4.5 Nanoparticles for Diagnosis of AD
4.5.2 Organic NPs for AD Diagnosis
On the other hand, Monosialogangliosides (GM1), exhibited much lower affi nity for Αβ (0.2 μM) [206]. 2-methyl-N-(2'-aminoethyl)-3-hydroxyl- 4-pyridinone (Iron chelator) [210], Sialic acid (Figure 4.11) [211, 212] and Maltose [213] were also ligated on dendrimers and the corresponding con- jugated nanoparticles were found to be eff ective Aβ aggregation inhibitors.
Table 4.7 NPs for AD diagnosis.
Type of NPs: Imaging agent- Ligands
Model Result Reference
Polymeric NPs Polystyrene/polybu-
tylcyanoacrylate -AChE inhibitor PE154
TTG Plaque detection by confocal laser- scanning microscopy
(295)
PBCA-NPs-
Alexa-488– AβMAb (6E10)
APP/PS1 Amyloid plaque detection in brain
(298)
PBCA- polystyrene NPs- Th iofl avin
In vitro Visualization of amyloid aggregates
(299) BCA NPs- Clioquinol
radioiodinated
AD mice AD brain section localized uptake of radiotracer
(296)
PLGA NPs-amyloid- binding aptamer Tet peptide
In vitro binding to amyloid plaques
(200)
Liposomes PA-Lips-PA
(Phosphatidic acid)
In vitro high affi nity (e.g., 22–60 nM) toward Aβ fi brils
(206) PA-LIP- PA and
RI7217 MAb
In vitro targeting amyloid-β peptide
(300) ApoE fragment
141-150
In vitro ↑uptake by cells ↑bind- ing to Aβ peptide
(301) Curcumin (or encap.
dyes) - Curcumin
In vitro high affi nity for amy- loid-β1-42 peptide.
(201) Curcumin- nanolipos-
omes-Curcumin
APPxPS1 stain the Aβ deposits in vivo
(202)
methoxy-XO4 APP/
PSEN1
iv delivery of Aβ-targeted NP to plaques in AD model
(302)
(Continued)
Type of NPs: Imaging agent- Ligands
Model Result Reference
USPIOs- OX-26 In vitro In vitro barrier crossing of liposomes contain- ing USPIOs
(303)
Iron oxide [IO] NPs Monocrystalline
IO-Abeta1-40 peptide
APP/PS1 Method to detect Abeta in AD transgenic mice
(304)
USPIO- Aβ1-42 peptide
APP/PS1 Amyloid plaques detected by T2*- weighted μMRI
(296)
SPIONs-anti-AβPP APP/PS1 MRI of Plaques (270) USPIO- Aβ1-42
peptide
APP/PS1 Detection of amyloid plaques in vivo
(305) Maghemite NPs-
Congo red, rhodamine
In vitro Th e hybrid system selec- tively marks Aβ40 fi brils
(306)
IONPs- anti-Aβ antibody (Aβ1-40
;Aβ1-42)
In vitro Assaying Aβ through immunomagnetic reduction
(271)
Gold NPs
Au - Aβ1-40 antibody In vitro Aβ (1-42) concentra- tions (10 fg/mL level)
(297) Au-sialic acid In vitro Amyloid-beta detection (295) Au- MAb specifi c to
ADDL(amyloid derived diff used ligands)
Ex vivo Bio-barcode assay to measure ADDL in CSF
(296)
Au-anti-tau MAb In vitro Two-photon scattering assay detection of tau protein
(295) Table 4.7 (Cont.)
Type of NPs: Imaging agent- Ligands
Model Result Reference
Au- Aβ(1–40) MAb In vitro Detection of Aβ Antigen or aggregates
(272, 273, 307) Quantum dots(QDs)
PEG-QDs - Aβ1–40, 1–42 peptides
In vitro Study of the Aβ peptide aggregation
(295) QDs-Gold NP-BACE1
peptide
In vitro Visualize BACE1 activ- ity in living cells
(308) QDs- Aβ peptides In vitro Visualisation of Aβ
plaques and inhibi- tion of fi brillation
(309)
Other NPs Manganese oxide
NPs- Aβ(1–40)MAb
APP/PS1 Detect amyloid plaque deposition in AD mouse models
(310)
Microbubbles- Gadolinium
APP/PS1 MRI imaging of amyloid plaques in the brain
(311) Co@Pt-Au core-shell
nanoparticles
In vitro MRI to monitor the structural evolution of Abeta assemblies
(312)
Silver NPs - ADDL antibody
In vitro Antigen detection;
determination of ADDL concentration
(297)
Silica nanoparticles anti-tau MAb
In vitro Detection of tau at 10pg/
mL in cerebral spinal fl uid (CSF)
(313)
Some of these are described in more detail below. Th e in vivo staining and detection of Aβ plaques by confocal laser-scanning microscopy with the use of polystyrene/polybutylcyanoacrylate (PS/PBCA)-NPs encapsulat- ing the fl uorescent biomarker PE154, was reported [295]. Briefl y PE154 a heterodimeric AChE inhibitor that allows histochemical staining of cortical Aβ plaques in triple-transgenic (TTG) mice was encapsulated
in biodegradable core-shell PS/PBCA-NPs and in vivo labelling of the plaques was demonstrated. Furthermore, it was shown that PE154 targeted only the Aβ plaques but not tau tangles nor reactive astrocytes (which surrounded the plaques). PBCA-dextran NPs coated with polysorbate 80 were recently proposed as systems to deliver BBB-impermeable molecular imaging probes into the brain [298]. It was indeed demonstrated in vivo (in a mouse model of AD) by using a non-BBB-permeable dye (Alexa-488) that these PBCA-dextran NPs accomplish visualization of amyloid plaques by successful targeting aft er conjugation to a specifi c AβMAb (6E10).
Additionally, the brain delivery of gadolinium-based contrast agents from similar NPs was proved by MRI. In fact the fi rst study reporting amyloid staining with PBCA NPs was from 2006 [299]. In that study Th iofl avin (a ligand for fi brillar Aβ peptides)-encapsulating PBCA NPs, showed sig- nifi cantly stronger fl uorescent staining compared to the free fl uorophore.
Indeed, aft er intracerebral injection, NP-thiofl avin selectively targeted fi brillar Abeta (following biodegradation-induced release from the NPs), in the cortices of APP/PS1 mice with age-dependent beta-amyloidosis.
Another study demonstrated that encapsulation of (125)I-clioquinol (CQ, 5-chloro-7-iodo-8-hydroxyquinoline) to PBCA nanoparticles improved its transport to the brain and its retention on amyloid plaques. (125)I-CQ- PBCA NPs successfully stained plaques on post-mortem frontal cortical sections of AD patients, and enhanced its retention in AD-mouse brains [296]. Th is combination makes the specifi c NPs a promising delivery vehicle for in vivo single photon emission tomography (SPECT) ((123) I) or PET ((124)I) amyloid imaging agent. Recently the development of Tet-1 targeted PLGA NPs encapsulating curcumin was reported [200]. It was observed that Tet-1 increased the neuronal uptake of curcumin from curcumin-PLGA NPs, compared to the non-targeted ones. Th ese NPs were able to attach to the amyloid aggregate surface and decrease the size of the aggregates within 12 hours of co-incubation.
Liposomes for Diagnosis of AD:As mentioned above, liposomes are colloidal, vesicular structures composed of one or more lipid bilayers. Th eir properties make them ideal candidates for the delivery of drugs or use for diagnosis of AD. Some liposomes with affi nity for Aβ peptides have been demonstrated to stain amyloid plaques in vitro and (in some cases) also in vivo, while on some NPs also BBB targeting ligands have been added with the aim to target brain-located Aβ species or plaques. However, specifi c diagnostic evaluations have not been yet carried out, and most studies are only in preclinical stage. As examples: liposomes and SLNs incorporating phosphatidic acid (PA) or cardiolipines (CL) as a way to target Aβ pep- tides were prepared, and Surface Plasmon Resonance (SPR) investigations
demonstrated that both PA/CL-containing liposomes and SLNs dis- played high affi nity (e.g., 22–60 nM) towards chip-immobilized Aβ fi brils, likely due to multivalent interactions [206]. Th e PA incorporating lipo- somes were subsequently further functionalized with a monoclonal anti- body (mAb) [RI7217] against the transferrin receptor, for BBB targeting [300]. SPR experiments revealed high affi nity of these nanoliposomes for Aβ-plaques and higher uptake and permeability of the targeted liposomes (compared to non-targeted ones) by cells which are good in vitro BBB models. In a similar approach the same PA liposomes were further func- tionalized with synthetic ApoE derived peptides in order to enhance their BBB targeting via the LDL receptor [301]. Results confi rmed enhanced targeting of human microvascular brain capillary endothelial cells in vitro (60% higher compared to the non-functionalized liposomes), while the functionalization with ApoE-derived peptide does not aff ect their previ- ously reported ability to bind amyloid-β. Additionally, in a recent study the functionalization of azido-decorated liposomes with an alkyne-deriva- tized curcumin was reported [201]. SPR experiments demonstrated that the later liposomes had the highest affi nity constant (in the 1–5 nM range) reported up-to-date for Aβ fi brils when decorated with a planar curcumin conjugate, while non planar curcumin-decorated liposomes did not show any binding. However, the later liposomes type (with non-planar cur- cumin conjugate) was recently reported to label amyloid deposits in post- mortem tissue of transgenic mice (APP-PS1) aft er IV administration (in vivo) and down-regulate the secretion of Aβ peptide in cells overexpressing hAPP (in vitro) [202]. Th ereby, the question is open about the importance of planar curcumin structure (as also mentioned before in section 4.4).
Others recently reported the preparation of Aβ-targeted stealth liposo- mal nanoparticles using the Aβ-targeted lipid conjugate DSPE-PEG-XO4 [302]. Th ese liposomal NPs maintain similar binding profi les to Aβ (1–40) as the free XO4 ligand in vitro. Th ey selectively bind to amyloid deposits in brain tissue sections of APP/PSEN1 transgenic mice in vitro. Ex vivo anal- yses of treated brain tissue show that when injected into mice, the targeted particles effi ciently bind both parenchymal plaques and CAA-associated amyloids throughout the brain. In vitro immunohistochemistry verifi ed co-localization of both the liposome encapsulated and bilayer membrane components on brain tissue sections obtained from treated animals, con- fi rming the ability of the particles to traverse the BBB and bind amyloid-β plaque deposits. Finally, in another study the encapsulation of USPIOs in liposomes (and formation of magnetoliposomes, MLs) functionalized with OX-26 antibody, which enables the NPs to pass through the BBB, has been reported [303]. In a second step, curcumin derivatives are additionally
immobilized on the ML surface for amyloid affi nity (A. Skouras et al, unpublished results). Ongoing in vitro and in vivo studies are currently carried out in order to demonstrate the potential of such multifunctional MLs to target Aβ plaques in the brain.