Enhanced Permeability and Retention-Like Extravasation of Nanoparticles from the Vasculature into Tuberculosis Granulomas in Zebrafish and Mouse Models.

The enhanced permeability and retention (EPR) effect is the only described mechanism enabling nanoparticles (NP) flowing in blood to reach tumours by a passive targeting mechanism. Here, using the transparent zebrafish model infected with Mycobacterium marinum we show that an EPR-like process also occurs allowing different types of NP to extravasate from the vasculature to reach granulomas that assemble during tuberculosis (TB) infection. PEGylated liposomes and other NP types cross endothelial barriers near infection sites within minutes after injection and accumulate close to granulomas. Although 100 nm and 190 nm NP concentrated most in granulomas even 700 nm liposomes reached these infection sites in significant numbers. We show by confocal microscopy that NP can concentrate in small aggregates in foci on the luminal side of the endothelium adjacent to the granulomas. These spots are connected to larger foci of NP on the ablumenal side of these blood vessels. EM analysis suggests that NP cross the endothelium via the paracellular route. PEGylated NP also accumulated efficiently in granulomas in a mouse model of TB infection with Mycobacterium tuberculosis, arguing that the zebrafish embryo model can be used to predict NP behaviour in mammalian hosts. In earlier studies we and others showed that uptake of NP by macrophages that are attracted to infection foci is one pathway for NP to reach TB granulomas. This study reveals that when NP are designed to avoid macrophage uptake they can also efficiently target granulomas via an alternative mechanism that resembles EPR.