Project description:In order to evaluate the mechanisms underlying hexavalent chromium (Cr(VI)) responses, mice and rats were treated with varying concentrations of Cr(VI) in drinking water, as sodium dichromate dihydrate (SDD). Potential transcriptomic responses were evaluated through microarray analysis.
Project description:In order to evaluate the mechanisms underlying hexavalent chromium (Cr(VI)) responses, mice and rats were treated with varying concentrations of Cr(VI) in drinking water, as sodium dichromate dihydrate (SDD). Potential transcriptomic responses were evaluated through microarray analysis.
Project description:Significant occupational and environmental exposures to hexavalent chromium, a metal with broad toxicity potential in humans, have been reported. In order to understand the mechanisms of dermal toxicity induced by hexavalent chromium, global gene expression profiling of human dermal fibroblasts exposed to a toxic concentration of potassium dichromate was performed. Microarray analysis of the gene expression profile in the fibroblasts treated with potassium dichromate identified significant differential expression of approximately 1,200 transcripts compared with the control cells. Hierarchical cluster analysis of the gene expression profile demonstrated a clear separation of the treated cells from the control group of cells. Functional categorization of the differentially expressed genes identified the enrichment of genes involved in several cellular processes, including apoptosis and oxidative stress, in the fibroblasts exposed to hexavalent chromium. Induction of apoptosis and generation of hydroxyl radicals indicative of oxidative stress in the dermal fibroblasts in response to their exposure to hexavalent chromium were independently confirmed by TUNEL assay and electron spin resonance (ESR) analysis, respectively. The potassium dichromate-induced cytotoxicity, differential gene expression, apoptosis, and oxidative stress were significantly blocked by the addition of ferrous sulfate, an agent known for its ability to reduce hexavalent chromium to the insoluble and therefore impermeable trivalent form, to the cell culture medium. Taken together, our data provide insights into the potential mechanisms underlying the dermal toxicity of hexavalent chromium and suggest a definite role for apoptosis and oxidative stress in Cr(VI)-induced cytotoxicity in human dermal fibroblasts.
Project description:Significant occupational and environmental exposures to hexavalent chromium, a metal with broad toxicity potential in humans, have been reported. In order to understand the mechanisms of dermal toxicity induced by hexavalent chromium, global gene expression profiling of human dermal fibroblasts exposed to a toxic concentration of potassium dichromate was performed. Microarray analysis of the gene expression profile in the fibroblasts treated with potassium dichromate identified significant differential expression of approximately 1,200 transcripts compared with the control cells. Hierarchical cluster analysis of the gene expression profile demonstrated a clear separation of the treated cells from the control group of cells. Functional categorization of the differentially expressed genes identified the enrichment of genes involved in several cellular processes, including apoptosis and oxidative stress, in the fibroblasts exposed to hexavalent chromium. Induction of apoptosis and generation of hydroxyl radicals indicative of oxidative stress in the dermal fibroblasts in response to their exposure to hexavalent chromium were independently confirmed by TUNEL assay and electron spin resonance (ESR) analysis, respectively. The potassium dichromate-induced cytotoxicity, differential gene expression, apoptosis, and oxidative stress were significantly blocked by the addition of ferrous sulfate, an agent known for its ability to reduce hexavalent chromium to the insoluble and therefore impermeable trivalent form, to the cell culture medium. Taken together, our data provide insights into the potential mechanisms underlying the dermal toxicity of hexavalent chromium and suggest a definite role for apoptosis and oxidative stress in Cr(VI)-induced cytotoxicity in human dermal fibroblasts. 16 samples were analyzed in this experiment. Exponentially growing human dermal fibroblasts (3x105 cells) were cultured in T25 cell culture flasks. When the cells were approximately 70% confluent, hexavalent potassium dichromate (5µM) was added to the medium with or without 40µM ferrous sulfate. Following 16 hours of culturing at 37oC, total RNA was isolated for gene expression studies. Details of the samples are: Control 4 Samples: Cr(0)-1, Cr(0)-2, Cr(0)-3, Cr(0)-4 Cr 5 µM 4 Samples: Cr(5)-5, Cr(5)-6, Cr(5)-7, Cr(5)-8 FeSO4 40 µM 4 Samples: Fe(40)-9, Fe(40)-10, Fe(40)-11, Fe(40)-12 Cr 5 µM + FeSO4 40 µM 4 Samples: Cr(5)+Fe(40)-13,Cr(5)+Fe(40)-14, Cr(5)+Fe(40)-15, Cr(5)+Fe(40)-16
Project description:High doses of sodium phenobarbital (NaPB), a constitutive androstane receptor (CAR) activator, have been shown to produce hepatocellular tumors in rodents by a mitogenic mode of action (MOA) involving CAR activation. The effect of 1 week dietary treatment with NaPB on liver weight and histopathology, hepatic CYP2B enzyme activity and CYP2B/3A mRNA expression, replicative DNA synthesis and selected genes related to cell proliferation and functional transcriptomic and metabolomic analyses was studied in male CD-1 mice, Wistar Hannover (WH) rats and chimeric mice with human hepatocytes. The treatment of chimeric mice with 1000-1500 ppm NaPB resulted in plasma levels around 3-5 fold higher than those observed in human subjects given therapeutic doses of NaPB. NaPB produced dose-dependent increases in hepatic CYP2B activity and CYP2B/3A mRNA levels in all animal models. Integrated functional metabolomic and transcriptomic analyses demonstrated the responses to NaPB in human liver were clearly different from those in rodents. While NaPB produced a dose-dependent increase in hepatocyte replicative DNA synthesis in CD-1 mice and WH rats, no increase in replicative DNA synthesis was observed in human hepatocyte-originated areas of chimeric mice. In addition, treatment with NaPB had no effect on Ki-67, PCNA, GADD45β, and MDM2 mRNA expression in chimeric mice, whereas significant increases were observed in CD-1 mice and/or WH rats. Thus, while NaPB could activate CAR in rodent and human hepatocytes, NaPB did not increase replicative DNA synthesis in human hepatocytes of chimeric mice, whereas it was mitogenic to rat and mouse hepatocytes. As human hepatocytes are refractory to the mitogenic effects of NaPB, the MOA for NaPB-induced rodent liver tumor formation is thus not relevant for humans. Male WH rats (4 animals/dose) were fed diets containing 0 (control) or 2500 ppm NaPB for 7 days. Liver samples were used for gene expression analysis.