Effects of carotenoids on lipid bilayers

Dynamic and Energetic Aspects of Carotenoids In-and-Around Model Lipid Membranes Revealed in Molecular Modelling

In contrast to plants, humans are unable to synthesise carotenoids and have to obtain them from diet. Carotenoids fulfil several crucial biological functions in the organism; however, due to poor solubility in water, their bioavailability from plant-based food is low. The processes of carotenoid absorption and availability in the human body have been intensively studied. The recent experimental findings concerning these processes are briefly presented in the introductory part of this review, together with a summary of such topics as carotenoid carriers, body transport and tissue delivery, to finally report on molecular-level studies of carotenoid binding by membrane receptors. The main message of the review is contained in the section describing computational investigations of carotenoid intercalation and dynamic behaviour in lipid bilayers. The relevance of these computational studies lies in showing the direct link between the microscopic behaviour of molecules and the characteristics of their macroscopic ensembles. Furthermore, studying the interactions between carotenoids and lipid bilayers, and certainly proteins, on the molecular- and atomic-level using computational methods facilitates the interpretation and explanation of their macroscopic properties and, hopefully, helps to better understand the biological functions of carotenoids.

Organization of Carotenoid Aggregates in Membranes Studied Selectively using Resonance Raman Optical Activity

In living organisms, carotenoids are incorporated in biomembranes, remarkably modulating their mechanical characteristics, fluidity, and permeability. Significant resonance enhancement of Raman optical activity (ROA) signals of carotenoid chiral aggregates makes resonance ROA (RROA), a highly selective tool to study exclusively carotenoid assemblies in model membranes. Hence, RROA is combined with electronic circular dichroism (ECD), dynamic light scattering (DLS), molecular dynamics, and quantum-chemical calculations to shed new light on the carotenoid aggregation in dipalmitoylphosphatidylcholine (DPPC) liposomes. Using representative members of the carotenoid family: apolar α-carotene and more polar fucoxanthin and zeaxanthin, the authors demonstrate that the stability of carotenoid aggregates is directly linked with their orientation in membranes and the monomer structures inside the assemblies. In particular, polyene chain distortion of α-carotene molecules is an important feature of J-aggregates that show increased orientational freedom and stability inside liposomes compared to H-assemblies of more polar xanthophylls. In light of these results, RROA emerges as a new tool to study active compounds and drugs embedded in membranes.

Inactivation of Carotenogenic-Biosynthesizing Genes Altered Lipids Composition and Intensity in Cronobacter sakazakii

Cronobacter sakazakii, an opportunistic milk-borne pathogen responsible for severe neonatal meningitis and bacteremia, can synthesize yellow pigment (various carotenoids) benefiting for bacterial survival, while little literature was available about the influence of various carotenoids on bacterial resistance to a series of stresses and the characteristics of cell membrane, obstructing the development of novel bactericidal strategies overcoming the strong tolerance of C. sakazakii. Thus in this study, for the first time, five carotenogenic genes of C. sakazakii BAA-894 were inactivated, respectively, to construct a series of mutants producing various carotenoids and their effects on the cell membrane properties, and resistances to food- and host-related stresses, were investigated systematically. Furthermore, to explore its possible mode of action, comparative lipidomics analysis was performed to reveal the change of lipids that were mainly located at cell membranes. The results showed that five mutants (ΔcrtB, ΔcrtI, ΔcrtY, ΔcrtZ, and ΔcrtX) displayed negligible change in growth rate but higher permeability of the outer membrane and lower fluidity of cell membrane compared to the wild type. Besides, these mutants exhibited poorer ability of biofilm formation and lower resistances to acid, oxidative, osmotic, and desiccation stresses, indicating that different carotenoid composition significantly affected environmental tolerance of C. sakazakii. To discover the possible causes, lipidomics analysis of C. sakazakii was conducted and more than 500 lipid species belonging to 27 classes had been identified at first. Compared to that of BAA-894, the composition and relative intensity of lipid species in five mutants varied significantly, especially the monounsaturated and biunsaturated phosphatidylethanolamine. The evidence presented in this study demonstrated that the varied composition of carotenoids in C. sakazakii significantly altered the lipid profile and intensity, which maybe a crucial means to influencing the characteristics of cell membranes and resistance to environmental stresses.

An Overview of Lutein in the Lipid Membrane

Lutein, zeaxanthin, and meso-zeaxanthin (a steroisomer of zeaxanthin) are macular pigments. They modify the physical properties of the lipid bilayers in a manner similar to cholesterol. It is not clear if these pigments are directly present in the lipid phase of the membranes, or if they form complexes with specific membrane proteins that retain them in high amounts in the correct place in the retina. The high content of macular pigments in the Henle fiber layer indicates that a portion of the lutein and zeaxanthin should not only be bound to the specific proteins but also directly dissolved in the lipid membranes. This high concentration in the prereceptoral region of the retina is effective for blue-light filtration. Understanding the basic mechanisms of these actions is necessary to better understand the carotenoid-membrane interaction and how carotenoids affect membrane physical properties-such as fluidity, polarity, and order-in relation to membrane structure and membrane dynamics. This review focuses on the properties of lutein.

Computational Exploration of Potential CFTR Binding Sites for Type I Corrector Drugs

Cystic fibrosis (CF) is a recessive genetic disease that is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The recent development of a class of drugs called "correctors", which repair the structure and function of mutant CFTR, has greatly enhanced the life expectancy of CF patients. These correctors target the most common disease causing CFTR mutant F508del and are exemplified by the FDA-approved VX-809. While one binding site of VX-809 to CFTR was recently elucidated by cryo-electron microscopy, four additional binding sites have been proposed in the literature and it has been theorized that VX-809 and structurally similar correctors may engage multiple CFTR binding sites. To explore these five binding sites, ensemble docking was performed on wild-type CFTR and the F508del mutant using a large library of structurally similar corrector drugs, including VX-809 (lumacaftor), VX-661 (tezacaftor), ABBV-2222 (galicaftor), and a host of other structurally related molecules. For wild-type CFTR, we find that only one site, located in membrane spanning domain 1 (MSD1), binds favorably to our ligand library. While this MSD1 site also binds our ligand library for F508del-CFTR, the F508del mutation also opens a binding site in nucleotide binding domain 1 (NBD1), which enables strong binding of our ligand library to this site. This NBD1 site in F508del-CFTR exhibits the strongest overall binding affinity for our library of corrector drugs. This data may serve to better understand the structural changes induced by mutation of CFTR and how correctors bind to the protein. Additionally, it may aid in the design of new, more effective CFTR corrector drugs.

Salt effects on mixed composition membranes containing an antioxidant lipophilic edaravone derivative: a computational-experimental study

The protection of lipid membranes against oxidation avoids diseases associated with oxidative stress. As a strategy to contrast it, functionalized lipids with antioxidant activity are used to become part of membranes thus protecting them. For this purpose, a lipophilic edaravone derivative has been synthesized, adding a C18 saturated chain to the original structure. The antioxidant activity of C18-Edv has been demonstrated in our previous work. In this study, molecular dynamics simulations have been performed to define the effects of NaCl, MgCl₂, KCl, and CaCl₂ salts on a palmitoyl-oleoyl-sn-glycero-phosphocholine (POPC) lipid bilayer encapsulating C18-Edv. The results showed how different salts influence POPC lateral diffusion, and the movements of C18-Edv heads, which are antioxidant moieties, were correlated to the ability of C18-Edv molecules to protect membranes. MgCl₂ showed a negative impact leading to C18-Edv clusterization and membrane stretching, while KCl and NaCl showed a moderate influence on the mixed lipid membrane structure. CaCl₂ increased the exposure of the C18-Edv heads to the lipid-water interface, resulting in the salt with a higher propensity to guarantee protection against radicals in the aqueous phase. Finally, C18-Edv-POPC liposomes have been prepared following the simulation conditions, and then an experimental Oxygen Radical Absorbance Capacity (ORAC) assay has been performed to confirm the in silico predicted results.

Carotenoids and Apocarotenoids in Planta: Their Role in Plant Development, Contribution to the Flavour and Aroma of Fruits and Flowers, and Their Nutraceutical Benefits

Carotenoids and apocarotenoids are diverse classes of compounds found in nature and are important natural pigments, nutraceuticals and flavour/aroma molecules. Improving the quality of crops is important for providing micronutrients to remote communities where dietary variation is often limited. Carotenoids have also been shown to have a significant impact on a number of human diseases, improving the survival rates of some cancers and slowing the progression of neurological illnesses. Furthermore, carotenoid-derived compounds can impact the flavour and aroma of crops and vegetables and are the origin of important developmental, as well as plant resistance compounds required for defence. In this review, we discuss the current research being undertaken to increase carotenoid content in plants and research the benefits to human health and the role of carotenoid derived volatiles on flavour and aroma of fruits and vegetables.

Computational and Experimental Approaches to Investigate Lipid Nanoparticles as Drug and Gene Delivery Systems

Lipid nanoparticles (LNPs) have been widely applied in drug and gene delivery. More than twenty years ago, DoxilTM was the first LNPs-based drug approved by the US Food and Drug Administration (FDA). Since then, with decades of research and development, more and more LNP-based therapeutics have been used to treat diverse diseases, which often offer the benefits of reduced toxicity and/or enhanced efficacy compared to the active ingredients alone. Here, we provide a review of recent advances in the development of efficient and robust LNPs for drug/gene delivery. We emphasize the importance of rationally combining experimental and computational approaches, especially those providing multiscale structural and functional information of LNPs, to the design of novel and powerful LNP-based delivery systems.

A carotenoid-deficient mutant of the plant-associated microbe Pantoea sp. YR343 displays an altered membrane proteome

Membrane organization plays an important role in signaling, transport, and defense. In eukaryotes, the stability, organization, and function of membrane proteins are influenced by certain lipids and sterols, such as cholesterol. Bacteria lack cholesterol, but carotenoids and hopanoids are predicted to play a similar role in modulating membrane properties. We have previously shown that the loss of carotenoids in the plant-associated bacteria Pantoea sp. YR343 results in changes to membrane biophysical properties and leads to physiological changes, including increased sensitivity to reactive oxygen species, reduced indole-3-acetic acid secretion, reduced biofilm and pellicle formation, and reduced plant colonization. Here, using whole cell and membrane proteomics, we show that the deletion of carotenoid production in Pantoea sp. YR343 results in altered membrane protein distribution and abundance. Moreover, we observe significant differences in the protein composition of detergent-resistant membrane fractions from wildtype and mutant cells, consistent with the prediction that carotenoids play a role in organizing membrane microdomains. These data provide new insights into the function of carotenoids in bacterial membrane organization and identify cellular functions that are affected by the loss of carotenoids.

Therapeutic Efficacy of Antioxidants in Ameliorating Obesity Phenotype and Associated Comorbidities

Obesity has been a worldwide epidemic for decades. Despite the abundant increase in knowledge regarding the etiology and pathogenesis of obesity, the prevalence continues to rise with estimates predicting considerably higher numbers by the year 2030. Obesity is characterized by an abnormal lipid accumulation, however, the physiological consequences of obesity are far more concerning. The development of the obesity phenotype constitutes dramatic alterations in adipocytes, along with several other cellular mechanisms which causes substantial increase in systemic oxidative stress mediated by reactive oxygen species (ROS). These alterations promote a chronic state of inflammation in the body caused by the redox imbalance. Together, the systemic oxidative stress and chronic inflammation plays a vital role in maintaining the obese state and exacerbating onset of cardiovascular complications, Type II diabetes mellitus, dyslipidemia, non-alcoholic steatohepatitis, and other conditions where obesity has been linked as a significant risk factor. Because of the apparent role of oxidative stress in the pathogenesis of obesity, there has been a growing interest in attenuating the pro-oxidant state in obesity. Hence, this review aims to highlight the therapeutic role of antioxidants, agents that negate pro-oxidant state of cells, in ameliorating obesity and associated comorbidities. More specifically, this review will explore how various antioxidants target unique and diverse pathways to exhibit an antioxidant defense mechanism.

Carotenoids promote lateral packing and condensation of lipid membranes

Carotenoids are pigment molecules that protect biomembranes against degradation and may be involved in the formation of functional bacterial membrane microdomains. Little is known on whether different types of carotenoids have different effects on the membrane or if there is any concentration dependence of these effects. In this work, we present results from molecular dynamics simulations of phospholipid bilayers containing different amounts of either β-carotene or zeaxanthin. Both β-carotene and zeaxanthin show the ability to laterally condense the membrane lipids and reduce their inter-leaflet interactions. With increasing concentrations, both carotenoids increase the bilayer thickness and rigidity. The results reveal that carotenoids have similar effects to cholesterol on regulating the behavior of fluid-phase membranes, suggesting that they could function as sterol substitutes and confirming their potential role in the formation of functional membrane domains.

Biophysical characterization of lutein or beta carotene-loaded cationic liposomes

The interactions between carotenoids and membrane constituents are vital for understanding the mechanism of their dynamic action. Lutein and beta-carotene were loaded separately into the bilayer of dipalmitoylphosphatidylcholine (DPPC) mixed at a molar ratio with l-α-phosphatidylethanolamine derived from sheep brain (cephalin) and stearylamine (SA) to form cationic liposomes. The molecular interaction between lutein or beta-carotene with cationic liposomes was studied using transmission electron microscopy (TEM), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. Encapsulation efficiency (EE %) and in vitro drug release were determined. The DLS measurements confirmed the mono-dispersity of all samples. TEM results revealed that liposomal samples were oval-shaped and there was a change in their morphology and size upon encapsulation of lutein or beta-carotene. Beta-carotene was observed to adhere to the boundary surface within the liposomal assembly with external morphological alterations. EE% of lutein and beta-carotene exceeded 98.8 ± 0.3% and 87 ± 4%, respectively. Lutein doped with cationic liposomes shows better in vitro release stability (about 30%) than beta-carotene (about 45%) between the 3^rd and the 6^th hour manifested by lower leakage rate percentage of lutein which would lead to higher lutein retention. The incorporated lutein resulted in broadening and shifting of the major endothermic peak of the co-liposomes, while the incorporation of beta-carotene did not induce a noticeable shift. An FTIR study was employed to reveal structure alterations in the vesicles after the encapsulation of lutein or beta-carotene into liposomes. Encapsulation of lutein or beta-carotene into liposomes induced a change in the frequency of the symmetric and asymmetric CH₂ stretching bands in the acyl chain that may influence the order of the membrane.

The interactions between carotenoids and membrane constituents are vital for understanding the mechanism of their dynamic action.

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.

The non-homogenous distribution and aggregation of carotenoids in the stratum corneum correlates with the organization of intercellular lipids in vivo

The human stratum corneum (SC) contains an abundant amount of carotenoid antioxidants, quenching free radicals and thereby protecting the skin. For the precise measurements of the depth-dependent carotenoid concentration, confocal Raman microscopy is a suitable method. The quantitative concentration can be determined by the carotenoid-related peak intensity of a Gaussian function approached at ≈1524 cm^-1 using non-linear regression. Results show that the carotenoid concentration is higher at the superficial layers of the SC then decreases to a minimum at 20% SC depth and increases again towards the bottom of the SC. In the present work, two carotenoid penetration pathways into the SC are postulated. The first pathway is from the stratum granulosum to the bottom of the SC, while in the second pathway, the carotenoids are delivered to the skin surface by sweat and/or sebum secretion and penetrate from outside. The carotenoids are aggregated at the superficial layers, which are shown by high correlation between the aggregation states of carotenoids and the lateral organization of lipids. At the 30%-40% SC depths, the ordered and dense lipid molecules intensify the lipid-carotenoid interactions and weaken the carotenoid-carotenoid interaction and thus exhibit the disaggregation of carotenoids. At 90%-100% SC depths, the carotenoid-lipid interaction is weakened and the carotenoids have a tendency to be aggregated. Thus, the molecular structural correlation of carotenoid and SC lipid might be reserved in the intercellular space of the SC and also serves as the skeleton of the intercellular lipids.

The interactions of an Aβ protofibril with a cholesterol-enriched membrane and involvement of neuroprotective carbazolium-based substances

Recent studies have shown that the aggregation of the amyloid-beta peptide (Aβ) in the brain cell membrane is responsible for the emergence of Alzheimer's disease (AD); the exploration of effective factors involved in the extension of the aggregation process and alternatively the examination of an effective inhibitor via theoretical and experimental tools are among the main research topics in the field of AD treatment. Therefore, in this study, we used all-atom molecular dynamics (MD) simulations to clarify the impact of cell membrane cholesterol on the interaction of Aβ with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) as a membrane model. Moreover, the effect of the P7C3-S243 molecule on the abovementioned process was investigated. The simulation results disclosed the neuroprotective property of the P7C3-S243 molecule. The MD simulation results indicate that the interaction of cholesterol molecules with the Aβ oligomer is negligible and cannot enhance membrane rupture. However, strong hydrogen bonding between the POPC molecules and the oligomers led to membrane perturbation. According to our modellings, the P7C3-S243 molecular layer can protect the cell membrane by inhibiting the direct interaction between the bilayer and Aβ. In addition, free-energy calculations were conducted to determine the possible penetration of Aβ fibrils into the cholesterol-enriched membrane.

Asymmetric Spontaneous Intercalation of Lutein into a Phospholipid Bilayer, a Computational Study

Lutein, a hydroxylated carotenoid, is a pigment synthesised by plants and bacteria. Animals are unable to synthesise lutein, nevertheless, it is present in animal tissues, where its only source is dietary intake. Both in plants and animals, carotenoids are associated mainly with membranes where they carry out important physiological functions. Their trafficking to and insertion into membranes are not well recognised due to experimental difficulties. In this paper, a computational approach is used to elucidate details of the dynamics and energetics of lutein intercalation from the water to the phospholipid bilayer phase. The dynamics is studied using molecular dynamics simulation, and the energetics using umbrella sampling. Lutein spontaneous insertion into the bilayer and translocation across it proceed via formation of hydrogen bonds between its hydroxyl groups and water and/or phospholipid oxygen atoms as well as desolvation of its polyene chain. As lutein molecule is asymmetric, its bilayer intercalation is also asymmetric. The course of events and timescale of the intercalation are different from those of helical peptides. The time of full lutein intercalation ranges from 20 to 100 ns and its final orientation is predominately vertical. Nevertheless, some lutein molecules are in the final horizontal position and some aggregate in the water phase and remain there for the whole simulation time. The highest energy barrier for the intercalation process is ~2.2 kcal/mol and the energy gain is ~18 kcal/mol. The results obtained for lutein can be applied to other xanthophylls and molecules of a similar structure.

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Lutein as an amphiphilic molecule readily intercalates into a lipid bilayer.

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MD simulations with dense sampling revealed details of the intercalation process.

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Time of full lutein membrane intercalation ranges from 20 to 100 ns.

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Lutein intercalation from the ε ring end is less probable than from the β ring end.

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Horizontal position of lutein in the bilayer is less probable than vertical.