Exposure to methyl tert-butyl ether (MTBE) is associated with mitochondrial dysfunction in rat

MTBE exposure may increase the risk of insulin resistance in male gas station workers

Insulin resistance is closely related to many metabolic diseases and has become a serious public health problem worldwide. So, it is crucial to find its environmental pathogenic factors. Methyl tert-butyl ether (MTBE), a widely used unleaded gasoline additive, has been proven to affect glycolipid metabolism. However, results from population studies are lacking. For this purpose, the potential relationships between MTBE exposure and the triglyceride glucose (TyG) index, a useful surrogate marker of insulin resistance, were evaluated using a small-scale occupational population. In this study, 201 participants including occupational and non-occupational MTBE exposure workers were recruited from the Occupational Disease Prevention and Control Hospital of Huaibei, and their health examination information and blood samples with informed consent were collected. The internal exposure levels were assessed by detecting blood MTBE using solid-phase-micro-extraction gas chromatography-mass spectrometry. Then the adjusted linear regression model was used to assess the relationship between MTBE exposure and fasting plasma glucose (FPG), or TyG index. Then, receiver-operating-characteristic (ROC) curves were performed to calculate the optimal cut-off points. Multivariable and hierarchical logistic regression models were used to analyze the impact of MTBE exposure on the risk of insulin resistance. Obvious correlations were observed between blood MTBE levels with TyG index (p = 0.016) and FPG (p = 0.001). Further analysis showed that using the mean of the TyG index (8.77) as a cutoff value had a good effect on reflecting the risk of insulin resistance. Multivariable logistic regression analysis also indicated that MTBE exposure was an independent risk factor for a high TyG index (OR = 1.088, p = 0.038), which indicated that MTBE exposure might be a new environmental pathogenic factor leading to insulin resistance, and MTBE exposure might increase the risk of insulin resistance by independently elevating the TyG index in male gas station workers.

Mediation effect of serum zinc on insulin secretion inhibited by methyl tert-butyl ether in gas station workers

Methyl tert-butyl ether (MTBE), a type of gasoline additive, has been found to affect insulin function and glucose homeostasis in animal experiments, but there is still no epidemiological evidence. Zinc (Zn) is a key regulatory element of insulin secretion and function, and Zn homeostasis can be disrupted by MTBE exposure through inducing oxidative stress. Therefore, we suspected that Zn might be involved and play an important role in the process of insulin secretion inhibited by MTBE exposure. In this study, we recruited 201 male subjects including occupational and non-occupational MTBE exposure from Anhui Province, China in 2019. Serum insulin and functional analog fibroblast growth factor 1 (FGF1) and blood MTBE were detected by Elisa and headspace solid-phase microextraction and gas chromatography-high-resolution mass spectrometry. According to MTBE internal exposure level, the workers were divided into low- and high-exposed groups and found that the serum insulin level in the high-exposed group was significantly lower than that in the low-exposed group (p = 0.003) while fasting plasma glucose (FPG) level increased obviously in the high-exposed group compared to the low-exposed group (p = 0.001). Further analysis showed that MTBE exposure level was positively correlated with FPG level, but negatively correlated with serum insulin level, which suggested that the FPG level increase might be related to the decrease of serum insulin level induced by MTBE exposure. The results of further mediation effect analysis showed that changes in serum zinc levels played a major intermediary role in the process of insulin secretion inhibition and blood glucose elevation caused by MTBE exposure. In addition, a significant negative correlation was found between MTBE exposure and serum Zn level, which might play a strong mediating effect on the inhibition of insulin secretion induced by MTBE exposure. In conclusion, our study provided evidence that MTBE could inhibit insulin secretion and interfere with Zn metabolism in gas station workers for the first time, and found that Zn might play an important mediation effect during the process of inhibiting insulin secretion and interfering with glucose metabolism induced by MTBE exposure.

Glutaminase 1 isoform up-regulation associated with lipid metabolism disorder induced by methyl tertiary-butyl ether in male rats

Methyl tertiary-butyl ether (MTBE) is a new unleaded gasoline additive, which is considered to be associated with abnormal lipid metabolism in many studies, but the metabolic characteristics and mechanism are still unclear. To observe the characteristics of lipid metabolism induced by MTBE and possible pathways, 21 male Wistar rats got intragastric administration for 24 weeks. The serum lipid metabolism indexes and metabolites were analyzed separately by a biochemical analyzer and untargeted metabolomics. And found that serum high-density lipoprotein cholesterol (HDL-C) levels in the exposure group were significantly reduced, and serum very low-density lipoprotein (VLDL) levels were significantly increased. In untargeted metabolomics, 190 differential metabolites were obtained. Among them, 23 metabolites were found to show the same trend in MTBE exposure groups, which might play a key role in systemic energy metabolism. Further metabolic pathways analysis showed that D-Glutamine, D-glutamate metabolism, and the other three pathways were affected by MTBE significantly. Therefore, we evaluated serum glutamine and glutamate levels and found that MTBE exposure significantly reduced glutamine levels and increased glutamate levels in rat serum and L-02 cells. Further, the key regulatory gene of glutamine metabolism, glutaminase 1 isoform (GLS1), was significantly up-regulated in rat liver and L-02 cells exposed to MTBE. While the effect of glutamine and glutamate metabolism induced by MTBE could be weakened by BPTES, an antagonist of GLS1. In conclusion, our results indicated that MTBE exposure could change the level of glutamine metabolism by promoting GLS1 expression and ultimately lead to abnormal lipid metabolism.

Investigating the Protective Role of Biochaga Drug on Structural Changes of Bovine Serum Albumin in the Presence of Methyl tert-butyl Ether

BACKGROUND

The health benefits of natural products have a long history. Chaga (Inonotus obliques) is used in traditional medicine and is an essential antioxidant for protecting the body from oxidants. Reactive oxygen species (ROS) are produced routinely due to metabolic processes. However, environmental pollution factors such as methyl tert-butyl ether (MTBE) can increase oxidative stress in the human body. MTBE is widely used as a fuel oxygenator that can harm health. The widespread use of MTBE has posed significant threats to the environment by polluting environmental resources, including groundwater. This compound can accumulate in the bloodstream by inhaling polluted air, with a strong affinity for blood proteins. The primary mechanism of MTBE's harmful effects is ROS production. The use of antioxidants may help reduce MTBE oxidation conditions. The present study proposes that biochaga, as an antioxidant, can reduce MTBE damage in the bovine serum albumin (BSA) structure.

METHODS AND RESULTS

This study investigated the role of different concentrations of biochaga in the structural change of BSA in the presence of MTBE by biophysical methods such as UV-Vis, fluorescence, FTIR spectroscopy, DPPH radical inhibition method, aggregation test, and molecular docking. Research at the molecular level is critical to investigate the structural change of proteins by MTBE and the protective effect of the ideal dose (2.5 µg/ml) of biochaga.

CONCLUSION

the results of spectroscopic examinations showed that the concentration of 2.5 µg/ml of biochaga has the least destructive effect on the structure of BSA in the presence and absence of MTBE, and it can play as an antioxidant.

Methyl tertiary-butyl ether inhibits THP-1 macrophage cholesterol efflux in vitro and accelerates atherosclerosis in ApoE-deficient mice in vivo

The biosafety of methyl tertiary-butyl ether (MTBE), mainly used as a gasoline additive, has long been a contentious topic. In addition to its routine toxicities, MTBE has been demonstrated to disrupt glucose and lipid metabolism and contribute to the development of type 2 diabetes as well as obesity. As one of the morbidities related to dyslipidemia, atherosclerosis is worthy of being investigated under MTBE exposure. Since foam cells derived from macrophages play pivotal roles during atherosclerosis development, we studied the effects of MTBE on macrophages in vitro and assessed the effect of MTBE on atherosclerosis plaque formation with the ApoE^-/- mouse model in vivo for the first time. Our results demonstrated that exposure to MTBE at environmentally relevant concentrations decreased the expression of ABCA1 and ABCG1, which are responsible for macrophage cholesterol efflux, at both mRNA and protein levels in THP-1 macrophages. Consequently, treatment with MTBE inhibited the transport of cholesterol from macrophages to High-density lipoprotein. ApoE^-/- mice exposed to MTBE at environmentally relevant concentrations (100, 1000 μg/kg) displayed significant increases in lesion area in the aorta and aortic root compared to vehicle-treated ones. Further analysis indicated that MTBE exposure enhanced the macrophage-specific marker Mac-2 contents within plaques in the aortic root, implying that MTBE could promote macrophage-derived foam cell formation and thus accelerate atherosclerosis plaque formation. We for the first time demonstrated the pro-atherogenic effect of MTBE via eliciting disruption of macrophage cholesterol efflux and accelerating foam cell formation and atherosclerosis plaque development.

Effect of methyl tert-butyl ether on adipogenesis and glucose metabolism in vitro and in vivo

Methyl tert-butyl ether (MTBE), as a widely used gasoline additive, is suspected of being environmentally toxic. MTBE accumulates mainly in adipose tissue, but its effect on obesity or obesity-related metabolic disorders has not been well understood yet. Therefore, we examined the effect of MTBE on the adipose function and the related metabolic processes with both 3T3-L1 cell line and C57BL/6J mice model. We found that exposure to MTBE at the environmental relevant concentration (100 μmol/L) could significantly induce differentiation of preadipocyte and disturb insulin-stimulated glucose uptake of mature adipocyte. The in vivo observation in male mice showed a positive correlation of visceral white adipose tissue (vWAT) expansion and cell size increase with MTBE treatment in 14 weeks. Glucose tolerance and insulin sensitivity tests demonstrated that MTBE at 1000 μg/(kg·day) disturbed the systemic glucose metabolism in a gender-specific manner, which might be partly attributed to the alterations of gut microbiota community at genus level with respect to Akkermansia, Clostridium XlVb, and Megamonas. In summary, our study characterized the effect of MTBE on adipose tissue function and glucose homeostasis in vitro and in vivo, and revealed that systemic disorders of the glucose metabolism might be modulated by the related gut microbiota.

SIRT1 attenuated oxidative stress induced by methyl tert-butyl ether in HT22 cells

Methyl tertiary-butyl ether (MTBE), an unleaded gasoline additive, can lead to oxidative stress, thus injuring the nervous system after long-term exposure. SIRT1, a NAD+-dependent histone deacetylase, can play a neuroprotective role in brain injury. However, the mechanism is unclear. This present study intended to define the role of SIRT1 during the process of MTBE-induced oxidative stress in mouse hippocampal neurons (HT22 cells). Our data showed that MTBE could directly trigger oxidative stress in HT22 cells by decreasing the activity of superoxide dismutase (SOD) and GSH/T-GSH level while increasing ROS, lipid peroxidation product malondialdehyde (MDA) and GSSG level. Similarly, the expression of SIRT1, an antioxidant, decreased in a dose-dependent manner. To further explore whether SIRT1 plays a key role during the process of oxidative stress, HT22 cells were transfected with siRNA-SIRT1 and preconditioned with the agonist of SIRT1 (SRT1720) for 2 h. The levels of oxidative stress (ROS, SOD, MDA, GSH/GSSG) were detected again after siRNA-SIRT1 HT22 cells and SRT1720 HT22 cells were exposed to MTBE for 6 h. In contrast to the non-pretreated group, levels of oxidative stress were tonic in siRNA-SIRT1 HT22 cells and attenuated in SRT1720 HT22 cells. Our results indicate that MTBE could directly cause oxidative stress in HT-22 cells, and SIRT1 might be an important antioxidant during MTBE-induced oxidative stress.