Presentation explores the Possibility of Fullerene and its derivatives to be used as a Therapeutic Agent in Alzheimer's and discusses the toxicity levels of different functional groups for the same.
2. i. Introduction
Fullerene
Alzheimerâs Disease
ii. Fullerene: Possible Therapeutic Agent
iii. Anti- Amyloid Beta activity
iv. Radical Scavenging
v. Acetylcholine esterase inhibition
vi. Discussion
vii. Future
viii. Conclusion
2
3. Fullerene (Buckministerfullerene)
â˘Carbon allotrope discovered in 1985 by Harry Kroto and his
team.
â˘60 equivalent carbon atoms arranged in spherical pattern
composed of 12pentagons and 20 hexagons
â˘Diameter of about 1nm to 10nm.
3
4. Applications in Medical sciences:
â˘Drug Delivery
â˘Diagnostic
â˘Probe
â˘Enzyme inhibition
â˘Site specific DNA photocleavage
â˘ROS quenching
4
5. ALZHEIMERâS DISEASE:
A progressive neurodegrading disease characterized by memory loss
and loss of cognitive functions .
Two hallmark pathologies:
ď§Extracellular plaque deposits of the β-amyloid peptide (Aβ)
ď§Neurofibrillary tangles of the microtubule binding protein tau.
Other mechanisms which signify AD:
ď§Oxidative stress
ď§Metal Homeostasis
ď§Dysfunction of acetylcholine esterase
ď§Mitochondrial dysfunction
5
6. Why Fullerene derivatives are being suggested as potential
therapeutic agents in AD?
ď§Hydrophobic core
ď§Membrane penetrating tendency
ď§ROS quenching
ď§Inhibitory action
ď§DNA photocleavage
ď§Low toxicity
ď§Potential to get variously functionalized
6
7. Amino acid sequence of amyloid beta. (Highlighted motif is a hydrophobic core)
Sisodia et al, The FASEB Journal, Vol. 9 March 1995
7
Ameloid Beta deposits in brain have been accounted as one of the early symptoms of
AD.
Ameloid beta are 39 to 43 amino acid sequence long proteins with a trans-membrane
and an extracellular domain.
Ameloid beta is formed from Ameloid Precursor Protein (APP) due to incorrect
cleavage by secretase enzyme at cell surface.
Mutations in APP sequence- secretase cleave at a different position resulting in
fibrillogenic ameloid beta.
Aggregation by nucleation and growth process
8. 8
Ameloid beta plagues are prominantly found in
hippocampus and neocortex regions of brain.
Plaques:-
Blocking vital cell to cell signaling, transport
Cause dys-functioning of mitochondria
(disrupting membrane)
ROS generation
Lipid peroxidation
Inhibition of key enzymes in respiratory
cycle
Form high affinity complex with copper ions
to generate hydrogen peroxide
Neuronal apoptosis
Figure: Shows brain severely
suffering from AD. Dark regions
shows the aggregated plagues in
brain and shrunken shape
represents damaged neurons.
(www.alz.org/braintour/healthy_vs
_alzheimers.asp)
9. 9
Fullerene + Functional group = Soluble derivative
Jeong et al. in 2003 had shown that DMF inhibits amyloid fibrils greatly via
Thioflavin T (ThT) fluorescence assay
No details on possible interaction behind this inhibition.
Xiaoying et. al in 2014 have provided a study on possible interaction of
fullerene derivative 1,2-dimethoxymethano fullerene (DMF) with insoluble
amyloid fibrils.
Three binding domains :
Central Hydrophobic core (17CVFFA21),
Turn site (27NKGAI31)
C-terminal β sheet site (31IIGLMVGGVVI41).
These regions have stronger hydrophobicity, aromatic residues and concave
surfaces which facilitates the binding of DMF molecule to these regions.
10. 10
Figure: (a) The structure of DMF. (b) The initial conformation of the Aβ42 protofibril with a
DMF molecule placed at three different positions. In the three initial states, the minimum
distance between DMF and Aβ42 is 2 nm. For DMF molecules, carbon atoms are in gray, oxgen
atoms are in red, and CH3 (united-atom) is in green. For Aβ42, different colors represent
different residues types: blue, positively charged; red, negatively charged; green, polar; gray,
hydrophobic. Xiaoying et. al in 2014
11. 11
Figure: Concave surface in turn region provides a potential binding site for DMF molecule. Binding in
turn region disrupts the salt bridges in fibrils and causing their disintegration. Xiaoying et. al in 2014
Podolski et. Al, 2007
Bobylev et al. 2010, fullerenol (FL), sodium
fullerenolate (NaFL) and NaPCF respectively.
Bobylev et al. 2011,
Nitroderivatives of fullerene C60. (a
methyl ester of LN[(2nitroglyceryl)
fullerenyl] proline; (c) methyl ester of
L N[(2,3dinitroglyceryl) fullerenyl]
proline; (e) 2nitroxyethyl ester of
LN([2(nitroxy) ethyl] fullerenyl)
proline.
12. 12
Figures: SEM images of Aggregated Amyloid beta fribrils. Podolski et. al, 2007
Figures: SEM images of
Aggregated Amyloid beta
fribrils incubated with
fullerenols. Image shows
disaggregation of plaques
on action of fullerene
derivates. Podolski et.
al, 2007
13. 13
A B C D E
A- Aggregated Fibrills
B- fullerenol (FL)
C- NaFL
D- NaPCF
E- Control
Graph: Thioflavin T (ThT) fluorescence assay on Aggregated amyloid beta fibrills after treatment
with fullerene derivatives. Bobylev et al. 2010
Tan-Yi Lu et al, 2011 : PEG-fullerene derivative Lee et al, 2011 a pentoxifylline derivative (PTX-fullerene)
14. 14
Oxidative stress :earliest symptom of the disease
Excessive generation of Reactive Oxygen Species (ROS) in brain due to
simultaneous dys-functionaling of a number of mechanisms in AD brain.
Zhi-You et al., 2007 : OS results in major damage to proteins and lipids
by increasing lipid peroxidation and causing unwanted oxidation of
proteins as well as nucleic acids
Julie K. Anderson, 2004, Zhao et al.,2013 : Effects of oxidative stress on
neurons in AD brain
Ranjana et al. 2012; Padurariu et al., 2013: sources of ROS:
Amyloid β accumulation,
Mitochondrial dysfunction
Metal homeostasis
15. 15
Zhao et al., 2013: Studies performed in Tg 19959 transgenic mice model and
Tg2576 mouse model
Amyloid β accumulation
Activation of N-methyl D-aspartate receptor
Calcium concentrations in neuronal cells
Mitochondira dysfunction (ATP generation and Krebs cycle, Adam-vizi et.al,
2010)
ROS generation
ROS
Increases β and γ secretase
JNK pathway activated
Amyloid β aggregation
16. 16
Mitochondrial dysfunction:
Amyloid β accumulation localized to mitochondrial regions
Damage to mitochondrial metabolism
Disrupting its lipid polarity
Increasing its membrane permeability
Release of cytochrome c
Disturbance in electron transport chain
Release of reactive oxygen species (ROS).
Amyloid β accumulation causes nitration and inactivation of MnSOD which is
a primary antioxidant enzyme present ion brain.
Figure: Dys-
functioning in
Mitochondria ,
results in
generation of
ROS species.
17. 17
Figure: Type I and Type II photosensitization
reactions by fullerene to generate free
radicals (Markovic et.al, 2008)
Figure: Surface coated soluble
fullerene,scavenging capability
depends on the porosity of
surfactant coating (Markovic
et.al, 2008)
Addition of extra functional side groups decreases the Ď electron
delocalization by breaking Ď bonds and hence decreses the role of fullerene as
a photosensitizer
18. 18
Fullerene scavenges ROS species by three mechanisms:
Physical Quenching is a weak mechanism where singlet oxygen is deactivated by
converting its electronic excitation energy to vibrational energy of oxygen and
fullerene. In derivatized fullerene molecule exhibits this type of ROS quenching
mechanism which is relatively weak with rate constant of or depending upon the
solvent. This quenching increases with addition of functional groups in the
fullerene cage.
Its been noted that fullerols are best quenchers and their ROS quenching ability
increases with each addition of âOH group.
Chemical quenching is mostly seen for Hydroxyl radicals as they react with
Carbon atoms attached to Ď double bond in cage. Thus as double bond decreases
on addition of functional groups, tendency of fullerene derivative to quench
Hydroxyl radicals decreases.
Catalytic quenching occurs for superoxide anion through catalytic dismutation.
Due to attachment of some carboxyl groups on ring, generation of some electron
deficient regions occur on cage which then take part in half reactions as catalyst
to deactivate superoxide anion (Bensasson et al., 2000).
19. 19
Figure: Structure of the C3 tris malonic acid C60 derivative,
showing the paired carboxylic acid groups attached to the
three cyclopropane carbons on the C60 molecule.
Figure: C3 decreases mitochondrial superoxide anion
production by cortical astrocytes. Cultured astrocytes
were loaded with dihydroethidium (DHE), then treated
with vehicle (H2O) or C3 for 1 h. DHE is oxidized to
ethidium, which is detected as increasing nuclear
Fuorescence in the astrocyte monolayer. C3 decreases
basal superoxide production by astrocytes, which derives
primarily from the mitochondrial electron transport
chain . (Dugan et.al, 2001)
20. 20
Figure: Fullerene derivatives. Metallo-fullerenols showed maximum ROS
scavenging activity. Yin et. al, 2009 , Biomaterials .
Bar Graph: Hydrogen peroxide scavenging
action of above fullerene derivatives in A549
mice cells. Yin et al., 2009 in their study
showed that metallo fullerols with a metal
atom present endohedrally in cage exhibits
greater antioxidant tendency by increasing
the electron affinity and polarizibility of the
fullerene cage. He also reported that these
endohedral fullerols showed less tendency to
aggregate as compared to fullerols alone.
21. 21
Acetylcholine esterase (ACh)
Loss of cholinergic neurotransmission by acetylcholine in cortex and
hippocampus
Amyloid β aggregates (Munoz et al., 1999)
Figure: Neurotransmission in
Synapsis. Image taken from
http://neuroanatomyblog.tu
mblr.com/post/35372201455/l
ostinretrosynthesis-
acetylcholine-ach-cycle
22. 22
Figure: Histochemical staining of AChE bound to amyloid Fibrils. Munoz et al., 1999
Graph: Efect of increasing concentrations of
AChE (25, 100 and 250 nM) on the formation of
fibrils nby using 70 nmol amyloid beta. Munoz
et al., FEBS Letters 450 (1999) 205^209
23. 23
Gonclaves et. Al, 2015: five fullerene (C60) derivatives designed to act as new
Human acetylcholinesterase (HssAChE) inhibitors by blocking its fasciculin II
(FASII) binding site.
Residues: Tyr72, Asp74, Trp286, Gln291, Tyr341 and Pro344
24. 24
Positively charged fullerene derivatives have affinity HssAChE entrane
Pyridine ring interacts with active site. Derivative 3 and 5 showed best inhibition
(Gonclaves et. Al, 2015)
Cavity of enzyme is hydrophobic, ideal for fullerenes to enter
Most effective inhibitors have tertiary amines or quaternary ammonium salts-
interacts with catalytic triad: Ser200, Glu327, His440 and Trp84 at base of gorge.
(Pastorin et. Al, 2006)
Figures: Left to right are Molecular structures of bis-N,N dimethylfulleropyrrolidinium salts, trans
forms while last one is cis form. It is shown that trans form with farther functional groups have
better orientation towards Trp84 and Trp 279 for both primary and secondary active site.
Pastorin et al, Org. Biomol. Chem., 2006, 4, 2556â2562
25. ď§Chemical and physical properties can be modified as per our
requirements by surface functionalization.
ď§Easy object to circulate in blood vessels around nervous system
ď§Lipophilicity of its carbon cage can make it possible for fullerene to
cross Blood Brain Barrier (BBB) (Ekkabut et. al, 2008, Nature)
ď§Cause target specific DNA cleavage can be utilized to not merely pause
the progression of AD but also stop it by causing mutations in AD causing
genes.
ď§Might have a toxic effect due to its tendency to generate oxygen radical
on being photosensitized, however, unless a light source is provided,
fullerene has no such effect. 25
27. Complications observed over choice of functionalized group for fullerene
to act as therapeutic agent in AD:
27
Groups ROS
scavenging
AChE
inhibition
Toxicity Deposition Clearance
from body
Hydroxyl Good Mildly High Low
Carbonyl Good No activity No Toxicity Moderate Low
Cationic grp Good activity Highly toxiz High Low
Metallo-C60 Good Less toxic Moderate Better
Surfactant
coated
Coating
dependent
doubtfull No toxicity
Yamago et al, 1995, Tsuchiya et al, 1996, Tang et al, 2007, Tzoupis et al, 2011,
Saathoff et al, 2011: compile some basic data about the biodistribution ,
toxicity and clearance of fullerene derivatives on basis of their respective
studies.
Fullerene molecule â no toxic effect, its choice of functional groups might
impart a significant toxicity to the fullerene derivative.
Anionic groups - very less toxic
Cationic groups - greater toxicity (Tang et.al, 2007)
28. 28
Mode of Fullerene intake:
â˘Orally - not adsorbed in body neither
metabolized and was found to have been
excreted via faeces and urine almost entirely
â˘On intravenous injection - widely adsorbed
in liver, kidney, bones and tissues and showed
extremely slow clearance rate. (Yamago et al,
1995)
Bar graph: Fecal excretion of
radioactive C14 labelled Fullerene
derivative after oral (blue) and
intravenous (red) dosing of compound
in rats. (Yamago et al, 1995, Chemistry
& Biology 1995, Vol 2 No 6 )
Thus, keeping the depository tendency of
fullerene in mind, it is likely that even if
toxicity of molecule is reduced, molecule might
still have some degree of harmful effects in
long run which are not yet brought to lime
light.
29. 29
ď§Work can be done in designing a single derivative with multi-functionalities
in adequate amount to counter all mechanisms responsible for progression
of AD.
ď§Since all these discussed therapies are to cease progression of AD once it
has started, efforts can be made to design a therapy using fullerene to cure
AD and stop it from arising.
ď§There are some genetic causes for amyloid-β aggregation and tau
hyperphosphorylation which have been clearly understood to this date
(Sisodie et al, 1995, Ballatore et al, 2007) and can be subjected to a gene
therapy mediated by fullerene derivatives since it is well known fullerene
also has property to perform site specific DNA cleavage.
30. 30
With many complications such as choice of functional group, toxicity, bio-
distribution, clearance, membrane permeability, absence of a reliable method to
generate exactly defined functional derivatives of fullerene and little knowledge
of its possible long term side effects; Fullerene has a long way yet to go to be an
AD therapeutic, possibility of which cannot be ruled out.
31. 31
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