Environmental Tobacco Smoke Alters Metabolic Systems in Adult Rats

Abstract

Human exposure to environmental tobacco smoke (ETS) is associated with an increased incidence of pulmonary and cardiovascular disease and possibly lung cancer. Metabolomics can reveal changes in metabolic networks in organisms under different physio-pathological conditions. Our objective was to identify spatial and temporal metabolic alterations with acute and repeated subchronic ETS exposure to understand mechanisms by which ETS exposure may cause adverse physiological and structural changes in the pulmonary and cardiovascular systems. Established and validated metabolomics assays of the lungs, hearts. and blood of young adult male rats following 1, 3, 8, and 21 days of exposure to ETS along with day-matched sham control rats (n = 8) were performed using gas chromatography time-of-flight mass spectrometry, BinBase database processing, multivariate statistical modeling, and MetaMapp biochemical mapping. A total of 489 metabolites were measured in the lung, heart, and blood, of which 142 metabolites were identified using a standardized metabolite annotation pipeline. Acute and repeated subchronic exposure to ETS was associated with significant metabolic changes in the lung related to energy metabolism, defense against reactive oxygen species, substrate uptake and transport, nucleotide metabolism, and substrates for structural components of collagen and membrane lipids. Metabolic changes were least prevalent in heart tissues but abundant in blood under repeated subchronic ETS exposure. Our analyses revealed that ETS causes alterations in metabolic networks, especially those associated with lung structure and function and found as systemic signals in the blood. The metabolic changes suggest that ETS exposure may adversely affects the mitochondrial respiratory chain, lung elasticity, membrane integrity, redox states, cell cycle, and normal metabolic and physiological functions of the lungs, even after subchronic ETS exposure.

Figure 1.

Metabolomics data sets and differentially altered metabolomes in ETS exposed organs. (a) Total metabolites detected in lungs, hearts, and blood. Numbers represent the metabolites that were detected with high confidence in each sample type. (b−e) The magnitude and dynamics of altered metabolomes in lungs, hearts, and blood. The number represents altered metabolites in ETS exposed organs compared to a filtered air treated organ (p < 0.05). Days 1, 3, 8, and 21 represent the time-points of sample collection during the time course experiment. (B = blood, H = heart, and L = lungs).

Figure 2.

Metabolic dysregulation in lungs of rats under ETS stress. Each node is a structurally identified metabolite. See Exeperimental Section for details about network graph construction and visualization. The graphs show five major clusters of compounds representing sugars and sugar phosphates, fatty acids, amino acids, aromatics, and organic acids. Red edges are KEGG reactant pair annotation, and blue edges are chemical similarity annotations. The graph was visualized using organic layout in Cytsocape. Red nodes are increased metabolites, and blue nodes are decreased metabolites. The size of nodes reflects fold changes. For clarity, only altered metabolites (p < 0.05) are labeled.

Figure 3.

Biological interpretation of the metabolic dysregulations in ETS-exposed lungs on acute and subchronic time-points. Altered pathways and biological mechanisms are highlighted as filled cells.