Monopolar and dipolar relaxation in spin ice Ho2Ti2O7

Ferromagnetically interacting Ising spins on the pyrochlore lattice of corner-sharing tetrahedra form a highly degenerate manifold of low-energy states. A spin flip relative to this "spin-ice" manifold can fractionalize into two oppositely charged magnetic monopoles with effective Coulomb interactions. To understand this process, we have probed the low-temperature magnetic response of spin ice to time-varying magnetic fields through stroboscopic neutron scattering and SQUID magnetometry on a new class of ultrapure Ho₂Ti₂O₇ crystals. Covering almost 10 decades of time scales with atomic-scale spatial resolution, the experiments resolve apparent discrepancies between prior measurements on more disordered crystals and reveal a thermal crossover between distinct relaxation processes. Magnetic relaxation at low temperatures is associated with monopole motion through the spin-ice vacuum, while at elevated temperatures, relaxation occurs through reorientation of increasingly spin-like monopolar bound states. Spin fractionalization is thus directly manifest in the relaxation dynamics of spin ice.

Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb_{2}Si_{2}O_{7}

The quantum dimer magnet (QDM) is the canonical example of quantum magnetism. The QDM state consists of entangled nearest-neighbor spin dimers and often exhibits a field-induced triplon Bose-Einstein condensate (BEC) phase. We report on a new QDM in the strongly spin-orbit coupled, distorted honeycomb-lattice material Yb_{2}Si_{2}O_{7}. Our single crystal neutron scattering, specific heat, and ultrasound velocity measurements reveal a gapped singlet ground state at zero field with sharp, dispersive excitations. We find a field-induced magnetically ordered phase reminiscent of a BEC phase, with exceptionally low critical fields of H_{c1}∼0.4 and H_{c2}∼1.4  T. Using inelastic neutron scattering in an applied magnetic field we observe a Goldstone mode (gapless to within δE=0.037  meV) that persists throughout the entire field-induced magnetically ordered phase, suggestive of the spontaneous breaking of U(1) symmetry expected for a triplon BEC. However, in contrast to other well-known cases of this phase, the high-field (μ_{0}H≥1.2  T) part of the phase diagram in Yb_{2}Si_{2}O_{7} is interrupted by an unusual regime signaled by a change in the field dependence of the ultrasound velocity and magnetization, as well as the disappearance of a sharp anomaly in the specific heat. These measurements raise the question of how anisotropy in strongly spin-orbit coupled materials modifies the field induced phases of QDMs.

Bone marrow mast cell immunophenotyping in adults with mast cell disease: a prospective study of 33 patients

The aberrant co-expression of CD2 and CD25 antigens is the immunophenotypic hallmark of neoplastic mast cells, and has been consistently identified on bone marrow mast cells from patients with indolent mast cell disease (MCD). We prospectively analyzed the bone marrow mast cell immunophenotype by multiparametric flow cytometry (FC) for 33 MCD cases, to examine the role of CD2 and CD25 expression in establishing diagnosis, detecting histologically occult bone marrow mast cell infiltration, and assessing treatment response. While CD25 was almost uniformly expressed, only 6 of 13 patients with indolent MCD, 1 of 8 with aggressive MCD, 2 of 7 with MCD and an associated hematological disorder, and none of the 2 patients with either mast cell leukemia or smoldering systemic mastocytosis, expressed CD2. One of three patients with cutaneous mastocytosis had an aberrant CD2+/CD25+ mast cell population suggesting histologically occult bone marrow involvement. CD25 expression was lost in one patient who achieved complete histologic remission with therapy, but not in two patients who achieved a partial remission. In conclusion, CD25, but not CD2, is a reliable marker for neoplastic mast cells, and CD25 expression indicates histologically occult bone marrow infiltration and residual disease after therapy.

Imatinib for systemic mast-cell disease

Imatinib has shown to be effective against malignant disease driven by ckit. We prospectively treated 12 adults with symptomatic systemic mast-cell disease at a dose of either 100 mg or 400 mg per day. Of the ten patients who we could assess for response, five (50%) had a measurable response to the drug, four of whom had important mast-cell cytoreduction and two who had complete clinical and histological remission. In the five patients with eosinophilia, three had complete clinical and haematological remission. The other two, who did not respond to treatment, were the only patients with the ckit D816V mutation. Our results suggest that imatinib either inhibits the growth-promoting role of wild type ckit, or targets an oncogenic kinase.

In vitro antiproliferative activity of the farnesyltransferase inhibitor R115777 in hematopoietic progenitors from patients with myelofibrosis with myeloid metaplasia

R115777 is an orally bioavailable farnesyltransferase inhibitor (FTI) that has displayed encouraging activity in patients with acute myeloid leukemia. To determine whether R115777 might exert similar activity in myelofibrosis with myeloid metaplasia (MMM), we evaluated its effects on circulating myeloid progenitor cells from patients with MMM (n=25) using in vitro colony-forming assays. The median R115777 concentrations that inhibited colony formation by 50% were 34 and 2.7 nM for myeloid and megakaryocytic colonies from MMM patients, respectively. Progenitors from normal controls and patients with other myeloproliferative disorders demonstrated similar sensitivity. Since the ras polypeptides are one putative target of FTIs, the potential role of ras effectors was examined by incubating parallel progenitor assays with the phosphatidyl-inositol-3 (PI-3) kinase inhibitor LY294002 and the mitogen-activated protein kinase 1 inhibitor PD98059. MMM progenitor colonies (n=7) were highly sensitive to LY294002 but not to PD98059, implying that the PI-3 kinase pathway may be critical for survival and proliferation of these cells. In addition to indicating that MMM progenitors are sensitive to clinically achievable R115777 concentrations in vitro, these results provide a potential explanation for the thrombocytopenia observed with R115777 during the treatment of other hematologic malignancies.

Transcription activation parameters at ara pBAD

We studied the formation of open complexes of RNA polymerase and promoter DNA as activated by the AraC protein at the Escherichia coli araBAD promoter pBAD and by the cyclic AMP receptor protein at the galKTE promoter P1. The DNA migration retardation assay was demonstrated to be suitable for the detection and quantitation of open complexes by the correspondence in the properties of open complexes in solution and retarded complexes observed in gels. These included, on the ara promoter, heparin resistance, lifetime, DNAseI footprinting, exonuclease III footprinting, permanganate footprinting and disappearance upon transcription, and on the gal promoter, the correspondence between the kinetic parameters Kd and k2 obtained with established techniques and those obtained with the migration retardation assay. On the pBAD promoter we obtained kinetic parameters of Kd = 0.3 nM and K2 = 1 minute(-1). The unusually tight binding of polymerase in the presence of AraC suggests that AraC binds polymerase tightly.

AraC protein can activate transcription from only one position and when pointed in only one direction

At the araBAD promoter, the RNA polymerase-proximal half-site for AraC binding partially overlaps the -35 region. Random and explicit spacing experiments show that both this partial overlapping and AraC binding to the polymerase-proximal half-site are necessary and sufficient for strong transcriptional activation. Normally, this occupancy is generated by the presence of arabinose, which shifts AraC from a DNA looping interaction involving the polymerase-distal half-site and the araO2 site 210 base-pairs away, to an interaction with the two half-sites adjacent to RNA polymerase. Changing the polymerase-proximal half-site to a higher affinity AraC binding site gives activation in the absence of arabinose. Thus, arabinose is not required to transform AraC into an activating conformation. Because the two half-sites of araI are direct repeats, the RNA polymerase proximal and distal surfaces of AraC are not identical. When the araI site was turned around, no spacings were found from which AraC could activate transcription. In light of the strict spacing and orientation requirements for AraC activation, the interactions between AraC and RNA polymerase are likely to be specific and inflexible.

An evaluation of human neurophysin production in Alzheimer's disease: preliminary observations

The concentrations of human neurophysins in the cerebrospinal fluid (CSF) of nine patients with Alzheimer's disease: Preliminary observations. (AD), and one patients with Pick's disease, were determined using specific radioimmunoassays (RIAs). Concentrations of vasopressin and oxytocin were also measured. Values were compared with those from 20 age-matched mentally normal individuals who were being treated for back pain. CSF levels of vasopressin-associated human neurophysin (VP-HNP) and oxytocin-associated human neurophysin (OT-HNP) in patients with AD (22 +/- 4 fmol/ml and 104 +/- 17 fmol/ml) were only 42% and 58% of those in the control subjects (p less than 0.0001, p less than 0.0004). Vasopressin levels for these patients (3.6 +/- 0.4 fmol/ml) were also significantly reduced to 51% of controls (p less than 0.007) and oxytocin levels were marginally (p = 0.092) reduced to 70% of controls. Because neurophysins and neuropeptides are gene-related products of vasopressin-neurons and oxytocin-neurons, the data indicate that these neurons are functionally impaired in patients with AD. Plasma neurophysin values suggest this impairment is confined to neurons with centrally-directed axons. Data from the one patient with Pick's disease demonstrates that reduced CSF levels of neurophysins and hormones is not confined to Alzheimer-type dementia.

Mapping, sequence, and apparent lack of function of araJ, a gene of the Escherichia coli arabinose regulon

We report the mapping, sequencing, and study of the physiological role of the fourth arabinose-inducible operon from Escherichia coli, araJ. It is located at 9 min on the chromosome and codes for a single 42-kDa protein that shows no significant homology to other known proteins. Destruction of the chromosomal araJ gene does not detectably affect either of the two arabinose transport systems, the ability of cells to grow on arabinose, or the induction kinetics of the araBAD operon, and thus the physiological role of AraJ, if any, remains unknown. We have also found a long open reading frame upstream of araJ. The sequence of this upstream open reading frame was found to be identical to the previously reported sequence of the sbcC gene (I. S. Naom, S. J. Morton, D. R. F. Leach, and R. G. Lloyd, Nucleic Acids Res. 17:8033-8044, 1989). The carboxyl region of SbcC has an amino acid sequence consistent with this region of SbcC forming an extended alpha-helical coiled-coil.

Continuous intratumoral infusion of methotrexate for recurrent glioblastoma: a pilot study

Five patients with documented recurrences of glioblastoma multiforme were given continuous infusions of methotrexate delivered intratumorally using implantable catheters and subcutaneous refillable pumps. A continuous infusion of methotrexate (1 mg/d) was begun with concomitant oral administration of folinic acid. The methotrexate dose was increased every 2 weeks to 3, 10, 30, and, ultimately, 75 mg/d in two patients. Samples of serum and ventricular cerebrospinal fluid (CSF) were obtained to determine the levels of methotrexate and total bioactive folates, and brain tissue was obtained from two patients for determination of methotrexate concentration. The patients survived from 7 to 49 weeks after the implantation of the infusion device. Neither the clinical examination nor sequential radiological studies gave clear evidence of reduction in tumor size. Pneumonia developed in one patient, and mild hepatitis and increased seizure frequency in another. Methotrexate was stable in the delivery system over 12 days, and ventricular CSF reached steady-state levels by 5 days. Steady-state ventricular CSF levels of methotrexate were higher than serum levels in some patients, while the reverse was true in others. Levels of total bioactive folates in the CSF did not increase above the normal range. Methotrexate concentrations were highest at the center of the tumor, but measurable amounts of methotrexate were detectable in all areas of the brain. At autopsy in four patients, variable liquefactive necrosis of the brain tumors was seen, and viable tumor was found at the periphery of the tumor bed. These preliminary results suggest that it is technically feasible to infuse methotrexate into brain tumor cavities, and show that little central nervous system or systemic toxicity was encountered in five patients. Better delineation of the safety and efficacy of this therapeutic approach will require further clinical trials.

The spectrum of imaging and neuropsychological findings in Pick's disease

To seek improved methods for the diagnosis of Pick's disease, we reviewed imaging studies of four women and two men (ages 48 to 65 years at onset) and psychometric testing of three of them with autopsy or biopsy-proved Pick's. The presence of Pick bodies was required for the diagnosis. Seven patients with biopsy-proved Alzheimer's disease served as a comparison group. In the Pick's patients, CT in five of six showed marked frontal pole or temporal pole atrophy, which clearly differed from the pattern of cerebral atrophy seen in the Alzheimer's patients. Psychometric testing showed performance patterns that tended to differ from those of the Alzheimer's patients in that recent memory was relatively preserved despite marked impairment of executive functions. The distinctive psychometric pattern in the Pick's patients was evanescent, however. Thus, there were imaging and psychometric findings of potential diagnostic value for Pick's disease, but, for different reasons, they were imperfect.