Inhalation toxicology and carcinogenesis studies of propylene glycol mono-t-butyl ether in rats and mice

Propylene oxide derived glycol ethers: A review of the alkyl glycol ethers potential to cause endocrine disruption

The 'propylene glycol ethers' (PGEs) are a group of chemical solvents and functional fluids produced through the reaction of propylene oxide (PO) and a monoalcohol. PGEs form different structural isomers, with possible permutations increasing with the number of PO units in the molecule. The dominant isomers have only secondary hydroxyl groups and are not able to be metabolized to the acid structures that are associated with reproductive toxicity. There have been published claims that glycol ethers are human endocrine disruptors. This review systematically evaluates all the available and relevant in vitro and in vivo data across the propylene glycol ether family of substances using an approach based around the EFSA/ECHA 2018 guidance for the identification of endocrine disruptors. The conclusion reached is that there is no evidence to show that PGEs target any endocrine organs or perturb endocrine pathways.

Efficacy of Prednisolone/Zn Metal Complex and Artemisinin Either Alone or in Combination on Lung Functions after Excessive Exposure to Electronic Cigarettes Aerosol with Assessment of Antibacterial Activity

The use of transition metal complexes as therapeutic compounds has become more and more pronounced. These complexes offer a great diversity of uses in their medicinal applications. Electronic cigarettes (ECs) are an electronic nicotine delivery system that contain aerosol (ECR). The ligation behavior of prednisolone, which is a synthetic steroid that is used to treat allergic diseases and asthma arthritis, and its Zn (II) metal complex were studied and characterized based on elemental analysis, molar conductance, Fourier-transform infrared (FT-IR) spectra, electronic spectra, XRD, scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and transmission electron microscopy (TEM). The FT-IR spectral data revealed that PRD acts as a mono-dentate ligand via oxygen atoms of the carbonyl group. Electronic and FT-IR data revealed that the PRD/Zn (II) metal complexes have square planner geometry. Artemisinin (ART) is the active main constituent of Artemisia annua extract, and it has been demonstrated to exert an excellent antimalarial effect. The experiment was performed on 40 male mice that were divided into the following 7 groups: Control, EC group, PRD/Zn, ART, EC plus PRD/Zn, EC plus ART, and PRD plus combination of PRD/Zn and ART. Serum CRP, IL-6, and antioxidants biomarkers were determined. Pulmonary tissue histology was evaluated. When in combination with Zn administration, PRD showed potent protective effects against pulmonary biochemical alterations induced by ECR and suppressed severe oxidative stress and pulmonary structure alterations. Additionally, PRD/Zn combined with ART prevented any stress on the pulmonary tissues via antioxidant regulation, reducing inflammatory markers CRP and Il-6 and improving antioxidant enzymatic levels more than either PRD or ART alone. Therefore, PRD/Zn combined with ART produced a synergistic effect against any sort of oxidative stress and also improved the histological structure of the lung tissues. These findings are of great importance for saving pulmonary function, especially during pandemic diseases, such as during the COVID-19 pandemic.

Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome

RATIONALE

E-cigarettes vaporize propylene glycol/vegetable glycerin (PG/VG), nicotine, and flavorings. However, the long-term health effects of exposing lungs to vaped e-liquids are unknown.

OBJECTIVES

To determine the effects of chronic vaping on pulmonary epithelia.

METHODS

We performed research bronchoscopies on healthy nonsmokers, cigarette smokers, and e-cigarette users (vapers) and obtained bronchial brush biopsies and lavage samples from these subjects for proteomic investigation. We further employed in vitro and murine exposure models to support our human findings.

MEASUREMENTS AND MAIN RESULTS

Visual inspection by bronchoscopy revealed that vaper airways appeared friable and erythematous. Epithelial cells from biopsy samples revealed approximately 300 proteins that were differentially expressed in smoker and vaper airways, with only 78 proteins being commonly altered in both groups and 113 uniquely altered in vapers. For example, CYP1B1 (cytochrome P450 family 1 subfamily B member 1), MUC5AC (mucin 5 AC), and MUC4 levels were increased in vapers. Aerosolized PG/VG alone significantly increased MUC5AC protein in human airway epithelial cultures and in murine nasal epithelia in vivo. We also found that e-liquids rapidly entered cells and that PG/VG reduced membrane fluidity and impaired protein diffusion.

CONCLUSIONS

We conclude that chronic vaping exerts marked biological effects on the lung and that these effects may in part be mediated by the PG/VG base. These changes are likely not harmless and may have clinical implications for the development of chronic lung disease. Further studies will be required to determine the full extent of vaping on the lung.

Evaluation of e-liquid toxicity using an open-source high-throughput screening assay

The e-liquids used in electronic cigarettes (E-cigs) consist of propylene glycol (PG), vegetable glycerin (VG), nicotine, and chemical additives for flavoring. There are currently over 7,700 e-liquid flavors available, and while some have been tested for toxicity in the laboratory, most have not. Here, we developed a 3-phase, 384-well, plate-based, high-throughput screening (HTS) assay to rapidly triage and validate the toxicity of multiple e-liquids. Our data demonstrated that the PG/VG vehicle adversely affected cell viability and that a large number of e-liquids were more toxic than PG/VG. We also performed gas chromatography-mass spectrometry (GC-MS) analysis on all tested e-liquids. Subsequent nonmetric multidimensional scaling (NMDS) analysis revealed that e-liquids are an extremely heterogeneous group. Furthermore, these data indicated that (i) the more chemicals contained in an e-liquid, the more toxic it was likely to be and (ii) the presence of vanillin was associated with higher toxicity values. Further analysis of common constituents by electron ionization revealed that the concentration of cinnamaldehyde and vanillin, but not triacetin, correlated with toxicity. We have also developed a publicly available searchable website (www.eliquidinfo.org). Given the large numbers of available e-liquids, this website will serve as a resource to facilitate dissemination of this information. Our data suggest that an HTS approach to evaluate the toxicity of multiple e-liquids is feasible. Such an approach may serve as a roadmap to enable bodies such as the Food and Drug Administration (FDA) to better regulate e-liquid composition.

alpha 2u-globulin nephropathy and renal tumors in national toxicology program studies

Chemically induced renal neoplasms in male rats, developed coincident with alpha(2u)-globulin nephropathy, are not considered predictive of risk to humans by the International Agency for Research on Cancer (IARC) and the U.S. Environmental Protection Agency. Criteria have been defined to establish the role of alpha(2u)-globulin nephropathy in renal carcinogenesis, based on a proposed mode of action involving sustained tubular cell proliferation resulting from alpha(2u)-induced nephropathy, with consequent development of neoplastic lesions. Recent NTP studies demonstrated inconsistencies with this proposed mechanism, including in some cases, far weaker kidney tumor responses than expected based on the extent of alpha(2u)-globulin nephropathy. NTP studies with decalin, propylene glycol mono-t-butyl ether and Stoddard solvent IIC included extended evaluations of alpha(2u)-related nephropathy, and were thus used in assessing the linkage between key events in 90-day studies with renal tumors in 2-year studies. This review revealed no or at best weak associations of tumor responses with renal alpha(2u)-globulin concentrations, indices of cell turnover, or microscopic evidence of alpha(2u)-associated nephropathy in prechronic studies. While tumor responses corresponded somewhat with a measure of cumulative alpha(2u)-associated nephropathy (linear mineralization of the papilla) at the end of the 2-year studies, the severity of chronic nephropathy was generally in best agreement with the pattern of tumor response. These results suggest that while alpha(2u)-globulin nephropathy may contribute to the renal tumor response, the critical component(s) of the nephropathy most closely associated with the development of tumors could not be clearly identified in this review.

Gender-dependent hepatic alterations in H-ras12V transgenic mice

BACKGROUND/AIMS

Although it has been proposed that Ras and related signal pathways play important roles in hepatocarcinogenesis, appropriate in vivo models are lacking.

METHODS

Two hepatocellular carcinoma lines were established using pronuclear microinjection techniques to create an insertion of the H-ras12V transgene under the control of the albumin enhancer/promoter. The resulting phenotypes and related molecular events were then examined.

RESULTS

Male (but not female) transgenic mice older than 2 months showed hepatic alterations with a high degree of reproducibility, as compared to the wild-type mice. The liver/body-weight ratios were lower for the females than for the males. The transgene-carrying line 28 was investigated extensively with respect to molecular differences between the genders. Male hepatocytes showed higher Ras activity and higher reactive oxygen species (ROS) levels than female hepatocytes. The female hepatocytes showed higher expression levels of p53 and p21Waf1/Cip1, enhanced cytochrome c release, which correlated with cell cycle arrest, and higher levels of hypodiploid cell formation, as compared to the male hepatocytes.

CONCLUSIONS

The gender-related differences in molecular responses to activated Ras may have implications for the prevalence of hepatic alterations in males. Our transgenic mice represent a potentially valuable animal model for future investigations.

Meeting report: summary of IARC monographs on formaldehyde, 2-butoxyethanol, and 1-tert-butoxy-2-propanol

An international, interdisciplinary working group of expert scientists met in June 2004 to develop IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans (IARC Monographs) on formaldehyde, 2-butoxyethanol, and 1-tert-butoxy-2-propanol. Each IARC Monograph includes a critical review of the pertinent scientific literature and an evaluation of an agent's potential to cause cancer in humans. After a thorough discussion of the epidemiologic, experimental, and other relevant data, the working group concluded that formaldehyde is carcinogenic to humans, based on sufficient evidence in humans and in experimental animals. In the epidemiologic studies, there was sufficient evidence that formaldehyde causes nasopharyngeal cancer, "strong but not sufficient" evidence of leukemia, and limited evidence of sinonasal cancer. The working group also concluded that 2-butoxyethanol and 1-tert-butoxy-2-propanol are not classifiable as to their carcinogenicity to humans, each having limited evidence in experimental animals and inadequate evidence in humans. These three evaluations and the supporting data will be published as Volume 88 of the IARC Monographs.