Levodopa is used as a [[prodrug]] to increase [[dopamine]] levels for the treatment of [[Parkinson's disease]], since it is able to cross the [[blood-brain barrier]] whereas dopamine itself cannot. Once levodopa has entered the [[central nervous system]] (CNS), it is metabolised to dopamine by [[aromatic-L-amino-acid decarboxylase]]. However,conversiontodopaminealsooccursintheperipheraltissues, causing adverse effects and decreasingtheavailabledopaminetothe CNS, soit is standard practice to co-administer a peripheral [[Aromatic-L-amino-aciddecarboxylase|DOPA decarboxylase]] inhibitor – [[carbidopa]] or [[benserazide]] – and often a [[catechol-O-methyl transferase]] (COMT) inhibitor.
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L-Dopa is used to increase [[dopamine]] levels for the treatment of [[Parkinson's disease]] and [[Dopa-Responsive Dystonia]], since it is able to cross the [[blood-brain barrier]], whereas dopamine itself cannot. Once levodopa has entered the [[central nervous system]] (CNS), it is metabolized to dopamine by [[aromaticL-aminoacid decarboxylase]]. [[Pyridoxalphosphate]](vitaminB6)isarequiredcofactor forthisdecarboxylation, and maybeadministeredalongwithlevodopa, usuallyas [[VitaminB6|pyridoxine]].
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==Adverse effects==
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Conversion to dopamine also occurs in the peripheral tissues, i.e. outside the brain. This may be the mechanism of the adverse effects of levodopa. It is standard clinical practice to co-administer a peripheral [[Aromatic-L-amino-acid decarboxylase|DOPA decarboxylase]] inhibitor—[[carbidopa]] or [[benserazide]]—and often a [[catechol-O-methyl transferase]] (COMT) inhibitor, to prevent synthesis of dopamine in peripheral tissue. Co-administration of pyridoxine without a decarboxylase inhibitor accelerates the extracerebral decarboxylation to such an extent that it cancels out the effects of levodopa administration, a circumstance which historically caused great confusion.
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For those taking it as a supplement, [[EGCG]] or [[green tea]] is a natural decarboxylase inhibitor.
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Levodopa, co-administered with a peripheral DOPA decarboxylase inhibitor, has been tested as a possible treatment for [[restless leg syndrome]] (RLS) and shown "no clear picture of reduced symptoms".<ref>{{cite web |title=L-dopa for RLS |url=http://www.medicine.ox.ac.uk/bandolier/booth/RLS/dopa.html |date=1 April 2007 |publisher=[[Bandolier (journal)|Bandolier]] |accessdate=2008-10-16}}</ref><!-- much claims for treatments in RLS, but this assertion of effectiveness needs a reliable source (ie not the 44% pharamaceutical funded Restless Legs Syndrome Foundation) -->
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==Adverse effects ==
Possible [[adverse drug reaction]]s include:
Possible [[adverse drug reaction]]s include:
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*[[Hypotension]], especially if the dosage is too high.
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*[[Hypotension]], especially if the dosage is too high
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*[[Arrhythmia]]s, although these are uncommon.
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*[[Arrhythmia]]s, although these are uncommon
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*[[Nausea]], which is often helped by taking the drug with food, although [[protein]] interferes with drug absorption.
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*[[Nausea]], which is often reduced by taking the drug with food, although [[protein]] interferes with drug absorption
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*Gastrointestinal bleeding.
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*Gastrointestinal bleeding
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*Disturbed [[Respiration (physiology)|respiration]].This is not always harmful, and can actually benefit patients with upper airway obstruction.
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*Disturbed [[Respiration (physiology)|respiration]],which is not always harmful, and can actually benefit patients with upper airway obstruction
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*[[Baldness|Hair loss]].
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*[[Baldness|Hair loss]]
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*Confusion.
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*Confusion
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*Extreme [[emotion|emotional]] states, particularly [[anxiety]], but also excessive [[libido]].
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*Extreme [[emotion]]al states, particularly [[anxiety]], but also excessive [[libido]]
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*Vivid [[dream]]s and/or fragmented sleep.
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*Vivid [[dream]]s and/or fragmented sleep
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*Visual and possibly auditory [[hallucination]]s.
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*Visual and possibly auditory [[hallucination]]s
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*Effects on learning.There is some evidence that it improves [[working memory]], while impairing other complex functions.
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*Effects on learning;there is some evidence that it improves [[working memory]], while impairing other complex functions
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*Sleepiness and sleep attacks.
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*Sleepiness and sleep attacks
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*a condition similar to [[amphetamine psychosis]].
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*A condition similar to [[amphetamine psychosis]].
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Although there are a number of adverse effects associated with levodopa, particularly psychiatric ones, it has fewer than other anti-Parkinson's drugs, including [[anticholinergic]]s, [[selegiline]], [[amantadine]], and [[dopamine agonist]]s.
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Although there are many adverse effects associated with levodopa, particularly psychiatric ones, it has fewer than other anti-Parkinson's drugs, including [[anticholinergic]]s, [[amantadine]], and [[dopamine agonist]]s.
More serious are the effects of chronic levodopa administration, which include:
More serious are the effects of chronic levodopa administration, which include:
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*End-of-dose deterioration of function.
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*End-of-dose deterioration of function
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*On/off oscillations.
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*On/off oscillations
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*Freezing during movement.
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*Freezing during movement
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*Dose failure ([[drug resistance]]).
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*Dose failure ([[drug resistance]])
*[[Dyskinesia]] at peak dose.
*[[Dyskinesia]] at peak dose.
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*Recent studies have demonstrated that use of L-dopa without simultaneously giving proper levels of serotonin percursors depletes serotonin.
Clinicians will try to avoid these by limiting levodopa dosages as far as possible until absolutely necessary.
Clinicians will try to avoid these by limiting levodopa dosages as far as possible until absolutely necessary.
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====Toxicity====
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Some studies suggest a cytotoxic role in the promotion and occurrence of adverse effects associated with levodopa treatment.<ref name="pmid9017256">{{cite journal |author=Cheng N, Maeda T, Kume T, ''et al'' |title=Differential neurotoxicity induced by L-DOPA and dopamine in cultured striatal neurons |journal=Brain research |volume=743 |issue=1-2 |pages=278–83 |year=1996 |month=December |pmid=9017256 |doi= |url=}}</ref> Though the drug is generally safe in humans, some researchers have reported an increase in [[cytotoxicity]] markers in [[rat]] pheochromocytoma PC12 cell lines treated with levodopa.<ref name="pmid7830076">{{cite journal |author=Basma AN, Morris EJ, Nicklas WJ, Geller HM |title=L-dopa cytotoxicity to PC12 cells in culture is via its autoxidation |journal=Journal of neurochemistry |volume=64 |issue=2 |pages=825–32 |year=1995 |month=February |pmid=7830076 |doi= |url=}}</ref> Other authors have attributed the observed [[toxic]] effects of levodopa in neural [[dopamine]] cell lines to enhanced formation of [[quinones]] through increased auto-oxidation and subsequent cell death in mesencephalic cell cultures.<ref name="pmid7552304">{{cite journal |author=Pardo B, Mena MA, Casarejos MJ, Paíno CL, De Yébenes JG |title=Toxic effects of L-DOPA on mesencephalic cell cultures: protection with antioxidants |journal=Brain research |volume=682 |issue=1-2 |pages=133–43 |year=1995 |month=June |pmid=7552304 |doi= |url=}}</ref><ref name="pmid8376999">{{cite journal |author=Mytilineou C, Han SK, Cohen G |title=Toxic and protective effects of L-dopa on mesencephalic cell cultures |journal=Journal of neurochemistry |volume=61 |issue=4 |pages=1470–8 |year=1993 |month=October |pmid=8376999 |doi= |url=}}</ref> Though levodopa is generally considered safe, some controversy surrounds use of the [[drug]] in [[Parkinson's Disease]] given some data indicating a deleterious effect on [[intracellular]] and [[neuronal]] tissue involved in the [[pathogenesis]] of the disease.<ref name="pmid10408739">{{cite journal |author=Simuni T, Stern MB |title=Does levodopa accelerate Parkinson's disease? |journal=Drugs & aging |volume=14 |issue=6 |pages=399–408 |year=1999 |month=June |pmid=10408739 |doi= |url=}}</ref>
==Biosynthesis==
==Biosynthesis==
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[[Image:Catecholamines biosynthesis.svg|thumb|right|400px|Biosynthesis of dopamine]]
<small>L</small>-DOPA is produced from the [[amino acid]] [[tyrosine]] by the enzyme [[tyrosine hydroxylase]]. It is also the precursor molecule for the [[catecholamine]] [[neurotransmitter]]s [[dopamine]] and [[norepinephrine]] (noradrenaline), and the [[hormone]] [[epinephrine]] (adrenaline). Dopamine is formed by the decarboxylation of <small>L</small>-DOPA.
<small>L</small>-DOPA is produced from the [[amino acid]] [[tyrosine]] by the enzyme [[tyrosine hydroxylase]]. It is also the precursor molecule for the [[catecholamine]] [[neurotransmitter]]s [[dopamine]] and [[norepinephrine]] (noradrenaline), and the [[hormone]] [[epinephrine]] (adrenaline). Dopamine is formed by the decarboxylation of <small>L</small>-DOPA.
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The prefix L- referencesitspropertyof [[levorotation]] (compared with [[dextrorotation]] or [[D-dopa]]).
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<small>L</small>-DOPAcanbedirectlymetabolized by [[catechol-O-methyl transferase]] (COMT) to 3-O-methyldopa (3-OMD) and then further to vanillactic acid (VLA). This metabolic pathway is non-existent in the healthy body but becomes important after peripheral <small>L</small>-DOPA administration in patients with Parkinson's Disease or in the rare cases of patients with [[aromatic L-amino acid decarboxylase]] (AADC) enzyme deficiency.<ref name="pmid1281049">{{cite journal |author=Hyland K, Clayton PT |title=Aromatic L-amino acid decarboxylase deficiency: diagnostic methodology |journal=Clinical chemistry |volume=38 |issue=12 |pages=2405–10 |year=1992 |month=December |pmid=1281049 |doi= |url=http://www.clinchem.org/cgi/reprint/38/12/2405.pdf |format=PDF}}</ref>
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The prefix <small>L</small>- references its property of [[levorotation]] (compared with [[dextrorotation]] or [[D-dopa|<small>D</small>-DOPA]]).
==History==
==History==
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In work that earned him a [[Nobel Prize in Physiology or Medicine|Nobel Prize]], Swedish scientist [[Arvid Carlsson]] first showed in the 1950s that administering levodopa to animals with Parkinsonian symptoms would cause a reduction of the symptoms. The [[neurology|neurologist]] [[Oliver Sacks]] describes this treatment in human patients with [[encephalitis lethargica]] in his book ''[[Awakenings]]'' on which the movie of the same name is based.
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In work that earned him a Nobel Prize in 2000, Swedish scientist Arvid Carlsson first showed in the 1950s that administering levodopa to animals with Parkinsonian symptoms would cause a reduction of the symptoms. The [[neurology|neurologist]] [[Oliver Sacks]] describes this treatment in human patients with [[encephalitis lethargica]] in his book ''[[Awakenings (book)|Awakenings]]'',upon which [[Awakenings|the movie of the same name]] is based.
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The 2001 Nobel Prize in Chemistry was also related to L-DOPA: the Nobel Committee awarded one-fourth of the prize to William S. Knowles for his work on chirally-catalysed [[hydrogenation]] reactions, the most noted example of which was used for the synthesis of L-DOPA.
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The 2001 Nobel Prize in Chemistry was also related to L-DOPA: the Nobel Committee awarded one-fourth of the prize to William S. Knowles for his work on chirally catalysed [[hydrogenation]] reactions, the most noted example of which was uses for the synthesis of L-DOPA.
Conversion to dopamine also occurs in the peripheral tissues, i.e. outside the brain. This may be the mechanism of the adverse effects of levodopa. It is standard clinical practice to co-administer a peripheral DOPA decarboxylase inhibitor—carbidopa or benserazide—and often a catechol-O-methyl transferase (COMT) inhibitor, to prevent synthesis of dopamine in peripheral tissue. Co-administration of pyridoxine without a decarboxylase inhibitor accelerates the extracerebral decarboxylation to such an extent that it cancels out the effects of levodopa administration, a circumstance which historically caused great confusion.
For those taking it as a supplement, EGCG or green tea is a natural decarboxylase inhibitor.
Levodopa, co-administered with a peripheral DOPA decarboxylase inhibitor, has been tested as a possible treatment for restless leg syndrome (RLS) and shown "no clear picture of reduced symptoms".[1]
Although there are many adverse effects associated with levodopa, particularly psychiatric ones, it has fewer than other anti-Parkinson's drugs, including anticholinergics, amantadine, and dopamine agonists.
More serious are the effects of chronic levodopa administration, which include:
Some studies suggest a cytotoxic role in the promotion and occurrence of adverse effects associated with levodopa treatment.[2] Though the drug is generally safe in humans, some researchers have reported an increase in cytotoxicity markers in rat pheochromocytoma PC12 cell lines treated with levodopa.[3] Other authors have attributed the observed toxic effects of levodopa in neural dopamine cell lines to enhanced formation of quinones through increased auto-oxidation and subsequent cell death in mesencephalic cell cultures.[4][5] Though levodopa is generally considered safe, some controversy surrounds use of the drug in Parkinson's Disease given some data indicating a deleterious effect on intracellular and neuronal tissue involved in the pathogenesis of the disease.[6]
L-DOPA can be directly metabolized by catechol-O-methyl transferase (COMT) to 3-O-methyldopa (3-OMD) and then further to vanillactic acid (VLA). This metabolic pathway is non-existent in the healthy body but becomes important after peripheral L-DOPA administration in patients with Parkinson's Disease or in the rare cases of patients with aromatic L-amino acid decarboxylase (AADC) enzyme deficiency.[7]
In work that earned him a Nobel Prize in 2000, Swedish scientist Arvid Carlsson first showed in the 1950s that administering levodopa to animals with Parkinsonian symptoms would cause a reduction of the symptoms. The neurologistOliver Sacks describes this treatment in human patients with encephalitis lethargica in his book Awakenings, upon which the movie of the same name is based.
The 2001 Nobel Prize in Chemistry was also related to L-DOPA: the Nobel Committee awarded one-fourth of the prize to William S. Knowles for his work on chirally-catalysed hydrogenation reactions, the most noted example of which was used for the synthesis of L-DOPA.
DOPA is a key molecule in the formation of marine adhesive proteins, such as those found in mussels. It is believed to be responsible for the water-resistance and rapid curing abilities of these proteins. DOPA may also be used to prevent surfaces from fouling by bonding antifouling polymers to a susceptible substrate.
Both levodopa and the related amino acid tyrosine are precursors to the biological pigment melanin. The enzyme tyrosinase catalyzes the oxidation of either substrate to the reactive intermediate dopaquinone, which reacts further, eventually leading to eumelanin oligomers.
Waite, J. Herbert, et al. (2005). Mussel Adhesion: Finding the Tricks Worth Mimicking. J Adhesion81: 1-21.
Messersmith, Phillip B., et al. (2006). Rapid Gel Formation and Adhesion in Photocurable and Biodegradable Block Copolymers with High DOPA Content. Macromolecules39: 1740-1748.
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