ROLE OF GLUTATHIONE IN FORMALDEHYDE METABOLISM AND TOXICITY

Glutathione (GSH) is involved in the detoxication of numerous chemicals exogenously exposed or endogenously generated. Exposure to these agents cause depletion of cellular GSH rendering these cells more susceptible to the toxic action of these same agents. Formaldehyde (CH(,2)O) was found to deplete cellular GSH, presumably by the formation of the GSH-CH(,2)O complex, S-hydroxymethylglutathione, and its rapid extrusion into the extracellular medium.^ The metabolism and toxicity of CH(,2)O were determined to be dependent upon cellular GSH in vitro and in vivo. The rate of CH(,2)O oxidation decreased and the extent of toxicity increased when isolated rat hepatocytes or strain A/J mice were pretreated with the GSH-depleting agent, diethyl maleate (DEM). Additional experiments were designed to further study the role GSH plays in detoxication using isolated rat hepatocytes.^ L-Methionine protected against the extent of lipid peroxidation and leakage of the cytosolic enzyme, lactate dehydrogenase (LDH), caused by CH(,2)O in DEM-pretreated hepatocytes, further supporting the protective role of GSH against cellular toxicity. The antioxidants, ascorbate, butylated hydroxytoluene, and (alpha)-tocopherol, were all protective against the extent of lipid peroxidation and leakage of LDH in isolated rat hepatocytes. Whereas L-methionine may be protective by increasing the cellular concentration of GSH which is used to detoxify free radicals or by facilitating the rate of CH(,2)O oxidation, the antioxidant, ascorbate, was protective without altering the rate of CH(,2)O oxidation or increasing cellular GSH levels. These results suggest that the free radical-mediated toxicity caused by CH(,2)O in DEM-pretreated hepatocytes is due to the further depletion of GSH by CH(,2)O and not to increased CH(,2)O persistence. How this further depletion in GSH by CH(,2)O in DEM-pretreated hepatocytes results in lipid peroxidation and cell death was further investigated.^ The further decrease in GSH caused by CH(,2)O in DEM-pretreated hepatocytes, suspected of stimulating lipid peroxidation and cell death, was found not to be due to depletion of mitochondrial GSH but to depletion of protein sulfhydryl groups. In addition, cellular toxicity appears more closely correlated with depletion of protein sulfhydryl groups than with an increase in cytosolic free Ca('2+). The combination of CH(,2)O and DEM may be a useful tool in identifying these critical sulfhydryl-protein(s) and to further understand the role GSH plays in detoxication. ^

A cross-sectional study of human symptomatology and residential formaldehyde concentrations

The cross-sectional study was performed to quantify the prevalence of symtomatology in residents of mobile homes as a function of indoor formaldehyde concentration. Formaldehyde concentrations were monitored for a seven hour period with an automated wet-chemical colorimetric analyzer. The health status of family members was ascertained by administration of questionnaires and physical exams. This is the first investigation to perform clinical assessments on residents undergoing concurrent exposure assessment in the home.^ Only 22.8% of households eligible for participation chose to cooperate. Monitoring data and health evaluations were obtained from 155 households in four Texas counties. A total of 428 residents (86.1%) were available for examination during the sampling hours. The study population included 45 infants, 126 children, and 257 adults.^ Formaldehyde concentration was not found to be significantly associated with increased risks for symptoms and signs of ocular irritation, dermal anomalies, or malaise. Three associations were identified that warrant further investigation. The relative odds associated with a doubling of formaldehyde concentration was significantly associated with parenchymal rales in adults and children. However, risk was modified by log respirable suspended particulate concentrations. Due to the presence of modification by a continuous variable, prevalence odds ratios (POR) and 95% confidence intervals (95% CI) for these associations are presented in tables. A doubling of formaldehyde concentration was also associated with an increased risk of perceived tightness in the chest in adults. Prevalence odds ratios are presented in a table due to effect modification by the average number of hours spent indoors on weekdays. Furthermore, a doubling of formaldehyde concentration was associated with an increased risk of drowsiness in children (POR = 2.60; 95% CI 1.04-6.51) and adults (POR = 1.94; 95% CI 1.20-3.14). ^

SYSTEMIC TOXICITY IN RODENTS FOLLOWING ACUTE AND SUBCHRONIC INHALATION OF FORMALDEHYDE (FLOW CYTOMETRY, CELL CYCLE KINETICS, ALKALINE ELUTION)

Systemic toxicity was evaluated in Sprague-Dawley (SD) rats and A-strain mice exposed to HCHO inhalation at 0, 0.5, 3, or 15 ppm for six hours/day, five days/week for up to 24 weeks. Toxicity was measured by flow cytometry to detect changes in cell cycle RNA and DNA content and by alkaline elution to detect DNA protein cross-link (DPC) formation.^ A G(,2)M block was detected in SD rat marrow following one week of exposure to 0.5, 3, or 15 ppm HCHO, but this block did not persist. No effect was noticed in mouse marrow. Only a minimal increase in RNA content was detected in rat or mouse marrow while exfoliated lung cells showed a significant increase in RNA activity after one week of exposure.^ Acute exposure in SD rats for four hours/day for one or three days at 150 ppm showed an increase in RNA activity in exfoliated lung cells but not in the marrow after one day. On the third day, dead cells were detected in exfoliated lung cells.^ In alkaline elution studies, no DPC were detected in marrow of SD rats after 24 weeks exposure up to 15 ppm. During acute exposures, a dose response relationship was detected in SD rat exfoliated lung cells which yielded cross-linking factors of 0.954, 1.237, and 1.417 following a four hour exposure to 15, 50, or 150 ppm, respectively. No DPC were detected in the marrow at 150 ppm. In vitro exposures to HCHO of CHO and SHE cells and rat marrow cells revealed the production of DPC and DNA-DNA cross-links.^ Cytoxan treatment of SD rats was used to provide positive controls for flow cytometry and alkaline elution. A drastic reduction in RNA content and cycling cells occurred one day following treatment. After four days, RNA content was greatly increased; and on day eleven the marrow had regenerated. DPCs were detected in both the marrow and the exfoliated lung cells.^ The lack of significant responses in SD rats and A-strain mice below 15 ppm HCHO is explainable by host defense mechanisms. Apparently, the mucociliary apparatus and enzymatic detoxification are sufficient to reduce systemic toxicity to low level concentrations of formaldehyde. ^

RESPIRATORY COMPENSATION MECHANISMS IN THE UPPER AND LOWER RESPIRATORY TRACTS OF AN ANIMAL MODEL AFTER SUBCHRONIC INHALATION EXPOSURE TO FORMALDEHYDE: IMPLICATIONS FOR TOXICOLOGY RISK ASSESSMENT (DEPOSITION, DOSE RECEIVED, RESPONSE)

The potential for significant human populations to experience long-term inhalation of formaldehyde and reports of symptomatology due to this exposure has led to a considerable interest in the toxicologic assessment of risk from subchronic formaldehyde exposures using animal models. Since formaldehyde inhalation depresses certain respiratory parameters in addition to its other forms of toxicity, there is a potential for the alteration of the actual dose received by the exposed individual (and the resulting toxicity) due to this respiratory effect. The respiratory responses to formaldehyde inhalation and the subsequent pattern of deposition were therefore investigated in animals that had received subchronic exposure to the compound, and the potential for changes in the formaldehyde dose received due to long-term inhalation evaluated. Male Sprague-Dawley rats were exposed to either 0, 0.5, 3, or 15 ppm formaldehyde for 6 hours/day, 5 days/week for up to 6 months. The patterns of respiratory response, deposition and the compensation mechanisms involved were then determined in a series of formaldehyde test challenges to both the upper and to the lower respiratory tracts in separate groups of subchronically exposed animals and age-specific controls (four concentration groups, two time points). In both the control and pre-exposed animals, there was a characteristic recovery of respiratory parameters initially depressed by formaldehyde inhalation to at or approaching pre-exposure levels within 10 minutes of the initiation of exposure. Also, formaldehyde deposition was found to remain very high in the upper and lower tracts after long-term exposure. Therefore, there was probably little subsequent effect on the dose received by the exposed individual that was attributable to the repeated exposures. There was a diminished initial minute volume response in test challenges of both the upper and lower tracts of animals that had received at least 16 weeks of exposure to 15 ppm, with compensatory increases in tidal volume in the upper tract and respiratory rate in the lower tract. However, this dose-related effect was probably not relevant to human risk estimation because this formaldehyde dose is in excess of that experienced by human populations. ^

AN INVESTIGATION OF THE EFFECT OF FORMALDEHYDE SPECIES ON ENVIRONMENTAL MEASUREMENT METHODS UNDER AMBIENT CONDITIONS

Species variations in formaldehyde solutions and gases were investigated by means of infrared spectral analysis. Double beam infrared spectrometry in conjunction with sodium chloride wafer technique and solvent compensation technique were employed. Formaldehyde species in various solutions were investigated. Formalin 37% was stable for many months. Refrigeration had no effects on its stability. Spectral changes were detected in 1000 ppm formaldehyde solutions. The absorbances of very diluted solutions up to 100 ppm were lower than the detection limit of the instruments. Solvent compensation improved resolution, but was associated with an observed lack of repeatability. Formaldehyde species in animal chambers containing animals and in mobile home air were analyzed with the infrared spectrophotometer equipped with a 10 cm gas cell. Spectra were not different from the spectrum of clean air. A portable single beam infrared spectrometer with a 20 meter pathlength was used for reinvestigation. Indoor formaldehyde could not be detected in the spectral; conversely, an absorption peak at 3.58 microns was found in the spectra of 3 and 15 ppm formaldehyde gas in animal chambers. This peak did not appear in the spectrum of the control chamber. Because of concerns over measurement bias among various analytical methods for formaldehyde, side-by-side comparisons were conducted in both laboratory and field measurements. The chromotropic acid method with water and 1% sodium bisulfite as collection media, the pararosaniline method, and a single beam infrared spectrometer were compared. Measurement bias was elucidated and the extent of the effects of temperature and humidity was also determined. The problems associated with related methods were discussed. ^