Physicochemical, pharmacokinetic and pharmacodynamic evaluation of liposomal tacrolimus (FK 506) in rats

Protective effects of selenium in tacrolimus-induced lung toxicity: potential role of heme oxygenase 1

The present study aimed to evaluate the protective effects of selenium (Sel) administration against tacrolimus (Tac) - induced lung toxicity and to assess the relation between heme oxygenase 1 (HO-1) and these effects. The study was conducted on 36 Wistar male albino rats equally divided into four groups: (i) normal control; (ii) Sel (0.1 mg/kg per day p.o. for four weeks); (iii) TAC 3 mg/mL as single oral dose on 27th day; and (iv) Tac + Sel. Lung tissues, lung homogenate, and bronchoalveolar lavage of the sacrificed animals were investigated biochemically and histopathologically, by immunohistochemistry or by PCR. The Tac group showed significantly lower expression of HO-1. Administration of Sel was associated with increased HO-1 expression. Oxidative (malondialdehyde, reduced glutathione, superoxide dismutase, myeloperoxidase, and glutathione peroxidase activity) and nitrosative stress (nitric oxide) markers and markers of inflammation (interleukin 1β (IL-1β), IL-6, and IL-10) showed changes corresponding to HO-1 levels in rat groups. Tac group showed the highest expression of caspase-3. Sel exerted a protective role against Tac-induced lung toxicity.

Study on Enhanced Dissolution of Azilsartan-Loaded Solid Dispersion, Prepared by Combining Wet Milling and Spray-Drying Technologies

The purpose of this study was to develop a combination method of wet milling and spray-drying technologies to prepare the solid dispersion and improve the dissolution rate of poorly water-soluble drug candidates. Azilsartan (AZL) was selected as the model drug for its poor water solubility. In the study, AZL-loaded solid dispersion was prepared with polyethylene glycol 6000 (PEG6000) and hydroxypropyl cellulose with super low viscosity (HPC-SL) as stabilizers by using combination of wet grinding and spray-drying methods. The high AZL loading solid dispersion was then characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR). Besides, dissolution test was carried out by the paddle method and stability investigation was also conducted. As a result, the dissolution rate of the solid dispersion tablets was found to be greater than conventional tablets, but in close agreement with market tablets. Furthermore, the formulation was shown to be stable at 40 ± 2°C and 75 ± 5% for at least 6 months, owing to its decreased particle size, morphology, and its crystal form. It was concluded that the combination of wet milling and spray-drying approaches to prepare solid dispersion would be a prospective method to improve the dissolution rate of poorly water-soluble drugs.

[Effect of tacrolimus on the pharmacokinetics and glucuronidation of SN-38, an active metabolite of irinotecan]

The present study has investigated the effect of tacrolimus on the pharmacokinetics of an active metabolite of irinotecan (CPT-11), 7-ethyl-10-hydroxy-camptothecin (SN-38) and SN-38 glucuronide (SN-38G) in rats. The effect of tacrolimus on SN-38 glucuronidation was also investigated in human and rat liver microsomes. When tacrolimus (0.5 mg/kg) was intravenously injected in rats 15 min before intravenous injection of CPT-11 (5 mg/kg), tacrolimus decreased the plasma concentration of SN-38G. Tacrolimus significantly decreased the area under plasma concentration-time curve (AUC) of SN-38G without change in the mean residence time. On the contrary, significant changes in the pharmacokinetic parameters of SN-38 were not observed. SN-38 glucuronidation in human and rat liver microsomes was inhibited dose-dependently by the presence of tacrolimus and the 50% inhibition concentration (IC50) values of tacrolimus in rat and human liver microsomes were 10.33 μM and 3.58 μM, respectively. When the inhibition type was determined by Lineweaver-Burk and Dixon plots, the inhibition was noncompetitive and the calculated inhibition constant (Ki) values for rat and human liver microsomes were 12.57 μM and 3.88 μM, respectively. These findings suggest that tacrolimus inhibits UGT1A1-mediated SN-38 glucuronidation. Considering the IC50 and Ki values for tacrolimus, it is likely that tacrolimus does not alter the pharmacokinetics of SN-38 and SN-38G at the clinically used dosages, suggesting the possibility that tacrolimus can use safely for cancer patients with irinotecan chemotherapy.

Preparation, characterization and pharmacokinetic studies of tacrolimus-dimethyl-β-cyclodextrin inclusion complex-loaded albumin nanoparticles

The purpose of the study is to develop a new formulation for clinically used anti-cancer agent tacrolimus (FK506) to minimize the severe side effects. Toward this end, a new formulation method has been developed by complexation of FK506 with an hydrophilic cyclodextrin derivative, heptakis (2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) using ultrasonic means. The resulting complex displays dramatically enhanced solubility of FK506. Then bovine serum albumin (BSA) nanoparticles were prepared directly from the preformed FK506/DM-β-CD inclusion complex by the desolvation-chemical crosslinking method, with the size of 148.4-262.9 nm. Stable colloidal dispersions of the nanoparticles were formed with zeta potentials of the range of -24.9 to -38.4 mV. The entrapment efficiency of FK506 was increased as high as 1.57-fold. Moreover, notably FK506 was released from the nanoparticles in a sustained manner. As demonstrated, pharmacokinetic studies reveal that, as compared with FK506-loaded BSA nanoparticles, the FK506/DM-β-CD inclusion complex-loaded BSA nanoparticles have significant increase at T(max), t(1/2), MRT and decrease at C(max). In summary, these results suggest that the drug/DM-β-CD inclusion complex-loaded BSA nanoparticles display significantly improved delivery efficiency for poorly soluble FK506 or its derivatives.

Pharmacokinetics and tissue distribution profile of icariin propylene glycol-liposome intraperitoneal injection in mice

Objectives

The pharmacokinetics and tissue distribution of icariin propylene glycol-liposome suspension (ICA-PG-liposomes) have been investigated.

Methods

ICA-PG-liposomes or ICA-PG-solution were prepared and intraperitoneally injected to mice. Morphology and size distribution of ICA-PG-liposomes were observed by transmission electron microscopy (TEM) and laser particle sizer. Plasma and tissues were collected at different times after intraperitoneal injection and icariin concentrations were determined by HPLC.

Key findings

From TEM, ICA-PG-liposomes showed spherical vesicles with a mean particle size of 182.4 nm. The encapsulation efficiency of ICA-PG-liposomes reached 92.6%. Pharmacokinetics of ICA-PG-liposomes displayed the three open compartments model. ICA-PG-liposomes enhanced icariin absorption from the abdominal cavity, prolonged mean retention time (MRT(0-t)), increased area under curve (AUC(0-t)) and maximum concentration in plasma. Compared with ICA-PG-solution, ICA-PG-liposomes resulted in larger amounts of icariin being distributed into spleen (60.38% total icariin), liver (16.68%), lung (6.21%), kidney (4.64%), heart (1.43%) and brain (1.83%). AUC(0-t) values in most tissues (except lung) of mice administered ICA-PG-liposomes were higher than those administered ICA-PG-solution, while Clearance in most tissues (except brain and lung) decreased. The MRT(0-t) values of ICA-PG-liposomes in all tissues and half lives of most tissues (except brain) were prolonged. From Targeted efficiency and relative uptake data, the spleen was the target tissue of the ICA-PG-liposomes.

Conclusions

ICA-PG-liposomes changed the pharmacokinetic behaviour and enhanced icariin distribution in tissues. With nanometer size, high encapsulation efficiency and improved pharmacokinetics, ICA-PG-liposomes might be developed as promising carriers for icariin injection.

Polyoxyl 60 hydrogenated castor oil free nanosomal formulation of immunosuppressant Tacrolimus: pharmacokinetics, safety, and tolerability in rodents and humans

OBJECTIVE

Develop Nanosomal formulation of Tacrolimus to provide safer alternative treatment for organ transplantation patients. Investigate safety, tolerability and pharmacokinetics of Nanosomal Tacrolimus formulation versus marketed Tacrolimus containing polyoxyl 60 hydrogenated castor oil (HCO-60) that causes side effects.

METHODS

Nanosomal Tacrolimus was prepared in an aqueous system. The particle size was measured by Particle Sizing Systems and structure morphology was determined by freeze-fracture electron microscopy. Investigational safety studies were conducted in mice and rats. Safety and pharmacokinetics of Nanosomal Tacrolimus were also evaluated in healthy human subjects.

RESULTS

The morphology of Nanosomal Tacrolimus showed a homogeneous population of nanosized particles with mean particle size of less than 100 nm. A 14 day consecutive administration of Nanosomal Tacrolimus up to 5 and 10mg/kg dose in rats and mice respectively, resulted in no mortality. Nanosomal Tacrolimus in human studies showed that it is safe and the pharmacokinetics profile is similar to the marketed HCO-60 based Tacrolimus. No significant change in peripheral blood lymphocyte percentage was noted in either mice or healthy human male subjects.

CONCLUSIONS

Nanosomal Tacrolimus is well characterized product which provides a new treatment option. It contains no alcohol or surfactants like HCO-60. Thus, Nanosomal Tacrolimus presents a new and improved therapeutic approach for organ transplant patients compared to the marketed HCO-60 based Tacrolimus product.

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.

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

A novel macromolecular prodrug of Tacrolimus (FK506), FK506-dextran conjugate, was developed and its physico-chemical, biological and pharmacokinetic characteristics were studied. The conjugate was estimated to contain 0.45% of FK506 and the coupling molar ratio was approximately 1:1 (dextran-FK-506). Adsorption experiments using ion exchangers indicated that FK506-dextran conjugate acted as a weakly negatively charged macromolecule. Low molecular weight radioactive compound(s), which was eluted in the same fractions as [(3)H]FK506, was released from [(3)H]FK506-dextran conjugate by chemical hydrolysis with a half-life of 150 h in phosphate buffer. In vitro immunosuppressive activity of the conjugate, as assessed by the rat lymphocyte stimulation test, was almost comparable to that of free FK506, suggesting that biologically active FK506 could be liberated from the conjugate. In vitro biodistribution studies demonstrated that conjugation with the dextran derivative dramatically changed the pharmacokinetic properties of FK506 after intravenous injection in rats. AUC of the FK506-dextran conjugate was almost 2000 times higher than that of free FK506 and organ uptake clearances of the conjugate were significantly smaller than those of the free drug. Thus, the present study has demonstrated that the FK506-dextran conjugate behaves as a prodrug of FK506 with an extended blood circulating time and can be expected to have an improved therapeutic potency.

Study of azathioprine encapsulation into liposomes

The factors influencing the encapsulation of azathioprine (AZA) into liposomes were investigated to find out the conditions for its optimal entrapment. Similar studies for comparison were also carried out on 6-mercaptopurine (6-MP), of which AZA is a prodrug. AZA and also 6-MP show higher encapsulation efficiencies in MLVs as compared to LUVs. Variation in phospholipid composition does not seem to affect the loading capacity of either of the two drugs. The encapsulation efficiency of both the drugs improves upon addition of cholesterol in the bilayer, but the effect is seen only up to 30% cholesterol. Thereafter the effect becomes constant. AZA shows better incorporation in the positively charged liposomes as compared to those with neutral or negative charge. The entrapment of 6-MP is, however, found to be independent of the charge on the liposomes. Entrapment efficiency for both the drugs markedly depends on the pH of the hydration medium, yielding better entrapment efficiencies at high pH values. The rise in solute concentration initially causes increase in the entrapment of the two drugs which is followed by a decreasing phase.

Biodistribution of cyclosporin encapsulated in liposomes modified with bioadhesive polymer

The purpose of this investigation was to study the possibility of renewing the immunosuppressive activity of cyclosporin by formulating the compound in liposomes modified with bioadhesive polymers. The liposomes prepared were evaluated both pharmacokinetically and pharmacodynamically. Tissue distribution and plasma pharmacokinetics of cyclosporin and model dye, sudan black, which is as hydrophobic as cyclosporin, were studied in rats after intravenous infusion (10 mg kg-1). The immunosuppressive efficacy of liposomal cyclosporin preparations was studied in the allogenic rat-heart-transplantation model, where cyclosporin therapy (10 mg kg-1) continued for one week. The entrapment of sudan black in liposomes modified with bioadhesive polymers resulted in higher sudan black delivery to the spleen and the liver than with standard sudan-black-loaded liposomes. Among the modified liposomes, those modified with carbopol 941 showed the most remarkable enhancing effect on the delivery of sudan black to these organs and total plasma clearance of sudan black decreased to 38.6 +/- 7.8 mL h-1 kg-1 (standard liposomes, 58.9 +/- 6.4 mL h-1 kg-1). Delivery of cyclosporin to the spleen and the liver was increased approximately twofold by modifying the liposomes with carbopol 941. In the preliminary study on the allogenic rat-heart-transplantation model, the mean survival days of the graft were 18.8 +/- 2.9 days for the group receiving cyclosporin liposomes modified with carbopol 941, 14.2 +/- 4.4 days for the group receiving standard cyclosporin liposomes and 7.6 +/- 0.5 days for the group receiving cyclosporin solution. The encapsulation of cyclosporin in liposomes modified with bioadhesive polymer enhanced the residence time of cyclosporin in the systemic circulation, resulting in approximately twofold greater delivery of cyclosporin to the spleen and liver. However, in the allogenic rat-heart-transplantation model no significant difference was detected between the immunosuppressive efficacy of cyclosporin encapsulated in bioadhesive polymer-modified liposomes and that encapsulated in standard liposomes.

The pharmacokinetics of water-in-oil-in-water-type multiple emulsion of a new tacrolimus formulation

We developed a water-in-oil-in-water-type (W/O/W)-type multiple emulsion of a new tacrolimus formulation. A potential approach to avoid the complications of systemic immunosuppression and simultaneously enhance immunosuppressive efficacy is to deliver immunosuppressive agents locally to the site of the target organs. The W/O/W emulsion is dispersed oil drops containing smaller water droplets that allow the delivery of drugs preferentially to the reticuloendothelial systems (RES). Since the liver and the spleen are primary components of the RES, and the brain and the kidney have a poor RES, we hypothesized that a W/O/W emulsion of tacrolimus would possess the pharmacokinetic benefits of local immunosuppression. We evaluated this hypothesis in a rat model. The tacrolimus levels of whole blood, the liver, spleen, brain, and kidney in rats given intravenous emulsions of tacrolimus (W/O/W group) were compared with a group administered tacrolimus alone (T group). There were no significant differences between the pharmacokinetic parameters of W/O/W group and T group based on whole blood data. However, the W/O/W group had significantly decreased tacrolimus levels in the brain and kidney, and significantly increased levels in the liver and spleen compared with the T group. These data suggest that the W/O/W emulsion is applicable as an intravenous drug carrier for local immunosuppression.

Clinical pharmacokinetics of tacrolimus

Tacrolimus, a novel macrocyclic lactone with potent immunosuppressive properties, is currently available as an intravenous formulation and as a capsule for oral use, although other formulations are under investigation. Tacrolimus concentrations in biological fluids have been measured using a number of methods, which are reviewed and compared in the present article. The development of a simple, specific and sensitive assay method for measuring concentrations of tacrolimus is limited by the low absorptivity of the drug, low plasma and blood concentrations, and the presence of metabolites and other drugs which may interfere with the determination of tacrolimus concentrations. Currently, most of the pharmacokinetic data available for tacrolimus are based on an enzyme-linked immunosorbent assay method, which does not distinguish tacrolimus from its metabolites. The rate of absorption of tacrolimus is variable with peak blood or plasma concentrations being reached in 0.5 to 6 hours; approximately 25% of the oral dose is bioavailable. Tacrolimus is extensively bound to red blood cells, with a mean blood to plasma ratio of about 15; albumin and alpha 1-acid glycoprotein appear to primarily bind tacrolimus in plasma. Tacrolimus is completely metabolised prior to elimination. The mean disposition half-life is 12 hours and the total body clearance based on blood concentration is approximately 0.06 L/h/kg. The elimination of tacrolimus is decreased in the presence of liver impairment and in the presence of several drugs. Various factors that contribute to the large inter- and interindividual variability in the pharmacokinetics of tacrolimus are reviewed here. Because of this variability, the narrow therapeutic index of tacrolimus, and the potential for several drug interactions, monitoring of tacrolimus blood concentrations is useful for optimisation of therapy and dosage regimen design.