To what extent are biomonitoring data available in chemical risk assessment?

1. Chemical risk assessment integrates the identification of hazards and the human exposure levels which can be established from external and/or internal exposure data. 2. The availability of biomonitoring and metabolism animal data, the skin penetration ability, and the existence of atmospheric threshold limit values were examined for twelve substances of the European first list of priority existing substances. This investigation was focused on workplace exposures and on urinary biomarkers of exposure. Appropriate biomonitoring data appeared to be available for two substances: styrene and trichloroethylene. Some biomonitoring research has been conducted on acrylonitrile, buta-1,3-diene, cyclohexane, 1,4-dichlorobenzene, hydrogen fluoride, 2-(2-methoxyethoxy)ethanol, however additional studies could be usefully carried out. No biomonitoring data are available for alkanes, C10-13, chloro; benzene, C10-13-alkyl derivatives; bis(pentabromophenyl)ether; diphenylether, octabromo-derivative. 3. It was concluded that in some cases, biomonitoring data are either lacking or scarce. This is rather surprising since the selection of the substances of the priority list was based on high tonnage, widespread use, extent of human exposure, and toxicological concern. The development of biomonitoring information could be helpful in assessing individual or population chemical exposure whatever the source and route, and would result in both more realistic and more accurate risk assessments.

The role of glutathione and cysteine conjugates in the nephrotoxicity of o-xylene in rats.

Moderate nephrotoxicity was induced in male and female rats exposed to o-xylene for 4 h at atmospheric concentrations of approximately 3000 ppm. The xylene in vivo nephrotoxicity resulted in low enzyme leakage from the kidney into the urine. This low leakage was confirmed in 24-h urine by an increase in gamma-glutamyltranspeptidase (gammaGT), N-acetyl-beta-D-glucosaminidase (NAG) and alkaline phosphatase (ALP) activities. Compared to the control, both the 24-h urine output and the glucose excretion increased in male and female rats. These increases were probably a result of damage to the renal proximal tubules. The role of the metabolic pathway of glutathione in the emergence of the renal damage observed with o-xylene was investigated in rats. Recent studies indicate that the metabolic pathway of glutathione may be a bioactivation pathway, which is responsible for nephrotoxic effects with several drugs or chemicals. The renal toxicity of three synthesized o-xylene thio-conjugates was investigated in several groups of female rats. Administration of S-(o-methylbenzyl)glutathione (i.p., 1 mmol/kg), S-(o-methylbenzyl)cysteine (per os, 1 mmol/kg) or N-acetyl-S-(o-methylbenzyl)cysteine (i.p., 0.75 mmol/kg) to female rats did not induce renal toxicity, as monitored by urinary biochemical parameters (gammaGT, NAG, ALP, glucose). The data obtained suggest that the glutathione pathway would appear to be only detoxication, and probably does not contribute to the renal toxicity of o-xylene in female rats. Thus, either another metabolic pathway or other intermediate metabolites are probably involved in the nephrotoxic action of o-xylene.

Role of extracellular glutathione and gamma-glutamyltranspeptidase in the disposition and kidney toxicity of inorganic mercury in rats.

The role of extracellular glutathione (GSH) and membrane-bound gamma-glutamyltranspeptidase (gamma-GT) as contributory factors in the disposition and toxicity of inorganic mercury (HgCl2, 1 mg kg-1, i.p.) was investigated in rats pretreated with acivicin (AT-125, 10 mg kg-1), a gamma-GT inhibitor. A high degree of gamma-GT inhibition (75%) and of protection (90%) against HgCl2-induced nephrotoxicity was obtained in gamma-GT-inhibited rats 24 h post-treatment. Pretreatment with acivicin affected the fractional distribution profile of 203 Hg, resulting in a twofold decrease in the renal incorporation of mercury 4 h post-treatment and a threefold increase in the 24-h urinary excretion of mercury. Plasma radioactivity remained constant over 24 h in rats dosed with 203Hg alone, whereas it decreased by 60% between 4 h and 24 h in gamma-GT-inhibited rats. In gamma-GT-inhibited rats treated with HgCl2 the renal and plasma reduced glutathione (GSH) content increased by 68% and 330% respectively, as compared to controls. The gamma-GT inhibition affected the distribution profile of mercury within urinary proteins, shifting the binding of mercury from the high-molecular-weight fraction (3% against 80%) to the low-molecular-weight fraction (72% against 10%). A significant but less impressive shift of mercury from the high- to the low-molecular-weight fraction also arose in the plasma. These results taken together support the pivotal role of extracellular GSH and membrane-bound gamma-GT in the renal incorporation, toxicity and excretion of inorganic mercury in rats.

Urinary thiodiglycolic acid and thioether excretion in male rats dosed with 1,2-dichloroethane.

1,2-dichloroethane (DCE) is extensively metabolized and partially excreted in urine as thioether compounds, which include thiodiglycolic acid (TDGA). In this study, we have compared the urinary excretion of TDGA and thioethers in the rat after administration of increasing doses of DCE. Male Sprague Dawley rats were given a single oral dose of labelled [14C]DCE (0.125 to 8.08 mmol kg-1 body wt.) and 24-h urine samples were collected. The TDGA and thioethers were determined in urine by a gas chromatography method and by the thioether assay after alkaline hydrolysis, respectively. The percentage of the administered radioactivity that was excreted in urine decreased with increasing dose of DCE and ranged between 63 and 7.4%. The amount of TDGA increased proportionally to the DCE dose up to 1.01 mmol DCE kg-1 body wt. and corresponded to 0.22 mmol TDGA mmol-1 DCE. Up to 0.25 mmol DCE kg-1 body wt., the amount of thioethers recovered in urine was not significantly different as compared to the vehicle control group (11.8 +/- 0.6 mumol SH equiv. kg-1 body wt., n = 10). From the 0.25-4.04 mmol DCE kg-1 body wt. dose, the amount of thioethers increased linearly with the dose of DCE and corresponded to 0.028 mmol SH equiv. mmol-1 DCE. The ratio between urinary thioethers and TDGA increased with the DCE dose and reached 0.17 +/- 0.01 (n = 5) at a dose of 8.08 mmol DCE kg-1 body wt. Moreover, TDGA contents determined in urine by gas chromatography before and after alkaline hydrolysis were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial contribution of biliary metabolites to nephrotoxicity, renal content and excretion of [14C]hexachloro-1,3-butadiene in rats.

Male Sprague Dawley rats with cannulated bile duct (BDC rats) received 100 or 200 mg kg-1 labelled hexachloro-1,3-butadiene ([14C]HCBD) by gavage 1 h (BDC1 rats) or 24 h (BDC24 rats) after surgical cannula implantation. Twenty-four hours after treatment with HCBD, rats were examined histochemically and biochemically for kidney damage. Urine, faeces, liver and kidney radioactivities were also measured in 24-h samples. Results were compared with those obtained from non-cannulated (NC) rats. Bile-duct cannulation did not completely protect against HCBD-induced kidney damage. The 24-h [14C] urinary excretion and tissue content was 30-50% lower in BDC rats compared to NC rats and correlated well with the toxicity findings. BDC1 rats appeared to be much more resistant to HCBD treatment than BDC24 rats. Since faecal [14C] radioactivity extractable by diethyl ether at neutral pH in BDC1 rats was twice that measured in BDC24 rats, the greater resistance was attributed to a higher deficiency in the gastrointestinal absorption of unchanged HCBD. The present results reveal that the biliary metabolites of HCBD are not solely responsible for kidney toxicity as previously assumed. They suggest a sinusoidal efflux of the HCBD conjugates from the liver.

Evaluation of the interaction of benzene and toluene on the urinary excretion of t,t-muconic acid in rats.

The influence of simultaneous exposure to benzene and toluene on the urine excretion of t,t-muconic acid (t,t-MA) was examined in rats. t,t-MA was measured from 24-h urine of rats subjected to a single 4-h exposure to 5 or 20 ppm benzene and/or 50, 100, 200 or 1000 ppm toluene. Coexposure lowered t,t-MA excretion in a concentration-dependent manner, especially in the 20 ppm benzene group where the decrease averaged 28, 44 and 85% after exposure to 100, 200 and 1000 ppm toluene, respectively, as compared to benzene-exposed groups alone. The data confirm the sensitivity of t,t-MA as an indicator of benzene exposure and point out that measurement of t,t-MA may underestimate the exposure to benzene in the presence of toluene.

Difference in liver and serum malathion carboxylesterase and glucose-6-phosphatase in detecting carbon tetrachloride-induced liver damage in rats.

Microsome, cytosol and serum malathion carboxylesterase (MaCEst) activity was assessed in rats after single i.p. administration of carbon tetrachloride (CCl4) in doses ranging from 0.05 to 1 ml kg-1. MaCEst activities were compared with those of glucose-6-phosphatase (G6-Pase) as an indicator of endoplasmic reticulum damage and serum glutamate dehydrogenase (GLDH) and sorbitol dehydrogenase (SHD) as indicators of liver cytolysis. The data showed a dose-dependent increase in GLDH and SDH serum activities (175% and 68%) from 0.05 ml kg-1; an increase in serum G6-Pase (31%) and a decrease in microsomal G6-Pase (38%) was apparent only after 0.5 or 1.0 ml kg-1 doses. MaCEst activity was unaffected. The results demonstrate that, under these experimental conditions, serum and subcellular measurements of MaCEst activity failed to reveal the liver toxicity of CCl4.

Changes in urinary proximal tubule parameters in neonatal rats exposed to cadmium chloride during pregnancy.

Pregnant Sprague-Dawley rats were injected intraperitoneally with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.0 or 2.5 mg kg-1 on days 8, 10, 12 and 14 of gestation. On postnatal day (PND) 3, 12 or 49, the offspring were examined for 8- or 24-h urinary excretion of beta 2-microglobulin (beta 2-m), metallothionein (MT) and urinary activity of three proximal tubular enzymes: gammaglutamyl transferase (GGT), alkaline phosphatase (ALP) and N-acetyl-beta-glucosaminidase (NAG). Treatment with CdCl2 did not affect growth or survival of offspring. Significant decreases in the urinary excretion of GGT, ALP and NAG were observed on PND 3, at both doses. Exposure to 4 x 2.5 mg kg-1 resulted in functional deficit of the proximal tubule on PND 3, as evidenced by the significant increase in beta 2-m. Except for a slight but significant increase of beta 2-m in 49-day-old males, all the other urinary parameters returned to control values on PND 12. There was no effect on MT. Results from this study show that prenatal exposure to CdCl2 can induce significant changes in the kidney biochemistry of rats in the early postnatal period.

Decrease in the rat bronchial acetylcholinesterase activity after toluene diisocyanate inhalation.

Acetylcholinesterase (AChE) activity was measured in bronchial tissue homogenate and blood from rats subjected to single and repeated 4-h daily inhalation exposure to toluene diisocyanate (TDI) or control atmospheres. A single 4-h exposure to TDI in the concentration range of 0.7-4.3 ppm did not decrease AChE activity in bronchial tissue but a 4-h exposure to 0.6 ppm TDI, or greater, for two consecutive days did reduce this activity (19% to 33% of the controls). Increasing the level of exposure to TDI for two consecutive days from 0.6 to 4.0 ppm and extending the length of exposure to 1.2 ppm TDI from 2 to 4, 9 or 14 days produced no further decrease in bronchial ACHE activity. Throughout these experiments, blood AChE activity remained unchanged. In rats exposed to 0.3 or 1 ppm TDI for 3 weeks, staining of the bronchial smooth muscle for AChE was reduced (36% of the controls) after exposure to 1 ppm TDI. These results support, for the first time, in vivo and localized anti-AChE activity by TDI.

Adrenal-dependent leucopenia after short-term exposure to various airborne irritants in rats.

Leucopenia without any change in differential or red blood cell counts was observed in rats exposed for 4 h to increasing concentrations of the following airborne irritants: acetic acid, benzyl chloride, 1,2-dichlorobenzene, ethyl acetate, ethyl acrylate, formaldehyde, isophorone, mesityl oxide, phenol, styrene, toluene diisocyanate and vinyl toluene. This effect was abolished by adrenalectomy. Vinyl toluene and 1,2-dichlorobenzene induced leucopenia at levels as low as their current occupational standards of 50 ppm. With the exception of 1,2-dichlorobenzene, the tested compounds caused leucopenia only when exposure reached the irritant level. It is discussed that stress associated with the irritative effect of chemicals can confound specific haematological effects.

Acetone compared to other ketones in modifying the hepatotoxicity of inhaled 1,2-dichlorobenzene in rats and mice.

The ability of acetone and 3 other ketone vapours to influence the hepatotoxicity of inhaled 1,2-dichlorobenzene (DCB) was examined in rats and mice. Methylethylketone, methylisobutylketone or cyclohexanone increased liver cytochrome P-450 content and glutathione-S-transferase (GST) activity, but did not affect serum glutamate dehydrogenase (GLDH) activity in rats. Pre-exposure to these ketones enhanced DCB-induced increase in serum GLDH activity (8-63-fold), while the increases in cytochrome P-450 content (33-86%) and GST activity (42-64%) were identical to those resulting from exposure to ketones alone. Each of the 3 levels of exposure to acetone elicited cytochrome P-450 and GST responses comparable with those caused by the other ketones. In spite of that, acetone pre-exposure potentiated (4785 ppm), reduced (10670 ppm) or suppressed (14790 ppm) DCB-induced liver toxicity. In mice, the 3 ketones mentioned above interacted with DCB on centrolobular liver glucose-6-phosphatase (G-6-Pase) while acetone pre-exposure elicited an interactive G-6-Pase response in the mediolobular area alone, suggesting topographic change.

Effects of prenatal methylmercury exposure on urinary proximal tubular enzyme excretion in neonatal rats.

The basal developmental pattern of excretion of 3 proximal tubular enzymes was determined in 8-h urinary specimens from neonatal rats. Gammaglutamyltransferase (GGT), alkaline phosphatase (ALP), and N-acetyl-beta-glucosaminidase (NAG) activities were measured at 3, 6, 9 and 12 days after birth. Subsequently, methylmercury chloride (CH3HgCl), known to induce foetotoxic changes in the proximal tubule was administered on days 8, 10 and 12 of gestation at 3 or 6 mg/kg and its effects on the enzyme activities were examined. Dose-related increases in the 3 enzyme activities occurred at dose levels that produced no maternal or postnatal toxicity, nor overt morphological malformation of the kidney. The peak of enzyme activities averaged about 200% and 130% of the control values for GGT, ALP, and NAG respectively, and occurred on days 3 and 6 in the treated groups. Urinary enzyme activities returned to the control levels from days 6 to 12. Our data point to the possibility of detecting CH3HgCl-induced prenatal effect on the kidney by measuring the 8-h urinary excretion of enzymes by rats in the early postnatal period.

Effect of SKF525-A on the glutathione-conjugating enzyme system and on liver toxicity.

SKF525-A given intraperitoneally (50 mg/kg body weight) to Sprague-Dawley rats in a single dose promoted a significant reduction in cytosolic glutathione S-transferase (GST) activities 0.5 and 1 h after injection. There was no decrease in liver non-protein sulfhydryls (NPSH) 0.5, 1 and 24 h after injection. Serum activities of glutamic pyruvic transaminase (GPT), sorbitol dehydrogenase (SDH), glutamic oxaloacetic transaminase (GOT) and glutamate dehydrogenase (GLDH) increased 1.8-, 2.9-, 3.8- and 41.2-fold respectively 8 h after injection, and the increased serum enzyme activities were maintained for up to 24 h. On the basis of these results, SKF525-A-induced blood manifestations of liver toxicity and decrease in GST activities may be regarded as confusing factors in the evaluation of the oxidative metabolism of compounds in Sprague-Dawley rats.

Concentration-related changes in blood and tissue parameters of hepatotoxicity and their interdependence in rats exposed to bromobenzene and 1,2-dichlorobenzene.

Liver damage resulting from 4 h exposure to bromobenzene (BB) (146-957 ppm) and 1,2-dichlorobenzene (DCB) (245-739 ppm) as model toxicants was evaluated in rats. The modifications considered were the increases in serum glutamate dehydrogenase (GLDH) and sorbitol dehydrogenase (SDH) activities and the decreases in centrolobular liver-cell glucose-6-phosphatase (G6-Pase) staining intensity. A linear inverse relationship was established between the logarithmic values of blood enzyme activities and liver G6-Pase staining intensity. In addition, the levels of exposure to each test chemical were found to be linearly related to liver G6-Pase staining intensity and to the logarithmic values of blood enzyme activities.

Short-term inhalation test for evaluating industrial hepatotoxicants in rats.

Liver damage was investigated in rat using serum enzyme activities measurements. Responses were recorded 24 h after whole body inhalation exposure to vapors of bromobenzene, carbon tetrachloride, chloroform, o-dichlorobenzene, 1,2-dichloroethane and dimethylformamide as model toxicants. First, rats were exposed during a single 4 h period to different concentrations of each solvent and the minimally active concentration was determined. Second, repeated exposures to chemicals at this concentration level (6 h daily, 2 or 4 days) were used in order to examine whether hepatotoxicity was enhanced. GLDH and SDH are more sensitive and more constant indices than GOT and GPT. It appears that a single exposure period induced more marked serum activities enhancement than repeated exposures.

Pseudo-clinical Fabry's disease without alpha galactosidase deficiency.

The authors describe two cases of clinical Fabry's disease. The first patient presents a deficiency of alpha galactosidase and a urinary excretion of ceramide trihexosides and dihexosides ; the second patient had a normal alpha galactosidase and normal excretion of urinary lipids. In this latter case the Km and the activity of the enzyme measured at different pH were similar to those of normal enzyme. The other lysosomal enzymes, beta galactosidase, beta glucosidase, hexosaminidases A and B, alpha fucosidase, arylsulfatases, phosphatase acids were also measured in patient 2 and all have normal activities. There is no urinary excretion of glycolipids or mucopolysaccharides. Yet this patient has an accumulation of material in his fibroblasts and renal cells. The authors also present a genetic study.