anat3029 treatments for alzheimer's disease georgios louloudis

LOULOUDIS 2016 Department of Neuroscience University College London

Treatments for Alzheimer’s Disease

Abstract

With Alzheimer’s disease patients on the increase, there is an imperative need for more

effective treatments. Current treatments of Alzheimer’s disease are only used to provide

symptomatic relief and decelerate cognitive decline. Despite having often been associated

with neuroprotective effects in preclinical studies, these treatments do not appear to exert

disease-modifying effects and patients may usually not respond to them. Combination of

symptomatic treatments has been shown to exert more beneficial effects than

monotherapeutic treatments in moderate to severe stage patients. Researchers are now

developing multimodal agents that will potentially be safer, more effective, and bind to

multiple targets with greater affinity. Immunotherapy has shown powerful disease-modifying

effects in preclinical studies, but has been ineffective in human trials. Researchers are

currently aiming to estimate whether immunotherapeutic agents will be more effective in the

presymptomatic stage. Reversal of cognitive decline has thus far been reported to have

occurred in two Alzheimer’s patients that underwent therapeutic programs, involving

physical exercise, dietary restrictions and drug intake. Treatments may need to be

administered early in the disease and provide more than just anti-amyloid or anti-tau effects,

with a focus on genetic and environmental risk factors, anti-apoptosis, synaptic potentiation

and plasticity, and regeneration.

Word count: 4848

Introduction

Alzheimer’s disease (AD) is associated with neuronal loss, cognitive dysfunction, impairment

of brain functions and dementia, and it is one of the greatest challenges the modern health

care system has to tackle (1). It is currently estimated that 46.8 million people are suffering

from dementia, a number which will double every 20 years, and the cost of treating dementia

is US$ 818 billion (2). This means that if the number of people with AD is not stabilised

soon, this lethal disease will only keep affecting more people and will be getting more

expensive and more difficult to treat. At the same time, Wu et al. (3) report that levels of

dementia in Western European countries could be stabilised as a result of enhanced living

conditions, and improved treatment of chronic and vascular illnesses. Whether the numbers

of AD patients could be stabilised by current and future treatments remains to be explored.

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The most common aim of clinical research is to ameliorate two features of AD: the amyloid

pathology and the tau pathology. The amyloid pathology of AD is characterised by the

increase in both extracellular and intracellular neuronal levels of amyloid-beta (Aβ) proteins,

and the deposition of extracellular amyloid plaques (4). The tau pathology is characterised by

the hyperphosphorylation, truncation and aggregation of tau, a microtubule-associated

protein, into neurofibrillary tangles (NFTs) (5). However, AD treatments can also target other

pathological features of the disease, such as the dysfunction of cholinergic systems in the

basal forebrain via the use of cholinesterase inhibitors (ChEIs) (6). Other research seeks to

establish whether counteracting environmental risk factors, e.g. high blood pressure,

dyslipidemia, etc, can help decelerate cognitive decline in AD (7). The last few years have

seen a lot being done on the field of AD treatments. From the development of Solanezumab

(8) to a 69-year old AD patient reversing his cognitive decline through a multitherapeutics

program (9), it would seem that research is on the right track to successfully manage and treat

AD. In the present paper, different types of AD treatment will be reviewed, focusing on their

potential to counteract the symptoms, neuropathology and progression of the disease.

Cholinesterase inhibitors (ChEIs)

As stated in the Introduction, cholinergic systems are impaired in AD as either cholinergic

neurons are lost, acetylcholine synthesis is impaired or acetylcholine is degraded, and ChEIs

act to delay the degradation of the neurotransmitter by inhibiting acetylcholinesterase (AChE)

(6,10). They thus act to prolong the effect of acetylcholine. Donepezil, rivastigmine and

galantamine have been approved for the treatment of mild to moderate AD as the first-line

treatment for the disease, with donepezil being also used against severe AD (6). A recent

review article reports that ChEIs delay cognitive decline over 6-12 months, with an initial

mild improvement in cognition over the first three months of treatment (6). However, ChEIs

are only used to relieve the symptoms of the disease, are poorly tolerated, have often been

associated with side effects, such as nausea and drowsiness, and their efficacy decreases with

more severe AD cases (11).

Despite their clinical use for symptomatic relief of AD, it has often been demonstrated that

neuroprotective effects may result from ChEIs. For example, exposure of SH-SY5Y

neuroblastoma cells with 100 nM ganstigmine, an AChEI, over 24 hours was shown to be

associated with a slight increase in sAPPα release (12). Additionally, Pakaski et al. (13)

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cultured primary rat basal forebrain neurons of 16- to 17-days old embryos with different

concentrations (10-4, 10-5 and 10-6 M) of metrifonate and ambenobium, two AChEIs, for 2

hours. AChE was stained with the technique of Tago et al. (14), which involves the use of

Karnovsky and Roots medium, diaminobenzidine and hydrogen peroxide, and protein lysates

from the neurons underwent 9% SDS-polyacrylamide gel electrophoresis, followed by

immunoblotting with 5 μg/ml monoclonal 22C11 antibody and anti-protein kinase C (PKC)

polyclonal antibody. The researchers noted that both APP release and expression of PKC

were increased following AChEI treatment. They attributed the increased APP release to the

enhanced non-amyloidogenic APP processing and α-secretase activity, which was potentially

brought about by the action of the ChEIs and PKC. Increased activation of PKC occurs as a

result of prolonged mAChR stimulation and activation of the Gq protein, which acts to raise

the levels of diacyglycerol, the effector that activates PKC. In turn, PKC is thought to

mediate the activation of α-secretase and the degradation of Aβ, in conjunction with the

MAPK pathway (15).

However, focusing only on one pathological feature of the disease can often be problematic.

Researchers tend to devote their attention to developing molecular techniques that allow for

the inhibition of the neurotoxic effects of Αβ, but all they are doing is shut the barn door after

the horse has bolted, given that it is tau pathology that is often better correlated with

cognitive deterioration in AD than amyloid pathology (16). It has been suggested that the

activation of the M1 and M3 mAChRs inhibits GSK-3β phosphorylation and, in turn, blocks

tau phosphorylation (17). However, Chalmers et al. (18) looked directly into the amyloid and

tau burden of the frontal and temporal cortices of matched cohorts of AD patients that were

treated with or without ChEIs via avidin-biotin immunohistochemistry and computer-assisted

image analysis. They observed that those who had received ChEIs exhibited greater levels of

phospho-tau compared to those that were not treated with ChEIs with Aβ levels only slightly

reduced. The evidence is rather contradictory, but it may be that both phospho-tau and Aβ

increase the expression of AChE, and that AChEIs contribute to AChE upregulation (19).

These expression changes may involve muscarinic and/or nicotinic acetylcholine receptor

transcriptional responses, such as the activation of c-fos (20). If AChEIs can contribute to the

increase in NFTs, then it could be that AChEIs upregulate AChE expression via signalling

pathways mediated by phospho-tau.

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All of the above could be used to explain why the efficacy of AChEI treatment decreases as

the severity of the disease progresses. For example, AChEI efficacy may decline due to the

upregulation of AChE, the enzyme that degrades acetylcholine, that may, in turn, be brought

about by Aβ and phospho-tau. Also, given that the drug acts to facilitate cholinergic

transmission, the efficacy of the drug may drop with progressive cell death. Novel multi-

modal ChEIs that are currently under development will be used to simultaneously target

many features of the disease, such as Aβ aggregation and procession, generation of oxygen

radicals and N-methyl-D-aspartate receptor (NMDAR) overactivation, and others, yielding

both symptomatic and disease-modifying effects (21). Nonetheless, ChEIs are important for

offering symptomatic relief to AD patients and should continue to be administered for that

reason.

Memantine

Another clinically approved drug for AD treatment is the NMDAR antagonist, memantine.

The rationale behind its use is that NMDA dysregylation and glutamate-triggered

excitotoxicity have been implicated in AD, with NMDAR-bearing neurons being more

vulnerable to AD-related neurotoxicity (22). The drug has been shown to improve cognition

and other AD-related behaviours in moderate to severe AD after 6 months of use (6). Its side

effects may include dizziness, agitation, confusion and headaches (6). Martinez-Coria et al.

(22) administered 20 mg/day memantine to three different groups of an AD mouse model for

three months: 6-, 9- and 15-months old 3xTg-AD mice. The mice showed improved

performance on the Water Morris maze, object recognition and contextual learning tasks.

Using the Enzyme-Linked Immunosorbent Assay (ELISA), the researchers detected less

severe amyloid pathology, with the effects being more profound in the older animals. By

Western Blotting with antibodies to tau, Martinez-Coria et al. (22) also noticed less

phosphorylated tau and greater levels of glycogen synthase kinase 3β (GSK3β)

phosphorylation at the Ser-9 residue, in the older mice. Finally, the researchers incubated

murine slices of the hippocampal CA1 region with 42 nmol/L Aβ oligomers and applied high

frequency stimuli (100 Hz/s) in the presence or absence of 1 μmol/L, and field excitatory

postsynaptic potentials (fEPSPs) were elicited by delivering electrical stimuli (0.033 Hz, 4-5

V, 20 μs). They observed that pre-treatment with memantine rescued the Aβ-induced long-

term potentiation (LTP) deficits that occurred in the absence of memantine.

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Martinez-Coria et al. (22) could not explain the cellular mechanisms by which memantine

could have decreased both the amyloid and tau pathologies in mice. The researchers

speculated that memantine acted to decrease GSK3β activity by reducing the levels of Aβ

oligomers, claiming that lower levels of Aβ oligomers are often correlated with decreased

GSK3β activity. However, they reveal that they found no differences in the phosphorylation

of other tau residues or tau kinases between the cohorts of mice, making it more difficult to

elucidate the mechanism of action of memantine in AD. It has also been reported that

memantine reduces the levels of Aβ40 and Aβ42 in rat primary cortical cultures and human

neuroblastoma cells alike, prevents the reduction of neurite outgrowth, blocks the

phosphorylation of tau that is mediated by kinases, e.g. Ca2+/calmodulin-dependent protein

kinase β (CaMKKβ), and reduces microglial-related inflammation (23). Given that

memantine acts to block the overactivation of NMDARs, the key signalling event in those

poorly understood pathways may be the influx of Ca2+ ions. Normally, neurons have active

and passive co-transporters and pumps that act to normalise intraneuronal Ca2+ levels after

brief Ca2+ influxes through protein complexes, e.g. NMDARs. Overactivation of NMDARs

would yield excessive levels of intraneuronal Ca2+, which, in turn, would trigger necrosis and

apoptotic pathways.

As Aβ can activate NMDARs via direct binding (23), memantine would act to inhibit all of

the apoptotic and necrotic cellular pathways that are mediated by excessive intraneuronal

Ca2+. Memantine also has the advantage of being a low affinity and activity-dependent

antagonist (23). It does not inhibit normal NMDAR activity and it thus has a high safety

profile (23). However, even in that case, memantine would offer no cure for AD. Aβ is

involved in a plethora of neurotoxic events, many of which may not involve Ca2+. Therefore,

it would seem best if memantine was used in combination therapeutics or co-administered

with other therapeutic agents, to also tackle AD signalling pathways that are not mediated by

excessive NMDAR activity. Indeed, co-administration of memantine with a ChEI has been

shown to reduce the rate of cognitive decline in moderate-to-severe AD patients compared to

ChEI treatment alone, and may yield beneficial effects that are maintained and even increased

over an extended period of time (24). Whether these effects are due to disease-modifying

effects or due to variation in sustained symptomatic effects is not currently known, but may

involve a synergistic effect on ACh levels (24). A potential mechanism for the combined

action of memantine and ChEIs is suggested under fig. 1 (25). A major issue of both ChEIs

and memantine is that at least half of AD patients that are treated with these drugs do not

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respond to them (26), which is quite problematic as they are the only clinically approved

drugs used against AD. Genetic polymorphisms, e.g. CYP2D6 and CYP3A4, may influence

the therapeutic outcome of combined ChEIs and memantine treatment (27). Therefore,

factors, such as the genetic profile of AD patients may have to be taken into consideration

when developing more efficacious therapeutic agents to be used against AD.

Fig. 1 The mechanism of action of combined memantine and AChEI treatment (25: p.363).

Parsons et al. (25) summarise the mechanism of action as shown here. Glutamatergic neurons

from the limbic regions form connections with cholinergic neurons of the basal forebrain.

Overactivation of NMDARs increases the background noise at glutamatergic neurons,

preventing the neurons from distinguishing physiological signal that is crucial for synaptic

neurotransmission. As the background noise results from excess Ca2+ influx, it eventually

leads to cell death. At the same time, the physiological signal at cholinergic neurons is low

due to loss of cholinergic transmission. Memantine alone acts to reduce background noise at

the glutamatergic neuron, but has limited effect on the physiological signal of the cholinergic

neuron as acetylcholine is also broken down by AChE. AChEIs alone have limited effect on

the physiological signal of the cholinergic neuron, as synaptic transmission from the

glutamatergic neuron is impaired by background noise. Only the combined administration of

these two drugs adequately facilitates neurotransmission, as memantine and AChEIs

combined act to greatly enhance, and preserve proper physiological signal. According to

Parsons et al. (25), this facilitates LTP and memory.

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Despite its potential roles in anti-apoptosis, memantine does not counteract the course of the

disease (28). Both memantine and ChEIs are symptomatic treatments that are not used to halt

or reverse the progression of the disease, and it is most unfortunate that they offer no cure.

However, as previously mentioned, researchers currently aim to develop analogues of these

drugs, which should present both disease-modifying and symptomatic properties. There are

two compounds under development that center upon memantine: nitromemantine, which is

produced by transferring a nitrooxy moiety –ONO2 from nitroglycerin vasodilator to

memantine (23), and the other is memagal, a combination of galantamine and memantine

(23,29). Information on both of these compounds is summarised below according to the

description offered by Zheng et al. (23). With its –ONO2 moiety, nitromemantine can activate

the S-nitrosylation site on NMDARs, an action that has been associated with reduction of

excessive NMDAR activity, inhibition of apoptotic cell death and enhancement of neuronal

survival, all without the induction of hypotension and other adverse effects that arise from the

action of nitroglycerine and nitric oxide (NO). Through its effects on extrasynaptic NMDARs

of 9-months old 3xTgAD mice, it has been observed that nitromemantine can restore the

number of synapses back to a normal level within a few months of treatment.

Nitromemantine is progressing to human trials. Memagal has been found to possess a high

affinity for both NMDARs and AChE, as it can inhibit AChE (IC50 = 0.696 μM) (23), while at

the same time it is an NMDAR inhibitor (IC50 = 0.28 nM) (29). Regardless of the absence of

clinical data on the efficacy of these two drugs, it would seem that multimodal therapeutics

are on the rise and may result in the advancement of AD treatments.

Immunotherapy

Immunotherapy is considered to be the most promising therapeutic approach against AD

(30). There is currently no clinically approved immunotherapeutic treatment against AD.

Clinical studies are currently being conducted to test the effectiveness of immunotherapeutic

approaches against the amyloid pathology, following the positive results that have been

yielded by preclinical studies. Preclinical studies, such as that of Wang et al. (31), have

attempted to shed light on the potential mechanisms of action of immunotherapeutic

approaches against AD and have also highlighted the potential of combination therapy. Wang

et al. (31) have shown that combined administration of anti-Aβ1-16 monoclonal IgG2a

antibody Ab9 and doxycycline, a tetracycline that acts as a suppressor of Aβ synthesis, can

collectively reduce amyloid plaque deposition by 52% and Aβ42 content by 28% compared

with pretreatment levels, in both young adult (6-12 months old) and geriatric (18-24 months

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old) tet-off APP mice. Some of their findings can be seen under fig. 2 (31). These results

have been attributed to enhanced internalisation of aggregated Aβ by microglia (31).

Additionally, it has been claimed that passive immunotherapy can rapidly increase structural

plasticity in the brains of PDAPP mice, even before the clearance of amyloid plaques (32).

Therefore, as immunotherapy may be able to reduce amyloid pathology, turn the immune

system against it and potentially provide rapid clinical results, it has justifiably progressed to

human trials.

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Fig. 2 Aβ reduction and amyloid clearance by combination treatment in APP/TTA transgenic

mice (31: p.4127). The results by Wang et al. (31) are summarised here. (a) Shown are silver-

stained amyloid plaques at the basal forebrain of 6.5 months old untreated APP/TTA

transgenic and of 12 months old transgenic mice that were either treated with doxycycline,

Ab9 antibody, or doxycycline plus Ab9, from 6-12 months. Plaques were visualised using

three different magnifications: 1X (top), 5X (middle), and 63X (bottom). It can be observed

that the combined doxycycline and Ab9 antibody caused the greatest reduction in amyloid

burden. (b,c,d) Amyloid burden (% surface area), Αβ42 levels (pmol/g) and SDS-soluble Aβ

levels (pmol/g) were quantified and all three were significantly lower in mice treated with

Ab9 plus doxycycline compared to all other conditions. (e) Amyloid plaque burden as it

progresses in untreated mice (6 and 12 months old). (f) The amyloid plaque burden

associated with monotherapy, combination therapy and no treatment are graphed.

Combination therapy was more efficacious in clearing amyloid plaques.

The clinical trials have not yielded positive results. The anti-Aβ vaccine, AN1792, which

included full-length Aβ42 peptide and QS21 adjuvant for activation of T-cell immune

responses, did decrease amyloid plaques in human patients, but it induced severe adverse

effects, e.g. meningoencephalitis, it did not prevent neurodegeneration and it did not improve

long-term clinical course (33). Solanezumab, a humanised anti-Aβ monoclonal antibody (34),

was reported to treat AD by 30% in patients suffering from mild-stage Alzheimer’s, and was

characterised as a “breakthrough” drug (8). The two phase III clinical trials that were funded

by Elli Lilly, EXPEDITION 1 and 2, did not ameliorate cognition or functional ability of

mild-to-moderate AD patients (34). It was after the extension trial (EXPEDITION-EXT) that

followed that researchers reported that solanezumab could reduce the severity of AD by 30%

(8). However, an analysis of the scores for cognitive function of the early-treated and

delayed-treated patients showed that these scores were not significantly different between the

two groups of patients (8). A likely explanation for the failure of solanezumab to treat AD is

that the treatment is not used early enough in the disease and not prior to plaque formation or

extensive damage by neurodegeneration (35). Current clinical trials with Gantenerumab and

Crenezumab, the latter of which binds Aβ monomers, oligomers and fibrils with greater

affinity than Solanezumab, will seek to determine when treatment has to be initiated, by

focusing on presymptomatic AD subjects or asymptomatic subjects with high risk for the

disease (35). Last but not least, 24 hours after having received a single dose of naturally

occurring human intravenous immunoglobulin G anti-Aβ antibodies (400 μg in 0.2 ml PBS),

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Tg2576 transgenic mice exhibited reduced amyloid fibrillation and release of toxic pro-

inflammatory cytokines, and enhanced synaptic plasticity and cognition (36). In the phase II

clinical trial by Dodel et al. (37), these intravenous antibodies were found to be safe and

tolerable in AD patients, but did not induce symptomatic effects on the cognitive and

functional levels (33). 89 patients, aged 50-85, participated in this trial for a total of 24 weeks

(37). The researchers claimed that the short duration of the trial and the small sample sizes

allowed neither for the proper detection of a disease-modifying effect nor for the

extrapolation of their data to other patients groups (37). Thus, more broad clinical trials will

be needed to properly assess the efficacy of anti-Aβ IgGs against AD (37).

Tau has also been considered in the development of immunotherapeutic agents. An in vitro

tau-tau interaction assay was performed to indicate a suitable immunotherapeutic agent

against tau pathology in transgenic Balb/c mice overexpressing mis-disordered human tau

protein 151-391/3R (38). The monoclonal antibody DC8E8 induced an 84% reduction in the

amount of oligomeric tau and targeted all developmental stages of tau in AD human brains,

including pretangles, intra- and extracellular tangles (38). It is rather noteworthy that kinetic

measurements with surface plasmon resonance highlighted DC8E8 as a greatly

discriminatory agent between pathological and physiological tau (38). DC8E8 was made into

an active vaccine, AADvac1, and was tested on an AD rat model expressing human tau (39).

The vaccine reduced the levels of tau oligomers and neurofibrillary tangles, it induced an

approximate 95% decrease in AD-type hyperphosphorylation, with an excellent safety and

tolerability profile (39). The vaccine is currently being tested in phase I human clinical trials

(39). Additionally, another, liposome-based, vaccine against pS396/pS404 tau, ACI-35,

improved long-term clinical course and reduced tauopathy in the brains of Tau.P301L mice,

without any adverse neuroinflammatory or neurological effects (40). ACI-35 is currently

undergoing Phase I clinical testing (41).

The preclinical studies that have been conducted with immunotherapeutic agents have thus

far shown that the agents hold great potential in counteracting the pathological effect of Aβ

and tau. If it is considered that anti-amyloid immunotherapeutics ought to be administered

before the onset of the disease, it is essential that developments in the field of immunotherapy

are also accompanied by developments in the field of diagnostics and biomarkers. There may

be additional factors that limit the efficacy of immunotherapeutics other than the time the

treatments are started. Antibodies are injected intravenously and have to cross the blood-brain

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barrier (BBB) to reach the brain (42). An approach that could be exploited to overcome this

limitation is to fuse the anti-Aβ antibodies with antibodies to the receptors of the BBB

endothelial cells, e.g. transferrin and low-density lipoprotein receptors, which act to facilitate

protein transfer to the neuronal side of the BBB (42). The reason why anti-amyloid therapies

have not yielded positive results in clinical trials, despite preclinical results on AD mouse

models, is still debated. It can be argued that AD mouse models, especially APP mice, do not

display hyperphosphorylated tau and significant neuronal loss (43), which would mean that

the immunotherapeutic drugs are more effective in mice than in humans. Similarly, studies

making use of tau mouse models in AD neglect the role of Aβ pathology of AD.

Additionally, the use of P301L tau mutant mice not only neglects the role of Aβ in AD, but is

not completely representative of AD, as mutations in the MAPT gene have not been directly

linked to the disease. Finally, the use of tau immunotherapeutics is justified by the fact that

tau is needed for Aβ to cause its neurotoxic effects (16) and that tau pathology is better

correlated with cognitive decline in AD (44). Other than their molecular interaction, Aβ and

tau can also independently induce neurotoxic effects, making the concept of combination

therapy and the targeting of both pathological amyloid and tau more favourable prospects

(44). It would also be best to also consider that, other than counteracting the effect of the key

players of AD, regeneration, plasticity and synaptic potentiation must also be stimulated in

the AD brain.

Therapeutic programs

A study with rather impressive results is that by Bredesen (9), which is summarised in this

paragraph. A 69-year old man had been suffering from progressive 12-year long memory

decline, which started with an incident as simple as not remembering his lock combination at

work to reading several chapters from a book before realising he had read it previously. The

patient was diagnosed with early AD by fluoro-deoxyglucose positron emission tomography

(FDG-PET) and was heterozygous for APOE4. He underwent a rather demanding and strict

therapeutic program, details of which are listed in table 1 (9). This therapeutic program

involved adhering to strict diet and sleeping patterns, physical exercise and the intake of

substances, such as vitamins, probiotics, herbs and omega-3 fatty acids. Six months after the

start of the program, the patient’s memory decline was reversed and he demonstrated major

improvements, as he was able to remember faces and function at work. It is worth mentioning

that this is not the only patient that Bredesen (9) focused on. Ten patients were used for the

study, all of them diagnosed with either amnestic mild cognitive impairment, subjective

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cognitive impairment, or AD. The therapeutic program differed between patients, but was

shown to be effective in nine of the patients. Out of the ten patients, three were diagnosed

with AD. Two of the AD patients benefited from the therapeutic program, whereas one

patient that was diagnosed with very late stage AD failed to show any signs of improvement

and continued exhibiting cognitive decline.

Activities & Supplements Approach & Intake Frequency

Physical exercise Swimming 3-4 times/week

Cycling 2 times/week

Running 1 time/week

Sleep & melatonin intake Sleep 8 hours/night

0.5mg Melatonin Each night

Diet Fasting Min. 3 hours between dinner

and bedtime; min. 12 hours

between breakfast and dinner

Increased consumption of

vegetables and fruits

Each day

Limited consumption of fish to

non-farmed, meat to occasional

grass-fed beef or organic chicken

Probiotics - -

Herbs 250mg Bacopa monniera 1 time/day

500mg Ashwagandha

400mg Turmeric

Omega-3 fatty acids 320mg Docosahexanoic acid

180mg Eicosapentanoic acid

Vitamins and others 1mg Methylcobalamin

0.8mg Methyltetrahydrofolate

50mg Pyridoxine-5-phosphate

1g Vitamin C

Vitamin D3 5000IU

Vitamin E 400IU

200mg CoQ10

50mg Zn picolinate

100mg α-lipoic acid

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500mg Citicoline 2 times/day

1tsp Coconut oil

Table 1 created to list all the details of the therapeutic program that the early stage AD

patient had to complete as part of the study by Bredesen (9: p.712).

The rationale behind the therapeutic program is that a multitherapeutic approach would target

a more extensive network of molecular interactions taking place in AD than a

monotherapeutic approach (9). Melatonin is administered and specific sleep patterns are

maintained as low levels of melatonin and poor sleep quality have been reported in the

pathology of the disease (45). Melatonin is claimed to possess antioxidant and

neuroprotective properties, as it can reduce free radicals, activate antioxidative defensive

enzymes, downregulate pro-oxidant enzymes, e.g. NO, and reverse inflammatory processes

(46). In terms of AD, melatonin has been reported to arrest tau hyperophosphorylation,

reduce Aβ production, inhibit Aβ-induced apoptosis and reverse memory and cognitive

deficits in APP695 transgenic mice (46). Physical activity may have been essential in

counteracting the effect of AD-conferring environmental factors, e.g. vascular risk factors

and lipid profile, suppressing inflammatory insults, modulating the formation of Aβ and

promoting the regeneration of new synapses and new neurons (47). The strict diet was

implemented to counteract the effect of blood pressure and lipid profile as AD risk factors.

Herbs, such as Ashwagandha (Withania somnifera) may be able to counteract the neurotoxic

effects of Aβ1-42 by restoring proper spine density, number and area, as well as proper

dendritic diameter and area (48). Supplementation of vitamins C and E may assist in reducing

AD-associated lipid peroxidation, but its effect on the course of the disease may not be strong

(49). Omega-3 fatty acids, e.g. docosahexanoic acid (DHA), may exert beneficial effects

against AD via a plethora of signalling events (50). Jicha and Markesbery (50) summarise

these potential signalling events as shown below. DHA may stimulate hippocampal

regeneration and the differentiation of neural stem cells, as it may induce alterations in gene

expression. It can also stimulate neuroprotectin D1 (NPD1), which in turn triggers anti-

apoptotic effects. It may also downregulate the activities of β-secretase, γ-secretase and

presenilin 1 via its effects on the lipid rafts that are associated with those proteins. However,

several clinical trials have tested the efficacy of DHA against AD without any success (50).

Jicha and Markesbery (50) suggest that its efficacy may rely on factors, such as the stage of

the disease and the APOE status of patients.

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The therapeutic program tested by Bredesen (9) offers support for the promise of

combination therapy in AD. As it can be seen this therapeutic program seems to provide more

than just an anti-amyloid or anti-tau effect, with an additional focus on anti-apoptosis, anti-

oxidation, regeneration, enhancement of structural plasticity and tackling the neurotoxic

effects of risk factors. As mentioned previously, vitamin or DHA supplementation on their

own may not have a positive effect against AD, but both of these could make a difference as

part of a therapeutic program. For example, multiple therapeutics may yield greater

neuropathological outcome than monotherapeutic approaches either due to synergistic effects,

the possibility that different treatments may enhance and/or accelerate the efficacy of one

another, or both (31). Given that the patient that was diagnosed with late stage AD did not

show any signs of improvement, the argument that treatments ought to be tested as early in

AD as possible also applies. A limitation of this therapeutic program is that it is extremely

difficult for mentally and, in many cases, physically incapacitated AD patients to comply

with, given that it involves a strict daily routine. Bredesen (9) reports that none of the patients

were able to comply with the entire protocol and patients often complained about the

difficulties they had to go through in completing it. Also, the way the therapeutic program is

formulated depends on diagnosis, patient history and evaluation of other factors, e.g. BMI,

lipid profile, APOE status (9). Given that we currently lack any reliable diagnostic methods

for AD, we have limited understanding of signalling events and risk factors in the disease,

and the fact that therapeutic programs are a newly introduced method for tackling AD, these

procedures may not always yield positive results in cases of progressive cognitive decline or

AD. The study made use of an extremely small number of patients, its results are still

anecdotal and more extensive clinical trials will be required to ensure the clinical efficacy of

these therapeutic programs (9). This case study could also be strengthened by following up

these patients after the completion of the therapeutic programs to ensure that the beneficial

effects of the programs persist in the long term and that patients do not relapse. It would also

be worthwhile to examine the effects of these programs at the level of neuronal tissues.

Conclusion

There is currently no established cure for AD. The clinically approved treatments for AD are

only used for symptomatic relief and have no effect on the progression of the disease. They

may potentially be associated with neuroprotective effects, but these appear to be limited,

weak and poorly understood. Current research seeks to modify the clinically approved

therapeutic compounds into more efficacious compounds that will bear both symptomatic and

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disease-modifying properties against the disease. With regards to immunotherapy, preclinical

studies making use of AD mouse models demonstrate that active and passive immunisation

can clear pathological Aβ and tau, and reverse cognitive decline. However, human trials have

failed to show any beneficial effects, despite public claim. This may be attributed to factors,

such as the differences in disease pathology in AD mouse models and humans and antibody

transfer through the blood-brain barrier, with failure to use the treatments early in the disease

being the most coined reason. The multitherapeutic approach by Bredesen (9) has noted a

reversal of cognitive decline in two AD patients, but the approach still requires further study.

Future directions could address the need for effective diagnostic methods for early and

presymptomatic AD and therapeutic approaches that can stimulate structural plasticity and

neuronal regeneration, in addition to anti-amyloid and anti-tau effects.

Literature search

Articles published between 2000 and 2016 were searched with Google Scholar and Pubmed,

using the search terms: “Alzheimer’s disease”, “amyloid”, “Aβ”, “tau”, “cholinesterase

inhibitors”, “memantine”, “immunotherapy”, “therapeutic program”, “clinical trials” and

combinations thereof, e.g. “Alzheimer’s disease cholinesterase inhibitors”, “amyloid

cholinesterase inhibitors”, “Alzheimer’s disease amyloid cholinesterase inhibitors”, etc.

Articles were not handsearched. All articles were written in English. For an update on agents

and their FDA status, www.alzforum.org/therapeutics was consulted. Original preclinical and

clinical studies, and review papers were all equally considered.

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