Groningen Addressing liver fibrosis with lipid - based drug carriers targeted to hepatic stellate cells

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 modified human serum albumin (M6P-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 [3H]-M6P-HSA-liposomes 90 % of the dose has cleared from the circulation. The blood elimination of these liposomes was counteracted by free M6P-HSA and polyinosinic acid, a competitive inhibitor of scavenger receptors. The M6PHSA-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 pharmacological interference in different pathways involved in the fibrosis. targeting liposomes to HSC in vivo chapter 3 Introduction The potential of liposomes as a drug carrier system has been extensively investigated. Various types of targeted liposomes have been developed aiming at specific populations of liver cells. Hepatocytes can be targeted using galactosylated liposomes (1-3) or asialofetuin grafted vesicles (4). Liposomes that are modified with aconitylated human serum albumin predominately accumulate in liver endothelial cells (LEC) (5) and mannosylated liposomes are recognised by Kupffer cells (KC) (6;7). So far, no studies have been reported on targeting of liposomes to hepatic stellate cells (HSC), which, in addition to KC and LEC, comprise an important population of non-parenchymal cells in the liver. In healthy organs, HSC are mainly responsible for storage of vitamin A (8). In contrast, during chronic liver injury, HSC become activated and transdifferentiate into myofibroblast-like cells. Activated HSC are characterised by loss of vitamin A and a high rate of proliferation (9). Moreover, they migrate towards the site of injury and on long run produce an excessive amounts of interstitial collagen, mainly type I and III, which leads to impairment of liver functions. HSC acquire also contractile properties that allow them to play a role in the control of sinusoidal blood flow (10). Thus, HSC contribute to the portal hypertension occurring in cirrhotic patients. Current antifibrotic therapies are often not effective because of lack of cell specificity. Therefore, drug carriers targeted to these pivotal cells represent an attractive prospect for future therapies. Liposomes are effective drug carriers because they can carry relatively large payloads. We designed a liposomal drug carrier to HSC by coupling mannose 6-phosphate-modified human serum albumin (M6P-HSA) to the surface of liposomes. In a rat model of liver fibrosis M6P-HSA was shown to accumulate in HSC (11) and the uptake of this protein by HSC was demonstrated to be mediated by mannose 6-phosphate/insulin like growth factor II (M6P/IGF II) receptor (12). In fibrotic livers, HSC express an increased amount of the M6P/IGF II receptor (13) that is involved in the activation of transforming growth factor β (TGF-β) (14;15), a key profibrotic cytokine. Previously, we demonstrated a high degree of association of M6P-HSA liposomes with cultured HSC and we showed that these liposomes can be targeted to HSC in fibrotic livers (16). In the current in vivo studies, using bile duct ligated (BDL) rats as a model of liver fibrosis, we determined the pharmacokinetic properties and the biodistribution of M6P-HSA liposomes in diseased animals. Subsequently, we analyzed whether next to HSC, KC and LEC play a role in the accumulation of M6P-HSA liposomes in BDL rats and tentatively characterised the receptors responsible for the in vivo uptake of these liposomes. Materials and Methods Chemicals Cholesterol (Chol), N-succinimidyl-S-acetylthioacetate (SATA) and polyinosinic acid (poly I) were from Sigma (St. Louis MO, USA). 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(4-(maleimidophenyl)bu tyramide) (MPB-PE) were purchased from Avanti Polar Lipids (Alabaster AL, USA). (3H)cholesteryloleyl ether (3H-COE) was obtained from Amersham Pharmacia Biotech (Buckinghamshire, UK). Human serum albumin fraction V was from Sanquin (Amsterdam, The Netherlands). All other chemicals were of analytical grade or the best grade available. Animals