Limbic encephalitis in children and adolescents

OBJECTIVE

Limbic encephalitis is rare in people <18 years of age and rarely given a formal diagnosis.

DESIGN

Retrospective study on presentation and outcome of children and adolescents with the clinico-radiological syndrome of limbic encephalitis tested for specific neuronal autoantibodies (Abs) over 3.5 years.

SETTING

Assessment, diagnosis, treatment and follow-up at 12 neuropaediatric and neurological departments in Europe, with Abs determined in Bonn, Germany and Oxford, UK.

PATIENTS

Ten patients <18 years of age who presented with a disorder mainly affecting the limbic areas of <5 years' duration with MRI evidence of mediotemporal encephalitis (hyperintense T2/FLAIR signal, resolving over time).

RESULTS

Median age at disease onset was 14 years (range 3-17). Eight patients had defined Abs: one each with Hu or Ma1/2 Abs, four with high titre glutamic acid decarboxylase (GAD) Abs, two of whom had low voltage-gated potassium channel (VGKC) Abs and two with only low titre VGKC Abs. A tumour was only found in the patient with Hu Abs (a neuroblastoma). After a median follow-up of 15 months with corticosteroid or intravenous immunoglobulin treatment, starting after a median of 4 months, two patients recovered, eight remained impaired and one died.

CONCLUSIONS

Limbic encephalitis is a disease that can occur in childhood or adolescence with many of the hallmarks of the adult disorder, suggesting that both result from similar pathogenic processes. Since most of the cases were non-paraneoplastic, as now also recognised in adults, more systematic and aggressive immunotherapies should be evaluated in order to improve outcomes.

Normal and pathological erythrocytes studied by atomic force microscopy

Erythrocytes (red blood cells, RBCs) are the most common type of blood cells in vertebrates. Many diseases and dysfunctions directly affect their structure and function. Employing the atomic force microscope (AFM) physical, chemical, and biological/physiological properties of RBCs can be studied even under near-physiological conditions. In this chapter, we present the application of different AFM techniques to investigate and compare normal and pathological RBCs. We give a detailed description for nondestructive immobilization of whole intact RBCs and explain preparation techniques for isolated native RBC membranes. High-resolution imaging of morphological details and pathological differences are demonstrated with healthy and systemic lupus erythematosus (SLE) erythrocytes revealing substructural changes due to SLE. We also present the technique of simultaneous topography and recognition imaging, which was used to map the distribution of cystic fibrosis transmembrane conductance regulator sites on erythrocyte membranes in healthy and cystic fibrosis-positive RBCs.

Detecting protein aggregates on untreated human tissue samples by atomic force microscopy recognition imaging

We apply topography and recognition (TREC) imaging to the analysis of whole, untreated human tissue for what we believe to be the first time. Pseudoexfoliation syndrome (PEX), a well-known cause of irreversible blindness worldwide, is characterized by abnormal protein aggregation on the anterior lens capsule of the eye. However, the development of effective therapies has been hampered by a lack of detailed knowledge of the protein constituents in these pathological deposits and their distribution. Using both TREC and immunofluorescence, one of the proteins implicated in the PEX pathology--the apolipoprotein clusterin--was detected, and differences in its distribution pattern on the surface of untreated human lens capsule tissue in both PEX and normal control samples were investigated. Our study shows the potential of TREC imaging for the analysis of whole, untreated human tissue samples.

Nanomechanical recognition measurements of individual DNA molecules reveal epigenetic methylation patterns

Atomic force microscopy (AFM) is a powerful tool for analysing the shapes of individual molecules and the forces acting on them. AFM-based force spectroscopy provides insights into the structural and energetic dynamics of biomolecules by probing the interactions within individual molecules, or between a surface-bound molecule and a cantilever that carries a complementary binding partner. Here, we show that an AFM cantilever with an antibody tether can measure the distances between 5-methylcytidine bases in individual DNA strands with a resolution of 4 Å, thereby revealing the DNA methylation pattern, which has an important role in the epigenetic control of gene expression. The antibody is able to bind two 5-methylcytidine bases of a surface-immobilized DNA strand, and retracting the cantilever results in a unique rupture signature reflecting the spacing between two tagged bases. This nanomechanical approach might also allow related chemical patterns to be retrieved from biopolymers at the single-molecule level.

Improved localization of cellular membrane receptors using combined fluorescence microscopy and simultaneous topography and recognition imaging

The combination of fluorescence microscopy and atomic force microscopy has a great potential in single-molecule-detection applications, overcoming many of the limitations coming from each individual technique. Here we present a new platform of combined fluorescence and simultaneous topography and recognition imaging (TREC) for improved localization of cellular receptors. Green fluorescent protein (GFP) labeled human sodium-glucose cotransporter (hSGLT1) expressed Chinese Hamster Ovary (CHO) cells and endothelial cells (MyEnd) from mouse myocardium stained with phalloidin-rhodamine were used as cell systems to study AFM topography and fluorescence microscopy on the same surface area. Topographical AFM images revealed membrane features such as lamellipodia, cytoskeleton fibers, F-actin filaments and small globular structures with heights ranging from 20 to 30 nm. Combined fluorescence and TREC imaging was applied to detect density, distribution and localization of YFP-labeled CD1d molecules on alpha-galactosylceramide (alphaGalCer)-loaded THP1 cells. While the expression level, distribution and localization of CD1d molecules on THP1 cells were detected with fluorescence microscopy, the nanoscale distribution of binding sites was investigated with molecular recognition imaging by using a chemically modified AFM tip. Using TREC on the inverted light microscope, the recognition sites of cell receptors were detected in recognition images with domain sizes ranging from approximately 25 to approximately 160 nm, with the smaller domains corresponding to a single CD1d molecule.

Molecular recognition imaging using tuning fork-based transverse dynamic force microscopy

We demonstrate simultaneous transverse dynamic force microscopy and molecular recognition imaging using tuning forks as piezoelectric sensors. Tapered aluminum-coated glass fibers were chemically functionalized with biotin and anti-lysozyme molecules and attached to one of the prongs of a 32kHz tuning fork. The lateral oscillation amplitude of the tuning fork was used as feedback signal for topographical imaging of avidin aggregates and lysozyme molecules on mica substrate. The phase difference between the excitation and detection signals of the tuning fork provided molecular recognition between avidin/biotin or lysozyme/anti-lysozyme. Aggregates of avidin and lysozyme molecules appeared as features with heights of 1-4nm in the topographic images, consistent with single molecule atomic force microscopy imaging. Recognition events between avidin/biotin or lysozyme/anti-lysozyme were detected in the phase image at high signal-to-noise ratio with phase shifts of 1-2 degrees. Because tapered glass fibers and shear-force microscopy based on tuning forks are commonly used for near-field scanning optical microscopy (NSOM), these results open the door to the exciting possibility of combining optical, topographic and biochemical recognition at the nanometer scale in a single measurement and in liquid conditions.

AFM imaging of functionalized carbon nanotubes on biological membranes

Multifunctional carbon nanotubes are promising for biomedical applications as their nano-size, together with their physical stability, gives access into the cell and various cellular compartments including the nucleus. However, the direct and label-free detection of carbon nanotube uptake into cells is a challenging task. The atomic force microscope (AFM) is capable of resolving details of cellular surfaces at the nanometer scale and thus allows following of the docking of carbon nanotubes to biological membranes. Here we present topographical AFM images of non-covalently functionalized single walled (SWNT) and double walled carbon nanotubes (DWNT) immobilized on different biological membranes, such as plasma membranes and nuclear envelopes, as well as on a monolayer of avidin molecules. We were able to visualize DWNT on the nuclear membrane while at the same time resolving individual nuclear pore complexes. Furthermore, we succeeded in localizing individual SWNT at the border of incubated cells and in identifying bundles of DWNT on cell surfaces by AFM imaging.

Topography and recognition imaging of protein-patterned surfaces generated by AFM nanolithography

Native-protein nanolithography is combined with topography and recognition imaging to synergistically use AFM tips to write and image nanoscale protein patterns on a surface (see picture). The approach is validated with different feedback modes, using surface-bound biotinylated bovine serum albumin (BSA) protein and AFM tips carrying streptavidin.

Stable, non-destructive immobilization of native nuclear membranes to micro-structured PDMS for single-molecule force spectroscopy

In eukaryotic cells the nucleus is separated from the cytoplasm by a double-membraned nuclear envelope (NE). Exchange of molecules between the two compartments is mediated by nuclear pore complexes (NPCs) that are embedded in the NE membranes. The translocation of molecules such as proteins and RNAs through the nuclear membrane is executed by transport shuttling factors (karyopherines). They thereby dock to particular binding sites located all over the NPC, the so-called phenylalanine-glycin nucleoporines (FG Nups). Molecular recognition force spectroscopy (MRFS) allows investigations of the binding at the single-molecule level. Therefore the AFM tip carries a ligand for example, a particular karyopherin whereas the nuclear membrane with its receptors is mounted on a surface. Hence, one of the first requirements to study the nucleocytoplasmatic transport mechanism using MRFS is the development of an optimized membrane preparation that preserves structure and function of the NPCs. In this study we present a stable non-destructive preparation method of Xenopus laevis nuclear envelopes. We use micro-structured polydimethylsiloxane (PDMS) that provides an ideal platform for immobilization and biological integrity due to its elastic, chemical and mechanical properties. It is a solid basis for studying molecular recognition, transport interactions, and translocation processes through the NPC. As a first recognition system we investigate the interaction between an important transport shuttling factor, importin beta, and its binding sites on the NPC, the FG-domains.

Reduced number of CFTR molecules in erythrocyte plasma membrane of cystic fibrosis patients

Cystic fibrosis (CF), the most common genetic disease among Caucasians, is caused by mutations in the gene encoding CFTR (cystic fibrosis transmembrane conductance regulator). The most frequent mutation, DeltaF508, results in protein misfolding and, as a consequence, prevents CFTR from reaching its final location at the cell surface. CFTR is expressed in various cell types including red blood cells. The functional role of CFTR in erythrocytes is still unclear. Since the number of CFTR copies in a single erythrocyte of healthy donors and CF patients with a homozygous DeltaF508 mutation is unknown, we counted CFTR, localized in erythrocyte plasma membrane, at the single molecule level. A novel experimental approach combining atomic force microscopy with quantum-dot-labeled anti-CFTR antibodies, used as topographic surface markers, was employed to detect individual CFTR molecules. Analysis of erythrocyte plasma membranes taken from healthy donors and CF patients with a homozygous DeltaF508 mutation reveals mean (SEM) values of 698 (12.8) (n=542) and 172 (3.8) (n=538) CFTR molecules per red blood cell, respectively. We conclude that erythrocytes reflect the CFTR status of the organism and that quantification of CFTR in a blood sample could be useful in the diagnosis of CFTR related diseases.

Long-term outcome of lesional posterior cortical epilepsy surgery in adults

OBJECTIVE

The aim of this study was to evaluate the short- and long-term seizure outcome and to find predictors of outcome after epilepsy surgery in lesional posterior cortical epilepsies (PCEs).

METHODS

The operative outcome in 80 consecutive adult patients with lesional PCEs who underwent resective surgery for intractable partial epilepsy between 1991 and 2006 was retrospectively studied.

RESULTS

The probability of remaining in Engel Class I was 66.3% (95% CI 60 to 72) at 6 months, 52.5% (95% CI 47 to 57) at 2 years, 52.9% (CI 45 to 59) at 5 years and 47.1% (CI 42 to 52) at 10 years. Factors predicting poor outcome were the presence of a somatosensory aura, extraregional spikes, incomplete resection, interictal epileptiform discharge (IED) in EEG 6 months and 2 years postsurgery, history of generalised tonic-clonic seizure (GT-CS) and the presence of focal cortical dysplasia in the resected specimen. Factors predicting good outcome were childhood onset of epilepsy, short epilepsy duration, ipsilateral spikes, visual aura, presence of well-circumscribed lesion in preoperative MRI and a pathologically defined tumour. In the multivariate analysis, predictors were different in the long and short term as follows: incomplete resection as proven by postoperative MRI (hazard ratio (HR) 2.059 (CI 1.19 to 3.67)) predicts seizure relapse in short-term follow-up. The presence of IED in the EEG performed 6 months after surgery (HR 2.3 (CI 1.128 to 4.734)) predicts seizure relapse in the long-term fellow-up. However, the absence of a history of GT-CS independently predicts seizure remission in short- and long-term follow-up.

CONCLUSIONS

Surgery in PCEs proved to be effective in short- and long-term follow-up. Lesional posterior cortical epilepsy may be a progressive process in a substantial number of cases.

Simultaneous topography and recognition imaging: physical aspects and optimal imaging conditions

Simultaneous topography and recognition imaging (TREC) allows for the investigation of receptor distributions on natural biological surfaces under physiological conditions. Based on atomic force microscopy (AFM) in combination with a cantilever tip carrying a ligand molecule, it enables us to sense topography and recognition of receptor molecules simultaneously with nanometre accuracy. In this study we introduce optimized handling conditions and investigate the physical properties of the cantilever-tip-sample ensemble, which is essential for the interpretation of the experimental data gained from this technique. In contrast to conventional AFM methods, TREC is based on a more sophisticated feedback loop, which enables us to discriminate topographical contributions from recognition events in the AFM cantilever motion. The features of this feedback loop were investigated through a detailed analysis of the topography and recognition data obtained on a model protein system. Single avidin molecules immobilized on a mica substrate were imaged with an AFM tip functionalized with a biotinylated IgG. A simple procedure for adjusting the optimal amplitude for TREC imaging is described by exploiting the sharp localization of the TREC signal within a small range of oscillation amplitudes. This procedure can also be used for proving the specificity of the detected receptor-ligand interactions. For understanding and eliminating topographical crosstalk in the recognition images we developed a simple theoretical model, which nicely explains its origin and its dependence on the excitation frequency.

Imaging and detection of single molecule recognition events on organic semiconductor surfaces

The combination of organic thin film transistors and biological molecules could open new approaches for the detection and measurement of properties of biological entities. To generate specific addressable binding sites on such substrates, it is necessary to determine how single biological molecules, capable of serving as such binding sites behave upon attachment to semiconductor surfaces. Here, we use a combination of high-resolution atomic force microscopy topographical imaging and single molecule force spectroscopy (TREC), to study the functionality of antibiotin antibodies upon adsorption on pentacene islands, using biotin-functionalized, magnetically coated AFM tips. The antibodies could be stably adsorbed on the pentacene, preserving their functionality of recognizing biotin over the whole observation time of more than one hour. We have resolved individual antigen binding sites on single antibodies for the first time. This highlights the resolution capacity of the technique.