Increased delivery of gallium-67 to tumors using serum-stable liposomes

Gallium-67 chelated to nitrilotriacetic acid was encapsulated in liposomes composed of various phospholipids, and 67Ga delivery potential to the tumor after intravenous injection of these liposomes was examined. Tumor uptake of the liposomes themselves and their stability in the serum were also studied. It was found that liposomes composed of distearoylphosphatidylcholine, diarachidoylphosphatidylcholine, or sphingomyelin with cholesterol (molar ratio of phospholipid:cholesterol, 2:1) could be taken by the tumor effectively and could deliver large amounts of 67Ga to the tumor. They could also give high 67Ga accumulation ratios (tumor to the other tissues). The study of liposomal stability in the serum suggested that the marked 67Ga accumulation in the tumor resulted from the serum stability of the liposomal bilayer, i.e., the stable liposomes in the blood circulation could reach the tumor in large quantities after i.v. injection. These observations indicate that liposomes with an appropriate lipid composition may be an excellent tool to accumulate 67Ga in tumors.     

Characterization of liposomes containing iodine-125-labeled radiographic contrast agents

Multilamellar liposomes were prepared containing either iodine-125-labeled (125I) diatrizoate or 125-I labeled iotrol in their aqueous phase. The in vitro permeabilities of liposomes containing both contrast agents were measured in the presence of saline and serum at 37 degrees C. Two different phospholipid compositions were studied: phosphatidylcholine/cholesterol/stearylamine (PC/C/S, 8: 1:1 molar ratio) and distearoylphosphatidylcholine/sphingomyelin (DSPC/SM, 5:2 mole ratio). In saline, similar permeabilities were observed for the four phospholipid-contrast agent combinations. In serum, however, leakage of 125I activity was 2 to 3 times greater from PC/C/S liposomes than from vesicles composed of DSPC/SM. When PC/C/S liposomes that contained 125I-diatrizoate were injected into rats, the clearance half-times for 125I activity from the liver, spleen, and whole body were 4.4 hours, 4.5 hours, and 2.8 hours, respectively. Liposomes composed of DSPC/SM cleared at a significantly slower rate from the liver, spleen, and whole body with half-times of 24.0 hours, 18.4 hours, and 17.2 hours observed from these tissues, respectively.     

泛影葡胺脂质体的制备及其肝脏靶向增强效应观察

目的：探讨泛影葡胺脂质体对肝脏靶向增强的可能。材料和方法：采用乙醚注射法（胆固醇与卵磷脂摩尔比１：１）制备包裹泛影葡胺的大单层脂质体;用ＣＴ观察其对大鼠肝炎型假瘤（ｎ＝４）的靶向增强效果。结果：（１）所制备的装载泛影葡胺脂质体粒径为０．８２±０．３２μｍ,面积为８．４±４．０μｍ２,体积为６．９±１．３μｍ３。造影剂包裹率为１０．１％。体外稳定试验表明泛影葡胺质体放置３ｄ时,含碘量仍保持９３．８％,７ｄ后造影剂大量渗漏,含碘量降至４１．８％。（２）泛影葡胺脂质体能靶向性分布于肝脏,使正常组织呈渐进式增强,３０ｍｉｎ达到高峰,以后逐渐下降,１２ｈ后恢复至基础水平。肝炎性假瘤灶在给药后３０ｍｉｎ显示最佳。结论：泛影葡胺脂质体能有效提高肝脏增强水平,对提高肝脏病变的显示有重要作用。     

Usefulness of liposomes carrying losefamate for CT opacification of liver and spleen

Losefamate, a hepatobiliary contrast agent, was encapsulated into liposomes to increase its ability to opacify the liver and spleen on computed tomographic (CT) images. Multilamellar lipid vesicles (lecithin, cholesterol, and stearylamine, in 4:1:1 molar ratio) containing iosefamate in their aqueous phase were prepared. Seven dogs received intravenous injections of 100-300 mg I/kg in one of three forms: encapsulated, unencapsulated, or a mixture of the two in equal parts. Animals that received the opaque vesicles had marked opacification of their livers, bile ducts, gallbladders, spleens (maximum 106 H enhancement), and gastrointestinal tracts. Spleen CT values (an indicator of encapsulated material uptake) were always higher in these dogs than in the animals receiving equivalent amounts of unencapsulated iosefamate alone. At the high-dose level, liver uptake of the encapsulated materials was also greater. Liposome-encapsulated hepatobiliary contrast agents are effective liver and spleen opacifiers for CT imaging in the dog.     

99mTc-HMPAO-labeled liposomes: an investigation into the effects of some formulation factors on labeling efficiency and in vitro stability

Technetium-99m complex of hexamethyl-propylene-amineoxime (HMPAO) is used as an efficient agent to label liposomes. For this, ^99mTc-HMPAO is incubated with preformed liposomes that contain glutathione (GSH). Effect of GSH and lipid concentration on labeling efficiency, as well as the effect of lipid composition on in vitro stability of labeled liposomes, was investigated in the present study. d,l-HMPAO was synthesized and kits including d,l-HMPAO and SnCl₂·2H₂O were optimized at 0.5 mg HMPAO, 5.0 μg SnCl₂·2H₂O and pH 7, and lyophilized. DSPC/CHOL (molar ratio 2:1) liposomes encapsulating GSH were labeled with ^99mTc-HMPAO prepared kits. Increase of GSH concentration in hydration buffer from 5 to 200 mM during liposome preparation resulted in a broad labeling efficiency of liposomes ranging from 4.16% to 69.81%. An initial approximate concentration of 100 mM GSH in the hydration buffer seems to be appropriate for a good labeling efficiency. At the optimum concentration of GSH, change of the total initial lipid concentration from 10 to 70 mM did not produce a remarkable difference in labeling efficiency. Study of the effect of lipid composition on the stability of liposomes showed that all three kinds of labeled liposomes composed of DSPC/CHOL, DPPC/CHOL and DMPC/CHOL (molar ratio 2:1) had good in vitro stability in human plasma at 37°C for 48 h; however, employing DSPC resulted in the most stable ones.     

MRI and <Superscript>1</Superscript>H MRS findings in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder characterized by a defect in cholesterol biosynthesis, associated with mental retardation and multisystem structural abnormalities. This study investigated the prevalence of congenital CNS abnormalities by MRI in a large series of patients with SLOS and the correlation of the clinical and biochemical findings with the results of MRI and ¹H MRS. Eighteen patients were studied; all underwent MRI of the brain, and 16 had ¹H MRS of the cerebral white matter. The ratios choline:NAA, lipid:NAA, and lipid:choline metabolite were found to be correlated with the clinical degree of disease severity, serum total sterol ratios (cholesterol/cholesterol + 7-dehydrocholesterol + 8-dehydrocholesterol) and in two cases with the effect of cholesterol therapy. Abnormal CNS findings were noted in five patients, including callosal abnormalities (n=4), Dandy-Walker variant (n=1), and arachnoid cyst (n=1). Holoprosencephaly was noted in one patient with a prevalence of 6%. Choline:NAA was elevated in seven patients. There was a statistically significant positive correlation between the lipid:choline ratio and the serum cholesterol precursor, 8-dehydrocholesterol. In two patients ¹H MRS demonstrated abnormally elevated lipids prior to cholesterol therapy, which improved on therapy. The use of MRI and ¹H MRS is an effective way to demonstrate brain structural abnormalities in patients with SLOS and may prove to be an effective method for the assessment of the effects of cholesterol replacement therapy in the brain.     

99Tcm-MIBI脂质体的制备及特征分析

目的 研究99Tcm-甲氧基异丁基异腈（MIBI）脂质体的制备方法,并对其特征进行分析。方法 采用乙醇注入-超声法制备99Tcm-MIBI脂质体,测定脂质体粒径大小和包封率,对超声时间、大豆卵磷脂与胆固醇的质量比等条件进行优化,观察99Tcm-MIBI脂质体的稳定性。结果 当制备的99Tcm-MIBI质量浓度为0.01 mg/mL时,平均粒径大小为（171.4±25.2）nm,包封率的平均值为（8.5±1.3）%。大豆卵磷脂与胆固醇的质量比为4:1和超声时间为5 min为最佳条件。电镜图显示,制备第1天后粒径较小,形态较为规则、均匀,呈完整球形或椭圆形;30 d后粒径大小及形态未见明显改变。结论 采用乙醇注入-超声法制备的99Tcm-MIBI脂质体粒径较小、包封率高,且较稳定。     

CT blood pool enhancement in primates with lopromide-carrying liposomes containing soy phosphatidyl glycerol

RATIONALE AND OBJECTIVES: The purpose of this study was to determine the feasibility of using iodinated liposomes as blood pool agents for computed tomography (CT) in nonhuman primates. MATERIALS AND METHODS: Five normal adult baboons (15-21 kg) were anesthetized and intravenously injected with iopromide containing soy phosphatidyl glycerol liposomes with a diameter of 195 nm. Each animal received a dose of 300 mg total iodine per kilogram (46% encapsulation). RESULTS: The animals tolerated the injections well, experiencing no measurable electrocardiographic changes, and recovered uneventfully from anesthesia. Sequential helical CT scans of the baboons from the base of the skull to the symphysis pubis acquired up to 40 minutes after injection showed persistent blood pool enhancement. Maximum mean enhancement of major vascular structures was 106 HU at 1 minute after contrast medium injection. Mean blood pool enhancement was 76, 72, and 67 HU at 10, 20, and 40 minutes after injection, respectively. Liver and spleen were enhanced by 40 and 41 HU, respectively, 40 minutes after injection. No significant enhancement was measured in the brain and pancreas. CONCLUSION: Soy phosphatidyl glycerol with iopromide liposomes produces prolonged vascular enhancement and has potential as a blood pool CT contrast agent in primates.     

细胞膜脂含量对结合血卟啉衍生物（HpD）及其载体的研究

应用电泳方法分离结合HpD的人血清,利用染色和HpD光照后产生红色荧光特性,证明了HpD与血清中脂蛋白和清蛋白组分结合。制备不同卵磷脂/胆固醇摩尔比的脂质体,将其与肝癌细胞融合后,分别加入HpD,经荧光光谱分析,光照后对脂质过氧化物(丙二醛)及荧光偏振度的测定,结果表明HpD与细胞膜上脂质相结合,其结合量与膜脂含量成正相关,光照后,丙二醛增加,膜流动性降低。     

Liposomal Gd-DTPA: preparation and characterization of relaxivity

Gadolinium diethylenetriaminepentaacetic acid (DTPA) has not proved particularly useful for hepatosplenic magnetic resonance imaging. However, by entrapping the Gd-DTPA within lipid vesicles, one may exploit the ability of the reticuloendothelial system to endocytose particulates, permitting passive delivery of contrast agent to the liver and spleen while decreasing the rate of clearance of Gd-DTPA from the vasculature. Liposomes of 70-400 nm diameter containing Gd-DTPA were prepared by a freeze-thaw extrusion process. These exhibited high trapping efficiencies and excellent stability during storage. For all sizes of liposomes, the relaxivity of the entrapped Gd-DTPA was less than that of free Gd-DTPA. Relaxivity varied linearly with the surface-area-to-volume ratio of the liposomes; the smaller the liposomes, the greater the relaxivity. Liposomes containing cholesterol had a lower relaxivity than liposomes without cholesterol. The authors suggest this reflects the decrease in the water permeability coefficient caused by the presence of cholesterol in the liposome membrane.     

T1 relaxivity of core-encapsulated gadolinium liposomal contrast agents--effect of liposome size and internal gadolinium concentration

RATIONALE AND OBJECTIVES: Long circulating core-encapsulated gadolinium (CE-Gd) liposomal nanoparticles that have surface conjugated polyethylene glycol are a promising platform technology for use as blood pool T1-based magnetic resonance (MR) contrast agents. The objective of this study was to investigate the effect of liposome size and internal (core) Gd concentration on the T1 relaxivity of CE-Gd liposomes. MATERIALS AND METHODS: Twelve different liposomal formulations were synthesized and characterized, resulting in a size (50, 100, 200, and 400 nm) and core Gd-concentration (200, 350, and 500 mM) "matrix" of test samples. Subsequently, CE-Gd liposomes were diluted in deionized water (four diluted samples) and molar T1 relaxivity (r1) measurements were performed at 2- and 7-T MR field strengths. RESULTS: The r1 of CE-Gd liposomes was inversely related to the liposome size. The largest change in r1 was observed between liposomes that were extruded through 50- and 100-nm filter membranes. At both field strengths, the variation in internal gadolinium concentration did not show any significant correlation (alpha 相似文献   

不同海拔梯度下小鼠脑含水量的改变及其与脑水肿的关系

目的；探讨急性高原脑水肿的发生机理；方法：实验观察了不同海拔梯度下小鼠脑含水量的改变其与脑水肿的关系；结果：小上低海拔区快速进入高海拔后脑组织的湿干幽会和含水量有增高，以进入高海拔区后的第７天为最高峰；结果；组织学观察表明，此时脑神经细胞肿胀，胞浆内有空泡变性，胶质细胞和微血管周围有明显空晕；结论：由低海拔区快速进入经拔区后可致脑水肿形成。     

Cholesterol enhances the delivery of liposome-encapsulated gallium-67 to tumors

The effect of incorporation of cholesterol (CH) into liposome membranes on the delivery of 67Ga encapsulated in liposomes to tumors was studied. The changes of the blood clearance of liposomes, liposome stability in serum and liposome uptake by the liver and spleen were also examined. Liposomes were prepared from distearoylphosphatidylcholine with various amounts of CH. It became clear that large amounts of CH (above 33 mol%) dramatically enhanced liposomal delivery of 67Ga to sarcoma 180 solid tumor in mice. Large amounts of CH increased the liposome stability in serum and decreased liposome uptake by the liver and spleen after intravenous injection, thus prolonging the blood clearance of liposomes. These observations suggested that the large delivery of 67Ga by CH-rich liposomes resulted from the extended retention and increased amount of liposomes in the circulation, caused by the incorporation of large amounts of CH. Small amounts of CH decreased liposome stability and hastened blood clearance, but had little effect on 67Ga delivery to the tumor. CH-rich liposomes showed high tumor uptake, with high tumor to blood and tumor to tissue ratios of 67Ga. It is anticipated that 67Ga-carrying liposomes will be an excellent tumor imaging agent for clinical use, provided that a correct choice of CH content is made.     

Improved visualization of vessels and hepatic tumors by micro-computed tomography (CT) using iodinated liposomes

OBJECTIVE: The goal of this study was to determine whether iodinated liposomes are a suitable tracer for mice microvessel and liver imaging by preclinical computed tomography (CT). MATERIALS AND METHODS: Iodinated liposomes were evaluated for vessel and liver imaging. A first group of nude mice was imaged by micro-CT after i.v. injection of liposomes at 1 or 2 gI/kg body weight (b.w.) for intervals up to 24 hours. A second group of mice bearing liver micrometastases was imaged after injection of liposomes at 2 gI/kg b.w. for intervals up to 24 hours. RESULTS: Vascular enhancements of 120 +/- 8 and 322 +/- 20 Hounsfield unit (HU) were obtained after injection of liposomes at 1 or 2 gI/kg b.w., respectively. This enhancement decreased with a blood half-life of 135 +/- 10 and 86 +/- 9 minutes, respectively. Liver enhancement of 157 +/- 5 and 235 +/- 23 HU were obtained after injection of iodinated liposomes at 1 and 2 gI/kg b.w., respectively. Liver micrometastases (250 microm) were detectable after injection of iodinated liposomes at 2 gI/kg b.w. CONCLUSIONS: Iodinated liposomes are a suitable contrast agent for vessels and liver imaging by micro-CT allowing clear vascular enhancement and detection of small liver metastases.     

Cholesterol effects on nonelectrolyte membrane transport in human erythrocytes: NMR magnetization transfer studies

The cholesterol content of human erythrocytes was altered by incubating them with sonicated dispersions of cholesterol/phosphatidylcholine at 37°C. ³¹P NMR saturation transfer experiments were used to measure the rate constant for efflux of dimethyl methylphosphonate (DMMP) from the cells, and thereby gain an estimate of the permeability coefficient. It was shown that up to 39% depletion of membrane cholesterol (cholesterol/phospholipid molar ratio of 0.46) increased the efflux rate constant and permeability coefficient of DMMP 1.55-and 1.86-fold, respectively. Enrichment of the membranes with cholesterol by 45% (cholesterol/phospholipid molar ratio of 1.57) on the other hand, decreased the efflux rate constant and permeability coefficient 1.63-and 1.79-fold, respectively. It was concluded that DMMP may be used as a probe molecule to study the functional consequences of changes in the lipid composition of erythrocytes in diseases that are associated with disorders of lipid metabolism.     

The physiology of lipoproteins

The seminal studies of Brown and Goldstein (Science 1986;232:34-47) coupled with the findings of the Framingham study revolutionized our understanding of the metabolic basis for vascular disease. These studies led to the widespread use of the coronary risk lipid profile, which uses the total cholesterol/high-density lipoprotein (HDL) ratio (or low-density lipoprotein [LDL]/HDL ratio) in predicting risk for vascular disease and as a tool for therapeutic management of patients at risk for vascular disease. However, although these methods are predictive of coronary artery disease (CAD) in general, it is also well known that the extent of occlusive disease and CAD varies greatly between individuals with similar cholesterol and HDL lipid profiles. For this reason, the National Cholesterol Education Program Expert Panel revised these guidelines and now recommends monitoring LDL and HDL cholesterol in the context of coronary heart disease risk factors and "risk equivalents." In addition, more recent findings indicate that specific alterations in individual lipoprotein subclasses may account for the variations in CAD in subjects with similar lipid profiles. For example, a preponderance of small, dense LDL particles correlates with a marked increase in risk for myocardial infarction independent of LDL levels. In particular, the association of small, dense LDL with elevated triglycerides (large, less dense VLDL) and reduced HDL has been defined as the atherogenic lipoprotein profile, and the key metabolic defect driving this profile may be elevated levels of triglycerides, specifically large, less dense VLDL. In an attempt to explain the physiologic basis for lipoprotein variations, this review describes the basic metabolic scheme underlying the traditional view of lipoprotein metabolism and physiology. It then examines the identity and role of the various lipoprotein subfractions in an attempt to distill a working model of how lipoprotein abnormalities might account for vascular disease in general and the metabolic syndrome in particular.     

Inhibition of vascular endothelial growth factor-mediated neointima progression with angiostatin or paclitaxel

PURPOSE: Therapeutic angiogenesis represents a new paradigm for treatment of ischemic vascular syndromes. However, vascular endothelial growth factor (VEGF) enhances the rate and degree of plaque formation. This study evaluates the potential to block these effects nonspecifically with paclitaxel or specifically with angiostatin. MATERIALS AND METHODS: Recombinant human VEGF(165) (rhVEGF) was administrated intramuscularly (2-microg/kg single injection) in combination with adventitial delivery of paclitaxel, angiostatin, or vehicle alone at the site of femoral arterial balloon overdilation injury in New Zealand White rabbits (n = 5 per treatment). Five additional animals with no rhVEGF and no adventitial delivery served as procedural controls. All rabbits were fed according to a 0.25% cholesterol diet beginning 28 days before angioplasty. Treated arteries were harvested after 7 days and evaluated to determine intima-to-media (I/M) ratios, macrophage infiltrate, and endothelial cell density. RESULTS: On histologic analysis, the rhVEGF/gel control group exhibited a mean I/M ratio of 0.337 +/- 0.028, a 77% increase over procedural controls, which exhibited a mean I/M of 0.190 +/- 0.010. rhVEGF/paclitaxel reduced I/M ratios to 0.151 +/- 0.007. In contrast, specific antiangiogenic therapy (rhVEGF/angiostatin) reduced I/M ratios to 0.032 +/- 0.003, a 91% decrease relative to rhVEGF/gel and an 83% decrease relative to procedural controls (P =.001 for each comparison). Local macrophages and endothelial cells also decreased with treatment. CONCLUSIONS: This study shows that paclitaxel and angiostatin each afford local protection against rhVEGF-mediated increases in neointima. Angiostatin further prevents progression of underlying neointima. These local therapies may allow broader use of therapeutic angiogenesis while avoiding and treating potentially undesirable effects.     

Engineered liposomes for potential alpha-particle therapy of metastatic cancer.

Disseminated, metastatic cancer is frequently incurable. Targeted alpha-particle emitters hold great promise as therapeutic agents for disseminated disease. (225)Ac is a radionuclide generator that has a 10-d half-life and results in alpha-emitting daughter elements ((221)Fr, (217)At, (213)Bi) that lead to the emission of a total of 4 alpha-particles. The aim of this study was to develop approaches for stable and controlled targeting of (225)Ac to sites of disseminated tumor metastases. Liposomes with encapsulated (225)Ac were developed to retain the potentially toxic daughters at the tumor site. METHODS: (225)Ac was passively entrapped in liposomes. To experimentally test the retention of actinium and its daughters by the liposomes, the gamma-emissions of (213)Bi were measured in liposome fractions, which were separated from the parent liposome population and the free radionuclides, at different times. Under equilibrium conditions the decay rate of (213)Bi was used to determine the concentration of (225)Ac. Measurements of the kinetics of (213)Bi activity were performed to estimate the entrapment of (213)Bi, the last alpha-emitting daughter in the decay chain. RESULTS: Stable pegylated phosphatidylcholine-cholesterol liposomes of different sizes and charge were prepared. Multiple (more than 2) (225)Ac atoms were successfully entrapped per liposome. (225)Ac retention by zwitterionic liposomes was more than 88% over 30 d. Retention by cationic liposomes was lower. A theoretical calculation showed that for satisfactory (213)Bi retention (>50%), liposomes of relatively large sizes (>650 nm in diameter) are required. (213)Bi retention was experimentally verified to be liposome-size dependent. For large liposomes, the measured (213)Bi retention was lower than theoretically predicted (less than 10%). CONCLUSION: This work supports the hypothesis that it may be possible to develop (225)Ac-based therapies by delivering multiple (225)Ac atoms in liposomes. Improvements in the retention of (225)Ac daughters will likely be necessary to fulfill this potential. Because of the size of the liposomal structures required to contain the daughters, the approach is ideally suited for locoregional therapy (e.g., intraperitoneal, intrahepatic artery, or intrathecal).     

The production and evaluation of contrast-carrying liposomes made with an automatic high-pressure system

An automatic, high-pressure system (Microfluidizer) has been found useful for producing contrast-carrying liposomes on an industrial scale. The goal of this investigation was to determine the feasibility of using this new microemulsification process to manufacture contrast-carrying microemulsified liposomes (MELs). Seven contrast media (three ionic, four nonionic) were encapsulated into the MELs. Light and electron microscopy, light scattering, radioisotope, and CT scan techniques were used to characterize these MELs, and the contrast entrapments among the studied media were compared. The contrast-carrying MELs had good properties for imaging normal reticuloendothelial tissues, selectively. They had a narrow size range (0.1-3.0 micron), a single bilayer wall, high liver and spleen upake, and low leakage rates. The nonionic media were significantly more effectively entrapped in the MELs than the ionic media (P less than .05). The iodine-to-lipid weight ratio was about 1:16 for ionic media and 1:4 for nonionic media. Physical properties of the contrast media such as osmotic pressure and charge appeared to affect contrast entrapment. It was concluded that the microemulsification process is a useful system for producing contrast-carrying liposomes continuously, on a large scale and in a reproducible manner.     

Cholesterol enhances the delivery of liposome-encapsulated gallium-67 to tumors

The effect of incorporation of cholesterol (CH) into liposome membranes on the delivery of ⁶⁷Ga encapsulated in liposomes to tumors was studied. The changes of the blood clearance of liposomes, liposome, stability in serum and liposome uptake by the liver and spleen were also examined. Liposomes were prepared from distearoylphosphatidylcholine with various amounts of CH. It became clear that large amounts of CH (above 33 mol%) dramatically enhanced liposomal delivery of ⁶⁷Ga to sarcoma 180 solid tumor in mice. Large amounts of CH increased the liposome stability in serum and decreased liposome uptake by the liver and spleen after intravenous injection, thus prolonging the blood clearance of liposomes. These observations suggested that the large delivery of ⁶⁷Ga by CH-rich liposomes resulted from the extended retention and increased amount of liposomes in the circulation, caused by the incorporation of large amounts of CH. Small amounts of CH decreased liposome stability and hastened blood clearance, but had little effect on ⁶⁷Ga delivery to the tumor. CH-rich liposomes showed high tumor uptake, with high tumor to blood and tumor to tissue ratios, of ⁶⁷Ga. It is anticipated that ⁶⁷Ga-carrying liposomes will be an excellent tumor imaging agent for clinical use, provided that a correct choice of CH content is made.