Testicular toxicity of 2-methoxyacetaldehyde, a possible metabolite of ethylene glycol monomethyl ether, in the rat

Therapeutic effects of thymoquinone or capsaicin on acrylamide-induced reproductive toxicity in rats mediated by their effect on oxidative stress, inflammation, and tight junction integrity

In the field of environmental toxicology, endocrine-disrupting effects have become a major concern. The present research set out to investigate the possible reproductive toxicity of acrylamide. The research was also expanded to explore the protective effects of two nutraceuticals, thymoquinone (TQ) and capsaicin, against acrylamide-induced reproductive toxicity. Six groups of sixty male albino rats were created. Group 1 was used as a control. Rats were administered a daily dose of acrylamide and acted as the model in Group 2. TQ was provided to rats once a day in Group 3. Capsaicin was administered to rats once a day in Group 4. TQ was given once daily to rats exposed to acrylamide in Group 5. Rats were given capsaicin once a day for eight weeks after being exposed to acrylamide in Group 6. Acrylamide induced oxidative stress, testicular NF-κB/p65 expression, and down-regulated the expression of occludin, all of which can contribute to its testicular toxicity, while TQ or capsaicin removes all of these toxicity signs. TQ and capsaicin have shown efficacy in alleviating all of the acrylamide's toxic insults in the current reproductive toxicity model. Both nutraceuticals upregulated the expression of occludin in testicular tissue and restored tight junction integrity, in addition to their well-known antioxidant and anti-inflammatory effects, which were confirmed in this study.

The influence of genetic polymorphisms on population variability in six xenobiotic-metabolizing enzymes

This review provides variability statistics for polymorphic enzymes that are involved in the metabolism of xenobiotics. Six enzymes were evaluated: cytochrome P-450 (CYP) 2D6, CYP2E1, aldehyde dehydrogenase-2 (ALDH2), paraoxonase (PON1), glutathione transferases (GSTM1, GSTT1, and GSTP1), and N-acetyltransferases (NAT1 and NAT2). The polymorphisms were characterized with respect to (1) number and type of variants, (2) effects of polymorphisms on enzyme function, and (3) frequency of genotypes within specified human populations. This information was incorporated into Monte Carlo simulations to predict the population distribution and describe interindividual variability in enzyme activity. The results were assessed in terms of (1) role of these enzymes in toxicant activation and clearance, (2) molecular epidemiology evidence of health risk, and (3) comparing enzyme variability to that commonly assumed for pharmacokinetics. Overall, the Monte Carlo simulations indicated a large degree of interindividual variability in enzyme function, in some cases characterized by multimodal distributions. This study illustrates that polymorphic metabolizing systems are potentially important sources of pharmacokinetic variability, but there are a number of other factors including blood flow to liver and compensating pathways for clearance that affect how a specific polymorphism will alter internal dose and toxicity. This is best evaluated with the aid of physiologically based pharmacokinetic (PBPK) modeling. The population distribution of enzyme activity presented in this series of articles serves as inputs to such PBPK modeling analyses.

Population distribution of aldehyde dehydrogenase-2 genetic polymorphism: implications for risk assessment

The role of genetic polymorphisms in modulating xenobiotic metabolism and susceptibility to cancer and other health effects has been suggested in numerous studies. However, risk assessments have generally not used this information to characterize population variability or adjust risks for susceptible subgroups. This paper focuses upon the aldehyde dehydrogenase-2 (ALDH2) system because it exemplifies the pivotal role genetic polymorphisms can play in determining enzyme function and susceptibility. Allelic variants in ALDH2 cause decreased ability to clear acetaldehyde and other aldehyde substrates, with homozygous variants (ALDH2*2/2) having no activity and heterozygotes (ALDH2*1/2) having intermediate activity relative to the predominant wild type (ALDH2*1/1). These polymorphisms are associated with increased buildup of acetaldehyde following ethanol ingestion and increased immediate symptoms (flushing syndrome) and long-term cancer risks. We have used Monte Carlo simulation to characterize the population distribution of ALDH2 allelic variants and inter-individual variability in aldehyde internal dose. The nonfunctional allele is rare in most populations, but is common in Asians such that 40% are heterozygotes and 5% are homozygote variants. The ratio of the 95th or 99th percentiles of the Asian population compared to the median of the U.S. population is 14- to 26-fold, a variability factor that is larger than the default pharmacokinetic uncertainty factor (3.2-fold) commonly used in risk assessment. Approaches are described for using ALDH2 population distributions in physiologically based pharmacokinetic-Monte Carlo refinements of risk assessments for xenobiotics which are metabolized to aldehyde intermediates (e.g., ethanol, toluene, ethylene glycol monomethyl ether).

Aldehyde dehydrogenase (ALDH) 2 associates with oxidation of methoxyacetaldehyde; in vitro analysis with liver subcellular fraction derived from human and Aldh2 gene targeting mouse

A principal pathway of 2-methoxyethanol (ME) metabolism is to the toxic oxidative product, methoxyacetaldehyde (MALD). To assess the role of aldehyde dehydrogenase (ALDH) in MALD metabolism, in vitro MALD oxidation was examined with liver subcellular fractions from Japanese subjects who carried three different ALDH2 genotypes and Aldh2 knockout mice, which were generated in this study. The activity was distributed in mitochondrial fractions of ALDH2*1/*1 and wild type (Aldh2+/+) mice but not ALDH2*1/*2, *2/*2 subjects or Aldh2 homozygous mutant (Aldh2-/-) mice. These data suggest that ALDH2 is a key enzyme for MALD oxidation and ME susceptibility may be influenced by the ALDH2 genotype.

Assessment of the U.S. Environmental Protection Agency methods for identification of hazards to developing organisms, Part I: The reproduction and fertility testing guidelines

BACKGROUND

Successful reproduction depends on the coordination of many processes, particularly the normal development and subsequent maturation of the sexual organs. The Food Quality Protection Act of 1996 mandates that the U.S. Environmental Protection Agency must protect infants and children from the effects of toxins, including those that affect the reproductive system. Therefore, the Agency finds itself at a critical juncture to make sure that the methods it requires for toxicity testing, the Health Effects Test Guidelines or Series 870 Guidelines, are adequate to determine possible toxicity to children.

METHODS AND RESULTS

We found that two testing protocols included in the core guidelines assess toxicological effects on developing animals. This article aims to provide a detailed analysis of the protocols included in the Reproduction and Fertility Effects Test Guideline. An accompanying article assesses the Developmental Toxicity Testing Guideline. We conducted this analysis on the basis of whether the test would yield the information needed to adequately determine risk to infants and children.

CONCLUSIONS

Our analysis concludes that given the limitations inherent in testing for reproduction and fertility effects during development, it is necessary to include a safety factor during risk assessment of chemicals. This action will fulfill the mandate expressed in the FQPA to protect infants and children from environmental hazards.

Induction of deletion mutations by methoxyacetaldehyde in Chinese hamster ovary (CHO)-AS52 cells

We have reported previously that methoxyacetaldehyde (MALD), a metabolite of 2-methoxyethanol, induces gpt gene mutations in Chinese hamster ovary (CHO)-AS52 cells but not hprt gene mutations in the standard CHO-K1-BH4 cells. In addition, MALD induces chromosome aberrations in both CHO cell lines. The data presented suggest that MALD induces deletion-type mutations. In this study, we analyzed MALD-induced CHO-AS52 mutants for deletion-type mutations using the nested-polymerase chain reaction (nested-PCR) assay. Spontaneous CHO-AS52 mutants are used as untreated control. Ethylnitrosourea (ENU)-induced CHO-AS52 mutants are used as negative control for multilocus deletions since ENU is a potent inducer of point mutations. The results show that the frequency of MALD-induced mutants containing total deletion of the gpt gene is 42.4% which is 2.3-fold higher than that from spontaneous mutants (18.6%). The frequency of ENU-induced deletion mutation is 3%. The data substantiate our hypothesis that MALD induces major deletion mutations.

Gaschromatographic determination of butoxyacetic acid after hydrolysis of conjugated metabolites in urine from workers exposed to 2-butoxyethanol

For the gaschromatographic determination of total butoxyacetic acid (BAA), i.e., free plus conjugated BAA in urine, we studied the acid hydrolysis condition to cleave the conjugate. The optimum condition for hydrolysis was chosen to be 60 min boiling of the mixture of 1 ml twofold diluted urine and 1.2 ml hydrochloric acid. For the biological monitoring of workers exposed to 2-butoxyethanol (BE), we applied our acid hydrolysis method to the urine from 6 workers exposed to the solvent for 7 days and determined total BAA as well as free BAA and conjugated BAA, which was calculated as the difference between the concentrations of free and conjugated BAA. The percentages of conjugated BAA vs. total BAA varied from 44.4% to 92.2% (mean value 71.1%) among 6 individual workers over 7 days and decreased gradually over the consecutive work days. In the latter half of the work week, free BAA comparatively accounted for the larger portion of urinary BAA. Significant correlations were found between urinary BAA concentrations and BE levels in the breathing-zone air (TWA). The correlation coefficients of urinary concentrations of total or conjugated BAA vs. BE levels was higher than that of free BAA concentrations vs. BE levels. Hence, the determination of total BAA in urine is a suitable test for the biological monitoring of BE exposure, because of the simplicity in procedures and the good agreement with BE exposure levels.

Cytogenetic effects of 2-methoxyethanol and its metabolite, methoxyacetaldehyde, in mammalian cells in vitro

Glycol ethers such as 2-methoxyethanol (2-ME) are reproductive toxins. The genotoxicity of 2-ME, especially its metabolites: methoxyacetaldehyde (MALD) and methoxyacetic acid (MAA), is not adequately investigated yet. We have shown previously that MALD induced mutation in the bacterial gpt gene which is inserted in an autosome of CHO-AS52 cell line but not in the hprt gene on the X chromosome of CHO-K1-BH4 cell line. These data suggest that MALD induces major deletion-type mutation. If this prediction is correct we would expect to observe that MALD is an efficient inducer of chromosome aberrations in both CHO cell lines. We have conducted a cytogenetic study using both CHO cell lines and human lymphocytes to investigate this phenomenon. Our results show that human lymphocytes treated with 10-30 mM MALD for 1 h or 0.05-0.5 mM MALD for 24 h induced significant dose-dependent increase of sister-chromatid exchanges (SCE) (p < 0.05). It also induced significant dose-dependent increase (p < 0.05) of chromosome aberrations in human lymphocytes (10-40 mM treated for 1 h, or 0.05-2.5 mM for 24 h) and in both CHO cell lines (1.25-20 mM for 3 h). Treatment of these cells with the parent compound, 2-ME did not induce chromosome aberrations nor SCE unless very high doses of the chemical were used. In conclusion, these results indicate that MALD is clastogenic to different cell types therefore it is potentially carcinogenic. The genotoxic effects of 2-ME in humans will be dependent upon the metabolic capability of individuals to bioactivate 2-ME to MALD.

Determination of urinary alkoxyacetic acids by a rapid and simple method for biological monitoring of workers exposed to glycol ethers and their acetates

In control subjects and workers exposed to glycol ethers and their acetates, we determined the urinary metabolites (three alkoxyacetic acids) by a simple and rapid method. Levels of urinary metabolites were significantly higher in the solvent workers than in the nonexposed subjects. The exposure levels measured by personal monitoring of breathing zone air were far below the threshold limit value. The present results indicate that determination of urinary alkoxyacetic acids by the practical method used here is useful for evaluating excessive exposure to solvents.

Exposure to ethylene glycol ethers and spermatogenic disorders in man: a case-control study

A case-control study was conducted among first time patients at a clinic for reproductive disorders. The study group consisted of 1019 cases, defined as patients diagnosed infertile or subfertile on the basis of a spermiogram and 475 controls who were diagnosed as normally fertile by the same procedure. Possible exposure to ethylene glycol ethers was assessed by the presence of the urinary metabolites methoxyacetic acid (MAA) and ethoxyacetic acid (EAA) respectively for 2-methoxyethanol and 2-ethoxyethanol or their acetates. In total, EAA was detected in 39 cases and six controls, with a highly significant odds ratio of 3.11 (p = 0.004). On the other hand, MAA was only found in one case and two controls. The presence of EAA in urine proved to be strongly associated with exposure to preparations containing solvents, especially paint products, and with some groups of occupations, the most important of which were also directly or possibly connected with paint products. The absence of a significant correlation between the concentration of urinary EAA and the various measures of sperm quality could be explained by the expected latent period between exposure and observed effects. Other temporal aspects of the relation between exposure as judged from the presence of urinary EAA and diagnosis are also discussed.

Mutagenicity and cytotoxicity of 2-methoxyethanol and its metabolites in Chinese hamster cells (the CHO/HPRT and AS52/GPT assays)

2-Methoxyethanol (ethylene glycol monomethyl ether) (EGME), is one of the most commonly used solvents for industrial and consumer products. Although the solvent has been shown to be a reproductive toxin the genotoxic activities of EGME especially its metabolites, have not been adequately investigated. The mutagenicity and cytotoxicity of EGME and its major metabolites, methoxyacetaldehyde (MALD) and methoxyacetic acid (MAA) in Chinese hamster ovary (CHO) cells were therefore examined by us. We have determined the mutagenicity of these compounds at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in CHO-K1-BH4 cells (CHO/HPRT assay) and the xanthine-guanine phosphoribosyl transferase (gpt) locus in CHO AS52 cells (AS52/GPT assay). The results show that these chemicals are not mutagenic to the hprt locus in CHO-K1-BH4 cells either with or without rat liver S9 mix as the metabolic activating system. With AS52 cells, only MALD is mutagenic in the absence of S9. It induced a dose-dependent mutagenic response. A dose-dependent cytotoxicity was induced by all compounds in both cell lines. MALD is the most and EGME is the least cytotoxic compounds. Our study shows that a metabolite of EGME, MALD, is highly cytotoxic and likely induces deletion-type mutations in AS52 cells. The genotoxic effect of EGME is, therefore, dependent upon its metabolism and its detection is dependent upon the assays used.

Testicular effects of bis(2-methoxyethyl) ether in the adult male rat

The onset of testicular pathology in the rat and possible recovery over an 8-week period were evaluated after the administration of up to 20 daily oral doses of bis(2-methoxyethyl) ether (diglyme) at 5.1 mmol/kg bw (684 mg/kg bw). Primary and secondary spermatocyte degeneration and spermatidic giant cells were observed after six to eight treatments. In addition, the testes-to-body weight ratio was significantly reduced by the tenth day of treatment and continued to be depressed eight weeks after discontinuation of the treatment. Testicular LDH-X activity, a pachytene spermatocyte marker enzyme, was significantly decreased in animals by the eighteenth day of treatment with diglyme.