Plasma Formate Is Greater in Fetal and Neonatal Rats Compared with Their Mothers.

BACKGROUND: Formate can be incorporated into 10-formyl-tetrahydrofolate (10-formyl-THF), which is a substrate for purine synthesis, and after further reduction of the one-carbon group, may be used as a substrate for thymidylate synthesis and for homocysteine remethylation. OBJECTIVE: We examined plasma formate concentrations and the expression of genes involved in the production and utilization of formate in fetal and neonatal rats and in pregnant and virgin female rats. METHODS: In 1 experiment, plasma formate was measured by GC-MS in rats aged 1-56 d. In a second experiment, virgin female (adult) rats, 19-d pregnant rats (P) and their male and female fetuses (F), and 3-d-old (N) and 7-d-old (J) offspring had plasma and amniotic fluid analyzed for formate by GC-MS, mRNA abundance in liver and placenta by qPCR, and several plasma amino acids by HPLC. RESULTS: The plasma formate concentration was significantly higher in fetuses at embryonic day 19 than in the mothers. It was also significantly higher in neonatal rats but slowly returned to adult concentrations by ∼3 wk. The abundance of mitochondrial monofunctional 10-formyl-tetrahydrofolate synthetase (Mthfd1l) mRNA was significantly higher in placenta (PP) and F liver than in liver of N or J. Expression of mitochondrial bifunctional NAD-dependent methylene-tetrahydrofolate dehydrogenase/methenyl-tetrahydrofolate cyclohydrolase (Mthfd2) was significantly enriched in PP and liver of P, intermediate in F liver, and much lower in liver of N and J, relative to PP. Serine hydroxymethyltransferase 2 (Shmt2), methylenetetrahydrofolate dehydrogenase 1 (Mthfd1), and glycine decarboxylase protein of the glycine cleavage system (Gldc) mRNA expression was significantly lower in PP compared with other groups. Cytoplasmic NAD(P)-dependent 10-formyl-tetrahydrofolate dehydrogenase (Aldh1/1) and mitochondrial NAD(P)-dependent 10-formyl-tetrahydrofolate dehydrogenase (Aldh1/2) , genes responsible for the catabolism of 10-formylTHF, were very weakly expressed in PP, low in livers of F and N, and reached the significantly higher adult levels in J. Serine, glycine, and methionine concentrations in plasma of F were significantly higher than in plasma of P. CONCLUSIONS: Formate metabolism is highly active in fetuses and in placenta of pregnant rats.

Pharmacometabonomics Analysis Reveals Serum Formate and Acetate Potentially Associated with Varying Response to Gemcitabine-Carboplatin Chemotherapy in Metastatic Breast Cancer Patients.

Gemcitabine-carboplatin (GC) chemotherapy was efficacious in metastatic breast cancer (MBC) patients probably resistant to anthracyclines and taxanes, but showed significant interindividual variation in treatment responses. Early prediction of response to treatment is clinically relevant to identify patients who will achieve clinical benefit. In this study, nuclear magnetic resonance (NMR) based pharmacometabonomics was used to noninvasively predict the response to GC chemotherapy of 29 MBC patients with prior exposure to both anthracyclines and taxanes from a phase II study. Formate and acetate levels in the baseline serum collected prior to GC chemotherapy were identified as potential predictive markers to select patients who will achieve clinical benefit and to identify those who should not be treated with the therapy to avoid futile treatment. The significantly lower baseline levels of serum formate and acetate in patients with resistant disease may reflect the higher demand of them as alternate/additional nutritional sources to fuel the accelerated proliferation of breast cancer cells that are biologically more aggressive or resistant to therapy. The results suggest that pharmacometabonomics can be a potential useful tool for predicting chemotherapy response in the context of precision medicine. Prospective studies with larger patient cohorts are required for validation of the findings.

FASD: folic acid and formic acid - an unholy alliance in the alcohol abusing mother.

Alcohol consumption during pregnancy remains a significant cause of preventable birth defects and developmental disabilities; however, the mechanism of toxicity remains unclear. Methanol is present as a congener in many alcoholic beverages and is formed endogenously. Because ethanol is preferentially metabolized over methanol, it has been found in the sera and cerebro-spinal fluid of alcoholics. Toxicity resulting from methanol has been attributed to formic acid. Formic acid is present in significantly higher quantities in the biofluids of alcoholics. These higher levels can be cytotoxic and cause neuronal cell death. However, the adverse effects can be mitigated by adequate levels of hepatic folic acid, because formic acid elimination depends on folic acid. During pregnancy, folate concentrations are at least 2-fold higher in cord blood then in maternal blood, owing to increased folate requirements. The reverse has been demonstrated in pregnancies with alcohol abuse, suggesting downregulation of folate transporters and low fetal folate levels. Moreover, formic acid can cross the placenta and its adverse effects can be mitigated by folic acid. Thus, the combination of low fetal folate levels and presence of formic acid form a potent cytotoxic combination that may play a significant role in the etiology of fetal alcohol spectrum disorder.

Formate: The Neglected Member of One-Carbon Metabolism.

Formate, the only non-tetrahydrofolate (THF)-linked intermediate in one-carbon metabolism, is produced in mammals from a variety of metabolic sources. It occurs in serum of adults at a concentration of approximately 30 µM. Its principal function lies as a source of one-carbon groups for the synthesis of 10-formyl-THF and other one-carbon intermediates; these are primarily used for purine synthesis, thymidylate synthesis, and the provision of methyl groups for synthetic, regulatory, and epigenetic methylation reactions. Although formate is largely produced in mitochondria, these functions mostly occur in the cytoplasm and nucleus. Formate plays a significant role in embryonic development, as evidenced by the effectiveness of formate in the pregnant dam's drinking water on the incidence of neural tube defects in some genetic models. High formate concentrations in fetal lambs may indicate a role in fetal development and suggest that extracellular formate may play a role in the interorgan distribution of one-carbon groups.

Riboflavin Deficiency in Rats Decreases de novo Formate Production but Does Not Affect Plasma Formate Concentration.

Background: The one-carbon metabolism pathway is highly dependent on a number of B vitamins in order to provide one-carbon units for purine and thymidylate biosynthesis as well as homocysteine remethylation. Previous studies have examined folate and vitamin B-12 deficiency and their effects on formate metabolism; as of yet, to our knowledge, no studies on the effects of riboflavin deficiency on formate metabolism have been published.Objective: Our objective was to determine the effects of riboflavin deficiency on formate metabolism.Methods: Weanling male rats were randomly assigned either to control, riboflavin-replete (RR) or to experimental, riboflavin-deficient (RD) versions of the AIN-93G diet for 13 d, at which time a constant infusion of [13C]-formate was carried out to ascertain the effects of deficiency on formate production. Gas chromatography-mass spectrometry was used to measure plasma formate concentration and [13C]-formate enrichment. HPLC, LC-mass spectrometry (MS)/MS, and enzymatic assays were used for the measurement of one-carbon precursors and other metabolites.Results: RD rats had significantly lower rates of formate production (15%) as well as significantly reduced hepatic methylenetetrahydrofolate reductase activity (69%) and protein concentration (54%) compared with RR rats. There was no difference in plasma formate concentrations between the groups. Plasma serine, a potential one-carbon precursor, was significantly higher in RD rats (467 ± 73 µM) than in RR rats (368 ± 52 µM).Conclusions: Although deficiencies in folate and vitamin B-12 lead to major changes in plasma formate concentrations, riboflavin deficiency results in no significant difference; this disagrees with the prediction of a published mathematical model. Our observation of a lower rate of formate production is consistent with a role for flavoproteins in this process.

1H nuclear magnetic resonance (NMR)-based serum metabolomics of human gallbladder inflammation.

OBJECTIVE AND DESIGN: We present in this article 1H nuclear magnetic resonance (NMR)-based metabolic approach to screen the serum metabolic alterations in human gallbladder inflammation with chronic cholecystitis (CC). MATERIAL/METHODS: Total of 71 human serum samples was divided into two groups, (n = 41, CC) and (n = 30 control). 1H NMR metabolic profiling was carried out for investigation of metabolic alterations. Multivariate statistical analysis was applied for pattern recognition and identification of metabolites playing crucial role in gallbladder inflammation. Receiver operating curve (ROC) and pathway analysis on NMR data were also carried out to validate the findings. RESULTS: Serum metabolites such as glutamine, low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), alanine, branch chained amino acids (BCAA), histidine and tyrosine were found to be depleted whereas formate, lactate, 1,2-propanediol were found to be elevated in CC. Metabolic pathways associated with metabolite alteration have also been reported. CONCLUSIONS: NMR has been established for disease diagnosis along with identification of metabolic pattern recognition in biofluids. Gallstones cause inflammation of the gallbladder in the form of CC. Inflammation plays a major role in causation of gall bladder cancer and leads the way to malignancy. Metabolic analysis of CC may lead to early diagnosis of disease and its progression to gallbladder cancer.

Nuclear enrichment of folate cofactors and methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) protect de novo thymidylate biosynthesis during folate deficiency.

Folate-mediated one-carbon metabolism is a metabolic network of interconnected pathways that is required for the de novo synthesis of three of the four DNA bases and the remethylation of homocysteine to methionine. Previous studies have indicated that the thymidylate synthesis and homocysteine remethylation pathways compete for a limiting pool of methylenetetrahydrofolate cofactors and that thymidylate biosynthesis is preserved in folate deficiency at the expense of homocysteine remethylation, but the mechanisms are unknown. Recently, it was shown that thymidylate synthesis occurs in the nucleus, whereas homocysteine remethylation occurs in the cytosol. In this study we demonstrate that methylenetetrahydrofolate dehydrogenase 1 (MTHFD1), an enzyme that generates methylenetetrahydrofolate from formate, ATP, and NADPH, functions in the nucleus to support de novo thymidylate biosynthesis. MTHFD1 translocates to the nucleus in S-phase MCF-7 and HeLa cells. During folate deficiency mouse liver MTHFD1 levels are enriched in the nucleus >2-fold at the expense of levels in the cytosol. Furthermore, nuclear folate levels are resistant to folate depletion when total cellular folate levels are reduced by >50% in mouse liver. The enrichment of folate cofactors and MTHFD1 protein in the nucleus during folate deficiency in mouse liver and human cell lines accounts for previous metabolic studies that indicated 5,10-methylenetetrahydrofolate is preferentially directed toward de novo thymidylate biosynthesis at the expense of homocysteine remethylation during folate deficiency.

A novel bedside diagnostic test for methanol poisoning using dry chemistry for formate.

BACKGROUND: The standard diagnostic approach to methanol poisoning is chromatographic measurement of methanol on centrally placed stationary equipment. Methanol poisoning in places where such equipment is unavailable is thus often not diagnosed. Methanol is metabolized to a toxic metabolite, formate; the presence of this compound indicates methanol poisoning. We have developed an enzymatic test for formate and modified it into a portable dry chemistry system that could be used anywhere. METHODS: The method consists of two enzymatic steps: Formation of NADH from NAD by formate dehydrogenase, and subsequent use of NADH as a reductant of a tetrazolium into a formazan dye that can be quantified photometrically or visually. RESULTS: The photometer gave a good correlation of R(2) = 0.9893 in serum and R(2) = 0.9949 in whole blood, showing an instrumental detection limit of less than 1 mM (4.5 mg/dL). The visual readings showed a correlation of R(2) = 0.8966. Users experienced some difficulty in separating the negative control from the low positives. CONCLUSIONS: We have documented the feasibility of an affordable formate strip test for bedside diagnosis of methanol poisoning and for screening of metabolic acidosis of unknown origin. Visual reading is possible, but a reader will improve reliability at lower levels of formate. Future studies are necessary to study the sensitivity and specificity towards other causes of metabolic acidosis and other acids present in human blood.

Severe Methanol Poisoning with Supralethal Serum Formate Concentration: A Case Report.

OBJECTIVE: To present a case of survival without visual and central nervous system sequelae at a formate concentration of twice the reported lethal level. CLINICAL PRESENTATION AND INTERVENTION: This was a case of a 33-year-old man who ingested 1 liter of a toxic mixture of methanol and ethanol. Upon admission, he presented with anxiety, tachycardia and hypertension and had a serum formate level of 1,400 mg/l (normal range 0.9-2.1 mg/l), a methanol level of 806 mg/l (normal range 2-30 mg/l), an undetectable ethanol concentration and a normal lactate level. A 10% solution of ethanol and folinic acid was administered intravenously and two 8-hour sessions of intermittent hemodialysis were performed. The patient was discharged on the fifth day without sequelae of poisoning. The follow-up examinations 3 months and 2 years later revealed no damage to the basal ganglia. The patient had normal visual-evoked potential and findings on optical coherence tomography. The genetic analysis revealed a rare minor allele for the gene coding CYP2E1 enzyme of the microsomal ethanol oxidizing system. CONCLUSION: The patient survived acute methanol poisoning without long-term sequelae despite a high serum level of formic acid upon admission.

[Distribution of Formic Acid after Methanol Intoxication in Rats].

OBJECTIVE: To investigate concentration and distribution in blood and tissues of formic acid after methanol intoxication in rats. METHODS: The Sprague-Dawley rats were divided into groups for control group and 3-day and 7-day intoxication treatment groups. The experimental groups were administered methanol by gavage with the initial dose of 8 mL/kg and followed with 4 mL/kg supplemental dose 24 h later. After 3 days and 7 days later, rats were killed by decapitation. Then samples of cardiac blood, liver, kidney, brain, heart and stomach of each group were collected. Formic acid concentrations were detected by high performance liquid chromatography. RESULTS: Formic acid concentrations in tissues were higher than in blood. Compared with 3-day intoxication group, there was an increase formic acid of concentration in brain and stomach in 7-day intoxication group, while a decrease in liver and kidney (P < 0.05). CONCLUSION: High performance liquid chromatography could be used to accurately detect formic acid. As the metabolite of methanol, formic acid accumulates in rat blood and tissues after intoxication and the concentrations in organs and tissues are obviously higher than in blood.

[Study of blood concentration analysis for formate in acute methanol poisoning].

A 53-year-old woman ingested about 300 mL of 95% methanol. After immediate ethanol antagonist therapy and hemodialysis, she recovered completely. Few days later, the plasma concentration of methanol and formate was measured. A gas chromatography was used for the plasma methanol concentration measurement, and a colorimetric method was used for plasma formate concentration measurement (Formate Colorimetric Assay Kit; BioVision, California, USA). Patient's plasma methanol concentration before hemodialysis was 676.9 mg/dL and plasma formate concentration was 16.9 mg/dL. By removing blood methanol and formate using hemodialysis before formate accumulations in the body, the patient was discharged without any sequelae. We were able to obtain correlation between a gas chromatography and colorimetric method without gas chromatography-mass spectrometry, with good correlation coefficients. The sensitivity was sufficient for analyzing blood sample. Monitoring formate concentration is useful in determining the treatment and evaluating the prognosis of methanol poisoning. We suggest that this colorimetric method is useful in a facility with no access to a gas chromatography in order to measure a plasma formate concentration.

Intermittent hemodialysis is superior to continuous veno-venous hemodialysis/hemodiafiltration to eliminate methanol and formate during treatment for methanol poisoning.

During an outbreak of methanol poisonings in the Czech Republic in 2012, we were able to study methanol and formate elimination half-lives during intermittent hemodialysis (IHD) and continuous veno-venous hemodialysis/hemodiafiltration (CVVHD/HDF) and the relative impact of dialysate and blood flow rates on elimination. Data were obtained from 11 IHD and 13 CVVHD/HDF patients. Serum methanol and formate concentrations were measured by gas chromatography and an enzymatic method. The groups were relatively comparable, but the CVVHD/HDF group was significantly more acidotic (mean pH 6.9 vs. 7.1 IHD). The mean elimination half-life of methanol was 3.7 and formate 1.6 h with IHD, versus 8.1 and 3.6 h, respectively, with CVVHD/HDF (both significant). The 54% greater reduction in methanol and 56% reduction in formate elimination half-life during IHD resulted from the higher blood and dialysate flow rates. Increased blood and dialysate flow on the CVVHD/HDF also increased elimination significantly. Thus, IHD is superior to CVVHD/HDF for more rapid methanol and formate elimination, and if CVVHD/HDF is the only treatment available then elimination is greater with greater blood and dialysate flow rates.

An isotope-dilution, GC-MS assay for formate and its application to human and animal metabolism.

Formate, a crucial component of one-carbon metabolism, is increasingly recognized as an important intermediate in production and transport of one-carbon units. Unlike tetrahydrofolate-linked intermediates, it is not restricted to the intracellular milieu so that circulating levels of formate can provide insight into cellular events. We report a novel isotope-dilution, GC-MS assay employing derivatization by 2,3,4,5,6-pentafluorobenzyl bromide for the determination of formate in biological samples. This assay is robust and sensitive; it may be applied to the measurement of formate in serum, plasma and urine. We demonstrate how this method may be applied by providing the first characterization of formate levels in a human population; formate levels were higher in males than in females. We also show how this procedure may be applied for the measurement of in vivo kinetics of endogenous formate production in experimental animals.

[Usefulness of blood formic acid detection in the methanol poisoning in the practice of clinical toxicology department-preliminary assessment]. / Ocena wstepna przydatnosci oznaczenia kwasu mrówkowego w diagnostyce zatruc metanolem w praktyce oddzialu toksykologii klinicznej.

BACKGROUND: Severe metabolic acidosis is one of the most difficult diagnostic and therapeutic challenges. The most common causes of this type of acid-base balance disorder are toxic alcohols, e.g. methanol poisoning. Metabolites of methanol, formaldehyde and formic acid are responsible for severe symptoms of this poisoning. OBJECTIVE: The aim of this study is a preliminary assessment of usefulness of formic acid detection by gas chromatography in the daily practice of clinical toxicology department in methanol poisoning confirmed by the designation of this alcohol in the blood. METHODS: The study included 9 patients from Greater Poland region diagnosed with methanol poisoning. Blood samples were collected during routine laboratory tests, on admission secured at-80°C, and then formic acid was determined by head-space gas chromatography. The relationship between the concentration of blood formic acid and methanol, ethanol, and the acid-base balance parameters were evaluated. RESULTS: The study group consisted of 9 men, aged 49.89 ± 6.17 years. All patients were diagnosed with alcohol dependence. In most cases (66.67%) and methanol poisoning occurred during ethanol abuse. The average blood methanol and ethanol concentrations were 2.48±1.74 g/L and 0.99±1.73 g/L respectively. The average blood formic acid concentration was 0.59±0.46 g/L, from 0.0 to 1.12 g/L. Acid-base balance parameters were (mean± SD): pH 7.00 ±0.36; pCO2 32.26 ± 14.54 mmHg; PO2 114.24±77.53 mmHg; BE -18.28 16.76 mmol/L; HCO3-12.70±11.53 mmol/L. There was a positive correlation be- tween the blood methanol and formic acid concentration. A negative correlation was found between the blood ethanol and formic acid concentration. In patients with positive blood ethanol concentration (1.74 to 5.0 g/L, mean 2.96±1.78 g/L) there was not any formic acid, despite the presence of methanol was confirmed. These patients did not demonstrate metabolic acidosis (mean±SD): pH 7.43 ±0.20; HCO3- 27.87 ± 2.36 mmol/L; BE 3.60 ±2.40 mmol/L. In contrast, in all patients with negative blood ethanol concentration, tests confirmed metabolic acidosis and elevated formic acid (mean SD): pH 6.80±0.20; HCO3- 5.12±1.67 mmol/L; BE-29.20±3.68 mmol/L; formic acid 0.89±0.16 g/L. CONCLUSION: Methanol poisoning cannot be confirmed by positive blood formic acid in patients with high blood ethanol concentration (≥1.74 g/L). In this kind of intoxication severe metabolic acidosis does not occur too. In patients with no detectable blood ethanol concentration, blood formic acid concentration can reach 1.12 g/L and correlates with the severity of metabolic acidosis.

Formate: an essential metabolite, a biomarker, or more?

Plasma and urinary formate concentrations were recently found to be elevated during vitamin B12 and folate deficiencies. It was proposed that formate may be a valuable biomarker of impaired one-carbon metabolism. Formate is an essential intermediary metabolite in folate-mediated one-carbon metabolism and, despite its importance, our knowledge of its metabolism is limited. Formate can be produced from several substrates (e.g., methanol, branched chain fatty acids, amino acids), some reactions being folate-dependent while others are not. Formate removal proceeds via two pathways; the major one being folate-dependent. Formate is a potentially toxic molecule and we suggest that formate may play a role in some of the pathologies associated with defective one-carbon metabolism.

Metabolomic signatures in guinea pigs infected with epidemic-associated W-Beijing strains of Mycobacterium tuberculosis.

With the understanding that the laboratory propagated strain of Mycobacterium tuberculosis H37Rv is of modest virulence and is drug susceptible, in the present study, we performed a nuclear magnetic resonance-based metabolomic analysis of lung tissues and serum obtained from guinea pigs infected by low dose aerosol exposure to clinical isolates of Mycobacterium tuberculosis. High Resolution Magic Angle Spinning NMR coupled with multivariate statistical analysis of 159 lung tissues obtained from multiple locations of age-matched naïve and 30 and 60 days of infected guinea pig lungs revealed a wide dispersal of metabolic patterns, but within these, distinct clusters of signatures could be seen that differentiated between naive control and infected animals. Several metabolites were identified that changed in concert with the progression of each infection. Major metabolites that could be interpreted as indicating host glutaminolysis were consistent with activated host immune cells encountering increasingly hypoxic conditions in the necrotic lung lesions. Moreover, glutathione levels were constantly elevated, probably in response to oxygen radical production in these lesions. Additional distinct signatures were also seen in infected serum, with altered levels of several metabolites. Multivariate statistical analysis clearly differentiated the infected from the uninfected sera; in addition, Receiver Operator Characteristic curve generated with principal component 1 scores showed an area under the curve of 0.908. These data raise optimism that discrete metabolomic signatures can be defined that can predict the progression of the tuberculosis disease process, and form the basis of an innovative and rapid diagnostic process.

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration.

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration. Am J Physiol Endocrinol Metab 301: E000-E000, 2011. First published September 20, 2011; 10.1152/ajpendo.00345.2011.-We carried out a (1)H-NMR metabolomic analysis of sera from vitamin B(12)-deficient rats. In addition to the expected increases in methylmalonate and homocysteine (Hcy), we observed an approximately sevenfold increase in formate levels, from 64 µM in control rats to 402 µM in vitamin B(12)-deficient rats. Urinary formate was also elevated. This elevation of formate could be attributed to impaired one-carbon metabolism since formate is assimilated into the one-carbon pool by incorporation into 10-formyl-THF via the enzyme 10-formyl-THF synthase. Both plasma and urinary formate were also increased in folate-deficient rats. Hcy was elevated in both the vitamin B(12)- and folate-deficient rats. Although plasma Hcy was also elevated, plasma formate was unaffected in vitamin B(6)-deficient rats (impaired transsulfuration pathway). These results were in accord with a mathematical model of folate metabolism, which predicted that reduction in methionine synthase activity would cause increased formate levels, whereas reduced cystathionine ß-synthase activity would not. Our data indicate that formate provides a novel window into cellular folate metabolism, that elevated formate can be a useful indicator of deranged one-carbon metabolism and can be used to discriminate between the hyperhomocysteinemia caused by defects in the remethylation and transsulfuration pathways.

Formate test for bedside diagnosis of methanol poisoning.

Methanol poisoning kills thousands of people every year and remains a diagnostic challenge, especially where the resources are scarce, but also in high-income countries worldwide. We are in the course of developing a bedside strip to detect formate - the toxic metabolite of methanol. We hereby present the first clinical methanol case where formate was detected bedside from a drop of blood: The patient, a 61-year-old male, was admitted with a suspect methanol poisoning and severe metabolic acidosis. The test strip was positive after 3 minutes. Sodium bicarbonate (500 mmol/L), fomepizole, dialysis and folinic acid were given based on the positive test. The diagnosis was some hours later confirmed by GC-MS, showing a methanol concentration of 62 mmol/L (200 mg/dL) and a formate concentration of 19 mmol/L. Implementation of this technology into routine clinical use can potentially offer an opportunity for a step change in the management of methanol poisoning.

COVID-19: A methyl-group assault?

The socio-economic implications of COVID-19 are devastating. Considerable morbidity is attributed to 'long-COVID' - an increasingly recognized complication of infection. Its diverse symptoms are reminiscent of vitamin B12 deficiency, a condition in which methylation status is compromised. We suggest why SARS-CoV-2 infection likely leads to increased methyl-group requirements and other disturbances of one-carbon metabolism. We propose these might explain the varied symptoms of long-COVID. Our suggested mechanismmight also apply to similar conditions such as myalgic encephalomyelitis/chronic fatigue syndrome. The hypothesis is evaluable by detailed determination of vitamin B12and folate status, including serum formate as well as homocysteine and methylmalonic acid, and correlation with viral and host RNA methylation and symptomatology. If confirmed, methyl-group support should prove beneficial in such individuals.

Species differences in methanol and formic acid pharmacokinetics in mice, rabbits and primates.

Methanol (MeOH) is metabolized primarily by alcohol dehydrogenase in humans, but by catalase in rodents, with species variations in the pharmacokinetics of its formic acid (FA) metabolite. The teratogenic potential of MeOH in humans is unknown, and its teratogenicity in rodents may not accurately reflect human developmental risk due to differential species metabolism, as for some other teratogens. To determine if human MeOH metabolism might be better reflected in rabbits than rodents, the plasma pharmacokinetics of MeOH and FA were compared in male CD-1 mice, New Zealand white rabbits and cynomolgus monkeys over time (24, 48 and 6h, respectively) following a single intraperitoneal injection of 0.5 or 2g/kg MeOH or its saline vehicle. Following the high dose, MeOH exhibited saturated elimination kinetics in all 3 species, with similar peak concentrations and a 2.5-fold higher clearance in mice than rabbits. FA accumulation within 6h in primates was 5-fold and 43-fold higher than in rabbits and mice respectively, with accumulation being 10-fold higher in rabbits than mice. Over 48 h, FA accumulation was nearly 5-fold higher in rabbits than mice. Low-dose MeOH in mice and rabbits resulted in similarly saturated MeOH elimination in both species, but with approximately 2-fold higher clearance rates in mice. FA accumulation was 3.8-fold higher in rabbits than mice. Rabbits more closely than mice reflected primates for in vivo MeOH metabolism, and particularly FA accumulation, suggesting that developmental studies in rabbits may be useful for assessing potential human teratological risk.