Breath, urine, and blood measurements as biological exposure indices of short-term inhalation exposure to methanol

In vitro antioxidant activity of Ficus carica L. latex from 18 different cultivars

As synthetic antioxidants that are widely used in foods are known to cause detrimental health effects, studies on natural additives as potential antioxidants are becoming increasingly important. In this work, the total phenolic content (TPC) and antioxidant activity of Ficus carica Linn latex from 18 cultivars were investigated. The TPC of latex was calculated using the Folin–Ciocalteu assay. 1,1-Diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and ferric ion reducing antioxidant power (FRAP) were used for antioxidant activity assessment. The bioactive compounds from F. carica latex were extracted via maceration and ultrasound-assisted extraction (UAE) with 75% ethanol as solvent. Under the same extraction conditions, the latex of cultivar ‘White Genoa’ showed the highest antioxidant activity of 65.91% ± 1.73% and 61.07% ± 1.65% in DPPH, 98.96% ± 1.06% and 83.04% ± 2.16% in ABTS, and 27.08 ± 0.34 and 24.94 ± 0.84 mg TE/g latex in FRAP assay via maceration and UAE, respectively. The TPC of ‘White Genoa’ was 315.26 ± 6.14 and 298.52 ± 9.20 µg GAE/mL via the two extraction methods, respectively. The overall results of this work showed that F. carica latex is a potential natural source of antioxidants. This finding is useful for further advancements in the fields of food supplements, food additives and drug synthesis in the future.

Estimations of the lethal and exposure doses for representative methanol symptoms in humans

Background

The aim of this review was to estimate the lethal and exposure doses of a representative symptom (blindness) of methanol exposure in humans by reviewing data from previous articles.

Methods

Available articles published from 1970 to 2016 that investigated the dose-response relationship for methanol exposure (i.e., the exposure concentration and the biological markers/clinical symptoms) were evaluated; the MEDLINE and RISS (Korean search engine) databases were searched. The available data from these articles were carefully selected to estimate the range and median of a lethal human dose. The regression equation and correlation coefficient (between the exposure level and urinary methanol concentration as a biological exposure marker) were assumed from the previous data.

Results

The lethal human dose of pure methanol was estimated at 15.8–474 g/person as a range and as 56.2 g/person as the median. The dose-response relationship between methanol vapor in ambient air and urinary methanol concentrations was thought to be correlated. An oral intake of 3.16–11.85 g/person of pure methanol could cause blindness. The lethal dose from respiratory intake was reported to be 4000–13,000 mg/l. The initial concentration of optic neuritis and blindness were shown to be 228.5 and 1103 mg/l, respectively, for a 12-h exposure.

Conclusion

The concentration of biological exposure indices and clinical symptoms for methanol exposure might have a dose-response relationship according to previous articles. Even a low dose of pure methanol through oral or respiratory exposure might be lethal or result in blindness as a clinical symptom.

Metabolic methanol: molecular pathways and physiological roles

Methanol has been historically considered an exogenous product that leads only to pathological changes in the human body when consumed. However, in normal, healthy individuals, methanol and its short-lived oxidized product, formaldehyde, are naturally occurring compounds whose functions and origins have received limited attention. There are several sources of human physiological methanol. Fruits, vegetables, and alcoholic beverages are likely the main sources of exogenous methanol in the healthy human body. Metabolic methanol may occur as a result of fermentation by gut bacteria and metabolic processes involving S-adenosyl methionine. Regardless of its source, low levels of methanol in the body are maintained by physiological and metabolic clearance mechanisms. Although human blood contains small amounts of methanol and formaldehyde, the content of these molecules increases sharply after receiving even methanol-free ethanol, indicating an endogenous source of the metabolic methanol present at low levels in the blood regulated by a cluster of genes. Recent studies of the pathogenesis of neurological disorders indicate metabolic formaldehyde as a putative causative agent. The detection of increased formaldehyde content in the blood of both neurological patients and the elderly indicates the important role of genetic and biochemical mechanisms of maintaining low levels of methanol and formaldehyde.

Biological exposure indices of pyrrole adducts in serum and urine for hazard assessment of n-hexane exposure

BACKGROUND

Pyrrole adducts might be used as a biomarker for monitoring occupational exposure to n-hexane, but the Biological Exposure Indices of pyrrole adducts in serum and urine are still unknown. The current study was designed to investigate the biological exposure limit of pyrrole adducts for hazard assessment of n-hexane.

METHODS

Male Wistar rats were given daily dose of 500, 1000, 1500, 2000, 4000 mg/kg bw n-hexane by gavage for 24 weeks. The levels of pyrrole adducts in serum and urine were determined at 8, 24 hours postdose once a week. The Biological Exposure Indices was evaluated by neurological evaluation and the levels of pyrrole adducts. The difference in pyrrole adducts formation between humans and rats were estimated by using in vitro test.

RESULTS

Dose-dependent effects were observed between the doses of n-hexane and pyrrole adducts in serum and urine, and the levels of pyrrole adduct in serum and urine approached a plateau at week 4. There was a significantly negative correlation between the time to paralysis and the level of pyrrole adducts in serum and urine, while a positive correlation between gait score and levels of pyrrole adducts in serum and urine was observed. In vitro, pyrrole adducts formed in human serum was about two times more than those in rat serum at the same level of 2,5-HD.

CONCLUSION

It was concluded that the BEIs of pyrrole adducts in humans were 23.1 ± 5.91 nmol/ml in serum 8 h postdose, 11.7 ± 2.64 nmol/ml in serum 24 h postdose, 253.8 ± 36.3 nmol/ml in urine 8 h postdose and 54.6 ± 15.42 nmol/ml in urine 24 h postdose.

Clinical breath analysis: discriminating between human endogenous compounds and exogenous (environmental) chemical confounders

Volatile organic compounds (VOCs) in exhaled breath originate from current or previous environmental exposures (exogenous compounds) and internal metabolic (anabolic and catabolic) production (endogenous compounds). The origins of certain VOCs in breath presumed to be endogenous have been proposed to be useful as preclinical biomarkers of various undiagnosed diseases including lung cancer, breast cancer, and cardio-pulmonary disease. The usual approach is to develop difference algorithms comparing VOC profiles from nominally healthy controls to cohorts of patients presenting with a documented disease, and then to apply the resulting rules to breath profiles of subjects with unknown disease status. This approach to diagnosis has a progression of sophistication; at the most rudimentary level, all measurable VOCs are included in the model. The next level corrects exhaled VOC concentrations for current inspired air concentrations. At the highest level, VOCs exhibiting discriminatory value also require a plausible biochemical pathway for their production before inclusion. Although these approaches have all shown some level of success, there is concern that pattern recognition is prone to error from environmental contamination and between-subject variance. In this paper, we explore the underlying assumptions for the interpretation and assignment of endogenous compounds with probative value for assessing changes. Specifically, we investigate the influence of previous exposures, elimination mechanisms and partitioning of exogenous compounds as confounders of true endogenous compounds. We provide specific examples based on a simple classical pharmacokinetic approach to identify potential misinterpretations of breath data and propose some remedies.

Effect of hemodialysis and diet on the exhaled breath methanol concentration in patients with ESRD

OBJECTIVES

End-stage renal disease (ESRD) causes accumulation of nitrogenous waste products and acid-base, mineral, fluid, and electrolyte disorders, which are partially corrected by hemodialysis (HD). While the effects of ESRD and dialysis on body fluid composition are well known, the effects on composition of expired breath are uncertain. Methanol is produced from unabsorbable complex carbohydrates by the colonic microbiome. Dietary restrictions of fruits and vegetables aimed at limiting potassium intake lower the intake of dietary fibers; the reduced fiber intake can in turn reduce production of methanol and its appearance in the exhaled breath. In this study, we investigated the inter- and intradialytic changes in the breath methanol levels.

DESIGN AND METHOD

Ten ESRD patients were studied during HD procedures at 3- and 2-day interdialytic intervals. On each occasion, 20 exhaled breath and room air samples were collected using evacuated canisters. Ten age-matched normal subjects served as controls. The samples were analyzed on a unique 6-column/detector gas chromatography system.

RESULTS

Seven ESRD patients consuming renal diet had lower methanol concentration (90 ± 29 ppbv) than the 3 patients consuming high-fiber diet (340 ± 48 ppbv, P ≤ .0006) and the 10 controls consuming unrestricted diets (202 ± 80 ppbv, P ≤ .001). HD significantly lowered breath methanol (60% ± 12%), paralleling the fall in serum urea concentration (70% ± 6%). The predialysis methanol concentration was slightly higher at 3-day than the 2-day interdialytic intervals.

CONCLUSION

Dietary restriction of fruits and vegetables lowers methanol production by the gut microbial flora in ESRD patients. Perhaps, methanol is a reliable breath biomarker to monitor individuals' daily fiber intake. Breath methanol is dramatically reduced by HD, reflecting its efficient removal.

Your prodrug releases formaldehyde: should you be concerned? No!

The title of this commentary contains a frequently asked question whenever someone presents or proposes a prodrug strategy that releases formaldehyde as a result of bioconversion of a prodrug to parent drug. Formaldehyde, a highly water-soluble one-carbon molecule, is endogenous to cells, tissues, and body fluids. Although formaldehyde is generated and incorporated into essential metabolic processes by the human body, exposure to large amounts of formaldehyde vapor can irritate the nasal mucosa and may potentially be carcinogenic. It also gives a positive Ames test. Metabolism of both endogenous and exogenous formaldehyde involves rapid oxidation to formic acid catalyzed by glutathione dependent and independent dehydrogenases in the liver and erythrocytes. Balancing this rapid detoxification pathway is endogenous formation from normal metabolic processes and exogenous formaldehyde input, resulting in approximately 0.1 mM systemic levels. The possibility that formaldehyde released upon bioconversion of prodrugs might induce toxicity has been repeatedly stated, but no convincing evidence for this perceived toxicity has been documented in experimental studies. Therefore, as pharmaceutical chemists and not as toxicologists, we present our perspective on the apparent concern with release of formaldehyde as a by-product of in vivo bioconversion of selective prodrugs, and suggest that in comparison to the total amount of daily endogenous formaldehyde production from metabolism, and exogenous exposure from food and the environment, the amount generated by prodrugs is minute and is unlikely to cause any systemic toxicity in humans. Such an argument does not preclude formaldehyde-based toxicity assessment of a prodrug. Instead, it reduces the risk that in vivo liberation of formaldehyde will cause undue toxicity.

Uptake and Disposition of Inhaled Methanol Vapor in Humans

Methanol is a widely used solvent and a potential fuel for motor vehicles. Human kinetic data of methanol are sparse. As a basis for biological exposure monitoring and risk assessment, we studied the inhalation toxicokinetics of methanol vapor in four female and four male human volunteers during light physical exercise (50 W) in an exposure chamber. The relative uptake of methanol was about 50% (range 47-53%). Methanol in blood increased from a background level of about 20 to 116 and 244 microM after 2 h exposure at 0, 100 ppm (131 mg/m3) and 200 ppm (262 mg/m3), respectively. Saliva showed substantially higher levels than blood immediately after exposure. This difference disappeared in a few minutes; thereafter the concentrations and time courses in blood, urine, and saliva were similar, with half times of 1.4, 1.7, and 1.3 h, respectively. The postexposure decrease of methanol in exhaled air was faster, with a half time of 0.8 h. The methanol concentrations were approximately twice as high in all four types of biological samples at 200 compared to 100 ppm. No increase in urinary formic acid was seen in exposed subjects. Our study indicates non-saturated, dose-proportional kinetics of methanol up to 200 ppm for 2 h. No gender differences were detected. Similar, parallel patterns were seen with regard to the methanol time courses in blood, urine, and saliva, whereas the concentration in exhaled air decreased markedly faster. Thus, apart from blood and urine, saliva also seems suitable for biomonitoring of methanol exposure.

NTP-CERHR Expert Panel report on the reproductive and developmental toxicity of methanol

The National Toxicology Program (NTP) and the National Institute of Environmental Health Sciences (NIEHS) established the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR) in June 1998. The purpose of the Center is to provide timely, unbiased, scientifically sound evaluations of human and experimental evidence for adverse effects on reproduction, including development, caused by agents to which humans may be exposed. Methanol was selected for evaluation by the CERHR based on high production volume, extent of human exposure, and published evidence of reproductive or developmental toxicity. Methanol is used in chemical syntheses and as an industrial solvent. It is a natural component of the human diet and is found in consumer products such as paints, antifreeze, cleaning solutions, and adhesives. It is used in race car fuels and there is potential for expanded use as an automobile fuel. This evaluation is the result of a 10-month effort by a 12-member panel of government and non-government scientists that culminated in a public Expert Panel meeting. This report has been reviewed by CERHR staff scientists, and by members of the Methanol Expert Panel. Copies have been provided to the CERHR Core Committee, which is made up of representatives of NTP-participating agencies. This report is a product of the Expert Panel and is intended to (1). interpret the strength of scientific evidence that a given exposure or exposure circumstance may pose a hazard to reproduction and the health and welfare of children; (2). provide objective and scientifically thorough assessments of the scientific evidence that adverse reproductive/development health effects are associated with exposure to specific chemicals or classes of chemicals, including descriptions of any uncertainties that would diminish confidence in assessment of risks; and (3). identify knowledge gaps to help establish research and testing priorities. The expert panel report becomes a central part of the subsequent NTP-CERHR Monograph. Each monograph includes the NTP Brief on the chemical under evaluation, the expert panel report, and all public comments on the expert panel report. The NTP Brief contains the NTP's conclusions on the potential for exposure to result in adverse effects on human development and reproduction. It is based on the expert panel report, public comments on the report, and relevant data published after the expert panel report was completed. NTP-CERHR Monographs are publicly available and are transmitted to appropriate health and regulatory agencies.

A proposed inhalation reference concentration for methanol

A biologically based approach was taken to developing an inhalation Reference Concentration (RfC) for methanol, a high production volume chemical with many commercial applications, including use as an alternative fuel for motor vehicles and as a hydrogen source for fuel cells. Benchmark Dose methodology was applied to the most sensitive toxic endpoint for assessing potential health risks in humans, cervical rib malformation data obtained using CD-1 mice. The concentration of methanol in circulating blood was employed as the dose metric, and the maximum likelihood estimate of the blood methanol increment causing a 10% extra risk of these malformations, was 215.4 mg/L, with a lower 95% confidence bound of 97.4 mg/L. A "Reference Increment" for blood methanol was then determined by dividing this value by a 3-fold factor for residual pharmacodynamic uncertainty between species and a 10-fold factor for interindividual variation in human sensitivity to methanol. The resulting Reference Increment in blood methanol was then converted to an equivalent inhalation Reference Concentration with a physiologically based pharmacokinetic model evaluated for continuous exposure conditions. The resulting maximum likelihood estimate for the inhalation RfC was 298 mg/m3, with a 95% lower confidence bound of 135 mg/m3.

American Academy of Clinical Toxicology practice guidelines on the treatment of methanol poisoning

EPIDEMIOLOGY

Almost all cases of acute methanol toxicity result from ingestion, though rarely cases of poisoning have followed inhalation or dermal absorption. The absorption of methanol following oral administration is rapid and peak methanol concentrations occur within 30-60minutes.

MECHANISMS OF TOXICITY

Methanol has a relatively low toxicity and metabolism is responsible for the transformation of methanol to its toxic metabolites. Methanol is oxidized by alcohol dehydrogenase to formaldehyde. The oxidation of formaldehyde to formic acid is facilitated by formaldehyde dehydrogenase. Formic acid is converted by 10-formyl tetrahydrofolate synthetase to carbon dioxide and water. In cases of methanol poisoning, formic acid accumulates and there is a direct correlation between the formic acid concentration and increased morbidity and mortality. The acidosis observed in methanol poisoning appears to be caused directly or indirectly by formic acid production. Formic acid has also been shown to inhibit cytochrome oxidase and is the prime cause of ocular toxicity, though acidosis can increase toxicity further by enabling greater diffusion of formic acid into cells.

FEATURES

Methanol poisoning typically induces nausea, vomiting, abdominal pain, and mild central nervous system depression. There is then a latent period lasting approximately 12-24 hours, depending, in part, on the methanol dose ingested, following which an uncompensated metabolic acidosis develops and visualfunction becomes impaired, ranging from blurred vision and altered visual fields to complete blindness.

MANAGEMENT

For the patient presenting with ophthalmologic abnormalities or significant acidosis, the acidosis should be corrected with intravenous sodium bicarbonate, the further generation of toxic metabolite should be blocked by the administration of fomepizole or ethanol and formic acid metabolism should be enhanced by the administration of intravenous folinic acid. Hemodialysis may also be required to correct severe metabolic abnormalities and to enhance methanol and formate elimination. For the methanol poisoned patient without evidence of clinical toxicity, the first priority is to inhibit methanol metabolism with intravenous ethanol orfomepizole. Although there are no clinical outcome data confirming the superiority of either of these antidotes over the other, there are significant disadvantages associated with ethanol. These include complex dosing, difficulties with maintaining therapeutic concentrations, the need for more comprehensive clinical and laboratory monitoring, and more adverse effects. Thus fomepizole is very attractive, however, it has a relatively high acquisition cost.

CONCLUSION

The management of methanol poisoning includes standard supportive care, the correction of metabolic acidosis, the administration of folinic acid, the provision of an antidote to inhibit the metabolism of methanol to formate, and selective hemodialysis to correct severe metabolic abnormalities and to enhance methanol and formate elimination. Although both ethanol and fomepizole are effective, fomepizole is the preferred antidote for methanol poisoning.

Partition coefficients for the trihalomethanes among blood, urine, water, milk and air

Chloroform, bromodichloromethane, chlorodibromomethane, and bromoform comprise the trihalomethanes, a group of widespread and mildly lipophilic compounds that result from water chlorination and other sources. Many animal studies show the chronic toxicity and carcinogenicity of these compounds, and recent work has demonstrated the importance of both ingestion and inhalation exposure pathways. This study presents partition coefficients describing the equilibrium among biological compartments (air, water, blood, milk, urine) for the four THMs based on results of headspace gas chromatographic analyses performed under equilibrium conditions and at 37 degrees C. The calculated partition coefficients ranged from 2.92 to 4.14 for blood/water, 1.54-2.85 for milk/blood, and 3.41-4.93 for blood/urine, with the lowest being chloroform and the highest being bromoform. Both human and cow milk were tested, with similar results. The available samples of human milk may not fully account for differences in lipid content and possibly other factors that affect estimates of partition coefficients. Simultaneous measurements of milk and blood in exposed individuals are suggested to confirm laboratory results. Partition coefficients are predicted using the octanol-air partition coefficient, also measured in this study, and the octanol-water partition coefficient. Results are similar to literature estimates for liquid/air partitioning of chloroform and chlorodibromomethane, but they differ from predictions based on hydrophobicity and lipid content. High correlations between the derived partitioned coefficients and the molecular structure (number of Br atoms) and physical properties (molecular weight and boiling point) are found for these analogous chemicals. In humans, THMs are both stored and metabolized with relatively rapid clearance rates. The derived partition coefficients can help to interpret results of biological monitoring and predict the potential for the accumulation and transfer of chemicals, specifically by the application of physiologically-based pharmacokinetic models. THM exposures to potentially susceptible populations, e.g. nursing infants, can be predicted using either such models.