Localization and activity of recombinant human CuZn superoxide dismutase after intratracheal administration

Recombinant Human Superoxide Dismutase and N-Acetylcysteine Addition to Exogenous Surfactant in the Treatment of Meconium Aspiration Syndrome

This study aimed to evaluate the molecular background of N-acetylcysteine (NAC) and recombinant human superoxide dismutase (rhSOD) antioxidant action when combined with exogenous surfactant in the treatment of meconium aspiration syndrome (MAS), considering redox signalling a principal part of cell response to meconium. Young New Zealand rabbits were instilled with meconium suspension (Mec) and treated by surfactant alone (Surf) or surfactant in combination with i.v. NAC (Surf + NAC) or i.t. rhSOD (Surf + SOD), and oxygen-ventilated for 5 h. Dynamic lung-thorax compliance, mean airway pressure, PaO₂/FiO₂ and ventilation efficiency index were evaluated every hour; post mortem, inflammatory and oxidative markers (advanced oxidation protein products, total antioxidant capacity, hydroxynonenal (HNE), p38 mitogen activated protein kinase, caspase 3, thromboxane, endothelin-1 and secretory phospholipase A₂) were assessed in pulmonary tissue homogenates. rhSOD addition to surfactant improved significantly, but transiently, gas exchange and reduced levels of inflammatory and oxidative molecules with higher impact; Surf + NAC had stronger effect only on HNE formation, and duration of treatment efficacy in respiratory parameters. In both antioxidants, it seems that targeting reactive oxygen species may be strong supporting factor in surfactant treatment of MAS due to redox sensitivity of many intracellular pathways triggered by meconium.

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Reduction of retinopathy of prematurity in extremely low gestational age newborns treated with recombinant human Cu/Zn superoxide dismutase

BACKGROUND

Reactive oxygen species have been implicated in the pathogenesis of retinopathy of prematurity (ROP). Extremely low gestational age (GA) newborns (ELGANs) have the highest risk of ROP and might benefit most from treatment with antioxidants.

OBJECTIVES

To determine whether recombinant human Cu/Zn superoxide dismutase (rhSOD) decreases the incidence or severity of ROP in ELGANs.

METHODS

A previous multicenter trial of intratracheal rhSOD for prevention of bronchopulmonary dysplasia randomized 302 preterm infants to receive intratracheal rhSOD or placebo at birth and every 48 h for 1 month. An analysis of the incidence and severity of ROP was performed in ELGANs.

RESULTS

The risk of ROP increased with decreasing GA. Within the entire cohort, no significant differences in ROP were found in the placebo versus rhSOD groups. Subgroup analysis on infants born at <26 weeks (n = 72) revealed a 22% reduction in ROP from 85% (placebo) to 66% (rhSOD) (p = 0.06). In subjects born at <25 weeks (n = 24), ROP was reduced by 53% from 85% (placebo) to 40% (rhSOD) (p = 0.03). ROP severity above stage 2 was found in 42% of placebo-treated infants but only 25% of rhSOD-treated subjects with ROP.

CONCLUSIONS

This post hoc analysis suggests that rhSOD reduces the risk of developing ROP in ELGANs, although further studies are required to confirm this observation.

Superoxide dismutase improves oxygenation and reduces oxidation in neonatal pulmonary hypertension

RATIONALE

Hyperoxic ventilation in the management of persistent pulmonary hypertension of the newborn (PPHN) can result in the formation of reactive oxygen species, such as superoxide anions, which can inactivate nitric oxide (NO) and cause vasoconstriction and oxidation.

OBJECTIVE

To compare the effect of intratracheal recombinant human superoxide dismutase (rhSOD) and/or inhaled NO (iNO) on systemic oxygenation, contractility of pulmonary arteries (PAs), and lung reactive oxygen species (isoprostane, 3-nitrotyrosine) levels in neonatal lambs with PPHN.

METHODS

Six newborn lambs with PPHN (induced by antenatal ductal ligation) were killed at birth. Twenty-six PPHN lambs were ventilated for 24 h with 100% O(2) alone (n = 6) or O(2) combined with rhSOD (5 mg/kg intratracheally) at birth (n = 4), rhSOD at 4 h of age (n = 5), iNO (20 ppm, n = 5), or rhSOD + iNO (n = 6). Contraction responses of fifth-generation PAs to norepinephrine and KCl, lung isoprostane levels, and 3-nitrotyrosine fluorescent intensity were measured.

RESULTS

Systemic oxygenation was impaired in PPHN lambs and significantly improved (up to threefold) in both rhSOD groups with or without iNO. Oxygenation improved more rapidly with the combination of rhSOD + iNO compared with either intervention alone. Norepinephrine- and KCl-induced contractions and lung isoprostane levels were significantly increased by 100% O(2) compared with nonventilated newborn lambs with PPHN. Both rhSOD and iNO mitigated the increased PA contraction response and lung isoprostane levels. Intratracheal rhSOD decreased the enhanced lung 3-nitrotyrosine fluorescence observed with iNO therapy.

CONCLUSION

Intratracheal rhSOD and/or iNO rapidly increase oxygenation and reduce both vasoconstriction and oxidation in newborn lambs with PPHN. This has important implications for clinical trials of rhSOD and iNO in newborn infants with PPHN.

Superoxide dismutase failed to attenuate allergen-induced nasal congestion in ragweed-sensitized dogs

We hypothesized that augmentation of antioxidant defenses with exogenous superoxide dismutase (SOD), an enzyme that provides an initial defense against oxidative injury, would attenuate allergen-induced nasal congestion in the canine model of allergic rhinitis. Nasal congestion was evaluated by the measurements of nasal resistance and the volume of the nasal passage. In five nonsensitized dogs, 30,000 U of SOD from bovine erythrocytes delivered by aerosol to the nasal passages before histamine challenge reduced the histamine-induced nasal congestion. At 30 min postchallenge, nasal resistance was 1.14 +/- 0.2 cmH2O.l(-1).min(-1) in the saline pretreatment study vs. 0.36 +/- 0.02 cmH2O.l(-1).min(-1) in the SOD pretreatment study (P < 0.05), and volume of nasal passage was 10.9 +/- 0.5 cm3 vs. 17.4 +/- 1.3 cm3 (P < 0.05), respectively. In five sensitized dogs, however, neither an analogous pretreatment with SOD nor intranasal aerosolized pretreatment with 30,000 U of SOD conjugated to polyethylene glycol attenuated ragweed-induced nasal congestion. Also, systemic application of SOD did not attenuate responses to challenges with histamine and ragweed in nonsensitized and sensitized dogs, respectively. The antioxidant-induced attenuation of nasal congestion in nonsensitized dogs confirms validity of the model and indicates the involvement of free radical-mediated damage in the genesis of the histamine-induced congestion. In sensitized dogs, the data do not support the hypothesis that oxidative stress is a clinically significant component of acute ragweed-induced nasal congestion. The data do not support the use of SOD for acute protection against allergic rhinitis.

Hypoxic constriction and reactive oxygen species in porcine distal pulmonary arteries

To determine whether reactive oxygen species (ROS) play an essential role in hypoxic pulmonary vasoconstriction (HPV) and the cellular locus of ROS production and action during HPV, we measured internal diameter (ID) at constant transmural pressure, lucigenin-derived chemiluminescence (LDCL), and electron paramagnetic resonance (EPR) spin adduct spectra in small distal porcine pulmonary arteries, and dichlorofluorescein (DCF) fluorescence in myocytes isolated from these arteries. Hypoxia (4% O2) decreased ID, increased DCF fluorescence, tended to increase LDCL, and in some preparations produced EPR spectra consistent with hydroxyl and alkyl radicals. Superoxide dismutase (SOD, 150 U/ml) or SOD + catalase (CAT, 200 U/ml) did not alter ID during normoxia but reduced or abolished the constriction induced by hypoxia. SOD also blocked HPV in endothelium-denuded arteries after restoration of the response by exposure to 10-10 M endothelin-1. Confocal fluorescence microscopy demonstrated that labeled SOD and CAT entered pulmonary arterial myocytes. SOD, SOD + CAT, and CAT blocked the increase in DCF fluorescence induced by hypoxia, but SOD + CAT and CAT also caused a stable increase in fluorescence during normoxia, suggesting that CAT diminished efflux of DCF from cells or oxidized the dye directly. We conclude that HPV required increased concentrations of ROS produced by and acting on pulmonary arterial smooth muscle rather than endothelium.

Pulmonary outcome at 1 year corrected age in premature infants treated at birth with recombinant human CuZn superoxide dismutase

OBJECTIVE

To examine whether treatment of premature infants with intratracheal recombinant human CuZn superoxide dismutase (r-h CuZnSOD) reduces bronchopulmonary dysplasia and improves pulmonary outcome at 1 year corrected age.

DESIGN

Three hundred two premature infants (600-1200 g birth weight) treated with exogenous surfactant at birth for respiratory distress syndrome were randomized to receive either intratracheal r-h CuZnSOD (5 mg/kg in 2 mL/kg saline) or placebo every 48 hours (as long as intubation was required) for up to 1 month of age. Short-term, as well as longer-term pulmonary outcome was assessed.

RESULTS

There were no differences between groups in the incidence of death or the development of bronchopulmonary dysplasia (oxygen requirement with an Edwards chest radiograph score of >or=3) at 28 days of life or 36 weeks' postmenstrual age. r-h CuZnSOD was well-tolerated and not associated with significant increases in any adverse event. At a median of 1 year corrected age, health assessments and physical examinations were performed on 209 (80%) surviving infants, with complete data available on 189 infants. Thirty-seven percent of placebo-treated infants had repeated episodes of wheezing or other respiratory illness severe enough to require treatment with asthma medications such as bronchodilators and/or corticosteroids compared with 24% of r-h CuZnSOD-treated infants, a 36% reduction. In infants <27 weeks' gestation, 42% treated with placebo received asthma medications compared with 19% of r-h CuZnSOD-treated infants, a 55% decrease. Infants <27 weeks' gestation who received r-h CuZnSOD also had a 55% decrease in emergency department visits and a 44% decrease in subsequent hospitalizations. Growth measurements and the results of physical examinations were comparable between groups.

CONCLUSIONS

These data indicate that treatment at birth with r-h CuZnSOD may reduce early pulmonary injury, resulting in improved clinical status when measured at 1 year corrected age. r-h CuZnSOD appears to be a safe and effective therapy that improves pulmonary outcome in high-risk premature infants.

Improved pulmonary distribution of recombinant human Cu/Zn superoxide dismutase, using a modified ultrasonic nebulizer

Prophylactic, intratracheal instillation of recombinant human Cu/Zn superoxide dismutase (rhSOD) has been shown to lessen lung injury produced by 48 h of hyperoxia and mechanical ventilation in neonatal piglets. However, instillation of small volumes of rhSOD intratracheally would not be expected to result in uniform pulmonary distribution. Aerosolization is a technique that may improve pulmonary distribution of drugs, but is limited by the poor efficiency of most nebulizers. A newly modified ultrasonic nebulizer was tested to assess pulmonary distribution of rhSOD compared to that achieved by intratracheal instillation. rhSOD was dual-labeled with technetium-99m (99mTc) and a fluorescent analog (permitting quantitative and qualitative assessments of pulmonary distribution), and administered to neonatal piglets by intratracheal instillation or by aerosolization. Intratracheal instillation of rhSOD to piglets when supine resulted in nonuniform distribution, with most of the drug being found in the right caudal lobe, and localized in airways. Placing animals in 30 degrees of Trendelenburg and administering half the dose in the left and half in the right lateral decubitus positions improved distribution, but alveolar deposition remained patchy. Aerosolization using a modified ultrasonic nebulizer uniformly delivered 45.8 +/- 3.8% of the rhSOD to the lungs that had been placed in the nebulizer. The rhSOD was still active and present in airways and alveoli in a homogeneous fashion. We conclude that intratracheal instillation of rhSOD in small volumes results in nonuniform pulmonary distribution, while aerosolization enhances rhSOD distribution and alveolar deposition. This has important implications for ongoing clinical trials of rhSOD for the prevention of acute and chronic lung injury in premature neonates.