Urea induces macrophage proliferation by inhibition of inducible nitric oxide synthesis.
BACKGROUND
Atherosclerosis is a major cause of morbidity and mortality in chronic renal failure and is associated with the proliferation of macrophages within atherosclerotic lesions.


METHODS
Because the progression of atherosclerosis as a consequence of decreased nitric oxide synthesis has been described, we investigated the correlation between the inhibition of inducible nitric oxide synthase (iNOS) by urea, macrophage proliferation as assayed by cell counting, tritiated thymidine incorporation and measurement of cell protein, and macrophage apoptosis.


RESULTS
Urea induces a dose-dependent inhibition of inducible nitric oxide synthesis in lipopolysaccharide-stimulated mouse macrophages (RAW 264.7) with concomitant macrophage proliferation. Macrophage proliferation, as determined by cell counting, became statistically significant at 60 mM urea, corresponding to a blood urea nitrogen level of 180 mg/100 ml, concentrations seen in uremic patients. iNOS protein expression showed a dose-dependent reduction, as revealed by immunoblotting when cells were incubated with increasing amounts of urea. The decrease of cytosolic DNA fragments in stimulated macrophages incubated with urea shows that the proliferative actions of urea are associated with a decrease of NO-induced apoptosis.


CONCLUSIONS
Our data demonstrate that the inhibition of iNOS-dependent NO production caused by urea enhances macrophage proliferation as a consequence of diminished NO-mediated apoptosis.
Moeslinger
T
T
Institute for Medical Physiology, Vienna, Austria. thomas.moeslinger@univie.ac.at
Friedl
R
R
Volf
I
I
Brunner
M
M
Baran
H
H
Koller
E
E
Spieckermann
P G
PG
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001161:Arteriosclerosis / Q000378:metabolism; D001565:Benzoates / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D053938:DNA Fragmentation; D004234:Diuretics, Osmotic / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006454:Hemoglobins / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D051379:Mice; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009603:Nitroso Compounds / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology*
D001565:Benzoates; D004234:Diuretics, Osmotic; D004791:Enzyme Inhibitors; D006454:Hemoglobins; D007093:Imidazoles; D008070:Lipopolysaccharides; C093285:NOC 18; D020030:Nitric Oxide Donors; D009603:Nitroso Compounds; C079393:1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole; D009569:Nitric Oxide; D014508:Urea; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D019331:NG-Nitroarginine Methyl Ester