The inhibition of myeloperoxidase by ceruloplasmin can be reversed by anti-myeloperoxidase antibodies. (1/796)

BACKGROUND: The purpose of this study was to characterize the recently reported inhibition of myeloperoxidase (MPO) by ceruloplasmin and to determine whether this may be disturbed in the presence of anti-MPO antibodies. METHODS: Specificity of the binding between ceruloplasmin and MPO was confirmed by Western blotting and enzyme-linked immunosorbent assay (ELISA), and the enzymatic activity of MPO was measured in the presence of ceruloplasmin, affinity-purified anti-MPO antibodies, or both. The affinity of the binding between MPO and ceruloplasmin and MPO and the anti-MPO antibodies was measured using a biosensor, with the results confirmed by chaotrope ELISA. RESULTS: Affinity-purified anti-MPO antibodies from patients with microscopic polyangiitis and florid renal vasculitis inhibited the binding between ceruloplasmin and MPO to a maximum of 72.9 +/- 12.8%, whereas those from patients with Wegener's granulomatosis and only minimal renal involvement inhibited the binding to a maximum of only 36.8 +/- 10.9% (P < 0. 001), with comparable reversal of the ceruloplasmin-mediated inhibition of MPO activity. Measurement of the affinity of the interactions demonstrated that binding between MPO and the anti-MPO antibodies is stronger than that between MPO and ceruloplasmin (1.61 x 107 to 1.33 x 108 vs. 7.46 x 106 m-1), indicating that binding to the autoantibody would be favored in vivo. CONCLUSIONS: This study confirms a role for ceruloplasmin as a physiological inhibitor of MPO, and demonstrates how the inhibition may be disrupted in the presence of anti-MPO antibodies. Because a majority (16 of 21) of the antibodies did not themselves inhibit MPO activity, their interference with the inhibition mediated by ceruloplasmin may be brought about by steric hindrance consequent upon the binding of the antibody to a dominant epitope at or near the active site.  (+info)

Ferroxidase activity of ferritin: effects of pH, buffer and Fe(II) and Fe(III) concentrations on Fe(II) autoxidation and ferroxidation. (2/796)

It is widely accepted that iron deposition in the iron storage protein ferritin in vitro involves Fe(II) oxidation, and that ferritin facilitates this oxidation at a ferroxidase site on the protein. However, these views have recently been questioned, with the protein ferroxidase activity instead being attributed to autoxidation from the buffer alone. Ligand exchange between another protein with ferroxidase activity and ferritin has been proposed as an alternative mechanism for iron incorporation into ferritin. In the present work, a pH stat apparatus is used to eliminate the influence of buffers on iron(II) oxidation. Here we show that the recent experiments questioning the ferroxidase activity of ferritin were flawed by inadequate pH control, that buffers actually retard rather than facilitate iron(II) oxidation, and that horse spleen ferritin has ferroxidase activity when measured under proper experimental conditions. Furthermore, high pH (7.0), a high Fe(II) concentration and the presence of Fe(III) all favour Fe(II) autoxidation in the presence or absence of ferritin.  (+info)

Copper metabolism in retinitis pigmentosa. (3/796)

Clinically and electrophysiologically confirmed cases of primary retinitis pigmentosa have been investigated regarding their copper metabolic state. It is observed that these patients show a normal or near normal serum copper concentration, very low plasma caeruloplasmin concentration, and a very high copper urinary excretion. A similarity between this condition and hepatolenticular degeneration is drawn and it is suggested that retinitis pigmentosa may also be a condition caused by an inborn error of copper metabolism.  (+info)

Caeruloplasmin isoforms in Wilson's disease in neonates. (4/796)

AIM: To investigate the neonatal diagnosis of Wilson's disease from caeruloplasmin isoforms in cord blood. METHODS: Serum caeruloplasmin isoforms were measured in 5-10 ml cord blood from 10 fresh umbilical cords using sodium dodecyl polyacrylamide gel electrophoresis (SDS PAGE) and western blotting and analysed by densitometry. Total caeruloplasmin concentrations were determined by nephelometry and caeruloplasmin oxidase by p-nitrophenyldiamine. RESULTS: Although total caeruloplasmin concentrations are reduced in neonates, the plasma isoform was significantly reduced or absent in patients with Wilson's disease. Sera from healthy neonates and from those with Wilson's disease had reduced biliary isoforms. CONCLUSION: Identification of caeruloplasmin isoforms may be a marker for Wilson's disease in neonates.  (+info)

The reactions of copper proteins with nitric oxide. (5/796)

Nitric oxide (NO) can act as a ligand for copper atoms and may also engage in redox chemistry with the metal once bound. Furthermore NO posses an unpaired electron which can couple with the unpaired electron on Cu2+. These properties have been exploited to probe the active sites of copper-containing enzymes and proteins. We review these studies. In addition to the use as a spectroscopic probe for the active site we draw attention to the rapid reactions of NO at the copper sites in Cytochrome c oxidase (CcO) and laccase. These reactions in CcO occur in the ms time range, at low NO concentrations and in the presence of oxygen and may therefore be of physiological relevance to the control of respiration. Finally we speculate on the wider role that NO may play in regulation of an important group of Type 2 copper containing enzymes.  (+info)

Abnormality in urinary protein excretion in Japanese men with impaired glucose tolerance. (6/796)

OBJECTIVE: To examine whether subjects with impaired glucose tolerance (IGT) for more than 2 years have any abnormality in the kidney. RESEARCH DESIGN AND METHODS: We measured urinary excretion rate and clearance of various plasma proteins with different molecular radii and different isoelectric points in 22 Japanese men with IGT (IGT group) and 37 age-matched healthy control subjects (control group). RESULTS: Clearance of ceruloplasmin (molecular radius approximately 45 A; isoelectric point 4.4), IgG4 (molecular radius 55 A; isoelectric point 5.4), and IgG (molecular radius 55 A; isoelectric point 7.4) was significantly higher in the IGT group than in the control group, whereas there were no significant differences in urinary excretion rate of albumin (molecular radius 36 A; isoelectric points 4.8-5.2) and clearance of alpha 2-macroglobulin (molecular radius 88 A; isoelectric point 5.4) between the two groups. CONCLUSIONS: In the present study, we found that clearance of neutral-charged IgG, negatively charged IgG4, and ceruloplasmin with molecular radii of approximately 45-55 A was selectively increased in IGT subjects. This finding does not seem to be explained by impairment of charge and pore-size selectivity in the glomerulus. Therefore, considering the present result together with our recent finding that enhanced glomerular filtration rate (GFR) after acute protein loading in healthy subjects induced a selective increase in clearance of IgG, IgG4, and ceruloplasmin, we suggest that increased intraglomerular hydraulic pressure, although enhanced GFR was not demonstrated, may be at work in these mildly hyperglycemic subjects.  (+info)

Hepatic hyperplasia and cancer in rats: alterations in copper metabolism. (7/796)

We previously demonstrated that rats exposed to the peroxisome proliferator (PP) diethylhexylphthalate (DEHP) had reduced serum ceruloplasmin (CP) oxidase activity, which suggests tissue copper deposition. Copper is highly toxic in excess, and results in cellular damage and hepatocellular carcinomas (HCC). This study addresses changes in expression of copper-related genes and metal accumulation in hyperplastic liver and tumors induced by PP. Male rats were fed diets containing DEHP or clofibrate (CLF) for 3-60 days (hyperplasia) and 4-chloro-6-(2,3 xylidino)-2-pyrimidinyl-thio(N-beta-hydroxyethyl) acetamide for 10 months (HCC). During hyperplasia, an immediate and progressive decrease in serum CP activity was observed (P < 0.05), as were reductions in mRNA levels for both CP and Wilson's disease gene (WD gene, a P-type ATPase) (P < 0.05). Tumor-bearing rats had lower serum CP activity (P < 0.05), and CP and WD gene mRNA levels were reduced in tumors (P < 0.05), and in liver surrounding tumors (SL) (P < 0.05). Metallothionein mRNA showed no consistent changes during hyperplasia. Tumors showed a 2.5-fold induction of metallothionein mRNA (P < 0.05), and a 1.2-fold increase in SL. Temporal increases in liver copper content occurred during hyperplasia, with increases of 2-fold (DEHP) and 3.3-fold (CLF) at 60 days (P < 0.05). Copper content was 2.2-fold higher in tumors (P < 0.05) and 1.7-fold higher in SL; iron did not increase and zinc decreased temporally. Thus, copper accumulation and changes in copper-related gene expression may be contributing factors in liver neoplasia in PP-treated rats. Loss of CP results in decreased free radical scavenger capacity and thus may enhance oxidative damage induced by PPs.  (+info)

Hemolytic activity of copper sulfate as influenced by epinephrine and chelating thiols. (8/796)

AIM: To study the effects of epinephrine, homocysteine, and other complexing agents on the cytotoxicity of copper sulfate. METHODS: In vitro suspensions of human red cells incubated with cupric sulfate were used, and hemolysis was determined by extracellular hemoglobin. RESULTS: The hemolytic activity of CuSO4 (0.3 mmol.L-1) was enhanced by the presence of epinephrine and to a lesser extent by homocysteine, whereas D-penicillamine, succimer, and mercaptodextran reduced the copper-induced hemolysis. The latter 3 chelating thiols also reduced the copper-epinephrine-induced hemolysis. The plasma protein ceruloplasmin reduced markedly the copper-epinephrine-induced hemolysis, even upon concentrations < 20% of that of copper. Chromic chloride, as well, acted anti-hemolytically. CONCLUSION: The latter protectors may interact with the production or activity of toxic oxygen, while classical copper chelators sequester cupric ions from interaction with epinephrine or homocysteine.  (+info)