The common oxidatively generated lesion, 8-oxo-7,8-dihydroguanine (8-oxoGua), is removed from DNA by base excision repair. The glycosylase primarily charged with recognition and removal of this lesion is 8-oxoGuaDNA glycosylase 1 (OGG1). When left unrepaired, 8-oxodG alters transcription and is mutagenic. Individuals homozygous for the less active OGG1 allele, Ser326Cys, have increased risk of several cancers. Here, small molecule enhancers of OGG1 were identified and tested for their ability to stimulate DNA repair and protect cells from the environmental hazard paraquat (PQ). PQ-induced mtDNA damage was inversely proportional to the levels of OGG1 expression whereas stimulation of OGG1, in some cases, entirely abolished its cellular effects. The PQ-mediated decline of mitochondrial membrane potential or nuclear condensation were prevented by the OGG1 activators. In addition, in Ogg1 mouse embryonic fibroblasts complemented with hOGG1, there was increased cellular and mitochondrial reactive oxygen species compared to their wild type counterparts. Mitochondrial extracts from cells expressing hOGG1 were deficient in mitochondrial 8-oxodG incision activity, which was rescued by the OGG1 activators. These data demonstrate that small molecules can stimulate OGG1 activity with consequent cellular protection. Thus, OGG1-activating compounds may be useful in select humans to mitigate the deleterious effects of environmental oxidants and mutagens.

Inhalation of airborne toxicants such as cigarette smoke and ozone is a shared health risk among the world's populations. The use of toxic herbicides like paraquat (PQ) is restricted by many countries, yet in the developing world PQ has demonstrable ill effects. The present study examined changes in pulmonary function, mitochondrial DNA (mtDNA) integrity and markers of DNA repair induced by acute or repeated exposure of PQ to rats. Similar to cigarette smoke and ozone, PQ promotes oxidative stress, and the impact of PQ on mtDNA was compared with that obtained with these agents. Tracheal instillation (i.t.) of PQ (0.01-0.075 mg/kg) dose dependently increased Penh (dyspnoea) by 48 h while body weight and temperature declined. Lung wet weight and the wet/dry weight ratio rose; for the latter, by as much as 52%. At low doses (0.02 and 0.03 mg/kg), PQ increased Penh by about 7.5-fold at 72 h. It quickly waned to near baseline levels. The lung wet/dry weight ratio remained elevated 7 days after administration coincident with marked inflammatory cell infiltrate. Repeated administration of PQ (1 per week for 8 weeks) resulted in a similar rise in Penh on the first instillation, but the magnitude of this response was markedly attenuated upon subsequent exposures. Pulmonary [lactate] and catalase activity, [8-oxodG] and histone fragmentation (cell death) were significantly increased. Repeated PQ instillation downregulated the expression of the mitochondrial-encoded genes, mtATP8, mtNd2 and mtcyB and nuclear ones for the DNA glycosylases, Ogg1, Neil1, Neil2 and Neil3. Ogg1 protein content decreased after acute and repeated PQ administration. mtDNA damage or changes in mtDNA copy number were evident in lungs of PQ-, cigarette smoke- and ozone-exposed animals. Taken together, these data indicate that loss of pulmonary function and inflammation are coupled to the loss of mtDNA integrity and DNA repair capability following exposure to airborne toxicants.

CD23 (low affinity IgE receptor, FcepsilonRII) is expressed as a Type II extracellular protein on a variety of cells such as B cells, monocytes and macrophages and is cleaved from the cell surface to generate several distinct fragments. The expression of CD23 on the cell surface as well as the generation of soluble fragments of CD23 has been shown to be involved in regulation of IgE synthesis. CD23 is released from the cell surface by a metalloprotease, analogous to the cleavage of other cell surface molecules such as TNF-alpha. This activity has been extensively studied with respect to biochemical characterization and ability to cleave specific mutants of CD23. Both local sequence and distal domains have been shown to affect cleavage of CD23. Selective dipeptide hydroxamic acid inhibitors of CD23 processing have been identified and demonstrated to very potently and selectively inhibit CD23 processing.

Abstract8-Oxoguanine DNA glycosylase (OGG1) initiates base excision repair of the oxidative DNA damage product 8-oxoguanine. OGG1 is bifunctional; catalyzing glycosyl bond cleavage, followed by phosphodiester backbone incision via a β-elimination apurinic lyase reaction. The product from the glycosylase reaction, 8-oxoguanine, and its analogues, 8-bromoguanine and 8-aminoguanine, trigger the rate-limiting AP lyase reaction. The precise activation mechanism remains unclear. The product-assisted catalysis hypothesis suggests that 8-oxoguanine and analogues bind at the product recognition (PR) pocket to enhance strand cleavage as catalytic bases. Alternatively, they may allosterically activate OGG1 by binding outside of the PR pocket to induce an active-site conformational change to accelerate apurinic lyase. Herein, steady-state kinetic analyses demonstrated random binding of substrate and activator. 9-Deazaguanine, which can’t function as a substrate-competent base, activated OGG1, albeit with a lower Emax value than 8-bromoguanine and 8-aminoguanine. Random compound screening identified small molecules with Emax values similar to 8-bromoguanine. Paraquat-induced mitochondrial dysfunction was attenuated by several small molecule OGG1 activators; benefits included enhanced mitochondrial membrane and DNA integrity, less cytochrome c translocation, ATP preservation, and mitochondrial membrane dynamics. Our results support an allosteric mechanism of OGG1 and not product-assisted catalysis. OGG1 small molecule activators may improve mitochondrial function in oxidative stress-related diseases.

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