High perfluorooctanoic acid exposure induces autophagy blockage and disturbs intracellular vesicle fusion in the liver

Abstract

Perfluorooctanoic acid (PFOA) has been shown to cause hepatotoxicity and other toxicological effects. Though PPARα activation by PFOA in the liver has been well accepted as an important mechanism of PFOA-induced hepatotoxicity, several pieces of evidence have shown that the hepatotoxic effects of PFOA may not be fully explained by PPARα activation. In this study, we observed autophagosome accumulation in mouse livers as well as HepG2 cells after PFOA exposure. Further in vitro study revealed that the accumulation of autophagosomes was not caused by autophagic flux stimulation. In addition, we observed that PFOA exposure affected the proteolytic activity of HepG2 cells while significant dysfunction of lysosomes was not detected. Quantitative proteomic analysis of crude lysosomal fractions from HepG2 cells treated with PFOA revealed that 54 differentially expressed proteins were related to autophagy or vesicular trafficking and fusion. The proteomic results were further validated in the cells in vitro and livers in vivo after PFOA exposure, which implied potential dysfunction at the late stage of autophagy. However, in HepG2 cells, it seemed that further inhibition of autophagy did not significantly alter the effects of PFOA on cell viability. Although these findings demonstrate that PFOA blocked autophagy and disturbed intracellular vesicle fusion in the liver, the changes in autophagy were observed only at high cytotoxic concentrations of PFOA, suggesting that autophagy may not be a primary target or mode of toxicity. Furthermore, since altered liver autophagy was not observed at concentrations of PFOA associated with human exposures, the relevance of these findings must be questioned.

Determination of Perflourooctanoic Acid Toxicity in a Human Hepatocarcinoma Cell Line

“…Nevertheless, humans are still exposed to PFOA through water, air and food, 1 – 3 , 25 even though a possible relationship between PFOA exposure and cardiovascular, pancreatic, testicular and liver disease has been reported. 1 , 6 – 9 Previous studies showed that PFOA accumulates in the liver of experimental animals, causing an increase in liver weight and enlargement of hepatocytes with necrotic features; cytoplasmic vacuolation and hepatocytic hypertrophy; acidophilic cytoplasm; and multifocal coagulation and liquefaction necrosis. 5 , 26 – 30 Alteration of the metabolic profile by PFOA, especially glucose and fatty acid metabolisms, and indirectly, mitochondrial dysfunction, are also thought to induce hepatotoxicity and inflammation response in the liver.…”

“…Perfluorooctanoic acid was found in several different biological samples, including in muscles, lungs, gonads and the liver. 1 – 9 The possible health effects have pushed many countries to restrict use of PFOA. 2 However, humans continue to be exposed to PFOA through contaminated food and water.…”

“… 1 , 6 – 7 , 10 It is thought that chronic exposure to PFOA could be associated with cardiovascular, kidney and liver diseases, as well as pancreatic, testicular and liver cancer. 1 , 6 – 9 , 11 …”

“… 2 , 11 – 16 The screening studies of fluorochemical production workers reported a positive relationship between PFOA exposure and serum alanine transaminase (ALT) levels, and a negative relationship with high-density lipoprotein (HDL) levels. 1 , 9 Previous data indicate that PFOA causes the death of primary and secondary hepatocytes. 17 – 19 Apoptosis is thought to be the main cell death pathway after exposure to PFOA.…”

Autophagy in exposure to environmental chemicals

“…It also causes the accumulation of autophagic vacuoles as well as disturbing autophagosomelysosome fusion in both mouse liver in vivo and in a human hepatocyte culture model in vitro (Table 2). A proteomic analysis further revealed that PFOA-exposure alters the expression of 54 proteins related to autophagy, vesicular trafficking and membrane fusions in mouse liver (Yan et al 2017).…”