Kinetic analysis of 65Zn and 70Zn metabolism in humans following simultaneous administration

The authors have previously studied Zn metabolism in humans with 65Zn and mathematical modeling. Radioisotopes cannot be used in some populations (e.g., children, pregnant women) in which Zn metabolism is of great interest but stable isotopes (e.g., 70Zn) can be used in these groups. To assess whether 70Zn is etabolized in the same manner as 65Zn they administered 10 μCi 65ZnCl2 and 2 mg 70Zn (enriched from 0.6 to 66%) orally, simultaneously to 4 normal subjects after an overnight fast. 70Zn and 65Zn were measured in plasma, red blood cells, urine and feces for 80d, and 65Zn, by external counting, over whole body liver and thigh. They used a previously developed model for Zn metabolism and SAAM/CONSAM to analyze data. They fitted data of each subject with the model and constrained parameter values to be the same for both tracers. From scatter of observed data about the model calculated values they could determined whether differences between the tracers were due to random error (seen as random scatter) or to differences in metabolism (seen as systematic deviations). They obtained a consistent fit of the model to both 65Zn and 70Zn data with only random scatter. These results show that 70Zn and 65Zn are not discriminated in the body and appear to be metabolized similarly. The model, based initially on 65Zn data, can now be applied to 70Zn studies to determine absorption, distribution and excretion of Zn in humans