Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chronic exposure to dimethylnitrosamine produces hepatic tumors through recurrent DNA alkylation, whereas acute exposure can cause liver necrosis through mechanisms that remain largely unknown. Our laboratory recently demonstrated that DNA fragmentation occurs early on and may be a causal event in dimethylnitrosamine-induced necrosis in liver. A challenge to interpreting these results is that up to 30% of liver cells are non-parenchymal and could account for the observed DNA fragmentation. In the present study, we have examined whether dimethylnitrosamine induces early genomic DNA fragmentation in cultured mouse hepatocytes. Hepatic parenchymal cells isolated from male ICR mice were cultured in Williams E medium. DNA damage was assessed quantitatively as a fragmented fraction that was not sedimented at 27,000 x g, and qualitatively from agarose gel electrophoresis. Cellular response to DNA damage was assessed by measuring induction of the DNA repair enzyme DNA ligase. Toxic cell death was estimated from release of lactate dehydrogenase (LDH) or adenine nucleotides from cells prelabeled with [3H]adenine. Dimethylnitrosamine produced a twofold increase in [3H]adenine release by 6 h and LDH release at 36 h. DNA fragmentation and DNA ligase activity increased by as early as 1 h. The Ca(2+)-endonuclease inhibitor aurintricarboxylic acid and the Ca2+ chelator ethylenediamine tetraacetic acid (EDTA) prevented DNA fragmentation through 6 h and virtually abolished cytotoxicity through 30 h. DNA ligase induction was strongly associated with DNA fragmentation. Early increases in DNA fragmentation and DNA ligase were highly correlated with later toxic cell death. Such results strongly suggest that dimethylnitrosamine-induced fragmentation of DNA in target parenchymal cells is a causal factor in the toxic death of these liver cells.
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PMID:Dimethylnitrosamine-induced DNA damage and toxic cell death in cultured mouse hepatocytes. 766 92

N-Nitrosodimethylamine (NDMA) is an acute hepatotoxin and potent carcinogen. The metabolic activation of NDMA to reactive metabolites is a critical step for the expression of its toxic and carcinogenic potential. We have previously demonstrated a strong correlation between methylation of cellular macromolecules and NDMA-mediated cytotoxicity, and we have demonstrated that reactive oxygen species may partially contribute to the toxic effects in P450 2E1-expressing cells. The mode of cell death in NDMA-treated monolayer cultures exhibited the following characteristics: (i) condensation of nuclear chromatin as demonstrated by using Hoechst 33258 staining, (ii) DNA fragmentation as detected by combining pulsed field and conventional agarose gel electrophoresis, and (iii) DNA double strand breaks determined by using the in situ terminal deoxynucleotidyl transferase assay and flow cytometric analysis. These results indicate that reactive metabolites of NDMA trigger activation of the signal pathway for apoptotic cell death in these P450-expressing cells. The NDMA-mediated cell death was partially prevented by the endonuclease inhibitor, aurintricarboxylic acid, as well as the caspase inhibitors, acetyl-Asp-Glu-Val-Asp-CHO and acetyl-Tyr-Val-Ala-Asp-CHO. The cell cycle distribution was altered in NDMA-treated cells resulting in an increase in the G2/M phase and a decrease in the G1 phase. Our results suggest that DNA degradation, the inability to complete DNA repair, the biochemical events associated with G2/M arrest, and the process of apoptotic death all result from P450 2E1-catalyzed metabolism of NDMA.
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PMID:N-Nitrosodimethylamine-mediated cytotoxicity in a cell line expressing P450 2E1: evidence for apoptotic cell death. 1036 44