Practical Schemes for Accurate Forces in Quantum Monte Carlo.

While the computation of interatomic forces has become a well-established practice within variational Monte Carlo (VMC), the use of the more accurate Fixed-Node Diffusion Monte Carlo (DMC) method is still largely limited to the computation of total energies on structures obtained at a lower level of theory. Algorithms to compute exact DMC forces have been proposed in the past, and one such scheme is also put forward in this work, but remain rather impractical due to their high computational cost. As a practical route to DMC forces, we therefore revisit here an approximate method, originally developed in the context of correlated sampling and named here the Variational Drift-Diffusion (VD) approach. We thoroughly investigate its accuracy by checking the consistency between the approximate VD force and the derivative of the DMC potential energy surface for the SiH and C2 molecules and employ a wide range of wave functions optimized in VMC to assess its robustness against the choice of trial function. We find that, for all but the poorest wave function, the discrepancy between force and energy is very small over all interatomic distances, affecting the equilibrium bond length obtained with the VD forces by less than 0.004 au. Furthermore, when the VMC forces are approximate due to the use of a partially optimized wave function, the DMC forces have smaller errors and always lead to an equilibrium distance in better agreement with the experimental value. We also show that the cost of computing the VD forces is only slightly larger than the cost of calculating the DMC energy. Therefore, the VD approximation represents a robust and efficient approach to compute accurate DMC forces, superior to the VMC counterparts.

Minimum energy pathways via quantum Monte Carlo.

We perform quantum Monte Carlo (QMC) calculations to determine minimum energy pathways of simple chemical reactions, and compare the computed geometries and reaction barriers with those obtained with density functional theory (DFT) and quantum chemistry methods. We find that QMC performs in general significantly better than DFT, being also able to treat cases in which DFT is inaccurate or even unable to locate the transition state. Since the wave function form employed here is particularly simple and can be transferred to larger systems, we suggest that a QMC approach is both viable and useful for reactions difficult to address by DFT and system sizes too large for high level quantum chemistry methods.

Excitation spectrum of a supersolid.

Conclusive experimental evidence of a supersolid phase in any known condensed matter system is presently lacking. On the other hand, a supersolid phase has been recently predicted for a system of spinless bosons in continuous space, interacting via a broad class of soft-core, repulsive potentials. Such an interaction can be engineered in assemblies of ultracold atoms, providing a well-defined pathway to the unambiguous observation of this fascinating phase of matter. In this Letter, we study by first principles computer simulations the elementary excitation spectrum of the supersolid, and show that it features two distinct modes, namely, a solidlike phonon and a softer collective excitation, related to broken translation and gauge symmetry, respectively.

Deparaffination time: a crucial point in histochemical detection of tissue copper.

The search for a sensitive histochemical method for revealing tissue copper has been the object of many workers in the past. In spite of multiple methods available, the occurrence in clinical practice of negative histochemical stains, even in cases with high copper levels demonstrated by quantitative methods is very high.This study was aimed at verifying the role of technical variations in the sensitivity of the Timm method and, in particular, the role of the dewaxing time of paraffin sections. To this end, 15 liver specimens, 10 from patients affected by Wilson's disease and 5 newborn livers were fixed in 10% formalin, paraffin embedded and routinaly processed. Four 4-micron sections from each case were rinsed in xylene for 10, 20, 60 min, and for 24 hrs. All sections were stained with Timm's method. In 13 out of the 15 liver biopsies utilized in this study, the sensitivity of Timm's method in revealing copper deposits in liver cells appeared to be dependent on the dewaxing time. In two other cases, reactivity of copper granules to Timm solution did not change significantly with the different deparaffination times. The best results were obtained by rinsing sections in xylene for 24 hrs, the worst in sections treated with xylen for 10 minutes. In particular, in five cases of Wilson's disease, Timm stain applied to sections following ten minutes of xylene were completely negative, while copper granules were clearly evidenced in the same section following an overnight bath in xylene. Our data show that an overnight bath of paraffin sections in xylene may completely change the sensitivity of Timm stain in revealing copper deposits in the liver, relaunching copper histochemistry in the diagnosis of copper-related liver diseases.

[Combined surgery of acute type A aortic dissections by ascending aorta replacement and bare stent]. / Chirurgie combinée des dissections aiguës de type A, par remplacement de l'aorte ascendante et endoprothèse non couverte.

UNLABELLED: Aim. After surgical treatment of type A aortic dissections a long segment of these aortas often remain dissected. Our goal was to analyse feasibility and first clinical and pathophysiological results of a combined treatment by ascending aorta replacement and stenting of the arch or descending aorta with Djumbodis(R) bare stents. PATIENTS AND METHODS: Twenty two cases from two centres were analyzed (Universitary Hospital of Parma and Rangueil Universitary Hospital of Toulouse). RESULTS: All the stents have been implanted with short times of circulatory arrest. Average follow-up was 278 days (0-2005). There were two peroperative deaths (9.1%). One year cumulate survival rate was 72.7%. Postoperative complications were mainly respiratory and renal. We have shown a reduction in number of perfused false lumen for aortic arches, more often stented, than for descending aortas (p=0.0104), and for dissected and stented segments versus dissected unstented segments (p=0.0083). CONCLUSION: Our study demonstrates feasibility of this combined procedure and its positive effect on pathophysiologic evolution. Long term results have to be evaluated, but we think promising to extend this treatment to the whole dissected aorta.

Thoracic aortic stents: a combined solution for complex cases.

OBJECTIVES: The combination of endovascular and standard surgical techniques may facilitate the management of complex aortic disease although the long-term durability of this approach needs to be confirmed. DESIGN: A retrospective review of our experience in the treatment of patients with complex aortic pathology using a combined endovascular and surgical approach. MATERIALS AND METHODS: Between 1998 and 2001, 27 patients with thoracic aortic aneurysm underwent stent-graft implantation. Eight required combined endovascular and surgical procedure because of complex pathology. In 3 cases, combined repair was carried out for a concomitant abdominal aortic aneurysm or aorto-iliac-femoral occlusive disease. In the other 5 cases, vessel relocation was performed to obtain safe landing zones: left subclavian artery to left carotid artery translocation in 3 patients, celiac trunk to superior mesenteric artery translocation in one and aorto-celiac-mesenteric bypass grafting in one. RESULTS: One of the 8 patients died on 12th post-operative day of intestinal bleeding and bowel infarction. No neurological sequelae were reported. The other patients are currently well at 11 months mean follow-up time. CONCLUSIONS: Simultaneous surgical and endovascular procedure is a feasible and may be a valuable adjunct to the treatment of complex aortic and peripheral vessel anatomy.

New perspectives for the treatment of thoracic aortic aneurysm with self-expanding endoprostheses. Preliminary experience.

We present our preliminary experience with the application of covered aortic stents to treat aneurysms and dissections of the thoracic artery, a technique that was developed in 1996. Seven selected patients were treated with World Medical Talent bare spring tip endoprostheses and followed up for a total of 67 months. All prostheses were implanted at the Parma General Hospital Cardiovascular Department. Seven patients, average age 57.8 years, range 44-73 years, were treated; a total of 11 prosthetic segments were implanted. Aortic pathologies included: 2 isthmic atherosclerotic aneurysms, 2 chronic dissections, 1 acute dissection, 1 thoracic aneurysm associated with an aneurysm of the abdominal aorta below the renal arteries. Dilation diameters ranged from 6-9 cm, lengths from 4-12 cm. All patients underwent computerized tomography and angiography before stent implantation. The procedure was carried out in an operating room with the patient under general anesthesia and in controlled hypotension. In 2 cases the common iliac artery, prepared for the extraperitoneal route by application of a No. 10 Dacron introducer sheath, was used as the insertion site; in 4 cases the common femoral artery was used, in the case of the double aneurysm the traditional surgical route was used to correct the abdominal aneurysm, and the thoracic aneurysm was repaired through the abdominal prosthesis. All patients were released in good condition; thrombosis of the aneurysm surrounding the graft was immediate in all cases except one which required the application of a second segment shortly after the initial procedure. There were no major complications; one case of iatrogenic dissection of the femoral artery used as the access site required a prosthetic bypass. No implant-related complications were observed during follow-up. Our initial experience has been favorable and demonstrates that stents can be utilized for aortic pathologies of varying etiologies; we had no mortality or major complications, and hospital stays were short. Long term results must be confirmed before the therapeutic potential of this technique can be fully evaluated.

Surgical repair of thoracic aortic aneurysms: results and complications.

Between January 1990 and February 2001 a total of 323 patients underwent following operations at our Institution: respectively 256 on the ascending aorta, 13 on the transverse arch and 54 on thoracic descending aorta. Sixteen patients with thoracic aortic aneurysms underwent endovascular stent graft implantation. The overall in-hospital mortality was respectively: 7% for ascending aortic aneurysms, 7.7% in the aortic arch aneurysms group and 5.5% for descending aortic aneurysms. The mortality was greater in case of emergency surgery and in the subgroup of patients with acute type A dissection. Stroke with permanent dysfunction occurred in 1.5% of ascending aneurysms, 7.7% of arch aneurysms and in 3.7% of thoracic descending aneurysms. In the latter group, all the major neurological events were related to conventional surgical procedures only: really no mortality or neurological morbidity occurred with endovascular stent graft implantation. Even if modern physiologic monitoring devices and new surgical techniques have been developed in the last years, the treatment of thoracic aortic aneurysms remains challenging. Endoluminal placement of stent grafts has developed as an alternative procedure for the treatment of thoracic aortic aneurysms, even if longer term follow-up is still necessary to fully define the efficacy of this approach.

Two waves of nuclear factor kappaB recruitment to target promoters.

Proinflammatory stimuli induce the rapid and transient translocation of nuclear factor (NF)-kappaB to the nucleus, where it activates transcription from several genes, including those encoding inflammatory cytokines and chemokines, adhesion molecules, and cytoprotective proteins. Using chromatin immunoprecipitation, we show that after an acute stimulation two distinct waves of NF-kappaB recruitment to target promoters occur: a fast recruitment to constitutively and immediately accessible (CIA) promoters and a late recruitment to promoters requiring stimulus-dependent modifications in chromatin structure to make NF-kappaB sites accessible (promoters with regulated and late accessibility [RLA]). Our results suggest that a mechanism of specificity in NF-kappaB-dependent transcriptional responses relies on the ability of individual stimuli to make RLA promoters accessible to NF-kappaB before its rapid extrusion from the nucleus.

Age-related changes in cytokine production by leukocytes in rhesus monkeys.

Using a variety of experimental rodent and human models, age-related alterations in cytokine production by immune cells have been described extensively. While the precise mechanism(s) responsible for such age-related changes in cytokine responses remain unclear, it seems likely that these changes may have a significant effect on immune cell function. In an attempt to clarify such changes in aging primates, we examined cytokine production by white cells derived from a controlled colony of rhesus monkeys (Macaca mulatta). Non-fractionated whole blood and peripheral blood mononuclear cells (PBMCs) were obtained from male monkeys of different ages (6-28 years), and were subsequently evaluated for their ability to express mRNA and protein for the cytokines, IL-10, IL-6, IFNgamma, IL-1beta, and TNFalpha, following in vitro stimulation with polyclonal mitogens. Our results suggest that white blood cells derived from aged rhesus monkeys exhibit a significant increase in their ability to produce the Th2-associated cytokine, IL-10, upon stimulation with lipopolysaccharide (LPS) when compared to white cells derived from younger counterparts. Similarly, a significant age-related decrease in the expression of the Th1-associated cytokine, IFNgamma, was also observed using phytohemagglutinin (PHA)-stimulated PBMCs. No significant age-related differences in the production of IL-1beta or TNFalpha were observed in response to any stimulation, but there was limited evidence of an age-related increase in IL-6 production. Overall, our results suggest that a possible systemic change from a Th0/Th1 to a Th2-like cytokine profile occurs in circulating leukocytes derived from aging primates. We believe that such age-related alterations in cytokine production may play a role in the reduced immune responses observed in elderly human populations.

Human cytomegalovirus harbors its own unique IL-10 homolog (cmvIL-10).

We identified a viral IL-10 homolog encoded by an ORF (UL111a) within the human cytomegalovirus (CMV) genome, which we designated cmvIL-10. cmvIL-10 can bind to the human IL-10 receptor and can compete with human IL-10 for binding sites, despite the fact that these two proteins are only 27% identical. cmvIL-10 requires both subunits of the IL-10 receptor complex to induce signal transduction events and biological activities. The structure of the cmvIL-10 gene is unique by itself. The gene retained two of four introns of the IL-10 gene, but the length of the introns was reduced. We demonstrated that cmvIL-10 is expressed in CMV-infected cells. Thus, expression of cmvIL-10 extends the range of counter measures developed by CMV to circumvent detection and destruction by the host immune system.

Redox regulation of chemokine receptor expression.

Cytokines and reactive oxygen intermediates (ROI) are frequent companions at sites of acute inflammation. We have shown previously that in human monocytes, bacterial lipopolysaccharide, IL-1, and tumor necrosis factor-alpha induce a rapid down-regulation of the monocyte chemotactic protein-1 receptor CCR2 (CC chemokine receptor-2). These stimuli also induce production of ROI. In this paper, we investigate the influence of antioxidants and/or ROI on chemokine-receptor expression. In human monocytes, the antioxidant pyrrolidine dithiocarbamate (PDTC) rapidly inhibited CCR2 (95-100% of inhibition) and CCR5 (77-100% of inhibition) mRNA expression by strongly decreasing transcript stability. CCR2 half-life was decreased from 1.5 h to 45 min; CCR5 half-life was decreased from 2 h to 70 min. This inhibitory activity also included CXCR4 (CXC chemokine receptor-4) but not CXCR2 receptor and, although to a lesser extent, was shared by the antioxidants N-acetyl-l-cysteine and 2-mercaptoethanol. In contrast, the ROI-generating system xanthine/xanthine oxidase increased CCR5 and CXCR4 mRNA expression and counteracted the inhibitory effect of PDTC. Accordingly, H(2)O(2) and the glutathione-depleting drug buthionine sulfoximine increased to different extents CCR2, CCR5, and CXCR4 mRNA expression. The PDTC-mediated inhibition of CCR5 and CXCR4 mRNA expression was associated with decreased chemotactic responsiveness (>90% inhibition) and with a marked inhibition of surface-receptor expression. In contrast, xanthine/xanthine oxidase opposed the bacterial lipopolysaccharide- and tumor necrosis factor-alpha-mediated inhibition of CCR5 and CXCR4 mRNA expression and increased both the CCR5 surface expression and the cell migration (3-fold) in response to macrophage inflammatory protein-1beta. These results suggest that the redox status of cells is a crucial determinant in the regulation of the chemokine system.

[Endoluminal repair of aortic aneurysms. Our experience]. / Correzione endoluminale degli aneurismi aortici. Nostra esperienza.

From February 1998 and March 2000 fourteen patients underwent "custom made" aortic self-expanding endoprostheses implantation (World Medical Talent Sunrise): nine of them for dilative pathology of thoracic aorta and 5 for abdominal aortic aneurysm below renal arteries. The etiology was degenerative in 8 patients, false aneurysm in 2, chronic dissection in 2 cases, acute dissection in one patient and post traumatic in the last one. All patients underwent preoperative Computed Tomography and Substraction Angiography studies. Stent-graft implantation was successful in all cases but one who required the conversion of the endovascular procedure in traditional surgery for technical problems. There were no perioperative deaths or major complications. We registered 2 cases of dissection of the femoral artery used to introduce the stent-graft, and treated with an iliac-femoral prosthetic bypass. There were no cases of paraplegia or renal failure or bowel ischemia. With the exception of one patient, died for a car accident, the others are alive and continue their scheduled follow-up controls. Our experience shows that this procedure is safe, allowing favorable results, if compared to traditional surgery, even if it requires further long-term evaluations.

Divergent effects of dithiocarbamates on AP-1-containing and AP-1-less NFAT sites.

Changes in the redox status of cells affect NF-kappaB and activator protein (AP)-1 nuclear expression and activity. In particular, antioxidants decrease NF-kappaB and increase AP-1 transcriptional activity, thereby regulating gene expression. In T cells, low concentrations of antioxidants enhance IL-2 and inhibit IL-4 expression. Since NFAT binding sites play an essential role in regulating IL-2 and IL-4 gene transcription, we studied the effects of dithiocarbamates, using the pyrrolidine derivative of dithiocarbamate (PDTC), on the activity of the distinct AP-1-containing IL-2 NFAT and AP-1-less IL-4 NFAT enhancers elements. Consistent with the presence of AP-1 proteins within the IL-2 NFAT complex, PDTC strongly enhanced phorbol 12-myristate 13-acetate/phytohemagglutinin-induced NFAT binding to the IL-2 NFAT enhancer and transcriptional activity of a reporter plasmid driven by this NFAT enhancer. In contrast, the activity of the IL-4 NFp enhancer, which does not bind AP-1, was abolished by PDTC treatment. In the Jurkat T cell line treated with PDTC, co-expression of the Ca2+/calmodulin-dependent phosphatase, calcineurin, completely restored the IL-4 NFp enhancer activity. Our data indicate that calcineurin-mediated NFAT activity is a target for antioxidants and provides new insights into the molecular mechanisms controlling differential cytokine gene expression.

Divergent effects of LPS on expression of IL-1 receptor family members in mononuclear phagocytes in vitro and in vivo.

Three molecules, interleukin 1 (IL-1) receptor I (IL-1RI), IL-1 receptor II (IL-1RII or decoy) and IL-1 receptor accessory protein (IL-1R AcP or IL-1RIII), are involved in IL-1 binding and signal transduction. In addition, three homologous genes (T1/ST2, MyD88 and rsc786) have been identified. Expression of the signal transducing type I R and of the decoy type II R in human monocytes is regulated by pro- and anti-inflammatory signals. The present study was designed to evaluate comprehensively how a prototypic pro-inflammatory signal, bacterial lipopolysaccharide (LPS), affects expression of IL-1R family members in mononuclear phagocytes in vitro and in vivo. Resting human monocytes expressed high levels of IL-1RII, IL-1R AcP, MyD88 and rsc786, whereas low levels of IL-1RI and T1/ST2 were present. In vitro exposure to LPS augmented expression of IL-1RI, T1/ST2 and MyD88, whereas it inhibited that of IL-1RII and rsc786. Expression of IL-1R AcP in monocytes was less substantially affected by LPS. The expression of IL-1R family members was also studied in organs of mice given LPS. As expected on the basis of in vitro results, organs (e.g. spleen, lungs and peritoneal exudate cells) from LPS-treated mice showed increased levels of IL-1RI, T1/ST2 and MyD88. Intriguingly, while expression of IL-1RII was inhibited in peritoneal macrophages after LPS, in accordance with in vitro results, increased IL-1RII mRNA was observed in organs such as liver, lungs and spleen. This unexpected effect of LPS was drastically reduced in mice rendered neutropenic by 5-fluorouracil. Therefore, we conclude that the apparent induction of IL-1RII in certain organs of LPS-treated mice is due to recruitment of myeloid cells which express high levels of decoy RII. Therefore, members of IL-1R family are independently and divergently regulated in mononuclear phagocytes exposed to the prototypic pro-inflammatory signal LPS in vitro and in vivo.

The human toll signaling pathway: divergence of nuclear factor kappaB and JNK/SAPK activation upstream of tumor necrosis factor receptor-associated factor 6 (TRAF6).

The human homologue of Drosophila Toll (hToll) is a recently cloned receptor of the interleukin 1 receptor (IL-1R) superfamily, and has been implicated in the activation of adaptive immunity. Signaling by hToll is shown to occur through sequential recruitment of the adapter molecule MyD88 and the IL-1R-associated kinase. Tumor necrosis factor receptor-activated factor 6 (TRAF6) and the nuclear factor kappaB (NF-kappaB)-inducing kinase (NIK) are both involved in subsequent steps of NF-kappaB activation. Conversely, a dominant negative version of TRAF6 failed to block hToll-induced activation of stress-activated protein kinase/c-Jun NH2-terminal kinases, thus suggesting an early divergence of the two pathways.

Gene transfer-mediated expression of physiological numbers of the type II decoy receptor in a myelomonocytic cellular context dampens the response to interleukin-1.

Available information suggests that the type II IL-1 receptor (RII) is a nonsignaling molecule which acts as a decoy for IL-1. The decoy function model for RII was supported by gene transfer experiments in fibroblasts and keratinocytes. Therefore, inhibition of IL-1 responsiveness after decoy RII gene transfer could reflect a non-physiological cellular context and receptor number. In the present study, constructs encoding RII or a cytoplasmic deletion mutant (delta 372-398) were transfected into U937 cells which express only low levels of RI detectable by RT-PCR. Gene transfer resulted in receptor numbers (approximately equal to 10(3)/cell) of the same order of magnitude as that found in normal myelomonocytic cells. Transfer of RII or a cytoplasmic deletion mutant into U937 did not increase responsiveness to IL-1, as assessed by IL-8 expression and production; it actually considerably dampened it. These results are consistent with the view that in a myelomonocytic cellular context, RII does not contribute to signaling and represents a unique pathway of negative regulation of the IL-1 system.

Regulated expression and release of the IL-1 decoy receptor in human mononuclear phagocytes.

The aim of this study was to investigate the expression and release of the IL-1 type II decoy receptor (R) in mononuclear phagocytes, which play a central role in immune and chronic inflammatory reactions. Human monocytes expressed both type I and type II R transcripts, the latter being two- to threefold more represented. By cross-linking and Ab blocking, the predominant surface IL-1-binding molecule was the decoy RII. IL-4, IL-13, and dexamethasone induced RI and RII transcripts and augmented the number of IL-1-binding sites with no modification of Kd values. The induced surface receptor was identified as the decoy RII. These stimuli induced the release of a soluble R with a m.w. of approximately 60 kDa, of which N-glycosylation contributed 22 kDa compared with 45 kDa released from polymorphonuclear leukocytes, of which N-glycosylation contributed 15 kDa. IL-13 and dexamethasone induced a release of 24 ng/ml/2 x 10(7) cells (from 8.7 to 43.2 ng/ml) and 25.6 ng/ml/2 x 10(7) cells (from 9.7 to 36.8 ng/ml) of decoy RII in 18 h, respectively (six donors). Thus, for instance, IL-13-treated (18 h) cells expressed 3.5 x 10(3) sites/cell and released 12 x 10(3) decoy RII/cell. The released decoy RII from monocytes bound IL-1apha and IL-1 receptor antagonist 30- and 2-fold less avidly than IL-1beta, respectively. In vitro-matured, monocyte-derived macrophages showed higher levels of surface expression and release of the IL-1 decoy RII. The results show that, on exposure to diverse molecules with anti-inflammatory properties, mononuclear phagocytes express and release copious amounts of a novel version of the soluble IL-1 decoy RII.

[Unilateral pulmonary embolectomy without extracorporeal circulation. A report of a clinical case]. / Embolectomia polmonare unilaterale senza circolazione extracorporea. Considerazioni su un caso clinico.

The surgical treatment of pulmonary embolectomy is currently indicated for acute massive obstruction of the pulmonary artery with severe haemodynamic failure and, as in this case, when medical treatment with anticoagulants or thrombolytic drugs is contraindicated. In this work, the Authors focus on the technique of unilateral pulmonary embolectomy through a median sternotomy; this approach allowed an easier and safer embolectomy without extracorporeal circulation.