1 © Patrick An Introduction to Medicinal Chemistry 3/e Chapter 19 CHOLINERGICS, ANTICHOLINERGICS &...

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Patrick Patrick An Introduction to Medicinal An Introduction to Medicinal

ChemistryChemistry 3/e 3/e

Chapter 19Chapter 19

CHOLINERGICS, CHOLINERGICS, ANTICHOLINERGICSANTICHOLINERGICS

& ANTICHOLINESTERASES& ANTICHOLINESTERASES

Part 3: Cholinergics & anticholinesterasesPart 3: Cholinergics & anticholinesterases

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ContentsContents

Part 3: Cholinergics & anticholinesterases

14. Acetylcholinesterase14.1. Role 14.2. Hydrolysis reaction catalysed14.3. Effect of inhibition14.4. Structure of enzyme complex14.5. Active site - binding interactions14.6. Active site - Mechanism of catalysis (3 slides)

15. Anticholinesterases15.1. Physostigmine15.2. Mechanism of action (3 slides)15.3. Physostigmine analogues15.4. Organophosphates (9 slides)15.5. Anticholinesterases as ‘Smart Drugs’ (2 slides)

[30 slides]

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14. Acetylcholinesterase14. Acetylcholinesterase

Acetylcholinesterase enzymeAcetylcholinesterase enzyme

......

...

Nerve 1Nerve 1Nerve 2Nerve 2

SignalSignal

14.1 Role14.1 Role • Hydrolysis and deactivation of acetylcholineHydrolysis and deactivation of acetylcholine• Prevents acetylcholine reactivating receptorPrevents acetylcholine reactivating receptor

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activeactive inactiveinactive

14.2 Hydrolysis reaction catalysed14.2 Hydrolysis reaction catalysed

Acetylcholine

CH3

C

O

O

Choline

+ NMe3

C

O

CH3 OH

Acetic acid

NMe3HO

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• Inhibitor blocks acetylcholinesteraseInhibitor blocks acetylcholinesterase• Ach is unable to bindAch is unable to bind• Ach returns to receptor and reactivates Ach returns to receptor and reactivates

itit• Enzyme inhibitor has the same effect as Enzyme inhibitor has the same effect as

a cholinergic agonista cholinergic agonist

22oo Message Message

Nerve 2Nerve 2

Enzyme inhibitorEnzyme inhibitor(Anticholinesterase)(Anticholinesterase)

14.3 Effect of inhibition14.3 Effect of inhibition

AchAch

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14.4 Structure of enzyme complex14.4 Structure of enzyme complex

S

S

SS

S

SS

S

S S

S

S

S

S

S S

S

S

Enzyme

EnzymeEnzyme

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:::OO

Serine

Histidine

Tyrosine

OH

N

N

HO

Aspartate


14.5 Active site - binding interactions14.5 Active site - binding interactions

• Anionic binding region similar to cholinergic receptor siteAnionic binding region similar to cholinergic receptor site• Binding and induced fit strains Ach and weakens bondsBinding and induced fit strains Ach and weakens bonds• Molecule positioned for reaction with His and SerMolecule positioned for reaction with His and Ser

vdwvdw

vdwvdw

hydrophobic pockets

Anionic binding regionEster binding region

Me

N

CH2 CH2

O

C

CH3

O

Me

Me

H-bondIonic

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14.6 Active site - Mechanism of catalysis14.6 Active site - Mechanism of catalysis

O H NNH

:

Serine Histidine(Nucleophile) (Base)

::

CH3 C

O

O CH2CH2NMe3

NNH

O

O

R

C

O

CH3

H

:

:

Histidine(Base catalyst)

::

NNH

O

OR

C

O

CH3

H

:

Histidine

:: ::

COR

O

CH3

O NNH

H

:

:

Histidine

Acid catalyst

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::

COR

O

CH3

O NNH

H

:

:

Histidine

H2O

NNH

OO

H

CCH3

O

H::

:

Histidine

ROH

CO

CH3

ON

NH

Histidine

C

O

OHCH3

O NNH

: _

H :

::

HistidineBasic catalyst

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C

O

OHCH3

O NNH

::

:

: H:

Histidine(Acid catalyst)

C

O

OHCH3

O NNH

: _

H

:

Histidine

::

C

O

OHCH3

O NNH

: _

H :

::

HistidineBasic catalyst

OHC

O

CH3

OH NNH

:

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• Serine and water are poor nucleophilesSerine and water are poor nucleophiles

• Mechanism is aided by histidine acting as a basic catalystMechanism is aided by histidine acting as a basic catalyst

• Choline and serine are poor leaving groupsCholine and serine are poor leaving groups

• Leaving groups are aided by histidine acting as an acid catalystLeaving groups are aided by histidine acting as an acid catalyst

• Very efficient - 100 x 10Very efficient - 100 x 1066 faster than uncatalysed hydrolysis faster than uncatalysed hydrolysis

• Acetylcholine hydrolysed within 100 Acetylcholine hydrolysed within 100 secs of reaching active secs of reaching active sitesite

• An aspartate residue is also involved in the mechanismAn aspartate residue is also involved in the mechanism

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The catalytic triadThe catalytic triad

• An aspartate residue interacts with the imidazole ring of An aspartate residue interacts with the imidazole ring of histidine to orientate and activate ithistidine to orientate and activate it

Serine Histidine(Nucleophile) (Base)

O H

NN

H

O

O

Aspartate

:

::::

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15. Anticholinesterases15. Anticholinesterases

• Inhibitors of acetylcholinesterase enzymeInhibitors of acetylcholinesterase enzyme

• Block hydrolysis of acetylcholineBlock hydrolysis of acetylcholine

• Acetylcholine is able to reactivate cholinergic receptorAcetylcholine is able to reactivate cholinergic receptor

• Same effect as a cholinergic agonistSame effect as a cholinergic agonist

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15. Anticholinesterases15. Anticholinesterases

15.1 Physostigmine15.1 Physostigmine

• Natural product from the African calabar beanNatural product from the African calabar bean• Carbamate is essential (equivalent to ester of Ach)Carbamate is essential (equivalent to ester of Ach)• Aromatic ring is important Aromatic ring is important • Pyrrolidine N is important (ionised at blood pH)Pyrrolidine N is important (ionised at blood pH)• Pyrrolidine N is equivalent to the quaternary nitrogen of AchPyrrolidine N is equivalent to the quaternary nitrogen of Ach

N N

MeOC

O

NMe

H

Me MeUrethane orCarbamate

Pyrrolidine N

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Physostigmine

O:N

NH

H

MeNHC

O

O Ar

::

15.2 Mechanism of action15.2 Mechanism of action

O ArC

O

MeNH

O

NHN:

:

H

::

O ArC

O

MeNH

O

NHNH

: ::

::

:

: :

O ArC

O

MeNH

O

NHN

:H

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:

: :

O ArC

O

MeNH

O

NHN

:H


Rate of hydrolysis slower by 40 x 10Rate of hydrolysis slower by 40 x 1066

Stable carbamoylintermediate

O H

NH:N

Hydrolysisvery slow

OC

O:N

NH

MeNH

-ArOH

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Carbonyl group'deactivated'

:

O

CON

Me

H: ::N

H

Me

CO

O

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15.3 Physostigmine analogues15.3 Physostigmine analogues

• Simplified analogueSimplified analogue• Susceptible to hydrolysisSusceptible to hydrolysis• Crosses BBB as free baseCrosses BBB as free base• CNS side effectsCNS side effects

• Fully ionisedFully ionised• Cannot cross BBBCannot cross BBB• No CNS side effectsNo CNS side effects• More stable to More stable to

hydrolysishydrolysis• Extra Extra NN-methyl group -methyl group

increases stabilityincreases stability

MiotineMiotine

C

N

O

O

H

Me

Me

CHNMe2

(ionised at blood pH)

NeostigmineNeostigmine

NMe3OMe

N

Me

C

O

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CN

O

OAr

H

Me

δδ

-

+

:Me

N

H

C OAr

O

OH

::

MeN

H

C

OH

OMeNH2

+CO2

Water

Hydrolysis mechanismsHydrolysis mechanisms

Possible mechanism 1Possible mechanism 1

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Me

N

H

COAr

O-H

CN O

Me MeNH2

+CO2

Compare:

CN

O

OAr

Me

Me-Me

No hydrolysis

Too reactive

Hydrolysis mechanismsHydrolysis mechanisms

Possible mechanism 2Possible mechanism 2

CN

O

OH

H

MeHH22OO

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Myasthenia gravis (sometimes abbreviated MG; from the Greek myastheneia, lit. 'muscle disease', and Latin gravis, 'serious') is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. At about 14 cases per 100,000 (in the U.S.), it is one of the lesser known autoimmune disorders. Weakness is typically caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated with immunosuppressants, cholinesterase inhibitors and, in selected cases, thymectomy.

Myasthenia gravis

http://www.healcentral.org/healapp/showMetadata?metadataId=3621

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Treatment

Myasthenia gravis can usually be controlled with medication. Medication is used for two different endpoints:Direct improvement of the weaknessReduction of the autoimmune processMuscle function is improved by cholinesterase inhibitors, such as neostigmine and pyridostigmine. These slow the natural enzyme cholinesterase that degrades acetylcholine in the motor end plate; the neurotransmitter is therefore around longer to stimulate its receptor. Usually doctors will start with a low dose, eg 3x20mg pyridostigmine, and increase until the desired result is achieved. If taken 30 minutes before a meal, symptoms will be mild during eating. Side effects, like perspiration and diarrhea can be countered by adding atropine. Pyridostigmine is a short-lived drug with a half-life of about 4 hours.

NMe3OMe2N

O

Neostigmine

N

OMe 2N

O

Me

Pyridostigmine

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http://www.healthtouch.com/bin/EContent_HT/dnoteShowLfts.asp?fname=04867&title=NEOSTIGMINE+(Injection)+(Injectable)+&cid=HTDRUG

http://www.healthtouch.com/bin/EContent_HT/dnoteShowLfts.asp?fname=04944&title=PYRIDOSTIGMINE+(Injection)+(Injectable)+&cid=HTDRUG

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Alzheimer's disease (AD), also known simply as Alzheimer's, is a neurodegenerative disease characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioral changes. It is the most common type of dementia.The most striking early symptom is loss of short term memory (amnesia), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and those functions (such as decision-making and planning) closely related to the frontal and temporal lobes of the brain as they become disconnected from the limbic system, reflecting extension of the underlying pathological process. These changes make up the essential human qualities, and thus AD is sometimes described as a disease where the victims suffer the loss of qualities that define human existence.This pathological process consists principally of neuronal loss or atrophy, principally in the temporoparietal cortex, but also in the frontal cortex, together with an inflammatory response to the deposition of amyloid plaques and neurofibrillary tangles.

Alzheimer's disease (AD)

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http://www.healthcentral.com/alzheimers/introduction-7-115.html

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Acetylcholinesterase inhibitorsAcetylcholinesterase (AChE) inhibition was thought to be important because there is a reduction in activity of the cholinergic neurons. AChE-inhibitors reduce the rate at which acetylcholine (ACh) is broken down and hence increase the concentration of ACh in the brain (combatting the loss of ACh caused by the death of the cholinergin neurons). Acetylcholinesterase-inhibitors seemed to modestly moderate symptoms but do not alter the course of the underlying dementing process.[67][68][69]Examples include:tacrine - no longer clinically useddonepezil - (marketed as Aricept)galantamine - (marketed as Razadyne in the U.S.A. Marketed as Reminyl or Nivalin in the rest of the world)rivastigmine - (marketed as Exelon)There is significant doubt as to the effectiveness of cholinesterase inhibitors. A number of recent articles have criticized the design of studies reporting benefit from these drugs, concluding that they have doubtful clinical utility, are costly, and confer many side effects.[70][71] The pharmaceutical companies, but also some independent clinicians, dispute the conclusions of these articles. A transdermal patch is under development that may ease administration of rivastigmine.[72]ivastigmine.

MeO

MeO

O

NDonepezil (Aricept)

ON

O

Rivastigmine (Exelon, Novartis)

Me

Et

Me

NMe 2

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15.4 Organophosphates15.4 Organophosphates

a) Nerve gasesa) Nerve gases

• Agents developed in World War 2Agents developed in World War 2• Agents irreversibly inhibit acetylcholinesteraseAgents irreversibly inhibit acetylcholinesterase• Permanent activation of cholinergic receptors by AchPermanent activation of cholinergic receptors by Ach• Results in deathResults in death

DyflosDyflos(Diisopropyl fluorophosphonate)(Diisopropyl fluorophosphonate)

iPrO

P

O

FiPrO

SarinSarin

P

Me F

OiPrO

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NS

P

O

O

VX Nerve Agent

The VX nerve agent is the most well-known of the V-series of nerve agents. Its chemical name is O-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothiolate and its molecular formula is C11H26NO2PS.The only countries known to possess VX are the United States and Russia. VX agent is considered an area denial weapon due to its physical properties.

With its high viscosity and low volatility VX has the texture and feel of high-grade motor oil. This makes it especially dangerous, as it has a high persistence in the environment. It is odorless and tasteless, and can be distributed as a liquid or, through evaporation, into small amounts of vapor. It works as a nerve agent by blocking the function of the enzyme acetylcholinesterase. Normally, an electric nerve pulse would cause the release of acetylcholine over a synapse that would stimulate muscle contraction. The acetylcholine is then broken down to non-reactive substances (acetic acid and choline) by the acetylcholinesterase enzyme. If more muscle tension is needed the nerve must release more acetylcholine. VX blocks the action of acetylcholinesterase, thus resulting in sustained contractions of all the muscles in the body. Sustained contraction of the diaphragm muscle causes death by asphyxiation.

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Often regarded as the deadliest nerve agent created to date, as little as 200 micrograms is enough to kill an average person, depending on method of absorption. Death can be avoided if the appropriate antidote is injected immediately after exposure. The most commonly used antidote is atropine and pralidoxime, which is issued for military personnel in the form of an autoinjector. Standard chemical agent resistance pills are also effective. Atropine works by binding and blocking a subset of acetylcholine receptors (known as muscarinic acetylcholine receptor, mAchR), so that the build up of acetylcholine produced by loss of the acetylcholinesterase function can no longer affect their target. This prevents involuntary muscle actions so that muscles like the diaphragm are not in constant contraction. The injection of pralidoxime regenerates bound acetylcholinesterase.

NS

P

O

O

VX Nerve Agent

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The chemist Ranajit Ghosh discovered the V-series nerve agents at the government research establishment at Porton Down, England in 1952; VX was passed over in favour of continuing with sarin as their chemical weapon of choice. The United Kingdom unilaterally renounced chemical and biological weapons in 1956. In 1958 the British government traded their research on VX technology with the United States of America in exchange for information on thermonuclear weapons. The US then went into production of large amounts of VX in 1961.

The US later destroyed all of its stockpiles of the deadly nerve agent (by incineration at Johnston Island in the South Pacific), as mandated by the US accession to the Chemical Weapons Convention. Earlier, pre-treaty disposal included the US Army's CHASE (Cut Holes And Sink 'Em) program, in which old ships were filled with chemical weapons stockpiles and then scuttled. CHASE 8 was conducted on June 15, 1967, in which the S.S. Cpl. Eric G. Gibson was filled with 7,380 VX rockets and scuttled in 7,200 feet of water, off the coast of Atlantic City, New Jersey. The long-term environmental ramifications of exposing large quantities of VX to seawater and marine life could pose a grave danger, but are ultimately unknown.

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The US is also destroying chemical weapons stockpiles containing VX in nine other locations, one of which is in Russia. On June 12, 2005, it was reported that more than 250,000 US gallons (950 m³) of the chemical weapon are stored at the Newport Chemical Depot in Newport, Indiana, about 30 miles (50 km) north of Terre Haute, Indiana. The VX is in the process of being hydrolyzed to much less toxic byproducts using concentrated caustic solution. The VX hydrolysate produced will contain mainly a phosphonate ester and a thiolamine, with 20 parts per billion or less of residual VX. (Interestingly, 20 ppb is the level of VX in water that is considered permissible for drinking by US combat troops.)

A plan was developed to truck the hydrolysate from Indiana to the DuPont Chambers Works Secure Environmental Facility at Deepwater, NJ where it was to be further treated to destroy the phosphonate ester and the thiolamine, and dumped into the Delaware River.[2] The governors of Delaware, New Jersey, Pennsylvania, and New York have opposed this plan and the New Jersey Governor Codey instructed the New Jersey Department of Transportation to deny entry to any trucks carrying the hydrolysate to the Deepwater facility. Prior to the current plan, it had been proposed that the hydrolysate be dumped into the Great Miami River, a tributary of the Ohio River, near Dayton, Ohio but the community there successfully defeated the proposal.

VX hydrolysis began on May 5 2005 and as of June 12 the facility had destroyed 2,894 US gallons (11 m³) of VX. A contained spill of 30 US gallons (100 L) drew attention to the disposal process, but authorities said no agent was released and no one was injured in the spill.Iraq under Saddam Hussein admitted to UNSCOM that it had researched VX, but denied weaponizing the agent due to production failure. [1] Subsequent investigation after the 2003 Invasion of Iraq indicates that Iraq had indeed weaponized VX in 1988 and had dropped three VX-filled bombs on Iran. [2]

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b) Mechanism of actionb) Mechanism of action

• Irreversible phosphorylationIrreversible phosphorylation• P-O bond very stableP-O bond very stable

PiPrO F

OiPrO

STABLE

-H

O

P O

iPrO

iPrO

Serine

OH

Serine

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c) Medicinal organophosphatec) Medicinal organophosphate

• Used to treat glaucomaUsed to treat glaucoma• Topical applicationTopical application• Quaternary N is added to improve binding interactionsQuaternary N is added to improve binding interactions• Results in better selectivity and lower, safer dosesResults in better selectivity and lower, safer doses

EcothiopateEcothiopateMe3N CH2 CH2 S P

O

OEt

OEt


NS

P

O

O

VX Nerve Agent

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d) Organophosphates as insecticidesd) Organophosphates as insecticides

• Relatively harmless to mammalsRelatively harmless to mammals• Agents act as prodrugs in insectsAgents act as prodrugs in insects• Metabolised by insects to produce a toxic metaboliteMetabolised by insects to produce a toxic metabolite

ParathionParathion

EtO

P

S

EtO O NO2

MalathionMalathion

CH

CH2CO2Et

CO2Et

S

P

MeO

SMeO


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d) Organophosphates as insecticidesd) Organophosphates as insecticides

MAMMALS INSECTS

NO2O

P

EtO

SEtO

PARATHION(Inactive Prodrug)

Active drug

Phosphorylates enzyme

DEATHDEATH

Mammalian Metabolism

EtO

P

S

EtO OH

INACTIVE& excreted

EtO

P

O

EtO O NO2InsectOxidative

desulphurisation


1©

N

N

O

POEt

S OEt

Diazinon

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http://www.physioviva.com/movies/neurotoxic_insecticides/index.html

N

N

Me

NCl

N NH

NNO2

Nicotine Imidacloprid

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e) Design of Organophosphate Antidotese) Design of Organophosphate Antidotes

StrategyStrategy• Strong nucleophile required to cleave strong P-O bondStrong nucleophile required to cleave strong P-O bond• Find suitable nucleophile capable of cleaving phosphate estersFind suitable nucleophile capable of cleaving phosphate esters• Water is too weak as a nucleophileWater is too weak as a nucleophile• Hydoxylamine is a stronger nucleophileHydoxylamine is a stronger nucleophile

• Hydroxylamine is too toxic for clinical useHydroxylamine is too toxic for clinical use• Increase selectivity by increasing binding interactions with active Increase selectivity by increasing binding interactions with active

sitesite

Hydroxylamine

+ +RO P

O

OR

ORH2N

O P

O

OR

OR

NH2OH ROH


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• Quaternary N is added to bind to the anionic regionQuaternary N is added to bind to the anionic region

• Side chain is designed to place the hydroxylamine moiety in Side chain is designed to place the hydroxylamine moiety in the correct position relative to phosphorylated serinethe correct position relative to phosphorylated serine

• Pralidoxime 1 million times more effective than Pralidoxime 1 million times more effective than hydroxylaminehydroxylamine

• Cannot act in CNS due to charge - cannot cross bbbCannot act in CNS due to charge - cannot cross bbb

PralidoximePralidoximeN

CH3

CH N

OH


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H

N CH NO

H

Me Me

NO

PNCH

O

OR

OR

CO2 OHSER

Active Site (Free)

CO2 O

P

OOR

OR

SER

Active Site (Blocked)


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• Prodrug for pralidoximeProdrug for pralidoxime• Passes through BBB as free basePasses through BBB as free base• Oxidised in CNS to pralidoximeOxidised in CNS to pralidoxime

ProPAMProPAM

N

HH

CH3

NOH


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15.5 Anticholinesterases as ‘Smart Drugs’15.5 Anticholinesterases as ‘Smart Drugs’

• Act in CNS Act in CNS

• Must cross blood brain barrierMust cross blood brain barrier

• Used to treat memory loss in Alzheimers diseaseUsed to treat memory loss in Alzheimers disease

• Alzheimers causes deterioration of cholinergic receptors in Alzheimers causes deterioration of cholinergic receptors in brainbrain

• Smart drugs inhibit Ach hydrolysis to increase activity at Smart drugs inhibit Ach hydrolysis to increase activity at remaining receptorsremaining receptors

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15.5 Anticholinesterases as ‘Smart Drugs’15.5 Anticholinesterases as ‘Smart Drugs’

Donepezil

Tacrine (Cognex)Toxic side effects

Rivastigmine (Exelon)(analogue of physostigmine)

Galanthamine(daffodil and snowdrop bulbs

Metrifonate(organophosphate)

Xanomeline

Anabaseine(ants and marine worms)

N

NH2

MeO

MeO

O

CH2 N

H

Cl

CH OC

N

O

Me

Et

Me

NMe2

MeOP CCl3

O

MeOOH

HN N

NMe

N

S

N

O MeN

O

MeO

Me

HO

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Nootropics (from Greek, 'acting on the mind'), popularly referred to as "smart drugs", are substances which boost human cognitive abilities (the functions and capacities of the brain). The word nootropic is derived from the Greek words noos or "mind" and tropein meaning "to ward." Typically, nootropics are alleged to work by increasing the brain's supply of neurochemicals (neurotransmitters, enzymes, and hormones), by improving the brain's oxygen supply, or by stimulating nerve growth.

Most alleged nootropic substances are nutrients or plant components (herbs, roots, beans, bark, etc.), available over the counter at health food and grocery stores, and are used as nutritional supplements. Some nootropics are drugs, used to treat people with cognitive learning difficulties, neural degradation (Alzheimer's and Parkinson's), and for cases of oxygen deficit to prevent hypoxia. These drugs have a variety of human enhancement applications as well, are marketed heavily on the World Wide Web, and are used by many people in personal cognitive enhancement regimens.

With some nootropics the effects are subtle and gradual, such as with most nerve growth inducers, and may take weeks or even months before any cognitive improvement is noticed. At the other end of the spectrum are nootropics which have effects that are immediate, profound, and obvious. While scientific studies support some of the claimed benefits, it is worth noting that many of the claims attributed to a variety of nootropics have not been formally tested.

Nootropics

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Dementia

Definition

The term dementia refers to symptoms, including changes in memory, personality, and behavior, that result from a change in the functioning of the brain. These declining changes are severe enough to impair the ability of a person to perform a function or to interact socially. This operating definition encompasses 70–80 different typesentia. They include changes due to diseases (Alzheimer's and Creutzfeld-Jakob diseases), changes due to a heart attack or repeated blows to the head (as suffered by boxers), and damage due to long-term alcohol abuse.

Dementia is not the same thing as delirium or mental retardation. Delirium is typically a brief state of mental confusion often associated with hallucinations. Mental retardation is a condition that usually dates from childhood and is characterized by impaired intellectual ability; mentally retarded individuals typically have IQ (intelligence quotient) scores below 70 or 75.

Description

The absent-mindedness and confusion about familiar settings and tasks that are hallmarks of dementia used to be considered as part of a typical aging pattern in the elderly. Indeed, dementia historically has been called senility. Dementia is now recognized not to be a normal part of aging. The symptoms of dementia can result from different causes. Some of the changes to the brain that cause dementia are treatable and can be reversed, while other changes are irreversible.

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The elderly are most prone to dementia, particularly those at risk for a stroke. The historical tendency of women to live longer than men has produced a higher prevalence of dementia in older women. However, women and men are equally prone to dementia. Over age 80, more than 20% of people have at least a mild form of dementia.

Dementia is especially prominent in older people. The three main irreversible causes are Alzheimer's disease, dementia with Lewy bodies, and multi-infarct dementia (also called vascular dementia).

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Neurotransmitter support - supplying the body with the precursors and cofactors it needs to produce neurotransmitters. Keeping the brain's neurotransmitters at high levels improves concentration, mental focus, calculation ability, memory encoding, recall, creativity, mood, and cures and prevents most depressions. The four main neurotransmitters are acetylcholine, dopamine, norepinephrine and serotonin.

Note that cardiovascular exercise performed on a regular basis also has nootropic effects, by increasing the body's capacity to supply brain cells with oxygen. Exercise is highly synergistic with nutritional supplementation, and a health regimen is incomplete without it.

What type of drugs will enhance cognition?

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Cholinergics are substances which affect the neurotransmitter acetylcholine or the components of the nervous system which utilize acetylcholine. Acetylcholine facilitates memory, concentration, focus, and high-order thought processes (abstract thought, calculation, innovation, etc.). Increasing the availability of this neurotransmitter in the brain may improve these functions and increase the duration in which they may be engaged without slowing down or stopping. Oversupplying the brain with acetylcholine may have the opposite effect, temporarily reducing rather than improving mental performance.

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Acetyl-L-carnitine (ALCAR) - Amino acid. Precursor of acetylcholine (donating the acetyl portion to the acetylcholine molecule). It is synergistic with lipoic acid.Centrophenoxine (Lucidril) - Drug. cholinergic agent, enhances color perception.Choline - precursor to acetylcholine (an essential component of the acetylcholine molecule).Alpha-GPC (L-alpha glycerylphosphorylcholine, Choline alfoscerate) - most effective choline precursor, readily crosses the blood-brain barrier.CDP-Choline (Cytidine Diphosphate Choline) - choline precursor, tends to be less expensive and similar in effect to Alpha GPC.Choline bitartrate - precursor of acetylcholine, general nootropic, anti-depressant.Choline citrate - precursor of the neurotransmitter acetylcholine, general nootropic, anti-depressant.DMAE - approved treatment for ADD/ADHD, precursor of acetylcholine, cholinergic agent, removes lipofuscin from the brain, anti-depressant.Huperzine A - potent acetylcholinesterase inhibitor derived from Chinese club-moss.Lecithin - precursor of acetylcholine.

Pyrrolidone derivatives:Piracetam (Nootropil) - Prescription drug (in Europe). The original (first)[2], and most commonly taken[3] nootropic drug. It is a cholinergic agent, synergistic with DMAE, centrophenoxine, choline, and Hydergine. Increases brain cell metabolism and energy levels[4], and speeds up interhemispheric flow of information (left-right brain hemisphere communication). Increases vigilance,[5], improves concentration, and enhances memory. Protects neurons from hypoxia,[2] and stimulates growth of acetylcholine receptors. May also cause nerves to regenerate. Piracetam markedly decreases the formation of neuronal lipofuscin.[6] It improves posture in elderly people.[7] It is not regulated in the US.Aniracetam - Drug. Analog of piracetam, and 4 to 8 times more potent. Like piracetam, aniracetam protects against some memory impairing chemicals, such as diethyldithiocarbamate and clonidine.[8] Also like piracetam, aniracetam may enhance memory in aging adults by increasing levels of brain biogenic monoamines, which are beneficial to learning and memory.[1] Both racetams have possible therapeutic use in treating fetal alcohol syndrome.[9] Aniracetam increases vigilance.[5]Etiracetam - It increases vigilance.[5]Nefiracetam - Drug. Analog of piracetam, and facilitates hippocampal neurotransmission.[10]Oxiracetam - Drug. Analog of piracetam, and 2 to 4 times stronger. Improves memory, concentration, and vigilance. When fed to pregnant rats, the offspring of those rats were more intelligent than the offspring of rats fed a saline solution placebo.Pramiracetam - Drug. Fifteen times stronger than piracetam, of which it is an analog.it is an analog.

Examples of Cholinergic Nootropic Drugs

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NO

O

NH2

Piracetam (brand name: Nootropil®, Myocalm®)

Piracetam (brand name: Nootropil®, Myocalm®), is a cerebral function regulating drug which is claimed to be able to enhance cognition as well as slow down brain aging. Piracetam's chemical name is 2-oxo-pyrrolidone, or 2-oxo-1-pyrrolidine acetamide. Piracetam is a cyclic derivative of GABA. It is one of the racetams, and is similar to the amino acid pyroglutamate. Though rare in the United States, piracetam is commonly prescribed in Europe for a variety of conditions.

Several meta-reviews of literature on piracetam indicate that piracetam increases performance on a variety of cognitive tasks among dyslexic children, though this may reflect its enhancement of cross-hemispheric communication and of cognitive function in general, rather than a specific improvement in whatever causes dyslexia. Piracetam also seems to inhibit brain damage caused by a variety of factors including hypoxia and excessive alcohol consumption.[1] [2]

Piracetam has been studied in an extensive number of clinical experiments, and has shown positive results in the treatment of post-stroke aphasia, epilepsy, cognitive decline following heart and brain surgery, dementia[3], and myoclonus,[4] [5]and some believe that understanding the mechanism through which it works can teach us about the role of inter-hemispheric communication in the brain.

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AphasiaDefinition

Aphasia is a communication disorder that occurs after language has been developed, usually in adulthood. Not simply a speech disorder, aphasia can affect the ability to comprehend the speech of others, as well as the ability to read and write. In most instances, intelligence per se is not affected.

Description

Aphasia has been known since the time of the ancient Greeks. However, it has been the focus of scientific study only since the mid-nineteenth century. Although aphasia can be caused by a head injury and neurologic conditions, its most common cause is stroke, a disruption of blood flow to the brain, which affects brain metabolism in localized areas of the brain.

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MyoclonusDefinition

Myoclonus is a brief, rapid, shock-like jerking movement.

Description

Myoclonus can be a symptom of a separate disorder, or can be the only or primary neurological finding, in which case it is termed "essential myoclonus." Myoclonus may occur in epilepsy, or following many different types of brain injury, such as lack of oxygen, stroke, trauma, or poisoning. Myoclonus can occur in one or more limbs, or may be generalized, involving much of the brain.

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Infarction

The process of anoxic tissue death. The usual cause is occlusion of an artery by a thrombus or embolus and sometimes by severe atherosclerosis.

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