title: Nitric oxide generation by renal proximal tubules: role of nitric oxide in the cytotoxicity of lipid A.
abstract: Lipid A, the biologically active component of lipopolysaccharide, stimulated nitric oxide (NO) production by isolated rat proximal tubules (as measured by NO2- release) in a time-dependent manner. At a concentration of 50 micrograms/ml, lipid A stimulated NO2- generation and guanosine 3',5'-cyclic phosphate (cGMP) production within 5 min. Both of these effects were blocked by NG-methyl-L-arginine (L-NMMA), an inhibitor of NO synthase or by 8-(N,N'-diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8), an inhibitor of intracellular Ca++ release. Because an increase in NO production may be cytotoxic, we examined the cytotoxic potential of lipid A. At 90 min, lipid A (50 micrograms/ml) produced significant lactate dehydrogenase release (42 +/- 5%) compared to control (25 +/- 5%; P < .05). Both L-NMMA (1 mM) and TMB-8 (100 microM) completely protected against lipid A-induced cytotoxicity. TMB-8 but not L-NMMA inhibited the rise intracellular Ca++ concentration ([Ca++]i) in isolated proximal tubules elicited by lipid A. L-NMMA but not TMB-8 inhibited proximal tubule soluble NO synthase activity. Thus, in the proximal tubule, lipid A stimulates a rise in [Ca++]i that in turn activates constitutive NO synthase. Furthermore, these events lead ultimately to NO-dependent cytotoxicity. Therefore, these findings suggest the potential for lipopolysaccharide to have a direct impact on proximal tubule physiology and renal function in vivo and support the potential therapeutic benefits of NO synthase inhibitors in the treatment of endotoxemia.
authors.affiliation: Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Traylor
authors.forename: J W
authors.initials: JW
authors.lastname: Proksch
authors.forename: V C
authors.initials: VC
authors.lastname: Beanum
authors.forename: P R
authors.initials: PR
authors.lastname: Mayeux
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D006152:Cyclic GMP / Q000096:biosynthesis; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008050:Lipid A / Q000633:toxicity*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D008050:Lipid A; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D007770:L-Lactate Dehydrogenase; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D002118:Calcium