The ability to down-regulate gene expression specifically through the use of silencing RNA (siRNA) techniques has revolutionized biology. Now Aouadi et al. report the development of oral delivery vehicles for siRNA in mammals. Noting that M cells in Peyer’s patches of the intestine will transfer micrometer-sized β1,2-D-glucan particles to gut-associated lymphatic tissues, where the particles will be phagocytosed by macrophages and then delivered to the tissues, the authors created β1,3-D-glucan–encapsulated siRNA particles (GeRPs), which released the siRNA upon encountering the acidic pH of the phagosome. Preliminary studies showed silencing of Tnf [encoding tumor necrosis factor–α (TNF-α)] in cultured macrophages with siRNA delivered in GeRPs. In a screen of peritoneal exudate macrophages for signaling proteins that regulated Tnf expression, the authors identified the serine-threonine protein kinase MAP4K4, which is also a mediator of TNF-α signaling. After various experiments with macrophages in culture to show that the GeRPs were readily taken up by the cells, that delivery of siRNA against Map4k4 through these particles was effective at knocking down the transcripts, and that TNF-α production was decreased in cells receiving the Map4k4 siRNA, the authors proceeded to examine the effectiveness of Map4k4 siRNA GeRPs in mice. Mice were given fluorescently labeled GeRPs with the Map4k4 siRNA or dye-labeled scrambled RNA orally. The GeRPs were detected in macrophages both in the gut-associated lymphatic tissues and in other tissues, such as lung, spleen, and liver, but not skeletal muscle. Knockdown of Mapk4k4 in macrophages from spleen, liver, and lung showed variable effectiveness, ranging from 40% to 80%. The mice receiving Map4k4 siRNA GeRPs were also protected from lethal inflammatory cytokine toxicity, and peritoneal exudate macrophages from the mice showed decreased production of TNF-α, as well as decreased serum TNF-α after challenge with lipopolysaccharide and D-GalN. This demonstration of oral delivery of siRNA has potentially important applications for human diseases that may be controlled by targeting macrophages.
M. Aouadi, G. J. Tesz, S. M. Nicoloro, M. Wang, M. Chouinard, E. Soto, G. R. Ostroff, M. P. Czech, Orally delivered siRNA targeting macrophage Map4k4 suppresses systemic inflammation. Nature 458, 1180–1184 (2009). [PubMed]