Local spin dynamics in magnetic molecular chains studied by NMR and μSR

We present NMR and μ⁺SR study of spin dynamics in one-dimensional and quasi-one-dimensional molecular magnets of recent synthesis. In particular, we focus on the so called Gd(hfac)₃NIT-R and CoPhOMe magnetic chains families. For Gd-R helimagnets we show some differences between “weakly frustrated systems” and “fully frustrated systems”. The different behaviour is due to the different radical inserted in the chains (R = Me, Ph for “weakly frustrated systems” and R = iPr, Et for “fully frustrated systems”). The existence of different phase transitions, particularly to 3D long-range magnetic order in Gd-Ph and to chiral order in Gd-iPr, is remarked together with a comparison between results obtained from macroscopic and microscopic investigating techniques. As regards CoPhOMe slowly relaxing chain, the ¹H NMR measurements confirm the freezing of the spins at low temperature, which prevents the 3D long-range order, and display the presence of two relaxation mechanisms related to distinct contributions to the local spin relaxation.     

Further characterization of mitochondrial protein phosphatase.

Mitochondrial protein phosphatase from rat liver exhibits rather wide substrate specificity, since it readily dephosphorylates, besides phosvitin, casein, and cytosol phosphoproteins, also ATP, ADP, inorganic pyrophosphate, p-nitrophenylphosphate.Aliphatic phosphate esters (β-glycerophosphate, glucose-6-P, serine-phosphate) are not dephosphorylated to any detectable extent.Evidence for the participation of a single enzyme in the dephosphorylation of phosvitin and ATP is provided. However, the different affinity toward the two substrates and other evidence suggest that the enzyme has in vivo the biological role of dephosphorylating, at least preferentially, the phosphoproteins.     

Fatigue of the plantar intrinsic foot muscles increases navicular drop

Our purpose was to assess the effect of foot intrinsic muscle fatigue on pronation, as assessed with navicular drop, during static stance. Twenty-one healthy young adults participated. Navicular drop was measured before and after fatiguing exercise of the plantar foot intrinsic muscles. Surface electromyography of the abductor hallucis muscle was recorded during maximum voluntary isometric contractions (MVIC) in order to find the baseline median frequency (MedF). Subjects then performed sets of 75 repetitions of isotonic flexion contractions of the intrinsic foot muscles against a 4.55 kg weight on a custom pulley system. After each set an MVIC was performed to track shifts in MedF. After a MedF shift of at least 10%, navicular drop measurements were repeated. Subjects exhibited 10.0 ± 3.8 mm of navicular drop at baseline and 11.8 ± 3.8 mm after fatigue (p < 0.0005). The change in navicular drop was significantly correlated with change in MedF (r = .47, p = .03). The intrinsic foot muscles play a role in support of the medial longitudinal arch in static stance. Disrupting the function of these muscles through fatigue resulted in an increase in pronation as assessed by navicular drop.     

Magnetic Nanoparticles from Magnetospirillum gryphiswaldense Increase the Efficacy of Thermotherapy in a Model of Colon Carcinoma

Magnetic nanoparticles (MNPs) are capable of generate heating power under the influence of alternating magnetic fields (AMF); this behaviour recently opened new scenarios for advanced biomedical applications, mainly as new promising tumor therapies. In this paper we have tested magnetic nanoparticles called magnetosomes (MNs): a class of MNPs naturally produced by magnetotactic bacteria. We extracted MNs from Magnetospirillum gryphiswaldense strain MSR-1 and tested the interaction with cellular elements and anti-neoplastic activity both in vitro and in vivo, with the aim of developing new therapeutic approaches for neoplastic diseases. In vitro experiments performed on Human Colon Carcinoma HT-29 cell cultures demonstrated a strong uptake of MNs with no evident signs of cytotoxicity and revealed three phases in the interaction: adherence, transport and accumulation in Golgi vesicles. In vivo studies were performed on subcutaneous tumors in mice; in this model MNs are administered by direct injection in the tumor volume, then a protocol consisting of three exposures to an AMF rated at 187 kHz and 23kA/m is carried out on alternate days, over a week. Tumors were monitored by Magnetic Resonance Imaging (MRI) to obtain information about MNs distribution and possible tissue modifications induced by hyperthermia. Histological analysis showed fibrous and necrotic areas close to MNs injection sites in mice subjected to a complete thermotherapy protocol. These results, although concerning a specific tumor model, could be useful to further investigate the feasibility and efficacy of protocols based on MFH. Magnetic nanoparticles naturally produced and extracted from bacteria seem to be promising candidates for theranostic applications in cancer therapy.     

Melphalan-induced DNA damage in p53(+/-) and wild type mice analysed by the comet assay

Melphalan is an alkylating substance used as a therapeutic agent; its mutagenicity is related to its ability to produce monoadducts and to form DNA cross-links. The alkaline comet assay is a useful test for the detection of DNA lesions. However, cross-links are not easily detected under standard conditions. Recently, modifications to the test have been introduced to measure cross-links by evaluating the reduction in induced DNA migration.

In this work, the standard comet assay and an assay modified by prolonging the electrophoresis time have been applied to evaluate DNA lesions induced by single, 4 or 26 weekly oral administrations of melphalan to p53^+/− knockout and to isotype parental mice. Cells were analysed from the liver, bone marrow, peripheral blood and the distal intestine. Moreover, a further protocol in which the presence of cross-links was inferred by the reduction in X-ray-induced DNA migration was applied to bone marrow cells and the sensitivity of the different methods was compared.

The majority of groups examined by the standard protocol showed no difference compared to controls, while the modified protocol (prolonged electrophoresis time) could detect a retarded DNA migration in cells from all the organs analysed with the exception of bone marrow cells.

Only the protocol based on X-ray in vitro irradiation showed the presence of melphalan-induced cross-links in bone marrow cells exposed to 2 mg/kg for 4 weeks, demonstrating that this was the most sensitive approach for detecting this type of lesion.

DNA lesions were evident in all the organs analysed. However, results suggest that the kinetics of cross-link repair could be different in bone marrow cells compared to other organs tested. After comparison between genotype-matched treated and control groups, a significant effect was shown more frequently in p53^+/− than in wild type groups.     

An investigation of the substrate specificity of protein phosphatase 2C using synthetic peptide substrates; comparison with protein phosphatase 2A

The synthetic phosphopeptide RRATpVA was found to be the most effective substrate for protein phosphatase 2C (PP2C) so far identified. Replacement of phosphothreonine by phosphoserine decreased activity over 20-fold and a striking preference for phosphothreonine was also observed with two other substrates (RRSTpTpVA and casein) that were phosphorylated on both serine and threonine. Replacement of the C-terminal valine in RRATpVA by proline abolished dephosphorylation, while exchanging the N-terminal alanine by proline had no effect. The preference for phosphothreonine and the effect of proline are similar to protein phosphatase 2A (PP2A). However, the peptide RRREEETpEEEAA, an excellent substrate for PP2A, was not dephosphorylated by PP2C, and substitution of the C-terminal valine in RRATpVA by glutamic acid reduced the rate of dephosphorylation by PP2C over 10-fold, without affecting dephosphorylation by PP2A. Addition of two extra N-terminal arginine residues to RRASpVA increased PP2A catalysed dephosphorylation 4- to 5-fold, without altering dephosphorylation by PP2C. These results represent the first study of the specificity of PP2C using synthetic peptides, and strengthen the view that this approach may lead to the development of more effective and specific substrates for the serine/threonine-specific protein phosphatases.