Extracellular vesicles: Roles and applications in drug-induced liver injury

Abstract

Extracellular vesicles (EV) are defined as nanosized particles, with a lipid bilayer, that are unable to replicate. There has been an exponential increase of research investigating these particles in a wide array of diseases and deleterious states (inflammation, oxidative stress, drug-induced liver injury) in large part due to increasing recognition of the functional capacity of EVs. Cells can package lipids, proteins, miRNAs, DNA, and RNA into EVs and send these discrete packages of molecular information to distant, recipient cells to alter the physiological state of that cell. EVs are innately heterogeneous as a result of the diverse molecular pathways that are used to generate them. However, this innate heterogeneity of EVs is amplified due to the diversity in isolation techniques and lack of standardized nomenclature in the literature making it unclear if one scientist's "exosome" is another scientist's "microvesicle." One goal of this chapter is to provide the contextual understanding of EV origin so one can discern between divergent nomenclature. Further, the chapter will explore the potential protective and harmful roles that EVs play in DILI, and the potential of EVs and their cargo as a biomarker. The use of EVs as a therapeutic as well as a vector for therapeutic delivery will be discussed.

Keywords: Acetaminophen; Biomarker; Drug-induced liver injury; Exosomes; Extracellular vesicles; Haptens; Idiosyncratic drug-induced liver injury; Microvesicle; Polycyclic aromatic hydrocarbons.

Fig. 1

Extracellular vesicles: biogenesis, transport, and release. A progenitor structure is first formed from the inward budding of the plasma membrane termed an early endosome. As the early endosome matures, intralumenal vesicles (ILVs) form driven by both ESCRT-dependent and ESCRT-independent (tetraspanins/lipids) mechanisms giving rise to a multivesicular body (MVB). These mechanisms dictating the formation of ILVs are also responsible for sorting and loading cargo (proteins, lipids, RNA, miRNA). The MVB can go to the lysosome for degradation or it can migrate to the plasma membrane via Rab proteins. SNARES, Rab GTPases and a rise in intracellular calcium help facilitate docking and fusion of the MVB to the plasma membrane. Once the ILVs are released into the extracellular environment they are now termed exosomes. Tetraspanin enriched membrane domains (TEMs), indicated by a triangle, help facilitate vesicular uptake and are highly concentrated on both the surface of exosomes and target cells. Microvesicles (MVs) form from the outward budding of the plasma membrane and are controlled through similar mechanisms as exosome formation. Unique mechanisms involved in MV formation, such as AARDC1, have been described. The overlap in the systems governing exosome and microvesicle formation highlight the difficulty in determining ex vivo the biogenesis pathway of the EV.

Fig. 2

Impact of xenobiotics on EV dynamics and the functional consequences. Xenobiotic exposure induces cellular stress resulting in a nearly ubiquitous response by increasing the release of EVs which are metabolically active and enriched in cytochrome P450 enzymes. These xenobiotic-EVs may deliver arginase to endothelial cells resulting in decreased intracellular arginine driving endothelial dysfunction. Extensive work has demonstrated in models of alcohol-induced injury that EVs can elicit a pro-inflammatory immune response by delivering specific molecular cargo. Additionally, drug-protein adducts are present in EVs which can be internalized by dendritic cells and may contribute to T cell proliferation. Ultimately, the cargo loaded into the EVs is xenobiotic-dependent which will dictate the downstream functional consequence.