Cellular and subcellular events in retinopathy of oxygen toxicity with a preliminary report on the preventive role of vitamin E and gamma-aminobutyric acid: a study in vitro.

Using freshly excised, pure, immature retinal vascular explants from neonatal rabbits as well as vascular cells harvested from such explants in a tissue culture environment, we established the direct cytocidal effect of hyperoxia on the vascular cells. One hundred percent oxygen at one atmosphere induced a marked cellular retraction after 4 to 6 hours of exposure and caused progressive increase in the number and size of lysosomal bodies and autophagic vacuoles. Between 12 to 18 hours, the Golgi apparatus enlarged and focal cytoplasmic degeneration ensued; the various changes in the endoplasmic reticulum, mitochondria, and nucleus became apparent between 18 to 24 hours. After 36 to 48 hours continuous exposure to hyperoxia, the cellular degradation with nuclear pyknosis led to granular and membranous debris. In contrast, the macrophages in the same culture were more resistant to the effect of hyperoxia. Our findings suggest multiple loci for oxygen toxicity in immature retinal vessels and cultured vascular cells. We believe that the cellular retraction is mediated through the prostanoid cascade. The initial event in cytotoxicity of hyperoxia is probably membrane injury, especially of the lysosomal system. The generation of the hydroxyl free radical invokes specific injury to the lysosomes; severe cellular damage occurs due to increased autophagocytosis, probably compounded upon by the inhibition of membrane pumps in the cell and the resulting intracellular acidosis. Injury to cell organelles such as mitochondria, endoplasmic reticulum, and nucleus which occurs at later stages and contributes to the final cell degeneration, may be partly related to the hyperoxic insult. The addition of vitamin E or gamma-aminobutryic acid to the culture medium partially retarded the hyperoxic injury to the vascular cells. In short term experiments, no significant damage occurred with exposure to 30% oxygen. The fact that immature, and not the mature, retinal vascular cells are rapidly and adversely affected by hyperoxia probably entails that the former are deficient in free radical scavenging enzymes but a protective mechanism against oxygen toxicity is acquired with the developmental maturity of these cells.