The ultrastructural investigation of mitochondria in B-CLL cells during apoptosis

Abstract

BACKGROUND: B-chronic lymphocytic leukemia (B-CLL) is an example of human malignancy caused by alternations in the pathways of apoptosis. Mitochondria play a critical role in the regulation of this process. The B-CLL cells dying in apoptosis showed typical morphological characteristics: the reduction of the nuclear volume is accompanied with the reduction of the cytoplasmatic volume, while many of organelles remain intact. The aim of our study was ultrastructural investigation of mitochondrial morphology in apoptotic B- CLL cells. METHODS: Our study included peripheral blood samples from 32 B-CLL patients. The samples were fixed in 4% glutar-aldehyde buffered in 0.1 cacodylate buffer and postfixed in 1% osmium tetroxide in the same buffer. The specimens were dehydrated in a graded series of alcohol and embedded in EPON 812. The ultra-thin sections were stained with uranyl acetate and lead citrate. Ultrastructural analysis of sections was performed on Philips electron microscope 208S at 80 kV. RESULTS: The most frequent mitochondrial abnormalities in apoptotic B-CLL cells were a reduction of size with a hyperdensity of their matrix (mitochondrial pyknosis), or markedly swollen mitochondria with peripherally placed, disorientated, and disintegrated cristae. In some apoptotic cells, we also detected close association of mitochondria with loops of rough endoplasmatic reticulum. CONCLUSION: The results of our study showed the numerous of mitochondria damages in B-CLL cells during apoptotic process. The correlation between ultrastructural damage and functional activity of mitochondria in apoptotic B-CLL cells is still not clear and requires further investigation.