Biomedical subjects
Publications and source records attributed to A Singer.
The escape of Brownian motion through a narrow absorbing window in an otherwise reflecting boundary of a domain is a rare event. In the presence of a deep potential well, there are two long time scales, the mean escape time from the well and the mean time to reach the absorbing window. We derive a generalized Kramers formula for the mean escape time through the narrow window.
The Brn-3a POU family transcription factor is overexpressed in human cervical carcinoma biopsies and is able to activate expression of the human papilloma virus type 16 (HPV-16) upstream regulatory region (URR), which drives the expression of the E6 and E7 oncoproteins. Inhibition of Brn-3a expression in human cervical cancer cells inhibits HPV gene expression and reduces cellular growth and anchorage independence in vitro as well as the ability to form tumours in vivo. Here, we show that Brn-3a differentially regulates different HPV-16 variants that have previously been shown to be associated with different risks of progression to cervical carcinoma. In human cervical material, Brn-3a levels correlate directly with HPV E6 levels in individuals infected with a high risk variant of HPV-16, whereas this is not the case for a low-risk variant. Moreover, the URRs of high- and intermediate-risk variants are activated by Brn-3a in transfection assays, whereas the URR of a low-risk variant is not. The change of one or two bases in a low-risk variant URR to their equivalent in a higher-risk URR can render the URR responsive to Brn-3a and vice versa. These results help explain why the specific interplay between viral and cellular factors necessary for the progression to cervical carcinoma only occurs in a minority of those infected with HPV-16.
OBJECTIVE: The objective of this double-blind, randomised, placebo-controlled, multicentre clinical study was to demonstrate the non-inferiority and safety of the hypericum extract STW3-VI in a once-daily dosage regime in the treatment of moderate depression. During the 6-week treatment phase, the course of depression was documented by use of HAMD (items 1-17), the von Zerssen's Adjective Mood Scale (BfS) and the CGI scales. The primary objective of this 3-arm design study was to demonstrate the non-inferiority of hypericum extract STW3-VI (900 mg) to the SSRI citalopram (20 mg) and superiority of hypericum over placebo. METHODS: Outpatients (N = 388) suffering from moderate depression were enrolled. The safety and tolerability of hypericum extract in comparison to citalopram and placebo was investigated on the basis of CGI, the occurrence of adverse events and the investigation of laboratory parameters and vital signs. RESULTS: From almost identical baseline values of 21.9 +/- 1.2 points (hypericum extract), 21.8 +/- 1.2 points (citalopram) and 22.0 +/- 1.2 points (placebo), the HAMD score was reduced to 10.3 +/- 6.4 (hypericum extract), 10.3 +/- 6.4 (citalopram) and 13.0 +/- 6.9 (placebo), respectively. Based on this data, the statistical significant therapeutic equivalence of hypericum extract STW3-VI to citalopram (p < 0.0001) and the superiority of this hypericum extract over placebo (p < 0.0001) was demonstrated. At the end of treatment 54.2 % (hypericum extract), 55.9 % (citalopram) and 39.2 % (placebo) of the patients were assessed as therapy responders. The secondary efficacy parameters, change in BfS, CGI and amount of therapy responders showed that the hypericum group was not statistically different from the citalopram group, and significantly superior to the placebo group. Significantly more adverse events with "certain", "probable" or "possible" relation to study medication were documented in the citalopram group (hypericum: 17.2 %, citalopram: 53.2 %, placebo: 30 %). In most cases, the investigators assessed the tolerability of hypericum extract, citalopram and placebo as "good" or "very good". CONCLUSION: The non-inferiority of hypericum extract as compared to citalopram and the superiority of both active compounds to placebo were demonstrated, as well as a better safety and tolerability of hypericum extract in comparison to citalopram. These results revealed that hypericum extract STW3-VI is a good alternative to chemically defined antidepressants in the treatment of outpatients with moderate depression.
Pomatoschistus minutus show paternal care in a resource defence mating system. We investigated the effect of nest-site availability on parasitic spawning. Each experimental pool contained four potentially nest-building males, four females and nests-sites in shortage (2) or excess (6). Both treatments were conducted in two populations; one with natural nest-sites in excess, one with a nest-site shortage. Microsatellite-DNA revealed that all nest-holders had fertilized most of the eggs they tended. Yet, 35% of the nests contained eggs fertilized by another male and 14.4% of the males had performed parasitic spawning. There was no site or treatment effect. Several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost to the nest-holder in terms of lost mating success. Nest-holders with and without eggs and non-nesting males all spawned parasitically, generating a significantly lower opportunity for sexual selection compared to if there had been no parasitic spawning.
A Langevin particle is initiated at the origin with positive velocity. Its trajectory is terminated when it returns to the origin. In 1945, Wang and Uhlenbeck posed the problem of finding the joint probability density function (PDF) of the recurrence time and velocity, naming it "the recurrence time problem". We show that the short-time asymptotics of the recurrence PDF is similar to that of the integrated Brownian motion, solved in 1963 by McKean. We recover the long-time t(-3/2) decay of the first arrival PDF of diffusion by solving asymptotically an appropriate variant of McKean's integral equation.
We consider the trajectories of particles diffusing between two infinite baths of fixed concentrations connected by a channel, e.g., a protein channel of a biological membrane. The steady state influx and efflux of Langevin trajectories at the boundaries of a finite volume containing the channel and parts of the two baths is replicated by termination of outgoing trajectories and injection according to a residual phase space density. We present a simulation scheme that maintains averaged fixed concentrations without creating spurious boundary layers, consistent with the assumed physics.
The prediction of ionic currents in protein channels of biological membranes is one of the central problems of computational molecular biophysics. Existing continuum descriptions of ionic permeation fail to capture the rich phenomenology of the permeation process, so it is therefore necessary to resort to particle simulations. Brownian dynamics (BD) simulations require the connection of a small discrete simulation volume to large baths that are maintained at fixed concentrations and voltages. The continuum baths are connected to the simulation through interfaces, located in the baths sufficiently far from the channel. Average boundary concentrations have to be maintained at their values in the baths by injecting and removing particles at the interfaces. The particles injected into the simulation volume represent a unidirectional diffusion flux, while the outgoing particles represent the unidirectional flux in the opposite direction. The classical diffusion equation defines net diffusion flux, but not unidirectional fluxes. The stochastic formulation of classical diffusion in terms of the Wiener process leads to a Wiener path integral, which can split the net flux into unidirectional fluxes. These unidirectional fluxes are infinite, though the net flux is finite and agrees with classical theory. We find that the infinite unidirectional flux is an artifact caused by replacing the Langevin dynamics with its Smoluchowski approximation, which is classical diffusion. The Smoluchowski approximation fails on time scales shorter than the relaxation time 1/gamma of the Langevin equation. We find that the probability of Brownian trajectories that cross an interface in one direction in unit time Deltat equals that of the probability of the corresponding Langevin trajectories if gammaDeltat=2 . That is, we find the unidirectional flux (source strength) needed to maintain average boundary concentrations in a manner consistent with the physics of Brownian particles. This unidirectional flux is proportional to the concentration and inversely proportional to sqrt[Deltat ] to leading order. We develop a BD simulation that maintains fixed average boundary concentrations in a manner consistent with the actual physics of the interface and without creating spurious boundary layers.
OBJECTIVE: The objective of this double-blind, multi-center clinical study was to demonstrate the non-inferiority of hypericum extract versus sertraline in the treatment of moderate depression. METHODS: A total of 241 patients with a diagnosis of moderate depressive disorder (according to ICD-10 criteria) were randomized with either 50 mg sertraline or 612 mg hypericum extract (hypericum group n = 123; sertraline group n = 118). According to the study protocol, 200 patients were treated for at least 12 weeks ( n = 102 hypericum extract; n = 98 sertraline); 81 patients in the hypericum group and 80 in the sertraline group were treated after week 12 for an additional 12 weeks. Thus, most patients were treated for a period of 6 months. The primary efficacy variable was the 17-item HAMD total score at the end of the first 12-week double-blind treatment period. RESULTS: After the first 12-week treatment period, the HAMD score decreased from almost identical initial values (22.0 +/- 1.1 for hypericum and 22.1 +/- 1.1 points for sertraline) to 8.3 +/- 5.5 points (hypericum) and 8.1 +/- 5.6 points (sertraline) (mean +/- SD) in the patients treated per-protocol (PP) population. The statistical test for non-inferiority (boundary delta = 3) revealed that hypericum extract is not inferior to sertraline ( P < 0.0001). The mean difference between the treatments was 0.1995 points, with a corresponding one-sided 97.5 % confidence interval (-infinity, 1.3772). In patients who continued treatment in the follow-up phase, the HAMD score at the end of the study was 5.7 +/- 4.8 points (hypericum group) and 7.1 +/- 6.3 points (sertraline group). Comparable improvement was also found for the von Zerssen's Adjective Mood Scale (BfS) and CGI during the first and second 12-week treatment period in both treatment groups. With 68.6 % of patients in the hypericum group and 70.4 % in the sertraline group, the percentage of patients rated as responders did not differ significantly between treatment groups (12 weeks). The adverse events of 12 patients in the hypericum group (9.8 %) and of 16 patients in the sertraline group (13.6 %) were possibly related to study medication. No basic differences in the treatment groups were observed and no interaction with concomitant medication was documented. In most cases , the investigators assessed the tolerability of hypericum extract and sertraline as "good" or "very good." CONCLUSIONS: The results indicate that hypericum extract STW 3 is not inferior to sertraline and that it is a well-tolerated drug for the treatment of moderate depression. These favorable effects were achieved with a once-daily dose of 612 mg of hypericum extract given for up to 24 weeks.
Flux between regions of different concentration occurs in nearly every device involving diffusion, whether an electrochemical cell, a bipolar transistor, or a protein channel in a biological membrane. Diffusion theory has calculated that flux since the time of Fick (1855), and the flux has been known to arise from the stochastic behavior of Brownian trajectories since the time of Einstein (1905), yet the mathematical description of the behavior of trajectories corresponding to different types of boundaries is not complete. We consider the trajectories of noninteracting particles diffusing in a finite region connecting two baths of fixed concentrations. Inside the region, the trajectories of diffusing particles are governed by the Langevin equation. To maintain average concentrations at the boundaries of the region at their values in the baths, a control mechanism is needed to set the boundary dynamics of the trajectories. Different control mechanisms are used in Langevin and Brownian simulations of such systems. We analyze models of controllers and derive equations for the time evolution and spatial distribution of particles inside the domain. Our analysis shows a distinct difference between the time evolution and the steady state concentrations. While the time evolution of the density is governed by an integral operator, the spatial distribution is governed by the familiar Fokker-Planck operator. The boundary conditions for the time dependent density depend on the model of the controller; however, this dependence disappears in the steady state, if the controller is of a renewal type. Renewal-type controllers, however, produce spurious boundary layers that can be catastrophic in simulations of charged particles, because even a tiny net charge can have global effects. The design of a nonrenewal controller that maintains concentrations of noninteracting particles without creating spurious boundary layers at the interface requires the solution of the time-dependent Fokker-Planck equation with absorption of outgoing trajectories and a source of ingoing trajectories on the boundary (the so called albedo problem).
Using a variational formulation, we derive the Kirkwood superposition approximation for systems at equilibrium in the thermodynamic limit. We define the entropy of the triplet correlation function and show that the Kirkwood closure brings the entropy to its maximal value. This approach leads to a different interpretation for the Kirkwood closure relation, usually explained by probabilistic considerations of dependence and independence of particles. The Kirkwood closure is generalized to finite volume systems at equilibrium by computing the pair correlation function in finite domains. Closure relations for high order correlation functions are also found using a variational approach. In particular, maximizing the entropy of quadruplets leads to the high order closure g(1234)=g(123)g(124)g(134)g(234)/[g(12)g(13)g(14)g(23)g(24)g(34)] used in the Born-Green-Yvon 2 equations which are a pair of integral equations for the triplet and pair correlation functions.
We report the ultrasound, computed tomographic, and magnetic resonance imaging findings in a case of extramedullary hematopoiesis presenting as a focal splenic mass in a patient with myelodysplastic syndrome. Ultrasound demonstrated a well-circumscribed hyperechoic mass, whereas computed tomography showed a heterogeneous mass better visualized after administration of intravenous contrast. On magnetic resonance imaging, the lesion was hypointense to the spleen on T1-weighted images, with increased signal on T2-weighted images, and demonstrated enhancement after intravenous contrast administration. Extramedullary hematopoiesis should be considered in the differential diagnosis for a splenic mass in any patient with a hematologic disorder.
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OBJECTIVE: To evaluate the incidence, outcome and predictive value of cytology showing glandular dyskaryosis. PARTICIPANTS: Fifty-seven women with a smear diagnosis of glandular dyskaryosis registered between January 1997 and December 2001. SETTING: Colposcopy and cytopathology units in a large district general hospital. RESULTS: Sixty smears in 57 women showing glandular dyskaryosis were identified from a cohort of 135,120 smears, giving an incidence of 0.05%. Hospital records were available for 50 women. Final diagnosis included 13 cases of cervical glandular intraepithelial neoplasia (CGIN), 4 microinvasive cervical adenocarcinomas, 2 undifferentiated tumours, 1 microinvasive squamous carcinoma, 21 cases of CIN and 13 cases of endometrial pathology (8 endometrial cancers). Twelve women had coexistent squamous and glandular disease. Forty-five out of 50 women had significant pathology (positive predictive value 90%). Colposcopy was seen to be of limited value in assessment of smears showing glandular dyskaryosis. Only 1 out of 13 glandular lesions was diagnosed by colposcopy. CONCLUSION: Smears showing glandular dyskaryosis are associated with significant pathology in 90% of cases and malignancy in 32% of cases. Hence, women with a smear showing glandular dyskaryosis should be referred urgently to a colposcopy clinic and flagged up as suspected cancer. Glandular dyskaryosis should be included in the national referral criteria for suspected gynaecological cancer.
This prospective observational study was carried out to evaluate the efficacy of large loop excision of the transformation zone (LLETZ) as a management strategy for women with four or more smears showing borderline changes or mild dyskaryosis. A total of 102 women with four or more smears showing minor abnormalities and no colposcopic evidence of high-grade disease opted to undergo LLETZ in preference to continued cytological surveillance. Histology of the LLETZ specimens showed 11 cases of CIN2/3, one CGIN, 32 CIN1 and 10 HPV changes. In 97 of the 102 (95%) women, the follow-up cervical smear reverted to negative.
Perineuronal nets (PNs) are known as chondroitin sulfate-rich, lattice-like coatings of the extracellular matrix ensheathing mainly GABAergic, parvalbumin-containing neurons especially in the cerebral cortex. PNs have also been detected around GABA-immunonegative cells which were shown to be not aminergic, cholinergic, nitrinergic or peptidergic in various brain regions of some mammalian species. To find out whether glycine and aspartate may occur in net-bearing neurons the present study was focused on the rat medial nucleus of the trapezoid body (MNTB) which contains a large portion of cells immunoreactive for these amino acids, but appears to be devoid of GABA-immunoreactive cell bodies. PNs were detected around many glycine- and aspartate-immunopositive neurons in the MNTB by carbocyanine double labeling and confocal laser scanning microscopy. An additional finding was that the lectin-cytochemically stained extracellular matrix surrounds the calretinin-immunoreactive calyces of Held known as giant glutamatergic endbulbs which cover glycinergic principal cells in the MNTB. As elucidated by triple fluorescence labeling, the vast majority of somata co-expressed the calcium-binding proteins parvalbumin and calbindin, but not calretinin. The observed co-localization of PNs and immunoreactivity for the voltage-dependent potassium channel Kv3.1b - as an established marker of fast-firing parvalbumin-containing neurons - supports the assumed function of PNs as a cation exchanger ensuring rapid ion transport as required by highly active nerve cells.
The t(15;17) translocation, found in 95% of acute promyelocytic leukemia, encodes a promyelocytic leukemia (PML)-retinoic acid receptor alpha (RARalpha) fusion protein. Complete remission of acute promyelocytic leukemia can be obtained by treating patients with all-trans retinoic acid, and PML-RARalpha plays a major role in mediating retinoic acid effects in leukemia cells. A main model proposed for acute promyelocytic leukemia is that PML-RARalpha exerts its oncogenic effects by repressing the expression of retinoic acid-inducible genes critical to myeloid differentiation. By applying subtraction cloning to acute promyelocytic leukemia cells, we identified a retinoic acid-induced gene, PRAM-1 (PML-RARalpha target gene encoding an Adaptor Molecule-1), which encodes a novel adaptor protein sharing structural homologies with the SLAP-130/fyb adaptor. PRAM-1 is expressed and regulated during normal human myelopoiesis. In U937 myeloid precursor cells, PRAM-1 expression is inhibited by expression of PML-RARalpha in the absence of ligand and de novo superinduced by retinoic acid. PRAM-1 associates with other adaptors, SLP-76 and SKAP-55HOM, in myeloid cell lines and with protein tyrosine kinase lyn. By providing the first evidence that PML-RARalpha dysregulates expression of an adaptor protein, our data open new insights into signaling events that are disrupted during transformation by PML-RARalpha and induced by retinoic acid during de novo differentiation of acute promyelocytic leukemia cells.
Immature double-positive (DP) thymocytes mature into CD4(+)CD8(-) cells in response to coengagement of TCR with any of a variety of cell surface "coinducer" receptors, including CD2. In contrast, DP thymocytes are signaled to undergo apoptosis by coengagement of TCR with CD28 costimulatory receptors, but the molecular basis for DP thymocyte apoptosis by TCR plus CD28 coengagement is not known. In the present study, we report that TCR plus CD28 coengagement does not invariably induce DP thymocyte apoptosis but, depending on the intensity of CD28 costimulation, can induce DP thymocyte maturation. We demonstrate that distinct but interacting signal transduction pathways mediate DP thymocyte maturation signals and DP thymocyte apoptotic signals. Specifically, DP maturation signals are transduced by the extracellular signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway and up-regulate expression of the antiapoptotic protein Bcl-2. In contrast, the apoptotic response stimulated by CD28 costimulatory signals is mediated by ERK/MAPK-independent pathways. Importantly, when TCR-activated thymocytes are simultaneously coengaged by both CD28 and CD2 receptors, CD28 signals can inhibit ERK/MAPK-dependent Bcl-2 protein up-regulation. Thus, there is cross-talk between the signal transduction pathways that transduce apoptotic and maturation responses, enabling CD28-initiated signal transduction pathways to both stimulate DP thymocyte apoptosis and also negatively regulate maturation responses initiated by TCR plus CD2 coengagement.
UNLABELLED: The city of Recife, northeastern Brazil, is reported to have the highest incidence of cervical cancer worldwide (83.2/100000 women). OBJECTIVE: To evaluate the efficacy of Hybrid Capture I (HC I) in cervical cancer detection and some risk factors in Recife. METHOD: Cervical scrapes for HC I analysis followed by colposcopy were collected from 140 women (70 with cervical cancer and 70 with normal cervix) from three screening services in Recife. RESULT: HC I sensitivity and specificity were 82.9 and 41.4%, respectively. The odds ratios for cervical cancer when Gesta > or = 5 and vaginal parity > or = 4 were, respectively, 5.30 and 4.27. CONCLUSION: HC I is a moderately sensitive method to detect cervical cancer, but it does not seem to be useful as a primary screening tool for it's low specificity. Early pregnancy, high Gesta/Para and living in rural areas were important local risk factors.