In fibrotic livers, collagen producing hepatic stellate cells (HSC) represent a major target for antifibrotic therapies. We designed liposomes with surface-coupled mannose 6-phosphate (M6P) modified human serum albumin (HSA) to target HSC via the M6P receptor. In this study we determined the pharmacokinetics and target specificity of M6P-HSA-liposomes in a rat model of liver fibrosis. Ten minutes after injection of [(3)H]-M6P-HSA-liposomes 90% of the dose has cleared the circulation. The blood elimination of these liposomes was counteracted by free M6P-HSA and polyinosinic acid, a competitive inhibitor of scavenger receptors. The M6P-HSA-liposomes accumulated in HSC. However, also Kupffer cells and endothelial cells contributed to the uptake of M6P-HSA-liposomes in the fibrotic livers. Polyinosinic acid inhibited the accumulation of the liposomes in Kupffer cells and liver endothelial cells, but not in HSC. PCR analysis revealed that cultured HSC express scavenger receptors. This was confirmed by Western blotting, although activation of HSC diminishes scavenger receptor protein expression. In conclusion, in a rat model for liver fibrosis M6P-HSA-liposomes can be efficiently targeted to non-parenchymal cells, including HSC. M6P receptors and scavenger receptors are involved in the cellular recognition of these liposomes, allowing multiple pharmacological interference in different pathways involved in the fibrosis.
Purpose. Delivery of apoptosis-inducing compounds to hepatic stellate cells (HSC) may be an effective strategy to reverse liver fibrosis. The aim of this study was therefore to examine the selective targeting of the apoptosis-inducing drug 15-deoxy-D12,14-prostaglandin J 2 (15dPGJ 2 ) with two different HSCcarriers: human serum albumin modified with the sugar mannose-6-phosphate (M6PHSA) or albumin modified with PDGF-receptor recognizing peptides (pPBHSA). Methods and Results. After chemical conjugation of 15dPGJ 2 to the carriers, the constructs displayed pharmacological activity and specific receptor-mediated binding to HSC in vitro. Unlike 15dPGJ 2 -pPBHSA, the cellular binding of 15dPGJ 2 -M6PHSA was reduced by a scavenger receptor antagonist. In vivo, both conjugates rapidly accumulated in fibrotic livers. Intrahepatic analysis revealed that 15dPGJ 2 -M6PHSA mainly accumulated in HSC, and to a lesser extent in Kupffer cells. 15dPGJ 2 -pPBHSA also predominantly accumulated in HSC with additional uptake in hepatocytes. Assessment of target receptors in human cirrhotic livers revealed that M6P/IGFII-receptor expression was present in fibrotic areas. PDGF-b receptor expression was abundantly expressed on human fibroblasts. Conclusions. These studies show that 15dPGJ 2 coupled to either M6PHSA or pPBHSA is specifically taken up by HSC and is highly effective within these cells. Both carriers differ with respect to receptor specificity, leading to differences in intrahepatic distribution. Nevertheless, both carriers can be used to deliver the apoptosis-inducing drug 15dPGJ 2 to HSC in vivo.
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