Infrared- and Raman-spectroscopy measurements of a transition in the crystal structure and a closing of the energy gap of BiTeI under pressure

BiTeI is a giant Rashba spin splitting system, in which a noncentrosymmetric topological phase has recently been suggested to appear under high pressure. We investigated the optical properties of this compound, reflectivity and transmission, under pressures up to 15 GPa. The gap feature in the optical conductivity vanishes above p∼9  GPa and does not reappear up to at least 15 GPa. The plasma edge, associated with intrinsically doped charge carriers, is smeared out through a phase transition at 9 GPa. Using high-pressure Raman spectroscopy, we follow the vibrational modes of BiTeI, providing additional clear evidence that the transition at 9 GPa involves a change of crystal structure. This change of crystal structure possibly inhibits the high-pressure topological phase from occurring.

Chronic treatment with tetrahydrobiopterin reverses endothelial dysfunction and oxidative stress in hypercholesterolaemia

BACKGROUND

Reduced availability of tetrahydrobiopterin (BH(4)), an essential cofactor of nitric oxide (NO) synthase (NOS), decreases NO production and increases reactive oxygen species. Both mechanisms contribute to atherosclerotic vascular disease. Although acute supplementation of BH(4) improves endothelial dysfunction, the effect of chronic BH(4) in humans is unknown.

OBJECTIVE

To investigate the effect of chronic BH(4) supplementation on endothelial function and oxidative stress in hypercholesterolaemia.

DESIGN

Randomised double-blind, placebo-controlled trial.

SETTING

University Hospital.

PATIENTS

22 hypercholesterolaemic patients (low-density lipoprotein (LDL) >4.5 mmol/l) were randomised to 4 weeks of oral BH(4) (400 mg twice daily) or placebo. Age-matched healthy volunteers served as controls.

MAIN OUTCOME MEASURES

Endothelium-dependent and -independent vasodilatation was assessed by venous occlusion plethysmography. To elucidate the mechanisms of BH(4) effect, NO release and superoxide anion (O(2)(-)) production were measured in human aortic endothelial cells exposed to native LDL (2.6 mmol cholesterol/l).

RESULTS

BH(4) plasma levels were significantly increased by oral supplementation. NO-mediated vasodilatation to acetylcholine was reduced in patients compared with controls and restored by BH(4). No effect of BH(4) on endothelium-independent vasodilatation was seen. Furthermore, 8-F(2 )isoprostane plasma levels, a marker of vascular oxidative stress, were reduced by BH(4). In LDL-treated endothelial cells, BH(4) levels and NO release were reduced and O(2)(-) production increased compared with control cells. Exogenous BH(4) normalised NO and O(2)(-) production.

CONCLUSIONS

In hypercholesterolaemia, endothelial dysfunction and oxidative stress can be reversed by chronic oral treatment with BH(4). Thus, BH(4) availability is essential for maintaining NO synthesis and low O(2)(-) production by endothelial NOS in vivo, and may provide a rational therapeutic approach to prevent cardiovascular disease.

Clinical comparison of xylazine and medetomidine for premedication of horses

OBJECTIVE

To compare the analgesic and cardiopulmonary effects of medetomidine and xylazine when used for premedication of horses undergoing general anesthesia.

DESIGN

Randomized clinical trial.

ANIMALS

40 horses.

PROCEDURE

Twenty horses were premedicated with medetomidine (10 microg/kg [4.5 microg/lb], i.m.) and the other 20 were premedicated with xylazine (2 mg/kg [0.9 mg/kg], i.m.). Horses were then anesthetized with a combination of guaifenesin and ketamine; anesthesia was maintained with halothane. Additional doses of medetomidine or xylazine were given if horses were not sufficiently sedated at the time of anesthetic induction. After induction of anesthesia, sodium pentothal was administered as necessary to prevent limb movements. Hypotension was treated with dobutamine; hypoventilation and hypoxemia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored.

RESULTS

Scores for the quality of the transition to inhalation anesthesia were significantly higher for horses premedicated with medetomidine than for horses premedicated with xylazine. However, other scores, recovery times, and numbers of attempts needed to achieve sternal recumbency and to stand were not significantly different between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that medetomidine is suitable for premedication of horses undergoing general anesthesia. Analgesic and cardiopulmonary effects of medetomidine were similar to those of xylazine, except that the transition to inhalation anesthesia was smoother when horses were premedicated with medetomidine, rather than xylazine.

Infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses

OBJECTIVE

To evaluate effects of infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses.

DESIGN

Randomized clinical trial.

ANIMALS

40 horses.

PROCEDURE

Horses were premedicated with xylazine and anesthetized with diazepam and ketamine. Anesthesia was maintained by infusion of guaifenesin, ketamine, and medetomidine and inhalation of sevoflurane (20 horses) or by inhalation of sevoflurane (20 horses). A surgical plane of anesthesia was maintained by controlling the inhaled concentration of sevoflurane. Sodium pentothal was administered as necessary to prevent movement in response to surgical stimulation. Hypotension was treated with dobutamine; hypoxemia and hypercarbia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored.

RESULTS

The delivered concentration of sevoflurane (ie, the vaporizer dial setting) was significantly lower and the quality of transition to inhalation anesthesia and of anesthetic maintenance were significantly better in horses that received the guaifenesin-ketamine-medetomidine infusion than in horses that did not. Five horses, all of which received sevoflurane alone, required administration of pentothal. Recovery time and quality of recovery were not significantly different between groups, but horses that received the guaifenesin-ketamine-medetomidine infusion required fewer attempts to stand.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that in horses, the combination of a guaifenesin-ketamine-medetomidine infusion and inhalation of sevoflurane resulted in better transition and maintenance phases while improving cardiovascular function and reducing the number of attempts needed to stand after the completion of anesthesia, compared with inhalation of sevoflurane.

Effects of intravenous infusion of lipid-free apo A-I in humans

Apolipoprotein (apo) A-I is the principal protein component of the plasma high density lipoproteins (HDLs). Tissue culture studies have suggested that lipid-free apo A-I may, by recruiting phospholipids (PLs) and unesterified cholesterol from cell membranes, initiate reverse cholesterol transport and provide a nidus for the formation, via lipid-poor, pre-beta-migrating HDLs, of spheroidal alpha-migrating HDLs. Apo A-I has also been shown to inhibit hepatic lipase (HL) and lipoprotein lipase (LPL) in vitro. To further study its functions and fate in vivo, we gave lipid-free apo A-I intravenously on a total of 32 occasions to six men with low HDL cholesterol (30 to 38 mg/dL) by bolus injection (25 mg/kg) and/or by infusion over 5 hours (1.25, 2.5, 5.0, and 10.0 mg.kg-1.h-1). The procedure was well tolerated: there were no clinical, biochemical, or hematologic changes, and there was no evidence of allergic, immunologic, or acute-phase responses. The 5-hour infusions increased plasma total apo A-I concentration in a dose-related manner by 10 to 50 mg/dL after which it decreased, with a half-life of 15 to 54 hours. Coinfusion of Intralipid reduced the clearance rate. The apparent volume of distribution exceeded the known extracellular space in humans, suggesting extensive first-pass clearance by one or more organs. No apo A-I appeared in the urine. Increases in apo A-I mass were confined to the pre-beta region on crossed immunoelectrophoresis of plasma and to HDL-size particles on size exclusion chromatography. Increases were recorded in HDL PL, but not in HDL unesterified or esterified cholesterol. Increases also occurred in LDL PL and in very low density lipoprotein cholesterol, triglycerides, and PL but not in plasma total apo B concentration. These results can all be explained by combined inhibition of HL and LPL activities. Owing to the effects that this would have had on HDL metabolism, no conclusions can be drawn from these data about the role of lipid-free apo A-I in the removal of PL and cholesterol from peripheral tissues in humans. The kinetic data suggest that the fractional catabolic rate of lipid-free apo A-I exceeds that of spheroidal HDLs and is reduced in the presence of surplus PL.

Chemical and biological properties of a cationic Tc-tetraamine complex

The complex of 99Tc with the ligand 1,4,8,11-tetraazaundecane (2,3,2-tet) was prepared and was compared with the similar 99Tc complexes with ethylenediamine and 1,4,8,11-tetraazacyclotetradecane. The results are all consistent with the formula [TcO2(2,3,2-tet)]+. The biological behavior was tested with 99mTc in Wistar rats. A fast clearance via the kidneys was found, and no accumulation in any other organ was observed.

Two detergent-insoluble proteins of the human lymphocyte membrane are enriched in an isolated membrane fraction

Human lymphocytes isolated from peripheral blood on Ficoll/Paque density gradients were surface-labelled by 125I/lactoperoxidase or 3H/reductive alkylation and lysed in buffer solutions containing non-ionic or amphoteric detergents (octylphenylpolyoxyethylenes, octylglucoside, cholylamidopropyldimethylammoniopropane sulfonate) under a variety of conditions. The cell lysate was fractionated by sedimentation or by density gradient centrifugation. The large majority of the labelled proteins is solubilized by the detergents. Two proteins of 45 000 and 30 000 molecular weight are the main detergent-insoluble, surface-labelled components. They can be fractionated from detergent lysates of cells in relatively pure form from the other membrane proteins and from nuclear material on density gradients. The same two proteins are specifically enriched in a membrane fraction isolated from a detergent-free cell homogenate by density gradient centrifugation. Cytoskeletal and other intracellular proteins remain associated with these two proteins when fractionated by either of these two independent methods.

Human lymphocyte membrane proteins treated with neuraminidase

Human peripheral blood lymphocytes were surface-iodinated, treated with neuraminidase from Vibrio cholerae and lysed with non-ionic detergent. In addition, surface membrane fractions were isolated from surface-iodinated cells in the absence of detergents and treated with neuraminidase after membrane isolation. The effect of neuraminidase treatment on the membrane proteins was studied by two-dimensional gel electrophoresis. One surface-labelled protein of 45 000 molecular weight which is characterized by its association with the detergent-resistant matrix of the cells and by its specific enrichment in an isolated membrane fraction, was found to be particularly sensitive to neuraminidase treatment both of intact cells and isolated membranes. A prominent labelled protein of apparent molecular weight of 60 000 is observed in the soluble fraction after neuraminidase treatment of intact cells. The analogous protein is detected when isolated membrane fractions are treated with neuraminidase.