Effect of beta-carotene on structural and dynamic properties of model phosphatidylcholine membranes. I. An EPR spin label study

Do carotenoids protect phytodetritus-associated bacteria from oxidative stress?

This study focused on how carotenoid pigments in bacteria attached to phytoplankton protect them from singlet oxygen produced by phytoplankton during senescence, specifically under illumination of the diatom Thalassiosira sp. Its effect was analyzed on bacterial membrane structure (photooxidation of bacterial membrane lipids such as mono-unsaturated fatty acids (MUFAs) and on DNA repair system in two bacterial species, non-pigmented Pseudomonas stutzeri and pigmented Dinoroseobacter shibae. In P. stutzeri cells, 1O₂ transferred from phytodetritus was not completely scavenged by bacterial membranous MUFAs and reached the cytoplasm, allowing both 1O₂ and UV radiation to cause a rapid response of DNA repair systems. In D. shibae, scavenging by bacterial membrane MUFAs and quenching by spheroidenone allowed only a small fraction of 1O₂ to reach the cytoplasm, as shown by a delayed and lower repair system activation. The fact that Rhodobacteriales is the dominant order in bacterioplankton communities associated with algal blooms could thus be partly due to the protective effect of its constituent carotenoids against 1O₂- and UV-induced damage.

Perspective on Integrative Simulations of Bioenergetic Domains

Bioenergetic processes in cells, such as photosynthesis or respiration, integrate many time and length scales, which makes the simulation of energy conversion with a mere single level of theory impossible. Just like the myriad of experimental techniques required to examine each level of organization, an array of overlapping computational techniques is necessary to model energy conversion. Here, a perspective is presented on recent efforts for modeling bioenergetic phenomena with a focus on molecular dynamics simulations and its variants as a primary method. An overview of the various classical, quantum mechanical, enhanced sampling, coarse-grained, Brownian dynamics, and Monte Carlo methods is presented. Example applications discussed include multiscale simulations of membrane-wide electron transport, rate kinetics of ATP turnover from electrochemical gradients, and finally, integrative modeling of the chromatophore, a photosynthetic pseudo-organelle.

Effects of flavonoids on membrane adaptation of food-associated bacteria

The effects of naringenin and the biflavonoids amentoflavone and tetrahydroamentoflavone on select bacterial lipids (carotenoids, fatty acids, and menaquinones) and membrane fluidity based on Laurdan generalized polarization were investigated. For this purpose, the pigment-forming food-associated microorganisms Staphylococcus xylosus (DSM 20266^T and J70), Staphylococcus carnosus DSM 20501^T, and Micrococcus luteus (ATCC 9341 and J3) were studied. The results suggest an envelope stress response by microorganisms due to flavonoids and an employment of adaptive mechanisms using carotenoids, fatty acids, and menaquinones. The flavonoid monomer naringenin impacted carotenoids, fatty acids, menaquinones, and membrane fluidity. Naringenin significantly influenced the carotenoid profile, particularly by an increase in the relative proportion of 4,4'-diaponeurosporenoic acid in Staphylococcus xylosus. Amentoflavone caused changes mainly in the membrane of Micrococcus luteus and decreased the menaquinone content. Tetrahydroamentoflavone mainly affected the carotenoids in the investigated strains. The noticeably different CCS value of tetrahydroamentoflavone compared to naringenin and amentoflavone revealed further insights into the structure-dependent effects of flavonoids. This study provides valuable insights into the response of pigment-forming food-associated microorganisms to naringenin, amentoflavone, and tetrahydroamentoflavone, which is important for the targeted and safe application of the latter as natural preservatives and useful for further research on the mechanisms of action.

Carotenoid biosynthesis is associated with low-temperature adaptation in Rhodosporidium kratochvilovae

BACKGROUND

Low temperatures greatly limit the growth of microorganisms. Low-temperature adaptation in microorganisms involves multiple mechanisms. Carotenoids are naturally occurring lipid-soluble pigments that act as antioxidants and protect cells and tissues from the harmful effects of free radicals and singlet oxygen. However, studies on the regulation of carotenoid biosynthesis at low temperatures in microorganisms are limited. In this study, we investigated the correlation between carotenoids and low-temperature adaptation in the cold-adapted strain of Rhodosporidium kratochvilovae YM25235.

RESULTS

Carotenoid biosynthesis in YM25235 was inhibited by knocking out the bifunctional lycopene cyclase/phytoene synthase gene (RKCrtYB) using the established CRISPR/Cas9 gene-editing system based on endogenous U6 promoters. The carotenoids were extracted with acetone, and the content and composition of the carotenoids were analyzed by spectrophotometry and HPLC. Then, the levels of reactive oxygen species (ROS) and the growth rate in YM25235 were determined at a low temperature. The results indicated that the carotenoid biosynthesis and ROS levels were increased in the YM25235 strain at a low temperature and inhibition of carotenoid biosynthesis was associated with higher ROS levels and a significant decrease in the growth rate of YM25235 at a low temperature.

CONCLUSIONS

The regulation of carotenoid biosynthesis was associated with low-temperature adaptation in YM25235. Our findings provided a strong foundation for conducting further studies on the mechanism by which YM25235 can adapt to low-temperature stress.

Modulation of Membrane Microviscosity by Protein-Mediated Carotenoid Delivery as Revealed by Time-Resolved Fluorescence Anisotropy

Carotenoids are potent antioxidants with a wide range of biomedical applications. However, their delivery into human cells is challenging and relatively inefficient. While the use of natural water-soluble carotenoproteins capable to reversibly bind carotenoids and transfer them into membranes is promising, the quantitative estimation of the delivery remains unclear. In the present work, we studied echinenone (ECN) delivery by cyanobacterial carotenoprotein AnaCTDH (C-terminal domain homolog of the Orange Carotenoid Protein from Anabaena), into liposome membranes labelled with BODIPY fluorescent probe. We observed that addition of AnaCTDH-ECN to liposomes led to the significant changes in the fast-kinetic component of the fluorescence decay curve, pointing on the dipole-dipole interactions between the probe and ECN within the membrane. It may serve as an indirect evidence of ECN delivery into membrane. To study the delivery in detail, we carried out molecular dynamics modeling of the localization of ECN within the lipid bilayer and calculate its orientation factor. Next, we exploited FRET to assess concentration of ECN delivered by AnaCTDH. Finally, we used time-resolved fluorescence anisotropy to assess changes in microviscosity of liposomal membranes. Incorporation of liposomes with β-carotene increased membrane microviscosity while the effect of astaxanthin and its mono- and diester forms was less pronounced. At temperatures below 30 °C addition of AnaCTDH-ECN increased membrane microviscosity in a concentration-dependent manner, supporting the protein-mediated carotenoid delivery mechanism. Combining all data, we propose FRET-based analysis and assessment of membrane microviscosity as potent approaches to characterize the efficiency of carotenoids delivery into membranes.

The C50 carotenoid bacterioruberin regulates membrane fluidity in pink-pigmented Arthrobacter species

Carotenoids have several crucial biological functions and are part of the cold adaptation mechanism of some bacteria. Some pink-pigmented Arthrobacter species produce the rare C₅₀ carotenoid bacterioruberin, whose function in these bacteria is unclear and is found mainly in halophilic archaea. Strains Arthrobacter agilis DSM 20550^T and Arthrobacter bussei DSM 109896^T show an increased bacterioruberin content if growth temperature is reduced from 30 down to 10 °C. In vivo anisotropy measurements with trimethylammonium-diphenylhexatriene showed increased membrane fluidity and a broadening phase transition with increased bacterioruberin content in the membrane at low-temperature growth. Suppression of bacterioruberin synthesis at 10 °C using sodium chloride confirmed the function of bacterioruberin in modulating membrane fluidity. Increased bacterioruberin content also correlated with increased cell resistance to freeze–thaw stress. These findings confirmed the adaptive function of bacterioruberin for growth at low temperatures for pink-pigmented Arthrobacter species.

Xanthophylls Modulate Palmitoylation of Mammalian β-Carotene Oxygenase 2

An extensive body of work has documented the antioxidant role of xanthophylls (lutein and zeaxanthin) in human health and specifically how they provide photoprotection in human vision. More recently, evidence is emerging for the transcriptional regulation of antioxidant response by lutein/lutein cleavage products, similar to the role of β-carotene cleavage products in the modulation of retinoic acid receptors. Supplementation with xanthophylls also provides additional benefits for the prevention of age-related macular degeneration (AMD) and attenuation of Alzheimer's disease symptoms. Mammalian β-carotene oxygenase 2 (BCO2) asymmetrically cleaves xanthophylls as well as β-carotene in vitro. We recently demonstrated that mouse BCO2 (mBCO2) is a functionally palmitoylated enzyme and that it loses palmitoylation when cells are treated with β-carotene. The mouse enzyme is the easiest model to study mammalian BCO2 because it has only one isoform, unlike human BCO2 with several major isoforms with various properties. Here, we used the same acyl-RAC methodology and confocal microscopy to elucidate palmitoylation and localization status of mBCO2 in the presence of xanthophylls. We created large unilamellar vesicle-based nanocarriers for the successful delivery of xanthophylls into cells. We demonstrate here that, upon treatment with low micromolar concentration of lutein (0.15 µM), mBCO2 is depalmitoylated and shows partial nuclear localization (38.00 ± 0.04%), while treatment with zeaxanthin (0.45 µM) and violaxanthin (0.6 µM) induces depalmitoylation and protein translocation from mitochondria to a lesser degree (20.00 ± 0.01% and 35.00 ± 0.02%, respectively). Such a difference in the behavior of mBCO2 toward various xanthophylls and its translocation into the nucleus in the presence of various xanthophylls suggests a possible mechanism for transport of lutein/lutein cleavage products to the nucleus to affect transcriptional regulation.

In Search for the Membrane Regulators of Archaea

Membrane regulators such as sterols and hopanoids play a major role in the physiological and physicochemical adaptation of the different plasmic membranes in Eukarya and Bacteria. They are key to the functionalization and the spatialization of the membrane, and therefore indispensable for the cell cycle. No archaeon has been found to be able to synthesize sterols or hopanoids to date. They also lack homologs of the genes responsible for the synthesis of these membrane regulators. Due to their divergent membrane lipid composition, the question whether archaea require membrane regulators, and if so, what is their nature, remains open. In this review, we review evidence for the existence of membrane regulators in Archaea, and propose tentative location and biological functions. It is likely that no membrane regulator is shared by all archaea, but that they may use different polyterpenes, such as carotenoids, polyprenols, quinones and apolar polyisoprenoids, in response to specific stressors or physiological needs.

A hypothesis about the origin of carotenoid lipid droplets in the green algae Dunaliella and Haematococcus

Hypercarotenogenesis in green algae evolved by mutation of PSY that increased its transcription at high light, disintegration of the eyespot in Dunaliella and acquisition of the capacity to export carotenoids from chloroplasts in Haematococcus. Carotenoids (Car) are lipid-soluble pigments synthesized in plants, algae, bacteria and fungi. Car have strong antioxidative properties and as such are utilized to reduce the danger of different diseases in humans. Two green microalgae are utilized as rich natural sources for Car: Dunaliella salina/bardawil accumulates 10% (w/w) β-carotene (βC), which is also pro-vitamin A, and Haematococcus pluvialis accumulates 4% (w/w) astaxanthin (Ast), the strongest antioxidant among Car. D. bardawil accumulates βC in plastoglobules within the chloroplast, whereas H. pluvialis deposits Ast in cytoplasmic lipid droplets (CLD). In this review we compare the hypercarotenogenic responses (HCR) in Dunaliella and in Haematococcus and try to outline hypothetical evolutionary pathways for its origin. We propose that a mutation in phytoene synthetase that increased its transcription level in response to high light stress had a pivotal role in the evolution of the HCR. Proteomic analyses indicated that in D. bardawil/salina the HCR evolved from dissociation and amplification of eyespot lipid globules. The more robust HCR in algae that accumulate carotenoids in CLD, such as H. pluvialis, required also acquisition of the capacity to export βC out of the chloroplast and its enzymatic conversion into Ast.

Morphology, compressibility and viscoelasticity of the mixed lipid monolayers in the presence of β-carotene

The aim of the present study was to investigate the interfacial behaviour of model biomembranes in the presence of β-carotene (βC). The Langmuir monolayer technique was used to form the mixed lipid film at the air/water interface. Using the surface pressure-area isotherms, the surface potential-area curves and the Brewster angle microscopy the nature of interactions between carotenoid and lipid components of the monolayers was investigated. The results were obtained for complex models of the lipid bilayer composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol (CHOL). It was found that β-carotene affected the membrane stability, fluidity and rigidity, however this influence varied with the DPPC/CHOL ratio. The membrane permeability which is significant for biological functions was found to be affected by the presence of β-carotene in the membrane. The morphology of mixed films visualized by Brewster angle microscopy was similar for DPPC/CHOL and DPPC/CHOL/βC films indicating incorporation of carotenoid into the film. In contrary to previous reports for individual lipids, we did not observed the aggregation of βC in the mixed lipid monolayer. Moreover, from dilatational rheology experiment we concluded about the significant role of β-carotene in modulation of the elastic behaviour of the membrane, especially in physiologically significant surface pressure, i.e. at π = 30 mN/m.

Multi-Carotenoids at Physiological Levels Inhibit VEGF-Induced Tube Formation of Endothelial Cells and the Possible Mechanisms of Action Both In Vitro and Ex Vivo

Carotenoids have been shown to exhibit antiangiogenic activities. Several studies have indicated that carotenoids used in combination were more effective on antioxidation and anticancer actions than carotenoids used singly. However, it is unclear whether multi-carotenoids have antiangiogenic effects. We investigated the effects of multi-carotenoids at physiological plasma levels of Taiwanese (abbreviated as MCT, with a total of 1.4 μM) and Americans (abbreviated as MCA, with a total of 1.8 μM), and of post-supplemental plasma levels (abbreviated as HMC with a total of 3.55 μM) on vascular endothelial growth factor (VEGF)-induced tube formation in human umbilical vein endothelial cells (HUVECs) and rat aortic rings. MCT, MCA, and HMC inhibited VEGF-induced migration, invasion, and tube formation of HUVECs as well as new vessels formation in rat aortic rings. MCT, MCA, and HMC inhibited activities o\f matrix metalloproteinase (MMP)-2, urokinase plasminogen activator, and phosphorylation of VEGF receptor 2 induced by VEGF. Moreover, MCT, MCA, and HMC significantly upregulated protein expression of tissue inhibitors of MMP-2 and plasminogen activator inhibitor-1. These results demonstrate the antiangiogenic effect of multi-carotenoids both in vitro and ex vivo with possible mechanistic actions involving attenuation of VEGF receptor 2 phosphorylation and extracellular matrix degradation.

Influence of polar and nonpolar carotenoids on structural and adhesive properties of model membranes

Carotenoids, which are known primarily for their photoprotective and antioxidant properties, may also strongly influence the physical properties of membranes. The localization and orientation of these pigments in the lipid bilayer depends on their structure and is determined by their interactions with lipid molecules. This affects both phase behavior and the mechanical properties of membranes. Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) allowed us to gain a direct insight into the differences between the interaction of the non-polar β-carotene and polar zeaxanthin embedded into DPPC liposomes. DSC results showed that zeaxanthin, having polar ionone rings, interacts more strongly with the membrane lipids than β-carotene. The decrease in molar heat capacity by a factor of 2 with a simultaneous broadening of the main phase transition (gel-to-liquid crystalline phase transition) as compared to the two other systems studied suggests some increased length of the coupled interactions between the polar xanthophyll and lipids. Long-distance interactions lead to the formation of larger clusters which may exhibit higher flexibility than small clusters when only short-distance interactions occur. AFM experiments show that adhesive forces are 2 and 10 times higher for DPPC membranes enriched in β-carotene and zeaxanthin, respectively, than those observed for an untreated system. Temperature dependent measurements of adhesion revealed that subphases can be formed in the gel lamellar state of DPPC bilayers. The presence of the non-polar carotenoid enhanced the effect and even a bifurcation of the substates was detected within a temperature range of 30.0-32.5°C prior to pretransition. It is the first time when the presence of subphases has been demonstrated. This knowledge can be helpful in better understanding the functioning of carotenoids in biological membranes. AFM seem to be a very unique and sensitive method for detecting such fine changes in the lipid bilayers.

Modulating effect of lipid bilayer-carotenoid interactions on the property of liposome encapsulation

Liposomes have become an attractive alternative to encapsulate carotenoids to improve their solubility, stability and bioavailability. The interaction mechanism of carotenoid with lipid bilayer is one of the major concerns in improving the delivery efficiency of liposomes. In this study, the microstructure and carotenoid encapsulation efficiency of liposomes composed of native phospholipid (egg yolk phosphatidylcholine, EYPC) and nonionic surfactant Tween 80 were investigated by atomic force microscopy, dynamic light scattering, and Raman spectroscopy, respectively. Subsequently, the effects of carotenoid incorporation on the physical properties of liposomal membrane were performed by Raman spectroscopy, fluorescence polarization, and electron paramagnetic resonance. Results showed that the incorporation of carotenoids affected the liposomes morphology, size and size distribution to various extents. Analysis on the Raman characteristic peaks of carotenoids revealed that lutein exhibited the strongest incorporating ability into liposomes, followed by β-carotene, lycopene, and canthaxanthin. Furthermore, it was demonstrated that carotenoids modulated the dynamics, structure and hydrophobicity of liposomal membrane, highly depending on their molecular structures and incorporated concentration. These modulations were closely correlated with the stabilization of liposomes, including mediating particle aggregation and fusion. These findings should guide the rationale designing for liposomal encapsulation technology to efficiently deliver carotenoids in pharmaceutics, nutraceuticals and functional foods.

Liposome as a delivery system for carotenoids: comparative antioxidant activity of carotenoids as measured by ferric reducing antioxidant power, DPPH assay and lipid peroxidation

This study was conducted to understand how carotenoids exerted antioxidant activity after encapsulation in a liposome delivery system, for food application. Three assays were selected to achieve a wide range of technical principles, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging, ferric reducing antioxidant powder (FRAP), and lipid peroxidation inhibition capacity (LPIC) during liposome preparation, auto-oxidation, or when induced by ferric iron/ascorbate. The antioxidant activity of carotenoids was measured either after they were mixed with preformed liposomes or after their incorporation into the liposomal system. Whatever the antioxidant model was, carotenoids displayed different antioxidant activities in suspension and in liposomes. The encapsulation could enhance the DPPH scavenging and FRAP activities of carotenoids. The strongest antioxidant activity was observed with lutein, followed by β-carotene, lycopene, and canthaxanthin. Furthermore, lipid peroxidation assay revealed a mutually protective relationship: the incorporation of either lutein or β-carotene not only exerts strong LPIC, but also protects them against pro-oxidation elements; however, the LPIC of lycopene and canthaxanthin on liposomes was weak or a pro-oxidation effect even appeared, concomitantly leading to the considerable depletion of these encapsulated carotenoids. The antioxidant activity of carotenoids after liposome encapsulation was not only related to their chemical reactivity, but also to their incorporation efficiencies into liposomal membrane and modulating effects on the membrane properties.

EPR spin labeling measurements of thylakoid membrane fluidity during barley leaf senescence

Physical properties of thylakoid membranes isolated from barley were investigated by the electron paramagnetic resonance (EPR) spin labeling technique. EPR spectra of stearic acid spin labels 5-SASL and 16-SASL were measured as a function of temperature in secondary barley leaves during natural and dark-induced senescence. Oxygen transport parameter was determined from the power saturation curves of the spin labels obtained in the presence and absence of molecular oxygen at 25°C. Parameters of EPR spectra of both spin labels showed an increase in the thylakoid membrane fluidity during senescence, in the headgroup area of the membrane, as well as in its interior. The oxygen transport parameter also increased with age of barley, indicating easier diffusion of oxygen within the membrane and its higher fluidity. The data are consistent with age-related changes of the spin label parameters obtained directly by EPR spectroscopy. Similar outcome was also observed when senescence was induced in mature secondary barley leaves by dark incubation. Such leaves showed higher membrane fluidity in comparison with leaves of the same age, grown under light conditions. Changes in the membrane fluidity of barley secondary leaves were compared with changes in the levels of carotenoids (car) and proteins, which are known to modify membrane fluidity. Determination of total car and proteins showed linear decrease in their level with senescence. The results indicate that thylakoid membrane fluidity of barley leaves increases with senescence; the changes are accompanied with a decrease in the content of car and proteins, which could be a contributing factor.

Differences in human meibum lipid composition with meibomian gland dysfunction using NMR and principal component analysis

PURPOSE

Nuclear magnetic resonance (NMR) spectroscopy has been used to quantify lipid wax, cholesterol ester terpenoid and glyceride composition, saturation, oxidation, and CH₂ and CH₃ moiety distribution. This tool was used to measure changes in human meibum composition with meibomian gland dysfunction (MGD).

METHODS

(1)H-NMR spectra of meibum from 39 donors with meibomian gland dysfunction (Md) were compared to meibum from 33 normal donors (Mn).

RESULTS

Principal component analysis (PCA) was applied to the CH₂/CH₃ regions of a set of training NMR spectra of human meibum. PCA discriminated between Mn and Md with an accuracy of 86%. There was a bias toward more accurately predicting normal samples (92%) compared with predicting MGD samples (78%). When the NMR spectra of Md were compared with those of Mn, three statistically significant decreases were observed in the relative amounts of CH₃ moieties at 1.26 ppm, the products of lipid oxidation above 7 ppm, and the =CH moieties at 5.2 ppm associated with terpenoids.

CONCLUSIONS

Loss of the terpenoids could be deleterious to meibum since they exhibit a plethora of mostly positive biological functions and could account for the lower level of cholesterol esters observed in Md compared with Mn. All three changes could account for the higher degree of lipid order of Md compared with age-matched Mn. In addition to the power of NMR spectroscopy to detect differences in the composition of meibum, it is promising that NMR can be used as a diagnostic tool.

Interactions between canthaxanthin and lipid membranes--possible mechanisms of canthaxanthin toxicity

Canthaxanthin (beta, beta-carotene 4, 4' dione) is used widely as a drug or as a food and cosmetic colorant, but it may have some undesirable effects on human health, mainly caused by the formation of crystals in the macula lutea membranes of the retina. This condition is called canthaxanthin retinopathy. It has been shown that this type of dysfunction of the eye is strongly connected with damage to the blood vessels around the place of crystal deposition. This paper is a review of the experimental data supporting the hypothesis that the interactions of canthaxanthin with the lipid membranes and the aggregation of this pigment may be the factors enhancing canthaxanthin toxicity towards the macula vascular system. All the results of the experiments that have been done on model systems such as monolayers of pure canthaxanthin and mixtures of canthaxanthin and lipids, oriented bilayers or liposomes indicate a very strong effect of canthaxanthin on the physical properties of lipid membranes, which may explain its toxic action, which leads to the further development of canthaxanthin retinopathy.

Mass spectrometry analysis of polyisoprenoids alcohols and carotenoids via ESI(Li(+))-MS/MS

Direct analysis of polyisoprenoid alcohols by electrospray ionization mass spectrometry (ESI-MS) often produces poor results requiring off-line time- and sample-consuming derivatization techniques. In this chapter, we describe a simple ESI-MS approach for the direct analysis of polyisoprenoid alcohols from biological samples. Lithium iodide is used to promote cationization by intense formation of [M+Li](+) adducts. Detection of polyisoprenoids with mass determination can thus be performed with high sensitivity (LOD near 100 pM), whereas characteristic collision-induced dissociations observed for both dolichols and polyprenols permit investigation of their structure. We also describe a simple ESI-MS approach for the direct analysis of carotenoids in biological samples using lithium iodide to promote their ionization and the analysis of several carotenoids as proof-of-principle cases. Finally, we applied ESI(Li(+))-MS and ESI(Li(+))-MS/MS to investigate the presence of carotenoids in Plasmodium falciparum.

Biologic activity of carotenoids related to distinct membrane physicochemical interactions

Carotenoids are naturally occurring organic pigments that are believed to have therapeutic benefit in treating cardiovascular disease (CVD) because of their antioxidant properties. However, prospective randomized trials have failed to demonstrate a consistent benefit for the carotenoid beta-carotene in patients at risk for CVD. The basis for this apparent paradox is not well understood but may be attributed to the distinct antioxidant properties of various carotenoids resulting from their structure-dependent physicochemical interactions with biologic membranes. To test this hypothesis, we measured the effects of astaxanthin, zeaxanthin, lutein, beta-carotene, and lycopene on lipid peroxidation using model membranes enriched with polyunsaturated fatty acids. The correlative effects of these compounds on membrane structure were determined using small-angle x-ray diffraction approaches. The nonpolar carotenoids, lycopene and beta-carotene, disordered the membrane bilayer and stimulated membrane lipid peroxidation (>85% increase in lipid hydroperoxide levels), whereas astaxanthin (a polar carotenoid) preserved membrane structure and exhibited significant antioxidant activity (>40% decrease in lipid hydroperoxide levels). These results suggest that the antioxidant potential of carotenoids is dependent on their distinct membrane lipid interactions. This relation of structure and function may explain the differences in biologic activity reported for various carotenoids, with important therapeutic implications.

Modification of membranes by quercetin, a naturally occurring flavonoid, via its incorporation in the polar head group

Quercetin is a naturally occurring flavonoid that has a lot of beneficial properties to human health. In this report, using the spin label technique, the influence of quercetin on the fluidity of multilamellar DPPC liposomes was studied. The polarity of the environment preferred by quercetin was also examined by determining the dependence of the position of electronic absorption maxima on dielectric properties of different environments. Autofluorescence of quercetin was also used to examine its distribution in cells. An additional aim of the study was to find how quercetin presence affects human skin fibroblasts. The results showed that incorporation of quercetin at physiological pH into DPPC liposomes caused changes in the partition coefficient of the Tempo spin label between water and polar head group phases. By determining the electronic absorption maxima, we observed that the chromophore of quercetin is localized in the polar head region. Fluorescence microscopy of HSF cells showed quercetin presence in the membrane, cytoplasm and inside the nucleus. Ultrastructural observation revealed some changes, especially in membranous structures, after flavonol treatment. From the results we have concluded that quercetin present in the membrane and other structures can cause changes within cells crucial for its pharmacological activity.

Thermotropic phase behaviour of lipid bilayers containing carotenoid pigment canthaxanthin: a differential scanning calorimetry study

In this study we address the problem of the effect of canthaxanthin on the thermotropic properties of lipid membranes formed with lipids which differ in the thickness of their hydrophobic core, size of polar heads or presence of the ester carbonyl group. For all the lipids a decrease in main transition enthalpy has been observed, indicating that canthaxanthin alters the membrane properties in its gel phase. The strongest influence of canthaxanthin on main phase transition and pretransition has been observed for the lipid having the thinnest hydrophobic region. Component analysis indicates a distinct cooperativity change, which most probably colligates with the formation of new thermotropic phases. The effect of canthaxanthin has been almost negligible in the case of phosphatidylethanolamines. The absence of the ester carbonyl group results in different thermotropic behavior, especially for low canthaxanthin concentrations. The effect of canthaxanthin is explained in terms of its organization within the membrane.

Differential effects of carotenoids on lipid peroxidation due to membrane interactions: X-ray diffraction analysis

The biological benefits of certain carotenoids may be due to their potent antioxidant properties attributed to specific physico-chemical interactions with membranes. To test this hypothesis, we measured the effects of various carotenoids on rates of lipid peroxidation and correlated these findings with their membrane interactions, as determined by small angle X-ray diffraction approaches. The effects of the homochiral carotenoids (astaxanthin, zeaxanthin, lutein, beta-carotene, lycopene) on lipid hydroperoxide (LOOH) generation were evaluated in membranes enriched with polyunsaturated fatty acids. Apolar carotenoids, such as lycopene and beta-carotene, disordered the membrane bilayer and showed a potent pro-oxidant effect (>85% increase in LOOH levels) while astaxanthin preserved membrane structure and exhibited significant antioxidant activity (40% decrease in LOOH levels). These findings indicate distinct effects of carotenoids on lipid peroxidation due to membrane structure changes. These contrasting effects of carotenoids on lipid peroxidation may explain differences in their biological activity.

Incorporation of carotenoid esters into liposomes

Carotenoid esters are investigated for their interaction with liposomal membranes and compared with their corresponding free (non-esterified) carotenoids. A monoester (beta-cryptoxanthin) and two diesters (zeaxanthin and lutein) were chosen. Egg yolk phosphatidylcholine liposomes served as the membrane model. We measured the sizes of the liposomes by photon correlation spectroscopy. The incorporation yields were determined spectrophotometrically. From liposomes simultaneously doped with the fluorescent dye Laurdan, fluidity changes of the liposomes were obtained. In summary, the results indicate that the carotenoid esters: (i) get incorporated, but at a lower yield than their corresponding free carotenoids, (ii) also increase the membrane rigidity as do the free carotenoids, and (iii) increase the liposome sizes significantly, but after extrusion through an 0.1 mum filter the sizes resemble with the exception of the liposomes incorporated with lutein diesters, they remain bigger indicating an elastic property due to two different accessible locations in the membrane.

Carotenoids as modulators of lipid membrane physical properties

Carotenoids are a group of pigments present both in the plant and animal kingdoms, which play several important physiological functions. The protection against active oxygen species, realised via the quenching of excited states of photosensitizing molecules, quenching of singlet oxygen and scavenging of free radicals, is one of the main biological functions of carotenoids. Several recent research indicate that the protection of biomembranes against oxidative damage can be also realised via the modification of the physical properties of the lipid phase of the membranes. This work presents an overview of research on an effect of carotenoids on the structural and dynamic properties of lipid membranes carried out with the application of different techniques such as Electron Paramagnetic Resonance, Nuclear Magnetic Resonance, Differential Scanning Calorimetry, X-ray diffractometry, monomolecular layer technique and other techniques. It appears that, in most cases, polar carotenoids span lipid bilayer and have their polar groups anchored in the opposite polar zones of the membrane. Owing to the van der Waals interactions of rigid rod-like molecules of carotenoid and acyl chains of lipids, pigment molecules rigidify the fluid phase of the membranes and limit oxygen penetration to the hydrophobic membrane core susceptible to oxidative degradation.

The behaviour of beta-carotene in the phosphatidylcholine bilayer as revealed by a molecular simulation study

A molecular dynamics (MD) simulation of the fully hydrated bilayer made of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and containing beta-carotene (beta-Car) molecules was carried out as a complementary approach to experimental techniques to investigate the orientation of beta-Car in the lipid membrane as well as its influence on the bilayer properties. The bilayer reached thermal equilibrium after 1200 ps of MD simulation and the productive run was carried out for 2800 ps. The results indicate that the carotene rings are located in the region occupied by the carbonyl groups of the POPC gamma-chain with no trace of penetration towards the centre of the bilayer. Carotene exhibits an ordering effect on both the beta- and the gamma-chain. While the fully saturated gamma-chain is affected evenly along, the order of the mono-unsaturated beta-chain is modified mainly below the double bond. In general, a high value of the order parameter and the chain tilt in the range from 11.4 degrees to 26.7 degrees were observed for the beta-Car molecules. However, for chain segment adjacent to methyl groups the value of the order parameter is low and the tilt angle is close to 75 degrees . Moreover, the probability of trans conformation being generally close to 1.0 along the beta-Car chain is reduced for these segments. Our MD simulation study suggests two pools of the preferential orientation of beta-Car: a slightly bent structure corresponding to a small chain tilt angle and a rather stretched structure that corresponds to a higher chain tilt. The results are discussed in the light of experimental findings.

The effect of polysialic acid on molecular dynamics of model membranes studied by 31P NMR spectroscopy

The paper reports the results of our study on the dynamics of model phospholipid membranes studied by 31P NMR spectroscopy. The 31P NMR spectra of multilamellar vesicles in temperatures below the main phase transition of PC are reported. The 31P NMR spectra revealed changes caused by an increase of the membrane fluidity when polysialic acid (polySia) was applied as a modifying agent. The presence of polySia in the external environment of the phospholipid vesicles changes the motional freedom in the region of phosphate group of lipids. Increase of polysialic acid concentration changes structural properties of a membrane by increasing its fluidity.

Thermotropic phase behaviour of alpha-dipalmitoylphosphatidylcholine multibilayers is influenced to various extents by carotenoids containing different structural features--evidence from differential scanning calorimetry

Carotenoids are the effective modulators of physical properties of model and natural membranes. To demonstrate the relationship between the structure of carotenoids and their effect on the molecular dynamics of membranes, we have investigated the influence of five structurally different carotenoids: beta-carotene, lycopene, lutein, violaxanthin, zeaxanthin and additionally carotane--a fully saturated derivative of beta-carotene, on thermotropic phase behaviour of dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles by means of differential scanning calorimetry (DSC). The results obtained indicate that the carotenoids used modulated the thermotropic properties of multibilayers to various extents, broadening the pretransition and the main phase transition peaks and shifting them to lower temperatures. Pronounced decrease of pretransition enthalpy (DeltaH(p)) proves that carotenoids very strongly alter the membrane properties in its gel phase. Comparison of the influence of several carotenoids shows that a rigid, polyisoprenoid chain plays a basic role in altering the thermotropic properties of such membranes and the presence of rings without oxygen-containing groups has a minor significance for the observed interactions. Carotenoids containing epoxy and/or hydroxy groups attached to their rings modify the thermotropic phase behaviour of DPPC multilamellar vesicles stronger than carotenes--a result of their orientation in the DPPC bilayer.

Different ways to insert carotenoids into liposomes affect structure and dynamics of the bilayer differently

We apply and quantify two techniques to incorporate carotenoids into liposomes: (i). preparation of unilamellar liposomes from mixtures of phospholipids and a carotenoid or cholesterol; (ii). insertion of carotenoids into prepared liposomes. Homogeneous liposomal fractions with a vesicle size diameter of approximately 50 nm were obtained by an extrusion method. The resulting vesicles were subjected to a three-dimensional light scattering cross-correlation measurement in order to evaluate their size distribution. The fluorescent dyes Laurdan, DiI-C(18), C(6)-NBD-PC were used to label the liposomes and to evaluate modulations of ordering, hydrophobicity and permeability to water molecules adjacent to the bilayer in the presence of carotenoids and/or cholesterol. Zeaxanthin incorporation (up to 0.1-1 mol%) attributes to the symmetric and ordered structure of the bilayer, causing both a strong hydrophobicity and a lower water permeability at the polar region of the membrane. The incorporation of lutein has similar effects, but its ordering effect is inferior in the polar region and superior in the non-polar region of the membrane. beta-Carotene, which can be incorporated at lower effective concentrations only, distributes in a more disordered way in the membrane, but locates preferentially in the non-polar region and, compared to lutein and zeaxanthin, it induces a less ordered structure, a higher hydrophobicity and a lower water permeability on the bilayer.

Low-temperature-induced accumulation of xanthophylls and its structural consequences in the photosynthetic membranes of the cyanobacterium Cylindrospermopsis raciborskii: an FTIR spectroscopic study

The effects of the growth temperature on the lipids and carotenoids of a filamentous cyanobacterium, Cylindrospermopsis raciborskii, were studied., The relative amounts of polyunsaturated glycerolipids and myxoxanthophylls in the thylakoid membranes increased markedly when this cyanobacterium was grown at 25 degrees C instead of 35 degrees C. Fourier transform infrared spectroscopy was used to analyze the low-temperature-induced structural alterations in the thylakoid membranes. Despite the higher amount of unsaturated lipids there, conventional analysis of the v(sym)CH(2) band (characteristic of the lipid disorder) revealed more tightly arranged fatty-acyl chains for the thylakoids in the cells grown at 25 degrees C as compared with those grown at 35 degrees C. This apparent controversy was resolved by a two-component analysis of the v(sym)CH(2) band, which demonstrated very rigid, myxoxanthophyll-related lipids in the thylakoid membranes. When this rigid component was excluded from the analysis of the thermotropic responses of the v(sym)CH(2) bands, the expected higher fatty-acyl disorder was observed for the thylakoids prepared from cells grown at 25 degrees C as compared with those grown at 35 degrees C. Both the carotenoid composition and this rigid component in the thylakoid membranes were only growth temperature-dependent; the intensity of the illuminating light during cultivation had no apparent effect on these parameters. We propose that, besides their well-known protective functions, the polar carotenoids in particular may have structural effects on the thylakoid membranes. These effects should be exerted locally--by forming protective patches, in-membrane barriers of low dynamics--to prevent the access of reactive radicals generated in either enzymatic or photosynthetic processes to sensitive spots of the membranes.

Molecular characteristics of astaxanthin and beta-carotene in the phospholipid monolayer and their distributions in the phospholipid bilayer

The molecular characteristics of the monolayers of astaxanthin with polar group on the beta-ionone ring in the molecule and beta-carotene without polar group and their interactions in mixed carotenoid-phospholipid monolayers and the effects of carotenoids on the phase behavior of the phospholipid bilayers were examined by the monolayer technique and differential scanning calorimetry (DSC). We found from the monolayer study that beta-carotene had an amphiphilic nature. The molecular assembly of astaxanthin in the monolayer at the hydrophobic/hydrophilic interface was more stable than that of beta-carotene. Dimyristoylphosphatidylcholine (DMPC) in the monolayer was miscible with astaxanthin in the range of 0-0.4 mol fractions of astaxanthin, but not fully miscible with beta-carotene even at low concentrations below 0.1 mol fraction of beta-carotene. Surface potential and compression/expansion cycles of beta-carotene monolayer indicated the formation of molecular aggregates by itself. DSC study showed that when small amount of astaxanthin was added, the transition temperature of dipalmitoylphosphatidylcholine (DPPC) was markedly shifted to lower temperatures and that the transition peak was asymmetrically broadened, indicative of a significant depression in cooperativity of the gel to liquid-crystalline transition. The asymmetric DSC endothermic bands of DPPC incorporating small amounts of astaxanthin were well fit by deconvolution into two to three domains containing different concentrations of astaxanthin. On the contrary, the incorporation of beta-carotene resulted in a small depression of the main transition temperature with a slight broadening of the transition peak, suggesting a small miscibility of beta-carotene with the phospholipid bilayer or a formation of aggregates of beta-carotene in the membranes. These results suggest that there would be a high localized concentration in the phase separated membrane for astaxanthin or beta-carotene to function effectively as scavenger.

Quenching of singlet oxygen by carotenoids produced in escherichia coli - attenuation of singlet oxygen-mediated bacterial killing by carotenoids

We examined the viability of Escherichia coli transformants harboring various carotenoids synthesizing genes in a medium containing an enzymatic singlet oxygen generating system, which contained myeloperoxidase, hydrogen peroxide and Br(-) at pH 4.5. Singlet oxygen quenching activities of various carotenoids in phosphatidyl choline micelles in aqueous media were also studied using the same enzymatic singlet oxygen generating system. Viability of the transformants producing carotenoids was higher than that of the wild type E. coli in the singlet oxygen generation mixture. Of the transformants tested, the viability of zeaxanthin-diglucoside producing transformant was the highest. Carotenoids in increasing order of k(q) values were beta-carotene, a cyclic carotene<zeaxanthin with hydroxy groups < or =lycopene, an acyclic carotene<canthaxanthin and astaxanthin with keto groups <<zeaxanthin-diglucoside. The k(q) value of zeaxanthin-diglucoside was 3.5 times higher than that of beta-carotene. These results suggest that orientation of the carotenoids in lipid layers of micelles and also in phospholipid membrane of bacteria is important for quenching of singlet oxygen. Furthermore, the viability of transformants producing lycopene and phytoene was almost as high as that of the transformant producing zeaxanthin-glucoside.

Exogenously incorporated ketocarotenoids in large unilamellar vesicles. Protective activity against peroxidation

The ability of astaxanthin and canthaxanthin as chain-breaking antioxidants was studied in Cu(2+)-initiated peroxidation of phosphatidylcholine large unilamellar vesicles (LUVs). Both carotenoids increased the lag period that precedes the maximum rate of lipid peroxidation, though astaxanthin showed stronger activity. For these experiments, different amounts of xanthophylls were exogenously added to previously made LUVs, non-incorporated pigment being afterwards removed. Differential scanning calorimetry assays with L-beta,gamma-dimyristoyl-alpha-phosphatidylcholine LUVs demonstrated that xanthophylls incorporated as described interact with the lipid matrix becoming interspersed among the phospholipid molecules.

Lycopene and beta-carotene protect against oxidative damage in HT29 cells at low concentrations but rapidly lose this capacity at higher doses

Epidemiological studies have clearly demonstrated a link between dietary carotenoids and the reduced incidence of certain diseases, including some cancers. However recent intervention studies (e.g. ATBC, CARET and others) have shown that beta-carotene supplementation has little or no beneficial effect and may, in fact, increase the incidence of lung cancers in smokers. This presents a serious dilemma for the scientific community - are carotenoids at high concentrations actually harmful in certain circumstances? Currently, a significant number of intervention studies are on-going throughout the world involving carotenoids (of both natural and synthetic origin). Our approach has been to study the ability of supplementary carotenoids in protecting cells against oxidatively-induced DNA damage (as measured by the comet assay), and membrane integrity (as measured by ethidium bromide uptake). Both lycopene and beta-carotene only afforded protection against DNA damage (induced by xanthine/xanthine oxidase) at relatively low concentrations (1-3 microM). These levels are comparable with those seen in the plasma of individuals who consume a carotenoid-rich diet. However, at higher concentrations (4-10 microM), the ability to protect the cell against such oxidative damage was rapidly lost and, indeed, the presence of carotenoids may actually serve to increase the extent of DNA damage. Similar data were obtained when protection against membrane damage was studied. This would suggest that supplementation with individual carotenoids to significantly elevate blood and tissue levels is of little benefit and, may, in fact, be deleterious. This in vitro data presented maybe significant in the light of recent intervention trials.

Evaluation of structurally different carotenoids in Escherichia coli transformants as protectants against UV-B radiation

Escherichia coli cells transformed with several carotenogenic genes to mediate the formation of zeta-carotene, neurosporene, lycopene, beta-carotene, and zeaxanthin were exposed to UV-B radiation. Short-term kinetics revealed that endogenous levels of neurosporene and beta-carotene protected E. coli against irradiation with UV-B. Zeaxanthin protected against only the photosensitized UV-B treatment. All other carotenoids were ineffective.

Zeaxanthin (dihydroxy-beta-carotene) but not beta-carotene rigidifies lipid membranes: a 1H-NMR study of carotenoid-egg phosphatidylcholine liposomes

1H-NMR technique was applied to study liposomes formed with egg-yolk phosphatidylcholine containing as an additional component two carotenoid pigments: beta-carotene or zeaxanthin (dihydrohy-beta-carotene). A strong rigidifying effect of zeaxanthin but not of beta-carotene with respect to hydrophobic core of lipid bilayer was concluded from the carotenoid-dependent broadening of the NMR lines assigned to -CH2- groups and terminal -CH3 groups of lipid alkyl chains. A similar effect of zeaxanthin with respect to polar headgroups was concluded on the basis of the effect of the pigment on the shape of NMR lines attributed to -N+(CH3)3 groups. In contrast, beta-carotene increases motional freedom of lipid polar headgroups. The inclusion of both carotenoids to liposomes resulted in the enhanced penetration of Pr3+ ions to the polar zone of the external layer of a membrane monitored by the splitting of the -N+(CH3)3 signal, the effect of beta-carotene being much more pronounced. Differences in the effect on membrane structure and molecular dynamics observed for beta-carotene and its polar derivative are discussed in terms of organization of a carotenoid-containing lipid membrane.

Changes in physical properties of vacuolar membrane during transformation of protein bodies into vacuoles in germinating pumpkin seeds

Changes in membrane molecular dynamics associated with the transformation of protein body membranes into vacuolar membranes during pumpkin seed germination, were monitored by EPR-spin probe technique. Using highly purified membrane preparations as well as 5-SASL and 16-SASL spin labels, parameters like general membrane lipid fluidity, order parameter, semicone angle, rotational correlation times tau 2B and tau 2C, ratio of immobilized to mobile lipids were determined and the activation energy for rotational diffusion of 16-SASL was calculated. Analysis of these parameters at different temperatures indicated a more rigid nature of protein body membrane comparing to vacuolar membrane, as a result of a more restricted motional freedom of lipids. These differences are discussed in terms of protein composition and various functional specialization of both types of membranes.

The importance of liposomes as models and tools in the understanding of photosensitization mechanisms

The various applications of liposomes in understanding photosensitization are described in this paper, with particular emphasis on the various kinds of information that these models allow to obtain in phototherapy. Liposomes are simple vesicles in which an aqueous phase is enclosed by a phospholipidic membrane. They are suitable models mimicking specific situations occurring in vivo and they allow study of the influence of physicochemical, photobiological and biochemical factors on the uptake of photosensitizers by tissues, their mechanisms of action and the subsequent photoinduced tumor necrosis. Moreover, solubilization of the sensitizer into the bilayer seems to improve its tumoral selectivity and its photodynamic efficiency.