Assessment of peroxisome proliferation is important in drug safety studies, since peroxisome proliferation often precedes tumor development in rodents. Proliferation can be measured morphometrically on sections by immunostaining for the peroxisomal enzyme catalase. Previous studies have used tissue embedded in acrylic resins such as LR White, which requires tissue sizes of 1-2 mm. Glycol methacrylate (GMA) is an acrylic resin that preserves antigenicity in much larger pieces of tissue. In this study we applied immunogold-silver staining (IGSS) to GMA sections for the quantitation of peroxisome proliferation in rat livers.

Sprague-Dawley rats were given clofibrate, a known peroxisome proliferator, for 14 days. Livers were removed, fixed in neutral buffered formalin for 4 hours, and embedded in GMA. Sections (3 μm thick) were incubated with antibody to catalase followed by protein A-gold (PAG), and the gold label was amplified using a commercial silver enhancement kit. Tissue sections were counterstained with propidium iodide (PI).