A toxicologic and dermatologic assessment of cinnamyl alcohol, cinnamaldehyde and cinnamic acid when used as fragrance ingredients.
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Acrolein↗
Biomedical subjects
I G Sipes
Publications and source records attributed to I G Sipes.
Absorption and elimination of D and C Red No. 28 in male F-344 rats.
D and C Red No. 28 (Red 28) is a US certified color additive used in drugs and cosmetics. Little is known about the extent of systemic absorption and pharmacokinetic behavior of Red 28. Therefore, these studies were performed to determine oral bioavailability and pharmacokinetic parameters of Red 28 in male F-344 rats following single and repeated oral dosing. Rats were administered either a single i.v. dose (50 mg/kg), a low oral gavage dose (50 mg/kg), or a high oral gavage dose (500 mg/kg) of Red 28. Plasma, urine and feces samples were subjected to solid phase extraction (SPE) and analyzed by HPLC for Red 28. Regardless of the dose or route of administration, the terminal t(1/2) of Red 28 was 2.5 h. The major route of elimination was fecal excretion, with 88% (i.v.) and 98% (50 mg/kg p.o.) of the dose recovered by 96 h. Urinary excretion of Red 28 accounted for 1% of the dose following i.v. administration. No Red 28 was detected in urine after p.o. administration. Biliary excretion was determined experimentally to be the primary route of elimination for systemically available Red 28. Bioavailability following p.o. administration was very low (1-2%) and was not altered significantly by 14 days of dietary pretreatment with Red 28.
Administration, Oral↗
A toxicologic and dermatologic assessment of linalool and related esters when used as fragrance ingredients.
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Acyclic Monoterpenes↗
Safety assessment of allylalkoxybenzene derivatives used as flavouring substances - methyl eugenol and estragole.
This publication is the seventh in a series of safety evaluations performed by the Expert Panel of the Flavor and Extract Manufacturers' Association (FEMA). In 1993, the Panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavouring substances under conditions of intended use. In this review, scientific data relevant to the safety evaluation of the allylalkoxybenzene derivatives methyl eugenol and estragole is critically evaluated by the FEMA Expert Panel. The hazard determination uses a mechanism-based approach in which production of the hepatotoxic sulfate conjugate of the 1'-hydroxy metabolite is used to interpret the pathological changes observed in different species of laboratory rodents in chronic and subchronic studies. In the risk evaluation, the effect of dose and metabolic activation on the production of the 1'-hydroxy metabolite in humans and laboratory animals is compared to assess the risk to humans from use of methyl eugenol and estragole as naturally occurring components of a traditional diet and as added flavouring substances. Both the qualitative and quantitative aspects of the molecular disposition of methyl eugenol and estragole and their associated toxicological sequelae have been relatively well defined from mammalian studies. Several studies have clearly established that the profiles of metabolism, metabolic activation, and covalent binding are dose dependent and that the relative importance diminishes markedly at low levels of exposure (i.e. these events are not linear with respect to dose). In particular, rodent studies show that these events are minimal probably in the dose range of 1-10 mg/kg body weight, which is approximately 100-1000 times the anticipated human exposure to these substances. For these reasons it is concluded that present exposure to methyl eugenol and estragole resulting from consumption of food, mainly spices and added as such, does not pose a significant cancer risk. Nevertheless, further studies are needed to define both the nature and implications of the dose-response curve in rats at low levels of exposure to methyl eugenol and estragole.
Animals↗
Disposition and metabolism of isoeugenol in the male Fischer 344 rat.
The primary objective of these studies was to determine the absorption, distribution, metabolism and excretion of isoeugenol following oral and intravenous administration to male Fischer-344 rats. Following a single oral dose of [14C]isoeugenol (156 mg/kg, 50 microCi/kg), greater than 85% of the administered dose was excreted in the urine predominantly as sulfate or glucuronide metabolites by 72 h. Approximately 10% was recovered in the feces, and less than 0.1% was recovered as CO(2) or expired organics. No parent isoeugenol was detected in the blood at any of the time points analyzed. Following iv administration (15.6 mg/kg, 100 microCi/kg), isoeugenol disappeared rapidly from the blood. The t(1/2) was 12 min and the Cl(s) was 1.9 l/min/kg. Excretion characteristics were similar to those of oral administration. The total amount of radioactivity remaining in selected tissues by 72 h was less than 0.25% of the dose following either oral or intravenous administration. Results of these studies show that isoeugenol is rapidly metabolized and is excreted predominantly in the urine as phase II conjugates of the parent compound.
Administration, Oral↗
Metabolism of bisphenol a in primary cultured hepatocytes from mice, rats, and humans.
Studies have shown that in the rat, bisphenol A (BPA) is metabolized and eliminated primarily as a monoglucuronide, a metabolite without estrogenic activity. The purpose of this study was to determine the extent of monoglucuronide formation in monolayers of hepatocytes from rats, mice, and humans. Noncytotoxic concentrations of BPA (10, 20, and 35 microM; 1.0 microCi), as assessed by lactate dehydrogenase leakage, were incubated with isolated hepatocytes for 0-6 h. Media were collected and analyzed for metabolites by radiochemical high performance liquid chromatography and liquid chromatography-tandem mass spectrometry. The metabolites identified include a monoglucuronide (major metabolite), a sulfate conjugate, and a glucuronide/sulfate diconjugate (minor metabolites). In hepatocytes of male Fischer-344 rats, the predominate metabolite was the diconjugate (glucuronide/sulfate). Under these conditions, the extent of metabolism by 3 h was similar in all species tested because all BPA was converted to conjugates by 3 h. Initial rates of metabolism in hepatocytes followed the order of mice > rats > humans. However, when extrapolated to the whole liver (i.e., cells per liver), the hepatic capacity for BPA glucuronidation is predicted to be humans > rats > mice. This research was supported in part by The Society of Plastics Industry Inc., and Southwest Environmental Health Science Center (ES 06694).
Air Pollutants, Occupational↗
Evaluation of hepatic cytochrome P4502E1 in the species-dependent bioactivation of 4-vinylcyclohexene.
4-Vinyl-1-cyclohexene (VCH), is converted by multiple forms of cytochrome P450 (CYP) to two monoepoxides (4-vinyl-1-cyclohexene 1,2-epoxide [VCH-1,2-epoxide], 4-vinyl-1-cyclohexene 7,8-epoxide [VCH-7,8-epoxide]), and 4-vinyl-1-cyclohexene diepoxide (VCD). A greater degree of formation of these epoxides by female B6C3F1 mice as compared to Fischer 344 rats correlates with the ovarian toxicity observed only in the mice. Understanding which isoforms of CYP are involved in VCH bioactivation will better explain the species-dependent ovotoxicity of VCH. Present studies focus on the role of CYP2E1, as this isoform is responsible for the bioactivation of several structurally related small molecular weight compounds, including 1,3-butadiene. Hepatic microsomes prepared from either mice or rats pretreated with the CYP inducer acetone demonstrated 2-fold increases in the formation of VCH-1,2-epoxide. However, incubations with microsomes from cyp2e1-deficient mice compared to those from wild type mice revealed no differences in the rates of bioactivation of VCH to the monoepoxides. Since repeated exposure to VCH is required for VCH-induced ovotoxicity, rodents were dosed with VCH for 5 or 10 d to observe effects on the hepatic concentration of CYP2E1 and/or associated activities. VCH pretreatment failed to increase the concentration of CYP2E1 or CYP2E1 activity in either species, as measured by immunoblotting analysis and p-nitrophenol hydroxylation. Based on these data, it is concluded that CYP2E1 does not play a role in the species differences between mice and rats in the bioactivation of VCH following repeated exposure to VCH. Other isoforms, such as those in CYP2A and CYP2B subfamilies, are likely involved in VCH bioactivation.
Animals↗
Mechanisms of ovotoxicity induced by environmental chemicals: 4-vinylcyclohexene diepoxide as a model chemical.
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Animals↗
Effect of 4-vinylcyclohexene diepoxide dosing in rats on GSH levels in liver and ovaries.
Repeated daily dosing of rats with the occupational chemical 4- vinylcyclohexene or its diepoxide metabolite (VCD) for 15 days destroys the smallest ovarian follicles. VCD acutely reduced hepatic levels of the antioxidant, glutathione (GSH); therefore, these studies were designed to evaluate whether GSH concentrations mediate VCD-induced ovotoxicity. Immature female Fischer 344 rats were dosed once or daily for 15 days with VCD (0.57 mmol/kg, ip) or the GSH synthesis inhibitor buthionine sulfoximine (BSO, 2 mmol/kg, ip). Animals were euthanized 2, 6, or 26 h following a single dose, and 2 or 26 h following 15 days of daily dosing. Reduced (p < 0.05) hepatic GSH was seen within 2 h of a single dose of either VCD (51 +/- 5% of control) or BSO (42 +/- 9%), but only BSO reduced ovarian GSH (71 +/- 5% at 6 h, p = 0.05) as measured by HPLC. Within 26 h, GSH levels had returned to control levels with either treatment. Hepatic GSH levels were reduced (< 0.05) 2 h after 15 daily doses with BSO (42 +/- 5%) or VCD (70 +/- 4%), but only BSO decreased ovarian GSH (64 +/- 3%). GSH levels in 15-day tissues were similar to controls 26 h after the final dose. Neither BSO nor VCD increased hepatic or ovarian concentrations of the oxidized dimer of GSH (GSSG) or thiobarbituric acid-reactive substances (TBARS), indicators of oxidative stress. These results suggest these treatments did not cause an oxidative stress. Histological counts of ovarian small follicle numbers were reduced (p < 0.05) in 15-day VCD-treated rats, whereas BSO did not affect follicle numbers, even though BSO reduced ovarian GSH content. These results support the conclusion that alterations in ovarian GSH levels are not involved in VCD-induced ovotoxicity.
Animals↗
Apoptosis induced in rats by 4-vinylcyclohexene diepoxide is associated with activation of the caspase cascades.
Previous studies have shown that ovotoxicity induced in rats by dosing with 4-vinylcyclohexene diepoxide (VCD) is likely via acceleration of the normal rate of atresia (apoptosis). The present study was designed to investigate the apoptosis-related caspase cascades as a component of this phenomenon in isolated ovarian small follicles. Female F344 rats were given a single dose of VCD (80 mg/kg, i.p., on Day 1; a time when ovotoxicity has not been initiated), or dosed daily for 15 days (80 mg/kg, i.p., on Day 15; a time when significant ovotoxicity is underway). Ovaries were collected after the final dose. Small preantral follicles (25-100 microm in diameter) were isolated, cellular fractions were prepared, and cleavage activity or protein expression levels of caspases-3, -8, and -9 were measured. Cytosolic caspase-3 activity was increased in small follicles (P < 0.01) by VCD treatment (Day 1, 2.86 +/- 0.23; Day 15, 3.25 +/- 0.64, VCD/control, n = 3). This activation was not seen in large or antral follicles (not targeted by VCD). Procaspase-3 protein was increased(P < 0.05) by VCD treatment 212% over controls in small ovarian follicles in Day 15, but not Day 1-dosed rats. Immunofluorescence staining intensity was evaluated by confocal microscopy. Caspase-3 protein, located in the cytosolic compartment of oocytes and granulosa cells of preantral follicles in various stages of development, was selectively increased (P < 0.05) in primordial and small primary follicles from Day 15 VCD-dosed rats. Caspase-8 activity was increased in small follicles in Day 15, but not in Day 1-treated rats; whereas caspase-9 activity was increased by VCD on Day 1 in the mitochondrial fraction. Thus, these data provide evidence that accelerated atresia induced in small ovarian follicles in rats by VCD is associated with activation of a caspase-mediated cascade.
Animals↗
Expression and redistribution of cellular Bad, Bax, and Bcl-X(L) protein is associated with VCD-induced ovotoxicity in rats.
Previous studies have shown that 4-vinylcyclohexene diepoxide (VCD)-induced ovotoxicity in rats is likely caused by acceleration of the normal rate of atresia (apoptosis). VCD-induced ovotoxicity is specific for small preantral follicles and is associated with increased activity of caspase cascades. The present study was designed to investigate the alteration of expression and distribution of several Bcl-2 family member proteins induced by dosing of VCD in rat small ovarian follicles. Female F344 rats were given a single dose of VCD (80 mg/kg, i.p., 1 day; a time when ovotoxicity is not initiated), or dosed daily for 15 days (80 mg/kg, i.p., 15 days; a time when significant ovotoxicity is underway). Four hours following the final dose, livers and ovaries were collected. Ovarian small (25-100 microm) and large (100-250 microm) preantral follicles were isolated, and subcellular fractions (cytosolic and mitochondrial) were prepared. Compared with controls, levels of the proapoptotic protein, Bad, were greater in both cytosolic and mitochondrial fractions of small preantral follicles collected from 15-day VCD-treated rats (cytosol, 1.97 +/- 0.16; mitochondria, 2.20 +/- 0.24, VCD/control, P < 0.05). After 15 days of daily VCD dosing, total cellular antiapoptotic Bcl-x(L) protein levels were unaffected in small preantral follicles, but its distribution in mitochondrial and cytosolic components was altered (mitochondria, 0.635 +/- 0.08; cytosol, 1.39 +/- 0.14, VCD/control, P < 0.05). Likewise, VCD did not affect protein levels of proapoptotic Bax in small follicles on Day 15. However, consistent with a Bax-mediated mechanism of apoptosis, the relative ratio of Bax/Bcl-x(L) in the mitochondrial fraction of small preantral follicles was significantly increased by VCD dosing (1.62 +/- 0.21, VCD/control, P < 0.05). Immunofluorescence staining intensity evaluated by confocal microscopy visualized cytochrome c protein in the cytosolic compartment in granulosa cells of preantral follicles in various stages of development. Relative to controls, within the population of small preantral follicles, staining intensity was less (P < 0.05) and presumably more diffuse, specifically in stage 1 primary follicles from VCD-treated animals (15 days). VCD caused none of these effects in large preantral follicles or liver (not targeted by VCD). These data provide evidence that the apoptosis induced by VCD in ovarian small preantral follicles of rats is associated with increased expression of Bad protein, redistribution of Bcl-x(L) protein and cytochrome c from the mitochondria to the cytosolic compartment, and an increase in the Bax/Bcl-x(L) ratio in the mitochondria. These observations are consistent with the involvement of Bcl-2 gene family members in VCD-induced acceleration of atresia.
Animals↗
Stereochemical aspects of vinylcyclohexene bioactivation in rodent hepatic microsomes and purified human cytochrome P450 enzyme systems.
The racemic mixture of 4-vinylcyclohexene (VCH) forms ovotoxic epoxides [VCH-1,2-epoxide, VCH-7,8-epoxide, and vinylcyclohexene diepoxide (VCD)] by cytochrome P450 (CYP) in B6C3F(1) female mice. These epoxides deplete primordial and primary follicles. The current studies compared in vitro epoxidation of (R)-VCH with that of (S)-VCH in hepatic microsomes prepared from adult female B6C3F(1) mice and Fischer 344 rats. Bioactivation of VCH in the rat was significantly less compared with that in the mouse. (R)-VCH formed significantly more VCH-1,2-epoxide as compared with (S)-VCH in both species, and less VCH-7,8-epoxide in the mouse. Neither of the enantiomers formed detectable amounts of VCD in the mouse or rat. Hepatic microsomes prepared from mice and rats pretreated with CYP-inducing agents (phenobarbital and acetone) were also incubated with (R)-VCH or (S)-VCH. Although monoepoxide formation was not increased enantioselectively in the mouse, VCD was formed preferentially from (R)-VCH as compared with (S)-VCH. Pretreatment with VCH resulted in nonstereoselective increases in both monoepoxide and diepoxide formation. In the rat, these pretreatments resulted in nonstereoselective increases in monoepoxide formation, but VCD formation was not detectable. Incubations with human CYP2E1 enzyme revealed that (R)-VCH formed significantly more VCH-1,2-epoxide and less VCH-7,8-epoxide than (S)-VCH. Human CYP2A6 was limited in its ability to form epoxides from either enantiomer of VCH. Human CYP2B6 preferentially formed VCH-7,8-epoxide compared with VCH-1,2-epoxide, and to a greater extent from (R)-VCH than from (S)-VCH. These results demonstrate regioselectivity and enantioselectivity in the bioactivation of VCH in rodent hepatic microsomes as well as in expressed human CYP enzymes.
Animals↗
Role of induction of specific hepatic cytochrome P450 isoforms in epoxidation of 4-vinylcyclohexene.
4-Vinyl-1-cyclohexene (VCH) is ovotoxic in B6C3F(1) mice but not in Fischer-344 rats, which can be partially attributed to greater formation of toxic epoxides from VCH in mice compared with rats. Since repeated exposure to VCH is necessary to cause ovotoxicity in mice, it is important to determine whether repeated exposure results in induction of cytochrome P450 (CYP) enzymes involved in its bioactivation. Hepatic microsomes prepared from mice or rats treated repeatedly with VCH demonstrated significantly increased VCH bioactivation in vitro, as assessed by VCH-1,2-epoxide, VCH-7,8-epoxide, or vinylcyclohexene diepoxide (VCD) formation. Mice and rats were then dosed with VCH, VCH-1,2-epoxide, or VCD for 10 days and measured for increases in hepatic microsomal CYP levels or activities. Total hepatic CYP levels were elevated only in microsomes from mice pretreated with VCH or VCH-1,2-epoxide. Immunoblotting analysis of microsomes from VCH-treated rodents revealed elevated levels of CYP2A and CYP2B in mice but not rats. VCH-1,2-epoxide pretreatment also increased CYP2B levels in the mouse. Activities toward specific substrates for CYP2A and CYP2B (coumarin and pentoxyresorufin, respectively) confirmed that VCH and VCH-1,2-epoxide pretreatments resulted in increased catalytic activities of CYP2A and CYP2B in the mouse but not the rat. Pretreatment with phenobarbital, a known inducer of CYP2A and CYP2B, increased VCH bioactivation in both species. Interestingly, metabolism studies with human CYP "Supersomes" reveal that, of eight isoforms tested, only human CYP2E1 and CYP2B6 were capable of significantly catalyzing VCH epoxidation, whereas CYP2B6, CYP2A6, CYP2E1, and CYP3A4 were capable of catalyzing the epoxidation of the monoepoxides.
Animals↗
Cytotoxicity and genotoxicity of methyleugenol and related congeners-- a mechanism of activation for methyleugenol.
Methyleugenol is a substituted alkenylbenzene found in a variety of foods, products, and essential oils. In a 2-year bioassay conducted by the National Toxicology Program, methyleugenol caused neoplastic lesions in the livers of Fischer 344 rats and B6C3F(1) mice. We were interested in the cytotoxicity and genotoxicity caused by methyleugenol and other alkenylbenzene compounds: safrole (a known hepatocarcinogen), eugenol, and isoeugenol. The endpoints were evaluated in cultured primary hepatocytes isolated from male Fischer 344 rats and female B6C3F(1) mice. Cytotoxicity was determined by measuring lactate dehydrogenase (LDH) release, while genotoxicity was determined by using the unscheduled DNA synthesis (UDS) assay. Rat and mouse hepatocytes showed similar patterns of toxicity for each chemical tested. Methyleugenol and safrole were relatively non-cytotoxic, but caused UDS at concentrations between 10 and 500 microM. In contrast, isoeugenol and eugenol produced cytotoxicity in hepatocytes with LC50s of approximately 200-300 microM, but did not cause UDS. Concurrent incubation of 2000 microM cyclohexane oxide (CHO), an epoxide hydrolase competitor, with a non-cytotoxic concentration of methyleugenol (10 microM) resulted in increased cytotoxicity but had no effect on genotoxicity. However, incubation of 15 microM pentacholorophenol, a sulfotransferase inhibitor, with 10 uM methyleugenol resulted in increased cytotoxicity but had a significant reduction of genotoxicity. These results suggest that methyleugenol is similar to safrole in its ability to cause cytotoxicity and genotoxicity in rodents. It appears that the bioactivation of methyleugenol to a DNA reactive electrophile is mediated by a sulfotransferase in rodents, but epoxide formation is not responsible for the observed genotoxicity.
Animals↗
Ovotoxicity in female Fischer rats and B6 mice induced by low-dose exposure to three polycyclic aromatic hydrocarbons: comparison through calculation of an ovotoxic index.
Extensive destruction of primordial follicles by exposure to ovarian toxicants can cause early menopause in women. Primordial follicle destruction is known to result from dosing of mice and rats with three polycyclic aromatic hydrocarbons (PAHs), contaminants commonly found in cigarette smoke. Therefore, the purpose of this study was to compare relative ovotoxicity in mice and rats using the PAHs, 9, 10-dimethylbenzanthracene (DMBA), 3-methylcholanthrene (3-MC), and benzo[a]pyrene (BaP). Female B6C3F(1) mice and Fischer 344 rats (age 28 days) were dosed daily (ip) with vehicle control or a range of doses of the PAHs. Two groups were dosed with the occupational chemicals 4-vinylcyclohexene (VCH; 500 mg/kg ip) or its diepoxide metabolite (VCD; 80 mg/kg ip), other known ovotoxicants. After 15 days, ovaries were collected, histologically prepared, and follicles were microscopically classified (primordial, primary, or secondary) and counted. The dose of each chemical that produced 50% loss of primordial follicles (p < 0.05) was determined (ED50) and used to calculate an ovotoxic index (OI) in mice and rats (ED50 x 15 days). Thus, a chemical with a lower OI is more toxic. Primordial follicles in mice displayed a lower OI than rats to all chemicals tested (mouse: DMBA, 0.0012; 3-MC, 0.003; BaP, 0.18; VCD, 6.8; VCH, 69; rat: DMBA, 0.45; 3-MC, >3.4; BaP, >3.6; VCD, 8.6; VCH, >69). In mice, DMBA targeted primordial follicles at a 10-fold lower concentration than primary and secondary follicles, whereas 3-MC exposure targeted primordial and primary follicles to a similar degree. BaP exposure targeted primordial and primary follicles at a 100-fold higher concentration than DMBA or 3-MC. Although BaP and 3-MC did not target secondary follicles in mice, secondary follicles in rats were most susceptible to 3-MC. Furthermore, all three PAHs were more ovotoxic (lower OI) with repeated low-dose exposure compared with OIs calculated from other studies using single high-dose exposures. The earliest day of impending primordial follicle loss (increase in percentage of unhealthy follicles, p < 0.05) in mice was factored into the OI (ED50 x first day of damage, p < 0.05 x % healthy follicles remaining, relative to control). The revised OI became DMBA d15, 0.0006; 3-MC d12, 0.0008; BaP d15, 0.132; and VCD d8, 2.96. These results predict that DMBA is the most potent ovarian toxicant (lower OI) in both species but VCD damages primordial follicles after shorter exposures. Calculation of the OI in mice and rats represents a method for comparing the relative potential risk of a variety of chemicals that produce ovarian damage at low levels following repeated exposures. The results also demonstrate that low-dose repeated exposures are substantially more toxic to the ovary than a single high-dose exposure. This finding is particularly important in view of the implications for chronic low-dose exposures of women to environmental chemicals.
9,10-Dimethyl-1,2-benzanthracene↗
1,2-Dichlorobenzene-mediated hepatocellular oxidative stress in Fischer-344 and Sprague-Dawley rats.
1,2-Dichlorobenzene (1,2-DCB) is a potent hepatotoxicant in male Fischer 344 (F-344) rats but not in Sprague-Dawley (SD) rats. While Kupffer cell-dependent oxidative stress plays a role in the progression of 1,2-DCB-mediated liver injury, we hypothesize that initiation of liver injury is due to oxidative events within the hepatocyte. This study compared hepatocellular oxidative stress marked by glutathione disulfide (GSSG) and glutathione (GSH) production in either bile, liver, or isolated hepatocytes of F-344 and SD rats following 1,2-DCB administration. Hepatic GSH concentrations were depleted at a greater rate in F-344 than in SD rats within 12 h of 1,2-DCB administration (3.6 mmol/kg ip). In bile, GSSG concentrations were threefold greater in F-344 rats compared to SD rats by 9 h of 1,2-DCB treatment. Moreover, 1-aminobenzotriazole but not gadolinium chloride pretreatment blocked the rise in biliary GSSG concentrations following 1,2-DCB administration. In in vitro studies, isolated hepatocytes of F-344 rats had a 15% increase in cellular GSSG concentrations following 1 h of 1,2-DCB (3.55 nmol) exposure, while GSH decreased 22% by 6.5 h compared to controls. In contrast, isolated SD hepatocytes exposed to 1,2-DCB had no increase in GSSG and only an 8% reduction in GSH. Furthermore, parameters of lipid peroxidation were increased in F-344 rats and not in SD rats. Collectively, these data suggest that hepatocellular oxidative stress is dependent upon bioactivation and the enhanced oxidative stress in the F-344 rat may explain its susceptibility to 1,2-DCB compared to the SD rat.
Animals↗
Diethyldithiocarbamate enhances production of nitric oxide and TNF-alpha by lipopolysaccharide-stimulated rat Kupffer cells.
Previous studies have shown that large doses of diethyldithiocarbamate (DDC) cause liver injury in rats and the pathogenesis of this injury involves, in part, release of superoxide anion by Kupffer cells. The purpose of this study was to evaluate if DDC was able to stimulate other potentially toxic mediators such as nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) using isolated rat Kupffer cells. DDC alone did not stimulate the release of NO and TNF-alpha by Kupffer cells. Interestingly, when Kupffer cells were stimulated by lipopolysaccharide (LPS), DDC (0-30 microM) enhanced the production of both NO and TNF-alpha in a concentration-dependent manner. Therefore, we further studied how DDC modulated the response of Kupffer cells to LPS. Immunocytochemical studies revealed that DDC increased the amount of inducible NO synthase and TNF-alpha protein in Kupffer cells after their exposure to LPS. The enhanced effects of DDC on the release of NO and TNF-alpha from Kupffer cells was inhibited by N-acetyl-L-cysteine (an inhibitor of transcription factor NF-kappaB activation). By using a specific antibody for NF-kappaBp65, it was found that DDC enhanced the LPS-activated nuclear translocation of NF-kappaB. There was no evidence of intracellular oxidative stress following either LPS alone or DDC + LPS exposure. The stimulatory effect of DDC on both NO and TNF-alpha release was inhibited by H-7 (an inhibitor of protein kinase C) but not H-8 (an inhibitor of cAMP-dependent protein kinase). These findings demonstrate that DDC enhances the production of NO and TNF-alpha by LPS-stimulated Kupffer cells and suggest that protein kinase C plays a critical role in mediating these effects of DDC.
Animals↗
Absorption and disposition of cobalt naphthenate in rats after a single oral dose.
The absorption and disposition of inorganic cobalt salts after oral administration have not been completely characterized. The objective of this project was to investigate the absorption and disposition of cobalt naphthenate in Fischer 344 rats following a single oral dose. Cobalt naphthenate was given orally at 3 doses: 0.333, 3.33, or 33.3 mg Co(II)/kg. Tissues, urine, and feces were collected over a 36-h period from the low- and high-dose groups; blood was collected from all 3 dose groups. The majority of the dose in both the low- and high-dose groups was excreted in the feces (42% and 73.1%, respectively), indicating that cobalt was incompletely absorbed from the gastrointestinal tract following oral dosing. The percent of the dose excreted in the urine was similar for low and high doses (31.8% and 26.3%, respectively). Cobalt concentrations were found to be highest in the liver and kidneys. The blood versus time cobalt concentration curves for the low-dose, intermediate-dose, and high-dose groups were elevated 4- to 5-fold, 14- to 25-fold, and 25- to 60-fold over control blood levels, respectively. The peak plasma concentrations of 0.6 and 1.7 microg Co(II)/ml occurred at approximately 4.3 h for the intermediate-dose group, and 3.3 h for the high-dose group. The terminal elimination half-lives were 24.7 and 24 h for the intermediate- and high-dose groups, respectively. Thus, although the extent of cobalt absorption as indicated by the blood concentrations and areas under the blood-time curves was not proportional to dose, the calculated pharmacokinetic values for the time to peak blood concentration and the apparent elimination rate constants were independent of dose. The amount excreted in the urine was also proportional to the dose. These apparent anomalies were not related to protein binding in blood.
Absorption↗