Changes in oxidative nucleic acid modifications and inflammation following one-week treatment with the bile acid sequestrant sevelamer: Two randomised, placebo-controlled trials

AIMS

Sevelamer has been reported to have anti-oxidative and anti-inflammatory effects as well as effects on glycaemic control and plasma lipids. The aim of this study was to determine the effects of one-week treatment with sevelamer on oxidative nucleic acid modifications and inflammation markers.

METHODS

Two double-blinded studies including 30 patients with type 2 diabetes (T2D) and 20 healthy individuals were conducted. Participants were randomised to one week of treatment with sevelamer (1600 mg three times daily) or placebo. RNA and DNA oxidation, measured by urinary excretion of 8-oxo-7,8-dihydroguanosine(8-oxoGuo) and (8-oxo-7,8-dihydro-2'-deoxyguanosine(8-oxodG), and markers of inflammation were determined before and after the intervention.

RESULTS

In patients with T2D there was no significant placebo-corrected reduction in 8-oxoGuo or 8-oxodG. However, a reduction in 8-oxoGuo was observed within the group treated with sevelamer (∆8-oxoGuo/creatinine (median[IQR]): -0.04 [-0.24; 0.01] nmol/mmol, p = 0.02). A sevelamer-mediated reduction in interleukin-2 (p = 0.04) and a trend towards reduction in interleukin-6 (p = 0.053) were found in patients with T2D.

CONCLUSIONS

This study reveals a potential effect of sevelamer treatment on inflammation and possible oxidative RNA modifications. The potential protective effects of sevelamer in terms of cardiovascular disease in patients with T2D need further investigation.

Interventions targeted at oxidatively generated modifications of nucleic acids focused on urine and plasma markers

Oxidative stress is associated with the development and progression of numerous diseases. However, targeting oxidative stress has not been established in the clinical management of any disease. Several methods and markers are available to measure oxidative stress, including direct measurement of free radicals, antioxidants, redox balance, and oxidative modifications of cellular macromolecules. Oxidatively generated nucleic acid modifications have attracted much interest due to the pre-mutagenic oxidative modification of DNA into 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), associated with cancer development. During the last decade, the perception of RNA has changed from that of a 'silent messenger' to an 'active contributor', and, parallelly oxidatively generated RNA modifications measured as 8-oxo-7,8-dihydro-guanosine (8-oxoGuo), has been demonstrated as a prognostic factor for all-caused and cardiovascular related mortality in patients with type 2 diabetes. Several attempts have been made to modify the amount of oxidative nucleic acid modifications. Thus, this review aims to introduce researchers to the measurement of oxidatively generated nucleic acid modifications as well as critically review previous attempts and provide future directions for targeting oxidatively generated nucleic acid modifications.

RNA oxidation and iron levels in patients with diabetes

AIM

The urinary biomarker for oxidative stress to RNA, 8-oxo-7,8-dihydro-guanosine (8-oxoGuo) is associated with mortality in patients with type 2 diabetes. Iron has also been linked to diabetes. In individuals with untreated hereditary iron overload it has been observed that 8-oxoGuo was higher compared to controls. In the current study, we hypothesized that 8-oxoGuo was associated with diagnosis of diabetes, and that iron confounded this association.

METHODS

Participants from a general Danish population were included in the study (n = 3567). UPLC-MS/MS method was used for 8-oxoGuo (nmol/mmol creatinine) measurement in spot urine. Iron biomarkers included total plasma iron, ferritin, transferrin saturation (TS) and transferrin.

RESULTS

8-oxoGuo was 17% higher in diabetes patients (n = 208) compared to non-diabetes controls. Unadjusted logistic regression model showed an odds ratio of diabetes of 1.38 (95%CI:1.21-1.57, P < 0.0001) per unit increase of 8-oxoGuo. When the model was adjusted for possible confounders the odds ratio was 1.09 (95%CI:0.94-1.26, P = 0.24). When additional adjustment was performed including ferritin, TS, or transferrin, respectively, the OR were 1.14 (95%CI:0.97-1.33, P = 0.09), 1.10 (95%CI: 0.95-1.28, P = 0.18), and 1.17 (95%CI:1.01-1.38, P = 0.04).

CONCLUSIONS

Our study indicates that 8-oxoGuo is higher in diabetes patients. The lack of association between 8-oxoGuo and diabetes in the adjusted model may be due to the cross-sectional design including post-treatment bias. Our data did not show consistent effect of all iron biomarkers in relation to diabetes. Most likely, the iron biomarkers were affected by inflammation thus not reflecting true iron levels.