Tiina M. Asikainen

Increased sensitivity of homozygous Sod2 mutant mice to oxygen toxicity

Induction or overexpression of pulmonary manganese superoxide dismutase (MnSOD) has been shown to protect against oxygen (O2) toxicity. Genetic inactivation of MnSOD (Sod2) results in multiple organ failure and early neonatal death. However, lungs or O2-tolerance of Sod2 knockout mice have not been investigated. We evaluated survival, lung histopathology, and other pulmonary antioxidants (glutathione cycle) of homozygous (-/-) and heterozygous (+/-) Sod2 mutant mice compared with wild-type controls (Sod2+/+) following 48 h exposure to either room air or to O2. The ability of antioxidant N-acetylcysteine to compensate for the loss of MnSOD was explored. Mortality of Sod2-/- mice increased from 0% in room air to 18 and 83% in 50 and 80% O2, respectively. N-acetylcysteine did not alter mortality of Sod2-/- mice. Histopathological analysis revealed abnormalities in saccules of Sod2-/- mice exposed either to room air or to 50% O2 suggestive of delayed postnatal lung development. In 50% O2, activities of glutamate-cysteine ligase (GCL) (previously known as gamma-glutamylcysteine synthetase, gamma-GCS) and glutathione peroxidase increased in Sod2-/- (35 and 70%, respectively) and Sod2+/- (12 and 70%, respectively) mice, but glutathione levels remained unaltered. We conclude that MnSOD is required for normal O2 tolerance and that in the absence of MnSOD there is a compensatory increase in pulmonary glutathione-dependent antioxidant defense in hyperoxia.

EXPRESSION OF ANTIOXIDANT ENZYMES DURING HUMAN LUNG DEVELOPMENT. † 226

Air breathing, and especially oxygen therapy, exposes the newborn lung to free radical effects. Antioxidant enzyme (AOE) activities are known to increase towards term in rat and rabbit lung, whereas the developmental profile of these enzymes in human lung is poorly understood. We investigated the expression of the key AOEs during human lung development. Fetal lung samples were obtained from legal abortions, newborn tissues from autopsies and adult tissues from surgical biopsies and donor lung transplantations. The activities of Mn-superoxide dismutase (SOD), Cu,ZnSOD, catalase (CAT) and glutathione peroxidase (Gpx) were measured using standard methods and mRNA-levels were quantitated by Northern analysis. We also measured the protein levels of MnSOD by Western blotting and localized the enzyme protein and mRNA using in situ methods. The mRNA levels of MnSOD and Cu,ZnSOD increased towards term and adulthood, whereas the specific activities were constant during intrauterine and postnatal life. However, the protein levels of MnSOD correlated well with the mRNA levels. MnSOD protein was localized in the developing bronchial epithelium in fetal lung and primarily in alveolar macrophages and type-II-pneumocytes in adult lung. MnSOD mRNA was localized to the same cell types. CAT and Gpx activity increased 3,0- and 1,9-fold by term, respectively, and the latter then decreased towards adulthood. CAT mRNA level increased towards term, whereas Gpx mRNA level remained constant. The regulation of the key AOEs in human lung appears to be both pre- and posttranslational. Factors other than AOEs may contribute to the adaptation of human lung to the increasing oxygen tension at birth.

Ontogeny of Antioxidant Enzymes (AOEs) in Human Lung and Liver 9

Background: Air breathing, especially oxygen therapy, exposes the newborn lung to free radical effects. AOE activities increase towards term in rat and rabbit lung. We studied the development of the key AOEs in human lung and liver.