Predicting the intrinsic membrane permeability of Caco-2/MDCK cells by the solubility-diffusion model

Membrane permeability is one of the main determinants for the absorption, distribution, metabolism and excretion of compounds and is therefore of crucial importance for successful drug development. Experiments with artificial phospholipid membranes have shown that the intrinsic membrane permeability (P0) of compounds is well-predicted by the solubility-diffusion model (SDM). However, using the solubility-diffusion model to predict the P0 of biological Caco-2 and MDCK cell membranes has proven unreliable so far. Recent publications revealed that many published P0 extracted from Caco-2 and MDCK experiments are incorrect. In this work, we therefore used a small self-generated set as well as a large revised set of experimental Caco-2 and MDCK data from literature to compare experimental and predicted P0. The P0 extracted from Caco-2 and MDCK experiments were systematically lower than the P0 predicted by the solubility-diffusion model. However, using the following correlation: log P0,Caco-2/MDCK = 0.84 log P0,SDM - 1.85, P0 of biological Caco-2 and MDCK cell membranes was well-predicted by the solubility-diffusion model.

Clinical Features and Voxel-Based-Symptom-Lesion Mapping of Silent Aspiration in Acute Infratentorial Stroke

Post-stroke dysphagia (PSD) is a severe and common complication after ischemic stroke. The role of silent aspiration as an important contributing factor in the development of a dysphagia-associated complications, in particular aspiration-associated pneumonia has been insufficiently understood. The aim of this study was to investigate the characteristics and risk factors of silent aspiration in patients with acute infratentorial stroke by FEES and to identify culprit lesions in stroke patient with a high risk of silent aspiration via voxel-based-symptom-lesion mapping (VBS/ML). This study is a retrospective observational study based on a prospectively collected FEES and stroke database. Consecutive patient cases with acute ischemic infratentorial stroke and FEES examination between 2017 and 2022 were identified. Group allocation was performed based on PAS scores. Imaging analysis was performed by manual assignment and by VBS/ML. Group comparisons were performed to assess silent aspiration characteristics. Binary logistic regression analysis was performed to determine if baseline clinical, demographic, and imaging parameters were helpful in predicting silent aspiration in patients. In this study 84 patient cases with acute infratentorial stroke who underwent FEES examination were included. Patients were moderately affected at admission (mean NIH-SS score at admission 5.7 SD ± 4.7). Most lesions were found pontine. Overall 40.5% of patients suffered from silent aspiration, most frequently in case of bilateral lesions. Patients with silent aspiration had higher NIH-SS scores at admission (p < 0.05), had a more severe swallowing disorder (p < 0.05) and were 4.7 times more likely to develop post-stroke pneumonia. Patients who underwent FEES examination later than 72 h after symptom onset were significantly more likely to suffer from silent aspiration and to develop pneumonia compared to patients who underwent FEES examination within the first 72 h (p < 0.05). A binary logistic regression model identified NIH-SS at admission as a weak predictor of silent aspiration. Neither in manual assignment of the lesions to brain regions nor in voxel-wise statistic regression any specific region was useful in prediction of silent aspiration. Silent aspiration is common in patients with infratentorial stroke and contributes to the risk for pneumonia. Patients with silent aspiration are more severely affected by stroke, but cannot reliably be identified by NIH-SS at admission or lesion location. Patients suffering from acute infratentorial stroke should been screened and examined for PSD and silent aspiration.

Pitfalls in evaluating permeability experiments with Caco-2/MDCK cell monolayers

When studying the transport of molecules across biological membranes, intrinsic membrane permeability (P0) is more informative than apparent permeability (Papp), because it eliminates external (setup-specific) factors, provides consistency across experiments and mechanistic insight. It is thus an important building block for modeling the total permeability in any given scenario. However, extracting P0 is often difficult, if not impossible, when the membrane is not the dominant transport resistance. In this work, we set out to analyze Papp values measured with Caco-2/MDCK cell monolayers of 69 literature references. We checked the Papp values for a total of 318 different compounds for the extractability of P0, considering possible limitations by aqueous boundary layers, paracellular transport, recovery issues, active transport, a possible proton flux limitation, and sink conditions. Overall, we were able to extract 77 reliable P0 values, which corresponds to about one quarter of the total compounds analyzed, while about half were limited by the diffusion through the aqueous layers. Compared to an existing data set of P0 values published by Avdeef, our approach resulted in a much higher exclusion of compounds. This is a consequence of stricter compound- and reference-specific exclusion criteria, but also because we considered possible concentration-shift effects due to different pH values in the aqueous layers, an effect only recently described in literature. We thus provide a consistent and reliable set of P0, e.g. as a basis for future modeling.

Effects of Aqueous Boundary Layers and Paracellular Transport on the Efflux Ratio as a Measure of Active Transport Across Cell Layers

The efflux ratio (ER), determined by Caco-2/MDCK assays, is the standard in vitro metric to establish qualitatively whether a compound is a substrate of an efflux transporter. However, others have also enabled the utilisation of this metric quantitatively by deriving a relationship that expresses the ER as a function of the intrinsic membrane permeability of the membrane (P0) as well as the permeability of carrier-mediated efflux (Ppgp). As of yet, Ppgp cannot be measured directly from transport experiments or otherwise, but the ER relationship provides easy access to this value if P0 is known. However, previous derivations of this relationship failed to consider the influence of additional transport resistances such as the aqueous boundary layers (ABLs) and the filter on which the monolayer is grown. Since single fluxes in either direction can be heavily affected by these experimental artefacts, it is crucial to consider the potential impact on the ER. We present a model that includes these factors and show both mathematically and experimentally that this simple ER relationship also holds for the more realistic scenario that does not neglect the ABLs/filter. Furthermore, we also show mathematically how paracellular transport affects the ER, and we experimentally confirm that paracellular dominance reduces the ER to unity and can mask potential efflux.

Revisiting the pKa-Flux method for determining intrinsic membrane permeability

Intrinsic membrane permeability is one of several factors that critically determine the intestinal absorption of a chemical. The intrinsic membrane permeability of a chemical is usually extracted from transwell experiments with Caco-2 or MDCK cells, preferably by the pKa-Flux method, which is considered the method of choice when aqueous boundary layer effects need to be excluded. The pKa-Flux method has two variants, the iso-pH method, where apical and basolateral pH are equal, and the gradient-pH method, where apical and basolateral pH are different. The most commonly used method is the gradient-pH method, as it is intended to reflect the pH-conditions in the gastrointestinal tract. However, concentration-shift effects caused by the applied pH-difference between apical and basolateral compartment in the gradient-pH method have not been considered in the evaluation of the experimental data in the past. Consequently, incorrect intrinsic membrane permeabilities have been determined. In this work, we present a revised method for extracting the intrinsic membrane permeability from gradient-pH data that considers concentration-shift effects in the basolateral aqueous boundary layer and filter as well as in the cytosol. Furthermore, we propose the use of the iso-pH method, where only concentration-shift effects in the cytosol need to be considered, as an alternative to the gradient-pH method. We use the five lipophilic bases amantadine, chloroquine, propranolol, venlafaxine and verapamil as examples to compare gradient-pH method and iso-pH method with regard to the extractability of the intrinsic membrane permeability. For lipophilic bases, the iso-pH method proves to be advantageous. All intrinsic membrane permeabilities determined in this work were substantially higher than the intrinsic membrane permeabilities reported in literature.

A framework for understanding the bioconcentration of surfactants in fish

Surfactants are a class of chemicals released in large quantities to water, and therefore bioconcentration in fish is an important component of their safety assessment. Their structural diversity, which encompasses nonionic, anionic, cationic and zwitterionic molecules with a broad range of lipophilicity, makes their evaluation challenging. A strong influence of environmental pH adds a further layer of complexity to their bioconcentration assessment. Here we present a framework that penetrates this complexity. Using simple equations derived from current understanding of the relevant underlying processes, we plot the key bioconcentration parameters (uptake rate constant, elimination rate constant and bioconcentration factor) as a function of its membrane lipid/water distribution ratio and the neutral fraction of the chemical in water at pH 8.1 and at pH 6.1. On this chemical space plot, we indicate boundaries at which four resistance terms (perfusion with water, transcellular, paracellular, and perfusion with blood) limit transport of surfactants across the gills. We then show that the bioconcentration parameters predicted by this framework align well with in vivo measurements of anionic, cationic and nonionic surfactants in fish. In doing so, we demonstrate how the framework can be used to explore expected differences in bioconcentration behavior within a given sub-class of surfactants, to assess how pH will influence bioconcentration, to identify the underlying processes governing bioconcentration of a particular surfactant, and to discover knowledge gaps that require further research. This framework for amphiphilic chemicals may function as a template for improved understanding of the accumulation potential of other ionizable chemicals of environmental concern, such as pharmaceuticals or dyes.

Mechanistic modeling of the bioconcentration of (super)hydrophobic compounds in Hyalella azteca

Bioconcentration tests using the freshwater amphipod Hyalella azteca as an alternative to conventional fish tests have recently received much attention. An appropriate computational model of H. azteca could help in understanding the mechanisms behind bioconcentration, in comparison to the fish as test organism. We here present the first mechanistic model for H. azteca that considers the single diffusive processes in the gills and gut. The model matches with the experimental data from the literature quite well when appropriate physiological information is used. The implementation of facilitated transport was essential for modeling. Application of the model for superhydrophobic compounds revealed binding to organic matter and the resulting decrease in bioavailable fraction as the main reason for the observed counterintuitive decrease in uptake rate constants with increasing octanol/water partition coefficient. Furthermore, estimations of the time needed to reach steady state indicated that durations of more than a month could be needed for compounds with a log Kow > 8, limiting the experimental applicability of the test. In those cases, model-based bioconcentration predictions could be a preferable approach, which could be combined with in vitro biotransformation measurements. However, our sensitivity analysis showed that the uncertainty in determining the octanol/water partition coefficients is a strong source of error for superhydrophobic compounds.

Impact of cholesterol and sphingomyelin on intrinsic membrane permeability

Transwell experiments with Caco-2 or MDCK cells are the gold standard for determining the intestinal permeability of chemicals. The intrinsic membrane permeability (P₀), that can be extracted from these experiments, might be comparable to P₀ measured in black lipid membrane (BLM) experiments and P₀ predicted by the solubility-diffusion model. Unfortunately, the overlap between experimental P_{0,Caco-2/MDCK} and P_0,BLM data is very small. So far, differences between both approaches have been attributed to the cholesterol and sphingomyelin content of cell membranes, but the database is too sparse to thoroughly test this theory. To create a diverse dataset, we measured P_0,BLM of ten chemicals in BLM experiments using DPhPC and DPhPC/cholesterol/sphingomyelin membranes. The results were compared to predicted BLM data and experimental Caco-2/MDCK data obtained from literature. While P_0,BLM of all chemicals was well predicted by the solubility-diffusion model, P_{0,Caco-2/MDCK} was only predictable for rather hydrophilic compounds with logarithmic hexadecane/water partition coefficients below -0.5. The effect of cholesterol and sphingomyelin on P_0,BLM was negligibly small.

Modeling of SGLT1 in Reconstituted Systems Reveals Apparent Ion-Dependencies of Glucose Uptake and Strengthens the Notion of Water-Permeable Apo States

The reconstitution of secondary active transporters into liposomes shed light on their molecular transport mechanism. The latter are either symporters, antiporters or exchangers, which use the energy contained in the electrochemical gradient of ions to fuel concentrative uptake of their cognate substrate. In liposomal preparations, these gradients can be set by the experimenter. However, due to passive diffusion of the ions and solutes through the membrane, the gradients are not stable and little is known on the time course by which they dissipate and how the presence of a transporter affects this process. Gradient dissipation can also generate a transmembrane potential (VM). Because it is the effective ion gradient, which together with VM fuels concentrative uptake, knowledge on how these parameters change within the time frame of the conducted experiment is key to understanding experimental outcomes. Here, we addressed this problem by resorting to a modelling approach. To this end, we mathematically modeled the liposome in the assumed presence and absence of the sodium glucose transporter 1 (SGLT1). We show that 1) the model can prevent us from reaching erroneous conclusions on the driving forces of substrate uptake and we 2) demonstrate utility of the model in the assignment of the states of SGLT1, which harbor a water channel.

Screening of 6000 Compounds for Uncoupling Activity: A Comparison Between a Mechanistic Biophysical Model and the Structural Alert Profiler Mitotox

Protonophoric uncoupling of phosphorylation is an important factor when assessing chemicals for their toxicity, and has recently moved into focus in pharmaceutical research with respect to the treatment of diseases such as cancer, diabetes, or obesity. Reliably identifying uncoupling activity is thus a valuable goal. To that end, we screened more than 6000 anionic compounds for in vitro uncoupling activity, using a biophysical model based on ab initio COSMO-RS input parameters with the molecular structure as the only external input. We combined these results with a model for baseline toxicity (narcosis). Our model identified more than 1250 possible uncouplers in the screening dataset, and identified possible new uncoupler classes such as thiophosphoric acids. When tested against 423 known uncouplers and 612 known inactive compounds in the dataset, the model reached a sensitivity of 83% and a specificity of 96%. In a direct comparison, it showed a similar specificity than the structural alert profiler Mitotox (97%), but much higher sensitivity than Mitotox (47%). The biophysical model thus allows for a more accurate screening for uncoupling activity than existing structural alert profilers. We propose to use our model as a complementary tool to screen large datasets for protonophoric uncoupling activity in drug development and toxicity assessment.

Predicting Uncoupling Toxicity of Organic Acids Based on Their Molecular Structure Using a Biophysical Model

We present a purely mechanistic model to predict protonophoric uncoupling activity EC_w of organic acids. All required input information can be derived from their chemical structure. This makes it a convenient predictive model to gain valuable information on the toxicity of organic chemicals already at an early stage of development of new commercial chemicals (e.g., in agriculture or pharmaceutical industries). A critical component of the model is the consideration of the possible formation of heterodimers from the neutral and anionic monomer, and its permeation through the membrane. The model was tested against literature data measured in chromatophores, submitochondrial particles, isolated mitochondria, and intact green algae cells with good success. It was also possible to reproduce pH-dependencies in isolated mitochondria and intact cells. Besides the prediction of the EC_w, the mechanistic nature of the model allows researchers to draw direct conclusions on the impact of single input factors such as pH- and voltage-gradients across the membrane, the anionic and neutral membrane permeability, and the heterodimerization constant. These insights are of importance in drug design or chemical regulation.

Membrane/Water Partitioning and Permeabilities of Perfluoroalkyl Acids and Four of their Alternatives and the Effects on Toxicokinetic Behavior

The search for alternatives to bioaccumulative perfluoroalkyl acids (PFAAs) is ongoing. New, still highly fluorinated alternatives are produced in hopes of reducing bioaccumulation. To better estimate this bioaccumulative behavior, we performed dialysis experiments and determined membrane/water partition coefficients, K_mem/w, of six perfluoroalkyl carboxylic acids (PFCAs), three perfluoroalkanesulfonic acids, and four alternatives. We also investigated how passive permeation might influence the uptake kinetics into cells, measuring the passive anionic membrane permeability P_ion through planar lipid bilayers for six PFAAs and three alternatives. Experimental K_mem/w and P_ion were both predicted well by the COSMO-RS theory (log RMSE 0.61 and 0.46, respectively). K_mem/w values were consistent with the literature data, and alternatives showed similar sorption behavior as PFAAs. Experimental P_ion values were high enough to explain observed cellular uptake by passive diffusion with no need to postulate the existence of active uptake processes. However, predicted pK_a and neutral permeabilities suggest that also the permeation of the neutral species should be significant in case of PFCAs. This can have direct consequences on the steady-state distribution of PFAAs across cell membranes and thus toxicity. Consequently, we propose a model to predict pH-dependent baseline toxicity based on K_mem/w, which considers the permeation of both neutral and anionic species.

Use of analgesics in acute stroke patients with inability to self-report pain: a retrospective cohort study

BACKGROUND

Pain is a common and burdensome complication in patients with acute stroke. We assessed the impact of impaired communication in stroke patients on pain assessment and treatment.

METHODS

We included 909 (507 male, mean age 71.8 years) patients admitted to our stroke unit from 01/2015 to 12/2015 in the analysis. Patients were assigned to four groups: able to communicate (AC), not able to communicate prior to index stroke (P-NAC), due to focal symptoms of index stroke (S-NAC), due to a reduced level of consciousness (C-NAC). Pain prevalence, documentation of pain and use of analgesics were evaluated. C-NAC patients were excluded from analyses regarding analgesic treatment due to relevant differences in patient characteristics.

RESULTS

746 patients (82.1%) were classified as AC, 25 (2.8%) as P-NAC, 90 (9.9%) as S-NAC and 48 (5.3%) as C-NAC. Pain was documented on the Numeric Rating Scale and in form of free text by nurses and physicians. Nurses documented pain more frequently than physicians (p < 0.001). Pain prevalence was 47.0% (n.s. between groups). The use of analgesic medication increased from 48.7% in the AC group, to 76.0% in the P-NAC group, and 77.8% in the S-NAC group (p < 0.001). Opioid use was significantly more frequent in NAC patients (p < 0.001). The response to the treatment was poorly documented with significantly lowest rates in S-NAC patients (p < 0.001).

CONCLUSIONS

Our study suggests that post-stroke pain in patients with inability to communicate is not attended enough, not systematically assessed and therefore not sufficiently treated.

[Interdisciplinary Management of Sellar Masses]

Interdisciplinary Management of Sellar Masses Abstract. Sellar masses may present with an impairment of pituitary function (hypopituitarism), hormone hypersecretion (prolactinoma, acromegaly, glucocorticoid excess) or neurological symptoms (visual impairment, headache). An increasing number of them is discovered as an incidentaloma. Among the various entities, benign pituitary adenomas and cystic lesions are most frequently encountered. The work-up includes a laboratory evaluation for hormone hyper- or hyposecretion and an MRI of the pituitary gland. If the optic chiasm is compromised, a visual field examination is mandatory. Except for prolactinomas, symptomatic sellar masses are usually resected via an endoscopic transsphenoidal approach. If a total resection is not feasible because of the invasion of surrounding structures, debulking to relieve pressure from the optic chiasm is the primary goal and radiotherapy may be considered. Residual hormone excess can be treated medically. In the early postoperative period special attention to the development and treatment of disordered body water homeostasis and hypopituitarism is crucial. Interdisciplinary work-up and decision making are of utmost importance and will offer the best management.

Passive Permeability of Planar Lipid Bilayers to Organic Anions

The membrane permeability P of organic ions was reported to be governed by the structure of the permeating molecule. Thus far, it is unclear whether the ion structure alters membrane partition or translocation proper across the membrane. Here, we obtained P values for 24 anionic compounds (18 concrete values, 6 upper limits) measuring the current that they carry through folded planar lipid bilayers. The P values range over more than 10 log units. Our measured permeability values correlate well (r = 0.95; logRMSE 0.74) with the hexadecane/water partition coefficients of the respective chemicals predicted by the COSMO-RS theory. Other attempts to predict P from the partition coefficient of the neutral molecule and from the solvation energy (Born energy) that opposes transfer into the membrane once the molecule is charged were unsuccessful. The uncertainties in assigning an effective radius to nonspherical molecules were much too large. The observation underlines that the actual structure of the molecules needs to be considered to predict partition and thus P by the solubility-diffusion model.

Effectiveness of syringe shieldings using radionuclides in radiation synovectomy

Aim: The radiation exposure in radiation synovectomy was investigated for technician and therapist using Erbium-169, Rhenium-186 and Yttrium-90 with and without syringe shieldings. Methods: Dose rates were measured in relation to the distance of the syringe containing the radionuclide. Measurements were repeated using syringe shieldings which consist of plastic surrounded by a lead layer. Results: The most relevant radiation exposure arises from Yttrium-90. Using syringe shieldings radiation exposure can be reduced by a factor of thousand. Conclusion: This kind of radiological protection is completely sufficient for the therapist. Concerning the technician preparing the radiopharmaceutics, the limit of the official German dosimetry service (500 mSv) might be exceeded if no special radiological protection is established. Thus, special dosimetry is recommended.

Anterior Cruciate Ligament Reconstruction - Does the Surgeon Risk Worsening of the Clinical Outcome During the Learning Curve if He Switches from Single Bundle Technique to Double Bundle Technique?

Background: Anatomical reconstruction of the anterior cruciate ligament (ACL) using the double-bundle (DB) technique is becoming increasingly popular. Despite its proved biomechanical and anatomical superiority, clinical studies have found little advantage for the DB technique. The aim of this study was therefore to evaluate whether an experienced surgeon is able to obtain his usual good results with ACL reconstruction with the single-bundle (SB) technique directly after changing to the DB technique. Patients/Material and Methods: In a prospective, non-randomised and controlled interventional study, we compared the first 19 patients in our clinic who had an anterior cruciate ligament reconstruction using the DB technique with 31 patients who underwent a SB ACL reconstruction performed by the same surgeon during the same period of investigation. The visual analog scale (VAS) for pain and function, the Tegner activity score, the International Knee Documentation Committee (IKDC), the Lysholm and the Marshall scores were used as evaluation methods, the anterior stability (KT-1000-arthrometer measurement) and the deficits in muscle strength in extension and flexion of both knees were measured in a standard manner one year after operation. Results: The Lysholm scores in the SB group (93.6 [± 3.8] points) and in the DB group (93.1 [± 4.2] points) were not significantly different (p > 0.05). Neither the VAS for pain (1 [± 2] points for both techniques), nor the VAS for function (8 [± 2] versus 7 [± 2] points) were significantly different (p > 0.05). For the anterior stability under Maximum Measurement Displacement (MMD), the SB group achieved a difference of 1.75 (± 1.94) mm, in comparison with 1.32 (± 1.89) mm for the DB group (p > 0.05). There was a trend to less deficit in muscle strength after DB ACL reconstruction. No complications were recorded in either group. Conclusion: Experienced surgeons in ACL reconstruction can change from the popular SB ACL reconstruction to the DB ACL reconstruction without causing clinical problems or additional complications. The well-known good results of the DB technique were attained in the first operations performed by an experienced surgeon and are compareable to the results of the SB technique.

Improving social perception in schizophrenia: the role of oxytocin

Previous research has shown that patients with schizophrenia are impaired in a wide range of social cognitive abilities, including emotion recognition, empathy for others, and mental perspective-taking. Recent studies suggest that a dysfunction of the oxytocinergic system contributes to the social impairment in schizophrenia. Accordingly, the present study sought to examine whether patients with schizophrenia would improve in a social perception task after taking a single dose of oxytocin, as compared to a placebo. Thirty-five patients diagnosed with schizophrenia were compared with 46 psychologically healthy matched controls on their recognition of kinship and intimacy, using the Interpersonal Perception Task. All participants received a single intranasal dose of 24 IU oxytocin or placebo, one week apart. Overall, the participants were more accurate in judging intimacy and kinship following the administration of oxytocin, as opposed to a placebo. However, when comparing patients with controls, only the recognition of kinship improved significantly in the patient group, whereas no such effect was observed in the control group or in the recognition of intimacy in either group. This is one of the first studies to demonstrate that social perception in schizophrenia can be improved by the administration of oxytocin and that patients show a greater treatment effect than controls.

[Tumour registry and reality: differential diagnosis of testicular tumours in childhood: survey and personal experience]

Painless scrotal swelling must always be considered as a potential malignant testicular tumour until proven otherwise. Prepubertal testicular tumours are seldom entities, for their differential diagnosis testicular sonography is gaining increasing importance. Although, according to national and international tumour registries, most patients tend to have malignant tumours, some clinical series from paediatric centres confirm that prepubertal testicular tumours are mainly benign lesions, especially up to the age of 12 years. Testis-sparing procedures are favoured when AFP is in a normal range and testicular parenchyma is detected sonographically. Oncological principles should be applied to paediatric patients consequently, staging examinations should be requested when a definite histology is proven. Cases should be reported to national tumour registries and, in addition to close surveillance, in some cases adjuvant therapy is necessary. In addition to the clinical guidelines from the tumour registries, differential diagnosis, testis-sparing surgery and the presence of TIN in the paediatric population should be discussed.

A novel mutation in CACNA1A associated with hemiplegic migraine, cerebellar dysfunction and late-onset cognitive decline

Hemiplegic migraine (HM) is a rare and severe subtype of migraine with aura, characterized by some degree of hemiparesis and other aura symptoms. Mutations in three genes (CACNA1A, ATP1A2 and SCN1A) have been detected in familial and, more rarely, in sporadic cases. The disease can be complicated by permanent neurological deficits, the most frequent one being a cerebellar syndrome; in addition, mental retardation has been recognized as part of the phenotypic spectrum. Here, we report a Caucasian male with a novel CACNA1A mutation and an unusual clinical phenotype: the patient, who had had a history of only two HM attacks, sought medical advice at age 49 primarily because of increasing cognitive decline accompanied by cerebellar dysfunction. While common neurodegenerative causes were excluded, neuropsychological evaluation revealed a distinct profile of deficits of a subcortico-prefrontal type as previously reported in patients with cerebellar dysfunction. This suggests a possible causal link between cerebellar and cognitive disturbances in this patient; in addition to these pathophysiological aspects, we review of the role of the cerebellum in cognition.

Validation of the German revised Addenbrooke's cognitive examination for detecting mild cognitive impairment, mild dementia in alzheimer's disease and frontotemporal lobar degeneration

BACKGROUND/AIMS

The diagnostic accuracy of the German version of the revised Addenbrooke's Cognitive Examination (ACE-R) in identifying mild cognitive impairment (MCI), mild dementia in Alzheimer's disease (AD) and mild dementia in frontotemporal lobar degeneration (FTLD) in comparison with the conventional Mini Mental State Examination (MMSE) was assessed.

METHODS

The study encompasses 76 cognitively healthy elderly individuals, 75 patients with MCI, 56 with AD and 22 with FTLD. ACE-R and MMSE were validated against an expert diagnosis based on a comprehensive diagnostic procedure. Statistical analysis was performed using the receiver operating characteristic method and regression analyses.

RESULTS

The optimal cut-off score for the ACE-R for detecting MCI, AD, and FTLD was 86/87, 82/83 and 83/84, respectively. ACE-R was superior to MMSE only in the detection of patients with FTLD [area under the curve (AUC): 0.97 vs. 0.92], whilst the accuracy of the two instruments did not differ in identifying MCI and AD. The ratio of the scores of the memory ACE-R subtest to verbal fluency subtest contributed significantly to the discrimination between AD and FTLD (optimal cut-off score: 2.30/2.31, AUC: 0.77), whereas the MMSE and ACE-R total scores did not.

CONCLUSION

The German ACE-R is superior to the most commonly employed MMSE in detecting mild dementia in FTLD and in the differential diagnosis between AD and FTLD. Thus it might serve as a valuable instrument as part of a comprehensive diagnostic workup in specialist centres/clinics contributing to the diagnosis and differential diagnosis of the cause of dementia.

Hydrogen Concentration Profiles at the Oxic-Anoxic Interface: a Microsensor Study of the Hindgut of the Wood-Feeding Lower Termite Reticulitermes flavipes (Kollar)

Molecular hydrogen is a key intermediate in lignocellulose degradation by the microbial community of termite hindguts. With polarographic, Clark-type H(inf2) microelectrodes, we determined H(inf2) concentrations at microscale resolution in the gut of the wood-feeding lower termite Reticulitermes flavipes (Kollar). Axial H(inf2) concentration profiles obtained from isolated intestinal tracts embedded in agarose Ringer solution clearly identified the voluminous hindgut paunch as the site of H(inf2) production. The latter was strictly coupled with both a low redox potential (E(infh) = -200 mV) and the absence of oxygen, in agreement with the growth requirements of the cellulolytic, H(inf2)-producing flagellates located in the hindgut paunch. Luminal H(inf2) partial pressures were much higher than expected (ca. 5 kPa) and increased more than threefold when the guts were incubated under a N(inf2) headspace. Radial H(inf2) concentration gradients showed a steep decrease from the gut center towards the periphery, indicating the presence of H(inf2)-consuming activities both within the lumen and at the gut epithelium. Measurements under controlled gas headspace showed that the gut wall was also a sink for externally supplied H(inf2), both under oxic and anoxic conditions. With O(inf2) microelectrodes, we confirmed that the H(inf2) sink below the gut epithelium is located within the microoxic gut periphery, but the H(inf2)-consuming activity itself, at least a substantial part of it, was clearly due to an anaerobic process. These results are in accordance with the recently reported presence of methanogens attached in large numbers to the luminal side of the hindgut epithelium of R. flavipes. If the oxygen partial pressure was increased, O(inf2) penetrated deeper and H(inf2) production was suppressed; it ceased completely as soon as the gut was fully oxic. In experiments with living termites, externally supplied H(inf2) (20 kPa) stimulated methane formation five- to sixfold to 0.93 (mu)mol (g of termite)(sup-1) h(sup-1), indicating that the methanogenic activity in R. flavipes hindguts is not saturated for hydrogen under in situ conditions. This rate was in good agreement with the H(inf2) uptake rates exhibited by isolated hindguts, which would account for more than half of the CH(inf4) formed by living termites under comparable conditions.