Asymmetric bilayers mimicking membrane rafts prepared by lipid exchange: Nanoscale characterization using AFM-Force spectroscopy

Sphingolipids-enriched rafts domains are proposed to occur in plasma membranes and to mediate important cellular functions. Notwithstanding, the asymmetric transbilayer distribution of phospholipids that exists in the membrane confers the two leaflets different potentials to form lateral domains as next to no sphingolipids are present in the inner leaflet. How the physical properties of one leaflet can influence the properties of the other and its importance on signal transduction across the membrane are questions still unresolved. In this work, we combined AFM imaging and Force spectroscopy measurements to assess domain formation and to study the nanomechanical properties of asymmetric supported lipid bilayers (SLBs) mimicking membrane rafts. Asymmetric SLBs were formed by incorporating N-palmitoyl-sphingomyelin (16:0SM) into the outer leaflet of preformed 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC)/Cholesterol SLBs through methyl-β-cyclodextrin–mediated lipid exchange. Lipid domains were detected after incorporation of 16:0SM though their phase state varied from gel to liquid ordered (Lo) phase if the procedure was performed at 24 or 37 °C, respectively. When comparing symmetric and asymmetric Lo domains, differences in size and morphology were observed, with asymmetric domains being smaller and more interconnected. Both types of Lo domains showed similar mechanical stability in terms of rupture forces and Young's moduli. Notably, force curves in asymmetric domains presented two rupture events that could be attributed to the sequential rupture of a liquid disordered (Ld) and a Lo phase. Interleaflet coupling in asymmetric Lo domains could also be inferred from those measurements. The experimental approach outlined here would significantly enhance the applicability of membrane models.     

Histological characteristics of the intestinal mucosa of the rat during the first year of life

In spite of the widespread use of rats in gastrointestinal research, there is a lack of information on the qualitative and quantitative histological characteristics. Therefore, a study was performed in 69 male Wistar rats with ages ranging from one day to one year old. The features studied included: height and number of villi in the duodenum, jejunum and ileum, and depth and number of crypts in the duodenum, jejunum, ileum, colon and rectum. Morphometric observations were expressed in a mathematical logarithmic curve that showed a normal, pattern of intestinal growth for each intestinal level. The number of villi in the small intestine decreased from 1 to 35 days of age, whereas the other intestinal parameters all increased during the same period. After 35 days the rates of increase or decrease were lower. The quantification of these intestinal changes provides a new complementary pattern as a reference for research as indicators of normality or malfunction in the rat intestine.     

Flavonoids and oxidative stress in Drosophila melanogaster

Flavonoids are a family of antioxidants that are widely represented in fruits, vegetables, dry legumes, and chocolate, as well as in popular beverages, such as red wine, coffee, and tea. The flavonoids chlorogenic acid, kaempferol, quercetin and quercetin 3β-d-glycoside were investigated for genotoxicity using the wing somatic mutation and recombination test (SMART). This test makes use of two recessive wing cell markers: multiple wing hairs (mwh) and flare (flr(3)), which are mutations located on the left arm of chromosome 3 of Drosophila melanogaster and are indicative of both mitotic recombination and various types of mutational events. In order to test the antioxidant capacities of the flavonoids, experiments were conducted with various combinations of oxidants and polyphenols. Oxidative stress was induced using hydrogen peroxide, the Fenton reaction and paraquat. Third-instar transheterozygous larvae were chronically treated for all experiments. The data obtained in this study showed that, at the concentrations tested, the flavonoids did not induce somatic mutations or recombination in D. melanogaster with the exception of quercetin, which proved to be genotoxic at only one concentration. The oxidants hydrogen peroxide and the Fenton reaction did not induce mutations in the wing somatic assay of D. melanogaster, while paraquat and combinations of flavonoids produced significant numbers of small single spots. Quercetin 3β-d-glycoside mixed with paraquat was shown to be desmutagenic. Combinations of the oxidants with the other flavonoids did not show any antioxidant activity.     

Attenuation of cardiac mitochondrial dysfunction by melatonin in septic mice

The existence of an inducible mitochondrial nitric oxide synthase has been recently related to the nitrosative/oxidative damage and mitochondrial dysfunction that occurs during endotoxemia. Melatonin inhibits both inducible nitric oxide synthase and inducible mitochondrial nitric oxide synthase activities, a finding related to the antiseptic properties of the indoleamine. Hence, we examined the changes in inducible nitric oxide synthase/inducible mitochondrial nitric oxide synthase expression and activity, bioenergetics and oxidative stress in heart mitochondria following cecal ligation and puncture-induced sepsis in wild-type (iNOS(+/+)) and inducible nitric oxide synthase-deficient (iNOS(-/-)) mice. We also evaluated whether melatonin reduces the expression of inducible nitric oxide synthase/inducible mitochondrial nitric oxide synthase, and whether this inhibition improves mitochondrial function in this experimental paradigm. The results show that cecal ligation and puncture induced an increase of inducible mitochondrial nitric oxide synthase in iNOS(+/+) mice that was accompanied by oxidative stress, respiratory chain impairment, and reduced ATP production, although the ATPase activity remained unchanged. Real-time PCR analysis showed that induction of inducible nitric oxide synthase during sepsis was related to the increase of inducible mitochondrial nitric oxide synthase activity, as both inducible nitric oxide synthase and inducible mitochondrial nitric oxide synthase were absent in iNOS(-/-) mice. The induction of inducible mitochondrial nitric oxide synthase was associated with mitochondrial dysfunction, because heart mitochondria from iNOS(-/-) mice were unaffected during sepsis. Melatonin treatment blunted sepsis-induced inducible nitric oxide synthase/inducible mitochondrial nitric oxide synthase isoforms, prevented the impairment of mitochondrial homeostasis under sepsis, and restored ATP production. These properties of melatonin should be considered in clinical sepsis.     

Suppressing Manganese Dissolution from Lithium Manganese Oxide Spinel Cathodes with Single‐Layer Graphene

Spinel‐structured LiMn₂O₄ (LMO) is a desirable cathode material for Li‐ion batteries due to its low cost, abundance, and high power capability. However, LMO suffers from limited cycle life that is triggered by manganese dissolution into the electrolyte during electrochemical cycling. Here, it is shown that single‐layer graphene coatings suppress manganese dissolution, thus enhancing the performance and lifetime of LMO cathodes. Relative to lithium cells with uncoated LMO cathodes, cells with graphene‐coated LMO cathodes provide improved capacity retention with enhanced cycling stability. X‐ray photoelectron spectroscopy reveals that graphene coatings inhibit manganese depletion from the LMO surface. Additionally, transmission electron microscopy demonstrates that a stable solid electrolyte interphase is formed on graphene, which screens the LMO from direct contact with the electrolyte. Density functional theory calculations provide two mechanisms for the role of graphene in the suppression of manganese dissolution. First, common defects in single‐layer graphene are found to allow the transport of lithium while concurrently acting as barriers for manganese diffusion. Second, graphene can chemically interact with Mn³⁺ at the LMO electrode surface, promoting an oxidation state change to Mn⁴⁺, which suppresses dissolution.     

Corporate and Product Carbon Footprint under Compound Hybrid Analysis: Application to a Spanish Timber Company

The European Union (EU) is advancing steadily toward the stabilization of atmospheric greenhouse gas concentrations. Various sectors are now obliged to make reductions, and new policies based on the carbon footprint are being encouraged. However, voluntary reporting of so‐called scope 3 emissions is hindering successful implementation of these policies. In this study, we present a tiered hybrid analysis to report emissions according to the ISO/TR 14069 standards and to obtain complete measures of scope 3 emissions. A process analysis for scope 1 and scope 2 emissions is complemented with a multiregional input‐output analysis for upstream scope 3 emissions. This novel approach is applied to the case study of a Spanish timber company. Its total carbon footprint in 2011 was 783,660 kilograms of carbon‐dioxide equivalent, of which 88% correspond to scope 3 emissions. These emissions are globally distributed; 71% are from European countries, followed by 8% from emerging economies (Brazil, Russia, India, Indonesia, Australia, and Turkey), 5% from China, and, finally, 16% from the rest of the world. We identify and discuss the advantages and disadvantages of this novel approach, the European implementation of which could be highly effective in reducing global carbon emissions.     

Reproductive strategies and population structure in Leishmania: substantial amount of sex in Leishmania Viannia guyanensis

Leishmania species of the subgenus Viannia and especially Leishmania Viannia guyanensis are responsible for a large proportion of New World leishmaniasis cases. Since a recent publication on Leishmania Viannia braziliensis, the debate on the mode of reproduction of Leishmania parasites has been reopened. A predominant endogamic reproductive mode (mating with relatives), together with strong Wahlund effects (sampling of strains from heterogeneous subpopulations), was indeed evidenced. To determine whether this hypothesis can be generalized to other Leishmania Viannia species, we performed a population genetic study on 153 human strains of L. (V.) guyanensis from French Guiana based on 12 microsatellite loci. The results revealed important homozygosity and very modest linkage disequilibrium, which is in agreement with a high level of sexual recombination and substantial endogamy. These results also revealed a significant isolation by distance with relatively small neighbourhoods and hence substantial viscosity of Leishmania populations in French Guiana. These results are of epidemiological relevance and suggest a major role for natural hosts and/or vectors in parasite strain diffusion across the country as compared to human hosts.     

Increased water‐use efficiency during the 20th century did not translate into enhanced tree growth

Aim The goals of this study are: (1) to determine whether increasing atmospheric CO₂ concentrations and changing climate increased intrinsic water use efficiency (iWUE, as detected by changes in Δ¹³C) over the last four decades; and if it did increase iWUE, whether it led to increased tree growth (as measured by tree‐ring growth); (2) to assess whether CO₂ responses are biome dependent due to different environmental conditions, including availability of nutrients and water; and (3) to discuss how the findings of this study can better inform assumptions of CO₂ fertilization and climate change effects in biospheric and climate models. Location A global range of sites covering all major forest biome types. Methods The analysis encompassed 47 study sites including boreal, wet temperate, mediterranean, semi‐arid and tropical biomes for which measurements of tree ring Δ¹³C and growth are available over multiple decades. Results The iWUE inferred from the Δ¹³C analyses of comparable mature trees increased 20.5% over the last 40 years with no significant differences between biomes. This increase in iWUE did not translate into a significant overall increase in tree growth. Half of the sites showed a positive trend in growth while the other half had a negative or no trend. There were no significant trends within biomes or among biomes. Main conclusions These results show that despite an increase in atmospheric CO₂ concentrations of over 50 p.p.m. and a 20.5% increase in iWUE during the last 40 years, tree growth has not increased as expected, suggesting that other factors have overridden the potential growth benefits of a CO₂‐rich world in many sites. Such factors could include climate change (particularly drought), nutrient limitation and/or physiological long‐term acclimation to elevated CO₂. Hence, the rate of biomass carbon sequestration in tropical, arid, mediterranean, wet temperate and boreal ecosystems may not increase with increasing atmospheric CO₂ concentrations as is often implied by biospheric models and short‐term elevated CO₂ experiments.