Dodecylglycerol. A new type of antibacterial agent which stimulates autolysin activity in Streptococcus faecium ATCC 9790

Synthesis, characterization, antibacterial and antifungal activities of 1-O-alkylglycerols

1-O-alkylglycerols are a class of natural existing lipids with broad biological activities. However, their use in food or agricultural fields remains to be investigated, especially for their antimicrobial activity. In this work, three 1-O-alkylglycerols, 1-O-octanylglycerol (C8Gly1), 1-O-dodecylglycerol (C12Gly1), and 1-O-hexadecylglycerol (C16Gly1), were synthesized in the isolated yields of 71.3-89.8 % and characterized by 1H NMR, 13C NMR, FITR, mass spectra, and HPLC-ESLD. The critical micelle concentration (CMC) of 1-O-alkylglycerols was determined to be 1.65 mmol/L (C8Gly1), 0.33 mmol/L (C12Gly1), and 0.23 mmol/L (C16Gly1) using the pyrene method. C12Gly1 and C16Gly1 had similar surface tensions that are lower than C8Gly1. C8Gly1 can form micelles in aqueous solution with excellent nano-dispersed uniformity and stability. Furthermore, C8Gly1 and C12Gly1 not only displayed good antibacterial activity against Staphylococcus aureus, but they also inhibited the growth of Botryosphaeria dothidea, Monilia fructigena, and Phytophthora capsicum at 400 μg/mL. Thus, the C8Gly1 and C12Gly1 can serve as novel antimicrobial agents in food preservation.

Natural and Enantiopure Alkylglycerols as Antibiofilms Against Clinical Bacterial Isolates and Quorum Sensing Inhibitors of Chromobacterium violaceum ATCC 12472

Resistance mechanisms occur in almost all clinical bacterial isolates and represent one of the most worrisome health problems worldwide. Bacteria can form biofilms and communicate through quorum sensing (QS), which allow them to develop resistance against conventional antibiotics. Thus, new therapeutic candidates are sought. We focus on alkylglycerols (AKGs) because of their recently discovered quorum sensing inhibition (QSI) ability and antibiofilm potential. Fifteen natural enantiopure AKGs were tested to determine their effect on the biofilm formation of other clinical bacterial isolates, two reference strains and their QSI was determined using Chromobacterium violaceum ATCC 12472. The highest biofilm inhibition rates (%) and minimum QS inhibitory concentration were determined by a microtiter plate assay and ciprofloxacin was used as the standard antibiotic. At subinhibitory concentrations, each AKG reduced biofilm formation in a concentration-dependent manner against seven bacterial isolates, with values up to 97.2%. Each AKG displayed QSI at different levels of ability without affecting the growth of C. violaceum. AKG (2S)-3-O-(cis-13’-docosenyl)-1,2-propanediol was the best QS inhibitor (20 μM), while (2S)-3-O-(cis-9’-hexadecenyl)-1,2-propanediol was the least effective (795 μM). The results showed for the first time the QSI activity of this natural AKG series and suggest that AKGs could be promising candidates for further studies on preventing antimicrobial resistance.

Functional lipidomics of vascular endothelial cells in response to laminar shear stress

Laminar shear stress generated by blood flow stimulates endothelial cells and activates signal transduction, which plays an important role in vascular homeostasis. Several lines of evidence indicate that membrane and intracellular lipids are involved in the signal transduction of biomechanical stresses. In this study, we performed global profiling of cellular lipids from human pulmonary artery endothelial cells (HPAEC) exposed to laminar shear stress. A total of 761 species of lipids were successfully annotated, with 198 of these species significantly changed in response to shear stress for 24 hours. Ether-linked lipids containing an alkyl moiety with a medium chain length (C11-C14) were uniquely upregulated, and the administration of their biosynthetic precursor 1-O-dodecyl-rac-glycerol attenuated phorbol 12-myristate 13-acetate (PMA) induced vascular cell adhesion molecule-1 (VCAM-1) expression. Given the pro-inflammatory and atherogenic roles of VCAM-1, our findings suggest that the induction of a specific group of lipids (ie, ether-linked lipids with medium length alkyl side chain) may confer atheroprotective and anti-inflammatory roles to vascular endothelial cells under flow conditions.

Characterizing the Membrane-Disruptive Behavior of Dodecylglycerol Using Supported Lipid Bilayers

Monoglycerides are esterified adducts of fatty acid and glycerol molecules that disrupt phospholipid membranes, leading to a wide range of biological functions such as antimicrobial activity. Among monoglycerides, glycerol monolaurate (GML) exhibits particularly high antimicrobial activity, although enzymatic hydrolysis of its ester group can diminish potency. Consequently, there have been efforts to identify more chemically stable versions of GML, most notably its alkylglycerol ether equivalent called dodecylglycerol (DDG). However, despite high structural similarity, biological studies indicate that DDG and GML are not functionally equivalent and it has been speculated that the two compounds might have different interaction profiles with phospholipid membranes. To address this outstanding question, herein, we employed supported lipid bilayer (SLB) platforms to experimentally characterize the interactions of DDG with phospholipid membranes. Quartz crystal microbalance-dissipation experiments identified that DDG causes concentration-dependent membrane morphological changes in SLBs and the overall extent of membrane remodeling events was greater than that caused by GML. In addition, time-lapsed fluorescence microscopy imaging experiments revealed that DDG causes extensive membrane tubulation that is distinct from how GML induces membrane budding. We discuss how differences in the head group properties of DDG and GML contribute to distinct membrane interaction profiles, offering insight into how the molecular design of DDG not only improves chemical stability but also enhances membrane-disruptive activity.

Synthesis, surfactant properties and antimicrobial activities of methyl glycopyranoside ethers

A series of amphiphilic methyl glucopyranoside ethers incorporating various alkyl chain lengths has been synthesized from commercially available methyl glucopyranosides following an acetalisation/hydrogenolysis sequence. The amphiphilic properties of ethers and acetal intermediates were evaluated. Both families exhibit excellent surfactant properties with a maximum efficiency obtained for compounds bearing a linear dodecyl chain (CMC = 0.012 mM, γ_sat. = 30 mN m^-1). Antimicrobial activity studies revealed an efficient activity (0.03 < MIC < 0.12 mM) against Gram-positive bacteria such as Listeria monocytogenes, Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus. More importantly, these compounds were found to be active against multi-resistant strains such as vancomycin-, methicillin- and daptomycin-resistant strains. Finally, it was found that antimicrobial activities are closely related to physicochemical properties and are also influenced by the nature of the carbohydrate moiety.

A thioesterase bypasses the requirement for exogenous fatty acids in the plsX deletion of Streptococcus pneumoniae

PlsX is an acyl-acyl carrier protein (ACP):phosphate transacylase that interconverts the two acyl donors in Gram-positive bacterial phospholipid synthesis. The deletion of plsX in Staphylococcus aureus results in a requirement for both exogenous fatty acids and de novo type II fatty acid biosynthesis. Deletion of plsX (SP0037) in Streptococcus pneumoniae did not result in an auxotrophic phenotype. The ΔplsX S. pneumoniae strain was refractory to myristic acid-dependent growth arrest, and unlike the wild-type strain, was susceptible to fatty acid synthesis inhibitors in the presence of exogenous oleate. The ΔplsX strain contained longer chain saturated fatty acids imparting a distinctly altered phospholipid molecular species profile. An elevated pool of 18- and 20-carbon saturated fatty acids was detected in the ΔplsX strain. A S. pneumoniae thioesterase (TesS, SP1408) hydrolyzed acyl-ACP in vitro, and the ΔtesS ΔplsX double knockout strain was a fatty acid auxotroph. Thus, the TesS thioesterase hydrolyzed the accumulating acyl-ACP in the ΔplsX strain to liberate fatty acids that were activated by fatty acid kinase to bypass a requirement for extracellular fatty acid. This work identifies tesS as the gene responsible for the difference in exogenous fatty acid growth requirement of the ΔplsX strains of S. aureus and S. pneumoniae.

Impact of fish oils on the outcomes of a mouse model of acutePseudomonas aeruginosapulmonary infection

Pseudomonas aeruginosais an opportunistic Gram-negative bacterium that causes pneumonia in immunocompromised humans and severe pulmonary damage in patients with cystic fibrosis. Imbalanced fatty acid incorporation in membranes, including increased arachidonic acid and decreased DHA concentrations, is known to play a critical role in chronic inflammation associated with bacterial infection. Other lipids, such as EPA and alkylglycerols, are also known to play a role in inflammation, particularly by stimulating the immune system, decreasing inflammation and inhibiting bacterial growth. In this context, the goal of the present study was to assess the effect of dietary DHA/EPA, in a 2:1 ratio, and alkylglycerols, as natural compounds extracted from oils of rays and chimeras, respectively, on the inflammatory reaction induced byP. aeruginosapulmonary infection in mice. To this end, mice were fed with a control diet or isolipidic, isoenergetic diets prepared with oils enriched in DHA/EPA (2:1) or alkylglycerols for 5 weeks before the induction of acuteP. aeruginosalung infection by endotracheal instillation. In our model, DHA/EPA (2:1) significantly improved the survival of mice after infection, which was associated with the acceleration of bacterial clearance and the resolution of inflammation leading to the improvement of pulmonary injuries. By contrast, alkylglycerols did not affect the outcomes ofP. aeruginosainfection. Our findings suggest that supplementation with ray oil enriched in DHA/EPA (2:1) can be considered as a preventive treatment for patients at risk forP. aeruginosainfection.

Ether-type moieties in the lipid part of glycoinositolphospholipids of Acanthamoeba rhysodes

Ether lipids were identified among components liberated with HF and nitrous acid deamination from Acanthamoeba rhysodes whole cells and its membrane glycoinositolphospholipids (GIPL). Liberated ether glycerols were converted to various derivatives that served characterization thereof. These included TMS and isopropylidene derivatives, oxidation with sodium periodate to aldehyde followed by reduction with NaBH4 to alcohol, and reaction of the alcohol with acetic anhydrite to form acetate derivatives. Periodate sensitivity demonstrated that the alkyl side chains were linked to the sn-1 position of glycerol. Combined information from TLC, GC-MS analysis, MALDI-TOF spectrometry, and chemical degradation experiments indicated the presence of ether-linked saturated normal and branched hydrocarbons with a length of C20-23 in the phospholipid fraction, C20-24 in free GPI, and C21-23 in the LPG polymer. The distribution of particular classes of alkylglycerols was similar for phospholipid and GPI fractions, and amounted to 2.62% (±0.04-0.28) 1-O-eicosanyl-sn-glycerol, 16.66% (±0.32-1.1) 1-O-uncosanyl-sn-glycerol, 9.18% (±0.33-1.37) anteiso-1-O-docosanyl-sn-glycerol, 47.56% (±0.32-2.14) 1-O-docosanyl-sn-glycerol, 20.56% (±0.58-1.67) anteiso-1-O-tricosanyl-sn-glycerol, and 2.34% (±0.12-0.63) 1-O-tricosanyl-sn-glycerol. For LPG preparation, the most abundant were anteiso-1-O-tricosanyl-sn-glycerol (57.26%) and 1-O-docosanyl-sn-glycerol (30.12%). The data from TLC and GC-MS analysis showed that ether lipids from phospholipids probably represent the lyso-alkylglycerol type, while those derived from GIPL are alkylacylglycerol moieties.

Host gene expression profiling and in vivo cytokine studies to characterize the role of linezolid and vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) murine sepsis model

Linezolid (L), a potent antibiotic for Methicillin Resistant Staphylococcus aureus (MRSA), inhibits bacterial protein synthesis. By contrast, vancomycin (V) is a cell wall active agent. Here, we used a murine sepsis model to test the hypothesis that L treatment is associated with differences in bacterial and host characteristics as compared to V. Mice were injected with S. aureus USA300, and then intravenously treated with 25 mg/kg of either L or V at 2 hours post infection (hpi). In vivo alpha-hemolysin production was reduced in both L and V-treated mice compared to untreated mice but the reduction did not reach the statistical significance [P = 0.12 for L; P = 0.70 for V). PVL was significantly reduced in L-treated mice compared to untreated mice (P = 0.02). However the reduction of in vivo PVL did not reach the statistical significance in V- treated mice compared to untreated mice (P = 0.27). Both antibiotics significantly reduced IL-1β production [P = 0.001 for L; P = 0.006 for V]. IL-6 was significantly reduced with L but not V antibiotic treatment [P<0.001 for L; P = 0.11 for V]. Neither treatment significantly reduced production of TNF-α. Whole-blood gene expression profiling showed no significant effect of L and V on uninfected mice. In S. aureus-infected mice, L altered the expression of a greater number of genes than V (95 vs. 42; P = 0.001). Pathway analysis for the differentially expressed genes identified toll-like receptor signaling pathway to be common to each S. aureus-infected comparison. Expression of immunomodulatory genes like Cxcl9, Cxcl10, Il1r2, Cd14 and Nfkbia was different among the treatment groups. Glycerolipid metabolism pathway was uniquely associated with L treatment in S. aureus infection. This study demonstrates that, as compared to V, treatment with L is associated with reduced levels of toxin production, differences in host inflammatory response, and distinct host gene expression characteristics in MRSA sepsis.

Orphan enzymes in ether lipid metabolism

Ether lipids are an emerging class of lipids which have so far not been investigated and understood in every detail. They have important roles as membrane components of e.g. lens, brain and testis, and as mediators such as platelet-activating factor. The metabolic enzymes for biosynthesis and degradation have been investigated to some extent. As most involved enzymes are integral membrane proteins they are tricky to handle in biochemical protocols. The sequence of some ether lipid metabolising enzymes has only recently been reported and other sequences still remain obscure. Defined enzymes without assigned sequence are known as orphan enzymes. One of these enzymes with uncharacterised sequence is plasmanylethanolamine desaturase, a key enzyme for the biosynthesis of one of the most abundant phospholipids in our body, the plasmalogens. This review aims to briefly summarise known functions of ether lipids, give an overview on their metabolism including the most prominent members, platelet-activating factor and the plasmalogens. A special focus is set on the description of orphan enzymes in ether lipid metabolism and on the successful strategies how four previous orphans have recently been assigned a sequence. Only one of these four was characterised by classical protein purification and sequencing, whereas the other three required alternative strategies such as bioinformatic candidate gene selection and recombinant expression or development of an inhibitor and multidimensional metabolic profiling.

Ether lipids

The naturally occurring 1-O-alkyl-sn-glycerols and their methoxylated congeners, 1-O-(2'-methoxyalkyl)-sn-glycerols, are biologically active compounds, ubiquitously found in nature as diacyl glyceryl ether lipids and phosphoether lipids. The chief objective of this article is to provide a comprehensive and up to date review on such ether lipids. The occurrence and distribution of these compounds in nature are extensively reviewed, their chemical structure and molecular variety, their biosynthesis and chemical synthesis and, finally, their various biological effects are described and discussed. An unprecedented biosynthesis of the 2'-methoxylated alkylglycerols is proposed. The first synthesis of enantiopure (Z)-(2'R)-1-O-(2'-methoxyhexadec-4'-enyl)-sn-glycerol, the most prevalent 2'-methoxylated type alkylglycerol present in cartilaginous fish, is described. It was accomplished by a highly convergent five step process.

An update on the therapeutic role of alkylglycerols

Scandinavian folk medicine used shark liver oil for the treatment of cancers and other ailments based on the rarity of tumors in sharks and their ability to resist infections. Shark liver oil is a source of alkylglycerols which have been studied as anti-cancer agents in several clinical trials. Moreover, alkylglycerols have been investigated for the treatment of radiation induced side effects and for their ability to boost the immune system. Several experimental studies have shown the ability of alkylglycerols to open the blood brain barrier to facilitate the access of therapeutic drugs to the central nervous system. This review covers the most important studies of alkylglycerols in both animals and humans.

Glycerol monolaurate and dodecylglycerol effects on Staphylococcus aureus and toxic shock syndrome toxin-1 in vitro and in vivo

Background

Glycerol monolaurate (GML), a 12 carbon fatty acid monoester, inhibits Staphylococcus aureus growth and exotoxin production, but is degraded by S. aureus lipase. Therefore, dodecylglycerol (DDG), a 12 carbon fatty acid monoether, was compared in vitro and in vivo to GML for its effects on S. aureus growth, exotoxin production, and stability.

Methodology/Principal Findings

Antimicrobial effects of GML and DDG (0 to 500 µg/ml) on 54 clinical isolates of S. aureus, including pulsed-field gel electrophoresis (PFGE) types USA200, USA300, and USA400, were determined in vitro. A rabbit Wiffle ball infection model assessed GML and DDG (1 mg/ml instilled into the Wiffle ball every other day) effects on S. aureus (MN8) growth (inoculum 3×10⁸ CFU/ml), toxic shock syndrome toxin-1 (TSST-1) production, tumor necrosis factor-α (TNF-α) concentrations and mortality over 7 days. DDG (50 and 100 µg/ml) inhibited S. aureus growth in vitro more effectively than GML (p<0.01) and was stable to lipase degradation. Unlike GML, DDG inhibition of TSST-1 was dependent on S. aureus growth. GML-treated (4 of 5; 80%) and DDG-treated rabbits (2 of 5; 40%) survived after 7 days. Control rabbits (5 of 5; 100%) succumbed by day 4. GML suppressed TNF-α at the infection site on day 7; however, DDG did not (<10 ng/ml versus 80 ng/ml, respectively).

Conclusions/Significance

These data suggest that DDG was stable to S. aureus lipase and inhibited S. aureus growth at lower concentrations than GML in vitro. However, in vivo GML was more effective than DDG by reducing mortality, and suppressing TNF-α, S. aureus growth and exotoxin production, which may reduce toxic shock syndrome. GML is proposed as a more effective anti-staphylococcal topical anti-infective candidate than DDG, despite its potential degradation by S. aureus lipase.

Characterization of monolaurin resistance in Enterococcus faecalis

There is increasing concern regarding the presence of vancomycin-resistant enterococci in domestically farmed animals, which may act as reservoirs and vehicles of transmission for drug-resistant enterococci to humans, resulting in serious infections. In order to assess the potential for the use of monolaurin as a food preservative, it is important to understand both its target and potential mechanisms of resistance. A Tn917 mutant library of Enterococcus faecalis AR01/DGVS was screened for resistance (MIC, >100 microg/ml) to monolaurin. Three mutants were identified as resistant to monolaurin and were designated DGRM2, DGRM5, and DGRM12. The gene interrupted in all three mutants was identified as traB, which encodes an E. faecalis pheromone shutdown protein and whose complementation in trans restored monolaurin sensitivity in all three mutants. DGRM2 was selected for further characterization. E. faecalis DGRM2 showed increased resistance to gentamicin and chloramphenicol (inhibitors of protein synthesis), while no difference in the MIC was observed with the cell wall-active antibiotics penicillin and vancomycin. E. faecalis AR01/DGVS and DGRM2 were shown to have similar rates (30% cell lysis after 4 h) of cell autolytic activity when activated by monolaurin. Differences in cell surface hydrophobicity were observed between the wild type and the mutant, with the cell surface of the parent strain being significantly more hydrophobic. Analysis of the cell wall structure of DGRM2 by transmission electron microscopy revealed an increase in the apparent cell wall thickness and contraction of its cytoplasm. Taken together, these results suggest that the increased resistance of DGRM2 was due to a change in cell surface hydrophobicity, consequently limiting the diffusion of monolaurin to a potential target in the cytoplasmic membrane and/or cytoplasm of E. faecalis.

In vitro and in vivo evaluations of the activities of lauric acid monoester formulations against Staphylococcus aureus

Due to increasing mupirocin resistance, alternatives for Staphylococcus aureus nasal decolonization are needed. Lauric acid monoesters combined with lactic, mandelic, malic, or benzoic acid are being evaluated as possible alternatives. We determined the in vitro activity of 13 lauric acid monoester (LAM) formulations and mupirocin against 30 methicillin-susceptible S. aureus (MSSA) isolates and 30 methicillin-resistant S. aureus (MRSA) isolates. We then used a murine model of MRSA nasopharyngeal colonization to compare the in vivo activity of mupirocin with three LAM formulations. MSSA and MRSA MIC(90) values were 0.25 microg/ml for mupirocin and </=4 microl/ml for all LAM formulations tested. Hsd:ICR mice were challenged with 10(8) CFU/naris MRSA. Five days later, S. aureus colonization was documented by culture. Treatment with bland, mupirocin, or one of three LAM ointments was then administered unblinded thrice daily for 2 days. Three days after treatment, both anterior nares were cultured for S. aureus. Administration of 128774-49E or 128774-53A was associated with greater eradication of MRSA carriage (24/34 [71%] or 33/40 [83%]) of animals, respectively) than bland ointment (12/38 [32%]) (P < 0.005). 128774-53A administration resulted in greater MRSA carriage eradication than mupirocin (19/38 [50%]) (P < 0.005) in this model. LAM formulations warrant evaluation for S. aureus nasal decolonization in humans.

1-O-Alkylglycerol vesicles (Algosomes): their formation and characterization

1-O-alkylglycerols (ALKG) have exhibited several biological activities and a prominent effect on blood-brain barrier permeability. They have markedly improved brain uptake of cancerostatic agents. Since ALKG are amphiphilic, we explored their tendency to assemble into bilayer vesicles, which can be applied as carriers for drugs. Vesicles (Algosomes) were formed by film hydration method using ALKG (tetra-, penta-, hexa-, hepta-, octa- or nona-decylglycerols) in combination with cholesterol (CHOL) and dicetyl phosphate (DCP) (1-O-alkylglycerol:CHOL:DCP in 45:45:10 molar ratio). On microscopic examination, the algosomes were found to be conspicuously spherical and the dispersion was a mixture of multi-lamellar and small-unilamellar vesicles. Phase transition temperatures of 1-O-hexadecylglycerol (HXDG) and CHOL mixtures were tested by differential scanning calorimetry (DSC). The changes in phase transition temperatures indicate the vesicle forming tendency of ALKG in presence of CHOL. Alkyl chain length dependent variations in vesicle size, zeta-potential (ZP) and capture volume (CV) could not be observed. Vesicles of 1-O-tetradecylglycerol (TTDG) showed improvement in CV with increase in CHOL content from 15 to 55 mol%. However the vesicle size decreased. On challenging algosomes with hypertonic salt solution [potassium iodide (KI) in water], vesicle size decreased and thus algosomes were found to be osmotically sensitive. Algosome dispersions on addition of higher concentrations of KI (40-100 mM) brought about increases in vesicle size and at concentrations 60 mM and above showed aggregation. All vesicular dispersions were stable for only a few days.

Synthesis of structured lipids and etherlipids with antioxidants: combination of a selena fatty acid and a selena fatty alcohol with a carotenoic acid in glyceride molecules

Selenium and carotenoids show similar and complementary properties and protect against a variety of pathological processes. Mixtures of both compounds are found in nutritional supplements and are used to prevent several diseases. The synthetic connection of carotenoids with selenium in glycerols may increase the chemopreventive activity of the individual compounds. Beta-apo-8'-carotenoic acid and 7-selenacapryloic acid were esterified with glycerol to highly unsaturated stable di- and triglycerides. Intramolecular selenium:carotenoid ratios of 1:1, 2:1 and 1:2 were obtained for 1-(7-selenaoctanoyl)-3-(3beta-apo-8 -carotenoyl)-glycerol, 1,3-di-(beta-apo-8'-carotenoyl)-2-(7-selenaoctanoyl)-glycero l and 1,2-di-(7-selenaoctanoyl)-3-(beta-apo-8'-carotenoyl)-glycero l, respectively. The carotenoic acid was likewise connected to the pharmacologically interesting 11-selenalaurylglycerolether forming an alkyl-acylglyceride: 1-(11-selenadodecyl)-3-(beta-apo-8'-carotenoyl)-glycerol.

Antibacterial activity of 7-aminocholesterol, a new sterol

A new sterol, 7-aminocholesterol, which inhibits growth of Saccharomyces cerevisiae, also displayed antibiotic activity against Gram-positive bacteria. The 50% growth inhibitory concentration against strains of Listeria innocua, L. monocytogenes, Staphylococcus aureus, Enterococcus hirae and Bacillus cereus was 3 microM.

Isolation and characterization of autolysis-defective mutants of Staphylococcus aureus created by Tn917-lacZ mutagenesis

Two autolysis-defective mutants (Lyt-1 and Lyt-2) of Staphylococcus aureus have been isolated by transposon Tn917-lacZ mutagenesis. The mutants exhibited normal growth rate, cell division, cell size, and adaptive responses to environmental changes. No autolytic activities were detected in a crude autolytic enzyme preparation from the Lyt- mutants. The rate of autolysis of whole cells and cell walls in the mutants were negligible, but mutant cell wall preparations were degraded by crude enzyme preparations from the wild-type strain. Zymographic analyses of enzyme extracts from the mutants showed a single autolytic enzyme band, compared with more than 10 autolytic enzyme bands from the parent strain. Analyses of intracellular and exoprotein fractions gave results similar to those in experiments with total-cell extracts. Southern blot analysis indicated the insertion of a single copy of the transposon into the chromosome of Lyt mutants. Isogenic Lyt mutants constructed by phage phi 11 transduction showed similar phenotypes. Because both Lyt- mutants had Tn917-lacZ inserted in the appropriate orientation, it was possible to determine gene activity under various conditions by measuring beta-galactosidase activity. The gene activity was found to be induced by low pH, low temperature, and high sucrose and high sodium chloride concentrations. From these data, we propose that the mutation lies in either a master regulatory gene or a structural gene which is responsible for the synthesis or processing of a majority of the autolytic enzyme bands.

Anti-neoplastic action of peritoneal macrophages following oral administration of ether analogues of lysophospholipids

Inflamed lesions of normal and cancerous tissues induce activation of phospholipase A in plasma membranes resulting in the release of various decomposed products of membranous lipids. Oral administration in mice of dodecylglycerol (DDG), a synthetic alkyglycerol, and an alkyl ether analogue of lysophospholipids, 1-0-octadecyl-2-0-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3-choline) efficiently activated peritoneal macrophages for enhanced Fc-mediated (fragment crystallisable) ingestion of red blood cells and direct cytotoxic action on retinoblastoma tumour cells. The activated macrophages not only inhibited tumour cell growth, but also markedly induced cytolysis of tumour cells. The antitumour capability of the macrophages was substantiated by luminol-enhanced chemiluminescence. These findings suggest that dodecylglycerol and ET-18-OCH3-choline administered orally retain their ability to induce a high level of macrophage activation and tumour cytotoxicity, just as occurs with intraperitoneal administration. Thus, these compounds have potential practical application in chemotherapy and immunotherapy of the tumour, which could be accomplished by simple oral rather than parenteral administration.

Regulation of neuronal differentiation in neuron-enriched primary cultures from embryonic rat cerebra by platelet activating factor and the structurally related glycerol ether lipid, dodecylglycerol

Primary cultures enriched in neurons dissociated from embryonic rat cerebra were used to demonstrate that platelet activating factor and the structurally related ether glycerolipid, dodecylglycerol, are readily taken up in small amounts by neurons and that they stimulate the differentiation of neurons. The stimulation of neuronal differentiation was observed as a precocious development of axon-like extensions which correlated with a concentration-dependent increase in neuronal-specific enzyme activities. This stimulation of morphological and neurochemical factors by either platelet activating factor or dodecylglycerol was almost completely abolished by triazolam, a known inhibitor of platelet activating factor function. Neither platelet activating factor nor dodecylglycerol at the concentrations used to achieve stimulation of neuronal differentiation compromised the plasma membrane, as indicated by the lack of leakage of cytoplasmic lactic acid dehydrogenase.

Induction of autolysis in Enterococcus faecalis S-47 by peptide AS-48

In addition to its bactericidal mode of action, the peptide antibiotic AS-48 exhibits a bacteriolytic effect on Enterococcus faecalis S-47 that is associated with autolysin activation. Bacteriolysis induced by the antibiotic can be modulated by addition of EDTA, divalent cations and autolysin activators (trypsin) or inhibitors (cardiolipin), suggesting that topologic regulation of the autolysins is involved in the process. In addition, inhibitors of protein and RNA synthesis interfere markedly with bacteriolysis, as do ionophores and the ATPase inhibitor DCCD, suggesting the participation of an internal messenger in autolysin activation in the presence of AS-48.

Synergism between penicillin G and the antimicrobial ether lipid, rac-1-dodecylglycerol, acting below its critical micelle concentration

rac-1-Dodecylglycerol (DDG) and penicillin G (Pen G) act synergistically to dramatically lower the minimum inhibitory concentration (MIC) of each other in four Gram-positive bacteria studied. At one-half its MIC, DDG ether lowered the MIC of Pen G 10- to 80-fold. Under the same conditions, Pen G lowered the MIC of DDG 4- to 7.5-fold. The critical micelle concentration of DDG was determined to be 7.93 mg/ml (0.0305 mM), which is approximately two-fold greater than the minimum inhibitory concentration of DDG determined in the presence of a protein-free chemically defined medium. This finding suggests that DDG is not killing bacteria through its detergent action. Pen G also did not alter the critical micelle concentration of DDG, which indicates that the synergism between these two agents is not related to micelle formation.

In vivo studies on stereospecificity of the monoglyceride kinase, lysophosphatidic acid acyltransferase, phosphatidic acid phosphatase and CDP-diglyceride synthase of Streptococcus mutans BHT using the stereoisomers of the ether lipid, dodecylglycerol

Streptococcus mutans BHT metabolizes radioactive 3-dodecyl-sn-glycerol (sn-3-DDG) almost exclusively to lysophosphatidic acid, phosphatidic acid and 1,3-diradyl-sn-glycerol, whereas the cells of this organism metabolize 1-dodecyl-sn-glycerol (sn-1-DDG) to all of the glycerol lipids of S. mutans BHT, with the largest amounts incorporated into phosphatidylglycerol and diradylglycerol (mostly the 1,2- but also the 1,3-isomer). (The common names of lipids, such as phosphatidic acid, are used in the broader sense to mean that the lipid may contain alkyl as well as acyl groups.) The addition of an equivalent amount of nonradioactive sn-3-DDG to radioactive sn-1-DDG causes more of the radioactivity to accumulate at phosphatidic acid. These results indicate that the monoglyceride kinase (EC 2.7.1.94), lysophosphatidic acid acyltransferase (EC 2.3.1.40) and the monoglyceride acyltransferase (EC 2.3.1.22) enzymatic reactions are not stereospecific, and that the CDP-diglyceride synthase (EC 2.7.7.41) and phosphatidic acid phosphatase (EC 3.1.3.4) metabolic steps are stereospecific in S. mutans BHT. The synthesis of phosphatidic acid and lysophosphatidic acid from sn-3-DDG provides a unique method for synthesizing these glycerol lipids with the uncommon stereochemical configuration in which the phosphate moiety is in the sn-1 position.

Biosynthesis and biotransformation of ether lipids

Some naturally occurring as well as synthetic ether lipids are biologically active. In certain cases, the effects of these substances are enhanced, in others, they are inhibited by compounds that were isolated from natural sources or prepared by chemical synthesis. The biotransformation of natural or "unnatural" ether lipids in microorganisms, plant or animal tissue also can lead to substances that elicit biological effects. The production of such compounds through various biotechnological techniques is a field wide open for future exploration. In addition to animal cell cultures, plant cell cultures may become useful tools in biomedical studies concerned with ether lipids.

Lysis of Bacillus subtilis Cells by Glycerol and Sucrose Esters of Fatty Acids

The lytic action of glycerol and sucrose esters of fatty acids with different carbon chain lengths on the exponentially growing cells of Bacillus subtilis 168 was investigated. Of each series of esters, glycerol dodecanoate and sucrose hexadecanoate were the most active. Lysis at 1 h after the addition of 0.1 mM glycerol dodecanoate or 20 μg of sucrose hexadecanoate per ml was 81 or 79%, respectively, as evaluated by the reduction in optical density. During this treatment a great loss of viability occurred that preceded lysis. The results that were obtained suggest that autolysis is induced by these esters. The esters caused morphological changes in the cells, but a seeming adaptation of the cells to esters was seen.

Use of resistant mutants to study the interaction of triton X-100 with Staphylococcus aureus

Staphylococcus aureus mutants resistant to the nonionic detergent Triton X-100, isolated from the wild-type strain H and the autolysin-deficient strain RUS3, could grow and divide in broth containing 5% (vol/vol) Triton X-100, while growth of the parental strains was markedly inhibited above the critical micellar concentration (0.02%) of the detergent. Growth-inhibitory concentrations of Triton X-100 killed wild-type cells without demonstrable cellular lysis. Triton X-100 stimulated autolysin activity of S. aureus cells under nongrowing conditions, and this lytic response was markedly reduced in energy-poisoned cells. In contrast, the detergent had no effect on the activity of autolysins in cell-free systems, and growth in the presence of Triton X-100 did not alter either the cellular autolysin activity or the susceptibility of cell walls to exogenous lytic enzymes. Treatment with either Triton X-100 or penicillin G in the growth medium stimulated release of predominantly acylated intracellular lipoteichoic acid and sensitized staphylococci to Triton X-100-induced autolysis. There was no significant difference in the cell wall and membrane compositions or Triton X-100 binding between the parental strains and the resistant mutants. The resistant mutant TXR1, derived from S. aureus H, had a higher level of L-alpha-glycerophosphate dehydrogenase activity, and its oxygen uptake was more resistant to inhibition by a submicellar concentration (0.008%) of Triton X-100. Growth in the presence of subinhibitory concentrations of Triton X-100 rendered S. aureus H cells phenotypically resistant to the detergent and greatly stimulated the level of oxygen uptake. Membranes isolated from such cells exhibited enhanced activity of the respiratory enzymes succinic dehydrogenase and L-alpha-glycerophosphate dehydrogenase.

Inhibition of peptidoglycan synthesis of Streptococcus faecium ATCC 9790 and Streptococcus mutans BHT by the antibacterial agent dodecyl glycerol

Dodecyl glycerol inhibits the synthesis of the peptidoglycans of Streptococcus faecium ATCC 9790 and Streptococcus mutans BHT. This metabolic regulation represents the second known mode by which dodecyl glycerol expresses antibacterial activity. The first mode of action of dodecyl glycerol was shown to stimulate autolysin activity which degrades cell-wall peptidoglycan (Ved HS, Gustow E, Mahadevan V and Pieringer RA, 1984, J. Biol. Chem. 259, 8115-8121).