Cytokines regulate endotoxin stimulation of endothelial cell arginine transport.
BACKGROUND
Endotoxin (lipopolysaccharide) stimulates transmembrane L-arginine transport in pulmonary artery endothelial cells (PAECs). The proinflammatory cytokines tumor necrosis factor (TNF) and interleukin-1 (IL-1) mediate many of the pathophysiologic effects of endotoxemia and sepsis. Endothelial cells secrete TNF and IL-1 in response to endotoxin. We hypothesize that lipopolysaccharide stimulation of plasma membrane L-arginine transport is mediated via an autocrine cytokine loop involving TNF and IL-1.


METHODS
Confluent porcine PAECs were incubated with various concentrations of lipopolysaccharide, TNF, or IL-1, and arginine uptake was determined by assaying the uptake of 3H-L-arginine in the presence or absence of Na+ at different time points. PAECs were then incubated with lipopolysaccharide or saline solution after pretreatment with either anti-TNF antibody or IL-1-receptor antagonist, and transport was measured 12 hours later.


RESULTS
Lipopolysaccharide, IL-1, and TNF all increased both Na+-dependent and Na+-independent carrier-mediated L-arginine transport in a fashion that was both time and dose dependent. Maximal increases in stimulated arginine uptake occurred 8 hours after exposure to the cytokines and 12 hours after exposure to lipopolysaccharide. Pretreatment of endothelial cells with anti-TNF antibody blocked lipopolysaccharide stimulation of both Na+-independent and Na+-dependent transport by 100% and 90%, respectively. In addition, IL-1-receptor antagonist inhibited lipopolysaccharide stimulation of both Na+-independent and Na+-dependent transport by 65% and 85%, respectively.


CONCLUSIONS
The marked increase in carrier-mediated L-arginine transport activity produced by lipopolysaccharide, IL-1, and TNF may represent an adaptive response by the pulmonary endothelium to support arginine-dependent biosynthetic pathways during sepsis. Furthermore, lipopolysaccharide stimulation of arginine transport is mediated in part through an autocrine mechanism involving IL-1 and TNF.
Department of Surgery, University of Florida, Gainesville 32610-0286.
J C
JC
Cendan
W W
WW
Souba
E M
EM
Copeland
D S
DS
Lind
D000818:Animals; D001120:Arginine / Q000493:pharmacokinetics*; D001692:Biological Transport; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D004731:Endotoxins / Q000494:pharmacology*; D007375:Interleukin-1 / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D011651:Pulmonary Artery / Q000166:cytology; D012964:Sodium / Q000378:metabolism; D013552:Swine; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
D004731:Endotoxins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; C044101:endotoxin, Escherichia coli; D001120:Arginine; D012964:Sodium