Aminoacetone Induces Oxidative Modification to Human Plasma Ceruloplasmin

Aerobic co-oxidation of hemoglobin and aminoacetone, a putative source of methylglyoxal

Aminoacetone (1-aminopropan-2-one), a putative minor biological source of methylglyoxal, reacts like other α-aminoketones such as 6-aminolevulinic acid (first heme precursor) and 1,4-diaminobutanone (a microbicide) yielding electrophilic α-oxoaldehydes, ammonium ion and reactive oxygen species by metal- and hemeprotein-catalyzed aerobic oxidation. A plethora of recent reports implicates triose phosphate-generated methylglyoxal in protein crosslinking and DNA addition, leading to age-related disorders, including diabetes. Importantly, methylglyoxal-treated hemoglobin adds four water-exposed arginine residues, which may compromise its physiological role and potentially serve as biomarkers for diabetes. This paper reports on the co-oxidation of aminoacetone and oxyhemoglobin in normally aerated phosphate buffer, leading to structural changes in hemoglobin, which can be attributed to the addition of aminoacetone-produced methylglyoxal to the protein. Hydroxyl radical-promoted chemical damage to hemoglobin may also occur in parallel, which is suggested by EPR-spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide and ethanol. Concomitantly, oxyhemoglobin is oxidized to methemoglobin, as indicated by characteristic CD spectral changes in the Soret and visible regions. Overall, these findings may contribute to elucidate the molecular mechanisms underlying human diseases associated with hemoglobin dysfunctions and with aminoacetone in metabolic alterations related to excess glycine and threonine.

Capacity of ceruloplasmin to scavenge products of the respiratory burst of neutrophils is not altered by the products of reactions catalyzed by myeloperoxidase

CP is a copper-containing ferroxidase of blood plasma, which acts as an acute phase reactant during inflammation. The effect of oxidative modification of CP induced by oxidants produced by MPO, such as HOCl, HOBr, and HOSCN, on its spectral, enzymatic, and anti-inflammatory properties was studied. We monitored the chemiluminescence of lucigenin and luminol along with fluorescence of hydroethidine and scopoletin to assay the inhibition by CP of the neutrophilic respiratory burst induced by PMA or fMLP. Superoxide dismutase activity of CP and its capacity to reduce the production of oxidants in respiratory burst of neutrophils remained virtually unchanged upon modifications caused by HOCl, HOBr, and HOSCN. Meanwhile, the absorption of type I copper ions at 610 nm became reduced, along with a drop in the ferroxidase and amino oxidase activities of CP. Likewise, its inhibitory effect on the halogenating activity of MPO was diminished. Sera of either healthy donors or patients with Wilson disease were co-incubated with neutrophils from healthy volunteers. In these experiments, we observed an inverse relationship between the content of CP in sera and the rate of H2O2 production by activated neutrophils. In conclusion, CP is likely to play a role of an anti-inflammatory factor tempering the neutrophil respiratory burst in the bloodstream despite the MPO-mediated oxidative modifications.

Ferricytochrome (c) directly oxidizes aminoacetone to methylglyoxal, a catabolite accumulated in carbonyl stress

Age-related diseases are associated with increased production of reactive oxygen and carbonyl species such as methylglyoxal. Aminoacetone, a putative threonine catabolite, is reportedly known to undergo metal-catalyzed oxidation to methylglyoxal, NH4(+) ion, and H2O2 coupled with (i) permeabilization of rat liver mitochondria, and (ii) apoptosis of insulin-producing cells. Oxidation of aminoacetone to methylglyoxal is now shown to be accelerated by ferricytochrome c, a reaction initiated by one-electron reduction of ferricytochrome c by aminoacetone without amino acid modifications. The participation of O2(•-) and HO (•) radical intermediates is demonstrated by the inhibitory effect of added superoxide dismutase and Electron Paramagnetic Resonance spin-trapping experiments with 5,5'-dimethyl-1-pyrroline-N-oxide. We hypothesize that two consecutive one-electron transfers from aminoacetone (E0 values = -0.51 and -1.0 V) to ferricytochrome c (E0 = 0.26 V) may lead to aminoacetone enoyl radical and, subsequently, imine aminoacetone, whose hydrolysis yields methylglyoxal and NH4(+) ion. In the presence of oxygen, aminoacetone enoyl and O2(•-) radicals propagate aminoacetone oxidation to methylglyoxal and H2O2. These data endorse the hypothesis that aminoacetone, putatively accumulated in diabetes, may directly reduce ferricyt c yielding methylglyoxal and free radicals, thereby triggering redox imbalance and adverse mitochondrial responses.

Evaluation of ceruloplasmin levels in patients undergoing surgical interventions with nasal polyps

OBJECTIVE

Oxidative stress is believed to have a role in the development of nasal polyps (NPs). It is also known that ceruloplasmin (CP), an acute phase protein, limits oxidative stress. The purpose of this study was to evaluate the ceruloplasmin levels in patients with NPs.

METHODS

One hundred and twenty patients with NPs, septal deviations and concha hypertrophies were recruited to the study. Patients were divided in two groups; group 1 (n=60) consisted of patients with NPs, and group 2 (n=60) consisted of septal deviations and concha hypertrophies. Polyp specimens were taken from all patients who underwent endoscopic surgery due to NPs, as well as control specimens were acquired who underwent an operation due to septoplasty or concha hypertrophy. Blood and tissue samples were obtained to assess CP levels.

RESULTS

There were no statistical differences in gender, age and biochemical values between two groups (p>0.05 for all). Compared to group 2, group 1 had significantly higher CP levels both in serum and the tissue samples (both p<0.001).

CONCLUSION

As a result of our study; CP levels both in serum and the tissue in patients with NPs were higher, may be consequence of the inflammation, than in patients without NPs.

Acetyl radical production by the methylglyoxal-peroxynitrite system: a possible route for L-lysine acetylation

Methylglyoxal is an α-oxoaldehyde putatively produced in excess from triose phosphates, aminoacetone, and acetone in some disorders, particularly in diabetes. Here, we investigate the nucleophilic addition of ONOO(-), known as a potent oxidant and nucleophile, to methylglyoxal, yielding an acetyl radical intermediate and ultimately formate and acetate ions. The rate of ONOO(-) decay in the presence of methylglyoxal [k(2,app) = (1.0 ± 0.1) × 10(3) M(-1) s(-1); k(2) ≈ 1.0 × 10(5) M(-1) s(-1)] at pH 7.2 and 25 °C was found to be faster than that reported with monocarbonyl substrates (k(2) < 10(3) M(-1) s(-1)), diacetyl (k(2) = 1.0 × 10(4) M(-1) s(-1)), or CO(2) (k(2) = 3-6 × 10(4) M(-1) s(-1)). The pH profile of the methylglyoxal-peroxynitrite reaction describes an ascendant curve with an inflection around pH 7.2, which roughly coincides with the pK(a) values of both ONOOH and H(2)PO(4)(-) ion. Electron paramagnetic resonance spin trapping experiments with 2-methyl-2-nitrosopropane revealed concentration-dependent formation of an adduct that can be attributed to 2-methyl-2-nitrosopropane-CH(3)CO(•) (a(N) = 0.83 mT). Spin trapping with 3,5-dibromo-4-nitrosobenzene sulfonate gave a signal that could be assigned to a methyl radical adduct [a(N) = 1.41 mT; a(H) = 1.35 mT; a(H(m)) = 0.08 mT]. The 2-methyl-2-nitrosopropane-CH(3)CO(•) adduct could also be observed by replacement of ONOO(-) with H(2)O(2), although at much lower yields. Acetyl radicals could be also trapped by added L-lysine as indicated by the presence of (ε)N-acetyl-L-lysine in the spent reaction mixture. This raises the hypothesis that ONOO(-)/H(2)O(2) in the presence of methylglyoxal is endowed with the potential to acetylate proteins in post-translational processes.

Ceruloplasmin induces polymorphonuclear leukocyte priming in localized aggressive periodontitis

BACKGROUND

Polymorphonuclear leukocytes (PMNs) from subjects with localized aggressive periodontitis (LAgP) present multiple functional abnormalities associated with a phenotypically primed PMN phenotype. Local inflammation is characterized by hypoxia, which leads to increased production of superoxide (O(2)(-)) by PMNs. Ceruloplasmin (CP) is also induced by hypoxia and inflammation. The aim of this study was to investigate the role of CP in O(2)(-) generation in PMNs from healthy subjects and patients with LAgP.

METHODS

PMNs were isolated from healthy subjects and those with LAgP (N = 36). Superoxide was measured by cytochrome-C reduction at 550 nm. Intracellular CP expression was analyzed by real-time polymerase chain reaction and Western blotting. Serum levels of CP were measured by enzyme-linked immunosorbent assay. Intracellular iron ion conversion was spectrophotometrically determined by measuring the absorbance of sigma-phenanthroline at 510 nm.

RESULTS

O(2)(-) generation was significantly higher in LAgP PMNs before and after stimulation with formyl-methionyl-leucyl-phenylalanine (100 nM). CP expression in PMNs and CP levels in serum were significantly higher in subjects with LAgP compared to the PMNs and serum samples from matched healthy donors (P <0.05). LAgP PMNs also had significantly higher levels of Fe(3+) and lower levels of Fe(2+) compared to healthy PMNs (P <0.05), suggesting increased iron conversion. Exogenous CP treatment of healthy PMNs resulted in significant increases in O(2)(-) generation and iron ion conversion similar to LAgP PMNs.

CONCLUSION

LAgP PMNs are primed to express higher levels of CP, leading to hypoxia-mediated O(2)(-) generation in PMNs and increased oxidative stress and neutrophil-mediated tissue injury in LAgP.

Aminoacetone, a putative endogenous source of methylglyoxal, causes oxidative stress and death to insulin-producing RINm5f cells

Aminoacetone (AA), triose phosphates, and acetone are putative endogenous sources of potentially cytotoxic and genotoxic methylglyoxal (MG), which has been reported to be augmented in the plasma of diabetic patients. In these patients, accumulation of MG derived from aminoacetone, a threonine and glycine catabolite, is inferred from the observed concomitant endothelial overexpression of circulating semicarbazide-sensitive amine oxidases. These copper-dependent enzymes catalyze the oxidation of primary amines, such as AA and methylamine, by molecular oxygen, to the corresponding aldehydes, NH4(+) ion and H2O2. We recently reported that AA aerobic oxidation to MG also takes place immediately upon addition of catalytic amounts of copper and iron ions. Taking into account that (i) MG and H2O2 are reportedly cytotoxic to insulin-producing cell lineages such as RINm5f and that (ii) the metal-catalyzed oxidation of AA is propagated by O2(*-) radical anion, we decided to investigate the possible pro-oxidant action of AA on these cells taken here as a reliable model system for pancreatic beta-cells. Indeed, we show that AA (0.10-5.0 mM) administration to RINm5f cultures induces cell death. Ferrous (50-300 microM) and Fe(3+) ion (100 microM) addition to the cell cultures had no effect, whereas Cu(2+) (5.0-100 microM) significantly increased cell death. Supplementation of the AA- and Cu(2+)-containing culture medium with antioxidants, such as catalase (5.0 microM), superoxide dismutase (SOD, 50 U/mL), and N-acetylcysteine (NAC, 5.0 mM) led to partial protection. mRNA expression of MnSOD, CuZnSOD, glutathione peroxidase, and glutathione reductase, but not of catalase, is higher in cells treated with AA (0.50-1.0 mM) plus Cu(2+) ions (10-50 microM) relative to control cultures. This may imply higher activity of antioxidant enzymes in RINm5f AA-treated cells. In addition, we have found that AA (0.50-1.0 mM) plus Cu(2+) (100 microM) (i) increase RINm5f cytosolic calcium; (ii) promote DNA fragmentation; and (iii) increase the pro-apoptotic (Bax)/antiapoptotic (Bcl-2) ratio at the level of mRNA expression. In conclusion, although both normal and pathological concentrations of AA are probably much lower than those used here, it is tempting to propose that excess AA in diabetic patients may drive oxidative damage and eventually the death of pancreatic beta-cells.

The dual face of endogenous alpha-aminoketones: pro-oxidizing metabolic weapons

Amino metabolites with potential prooxidant properties, particularly alpha-aminocarbonyls, are the focus of this review. Among them we emphasize 5-aminolevulinic acid (a heme precursor formed from succinyl-CoA and glycine), aminoacetone (a threonine and glycine metabolite), and hexosamines and hexosimines, formed by Schiff condensation of hexoses with basic amino acid residues of proteins. All these metabolites were shown, in vitro, to undergo enolization and subsequent aerobic oxidation, yielding oxyradicals and highly cyto- and genotoxic alpha-oxoaldehydes. Their metabolic roles in health and disease are examined here and compared in humans and experimental animals, including rats, quail, and octopus. In the past two decades, we have concentrated on two endogenous alpha-aminoketones: (i) 5-aminolevulinic acid (ALA), accumulated in acquired (e.g., lead poisoning) and inborn (e.g., intermittent acute porphyria) porphyric disorders, and (ii) aminoacetone (AA), putatively overproduced in diabetes mellitus and cri-du-chat syndrome. ALA and AA have been implicated as contributing sources of oxyradicals and oxidative stress in these diseases. The end product of ALA oxidation, 4,5-dioxovaleric acid (DOVA), is able to alkylate DNA guanine moieties, promote protein cross-linking, and damage GABAergic receptors of rat brain synaptosome preparations. In turn, methylglyoxal (MG), the end product of AA oxidation, is also highly cytotoxic and able to release iron from ferritin and copper from ceruloplasmin, and to aggregate proteins. This review covers chemical and biochemical aspects of these alpha-aminoketones and their putative roles in the oxidative stress associated with porphyrias, tyrosinosis, diabetes, and cri-du-chat. In addition, we comment briefly on a side prooxidant behaviour of hexosamines, that are known to constitute building blocks of several glycoproteins and to be involved in Schiff base-mediated enzymatic reactions.

Ceruloplasmin and what it might do

The blue coloured plasma protein ceruloplasmin binds up to 95% of circulating copper, and has several possible functions. It has been proposed to function in copper transport, oxidation of organic amines, iron(II) oxidation and the regulation of cellular iron levels, and catechols, radical scavenging and other antioxidant processes. This account will consider the relative importance of these multiple functions in terms of the physiological roles of ceruloplasmin.