Light and electron microscopic detection of inflammation-targeting liposomes encapsulating high-density colloidal gold in arthritic mice

Light and electron microscopic detection of inflammation-targeting liposomes encapsulating high-density colloidal gold in arthritic mice

Ami Maehara, Keiichiro Nishida, Masumi Furutani, Emi Matsumoto, Aiji Ohtsuka, Yoshifumi Ninomiya, Toshitaka Oohashi 

Objective: We have previously demonstrated the efficient and time-dependent transvascular localization of Sialyl Lewis X (SLX)-liposomes to inflammatory sites, but the final target of the SLX-liposomes remained uncertain. The aim of this study was to identify the target cells of the liposomes within the inflamed joints of collagen antibody-induced arthritis (CAIA) model mice.

Methods: SLX-liposomes and unlabeled liposomes encapsulating high-density colloidal gold were administered intravenously into the caudal vein of CAIA mice on day 5 after induction of arthritis when the inflammatory score was maximal (n = 6 per group). Six hours or 24 h after liposome administration, animals were euthanized and hind limbs and ankles were excised without perfusion. After fixation, synovial tissues were examined by light microscopy after silver enhancement of colloidal gold or by transmission electron microscopy.

Results: Silver-enhanced signals were detected within the cells around E-selectin-positive blood vessels in the synovium of the SLX-liposome group. These cells were positive for the macrophage/monocyte marker F4/80 or neutrophil marker Ly-6G. Transmission electron microscopy detected the colloidal gold signals together with liposome-like structures within the phagosomes of synovial macrophages. Transmission electron microscopy and energy dispersive X-ray spectrometry could determine gold elements in the lysosomes of synovial macrophages.

Conclusions: The results of the current study demonstrate that SLX-liposomes primarily targeting E-selectin in activated endothelial cells could potentially deliver their contents into inflammatory cells around synovial blood vessels in arthritic joints.