Estimates of parameters for formaldehyde emission model from plywood panel under various temperature and relative humidity conditions

The initial emittable concentration, C_m,0, the material phase diffusion coefficient, D_m, and the air/material partition coefficient, K, are the key parameters used to predict the formaldehyde emissions from indoor building materials. This work presents formaldehyde emission experiments of plywood panels in a climatic chamber under various environmental conditions, which provides information on how relative humidity, temperature, and loading degree affect the formaldehyde emission. The experimental results showed that formaldehyde concentration in the climatic chamber increased rapidly during the initial 3 h, and then reached equilibrium after 7 h. The equilibrium concentration of formaldehyde in the closed chamber was increased by 1.1-1.3 times with the relative humidity increased by 20%, and 1.3-2.5 times with the temperature increased by 5 °C, respectively. In agreement with the experimental treatment, a new method of estimating parameters was carried out in a theoretical model from formaldehyde emission, opening the way to a factorial analysis of the relevant parameters for relative humidity and temperature. The theoretical model with estimated parameters was further validated by experiments with different environmental conditions, which should help to quickly determine the parameters needed to predict formaldehyde emissions.

Inhaled formaldehyde induces DNA-protein crosslinks and oxidative stress in bone marrow and other distant organs of exposed mice

Formaldehyde (FA), a major industrial chemical and ubiquitous environmental pollutant, has been classified as a leukemogen. The causal relationship remains unclear, however, due to limited evidence that FA induces toxicity in bone marrow, the site of leukemia induction, and in other distal organs. Although induction of DNA-protein crosslinks (DPC), a hallmark of FA toxicity, was not previously detected in the bone marrow of FA-exposed rats and monkeys in studies published in the 1980s, our recent studies showed increased DPC in the bone marrow, liver, kidney, and testes of exposed Kunming mice. To confirm these preliminary results, in the current study we exposed BALB/c mice to 0, 0.5, 1.0, and 3.0 mg m(-3) FA (8 hr per day, for 7 consecutive days) by nose-only inhalation and measured DPC levels in bone marrow and other organs of exposed mice. As oxidative stress is a potential mechanism of FA toxicity, we also measured glutathione (GSH), reactive oxygen species (ROS), and malondialdehyde (MDA), in the bone marrow, peripheral blood mononuclear cells, lung, liver, spleen, and testes of exposed mice. Significant dose-dependent increases in DPC, decreases in GSH, and increases in ROS and MDA were observed in all organs examined (except for DPC in lung). Bone marrow was among the organs with the strongest effects for DPC, GSH, and ROS. In conclusion, exposure of mice to FA by inhalation induced genotoxicity and oxidative stress in bone marrow and other organs. These findings strengthen the biological plausibility of FA-induced leukemogenesis and systemic toxicity.

Accumulated hippocampal formaldehyde induces age-dependent memory decline

Aging is an important factor in memory decline in aged animals and humans and in Alzheimer's disease and is associated with the impairment of hippocampal long-term potentiation (LTP) and down-regulation of NR1/NR2B expression. Gaseous formaldehyde exposure is known to induce animal memory loss and human cognitive decline; however, it is unclear whether the concentrations of endogenous formaldehyde are elevated in the hippocampus and how excess formaldehyde affects LTP and memory formation during the aging process. In the present study, we report that hippocampal formaldehyde accumulated in memory-deteriorating diseases such as age-related dementia. Spatial memory performance was gradually impaired in normal Sprague-Dawley rats by persistent intraperitoneal injection with formaldehyde. Furthermore, excess formaldehyde treatment suppressed the hippocampal LTP formation by blocking N-methyl-D-aspartate (NMDA) receptor. Chronic excess formaldehyde treatment over a period of 30 days markedly decreased the viability of the hippocampus and down-regulated the expression of the NR1 and NR2B subunits of the NMDA receptor. Our results indicate that excess endogenous formaldehyde is a critical factor in memory loss in age-related memory-deteriorating diseases.

Recent trend in risk assessment of formaldehyde exposures from indoor air

Studies about formaldehyde (FA) published since the guideline of 0.1 mg/m(3) by the World Health Organization (WHO) in 2010 have been evaluated; critical effects were eye and nasal (portal-of-entry) irritation. Also, it was considered to prevent long-term effects, including all types of cancer. The majority of the recent toxicokinetic studies showed no exposure-dependent FA-DNA adducts outside the portal-of-entry area and FA-DNA adducts at distant sites were due to endogenously generated FA. The no-observed-adverse-effect level for sensory irritation was 0.5 ppm and recently reconfirmed in hypo- and hypersensitive individuals. Investigation of the relationship between FA exposure and asthma or other airway effects in children showed no convincing association. In rats, repeated exposures showed no point mutation in the p53 and K-Ras genes at ≤15 ppm neither increased cell proliferation, histopathological changes and changes in gene expression at 0.7 ppm. Repeated controlled exposures (0.5 ppm with peaks at 1 ppm) did not increase micronucleus formation in human buccal cells or nasal tissue (0.7 ppm) or in vivo genotoxicity in peripheral blood lymphocytes (0.7 ppm), but higher occupational exposures were associated with genotoxicity in buccal cells and cultivated peripheral blood lymphocytes. It is still valid that exposures not inducing nasal squamous cell carcinoma in rats will not induce nasopharyngeal cancer or lymphohematopoietic malignancies in humans. Reproductive and developmental toxicity are not considered relevant in the absence of sensory irritation. In conclusion, the WHO guideline has been strengthened.

The human lung cell line A549 does not develop adaptive protection against the DNA-damaging action of formaldehyde

The alkaline comet assay was used to further characterize the induction of DNA-protein crosslinks (DPX) by formaldehyde (FA) and their removal in the human lung cell line A549. DPX were indirectly measured as the reduction of gamma ray-induced DNA migration. Repeated treatments of A549 cells with low FA concentrations (up to 100 microM) did not lead to significant differences in the induction of DPX in comparison with a single treatment. Pretreatment with higher FA-concentrations (200 microM and above) enhanced the crosslinking effect. There was no indication for an adaptive protection against the induction of DPX by FA. These findings are in agreement with RT-PCR measurements of the expression of genes that encode the main enzymes involved in FA detoxification. A549 cells exposed to FA (50-300 microM) for 1, 4, or 24 hr did not reveal altered expression of the GSH-dependent formaldehyde dehydrogenase (FDH, which is identical to alcohol dehydrogenase 3; ADH3), the cytosolic aldehyde dehydrogenase 1 (ALDH1A1) and the mitochondrial ALDH2. Pretreatment of A549 cells with a low FA concentration (50 microM) also did not enhance the removal of DPX induced by higher FA concentrations. Taken together, these results suggest that A549 cells do not develop adaptive protection against the genotoxic action of FA. Neither metabolic inactivation of FA nor the repair of FA-induced DPX seems to be enhanced in cells pretreated with FA.

Bayesian analysis of a rat formaldehyde DNA-protein cross-link model

As the initial effort in a multi-step uncertainty analysis of a biologically based cancer model for formaldehyde, a Markov chain Monte Carlo (MCMC) analysis was performed for a compartmental model that predicts DNA-protein cross-links (DPX) produced by formaldehyde exposure. The Bayesian approach represented by the MCMC analysis integrates existing knowledge of the model parameters with observed, formaldehyde-DPX-specific data, providing a statistically sound basis for estimating model output uncertainty. Uncertainty and variability were evaluated through a hierarchical structure, where interindividual variability was considered for all model parameters and that variability was assumed to be uncertain on population levels. The uncertainty of the population mean and that of the population variance were significantly reduced through the MCMC analysis. Our investigation highlights several issues that must be dealt with in many real-world analyses (e.g., issues of parameters' nonidentifiability due to limited data) while demonstrating the feasibility of conducting a comprehensive quantitative uncertainty evaluation. The current analysis can be viewed as a case study, for a relatively simple model, illustrating some of the constraints that analysts will face when applying Bayesian approaches to biologically or physiologically based models of increasing complexity.

Purification capability of tobacco transformed with enzymes from a methylotrophic bacterium for formaldehyde

Plants have the ability to remediate environmental pollution. Especially, they have a high purification capability for airpollution. We have measured the purification characteristics of foliage plants for indoor airpollutants--for example, formaldehyde (HCHO), toluene, and xylene--using a tin oxide gas sensor. HCHO is an important intermediate for biological fixation of C1 compounds in methylotrophs. The ribulose monophosphate pathway of HCHO fixation is inherent in many methylotrophic bacteria, which can grow on Cl compounds. Two genes for the key enzymes, HPS and PHI, from the methylotrophic bacterium Mycobacterium gastri MB19 were introduced into tobacco. In this article, the HCHO-removal characteristic of the transformant was examined by using the gas sensor in order to evaluate quantitatively. The purification characteristics of the transformant for toluene, xylene, and styrene were also measured. The results confirmed an increase of 20% in the HCHO-removal capability. The differences of the purification capabilities for toluene, xylene, and styrene were not recognized.

Persuasive evidence that formocresol use in pediatric dentistry is safe

Concern has been expressed about the safety of formocresol use in pediatric dentistry. Formaldehyde, a primary component in formocresol, is a hazardous substance and is considered a probable human carcinogen by Health Canada. However, humans inhale and ingest formaldehyde daily and also produce this compound as part of normal cellular metabolism. The human body is physiologically equipped to handle this exposure through multiple pathways for oxidation of formaldehyde to formate and incorporation into biological macromolecules via tetrahydrofolate-dependent one-carbon biosynthetic pathways. Recent re-evaluation of earlier research that examined potential health risks associated with formaldehyde exposure has shown that the research was based on flawed assumptions, which resulted in erroneous conclusions. This review examines more recent research about formaldehyde metabolism, pharmacokinetics and carcinogenicity, the results of which indicate that formaldehyde is probably not a potent human carcinogen under conditions of low exposure. Extrapolation of these research results to pediatric dentistry suggests an inconsequential risk of carcinogenesis associated with formaldehyde use in pediatric pulp therapy. Areas for further investigation are suggested.

A mathematical model for the absorption and metabolism of formaldehyde vapour by humans

Epidemiological studies of occupational exposure to formaldehyde gas (HCHO) have suggested possible links between concentration and duration of exposure, and elevated risks of leukaemia and other cancers at sites distant from the site of contact. Formaldehyde is a highly water soluble gas which, when inhaled, reacts rapidly at the site of contact and is quickly metabolised by enzymes in the respiratory tissue. Inhaled formaldehyde is almost entirely absorbed in the respiratory tract and, for formaldehyde induced toxicity to occur at distant sites, HCHO must enter the blood and be transported to systemic tissues via the circulatory system. A mathematical model describing the absorption and removal of inhaled formaldehyde in the nasal tissue is therefore formulated to predict the proportion of formaldehyde entering into the blood. Accounting for the spatial distribution of the formaldehyde concentration and the metabolic activity within the mucosa, the concentration of formaldehyde in the mucus, the epithelium and the blood has been determined and was found to attain a steady-state profile within a few seconds of exposure. The increase of the formaldehyde concentration in the blood was predicted to be insignificant compared with the existing pre-exposure levels in the body, indicating that formaldehyde is rapidly removed in the nasal tissue. The results of the model thus suggest that it is highly unlikely that following inhalation by the nose, formaldehyde itself will cause toxicity at sites other than the initial site of contact in the respiratory tract.

[Effect of the interaction of formaldehyde and nitric oxide metabolism pathways in mechanism of their toxic action. I. Exo- and endogenous sources of formaldehyde and nitric oxide. Toxic action of formaldehyde]

Possible exogenous sources of formaldehyde and nitric oxide have been considered; the environment pollution conditions under which these compounds and their precursors have mutual effect on the organism; endogenous sources of FA and NO which are intermediates of the metabolism and key enzymes of their transformation (semicarbazide-sensitive amine oxidase and NO-synthase) the role of the C1 metabolic cycle pathways and methyl cycles in the FA formation and accumulation have been considered as well, various paths of FA toxic action have been characterized.

Dose-dependent transitions in mechanisms of toxicity: case studies

Experience with dose response and mechanisms of toxicity has shown that multiple mechanisms may exist for a single agent along the continuum of the full dose-response curve. It is highly likely that critical, limiting steps in any given mechanistic pathway may become overwhelmed with increasing exposures, signaling the emergence of new modalities of toxic tissue injury at these higher doses. Therefore, dose-dependent transitions in principal mechanisms of toxicity may occur, and could have significant impact on the interpretation of reference data sets for risk assessment. To illustrate the existence of dose-dependent transitions in mechanisms of toxicity, a group of academic, government, and industry scientists, formed under the leadership of the ILSI Health and Environmental Sciences Institute (HESI), developed a series of case studies. These case studies included acetaminophen, butadiene, ethylene glycol, formaldehyde, manganese, methylene chloride, peroxisome proliferator-activated receptor (PPAR), progesterone/hydroxyflutamide, propylene oxide, vinyl acetate, vinyl chloride, vinylidene chloride, and zinc. The case studies formed the basis for technical discourse at two scientific workshops in 2003.

Antiestrogen Binding Site and Estrogen Receptor Mediate Uptake and Distribution of 4-Hydroxytamoxifen-Targeted Doxorubicin−Formaldehyde Conjugate in Breast Cancer Cells

The anthracycline antitumor drug, doxorubicin (DOX), has long been used as a broad spectrum chemotherapeutic. The literature now documents the role of formaldehyde in the cytotoxic mechanism, and anthracycline-formaldehyde conjugates possess substantially enhanced activity in vitro and in vivo. We have recently reported the design, synthesis, and preliminary evaluation of a doxorubicin-formaldehyde conjugate targeted, via 4-hydroxytamoxifen, to the estrogen receptor (ER) and antiestrogen binding site (AEBS), which are commonly present in breast cancer cells. The lead targeted doxorubicin-formaldehyde conjugate, called DOX-TEG-TAM, was found to possess superior cell growth inhibition characteristics relative to clinical doxorubicin and an untargeted control conjugate, especially in ER-negative, multidrug resistant MCF-7/Adr cells. The enhanced activity in the absence of estrogen receptor raised the possibility that targeting was also mediated via AEBS. Fluorescence microscopy of an ER-negative, AEBS-positive cell line as a function of time showed initial DOX-TEG-TAM localization in cytosol, in contrast to initial DOX and untargeted doxorubicin-formaldehyde conjugate localization in the nucleus. DOX-TEG-TAM was taken up by four AEBS-positive cell lines to a greater extent than doxorubicin and an untargeted doxorubicin-formaldehyde conjugate. Of the four cell lines, three were ER negative. DOX-TEG-TAM uptake was inhibited in a dose-dependent manner by the presence of a competing AEBS ligand. DOX-TEG-TAM retains 60% of the affinity of 4-hydroxytamoxifen for AEBS. DOX-TEG-TAM was also taken up by the AEBS-negative, ER-positive cancer cell line Rtx-6; with these cells uptake was inhibited in a dose-dependent manner by the ER ligand, estradiol. The data support the hypothesis that uptake of 4-hydroxytamoxifen targeted doxorubicin-formaldehyde conjugate is mediated by both the antiestrogen binding site and estrogen receptor.

Alcohol dehydrogenases that catalyse methyl formate synthesis participate in formaldehyde detoxification in the methylotrophic yeast Candida boidinii

Methyl formate synthesis during growth on methanol by methylotrophic yeasts has been considered to play a role in formaldehyde detoxification. An enzyme that catalyses methyl formate synthesis was purified from methylotrophic yeasts, and was suggested to belong to a family of alcohol dehydrogenases (ADHs). In this study we report the gene cloning and gene disruption analysis of three ADH-encoding genes in the methylotrophic yeast Candida boidinii (CbADH1, CbADH2 and CbADH3) in order to clarify the physiological role of methyl formate synthesis. From the primary structures of these three genes, CbAdh1 was shown to be cytosolic and CbAdh2 and CbAdh3 were mitochondrial enzymes. Gene products of CbADH1, CbADH2 and CbADH3 expressed in Escherichia coli showed both ADH- and methyl formate-synthesizing activities. The results of gene-disruption analyses suggested that methyl formate synthesis was mainly catalysed by a cytosolic ADH (CbAdh1), and this enzyme contributed to formaldehyde detoxification through glutathione-independent formaldehyde oxidation during growth on methanol by methylotrophic yeasts.

A distributed-parameter model for formaldehyde uptake and disposition in the rat nasal lining

DNA-protein cross-links (DPX) serve as a dosimeter for inhaled formaldehyde and are associated with tumor induction in rat nasal passages after chronic exposure to 6 ppm and above. To determine the role of epithelium-specific morphometry in formaldehyde-induced patterns of injury, we developed a mathematical model that links airflow-driven formaldehyde uptake with DPX formation in regions of the rat nose with high and low tumor incidence. A three-dimensional, anatomically accurate computational fluid dynamics model of rat nasal airflow and inhaled gas uptake was integrated with a physiologically based mathematical model incorporating tissue thickness, formaldehyde diffusion, its removal by enzymatic and nonenzymatic processes, and DNA distribution in the nasal mucosa to predict DPX formation. The model implicitly incorporates the reversible conversion of formaldehyde to methylene glycol. Where possible, parameter values were taken from the literature or estimated using published correlations. The Michaelis-Menten kinetic constants Vmax and Km, as well as a first-order constant for formaldehyde removal, were left as fitted parameters. The resultant model fit to the experimentally measured DPX in the high- and low-tumor-incidence regions of the rat nasal passages was very good. Sensitivity analysis indicates that among the fitted parameters, model fits are most sensitive to Vmax and that predictions were sensitive to changes in tissue thickness when all other parameters are held constant. The model structure facilitates extrapolation to primates and humans and application to other soluble, reactive gases.

Benchmark dose risk assessment for formaldehyde using airflow modeling and a single-compartment, DNA-protein cross-link dosimetry model to estimate human equivalent doses

Formaldehyde induced squamous-cell carcinomas in the nasal passages of F344 rats in two inhalation bioassays at exposure levels of 6 ppm and above. Increases in rates of cell proliferation were measured by T. M. Monticello and colleagues at exposure levels of 0.7 ppm and above in the same tissues from which tumors arose. A risk assessment for formaldehyde was conducted at the CIIT Centers for Health Research, in collaboration with investigators from Toxicological Excellence in Risk Assessment (TERA) and the U.S. Environmental Protection Agency (U.S. EPA) in 1999. Two methods for dose-response assessment were used: a full biologically based modeling approach and a statistically oriented analysis by benchmark dose (BMD) method. This article presents the later approach, the purpose of which is to combine BMD and pharmacokinetic modeling to estimate human cancer risks from formaldehyde exposure. BMD analysis was used to identify points of departure (exposure levels) for low-dose extrapolation in rats for both tumor and the cell proliferation endpoints. The benchmark concentrations for induced cell proliferation were lower than for tumors. These concentrations were extrapolated to humans using two mechanistic models. One model used computational fluid dynamics (CFD) alone to determine rates of delivery of inhaled formaldehyde to the nasal lining. The second model combined the CFD method with a pharmacokinetic model to predict tissue dose with formaldehyde-induced DNA-protein cross-links (DPX) as a dose metric. Both extrapolation methods gave similar results, and the predicted cancer risk in humans at low exposure levels was found to be similar to that from a risk assessment conducted by the U.S. EPA in 1991. Use of the mechanistically based extrapolation models lends greater certainty to these risk estimates than previous approaches and also identifies the uncertainty in the measured dose-response relationship for cell proliferation at low exposure levels, the dose-response relationship for DPX in monkeys, and the choice between linear and nonlinear methods of extrapolation as key remaining sources of uncertainty.

Detoxification in relation to toxin tolerance in desert woodrats eating creosote bush

We studied the relationship between the use of three detoxification pathways and urine pH and the tolerance of desert woodrats from two populations to a mixture of naturally occurring plant secondary metabolites (mostly phenolics) in resin from creosote bush (Larrea tridentata). The two populations of desert woodrats came from the Mojave desert (Mojave woodrats), where woodrats consume creosote bush, and from the Great Basin desert (Great Basin woodrats), where the plant species is absent. We fed woodrats alfalfa pellets containing increasing levels of the phenolic resin and measured three detoxification pathways and urine pH that are related to detoxification of allelochemicals. We found that the excretion rate of two phase II detoxification conjugates, glucuronides and sulfides. increased with increasing resin intake, whereas excretion of hippuric acid was independent of resin intake, although it differed between populations. Urine pH declined with increasing resin ingestion. The molar proportion of glucuronides in urine was three times that of the other conjugates combined. Based on an evaluation of variation in the three detoxification pathways and urine pH in relation to resin intake, we rejected the hypotheses that woodrats' tolerance to resin intake is related to capacity for amination, sulfation, or pH regulation. However, Mojave woodrats had higher maximum glucuronide excretion rates, and we accepted the hypothesis that within and between populations woodrats tolerate more resin because they have a greater capacity for glucuronide excretion.

Molecular basis for the synergistic interaction of adriamycin with the formaldehyde-releasing prodrug pivaloyloxymethyl butyrate (AN-9)

The interaction of Adriamycin and pivaloyloxymethyl butyrate (AN-9) was investigated in IMR-32 neuroblastoma and MCF-7 breast adenocarcinoma cells. Adriamycin is a widely used anticancer drug, whereas AN-9 is an anticancer agent presently undergoing Phase II clinical trials. The anticancer activity of AN-9 has been attributed to its ability to act as a butyric acid prodrug, although it also releases formaldehyde and pivalic acid. Adriamycin and AN-9 in combination display synergy when exposed simultaneously to cells or when AN-9 treatment is up to 18 h after Adriamycin administration. However, the reverse order of addition results in antagonism. These interactions have been established using cell viability assays and classical isobologram analysis. To understand the molecular basis of this synergy, the relative levels of Adriamycin-DNA adducts were determined using various treatment combinations. Levels of Adriamycin-DNA adducts were enhanced when treatment combinations known to be synergistic were used and were diminished using those treatments known to be antagonistic. The relative timing of the addition of Adriamycin and AN-9 was critical, with a 20-fold enhancement of Adriamycin-DNA adducts occurring when AN-9 was administered 2 h after the exposure of cells to Adriamycin. The enhanced levels of these adducts and the accompanying decreased cell viability were directly related to the esterase-dependent release of formaldehyde from AN-9, providing evidence for the formaldehyde-mediated activation of Adriamycin.

Dosimetry modeling of inhaled formaldehyde: comparisons of local flux predictions in the rat, monkey, and human nasal passages

Formaldehyde-induced nasal squamous cell carcinomas in rats and squamous metaplasia in rats and rhesus monkeys occur in specific regions of the nose with species-specific distribution patterns. Experimental approaches addressing local differences in formaldehyde uptake patterns and dose are limited by the resolution of dissection techniques used to obtain tissue samples and the rapid metabolism of absorbed formaldehyde in the nasal mucosa. Anatomically accurate, 3-dimensional computational fluid dynamics models of F344 rat, rhesus monkey, and human nasal passages were used to estimate and compare regional inhaled formaldehyde uptake patterns predicted among these species. Maximum flux values, averaged over a breath, in nonsquamous epithelium were estimated to be 2620, 4492, and 2082 pmol/(mm(2)-h-ppm) in the rat, monkey, and human respectively. Flux values predicted in sites where cell proliferation rates were measured as similar in rats and monkeys were also similar, as were fluxes predicted in a region of high tumor incidence in the rat nose and the anterior portion of the human nose. Regional formaldehyde flux estimates are directly applicable to clonal growth modeling of formaldehyde carcinogenesis to help reduce uncertainty in human cancer risk estimates.

Dosimetry modeling of inhaled formaldehyde: binning nasal flux predictions for quantitative risk assessment

Interspecies extrapolations of tissue dose and tumor response have been a significant source of uncertainty in formaldehyde cancer risk assessment. The ability to account for species-specific variation of dose within the nasal passages would reduce this uncertainty. Three-dimensional, anatomically realistic, computational fluid dynamics (CFD) models of nasal airflow and formaldehyde gas transport in the F344 rat, rhesus monkey, and human were used to predict local patterns of wall mass flux (pmol/[mm(2)-h-ppm]). The nasal surface of each species was partitioned by flux into smaller regions (flux bins), each characterized by surface area and an average flux value. Rat and monkey flux bins were predicted for steady-state inspiratory airflow rates corresponding to the estimated minute volume for each species. Human flux bins were predicted for steady-state inspiratory airflow at 7.4, 15, 18, 25.8, 31.8, and 37 l/min and were extrapolated to 46 and 50 l/min. Flux values higher than half the maximum flux value (flux median) were predicted for nearly 20% of human nasal surfaces at 15 l/min, whereas only 5% of rat and less than 1% of monkey nasal surfaces were associated with fluxes higher than flux medians at 0.576 l/min and 4.8 l/min, respectively. Human nasal flux patterns shifted distally and uptake percentage decreased as inspiratory flow rate increased. Flux binning captures anatomical effects on flux and is thereby a basis for describing the effects of anatomy and airflow on local tissue disposition and distributions of tissue response. Formaldehyde risk models that incorporate flux binning derived from anatomically realistic CFD models will have significantly reduced uncertainty compared with risk estimates based on default methods.

Dosimetry modeling of inhaled formaldehyde: the human respiratory tract

Formaldehyde (HCHO), which has been shown to be a nasal carcinogen in rats and mice, is used widely and extensively in various manufacturing processes. Studies in rhesus monkeys suggest that the lower respiratory tract may be at risk and some epidemiologic studies have reported an increase in lung cancer associated with HCHO; other studies have not. Thus, an assessment of possible human risk to HCHO exposure based on dosimetry information throughout the respiratory tract (RT) is desirable. To obtain dosimetry estimates for a risk assessment, two types of models were used. The first model (which is the subject of another investigation) used computational fluid dynamics (CFD) to estimate local fluxes in a 3-dimensional model of the nasal region. The subject of the present investigation (the second model) applied a 1-dimensional equation of mass transport to each generation of an adult human symmetric, bifurcating Weibel-type RT anatomical model, augmented by an upper respiratory tract. The two types of modeling approaches were made consistent by requiring that the 1-dimensional version of the nasal passages have the same inspiratory air-flow rate and uptake during inspiration as the CFD simulations for 4 daily human activity levels. Results obtained include the following: (1) More than 95% of the inhaled HCHO is predicted to be retained by the RT. (2) The CFD predictions for inspiration, modified to account for the difference in inspiration and complete breath times, are a good approximation to uptake in the nasal airways during a single breath. (3) In the lower respiratory tract, flux is predicted to increase for several generations and then decrease rapidly. (4) Compared to first pulmonary region generation fluxes, the first few tracheobronchial generations fluxes are over 1000 times larger. Further, there is essentially no flux in the alveolar sacs. (5) Predicted fluxes based on the 1-dimensional model are presented that can be used in a biologically based dose-response model for human carcinogenesis. Use of these fluxes will reduce uncertainty in a risk assessment for formaldehyde carcinogenicity.

Uniform expression of alcohol dehydrogenase 3 in epithelia regenerated with cultured normal, immortalised and malignant human oral keratinocytes

The human oral epithelium is a target for damage from the inhalation of formaldehyde. However, most experimental studies on this chemical have relied on laboratory animals that are obligatory nose breathers, including rats and mice. Therefore, in vitro model systems that mimic the structure of the human oral epithelium and which retain normal tissue-specific metabolic competence are desirable. Based on the established role of alcohol dehydrogenase 3 (ADH3), also known as glutathione-dependent formaldehyde dehydrogenase, as the primary enzyme catalysing the detoxification of formaldehyde, the aim of this study was to investigate the expression of ADH3 in organotypic epithelia regenerated with normal (NOK), immortalised (SVpgC2a) and malignant (SqCC/Y1) human oral keratinocytes. Organotypic epithelia, usually consisting of 5-10 cell layers, were produced at the air-liquid interface of collagen gels containing human oral fibroblasts, after culture for 10 days in a standardised serum-free medium. Immunochemical staining demonstrated uniform expression of ADH3 in these organotypic epithelia, as well as in the epithelial cells of oral tissue. The specificity of the ADH3 antiserum was ascertained from the complete neutralisation of the immunochemical reaction with purified ADH3 protein. Assessment of the staining intensities indicated that the expression levels were similar among the regenerated epithelia. Furthermore, the regenerated epithelia showed similar ADH3 expression to the epithelium in oral tissue. Therefore, a tissue-like expression pattern for ADH3 can be generated from the culture of various oral keratinocyte lines in an organotypic state. Similar expression levels among the various cell lines indicate the preservation of ADH3 during malignant transformation, and therefore that NOK, SVpgC2a and SqCC/Y1 represent functional models for in vitro studies of formaldehyde metabolism in human oral mucosa.

Applications of mechanistic data in risk assessment: the past, present, and future

Mechanistic data, when available, have long been considered in risk assessment, such as in the development of the nitrate RfD based on effects in a sensitive group (infants). Recent advances in biology and risk assessment methods have led to a tremendous increase in the use of mechanistic data in risk assessment. Toxicokinetic data can improve extrapolation from animals to humans and characterization of human variability. This is done by the development of improved tissue dosimetry, by the use of uncertainty factors based on chemical-specific data, and in the development of physiologically based pharmacokinetic (PBPK) models. The development of the boron RfD illustrates the use of chemical-specific data in the improved choice of uncertainty factors. The draft cancer guidelines of the U.S. Environmental Protection Agency emphasize the use of mode of action data. The first choice under the guidelines is to use a chemical-specific, biologically based dose-response (BBDR) model. In the absence of a BBDR model, mode of action data are used to determine whether low-dose extrapolation is done using a linear or nonlinear (margin of exposure) approach. Considerations involved in evaluating a hypothesized mode of action are illustrated using 1,3-dichloropropene, and use of a BBDR model is illustrated using formaldehyde. Recent developments in molecular biology, including transgenic animals, microarrays, and the characterization of genetic polymorphisms, have significant potential for improving risk assessments, although further methods development is needed. Overall, use of mechanistic data has significant potential for reducing the uncertainty in assessments, while at the same time highlighting the areas of uncertainty.

Sites and mechanisms for uptake of gases and vapors in the respiratory tract

Inhalation is a common route by which individuals are exposed to toxicants. The air contains a multitude of gases and vapors that are brought into the respiratory tract with each breath. Depending upon the physical and chemical characteristics of the toxicant, the respiratory tract can be considered as a target organ in addition to a portal of entry. Sufficient information is not always available on the fate or effects of an inhaled gas or vapor. Two physiochemical principles, water solubility and reactivity, can be used to predict the site of uptake of gases and vapors in the respiratory tract and potential mechanisms for reaction with respiratory tract tissue and absorption into the blood. Four model compounds, formaldehyde, ozone, dibasic esters, and butadiene are discussed as examples of how knowledge of aqueous solubility and chemical reactivity can help toxicologists predict sites and mechanisms by which inhaled gases and vapors interact with respiratory tract tissues.

Methanol solvent may cause increased apparent metabolic instability in in vitro assays

Methanol was widely used as a substrate-delivering solvent in in vitro metabolic stability screenings. Its interaction with enzyme activities, particularly those of cytochrome P450s, has been investigated extensively in the past. Little was known about the interaction of methanol, whether direct or indirect, with substrates. The present study provided data for the first time to show that use of methanol may result in the formation of artifacts, which could mislead the metabolic stability information. The disappearance of LAQ094, metaraminol, and (-)-isoproterenol following 1-h incubation with human liver microsomes was 73, 85, and 66%, respectively, in the presence of 1% methanol, but was only 3, 15, and 24%, respectively, in the absence of organic solvent. The dramatically increased instability in the presence of methanol of these three compounds, each with 1,2-diamino or 1,2-amino hydroxy functional groups, was due to the formation of [M + 12] products resulting from condensation reaction of the substrates with formaldehyde. Formaldehyde was formed from methanol by human liver microsomal enzymes with an apparent K(m) of 35 mM and a V(max) of 7.9 nmol/min/mg of protein. The concentration of formaldehyde reached as high as 600 microM following a 60-min incubation. The [M + 12] products were characterized as five-membered heterocycles by liquid chromatography and tandem mass spectrometry analysis. Inclusion of 10 mM glutathione prevented the formation of such artifacts and is therefore suggested for future in vitro screenings. Our study also documented the novel finding of enzyme-dependent conversion of NADPH to nicotinamide in microsomal incubations.

The formaldehyde metabolic detoxification enzyme systems and molecular cytotoxic mechanism in isolated rat hepatocytes

The toxicity and carcinogenicity of formaldehyde (HCHO) has been attributed to its ability to form adducts with DNA and proteins. A marked decrease in mitochondrial membrane potential and inhibition of mitochondrial respiration that was accompanied by reactive oxygen species formation occurred when isolated rat hepatocytes were incubated with low concentrations of HCHO in a dose-dependent manner. Hepatocyte GSH was also depleted by HCHO in a dose-dependent manner. At higher HCHO concentrations, lipid peroxidation ensued followed by cell death. Cytotoxicity studies were conducted in which isolated hepatocytes exposed to HCHO were treated with inhibitors of HCHO metabolising enzymes. There was a marked increase in HCHO cytotoxicity when either alcohol dehydrogenase or aldehyde dehydrogenase was inhibited. Inhibition of GSH-dependent HCHO dehydrogenase activity by prior depletion of GSH markedly increased hepatocyte susceptibility to HCHO. In each case, cytotoxicity was dose-dependent and corresponded with a decrease in hepatocyte HCHO metabolism and increased lipid peroxidation. Antioxidants and iron chelators protected against HCHO cytotoxicity. Cytotoxicity was also prevented, when cyclosporine or carnitine was added to prevent the opening of the mitochondrial permeability transition pore which further suggests that HCHO targets the mitochondria. Thus, HCHO-metabolising gene polymorphisms would be expected to have toxicological consequences on an individual's susceptibility to HCHO toxicity and carcinogenesis.

Relative roles of convection and chemical reaction for the disposition of formaldehyde and ozone in nasal mucus

The mucociliary apparatus is an important respiratory-tract defense system that may provide significant protection of the underlying epithelium from gases and vapors. Limiting-case calculations were performed to determine the significance of convective mucus transport and chemical reaction for formaldehyde (HCHO) and ozone (O(3)) in rat nasal respiratory epithelial mucus. Less than 4.6% of absorbed HCHO can be bound to amino groups (serum albumin) after 20 min of exposure. Thus, at the slowest measured mucus flow rates in rats, approximately 1 mm/min, a fluid element of mucus could travel more than 2 cm before binding 5% of absorbed HCHO, by which time the element would probably leave the nose (the site of toxic responses). In other calculations, HCHO removed by chemical reaction from a volume of mucus exposed for longer times was determined to be less than 0.54% of that removed by mucus flow (convection). Given the solubility of HCHO in mucus (water) and estimates of total mucus flow, however, as much as 22-42% of inhaled HCHO may be removed by total mucus flow. Alternately, O(3) dissolved in mucus would react completely with unsaturated fatty acids in 8.3 x 10(-4) s, in which time the mucus could flow no more than approximately 0.42 microm at the maximum reported flow rate of 30 mm/min. Even if a volume of mucus is flushed by net flow in 1 s, the amount of O(3) removed by flow would only be 0.12% of that removed by chemical reaction. Finally, based on the solubility of ozone, less than 8.0 x 10(-5)% of inhaled material could be removed from the nose by mucus flow. These results indicate which mucociliary processes are significant in site-specific dosimetry modeling.

Acute airway effects of formaldehyde and ozone in BALB/c mice

1. Concentration and time-effect relationships of formaldehyde and ozone on the airways were investigated in BALB/c mice. The effects were obtained by continuous monitoring of the respiratory rate, tidal volume, expiratory flow rate, time of inspiration, time of expiration, and respiratory patterns. 2. With concentrations up to 4 p.p.m., formaldehyde showed mainly sensory irritation effects of the upper airways that decrease the respiratory rate from a trigeminal reflex. The no-effect level (NOEL) was about 0.3 p.p.m. This value is close to the human NOEL, which is about 0.08 p.p.m. 3. Ozone caused rapid, shallow breathing in BALB/c mice. Later on, the respiratory rate decreased due to another vagal response that indicated an incipient lung oedema. The NOEL in mice was about 1 p.p.m. during 30 min of ozone exposure. No major effect occurs in resting humans at about 0.4 p.p.m. 4. Thus, the upper airway irritant, formaldehyde, and the deep lung irritant, ozone, showed the same types of respiratory effects in humans and in BALB/c mice. Also, the sensitivity was nearly identical. Continuous monitoring of respiratory effects in BALB/c mice, therefore, may be a valuable method for the study of effects of other environmental pollutants, which, however, should be confirmed in further studies.

Thiols in formaldehyde dissimilation and detoxification

Glutathione is not a universal coenzyme for formaldehyde oxidation. MySH (mycothiol, 1-O-(2'-[N-acetyl-L-cysteinyl]amido-2'-deoxy-alpha-D-glucopyranosyl)-D-m yo-inositol) is GSH's counterpart as coenzyme in formaldehyde dehydrogenase from certain gram-positive bacteria. However, formaldehyde dissimilation and detoxification not only proceed via thiol-dependent but also via thiol-independent dehydrogenases. The distinct structures and enzymatic properties of MySH-dependent and GSH-dependent formaldehyde dehydrogenases could provide clues for development of selective drugs against pathogenic Mycobacteria. It is to be expected that other new types of thiol-dependent formaldehyde dehydrogenases will be discovered in the future. Indications exist that the product of thiol-dependent formaldehyde oxidation, the thiol formate ester, is not only hydrolytically converted into thiol and formate but can also be oxidatively converted in some cases by a molybdoprotein aldehyde dehydrogenase into the corresponding carbonate ester, decomposing spontaneously into CO2 and the thiol.

Increase of formation of methylamine and formaldehyde in vivo after administration of nicotine and the potential cytotoxicity

Methylamine is a constituent of cigarette smoke and the major end product of nicotine metabolism. Smoking or nicotine can induce the release of adrenaline, which is in turn deaminated by monoamine oxidase, also producing methylamine. We found that the urinary level of methylamine was significantly elevated following administration of nicotine (25 mg/Kg, i.p.). Semicarbazide-sensitive amine oxidase (SSAO) inhibitors further increased the excretion of methylamine induced by nicotine. Following administration of L-(-)-[N-methyl-3H]nicotine long-lasting irreversible radioactive adducts were detected in different mouse tissues and such adduct formation could be blocked by selective SSAO inhibitors. These adducts are probably cross-linked oligoprotein complexes cross-linked by formaldehyde. The findings support the idea that nicotine can enhance SSAO/methylamine-mediated increase of formaldehyde and oxidative stress and this could in part contribute the adverse effect of health associated with smoking.

Mechanical, histologic, and biochemical effects of canine rectal formalin instillation

Instillation of 4 percent formalin effectively treats radiation hemorrhagic proctitis; however, little is known regarding its side effects.

PURPOSE

The study contained herein was undertaken to determine rectal compliance and collagen content, mucosal and vascular histologic changes, and kinetics of formalin absorption following instillation.

METHODS

Fifteen mongrel dogs (50-60 pounds) were randomized into five experimental groups according to time elapsed from formalin treatment: control, acute, one week, two weeks, and four weeks. Formalin was instilled in 30-ml aliquots to a total volume of 400 ml. Rectal compliance (closed manometry system) was assessed pre-formalin and post-formalin at the designated time interval. Serum formalin metabolites were determined at time 0, 0.5, 1, and 3 hours. A segment of rectal wall was analyzed for collagen content, mucosal injury, and blood vessel density.

RESULTS

Serum formalin levels peaked within 30 minutes, returning to normal by 3 hours. With the exception of one dog, toxic levels were not reached at any time during the study. No dogs experienced sepsis, fever, or altered gastrointestinal function. Acute and one-week dogs showed mild diffuse proctitis and mucosal slough, which healed within two weeks. Rectal compliance and collagen content were unchanged. Mucosal blood vessels decreased in number early (P = 0.03).

CONCLUSIONS

Instillation of 4 percent formalin in sequential aliquots of a small volume that is kept in contact for a short period of time is safe. Serum formalin levels generally do not reach toxic levels, and the slight elevation in formalin concentration that was seen returns to normal within three hours. Formalin-induced proctitis heals within two weeks, and no long-term changes in rectal compliance or collagen content were seen.

Absorption kinetics of rectal formalin instillation

Formalin instillation has become an accepted treatment of radiation-induced hemorrhagic cystitis and proctitis since the initial report by Brown in 1969 (Med. J. Aust. 1:23, 1969). Although its use is widespread, no studies have been performed to determine the safest, volume or duration of formalin exposure. The purpose of our study was to determine the optimum technique for instillation and the safety margin regarding the maximum time that formalin can be in contact with the rectal mucosa without causing serum toxicity. In a pilot canine study, 4% neutral buffered formalin was instilled into the rectum in 30 ml aliquots for 60 seconds each after which each aliquot was withdrawn; a total volume of 400 ml was used. Our subsequent experiment involved rectal instillation of a single formalin bolus of 100 ml for 1 hour without removal during this time. Formalin metabolites were measured in the blood and urine to assess toxicity. Results indicate that with the latter technique serum formic acid reaches toxic levels within 15 minutes of instillation and may stay elevated for several hours. Metabolites in the urine similarly increase within 15 minutes, lagging only shortly behind the rise in serum levels. Performing formalin instillation in a series of 30 ml aliquots appears to be a safer treatment, as toxic serum levels were not reached and their slight rise above baseline returned to normal within 3 hours.

Comparison of inhaled formaldehyde dosimetry predictions with DNA-protein cross-link measurements in the rat nasal passages

Kimbell and coworkers (Toxicol, Appl. Pharmacol, 121, 253-263, 1993) developed a computational fluid dynamics (CFD) model of a F344 rat nasal passage to quantify local wall mass flux (uptake rate) of inhaled chemical. To simulate formaldehyde uptake, Kimbell et al. assumed that mass transfer of formaldehyde from the air into the nasal lining was fast and complete. This was approximated in the CFD model by setting the formaldehyde concentration at the airway walls to zero. Experimental confirmation of formaldehyde mass-flux predictions is desirable if the CFD model is to be used for predicting formaldehyde dosimetry. The purpose of this study was to see if the CFD model predictions of formaldehyde mass flux are consistent with laboratory data on formaldehyde dosimetry. In this study, a mathematical model of the nasal lining was modified to link CFD dosimetry predictions for inhaled formaldehyde with measured tissue disposition of inhaled gas. This model treats the nasal lining as a single, well-stirred compartment, accounts for formaldehyde reaction via saturable and first-order pathways, and allows comparison of model-predicted DNA-protein cross-links (DPX) with regional DPX measured in formaldehyde-exposed rats. Effective Michaelis-Menten kinetic parameters (Vmax = 3040 microM/min and Km = 59 microM) and a pseudo-first-order rate constant for elimination of formaldehyde by nonsaturable pathways (kf = 6 min-1) were estimated (fit) using an average mass flux derived from experimentally measured uptake of formaldehyde. DPX predictions obtained using the estimated kinetic parameters and linking the CFD model to the nasal-lining model compared well with experimentally measured DPX. The close correlation between predicted and measured DPX in the rat nasal passage supports the CFD model predictions of formaldehyde mass flux at the level of resolution provided by the experimental data.

Formaldehyde replaces glutaraldehyde in porcine bioprosthetic heart valves

BACKGROUND AND AIMS OF THE STUDY

In the production of porcine bioprostheses, the initial glutaraldehyde treatment is often followed by a short incubation in formaldehyde to ensure sterility of the valve. It is assumed that the glutaraldehyde cross links are stable and that the formaldehyde step does not alter the glutaraldehyde incorporated. The objective of this study was to determine whether the formaldehyde interacts with the tissue to cause changes in the glutaraldehyde composition.

MATERIALS AND METHODS

Two methods of tissue treatment were investigated: (i) fresh porcine leaflet tissue was treated with glutaraldehyde, followed by storage in formaldehyde, (ii) tissue processed in glutaraldehyde and transferred to formaldehyde for six hours was returned to glutaraldehyde for storage. The content of the two aldehydes was estimated by high performance liquid chromatography (HPLC), using an adaptation of the method developed by Hughes et al, which measures the acid labile Schiff bases formed between the collagen and the aldehyde.

RESULTS

The initial content of glutaraldehyde in the tissue declined from 63 +/- 10 nmol/mg dry weight to 21 +/- 4 nmol/mg dry weight when the leaflets were placed in formaldehyde for 24 hours. The initial uptake of formaldehyde was 800 +/- 144 nmol/mg dry weight after 24 hours and this declined to 370 +/- 33 nmol/mg dry weight over a 16 week period of storage in formaldehyde. By this stage, the level of glutaraldehyde had decreased to 2.4 +/- 0.2 nmol/mg dry weight. There was a sharp decline in the glutaraldehyde concentration from 89 +/- 6 nmol/mg dry weight to 14 +/- 1 nmol/mg dry weight when the tissue was placed in 4% formaldehyde solution for six hours. The formaldehyde uptake was 770 +/- 54 nmol/mg dry weight. After return to 0.625% glutaraldehyde solution the formaldehyde concentration declined whilst the glutaraldehyde concentration initially increased.

CONCLUSIONS

These results show that the formaldehyde reacts with the epsilon amino groups of lysine which had not reacted with glutaraldehyde, probably for steric reasons; and that formaldehyde replaces some glutaraldehyde in the tissue by a mass action effect. The tissue concentration of both aldehydes subsequently declined over the study period.

Formaldehyde mechanistic data and risk assessment: endogenous protection from DNA adduct formation

Exposures of rodents to airborne formaldehyde (FA) produce dose-related toxicity, enhanced cell proliferation and squamous cell carcinomas in the nasal passages. The mechanism of FA-induced tumor formation involves DNA-protein crosslink formation and enhanced cell proliferation secondarily to cytotoxicity. The mucociliary apparatus and glutathione protect against low-dose FA-induced effects. Consequently, the mechanistic information is consistent with a very sublinear dose-response curve for tumor formation. The sublinear dose-response of nasal DNA-protein crosslinks levels in rodents and monkeys has been used in the risk assessment of FA.

Use of mechanistic information in risk assessment for toxic chemicals

Risk assessment (RA) for toxic chemicals is assumed to be a scientific activity providing a framework of principles for the complication and evaluation of all available scientific information and the rational extrapolation to human health effects in as quantitative terms as possible and with a high degree of certainty. Sensible public health decisions are made more certain through the use of mechanistic information throughout the 4 steps in RA: hazard identification, dose-response assessment, exposure (dose) assessment and risk characterisation. Examples of the use of mechanistic information to assess risks of systemic, developmental/reproductive and neurotoxic effects show how to move away from the presently used threshold/no observable adverse effect/uncertainty factor default methodology towards an evaluation based on all available scientific data. The experience gained in cancer RA in the use of metabolic and tissue binding (receptor) models as well as physiologically based pharmacokinetic (PBPK) and pharmacodynamic (PBPD) models can be transferred to non-cancer RA. A good example is the use of a PBPK model for the hepatoxicity of chloroform. As in cancer RA, as default positions are replaced by biological data the risk assessments become less uncertain when extrapolating between species. Combining information on tissue dosimetry and response data can also provide an estimate of variability within populations, which is impossible with present default type methodology but essential for adequate risk characterisation. Unlike the cancer field there is no single hypothesis for the mechanism of action for the multitude of non-cancer end-points studied.

Intra-canal dissolution of Sargenti paste

Although the efficacy and safety of the Sargenti technique have remained controversial for more than a decade, the technique still is widely used by many dentists throughout the world. The following report describes a retrospective analysis of 367 cases that looked at the contribution of instrumentation technique and fill adequacy to paste dissolution.

Changes in receptor-mediated endocytosis in liver sinusoidal cells after partial hepatectomy in the rat

Liver sinusoidal cells play an important role in host defense by clearing particulate matter and macromolecules from the circulation. In this study, receptor-mediated endocytosis in sinusoidal cells was examined in two-thirds hepatectomized rats using 125I-labeled formaldehyde-treated bovine serum albumin (fBSA) as an endocytable macromolecule. The liver-weight to body-weight ratio in hepatectomized rats returned to the control value 10 days after hepatectomy. The endocytotic index for fBSA in sinusoidal cells decreased significantly to 0.0210 +/- 0.0017 (controls, 0.0598 +/- 0.0019) on the first day, then returned to the control level at 5 days (0.0554 +/- 0.0030). The changes in hepatic uptake for fBSA showed a similar time course of the endocytotic index. A transient increase in the uptake of fBSA per unit weight of liver of 22-39% above control occurred 2 to 3 days after hepatectomy. In contrast to fBSA, the endocytotic index in hepatocytes evaluated with 125I-labeled asialofetuin reached the minimum level on the second day, and then recovered to the control level 10 days after hepatectomy. These results suggest that endocytosis of fBSA by sinusoidal cells decreases after hepatectomy and rapidly recovers to normal before the completion of liver regeneration, whereas endocytosis of asialofetuin by hepatocytes decreases following hepatic resection and returns to normal when regeneration is substantially complete.

Receptor-mediated endocytosis of chemically modified albumins by sinusoidal endothelial cells and Kupffer cells in rat and human liver

Human serum albumin (HSA), formaldehyde-treated HSA (FHSA), and HSA polymerized with glutaraldehyde (pHSA) were conjugated with colloidal gold (15 (15G) or 50 (50G) nm in diameter). The labeled proteins were injected into the portal veins of rats and followed by electron microscopy. Both 15G-FHSA and 15G-pHSA were taken up by sinusoidal endothelial cells (Ec) and Kupffer cells (Kc). Five minutes after injection, gold particles were observed on the surface of Ec and Kc. At 10 min, most gold particles were gathered in the coated pits and vesicles of Ec. In Kc, gold particles were observed in both coated vesicles and macropinocytotic vesicles. At 15 min, the gold particles were localized mainly in the endosomes and some lysosomes of Ec and in the large vacuoles of Kc. At 30 min, the gold particles had been gathered into the secondary lysosomes and condensed. At 60 min, some gold particles were observed in the cytoplasm of Ec. The fate of 15G-pHSA was the same as that of 15G-FHSA. Simultaneous injection of 15G-pHSA and 50G-FHSA revealed that particles of both sizes were taken up together into the coated pits and vesicles of Ec. Preperfusion of livers with unlabeled FHSA, pHSA, or formaldehyde-treated bovine serum albumin (FBSA) inhibited the uptake of 15G-FHSA or 15G-pHSA by Ec. In a human liver biopsy specimen, both 15G-FHSA and 15G-pHSA were taken up by Ec and Kc through coated vesicles, as in the rat liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic studies of formaldehyde binding in tissue

Specimens of rabbit liver were fixed for various periods up to 6 days in buffered 14C-formaldehyde. Binding of the isotope reached a plateau after fixation for approximately 24 hr; the half-maximal binding level was reached after approximately 100 min. Formaldehyde binding at 37 C was faster than at 25 C, and faster at pH 7.0 than at pH 4.0. During rinsing of the fixed tissue in water for up to 26 days there was a progressive decrease in isotope content to 10-20% of the pre-rinse level, indicating that formaldehyde fixation is a reversible process.

Chronic ethanol administration impairs degradation of formaldehyde-treated albumin by the perfused rat liver

Nonparenchymal cells of the liver appear to be important in the pathogenesis of various liver diseases, including that caused by ethanol. It is known that chronic ethanol administration impairs the process of receptor-mediated endocytosis in hepatocytes. Liver endothelial cells are also actively endocytic cells, playing a prominent role in the clearance from the circulation of a variety of macromolecules. In this study, we assessed the effect of ethanol administration on this "scavenger" function of liver endothelial cells by measuring the degradation of formaldehyde-treated albumin in isolated, perfused livers of ethanol-fed rats. Rats were pair-fed for 1 or 4 weeks with a liquid diet containing either ethanol as 36% of total calories or an isocaloric amount of carbohydrate. Chronic ethanol administration in this manner for 1 or 4 weeks significantly impaired the degradation of this endothelial cell ligand (by 60 +/- 9% and 37 +/- 9%, respectively). Liver perfusions were also performed on rats that had been administered ethanol acutely or in which ethanol was added to the perfusate. No acute effect of ethanol on the degradation of this ligand was seen. These results demonstrate that chronic ethanol ingestion impairs receptor-mediated endocytosis of formaldehyde-treated albumin by liver endothelial cells, indicating that the adverse effects of ethanol on protein trafficking within the liver are not limited to the hepatocytes.

The penetration of root canal sealers into dentinal tubules. A scanning electron microscopic study

The purpose of this study was to evaluate the effect of smear layer on penetration of four root sealers into dentinal tubules. Sixty-four, recently extracted, human maxillary and mandibular incisors were used. Following removal of the crowns, the pulps were extirpated and the root canals instrumented. The teeth were then divided into two groups. The teeth in the control group were irrigated with saline solution and the experimental group treated with EDTA and NaOCl. Each main group was then divided into four sub-groups and the root canals filled with Diaket, N2 Universal, SPAD and Forfenan as recommended by the manufacturers. The teeth were split longitudinally and examined using scanning electron microscopy. A quantitative assessment was made of sealer penetration into the dentinal tubules in the coronal, middle and apical parts of each root canal. It was observed that the smear layer obstructed the penetration of the tubules by the sealers. However, in the experimental group, the penetration into dentinal tubules was better with Diaket, N2 and SPAD, than with Forfenan (P < 0.01). It was concluded that this penetration could be affected by physical and chemical properties of root canal filling materials.

Distribution of radioactivity from 14C-formaldehyde in pregnant mice and their fetuses

The distribution of 14C after the administration of 14C-formaldehyde was studied in pregnant mice by a whole body low temperature autoradiographic technique. The concentrations of formaldehyde and its metabolites in maternal and fetal blood and tissues were determined in unsectioned tissues by liquid scintillation spectrophotometry. The binding of 14C from 14C-formaldehyde to cells and DNA in maternal and fetal mouse liver was also measured. Radioactivity of 14C deriving from 14C-formaldehyde was found immediately after injection, and showed strong accumulation and retention three hours after injection. The organs that had high concentrations at all studied survival intervals were maternal liver, intestinal mucosa, bone marrow, kidneys, and salivary glands. Considerable amounts of radioactivity were found in the fetuses at six hours after injection, and the concentrations were almost the same as in the maternal tissues. The elimination of 14C-formaldehyde and metabolites from the placenta and fetus occurred more slowly than from maternal tissue.

[The effect of milk consumption on the activity of the formaldehyde detoxification system in sensitization to this compound]

The activity of formaldehyde dehydrogenase (FDG) and total nonspecific formaldehyde oxidative activity of nasal mucosa and liver and the amount of reduced glutathione in the liver were measured in guinea pig subjected to epicutaneous or inhalative action of formaldehyde and additionally fed with cow milk. Glutathione-deficient animals demonstrated an increase in FDG activity following formaldehyde sensitization both in the liver and in nasal mucosa, whereas FDG activity in glutathione-supplied animals did not change significantly. The concentration of formaldehyde in the internal environment is supposed to be controlled by the levels of coenzyme (reduced glutathione) and FDG activity.

Effects of formaldehyde on xenotransplanted human respiratory epithelium

A laboratory animal model that permits the exposure of xenotransplanted human respiratory epithelium to formaldehyde was used to study the effects of formaldehyde alone or in combination with the ultimate carcinogenic metabolite of benzo[a]pyrene, benzo[a]pyrene diol epoxide. Epithelial cells obtained from autopsies of full-term human fetuses or infants less than one year old were isolated, amplified in primary cultures, and then inoculated into rat tracheas from which the epithelial layer had been removed. These tracheas then were sealed and transplanted subcutaneously into irradiated athymic nude mice. Four weeks after transplantation, the tracheal lumen was completely covered by epithelium, most of which was of the mucociliary respiratory type. At this stage, tracheal transplants containing tracheobronchial epithelium from 20 different human infant donors were exposed to silastic devices containing 0, 0.5, 1, or 2 mg of formaldehyde. The tracheal transplants were examined histologically 2, 4, 8, or 16 weeks after transplantation. Before being killed, all animals were injected with a single pulse of tritiated thymidine. Important epithelial alterations were seen in the transplants treated with formaldehyde, with a maximum effect visible two weeks after exposure. In most cases, the highest dose of 2 mg produced numerous areas of epithelial erosion and inflammation; however, this effect was not as evident with the lower doses. All doses produced areas of hyperplastic epithelium alternating with areas of atrophic epithelium. Although the differences in predominance of different types of epithelium were not clearly dependent on dose, the labeling index showed dose dependence between two and four weeks after the initiation of exposure. The maximum mean labeling index was three to four times higher than normal, although in some focal hyperplastic-metaplastic lesions the labeling index increased up to 20 times. These studies show that formaldehyde, although toxic at higher doses, is able to elicit at lower doses a proliferative response of the human infant tracheobronchial epithelium that is not preceded by a massive toxic effect. Similar studies were performed using xenotransplanted human adult nasal respiratory epithelium (Study 2). The response pattern was very similar to that of the xenotransplanted human tracheobronchial epithelium from human infants (Study 1). In Study 3, using cells obtained from 11 human infant tracheobronchial epithelia, the formaldehyde applied simultaneously or sequentially with benzo[a]pyrene diol epoxide did not induce epithelial alterations different from those observed with formaldehyde treatments alone.(ABSTRACT TRUNCATED AT 250 WORDS)

[Formic acid in urine--a significant parameter in environmental diagnosis?]

Reference intervals of formic acid excretion in urine of healthy occupational unexposed adults were determined. Within the range of specific gravity between 1.016-1.032 g/cm3 normalization by creatinine or gravity is unnecessary. The mean formic acid concentration in urine of female and male adults aged 20-80 years was 21 mg/l +/- 30 mg/l (95. percentile 60 mg/l) with slightly higher values in elder persons. Smoking and dietary habits had no influence on formic acid excretion but age was positively correlated with increased concentrations. An oral methanol intake of 10 mg/kg body weight had no significant impact on urine excretion of formic acid. Excretion in the general population is determined by endogenous metabolism of amino acids, purine- and pyrimidine-bases rather than the uptake and metabolism of precursors like formaldehyde. Hence in contrast to recent recommendations in environmental medicine, formic acid in urine is not an appropriate parameter for biological-monitoring of low level exposure to formaldehyde.

[Hepatocellular mechanisms of compensatory processes influenced by environmental chemical factors]

The hepatocellular compensatory mechanisms against chemical pollutants were investigated. They expressed in hypertrophic nucleus-nucleolus structures, increased DNA-synthetizing and proliferative activity of hepatocytes, activated hepatic bile secretion and metabolic rearrangement in hepatocytes.

Covalent binding of inhaled formaldehyde to DNA in the respiratory tract of rhesus monkeys: pharmacokinetics, rat-to-monkey interspecies scaling, and extrapolation to man

DNA-protein cross-links were formed in the respiratory tract of rhesus monkeys exposed to [14C]formaldehyde (0.7, 2, or 6 ppm; 6 hr). Concentrations of cross-links (pmol/mg DNA) were highest in the mucosa of the middle turbinates; lower concentrations were produced in the anterior lateral wall/septum and nasopharynx. Very low concentrations were found in the larynx/trachea/carina and in the proximal portions of the major bronchi of some monkeys exposed to 6 ppm but not to 0.7 ppm. No cross-links were detected in the maxillary sinuses or lung parenchyma. The pharmacokinetics of cross-link formation in the nose were interpreted using a model in which the rate of formation is proportional to the tissue concentration of formaldehyde. The model includes both saturable and nonsaturable elimination pathways and describes regional differences in DNA binding as having an anatomical rather than a biochemical basis. Using this model, the concentration of cross-links formed in corresponding tissues of different species can be predicted by scaling the pharmacokinetic parameter that depends on minute volume (V) and quantity of nasal mucosal DNA (MDNA). The concentration-response curve for the average rate of cross-link formation in the turbinates, lateral wall, and septum of rhesus monkeys was predicted from that of F-344 rats exposed under similar conditions. There was significant overlap between predicted and fitted curves, implying that V and MDNA are major determinants of the rate of cross-link formation in the nasal mucosa of different species. Concentrations of cross-links that may be produced in the nasal mucosa of adult men were predicted based on experimental data in rats and monkeys. The results suggest that formaldehyde would generate lower concentrations of cross-links in the nasal mucosa of humans than of monkeys, and much lower concentrations in humans than in rats. The rate of formation of DNA-protein cross-links can be regarded as a surrogate for the delivered concentration of formaldehyde. Use of this surrogate should decrease the uncertainty of human cancer risk estimates derived by interspecies extrapolation by providing a more realistic measure of the delivered concentration at critical target sites.

Clearance of desialylated mouse alpha-macroglobulin and murinoglobulin in the mouse

Mouse alpha-macroglobulin and murinoglobulin were labeled with 125I and utilized for plasma clearance studies performed with mice. Desialylated murinoglobulin was rapidly cleared from the circulation with a half-life of about 5 min. On the other hand, desialylated alpha-macroglobulin showed a biphasic curve: about half was cleared at a rate similar to that of the intact molecule while the remaining half had a shorter half-life of about 20 min which was prolonged by a simultaneous injection of a 200-fold excess of unlabeled asialoorosomucoid. Virtually no cross competition was observed between these asialoglobulins and formaldehyde-treated bovine serum albumin or trypsin-bound alpha-macroglobulin. These results suggest that the intravascular elimination of desialylated alpha-macroglobulin and murinoglobulin is independent of the clearance systems responsible for formaldehyde-modified proteins or proteinase-bound alpha-macroglobulins, and that the structure or spatial arrangement, or both, of oligosaccharide units of alpha-macroglobulin is somewhat different from that of murinoglobulin, resulting in a difference of avidity of interaction with the asialoglycoprotein receptor. The desialylated alpha-macroglobulin and murinoglobulin accumulated principally in the liver.