Changes in muntjac fibroblasts associated with the acquisition of cadmium resistance. A pre-resistance, transitional and post-resistance study

Autophagy as an ultrastructural marker of heavy metal toxicity in human cord blood hematopoietic stem cells

Stem cells are a key target of environmental toxicants, but little is known about their toxicological responses. We aimed at developing an in-vitro model based on adult human stem cells to identify biomarkers of heavy metal exposure. To this end we investigated the responses of human CD34+ hematopoietic progenitor cells to hexavalent chromium (Cr[VI]) and cadmium (Cd). Parallel cultures of CD34+ cells isolated from umbilical cord blood were exposed for 48 h to 0.1 microM and 10 microM Cr(VI) or Cd. Cultures treated with 10 microM Cr(VI) or Cd showed marked cell loss. Ultrastructural analysis of surviving cells revealed prominent autophagosomes/autophagolysosomes, which is diagnostic of autophagy, associated with mitochondrial damage and replication, dilatation of the rough endoplasmic reticulum and Golgi complex, cytoplasmic lipid droplets and chromatin condensation. Treated cells did not show the morphologic hallmarks of apoptosis. Treatment with 0.1 microM Cr(VI) or Cd did not result in cell loss, but at the ultrastructural level cells showed dilated endoplasmic reticulum and evidence of mitochondrial damage. We conclude that autophagy is implicated in the response of human hematopoietic stem cells to toxic concentrations of Cr(VI) and Cd. Autophagy, which mediates cell survival and death under stress, deserves further evaluation to be established as biomarker of metal exposure.

Cadmium-induced multistep transformation of cultured Indian muntjac skin fibroblasts

During the past five years we have made a series of cadmium-transformed and resistant fibroblast cell lines by continuous low-level exposure to cadmium. In the present paper we describe the use of four of these lines with varying degrees of transformation to investigate the multistep nature of cadmium carcinogenesis. These include: (a) M cell, an immortal but nontransformed muntjac skin fibroblast line; (b) CCR5, a morphologically transformed and cadmium-resistant line derived from M cells after 20-months continuous exposure to small step-wise increases in cadmium; (c) SCR5, a tumorigenic line derived by selection (in the absence of cadmium) of rapidly growing CCR5 agar colonies; (d) T1, a line derived from an SCR5 tumour growing in a nude mouse. We have compared the morphological characteristics of the four cell lines using light and electron microscopy and evaluated their ability to grow in liquid culture, soft agar and nude mice. We have also examined the changes which have occurred in their cytoskeletons and extracellular matrices using fluorescent antibodies to actin, tubulin and fibronectin and related these to the strength of their cell-cell and cell-substrate attachments and to their levels of transformation and tumorigenesis. We have shown that, while some changes occur in a single step (e.g. intracellular cytoskeletal changes), others are gradual (e.g. changes in extracellular matrix, focus formation and ability to grow in soft agar). We conclude that continuous exposure to low levels of cadmium can initiate growth and structural changes which subsequently lead to cell transformation and tumorigenesis on the removal of cadmium. Though change with cadmium was slow, many of the transformed characteristics are similar to those reported for viral and chemically transformed cells.