Exploring the potential benefit of natural product extracts in paraquat toxicity.

Paraquat dichloride, a herbicide used for weed and grass control, is extremely toxic to humans and animals. The mechanisms of toxicity involve the redox cycling of paraquat resulting in the generation of reactive oxygen species and the depletion of the cellular NADPH. The major cause of death in paraquat poisoning is respiratory failure due to its specific uptake by and oxidative insult to the alveolar epithelial cells and inflammation with subsequent obliterating fibrosis. Paraquat also causes selective degeneration of dopaminergic neurons in the substantia nigra pars compacta, reproducing an important pathological feature of Parkinson disease. Currently, there are no antidotes for the treatment of paraquat poisoning and therapeutic management is mostly supportive and directed towards changing the disposition of the poison. The lack of effective treatments against paraquat poisoning has led to the exploration of novel compounds with antioxidant and/or anti-inflammatory properties. Recently, there is an interest in plant compounds, particularly those used in traditional medicine. Phytochemicals have been highlighted as a possible therapeutic modality for a variety of diseases due to their putative efficacies and safety. In this review, the status of plant extracts and traditional medicines in ameliorating the toxicity of paraquat is discussed.

The antimicrobial properties of ginseng and ginseng extracts.

Ginseng is commonly used in traditional Chinese medicine as a tonic and an adaptogen to reduce fatigue and boost the immune system. In recent years, ginseng extracts are shown to have both bacteriostatic and bactericidal actions and seem to exert their effects by several mechanisms, including disruption of biofilms, inhibition of quorum-sensing and virulence factors, and altering motility. Also, ginseng extracts are shown to have antifungal properties as demonstrated by their ability to inhibit the growth of several mold and yeast species. Extracts from ginseng root have a strong antiviral activity against the RNA viruses in cell cultures and animal models. In addition to the antimicrobial activities, ginseng extracts are shown to possess immunomodulatory properties involved in the amelioration of infections. The present paper describes the antimicrobial effects of ginseng and its extracts.

The bioactivity and toxicological actions of carvacrol.

Carvacrol is a monoterpenic phenol produced by an abundant number of aromatic plants, including thyme and oregano. Presently, carvacrol is used in low concentrations as a food flavoring ingredient and preservative, as well as a fragrance ingredient in cosmetic formulations. In recent years, considerable research has been undertaken in an effort to establish the biological actions of carvacrol for its potential use in clinical applications. Results from in vitro and in vivo studies show that carvacrol possess a variety of biological and pharmacological properties including antioxidant, antibacterial, antifungal, anticancer, anti-inflammatory, hepatoprotective, spasmolytic, and vasorelaxant. The focus of this review is to evaluate the existing knowledge regarding the biological, pharmacological, and toxicological effects of carvacrol.

Liposomal antibiotic formulations for targeting the lungs in the treatment of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a Gram-negative bacterium that causes serious lung infections in cystic fibrosis, non-cystic fibrosis bronchiectasis, immunocompromised, and mechanically ventilated patients. The arsenal of conventional antipseudomonal antibiotic drugs include the extended-spectrum penicillins, cephalosporins, carbapenems, monobactams, polymyxins, fluoroquinolones, and aminoglycosides but their toxicity and/or increasing antibiotic resistance are of particular concern. Improvement of existing therapies against Pseudomonas aeruginosa infections involves the use of liposomes - artificial phospholipid vesicles that are biocompatible, biodegradable, and nontoxic and able to entrap and carry hydrophilic, hydrophobic, and amphiphilic molecules to the site of action. The goal of developing liposomal antibiotic formulations is to improve their therapeutic efficacy by reducing drug toxicity and/or by enhancing the delivery and retention of antibiotics at the site of infection. The focus of this review is to appraise the current progress of the development and application of liposomal antibiotic delivery systems for the treatment pulmonary infections caused by P. aeruginosa.

Co-administration of aqueous ginseng extract with tobramycin stimulates the pro-inflammatory response and promotes the killing of Pseudomonas aeruginosa in the lungs of infected rats.

North American ginseng is known to have immunomodulatory and antipseudomonal properties in vitro. In this study we investigated the effects of aqueous ginseng extract, either alone or in a combination with the antibiotic tobramycin, in an animal model of chronic Pseudomonas aeruginosa lung infection. The lungs of male rats (n = 5) were infected with P. aeruginosa (2 × 10(8) cfu/mL) in agar-beads by intratracheal instillation. Starting on day 7 post-infection, animals were treated daily for 3 consecutive days with saline, tobramycin (300 µg/kg body mass, intratracheal), and (or) ginseng (100 mg/kg body mass, subcutaneous); animals were sacrificed 24 h after the third drug treatment. Lung bacteria counts, cytokine levels in sera, and lung histopathology were examined. The treatment of infected animals with tobramycin [6.6 × 10(4) colony forming units (cfu)], ginseng (5.3 × 10(4) cfu), or tobramycin plus ginseng (2.0 × 10(3) cfu) lessened the lung infection compared with the control group (saline treated) (6.0 × 10(6) cfu). The levels of pro-inflammatory cytokines (IL-2, IL-4, IL-6, IL-12p70, IFN-γ, GM-CSF, TNF-α) in infected animals were significantly increased with co-treatment of ginseng plus tobramycin. These data suggest that co-administration of aqueous ginseng extract and tobramycin stimulated the pro-inflammatory response and promoted the killing of P. aeruginosa.

Therapeutic effect of liposomal-N-acetylcysteine against acetaminophen-induced hepatotoxicity.

BACKGROUND: Acetaminophen (APAP) is an antipyretic analgesic drug that when taken in overdose causes depletion of glutathione (GSH) and hepatotoxicity. N-acetylcysteine (NAC) is the antidote of choice for the treatment of APAP toxicity; however, due to its short-half-life repeated dosing of NAC is required. PURPOSE: To determine whether a NAC-loaded liposomal formulation (Lipo-NAC) is more effective than the conventional NAC in protecting against acute APAP-induced hepatotoxicity. METHODS: Male Sprague-Dawley rats were challenged with an intragastric dose of APAP (850 mg/kg b.wt.); 4 h later, animals were administered saline, NAC, Lipo-NAC or empty liposomes and sacrificed 24 h post-APAP treatment. RESULTS: APAP administration resulted in hepatic injury as evidenced by increases in plasma bilirubin, alanine (AST) and aspartate (ALT) aminotransferase levels and tissue levels of lipid peroxidation and myeloperoxidase as well as decreases in hepatic levels of reduced GSH, GSH peroxidase and GSH reductase. Treatment of animals with Lipo-NAC was significantly more effective than free NAC in reducing APAP-induced hepatotoxicity. Histological evaluation showed that APAP caused periacinar hepatocellular apoptosis and/or necrosis of hepatocytes around the terminal hepatic venules which was reduced by NAC treatment, the degree of reduction being greater for Lipo-NAC. CONCLUSION: These data suggest that administration of Lipo-NAC ameliorated the APAP-induced hepatotoxicity.

Safety and pharmacokinetic studies of liposomal antioxidant formulations containing N-acetylcysteine, α-tocopherol or γ-tocopherol in beagle dogs.

The safety and pharmacokinetic profile of liposomal formulations containing combinations of the antioxidants α-tocopherol, γ-tocopherol or N-acetylcysteine in beagle dogs was examined. Each group consisted of beagle dogs of both genders with a control group receiving empty dipalmitoylphosphatidylcholine (DPPC) liposomes (330 mg/kg DPPC, EL), and test groups receiving liposomes prepared from DPPC lipids with (i) N-acetylcysteine (NAC) (60 mg/kg NAC [L-NAC]); (ii) NAC and α-tocopherol (αT) (60 mg/kg NAC and 25 mg/kg α-tocopherol [L-αT-NAC]) and (iii) NAC and γ-tocopherol (60 mg/kg NAC and 25 mg/kg γ-tocopherol (γT) [L-γT-NAC]). The dogs in the control group (EL) and three test groups exhibited no signs of toxicity during the dosing period or day 15 post treatment. Weight gain, feed consumption and clinical pathology findings (hematology, coagulation, clinical chemistry, urinalysis) were unremarkable in all dogs and in all groups. Results from the pharmacokinetic study revealed that the inclusion of tocopherols in the liposomal formulation significantly increased the area under the curve (AUC) and ß-half life for NAC; the tocopherols had greater impact on the clearance of NAC, where reductions of central compartment clearance (CL) ranged from 56% to 60% and reductions of tissue clearance (CL2) ranged from 73% to 77%. In conclusion, there was no treatment-related toxicity in dogs at the maximum feasible dose level by a single bolus intravenous administration while the addition of tocopherols to the liposomal formulation prolonged the circulation of NAC in plasma largely due to a decreased clearance of NAC.

Toxicity of ricin toxin A chain in rats.

Ricin toxin A chain (RTA) is the cytotoxic component of the dimeric protein, ricin, one of the most potent and deadly plant toxins extracted from the seeds of Ricinus communis. RTA has been investigated as a potential candidate for cancer chemotherapy, in the form of immunotoxins, and as a method for depleting macrophages in vivo. The toxicity of RTA immunotoxins is mostly characterized by inflammation and necrosis and has been attributed to the RTA moiety of the conjugate. The present study was carried out to investigate the toxicity of intravenously (i.v.) administered RTA alone and to assess whether the observed tissue injuries are associated with increases in oxidative stress (OS) and inflammation. RTA (10 or 90 µg/kg body weight) was administered to animals i.v., and 5 or 24 hours later, liver, lungs, kidneys, and hearts were examined. RTA, at a dose of 90 µg/kg (i.v.), resulted in significant increases (P < 0.05) in an inflammatory response (i.e., increases in hepatic and lung myeloperoxidase activity) and increases in oxidant response (increases in lipid peroxidation and decreases in glutathione levels in hepatic and lung homogenates). These data suggest that i.v. administration of RTA resulted in organ injuries that were associated with inflammation and OS.

Acute toxicity study of liposomal antioxidant formulations containing N-acetylcysteine, α-tocopherol, and γ-tocopherol in rats.

Liposomes have been used for the delivery of antioxidants to different tissues and organs for the treatment of oxidative stress-induced injuries. In this study, the acute toxicity of a single dose of intravenously (i.v.) administered liposomal antioxidant formulation, containing N-acetylcysteine (NAC) with or without α-tocopherol (α-T) or γ-tocopherol (γ-T), in rats was examined. Each group consisted of 5 male and 5 female Sprague-Dawley rats, with a control group receiving empty dipalmitoylphosphatidylcholine (DPPC) liposomes (660 mg/kg) and test groups receiving DPPC liposomes (660 mg/kg) entrapped with 1) NAC (200 mg/kg), 2) NAC (200 mg/kg) and α-T (83.3 mg/kg), and 3) NAC (200 mg/kg) and γ-T (71.4 mg/kg). These dose levels were determined from the dose-range-finding study and were considered to be the maximum feasible dose (MFD) levels, based on the volume of 10 mL/kg and physical properties and viscosity of the test articles that could be safely administered to rats by an i.v. injection. Two weeks after treatment (day 15), rats in the control group and three test groups exhibited no clinical signs of toxicity during the dosing period or during the 14-day post-treatment period. Weight gain and food consumption in all animals was appropriate for the age and sex of animals. Clinical pathology findings (e.g., hematology, coagulation, clinical chemistry, and urinalysis) were unremarkable in all rats and in all groups. In conclusion, the results of this study showed no treatment-related toxicity in rats at the MFD level by a single bolus i.v. administration.

Liposomal Antioxidants for Protection against Oxidant-Induced Damage.

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, can be formed as normal products of aerobic metabolism and can be produced at elevated rates under pathophysiological conditions. Overproduction and/or insufficient removal of ROS result in significant damage to cell structure and functions. In vitro studies showed that antioxidants, when applied directly and at relatively high concentrations to cellular systems, are effective in conferring protection against the damaging actions of ROS, but results from animal and human studies showed that several antioxidants provide only modest benefit and even possible harm. Antioxidants have yet to be rendered into reliable and safe therapies because of their poor solubility, inability to cross membrane barriers, extensive first-pass metabolism, and rapid clearance from cells. There is considerable interest towards the development of drug-delivery systems that would result in the selective delivery of antioxidants to tissues in sufficient concentrations to ameliorate oxidant-induced tissue injuries. Liposomes are biocompatible, biodegradable, and nontoxic artificial phospholipid vesicles that offer the possibility of carrying hydrophilic, hydrophobic, and amphiphilic molecules. This paper focus on the use of liposomes for the delivery of antioxidants in the prevention or treatment of pathological conditions related to oxidative stress.

Ginseng aqueous extract attenuates the production of virulence factors, stimulates twitching and adhesion, and eradicates biofilms of Pseudomonas aeruginosa.

This study was carried out to examine the antimicrobial activity of the aqueous extract of Panax quinquefolius from North American ginseng (NAGE) root against Pseudomonas aeruginosa . The minimum inhibitory concentrations of reference and clinical isolates of Pseudomonas aeruginosa were measured by a standard agar-dilution method. At subinhibitory NAGE concentrations, the secretion of virulence factors, motility on agar, and adhesion to 96-well microplates were studied on the nonmucoid Pseudomonas aeruginosa O1 strain. At suprainhibitory concentrations, the activity of NAGE against mature biofilm complexes formed in the Calgary Biofilm Device and the Stovall flow cell were assessed. NAGE possessed an antibacterial activity against all the Pseudomonas aeruginosa strains at 1.25%-2.5% w/v. NAGE also significantly attenuated pyocyanin, pyoverdine, and lipase concentrations, stimulated twitching, and attenuated swarming and swimming motility. At 1.25% w/v, NAGE augmented adhesion, and at 5% w/v detached 1-day-old biofilms in microplates. The extract also eradicated 6-day-old mature biofilms (5% w/v), and fluorescence microscopy displayed a reduction of live cells and biofilm complexes compared with nontreated biofilms. These data suggest that the aqueous extract from North American ginseng possesses antimicrobial activities in vitro.

N-acetylcysteine modulates the cytotoxic effects of Paclitaxel.

BACKGROUND: Paclitaxel is a microtubule-stabilizing drug known to cause mitotic G2/M arrest and apoptosis. It also increases the generation of reactive oxygen species (ROS) known to be involved in both apoptotic and necrotic cell death. Antioxidants, such as N-acetylcysteine (NAC), prevent the deleterious effects of ROS and modulate the regulation of apoptotic-linked cellular proteins. METHODS: A549 human adenocarcinoma alveolar epithelial cells were treated with 5.0 mM NAC, 1.0 µM paclitaxel, or co-incubated with both NAC and paclitaxel for a 24-hour incubation period. The effects of NAC in paclitaxel-induced cytotoxicity were evaluated by measuring cell viability, production of ROS, and apoptosis. RESULTS: Challenge of cells with paclitaxel resulted in time/concentration-dependent decreases in cell viability and increases in intracellular levels of ROS, and apoptosis, all effects being abrogated by co-treatment with NAC. NAC reduced the paclitaxel-induced increase in activated caspase-10 levels, but potentiated that for caspase-3. CONCLUSIONS: NAC alters the cytotoxicity of paclitaxel in vitro by decreasing the levels of ROS, preventing apoptosis, and modulating apoptotic cellular proteins.

Bismuth-ethanedithiol incorporated in a liposome-loaded tobramycin formulation modulates the alginate levels in mucoid Pseudomonas aeruginosa.

OBJECTIVES: This study examined the antibacterial activity, alginate modulation, and deposition of a tobramycin bismuth-ethanedithiol (Tob-Bi) conventional (free) or vesicle-entrapped (lipo) formulation against two mucoid Pseudomonas aeruginosa clinical isolates. METHODS: The inhibitory, bactericidal and biofilm eradication concentrations (in presence or absence of alginate lyase) were determined. The modulation of alginate was assessed by the carbazole assay and fluorescent-labelling of live alginate-producing biofilms by confocal microscopy. The deposition of the formulations was assessed using the immunogold-labelling technique, transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDS). KEY FINDINGS: The inhibitory and bactericidal concentrations for lipo Tob-Bi compared with free Tob-Bi were reduced in all strains by 2- to 8-fold, and 2- to 32-fold, respectively. The biofilm eradication concentrations for lipo Tob-Bi compared with free Tob-Bi were reduced by 4- to 32-fold in the mucoid strains. The addition of alginate lyase transiently enhanced eradication for one mucoid strain only. The alginate levels were attenuated by more than half, and free Tob-Bi fared better than lipo Tob-Bi determined by the carbazole assay. Under confocal microscopy, alginate lyase reduced alginate levels and detached mucoid biofilms. Free and lipo Tob-Bi did not detach the bacteria from the surface, but attenuated alginate levels. Tobramycin was detected by immunogold-labelling inside the bacterium, but EDS did not detect bismuth deposits. CONCLUSIONS: These findings substantiate a role in which tobramycin, bismuth, and alginate lyase play in eradicating mucoid P. aeruginosa growth and modulate alginate levels.

Treatment of ricin A-chain-induced hepatotoxicity with liposome-encapsulated N-acetylcysteine.

BACKGROUND: The toxicity of ricin resides in the ricin A-chain (RTA) and is attributed to the inhibition of protein synthesis but inflammation and oxidative stress have also been implicated. RTA can independently enter cells producing comparable tissue injury and inflammation, although at much higher concentrations than intact ricin. Treatment for exposure to ricin or RTA is supportive. PURPOSE: To examine the effectiveness of conventional or liposome-encapsulated N-acetylcysteine (Lipo-NAC) in ameliorating RTA-induced hepatotoxicity. METHODS: Four hours after RTA administration (90 µg/kg b.wt, iv), rats were treated with conventional NAC or Lipo-NAC (25 mg/kg NAC). The hepatoprotective effects of the antioxidant formulations were assessed by measuring indexes for liver injury (alanine [ALT] and aspartate [AST] aminotransferase activities), inflammation (myeloperoxidase, tumor necrosis factor-α, chloramine levels), and oxidant response (lipid peroxidation, nitrotyrosine, glutathione levels) 24-h post-RTA exposure. RESULTS: Administration of RTA to animals resulted in hepatotoxicity as demonstrated by elevated plasma ALT and AST levels, increases in an inflammatory response, and increases in oxidant response. Treatment of animals with the antioxidant formulations reversed the RTA-induced hepatotoxicity, being most evident following the administration of Lipo-NAC. CONCLUSION: NAC, administered in a liposomal form, may serve as a potentially effective pharmacological agent in the treatment of RTA-induced liver injuries.

Protective Effects of Liposomal N-Acetylcysteine against Paraquat-Induced Cytotoxicity and Gene Expression.

Paraquat (PQ) is a herbicide that preferentially accumulates in the lung and exerts its cytotoxicity via the generation of reactive oxygen species (ROS). There is no specific treatment for paraquat poisoning. Attempts have been made to increase the antioxidant status in the lung using antioxidants (e.g., superoxide dismutase, vitamin E, N-acetylcysteine) but the outcome from such treatments is limited. Encapsulation of antioxidants in liposomes improves their therapeutic potential against oxidant-induced lung damage because liposomes facilitate intracellular delivery and prolong the retention of entrapped agents inside the cell. In the present study, we compared the effectiveness of conventional N-acetylcysteine (NAC) and liposomal-NAC (L-NAC) against PQ-induced cytotoxicity and examined the mechanism(s) by which these antioxidant formulations conferred cytoprotection. The effects of NAC or L-NAC against PQ-induced cytotoxicity in A549 cells were assessed by measuring cellular PQ uptake, intracellular glutathione content, ROS levels, mitochondrial membrane potential, cellular gene expression, inflammatory cytokine release and cell viability. Pretreatment of cells with L-NAC was significantly more effective than pretreatment with the conventional drug in reducing PQ-induced cytotoxicity, as indicated by the biomarkers used in this study. Our results suggested that the delivery of NAC as a liposomal formulation improves its effectiveness in counteracting PQ-induced cytotoxicity.

Cytotoxicity and gene array analysis of alveolar epithelial A549 cells exposed to paraquat.

Paraquat (PQ), a commonly used herbicide, is highly toxic to humans and animals. The primary injury occurs in the lung, where PQ is actively taken up by alveolar epithelial cells and consequently produces damaging reactive oxygen species (ROS) via redox cycling. ROS have also been shown to induce expression of several early response genes and to activate transcription factors, which may contribute to the inflammatory response associated with PQ injury. In order to further elucidate the mechanism(s) of PQ injury, we investigated its effects on the cellular status and gene expression profile of immortalized human alveolar epithelial A549 cells in vitro. Incubation of cells with PQ resulted in concentration- and time-dependent PQ uptake, which correlated with increases in intracellular ROS levels and decreases in intracellular glutathione content, mitochondrial membrane potential, and cell viability. Gene array analysis showed differential expression in response to PQ exposure over time, particularly increases in: (i) the expression of growth arrest and cell cycle-related genes (e.g. CDKN1A, DDIT3 GADD45A, GDF15, MDM2, EGR1, CASP10, CASP8) and (ii) the expression of pro-inflammatory genes (e.g. IL1A, IL6, IL18, NFKB1, SERPINE1), which correlated with increases in the secretion of pro-inflammatory cytokines (e.g. IL-8, IL-6). These data suggest that uptake of PQ by A549 cells altered the cellular redox status and the expression of several early response genes, including the inflammatory response, all of which might contribute to the overall cytotoxicity of PQ.

Attenuation of Pseudomonas aeruginosa virulence factors and biofilms by co-encapsulation of bismuth-ethanedithiol with tobramycin in liposomes.

OBJECTIVES: This study examined the activities of tobramycin and bismuth against quorum sensing, virulence factors and biofilms of Pseudomonas aeruginosa by co-encapsulating the agents in liposomes in order to achieve greater delivery of the agents. METHODS: The inhibitory effects of the agents, in either their conventional (free) or vesicle-entrapped (liposomal) formulations, were assessed by measuring the changes in the quorum-sensing signal molecule N-acyl homoserine lactone, pyoverdine, pyocyanin, elastase, protease, chitinase, bacterial attachment and biofilms in vitro. RESULTS: The effectiveness of tobramycin and bismuth was superior when they were co-administered as a liposomal formulation as measured by their ability to attenuate the production of N-acyl homoserine lactone, elastase (P < 0.01), protease (P < 0.05) and chitinase (P < 0.01). In the presence of non-lethal concentrations of free and liposomal tobramycin and bismuth, bacterial attachment was attenuated. Biofilm formation was also attenuated with free tobramycin and bismuth, yet, in the presence of liposomal tobramycin and bismuth, biofilm complexes could form but contained mostly dead bacteria. When established biofilms were treated with higher concentrations, free tobramycin and bismuth killed and detached bacteria, while the liposomal tobramycin and bismuth penetrated and killed bacteria in the cores of the biofilms. CONCLUSIONS: These data suggest that treatment of P. aeruginosa with tobramycin and bismuth, as measured by the changes in quorum sensing, virulence factors and biofilms, is most effective when delivered as a liposomal formulation at a lower concentration compared with the free formulation.

Importance of DNase and alginate lyase for enhancing free and liposome encapsulated aminoglycoside activity against Pseudomonas aeruginosa.

OBJECTIVES: This study evaluated the potential of DNase, alginate lyase (AlgL) and N-acetylcysteine (NAC) in enhancing the in vitro bactericidal activity of conventional (free) and vesicle-entrapped (liposomal) gentamicin, amikacin and tobramycin. METHODS: The MICs and biofilm eradication for two clinical isolates of Pseudomonas aeruginosa (a mucoid strain and a non-mucoid strain) were determined in the presence and absence of AlgL. The co-activity of aminoglycosides with DNase and/or AlgL against endogenous P. aeruginosa in cystic fibrosis (CF) sputum was also measured. The inhibitory effects of mucin in the presence and absence of the mucolytic agent NAC on aminoglycosidic activity were also examined. RESULTS: The MIC values of the liposomal aminoglycosides were similar to or lower than those of free aminoglycosides. Biofilm formation increased the bactericidal concentrations of these drugs by 8- to 256-fold and treatment with AlgL improved killing of the mucoid strain. The activity of some aminoglycosides against the sputum was increased by the addition of DNase or AlgL (P < 0.05), and was increasingly evident with concurrent DNase and AlgL administration. Addition of mucin inhibited liposomal aminoglycosidic activity (up to 32-fold) evidently more than the free aminoglycosides (up to 8-fold). The addition of NAC did not improve activity significantly (P > 0.05). Tobramycin was the most effective aminoglycoside to reduce biofilms and sputum. CONCLUSIONS: Liposomal aminoglycosides do not fare better than conventional forms. The co-administration of DNase and AlgL is essential for enhanced activity in reducing biofilm growth and sputum bacterial counts. While mucin retards bactericidal activity, NAC does not improve aminoglycosidic activity.

Activity and interactions of liposomal antibiotics in presence of polyanions and sputum of patients with cystic fibrosis.

BACKGROUND: To compare the effectiveness of liposomal tobramycin or polymyxin B against Pseudomonas aeruginosa in the Cystic Fibrosis (CF) sputum and its inhibition by common polyanionic components such as DNA, F-actin, lipopolysaccharides (LPS), and lipoteichoic acid (LTA). METHODOLOGY: Liposomal formulations were prepared from a mixture of 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) or 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) and Cholesterol (Chol), respectively. Stability of the formulations in different biological milieus and antibacterial activities compared to conventional forms in the presence of the aforementioned inhibitory factors or CF sputum were evaluated. RESULTS: The formulations were stable in all conditions tested with no significant differences compared to the controls. Inhibition of antibiotic formulations by DNA/F-actin and LPS/LTA was concentration dependent. DNA/F-actin (125 to 1000 mg/L) and LPS/LTA (1 to 1000 mg/L) inhibited conventional tobramycin bioactivity, whereas, liposome-entrapped tobramycin was inhibited at higher concentrations--DNA/F-actin (500 to 1000 mg/L) and LPS/LTA (100 to 1000 mg/L). Neither polymyxin B formulation was inactivated by DNA/F-actin, but LPS/LTA (1 to 1000 mg/L) inhibited the drug in conventional form completely and higher concentrations of the inhibitors (100 to 1000 mg/L) was required to inhibit the liposome-entrapped polymyxin B. Co-incubation with inhibitory factors (1000 mg/L) increased conventional (16-fold) and liposomal (4-fold) tobramycin minimum bactericidal concentrations (MBCs), while both polymyxin B formulations were inhibited 64-fold. CONCLUSIONS: Liposome-entrapment reduced antibiotic inhibition up to 100-fold and the CFU of endogenous P. aeruginosa in sputum by 4-fold compared to the conventional antibiotic, suggesting their potential applications in CF lung infections.

Bismuth-thiol incorporation enhances biological activities of liposomal tobramycin against bacterial biofilm and quorum sensing molecules production by Pseudomonas aeruginosa.

Recurrent pulmonary infection and inflammation are major risk factors for high morbidity and mortality in patients with cystic fibrosis (CF). As such, frequent antibiotic use and drug resistant bacterial strains are main concerns in individuals with CF. Bacterial virulence and resistance are influenced by unique CF airways fluid lining and Pseudomonas aeruginosa quorum sensing (QS) and biofilm formation. We have developed a novel liposome formulation consist of bismuth-thiol and tobramycin (LipoBiEDT-TOB) that is non-toxic and highly effective against planktonic bacteria. In this study, we examined the effect of LipoBiEDT-TOB on QS molecule N-acyl homoserine lactone (AHL) secretion by P. aeruginosa isolates in the presence of Agrobacterium tumefaciens reporter strain (A136). LipoBiEDT-TOB activity against biofilm forming P. aeruginosa was compared to free tobramycin using the Calgary Biofilm Device (CBD). Our data indicate that LipoBiEDT-TOB prevents AHL production at low tobramycin concentration (as low as 0.012 mg/l) and stops biofilm forming P. aeruginosa growth at 64 mg/l. The formulation is stable in different biological environments (biofilm, sputum, and bronchoalveolar lavage) and is able to penetrate CF sputum. Taken together, co-encapsulation of bismuth-thiol metal with tobramycin in liposome improves its antimicrobial activities in vitro.