46 research outputs found
Isoniazid as a substrate and inhibitor of myeloperoxidase: Identification of amine adducts and the influence of superoxide dismutase on their formation
Neutrophils ingest Mycobacteria tuberculosis (Mtb) in the lungs of infected individuals. During
phagocytosis they use myeloperoxidase (MPO) to catalyze production of hypochlorous acid (HOCl), their
most potent antimicrobial agent. Isoniazid (INH),the foremost antibiotic in the treatment oftuberculosis,
is oxidized by MPO. It rapidly reduced compound I of MPO [k = (1.22 0.05) 106 M 1 s
1
] but reacted less
favorably with compound II [(9.8 0.6) 102 M 1 s
1
]. Oxidation of INH by MPO and hydrogen peroxide was
unaffected by chloride,the physiological substrate for compound I, and the enzyme was partially converted
to compound III. This indicates that INH is oxidized outside the classical peroxidation cycle. In combination
with superoxide dismutase (SOD), MPO oxidized INH without exogenous hydrogen peroxide. SOD must
favor reduction of oxygen by the INH radical to give superoxide and ultimately hydrogen peroxide. In both
oxidation systems, an adduct with methionine was formed and it was a major product with MPO and SOD.
We show that it is a conjugate of an acyldiimide with amines. INH substantially inhibited HOCl production
by MPO and neutrophils below pharmacological concentrations. The reversible inhibition is explained by
diversion of MPO to its ferrous and compound III forms during oxidation of INH. MPO, along with SOD
released by Mtb, will oxidize INH at sites of infection and their interactions are likely to limit the efficacy of
the drug, promote adverse drug reactions via formation of protein adducts, and impair a major bacterial
killing mechanism of neutrophils
Myeloperoxidase and oxidation of uric acid in gout: implications for the clinical consequences of hyperuricaemia
Objectives. The aims of this study were to establish whether, in patients with gout, MPO is released from
neutrophils and urate is oxidized to allantoin and if these effects are attenuated by allopurinol.
Methods. MPO, urate, allantoin and oxypurinol were measured in plasma from 54 patients with gout and
27 healthy controls. Twenty-three patients had acute gout, 13 of whom were receiving allopurinol, and 31
had intercritical gout, 20 of whom were receiving allopurinol. Ten additional gout patients had samples
collected before and after 4 weeks of allopurinol.
Results. Plasma MPO and its specific activity were higher (P < 0.05) in patients with acute gout not
receiving allopurinol compared with controls. MPO protein in patients’ plasma was related to urate concentration (r = 0.5, P < 0.001). Plasma allantoin was higher (P < 0.001) in all patient groups compared with
controls. In controls and patients not receiving allopurinol, allantoin was associated with plasma urate
(r = 0.62, P < 0.001) and MPO activity (r = 0.45, P < 0.002). When 10 patients were treated with allopurinol,
it lowered their plasma urate and allantoin (P = 0.002). In all patients receiving allopurinol, plasma allantoin
was related to oxypurinol (r = 0.65, P < 0.0001). Oxypurinol was a substrate for purified MPO that
enhanced the oxidation of urate.
Conclusion. Increased concentrations of urate in gout lead to the release of MPO from neutrophils and
the oxidation of urate. Products of MPO and reactive metabolites of urate may contribute to the pathology
of gout and hyperuricaemia. At low concentrations, oxypurinol should reduce inflammation, but high
concentrations may contribute to oxidative stress
Measuring chlorine bleach in biology and medicine
Background: Chlorine bleach, or hypochlorous acid, is the most reactive two-electron oxidant produced in appreciable amounts in our bodies. Neutrophils are the main source of hypochlorous acid. These champions of the innate immune system use it to fight infection but also direct it against host tissue in inflammatory diseases.
Neutrophils contain a rich supply of the enzyme myeloperoxidase. It uses hydrogen peroxide to convert chloride
to hypochlorous acid.
Scope of review: We give a critical appraisal of the best methods to measure production of hypochlorous acid by
purified peroxidases and isolated neutrophils. Robust ways of detecting it inside neutrophil phagosomes where
bacteria are killed are also discussed. Special attention is focused on reaction-based fluorescent probes but their
visual charm is tempered by stressing their current limitations. Finally, the strengths and weaknesses of biomarker assays that capture the footprints of chlorine in various pathologies are evaluated.
Major conclusions: Detection of hypochlorous acid by purified peroxidases and isolated neutrophils is best
achieved by measuring accumulation of taurine chloramine. Formation of hypochlorous acid inside neutrophil
phagosomes can be tracked using mass spectrometric analysis of 3-chlorotyrosine and methionine sulfoxide in
bacterial proteins, or detection of chlorinated fluorescein on ingestible particles. Reaction-based fluorescent probes
can also be used to monitor hypochlorous acid during phagocytosis. Specific biomarkers of its formation during inflammation include 3-chlorotyrosine, chlorinated products of plasmalogens, and glutathione sulfonamide.
General significance: These methods should bring new insights into how chlorine bleach is produced by peroxidases, reacts within phagosomes to kill bacteria, and contributes to inflammation. This article is part of a Special
Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn
Myeloperoxidase and oxidative stress in rheumatoid arthritis
Objective. To determine whether MPO contributes to oxidative stress and disease activity in RA and
whether it produces hypochlorous acid in SF.
Methods. Plasma and where possible SF were collected from 77 RA patients while 120 healthy controls
supplied plasma only. MPO and protein carbonyls were measured by ELISAs. 3-Chlorotyrosine in proteins
and allantoin in plasma were measured by mass spectrometry.
Results. Plasma MPO concentrations were significantly higher in patients with RA compared with
healthy controls [10.8 ng/ml, inter-quartile range (IQR): 7.214.2; P < 0.05], but there was no significant
difference in plasma MPO protein concentrations between RA patients with high disease activity
(HDA; DAS-28 >3.2) and those with low disease activity (LDA; DAS-28 43.2) (HDA 27.9 ng/ml,
20.234.1 vs LDA 22.1 ng/ml, 16.934.9; P > 0.05). There was a significant relationship between plasma
MPO and DAS-28 (r = 0.35; P = 0.005). Plasma protein carbonyls and allantoin were significantly higher in
patients with RA compared with the healthy controls. MPO protein was significantly higher in SF compared with plasma (median 624.0 ng/ml, IQR 258.42433.0 vs 30.2 ng/ml, IQR 25.150.9; P < 0.0001). The
MPO present in SF was mostly active. 3-Chlorotyrosine, a specific biomarker of hypochlorous acid, was
present in proteins from SF and related to the concentration of MPO (r = 0.69; P = 0.001). Protein carbonyls
in SF were associated with MPO protein concentration (r = 0.40; P = 0.019) and 3-chlorotyrosine (r = 0.66;
P = 0.003).
Conclusion. MPO is elevated in patients with RA and promotes oxidative stress through the production of
hypochlorous acid
Uric acid and thiocyanate as competing substrates of lactoperoxidase
The physiological function of urate is poorly understood. It
may act as a danger signal, an antioxidant, or a substrate for
heme peroxidases. Whether it reacts sufficiently rapidly with
lactoperoxidase (LPO) to act as a physiological substrate remains unknown. LPO is a mammalian peroxidase that plays a
key role in the innate immune defense by oxidizing thiocyanate
to the bactericidal and fungicidal agent hypothiocyanite. We
now demonstrate that urate is a good substrate for bovine LPO