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Thiols enhance NO formation from nitrate photolysis

Dejam, André, Kleinbongard, Petra, Rassaf, Tienush, Hamada, Sandra, Gharini, Putrika, Rodriguez, Juan, Feelisch, Martin and Kelm, Malte (2003) Thiols enhance NO formation from nitrate photolysis Free Radical Biology & Medicine, 35, (12), pp. 1551-1559. (doi:10.1016/j.freeradbiomed.2003.09.009). (PMID:14680678).

Record type: Article


Nitrate is generally considered an inert oxidative breakdown product of nitric oxide (NO). Whereas it has been shown that limited amounts of NO are produced during the photolysis of nitrate in aqueous solution, the photochemistry of nitrate in biological matrices such as plasma is unknown. We hypothesized that thiols, which are ubiquitously present in biological systems, may significantly enhance NO-quantum yields from nitrate photolysis. Exposure of fresh human plasma to high-intensity UV-light resulted in NO-formation (19 +/- 3 nmol/l/min) as measured by gas phase chemiluminescence, and this signal was almost completely abolished by the removal of plasma N-oxides (2 +/- 1 nmol/l/min). Reconstitution of NOx-depleted plasma samples with a physiological concentration of nitrate, but not nitrite, restored photolytic NO-generation to values comparable to naïve plasma. Addition of the thiol-reducing agent, dithiothreitol or the sulfhydryl-bearing amino acid, L-cysteine increased NO-formation above control levels. Thiol-blockade by either N-ethylmaleimide (NEM) or mercuric chloride (HgCl2) reduced basal NO formation from 19 +/- 3 to 7 +/- 2 and 4 +/- 1 nmol/l/min, respectively. Exposure of plasma to UV-light increased NO-adduct concentrations from 18 +/- 5 to 1662 +/- 658 nmol/l. Collectively, our results show that thiols facilitate photolytic conversion of nitrate to NO and NO-adducts such as S-nitrosothiols. This may lead to substantial overestimation of the latter when photolysis-based methodologies are used for their determination. Whether this novel reaction channel also has in vivo relevance remains to be investigated.

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e-pub ahead of print date: 11 December 2003
Published date: 15 December 2003
Keywords: nitrate photolysis, n-oxides, nitrate, nitrite, uv-light, thiols, free radicals
Organisations: Clinical & Experimental Sciences


Local EPrints ID: 337849
ISSN: 0891-5849
PURE UUID: 8f3591f5-4db9-40b9-8d4d-c8762e3df5f5
ORCID for Martin Feelisch: ORCID iD

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Date deposited: 22 Jun 2012 09:40
Last modified: 18 Jul 2017 06:00

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Author: André Dejam
Author: Petra Kleinbongard
Author: Tienush Rassaf
Author: Sandra Hamada
Author: Putrika Gharini
Author: Juan Rodriguez
Author: Martin Feelisch ORCID iD
Author: Malte Kelm

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