A new, simple method for linking of antibodies to atomic force microscopy tips

Functionalization of atomic force microscope (AFM) tips with bioligands converts them into monomolecular biosensors which can detect complementary receptor molecules on the sample surface. Flexible PEG tethers are preferred because the bioligand can freely reorient and locally palpate the sample surface while the AFM tip is moved along. In a well-established coupling scheme [Hinterdorfer et al. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 3477-3481], a heterobifunctional PEG linker is used to tether thiol-containing bioligands to amino-functionalized AFM tips. Since antibodies contain no free thiol residues, prederivatization with N-succinimidyl 3-(acetylthio)propionate (SATP) is needed which causes a relatively high demand for antibody. The present study offers a convenient alternative with minimal protein consumption (e.g., 5 microg of protein in 50 microL of buffer) and no prederivatization, using a new heterobifunctional cross-linker that has two different amino-reactive functions. One end is an activated carboxyl (N-hydroxysuccinimide ester) which is much faster to react with the amino groups of the tips than the benzaldehyde function on its other end. The reactivity of the latter is sufficient, however, to covalently bind lysine residues of proteins via Schiff base formation. The method has been critically examined, using biotinylated IgG as bioligand on the tip and mica-bound avidin as complementary receptor. These experiments were well reproduced on amino-functionalized silicon nitride chips where the number of specifically bound IgG molecules (approximately 2000 per microm2) was estimated from the amount of specifically bound ExtrAvidin-peroxidase conjugate. For a bioscientific application, human rhinovirus particles were tethered to the tip, very-low-density lipoprotein receptor fragments were tethered to mica, and the specific interaction was studied by force microscopy.

Presurgical seizure frequency and tumoral etiology predict the outcome after extratemporal epilepsy surgery

OBJECTIVE

To examine the predictive value of demographic data for the seizure outcome after extratemporal epilepsy surgery.

METHODS

Eightyone patients who underwent resective extratemporal epilepsy surgery were retrospectively studied concerning (a) age at surgery, (b) onset of epilepsy, (c) duration of epilepsy, (d) number of seizures at the time of presurgical evaluation, (d) number of presurgically tested antiepileptic substances and (f) number of seizure types. The data were correlated to the postoperative seizure outcome after two years.

RESULTS

33 patients (40.7%) were seizure free two years after surgery. Univariate and multivariate analysis revealed that both tumor etiology and low presurgical seizure frequency were independently associated with seizure freedom after epilepsy surgery. The recurrence rate in patients with one or more seizures per day was more than two-fold if compared with patients with fewer seizures. The remaining demographic factors did not show a significant association with seizure outcome in our 81 patients.

CONCLUSIONS

Fewer than daily seizures prior to surgery and a tumoral etiology independently increase the likelihood of remaining seizure free two years after extratemporal epilepsy surgery.

Assessment of cognitive functions before and after stereotactic interstitial radiosurgery of hypothalamic hamartomas in patients with gelastic seizures

We assessed cognitive functions before and 3 months after interstitial radiotherapy in 14 patients with gelastic seizures caused by hypothalamic hamartoma. Cognitive functioning was assessed before temporary implantation of (125)I-seed and 3 months after seed explantation. Performance was compared with that of a selected control group of conservatively treated patients with symptomatic focal epilepsy tested before add-on treatment with a new antiepileptic drug and after reaching steady state. No short-term negative side effects of the interstitial radiosurgery could be observed for the domains of attention and executive functions and verbal and figural memory performance. Cognitive development of the patients treated with seeds was comparable to that of the control group at both assessments. Thus, the stereotactic implantation of (125)I-seeds in this patient group with gelastic seizures caused by hypothalamic hamartoma provides a well-tolerated minimally invasive method in the treatment of this severe epileptic syndrome without negative cognitive side effects.

Patients' ability to react before complex partial seizures

OBJECTIVE

The purpose of the study described here was to investigate the pathophysiology of patients' ability to react during the conscious (aura) phase of complex partial seizures (CPS) originating from the temporal lobe.

METHODS

We reviewed video recordings of CPS experienced by 130 adult patients who had undergone epilepsy surgery for intractable medial temporal lobe epilepsy. All patients were instructed to push the alarm button when they felt an aura. We defined the preictal reactivity as the ability to push the alarm button before the complex partial (unconscious) phase of seizures.

RESULTS

Seventy-seven patients (59%) pushed the alarm button before seizures. Patients with preictal reactivity were significantly younger, more often had lateralized EEG seizure patterns, and had a better postoperative outcome. Patients who did not push the alarm button had secondarily generalized seizures more often.

CONCLUSIONS

Ability to react before CPS is associated with a circumscribed region involved at seizure onset and spread, and with a seizure-free postoperative outcome.

Antibody linking to atomic force microscope tips via disulfide bond formation

Covalent binding of bioligands to atomic force microscope (AFM) tips converts them into monomolecular biosensors by which cognate receptors can be localized on the sample surface and fine details of ligand-receptor interaction can be studied. Tethering of the bioligand to the AFM tip via a approximately 6 nm long, flexible poly(ethylene glycol) linker (PEG) allows the bioligand to freely reorient and to rapidly "scan" a large surface area while the tip is at or near the sample surface. In the standard coupling scheme, amino groups are first generated on the AFM tip. In the second step, these amino groups react with the amino-reactive ends of heterobifunctional PEG linkers. In the third step, the 2-pyridyl-S-S groups on the free ends of the PEG chains react with protein thiol groups to give stable disulfide bonds. In the present study, this standard coupling scheme has been critically examined, using biotinylated IgG with free thiols as the bioligand. AFM tips with PEG-tethered biotin-IgG were specifically recognized by avidin molecules that had been adsorbed to mica surfaces. The unbinding force distribution showed three maxima that reflected simultaneous unbinding of 1, 2, or 3 IgG-linked biotin residues from the avidin monolayer. The coupling scheme was well-reproduced on amino-functionalized silicon nitride chips, and the number of covalently bound biotin-IgG per microm2 was estimated by the amount of specifically bound ExtrAvidin-peroxidase conjugate. Coupling was evidently via disulfide bonds, since only biotin-IgG with free thiol groups was bound to the chips. The mechanism of protein thiol coupling to 2-pyridyl-S-S-PEG linkers on AFM tips was further examined by staging the coupling step in bulk solution and monitoring turnover by release of 2-pyridyl-SH which tautomerizes to 2-thiopyridone and absorbs light at 343 nm. These experiments predicted 10(3)-fold slower rates for the disulfide coupling step than actually observed on AFM tips and silicon nitride chips. The discrepancy was reconciled by assuming 10(3)-fold enrichment of protein on AFM tips via preadsorption, as is known to occur on comparable inorganic surfaces.

Unilateral hand automatisms in temporal lobe epilepsy

OBJECTIVES

To analyse the lateralising value of unilateral manual automatism (UMA), its relation to contralateral dystonia and the hand by which the UMA was performed.

METHODS

In this retrospective study, we reviewed video recordings of 141 patients (mean age 34.1+/-10) who had consecutively undergone presurgical evaluations with ictal video-EEG recordings and high-resolution MRI, had had epilepsy surgery due to intractable medial temporal lobe epilepsy with complex partial seizures due to unilateral medial temporal lobe lesions. The video recordings were prospectively reviewed by one of the authors blinded to patient's clinical data except the diagnosis of medial temporal lobe epilepsy. Altogether 310 archived seizures were analysed.

RESULTS

Hand automatisms occurred in 86.5% of patients. UMA occurred in 53% of patients. If UMA was accompanied by contralateral hand dystonia, it had a high lateralising value to the ipsilateral epileptic focus (EF), it was ipsilateral in 85% of patients. Conversely, if UMA occurred without contralateral dystonia, it had only a limited lateralising value because it was ipsilateral to the EF in only 63% of patients. However, we found that left-sided UMA without dystonia had a high lateralising value to the left hemisphere (ipsilateral to the EF in 82%), while right-sided UMA without dystonia has practically no lateralising value.

CONCLUSIONS

UMA with contralateral dystonia has a high lateralising value to the ipsilateral hemisphere. Left-sided UMA without contralateral dystonia has a lateralising value to the left hemisphere. Right-sided UMA without contralateral dystonia has no lateralising value.

[Correlation between sex, intrauterine position and familial predisposition and neonatal hip ultrasound results]

AIM

To correlate findings of hip ultrasound on day 4-10 of life with sex, intrauterine position and a positive family history for congenital hip anomalies.

METHODS

The SNiP-study ( Survey of Neonates In Pommerania) registered 2256 neonates (2030 term, 226 preterm) between May 2002 and March 2004. Hip ultrasound results of 1043 term and since October 2003 33 preterm neonates were analysed. Time of ultrasound was day 4-10 after birth. Preterm neonates were examined when reaching their corrected term gestational age. Ultrasound was applied with a 7.5 MHz linear scanner and results were classified according to Graf. Chi-square and Fishers exact test were used for statistical analysis.

RESULTS

4.9 % of the screened hips were classified as IIc or higher, 3.1 % were unilateral and 1.7 % bilateral. Incidence was significantly higher (p < 0.023) in females (6.6 %) than in males (3.2 %). There was no significant difference in intrauterine position or positive family history for hip anomalies with 3.7 % for mothers, 1.2 % of fathers and 2.4 % of siblings positive. There was a higher incidence for congenital hip dysplasia in preterms with 6.1 %, which is not significant due to the limited number.

DISCUSSION

Current screening methods miss up to 18 % of newborns with severe hip dysplasia. We were able to demonstrate that screening for congenital hip dysplasia with ultrasound is a diagnostic tool even during the first days of life. There is a significantly higher incidence of congenital hip dysplasia in females, but in contrast to other studies we found no significant difference in intrauterine position or familial history. Earlier diagnosis and therapy on the base of relevant risk factors might correspond with an improved prognosis and outcome. Further studies are warranted to evaluate the significance in preterm neonates.

Vorschlag für eine neue patientenorientierte Epilepsieklassifikation

The recent proposal by the ILAE Task Force for Epilepsy Classification is a multiaxial, syndrome-oriented approach. Epilepsy syndromes--at least as defined by the ILAE Task Force--group patients according to multiple, usually poorly defined parameters. As a result, these syndromes frequently show significant overlap and may change with patient age. We propose a five-dimensional and patient-oriented approach to epilepsy classification. This approach shifts away from syndrome orientation, using independent criteria in each of the five dimensions similarly to the diagnostic process in general neurology. The main dimensions of this new classification consist of (1) localizing the epileptogenic zone, (2) semiology of the seizure, (3) etiology, (4) seizure frequency, and (5) related medical conditions. These dimensions characterize all information necessary for patient management, are independent parameters, and include information more pertinent than the ILAE axes with regard to patient management. All cases can be classified according to this five-dimensional system, even at initial encounter when no detailed test results are available. Information from clinical tests such as MRI and EEG are translated into the best possible working hypothesis at the time of classification, allowing increased precision of the classification as additional information becomes available.

Laughter and the mesial and lateral premotor cortex

We report the induction of laughter and smiling by cortical electrical stimulation of the frontal lobe of two patients: an 18-month-old boy with a left frontal cortical lesion extending to the vertex and the central gyrus, and a 35-year-old woman with a lesion in the right supplementary sensorimotor area (SSMA). The subjects underwent presurgical epilepsy evaluation with subdural grid electrodes to determine surgical candidacy. Stimulation of the prefrontal area reproducibly induced laughter. The adult patient reported absence of emotional content. Slowing of speech occurred under stimulation of electrodes in the upper and posterior vicinity. In this patient laughter was elicited in the anterior part of the SSMA. In the child, this response was induced by stimulation of the lateral prefrontal cortex near the midline. We conclude that the anterior portion of the SSMA/lateral premotor cortex is involved in generating the motor pattern of laughter.

Improving the contrast of topographical AFM images by a simple averaging filter

New image-processing methods were applied to atomic force microscopy images in order to visualize small details on the surface of virus particles and living cells. Polynomial line flattening and plane fitting of topographical images were performed as first step of the image processing. In a second step, a sliding window approach was used for low-pass filtering and data smoothing. The size of the filtering window was adjusted to the size of the small details of interest. Subtraction of the smoothed data from the original data resulted in images with enhanced contrast. Topographical features which are usually not visible can be easily discerned in the processed images. The method developed in this study rendered possible the detection of small patterns on viral particles as well as thin cytoskeleton fibers of living cells. It is shown that the sliding window approach gives better results than Fourier-filtering. Our method can be generally applied to increase the contrast of topographical images, especially when small features are to be highlighted on relatively high objects.

Transient lesion in the splenium of the corpus callosum and antiepileptic drug withdrawal

OBJECTIVE

To test pathophysiologic hypotheses regarding the occurrence of a splenial lesion in patients with epilepsy.

METHODS

The authors studied 16 patients with a splenial lesion and 32 control patients, all of whom had MRI examination immediately after presurgical EEG long-term monitoring (LTM). The authors compared the number of generalized tonic-clonic and partial seizures during LTM, antiepileptic drug (AED) withdrawal, and laboratory results.

RESULTS

All of the patients with a splenial lesion had their AEDs stopped completely, vs 47% of the controls (p = 0.001). Patients with SCC lesion had a longer duration of complete withdrawal (median 3.5 vs 2 days, p = 0.03). There was no correlation with seizure frequency or the introduction of new AEDs.

CONCLUSION

A lesion of the splenium of the corpus callosum in patients with epilepsy is not associated with toxic drug effects or high seizure frequency, but might be induced by a rapid and relatively long-lasting reduction of antiepileptic drugs. Its frequency might be underestimated as MRI after long-term monitoring is rarely done.

Prognostic factors for surgery of neocortical temporal lobe epilepsy

OBJECTIVES

In the current classification of epilepsies two forms of temporal lobe epilepsy (TLE) were included: mesial and lateral (neocortical) TLE. We aimed at identifying prognostic factors for the surgical outcome of lesional neocortical TLE.

METHODS

We included consecutive patients who had undergone presurgical evaluation including ictal video-EEG and high-resolution MRI, who had TLE due to neocortical lateral epileptogenic lesions, who had a lesionectomy and who had >2-year follow-up.

RESULTS

There were 29 patients who met the inclusion criteria. Twenty of them became postoperatively seizure-free. Patients' mean age was 34.8+/-9 years (range 18-52). The age at epilepsy onset was 20.1+/-8 years. We found that left-sided surgery (p=0.048) and focal cortical dysplasia (FCD) on MRI (p=0.005) were associated with non-seizure-free outcome, while lateralized/localized EEG seizure pattern (p=0.032), tumors on the MRI (p=0.013), and a favorable seizure situation at the 6-month postoperative evaluation were associated with 2-year postoperative seizure-freedom (p<0.001). Multivariate analysis indicated that the side of surgery was not an independent predictor.

CONCLUSION

More than two-thirds of the patients with neocortical TLE became seizure-free postoperatively. Lateralized/localized EEG seizure pattern and tumors on the MRI were associated with postoperative seizure-freedom, while FCD were associated with a poor outcome. The 6-month postoperative outcome is a reliable predictor for the long-term outcome.