Table 1.

The contrast between lipid droplets and extracellular vesicles

	Lipid Droplets (LDs)	Extracellular Vesicles (EVs)
The Structure and Composition	As previously mentioned, the outer layer of LDs consists of a monolayer composed of phospholipid membrane, while the contents primarily consist of neutral lipid TAG and CE, along with a small quantity of lipophilic compounds. Currently, there is no available information regarding the presence of proteins or nucleic acids within the contents [309]. LD proteins are exclusively localized on the phospholipid monolayer and play crucial roles in various processes such as LD formation, development, maturation, degradation, and interaction with intracellular organelles	The outer layer of EVs is composed of a bilayer of phospholipids, while their contents encompass nucleic acids, proteins, lipids, cytokines, metabolites and other biomolecules that can reflect the status of parental cells [306, 322, 323]. The composition and abundance of these vesicular contents will undergo dynamic changes in accordance with different cell types and conditions [324–326]. Furthermore, these contents serve as crucial mediators for intercellular communication by being exchanged with different target cells to exert specific biological effects based on varying requirements [327, 328]
Size	40–100 nm The size of LDs can dynamically alter in response to various stimuli	Small (20–200 nm): exomeres (> 50 nm), supermeres (> 25 nm), exosomes (40–200 nm) and defensosomes Large (200 nm-10 μm): Microvesicles (100 nm-1 μm), migrasomes (500–3000 nm), apoptotic bodies(50 nm-5 μm) and large oncosomes (1–10 μm) [309]
Biogenesis	Neutral lipids are synthesized and accumulated within the lumen of the endoplasmic reticulum (ER), undergoing a series of sequential stages including nucleation, expansion, budding, and detachment to ultimately form mature LDs	Endocytic pathway: The cytosol undergoes invagination to generate early sorting endosomes (ESEs) and matures into late sorting endosomes (LSEs), which are facilitated by ESCRT (endosomal sorting complex required for transport) proteins and cargo sorting, resulting in the formation of intraluminal vesicles (ILVs). Eventually, LSEs transition into multivesicular bodies (MVBs), which subsequently merge with the plasma membrane, leading to the extracellular release of ILVs [329–331] Plasma membrane pathway: The extracellular microvesicles generated through this pathway are typically large in size and result from the outward budding of the plasma membrane. Subsequently, they are released into the extracellular space after selectively incorporating proteins, nucleic acids, and lipids [332, 333]
Categorization	The current classification standard is not yet clearly defined	The classification of EVs is based on their biogenesis pathway, size, density, and biophysical characteristics [306, 309]
Degradation	Lipolysis, chaperone-mediated autophagy and macrolipophagy	The recipient cells have the ability to internalize EVs, which can subsequently undergo degradation through the autophagolysosomal pathway [334]
Cell origin	LDs can be observed in various types of brain cells during pathological conditions, with astrocytes and microglia being the most frequently affected. However, ependymal cells are the sole cell type within the brain that is capable of physiologically generating LDs	The release of EVs is a capability possessed by nearly all types of cells [307]
Site of action	The LDs typically engage in intracellular interactions with organelles such as mitochondria and endoplasmic reticulum, or actively participate in cell signaling pathways through their own protein or lipid constituents. In essence, their primary localization is within the cytoplasm	The EVs in the central nervous system (CNS) have the ability to traverse the blood–brain barrier and be released into both the bloodstream and cerebrospinal fluid (CSF), or they can be internalized by neighboring cells to facilitate intercellular communication [308, 335, 336]
Isolation	The isolation of LDs is typically performed from cell or tissue lysates rather than from cell culture media or biological fluids. Currently, there are no established guidelines for the isolation process	EVs are typically isolated from cell culture media or biological fluids based on their size, density, subcellular origin, and molecular composition. The focus is primarily on eliminating extracellular contaminants such as proteins, cell debris, and other overlapping subsets of EVs [309, 337]. However, achieving complete isolation and purification of EVs remains challenging; therefore, it is recommended to employ a combined complementation method. The method of density gradient ultracentrifugation is extensively employed for the isolation of EVs [338–340]
Detection	The intracellular LD was primarily subjected to analysis. Fluorescence-based microscopy: Bodipy, a fluorescently labeled antibody targeting LD protein markers [341]. Non-fluorescence based microscopy: stimulated Raman light scattering microscopy, atomic force microscopy (AFM) [342, 343]	The isolated EVs were detected. The commonly used testing methods include Nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), high-resolution flow cytometry etc. [344–346]