Sharpening the Interfaces of Axial Heterostructures in Self-Catalyzed AlGaAs Nanowires: Experiment and Theory

The growth of III-III-V axial heterostructures in nanowires via the vapor-liquid-solid method is deemed to be unfavorable because of the high solubility of group III elements in the catalyst droplet. In this work, we study the formation by molecular beam epitaxy of self-catalyzed GaAs nanowires with AlxGa1-xAs insertions. The composition profiles are extracted and analyzed with monolayer resolution using high-angle annular dark-field scanning transmission electron microscopy. We test successfully several growth procedures to sharpen the heterointerfaces. For a given nanowire geometry, prefilling the droplet with Al atoms is shown to be the most efficient way to reduce the width of the GaAs/AlxGa1-xAs interface. Using the thermodynamic data available in the literature, we develop numerical and analytical models of the composition profiles, showing very good agreement with experiments. These models suggest that atomically sharp interfaces are attainable for catalyst droplets of small volumes.

Enhanced plasmonic properties of gold-catalysed semiconductor nanowires

A key challenge for the development of plasmonic nanodevices is their integration into active semiconducting structures. Gold-catalysed semiconductor nanowires are promising candidates for their bottom-up growth process that aligns a single gold nanoparticle at each nanowire apex. Unfortunately these show extremely poor plasmonic properties. In this work, we propose a way to enhance their plasmonic resonance up to those of ideal and isolated gold nanoparticles. A suitable purification protocol compatible with GaAs and ZnSe molecular beam epitaxy of nanowires is used to produce plasmonic active nanowires, which were used to enhance the Raman signal of pentacene and graphene oxide. Enhancement factors up to three orders of magnitude are demonstrated.

Bundling of GaAs nanowires: a case of adhesion-induced self-assembly of nanowires

The origin of deflections of semiconductor nanowires (NWs) induced by an electron beam in scanning electron microscopy has been subject to different interpretations. Similarly, the subsequent clumping together of NWs into bundles is frequently observed, but no interpretation has yet been advanced. Here we present results on the bundling of NWs following the intentional bending by an electron beam. Furthermore, we extend the concept of lateral collapse, usually applied to fibrillar architectures mimicking the adhesiveness of natural surfaces (the so-called Gecko effect), to analyze the mechanism of the NW bundle formation. We demonstrate how the geometry of the NW arrays and the mechanical properties of the composing materials govern bundling and how these parameters should be taken into account in the design of NW arrays both for avoiding vertical misalignment when detrimental and for achieving patterning of NW arrays into nanoarchitectures.

Eicosapentaenoic acid modulates CyA-induced proinflammatory cytokine over-expression in osteoblastic cells in vitro

Several adverse outcomes are reported in subjects undergoing long term Cyclosporin A (CyA) treatment. Severe osteopenia has been described in clinical and experimental reports, while beneficial effects of n-3 polyunsaturated fatty acids (PUFAs) on bone metabolism are recognized. In the present study we investigated the effects of n-3 versus n-6 PUFAs on osteoblastic cells treated with CyA, evaluating the expression of interleukin (IL)-1ß, interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) in two different experimental protocols and the production of IL-6, IL-1ß, and tumor necrosis factor alpha (TNFalpha) in cells challenged simultaneously with CyA and eicosapentaenoic acid (EPA) for 48h. IL-1ß and IL-6 up-regulation, induced by CyA, was counteracted by the addition of EPA in both protocols; on the contrary, arachidonic acid (AA) magnified CyA the effects. COX-2 and iNOS levels were not modified by CyA treatment. These in vitro results, that substantiate clinical reports of CyA-induced osteopenia, demonstrate a beneficial effect of EPA on CyA-altered cytokine profile, opening new perspectives in the non-pharmacological management of adverse outcomes in CyA-treated patients.

Polyunsaturated fatty acids and renal fibrosis: pathophysiologic link and potential clinical implications

The role of polyunsaturated fatty acids in renal fibrosis. Several studies suggest a close relationship between polyunsaturated fatty acids (PUFA) and renal inflammation and fibrosis, which are crucial stages in chronic kidney disease (CKD). Beneficial effects of n-3 PUFA on the course of experimental and human nephropathies have been reported. PUFA can ameliorate chronic, progressive renal injury beyond the simple reduction of serum lipid levels. These pleiotropic effects of PUFA are due to their properties of interfering with the synthesis of a variety of inflammatory factors and events, through effects related both to the modulation of the balance of n-6 and n-3-derived eicosanoids and to direct action on the cellular production of the major cytokine mediators of inflammation and on endothelium function. The mechanisms by which PUFA can favorably interfere with some stages in renal fibrosis processes, such as mesangial cell activation and proliferation and extracellular matrix protein synthesis, include the regulation of some pro-inflammatory cytokine production, renin and nitric oxide (NO) systems and peroxisome proliferator-activated receptor gene expression. An optimal n-6/n-3 PUFA ratio dietary intake could offer new therapeutic strategies aimed at interrupting the irreversible process of renal fibrosis and ameliorating chronic renal injury. However, further experimental, epidemiological and clinical investigations are needed to confirm the role of PUFA in the renal fibrosis pathway and the natural history of chronic nephropathies.

Fatty acids and cytokine mRNA expression in human osteoblastic cells: a specific effect of arachidonic acid

Epidemiological, clinical and experimental evidence suggests that fatty acids have a modulatory effect on bone metabolism in animals and humans. To investigate this hypothesis, we evaluated the effects of three different fatty acids, arachidonic acid (AA), eicosapentaenoic acid (EPA) and oleic acid (OA), on the expression of cytokines involved in bone remodelling. Cytokine mRNAs in the human osteoblast-like cell line MG-63 were quantified by reverse transcription-PCR. AA induced increased expression of interleukin-1alpha, interleukin-1beta, tumour necrosis factor-alpha and macrophage colony-stimulating factor mRNAs in a time- and dose-dependent manner. EPA and OA had no stimulatory effects, but instead caused a significant inhibition of AA-induced cytokine mRNA expression. Cell treatment with calphostin C, an inhibitor of protein kinase C (PKC), and cellular PKC down-regulation experiments independently resulted in significant inhibition of AA-induced cytokine expression, suggesting that a PKC-dependent mechanism accounts for the effects of AA on cytokine production. In conclusion, our study demonstrates specific effects of fatty acids on cytokine gene expression in human osteoblast-like cells. The clinical relevance of our findings requires further investigation.

Stage-specific expression of Gadd45 induced by X-irradiation in rat spermatogenesis

PURPOSE

Gadd45 is involved in the response to DNA damage in somatic cells. The effect of X-irradiation and chemical treatments on expression of Gadd45 and two other 53-regulated genes, p21 and cyclin-G, was studied in rat testis.

MATERIALS AND METHODS

The reverse-transcriptase polymerase chain reaction (RT-PCR) was performed on testis extracts of control, X-irradiated (6Gy), etoposide (10 mg kg(-1)) and adriamycin (5mg kg(-1))-treated rats. For stage-specific analysis, seminiferous tubules were isolated and segments representing the 14 epithelial stages were obtained.

RESULTS

In whole testis extracts, increases in Gadd45, p21 and cyclin-G expression were detectable after irradiation, but not after etoposide or adriamycin treatments. Analysis of fractions consisting of defined epithelial stages showed a high expression of Gadd45 in stages VII-XII and of p21 in stages VII-VIII. Irradiation significantly increased the level of Gadd45 mRNA in stages VI-VIII and of p21 mRNA in stages VI-I. Although no overall increase could be observed in whole testis samples of the etoposide-treated rat, stage-specific analysis revealed an induction of p21 expression in stages XIII-I. Gadd45 and cyclin-G mRNA were localized to spermatocytes and round spermatids known to express p21.

CONCLUSIONS

Although X-irradiation, etoposide and adriamycinare known spermatogenic mutagens and activators of apoptosis, only X-rays induce slightly Gadd45 expression in testis. This small induction was very stage specific.

Specific modulatory effect of arachidonic acid on human red blood cell oxalate transport: clinical implications in calcium oxalate nephrolithiasis

Greater arachidonic acid (AA) contents, which were correlated with erythrocyte transmembrane oxalate (Ox) transport, were observed in plasma and erythrocyte membrane phospholipids of patients with idiopathic calcium renal stones, suggesting a link between membrane phospholipid fatty acid composition and cellular Ox transport. To confirm this hypothesis, the effects of exogenous red blood cell incorporation of three different fatty acids (i.e., oleic acid, AA, and eicosapentaenoic acid) on Ox transport and the phosphorylation status of band 3 protein, which has been shown to mediate red blood cell Ox flux, were investigated. Preincubation of erythrocytes with AA induced a dose-dependent increase in the phosphorylation level of band 3 protein and an increase in transmembrane Ox self-exchange. In contrast, inhibitory effects on both parameters were observed after the incorporation of oleic and eicosapentaenoic acids. These data, together with previous observations of dietary effects on erythrocyte Ox transport and urinary Ox excretion, indicate that genetic and/or nutritional changes in membrane phospholipid fatty acid composition play a crucial role in modulating cellular Ox transport in idiopathic calcium Ox nephrolithiasis.

PRINS localization of centromeres and telomeres in micronuclei indicates that in mouse splenocytes chromatid non-disjunction is a major mechanism of aneuploidy

Primed In Situ DNA Synthesis (PRINS) of telomeric and centromeric (minor satellite DNA) sequences has been applied together with the cytokinesis block micronucleus (MN) assay in mouse splenocytes, with the aim of understanding the mechanism of origin of spontaneous and induced MN. Splenocyte cultures were treated in vitro either with the clastogenic agent mitomycin C or with the aneugenic compound colcemid. The relative proportions of MN carrying 1 to 4 telomeric signals were in agreement with the known mechanism of action of the chemicals tested, i.e., an higher number of MN with less than 4 telomeres were found in MMC-than in colcemid-treated cultures. No MN lacking the telomeric sequences (0 spot) were found, indicating that the observed distributions should not be affected by false-negative data. Furthermore, all MN carrying a single telomere were negative for the centromere, thus indicating that this class represents true chromosome acentric fragments. Finally, MN with 4 telomeric spots always carried the centromeric sequence, as expected on the hypothesis that these MN correspond to whole chromosomes. With respect to centromere-positive MN, more than one half carried 4 telomeric signals (whole chromosomes), and only 1/4 or less showed 2 telomeric signals (probably corresponding to a single chromatid). This difference was statistically significant, either in untreated cultures or in cultures exposed to mitomycin C or colcemid. On the whole, these data indicate that non-disjunction followed by whole chromosome loss (with the production of two daughter monosomic nuclei) may be the main mechanism of malsegregation leading to MN formation.