Heme-oxygenase 1 Gene Expression is a Marker for Hexavalent Chromium-Induced Stress and Toxicity in Human Dermal Fibroblasts

Abstract

Several adverse health effects, including irritant and allergic contact dermatitis, have been reported among workers who are occupationally exposed to chromium-containing compounds. Human dermal fibroblasts were used as an in vitro experimental model to study the potential mechanisms underlying hexavalent chromium [Cr(VI)]-induced dermal toxicity. Exposure of the fibroblasts to 5 microM Cr(VI) (LC50 for a 24-h exposure period) followed by microarray analysis of the gene expression profile revealed overexpression of several genes including those involved in cell stress response. The cellular level of glutathione, the major antioxidant molecule present in the cells, was significantly lower in the Cr(VI)-treated cells compared to the corresponding control cells. The Cr(VI)-induced overexpression of heme-oxygenase 1 messenger RNA (HO-1) in the fibroblasts was significantly blocked by actinomycin D and by inhibitors of MAP kinase pathways. The Cr(VI)-induced cytotoxicity and the overexpression of the HO-1 gene were dependent on the glutathione level of the fibroblasts. Buthionine sulfoximine-mediated GSH depletion resulted in enhanced Cr(VI) cytotoxicity and further overexpression of the HO-1 gene. On the other hand, elevated cellular levels of glutathione resulting from pretreating the cells with GSH significantly protected the cells against the Cr(VI)-induced cytotoxicity and blocked the HO-1 gene's overexpression. Pretreating the fibroblasts with N-acetyl cysteine also significantly reduced the Cr(VI)-induced cytotoxicity and overexpression of the HO-1 gene. In conclusion, depletion of GSH leading to cellular stress is a major mechanism responsible for Cr(VI)-induced cytotoxicity. Furthermore, the expression level of HO-1 gene is a marker for Cr(VI)-induced cell stress leading to cytotoxicity.

Transcriptomics Evaluation of Hexavalent Chromium Toxicity in Human Dermal Fibroblasts

“…The cytotoxicity data obtained in the present investigation is in agreement with our previous report [1] and further supports the dermal toxicity potential of Cr(VI) [7]. Many of the genes that were differentially expressed in our previous study [1] were also found differentially expressed in the current study. However, quantitative differences in the expression of those genes were noticed between the two studies.…”

“…These results were essentially similar to those of our previous publication [1] and are, therefore, not presented here. Exposure of fibroblasts to 5 µM Cr(VI) for 16-hours (the time interval employed in the case of gene expression experiment) resulted in <30% cell death (data not presented).…”

“…The present study is a follow-up of one of our previous publications [1] in which we employed a microarray that contained 263 genes, whose expression are indicative of stress and toxicity, to determine the mechanisms underlying Cr(VI)-induced dermal toxicity. The microarray employed in the present study contained more than 22,000 genes involved in a variety of cellular functions and, therefore, is expected to provide a broader understanding of the dermal toxicity potential of Cr(VI) as well as further insight into the possible mechanisms underlying the toxicity.…”

“…Culturing of mycoplasma-free human dermal fibroblasts (Catalogue number CRL 2076, ATCC, Manassas, VA) in Iscove's modified Dulbecco's medium and determination of cytotoxicity induced by hexavalent potassium dichromate [K 2 Cr 2 O 7 , abbreviated Cr(VI), Sigma Chemical Company, St Louis, MO] were done exactly as described in our previous publication [1].…”

“…The potential of chromium, especially its hexavalent form, to result in toxicity has been recognized for a long period of time. Treating cells cultured in vitro with hexavalent chromium resulted in cytotoxicity [1], genotoxicity [2], apoptosis [3], and cell transformation [4]. Similarly, administration of hexavalent chromium to experimental animals results in toxicity of the lungs [5], kidney [6], skin [7], and reproductive system [8].…”