Impact of hexavalent chromium on mammalian cell bioenergetics: phenotypic changes, molecular basis and potential relevance to chromate-induced lung cancer.

Occupational exposure to hexavalent chromium [Cr(VI)] has been firmly associated with the development of several pathologies, notably lung cancer. According to the current paradigm, the evolution of normal cells to a neoplastic state is accompanied by extensive metabolic reprogramming, namely at the level of energy-transducing processes. Thus, a complete understanding of the molecular basis of Cr(VI)-induced lung cancer must encompass the elucidation of the impact of Cr(VI) on metabolism. Research in this area is still in its infancy. Nonetheless, Cr(VI)-induced metabolic phenotypes are beginning to emerge. Specifically, it is now well documented that Cr(VI) exposure inhibits respiration and negatively affects the cellular energy status. Furthermore, preliminary results suggest that it also upregulates glucose uptake and lactic acid fermentation. From a mechanistic point of view, there is evidence that Cr(VI) exposure can interfere with energy transducing pathways at different levels, namely gene expression, intracellular protein levels and/or protein function. Loss of thiol redox control likely plays a key role in these processes. The transcriptional networks that control energy transduction can likewise be affected. Data also suggest that Cr(VI) exposure might compromise energy transducing processes through changes in the intracellular pools of their substrates. This article reviews, for the first time, the information available on Cr(VI) impact on mammalian cell bioenergetics. It aims to provide a framework for the understanding of the role played by bioenergetics in Cr(VI)-induced carcinogenesis and is also intended as a guide for future research efforts in this area.

Molecular and cellular mechanisms of hexavalent chromium-induced lung cancer: an updated perspective.

For over a century, chromium (Cr) has found widespread industrial and commercial use, namely as a pigment, in the production of stainless steel and in chrome plating. The adverse health effects to the skin and respiratory tract of prolonged exposure to Cr have been known or suspected for a long time, but it was much more recently that the toxicity of this element was unequivocally attributed to its hexavalent state. Based on the combined results of extensive epidemiological studies, animal carcinogenicity studies and several types of other relevant data, authoritative regulatory agencies have found sufficient evidence to classify hexavalent chromium [Cr(VI)] compounds as encountered in the chromate production, chromate pigment production and chromium plating industries as carcinogenic to humans. Crucial for the development of novel strategies to prevent, detect and/or treat Cr(VI)-induced cancers is a detailed knowledge of the molecular and cellular mechanisms underlying these pathologies. Unfortunately, in spite of a considerable research effort, crucial facets of these mechanisms remain essentially unknown. This review is intended to provide a concise, integrated and critical perspective of the current state of knowledge concerning multiple aspects of Cr(VI) carcinogenesis. It will present recent theories of Cr(VI)-induced carcinogenesis and will include aspects not traditionally covered in other reviews, such as the possible involvement of the energy metabolism in this process. A brief discussion on the models that have been used in the studies of Cr(VI)-induced carcinogenicity will also be included, due to the impact of this parameter on the relevance of the results obtained.

Metabolic reprogramming of the tumor.

Cancer is classically considered as a genetic and, more recently, epigenetic multistep disease. Despite seminal studies in the 1920s by Warburg showing a characteristic metabolic pattern for tumors, cancer bioenergetics has often been relegated to the backwaters of cancer biology. This review aims to provide a historical account on cancer metabolism research, and to try to integrate and systematize the metabolic strategies in which cancer cells engage to overcome selective pressures during their inception and evolution. Implications of this renovated view on some common concepts and in therapeutics are also discussed.