitter systems, (5) Synaptic density, (6) Cerebral energy metabolism (glucose transport/ hexokinase), and (7) Various other proteins. This last category contains proteins involved in mechanisms underlying neuroinflammation or cognitive impairment, which may also be potential therapeutic targets. Many receptors belong to this category: AMPA, cannabinoid, colony stimulating factor 1, metabotropic glutamate receptor 1 and 5 (mGluR1, mGluR5), opioid (kappa, mu), purinergic (P2X7, P2Y12), sigma-1, sigma-2, receptor for advanced glycation endproducts, and triggering receptor expressed on myeloid cells-1, besides several enzymes: cyclooxygenase-1 and 2 (COX-1, COX-2), phosphodiesterase-5 and 10 (PDE5, PDE10), and tropomyosin receptor kinase. Significant advances in neuroimaging have been made in the last 15 years. The use of 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) for quantification of regional cerebral glucose metabolism is well-established. Three tracers for beta-amyloid plaques have been approved by the Food and Drug Administration and European Medicines Agency. Several tracers for tau neurofibrillary tangles are already applied in clinical research. Since many novel agents are in the preclinical or experimental stage of development, further advances in nuclear medicine imaging can be expected in the near future. PET studies with established tracers and tracers for novel targets may result in early diagnosis and better classification of neurodegenerative disorders and in accurate monitoring of therapy trials which involve these targets. PET data have prognostic value and may be used to assess the response of the human brain to interventions, or to select the appropriate treatment strategy for an individual patient. (C) 2021 The Authors. Published by Elsevier Inc

Potential biomarkers and novel pharmacological targets in protein aggregation-related neurodegenerative diseases

The aggregation of specific proteins plays a pivotal role in the etiopathogenesis of several neurodegenerative diseases (NDs). β-Amyloid (Aβ) peptide-containing plaques and intraneuronal neurofibrillary tangles composed of hyperphosphorylated protein tau are the two main neuropathological lesions in Alzheimer's disease. Meanwhile, Parkinson's disease is defined by the presence of intraneuronal inclusions (Lewy bodies), in which α-synuclein (α-syn) has been identified as a major protein component. The current literature provides considerable insights into the mechanisms underlying oligomeric-related neurodegeneration, as well as the relationship between protein aggregation and ND, thus facilitating the development of novel putative biomarkers and/or pharmacological targets. Recently, α-syn, tau and Aβ have been shown to interact each other or with other "pathological proteins" to form toxic heteroaggregates. These latest findings are overcoming the concept that each neurodegenerative disease is related to the misfolding of a single specific protein. In this review, potential opportunities and pharmacological approaches targeting α-syn, tau and Aβ and their oligomeric forms are highlighted with examples from recent studies. Protein aggregation as a biomarker of NDs, in both the brain and peripheral fluids, is deeply explored. Finally, the relationship between biomarker establishment and assessment and their use as diagnostics or therapeutic targets are discussed

Diffusion imaging markers of cerebral small vessel disease

Diffusion magnetic resonance imaging (MRI) is widely used as a research tool to assess (subtle) alterations of the cerebral white matter. Measures derived from diffusion MRI appear to be valuable markers for cerebral small vessel disease (SVD). However, SVD is frequently co-occurring with Alzheimer’s disease (AD), and disturbed white matter integrity and altered diffusion measures are considered key findings in both conditions. Yet, the contribution of SVD and AD to diffusion alterations is unclear, which hampers the interpretation of research studies in patients with mixed disease, e.g. memory clinic patients. Study 1 of this thesis aimed to clarify the effect of SVD and AD on diffusion measures by including multiple (memory clinic) samples covering the entire spectrum of SVD, mixed disease, and AD. We calculated diffusion measures from diffusion tensor imaging (DTI) and free water imaging. Within each sample of the disease spectrum, we applied simple regression analyses and multivariable random forest analyses between AD biomarkers (amyloid-beta, tau), conventional MRI markers of SVD, and global diffusion measures. Furthermore, we investigated regional associations between tau on positron emission tomography (PET) and diffusion measures in voxel-wise analyses. Our main findings are that conventional MRI markers of SVD were strongly associated with diffusion measures and showed a higher contribution than AD biomarkers in multivariable analyses across all memory clinic samples. Regional analyses between tau PET and diffusion measures were not significant. We conclude that SVD rather than AD determines diffusion alterations in memory clinic patients. Our findings validate diffusion measures as markers for SVD. Study 2 applied diffusion MRI markers to study gait impairment in SVD. Gait impairment is a commonly reported clinical deficit in SVD patients, but the underlying mechanisms are still debated. The proposed mechanisms include SVD-related white matter alterations resulting in impaired supraspinal locomotor control, cognitive deficits (e.g. planning and execution of movements), and factors independent of SVD, such as age-related instability (e.g. joint wear, sarcopenia) and comorbidities (e.g. neurodegenerative pathology). A reason for the lack of knowledge on gait impairment in SVD is that studies in elderly, sporadic SVD patients are typically confounded by effects of normal-aging and age-related comorbidities. Therefore, Study 2 of this thesis aimed to study the effect of pure SVD on gait performance in a relatively young sample of genetically defined SVD patients without age-related confounding. We performed comprehensive gait assessment using an electronic walkway to obtain multiple spatio-temporal gait parameters standardized based on data from healthy controls. Importantly, we tested the association between diffusion MRI markers of SVD-related white matter alterations and gait performance, since (strategic) white matter alterations are discussed as a major cause of gait decline in the elderly. Furthermore, we assessed the relation between cognitive deficits and gait performance. Our main finding is that, despite severe white matter alterations in pure SVD patients, gait performance was relatively preserved. Cognitive deficits in our study participants were not related to gait impairment. Thus, our results query isolated white matter alterations, in the absence of comorbidities, as a main factor of gait impairment in SVD and suggest that their combination with age-related comorbidities and/or normal-aging may play a crucial role in gait decline. In conclusion, diffusion measures are valid MRI markers of SVD-related white matter alterations. They have significant value both in future research on altered white matter and potentially also in the diagnostic work-up of memory clinic patients, to differentiate between vascular and neurodegenerative disease. Researchers may select target populations for clinical trials based on diffusion measures, e.g. to identify patients with a low SVD burden as targets for prevention and early intervention in SVD. Clinicians and researchers should always consider SVD as the origin of diffusion alterations in patients with mixed pathology. The field of application of diffusion measures is wide and may provide new insights into effects of subtle white matter alterations on clinical deficits, as shown in Study 2 on gait impairment in pure SVD. Future studies should investigate measures from advanced diffusion models and diffusion-based brain network analysis, to further elucidate the mechanisms of clinical deficits in SVD patients

Diffusion imaging markers of cerebral small vessel disease

Diffusion magnetic resonance imaging (MRI) is widely used as a research tool to assess (subtle) alterations of the cerebral white matter. Measures derived from diffusion MRI appear to be valuable markers for cerebral small vessel disease (SVD). However, SVD is frequently co-occurring with Alzheimer’s disease (AD), and disturbed white matter integrity and altered diffusion measures are considered key findings in both conditions. Yet, the contribution of SVD and AD to diffusion alterations is unclear, which hampers the interpretation of research studies in patients with mixed disease, e.g. memory clinic patients. Study 1 of this thesis aimed to clarify the effect of SVD and AD on diffusion measures by including multiple (memory clinic) samples covering the entire spectrum of SVD, mixed disease, and AD. We calculated diffusion measures from diffusion tensor imaging (DTI) and free water imaging. Within each sample of the disease spectrum, we applied simple regression analyses and multivariable random forest analyses between AD biomarkers (amyloid-beta, tau), conventional MRI markers of SVD, and global diffusion measures. Furthermore, we investigated regional associations between tau on positron emission tomography (PET) and diffusion measures in voxel-wise analyses. Our main findings are that conventional MRI markers of SVD were strongly associated with diffusion measures and showed a higher contribution than AD biomarkers in multivariable analyses across all memory clinic samples. Regional analyses between tau PET and diffusion measures were not significant. We conclude that SVD rather than AD determines diffusion alterations in memory clinic patients. Our findings validate diffusion measures as markers for SVD. Study 2 applied diffusion MRI markers to study gait impairment in SVD. Gait impairment is a commonly reported clinical deficit in SVD patients, but the underlying mechanisms are still debated. The proposed mechanisms include SVD-related white matter alterations resulting in impaired supraspinal locomotor control, cognitive deficits (e.g. planning and execution of movements), and factors independent of SVD, such as age-related instability (e.g. joint wear, sarcopenia) and comorbidities (e.g. neurodegenerative pathology). A reason for the lack of knowledge on gait impairment in SVD is that studies in elderly, sporadic SVD patients are typically confounded by effects of normal-aging and age-related comorbidities. Therefore, Study 2 of this thesis aimed to study the effect of pure SVD on gait performance in a relatively young sample of genetically defined SVD patients without age-related confounding. We performed comprehensive gait assessment using an electronic walkway to obtain multiple spatio-temporal gait parameters standardized based on data from healthy controls. Importantly, we tested the association between diffusion MRI markers of SVD-related white matter alterations and gait performance, since (strategic) white matter alterations are discussed as a major cause of gait decline in the elderly. Furthermore, we assessed the relation between cognitive deficits and gait performance. Our main finding is that, despite severe white matter alterations in pure SVD patients, gait performance was relatively preserved. Cognitive deficits in our study participants were not related to gait impairment. Thus, our results query isolated white matter alterations, in the absence of comorbidities, as a main factor of gait impairment in SVD and suggest that their combination with age-related comorbidities and/or normal-aging may play a crucial role in gait decline. In conclusion, diffusion measures are valid MRI markers of SVD-related white matter alterations. They have significant value both in future research on altered white matter and potentially also in the diagnostic work-up of memory clinic patients, to differentiate between vascular and neurodegenerative disease. Researchers may select target populations for clinical trials based on diffusion measures, e.g. to identify patients with a low SVD burden as targets for prevention and early intervention in SVD. Clinicians and researchers should always consider SVD as the origin of diffusion alterations in patients with mixed pathology. The field of application of diffusion measures is wide and may provide new insights into effects of subtle white matter alterations on clinical deficits, as shown in Study 2 on gait impairment in pure SVD. Future studies should investigate measures from advanced diffusion models and diffusion-based brain network analysis, to further elucidate the mechanisms of clinical deficits in SVD patients

生体数学モデルを用いたアミロイドおよびタウトレーサーのスクリーニング

Tohoku University渡部浩司課

Imaging glucose metabolism, neuroinflammation, and cannabinoid receptor 1 in transgenic mouse models of Alzheimer’s disease

The pathophysiological cascade leading to Alzheimer’s disease is characterized by the accumulation of destructive β-amyloid in the brain. Convincing evidence has also shown that cerebral energy hypometabolism and an overproduction of translocator protein during neuroinflammation, as well as deficits in the endocannabinoid system, play major roles in progression of the disease. Monitoring temporal changes inside the diseased brain with noninvasive positron emission tomography (PET) would be a unique translational tool, bridging the gap between disease models and patients and aiding in the discovery of disease-modifying therapies against Alzheimer’s disease. The aim of this thesis was to evaluate the translational feasibility of cerebral glucose metabolism targeting PET tracer 18F-FDG in APPswe-PSIdE9, Tg2576, and APP/PS1-21 mouse models of Alzheimer’s disease. In addition, this thesis aimed to examine the suitability of neuroinflammation-specific protein targeting tracer 18F-DPA-714 for longitudinal follow-up in aging APP/PS1-21 mice and whether it correlates with changes in glucose metabolism. Furthermore, the translational applicability of 18F-FMPEP-d2 was evaluated as a tool to assist in preclinical research targeting cannabinoid receptor 1 (CB1R) in wild-type and APP/PS1-21 mice. Of the tested models, APP/PS1-21 mice demonstrated the most aggressive β-amyloid pathology. Furthermore, repeated PET scans with 18F-FDG and 18F-DPA-714 detected progressive glucose hypometabolism and neuroinflammation in the APP/PS1-21 model as the mice aged. However in the APPswe-PSIdE9 and Tg2576 mouse models, only a weak or non-altered glucose metabolism was observed. 18F-FMPEP-d2 was able to reveal altered CB1R availability when aging APP/PS1- 21 mice were followed with repeated PET scans. This thesis work demonstrated that Alzheimer’s disease mouse models differ in terms of amyloidosis and cerebral glucose metabolism, which creates challenges when comparing the research results between the models. The feasibility of 18F-FDG small animal PET depends on the chosen disease model and environmental factors. In the APP/PS1-21 model, longitudinal 18FFMPEP- d2 and 18F-DPA-714 PET scans were able to demonstrate pathological features related to Alzheimer´s disease, which were confirmed by ex vivo examinations.Aivojen energia-aineenvaihdunnan, tulehduksen ja tyypin 1 kannabinoidireseptorin kuvantaminen Alzheimerin taudin muuntogeenisissä hiirimalleissa Alzheimerin taudin keskeisimmät aivomuutokset ovat sakkautuvien β-amyloidipeptidien muodostuminen plakeiksi, aivojen heikentynyt energia-aineenvaihdunta, tulehduksen lisääntyminen ja endokannabinoidijärjestelmässä tapahtuvat muutokset, jotka lopulta johtavat hermosolujen vaurioitumiseen ja tyypillisten kognitiivisten häiriöiden ilmentymiseen. Aivomuutoksia on mahdollista seurata elävässä tutkittavassa kajoamattoman positroniemissiotomografia (PET)-kuvantamisen avulla. Muuntogeenisten Alzheimerin taudin eläinmallien PET-kuvantaminen antaa ainutlaatuisen mahdollisuuden selvittää sairauden monimutkaisia patologisia tapahtumia ja seurata uusien lääkeaineiden vaikutusta ja turvallisuutta. Tämän tutkimuksen tavoitteena oli arvioida aivojen glukoosiaineenvaihduntaa mallintavan 18FFDG-merkkiaineen soveltuvuutta muuntogeenisten APPswe-PSIdE9, Tg2576 ja APP/PS1-21 hiirimallien pieneläinPET-kuvantamiseen. Toisena tavoitteena oli arvioida tulehdusproteiiniin sitoutuvan PET-merkkiaineen, 18F-DPA-714, soveltuvuutta aivoissa etenevän tulehduksen seuraamiseen muuntogeenisessä APP/PS1-21 hiirimallissa. Kolmantena tavoitteena oli tutkia tyypin 1 kannabinoidireseptori-PET-merkkiaineen, 18F-FMPEP-d2, soveltuvuutta pieneläinkuvantamiseen villityypin hiirillä ja Alzheimerin taudin reseptorimuutosten seuraamiseen APP/PS1-21 hiirimallilla. APP/PS1-21 hiirimallin β-amyloidipatologia eteni muita malleja nopeammin. Lisäksi hiirimallin aivojen glukoosiaineenvaihduntaa mallintavan merkkiaineen kertymä heikentyi ja tulehdusproteiiniin sitoutuvan merkkiaineen määrä kasvoi, kun hiiriä kuvattiin toistuvasti PETmenetelmällä. Vastaavasti APPswe-PSIdE9 ja Tg2576 hiirimalleilla havaittiin vain lievää tai olematonta glukoosiaineenvaihdunnan heikkenemistä. 18F-FMPEP-d2 PET-tutkimukset osoittivat alentunutta merkkiainekertymää APP/PS1-21 hiirimallissa verrattuna terveisiin eläimiin, ja soveltuvuutta tuleviin pieneläinkuvantamistutkimuksiin. Tutkimustulokset osoittivat, että muuntogeeniset eläinmallit eroavat merkittävästi toisistaan, mikä asettaa haasteita tutkimustulosten vertaamiseen mallien kesken. Aivojen 18F-FDG-kertymä vaihtelee tautimallin ja ympäristötekijöiden mukaan, mikä tuo rajoitteita pieneläinkuvantamisen toteuttamiseen. Sekä 18F-DPA-714- ja 18F-FMPEP-d2-merkkiaineet pystyivät osoittamaan Alzheimerin taudille tyypillisiä aivomuutoksia APP/PS1-21 hiirissä, mitkä voitiin varmentaa ex vivo menetelmin hiirten aivoleikkeistä

Early detection of Alzheimer’s disease - Twin study on episodic memory and imaging biomarkers of neuroinflammation and β-amyloid

The disease process of Alzheimer’s disease (AD) causes damage to the brain for several years leading to the development of mild cognitive impairment (MCI) and finally to dementia which interferes with independent living. The early detection of AD disease process is key for the prevention and treatment of disease. The aim of this thesis was to improve the assessment of episodic memory (EM) and cognitive performance with a telephone interview and neuroimaging of early AD. The study population belonged to the older Finnish Twin Cohort study. 2631 twins (856 pairs) participated in the telephone interview (TELE, TICS) during 1999–2007 and 1817 twins (559 pairs) participated in the interview (TELE, TICS, TICS-m) during 2013– 2017. Cognitively discordant twin pairs were asked to participate in more detailed examinations. 11 twin pairs participated in [11C]PBR28 positron emission tomography (PET) imaging measuring neuroinflammation during 2014–2017 and 45 twin pairs participated in [11C]PiB PET imaging measuring β-amyloid (Aβ) deposits during 2005–2017. Twins who had co-twins with dementia (n=101) performed poorer than average in a word list learning test. When using the telephone interview TICS-m, the education‐adjusted classification resulted in a higher proportion of apolipoprotein (APOE) ε4 allele carriers among those identified as having MCI. Twins with poorer EM performance (n=10) had higher cortical [11C]PBR28 uptake compared to their better-performing co-twins. In addition, higher cortical [11C]PiB uptake was associated with poorer EM performance. The results from the telephone interview studies indicate that poorer word list learning performance may be an early marker of dementia risk and that the use of education‐adjustment may increase the accuracy of MCI classification. The twin pair setting controlling for genetic and environmental effects indicated that brain Aβ load and neuroinflammation have a negative association with EM performance.Alzheimerin taudin varhainen havaitseminen – Kaksostutkimus episodisesta muistista ja neuroinflammaation ja β-amyloidin kuvantamisbiomarkkereista Alzheimerin taudin (AT) prosessi vaurioittaa aivoja vuosien ajan ja johtaa lievään kognitiiviseen heikentymiseen (MCI) ja lopulta itsenäistä selviytymistä häiritsevään dementiaan. AT:n dementiaan johtavan prosessin varhainen havaitseminen on avainasemassa ehkäisyn ja hoidon kannalta. Tämän väitöskirjatutkimuksen tavoitteena oli kehittää puhelinhaastattelun käyttöä episodisen muistin (EM) ja muiden tiedonkäsittely- eli kognitiivisten toimintojen arvioimisessa sekä AT:n varhaista kuvantamista. Tutkimusjoukko kuului vanhempaan suomalaisen kaksoskohorttitutkimukseen. 2631 kaksosta (856 paria) osallistui puhelinhaastatteluun (TELE, TICS) 1999–2007 aikana ja 1817 kaksosta (559 paria) osallistui haastatteluun (TELE, TICS, TICS-m) 2013–2017 aikana. Kognitiivisesti diskordantit kaksosparit kutsuttiin tarkempiin jatkotutkimuksiin. 11 kaksosparia osallistui neuroinflammaatiota mittaavaan [11C]PBR28-merkkiaineen positroniemissiotomografia (PET) - kuvaukseen 2014–2017 aikana ja 45 kaksosparia osallistui aivojen β-amyloidikertymää mittaavaan [11C]PiB-merkkiaineen PET-kuvaukseen 2005–2017 aikana. Sellaisten kognitiivisesti normaalien ikääntyneiden kaksosten (n=101), joiden sisaruksella oli dementia, havaittiin suoriutuvan keskimääräistä heikommin sanalistan oppimista mittaavassa testissä. Käytettäessä TICS-m-puhelinhaastattelua koulutuskorjauksen käyttäminen johti siihen, että MCI:tä sairastavien joukossa oli suurempi osuus apolipoproteiini E:n (APOE) ε4-alleelin kantajia. Kaksosilla (n=10), jotka suoriutuivat heikommin EM-testeissä, oli suurempi aivokuoren [11C]PBR28-kertymä verrattuna paremmin suoriutuviin sisaruksiinsa. Myös suurempi aivokuoren [11C]PiB-kertymä oli yhteydessä heikompaan EM-suoritukseen. Puhelinhaastattelujen tulokset viittaavat siihen, että sanalistan oppiminen voi olla dementiariskistä kertova varhainen merkki ja että koulutuskorjauksen käyttö voi lisätä MCI-luokittelun tarkkuutta. Kaksosasetelma, joka kontrolloi geneettisten ja ympäristötekijöiden vaikutusta, osoitti, että aivojen β-amyloidikertymä ja neuroinflammaatio ovat negatiivisessa yhteydessä EM:n toiminnan kanssa

12 Chapters on Nuclear Medicine

The development of nuclear medicine as a medical specialty has resulted in the large-scale application of its effective imaging methods in everyday practice as a primary method of diagnosis. The introduction of positron-emitting tracers (PET) has represented another fundamental leap forward in the ability of nuclear medicine to exert a profound impact on patient management, while the ability to produce radioisotopes of different elements initiated a variety of tracer studies in biology and medicine, facilitating enhanced interactions of nuclear medicine specialists and specialists in other disciplines. At present, nuclear medicine is an essential part of diagnosis of many diseases, particularly in cardiologic, nephrologic and oncologic applications and it is well-established in its therapeutic approaches, notably in the treatment of thyroid cancers. Data from official sources of different countries confirm that more than 10-15 percent of expenditures on clinical imaging studies are spent on nuclear medicine procedures