Introduction: A complex cocktail of endocrine-disrupting and other chemicals is ubiquitous in the modern environment. Exposure to such chemicals contributes to diseases including metabolic syndrome and infertility. The liver is the primary defence organ against xenotoxicants, but also the source of major of plasma proteins, and growth factors/hormones.
Aim: To understand how chronic exposure to complex mixtures of chemicals at human and environmentally relevant concentrations affects liver function and contributes to disease outcomes.
Methods: Liver protein extracts from adult sheep that grazed on control or sewage sludge-fertilised pastures throughout their lives (gestation and lactation via the mother and post-weaning grazing) were divided in four groups (n=1012/group) according sex and treatment. Proteins were resolved using 2D differential in-gel electrophoresis and compared using SameSpots Software. Differentially expressed protein spots were identified by liquid chromatography/tandem mass spectroscopy (LCMS/MS). Western blots were used to measure total protein levels and post-translational modifications.
Results: Chronic exposure to sewage sludge grossly altered the liver proteome in a sex-specific manner. Out of the observable 445 protein spots, 143 spots in ewes, and 94 spots in rams (with an overlap of 44 spots) showed statistically significant (P<0.05) spot volume alterations compared to controls. Proteins identified in 29 treatment-affected spots included: major plasma-secreted proteins (albumin, transferrin, and apolipoprotein A1), detoxification enzymes (GSTM, GSTT, and INMT), and fatty acid β-oxidation enzymes (ACAA2 and ECHS1). Albumin and transferrin were increased in a subset of treated rams and transferrin glycosylation patterns were altered in ewes. Reproductive system development and function, endocrine system and cancer pathways affected in males and cell death and survival, developmental disorders, haematological disease pathways affected in females.
Conclusions: Major alterations by environmental chemical exposure to liver function are likely to affect multiple systems in the body thereby providing a strong link between exposure and disease progression and/or development.