Interaction of lymphocytes with Kupffer cells from halothane-exposed guinea pigs

BACKGROUND

The purpose of this study was to investigate lymphocyte adhesion to Kupffer cells as a component of an immune-mediated mechanism for halothane hepatitis.

METHODS

Kupffer cells were isolated from guinea pigs exposed to 1.0% halothane/40% oxygen and cultured with various synthetic antigens (trifluoroacetyl-protein adducts or hepatocyte homogenate from halothane-exposed animals). Latex beads were also added to Kupffer cell cultures to determine if activation of these macrophages would result in an increased cellular adhesion. Lymphocytes which had been surfaced-labeled with biotin were added to treated Kupffer cells, and lymphocyte adhesion was determined using a streptavidin-peroxidase reagent for colorimetric detection.

RESULTS

Trifluoroacetyl-lysine, trifluoroacetyl-rabbit albumin or guinea pig albumin did not induce lymphocyte adhesion. Latex beads also had no effect on cellular adhesion. A noticeable increase in lymphocyte adhesion to Kupffer cells previously treated with either trifluoroacetyl-guinea pig albumin or hepatocyte homogenate was observed. Stimulation of lymphocytes with phorbol myristate acetate did not have an effect on adhesion. Addition ofantimajor histocompatibility complex II antibody had a significant inhibitory effect on lymphocyte adhesion to Kupffer cells treated with trifluoroacetyl-guinea pig albumin or homogenate.

CONCLUSION

These results demonstrate that the halothane trifluoroacetyl-guinea pig albumin antigen and hepatocyte homogenate enhances the adhesion of lymphocytes to cultured Kupffer cells and that this interaction involves major histocompatibility complex II expression on stimulated Kupffer cells. The interaction between Kupffer cells which present specific trifluoroacetyl-antigens and lymphocytes from halothane-exposed animals may play an important role in the pathogenesis of halothane hepatitis.

Kupffer cells from halothane-exposed guinea pigs carry trifluoroacetylated protein adducts

The anesthetic, halothane, is bioactivated by the liver cytochrome P450 system to trifluoroacetyl-chloride, which can readily acylate liver protein. Covalent binding of the trifluoroacetyl moiety may result in hapten formation leading to the induction of an immune response and ultimately halothane hepatitis. In this study the presence of trifluoroacetylated-protein adducts in Kupffer cells was investigated to learn how the immune system might come in contact with the proteins. Guinea pigs were exposed to 1.0% halothane, 40% oxygen for 4 h. Kupffer cells were isolated on days 1 through 9 post-exposure, by liver perfusion and purification by elutriation. Using gel electrophoresis and Western blotting techniques, it has been demonstrated that Kupffer cells obtained from halothane-treated guinea pigs, do carry trifluoroacetyl-protein adducts as recognized by an anti-trifluoroacetyl-rabbit serum albumin antibody. Apparent molecular weights of polypeptides bound by trifluoroacetyl were of a wide range, 25-152 kDa. Bands were most prominent in the larger Kupffer cells with more appearing at lower molecular weights. Trifluoroacetyl-protein adducts were not detected in lung, spleen, lymph node or peripheral blood macrophages. This work suggests a role for Kupffer cells in the presentation of altered proteins in the liver to cells of the immune system.

Demonstration of a cellular immune response in halothane-exposed guinea pigs

Halothane hepatitis is considered to be a result of an idiosyncratic autoimmune reaction brought about by the formation of neoantigens that have been generated by covalent binding of halothane biotransformation intermediates. The guinea pig is being examined as an animal model to investigate an immune-mediated mechanism for halothane hepatotoxicity. Male Hartley guinea pigs were exposed to 1% halothane/40% oxygen for 4 hr, three times with 40-day intervals. Kupffer cells and splenocytes were isolated from animals on various days after each halothane exposure. Splenocytes were cocultured in a lymphocyte transformation test with various concentrations of TFA(trifluoroacetylated)-antigens for 7 days and proliferation was measured by 3H-thymidine incorporation. In a second experiment, Kupffer cells were cocultured with autologous as well as allogeneic splenocytes with or without concanavalin A to determine whole cell sensitization and accessory function by Kupffer cells from treated animals. A 4-fold increase in splenocyte proliferation occurred in response to TFA-guinea pig albumin. No significant increase in proliferation could be detected with TFA-lysine or guinea pig albumin. A 14-fold increase in splenocyte proliferation also occurred in response to Kupffer cells from halothane-exposed animals. Autologous splenocytes demonstrated more of a response from treated versus control animals, indicating possible involvement of major histocompatibility complex II antigens. These results indicate recognition of TFA-antigens and Kupffer cells as antigen-presenting cells in halothane-exposed guinea pigs. This study provides good evidence that a cellular immune response is involved in the guinea pig after halothane exposure.

Utilization of renal slices to evaluate the efficacy of chelating agents for removing mercury from the kidney

Mercury is an environmental contaminant that preferentially accumulates in the kidney. It has been previously shown using proton-induced X-ray emission analysis that mercury (HgCl2) accumulated in precision-cut rabbit renal cortical slices. In this study, the efficacy of seven chelating agents for the removal of Hg from renal slices has been examined. Rabbits were injected with HgCl2 (10 mg/kg) and 3 h later kidneys were sliced, or renal slices were exposed in vitro to a mildly toxic concentration of HgCl2 (5 x 10(-5)M, 4 h). The slices were then treated in vitro with 10 mM concentrations of EDTA, lipoic acid (LA), penicillamine (PA), glutathione (GSH), 1,4-dithiothreitol (DTT), DMSA, or DMPS. DMPS proved to be the most effective in mobilizing Hg from in vivo or in vitro HgCl2-exposed renal tissue ( > 85% of control after 3 h incubation). Relative efficacies for the seven agents were DMPS > DMSA, PA > DTT, GSH > LA, EDTA. The use of renal slices appears to be a useful in vitro tool for assessing the efficacy of chelating agents on mobilizing accumulated Hg from renal tissue.

Late dimethyl sulfoxide administration provides a protective action against chemically induced injury in both the liver and the kidney

Dimethyl sulfoxide (DMSO) can protect the liver from injury produced by a variety of hepatotoxicants when administered prior to or concomitant with the toxicants. This protective action has previously been attributed to DMSO-induced inhibition of bioactivation of the compounds to toxic intermediates. In these studies, the ability of DMSO to provide protection when administered 10 hr after a toxicant was evaluated in several animal models of xenobiotic-induced liver and kidney injury. In the guinea pig model of halothane-associated hepatotoxicity, male outbred Hartley guinea pigs received 2 ml/kg DMSO 10 hr after an inhalation exposure to 1.0% halothane, 40% O2 for 4 hr. DMSO decreased the extent of liver necrosis as indicated by a threefold decrease in plasma alanine aminotransferase activity 48 hr after exposure and a reduction in the incidence and extent of zone 3 necrosis. These results do not appear to be due to alterations in halothane biotransformation since DMSO administered at 10 hr after halothane had no affect on plasma concentrations of the halothane metabolite tritluoroacetic acid or covalent binding by reactive halothane biotransformation intermediates to hepatic protein. In addition, administration of the structurally analogous biotransformation inhibitor diallyl sulfide at 10 hr after halothane also had no affect on biotransformation or covalent binding but provided no protection from liver injury. Hepatic glutathione concentrations in the guinea pigs 24 hr after halothane exposure were also unaffected by late treatment with DMSO. Further studies in male Sprague-Dawley rats demonstrated the ability of DMSO to decrease the hepatic injury resulting from oral administration of 1.0 ml/kg chloroform or 0.5 ml/kg bromobenzene when administered 10 hr after either toxicant. The chloroform-treated rats also developed renal tubular necrosis with large increases in plasma creatinine and urea nitrogen, which were completely ameliorated by DMSO. Elucidating the mechanism(s) of this protective action of late DMSO administration should provide insight into the cascade of events that lead to liver and kidney injury from toxicants and, hopefully, therapeutic modalities for individuals suffering from acute, progressing, xenobiotic-induced hepatitis.

Vitamin A potentiation of vinylidene chloride hepatotoxicity in rats and precision-cut rat liver slices

Pretreatment of large doses of vitamin A (VA) is known to potentiate the hepatotoxicity of carbon tetrachloride. Therefore the effects of 1-day VA pretreatment on VDC hepatotoxicity was examined both in vivo and in an in vitro system of precision-cut rat liver slices. Male Sprague-Dawley rats were pretreated with 250,000 IU/kg VA by oral gavage. After 24 hr rats were administered 50, 100, or 200 mg/kg VDC ip. Precision-cut liver slices were prepared from VA pretreated rats 24 hr later and the liver slices were exposed for 2-8 hr to 0.025-1.0 microliter VDC evaporated into the gas phase of the incubation vials. VA pretreatment resulted in an enhancement of VDC toxicity, both in vivo and in vitro. There was a dose-dependent increase in plasma ALT 24 hr after VDC treatment of rats and an increase in K+ leakage from liver slices after VDC exposure. Histological analysis of the liver or the liver slices revealed that VA + VDC treatment resulted in centrilobular necrosis of the liver. When GdCl3 (10 mg/kg iv) was administered just before VA pretreatment of rats, VDC toxicity was partially reversed as observed by a decrease in ALT in vivo and a decrease in the loss of K+ in vitro. These results indicated that Kupffer cells, the resident macrophages of the liver, were partially responsible for the VA-potentiated VDC hepatotoxicity. One-day pretreatment of VA induced cytochrome P450IIE1 protein content as well as its enzymatic activity as measured by pnitrophenol hydroxylation. Because VDC is bioactivated by cytochrome P450IIE1, the increase in VDC hepatotoxicity after VA may be due to an increased bioactivation of VDC in the liver and in precision-cut liver slices. Thus, more than one mechanism may be involved in the VA enhancement of VDC hepatotoxicity.

Protein arylation precedes acetaminophen toxicity in a dynamic organ slice culture of mouse kidney

Acetaminophen (APAP) is an analgesic and antipyretic agent which may cause hepatotoxicity and nephrotoxicity with overdose in man and laboratory animals. In vivo studies suggest that in situ activation of APAP contributes to the development of nephrotoxicity. Associated with target organ toxicity is selective arylation of proteins, with a 58-kDa acetaminophen binding protein (58-ABP) being the most prominent cytosolic target. In this study a mouse kidney slice model was developed to further evaluate the contribution of in situ activation of APAP to the development of nephrotoxicity and to determine the selectivity of protein arylation. Precision cut kidney slices from male CD-1 mice were incubated with selected concentrations of APAP (0-25 mM) for 2 to 24 hr. APAP caused a dose- and time-dependent decrease in nonprotein sulfhydryls (NPSH), ATP content, and K+ retention. Preceding toxicity was arylation of cytosolic proteins, the most prominent one being the 58-ABP. The association of 58-ABP arylation with APAP toxicity in this mouse kidney slice model is consistent with earlier, in vivo results and demonstrates the importance of in situ activation of APAP for the development of nephrotoxicity. Precision cut renal slices and dynamic organ culture are a good model for further mechanistic studies of APAP-induced renal toxicity.

Cold- and cryopreservation of dog liver and kidney slices

The use of tissue slices in culture could decrease the number of animals used in health-related research and decrease experimental variation. This reduction may come about particularly if the methods of cold- and cryopreserving tissue slices are perfected, and one can conduct sequential in vitro experiments into xenobiotic metabolism, organ-specific toxicity, or organ-specific biochemical processes with tissue slices. With this goal in mind, dog liver and kidney slices were placed in cold storage at 0 degrees C using Viaspan (UW), Euro-Collins (EC), Sacks + prostacyclin (SP), and V-7 (V7) cold-preservation solutions for 10 days. Viability was assessed each day by measuring K+ content and protein synthesis after 4 h of incubation in Waymouth + 10% fetal calf serum (FCS). Dog liver slices can be cold-preserved in V7 for up to 7 days using K+ retention as the viability criterion but only up to 4 days using protein synthesis. Dog kidney slices can be cold-preserved in UW, EC, and V7 for up to 10 days using K+ retention, but only V7 could maintain protein synthesis for 10 days. Cryopreserved dog liver and kidney slices retained 63-68% of control viability after 4 h of incubation in FCS. The cryopreservation regimen included using 10% dimethyl sulfoxide in FCS as the cryoprotectant, a freezing rate of 0.5 degrees C/min for liver slices and 12 degrees C/min for kidney slices, and thawing in 37 degrees C FCS. Continued development of cold- and cryopreserving tissue slices could reduce the numbers of animals used and provide accurate and reproducible data.

Use of precision-cut liver slices as an in vitro tool for evaluating liver function

Precision-cut liver slices have been developed as an in vitro tool for assessing liver viability and function and for examining hepatotoxicants. Liver slices from a variety of species (including human) are prepared using mechanical slicers that produce reproducible slices of a uniform thickness, which allows optimum exchange of nutrients, waste, and gases. Slices are incubated in dynamic systems that allow the slices to be maintained viable in culture for 1-10 days. The viability of slices can be assessed by ion content (K+, Na+ ATPase status), intermediary metabolism, energy status (ATP), respiration, biosynthetic ability, and biotransformation activity. In addition, liver tissue slices allow the opportunity for extensive microscopic evaluation (light and electron) as well as newer technologies such as confocal microscopy. Assessment of the toxic potential of a chemical can be performed after a short-term or constant exposure by evaluating the viability parameters. Liver slices have been used extensively for rank-ordering the toxicity of chemicals as well as for examining the mechanisms of liver injury. Liver slices in culture also can be used for an examination of the induction of new enzymes such as cytochrome P-450 and the expression of stress proteins or peroxisomal enzymes. Finally, liver slices offer a system for evaluating whole or cryopreserved liver as well as regeneration of liver tissue after toxic insult. Liver slices have been shown to be a valid in vitro system for examining liver function and offer a bridge between in vivo and cell culture systems.

Use of tissue slices in chemical mixture toxicology and interspecies investigations

Precision-cut tissue slices have proven to be a useful in vitro system for biotransformation and toxicity studies. Since tissue slices can be readily prepared from a variety of tissues and species, they can easily be used for interspecies investigations and comparisons. Furthermore, slices can be readily prepared from human tissue, thus comparisons (extrapolation) can be made between laboratory animals and humans. Slices can also be used to examine the toxic interactions of chemicals in vitro. It is important to use the correct experimental design to demonstrate toxic interactions and to assure that the tissue slices are properly exposed to the chemicals. Overall, tissue slices offer a valid in vitro system for performing species comparisons and chemical-chemical interaction studies.

Sodium arsenite and heat shock induce stress proteins in precision-cut rat liver slices

The present study was undertaken to investigate the usefulness of stress proteins as early, sensitive indicators of hepatotoxicity. Induction of stress protein synthesis in precision-cut rat liver slices was examined following in vitro exposure to sodium arsenite or heat shock. Precision-cut rat liver slices were incubated with 10(-5) or 10(-6) M sodium arsenite for 2, 4 or 8 h in the presence of 35S-methionine or exposed to hyperthermia (42.5 +/- 0.5 degrees C) for 45 min and then incubated with 35S-methionine for 2, 4 or 8 h. Fluorographic analysis indicated an increase in the synthesis of HSP 70 and HSP 90 family of proteins by both treatments. Immunoblot analysis demonstrated that there was a specific induction of HSP 72 and HSP 90. Induction of HSP 70 was greater than that of HSP 90 by both treatments. Stress protein induction occurred at earlier times by concentrations of arsenite which did not alter other viability parameters such as leakage of intracellular K+ or total protein synthesis. The results indicated that induction of stress proteins has the potential usefulness as an early biomarker of arsenite toxicity.

Peritubular paraquat transport in isolated renal proximal tubules

To better understand the characteristics of peritubular transport of organic cations (OCs), the uptake of the polyvalent OC dimethylbipyridinium (paraquat) and the structurally similar monovalent OC 1-methyl-4-phenylpyridinium (MPP+) was measured in suspensions of rabbit renal proximal tubules. Compared to the uptake of MPP+, the uptake of paraquat across the peritubular membrane was a low affinity, low capacity carrier-mediated process with a Jmax of 0.52 +/- 0.19 nmol.mg of protein.-1 min-1 and a Km of 162 +/- 25 microM. The uptake of MPP+ was a carrier-mediated process with a measured Jmax and Km of 1.8 +/- 0.09 nmol.mg of protein.-1min-1 and 28 +/- 8 microM, respectively. To determine whether paraquat is a substrate for the monovalent OC pathway, the effect of unlabeled MPP+ and tetraethylammonium (TEA) on paraquat uptake was examined. A 1 mM concentration of the monovalent OC MPP+ and TEA reduced the uptake of [14C]paraquat and [3H]MPP+ by approximately 30 and 90%, respectively, whereas 1 mM paraquat had no effect on [3H]MPP+ or [14C]TEA uptake. Thus, MPP+, but not paraquat, appears to interact with the monovalent OC transporter. On the other hand, the polyvalent OC substrates, including the polyamines putrescine and spermine, the herbicide diquat and the divalent hexamethonium bromidehydrate had no effect on either paraquat or MPP+ uptake. However, the synthetic polyamine methylglyoxal bis(guanyl-hydrazone)dihydrochloride (MGBG; 1 mM) reduced both paraquat and MPP+ uptake (by 60 and 90%, respectively). The ability of MGBG, unlike the other polyvalent substrates, to interact with paraquat transport may be related to structural similarities in the relative location of the two charged nitronium moieties in paraquat and MGBG.(ABSTRACT TRUNCATED AT 250 WORDS)

Precision-cut tissue slices: applications in pharmacology and toxicology

Almost a decade has passed since the first paper describing the isolation and maintenance of precision-cut liver slices produced using a mechanical tissue slicer was published (1). Although tissue slices of various organs have been employed as an in vitro system for several decades, the lack of reproducibility within the slices and the relatively limited viability of the tissue preparations has prevented a widespread acceptance of the technique. The production of an automated slicer, capable of reproducibly producing relatively thin slices of tissue, as well as the development of a dynamic organ culture system, overcame several of these obstacles. Since that time, significant advances in the methods to produce and culture tissue slices have been made, as well as the application of the technique to several other organs, including kidney, lung and heart. This review will i) summarize the historical use of tissue slices prior to the development of the precision-cut tissue slice system; ii) briefly analyze current methods to produce precision-cut liver, kidney, lung and heart slices; and iii) discuss the applications of this powerful in vitro system to the disciplines of pharmacology and toxicology.

Biotransformation and hepatotoxicity of HCFC-123 in the guinea pig: potentiation of hepatic injury by prior glutathione depletion

The chlorofluorocarbon substitute 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) is a structural analog of halothane. Both are oxidatively metabolized by CYP2EI, producing a reactive trifluoroacyl acid chloride intermediate and have been shown to cause acute liver necrosis in the guinea pig. With halothane, liver injury has been associated with the degree of reactive intermediate binding to hepatic protein. This injury can be potentiated by prior glutathione (GSH) depletion. Thus, the combination of GSH depletion and HCFC-123 exposure was evaluated for its hepatotoxic potential in this species. Male outbred Hartley guinea pigs were injected with either 0.8 g/kg l-buthionine-(S,R)-sulfoximine (BSO) to deplete hepatic glutathione or vehicle control solution 24 hr before a 4-hr inhalation exposure to 1.0% (v/v) HCFC-123 with 40% O2. HCFC-123 caused minimal liver injury with only 1 of 8 exposed animals displaying confluent zone 3 necrosis. GSH depletion potentiated injury producing submassive to massive liver necrosis in some animals. This potentiation was associated with a 36% increase in covalent binding of reactive HCFC-123 intermediates to hepatic protein. These results were not due to alterations in the biotransformation of HCFC-123 as indicated by plasma concentrations of the metabolites trifluoroacetic acid and fluoride ion which were not affected by BSO pretreatment. HCFC-123 was also found to cause a decrease in liver GSH concentrations following exposure. These findings demonstrate a role for hepatic GSH in helping to prevent covalent binding by the trifluoroacyl acid chloride intermediate. Inhalation of HCFC-123 can cause acute hepatic injury in the guinea pig that is worsened by low hepatic GSH concentrations.

Halogenated anesthetics form liver adducts and antigens that cross-react with halothane-induced antibodies

Two halogenated anesthetics, enflurane and isoflurane, have been associated with an allergic-type hepatic injury both alone and following previous exposure to halothane. Halothane hepatitis appears to involve an aberrant immune response. An antibody response to a protein-bound biotransformation product (trifluoroacetyl adduct) has been detected on halothane hepatitis patients. This study was performed to determine cross-reactivity between enflurane and isoflurane with the hypersensitivity induced by halothane. The subcellular and lobular production of hepatic neoantigens recognized by halothane-induced antibodies following enflurane and isoflurane, and the biochemical nature of these neoantigens was investigated in two animal models. Enflurane administration resulted in neoantigens detected in both the microsomal and cytosolic fraction of liver homogenates and in the centrilobular region of the liver. In the same liver, biochemical analysis detected fluorinated liver adducts that were up to 20-fold greater in guinea pigs than in rats. This supports and extends previous evidence for a mechanism by which enflurane and/or isoflurane could produce a hypersensitivity condition similar to that of halothane hepatitis either alone or subsequent to halothane administration. The guinea pig would appear to be a useful model for further investigations of the immunological response to these antigens.

The lipoic acid containing components of the 2-oxoacid dehydrogenase complexes mimic trifluoroacetylated proteins and are autoantigens associated with halothane hepatitis

Anti-CF3CO antibodies, monospecific toward trifluoroacetylated proteins (CF3CO-proteins), which are elicited in experimental animals and humans exposed to the anesthetic agent halothane, cross-react with an unknown protein of approximately 52 kDa, constitutively expressed in tissues of experimental animals and humans not previously exposed to the agent. Using anti-CF3CO antibody, the protein(s) of 52 kDa could be immunoprecipitated from solubilized rat heart homogenate. Two-dimensional gel electrophoretic analysis revealed the presence of distinct major (P1, P2) and minor (P3, P4, P5) protein components with apparent molecular masses of 52 kDa. From each of the components P1 and P2, the amino acid sequences of three peptides were determined and found to exhibit 100% identity with the corresponding amino acid sequences of the E2 subunit of the rat 2-oxoglutarate dehydrogenase complex (OGDC). Additionally to the E2 subunit of OGDC, anti-CF3CO antibody also recognized on immunoblots the purified E2 subunit of the branched chain 2-oxoacid dehydrogenase complex (BCOADC) and protein X, a constituent of the pyruvate dehydrogenase complex (PDC), in a manner sensitive to competition by N6-(trifluoroacetyl)-L-lysine (CF3CO-Lys), 6(RS)-lipoic acid, and N6-(6(RS)-lipoyl)-L-lysine (lipoyl-Lys). Furthermore, a discrete population of autoantibodies was identified in sera of patients with halothane hepatitis which could not discriminate between the lipoylated target epitope present on the E2 subunit of OGDC and epitopes on CF3CO-RSA, used as model for CF3CO-proteins. These data suggest that the autoantigenicity of these proteins in halothane hepatitis is based on the molecular mimicry of CF3CO-Lys by lipoic acid, the prosthetic group common to protein X and the E2 subunits of OGDC and BCOADC.

Comparative metabolism and toxicity of dichlorobenzenes in Sprague-Dawley, Fischer-344 and human liver slices

1. Precision-cut liver slices, prepared from Sprague-Dawley and Fischer-344 rats and donated human liver tissue, were used to identify differences in 1,2-dichlorobenzene (1,2-DCB), 1,3-dichlorobenzene (1,3-DCB) and 1,4-dichlorobenzene (1,4-DCB) metabolism and how it may relate to toxicity. 2. Rat and human liver slices were incubated with 1 mM of either dichlorobenzene to determine metabolism and toxicity, at 2 and 6 h of organ culture. 3. The human liver slices metabolised the dichlorobenzenes to a greater extent than those from either of the rat strains. Liver slices from the Fischer-344 strain had a higher metabolic rate than the slices from the Sprague-Dawley rat strain. 4. The metabolic rate of dichlorobenzene isomers did not consistently correlate with its toxicity. For example, human slices did not exhibit any hepatoxicity, even though they metabolised these compounds to a greater extent than either rat strain. 5. Cross species covalent binding did not correlate with toxicity endpoints measured in this study. 6. The phase two metabolite profiles for each of the isomers in human and rat slices were similar in that the glutathione-cysteine conjugate was the major metabolite. 7. The use of an in vitro system which utilises human liver slices might provide an important bridge between animal derived data and the human situation.

Biotransformation of sevoflurane by rat neonate liver slices

Sevoflurane [CF3-CH(OCH2F)-CF3] is biotransformed to inorganic fluoride (F-) and hexafluoroisopropanol, which forms a glucuronide conjugate. Although sevoflurane may be used in newborns without fully developed biotransformation activity, studies were performed using liver slices from rat neonates to determine sevoflurane disposition. Sevoflurane was vaporized in sealed roller culture vials to produce a continuous saturating dose (0.5 mM). After incubation, slices and incubation media were sonicated and centrifuged to remove debris. The supernatant fraction was analyzed for F-, hexafluoroisopropanol, and hexafluoroisopropanol-glucuronide conjugate. The metabolism of sevoflurane by liver slices increased proportionately with time with a stoichiometric production (1:1) of hexafluoroisopropanol and F- in all age groups. Only glucuronide conjugates of hexafluoroisopropanol were found. The rate of sevoflurane biotransformation measured as fluoride production was similar among slices prepared from all neonate age groups. Although no hexafluoroisopropanol-glucuronide was generated by slices from 4-, 6-, and 8-day-old neonates, by day 21, 17% of the total hexafluoroisopropanol is glucuronidated. This contrasts with the lower levels of free hexafluoroisopropanol typically seen in adults liver slices, wherein 51% of the hexafluoroisopropanol was glucuronidated. These studies indicate that sevoflurane is equally metabolized to hexafluoroisopropanol and F-, but a deficiency in glucuronosyltransferase occurs in neonates.

Interaction of metals during their uptake and accumulation in rabbit renal cortical slices

The uptake and accumulation of metals occurs in the kidney, which is a key site for interaction between metal nephrotoxicants. The uptake/accumulation and interaction of CdCl2, HgCl2, K2Cr2O7, and NaAsO2 was examined in precision-cut rabbit renal cortical slices. Slices were incubated with 10(-6) to 10(-3) M of a single metal toxicant or combinations of metal toxicants for 12 hr in DME-F12 media. Slices were blotted and sandwiched between two mylar films stretched across XRF sample cups. Quantitation of the metal in the slices was performed by proton-induced X-ray emission analysis (PIXE). The uptake of the metals was rapid, often reaching a maximum between 3 to 6 hr; the accumulation of Hg was highest, followed in order by Cd, Cr, and As. When two metals were present together, substantial alterations were observed in the uptake of the metals in the slices. HgCl2 hindered the uptake of K2Cr2O7, NaAsO2, CdCl2 (in this order), whereas these metals facilitated the uptake of HgCl2. However, a decreased uptake of both metals was often noted after exposure to other combinations of metals. PIXE analysis of metal content in slices is attractive since all elements (atomic number > 20) can be determined simultaneously. This information will be particularly useful in studying potential toxic interactions.

Trifluoroacetylation potentiates the humoral immune response to halothane in the guinea pig

Halothane hepatitis appears to result from an inappropriate immune response to the products of halothane metabolism. Attempts to produce an animal model for halothane hepatitis have been largely unsuccessful. Although guinea pigs produce neoantigens following treatment with halothane, the subsequent antibody response is weak, possibly accounting for the failure to produce halothane hepatitis in these animals. In order to increase the antibody response to halothane neoantigens, three methods for trifluoroacetylating proteins were used. Guinea pigs were either treated with S-ethylthiotrifluoroacetate, autologous lymphocytes trifluoroacetylated ex vivo, or immunized with trifluoroacetylated mycobacterial protein, followed by exposure to halothane, and examined for anti-halothane metabolite antibodies (anti-TFA antibodies). Animals treated with S-ethylthiotrifluoroacetate developed anti-TFA antibodies, and following exposure to halothane exhibited an enhanced antibody response. Treatment with trifluoroacetylated lymphocytes also resulted in an enhanced anti-TFA antibody response following halothane exposure. Immunization with trifluoroacetylated mycobacterial proteins resulted in very high anti-TFA antibody titers. However, subsequent exposure to halothane had no observable effect on specific antibody titers. Exposure to halothane, regardless of treatment, resulted in the production of anti-microsomal protein antibodies. Signs of halothane hepatitis were not observed, indicating that enhancement of the humoral immune response does not appear to be sufficient for production of halothane hepatitis.

Glutathione effects on toxicity and uptake of mercuric chloride and sodium arsenite in rabbit renal cortical slices

The mechanism of renal uptake of nephrotoxic heavy metals such as HgCl2 and NaAsO2 is not clear. The metals are known to react with endogenous sulfhydryls such as glutathione (GSH), so metal-GSH conjugates may be delivered to the kidney. To study this possibility, renal cortical slices from male New Zealand white rabbits were incubated with 10(-4) M HgCl2 or 10(-3) M NaAsO2 +/- stoichiometric amounts (1-3x) of GSH; or synthetic metal-GSH conjugates [10(-4) M Hg(SG)2 or 10(-3) M As(SG)3]. Incubations were performed at 37 degrees C in DME-F12 buffer (95/5 O2/CO2) for 8 hr. Hg(SG)2 reduced slice K+/DNA content, as an indicator of viability, significantly less than HgCl2. As(SG)3 exhibited a 2-hr delay in K+/DNA content reduction compared to NaAsO2. This delay in toxicity was not correlated to changes in uptake. Arsenic and mercury accumulation, determined by proton-induced X-ray emission, were also identical between the metal salts and the metal-GSH conjugates. Exogenous GSH decreased HgCl2 cytotoxicity and was correlated to a decrease in Hg accumulation in the slice. Exogenous GSH had limited if any protective effects against cytotoxicity by NaAsO2 and a decrease in As accumulation was not observed. Complex metal-GSH interactions appear to exist and impact on the uptake and toxicity of these metals.

Novel mechanisms in chemically induced hepatotoxicity

This review focuses on cellular events that modulate hepatotoxicity subsequent to initial liver insult. Cellular events that determine the nature and extent of hepatotoxic injury and the ultimate outcome of that injury are also discussed. The roles of cell types other than hepatocytes, hepatocyte organelle-specific processes, and regeneration in progression or recovery from liver injury are emphasized. Leukocyte activities are key events in two distinct hepatotoxicities. Neutrophil-mediated, periportal inflammation appears to play a primary role in progression of alpha-naphthylisothiocyanate-induced cholangiolitic hepatitis. However, a humorally mediated autoimmune response to protein adducts that occurs after anesthesia is critical in onset of halothane-induced hepatitis. New insights into specific events at the hepatocyte level are also emerging. Although reducing gap junctional communication between hepatocytes can protect against progression of liver injury, down-regulation of the subunit proteins (connexins) can isolate neoplastic cells from growth regulation. Acidic intracellular pH characteristic of hypoxia is protective against both hypoxic and toxicant-induced cell injury. In oxidative injury, a pH-mediated mitochondrial permeability transition causes mitochondrial uncoupling and ATP loss and leads to cell death. The ultimate outcome of hepatotoxic injury depends on the extent of tissue repair. Stimulation of tissue repair after a sublethal dose of CCl4 appears to be the central mechanism in protection against death from a subsequent large dose. Taken together, these examples illustrate the importance of events subsequent to initial liver injury as determinants of extent of liver damage.

Phenobarbital induces cytosolic acidification in an established liver epithelial cell line

Phenobarbital (PB), a long-acting barbiturate, is also a known tumor promoter. The mechanism responsible for the promoting effect of PB has not yet been elucidated. Changes in intracellular pH (pHin) have been associated with both early and late events of multistage carcinogenesis. We conducted this study to evaluate whether PB alters pH homeostasis. Adult rat liver (ARL) epithelial cells were cultured for 48 h on glass coverslips, loaded with the intracellular pH indicator SNARF-1, and perfused with various concentrations of PB to evaluate its effect on pHin. Our results show that PB treatment of cultured cells induces a concentration-dependent cytosolic acidification. These results indicate that its ability to decrease pHin may be involved in the mechanism of tumor promotion by PB.

Identification of the dihydrolipoamide acetyltransferase subunit of the human pyruvate dehydrogenase complex as an autoantigen in halothane hepatitis. Molecular mimicry of trifluoroacetyl-lysine by lipoic acid

Trifluoroacetylated (CF3CO-) proteins, elicited upon exposure of animals or humans to halothane, were recognized by anti-CF3CO antibody, monospecific for the hapten derivative N6-trifluoroacetyl-L-lysine. Anti-CF3CO antibodies cross-reacted with the dihydrolipoamide acetyltransferase (E2 subunit) of pyruvate dehydrogenase, indicating that epitopes on the E2 subunit of pyruvate dehydrogenase molecularly mimic those on CF3CO-proteins. Lipoic acid, the prosthetic group of the E2 subunit of pyruvate dehydrogenase was essential in this process, in that only the lipoylated form of the recombinantly expressed inner lipoyl domain of the human E2 subunit of pyruvate dehydrogenase, but not the unlipolyated form, was recognized by anti-CF3CO antibody. Furthermore, based on a high degree of structural relatedness, both CF3CO-Lys and (6RS)-lipoic acid, as well as the lipoylated peptide ETDK(lipoyl)ATIG specifically inhibited the recognition by anti-CF3CO antibody of the E2 subunit of pyruvate dehydrogenase, of trifluoroacetylated rabbit serum albumin and of human liver CF3CO-proteins. In sera of patients with halothane hepatitis, autoantibodies with properties identical to those of anti-CF3CO antibody were identified which could not discriminate between CF3CO-proteins and the E2 subunit of pyruvate dehydrogenase. These data suggest that the E2 subunit pyruvate of dehydrogenase is an autoantigen in halothane hepatitis and that molecular mimicry of CF3CO-proteins by the E2 subunit of pyruvate dehydrogenase is due to the similar structures of CF3CO-Lys and lipoic acid.