Identification and quantification of isoguanosine in humans and mice

Abstract

Isoguanine (2-hydroxyadenine), considered to be a non-natural nucleobase has, however, been shown to occur in the croton bean, butterfly wings and a mollusk. For the first time, to the best of our knowledge, we report the identification of isoguanosine (2-hydroxyadenosine), the ribonucleoside, in humans and mouse. Isoguanosine is identified and quantified in RNA from mouse liver samples and in human urine and cerebrospinal fluid. Isoguanine could not be detected as the 2′-deoxyribonucleoside in mouse liver DNA. It could be speculated that the source of isoguanosine was formation from adenosine during oxidative stress in the body. However, the urinary concentrations of isoguanosine and the levels in the liver found here by using isotope dilution liquid chromatography–tandem mass spectrometry are identical to or exceed those of 8-oxo-7,8-dihydro-2′-deoxyguanosine and 8-oxo-7,8-dihydro-guanosine. Guanine is the nucleobase that is oxidized the easiest, so it appears spectacular that the levels of isoguanosine are higher than the levels of 8-oxo-7,8-dihydro-2′-deoxyguanosine and 8-oxo-7,8-dihydro-guanosine. It also appears intriguing that it was only possible to detect the ribonucleoside isoguanosine and not the 2′-deoxyribonucleoside. These observations could indicate that the isoguanosine found is not formed by oxidative stress and could have biological functions.

Keywords:

• Humans
• chromatography
• liquid
• mass spectrometry
• RNA
• nucleosides
• mammals

Acknowledgements

The authors would like to thank Lis Kjaer Hansen and Stine Willum Frederiksen for expert technical assistance.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The Toyota Foundation Denmark and Research Foundation of the Capital Region of Copenhagen are acknowledged for financial support.