Long term depleted uranium exposure in Gulf War I veterans does not cause elevated numbers of micronuclei in peripheral blood lymphocytes.

Depleted uranium (DU) is a high density heavy metal that has been used in military munitions since the 1991 Gulf War. DU is weakly radioactive and chemically toxic. Long term exposure can cause adverse health effects. This study assessed genotoxic effects in DU exposed Gulf War I veterans as a function of uranium (U) body burden. Levels of urine U were used to categorize the cohort into low and high exposure groups. Exposure to DU occurred during friendly fire incidents in 1991 involving DU munitions resulting in inhalation and ingestion exposure to small particles of DU and soft tissue DU fragments from traumatic injuries. All of these Veterans are enrolled in a long term health surveillance program at the Baltimore Veterans Administration Medical Center. Blood was drawn from 35 exposed male veterans aged 36-59 years, then cultured and evaluated for micronuclei (MN) using the cytokinesis block method. The participants were divided into two exposure groups, low and high, based on their mean urine uranium (uU) concentrations. Poisson regression analyses with mean urine U concentrations, current smoking, X-rays in the past year and donor age as dependent variables revealed no significant relationships with MN frequencies. Our results indicate that on-going systemic exposure to DU occurring in Gulf War I Veterans with DU embedded fragments does not induce significant increases in MN in peripheral blood lymphocytes compared to MN frequencies in Veterans with normal U body burdens.

Longitudinal health surveillance in a cohort of Gulf War veterans 18 years after first exposure to depleted uranium.

As part of a longitudinal surveillance program, 35 members of a larger dynamic cohort of 79 Gulf War I veterans exposed to depleted uranium (DU) during combat underwent clinical evaluation at the Baltimore Veterans Administration Medical Center. Health outcomes and biomonitoring results were obtained to assess effects of DU exposure and determine the need for additional medical intervention. Clinical evaluation included medical and exposure histories, physical examination, and laboratory studies including biomarkers of uranium (U) exposure. Urine collections were obtained for U analysis and to measure renal function parameters. Other laboratory measures included basic hematology and chemistry parameters, blood and plasma U concentrations, and markers of bone metabolism. Urine U (uU) excretion remained above normal in participants with embedded DU fragments, with urine U concentrations ranging from 0.006 to 1.88 µg U/g creatinine. Biomarkers of renal effects showed no apparent evidence of renal functional changes or cellular toxicity related to U body burden. No marked differences in markers of bone formation or bone resorption were observed; however, a statistically significant decrease in levels of serum intact parathyroid hormone and significant increases in urinary calcium and sodium excretion were seen in the high versus the low uU groups. Eighteen years after first exposure, members of this cohort with DU fragments continue to excrete elevated concentrations of uU. No significant evidence of clinically important changes was observed in kidney or bone, the two principal target organs of U. Continued surveillance is prudent, however, due to the ongoing mobilization of uranium from fragment depots.

Surveillance results of depleted uranium-exposed Gulf War I veterans: sixteen years of follow-up.

As part of a longitudinal surveillance program, 35 members of a larger cohort of 77 Gulf War I veterans who were victims of depleted uranium (DU) "friendly fire" during combat underwent a 3-day clinical assessment at the Baltimore Veterans Administration Medical Center (VAMC). The assessment included a detailed medical history, exposure history, physical examination, and laboratory studies. Spot and 24-h urine collections were obtained for renal function parameters and for urine uranium (U) measures. Blood U measures were also performed. Urine U excretion was significantly associated with DU retained shrapnel burden (8.821 mug U/g creatinine [creat.] vs. 0.005 mug U/g creat., p = .04). Blood as a U sampling matrix revealed satisfactory results for measures of total U with a high correlation with urine U results (r = .84) when urine U concentrations were >/=0.1 mug/g creatinine. However, isotopic results in blood detected DU in only half of the subcohort who had isotopic signatures for DU detectable in urine. After stratifying the cohort based on urine U concentration, the high-U group showed a trend toward higher concentrations of urine beta(2) microglobulin compared to the low-U group (81.7 v. 69.0 mug/g creat.; p = .11 respectively) and retinol binding protein (48.1 vs. 31.0 mug/g creat.; p = .07 respectively). Bone metabolism parameters showed only subtle differences between groups. Sixteen years after first exposure, this cohort continues to excrete elevated concentrations of urine U as a function of DU shrapnel burden. Although subtle trends emerge in renal proximal tubular function and bone formation, the cohort exhibits few clinically significant U-related health effects.

Health surveillance of Gulf War I veterans exposed to depleted uranium: updating the cohort.

A cohort of seventy-four 1991 Gulf War soldiers with known exposure to depleted uranium (DU) resulting from their involvement in friendly-fire incidents with DU munitions is being followed by the Baltimore Veterans Affairs Medical Center. Biennial medical surveillance visits designed to identify uranium-related changes in health have been conducted since 1993. On-going systemic exposure to DU in veterans with embedded metal fragments is indicated by elevated urine uranium (U) excretion at concentrations up to 1,000-fold higher than that seen in the normal population. Health outcome results from the subcohort of this group of veterans attending the 2005 surveillance visit were examined based on two measures of U exposure. As in previous years, current U exposure is measured by determining urine U concentration at the time of their surveillance visit. A cumulative measure of U exposure was also calculated based on each veteran's past urine U concentrations since first exposure in 1991. Using either exposure metric, results continued to show no evidence of clinically significant DU-related health effects. Urine concentrations of retinol binding protein (RBP), a biomarker of renal proximal tubule function, were not significantly different between the low vs. high U groups based on either the current or cumulative exposure metric. Continued evidence of a weak genotoxic effect from the on-going DU exposure as measured at the HPRT (hypoxanthine-guanine phosphoribosyl transferase) locus and suggested by the fluorescent in-situ hybridization (FISH) results in peripheral blood recommends the need for continued surveillance of this population.

Production of low molecular weight cadmium-binding proteins in rabbit lung following exposure to cadmium chloride.

Low molecular weight cadmium-binding proteins were studed in lung tissue from rabbits exposed to aerosols of CdCl2. Lungs obtained from animals exposed by inhalation to aerosols of 800 or 1600 micrograms/m3 CdCl2 for 2-hr periods/day, every other day for a 5-day period, were found to contain at least three low molecular weight cadmium-binding proteins, two of which were similar electrophoretically and spectrally to rabbit liver metallothionein. The third protein(s), which accounted for the majority of the cadmium in the soluble fraction of the tissue, did not bind to an anionic exchange gel and did not appear to be a polymerized form of metallothionein. Translocation studies of lung cadmium suggest a long half-life for cadmium in lung tissue following inhalation exposure, due perhaps to the high affinity of cadmium for specific lung cadmium-binding proteins. A small but significant redistribution of lung cadmium did occur to both kidney and liver tissue with time.

Relationship between metal toxicity to subcellular systems and the carcinogenic response.

The effects of metals on subcellular organelle functions have been reviewed in relation to carcinogenesis. Perturbations of the normal uptake and metabolism of carcinogens can arise through changes in microsomal enzyme activities, membrane permeabilities, and cell turnover. Metal effects on heme-dependent oxidative functions are well documented and are primarily manifested by increased heme degradation rates (microsomal heme oxygenase activity), decreased heme production (mitochondrial and cytosolic heme biosynthetic enzymes) and, in the case of a few metals, through nuclear effects of metals on the induction of microsomal enzymes. Many metals are accumulated by lysosomes, but known effects of metals on the function of these organelles in sequestering and storing organic compounds are few. Studies of changes in plasma or mitochondrial membrane permeabilities by metals have centered mainly on the susceptibility of membrane ATPase activities to metal ion alteration and on the involvement of metals in lipid peroxidation and free radical formation. Knowledge of the effects of metals on subcellular organelle functions should aid in the understanding of the mechanisms by which metal ions may play a role in the carcinogenic response.

Intracellular metabolism and effects of circulating cadmium-metallothionein in the kidney.

The mechanism of cadmium-metallothionein (CdMT)-mediated nephrotoxicity is being studied in rats using an acute dose regimen. Results of metabolism studies have shown that injected CdMT is rapidly degraded by the kidney with the release of Cd2+ into the cell cytoplasm. Ultrastructural studies indicate that an increase in the number of small lysosomes is the first measurable effect of CdMT in the kidney at 1 hr. This is followed by an increase in the number of small vesicles at 4 hr. It is proposed that these effects are the result of decreased primary lysosome formation and an inhibition of the fusion of pinocytotic vesicles with cell lysosomes by Cd. Functional alterations measured 8 hr after CdMT injection include an increase in urine volume and increased excretion of the low molecular weight protein, RNAase. Prior induction of renal MT by Zn pretreatment prevents the induction of polyuria and low molecular weight proteinuria by CdMT. These data provide further evidence that CdMT nephrotoxicity occurs as a result of Cd2+ toxicity within the cell.

Early cellular effects of circulating cadmium-thionein on kidney proximal tubules.

Circulating cadmium-thionein (Cd-MT) is cleared from the mammalian circulatory system by filtration through the kidney glomerulus with subsequent reabsorption by kidney proximal tubules. Damage to the tubules results following uptake of Cd-MT, which is dependent upon time and the dose level of cadmium administered. Intravenous administration of 109Cd-MT at doses of 0.017 and 0.17 mg Cd/kg body weight with examination of total renal uptake of 109Cd at 0.5, 3, and 24 hr disclosed that the rate of clearance from the blood and uptake by the kidney was significantly more rapid at the 0.017 mg Cd/kg dose. Ultrastructural changes resulting from intravenous injection of either form A or B of Cd-MT were characterized by increased numbers of pinocytotic vesicles and small, dense lysosomal structures. There was no evidence of mitochondrial swelling or cell death at either 3 or 6 hr after injection. The subcellular distribution of cadmium in kidney tissue at various times after administration of Cd-MT was determined by using differential centrifugation techniques with 109Cd and in situ by using x-ray microanalysis. At 30 min after injection of Cd-MT, significant amounts of cadmium were present in lysosomal fractions indicating an interaction between the tubular lysosome system and Cd-MT prior to the onset of overt cellular toxicity. Results suggest that Cd-MT is reabsorbed and broken down by kidney tubule cells in a physiological manner with possible subsequent release of the toxic cadmium ion.

Elevated urine uranium excretion by soldiers with retained uranium shrapnel.

The use of depleted uranium in munitions has given rise to a new exposure route for this chemically and radioactively hazardous metal. A cohort of U.S. soldiers wounded while on or in vehicles struck by depleted uranium penetrators during the Persian Gulf War was identified. Thirty-three members of this cohort were clinically evaluated, with particular attention to renal abnormalities, approximately 3 y after their injury. The presence of retained shrapnel was identified by x ray, and urine uranium concentrations were measured on two occasions. The absorption of uranium from embedded shrapnel was strongly suggested by measurements of urine uranium excretion at two time intervals: one in 1993/1994 and one in 1995. Mean urine uranium excretion was significantly higher in soldiers with retained shrapnel compared to those without shrapnel at both time points (4.47 vs. 0.03 microg g(-1) creatinine in 1993/1994 and 6.40 vs. 0.01 microg g(-1) creatinine in 1995, respectively). Urine uranium concentrations measured in 1995 were consistent with those measured in 1994/1993, with a correlation coefficient of 0.9. Spot urine measurements of uranium excretion were also well correlated with 24-h urine collections (r = 0.95), indicating that spot urine samples can be reliably used to monitor depleted uranium excretion in the surveillance program for this cohort of soldiers. The presence of uranium in the urine can be used to determine the rate at which embedded depleted uranium fragments are releasing biologically active uranium ions. No evidence of a relationship between urine uranium excretion and renal function could be demonstrated. Evaluation of this cohort continues.

Detection of depleted uranium in biological samples from Gulf War veterans.

During the Persian Gulf War, soldiers may have inhaled, ingested, and/or experienced wound contamination by depleted uranium (DU), which is used in military projectiles and armor. DU is produced by depleting natural uranium of 234U and 235U during the uranium-enrichment process. Although the long-term effects of significant DU exposures require investigation, many veterans express fears about its impact on health. An assay by which DU exposure can be assessed would not only be a useful research tool, but the information could help mitigate the concerns of exposed individuals. In this study, urine samples from individuals enrolled in the Depleted Uranium Follow-Up Program at the Baltimore Veterans Administration Medical Center were examined for uranium content. Isotopic composition of urine uranium was determined by measuring the 235U/238U ratio, using an inductively coupled plasma mass spectrometer. Using this method, natural and depleted uranium could be readily differentiated. By demonstrating the absence of DU in soldiers who suspect exposure by inhalation or ingestion, the assay should reduce psychological stress in these individuals.

Degradation of cadmium-thionein in rat liver and kidney.

3H-cystine and 115mCd were incorporated into hepatic and renal cadmium-thionein in response to a subcutaneous administration of 4.4 micronmol of Cd2+ containing 115mCd. Cadmium-thionein bound 115mCd reached a plateau by 24 hrs. and 72 hrs. after the Cd2+ injection in liver and kidney, respectively. The half-life (t 1/2) of 3-H-labeled hepatic cadmium-thionein was 3.5 days, whereas the average t 1/2 of the soluble proteins was 3.7 days. The t 1/2 of the soluble renal proteins was 3.8 days. In marked contrast, the 115mCd content of both hepatic and renal cadmium-thionein was virtually unchanged even 9 days after administration of this radionuclide. These data indicate that the protein moiety of metallothionein is degraded, although there appears to be a concomitant rebinding of Cd2+ to nascent thionein polypeptide chains. Thus the lack of metallothionein degradation, per se, does not account for the long-term retention of Cd2+ in liver and kidney during chronic exposure.

Degradation of cadmium-thionein in rat liver and kidney.

[3 H] Cystine and 115mCd were incorporated into hepatic and renal Cd-thionein in response to sc administration of 4.4 mumol of Cd2+ containing 115mCd. Cd-thionein-bound 115mCd reached a plateau by 24 and 72 h after the Cd2+ injection in liver and kidney, respectively. The half-life (t1/2) of 3 H-labeled hepatic Cd-thionein was 3.5 d, whereas the average t1/2 of the soluble proteins was 3.7 d. The t1/2 of 3 H-labeled renal Cd-thionein was 3.7 d, whereas the average t1/2 of the soluble renal proteins was 3.8 d. In marked contrast, the 115mCd content of both hepatic and renal Cd-thionein was virtually unchanged, even 9 d after administration of this radionuclide. These data indicate that the protein moiety of metallothionein is degraded, although there appears to be a concomitant rebinding of Cd2+ to nascent thionein polypeptide chains. Thus the lack of metallothionein degradation per se does not account for the long-term retention of Cd2+ in liver and kidney during chronic exposure.

Development of a pharmacokinetic model for chromium in the rat following subchronic exposure. I. The importance of incorporating long-term storage compartment.

A pharmacokinetic model of chromium depuration in the rat has been developed under subchronic exposure conditions. Rats were exposed to 100 ppm Cr(VI) in their drinking water for 6 weeks, followed by a 140-day period of depuration. Tissue concentrations of Cr at the end of the 6-week exposure period were greatest in the bone, spleen, and kidney, with lower concentrations present in the liver and blood. The overall kinetics of Cr depuration from the tissues were relatively slow, especially for the largest compartment which included bone. The results indicated that the half-life of Cr in bone exceeded 100 days. A three-compartment model was developed to fit the data. Liver, kidney, and spleen were grouped into a single compartment which was linked to a major storage compartment (i.e., bone, skin, hair, and muscle) via the blood. Using this model, the time to a 50% reduction of whole body Cr (i.e., loss of total Cr mass for the whole rat) was calculated to be about 80 days. The higher half-life for the storage compartment of 100 days is due to the relative weights of the compartments and the more rapid loss of Cr from the liver, kidney, and spleen compartment. The data suggest that Cr may be sequestered and release of Cr by the storage compartment over an extended period of time, thereby, may play an important role in maintaining elevated body burdens and tissue concentrations of Cr following long-term exposure to this toxic metal.

Mechanism of cadmium-metallothionein-induced nephrotoxicity: relationship to altered renal calcium metabolism.

Prolonged cadmium exposure has been associated with proteinuria, calcuria and loss of calcium from bones in humans. Previous studies have shown that kidney uptake of cadmium in vivo results from proximal tubule absorption of the circulating cadmium metallothionein complex (CdMT), and intracellular release of the Cd2+ ion prior to induction of renal metallothionein. Parenteral administration of CdMT has been found to selectively damage the proximal tubule cell lysosome system with development of a tubular proteinuria pattern similar to that observed under chronic exposure conditions. The present studies also demonstrate a concomitant calcuria but no changes in the excretion of other electrolytes or glucose using this model. These marked changes in renal calcium metabolism occurred in the absence of mitochondrial damage, changes in total, Na/K or Mg-stimulated ATPase activities, renal ATP levels, membrane 45Ca2+ transport or overt tubule cell necrosis during an 8 hour period following CdMT injection. Proteinuria and calcuria were prevented by prior zinc induction of the renal MT pool. Data from these studies indicate that renal proximal tubule cell uptake and degradation of the circulating CdMT complex produces both a marked proteinuria and calcuria. The calcuria does not appear to stem from changes in renal energy metabolism or membrane transport of this element but is probably a secondary result of calcium binding to excreted proteins which are increased in urine to a similar extent. The studies also suggest that zinc status and maintenance of the renal ZnMT pool may play an important role in regulating cadmium-induced renal proteinuria and calcuria by preventing Cd2+ perturbation of the proximal tubule cell lysosome system.

Control of zinc-thionein synthesis in rat liver.

The rate of [35S]cystine incorporation into hepatic zinc-thionein (a metallothionein) was stimulated, with a maximum of 5-6h, after parenteral administration of 2mg of Zn2+ containing 65Zn. The binding of 65Zn to zinc-thionein was measurable by 2-1/2h and reached a plateau by 18h after the injection. A net increase in the hepatic 65Zn content was observed subsequent to the decrease in the rate of zinc-thionein synthesis. The incorporation of both 65Zn and [35S]cystine into zinc-thionein was inhibited by prior administration of either actinomycin D or cordycepin. A second injection of Zn2+, 20h after the initial injection, yielded a 4.9-fold greater increase in zinc-thionein synthesis compared with that after only one injection; however, this synthesis was also inhibitable by actinomycin D. These data support the concept that hepatic zinc-thionein synthesis responds quickly to changes in Zn2+ status and that Zn2+ is bound subsequent to synthesis of nascent thionein chains. The mechanism of control of zinc-thionein synthesis by Zn2+ appears to involve changes in the amounts of a short-lived, poly(A)-containing RNA whose translation can be derepressed by additional exposure to Zn2+.

Cadmium-Metallothionein nephropathy: relationships between ultrastructural/biochemical alterations and intracellular cadmium binding.

Cadmium metallothionein (CdMT) nephrotoxicity was studied in rats injected i.p. with a single nonlethal dose of CdMT (0.6 mg of Cd per kg). Within 8 hr of CdMT injection, urine volume and urine sodium excretion were increased and sodium dodecyl sulfate gel electrophoresis of urine proteins showed that elevated levels of low molecular weight proteins were present in the urines of CdMT-treated rats. Urine RNAase activity was also elevated, approximately 7-fold, by CdMT but not by zinc metallothionein (ZnMT) or lysozyme at equivalent protein doses, demonstrating that a proteinuria indicative of proximal tubule cell dysfunction develops as an early response to CdMT exposure. Ultrastructural alterations were also present in animals injected with CdMT but not ZnMT or lysozyme. The earliest alterations occurred in the lysosome compartment of the cell. By 1 hr, the number of small lysosomes in renal proximal convoluted tubule cells increased significantly with no changes in other organelle compartments. By 4 and 8 hr, there was a further increase in lysosome number with a concomitant decrease in size and a marked increase in the number of small clear apical vacuoles. Lysosomal cathepsin D activity was decreased at 4 and 8 hr after CdMT injection, and in vitro studies indicated that this effect was not due to a direct inhibition of the enzyme by Cd++ or CdMT. Thus, both lysosome size and protease activity were rapidly altered by CdMT exposure. Studies of Cd binding in the kidney suggest that non-MT-bound Cd is an important factor in CdMT-associated toxicity. Approximately 97% of the Cd present in the cytoplasm at 1 hr was non-MT-bound. Prior induction of renal MT by treatment with zinc (20 mg of Zn per kg as ZnSO4, i.p. 16 hr before CdMT injection) markedly reduced non-MT binding of Cd++ in kidneys of treated animals and inhibited the alterations in urine volume and low molecular weight protein reabsorption induced by CdMT. These data suggest that acute CdMT exposure provides an excellent system for studying the mechanism of cadmium tubular proteinuria and that the intracellular renal MT pool plays a key role in regulating this process.

Time-varying conjugation of 7,12-dimethylbenz[a]anthracene metabolites in rainbow trout (Oncorhynchus mykiss).

Sexually immature rainbow trout were dosed via gavage with 7,12-[14C]dimethylbenz[a]anthracene (DMBA) in order to study hepatic metabolite formation over time and at single and multiple doses. beta-Glucuronidase and aryl sulfatase hydrolyses of bile extracts and subsequent high-pressure liquid chromatography analysis demonstrated significant levels of sulfate conjugates formed after 12 hr of exposure to a single dose. By 72 hr, glucuronide conjugates had increased and after three doses of [14C]DMBA, glucuronides exceeded the amount of sulfates by almost an order of magnitude. Of the metabolites that could be tentatively identified, the majority were oxidative derivatives of the aromatic rings 3-OH DMBA and 3,4-trans-OHDMBA, the latter of which is mutagenic and a precursor to the proposed ultimate carcinogen of DMBA.

Distribution of chromium within cells of the blood.

Although a number of investigators have examined the uptake of chromium in red blood cells (RBC) or whole blood, little is known about chromium uptake in white blood cells (WBC). Radiolabeled chromium (51Cr) was used to determine chromium uptake and distribution. Isolated RBC and enriched WBC populations were exposed in vitro to potassium chromate (Cr+6) and uptake was determined over a 2-hr time period. Exposure of either rat or human blood cells to 50 microM K2CrO4 for 2 hr resulted in greater accumulation of chromium within WBC than RBC. Uptake by rat WBC was significantly greater than that of human; whereas, uptake by human RBC was greater than that of the rat. Exposure of human whole blood to 50 microM K2CrO4, prior to isolation of WBC, also resulted in an increased uptake of chromium by WBC. Fisher 344 rats were exposed either orally or intravenously to a single dose of K2CrO4 and the distribution of chromium within blood cells was determined 1 hr, 24 hr, or 7 days following exposure. Regardless of the route or time following exposure, WBC chromium levels were consistently greater than those of RBC. However, the absolute levels of chromium did change with time. A comparison of chromium distribution 24 hr following a single oral exposure (1 ppm Cr+6) to the distribution 7 days following exposure demonstrated a reduction in chromium levels for RBC (10-fold) and for WBC (approximately 2.5-fold). In contrast, intravenous administration of chromate resulted in no significant decrease in RBC chromium levels when compared 1 hr, 24 hr, and 7 days following exposure. Although no difference in WBC chromium content was observed at 1 and 24 hr after exposure, an approximate 1.7-fold decrease in chromium content was detected at Day 7 for WBC. Intravenous administration of chromic chloride (Cr+3) resulted in a low level of chromium associated with RBC following 1 hr, and chromium was undetected in the WBC. These data demonstrate that WBC accumulate hexavalent chromium following both in vitro and in vivo exposure. In addition, white blood cells accumulate chromium to a greater extent than red blood cells. Since WBC accumulate chromium, their use as a target for the development of biomarkers of chromium exposure may be warranted.

Differential DNA-protein crosslinking in lymphocytes and liver following chronic drinking water exposure of rats to potassium chromate.

Carcinogenic chromium (VI) compounds are persistent environmental contaminants with potential for human exposure through drinking water. One lesion associated with chromium (VI) exposure is the formation of DNA-protein crosslinks (DPC). In an attempt to develop markers of chromium exposure, the formation of DPC in lymphocytes was investigated. Fisher 344 rats were exposed to K2CrO4 in their drinking water for 3 and 6 weeks at concentrations of 100 and 200 ppm chromium. No DPC could be detected in isolated splenic lymphocytes using the alkaline elution technique or by using a polyclonal antibody to chromate-induced DPC. However, increased complexing of proteins with DNA was demonstrated in liver following 3 weeks of exposure at both 100 and 200 ppm chromium. Intraperitoneal administration of potassium chromate did not induce detectable DPC in lymphocytes; however, an increased association of proteins with isolated DNA was detected in the liver. DPC were also induced in isolated splenic lymphocytes following a 2-hr exposure in vitro to 100 microM K2CrO4 in a salts-glucose medium. Although chromium was detected in blood, liver, and kidney, blood levels were comparatively much lower. A comparison of chromium levels required to induce DPC in lymphocytes in vitro and the amount absorbed orally suggests that the white blood cell chromium levels following oral exposure may be too low to induce measurable DNA-protein crosslinks in lymphocytes.

Detection of cadmium exposure in rats by induction of lymphocyte metallothionein gene expression.

The induction of metallothionein (MT) gene expression in lymphocytes of rats was determined in order to detect exposure in vivo to cadmium. Both acute and chronic CdCl2 exposures resulted in the induction of the MT-1 gene in lymphocytes as measured by standard RNA Northern blot analysis. Twenty-four hours following an ip injection of 3.4 mg/kg CdCl2, a ninefold increase in MT gene expression was observed in lymphocytes, as well as five- and sevenfold increases in liver and kidney, respectively. Oral exposure of rats to 1-100 ppm CdCl2 via drinking water resulted in an approximate twofold enhanced MT signal in lymphocytes after 6 wk, and a threefold increase after 13 wk of exposure to 100 ppm Cd. No increases in lymphocyte MT gene expression were observed after 3 wk of Cd exposure. Liver MT gene expression was substantially induced following chronic Cd exposure, while kidney was not, although this organ had a higher basal expression of the MT-1 gene. Analysis of tissue Cd burdens demonstrated a dose-response Cd accumulation in liver and kidney, but only kidney burdens increased substantially with prolonged Cd exposure. These results demonstrate the utility of lymphocyte gene expression assays to detect in vivo toxicant exposure, and thus their applicability as molecular biomarker assays for human exposure assessment.