Long-term physiologic tracing of nutrients, toxins, and drugs in healthy subjects is not possible using traditional decay counting of radioisotopes or stable isotope mass spectrometry due to radiation exposure and limited sensitivity, respectively. A physiologic dose of 14C-labeled folic acid (35 μg, 100 nCi) was ingested by a healthy adult male and followed for 202 days in plasma, erythrocytes, urine, and feces using accelerator mass spectrometry. All samples and generated wastes were classified nonradioactive and the subject received a life-time-integrated radiological effective dose of only 11 μSv. Radiolabeled folate appeared in plasma 10 min after ingestion but did not appear in erythrocytes until 5 days later. Approximately 0.4% of the erythrocytes were intrinsically labeled with an average of 130 14C atoms during erythropoiesis from the pulse of plasma [14C]folate. An appropriate radiocarbon-labeled precursor can intrinsically label DNA or a specific protein during synthesis and obtain limits of quantitation several orders of magnitude below that of stable isotope methods.
- Accelerator mass spectrometry
- Intrinsic labeling
- Physiologic dose
ASJC Scopus subject areas
- Molecular Biology