Free radical production requires both inducible nitric oxide synthase and xanthine oxidase in LPS-treated skin

Abstract

Free radical formation has been investigated in diverse experimental models of LPS-induced inflammation. Here, using electron spin resonance (ESR) and the spin trap ␣-(4-pyridyl-1-oxide)-N-tertbutylnitrone, we have detected an ESR spectrum of ␣-(4-pyridyl-1-oxide)-N-tert-butylnitrone radical adducts in the lipid extract of mouse skin treated with LPS for 6 h. The ESR spectrum was consistent with the trapping of lipid-derived radical adducts. In addition, a secondary radical-trapping technique using dimethyl sulfoxide (DMSO) demonstrated methyl radical formation, revealing the production of hydroxyl radical. Radical adduct formation was suppressed by aminoguanidine, N-(3-aminomethyl)benzylacetamidine (1400W), or allopurinol, suggesting a role for both inducible nitric oxide synthase (iNOS) and xanthine oxidase (XO) in free radical formation. The radical formation was also suppressed in iNOS knockout (iNOS ؊/؊ ) mice, demonstrating the involvement of iNOS. NADPH oxidase was not required in the formation of these radical adducts because the ESR signal intensity was increased by LPS treatment in NADPH oxidase knockout (gp91 phox؊/؊ ) mice as much as it was in the wild-type mouse. Nitric oxide ( • NO) end products were increased in LPS-treated skin. As expected, the • NO end products were not suppressed by allopurinol but were by aminoguanidine. Interestingly, nitrotyrosine formation in LPStreated skin was also suppressed by aminoguanidine and allopurinol independently. Pretreatment with the ferric iron chelator Desferal had no effect on free radical formation. Our results imply that both iNOS and XO, but neither NADPH oxidase nor ferric iron, work synergistically to form lipid radical and nitrotyrosine early in the skin inflammation caused by LPS.lipopolysaccharide ͉ mouse skin L ipopolysaccharide (LPS), an outer-membrane component of Gram-negative bacteria, interacts with CD14, which then presents LPS to the Toll-like receptor 4 (1, 2); filling of this receptor activates inflammatory gene expression through nuclear factor B and mitogen-activated protein kinase signaling (3, 4). Over the years, LPS has frequently been used in experimental models of inflammation. The inflammatory response includes activation of free radical-generating enzymes in various types of cells that initiate host lipid peroxidation. For the detection and identification of these generated free radicals, the use of spin-trapping compounds appears to be the best method in vivo (5, 6). By using the electron spin resonance (ESR) spin-trapping technique, we have detected in vivo free radical production in lungs treated with LPS (7) or low-dose LPS plus diesel exhaust particles (8). In these articles, we have discussed the involvement of free radical-generating enzymes such as NADPH oxidase, xanthine oxidase (XO), and inducible nitric oxide synthase (iNOS).NADPH oxidase is generally activated in neutrophils that infiltrate the skin (9). It is also present in keratinocytes (10, 11) and fibroblasts (12). XO is activated in 12-O-tetradecanoyl-13-phorbol...

Involvement of inducible nitric oxide synthase in hydroxyl radical-mediated lipid peroxidation in streptozotocin-induced diabetes

“…GdCl 3 (10 mg/kg) was injected intravenously 24 h before the spin-trapping experiments [36]. Aminoguanidine (200 mg/kg) or 1400W (15 mg/kg) was administered 30 min or 1 h prior to spin trapping, respectively [37]. L-arginine (100 mg/kg) was administered 30 min prior to spin trapping.…”

Protective Effect Against Hydroxyl Radical-induced DNA Damage and Antioxidant Mechanism of [6]-gingerol: A Chemical Study

“…15 The product of •OH reaction with DMSO has been demonstrated to be •CH 3 . 16 In addition, in xanthineluminal-xanthine oxidase assay, since alkaline DMSO can generate superoxide anion radicals, 17,18 DMSO as the solvent undoubtedly cause interference with the determination of superoxide radical scavenging.…”

Xanthine Oxidoreductase Function Contributes to Normal Wound Healing

“…We and others have reported that nitrite can serve as a source of NO through XOR in models of vascular injury and pulmonary hypertension (23,24). XOR has been detected in skin, where it is involved in ROS production in response to lipopolysaccharide (LPS) (25) and ultraviolet irradiation (26). Thus, we hypothesize that XOR participates in normal wound healing through ROS/RNS and NO production.…”

“…We and others have shown that XOR is required for the beneficial actions of supplemental nitrite in the inhibition of intimal hyperplasia after vascular injury (23) and in reversing pulmonary hypertension (24). XOR expression in skin has been previously reported, linked to the pathogenesis of sunburn and skin inflammation (24,25). Beyond that, little is known about the role of XOR in the skin.…”