Molecular dynamics study of nanoconfined TIP4P/2005 water: how confinement and temperature affect diffusion and viscosity.

In the past few decades great effort has been devoted to the study of water confined in hydrophobic geometries at the nanoscale (tubes and slit pores) due to the multiple technological applications of such systems, ranging from drug delivery to water desalination devices. To our knowledge, neither numerical/theoretical nor experimental approaches have so far reached a consensual understanding of structural and transport properties of water under these conditions. In this work, we present molecular dynamics simulations of TIP4P/2005 water under different nanoconfinements (slit pores or nanotubes, with two degrees of hydrophobicity) within a wide temperature range. It has been found that water is more structured near the less hydrophobic walls, independently of the confining geometries. Meanwhile, we observe an enhanced diffusion coefficient of water in both hydrophobic nanotubes. Finally, we propose a confined Stokes-Einstein relation to obtain the viscosity from diffusivity, whose result strongly differs from the Green-Kubo expression that has been used in previous works. While viscosity computed with the Green-Kubo formula (applied for anisotropic and confined systems) strongly differs from that of the bulk, viscosity computed with the confined Stokes-Einstein relation is not so much affected by the confinement, independently of its geometry. We discuss the shortcomings of both approaches, which could explain this discrepancy.

NMR investigations of protein-carbohydrate interactions: insights into the topology of the bound conformation of a lactose isomer and beta-galactosyl xyloses to mistletoe lectin and galectin-1.

A hallmark of oligosaccharides is their often limited spatial flexibility, allowing them to access a distinct set of conformers in solution. Viewing each individual or even the complete ensemble of conformations as potential binding partner(s) for lectins in protein-carbohydrate interactions, it is pertinent to address the question on the characteristics of bound state conformation(s) in solution. Also, it is possible that entering the lectin's binding site distorts the low-energy topology of a glycosidic linkage. As a step to delineate the strategy of ligand selection for galactosides, a common physiological docking point, we have performed a NMR study on two non-homologous lectins showing identical monosaccharide specificity. Thus, the conformation of lactose analogues bound to bovine heart galectin-1 and to mistletoe lectin in solution has been determined by transferred nuclear Overhauser effect measurements. It is demonstrated that the lectins select the syn conformation of lactose and various structural analogues (Galbeta(1-->4)Xyl, Galbeta(1-->3)Xyl, Galbeta(1-->2)Xyl, and Galbeta(1-->3)Glc) from the ensemble of presented conformations. No evidence for conformational distortion was obtained. Docking of the analogues to the modeled binding sites furnishes explanations, in structural terms, for exclusive recognition of the syn conformer despite the non-homologous design of the binding sites.

[Inflation of the endotracheal tube cuff as an aid for blind nasotracheal intubation in patients with predicted difficult laryngoscopy]. / El inflado del neumotaponamiento como ayuda para la intubación nasotraqueal a ciegas en pacientes con predicción de laringoscopia difícil.

HYPOTHESIS AND OBJECTIVES: Inflation of the tracheal tube cuff to facilitate blind nasal intubation as described by Gobarck in 1987 has been shown to be effective for increasing the rate of successful intubation from 45 to 95% in patients with no airway alterations. We aimed to assess the usefulness of this technique in patients with anatomical alterations of the airway, in whom difficult intubation was predicted. PATIENTS AND METHODS: We enrolled 25 patients with airway alterations that made laryngoscopy likely to be difficult and who were scheduled for neoplastic maxillofacial surgery. RESULTS: Twelve patients (48%) were intubated on the first try, 5 (20%) on the second try and 6 (24%) on the third try. We were unable to intubate 2 patients (8%) after three tries, and therefore opted to intubate with a fiberoptic endoscope. CONCLUSIONS: Inflation of the tracheal tube cuff is useful for facilitating nasotracheal intubation in the awake patient.

Molecular modeling of the amyloid-beta-peptide using the homology to a fragment of triosephosphate isomerase that forms amyloid in vitro.

The main component of the amyloid senile plaques found in Alzheimer's brain is the amyloid-beta-peptide (A beta), a proteolytic product of a membrane precursor protein. Previous structural studies have found different conformations for the A beta peptide depending on the solvent and pH used. In general, they have suggested an alpha-helix conformation at the N-terminal domain and a beta-sheet conformation for the C-terminal domain. The structure of the complete A beta peptide (residues 1-40) solved by NMR has revealed that only helical structure is present in A beta. However, this result cannot explain the large beta-sheet A beta aggregates known to form amyloid under physiological conditions. Therefore, we investigated the structure of A beta by molecular modeling based on extensive homology using the Smith and Waterman algorithm implemented in the MPsrch program (Blitz server). The results showed a mean value of 23% identity with selected sequences. Since these values do not allow a clear homology to be established with a reference structure in order to perform molecular modeling studies, we searched for detailed homology. A 28% identity with an alpha/beta segment of a triosephosphate isomerase (TIM) from Culex tarralis with an unsolved three-dimensional structure was obtained. Then, multiple sequence alignment was performed considering A beta, TIM from C.tarralis and another five TIM sequences with known three-dimensional structures. We found a TIM segment with secondary structure elements in agreement with previous experimental data for A beta. Moreover, when a synthetic peptide from this TIM segment was studied in vitro, it was able to aggregate and to form amyloid fibrils, as established by Congo red binding and electron microscopy. The A beta model obtained was optimized by molecular dynamics considering ionizable side chains in order to simulate A beta in a neutral pH environment. We report here the structural implications of this study.

A structural motif of acetylcholinesterase that promotes amyloid beta-peptide fibril formation.

Acetylcholinesterase (AChE) has been found to be associated with the core of senile plaques. We have shown that AChE interacts with the amyloid beta-peptide (Abeta) and promotes amyloid fibril formation by a hydrophobic environment close to the peripheral anionic binding site (PAS) of the enzyme. Here we present evidence for the structural motif of AChE involved in this interaction. First, we modeled the docking of Abeta onto the structure of Torpedo californica AChE, and identified four potential sites for AChE-Abeta complex formation. One of these, Site I, spans a major hydrophobic sequence exposed on the surface of AChE, which had been previously shown to interact with liposomes [Shin et al. (1996) Protein Sci. 5, 42-51]. Second, we examined several AChE-derived peptides and found that a synthetic 35-residue peptide corresponding to the above hydrophobic sequence was able to promote amyloid formation. We also studied the ability to promote amyloid formation of two synthetic 24-residue peptides derived from the sequence of a Omega-loop, which has been suggested as an AChE-Abeta interacting motif. Kinetic analyses indicate that only the 35-residue hydrophobic peptide mimics the effect of intact AChE on amyloid formation. Moreover, RP-HPLC analysis revealed that the 35-residue peptide was incorporated into the growing Abeta-fibrils. Finally, fluorescence binding studies showed that this peptide binds Abeta with a K(d) = 184 microM, independent of salt concentration, indicating that the interaction is primarily hydrophobic. Our results indicate that the homologous human AChE motif is capable of accelerating Abeta fibrillogenesis.

Factors influencing collection and engraftment of CD34+ cells in patients with breast cancer following high-dose chemotherapy and autologous peripheral blood progenitor cell transplantation.

Although autologous PBPC transplantation is being used increasingly for the treatment of breast cancer, there are few data on factors influencing mobilization and engraftment in these patients. We have analyzed these factors in 70 patients with advanced or metastatic breast cancer undergoing autologous PBPC transplantation. All patients were mobilized after stimulation with G-CSF, and a median of 3.16 x 10(6)/kg CD34+ cells (range 0.75-23.33) were infused. All patients received conditioning with a combination of cyclophosphamide, thiotepa, and carboplatin, and postinfusion G-CSF was administered to 60 patients. The median times to reach 0.5 x 10(9)/L and 1 x 10(9)/L neutrophils were 10 and 11 days, respectively. The median times to obtain 20 x 10(9)/L and 50 x 10(9)/L platelets were 12 and 18 days, respectively. An analysis of factors that influence CD34+ cell collection was performed by linear regression. Previous radiation therapy and increasing age were associated with lower numbers of CD34+ cells collected. Those variables that could influence the tempo of engraftment were examined by multivariate analysis using Cox regression models. The number of CD34+ cells infused was found to influence both neutrophil and platelet recovery. The use of G-CSF after transplant, accelerated neutrophil recovery, and having more than six cycles of previous chemotherapy was an unfavorable factor for recovering >50 x 10(9)/L platelets.

Salvage chemotherapy with mini-BEAM for relapsed or refractory Hodgkin's disease prior to autologous peripheral blood stem cell transplantation.

BACKGROUND AND OBJECTIVE: High-dose chemotherapy and autologous bone marrow transplantation (ABMT) has become the standard approach for most patients with relapsed or refractory Hodgkin's disease. Disease status at transplant has been correlated with outcome following ABMT. In light of this, we employ mini-BEAM (BCNU, etoposide, cytarabine and melphalan) salvage therapy in order to achieve a state of minimal residual disease prior to transplantation. DESIGN AND METHODS: From February 1992 to June 1998 twenty-four patients receiving mini-BEAM therapy for resistance or relapse of their Hodgkin's disease were included. Four patients had obtained no response with initial chemotherapy (refractory), eight had obtained an incomplete response, seven were in first relapse and five in second or subsequent relapse. Fifteen patients received mini-BEAM as first salvage chemotherapy regimen. The remaining nine patients had previously been exposed to a median of one salvage regimen. Patients received a median of three cycles of mini-BEAM. RESULTS: Sixteen patients achieved complete remission and four partial remission, yielding an overall response rate of 83%. No significant differences in response were observed between patients who received mini-BEAM as initial salvage therapy and those who had received a prior salvage regimen. Eighteen out of the twenty responding patients went on to intensive therapy and peripheral blood stem cell transplantation. With a median follow-up of 52 months, the cumulative probability of 7-year overall survival is 71% for the responders and that of the 6-year disease-free survival is 42%. No treatment-related deaths were observed. INTERPRETATION AND CONCLUSIONS: Mini-BEAM is an effective salvage regimen with moderate toxicity that may be useful for cytoreduction prior to stem cell procedures.

Long-term follow-up in patients treated with Mini-BEAM as salvage therapy for relapsed or refractory Hodgkin's disease.

Several studies have focused on investigation of the optimal salvage regimen to induce maximum response before autologous stem cell transplantation (ASCT) in patients with relapsed or refractory Hodgkin's disease (HD). However, in most of these studies, the follow-up is relatively short. In the present study, we report on long-term results of 55 consecutive patients with HD who received Mini-BEAM [BCNU (carmustine), etoposide, cytarabine, melphalan] as salvage therapy before ASCT. Eleven patients were refractory to front-line therapy, 17 were partial responders, and 27 patients had relapsed from HD. Twenty-eight patients achieved complete response, and 18 achieved partial response with a median of two cycles of Mini-BEAM, giving a total response rate of 84%. Significant factors predicting poor response (P < 0.05) were: initial treatment with MOPP (mechloroethamine, oncovin, procarbazine, prednisolone), > or = two previous chemotherapy regimens and three disease characteristics at Mini-BEAM treatment: presence of B symptoms, extranodal involvement or low serum albumin. However, only the last two factors retained independent influence on multivariate analysis. In total, 45/55 patients have been transplanted. Median follow-up after Mini-BEAM administration for living patients is 68 months. At the time of reporting, 31 out of 55 patients (56.4%) are still alive, 21 patients (38%) have relapsed, three (5.4%) have developed secondary neoplasias, and five have died of other complications not related to disease progression. The actuarial 7-year overall survival (OS) was 52%, the progression-free survival (PFS) 54% and the event-free survival (EFS) 36%. The response to Mini-BEAM was the most important prognostic factor for predicting the long-term probability of surviving the disease: none of the eight patients who did not respond to Mini-BEAM were alive at 3 years. On multivariate analysis, response to Mini-BEAM and extranodal involvement before Mini-BEAM had a significant influence on OS. Our results show the safety and efficacy of Mini-BEAM before ASCT for refractory or relapsed HD patients.

Identification of factors associated with poor peripheral blood progenitor cell mobilization in Hodgkin's disease.

BACKGROUND AND OBJECTIVES: Although the use of drugs which damage stem cells is common in patients with Hodgkin's disease (HD), factors affecting peripheral blood progenitor cell (PBPC) mobilization have not been clearly established in this group of patients. The aim of this study was to identify factors associated with poor PBPC mobilization in patients with HD. DESIGN AND METHODS: In order to address this issue we have evaluated in 54 patients with HD mobilized with G-CSF alone the following factors: sex, age, histologic subtype, B symptoms at diagnosis, status of remission, previous chemotherapy and radiotherapy, interval from diagnosis and last chemotherapy cycle to harvest, and dose of G-CSF. Univariate analysis was performed using Student's t-test, Pearson's correlation and Spearman's correlation. A stepwise regression model was used to determine which of the variables was the most predictive of PBPC mobilization. RESULTS: In univariate analysis poorer PBPC mobilization was observed in patients who had previously received at least two courses of mini-BEAM (p=0.006), a high number of different chemotherapy regimens (p=0.002), a chemotherapy score >30 (p=0.02) and more than 9 months of alkylating agents (p=0.07). We did not find radiotherapy to be a significant factor affecting progenitor cell yield (p=0.59). In the stepwise regression model, only the previous administration of two or more mini-BEAM cycles predicted a poor PBPC yield (p=0.006). INTERPRETATION AND CONCLUSIONS: Previous chemotherapy, principally exposure to a mini-BEAM regimen, seems to be the principal factor affecting collection of PBPC in patients with HD mobilized with G-CSF alone. Since mini-BEAM is an effective salvage regimen in relapsed or refractory HD, collection of PBPC should be planned when there has been no or only minimal exposure to a mini-BEAM regimen.