DNA dynamics in complex coacervate droplets and micelles.

Single stranded DNA (ssDNA), or another polyanion, can be mixed with polycations to form liquid-like complex coacervates. When the polycations are replaced by cationic-neutral diblock copolymers, complex coacervate core micelles (C3Ms) can be formed instead. In both complex coacervates and C3Ms, dynamics plays an important role. Yet, to date, the effect of chain length on the dynamics effect is still not fully understood. The DNA complexes provide a versatile platform to further elucidate these chain length effects because the DNA is monodisperse and its length can be easily adapted. Therefore, we study in this paper the dynamics of fluorescently labelled ssDNA in both complex coacervate droplets and micelles. The DNA dynamics in the complex coacervate droplets is probed by fluorescence recovery after photobleaching (FRAP). We observe that the DNA diffusion coefficient depends more strongly on the DNA length than predicted by the sticky Rouse model and we show that this can be partly explained by changes in complex coacervate density, but that also other factors might play a role. We measure the molecular exchange of C3Ms by making use of Förster resonance energy transfer (FRET) and complement these measurements with Langevin dynamics simulations. We conclude that chain length polydispersity is the main cause of a broad distribution of exchange rates. We hypothesise that the different exchange rates that we observe for the monodisperse DNA are mainly caused by differences in dye interactions and show that the dye can indeed have a large effect on the C3M exchange. In addition, we show that a new description of the C3M molecular exchange is required that accounts among others for the effect of the length of the oppositely charged core species. Together our findings can help to better understand the dynamics in both specific DNA systems and in complex coacervate droplets and micelles in general.

FRET-Based Determination of the Exchange Dynamics of Complex Coacervate Core Micelles.

Complex coacervate core micelles (C3Ms) are nanoscopic structures formed by charge interactions between oppositely charged macroions and used to encapsulate a wide variety of charged (bio)molecules. In most cases, C3Ms are in a dynamic equilibrium with their surroundings. Understanding the dynamics of molecular exchange reactions is essential as this determines the rate at which their cargo is exposed to the environment. Here, we study the molecular exchange in C3Ms by making use of Förster resonance energy transfer (FRET) and derive an analytical model to relate the experimentally observed increase in FRET efficiency to the underlying macromolecular exchange rates. We show that equilibrated C3Ms have a broad distribution of exchange rates. The overall exchange rate can be strongly increased by increasing the salt concentration. In contrast, changing the unlabeled homopolymer length does not affect the exchange of the labeled homopolymers and an increase in the micelle concentration only affects the FRET increase rate at low micelle concentrations. Together, these results suggest that the exchange of these equilibrated C3Ms occurs mainly by expulsion and insertion, where the rate-limiting step is the breaking of ionic bonds to expel the chains from the core. These are important insights to further improve the encapsulation efficiency of C3Ms.

Chemical Feedback in Templated Reaction-Assembly Networks.

Chemical feedback between building block synthesis and their subsequent supramolecular self-assembly into nanostructures has profound effects on assembly pathways. Nature harnesses feedback in reaction-assembly networks in a variety of scenarios including virion formation and protein folding. Also in nanomaterial synthesis, reaction-assembly networks have emerged as a promising control strategy to regulate assembly processes. Yet, how chemical feedback affects the fundamental pathways of structure formation remains unclear. Here, we unravel the pathways of a templated reaction-assembly network that couples a covalent polymerization to an electrostatic coassembly process. We show how the supramolecular staging of building blocks at a macromolecular template can accelerate the polymerization reaction and prevent the formation of kinetically trapped structures inherent to the process in the absence of feedback. Finally, we establish a predictive kinetic reaction model that quantitatively describes the pathways underlying these reaction-assembly networks. Our results shed light on the fundamental mechanisms by which chemical feedback can steer self-assembly reactions and can be used to rationally design new nanostructures.

Langevin Dynamics Simulations of the Exchange of Complex Coacervate Core Micelles: The Role of Nonelectrostatic Attraction and Polyelectrolyte Length.

Complex coacervate core micelles (C3Ms) are promising encapsulators for a wide variety of (bio)molecules. To protect and stabilize their cargo, it is essential to control their exchange dynamics. Yet, to date, little is known about the kinetic stability of C3Ms and the dynamic equilibrium of molecular building blocks with micellar species. Here we study the C3M exchange during the initial micellization by using Langevin dynamics simulations. In this way, we show that charge neutral heterocomplexes consisting of multiple building blocks are the primary mediator for exchange. In addition, we show that the kinetic stability of the C3Ms can be tuned not only by the electrostatic interaction but also by the nonelectrostatic attraction between the polyelectrolytes, the polyelectrolyte length ratio, and the overall polyelectrolyte length. These insights offer new rational design guides to aid the development of new C3M encapsulation strategies.

Two-dimensional crystals of star polymers: a tale of tails.

The formation of non-hexagonal crystalline structures by the organisation of colloidal nanoparticles often involves the use of complex particles with anisotropic shape or interactions or the imposition of non-uniform external fields. Here we explore how unusual symmetries can be created using experimentally realistic particles that interact through isotropic and purely repulsive potentials. In particular, we use simulations to explore the phase behavior of two-dimensional systems of star polymers. We uncover how the tail of the pair potential has a large role in dictating the phase behavior. Star polymers interacting in the far field with a Gaussian potential only form hexagonal phases, while an exponential tail gives rise to stable primitive oblique and honeycomb lattices. We identify the ratio in strength between long and short range interactions and the nature of the transition between these regimes as crucial parameters to predict when non-hexagonal crystals of star polymers can be stable. This leads to experimental design rules for creating star polymers which should exhibit unusual lattice formation.

Design of binary polymer brushes with tuneable functionality.

Using coarse grained molecular dynamics simulations, we study how functionalized binary brushes may be used to create surfaces whose functionality can be tuned. Our model brushes consist of a mixture of nonresponsive polymers with functionalized responsive polymers. The functional groups switch from an exposed to a hidden state when the conformations of the responsive polymers change from extended to collapsed. We investigate quantitatively which sets of brush parameters result in optimal switching in functionality, by analyzing to which extent the brush conformation allows an external object to interact with the functional groups. It is demonstrated that brushes with species of comparable polymer lengths, or with longer responsive polymers than nonresponsive polymers, can show significant differences in their functionality. In the latter case, either the fraction of responsive polymers or the total grafting density has to be reduced. Among these possibilities, a reduction of the fraction of responsive polymers is shown to be most effective.

Multiple LHCII antennae can transfer energy efficiently to a single Photosystem I.

Photosystems I and II (PSI and PSII) work in series to drive oxygenic photosynthesis. The two photosystems have different absorption spectra, therefore changes in light quality can lead to imbalanced excitation of the photosystems and a loss in photosynthetic efficiency. In a short-term adaptation response termed state transitions, excitation energy is directed to the light-limited photosystem. In higher plants a special pool of LHCII antennae, which can be associated with either PSI or PSII, participates in these state transitions. It is known that one LHCII antenna can associate with the PsaH site of PSI. However, membrane fractions were recently isolated in which multiple LHCII antennae appear to transfer energy to PSI. We have used time-resolved fluorescence-streak camera measurements to investigate the energy transfer rates and efficiency in these membrane fractions. Our data show that energy transfer from LHCII to PSI is relatively slow. Nevertheless, the trapping efficiency in supercomplexes of PSI with ~2.4 LHCIIs attached is 94%. The absorption cross section of PSI can thus be increased with ~65% without having significant loss in quantum efficiency. Comparison of the fluorescence dynamics of PSI-LHCII complexes, isolated in a detergent or located in their native membrane environment, indicates that the environment influences the excitation energy transfer rates in these complexes. This demonstrates the importance of studying membrane protein complexes in their natural environment.

Brain-derived neurotrophic factor as a driving force behind neuroplasticity in neuropathic and central sensitization pain: a new therapeutic target?

INTRODUCTION: Central sensitization is a form of maladaptive neuroplasticity underlying many chronic pain disorders, including neuropathic pain, fibromyalgia, whiplash, headache, chronic pelvic pain syndrome and some forms of osteoarthritis, low back pain, epicondylitis, shoulder pain and cancer pain. Brain-derived neurotrophic factor (BDNF) is a driving force behind neuroplasticity, and it is therefore crucial for neural maintenance and repair. However, BDNF also contributes to sensitization of pain pathways, making it an interesting novel therapeutic target. AREAS COVERED: An overview of BDNF's sensitizing capacity at every level of the pain pathways is presented, including the peripheral nociceptors, dorsal root ganglia, spinal dorsal horn neurons, and brain descending inhibitory and facilitatory pathways. This is followed by the presentation of several potential therapeutic options, ranging from indirect influencing of BDNF levels (using exercise therapy, anti-inflammatory drugs, melatonin, repetitive transcranial magnetic stimulation) to more specific targeting of BDNF's receptors and signaling pathways (blocking the proteinase-activated receptors 2-NK-κß signaling pathway, administration of phencyclidine for antagonizing NMDA receptors, or blockade of the adenosine A2A receptor). EXPERT OPINION: This section focuses on combining pharmacotherapy with multimodal rehabilitation for balancing the deleterious and therapeutic effects of BNDF treatment in chronic pain patients, as well as accounting for the complex and biopsychosocial nature of chronic pain.

Physical activity, air pollution and the brain.

This review introduces an emerging research field that is focused on studying the effect of exposure to air pollution during exercise on cognition, with specific attention to the impact on concentrations of brain-derived neurotrophic factor (BDNF) and inflammatory markers. It has been repeatedly demonstrated that regular physical activity enhances cognition, and evidence suggests that BDNF, a neurotrophin, plays a key role in the mechanism. Today, however, air pollution is an environmental problem worldwide and the high traffic density, especially in urban environments and cities, is a major cause of this problem. During exercise, the intake of air pollution increases considerably due to an increased ventilation rate and particle deposition fraction. Recently, air pollution exposure has been linked to adverse effects on the brain such as cognitive decline and neuropathology. Inflammation and oxidative stress seem to play an important role in inducing these health effects. We believe that there is a need to investigate whether the well-known benefits of regular physical activity on the brain also apply when physical activity is performed in polluted air. We also report our findings about exercising in an environment with ambient levels of air pollutants. Based on the latter results, we hypothesize that traffic-related air pollution exposure during exercise may inhibit the positive effect of exercise on cognition.

Active workstations to fight sedentary behaviour.

BACKGROUND: The impact of active workstations has been studied in several settings, and several outcomes have been investigated. However, the effects on health, work performance, quality of life, etc., have never been systematically reviewed. OBJECTIVE: To evaluate the existing literature about active workstations and their possible positive health and work performance effects. DATA SOURCES: We searched the electronic databases PubMed and Web of Science (up until 28 February 2014). The search terms we used were 'active workstation', 'standing workstation', 'standing desk', 'stand up workstation', 'stand up desk', 'walking desk', 'walking workstation', 'treadmill workstation', 'treadmill desk', 'cycling workstation', 'cycling desk' and 'bike desk', in combination with 'health', 'quality of life', 'cognition', 'computer task performance', 'absenteeism', 'productivity', 'academic achievement', 'cognitive decline', and 'independent living'. In addition, we searched the reference lists of relevant published articles. STUDY SELECTION: Randomized controlled trials, non-randomized controlled trials and non-randomized non-controlled trials investigating the introduction of active workstations in humans were included in this systematic review. Only original studies were included, and we did not accept studies combining the introduction of active workstations with other interventions. Outcomes concerning health, energy expenditure, cognition, quality of life and work performance were included. RESULTS: We included 32 studies, of which five were longitudinal studies in school-aged children, 10 were longitudinal studies in adults and 17 were non-longitudinal studies in adults. Sixteen studies investigated standing desks, 15 investigated walking desks, and one investigated a cycling workstation. The general findings were decreased sitting time, increased energy expenditure, a positive effect on several health markers, no detrimental effect on work performance, no acute effect on cognitive function and no straightforward findings concerning computer task performance. CONCLUSION: The implementation of active workstations might contribute to improving people's health and physical activity levels. The effect of the use of these active workstations on cognition and applied work tasks, such as computer task performance, needs further investigation before conclusions can be drawn. Another aspect that needs further investigation is the implementation of the different active workstations in all age groups.

Differentiation and histogenesis of syringomatous tumour of the nipple and low-grade adenosquamous carcinoma: evidence for a common origin.

AIMS: Syringomatous tumour of the nipple and low-grade adenosquamous carcinoma (LGAdSC) of the breast are regarded as distinct entities. To clarify the nature of these two lesions, we compared the expression of different lineage/differentiation markers in 12 syringomatous tumours of the nipple, nine LGAdSCs, and normal breast epithelium. METHODS AND RESULTS: Using triple immunofluorescence labelling and quantitative RT-PCR for keratins, p63, and smooth muscle actin, we demonstrated that syringomatous tumour and LGAdSC contain p63+/K5/14+ tumour cells, K10+ squamous cells, and K8/18+ glandular cells, with intermediary cells being found in both lineages. Identical p63+/K5/14+ cells were also found in the normal breast duct epithelium. CONCLUSIONS: Our data provide evidence that syringomatous tumour of the nipple and LGAdSC are identical or nearly identical lesions. They contain p63+/K5/14+ cells as the key cells from which the K10+ squamous lineage and the K8/18+ glandular lineage arise. On the basis of our findings in normal breast tissue and associated benign lesions, we suggest that p63+/K5/14+ cells of the normal breast duct epithelium or early related cells might play a key role in the neoplastic transformation of both syringomatous tumour and LGAdSC. We propose that the differentiation patterns found in both lesions reflect the early ontogenetic stages of the normal breast epithelium.

Removal of collagen nerve conduits (NeuraGen) after unsuccessful implantation: focus on histological findings.

Nerve conduits are nonneural, hollow tubular structures designed to bridge the gap of a sectioned nerve, to protect the nerve from scar formation, and to guide the regenerating fibers into the distal nerve stump. In the 8-year experience of our department, four patients aged 14 to 50 years had an unsuccessful implantation of a nerve conduit (NeuraGen, Integra, Plainsboro, NJ). In these four patients, the collagen tubes were replaced by an autogenous nerve graft. The histological specimens showed characteristic histological findings of a scar neuroma without any signs of foreign body reaction in three cases and with minimal foreign body reaction in one case. The collagen nerve tube was completely resorbed in all cases after a time period of 6 to 17 months and could not be detected marco- or microscopically.To our knowledge, this is the first report in the English and German literature describing the histological characteristics of explanted collagen nerve tubes in humans.

Subclinical effects of aerobic training in urban environment.

PURPOSE: Particulate matter (PM) exposure is linked to inflammation, neuroinflammation, and cognitive decline, whereas aerobic training improves cognition. We investigated the effects of PM exposure during aerobic training on inflammatory biomarkers, serum brain-derived neurotrophic factor (BDNF), an assumed mediator of exercise-induced cognitive improvements, and cognitive performance. METHODS: Two groups of untrained volunteers completed an aerobic training program of 12 wk, 3 sessions a week: one group (n = 15) in an urban and another group (n = 9) in a rural environment. Ultrafine PM (UFPM) concentrations were measured during each training session. Aerobic fitness (Cooper test), BDNF serum levels, blood total and differential leukocyte counts, exhaled nitric oxide levels, and cognitive performance (Stroop task, Operation Span, and Psychomotor Vigilance task) were analyzed before and after the program. RESULTS: UFPM concentrations were significantly higher in the urban environment compared with the rural environment (P = 0.006). Fitness levels improved equally (P < 0.0001) in both groups. Leukocyte counts (P = 0.02), neutrophil counts (P = 0.04), and exhaled nitric oxide levels (P = 0.002) increased after training in the urban group, whereas these parameters did not change in the rural group. The changes in these markers' levels after training showed a positive correlation with the personal average UFPM exposure during training. Reaction times on the Stroop task improved in the rural group (P = 0.001), but not in the urban group. No effects were found on BDNF levels, Operation Span, and Psychomotor Vigilance test performances. CONCLUSION: Aerobic training in an urban environment with high traffic-related air pollution increased inflammatory biomarkers, and, in contrast to aerobic training in a rural environment, cognitive performance on the Stroop task did not improve.

Changed gene expression in brains of mice exposed to traffic in a highway tunnel.

CONTEXT: Air pollution has been suggested to have an impact on the brain. OBJECTIVE: The objective was to assess the expression of inflammation-related genes in the brains of mice that had been exposed for 5 days to a well-characterized traffic-polluted environment, i.e. a highway tunnel. MATERIALS AND METHODS: Twenty C57BL6 mice were randomly allocated to four groups of five animals. Two groups were placed in the tunnel for 5 days (mean PM 2.5, 55.1 µg/m³, mean elemental carbon, EC 13.9 µg/m³) in cages with or without filter, two control groups were housed outside the tunnel. Animals were assessed within 24 hours after the last exposure day. Lung injury and inflammation were assessed by bronchoalveolar lavage (BAL) and histology. Blood leukocytosis and coagulation parameters were determined in peripheral blood. The olfactory bulb and hippocampus were analyzed for changes in expression of inflammatory genes and brain-derived neurotrophic factor (BDNF). RESULTS AND DISCUSSION: Although carbon particles were abundant in alveolar macrophages of exposed mice and absent in non-exposed mice, there was no evidence of pulmonary or systemic inflammation. There was an increased expression of genes involved in inflammatory response (COX2, NOS2, NOS3, and NFE2L2) in the hippocampus of the exposed mice. In the olfactory bulb, a downregulation was found for IL1α, COX2, NFE2L2, IL6, and BDNF. CONCLUSION: Although this short-term exposure to traffic-related pollution did not induce pulmonary or systemic inflammation, the expression of inflammatory genes was affected in different brain areas. The decreased BDNF expression in the olfactory bulb suggests lower brain neurotrophic support in response to traffic-related air pollution.

Acute running stimulates hippocampal dopaminergic neurotransmission in rats, but has no influence on brain-derived neurotrophic factor.

Hippocampal brain-derived neurotrophic factor (BDNF) protein is increased with exercise in rats. Monoamines seem to play a role in the regulation of BDNF, and monoamine neurotransmission is known to increase with exercise. The purpose of this study was to examine the influence of acute exercise on monoaminergic neurotransmission and BDNF protein concentrations. Hippocampal microdialysis was performed in rats that were subjected to 60 min of treadmill running at 20 m/min or rest. Two hours postexercise, the rats were killed, and the hippocampus was dissected. In experiments without microdialysis, hippocampus and serum samples were collected immediately after exercise. Exercise induced a twofold increase in hippocampal dopamine release. Noradrenaline and serotonin release were not affected. Hippocampal BDNF levels were not influenced, whether they were measured immediately or 2 h after the exercise protocol. Serum BDNF levels did not change either, but serum BDNF was negatively correlated to peripheral corticosterone concentrations, indicating a possible inhibitory reaction to the stress of running. Sixty minutes of exercise enhances dopamine release in the hippocampus of the rat in vivo. However, this increase is not associated with changes in BDNF protein levels immediately nor 2 h after the acute exercise bout. An increased corticosterone level might be the contributing factor for the absence of changes in BDNF.

Does a period of detraining cause a decrease in serum brain-derived neurotrophic factor?

Brain-derived neurotrophic factor (BDNF) is one of the neurotrophins promoting cognitive function and contributing to neurogenesis and neuroprotection. Available evidence suggests that exercise influences serum BDNF concentrations, but that the effect is transient. The purpose of this study is to determine whether a period of aerobic training, followed by a period of detraining, can influence basal serum BDNF levels in humans. Sixteen young, sedentary subjects were assigned to an experimental group (n=9) and a control group (n=7). The experimental group performed an aerobic training program during 8 weeks, followed by 8 weeks of detraining, during which subjects returned to their previous, sedentary activity level. The control group remained physically inactive during 16 weeks. In both groups, performance on short-term (Digit Span test) and mid-term memory (Recall of Images) was assessed. Aerobic training significantly increased the VO(2) peak in the experimental group, and these values returned to baseline after 8 weeks of detraining. Basal serum BDNF was not influenced by 8 weeks of aerobic training and detraining did not seem to have an effect on basal peripheral BDNF concentrations. Both training and detraining did not clearly influence short-term memory performance on the Digit Span test and no differences were present between the experimental and control group on the mid-term memory test. Future studies should focus on patient groups and elderly to further investigate the effect of training and detraining on neurotrophic factors and cognitive function, and on the effects of training and detraining on the BDNF response to acute exercise.

Influence of different intravenous lipid emulsions on hepatobiliary dysfunction in a rabbit model.

OBJECTIVES: Long-term total parenteral nutrition (TPN) in children is often complicated by the development of cholestasis, liver fibrosis, and liver failure. High doses of intravenous lipids may be involved in the pathogenesis of hepatobiliary dysfunction. The purpose of this study was to determine whether the use of 2 newly developed lipid emulsions could reduce liver damage. MATERIALS AND METHODS: Three groups of prepubescent rabbits received TPN including a lipid emulsion either based on soybean oil, olive oil, or soybean oil with n-3 fatty acids added. Enterally fed animals served as controls. After 21 d the animals were killed. Serum samples were obtained at the beginning and end of the study period. Specimens were processed for histological evaluation using a specific score to assess the severity of liver damage. RESULTS: Biochemical parameters did not predict the extent of liver damage. Hydropic degeneration as an indicator of toxic liver injury was the predominant histological alteration regardless of the type of lipids infused. The extent of fibrosis did not significantly differ among treatment groups except for animals infused with n-3 fatty acids exhibiting increased fibrotic transformation as compared with controls. CONCLUSION: In our animal model, the use of a lipid emulsion with a reduced amount of polyunsaturated fatty acids was not superior to a lipid emulsion based on soybean oil. Long-term application of n-3 fatty acids was associated with more extensive fibrosis. Therefore, intravenous n-3 fatty acids containing lipid preparations (fish oil) should not be used in patients for long-term TPN.

Histopathologic findings in a novel decellularized pulmonary homograft: an autopsy study.

Innovative valved conduits for reconstruction of the right ventricular outflow tract are desirable to overcome the risk of valve deterioration of conventional homografts. This study describes the histopathology of a novel decellularized pulmonary homograft (SynerGraft) implanted in the right ventricular outflow tract of a 60-year-old man 5 weeks before death. The histomorphology of this decellularized homograft showed integrity of its extracellular matrix and a gradual cellular infiltrate consisting predominantly of macrophages, resembling an early nonspecific inflammatory phase of recellularization without any signs of a specific immunologic interference 5 weeks after implantation. Whether this morphologic appearance precedes the desired repopulation with autologous fibroblasts remains to be established.