Guinea DNA nitrogen and carbon isotope ratios are depleted relative to tissue and mildly responsive to physiological state

Abstract

Background. Natural, endogenous, δ13C and δ15N isotope ratios are routinely used to probe environmental systems but have not been much exploited for nutritional studies. Cerebellar neuronal DNA maintains a long-lived record of isotope ratio because it does not turnover. We investigated the endogenous δ13C and δ15N of DNA and bulk tissue of cerebellum to determine baseline isotope ratios and whether in utero physiology influences isotope ratios at this level. Methods. Pregnant guinea pigs were randomized to five different groups: Control (C), low protein (LP), high protein (HP), feed restricted (FR), and diabetic (D). Pups were fed the C diet from birth. Pup cerebellum δ13C and δ15N was analyzed for DNA and bulk by elemental analysis-isotope ratio mass spectrometry at 2 da and 120 da of age. All isotope ratios are expressed relative to that of the feed. Results. Cerebellar DNA averaged about δ15N = −5‰ at both 2 and 120 da of age. Bulk cerebellum was δ15N = +4‰. Cerebellar DNA δ13C was +3.4‰ at 2 da and about +5.4% at 120 da. Bulk cerebellar δ13C at 120 days followed the in utero protein level: −0.85, +1.3, +4.9‰ for LP, C and HP, respectively. Conclusions. We show for the first time that δ15N of DNA is depleted relative to feed and that it is largely unresponsive to physiological state. δ13C of whole tissue increased with in utero dietary protein level. Funding: NIH GM071534.