Abstracts
1997 Digestive Disease Week

Chylomicrons alter the clearance and response to endotoxin by hepatocytes.

HW Harris, P Chau, JH Rapp, JP Kane, DCRockey. Departments of Surgery and Medicine, San Francisco General Hospital, University of California, San Francisco.

Chylomicrons (CM) can bind endotoxin (LPS) and prevent endotoxic shock and death in rodents. While CM increase the uptake of LPS by the liver, the hepatic cell type responsible for this increase is unclear. We hypothesized that CM protect by shunting LPS to hepatocytes. Since hepatocytes are less responsive to endotoxin, as compared to Kupffer cells, the redistribution of this toxic macromolecule could reduce the host inflammatory response and thus be protective. Methods. To examine the effect of CM on the uptake of LPS and on cytokine-induced NO production by hepatocytes, rats were injected with saline, CM, or ¹²⁵I-LPS that was either CM-bound or in saline. After 1 h, blood and liver were sampled, purified hepatocytes isolated via standard methods, and the ¹²⁵I-LPS content quantified where indicated. Hepatocyte nitric oxide (NO) production after in vitro stimulation was determined as a measure of hepatocellular activation by LPS in vivo. Results. The levels of ¹²⁵I-LPS were lower in blood (44.8 ± 5.2 v. 54.5 ± 6.7, p<0.02) and higher in liver (30.5 ± 5.4 v. 12.7 ± 0.8, p<0.001) from rats given CM-LPS as compared to controls. There was a greater than three-fold increase in the uptake of CM-LPS by hepatocytes compared to controls (7.0 ± 2.6 v. 1.9 ± 0.1 cpm/µg DNA, p<0.03). Also, there was reduced NO production by hepatocytes from rats injected with CM-LPS as compared to saline, CM or LPS alone (p<0.05, Table I). Data shown are mean ± SD nitrite levels (nmoles/10⁶ cells) from isolated hepatocytes, 24h after exposure to standard culture medium (control) v. TNF-lpha (10 ng/ml) + IL-1ß (5 ng/ml) + IFN-gamma (50 U/ml)

TABLE I.                                     treatment groups
 in vitro stimulant                 saline       CM      LPS     CM-LPS
 control                            1 ± 0      1 ± 0    0 ± 0     4 ± 3
 TNF-lpha + IL-1ß + IFN-gamma   49 ± 8     56 ± 21  52 ± 6    31 ± 5

Summary. These data demonstrate that CM increase the plasma clearance and uptake of LPS by the liver, and that hepatocytes are largely responsible for the increased hepatic clearance of CM-bound LPS in rats. In addition, CM-LPS complexes appear to downregulate the stimulatory effect of pro-inflammatory cytokines on hepatocytes. These findings add further insight into the mechanism by which chylomicrons protect against endotoxic shock and death in rodents.