Infrared spectroscopy of glycolipids

Electrochemical and Infrared Studies of a Model Bilayer of the Outer Membrane of Gram-Negative Bacteria and its Interaction with polymyxin─the Last-Resort Antibiotic

A model bilayer of the outer membrane (OM) of Gram-negative bacteria, composed of lipid A and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), was assembled on the β-Tg modified gold (111) single crystal surface using a combination of Langmuir-Blodgett and Langmuir-Schaefer transfer. Electrochemical and spectroscopic methods were employed to study the properties of the model bilayer and its interaction with polymyxin. The model bilayer is stable on the gold surface in the transmembrane potential region between 0.0 and -0.7 V. The presence of Mg2+ coordinates with the phosphate and carboxylate groups in the leaflet of lipid A and stabilizes the structure of the model bilayer. Polymyxin causes the model bilayer leakage and damage in the transmembrane potential region between 0.2 and -0.4 V. At transmembrane potentials lower than -0.5 V, polymyxin does not affect the membrane integrity. Polymyxin binds to the phosphate and carboxylate groups in lipid A molecules and causes the increase of the tilt angle of acyl chains and the decrease of the tilt of the C═O bond. The results in this paper indicate that the antimicrobial activity of polymyxin depends on the transmembrane potential at the model bilayer and provides useful information for the development of new antibiotics.

Cardiolipin Strongly Inhibits the Leakage Activity of the Short Antimicrobial Peptide ATRA-1 in Comparison to LL-37, in Model Membranes Mimicking the Lipid Composition of Staphylococcus aureus

Cardiolipin is one of the main phospholipid components of Staphylococcus aureus membranes. This lipid is found at varying concentrations in the bilayer, depending on the growth stage of the bacteria, and as a response to environmental stress. Cardiolipin is an anionic phospholipid with four acyl chains, which modulates the bending properties of the membrane due to its inverted conical shape. It has been shown to inhibit the pore forming activity of several antimicrobial peptides, in general doubling the peptide concentration needed to induce leakage. Here we find that the short snake-derived antimicrobial peptide ATRA-1 is inhibited by several orders of magnitude in the presence of cardiolipin in saturated membranes (DMPG) compared to the human cathelicidin LL-37, which is only inhibited two-fold in its leakage-inducing concentration. The ATRA-1 is too short to span the membrane and its leakage activity is likely related to detergent-like alterations of bilayer structure. Fluorescence spectroscopy shows only a minor effect on ATRA-1 binding to DMPG membranes due to the presence of cardiolipin. However, FTIR spectroscopy shows that the acyl chain structure of DMPG membranes, containing cardiolipin, become more organized in the presence of ATRA-1, as reflected by an increase in the gel to liquid-crystalline phase transition temperature. Instead, a depression in the melting temperature is induced by ATRA-1 in DMPG in the absence of cardiolipin. In comparison, LL-37 induces a depression of the main phase transition of DMPG even in the presence of cardiolipin. These data suggest that cardiolipin inhibits the penetration of ATRA-1 into the membrane core, impeding its capacity to disrupt lipid packing.

Infrared Spectroscopic Study of Multi-Component Lipid Systems: A Closer Approximation to Biological Membrane Fluidity

Membranes are essential to cellular organisms, and play several roles in cellular protection as well as in the control and transport of nutrients. One of the most critical membrane properties is fluidity, which has been extensively studied, using mainly single component systems. In this study, we used Fourier transform infrared spectroscopy to evaluate the thermal behavior of multi-component supported lipid bilayers that mimic the membrane composition of tumoral and non-tumoral cell membranes, as well as microorganisms such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus. The results showed that, for tumoral and non-tumoral membrane models, the presence of cholesterol induced a loss of cooperativity of the transition. However, in the absence of cholesterol, the transitions of the multi-component lipid systems had sigmoidal curves where the gel and fluid phases are evident and where main transition temperatures were possible to determine. Additionally, the possibility of designing multi-component lipid systems showed the potential to obtain several microorganism models, including changes in the cardiolipin content associated with the resistance mechanism in Staphylococcus aureus. Finally, the potential use of multi-component lipid systems in the determination of the conformational change of the antimicrobial peptide LL-37 was studied. The results showed that LL-37 underwent a conformational change when interacting with Staphylococcus aureus models, instead of with the erythrocyte membrane model. The results showed the versatile applications of multi-component lipid systems studied by Fourier transform infrared spectroscopy.

Fourier Transform Infrared (FTIR) Spectroscopy to Analyse Human Blood over the Last 20 Years: A Review towards Lab-on-a-Chip Devices

Since microorganisms are evolving rapidly, there is a growing need for a new, fast, and precise technique to analyse blood samples and distinguish healthy from pathological samples. Fourier Transform Infrared (FTIR) spectroscopy can provide information related to the biochemical composition and how it changes when a pathological state arises. FTIR spectroscopy has undergone rapid development over the last decades with a promise of easier, faster, and more impartial diagnoses within the biomedical field. However, thus far only a limited number of studies have addressed the use of FTIR spectroscopy in this field. This paper describes the main concepts related to FTIR and presents the latest research focusing on FTIR spectroscopy technology and its integration in lab-on-a-chip devices and their applications in the biological field. This review presents the potential use of FTIR to distinguish between healthy and pathological samples, with examples of early cancer detection, human immunodeficiency virus (HIV) detection, and routine blood analysis, among others. Finally, the study also reflects on the features of FTIR technology that can be applied in a lab-on-a-chip format and further developed for small healthcare devices that can be used for point-of-care monitoring purposes. To the best of the authors’ knowledge, no other published study has reviewed these topics. Therefore, this analysis and its results will fill this research gap.

Membrane Potentials Trigger Molecular-Scale Rearrangements in the Outer Membrane of Gram-Negative Bacteria

The structural complexity of the cell envelope of Gram-negative bacteria limits the fabrication of realistic models of bacterial cell membranes. A vertical Langmuir-Blodgett withdrawing was used to deposit a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) monolayer on the Au(111) surface. The second leaflet composed of di[3-deoxy-D-manno-octulosonyl]-lipid A (KLA) was deposited using Langmuir-Schaefer transfer. The use of an electrode material as a support for the POPE-KLA bilayer allowed electrochemical control of the membrane's stability, compactness, and structure. Capacitance-potential curves showed a typical pattern for the supported lipid bilayers electrochemical characteristic. The minimum membrane capacitance was ∼4 μF cm^-2 and did not change in the following desorption-adsorption cycles, indicating the presence of a stable bilayer structure with an asymmetric composition of both leaflets. However, at a molecular scale, as elucidated in spectroelectrochemical experiments, large differences in the response of both leaflets to electric potentials were observed. The acyl chains in POPE and KLA existed in a liquid state. The quantitative analysis of the CH stretching modes indicated potential-driven reorientations in the hydrophobic fragment of the bilayer, already in the adsorbed state. To assign observed rearrangements to POPE and KLA lipids in both leaflets, per-deuterated d₃₁-POPE was transferred into the inner leaflet. Since no potential-dependent changes of the CD₂ stretching modes in the d₃₁-POPE-KLA bilayer were observed, reorientations in the acyl chain region were assigned to the KLA molecules. Mg²⁺ ions were bound to the polar head groups of KLA. The strength of electrostatic interactions in the polar head group region of KLA was dependent on the direction of the electric field. At negative electric potentials, the binding of divalent cations weakened, which gave the KLA molecules increased orientational flexibility. This behavior in electric fields is peculiar for the outer membrane and indicates that the microbial cell membranes have different electrochemical properties than phospholipid bilayers.

FTIR Spectroscopic Imaging Supports Urine Cytology for Classification of Low- and High-Grade Bladder Carcinoma

Simple Summary

Human urine cytological samples were investigated using Fourier transform infrared spectroscopic imaging in terms of recognition of bladder cancer. The clustering of IR spectra of whole cytological smears revealed very good spectral correlation with normal urothelial cell features. Next, the combination of spectral information derived from unsupervised hierarchical cluster analysis and partial least square discriminant analysis (PLS-DA) classified normal vs. low- and high-grade bladder urothelial carcinoma with sensitivity and specificity of 90–97%.

Abstract

Bladder urothelial carcinoma (BC) is a common, recurrent, life-threatening, and unpredictable disease which is difficult to diagnose. These features make it one of the costliest malignancies. Although many possible diagnostic methods are available, molecular heterogeneity and difficulties in cytological or histological examination induce an urgent need to improve diagnostic techniques. Herein, we applied Fourier transform infrared spectroscopy in imaging mode (FTIR) to investigate patients’ cytology samples assigned to normal (N), low-grade (LG) and high-grade (HG) BC. With unsupervised hierarchical cluster analysis (UHCA) and hematoxylin-eosin (HE) staining, we observed a correlation between N cell types and morphology. High-glycogen superficial (umbrella) and low-glycogen piriform urothelial cells, both with normal morphology, were observed. Based on the spectra derived from UHCA, principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were performed, indicating a variation of protein content between the patient groups. Moreover, BC spectral cytology identified a low number of high-glycogen cells for which a shift of the carbohydrate/phosphate bands was also observed. Despite high cellular heterogeneity, PLS-DA was able to classify the spectra obtained. The voided urine FTIR cytology is one of the options that might be helpful in BC diagnosis, as high sensitivity and specificity up to 97% were determined.

In Vitro Spectroscopy-Based Profiling of Urothelial Carcinoma: A Fourier Transform Infrared and Raman Imaging Study

Simple Summary

The mortality and recurrence associated with urothelial carcinoma are high. High heterogeneity makes it hard to detect with currently available methods such as cytology and histology. We propose here vibrational spectroscopic imaging as an additional diagnostic tool for the classification of bladder cancer. Our study revealed that chemism-induced spectroscopic features of the cancer cells of various stages and invasiveness were specifically detected.

Abstract

Markers of bladder cancer cells remain elusive, which is a major cause of the low recognition of this malignant neoplasm and its recurrence. This implies an urgent need for additional diagnostic tools which are based on the identification of the chemism of bladder cancer. In this study, we employed label-free techniques of molecular imaging—Fourier Transform Infrared and Raman spectroscopic imaging—to investigate bladder cancer cell lines of various invasiveness (T24a, T24p, HT-1376, and J82). The urothelial HCV-29 cell line was the healthy control. Specific biomolecules discriminated spatial distribution of the nucleus and cytoplasm and indicated the presence of lipid bodies and graininess in some cell lines. The most prominent discriminators are the total content of lipids and sugar moieties as well as the presence of glycogen and other carbohydrates, un/saturated lipids, cytochromes, and a level of S-S bridges in proteins. The combination of the obtained hyperspectral database and chemometric methods showed a clear differentiation of each cell line at the level of the nuclei and cytoplasm and pointed out spectral signals which differentiated bladder cancer cells. Registered spectral markers correlated with biochemical composition changes can be associated with pathogenesis and potentially used for the diagnosis of bladder cancer and response to experimental therapies.

Biophysical Stress Responses of the Yeast Lachancea thermotolerans During Dehydration Using Synchrotron-FTIR Microspectroscopy

During industrial yeast production, cells are often subjected to deleterious hydric variations during dehydration, which reduces their viability and cellular activity. This study is focused on the yeast Lachancea thermotolerans, particularly sensitive to dehydration. The aim was to understand the modifications of single-cells biophysical profiles during different dehydration conditions. Infrared spectra of individual cells were acquired before and after dehydration kinetics using synchrotron radiation-based Fourier-transform infrared (S-FTIR) microspectroscopy. The cells were previously stained with fluorescent probes in order to measure only viable and active cells prior to dehydration. In parallel, cell viability was determined using flow cytometry under identical conditions. The S-FTIR analysis indicated that cells with the lowest viability showed signs of membrane rigidification and modifications in the amide I (α-helix and β-sheet) and amide II, which are indicators of secondary protein structure conformation and degradation or disorder. Shift of symmetric C–H stretching vibration of the CH₂ group upon a higher wavenumber correlated with better cell viability, suggesting a role of plasma membrane fluidity. This was the first time that the biophysical responses of L. thermotolerans single-cells to dehydration were explored with S-FTIR. These findings are important for clarifying the mechanisms of microbial resistance to stress in order to improve the viability of sensitive yeasts during dehydration.

Characterization of biosurfactant produced by the endophyte Burkholderia sp. WYAT7 and evaluation of its antibacterial and antibiofilm potentials

The endophyte Burkholderia sp. WYAT7 isolated from the medicinal plant Artemisia nilagirica (Clarke) Pamp. was analyzed for its ability to produce biosurfactant. The evaluation of biosurfactant production was conducted using different screening methods which confirmed the presence of biosurfactant in the culture supernatant. CTAB- methylene blue agar plate method was used for the screening of glycolipid biosurfactant production. The biosurfactant produced by the bacteria effectively metabolized hydrocarbons present in the bacterial culture media. Fourier transform infrared spectroscopic (FTIR) analysis of biosurfactant provided the details regarding OH stretching, stretching vibrations of acyl chain, CO stretching, stretching vibrations of ether and vibrations of glycosidic linkages in the biosurfactant. The stretching vibrations of glycosidic linkage in the fingerprint regions of FTIR spectrum (1200 cm^-1 to 800 cm^-1 regions) confirms that the biosurfactant produced was a glycolipid. The GC-MS analysis confirmed the methyl and ethyl esters of fatty acids. The biosurfactant from the bacteria exhibited antibacterial activity against bacterial pathogens such as Pseudomonas aeruginosa (MTCC 2453), Escherichia coli (MTCC 1610), Salmonella paratyphi and Bacillus subtilis. The glycolipid biosurfactant had antibiofilm activity as evidenced in Staphylococcus aureus (MTCC 1430). All these results indicated the beneficial effect of the biosurfactant in plant-endophyte interactions. The properties exhibited by the biosurfactant suggest that it can be exploited commercially for the production of novel antibiotics.

Supramolecular structure of enterobacterial wild-type lipopolysaccharides (LPS), fractions thereof, and their neutralization by Pep19-2.5

Lipopolysaccharides (LPS) belong to the strongest immune-modulating compounds known in nature, and are often described as pathogen-associated molecular patterns (PAMPs). In particular, at higher concentrations they are responsible for sepsis and the septic shock syndrome associated with high lethality. Since most data are indicative that LPS aggregates are the bioactive units, their supramolecular structures are considered to be of outmost relevance for deciphering the molecular mechanisms of its bioactivity. So far, however, most of the data available addressing this issue, were published only for the lipid part (lipid A) and the core-oligosaccharide containing rough LPS, representing the bioactive unit. By contrast, it is well known that most of the LPS specimen identified in natural habitats contain the smooth-form (S-form) LPS, which carry additionally a high-molecular polysaccharide (O-chain). To fill this lacuna and going into a more natural system, here various wild-type (smooth form) LPS including also some LPS fractions were investigated by small-angle X-ray scattering with synchrotron radiation to analyze their aggregate structure. Furthermore, the influence of a recently designed synthetic anti-LPS peptide (SALP) Pep19-2.5 on the aggregate structure, on the binding thermodynamics, and on the cytokine-inducing activity of LPS were characterized, showing defined aggregate changes, high affinity binding and inhibition of cytokine secretion. The data obtained are suitable to refine our view on the preferences of LPS for non-lamellar structures, representing the highest bioactive forms which can be significantly influenced by the binding with neutralizing peptides such as Pep19-2.5.

Self-Organisation, Thermotropic and Lyotropic Properties of Glycolipids Related to their Biological Implications

Glycolipids are amphiphilic molecules which bear an oligo- or polysaccharide as hydrophilic head group and hydrocarbon chains in varying numbers and lengths as hydrophobic part. They play an important role in life science as well as in material science. Their biological and physiological functions are quite diverse, ranging from mediators of cell-cell recognition processes, constituents of membrane domains or as membrane-forming units. Glycolipids form an exceptional class of liquid-crystal mesophases due to the fact that their self-organisation obeys more complex rules as compared to classical monophilic liquid-crystals. Like other amphiphiles, the supra-molecular structures formed by glycolipids are driven by their chemical structure; however, the details of this process are still hardly understood. Based on the synthesis of specific glycolipids with a clearly defined chemical structure, e.g., type and length of the sugar head group, acyl chain linkage, substitution pattern, hydrocarbon chain lengths and saturation, combined with a profound physico-chemical characterisation of the formed mesophases, the principles of the organisation in different aggregate structures of the glycolipids can be obtained. The importance of the observed and formed phases and their properties are discussed with respect to their biological and physiological relevance. The presented data describe briefly the strategies used for the synthesis of the used glycolipids. The main focus, however, lies on the thermotropic as well as lyotropic characterisation of the self-organised structures and formed phases based on physico-chemical and biophysical methods linked to their potential biological implications and relevance.

Dual drug encapsulation in a novel nano-vesicular carrier for the treatment of cutaneous melanoma: characterization and in vitro/in vivo evaluation

The objective of this research was to develop and evaluate a dual drug-loaded dermal targeted vesicle for the treatment of cutaneous melanoma.

Biophysical analysis of the interaction of the serum protein human β2GPI with bacterial lipopolysaccharide

There are several human serum proteins for which no clear role is yet known. Among these is the abundant serum protein beta2-glycoprotein-I (β2GPI), which is known to bind to negatively charged phospholipids as well as to bacterial lipopolysaccharides (LPS), and was therefore proposed to play a role in the immune response. To understand the details of these interactions, a biophysical analysis of the binding of β2GPI to LPS and phosphatidylserine (PS) was performed. The data indicate only a moderate tendency of the protein (1) to influence the LPS-induced cytokine production in vitro, (2) to react exothermally with LPS in a non-saturable way, and (3) to change its local microenvironment upon LPS association. Additionally, we found that the protein binds more strongly to phosphatidylserine (PS) than to LPS. Furthermore, β2GPI converts the LPS bilayer aggregates into a stronger multilamellar form, and reduces the fluidity of the hydrocarbon moiety of LPS due to a rigidification of the acyl chains. From these data it can be concluded that β2GPI plays a role as an immune-modulating agent, but there is much less evidence for a role in immune defense against bacterial toxins such as LPS.

Percutaneous penetration modifiers and formulation effects: thermal and spectral analyses

The study investigated the formulation effects of laurocapram and iminosulfurane derived penetration modifiers on human stratum corneum using thermal and spectral analyses. Firstly, formulations of penetration modifiers were assessed as enhancers/retardants using the model permeant, diethyl-m-toluamide followed by investigation of their mechanisms of action using differential scanning calorimetry (DSC) and attenuated total reflectance Fourier-transform infra-red spectroscopy. The penetration modifiers investigated were laurocapram, 3-dodecanoyloxazolidin-2-one (N-0915), S,S-dimethyl-N-(4-bromobenzoyl) iminosulfurane (DMBIS), S,S-dimethyl-N-(2-methoxycarbonylbenzenesulfonyl) iminosulfurane (DMMCBI) and tert-butyl 1-dodecyl-2-oxoazepan-3-yl-carbamate (TBDOC) that were formulated in either water, propylene glycol (PG), ethanol or polyethylene glycol 400 (PEG 400). The results explain the mechanism for the first time why an enhancer can become a retardant or vice versa depending upon the vehicle in which it is applied to the skin. DSC indicated that penetration modifier formulations enhanced permeation of active mainly by disruption and fluidization of the stratum corneum lipid bilayers while IR data indicated characteristic blue shifts with decreases in peak intensity. On the other hand, DSC of penetration modifier formulations showing retardation depicted elevated T (m2) with a strengthening of lipid-protein complex while IR results indicated formation of multiple peaks around 1,738 cm(-1) transition in stratum corneum spectra suggesting retardation may be caused by organization of SC lipids by increased H-bonding.

Endotoxins: relationship between structure, function, and activity

Endotoxins as amphiphilic components of the outer layer of the outer membrane of Gram-negative bacteria exert their immunostimulatory activity after release from bacterial cells. Thus, the characterization of the physicochemical properties of this glycolipid in physiological fluids is of utmost importance for an understanding of cell activation processes. Here, the essential physicochemical parameters describing endotoxins such as critical micellar concentration, acyl chain fluidity, intramolecular conformation, supramolecular structures, and size as well as morphology of the aggregates are discussed and assessed with respect to their importance for an understanding of the interaction mechanisms with immunorelevant cells. The reviewed data clearly indicate that knowledge of these parameters is essential for understanding the bioactivity of not only endotoxins, but also endotoxin-like amphiphiles.

Physicochemical characterization and biological activity of lipooligosaccharides and lipid A from Neisseria meningitidis

Meningococcal endotoxin is the major contributor to the pathogenesis of fulminant sepsis and meningitis of meningococcal disease and is a potent activator of the MyD88-dependent and MyD88-independent pathways via the MD-2/TLR4 receptor. To understand better the biological properties of meningococcal endotoxin that initiates these events, the physicochemical structure of Neisseria meningitidis lipopoly(oligo)saccharide (LOS) of the serogroup B wild-type strain NMB (NeuNAc-Gal beta-GlcNAc-Gal beta-Glc beta-Hep2(GlcNAc,Glc alpha)PEA-Kdo2-lipid A, 1,4'-bisphosphorylated +/- PEA, PEtN) and the genetically-defined mutants (gmhB, Kdo2 -lipid A; kdtA, meningococcal lipid A; gmhB-lpxL1, Kdo2penta-acylated lipid A and NMB-lpx1, penta-acylated meningococcal LOS) were assessed in relation to bioactivity. Confirming previous work, Kdo2lipid A was the minimal structure required for optimal activation of the MD-2/TLR4 pathway of human macrophages. Meningococcal lipid A alone was a very weak agonist in stimulating human macrophages, even at high doses. Penta-acylated LOS structures demonstrated a moderate reduction in TLR4/MyD88-dependent signaling and a dramatic decrease in TLR4-TRIF-dependent signaling. For a better understanding of these results, we have performed an analysis of physicochemical parameters of the LOS structures such as the gel-to-liquid crystalline phase transition of the acyl chains, the inclination angle of the diglucosamine backbone with respect to the membrane surface, and the aggregate structure, and have found a very significant correlation of these parameters with biological activities extending our concept of endotoxicity.

Analysis of Quil A–phospholipid mixtures using drift spectroscopy

The aim of this study was to investigate molecular interactions between Quil A and phosphatidylcholine in the solid state using diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Analysis of the interactions was characterized on the different regions of phosphatidylcholine: hydrophobic chain, interfacial and headgroup regions. The spectra of the hydrocarbon region of phosphatidylcholine alone compared to that for the binary mixture of Quil A and phosphatidylcholine were similar. These findings suggest that Quil A did not cause conformational disorder of the fatty acyl chains of the phospholipid. In contrast, a shift in the wavenumber of the choline group and a broad band in this moiety indicate a modification of the phospholipid in the headgroup region due to interaction between Quil A and phosphatidylcholine. These results suggest possibly ionic interactions between the negatively charged glucuronic acid moiety of the Quil A molecule with the positively charged choline group. The findings could also be the result of conformational changes in the choline group because of the intercalation of sugar moieties in Quil A between the choline and phosphate groups due to hydrogen bonding. Shift of wavenumbers to lower values on the carbonyl group was observed suggesting hydrogen bonding between Quil A and phosphatidylcholine. The difference in degrees of wavenumber shift (choline>phosphate>carbonyl group) and observed broad bands indicated that Quil A preferentially interacted with phosphatidylcholine on the hydrophilic headgroup. Cholesterol influenced such interactions at relatively high concentration (60%, w/w).

Glycolipid Membranes through Atomistic Simulations: Effect of Glucose and Galactose Head Groups on Lipid Bilayer Properties

Though glycolipids are involved in a multitude of cellular functions, the understanding of their atom-scale properties in lipid membranes has remained very limited due to the lack of atomistic simulations. In this work, we employ extensive simulations to characterize one-component membranes comprised of glycoglycerolipids, focusing on two common glyco head groups, namely glucose and galactose. The properties of these two glycoglycerolipid bilayers are compared in a systematic manner with membranes consisting of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) lipids, whose structures aside from the head group are identical with those of the two glycolipids. We find that the glycolipid systems are characterized by a substantial number of hydrogen bonds in the head group region, leading to membrane packing that is stronger than in a PC but less significant than that in a PE bilayer. The role played by the glyco head group is especially evident in the electrostatic membrane potential, which is particularly large in the glycolipid membranes. For the same reason, the interfacial forces near glycolipid bilayers are significantly different from those found in PC and PE bilayers, affecting, e.g., the ordering of water close to the membrane. These effects are particularly important for the case of galactose, an important component in thylacoids.

Biophysical analysis of the interaction of granulysin-derived peptides with enterobacterial endotoxins

To combat infections by Gram-negative bacteria, it is not only necessary to kill the bacteria but also to neutralize pathogenicity factors such as endotoxin (lipopolysaccharide, LPS). The development of antimicrobial peptides based on mammalian endotoxin-binding proteins is a promising tool in the fight against bacterial infections, and septic shock syndrome. Here, synthetic peptides derived from granulysin (Gra-pep) were investigated in microbiological and biophysical assays to understand their interaction with LPS. We analyzed the influence of the binding of Gra-pep on (1) the acyl chain melting of the hydrophobic moiety of LPS, lipid A, by Fourier-transform spectroscopy, (2) the aggregate structure of LPS by small-angle X-ray scattering and cryo-transmission electron microscopy, and 3) the enthalpy change by isothermal titration calorimetry. In addition, the influence of Gra-pep on the incorporation of LPS and LPS-LBP (lipopolysaccharide-binding protein) complexes into negatively charged liposomes was monitored. Our findings demonstrate a characteristic change in the aggregate structure of LPS into multilamellar stacks in the presence of Gra-pep, but little or no change of acyl chain fluidity. Neutralization of LPS by Gra-pep is not due to a scavenging effect in solution, but rather proceeds after incorporation into target membranes, suggesting a requisite membrane-bound step.

Thermodynamic analysis of the lipopolysaccharide-dependent resistance of gram-negative bacteria against polymyxin B

Cationic antimicrobial cationic peptides (CAMP) have been found in recent years to play a decisive role in hosts' defense against microbial infection. They have also been investigated as a new therapeutic tool, necessary in particular due to the increasing resistance of microbiological populations to antibiotics. The structural basis of the activity of CAMPs has only partly been elucidated and may comprise quite different mechanism at the site of the bacterial cell membranes or in their cytoplasm. Polymyxin B (PMB) is a CAMP which is effective in particular against Gram-negative bacteria and has been well studied with the aim to understand its interaction with the outer membrane or isolated membrane components such as lipopolysaccharide (LPS) and to define the mechanism by which the peptides kill bacteria or neutralize LPS. Since PMB resistance of bacteria is a long-known phenomenon and is attributed to structural changes in the LPS moiety of the respective bacteria, we have performed a thermodynamic and biophysical analysis to get insights into the mechanisms of various LPS/PMB interactions in comparison to LPS from sensitive strains. In isothermal titration calorimetric (ITC) experiments considerable differences of PMB binding to sensitive and resistant LPS were found. For sensitive LPS the endothermic enthalpy change in the gel phase of the hydrocarbon chains converts into an exothermic reaction in the liquid crystalline phase. In contrast, for resistant LPS the binding enthalpy change remains endothermic in both phases. As infrared data show, these differences can be explained by steric changes in the headgroup region of the respective LPS.

Instrumental analysis of bacterial cells using vibrational and emission Mössbauer spectroscopic techniques

In biosciences and biotechnology, the expanding application of physicochemical approaches using modern instrumental techniques is an efficient strategy to obtain valuable and often unique information at the molecular level. In this work, we applied a combination of vibrational (Fourier transform infrared (FTIR), FT-Raman) spectroscopic techniques, useful in overall structural and compositional analysis of bacterial cells of the rhizobacterium Azospirillum brasilense, with 57Co emission Mössbauer spectroscopy (EMS) used for sensitive monitoring of metal binding and further transformations in live bacterial cells. The information obtained, together with ICP-MS analyses for metals taken up by the bacteria, is useful in analysing the impact of the environmental conditions (heavy metal stress) on the bacterial metabolism and some differences in the heavy metal stress-induced behaviour of non-endophytic (Sp7) and facultatively endophytic (Sp245) strains. The results show that, while both strains Sp7 and Sp245 take up noticeable and comparable amounts of heavy metals from the medium (0.12 and 0.13 mg Co, 0.48 and 0.44 mg Cu or 4.2 and 2.1 mg Zn per gram of dry biomass, respectively, at a metal concentration of 0.2 mM in the medium), their metabolic responses differ essentially. Whereas for strain Sp7 the FTIR measurements showed significant accumulation of polyhydroxyalkanoates as storage materials involved in stress endurance, strain Sp245 did not show any major changes in cellular composition. Nevertheless, EMS measurements showed rapid binding of cobalt(II) by live bacterial cells (chemically similar to metal binding by dead bacteria) and its further transformation in the live cells within an hour.

Biologically active lipid A antagonist embedded in a multilayered polyelectrolyte architecture

Recently [Jessel N, Schwinte P, Donohue R, Lavalle P, Boulmedais F, Darcy R, et al. Pyridylamino-beta-cyclodextrin as a molecular chaperone for lipopolysaccharide embedded in a multilayered polyelectrolyte architecture. Adv Funct Mater 2004;14:963-9], we demonstrated the biological activity of a lipopolysaccharide from Escherichia coli incorporated into layer-by-layer films made of poly (l-lysine) and poly (l-glutamic acid) and containing a polycationic beta-cyclodextrin (CD) with chaperone properties. Here we develop innovative architectures containing a complex made of a charged beta-cyclodextrin and a lipid A antagonist (LAA) as potential systems for local endotoxin antagonistic activity. We examine the biological activity of these architectures. The CD-LAA complex adsorbed on top, or embedded into the polyelectrolyte films keeps its LPS antagonistic activity on both murine and human macrophages for at least 24h.

Continuous monitoring of WBC (biochemistry) in an adult leukemia patient using advanced FTIR-spectroscopy

Fourier transform infrared (FTIR)-spectroscopy has been found useful for monitoring the effectiveness of drugs during chemotherapy in leukemia patients. In the present work, spectral changes that occurred in the white blood cells (WBC) of an adult acute myeloid leukemia (AML) patient and their possible utilization for monitoring biochemistry of WBC were investigated. The phosphate absorbance from nucleic acids and the lipid-protein ratio in the WBC decreased immediately after treatment and then increased to levels of a control group. Similar observations were recorded in child patients with acute lymphoblastic leukemia (ALL) who were used as test cases. These parameters maybe used as possible markers to indicate successful remission and suggest that FTIR-spectroscopy may provide a rapid optical method for continuous monitoring or evaluation of a WBC population.

The use of FTIR microscopy for evaluation of herpes viruses infection development kinetics

The kinetics of Herpes simplex infection development was studied using an FTIR microscopy (FTIR-M) method. The family of herpes viruses includes several members like H. simplex types I and II (HSV I, II), Varicella zoster (VZV) viruses which are involved in various human and animal infections of different parts of the body. In our previous study, we found significant spectral differences between normal uninfected cells in cultures and cells infected with herpes viruses at early stages of the infection. In the present study, cells in cultures were infected with either HSV-I or VZV and at various times post-infection they were examined either by optical microscopy or by advanced FTIR-M. Spectroscopic measurements show a consistent decrease in the intensity of the carbohydrate peak in correlation with the viral infection development, observed by optical microscopy. This decrease in cellular carbohydrate level was used as indicator for herpes viruses infection kinetics. This parameter could be used as a basis for applying a spectroscopic method for the evaluation of herpes virus infection development. Our results show also that the development kinetics of viral infection has an exponential character for these viruses.

Studies on acute human infections using FTIR microspectroscopy and cluster analysis

A novel methodology for the diagnosis of acute infections using FTIR microspectroscopy (FTIR-MSP) data on blood components and cluster analysis is presented. Blood samples were collected from 11 patients suffering from various infections and 16 age-matched healthy human controls. Blood components such as white blood cells, red blood cells, and plasma were isolated using standard procedures and FTIR-MSP of these components was utilized. A cluster analysis of the FTIR spectra was performed. The spectra obtained from the three blood components of patients were different from those of controls. The FTIR spectra of white blood cells from patients suffering infections were significantly different from the controls. Cluster analyses of averaged FTIR-MSP spectra of white blood cells provided 100% classification between patients and healthy controls.

Intermolecular interactions in dry and rehydrated pure and mixed bilayers of phosphatidylcholine and digalactosyldiacylglycerol: a Fourier transform infrared spectroscopy study

Glycolipids are an important part of almost all biological membranes. Their effects on membrane structure and their interactions with phospholipids, however, have not been extensively studied so far. We have investigated the phase behavior and intermolecular interactions in dry and rehydrated bilayers made from the phospholipid egg phosphatidylcholine (EPC) and the plant chloroplast glycolipid digalactosyldiacylglycerol (DGDG), or from a mixture (1:1) of these lipids, using Fourier transform infrared spectroscopy. We show that there are extensive interactions between EPC and DGDG in mixed membranes, and also between DGDG molecules in pure DGDG membranes, involving sugar OH groups and C[double bond]O, P[double bond]O, and choline moieties in dry membranes. These interactions persist to a certain degree even after rehydration. We present evidence that these interactions influence the mixing behavior in phosphatidylcholine/DGDG membranes and also the phase behavior of both EPC/DGDG and pure DGDG membranes in the dry state.

Spectroscopic evaluation of the effect of a red microalgal polysaccharide on herpes-infected Vero cells

The sulfated polysaccharide obtained from a species of red microalga has proved to be a potent antiviral agent against various members of the herpes family. In the present study, we used microscopic Fourier transform infrared spectroscopy (FT-IR) to investigate differences between normal cells, those infected with herpes viruses, and infected cells treated with red microalgal polysaccharide. FT-IR enables the characterization of cell or tissue pathology based on characteristic molecular vibrational spectra of the cells. The advantage of microscopic FT-IR spectroscopy over conventional FT-IR spectroscopy is that it facilitates inspection of restricted regions of cell cultures or tissue. Our results showed significant spectral differences at early stages of infection between infected and noninfected cells, and between infected cells treated with the polysaccharide and those not treated. In infected cells, there was an impressive decrease in sugar content and a considerable increase in phosphate levels in conjunction with the infection progress. Our results also proved that sugars penetrated and accumulated inside cells treated with the red microalgal polysaccharide. These could have been sugar fragments of low molecular weight present in the polysaccharide solution, despite purification by dialysis. Such sugar accumulation might be responsible for a breakdown in the internal steps of the viral replication cycle.

Phase transitions and hydrogen bonding in a bipolar phosphocholine evidenced by calorimetry and vibrational spectroscopy

As a model for natural archaebacterial bolalipids, we have synthesized omega-hydroxybehenylphosphocholine (HBPC, HO-(CH(2))(22)-OP(O(-)(2))O-(CH(2))(2)-N+(CH(3))(3)) and investigated it, by Fourier-transform infrared and Raman spectroscopy and differential scanning calorimetry, both as fully hydrated dispersions (varying temperature) and as aligned films (varying hydration) in terms of particular structural features predestining such bipolar lipids for their occurrence in extremophilic organisms. The phase behavior of HBPC in dispersions depends on sample pretreatment as it comprises metastabilities in annealed samples. However, main transition proceeds consistently near 81 degrees C. Some (extra) deal of headgroup (phosphate) hydration accompanying a gel-gel phase transition near 66 degrees C appears to precede chain melting. Studies with HBPC films revealed lamellar interdigitated-like solid phases with an extraordinarily strong omega-OH--OPO(-) omega-OH--OPO(-) omega-OH hydrogen-bond pattern formed along both sides of the resulting monolayers. The "clamping" effect inherent to such structures provides a clue to explain the relatively high main-transition temperature of HBPC assemblies.