Niemann-Pick disease (types A and B), or
acid sphingomyelinase deficiency, is an inherited deficiency of
acid sphingomyelinase, resulting in intralysosomal accumulation of
sphingomyelin in cells throughout the body, particularly within those of the reticuloendothelial system. These cellular changes result in hepatosplenomegaly and pulmonary infiltrates in humans. A knockout mouse model mimics many elements of human ASMD and is useful for studying disease histopathology. However, traditional
formalin-fixation and
paraffin embedding of ASMD tissues dissolves
sphingomyelin, resulting in tissues with a foamy cell appearance, making quantitative analysis of the substrate difficult. To optimize substrate fixation and staining, a modified
osmium tetroxide and
potassium dichromate postfixation method was developed to preserve
sphingomyelin in
epon-
araldite embedded tissue and pulmonary cytology specimens. After processing, semi-thin sections were incubated with
tannic acid solution followed by staining with
toluidine blue/
borax. This modified method provides excellent preservation and staining contrast of
sphingomyelin with other cell structures. The resulting high-resolution light microscopy sections permit digital quantification of
sphingomyelin in light microscopic fields. A
lysenin affinity
stain for
sphingomyelin was also developed for use on these semi-thin
epon sections. Finally, ultrathin serial sections can be cut from these same tissue blocks and stained for ultrastructural examination by electron microscopy.