Its primary action is as a mucolytic, but at a molecular level, Carbocysteine attenuates the phosphorylation of NF-κB p65 and ERK1/2. It also modulates the interplay between the Nrf2/HO-1 and NF-κB pathways and inhibits apoptosis.

In vitro, Carbocysteine modulates key inflammatory and oxidative stress pathways. It inhibits the phosphorylation of NF-κB p65 and ERK1/2, which are crucial for inflammatory signaling. By modulating the Nrf2/HO-1 and NF-κB interplay, it helps to balance the cellular response to oxidative stress and inflammation. It also demonstrates anti-apoptotic effects.

Carbocysteine's in vivo activity is primarily demonstrated through its clinical efficacy. As an orally active agent, it is used to reduce mucus viscosity in the respiratory tract, making it easier to expel. Its anti-inflammatory and antioxidant properties contribute to its therapeutic benefits in chronic respiratory conditions like COPD.

The in vitro mechanism is typically studied in cell culture models of inflammation. Cells, such as human airway epithelial cells, are stimulated with pro-inflammatory agents (e.g., TNF-α or LPS) in the presence or absence of Carbocysteine. The readout involves measuring the phosphorylation status of NF-κB p65 and ERK1/2 via Western blotting, as well as assessing the expression of Nrf2 and its downstream targets.

In vitro cell-based assays are used to evaluate the compound's effects on apoptosis and inflammatory signaling. Cells are treated with Carbocysteine, and apoptosis is assessed using methods like Annexin V/PI staining or caspase activity assays. The modulation of NF-κB and Nrf2 pathways is confirmed by analyzing the nuclear translocation of these transcription factors and the expression of their target genes.

Carbocysteine is an orally active drug, and its in vivo activity is evaluated in clinical settings. Animal models of COPD or acute lung injury are used to study its efficacy. The primary endpoints include the measurement of mucus production, inflammatory cell infiltration in the lungs, and levels of inflammatory cytokines in bronchoalveolar lavage fluid.

Absorption, Distribution and Excretion
Following oral administration, carbocysteine is rapidly absorbed from the gastrointestinal tract, reaching peak serum concentrations within 1–1.7 hours. Approximately 30%–60% of the oral dose is excreted unchanged in the urine. Carbocysteine penetrates well into pulmonary and bronchial secretions. Information regarding the clearance rate of carbocysteine in the literature is unclear. Metabolism/Metabolites The metabolic pathway of carbocysteine involves acetylation, decarboxylation, and sulfoxide formation, ultimately producing pharmacologically inactive carbocysteine derivatives. Due to genetic polymorphism in sulfoxide formation capacity, its metabolism varies significantly. Two cytoplasmic enzymes are responsible for the metabolism of carbocysteine: cysteine dioxygenase and phenylalanine 4-hydroxylase. Decreased metabolism leads to increased carbocysteine exposure, which explains the differences in clinical response among patients, who may have polymorphisms affecting the enzymes that metabolize carbocysteine. Sulfonation is generally considered to be the main metabolic pathway of carbocysteine; however, a team of researchers discovered a novel urinary metabolite, S-(carboxymethylthio)-L-cysteine (CMTC). In this study, cysteine sulfoxide metabolites were not detected in the urine of patients taking carbocysteine.

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Biological Half-Life
The plasma half-life of carbocysteine is 1.33 hours.
As an orally administered drug, Carbocysteine is well-absorbed and distributed. Its pharmacokinetic profile supports once- or twice-daily dosing regimens for respiratory conditions. The compound undergoes metabolism, and its systemic exposure is sufficient to exert its mucolytic and anti-inflammatory effects in the respiratory tract.

Protein Binding
There is no information in the literature regarding the plasma protein binding of carboxymethylcysteine.
Carbocysteine is generally well-tolerated in clinical use. However, there have been reports of severe and even fatal paradoxical reactions in children treated with the drug, leading to the withdrawal of some marketing authorizations. The specific mechanisms of these adverse events are not fully understood.

[1]. Efficacy and safety profile of mucolytic/antioxidant agents in chronic obstructive pulmonary disease: a comparative analysis across erdosteine, carbocysteine, and N-acetylcysteine. Respir Res. 2019 May 27;20(1):104.

S-Carboxymethyl-L-cysteine is an L-cysteine thioether with the structure L-cysteine, in which the hydrogen on the thiol group is replaced by a carboxymethyl group. It has expectorant properties. It is an L-cysteine thioether and also a non-protein L-α-amino acid. It is the conjugate acid of S-carboxymethyl-L-cysteine (1-). Dyspnea and cough are common symptoms of chronic obstructive pulmonary disease (COPD) and other respiratory diseases characterized by increased mucus secretion. COPD patients are at higher risk of lung infections because viruses and bacteria grow and accumulate in thick bronchial mucus. Carbocysteine is an expectorant that relieves respiratory symptoms and infections by reducing the viscosity of mucus, making it easier to expel. Several marketing authorizations for the drug have been withdrawn after severe and even fatal paradoxical reactions in children treated with carbocysteine. Doctors in France and Italy have reported symptoms such as dyspnea, shortness of breath, and worsening cough after taking carbocysteine. Currently, carboxymethylcysteine has not been approved by the U.S. Food and Drug Administration (FDA) or Health Canada, but it is approved for use in Asia, Europe, and South America. S-carboxymethyl-L-cysteine is a metabolite of E. coli (K12 strain, MG1655 strain), produced or discovered by E. coli. It is a compound formed by the reaction of iodoacetic acid with sulfhydryl groups in proteins. It has been used as an anti-infective nasal spray with expectorant and antitussive effects. Drug Indications Carboxymethylcysteine is available as an over-the-counter or prescription drug for clearing respiratory secretions associated with increased mucus production. Mechanism of Action Excessive mucus production is characteristic of serious respiratory diseases including asthma, cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD). It blocks bacterial adhesion to cells, thereby preventing lung infections. Glycoproteins (fucoprotein, sialic acid mucin, and sulfated mucin) regulate the viscoelasticity of bronchial mucus. The levels of fucoglycoprotein in the mucus of patients with chronic obstructive pulmonary disease (COPD) are elevated. Carboxycysteine may reduce mucus viscosity by stimulating intracellular sialyltransferase to restore the balance between sialic acid mucin and fucoglycoprotein. One study found that L-carboxycysteine can inhibit hydrogen peroxide (H₂O₂)-induced cell damage by activating protein kinase B (Akt) phosphorylation, suggesting that L-carboxycysteine may have antioxidant effects and prevent lung cell apoptosis. Some evidence suggests that L-carboxycysteine can inhibit the NF-κB and ERK1/2 MAPK signaling pathways, thereby reducing TNF-α-induced inflammation in the lungs and other inflammatory pathways. An in vitro study found that L-carboxycysteine can reduce the expression of intercellular adhesion molecule 1 (ICAM-1), thereby inhibiting rhinovirus 14 infection and alleviating airway inflammation.

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Pharmacodynamics
Due to its mucolytic properties, carbocysteine can significantly reduce sputum viscosity, relieving cough, dyspnea, and fatigue. Furthermore, it can reduce respiratory mucus accumulation, thereby preventing lung infections; this is particularly beneficial for preventing acute exacerbations of chronic obstructive pulmonary disease (COPD) caused by bacteria and viruses. In vitro studies have shown that it possesses anti-inflammatory activity and a certain degree of free radical scavenging effect.

Carbocysteine is approved for clinical use as an over-the-counter and prescription mucolytic in many countries. It is used to relieve respiratory symptoms associated with conditions like COPD and other disorders with increased mucus viscosity. Its mechanism involves a combination of mucolytic, anti-inflammatory, and antioxidant actions.

C5H9NO4S

179.19

179.025

638-23-3

(RS)-Carbocisteine;25390-17-4

193653

White to off-white solid powder

1.5±0.1 g/cm3

417.3±45.0 °C at 760 mmHg

208-213 °C (dec.)

206.2±28.7 °C

0.0±2.1 mmHg at 25°C

1.588

0.32

3

6

5

11

161

1

C([C@@H](C(=O)O)N)SCC(=O)O

GBFLZEXEOZUWRN-VKHMYHEASA-N

InChI=1S/C5H9NO4S/c6-3(5(9)10)1-11-2-4(7)8/h3H,1-2,6H2,(H,7,8)(H,9,10)/t3-/m0/s1

(2R)-2-amino-3-(carboxymethylsulfanyl)propanoic acid

Mucofan; DF 1794Y; Carbocysteine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment (e.g. under nitrogen), avoid exposure to moisture.

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

H2O : ~6 mg/mL (~33.48 mM)

Solubility in Formulation 1: 2 mg/mL (11.16 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication (<60°C).

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