Carbon nanotubes: an insight into the mechanisms of their potential genotoxicity

After the health catastrophe resulting from the widespread use of asbestos which was once hailed as a new miracle material, the increasing use of carbon nanotubes (CNTs) has spawned major concern due to their similarities in terms of size, shape and poor solubility. Assessment of genotoxicity has shown that CNTs can damage DNA in vitro and in vivo. The genotoxic potential of different CNT samples varies considerably, however, with negative findings reported in a number of studies, probably due to the enormous heterogeneity of CNTs. The observed spectrum of genotoxic effects shows similarities with those reported for asbestos fibres. Mutagenicity has been found in vivo but in bacterial assays both asbestos and CNTs have mostly tested negative. An overview of key experimental observations on CNT-induced genotoxicity is presented in the first half of this review.In the second part, the potential mechanisms of CNT-elicited genotoxicity are discussed. Whereas CNTs possess intrinsic ROS-scavenging properties they are capable of generating intracellular ROS upon interaction with cellular components, and can cause antioxidant depletion. These effects have been attributed to their Fenton-reactive metals content. In addition, CNTs can impair the functionality of the mitotic apparatus. A noteworthy feature is that frustrated phagocytosis, which is involved in asbestos-induced pathology, has been observed for specific CNTs as well. The involvement of other mechanisms generally implicated in particle toxicity, such as phagocyte activation and impairment of DNA repair, is largely unknown at present and needs further investigation

Fiber-induced crystallization in elongational flows

Morphology development at the fiber/matrix interphase in fiber-reinforced isotactic polypropylene composites is a widely studied topic. While the application of shear flow may strongly enhance the nucleation density around the fiber, little is known about the influence of fibers on the crystallization of polypropylene subjected to an extensional flow. In this work, the flow around a single glass fiber upon uniaxial elongation of the melt is examined using X-ray scattering and diffraction techniques and compared to the response measured for the neat matrix. A comparison between a neat and compatibilized matrix is made given the strong influence of the addition of an adhesion modifier on the bulk crystallization kinetics of polypropylene. The flow is applied using an in-house-built filament stretching extensional rheometer, which, due to its midfilament control scheme, allows for in situ X-ray experiments. Combined small-angle X-ray scattering/wide-angle X-ray diffraction patterns are acquired during the flow and subsequent crystallization step. Postcrystallization area scans of the filament show that the introduction of a single glass fiber gives rise to the development of β-phase crystals, particularly in the area around the fiber ends, and in contrast to what is observed for the matrix materials alone, where solely α-phase is found. Surprisingly enough, the addition of a single fiber (0.00045 vol %) alters the crystallizing polymorph in almost the entire filament. However, the addition of the adhesion modifier hinders the formation of β-phase crystals around the fiber due to an acceleration of the bulk crystallization kinetics. Finite element simulations provide insight into the flow field around the fiber during stretching and demonstrate that the flow is no longer uniaxial extension, but dominated by shear, even though the volumetric amount of fiber as compared to the matrix is negligible. These findings explain the experimental observation of substantial β-phase formation after the introduction of a single fiber, while this is not observed in the matrix material. Worth noting, the formation of β-phase polypropylene depends not only on the presence and the strength of the flow but predominantly on the type of flow, i.e., shear as opposed to elongation

Low relationship quality predicts scratch contagion during tense situations in orangutans (Pongo pygmaeus)

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Torsional fracture of viscoelastic liquid bridges

Short liquid bridges are stable under the action of surface tension. In applications like electronic packaging, food engineering, and additive manufacturing, this poses challenges to the clean and fast dispensing of viscoelastic fluids. Here, we investigate how viscoelastic liquid bridges can be destabilized by torsion. By combining high-speed imaging and numerical simulation, we show that concave surfaces of liquid bridges can localize shear, in turn localizing normal stresses and making the surface more concave. Such positive feedback creates an indent, which propagates toward the center and leads to breakup of the liquid bridge. The indent formation mechanism closely resembles edge fracture, an often undesired viscoelastic flow instability characterized by the sudden indentation of the fluid\u27s free surface when the fluid is subjected to shear. By applying torsion, even short, capillary stable liquid bridges can be broken in the order of 1 s. This may lead to the development of dispensing protocols that reduce substrate contamination by the satellite droplets and long capillary tails formed by capillary retraction, which is the current mainstream industrial method for destabilizing viscoelastic liquid bridges

Multi-tier Loyalty Programs to Stimulate Customer Engagement

Customers differ in their purchase behavior, profitability, attitude toward the firm, and so on. These differences between customers have led to numerous firms introducing multi-tier loyalty programs. A multi-tier loyalty program explicitly distinguishes between customers by means of hierarchical tiers (e.g. Silver, Gold, Platinum) and assigns customers to different tiers based on their past purchase behavior. Next, customers in different tiers are provided varying levels of tangible rewards and intangible benefits, which are potentially powerful instruments to stimulate customer engagement. In this chapter, we focus on the design and effectiveness of such multi-tier loyalty programs. Building on loyalty program and customer prioritization research, we discuss whether, why, and how multi-tier loyalty programs are effective (or not) in influencing customer behavior, thereby enhancing customer engagement and financial performance

Towards the reconstruction of integrated genome-scale models of metabolism and gene expression

The reconstruction of integrated genome-scale models of metabolism and gene expression has been a challenge for a while now. In fact, various methods that allow integrating reconstructions of Transcriptional Regulatory Networks, gene expression data or both into Genome-Scale Metabolic Models have been proposed. Several of these methods are surveyed in this article, which allowed identifying their strengths and weaknesses concerning the reconstruction of integrated models for multiple prokaryotic organisms. Additionally, the main resources of regulatory information were also surveyed, as the existence of novel sources of regulatory information and gene expression data may contribute for the improvement of methodologies referred herein.This study was supported by the Portuguese Foundation for Science andTechnology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit andBioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European RegionalDevelopment Fund under the scope of Norte2020-Programa Operacional Regional do Norte. Fernando Cruz holds a doctoral fellowship (SFRH/BD/139198/2018) funded by the FCT. The authors thank project SHIKIFACTORY100 - Modular cell factories for the production of 100 compounds from the shikimate pathway (814408) funded by the European Commission.info:eu-repo/semantics/publishedVersio

Human autoreactive T cells recognize CD1b and phospholipids

In contrast with the common detection of T cells that recognize MHC, CD1a, CD1c, or CD1d proteins, CD1b autoreactive T cells have been difficult to isolate in humans. Here we report the development of polyvalent complexes of CD1b proteins and carbohydrate backbones (dextramers) and their use in identifying CD1b autoreactive T cells from human donors. Activation is mediated by αβ T-cell receptors (TCRs) binding to CD1b-phospholipid complexes, which is sufficient to activate autoreactive responses to CD1b-expressing cells. Using mass spectrometry and T-cell responses to scan through the major classes of phospholipids, we identified phosphatidylglycerol (PG) as the immunodominant lipid antigen. T cells did not discriminate the chemical differences that distinguish mammalian PG from bacterial PG. Whereas most models of T-cell recognition emphasize TCR discrimination of differing self and foreign structures, CD1b autoreactive T cells recognize lipids with dual self and foreign origin. PG is rare in the cellular membranes that carry CD1b proteins. However, bacteria and mitochondria are rich in PG, so these data point to a more general mechanism of immune detection of infection- or stress-associated lipids

Influences of the G2350A polymorphism in the ACE Gene on cardiac structure and function of ball game players

<p>Abstract</p> <p>Background</p> <p>Except for the I/D polymorphism in the angiotensin I-converting enzyme (ACE) gene, there were few reports about the relationship between other genetic polymorphisms in this gene and the changes in cardiac structure and function of athletes. Thus, we investigated whether the G2350A polymorphism in the <it>ACE </it>gene is associated with the changes in cardiac structure and function of ball game players. Total 85 healthy ball game players were recruited in this study, and they were composed of 35 controls and 50 ball game players, respectively. Cardiac structure and function were measured by 2-D echocardiography, and the G2350A polymorphism in the <it>ACE </it>gene analyzed by the SNaPshot method.</p> <p>Results</p> <p>There were significant differences in left ventricular mass index (LVmassI) value among each sporting discipline studied. Especially in the athletes of basketball disciplines, indicated the highest LVmassI value than those of other sporting disciplines studied (p < 0.05). However, there were no significant association between any echocardiographic data and the G2350A polymorphism in the <it>ACE </it>gene in the both controls and ball game players.</p> <p>Conclusions</p> <p>Our data suggests that the G2350A polymorphism in the <it>ACE </it>gene may not significantly contribute to the changes in cardiac structure and function of ball game players, although sporting disciplines of ball game players may influence the changes in LVmassI value of these athletes. Further studies using a larger sample size and other genetic markers in the <it>ACE </it>gene will be needed.</p