Protection or sensitization by thiols or ascorbate in irradiated solutions of DNA or deoxyguanosine.

The initial aim of this study was to investigate how charge and other chemical properties of some radical scavengers influence the radiation-induced formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) in two model systems. The target molecule, deoxyguanosine (dG), was either organized in the DNA-helix form or present as a free nucleoside in an aerated aqueous phosphate buffer. Samples were irradiated with 137Cs gamma rays, alone or in the presence of different thiols, alcohols or ascorbate with net charges from -1 to +1. The formation of 8-oxo-dG was assayed with reverse-phase HPLC coupled to an electrochemical detector. In the absence of radical scavengers, the radiation-induced formation of 8-oxo-dG in DNA was extensive, and the ratio for formation of 8-oxo-dG was 20-fold higher for DNA compared to dG. The yields of 8-oxo-dG in DNA and dG were 7.7 x 10(-3) micromol J(-1) and 3.8 x 10(-4) micromol J(-1), respectively. Yield-dose plots showed that the efficiency of the positively charged thiol cysteamine to counteract the radiation-induced formation of 8-oxo-dG in DNA was significantly (P < 0.001) greater compared to the uncharged or negatively charged thiols. Uncharged thiols were significantly (0.001 < P < 0.05) more effective in protecting DNA compared to negatively charged thiols. In contrast to the protection against oxidative damage provided by thiols and ascorbate when they were present during irradiation of DNA, the formation of 8-oxo-dG was significantly increased when these compounds were present during irradiation of dG in solution. Compared to the irradiated control, the increase was 11- to 116-fold for thiols and ascorbate, respectively. The enhanced oxidative damage of dG observed in the presence of ascorbate or thiols suggests that secondarily formed radicals from thiols or ascorbate may react with dG, or that transformation of different primary sites of damage on dG to 8-oxo-dG is enhanced.     

Aldehydes or dicarbonyls in non-enzymic glycosylation of proteins.

The non-enzymic post-translational glycosylation of certain proteins has been implicated in the production of diabetic sequelae. In the present paper the possibility that it is not the glucose aldehyde that binds to proteins but a dicarbonyl autoxidation product is investigated. Earlier experiments may not have distinguished between these two possibilities. The rate of binding of 2-deoxyglucose (a non-autoxidizable sugar) to lens alpha-crystallin is compared with that of glucose (an autoxidizable sugar). The stabilized Schiff-base adducts was investigated by using proton n.m.r. and fast-atom-bombardment mass spectroscopy to distinguish whether they are the product of aldehyde or dicarbonyl addition. We conclude that it is the open-chain aldehyde of glucose that binds initially to amino groups and that there is no participation of dicarbonyl autoxidation products in the initial non-enzymic protein glycosylation reaction.     

Retention or loss of v-mil sequences after propagation of MH2 virus in vivo or in vitro.

During propagation of the defective avian retrovirus MH2 in the presence of replication-competent helper virus, deletion of portions of the viral genome occurred frequently. After transformation of quail cells in vitro, v-mil sequences were lost, leading to populations of MH2 viruses which were highly deficient for mil gene expression but which could transform macrophage and fibroblast cells in vitro with high efficiency. In contrast, after induction of tumors in quail with mil-deficient MH2 viral stocks, a majority of the tumor DNAs contained mil+ proviruses, suggesting that there is selection for retention of the v-mil gene in vivo and that the mil protein may play a role in the oncogenicity of MH2 virus. We also isolated MH2-transformed cell lines which contained deleted proviruses arising from packaging and subsequent integration of the subgenomic v-myc-encoding mRNA. Some of these cell lines produced viruses which encoded abnormal v-myc proteins and had altered in vitro transforming properties. These altered phenotypes may be caused by mutations within the v-myc gene.