PEG‐asparaginase‐induced hepatic steatosis is associated with PKA activation and white adipose tissue lipolysis

Abstract

BackgroundPEGylated L‐asparaginase (PEG‐ASNase) is an essential chemotherapeutic agent used in the treatment of pediatric acute lymphoblastic leukemia (ALL) that depletes L‐asparagine and leads to leukemic cell apoptosis. However, this agent is avoided in adult ALL protocols due to its high risk of liver toxicity. Clinical studies have implied that the mechanism of PEG‐ASNase‐induced liver toxicity is due to defect in hepatic β oxidation; however, no study has investigated the mechanism or the role of β oxidation in PEG‐ASNase‐induced hepatic toxicity. Our study aims to demonstrate that PEG‐ASNase‐induced liver toxicity is not due to hepatic defects in fatty acid oxidation, VLDL secretion, or fatty acid synthesis. Rather, our data suggest that the toxicity may be due to a novel mechanism of fatty liver involving drug‐induced adipose lipolysis.Methods8‐week‐old male Balb/c mice received 1,500 IU/kg of PEG‐ASNase and were sacrifice at 1, 3, 5, or 7 days after drug administration. Blood, liver, and white adipose tissue (WAT) were harvested after sacrifice. Liver lipids were directly quantified and further assessed via Oil red O and H&E staining. Total and direct bilirubin, ALT, AST, and non‐esterified fatty acids (NEFA) were measure in plasma. The mRNA and protein levels of genes involved in hepatic fatty acid oxidation, lipid synthesis, and VLDL secretion were determined. To assess the effect of PEG‐ASNase on WAT lipolysis, the protein levels of Atgl, phosphorylated Hsl, and protein kinase A (PKA) were measured.ResultsPEG‐ASNase treatment in mice led to total body, liver, and WAT weight loss. Mice developed hepatic microvesicular steatosis after 3–7 days of drug administration. Plasma direct and total bilirubin levels were elevated 8‐fold relative to controls, whereas ALT, AST, and NEFA concentrations were elevated 2‐fold 3–7 days after PEG‐ASNase. Furthermore, we found, that the hepatic mRNA and protein levels of Srebp‐1c and Fas, which are involved in fatty acid synthesis, were downregulated suggesting a decrease in lipid synthesis after PEG‐ASNase. Furthermore, the hepatic gene and protein expression of Pparα, Lcad, and Mcad, which are involved in fatty acid oxidation, were upregulated after PEG‐ASNase. In vivo VLDL secretion was also increased 3 days after PEG‐ASNase administration. Taken together, our data indicate that other lipid sources are mediating the drug‐induced fatty liver. Among WAT, we found that PEG‐ASNase elevated ATGL, phosphorylated HSL, and PKA protein levels, consistent with the WAT weight loss and the increased plasma NEFA levels.ConclusionOur data suggest that PEG‐ASNase‐induced WAT lipolysis leads to the development of microvesicular hepatic steatosis and toxicity. Our future studies will determine whether PEG‐ASNase hepatic steatosis can be inhibited via the pharmacological or genetic inhibition of adipose lipolysis and identify the molecular mechanism leading to PKA activation and lipolysis.Support or Funding InformationNIH Grants RO1 CA216815. University of Pittsburgh School of Pharmacy, Pittsburgh, PA 15261.