Simultaneous analysis of methylprednisolone, methylprednisolone succinate, and endogenous corticosterone in rat plasma

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

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.

Development of superparamagnetic high-magnetization C18-functionalized magnetic silica nanoparticles as sorbents for enrichment and determination of methylprednisolone in rat plasma by high performance liquid chromatography

In this study, a novel extraction and enrichment technique based on superparamagnetic high-magnetization C(18)-functionalized magnetic silica nanoparticles (C(18)-MNPs) as sorbents was successfully developed for the determination of methylprednisolone (MP) in rat plasma by high performance liquid chromatography (HPLC). The synthesized silica-coated magnetite modified with chlorodimethyl-n-octadecylsilane was about 320 nm in diameter with strong magnetism and high surface area. It provided an efficient way for extraction and concentration of MP in the samples through hydrophobic interaction by the interior C(18) groups. Moreover, MP adsorbed with C(18)-MNPs could be simply and rapidly isolated through placing a strong magnet on the bottom of container, and then easily eluted from C(18)-MNPs by n-hexane solution. Extraction conditions such as amounts of C(18)-MNPs added, adsorption time and desorption solvent, were investigated. Method validations including linear range, detection limit, precision, and recovery were also studied. The results showed that the proposed method based on C(18)-MNPs was a simple, accurate and high efficient approach for the analysis of MP in the complex plasma samples.

A sensitive and specific precursor ion scanning approach in liquid chromatography/electrospray ionization tandem mass spectrometry to detect methylprednisolone acetate and its metabolites in rat urine

A new, simple, sensitive and specific liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method in precursor ion scanning (PIS) mode has been developed for the rapid detection of methylprednisolone acetate (MPA) and its metabolites in rat urine. A suitable product ion specific for methylprednisolone (MP) and MPA was selected after a fragmentation study on 20 (cortico)steroids at different collision energies (5-40 eV). Urine samples were simply treated with acetonitrile then dried in a SpeedVac system. The method was validated and compared with other PIS methods for detecting corticosteroids in human urine. It was more sensitive, with limit of detection (LOD) and lower limit of quantitation (LLOQ), respectively, of 5 and 10 ng mL(-1). The method was applied for the analysis of rat urine collected before and after (24, 48, 72 h) intra-articular (IA) injection of a marketed formulation of MPA (Depo-Medrol(R)). MS/MS acquisitions were taken at different collision energies for the precursor ions of interest, detected in PIS mode, to verify the MP-related structure. Six different metabolites were detected in rat urine, and their chemical structures were assigned with a computational study.

Plasma pharmacokinetics and tissue disposition of novel dextran-methylprednisolone conjugates with peptide linkers in rats

The plasma and tissue disposition of two novel dextran prodrugs of methylprednisolone (MP) containing one (DMP-1) or five (DMP-5) amino acids as linkers were studied in rats. Single 5-mg/kg doses (MP equivalent) of each prodrug or MP were administered intravenously, and blood and tissue samples were collected. Prodrug and drug concentrations were quantitated using HPLC, and noncompartmental pharmacokinetic parameters were estimated. Whereas conjugation of MP with dextran in both prodrugs substantially decreased the clearance of the drug by approximately 200-fold, the accumulations of the drug in the liver, spleen, and kidneys were significantly increased by conjugation. However, the extent of accumulation of DMP-1 in these tissues was substantially greater than that for DMP-5. Substantial amounts of MP were regenerated from both prodrugs in the liver and spleen, with the rate of release from DMP-5 being twice as fast as that from DMP-1. However, the AUCs of MP regenerated from DMP-1 in the liver and spleen were substantially higher than those after DMP-5. In contrast, in the kidneys, the AUC of MP regenerated from DMP-5 was higher than that after DMP-1 administration. These data suggest that DMP-1 may be more suitable than DMP-5 for targeting immunosuppression to the liver and spleen.

Desenvolvimento de um método analítico rápido e eficiente para a determinação de corticosteróides plasmáticos por injeção direta em coluna cromatográfica ISRP-C18 por CLAE

O presente trabalho teve como objetivo o desenvolvimento de um método analítico simples, rápido e eficiente para a determinação de corticosteróides (cortisona, corticosterona, acetato de hidrocortisona e acetato de dexametasona) em amostras sangüíneas de ratos empregando um sistema isocrático de cromatografia líquida de alta eficiência (CLAE) com detecção ultravioleta. O método envolveu a injeção direta da amostra sangüínea em uma coluna cromatográfica com superfície interna de fase reversa (ISRP-C18), empregando a fase móvel composta por tampão fosfato pH 4,0: acetonitrila (65:35 v/v). A detecção dos analitos foi obtida, através de um detector de ultravioleta de comprimento de onda variável (Varian Modelo 2550) ajustado em 240 nm e um integrador SP 4400 Chromaject (Varian Associates, Inc, Sunnyvale, CA, USA). A extração do analito resultou em valores de recuperação entre 90% e 108%, e coeficiente de variação entre 1,1% a 2,5%. Os limites de detecção e quantificação do método foram de 0,02 e 0,04 µg mL-1, respectivamente. Assim, o método analítico proposto possibilitou a injeção direta (on-line) da amostra sem tratamento prévio apresentando também várias vantagens, tais como: rapidez, exatidão, precisão e especificidade.

A rapid and sensitive LC-ESI-MS/MS method for detection and quantitation of methylprednisolone and methylprednisolone acetate in rat plasma after intra-articular administration

A rapid, sensitive and specific liquid chromatography-electrospray-tandem mass spectrometric (LC-ESI-MS/MS) method for the simultaneous detection and quantitation of methylprednisolone acetate (MPA) and methylprednisolone (MP) in rat plasma, using a triple-stage quadrupole, has been developed and validated. MP-D(2) was used as internal standard (IS) and acetonitrile was added to plasma samples for protein precipitation. After extraction with dichloromethane, the analytes were separated on a C-12 reversed-phase column by isocratic elution (6min at a flow rate 0.2mLmin(-1)) with water containing 0.01% formic acid (A) and acetonitrile (B) (50:50, v/v). Quantitation was performed in positive ion multiple reaction monitoring (MRM) mode by applying the following precursor-to-product ion transitions: MPA m/z 417-->135+161+253; MP m/z 375-->135+161+253; IS m/z 377-->135+161+253. The method, validated over the concentration range 6-600ngmL(-1), has been shown to meet the current requirements of bioananalytical validation, providing satisfactory results in terms of linearity, recovery, intra-day and inter-day precision and accuracy. The lower limit of quantitation (LLOQ) was 6ngmL(-1) for both the analytes (0.080 and 0.072pmol injected for MP and MPA, respectively). The method was successfully applied to monitor the plasma levels of MPA and MP following intra-articular (IA) injections of a low MPA (Depo-Medrol((R))) dose in rats.

Liquid chromatography-tandem mass spectrometry for the determination of methylprednisolone in rat plasma and liver after intravenous administration of its liver-targeted dextran prodrug

A specific and sensitive liquid chromatography (LC)-tandem mass spectrometric method for quantitative determination of methylprednisolone (MP) in rat plasma and liver was developed and validated using triamcinolone acetonide as an internal standard. Liquid-liquid extraction using tert-butyl methyl ether was used to extract the drug and the internal standard from plasma and liver. The separation of MP was performed on a C(18) column with a mobile phase of acetonitrile:0.5% formic acid aqueous solution (85:15, v/v) over 4min. The assay was based on the selected reaction monitoring transitions at m/z 375-->161 for MP in plasma, 375-->357 for MP in liver, and 435-->415 for internal standard in both plasma and liver. The lower limit of quantification was 20ng/mL based on 100microL of plasma or liver homogenate. Intra- and inter-day assay variations were Collapse

Key Words

• methylprednisolone
• dextran-methylprednisolone prodrug
• rat plasma
• rat liver
• liquid chromatography-tandem mass spectrometry
• pharmacokinetics

Collapse

MESH Headings

• Animals
• Chromatography, Liquid/methods
• Dextrans/administration & dosage
• Dextrans/pharmacokinetics
• Liver/chemistry
• Liver/metabolism
• Male
• Methylprednisolone/analysis
• Methylprednisolone/blood
• Methylprednisolone/pharmacokinetics
• Prodrugs/administration & dosage
• Prodrugs/pharmacokinetics
• Rats
• Rats, Sprague-Dawley
• Tandem Mass Spectrometry/methods

Collapse

Grants

• R01 GM069869 NIGMS NIH HHS

Collapse

Affiliation(s)

Shuang-Qing Zhang Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA
Helen R. Thorsheim Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA
Suman Penugonda Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA
Venkateswaran C. Pillai Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA
Quentin R. Smith Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA
Reza Mehvar Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA

Collapse

Collaborators Collapse

A mouse model for glucocorticoid-induced osteonecrosis: effect of a steroid holiday

Glucocorticoid-induced osteonecrosis is a common and dose-limiting adverse event. The goal of this study was to establish a mouse model of glucocorticoid-induced osteonecrosis suitable for testing the effects of different treatment strategies on its frequency. Fourteen murine strains were screened using various glucocorticoids, routes of administration, and diets. Four-week-old male BALB/cJ mice were treated with oral dexamethasone for up to 12 weeks either by continuous dosing or by discontinuous dosing, with or without asparaginase. Histopathological features of the distal femurs were examined by light microscopy. Osteonecrotic lesions were characterized by empty lacunae and osteocyte ghosts in trabecular bone surrounded by necrotic marrow and edema. The incidence of dexamethasone induced osteonecrosis in BALB/cJ mice was 40-45% (4/10 or 5/11) at 12 weeks. The frequency of osteonecrosis trended lower after discontinuous compared to continuous dosing for 12 weeks (8 vs. 45%) (p = 0.06) despite comparable cumulative plasma exposure. Asparaginase hastened the occurrence of osteonecrosis, which was observed as early as 4 weeks and the incidence was 50% after 6 weeks. A mouse model of glucocorticoid-induced osteonecrosis was established. Discontinuous was less osteonecrotic than continuous dexamethasone treatment, consistent with the possible benefits of a "steroid holiday" seen in clinical settings. Moreover, asparaginase hastened osteonecrosis, indicating that drugs may interact with glucocorticoids to affect osteonecrosis risk.

Synthesis and in vitro characterization of novel dextran-methylprednisolone conjugates with peptide linkers: effects of linker length on hydrolytic and enzymatic release of methylprednisolone and its peptidyl intermediates

To control the rate of release of methylprednisolone (MP) in lysosomes, new dextran-MP conjugates with peptide linkers were synthesized and characterized. Methylprednisolone succinate (MPS) was attached to dextran 25 kDa using linkers with 1-5 Gly residues. The release characteristics of the conjugates in pH 4.0 and 7.4 buffers, blood, liver lysosomes, and various lysosomal proteinases were determined using a size-exclusion and/or a newly developed reversed-phase HPLC method capable of simultaneous quantitation of MP, MPS, and all five possible MPS-peptidyl intermediates. We synthesized conjugates with >or=90% purity and 6.9-9.5% (w/w) degree of MP substitution. The conjugates were stable at pH 4.0, but released MP and intact MPS-peptidyl intermediates in the pH 7.4 buffer and rat blood, with faster degradation rates for longer linkers. Rat lysosomal fractions degraded the conjugates to MP and all the possible intermediates also at a rate directly proportional to the length of the peptide. Whereas the degradation of the conjugates by cysteine peptidases (papain or cathepsin B) was relatively substantial, no degradation was observed in the presence of aspartic (cathepsin D) or serine (trypsin) proteinases, which do not cleave peptide bonds with Gly. These newly developed dextran conjugates of MP show promise for controlled delivery of MP in lysosomes.

Quantitation of hepcidin from human and mouse serum using liquid chromatography tandem mass spectrometry

The hepatic peptide hormone hepcidin is considered the central regulator of iron metabolism. Characterizing the circulating levels of this peptide is critical to understanding its role in the development of clinically relevant syndromes, such as anemia of inflammation/chronic disease, and may provide insight into potential clinical interventions. While quantitative methods have been published for the determination of urinary hepcidin and serum prohepcidin, no definitive methods have been published for the determination of hepcidin in serum. In this report, we describe a quantitative method for the determination of both human and mouse hepcidin in serum and plasma. The method employs protein precipitation and solid-phase extraction followed by liquid chromatographic separation and tandem mass spectrometry detection. The method has a quantitative range of 0.25 ng/mL to 500 ng/mL serum for mouse hepcidin and 1 ng/mL to 500 ng/mL serum for human hepcidin. The method uses small sample volumes (50 microL for mice and 100 microL for humans) and 96-well formats for rapid sample processing. The method was used to establish baseline serum and plasma concentrations of hepcidin in normal C57Bl/6 mice and healthy human volunteers.

Comparison of the use of anionic and cationic surfactants for the separation of steroids based on MEKC and sweeping-MEKC modes

In attempts to improve the selectivity and sensitivity of steroid separation and to determine their migration order, a comparison of the use of anionic and cationic surfactants based on the MEKC and sweeping-MEKC modes was made. A mixture of six steroids (progesterone, 17-hydroxy progesterone, 11-deoxycortisol, corticosterone, cortisone, and cortisol) could be separated and detected by means of the CE/UV-absorption method. The order of migration time for these steroids was compared under various conditions, including acidic/alkaline buffers, anionic/cationic surfactants, and positive/negative applied voltage, causing the direction of the EOF and the migration of micelles to change. The major rules for generally predicting the migration order of steroids are summarized. The detection limits were significantly improved when the sweeping-MEKC mode was applied.

Effects of duration of ischemia and donor pretreatment with methylprednisolone or its macromolecular prodrug on the disposition of indocyanine green in cold-preserved rat livers

PURPOSE

Cold preservation of the liver before transplantation may change uptake and excretory functions of hepatocytes. We hypothesized that an increase in the duration of preservation would result in a progressive decrease in the hepatic uptake and/or biliary excretion of indocyanine green (ICG), which would be attenuated by pharmacologic interventions.

METHODS

Donor rats (n = 40) were administered saline (control) or single 5 mg/kg doses of methylprednisolone (MP) or its liver-targeted prodrug (DMP) 2 h prior to liver harvest. Following preservation in cold University of Wisconsin solution for 0, 24, 48, or 72 h, livers were reperfused in a single-pass manner for 30 min in the presence of ICG (approximately 4 microg/ml), followed by 60 min of ICG-free perfusion. The inlet, outlet, and bile concentrations of ICG were measured periodically by high performance liquid chromatography (HPLC), and kinetic parameters were estimated.

RESULTS

Effects of duration of preservation: In unpreserved livers, a significant portion of ICG dose (16%) was effluxed from the liver during the washout period. Cold preservation for 24-72 h progressively increased (p < 0.05) the efflux of ICG (>2-fold at 72 h). Similarly, average extraction ratio showed a modest (30-40%) decrease with increasing preservation time (p < 0.05). However, biliary excretion of ICG showed the most sensitivity to the preservation time (14 to >800-fold decline). Effects of pretreatment: DMP caused significant (p < 0.05) increases in biliary ICG levels (>12-fold) and bile flow rates (6-15-fold) of preserved livers. Although MP pretreatment significantly (p < 0.05) increased (6-fold) bile flow rates in 48-h preserved livers, its effects on biliary ICG levels were not significant (p > 0.05).

CONCLUSIONS

Biliary excretion of ICG is the most sensitive kinetic parameter to prolonged cold ischemia-reperfusion injury in a rat liver perfusion model. The injury may be significantly attenuated by pharmacologic pretreatment of the liver donors.

Attenuation of Kupffer cell activation in cold-preserved livers after pretreatment of rats with methylprednisolone or its macromolecular prodrug

PURPOSE

Activation of hepatic Kupffer cells (KCs) during organ preservation and subsequent reperfusion causes release of proinflammatory mediators and is responsible, at least in part, for rejection of transplanted livers. Our hypothesis was that donor pretreatment, before liver harvest, with methylprednisolone (MP) or its dextran prodrug (DMP) would reduce KC activation.

METHODS

Adult donor rats were administered a single 5-mg/kg (MP equivalent) IV dose of MP or DMP or saline 2 h before liver harvest. The livers were then stored in University of Wisconsin solution for 24, 48, or 96 h (n = 4/treatment/time). A recirculating perfusion model was used to study, for 180 min, the release of KC activation markers, tumor necrosis factor (TNF)-alpha and acid phosphatase, and other biochemical indices from the cold-preserved livers.

RESULTS

Cold ischemia-reperfusion resulted in release of substantial levels of TNF-alpha in untreated groups. Pretreatment of rats with MP or DMP caused a significant (p < 0.0001) reduction in TNF-alpha AUC in the perfusate, with no significant differences between MP and DMP. The maximum inhibitory effect of MP (77.5 +/- 10.2%) was observed after 48 h of preservation, whereas DMP showed maximal inhibition of TNF-alpha AUC at both 24 (74.5 +/- 15.8%) and 48 (74.8 +/- 12.6%) h of preservation. Similarly, both MP and DMP resulted in a significant (p < 0.0004) decrease in acid phosphatase levels of cold-preserved livers. However, neither pretreatment had any substantial effect on the levels of other biochemical markers.

CONCLUSIONS

Both MP and DMP pretreatments decreased the release of TNF-alpha and acid phosphatase from livers subjected to cold ischemia preservation. Therefore, pretreatment of liver donors with MP or its prodrug decreases KC activation by cold ischemia-reperfusion.

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: local immunosuppressive effects in liver after systemic administration to rats

PURPOSE

The purpose of this work was to study the local immunosuppressive effects of systemically administered methylprednisolone (MP) and its prodrug, dextran-methylprednisolone (DMP), in rat livers.

METHODS

Single 5 mg/kg (MP equivalent) doses of MP or DMP were injected intravenously to rats, and livers were isolated at different time points (0-72 h; n = 4/time point). Isolated livers were stimulated ex vivo with bacterial lipopolysaccharide, and outlet perfusate and bile samples were analyzed for their concentrations of tumor necrosis factor (TNF)-alpha by enzyme-linked immunosorbent assay. The area under the perfusate TNF-alpha concentration-time curve (AUC) was used as a measure of immune response. Hepatic concentrations of MP and DMP were also measured by high-performance liquid chromatography.

RESULTS

Both MP and DMP resulted in a decrease in lipopolysaccharide-induced increase in TNF-alpha AUC. MP injection 8 h before liver isolation resulted in a maximum of 50% decrease in TNF-alpha AUC. Compared with MP, the maximum effect of the prodrug (DMP) was both more intense (approximately 80% reduction in TNF-alpha AUC) and delayed (maximum inhibition at 24 h). Overall, the area under the effect (% inhibition of TNF-alpha)-time (%inhibition-h) for DMP (3,680 +/- 406) was approximately four times more than that for the parent drug (846 +/- 114). Whereas the MP concentrations in the liver were not quantifiable after the injection of the parent drug, relatively large concentrations of DMP and regenerated MP were found in the liver of DMP-injected rats.

CONCLUSIONS

After systemic administration to rats, both MP and DMP exhibit local immunosuppressive effects in the liver. The local effects of the prodrug (DMP), however, appear to be more intense and sustained than those of the parent drug (MP).

Determination of corticosterone in rat and mouse plasma by gas chromatography-selected ion monitoring mass spectrometry

A simple, highly sensitive and specific method based on gas-chromatography-selected ion monitoring (SIM) mass spectrometry has been developed for the quantitation of corticosterone in rat and mouse plasma. After extraction of the plasma with ethyl acetate, the residue was trimethy-silylated with pentafluorobenzyl hydroxylamine-trimethylsilyl (PFBO-TMS). Detection of the derivatives was accomplished by a quadruple mass spectrometer in the selected ion monitoring mode (m/z of 316, 648, 663 and 678). The detection limit of the assay was 0.1 pg on column. The results show that in the plasma of non-stressed animals, only minor amounts of corticosterone were found; whereas in the plasma of stressed animals, it was dramatically increased. The method developed here can be used to examine corticosterone levels as a marker of stress in rats and mice and may also be used for estimation of the effect of stress-release medications.

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: plasma and tissue disposition

Plasma and tissue disposition of a macromolecular prodrug of methylprednisolone (MP), dextran (70 kDa)-methylprednisolone succinate (DMP), was studied in rats. Single 5-mg/kg doses of DMP or unconjugated MP were administered into the tail veins of different groups of rats (n = 4/group/time point). Blood (cardiac puncture) and tissues (liver, spleen, kidney, heart, lung, thymus, and brain) were collected at various times after DMP (0-96 h) or MP (0-2 h) injections. Concentrations of DMP and MP in samples were analyzed by size-exclusion chromatography (SEC) and reversed-phase high-performance liquid chromatography (HPLC), respectively. Conjugation of MP with 70-kDa dextran resulted in 22-, 300-, and 30-fold decreases in the steady-state volume of distribution, clearance, and terminal plasma rate constant of the steroid, respectively. As for tissue distribution, the conjugate delivered the steroid primarily to the spleen and liver as indicated by 19- and 3-fold increases, respectively, in the tissue/plasma area under the curve (AUC) ratios of the steroid. On the other hand, the tissue/plasma AUC ratios of the prodrug in other organs were negligible. Active MP was released from DMP slowly in the spleen and liver, and AUCs of the regenerated MP in these tissues were 55- and 4.8-fold, respectively, higher than those after the administration of the parent drug. In contrast, no parent drug was detected in the plasma of DMP-injected rats. These results indicate that DMP may be useful for the targeted delivery of MP to the spleen and liver where the active drug is slowly released.

Gas chromatography and high-performance liquid chromatography of natural steroids

This review article underlines the importance of gas chromatography (GC), high-performance liquid chromatography (HPLC) and their hyphenated techniques using mass spectrometry (MS) for the determination of natural steroids, especially in human biological fluids. Steroids are divided into eight categories based on their structures and functions, and recent references using the above methodologies for the analysis of these steroids are cited. GC and GC-MS are commonly used for the determination of volatile steroids. Although HPLC is a widely used analytical method for the determination of steroids including the conjugated type in biological fluids, LC-MS is considered to be the most promising one for this purpose because of its sensitivity, specificity and versatility.

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: dose-dependent pharmacokinetics in rats

The dose-dependency in the pharmacokinetics of a macromolecular prodrug of methylprednisolone (MP), dextran-methylprednisolone succinate (DMP), was investigated in rats. Single doses (MP equivalent) of 2.5, 5.0, 10, 20, and 30 mg/kg of DMP were administered intravenously to rats (n=5/group), and serial blood samples (0-96 h) and spleen and liver tissues (96 h) were collected. The concentrations of DMP in plasma and spleen were analyzed using a size-exclusion chromatographic method. The concentrations of DMP in the liver samples were determined by an indirect method after sequential hydrolysis by dextranase and esterase enzymes, followed by HPLC analysis of MP. The kinetics of DMP were analyzed by non-compartmental methods. The systemic clearance of DMP decreased approximately 5-fold (from 42.1+/-11.0 to 7.72+/-1.84 ml/h per kg) when the dose was increased from 2.5 to 30 mg/kg. The nonlinearity in the clearance of DMP could be adequately described by a Michaelis-Menten type elimination with a maximum velocity of elimination of 1.72 mg/h per kg and a constant of 24.9 microg/ml. Additionally, the percent of the dose of DMP found at 96 h in the liver and spleen, where the prodrug is sequestered and gradually eliminated, significantly decreased with an increase in the dose. It is concluded that the clearance of DMP in rats is modestly dose-dependent in the dosage range of 2.5-30 mg/kg.

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: immunosuppressive effects after in vivo administration to rats

PURPOSE

To study the immunosuppressive activities of a macromolecular prodrug of methylprednisolone (MP), dextran-methylprednisolone succinate (DEX-MPS), in rats.

METHODS

Single 5 mg/kg (MP equivalent) doses of MP or DEX-MPS were administered intravenously to rats, and blood and spleen samples were collected over 96 h. The immunosuppressive activity was determined by the effects of the free or dextran-conjugated drug on the mitogen-stimulated spleen lymphocyte proliferation. Additionally, the number of lymphocytes in the spleen cell suspensions was estimated. Further, the plasma and spleen concentrations of the conjugated and free MP were determined using size-exclusion and reversed-phase chromatographic methods, respectively.

RESULTS

Both MP and DEX-MPS injections resulted in the inhibition of the spleen lymphocyte proliferation. However, the maximal effect of DEX-MPS was significantly (P < 0.003) more intense (approximately 100% inhibition) and delayed (24 h) relative to that of MP (approximately 50% inhibition at 2 h). The DEX-MPS injection also resulted in a significantly (P < 0.0001) higher decline in the estimated number of spleen lymphocytes (approximately 80% at 24 h), compared with the MP injection (approximately 30% at 2 hr). Whereas the plasma and spleen concentrations of MP could not be measured at > or = 2 h after the drug injection, relatively high concentrations of DEX-MPS persisted in plasma and spleen for 24 h and 96 h, respectively.

CONCLUSION

Dextran-methylprednisolone conjugate can effectively deliver the corticosteroid to its site of action for immunosuppression, resulting in more intense and sustained effects when compared with the free drug administration.

Kinetics of hydrolysis of dextran-methylprednisolone succinate, a macromolecular prodrug of methylprednisolone, in rat blood and liver lysosomes

A macromolecular prodrug of methylprednisolone (MP) was synthesized by conjugating MP with dextran with a M(W) of 70000 through a succinic acid linker. It has been shown previously that the dextran-MP conjugate (DMP) releases MP directly or indirectly through formation of methylprednisolone succinate (MPS) which is further hydrolyzed to MP. To investigate the suitability of DMP conjugate as a prodrug of MP for systemic administration, the kinetics of hydrolysis of the conjugate was studied in vitro in rat blood and liver lysosomes. In blood, the hydrolysis of MPS to MP was approximately ten-fold faster than that in buffer. However, the hydrolysis rate constants of DMP conjugate to MP or MPS in blood were not different from those in buffer. Overall, the hydrolysis of DMP in the rat blood occurred with a half life of approximately 25 h. Hydrolysis of MPS to MP also occurred in the liver lysosomal fraction, but not in the control samples lacking lysosomes. However, the rate constants for the hydrolysis of DMP conjugate to MP and MPS in the lysosomal fraction were not significantly different from those in the control samples. These data suggest that the slow hydrolysis of DMP conjugate to MP or MPS in both rat blood and liver lysosomes occurs mostly, if not completely, via chemical hydrolysis. However, the conversion of MPS to MP is apparently enzymatic. The data may have significant implications for systemic administration of the prodrug.