Increased plasma levels of 8-oxoguanine DNA glycosylase-1 in bipolar disorder

A comparative meta-analysis of peripheral 8-hydroxy-2'-deoxyguanosine (8-OHdG) or 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) levels across mood episodes in bipolar disorder

OBJECTIVE

Oxidative DNA damage has been associated with the pathophysiology of bipolar disorder (BD) as one of the common pathways between increased medical comorbidity and premature aging in BD. Previous evidence shows increased levels of oxidatively induced DNA damage markers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) or its tautomer 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), in patients with BD in comparison to healthy individuals. With the current research, we aim to analyze data on peripheral (blood or urine) 8-OHdG/8-oxo-dG levels across mood states of BD using a meta-analytical approach.

METHOD

A literature search was conducted using the databases PubMed, Scopus, and Web of Science to identify eligible studies (January 1989 to July 2022). Relevant studies were systematically reviewed; a random-effects meta-analysis and a meta-regression analysis were conducted.

RESULTS

The current meta-analysis included 12 studies consisting of 808 BD patients (390 in euthymia, 156 in mania, 137 in depression, 16 in mixed episode, 109 not specified) and 563 healthy controls. BD patients that were currently depressed had significantly higher levels of 8-OHdG/8-oxo-dG than healthy controls, while euthymic or manic patients did not differ from healthy controls. A meta-regression analysis showed sex distribution (being female) and older age to be significantly related to increased 8-OHdG/8-oxo-dG levels.

CONCLUSION

Our findings suggest that 8-OHdG/8-oxo-dG may be a state-related marker of depression in BD and may be affected by older age and female gender.

The role of base excision repair in major depressive disorder and bipolar disorder

BACKGROUND

In vivo and in vitro studies suggest that inflammation and oxidative damage may contribute to the pathogenesis of major depressive disorder (MDD) and bipolar disorder (BD). Imbalance between DNA damage and repair is an emerging research area examining pathophysiological mechanisms of these major mood disorders. This systematic review sought to review DNA repair enzymes, with emphasis on the base excision repair (BER), in mood disorders.

METHODS

We conducted a comprehensive literature search of Ovid MEDLINE® Epub Ahead of Print, Ovid MEDLINE® In-Process & Other Non-Indexed Citations, Ovid MEDLINE® Daily, EMBASE (1947), and PsycINFO for studies investigating the alterations in base excision repair in patients with MDD or BD.

RESULTS

A total of 1364 records were identified. 1352 records remained after duplicates were removed. 24 records were selected for full-text screening and a remaining 12 articles were included in the qualitative synthesis. SNPs (single nucleotide polymorphisms) of several BER genes have been shown to be associated with MDD and BD. However, it was difficult to draw conclusions from BER gene expression studies due to conflicting findings and the small number of studies.

LIMITATIONS

All studies were correlational so it was not possible to draw conclusions regarding causality.

CONCLUSION

Future studies comparing DNA repair during the manic or depressive episode to remission will give us a better insight regarding the role of DNA repair in mood disorders. These alterations might be utilized as diagnostic and prognostic biomarkers as well as measuring treatment response.

The Effect of Organic Lithium Salts on Plasma 8-Hydroxy-2'-Deoxyguanosine in Bipolar Patients In Vitro

Objective

An important step in the development of new drugs for the treatment of bipolar disorder (BD) is the study of the extent to which novel lithium salts whose anionic component has an antioxidant effect can reduce oxidative DNA damage in human blood plasma in vitro. We investigated the effects of lithium salts containing different organic anionic components (lithium carbonate (Li-CAR), pyruvate (Li-PYR), succinate (Li-SUC), fumarate (Li-FUM) and ascorbate (Li-ASC)) on levels of the oxidative damage product of DNA-8-hydroxy-2'-deoxyguanosine (8-OH-dG) in blood plasma after incubation of blood samples from healthy individuals (healthy group) and patients with bipolar disorder (BD-group) with these chemical compounds.

Methods

Blood incubation was carried out in the presence of lithium salts (1.2 mM) for 1 hour at 37°C. Measurement of 8-OH-dG concentrations in blood plasma was carried out by enzyme immunoassay using a DNA Damage Competitive Elisa Kit (Thermo Fisher Scientific, USA).

Results

In samples without compounds (control), concentrations of 8-OH-dG in the BD-group did not differ from the group of healthy individuals. None of the tested compounds had a significant effect on 8-OH-dG in healthy individuals. In BD patients, Li-PYR significantly reduced levels of plasma 8-OH-dG, while other compounds did not have a noticeable effect.

Conclusion

Lithium pyruvate reduces oxidative DNA damage in the blood of BD patients in vitro, demonstrating the potential of this compound to function not only as a mood stabilizer, but also as an antioxidant and cytoprotector.