Lymphocyte metallothionein mRNA responds to marginal zinc intake in human volunteers

Marginal Zn deficiency is thought to be prevalent in both developed and dev eloping countries. However, the extent of Zn deficiency is not known, due t o the lack of a reliable diagnostic indicator. Blood plasma and erythrocyte concentrations of metallothionein (MT) reflect Zn status, but measurement of MT is dependent on the availability of sensitive immunoassays. Our aim w as to show whether measurement of T lymphocyte MT-2A mRNA, using a competit ive reverse transcriptase (RT)-polymerase chain reaction (PCR) assay, could indicate Zn status in human subjects in a residential Zn-depletion study. In the study, the Zn intake of seven volunteers was maintained at 13.7 mg/d for 5 weeks (baseline) followed by 4.6 mg/d for 10 weeks (marginal intake) and then 13.7 mg/d (repletion) for 5 weeks. The quantitative assay was dev eloped using standard techniques and concentrations of MT-2A mRNA were norm alized by reference to beta -actin mRNA which was also measured by competit ive RT-PCR assay. An alternative method of measuring the PCR product using capillary electrophoresis with laser-induced fluorescence detection was als o evaluated. There was considerable inter-individual variation in MT-2A mRN A concentration and the mean level at the end of the baseline period was 10 .3 (se 3.7) fg MT-2A mRNA/pg beta -actin mRNA, which then decreased by 64 % during the low Zn intake period. After repletion, MT-2A mRNA returned to b aseline concentrations. In contrast, plasma Zn was unchanged by marginal Zn intake or repletion. The effect of low Zn in all individuals was consisten t. We conclude that this assay is a sensitive method of evaluating marginal changes in dietary Zn intake.