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Selected tissue distribution of liposomal methylprednisolone in rats
1Department of Pharmaceutics, School of Pharmacy, State University of New York at Buffalo, NY 14260.
Abstract:
The distribution of methylprednisolone (MPL) in various rat tissues following 2 mg/kg IV bolus doses of liposomal drug (L-MPL) and drug in solution was investigated. Animals were sacrificed at selected times post-dosing until 120 h. Liver, spleen, thymus, heart, lungs, muscle, kidney and brain were excised and the concentrations of MPL were measured using HPLC after homogenizing organs in buffer. The incorporation of MPL in liposomes did not alter the uptake of drug by heart, lung and muscle. Drug concentrations in brain were undetectable. In the kidney the MPL concentrations after 1 h were higher for liposomal drug and not detectable at later time points. Tissue to plasma partition coefficients were close to unity in lung, heart, and muscle at 1-2 h after the dose of drug in solution and increased by 7.5 times for spleen and 6 times for thymus after the dose of L-MPL. There were no significant differences between the weights of organs expressed in percent of body weight. These results demonstrate that, while the sequestration of L-MPL by lymphatic tissues occurred, the uptake of drug by the other tissues did not increase. This may be beneficial for preferential targeting of the immune system.
Insights
Liposomal methylprednisolone (L-MPL) distribution in rats showed increased concentrations in lymphatic tissues like the spleen and thymus. Other tissues, including the brain, heart, and lungs, did not show altered drug uptake.
Area of Science:
- Pharmacokinetics
- Drug Delivery Systems
Background:
- Methylprednisolone (MPL) is a corticosteroid with anti-inflammatory properties.
- Liposomal formulations aim to alter drug distribution and potentially improve therapeutic targeting.
Purpose of the Study:
- To investigate the tissue distribution of liposomal methylprednisolone (L-MPL) compared to conventional MPL solution in rats.
- To evaluate the pharmacokinetic profile and tissue partitioning of MPL after intravenous administration.
Main Methods:
- Rats received intravenous bolus doses of L-MPL or MPL solution (2 mg/kg).
- Tissues (liver, spleen, thymus, heart, lungs, muscle, kidney, brain) were collected at various time points up to 120 hours.
- MPL concentrations were quantified using High-Performance Liquid Chromatography (HPLC).
Main Results:
- L-MPL did not alter MPL uptake in the heart, lungs, or muscles compared to the solution.
- MPL concentrations in the brain were undetectable.
- Kidney showed higher MPL concentrations at 1 hour with L-MPL, but levels were undetectable later.
- Tissue-to-plasma partition coefficients increased significantly for spleen (7.5-fold) and thymus (6-fold) with L-MPL.
Conclusions:
- Liposomal encapsulation of MPL led to sequestration in lymphatic tissues (spleen, thymus).
- Uptake of MPL by other non-lymphatic tissues was not increased.
- This preferential targeting of immune system tissues may offer therapeutic advantages.