4-Hydroxy-2-nonenal attenuates 8-oxoguanine DNA glycosylase 1 activity

Elevated cellular oxidative stress and oxidative DNA damage are key contributors to impaired cardiac function in diabetes. During chronic inflammation, reactive oxygen species (ROS)-induced lipid peroxidation results in the formation of reactive aldehydes, foremost of which is 4-hydroxy-2-nonenal (4HNE). 4HNE forms covalent adducts with proteins, negatively impacting cellular protein function. During conditions of elevated oxidative stress, oxidative DNA damage such as modification by 8-hydroxydeoxyguanosine (8OHdG) is repaired by 8-oxoguanine glycosylase-1 (OGG-1). Based on these facts, we hypothesized that 4HNE forms adducts with OGG-1 inhibiting its activity, and thus, increases the levels of 8OHG in diabetic heart tissues. To test our hypothesis, we evaluated OGG-1 activity, 8OHG and 4HNE in the hearts of leptin receptor deficient db/db mice, a type-2 diabetic model. We also treated the recombinant OGG-1 with 4HNE to measure direct adduction. We found decreased OGG-1 activity (P > .05), increased 8OHG (P > .05) and increased 4HNE adducts (P > .05) along with low aldehyde dehydrogenase-2 activity (P > .05). The increased colocalization of OGG-1 and 4HNE in cardiomyocytes suggest 4HNE adduction on OGG-1. Furthermore, colocalization of 8OHG and OGG-1 with mitochondrial markers TOM 20 and aconitase, respectively, indicated significant levels of oxidatively-induced mtDNA damage and implicated a role for mitochondrial OGG-1 function. In vitro exposure of recombinant OGG-1 (rOGG-1) with increasing concentrations of 4HNE resulted in a concentration-dependent decrease in OGG-1 activity. Mass spectral analysis of trypsin digests of 4HNE-treated rOGG-1 identified 4HNE adducts on C28, C75, C163, H179, H237, C241, K249, H270, and H282. In silico molecular modeling of 4HNE-K249 OGG-1 and 4HNE-H270 OGG-1 mechanistically supported 4HNE-mediated enzymatic inhibition of OGG-1. In conclusion, these data support the hypothesis that inhibition of OGG-1 by direct modification by 4HNE contributes to decreased OGG-1 activity and increased 8OHG-modified DNA that are present in the diabetic heart.