Glycerol contained in vaping liquids affects the liver and aspects of energy homeostasis in a sex‐dependent manner

Abstract

Vaping is increasingly popular among the young and adult population. Vaping liquids contained in electronic cigarettes (e‐cigarettes) are mainly composed of propylene glycol and glycerol, to which nicotine and flavors are added. Among several biological processes, glycerol is a metabolic substrate used for lipid synthesis in fed state as well as glucose synthesis in fasting state. We aimed to investigate the effects of glycerol e‐cigarette aerosol exposure on the aspects of glycerol and glucose homeostasis. Adult and young male and female mice were exposed to e‐cigarette aerosols with glycerol as vaping liquid using an established whole‐body exposure system. Mice were exposed acutely (single 2‐h exposure) or chronically (2 h/day, 5 days/week for 9 weeks). Circulating glycerol and glucose levels were assessed and glycerol as well as glucose tolerance tests were performed. The liver was also investigated to assess changes in the histology, lipid content, inflammation, and stress markers. Lung functions were also assessed as well as hepatic mRNA expression of genes controlling the circadian rhythm. Acute exposure to glycerol aerosols generated by an e‐cigarette increased circulating glycerol levels in female mice. Increased hepatic triglyceride and phosphatidylcholine concentrations were observed in female mice with no increase in circulating alanine aminotransferase or evidence of inflammation, fibrosis, or endoplasmic reticulum stress. Chronic exposure to glycerol e‐cigarette aerosols mildly impacted glucose tolerance test in young female and male mice. Fasting glycerol, glucose, and insulin remained unchanged. Increased pulmonary resistance was observed in young male mice. Taken together, this study shows that the glycerol contained in vaping liquids can affect the liver as well as the aspects of glucose and glycerol homeostasis. Additional work is required to translate these observations to humans and determine the biological and potential pathological impacts of these findings.

Melosira nummuloides Ethanol Extract Ameliorates Alcohol-Induced Liver Injury by Affecting Metabolic Pathways

“…34 Excess glycerol can be converted into lipids and stored in the liver. 35 Studies have highlighted the association between amino acids and lipid metabolism. Elevated levels of essential amino acids, including isoleucine and valine, have been observed in the sera of obese individuals, suggesting their potential role in regulating lipid metabolism in humans and mice.…”

“…Glycerol serves as a precursor for lipid biosynthesis, specifically glycerol-3-phosphate, which is important for lipid production . Excess glycerol can be converted into lipids and stored in the liver . Studies have highlighted the association between amino acids and lipid metabolism.…”

Association between the dual use of electronic and conventional cigarettes and NAFLD status in Korean men

“…Moreover, components of e-liquids other than nicotine, such as glycerol, may exert a genderdependent effect on hepatic steatosis. Propylene glycol and glycerol are the main ingredients of vaping liquids, to which nicotine and flavoring are added 32 . In an experimental study, female mice, but not male mice, displayed elevated hepatic triglyceride and phosphatidylcholine levels after exposure to e-vapor composed only of glycerol (without nicotine or flavoring) 32 .…”

“…Propylene glycol and glycerol are the main ingredients of vaping liquids, to which nicotine and flavoring are added 32 . In an experimental study, female mice, but not male mice, displayed elevated hepatic triglyceride and phosphatidylcholine levels after exposure to e-vapor composed only of glycerol (without nicotine or flavoring) 32 . Also, pregnant female mice and offspring that were exposed to nicotine-free e-vapor showed liver damage and metabolic changes 33 .…”