Lipid composition and dynamics of cell membranes of Bacillus stearothermophilus adapted to amiodarone

Rapeseed oil-rich diet alters hepatic mitochondrial membrane lipid composition and disrupts bioenergetics

Diet is directly related with physiological alterations occurring at a cell and subcellular level. However, the role of diet manipulation on mitochondrial physiology is still largely unexplored. Aiming at correlating diet with alterations of mitochondrial membrane composition and bioenergetics, Wistar-Han male rats were fed for 11, 22 and 33 days with a rapeseed oil-based diet and mitochondrial bioenergetics, and membrane composition were compared at each time point with a standard diet group. Considerable differences were noticed in mitochondrial membrane lipid composition, namely in terms of fatty acyl chains and relative proportions of phospholipid classes, the modified diet inducing a decrease in the saturated to unsaturated molar ratio and an increase in the phosphatidylcholine to phosphatidylethanolamine molar ratio. Mass spectrometry lipid analysis showed significant differences in the major species of cardiolipin, with an apparent increased incorporation of oleic acid as a result of exposure to the modified diet. Rats fed the modified diet during 22 days showed decreased hepatic mitochondrial state 3 respiration and were more susceptible to Ca(2+)-induced transition pore opening. Rapeseed oil-enriched diet also appeared to promote a decrease in hydroperoxide production by the respiratory chain, although a simultaneous decrease in vitamin E content was detected. In conclusion, our data indicate that the rapeseed oil diet causes negative alterations on hepatic mitochondrial bioenergetics, which may result from membrane remodeling. Such alterations may have an impact not only on energy supply to the cell, but also on drug-induced hepatic mitochondrial liabilities.

Lipid raft involvement in yeast cell growth and death

The notion that cellular membranes contain distinct microdomains, acting as scaffolds for signal transduction processes, has gained considerable momentum. In particular, a class of such domains that is rich in sphingolipids and cholesterol, termed as lipid rafts, is thought to compartmentalize the plasma membrane, and to have important roles in survival and cell death signaling in mammalian cells. Likewise, yeast lipid rafts are membrane domains enriched in sphingolipids and ergosterol, the yeast counterpart of mammalian cholesterol. Sterol-rich membrane domains have been identified in several fungal species, including the budding yeast Saccharomyces cerevisiae, the fission yeast Schizosaccharomyces pombe as well as the pathogens Candida albicans and Cryptococcus neoformans. Yeast rafts have been mainly involved in membrane trafficking, but increasing evidence implicates rafts in a wide range of additional cellular processes. Yeast lipid rafts house biologically important proteins involved in the proper function of yeast, such as proteins that control Na⁺, K⁺, and pH homeostasis, which influence many cellular processes, including cell growth and death. Membrane raft constituents affect drug susceptibility, and drugs interacting with sterols alter raft composition and membrane integrity, leading to yeast cell death. Because of the genetic tractability of yeast, analysis of yeast rafts could be an excellent model to approach unanswered questions of mammalian raft biology, and to understand the role of lipid rafts in the regulation of cell death and survival in human cells. A better insight in raft biology might lead to envisage new raft-mediated approaches to the treatment of human diseases where regulation of cell death and survival is critical, such as cancer and neurodegenerative diseases.

Cell-penetrating peptide-based systems for nucleic acid delivery: a biological and biophysical approach

The increasing knowledge on the genetic basis of disease provides a platform for the development of promising gene-targeted therapies that can be applied to numerous pathological conditions, including cancer. Such genetic-based approaches involve the use of nucleic acids as therapeutic agents, either for the insertion or for the repair and regulation of specific genes. However, despite the huge pharmacological potential of these molecules, their application remains highly dependent on the development of delivery systems capable of mediating efficient cellular uptake. The discovery of a class of small peptides, the so-called cell-penetrating peptides (CPPs), which are able to very efficiently cross cell membranes through a mechanism that is independent of membrane receptors or transporters and avoids lysosomal enzymatic degradation, has been enthusiastically considered of key interest to improve noninvasive cellular delivery of therapeutic molecules. A large number of CPPs have been applied successfully to mediate the intracellular delivery of nucleic acids, including the S4(13)PV peptide for which interactions with membranes and resulting biological effects are illustrated in this chapter. Here, we provide a description of the experimental procedures for the preparation of CPP-based nucleic acid complexes and assessment of their formation, the selection of those protocols leading to the most efficient complexes, the biophysical characterization of CPP membrane interactions, and the evaluation of the biological and cytotoxic activity of the complexes.

Toxicity assessment of the herbicide metolachlor comparative effects on bacterial and mitochondrial model systems

Metolachlor is one of the most intensively used chloroacetamide herbicides. However, its effects on the environment and on non-target animals and humans as well as its interference at a cell/molecular level have not yet been fully elucidated. The aim of this study was: firstly, to evaluate the potential toxicity of metolachlor at a cell/subcellular level by using two in vitro biological model systems (a strain of Bacillus stearothermophilus and rat liver mitochondria); secondly, to evaluate the relative sensibility of these models to xenobiotics to reinforce their suitability for pollutant toxicity assessment. Our results show that metolachlor inhibits growth and impairs the respiratory activity of B.stearothermophilus at concentrations two to three orders of magnitude higher than those at which bacterial cells are affected by other pesticides. Also at concentrations significantly higher than those of other pesticides, metolachlor depressed the respiratory control ratio, membrane potential and respiration of rat liver mitochondria when malate/glutamate or succinate were used as respiratory substrates. Moreover, metolachlor impaired the respiratory activity of rat liver mitochondria in the same concentration range at which it inhibited bacterial respiratory system (0.4-5.0 micromol/mg of protein). In conclusion, the high concentration range at which metolachlor induces toxicity in vitro suggests that this compound is safer than other pesticides previously studied in our laboratory, using the same model systems. The good parallelism between metolachlor effects on both models and the toxicity data described in the literature, together with results obtained in our laboratory with other compounds, indicate the suitability of these systems to assess toxicity in vitro.

Membrane hyperpolarization drives cation influx and fungicidal activity of amiodarone

Cationic amphipathic drugs, such as amiodarone, interact preferentially with lipid membranes to exert their biological effect. In the yeast Saccharomyces cerevisiae, toxic levels of amiodarone trigger a rapid influx of Ca(2+) that can overwhelm cellular homeostasis and lead to cell death. To better understand the mechanistic basis of antifungal activity, we assessed the effect of the drug on membrane potential. We show that low concentrations of amiodarone (0.1-2 microm) elicit an immediate, dose-dependent hyperpolarization of the membrane. At higher doses (>3 microm), hyperpolarization is transient and is followed by depolarization, coincident with influx of Ca(2+) and H(+) and loss in cell viability. Proton and alkali metal cation transporters play reciprocal roles in membrane polarization, depending on the availability of glucose. Diminishment of membrane potential by glucose removal or addition of salts or in pma1, tok1Delta, ena1-4Delta, or nha1Delta mutants protected against drug toxicity, suggesting that initial hyperpolarization was important in the mechanism of antifungal activity. Furthermore, we show that the link between membrane hyperpolarization and drug toxicity is pH-dependent. We propose the existence of pH- and hyperpolarization-activated Ca(2+) channels in yeast, similar to those described in plant root hair and pollen tubes that are critical for cell elongation and growth. Our findings illustrate how membrane-active compounds can be effective microbicidals and may pave the way to developing membrane-selective agents.

Fungicidal activity of amiodarone is tightly coupled to calcium influx

The antiarrhythmic drug amiodarone has microbicidal activity against fungi, bacteria and protozoa. In Saccharomyces cerevisiae, amiodarone triggers an immediate burst of cytosolic Ca2+, followed by cell death markers. Ca2+ transients are a common response to many forms of environmental insults and toxic compounds, including osmotic and pH shock, endoplasmic reticulum stress, and high levels of mating pheromone. Downstream signaling events involving calmodulin, calcineurin and the transcription factor Crz1 are critical in mediating cell survival in response to stress. In this study we asked whether amiodarone induced Ca2+ influx was beneficial, toxic or a bystander effect unrelated to the fungicidal effect of the drug. We show that downregulation of Ca2+ channel activity in stationary phase cells correlates with increased resistance to amiodarone. In actively growing cells, extracellular Ca2+ modulated the size and shape of the Ca2+ transient and directly influenced amiodarone toxicity. Paradoxically, protection was achieved both by removal of external Ca2+ or by adding high levels of CaCl2 (10 mM) to block the drug induced Ca2+ burst. Our results support a model in which the fungicidal activity of amiodarone is mediated by Ca2+ stress, and highlight the pathway of Ca2+ mediated cell death as a promising target for antifungal drug development.

Global disruption of cell cycle progression and nutrient response by the antifungal agent amiodarone

The antiarrhythmic drug amiodarone has fungicidal activity against a broad range of fungi. In Saccharomyces cerevisiae, it elicits an immediate influx of Ca(2+) followed by mitochondrial fragmentation and eventual cell death. To dissect the mechanism of its toxicity, we assessed the transcriptional response of S. cerevisiae to amiodarone by DNA microarray. Consistent with the drug-induced calcium burst, more than half of the differentially transcribed genes were induced by high levels of CaCl(2). Amiodarone also caused rapid nuclear accumulation of the calcineurin-regulated Crz1. The majority of genes induced by amiodarone within 10 min were involved in utilization of alternative carbon and nitrogen sources and in mobilizing energy reserves. The similarity to nutrient starvation responses seen in stationary phase cells, rapamycin treatment, and late stages of shift to diauxic conditions and nitrogen depletion suggests that amiodarone may interfere with nutrient sensing and regulatory networks. Transcription of a set of nutrient-responsive genes was affected by amiodarone but not CaCl(2), indicating that activation of the starvation response was independent of Ca(2+). Genes down-regulated by amiodarone were involved in all stages of cell cycle control. A moderate dose of amiodarone temporarily delayed cell cycle progression at G(1), S, and G(2)/M phases, with the Swe1-mediated delay in G(2)/M phase being most prominent in a calcineurin-dependent manner. Overall, the transcriptional responses to amiodarone revealed by this study were found to be distinct from other classes of antifungals, including the azole drugs, pointing toward a novel target pathway in combating fungal pathogenesis.

Tamoxifen induces ultrastructural alterations in membranes of Bacillus Stearothermophilus

Tamoxifen (TAM), a non-steroid antiestrogen, is the mostly used drug for chemotherapy and chemoprevention of breast cancer. However, the mechanisms by which TAM inhibits cell proliferation in breast cancer are not fully understood. TAM strongly incorporates in biomembranes and a variety of effects have been assigned to biophysical and biochemical interactions with membranes. Therefore, a better understanding of the physicochemical basis of interaction of TAM with biomembranes is essential to elucidate the molecular mechanisms of action. A strain of Bacillus stearothermophilus has been used as a model to clarify the interaction of TAM with the cell membrane. TAM effects on the ultrastructure of membranes of this bacterium were evaluated by electron microscopy. Important ultrastructural alterations were observed in B. stearothermophilus treated with TAM, namely change in the geometry of the membrane profile from asymmetric to symmetric, disaggregation of ribosomes, coagulation of the cytoplasmic matrix, occurrence of mesossomes, appearance of fractures in membranes and the alteration of the ultrastructure of cell wall. These ultrastructural alterations confirm that TAM is a membrane-active drug and that membrane damage may be involved in molecular mechanisms of cell death induced by this drug.

Molecular mechanisms of the metabolite 4-hydroxytamoxifen of the anticancer drug tamoxifen: use of a model microorganism

A strain of the thermophilic eubacterium Bacillus stearothermophilus was used as a model system to identify membrane mediated cytotoxic effects of 4-hydroxytamoxifen, following previous studies with tamoxifen. With this experimental approach we attempted to further clarify tamoxifen and 4-hydroxytamoxifen membrane interactions often evoked as responsible for their multiple cellular effects. Bacterial growth and the oxygen consumption rate provided quantitative data of the cytotoxic action of hydroxytamoxifen. The effects of hydroxytamoxifen on the physical properties of bacterial lipid membrane preparations were also evaluated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene. Cultures of B. stearothermophilus grown in a complex medium containing hydroxytamoxifen in the concentration range of 1 to 7 microM exhibited progressively longer lag adapting periods, decreased specific growth rates and lower growth yields, as compared to control cultures. Hydroxytamoxifen also affected the electron redox flow of B. stearothermophilus protoplasts and induced significant perturbation of the structural order of bacterial lipid dispersions. We concluded that the bacterial model provides useful information about the nature and repercussion of membrane physical interactions of this lipophilic drug, on the basis of an easy and economic methodology.

Use of the microorganism Bacillus stearothermophilus as a model to evaluate toxicity of the lipophilic environmental pollutant endosulfan

Microorganisms are very powerful tools for the supply of information about the toxic effects of lipophilic compounds, since an impairment of cell growth usually occurs as a result of perturbations related, in most cases, with the partition of toxicants in membranes. The thermophilic eubacterium Bacillus stearothermophilus has been used as a model system to identify alpha- and beta-endosulfan interactions with the membrane possibly related with the insecticide toxicity. Two approaches have been pursued: (a) bacterial growth is followed and the effects of endosulfan isomers determined; (b) biophysical studies with the fluorescent fluidity probe 1,6-diphenyl-1,3,5-hexatriene (DPH) were performed to assess the effects of alpha- and beta-endosulfan on the organization of the membrane lipid bilayer. The effects on growth were quantitatively evaluated by determination of growth parameters, namely the lag phase, the specific growth rate and the cell density reached by cultures in the stationary phase. Growth inhibition by alpha and beta-endosulfan dependent on the concentration is diminished or removed by the addition of 2.5 mM Ca2+ to bacterial cultures. Fluorescence DPH polarization consistently showed opposite effects of Ca2+ and alpha- and beta-endosulfan on the physical state of bacterial polar lipid dispersions.

Influence of the growth substrate on ester-linked phospho- and glycolipid fatty acids of PAH-degrading Mycobacterium sp. LB501T

The influences of poorly water-soluble anthracene on ester-linked phospholipid fatty acid (PLFA) and glycolipid fatty acid (GLFA) profiles of Mycobacterium sp. LB501T were studied. Bacteria were cultivated on either anthracene or glucose (one culture with successively amended small doses of this substrate and one with excess concentrations) to distinguish between influences of the chemical structure and the bioavailability of the growth substrate. Results revealed that GLFA and PLFA profiles of M. sp. LB501T depended on the availability and the structure of the carbon source. Fatty acid profiles obtained with anthracene differed from those obtained with excess glucose. They were interpreted as a specific adaptation to this poorly bioavailable polycyclic aromatic hydrocarbon (PAH). In contrast, profiles obtained with low glucose concentrations showed clear signs of starvation stress. Stable carbon isotopic ratios (delta13C) of GLFA and PLFA of M. sp. LB501T were analysed to characterize the 13C-fractionation during the biosynthesis of individual fatty acids and to evaluate their value as markers for substrate usage. Although the delta13C values of PLFA and GLFA showed differential isotope fractionation during anthracene- and glucose-degradation, they were sufficiently distinct to be used as signatures of bacterial substrate usage.