Lack of Pseudomelanosis coli in colonic adenomas suggests different pathways of apoptotic bodies in normal and neoplastic colonic mucosa.

Pseudomelanosis coli is characterized by pigment deposition in the lamina propria and caused by increased epithelial apoptosis. Pseudomelanosis coli is absent in colonic neoplasia. The aim of our studies was to investigate this phenomenon in more detail. Apoptotic fragments of epithelial cells and their distribution, cell proliferation (Ki-67, MIB 1 immunostaining), macrophages (CD68 immunostaining), Bcl-2 expression and apoptosis [terminal-deoxynucleotidyl-transferase mediated dUTP fluorescein nick end labeling (TUNEL) assay] were studied in adenomas arising in normal and melanotic colonic mucosa, in normal colonic mucosa and colonic mucosa with pseudomelanosis alone. In adenomas, we found 7.0 apoptotic bodies per 100 epithelial cells in the epithelial layer and only 0.2 apoptotic bodies per high power field (HPF) in the lamina propria. In contrast, in melanotic mucosa 1.7 apoptotic bodies per 100 epithelial cells in the epithelial layer and 2.5 per HPF in the lamina propria were found. Our results show that apoptotic fragments remain in the neoplastic (adenomatous) epithelium and do not reach (at least in higher amounts) the lamina propria. They can, therefore, not contribute to the development of pseudomelanosis in these lesions. However, macrophages are diminished in adenomas. Proliferation (Ki-67) and also Bcl-2 expression are highly increased in adenomas. The pathway of mucosal macrophages is also discussed.