Mechanosensing at the Nuclear Envelope by Nuclear Pore Complex Stretch Activation and Its Effect in Physiology and Pathology

Cell fate is correlated to mechanotransduction, in which forces transmitted by the cytoskeleton filaments alter the nuclear shape, affecting transcription factor import/export, cells transcription activity and chromatin distribution. There is in fact evidence that stem cells cultured in 3D environments mimicking the native niche are able to maintain their stemness or modulate their cellular function. However, the molecular and biophysical mechanisms underlying cellular mechanosensing are still largely unclear. The propagation of mechanical stimuli via a direct pathway from cell membrane integrins to SUN proteins residing in the nuclear envelop has been demonstrated, but we suggest that the cells’ fate is mainly affected by the force distribution at the nuclear envelope level, where the SUN protein transmits the stimuli via its mechanical connection to several cell structures such as chromatin, lamina and the nuclear pore complex (NPC). In this review, we analyze the NPC structure and organization, which have not as yet been fully investigated, and its plausible involvement in cell fate. NPC is a multiprotein complex that spans the nuclear envelope, and is involved in several key cellular processes such as bidirectional nucleocytoplasmic exchange, cell cycle regulation, kinetochore organization, and regulation of gene expression. As several connections between the NPC and the nuclear envelope, chromatin and other transmembrane proteins have been identified, it is reasonable to suppose that nuclear deformations can alter the NPC structure. We provide evidence that the transmission of mechanical forces may significantly affects the basket conformation via the Nup153-SUN1 connection, both altering the passage of molecules through it and influencing the state of chromatin packing. Finally, we review the known correlations between a pathological NPC structure and diseases such as cancer, autoimmune disease, aging and laminopathies.

Diagnosis of chronic anaemia in gastrointestinal disorders: A guideline by the Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO) and the Italian Society of Paediatric Gastroenterology Hepatology and Nutrition (SIGENP)

Anaemia is a common pathologic condition, present in almost 5% of the adult population. Iron deficiency is the most common cause; other mechanisms can be involved, making anaemia a multi-factorial disorder in most cases. Anaemia being a frequent manifestation in the diseases of the gastrointestinal tract, patients are often referred to gastroenterologists. Furthermore, upper and lower endoscopy and enteroscopy are pivotal to the diagnostic roadmap of anaemia. In spite of its relevance in the daily clinical practice, there is a limited number of gastroenterological guidelines dedicated to the diagnosis of anaemia. For this reason, the Italian Association of Hospital Gastroenterologists and Endoscopists and the Italian Society of Paediatric Gastroenterology, Hepatology and Nutrition commissioned a panel of experts to prepare a specific guideline on anaemia and its diagnostic roadmap in the gastroenterological scenario. The panel also discussed about the potential involvement of gastroenterologists and endoscopists in the management of patients with anaemia, with particular attention to the correct use of investigations. The panel paid particular attention to practical issues with the aim to support gastroenterologists in their clinical practice when dealing with patients with anaemia.

Five common errors to avoid in clinical practice: the Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO) Choosing Wisely Campaign

Modern medicine provides almost infinite diagnostic and therapeutic possibilities if compared to the past. As a result, patients undergo a multiplication of tests and therapies, which in turn may trigger further tests, often based on physicians' attitudes or beliefs, which are not always evidence-based. The Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO) adhered to the Choosing Wisely Campaign to promote an informed, evidence-based approach to gastroenterological problems. The aim of this article is to report the five recommendations of the AIGO Choosing Wisely Campaign, and the process used to develop them. The AIGO members' suggestions regarding inappropriate practices/interventions were collected. One hundred and twenty-one items were identified. Among these, five items were selected and five recommendations were developed. The five recommendations developed were: (1) Do not request a fecal occult blood test outside the colorectal cancer screening programme; (2) Do not repeat surveillance colonoscopy for polyps, after a quality colonoscopy, before the interval suggested by the gastroenterologist on the colonoscopy report, or based on the polyp histology report; (3) Do not repeat esophagogastroduodenoscopy in patients with reflux symptoms, with or without hiatal hernia, in the absence of different symptoms or alarm symptoms; (4) Do not repeat abdominal ultrasound in asymptomatic patients with small hepatic haemangiomas (diameter < 3 cm) once the diagnosis has been established conclusively; (5) Do not routinely prescribe proton pump inhibitors within the context of steroid use or long-term in patients with functional dyspepsia. AIGO adhered to the Choosing Wisely Campaign and developed five recommendations. Further studies are needed to assess the impact of these recommendations in clinical practice with regards to clinical outcome and cost-effectiveness.

Multi-Scale Analysis of the Toraymyxin Adsorption Cartridge Part II: Computational Fluid-Dynamic Study

Extracorporeal endotoxin removal by means of the Toraymyxin device is based on the ability of polymyxin B to bind endotoxins with a high specificity. The endotoxins/polymyxin molecular interactions were computationally analyzed in a parallel work (Part I). In this paper we investigate with a multi-scale approach the phenomena involving blood and plasma fluid dynamics inside the device. The macro- and mesoscale phenomena were studied by means of 3D models using computational fluid dynamics. The flow behavior in the sorbent material was focused, modeling the sorbent as a homogeneous porous medium at the macroscale level, or accounting for the realistic geometry of its knitted fibers at the mesoscale level. A microscale model was then developed to analyze the behavior of endotoxin molecules subjected to the competition of flow drag and molecular attraction by fibergrafted polymyxin B. The macroscale results showed that a very regular flow field develops in the sorbent, furthermore supplying the peak velocity to be input in the lower-scale model. The mesoscale analysis yielded the realistic range for wall shear stresses (WSSs) acting on fiber walls. With WSS values in the entire range, the results of the microscale analysis demonstrated that the capability of polymyxin B to capture endotoxin molecules from the flow extends at distances one order of magnitude greater than the characteristic distance of the stable intermolecular bond. We conclude that the use of an integrated, multi-scale analysis allows for a comprehensive understanding of the complex mechanisms involved in endotoxin sorption phenomena with immobilized polymyxin B.

Implications of small-bowel transit time in the detection rate of capsule endoscopy: A multivariable multicenter study of patients with obscure gastrointestinal bleeding

AIM

To define the role of small-bowel transit time in the detection rate of significant small-bowel lesions.

METHODS

Small-bowel capsule endoscopy records, prospectively collected from 30 participating centers in the Lombardy Registry from October 2011 to December 2013, were included in the study if the clinical indication was obscure gastrointestinal bleeding and the capsule reached the cecum. Based on capsule findings, we created two groups: P2 (significant findings) and P0-1 (normal/negligible findings). Groups were compared for age, gender, small-bowel transit time, type of instrument, modality of capsule performance (outpatients vs inpatients), bowel cleanliness, and center volume.

RESULTS

We retrieved and scrutinized 1,433 out of 2,295 capsule endoscopy records (62.4%) fulfilling the inclusion criteria. Patients were 67 ± 15 years old, and 815 (57%) were males. In comparison with patients in the P0-1 group, those in the P2 group (n = 776, 54%) were older (P < 0.0001), had a longer small-bowel transit time (P = 0.0015), and were more frequently examined in low-volume centers (P < 0.001). Age and small-bowel transit time were correlated (P < 0.001), with age as the sole independent predictor on multivariable analysis. Findings of the P2 group were artero-venous malformations (54.5%), inflammatory (23.6%) and protruding (10.4%) lesions, and luminal blood (11.5%).

CONCLUSION

In this selected, prospectively collected cohort of small-bowel capsule endoscopy performed for obscure gastrointestinal bleeding, a longer small-bowel transit time was associated with a higher detection rate of significant lesions, along with age and a low center volume, with age serving as an independent predictor.

Hospital care services for digestive diseases in Italy: the first quantitative assessment

The scarcity of human and structural resources for specialized gastroenterology care is a problem in many Western countries. Data regarding the resources for Italian Gastroenterology, so far lacking, have been thus searched and evaluated. Based on an agreement protocol between the Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO) and the Ministry of Health, national data regarding all Institutions providing gastroenterological care were analysed. Hospital beds in Gastroenterology units are presented by region, regimen of stay and per million inhabitants as of January 2011. Association of Hospital Gastroenterologists and Endoscopists also performed a survey of gastroenterology units in all Italian regions regarding number of ordinary/day hospital beds and the number of staff gastroenterologists. The Ministry data showed a total of 174 Gastronterology Units in Italy, a total of 2062 hospital beds for the discipline, for a proportion of 34.2 beds per million inhabitants. The Association of Hospital Gastroenterologists and Endoscopists survey showed a total of 1425 gastroenterologists in Italy. These data should represent a key reference for appropriate planning of specialized care for digestive diseases.

Electrical conditioning of adipose-derived stem cells in a multi-chamber culture platform

In tissue engineering, several factors play key roles in providing adequate stimuli for cells differentiation, in particular biochemical and physical stimuli, which try to mimic the physiological microenvironments. Since electrical stimuli are important in the developing heart, we have developed an easy-to-use, cost-effective cell culture platform, able to provide controlled electrical stimulation aimed at investigating the influence of the electric field in the stem cell differentiation process. This bioreactor consists of an electrical stimulator and 12 independent, petri-like culture chambers and a 3-D computational model was used to characterize the distribution and the intensity of the electric field generated in the cell culture volume. We explored the effects of monophasic and biphasic square wave pulse stimulation on a mouse adipose-derived stem cell line (m17.ASC) comparing cell viability, proliferation, protein, and gene expression. Both monophasic (8 V, 2 ms, 1 Hz) and biphasic (+4 V, 1 ms and -4 V, 1 ms; 1 Hz) stimulation were compatible with cell survival and proliferation. Biphasic stimulation induced the expression of Connexin 43, which was found to localize also at the cell membrane, which is its recognized functional mediating intercellular electrical coupling. Electrically stimulated cells showed an induced transcriptional profile more closely related to that of neonatal cadiomyocytes, particularly for biphasic stimulation. The developed platform thus allowed to set-up precise conditions to drive adult stem cells toward a myocardial phenotype solely by physical stimuli, in the absence of exogenously added expensive bioactive molecules, and can thus represent a valuable tool for translational applications for heart tissue engineering and regeneration.

A dynamic distention protocol for whole-organ bladder decellularization: histological and biomechanical characterization of the acellular matrix

A combined physical-chemical protocol for whole full-thickness bladder decellularization is proposed, based on organ cyclic distention through repeated infusion/withdrawal of the decellularization agents through the urethra. The dynamic decellularization was intended to enhance cell removal efficiency, facilitating the delivery of detergents within the inner layers of the tissue and the removal of cell debris. The use of mild chemical detergents (hypotonic solution and non-ionic detergent) was employed to limit adverse effects upon matrix 3D ultrastructure. Inspection of the presence of residual DNA and RNA was carried out on decellularized matrices to verify effective cell removal. Histological investigation was focused on assessing the retention of adequate structural and functional components that regulate the biomechanical behaviour of the acellular tissue. Biomechanical properties were evaluated through uniaxial tensile loading tests of tissue strips and through ex vivo filling cystometry to evaluate the whole-organ mechanical response to a physiological-like loading state. According to our results, a dynamic decellularization protocol of 17 h duration with a 5 ml/min detergent infusion flow rate revealed higher DNA removal efficiency than standard static decellularization, resulting in residual DNA content < 50 ng/mg dry tissue weight. Furthermore, the collagen network and elastic fibres distribution were preserved in the acellular ECM, which exhibited suitable biomechanical properties in the perspective of its future use as an implant for bladder augmentation.

Defensive medicine practices among gastroenterologists in Lombardy: between lawsuits and the economic crisis

BACKGROUND

Defensive medicine is becoming more frequent behaviour and has an impact on the economic 'health' of national healthcare systems.

AIM

The aim of this study was to clarify the impact of defensive medicine on gastroenterological practices in Lombardy.

METHODS

Gastroenterologists attending the Lombardy Annual Gastroenterological Conference received a questionnaire based on multiple choice tests and visual analogue scales. The questionnaire was divided into three parts evaluating the respondent's characteristics, the number of procedures prescribed, and the percentage of those performed with a defensive purpose.

RESULTS

Sixty-four of 107 participants (60%) completed the questionnaire, 94% of whom reported practising defensive medicine. The percentage of defensively requested procedures amounted to 18% of all digestive endoscopies, 8.9% of abdominal ultrasonography scans, 4.9% of abdominal computed tomography or magnetic resonance scans, and 12.2% of all consultations. The total number of defensive procedures prescribed per month by the participants was 878, and 31.7% of the performed procedures (n=4897) were reported to defensively based. On the basis of the 2012 regional reimbursement fees, the yearly cost of defensive procedures prescribed and/or performed by all gastroenterologists in Lombardy was estimated to be € 8,637,835.

CONCLUSIONS

Our findings indicate that defensive medicine profoundly affects current medical practices among gastroenterologists, and has a considerable economic impact.

Can we improve the detection rate and interobserver agreement in capsule endoscopy?

BACKGROUND

Data about strategies for improving the diagnostic ability of capsule endoscopy readers are lacking.

AIM

(1) To evaluate the detection rate and the interobserver agreement among readers with different experience; (2) to verify the impact of a specific training (hands-on training plus expert tutorial) on these parameters.

METHODS

17 readers reviewed 12 videos twice; between the two readings they underwent the training. The identified small bowel findings were described by a simplified version of Structured Terminology and classifies as clinically significant/non-significant. Findings identified by the readers were compared with those identified by three experts (Reference Standard).

RESULTS

The Reference Standard identified 26 clinically significant findings. The mean detection rate of overall readers for significant findings was low (about 50%) and did not change after the training (46.2% and 46.4%, respectively). There was no difference in the detection rate among readers with different experience. The interobserver agreement with the Reference Standard in describing significant findings was moderate (k = 0.44; CI95%: 0.39-0.50) and did not change after the training (k = 0.44; CI95%: 0.38-0.49) or stratifying readers according to their experience.

CONCLUSIONS

Both the interobserver agreement and the detection rate of significant findings are low, regardless of the readers' experience. Our training did not significantly increase the performance of readers with different experience.

Capsule endoscopy of the small bowel in the clinical practice: outpatient management is feasible and cheaper

AIM

Four Italian regions have cost coding for outpatient capsule-endoscopy. Elsewhere it is performed in ordinary hospital admission. To identify, in a cohort of patients of a Gastroenterology Unit, those feasible for outpatient versus inpatient treatment; to analyze costs distribution in both management areas.

METHODS

We retrospectively analysed 100 clinical records of admissions to A.O. San-Carlo-Borromeo, Milan between 2005-2008. Hospitalization criteria (at least 3): 1) occult/obscure gastrointestinal bleeding; 2) hemoglobin ≤ 8 gr/dL; 3) indication for blood transfusions; 4) urgent hospital admission.

RESULTS

A total of 62 patients had urgent admission, 60 blood transfusions, 81 underwent EGD and colonoscopy, 8 enteroscopy and 5 surgery. Mean haemoglobin value was 8.67 g/dL. Capsule-endoscopy was positive in 70, uncertain in 8, negative in 22. Positive cases: 33 angiodyplasia, 18 ulcers/erosions, 13 polyps/masses, 5 overt bleeding, 1 celiac disease. 47/100 were appropriate as outpatient, saving 432 days of hospital stays. Admission coding was grouped into 7 DRGs (overall expense: 98,366 Euros). Considering EGD/colonoscopy outpatient costs and 1.100 euros as estimated value for capsule-endoscopy, the total expense could be 53.919.

CONCLUSION

Outpatient capsule-endoscopy small bowel examination is feasible in half of the cases. It is cost saving, (about 45.000 Euros/100 patients), reducing inappropriate hospital stays.

Cost estimation of small bowel capsule endoscopy based on "real world" data: inpatient or outpatient procedure?

BACKGROUND

Although capsule endoscopy is the cornerstone for the evaluation of the small bowel in patients with obscure GI bleeding data about costs are lacking.

AIM

To evaluate, from a third party payer point of view, whether performing capsule endoscopy as an outpatient instead of an inpatient procedure can reduce costs.

MATERIALS AND METHODS

The data source is a multicentre survey collecting data for 2921 patients; 1486 of them underwent capsule endoscopy for obscure GI bleeding or chronic unexplained iron-deficiency anaemia as inpatients (814 with positive, 211 with inconclusive and 461 with negative result). We estimated costs of inpatient procedures based on the diagnosis related groups (DRG) system, while those of outpatient procedures on reimbursement provided in five Italian regions.

RESULTS

We estimated that the cost for each inpatient undergoing capsule endoscopy is about € 1775.90. Assuming that all these patients had undergone the same procedure as outpatients, € 175.00-741.00 per patient (depending on the reimbursement and/or on diagnosis related group codes applied) would have been saved.

CONCLUSIONS

Our estimate suggests that, from the third party payer's perspective and using the diagnosis related group reimbursement system, shifting capsule endoscopy from inpatient to outpatient procedure, would be potentially cost saving at least for patients referred for obscure GI bleeding or chronic unexplained anaemia.

Mechanisms of polymyxin B endotoxin removal from extracorporeal blood flow: molecular interactions

The outer leaflet of Gram-negative bacteria membrane contains a great amount of lipopolysaccharides, also known as endotoxins, which play a central role in the pathogenesis of septic shock. It has been demonstrated that the polymyxin B (PMB) molecule has both antibacterial and antiendotoxin capabilities; in fact, it is able to compromise the bacterial outer membrane and bind lipopolysaccharides, thereby neutralizing its toxic effects. Extracorporeal hemoperfusion treatments based on cartridges containing PMB-immobilized fibers (Toraymyxin PMX-F; Toray Industries, Tokyo, Japan) are used to remove endotoxins circulating in the blood flow. In this study, we focused on the characterization of the interactions occurring in the formation of the PMB-endotoxin complex at the molecular level. In particular, the molecular mechanics approach was used to evaluate the interaction energy and eventually the interaction force between the two molecules. PMB was faced with five molecular portions of lipopolysaccharides differing in their structure. The interaction energy occurring for each molecular complex was calculated at different intermolecular distances and the binding forces were estimated by fitting interaction energy data. Results show that the short-range interactions between PMB and endotoxins are mediated mainly by hydrophobic forces, while in the long term, the complex formation is driven by ionic forces only. Maximum binding forces calculated via molecular mechanics for the PMB-endotoxin complex are in the range of 1.39-3.79 nN. Understanding the interaction mechanism of the single molecular complex is useful both in order to figure out the molecular features of such interaction and to perform higher scale level analysis, where such nanoscale detail is impractical but could be used to account for molecular behavior at a coarse level of discretization.

Gastroenterology in Italian clinical practice. The RING Study: six years' data from gastroenterology departments

AIM

Computer systems in hospitals provide information on the work of each single operative unit and the complexity of its caselist. However, in Italy, there is no official data-base for Gastroenterology Departments, to summarize their work.

METHODS

The RING (Ricerca-INformatizzata-in-Gastroenterologia) study has collected, through a software made on purpose, 113 237 hospital discharge files (HDF) from 55 Italian hospital Gastroenterology Units, since 2001. This caselist provides a picture of the patients and is useful for clinical/management evaluation.

RESULTS

Between January 2001 and December 2006, 55 Gastroenterology Units gathered 88240 HDF referring to ''ordinary admissions''. The male:female rate was 1:1, mean age was 61.3+/-18.5 years. Mean hospital stay was around eight days. Over the years there was a significant drop in DRG183 (miscellaneous digestive disorders-without complications) from 11.5% to 7.4% (P<0.0001), with no similar increase in DRG182 (with complications) which rose from 3.1% to 4.0%. Principal discharge diagnoses are post-hepatic and alcohol-related cirrhosis, hepatocarcinoma, acute pancreatitis, duodenal/gastric ulcer.

CONCLUSIONS

The RING data show that the gastroenterologist has been working increasingly with patients whose pathologies would have been ''inappropriately'' treated surgically (DRGs 204 and 174). Inappropriate gastroenterological treatment seems to have decreased as well as the DRG183 with no apparent ''opportunistic'' compensatory increase in DRGs with complications, such as 182.

Management of patients with nonvariceal upper gastrointestinal hemorrhage before and after the adoption of the Rockall score, in the Italian Gastroenterology Units

OBJECTIVES

Nonvariceal upper gastrointestinal hemorrhage is a frequent reason for ordinary hospital admission. In Italy the use of prognostic scores to stratify the risk has not been adequately validated: the impact on clinical management of a rating system like the Rockall score remains to be established. RING is a 'register' that has been collecting hospital discharge files from hospital gastroenterology units, giving a broad picture of the patients admitted for this pathology.

METHODS

We analyzed the hospital discharge files collected between 2001 and 2005 from 12 gastroenterology units, which issued more than 26,000 hospital discharge files for ordinary hospital admission and have been using the Rockall score for defining nonvariceal upper gastrointestinal hemorrhage since 2003.

RESULTS

There were 2832 hospital discharge files with a main diagnosis of nonvariceal upper gastrointestinal hemorrhage: 1335 'before' the Rockall score was introduced, 1497 'after' the introduction. Patients' mean age was 67.7+/-16.7 years, with a male/female ratio of 1.7 and no significant changes over the years. There were no differences in the distribution of diagnoses in nonvariceal upper gastrointestinal hemorrhage patients before/after the introduction of the Rockall score, though the mean hospital stay became shorter (7.1+/-5.0 vs. 6.3+/-4.5 days), and mortality declined (2.8 vs. 2.3%), in parallel with the caselist as a whole. For 1102 ordinary hospital admission Rockall score was calculated. Diagnoses were more accurate: significantly fewer undefined causes and an increase in peptic ulcer. The mean Rockall score was 4.6+/-2.2: 17.8% low (0-2), 48.7% intermediate (3-5), and 33.5% high (>or=6). Mean hospital stay, rebleeding, and mortality were correlated with the severity of the score.

CONCLUSION

The Rockall score enables the clinician to formulate a more precise diagnosis and substantially shortens the time in hospital, especially for patients at low-risk of rebleeding and death, so more resources can be dedicated to critically ill patients.

Management and outcomes of hepatic cirrhosis: Findings from the RING study

BACKGROUND/AIM

Hepatic cirrhosis is a frequent reason for ordinary hospital admission (OA). The RING study collected hospital discharge files (HDF) from Italian hospital gastroenterology units (IGU). This caselist provides a broad picture of the patients admitted for this pathology.

MATERIAL/METHODS

More than 50,000 HDF for OA were collected between 2001 and 2004 from 26 IGU.

RESULTS

Eight thousand four hundred and eighty-seven HDF (16%) had a diagnosis of hepatic cirrhosis; Child-Pugh classes were 20.2% A, 34.8% B and 45.0% C. Patients' mean age was 63.7+/-12.1 years and 62.5% were male. A 61.1% of the cirrhosis cases had ascites, 29.9% portal-systemic encephalopathy, 29.2% hepatocellular carcinoma (HCC), 10% bleeding varices, 3.0% hepatorenal syndrome (HRS). Mortality for OA for cirrhosis was 5.7% versus 2.6% for other diagnoses. The proportion varied with the severity of the cirrhosis: 0% for Child A, 1.1% B, 10.5% C. Mortality was significantly associated with: Child-Pugh at admission (odds ratio: OR 9.2), HRS (OR 11.7), bleeding varices (OR 2.2), HCC (OR 1.8).

CONCLUSIONS

Hepatic cirrhosis was found in 16% of the OA to IGU and mortality was double the rate for all the other pathologies in the same wards. Child-Pugh is a useful prognostic tool, higher classes implying a greater risk of death. HRS and bleeding varices were the complications with most influence on in-hospital mortality.

Seasonal patterns of hospital treatment for inflammatory bowel disease in Italy

AIM

It is still debated whether clinical flare-ups of chronic inflammatory bowel disease follow a seasonal pattern, and the various reports are based on general practitioners' records or hospital discharge charts. There are, however, no specific figures for treatment in hospital gastroenterology units, which serve as a reference point for these disorders. This study was therefore designed to investigate whether there is a seasonal pattern in admissions for inflammatory intestinal disease in Italy, differing from what is generally known about gastrointestinal pathologies, since there are no nation-wide figures on the subject.

METHODS

The RING (Ricerca Informatizzata in Gastroenterologia) project is an observational study collecting hospital discharge forms from 22 centers in Italy.

RESULTS

From winter 2000 to autumn 2003, the 22 gastroenterology units participating in the RING project discharged 32,357 patients following ordinary hospital admissions. Of these, 2,856 (8.8%) had a main diagnosis of inflammatory bowel disease: 1,541 Crohn's disease, and 1,315 ulcerative colitis. No seasonal patterns were detected for either category, or when the analysis was done by age, sex and site of disease.

CONCLUSIONS

The most serious flare-ups of inflammatory bowel disease, i.e. those requiring routine hospital treatment, do not appear to follow any seasonal pattern, regardless of the site of the disease or the patient's age or sex.

Multi-scale analysis of the toraymyxin adsorption cartridge. Part I: molecular interaction of polymyxin B with endotoxins

Endotoxins or lipopolysaccharides are the main constituents of the outer leaflet of Gram-negative bacteria membrane and play a central role in the pathogenesis of the septic shock. Polymyxin B has both antibacterial and antiendotoxin capability; indeed it is able to destroy the bacterial outer membrane and bind endotoxin neutralizing its toxic effects. Cartridges containing polymyxin B-immobilized fibers (Toraymyxin PMX-F, Toray Industries, Japan) are used in extracorporeal hemoperfusion to remove circulating endotoxin. The aim of this study is the characterization of the polymyxin B-endotoxin system at the molecular level, thus providing quantitative evaluation of the binding forces exerted in the molecular complex. Polymyxin B was interfaced with five molecular models of lipopolysaccharides differing in their structure and molecular mechanics simulations were performed at different intermolecular distances aimed at calculating the interaction energies of the complex. Binding forces were calculated by fitting interaction energies data. Results show that in the short range the polymyxin B-endotoxin complex is mediated by hydrophobic forces and in the long range the complex is driven by ionic forces only. From a mechanical standpoint, polymyxin B-endotoxin complex is characterized by maximum binding forces ranging between 1.39 nN to 3.79 nN. The knowledge of the binding force behavior at different intermolecular distances allows further investigations at higher scale level (Part II).

A numerical and experimental study of compliance and collapsibility of preterm lamb tracheae

Knowledge of the mechanical behaviour of immature tracheae is crucial in order to understand the effects exerted on central airways by ventilatory treatments, particularly of Total Liquid Ventilation. In this study, a combined experimental and computational approach was adopted to investigate the compliance and particularly collapsibility of preterm lamb tracheae in the range of pressure likely applied during Total Liquid Ventilation (-30 to 30 cmH2O). Tracheal samples of preterm lambs (n = 5; gestational age 120-130 days) were tested by altering transmural pressure from -30 to 30 cmH2O. Inflation (Si) and collapsing (Sc) compliance values were calculated in the ranges 0 to 10 cmH2O and -10 to 0 cmH2O, respectively. During the tests, an asymmetric behaviour of the DeltaV/V0 vs. P curves at positive and negative pressure was observed, with mean Si = 0.013 cmH2O(-1) and Sc = 0.053 cmH2O(-1). A different deformed configuration of the sample regions was observed, depending on the posterior shape of cartilaginous ring. A three-dimensional finite-element structural model of a single tracheal ring, based on histology measurements of the tested samples was developed. The model was parameterised in order to represent rings belonging to three different tracheal regions (craniad, median, caudal) and numerical analyses replicating the collapse test conditions were performed to evaluate the ring collapsibility at pressures between 0 and -30 cmH2O. Simulation results were compared to experimental data to verify the model's reliability. The best model predictions occurred at pressures -30 to -10 cmH2O. In this range, a model composed of median rings best interpreted the experimental data, with a maximum error of 2.7%; a model composed of an equal combination of all rings yielded an error of 12.6%.

Pressure drop vs flow relationship in isolated preterm lamb tracheae

Knowledge of immature tracheae mechanical behavior is fundamental in understanding the effects exerted on the upper airways by tidal liquid ventilation (TLV). Particularly, negative pressure can take place along the airways during expiration, which can cause airway collapse and flow limitation; therefore, representing a critical issue in preterm infant patients, whose airways are less stiff than adult ones. In this study, we investigated the expiratory pressure drop vs flow relationship of isolated preterm lamb tracheal samples to determine their hydraulic resistance, collapse pressure and collapse flow rate; a liquid flow through the samples was obtained by applying negative pressure at the outlet (cephalad) extremity of the tra-cheal sample, while keeping the inlet (caudal) extremity at atmospheric pressure. Histological analyzes were performed on the tracheal samples after each test session, in order to examine the morphological structure of the tracheal wall. Flow resistance tests demonstrated progressive lumen narrowing at increasing pressure drop (&#8710;P=P in -P out ). The flow rate increased with &#8710;P un-til a plateau was reached, and then decreased, describing the onset of a collapse phenomenon; however, complete occlusion was not reached. The tracheal samples demonstrated a similar behavior to that of a Starling resistor during the collapse phase: when a critical &#8710;P was reached, collapse was observed starting at the outlet region, which was subjected to the greatest negative pressure, then propagating towards the caudal direction. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 177-82).

Myosin head mechanical performance under different conformational change mechanisms

The present paper puts forward a mathematical approach to model the conformational changes of the myosin head due to ATP hydrolysis, which determine the head swinging and consequent sliding of the actin filament. Our aim is to provide a simple but effective model simulating myosin head performance to be integrated into the overall model of sarcomere mechanics under development at our Laboratory (J. Biomech. 34 (2001) 1607). We began by exploring myosin head mechanics in recent findings about myosin ultrastructure, morphology and energetics in order to calculate the working stroke distance (WS) and the force transmitted to the actin filament during muscle contraction. Two different working stroke mechanisms were investigated, assuming that the swinging of the myosin head occurs either as a consequence of purely conformational changes (Science 261 (1993a) 58) or by thermally driven motion (ratchet mechanism) followed by conformational changes (Cell 99 (1999) 421). Our results show that force and WS values vary markedly between the two models. The maximum force generated is about 10 pN for the first model and 31 pN for the second model, and the WSs are about 13 and 4 nm, respectively. These results are then discussed and compared with published data. The experimental data used for comparison are scarce and non-homogeneous; hence, the final remarks do not lead to definite conclusions. In any event, relatively speaking, the first model is more coherent with experimental findings.