High-fat diet-induced lipidome perturbations in the cortex,hippocampus, hypothalamus,and olfactory bulb of mice

Given their important role in neuronal function, there has been an increasing focus on altered lipid levels in brain disorders. The effect of a high-fat (HF) diet on the lipid profiles of the cortex, hippocampus, hypothalamus, and olfactory bulb of the mouse brain was investigated using nanoflow ultrahigh pressure liquid chromatography-electrospray ionization-tandem mass spectrometry in the current study. For 8?weeks, two groups of 5-week-old mice were fed either an HF or normal diet (6 mice from each group analyzed as the F and N groups, respectively). The remaining mice in both groups then received a 4-week normal diet. Each group was then subdivided into two groups for another 4-week HF or normal diet. Quantitative analysis of 270 of the 359 lipids identified from brain tissue revealed that an HF diet significantly affected the brain lipidome in all brain regions that were analyzed. The HF diet significantly increased diacylglycerols, which play a role in insulin resistance in all regions that were analyzed. Although the HF diet increased most lipid species, the majority of phosphatidylserine species were decreased, while lysophosphatidylserine species, with the same acyl chain, were substantially increased. This result can be attributed to increased oxidative stress due to the HF diet. Further, weight-cycling (yo-yo effect) was found more critical for the perturbation of brain lipid profiles than weight gain without a preliminary experience of an HF diet. The present study reveals systematic alterations in brain lipid levels upon HF diet analyzed either by lipid class and molecular levels.     

Modern geochemical and molecular tools for monitoring in-situ biodegradation of MTBE and TBA

Methyl tert-butyl ether (MTBE) is a major gasoline oxygenate worldwide and a widespread groundwater contaminant. Natural attenuation of MTBE is of practical interest as a cost effective and non-invasive approach to remediation of contaminated sites. The effectiveness of MTBE attenuation can be difficult to demonstrate without verification of the occurrence of in-situ biodegradation. The aim of this paper is to discuss the recent progress in assessing in-situ biodegradation. In particular, compound-specific isotope analysis (CSIA), molecular techniques based on nucleic acids analysis and in-situ application of stable isotope labels will be discussed. Additionally, attenuation of tert-butyl alcohol (TBA) is of particular interest, as this compound tends to occur alongside MTBE introduced from the gasoline or produced by (mainly anaerobic) biodegradation of MTBE.     

Non-significance of rhizosphere degradation during phytoremediation of MTBE

Methyl tertiary butyl ether (MTBE) is a gasoline additive associated with groundwater pollution at gas station sites. Previous research on poplar trees in hydroponic systems suggests that phytovolatilization is an effective mechanism for phytoremediation of MTBE (Rubin and Ramaswami, 2001), but the potential for microbial degradation of MTBE in the rhizosphere of trees had not been assessed. MTBE had largely been considered recalcitrant to microbial processes, but recent fieldwork suggests rapid biodegradation may occur in certain cases. This paper investigates the potential for rhizosphere degradation of MTBE at time frames relevant for phytoremediation. Three experiments were conducted at different levels of aggregation to examine possible degradation of MTBE by rhizosphere microorganisms that had been acclimated to low levels of MTBE for 6 weeks. MTBE soil die-away studies, conducted with both poplar trees and fescue grass, found no significant differences between MTBE concentration in vegetated and unvegetated soils over a two-week attenuation period. Closed chamber tests comparing hydroponic and rhizospheric poplar tree systems also showed essentially complete recovery of MTBE mass in both systems, suggesting an absence of degradation. Finally, rhizosphere microbes tested in aerated bioreactors were found to be thriving and metabolizing root materials, but did not show measurable degradation of MTBE. In all tests, the MTBE degradation product, Tert Butyl Alcohol (TBA), was not detected. The insignificance of MTBE degradation by rhizosphere microorganisms suggests that plant processes be the primary focus of further research on MTBE phytoremediation.     

Bioremediation of MTBE: a review from a practical perspective

The addition of methyl tert-butyl ether (MTBE) to gasoline has resulted in public uncertainty regarding the continued reliance on biological processes for gasoline remediation. Despite this concern, researchers have shown that MTBE can be effectively degraded in the laboratory under aerobic conditions using pure and mixed cultures with half-lives ranging from 0.04 to 29 days. Ex-situ aerobic fixed-film and aerobic suspended growth bioreactor studies have demonstrated decreases in MTBE concentrations of 83% and 96% with hydraulic residence times of 0.3 hrs and 3 days, respectively. In microcosm and field studies, aerobic biodegradation half-lives range from 2 to 693 days. These half-lives have been shown to decrease with increasing dissolved oxygen concentrations and, in some cases, with the addition of exogenous MTBE-degraders. MTBE concentrations have also been observed to decrease under anaerobic conditions; however, these rates are not as well defined. Several detailed field case studies describing the use of ex-situ reactors, natural attenuation, and bioaugmentation are presented in this paper and demonstrate the potential for successful remediation of MTBE-contaminated aquifers. In conclusion, a substantial amount of literature is available which demonstratesthat the in-situ biodegradation of MTBE is contingent on achieving aerobic conditions in the contaminated aquifer.     

Toxicological evaluation of methyl tertiary butyl ether (MTBE): Testing performed under TSCA consent agreement

MTBE is a colorless, relatively volatile liquid that has found widespread use as an octane‐enhancing gasoline additive. In 1987, the Environmental Protection Agency's (EPA) Interagency Testing Committee identified MTBE for priority testing consideration based on large production volume, potential widespread exposure, and limited data on chronic health effects. In response, the industry formed the MTBE Health Effects Testing Task Force, which in 1988 signed a Consent Agreement with the EPA requiring the task force member companies to perform toxicological testing on MTBE.

The testing program, which began in the second quarter of 1988, consists of a full complement of short‐ and long‐term tests. The testing completed to date includes genotoxicity (in vivo bone marrow cytogenetics and Drosophila sex‐linked recessive lethal assays), developmental toxicity, acute and subchronic neurotoxicity (motor activity, functional observation battery, and neuropathology), subchronic toxicity, reproductive/fertility effects, and pharmacokinetic studies. There is also an ongoing oncogenicity study in rats and mice. The final report for this chronic study is expected at the end of 1992. The total cost for the program is approximately $3.75 million, which is funded by the 11 Task Force member companies based on market share.

These studies were sponsored by the MTBE Health Effects Testing Task Force, Oxygenated Fuels Association, Washington, D.C.     

Monte Carlo Vadose Zone Model for Soil Remedial Criteria

Many vadose zone models are available for environmental remediation, but few offer the procedures for verifying model predictions with field data and for dealing with uncertainties associated with model input parameters. This article presents a modified model combining a one-dimensional vadose-zone transport model and a simple groundwater mixing model with a function of Monte Carlo simulation (MCS). The modified model is applied to determine soil remedial concentrations for methyl tertiary butyl ether (MTBE). The modified model generates a distribution of MTBE ground-water concentrations at the point of compliance. This distribution can be used to estimate the risk of exceeding groundwater quality standard given soil remedial concentrations. In a case study, soil remedial concentration for MTBE is established to be 5?µg/kg, with a 95% and 10?µg/kg with a 50% probability that groundwater concentration will not exceed the water quality objective of 13?µg/L. Furthermore, this study uses MCS to investigate uncertainties of model input parameter hydraulic conductivity (K). One set of data (K1) is based on the results of hydraulic conductivity laboratory tests, and the other (K2) is based on the results of slug tests conducted in the field. As expected, the laboratory data show smaller K values than the field data. The comparison of the MCS results obtained from the two sets of K data indicates that the MTBE groundwater concentrations calculated based on K1 are generally 160 to 625% greater than those calculated based on K2 at the same percentiles of the MCS distribution. A higher soil remedial concentration of9jig/kg is then calculated based on the MCS results from K2 at 95%ile and 19?µg/kg at 50%ile.     

Biodegradation of methyl tert-butyl ether as a sole carbon source by aerobic granules cultivated in a sequencing batch reactor

Aerobic granules efficient at degrading methyl tert-butyl ether (MTBE) were successfully developed in a well-mixed sequencing batch reactor (SBR). Treatment efficiency of MTBE in the reactor during the stable operations exceeded 99.8%, and effluent MTBE was consistently below 800 mug/L. The specific MTBE degradation rate was observed to increase with increasing MTBE initial concentrations from 25 to 400 mg/L, peaked at 18.2 mg-MTBE/g-VSS h, and declined with further increases in MTBE concentration as substrate inhibition effects became significant. There was a good fit between these biodegradation data and the Haldane equation (R (2) = 0.976). Microbial community DNA profiling was carried out using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction amplified 16S rDNA. The aerobic granule was found to contain a wide diversity of microorganisms. More than 70% similarity among the samples in the time period examined indicated a highly stable microbial community as the reactor reached the stable operation.     

Quantitative analysis of 3α,6α,24-trihydroxy-24,24-di(trifluoromethyl)-5β-cholane,a potent synthetic steroidal liver X receptor agonist in plasma using liquid chromatography–tandem mass spectrometry

The steroidal liver X receptor agonist, 3α,6α,24-trihydroxy-24,24-di(trifluoromethyl)-5β-cholane (ATI-829) is a potential therapeutic agent for the treatment of atherosclerosis. A sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS–MS) method for the quantification of ATI-829 in mouse plasma was developed and validated. Proteins in a 25 μL aliquot of mouse plasma were precipitated, and ATI-829 was extracted from the precipitate by the addition of 125 μL methanol. The overall extraction efficiency was greater than 99%. LC–MS–MS with negative ion electrospray and selected reaction monitoring was used for the quantitative analysis of ATI-829. The lower limit of quantitation of ATI-829 corresponded to 5.0 ng/mL (9.7 nM) plasma. Interference from matrix was negligible. The calibration curve was linear over the range 5–2000 ng/mL. The intra-day precision and inter-day precision of the analyses were <4.5% and <6%, respectively, and the accuracy ranged from 92% to 103%. ATI-829 in plasma was stable for at least 6 h at room temperature, 1 week at 4 °C, and 3 weeks at −20 °C. The validated method was then utilized for pharmacokinetic studies of ATI-829 administered to mice.     

Kinetics and mechanism of gas phase MTBE and ETBE formation on Keggin and Wells-Dawson heteropolyacids as catalysts

The paper reviews the work of the authors concerning the mechanism and kinetics of catalytic gas phase formation of tertiary ethers: methyl-tert-butyl ether (MTBE) and ethyl-tert-butyl ether (ETBE). The mechanism of tertiary ethers synthesis from alcohol and isobutene was proposed. Basing on the sorption of reagents and IR investigations the elementary steps of reactions were proposed. As the rate determining step two possible reactions: formation of carbocation and formation of ether from alcohol supplied from the bulk and protonated isobutene were discussed. The general rate equation was formulated.