ALDH2 polymorphism and biological monitoring of toluene

[Importance of an Aldehyde Dehydrogenase 2 Polymorphism in Preventive Medicine]

Unlike genetic alterations in other aldehyde dehydrogenase (ALDH) isozymes, a defective ALDH2 polymorphism (rs671), which is carried by almost half of East Asians, does not show a clear phenotype such as a shortened life span. However, impacts of a defective ALDH2 allele, ALDH2*2, on various disease risks have been reported. As ALDH2 is responsible for the detoxification of endogenous aldehydes, a negative effect of this polymorphism is predicted, but bidirectional effects have been actually observed and the mechanisms underlying such influences are often complex. One reason for this complexity may be the existence of compensatory aldehyde detoxification systems and the secondary effects of these systems. There are many issues to be addressed with regard to the ALDH2 polymorphism in the field of preventive medicine, including the following concerns. First, ALDH2 in the fetal stage plays a role in aldehyde detoxification; therefore, prenatal health effects of environmental aldehyde exposure are of concern for ALDH2*2-carrying fetuses. Second, ALDH2*2 carriers are at high risk of drinking-related cancers. However, their drinking habits result in less worsening of physiological findings, such as energy metabolism index and liver functions, compared with non-ALDH2*2 carriers, and therefore opportunities to detect excessive drinking can be lost. Third, personalized medicine such as personalized prescriptions for ALDH2*2 carriers will be required in the clinical setting, and accumulation of evidence is awaited. Lastly, since the ALDH2 polymorphism is not considered in workers' limits of exposure to aldehydes and their precursors, efforts to lower exposure levels beyond legal standards are required.

Significant association between decreased ALDH2 activity and increased sensitivity to genotoxic effects in workers occupationally exposed to styrene

ALDH2 is involved in the metabolism of styrene, a widely used industrial material, but no data are available regarding the influence of this enzyme on the metabolic fate as well as toxic effects of this chemical. In this study, we recruited 329 workers occupationally exposed to styrene and 152 unexposed controls. DNA strand breaks, DNA-base oxidation in leukocytes and urinary 8-hydroxydeoxyguanosine (8-OH-dG) were assayed as biomarkers to measure genotoxic effects. Meanwhile, we examined the genetic polymorphisms, including ALDH2, EXPH1, GSTM1, GSTT1 and CYP2E1, and also analyzed the levels of styrene exposure through detecting urinary styrene metabolites and styrene concentration in air. In terms of DNA damage, the three genotoxic biomarkers were significantly increased in exposed workers as compared with controls. And the styrene-exposed workers with inactive ALDH2 *2 allele were subjected to genotoxicity in a higher degree than those with ALDH2 *1/*1 genotype. Also, lower levels of urinary styrene metabolites (MA + PGA) were observed in styrene-exposed workers carrying ALDH2 *2 allele, suggesting slower metabolism of styrene. The polymorphisms of other enzymes showed less effect. These results suggested that styrene metabolism and styrene-induced genotoxicity could be particularly modified by ALDH2 polymorphisms. The important role of ALDH2 indicated that the accumulation of styrene glycoaldehyde, a possible genotoxic intermediate of styrene, could account for the genotoxicity observed, and should be taken as an increased risk of cancer.

Evaluation of genetic polymorphisms in patients with multiple chemical sensitivity

Objective

Multiple chemical sensitivity (MCS) is a chronic medical condition characterized by symptoms that the affect an individual’s response to low-level chemical exposure. In this study, we identified a chemical sensitive population (CSP) and investigated the effect of genetic polymorphisms on their risk of chemical sensitivity.

Methods

A quick environment exposure sensitivity (QEESI) questionnaire was used to survey 324 Japanese male workers whose DNA samples had been collected and stored. The following genes, which encode enzymes affecting the metabolic activation of a large number of xenobiotic compounds, were selected and analyzed in order to determine their influence on genetic predisposition to CSP: cytochrome P450 (CYP) 2E1, N-acetyl transferase (NAT) 2, glutathione S-transferase (GST) M1, GSTT1, GSTP1, low Km aldehyde dehydrogenase (ALDH2), and superoxide dismutase (SOD) 2.

Results

Significant case-control distributed differences were observed in SOD2 polymorphisms and allele frequency distribution in high chemical sensitive subjects. Both the significant adjusted OR of 4.30 (95% CI, 1.23–15.03) and 4.53 (95% CI, 1.52-13.51) were observed in SOD2 Ala/Ala and Val/Ala compared to Val/Val and in SOD2 Ala/Ala compared to Val/Ala compared to Val/Val genetic analysis in the high chemical sensitivity case-control study.

Conclusions

We observed that high chemical sensitive individuals diagnosed by using Japanese criteria as MCS patients were more significantly associated with SOD2 polymorphisms.

Modification of the relationship between urinary 8-OHdG and hippuric acid concentration by GSTM1, GSTT1, and ALDH2 genotypes

Urinary hippuric acid (HA) has been widely used as a biological marker of occupational exposure to toluene, although it is no longer valid for low levels of toluene exposure. Toluene exposure is known to induce oxidative DNA damage and the metabolism is affected by genetic polymorphisms of some metabolizing enzymes. Therefore, genetic polymorphisms of these metabolizing enzymes must be considered in the evaluation of oxidative stress caused by toluene exposure. We evaluated the relationship between urinary 8-hydroxydeoxyguanosine (8-OHdG), a marker of oxidative DNA damage, and urinary HA in individuals without occupational exposure to toluene and characterized the possible roles of GSTM1, GSTT1, and aldehyde dehydrogenase 2 (ALDH2) genotypes in the relationships between these markers. In this study, we enrolled 92 healthy Koreans. Urinary HA and 8-OHdG levels were measured and the correlations between them were statistically tested according to the GSTM1, GSTT1, and ALDH2 genotypes. HA did not significantly correlate with urinary 8-OHdG in overall subjects. However, the correlation between them showed a statistical significance in individuals with GSTM1-null, GSTT1-null, and ALDH2 *2/*2 genotypes (r = 0.766, p < 0.01). This study shows that the relationship between urinary HA and 8-OHdG concentration is modified by genetic polymorphisms of some metabolizing enzymes such as GSTM1, GSTT1, and ALDH2.

Increased frequencies of micronucleated reticulocytes and T-cell receptor mutation in Aldh2 knockout mice exposed to acetaldehyde

Aldehyde dehydrogenase-2 (ALDH2) metabolizes acetaldehyde produced from ethanol into acetate and plays a major role in the oxidation of acetaldehyde in vivo. About half of all Japanese people have inactive ALDH2. We generated homozygous Aldh2 null (Aldh2-/-) mice by gene targeting knockout as a model of ALDH2-deficient humans. To investigate the mutagenicity of acetaldehyde, a micronucleus assay and a T-cell receptor (TCR) gene mutation assay were performed in Aldh2-/- mice and wild-type (Aldh2 +/+) mice exposed to acetaldehyde. The mice were continuously exposed to 125 and 500 ppm of acetaldehyde vapor for 2 weeks. Another group was orally administered 100 mg/kg once a day for 2 weeks continuously. The mice were killed after 2 weeks of exposure to acetaldehyde, and the frequency of micronucleated reticulocytes was measured by flow cytometry. We also observed the incidence of TCR gene mutations in T-lymphocytes by measuring the variant CD3(-CD4+) expression by flow cytometry. The frequency of micronucleated reticulocytes induced by acetaldehyde was significantly increased in Aldh2 -/- mice, but not in Aldh2 +/+ mice. TCR mutant frequency was also associated with acetaldehyde exposure in Aldh2-/ - mice, especially after oral administration; however, it was not associated with acetaldehyde exposure in Aldh2 +/+ mice. In conclusion, Aldh2 -/- mice showed high sensitivity in the micronuclei and TCR mutation assays compared with Aldh2 +/+ mice after exposure to acetaldehyde.

[Review of sick house syndrome]

'Sick house syndrome' (SHS) is a health issue that closely resembles sick building syndrome (SBS) that had occurred in European countries. The aim of this review is to clarify the characteristics of SHS by reviewing previous reports rigorously. We propose the definition of SHS as "health impairments caused by indoor air pollution, regardless of the place, causative substance, or pathogenesis". Cases of SBS are reported to occur predominantly in offices and sometimes schools, whereas those of SHS are usually found in general dwellings. In many cases, SHS is caused by biologically and/or chemically polluted indoor air. Physical factors might affect the impairments of SHS in some cases. It is considered that symptoms of SHS develop through toxic, allergic and/or some unknown mechanisms. Psychological mechanisms might also affect the development of SHS. It is still unclear whether SBS and SHS are very close or identical clinical entities, mostly because a general agreement on a diagnostic standard for SHS has not been established. Previous research gradually clarified the etiology of SHS. Further advances in research, diagnosis, and treatment of SHS are warranted with the following measures. Firstly, a clinical diagnostic standard including both subjective and objective findings must be established. Secondly, a standard procedure for assessing indoor air contamination should be established. Lastly, as previous research indicated multiple causative factors for SHS, an interdisciplinary approach is needed to obtain the grand picture of the syndrome.

Urinary 8-hydoxydeoxyguanosine (8-OHdG) and plasma malondialdehyde (MDA) levels in Aldh2 knock-out mice under acetaldehyde exposure

To clarify the carcinogenicity of acetaldehyde when associated with ALDH (aldehyde dehydrogenase) 2 polymorphism, Aldh2 knock-out (Aldh2-/-) mice and their wild type (Aldh2+/+) mice were exposed to two different concentrations of acetaldehyde (125 ppm and 500 ppm) for two weeks. Aldh2-/- mice, which have the same genetic background as C57BL/6J (wild mice) except for the Aldh2 gene, were used as models of humans who lack ALDH2 activity. Urinary 8-hydroxydeoxyguanosine (8-OHdG) and plasma malondialdehyde (MDA) levels were measured as indicators of oxidative DNA damage and lipid peroxidation, respectively. At 125 ppm acetaldehyde exposure for 12 d, urinary 8-OHdG levels in Aldh2+/+ mice did not increase. However, urinary 8-OHdG levels in Aldh2-/- mice were slightly increased by the end of the exposure. On the other hand, plasma MDA levels did not increase in either Aldh2-/- orAldh2+/+ mice. At 500 ppm, urinary 8-OHdG levels in both Aldh2-/- and Aldh2+/+ mice significantly increased after 6 and 12 d, but there was no genetic difference. On the other hand, plasma MDA levels in Aldh2+/+ and Aldh2-/- mice did not increase at either 125 ppm or 500 ppm after two weeks of exposure. In conclusion, it is suspected that DNA was damaged by acetaldehyde inhalation, and that susceptibility to acetaldehyde varies according to Aldh2 genotype.

Genetic deficiency of a mitochondrial aldehyde dehydrogenase increases serum lipid peroxides in community-dwelling females

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) plays a major role in acetaldehyde detoxification. The alcohol sensitivity is associated with a genetic deficiency of ALDH2. We and others have previously reported that such a deficiency influences the risk for late-onset Alzheimer's disease (LOAD), hypertension, and myocardial infarction. Then we tried to find phenotypes to which the ALDH2 polymorphism contributes by conducting several evaluations including biochemical and functional analyses of various tissues in a community-dwelling population. Several serum proteins, lipids, and lipid peroxides (LPO) levels showed differences between the nondefective (ALDH2*1/1) and defective (ALDH2*1/2 and ALDH2*2/2) ALDH2 individuals. However, alcohol-drinking behavior is known to affect these evaluations. Thus, we excluded the effects of alcohol-drinking behavior from the association with the ALDH2-deficient genotype through correction and found that the concentration of LPO was significantly lower in the nondefective ALDH2 females than the defective females. The effect of frequent alcohol-drinking behavior in males seems to override the phenotype of the high serum LPO level. These results indicate that the ALDH2 deficiency may enhance oxidative stress in vivo. Thus, these findings suggest that ALDH2 functions as a protector against oxidative stress and the decrease in protection may influence the onset of AD, hypertension, and myocardial infarction.

Deficiency in a mitochondrial aldehyde dehydrogenase increases vulnerability to oxidative stress in PC12 cells

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) plays a major role in acetaldehyde detoxification. The alcohol sensitivity is associated with a genetic deficiency of ALDH2. We have previously reported that this deficiency influences the risk for late-onset Alzheimer's disease. However, the biological effects of the deficiency on neuronal cells are poorly understood. Thus, we obtained ALDH2-deficient cell lines by introducing mouse mutant Aldh2 cDNA into PC12 cells. The mutant ALDH2 repressed mitochondrial ALDH activity in a dominant negative fashion, but not cytosolic activity. The resultant ALDH2-deficient transfectants were highly vulnerable to exogenous 4-hydroxy-2-nonenal, an aldehyde derivative generated by the reaction of superoxide with unsaturated fatty acid. In addition, the ALDH2-deficient transfectants were sensitive to oxidative insult induced by antimycin A, accompanied by an accumulation of proteins modified with 4-hydroxy-2-nonenal. Thus, these findings suggest that mitochondrial ALDH2 functions as a protector against oxidative stress.

Teratogen update: toluene

Extrapolating from animal data, at the level at which well-controlled occupational exposure to toluene vapor is encountered, in utero exposure does not pose a significant fetal risk. However, following chronic and excessive industrial accidents or intentional abuse, toluene exposure several orders of magnitude greater exists, and at these levels in utero exposures in both animals and humans have been shown to produce significant delays in fetal growth. At these greater exposure levels, both dose and gestational timing relationships can be demonstrated in animal models. Of note, in both animals and humans, postnatal persistence of growth deficiency has been observed. A pattern of teratogenicity similar to that of the fetal alcohol syndrome is prevalent in all human studies of excessive in utero exposure to toluene. In humans, the effects of in utero toluene exposure among intentional abusers is confounded by such variables as general health and exposure to other teratogens. Chronic toluene abuse produces a renal tubular acidosis with maternal hypokalemia and profoundly lowered serum pH. Further evaluation of greater numbers of infants with respect to maternal renal tubular acidosis will be needed to fully assess the contribution of chronic acidosis. The contribution of maternal acidosis to fetal teratogenicity remains speculative. Coabuse of additional agents, in particular alcohol, may increase the teratogenic risks. The overlap of features following in utero toluene abuse with those of fetal alcohol syndrome suggests a possible common pathway of craniofacial teratogenesis. Lastly, genetic variations that result in deficiency of ALDH2, an enzyme involved in toluene metabolism, may increase the risks of toluene teratogenicity in at-risk individuals at lower levels of exposure. Prospective studies of toluene-exposed pregnancies would provide more information on the fetal effects at these levels.

The central nervous system and exposure to toluene: a risk characterization

The principal health outcome of exposure to toluene is dysfunction of the central nervous system. Effects range from fatalities and severe neurological disorders in toluene abuse situations to deficits in neurobehavioral function in occupational populations. An Inhalation Reference Concentration (RfC) of 0.4 mg toluene/m3 or 0.1 ppm was developed by the U.S. EPA to protect general populations chronically exposed to toluene. The RfC was derived from results of an occupational study involving Asian workers who developed neurobehavioral deficits at a mean toluene exposure level at the time of the study of 88 ppm. The derivation incorporated several uncertainty factors, one of which was a factor of 10 to account for sensitive subpopulations. Recent evidence indicates that some Japanese and possibly other Asian populations harbor a defective gene for aldehyde dehydrogenase, and thus exhibit a decreased rate of toluene metabolism. Although it is not known if reduced metabolism by aldehyde dehydrogenase also was a factor in the occupational study, preshift blood levels of toluene were considerably higher than preshift levels from non-Asian workers exposed to similar air levels of toluene. The elevated blood levels are consistent with defective metabolism but remain to be confirmed. Inasmuch as air levels of toluene in urban environments are about 10-fold lower than the RfC, an adequate measure of protection is afforded by the RfC with or without an uncertainty factor for sensitive subgroups. However, the uncertainty factor for sensitive subgroups should be retained because there is no information regarding toluene metabolism in children.