Hepatic immunosuppressive effects of systemically administered novel dextran-methylprednisolone prodrugs with peptide linkers in rats

Abstract

The hepatic immunosuppressive activities of two novel dextran prodrugs of methylprednisolone (MP) containing one (DMP1) or five (DMP5) amino acids as linkers were studied in rats. At various times (0-2 weeks) after intravenous administration of single 5 mg/kg (MP equivalent) doses of each prodrug or MP succinate (MPS), livers were isolated and immunologically stimulated ex vivo with lipopolysaccharide. The concentrations of tumor necrosis factor (TNF)-α in the outlet perfusate were then quantitated to assess immune response. Additionally, the concentrations of DMP1, DMP5, and/or MP were measured in the liver. MPS, DMP5, or DMP1 injections caused a maximum of 48.9%, 63.5%, or 85.7% decrease in the TNF-α secretion into the perfusate, with the time above the 50% inhibitory effect being <5, <24, or 120 h, respectively. Additionally, the area under the effect-time curve for DMP1 was 11-fold or fourfold higher than that after the administration of MPS or DMP5, respectively. Relatively high concentrations of DMP1 were present in the liver even at the last sampling time of 2 weeks. These data suggest that a single intravenous dose of DMP1 produces an intense and sustained immunosuppression in the liver for a relatively long time, which may be useful in liver transplantation.

Figure 1

Average bile flow rates of livers during 2 h of ex vivo perfusion. The livers were isolated at different times following pretreatment of animals with a single 5-mg/kg (MP equivalent) dose of MPS, DMP1, or DMP5. The columns and bars represent the mean and SD values, respectively (n = 3–5/group).

Figure 2

The concentration-time profiles of TNF-α in the outlet perfusate of livers isolated from untreated animals (negative and positive controls) and the animals pretreated with a single 5-mg/kg (MP equivalent) dose of MPS, DMP5, or DMP1 at 5, 12, or 24 h before the liver isolation, respectively. Except for the negative control group, all the livers were stimulated with 300 μg of LPS during the first 20 min of ex vivo perfusion. The symbols and bars represent the mean and SD values, respectively (n = 3–5/group).

Figure 3

The time course of the inhibitory effects of a single 5-mg/kg (MP equivalent) dose of MPS, DMP1, or DMP5 on the release of TNF-α into the outlet perfusate of livers stimulated with 300 μg of LPS during the first 20 min of ex vivo perfusion. The symbols and bars represent the mean and SD values, respectively (n = 3–5/group).

Figure 4

The hepatic concentration time courses of DMP1, DMP5, and MP regenerated from the prodrugs following a single 5-mg/kg (MP equivalent) dose of the prodrugs. The symbols and bars represent the mean and SD values, respectively (n = 3/group), and the lines for DMP1 and DMP5 are based on the biexponential model with parameters in Table 4.

Figure 5

The effect-hepatic concentration time profiles following a single 5-mg/kg (MP equivalent) dose of DMP1 or DMP5. The symbols and arrows represent the mean and the progression of sampling time, respectively ((n = 3–5/group).