Beyond the lungs: Exploring diverse applications of bromhexine and ambroxol.

The respiratory tract is commonly affected in multisystem disorders. Although many drugs have been developed to target various components of these diseases, there is still a need for effective treatments that can address both respiratory and non-respiratory symptoms. Bromhexine and ambroxol are mucolytic agents with a good safety profile that are widely used to treat respiratory conditions. These compounds seem to present several unresolved questions when carrying out their therapeutic effects, suggesting that they may not merely improve mucociliary clearance. These assumptions have provided the basis for researchers to investigate the specific characteristics of bromhexine and ambroxol. This has led to the emergence of several repositionings for this compound. Accordingly, these compounds have also shown potential benefits in the treatment of various extrapulmonary disorders, including neurological disorders, and inflammatory bowel disease. We gathered findings from relevant studies published in English between 1970 and December 2023 by searching databases including PubMed, Google Scholar, Scopus, Embase, and the Cochrane Library. Our findings revealed that most of the research on extrapulmonary uses has been conducted at the preclinical level. Accordingly, more clinical studies are needed to determine the effectiveness of bromhexine and ambroxol in these conditions. This article provides an overview of the potential extrapulmonary applications of bromhexine and ambroxol and discusses the potential advantages of using these drugs in multisystem disorders.

Thiolated polyglycerol sulfate as potential mucolytic for muco-obstructive lung diseases.

Increased disulfide crosslinking of secreted mucins causes elevated viscoelasticity of mucus and is a key determinant of mucus dysfunction in patients with cystic fibrosis (CF) and other muco-obstructive lung diseases. In this study, we describe the synthesis of a novel thiol-containing, sulfated dendritic polyglycerol (dPGS-SH), designed to chemically reduce these abnormal crosslinks, which we demonstrate with mucolytic activity assays in sputum from patients with CF. This mucolytic polymer, which is based on a reportedly anti-inflammatory polysulfate scaffold, additionally carries multiple thiol groups for mucolytic activity and can be produced on a gram-scale. After a physicochemical compound characterization, we compare the mucolytic activity of dPGS-SH to the clinically approved N-acetylcysteine (NAC) using western blot studies and investigate the effect of dPGS-SH on the viscoelastic properties of sputum samples from CF patients by oscillatory rheology. We show that dPGS-SH is more effective than NAC in reducing multimer intensity of the secreted mucins MUC5B and MUC5AC and demonstrate significant mucolytic activity by rheology. In addition, we provide data for dPGS-SH demonstrating a high compound stability, low cytotoxicity, and superior reaction kinetics over NAC at different pH levels. Our data support further development of the novel reducing polymer system dPGS-SH as a potential mucolytic to improve mucus function and clearance in patients with CF as well as other muco-obstructive lung diseases.

Antitussive, Expectorant and Antipyretic Effect of the Ethanolic Extract of the Leaves of Momordica charantia L.

The traditional use of the M. charantia L. plant to treat coughs, fever and expectoration is widely practiced in different cultures, but its effectiveness and safety still require scientific investigation. This study sought to perform a chemical analysis and evaluate the antitussive, expectorant and antipyretic effects of the ethanolic extract of M. charantia leaves (EEMc) in rats and mice. The EEMc was subjected to chemical analysis by HPLC-DAD, revealing the presence of the flavonoids astragalin and isoquercetin. Acute oral toxicity in mice did not result in deaths, although changes in liver weight and stool consistency were observed. EEMc demonstrated an antitussive effect at doses of 100 and 300 mg/kg in mice subjected to cough induction by citric acid nebulization. Furthermore, it showed expectorant activity at a dose of 300 mg/kg, assessed based on the elimination of the phenol red marker in bronchoalveolar lavage. In the evaluation of antipyretic activity in rats, fever induced by Saccharomyces cerevisiae was reduced at all doses tested during the first hour after treatment. This innovative study identified the presence of astragalin and isoquercetin in EEMc and indicated that the extract has antitussive, expectorant and antipyretic properties. Therefore, EEMc presents itself as a promising option in herbal medicine for the treatment of respiratory symptoms and fever.

Proposed mechanisms of action of herbal drugs and their biologically active constituents in the treatment of coughs: an overview.

Various medicinal plants find their use in cough treatment, based on traditions and long-term experience. Pharmacological principles of their action, however, are much less known. Herbal drugs usually contain a mixture of potentially active compounds, which can manifest diverse effects. Expectorant or antitussive effects, which can be accompanied by others, such as anti-inflammatory or antibacterial, are probably the most important in the treatment of coughs. The aim of this review is to summarize the current state of knowledge of the effects of medicinal plants or their constituents on cough, based on reliable pharmacological studies. First, a comprehensive description of each effect is provided in order to explain the possible mechanism of action in detail. Next, the results related to individual plants and substances are summarized and critically discussed based on pharmacological in vivo and in vitro investigation.

Anti-Inflammatory Actions of Expectorants in a Rat Carrageenan-Induced Footpad Edema Model.

S-Carboxymethyl-L-cysteine (SCMS) exhibits sputum-regulating and anti-inflammatory actions. Previous studies reported the anti-inflammatory effects of SCMS on chronic inflammatory diseases, but no study has examined these effects on acute inflammatory diseases. In this study, we investigated the anti-inflammatory effects of SCMS in a rat carrageenan-induced footpad edema model, which is routinely used as an acute inflammation model. Expectorants were administered to rats with footpad edema induced by subcutaneously administering 1%λ-carrageenan to the footpad of the left posterior limb, and the dose dependency of the anti-inflammatory effects was evaluated. As a result, even when the dose of SCMS was increased to 400 mg/kg, there were no inhibitory effects on edema. Furthermore, we examined the inhibitory effects of other expectorants (ambroxol hydrochloride, N-acetyl-L-cysteine, L-cysteine ethylester hydrochloride, and L-cysteine methylester hydrochloride), which were reported to exhibit anti-inflammatory effects on chronic inflammation, on edema. However, none of these expectorants inhibited edema.

Effect of Nebulized BromAc on Rheology of Artificial Sputum: Relevance to Muco-Obstructive Respiratory Diseases.

Respiratory diseases such as cystic fibrosis, COPD, and COVID-19 are difficult to treat owing to viscous secretions in the airways that evade mucocilliary clearance. Earlier studies have shown success with BromAc as a mucolytic agent. Hence, we tested the formulation on two gelatinous airway representative sputa models, to determine whether similar efficacy exist. Sputum lodged in an endotracheal tube was treated to aerosol N-acetylcysteine, bromelain, or their combination (BromAc). After measuring the particle size of aerosolized BromAc, the apparent viscosity was measured using a capillary tube method, whilst the sputum flow was assessed using a 0.5 mL pipette. Further, the concentration of the agents in the sputa after treatment were quantified using chromogenic assays. The interaction index of the different formulations was also determined. Results indicated that the mean particle size of BromAc was suitable for aerosol delivery. Bromelain and N-acetylcysteine affected both the viscosities and pipette flow in the two sputa models. BromAc showed a greater rheological effect on both the sputa models compared to individual agents. Further, a correlation was found between the rheological effects and the concentration of agents in the sputa. The combination index using viscosity measurements showed synergy only with 250 µg/mL bromelain + 20 mg/mL NAC whilst flow speed showed synergy for both combinations of bromelain (125 and 250 µg/mL) with 20 mg/mL NAC. Hence, this study indicates that BromAc may be used as a successful mucolytic for clearing airway congestion caused by thick mucinous immobile secretions.

Ameliorative Effect of Imperatorin on Dermatophagoides pteronyssinus-Induced Allergic Asthma by Suppressing the Th2 Response in Mice.

Imperatorin is a furanocoumarin derivative and an effective ingredient in several Chinese medicinal herbs. It has favorable expectorant, analgesic, and anti-inflammatory effects. In this study, we investigated whether imperatorin has protective effects against Dermatophagoides pteronyssinus (Der p)-induced asthma in mice. Lung and bronchial tissues were histopathologically examined through hematoxylin-eosin staining. The concentrations of immunoglobin E (IgE), IgG1, IgG2a in serum and those of T helper 1 (Th1) and two cytokines and eosinophil-activated chemokines in bronchoalveolar lavage fluid (BALF) were detected using an enzyme immunoassay. Histological examination revealed that imperatorin reduced inflammatory cell infiltration, mucus hypersecretion, and endothelial cell hyperplasia. The examination also indicated that imperatorin could reduce the inflammatory cell count in BALF as well as IgE and IgG1 expression in serum, but IgG2a expression was significantly increased. Imperatorin reduced the production of interleukin (IL)-4, IL-5, and IL-13 by Th2, promoted the production of interferon-γ and IL-12 by Th1, and increased the production of IL-10 in bronchoalveolar lavage fluid. These findings suggest that imperatorin has a considerable anti-inflammatory effect on Der p-induced allergic asthma in mice.

Short-term supplementation with ω-3 polyunsaturated fatty acids modulates primarily mucolytic species from the gut luminal mucin niche in a human fermentation system.

Consumption of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) provides multifaceted health benefits. Recent studies suggest that ω-3 PUFAs modulate the gut microbiota by enhancing health-promoting bacteria, such as the mucin specialist Akkermansia muciniphila. However, these prebiotic properties have been poorly investigated and direct effects on the gut microbiome have never been explored dynamically across gut regions and niches (lumen vs. mucus-associated microbiota). Thus, we studied the effects of 1 week EPA- and DHA-enriched ω-3 fish-oil supplementation on the composition and functionality of the human microbiome in a Mucosal Simulator of the Human Intestinal Microbial Ecosystem (M-SHIME®). Gut microbial communities derived from one individual harvested in two different seasons were tested in duplicate. Luminal and outer mucus-associated microbiota of the ileum, ascending, transverse and descending colons were cultivated over 28 d from fecal inoculates and supplemented with ω-3 PUFAs for the last 7 d. We show that ω-3 PUFA supplementation modulates the microbiota in a gut region- and niche-dependent fashion. The outer mucus-associated microbiota displayed a higher resilience than the luminal mucin habitat to ω-3 PUFAs, with a remarkable blooming of Akkermansia muciniphila in opposition to a decrease of Firmicutes-mucolytic bacteria. The ω-3 PUFAs also induced a gradual and significant depletion of non-mucolytic Clostridia members in luminal habitats. Finally, increased concentrations of the short chain fatty acids (SCFA) propionate in colon regions at the end of the supplementation was associated positively with the bloom of Akkermansia muciniphila and members of the Desulfovibrionia class.

Ambroxol, a mucolytic agent, boosts HO-1, suppresses NF-κB, and decreases the susceptibility of the inflamed rat colon to apoptosis: A new treatment option for treating ulcerative colitis.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease of unknown etiology that increases the risk of developing colorectal cancer and imposes a lifelong healthcare burden on millions of patients worldwide. Current treatment strategies are associated with significant risks and have been shown to be fairly effective. Hence, discovering new therapies that have better efficacy and safety profiles than currently exploited therapeutic strategies is challenging. It has been well delineated that NF-κB/Nrf2 crosstalk is a chief player in the interplay between oxidative stress and inflammation. Ambroxol hydrochloride, a mucolytic agent, has shown antioxidant and anti-inflammatory activity in humans and animals and has not yet been examined for the management of UC. Therefore, our approach was to investigate whether ambroxol could be effective to combat UC using the common acetic acid rat model. Interestingly, a high dose of oral ambroxol (200 mg/kg/day) reasonably improved the microscopic and macroscopic features of the injured colon. This was linked to low disease activity and a reduction in the colonic weight/length ratio. In the context of that, ambroxol boosted Nrf2 activity and upregulated HO-1 and catalase to augment the antioxidant defense against oxidative damage. Besides, ambroxol inactivated NF-κB signaling and its consequent target pro-inflammatory mediators, IL-6 and TNF-α. In contrast, IL-10 is upregulated. Consistent with these results, myeloperoxidase activity is suppressed. Moreover, ambroxol decreased the susceptibility of the injured colon to apoptosis. To conclude, our findings highlight the potential application of ambroxol to modify the progression of UC by its anti-inflammatory, antioxidant, and antiapoptotic properties.

Mucus interaction to improve gastrointestinal retention and pharmacokinetics of orally administered nano-drug delivery systems.

Oral delivery of therapeutics is the preferred route of administration due to ease of administration which is associated with greater patient medication adherence. One major barrier to oral delivery and intestinal absorption is rapid clearance of the drug and the drug delivery system from the gastrointestinal (GI) tract. To address this issue, researchers have investigated using GI mucus to help maximize the pharmacokinetics of the therapeutic; while mucus can act as a barrier to effective oral delivery, it can also be used as an anchoring mechanism to improve intestinal residence. Nano-drug delivery systems that use materials which can interact with the mucus layers in the GI tract can enable longer residence time, improving the efficacy of oral drug delivery. This review examines the properties and function of mucus in the GI tract, as well as diseases that alter mucus. Three broad classes of mucus-interacting systems are discussed: mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems. For each class of system, the basis for mucus interaction is presented, and examples of materials that inform the development of these systems are discussed and reviewed. Finally, a list of FDA-approved mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems is reviewed. In summary, this review highlights the progress made in developing mucus-interacting systems, both at a research-scale and commercial-scale level, and describes the theoretical basis for each type of system.

Mucolytic and Antioxidant Effects of Intranasal Acetylcysteine Use on Acute Rhinosinusitis in Rats with an Acute Rhinosinusitis Model.

INTRODUCTION: The aim of this study was to investigate whether N-acetylcysteine (NAC) is effective in the treatment murine model of acute rhinosinusitis in rats. MATERIALS AND METHODS: Twelve rats were included in the study. The left nasal cavity of all rats was infected with Streptococcus pneumoniae. Group 1 was the group in which NAC was administered into the left nasal cavity twice daily. Group 2 was selected as the control group. All rats were then sterilely sacrificed under anesthesia after intracardiac blood sampling. After sacrifice, sterile culture samples were collected from the posterior nasal cavity. RESULTS: Total oxidant status and oxidative stress index (OSI), interleukin 1ß, interleukin 6, and tumor necrosis factor α levels decreased significantly in the treatment group. Total antioxidant status was significantly increased. There was a statistically significant increase in total serum thiol levels and native thiol levels. Histopathologic evaluation showed a statistically significant decrease in submucosal gland hypertrophy in the treatment group. CONCLUSION: According to our study, intranasal application of NAC can decrease the inflammatory findings in murine acute rhinosinusitis.

Active microbial metabolites study on antitussive and expectorant effects and metabolic mechanisms of platycosides fraction of Platycodonis Radix.

A new method involving gut microbiota biotransformation, spectrum-effect relationship analysis and metabolomics analysis was developed to study the antitussive and expectorant microbial metabolites of platycosides fraction (MPFs) of Platycodonis Radix. Furthermore, their possible metabolic mechanisms were studied for the first time. The findings showed that the antitussive and expectorant effects of the platycosides fraction (PF) were significantly enhanced by the gut microbiota biotransformation. 11 active antitussive microbial metabolites and 12 active expectorant microbial metabolites, which shared 8 components, were successfully screened out via spectrum-effect relationship analysis. The prototypes of the active microbial metabolites could be reversely traced according to the gut microbiota biotransformation pathways. It was found out that one platycoside could produce several active microbial metabolites and several different platycosides could produce the same active microbial metabolite. In addition, the metabolomics analysis showed that both the PF and its active microbial metabolites could regulate the same metabolomic pathways of Linoleic acid metabolism, Arachidonic acid metabolism and Glycerophospholipid metabolism to exert antitussive activity, and regulate the same metabolomic pathway of Arachidonic acid metabolism to exert expectorant activity. These findings suggested the microbial metabolites may be the active forms of the platycosides. Overall, the proposed approach was useful in screening the active microbial metabolites; this work explained the in vivo antitussive and expectorant metabolic mechanisms of multi-constituents, multi-targets and synergistic effects of PF of Platycodonis Radix.

Ex-vivo mucolytic and anti-inflammatory activity of BromAc in tracheal aspirates from COVID-19.

COVID-19 is a lethal disease caused by the pandemic SARS-CoV-2, which continues to be a public health threat. COVID-19 is principally a respiratory disease and is often associated with sputum retention and cytokine storm, for which there are limited therapeutic options. In this regard, we evaluated the use of BromAc®, a combination of Bromelain and Acetylcysteine (NAC). Both drugs present mucolytic effect and have been studied to treat COVID-19. Therefore, we sought to examine the mucolytic and anti-inflammatory effect of BromAc® in tracheal aspirate samples from critically ill COVID-19 patients requiring mechanical ventilation. METHOD: Tracheal aspirate samples from COVID-19 patients were collected following next of kin consent and mucolysis, rheometry and cytokine analysis using Luminex kit was performed. RESULTS: BromAc® displayed a robust mucolytic effect in a dose dependent manner on COVID-19 sputum ex vivo. BromAc® showed anti-inflammatory activity, reducing the action of cytokine storm, chemokines including MIP-1alpha, CXCL8, MIP-1b, MCP-1 and IP-10, and regulatory cytokines IL-5, IL-10, IL-13 IL-1Ra and total reduction for IL-9 compared to NAC alone and control. BromAc® acted on IL-6, demonstrating a reduction in G-CSF and VEGF-D at concentrations of 125 and 250 µg. CONCLUSION: These results indicate robust mucolytic and anti-inflammatory effect of BromAc® ex vivo in tracheal aspirates from critically ill COVID-19 patients, indicating its potential to be further assessed as pharmacological treatment for COVID-19.

Preparation of Naringenin Nanosuspension and Its Antitussive and Expectorant Effects.

Naringenin (NRG) is a natural flavonoid compound abundantly present in citrus fruits and has the potential to treat respiratory disorders. However, the clinical therapeutic effect of NRG is limited by its low bioavailability due to poor solubility. To enhance the solubility, naringenin nanosuspensions (NRG-NSps) were prepared by applying tocopherol polyethylene glycol succinate (TPGS) as the nanocarrier via the media-milling method. The particle size, morphology, and drug-loading content of NRG-NSps were examined, and the stability was evaluated by detecting particle size changes in different physiological media. NRG-NSps exhibited a flaky appearance with a mean diameter of 216.9 nm, and the drug-loading content was 66.7%. NRG-NSps exhibited good storage stability and media stability. NRG-NSps presented a sustainable release profile, and the cumulative drug-release rate approached approximately 95% within 7 d. NRG-NSps improved the antitussive effect significantly compared with the original NRG, the cough frequency was decreased from 22 to 15 times, and the cough incubation period was prolonged from 85.3 to 121.6 s. Besides, NRG-NSps also enhanced expectorant effects significantly, and phenol red secretion was increased from 1.02 to 1.45 µg/mL. These results indicate that NRG-NSps could enhance the bioavailability of NRG significantly and possess a potential clinical application.

GesEPOC 2021 y GOLD 2021. ¿Más cerca o más lejos? / GesEPOC 2021 and GOLD 2021. Closer Together or Further Apart?

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Chemical Analysis by LC-MS of Cannabis sativa Root Samples from Northeast Brazil and Evaluation of Antitussive and Expectorant Activities.

Cannabis sativa is a millenary medicinal plant. However, contrary to worldwide paradigm-shifting, countries like Brazil still prohibit C. sativa cultivation and its medicinal use, even though many populations use aerial parts and roots of this plant for healthcare. As such, the objective of this work was to identify substances in the samples of the C. sativa roots, tracing a correlation with antitussive and expectorant effects. Therefore, samples of C. sativa roots were donated by the Polícia Federal Brasileira, and its aqueous extract (AECsR) was prepared with subsequent lyophilization, to maintain the material stability. After that, the material was analyzed by LC-MS to observe its chemical profile. Four samples (AECsR-A, B, C, and D) were tested in animal models of citric acid-induced cough (0.4 M) and phenol red expectoration (500 mg/kg). Using LC-MS it was possible to identify 5 molecules in C. sativa roots: p-coumaroyltyramine, tetrahydrocannabinol-C4, feruoiltyramine, anhydrocanabisativine, and cannabisativine. In experimental protocols, male mice (Mus musculus) were treated with samples of AECsR at doses of 12.5, 25, or 50 mg/kg regardless of the pharmacological test. In these tests, all samples showed the potential to treat cough and promote fluid expectoration, differing only in the dose at which these effects were observed. Therefore, the data showed that the C. sativa roots of the Brazilian Northeast showed antitussive and expectorant effects, even with intense secondary metabolites' variation, which alters its potency, but not its effect. This highlights the importance of this medicinal plant for future therapy and corroborates to traditional use.

Bromhexine and its inhibitory effect on lipase - kinetics and structural study.

Lipase hydrolyses the ester bonds in triglyceride. It is an important enzyme in medicine and industry. Some pathogen bacteria use this exoenzyme to disrupt the extracellular matrix of host organisms. Pseudomonas uses various extracellular enzymes such as lipase to invade its host. In this report, for the first time, bromhexine was introduced as an inhibitor of lipase. Bromhexine is a mucolytic drug which is used in the treatment of respiratory tract disorders. The results showed that bromhexine inhibited the enzyme by competitive inhibition. IC50 and Ki values of the drug were 0.049 mM and 0.02 mM, respectively. Arrhenius plot showed that the drug reduced the activation energy. The enzyme was purified and SDS-PAGE showed that its molecular weight is 13 kDa. Fluorescence measurement revealed that binding of the drug to lipase could make structural changes in the enzyme. Inhibition of lipase by bromhexine could be applicable in medicine.

Anti-inflammatory, expectorant, and antitussive properties of Kyeongok-go in ICR mice.

CONTEXT: Kyeongok-go (KOG) is a traditional mixed herb preparation consisting of Panax ginseng CA Meyer (Araliaceae), Poria cocos Wolf (Polyporaceae), Rehmannia glutinosa (Gaertner) Liboschitz ex Steudel (Orobanchaceae), and honey. Various pharmacological effects of KOG are reported, but the efficacy on respiratory diseases has not been evaluated. OBJECTIVE: The anti-inflammatory, expectorant, and antitussive properties of KOG were examined using animal models of respiratory diseases. MATERIALS AND METHODS: KOG (100, 200, and 400 mg/kg) was orally administered to ICR mice (n = 8) once a day for 11 days. Anti-inflammatory effects of vehicle, xylene, KOG and DEXA (1 mg/kg) were determined by monitoring edoema and redness of treated ears, and measuring the relative and absolute weight of each ear. Expectorant properties of vehicle, KOG and AM (250 mg/kg) were evaluated by observing body surface redness, and the amount of mucous secreted by the trachea. The antitussive potential of vehicle, NH4OH, KOG and TB (50 mg/kg) was evaluated by monitoring changes in the number of coughs (for 6 min). RESULTS: KOG (400 mg/kg) treated mice showed 31.29% and 30.72% (p < 0.01) decreases in the relative and absolute weights of each ear relative to xylene control mice, 39.06% increases (p < 0.01) in TLF OD values relative to intact vehicle control mice, and 59.53% decrease (p < 0.01) in coughing compared to NH4OH control mice. Dose-dependent changes were observed in all experimental models. CONCLUSIONS: KOG may be a potential therapeutic agent for the treatment of various respiratory diseases, particularly those caused by environmental toxins.

Disulfide disruption reverses mucus dysfunction in allergic airway disease.

Airway mucus is essential for lung defense, but excessive mucus in asthma obstructs airflow, leading to severe and potentially fatal outcomes. Current asthma treatments have minimal effects on mucus, and the lack of therapeutic options stems from a poor understanding of mucus function and dysfunction at a molecular level and in vivo. Biophysical properties of mucus are controlled by mucin glycoproteins that polymerize covalently via disulfide bonds. Once secreted, mucin glycopolymers can aggregate, form plugs, and block airflow. Here we show that reducing mucin disulfide bonds disrupts mucus in human asthmatics and reverses pathological effects of mucus hypersecretion in a mouse allergic asthma model. In mice, inhaled mucolytic treatment loosens mucus mesh, enhances mucociliary clearance, and abolishes airway hyperreactivity (AHR) to the bronchoprovocative agent methacholine. AHR reversal is directly related to reduced mucus plugging. These findings establish grounds for developing treatments to inhibit effects of mucus hypersecretion in asthma.

The Multifaceted Therapeutic Role of N-Acetylcysteine (NAC) in Disorders Characterized by Oxidative Stress.

Oxidative stress, which results in the damage of diverse biological molecules, is a ubiquitous cellular process implicated in the etiology of many illnesses. The sulfhydryl-containing tripeptide glutathione (GSH), which is synthesized and maintained at high concentrations in all cells, is one of the mechanisms by which cells protect themselves from oxidative stress. N-acetylcysteine (NAC), a synthetic derivative of the endogenous amino acid L-cysteine and a precursor of GSH, has been used for several decades as a mucolytic and as an antidote to acetaminophen (paracetamol) poisoning. As a mucolytic, NAC breaks the disulfide bonds of heavily cross-linked mucins, thereby reducing mucus viscosity. In vitro, NAC has antifibrotic effects on lung fibroblasts. As an antidote to acetaminophen poisoning, NAC restores the hepatic GSH pool depleted in the drug detoxification process. More recently, improved knowledge of the mechanisms by which NAC acts has expanded its clinical applications. In particular, the discovery that NAC can modulate the homeostasis of glutamate has prompted studies of NAC in neuropsychiatric diseases characterized by impaired glutamate homeostasis. This narrative review provides an overview of the most relevant and recent evidence on the clinical application of NAC, with a focus on respiratory diseases, acetaminophen poisoning, disorders of the central nervous system (chronic neuropathic pain, depression, schizophrenia, bipolar disorder, and addiction), cardiovascular disease, contrast-induced nephropathy, and ophthalmology (retinitis pigmentosa).