Nephrotoxicity of 4-amino-2-chlorophenol and 2-amino-4-chlorophenol in the Fischer 344 rat

Role of Free Radicals and Biotransformation in Trichloronitrobenzene-Induced Nephrotoxicity In Vitro

This study determined the comparative nephrotoxic potential of four trichloronitrobenzenes (TCNBs) (2,3,4-; 2,4,5-; 2,4,6-; and 3,4,5-TCNB) and explored the effects of antioxidants and biotransformation inhibitors on TCNB-induced cytotoxicity in isolated renal cortical cells (IRCC) from male Fischer 344 rats. IRCC were incubated with a TCNB up to 1.0 mM for 15–120 min. Pretreatment with an antioxidant or cytochrome P450 (CYP), flavin monooxygenase (FMO), or peroxidase inhibitor was used in some experiments. Among the four TCNBs, the order of decreasing nephrotoxic potential was approximately 3,4,5- > 2,4,6- > 2,3,4- > 2,4,5-TCNB. The four TCNBs exhibited a similar profile of attenuation of cytotoxicity in response to antioxidant pretreatments. 2,3,4- and 3,4,5-TCNB cytotoxicity was attenuated by most of the biotransformation inhibitors tested, 2,4,5-TCNB cytotoxicity was only inhibited by isoniazid (CYP 2E1 inhibitor), and 2,4,6-TCNB-induced cytotoxicity was inhibited by one CYP inhibitor, one FMO inhibitor, and one peroxidase inhibitor. All of the CYP specific inhibitors tested offered some attenuation of 3,4,5-TCNB cytotoxicity. These results indicate that 3,4,5-TCNB is the most potent nephrotoxicant, free radicals play a role in the TCNB cytotoxicity, and the role of biotransformation in TCNB nephrotoxicity in vitro is variable and dependent on the position of the chloro groups.

The role of biotransformation and oxidative stress in 3,5-dichloroaniline (3,5-DCA) induced nephrotoxicity in isolated renal cortical cells from male Fischer 344 rats

Among the mono- and dichloroanilines, 3,5-dichloroaniline (3,5-DCA) is the most potent nephrotoxicant in vivo and in vitro. However, the role of renal biotransformation in 3,5-DCA induced nephrotoxicity is unknown. The current study was designed to determine the in vitro nephrotoxic potential of 3,5-DCA in isolated renal cortical cells (IRCC) obtained from male Fischer 344 rats, and the role of renal bioactivation and oxidative stress in 3,5-DCA nephrotoxicity. IRCC (∼ 4 million cells/ml) from male rats were exposed to 3,5-DCA (0-1.0mM) for up to 120 min. In IRCC, 3,5-DCA was cytotoxic at 1.0mM by 60 min as evidenced by the increased release of lactate dehydrogenase (LDH), but 120 min was required for 3,5-DCA 0.5mM to increase LDH release. In subsequent studies, IRCC were exposed to a pretreatment (antioxidant or enzyme inhibitor) prior to exposure to 3,5-DCA (1.0mM) for 90 min. Cytotoxicity induced by 3,5-DCA was attenuated by pretreatment with inhibitors of flavin-containing monooxygenase (FMO; methimazole, N-octylamine), cytochrome P450 (CYP; piperonyl butoxide, metyrapone), or peroxidase (indomethacin, mercaptosuccinate) enzymes. Use of more selective CYP inhibitors suggested that the CYP 2C family contributed to 3,5-DCA bioactivation. Antioxidants (glutathione, N-acetyl-l-cysteine, α-tocopherol, ascorbate, pyruvate) also attenuated 3,5-DCA nephrotoxicity, but oxidized glutathione levels and the oxidized/reduced glutathione ratios were not increased. These results indicate that 3,5-DCA may be activated via several renal enzyme systems to toxic metabolites, and that free radicals, but not oxidative stress, contribute to 3,5-DCA induced nephrotoxicity in vitro.

3,4,5-Trichloroaniline nephrotoxicity in vitro: potential role of free radicals and renal biotransformation

Chloroanilines are widely used in the manufacture of drugs, pesticides and industrial intermediates. Among the trichloroanilines, 3,4,5-trichloroaniline (TCA) is the most potent nephrotoxicant in vivo. The purpose of this study was to examine the nephrotoxic potential of TCA in vitro and to determine if renal biotransformation and/or free radicals contributed to TCA cytotoxicity using isolated renal cortical cells (IRCC) from male Fischer 344 rats as the animal model. IRCC (~4 million cells/mL; 3 mL) were incubated with TCA (0, 0.1, 0.25, 0.5 or 1.0 mM) for 60–120 min. In some experiments, IRCC were pretreated with an antioxidant or a cytochrome P450 (CYP), flavin monooxygenase (FMO), cyclooxygenase or peroxidase inhibitor prior to incubation with dimethyl sulfoxide (control) or TCA (0.5 mM) for 120 min. At 60 min, TCA did not induce cytotoxicity, but induced cytotoxicity as early as 90 min with 0.5 mM or higher TCA and at 120 min with 0.1 mM or higher TCA, as evidenced by increased lactate dehydrogenase (LDH) release. Pretreatment with the CYP inhibitor piperonyl butoxide, the cyclooxygenase inhibitor indomethacin or the peroxidase inhibitor mercaptosuccinate attenuated TCA cytotoxicity, while pretreatment with FMO inhibitors or the CYP inhibitor metyrapone had no effect on TCA nephrotoxicity. Pretreatment with an antioxidant (α-tocopherol, glutathione, ascorbate or N-acetyl-l-cysteine) also reduced or completely blocked TCA cytotoxicity. These results indicate that TCA is directly nephrotoxic to IRCC in a time and concentration dependent manner. Bioactivation of TCA to toxic metabolites by CYP, cyclooxygenase and/or peroxidase contributes to the mechanism of TCA nephrotoxicity. Lastly, free radicals play a role in TCA cytotoxicity, although the exact nature of the origin of these radicals remains to be determined.

4-Amino-2-chlorophenol: Comparative in vitro nephrotoxicity and mechanisms of bioactivation

Chlorinated anilines are nephrotoxicants both in vivo and in vitro. The mechanism of chloroaniline nephrotoxicity may occur via more than one mechanism, but aminochlorophenol metabolites appear to contribute to the adverse in vivo effects. The purpose of this study was to compare the nephrotoxic potential of 4-aminophenol (4-AP), 4-amino-2-chlorophenol (4-A2CP), 4-amino-3-chlorophenol (4-A3CP) and 4-amino-2,6-dichlorophenol (4-A2,6DCP) using isolated renal cortical cells (IRCC) from male Fischer 344 rats as the model and to explore renal bioactivation mechanisms for 4-A2CP. For these studies, IRCC (∼4×10(6)cells/ml) were incubated with an aminophenol (0.5 or 1.0mM) or vehicle for 60min at 37°C with shaking. In some experiments, cells were pretreated with an antioxidant or cytochrome P450 (CYP), flavin-containing monooxygenase (FMO), peroxidase or cyclooxygenase inhibitor prior to 4-A2CP (1.0mM). Lactate dehydrogenase (LDH) release served as a measure of cytotoxicity. The order of decreasing nephrotoxic potential in IRCC was 4-A2,6-DCP>4-A2CP>4-AP>4-A3CP. The cytotoxicity induced by 4-A2CP was reduced by pretreatment with the peroxidase inhibitor mercaptosuccinic acid, and some antioxidants (ascorbate, glutathione, N-acetyl-l-cysteine) but not by others (α-tocopherol, DPPD). In addition, pretreatment with the iron chelator deferoxamine, several CYP inhibitors (except for the general CYP inhibitor piperonyl butoxide), FMO inhibitors or indomethacin (a cyclooxygenase inhibitor) failed to attenuate 4-A2CP cytotoxicity. These results demonstrate that the number and ring position of chloro groups can influence the nephrotoxic potential of 4-aminochlorophenols. In addition, 4-A2CP may be bioactivated by cyclooxygenase and peroxidases, and free radicals appear to play a role in 4-A2CP cytotoxicity.

Mechanistic aspects of 4-amino-2,6-dichlorophenol-induced in vitro nephrotoxicity

4-Amino-2,6-dichlorophenol (ADCP) is a potent acute nephrotoxicant in vivo inducing prominent renal corticomedullary necrosis. In vitro, ADCP exposure increases lactate dehydrogenase (LDH) release from rat renal cortical slices at 0.05 mM or greater. The purpose of this study was to examine the ability of antioxidants, cytochrome P450 (CYP) and flavin adenine dinucleotide monooxygenase (FMO) activity modulators, indomethacin, glutathione and inhibitors of glutathione conjugate metabolism to attenuate ADCP cytotoxicity in vitro. Renal cortical slices prepared from untreated male Fischer 344 rats (N=4/group) were preincubated at 37 degrees C under a 100% oxygen atmosphere with an inhibitor or vehicle for 5-30 min. ADCP (0.05-0.5mM) or vehicle was added and incubations continued for 120 min. At the end of the incubation period, LDH release was measured as an index of nephrotoxicity. ADCP cytotoxicity was partially attenuated by ascorbate (1.0 or 2.0mM), but not by N,N'-diphenyl-p-phenylenediamine (DPPD), alpha-tocopherol or deferoxamine. Inhibitors of CYP (metyrapone, piperonyl butoxide and isoniazid) and FMO activity modulators (methimazole, N-octylamine) had no effect on ADCP cytotoxicity. Indomethacin or glutathione 1.0mM completely and partially blocked ADCP 0.1 and 0.5mM cytotoxicity, respectively. N-acetylcysteine, AOAA (an inhibitor of cysteine conjugate beta-lyase) and probenecid (an organic anion transport inhibitor), but not AT-125 (an inhibitor of gamma-glutamyl transferase), partially attenuated ADCP 0.1mM cytotoxicity. Overall, these results suggest that reactive metabolites may be produced from ADCP primarily via a co-oxidation-mediated mechanism. The difference in the ability of ascorbate and glutathione to attenuate ADCP-induced cytotoxicity in vitro in kidney cells could indicate that alkylation via the reactive benzoquinoneimine metabolite might be responsible for cytotoxicity rather than a free radical-mediated mechanism.

Final report on the safety assessment of 6-Amino-m-Cresol, 6-Amino-o-Cresol, 4-Amino-m-Cresol, 5-Amino-4-Chloro-o-Cresol, 5-Amino-6-Chloro-o-Cresol, and 4-Chloro-2-Aminophenol

Each of these ingredients function as hair colorants. 5-Amino-4-Chloro-o-Cresol and 5-Amino-6-Chloro-o-Cresol are identified as oxidative hair dyes, that is, they are combined with an oxidizing agent before being applied to the hair. 6-Amino-m-Cresol, 6-Amino-o-Cresol, 4-Amino-m-Cresol, and 5-Amino-4-Chloro-o-Cresol are used in oxidative hair dyes, but it is not known if they are also used in nonoxidative (semipermanent) hair dyes. No toxicologically significant impurities are present with these two ingredients. To supplement the safety test data on these ingredients, available data on related ingredients (4-amino-2-hydroxytoluene and p-,m-, and o-aminophenol) previously found safe as used by the Cosmetic Ingredient Review (CIR) Expert Panel were summarized. 5-Amino-4-Chloro-o-Cresol and 5-Amino-6-Chloro-o-Cresol do not absorb significant ultraviolet radiation in the UVB region and none in the UVA region, although 4-Amino-m-Cresol had a symmetrical UV absorption peak at 300 nm. Percutaneous penetration of 5-Amino-4-Chloro-o-Cresol and 5-Amino-6-Chloro-o-Cresol alone was significant, but when combined with oxidative developer, skin absorption was extremely low. Both of these dyes are excreted rapidly via the urine. Repeated exposure of animal skin to 5-Amino-4-Chloro-o-Cresol and 5-Amino-6-Chloro-o-Cresol failed to produce any cumulative irritation and single exposures up to 10%were not irritating to animal skin. 5-Amino-4-Chloro-o-Cresol and 5-Amino-6-Chloro-o-Cresol combined with oxidizer were not sensitizers in guinea pig maximization tests. Ocular irritation resulted from exposure of animals to undiluted 5-Amino-4-Chloro-o-Cresol, but not to a 5%solution. Only minor irritation was observed with 5%5-Amino-6-Chloro-o-Cresol. Subchronic toxicity testing in animals using 5-Amino-4-Chloro-o-Cresol, 5-Amino-6-Chloro-o-Cresol, and 4-Amino-m-Cresol did not yield any adverse reactions. 6-Amino-m-Cresol and 4-Amino-m-Cresol were generally not mutagenic in in vitro and in vivo tests. Exposure to 5-Amino-4-Chloro-o-Cresol, 5-Amino-6-Chloro-o-Cresol, 6-Amino-m-Cresol and 4-Amino-m-Cresol from cosmetics were several orders of magnitude below developmental toxicity no-observed-adverse effect levels (NOAELs). Although irritation data on several ingredients are absent, products containing these ingredients must include a caution statement and patch test instructions for determining whether the product causes skin irritation. The Expert Panel expects that following this procedure would identify individuals who would have an adverse reaction and allow them to avoid significant exposures. These compounds, when tested alone, are moderate skin sensitizers, but when combined with the developer, these ingredients are not sensitizers in animal tests. This information, coupled with the available animal test data, supports the safety of these ingredients in oxidative hair dyes. In the absence of systemic toxicity data, however, the available data are insufficient to support the safety of 6-Amino-o-Cresol and 4-Chloro-2-Aminophenol in semipermanent hair dyes. The types of data required for these two ingredients for this use include (1) physical and chemical properties, including the octanol/water partition coefficient; (2) impurities data, especially regarding the presence of m-cresol, other organic molecules, and heavy metals; (3) data demonstrating that the metabolism is similar to that of 4-amino-2-hydroxytoluene and/or p-,m-, and o-aminophenol, or 28-day dermal toxicity with histopathology, dermal reproductive toxicity data, and an in vitro genotoxicity study for 6-Amino-o-Cresol and one genotoxicity study in a mammalian system; if positive, a 2-year dermal carcinogenicity study using National Toxicology Program methods may be needed.