Subchronic inhalation toxicity of methanol

Wound Healing Properties of Natural Products: Mechanisms of Action

A wound is the loss of the normal integrity, structure, and functions of the skin due to a physical, chemical, or mechanical agent. Wound repair consists of an orderly and complex process divided into four phases: coagulation, inflammation, proliferation, and remodeling. The potential of natural products in the treatment of wounds has been reported in numerous studies, emphasizing those with antioxidant, anti-inflammatory, and antimicrobial properties, e.g., alkaloids, saponins, terpenes, essential oils, and polyphenols from different plant sources, since these compounds can interact in the various stages of the wound healing process. This review addresses the most current in vitro and in vivo studies on the wound healing potential of natural products, as well as the main mechanisms involved in this activity. We observed sufficient evidence of the activity of these compounds in the treatment of wounds; however, we also found that there is no consensus on the effective concentrations in which the natural products exert this activity. For this reason, it is important to work on establishing optimal treatment doses, as well as an appropriate route of administration. In addition, more research should be carried out to discover the possible side effects and the behavior of natural products in clinical trials.

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

RIFM fragrance ingredient safety assessment, cis-3-hexenyl methyl carbonate, CAS Registry Number 67633-96-9

The following paper presents the method of determination of the percolation threshold in cement composites with expanded graphite by impedance spectroscopy. Most of the applications of cement composites with conductive additives require exceeding the percolation threshold. The ionic conductivity of cement matrix below the percolation threshold has a major impact on the conductivity of the composite, as a result, it significantly hinders the exploitation of these composites. The electric properties of cement composites with expanded graphite were evaluated by DC measurements and impedance spectroscopy (IS). Based on Nyquist plots, two equivalent circuits were adopted for the composites. Next, the values of capacitance and inductance of cement composites with expanded graphite were calculated from the fitted equivalent circuits. The analysis of the results shows that the percolation threshold occurs when the reactance of the composite changes from captative to inductive. Comparison between the values of percolation threshold obtained from DC measurements and IS shows that the method is effective for cement composites with conductive additives.

Adaptable sensor for employing fluorometric detection of methanol molecules: theoretical aspects and DNA binding studies

The multifunctional ligand NO2-H2SALNN has been synthesized and employed for the selective fluorometric detection of methanol and its interaction with DNA.

Toxicity of Methanol to Fish, Crustacean, Oligochaete Worm, and Aquatic Ecosystem

Static renewal bioassays were conducted in the laboratory and in outdoor artificial enclosures to evaluate toxic effects of methanol to one teleost fish and two aquatic invertebrates and to limnological variables of aquatic ecosystem. Ninety-six-hour acute toxicity tests revealed cladoceran crustacea Moina micrura as the most sensitive to methanol (LC50, 4.82 g/L), followed by freshwater teleost Oreochromis mossambicus (LC50, 15.32 g/L) and oligochaete worm Branchiura sowerbyi (LC50, 54.89 g/L). The fish, when exposed to lethal concentrations of methanol, showed difficulties in respiration and swimming. The oligochaete body wrinkled and fragmented under lethal exposure of methanol. Effects of five sublethal concentrations of methanol (0, 23.75, 47.49, 736.10, and 1527.60 mg/L) on the feeding rate of the fish and on its growth and reproduction were evaluated by separate bioassays. Ninety-six-hour bioassays in the laboratory showed significant reduction in the appetite of fish when exposed to 736.10 mg/L or higher concentrations of methanol. Chronic toxicity bioassays (90 days) in outdoor enclosures showed a reduction in growth, maturity index and fecundity of fish at 47.49 mg/L or higher concentrations of methanol. Primary productivity, phytoplankton population, and alkalinity of water were also reduced at these concentrations. Chronic exposure to 1527.60 mg/L methanol resulted in damages of the epithelium of primary and secondary gill lamellae of the fish. The results revealed 23.75 mg/L as the no-observed-effect concentration (NOEC) of methanol to freshwater aquatic ecosystem.

Chronic maternal methanol inhalation in nonhuman primates (Macaca fascicularis): reproductive performance and birth outcome

The present study was designed to characterize maternal reproductive performance and early offspring effects following exposure to methanol (MeOH) vapor in a nonhuman primate model. The two-cohort study design used 48 adult female Macaca fascicularis (24/cohort) monkeys exposed to 0, 200, 600, or 1800 ppm MeOH vapor for approximately 2.5 h/day, 7 days/week prior to breeding and throughout pregnancy. Maternal body weight measurement, clinical observations and health assessments were conducted routinely throughout the study. Menstrual cyclicity was monitored during the pre-breeding and breeding periods and timed matings were conducted with nonexposed males. Females were monitored closely during the last month of pregnancy. At birth, infant physical characteristics were measured and a newborn health assessment was conducted. Methanol exposure did not alter menstrual cycles, the number of breedings to conception or conception rate. A total of 34 live-born infants were delivered (control=8, 200 ppm=9, 600 ppm=8, 1800 ppm=9). One female each in the control and 600-ppm group delivered a stillborn infant and a cesarean section (C-section) was required to deliver a hydrocephalic infant who died in utero in the maternal 1800-ppm group. Although not statistically significant, five MeOH-exposed females were C-sectioned due to pregnancy complications such as uterine bleeding and prolonged unproductive labor. These complications were not observed in the control group. The mean length of pregnancy in the MeOH-exposed groups was significantly decreased by 6 to 8 days when compared to controls. There were no MeOH-related effects on offspring birthweight or newborn health status. The consistent reduction in length of pregnancy observed in the MeOH females may reflect a treatment effect on the fetal neuroendocrine system. Given that the fetal hypothalamic--pituitary-adrenal axis controls pregnancy length in most species, these results suggest a modest but significant effect of MeOH on the biochemical events that control the timing of birth.

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.

Evaluation of potential neurotoxic effects of occupational exposure to (L)-lactates

Organo psycho syndrome (OPS) or chronic toxic encephalopathy (CTE) is a neurotoxic condition reported following long-term exposure to paints containing organic solvent and to other solvents. Lactate esters are finding wider use as solvents. Lactate esters have been well studied in standard toxicity tests, but specific neurotoxicity studies have not been conducted. No clinical signs of chronic neurotoxicity have been observed in standard toxicity tests. Lactate esters are rapidly hydrolyzed in the body to lactic acid and the corresponding alcohol. Alcohols have been reported to have acute neurotoxic effects, usually following high levels of ingestion. The literature on alcohols was reviewed to establish the no-observed-adverse-effect level (NOAEL) for acute neurotoxicity and to look for any evidence of chronic neurotoxicity from the alcohols produced by hydrolysis of the lactate esters. The NOAELs were compared with the potential amounts of alcohol produced by hydrolysis of different lactate esters at 200 mg//m(3) (the NOAEL for most of the lactate esters). In all cases neither acute nor chronic neurotoxicity would be expected based on the amounts of alcohol produced by hydrolysis of the lactate esters at their NOAELs. L-Lactic acid is a normal metabolite in the body and is not considered neurotoxic. Based on this information there is no evidence to suggest that L-lactate esters can cause any chronic neurotoxicity, OPS, or CTE.

Proposal for reference concentrations (RfC) for inhalation exposure to methanol

A tentative reference concentration (RfC) for methanol in ambient air, i.e. an exposure concentration below which adverse effects are not expected to occur, was derived from the analysis of the toxicological data available in the literature. Well-documented studies that correlate environmental levels of methanol with observed toxic effects have not been found in the literature, nor have any long-term epidemiological studies of chronic low-level occupational exposure been found. Assessment of RfC for acute inhalation exposure is based on a human study (n=26 subjects) with a 'tentative' NOAEL of 262 mg/m(3). The calculated RfC for 1 h exposure is 104.8 mg/m(3). The RfC is given a low confidence rating as there was only one methanol concentration used. A well designed study on monkeys served as the basis for the assessment of RfC for chronic inhalation exposure. In this study, 13.1 and 131 mg/m(3) were considered as NOAEL and LOAEL, respectively. The calculated RfC is 0.38 mg/m(3). The overall database is weak, lacking data on reproductive and developmental endpoints in human or non-human primates. Nevertheless, the RfC is given a medium confidence rating because of the strength of the principal study.

Inhalation toxicity of methanol/gasoline in rats: effects of 13-week exposure

The subchronic inhalation toxicity of a methanol/gasoline blend (85% methanol, 15% gasoline, v/v) was studied in rats. Sprague Dawley rats (10 animals per group) of both sexes were exposed to vapours of methanol/gasoline at 50/3, 500/30 and 5000/300ppm for 6 hours per day, 5 days per week, for 13 weeks. Control animals inhaled filtered room air only. Control recovery and high dose recovery groups were also included which inhaled room air for an extra 4 weeks following the treatment period. No clinical signs of toxicity were observed in the treatment group and their growth curves were not significantly different from the control. Except for decreased forelimb grip strength in high dose females, no treatment-related neurobehavioural effects (4-6 hours post inhalation) were observed using screening tests which included cage-side observations, righting reflex, open field activities, and forelimb and hindlimb grip strength. At necropsy, the organ to body weight ratios for the liver, spleen, testes, thymus and lungs were not significantly different from the control group. There were no treatment-related effects in the hematological endpoints and no elevation in serum formate levels. Minimal serum biochemical changes were observed with the only treatment-related change being the decreased creatinine in the females. A dose-related increase in urinary ascorbic acid was detected in males after 2, 4 and 8 weeks of exposure, but not after the 12th week, and in females only at week-2. Increased urinary albumin was observed in treated males starting at the lowest dose and at all exposure periods, but not in females. A treatment-related increase in urinary beta 2-microglobulin was detected in males at week-2 only. Except for mild to moderate mucous cell metaplasia in nasal septum B, which occurred more often and with a slightly higher degree of severity in the low dose groups of both sexes, and presence of a minimal degree of interstitial lymphocyte infiltration in the prostate glands in the high dose males. No other significant microscopic changes were observed in the tissues of treated animals. Based on the marked increase in urinary ascorbic acid and albumin in the high dose males and the decreased forelimb grip strength in the high dose females, we concluded that the no-observed adverse effect level (NOAEL) of methanol/gasoline vapour is 500/30 ppm.

Short-term inhalation toxicity of methanol, gasoline, and methanol/gasoline in the rat

Four- to five-week-old male and female Sprague Dawley rats were exposed to vapors of methanol (2500 ppm), gasoline (3200 ppm), and methanol/gasoline (2500/3200 ppm, 570/3200 ppm) six hours per day, five days per week for four weeks. Control animals were exposed to filtered room air only. Depression in body weight gain and reduced food consumption were observed in male rats, and increased relative liver weight was detected in rats of both sexes exposed to gasoline or methanol/gasoline mixtures. Rats of both sexes exposed to methanol/gasoline mixtures had increased relative kidney weight and females exposed to gasoline and methanol/gasoline mixtures had increased kidney weight. Decreased serum glucose and cholesterol were detected in male rats exposed to gasoline and methanol/gasoline mixtures. Decreased hemoglobin was observed in females inhaling vapors of gasoline and methanol/gasoline at 570/3200 ppm. Urine from rats inhaling gasoline or methanol/gasoline mixtures had up to a fourfold increase in hippuric acid, a biomarker of exposure to the toluene constituent of gasoline, and up to a sixfold elevation in ascorbic acid, a noninvasive biomarker of hepatic response. Hepatic mixed-function oxidase (aniline hydroxylase, aminopyrine N-demethylase and ethoxyresorufin O-deethylase) activities and UDP-glucuronosyltransferase activity were elevated in rats exposed to gasoline and methanol/gasoline mixtures. Histopathological changes were confined to very mild changes in the nasal passages and in the uterus, where decreased incidence or absence of mucosal and myometrial eosinophilia was observed in females inhaling gasoline and methanol/gasoline at 570/3200 ppm. It was concluded that gasoline was largely responsible for the adverse effects, the most significant of which included depression in weight gain in the males, increased liver weight and hepatic microsomal enzyme activities in both sexes, and suppression of uterine eosinophilia. No apparent interactive effects between methanol and gasoline were observed.

Inhalation toxicity study of methanol, toluene, and methanol/toluene mixtures in rats: effects of 28-day exposure

The inhalation toxicity of methanol and toluene was investigated in rats. Young Sprague Dawley rats of both sexes were exposed to vapors of methanol (300 ppm, 3000 ppm), toluene (30 ppm, 300 ppm) or methanol/toluene (300/30 ppm, 300/300 ppm, 3000/30 ppm, and 3000/300 ppm) six hrs per day, five days/week for four weeks. Control animals inhaled air only. Increased serum alkaline phosphatase activity was observed in males exposed to high-dose toluene, and decreased creatinine was noted in the group exposed to high-dose methanol/toluene. The thyroid gland in females appeared to be a target organ for inhaled methanol, toluene, and methanol/toluene, although the changes were confined to a mild, and occasionally moderate, reduction in follicle size. Histopathological changes of the nasal passages, consisting of subepithelial nonsuppurative inflammation, occurred in higher incidences in rats exposed to methanol/toluene than in those exposed to the individual vapors. Inhalation of methanol, toluene, or methanol/toluene produced no changes in liver weights, hepatic mixed-function oxidases, or serum aspartate transaminase activities, and onlly minimal changes in liver histopathology. The only liver changes were decreased liver weight and increased cytoplasmic density of the periportal areas in females exposed to high-dose methanol/toluene. These data indicated that exposure to methanol, toluene, or a mixture of both produced mild biochemical effects and histological changes in the thyroid and nasal passage. No apparent interactive effects were observed.

Methanol inhalation toxicity

Significant toxicity can result from intentional methanol inhalation. We report seven cases, involving four patients, of intentional inhalation of CARB-MEDIC carburetor cleaner containing toluene (43.8%), methanol (23.2%), methylene chloride (20.5%), and propane (12.5%). Patients arrived at the emergency department with central nervous system depression, nausea, vomiting, shortness of breath, photophobia, and/or decreased visual acuity. Treatment included correction of acidosis, leucovorin and/or folic acid, ethanol infusions, and supportive care. Hemodialysis was necessary in three cases. Measured blood methanol levels ranged from 50.4 to 128.6 mg/dL. Blood formic acid levels were 120, 193, and 480 micrograms/mL, respectively, in three patients. Ophthalmic examinations revealed hyperemic discs and decreased visual acuity in one patient. One individual was found pulseless with several CARB-MEDIC cans nearby. Attempts at revival were unsuccessful. Clinicians should be aware that significant blood methanol and formic acid levels may occur after inhalation of methanol.

Physiologically based pharmacokinetic model for methanol in rats, monkeys, and humans

The pharmacokinetics of methanol and formate were characterized in male Fischer-344 rats and rhesus monkeys exposed to methanol vapor concentrations between 50 and 2000 ppm for 6 hr. End-of-exposure blood methanol concentrations were not directly proportional to the atmospheric concentration. The methanol exposures did not cause an elevation in blood formate concentrations. After an intravenous dose of [14C]methanol in rats, metabolism, exhalation, and renal excretion contributed 96.6, 2.6, and 0.8%, respectively, to the elimination of blood methanol concentrations. These values and the calculated renal methanol extraction efficiency (0.007) are nearly identical to those for humans after low doses of methanol. A physiologically based pharmacokinetic model was developed to simulate the in vivo data. In order to simulate the observed blood methanol concentrations in the inhalation studies in rats, a double pathway for methanol metabolism to formaldehyde was used. One path used rodent catalase Km and Vmax values and the other used a smaller Km and Vmax to simulate an enzyme with a higher affinity and lower capacity. The lack of proportionality observed in end-of-exposure blood methanol concentrations may be due to saturation of an enzyme with higher affinity and lower capacity than catalase. The physiologically based pharmacokinetic model was modified to simulate the monkey data and was scaled-up for humans. In order to simulate the monkey blood methanol concentrations, the use of rodent catalase parameters for methanol metabolism was required. This finding suggests that primates and rodents may be similar in the initial step of methanol metabolism after low methanol doses. Previously published human urinary methanol excretion data was successfully simulated by the model. The models were used to predict the atmospheric methanol concentration range over which the laboratory species exhibit quantitative similarities with humans. Below 1200 ppm, all three species exhibit similar end-of-exposure blood methanol concentrations and a linear relationship between atmospheric and blood methanol concentrations. At higher atmospheric concentrations, external and internal methanol concentrations increase desparately, suggesting that delivered dose rather than exposure concentration should be used in interpreting data from high-dose studies.

Toxicity to rats of methanol-fueled engine exhaust inhaled continuously for 28 days

Fischer 344 rats were exposed to three concentrations of exhaust generated by an M85 methanol-fueled engine (methanol with 15% gasoline) without catalyst for 8 h/d, 7 d/wk for 7, 14, 21, or 28 d. Concentration- and time-dependent yellowing of the fur was prominent in all treated groups. Concentration-dependent increases in the erythrocyte count, hematocrit, hemoglobin concentration, formaldehyde in plasma, and carboxyhemoglobin in the erythrocytes, and decrease in serum alkaline phosphatase activity were seen after all exposure periods. Histopathologically, lesions were found in the nasal cavity and lungs after 7 d of exposure. Squamous metaplasia of the respiratory epithelium of level 1 (level of the posterior edge of the upper incisor teeth) lining of the nasoturbinate and/or maxilloturbinate and infiltration of neutrophils into the submucosa, and decreases of Clara cells in the terminal bronchiolus and of cilia in the bronchiolar epithelium, were observed in the high-concentration group (carbon monoxide, 94 ppm; formaldehyde, 6.9 ppm; methanol, 17.9 ppm; nitrogen oxides, 52.7 ppm; nitrogen dioxide, 10.6 ppm). The histopathological extents of several lesions increased slightly with the exposure time. Slight squamous metaplasia and hyperplasia of the respiratory epithelium at level 1 were also observed in the medium-concentration group (one in three of the high-concentration group). No histopathological changes were found in the olfactory epithelium of the nasal cavity. In the low-concentration group (one in nine of the high-concentration group), no marked histopathological changes in these organs were observed. These results may suggest that the lesions observed in the nasal cavity of rats exposed to methanol-fueled engine exhaust were mainly caused by formaldehyde, although other components in the exhaust also may have affected nasal cavity and/or lungs to less extent.

Evidence that methanol inhalation does not induce chromosome damage in mice

Mice were exposed by inhalation to 800 or 4000 ppm methanol for 5 days, and cytogenetic effects were analyzed in blood erythrocytes, lung cells, and testicular germ cells. The results were uniformly negative; no increased frequencies of micronuclei in blood cells, of sister-chromatid exchanges, chromosome aberrations, or micronuclei in lung cells, or of synaptonemal complex damage in spermatocytes were found. From the standpoint of risk assessment, these experimental studies do not reveal any evidence of a cytogenetic hazard associated with inhalation of methanol.

The toxicity of inhaled methanol vapors

Methanol could become a major automotive fuel in the U.S., and its use may result in increased exposure of the public to methanol vapor. Nearly all of the available information on methanol toxicity in humans relates to the consequences of acute, rather than chronic, exposures. Acute methanol toxicity evolves in a well-understood pattern and consists of an uncompensated metabolic acidosis with superimposed toxicity to the visual system. The toxic properties of methanol are rooted in the factors that govern both the conversion of methanol to formic acid and the subsequent metabolism of formate to carbon dioxide in the folate pathway. In short, the toxic syndrome sets in if formate generation continues at a rate that exceeds its rate of metabolism. Current evidence indicates that formate accumulation will not challenge the metabolic capacity of the folate pathway at the anticipated levels of exposure to automotive methanol vapor.