Optimization of techniques for the maximal detection and quantification of Alzheimer's-related neuropathology with digital imaging.

Prior to undertaking quantitative neuropathological studies of Alzheimer's disease, methods for detecting plaques and tangles must be optimized. While suitable antibodies have been developed with great sensitivity, specificity, and reliability, there is no standard pre-treatment protocol for key AD-related pathology. It is well known that formic acid treatment enhances the detection of beta-amyloid. But what concentration of formic acid is best; can similar methods enhance the detection of tau-related pathology? This study compared multiple antigen retrieval techniques (e.g. boiling in citrate or glycine buffer, microwaves, formic acid concentrations), to develop an optimal, standardized protocol for quantitative digital microscopy. Free-floating (40 microm) and paraffin-embedded (12 microm) sections of formalin fixed frontal cortex from mild, moderate, and severe AD cases (n = 18) were pretreated with fifteen different protocols and stained with each of the following antibodies: beta42, PHF-1, MC-1 and AT8. Random fields were digitally captured and images were thresholded to select for positively stained areas versus background (e.g. "load"). As previously reported, high concentrations of formic acid were extremely effective in enhancing the detection of beta-amyloid; as much as a 2-fold enhancement in Abeta "load" values were observed. Surprisingly, tau-related pathology detection also increased significantly following pretreatment. Depending on the antibody, between a 3-fold and 6-fold enhancement was possible relative to no pretreatment. Comparable results were found in paraffin-embedded sections. Similar enhancements in the detection of pathology were obtained following 99% formic acid exposure, microwaving in citrate buffer (pH 9.0) or exposure to 99% formic acid then boiling in citrate buffer (pH 6.0). Because the latter treatments were often harsh on the tissue and more difficult to control, we recommend a standard tissue pretreatment of 99% formic acid for seven minutes for both beta-amyloid and tau-related pathology.