Improvement of therapeutic effect of human recombinant superoxide dismutase on ischemic acute renal failure in the rat via cationization and conjugation with polyethylene glycol

Single enzyme nanoparticle, an effective tool for enzyme replacement therapy

The term "single enzyme nanoparticle" (SEN) refers to a chemically or biologically engineered single enzyme molecule. SENs are distinguished from conventional protein nanoparticles in that they can maintain their individual structure and enzymatic activity following modification. Furthermore, SENs exhibit enhanced properties as biopharmaceuticals, such as reduced antigenicity, and increased stability and targetability, which are attributed to the introduction of specific moieties, such as poly(ethylene glycol), carbohydrates, and antibodies. Enzyme replacement therapy (ERT) is a crucial therapeutic option for controlling enzyme-deficiency-related disorders. However, the unfavorable properties of enzymes, including immunogenicity, lack of targetability, and instability, can undermine the clinical significance of ERT. As shown in the cases of Adagen®, Revcovi®, Palynziq®, and Strensiq®, SEN can be an effective technology for overcoming these obstacles. Based on these four licensed products, we expect that additional SENs will be introduced for ERT in the near future. In this article, we review the concepts and features of SENs, as well as their preparation methods. Additionally, we summarize different types of enzyme deficiency disorders and the corresponding therapeutic enzymes. Finally, we focus on the current status of SENs in ERT by reviewing FDA-approved products.

Development of PEGylated serum albumin with multiple reduced thiols as a long-circulating scavenger of reactive oxygen species for the treatment of fulminant hepatic failure in mice

Reactive oxygen species (ROS) are involved in the pathophysiology of fulminant hepatic failure. Therefore, we developed polyethylene glycol-conjugated bovine serum albumin with multiple reduced thiols (PEG-BSA-SH) for the treatment of fulminant hepatic failure. As a long-circulating ROS scavenger, PEG-BSA-SH effectively scavenged highly reactive oxygen species and hydrogen peroxide in buffer solution. PEG-BSA-SH showed a long circulation time in the plasma after intravenous injection into mice. Fulminant hepatic failure was induced by intraperitoneal injection of lipopolysaccharide and D-galactosamine (LPS/D-GalN) into mice. The LPS/D-GalN-induced elevation of plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels was significantly inhibited by a bolus intravenous injection of PEG-BSA-SH. Furthermore, the changes in hepatic lipid peroxide and hepatic blood flow were effectively suppressed by PEG-BSA-SH. In contrast, L-cysteine, glutathione, and dithiothreitol, three traditional reduced thiols, had no statistically significant effects on the serum levels of ALT or AST. These findings indicate that PEG-BSA-SH is a promising ROS scavenger and useful in the treatment of fulminant hepatic failure.

Pharmacokinetic considerations for targeted drug delivery

Drug delivery systems involve technology designed to maximize therapeutic efficacy of drugs by controlling their biodistribution profile. In order to optimize a function of the delivery systems, their biodistribution characteristics should be systematically understood. Pharmacokinetic analysis based on the clearance concepts provides quantitative information of the biodistribution, which can be related to physicochemical properties of the delivery system. Various delivery systems including macromolecular drug conjugates, chemically or genetically modified proteins, and particulate drug carriers have been designed and developed so far. In this article, we review physiological and pharmacokinetic implications of the delivery systems.

Protective role of extracellular superoxide dismutase in renal ischemia/reperfusion injury

Extracellular superoxide dismutase (SOD3) is highly expressed in renal tissues and a critical regulator of vascular function. We hypothesized that deletion of SOD3 would attenuate recovery of renal blood flow (RBF) and increase oxidative stress and injury following renal ischemia/reperfusion (I/R). To test this, we evaluated SOD expression and activity, basal superoxide production, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in kidneys from male and female wild-type (WT) and SOD3-knockout mice. RBF, measured using an ultrasonic flow probe, and histological indices of oxidative stress and injury were assessed after 1 h of ischemia. Following ischemia, RBF was attenuated in kidneys from male, but not female, knockout mice compared with their WT counterparts. Total SOD activity was significantly reduced in male knockout compared with WT male mice but was similar in female mice of both genotypes, suggesting upregulated SOD1 activity. Basal superoxide production and NADPH oxidase activity were unrelated to the differences in RBF. After 24 h, kidneys from both genders of knockout mice were found to have more oxidative stress (3-nitrotyrosine immunohistochemistry) and renal cast formation than those from WT mice. Thus, our study found a key role for SOD3 in regulating renal I/R injury.

Prevention of ischemia/reperfusion injury by hepatic targeting of nitric oxide in mice

Macromolecular nitric oxide (NO) donors possessing the ability to target a specific type of liver cells were developed for delivering NO to the liver. Six NO molecules were covalently bound to mannosylated (Man) or galactosylated (Gal) bovine serum albumin (BSA) through an S-nitrosothiol linkage to obtain Man-poly SNO-BSA and Gal-poly SNO-BSA, respectively. The carrier parts of Man-poly SNO-BSA and Gal-poly SNO-BSA predominantly accumulated in the liver after intravenous injection in mice. In an ischemia/reperfusion injury mouse model, in which hepatic injury was induced by occluding the portal vein for 15 min followed by a 6 h reperfusion, the elevation of plasma alanine aminotransferase and aspartate aminotransferase levels was significantly inhibited by a bolus intravenous injection of Man-poly SNO-BSA or Gal-poly SNO-BSA, just before the start of reperfusion. In marked contrast, S-nitroso-N-acetyl penicillamine and NO-conjugated BSA, two classical S-nitrosothiols, had no statistically significant effects on the serum levels of the markers. The released NO in mouse liver was detected by electron spin resonance spectrometry only in the liver of mice receiving Man-poly SNO-BSA or Gal-poly-SNO-BSA. These findings indicate that Man-poly SNO-BSA and Gal-poly SNO-BSA are promising compounds for preventing hepatic ischemia/reperfusion injury by delivering pharmacologically active NO to the liver.

Catalase delivery for inhibiting ROS-mediated tissue injury and tumor metastasis

Reactive oxygen species (ROS) have been suggested to be involved in a variety of human diseases. Catalase, an enzyme degrading hydrogen peroxide, can be used as a therapeutic agent for such diseases, but its successful application will depend on the distribution of the enzyme to the sites where ROS are generated. Chemical modification techniques have been used to control the tissue distribution of catalase, and delivery to hepatocytes (galactosylation), liver nonparenchymal cells (mannosylation or succinylation), kidney (cationization) and the blood pool (PEGylation) has been achieved. The effectiveness of catalase delivery has been demonstrated in animal models for hepatic ischemia/reperfusion injury, chemical-induced tissue injuries and tumor metastasis to the liver, lung and peritoneal organs. Significant inhibition was observed in the ROS-mediated oxidative tissue damages and ROS-mediated upregulation of expression of genes responsible for recruitment of inflammatory cells and for metastatic growth of tumor cells. Because oxygen plays a fundamental key role in our life and oxidative stress is implicated in a wide variety of human diseases, catalase delivery could have wide application in the near future.

Combining cisplatin with cationized catalase decreases nephrotoxicity while improving antitumor activity

Cisplatin is frequently used to treat solid tumors; however, nephrotoxicity due to its reactive oxygen species-mediated effect limits its use. We tested the ability of cationized catalase, a catalase derivative, to inhibit nephrotoxicity in cisplatin-treated mice. Immunohistochemical analysis showed that the catalase derivative concentrated in the kidney more efficiently than native catalase. Repeated intravenous doses of cationized catalase significantly decreased cisplatin-induced changes in serum creatinine, blood urea nitrogen, nitrite/nitrate levels, lactic dehydrogenase activity, and renal total glutathione and malondialdehyde contents. In addition, cationized catalase effectively blunted cisplatin-induced proximal tubule necrosis but had no significant effect on the cisplatin-induced inhibition of subcutaneous tumor growth. Repeated doses of catalase, especially cationized catalase, significantly increased the survival of cisplatin-treated tumor-bearing mice preventing cisplatin-induced acute death. Our studies suggest that catalase and its derivatives inhibit cisplatin-induced nephrotoxicity, thus improving the efficiency of cisplatin to treat solid tumors.

Inhibition of tumour metastasis by targeted delivery of antioxidant enzymes

Metastasis is one of the most harmful aspects of malignant neoplasm. Interaction of tumour cells with normal cells such as tissue macrophages may generate reactive oxygen species, which would affect various aspects of tumour metastasis. Reactive oxygen species cause damage to both tumour and normal cells and some of them, especially hydrogen peroxide, can also act as intracellular second messengers at sublethal concentrations to increase the transcription of various genes, which can then accelerate the proliferation of tumour cells in metastatic colonies. Therefore, eliminating hydrogen peroxide is one approach to inhibiting tumour metastasis. In this article, the roles of reactive oxygen species in tumour metastasis are reviewed, and the strategies to inhibit tumour metastasis by the targeted delivery of catalase, an enzyme that detoxifies hydrogen peroxide, are discussed.

Improved anti-oxidant activity of superoxide dismutase by direct chemical modification

Chemically modified derivatives of superoxide dismutase (SOD), i.e., cationized (Cat-SOD) and mannosylated SOD (Man-SOD), were designed to improve an ability of SOD to suppress reactive oxygen species (ROS)-mediated injury in the alveolar epithelium. To evaluate their effectiveness, an in vitro model of paraquat poisoning was developed with primary cultured rabbit alveolar type II cells. Despite a 5.6-fold higher cellular association than native SOD, Man-SOD did not protect cell injury due to paraquat following evaluation by MTT assay. In contrast, Cat-SOD exhibited a 140-fold higher cellular association than native SOD and greatly suppressed paraquat-induced cell injury, as well as lipid peroxidation. Incubation with 300 U/ml Cat-SOD for 2 h increased intracellular SOD activity 5.3-fold. The increase in intracellular SOD activity was significantly inhibited in the presence of cytochalasin B, an endocytosis inhibitor. Internalization of Cat-SOD was also confirmed by confocal laser scanning fluorescein microscopy. In addition, the protective effect of Cat-SOD against paraquat-induced cell injury was completely abolished by the presence of cytochalasin B. In conclusion, this study demonstrated that cationization of SOD greatly enhances its intracellular delivery and, as a consequence, produces a significant protective effect against ROS-mediated injury of the alveolar epithelium.

Inhibition of experimental hepatic metastasis by targeted delivery of catalase in mice

Bovine liver catalase derivatives possessing diverse tissue distribution properties were synthesized, and their effects on hepatic metastasis of colon carcinoma cells were examined in mice. An intraportal injection of 1 x 10(5) colon 26 cells resulted in the formation of more than 50 metastatic colonies on the surface of the liver at 14 days after injection. An intravenous injection of catalase (CAT; 35000 units/kg of body weight) significantly (P < 0.001) reduced the number of the colonies in the liver. Galactosylated (Gal-), mannosylated (Man-) and succinylated (Suc-) CAT were also tested in the same system. Of these derivatives, Gal-CAT showed the greatest inhibitory effect on hepatic metastasis, and the number of colonies was significantly (P < 0.001) smaller than following treatment with catalase. High activities of matrix metalloproteinases (MMPs), especially MMP-9, were detected in the liver of mice bearing metastatic tumor tissues, which was significantly (P < 0.05) reduced by Gal-CAT. These results, combined with our previous finding that Gal-CAT can be efficiently delivered to hepatocytes, indicate that the targeted delivery of catalase to the liver by galactosylation is a promising approach to suppress hepatic metastasis. Decreased MMP activity by catalase delivery seems to be involved in its anti-metastatic effect.

Poly(vinylpyrrolidone-co-dimethyl maleic acid) as a novel renal targeting carrier

Poly(vinylpyrrolidone-co-dimethyl maleic acid) (PVD) was found to have high renal-targeting capability and safety as a drug carrier. To optimize the renal drug delivery system using PVD, the relationship between the molecular weight of PVD and its renal accumulation were evaluated in mice by their intravenous injection. It was found that the molecular size of 6-8 kDa was associated with the highest renal accumulation. The specific bioactivity of PVD-conjugated superoxide dismutase (SOD) relative to that of unmodified SOD gradually decreased with an increase in the degree of modification to SOD with PVD6K. The conjugated SOD (L-PVD-SOD) with the molecular size of 73 kDa, which had comparable specific bioactivity with native SOD, showed longer plasma half-life than native SOD. About sixfold more L-PVD-SOD was distributed to the kidneys than native SOD 3 h after intravenous injection, whereas extensive PVD modification did not enhance the renal accumulation of SOD. This L-PVD-SOD effectively accelerated recovery from mercuric chloride-induced acute renal failure in vivo. These results suggest that L-PVD-SOD may be the optimal derivative as a potential therapeutic agent to various renal diseases.

Polyethylene glycol-superoxide dismutase, a conjugate in search of exploitation

Without a doubt PEG-SOD has been the enzyme most studied in PEGylation. One can say that it represents the preferred model to assess chemistries for PEG activation, analytical procedures suitable for conjugate characterization, the influence of PEG size in conjugate removal from circulation and elimination of immunogenicity and antigenicity, and the effect of route of administration. The effect of PEG conjugation was studied in vitro and in vivo models in comparison with the free enzyme and the following conclusions may be drawn: (1) At the blood vessel level, PEG-SOD has been shown to provide a greater resistance to oxidant stress, to improve endothelium relaxation and inhibit lipid oxidation. (2) In the heart, PEG-SOD proved to be at least as effective as native SOD in treatment of reperfusion-induced arrhythmias and myocardial ischemia. (3) In the lung, PEG-SOD appeared to be able to reduce oxygen toxicity and E. coli-induced lung injury, but not in the treatment of lung physiopathology associated with endotoxin-induced acute respiratory failure and in the reduction of asbestos-induced cell damage. (4) On cerebral ischemia/reperfusion injuries the effect of PEG-SOD was uncertain, also due to the difficulty of cerebral cell penetration. (5) In kidney and liver ischemia both enzyme forms were found to ameliorate reperfusion damage. In view of so much positive research on PEG-SOD, it is surprising that no approved application in human therapy has been established and approved.

Electrical charge on protein regulates its absorption from the rat small intestine

The effect of the electrical charge on the intestinal absorption of a protein was studied in normal adult rats. Chicken egg lysozyme (Lyz), a basic protein with a molecular weight of 14,300, was selected and several techniques for chemical modification were applied. Then the intestinal absorption of Lyz derivatives was evaluated by measuring the radioactivity in plasma and tissues, after the administration of an (111)In-labeled derivative to an in situ closed loop of the jejunum. After the administration of (111)In-Lyz, the level of radioactivity in plasma was comparable with the lytic activity of Lyz, supporting the fact that the radioactivity represents intact Lyz. (111)In-cationized Lyz showed a 2-3 times higher level of radioactivity in plasma, whereas the radioactivity of (111)In-anionized Lyz was much lower. The absorption rate of (111)In-Lyz derivatives calculated by a deconvolution method was correlated for the strength of their positive net charge. A similar relationship was observed using superoxide dismutase. These findings indicate that the intestinal absorption of a protein is, at least partially, determined by its electrical charge.

Targeting of superoxide dismutase and catalase to vascular endothelium

Reactive oxygen species, such as superoxide anion (O2(-)) and H2O2, cause oxidative stress in endothelial cells, a condition implicated in the pathogenesis of many cardiovascular and pulmonary diseases. Antioxidant enzymes, superoxide dismutases (SOD, converting superoxide anion into H2O2) and catalase (converting H2O2 into water), are candidate drugs for augmentation of antioxidant defenses in endothelium. However, SOD and catalase undergo fast elimination from the bloodstream, which compromises delivery and permits rather modest, if any, protection against vascular oxidative stress. Coupling of polyethylene glycol (PEG) to the enzymes and encapsulating them in liposomes increases their bioavailability and enhances their protective effect. Chemical modifications and genetic manipulations of SOD and catalase have been proposed in order to provide more effective delivery to endothelium. For example, chimeric protein constructs consisting of SOD and heparin-binding peptides have an affinity for charged components of the endothelial glycocalix. However, the problem of developing a more effective and precise delivery of the drugs to endothelial cells persists. Endothelial surface antigens may be employed to provide targeting and subcellular addressing of drugs (vascular immunotargeting strategy). Thus, SOD and catalase conjugated to antibodies directed against the constitutively expressed endothelial antigens, angiotensin-converting enzyme (ACE) and adhesion molecules (ICAM-1 or PECAM-1), bind to endothelium in intact animals after intravascular administration, accumulate in the pulmonary vasculature, enter endothelial cells and augment their antioxidant defenses. Such immunotargeting strategies may provide secondary therapeutic benefits by inhibiting the function of target antigens. For example, blocking of ICAM-1 and PECAM-1 by carrier antibodies may attenuate inflammation and leukocyte-mediated vascular damage. Additional studies in animal models of vascular oxidative stress are necessary in order to more fully characterize potential therapeutic effects and limitations of targeting of antioxidant enzymes to endothelial cells.

Delivery of antioxidant enzyme proteins to the lung

Protection of alveolar epithelial cells (alveolocytes) and vascular endothelial cells against pulmonary oxidative stress is an important problem. An inadequate delivery to the target cells limits the protective utility of the antioxidant enzymes, superoxide dismutase (SOD) and catalase. SOD and catalase modifications, such as coupling with polyethylene glycol and encapsulation in liposomes, prolong the life span of the active enzymes in vivo. The airway administration of SOD and catalase protects alveolocytes against hyperoxic oxidative stress. Although pulmonary endothelium is poorly accessible from the airways, it is accessible from circulation. However, antioxidant enzymes and their derivatives display poor targeting to pulmonary endothelium. To improve the targeting and provide intracellular delivery to endothelium, the enzymes can be conjugated with antibodies against endothelial antigens, such as angiotensin-converting enzyme and adhesion molecules [intercellular adhesion molecule-1 (ICAM-1) or platelet-endothelial cell adhesion molecule-1 (PECAM-1)]. These immunoconjugates accumulate in the pulmonary vasculature in intact animals, enter endothelium, and augment the antioxidant defenses. The immunoconjugates directed against ICAM-1 and PECAM-1 may also provide a secondary therapeutic benefit by blocking of sequestration and infiltration of leukocytes in the lungs. Further investigations are necessary to evaluate the therapeutic effectiveness of the vascular immunotargeting of antioxidant enzymes and solve technical problems associated with production of safe, clinically useful conjugates.

Targeting of superoxide dismutase to the liver results in anti-inflammatory effects in rats with fibrotic livers

BACKGROUND/AIMS

The rapid clearance from plasma and the limited uptake of superoxide dismutase (SOD) in the liver hampers the effectiveness of this enzyme in liver diseases. We therefore compared the pharmacokinetics and in vivo efficacy of SOD with two modified forms of this protein: SOD coupled to the copolymer DIVEMA and mannosylated-SOD.

METHODS

Reactive oxygen scavenging activity of SOD conjugates was tested in livers of bile duct ligated rats. Intrahepatic production of reactive oxygen species (ROS) and neutrophil infiltration were studied immunohistochemically and related to the organ and cellular distribution of radiolabeled SOD conjugates.

RESULTS

Native SOD was rapidly cleared from the circulation and accumulated in renal tubuli. The enzyme had no effect on the intrahepatic ROS production. Covalent attachment of SOD to DIVEMA yielded a polyanionic conjugate with a prolonged elimination half-life compared to native SOD. In contrast to native SOD, DIVEMA-SOD was taken up by the liver via scavenger receptors. Mannosylation of SOD (Man-SOD) resulted in a conjugate that was rapidly cleared from the blood. This Man-SOD was taken up by non-parenchymal liver cells. The pharmacokinetics of SOD and its derivatives were similar in normal and bile duct ligated rats. Efficacy studies with Man-SOD revealed only a slight decrease in intrahepatic ROS production. However, DIVEMA-SOD exhibited a potent inhibitory effect on ROS production in the liver. Nearly complete ROS-scavenging activity was observed in the portal areas.

CONCLUSIONS

Considering the prolonged half-life, the increased delivery of SOD to the target cells, and the concomitant increased effectiveness, application of DIVEMA-SOD seems a promising new approach to attenuate intrahepatic inflammatory processes.

Hepatocyte-specific distribution of catalase and its inhibitory effect on hepatic ischemia/reperfusion injury in mice

To explore the possibility of using catalase for the treatment of reactive oxygen species (ROS)-mediated injuries, the pharmacokinetics of bovine liver catalase (CAT) labeled with 111In was investigated in mice. At a dose of 0.1 mg/kg, more than 70% of 111In-CAT was recovered in the liver within 10 min after intravenous injection. In addition, 111In-CAT was predominantly recovered from the parenchymal cells (PC) in the liver. Increasing the dose retarded the hepatic uptake of 111In-CAT, suggesting saturation of the uptake process. This cell-specific uptake could not be inhibited by coadministration of various compounds which are known to be taken up by liver PC, indicating that the uptake mechanism of CAT by PC is very specific to this compound. The preventive effect of CAT on a hepatic ischemia/reperfusion injury was examined in mice by measuring the GOT and GPT levels in plasma. A bolus injection of CAT at 5 min prior to the reperfusion attenuated the increase in the levels of these indicators in a dose-dependent manner. These results suggest that catalase can be used for various hepatic injuries caused by ROS.

Augmented inhibitory effect of superoxide dismutase on superoxide anion release from macrophages by direct cationization

Superoxide dismutase (SOD) was modified into cationized form (Cat-SOD) in order to enhance its pharmacological efficacy based on an electrostatic interaction. The inhibitory effect of Cat-SOD on superoxide anion release from inflammatory macrophages and its cellular interaction were studied in vitro. Cat-SOD exhibited an excellent inhibitory effect on superoxide anion release from the macrophages, and this effect surpassed those of native SOD and SOD modified with mannose (Man-SOD) which is taken up via mannose receptor-mediated endocytosis by macrophages. In the presence of colchicine, a microtubule-disruptive agent, the inhibitory effect of Cat-SOD was slightly impaired, whereas the effect of Man-SOD completely disappeared. The intracellular localization of fluorescein isothiocyanate-labeled SOD, Cat-SOD and Man-SOD observed by confocal laser microscopy supported the difference in their abilities to eliminate superoxide anions. The different sensitivities of Cat-SOD and Man-SOD to colchicine were also confirmed by the confocal laser microscopic images, suggesting their distinct intracellular trafficking pathways in the macrophages. In conclusion, Cat-SOD is desirable for its pharmacological activity, which is probably the result of its ability to be delivered to the vicinity of NADPH-oxidase which locates in the cell membrane and generates superoxide anions.

Macromolecular carrier systems for targeted drug delivery: pharmacokinetic considerations on biodistribution

This review article describes the current status and future perspectives of site-specific drug delivery by means of macromolecular carrier systems. Basic aspects and recent advances of targeted delivery of 1) conventional drugs, 2) protein drugs, and 3) gene medicines including antisense oligonucleotides and plasmid DNA, are reviewed from a pharmacokinetic perspective. Successful in vivo application of macromolecular carrier systems requires pharmacokinetic considerations at whole body, organ, cellular and subcellular levels. The integration of simultaneous research progress in the multidisciplinary fields such as biochemistry, cell and molecular biology, pharmacology, and pharmacokinetics will accelerate the emergence of marketed drugs with macromolecular carrier systems.

Characterization of LLC-PK1 kidney epithelial cells as an in vitro model for studying renal tubular reabsorption of protein drugs

PURPOSE

The purpose of this study was to assess whether LLC-PK1 renal epithelial cells could serve as an in vitro model for studying the renal tubular reabsorption of protein drugs.

METHODS

The association of 111In-labeled model protein drugs, bovine serum albumin (BSA), superoxide dismutase (SOD), soybean trypsin inhibitor (STI), and [Asu1.7]-eel calcitonin (Asu-ECT), with the monolayers of LLC-PK1 renal epithelial cells was characterized under various conditions.

RESULTS

The cellular association of these proteins was temperature-dependent and varied according to the protein. Saturation kinetics were observed for STI association, with the apparent Km and Vmax values determined to be 66.3 micrograms/ml and 250 ng/mg protein/min, respectively. The association of STI decreased with increases in medium pH from 5.4 to 8.4 and was inhibited significantly by 2,4-dinitrophenol, sodium azide, cytochalasin B, and colchicine, suggesting that the cellular association involved endocytosis. Mutual inhibition was observed in competitive binding experiments with the four protein drugs, suggesting that they shared a common binding site on the luminal membrane of LLC-PK1 cells. Taken together, these findings show that a variety of protein drugs bind to LLC-PK1 cells in a non-specific manner and possibly undergo endocytosis, a phenomenon that is similar to in vivo proximal tubular reabsorption.

CONCLUSIONS

LLC-PK1 renal epithelial cells would be a suitable model system for the study of the renal proximal tubular reabsorption of protein drugs.