Uranium quantification in semen by inductively coupled plasma mass spectrometry.

In this study we report uranium analysis for human semen samples. Uranium quantification was performed by inductively coupled plasma mass spectrometry. No additives, such as chymotrypsin or bovine serum albumin, were used for semen liquefaction, as they showed significant uranium content. For method validation we spiked 2g aliquots of pooled control semen at three different levels of uranium: low at 5 pg/g, medium at 50 pg/g, and high at 1000 pg/g. The detection limit was determined to be 0.8 pg/g uranium in human semen. The data reproduced within 1.4-7% RSD and spike recoveries were 97-100%. The uranium level of the unspiked, pooled control semen was 2.9 pg/g of semen (n=10). In addition six semen samples from a cohort of Veterans exposed to depleted uranium (DU) in the 1991 Gulf War were analyzed with no knowledge of their exposure history. Uranium levels in the Veterans' semen samples ranged from undetectable (<0.8 pg/g) to 3350 pg/g. This wide concentration range for uranium in semen is consistent with known differences in current DU body burdens in these individuals, some of whom have retained embedded DU fragments.

Uranium analysis in urine by inductively coupled plasma dynamic reaction cell mass spectrometry.

Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of 235U/238U in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uranium's 235U/238U ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the 235U/238U ratio. The quantitative analysis was achieved using 233U as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized 235U+ and 238U+ into 235UO2+ (m/z = 267) and 238UO2+ (m/z = 270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the 235U signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL(-1) urine and an average coefficient of variation (CV) of 1-2% within the sample measurements. The method detection limit for determining 235U/238U ratio was 3.0 pg U mL(-1) urine. An additional 21 patient samples were analyzed with no information about medical history. The measured 235U/238U ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.

Environmental exposure to trace elements and prostate cancer in three New Zealand ethnic groups.

A stratified random sample of 176 men was taken from a larger community prostate study group of 1405 eligible subjects from three ethnic groups in the Wellington region of New Zealand, in order to examine ethnic differences in exposure to cadmium (Cd), selenium (Se) and zinc (Zn) and possible associations of blood levels of Cd, Se and Zn with the prevalence of elevated serum Prostate Specific Antigen (PSA); a marker of prostate cancer. Maori and Pacific Islands men were found likely to have higher Cd exposure than New Zealand Europeans through diet, occupation and smoking. However, there was no significant difference between ethnic groups in mean blood Cd levels. Pacific Islands men had significantly higher levels of blood Se than both New Zealand European men and Maori men. Maori men had significantly higher levels of blood Zn than both New Zealand European men and Pacific Islands men. A positive association was found between blood Cd and total serum PSA. Se and Zn levels were not associated with elevated PSA. Maori and Pacific Islands men have higher prostate cancer mortality rates than New Zealand European men. Ethnic differences in mortality could be contributed to by differences in rates of disease progression, influenced by exposure and/or deficiency to trace elements. However, results did not reflect a consistent ethnic trend and highlight the complexity of the risk/protective mechanisms conferred by exposure factors. Further research is needed to ascertain whether the associations found between Cd and PSA levels are biologically important or are merely factors to be considered when interpreting PSA results clinically.

Structural consequences of metallothionein dimerization: solution structure of the isolated Cd4-alpha-domain and comparison with the holoprotein dimer.

The NMR determination of the structure of Cd(7)-metallothionein was done previously using a relatively large protein concentration that favors dimer formation. The reactivity of the protein is also affected under this condition. To examine the influence of protein concentration on metallothionein conformation, the isolated Cd(4)-alpha-domain was prepared from rabbit metallothionein-2 (MT 2), and its three-dimensional structure was determined by heteronuclear, (1)H-(111)Cd, and homonuclear, (1)H-(1)H NMR, correlation experiments. The three-dimensional structure was refined using distance and angle constraints derived from these two-dimensional NMR data sets and a distance geometry/simulated annealing protocol. The backbone superposition of the alpha-domain from rabbit holoprotein Cd(7)-MT 2 and the isolated rabbit Cd(4)-alpha was measured at a RMSD of 2.0 A. Nevertheless, the conformations of the two Cd-thiolate clusters were distinctly different at two of the cadmium centers. In addition, solvent access to the sulfhydryl ligands of the isolated Cd(4)-alpha cluster was 130% larger due to this small change in cluster geometry. To probe whether these differences were an artifact of the structure calculation, the Cd(4)-alpha-domain structure in rabbit Cd(7)-MT 2 was redetermined, using the previously defined set of NOEs and the present calculation protocol. All calculations employed the same ionic radius for Cd(2+) and same cadmium-thiolate bond distance. The newly calculated structure matched the original with an RMSD of 1.24 A. It is hypothesized that differences in the two alpha-domain structures result from a perturbation of the holoprotein structure because of head-to-tail dimerization under the conditions of the NMR experiments.