Antioxidant activity of hyaluronic acid investigated by means of chemiluminescence of equine neutrophil bursts and electron paramagnetic resonance spectroscopy.

Activated neutrophils (PMNs), the ROS/RNS released by PMNs and the derived inflammatory processes are involved in the pathogenesis and progression of human inflammatory airway diseases. Similar diseases are also present in horses which suffer from recurrent airway obstruction (RAO), exercise-induced pulmonary haemorrhage (EIPH) and inflammatory airway diseases (IAD). Hyaluronic acid (HA) plays numerous roles in modulating inflammatory processes. The aim of this study was to examine whether a preparation of HA (MW 900 000 Da) interferes with ROS/RNS during the course of equine PMN respiratory bursts, and to establish the lowest concentration at which it still has antioxidant activity by means of luminol-amplified chemiluminescence (LACL). Electron paramagnetic resonance (EPR) spectroscopy was also used to investigate the direct antiradical activity of HA. The hydroxyl radical was significantly scavenged in a concentration-dependent manner at HA concentrations ranging from 2.5 to 0.16 mg/mL. Superoxide anion, Tempol radical and the ABTS(•+) were significantly inhibited at concentrations ranging from 2.5 to 0.62 mg/mL. The LACL of stimulated equine neutrophils showed that HA induced a statistically significant concentration-effect reduction from 5 mg/mL to 1.25 mg/mL. These findings were confirmed also when l-Arg was added to investigate the inhibition of the resulting peroxynitrite anion. Our findings indicate that, in addition to the human use, HA can also be used to antagonize the oxidative stress generated by free radicals in horses peripheral blood mononuclear cells (PBMCs). In order to achieve therapeutic concentrations, a direct aerosol administration to horses with horse respiratory diseases can be considered, as this route of application is also recommended in human medicine.

Diclofenac-Choline Antioxidant Activity Investigated by means of Luminol Amplified Chemiluminescence of Human Neutrophil Bursts and Electron Paramagnetic Resonance Spectroscopy.

A new diclofenac salt called diclofenac-choline (DC) has recently been proposed for the symptomatic treatment of oropharyngeal inflammatory processes and pain because its greater water solubility allows the use of high concentrations, which are useful when the contact time between the drug and the oropharyngeal mucosa is brief, as in the case of mouthwashes or spray formulations. The antioxidant activity of DC has not yet been investigated, and so the aim was to use luminol-amplified-chemiluminescence (LACL) to verify whether various concentrations of DC (1.48, 0.74 and 0.37 mg/mL for incubation times of 2, 4 and 8 min) interfere with oxygen and nitrogen radicals during the course of human neutrophils respiratory bursts; electron paramagnetic resonance (EPR) spectroscopy was used to investigate its direct antiradical (scavenger) activity. The EPR findings showed that DC has concentration-dependent scavenging activity against the ABTS, the DPPH, and the hydroxyl radicals, but no activity on superoxide anion, as has been previously reported in the case of other NSAIDs. LACL revealed an inhibitory effect that was statistically significant after only 2 min of incubation, and similar after 4 and 8 min. The effects on the peroxynitrite radical paralleled those observed in the previous test. High concentrations and short incubation times showed that there is no interference on PMN viability, and so the inhibitory findings must be attributed to the effect of the drug. The anti-inflammatory effects of DC cannot be attributed solely to the inhibition of prostaglandin synthesis, but its effects on free radicals and neutrophil bursts suggest that they may contribute to its final therapeutic effect.

Comparative antioxidant activity of cultivated and wild Vaccinium species investigated by EPR, human neutrophil burst and COMET assay.

OBJECTIVES: The Vaccinium (V.) spp. berries are considered a source of antioxidants, mainly belonging to polyphenols, specifically flavonoids and anthocyanins. Wild genotypes generally contain more antioxidants than cultivated counterparts. So, seven different antioxidants assays on extracts from cultivated and wild Vaccinium berries were performed, to evaluate their difference in terms of bioactivity on oxidative protection and minimum dosage to have a significant action. MATERIALS AND METHODS: Four cell-free antioxidant assays (ABTS radical scavenging and electronic paramagnetic resonance using Fremy's salt, superoxide anion and hydroxyl radical), and three assays on human cells (two luminol amplified chemiluminescence, LACL, one on DNA damage, COMET) were used to measure the effects of cultivated blueberry (V. corymbosum) and wild bilberry (V. myrtillus) on the differently induced oxidative stress. Concentrations vs activity patterns were obtained by successive dilutions of extracts in order to identify both EC50 and minimum significant activity (MSA). RESULTS: All the assays (except for the hydroxyl radical scavenging) showed a good relationship mainly with anthocyanin and polyphenol content and the significant greater activity of wild Vaccinium extracts. In fact, LACL data gave an EC50 of 11.8 and an MSA of 5.2 g were calculated as fresh weight dosage in cultivated berries, compared with lower doses in wild berries, EC50 of 5.7 g and MSA of 3.4 g. CONCLUSIONS: Wild Vaccinium extracts averaged 3.04 and 2.40 fold more activity than cultivated extracts by EC50 and MSA, respectively. COMET assay confirmed the stronger action on DNA protection in wild samples.

Characterisation of the antioxidant effects of Aesculus hippocastanum L. bark extract on the basis of radical scavenging activity, the chemiluminescence of human neutrophil bursts and lipoperoxidation assay.

OBJECTIVES: Oxidative stress is increasingly recognised as a pivotal factor that plays a number of roles in the inflammatory response to environmental signals. It has been claimed that Aesculus hippocastanum extracts have antioxidant and anti-inflammatory activity, but these claims are mainly based on the results of chemical reactions and folk-medicine. MATERIALS AND METHODS: The aim of this study was to examine whether a bark extract of Aesculus hippocastanum interferes with reactive oxygen/nitrogen species (ROS/RNS) during the course of human neutrophil respiratory bursts, and to establish the lowest concentration at which it still has antioxidant activity by means of luminol amplified chemiluminescence (LACL). We also studied its ability to counteract lipid peroxidation (LPO) in human cells. Before investigating its antioxidant effects on human cells, we analysed its scavenging activity against ABTS*+, hydroxyl radical, superoxide anion, and Fremy's salt (those last three by means of electron paramagnetic resonance (EPR) spectrometry). RESULTS: The extract of Aesculus hippocastanum exerted its anti-ROS/RNS activity in a concentration-dependent manner with significant effects being observed for even very low concentrations: 10 microg/ml without L-Arg, and 5 microg/ml when L-Arg was added to the fMLP test. The LPO assay confirmed these results, which were paralleled by the EPR study. CONCLUSIONS: These findings are interesting for improving the antioxidant network and restoring redox balance in human cells, and extend the possibility of using plant-derived molecules to antagonise the oxidative stress generated in living organisms when the balance is in favour of free radicals as a result of the depletion of cell antioxidants.

Visual analysis of vaginal cell binding and retention of a gynecological douche.

AIM: Gynecological douches may contain various molecules that need to cover and be retained by cutaneous and mucosal cells if they are to act efficaciously in treating local conditions. The aim of this study was to investigate the possibility of directly visualising the ability of a commercial medical gynecological douche to bind to, and be retained by human vaginal cells. METHODS: The commercial gynecological douche under study was "Saugella Attiva douche", bought at local chemist. The vaginal epithelial cells were obtained from healthy, non-pregnant, regularly menstruating women aged 24-52 years. The cells were obtained from the mucosal surface of the mid-vaginal wall by means of gentle scraping with a sterile spatula. Ferric oxide particles and Escherichia coli were used as inorganic and organic markers in order to visualize the adherence of the transparent thin film of a gynecological douche to human vaginal cells by means of Nomarski interference contrast microscopy and scanning electron microscopy. RESULTS: Both markers made it possible to clearly visualize the binding and retention of the transparent thin layer of the douche also at the dilution 1:2 and 1:4. CONCLUSIONS: The fact that the douche can be locally retained is useful because its formulation contains thymol and eugenol, which are known to have antibacterial, antifungal and antioxidant effects but need a period of contact before they act fully.

A prospective, randomized, double-blind comparison between parecoxib and ketorolac for early postoperative analgesia following nasal surgery.

BACKGROUND: The aim of this prospective, randomized, double-blind study was to compare the efficacy of parecoxibfor postoperative analgesia after endoscopic turbinate and sinus surgery, with the non-selective non-steroid anti-inflammatory drug (NSAID), ketorolac. METHODS: A total of 50 patients with an ASA physical status I-II, receiving functional endoscopic sinus surgery (FESS) and endoscopic turbinectomy after local infiltration with 1% mepivacaine, were randomly assigned to receive intravenous administration of either 40 mg parecoxib (N.=25) or 30 mg ketorolac (N.=25), 15 min before the discontinuation of anaesthesia and then every 8 h postoperatively. A blinded observer recorded the incidence and severity of pain upon admission to the postanesthesia care unit (PACU), as well as 10, 20, and 30 min after PACU admission. Thereafter, observations continued every 1 h for the first 6 h, and then 12 h and 24 h after surgery. RESULTS: The area under the curve of the visual analogue scale (AUCVAS) calculated during the study period was 635 (26-1 413) in the Parecoxib group and 669 (28-1 901) in the Ketorolac group (P=0.54). Rescue morphine analgesia was required by 12 patients (48%) in the Parecoxib group and 11 patients (44%) in the Ketorolac group (P<0.05); while mean morphine consumption was 5 +/- 2.5 mg and 5 +/- 2.0 mg in Ketorolac and Parecoxib groups, respectively (P<0.05). No differences in the incidence of side effects were recorded between the two groups. Patient satisfaction was similarly high in both groups, and all patients were discharged uneventfully 24 h after surgery. CONCLUSION: In patients undergoing endoscopic nasal surgery and local infiltration with 1% mepivacaine, parecoxib administered before discontinuing general anesthesia is as effective in treating early postoperative pain as ketorolac.

Inhibitory activity of thymol against the formation and viability of Candida albicans hyphae.

As the capacity of Candida albicans to produce hyphae is considered an important virulence factor in the pathogenesis of candiasis, the aim of this study was to investigate whether thymol, the major component of thyme oil, can interfere with the filamentous forms of Candida albicans and their viability. The morphological transition from yeasts to filamentous forms was investigated by analysing the morphological index (MI), which classifies the differentiated forms and blastoconidia; viability was investigated by means of fluorescence microscopy using a new SYTO-9 and propidium iodide method previously used to stain only blastoconidia. Without thymol, there was an average of 94.00 +/- 3.06% hyphal forms. After 6 h of incubation with 1x MIC (125 microg ml(-1)), 1/2x MIC and 1/4x MIC of thymol, filamentation was, respectively, 14.33 +/- 8.25%, 28.33 +/- 7.17% and 45.67 +/- 8.09% in comparison with control (all statistically significant). In the absence of thymol, viable cells accounted for an average of 93.00 +/- 4.00% whereas, after 6 h of incubation with 1x MIC, 1/2x MIC and 1/4x MIC of thymol, the presence of 54.33 +/- 1.86%, 29.00 +/- 3.61% and 23.00 +/- 2.52% of yellow-orange coloured forms indicated damaged membranes and reduced viability. Our findings show that thymol interferes with the formation and viability of hyphae. This can be attributed to the characteristics of thymol disturbing Candida cell membranes and metabolism, probably by affecting fungal cell-wall synthesising enzymes.

The post-antibiotic effects of rokitamycin (a 16-membered ring macrolide) on susceptible and erythromycin-resistant strains of Streptococcus pyogenes.

The post-antibiotic effects (PAEs) on susceptible and erythromycin-resistant strains of Streptococcus pyogenes (M phenotype and inducibly resistant) of rokitamycin and erythromycin were investigated in vitro using microbiological impedance measurement. Exposure of susceptible S. pyogenes strains to 1/4, 1/2, 1 and 2 MIC erythromycin and rokitamycin resulted in PAEs of rokitamycin in the same order of magnitude as those of erythromycin and that were dose dependent. The duration of rokitamycin PAEs in erythromycin-resistant S. pyogenes strains (M phenotype and those with inducible resistance) were comparable with those observed in susceptible strains. This was not the case for erythromycin. The investigation showed that a 16-membered ring macrolide such as rokitamycin has different PAEs from those of a 14-membered ring macrolide such as erythromycin. They also indicated that, as the PAEs of rokitamycin on the M phenotype and inducible resistant strains were comparable with those on susceptible strains, no re-evaluation of therapeutic dosing regimens was required.

Gemifloxacin: effects of sub-inhibitory concentrations on various factors affecting bacterial virulence.

This study investigated the ability of sub-MICs of gemifloxacin to interfere with the bacterial virulence parameters of adhesiveness, haemagglutination, hydrophobicity and motility, as well as their interactions with host neutrophilic defences such as phagocytosis, killing and respiratory bursts. The adhesiveness of both Escherichia coli and Staphylococcus aureus was significantly reduced to a subinhibitory concentration of 1/32 MIC. Indirect fimbriation parameters, such as hydrophobicity and haemagglutination were significantly reduced at a concentration of 1/8 MIC, as was migration (swarming). Phagocytosis and the respiratory burst measured by means of chemiluminescence were not affected, but killing was significantly increased from 1/2 to 1/8 MIC. The interpolation of these pharmacodynamic findings with pharmacokinetic curves indicates that sub-MIC concentrations of gemifloxacin can prolong antimicrobial effects on virulence determinants up to 27 h after the antimicrobial concentration has fallen below the MIC value.

Morphostructural damage and the inhibition of bacterial adhesiveness of Staphylococcus aureus and Moraxella catarrhalis induced by moxifloxacin.

The aim of this study was to investigate the ability of moxifloxacin to interfere with the mechanism of bacterial adhesion and disrupt the morphological and structural integrity of bacteria. Three Staphylococcus aureus and three Moraxella catarrhalis strains were grown in the presence of 1/2-1/128 minimum inhibitory concentration (MIC) serial dilutions and incubated with human epithelial cells. A significant decrease in adhesion was observed from 1/2 MIC to 1/64 MIC for S. aureus, and from 1/2 MIC to 1/16 MIC for M. catarrhalis. The use of atomic force microscopy, a new technique capable of revealing surface structures in three-dimensional detail and at very high resolution, showed the rapid onset and time course of the sequence of disruptive morphostructural events following the incubation of both S. aureus and M. catarrhalis with sub-MICs of moxifloxacin. Our findings suggest that less than conventional MIC moxifloxacin concentrations may be effective in reducing bacterial adhesiveness and structural integrity on which the maintenance of bacterial activity depends.

Interference of sub-inhibitory concentrations of gatifloxacin on various determinants of bacterial virulence.

The physico-chemical characteristics of the molecular array on the outermost surface of bacteria modulate various bacterial functions which, when expressed in the human environment, constitute important determinants of bacterial virulence. The present study investigated the ability of subinhibitory concentrations of gatifloxacin to interfere with various virulence determinants of Escherichia coli and with the adhesiveness of Staphylococcus aureus. The adhesiveness of S. aureus and E. coli to human epithelial cells was inhibited at gatifloxacin concentrations down to 1/32 and 1/64 the minimum inhibitory concentration (MIC). Sub-MICs of gatifloxacin down to 1/8-MIC significantly reduced hemagglutination and hydrophobicity, which are correlated with fimbriation and provide clues relating to the physico-chemical characteristics of the outer surface of bacteria. Swarming (motility) was reduced at concentrations down to 1/8 MIC. Phagocytosis was not affected but killing significantly increased from 1/8 to 1/2 MIC. The respiratory bursts of neutrophils investigated by a chemiluminescence procedure were not modified. The interpolation of these pharmacodynamic findings with pharmacokinetic curves indicates that the effect of sub-MIC concentrations of gatifloxacin can engender activity, prolonging antimicrobial effects on virulence determinants over 30 hours after the antimicrobial concentration has fallen below the MIC.

Daptomycin morphostructural damage in Bacillus cereus visualized by atomic force microscopy.

Daptomycin is a novel, rapidly bactericidal in vitro antibiotic that is under investigation for the treatment of serious Gram-positive infections. Although daptomycin appears to disrupt membrane function, the precise mechanism of action has not been fully elucidated. Atomic force microscopy (AFM) is an innovative technique that allows high-resolution visualization and digital image manipulation of cell surface structures in 3 dimensions without the use of photons and electrons. The aim of this study was to use AFM to investigate the morphostructural changes in Bacillus cereus that occur upon daptomycin administration. The effects of daptomycin at 4x and 8x the minimal inhibitory concentration were visualized during an 8-hour incubation period. Atomic force microscopy images showed aberrant bacterial surface formations, including flattening and shrinking of cells and leakage of cytoplasm through the membrane. In addition to structural changes, the destabilization of flagella was also observed. These results support previous data suggesting that daptomycin disrupts membrane function.

The combination of the SH metabolite of erdosteine (a mucoactive drug) and ciprofloxacin increases the inhibition of bacterial adhesiveness achieved by ciprofloxacin alone.

Exposure to ciprofloxacin and other fluoroquinolone antibiotics at less than minimum inhibitory concentrations (MICs) reduces the production of some of the factors that contribute to bacterial virulence, particularly bacterial adhesiveness. Once metabolized, erdosteine (a mucoactive drug) produces an active metabolite (Met I) with a reducing sulfhydryl group that is capable of opening the disulfide bonds present in tracheobronchial mucins and pilins, a protein of bacterial fimbriae (adhesins). This induces stereoconformational changes that interfere with the binding of bacterial adhesins to the receptors on mucosal cells. The combination of 5 and 10 micrograms/ml of Met I and 1/4, 1/8, 1/16 MICs of ciprofloxacin potentiated the inhibition of Staphylococcus aureus and Escherichia coli adhesiveness to human mucosal cells in comparison with ciprofloxacin alone. This finding opens up an interesting new possibility for interfering with bacterial adhesiveness and the resulting virulence by combining antibiotics with agents devoid of antibacterial activity.

Effects of gatifloxacin on phagocytosis, intracellular killing and oxidant radical production by human polymorphonuclear neutrophils.

The ingestion and killing of bacteria by phagocytic cells is an important step in the sequence of interactions between invading microorganisms and host defense systems and may be affected by antibiotics. We investigated the effects of gatifloxacin on the phagocytosis, killing and oxidative bursts of human polymorphonuclear neutrophils (PMNs). The percentage phagocytosis and the phagocytosis index were unaffected by exposure of Escherichia coli strains to sub-MICs of gatifloxacin to a 1/64 dilution. However a significant increase in percentage intraphagocytic killing and the killing index occurred in one E. coli strain at 1/32 MIC and in two strains at 1/16 MIC. The incubation of PMNs with sub-MICs and supra-MICs of gatifloxacin (to 32 MIC) did not affect the oxidative bursts.

Staphylococcus aureus and Escherichia coli adhesion to human cells is reduced by sub-MICs of gemifloxacin.

This study was designed to investigate the capacity of subinhibitory concentrations of the newly developed fluoroquinolone antibiotic gemifloxacin to interfere with the mechanism of bacterial adhesion. Human buccal epithelial cells were incubated with Staphylococcus aureus and Escherichia coli, and grown in the presence of serial dilutions of gemifloxacin from 1/2 MIC to 1/128 MIC. A significant decrease in the adhesion of both S. aureus and E. coli was observed from 1/2 MIC to 1/32 MIC. Morphological changes including filamentous forms of E. coli and cluster formation and swelling of S. aureus were also observed, mainly from 1/2 MIC to 1/8 and 1/16 MIC. These findings are discussed in terms of dose-effect relationships and the interpolation of this pharmacodynamic data with the pharmacokinetics curve of gemifloxacin.

Inhibitory effects of zafirlukast on respiratory bursts of human neutrophils.

The effects of zafirlukast, a cysteinyl-leukotriene receptor antagonist, on the generation of the reactive oxygen species (ROS) released during respiratory bursts of human polymorphonuclear neutrophils (PMNs) is still unknown. The aim of this study was to investigate the ability of zafirlukast to interfere with the respiratory burst of PMNs. Respiratory burst responses of PMNs were investigated by luminol-amplified chemiluminescence (LACL) using particulate (Candida albicans and zymosan) and soluble stimulants [N-formyl-methionylleucyl-phenylalanine (fMLP) and phorbol 12 myristate 13 acetate (PMA)]. When incubated with PMNs for 10 min at concentrations ranging from 5 x 10(-9) M to 5 x 10(-6) M, zafirlukast did not significantly affect the respiratory bursts of PMNs induced by either the particulate or soluble stimuli. However, after incubation for 60 min, it did reduce the respiratory bursts of PMNs in a concentration-related fashion when the PMNs were stimulated with fMLP, and at a concentration of 5 x 10(-6) M when the stimulus was PMA. No significant effects were seen when the PMNs were challenged with particulate stimuli. Zafirlukast is able to interfere with the activation of the PMNs respiratory burst induced by soluble stimulants. The different behavior determined by different times of contact and different stimuli opens the way to interpretations concerning the antioxidant effect of zafirlukast.

The SH-metabolite I of erdosteine, a mucolytic drug, enhances the inhibitory effect of salbutamol on the respiratory burst of neutrophils.

Reactive oxygen species (ROS) are a common denominator of airway inflammation associated with chronic obstructive pulmonary disease (COPD) and asthma, as well as with less frequent lung diseases such as idiopathic pulmonary fibrosis (IPF), acute respiratory distress syndrome (ARDS) and cystic fibrosis (CF). The most frequently administered drugs used to treat these diseases are bronchodilators, antioxidant/antiphlogistic agents and mucoactive drugs. The metabolization of the mucoactive drug erdosteine produces an active metabolite (Met I) with a reducing SH group. In addition to its mucolytic action, Met I also has useful antioxidant activity. The various activities of beta 2-agonists include their ability to reduce the respiratory burst of neutrophils and the subsequent release of ROS. beta 2-Agonists and mucoactive drugs may be administered to the same patients during the treatment of lung diseases. The aim of this study was to investigate the ability of Met I to potentiate the activity of salbutamol in inhibiting the in vitro respiratory burst of neutrophils by means of chemiluminescence. The combination of Met I 5 and 10 micrograms/ml with salbutamol 10(-5), 10(-6) and 10(-7) M led to a significant reduction in respiratory bursts when the neutrophils were stimulated with the soluble stimulant N-formyl-methionylleucyl-phenylalanine (fMLP). The combinations of the two drugs that reduced the respiratory bursts when a particulate stimulus (Candida albicans) was used were those containing 10(-5) M of salbutamol. The reasons for this different behavior remain unclear and raise questions about the specific roles, sites and mechanisms of action of the different types of stimulation undergone by the respiratory airways.

Bacterial adhesiveness: effects of the SH metabolite of erdosteine (mucoactive drug) plus clarithromycin versus clarithromycin alone.

After metabolization, erdosteine (a mucoactive drug) produces an active metabolite (Met I) with an SH group that is capable of opening disulphide bonds, including those of pilin, a protein of bacterial fimbriae. This induces stereochemical conformational changes that interfere with the binding of bacterial adhesins (fimbriae) to receptors on eukaryotic cells. At subinhibitory concentrations, the macrolide clarithromycin inhibits the expression of adhesins on bacterial cell surfaces. The addition of 5 and 10 microg/ml of Met I to 1/8, 1/16 and 1/32 MIC of clarithromycin potentiated the inhibition of Staphylococcus aureus adhesiveness to human mucosal cells in comparison with the antibiotic alone. This finding opens up a new possibility of interfering with bacterial adhesiveness and its resulting pathogenicity not only by using antibiotics but also by means of their combination with agents devoid of antibacterial activity.

Assessment of the antioxidant activity of the SH metabolite I of erdosteine on human neutrophil oxidative bursts.

Acute and chronic lung diseases both lead to an extensive recruitment of neutrophils in the lungs. These cells play a major defensive role but, when activated, they are also an important source of reactive oxygen species, which generate a cytotoxic oxidant stress that triggers a self-sustaining phlogogenic loop. Erdosteine (CAS 84611-23-4) is a mucoactive drug whose metabolization leads to active metabolites with an SH group, and molecules bearing an SH group are also considered to have antioxidant activity. Luminol amplified chemiluminescence was used to investigate the oxidative bursts of human neutrophils and it was found that concentrations of 2.5, 5, 10 and 20 micrograms/ml of metabolite I of erdosteine significantly inhibit oxidative bursts in a concentration-related manner that overlaps the inhibition induced by the control drug N-acetylcysteine. Chemiluminescence was also studied in cell-free systems to see whether the drug also has direct scavenger activity, which was observed from 2.5 to 20 micrograms/ml of metabolite I using the xanthine/xanthine oxidase assay and at concentrations of 0.039 to > or = 2.5 micrograms/ml using the highly-sensitive hypochlorous acid/H2O2 assay. The findings indicate that the metabolite I of erdosteine has antioxidant activity which, together with the drug's mucomodifying activity, may lead to a useful antiphlogistic effect.

Effects of erdosteine and its metabolites on bacterial adhesiveness.

Erdosteine (CAS 84611-23-4) is administered as a mucolytic drug in patients with pulmonary disorders who suffer from a thickening of bronchial mucus with altered physico-chemical characteristics. Erdosteine itself does not have a free thiol group but its metabolization produces active metabolites with a -SH group that is capable of breaking disulfide bonds of mucins and improving the mucociliary clearance of the airways, and thus reproducing the effects of the class of muco-active drugs having a thiol group. It has also been reported that muco-active drugs with this group reduce bacterial adhesiveness to human mucosal cells. The aim of this study was to investigate whether erdosteine and its SH-metabolites are capable of interfering with bacterial adhesiveness. Metabolite I significantly reduces both S. aureus and E. coli adhesiveness to human mucosal epithelial cells at concentrations of 2.5, 5 and 10 micrograms/ml. The same concentrations of erdosteine, metabolite II, metabolite III and N-acetylcysteine (as a control drug) were devoid of such activity, whereas the results of hemagglutination and hydrophobicity assays showed that the behaviour of metabolite I overlapped that of bacterial adhesiveness, thus indicating that interference takes place at a fimbrial level. This is confirmed by the fact that the incubation of human buccal cells with drugs does not reduce the adhesiveness of untreated bacteria. The presence of this additional activity in a muco-active drug is useful because bacteria not only adhere to epithelial cells but also to tracheobronchial secretions.