Aromatic L-amino acid decarboxylase (DOPA decarboxylase), the enzyme responsible for the decarboxylation of levodopa to dopamine in peripheral tissues. Carbidopa is a competitive inhibitor of aromatic L-amino acid decarboxylase that does not cross the blood-brain barrier. By inhibiting peripheral DOPA decarboxylase, carbidopa prevents the conversion of levodopa to dopamine outside the central nervous system.

In B\PC3 and Capan-2 cells, carbidetopa ((S)-(-)-carbidopa) monohydrate demonstrates activity akin to those of other AhR ligands, specifically inducing CYP1A1 and CYP1A2, which can be controlled by AhR Antagonists (e.g., CH223191) block [1]. Carbidopa is an inhibitor of aromatic-L-amino acid decarboxylase that exhibits specific cytotoxicity against small cell lung cancer cells and human lung carcinooids. Carbidopa's fatal dose is 29 μM (IC50)[3].
Carbidopa inhibits peripheral DOPA decarboxylase, preventing the conversion of levodopa to dopamine in peripheral tissues. This reduces the amount of levodopa that is decarboxylated outside the brain, increasing the amount of levodopa that reaches the central nervous system and reducing peripheral side effects. Carbidopa has no antiparkinson activity by itself and has not been demonstrated to have any overt pharmacodynamic actions in the recommended doses.

In vivo research revealed that a dose of 1 mg/mouse of carbidopa greatly suppressed tumor growth in athymic nude mice carrying BχPC3 cells as xenografts [1]. Carbidopa monohydrate also stimulates nuclear absorption of AhR.
In vivo, carbidopa is used in combination with levodopa for the treatment of Parkinson's disease. When administered with levodopa, carbidopa increases both plasma levels and the plasma half-life of levodopa, and decreases plasma and urinary dopamine and homovanillic acid. This allows for a lower dose of levodopa to achieve therapeutic effects, reducing the incidence of levodopa-induced side effects such as nausea, vomiting, and cardiac arrhythmias.

In vitro enzyme assays for carbidopa involve measuring DOPA decarboxylase inhibition using radiometric or colorimetric methods. The enzyme is incubated with its substrate (levodopa or other aromatic amino acids) and various concentrations of carbidopa, and the production of dopamine is measured by HPLC or other methods. IC50 values are determined from concentration-response curves. These assays confirm the competitive inhibition of DOPA decarboxylase by carbidopa.

Cellular assays for carbidopa involve treating cells expressing DOPA decarboxylase with the compound and measuring the conversion of levodopa to dopamine. The compound's ability to inhibit DOPA decarboxylase activity in cellular contexts is demonstrated in these assays. These studies confirm that carbidopa inhibits peripheral DOPA decarboxylase and increases the amount of levodopa available for transport into the brain.

In vivo animal studies for carbidopa typically involve administration to rodent or other animal models of Parkinson's disease, often in combination with levodopa. The effects of carbidopa on levodopa pharmacokinetics, brain dopamine levels, and behavioral outcomes are assessed. These studies establish the dose-response relationship and efficacy of carbidopa as an adjunct to levodopa therapy.

Absorption, Distribution and Excretion
Following oral administration of levodopa/carbidopa, 40-70% of the administered dose is absorbed. After absorption, the bioavailability of carbidopa is 58%. The maximum concentration of 0.085 mcg/ml is reached after 143 minutes, with an AUC of 19.28 mcg·min/ml. Animal studies show that 66% of the administered carbidopa dose is excreted in the urine and 11% in the feces. These studies were conducted in humans, where urinary excretion was observed to account for 50% of the administered dose. The volume of distribution for carbidopa/levodopa combination therapy is 3.6 L/kg. However, carbidopa is widely distributed in tissues other than the brain. After one hour, carbidopa is primarily distributed in the kidneys, lungs, small intestine, and liver. The clearance rate of levodopa/carbidopa combination therapy has been reported to be 51.7 L/h.

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Metabolic/Metabolites
The loss of the hydrazine functional group (possibly in the form of molecular nitrogen) is the main metabolic pathway of carbidopa. Carbidopa metabolites include various products, including 3-(3,4-dihydroxyphenyl)-2-methylpropionic acid, 3-(4-hydroxy-3-methoxyphenyl)-2-methylpropionic acid, 3-(3-hydroxyphenyl)-2-methylpropionic acid, 3-(4-hydroxy-3-methoxyphenyl)-2-methyllactic acid, 3-(3-hydroxyphenyl)-2-methyllactic acid, and 3,4-dihydroxyphenylacetone (1,2).

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Biological Half-Life
The half-life of carbidopa has been reported to be approximately 107 minutes.
Pharmacokinetic studies of carbidopa show that the compound is absorbed following oral administration but does not cross the blood-brain barrier. Carbidopa reduces the amount of levodopa required to produce a given response by about 75% and, when administered with levodopa, increases both plasma levels and the plasma half-life of levodopa, and decreases plasma and urinary dopamine and homovanillic acid. Carbidopa is eliminated primarily by renal excretion.

Protein Binding
It is currently generally accepted that carbidopa has a protein binding rate of 76%. However, further research or sources for this information are needed.
Preclinical toxicity studies of carbidopa have established its safety profile. Carbidopa has not been demonstrated to have any overt pharmacodynamic actions in the recommended doses. The compound is generally well tolerated, and adverse effects are primarily related to the increased delivery of levodopa to the brain, which can exacerbate levodopa-induced dyskinesias or psychiatric effects. Carbidopa is considered safe for long-term use in combination with levodopa.

[1]. Safe S. Carbidopa: a selective Ah receptor modulator (SAhRM). Biochem J. 2017;474(22):3763-3765. Published 2017 Nov 6.

[2]. Fermaglich J. Treatment of Parkinson's disease with carbidopa, a peripheral decarboxylase inhibitor, and levodopa. Med Ann Dist Columbia. 1974;43(12):587-591.

[3]. The aromatic-L-amino acid decarboxylase inhibitor carbidopa is selectively cytotoxic to human pulmonary carcinoid and small cell lung carcinoma cells. Clin Cancer Res. 2000;6(11):4365-4372.

Carbidopa is the hydrate of 3-(3,4-dihydroxyphenyl)propionic acid, in which the hydrogen atom at the α-position of the carboxyl group is replaced by a hydrazine group and a methyl group (S configuration). Carbidopa is a dopa decarboxylase inhibitor, thus preventing the conversion of levodopa to dopamine. It does not possess anti-Parkinson's activity itself, but is used in the treatment of Parkinson's disease to reduce the peripheral adverse effects of levodopa. It has multiple functions, including as an EC 4.1.1.28 (aromatic-L-amino acid decarboxylase) inhibitor, an anti-Parkinson's drug, a dopaminergic drug, and an anti-movement disorder drug. It belongs to the hydrazine class of compounds, hydrates, monocarboxylic acids, and catechols. This product contains anhydrous carbidopa. The chemical name of carbidopa is N-amino-α-methyl-3-hydroxy-L-tyrosine monohydrate. It potently inhibits aromatic amino acid decarboxylases (DDCs) and, due to its chemical properties, cannot cross the blood-brain barrier. Due to its activity, carbidopa is often used in combination with levodopa. For patients whose nausea is not effectively relieved by levodopa/carbidopa combination therapy, we developed a carbidopa-only monotherapy. The first FDA-approved carbidopa-only product was developed by Amerigens Pharmaceuticals Ltd. and approved in 2014. On the other hand, carbidopa/levodopa combination therapy was initially developed by Watson Labs, but FDA history shows that Mayne Pharma approved the combination therapy as early as 1992. Carbidopa is an aromatic amino acid decarboxylase inhibitor. Its mechanism of action is as a dopa decarboxylase inhibitor. Carbidopa is a hydrazine derivative of dopa. It is a peripheral dopa decarboxylase inhibitor and can be used as an adjunct to levodopa to prevent the conversion of levodopa to dopamine in peripheral tissues, thereby reducing peripheral side effects. Carbidopa cannot cross the blood-brain barrier. Therefore, once levodopa reaches the brain, it is metabolized into dopamine by dopa decarboxylase and exerts its effects on dopamine receptors. Carbidopa is a dopa decarboxylase inhibitor that prevents the conversion of levodopa to dopamine. It is used in Parkinson's disease to reduce the peripheral adverse effects of levodopa. Carbidopa itself does not have anti-Parkinson's activity. Drug Indications Carbidopa, used in combination with levodopa, is used to treat idiopathic Parkinson's disease, post-encephalitis Parkinson's syndrome, and symptomatic Parkinson's syndrome following carbon monoxide or manganese poisoning. Combination therapy can reduce nausea and vomiting caused by levodopa. Carbidopa formulations should be used when the carbidopa/levodopa combination therapy does not provide an adequate daily dose. Additionally, carbidopa formulations may be used when individualized adjustments to the dosage of carbidopa and levodopa are required.
FDA Label

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Mechanism of Action
Carbidopa is an inhibitor of dopamine transporter (DDC), thereby inhibiting the peripheral metabolism of levodopa. DDC plays a crucial role in the conversion of L-tryptophan to serotonin and L-dopa to dopamine. DDC is present in peripheral tissues and the blood-brain barrier. Because carbidopa cannot cross the blood-brain barrier, its action is primarily concentrated in the peripheral DDC. Therefore, carbidopa inhibits the peripheral metabolism of levodopa without affecting dopamine production in the brain.

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Pharmacodynamics
When carbidopa is used in combination with levodopa, it inhibits the peripheral conversion of levodopa to dopamine and inhibits aromatic L-amino acid decarboxylases from decarboxylating oxithtriptan to serotonin. This results in more levodopa and oxithtriptan being available for transport to the central nervous system. Carbidopa also inhibits the metabolism of levodopa in the gastrointestinal tract, thereby increasing the bioavailability of levodopa. Increased circulation of levodopa can enhance the potency of still-functional dopaminergic neurons and has been shown to temporarily relieve symptoms. Carbidopa's role is crucial because levodopa can cross the blood-brain barrier, while dopamine cannot. Therefore, taking carbidopa is essential to prevent exogenous levodopa from being converted into dopamine before reaching its primary sites of action in the brain. Studies have shown that combined use of carbidopa and levodopa can prolong the half-life of levodopa by more than 1.5 times, while increasing plasma concentration and decreasing clearance. Combined therapy also showed a higher urinary recovery rate of levodopa than dopamine, indicating reduced metabolism. This effect has been well-documented by significantly reducing levodopa requirements and significantly decreasing side effects such as nausea. Studies have found that the effect of carbidopa is dose-independent.
Carbidopa hydrate is a competitive inhibitor of aromatic L-amino acid decarboxylase used in combination with levodopa for the treatment of Parkinson's disease. Carbidopa does not cross the blood-brain barrier and acts peripherally to prevent the conversion of levodopa to dopamine, increasing the amount of levodopa that reaches the brain and reducing peripheral side effects. Carbidopa reduces the required levodopa dose by about 75%. It has no antiparkinson activity by itself.

C10H16N2O5

244.2444

244.105

38821-49-7

Carbidopa;28860-95-9;Carbidopa-d3 monohydrate;1276197-58-0

38101

White to off-white solid powder

1.42 g/cm3

528.7ºC at 760 mmHg

203-208 °C

273.5ºC

0.973

6

7

4

17

261

1

C[C@](CC1=CC(=C(C=C1)O)O)(C(=O)O)NN.O

QTAOMKOIBXZKND-PPHPATTJSA-N

InChI=1S/C10H14N2O4.H2O/c1-10(12-11,9(15)16)5-6-2-3-7(13)8(14)4-6;/h2-4,12-14H,5,11H2,1H3,(H,15,16);1H2/t10-;/m0./s1

(2S)-3-(3,4-dihydroxyphenyl)-2-hydrazinyl-2-methylpropanoic acid;hydrate

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)