Synthesis and pharmacokinetics of a novel macromolecular prodrug of Tacrolimus (FK506), FK506-dextran conjugate

Redox-Responsive Hyaluronic Acid-Tacrolimus Conjugate: Synthesis, Characterization, and In Vitro Immunosuppressive Activity

A redox-responsive macromolecular prodrug of tacrolimus, HA-ss-Tac, was constructed by conjugation of tacrolimus (TAC, FK506) through its succinate ester to cystamine-modified hyaluronic acid (HA-Cys), and its physicochemical properties and immunosuppressive activity were studied. The synthesized HA-ss-TAC was determined to contain 8% of chemically loaded TAC with significantly enhanced water solubility. The release study showed a sustained release of drug through slow degradation of linker-drug bonds. In vitro inhibition of proliferation of T- and B-lymphocytes was almost comparable to that of TAC, implying that the biologically active compound could be released from the conjugate. The polymeric prodrug lacks obvious cytotoxicity on Raw 264.7 macrophages and significantly suppressed the production of inflammatory cytokines IL-2 and IL-1β by LPS-activated cells. Additionally, the cellular uptake study of the FITC-labeled conjugate confirmed the HA receptor-mediated internalization of the conjugate into targeted cells, thus avoiding systemic side effects. Taken together, the HA-ss-TAC prodrug could be an optimal prodrug for intravenous administration based on this preliminary data and can be expected to have improved therapeutic efficacy.

Sustained A1 Adenosine Receptor Antagonist Drug Release from Nanoparticles Functionalized by a Neural Tracing Protein

Respiratory dysfunction is a major cause of death in people with spinal cord injury (SCI). A remaining unsolved problem in treating SCI is the intolerable side effects of the drugs to patients. In a significant departure from conventional targeted nanotherapeutics to overcome the blood-brain barrier (BBB), this work pursues a drug-delivery approach that uses neural tracing retrograde transport proteins to bypass the BBB and deliver an adenosine A1 receptor antagonist drug, 1,3-dipropyl-8-cyclopentyl xanthine, exclusively to the respiratory motoneurons in the spinal cord and the brainstem. A single intradiaphragmatic injection at one thousandth of the native drug dosage induces prolonged respiratory recovery in a hemisection animal model. To translate the discovery into new treatments for respiratory dysfunction, we carry out this study to characterize the purity and quality of synthesis, stability, and drug-release properties of the neural tracing protein (wheat germ agglutinin chemically conjugated to horseradish peroxidase)-coupled nanoconjugate. We show that the batch-to-batch particle size and drug dosage variations are less than 10%. We evaluate the nanoconjugate size against the spatial constraints imposed by transsynaptic transport from pre to postsynaptic neurons. We determine that the nanoconjugate formulation is capable of sustained drug release lasting for days at physiologic pH, a prerequisite for long-distance transport of the drug from the diaphragm muscle to the brainstem. We model the drug-release profiles using a first-order reaction model and the Noyes-Whitney diffusion model. We confirm via biological electron microscopy that the nanoconjugate particles do not accumulate in the tissues at the injection site. We define the nanoconjugate storage conditions after monitoring the solution dispersion stability under various conditions for 4 months. This study supports further development of neural tracing protein-enabled nanotherapeutics for treating respiratory problems associated with SCI.

Distinct effects of calcineurin dependent and independent immunosuppressants on endotoxaemia-induced nephrotoxicity in rats: Role of androgens

Evidence suggests that immunosuppressant therapies protect against harmful effects of endotoxaemia. In this study, we tested whether calcineurin-dependent (cyclosporine/tacrolimus) and -independent (sirolimus) immunosuppressants variably influence nephrotoxicity induced by endotoxaemia and whether this interaction is modulated by testosterone. We investigated the effects of immunosuppressants on renal histopathological, biochemical and inflammatory profiles in endotoxic male rats and the role of androgenic state in the interaction. Six-hour treatment of rats with lipopolysaccharide (LPS, 3 mg/kg) increased (i) serum urea/creatinine, (ii) width of proximal/distal tubules, (iii) tubular degeneration and vacuolation, (iv) Western protein expressions of renal toll-like receptor 4, monocyte chemoattractant protein-1, and NADPH oxidase-2, and (v) serum tumour necrosis factor-α and myeloperoxidase. These endotoxic manifestations were intensified and eliminated upon concurrent exposure to cyclosporine and sirolimus, respectively. The cyclosporine actions appear to be a class rather than a drug effect because similar exacerbation of LPS nephrotoxicity was observed in rats treated with tacrolimus, another calcineurin inhibitor (CNI). Moreover, the deteriorated renal outcomes in LPS/tacrolimus-treated rats were reduced after castration or androgen receptor blockade by flutamide. The data suggest opposite effects for calcineurin-dependent (exaggeration) and -independent immunosuppressants (amelioration) on renal defects of endotoxaemia and implicate androgenic pathways in the worsened endotoxic renal profile induced by CNIs.

Topical tacrolimus nanocapsules eye drops for therapeutic effect enhancement in both anterior and posterior ocular inflammation models

Tacrolimus has shown efficacy in eye inflammatory diseases. However, due to the drug lability, its formulation into a stable ophthalmic product remains a challenge. Tacrolimus-loaded nanocapsules (NCs) were designed for ocular instillation. Further, the stability and effects of the formulation were analyzed under different experimental conditions. Physicochemical characterization of the NCs revealed suitable homogeneous size and high encapsulation efficiency. Moreover, the lyophilized formulation was stable at ICH long term and accelerated storage conditions, for at least 18 and 3 months, respectively. The tacrolimus NCs did not elicit any eye irritation in rabbits after single- and multiple-dose applications. Additionally, ex vivo penetration assays on isolated porcine cornea and pharmacokinetics analyses in various rabbit eye compartments demonstrated the superiority of the NCs in retention and permeation into the anterior chamber of the eye compared to the free drug dissolved in oil. Moreover, multiple dose ocular instillation of the NCs in rats allowed high tacrolimus levels in the eye with very low plasma concentrations. Finally, the developed delivery system achieved a significant decrease in four typical inflammatory markers in a murine model of keratitis, an anterior chamber inflammation. Furthermore, these NCs, applied as eye drops, displayed clinical and histological efficacy in the mainly posterior chamber inflammation model of murine, experimental auto-immune uveitis.

Head-to-head comparative pharmacokinetic and biodistribution (PK/BD) study of two dexamethasone prodrug nanomedicines on lupus-prone NZB/WF1 mice

HPMA copolymer-based dexamethasone prodrug (P-Dex) and PEG-based dexamethasone prodrug (PEG-Dex, ZSJ-0228) were previously found to passively target the inflamed kidney and provide potent and sustained resolution of nephritis in NZB/WF1 lupus-prone mice. While both prodrug nanomedicines effectively ameliorate lupus nephritis, they have demonstrated distinctively different safety profiles. To explore the underlining mechanisms of these differences, we conducted a head-to-head comparative PK/BD study of P-Dex and PEG-Dex on NZB/WF1 mice. Overall, the systemic organ/tissue exposures to P-Dex and Dex released from P-Dex were found to be significantly higher than those of PEG-Dex. The high prodrug concentrations were sustained in kidney for only 24 h, which cannot explain their lasting therapeutic efficacy (>1 month). P-Dex showed sustained presence in liver, spleen and adrenal gland, while the presence of PEG-Dex in these organs was transient. This difference in PK/BD profiles may explain PEG-Dex' superior safety than P-Dex.

Diaphragmatic recovery in rats with cervical spinal cord injury induced by a theophylline nanoconjugate: Challenges for clinical use

Context: Following a spinal cord hemisection at the second cervical segment the ipsilateral hemidiaphragm is paralyzed due to the disruption of the rostral ventral respiratory group (rVRG) axons descending to the ipsilateral phrenic motoneurons (PN). Systemically administered theophylline activates a functionally latent crossed phrenic pathway (CPP) which decussates caudal to the hemisection and activates phrenic motoneurons ipsilateral to the hemisection. The result is return of function to the paralyzed hemidiaphragm. Unfortunately, in humans, systemically administered theophylline at a therapeutic dose produces many unwanted side effects.Design and setting: A tripartite nanoconjugate was synthesized in which theophylline was coupled to a neuronal tracer, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), using gold nanoparticles as the coupler. Following intradiaphragmatic injection of the nanoconjugate, WGA-HRP selectively targets the theophylline-bound nanoconjugate to phrenic motoneurons initially, followed by neurons in the rVRG by retrograde transsynaptic transport.Participants: (N/A)Interventions: (N/A)Outcome Measures: Immunostaining, Electromyography (EMG).Results: Delivery of the theophylline-coupled nanoconjugate to the nuclei involved in respiration induces a return of respiratory activity as detected by EMG of the diaphragm and a modest return of phrenic nerve activity.Conclusion: In addition to the modest return of phrenic nerve activity, there were many difficulties using the theophylline nanoconjugate because of its chemical instability, which suggests that the theophylline nanoconjugate should not be developed for clinical use as explained herein.

A perspective on magnetic core-shell carriers for responsive and targeted drug delivery systems

Magnetic core-shell nanocarriers have been attracting growing interest owing to their physicochemical and structural properties. The main principles of magnetic nanoparticles (MNPs) are localized treatment and stability under the effect of external magnetic fields. Furthermore, these MNPs can be coated or functionalized to gain a responsive property to a specific trigger, such as pH, heat, or even enzymes. Current investigations have been focused on the employment of this concept in cancer therapies. The evaluation of magnetic core-shell materials includes their magnetization properties, toxicity, and efficacy in drug uptake and release. This review discusses some categories of magnetic core-shell drug carriers based on Fe2O3 and Fe3O4 as the core, and different shells such as poly(lactic-co-glycolic acid), poly(vinylpyrrolidone), chitosan, silica, calcium silicate, metal, and lipids. In addition, the review addresses their recent potential applications for cancer treatment.

Preclinical characterization and clinical evaluation of tacrolimus eye drops

Severe allergic ocular diseases as atopic keratoconjunctivitis can induce corneal damage due to inflammatory substances released from giant papillae. Tacrolimus eye drops are one of the current therapeutic alternatives for its treatment. This work is aimed at developing and characterizing a 0.03% tacrolimus ophthalmic formulation, which was introduced in three types of vehicles (BBS, PVA and Hyaluronic Acid). For this, we have performed in vitro (stability studies) and in vivo assays (corneal permanence time measured directly by Positron Emission Tomography) of three potential formulations. Next, the best formulation was selected, and its toxicological profile and clinical effectiveness have been evaluated. The biopermanence studies (direct measurements and PET/CT) showed that the formulations with PVA and Hyaluronic Acid present more retention time on the ocular surface of rats than PBS. From the stability study, we have determined that tacrolimus with PVA in cold storage is the best option. Tacrolimus with PVA has shown lower cytotoxicity than cyclosporine at early times. On the other hand, the pilot study performed has shown significant improvements in patients, with no noticeable adverse reactions. Based on stability, biopermanence, safety and clinical effectiveness studies, we concluded that tacrolimus-PVA eye drops are a suitable candidate for its clinical application in inflammatory ophthalmology diseases.

Design, Characterization, and In Vivo Pharmacokinetics of Tacrolimus Proliposomes

The objective of this study was to develop proliposomal formulation for a poorly bioavailable drug, tacrolimus. Proliposomes were prepared by thin film hydration method using different lipids such as hydrogenated soy phosphatidylcholine (HEPC), soy phosphatidylcholine (SPC), distearyl phosphatidylcholine (DSPC), dimyristoylphosphatidylcholine (DMPC), and dimyristoylphosphatidylglycerol sodium (DMPG) and cholesterol in various ratios. Proliposomes were evaluated for particle size, zeta potential, in vitro drug release, in vitro permeability, and in vivo pharmacokinetics. In vitro drug release was carried out in purified water using USP type II dissolution apparatus. In vitro drug permeation was studied using parallel artificial membrane permeation assay (PAMPA) and everted rat intestinal perfusion techniques. In vivo pharmacokinetic studies were conducted in male Sprague-Dawley (SD) rats. Among the different formulations, proliposomes with drug/DSPC/cholesterol in the ratio of 1:2:0.5 demonstrated the desired particle size and zeta potential. Enhanced drug release was observed with proliposomes compared to pure tacrolimus in purified water after 1 h. Tacrolimus permeability across PAMPA and everted rat intestinal perfusion models was significantly higher with proliposomes. The optimized formulation of proliposomes indicated a significant improvement in the rate and absorption of tacrolimus. Following a single oral administration, a relative bioavailability of 193.33% was achieved compared to pure tacrolimus suspension.

Therapeutic effect of 0.1% Tacrolimus Eye Ointment in Allergic Ocular Diseases

INTRODUCTION

Allergic Ocular Diseases (AODs) like Atopic Keratoconjunctivitis (AKC) and Vernal Keratoconjunctivitis (VKC) are chronic forms of ocular allergy that can cause severe visual complications. Pathogenesis of AODs is uncertain and treatment has been a challenge for ophthalmologists. Tacrolimus, a 23-member cyclic macrolide lactone derived from [streptomyces tsukubaensis] now in ointment form has been successfully used in AODs.

AIM

To study the therapeutic effect of 0.1% Tacrolimus eye ointment in patients with Allergic Ocular Diseases (AODs).

MATERIALS AND METHODS

This prospective observational study was conducted on 36 patients with severe AOD and moderate cases not responding to conventional treatment. They were treated with 0.1% tacrolimus eye ointment twice daily for minimum three months in addition to conventional treatment and observed for a period of 6 months. Symptoms and signs after treatment were evaluated. Grades of clinical signs were assessed based on slit lamp clinical photographs; development of possible complications was assessed and analysed by Wilcoxon signed rank test.

RESULTS

Mean age of patients was 9.3±4.3 years and mean duration of AODs was 3.1±1.8 years. The scores on both the four point scales for signs and symptoms decreased significantly (p<0.0001) after 1 month of 0.1% Tacrolimus eye ointment treatment. Itching was the first symptom to show dramatic relief and conjunctival hyperaemia was the first sign to show improvement. 88.88% of patients were successfully weaned off topical steroids in 6 months into Tacrolimus treatment. Even in patients unresponsive to 0.1% topical Cyclosporine, symptoms and signs scores decreased significantly (p<0.0001). The most common adverse reaction was a transient burning sensation (36.11%).

CONCLUSION

Topical 0.1% Tacrolimus eye ointment was found to be a safe and effective treatment in cases of AODs and also worked as steroid sparing and replacing agent. It was also found effective in patient's refractory to topical Cyclosporine.

Therapeutic effects of 0.1% tacrolimus eye drops for refractory allergic ocular diseases with proliferative lesion or corneal involvement

Background

The objective of this study was to investigate the efficacy of topical 0.1% tacrolimus in treating refractory allergic conjunctivitis with proliferative lesions and/or corneal involvement.

Methods

This prospective observational study included 1436 patients with refractory allergic conjunctivitis whose condition had responded poorly to conventional antiallergic drugs and/or topical steroids and/or topical cyclosporine. All patients received tacrolimus eye drops twice daily during the study period. Ten clinical signs and six clinical symptoms were rated on a four-grade scale. The primary endpoint was the change from baseline in total clinical signs and symptoms score at the last observation or following 6 months of treatment.

Results

Total signs and symptoms score significantly decreased after 1 month of treatment (p<0.001). Giant papillae and corneal lesions were also reduced by tacrolimus eye drop use (p<0.001). The drug proved effective in patients whose condition did not respond well to topical cyclosporine therapy. About 50% of all patients using topical steroids were weaned. The most common adverse reaction was a transient burning sensation (3.20%).

Conclusions

Tacrolimus eye drops are highly effective in treating refractory allergic conjunctivitis with proliferative lesions and/or corneal involvement, and may reduce or replace topical steroid use.

Trial registration number

UMIN 000008640.

Formulation strategies for drug delivery of tacrolimus: An overview

Tacrolimus (FK 506) is a potent macrolide lactone immunosuppressive agent used for prophylaxis of organ rejection after transplantation and graft-versus-host disease after bone marrow transplantation in patients. Moreover, tacrolimus is a drug of choice in the treatment of atopic dermatitis for decreasing side effects associated with the use of topical corticosteroids. In spite of its success in ensuring graft survival, therapeutic use of tacrolimus is complicated due to its narrow therapeutic index (between 5 and 15 ng/ml). Tacrolimus has a large inter-/intra-patient variability in pharmacokinetics profile and a poor oral bioavailability because of its poor solubility, P-gp efflux, marked pre-systemic metabolism by CYP3A in the enterocytes and liver first pass effect. Several formulation approaches such as oily solution, solid dispersions, complexation with cyclodextrins, liposomes etc., have been investigated to improve oral delivery of FK 506. In this review, we have discussed various formulation approaches that have been undertaken by various researchers to solve the problems related to the drug delivery of tacrolimus.

Treatment of cerebral ischemia-reperfusion injury with PEGylated liposomes encapsulating FK506

FK506 (Tacrolimus) has the potential to decrease cerebral ischemia-reperfusion injury. However, the clinical trial of FK506 as a neuroprotectant failed due to adverse side effects. This present study aimed to conduct the selective delivery of FK506 to damaged regions, while at the same time reducing the dosage of FK506, by using a liposomal drug delivery system. First, the cytoprotective effect of polyethylene glycol-modified liposomes encapsulating FK506 (FK506-liposomes) on neuron-like pheochromocytoma PC12 cells was examined. FK506-liposomes protected these cells from H2O2-induced toxicity in a dose-dependent manner. Next, we investigated the usefulness of FK506-liposomes in transient middle cerebral artery occlusion (t-MCAO) rats. FK506-liposomes accumulated in the brain parenchyma by passing through the disrupted blood-brain barrier at an early stage after reperfusion had been initiated. Histological analysis showed that FK506-liposomes strongly suppressed neutrophil invasion and apoptotic cell death, events that lead to a poor stroke outcome. Corresponding to these results, a single injection of FK506-liposomes at a low dosage significantly reduced cerebral cell death and ameliorated motor function deficits in t-MCAO rats. These results suggest that liposomalization of FK506 could reduce the administration dose by enhancing the therapeutic efficacy; hence, FK506-liposomes should be a promising neuroprotectant after cerebral stroke.

FK506-binding protein (FKBP) partitions a modified HIV protease inhibitor into blood cells and prolongs its lifetime in vivo

HIV protease inhibitors are a key component of anti-retroviral therapy, but their susceptibility to cytochrome P(450) metabolism reduces their systemic availability and necessitates repetitive dosing. Importantly, failure to maintain adequate inhibitor levels is believed to provide an opportunity for resistance to emerge; thus, new strategies to prolong the lifetime of these drugs are needed. Toward this goal, numerous prodrug approaches have been developed, but these methods involve creating inactive precursors that require enzymatic processing. Using an alternative strategy inspired by the natural product FK506, we have synthetically modified an HIV protease inhibitor such that it acquires high affinity for the abundant, cytoplasmic chaperone, FK506-binding protein (FKBP). This modified protease inhibitor maintains activity against HIV-1 protease (IC(50) = 19 nM) and, additionally, it is partitioned into the cellular component of whole blood via binding to FKBP. Interestingly, redistribution into this protected niche reduces metabolism and improves its half-life in mice by almost 20-fold compared with the unmodified compound. Based on these findings, we propose that addition of FKBP-binding groups might partially overcome the poor pharmacokinetic properties of existing HIV protease inhibitors and, potentially, other drug classes.

Preliminary study of the effect of FK506 nanospheric-suspension eye drops on rejection of penetrating keratoplasty

OBJECTIVE

The aim of this study was to investigate the effect of a topical FK506 nanospheric suspension in a rat model of penetrating keratoplasty.

METHODS

FK506 nanospheres were prepared by using a biodegradable poly (lactic-co-glycolic acid) copolymer (PLGA). Its distribution in the eye and blood after a single instillation was examined in rabbits. Sprague-Dawley (SD) rats received corneal heterografts and were topically treated with phosphate-buffered saline (PBS), PLGA, FK-506 0.01% (nanospheres), or dexamethasone 0.05% solutions twice a day for 28 days. Rejection index and graft-survival time were recorded and compared between the four groups. Three grafts were collected at different time points for immunohistochemical studies.

RESULTS

In the cornea, the FK-506 concentration reached its peak within 1 h of a single eye-drop instillation and then decreased by half (1667.85 +/- 611.87 ng/g) at 8 h. FK-506 cannot be detected in rabbit blood. There were significant differences in the graft-survival time between the FK-506 nanosphere group (15.09 +/- 4.81 days) and the other three groups [PBS (7.90 +/- 1.20, t = -4.594, P < 0.001), PLGA (8.44 +/- 0.88, t = - 4.074, P = 0.001) and dexamethasone (10.44 +/- 1.42, t = -2.790, P = 0.012)]. The rejected corneas in the FK506 nanosphere group showed significantly fewer CD4, CD8, CD68, CD79, vascular endothelial growth factor, ICAM, and tumor growth factor-beta(1)-positive cells than those in the other groups.

CONCLUSIONS

FK506 0.01% nanospheric-suspension eye drops delayed the occurrence of corneal allograft rejection and prolonged allograft survival time. The FK506 nanospheres may be valuable in suppressing corneal graft rejection.

The protein-binding and drug release properties of macromolecular conjugates containing daptomycin and dextran

Prototype daptomycin-dextran macromolecular conjugates were prepared in an attempt to modify the biodistribution and protein-binding properties of daptomycin. Synthesis of daptomycin macromolecular conjugates involved dextran activation, daptomycin-dextran coupling, and purification. The reaction mixtures were separated on a Sephadex G-100 column using 10% acetronitrile in water as a mobile phase. UV and fluorescence characteristics of high molecular weight fractions demonstrated imine product formation while the lower molecular weight fractions contained free daptomycin, imine, and anilide products. Daptomycin macromolecular conjugates were characterized by drug loading, drug release, and binding affinity for fibrinogen using HPLC analysis and surface plasmon resonance. Drug loading was calculated to be 160mg of daptomycin per gram of macromolecule. Approximately 9% of the conjugated daptomycin was released from the macromolecular conjugates in aqueous media in the pH range of 1-7.4. The conjugates possessed higher affinity for fibrinogen than that of daptomycin.

Attenuation of acute rejection in a rat liver transplantation model by a liver-targeted dextran prodrug of methylprednisolone

BACKGROUND

The use of methylprednisolone (MP) and other corticosteroids for the treatment of acute liver allograft rejection is associated with severe toxicities in nontarget tissues. Therefore, selective delivery of MP to the liver may improve its efficacy and alleviate its side effects. We investigated the effects of a novel liver-targeted dextran prodrug of MP (DMP) in an orthotopic rat liver transplantation (OLT) model.

METHODS

The model consisted of a high responder rejection strain combination (Dark Agouti donors and Lewis recipients). Liver recipients were intravenously administered saline or a single subtherapeutic dose of MP (5 mg/kg) as the parent drug (MP) or its prodrug (DMP). Different groups were then monitored for graft survival or euthanized 5 or 9 days posttransplantation. Plasma chemistry, including alkaline phosphatase and bilirubin, allograft histology, and survival duration were determined.

RESULTS

Untreated recipients exhibited elevated plasma levels of liver injury markers, progressive portal and venous inflammation and cellular infiltration in liver allografts, and a mean graft survival time (MST) of 10.5 days. MP treatment did not alter any of these parameters. In contrast, a single dose of DMP resulted in a decrease in plasma levels of liver injury markers, a decrease in histological grade of rejection on day 5, and a substantial increase in MST (27.5 days).

CONCLUSIONS

These results demonstrate attenuation of acute rejection following local (allograft) immunosuppression with a single subtherapeutic dose of MP delivered as a liver-targeted prodrug. Dextran prodrugs may be useful for selective delivery of immunosuppressants to the liver following liver transplantation.

Biodegradable microsphere-loaded tacrolimus enhanced the effect on mice islet allograft and reduced the adverse effect on insulin secretion

The adverse effects of tacrolimus have limited the use of this potent immunosuppressive drug in clinical transplantation. To improve the therapeutic effects, we developed a new type of tacrolimus with biodegradable microsphere technology and examined the immunosuppressive effects on allogeneic islet transplantation and the side-effects on insulin secretion in vivo. With a single subcutaneous injection, mouse blood concentrations of tacrolimus (M-FK) carried in biodegradable microspheres remained flat for 2 weeks (only 10 h for conventional tacrolimus). A single subcutaneous administration of 20 mg/kg of M-FK significantly prolonged the survival of islet allografts (MST = 28 days) compared with the control group (MST = 10 days). Series administration of 10 mg/kg of M-FK at 7-day intervals markedly prolonged the survival of islet grafts, and resulted in 60% allograft acceptance. In mice with syngeneic islet transplantations, a single administration of 30 mg/kg of tacrolimus inhibited insulin secretion, whereas a single administration of an equal dosage of M-FK did not. The results suggested that M-FK enhanced the immunosuppressive effects on islet allograft rejection more effectively with reduced side-effects on insulin secretion.

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).

Mechanisms of clinically relevant drug interactions associated with tacrolimus

The clinical management of tacrolimus, a macrolide used as immunosuppressant after transplantation, is complicated by its narrow therapeutic index in combination with inter- and intraindividually variable pharmacokinetics. As a substrate of cytochrome P450 (CYP) 3A enzymes and P-glycoprotein, tacrolimus interacts with several other drugs used in transplantation medicine, which also are known CYP3A and/or P-glycoprotein inhibitors and/or inducers. In clinical studies, CYP3A/P-glycoprotein inhibitors and inducers primarily affect oral bioavailability of tacrolimus rather than its clearance, indicating a key role of intestinal P-glycoprotein and CYP3A. There is an almost complete overlap between the reported clinical drug interactions of tacrolimus and those of cyclosporin. However, in comparison with cyclosporin, only few controlled drug interaction studies have been carried out, but tacrolimus drug interactions have been extensively studied in vitro. These results are inconsistent and are of poor predictive value for clinical drug interactions because of false negative results. P-glycoprotein regulates distribution of tacrolimus through the blood-brain barrier into the brain as well as distribution into lymphocytes. Interaction of other drugs with P-glycoprotein may change tacrolimus tissue distribution and modify its toxicity and immunosuppressive activity. There is evidence that ethnic and gender differences exist for tacrolimus drug interactions. Therapeutic drug monitoring to guide dosage adjustments of tacrolimus is an efficient tool to manage drug interactions. In the near future, progress can be expected from studies evaluating potential pharmacokinetic interactions caused by herbal preparations and food components, the exact biochemical mechanism underlying tacrolimus toxicity, and the potential of inhibition of CYP3A and P-glycoprotein to improve oral bioavailability and to decrease intraindividual variability of tacrolimus pharmacokinetics.

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.

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.

Dextrans for targeted and sustained delivery of therapeutic and imaging agents

Dextrans are glucose polymers which have been used for more than 50 years as plasma volume expanders. Recently, however, dextrans have been investigated for delivery of drugs, proteins/enzymes, and imaging agents. These highly water soluble polymers are available commercially as different molecular weights (M(W)) with a relatively narrow M(W) distribution. Additionally, dextrans contain a large number of hydroxyl groups which can be easily conjugated to drugs and proteins by either direct attachment or through a linker. In terms of pharmacokinetics, the intact polymer is not absorbed to a significant degree after oral administration. Therefore, most of the applications of dextrans as macromolecular carriers are through injectable routes. However, a few studies have reported the potential of dextrans for site (colon)-specific delivery of drugs via the oral route. After the systemic administration, the pharmacokinetics of the conjugates of dextran with therapeutic/imaging agents are significantly affected by the kinetics of the dextran carrier. Animal and human studies have shown that both the distribution and elimination of dextrans are dependent on the M(W) and charge of these polymers. Pharmacodynamically, conjugation with dextrans has resulted in prolongation of the effect, alteration of toxicity profile, and a reduction in the immunogenicity of drugs and/or proteins. A substantial number of studies on dextran conjugates of therapeutic/imaging agents have reported favorable alteration of pharmacokinetics and pharmacodynamics of these agents. However, most of these studies have been carried out in animals, with only a few being extended to humans. Future studies should concentrate on barriers for the clinical use of dextrans as macromolecular carriers for delivery of drugs, proteins, and imaging agents.

PCL-b-PEO micelles as a delivery vehicle for FK506: assessment of a functional recovery of crushed peripheral nerve

The aim of this work was to test in vivo a new block copolymer-based delivery system containing lipophilic drug FK506, known as Tacrolimus. Tacrolimus is currently used in clinics as an immunosupressant agent, and more recently it has been shown that it can exert neurotrophic effects. We prepared, characterized, and assessed polycaprolactone-b-polyethylenoxyde (PCL-b-PEO) micelles containing FK506 in vitro and in vivo. By using well-established animal model of peripheral nerve injury (crushed sciatic nerve), we show that the rate of functional recovery of injured nerve is significantly enhanced in rats treated with micellar FK506. These findings support the notion that PCL-b-PEO is a suitable polymer material for FK506 and suggest its wider applicability as a delivery vehicle for other biologically active, poorly soluble therapeutic agents.