The effects of low-flow sevoflurane and isoflurane anesthesia on renal function in patients with stable moderate renal insufficiency

Sevoflurane degrades to Compound A, which is nephrotoxic in rats. Therefore, the renal effects of Compound A is an area of intense debate. We investigated the effects of low-flow sevoflurane and isoflurane anesthesia on renal function in patients with stable renal insufficiency. Seventeen patients with a serum creatinine level of more than 1.5 mg/dL were anesthetized with sevoflurane or isoflurane at a total flow of 1 L/min. Serum creatinine and blood urea nitrogen were measured before anesthesia and again 1, 2, 3, 5, 7, and 14 days after anesthesia. The 24-h creatinine clearance was measured before anesthesia and 7 days after anesthesia. There were no significant differences in the blood urea nitrogen levels, serum creatinine concentrations, or creatinine clearance before and after anesthesia within each group. These results suggest that sevoflurane and isoflurane have similar effects on renal function in patients with moderately impaired renal function. Further study of the effects of low-flow sevoflurane anesthesia on impaired renal function with a larger sample size than ours is required to resolve the issue of sevoflurane safety in patients with renal insufficiency.

IMPLICATIONS

The serum creatinine and blood urea nitrogen data indicate that, for exposures of <130 ppm/h in Compound A inspired area under the curve, renal effects of low-flow sevoflurane are similar to those of isoflurane in patients with stable renal insufficiency.

Effects of the ethyl and benzyl ethers of indenestrols A and B on cytotoxicity in Chinese hamster V79 cells

We recently investigated the relationship between the structures of various indenestrols and their cytotoxicity, and reported that indenestrol A (IA), a metabolite of the synthetic nonsteroidal estrogen diethylstilbestrol, and indenestrol B (IB), an analog of IA, disrupt the microtubule architecture of Chinese hamster V79 cells in vitro. We then synthesized 16 optically active indenestrol derivatives by substituting monoethyl, monobenzyl and diethyl ether groups at the 6- and/or 4'-hydroxyl positions, and examined their cytotoxic activities in Chinese hamster V79 cells. The results indicated that the monoethyl ethers had cytotoxic activities similar to monomethyl ethers. However, the (+)- and (-)-monobenzyl ethers were less cytotoxic than the corresponding monomethyl and monoethyl derivatives.

Cell transformation and genotoxicity induced by bis(2, 3-dichloro-1-propyl) ether

Bis(dichloropropyl) ether isomers have been identified in a petrochemical plant effluent through a toxicity identification evaluation study in the United States. They have also been observed in the microgram per liter range along one of the largest rivers in Europe, the Elbe River. In the present investigation, the genotoxic and transforming activity of a bis(dichloropropyl) ether isomer, bis(2,3-dichloro-1-propyl) ether, was assayed in vitro. The results demonstrate that bis(2,3-dichloro-1-propyl) ether is a potent mutagen in Salmonella typhimurium strains TA 100, TA 1535, and to a lesser extent in strain TA 98, but only when tested in the presence of a metabolic activation system (S9 mix). We have also investigated the induction of micronuclei by bis(2,3-dichloro-1-propyl) ether in the metabolically competent cell line, MCL-5. A linear, dose-dependent increase in micronuclei was observed following exposure to bis(2,3-dichloro-1-propyl) ether. The DNA strand-breaking capacity of this chemical was assessed in the alkaline single-cell gel electrophoresis ("comet") assay with MCL-5 cells. Bis(2,3-dichloro-1-propyl) ether clearly induced DNA strand breaks in the 4.5-45.5 microg/ml dose range. The ether also induced malignant transformation in C3H/M2 mouse fibroblasts after metabolic activation (S9 mix). Thus, it must be suspected that bis(2, 3-dichloro-1-propyl) ether may possess a carcinogenic potential. Since the compound along with its isomers is present in considerable concentrations in surface water, their elimination is a matter of significant public concern.

Nonimmobilizers and transitional compounds may produce convulsions by two mechanisms

Some inhaled compounds cause convulsions. To better appreciate the physical basis for this property, we correlated the partial pressures that produced convulsions in rats with the lipophilicity (nonpolarity) and hydrophilicity (polarity) of 45 compounds: 3 n-alkanes, 18 n-haloalkanes, 3 halogenated aromatic compounds, 3 cycloalkanes and 3 halocycloalkanes, 13 halogenated ethers, and 2 noble gases (He and Ne). In most cases, convulsions were quantified by averaging the alveolar partial pressures just below the pressures that caused and slightly higher pressures that did cause clonic convulsions (ED50). The ED50 did not correlate with hydrophilicity (the saline/gas partition coefficient), nor was there an obvious correlation with molecular structure. For 80% of compounds (36 of 45), the ED50 correlated closely (r2 = 0.99) with lipophilicity (the olive oil/gas partition coefficient). Perhaps because they block the effect of GABA on GABA(A) receptors, five compounds were more potent than would be predicted from their lipophilicity. Conversely, four compounds may have been less potent than would be predicted because they (like conventional inhaled anesthetics) enhance the effect of GABA on GABA(A) receptors.

IMPLICATIONS

Nonimmobilizers and transitional compounds may produce convulsions by two mechanisms. One correlates with lipophilicity (nonpolarity), and the other correlates with an action on GABA(A) receptors.

Immunochemical evidence against the involvement of cysteine conjugate beta-lyase in compound A nephrotoxicity in rats

BACKGROUND

Compound A, a degradation product of sevoflurane, causes renal corticomedullary necrosis in rats. Although the toxicity of this compound was originally hypothesized to result from the biotransformation of its cysteine conjugates into toxic thionoacyl halide metabolites by renal cysteine conjugate beta-lyase, recent evidence suggests that alternative mechanisms may be responsible for compound A nephrotoxicity. The aim of this study was to evaluate these issues by determining whether mercapturates and glutathione conjugates of compound A could produce renal corticomedullary necrosis in rats, similar to compound A, and whether renal covalent adducts of the thionacyl halide metabolite of compound A could be detected immunochemically.

METHODS

Male Wistar rats were administered, intraperitoneally, N-acetylcysteine conjugates (mercapturates) of compound A (90 or 180 micromol/kg) or glutathione conjugates of compound A (180 micromol/kg) with or without intraperitoneal pretreatments with aminooxyacetic acid (500 micromol/kg) or acivicin (250 micromol/kg). Rats were killed after 24 h, and kidney tissues were analyzed for toxicity by histologic examination or for protein adducts by immunoblotting or immunohistochemical analysis, using antisera raised against the covalently bound thionoacyl halide metabolite of compound A.

RESULTS

Mercapturates and glutathione conjugates of compound A both produced renal corticomedullary necrosis similar to that caused by compound A. Aminooxyacetic acid, an inhibitor of renal cysteine conjugate beta-lyase, did not inhibit the toxicity of the mercapturates, whereas acivicin, an inhibitor of gamma-glutamyltranspeptidase, potentiated the toxicity of both classes of conjugates. No immunochemical evidence for renal protein adducts of the thionacyl halide metabolite was found in rats 24 h after the administration of the mercapturates of compound A or in the kidneys of rats, obtained from a previous study, 5 and 24 h after the administration of compound A.

CONCLUSION

The results of this study are consistent with the idea that a mechanism other than the renal cysteine conjugate beta-lyase pathway of metabolic activation is responsible for the nephrotoxicity of compound A and its glutathione and mercapturate conjugates in male Wistar rats.

Recent advances in molecular mechanisms of nephrotoxicity

Numerous drugs and endogenous compounds are efficiently excreted from the renal proximal tubule via two carrier-mediated pathways, that are organic anion and organic cation transport systems. Since most nephrotoxicants are taken up into renal target cells for further actions, these transport systems seem to be an early event for nephrotoxicity. Recent advances in nephrotoxicity are molecular cloning of several transporters related to important toxic compounds in the kidney. An organic cation transporter 1 (OCT1) was cloned in 1994. On the other hand, we recently isolated a complementary DNA that encodes an organic anion transporter 1 (OAT1) as an anion/dicarboxylate exchanger of the basolateral membrane of proximal tubule. Transepithelial secretion of organic anion consists of an influx of anionic substrates into the cell through the basolateral membrane and their efflux to the urine across the apical membrane. OAT1 displays a remarkably wide substrate specificity, including endogenous substrates, a variety of drugs with different structures and natural toxins. We further isolated homologs of OAT series such as liver-specific OAT2 and kidney-, liver- and brain-expressing OAT3. Because the amino acid sequence of OAT1 shows 38% identity to OCT1, a newly defined 'multispecific organic ion transporter superfamily' will provide potential tools to assess mechanisms of many nephrotoxicants including drugs and xenobiotics, and contribute also in understanding more precisely nephrotoxic mechanisms of chemicals.

Evaluation of the cytotoxic activity of polyethers isolated from Laurencia

In this paper, we report on the conformational analysis of several polyether triterpenes with a squalene carbon skeleton which exhibited significant cytotoxic activity using a Monte Carlo conformational search and spectroscopical data. These studies indicate that the conformation of the side chain C-14/C-19 and the arrangement and direction of this chain may be among the fundamental factors related to the activity of this type of metabolites.

[Occupational exposure and environmental pollution: the role of inhalation anesthetics with special consideration of sevoflurane]

There are a number of assays available to study genetic toxicity of inhalation anaesthetics. Those discussed in this review are the Ames Salmonella mutagenesis test and assays for structural chromosome aberrations, micronuclei (MN) and sister chromatid exchanges (SCEs). None of these assays showed abnormalities induced by volatile inhalation anaesthetics. Only Compound A induced a slight increase in the number of SCEs. However, the implications of this in vitro study are unclear. Results of studies focussing on the effects of long-term occupational exposure to inhalation anaesthetics are controversial. Neither harmfulness nor safety of chronic exposure to low concentrations of inhalation anaesthetics have been proven. Although there is no clear evidence of harmfulness, there is general agreement that occupational exposure should be minimized for precautionary reasons. This particularly applies to N2O. Therefore, occupational exposure standards have been established in many countries, though not yet for sevoflurane and desflurane. In Germany, occupational exposure can be kept below the threshold values, when working in operation theatres with a standard air conditioning system, a high-flow scavenging system, low leakage anaesthesia machines and preventative maintenance of equipment. Under these conditions occupational exposure is low even when using laryngeal mask airways and uncuffed tracheal tubes. Sevoflurane is a halocarbon, but is only partially halogenated and the only halogen it contains is fluorine. Sevoflurane, therefore, appears to have an insignificant effect on ozone depletion and its contribution to the greenhouse effect is negligible.

Fate and toxicity of 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A)-derived mercapturates in male, Fischer 344 rats

BACKGROUND

2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) is formed in the anesthesia circuit by the degradation of sevoflurane. Compound A is nephrotoxic in rats and undergoes metabolism by the mercapturic acid pathway in rats and humans to yield the mercapturates S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-N-acetyl-L -cysteine (compound 3) and S-[2(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-N-acetyl-L-cys teine (compound 5). These experiments were designed to examine the fate and nephrotoxicity of compound A-derived mercapturates in rats.

METHODS

The deacetylation of compounds 3 and 5 by human and rat kidney cytosol and with purified acylases I and III was measured, and their nephrotoxicity was studied in male Fischer 344 rats. The metabolism of the deuterated analogs of compounds 3 and 5, [acetyl-2H3]S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl ]-N-acetyl-L-cysteine (compound 3-d3) and [acetyl-2H3]S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-N -acetyl-L-cysteine (compound 5-d3), respectively, was measured.

RESULTS

Compound 5, but not compound 3, was hydrolyzed by human and rat kidney cytosols and by acylases I and III. 19F nuclear magnetic resonance spectroscopic analysis showed no urinary metabolites of compound 3, but unchanged compound 5 and its metabolites 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid and 2-[1-(fluoromethoxy)-2,2,2-trifluoroethyl]-4,5-dihydro-1,3-thiazol e-4-carboxylic acid were detected in urine. Compound 5 (250 microM/kg) produced clinical chemical and morphologic evidence of renal injury in two of three animals studied.

CONCLUSIONS

Compounds 3 and 5 underwent little metabolism. Compound 5, but not compound 3, was mildly nephrotoxic. These results indicate that compound A-derived mercapturate formation constitutes a detoxication pathway for compound A.

[Compound A: toxicology and clinical relevance]

Sevoflurane, like all currently used volatile anaesthetics, is degraded by carbon dioxide absorbents. The most significant degradant is a haloalkene known trivially as "compound A". Compound A is nephrotoxic in rats and, at higher doses, in nonhuman primates, causing proximal tubular necrosis. There has been much interest in the potential for compound A toxicity in humans. Inhaled compound A concentrations are greatest at low flow rates, high sevoflurance concentrations, warmer absorbent, barium hydroxide vs soda lime, and drier absorbent. Typical inspired compound A concentrations during low-flow and closed-circuit sevoflurane anaesthesia in humans are 8-24 and 20-32 ppm with soda lime and barium hydroxide lime, respectively. Renal effects of compound A production during sevoflurane anesthesia have been examined in surgical patients and volunteers, using standard (creatinine clearance, serum BUN and creatinine) and experimental (urine excretion of protein, glucose, NAG, GST, AAP) markers of renal function. Investigations to date in surgical patients show similar renal effects of low-flow sevoflurane, low-flow isoflurane or high-flow sevoflurane. There have been no case reports of compound A-associated renal injuryin humans. In volunteers, one study found changes in experimental but not conventional renal markers, while other investigations show no significant changes in either standard or experimental markers. The mechanism of compound A nephrotoxicity in rats appears to involve metabolism to glutathione and cysteine conjugates, and their subsequent renal uptake and metabolism by pathways that are different in rats and humans.

Acute toxicity of ethylene glycol mono-n-butyl ether in the guinea pig

Acute toxicity values, such as oral and percutaneous LD50s, are often used as the basis for classifying chemicals into toxicity categories, and their subsequent regulation. Such values obtained for ethylene glycol mono-n-butyl ether (EGBE; 2-butoxyethanol) in rats and rabbits indicate that it is moderately toxic. However, the cause of death in these acute studies appeared to be secondary to acute intravascular haemolysis, an effect for which guinea pigs and humans are much less sensitive than rats, mice and rabbits. Recently-conducted acute toxicity studies in the guinea pig resulted in an acute oral LD50 of 1400 mg/kg, an acute percutaneous LD50 of greater than 2000 mg/kg, and a 1-hr LC50 greater than 633 ppm. These data are compared with published acute toxicity values, and indicate that the predicted acute toxicity of EGBE in humans, based on data from the guinea pig, would be less than that observed in other animal species. Based in part on the guinea pig data, EBGE is no longer classified as a poisonous substance by either the United Nations or US Department of Transportation.

Role of the renal cysteine conjugate beta-lyase pathway in inhaled compound A nephrotoxicity in rats

BACKGROUND

The sevoflurane degradation product compound A is nephrotoxic in rats and undergoes metabolism to glutathione and cysteine S-conjugates, with further metabolism by renal cysteine conjugate beta-lyase to reactive intermediates. Evidence suggests that toxicity is mediated by renal uptake of compound A S-conjugates and metabolism by beta-lyase. Previously, inhibitors of the beta-lyase pathway (aminooxyacetic acid and probenecid) diminished the nephrotoxicity of intraperitoneal compound A. This investigation determined inhibitor effects on the toxicity of inhaled compound A.

METHODS

Fischer 344 rats underwent 3 h of nose-only exposure to compound A (0-220 ppm in initial dose-response experiments and 100-109 ppm in subsequent inhibitor experiments). The inhibitors (and targets) were probenecid (renal organic anion transport mediating S-conjugate uptake), acivicin (gamma-glutamyl transferase), aminooxyacetic acid (renal beta-lyase), and aminobenzotriazole (cytochrome P450). Urine was collected for 24 h, and the animals were killed. Nephrotoxicity was assessed by histology and biochemical markers (serum BUN and creatinine; urine volume; and excretion of protein, glucose, and alpha-glutathione-S-transferase, a predominantly proximal tubular cell protein).

RESULTS

Compound A caused dose-related proximal tubular cell necrosis, diuresis, proteinuria, glucosuria, and increased alpha-glutathione-S-transferase excretion. The threshold for toxicity was 98-109 ppm (294-327 ppm-h). Probenecid diminished (P < 0.05) compound A-induced glucosuria and excretion of alpha-glutathione-S-transferase and completely prevented necrosis. Aminooxyacetic acid diminished compound A-dependent proteinuria and glucosuria but did not decrease necrosis. Acivicin increased nephrotoxicity of compound A, and aminobenzotriazole had no consistent effect on nephrotoxicity of compound A.

CONCLUSIONS

Nephrotoxicity of inhaled compound A in rats was associated with renal uptake of compound A S-conjugates and cysteine conjugates metabolism by renal beta-lyase. Manipulation of the beta-lyase pathway elicited similar results, whether compound A was administered by inhalation or intraperitoneal injection. Route of administration does not apparently influence nephrotoxicity of compound A in rats.

Dehydration of Baralyme increases compound A resulting from sevoflurane degradation in a standard anesthetic circuit used to anesthetize swine

In a model anesthetic circuit, dehydration of Baralyme brand carbon dioxide absorbent increases degradation of sevoflurane to CF2=C(CF3)OCH2F, a nephrotoxic vinyl ether called Compound A. In the present study, we quantified this increase using "conditioned" Baralyme in a circle absorbent system to deliver sevoflurane anesthesia to swine. Mimicking continuing oxygen delivery for 2 days after completion of an anesthetic, we directed a conditioning fresh gas flow of 5 L/min retrograde through fresh absorbent in situ in a standard absorbent system for 40 h. The conditioned absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit to deliver sevoflurane to swine weighing 78 +/- 2 kg. The initial inflow rate of fresh gas flow was set at 10 L/min with the vaporizer at 8% to achieve the target end-tidal concentration of 3.0%-3.2% sevoflurane in approximately 20 min. The flow was later decreased to 2 L/min, and the vaporizer concentration was decreased to sustain the 3.0%-3.2% value for a total of 2 h (three pigs) or 4 h (eight pigs). Inspired Compound A increased over the first 30 +/- 60 min to a peak concentration of 357 +/- 49 ppm (mean +/- SD), slowly decreasing thereafter to 74 +/- 6 ppm at 4 h. The average concentration over 2 h was 208 +/- 25 ppm, and the average concentration over 4 h was 153 +/- 19 ppm. Pigs were killed 1 or 4 days after anesthesia. The kidneys from pigs anesthetized for both 2 h and 4 h showed mild inflammation but little or no tubular necrosis. These results suggest that dehydration of Baralyme may produce concentrations of Compound A that would have nephrotoxic effects in humans in a shorter time than would be the case with normally hydrated Baralyme.

IMPLICATIONS

The vapor known as Compound A can injure the kidney. Dehydration of Baralyme, a standard absorbent of carbon dioxide in inhaled anesthetic delivery systems, can cause a 5- to 10-fold increase in Compound A concentrations produced from the inhaled anesthetic, sevoflurane, given at anesthetizing concentrations in a conventional anesthetic system.

Nephrotoxicity of the glutathione and cysteine S-conjugates of the sevoflurane degradation product 2-(fluoromethoxy)-1,1,3,3, 3-pentafluoro-1-propene (Compound A) in male Fischer 344 rats

2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (Compound A) is a halogenated alkene that is nephrotoxic in rats when administered by inhalation or intraperitoneally. Compound A undergoes glutathione-dependent metabolism: Compound A-derived glutathione S-conjugates and mercapturates are excreted in the bile and urine, respectively, of rats given Compound A. The present experiments were designed to study the nephrotoxicity of the Compound A-derived glutathione and cysteine S-conjugates, S-[2-(fluoromethoxy)-1,1,3,3, 3-pentafluoropropyl]glutathione , S-[2-(fluoromethoxy)-1,3,3, 3-tetrafluoro-1-propenyl]glutathione , S-[2-(fluoromethoxy)-1,1,3,3, 3-pentafluoropropyl]-L-cysteine and S-[2-(fluoromethoxy)-1,3,3, 3-tetrafluoro-1-propenyl]-L-cysteine . Conjugates , and given intraperitoneally produced dose-dependent nephrotoxicity that was characterized by diuresis, increased excretion of glucose and protein, elevated blood urea nitrogen concentrations and severe morphological changes in the kidneys, particularly in the proximal tubules. Glutathione S-conjugate , at a dose of 500 micromol/kg, was hepatotoxic. Cysteine S-conjugate was not nephrotoxic, apparently because of its facile cyclization to the thiazoline 2-[1-(fluoromethoxy)-2,2,2-trifluoroethyl]-4,5-dihydro-1, 3-thiazole-4-carboxylic acid, which is not a beta-lyase substrate. Also, the alpha-methyl analog of cysteine S-conjugate S-[2-(fluoromethoxy)-1,1,3,3, 3-pentafluoropropyl]-DL-alpha-methylcysteine, which cannot undergo beta-lyase-dependent bioactivation, was not nephrotoxic. These in vivo data show that Compound A-derived S-conjugates are nephrotoxic and that the toxicity is associated with beta-lyase-dependent bioactivation.

Quantitative differences in the production and toxicity of CF2=BrCl versus CH2F-O-C(=CF2)(CF3) (compound A): the safety of halothane does not indicate the safety of sevoflurane

Carbon dioxide absorbents degrade both halothane and sevoflurane to toxic unsaturated compounds (CF2=CBrCl and CH2F-O-C[=CF2][CF3] [i.e., Compound A], respectively). Given the long history of safe administration of halothane, comparable toxicities of these degradation products would imply a similar safety of sevoflurane. We therefore examined CF2=CBrCl in the context of four issues relevant to previous studies of the toxicity of Compound A: 1) reactivity of the degradation product in vitro; 2) rate of its production in vitro; 3) its in vivo toxicity; 4) importance of the beta-lyase pathway to the toxicity in vivo. We found the following. 1) CF2=CBrCl is less reactive than Compound A, degrading in human serum albumin at one-fifth the rate of Compound A. 2) Over a 3-h period of "anesthesia," a standard circle system containing Baralyme (Allied Healthcare Products, Inc., St. Louis, MO) produces 30 times as much Compound A from a minimum alveolar anesthetic concentration (MAC) concentration of sevoflurane as CF2=CBrCl from a MAC concentration of halothane; with soda lime, the difference is 60-fold. Correcting for differences in uptake of halothane versus sevoflurane decreases the differences to 20-40 times. 3) For a 3-h administration to rats, the partial pressure of Compound A causing minimal renal injury or necrosis of half the affected tubule cells exceeds the partial pressure of CF2=CBrCl causing minimal injury or necrosis of half the affected tubule cells by a factor of approximately 4-6. Thus, the ratio of production (Item 2 above) to the partial pressure causing injury with CF2=CBrCl is approximately a quarter of that ratio for Compound A. 4) Compounds that block the beta-lyase pathway either do not change (acivicin) or decrease (aminooxyacetic acid; AOAA) renal injury from CF2=CBrCl in rats, whereas these compounds increase (acivicin) or do not change (AOAA) injury from Compound A. We conclude that the safety of halothane cannot be used to support the safety of sevoflurane.

IMPLICATIONS

Carbon dioxide absorbents degrade halothane and sevoflurane to unsaturated compounds nephrotoxic to rats. Relative to sevoflurane's degradation product, halothane's degradation product has less toxicity relative to production, less reactivity, and a different mechanism of injury. The clinical absence of halothane nephrotoxicity does not necessarily indicate a similar absence for sevoflurane.

Maternal and developmental toxicity of polychlorinated diphenyl ethers (PCDEs) in Swiss-Webster mice and Sprague-Dawley rats

Polychlorinated diphenyl ethers (PCDEs) are industrial byproducts found in many ecosystems at low levels. PCDEs are not markedly toxic to adult rodents, but their developmental toxicity has not previously been examined. We evaluated the maternal and perinatal toxicity of nine PCDE congeners to outbred mice when compounds were administered from gestation day (GD) 6 through GD 15. 2,2',4,4',5,6'-hexaCDE and 2,3',4',6-tetraCDE decreased the number of pups born per female mated and the number of pups surviving per litter born. 2,2',4,4',5,5'-hexaCDE and 2,2',4,5,6'-pentaCDE decreased the number of litters born per female mated, without decreasing postnatal survival. The other PCDEs did not decrease survival either pre- or postnatally. None of the PCDEs caused absence of Harderian glands in surviving offspring at the doses administered. Neither induction of cytochromes P450 nor tissue residues of individual congeners correlated well with developmental toxicity. Three PCDEs were also evaluated in outbred (Sprague-Dawley) rats: 2,2',4,5,6'-pentaCDE and 2,3',4',6-tetraCDE, because of their toxicity to mice; 2,2',4,4',5,5'-hexaCDE, because it should exhibit PCB-like toxicity. Each congener was administered at three dose levels from GD 6 through GD 15. 2,2',4,5,6'-pentaCDE decreased the number of litters born at 100 mg/kg/day, and the survival of pups in litters carried to term, at both 50 and 100 mg/kg per day. Postnatal weight gain was also reduced. In contrast to its action in mice, 2,3',4',6-tetraCDE decreased neither the numbers of litters born nor postnatal survival of rat offspring, but did suppress postnatal weight gain at least through PD 5. As in mice, induction of cytochromes P450 was not well correlated with the developmental toxicity of individual congeners.

[Evaluation of risks of glycol ethers for the reproductive health]

Glycol ethers (Ge) are a family of substances with a growing use in industrial and domestic products for the two last decades. Ge (group 1 and 2) are experimentally toxic for reproduction and development, at various levels. That begins to be found in humans. Epidemiological studies confirm toxicokinetic data showing humans are more sensitive than animals, because of a low excretion rate of the toxic metabolites. Occupational and consumer exposures are frequently higher than reference concentrations deducted from animal data. They may be involved in the growing number of genital reproductive system and reproduction anomaly, observed in most developed countries. Genetic toxicity is suspected from experimental data, but further investigations are needed.

Spectrum and subcellular determinants of fluorinated anesthetic-mediated proximal tubular injury

Currently used fluorinated anesthetics are chemically related to methoxyflurane (MF), a drug that caused many cases of clinical acute renal failure during previous widespread use. To determine whether newer fluorinated anesthetics might also have nephrotoxic effects, three currently used agents (isoflurane (IF), sevoflurane (SF), and desflurane) or MF were added to rat proximal tubular segments, followed by assessments of cell integrity (ATP levels and percent lactic dehydrogenase release). Ether served as a negative control. MF, IF, and SF each induced lethal proximal tubular segment injury (up to 92, 71, and 30% lactic dehydrogenase release, respectively) and massive ATP depletion. ATP losses were observed at or near clinically relevant drug levels, they preceded lethal injury, and they correlated with approximately 50% and approximately 100% reductions in total and Na,K-ATPase-driven respiration, respectively. Clinically relevant inorganic fluoride levels simulated fluorinated anesthetic toxicity. However, fluoride release from the anesthetics (a cytochrome P450 process) did not appear to be required for toxicity (no protection with P450 inhibitors and no detectable inorganic fluoride release). As IF was judged to be one-third as toxic as MF, subclinical tubular injury (increased urine N-acetyl-beta-D-glucosaminidase (NAG) levels) after its use was sought in 19 surgical patients. Fifteen patients undergoing comparable operations with SF (approximately one-half as toxic as IF in vitro) and nine patients undergoing regional/ local anesthesia were controls. The IF group doubled its urinary NAG levels by the end of surgery (P < 0.005). Conversely, NAG levels remained stable in both control groups. The conclusions are that 1) currently used fluorinated anesthetics, particularly IF, share (but to a lesser degree) MFs tubulotoxic effects, 2) ATP depletion (probably due to decreased production) and Na,K-ATPase inhibition are likely contributing mechanisms, 3) fluoride is a prime determinant of this toxicity, and 4) tubular injury can be expressed at or near clinically relevant anesthetic/inorganic fluoride levels. That increased enzymuria can develop in patients after IF anesthesia suggests that the above in vitro data could have potential clinical relevance in selected patients.

Effects of maternal exposure to chlorinated diphenyl ethers on thyroid hormone concentrations in maternal and juvenile rats

Polychlorinated diphenyl ethers (PCDEs) are industrial byproducts and widespread environmental contaminants. Their structural similarity to PCBs suggests that they may exhibit subtle effects on both adult and juvenile mammals. We examined the effects of 3 PCDEs (2,2',4,5,6'-pentachlorodiphenyl ether, 2',3,4,6'-tetrachlorodiphenyl ether, and 2,2',4,4',5,5'-hexachlorodiphenyl ether) on maternal rat thyroid levels shortly after exposure, and on the thyroid levels of 16 day old juvenile rats that had been prenatally exposed. Both 2,2',4,5, 6'-pentachlorodiphenyl ether and 2',3,4,6'-tetrachlorodiphenyl ether depressed thyroxine (T4) levels in the maternal females as well as in both sexes of juvenile rats. 2,2',4,4',5,5'-hexachlorodiphenyl ether did not alter T4 levels in the pregnant females, but depressed juvenile T4 levels. None of the congeners studied significantly altered T3 levels. Effects on thyroid hormones did not correlate with the congeners' induction of cytochrome P450.

compound A induces sister chromatid exchanges in Chinese hamster ovary cells

BACKGROUND

Compound A [CF2 = C(CF3)OCH2F], a degradation product of sevoflurane [(CF3)2CHOCH2F], is a vinyl ether and may be an alkylating agent. Thus it is a potential genotoxin.

METHODS

The capacity of compound A to produce sister chromatid exchanges was measured in Chinese hamster ovary cells with and without metabolic activation. Concentrations of 11 to 468 ppm compound A were applied for 2 h, the Chinese hamster ovary cells were incubated for a further 34 h in the presence of bromodeoxyuridine, and then colcemid was added to produce arrest in metaphase. Coded slides of cells were examined blindly, and 50 chromosome spreads were counted for each test concentration.

RESULTS

The lowest concentration of compound A applied without metabolic activator (27 ppm) significantly increased (P < 0.001) sister chromatid exchanges, and increasing concentrations of compound A increased the incidence of exchanges. Metabolic activation did not increase the incidence of exchanges.

CONCLUSIONS

Compound A increases sister chromatid exchanges at concentrations (27 ppm) obtained in low-flow systems when sevoflurane is used at concentrations approximating minimum alveolar concentration.

[Repeated low-flow sevoflurane anesthesia: effects on hepatic and renal function in beagles]

We studied the effects of repeated low-flow sevoflurane anesthesia for 6 hours. Five beagle dogs received 1.3 MAC (3%) sevoflurane anesthesia. Anesthesia of 6 hours was repeated on at the 7th day after the first anesthesia. Compound A gas samples were collected from the inspiratory limb during anesthesia. Concentrations of serum and renal fluoride, hepatic and renal function parameters were measured during and up to 7 days after the first and second anesthesia. The peak concentration of compound A was 23.7 +/- 3.6 ppm at 2 hours and the same level remained during the anesthesia. Plasma fluoride level exceeded 50 mmol.l-1 during anesthesia and rapidly decreased to the preanesthesia level thereafter. Serum GOT increased slightly only on the first postanesthesia day. No significant changes in other blood chemistry studies were observed. The excretion of renal tubular enzymes did not increase during and after anesthesia. Repeated low flow sevoflurane anesthesia in beagles did not affect hepatic and renal function significantly.

Effect of 2,4,4'-trichloro-2'-hydroxydiphenyl ether on cytochrome P450 enzymes in the rat liver

We examined the effect of 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300) on microsomal cytochrome P450 (P450) enzymes in rat liver. Rats were treated intraperitoneally with Irgasan DP300 daily for 4 days, at doses of 0.2, 0.4 and 0.8 mmol/kg. Among the P450-dependent monooxygenase activities, 7-benzyloxyresorufin O-debenzylase (BROD) and 7-pentoxyresorufin O-depentylase (PROD) in rats, which are associated with CYP2B1, were remarkably induced by all doses of Irgasan DP300. The relative induction to each control activity were from 5.6- to 22.3-fold and 4.9- to 20.2-fold, respectively. Furthermore, immunoblotting showed that CYP2B1/2 protein level in rat liver microsomes was increased from 10.8- to 34.4-fold by Irgasan DP300. In addition, 7-ethoxycoumarin O-deethylase (ECOD) and p-nitrophenol hydroxylase (PNPH) activities were significantly increased by Irgasan DP300 at all doses (from 1.4- to 4.9-fold). Although the activities of other P450-dependent monooxygenases, namely aminopyrine N-demethylase (APND), aniline p-hydroxylase (ANPH), erythromycin N-demethylase (EMND), lauric acid omega-hydroxylase (LAOH) and testosterone 6 beta-hydroxylase (TS6BH) were increased at high doses (> or = 0.4 mmol/kg) of Irgasan DP300, the relative level was lower than those of the CYP2B1-dependent monooxygenases such as BROD and PROD. However, 7-ethoxyresorufin O-deethylase (EROD), 7-methoxyresorufin O-demethylase (MROD), testosterone 2 alpha-hydroxylase (TS2AH) and testosterone 7 alpha-hydroxylase (TS7AH) activities were not affected by any doses of Irgsan DP300. Immunoblotting showed that CYP3A2/1 and CYP4A1 protein levels were significantly induced from 1.3- to 2.2-fold by Irgasan DP300 (> or = 0.4 mmol/kg), whereas those of CYP1A1/2, CYP2C11/6 and CYP2E1 were not affected by any doses of Irgasan DP300. These results suggest that Irgasan DP300 induces the P450 isoforms of CYP2B subfamily in the rat liver, and that the induced P450 isozymes closely relates to the toxicity of Irgasan DP300 or its chlorinated derivatives.

Reproductive assessment by continuous breeding: evolving study design and summaries of ninety studies

The Reproductive Assessment by Continuous Breeding (RACB) design has been used by the National Toxicology Program for approximately 15 years. This article details the evolutions in the thinking behind the design and the end points used in the identification of hazards to reproduction. Means of nominating chemicals are provided, and both early and current designs are described as well as some proposed changes for the future. This introduction is followed by a text and tabular summary of each study performed to date. We hope that this will not only be an explicit presentation of the findings of this testing program to date, but will help stimulate thinking about new ways to detect and measure reproductive toxicity in rodents, and help identify new relationships among the end points that are measured in such studies.