Cationic vesicles based on biocompatible diacyl glycerol-arginine surfactants: physicochemical properties, antimicrobial activity, encapsulation efficiency and drug release.

Physicochemical characteristics of cationic vesicular systems prepared from biocompatible diacyl glycerol-arginine surfactants are investigated. These systems form stable cationic vesicles by themselves and the average diameter of the vesicles decreases as the alkyl chain length of the surfactant increases. The addition of DPPC also modifies the physicochemical properties of these vesicles. Among the drugs these cationic formulations can encapsulate, we have considered Ciprofloxacin and 5-Fluorouracil (5-FU). We show that the percentage of encapsulated drug depends on both the physicochemical properties of the carrier and the type of drug. The capacity of these systems to carry different molecules was evaluated performing in vitro drug release studies. Finally, the antimicrobial activity of empty and Ciprofloxacin-loaded vesicles against Gram-positive and Gram-negative bacteria has been determined. Three bacteria were tested: Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. The in vitro drug release from all formulations was effectively delayed. Empty cationic vesicles showed antimicrobial activity and Ciprofloxacin-loaded vesicles showed similar or higher antimicrobial activity than the free drug solution. These results suggest that our formulations represent a great innovation in the pharmaceutical field, due to their dual pharmacological function: one related to the nature of the vehiculated drug and the other related to the innate antibacterial properties of the surfactant-based carriers.

The role of counterions in the membrane-disruptive properties of pH-sensitive lysine-based surfactants.

Surfactants are among the most versatile and widely used excipients in pharmaceuticals. This versatility, together with their pH-responsive membrane-disruptive activity and low toxicity, could also enable their potential application in drug delivery systems. Five anionic lysine-based surfactants which differ in the nature of their counterion were studied. Their capacity to disrupt the cell membrane was examined under a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model for endosomal membranes. The surfactants showed pH-sensitive hemolytic activity and improved kinetics at the endosomal pH range. Low concentrations resulted in negligible hemolysis at physiological pH and high membrane lytic activity at pH 5.4, which is in the range characteristic of late endosomes. With increasing concentration, the surfactants showed an enhanced capacity to lyse cell membranes, and also caused significant membrane disruption at physiological pH. This observation indicates that, at high concentrations, surfactant behavior is independent of pH. The mechanism of surfactant-mediated membrane destabilization was addressed, and scanning electron microscopy studies were also performed to evaluate the effects of the compounds on erythrocyte morphology as a function of pH. The in vitro cytotoxicity of the surfactants was assessed by MTT and NRU assays with the 3T3 cell line. The influence of different types of counterion on hemolytic activity and the potential applications of these surfactants in drug delivery are discussed. The possibility of using pH-sensitive surfactants for endosome disruption could hold great promise for intracellular drug delivery systems in future therapeutic applications.

Cationic surfactants derived from lysine: effects of their structure and charge type on antimicrobial and hemolytic activities.

Three different sets of cationic surfactants from lysine have been synthesized. The first group consists of three monocatenary surfactants with one lysine as the cationic polar head with one cationic charge. The second consists of three monocatenary surfactants with two amino acids as cationic polar head with two positive charges. Finally, four gemini surfactants were synthesized in which the spacer chain and the number and type of cationic charges have been regulated. The micellization process, antimicrobial activity, and hemolytic activity were evaluated. The critical micelle concentration was dependent only on the hydrophobic character of the molecules. Nevertheless, the antimicrobial and hemolytic activities were related to the structure of the compounds as well as the type of cationic charges. The most active surfactants against the bacteria were those with a cationic charge on the trimethylated amino group, whereas all of these surfactants showed low hemolytic character.

Aggregation properties of diacyl lysine surfactant compounds: hydrophobic chain length and counterion effect.

In this paper, we report on the study of aqueous solution and aggregation properties of diacyl Lysine surfactant salts with several surfactant counterions at a fixed hydrophobic chain length. They present a critical micellar concentration nearly independent of the counterion. The area per surfactant molecule is around 1.3 nm (2) also independent of the counterion. We have also studied the dry state crystallization of these surfactant salts. We show that small counterion systems tend to form bicontinuous cubic structures and that the increase in counterion size tends to form lamellar structures. We have compared this behavior with the dry state crystallization of the diacyl Lysine surfactants as a function of hydrophobic chain length. For long hydrophobic chains, the crystal structure is lamellar, while for intermediate, length is cubic. Among the structures studied, the one with the shortest chain length crystallizes in a hexagonal inverse phase.

The biological properties of lysine-derived surfactants.

We examine the effects of aquatic toxicity on Daphnia magna, the antimicrobial activity of new anionic lysine-derivative surfactants, and the influence of different-sized counterions associated with the surfactants. Surfactants with Tris and Lithium had less of a toxic effect on Daphnia, while all surfactants proved highly active against yeasts and the gram-negative bacteria Bordetella bronchiseptica. Counterion size was found to have no effect on aquatic toxicity or antimicrobial activity.

Disturbance of erythrocyte lipid bilayer by amino acid-based surfactants.

In an attempt to increase our knowledge regarding the mechanisms of surfactant membrane interaction, we studied the action of several anionic and cationic amino acid-based surfactants on membrane fluidity using fluorescence anisotropy. Anisotropy measurements demonstrated that almost all of the surfactants studied disturbed the external region of the erythrocyte membrane without affecting the core of the bilayer. How the physico-chemical properties and structure of these compounds affect dynamics of the lipid bilayer is discussed in detail.

Determination of interleukin-1alpha in human NCTC 2544 keratinocyte cells as a predictor of skin irritation from lysine-based surfactants.

Lysine derivative surfactants are a class of amino acid-based surfactants synthesized as lecithin analogues that deserve particular attention because of their low toxicity and high biocompatibility. To complete the toxicological profile of these surfactants, IL-1 alpha production (cell-associated and release to the culture medium) was determined as an in vitro method for predicting skin irritation. In addition, an MTT assay was used as a viability marker in keratinocytes NCTC 2544. Keratinocytes are a biologically relevant target for developing in vitro techniques to assess skin irritants: moreover, they are the principal source of the proinflammatory cytokine IL-1 alpha in the epidermis. Lysine derivatives proved to be less potent in stimulating IL-1 alpha synthesis and induced a lower release of this cytokine into the culture medium when compared to the anionic surfactant sodium dodecyl sulfate. Due to their low irritancy potential, lysine-based surfactants may offer promising applications in pharmaceutical and cosmetic preparations.

Potential irritation of lysine derivative surfactants by hemolysis and HaCaT cell viability.

Surfactants represent one of the most common constituents in topical pharmaceutical and cosmetic applications or cleansers. Since adverse skin and ocular reactions can be caused by them, it is important to evaluate damaging effects. Amino acid-based surfactants deserve particular attention because of their low toxicity and environmental friendly properties. New lysine derivative surfactants associated with heavy and light counterions were tested. The ocular irritancy was assessed by hemolysis, and photohemolysis was employed to evaluate their phototoxicity. Cytotoxicity on HaCaT cells was determined by neutral red uptake and MTT assay to predict skin irritation. All lysine derivative surfactants were less hemolytic and thus less eye-irritating than the commercial surfactants used as model irritants. No phototoxic effects were found. All surfactants presented cytotoxic effects as demonstrated by decrease of neutral red uptake and reduction of MTT salt, with clear concentration-effect profiles. However, the rates of cytotoxicity on HaCaT for the new surfactants suggested that they were less cytotoxic and then, less skin-irritating than the reference ones; surfactants with heavy counterions were the less cytotoxic. The anionic surfactants investigated in the present work may constitute a promising class of surfactants given their low irritancy potential for pharmaceutical and cosmetic preparations.

Assessment of the potential skin irritation of lysine-derivative anionic surfactants using mouse fibroblasts and human keratinocytes as an alternative to animal testing.

PURPOSE: The aim of this study was to identify new surfactants with low skin irritant properties for use in pharmaceutical and cosmetic formulations, employing cell culture as an alternative method to in vivo testing. In addition, we sought to establish whether potential cytotoxic properties were related to the size of the counterions bound to the surfactants. METHODS: Cytotoxicity was assessed in the mouse fibroblast cell line 3T6 and the human keratinocyte cell line NCTC 2544 using the MTT assay and uptake of the vital dye neutral red 24 h after dosing (NRU). RESULTS: Lysine-derivative surfactants showed higher IC50s than did commercial anionic irritant compounds such as sodium dodecyl sulfate, proving to be no more harmful than amphoteric betaines. The aggressiveness of the surfactants depended on the size of their constituent counterions: surfactants associated with lighter counterions showed a proportionally higher aggressivity than those with heavier ones. CONCLUSIONS: Synthetic lysine-derivative anionic surfactants are less irritant than commercial surfactants such as sodium dodecyl sulfate and hexadecyltrimethylammonium bromide and are similar to betaines. These surfactants may offer promising applications in pharmaceutical and cosmetic preparations, representing a potential alternative to commercial anionic surfactants as a result of their low irritancy potential.

A synthetic alternative to natural lecithins with antimicrobial properties.

Two soft biocompatible cationic surfactants from the amino acid arginine, 1,2-dilauroyl-3-acetylarginyl-rac-glycerol (1212RAc) and 1,2-dimirystoyl-3-acetylarginyl-rac-glycerol (1414RAc), were prepared. Their physicochemical properties show that they can be classified as multifunctional surfactants with self-aggregation behaviour comparable to that of short-chain lecithins. The two surfactants can simultaneously stabilise water-in-oil (W/O) droplets and oil-in-water (O/W) droplets, forming multiple emulsions. They have antimicrobial activity similar to that of conventional cationic surfactants and are as harmless as amphoteric betaines. These surfactants constitute an interesting alternative to the diglycerides and lecithins in formulations that require antimicrobial properties.

Assessment of primary eye and skin irritants by in vitro cytotoxicity and phototoxicity models: an in vitro approach of new arginine-based surfactant-induced irritation.

Extensive efforts have been made, recently, to find surfactants with lower irritation potential than those presently commercially available, for use in pharmaceutical and cosmetic preparations. Cytotoxic and phototoxic effects of a novel family of dicationic arginine-diglyceride surfactant compounds, 1,2-diacyl,3-O-(l-arginyl)-rac-glycerol with alkyl chain lengths in the range from 8 to 14 carbon atoms, were compared to three commercial surfactants. The end-points used to assess toxicity were the red blood cell lysis assay and uptake of the vital dye neutral red 24h after dosing (NRU), respectively. Two immortalized cell lines, murine fibroblast cell line, 3T3, and one human keratinocyte cell line, HaCaT, were used as in vitro models to predict the potential phototoxicity which could result in irritation, determined by resazurin reduction to resorufin and neutral red uptake (NRU). All tested surfactants had cytotoxicity effects as demonstrated by and decrease of NR uptake, which showed a clear concentration-response relationship. Concentrations resulting in 50% inhibition of NR uptake (IC(50)) range from 1 microM(-1) (hexadecyl trimethyl ammonium bromide) to 565 microM(-1) (12,12-l-arginine). Erythrocyte haemolysis also showed a clear concentration-response relationship, the 50% of haemolysis ranged from 37 microM(-1) (10,10-l-arginine) to 151 microM(-1) (sodium lauryl sulphate). Phototoxicity was performed with 12,12-l-acetyl-arginine, the most stable chemical structure. The validated 3T3 NRU photoxicity assay was used and revealed a phototoxic potential.

Physicochemical characterization and antimicrobial properties of rhamnolipids produced by Pseudomonas aeruginosa 47T2 NCBIM 40044.

Pseudomonas aeruginosa 47T2, grown in submerged culture with waste frying oil as a carbon source, produced a mixture of rhamnolipids with surface activity. Up to 11 rhamnolipid homologs (Rha-Rha-C(8)-C(10); Rha-C(10)-C(8)/Rha-C(8)-C(10);Rha-Rha-C(8)-C(12:1); Rha-Rha-C(10)-C(10); Rha-Rha-C(10)-C(12:1); Rha-C(10)-C(10); Rha-Rha-C(10)-C(12)/Rha-Rha-C(12)-C(10); Rha-C(10)-C(12:1)/Rha-C(12:1)-C(10); Rha-Rha-C(12:1)-C(12); Rha-Rha-C(10)-C(14:1); Rha-C(10)-C(12)/Rha-C(12)-C(10)) were isolated from cultures of P. aeruginosa 47T2 from waste frying oil and identified by HPLC-MS analysis. This article deals with the production, isolation, and chemical characterization of the rhamnolipid mixture RL(47T2). The physicochemical and biological properties of RL(47T2) as a new product were also studied. Its surface tension decreased to 32.8 mN/m; and the interfacial tension against kerosene to 1 mN/m. The critical micellar concentration for RL(47T2) was 108.8 mg/mL. The product showed excellent antimicrobial properties. Antimicrobial activity was evaluated according to the minimum inhibitory concentration (MIC), the lowest concentration of an antimicrobial agent that inhibits development of visible microbial growth. Low MIC values were found for bacteria Serratia marcescens (4 microg/mL), Enterobacter aerogenes (8 microg/mL), Klebsiella pneumoniae (0.5 microg/mL), Staphylococcus aureus and Staphylococcus epidermidis (32 microg/mL), Bacillus subtilis (16 microg/mL), and phytopathogenic fungal species: Chaetonium globosum (64 microg/mL), Penicillium funiculosum (16 microg/mL), Gliocadium virens (32 microg/mL) and Fusarium solani (75 microg/mL).

Interactions of surfactants with living cells. Induction of apoptosis by detergents containing a beta-lactam moiety.

The toxicity of new surfactants containing a beta-lactam ring has been established by studying their interaction with a hybridoma cell line. An hour of contact is sufficient to generate an apoptotic signal after two days of culture. Under the experimental conditions chosen for the experiments, surfactants have been divided into three categories: i) biocompatible and non-apogenic; ii) surfactants triggering an apoptotic signal without inducing cell necrosis; iii) surfactants triggering an apoptotic signal at low concentrations and destroying the cells by necrosis at higher concentrations. The necrosis inducing surfactants also had haemolytic properties. These properties were related to the values of the hydrophilic-lipophilic balance of the molecules.

Purification of non-toxic, biodegradable arginine-based gemini surfactants, bis(Args), by ion exchange chromatography.

This paper presents an environmentally improved procedure for the preparative purification of a series of arginine-based gemini surfactants. The technique used was cation-exchange chromatography. Mixtures of boric-borate buffer, co-solvent (ethanol), and sodium chloride were tested as eluents. The influence of the buffer pH and the amount of co-solvent on the chromatographic process was studied for the model compound bis(Nalpha-lauroyl-L-arginine) 1,3-propanediamide dihydrochloride, C3(LA)2, and purification conditions were established. The method was scaled-up to the multigram level for C3(LA)2 and the rest of the series. The proposed preparative procedure involves simple equipment, low cost materials, and minimal amounts of solvent (water/ethanol), with low toxicity.

Possible effects of counterions on biological activities of anionic surfactants.

The aggressiveness in terms of apogenic and necrotic activities of lysine-derived anionic surfactants towards a mammalian cell line (U937) were studied. We used N(alpha)N(epsilon)-dioctanoyl lysine as the model surfactant with lysine, tris, Na(+) or Li(+) as counterions. The aggressiveness of the different surfactants was assessed as the concentrations leading to apoptosis or necrosis after the cells were incubated in the presence of surfactants and then cultivated in their absence. Used in the same conditions, acetates associated with the same cations, had no effects on the cells. Our results show that the aggressiveness of the surfactants depended on the nature of the counterions: it was high when surfactants were associated with small counterions, and low with large counterions.

Chemo-enzymatic synthesis of arginine-based gemini surfactants.

A novel chemo-enzymatic synthesis of arginine-based gemini cationic surfactants bis(Args) is reported. These compounds consist of two single N(alpha)-acyl-arginine structures connected through the alfa-carboxylic groups of the arginine residues by a alpha, omega-diaminoalkane spacer chain. N(alpha)-Acyl-L-arginine alkyl ester derivatives were the starting building blocks for the synthesis. The best strategy found consisted of two steps. First, the quantitative acylation of one amino group of the spacer by the carboxylic ester of the N(alpha)-acyl-arginine took place spontaneously, at the melting point of the alpha,omega-diaminoalkane, in a solvent-free system. The second step was the papain-catalyzed reaction between another N(alpha)-acyl-arginine alkyl ester and the free aliphatic amino group of the derivative formed in the first step. Reactions were carried out in solid-to-solid and solution systems using low-toxic potential solvents. Changes in reaction performance and product yield were studied for the following variables: organic solvent, support for enzyme deposition and substrate concentration. The best yields (70%) were achieved in solid-to-solid systems and in ethanol at a(w) = 0.07. Bis(Args) analogs of 8, 10 and 12 carbon atoms using 1,3-diaminopropane and 1, 3-diamino-2-hydroxy-propane as hydrocarbon spacers were prepared at the 6-7 gram level employing the methodology developed. The overall yields which include reaction and purification varied from 51% to 65% of pure (97-98% by HPLC) product.

Qualitative and quantitative analysis of new alkyl amide arginine surfactants by high-performance liquid chromatography and capillary electrophoresis.

A protocol for the qualitative and quantitative analysis of novel arginine-based cationic surfactants using HPLC and CE was studied and compared. The optimization of the analytical conditions was carried out through a systematic variation of the experimental parameters such as mobile phase, eluent conditions, ion pairing and amount of sample for HPLC, and type of buffer, ion strength, type and amount of organic solvent, sample injection time, applied voltage and column washing and conditioning for CE.

Preparation and antibiotic activity of monobactam analogues of nocardicins.

A series of diverse beta-lactam analogues of nocardicins with interesting antimicrobial properties were prepared. Coupling of glucosamine to these compounds improved their water solubility. Aminoacid derivatives produced a stereoinduction on the quaternary enantiotopic carbon of the starting compound 1. Evaluation of their antimicrobial activity showed that the introduction of alpha-amninoacids to monobactams increased their activity. The importance of asymmetric carbon is exemplified by the higher antibiotic activity of L-alpha-aminoacids than the D-series. No significant difference was observed between fluorinated and non-fluorinated monobactams.

Erythrocyte hemolysis and shape changes induced by new lysine-derivate surfactants.

The effects of new synthetic lysine-derived anionic surfactants on human and rat erythrocytes were studied. The surfactants were salts of Nalpha,Nepsilon-dioctanoyl lysine with different counterions: lysine (77KK), tris (trishydroxymethyl amminomethane) (77KT), sodium (77KS), and lithium (77KL). 77KK and 77KT showed a biphasic hemolytic behavior in the erythrocytes. The surfactants 77KS and 77KL showed concentration-dependent hemolysis with a CH50 of about 3.4 and 2.6 mmol/l, respectively. 77KK and 77KT induced protection against hypotonic hemolysis in rat erythrocytes at the concentration which showed the least hemolytic activity under isotonic conditions. With human erythrocytes, 77KT did not show biphasic behavior in isotonic medium, but under hypotonic conditions biphasic behavior was present. Changes in shape of the erythrocyte, from discocytic to stomatocytic were observed after incubation with the anionic surfactants studied. Such shape changes occurred progressively over time, with total alteration in shape occuring after about 20 min of incubation.

Enzymatic synthesis of arginine-based cationic surfactants.

A novel enzymatic approach for the synthesis of arginine N-alkyl amide and ester derivatives is reported. Papain deposited onto solid support materials was used as catalyst for the amide and ester bond formation between Z-Arg-OMe and various long-chain alkyl amines and alcohols (H2N-Cn2, HO-Cn; n = 8-16) in organic media. Changes in enzymatic activity and product yield were studied for the following variables: organic solvent, aqueous buffer content, support for the enzyme deposition, presence of additives, enzyme loading, substrate concentration, and reaction temperature. The best yields (81-89%) of arginine N-alkyl amide derivatives were obtained at 25 degrees C in acetonitrile with an aqueous buffer content ranging from 0 to 1% (v/v) depending on the substrate concentration. The synthesis of arginine alkyl ester derivatives was carried out in solvent-free systems at 50 or 65 degrees C depending on the fatty alcohol chain length. In this case, product yields ranging from 86 to 89% were obtained with a molar ratio Z-Arg-OMe/fatty alcohol of 0.01. Papain deposited onto polyamide gave, in all cases, both the highest enzymatic activities and yields. Under the best reaction conditions the syntheses were scaled up to the production of 2 g of final product. The overall yields, which include reaction, Nalpha-benzyloxycarbonyl group (Z) deprotection and purification, varied from 53 to 77% of pure (99.9% by HPLC) product.