Rapamycin-induced hypophosphatemia and insulin resistance are associated with mTORC2 activation and Klotho expression.

Rapamycin, an immunosuppressive drug used to prevent rejection after kidney transplantation, influences phosphate homeostasis, induces insulin resistance and has been shown to prolong lifespan in animal models. Because Klotho is an aging-suppressor gene controlling phosphate metabolism and insulin sensitivity, we investigated the influence of rapamycin on Klotho expression. A total of 100 kidney transplant recipients, 50 chronically treated with rapamycin and 50 with calcineurin inhibitors, were enrolled; 20 healthy subjects were employed as control. In the rapamycin group, serum phosphate was lower than in the CNI group with an increase in phosphate excretion and a reduction in its reabsorption. In addition, rapamycin increased insulin resistance as shown by HOMA index. Rapamycin treatment of an immortalized proximal tubular cell line induced the expression of Klotho, the phosphorylation of AKT in Ser473, downstream target of mTORC2 and the expression of RICTOR, mTORC2 main component. AKT inhibition reduced the rapamycin-induced expression of Klotho. In vivo rapamycin treatment induced higher degree of RICTOR and AKT Ser(473) expression directly correlating with long-term rapamycin exposure, FE(PO4) and HOMA index. In conclusion, our data would suggest that rapamycin may influence phosphate homeostasis and insulin resistance modulating Klotho expression through mTORC2 activation.

Eley-Rideal recombination of hydrogen atoms on a tungsten surface.

The Eley-Rideal recombination reaction of H chemisorbed on the four-fold site of W(001) at a surface temperature T(S) = 500 K is studied using the fully three-dimensional semiclassical collisional model and an accurate potential energy surface for the H-W(001) system. The recombination probability, calculated at different collisional energies in the range (0.05-5) eV, shows a broad maximum around 0.4 for energies between 0.1 eV and 2.5 eV. The exothermic energy partitioning in the final states of the desorbing H(2) molecules shows that, at low impact energies, only the first three vibrational levels of the hydrogen molecule are energetically accessible, while at the higher impact energies vibrational levels up to v = 7 can be populated. The energy exchanged with the phonons surface is small but not negligible.

Depolarization and muscarinic excitation induced in a sympathetic ganglion by vasoactive intestinal polypeptide.

The effects of vasoactive intestinal polypeptide (VIP) in the superior cervical ganglion of the cat were studied in vitro and in vivo with sucrose gap and multiunit recording, respectively. At a dose of 0.03 to 0.12 nanomole, VIP produced a dose-dependent, prolonged (3 to 15 minutes) depolarization of the ganglion and enhanced the ganglionic depolarization elicited by the muscarinic agonist acetyl-beta-methylcholine. At a dose of 1.8 to 10 nanomoles, the peptide enhanced and prolonged the postganglionic discharge elicited by acetyl-beta-methylcholine, enhanced muscarinic transmission in ganglia treated with an anticholinesterase agent, and enhanced the late muscarinic discharge elicited by acetylcholine. VIP did not affect the early nicotinic discharge elicited by acetylcholine or by electrical stimulation of the preganglionic nerve. It is concluded that VIP has a selective facilitatory action on muscarinic excitatory mechanisms in the superior cervical ganglion of the cat.

Oxygen adsorption on beta-cristobalite polymorph: ab initio modeling and semiclassical time-dependent dynamics.

The adsorption dynamics of atomic oxygen on a model beta-cristobalite silica surface has been studied by combining ab initio electronic structure calculations with a molecular dynamics semiclassical approach. We have evaluated the interaction potential of atomic and molecular oxygen interacting with an active Si site of a model beta-cristobalite surface by performing DFT electronic structure calculations. As expected, O is strongly chemisorbed, E(b) = 5.57 eV, whereas molecular oxygen can be weakly adsorbed with a high-energy barrier to the adsorption state of approximately 2 eV. The binding energies calculated for silica clusters of different sizes have revealed the local nature of the O,O(2)-silica interaction. Semiclassical collision dynamic calculations show that O is mainly adsorbed in single-bounce collisions, with a smaller probability for adsorption via a multicollision mechanism. The probability for adsorption/desorption (reflected) collisions at the three impact energies is small but not negligible at the higher energy considered in the trajectory calculations, about P(r) = 0.2 at E(kin) = 0.8 eV. The calculations give evidence of a complex multiphonon excitation-deexcitation mechanism underlying the dynamics of stable adsorption and inelastic reflection collisions.

Isotope and surface temperature effects for hydrogen recombination on a graphite surface.

We highlight the isotope and surface temperature effects for hydrogen atom recombination on a graphite surface. The reaction dynamics is studied using the semiclassical collisional method, according to which the mass and temperature effects are due to the coupling between the H/D dynamics and the dynamics of the phonon excitation/de-excitation mechanism of the substrate. All possible collisional schemes with H/D adsorbed on the surface and H/D impinging from the gas phase are considered. In particular, we focus on the recombination reaction between an H atom colliding with a D atom adsorbed on the surface and a D atom incident on an H adatom. For H(2) and D(2) formation, the surface temperature effect is investigated by comparing the results obtained for T(S)=800 K with those obtained at T(S)=500 K and T(S)=100 K. Despite the low masses involved in the dynamics, effective isotope and temperature effects were observed on the recombination probabilities, reaction energetics, and roto-vibrational states of formed molecules. The results show the need for correct treatment of the multiphonon excitation mechanism in molecule-surface interactions.

Selective facilitatory effect of vasoactive intestinal polypeptide (VIP) on muscarinic firing in vesical ganglia of the cat.

VIP immunoreactivity was identified in nerve fibers and in 10-13% of the neurons in pelvic and bladder ganglia of the cat. Ninety percent of the VIP positive neurons contained acetylcholinesterase. VIP immunoreactivity was not altered in decentralized ganglia 1 week to 8 months after transection of the pelvic and hypogastric nerves indicating that VIP fibers arose from neurons within the peripheral nervous system. The intra-arterial administration of VIP (1-50 micrograms/kg) enhanced the postganglionic discharge elicited by the muscarinic agonist, acetyl-beta-methylcholine, but did not alter the postganglionic firing elicited by the nicotinic agonist, tetramethylammonium or by electrical stimulation of preganglionic axons in the pelvic nerve. VIP did not elicit a postganglionic discharge in untreated ganglia, but did evoke a prolonged discharge in ganglia treated with an irreversible anticholinesterase agent, 217AO. This discharge was not affected by hexamethonium but was blocked by atropine. VIP suppressed the muscarinic inhibition of ganglionic transmission produced by acetyl-beta-methylcholine without altering the response to other inhibitory agents (norepinephrine, leucine-enkephalin and gamma-aminobutyric acid (GABA). VIP (0.1-0.3 micrograms/kg) also had a direct inhibitory effect on bladder smooth muscle. These findings raise the possibility that intraganglionic pathways containing VIP may exert a selective modulatory influence on muscarinic transmission in vesical parasympathetic ganglia.

Vasoactive intestinal polypeptide elicits a discharge in chronically decentralized sympathetic ganglia.

Vasoactive intestinal polypeptide (VIP, 5-50 micrograms) injected intraarterially to the chronically decentralized cat superior cervical ganglion elicited a prolonged (2-5 min) postganglionic discharge which was resistant to cholinergic blocking agents but was blocked by [Leu5]enkephalin and GABA (10-200 micrograms i.a.). VIP did not elicit a discharge in acutely decentralized ganglia. These findings indicate that VIP has direct excitatory effects on ganglion cells and that these excitatory effects are enhanced following degeneration of the preganglionic nerve terminals.

Vasoactive intestinal polypeptide facilitates the late component of the 5-hydroxytryptamine-induced discharge in the cat superior cervical ganglion.

The intra-arterial administration of vasoactive intestinal polypeptide (VIP, 1-10 micrograms, i.a.) to the cat superior cervical ganglion facilitated or unmasked the late component but not the early component of the 5-hydroxytryptamine (5-HT, 0.5-50 micrograms, i.a.)-induced postganglionic discharge. The facilitation occurred in acutely and chronically decentralized ganglia. The early and late 5-HT discharges were blocked by MDL-72222, a 5-HT antagonist, but not by cholinergic antagonists. These data together with previous observations indicate that VIP selectively facilitates slow cholinergic and non-cholinergic excitatory mechanisms in autonomic ganglia.

Use of acetazolamide-challenge xenon CT in the assessment of cerebral blood flow dynamics in patients with arteriovenous malformations.

Arteriovenous malformations (AVMs) may cause symptoms related to a reduction of cerebral blood flow (CBF) to surrounding brain parenchyma. To evaluate this compromise of hemodynamic reserve (commonly referred to as steal phenomenon), we used acetazolamide challenge and stable-xenon CT (Xe/CT). Baseline Xe/CT studies in 13 patients with AVMs were followed by an acetazolamide challenge to the vascular reserve. Blood flow maps were quantitated by using region-of-interest (ROI) software. ROI findings were categorized into four groups on the basis of the presence or absence of normal baseline CBF and presence or absence of normal augmentation of CBF. ROIs were designated as near site (within the vascular territory supplying the AVM) or far site (outside the vascular territory supplying the AVM). One patient had a normal baseline and normal augmentation of CBF (group 1). The other patients had a combination of one or more of the other three categories. Ten patients had parenchymal areas that exhibited either a normal or low baseline CBF with decreased augmentation; both conditions were interpreted as decreased vascular reserve (groups 2 and 3). Eleven patients had parenchymal areas that showed a low baseline CBF and normal augmentation with acetazolamide (group 4), interpreted as having a decreased demand for CBF but having a normal vascular reserve. Decreased vascular reserve was found in 27% of the nearsite areas and 17% of the far-site areas. No patients had only far-site abnormal vascular reserve. We believe that compromised vascular reserve can best be evaluated with a challenge study, such as this acetazolamide-challenge Xe/CT study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cost effectiveness analysis: a review.

Medical treatments and strategies are increasingly being subjected to evaluations of economic efficiency. Although the reasons for this are many, it is becoming ever more important for physicians to have an understanding of the uses and limitations of such evaluations. Cost effectiveness analysis (CEA) is a technique that measures the cost of medical technology per unit of a defined health output, usually life years saved with an adjustment for quality of survival. CEA is a popular method of economic evaluation for policy markers, because it can provide direct comparisons among many medical technologies, resulting in a ranked order of procedures based on economic efficiency. The proper interpretation of a CEA requires an understanding of the component parts of the analysis, their theoretical bases, and their limitations. The components of a CEA include the determination of relevant costs, an appropriate analysis viewpoint, the use of discounting for both costs and benefits, and a sensitivity analysis of the assumptions and probabilities that drive the analysis. Marginal and incremental CEAs are techniques that help to address the cost effectiveness of different amounts of a particular treatment and the differential costs and benefits of competing strategies, respectively. A review is presented of the theoretical basis of CEA and its component parts. Emphasis is placed on generating an understanding of the method rather than providing a step-by-step protocol for the undertaking of such studies.

The cost effectiveness of stereotactic radiosurgery versus surgical resection in the treatment of solitary metastatic brain tumors.

Solitary metastatic brain tumors are the most common intracranial neoplasms encountered by neurosurgeons. Surgical resection of brain metastasis with whole brain radiotherapy (WBR) significantly increases survival in comparison with WBR alone. Stereotactic radiosurgery (SR) seems to provide results that are similar to those of surgical resection. To analyze the economic efficiency of these different treatments, we compared the results of surgical resection and SR as reported in the medical literature between 1974 and 1994. We included studies in which: 1) at least 75% of patients received WBR; 2) study dates were in the computed tomography era (after 1975); 3) operative morbidity, mortality, and median survival were reported; 4) study dates were not included in a more recent update or review; 5) tumor histologies were reported; and 6) the cobalt-60 gamma unit was used for SR. Three surgical resection studies and one SR study met all entry requirements. The WBR baseline was developed from two prospective, randomized trials and used for incremental cost effectiveness analysis. We developed a model of typical resource usage for uncomplicated procedures, reported complications, and subsequent craniotomies (for recurrent tumor or radiation necrosis) for both treatment options. Costs were estimated from the societal viewpoint using the 1992 Medicare Provider Analysis and Review database with average cost:charge ratios for surgery and WBR. A survey of capital and operating costs from five sites was used for radiosurgery. Our analysis revealed that radiosurgery had a lower uncomplicated procedure cost ($20,209 versus $27,587), a lower average complication cost per case ($2,534 versus $2,874), and a lower total cost per procedure ($22,743 versus $30,461), was more cost effective ($24,811 versus $32,149 per life year), and had a better incremental cost effectiveness ($40,648 versus $52,384 per life year) than surgical resection. A sensitivity analysis revealed that large changes in key assumptions would be required to change the analysis outcome. Equalization of the incremental cost effectiveness of the two treatments would require one of the following: 1) a 38.7% reduction in SR annual case volume, 2) a 34.7% increase in SR procedure cost, 3) a 18.8% reduction in surgical resection procedure cost, 4) a 240.5% increase in SR morbidity cost, 5) a 12.7% reduction in SR median survival, 6) a 16.8% increase in surgical resection median survival. Elimination of all surgical resection morbidity cost would still result in superior incremental cost effectiveness for SR.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracranial infantile myofibromatosis.

Infantile myofibromatosis is a proliferative disorder of infancy and early childhood characterized by nodular or diffuse growth of lesions that are comprised of a mixture of mesenchymal elements within the skin, subcutaneous tissues, skeletal muscle, bone, and/or visceral organs. Although these pseudotumors are considered to be the most common fibrous "neoplasm" of infancy, central nervous system involvement is reportedly rare. During the last 7 years, the authors have treated three children with intracranial myofibromas who presented at 6 weeks, 7 months, and 3 3/4 years of age, respectively. Each child had a large calvarial mass that produced significant brain compression despite a paucity of neurological signs. On computerized tomography, these tumors were isodense to brain tissue, enhanced strongly with intravenous contrast material, and showed smoothly marginated bone erosion without surrounding sclerosis. On magnetic resonance imaging, the tumors were hypointense on T1-weighted images, with dense enhancement following the administration of intravenous contrast medium, and hyperintense on T2-weighted images. At operation, the tumors were highly vascular and appeared to arise from within the leaves of the dura, eroding through the overlying bone, but not violating the galeal or arachnoidal layers. Two of the lesions were adherent to major dural venous sinuses. Both of these lesions were completely resected in continuity with the involved dura, and have not recurred 6 years and 1 year, respectively, postoperatively. However, in one patient in whom the involved dura was not resected at the initial procedure, the tumor recurred rapidly. A complete excision of the tumor and involved dura was then performed and the patient is now recurrence-free, 5 1/2 years after the second surgical resection. All patients tolerated resection well, but two have required cranioplasty for persistent calvarial defects. The surgical experience with these lesions is reviewed and the distinctive features of their clinical presentation, radiographic appearance, operative management, and outcome are discussed.

Optimization of analytical and pre-analytical conditions for MALDI-TOF-MS human urine protein profiles.

Protein analysis in biological fluids, such as urine, by means of mass spectrometry (MS) still suffers for insufficient standardization in protocols for sample collection, storage and preparation. In this work, the influence of these variables on healthy donors human urine protein profiling performed by matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was studied. A screening of various urine sample pre-treatment procedures and different sample deposition approaches on the MALDI target was performed. The influence of urine samples storage time and temperature on spectral profiles was evaluated by means of principal component analysis (PCA). The whole optimized procedure was eventually applied to the MALDI-TOF-MS analysis of human urine samples taken from prostate cancer patients. The best results in terms of detected ions number and abundance in the MS spectra were obtained by using home-made microcolumns packed with hydrophilic-lipophilic balance (HLB) resin as sample pre-treatment method; this procedure was also less expensive and suitable for high throughput analyses. Afterwards, the spin coating approach for sample deposition on the MALDI target plate was optimized, obtaining homogenous and reproducible spots. Then, PCA indicated that low storage temperatures of acidified and centrifuged samples, together with short handling time, allowed to obtain reproducible profiles without artifacts contribution due to experimental conditions. Finally, interesting differences were found by comparing the MALDI-TOF-MS protein profiles of pooled urine samples of healthy donors and prostate cancer patients. The results showed that analytical and pre-analytical variables are crucial for the success of urine analysis, to obtain meaningful and reproducible data, even if the intra-patient variability is very difficult to avoid. It has been proven how pooled urine samples can be an interesting way to make easier the comparison between healthy and pathological samples and to individuate possible differences in the protein expression between the two sets of samples.

Atomic oxygen recombination on quartz at high temperature: experiments and molecular dynamics simulation.

A joint experimental and theoretical approach has been developed to study oxygen atom recombination on a beta-quartz surface. The experimental MESOX setup has been applied for the direct measurement of the atomic oxygen recombination coefficient gamma at T(S) = 1000 K. The time evolution of the relative atomic oxygen concentration in the cell is described by the diffusion equation because the mean free path of the atoms is less than the characteristic dimension of the reactor. The recombination coefficient gamma is then calculated from the concentration profile obtained by visible spectroscopy. We get an experimental value of gamma = 0.008, which is a factor of about 3 less than the gamma value reported for O recombination over beta-cristobalite. The experimental results are discussed and compared with the semiclassical collision dynamics calculations performed on the same catalytic system aimed at determining the basic features of the surface catalytic activity. Agreement, both qualitative and quantitative, between the experimental and the theoretical recombination coefficients has been found that supports the Eley-Rideal recombination mechanism and gives more evidence of the impact that surface crystallographic variation has on catalytic activity. Also, several interesting aspects concerning the energetics and the mechanism of the surface processes involving the oxygen atoms are pointed out and discussed.

The acetazolamide challenge: imaging techniques designed to evaluate cerebral blood flow reserve.

Cerebral blood flow was analyzed by the stable xenon (Xe)/CT scanning technique in 29 patients with significant vascular lesions before and after administration of an acetazolamide (Diamox) vasodilatory challenge. Three response types were identified: I, normal flow before Diamox with flow augmentation after Diamox; II, low flow before Diamox with flow augmentation after Diamox; and III, low or normal flow before Diamox with no augmentation or decreased flow after Diamox. Twenty-four percent of the patients studied qualified for category III. We believe that patients in this category represent a group of individuals without blood flow reserve whose clinical management should include careful consideration of their hemodynamic status. The Xe/CT scanning technique with the addition of Diamox flow challenge is a clinically accessible and effective method for assessing cerebral blood flow and blood flow reserve.

Single-stage stereotactic diagnosis and radiosurgery: feasibility and cost implications.

We compared the efficacy and the hospital charges of either single-stage or two-stage stereotactic diagnosis and radiosurgery procedures. Twelve patients underwent either one-stage or two-stage diagnosis and management of their brain tumors. Both techniques utilize high-resolution intraoperative stereotactic image-guided technology and rapid touch preparation (imprint) cytopathological techniques to confirm the presence of neoplasm. Following this pathologic diagnosis, six patients immediately underwent stereotactic radiosurgery employing the same frame application and dose planning based on preoperative and intraoperative images. Six patients underwent two-stage procedures, i.e., discharge from the hospital after histopathological diagnosis followed by readmission, reapplication of the stereotactic head frame, and repeat neuroradiological imaging prior to radiosurgery. Requirements for success of the single-stage procedure include intraoperative stereotactic high-resolution imaging, a hospital-wide ethernet system for transferring neurodiagnostic images, and expertise in rapid touch-preparation histopathological technique for accurate diagnosis. Intraoperative computed tomography imaging after biopsy confirmed the target accuracy and lack of movement of the target after brain biopsy. The advantages of the single-stage approach include reduced length of overall hospital stay, simultaneous histopathological diagnosis and therapy in a single hospital admission, and reduced total hospital charges. For patients highly suspected of having brain tumors and for whom stereotactic radiosurgery will be utilized in the treatment, single-stage stereotactic diagnosis immediately followed by radiosurgery is an accurate, effective, and potentially less costly management strategy than a two-stage approach.