Damage and repair of mouse lung DNA induced by 1-nitropyrene

Biological effects of diesel exhaust particles. I. In vitro production of superoxide and in vivo toxicity in mouse

The problem of whether or not active oxygen species are involved in pulmonary injury by diesel exhaust particles (DEP) was investigated. We found that DEP could produce superoxide O2.- and hydroxyl radical (.OH) in vitro without any biological activating systems. In this reaction system, O2.- and .OH productions were inhibited by addition of superoxide dismutase (SOD) and dimethylsulfoxide, respectively. DEP which were washed with methanol could no longer produce O2.- and .OH, indicating that active components were extractable with organic solvents. These oxygen radicals were also identified by electron spin resonance (ESR) measurement. Furthermore, DEP instilled intratracheally to mouse caused high mortality at low dose, although methanol-washed DEP did not kill any mouse. The cause of death seemed to be pulmonary edema mediated by endothelial cell damage. The instilled DEP markedly decreased the activities of SOD, glutathione peroxidase, and glutathione S-transferase in mouse lungs. On the other hand, the death rate and lung injury were markedly prevented by polyethylene glycol conjugated SOD (PEG-SOD) pretreatment prior to DEP administration. The mortality and lung injury by DEP were also suppressed by butylated hydroxytoluene (BHT) pretreatment. From these results, it was suggested that most parts of DEP toxicity in lungs are due to active oxygen radicals such as O2.- and .OH, and that the cause of death is due to pulmonary edema mediated by endothelial cell damage.

Application of alkaline unwinding to analysis of strand breaks induced by bleomycin in hamster lung DNA in vivo

Strand breaks in hamster lung DNA were analyzed following in vivo exposure to bleomycin. An alkaline unwinding procedure involving separation of single-strand from double-strand DNA by hydroxylapatite chromatography followed by fluorescence detection of DNA with bisbenzimide was adapted for these studies. Procedures were developed that allowed preparation of DNA from lungs of control animals with a relatively low amount of single-strand DNA relative to double-strand DNA. Time dependence of unwinding was demonstrated using samples that were damaged deliberately by brief probe sonication. To verify that residual bleomycin remaining in lungs at the time of sacrifice did not cause strand breaks during sample preparation, bleomycin was added to minced lung in vitro. Under these conditions, the ratio of single-strand to double-strand DNA was not increased significantly. Substantial strand breaks were produced in vivo at 15 min and 1 h following intratracheal instillation of bleomycin into hamsters, as evidenced by a 5-6-fold increase in the ratio of single-strand to double-strand DNA relative to controls. The DNA damage appeared to be repaired within 1 day following exposure.

Binding of polycyclic and nitropolycyclic aromatic hydrocarbons to specific fractions of rat lung chromatin

Carcinogen-induced damage to nuclear matrix DNA, the site of DNA replication and transcription, could have profound effects on gene regulation and mutation. 1,6-Dinitropyrene (1,6-DNP), 1-nitropyrene (1-NP), 6-nitrobenzo[a]pyrene (6-NBP), benzo[a]pyrene (BP) and benzo[a]pyrene diolepoxide (BPDE) were investigated for their abilities to bind to selected regions of DNA in rat lung cell nuclei. Following in vitro exposure to carcinogen, nuclei were fractionated into active chromatin (AC), nuclear matrix (NM) and bulk (low and high salt) chromatin fractions. At an equivalent molar concentration, the highest binding to unfractionated (total) DNA was obtained with BPDE, followed in order by BP, 1,6-DNP, 6-NBP and 1-NP. BPDE, a direct alkylating compound, was bound approximately 18 times higher than the other compounds. All compounds were bound to AC (mononucleosomal DNA approximately 185 bp) and to NM in greater amounts than to bulk DNA. The binding ratios (AC + NM)/(LS + HS) varied from 2 to 21, depending upon the compound. The selective binding to specific DNA regions did not appear to be significantly related to the structures of the parent compounds or to their inferred metabolites. Thus, it appears that selective binding to specific regions is a general phenomenon that is related to the open state of the chromatin structure.