Antioxidative activity of new N-oxides of tertiary amines: membrane model and chromogen studies

Potential antioxidative activities of three series of newly synthesized N-oxides were studied. Individual components in each of the series differed in the lipophilicities and number of free radical scavenging groups. Various methods were used to determine their antioxidative efficiencies: Prevention of erythrocyte membrane lipid oxidation induced by UV irradiation and chromogen experiments in which antioxidative efficiencies of compounds were compared to that of the standard antioxidant Trolox (a water-soluble vitamin E analogue). Additionally, some hemolytic (pig erythrocytes) and differential scanning calorimetry (DSC) measurements were performed to determine a mechanism of the interaction between membranes and N-oxides. It was found that N-oxides, especially those of long alkyl chains (> C12H25), readily interacted with both, erythrocyte and liposomal membranes. No marked differences were found in their protection of erythrocytes against oxidation. In most cases inhibition of oxidation changed between 15% and 25%. Still, it was far better than in chromogen experiments where suppression of free radicals reached 20% in the best case. It may be concluded that antioxidative capabilities of N-oxides are moderate. Studies on the interaction mechanism showed that incorporation of particular compounds into model membranes varied. Hemolysing activities of compounds increased with the elongation of the alkyl chain but differed for corresponding compounds of particular series indicating that lipophilicity of compounds is not the only factor determing their interaction with erythrocyte membranes. DSC experiments showed that N-oxides, upon incorporation into 1,2-dipalmitoyl-3-sn-phosphatidylcholine liposomes, shifted the subtransition (Tp) and the main transition (Tm). The shifts observed depended on the alkyl chain length. The effects differed for each series. It seems that in the case of long alkyl chain compounds the domain formation may take place. Generally, the decrease of Tm was greatest for the same compounds that exhibited the best hemolytic efficacy. The same conclusion concerns the decrease of cooperativity of the main transition and the observed changes suggest an increase in membrane fluidity. Both, erythrocyte and DSC experiments seem to indicate that compounds of particular series incorporate in a somewhat different way into membranes.     

Antioxidative activity of some quaternary ammonium salts incorporated into erythrocyte membranes

The antioxidative activity of two series of amphiphilic compounds from a group of quaternary ammonium salts has been investigated. They were so-called bifunctional surfactants synthesized to be used as common pesticides or as antioxidants. The latter application was to be ensured by providing the compounds studied with an antioxidant group. Studies on antioxidative possibilities of those compounds were performed on pig erythrocytes. Due to their hydrophobic parts, they anchor in the erythrocyte membrane and influence the degree of lipid oxidation in the erythrocyte membrane subjected to UV radiation. It was found that compounds of both series decreased the oxidation of the membrane lipids. The inhibition of this oxidation increased with the length of their hydrophobic chains up to fourteen carbon atoms. The compounds of the longest hydrophobic chains showed a somewhat weaker antioxidative activity. Of the two series studied compounds were more effective having bromide ions as counterions. The corresponding compounds of a second series (chlorides) protected erythrocyte significantly weaker against oxidation. The effect of the compounds on fluidity of the erythrocyte membrane has been studied in order to explain the oxidation results. Change in fluidity of the erythrocyte ghost membranes was found also dependent on length of the hydrophobic part of the compounds and was more pronounced in the case of bromide surfactants. The final conclusion is that the compounds studied can be succesfully used as antioxidant agents of good efficacy.     

Membrane-protective properties of isobornylphenols-a new class of antioxidants

The membrane protective and membrane active properties and the antioxidative activity of new semisynthetic antioxidants—isobornylphenols were studied. The presence of oxidant and cytotoxic properties of the compounds were evaluated considering the degree of hemolysis of erythrocytes, either spontaneous or induced by hydrogen peroxide. All the studied compounds were found to have significant antioxidative activity in certain conditions. But their capacity to protect membrane erythrocytes from oxidative stress substantially depended on the structure and concentration of the compound. The highest membrane protective activity was observed for 2,6-diisobornyl-4-methylphenol, which has isobornyl in both of its ortho-positions. Scanning electron microscopy of blood erythrocyte surface architectonics confirmed the ability of the studied compounds to interact with the cell membrane and to change its structure. A relationship between erythrocyte morphological transformation according to bilayer-couple hypothesis depending on isobornylphenols membrane behavior and the cytotoxic effect of certain compound high concentrations reflected in low membrane protective activity in the model cell system was shown. The data obtained allow us to conclude that the biological activity of isobornylphenols is due to both their antioxidative properties and their ability to interact with the cell membranes.     

Assessment of potential application of binary mixtures of 2,4-d with novel aminophosphonates

A series of new aminoalkane- and aminofluorenephosphonates was synthesized for agrochemical application. The particular compounds had different alkyl substituents at the carbon, nitrogen and phosphorus atoms. Their pesticidal activity was checked by applying various experimental methods. These included the measurements of compounds' potency: to inhibit growth of cucumber and germination of white mustard seeds, to influence on the membrane potential of algae and to damage human erythrocyte membranes resulting in hemolysis. All the aminophosphonates were also used in equimolar binary mixtures with the well-known herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), to check, if using such mixtures, the biological efficiencies found for particular compounds could be enhanced due to interactions between aminophosphonates and 2,4-D. The results demonstrated, that depending on the structural features of the compounds, the final effects differed from antagonistic, through additive to the most promising synergistic ones. However, the type of interaction between 2,4-D and the compounds studied found in different experiments was somewhat different. In order to estimate those effects various statistical methods were used (toxic unit method, isobole method).     

Interactions of biocidal guanidine hydrochloride polymer analogs with model membranes: a comparative biophysical study

Four synthesized biocidal guanidine hydrochloride polymers with different alkyl chain length, including polyhexamethylene guanidine hydrochloride and its three new analogs, were used to investigate their interactions with phospholipids vesicles mimicking bacterial membrane. Characterization was conducted by using fluorescence dye leakage, isothermal titration calorimetry, and differential scanning calorimetry. The results showed that the gradually lengthened alkyl chain of the polymer increased the biocidal activity, accompanied with the increased dye leakage rate and the increased binding constant and energy change value of polymer-membrane interaction. The polymer-membrane interaction induced the change of pretransition and main phase transition (decreased temperature and increased width) of phospholipids vesicles, suggesting the conformational change in the phospholipids headgroups and disordering in the hydrophobic regions of lipid membranes. The above information revealed that the membrane disruption actions of guanidine hydrochloride polymers are the results of the polymer's strong binding to the phospholipids membrane and the subsequent perturbations of the polar headgroups and hydrophobic core region of the phospholipids membrane. The alkyl chain structure significantly affects the binding constant and energy change value of the polymer-membrane interactions and the perturbation extent of the phospholipids membrane, which lead to the different biocidal activity of the polymer analogs. This work provides important information about the membrane disruption action mechanism of biocidal guanidine hydrochloride polymers.     

Effect of 8-alkylberberine homologues on erythrocyte membrane

8-alkylberberine homologues (Ber-C8-n, where n indicates carbon atom number of gaseous normal alkyl at 8 position, n = 0, 2, 4, 6, 8, 10, 12, or 16) were synthesized and their effects on the hemolysis of rabbit erythrocyte, the fluidity of membrane and the fluorescence of membrane protein were investigated by fluorescence analysis technique. Ber-C8-n with mediate length alkyl (4 < n < 10) exhibited obvious hemolysis effect on rabbit erythrocyte when their concentration exceed 1.25 x10(-4) mol/L, and Ber-C8-8 displayed the highest hemolysis effect among all tested homologues. All of Ber-C8-n influenced the fluidity of erythrocyte membrane to different extents, which exhibited an obvious dose-effect relationship. The effect of Ber-C8-n on fluidity increased as the length of alkyl chain was elongated and decreased gradually when the alkyl carbon atoms exceeded 8. The fluorescence of erythrocyte membrane protein was quenched by Ber-C8-n, which showed a similar changing tendency on membrane fluidity. Experiments in vitro suggested that disturbing effects of Ber-C8-n on the conformation and function of membrane protein leaded to the changes of membrane fluidity and stability, and then the membrane was broken down.     

Effects of long-chain cis-unsaturated fatty acids and their alcohol analogs on aggregation of bovine platelets and their relation with membrane fluidity change

The effects of long-chain cis-unsaturated fatty acids with different alkyl chain lengths and different numbers of double bonds on aggregation of bovine platelets and membrane fluidity were investigated. All the cis-unsaturated fatty acids tested inhibited aggregation and at the same time increased membrane fluidity in accordance with their inhibitory effects. The saturated fatty acids and trans-unsaturated fatty acid tested for comparison had much lower or no effects on aggregation and membrane fluidity. The inhibitory effects of mono cis-unsaturated fatty acids increased with increase of their alkyl chain length. cis-Unsaturated fatty acids with two or more double bonds had more inhibitory effects than mono-unsaturated fatty acids. The position of the double bonds had less influence than the number of double bonds. We also examined the effects of cis-unsaturated fatty acids on membrane fluidity with diphenylhexatriene and anthroyloxy derivatives of fatty acids as probes and observed increased fluidity to be considerable in the membrane. The alcohol analogs of cis-unsaturated fatty acids also inhibited aggregation and increased membrane perturbation. These results suggest that the inhibition of platelet aggregation by cis-unsaturated compounds is due to perturbation of the lipid layer.     

Membrane-destabilizing activity of pH-responsive cationic lysine-based surfactants: role of charge position and alkyl chain length

Many strategies for treating diseases require the delivery of drugs into the cell cytoplasm following internalization within endosomal vesicles. Thus, compounds triggered by low pH to disrupt membranes and release endosomal contents into the cytosol are of particular interest. Here, we report novel cationic lysine-based surfactants (hydrochloride salts of N(ε)- and N(α)-acyl lysine methyl ester) that differ in the position of the positive charge and the length of the alkyl chain. Amino acid-based surfactants could be promising novel biomaterials in drug delivery systems, given their biocompatible properties and low cytotoxic potential. We examined their ability to disrupt the cell membrane in a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model of endosomal membranes. Furthermore, we addressed the mechanism of surfactant-mediated membrane destabilization, including the effects of each surfactant on erythrocyte morphology as a function of pH. We found that only surfactants with the positive charge on the α-amino group of lysine showed pH-sensitive hemolytic activity and improved kinetics within the endosomal pH range, indicating that the positive charge position is critical for pH-responsive behavior. Moreover, our results showed that an increase in the alkyl chain length from 14 to 16 carbon atoms was associated with a lower ability to disrupt cell membranes. Knowledge on modulating surfactant-lipid bilayer interactions may help us to develop more efficient biocompatible amino acid-based drug delivery devices.     

The efficiency of various detergents for extraction and stabilization of acetylcholinesterase from bovine erythrocytes

The efficiency of several nonionic detergents and a homologous series of zwitterionic detergents for the extraction of acetylcholinesterase (EC 3.1.1.7) from bovine erythrocyte membranes was examined. Of the nonionic detergents examined, the polyoxyethylene-based Tweens were the least effective solubilizing agents. Within this series, increasing the length of the saturated fatty acid chain progressively decreased the efficiency of enzyme recovery, while unsaturation in the side chain reversed this trend. In the Lubrol detergents, where the chain length of the alcohol group is variable, an increase in the length of the polyoxyethylene glycol group decreased the recovery of acetylcholinesterase in the solubilized state, without affecting the efficiency of extraction of total erythrocyte protein. As with the other nonionic detergents examined, Triton X-100 and octyl beta-D-glucoside were maximally effective in solubilizing acetylcholinesterase activity at concentrations greater than their respective critical micelle concentrations. In the sulfobetaine (N-alkyldimethylaminopropane sulphonate) zwitterionic detergent series, the longer alkyl chain zwittergents Z 316 and Z 314 were more efficient than the shorter chain length members of the series (Z 310 and Z 312). In contrast to the higher chain length compounds, short chain analogs were maximally effective at or below their critical micelle concentrations. After purification by ion-exchange chromatography and affinity chromatography, the enzyme extracted with the various detergents gave sedimentation coefficients between 6.8S and 7.6S, consistent with a dimeric structure. Acetylcholinesterase could also be efficiently released by 0.2 mM EDTA or 0.5 M NaCl from bovine erythrocyte membranes previously depleted of 70-80% of the membrane lipids by butanol. Nonlinear Arrhenius plots of enzyme activity were found whether acetylcholinesterase was solubilized with Tween 20, Lubrol PX, or Triton X-100. The present work confirms that bovine erythrocyte acetylcholinesterase requires detergents to solubilize it from membranes and that its activity depends on the structure of the amphiphiles used to solubilize the enzyme.     

Amphiphilic amine-N-oxides with aliphatic alkyl chain act as efficient superoxide dismutase mimics, antioxidants and lipid peroxidation blockers in yeast

Amphiphilic 3-(alkanoylamino)propyldimethylamine-N-oxides with different length of the alkyl chain, i.e. different hydrophilic-lipophilic balance, act in micromolar concentrations as SOD mimics by lifting the inhibition of aerobic growth caused by SOD deletions in Saccharomyces cerevisiae. They also enhance the survival of sod mutants of S. cerevisiae exposed to the hydrophilic superoxide-generating prooxidant paraquat and the amphiphilic hydroperoxide-producing tert-butylhydroperoxide (TBHP), and largely prevent TBHP-induced peroxidation of isolated yeast plasma membrane lipids. Unlike the SOD-mimicking effect, the magnitude of these effects depends on the alkyl chain length of the amine-N-oxides, which incorporate into S. cerevisiae membranes, causing fluidity changes in both the hydrophilic surface part of the membrane and the membrane lipid matrix. Unlike wild-type strains, the membranes of sod mutants were found to contain polyunsaturated fatty acids; the sensitivity of the mutants to lipophilic pro-oxidants was found to increase with increasing content of these acids. sod mutants are useful in assessing pro- and antioxidant properties of different compounds.     

A PAMPA Study of the Permeability‐Enhancing Effect of New Ceramide Analogues

There is a major need in drug discovery for quick, precise, and cost‐effective high‐throughput screening (HTS) systems in the early stages of drug research. The Parallel Artificial Membrane Permeability Assay (PAMPA) aims at predicting the passive membrane properties of drugs. Since 1998, model membranes have been developed to predict gastro‐intestinal absorption or transport through the blood–brain barrier. This paper presents recent results in a project aiming to improve the prediction of transdermal penetration. Using the PAMPA system, we investigated the effect of four newly synthetized ceramide analogues (certramides) on the permeability of three model compounds (ciprofloxacin, nifedipine, and verapamil). The certramides differ in the length of one alkyl chain, while the other alkyl chain and the head group remained the same. A relationship between the membrane concentration of certramides (from 0 to 100%) and the permeability of compounds was found, and the results of different certramides were compared. The strongest effect on permeability was caused by the ceramide analogue CTR(C₁₂–C₁₆). The reproducibility of the experiments and the impact of presence or absence of organic solvents (dodecane and CHCl₃) in the membrane were also investigated.     

Gemini ester quat surfactants and their biological activity

Cationic gemini surfactants are an important class of surface-active compounds that exhibit much higher surface activity than their monomeric counterparts. This type of compound architecture lends itself to the compound being easily adsorbed at interfaces and interacting with the cellular membranes of microorganisms. Conventional cationic surfactants have high chemical stability but poor chemical and biological degradability. One of the main approaches to the design of readily biodegradable and environmentally friendly surfactants involves inserting a bond with limited stability into the surfactant molecule to give a cleavable surfactant. The best-known example of such a compound is the family of ester quats, which are cationic surfactants with a labile ester bond inserted into the molecule. As part of this study, a series of gemini ester quat surfactants were synthesized and assayed for their biological activity. Their hemolytic activity and changes in the fluidity and packing order of the lipid polar heads were used as the measures of their biological activity. A clear correlation between the hemolytic activity of the tested compounds and their alkyl chain length was established. It was found that the compounds with a long hydrocarbon chain showed higher activity. Moreover, the compounds with greater spacing between their alkyl chains were more active. This proves that they incorporate more easily into the lipid bilayer of the erythrocyte membrane and affect its properties to a greater extent. A better understanding of the process of cell lysis by surfactants and of their biological activity may assist in developing surfactants with enhanced selectivity and in widening their range of application.     

Interaction of amphiphiles with integral membrane proteins. I. Structural destabilization of the anion transport protein of the erythrocyte membrane by fatty acids, fatty alcohols, and fatty amines

The effect of model amphiphiles on the structural stability of the anion exchange protein (band 3) of the human erythrocyte membrane was studied by differential scanning calorimetry. The concentration of membranes, as well as the concentration, head group, alkyl chain length, degree of unsaturation, and double bond configuration of a variety of alkane derivatives were all varied in a systematic way. The depression of the denaturation temperature of band 3 per unit membrane concentration of the amphiphile was then determined in order to quantitate the potency of each drug. Saturated fatty acids of chain length C8 to C24 displayed a monotonic decrease in potency up to C20, followed by a dramatic diminution in potency at C22 and C24. Unsaturation caused only minor increases in the abilities of fatty acids to perturb the anion exchanger, and surprisingly, there was neither a trend for the number of double bonds nor a significant cis-trans distinction. Arachidonic acid, as an exception, was much more effective than any other amphiphile in destabilizing band 3. Fatty acids were about three times more potent than fatty amines and fatty alcohols; however, the enhanced partitioning of the latter into the membrane compensated at certain membrane/buffer ratios for its reduced intrinsic potency. A quantitative model interpretation of the data is presented in an accompanying paper.     

Effects of platelet activating factor and related lipids on phase transition of dipalmitoylphosphatidylcholine

Recent evidence localizing the inflammatory mediator, platelet activating factor, (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) to the membranes of stimulated neutrophils raises the possibility that PAF may, in addition to its activities as a mediator, alter the physical properties of membranes. Accordingly, the effects of PAF and related alkyl ether and acyl analogs on phase transition thermodynamics of dipalmitoylphosphatidylcholine (DPPC) were studied using fluorescence polarization of the fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH). PAF, its ester analog (1-palmitoyl-2-acetylphosphatidylcholine) and both the corresponding alkyl and acyl lysophospholipid analogs (each at a concentration of 10 mol%) significantly decreased the phase transition temperature and broadened the phase transition of DPPC (P less than 0.05). The relative potency of the lipids in causing this effect was ester-PAF greater than or equal to PAF greater than or equal to lyso-PAF greater than lyso-PC suggesting that the fluidization of the synthetic membranes was attributable to both the 2-position acetyl group and the 1-position alkyl linkage. Furthermore, using various related compounds, increases in chain length and degree of unsaturation in the 2-position were shown to enhance the depression in transition temperature and broadening of the phase transition. Phase transition thermodynamics were also assessed using differential scanning calorimetry. Similar depression in the phase transition temperature was measured for PAF and both the alkyl and acyl lysophospholipids. Broadening of the phase transition for DPPC by the various analogs was assessed by calculation of transition peak width and cooperative unit. Data from fluorescence polarization and differential scanning calorimetry provide similar though not identical results and support the hypothesis that the unique features of PAF may alter membrane physical properties and could ultimately explain some of its biologic actions.     

Nonallergenic urushiol derivatives inhibit the oxidation of unilamellar vesicles and of rat plasma induced by various radical generators

Urushiols consist of an o-dihydroxybenzene (catechol) structure and an alkyl chain of 15 or 17 carbons in the 3-position of a benzene ring and are allergens found in the family Anacardiaceae. We synthesized various veratrole (1,2-dimethoxybenzene)-type and catechol-type urushiol derivatives that contained alkyl chains of various carbon atom lengths, including –H, –C₁H₃, –C₅H₁₁, –C₁₀H₂₁, –C₁₅H₃₁, and –C₂₀H₄₁, and investigated their contact hypersensitivities and antioxidative activities. 3-Decylcatechol and 3-pentadecylcatechol displayed contact hypersensitivity, but the other compounds did not induce an allergic reaction, when the ears of rats were sensitized by treatment with the compounds every day for 20 days. Catechol-type urushiol derivatives (CTUDs) exerted very high radical-scavenging activity on the 1,1-diphenyl-2-picrylhydrazyl radical and inhibited lipid peroxidation in a methyl linoleate solution induced by 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN). However, veratrole-type urushiol derivatives did not scavenge or inhibit lipid peroxidation. CTUDs also acted as effective inhibitors of lipid peroxidation of the egg yolk phosphatidylcholine large unilamellar vesicle (PC LUV) liposome system induced by various radical generators such as AMVN, 2,2′-azobis(2-amidino-propane) dihydrochloride, and copper ions, although their efficiencies differed slightly. In addition, CTUDs suppressed formation of cholesteryl ester hydroperoxides in rat blood plasma induced with copper ions. CTUDs containing more than five carbon atoms in the alkyl chain showed excellent lipophilicity in a n-octanol/water partition experiment. These compounds also exhibited high affinities to the liposome membrane using the ultrafiltration method of the PC LUV liposome system. Therefore, CTUDs seem to act as efficient antioxidative compounds against membranous lipid peroxidation owing to their localization in the phospholipid bilayer. These results suggest that nonallergenic CTUDs act as antioxidants to protect against oxidative damage of cellular and subcellular membranes.     

Antioxidative activity of some phenoxy and organophosphorous compounds

Experiments were performed in order to check whether biological activity of some organophosphorous compounds widely applied as herbicides: 2,4-dichlorophenoxyacetic acid (1) and its sodium salt (2), N-phosphonomethylglycine acid (3) and its sodium salt (4), diethyl 1-butylamino-1-cyclohexanephosphonate (5) and diethyl 9-butylamino-9-fluorenephosphonate (6) followed from their oxidative activity. The compounds studied differed in their polarity and hydrophobicity. On the contrary, it was found that all herbicides protected erythrocyte membranes against partial peroxidation induced by UV irradiation. The effect was somewhat differentiated and followed the sequence: 5 >1 >2 >6 >3 >4. The observed differences between the antioxidative activities of the compounds are probably related to differences in their ability to incorporate into the lipid phase of the erythrocyte membrane. Once incorporated, they change fluidity of the membranes. The extent of the changes was determined in fluorescence measurements. Polarization and anisotropy coefficients of erythrocyte membranes modified by micromolar concentrations of herbicides at different temperatures were measured for that purpose. Generally, they followed the sequence found for antioxidative activity of the herbicides studied, which confirms the assumption of close correlation between the depth of incorporation of a herbicide into the erythrocyte membrane and its protective efficiency.     

Effects of alkyl chain length of gallate on self-association and membrane binding

Alkyl gallates are anticipated for their use as anti-bacterial and anti-viral agents. Although their pharmacological activities depend on their alkyl chain length, no mechanism has yet been clarified. As described herein, we investigated the membrane binding properties of a series of alkyl gallates using fluorescence measurement to elucidate their different pharmacological activities. Membrane binding of the alkyl gallates increased concomitantly with increasing alkyl chain length, except for cetyl gallate and stearyl gallate. Dynamic light scattering revealed that alkyl gallates with a long alkyl chain are prone to self-association in the solution. Membrane binding abilities of the alkyl gallates are correlated with anti-bacterial and anti-virus activities, as described in previous reports. The partition constants of the alkyl gallates to lipid membranes depend on the membrane components and the membrane phase. Self-association and lipid binding of the alkyl gallates might be primary biophysical factors associated with their pharmacological activities.     

Glycoalkaloids selectively permeabilize cholesterol containing biomembranes

The effects of the glycoalkaloids α-solanine, α-chaconine and α-tomatine on different cell types were studied in order to investigate the membrane action of these compounds. Hemolysis of erythrocytes was compared to 6-carboxyfluorescein leakage from both ghosts and erythrocyte lipid vesicles, whereas leakage of enzymes from mitochondria and the apical and baso-lateral side of Caco-2 cells was determined. Furthermore, the effects of glycoalkaloids on the gap-junctional communication between Caco-2 cells was studied. From these experiments, it was found that glycoalkaloids specifically induced membrane disruptive effects of cholesterol containing membranes as was previously reported in model membrane studies. In addition, α-chaconine was found to selectively decrease gap-junctional intercellular communication. Furthermore, the glycoalkaloids were more potent in permeabilizing the outer membrane of mitochondria compared to digitonin at the low concentrations used.     

Caffeic acid phenolipids in the protection of cell membranes from oxidative injuries. Interaction with the membrane phospholipid bilayer

Caffeic acid (CA) has demonstrated a strong intracellular antioxidant ability by scavenging ROS, contributing to the maintenance of cell membrane structural integrity and to reduce oxidative injuries in other cell components. Nevertheless, caffeic acid has limited usage, due to its hydrophilic character. In this work, the introduction of alkyl chains in the caffeic acid molecule by esterification (methyl - C1, ethyl - C2, butyl - C4, hexyl - C6, octyl - C8 and hexadecyl - C16), significantly increased its lipophilicity. All caffeates tested showed a much higher protective activity than caffeic acid against red blood cells (RBCs) AAPH-induced oxidative stress; this protection was heavily dependent on the length of the alkyl chain of the esters, and on their concentration. At 2.5 and 5 μM, the more lipophilic compounds (C8 and C16) showed a remarkable antioxidant activity, inhibiting hemolysis; probably, their better location within the membrane leads to a better antioxidative protection; however, at 50 μM, the more hydrophilic compounds (C1-C4) showed a better activity against hemolysis than the more lipophilic ones (C8-C16). At this higher concentration, the better interaction of the more lipophilic compounds with the membrane seems to cause changes in RBC membrane fluidity, disturbing membrane integrity. Our data show that the antioxidant activity of these compounds could play an important role for the protection of different tissues and organs, by protecting cell membranes from oxidative injuries.     

Synergistic effects of anacardic acids and methicillin against methicillin resistant Staphylococcus aureus

The synergistic effects of 6-alk(en)ylsalcylic acids, also known as anacardic acids, in combination with methicillin against Staphylococcus aureus ATCC 33591 (MRSA) was investigated. The double bond in C15-anacardic acids is not essential in eliciting the antibacterial activity but is associated with increasing the activity. The synergistic effects decreased with increasing the number of double bonds in the alkyl chain. On the other hand, the antibacterial activity of anacardic acids possessing different alkyl chain lengths against the same MRSA strain was found to be a parabolic function of their lipophilicity and maximized with the alkyl chain length of C10 and C12. Notably, the synergistic effects were noted to increase with increasing the alkyl chain length.