Transient effects of empty liposomes on hepatic macrophage populations in rats

Liposomes have been used as a vehicle for encapsulating chemicals or toxins in toxicological studies. We investigated the transient effects of empty liposomes on hepatic macrophages by applying a single intravenous injection at a dose of 10 ml/kg body weight in 6-week-old male F344 rats. One day after injection, the numbers of hepatic macrophages reacting to CD163, CD68, Iba-1, MHC class II, Gal-3 and CD204 were significantly increased in liposome-treated rats. CD163(+) Kupffer cells and CD68(+) macrophages with increased phagocytic activity in hepatic lobules were most sensitive. The histological architecture of the liver was not changed following liposome injection; however, hepatocytes showed increased proliferating activity, demonstrable with proliferation marker immunostaining and by an increase in gene profiles related to the cell cycle. In the liposome-treated rats, interestingly, AST and ALT values were significantly decreased, and MCP-1, IL-1β and TGF-β1 mRNAs were significantly increased. Collectively, the present study found that hepatic macrophages activated by liposomes can influence liver homeostasis. This information would be useful for background studies on liposomes.