Loss of 51chromium, lactate dehydrogenase, and 111indium as indicators of endothelial cell injury

Injury to endothelial cells appears to be an important initial event in the pathogenesis of many diseases such as acute lung injury, venous and arterial thromboembolism, and atherosclerosis. Different methods for detecting damage to cultured endothelial cells have been described. However, their relative sensitivity as markers of endothelial cell damage has not been adequately determined. We compared the loss of 51Chromium (51Cr), the cytoplasmic enzyme lactate dehydrogenase (LDH), and 111Indium (111In) from endothelial cells upon exposure to several injurious agents. Cultured bovine pulmonary artery endothelial cells in confluent monolayers were labeled with 51Cr or 111Inoxine and exposed to increasing concentrations of the nonionic detergent, Triton X-100 (0.2 to 1%), hydrogen peroxide (1 to 500 microM), or neutrophils stimulated with phorbol myristate acetate. With all forms of injury, loss of 51Cr occurred earlier and to a greater extent than LDH loss which in turn was greater than loss of 111In. Substantial loss of 51Cr was observed in the absence of appreciable ultrastructural damage to endothelial cell external membranes. The findings may reflect the relative ease with which small molecules such as adenine nucleotides (51Cr-labeled) escape whereas larger molecules such as LDH and proteins binding 111In are retained intracellularly. Thus, 51Cr loss appears to be a more sensitive indicator of sublytic endothelial cell injury than either 111In or LDH release.