Lipo-prostaglandin preparations

Therapeutic effect of epidurally administered lipo-prostaglandin e1 agonist in a rat spinal stenosis model

BACKGROUND

A lipo-prostaglandin E1 agonist is effective for the treatment of neurological symptoms of spinal stenosis when administered by an oral or intravenous route. we would like to reveal the therapeutic effect of an epidural injection of lipo-prostaglandin E1 on hyperalgesia in foraminal stenosis.

METHODS

A total of 40 male Sprague-Dawley rats were included. A small stainless steel rod was inserted into the L5/L6 intervertebral foramen to produce intervertebral foraminal stenosis and chronic compression of the dorsal root ganglia (DRG). The rats were divided into three groups: epidural PGE1 (EP) (n = 15), saline (n = 15), and control (n = 10). In the EP group, 0.15 µg.kg-1 of a lipo-PGE1 agonist was injected daily via an epidural catheter for 10 days from postoperative day 3. In the saline group, saline was injected. Behavioral tests for mechanical hyperalgesia were performed for 3 weeks. Then, the target DRG was analyzed for the degree of chromatolysis, chronic inflammation, and fibrosis in light microscopic images.

RESULTS

From the fifth day after lipo-PGE1 agonist injection, the EP group showed significant recovery from mechanical hyperalgesia, which was maintained for 3 weeks (P < 0.05). Microscopic analysis showed much less chromatolysis in the EP group than in the saline or control groups.

CONCLUSIONS

An epidurally administered lipo-PGE1 agonist relieved neuropathic pain, such as mechanical hyperalgesia, in a rat foraminal stenosis model, with decreasing chromatolysis in target DRG. We suggest that epidurally administered lipo-PGE1 may be a useful therapeutic candidate for patients with spinal stenosis.

Prostaglandin E1 -containing nanoparticles improve walking activity in an experimental rat model of intermittent claudication

OBJECTIVES

Due to the low stability of lipid emulsions, a lipid emulsion of prostaglandin E1 (Lipo-PGE1 ) necessitates daily intravenous drip infusions. To overcome this issue, we developed nanoparticles containing PGE1 (Nano-PGE1 ). Nano-PGE1 showed a good sustained-release profile of PGE1 from the nanoparticles in vitro, which may permit a longer-lasting therapeutic effect to be achieved. We here examined the pharmacological activity of Nano-PGE1 in a rat experimental model of intermittent claudication induced by femoral artery ligation.

METHODS

The walking activity of the rat was tested on a rodent treadmill. Tissue levels of PGE1 were determined by enzyme immunoassay, and skeletal muscle angiogenesis (capillary growth) was monitored by immunohistochemical analysis.

KEY FINDINGS

PGE1 could be detected in the lesion site one day after the intravenous administration of Nano-PGE1 but not of Lipo-PGE1 . An increased accumulation of Nano-PGE1 in the lesion site compared with control (unlesioned) site was also observed. The ligation procedure reduced the walking activity, which in turn was improved by a single administration of Nano-PGE1 but not of Lipo-PGE1 . The single administration of Nano-PGE1 also stimulated angiogenesis in the skeletal muscle around the ligated artery.

CONCLUSIONS

The findings of this study suggest that Nano-PGE1 improves the walking activity of femoral artery-ligated rats through the accumulation and sustained release of PGE1 .

Accelerated blood clearance phenomenon upon repeated injection of PEG-modified PLA-nanoparticles

PURPOSE

We recently developed prostaglandin E(1) (PGE(1))-encapsulated nanoparticles, prepared with a poly(lactide) homopolymer (PLA, Mw = 17,500) and monomethoxy poly(ethyleneglycol)-PLA block copolymer (PEG-PLA) (NP-L20). In this study, we tested whether the accelerated blood clearance (ABC) phenomenon is observed with NP-L20 and other PEG-modified PLA-nanoparticles in rats.

METHODS

The plasma levels of PGE(1) and anti-PEG IgM antibody were determined by EIA and ELISA, respectively.

RESULTS

Second injections of NP-L20 were cleared much more rapidly from the circulation than first injections, showing that the ABC phenomenon was induced. This ABC phenomenon, and the accompanying induction of anti-PEG IgM antibody production, was optimal at a time interval of 7 days between the first and second injections. Compared to NP-L20, NP-L33s that were prepared with PLA (Mw = 28,100) and have a smaller particle size induced production of anti-PEG IgM antibody to a lesser extent. NP-L20 but not NP-L33s gave rise to the ABC phenomenon with a time interval of 14 days. NP-L33s showed a better sustained-release profile of PGE(1) than NP-L20.

CONCLUSIONS

This study revealed that the ABC phenomenon is induced by PEG-modified PLA-nanoparticles. We consider that NP-L33s may be useful clinically for the sustained-release and targeted delivery of PGE(1).

DDS for anti-aging and regenerative medicine (review)

In this paper we summarized, first the present status and history of the development of research in anti-aging and regenerative medicine in Japan, and secondly some of our research using DDS in the field of both medicine. The regenerative medicine has been developed in Japan by using the fund from the Government, particularly as the Millennium Project. While anti-aging medicine developed following the social interest on it in Japan and it was influenced by American Society (A4M). Next, we summarized our research on DDS for anti-aging and regenerative medicine. In most cases we used oily or solid nanoparticles as carriers of drug. Those particles have a property of both of targeting and slow release in the DDS technology. The two properties are important for anti-aging and regenerative medicine, since drugs have to be administered safely and for long time. We applied prostaglandin E1, granulocyte-colony stimulate factor (G-CSF), and retinoid into the systems.

Drug-incorporating calcium carbonate nanoparticles for a new delivery system

We devised a simple method for incorporating drugs into solid calcium carbonate nanoparticles (nano-CaCO3). The size of nano-CaCO3 was controlled by mixing speed. Washing the nanoparticles released little incorporated drug but much drug that was adsorbed on the surface. In an in vitro releasing test, granulocyte colony-stimulating factor incorporated in nano-CaCO3 was chemically stable and released very slowly. Subcutaneous injection of nano-CaCO3 incorporating betamethasone phosphate (BP) resulted in a smaller initial increase in plasma concentration and a subsequent sustained release in compared with betamethasone phosphate solution. Nano-CaCO3 may be useful to deliver hydrophilic drugs and bioactive proteins.

Endothelial cell protection against ischemia/reperfusion injury by lecithinized superoxide dismutase

BACKGROUND

Organs used for transplantation may experience long periods of cold ischemic preservation and consequently oxygen free radical-mediated damage following reperfusion. Lecithinized superoxide dismutase (lec-SOD) is a novel free radical scavenger that has been shown to bind with high affinity to cell membranes. The aim of this study was to determine whether lec-SOD bound to endothelial cells under organ preservation conditions to mediate direct antioxidant activity at the endothelial cell surface and thus offer protection against the harmful effects of ischemia/reperfusion injury.

METHODS

An in vitro study was performed on large vessel endothelial cells (HUVEC) and a human microvascular endothelial cell line HMEC-1, to investigate the potential therapeutic benefits of incorporating lec-SOD into organ preservation solution. A cold hypoxia/reoxygenation system was developed to examine lec-SOD binding affinity to endothelial cells, protection against hypoxia/reoxygenation-induced cell death, and neutrophil adhesion.

RESULTS

Lec-SOD bound to endothelial cells with higher affinity than unmodified recombinant human superoxide dismutase (rhSOD) and significantly protected both HUVEC and HMEC-1 from cell death following 27 hours of cold hypoxia (P < 0.01). Furthermore, neutrophil adhesion to the endothelium stimulated by hypoxia and reoxygenation was significantly inhibited by treatment with lec-SOD but not by lecithin or rhSOD (P < 0.01). Analysis by flow cytometry demonstrated that E-selectin and ICAM-1 were up-regulated by hypoxia/reoxygenation that was inhibited in part by lec-SOD.

CONCLUSIONS

The results from this study suggest that incorporation of lec-SOD into organ preservation solutions provides effective protection to endothelial cells against cold ischemia and reperfusion injury following transplantation.

Marked hypotensive and blood flow-increasing effects of a new lipo-PGE(1) (lipo-AS013) due to vascular wall targeting

Lipo-AS013 is being developed as an improved formulation of lipo-PGE(1), which is widely used in clinical practice in Japan and some Asian countries. We have previously reported that lipo-AS013, which is a lipid microsphere (LM) preparation of a chemically stable and lipophilic PGE(1) prodrug (AS013, Fig. 1), slowly releases small amounts of the active ingredient (AS013) in human plasma. In the present study, to estimate the vascular wall targeting ability and efficacy of lipo-AS013, we determined the hypotensive and blood flow-increasing effects of lipo-AS013, lipo-PGE(1), PGE(1)CD, and AS013. Lipo-AS013 was found to have longer-lasting hypotensive and blood flow-increasing effects than the other agents. The two LM preparations, lipo-PGE(1) and lipo-AS013, had a markedly stronger effect than PGE(1)CD and AS013 alone, demonstrating the benefit of drug delivery using LM. In spontaneously hypertensive rats (SHR), lipo-AS013 also had a significant hypotensive effect. To confirm vascular wall targeting by lipo-AS013, the localization of PGE(1) in the aorta and neovascular capillaries of rat was investigated by immunostaining. The results indicated that lipo-AS013 was more efficient at delivering the active ingredient (AS013) to the vessel wall. In conclusion, lipo-AS013 could supersede lipo-PGE(1) and PGE(1)CD in clinical use.

In vitro and in vivo activities of NS-718, a new lipid nanosphere incorporating amphotericin B, against Aspergillus fumigatus

We evaluated the in vitro and in vivo potencies of a new lipid nanosphere that incorporates amphotericin B (AmB), NS-718, against Aspergillus fumigatus. The in vitro activity of NS-718 (the MIC at which 90% of strains are inhibited [MIC90], 0.25 microgram/ml) against 18 isolates of A. fumigatus was similar to that of deoxycholate AmB (D-AmB; Fungizone; MIC90, 0.25 microgram/ml), but NS-718 was more potent than liposomal AmB (L-AmB; AmBi-some; MIC90, 1.0 microgram/ml). The in vivo efficacy of NS-718 in a rat model of invasive pulmonary aspergillosis was compared with those of D-AmB and L-AmB. A low dose (1 mg/kg of body weight) of L-AmB was ineffective (survival rate, 0%), although equivalent doses of D-AmB and NS-718 were more effective (survival rate, 17%). However, a higher dose of NS-718 (3 mg/kg) was more effective (survival rate, 100%) than equivalent doses of D-AmB and L-AmB (survival rate, 0%). To explain these differences, pharmacokinetic studies showed higher concentrations of AmB in the plasma of rats treated with NS-718 than in the plasma of those treated with D-AmB. Our results suggest that NS-718, a new preparation of AmB, is a promising antifungal agent with activity against pulmonary aspergillosis.

Effect of composition on biological fate of oil particles after intravenous injection of O/W lipid emulsions

Plasma concentrations of oil particles after intravenous injection of oil-in-water (O/W) lipid emulsions were monitored based on the plasma concentration of phospholipids (PL) and triglycerides (TG), and the light scattering intensity (LSI) of plasma. Previously, we found that their time profiles after injection of the standard O/W lipid emulsion composed of soybean oil (SO) and egg yolk phosphatides (EYP) were similar and suggested that the oil particles with diameter of about 200 nm were entrapped by reticuloendothelial system (RES). Herein, in order to develop a delivery system to avoid the RES uptake by using the lipid emulsions, biological fate of lipid emulsions with oil particles of various sizes or those emulsified by surfactants with polyoxyethylene segments were subjected to the investigations. Lipid emulsions with oil particles of various sizes (about 150-550 nm) were prepared by altering EYP content. The oil particles were stable in plasma in vitro, but oil particle size decreased time-dependently after intravenous injection. Plasma clearance of oil particles depended on their initial size and was decreased by pretreatment with dextran sulfate 500 (DS500), a known RES suppressor. These results suggested that oil particles are still entrapped by RES, even for small-sized oil particles (about 150 nm). Lipid emulsion with small-sized oil particles was also prepared using medium chain triglycerides. The oil particles were stable in vitro, but the time profiles of plasma concentrations of PL and TG, and LSI of plasma were different, and oil particle size decreased time-dependently after intravenous injection. Plasma clearance of the oil particles also depended on their initial size and was decreased by DS500, suggesting that in vivo instability could be due to RES-mediated processes. Artificial surfactants with polyoxyethylene segments, HCO-60 (HCO60) and polysorbate 80 (PS80), were used for RES avoidance. HCO60 resulted in drastic reduction of the plasma clearance of the oil particles for both lipid emulsions composed of soybean oil and medium chain triglycerides. The time-dependent decrease of oil particle size after intravenous injection was marginal. In contrast, PS80 could not prolong the circulation time of the oil particles, and their size decreased time-dependently after intravenous injection.

O/W lipid emulsions for parenteral drug delivery. IV. Changes in the pharmacokinetics and pharmacodynamics of a highly lipophilic drug, menatetrenone

The pharmacokinetics and pharmacodynamics of antihemorrhagic vitamin, menatetrenone after intravenous injection as the lipid emulsion, were compared to those as the micellar solutions. Menatetrenone was selectively delivered to the liver, lungs and spleen and retained in them. Hepatic and splenetic concentration at 6 h (C6h) increased 21.6- and 27.1-fold, respectively, and the area under the tissue concentration-time curve up to 6 h (AUC(0-6h)) were 2.3- and 11.4-fold, respectively, when compared with its micellar solution. Antihemorrhagic effect of menatetrenone was assessed using warfarin-induced hypoprothrombinemic rats. The lipid emulsion of menatetrenone decreased the prothrombin time at 6h after intravenous injection more effectively than micellar solution. The dose response curves indicated that the efficacy of the lipid emulsion was 2.4-2.9 times that of a micellar solution, and this was correlated with AUC(0-6h) rather than C6h. The plasma level of clotting factor VII and the hepatic level of descarboxyprothrombin were also recovered more effectively, while no significant differences were noted between the two formulations for the plasma level of factor II or descarboxyprothrombin at the dose levels examined. Although selective delivery of menatetrenone in the liver by the lipid emulsion was due to phagocytosis by non-parenchymal cells, menatetrenone in the whole liver appeared to contribute to recovery from hypoprothrombinemia.

O/W lipid emulsions for parenteral drug delivery. III. Lipophilicity necessary for incorporation in oil particles even after intravenous injection

The potential usefulness of oil-in-water (O/W) lipid emulsions as injectable drug delivery systems was examined. Plasma concentrations of oil particles after intravenous injection of a standard lipid emulsion composed of soybean oil and egg yolk phosphatides were monitored based on the plasma concentrations of phospholipids and triglycerides, and the light scattering intensity of the plasma. Their time profiles were similar to each other, and the oil particle size decreased time-dependently. Pretreatment with dextran sulfate, a known reticuloendothelial system (RES) suppressor, resulted in marked reduction of the plasma clearance of the oil particles and of the time-dependent alteration of oil particle size, suggesting that oil particles were trapped by RES. The lipophilicity of the drug needed for its incorporation in the oil particles even after intravenous injection was found to be clog P > 8, where clog P is the calculated logarithm of the partition coefficient between n-octanol and water. In the case of sudan II (clog P = 5.4), the release from the oil particles was very quick after intravenous injection, resulting in slight alteration in biodistribution when compared with its micellar solution. In contrast, menatetrenone (clog P = 9.5) was selectively delivered to the liver, lungs and spleen, being consistent with the oil particles taken up by RES.

Randomized, double-blind, placebo-controlled study evaluating the efficacy and safety of AS-013, a prostaglandin E1 prodrug, in patients with intermittent claudication

BACKGROUND

Intermittent claudication due to peripheral arterial occlusive disease (PAOD) is a common cause of pain and disability in the middle-aged. Clinical trials of the potent vasodilator prostaglandin E1 have been disappointing. This is the first report of a controlled clinical trial of AS-0:3, a novel prodrug of prostaglandin E1 incorporated into lipid microspheres that has been developed to improve delivery of the active compound to blood vessel walls.

METHODS AND RESULTS

Eighty patients with stenosis or occlusion, symptoms of intermittent claudication, and maximum walking distance of > or = 30 and < or = 300 m on a standard treadmill test were randomized to placebo or one of three dosage regimens of AS-013. Drug was administered by intravenous injection 5 d/wk for 4 weeks. Treadmill tests and other assessments were completed at weeks 0, 4, and 8. A statistically significant increase in maximum walking distance was observed at 4 weeks (for placebo: median, 4.5 m; interquartile range [IQR], 20; for active treatment: median, 28.0 m; IQR, 81; P < .01, Mann-Whitney test). A similar response was seen at 8 weeks (for placebo; median, -11.2 m; IQR, 35; for active treatment: median, 35 m; IQR, 68; P < .01, Mann-Whitney test). Dose-related improvements in pain-free walking distance and quality of life were observed. No serious safety issues were noted.

CONCLUSIONS

These promising clinical data indicate that AS-013, a new prodrug of prostaglandin E1, could provide an effective and acceptable treatment for patients with intermittent claudication. Studies to investigate the optimal dosing regimen, duration of clinical benefit, and effects in more severe forms of peripheral arterial disease are warranted.

Changes in the fatty acid composition of immune cells and plasma by intravenous injection of dihomo-gamma-linolenic acid in mice

An injectable emulsion of 10% tridihomo-gamma-linolenoyl glycerol (DGLA-TG, 96% pure) was prepared. 0.5 ml of the emulsion was injected into tail veins of 6-week-old C3H/HeSlc mice. They were killed 1, 3, 6, 12 and 24 h after the injection. The fatty acid composition of the phospholipid (PL) fraction of plasma, splenocytes and thymocytes was analysed along with that of control mice. DGLA concentrations increased markedly 1 h after the injection in the plasma (from 2.2% to 13.2%) and splenocyte (from 1.1% to 10.1%) PL fractions; they decreased rapidly thereafter. On the other hand, DGLA concentrations in the thymocyte PL fraction did not increase markedly. These data may be useful for planning animal experiments with DGLA emulsions, should these be developed as an experimental drug in the future.

Effects of a single drip infusion of lipo-prostaglandin E1 on vibratory threshold in patients with diabetic neuropathy

We evaluated acute effects of prostaglandin E1 encapsulated in lipid microspheres (lipo-PGE1), in 14 type 2 diabetic patients with neuropathy. Nerve conduction velocity (NCV), vibratory threshold (VT), skin temperature and subjective symptoms were evaluated for 24 hours after a single drip infusion of lipo-PGE1. In 6 of the 14 patients, the decrease in VT (P < 0.05) more than 50% measured by an SMV-5 vibrometer was observed at 6 hours after the infusion (responders). Subjective symptoms were improved (P < 0.05) in 5 of the 6 responders, whereas it improved in only 1 of the 8 patients who had no change in VT (nonresponders). NCV did not change (P > 0.05) either in the responders or in the nonresponders by the infusion. The responders had less impairment in VT and milder retinopathy and nephropathy than the nonresponders (P < 0.05). Our results demonstrate that vibratory sensation and subjective symptoms can be improved by a single infusion of lipo-PGE1 in type 2 diabetic patients with mild neuropathy.

O/W lipid emulsions for parenteral drug delivery. II. Effect of composition on pharmacokinetics of incorporated drug

The potential usefulness of O/W lipid emulsions as injectable drug delivery systems for lipophilic drugs was examined using a model lipophilic drug, sudan II (clogP = 5.4) in the normal rats. The standard lipid emulsion composed of soybean oil and egg yolk phosphatides increased the blood concentration of sudan II after i.v. injection when compared with its solubilized solution by plasma. However, it was still lower than that of the oil particles, and the distribution of sudan II to liver, lungs, adipose tissue, heart, and muscle was not altered, and only that to brain and kidneys was decreased. Herein, the effect of extensive alterations in the lipid emulsion composition on the blood concentration and organ distribution of sudan II was examined in comparison with the standard formulation. Addition of cholesterol, use of pure egg yolk phosphatidylcholine, use of phospholipids with saturated alkyl chain, use of saturated long chain triglycerides, and use of saturated medium chain triglycerides were tested. The oil particles of all tested lipid emulsions were still located in plasma space, and use of saturated medium chain triglycerides was the most effective way to increase blood concentration of sudan II, resulting in higher distribution to liver, lungs, spleen, and brain. This was caused by the increase of the steady-state partition of sudan II to the oil particles, and not by alteration of their organ distribution clearance.

Lipo-PGE1, a new lipid-encapsulated preparation of prostaglandin E1: placebo-and prostaglandin E1-controlled multicenter trials in patients with diabetic neuropathy and leg ulcers

Several clinical trials have shown that prostaglandin E1 (PGE1) is effective in treating peripheral occlusive vascular disease, but not definitely for diabetic neuropathy. We developed a new preparation of PGE1 incorporated in lipid microspheres (lipo-PGE1) that was designed to accumulate at vascular lesions. The effect of lipo-PGE1 (10 micrograms/day) was compared with placebo and the normal dose of a free PGE1 preparation (PGE1-CD, 40 micrograms/day) in two studies (double-blind and well-controlled) which enrolled 364 diabetic patients with neuropathy and/or leg ulcers. The drugs were given intravenously (bolus or drip infusion) for 4 weeks. Clinical improvement was noted in 61.6% of the lipo-PGE1 group and 30.0% of the placebo group in Trial 1 (p < 0.01), while the figures were 58.3% in the lipo-PGE1 group and 37.1% in the PGE1-CD group in Trial 2 (p < 0.01). Leg ulcers became smaller in the lipo-PGE1 groups in both trials (p < 0.01). In Trial 2, motor conduction velocity improved in the lipo-PGE1 group (p = 0.016). Side effects occurred in few patients receiving lipo-PGE1 or placebo, but more patients developed local side effects in the PGE1-CD group (p < 0.01). Thus, bolus intravenous injection of lipo-PGE1 improved diabetic neuropathy and leg ulcers with minimal side effects.

Intravenous injection of tridihomo-gamma-linolenoyl-glycerol into mice and its effects on delayed-type hypersensitivity

Highly purified tridihomo-gamma-linolenoyl-glycerol (DGLA-TG) was emulsified with egg yolk lecithin as a 10% (wt/vol) DGLA-TG emulsion. We injected 0.05 or 0.5 mL of the emulsion into mice through the tail vein and investigated its effects on the fatty acid composition of spleen cells and on delayed-type hypersensitivity (DTH) response. At 1 h after the injection, dihomo-gamma-linolenic acid (DGLA) concentrations were increased significantly in the total phospholipid fraction of spleen cells from 1.21 +/- 0.13 mol% to 2.09 +/- 0.74 mol% (P < 0.02) and 7.95 +/- 1.25 mol% (P < 0.001) in the 0.05-mL and 0.5-mL groups, respectively. Mice, which had already been immunized with sheep red blood cells (SRBC), were challenged by the injection of SRBC into the right-hind footpad. Intravenous injection into mice with 0.5 mL of the emulsion immediately before the challenge almost completely suppressed DTH response measured by the swelling of the right-hind footpads 24 h thereafter. This inhibitory effect on the DTH response was significant with as little as 0.05 mL of the emulsion, whereas a soybean oil emulsion was not effective at all. In conclusion, intravenous injection of a DGLA emulsion increased DGLA concentrations in immune cells within 1 h and suppressed the DTH reaction.

Enhanced antitumor activity and reduced toxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea administered in lipid microspheres to tumor-bearing mice

Stable lipid microspheres (LM) and lipid nanospheres (LN) with average diameters of 200 nm and 50 nm, respectively, were used to encapsulate an lipophilic antitumor agent, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). LM and LN containing BCNU (lipo BCNU and s-lipo BCNU, respectively) were prepared by homogenizing a soybean oil solution of BCNU with egg yolk lecithin, and their antitumor activity via the intravenous route was tested against L1210 leukemia in mice and compared with that of BCNU dissolved in saline. Both lipo-BCNU and s-lipo BCNU showed significantly enhanced antitumor activity with reduced toxicity, when compared with the corresponding doses of BCNU alone. These results suggest that LM and LN may be suitable carriers for lipophilic antitumor agents and may enhance their efficacy.

Review: recent advances in lipid microsphere technology for targeting prostaglandin delivery

Although prostaglandin E1 (PGE1) and prostacyclin (PGI2) exhibit pharmacological activities in free form, it has been hypothesized and experimentally verified that carrier preparations can target them more effectively at lower doses, thus causing fewer side effects. Lipid microspheres (LM) with a diameter of 0.2 micron are drug carriers prepared from soybean oil and lecithin, and the drug is incorporated within the LM. Lipo-PGE1 and lipo-PGI2 are LM preparations of PGE1 and a PGI2 derivative that are designed to accumulate at the vascular lesions. The authors have achieved remarkable clinical effects against neuropathy and ulcers, severe hepatitis, congenital heart diseases, and acute cerebral thrombosis using these preparations. In this review, clinical observations, some basic studies including targeting delivery of lipo-PGE1 to the liver, and future indications for these preparations are introduced. Development of a new lipo-PGE1 (lipo-AS013) that overcomes the disadvantages of the preparation currently available is also discussed. Lipo-AS013, a prodrug of PGE1, is considered superior to free PGE1 in terms of its chemical stability in LM and the retention ratio of the drug in LM in the body.

Controlled biodistribution of highly lipophilic drugs with various parenteral formulations

Lipid carrier systems are considered effective for targeting highly lipophilic drugs, but little systematic information about the effect of the physicochemical and pharmaceutical characteristics of drugs and formulations on their performance has been obtained. 3H-Retinoic acid and 14C-cholesteryl oleate with different lipophilicities (log PCoct = 6.6 and 18, respectively) were selected as model drugs and the potential of formulations such as oil in water (o/w) emulsion, micellar solution, and liposomes for controlling their biodistribution was demonstrated. After intravenous injection in mice, 3H-retinoic acid showed similar disposition profiles irrespective of formulation type, suggesting its rapid dissociation from carriers. 14C-Cholesteryl oleate with extremely high lipophilicity revealed widely varied disposition profiles reflecting the distribution patterns of carriers: micellar solution and liposomes showed large AUC values and low hepatic clearances, while the use of emulsion as a carrier resulted in rapid clearance from blood circulation into the liver. The results suggested that these formulations can be used as targeting carriers for lipophilic drugs which, however, should have a sufficiently high lipophilicity of about log PCoct 9-16.