Glutathione depletion modulates methanol, formaldehyde and formate toxicity in cultured rat conceptuses

The proposed use of methanol (H3COH) as an alternative to fossil fuels has prompted concern about potential health risks resulting from widespread environmental exposure. Methanol is teratogenic in rodents and, although the exact toxic species is not known, teratogenesis may result from the enzymatic biotransformation of H3COH to formaldehyde (CH2O) and formic acid causing increased biological reactivity and toxicity. A protective role for the antioxidant glutathione (GSH) has been described for H3COH, CH2O and formic acid toxicity in various biological systems but has yet to be evaluated in the developing conceptus. Whole embryo culture studies were conducted using GD 10-11 rat conceptuses to elucidate the relationship between H3COH and its metabolites and GSH status. Methanol exposure produced a decrease in normal growth parameters and a dose-dependent loss of viability. CH2O had deleterious effects on embryo growth and viability. Sodium formate (HCOONa) exposure resulted in a high mortality rate but viable embryos did not manifest any abnormalities. Methanol, CH2O, and HCOONa all produced a significant depletion of GSH in both embryo and VYS. Inhibition of GSH synthesis by L-buthionine-S,R-sulfoximine (BSO) treatment exacerbated H3COH, CH2O and HCOONa embryotoxicity. Interestingly, only H3COH/BSO and CH2O/BSO co-treatments caused increased malformation, while embryos treated with HCOONa/BSO did not produce any developmental deformities. These results implicate CH2O as the most embryotoxic H3COH metabolite, on a molar basis, in terms of causing dysmorphogenesis, alterations of normal growth parameters and embryolethality. HCOONa was selectively embryolethal and did not produce dysmorphogenesis. CH2O toxicity is potentiated by GSH depletion, indicating that GSH may be more directly involved in its detoxication in the embryo.     

Methanol, formaldehyde, and sodium formate exposure in rat and mouse conceptuses: a potential role of the visceral yolk sac in embryotoxicity

BACKGROUND: Methanol (CH3OH) is believed to be teratogenic based on rodent studies. The mouse is more sensitive than the rat, but mechanisms of toxicity and identification of teratogenic metabolites are uncertain. METHODS: Rat and mouse whole embryo cultures are used to distinguish toxicity of CH3OH and its metabolites, formaldehyde (HCHO) and formate (HCOONa), which are produced following transit through the visceral yolk sac (VYS), via addition to culture medium, or by direct embryonic exposure through microinjection into the amnion. RESULTS: Embryonic viability, increased dysmorphogenesis, and decreased growth parameters were altered in a dose-dependent fashion for each compound. Mouse embryos were more sensitive than rat, as indicated by significant decreases in viability at comparable, lower concentrations. HCHO produced dysmorphogenesis and caused embryolethality at nearly 1000-fold lower concentrations (0.004 mg/ml) than seen with either CH3OH or HCOONa. All agents produced incomplete axial rotation and delayed neural tube closure in mice, but only CH3OH elicited similar effects in the rat. Increased growth retardation, blood pooling in the head and VYS, enlarged pericardium, accumulation of necrotic matter in the amnion, and hypoplastic prosencephalon were observed in both species with all compounds. Microinjection of compounds into the amnion produced higher mortality in mouse and rat, compared to equimolar amounts added to the culture medium. CH3OH did not prevent neural tube closure in the rat when microinjected. CONCLUSIONS: HCHO is the most embryotoxic CH3OH metabolite and elicits the entire spectrum of lesions produced by CH3OH. The VYS serves a general protective role against toxicity and inherent differences in the embryonic metabolism of CH3OH may determine species sensitivity.     

Conversion and toxicity characteristics of formaldehyde in acetoclastic methanogenic sludge

An unadapted mixed methanogenic sludge transformed formaldehyde into methanol and formate. The methanol to formate ratio obtained was 1:1. Formaldehyde conversion proceeded without any lag phase, suggesting the constitutive character of the formaldehyde conversion enzymes involved. Because the rate of formaldehyde conversion declined at increased formaldehyde additions, we hypothesized that some enzymes and/or cofactors might become denatured as a result of the excess of formaldehyde. Furthermore, formaldehyde was found to be toxic to acetoclastic methanogenesis in a dual character. Formaldehyde toxicity was partly reversible because once the formaldehyde concentration was extremely low or virtually removed from the system, the methane production rate was partially recovered. Because the degree of this recovery was not complete, we conclude that formaldehyde toxicity was partly irreversible as well. The irreversible toxicity likely can be attributed to biomass formaldehyde-related decay. Independent of the mode of formaldehyde addition (i.e., slug or continuous), the irreversible toxicity was dependent on the total amount of formaldehyde added to the system. This finding suggests that to treat formaldehyde-containing waste streams, a balance between formaldehyde-related decay and biomass growth should be attained.     

Bacterial yields on methanol,methylamine, formaldehyde,and formate

Several bacteria utilizing C₁-compounds as sole carbon sources were grown on these substrates in continuous culture. The molar yield values (g of cell dry wt/mol of substrate utilized) of bacteria which utilize C₁-compounds via the ribulose monophosphate pathway were between 15.7 to 17.3 when grown on methanol; while the molar yield values of bacteria which use the serine pathway for the assimilation of C₁-compounds varied between 9.8 and 13.1. The molar yield values of different bacteria which use the serine pathway decreased as the oxidation levels of the C₁-growth substrates increased. On formaldehyde the values were between 7.2 to 9.6, whereas on formate the values varied from 3.3 to 6.9. It appears that bacteria utilize C_l-compounds more efficiently via the ribulose monophosphate pathway than via the serine pathway. The oxidation step from methanol to formaldehyde (and from methylamine to formaldehyde) in the bacteria studied may be energy yielding. A comparison has been made between the experimental yield values obtained and theoretical values.     

Oxidation of methanol,formaldehyde and formate by catalase purified from methanol-grown Hansenula polymorpha

Catalase has been partially purified from cell-free extracts of methanol-grown Hansenula polymorpha and its peroxidative properties were studied. It was shown that the enzyme is capable of oxidizing methanol, formaldehyde and formate in the presence of hydrogen peroxide. The physiological significance of these reactions in the transduction of energy from the oxidation of methanol in yeasts is discussed.     

In vitro enhancing effects of thymic dendritic cells on apoptotic cell death of thymocytes

Using terminal deoxynucleotide transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay and propidium iodide-DNA staining flow cytometry assay, the effects of mouse thymic dendritic cells (MTSC4) on the process of programmed cell death of thymocytesin vitro were investigated. It was noticed that thymocytes bound to MTSC4 used in this study. That the percentages of apoptotic nuclei of the bound thymocytes on MTSC4 were much higher than those of medium-cultured thymocytes, while the bound thymocytes on mouse thymic epithelial cell (MTEC1) showed much lower percentages of apoptosis. FACS analysis quantitatively confirmed the observation. Phenotype analysis showed that MTSC4 induced the deletion of CD4 + CD8 + cells and CD4 + CD8-.cells in 18 h of coculture. The results suggest that the negative selection of medullary thymocytes may be achieved by thymic dendritic cells through their enhancing effects on apoptosis. Project supported by the National Natural Science Foundation of China (Grant No.39670685) and FokYin Tung Education Foundation.     

In vitro enhancing effects of thymic dendritic cells on apoptotic cell death of thymocytes

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The effect of age on the recognition thresholds of three sweeteners: sucrose,saccharin and aspartame

It iS believed that people's sensitivity to taste declines with age but the evidence is inconclusive. This study was designed to test the hypothesis that taste recognition thresholds (TRTs) for sweetness are higher in older than in younger individuals, using groups of 16 younger subjects (18–30) and 16 older subjects (60–85). Three test substances were used: sucrose, aspartame and saccharin. A questionnaire recorded variables which might have affected TRTs, but data failed to show any trend that might have biased the principle variate-age. There was a significant alteration with age of recognition thresholds, at least for sucrose and saccharin. The differences between the groups for the three sweeteners were due to the fact that all the very sensitive subjects were young. None of the older subjects had particularly poor discrimination: all but one had TRTs within the range of younger subjects. Although there are age-related taste changes, they are much less dramatic than commonly occurs with other senses, such as sight and hearing. The findings of this study have implications for institutional catering and the dietary management of older people using non-sugar sweeteners.     

微生物对甲醛的净化效应与作用机制

甲醛是一种无色、强刺激性、危害人体嗅觉及免疫功能的有毒气体。目前工业的快速发展和室内装修的盛兴使得甲醛成为工业废气和室内空气污染的重要来源之一,也是当前威胁人类健康的主要杀手之一。开发高效净化甲醛的新技术是解决空气污染的重要途径。生物因能动态、持续地吸收利用甲醛,使得生物净化成为一种新兴、高效、绿色的甲醛污染防治技术。甲基营养菌等微生物可特异地吸收、同化甲醛等一碳化合物,逐渐成为生物净化甲醛的新宠。本文在分析甲醛的危害及其净化技术现状的基础上,从种群多样性、作用机理和应用等方面综述了微生物净化甲醛的研究进展。     

Synthesis and characteristics of an aspartame analogue, L-asparaginyl L-3-phenyllactic acid methyl ester

Aspartame (L-aspartyl L-phenylalanine methyl ester) isan artificial sweetener as shown in Fig.1 (A) [1]. Studieson its structure and function showed that its N-terminalL-aspartyl residue could only be replaced by aminomalonyl[2] or L-asparaginyl [3] residue. When its peptide bondwas replaced by an ester bond [Fig. 1(B)] or the hydrogenof amide in the peptide bond replaced by a methyl group[Fig. 1(C)], its sweetness was lost [4]. According to thecrystal structure of aspartame, between the …     

Protective effects of taxifolin on pazopanib-induced liver toxicity: an experimental rat model

Pazopanib is a tyrosine kinase inhibitor that is generally used for the treatment of metastatic renal cell cancer and advanced soft tissue sarcoma. It can cause various degrees of hepatotoxicity. Our study aimed to investigate the effect of taxifolin on pazopanib-induced liver toxicity. A total of 18 rats were divided into three groups: the pazopanib (PP), pazopanib plus taxifolin (TPP), and control (C) group. Taxifolin was administered to the TPP (n=6) group with a dose of 50 mg/kg. Distilled water was orally admnistered to the C (n=6) and PP (n=6) groups as a solvent. Subsequently, pazopanib 200 mg/kg was administered to the TPP and PP groups via the stomach. This procedure was repeated once a day for four weeks. Then, all rats were sacrificed, and their livers were removed. Malondialdehyde (MDA), total glutathione (tGSH), total oxidant status (TOS), and total antioxidant status (TAS) levels were evaluated. MDA and TOS levels were higher in the PP group compared with the levels of the other parameters (P<0.001). tGSH and TAS levels were lower in the PP group than in the TPP and C groups (P<0.001), and the aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) levels were higher. Furthermore, liver tissue damage, including hemorrhage, hydropic degeneration, and necrosis was observed in the PP group. Administration of taxifolin before pazopanib significantly improved degenerative changes. Our study demonstrated that the administration of taxifolin is significantly effective in preventing pazopanib-induced hepatotoxicity in rats.     

Relationships between formaldehyde metabolism and toxicity and glutathione concentrations in isolated rat hepatocytes

The metabolism and toxicity of formaldehyde (CH2O) in isolated rat hepatocytes was found to be dependent upon the intracellular concentration of glutathione (GSH). Using hepatocytes depleted of GSH by treatment with diethyl maleate (DEM), the rate of CH2O (5.0 mM) disappearance was significantly decreased. Formaldehyde decreased the concentration of GSH in hepatocytes, probably by the extrusion of the CH2O-GSH adduct, S-hydroxymethylglutathione. Formaldehyde toxicity was potentiated in cells pretreated with 1.0 mM DEM as measured by the loss of membrane integrity (NADH stimulation of lactate dehydrogenase (LDH) activity) and an increase in lipid peroxidation (formation of thiobarbituric acid-reactive compounds). This potentiation of toxicity was both CH2O concentration-dependent and time-dependent. There was an excellent correlation between the increase in lipid peroxidation and the decrease in cell viability. L-Methionine (1.0 mM) both protected the cells from toxicity caused by the combination of 8.0 mM CH2O and 1.0 mM DEM and increased the cellular GSH concentration. The antioxidants, ascorbate, butylated hydroxytoluene (BHT) and alpha-tocopherol (10, 25 and 125 microM), all exhibited dose-dependent protection against toxicity produced by 8.0 mM CH2O and 1.0 mM DEM. At toxic concentrations of CH2O (10.0-13.0 mM), administered by itself, lipid peroxidation did not increase concomitantly with the decrease in cell viability and the addition of antioxidants (125 microM) did not influence CH2O toxicity. These results suggest that CH2O toxicity in GSH-depleted hepatocytes may be mediated by free radicals as a result of the effect of CH2O on a critical cellular pool of GSH. However, cells with normal concentrations of GSH are damaged by CH2O by a different mechanism.     

A rapid method for the separation of large and small thymocytes from rats and mice

Thymocytes from rats and mice have been separated into large and small cell populations in high yield and purity by isopycnic centrifugation in a discontinuous (three-layered) gradient of Percoll. Cells are mixed with the middle layer and during low-speed centrifugation the small, denser cells sediment to the bottom interface whilst the large, less dense cells float to the top interface. Red blood cells, and small debris particles separate into the bottom and top layers respectively. Studies on the uptake of [3H]TdR show that the small cells are non-dividing while more than half of the large cells are capable of division.     

Effects of methylprednisolone on the energy metabolism of quiescent and conA-stimulated thymocytes of the rat

The short-term effects of high concentrations of Methylprednisolone (MP) on the energy metabolism of quiescent and Concanavalin A-stimulated rat thymocytes were investigated in vitro. Concanavalin A (ConA) stimulated the respiration rate of quiescent thymocytes by 35%. Addition of more than 0.15 mg MP/10⁷ cells to ConA-stimulated cells reversed this respiratory stimulation; in addition, higher concentrations of MP caused a similar progressive decrease in the rate of respiration of both quiescent and ConA-stimulated cells. Similarly, the stimulation of respiration by ConA was greatly reduced in MP-treated cells. MP addition lowered cytoplasmic [Ca²⁺] and, at high concentrations, abolished the ability of ConA to increase [Ca²⁺]. Thus MP both reverses and prevents the immediate stimulation of thymocytes by ConA.In quiescent thymocytes, MP strongly inhibited that part of the oxygen consumption used to drive the cycle of Na⁺ influx across the plasma membrane and Na⁺ efflux on the Na⁺K⁺-ATPase, but did not inhibit oxygen consumption used to drive protein synthesis. In ConA-stimulated thymocytes MP had the same effects and also strongly inhibited oxygen consumption dependent on the cycle of Ca²⁺ influx across the plasma membrane and Ca²⁺ efflux on the Ca²⁺-ATPase, but had little effect on oxygen consumption used to drive RNA and DNA synthesis.These results show that MP prevents cation cycling in thymocytes (either by preventing cation influx or by inhibiting cation pumps) and prevents mitogenic stimulation of the cells. The high MP concentration required and the speed of onset of the effect (lless than 30s) provide strong evidence that these effects of MP are not mediated by glucocorticoid receptors and subsequent activation of gene expression. They may be caused by direct effects of MP on the properties of the plasma membrane. These effects are considered to be, at least partially, responsible for the beneficial results that currently have been obtained using MP megadoses in various clinical situations.     

Comparative toxicity,growth inhibitory and biochemical effects of terpenes and phenylpropenes on Spodoptera littoralis (Boisd.)

Eleven monoterpenes, phenylpropenes and sesquiterpenes were evaluated for their insecticidal and growth inhibitory activities against the second and fourth larval instars of Spodoptera littoralis. Among the tested compounds, 1,8-cineole revealed the highest fumigant toxicity against the 2nd and 4th larval instars with LC₅₀ values of 2.32 and 3.13 mg/L air, respectively. The monoterpenes, p-cymene, α-terpinene, (−)α-pinene and (−)-carvone were highly toxic to both larval stages as their LC₅₀ values ranged between 7.35 and 13.79 mg/L air against 2nd larval instar and between 14.66 and 32.02 mg/L air against 4th larval instar. In topical application assay against the 4th larval instar, (−)-carvone (LD₅₀ = 0.15 mg/larva) and cuminaldehyde (LD₅₀ = 0.27 mg/larva) were the most potent contact toxicants. In residual film assay, trans-cinnamaldehyde, (−)-citronellal and p-cymene showed the highest insecticidal activity against the 2nd larval instar, while α-terpinene and (−)-carvone were most effective compounds against the 4th larval instar. Moreover, the tested compounds caused strong growth reduction of both larval stages with growth inhibition higher than 80% in the 2nd larval instar and higher than 70% in the 4th larval instar. On the other hand, (−)-carvone, cuminaldehyde and (Z,E)-nerolidol showed pronounced inhibitory effects on acetylcholinesterase (AChE) and adenosine triphosphatases (ATPases) activity of S. littoralis larvae. Cuminaldehyde (IC₅₀ = 1.04 mM) and (Z,E)-nerolidol (IC₅₀ = 0.02 mM) caused the highest inhibition of AChE and ATPases, respectively. Taken together, the results indicate that monoterpenes, phenylpropenes and phenylpropenes could be used to develop new botanical insecticides for S. littoralis management.     

A study on specific behavioral effects of formaldehyde in the rat

It has been reported that single exposure of rats of low-level formaldehyde vapor concentrations causes significant alteration in their motor activity in the inhalation chamber. In this study, we determined the effects of formaldehyde on the locomotor activity and behavior of adult male and female Lew. 1K rats in an open field two hours after termination of a single two hours lasting inhalative exposure to approximately 0.1, 0.5, or 5 ppm. Following behavioral parameters were quantitatively examined: numbers of crossed floor squares, occurrence frequencies of air and floor sniffing, grooming, rearing, and wall climbing, as well as the incidence of fecal boli. In the open field situation, the males of all formaldehyde groups crossed significantly lower numbers of floor squares. Furthermore, significant decrease in the occurrence frequencies of floor sniffing, rearing, and wall climbing were observed. Within the female rat groups exposed to 0.5 or 5 ppm formaldehyde, a significantly decreased numbers of crossed squares were registered, while this parameter remained unchanged in the 0.1 ppm group. Other parameters were also affected by the formaldehyde inhalation (e.g. significant increase in the occurrence frequencies of air sniffing in the 0.1 and 0.5 ppm groups and significant decrease in the numbers of floor sniffing in the 0.5 and 5 ppm groups, respectively). The incidence of fecal boli was not affected in any exposure group neither in males nor in females. It is concluded from the results obtained that formaldehyde significantly affects the locomotor behavior of adult male and female rats in the open field after a single inhalative exposure to the above mentioned concentrations.     

The effects of dietary flaxseed on the Fischer 344 rat: I. Development, behaviour, toxicity and the activity of liver gamma-glutamyltranspeptidase

The effect of exposure to, followed by consumption of, 10% flax chow from the 18th day of gestation to the 86th day after birth was examined in male and female Fischer 344 rats. Growth curves of the flax chow-fed rats were identical to those of regular chow-fed rats, as were such developmental milestones as pinna development, growth of hair and eye opening. Acoustical startle and the righting reflexes, developmental behavioural indices, were also the same. Blood glucose levels were comparable in flax chow-fed and regular chow-fed rats at all stages of development, indicating that flax is without effect on glucose balance. There were no signs of toxicity in the flax chow-fed rats since their plasma levels of alanine aminotransferase and gamma-glutamyltranspeptidase (gammaGT) were the same as those of regular chow-fed rats. The activity of gammaGT displayed an increase in the livers of flax chow-fed rats after puberty, more so in the male-four-fold-than in the female-1.38-fold. This is suggestive of an estrogenic effect which implicates an effect of an estrogenic flax lignan. An hepatobeneficial effect of the flax-induced increase in liver gammaGT is discussed. In summary, dietary 10% flax chow is without long-term effect on growth, development and behaviour, is non-toxic and may be hepatoprotective.     

Interactive effects of prenatal cocaine and nicotine exposure on maternal toxicity,postnatal development,and behavior in the rat

Two experiments were performed to investigate the interactive effects of prenatal coadministration of cocaine hydrochloride (C) and nicotine tartrate (N). Experiment I was designed to determine doses of C and N that could be coadministered without altering maternal gestational parameters and/or fetal viability. Exposure of Sprague-Dawley rats to combined high-dose C (20 mg/kg) and high-dose N (5.0 mg/kg) on gestation days 8–21 was not more toxic to dam or fetus than that of exposure to C alone. Experiment II investigated pregnancy outcome, postnatal development, and behavior of the offspring following drug exposure to either high-dose cocaine (20 mg/kg: CS), high-dose nicotine (5.0 mg/kg: NS), or both (NC) on gestation days 8–21. N was administered by osmotic minipump and C by sc injection. Saline-injected dams, fitted with saline-filled pumps (SS), and untreated dams, pair-fed (PF) to NC females, served as controls. Alterations in maternal variables were limited to a 10–15% decrease in food consumption in NC and CS groups. Pregnancy outcome and birth statistics were unaffected by prenatal treatment, as was offspring body weight during the first four postnatal weeks. However, the development of surface righting was delayed in CS pups, and only CS offspring were underresponsive to the stimulatory effects of dopamine agonists on activity and stereotypy. Behavioral responses to N challenge were similar in all groups. In addition, only CS offspring showed altered behavioral responses in a spontaneous alternation task. Treatment effects on dopamine D₁ and D₂ binding in the caudate nucleus were not observed. The combination of N and C did not exacerbate any of the behavioral changes seen in CS offspring. These results support the hypothesis that C is a behavioral teratogen in rodents, and suggest that in the present model, nicotine can mitigate some of the consequences ofin utero exposure to cocaine.     

Growth of Pseudomonas C on C1 compounds: enzyme activites in extracts of Pseudomonas C cells grown on methanol, formaldehyde, and formate as sole carbon sources.

Pseudomonas C can grow on methanol, formaldehyde, or formate as sole carbon source. It is proposed that the assimilation of carbon by Pseudomonas C grown on different C1 growth substrates proceeds via one of two metabolic pathways, the serine pathway or the allulose pathway (the ribose phosphate cycle of formaldehyde fixation). This contention is based on the distribution of two key enzymes, each of which appears to be specifically involved in one of the assimilation pathways, glycerate dehydrogenase (serine pathway) and hexose phosphate synthetase (allulose pathway). The assimilation of methanol in Pseudomonas C cells appears to occur via the allulose pathway, whereas the utilization of formaldehyde or formate in cells grown on formaldehyde or formate as sole carbon sources appears by the serine pathway. When methanol is present together with formaldehyde or formate in the growth medium, the formaldehyde or formate is utilized by the allulose pathway.