High‐Performance Liquid Chromatographic Resolution of Neutral and Cationic Hetero[6]Helicenes

Cationic hetero[6]helicenes 1⁺ , 2⁺ and 3⁺ have been recently disclosed. Herein we report on their enantiomeric separation using high‐performance liquid chromatography. Separation of the antipodes can be achieved in preparative scale on neutral adducts with Chiralcel OD‐I or Chiralpak ID CSP. Selectivity factors of 1.90, 1.67, and 1.96 were obtained for 1-H , 2-H , and 3-H , respectively. Separation can also be performed on the carbenium ions on regular Chiralpak IA CSP using water‐containing eluents, thus allowing for enantiomeric purity determinations in aqueous environments. Resolution of neutral and cationic helicenes is also achieved on more recently developed LARIHC columns. The versatility of the cyclofructan phases allows for baseline separations for both cases and their loading capabilities are demonstrated. Finally, the configurational stability of 1⁺ , 2⁺ , and 3⁺ was measured. For each replacement of an oxygen atom by an amino group, the racemization barrier increases significantly (ΔG^? = 29.8, 36.3 and >37 kcal mol^‐1 for 1⁺ , 2⁺ , and 3⁺ respectively). Chirality 28:282–289, 2016. © 2016 Wiley Periodicals, Inc.     

Preclinical Models for Studying NASH-Driven HCC: How Useful Are They?

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Climate change reduces resilience to fire in subalpine rainforests

Climate change is affecting the distribution of species and the functioning of ecosystems. For species that are slow growing and poorly dispersed, climate change can force a lag between the distributions of species and the geographic distributions of their climatic envelopes, exposing species to the risk of extinction. Climate also governs the resilience of species and ecosystems to disturbance, such as wildfire. Here we use species distribution modelling and palaeoecology to assess and test the impact of vegetation–climate disequilibrium on the resilience of an endangered fire‐sensitive rainforest community to fires. First, we modelled the probability of occurrence of Athrotaxis spp. and Nothofagus gunnii rainforest in Tasmania (hereon “montane rainforest”) as a function of climate. We then analysed three pollen and charcoal records spanning the last 7,500 cal year BP from within both high (n = 1) and low (n = 2) probability of occurrence areas. Our study indicates that climatic change between 3,000 and 4,000 cal year bp induced a disequilibrium between montane rainforests and climate that drove a loss of resilience of these communities. Current and future climate change are likely to shift the geographic distribution of the climatic envelopes of this plant community further, suggesting that current high‐resilience locations will face a reduction in resilience. Coupled with the forecast of increasing fire activity in southern temperate regions, this heralds a significant threat to this and other slow growing, poorly dispersed and fire sensitive forest systems that are common in the southern mid to high latitudes.     

Ecosystem services provided by bromeliad plants: A systematic review

The unprecedented loss of biological diversity has negative impacts on ecosystems and the associated benefits which they provide to humans. Bromeliads have high diversity throughout the Neotropics, but they have been negatively affected by habitat loss and fragmentation, climate change, invasive species, and commercialization for ornamental purpose. These plants provide direct benefits to the human society, and they also form microecosystems in which accumulated water and nutrients support the communities of aquatic and terrestrial species, thus maintaining local diversity. We performed a systematic review of the contribution of bromeliads to ecosystem services across their native geographical distribution. We showed that bromeliads provide a range of ecosystem services such as maintenance of biodiversity, community structure, nutrient cycling, and the provisioning of food and water. Moreover, bromeliads can regulate the spread of diseases, and water and carbon cycling, and they have the potential to become important sources of chemical and pharmaceutical products. The majority of this research was performed in Brazil, but future research from other Neotropical countries with a high diversity of bromeliads would fill the current knowledge gaps and increase the generality of these findings. This systematic review identified that future research should focus on provisioning, regulating, and cultural services that have been currently overlooked. This would enhance our understanding of how bromeliad diversity contributes to human welfare, and the negative consequences that loss of bromeliad plants can have on communities of other species and the healthy functioning of the entire ecosystems.     

Review of methodology for the determination of benzimidazole residues in biological matrices

Benzimidazoles are anthelmintic agents widely used in the treatment of parasitic infections in a range of species and as fungicidal agents in the control of spoilage of crops during storage and transport. In this paper, the more important benzimidazoles are introduced and their pharmacological effects and physiochemical properties discussed. The metabolism of these drugs is described relating to the occurrence and persistence of residues in biological matrices, providing information for selection of suitable matrices and target residues for testing. Methods for determination of benzimidazoles are reviewed for a range of biological matrices. The importance of selecting suitable extraction and clean-up procedures is discussed, along with the difficulties encountered in adapting single residue methods to multi-residue methods. The importance of suitable detection systems for determination of benzimidazoles, namely, screening, HPLC, GC and confirmatory methods is described in detail. The future for benzimidazole residue analysis is discussed, focusing on selection of appropriate residues for screening methods and protocols for confirmation of benzimidazole residues.     

Conserved regulation of MAP kinase expression by PUF RNA-binding proteins

Mitogen-activated protein kinase (MAPK) and PUF (for Pumilio and FBF [fem-3 binding factor]) RNA-binding proteins control many cellular processes critical for animal development and tissue homeostasis. In the present work, we report that PUF proteins act directly on MAPK/ERK-encoding mRNAs to downregulate their expression in both the Caenorhabditis elegans germline and human embryonic stem cells. In C. elegans, FBF/PUF binds regulatory elements in the mpk-1 3′ untranslated region (3′ UTR) and coprecipitates with mpk-1 mRNA; moreover, mpk-1 expression increases dramatically in FBF mutants. In human embryonic stem cells, PUM2/PUF binds 3′UTR elements in both Erk2 and p38α mRNAs, and PUM2 represses reporter constructs carrying either Erk2 or p38α 3′ UTRs. Therefore, the PUF control of MAPK expression is conserved. Its biological function was explored in nematodes, where FBF promotes the self-renewal of germline stem cells, and MPK-1 promotes oocyte maturation and germ cell apoptosis. We found that FBF acts redundantly with LIP-1, the C. elegans homolog of MAPK phosphatase (MKP), to restrict MAPK activity and prevent apoptosis. In mammals, activated MAPK can promote apoptosis of cancer cells and restrict stem cell self-renewal, and MKP is upregulated in cancer cells. We propose that the dual negative regulation of MAPK by both PUF repression and MKP inhibition may be a conserved mechanism that influences both stem cell maintenance and tumor progression.     

Genetic variation in the mitochondrial enzyme carbamyl-phosphate synthetase I predisposes children to increased pulmonary artery pressure following surgical repair of congenital heart defects: a validated genetic association study

Increased pulmonary artery pressure (PAP) can complicate the postoperative care of children undergoing surgical repair of congenital heart defects. Endogenous NO regulates PAP and is derived from arginine supplied by the urea cycle. The rate-limiting step in the urea cycle is catalyzed by a mitochondrial enzyme, carbamoyl-phosphate synthetase I (CPSI). A well-characterized polymorphism in the gene encoding CPSI (T1405N) has previously been implicated in neonatal pulmonary hypertension. A consecutive modeling cohort of children (N=131) with congenital heart defects requiring surgery was prospectively evaluated to determine key factors associated with increased postoperative PAP, defined as a mean PAP>20 mmHg for at least 1h during the 48h following surgery measured by an indwelling pulmonary artery catheter. Multiple dimensionality reduction (MDR) was used to both internally validate observations and develop optimal two-variable through five-variable models that were tested prospectively in a validation cohort (N=41). Unconditional logistic regression analysis of the modeling cohort revealed that age (OR=0.92, p=0.01), CPSI T1405N genotype (AC vs. AA: OR=4.08, p=0.04, CC vs. AA: OR=5.96, p=0.01), and Down syndrome (OR=5.25, p=0.04) were independent predictors of this complex phenotype. MDR predicted that the best two-variable model consisted of age and CPSI T1405N genotype (p<0.001). This two-variable model correctly predicted 73% of the outcomes from the validation cohort. A five-variable model that added race, gender and Down's syndrome was not significantly better than the two-variable model. In conclusion, the CPSI T1405N genotype appears to be an important new factor in predicting susceptibility to increased PAP following surgical repair of congenital cardiac defects in children.     

Critical role of Ena/VASP proteins for filopodia formation in neurons and in function downstream of netrin-1

Ena/VASP proteins play important roles in axon outgrowth and guidance. Ena/VASP activity regulates the assembly and geometry of actin networks within fibroblast lamellipodia. In growth cones, Ena/VASP proteins are concentrated at filopodia tips, yet their role in growth cone responses to guidance signals has not been established. We found that Ena/VASP proteins play a pivotal role in formation and elongation of filopodia along neurite shafts and growth cone. Netrin-1-induced filopodia formation was dependent upon Ena/VASP function and directly correlated with Ena/VASP phosphorylation at a regulatory PKA site. Accordingly, Ena/VASP function was required for filopodial formation from the growth cone in response to global PKA activation. We propose that Ena/VASP proteins control filopodial dynamics in neurons by remodeling the actin network in response to guidance cues.     

Arp2/3 is a negative regulator of growth cone translocation

Arp2/3 is an actin binding complex that is enriched in the peripheral lamellipodia of fibroblasts, where it forms a network of short, branched actin filaments, generating the protrusive force that extends lamellipodia and drives fibroblast motility. Although it has been assumed that Arp2/3 would play a similar role in growth cones, our studies indicate that Arp2/3 is enriched in the central, not the peripheral, region of growth cones and that the growth cone periphery contains few branched actin filaments. Arp2/3 inhibition in fibroblasts severely disrupts actin organization and membrane protrusion. In contrast, Arp2/3 inhibition in growth cones minimally affects actin organization and does not inhibit lamellipodia protrusion or de novo filopodia formation. Surprisingly, Arp2/3 inhibition significantly enhances axon elongation and causes defects in growth cone guidance. These results indicate that Arp2/3 is a negative regulator of growth cone translocation.     

FTIR spectroelectrochemical study of the activation and inactivation processes of [NiFe] hydrogenases: effects of solvent isotope replacement and site-directed mutagenesis

The kinetics of the activation and anaerobic inactivation processes of Desulfovibrio gigas hydrogenase have been measured in D₂O by FTIR spectroelectrochemistry. A primary kinetic solvent isotope effect was observed for the inactivation process but not for the activation step. The kinetics of these processes have been also measured after replacement of a glutamic residue placed near the active site of an analogous [NiFe] hydrogenase from Desulfovibrio fructosovorans. Its replacement by a glutamine affected greatly the kinetics of the inactivation process but only slightly the activation process. The interpretation of the experimental results is that the rate-limiting step for anaerobic inactivation is the formation from water of a -OH^– bridge at the hydrogenase active site, and that Glu25 has a role in this step.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00775-004-0559-7