Different responses of cytosolic and mitochondrial glutathione in rat livers after ethylene oxide exposure

Ethylene oxide exposure increases impaired glucose metabolism in the US general population: a national cross-sectional study

BACKGROUND

Current experimental evidence supports that ethylene oxide (EO) exposure-related pathophysiologies may affect glucose metabolism, but few population-based studies have explored the potential links.

METHODS

This study used cross-sectional data from 15560 participants in the National Health and Nutrition Examination Survey (NHANES) from 2017 to 2020. EO exposure levels were calculated by testing hemoglobin adducts of EO (HbEO) via a modified Edman reaction. We focused on the association of EO exposure with prediabetes and diabetes as well as indicators of impaired glucose metabolism and further analyzed the potential pathogenic mechanisms. Statistics included logistic regression, generalized additive model fitting, penalized spline method, two-piecewise linear regression, recursive algorithm, mediation analysis, and Pearson's analysis.

RESULTS

EO exposure was associated with changes in glucose metabolic indicators and increased prevalence of prediabetes and diabetes, showing age-consistency and being more pronounced in obese and non-smoking populations. For each one pmol/g Hb, one SD, or two-fold SD increase in log2-HbEO, the risk of prediabetes increased by 12%, 16%, and 33%, with an increased risk of diabetes by 18%, 26%, and 61%, respectively. Dose-response curves revealed that this positive correlation was approximately linear with prediabetes and "J" shaped with diabetes. When log2-HbEO > 8.03 pmol/g Hb, the risk of diabetes would be further increased. Pearson's correlation revealed that EO exposure was associated with reduced fasting insulin and elevated HbA1c in the prediabetic stage. While in the diabetes stage, EO exposure was correlated with elevated fasting glucose, HbA1c, and HOMA-IR, suggesting an exacerbation of diabetes progression by EO exposure. A potential mechanism that the early stages of impaired glucose metabolism may be initiated by EO-related inflammation and oxidative stress damaging pancreatic β-cells, resulting in decreased insulin secretion. These speculations were partially supported by mediation analysis and mediators' Pearson analysis.

CONCLUSION

Elevated ethylene oxide exposure increases the incidence of impaired glucose metabolism in the general U.S. population and a potential intervention may be to effectively suppress inflammation and oxidative stress imbalances.

A physiologically based pharmacokinetic model for butadiene and its metabolite butadiene monoxide in rat and mouse and its significance for risk extrapolation

The gas 1,3-butadiene (BU) is an important industrial chemical and an environmental air pollutant. BU has been shown to be a weak carcinogen in the rat but a potent carcinogen in the B6C3F1 mouse. This species difference makes risk extrapolation to humans difficult and the underlying mechanism should be clarified before meaningful risk extrapolation to humans can be made. One possible explanation for the species differences in cancer response is that there are quantitative species differences in the formation of genotoxic epoxides. To investigate this possibility a physiologically based pharmacokinetic (pbpk) model for BU together with its first reactive metabolite 1,2-epoxybutene-3 (butadiene monoxide, BMO) was developed. Previously reported values on hepatic glutathione (GSH) turnover, depletion of hepatic GSH in rodents exposed to BU, and in vitro metabolic data of BU and BMO were included in the model, which incorporates intrahepatic first-pass hydrolysis of BMO and the ordered sequential, ping-pong mechanism to describe the enzyme kinetics of BMO-GSH conjugation. In vitro studies were carried out to obtain tissue: air partition coefficients of BU and BMO in rat tissue homogenates. The simulated pharmacokinetics of BU, BMO, and GSH agreed with previously published experimental observations in rat and mouse obtained in closed and open chamber experiments. According to the model, the internal dose of BMO (expressed either as the concentration in mixed venous blood or as the area under the concentration-time curve) is approximately 1.6 times higher in the mouse than in the rat for exposure to BU below 1000 ppm. At higher exposure levels, GSH depletion occurs in the mouse, but not in the rat, after about 6-9 h. This GSH depletion results in up to 2-3 times higher internal doses in the mouse than in the rat. The clear but relatively small species differences in body burdens of BMO indicated from our model can only partly explain the marked species difference in cancer response between mice and rats exposed to BU.

In vivo modulation of total and mitochondrial glutathione in rat liver. Depletion by phorone and rescue by N-acetylcysteine

The aim of the present work was to modulate in vivo the level of hepatic mitochondrial glutathione (GSH). Rats were given phorone (diisopropylidene acetone), which in vivo becomes enzymatically conjugated to GSH, and were subsequently treated with N-acetylcysteine (NAC) to rescue GSH. In liver homogenate, a rapid and biphasic (T1/2 less than or equal to 15 min and 1.5 hr) drop of GSH was observed upon phorone administration. NAC treatment led to a restoration (T1/2 about 1 hr) of GSH in the homogenate above control values within 3 hr. The mitochondrial GSH level decreased with T1/2 of about 1.5 hr upon phorone treatment, and was 75% restored by NAC treatment within 3 hr. Hydroperoxide-induced mitochondrial pyridine nucleotide oxidation and Ca2+ release were impeded in GSH-depleted organelles, and NAC treatment restored these processes. The GSH status had no influence on mitochondrial pyridine nucleotide oxidation and Ca2+ released induced by alloxan, which reacts directly and non-enzymatically with pyridine nucleotides. It is concluded that NAC is able to rescue mitochondrial GSH in vivo and restore important mitochondrial functions. The data suggest that NAC may be a useful antidote in oxidative stress-related diseases.