Modification of liposomes for liver targeting

Artificial cells delivering itaconic acid induce anti-inflammatory memory-like macrophages to reverse acute liver failure and prevent reinjury

Hepatic macrophages represent a key cellular component of the liver and are essential for the progression of acute liver failure (ALF). We construct artificial apoptotic cells loaded with itaconic acid (AI-Cells), wherein the compositions of the synthetic plasma membrane and surface topology are rationally engineered. AI-Cells are predominantly localized to the liver and further transport to hepatic macrophages. Intravenous administration of AI-Cells modulates macrophage inflammation to protect the liver from acetaminophen-induced ALF. Mechanistically, AI-Cells act on caspase-1 to suppress NLRP3 inflammasome-mediated cleavage of pro-IL-1β into its active form in macrophages. Notably, AI-Cells specifically induce anti-inflammatory memory-like hepatic macrophages in ALF mice, which prevent constitutive overproduction of IL-1β when liver reinjury occurs. In light of AI-Cells' precise delivery and training of memory-like hepatic macrophages, they offer promising therapeutic potential in reversing ALF by finely controlling inflammatory responses and orchestrating liver homeostasis, which potentially affect the treatment of various types of liver failure.

Chitosan-based nanoscale delivery systems in hepatocellular carcinoma: Versatile bio-platform with theranostic application

The field of nanomedicine has provided a fresh approach to cancer treatment by addressing the limitations of current therapies and offering new perspectives on enhancing patients' prognoses and chances of survival. Chitosan (CS) is isolated from chitin that has been extensively utilized for surface modification and coating of nanocarriers to improve their biocompatibility, cytotoxicity against tumor cells, and stability. HCC is a prevalent kind of liver tumor that cannot be adequately treated with surgical resection in its advanced stages. Furthermore, the development of resistance to chemotherapy and radiotherapy has caused treatment failure. The targeted delivery of drugs and genes can be mediated by nanostructures in treatment of HCC. The current review focuses on the function of CS-based nanostructures in HCC therapy and discusses the newest advances of nanoparticle-mediated treatment of HCC. Nanostructures based on CS have the capacity to escalate the pharmacokinetic profile of both natural and synthetic drugs, thus improving the effectiveness of HCC therapy. Some experiments have displayed that CS nanoparticles can be deployed to co-deliver drugs to disrupt tumorigenesis in a synergistic way. Moreover, the cationic nature of CS makes it a favorable nanocarrier for delivery of genes and plasmids. The use of CS-based nanostructures can be harnessed for phototherapy. Additionally, the incur poration of ligands including arginylglycylaspartic acid (RGD) into CS can elevate the targeted delivery of drugs to HCC cells. Interestingly, smart CS-based nanostructures, including ROS- and pH-sensitive nanoparticles, have been designed to provide cargo release at the tumor site and enhance the potential for HCC suppression.

Effect of hydrophile-lipophile balance of the linker in Gal/GalNAc ligands on high-affinity binding of galactosylated liposomes by the asialoglycoprotein receptor

In this study, we explored the effect of the hydrophile-lipophile balance (HLB) in the linker unit of Galactose (Gal)/N-acetylgalactosamine (GalNAc) ligands on their affinity toward asialoglycoprotein receptors (ASGPRs). Two Gal/GalNAc ligands with lipophilic linkers-{(5-cholesten-3b-ol)[(2-acetamido-2-deoxy-d-galactopyranose-6-o)sebacate]} (CHS-6-GalNAc) and {(5-cholesten-3b-ol)[(d-galactopyranose-6-o)sebacate]} (CHS-6-Gal)-and two with hydrophilic linkers-{(5-cholesten-yl)[(4-O-b-D-galactopyranosyl)-D-glucitol-6-yl]sebacate} (CHS-1-Gal) and {(5-cholesten-3a-ol)[(2-acetamido-2-deoxy-d-galactopyranose-6-o)3,6-dioxa-octanedioate]} (CHS-PEG₂-6-GalNAc)-were synthesized by enzymatic catalysis. Compared with unmodified liposomes, all Gal/GalNAc ligand-modified liposomes showed higher efficiency toward the hepatocyte target as evaluated by weighted-average overall drug-targeting efficiency (Te*) in vivo and HepG2 cell uptake efficiency in vitro. The ligands containing linkers with high HLB values (i.e., CHS-PEG₂-6-GalNAc and CHS-1-Gal) exhibited higher ASGPR affinity than those containing linkers with low HLB values (i.e., CHS-6-GalNAc and CHS-6-Gal). We used molecular-dynamics (MD) simulations to investigate the structure-activity relationship between the HLB value of the linker in a ligand and ASGPR affinity. MD simulation results indicated that a Gal/GalNAc ligand with a more hydrophilic linker (i.e., higher HLB value) unit tended to have a higher solvent-accessible surface area (SASA), leading to lower steric hindrance for effective ASGPR recognition. The results of this study will provide an improved design for Gal/GalNAc ligand-based surface-modified liposomes with high ASGPR affinity.

The hepatic lipidome: From basic science to clinical translation

The liver is the key organ involved in lipid metabolism and transport. Excessive lipid accumulation due to dysregulated lipid metabolism predisposes the liver to steatosis, cirrhosis, and hepatocellular carcinoma. Lipids are generally compartmentalized in specialized organelles called lipid droplets that enable cells to store and release lipids in a regulated manner. However, during flux-in and flux-out of droplets, lipids are converted into toxic species leading to lipid-mediated liver damage. Lipids are categorized into 'toxic' or 'healthy' lipids that are involved in liver disease pathogenesis or resolution, respectively. Lipidomic analysis have revealed unique lipid signature that correlates with the disease progression therefore being used for disease diagnosis. In this comprehensive review, we provide an overview on hepatic lipid homeostasis, lipid compartmentalization mechanisms and lipidomic profiles in different liver diseases. We further discuss promising therapeutics targeting the hepatic lipidome including pro-resolving lipids, liposomes, and small-molecule inhibitors for the treatment of liver diseases.

Chitosan-coated liposomes loaded with butyric acid demonstrate anticancer and anti-inflammatory activity in human hepatoma HepG2 cells

Butyric acid (BA) has been reported to induce anticancer effects on hepatocellular carcinoma (HCC) cells both in vitro and in vivo. However, its delivery and release in cancer tissues must be optimized. On the basis of these requirements, we prepared liposomes coated with chitosan and uncoated liposomes and both types were loaded with BA through a thin-film hydration method. The liposomes coated or uncoated with chitosan had a mean hydrodynamic size of 83.5 and 110.3 nm, respectively, with a homogeneous size distribution of the particles. For evaluation of the biological effects of the nanoformulations, the hepatoblastoma (HB) HepG2 cell line was utilized. BA-loaded liposomes coated with chitosan showed a considerable higher cytotoxicity than both uncoated liposomes and free BA, with IC50 values, after 72 h of incubation, of 7.5, 2.5 and 1.6 mM, respectively. Treatment of HepG2 cells for 5 h with the BA-loaded liposomes coated with chitosan at 5 mM lowered the extent of the increase in IL-8, IL-6, TNF-α and TGF-β expression of approximately 64, 58, 85 and 73.8%, respectively, when compared to the untreated cells. The BA-loaded liposomes coated with chitosan had marked capacity to be internalized in human HB cells showing an increased cytotoxic activity when compared with free BA and important anti-inflammatory effects by inhibiting production of cytokines with a central role in liver cell survival.

Hepatic Stellate Cells in Liver Fibrosis and siRNA-Based Therapy

Hepatic fibrosis is a reversible wound-healing response to either acute or chronic liver injury caused by hepatitis B or C, alcohol, and toxic agents. Hepatic fibrosis is characterized by excessive accumulation and reduced degradation of extracellular matrix (ECM). Excessive accumulation of ECM alters the hepatic architecture leading to liver fibrosis and cirrhosis. Cirrhosis results in failure of common functions of the liver. Hepatic stellate cells (HSC) play a major role in the development of liver fibrosis as HSC are the main source of the excessive production of ECM in an injured liver. RNA interference (RNAi) is a recently discovered therapeutic tool that may provide a solution to manage multiple diseases including liver fibrosis through silencing of specific gene expression in diseased cells. However, gene silencing using small interfering RNA (siRNA) is encountering many challenges in the body after systemic administration. Efficient and stable siRNA delivery to the target cells is a key issue for the development of siRNA therapeutic. For that reason, various viral and non-viral carriers for liver-targeted siRNA delivery have been developed. This review will cover the current strategies for the treatment of liver fibrosis as well as discussing non-viral approaches such as cationic polymers and lipid-based nanoparticles for targeted delivery of siRNA to the liver.

Liver-targeting liposome drug delivery system and its research progress in liver diseases

Liposome-based targeted therapy is mainly divided into active targeting, passive targeting, and physical and chemical targeting. In terms of liver targeting, because of specificity, active liver-targeting liposomes have received more and more attention, and these types of liposomes can be used in liver fibrosis, hepatitis and other chronic liver diseases. In addition, the particle size could control the passive liver targeting of liposomes, while the liver-targeted liposomes of the physical and chemical targeting type have advantages in treating hepatic carcinoma. In this paper, we focus on the basics and application of liver-targeting liposome drug delivery system in hepatic diseases.

Improved antitumor activity and reduced cardiotoxicity of epirubicin using hepatocyte-targeted nanoparticles combined with tocotrienols against hepatocellular carcinoma in mice

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death worldwide. Epirubicin (EPI), an anthracycline derivative, is one of the main line treatments for HCC. However, serious side effects including cardiomyopathy and congestive heart failure limit its long term administration. Our main goal is to develop a delivery strategy that ensures improved efficacy of the chemotherapeutic agent together with reduced cardiotoxicity. In this context, EPI was loaded in chitosan-PLGA nanoparticles linked with asialofetuin (EPI-NPs) selectively targeting hepatocytes. In an attempt to reduce cardiotoxicity, targeted EPI-NPs were coadministered with tocotrienols. EPI-NPs significantly enhanced the antiproliferative effect compared to free EPI as studied on Hep G2 cell line. Nanoencapsulated EPI injected in HCC mouse model revealed higher p53-mediated apoptosis and reduced angiogenesis in the tumor. Combined therapy of EPI-NPs with tocotrienols further enhanced apoptosis and reduced VEGF level in a dose dependent manner. Assessment of cardiotoxicity indicated that EPI-NPs diminished the high level of proinflammatory cytokine tumor necrosis factor-α (TNF-α) as well as oxidative stress-induced cardiotoxicity as manifested by reduced level of lipid peroxidation products (TBARS) and nitric oxide (NO). EPI-NPs additionally restored the diminished level of superoxide dismutase (SOD) and reduced glutathione (GSH) in the heart. Interestingly, tocotrienols provided both antitumor activity and higher protection against oxidative stress and inflammation induced by EPI in the heart. This hepatocyte-targeted biodegradable nanoparticle/tocotrienol combined therapy represents intriguing therapeutic strategy for EPI providing not only superior efficacy but also higher safety levels.

Galactosylated nanostructured lipid carriers for delivery of 5-FU to hepatocellular carcinoma

The aim of the present study was to design a targeted delivery system of 5-fluorouracil (5-FU) for hepatocellular carcinoma (HCC). Lactobionic acid (LB) was conjugated to stearyl amine (SA) by a chemical reaction. The nanostructured lipid carriers (NLCs), containing LB conjugate, lecithin, glyceryl monostearate, oil [oleic acid (OA) or Labrafac 5 or 10%], and 5-FU, were dissolved in alcohol/acetone, the oil phase was added to the aqueous phase containing Tween 80 or Solutol(®) HS15 (0.25 or 0.5%), and NLCs were prepared by an emulsification-solvent diffusion method. Physical properties and drug release were studied in NLCs. The thiazolyl blue tetrazolium bromide assay was used to study the cytotoxicity of NLCs on HepG(2) cells, and the cellular uptake of NLCs was determined by flow cytometry. Fourier transform infrared spectroscopy and (1)H-NMR spectra confirmed the successful conjugation of LB and SA. The optimized NLCs consisted of 0.5% Solutol HS15 and 10% OA oil. The particle size of these nanoparticles was 139.2 nm, with a zeta potential of -18 mV, loading efficiency of 34.2%, release efficiency after 2 hours of the release test was 72.6%, and crystallinity was 0.63%. The galactosylated NLCs of 5-FU were cytotoxic on the HepG(2) cell line in a half concentration of 5-FU and seems promising in reducing 5-FU dose in HCC.

N-trimethyl chitosan nanoparticle-encapsulated lactosyl-norcantharidin for liver cancer therapy with high targeting efficacy

N-Trimethyl chitosan (TMC) was synthesized and used to prepare lactosyl-norcantharidin TMC nanoparticles (Lac-NCTD-TMC-NPs) using an ionic cross-linkage process. Lac-NCTD-TMC-NPs with an average particle size of 120.6 ± 1.7 nm were obtained, with an entrapment efficiency of 69.29% ± 0.76%, and a drug-loading amount of 9.1% ± 0.07%. The release of Lac-NCTD-TMC-NPs in vitro was investigated through a dialysis method, and its sustained effect was evident. In the human liver cancer cell line HepG2, the half-maximum inhibiting concentration (IC(50)) of TMC-encapsulated Lac-NCTD (Lac-NCTD-TMC-NPs) was only 24.2% that of free Lac-NCTD at 24 hours. Lac-NCTD induced HepG2 cell death by triggering apoptosis. In vitro cellular uptake and in vivo NIR fluorescence real-time imaging both indicated a high targeting efficacy. In comparison with Lac-NCTD and Lac-NCTD chitosan NPs (Lac-NCTD-CS-NPs ), Lac-NCTD-TMC-NPs had the strongest antitumor activity on the murine hepatocarcinoma 22 subcutaneous model.

FROM THE CLINICAL EDITOR

In this article the preparation of N-trimethyl chitosan-encapsulated lactosyl-norcantharidin nanoparticles is described that displayed efficient targeting and sustained release in a hepatocarcinoma SC murine model.

In vivo targeted gene delivery by cationic nanoparticles for treatment of hepatocellular carcinoma

BACKGROUND

Transgene expression in vivo for therapeutic purposes will require methods that allow for efficient gene transfer into cells. Although current vector technologies are being improved, the development of novel vector systems with improved targeting specificity, higher transduction efficiencies and improved safety is necessary.

METHODS

Asialoglycoprotein receptor-targeted cationic nanoparticles for interleukin (IL)-12 encapsulation (NP1) or adsorption (NP2) have been formulated by blending poly(D,L-lactic-co-glycolic) acid (PLGA) (50 : 50) with the cationic lipid 1,2-dioleoyl-3-(trimethylammonium) propane (DOTAP) and the ligand asialofetuin (AF), by using a modified solvent evaporation process.

RESULTS

We present a novel targeted lipopolymeric vector, which improves significantly the levels of luciferase gene expression in the liver upon i.v. administration. Targeted-NP2 particles showed a five- and 12-fold higher transfection activity in the liver compared to non-targeted (plain) complexes or naked pCMV DNA, respectively. On the other hand, BNL tumor-bearing animals treated with AF-NP1 containing the therapeutic gene IL-12, showed tumor growth inhibition, leading to a complete tumor regression in 75% of the treated mice, without signs of recurrence. High levels of IL-12 and interferon-gamma were detected in the sera of treated animals. Mice survival also improved considerably. Tumor treatment with AF-NP2 formulations lead only to a retardation in the tumor growth.

CONCLUSIONS

In the present study, we have developed an efficient targeted non-viral vector for IL-12 gene transfer in hepatocellular carcinoma in vivo, by employing non-toxic cationic PLGA/DOTAP/AF nanoparticles. These results demonstrate for the first time that this cationic system could be used successfully and safely for delivery of therapeutic genes with antitumor activity into liver tumors with targeting specificity.

Toxicity of hepatotoxins: new insights into mechanisms and therapy

Liver injury caused by hepatotoxins, such as carbon tetrachloride (CCl4), ethanol, and acetaminophen (APAP), is characterised by varying degrees of hepatocyte degeneration and cell death via either apoptosis or necrosis. The generation of reactive intermediate metabolites from the metabolism of hepatotoxins, and the occurrence of reactive oxygen species (ROS) during the inflammatory reaction account for a variety of pathophysiologic pathways leading to cell death, such as covalent binding, disordered cytosolic calcium homeostasis, glutathione (GSH) depletion, onset of mitochondrial permeability transition (MPT) and associated lipid peroxidation. The metabolism of hepatotoxins by cytochrome P-450 enzyme subtypes is a key step of the intoxication; therefore, enzyme inhibitors are shown to minimise the hepatotoxin-associated liver damage. Understanding the function of transcription factors, such as nuclear factor kappaB (NF-kappaB) in acute liver injury, may provide some answers as to the molecular mechanisms of toxic insults. Moreover, substantial evidence exists that MPT is involved in ROS-associated hepatocellular injury and new findings offer a novel therapeutic approach to attenuate cell damage by blocking the onset of MPT. Thus, oxidant stress and lipid peroxidation are crucial elements leading to hepatotoxin-associated liver injury. In addition to specific treatment for a given hepatotoxin, the general strategy for prevention and treatment of the damage includes reducing the production of reactive metabolites of the hepatotoxins, using anti-oxidative agents, and selectively targeting therapeutics to Kupffer cells or hepatocytes for on-going processes, which play a role in mediating a second phase of the injury.

Liposomal irinotecan: formulation development and therapeutic assessment in murine xenograft models of colorectal cancer

PURPOSE

The purpose is to demonstrate whether an appropriately designed liposomal formulation of irinotecan is effective in treating mice with liver-localized colorectal carcinomas.

EXPERIMENTAL DESIGN

Irinotecan was encapsulated in 1,2-distearoyl-sn-glycero-3-phosphocholine/cholesterol (55:45 molar ratio) liposomes using an ionophore (A23187)-generated transmembrane proton gradient. This formulation was evaluated in vivo by measuring plasma elimination of liposomal lipid and drug after i.v. administration. Therapeutic activity was determined in SCID/Rag-2M mice bearing s.c. LS180 tumors or orthotopic LS174T colorectal metastases.

RESULTS

Drug elimination from the plasma was significantly reduced when irinotecan was administered in the liposomal formulation. At 1 hour after i.v. administration, circulating levels of the liposomal drug were 100-fold greater than that of irinotecan given at the same dose. High-performance liquid chromatographic analysis of plasma samples indicated that liposomal irinotecan was protected from inactivating hydrolysis to the carboxylate form. This formulation exhibited substantially improved therapeutic effects. For the LS180 solid tumor model, it was shown that after a single injection of liposomal irinotecan at 50 mg/kg, the time to progress to a 400-mg tumor was 34 days (as compared with 22 days for animals treated with free drug at an equivalent dose). In the model of colorectal liver metastases (LS174T), a median survival time of 79 days was observed after treatment with liposomal irinotecan (50 mg/kg, given every 4 days for a total of three doses). Saline and free drug treated mice survived for 34 and 53 days, respectively.

CONCLUSIONS

These results illustrate that liposomal encapsulation can substantially enhance the therapeutic activity of irinotecan and emphasize the potential for using liposomal irinotecan to treat liver metastases.

The prospects of hepatic drug delivery and gene therapy

Liver targeted therapy is designed to deliver a substance preferentially to the organ in order to increase the accumulation, improve the therapeutic effect and reduce toxicity to other organs. The aim of selective targeting is to deliver a substance to a specific cell type in the liver. A variety of vehicles have been designed and further modified for selective targeting of therapeutics to the liver. The targeting properties and strategies of commonly used agents, such as liposomes, microspheres and recombinant chylomicrons, are discussed. Viral and non-viral vectors, such as cationic liposomes, reconstituted chylomicron remnants, adenoviruses, adeno-associated viruses, retroviruses, and SV-40, are currently being evaluated for the delivery of DNA to the liver. New developments in improving the targeting efficiency of the available vectors while avoiding their disadvantages have made their use in clinical trials of various genetic disorders possible. For viral hepatitis, antisense and ribozyme techniques are being employed with selective targeting approaches. A commonly employed current strategy for targeting hepatocellular carcinoma cells is to make the tumour cells convert non-toxic 'prodrugs' to toxic metabolites in situ, achieving a high concentration of the toxic product in the local milieu, while avoiding systemic toxicity. Although gene therapy itself is in its infancy, some encouraging results have been developed in studies of familial hypercholesterolaemia, haemophilia, alpha1-antitrypsin deficiency and Crigler-Najjar syndrome. The potential strengths as well as the problems with these studies are discussed.

Gene therapy of hepatocarcinoma: a long way from the concept to the therapeutical impact

Hepatocellular carcinoma (HCC), the most prevalent histological form of primary liver cancer is one of the most frequent cancer worldwide. This pathology still requires the development of new therapeutical approaches. Gene therapy strategies focusing on the genetic manipulation of accessory cells involved in the immune reaction against cancer cells, or on the direct transduction of tumor cells with transgenes able to "suicide" cancer cells have been largely developed for more than ten years.

Gene delivery to the rat liver using cationic lipid emulsion/DNA complex: comparison between intra-arterial, intraportal and intravenous administration

Objective

To compare the efficiency of intra-arterial, intraportal, and intravenous administration of cationic lipid emulsion/DNA complex, as used for gene transfer to rat liver.

Materials and Methods

DNA-carrier complex for the in-vivo experiment was prepared by mixing DNA and a cationic lipid emulsion. According to the administration route used (intra-arterial, intraportal, or intravenous), the animals were assigned to one of three groups. The heart, lung, liver, spleen and kidneys were removed and assayed for total protein and luciferase concentration.

Results

The cationic lipid emulsion/DNA complex used successfully transfected the various organs via the different administration routes employed. Luciferase activity in each organ of untreated animals was negligible. Liver luciferase values were significantly higher in the groups in which intra-arterial or intraportal administration was used.

Conclusion

The intra-arterial or intraportal administration of cationic lipid emulsion/DNA complex is superior to intravenous administration and allows selective gene transfer to the liver.

Increased receptor-mediated gene delivery to the liver by protamine-enhanced-asialofetuin-lipoplexes

A novel lipidic vector composed of DOTAP/Chol liposomes, asialofetuin (AF), protamine sulfate and DNA has been developed. The resulting protamine-AF-lipoplexes improved significantly the levels of gene expression in cultured cells and in the liver upon i.v. administration. Lipoplexes containing the optimal amount of AF (1 microg/microg DNA) showed a 16-fold higher transfection activity in HepG2 cells than non-targeted (plain) complexes. The uptake by cells having asialoglycoprotein receptors (ASGPr) on their plasma membrane was decreased by the addition of free AF, indicating that AF-lipoplexes were taken up specifically by cells via ASGPr-mediated endocytosis. Results from transfections performed in cells defective in ASGPr, ie HeLa cells, confirmed this mechanism. By addition of the condensing peptide, protamine sulfate, smaller complexes were obtained, which enhanced even more the uptake of AF-complexes in HepG2 cells and in the liver. The optimal amount of protamine was 0.4 microg/mcirog DNA, and gene expression was about 5-fold over that obtained with AF-lipoplexes in the absence of the peptide, and 75-fold higher than that with plain conventional lipoplexes. Protamine-AF-lipoplexes increased by a factor of 12 luciferase gene expression in the liver of mice administered systemically via the tail vein, compared to plain complexes. In summary, our findings extend the scope of previous studies where AF-lipoplexes were used to introduce DNA into hepatocytes. The combination of targeting and protamine condensation obviated the need for partial hepatectomy, commonly required to obtain efficient gene delivery in this organ. Since protamine sulfate has been proven to be non-toxic in humans, the novel liver-specific vector described here may be useful for the delivery of clinically important genes to this organ.

In vivo liver-directed gene transfer in rats and pigs with large anionic multilamellar liposomes: routes of administration and effects of surgical manipulations on transfection efficiency

Conventional large (500-800 nm) multilamellar liposomes encapsulating DNA have been used in vivo as gene vectors into rat and pig liver. By using the intraportal vein route, high dose DNA (10 mg/kg) provided low efficiency and transient luciferase gene expression in the liver. This gene expression was, however, increased by liver resection (> 50%), ischemia (20 min) or orthotopic transplantation. As evidenced by histochemical analysis of beta-galactosidase expression, the gene transfection mainly ensued in Kupffer cells, but spleen and lung were contaminated. In comparison, injection into the bile duct of even 25-fold lower dose of liposome-encapsulated DNA (0.4 mg/kg) produced higher (100-fold) and long-lasting (during 6 days, at least) luciferase expression in rat liver. The gene expression was restricted to the liver and enhanced by liver resection. By this route, transgene-expressing cells were mainly hepatocytes. A treatment with colchicine prior to the administration of the vector allowed the persistence of relative high gene expression for at least 7 days. In pigs, qualitatively similar, but quantitatively less efficient gene expression was obtained by either the portal vein or the bile duct route. These results indicate that intrabile duct route might render large non-viral vectors applicable to gene transfer into the hepatocytes. The efficiency of liposome-mediated gene transfer into the liver can be increased by liver resection, ischemia or transplantation performed before DNA injection.

Liver-directed gene therapy: promises, problems and prospects at the turn of the century

Although liver-directed gene therapy arrived later than gene therapy directed at bone marrow cells, intrinsic advantages of the liver as a target organ make it likely that gene therapy for liver diseases will be among the first therapeutically relevant applications of this treatment modality at the onset of the 21st century. Vectorology for gene transfer to the liver is advancing rapidly, and it is safe to predict that gene therapy vehicles that will be in clinical use a decade from now, have not yet been developed. None of the currently available modes of gene transfer to the liver is optimal for all types of applications. Nonetheless, the concerted effort of many investigators has provided a wide choice of non-viral and viral vectors for gene transfer to the liver for use in specific situations. Original strategies for liver-directed gene therapy included substitution of missing gene products, overexpression of intrinsic or extrinsic genes and inhibition of expression of specific genes. To the list is now added the possibility of site-specific correction or generation of mutations within specific genes in somatic cells of living adult animals. Thus, despite some initial faux pas, liver-directed gene therapy is poised to make an important impact on health care in the year 2000 and beyond.

Administration of the tris salt of alpha-tocopheryl hemisuccinate inactivates CYP2E1, enhances microsomal alpha-tocopherol levels and protects against carbon tetrachloride-induced hepatotoxicity

A series of tocopherol compounds were examined for their capacity to protect against carbon tetrachloride (CCl4)-induced hepatotoxicity in rats. Of the tocopherol compounds tested in our study, only the tris salt of d-alpha-tocopheryl hemisuccinate (TS-tris) protected against CCl4-induced hepatotoxicity. The administration of d-alpha-tocopherol (alpha-T) and the nonhydrolyzable tocopherol ether, d-alpha-tocopheryloxybutyrate tris salt (TSE-tris), failed to protect against CCl4-induced hepatotoxicity. TS-tris was the only tocopherol which significantly decreased CYP2E1 activity after 18 h. This decrease in CYP2E1 activity is likely to limit the activation of CCl4 and protect against CCl4-induced hepatotoxicity. Our results also suggest that TS-tris protection against CCl4-induced hepatotoxicity correlates with the enhanced capacity of TS-tris to deliver alpha-T and increase the antioxidant status of hepatocytes. TSE-tris did not increase cellular alpha-T levels, while administration of TS-tris produced large increases in alpha-T levels in liver homogenates as well as in liver nuclei, microsomes, mitochondria and plasma membranes. This enhanced ability to deliver tocopherol equivalents to parenchymal liver cells may be related in part to the ability of TS-tris to form liposomes in aqueous solutions. TS-tris administration protected against CCl4-induced microsomal lipid peroxide formation and inactivation of the microsomal enzyme glucose-6-phosphatase (G6Pase). Supplementation of animals with alpha-T protected against microsomal lipid peroxide formation but not against the inactivation of G6Pase. Based on our findings, we propose that high cellular levels of alpha-T protect against CCl4-induced hepatotoxicity by scavenging CCl4 radicals as well as protecting against lipid peroxidation. Our results do not support the importance of microsomal lipid peroxidation as an early event in acute CCl4-induced hepatic necrosis.

Increased liver uptake of liposomes and improved targeting efficacy by labeling with asialofetuin in rodents

To improve liposome-directed therapy of liver disease and gene delivery, it would be beneficial to selectively target hepatocytes. For this purpose, conventional liposomes (CL) were labeled with asialofetuin (AF), an asialoglycoprotein. The biodistribution of AF-labeled liposomes (AF-L) in mice and their incorporation into rat hepatocytes, and their potential use in acute liver injury, were investigated. AF-L displayed a quicker plasma clearance than CL, and 25.4%, 2.7%, and 1.2% of the injected dose remained in the plasma versus 47.0%, 26.1%, and 9.5% of CL, respectively at 2, 4, and 20 hours after the injection. Total liver uptake of AF-L (73%+/-3.9%) was markedly higher (P < .005) than CL (16.5%+/-1.8%) 4 hours after the injection. Liposomal radioactivity (cpm/mg) was greatly enhanced in the liver (11-fold) during the first 4 hours after the administration of 14C-AF-L, and was much higher than in 14C-CL-injected mice (1.5-fold). In vitro incubation of isolated rat hepatocytes with 14C-AF-L or intravenous injection of 14C-AF-L in rats resulted in higher hepatocyte-bound radioactivity compared with 14C-CL (P < .01-.005). AF-L-associated 1,1'-dilinoleyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) fluorescent signals were not only located in Kupffer cells, but also in hepatocytes, in which bile canaliculus networks were imaged. Intravenous administration of vitamin E (VE)-associated CL (VE-CL, 1 mg/mouse) significantly lowered alanine transaminase (ALT) levels in CCl4-treated mice (196+/-79 vs. 2,107+/-235 U/mL; P < .01). The ALT level in CCl4 + VE-AF-L group was decreased to 38+/-16 units/mL, which was significantly lower than the CC14 + VE-CL group (P < .05). In conclusion, labeling liposomes with AF led to a shortened liposome plasma half-life and greatly enhanced uptake of AF-L liposome by the liver. The enhanced uptake resulted from an increased incorporation of hepatocytes with AF-L liposomes. VE-associated AF liposomes further improved the protective effect of VE liposomes on CC14-induced acute liver injury in mice. Preferential hepatocyte incorporation of AF-L liposomes suggests a useful hepatocyte-targeting approach for drug delivery and gene transfection.