Methods for reducing nonspecific interaction in antibody–antigen assay via atomic force microscopy

We developed a method to measure the rupture forces between antibody and antigen by atomic force microscopy (AFM). Previous studies have reported that in the measurement of antibody–antigen interaction using AFM, the specific intermolecular forces are often obscured by nonspecific adhesive binding forces between antibody immobilized cantilever and substrate surfaces on which antigen or nonantigen are fixed. Here, we examined whether detergent and nonreactive protein, which have been widely used to reduce nonspecific background signals in ordinary immunoassay and immunoblotting, could reduce the nonspecific forces in the AFM measurement. The results showed that, in the presence of both nonreactive protein and detergent, the rupture forces between anti-ferritin antibodies immobilized on a tip of cantilever and ferritin (antigen) on the substrate could be successfully measured, distinguishing from nonspecific adhesive forces. In addition, we found that approach/retraction velocity of the AFM cantilever was also important in the reduction of nonspecific adhesion. These insights will contribute to the detection of specific molecules at nanometer scale region and the investigation of intermolecular interaction by the use of AFM.

ARTICLE

FERRITIN: Augmentation in restless legs syndrome -low ferritin

Abstract
Background and purpose: Augmentation is a major problem with dopaminergic therapy for restless legs syndrome (RLS), and predictors of augmentation have not yet been identified. We aimed to analyze the relationship between baseline ferritin level and occurrence of augmentation in a retrospective analysis of a prospective double-blind trial of cabergoline versus levodopa on augmentation in RLS.

Patients and methods: Patients who experienced augmentation were compared to patients who did not experience augmentation.

Results: Augmentation symptoms causing premature discontinuation from the study or which were tolerated (n = 36, ferritin: 85 + 59 ng/ml) were associated with lower levels of serum ferritin compared to patients without augmentation (n = 302, ferritin : 118 + 108 ng/ml, p = 0.0062).

Conclusions: Ferritin as a marker of iron storage may play an important role in the pathophysiology of RLS and may prove to be a biomarker for the development of augmentation under dopaminergic therapy.

Keywords: Restless legs syndrome; Augmentation; Dopaminergic therapy; Ferritin; Iron storage; Cabergoline; Levodopa


Corresponding author. Address: Paracelsus-Elena Klinik, Klinikstrasse 16, 34128 Kassel, Germany. Tel.: +49 561 6009 200; fax: +49 561 6009 126.
doi:10.1016/j.sleep.2007.07.020