Reduction of cold injury by superoxide dismutase and catalase

Therapeutic uses of antioxidant liposomes

This review will focus on the therapeutic uses of antioxidant liposomes. Antioxidant liposomes have a unique ability to deliver both lipid- and water-soluble antioxidants to tissues. This review will detail the varieties of antioxidants which have been incorporated into liposomes, their modes of administration, and the clinical conditions in which antioxidant liposomes could play an important therapeutic role. Antioxidant liposomes should be particularly useful for treating diseases or conditions in which oxidative stress plays a significant pathophysiological role because this technology has been shown to suppress oxidative stress. These diseases and conditions include cancer, trauma, irradiation, retinotherapy or prematurity, respiratory distress syndrome, chemical weapon exposure, and pulmonary infections.

Therapeutic uses of antioxidant liposomes

This chapter focuses on the use of antioxidant liposomes in the general area of free radical biology and medicine. The term antioxidant liposome is relatively new and refers to liposomes containing lipid-soluble chemical antioxidants, water-soluble chemical antioxidants, enzymatic antioxidants, or combinations of these various antioxidants. The role of antioxidants in health and disease has been extensively discussed, and many excellent reviews and books are available (1–3). Antioxidant liposomes hold great promise in the treatment of many diseases in which oxidative stress plays a prominent role. Oxidative stress is a physiological condition in which the production of damaging free radicals exceeds the in vivo capacity of antioxidant protection mechanisms to prevent pathophysiology. Free radicals are molecules with unpaired electrons, often highly reactive and damaging to biological systems. The biological membranes of subcellular organelles are a major site of free radical damage but proteins and DNA are also significant targets. Moreover, free radicals can alter cellular signal transduction pathways and stimulate the synthesis of inflammatory cytokines. Oxygen radicals and other reactive oxygen species (ROS) arise from the single electron reductions of oxygen.

Maternal administration of superoxide dismutase and catalase in phenytoin teratogenicity

Embryonic bioactivation and formation of reactive oxygen species (ROS) are implicated in the mechanism of phenytoin teratogenicity. This in vivo study in pregnant CD-1 mice evaluated whether maternal administration of the antioxidative enzymes superoxide dismutase (SOD) and/or catalase conjugated with polyethylene glycol (PEG) could reduce phenytoin teratogenicity. Initial studies showed that pretreatment with PEG-SOD alone (0.5-20 KU/kg i.p. 4 or 8 h before phenytoin) actually increased the teratogenicity of phenytoin (65 mg/kg i.p. on gestational days [GD] 11 and 12, or 12 and 13) (p < .05), and appeared to increase embryonic protein oxidation. Combined pretreatment with PEG-SOD and PEG-catalase (10 KU/kg 8 or 12 h before phenytoin) was not embryo-protective, nor was PEG-catalase alone, although PEG-catalase alone reduced phenytoin-initiated protein oxidation in maternal liver (p < .05). However, time-response studies with PEG-catalase (10 KU/kg) on GDs 11, or 11 and 12, showed maximal 50-100% increases in embryonic activity sustained for 8-24 h after maternal injection (p < .05), and dose-response studies (10-50 KU/kg) at 8 h showed maximal respective 4-fold and 2-fold increases in maternal and embryonic activities with a 50 KU/kg dose (p < .05). In controls, embryonic catalase activity was about 4% of that in maternal liver, although with catalase treatment, enhanced embryonic activity was about 2% of enhanced maternal activity (p < .05). PEG-catalase pretreatment (10-50 KU/kg 8 h before phenytoin) also produced a dose-dependent inhibition of phenytoin teratogenicity, with maximal decreases in fetal cleft palates, resorptions and postpartum lethality at a 50 KU/kg dose (p < .05). This is the first evidence that maternal administration of PEG-catalase can substantially enhance embryonic activity, and that in vivo phenytoin teratogenicity can be modulated by antioxidative enzymes. Both the SOD-mediated enhancement of phenytoin teratogenicity, and the inhibition of phenytoin teratogenicity by catalase, indicate a critical role for ROS in the teratologic mechanism, and the teratologic importance of antioxidative balance.

Therapeutic effect of liposomal superoxide dismutase in an animal model of retinopathy of prematurity

A newborn rat model of retinopathy of prematurity was used to test the hypothesis that a lack of superoxide dismutase contributes to the retinal vaso-attenuation seen during exposure of the animals to hyperoxic conditions. To determine the endogenous superoxide dismutase activity of the retina under hyperoxic conditions, litters of albino rats were placed in either constant 80% ambient oxygen (constant hyperoxia), or placed in 21% oxygen (room air) immediately after birth. Every other day, for 14 days, several rat pups were sacrificed and their retinas removed for the determination of total superoxide dismutase (SOD) activity and manganese-associated SOD activity. An attempt was made to increase retinal SOD activity by intraperitoneal administration of exogenous SOD encapsulated in polyethylene glycol-modified liposomes. Additional litters were exposed to the same oxygen treatments and supplemented twice daily with either liposome-encapsulated superoxide dismutase in saline or liposomes containing saline without SOD. Animals were sacrificed at various time points for the determination of total superoxide dismutase activity and computer-assisted analysis of vessel density and avascular area. Animals raised in an atmosphere of constant 80% oxygen had significantly reduced levels of retinal superoxide dismutase activity through 6 days of life when compared to their room air-raised littermates. At 6 days of age, daily supplementation with liposome-encapsulated SOD had significantly increased retinal superoxide dismutase activity and reduced oxygen-induced vaso-attenuation as evidenced by increased vessel density and decreased avascular area, when compared to littermates exposed to constant hyperoxia that received control liposomes. Superoxide dismutase had no adverse effects on any of the animals regardless of treatment. Tracing experiments demonstrated that liposomes entered the retina and were found in cells morphologically resembling microglia. Delivery of SOD to the retina via long-circulating liposomes proved beneficial, suggesting that restoration and/or supplementation of endogenous antioxidants in oxygen-damaged retinal tissue is a potentially valuable therapeutic strategy.

Therapeutic effect of liposomal superoxide dismutase in an animal model of retinopathy of prematurity

A newborn rat model of retinopathy of prematurity was used to test the hypothesis that a lack of superoxide dismutase contributes to the retinal vaso-attenuation seen during exposure of the animals to hyperoxic conditions. To determine the endogenous superoxide dismutase activity of the retina under hyperoxic conditions, litters of albino rats were placed in either constant 80% ambient oxygen (constant hyperoxia), or placed in 21% oxygen (room air) immediately after birth. Every other day, for 14 days, several rat pups were sacrificed and their retinas removed for the determination of total superoxide dismutase (SOD) activity and manganese-associated SOD activity. An attempt was made to increase retinal SOD activity by intraperitoneal administration of exogenous SOD encapsulated in polyethylene glycol-modified liposomes. Additional litters were exposed to the same oxygen treatments and supplemented twice daily with either liposome-encapsulated superoxide dismutase in saline or liposomes containing saline without SOD. Animals were sacrificed at various time points for the determination of total superoxide dismutase activity and computer-assisted analysis of vessel density and avascular area. Animals raised in an atmosphere of constant 80% oxygen had significantly reduced levels of retinal superoxide dismutase activity through 6 days of life when compared to their room air-raised littermates. At 6 days of age, daily supplementation with liposome-encapsulated SOD had significantly increased retinal superoxide dismutase activity and reduced oxygen-induced vaso-attenuation as evidenced by increased vessel density and decreased avascular area, when compared to littermates exposed to constant hyperoxia that received control liposomes. Superoxide dismutase had no adverse effects on any of the animals regardless of treatment. Tracing experiments demonstrated that liposomes entered the retina and were found in cells morphologically resembling microglia. Delivery of SOD to the retina via long-circulating liposomes proved beneficial, suggesting that restoration and/or supplementation of endogenous antioxidants in oxygen-damaged retinal tissue is a potentially valuable therapeutic strategy.

Comparison of the effects of nerve growth factor and superoxide dismutase on vascular extravasation in experimental burns

Superoxide dismutase (SOD), a free-radical scavenger, inhibits the increase of vascular permeability in experimental burn lesions in rats. In this study the aim was to determine whether Nerve Growth Factor (NGF), which has been implicated in the modulation of some inflammatory reactions, behaves in an analogous way. The study compares the haematocrit (Ht) and haemoglobin (Hb) variations in three groups of rats treated respectively with saline solution, SOD and NGF, immediately after causing a 25 per cent dermal burn injury. Statistical comparison (Student's t test) of the Ht and Hb variations between the Control group (Ht and Hb increase) and the NGF group (Ht and Hb decrease), shows significant differences in the intervals between 15 and 60 min (P < 0.01) and between 60 and 120 min (P < 0.05). Although SOD is able to control extravasation in the immediate postburn period (basal-15 min), NGF has a comparable effect in subsequent periods. The overall action of NGF shows that this agent is able to maintain Ht and Hb values at basal levels even after 120 min postburn. These results seem to be the first evidence of an inhibitory effect of NGF on the vascular permeability in burn lesions.

Neurotoxicity, drugs and abuse, and the CuZn-superoxide dismutase transgenic mice

Administration of methamphetamine (METH) to animals causes loss of DA terminals in the brain. The manner by which METH causes these changes in neurotoxicity is not known. We have tested the effects of this drug in copper/zinc (CuZn)-superoxide dismutase transgenic (SOD Tg) mice, which express the human CuZnSOD gene. In nontransgenic (non-Tg) mice, acute METH administration causes significant decreases in DA and dihydroxyphenylacetic acid (DOPAC) in the striata of non-Tg mice. In contrast, there were on significant decreases in striatal DA in the METH administration caused decreases in striatal DA and DOPAC in the non-Tg mice, but not in the SOD-Tg mice. Similar studies were carried out with 1-methyl-1,2,3,6-tetrahydropyridine (MPTP), which also causes striatal DA and DOPAC depletion. As in the case of METH, MPTP causes marked depletion of DA and DOPAC in the non-Tg mice, but not in the SOD Tg mice. These results suggest that the mechanisms of toxicity of both METH and MPTP involved superoxide radical formation.

The role of free radicals in cold injuries

Cold injury is a tissue trauma produced by exposure to freezing temperatures and even brief exposure to a severely cold and windy environment. Rewarming of frozen tissue is associated with blood reperfusion and the simultaneous generation of free oxygen radicals. In this review is discussed the current understanding of the mechanism of action of free oxygen radicals as related to cold injury during rewarming. Decreased energy stores during ischaemia lead to the accumulation of adenine nucleotides and liberation of free fatty acids due to the breakdown of lipid membranes. On rewarming, free fatty acids are metabolized via cyclo-oxygenase and adenine nucleotides are metabolized via the xanthine oxidase pathway. These may be the source of free oxygen radicals. Leukocytes may also play a major role in the pathogenesis of cold injury. Oxygen radical scavengers, such as superoxide dismutase and catalase, may help to reduce the cold induced injury but their action is limited due to the inability readily to cross the plasma membrane. Lipid soluble antioxidants are likely to be more effective scavengers because of their presence in membranes where peroxidative reactions can be arrested.

Restoration of the cAMP second messenger pathway enhances cardiac preservation for transplantation in a heterotopic rat model

Current organ preservation strategies subject graft vasculature to severe hypoxia (PO2 approximately 20 Torr), potentially compromising vascular function and limiting successful transplantation. Previous work has shown that cAMP modulates endothelial cell (EC) antithrombogenicity, barrier function, and leukocyte/EC interactions, and that hypoxia suppresses EC cAMP levels. To explore the possible benefits of cAMP analogs/agonists in organ preservation, we used a rat heterotopic cardiac transplant model; dibutyryl cAMP added to preservation solutions was associated with a time- and dose-dependent increase in the duration of cold storage associated with successful graft function. Preservation was also enhanced by 8-bromo-cAMP, the Sp isomer of adenosine 3',5'monophosphorothioate, and types III (indolidan) and IV (rolipram) phosphodiesterase inhibitors. Neither butyrate alone nor 8-bromoadenosine were effective, and the cAMP-dependent protein kinase antagonist Rp isomer of adenosine 3',5'monophosphorothioate prevented preservation enhancement induced by 8-bromo-cAMP. Grafts stored with dibutyryl cAMP demonstrated a 5.5-fold increase in blood flow and a 3.2-fold decreased neutrophil infiltration after transplantation. To explore the role of cAMP in another cell type critical for vascular homeostasis, vascular smooth muscle cells were subjected to hypoxia, causing a time-dependent decline in cAMP levels. Although adenylate cyclase activity was unchanged, diminished oxygen tensions were associated with enhanced phosphodiesterase activity (59 and 30% increase in soluble types III and IV activity, respectively). These data suggest that hypoxia or graft ischemia disrupt vascular homeostasis, at least in part, by perturbing the cAMP second messenger pathway. Supplementation of this pathway provides a new approach for enhancing cardiac preservation, promoting myocardial function, and maintaining vascular homeostatic properties.

Protection from cold injury by deferoxamine, an iron chelator

The presence of hydroxyl radical (OH) has been implicated in the pathogenesis of cold injury. Since iron is known to catalyze the OH formation responsible for cellular injury, this study was designed to examine whether an iron chelator such as deferoxamine can salvage a tissue from cold injury. Cold injury was induced in the hind limbs of rabbits. The experimental group received 0.6 mM of deferoxamine through the femoral vein prior to cooling of the limbs. Deferoxamine reduced the tissue injury, as evidenced by the decreased release of lactate dehydrogenase, a nonspecific marker for cellular injury. In addition, this drug inhibited OH formation and lipid peroxidation when examined by monitoring the formation of conjugated dienes and malonaldehyde, presumptive markers for lipid peroxidation. Rewarming of the cooled limbs was also associated with the loss of membrane phospholipids, with the corresponding accumulation of lysophosphoglycerides and free fatty acids, especially linoleic and arachidonic acids. Deferoxamine prevented the loss of phospholipids and inhibited the accumulation of amphipathic lipid products. These results indicates that deferoxamine salvaged the tissue from cold injury, possibly by preventing the formation of OH presumably by chelating iron, thus protecting the phospholipids from free radical attack.