Induction of apoptosis in the lung but not in the liver of rats receiving intra-tracheal instillations of chromium(VI).
Several studies have shown that hexavalent chromium [Cr(VI)] induces apoptosis in a variety of in vitro test systems. We instilled intra-tracheally either saline or sodium dichromate (0.25 mg/kg body weight), for three consecutive days, to Sprague-Dawley rats. TUNEL analyses showed a marked increase of the apoptotic index in both bronchial epithelium and lung parenchyma of Cr(VI)-treated rats, but no effect was detected in their liver. In parallel, the expression of 13 out of 18 apoptosis-related genes, evaluated by cDNA array analysis, was significantly enhanced in rat lung. The overexpressed genes included c-Jun N-terminal kinases 1, 2 and 3, bcl-x, bcl-2-associated death promoter and bcl-2-related ovarian killer protein, caspases 1, 3 and 6, DNase I precursor, DNA topoisomerases I and II alpha, and poly(ADP-ribose) polymerase. The enhancement of p53 expression in the lung was borderline to statistical significance. Expressions of bcl-2, bax-alpha, mdm2 and DNA topoisomerase IIB were not enhanced to a significant extent in lung. No induction of gene expression was observed in rat liver. RT-PCR analyses confirmed that Cr(VI) enhances the expression of c-Jun N-terminal kinase 1, caspase 6, and DNase I precursor but not that of bcl-2 in lung, while none of these genes was overexpressed in the liver of Cr(VI)-treated rats. The lack of stimulation of apoptosis in the liver parallels the failure of Cr(VI) to produce genotoxic damage, as we previously observed under identical experimental conditions. These negative findings may be ascribed to reduction of Cr(VI) to Cr(III) when traveling from the respiratory tract to the liver. On the other hand, induction of apoptosis in the respiratory tract parallels the occurrence of genotoxic effects and oxidative DNA damage produced by Cr(VI) in the same tissue. As previously shown in another laboratory, Cr(VI) did not induce lung tumors after 30 months of administration of the same daily dose. Therefore, apoptosis is likely to provide a protective mechanism at a post-genotoxic stage of Cr(VI) carcinogenesis.
D'Agostini
Francesco
F
Department of Health Sciences, University of Genoa, Via A. Pastore 1, I-16132 Genoa, Italy.
Izzotti
Alberto
A
Bennicelli
Carlo
C
Camoirano
Anna
A
Tampa
Elena
E
De Flora
Silvio
S
D000818:Animals; D017209:Apoptosis; D002274:Carcinogens, Environmental; D053178:Caspase 6; D020169:Caspases / Q000096:biosynthesis; D002840:Chromates / Q000494:pharmacology; D002857:Chromium / Q000008:administration & dosage* / Q000494:pharmacology*; D004250:DNA Topoisomerases, Type II / Q000096:biosynthesis; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins; D003850:Deoxyribonuclease I / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D020287:In Situ Nick-End Labeling; D048031:JNK Mitogen-Activated Protein Kinases; D008099:Liver / Q000187:drug effects / Q000473:pathology*; D008168:Lung / Q000187:drug effects / Q000473:pathology*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis; D009687:Nuclear Proteins; D020411:Oligonucleotide Array Sequence Analysis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2; D051736:Proto-Oncogene Proteins c-mdm2; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014132:Trachea / Q000378:metabolism; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D002274:Carcinogens, Environmental; D002840:Chromates; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D002857:Chromium; C074702:chromium hexavalent ion; C016104:sodium bichromate; C497208:Mdm2 protein, rat; D051736:Proto-Oncogene Proteins c-mdm2; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D003850:Deoxyribonuclease I; C505518:Casp6 protein, rat; D053178:Caspase 6; D020169:Caspases; D004250:DNA Topoisomerases, Type II