Perfluorodecalin Emulsion Research Articles

Effect of Combined Perftoran and Indocyanine Green-Photodynamic Therapy on HypoxamiRs and OncomiRs in Lung Cancer Cells.

Indocyanine green (ICG) is a nontoxic registered photosensitizer used as a diagnostic tool and for photodynamic therapy (PDT). Hypoxia is one the main factors affecting PDT efficacy. Perfluorodecalin emulsion (Perftoran®) is a known oxygen carrier. This study investigated the effect of Perftoran® on ICG/PDT efficacy in presence and absence of Perftoran® via evaluation of phototoxicity by MTT; hypoxia estimation by pimonidazole, HIF-1α/β by ELISA, and 17 miRNAs (tumor suppressors, oncomiRs, and hypoxamiRs) were analyzed by qPCR. Compared to ICG/PDT, Perftoran®/ICG/PDT led to higher photocytotoxicity, inhibited pimonidazole hypoxia adducts, inhibited HIF-1α/β concentrations, induced the expression of tumor-suppressing miRNAs let-7b/d/f/g, and strongly inhibited the pro-hypoxia miRNA let-7i. Additionally, Perftoran®/ICG/PDT suppressed the expression of the oncomiRs miR-155, miR-30c, and miR-181a and the hypoxamiRs miR-210 and miR-21 compared to ICG/PDT. In conclusion, Perftoran® induced the phototoxicity of ICG/PDT and inhibited ICG/PDT-hypoxia via suppressing HIF-α/β, miR-210, miR-21, let-7i, miR-15a, miR-30c, and miR-181a and by inducing the expression of let-7d/f and miR-15b.

Perftoran improves Visudyne-photodynamic therapy via suppressing hypoxia pathway in murine lung cancer

Perfluorodecalin emulsion (Perftoran®) is an oxygen carrier. Verteporfin, a photosensitizer, is used for cancer photodynamic therapy (PDT) in its liposomal form (Visudyne®). Hypoxia affects PDT efficacy. The study aimed to investigate the effect of Perftoran® on the efficacy of Visudyne®/PDT and on the hypoxia pathway in lung cancer. Lung cancer was induced in mice by diethylnitrosamine and carbon tetrachloride. Lung tissues have been analyzed for apoptosis and necrosis detection by dual DNA staining; mitochondrial transmembrane potential (ΔΨm) staining by Red CMX-Ros, hypoxia estimation by pimonidazole, miRNA-21-5p and miRNA-210-3p evaluation by qPCR, and HIF-1α and VEGF determination by ELISA. Compared to Visudyne®/PDT, Perftoran®/Visudyne®/PDT led to severe apoptosis and necrosis regions in the bronchiolar epithelium, induced late apoptosis and necrosis and suppressed ΔΨm and total hypoxia level more than Visudyne®/PDT. The expression of miR-21 and miR-210 and the concentration of HIF-1α and VEGF were significantly induced in tumor-bearing mice. Compared to Visudyne®/PDT, Perftoran®/Visudyne®/PDT dramatically suppressed the expression of miR-21 and miR-210 and the concentration of HIF-1α and VEGF. In conclusion, these findings indicate the potential role of Perftoran® in suppressing hypoxia through the inhibition of the hypoxamiRs expression and HIF-1α, which in turn led to the inhibition of VEGF, during Visudyne®/PDT.

The adverse effects of hypoxia on hiHep functions via HIF-1α/PGC-1α axis are alleviated by PFDC emulsion

Human-induced hepatocyte-like cells (hiHeps) are new cell sources for bio-artificial liver (BAL), as a potential treatment for acute liver failure (ALF), which calls for 1010 cells at a minimum. However, high-density hiHeps loaded in BAL have a high demand for oxygen, leading to hypoxia during culture. At present, the effects of hypoxia on hiHep proliferation and functions are still unclear. Here, it was proved that hiHeps were hypoxic at day 8 of culture, even though the seeding density were 4 × 107 cells/cm3 in the PET-loaded bioreactor. Hypoxia impaired hiHep functions, such as albumin secretion, urea synthesis and drug metabolism. HIF-1α up-regulated its downstream genes related to glucose metabolism, including PDK-1, Glut1 and LDHA under hypoxia. Meanwhile, HIF-1α down-regulated the gene expressions of PGC-1α, NRF-1, TFAM, TFB1M and TFB2M. This study found that PGC-1α was a downstream mediator of HIF-1α, and HIF-1α/PGC-1α axis repressed the protein expressions of CYP1A2 and CYP3A4. Our findings revealed that hypoxia affected the proliferation and functions of hiHeps via HIF-1α/PGC-1α axis, and showed that perfluorodecalin (PFDC) emulsion reversed the adverse effects of hypoxia during high-density perfusion culture.

Development of fluorinated polyplex nanoemulsions for improved small interfering RNA delivery and cancer therapy

We report the development of a small interfering RNA (siRNA) delivery vector based on cationic perfluorocarbon nanoemulsions. We have prepared perfluorodecalin (PFD) emulsions with a positive surface charge provided by a fluorinated poly(ethylenimine) (F-PEI). The fluorinated emulsion (F-PEI@PFD) reduced cytotoxicity of F-PEI and demonstrated effective binding with siRNAs to form nanosized emulsion polyplexes. The prepared emulsion polyplexes enhanced cellular uptake and improved endosomal escape of the siRNA. In addition to increased reporter gene silencing in multiple cancer cell lines, when compared with control F-PEI and PEI polyplexes, the siRNA emulsion polyplexes showed an excellent resistance to serum deactivation and maintained high activity, even in high-serum conditions. The F-PEI@PFD emulsion polyplexes carrying an siRNA to silence the expression of Bcl2 gene induced apoptosis and inhibited tumor growth in a melanoma mouse model in vivo and showed potential for in vivo ultrasound imaging. This study demonstrates the potential of F-PEI@PFD emulsions as a multifunctional theranostic nanoplatform for safe siRNA delivery, with integrated ultrasound imaging functionality.

A study on improving the outcome of cryosurgery using low thermal conductivity emulsions

This study proposes a novel approach that utilises low thermal conductivity emulsions of perfluorodecalin as insulation around the tumour interface. The study reports the preparation of low thermal conductivity perfluorodecalin (PFD) emulsions (30%, 50%, 70% and 90% (w/v)) using probe sonication. The determination of thermal conductivity of these emulsions experimentally reveals a decrease in magnitude with the increase in the concentration of perfluorodecalin. The dynamic light scattering (DLS) and zeta potential studies indicate monodisperse and stable emulsions. Fourier transform infrared spectroscopy (FTIR) analysis confirms the presence of perfluorocarbon phase in the emulsion. The results of differential scanning calorimetry and theoretical estimation of thermal conductivity demonstrate that the increase of perfluorodecalin concentration lowers the specific heat and thermal conductivity of the emulsions. Experimental studies have been performed during cryosurgical freezing on an agarose gel phantom in the presence of a low thermal conductivity emulsion layer. The results suggest that in the presence of PFD 90 emulsion layer around the gel phantom the temperature at the 10 mm axial thermocouple the temperature is found to be 11 ∘C, whilst in the absence of this emulsion layer, the temperature is − 4 ∘C at the same thermocouple location, suggesting the insulating ability of perfluorocarbon emulsion layer. In conclusion, this study proposes a new approach that utilises low thermal conductivity emulsions for enhancing the cryosurgical freezing and minimising the damage to a defined region.

Effect of cold perfusion and perfluorocarbons on liver graft ischemia in a donation after cardiac death model

BackgroundEffects of two perfluorocarbon (PFC) formulations (perfluorodecalin emulsion and perfluorodecalin liquid) on the quality of liver graft preservation, in a donation after cardiac death (DCD) rat model, were investigated. The significance of continuous graft perfusion during cold preservation was also explored. Materials and methodsDCD model: 30 min after cardiopulmonary arrest was initiated, livers were excised and flushed with cold University of Wisconsin (UW) solution (± PFC) and preserved in the same solution for 8 h. The study groups were preserved as follows: group 1: no perfusion; group 2: perfusion with UW; group 3: PFC was administered before cardiac arrest and the liver was perfused with UW alone; and groups 4 and 5: perfused with UW + 1 of two PFCs. In a baseline group used only for comparison of gene expression, livers were quick-frozen after cardiac arrest. Microarrays were used to analyze liver messenger RNA transcripts. Histopathologic, immunohistochemical, and ADP/ATP ratio evaluations were performed to assess the quality of graft preservation. ResultsSignificant decreases in downregulation and increases in upregulation of hepatic genes (relative to baseline) were demonstrated in all perfusion groups. This trend was most pronounced in the PFC groups. Lower fat content and ADP/ATP ratio and a reduction in Caspase 3 activation were found in all perfusion groups. ConclusionHypothermic perfusion of rat DCD liver grafts with oxygenated UW solution (± PFC) produced superior preservation compared with nonperfusion storage. The observed changes in expression of hepatic genes may represent a protective effect in the DCD model.

Artificial oxygen carriers based on perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules

Poly(n-butyl-cyanoacrylate)-nanocapsules filled by perfluorodecalin (PFD) are proposed as potential oxygen carriers for blood substitute. The capsule dispersion is prepared via interfacial polymerisation from a PFD emulsion in water which in turn is generated by spontaneous phase separation. The resulting dispersion is capable of carrying approximately 10% of its own volume of gaseous oxygen, which is approximately half of the capacity of human blood. The volumes of the organic solvents and water are varied within a wide range, connected to a change of the capsule radius between 200 and 400 nm. The principal suitability of the capsule dispersion for intravenous application is proven in first physiological experiments. A total amount of 10 ml/kg body weight has been infused into rats, with the dispersion supernatant and a normal saline solution as controls. After the infusion of nanocapsules, the blood pressure as well as the heart rate remains constant on a normal level.

Uptake of concentrated perfluorocarbon emulsions into rat lymphoid tissues.

The effects of injecting (10-30 mL kg-1) either perfluorodecalin (FDC) emulsions of increasing phase fraction (20-60% w/v) or the commercial formulation, Fluosol, on lymphoid tissues have been studied for up to 7 days in male rats. Tissue weights increased by up to 123% (P < 0.05) in proportion with quantity of perfluorochemical (PFC) injected, with spleen responses consistently greater than those of the liver. PFC droplets recovered from these tissues at 72 h after injection of 30% (w/v) FDC emulsion (10 mL kg-1) had mean diameters in the 1-10 microns range, with those from the spleen being larger than those from the liver. Recovered droplet diameters were considerably greater than freshly-prepared emulsion mean particle sizes (0.21-0.25 microns). These results suggest that coalescence of emulsion droplets following accumulation in lymphoid tissue is a pre-requisite for the eventual excretion of PFC vapour through the lungs.

Emulsified perfluorochemicals as respiratory gas carriers: recovery of perfluorodecalin emulsion droplets from rat tissues.

To further understand the in-vivo biokinetic behaviour of perfluorochemical (PFC) emulsions, male rats were injected (10 mL kg-1) with 30% (w/v) emulsified perfluorodecalin (FDC) and uptake into tissues assessed. At 72 h after injection, the mean (+/- s.e.m.) diameters of FDC droplets recovered from liver and spleen were 2.24 +/- 0.04 and 2.78 +/- 0.10 microns, respectively; droplets recovered from lung after 72 h (mean: 1.73 +/- 0.13 micron) were significantly smaller (P < 0.01). After 7 days, FDC droplet diameters in liver had increased to 3.31 +/- 0.13 microns (P < 0.01) and those in lung to 2.71 +/- 0.14 microns (P < 0.01); droplets in spleen after 7 days (2.22 +/- 0.09 microns) were similar to those at 72 h. These data support the hypothesis that significant initial coalescence of FDC droplets occurs in the rat liver and spleen, with further coalescence in the liver up to 7 days. The mean percentage of the injected FDC dose recovered from the liver after 72 h was 2.2 +/- 0.4%, and after 7 days was 0.07 +/- 0.05% (P < 0.01). A smaller decrease in the percent injected FDC in spleen also occurred over the same period (72 h: 1.9 +/- 0.3%; 7 days: 0.8 +/- 0.5%; P < 0.01). The percent injected FDC in lung was similar at 72 h (0.007 +/- 0.004%) and 7 days (0.005 +/- 0.001%). FDC was undetectable (< 0.001%) in all blood samples. The greater rate of FDC elimination from the liver than from the spleen may be related to differences in the rates of reticuloendothelial system processing between these organs.

In VitroComparison of Dodecafluoropentane (DDFP), Perfluorodecalin (PFD), and Perfluoroctylbromide (PFOB) in the Facilitation of Oxygen Exchange

The purpose is to prepare 2% w/v emulsions of dodecafluoropentane, perfluorodecalin, and perfluoroctylbromide and compare them for their ability to absorb oxygen. The oxygen uptake capability and volume expansion of each emulsion and the blank vehicle were evaluated in water at 21 degrees C and 37 degrees C. The average particle size of the dodecafluoropentane emulsion is < 400 nm stored at room temperature for 6 months. In comparison to water treated with either the blank vehicle, the perfluorodecalin emulsion, or the perfluoroctylbromide emulsion, the dodecafluoropentane emulsion absorbs 3 times more oxygen at 21 degrees C and 7 times more oxygen at 37 degrees C. Furthermore, a significantly higher in vitro expansion (5 times) is observed with the dodecafluoropentane emulsion at 37 degrees C. As such, DDFP has been hypothesized to be a better oxygen carrier and delivery agent in vivo. This may be applicable to a variety of hypoxic medical conditions where oxygen delivery might be therapeutically beneficial.

A system establishment compatibility profiles for artificial oxygen carriers and other substances.

Worldwide, great efforts are being made to develop a clinically useful artificial oxygen carrier. Toxicological and immunological compatibility is generally tested using animal experiments but inflammatory parameters in particular show large species-specific differences. Therefore, we developed an in vitro system using human components to establish a compatibility profile of unknown compounds. The test system comprises induction of hemolysis, activation of complement (C3a), induction/suppression of cytokine production, influence on cell proliferation, direct toxicity on peripheral leukocytes, and phagocytosis of the material under test and of microbes. The test system will be described, along with results of various perfluorocarbon emulsions. When testing lecithin-based perfluorodecalin (PFD) emulsions, and comparing them to Pluronic-based PFD emulsions, we could show that Pluronic-based emulsions were virtually untoxic to peripheral human leukocytes. They neither inhibited cell proliferation nor caused any hemolysis, but caused mild to moderate inhibition of endotoxin-induced cytokine production. At the same time, lecithin-based PFD emulsion caused substantial cytotoxicity in phagocytic cells like monocytes (60-100% after 24 h incubation) and granulocytes (10-20% after 24 h incubation). They also suppressed endotoxin-induced cytokine production in monocytes to more than 98% and inhibited cell proliferation of an endothelial (ECV 304) and a monocytic cell line (MonoMac6) to more than 95%.

Perfluoroalkylated telomers derived from tris(hydroxymethyl)acrylamidomethane as surfactants and co-surfactants in fluorocarbon emulsions

The ability of perfluoroalkylated telomers derived from tris(hydroxymethyl)acrylamidomethane (TAC) to stabilize fluorocarbon emulsions has been investigated. For this purpose, 50% w/v emulsions of perfluorodecalin (FDC) and perfluoro-octyl bromide (PFOB) were prepared with a total 3% w/v of surfactant and were compared with emulsions prepared with Pluronic F-68 ® or egg yolk phospholipids (EYP). When used as the sole surfactant, telomers 1 (TAC with a C 6F 13 chain and a number average degree of polymerization n ∼ 6) and 2 (C 8F 17TAC, n ∼ 6) produced FDC emulsions that were more stable than with Pluronic F-68 alone; when compared to EYP no improvement was found. When associated to other, less hydrophilic perfluoroalkylated surfactants, such as the monoadduct 3 (C 6F 13TAC, n = 1) or [1- O-(perfluoro-octyl)-2′-propenyl]xylitol ( 4), for certain formulations these telomers resulted in somewhat enhanced stabilization of both FDC and PFOB emulsions. In some cases, the emulsions were as stable as those prepared with EYP alone. When telomer 1 was used as a co-emulsifier with EYP, no noticeable stabilization was observed; with Pluronic F-68 emulsion stability was reduced.

Perfluorodecalin Emulsion Tested for Biocompatibility in Macrophages by Means of a Magnetometric Method

The effect of a stable perfluorodecalin (FDC) emulsion, based on addition of 0.2-0.5% (W/V) of perfluoroperhydrophenanthrene and 4% egg yolk lecithin was tested for its influence on Kupffer cells in vivo by means of a magnetometric procedure in rats. It was also compared with the effect of a perfluoro-chemical emulsion (PFC) of the first generation (FluosolR-DA, FDA). While doses of 0.1 g/kg body weight of both PFCs caused a small increase of activity in these cells (as measured by an increase in a ratio factor r after magnetization), doses of 1 g/kg b.wt. led to a significant retardation of intracellular movements after FDC and FDA for two and four days, respectively. A dose of 3 g/kg b.wt. of FDC effected a significant depression for 8 days, whereas after the same dose of Fluosol-DA the intracellular motility remained depressed for as long as 32 days.

Room Temperature Stable Perfluorocarbon Emulsions with Acceptable Half-Lives in the Reticuloendothelial System

Prolonged room temperature stability (i.e. zero particle growth) can be achieved for concentrated emulsions of perflubron (perfluorooctyl bromide) or perfluorodecalin via addition of a secondary high molecular weight, lipophilic fluorocarbon component. Due to their enhanced lipophilic character, the secondary fluorocarbon components have acceptable half-lives in the organs of the reticuloendothelial system.

The Elimination Peculiarities of Perfluorocarbon Emulsions Stabilized with Egg Yolk Phospholipid

In order to examine the elimination rate of Perfluorodecalin (FDC) emulsions stabilized with different emulsifiers--yolk phospholipid (EYP) and procsanol P-268 (analog of Pluronic F-68)--we performed controlled trials on excretion of FDC in exhaled air, elimination from blood and accumulation in the liver. Adult Wistar rats were injected intravenously with FDC emulsions stabilized with different emulsifiers at a dose of 11.5 g FDC per kg body weight. The concentration of FDC in blood, exhaled air and liver tissue was examined by means of the gas chromatography method. The circulation time in blood for the emulsion stabilized with EYP was much longer comparatively to the emulsion containing the synthetic emulsifier procsanol P-268. The injection of EYP dispersions prolonged the circulation time of lipid-stabilised FDC emulsions. The rate of PFC elimination in exhaled air from such an emulsion and the rate of its accumulation in liver during the initial period after injection are reduced compared to the procsanol-stabilized emulsion. These data are interpreted as the result of a reduction of phagocytic activity of blood monocytes toward the lipid-coated particles of the emulsion. The circulation time of PFC emulsion can be prolonged by using lipid emulsifier and additional injections of EYP dispersion.

Amphiphilic Sugar Phosphates with Single or Double Perfluoroalkylated Hydrophobic Chains for Use in Oxygen and Drug Delivery Systems

New anionic amphiphiles with a phosphate ester junction between the fluorophilic-lipophilic tail and the sugar-based hydrophilic head were synthesized and evaluated. The single hydrophobic chain surfactants 1 a, b and 2a allowed the preparation of stable and fine highly concentrated emulsions of perfluorodecalin or perfluoroocytl bromide, either when used alone or in conjunction with egg yolk phospholipids (EYP). Surfactants 3d, 5d, 6d and 6e, with two hydrophobic chains, one fluorinated the other not, gave liposomal structures, and displayed encapsulation properties for carboxyfluorescein. The phosphodiesters tested cause no significant inhibition of the growth and viability of Namalva cell cultures (0.1-1 g/L range). Single chain phosphodiesters manifest no detectable hemolytic activity (at 100 g/L for 1a) whereas double chain compounds do moderately (ca 20% hemolysis at 20 g/L). The maximum tolerated dose compatible with the survival of all of a series of 10 intravenously injected mice is in 130 mg/kg body weight range.

Improvement in emulsification particle size reduction and stabilization of concentrated fluorocarbon emulsions by small amounts of ( d-glucosyl)[2-(perfluoroalkyl)ethyl] phosphates as surfactants

The achievement of an effective intravenously injectable oxygen carrier based on fluorocarbons requires highly concentrated, stable emulsions. Significant progress has now been achieved by using minor amounts of sodium (3- or 6- d-glucosyl)[2-(perfluoroalkyl)ethyl] phosphates as surfactants, or as co-surfactants with egg yolk phospholipids (EYP). A preliminary comparative evaluation of these water-soluble anionic surfactants in 50% (w/v) perfluorodecalin (FDC) emulsions indicates significantly better emulsifying properties than those of natural EYP, the surfactant most commonly used in intravenously injectable emulsions. The fluorinated surfactants, either alone or in conjunction with EYP, give smaller particles, both at the time of preparation and after one month at 40°C, than does EYP alone. The perfluorooctyl derivatives, independent of the location of the phosphate on the glucose moiety, are more effective than the perfluorohexyl one. The remarkable emulsifying properties of these compounds are established to be related to the presence of the anionic P(O)O connector, they are also greatly enhanced by the introduction of the perfluoroalkylated chain. These effects are even more pronounced with the more concentrated (90% (w/v)) perfluorooctyl bromide (PFOB) emulsions. Replacement of a small amount (one eighth) of the EYP by [2-(perfluorooctyl)ethyl](6- d-glucosyl) (sodium) phosphate in PFOB/EYP emulsions facilitates the emulsification process, reduces the average particle size significantly, and achieves strong stabilization of the emulsions. Increasing the fluorinated surfactant/EYP ratio resulted in no significant additional benefit. Concentrated (90% (w/v)) PFOB emulsions, markedly more stable than those containing 4% EYP, were obtained with only 1% of [2-(perfluorooctyl)ethyl](6- d-glucosyl) (sodium) phosphate as the sole surfactant.

Perfluoroalklylated phospholipids as surfactants and co-surfactants forinjectable fluorocarbon emulsions.

Highly fluorinated phospholipids were investigated as sole surfactant, and as co-surfactant with egg yolk phospholipids (EYP), in the formulation of 50% and 100% w/v perfluorodecalin emulsions. The surfactant's capability to stabilize such emulsions improves with the length of the perfluoroalklylated tail and with the increase of its relative weight in the hydrophobic chain. As sole surfactant, 2, which has the longest fluorinated tail has the highest efficacy. As co-surfactant with EYP, a strong stabilizing effect is found when the total hydrophobic chain length is adjusted to the EYP membrane's thickness, which is the case of 1. Dispersions of the F-phospholipids do not modify cell growth and viability and show no hemolytic activity on human red blood cells at concentrations in the 60-100g/L range. Acute toxicity tests in mice indicate - i.v. DL50 greater than 2.75 g/Kg body wt.

Co-surfactant effect of perfluoroalkylated glycerophosphocholines in fluorocarbon emulsions: Dependence on the co-surfactant's hydrophobic chain length

Unexpectedly large differences were found when new perfluoroalkylated glycerophosphocholines with slightly different lipidic chains were evaluated as co-surfactants with egg yolk phospholipids (EYP) in the preparation of concentrated buffered (100% w v , i.e., 51.5% v v ) perfluorodecalin emulsions. As co-emulsifier, 1 shows a strong stabilizing effect when compared to a reference emulsion based on natural EYP alone. No significant effect on the emulsion's stability was observed with 2 in spite of the fact that it has the longest fluorophilic F-alkyl tail. Compound 3, which has the shortest lipidic chain length, demonstrated strong destabilizing properties at the time of the preparation of the emulsion. These stabilizing/destabilizing effects are rationalized in terms of interactions of the surfactant's perfluoroalkylated tail with the fluorocarbon phase or with the hydrocarbon chains of the EYP. Stabilizing effects become predominant only when the surfactant's total chain length is comparable to the EYP monolayer's thickness, which is the case for 1.

Acute toxicity of perfluorodecalin emulsion for rabbits

The toxicity of injected intravenously to rabbits perfluorodecalin (PFD) emulsion (10% vol/vol) with 4% Proxanol 268 (USSR analog of Pluronic F-68) as a stabilizer was studied. LD 50 of PFD emulsion was approximately 13 ml/kg, corresponding to the data, reported previously[l]. Perfluoro-p-methylcyclohexyl- piperidine (PFMCP) emulsion at a dose 10 ml/kg effectively eliminated the PFD emulsion toxicity while using any mode of injection: simultaneous injection of PFD and PFMCP emulsions; administration of PFMCP emulsion 5–7 days before or 5–12 days after administration of PFD emulsion. Perfluorotripropylamine (PFTPA) emulsion wasn't toxic for rabbits, suggesting that gas embolia couldn't cause animal death under administration of PFD emulsion (P v of PFD and PFTPA are 12 and 20 mm Hg respectively). Rabbits death also couldn't be caused by liver cytochrome P-450 induction and some other membrane effects of PFD, because emulsion of even more lipophilic perfluorooctylbromide(PFOB) wasn't toxic (CST of PFD and PFOB are 22 and 5°C respectively). It is suggested that the cause of rabbit death after administration of PFD emulsion is unstability of the letter in circulatory system, which results in thrombosis of pulmonary capillaries. Freeze-fracture electron microscopy revealed the large dense aggregates of PFD particles in rabbits blood 1–2 days after PFD emulsion injection.