Depressant effect of ambroxol on stimulated functional responses and cell death in rat alveolar macrophages exposed to silica in vitro

Ambroxol for the treatment of fibromyalgia: science or fiction?

Fibromyalgia appears to present in subgroups with regard to biological pain induction, with primarily inflammatory, neuropathic/neurodegenerative, sympathetic, oxidative, nitrosative, or muscular factors and/or central sensitization. Recent research has also discussed glial activation or interrupted dopaminergic neurotransmission, as well as increased skin mast cells and mitochondrial dysfunction. Therapy is difficult, and the treatment options used so far mostly just have the potential to address only one of these aspects. As ambroxol addresses all of them in a single substance and furthermore also reduces visceral hypersensitivity, in fibromyalgia existing as irritable bowel syndrome or chronic bladder pain, it should be systematically investigated for this purpose. Encouraged by first clinical observations of two working groups using topical or oral ambroxol for fibromyalgia treatments, the present paper outlines the scientific argument for this approach by looking at each of the aforementioned aspects of this complex disease and summarizes putative modes of action of ambroxol. Nevertheless, at this point the evidence basis for ambroxol is not strong enough for clinical recommendation.

Biofilm-dependent airway infections: a role for ambroxol?

Biofilms are a key factor in the development of both acute and chronic airway infections. Their relevance is well established in ventilator associated pneumonia, one of the most severe complications in critically ill patients, and in cystic fibrosis, the most common lethal genetic disease in Caucasians. Accumulating evidence suggests that biofilms could have also a role in chronic obstructive pulmonary disease and their involvement in bronchiectasis has been proposed as well. When they grow in biofilms, microorganisms become multidrug-resistant. Therefore the treatment of biofilm-dependent airway infections is problematic. Indeed, it still largely based on measures aiming to prevent the formation of biofilms or remove them once that they are formed. Here we review recent evidence suggesting that the mucokinetic drug ambroxol has specific anti-biofilm properties. We also discuss how additional pharmacological properties of this drug could be beneficial in biofilm-dependent airway infections. Specifically, we review the evidence showing that: 1-ambroxol exerts anti-inflammatory effects by inhibiting at multiple levels the activity of neutrophils, and 2-it improves mucociliary clearance by interfering with the activity of airway epithelium ion channels and transporters including sodium/bicarbonate and sodium/potassium/chloride cotransporters, cystic fibrosis transmembrane conductance regulator and aquaporins. As a whole, the data that we review here suggest that ambroxol could be helpful in biofilm-dependent airway infections. However, considering the limited clinical evidence available up to date, further clinical studies are required to support the use of ambroxol in these diseases.

Ambroxol in the 21st century: pharmacological and clinical update

BACKGROUND

Belonging to the group of expectorants, ambroxol is an active substance with a long history that influences parameters considered to be the basis for the physiological production and the transport of the bronchial mucus. Therefore, ambroxol's indication is 'secretolytic therapy in acute and chronic bronchopulmonary diseases associated with abnormal mucus secretion and impaired mucus transport'.

OBJECTIVE

The aim of this review is to evaluate the pharmacological and clinical data on the mucokinetic compound ambroxol.

METHODS

The existing database that covers >40 years of pharmacological research and clinical development was analysed. Only studies with adequate study design were evaluated.

CONCLUSION

Ambroxol is shown to exert several activities: i) secretolytic activity (i.e., promotes mucus clearance, facilitates expectoration, and eases productive cough); ii) anti-inflammatory and antioxidant activity; and iii) a local anaesthetic effect through sodium channel blocking at the level of the cell membrane. The reduction on chronic obstructive pulmonary disease exacerbations is consistent and clinically relevant. The anaesthetic effect is a new pharmacological action that could be beneficial in the management of acute respiratory tract infections. The efficacy and safety of ambroxol is well established.

Ambroxol: a CNS drug?

For almost three decades ambroxol has been used in the therapy of airway diseases. In 2002, ambroxol lozenges were marketed for the treatment of sore throat making use of its local anesthetic effect. Detailed investigations of ambroxol with modern pharmacological methods yielded additional interesting results: ambroxol has been found to have profound effects on neuronal voltage-gated Na(+), as well as Ca(2+) channels, and to effectively reduce chronic inflammatory and neuropathic pain in rodents. The question was raised whether ambroxol affects the central nervous system (CNS) directly, or whether its effects can be explained solely by a peripheral action. This issue was addressed by re-examining pharmacokinetics, as well as toxicology of ambroxol. It has been concluded that even at the highest clinically used doses ambroxol does not have significant direct effects on the CNS. At clinically relevant plasma concentrations ambroxol either does not penetrate blood-brain barrier, or its brain levels are too low to cause relevant effects. The analgesic effects of ambroxol by either systemic administration to animals, or by topical application in humans can be explained by ambroxol-induced blockade of ion channels in peripheral neurons.

Silica induces macrophage cytokines through phosphatidylcholine-specific phospholipase C with hydrogen peroxide

Silica particle-associated inflammation is implicated in the genesis of several pulmonary diseases, including silicosis and lung cancer. In this study we investigated the role of phosphatidylcholine-specific phospholipase C (PC-PLC) in silica-stimulated induction of TNF-alpha and IL-1beta and how PC-PLC activity is regulated by silica in a rat alveolar macrophage model. We demonstrated that inhibition of PC-PLC, which was achieved with tricychodecan-9-yl-xanthate (D609), blocked the silica-stimulated induction of TNF-alpha and IL-1beta in alveolar macrophage, suggesting that PC-PLC is involved in the silica-associated inflammatory response. PC-PLC activity was increased significantly by silica exposure, and this could be inhibited by MnTBAP, which catalyzes both the dismutation of O2.- to O2 and H2O2 and the dismutation of H2O2 to O2 and H2O, revealing that PC-PLC activity is regulated in a redox-dependent manner. This is further confirmed by the finding that PC-PLC activity was increased by exogenous H2O2. The intracellular calcium chelator BAPTA blocked the H2O2-increased PC-PLC activity, while the calcium ionophore, A23187, enhanced PC-PLC activity. The data indicate that PC-PLC plays critical roles in the silica-associated inflammatory response and that PC-PLC is regulated through redox- and calcium-dependent manners in alveolar macrophages.

Phospholipid concentration in lung lavage fluid as biomarker for pulmonary fibrosis

Pulmonary surfactant comprised primarily of phospholipids is a phospholipid-protein complex synthesized by type II alveolar epithelial cells or Clara cells and secreted to the pulmonary alveoli. As changes have been found in phospholipid concentrations in the bronchoalveolar lavage fluid (BALF) of patients with pulmonary fibrosis, phospholipid is considered to be involved in the process of fibrois/fibrotic process. Therefore, we made a crystalline silica rat model and measured phospholipid concentrations in lung lavage fluid in order to study the relationship of phospholipid to particle-induced pulmonary fibrosis. Eight-week-old Wistar male rats (n = 35) were injected with 2 mg crystalline silica particles suspended in 0.4 ml physiological saline. Rats in the control group (n = 35) were injected with physiological saline only. There were 7 rats in each of the ten subgroups. Rats were sacrificed and dissected at 3 days, 1 wk, 1 mo, 3 mo, and 6 mo after injection. Bronchoalveolar lavage was conducted on bronchoalveoli recovered from the right lung of each rat, the lavage fluid was centrifuged, and the supernatant was used to measure phospholipid concentration. The results were compared with previously reported inflammation scores. Phospholipid concentrations in lung lavage fluid for the exposed group showed a statistically significant increase compared to the control group throughout the observation period. Moreover, when compared to histopathologically examined inflammation scores, a positive correlation was found between the two. Judging from the facts that phospholipid concentrations in lung lavage fluid increased and that this increase correlated with the severity of inflammation, this experiment indicated that phospholipids are involved in particle-induced lung disorders.

Leukotrienes enhance the bactericidal activity of alveolar macrophages against Klebsiella pneumoniae through the activation of NADPH oxidase

Leukotrienes (LTs) are lipid mediators that participate in inflammatory diseases and innate immune function. We sought to investigate the importance of LTs in regulating the microbicidal activity of alveolar macrophages (AMs) and the molecular mechanisms by which this occurs. The role of LTs in enhancing AM microbicidal activity was evaluated pharmacologically and genetically using in vitro challenge with Klebsiella pneumoniae. Exogenous LTs increased AM microbicidal activity in a dose- and receptor-dependent manner, and endogenous production of LTs was necessary for optimal killing. Leukotriene B4 (LTB4) was more potent than cysteinyl LTs. An important role for nicotinamide adenine dinucleotide (NADPH) oxidase in LT-induced microbicidal activity was indicated by the fact that bacterial killing was abrogated by the NADPH oxidase inhibitor diphenyleneiodonium (DPI; 10 microM) and in AMs derived from gp91phox-deficient mice. By contrast, LT-induced microbicidal activity was independent of the generation of nitric oxide. LTs increased H2O2 production, and LTB4 was again the more potent agonist. Both classes of LTs elicited translocation of p47phox to the cell membrane, and LTB4 induced phosphorylation of p47phox in a manner dependent on protein kinase C-delta (PKC-delta) activity. In addition, the enhancement of microbicidal activity by LTs was also dependent on PKC-delta activity. Our results demonstrate that LTs, especially LTB4, enhanceAM microbicidal activity through the PKC-delta-dependent activation of NADPH oxidase.

Inhibition of bleomycin-induced cell death in rat alveolar macrophages and human lung epithelial cells by ambroxol

The mitochondrial permeability transition is recognized to be involved in toxic and oxidative forms of cell injury. In the present study, we investigated the effect of ambroxol against the cytotoxicity of bleomycin (BLM) by looking at the effect on the mitochondrial membrane permeability in alveolar macrophages and lung epithelial cells. Alveolar macrophages or lung epithelial cells exposed to BLM revealed the loss of cell viability and increase in caspase-3 activity. Ambroxol (10-100 microM) reduced the 75 mU/mL BLM-induced cell death and activation of caspase-3 in macrophages or epithelial cells. It reduced the condensation and fragmentation of nuclei caused by BLM in macrophages. Ambroxol alone did not significantly cause cell death. Treatment of alveolar macrophages with BLM resulted in the decrease in transmembrane potential in mitochondria, cytosolic accumulation of cytochrome c, increase in formation of reactive oxygen species (ROS) and depletion of GSH. Ambroxol (10-100 microM) inhibited the increase in mitochondrial membrane permeability, ROS formation and decrease in GSH contents due to BLM in macrophages. Ambroxol exerted a scavenging effect on hydroxyl radicals and nitric oxide and reduced the iron-mediated formation of malondialdehyde and carbonyls in liver mitochondria. It prevented cell death due to SIN-1 in lung epithelial cells. The results demonstrate that ambroxol attenuates the BLM-induced viability loss in alveolar macrophages or lung epithelial cells. This effect may be due to inhibition of mitochondrial damage and due to the scavenging action on free radicals.

Depressant effects of ambroxol and erdosteine on cytokine synthesis, granule enzyme release, and free radical production in rat alveolar macrophages activated by lipopolysaccharide

The present study examined the effects of ambroxol and erdosteine, bronchial expectorants, on the cytokine synthesis, granule enzyme release, and free radical production in rat alveolar macrophages activated by lipopolysaccharide. Ambroxol and erdosteine significantly decreased the production of tumour necrosis factors-alpha, interleukin-1beta, and interleukin-6 in alveolar macrophages activated by lipopolysaccharide. These drugs significantly reduced the production of superoxide anion, hydrogen peroxide, and nitric oxide and the release of acid phosphatase and lysozyme in lipopolysaccharide-activated macrophages. Ambroxol and erdosteine showed no scavenging effect on superoxide anion and hydrogen peroxide, whereas both drugs effectively decomposed nitric oxide. The results show that ambroxol and erdosteine may inhibit the responses, including cytokine synthesis and free radical production, in rat alveolar macrophages activated by lipopolysaccharide. Unlike the production of reactive oxygen species, the inhibitory effect of ambroxol and erdosteine on the production of nitric oxide in lipopolysaccharide-activated alveolar macrophages may be accomplished by a scavenging action on the species and inhibition of the respiratory burst.

Ambroxol inhibits peroxynitrite-induced damage of alpha1-antiproteinase and free radical production in activated phagocytic cells

The present study examined the effect of ambroxol on toxic action of peroxynitrite and the respiratory burst in activated phagocytic cells. Ambroxol decreased the inactivation or destruction of alpha1-antiproteinase induced by peroxynitrite (ONOO-) or hypochlorous acid (HOCl), which was similar to penicillamine and glutathione and was greater than diclofenac sodium and naproxen sodium. Ambroxol significantly decreased ONOO--mediated tyrosine nitration and iron plus EDTA-mediated degradation of 2-deoxy-D-ribose. Ambroxol significantly attenuated the production of superoxide, hydrogen peroxide, HOCl, and nitric oxide in fMLP- or IL-1-activated phagocytic cells, while the inhibitory effects of antiinflammatory and thiol compounds were only observed in HOCl production. Ambroxol and antiinflammatory drugs did not show a cytotoxic effect on macrophages. The results suggest that ambroxol protects tissue components against oxidative damage by an action different from antiinflammatory drugs. Ambroxol may interfere with oxidative damage of alpha1-antiproteinase through a scavenging action on ONOO- and HOCl and inhibition of the respiratory burst of phagocytic cells.