Microscopic dynamics of gas molecules confined in porous channel-like ice structure.

In the rich ice polymorphism landscape, ice XVII, metastable at ambient pressure and at temperatures below 130 K, is surely one of the most interesting from both fundamental and technological perspectives due to its porosity, i.e., its capability to repeatedly absorb and desorb molecular hydrogen by dosing the gas at pressures even below the ambient one. Here, owing to this exceptional key feature, we investigate the roto-vibrational dynamics of the H2 molecules trapped in the fully deuterated ice XVII structure. Making use of the high-resolution and brilliance of the TOSCA neutron vibrational spectrometer, combined with high-resolution Raman data, we are able to efficiently distinguish the center-of-mass translational bands from the rotational ones and to study them as a function of the guest filling of the ice structure, unraveling a peculiar behavior for the confined particle in a low-dimensional system. Moreover, we also report the study of the microscopic dynamics of confined nitrogen and oxygen, which are the most abundant molecular species in the atmosphere and are of paramount interest for technological applications. Finally, we show that the ice XVII porosity is a unique feature, especially in the low pressure regime, within the emptied-hydrate phases discovered to date.

Effects of bilateral lung transplantation on cardiac autonomic modulation and cardiorespiratory coupling: a prospective study.

BACKGROUND: Although cardiac autonomic modulation has been studied in several respiratory diseases, the evidence is limited on lung transplantation, particularly on its acute and chronic effects. Thus, we aimed to evaluate cardiac autonomic modulation before and after bilateral lung transplantation (BLT) through a prospective study on patients enrolled while awaiting transplant. METHODS: Twenty-two patients on the waiting list for lung transplantation (11 women, age 33 [24-51] years) were enrolled in a prospective study at Ospedale Maggiore Policlinico Hospital in Milan, Italy. To evaluate cardiac autonomic modulation, ten minutes ECG and respiration were recorded at different time points before (T0) and 15 days (T1) and 6 months (T2) after bilateral lung transplantation. As to the analysis of cardiac autonomic modulation, heart rate variability (HRV) was assessed using spectral and symbolic analysis. Entropy-derived measures were used to evaluate complexity of cardiac autonomic modulation. Comparisons of autonomic indices at different time points were performed. RESULTS: BLT reduced HRV total power, HRV complexity and vagal modulation, while it increased sympathetic modulation in the acute phase (T1) compared to baseline (T0). The HRV alterations remained stable after 6 months (T2). CONCLUSION: BLT reduced global variability and complexity of cardiac autonomic modulation in acute phases, and these alterations remain stable after 6 months from surgery. After BLT, a sympathetic predominance and a vagal withdrawal could be a characteristic autonomic pattern in this population.

Particulate matter phagocytosis induces tissue factor in differentiating macrophages.

Airborne exposure to particulate matter with diameter < 10 mcM (PM10) has been linked to an increased risk of thromboembolic events, but the mechanisms are not completely understood. The aim of this study was to evaluate the effect of PM10 phagocytosis on the release of procoagulant molecules in human differentiating macrophages, and that of PM10 inhalation in an experimental model in rats. Human monocytes were separated from the peripheral blood by the lymphoprep method, differentiated in vitro and treated with standard PM10 or vehicle. Sprague-Dawley rats were instilled intratracheally with PM10 or vehicle alone. The outcome was expression of proinflammatory genes and of tissue factor (TF). In human differentiating macrophages, PM10 exposure upregulated inflammatory genes, but most consistently induced TF mRNA and protein levels, but not TF protein inhibitor, resulting in increased TF membrane expression and a procoagulant phenotype. Differentiation towards the anti-inflammatory M2 phenotype inhibited PM10 -mediated TF expression. TF induction required phagocytosis of PM10 , whereas phagocytosis of inert particles was less effective. PM10 phagocytosis was associated with a gene expression profile consistent with intracellular retention of iron, inducing oxidative stress. Both PM10 and iron activated the stress kinases ERK1/2 pathway, involved in the induction of TF expression. In rats, alveolar exposure to PM10 was associated with pulmonary recruitment of inflammatory cells and resulted in local, but not systemic, induction of TF expression, which was sufficient to increase circulating TF levels. In conclusion, TF induction by differentiating lung macrophages, activated following phagocytosis, contributes to the increased risk of thromboembolic complications associated with PM10 exposure.

Measuring endogenous changes in serotonergic neurotransmission in humans: a [11C]CUMI-101 PET challenge study.

Serotonin (5-HT) neurotransmission is implicated in cognitive and emotional processes and a number of neuropsychiatric disorders. The use of positron emission tomography (PET) to measure ligand displacement has allowed estimation of endogenous dopamine release in the human brain; however, applying this methodology to assess central 5-HT release has proved more challenging. The aim of this study was to assess the sensitivity of a highly selective 5-HT(1A) partial agonist radioligand [(11)C]CUMI-101 to changes in endogenous 5-HT levels induced by an intravenous challenge with the selective 5-HT re-uptake inhibitor (SSRI), citalopram, in healthy human participants. We studied 15 healthy participants who underwent PET scanning in conjunction with [(11)C]CUMI-101 after receiving an intravenous infusion of citalopram 10 mg or placebo in a double-blind, crossover, randomized design. Regional estimates of binding potential (BP(ND)) were obtained by calculating total volumes of distribution (V(T)) for presynaptic dorsal raphe nucleus (DRN) and postsynaptic cortical regions. Relative to placebo, citalopram infusion significantly increased [(11)C]CUMI-101 BP(ND) at postsynaptic 5-HT(1A) receptors in several cortical regions, but there was no change in binding at 5-HT(1A) autoreceptors in the DRN. Across the postsynaptic brain regions, citalopram treatment induced a mean 7% in [(11)C]CUMI-101 BP(ND) (placebo 1.3 (0.2); citalopram 1.4 (0.2); paired t-test P=0.003). The observed increase in postsynaptic [(11)C]CUMI-101 availability identified following acute citalopram administration could be attributable to a decrease in endogenous 5-HT availability in cortical terminal regions, consistent with preclinical animal studies, in which acute administration of SSRIs decreases DRN cell firing through activation of 5-HT(1A) autoreceptors to reduce 5-HT levels in postsynaptic regions. We conclude that [(11)C]CUMI-101 may be sensitive to changes in endogenous 5-HT release in humans.

GH levels and insulin sensitivity are differently associated with biomarkers of cardiovascular disease in active acromegaly.

CONTEXT: Acromegaly is characterized by GH excess and insulin resistance. It is not known which of these disorders is responsible for the increased atherogenic risk in these patients. OBJECTIVE: To analyse the associations of GH and homoeostasis model assessment (HOMA) with biomarkers of cardiovascular disease and to compare the above-mentioned variables between patients with active acromegaly and controls. DESIGN AND SETTING: This open cross-sectional study was conducted at a University Hospital. PATIENTS: Twenty-two outpatients were compared with sex- and age-matched control subjects. MAIN OUTCOMES: Included clinical features, hormonal status, markers of insulin resistance, lipoprotein profile and biomarkers of cardiovascular disease. RESULTS: Patients presented higher triglyceride (median [IQR]) (1·2[1·1-1·6] vs 0·9[0·6-1·1] mm, P < 0·05), low-density lipoprotein-cholesterol (LDL-C) (mean ± SD) (3·5 ± 0·9 vs 3·0 ± 0·7mm, P < 0·05), apoB (0·98 ± 0·23 vs 0·77 ± 0·22 g/l, P < 0·05), free fatty acid (0·69 ± 0·2 vs 0·54 ± 0·2 mM, P < 0·05), oxidized-LDL (120 ± 22 vs 85 ± 19 U/l, P < 0·05) and endothelin-1 (0·90 ± 0·23 vs 0·72 ± 0·17 ng/l, P < 0·05) levels, increased cholesteryl ester transfer protein (CETP) activity (179 ± 27 vs 138 ± 30%/ml/h, P < 0·01) and lower C reactive protein (CRP) (0·25[0·1-0·9] vs 0·85[0·4-1·4] mg/l; P < 0·05) levels than control subjects. Vascular cell adhesion molecule (VCAM-1) concentration was not different. By multiple linear regression analyses, HOMA explained the variability of triglycerides (25%), high-density lipoprotein-cholesterol (HDL-C) (30%) and CETP activity (28%), while GH independently predicted LDL-C (18%), oxidized-LDL (40%) and endothelin-1 levels (19%). CONCLUSIONS: In patients with active acromegaly, GH excess contributes to the development of insulin resistance, and the interaction between both disturbances would be responsible for the appearance of atherogenic pro-oxidative and pro-inflammatory factors. Insulin resistance would be preferably associated with an atherogenic lipoprotein profile and to high CETP activity, while high GH levels would independently predict the increase in LDL-C, ox-LDL and endothelin-1.

Evidence of Air Trapping During Ex Vivo Lung Perfusion: A Swine Experimental Lung Imaging and Mechanics Study.

Ex vivo lung perfusion (EVLP) allows the ventilation and perfusion of lungs to evaluate their viability for transplantation. The aim of this study is to compare the mechanical, morphologic and functional properties of lungs during EVLP with values obtained in vivo to guide a safe mechanical ventilation strategy. Lungs from 5 healthy pigs were studied in vivo and during 4 hours of EVLP. Lung compliance, airway resistance, gas exchange, and hemodynamic parameters were collected at positive end-expiratory pressure (PEEP) of 5 cm H2O. Computed tomography was performed at PEEP 0, PEEP 5, and total lung capacity (TLC). Lung pressure-volume (PV) curves were performed from PEEP 0 to TLC. Lung compliance decreased during EVLP (53 ± 5 mL/cm H2O vs 29 ± 7 mL/cm H2O, P < .05), and the PV curve showed a lower inflection point. Gas content (528 ± 118 mL vs 892 ± 402 mL at PEEP 0) and airway resistance (25 ± 5 vs 44 ± 9 cmH2O/L∗s-1, P < .05) were higher during EVLP. Alveolar dead space (5% ± 2% vs 17% ± 6%, P < .05) and intrapulmonary shunt (9% ± 2% vs 28% ± 13%, P < .05) increased ex vivo compared to in vivo, while the partial pressure of oxygen to inspired oxygen fraction ratio (PO2/FiO2) did not differ (468 ± 52 mm Hg vs 536 ± 14 mm Hg). In conclusion, during EVLP lungs show signs of air trapping and bronchoconstriction, resulting in low compliance and increased alveolar dead space. Intrapulmonary shunt is high despite oxygenation levels acceptable for transplantation.

Increased oxidized low density lipoprotein associated with high ceruloplasmin activity in patients with active acromegaly.

OBJECTIVE: Active acromegaly is associated with increased mortality from cardiovascular causes. Several studies have shown increased atherogenic risk factors and biomarkers of inflammation and atherosclerosis in association with growth hormone excess. The aim of this study was to evaluate oxidized low density lipoprotein (oxLDL) levels and some modulators of LDL oxidative modification in patients with acromegaly. DESIGN: Open transversal study. PATIENTS: Fifteen patients with active acromegaly and 15 controls were studied. MEASUREMENTS: We evaluated the levels of oxLDL, thiobarbituric acid reactive substances (TBARS), ceruloplasmin, bilirubin, uric acid and total reactive antioxidant potential, and the activities of ceruloplasmin, myeloperoxidase, superoxide distmutase, paraoxonase 1, and platelet activating factor acethylhydrolase. Statistical analysis was performed including body mass index as a covariate or as a fixed variable. RESULTS: Patients with acromegaly showed significantly higher levels of oxLDL (120 +/- 19 vs. 86 +/- 20 U/l, P < 0.001) and endothelin (P < 0.05), increased ceruloplasmin activity (P < 0.01) and a trend towards higher values in TBARS concentration (P = 0.07) in comparison to healthy controls. OxLDL was positively associated with GH, IGF-I and its binding protein 3 (r = 0.63, P < 0.001; r = 0.53, P < 0.01; and r = 0.56, P < 0.01; respectively). OxLDL showed direct associations with endothelin-1 (r = 0.53, P < 0.01) and ceruloplasmin activity (r = 0.43, P < 0.05). The other parameters evaluated were similar in both groups. CONCLUSIONS: The increase in plasma oxLDL levels, a direct marker of the plaque formation, could constitute a link between atherosclerosis and active acromegaly. LDL oxidation would not be the consequence of diminished antioxidant defences, but of an enhancement in prooxidant factors like ceruloplasmin.

Alterations in biomarkers of cardiovascular disease (CVD) in active acromegaly.

OBJECTIVES: In acromegalic patients, cardiovascular and metabolic comorbidities contribute to enhance mortality. Available data on the lipoprotein profile of these patients are controversial. Our aim was to characterize the lipoprotein profile and emergent biomarkers of cardiovascular disease in active acromegalic patients in comparison with sex- and age-matched healthy controls. PATIENTS: Eighteen patients with active acromegaly and 18 controls were studied. MEASUREMENTS: Glucose levels, hormonal status, lipoprotein profile and C reactive protein (CRP) were evaluated by standardized methods. Cholesteryl ester transfer protein (CETP) and lipoprotein-associated phospholipase A(2 )(Lp-PLA(2)) were measured by radiometric techniques, endothelin-1 and vascular cell adhesion molecule (VCAM)-1 by enzyme-linked immunosorbent assay, and leucocytes CD18, CD49d and CD54 by flow cytometry. RESULTS: After adjusting for body mass index (BMI), acromegalic patients presented a more atherogenic lipoprotein profile, consisting of higher levels of triglycerides and apolipoprotein B and alterations in the ratios which estimate insulin resistance and atherogenic risk. CETP activity was significantly increased in acromegalic patients as compared to controls (168 +/- 17 vs. 141 +/- 30% per ml h, respectively; P < 0.05). Endothelin-1 levels evidenced an increase in the patients' group (0.9 +/- 0.2 vs. 0.7 +/- 0.2 ng/l, respectively; P < 0.01) and showed positive and significant correlations with GH, IGF-1 and IGFBP-3 (r = 0.45, 0.42 and 0.44, respectively; P < 0.01 for all of them; with BMI as a fixed variable). Lymphocytes from acromegalic patients showed increased CD49d content (282 +/- 59 vs. 246 +/- 48 arbitrary units, respectively; P < 0.05). CONCLUSIONS: Taken together, the alterations described seem to contribute to constituting a state of higher propensity for the development of atherosclerotic cardiovascular disease, which adds to the presence of specific cardiomyopathy.

Low adiponectin levels in primary hypertriglyceridemic male patients.

BACKGROUND AND AIMS: Adiponectin is an adipokine highly and specifically expressed by adipose cells with antiatherogenic and antiinflammatory activities. The aim of the present study was to evaluate plasma adiponectin concentration in patients with primary hypertriglyceridemia and its relationship with metabolic parameters. METHODS AND RESULTS: Male patients with primary hypertriglyceridemia and without the metabolic syndrome (n=22) were compared with normotriglyceridemic individuals (n=25). Plasma adiponectin concentration was measured by standardised enzyme-linked immunosorbent assay. Body mass index, waist circumference, glucose, insulin and non-esterified fatty acid levels, lipoprotein profile, and CETP activity were evaluated. Adiponectin levels were significantly decreased in hypertriglyceridemic patients in comparison with normotriglyceridemic subjects (4292+/-1717 vs. 6939+/-3249 ng/ml, p<0.005, respectively). Adiponectin was negatively associated with glucose (r=-0.44, p<0.01), insulin (r=-0.37, p<0.01), HOMA (r=-0.40, p<0.01), triglycerides (r=-0.36, p<0.01), VLDL-C (r=-0.34, p<0.05), and CETP (r=-0.47, p<0.001). Positive and significant correlations were observed with QUICKI (r=0.49, p<0.001) and HDL-C (r=0.33, p<0.05). In the multiple linear regression analysis, considering waist circumference, QUICKI, Log-triglycerides, HDL-C, and CETP as independent variables, Log-adiponectin showed a positive correlation with QUICKI, with an r(2)=0.229 and p<0.001. Therefore, the independent variable QUICKI explained the 23% of the variance in Log-adiponectin concentration. CONCLUSIONS: We found low adiponectin levels in a population of primary hypertriglyceridemic men without the metabolic syndrome and an independent relationship between adiponectin concentration and insulin resistance. A reduction in insulin sensitivity and its impact on adiponectin concentration could be linked to high non-esterified fatty acid levels, increased triglyceride synthesis in the liver and impaired catabolism of triglyceride-rich lipoproteins.

Lung Transplant From Donor With Tracheal Bronchus: Case Report and Literature Review.

Donor lung abnormalities are quite rare; one of them is the presence of bronchial anomalies, whose incidence range is from 0.1% to 0.5%. The upper right tracheal bronchus is one of the most frequent anatomic variations. We present a case of successful double lung transplant in a young female patient affected by cystic fibrosis from a donor with upper right tracheal bronchus, emerging 2 rings before the tracheal carina. During implantation of the left lung, we performed a double apical segmentectomy on back table; therefore, the right lung was implanted with the standard technique. Four cases of graft transplant characterized by the presence of tracheal bronchus are reported in the scientific literature; the authors report 4 different technical solutions to tackle the problem of anatomic anomaly. We report the first case of graft segmentectomy at back table suggesting a simple, safe, and time-sparing procedure. In conclusion, provided that the team has sufficient skill in reductive surgery at the back table and the anthropometric data are permissive, we stress the opportunity to downsize the graft in order to minimize anastomotic risks and save time.

Epstein-Barr Virus-Related Post-Transplant Lymphoproliferative Disorders in Cystic Fibrosis Lung Transplant Recipients: A Case Series.

BACKGROUND: Solid organ transplantation is associated with a higher risk of Epstein-Barr virus (EBV)-related lymphoproliferative disease due to immunosuppressive regimen. Little evidence is currently available on post-transplant lymphoproliferative disorders (PTLDs) in the lung transplant (LuTx) setting, particularly in cystic fibrosis (CF) recipients. METHODS: We retrospectively analyzed all the cases of PTLDs that occurred in our LuTx center between January 2015 and December 2017. We reviewed clinical and radiologic data, donor and recipient EBV serostatus, immunosuppressive therapy, histologic data, and follow-up of these patients. RESULTS: A total of 77 LuTxs were performed at our center in the study period; 39 (50.6%) patients had CF; 4 developed EBV-related PTLDs. They were all young (17-26 years) CF patients with high serum EBV DNA load. Disease onset was within the first 3 months after LuTx. In 3 cases presentation was associated with fever and infection-like symptoms, whereas in 1 case radiologic suspicion arose unexpectedly from a CT scan performed for different clinical reasons. Diagnosis was reached through lung biopsy in all cases. All patients received rituximab, cyclophosphamide, doxorubicin hydrochloride (hydroxydaunomycin), vincristine sulfate (Oncovin), and prednisone with variable response and complications. CONCLUSION: In our experience, the early development of EBV-related PTLD was a highly aggressive, life-threatening condition, which exclusively affected young CF patients in the early post-transplant period. The rate of this complication was relatively high in our population. Diagnosis with lung biopsy is crucial in all suspected cases and regular monitoring of EBV DNA levels is of utmost importance given the high correlation with PTLDs in patients at increased risk.

Surveillance Transbronchial Biopsy Program to Evaluate Acute Rejection After Lung Transplantation: A Single Institution Experience.

BACKGROUND: There is no unanimity in the literature regarding the value of transbronchial biopsies (TBBs) performed at a scheduled time after lung transplantation (surveillance TBBs [SBs]), compared to biopsies performed for suspected clinical acute rejection (clinically indicated TBBs [CIBs]). This study exposes an assessment of our experience over the last 4 years through a retrospective analysis of the data collected. METHODS: In our center, SBs are performed at 3, 6, and 12 months after a transplant. Data from 110 patients who underwent a TBB were collected from January 2013 to November 2017. Clinical and functional data along with the histologic results and complications were collected. RESULTS: Overall 251 procedures were performed: 223 for surveillance purposes and 28 for clinical indications. The SBs diagnostic rate was 84%. A grade 2 acute rejection (AR) was detected in 9 asymptomatic patients, all of whom were medically treated, with downgrading of AR documented in all cases. The rate of medical intervention in the SB group was 8%. The CIBs diagnostic rate was 96%. The rate of AR detected by CIBs was significantly higher than by SBs (36% versus 4%; P < .0001). Overall the major complication rate was 4%; no patients required transfusions and no mortality occurred in the patient cohort. CONCLUSIONS: The surveillance protocol did not eliminate the necessity of CIBs, but in 8% of patients early rejection was histologically assessed. The correlation between histologic and clinical data allows a more careful approach to transplanted patients.

Immunocytochemical detection of occult tumor cells in the bone marrow: prognostic impact on early stages of lung cancer.

OBJECTIVES: This study was designed to verify the prognostic impact of occult tumor cells in the bone marrow of stage I and II non-small-cell lung cancer patients using cytokeratin as a micrometastatic marker. METHODS: One hundred and fifty-two patients with stage I and II non-small-cell lung cancer, who underwent radical surgery by pulmonary lobectomy, were entered into the study. Bone marrow from fragments of resected ribs, and primary tumors were stained by anti-cytokeratin 18 antibody. Fourteen bone marrow specimens from patients without malignancy were used as a control group. Cancer recurrence was the study end point. RESULTS: All the primary tumors were positive for cytokeratin; occult tumor cells were detected in 38 bone marrow specimens (25%). The prevalence of the occult tumor cells was not related to age, gender, tumor stage, histological differentiation or grade. The mean follow-up time was 35.3 months; 68 patients developed recurrence; the mean time for recurrence was 21.2 months. The general disease-free interval was not related to the presence of occult tumor cells in the bone marrow. This result did not change when grouping the patients by tumor stage. The stage was the best predictor of cancer recurrence (Cox proportional hazards model ratio: 2.09; p = 0.0026). CONCLUSIONS: This study confirms that immunocytochemical analysis detects occult tumor cells in the bone marrow of at least 25% of patients surgically treated for stage I and II non-small-cell lung cancer. These occult tumor cells do not have any impact on the disease-free interval.

Lobar Lung Transplantation From Deceased Donor: Monocentric Experience.

INTRODUCTION: Lung transplantation is considered a therapeutic option in selected patients affected by end-stage pulmonary disease. The mortality on the waiting list is mainly attributed to the shortage of the donor pool available for transplantation. There are various strategies to overcome this shortage; one of them is lobar transplantation. METHODS: The aim of the current study was to analyze the outcome of lobar lung transplantation from deceased donors in our Lung Transplant Center. Overall survival, perioperative mortality and morbidity, problem on bronchial anastomosis, and chronic rejection were prospectively recorded in a 5-year time-frame. RESULTS: From November 2010 to October 2015, we performed 100 lung transplantations; 6 of which (6%) were lobar transplantations from deceased donors. Three recipients were on an emergency list due to preoperative extracorporeal support. The causes of lobectomy leading to lobar transplantation were: size mismatch (3), iatrogenic vascular damage (2), and chronic atelectasis (1). One patient died 5 months after surgery for sepsis; and 5 patients were alive at the study end (median follow-up: 17.5 months). Prevalence of grade 3 primary graft dysfunction at 72 hours was 50%. One patient developed bronchial stenosis. No cases of chronic rejection were recorded. CONCLUSIONS: Lobar transplantation can be considered a valid tool to overcome the donor pool shortage in selected cases; such a technique has proved particularly useful in critically ill patients who were scheduled in an emergency transplant program.

Lung Allocation Score: A Single-Center Simulation.

BACKGROUND: The lung allocation score (LAS) was introduced in the United States in May 2005 with the main goal of reducing the waiting list mortality of patients with end-stage lung diseases, but also to enhance the lung transplant benefit and improve the management of urgent candidates. Several papers have reported that LAS resulted in a reduction of the waiting list mortality but no significant survival benefit was noted. METHODS: We evaluate the usefulness of LAS as a predictor for lung transplantation outcome in 123 patients listed for lung transplantation in an Italian center. Primary endpoints were waiting list mortality and posttransplant mortality at 1 year; secondary endpoints included perioperative circulatory support, cardiopulmonary bypass, primary graft dysfunction, and long-term survival after transplantation. RESULTS: We observed the absence of correlation between LAS and waiting list mortality. The LAS did not affect the long-term survival in our population. CONCLUSIONS: High LAS was predictive of primary graft dysfunction of grade 3 in the first 72 hours after transplantation.

Reflections on the use of robust and least-squares non-linear regression to model challenge tests conducted in/on food products.

In this research, we question the straight-forward use of the classical sum of squared error criterion for identifying the typical parameters of a primary model (like growth rate mumax and lag time lambda) when applied to growth curves obtained in and on food products. Firstly, we base our reflections on 62 Listeria monocytogenes laboratory challenge tests collected in various environments (broth, crushed cold-smoked salmon, and surface of cold-smoked salmon slices). Whereas growth data in broth resulted in residual values consistent with a Gaussian distribution, growth data in the crushed product and even more on the surface of slices appeared different. Secondly, we propose the use of an alternative so-called robust non-linear regression method suitable when experimental error is non-normally distributed, which seems, according to this research, typical for microbial challenge tests in/on food products, and which lead to apparent outliers or leverage points in the experimental data. Properties of the robust regression procedure are illustrated on simulated data first, whereafter its use on the considered challenge tests is illustrated. To conclude, reflections on the assumptions and related realism underlying challenge tests and recommendations for fitting growth curves obtained in and on food products are presented.

Putative physiological significance of vasopressin V1a receptor activation in rat pituicytes.

Physiological stimuli operative during, for example, dehydration or lactation, induce neurohypophysial astrocytes (pituicytes) to undergo reversible morphological changes, which in turn may modulate the release of vasopressin and oxytocin. To study the molecular mechanisms of this morphological plasticity, we used primary cultures of rat pituicytes. During stimulation with adenosine, pituicytes become stellate, which is characterized by a round, phase-bright soma and complex arborization, implying major cytoskeletal modifications. Following addition of vasopressin or oxytocin, stellate pituicytes revert to a flat shape. The effects of both hormones are mediated by V(1a) receptor activation, which also induces biphasic Ca(2+) (i) signals in pituicytes. Stellation reversal requires Ca(2+)-dependent activation of Cdc42, a small GTPase known to impact on the cytoskeleton. V(1a) receptor activation by vasopressin or oxytocin also stimulates [(3)H]taurine efflux from cultured pituicytes. As taurine inhibits vasopressin output from neurohypophysial terminals, we postulate a negative-feedback mechanism whereby secreted vasopressin limits its own availability. This stop signal might be reinforced by shape changes elicited by vasopressin in pituicytes. These results support the concept that, during specific physiological states, pituicyte V(1a) receptor activation modulates the release of neurohypophysial hormones.

Estimation of temperature dependent growth rate and lag time of Listeria monocytogenes by optical density measurements.

An automated turbidimetric system, Bioscreen C, was used to monitor growth of ten strains of Listeria monocytogenes at different temperatures. Several methods for estimation of maximum specific growth rate (mu(max)) and lag time (lag) from turbidimetric data were compared to values estimated from viable count data. By using a calibration factor, reliable estimations of mu(max) could be obtained from turbidimetric measurements. On the other hand, accurate estimations of lag required some viable count data.

Biological variability and exposure assessment.

Predictive models are now commonly used for exposure assessment, with growth parameters defined for each microbial species. In this study, we tried to take into account microbial growth variability among strains of a single species. Bacillus cereus in pasteurized milk was chosen to illustrate the influence of the biological variability on the outcome of exposure assessment. Each parameter of the exposure assessment (growth parameters, shelf-life conditions) was characterized by a probability distribution describing variability and/or uncertainty. The impact of the intra-species variability on the result of the exposure assessment was then quantified and discussed. Two simple domestic shelf life conditions were tested. The results confirm that the biological variability has a great impact on the accuracy of the result and should not be systematically neglected.

A quantitative approach for studying the effect of heat treatment conditions on resistance and recovery of Bacillus cereus spores.

When a bacterial population undergoes an unfavourable transient increase in temperature, a death phase followed by a lag and growth phase are observed for the surviving and cultivable population. The lag phase is of great interest in regard to food safety, but for bacterial spores, very few studies have been carried out on the evolution of lag time versus heat treatment duration. The experiments monitored on spores of two strains of Bacillus cereus showed a biphasic evolution of the lag time for germination of stressed spores with increase in heat treatment duration, at 90 degrees C, 95 degrees C and 100 degrees C and for different recovery conditions in laboratory medium. Initially, the lag time increased with the duration of the thermal stress up to an optimum. Subsequently, the lag time decreased, with increasing stress duration, to a threshold. The evolution of the lag time to germination of surviving spores, under the range of temperature tested, was similar to the evolution of the lag time to growth after mild-temperature treatments observed with vegetative cells of Escherichia coli and Listeria monocytogenes by Breand et al. (1997) [Breand, S., Fardel, G., Flandrois, J.-P., Rosso, L., Tomassone, R., 1997. A model describing the relationship between lag time and mild temperature increase duration. Int. J. Food Microbiol. 38, 157-167]. The mathematical model established from these investigations could also be applied in the case of heat-stressed spores. Moreover, it was observed that there was a significant linear relationship between the D-value and the treatment duration that gave the maximum lag time.