Blood Metallothionein Transcript as a Biomarker for Metal Sensitivity: Low Blood Metallothionein Transcripts in Arsenicosis Patients from Guizhou, China

BACKGROUND: Because metallothionein (MT) is a metal-binding protein that protects against metal intoxication, it could be a biomarker for individual sensitivity to metal toxicity. OBJECTIVE: We assessed the use of bloodborne MT transcript as a reflection of tissue MT levels and examined the potential role of MT in arsenic toxicity in an environmentally exposed human population. METHOD: Rodents were treated with zinc or nonmetallic MT inducers for 4 days, and the blood and tissues were collected for MT transcript analysis by real-time reverse transcriptase-polymerase chain reaction and MT protein determination by the cadmium-hemoglobin assay. Blood and buccal cell samples were collected from arsenicosis patients and healthy subjects residing in Guizhou, China, and total RNA was isolated for MT transcript analysis. RESULTS: There was a positive correlation between blood MT-1 and MT-2 transcripts and corresponding hepatic or renal MT transcript levels in rats and mice. Furthermore, there was a positive correlation between blood MT-1 and MT-2 transcript and tissue MT protein levels in these animals. A positive correlation also occurred between human blood MT and buccal cell MT transcript levels. MT-1A and MT-2A were the major isoform transcripts in human blood and buccal cells, and significantly lower MT levels were seen in arsenicosis patients compared with healthy subjects. CONCLUSIONS: Blood MT transcript appears to be a useful biomarker of tissue MT levels. Arsenicosis patients in Guizhou show significantly lower MT transcript levels in blood, which may have predisposed this population to arsenic intoxication.