Pitfalls in the detection of lipid vectors in neural cell culture and in brain tissue

Lipid particles (liposomes and lipid-coated microbubbles) are currently studied as vectors for drug delivery to the central nervous system. The visualization of these particles is usually based on their labeling with a lipophilic fluorescent dye (3,3'-dioctadecycloxacarbocyanine perchlorate) or staining with Oil Red O. The purpose of this article was to highlight the difficulties and pitfalls encountered with the use of these techniques in the detection of lipid particles in neural cell cultures and in brain tissue. In vitro and in vivo studies were conducted on different neural cell cultures (rat and human tumors, microglial cells) and animal models of brain lesion (lipopolysaccharide and quinolinic acid-induced lesion, induced brain tumor). The cells or brain slices were observed with optical microscopy after staining with Oil Red O, fluorescent microscopy, or scanning electron microscopy. Intra and extracytoplasmic lipid particles (stained with Oil Red O or autofluorescent or visualized by scanning electron microscopy) were naturally found in the cells and tissues studied. Intracytoplasmic lipid microparticles were present in tumoral and microglial cells. These lipid microparticles were also observed with some extracytoplasmic lipid droplets in the induced brain lesions. These images could be misinterpreted as lipid vectors if the cells or animals would have been treated with such a vector.