Precise Zn isotopic ratio measurements of human red blood cell and hair samples by multiple collector-ICP-mass spectrometry.

Precise 66Zn/64Zn and 68Zn/64Zn isotopic ratios of biochemical samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). In order to eliminate the mass spectrometric interferences on Zn isotopes (e.g., 64Ni+ and 136Ba2+), we chemically purified the analyte using an ion chromatographic technique. The resulting precisions of the 66Zn/64Zn and 68Zn/64Zn ratio measurements were 0.05/1000 and 0.10/1000 (2SD), respectively, which were enough to detect the isotopic variation of Zn in nature. Red blood cell (RBC) samples were collected from five volunteers (four males and one female), including a series of 12 RBC samples from one person through monthly-based sampling over a year. These were analyzed to test possible seasonal changes and variations in 66Zn/64Zn and 68Zn/64Zn ratios among the individuals. The 66Zn/64Zn and 68Zn/64Zn ratios for a series of 12 RBC samples collected over a year were 0.43/1000 and 0.83/1000 higher than the values of highly purified Zn metal (JMC Zn), and no seasonal change could be found. The 66Zn/64Zn and 68Zn/64Zn ratios for RBC samples collected from five volunteers did not vary significantly. In order to investigate Zn isotopic heterogeneity in a human body, Zn isotopic ratios of a hair sample collected from one of the volunteers was also analyzed. The 66Zn/64Zn and 68Zn/64Zn ratios for the hair sample were 0.59/1000 and 1.14/1000 lower than the mean value of RBC samples. This result demonstrates that detectable isotopic fractionation occurs in the human body. The data obtained here suggest that the isotopic ratios of trace metals could provide new information about transportation of metal elements in vivo.

Pharmacokinetics of intravascularly administered (65)Zinc in channel catfish (Ictalurus punctatus).

Comparison was made of the pharmacokinetics of the radioisotope (65)Zinc ((65)Zn) in blood, plasma, and whole body of adult channel catfish (Ictalurus punctatus) following intravascular (iv) administration. A two-compartment model described the pharmacokinetics of (65)Zn in plasma and blood during the first 40 days following iv administration, but was unable to describe the long-term disposition of (65)Zn. Whole-body counting revealed that approximately half of the (65)Zn dose was sequestered in a slowly exchangeable pool with a half-life of 1.5 years. Greater than 99% of the circulating (65)Zn was bound to plasma proteins, whereas there was less than 1% binding to red blood cells. Synthesis of the results for channel catfish and existing data in other species indicates three phases in the pharmacokinetics of zinc. The first phase consists of initial distribution outside the vascular system to kidney, liver, and other organs (alpha phase in blood and plasma; t(1/2) of 4 to 5 h). The second phase involves distribution from organs to a slowly exchangeable zinc pool, likely consisting of bone (beta phase in blood and plasma; alpha phase in whole body; t(1/2) of 4 to 20 days). The third phase appears to involve a slow turnover of sequestered zinc (t(1/2) greater than 1 year). Blood sampling or short-term whole-body measurements will underestimate the persistence of zinc in fish, thus prolonged sampling and measurement of whole-body concentrations are necessary to characterize the pharmacokinetics of zinc.

Zinc65 absorption in patients with carcinoma of the prostate.

The intestinal absorption of 65 Zn was determined in patients with carcinoma of the prostate prior to treatment and during estrogen therapy. Following an oral tracer dose of 65 ZnCl2, plasma levels and urinary and fecal excretions of 65 Zn were determined. The absorption of 65 Zn was low in six of eight patients, particularly in three patients who had extensive metastatic bone involvement. During estrogen therapy the absorption of 65 Zn increased markedly in these patients, and this increase correlated with the clinical remission of the neoplastic process. In one patient who did not respond to estrogen therapy, 65 Zn absorption was normal prior to treatment and did not increase during estrogen therapy. In patients free of neoplasia estrogen administration did not increase 65 Zn absorption, and even decreased it. These results indicate that the intestinal absorption of 65 Zn is decreased during the active phase of carcinoma of the prostate and improves during clinical remission induced by estrogen therapy.