Pharmacokinetics Of Liposomes Research Articles

The pharmacokinetics of PEGylated liposomal doxorubicin are not significantly affected by sex in rats or humans, but may be affected by immune dysfunction

PEGylated liposomal doxorubicin (PLD, Caelyx®, Doxil®) has been suggested to show significant sex-based differences in plasma clearance, as well as high inter-individual variability that may be driven by monocyte counts in cancer patients. This study aimed to establish if these differences are similarly observed in rats, which exhibit similar liposome clearance mechanisms to humans, and to use this model to identify sources of inter-individual and sex-based pharmacokinetic variability. The plasma and lymphatic pharmacokinetics of PLD were evaluated in male and female rats by quantifying doxorubicin as well as the 3H-labelled liposome. In general, the pharmacokinetics of doxorubicin and the 3H-liposome did not differ significantly between male and female rats when corrected for body surface area. Female rats did, however, show significantly higher doxorubicin concentrations in lymph compared to male rats. With the exception of serum testosterone concentrations in males, none of the physiological parameters evaluated correlated with plasma clearance. Further, reanalysis of published human data that formerly reported sex-differences in PLD plasma clearance similarly revealed no significant differences in PLD plasma clearance between males and females with solid tumours, but increased plasma clearance in patients with Kaposi's sarcoma (generally HIV+/immunocompromised). These data suggest that with the exception of lymphatic exposure, there are unlikely to be significant sex effects in the pharmacokinetics of liposomes, but immune function may contribute to inter individual variability.

Role of Liposome Size, Surface Charge, and PEGylation on Rheumatoid Arthritis Targeting Therapy.

Rheumatoid arthritis (RA) is a chronic, systemic, progressive autoimmune disease. The vascular permeability of inflamed joints in RA makes it a natural candidate for passive targeting, similar to the enhanced permeability and retention (EPR)effect in solid tumors. Thus, various therapeutic drugs have been encapsulated in nanocarriers to achieve longer in vivo circulation times and improve RA targeting. Although liposomes are the most widely used nanocarriers for RA treatment, the effects of physical and chemical characteristics of liposomes, such as particle sizes, surface charge, polyethylene glycol (PEG) chain length, and PEG concentration, on their passive RA targeting effect have not been fully elucidated. Here, we systematically investigated the effects of physical and chemical properties of liposomes on circulation time and conducted preliminary studies on their passive targeting mechanisms. A series of liposomes with different particle sizes (70, 100, 200, and 350 nm), surface charges (positive, negative, slight positive, and slight negative), PEG chain lengths (1, 2, and 5 kDa), and concentrations (5, 10, and 20% w/w of total lipid) were prepared by lipid film dispersion and extrusion. The pharmacokinetics of liposomes with different formulas were evaluated with a fluorescence microplate reader. A collagen-induced arthritis (CIA) mouse model was utilized to mimic RA pathological conditions and to evaluate the targeting and efficacy of liposomes with different properties using a near-infrared fluorescence imaging system. Uptake of fluorescent liposomes by various synovial cells was measured by flow cytometry. The results indicated that liposomes with 100 nm diameter, a slight negative charge, and 10% incorporation of 5 kDa PEG had better in vivo circulation time and inflamed joint targeting than did other liposomes. Dexamethasone (Dex) was encapsulated into optimized liposomes as an active ingredient for RA treatment. Pharmacodynamic studies demonstrated that Dex liposomes could significantly improve the antiarthritic efficacy of Dex in a CIA mouse model of RA. This study also found that the retention mechanism of RA was mainly increased because of the uptake of liposomes by fibroblasts and macrophages in inflamed joints. This study provides a persuasive explanation for passive RA targeting by liposomes and advances our ability to treat RA with nanomedicine.

The ability of liposomes, tailored for blood-brain barrier targeting, to reach the brain is dramatically affected by the disease state.

To investigate if and how the ability of liposomes, previously designed for Alzheimer's therapy, to reach the brain changes in aging/pathological conditions with respect to the healthy state. Biodistribution and pharmacokinetics of liposomes in young or aged healthy mice and in an Alzheimer's mouse model were measured by radiochemical techniques. The expression of brain receptors and structural proteins was evaluated by Western blot. At equal blood levels, the amount and integrity of liposomes in the brain were dramatically lower in Alzheimer's or aged mice, with respect to young animals. These differences are likely attributable to molecular alterations in the brain vasculature. Brain alterations in pathology or aging should be considered in the design of drug delivery systems for brain targeting.

Enhanced Distribution and Anti-Tumor Activity of Ergosta-4,6,8(14),22-Tetraen-3-One by Polyethylene Glycol Liposomalization

Ergosta-4,6,8(14),22-tetraen-3-one (ergone) was isolated from P. umbellatus, which has been demonstrated to possess a variety of pharmacological activities in vivo and in vitro. The purpose of this study was to evaluate the potent ergone formulations for cancer chemotherapy, the liposomal formulations were less toxic and provide longer systemic circulation time were selected as candidates of nanocarriers for ergone. The effect of modification polyethylene glycol (PEG) on the pharmacokinetics of liposome showed that the retaining time of ergone in blood circulation was prolonged by modified PEG. Moreover, the results of pharmacokinetic analysis showed that of PEG liposome was about 2.8 times higher than that of free PEG liposome after intravenous injection into normal rats due to the lower distribution into the reticuloendothelial system tissues. Since PEG liposome was able to stably encapsulate ergone in blood, area under plasma concentration-time curve of ergone was also extensively enhanced after intravenous dosing of ergone-PEG liposome into normal rats. In the in vivo studies utilizing solid tumor-bearing mice, it was confirmed that ergone-PEG liposome delivered remarkably larger amount of ergone to tumor tissue and provided more significant anti-tumor activity than free ergone. In conclusion, PEG liposome was an effective delivery formulation to achieve increased ergone release in tumor and therapeutic efficacy.

PET imaging of liposomes labeled with an [18F]-fluorocholesteryl ether probe prepared by automated radiosynthesis

A novel [18F]-labeled cholesteryl ether lipid probe was prepared by synthesis of the corresponding mesylate, which was [18F]-fluorinated by a [18F]KF, Kryptofix-222, K2CO3 procedure. Fluorination was done for 10 minutes at 165°C and took place with conversion between 3 and 17%, depending on conditions. Radiolabelling of the probe and subsequent in situ purification on SEP-Paks were done on a custom-built, fully automatic synthesis robot. Long-circulating liposomes were prepared by hydration (magnetic stirring) of a lipid film containing the radiolabeled probe, followed by fully automated extrusion through 100-nm filters. The [18F]-labeled liposomes were injected into nude, tumor-bearing mice, and positron emission tomography (PET) scans were performed several times over 8 hours to investigate the in vivo biodistribution. Clear tumor accumulation, as well as hepatic and splenic uptake, was observed, corresponding to expected liposomal pharmacokinetics. The tumor accumulation 8 hours postinjection accounted for 2.25 ± 0.23 (mean ± standard error of the mean) percent of injected dose per gram (%ID/g), and the tumor-to-muscle ratio reached 2.20 ± 0.24 after 8 hours, which is satisfactorily high for visualization of pathological lesions. Moreover, the blood concentration was still at a high level (13.9 ± 1.5 %ID/g) at the end of the 8-hour time frame. The present work demonstrates the methodology for automated preparation of radiolabeled liposomes, and shows that [18F]-labeled liposomes could be suitable as a methodology for visualization of tumors and obtaining short-term pharmacokinetics in vivo.

Preparation, characterization, cytotoxicity and pharmacokinetics of liposomes containing lipophilic gemcitabine prodrugs

Gemcitabine is a known anticancer agent rapidly deaminated to the inactive metabolite 2′,2′-difluorodeoxyuridine; it must therefore be administered at very high dose. Many different approaches have been tried to improve the metabolic stability; we synthesized a series of increasingly lipophilic prodrugs of gemcitabine by linking the 4-amino group with valeroyl, heptanoyl, lauroyl and stearoyl linear acyl derivatives. We studied their stability at storage, in plasma and with the lysosomal intracellular enzyme cathepsins. We studied incorporation of these lipophilic prodrugs in liposomes, where their encapsulation efficiency (EE) closely depends on the length of the saturated 4-( N)-acyl chain, the phospholipids chosen and the presence of cholesterol. A maximum EE of 98% was determined for 4-( N)-stearoyl-gemcitabine incorporated in DSPC/DSPG 9:1. This formulation was correlated with the highest stability in vitro and in vivo. Cytotoxicity of gemcitabine prodrugs, free or encapsulated in liposomes, was between two- and sevenfold that of free gemcitabine. Encapsulation of long-chain lipophilic prodrugs of gemcitabine in liposomes protected the drug from degradation in plasma, assuring a long plasma half-time and intracellular release of the free drug.

The modulation of thermal properties of vinblastine by cholesterol in membrane bilayers

It has been shown that the partitioning of vinblastine in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) single and multiple bilayer dispersions induces partial interdigitation of the lipid alkyl chains. Similar behavior has been observed for abietic and ursodeoxycholic acids and may well be generalized for the partitioning of bulky amphoteric molecules, which tend to localize in the vicinity of the polar heads. For the present study, differential scanning calorimetry (DSC) has been employed to investigate the role of lipid molecular characteristics such as the alkyl chain length and the polarity of the head-group, as well as the impact of cholesterol upon vinblastine-induced interdigitation. It is found that vinblastine does not induce interdigitation in lipids with either shorter or longer alkyl chains than DPPC, or having head-groups of different polarity. In addition, it is shown that the presence of cholesterol in the lipid bilayer tends to modulate the phase behavior of the lipid/vinblastine bilayer system. Preliminary studies show that such properties directly affect the encapsulation efficiency and the pharmacokinetics of liposomes.

Preparation, characterization, cytotoxicity and pharmacokinetics of liposomes containing docetaxel

The taxanes, paclitaxel and docetaxel, are anticancer agents used in clinical trials against ovarian carcinoma, breast, lung and head/neck cancer. Paclitaxel, very insoluble in water, is generally formulated using Cremophor EL. Docetaxel, more soluble in water, is formulated using Tween 80 and ethanol. Tween 80, albeit less toxic than Cremophor EL, may be responsible of some toxic effects. To eliminate these vehicles and improve the drug’s antitumor efficacy, taxanes have been incorporated in liposomes. We compared formulation, stability, biodistribution and pharmacokinetics of docetaxel in conventional and PEGylated liposomes. Of the several formulations examined, docetaxel-liposomes composed of ePC/PG/CHOL 9:1:2 and ePC/PG/DSPE-PEG 2000/CHOL 9:1:2:0.7 were the most effective. Both conventional and PEGylated docetaxel-liposomes were stable at 4 °C after 15 days, whereas in the presence of serum at 37 °C they were less stable. The IC 50 values of docetaxel-liposomes, evaluated on HT-29 and Igrov1 cell lines, remained very high. Pharmacokinetics and biodistribution were evaluated in Balb/c mice after i.v. injection of [ 14C]docetaxel, formulated in Tween 80 or in 3H-labeled conventional or PEGylated liposomes. The t 1/2 β, which was low for docetaxel (52.3 min), rose to 260 min for conventional docetaxel-liposomes and to 665 min for PEGylated docetaxel liposomes. Biodistribution studies confirmed the pharmacokinetics.

Preparation, characterization, cytotoxicity and pharmacokinetics of liposomes containing water-soluble prodrugs of paclitaxel

Paclitaxel (Taxol) is a diterpenoid isolated from Taxus brevifolia, used clinically for the treatment of ovarian and breast cancer. Due to its aqueous insolubility it is administered dissolved in ethanol and Cremophor EL (polyethoxylated castor oil), which has serious side effects. In order to eliminate this vehicle, in previous work we entrapped paclitaxel in conventional and in polyethylene glycol coated liposomes. However, in neither formulation did we obtain satisfactory entrapment efficiency. In this study we increased the paclitaxel concentration entrapped in liposomes by incorporating different water-soluble prodrugs, such as the 2′-succinyl, 2′-methylpyridinium acetate and 2′-mPEG ester paclitaxel derivatives, in the lipid vesicles. Liposomes containing 2′-mPEG (5000)–paclitaxel showed the best performance in terms of stability, entrapment efficiency and drug concentration (6.5 mgml−1). The in vitro cytotoxic activity of this liposomal prodrug was similar to that of the parent drug. The pharmacokinetic parameters for the free and for the liposomal prodrugs fitted a bi-exponential plasma disposition. The most important change in pharmacokinetic values of the prodrug vs. the free drug liposomal formulations was t1/2β, plasma lifetime, which was longer in liposomes containing 2′-mPEG (5000)–paclitaxel.

The size of liposomes: a factor which affects their targeting efficiency to tumors and therapeutic activity of liposomal antitumor drugs

The size of liposomes has been shown to be an important factor in the efficient delivery of an antitumor agent to a tumor. In this paper, the effects of the size of liposomes on the pharmacokinetics of liposomes and liposome-encapsulated drugs are discussed with reference to: (1) the circulation amount and residence time of liposomes in the blood, (2) the accumulation of liposomes in the tumor, and (3) in vivo drug release from liposomes. In addition, the effect of size on therapeutic activity (antitumor efficacy and toxicity) of a liposomal anticancer preparation is discussed. Finally we discuss the importance of liposome size in the design of a more effective liposomal antitumor preparation.

Synergistic effect between size and cholesterol content in the enhanced hepatic uptake clearance of liposomes through complement activation in rats.

The effect of liposome size and cholesterol (CH) content on the pharmacokinetics of liposomes was investigated in rats. The pharmacokinetics of liposomes was examined using 5(6)-carboxyfluorescein (CF) as an aqueous phase marker. The extent of complement activation (ECA) was also measured by the release of CF from liposomes in serum. Both the size and the CH content influenced the mean residence time, total body clearance, and the hepatic uptake clearance (CLh) of liposomes. The increase of the size of liposomes increased the CLh at each CH content. There was no CH dependency of CLh in small liposomes (200 nm in diameter), although the CLh increased with the increase in the CH content in large (800 nm) and medium (400 nm) liposomes. A significant interaction effect was observed between liposome size and the CH content on CLh according to the analysis of variance. The good correlation between CLh and ECA indicated the role of complements as opsonins in enhancing the hepatic uptake of liposomes. The interaction effect between the size and CH content on CLh was explained principally by the product of the size and CH content. A synergistic effect was observed between the size and the CH content on CLh. An underlying hypothesis of the synergistic effect was postulated based on the size dependent recognition of liposomes by complement system.

Species difference in the disposition of liposomes among mice, rats, and rabbits: allometric relationship and species dependent hepatic uptake mechanism.

The species difference in the pharmacokinetics of liposomes was investigated in mice, rats and rabbits. Liposomes were intravenously injected at doses of 1, 10 and 100 (nmol/g body weight), and the time courses of liposomes in blood, liver and spleen were measured. Pharmacokinetic parameters were regressed as a function of body weight (BW) and dose of liposomes (D). The uptake mechanism of liposomes was also examined with the isolated perfused liver between rats and mice. Mean residence time increased with the increase of BW and D of liposomes. This increase of mean residence time resulted from the decreased total body clearance, which was principally explained by the species difference in the hepatic uptake clearance (CLh) of liposomes. The parameter CLh was regressed well by a multiple regression as a function of BW and D. In this analysis, an exponent for BW was around 0.5, which clearly indicates that smaller animals have higher uptake clearance per unit BW. Immunohistochemical analysis revealed that there was no significant difference in the density of Kupffer cells among these species. This suggest that the species difference in CLh resulted not from the density of Kupffer cells but from the uptake ability of Kupffer cells among species. In the isolated perfused liver, the hepatic uptake of liposomes was mainly explained by opsonin dependent uptake in rats, while opsonin independent uptake in mice. These quantitative and qualitative information on the species difference of liposome disposition will provide an useful information for constructing a drug delivery system using liposomes.

Liposome preparations: A step forward in topical drug therapy for skin disease?: A review

The production of liposomes, which was described in 1961, soon was claimed to be a useful technology for drug encapsulation. The first preparation (containing a topical antifungal agent), however, was registered only recently. Additional preparations, including some for topical therapy of skin disease, are under clinical investigation. Moreover, a variety of cosmetic products that contain liposomes is available today. In this article we review the literature on liposomes as it pertains to dermatology, including the basic principles of liposome structures and preparations, pharmacokinetics of liposomes and liposome-encapsulated drugs, and the influence on drug activity. Moreover, future applications of liposome preparations are discussed.

Effects of dose and vesicle size on the pharmacokinetics of liposomes.

The blood concentration and urinary excretion after intravenous injection of liposomes containing 3H-inulin at three dose levels were examined in rats. A pharmacokinetic model for the dose dependency is postulated based on the results. The effects of vesicle size were also examined and the biological disposition was simulated. Factors affecting the liposomal disposition are discussed.Dose dependency of the disposition was observed at three dose levels (1.8, 14.9 and 70.3μmol total lipids/rat) of liposomes having a mean diameter of 0.22μm. The results suggest the existence of saturable processes in the uptake of liposomes by the reticuloendothelial system (RES) and leakage of inulin from liposomes, and a first-order rate process in the release of inulin from the cell after degradation of liposomes taken up by the RES. However, simulation of the data obtained after high-dose administration was unsuccessful with this model, the blood clearance of liposomes being faster than calculated. It is suggested that first-order processes may operate in parallel with the saturable processes of uptake and leakage.The effects of the size of liposomes (mean diameter : 0.15, 0.22 and 0.43μm) on the disposition were also examined. The patterns of the blood levels and urinary excretion of small liposomes and large liposomes were very similar to those of the high-dose and low-dose experiments, respectively, in spite of the very similar dose levels of total lipids administered.Simulation suggested that the dose expressed in terms of the number of vesicles was suitable for evaluation of the liposomal disposition. The results indicate that the size and number of liposomes are important variables affecting the disposition of liposomes and they should be controlled strictly in liposomes for in vivo use.