What Is the Benefit of Ramped Pulse Shapes for Activating Auditory Cortex Neurons? An Electrophysiological Study in an Animal Model of Cochlear Implant

In all commercial cochlear implant (CI) devices, the activation of auditory nerve fibers is performed with rectangular pulses that have two phases of opposite polarity. Recently, several papers proposed that ramped pulse shapes could be an alternative shape for efficiently activating auditory nerve fibers. Here, we investigate whether ramped pulse shapes can activate auditory cortex (ACx) neurons in a more efficient way than the classical rectangular pulses. Guinea pigs were implanted with CI devices and responses of ACx neurons were tested with rectangular pulses and with four ramped pulse shapes, with a first-phase being either cathodic or anodic. The thresholds, i.e., the charge level necessary for obtaining significant cortical responses, were almost systematically lower with ramped pulses than with rectangular pulses. The maximal firing rate (FR) elicited by the ramped pulses was higher than with rectangular pulses. As the maximal FR occurred with lower charge levels, the dynamic range (between threshold and the maximal FR) was not modified. These effects were obtained with cathodic and anodic ramped pulses. By reducing the charge levels required to activate ACx neurons, the ramped pulse shapes should reduce charge consumption and should contribute to more battery-efficient CI devices in the future.

Current distribution of distributed all-polar cochlear implant stimulation mode measured in-situ

Oticon Medical cochlear implants use a stimulation mode called Distributed All-Polar (DAP) that connects all non-stimulating available intracochlear electrodes and an extracochlear reference electrode. It results in a complex distribution of current that is yet undescribed. The present study aims at providing a first characterization of this current distribution. A Neuro Zti was modified to allow the measurement of current returning to each electrode during a DAP stimulation and was implanted in an ex-vivo human head. Maps of distributed current were then created for different stimulation conditions with different charge levels. Results show that, on average, about 20% of current returns to the extracochlear reference electrode, while the remaining 80% is distributed between intracochlear electrodes. The position of the stimulating electrode changed this ratio, and about 10% more current to the extracochlear return in case of the first 3 basal electrodes than for apical and mid position electrodes was observed. Increasing the charge level led to small but significant change in the ratio, and about 4% more current to the extracochlear return was measured when increasing the charge level from 11.7 to 70 nC. Further research is needed to show if DAP yields better speech understanding than other stimulation modes.

Increased Threshold and Reduced Firing Rate of Auditory Cortex Neurons after Cochlear Implant Insertion

The cochlear implant (CI) is the most successful neuroprosthesis allowing thousands of patients with profound hearing loss to recover speech understanding. Recently, cochlear implants have been proposed to subjects with residual hearing and, in these cases, shorter CIs were implanted. To be successful, it is crucial to preserve the patient’s remaining hearing abilities after the implantation. Here, we quantified the effects of CI insertion on the responses of auditory cortex neurons in anesthetized guinea pigs. The responses of auditory cortex neurons were determined before and after the insertion of a 300 µm diameter CI (six stimulating electrodes, length 6 mm). Immediately after CI insertion there was a 5 to 15 dB increase in the threshold for cortical neurons from the middle to the high frequencies, accompanied by a decrease in the evoked firing rate. Analyzing the characteristic frequency (CF) values revealed that in large number of cases, the CFs obtained after insertion were lower than before. These effects were not detected in the control animals. These results indicate that there is a small but immediate cortical hearing loss after CI insertion, even with short length CIs. Therefore, efforts should be made to minimize the damages during CI insertion to preserve the cortical responses to acoustic stimuli.

Dexamethasone-loaded cochlear implants: How to provide a desired "burst release"

Cochlear implants containing iridium platinum electrodes are used to transmit electrical signals into the inner ear of patients suffering from severe or profound deafness without valuable benefit from conventional hearing aids. However, their placement is invasive and can cause trauma as well as local inflammation, harming remaining hair cells or other inner ear cells. As foreign bodies, the implants also induce fibrosis, resulting in a less efficient conduction of the electrical signals and, thus, potentially decreased system performance. To overcome these obstacles, dexamethasone has recently been embedded in this type of implants: into the silicone matrices separating the metal electrodes (to avoid short circuits). It has been shown that the resulting drug release can be controlled over several years. Importantly, the dexamethasone does not only act against the immediate consequences of trauma, inflammation and fibrosis, it can also be expected to be beneficial for remaining hair cells in the long term. However, the reported amounts of drug released at “early” time points (during the first days/weeks) are relatively low and the in vivo efficacy in animal models was reported to be non-optimal. The aim of this study was to increase the initial “burst release” from the implants, adding a freely water-soluble salt of a phosphate ester of dexamethasone. The idea was to facilitate water penetration into the highly hydrophobic system and, thus, to promote drug dissolution and diffusion. This approach was efficient: Adding up to 10% dexamethasone sodium phosphate to the silicone matrices substantially increased the resulting drug release rate at early time points. This can be expected to improve drug action and implant functionality. But at elevated dexamethasone sodium phosphate loadings device swelling became important. Since the cochlea is a tiny and sensitive organ, a potential increase in implant dimensions over time must be limited. Hence, a balance has to be found between drug release and implant swelling.

Temporal integration of short-duration pulse trains in cochlear implant listeners: Psychophysical and electrophysiological measurements

While electrically-evoked auditory brainstem response (eABR) thresholds for low-rate pulse trains correlate well with behavioral thresholds measured at the same rate, the correlation is much weaker with behavioral thresholds measured at high rates, such as used clinically. This implies that eABRs to low-rate stimuli cannot be reliably used for objective programming of threshold levels in cochlear implant (CI) users. Here, we investigate whether the use of bunched-up pulses (BUPS), consisting of groups of closely-spaced pulses may be used as an alternative stimulus. Experiment 1 measured psychophysical detection thresholds for several stimuli having a period of 32 ms in nine CI subjects implanted with a Med-EL device. The stimuli differed in the number of pulses present in each period (from 1 to 32), the pulse rate within period (1000 pps and as high as possible for BUPS) and the electrode location (apical or basal). The correlation between psychophysical thresholds obtained for a high-rate (1000 pps) clinical stimulus and for the BUPS stimuli increased as the number of pulses per period of BUPS increased from 1 to 32. This first psychophysical experiment suggests that the temporal processes affecting the threshold of clinical stimuli are also present for BUPS. Experiment 2 measured eABRs on the apical electrode of eight CI subjects for BUPS having 1, 2, 4, 8, 16 or 32 pulses per period. For most subjects, wave V was visible for BUPS having up to 16 pulses per period. The latency of wave V at threshold increased as a function of the number of pulses per period, suggesting that the eABR reflects the integration of multiple pulses at such low levels or that the neural response to each individual pulse increases along the sequence due to facilitation processes. There was also a strong within-subject correlation between electrophysiological and behavioral thresholds for the different BUPS stimuli. This demonstrates that the drop in behavioral threshold obtained when increasing the number of pulses per period of the BUPS can be measured electrophysiologically using eABRs. In contrast, the across-subject correlation between eABR thresholds for BUPS and clinical thresholds remained relatively weak and did not increase with the number of pulses per period. Implications of the use of BUPS for objective programming of CIs are discussed.

Level coding by phase duration and asymmetric pulse shape reduce channel interactions in cochlear implants

Conventional loudness coding with CIs by pulse current amplitude has a disadvantage: Increasing the stimulation current increases the spread of excitation in the auditory nerve, resulting in stronger channel interactions at high stimulation levels. These limit the number of effective information channels that a CI user can perceive. Stimulus intensity information (loudness) can alternatively be transmitted via pulse phase duration. We hypothesized that loudness coding by phase duration avoids the increase in the spread of the electric field and thus leads to less channel interactions at high stimulation levels. To avoid polarity effects, we combined this coding with pseudomonophasic stimuli. To test whether this affects the spread of excitation, 16 acutely deafened guinea pigs were implanted with CIs and neural activity from the inferior colliculus was recorded while stimulating with either biphasic, amplitude-coded pulses, or pseudomonophasic, duration- or amplitude-coded pulses. Pseudomonophasic stimuli combined with phase duration loudness coding reduced the lowest response thresholds and the spread of excitation. We investigated the channel interactions at suprathreshold levels by computing the phase-locking to a pulse train in the presence of an interacting pulse train on a different electrode on the CI. Pseudomonophasic pulses coupled with phase duration loudness coding reduced the interference by 4-5% compared to biphasic pulses, depending on the place of stimulation. This effect of pseudomonophasic stimuli was achieved with amplitude coding only in the basal cochlea, indicating a distance- or volume dependent effect. Our results show that pseudomonophasic, phase-duration-coded stimuli slightly reduce channel interactions, suggesting a potential benefit for speech understanding in humans.

ECAP growth function to increasing pulse amplitude or pulse duration demonstrates large inter-animal variability that is reflected in auditory cortex of the guinea pig

Despite remarkable advances made to ameliorate how cochlear implants process the acoustic environment, many improvements can still be made. One of most fundamental questions concerns a strategy to simulate an increase in sound intensity. Psychoacoustic studies indicated that acting on either the current, or the duration of the stimulating pulses leads to perception of changes in how loud the sound is. The present study compared the growth function of electrically evoked Compound Action Potentials (eCAP) of the 8^th nerve using these two strategies to increase electrical charges (and potentially to increase the sound intensity). Both with chronically (experiment 1) or acutely (experiment 2) implanted guinea pigs, only a few differences were observed between the mean eCAP amplitude growth functions obtained with the two strategies. However, both in chronic and acute experiments, many animals showed larger increases of eCAP amplitude with current increase, whereas some animals showed larger of eCAP amplitude with duration increase, and other animals show no difference between either approaches. This indicates that the parameters allowing the largest increase in eCAP amplitude considerably differ between subjects. In addition, there was a significant correlation between the strength of neuronal firing rate in auditory cortex and the effect of these two strategies on the eCAP amplitude. This suggests that pre-selecting only one strategy for recruiting auditory nerve fibers in a given subject might not be appropriate for all human subjects.

A New Method to Test the Efficiency of Cochlear Implant Artifacts Removal From Auditory Evoked Potentials

Auditory evoked potentials are of great interest to objectively evaluate the audition in cochlear implant (CI) recipients. However, these measures are impeded by CI stimulation electrical artifacts present in the EEG. In the first part, this paper investigates the use of a hybrid model approximating CI patient data. This model gives access to both uncontaminated and denoised data, thus allowing for the evaluation of CI artifact removal methods. Here the efficiency of independent component analysis (ICA) is evaluated in the context of auditory steady-state responses (ASSRs). A dedicated experimental setup was developed to simultaneously record EEG data from a normal hearing (NH) participant and CI artifact data from a phantom equipped with a CI. Hybrid data were obtained as a linear mixture of both sources. Amplitude-modulated continuous tones were used as stimuli to elicit ASSRs. After denoising, the comparison of denoised hybrid data and original NH data showed high correlations between the two datasets, demonstrating the efficiency of ICA. In the second part, the ICA was applied to real clinical CI ASSR data. Results support the usefulness of the methodology as regards the performance evaluation of signal processing methods applied to CI patient data prior to clinical application.

MALDI imaging mass spectrometry reveals multiple clinically relevant masses in colorectal cancer using large-scale tissue microarrays

For identification of clinically relevant masses to predict status, grade, relapse and prognosis of colorectal cancer, we applied Matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) to a tissue micro array containing formalin-fixed and paraffin-embedded tissue samples from 349 patients. Analysis of our MALDI-IMS data revealed 27 different m/z signals associated with epithelial structures. Comparison of these signals showed significant association with status, grade and Ki-67 labeling index. Fifteen out of 27 IMS signals revealed a significant association with survival. For seven signals (m/z 654, 776, 788, 904, 944, 975 and 1013) the absence and for eight signals (m/z 643, 678, 836, 886, 898, 1095, 1459 and 1477) the presence were associated with decreased life expectancy, including five masses (m/z 788, 836, 904, 944 and 1013) that provided prognostic information independently from the established prognosticators pT and pN. Combination of these five masses resulted in a three-step classifier that provided prognostic information superior to univariate analysis. In addition, a total of 19 masses were associated with tumor stage, grade, metastasis and cell proliferation. Our data demonstrate the suitability of combining IMS and large-scale tissue micro arrays to simultaneously identify and validate clinically useful molecular marker. Copyright © 2017 John Wiley & Sons, Ltd.

Rate discrimination at low pulse rates in normal-hearing and cochlear implant listeners: Influence of intracochlear stimulation site

Temporal pitch perception in cochlear implantees remains weaker than in normal hearing listeners and is usually limited to rates below about 300 pulses per second (pps). Recent studies have suggested that stimulating the apical part of the cochlea may improve the temporal coding of pitch by cochlear implants (CIs), compared to stimulating other sites. The present study focuses on rate discrimination at low pulse rates (ranging from 20 to 104 pps). Two experiments measured and compared pulse rate difference limens (DLs) at four fundamental frequencies (ranging from 20 to 104 Hz) in both CI and normal-hearing (NH) listeners. Experiment 1 measured DLs in users of the (Med-El CI, Innsbruck, Austria) device for two electrodes (one apical and one basal). In experiment 2, DLs for NH listeners were compared for unresolved harmonic complex tones filtered in two frequency regions (lower cut-off frequencies of 1200 and 3600 Hz, respectively) and for different bandwidths. Pulse rate discrimination performance was significantly better when stimulation was provided by the apical electrode in CI users and by the lower-frequency tone complexes in NH listeners. This set of data appears consistent with better temporal coding when stimulation originates from apical regions of the cochlea.

Identificación de fallas mecanicas utilizando la Transformada Wavelet y Labview

Se pretende validar, con dos ejemplos, el uso de la Transformada Wavelet en la detección de fallas mecánicas. El primero de ellos, un engrane con un diente roto es sometido a rotación en una máquina de pruebas, de donde se extraen las señales de vibración por medio de una red de acelerómetros. El último es una barra de aluminio con una fractura.  Las señales son procesadas y se analizan en el dominio de la frecuencia y del tiempo por medio de la Transformada Rápida de Fourier (solo en el primer caso) y la transformada Wavelet respectivamente, mismas que han sido programadas en una aplicación en LabVIEW.  En el análisis se obtiene claramente los resultados predichos según un análisis mecánico de los componentes de la máquina.

[On-scene times for helicopter services. Influence of central dispatch center strategy]

BACKGROUND

Previous studies have suggested that when using several emergency systems and air rescue prehospital and on-scene times are extended, depending on the dispatch strategy. Emergency medical services (EMS) in Germany are delivered by ambulances (AMB) staffed by paramedics alone or with physicians (EMD) and by helicopter emergency medical services (HEMS) always staffed by both. The advantages of HEMS in countries with short transport distances and high hospital density are controversial. The best dispatching strategy for HEMS has not been determined

OBJECTIVE

The BoLuS study in the German state of Hessen was designed to evaluate the influence of dispatch strategy on prehospital times for responses involving both HEMS and EMS.

METHODS

Rescue responses involving HEMS were prospectively evaluated in 12 regions of Hessen from July 2010 to September 2011. Although all regions had access to HEMS, only one had its own service. Data from both central dispatch centers and helicopter services were collected and combined to calculate the on-scene time (OST) and correlate it with dispatch strategy.

RESULTS

A total of 2111 emergency interventions were evaluated. Internal medicine emergencies accounted for 42.9 % of cases and trauma for 36.7 %. Just one patient was involved in 87.9 % of rescues. Two services were involved in 65.3 % of rescues and three or more in 31.5 %. The most common dispatch categories were initial dispatch of EMS and HEMS (50.6 %), initial dispatch of EMS with later request for HEMS (19.7 %) and initial dispatch of both EMS and EMD with later request for HEMS (17.4 %). The OST for these categories were 31.0 ± 13.7 min, 43.7 ± 16.2 min and 54.6 ± 21.3 min (p < 0.01), respectively.

CONCLUSION

OST varies significantly depending on the number of EMS involved and the dispatch strategy. Sequential dispatching of ground and later HEMS wastes time. Getting an emergency physician to the scene as quickly as possible, reducing transport time to an appropriate hospital and caring for more complex emergencies are the main indications for HEMS. If HEMS appears likely to be needed, it should be dispatched immediately.

Effects of di-isopropyl phosphorofluoridate on rat liver microsomal and lysosomal beta-glucuronidase

iPr(2)P-F (di-isopropyl phosphorofluoridate) administration to rats produces a liver-dependent specific elevation of plasma beta-glucuronidase activity. The response is unaffected by puromycin pretreatment. By using subcellular-fractionation techniques, the rise in plasma beta-glucuronidase activity was correlated temporally with a fall in liver microsomal beta-glucuronidase activity. After iPr(2)P-F treatment, liver microsomal membranes are depleted of beta-glucuronidase but slowly return to normal over 1 week. On the other hand, liver lysosomal beta-glucuronidase activity is high at early time points (less than 60min) after iPr(2)P-F administration but decreases to below control values; this lasts for a few days. The response to iPr(2)P-F was demonstrated in isolated hepatocytes prepared from iPr(2)P-F-treated rats. In such preparations, microsomal beta-glucuronidase is lost rapidly, followed by a specific decrease in hepatocyte lysosomal beta-glucuronidase. The results suggest that a pool of microsomal beta-glucuronidase serves as precursor to plasma beta-glucuronidase in iPr(2)P-F-treated rats, and further, that microsomal beta-glucuronidase may serve as precursor to lysosomal beta-glucuronidase.

[Time in care of trauma patients in the air rescue service: implications for disposition?]

BACKGROUND

Time plays a crucial role in treating multiple traumatized patients and delays in management worsen the prognosis. Furthermore, current studies show that trauma patients profit from primary delivery to a trauma center. Therefore, the goal of physician-staffed ground and air rescue services in Germany is to treat these patients as quickly as possible and deliver them to a suitable trauma center. The aim of the present study was to investigate prehospital treatment times for the air rescue team in terms of disposition and efficiency when a ground rescue team was already present at the scene.

METHODS

In a nationwide, multicenter analysis emergency missions carried out for traumatological emergencies in 2006 by 28 air rescue centers (ARC) of the TeamDRF and 6 ARC of the federal police were evaluated using the medical database MEDAT of the German Air Rescue Service. A distinction was made between combined missions with (MEDAT 1 group) and without (MEDAT 2 group) physician-staffed ground emergency medical services already being present at the emergency site and in particular the rescue helicopter treatment times for both groups were investigated. Furthermore, combined missions (MAN 1 group) and solo missions (MAN 2 group) for traumatological emergencies in the period 01.05.2006 to 31.01.2007 were investigated in a complementary prospective regional study at the ARC Heidelberg/Mannheim "Christoph 53". In both groups the total treatment times for all physician-staffed emergency systems involved in treatment at the scene were investigated.

RESULTS

Nationwide, 26,010 primary missions could be evaluated and of these, 11,464 missions were traumatological emergencies (44.1%) with 2,229 (19.4%) carried out by the MEDAT 1 group and 9,235 (80.6%) by the MEDAT 2 group. For both groups the helicopter treatment times depended on the severity of the injuries (NACA classification) and were between 17+/-12 min (NACA I) and 34+/-19 min (NACA VII) in MEDAT group 1 versus 21+/-10 and 36+/-19 min in MEDAT group 2 (p<0.05, p<0.001), respectively. In the MEDAT 1 group, the average treatment times were between 2.8 min (NACA VII) and 8.1 min (NACA VI) shorter compared with the MEDAT 2 group. Moreover, when taking the severity of the injury into consideration, a regular and significantly higher treatment effort (e.g. intubation, repositioning and chest tube insertion) and a greater proportion of patients who were transported to the clinic via rescue helicopter were observed for the MEDAT 1 group than for the MEDAT 2 group. In the regional study 670 primary missions were evaluated including 382 traumatological emergencies (57%). From these, 90 multiple trauma patients (NACA V) were not resuscitated or died at the scene, 58 from the MAN 1 group and 32 from the MAN 2 group, and were investigated more closely. The helicopter treatment times were comparable to those observed in the nationwide study and were found to be 26+/-12 min and 35+/-20 min (p<0.05), respectively. In the MAN 1 group the treatment times for the ground rescue services up to the time when the helicopter arrived was 22+/-11 min on average; the total treatment time was 48+/-15 min and 12+/-8 min longer than the time for the MAN 2 group, which was statistically significant. In the MAN 1 group the helicopter was alerted on average 17+/-15 min after the physician-staffed ground rescue services arrived at the emergency site. Treatment by the rescue helicopter teams was significantly more extensive in the MAN 1 group.

CONCLUSIONS

The treatment times for the helicopter were several minutes shorter when a physician-staffed ground rescue team had already arrived at the emergency site. However, it must be assumed that the total prehospital time is significantly longer for such missions. These results directly affect the disposition at the emergency dispatch center and indicate that when air rescue is required to transport a patient to hospital, the helicopter should be alerted at an early stage. In such settings, it is likely that initiating the operation in this way would improve the prognosis of severely injured patients and save costs.

[Maillard reaction products in food as pro-inflammatory and pro-arteriosclerotic factors of degenerative diseases]

Heating of food induces the formation of Maillard reaction products (MRPs) caused by the reaction of reducing sugars with proteins or amino acids. Analogous reactions occur in the human body, eventually forming "Advanced Glycation Endproducts" (AGEs). AGEs accumulate in aging tissues accelerating degenerative-inflammatory and proliferative processes. MRPs present in food can also directly cause inflammatory processes in the intestines and, once absorbed, would support and reinforce any inflammatory and degenerative process occurring in the body. The contribution of AGEs (and additional MRPs) in the development of diabetic complications as well as nephropathy, neuropathy, micro- and macroangiopathies is now well established. Which of the MRPs or AGEs in particular induce these cellular processes is currently unknown. Thus the exact knowledge of the chemical structures of the MRPs could help to minimize the formation of "harmful MRPs" that occur due to heating in food processing. Because MRPs play a decisive role in the successful marketing of edibles due to their characteristics as flavor components, it is important to increase the amount of innocuous and palatable MRPs, and minimize signal active pro-inflammatory MRPs by the use of defined preparation methods. It is practicable to use low-priced immunological methods for the quantitative determination of specific MRPs or AGEs. In the medical area, the knowledge of the signal active MRP/AGE structures provides the opportunity to measure their concentrations in body fluids and tissues and thus determine their influence on inflammatory and age-related degenerative processes (e. g., late diabetic complications, arteriosclerosis, degeneration of neurons). From a clinical perspective, the application of RAGE antagonists after an appropriate chemical diagnosis could be effective in supporting the treatment of affected patient groups, especially older diabetic and dialysis patients.

Evaluation of the Maillard Reaction in Infant Formulas by Means of Front-Face Fluorescence

Foods are complex mixtures of macro- and micronutrients, which interact, leading to oxidation, glycation, and hydrolysis upon heating (e.g., sterilization, cooking) and storage. Their nutritional quality and safety are consequently affected, justifying the need for accurate monitoring of the evolution of the food composition during processing and shelf life. Classical chromatographic analysis as well as newly proposed rapid methods based on fluorescence spectrometry analyses were applied on whey powder-based models and commercial samples (in powdered form and ultrahigh temperature [UHT] sterilized), some of which had been previously submitted to protein hydrolysis. These samples were incubated for 48 h at 60 degrees C to mimic accelerated storage. Fluorescence fingerprints addressing modifications in the product composition during processing were recorded and analyzed by chemometric methods. Carboxymethyllysine (Nepsilon-[carboxymethyl]lysine; CML) was measured using an ELISA method. Fluorescence, recorded in a front-face mode on intact samples, is very sensitive to pertinent physicochemical changes induced by heat treatment, formulation (the moisture level in powders, presence of vitamin C and iron), and storage. Similar trends were observed between powders' fluorescence and CML-for example, a strong effect of protein hydrolysis and increasing water content. Addition of vitamin C was associated with an antioxidant effect despite the presence of iron. Good calibration models were obtained for predicting CML from fluorescence spectra both in food models and in commercial samples, although more work is needed to obtain accurate and robust calibration models. Results show the potential of nondestructively applied fluorescence spectrometry for measuring CML in formulas, a rapid, simple, and cost-effective method to monitor formula quality.

Elevated serum levels of N(epsilon)-carboxymethyl-lysine, an advanced glycation end product, are associated with proliferative diabetic retinopathy and macular oedema

AIMS/HYPOTHESIS

Diabetic retinopathy is a frequent microvascular complication. In search of novel risk markers, we analysed the association between serum levels of the major advanced glycation end product N(epsilon)-carboxymethyl-lysine (CML) and prevalence of advanced stages of retinopathy in Type 2 diabetic patients without nephropathy.

METHODS

We carried out a case-control study of Type 2 diabetic patients with and without advanced stages of diabetic retinopathy. Retinopathy and macular oedema were defined according to standard criteria. Serum levels of CML were estimated by means of a novel competition-based ELISA assay.

RESULTS

Serum levels of CML were significantly different between age-matched controls (n=792; mean value +/- SD: 521+/-134 ng/ml), Type 2 diabetic patients without severe retinopathy (821+/-141 ng/ml; p<0.0001) and Type 2 diabetic patients with proliferative retinopathy (1182+/-346 ng/ml; p<0.0001). Levels of CML greater than 1000 ng/ml represented a 25-fold increase in risk of proliferative retinopathy. Receiver operating characteristics analysis revealed a CML threshold of 1087 ng/ml (100% sensitivity, 93% specificity) for clinically significant macular oedema.

CONCLUSIONS/INTERPRETATION

High serum levels of CML were associated with advanced stages of retinopathy. Serum levels were shown to be a progressive risk marker, whereby a level of more than 1000 ng/ml induced a 25-fold increase in risk of proliferative retinopathy and clinically significant macular oedema. Our data suggest that serum levels of CML provide a novel risk marker for advanced stages of diabetic retinopathy in Type 2 diabetic patients.

Total synthesis and biological evaluation of the nakijiquinones

The Her-2/Neu receptor tyrosine kinase is vastly overexpressed in about 30% of primary breast, ovary, and gastric carcinomas. The nakijiquinones are the only naturally occurring inhibitors of this important oncogene, and structural analogues of the nakijiquinones may display inhibitory properties toward other receptor tyrosine kinases involved in cell signaling and proliferation. Here, we describe the first enantioselective synthesis of the nakijiquinones. Key elements of the synthesis are (i) the reductive alkylation of a Wieland-Miescher-type enone with a tetramethoxyaryl bromide, (ii) the oxidative conversion of the aryl ring into a p-quinoid system, (iii) the regioselective saponification of one of the two vinylogous esters incorporated therein, and (iv) the selective introduction of different amino acids via nucleophilic conversion of the remaining vinylogous ester into the corresponding vinylogous amide. The correct stereochemistry and substitution patterns are completed by conversion of two keto groups into a methyl group and an endocyclic olefin via olefination/reduction and olefination/isomerization sequences, respectively. This synthesis route also gave access to analogues of nakijiquinone C with inverted configuration at C-2 or with an exocyclic instead of an endocyclic double bond. Investigation of the kinase-inhibiting properties of the synthesized derivatives revealed that the C-2 epimer 30 of nakijiquinone C is a potent and selective inhibitor of the KDR receptor, a receptor tyrosine kinase involved in tumor angiogenesis. Molecular modeling studies based on the crystal structure of KDR and a model of the ATP binding site built from a crystal structure of FGF-R revealed an insight into the structural basis for the difference in activity between the natural product nakijiquinone C and the C-2 epimer 30.

Trypanosoma cruzi: phosphatidylinositol 3-kinase and protein kinase B activation is associated with parasite invasion

Multiple signal transduction events are triggered in the host cell during invasion by the protozoan parasite Trypanosoma cruzi. Here, we report the regulation of host cell phosphatydilinositol 3-kinase (PI3K) and protein kinase B (PKB/Akt) activities by T. cruzi during parasite-host cell interaction. Treatment of nonphagocytic cells (Vero, L(6)E(9), and NIH 3T3) and phagocytic cells (human and J774 murine macrophages) with the selective PI3K inhibitors Wortmannin and LY294002 significantly impaired parasite invasion in a dose-dependent fashion. A strong activation of PI3K and PKB/Akt activities in Vero cells was detected when these cells were incubated with trypomastigotes or their isolated membranes. Consistently, we were unable to detect activation of PI3K or PKB/Akt activities in host cells during epimastigote (noninfective) membrane-host cell interaction. Infection of transiently transfected cells containing an inactive mutant PKB showed a significant inhibition of invasion compared with the active mutant-transfected cells. T. cruzi PI3K-like activity was also required in host cell invasion since treatment of trypomastigotes with PI3K inhibitors prior to infection reduced parasite entry. Taken together, these results indicate that PI3K and PKB/Akt activation in parasites, as in host cells induced by T. cruzi, is an early invasion signal required for successful trypomastigote internalization.

Prevalence and pathogenicity of retroviruses in wildcats in France

Feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) are frequently encountered in domestic cats (Felis catus) and in wild felids, but only FeLV has been previously identified in wildcats (Fellis silvestris). Thirty-eight wildcats, either captured alive or found dead, were sampled in eastern and central France. Nine of them (23.7 per cent) carried the FeLV p27 antigen, and three (7.9 per cent) had antibodies to FIV. There was a significant relationship between two measures of body condition and FeLV status; the FeLV-positive cats being in poorer condition than the FeLV-negative cats. The results suggest that FeLV is common in wildcats and may increase mortality in this species. The FIV-positive results constitute the first indication of a FIV-related virus in wildcats.

Identification of naturally processed T cell epitopes from glutamic acid decarboxylase presented in the context of HLA-DR alleles by T lymphocytes of recent onset IDDM patients

Glutamic acid decarboxylase (GAD) has been defined as a major target antigen in insulin-dependent diabetes mellitus (IDDM). To identify the molecular ligands triggering a T cell response to GAD, a panel of human GAD65-specific T lymphocyte lines was generated from peripheral blood of three recent onset IDDM patients. All lines derived from a patient expressing the high-risk-conferring HLA-DR*0301/ *0401 haplotypes recognized a single epitope localized between amino acid positions 270 and 283 of GAD65, a stretch that is located in close proximity to the homology region shared with Coxsackie virus P2-C protein. All lines with this specificity were restricted to the DRA, B1*0401 product of the DR4 haplotype. Analysis of the GAD-specific T cell response in a second patient homozygous for DR4 haplotypes demonstrated that the same DRA, B1*0401 allele selected T cells specific for a different determinant. The T cell response profile in a third patient showed that DR*1501/ *1601-encoding haplotypes could present at least three different epitopes to GAD65-specific T lymphocytes. One of these epitopes was presented by a DR allele associated with the resistance-conferring DRB1*1501 haplotype. GAD-specific T cell lines could not be isolated from HLA class II-matched normal individuals. Our data reveal that (a) the T cell response to GAD65 is quite heterogenous in recent onset IDDM patients; (b) HLA-DR, not DQ, seems to be the principal restriction element used by T cells present at the onset of the disease; and (c) T cells responding to epitopes containing identical sequences to Coxsackie virus P2-C protein were not detected.

Bee venom phospholipase A2 is recognized by the macrophage mannose receptor

A high affinity and a specific binding site for bee venom PLA2 was found on the surface of J774E macrophages. The binding sites for bee venom PLA2 are entirely different from the binding sites for pancreatic and snake venom PLA2 as revealed by competition experiments. Binding and uptake of bee venom PLA2 by J774E macrophages was shown to be competed by mannose-BSA, glucose-BSA, N-acetylglucosamine-BSA, but not by galactose-BSA, indicating that the binding of bee venom PLA2 is probably mediated by macrophage mannose receptor. An affinity labeling experiment revealed that the bee venom PLA2 specifically binds to a single polypeptide with a mass of approximately 180 kDa. Moreover, the affinity labeled protein component, i.e., the binding site, was not detected in the presence of excess mannose-BSA, suggesting that mannose-BSA and the bee venom PLA2 bind to the same site on macrophages. These observations were further supported by the binding of bee venom PLA2 to cells which are known to express the mannose receptor and by specific binding of bee venom PLA2 to the purified mannose receptor. These data confirm that bee venom PLA2 binding to macrophages is mediated through the mannose receptor.

Control of protein traffic between distinct plasma membrane domains. Requirement for a novel 108,000 protein in the fusion of transcytotic vesicles with the apical plasma membrane

We have developed a cell-free system that reconstitutes the last step in transcytosis, i.e. the fusion of transcytotic transport vesicles with the apical plasma membrane (PM). Subcellular fractions containing transcytotic vesicles (the donor) or apical PM (the acceptor) were prepared from rat liver by sucrose density centrifugation. Fusion between the donor and acceptor fractions was measured by the conversion of the 120,000 transmembrane form of the polymeric IgA receptor (pIgA-R), an endogenous protein of transcytotic vesicles, to a processed fragment by a protease endogenous to the apical PM. Fusion occurred only at 37 degrees C and was critically dependent on the presence of ATP and cytosol. Fusion was inhibited by treating the in vitro fusion reaction with N-ethylmaleimide or by adding antibodies against N-ethylmaleimide-sensitive factor (NSF). We have previously identified a specific transcytotic vesicle-associated protein (TAP) and here show that TAP exists in both cytosolic and membrane-associated pools. Because of its exclusive interaction with transcytotic vesicles, we tested the involvement of TAP in distinct fusion processes. Removal of TAP inhibited fusion in an in vitro transcytotic fusion reaction but had no inhibitory effect in an in vitro endosome-endosome fusion system or in an in vitro intra-Golgi transport reaction. We propose that TAP represents part of the molecular machinery specifically involved in targeting and/or fusion of transcytotic vesicles with the apical PM.

Characterization of trypsin-sensitive factor(s) required for endosome-endosome fusion

Fusion of endosomes appears to be required at early steps of receptor-mediated endocytosis. These fusion events have been reconstituted using a cell-free assay and have been shown to require both cytosolic and membrane-associated proteins. We report here that trypsinization of endosomes completely inhibited fusion. Addition of untreated cytosol cannot restore fusion of trypsinized endosomes. However, fusion activity is restored by the addition of either untreated vesicles or a high salt extract containing peripheral membrane proteins (KE). KE contains both the membrane-associated factor(s) required for the reconstitution of fusion using trypsinized endosomes and the factors that are normally provided by the cytosol. The restorative activity of KE was sensitive to trypsin treatment or incubation at 100 degrees C, but was largely N-ethylmaleimide (NEM)-resistant. This and other criteria demonstrated that the trypsin-sensitive factor is distinct from N-ethylmaleimide-sensitive factor (NSF), an NEM-sensitive protein involved in vesicular fusion, and from other known factors that may participate in membrane fusion events. Preliminary fractionation studies indicate that the restorative activity of KE is associated with one or more high molecular weight proteins. The present study indicates that a novel trypsin-sensitive protein(s) is involved in endosome-endosome fusion. This factor is membrane-associated and is not found in an active form in cytosol as prepared.

Endosomal density shift is related to a decrease in fusion capacity

Dinitrophenol (DNP)-beta-glucuronidase and mannosylated anti-DNP IgG, which are endocytosed by the mannose receptor and delivered to lysosomes, were previously developed as probes for examination of fusion between early endosomes in a cell-free system. In this study, these probes were found to be transported by intact cells to endocytic vesicles with heavy buoyant density at different rates, as determined by Percoll gradient fractionation of cell homogenates. There was a concomitant loss of in vitro fusion activity as the ligands moved to dense compartments. In monensin-treated cells, DNP-beta-glucuronidase was retained in a light compartment corresponding to intracellular vesicles capable of fusion in vitro. Pulse-chase studies using a DNP-derivatized transferrin-alkaline phosphatase conjugate showed that a recycling ligand was always found in light intracellular vesicles that were capable of fusion to early endosomes in vitro. In contrast to cell-free systems, intact cells sequentially labeled with DNP-beta-glucuronidase and then mannosylated anti-DNP IgG showed ligand mixing in both early and late endocytic compartments. Treatment with nocodazole or colchicine did not affect the rate of DNP-beta-glucuronidase transport to heavy vesicles in intact cells, however, the extent of ligand mixing in late endosomes was decreased by microtubule disruption. Using sequentially labeled cells split into two groups, we directly compared ligand mixing in vitro to mixing by intact cells. Fusion alone does not mediate increases in vesicle density, since DNP-beta-glucuronidase/anti-DNP IgG complexes formed in vitro were found in light vesicles, while intact cells showed immune complexes predominantly in heavy vesicles. These results suggest that the density shift is an initial step in targeting to lysosomes.

Contact formation and transfer of mannose BSA gold from macrophages to cocultured fibroblasts

When macrophages were cocultured with fibroblasts many of the cells formed firm contacts. In some of these contacts both cell types were closely apposed and in others they were more clearly separated with numerous pseudopodia extending from macrophages toward the fibroblasts. Many small vesicles similar in structure to caveoli were observed immediately beneath the plasma membrane of some fibroblasts in regions immediately adjacent to areas of contact with macrophages. The membrane integrity of both cell types was always maintained and no connecting cytoplasmic strands were observed between contacting cells. Junctions were freely permeable to ruthenium red and less permeable to the larger cationized ferritin. Gold conjugated to mannose BSA was taken up readily by macrophages but not by fibroblasts. When fibroblasts were cocultured with macrophages that had been labeled with endocytosed gold, increasing amounts were transferred to them. Gold was observed within gaps formed between cocultured cells and within recipient fibroblasts in vesicles anatomically similar to lysosomes. These points of contact thus appear to provide a series of specialized protected clefts into which directed exocytosis of ligands from donor cells can take place and from which endocytosis into recipient cells is facilitated.

In vitro clustering and multiple fusion among macrophage endosomes

Early steps of receptor-mediated endocytosis appear to require the fusion of endosomes with each other. Recently, these fusion events have been reconstituted in vitro using vesicle preparations from J774 macrophages which have internalized ligands via the mannose receptor (Diaz, R., Mayorga, L., and Stahl, P. (1988) J. Biol. Chem. 263, 6093-6100). The present studies indicate that endosomes first form clusters when incubated under fusogenic conditions. Aggregation state was determined by electron microscopy using vesicles containing ligand-coated colloidal gold of different sizes previously internalized via the mannose receptor. Aggregation required cytosol and ATP. Afterwards, the limiting membranes of the vesicles composing these aggregates undergo multiple fusion and bring about the formation of large diameter vesicles that maintained the same density as endosomes when analyzed by Percoll gradient sedimentation. These large diameter vesicles were no longer fusogenic in the fusion assay. Multiple fusion was determined morphologically by the co-localization of three different size colloidal gold vesicles inside endocytic vesicles and biochemically by the fusion-dependent formation of triple immune complexes between three endocytic ligands internalized by receptor-mediated endocytosis: anti-dinitrophenol mouse IgG and dinitrophenol-derivatized beta-glucuronidase, ligands for the mannose receptor, and aggregated rabbit anti-mouse IgG, a ligand for the macrophage Fc receptor.

The use of permeabilized cells to study the ion requirements of receptor-ligand dissociation in endosomes

The mannose receptor mediates the transport of high-mannose glycoproteins from the cell surface to lysosomes in macrophages. The binding of ligand to the receptor is dependent on both pH and Ca2+. Upon internalization, ligands enter an acidic pre-lysosomal compartment where receptor-ligand dissociation takes place. Acidification is driven by an endosomal proton pump and anion transport is coupled to this acidification step. A permeabilized-cell assay has been designed to characterize the ionic requirements for receptor-ligand dissociation in endosomes. The plasma membrane of macrophages has been permeabilized selectively with digitonin without affecting endosomal membranes. Receptor-ligand dissociation in permeabilized cells required ATP and was blocked by proton ionophores. Di-isothiocyanostilbene-disulphonic acid and N-ethylmaleimide also blocked dissociation, but mitochondrial ATPase inhibitors and vanadate were ineffective. To explore the nature of the anion requirement for acidification, the ability of different anions to compensate for Cl- was tested. For the halide series, Br- was as equally effective as Cl- in supporting receptor-ligand dissociation, but I- was inhibitory. Citrate and gluconate were only partially effective, while SO4(2-), NO3- and PO4(2-) blocked dissociation. Addition of Ca2+ to permeabilized-cell preparations impaired ATP-dependent dissociation without affecting endosome acidification. These results suggest that the endosomal membrane has a Ca2+ conductance that would permit the rapid efflux of Ca2+ from endosomes during acidification, and this would appear to be a necessary step for efficient sorting of Ca2+-dependent receptors from their ligands.

Use of ricin A-chain to selectively deplete Kupffer cells

We used the A-chain of the toxin ricin (RTA) as a toxin specific to Kupffer cells in mice. RTA is specifically taken up by the mannose receptor present exclusively in macrophages. Kupffer cells were quantitated by shifts in beta-glucuronidase clearance and microscopic counts of cells which phagocytosed India ink. When compared to saline controls, 20 mg/kg of RTA intraperitoneally (divided over 4 days) or intraportally (single doses) significantly prolonged the t 1/2 half-life of beta-glucuronidase by 270 +/- 37 and 210 +/- 8%, respectively. Kupffer cell numbers were significantly decreased by 27 +/- 8 and 33 +/- 16%. This effect persisted for at least 3 days after toxin administration. Despite effects on Kupffer cell number, minimal histological damage to liver, spleen, lung, and heart was noted. Higher doses of RTA or doses potentiated by ureteral ligation to prevent renal clearance resulted in prohibitive mortalities and histologic liver damage. Doses of Hura crepitans inhibitor, a toxin similar to RTA but not mannose-receptor specific, did not affect Kupffer cell numbers. We conclude that RTA given both intraperitoneally and intraportally at low doses is toxic specifically to Kupffer cells. Kupffer cell numbers can be indirectly measured by beta-glucuronidase clearance.

Cell contact and direct transfer between co-cultured macrophages and fibroblasts

Mouse peritoneal macrophages formed attachments with beta-glucuronidase deficient human fibroblasts within an hour after co-cultures were initiated. Some of these attachments were transitory, while in others macrophages remained in firm contact with fibroblasts for many hours. Attachment of one macrophage did not prevent attachment of others, since many fibroblasts made firm contact with four or five other cells. Not all macrophages, however, attached themselves to fibroblasts. Macrophages injected with Lucifer yellow did not transfer the dye to fibroblasts with which they had made contact, nor was there any reverse transfer from injected fibroblasts to macrophages. Lucifer yellow was, however, transferred rapidly from injected fibroblasts to other adjacent fibroblasts with which they had formed gap junctions. Macrophages whose lysosomes had been pre-loaded with FITC-dextran did transfer this ligand to recipient fibroblasts, where it became localised in a perinuclear pattern with many bright punctate patches adjacent to donor macrophages. Transfer of FITC-dextran was blocked when cells were separated by nucleopore membranes in an analogous manner to transfer of endogenous lysosomal beta-glucuronidase.

In vitro fusion of endosomes following receptor-mediated endocytosis

Receptor-mediated endocytosis and receptor recycling involve a series of intracellular membrane fusion events that appear to play an important role in the regulation of the overall rate and efficiency of the process. An endosome-endosome fusion assay is described using two ligands that (i) rapidly and efficiently enter the endosomal compartment via the macrophage mannose receptor and (ii) that mutually recognize each other. Dinitrophenol-derivatized beta-glucuronidase (DNP-beta-glucuronidase), a ligand for the mannose receptor, was endocytosed by one population of J774 E clone cells, and mannose-derivatized monoclonal anti-DNP IgG (Man-IgG) was internalized by a second set of cells. Both ligands were localized in endosomes as determined by fractionation on Percoll gradients. Incubation of vesicles prepared from the two set of cells resulted in vesicle fusion as indicated by the formation of DNP-beta-glucuronidase-Man-IgG complexes. Under standard conditions, fusion was time-, ATP-, and temperature-dependent. KCl was required for fusion. Fusion required both cytosolic- and membrane-associated proteins. N-Ethylmaleimide treatment of cytosol inhibited fusion. Proton ionophores and amines had no effect on the fusion reaction. ATP-dependent fusion was only observed between early endocytic compartments. While in the presence of a Ca2+ chelator fusion was ATP-dependent, in its absence fusion was also observed in an ATP-independent fashion.