Urinary gamma-glutamyl transferase as a specific marker for mercury after heavy metal treatment of rats

Hair mercury association with selenium, serum lipid spectrum, and gamma-glutamyl transferase activity in adults

The primary objective of the research is to estimate the dependence between hair mercury content, hair selenium, mercury-to-selenium ratio, serum lipid spectrum, and gamma-glutamyl transferase (GGT) activity in 63 adults (40 men and 23 women). Serum triglyceride (TG) concentration in the high-mercury group significantly exceeded the values obtained for low- and medium-mercury groups by 72 and 42 %, respectively. Serum GGT activity in the examinees from high-Hg group significantly exceeded the values of the first and the second groups by 75 and 28 %, respectively. Statistical analysis of the male sample revealed similar dependences. Surprisingly, no significant changes in the parameters analyzed were detected in the female sample. In all analyzed samples, hair mercury was not associated with hair selenium concentrations. Significant correlation between hair mercury content and serum TG concentration (r = 0.531) and GGT activity (r = 0.524) in the general sample of the examinees was detected. The respective correlations were observed in the male sample. Hair mercury-to-selenium ratios significantly correlated with body weight (r = 0.310), body mass index (r = 0.250), serum TG (r = 0.389), atherogenic index (r = 0.257), and GGT activity (r = 0.393). The same correlations were observed in the male sample. Hg/Se ratio in women did not correlate with the analyzed parameters. Generally, the results of the current study show the following: (1) hair mercury is associated with serum TG concentration and GGT activity in men, (2) hair selenium content is not related to hair mercury concentration, and (3) mercury-to-selenium ratio correlates with lipid spectrum parameters and GGT activity.

The relevance of the individual genetic background for the toxicokinetics of two significant neurodevelopmental toxicants: mercury and lead

The heavy metals mercury and lead are well-known and significant developmental neurotoxicants. This review summarizes the genetic factors that modify their toxicokinetics. Understanding toxicokinetics (uptake, biotransformation, distribution, and elimination processes) is a key precondition to understanding the individual health risks associated with exposure. We selected candidate susceptibility genes when evidence was available for (1) genes/proteins playing a significant role in mercury and lead toxicokinetics, (2) gene expression/protein activity being induced by these metals, and (3) mercury and lead toxicokinetics being affected by gene knockout/knockdown or (4) by functional gene polymorphisms. The genetic background is far better known for mercury than for lead toxicokinetics. Involved are genes encoding L-type amino acid transporters, organic anion transporters, glutathione (GSH)-related enzymes, metallothioneins, and transporters of the ABC family. Certain gene variants can influence mercury toxicokinetics, potentially explaining part of the variable susceptibility to mercury toxicity. Delta-aminolevulinic acid dehydratase (ALAD), vitamin D receptor (VDR) and hemochromatosis (HFE) gene variants are the only well-established susceptibility markers of lead toxicity in humans. Many gaps remain in our knowledge about the functional genomics of this issue. This calls for studies to detect functional gene polymorphisms related to mercury- and lead-associated disease phenotypes, to demonstrate the impact of functional polymorphisms and gene knockout/knockdown in relation to toxicity, to confirm the in vivo relevance of genetic variation, and to examine gene-gene interactions on the respective toxicokinetics. Another crucial aspect is knowledge on the maternal-fetal genetic background, which modulates fetal exposure to these neurotoxicants. To completely define the genetically susceptible risk groups, research is also needed on the genes/proteins involved in the toxicodynamics, i.e., in the mechanisms causing adverse effects in the brain. Studies relating the toxicogenetics to neurodevelopmental disorders are lacking (mercury) or very scarce (lead). Thus, the extent of variability in susceptibility to heavy metal-associated neurological outcomes is poorly characterized.

Fumonisin B1 toxicity in male Sprague-Dawley rats

Male rats were gavaged with fumonisin B1 (FB1) once daily for 11 consecutive days at doses of 0, 1, 5, 15, 35, and 75 mg FB1/kg body weight. Urine osmolality (at 5-75 mg FB1/kg) and organic ion transport in kidney slices (at 5-75 mg FB1/kg) were reduced. Urinary excretion of protein (at 15-75 mg FB1/kg) and of the enzymes LDH (at 5-75 mg FB1/kg), NAG (at 5-75 mg FB1/kg) and GGT (at 15-75 mg FB1/kg) were increased. These findings were indicative of glomerular and tubular toxicity. Histopathologic changes in the kidney consisted of necrosis of tubular epithelia of variable extent accentuated in the inner cortex. These changes were present at 1 and 5 mg FB1/kg and were more pronounced at 15-75 mg FB1/kg. Serum enzymes indicative of hepatotoxicity (ALT, GGT) were elevated compared to controls at 75 mg FB1/kg only. There were noticeable increases in mitotic figures in hepatocytes at 35-75 mg FB1/kg, while single cell necroses were increasingly numerous from 15-75 mg FB1/kg. The kidneys were considered to be the primary target organs in this study.

Arsenic induces and enhances rat hepatic metallothionein production in vivo

Metallothionein genes (MT) are inducible by a variety of agents, including heavy metals. We report the induction of MT expression by arsenite (As3+) in rat liver in vivo. As3+ (but not arsenate [As5+]) injection increased MT protein and MT-1 and MT-2 mRNA accumulation in liver only, but not in kidney or pancreas. In addition, As3+ enhanced zinc-induced MT protein accumulation in liver without any increase in MT mRNA levels. These data indicate that arsenic may increase MT expression either directly (by inducing MT mRNA accumulation), or indirectly by altering post-transcriptional events. This constitutes an unusual mechanism of enhancement of MT gene expression and appears to be mediated by processes not specifically associated with binding of arsenite to MT in vivo.

Zirconium. An abnormal trace element in biology

The action of Zirconium (Zr) on biological systems presents an enigma. It is ubiquitous, being present in nature in amounts higher than most trace elements. It is taken up by plants from soil and water and accumulated in certain tissues. The entry into animal systems in vivo is related to the mode of exposure and the concentration in the surrounding environment. Retention is initially in soft tissues and then slowly in the bone. The metal is able to cross the blood brain-barrier and is deposited in the brain and the placental barrier to enter milk. The daily human uptake has been known to be as high as 125 mg. The level of toxicity has been found to be moderately low, both in histological and cytological studies. The toxic effects induced by very high concentrations are nonspecific in nature. Despite the presence and retention in relatively high quantities in biological systems, Zr has not yet been associated with any specific metabolic function. Very little information is available about its interaction with the compounds of the genetical systems, such as nucleic acids. Apparently, the metal is neither an essential nor toxic element in the conventional sense. However, the increasing exposure to this element through its increasing use in new materials and following radioactive fallout, has increased the importance of the study of its effects on living organisms. The tetravalent nature of the ionic state and the high stability of the compounds formed are important factors that need to be considered, as also the accumulation of this element in the brain, reminiscent of the relationship between Al3+ and Alzheimer's disease.

Biochemical response to cadmium. Dose-time effect

Dose- and time-related effects of Cd (II) (0.5 or 1.0 mg/kg, Cd as CdCl2.H2O, subcutaneously, daily for 48 h, 1, 3, or 6 wk) were investigated in rats. A dose-related increase in the activity of plasma alkaline phosphatase (ALP), lactate dehydrogenase (LDH), aspartate aminotransferase (GOT), and alanine aminotransferase (GPT) was evident only at 6 wk, whereas an early rise in ALP and LDH was seen at 3 wk in 1.0 mg Cd group only. The hepatic and renal metallothionein (MT) induction displayed a dose- as well as time-related increase with Cd accumulation. A significant increase in hepatic Zn and renal Cu, no change in hepatic Cu, and a slight increase in renal Zn was observed. Urinary ALP and leucine aminopeptidase (LAP) showed an initial increase at 48 h, thereafter returned to near normal. A second phase of enzymuria (ALP, LAP, GOT, GPT, gamma-glutamyl transpeptidase), proteinuria, and aminoaciduria occurred at 6 wk in a dose-related manner. The urinary excretion of specific renal enzymes appeared closely related to the MT induction and organ Cd levels.

Relationship of clastogenic effects of zirconium oxychloride to dose and duration of exposure in bone marrow cells of mice in vivo

Zirconium oxychloride was administered as a single oral dose to laboratory-bred Swiss albino mice corresponding to 1/2, 1/6 and 1/20 of the LD50 values. Bone marrow cells were screened after 6, 12 and 24h for chromosomal aberrations following an air-drying-Giemsa schedule. The frequencies of chromosomal breaks and alterations induced increased significantly at a rate directly proportional to the concentration used. The increase was also related to the period after exposure, although to a less extent than the concentration used. No direct relationship could be observed to the sex of the animal.

Effects of inhibition of cystathionase activity on glutathione and metallothionein levels in the adult rat

The effects of alterations in sulfur metabolism on hepatic and renal metallothionein and glutathione metabolism were studied in the adult rat using inhibition of two enzymes of these pathways, hepatic cystathionase and renal gamma-glutamyl transpeptidase. Rats were fed a diet containing both methionine (0.66%) and cystine (0.20%) for 1 week before receiving three consecutive daily intraperitoneal injections of propargylglycine, a selective cystathionase inhibitor, at various doses (2.5-375 mumol/kg). When hepatic cystathionase was inhibited greater than 90% (greater than or equal to 50 mumol propargylglycine/kg), renal and hepatic metallothionein and hepatic glutathione were unaltered except at the highest dose. On the other hand, renal glutathione was increased two-fold with a concomitant decrease in renal gamma-glutamyl transpeptidase activity (50% of control). In another experiment, when renal gamma-glutamyl transpeptidase was inhibited greater than 90% with three consecutive daily injections of acivicin, a selective gamma-glutamyl transpeptidase inhibitor (10 mg/kg IP), renal glutathione content was unaltered while hepatic glutathione was decreased. Renal and hepatic metallothionein were not changed. Thus, the cysteine pools for metallothionein and glutathione appear unrelated under the present experimental conditions. In addition, following either proparglyglycine or acivicin injections, renal and hepatic glutathione pools appear to be altered differently. These results suggest that renal glutathione may be preferentially maintained even when hepatic glutathione is decreased.

Protection against mercuric chloride nephrotoxicity by cold exposure in rats

The influence of cold exposure (+ 1 degree C for 24 h) was studied in rats dosed i.p. with 0, 2.5 or 5.0 mumol HgCl2/kg. Cold exposure of controls caused an increased diuresis and solute elimination, except sodium, with almost no variations in urine alkaline phosphatase (ALP) and gammaglutamyl transferase (GGT). Proximal tubule brush border damage was demonstrated by a marked increase in ALP and GGT in HgCl2-dose animals at room temperature. Cold exposure protected against this kidney damage.

Urinary gamma-glutamyl transferase as an indicator of acute nephrotoxicity in rats

A series of nephrotoxic compounds dissolved in 0.9% NaCl was given to groups of five male Wistar rats in a single i.p. injection. Mercuric acetate and mercuric trifluoroacetate at 1 mg Hg/kg induced a sharp increase in urinary gamma-glutamyl transferase (GGT) activity on day 1, followed by a decrease below control values on day 3. Sodium ethylmercurithiosalicylate induced a relatively small urinary GGT increase, explained by its low Hg-bioavailability. An increased urinary GGT activity was noted after treatment with the aminoglycoside antibiotics kanamycin, neomycin, paramomycin, and streptomycin (100 and 800 mg/kg), ammonium fluoride (18.5 and 37 mg/kg), potassium bichromate (7.5 and 30 mg/kg), sodium tetrathionate (62.5 and 125 mg/kg), and cis-diamminedichloroplatinum (2 and 4 mg/kg). This was lower than for the mercury compounds, but clearly different from the controls. The urinargy GGT increase was an acute phenomenon. It is concluded that the measurement of urinary GGT can be used as an indicator of acute nephrotoxicity.

Gel filtration of urine: a method to detect nephrotoxicity in rats

Sephadex G-100 gel filtration of urine from male Wistar rats revealed 3 protein peaks: peak I (eluted with the void volume of the column), peak II (Mr between 67 000 and 43 000), and peak III (Mr about 13 700). Nephrotoxic compounds were given as a single i.p. injection. Peak I, and especially peak II were significantly increased in 24-h urine samples from rats receiving mercuric acetate (1.58 mg/kg), mercuric trifluoroacetate (MTFA) (2.22 mg/kg), sodium ethylmercurithiosalicylate (EMTSA) (20.2 mg/kg), sodium tetrathionate (250 mg/kg), ammonium fluoride (18.5 mg/kg), paramomycin sulfate (800 mg/kg), ochratoxin A (5 mg/kg) and cis-platinum (4 mg/kg). It is concluded that gel filtration of urine can be used as a method to detect nephrotoxicity in rats.