Reactive nitrogen and oxygen radicals formed during hepatic ischemia-reperfusion kill weakly metastatic colorectal cancer cells

Microscopic infarcts develop within the Livers of athymic nude mice during the first 24 h after human colorectal carcinoma (CRC) cells arrest within h epatic sinusoids, Because these regions are reperfused, essentially all wea kly metastatic clone A and MIP-101 CRC cells die, whereas many highly metas tatic CX-1 CRC cells survive. Because hepatic sinusoidal endothelial cells kill tumor cells in vitro by producing nitric oxide, superoxide anion, and other reactive oxygen and nitrogen species, our purpose was to determine wh ether reoxygenation of ischemic hepatic cultures in vitro forms toxic oxyge n and nitrogen radicals that kill weakly but not highly metastatic CRC cell s. CRC cells (10(7)) were labeled with rhodamine-dextran and calcein AM, cu ltured with cells from one mouse Liver in a rotating suspension culture sys tem for up to 24 h, and the metabolic activity of the CRC cells was determi ned. Liver fragments oxygenated normally before harvest were not toxic to e ither CRC cell line, but coculture with liver made ischemic by a 3-min liga tion of the portal vein and hepatic artery in vivo before harvest and then cultured in oxygenated medium killed 50-70% of weakly metastatic clone A an d MIP-101 cells at 24 h but <15% of highly metastatic CX-I cells. Inhibitio n of nitric oxide synthase, addition of exogenous superoxide dismutase, but not catalase or hypoxia, during coculture blocked the killing of weakly me tastatic CRC cells, Thus, reoxygenation of hepatic parenchymal and nonparen chymal cells after ischemia may form toxic species that eliminate weakly me tastatic CRCs within 24 h of their arrest in the liver.