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 hepatic sinusoids. Because these regions are reperfused, essentially all weakly metastatic clone A and MIP-101 CRC cells die, whereas many highly metastatic 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 whether reoxygenation of ischemic hepatic cultures in vitro forms toxic oxygen and nitrogen radicals that kill weakly but not highly metastatic CRC cells. CRC cells (10(7)) were labeled with rhodamine-dextran and calcein AM, cultured with cells from one mouse liver in a rotating suspension culture system for up to 24 h, and the metabolic activity of the CRC cells was determined. Liver fragments oxygenated normally before harvest were not toxic to either CRC cell line, but coculture with liver made ischemic by a 3-min ligation 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 and MIP-101 cells at 24 h but <15% of highly metastatic CX-1 cells. Inhibition of nitric oxide synthase, addition of exogenous superoxide dismutase, but not catalase or hypoxia, during coculture blocked the killing of weakly metastatic CRC cells. Thus, reoxygenation of hepatic parenchymal and nonparenchymal cells after ischemia may form toxic species that eliminate weakly metastatic CRCs within 24 h of their arrest in the liver.

Carcinoembryonic antigen facilitates experimental metastasis through a mechanism that does not involve adhesion to liver cells.

Carcinoembryonic antigen (CEA) injected intravenously into athymic nude mice increases the ability of weakly metastatic human colorectal carcinoma (CRC) cells to colonize liver in an experimental metastasis assay. Since CEA acts as an intercellular adhesion molecule in vitro, several investigators have postulated that this facilitation of experimental metastasis may be mediated through adhesion between CEA on CRC and CEA-binding proteins on Kupffer or other cells lining the hepatic sinusoid. The present work tested this postulate both by intravital fluorescence videomicroscopy in vivo and in adhesion assays in vitro to enriched populations of Kupffer cells and hepatic sinusoidal endothelial cells (SEC). The data indicate that CEA expression does not effect adhesion to enriched Kupffer cells or SEC in vitro. These data suggest that CEA enhances liver colonization through another mechanism, possibly one that involves modulation of the hepatic response to tumor cell implantation.

Role of nitric oxide and superoxide anion in elimination of low metastatic human colorectal carcinomas by unstimulated hepatic sinusoidal endothelial cells.

Human colorectal carcinoma (CRC) cell survival for the first 24 h after implantation in the hepatic sinusoid determines its potential to colonize the liver. Nearly 10-fold more highly metastatic CX-1 cells survive within the livers of nude mice 24 h after intrasplenic injection than weakly metastatic clone A cells. Because CRCs contact sinusoidal endothelial cells (SECs) during implantation, we sought to determine whether SECs were more toxic to clone A than to CX-1 cells. When 2 x 10(4) vital dye-labeled CRC cells were added to murine SEC monolayers, more than 30% of clone A cells lost calcein AM fluorescence compared to fewer than 5% of CX-1 cells after 24 h of coculture with SECs. Kupffer cells did not mediate this effect, because neither enriched Kupffer cells nor SECs treated with a Kupffer cell inhibitor altered the SEC-mediated toxic effect to clone A cells. Pretreatment with a nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine, superoxide dismutase, or dexamethasone, blocked SEC-mediated toxicity to clone A cells, whereas calcium chelation and catalase did not. In addition, clone A cells were more sensitive to a superoxide donor, 3-morpholinosydnonimine N-ethylcarbamide, than were CX-1 cells, and neither cell line was sensitive to sodium nitroprusside, a nitric oxide donor. Thus, unstimulated murine SECs produce reactive oxygen species that are selectively toxic to weakly metastatic clone A cells. This may be a mechanism by which host liver cells eliminate weakly metastatic neoplastic cells.

In vivo induction of murine cytokine production by carcinoembryonic antigen.

Carcinoembryonic antigen (CEA) may promote experimental metastasis through production of cytokines. The effect of systemic CEA on the production of proinflammatory cytokines was investigated in mice and compared to levels induced by lipopolysaccharide (LPS). Serum concentrations of interleukin (IL)-6 peaked 1 h after an i.v. CEA injection of 40 microg/mouse to 37-54% of the maximal level induced by a 1 microg/mouse injection of LPS in both normal and immunoincompetent mice. The CEA induction of IL-6 was a specific response, because the peptide PELPK (the pentapeptide on CEA that is the ligand for the CEA receptor on Kupffer cells) conjugated to albumin induced 30% of the maximal CEA response for IL-6, whereas the specificity control PELGK-conjugated albumin did not. IL-1alpha and tumor necrosis factor (TNF)-alpha levels after i.v. injection of CEA were only 3-5% of those induced by LPS. The IL-6 responses of mice pretreated with 100 microg/kg genistein were decreased by more than 40%. However, genistein inhibited the TNF-alpha response to LPS by 46% but increased the CEA-induced response by 300%. When murine Kupffer cells were stimulated with LPS or CEA in vitro, LPS increased tyrosine phosphorylation of a Mr 30,000 protein, whereas CEA decreased phosphorylation of a Mr 60,000 protein and did not increase phosphorylation of the Mr 30,000 protein. Thus, i.v. CEA stimulates production of IL-6 and TNF-alpha after binding to Kupffer cells through signal transduction pathways that appear to be different from those stimulated by LPS.