Interactions between components in biological membranes and their implications for membrane function

Tuning of the Anti-Breast Cancer Activity of Betulinic Acid via Its Conversion to Ionic Liquids

Betulinic acid (BA) is a natural pentacyclic triterpene with diverse biological activities. However, its low water solubility limits its pharmaceutical application. The conversion of pharmaceutically active molecules into ionic liquids (ILs) is a promising strategy to improve their physicochemical properties, stability, and/or potency. Here, we report the synthesis and characterization of 15 novel ILs containing a cation ethyl ester of a polar, non-polar, or charged amino acid [AAOEt] and an anion BA. Except for [ValOEt][BA], we observed preserved or up to 2-fold enhanced cytotoxicity toward hormone-dependent breast cancer cells MCF-7. The estimated IC50 (72 h) values within the series varied between 4.8 and 25.7 µM. We found that the most cytotoxic IL, [LysOEt][BA]2, reduced clonogenic efficiency to 20% compared to that of BA. In addition, we evaluated the effect of a 72 h treatment with BA or [LysOEt][BA]2, the most cytotoxic compound, on the thermodynamic behavior of MCF-7 cells. Based on our data, we suggest that the charged amino acid lysine included in the novel ILs provokes cytotoxicity by a mechanism involving alteration in membrane lipid organization, which could be accompanied by modulation of the visco-elastic properties of the cytoplasm.

Consequences of Aging on Bone

With the aging of the global population, the incidence of musculoskeletal diseases has been increasing, seriously affecting people's health. As people age, the microenvironment within skeleton favors bone resorption and inhibits bone formation, accompanied by bone marrow fat accumulation and multiple cellular senescence. Specifically, skeletal stem/stromal cells (SSCs) during aging tend to undergo adipogenesis rather than osteogenesis. Meanwhile, osteoblasts, as well as osteocytes, showed increased apoptosis, decreased quantity, and multiple functional limitations including impaired mechanical sensing, intercellular modulation, and exosome secretion. Also, the bone resorption function of macrophage-lineage cells (including osteoclasts and preosteoclasts) was significantly enhanced, as well as impaired vascularization and innervation. In this study, we systematically reviewed the effect of aging on bone and the within microenvironment (including skeletal cells as well as their intracellular structure variations, vascular structures, innervation, marrow fat distribution, and lymphatic system) caused by aging, and mechanisms of osteoimmune regulation of the bone environment in the aging state, and the causal relationship with multiple musculoskeletal diseases in addition with their potential therapeutic strategy.

Light and Scanning Electron Microscopy of Red Blood Cells From Humans and Animal Species Providing Insights into Molecular Cell Biology

We reviewed the many discoveries in cell biology, made since the 17^th century, which have been based on red blood cells (RBCs). The advances in molecular and structural biology in the past 40 years have enabled the discovery with these cells, most notably, of the first water channel protein (WCP) called today aquaporin1 (AQP1). The main aim of our work reviewed was to examine by light and electron microscopy a very wide range of RBCs from reptiles, birds, monotremes, marsupials and placentals, in order to estimate from these images the RBC cell volume and surface area. The diffusional water permeability of the RBC membrane from these species has further been measured with a nuclear magnetic resonance (NMR) spectroscopy technique. The significance of the observed permeability of RBCs to water and possible influences on the whole body are discussed.

Photolytic Controlled Release Formulation of Methotrexate Loaded in Chitosan/TiO2 Nanoparticles for Breast Cancer

A new system composed of chitosan nanoparticles loaded with methotrexate (MTX-CS-NPs) and functionalized with photocatalytic TiO₂ nanoparticles (TiO₂-NPs) was prepared. This system is expected to initiate polymeric rupture of MTX-CS-NPs and subsequently release MTX, upon illumination with UV light. MTX-CS-NPs were prepared and characterized in terms of particle size, charge, polydispersity and drug release before and after coating with TiO₂-NPs. The release of MTX in vitro was studied in dark, light and UV light. Finally, coated and uncoated MTX-CS-NPs were studied in vitro using MCF-7 cell line. The functionalized NPs were larger in size, more polydisperse and carried higher positive charges compared to the unfunctionalized NPs. The entrapment efficacy was high reaching 75% and was not affected by coating with MTX-CS-NPs. Further, less than 5% of methotrexate was released after 80 h from uncoated NPs and the release was not enhanced by UV illumination of the particles. In contrast, the release from functionalized NPs was enhanced, reaching 40% after 80 h, as the particles were stroked with UV light and as the amount of TiO₂-NPs used in coating increased. Finally, coating the MTX-CS-NPs with TiO₂-NPs significantly enhanced their cytotoxicity on MCF-7 cells. The coated MTX-CS-NPs recorded low cell viabilities compared to the other formulations. In conclusion, the drug release of MTX-CS-NPs could be triggered and controlled remotely by coating with TiO₂-NPs, which maybe more effective in cancer treatment.

Protein Transport Studied by a Model Asymmetric Membrane Army Arranged in a Dimple Chip

Reconstituted model membrane systems are powerful platforms to tackle interesting problems existing in membrane biology. One of the barriers to efficient drug delivery, as therapeutics to disease, is the physical membrane barrier of the cell. Small molecule can typically diffuse through the membrane; however, biomolecules such as proteins or nucleic acids cannot passively diffuse the bilayer and thus much research has been geared to engineering protein and/or nucleic acids delivery methods. One delivery method uses cell penetrating peptides (CPPs). In this chapter, we introduce the model "membrane army" arranged in dimple chip to study the delivery of β-galactosidase by a CPP known as Pep-1. This method uses droplet interface bilayer technology (DIB). It accelerates the speed to screen through the working conditions in CPP-assisted protein translocations because each chip provides dimples that can accommodate 36 pairs of droplets or 18 model bilayers. We will use one of the successful translocation conditions of β-galactosidase delivery as the example to illustrate how the model "membrane army" is built and utilized.

The Modulating Effect of p-Coumaric Acid on The Surface Charge Density of Human Glioblastoma Cell Membranes

p-Coumaric acid (p-CoA), a phenolic acid belonging to the hydroxycinnamic acids family, is a compound with tentative anticancer potential. Microelectrophoretic mobility measurements conducted at various pH values of electrolyte solution were applied to study p-CoA effects on electrical properties of human glioblastoma cell membranes. The obtained results demonstrated that after the p-CoA treatment, the surface charge density of cancer cells changed in alkaline pH solutions, while no noticeable changes were observed in cell membranes incubated with p-CoA compared to control at acidic pH solutions. A four-equilibrium model was used to describe the phenomena occurring on the cell membrane surface. The total surface concentrations of both acidic and basic functional groups and their association constants with solution ions were calculated and used to define theoretical curves of membrane surface charge density versus pH. The resulting theoretical curves and the experimental data were compared to verify the reliability and validity of the adopted model. The deviation of both kinds of data obtained at a higher pH may be caused by disregarding interactions between the functional groups of cancer cells. Processes occurring in the cell membranes after their incubation with p-CoA can lead to disorders of existing equilibria, which result in changes in values of the parameters describing these equilibria.

Physicochemical characterization of diacyltetrol-based lipids consisting of both diacylglycerol and phospholipid headgroups

Synthesis and physicochemical properties of a family of diacyltetrol-based hybrid lipids, containing both diacylglycerol and anionic lipid headgroups within the same moiety, have been reported for the first time.

Effects of novel dinuclear cisplatinum(II) complexes on the electric properties of human breast cancer cells

The aim of this study was to determine the influence of cisplatin and novel dinuclear platinum(II) complexes on the electrical properties of the membrane and the level of lipid peroxidation in the human breast cancer cell lines MDA-MB-231 and MCF-7. The basal electrical surface properties of cells are known. Changes in cell function may affect these surface properties, and those changes can be detected by electrokinetic measurements. The surface charge density of the breast cancer cell lines MDA-MB-231 and MCF-7 were measured as a function of pH. A four-component equilibrium model was used to describe the interaction between the solution ions and the breast cancer cell surface. The experimental and the theoretical charge variation curves of the breast cancer cells at pH 2.5-9 were in agreement. Measurements of the cellular malondialdehyde levels with high performance liquid chromatography were used to determine the extent of lipid peroxidation. The acid and base functional group concentrations and average association constants with hydroxyl ions were smaller in breast cancer cell membranes treated with cisplatin or novel dinuclear platinum(II) complexes compared with untreated cancer cells, and the average association constants with hydrogen ions were higher. The levels of lipid peroxidation products in breast cancer cells treated with cisplatin or novel dinuclear platinum(II) complexes were also higher than in untreated cancer cells.

Biosynthetic alginate–polyester hydrogels with inherent free radical scavenging activity promote cellular response

The prevention of deleterious effects of reactive oxygen species on the cell growth by biosynthetic hydrogels based on alginate–polyester copolymer was studied using H2O2 as the model ROS molecule. Chemically cross-linked biosynthetic hydrogels of alginate- co-poly(propylene fumarate)–n-butyl methacrylate, alginate- co-poly(propylene fumarate)–methyl methacrylate, alginate- co-poly(propylene fumarate)–2-hydroxyethyl methacrylate, and alginate- co-poly(propylene fumarate)– N,N′-methylene bisacrylamide with different biostabilities were prepared. We found that they were able to resist reactive oxygen species penetration into the cell to a greater extent which was evident from the live/dead assay, and increased intracellular glutathione levels compared to the H2O2-treated control. The hydrogels maintained the genomic integrity which was confirmed by comet assay. The inherent protective effects of these hydrogels without any antioxidant moiety may be mediated by dual mechanism: (a) prevention of migration of H2O2 into the cells by calcium-induced conformational changes and rigidity in phospholipids present in the surface membrane of cells by the calcium generated from degradation of hydrogel and (b) by the dilution of H2O2 by the free water in the hydrogel. These hydrogels have potential as injectable hydrogels to manage myocardial infarction and ischemia.

Changes in electric properties of human breast cancer cells

Studies of the electrical surface properties of biological cells have provided fundamental knowledge about the cell surface. The change in biological functions of cells may affect the surface properties and can be detected by electrokinetic measurements. The surface density of fibroblasts and breast cancer cells (MDA-MB-231 and MCF-7) as a function of pH was measured by electrophoresis. The interaction between solution ions and the breast cancer cell or fibroblast surface was described by a four-component equilibrium model. The agreement between the experimental and theoretical charge variation curves of the breast cancer cells and fibroblasts was good at pH 2.5–9. The extent of fibroblast and breast cancer cell lipid peroxidation was estimated by HPLC measurement of the malondialdehyde level. The acid (C_TA) and basic (C_TB) functional group concentrations and the average association constant with hydroxyl (K_BOH) ions values of the breast cancer cell membranes were higher than in normal cells, while the average association constant with hydrogen (K_AH) value was smaller. The level of lipid peroxidation products was higher in breast cancer cells than in normal cells.

Comparative studies of water permeability of red blood cells from humans and over 30 animal species: an overview of 20 years of collaboration with Philip Kuchel

NMR measurements of the diffusional permeability of the human adult red blood cell (RBC) membrane to water (P(d)) and of the activation energy (E(a,d)) of the process furnished values of P(d) ~ 4 × 10(-3) cm/s at 25 °C and ~6.1 × 10(-3) cm/s at 37 °C, and E(a,d) ~ 26 kJ/mol. Comparative NMR measurements for other species showed: (1) monotremes (echidna and platypus), chicken, little penguin, and saltwater crocodile have the lowest P(d) values; (2) sheep, cow, and elephant have P(d) values lower than human P(d) values; (3) cat, horse, alpaca, and camel have P(d) values close to those of humans; (4) guinea pig, dog, dingo, agile wallaby, red-necked wallaby, Eastern grey kangaroo, and red kangaroo have P(d) values higher than those of humans; (5) mouse, rat, rabbit, and "small and medium size" marsupials have the highest values of P(d) (>8.0 × 10(-3) cm/s at 25 °C and >10.0 × 10(-3) cm/s at 37 °C). There are peculiarities of E(a,d) values for the RBCs from different species. The maximum inhibition of diffusional permeability of RBCs induced by incubation with p-chloromercuribenzene sulfonate varied between 0% (for the chicken and little penguin) to ~50% (for human, mouse, cat, sheep, horse, camel, and Indian elephant), and ~60-75% (for rat, guinea pig, rabbit, dog, alpaca, and all marsupials). These results indicate that no water channel proteins (WCPs) or aquaporins are present in the membrane of RBCs from monotremes (echidna, platypus), chicken, little penguin and saltwater crocodile whereas WCPs from the membranes of RBCs from marsupials have peculiarities.

Implication of BBM lipid composition and fluidity in mitigated alkaline phosphatase activity in renal cell carcinoma

Previous study has documented reduced alkaline phosphatase (ALP) activity in brush border membrane (BBM) isolated from renal cell carcinoma (RCC). Diminished activity of ALP is associated with alteration in both increased K(m) as well as decreased V(max) of enzyme suggests that there may be a change in the conformation of enzyme as well as decreased number of ALP active molecules. The present study was conducted to find out any role of BBM lipid composition and its fluidity in diminished activity of alkaline phosphatase in renal cell carcinoma. Total phospholipids and glycolipids were significantly augmented in BBM from RCC as compared to control. Fractional analysis of total phospholipids revealed significantly increased phosphatidylethanolamine. Decreased fractions of sphingomyelin and phosphatidylinositol were observed. Cholesterol-to-total phospholipid molar ratios in tumor BBM was a significantly lower in tumor BBM. A significant reduction in polarization and microviscosity was found in BBM from RCC. Therefore, we conclude that alteration in membrane lipid composition and fluidity may play a substantial role in reduced activity of ALP in RCC.

Impacts of the osmolality and the lumenal ionic strength on osmosensory transporter ProP in proteoliposomes

H(+) symporter ProP serves as a paradigm for the study of osmosensing. ProP attains the same activity at the same osmolality when the medium outside cells or proteoliposomes is supplemented with diverse, membrane-impermeant solutes. The osmosensory mechanism of ProP has been probed by varying the solvent within membrane vesicles and proteoliposomes. ProP activation was not ion specific, did not require K(+), and could be elicited by large, uncharged solutes polyethylene glycols (PEGS). We hypothesized that ProP is an ionic strength sensor and lumenal macromolecules activate ProP by altering ion activities. The attainable range of lumenal ionic strength was expanded by lowering the phosphate concentration within proteoliposomes. ProP activity at high osmolality, but not the osmolality, yielding half-maximal activity (Π(1/2)/RT), decreased with the lumenal phosphate concentration. This was attributed to acidification of the proteoliposome lumen due to H(+)-proline symport. The ionic strength yielding half-maximal ProP activity was more anion-dependent than Π(1/2)/RT for proteoliposomes loaded with citrate, sulfate, phosphate, chloride, or iodide. The anion effects followed the Hofmeister series. Lumenal bovine serum albumin (BSA) lowered the lumenal ionic strength at which ProP became active. Osmolality measurements documented the non-idealities of solutions including potassium phosphate and other solutes. The impacts of PEGS and BSA on ion activities did not account for their impacts on ProP activity. The effects of the tested solutes on ProP appear to be non-coulombic in nature. They may arise from effects of preferential interactions and macromolecular crowding on the membrane or on ProP.

The first discovered water channel protein, later called aquaporin 1: molecular characteristics, functions and medical implications

After a decade of work on the water permeability of red blood cells (RBC) Benga group in Cluj-Napoca, Romania, discovered in 1985 the first water channel protein in the RBC membrane. The discovery was reported in publications in 1986 and reviewed in subsequent years. The same protein was purified by chance by Agre group in Baltimore, USA, in 1988, who called in 1991 the protein CHIP28 (CHannel forming Integral membrane Protein of 28 kDa), suggesting that it may play a role in linkage of the membrane skeleton to the lipid bilayer. In 1992 the Agre group identified CHIP28's water transport property. One year later CHIP28 was named aquaporin 1, abbreviated as AQP1. In this review the molecular structure-function relationships of AQP1 are presented. In the natural or model membranes AQP1 is in the form of a homotetramer, however, each monomer has an independent water channel (pore). The three-dimensional structure of AQP1 is described, with a detailed description of the channel (pore), the molecular mechanisms of permeation through the channel of water molecules and exclusion of protons. The permeability of the pore to gases (CO(2), NH(3), NO, O(2)) and ions is also mentioned. I have also reviewed the functional roles and medical implications of AQP1 expressed in various organs and cells (microvascular endothelial cells, kidney, central nervous system, eye, lacrimal and salivary glands, respiratory apparatus, gastrointestinal tract, hepatobiliary compartments, female and male reproductive system, inner ear, skin). The role of AQP1 in cell migration and angiogenesis in relation with cancer, the genetics of AQP1 and mutations in human subjects are also mentioned. The role of AQP1 in red blood cells is discussed based on our comparative studies of water permeability in over 30 species.

Bacterial osmoregulation: a paradigm for the study of cellular homeostasis

To thrive, cells must control their own physical and chemical properties. This process is known as cellular homeostasis. The dilute solutions traditionally favored by experimenters do not simulate the cytoplasm, where macromolecular crowding and preferential interactions among constituents may dominate critical processes. Solutions that do simulate cytoplasmic conditions are now being characterized. Corresponding cytoplasmic properties can be varied systematically by imposing osmotic stress. This osmotic stress approach is revealing how cytoplasmic properties modulate protein folding and protein?nucleic acid interactions. Results suggest that cytoplasmic homeostasis may require adjustments to multiple, interwoven cytoplasmic properties. Osmosensory transporters with diverse structures and bioenergetic mechanisms activate in response to osmotic stress as other proteins inactivate. These transporters are serving as paradigms for the study of in vivo protein-solvent interactions. Experimenters have proposed three different osmosensory mechanisms. Distinct mechanisms may exist, or these proposals may reflect different perceptions of a single, unifying mechanism.

Neutrophil fatty acid composition: effect of a single session of exercise and glutamine supplementation

The fatty acid composition of immune cells appears to contribute to variations of cell function. The independent and combined effects of a single session of exercise (SSE) and glutamine supplementation (GS) on neutrophil fatty acid composition were investigated. Compared to control (no treatment given--i.e. neither SSE or GS), single session of exercise decreased myristic, palmitic and eicosapentaenoic (EPA) acids, and increased lauric, oleic, linoleic, arachidonic (AA) and docosahexaenoic (DHA) acids whereas glutamine supplementation combined with SSE (GS+SSE) increased oleic acid. Polyunsaturated/saturated fatty acid ratio and Unsaturation index were higher in neutrophils from the SSE and GS groups as compared with control. These findings support the proposition that SSE and GS may modulate neutrophil function through alterations in fatty acid composition.

Ectopic expression of alkaline phosphatase in proximal tubular brush border membrane of human renal cell carcinoma

The present study was conducted to find out any alteration in the expression and activity of alkaline phosphatase in the brush border membrane (BBM) from renal cell carcinoma (RCC) in comparison to normal renal BBM. The specific activity of alkaline phosphatase was drastically reduced in homogenate as well as BBM from RCC kidney when compared to ALP activity in BBM of normal kidney. Kinetic studies revealed that diminished activity of alkaline phosphatase in BBM isolated from RCC was fraternized with decrease in maximal velocity (V(max)) and increase in affinity constant (K(m)) of the enzyme. SDS-PAGE studies showed that the BBM proteins having molecular weights ranging from 95 to 170 kDa were poorly expressed in RCC BBM in relative to normal kidney BBM. Incubation of SDS-PAGE gel with BCIP/NBT dye clearly showed that the expression of ALP in tumor renal BBM was markedly reduced as compared to normal kidney. Further, Western blot analysis using anti-alkaline phosphatase antibody also confirmed the reduced expression of ALP in tumor renal BBM. Lipid composition in reference to phospholipids, glycolipids and cholesterol in tumor renal BBM was altered to that of normal renal BBM, indicating alteration in membrane fluidity of tumor renal BBM.

Parameters characterizing acid-base equilibria between cell membrane and solution and their application to monitoring the effect of various factors on the membrane

The cell membrane is an extremely complicated object. It participates in a large number of equilibria. For this reason, it is impossible to determine the parameters of all of them. It is the purpose of this work to define a limited number of averaged parameters in order to describe the equilibria between cell membrane components and environmental components. These parameters are the total acidic functional group concentration as well as the basic group concentration and their association constants with hydrogen or hydroxyl ions. The parameters were determined using the pH dependence of the electric surface charge density. The usefulness of these parameters was checked by studying the effect of green tea on liver cells in ethanol poisoning. Ethanol provokes an increase in concentration of functional groups, positively and negatively charged, as well as an increase in the basic groups association constant and a decrease in acidic groups association constant. Administering green tea partly compensates the changes provoked by ethanol poisoning. The parameters proposed in this work, C(TA), C(TB), K(AH) and K(BOH), are suited for monitoring the changes caused by various factors.

Thyroid hormones increase Na+–Pi co-transport activity in intestinal brush border membrane: Role of membrane lipid composition and fluidity

In the present study, we documented the promising role of thyroid hormones status in animals in modulation of Na+-Pi transport activity in intestinal brush border membrane vesicles (BBMV) which was accompanied with alterations in BBM lipid composition and fluidity. Augmentation of net Pi balance in hyperthyroid (Hyper-T) rats was fraternized with accretion of Pi transport across BBMV isolated from intestine of Hyper-T rats as compared to hypothyroid (Hypo-T) and euthyroid (Eu-T) rats while Na+-Pi transport across BBMV was decreased in Hypo-T rats relative to Eu-T rats. Increment in Na+-Pi transport in intestinal BBMV isolated from Hyper-T rats was manifested as an increase in the maximal velocity (Vmax) of Na+-Pi transport system. Furthermore, BBMV lipid composition profile in intestinal BBM from Hyper-T was altered to that of Hypo-T rats and Eu-T rats. The molar ratio of cholesterol/phospholipids was higher in intestinal BBM from Hypo-T rats. Fluorescence anistropy of diphenyl hexatriene (rDPH) and microviscosity were significantly decreased in the intestinal BBM of Hyper-T rats and decreased in Hypo-T rats as compared to Eu-T rats which corroborated with the alteration in membrane fluidity in response to thyroid hormone status of animals. Therefore, thyroid hormone mediated change in membrane fluidity might play an important role in modulating Na+-Pi transport activity of intestinal BBM.

Thyroid hormones stimulate Na+-Pi transport activity in rat renal brush-border membranes: role of membrane lipid composition and fluidity

Antecedent studies have suggested that lipid composition and fluidity of cellular membranes of various organs are altered in response to thyroid hormone status. To date, the effects of thyroid hormone status on these parameters have not been examined in rat renal apical membrane in regard to sodium-dependent phosphate transport. In the present study, we determined the potential role of alterations in cortical brush-border membrane lipid composition and fluidity in modulation of Na+-Pi transport activity in response to thyroid hormone status. Thyroid hormone status influences the fractional excretion of Pi, which is associated with alteration in renal brush-border membrane phosphate transport. The increment in Na+-Pi transport in renal BBMV isolated from Hyper-T rats is manifested as an increase in the maximal velocity (Vmax) of Na+-Pi transport. Further, the cholesterol content was significantly increased in renal BBM of Hypo-T rats and decreased in Hyper-T rats as compared to the Eu-T rats. The molar ratio of cholesterol/phospholipids was also higher in renal BBM from hypo-T rats. Subsequently, fluorescence anisotropy of diphenyl hexatriene (rDPH) and microviscosity were significantly decreased in the renal BBM of the Hyper-T rats and increased in the Hypo-T rats as compared to Eu-T rats. The result of this study, therefore, suggest that alteration in renal BBM cholesterol, cholesterol/phospholipid molar ratio, and membrane fluidity play an important role in the modulation of renal BBM Na+-Pi transport in response to thyroid hormone status of animals.

Supragingival calculus: formation and control

Dental calculus is composed of inorganic components and organic matrix. Brushite, dicalcium phosphate dihydrate, octacalcium phosphate, hydroxyapatite, and whitlockite form the mineral part of dental calculus. Salivary proteins selectively adsorb on the tooth surface to form an acquired pellicle. It is followed by the adherence of various oral micro-organisms. Fimbriae, flagella, and some other surface proteins are essential for microbial adherence. Microbial co-aggregation and co-adhesion enable some micro-organisms, which are incapable of adhering, to adhere to the pellicle-coated tooth surface. Once organisms attach to the tooth surface, new genes could be expressed so that mature dental plaque can form and biofilm bacteria assume increased resistance to antimicrobial agents. Supersaturation of saliva and plaque fluid with respect to calcium phosphates is the driving force for plaque mineralization. Both salivary flow rate and plaque pH appear to influence the saturation degree of calcium phosphates. Acidic phospholipids and specific proteolipids present in cell membranes play a key role in microbial mineralization. The roles of crystal growth inhibitors, promoters, and organic acids in calculus formation are discussed. Application of biofilm culture systems in plaque mineralization is concisely reviewed. Anti-calculus agents used--centering on triclosan plus polyvinyl methyl ether/maleic acid copolymer, pyrophosphate plus polyvinyl methyl ether/maleic acid copolymer, and zinc ion-in commercial dentifrices are also discussed in this paper.

Molecular basis of renal handling of calcium in response to thyroid hormone status of rat

We investigated the effect of thyroid hormone status on renal handing of Ca2+. Further, like kinetics of Ca2+ transport across brush-border membrane (BBM) and basolateral membrane (BLM) of renal epithelial cells was carried out. FE(Ca) was decreased in hyperthyroid (Hyper-T) rats and increased in hypothyroid (Hypo-T) rats as compared to euthyroid (Eu-T) rats. Ca2+ uptake into renal brush-border membrane vesicles (BBMV) was increased in Hyper-T rats and decreased in Hypo-T rats as compared to Eu-T rats. K(m) was lower in Hyper-T rats and higher in Hypo-T rats as compared to Eu-T rats whereas, V(max) remained unaltered. The transition temperature for calcium uptake varied inversely with the thyroid hormone status. Renal BBM of Hyper-T rats showed decreased anisotropy and polarisation of DPH as compared to EU-T rats whereas these values were increased in Hypo-T rats. Thus, the altered BBM fluidity appears to modulate Ca2+ transport across BBM. Na+/Ca2+ exchange activity of renal cells was increased in Hyper-T and decreased in Hypo-T rats as compared to Eu-T rats. V(max) for Na+/Ca2+ exchange was increased in Hyper-T rats and deceased in Hypo-T rats as compared to Eu-T rats, whereas, [Na+](0.5) was similar in all three groups. The c-AMP levels of renal cortex of Hyper-T rats was increased and that of Hypo-T rats decreased as compared to Eu-T rats. Thus, thyroid hormones increased Ca2+ reabsorption in the kidney of rat. Thyroid hormone-mediated modulation of BBM fluidity appears to stimulate Ca2+ uptake into renal BBMV. Thyroid hormones possibly activated the Na+/Ca2+ exchanger through cAMP-dependent pathway.

Acetyl-L-carnitine physical-chemical, metabolic, and therapeutic properties: relevance for its mode of action in Alzheimer's disease and geriatric depression

Acetyl-L-carnitine (ALCAR) contains carnitine and acetyl moieties, both of which have neurobiological properties. Carnitine is important in the beta-oxidation of fatty acids and the acetyl moiety can be used to maintain acetyl-CoA levels. Other reported neurobiological effects of ALCAR include modulation of: (1) brain energy and phospholipid metabolism; (2) cellular macromolecules, including neurotrophic factors and neurohormones; (3) synaptic morphology; and (4) synaptic transmission of multiple neurotransmitters. Potential molecular mechanisms of ALCAR activity include: (1) acetylation of -NH2 and -OH functional groups in amino acids and N terminal amino acids in peptides and proteins resulting in modification of their structure, dynamics, function and turnover; and (2) acting as a molecular chaperone to larger molecules resulting in a change in the structure, molecular dynamics, and function of the larger molecule. ALCAR is reported in double-blind controlled studies to have beneficial effects in major depressive disorders and Alzheimer's disease (AD), both of which are highly prevalent in the geriatric population.

Interaction of albumins from different species with phospholipid liposomes. Multiple binding sites system

The interactions of three serum albumin species (rat, human, and bovine) with liposomes containing dimyristoylphosphatidylcholine, distearoylphosphatidylcholine or mixtures of both under different membrane fluidity conditions have been investigated using isothermal titration calorimetry and steady-state fluorescence anisotropy. Calorimetric titration studies of the binding of liposomes to the albumin species indicate in all cases exothermic processes with multiple sites of binding in the albumin molecules. Distinct saturation of the protein-lipid binding processes was observed at low or high molar lipid/protein ratio depending on the particular system. The thermodynamic parameters, including the association enthalpy and entropy, and the optimal values for the binding constants were thoroughly varied as a function of the number of identical binding sites, defining the best value of the parameter. Our experimental results, obtained using complementary biophysical techniques, provide experimental evidence for a significant difference in the association of the three protein species to phospholipid membranes. These observations also suggest a close relation between the binding parameters of the protein/lipid association and the lipid state of the phospholipid membranes.

Crystallization of the isobutylphosphocholine-cholesterol-isobutanol (1:3:3) complex and its investigation by X-ray analysis: interaction of phopholipid headgroups with cholesterol

A crystal complex consisting of the isobutyl analog of phosphatidylcholine (PC) (isobutylphosphocholine), cholesterol, and isobutanol with molecular ratio 1:3:3 was obtained and investigated by means of X-ray analysis. The complex was shown to correspond to the monoclinic system (sp. gr. P2(1)): a=16.994(10), b=11.314(7), c=28.164(15), beta=104.07(3), V=5252.63 A(3), Z=2, D(calc)=1.0273 g/cm(3). The isobutylphosphocholine molecule is the key component of the complex. Pairs of hydrogen bonds are formed between the (-delta)O-P-O(delta-) group of the isobutylphosphocholine molecule and C-OH groups of two cholesterol and two isobutanol molecules. The third molecules of cholesterol and isobutanol are H-bonded with the (-delta)O-P-O(delta-) group of the isobutylphosphocholine molecule via C-OH groups of isobutanol and cholesterol, respectively. The crystal structure is built up by translation of the complex in multiplicate along the two-fold axis in the direction of axis b. It contains bands formed by isobutylphosphocholine molecules alternately changing their direction. They are fixed by virtue of two zones of electrostatic interactions of the type (-delta)O-P-O(delta-)ellipsis(+)N(CH(3))(3) and are more or less parallel to the bc plane. The structure also contains three-layer domains formed by cholesterol molecules perpendicular to isobutylphosphocholine bands. In the direction of the c-axis isobutylphosphocholine bands alternate with the layers of cholesterol molecules herewith reproducing repeated blocks. The obtained structure is compared with that of crystals of phospholipids and cholesterol and its derivatives.

Protective effect of N-acetylcysteine on rat liver cell membrane during methanol intoxication

Methanol is oxidized in-vivo to formaldehyde and then to formate, and these processes are accompanied by the generation of free radicals. We have studied the effect of N-acetylcysteine on liver cell membrane from rats intoxicated with methanol (3.0 g kg(-1)). Evaluation of the effect was achieved by several methods. Lipid peroxidation and surface charge density were measured. An ultrastructural study of the liver cells was undertaken. The concentration of marker enzymes of liver damage (alanine aminotransferase and aspartate aminotransferase) in blood serum was measured. Methanol administration caused an increase in lipid peroxidation products (approximately 30%) as well as in surface charge density (approximately 60%). This might have resulted in the membrane liver cell damage visible under electron microscopy and a leak of alanine aminotransferase and aspartate aminotransferase into the blood (increase of approximately 70 and 50%, respectively). Ingestion of N-acetylcysteine with methanol partially prevented these methanol-induced changes. Compared with the control group, lipid peroxidation was increased by approximately 3% and surface charge density by approximately 30%. Alanine aminotransferase and aspartate aminotransferase activity increased by 9 and 8%, respectively, compared with the control group. The results suggested that N-acetylcysteine was an effective antioxidant in methanol intoxication. It may have efficacy in protecting free radical damage to liver cells following methanol intoxication.

Capillary interactions between particles bound to interfaces, liquid films and biomembranes

This article is devoted to an overview, comparison and discussion of recent results (both theoretical and experimental) about lateral capillary forces. They appear when the contact of particles or other bodies with a fluid phase boundary causes perturbations in the interfacial shape. The capillary interaction is due to the overlap of such perturbations which can appear around floating particles, vertical cylinders, particles confined in a liquid film, inclusions in the membranes of lipid vesicles or living cells, etc. In the case of floating particles the perturbations are due to the particle weight; in this case the force decreases with the sixth power of the particle size and becomes immaterial for particles smaller than approximately 10 microm. In all other cases the interfacial deformations are due to the particle wetting properties; the resulting 'immersion' capillary forces can be operative even between very small particles, like protein globules. In many cases such forces can be responsible for the experimentally observed two-dimensional particle aggregation and ordering. An analogy between capillary and electrostatic forces enables one to introduce 'capillary charges' of the attached particles, which characterize the magnitude of the interfacial deformation and could be both positive and negative. Moreover, the capillary interaction between particle and wall resembles the image force in electrostatics. When a particle is moving bound to an interface under the action of a capillary force, one can determine the surface drag coefficient and the surface viscosity supposedly the magnitude of the capillary force is known. Alternative (but equivalent) energy and force approaches can be used for the theoretical description of the lateral capillary interactions. Both approaches require the Laplace equation of capillarity to be solved and the meniscus profile around the particles to be determined. The energy approach accounts for contributions due to the increase of the meniscus area, gravitational energy and/or energy of wetting. The second approach is based on calculating the net force exerted on the particle, which can originate from the hydrostatic pressure, interfacial tension and bending moment. In the case of small perturbations, the superposition approximation can be used to derive an asymptotic formula for the capillary forces, which has been found to agree well with the experiment. Capillary interactions between particles bound to spherical interfaces are also considered taking into account the special geometry and restricted area of such phase boundaries. A similar approach can be applied to quantify the forces between inclusions (transmembrane proteins) in lipid membranes. The deformations in a lipid membrane, due to the inclusions, can be described theoretically in the framework of a mechanical model of the lipid bilayer, which accounts for its 'hybrid' rheology (neither elastic body nor fluid). In all considered cases the lateral capillary interaction originates from the overlap of interfacial deformations and is subject to a unified theoretical treatment, despite the fact that the characteristic particle size can vary from 1 cm down to 1 nm.

Influence of trolox derivative and N-acetylcysteine on surface charge density of erythrocytes in methanol intoxicated rats

Methanol is oxidized in vivo to formaldehyde and then to formate and these processes are accompanied by free radicals generation. This paper reports the effect of antioxidants: trolox derivative (U-83836E) and N-acetylcysteine (NAC) on lipid peroxidation, surface charge density and hematological parameters of erythrocytes from rats intoxicated with methanol (3.0 g/kg body weight). Methanol administration caused increase in erythrocyte lipid peroxidation products and changes in surface charge density. Ingestion of methanol with U-83836E and NAC partially prevented these methanol-induced changes. This suggests that U83836E and NAC act as effective antioxidants and free radicals scavengers. They may have efficacy in protecting free radical damage to erythrocytes following methanol intoxication.

Thyroid hormones modulate zinc transport activity of rat intestinal and renal brush-border membrane

Thyroid hormone status influences the Zn2+ and metallothionein levels in intestine, liver, and kidney. To evaluate the impact of thyroid hormones on Zn2+ metabolism, Zn2+ uptake studies were carried out in intestinal and renal brush-border membrane vesicles (BBMV). Steady-state Zn2+ transport in intestinal and renal cortical BBMV was increased in hyperthyroid (Hyper-T) rats and decreased in the hypothyroid (Hypo-T) rats relative to euthyroid (Eu-T) rats. In both the intestinal and renal BBMV, Hyper-T rats showed a significant increase in maximal velocity compared with Eu-T and Hypo-T rats. Apparent Michaelis constant was unaltered in intestinal and renal BBMV prepared from the three groups. Fluorescence anisotropy of diphenyl hexatriene was decreased significantly in intestinal and renal brush-border membrane (BBM) isolated from Hyper-T rats compared with Hypo-T and Eu-T rats. A significant reduction in the microviscosity and transition temperature for Zn2+ uptake in intestinal and renal BBM from Hyper-T rats is in accordance with the increased fluidity of these BBMs. These findings suggest that the increased rate of Zn2+ transport in response to thyroid hormone status could be associated with either an increase in the number of Zn2+ transporters or an increase in the active transporters due to alteration in the membrane fluidity. Thus the thyroid hormone-mediated change in membrane fluidity might play an important role in modulating Zn2+ transport activity of intestinal and renal BBM.

Miscibility of phospholipids with identical headgroups and acyl chain lengths differing by two methylene units: effects of headgroup structure and headgroup charge

We have investigated the influence of the chemical structure and charge of the hydrophillic headgroup on the miscibility of saturated phospholipids with acyl chain lengths differing by two methylene units, namely DMPA/DPPA, DMPC/DPPC, DMPE/DPPE and DMPG/DPPG (0.1 M NaCl). All four mixtures were analysed by DSC at pH 7. To study the influence of a change in headgroup charge, we additionally investigated DMPA/DPPA mixtures at pH 4 and 12, and DMPG/DPPG mixtures at pH 2. The experimental DSC thermograms were fitted using methods described before [Johann et al., Biophys. J. 71 (1996), 3215-3228] to obtain the temperatures of onset and end of melting and first approximations for the non-ideality parameters as a function of composition. The resulting phase diagrams were then fitted using a four non-ideality parameter model for non-ideal, non-symmetric mixing in both phases. The phase diagram of the system DMPG/DPPG has a lens-like shape, the non-ideality parameters rhog and rhol for the gel and the liquid-crystalline phase, respectively, are zero, indicating ideal mixing in both phases. For the other mixtures, differences in miscibility are observed depending on the structure of the headgroup. At pH 7, rhog > rhol, i.e., the miscibility in the liquid-crystalline phase is more ideal than in the gel state. All rhog values are positive and the sequence for rhog observed is PA>PE>PC>PG. Partial protonation of PA at pH 4 or complete deprotonation at pH 12 leads to negative non-ideality parameters for both phases, indicating a preference for mixed pair formation. Protonation of PG in DMPG/DPPG mixtures at pH 2 leads to positive non-ideality parameters for both phases, indicating a tendency for demixing. The results show, that the miscibility of phospholipids with identical headgroups but chain lengths differing by two methylene groups is dependent on headgroup structure and on headgroup charge.

Nonideal mixing and phase separation in phosphatidylcholine-phosphatidic acid mixtures as a function of acyl chain length and pH

The miscibilities of phosphatidic acids (PAs) and phosphatidylcholines (PCs) with different chain lengths (n = 14, 16) at pH 4, pH 7, and pH 12 were examined by differential scanning calorimetry. Simulation of heat capacity curves was performed using a new approach that incorporates changes of cooperativity of the transition in addition to nonideal mixing in the gel and the liquid-crystalline phase as a function of composition. From the simulations of the heat capacity curves, first estimates for the nonideality parameters for nonideal mixing as a function of composition were obtained, and phase diagrams were constructed using temperatures for onset and end of melting, which were corrected for the broadening effect caused by a decrease in cooperativity. In all cases the composition dependence of the nonideality parameters indicated nonsymmetrical mixing behavior. The phase diagrams were therefore further refined by simulations of the coexistence curves using a four-parameter approximation to account for nonideal and nonsymmetrical mixing in the gel and the liquid-crystalline phase. The mixing behavior was studied at three different pH values to investigate how changes in headgroup charge of the PA influences the miscibility. The experiments showed that at pH 7, where the PA component is negatively charged, the nonideality parameters are in most cases negative, indicating that electrostatic effects favor a mixing of the two components. Partial protonation of the PA component at pH 4 leads to strong changes in miscibility; the nonideality parameters for the liquid-crystalline phase are now in most cases positive, indicating clustering of like molecules. The phase diagram for 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid:1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine mixtures at pH 4 indicates that a fluid-fluid immiscibility is likely. The results show that a decrease in ionization of PAs can induce large changes in mixing behavior. This occurs because of a reduction in electrostatic repulsion between PA headgroups and a concomitant increase in attractive hydrogen bonding interactions.

Selective association of phospholipids as a clue for the passive flip-flop diffusion through bilayer lipid membranes

We showed that the investigation of the selective association of phospholipids might contribute to the insight of the flip-flop diffusion processes. The process of selective association was studied quantitatively by testing the association probabilities for both parallel and anti-parallel orientations of the polar headgroups. The model of double chain binary mixture confirms a high capacity of phospholipids for self-association in parallel configuration of the electric dipole moments whether the cross-sectional area of the polar headgroups are in an usual range of 25-55 A2. It is demonstrated that the aggregation of a class of phospholipids from a binary mixture is strongly dependent on the dipole-dipole interaction between the same phospholipids and is modulated by the magnitude of the electric dipole moment of the other phospholipids from that binary mixture. There are a great number of mechanisms involved in the transbilayer movement of phospholipids. We referred here only to the passive transport of lipids from one monolayer to the other. The flip-flop mechanisms raised in this paper are the breakdown of bilayer due to the increase of the packing density and the inversion of the coupled phospholipids from the opposite monolayers of the same bilayer. Thus, the pair formation promoting a drop in occupied volume decreases the packing pressure in the respective monolayer and consequently triggers a flip-flop into the other direction since the packing pressure in the other monolayer has not dropped. According to the present model for the binary mixtures of double-chain lipids, the rate of the flip-flop diffusion decreased by increasing the number of the methylene groups added to the acyl chain. This dependence may be perturbed whether the phospholipids possesses a very high cross-section area of the polar headgroups (a > 55 A2). We think that the selective association of phospholipids is neither exclusively, nor only involved in promoting the transbilayer diffusion of phospholipids. Most probably, the selective association determines some phospholipid domains that attract certain particular proteins so that it can modulate the protein activity.

Amino acid composition of rat and human liver microsomes in normal and pathological conditions

The amino acid composition of proteins from liver microsomes has been studied in rats and in human subjects with normal liver, with obstructive jaundice or liver cirrhosis. The pattern of the amino acid composition of microsomes appeared to be species-specific. Phenylalanine, threonine, serine, proline, histidine and [aspartic acid plus asparagine] were increased, while alanine, tyrosine, glycine and arginine were decreased in the human compared to the rat microsomes. In patients with obstructive jaundice of short duration (less than two months) only a slight decrease in leucine and phenylalanine could be noticed, while in the case of liver cirrhosis amino acid composition was markedly changed.

Acyl-CoA synthetase activity depends on the phospholipid composition of rat liver plasma membranes

The dependence of acyl-CoA synthetase on the lipid composition of rat liver plasma membranes has been investigated. For this purpose the composition of the membranes was modified by incorporation of different phospholipids in the presence of partially purified lipid transfer proteins. Another approach to the modification of the membrane phospholipid composition was treatment with exogenous phospholipase C and subsequent enrichment with different phospholipids. The experiments performed in vitro indicated that the presence of certain phospholipids such as phosphatidylnositol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylserine was essential for the activation of long chain fatty acids by acyl-CoA synthetase. However, some differences were observed when oleate and palmitate were used as substrates. Sphingomyelin was found to inhibit this activity especially when oleic acid served as substrate. In addition, we tried to modify in vivo the membrane lipid composition by treatment with D-galactosamine, which is known to induce acute hepatitis and cause biochemical and biophysical alterations in liver membranes. The results thus obtained confirmed the idea that the augmentation of the membrane lipids and especially of PI, PE and PG was accompanied by acyl-CoA synthetase activation. The presence of two different enzymes, activating the saturated and unsaturated fatty acids is discussed.

Lipid domains and lipid/protein interactions in biological membranes

In the fluid mosaic model of membranes, lipids are organized in the form of a bilayer supporting peripheral and integral proteins. This model considers the lipid bilayer as a two-dimensional fluid in which lipids and proteins are free to diffuse. As a direct consequence, both types of molecules would be expected to be randomly distributed within the membrane. In fact, evidences are accumulating to indicate the occurrence of both a transverse and lateral regionalization of membranes which can be described in terms of micro- and macrodomains, including the two leaflets of the lipid bilayer. The nature of the interactions responsible for the formation of domains, the way they develop and the time- and space-scale over which they exist represent today as many challenging problems in membranology. In this report, we will first consider some of the basic observations which point to the role of proteins in the transverse and lateral regionalization of membranes. Then, we will discuss some of the possible mechanisms which, in particular in terms of lipid/protein interactions, can explain lateral heterogenities in membranes and which have the merit of providing a thermodynamic support to the existence of lipid domains in membranes.

Effect of membrane phospholipid composition and fluidity on rat liver plasma membrane tyrosine kinase activity

1. The effect of membrane phospholipid composition and fluidity on tyrosine kinase activity was investigated in rat liver plasma membranes. 2. The phospholipid composition has been modified by in vitro enrichment of plasma membranes with different phospholipids in the presence of lipid transfer proteins and by partial delipidation with exogenous phospholipases A2, C and D and subsequent enrichment with phosphatidylglycerol. 3. Phosphatidylglycerol and dioleoylglycerophosphocholine caused dramatic elevation of this activity, while phosphatidylserine and phosphatidylethanolamine were less effective. Enrichment with dipalmitoylglycerophosphocholine and sphingomyeline reduced tyrosine kinase activity.

The effects of lipids and detergents on ATPase-active P-glycoprotein

We previously isolated and characterized a partially purified preparation of ATPase-active P-glycoprotein, the multidrug transporter (Doige, C.A., Yu, X. and Sharom, F.J. (1992) Biochim. Biophys. Acta 1109, 149-160). The effect of various detergents and membrane phospholipids on the ATPase activity of P-glycoprotein has now been investigated. P-Glycoprotein ATPase activity was most stable in CHAPS, with over 50% of the activity retained at a concentration of 8 mM. Octyl glucoside in the low mM range also supported the ATPase, while deoxycholate destroyed all activity at 1 mM. Digitonin and SDS inhibited ATPase activity at very low concentrations. Triton X-100 at 2-10 microM stimulated the ATPase almost 2-fold, while higher levels inhibited activity. Although P-glycoprotein ATPase was sensitive to thermal inactivation, full activity was preserved in the presence of asolectin, but not phosphatidylcholine species. Further studies revealed that asolectin, both saturated and unsaturated phosphatidylethanolamines, and phosphatidylserine, were best able to maintain ATPase activity at 23 degrees C. Saturated phosphatidylethanolamine species activated P-glycoprotein ATPase up to 40% at 23 degrees C, and 80% at 4 degrees C. Following detergent delipidation, various lipids were able to restore P-glycoprotein ATPase activity. Unsaturated phosphatidylcholine and phosphatidylserine were most effective, while saturated species were not able to restore catalytic activity. These results indicate that membrane lipids are necessary for catalytic activity of the ATPase domains of P-glycoprotein. P-Glycoprotein has well-defined lipid preferences, with saturated phosphatidylethanolamines both activating the ATPase and providing protection from thermal inactivation, while fluid lipid mixtures are able to restore activity following delipidation.