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Nonlinear pharmacokinetics of recombinant human macrophage colony-stimulating factor (M-CSF) in rats
R J Bauer1, J A Gibbons, D P Bell
1Department of Pharmacology, Pharmacokinetics and Toxicology, Chiron Corporation, Emeryville, California.
Abstract:
The pharmacokinetics and mechanisms of elimination of recombinant human macrophage-colony stimulating factor (M-CSF) were investigated in rats. Intravenous injections of 0.1, 1 or 10 mg/kg M-CSF were administered and plasma samples were measured for M-CSF by bioassay. Systemic clearance decreased and the shape of the concentration-time curve changed with increasing dose, indicating nonlinear pharmacokinetics. At 10 mg/kg, two half-lives were initially observed, but after about 20 hr the plasma M-CSF suddenly declined with a steep slope. The rapidly declining phase suggested a saturable clearance mechanism that was prominent at low plasma concentrations of M-CSF (below 300 ng/ml) and obscured at high plasma concentrations of M-CSF. The rapid decline of plasma M-CSF occurred at earlier times with multiple daily injections of M-CSF, indicating induction of the saturable clearance mechanism. The rapidly declining phase was inhibited by carrageenan, indicating that saturable clearance might be due to metabolism of M-CSF by macrophages. With ligation of either the renal pedicles or ureters, the apparent half-lives of M-CSF increased by a factor of 2- to 3-fold, while the occurrence of the rapidly declining phase was delayed, but not eliminated. Overall, the results are well described by a two-compartment, first-order elimination model with a parallel Michaelis-Menten elimination pathway. First-order elimination is largely performed by the kidneys and the saturable Michaelis-Menten elimination pathway appears to be mediated by cells of the monocyte-macrophage lineage.
Insights
Recombinant human macrophage-colony stimulating factor (M-CSF) exhibits nonlinear pharmacokinetics in rats, with clearance primarily involving kidneys and macrophages. Saturable elimination pathways are induced by repeated M-CSF administration.
Area of Science:
- Pharmacology
- Immunology
Background:
- Recombinant human macrophage-colony stimulating factor (M-CSF) is a key cytokine in hematopoiesis and immune response.
- Understanding its pharmacokinetic profile and elimination pathways is crucial for therapeutic applications.
Purpose of the Study:
- To investigate the pharmacokinetics and elimination mechanisms of M-CSF in rats.
- To elucidate the dose-dependent and saturable clearance of M-CSF.
Main Methods:
- Intravenous administration of varying M-CSF doses (0.1, 1, 10 mg/kg) to rats.
- Plasma M-CSF levels measured by bioassay over time.
- Pharmacokinetic modeling using a two-compartment model with Michaelis-Menten kinetics.
- Investigated effects of renal pedicle/ureter ligation and carrageenan administration.
Main Results:
- M-CSF displayed nonlinear pharmacokinetics with dose-dependent systemic clearance.
- A saturable clearance mechanism, prominent at low M-CSF concentrations, was identified.
- Repeated M-CSF injections induced this saturable pathway, inhibited by carrageenan, suggesting macrophage involvement.
- Renal elimination contributed to first-order clearance, while macrophage-mediated pathways handled saturable elimination.
Conclusions:
- M-CSF elimination in rats involves both renal (first-order) and macrophage-mediated (saturable Michaelis-Menten) pathways.
- The saturable pathway is inducible and plays a significant role at therapeutic M-CSF concentrations.
- These findings are essential for optimizing M-CSF dosing strategies in clinical settings.