The effects of mixtures of dichloroacetate and trichloroacetate on induction of oxidative stress in livers of mice after subchronic exposure

Haloacetamides disinfection by-products, a potential risk factor for nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder characterized by abnormal lipid deposition, with oxidative stress being a risk factor in its onset and progression. Haloacetamides (HAcAms), as unregulated disinfection by-products in drinking water, may alter the incidence and severity of NAFLD through the production of oxidative stress. We explored whether HAcAms at 1, 10, and 100-fold concentrations in Shanghai drinking water perturbed lipid metabolism in normal human liver LO-2 cells. CRISPR/Cas9 was used to construct a LO-2 line with stable NRF2 knock-down (NRF2-KD) to investigate the mechanism underlying abnormal lipid accumulation and hepatocyte damage caused by mixed exposure to HAcAms. At 100-fold real-world concentration, HAcAms caused lipid deposition and increased triglyceride accumulation in LO-2 cells, consistent with altered de novo lipogenesis. Differences in responses to HAcAms in normal and NRF2-KD LO-2 cells indicated that HAcAms caused hepatocyte lipid deposition and triglyceride accumulation by activation of the NRF2/PPARγ pathway and aggravated liver cell toxicity by inducing ferroptosis. These results indicate that HAcAms are important risk factors for NAFLD. Further observations and verifications of the effect of HAcAms on NAFLD in the population are warranted in the future.

Dichloroacetate for Cancer Treatment: Some Facts and Many Doubts

Rarely has a chemical elicited as much controversy as dichloroacetate (DCA). DCA was initially considered a dangerous toxic industrial waste product, then a potential treatment for lactic acidosis. However, the main controversies started in 2008 when DCA was found to have anti-cancer effects on experimental animals. These publications showed contradictory results in vivo and in vitro such that a thorough consideration of this compound's in cancer is merited. Despite 50 years of experimentation, DCA's future in therapeutics is uncertain. Without adequate clinical trials and health authorities' approval, DCA has been introduced in off-label cancer treatments in alternative medicine clinics in Canada, Germany, and other European countries. The lack of well-planned clinical trials and its use by people without medical training has discouraged consideration by the scientific community. There are few thorough clinical studies of DCA, and many publications are individual case reports. Case reports of DCA's benefits against cancer have been increasing recently. Furthermore, it has been shown that DCA synergizes with conventional treatments and other repurposable drugs. Beyond the classic DCA target, pyruvate dehydrogenase kinase, new target molecules have also been recently discovered. These findings have renewed interest in DCA. This paper explores whether existing evidence justifies further research on DCA for cancer treatment and it explores the role DCA may play in it.

Associations between Urinary Concentrations of Disinfection Byproducts and in Vitro Fertilization Outcomes: A Prospective Cohort Study in China

BACKGROUND

Experimental studies show that disinfection byproducts (DBPs) can inhibit oocyte maturation, decrease fertilization capacity, and impair embryo development, but human evidence is lacking.

OBJECTIVES

We aimed to evaluate the associations between exposure to drinking water DBPs and in vitro fertilization (IVF) outcomes.

METHODS

The study included 1,048 women undergoing assisted reproductive technology (ART) treatment between December 2018 and January 2020 from a prospective cohort study, the Tongji Reproductive and Environmental study in Wuhan, China. Exposure to DBPs was assessed by dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in up to four urine samples, which were collected on the day of both enrollment and oocyte retrieval. Multivariable generalized linear mixed models, accounting for multiple IVF cycles per woman, were applied to evaluate the associations between urinary biomarkers of DBP exposures and IVF outcomes. Stratified analyses were used to explore the potential effect modifiers.

RESULTS

The included 1,048 women underwent 1,136 IVF cycles, with 960 (91.6%), 84 (8.0%), and 4 (0.4%) women contributing one cycle, two cycles, and three cycles, respectively. We found that elevated quartiles of urinary DCAA and TCAA concentrations were associated with reduced numbers of total oocytes and metaphase II oocytes and that urinary DCAA concentrations with a lower proportion of best-quality embryos (all p for trends < 0.05 ). Moreover, elevated quartiles of urinary DCAA concentrations were associated with decreased proportions of successful implantation, clinical pregnancy, and live birth (14%, 15%, and 15% decreases in adjusted means comparing the extreme quartiles, respectively; all p for trends < 0.05 ). Stratification analyses showed that the inverse associations of urinary TCAA concentrations with multiple IVF outcomes were stronger among women ≥ 30 y of age (p for interactions < 0.05 ).

DISCUSSION

Exposure to drinking water DBPs was inversely associated with some IVF outcomes among women undergoing ART treatment. Further study is necessary to confirm our findings. https://doi.org/10.1289/EHP12447.

Associations of Urinary Trichloroacetic Acid Concentrations with Spermatozoa Apoptosis and DNA Damage in a Chinese Population

Exposure to trichloroacetic acid (TCAA) has been associated with impaired semen quality; however, its association with spermatozoa apoptosis and DNA damage remains unclear. We, therefore, collected single semen and repeated urine samples from male partners of couples attending a reproductive center, which were measured for spermatozoa apoptosis and DNA damage parameters and TCAA concentrations, respectively. Multivariable linear regression models were used to explore the associations between urinary TCAA concentrations and spermatozoa apoptosis (n = 462) and DNA damage parameters (n = 512). After adjusting for potential confounders, positive dose-response relationships were found between urinary TCAA concentrations and percentage of tail DNA (tail%) and tail-distributed moment (TDM) (both p for trend <0.10). Compared with men in the lowest tertile of urinary TCAA concentrations, men in the highest tertile had a greater tail% and TDM of 6.2% (95% CI: 0.7, 12.2%) and 8.9% (95% CI: -1.9, 20.5%), respectively. Urinary TCAA concentrations were unrelated to spermatozoa apoptosis parameters in a dose-response manner. However, urinary TCAA concentrations were positively associated with the percentage of Annexin V⁺/PI^- spermatozoa (apoptotic cells), when urinary TCAA concentrations were modeled as continuous variables. Our results suggest that exposure to TCAA at concentrations in real-world scenarios may be associated with spermatozoa apoptosis and DNA damage.

Oxidative stress and EROD activity in Caco-2 cells upon exposure to chlorinated hydrophobic organic compounds from drinking water reservoirs

Our previous studies showed hydrophobic organic compounds (HOCs) in the sediments of drinking water reservoirs caused DNA damage in human cells (Caco-2) after chlorination. However, the main mechanisms remained unclear. This study compared oxidative damage and EROD activity in Caco-2 cells upon exposure to chlorinated HOCs, and the role of antioxidants (catalase, vitamin C and epigallocatechin gallate (EGCG)) in reducing the toxicities was examined. The result showed that chlorinated HOCs induced a 4-fold increase in production of reactive oxygen species (ROS) compared with HOCs. Antioxidants supplement significantly reduced ROS yields and DNA peroxidation. HOCs with relatively higher TEQ_bio were greatly reduced (about 98%) after chlorination, indicating dioxin-like toxicity is not the main factor inducing oxidative damage by chlorinated HOCs. Yet, ROS and the associated oxidative damage seem to be more responsible for causing DNA damage in the cells. Antioxidants including catalase, Vitamin C and EGCG showed protective effect against chlorination.

Synergistic cytotoxicity of bromoacetic acid and three emerging bromophenolic disinfection byproducts against human intestinal and neuronal cells

Halogenated disinfection byproducts (halo-DBPs) are drinking water contaminants of great public health concern. Nine haloaliphatic DBPs have been regulated by the U.S. Environmental Protection Agency and various halophenolic compounds have been identified as emerging DBPs. In this study, we evaluated the cytotoxic interactions of the regulated bromoacetic acid and three emerging bromophenolic DBPs, i.e., 2,4,6-tribromophenol, 3,5-dibromo-4-hydroxybenzoic acid, and 3,5-dibromo-4-hydroxybenzaldehyde. Cytotoxicity was measured for each DBP individually as well as each of their mixtures using in vitro human epithelial colorectal adenocarcinoma (Caco-2) and neuroblastoma (SH-SY5Y) cells. Concentration addition (CA) model and isobolographic analysis were employed to characterize the interactions among the DBPs. Our results show that the cytotoxicity of four bromo-DBPs against both cell-types followed the descending rank order of bromoacetic acid > 2,4,6-tribromophenol > 3,5-dibromo-4-hydroxybenzaldehyde > 3,5-dibromo-4-hydroxybenzoic acid. Compared with the toxicity data in literature, our finding that bromoacetic acid showed higher cytotoxicity than bromophenolic DBPs was consistent with the results from Chinese hamster ovary cells (a commonly used in vitro model of DBP toxicological studies); but different from the results obtained from in vivo biological models. Significantly, with CA model prediction, we found that mixtures of four bromo-DBPs exhibited synergistic cytotoxic effects on both human cell types. Isobolographic analysis of binary DBP mixtures revealed that, for Caco-2 cells, bromoacetic acid, 2,4,6-tribromophenol, and 3,5-dibromo-4-hydroxybenzoic acid induced synergism; for SH-SY5Y cells, bromoacetic acid induced synergism with all three bromophenolic DBPs. The production of reactive oxidative species (ROS) induced by DBP mixtures could be an important reason for the synergistic cytotoxicity.

Environmental toxicant-induced maladaptive mitochondrial changes: A potential unifying mechanism in fatty liver disease?

Occupational and environmental exposures to industrial chemicals are well known to cause hepatotoxicity and liver injury. However, despite extensive evidence showing that exposure can lead to disease, current research approaches and regulatory policies fail to address the possibility that subtle changes caused by low level exposure to chemicals may also enhance preexisting conditions. In recent years, the conceptual understanding of the contribution of environmental chemicals to liver disease has progressed significantly. Mitochondria are often target of toxicity of environmental toxicants resulting in multisystem disorders involving different cells, tissues, and organs. Here, we review persistent maladaptive changes to mitochondria in response to environmental toxicant exposure as a mechanism of hepatotoxicity. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of toxicant-induced liver disease, rational targeted therapy can be developed to better predict risk, as well as to treat or prevent this disease.

The role of oxidative stress in association between disinfection by-products exposure and semen quality: A mediation analysis among men from an infertility clinic

Toxicological and epidemiologic evidence has suggested that exposure to disinfection by-products (DBPs) impairs semen quality, while the underlying biological mechanisms remain unclear. This study aimed to examine the mediating role of oxidative stress in association between DBP exposure and semen quality. We measured a urinary biomarker of DBP exposure [trichloroacetic acid (TCAA)] and three urinary biomarkers of oxidative stress [8-hydroxy-2-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F2_α (8-isoPGF2_α) and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA)] among men from an infertility clinic (n = 299). The associations of oxidative stress biomarkers with urinary TCAA and semen quality were evaluated using multivariable linear regression models, and the mediating role of oxidative stress biomarkers was assessed by a mediation analysis. Urinary TCAA was positively associated with urinary 8-OHdG and 8-isoPGF2_α in a dose-response manner (both P for trend < 0.001). Significantly inverse dose-response associations were observed between urinary 8-isoPGF2_α and sperm concentration and between urinary 8-OHdG and sperm motility (both P for trend < 0.05). The mediation analysis indicated a significant indirect effect of urinary 8-isoPGF2_α in the association between urinary TCAA and decreased sperm concentration (P = 0.01). Our results suggest that lipid peroxidation may be an intermediate mechanism by which DBP exposure impairs semen quality.

Assessing Additivity of Cytotoxicity Associated with Disinfection Byproducts in Potable Reuse and Conventional Drinking Waters

Recent studies used the sum of the measured concentrations of individual disinfection byproducts (DBPs) weighted by their Chinese hamster ovary (CHO) cell cytotoxicity LC₅₀ values to estimate the DBP-associated cytotoxicity of disinfected waters. This approach assumed that cytotoxicity was additive rather than synergistic or antagonistic. In this study, we evaluated whether this assumption was valid for mixtures containing DBPs at the concentration ratios measured in authentic disinfected waters. We examined the CHO cell cytotoxicity of defined DBP mixtures based on the concentrations of 43 regulated and unregulated DBPs measured in eight drinking and potable reuse waters. The hypothesis for additivity was supported using three experimental approaches. First, we demonstrated that the calculated additive toxicity (CAT) and bioassay-based calculated additive toxicity (BCAT) of the DBP mixtures agree within 12% on a median basis. We also found an additive toxicity response (CAT ≈ BCAT) between the regulated and unregulated DBP classes. Finally, the empirical biological cytotoxicity of the DBP subset mixtures, independent of the calculated toxicity, was additive. These results support the validity of using the sum of cytotoxic potency-weighted DBP concentrations as an estimate of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters.

Blood and urinary biomarkers of prenatal exposure to disinfection byproducts and oxidative stress: A repeated measurement analysis

BACKGROUND

Toxicological studies have demonstrated that disinfection by-products (DBPs) can induce oxidative stress, a proposed mechanism that is relevant to adverse birth outcomes.

OBJECTIVE

To examine the associations of blood trihalomethanes (THMs) and urinary haloacetic acids (HAAs) with urinary biomarkers of oxidative stress among pregnant women.

METHODS

From 2015 to 2017, a total of 4150 blood and 4232 urine samples were collected from 1748 Chinese women during pregnancy. We determined concentrations of 4 blood THMs [chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)] and 2 urinary HAAs [dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA)]. The summary measures of exposure for brominated THMs (Br-THMs; a molar sum of BDCM, DBCM, and TBM) and total THMs (TTHMs; a molar sum of TCM and Br-THMs) were also calculated. Associations of categorical (i.e., tertiles) and continuous measures of DBPs with urinary concentrations of oxidative stress (OS) biomarkers, 8-hydroxy-2-deoxyguanosine (8-OHdG), 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), and 8-iso-prostaglandin F_2α (8-isoPGF_2α), were assessed using linear mixed regression models.

RESULTS

After adjusting for relevant confounding factors, we observed positive dose-response relationships between blood Br-THM tertiles and urinary HNE-MA (P for trend < 0.001). We also found positive associations between tertiles of blood TCM and TTHMs and urinary 8-OHdG and HNE-MA (all P for trend < 0.05). Urinary HAAs were also positively associated with 8-OHdG, HNE-MA, and 8-isoPGF_2α in a dose-response manner (all P for trend < 0.001). These associations were further confirmed when we modeled DBP exposures as continuous variables in linear mixed regression models, as well as in penalized regression splines based on generalized additive mixed models.

CONCLUSIONS

Exposure to DBPs during pregnancy may increase maternal OS status.

In vitro toxicity and molecular interacting mechanisms of chloroacetic acid to catalase

Chloroacetic acid (CAA), one of typical disinfection by-products (DBPs), has attracted considerable concerns for its biological safety. Antioxidant enzyme catalase (CAT) plays a crucial part in the regulation of redox state balance. Herein, CAA was used to test its adverse effects on CAT and explore the underlying mechanism. The cell viability of mouse primary hepatocytes decreased under CAA exposure. A bell-shaped response to CAA exposure was observed in intracellular CAT activity, whose change was partly influenced by molecular CAT activity. CAA binds to CAT mainly via van der Waals forces and hydrogen bonds with a stoichiometry of 9.2. The binding caused structural changes in CAT with the unfolding of polypeptide chains and the decrease of α-helical content. CAA interacts with the amino acid residues surrounding the active sites and substrate channel of CAT. These interactions result in the decrease of molecular CAT activity, which could be restored by high ionic strength. This study has provided a combined molecular and cellular tactics for studying the adverse effects of DBPs on biomarkers and the underlying mechanisms.

Mechanisms of Environmental Contributions to Fatty Liver Disease

PURPOSE

Fatty liver disease (FLD) affects over 25% of the global population and may lead to liver-related mortality due to cirrhosis and liver cancer. FLD caused by occupational and environmental chemical exposures is termed "toxicant-associated steatohepatitis" (TASH). The current review addresses the scientific progress made in the mechanistic understanding of TASH since its initial description in 2010.

RECENT FINDINGS

Recently discovered modes of actions for volatile organic compounds and persistent organic pollutants include the following: (i) the endocrine-, metabolism-, and signaling-disrupting chemical hypotheses; (ii) chemical-nutrient interactions and the "two-hit" hypothesis. These key hypotheses were then reviewed in the context of the steatosis adverse outcome pathway (AOP) proposed by the US Environmental Protection Agency. The conceptual understanding of the contribution of environmental exposures to FLD has progressed significantly. However, because this is a new research area, more studies including mechanistic human data are required to address current knowledge gaps.

Interaction of volatile organic compounds and underlying liver disease: a new paradigm for risk

Occupational and environmental exposures to industrial chemicals are known to cause hepatotoxicity and liver injury, in humans and in animal models. Historically, research has focused on severe acute liver injury (e.g. fulminant liver failure) or endstage diseases (e.g. cirrhosis and HCC). However, it has become recently recognized that toxicants can cause more subtle changes to the liver. For example, toxicant-associated steatohepatitis, characterized by hepatic steatosis, and inflammation, was recently recognized in an occupational cohort exposed to vinyl chloride. At high occupational levels, toxicants are sufficient to cause liver damage and disease even in healthy subjects with no comorbidities for liver injury. However, it is still largely unknown how exposure to toxicants initiate and possibly more importantly exacerbate liver disease, when combined with other factors, such as underlying non-alcoholic fatty liver disease caused by poor diet and/or obesity. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of toxicant-induced liver disease, rational targeted therapy can be developed to better predict risk, as well as to treat or prevent this disease. The purpose of this review is to summarize established and proposed mechanisms of volatile organic compound-induced liver injury and to highlight key signaling events known or hypothesized to mediate these effects.

Fatal Liver and Bone Marrow Toxicity by Combination Treatment of Dichloroacetate and Artesunate in a Glioblastoma Multiforme Patient: Case Report and Review of the Literature

A 52-year-old male patient was treated with standard radiochemotherapy with temozolomide for glioblastoma multiforme (GBM). After worsening of his clinical condition, further tumor-specific treatment was unlikely to be successful, and the patient seeked help from an alternative practitioner, who administered a combination of dichloroacetate (DCA) and artesunate (ART). A few days later, the patient showed clinical and laboratory signs of liver damage and bone marrow toxicity (leukopenia, thrombocytopenia). Despite successful restoration of laboratory parameters upon symptomatic treatment, the patient died 10 days after the infusion. DCA bears a well-documented hepatotoxic risk, while ART can be considered as safe concerning hepatotoxicity. Bone marrow toxicity can appear upon ART application as reduced reticulocyte counts and disturbed erythropoiesis. It can be assumed that the simultaneous use of both drugs caused liver injury and bone marrow toxicity. The compassionate use of DCA/ART combination therapy outside of clinical trials cannot be recommended for GBM treatment.

4-Hydroxynonenal: A Superior Oxidative Biomarker Compared to Malondialdehyde and Carbonyl Content Induced by Carbon Tetrachloride in Rats

Carbon tetrachloride (CCl4), a halogenated substance that generates free radical species during metabolism in vivo, induces hepatotoxicity, produces oxidative DNA damage, and increased levels of protein carbonyl, malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE). In this study, Sprague-Dawley rats received single or repeated ip injections of carbon tetrachloride (CCl4), and formation and persistence of carbonyls, MDA, and 4-HNE in plasma were measured using gas chromatography-mass spectrometry. After a single injection of 500 mg/kg CCl4 the in vivo half-lives of MDA and carbonyl content were 1.5 d and 2 d, respectively, while that of 4-HNE was approximately 10 d. Treatment with CCl4 (50, 100, 500, or 1000 mg/kg) dose-dependently increased these oxidative biomarkers in blood. However, formation of protein carbonyls and MDA was less sensitive than 4-HNE to CCl4. Levels of serum glutamic oxaloacetic transaminase (SGOT) and glutamic pyruvic transaminase (SGPT) (hepatotoxicity markers) rose with CCl4 doses. After a single injection (500 mg/kg), the peak level of SGOT was observed after 8 h but SGPT after 24 h. Overall, 4-HNE was more dose-sensitive and showed greater formation subchronically than other biomarkers. Multiple ip treatments with 300 mg CCl4 /kg (d 1, 3, 6, 10, 14, and 21) demonstrated that 4-HNE formation was highest (18-fold, peak/control) and subchronic up to d 21 (last treatment day), unlike other biomarkers. Data suggest that 4-HNE, MDA, and carbonyl content may be useful oxidative biomarkers for exposure to free radical generating halogenated compounds. However, 4-HNE appears to be a more sensitive and sustainable biomarker for toxicological and risk assessments.

Dichloroacetate and Trichloroacetate Toxicity in AML12 Cells: Role of Oxidative Stress

The toxicity of the drinking water disinfection by products dichloroacetate (DCA) and trichloroacetate (TCA) was studied in the alpha mouse liver (AML12) cells at concentrations ranging between 770 and 4100 ppm and at incubation times ranging from 24 to 72 h. Cellular viability, superoxide anion (SA) and lipid peroxidation (LP) production, as well as superoxide dismutase (SOD) activity were determined. DCA and TCA resulted in time- and concentration-dependent decreases in cellular viability, and also in significant increases in SA and LP production, and in SOD activity at specific concentrations and time points. The effective toxic concentrations of the compounds in these cells were found to be 10-fold higher than those producing similar effects in the mouse liver. It has been concluded that the AML12 is a good screening system to identify toxic concentrations of the halaocetates present in the drinking water that may need further in vivo testing.

Do Antioxidant Enzymes and Glutathione Play Roles in the Induction of Hepatic Oxidative Stress in Mice upon Subchronic Exposure to Mixtures of Dichloroacetate and Trichloroacetate?

Dichloroacetate (DCA) and trichloroacetate (TCA) are water chlorination byproducts, and their mixtures were previously found to induce additive to greater than additive effects on hepatic oxidative stress (OS) induction in mice after subchronic exposure. To investigate the roles of antioxidant enzymes and glutathione (GSH) in those effects, livers of B6C3F1 mice treated by gavage with 7.5, 15, or 30 mg DCA/kg/day, 12.5, 25, or 50 mg TCA/kg/day, and mixtures (Mix I, Mix II and Mix III) at DCA:TCA ratios corresponding to 7.5:12.5, 15:25 and 25:50 mg/kg/day, respectively, for 13 weeks. Livers were assayed for superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), as well as for GSH levels. In general, DCA suppressed SOD and GSH-Px activities and GSH levels but caused no changes in CAT activity; TCA increased SOD and CAT activities, suppressed GSH-Px activity, but did not change GSH levels; mixtures of DCA and TCA increased SOD and CAT activities and suppressed GSH-Px activity and GSH levels. In conclusion, antioxidant enzymes contribute to DCA-, TCA- and mixtures-induced OS, but not to changes from additive to greater than additive effects produced by different mixture compositions of the compounds. GSH on the hand may contribute to these changes.

Nephrotoxic potential and toxicokinetics of melamine combined with cyanuric acid in rats

To investigate the nephrotoxic potential of melamine (MEL) and cyanuric acid (CA) in male Sprague-Dawley rats, 7-d repeated-dose studies were performed. The experimental groups of MEL100 and CA100 were orally administered with MEL and CA at 100 mg/kg/d for 7 d, respectively. In groups dosed with MEL-CA mixtures, melamine and cyanuric acid (1:1) were simultaneously administered at 4, 20, or 100 mg/kg/d for 7 d (i.e., MEL-CA4, MEL-CA20, or MEL-CA100, respectively). Body weights were not markedly affected in MEL100, CA100, and MEL-CA4 groups, but significantly reduced in MEL-CA 20 and 100 rats. Most parameters determined in sera and tissues were not markedly altered in MEL100, CA100, and MEL-CA4-treated rodents. However, BUN, creatinine, total protein, and kidney weights were significantly increased in MEL-CA20- and MEL-CA100-treated animals. Renal histopathologic findings also revealed signs of toxicity, including tubular dilatation, crystal deposition, granulomatous tubulo-interstitial inflammation, and tubular necrosis with regeneration. Data suggested that the combination of MEL and CA might be responsible for observed nephrotoxicity that was not seen following individual exposure to either MEL or CA alone. Subsequently, the concentrations of MEL and CA were determined in serum, urine, and kidney tissues by using liquid chromatography-mass spectrometry. Toxicokinetic studies indicated that MEL or CA alone might be eliminated almost completely within 24 h after dosing showing no accumulation in kidney. However, the combined MEL-CA dose produced marked accumulation of chemicals in blood and kidneys. These results suggested that combined MEL and CA might produce renal toxicity due to significant chemical accumulation in kidney accompanied by low excretion.