l-DOPA, also known as levodopa and l-3,4-dihydroxyphenylalanine, is made and used as part of the normal biology of some plants[3] and animals, including humans. Humans, as well as a portion of the other animals that utilize l-DOPA, make it via biosynthesis from the amino acidl-tyrosine. l-DOPA is the precursor to the neurotransmittersdopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), which are collectively known as catecholamines. Furthermore, l-DOPA itself mediates neurotrophic factor release by the brain and CNS.[4][5] In some plant families (of the order Caryophyllales), l-DOPA is the central precursor of a biosynthetic pathway that produces a class of pigments called betalains.[6]l-DOPA can be manufactured and in its pure form is sold as a psychoactive drug with the INN levodopa; trade names include Sinemet, Pharmacopa, Atamet, and Stalevo. As a drug, it is used in the clinical treatmentofParkinson's disease and dopamine-responsive dystonia.
l-DOPA has a counterpart with opposite chirality, d-DOPA. As is true for many molecules, the human body produces only one of these isomers (the l-DOPA form). The enantiomeric purityofl-DOPA may be analyzed by determination of the optical rotation or by chiral thin-layer chromatography.[7]
In humans, conversion of l-DOPA to dopamine does not only occur within the central nervous system. Cells in the peripheral nervous system perform the same task. Thus administering l-DOPA alone will lead to increased dopamine signaling in the periphery as well. Excessive peripheral dopamine signaling is undesirable as it causes many of the adverse side effects seen with sole L-DOPA administration. To bypass these effects, it is standard clinical practice to coadminister (with l-DOPA) a peripheral DOPA decarboxylase inhibitor (DDCI) such as carbidopa (medicines containing carbidopa, either alone or in combination with l-DOPA, are branded as Lodosyn[10] (Aton Pharma)[11]Sinemet (Merck Sharp & Dohme Limited), Pharmacopa (Jazz Pharmaceuticals), Atamet (UCB), Syndopa and Stalevo (Orion Corporation) or with a benserazide (combination medicines are branded Madopar or Prolopa), to prevent the peripheral synthesis of dopamine from l-DOPA). However, when consumed as a botanical extract, for example from M pruriens supplements, a peripheral DOPA decarboxylase inhibitor is not present.[3]
Inbrija (previously known as CVT-301) is an inhaled powder formulation of levodopa indicated for the intermittent treatment of "off episodes" in patients with Parkinson's disease currently taking carbidopa/levodopa.[12] It was approved by the United States Food and Drug Administration on December 21, 2018, and is marketed by Acorda Therapeutics.[13]
Coadministration of pyridoxine without a DDCI accelerates the peripheral decarboxylationofl-DOPA to such an extent that it negates the effects of l-DOPA administration, a phenomenon that historically caused great confusion.
In addition, l-DOPA, co-administered with a peripheral DDCI, is efficacious for the short-term treatment of restless leg syndrome.[14]
The two types of response seen with administration of l-DOPA are:
The short-duration response is related to the half-life of the drug.
The longer-duration response depends on the accumulation of effects over at least two weeks, during which ΔFosB accumulates in nigrostriatal neurons. In the treatment of Parkinson's disease, this response is evident only in early therapy, as the inability of the brain to store dopamine is not yet a concern.
l-DOPA is produced from the amino acid l-tyrosine by the enzyme tyrosine hydroxylase. l-DOPA can act as an l-tyrosine mimetic and be incorporated into proteins by mammalian cells in place of L-tyrosine, generating protease-resistant and aggregate-prone proteinsin vitro and may contribute to neurotoxicity with chronic l-DOPA administration.[18]
It is also the precursor for the monoamineorcatecholamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). Dopamine is formed by the decarboxylation of l-DOPA by aromatic l-amino acid decarboxylase (AADC).
l-DOPA can be directly metabolized by catechol-O-methyl transferaseto3-O-methyldopa, and then further to vanillactic acid. This metabolic pathway is nonexistent 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 AADC enzyme deficiency.[19]
l-Phenylalanine, l-tyrosine, and l-DOPA are all precursors to the biological pigmentmelanin. The enzyme tyrosinasecatalyzes the oxidationofl-DOPA to the reactive intermediate dopaquinone, which reacts further, eventually leading to melanin oligomers. In addition, tyrosinase can convert tyrosine directly to l-DOPA in the presence of a reducing agent such as ascorbic acid.[20]
l-DOPA is a key compound in the formation of marine adhesive proteins, such as those found in mussels.[21][22] It is believed to be responsible for the water-resistance and rapid curing abilities of these proteins. l-DOPA may also be used to prevent surfaces from fouling by bonding antifouling polymers to a susceptible substrate.[23] The versatile chemistry of L-DOPA can be exploited in nanotechnology.[24] For example, DOPA-containing self-assembling peptides were found to form functional nanostructures, adhesives and gels.[25][26][27][28]
Nausea, which is often reduced by taking the drug with food, although protein reduces drug absorption. l-DOPA is an amino acid, so protein competitively inhibits l-DOPA absorption.
Gastrointestinal bleeding
Disturbed respiration, which is not always harmful, and can actually benefit patients with upper airway obstruction
Possible dopamine dysregulation: The long-term use of l-DOPA in Parkinson's disease has been linked to the so-called dopamine dysregulation syndrome.[29]
Clinicians try to avoid these side effects and adverse reactions by limiting l-DOPA doses as much as possible until absolutely necessary.
The long term use of L-Dopa increases oxidative stress through monoamine oxidase led enzymatic degradation of synthesized dopamine causing neuronal damage and cytotoxicity. The oxidative stress is caused by the formation of reactive oxygen species (H2O2) during the monoamine oxidase led metabolism of dopamine. It is further perpetuated by the richness of Fe2+ ions in striatum via the Fenton reaction and intracellular autooxidation. The increased oxidation can potentially cause mutations in DNA due to the formation of 8-oxoguanine, which is capable of pairing with adenosine during mitosis.[30]
In work that earned him a Nobel Prize in 2000, Swedish scientist Arvid Carlsson first showed in the 1950s that administering l-DOPA to animals with drug-induced (reserpine) Parkinsonian symptoms caused a reduction in the intensity of the animals' symptoms. In 1960/61 Oleh Hornykiewicz, after discovering greatly reduced levels of dopamine in autopsied brains of patients with Parkinson's disease,[31] published together with the neurologist Walther Birkmayer dramatic therapeutic antiparkinson effects of intravenously administered l-DOPA in patients.[32] This treatment was later extended to manganese poisoning and later Parkinsonism by George Cotzias and his coworkers,[33] who used greatly increased oral doses, for which they won the 1969 Lasker Prize.[34][35] The neurologistOliver Sacks describes this treatment in human patients with encephalitis lethargica in his 1973 book Awakenings, upon which the 1990 movie of the same name is based. The first study reporting improvements in patients with Parkinson's disease resulting from treatment with L-dopa was published in 1968.[36]
The 2001 Nobel Prize in Chemistry was also related to l-DOPA: the Nobel Committee awarded one-quarter 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.[37][38][39]
Synthesis of l-DOPA via hydrogenation with C2-symmetric diphosphine.
In 2015, a retrospective analysis comparing the incidence of age-related macular degeneration (AMD) between patients taking versus not taking l-DOPA found that the drug delayed onset of AMD by around 8 years. The authors state that significant effects were obtained for both dry and wet AMD.[40][non-primary source needed]
In plants, L-DOPA functions as an allelochemical which inhibits the growth of certain species, and is produced and secreted by a few legume species such as the broad bean Vicia faba and the velvet bean Mucuna pruriens.[41] Its effect is strongly dependent on the pH and the reactivity of iron in the soil.[42]
^Martens J, Günther K, Schickedanz M (1986). "Resolution of Optical Isomers by Thin-Layer Chromatography: Enantiomeric Purity of Methyldopa". Arch. Pharm.319 (6): 572–574. doi:10.1002/ardp.19863190618. S2CID97903386.
^Hardebo JE, Owman C (July 1980). "Barrier mechanisms for neurotransmitter monoamines and their precursors at the blood-brain interface". Annals of Neurology. 8 (1): 1–31. doi:10.1002/ana.410080102. PMID6105837. S2CID22874032.
^Lindemann L, Hoener MC (May 2005). "A renaissance in trace amines inspired by a novel GPCR family". Trends in Pharmacological Sciences. 26 (5): 274–281. doi:10.1016/j.tips.2005.03.007. PMID15860375.
^Wang X, Li J, Dong G, Yue J (February 2014). "The endogenous substrates of brain CYP2D". European Journal of Pharmacology. 724: 211–218. doi:10.1016/j.ejphar.2013.12.025. PMID24374199.
^Giuri D, Ravarino P, Tomasini C (June 2021). "L-Dopa in small peptides: an amazing functionality to form supramolecular materials". Organic & Biomolecular Chemistry. 19 (21): 4622–4636. doi:10.1039/D1OB00378J. hdl:11585/840774. PMID33978030. S2CID234474122.
^Maity S, Nir S, Zada T, Reches M (October 2014). "Self-assembly of a tripeptide into a functional coating that resists fouling". Chemical Communications. 50 (76): 11154–11157. doi:10.1039/C4CC03578J. PMID25110984.
^Merims D, Giladi N (2008). "Dopamine dysregulation syndrome, addiction and behavioral changes in Parkinson's disease". Parkinsonism & Related Disorders. 14 (4): 273–80. doi:10.1016/j.parkreldis.2007.09.007. PMID17988927.
^Ehringer H, Hornykiewicz O (December 1960). "[Distribution of noradrenaline and dopamine (3-hydroxytyramine) in the human brain and their behavior in diseases of the extrapyramidal system]". Klinische Wochenschrift. 38 (24): 1236–9. doi:10.1007/BF01485901. PMID13726012. S2CID32896604.
^Birkmayer W, Hornykiewicz O (November 1961). "[The L-3,4-dioxyphenylalanine (DOPA)-effect in Parkinson-akinesia]". Wiener Klinische Wochenschrift. 73: 787–8. PMID13869404.
^Cotzias GC, Papavasiliou PS, Gellene R (July 1969). "L-dopa in parkinson's syndrome". The New England Journal of Medicine. 281 (5): 272. doi:10.1056/NEJM196907312810518. PMID5791298.
^Knowles WS (March 1986). "Application of organometallic catalysis to the commercial production of L-DOPA". Journal of Chemical Education. 63 (3): 222. Bibcode:1986JChEd..63..222K. doi:10.1021/ed063p222.
^Fujii Y, Shibuya T, Yasuda T (1991). "L-3,4-Dihydroxyphenylalanine as an Allelochemical Candidate from Mucuna pruriens (L.) DC. var. utilis". Agricultural and Biological Chemistry. 55 (2): 617–618. doi:10.1080/00021369.1991.10870627.
