Inhibition of interleukin-1-alpha-induced nitric oxide synthase in vascular smooth muscle and full reversal of interleukin-1-alpha-induced hypotension by N omega-amino-L-arginine.
BACKGROUND
Interleukin-1-alpha (IL-1) is a cytokine with potentially therapeutic immunoproliferative and tumoricidal activities. Preliminary clinical studies suggest that use of IL-1 may be restricted by dose-limiting hypotension.


OBJECTIVE
The purpose of this study was to investigate the role of nitric oxide (NO.) as a possible mediator of this hypotension.


METHODS
Cytokine-treated rat aortic smooth muscle cells were assayed for nitrite production, a stable breakdown product of nitric oxide. Nitric oxide synthase from smooth muscle cells was partially characterized in cytosol preparations using a novel Fe(2+)-myoglobin method to test for nitric oxide production. To determine the role of NO. on the immunorestorative and antineoplastic activity of IL-1, N omega-amino-L-arginine (NAA) or N omega-monomethyl-L-arginine (NMA), inhibitors of nitric oxide synthase, were added to either cultures of IL-1-dependent T cells or A375 melanoma cells exposed to IL-1. To investigate the effects of NAA in vivo, pentobarbital anesthetized dogs, which were made hypotensive by administration of IL-1, received a single intravenous bolus dose of NAA. The effects of NAA were then reversed by the administration of L-arginine.


RESULTS
Our results show that cultured IL-1-activated rat aortic smooth muscle cells synthesize nitric oxide, a potent vasodilator. Induction of nitric oxide synthase is augmented by interferon-gamma and blocked by IL-1 receptor antagonist and by inhibitors of RNA or protein synthesis. Nitric oxide synthesis by IL-1-activated smooth muscle cells is inhibited by NAA, NMA, and N omega-nitro-L-arginine (NNA) with ED50 (i.e., effective dose for 50% inhibition) values of 20, 60, and 1000 microM, respectively; this rank order of inhibition is characteristic of an agonist-unregulated, inducible isoform of nitric oxide synthase. In smooth muscle cells, inhibition of NO. synthesis by NAA is reversed by excess L-arginine. Consistent with the induction of unregulated NO. synthesis in vascular smooth muscle in vivo, administration of IL-1 (50 micrograms/kg) to dogs caused a 33.5% decrease in systemic vascular resistance and a 28% decrease in blood pressure within 3 hours. Subsequent administration of NAA (20 mg/kg) rapidly and completely reversed the hypotension and increased systemic vascular resistance; these effects of NAA were reversed by L-arginine. Neither the immunoproliferative nor the tumoricidal activity of IL-1 was diminished by NAA.


CONCLUSIONS
Our results indicate that (a) vascular smooth muscle is a likely source as well as a target of IL-1-induced NO. synthesis, causing vasodilatation and hypotension, (b) nitric oxide synthase inhibitors can fully reverse this hypotension, and (c) the therapeutically useful properties of IL-1 are not diminished by nitric oxide synthase inhibitors.


CONCLUSIONS
Administration of inhibitors of nitric oxide synthase can reverse the pathological cardiovascular effects of IL-1 at concentrations that do not interfere with the potentially useful immunoproliferative or tumoricidal effects of this cytokine. In the context of the current clinical trials of IL-1, this finding would represent a very significant advantage.
Kilbourn
R G
RG
Department of Medical Oncology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Gross
S S
SS
Lodato
R F
RF
Adams
J
J
Levi
R
R
Miller
L L
LL
Lachman
L B
LB
Griffith
O W
OW
D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000187:drug effects*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D002455:Cell Division / Q000187:drug effects; D004285:Dogs; D004790:Enzyme Induction / Q000187:drug effects; D006801:Humans; D007022:Hypotension / Q000139:chemically induced / Q000188:drug therapy*; D007375:Interleukin-1 / Q000009:adverse effects / Q000037:antagonists & inhibitors*; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D019001:Nitric Oxide Synthase; D051381:Rats; D011916:Rats, Inbred F344; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects
D007375:Interleukin-1; C063904:N(G)-aminoarginine; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases