Secondary radicals derived from chloramines of apolipoprotein B-100 contribute to HOCl-induced lipid peroxidation of low-density lipoproteins. (1/711)

Oxidation of low-density lipoproteins (LDL) is thought to contribute to atherogenesis. Although there is increasing evidence for a role of myeloperoxidase-derived oxidants such as hypochlorite (HOCl), the mechanism by which HOCl modifies LDL remains controversial. Some studies report the protein component to be the major site of attack, whereas others describe extensive lipid peroxidation. The present study addresses this controversy. The results obtained are consistent with the hypothesis that radical-induced oxidation of LDL's lipids by HOCl is a secondary reaction, with most HOCl consumed via rapid, non-radical reaction with apolipoprotein B-100. Subsequent incubation of HOCl-treated LDL gives rise to lipid peroxidation and antioxidant consumption in a time-dependent manner. Similarly, with myeloperoxidase/H2O2/Cl- (the source of HOCl in vivo), protein oxidation is rapid and followed by an extended period of lipid peroxidation during which further protein oxidation does not occur. The secondary lipid peroxidation process involves EPR-detectable radicals, is attenuated by a radical trap or treatment of HOCl-oxidized LDL with methionine, and occurs less rapidly when the lipoprotein was depleted of alpha-tocopherol. The initial reaction of low concentrations of HOCl (400-fold or 800-fold molar excess) with LDL therefore seems to occur primarily by two-electron reactions with side-chain sites on apolipoprotein B-100. Some of the initial reaction products, identified as lysine-residue-derived chloramines, subsequently undergo homolytic (one-electron) reactions to give radicals that initiate antioxidant consumption and lipid oxidation via tocopherol-mediated peroxidation. The identification of these chloramines, and the radicals derived from them, as initiating agents in LDL lipid peroxidation offers potential new targets for antioxidative therapy in atherogenesis.  (+info)

When and why a water-soluble antioxidant becomes pro-oxidant during copper-induced low-density lipoprotein oxidation: a study using uric acid. (2/711)

The inclusion of uric acid in the incubation medium during copper-induced low-density lipoprotein (LDL) oxidation exerted either an antioxidant or pro-oxidant effect. The pro-oxidant effect, as mirrored by an enhanced formation of conjugated dienes, lipid peroxides, thiobarbituric acid-reactive substances and increase in negative charge, occurred when uric acid was added late during the inhibitory or lag phase and during the subsequent extensive propagation phase of copper-stimulated LDL oxidation. The pro-oxidant effect of uric acid was specific for copper-induced LDL oxidation and required the presence of copper as either Cu(I) or Cu(II). In addition, it became much more evident when the copper to LDL molar ratio was below a threshold value of approx. 50. In native LDL, the shift between the antioxidant and the pro-oxidant activities was related to the availability of lipid hydroperoxides formed during the early phases of copper-promoted LDL oxidation. The artificial enrichment of isolated LDL with alpha-tocopherol delayed the onset of the pro-oxidant activity of uric acid and also decreased the rate of stimulated lipid peroxidation. However, previous depletion of alpha-tocopherol was not a prerequisite for unmasking the pro-oxidant activity of uric acid, since this became apparent even when alpha-tocopherol was still present in significant amounts (more than 50% of the original values) in LDL. These results suggest, irrespective of the levels of endogenous alpha-tocopherol, that uric acid may enhance LDL oxidation by reducing Cu(II) to Cu(I), thus making more Cu(I) available for subsequent radical decomposition of lipid peroxides and propagation reactions.  (+info)

Stabilized polynuclear iron hydroxide is an efficient oral phosphate binder in uraemic patients. (3/711)

BACKGROUND: There is a continuing need for non-aluminium and non-calcium-containing oral phosphate binders. A novel product, i.e. stabilized polynuclear iron hydroxide, has experimentally been shown to be an effective phosphate binder. The purpose of the study was to test the efficacy and tolerability of the compound in hyperphosphataemic patients with stable preterminal renal failure. METHODS: In an open uncontrolled study we examined a total of 13 patients with stable preterminal renal failure (median serum-creatinine 5.4 mg/dl, range 4.2-7.3 mg/dl) and hyperphosphataemia (median fasting plasma-Pi 2.2 mmol/l, range 1.95 3.0 mmol/l). Patients were given dietary advise to maintain a constant intake of phosphate and this was verified by measuring urinary Pi excretion. After 2 weeks on no oral phosphate binders, patients were given daily 3 x 2.5 g stabilized polynuclear iron hydroxide with meals for 4 weeks. In a blinded fashion plasma-Pi and urinary-Pi as well as 1,84 i-PTH, vitamin D metabolites, serum-iron and ferritin were measured in a central laboratory. RESULTS: Compared to baseline (no oral phosphate binders), the median per cent decrease of fasting plasma-Pi at day 14 was 20% (7.2-41%) (P<0.001 by Wilcoxon test) and the median per cent decrease of urinary P excretion was 37% (9.6-56.6%) (P<0.0003 by Wilcoxon test for paired differences). Ferritin levels did not differ significantly during the study. Apart from a certain laxative action and black discolouration of the faeces, no side effects were noted in this short-term study. CONCLUSION: Stabilized polynuclear iron hydroxide is a promising, efficaceous and well tolerated phosphate binder.  (+info)

Bilirubin-Cu(II) complex degrades DNA. (4/711)

It has recently been reported that bilirubin forms a complex with Cu(II). In this paper we show that the formation of the complex results in the reduction of Cu(II) to Cu(I) and the redox cycling of the metal gives rise to the formation of reactive oxygen species, particularly hydroxyl radical. The bilirubin-Cu(II) complex causes strand breakage in calf thymus DNA and supercoiled plasmid DNA. Cu(I) was shown to be an essential intermediate in the DNA cleavage reaction by using the Cu(I) specific sequestering reagent neocuproine. Bilirubin-Cu(II) produced hydroxyl radical and the involvement of active oxygen species was established by the inhibition of DNA breakage by various oxygen radical quenchers.  (+info)

Effects of aluminum on plasma membrane as revealed by analysis of alkaline band formation in internodal cells of Chara corallina. (5/711)

To study the mechanism of aluminum toxicity in plant cells, the effects of aluminum on alkaline band formation were analyzed in the internodal cells of Chara. After cells were treated with AlCl3, they were examined for their capacity to develop alkaline bands. Treating cells with AlCl3 medium at pH 4.5 completely inhibited alkaline band formation. When either CaCl2 or malic acid was added to the AlCl3 medium (pH 4.5), it did not produce an ameliorative effect, whereas addition of both CaCl2 and malic acid induced a significant ameliorative effect. It was found that treatment at pH 4.5 in the absence of AlCl3 strongly inhibited alkaline band formation. This inhibition by the low pH (4.5) treatment was effectively ameliorated by CaCl2. At higher pH (5.0), malic acid alone produced a significant ameliorative effect on aluminum inhibition of alkaline band formation, but CaCl2 did not. Recovery from aluminum inhibition was also studied. When cells treated with AlCl3 at pH 4.5 were incubated in artificial pond water, they could not recover the capacity to develop alkaline band. When either malic acid or CaCl2 was added to artificial pond water, cells recovered their alkaline band formation. It was concluded that one of the primary targets of aluminum is the plasma membrane and that aluminum affects the plasma membrane from the cell exterior at the beginning of the treatment (within 24 h). It was also suggested that the aluminum treatment impairs the HCO3- influx mechanism but not the OH- efflux mechanism.  (+info)

Carboxylate binding modes in zinc proteins: a theoretical study. (6/711)

The relative energies of different coordination modes (bidentate, monodentate, syn, and anti) of a carboxylate group bound to a zinc ion have been studied by the density functional method B3LYP with large basis sets on realistic models of the active site of several zinc proteins. In positively charged four-coordinate complexes, the mono- and bidentate coordination modes have almost the same energy (within 10 kJ/mol). However, if there are negatively charged ligands other than the carboxylate group, the monodentate binding mode is favored. In general, the energy difference between monodentate and bidentate coordination is small, 4-24 kJ/mol, and it is determined more by hydrogen-bond interactions with other ligands or second-sphere groups than by the zinc-carboxylate interaction. Similarly, the activation energy for the conversion between the two coordination modes is small, approximately 6 kJ/mol, indicating a very flat Zn-O potential surface. The energy difference between syn and anti binding modes of the monodentate carboxylate group is larger, 70-100 kJ/mol, but this figure again strongly depends on interactions with second-sphere molecules. Our results also indicate that the pK(a) of the zinc-bound water ligand in carboxypeptidase and thermolysin is 8-9.  (+info)

Cytoplasmic delayed neuronal death in the myenteric plexus of the rat small intestine after ischemia. (7/711)

The present study demonstrates light and electron microscopic changes in neurons in the myenteric plexus of the rat ileum following four-hour ischemia. Macroscopically, an intestinal constriction occurred at the damaged portion at three weeks after ischemia; the segment oral to the constriction markedly swelled at four weeks. In light microscopy, at three weeks after ischemia, the myenteric neurons appeared spongy or foamy, containing many vacuoles in their somatic cytoplasm. At four weeks, the neuronal cytoplasm and nerve fiber bundles had disintegrated to form vacant spaces in the myenteric plexus. The neuronal nucleus of the damaged plexus did not show positive nick-end labeling. In electron microscopy, neuronal cytoplasm revealed degenerative signs already at one week after ischemia: a distended endoplasmic reticulum and swollen mitochondria with fragmentary cristae. The nerve fibers also showed destruction of the mitochondria, and degenerative changes in the postsynaptic sites appeared earlier than the presynaptic terminals. The results suggest that intestinal ischemia causes delayed neuronal death, which differs from the apoptotic process previously demonstrated in the ischemia-damaged brain.  (+info)

Diagnosing dermatomycosis in general practice. (8/711)

BACKGROUND: Diagnosing dermatomycosis from a clinical image is not always easy. Microscopy of a potassium hydroxide preparation (KOH-test) and culturing are seldomly used in general practice. Cyanoacrylate surface skin scraping (CSSS) is a new diagnostic tool that may be useful and simple. OBJECTIVES: We aimed to investigate the diagnostic value of signs and symptoms, the KOH-test and the CSSS, in patients with erythematosquamous skin lesions, using the culture as the gold standard. Our goal is to formulate an optimal algorithm for the diagnosis of mycosis, based on one or more of these tests and including both optimal accuracy and costs. METHODS: Scales from 148 consecutive general practice patients were tested using a KOH-test, CSSS and culture. Clinical data were collected using a questionnaire. RESULTS: Twenty-six (18%) positive fungal cultures were identified. The sensitivity of the clinical diagnosis was 81% and its specificity 45%; for the KOH-test, these figures were 12 and 93% respectively; and for the CSSS, 62 and 88%, respectively. The positive predictive value of the clinical diagnosis was 24% and the negative predictive value 92%; for the KOH-test these figures were 25 and 83%, respectively, and for the CSSS, 52 and 92%, respectively. Determining CSSS in all patients proved to be the most accurate policy (accuracy = 83%). The likelihood ratio of CSSS in all patients was 5.17 for a positive test result and 0.43 for a negative test result. An approach in which CSSS is obtained in only those patients whom the physician considers by clinical examination to have dermatomycosis, with no testing in other patients, results in positive and negative likelihood ratios of 4.69 and 0.56, respectively. Such a policy would result in an overall sensitivity of 50%, a specificity of 89%, a positive predictive value of 50% and a negative predictive value of 89%. DISCUSSION: The clinical picture of dermatomycosis is not very reliable. The combination of a clinical judgement if this is negative and an additional CSSS in the case of a positive clinical judgement provides us with the best cost-benefit ratio, if both diagnostic accuracy and logistic considerations are taken into consideration.  (+info)