Two Aldehyde Clearance Systems Are Essential to Prevent Lethal Formaldehyde Accumulation in Mice and Humans.

Reactive aldehydes arise as by-products of metabolism and are normally cleared by multiple families of enzymes. We find that mice lacking two aldehyde detoxifying enzymes, mitochondrial ALDH2 and cytoplasmic ADH5, have greatly shortened lifespans and develop leukemia. Hematopoiesis is disrupted profoundly, with a reduction of hematopoietic stem cells and common lymphoid progenitors causing a severely depleted acquired immune system. We show that formaldehyde is a common substrate of ALDH2 and ADH5 and establish methods to quantify elevated blood formaldehyde and formaldehyde-DNA adducts in tissues. Bone-marrow-derived progenitors actively engage DNA repair but also imprint a formaldehyde-driven mutation signature similar to aging-associated human cancer mutation signatures. Furthermore, we identify analogous genetic defects in children causing a previously uncharacterized inherited bone marrow failure and pre-leukemic syndrome. Endogenous formaldehyde clearance alone is therefore critical for hematopoiesis and in limiting mutagenesis in somatic tissues.

Normative formaldehyde-hemoglobin adduct levels among the US Population: Analysis of the 2013-2016 National Health and Nutrition Examination Survey.

INTRODUCTION: Formaldehyde (FA) is currently classified as a known carcinogen. In addition to being a ubiquitous compound with many common exogenous exposure sources, it is also part of multiple metabolic pathways and present in every living cell. The objectives of this study were to determine normative levels of FA as measured by FA-Hemoglobin (Hb) adducts in the United States (US) and to determine if FA-Hb levels differ based on a variety of demographic factors. METHODS: Data collected between 2013 and 2016 by the National Health and Nutrition Examination Survey were assessed from 4521 participants representing approximately 244 million individuals living in the US. General linear models were used to examine associations between FA-Hb adducts and sample characteristics. FA-Hb levels were summarized using geometric mean concentrations (GMC) and associated 95% confidence intervals (CI). RESULTS: The overall GMC was 131.10 nmol/g Hb (95% CI 129.39-132.83). Analyses revealed no evidence to support associations between FA-Hb levels and age, gender, income, or nicotine use. Among adults, non-Hispanic Black race was associated with lower FA-Hb levels compared to all other race/ethnicity groups, P < 0.01. CONCLUSION: The study provides the first normative values for FA in adults and children. These data could be a tool to assess the body's response to acute and chronic exposure.

Plasma from some patients with amyotrophic lateral sclerosis exhibits elevated formaldehyde levels.

INTRODUCTION: The aim of this study was to determine whether patients with amyotrophic lateral sclerosis (ALS) exhibit higher plasma levels of formaldehyde (FA) than controls, and to look for alterations in levels of FA precursors. METHODS: We studied 40 heathy controls and 50 ALS patients from the Motor Neuron Disease clinic at the Royal Brisbane & Women's Hospital. Plasma FA levels were quantified using a FA detection assay. Trimethylamine (TMA) and trimethylamine oxide (TMAO) in plasma were quantified by multiple reaction monitoring (MRM) mass spectrometry. Plasma levels in patients and controls were compared using Mann-Whitney U test and Spearman's correlation test was used to assess the correlation between levels of FA, TMA, TMAO and other variables. RESULTS: The levels of plasma FA were significantly greater in ALS subjects than controls. TMA and TMAO levels were not significantly different between healthy controls and patients, but were greater in ALS subjects with elevated FA levels than those with normal levels. Of note, levels of TMA and TMAO demonstrated a significant positive correlation with plasma FA levels (spearman's correlation coefficients of TMA with FA [r = 0.451, p = 0.010] and TMAO [r = 0.401, p = 0.023]). There was no association of FA levels with disability measured with the ALS functional rating scale, with the duration of disease or with the age of the subjects. CONCLUSION: Elevated FA is found in some patients with ALS. FA is neurotoxic and could contribute to disease pathogenesis.

Investigation of serum amino acids involved in gallic acid detoxification of formaldehyde by liquid chromatography/tandem mass spectrometry and neutral loss scan.

RATIONALE: Gallic acid is one of the most common polyphenols in natural products and human diet. The consumption of gallic acid reduces the incidence of cardiovascular diseases, chronic metabolic disorders and cancers. Most previous publications focused on the antioxidative or prooxidative properties of gallic acid. In the present work, gallic acid as a trapping agent of blood formaldehyde was investigated by liquid chromatography/tandem mass spectrometry (LC/MS/MS) and neutral loss scan. METHODS: Serum samples incubated with gallic acid were subjected to LC/MS/MS analysis using an LTQ XL ion trap mass spectrometer. The adduct ions of gallic acid-formaldehyde-amino acids were explored by investigation of their fragmentation patterns and neutral loss scan experiments. RESULTS: A series of Mannich adducts (namely, gallic acid-formaldehyde-alanine, gallic acid-formaldehyde-proline, gallic acid-formaldehyde-leucine or gallic acid-formaldehyde-isoleucine and gallic acid-formaldehyde-phenylalanine) were identified as metabolites by neutral loss scan experiments. CONCLUSIONS: This work demonstrated that serum amino acids are involved in gallic acid detoxification of formaldehyde. Because excessive formaldehyde in blood is implicated in a variety of disease pathologies, detoxification of formaldehyde, especially endogenous formaldehyde, may be another health beneficial effect of gallic acid. It also suggested that more attention should be paid to Mannich-type metabolites of polyphenol-formaldehyde-amino acids in research into the pharmacokinetics and bioavailability of polyphenols.

Super-quenched Molecular Probe Based on Aggregation-Induced Emission and Photoinduced Electron Transfer Mechanisms for Formaldehyde Detection in Human Serum.

Energy transfer between fluorescent dyes and quenchers is widely used in the design of light-up probes. Although dual quenchers are more effective in offering lower background signals and higher turn-on ratios than one quencher, such probes are less explored in practice as they require both quenchers to be within the proximity of the fluorescent core. In this contribution, we utilized intramolecular motion and photoinduced electron transfer (PET) as quenching mechanisms to build super-quenched light-up probes based on fluorogens with aggregation-induced emission. The optimized light-up probe possesses negligible background and is able to detect not only free formaldehyde (FA) but also polymeric FA, with an unprecedented turn-on ratio of >4900. We envision that this novel dual quenching strategy will help to develop various light-up probes for analyte sensing.

Formaldehyde induces diabetes-associated cognitive impairments.

Patients with type 2 diabetes mellitus (T2DM) often develop cognitive impairments and have an increased risk of developing Alzheimer's disease. Hyperglycemia is a major characteristic of T2DM, but how elevated glucose levels lead to cognitive decline remains elusive. Here, we report that patients with T2DM and mutations in the formaldehyde (FA)-degrading enzyme aldehyde dehydrogenase 2 ( ALDH2) gene had higher levels of FA and more severe dementia. Injection of FA induced hyperglycemia and cognitive deficits in rats. Ablation of gene expression of ALDH2, the main enzyme to oxidize FA, resulted in abnormally high levels of hippocampal FA, leading to hyperglycemia and cognitive impairments as well as potentiating streptozotocin-induced diabetes development in ALDH2 knockout mice. We found that FA interacts with insulin to form FA-insulin adducts, and these FA-insulin adducts caused insulin deficiency, contributing to memory decline in diabetic rodent models. Reduction of FA by transgenic overexpression of human ALDH2 attenuates hyperglycemia and alleviates cognitive deficits in diabetic mouse models. These findings suggest that excess FA plays a critical role in mediating diabetes-related dementia. Targeting FA and its metabolizing enzyme ALDH2 may be a valid approach for preventing and treating dementia in diabetes mellitus.-Tan, T., Zhang, Y., Luo, W., Lv, J., Han, C., Hamlin, J. N. R., Luo, H., Li, H., Wan, Y., Yang, X., Song, W., Tong, Z. Formaldehyde induces diabetes-associated cognitive impairments.

Association between formaldehyde exposure and miscarriage in Chinese women.

The aim of this study was to assess whether higher plasma formaldehyde concentration existed in women diagnosed with miscarriage and whether it contributed to higher risk of miscarriage in Chinese women.A case-control study was conducted in 118 women with a diagnosed miscarriage at the first trimester and 191 healthy women who delivered at term. Plasma levels of formaldehyde were measured by gas chromatography in conjunction with mass spectrometry after derivatization of the formaldehyde to the pentafluorophenylhydrazone and characteristics of the subjects including age, education level, occupation, family income, home decoration status, and exposure to second-hand smoke were recorded. Logistic regression analyses were performed to investigate the relationship between miscarriage and levels of formaldehyde.Women with miscarriage were comparable to controls in terms of age, education level, occupation, family income, and home decoration status. They were, however, more likely to be exposed to second-hand smoke. Plasma levels of formaldehyde were significantly higher in women with miscarriage (0.0944 ±â€Š0.0105 vs. 0.0239 ±â€Š0.0032 µg/mL, P < .001). Multivariate logistic regression showed that higher level of formaldehyde (odds ratio [OR]: 8.06, 95% confidence interval [CI]: 4.96-13.09) and exposure to second-hand smoke (OR: 3.60, 95% CI: 1.58-8.20) were independently and significantly associated with higher risk of miscarriage.Plasma levels of formaldehyde were significantly higher in women who were diagnosed with miscarriage than those who delivered at term and higher levels of formaldehyde was an independent risk factor for miscarriage, with higher levels being associated with higher risk of miscarriage.

Plasma Level Formaldehyde in Children Receiving Pulpotomy Treatment under General Anesthesia.

OBJECTIVES: Formocresol has long been used by dentists for pulpotomy of primary teeth. Due to some concerns regarding its possible carcinogenicity, formocresol has been the topic of numerous studies. This study sought to assess the changes in plasma level of formaldehyde of children after receiving pulpotomy under general anesthesia. STUDY DESIGN: Twenty-five children between 2-6 years requiring dental treatments under general anesthesia were studied. Blood samples were taken of children before and after the procedure. Plasma level of formaldehyde was measured using high performance liquid chromatography (HPLC). RESULTS: A total of 106 pulpotomy treatments were performed in 25 children using 126 cotton pellets dipped in formocresol. An increase and a decrease in plasma level of formaldehyde were noted in 5 (20%) and 20 (80%) children, respectively post-operatively compared to baseline. The t-test showed no significant difference in plasma level of formaldehyde pre- and postoperatively (P=0.12). the plasma level of formaldehyde in children who had higher levels of formaldehyde prior to the operation was also higher than that of others after the operation and this association was statistically significant (P=0.001, r=0.64). CONCLUSIONS: The results showed no significant change in the mean plasma level of formaldehyde in children who received pulpotomy under general anesthesia compared to its baseline value.

Using lysine adducts of human serum albumin to investigate the disposition of exogenous formaldehyde in human blood.

Formaldehyde is a human carcinogen that readily binds to nucleophiles, including proteins and DNA. To investigate whether exogenous formaldehyde produces adducts in extracellular fluids, we characterized modifications to human serum albumin (HSA) following incubation of whole blood, plasma, and saliva with formaldehyde at concentrations of 1, 10 and 100µM. The only HSA locus that showed the presence of formaldehyde modifications was Lys199. A N(6)-Lys adduct with added mass of 12Da, representing a putative intramolecular crosslink, was detected in biological fluids that had been incubated with formaldehyde but not in control fluids. An adduct representing N(6)-Lys formylation was detected in all fluids, but levels did not increase above control values over the tested range of formaldehyde concentrations. An adduct representing N(6)-Lys199 acetylation was also measured in all samples. We then applied the assay to repeated samples of human plasma from 6 nonsmoking volunteer subjects (from Berkeley, CA), and single samples of serum from 15 workers exposed to airborne formaldehyde at about 1.5ppm in a production facility and 15 control workers from Tianjin, China. Although all human plasma/serum samples contained basal levels of the products of N(6)-Lys formylation and acetylation, the putative crosslink product was not detected. Since the putative crosslink was observed in plasma incubated with formaldehyde at 1µM, this suggests that the endogenous concentration of formaldehyde in serum was much lower than reported in the literature. Furthermore, concentrations of the formyl adduct were not higher in workers exposed to formaldehyde at about 1.5ppm than in controls. Follow-up in vitro experiments with gaseous formaldehyde at 1.4ppm detected the putative crosslink in plasma but not whole blood. This combination of results suggests that N(6) formylation occurs within cells with subsequent release of adducted HSA to the systemic circulation. Comparing across human samples, levels of N(6)-Lys199 formyl adducts were present at similar concentrations in subjects from California and China (about 1mmol/mol HSA), but N(6)-Lys199 acetyl adducts were present at higher concentrations in Chinese subjects (0.34 vs. 0.13mmol/mol HSA).

[Health risks for residents of cities with developed copper industry].

The study results stressed considerable contribution of technogenic environmental pollution in cities with developed copper industry into individual health risk of Sverdlovsk region population.

[Cognitive disorders in workers engaged into formaldehyde and methanol production].

The authors studied cognitive functions state in workers engaged into chemical production under exposure to combination of factors with prevalent methanol and formaldehyde. Study covered 128 examinees of main occupations and 89 individuals of reference group. Through periodic medical examinations, state of cognitive functions was assessed by Montreal scale (MCA). Findings are increased serum levels of methanol and formaldehyde in the main group members. Moderate cognitive disorders of multifunctional type were seen. Associations of these disorders with acting agents were studied, and high degree of their correlations with occupation was revealed.

Effects of formaldehyde on lymphocyte subsets and cytokines in the peripheral blood of exposed workers.

Formaldehyde (FA) is a well-known irritant, and it is suggested to increase the risk of immune diseases and cancer. The present study aimed to evaluate the distribution of major lymphocyte subsets and cytokine expression profiles in the peripheral blood of FA-exposed workers. A total of 118 FA-exposed workers and 79 controls were enrolled in the study. High performance liquid chromatography, flow cytometry, and cytometric bead array were used to analyze FA in air sample and formic acid in urine, blood lymphocyte subpopulations, and serum cytokines, respectively. The FA-exposed workers were divided into low and high exposure groups according to their exposure levels. The results showed that both the low and high FA-exposed groups had a significant increase of formic acid in urine when compared to the controls. Both the low and high exposure groups had a significant increase in the percentage of B cells (CD19+) compared to the control group (p<0.01). A significant increase in the percentage of the natural killer (NK) cells (CD56+) was observed in the low exposure group compared to the control (p = 0.013). Moreover, the FA-exposed workers in both exposure groups showed a significant higher level of IL-10 but lower level of IL-8 than the control (p<0.01). Subjects in the high exposure group had a higher level of IL-4 but a lower level of IFN-γ than the control (p<0.05). Finally, there is a significant correlation between the levels of IL-10, IL-4, and IL-8 and formic acid (p<0.05). The findings from the present study may explain, at least in part, the association between FA exposure and immune diseases and cancer.

The determination of exogenous formaldehyde in blood of rats during and after inhalation exposure.

Formaldehyde (FA) is suspected of being associated with the development of leukemia. An inhalation experiment with FA was performed in rats to study whether FA can enter the blood and could thus cause systemic toxicity in remote tissues such as the bone marrow. Therefore, a sophisticated analytical method was developed to detect blood concentrations of FA during and after single 6-h exposure by inhalation. In order to differentiate between exogenous and endogenous FA the rats were exposed to stable isotope ((13)C) labeled FA by inhalation. During and after exposure of the rats to (13)C-FA their blood was analyzed to determine the ratio between labeled and natural FA in blood and the total blood concentration of FA. With respect to sensitivity, with the applied method exogenous (13)C-FA could have been detected in blood at a concentration approximately 1.5% of the endogenous FA blood concentration. Exogenous (13)C-FA was not detectable in the blood of rats either during or up to 30 min after the exposure. It was concluded that the inhalation of (13)C-FA at 10 ppm for 6h did not result in an increase of the total FA concentration in blood.

[The increase of micronuclei frequencies of peripheral blood lymphocyte in plywood workers exposed accumulatively to formaldehyde].

OBJECTIVE: To investigate the effects of occupational exposure to formaldehyde on the micronuclei frequencies in peripheral blood lymphocytes of workers. METHODS: Two hundred thirty six plywood workers were divided into 3 exposure groups (low, middle and high) according to internal exposure biomarker (formaldehyde human serum albumin conjugate, FA-HSA), which was detected by ELISA. The concentrations of formaldehyde (FA) in air of two workshops were measure using the high performance liquid chromatography. Cytokinesis-block micronucleus (CBMN) test was used to detect the micronuclei frequencies of peripheral blood lymphocyte in 236 workers. RESULTS: The average concentrations of FA in the low and high exposure workshops were 0.58 +/- 0.20 and 1.48 +/- 0.61 mg/m3, respectively, there was significant difference (P < 0.01). The average concentrations of serum FA-HAS of workers in two workshops were 69.22 +/- 15.37 and 136.29 +/- 89.49 pg/ml, respectively, there was significant difference (P < 0.01). The results of CBMN test showed that the micronucleus frequencies in low, middle and high exposure groups were 1.94 +/- 1.72, 2.10 +/- 1.92 and 2.10 +/- 1.70 per thousand, respectively, there were no significant differences between groups. However, the micronucleus frequencies in accumulative low, middle and high exposure groups were 1.36 +/- 1.36, 2.31 +/- 1.81 and 2.49 +/- 1.92 per thousand, respectively, there were significant differences between different accumulative exposure groups (P < 0.01). The results of correlation analysis indicated that there was a positive correlation between accumulative exposure levels and micronucleus frequencies (r(s) = 0.321, P < 0.01). The accumulative exposure doses may be a risk factor for high micronucleus frequencies in workers exposed to FA (P(trend) = 0.002). CONCLUSION: FA-HSA levels can serve as an internal exposure biomarker for assessing the exposure level of workers exposed to FA. Accumulative formaldehyde exposure resulted in an increase of micronuclei frequencies of peripheral blood lymphocyte in plywood workers.

Reaction of homopiperazine with endogenous formaldehyde: a carbon hydrogen addition metabolite/product identified in rat urine and blood.

Drug reactivity and bioactivation are of major concern to the development of potential drug candidates in the pharmaceutical industry (Chem Res Toxicol 17:3-16, 2004; Chem Res Toxicol 19:889-893, 2006). Identifying potentially problematic compounds as soon as possible in the discovery process is of great importance, so often early in vitro screening is used to speed up attrition. Identification of reactive moieties is relatively straightforward with appropriate in vitro trapping experiments; however, on occasion unexpected reactive intermediates can be found later during more detailed in vivo studies. Here, we present one such example involving a series of compounds from an early drug discovery campaign. These compounds were found to react with endogenous formaldehyde from a rat in vivo study, resulting in the formation of novel +13-Da bridged homopiperazine products (equivalent to the addition of one carbon and one hydrogen atom), which were detected in urine and blood. The identification of these +13-Da products and their origin and mechanism of formation are described in detail through analyses of a representative homopiperazine compound [N-(3-(3-fluorophenyl)-1,2,4-thiadiazol-5-yl)-4-(4-isopropyl-1,4-diaze-pane-2-carbonyl)piperazine-1-carboxamide (AZX)] by liquid chromatography-UV-mass spectrometry, (1)H NMR, and chemical tests.

Formaldehyde up-regulates TRPV1 through MAPK and PI3K signaling pathways in a rat model of bone cancer pain.

OBJECTIVE: Our previous study showed that tumor tissue-derived formaldehyde at low concentrations plays an important role in bone cancer pain through activating transient receptor potential vanilloid subfamily member 1 (TRPV1). The present study further explored whether this tumor tissue-derived endogenous formaldehyde regulates TRPV1 expression in a rat model of bone cancer pain, and if so, what the possible signal pathways are during the development of this type of pain. METHODS: A rat model of bone cancer pain was established by injecting living MRMT-1 tumor cells into the tibia. The formaldehyde levels were determined by high performance liquid chromatography, and the expression of TRPV1 was examined with Western blot and RT-PCR. In primary cultured dorsal root ganglion (DRG) neurons, the expression of TRPV1 was assessed after treatment with 100 µmol/L formaldehyde with or without pre-addition of PD98059 [an inhibitor for extracellular signal-regulated kinase], SB203580 (a p38 inhibitor), SP600125 [an inhibitor for c-Jun N-terminal kinase], BIM [a protein kinase C (PKC) inhibitor] or LY294002 [a phosphatidylinositol 3-kinase (PI3K) inhibitor]. RESULTS: In the rat model of bone cancer pain, formaldehyde concentration increased in blood plasma, bone marrow and the spinal cord. TRPV1 protein expression was also increased in the DRG. In primary cultured DRG neurons, 100 µmol/L formaldehyde significantly increased the TRPV1 expression level. Pre-incubation with PD98059, SB203580, SP600125 or LY294002, but not BIM, inhibited the formaldehyde-induced increase of TRPV1 expression. CONCLUSION: Formaldehyde at a very low concentration up-regulates TRPV1 expression through mitogen-activated protein kinase and PI3K, but not PKC, signaling pathways. These results further support our previous finding that TRPV1 in peripheral afferents plays a role in bone cancer pain.

Assessment of genotoxic effects and changes in gene expression in humans exposed to formaldehyde by inhalation under controlled conditions.

Forty-one volunteers (male non-smokers) were exposed to formaldehyde (FA) vapours for 4 h/day over a period of five working days under strictly controlled conditions. For each exposure day, different exposure concentrations were used in a random order ranging from 0 up to 0.7 p.p.m. At concentrations of 0.3 and 0.4 p.p.m., four peaks of 0.6 or 0.8 p.p.m. for 15 min each were applied. During exposure, subjects had to perform bicycle exercises (∼80 W) four times for 15 min. Blood samples, exfoliated nasal mucosa cells and nasal biopsies were taken before the first and after the last exposure. Nasal epithelial cells were additionally sampled 1, 2 and 3 weeks after the end of the exposure period. The alkaline comet assay, the sister chromatid exchange test and the cytokinesis-block micronucleus test were performed with blood samples. The micronucleus test was also performed with exfoliated nasal mucosa cells. The expression (mRNA level) of the glutathione (GSH)-dependent formaldehyde dehydrogenase (FDH, identical to alcohol dehydrogenase 5; ADH5; EC 1.2.1.46) was measured in blood samples by quantitative real-time reverse transcription-polymerase chain reaction with TaqMan probes. DNA microarray analyses using a full-genome human microarray were performed on blood samples and nasal biopsies of selected subgroups with the highest FA exposure at different days. Under the experimental conditions of this study, inhalation of FA did not lead to genotoxic effects in peripheral blood cells and nasal mucosa and had no effect on the expression of the FDH gene. Inhalation of FA did also not cause alterations in the expression of genes in a microarray analysis with nasal biopsies and peripheral blood cells.

Determination of trace formaldehyde in blood plasma by resonance fluorescence technology.

A novel method for the determination of trace formaldehyde in blood plasma has been established by using resonance fluorimetry technique. It was based on the fact that oxidation of pyronine Y by potassium bromate was catalyzed by formaldehyde in sulfuric acid. When the wavelength interval was at Δλ=0 nm, it was found that the decreased intensity (ΔF) of resonance fluorescence at 574.6 nm was proportional to the concentration of formaldehyde in the range of 1.27×10(-2) to 2.28 µg mL(-1). The limit of detection and the average recovery for formaldehyde were 3.80 ng mL(-1) and 101.6% (n=6), respectively. The present method had been applied to the determination of trace formaldehyde in blood plasma, and the obtained results were in good agreement with those obtained by the resonance light scattering method.

Hematological and toxicological evaluation of formaldehyde as a potential cause of human leukemia.

Epidemiological findings suggesting that formaldehyde exposure is associated with a higher risk of acute myelogenous leukemia (AML) and other hematological cancers have led to consideration of the potential mechanism of action by which inhalation of this rapidly reactive agent can cause bone marrow cancer. Two major mechanism-based arguments against formaldehyde as a leukemogen have been the difficulty in envisioning how inhaled formaldehyde might penetrate to the bone marrow; and the lack of similarity of non-cancer effects to other known human myeloleukemogens, particularly the absence of pancytopenia in humans or laboratory animals exposed to high levels. However, both of these arguments have been addressed by the recent finding of a pancytopenic effect and chromosomal abnormalities in heavily exposed Chinese workers which, if replicated, are indicative of a genotoxic effect of formaldehyde on hematopoietic stem cells that is in keeping with other known human leukemogens. Review of the body of evidence suggests an apparent discrepancy between studies in laboratory animals, which generally fail to show evidence of penetration of formaldehyde into the blood or evidence of blood or bone marrow genotoxicity, and studies of exposed humans in which there tends to be evidence of genotoxicity in circulating blood cells. One possible explanation for this discrepancy is species difference. Another possible explanation is that myeloid precursors within the nasal mucosa may be the site for leukemogenesis. However, chloromas, which are local collections of myeloid tumor cells, are rarely if ever found in the nose. Other proposed mechanisms for formaldehyde leukemogenesis are reviewed, and dose issues at the interface between the epidemiological and hematotoxicological findings are explored.

Clear differences in levels of a formaldehyde-DNA adduct in leukocytes of smokers and nonsmokers.

Formaldehyde is considered carcinogenic to humans by the IARC, but there are no previous reports of formaldehyde-DNA adducts in humans. In this study, we used liquid chromatography-electrospray ionization-tandem mass spectrometry to quantify the formaldehyde-DNA adduct N(6)-hydroxymethyldeoxyadenosine (N(6)-HOMe-dAdo) in leukocyte DNA samples from 32 smokers of >or=10 cigarettes per day and 30 nonsmokers. Clear peaks coeluting with the internal standard in two different systems were seen in samples from smokers but rarely in nonsmokers. N(6)-HOMe-dAdo was detected in 29 of 32 smoker samples (mean +/- SD, 179 +/- 205 fmol/micromol dAdo). In contrast, it was detected in only 7 of 30 nonsmoker samples (15.5 +/- 33.8 fmol/micromol dAdo; P < 0.001). The results of this study show remarkable differences between smokers and nonsmokers in levels of a leukocyte formaldehyde-DNA adduct, suggesting a potentially important and previously unrecognized role for formaldehyde as a cause of cancer induced by cigarette smoking.