Functional models of nonheme diiron enzymes: kinetic and computational evidence for the formation of oxoiron(iv) species from peroxo-diiron(iii) complexes, and their reactivity towards phenols and H2O2.

The reactivity of the previously reported peroxo adducts [Fe2(µ-O2)(L(1))4(CH3CN)2](2+), and [Fe2(µ-O2)(L(2))4(CH3CN)2](2+), (L(1) = 2-(2'-pyridyl)benzimidazole and L(2) = 2-(2'-pyridyl)-N-methylbenzimidazole) towards H2O2 as catalase mimics, and towards various phenols as functional RNR-R2 mimics, is described. Kinetic, mechanistic and computational studies gave direct evidence for the involvement of the (µ-1,2-peroxo)diiron(iii) intermediate in the O-H activation process via formation of low-spin oxoiron(iv) species.

Red cells, hemoglobin, heme, iron, and atherogenesis.

OBJECTIVE: We investigated whether red cell infiltration of atheromatous lesions promotes the later stages of atherosclerosis. METHODS AND RESULTS: We find that oxidation of ferro (FeII) hemoglobin in ruptured advanced lesions occurs generating ferri (FeIII) hemoglobin and via more extensive oxidation ferrylhemoglobin (FeIII/FeIV=O). The protein oxidation marker dityrosine accumulates in complicated lesions, accompanied by the formation of cross-linked hemoglobin, a hallmark of ferrylhemoglobin. Exposure of normal red cells to lipids derived from atheromatous lesions causes hemolysis and oxidation of liberated hemoglobin. In the interactions between hemoglobin and atheroma lipids, hemoglobin and heme promote further lipid oxidation and subsequently endothelial reactions such as upregulation of heme oxygenase-1 and cytotoxicity to endothelium. Oxidative scission of heme leads to release of iron and a feed-forward process of iron-driven plaque lipid oxidation. The inhibition of heme release from globin by haptoglobin and sequestration of heme by hemopexin suppress hemoglobin-mediated oxidation of lipids of atheromatous lesions and attenuate endothelial cytotoxicity. CONCLUSIONS: The interior of advanced atheromatous lesions is a prooxidant environment in which erythrocytes lyse, hemoglobin is oxidized to ferri- and ferrylhemoglobin, and released heme and iron promote further oxidation of lipids. These events amplify the endothelial cell cytotoxicity of plaque components.

Supression of hemin-mediated oxidation of low-density lipoprotein and subsequent endothelial reactions by hydrogen sulfide (H(2)S).

Heme-mediated oxidative modification of low-density lipoprotein (LDL) plays a crucial role in early atherogenesis. It has been shown that hydrogen sulfide (H(2)S) produced by vascular smooth muscle cells is present in plasma at a concentration of about 50 micromol/L. H(2)S is a strong reductant which can react with reactive oxygen species like superoxide anion and hydrogen peroxide. The current study investigated the effect of H(2)S on hemin-mediated oxidation of LDL and oxidized LDL (oxLDL)-induced endothelial reactions. H(2)S dose dependently delayed the accumulation of lipid peroxidation products-conjugated dienes, lipid hydroperoxides (LOOH), and thiobarbituric acid reactive substances-during hemin-mediated oxidation. Moreover, H(2)S decreased the LOOH content of both oxidized LDL and lipid extracts derived from soft atherosclerotic plaque, which was accompanied by reduced cytotoxicity. OxLDL-mediated induction of the oxidative stress responsive gene, heme oxygenase-1, was also abolished by H(2)S. Finally we have shown that H(2)S can directly protect endothelium against hydrogen peroxide and oxLDL-mediated endothelial cytotoxicity. These results demonstrate novel functions of H(2)S in preventing hemin-mediated oxidative modification of LDL, and consequent deleterious effects, suggesting a possible antiatherogenic action of H(2)S.

Identification of sulfhemoglobinemia after surgical polypectomy.

Sulfhemoglobinemia (SHb) is an uncommon cause of cyanosis that is predominantly drug-induced in adults. We report an unusual case of sodium sulfate-induced sulfhemoglobinemia in a 61-year-old woman after surgical polypectomy. Fractional hemoglobin derivates were assayed by spectrophotometry and high-performance liquid chromatography. The SHb ratio was 8.6% in the first sample and 3.77% a month later measured by spectrophotometry. In the blood hemolysate, a new peak was identified as SHb with high-performance liquid chromatography (HPLC). HPLC showed the presence of 9.37% SHb in the first sample and 4.88% a month later. After removing the suspected toxic agent the cyanosis decreased significantly. The findings underline the importance of routine SHb detection in cyanosis of unknown origin especially in emergency cases.

Serum levels of platelet released CD40 ligand are increased in early onset occlusive carotid artery disease.

OBJECTIVE: Soluble CD40 ligand (sCD40L) has been suggested as a key mediator between inflammation and atherosclerosis, and the CD40-CD40L interaction has a role in atherosclerotic lesion progression. We evaluated if platelet released serum sCD40L and sCD40 levels differ between patients with early onset occlusive carotid artery disease and age-matched controls. METHODS: sCD40L and sCD40 levels were measured in serum samples of 60 patients with occlusive carotid artery disease and 30 age-matched controls using ELISA. Degree of stenosis of the internal carotid artery (ICA), and intima-media thickness (IMT) in the common carotid artery were measured by high resolution ultrasound. Values are given as mean +/- SD. RESULTS: Mean age was 50.9 +/- 3.5 and 50.1 +/- 3.5 years in the patient and control groups. IMT was significantly thicker in patients than in controls (0.89 +/- 0.14 vs. 0.78 +/-0.12 mm, p=0.0003). Serum levels of sCD40L were significantly higher (6.9 +/- 5 vs. 4.5 +/- 3.0 ng/mL, p=0.038) in patients, whereas sCD40 did not differ significantly between patients and controls (85 +/- 56.9 vs. 79.3 +/- 18.7 pg/mL, p=0.34). IMT did not correlate with sCD40L or sCD40 levels (R=-0.03, p=0.77; and R=0.109, p=0.308, respectively). CONCLUSIONS: sCD40L but not sCD40 levels are significantly higher in patients with occlusive carotid artery disease. Platelet derived sCD40L may be a key mediator among inflammation, thrombosis and atherosclerosis.

The antifungal protein AFP secreted by Aspergillus giganteus does not cause detrimental effects on certain mammalian cells.

The antifungal protein AFP is a small, cystein-rich protein secreted by the imperfect ascomycete Aspergillus giganteus. The protein efficiently inhibits the growth of filamentous fungi, including a variety of serious human and plant pathogens mainly of the genera Aspergillus and Fusarium, whereas AFP does not affect the growth of yeast and bacteria. This restricted susceptibility range makes it very attractive for medical or biotechnological use to combat fungal infection and contamination. We, therefore, analyzed whether AFP affects the growth or function of a number of mammalian cells. Here we show that the protein neither provokes any cytotoxic effects on human endothelial cells isolated from the umbilical vein nor activates the immune system. Moreover, potassium currents of neurons and astrocytes do not change in the presence of AFP and neither excitatory processes nor the intracellular calcium homeostasis of cultured skeletal muscle myotubes are affected by AFP. Our data, therefore, suggest that AFP is indeed a promising candidate for the therapeutic or biotechnological use as a potential antifungal agent.

The Penicillium chrysogenum-derived antifungal peptide shows no toxic effects on mammalian cells in the intended therapeutic concentration.

Certain filamentous fungi, such as the penicillin-producing strain Penicillium chrysogenum, secrete small, highly basic and cysteine-rich proteins with antifungal effects. Affected fungi include a number of important zoopathogens, including those infecting humans. Recent studies, however, have pointed to a membrane-perturbing effect of these antifungal compounds, apparent as a potassium efflux from affected fungal cells. If present on mammalian cells, this would severely hinder the potential therapeutic use of these molecules. Here we studied the effects of the P. chrysogenum-derived antifungal peptide (PAF) on a number of mammalian cells to establish whether the protein has any cytotoxic effects, alters transmembrane currents on excitable cells or activates the immune system. PAF, in a concentration range of 2-100 mug/ml, did not cause any cytotoxicity on human endothelial cells from the umbilical vein. Applied at 10 mug/ml, it also failed to modify voltage-gated potassium channels of neurones, skeletal muscle fibers, and astrocytes. PAF also left the hyperpolarization-activated non-specific cationic current (I(h)) and the L-type calcium current unaffected. Finally, up to 2 mug/ml, PAF did not induce the production of pro-inflammatory cytokines such as IL-6, IL-8, and TNF-alpha. These results suggest that PAF should have only minor, if any, effects on mammalian cells in the intended therapeutic concentration range.

Haem, haem oxygenase and ferritin in vascular endothelial cell injury.

Iron-derived reactive oxygen species (ROS) are implicated in the pathogenesis of numerous vascular disorders including atherosclerosis, microangiopathic haemolytic anaemia, vasculitis and reperfusion injury. One abundant source of redox-active iron is haem, which is inherently dangerous when released from intracellular haem proteins. The present review concerns the likely involvement of haem in vascular endothelial cell damage and the strategies used by endothelium to minimize such damage. Exposure of endothelial cells to haem greatly potentiates cell killing mediated by polymorphonuclear leukocytes and other sources of ROS. Free haem also promotes the conversion of low-density lipoprotein to cytotoxic oxidized products. If only because of its abundance, haemoglobin probably represents the most important potential source of haem within the vascular endothelium; free haemoglobin in plasma, when oxidized, can transfer haem to endothelium, thereby enhancing cellular susceptibility to oxidant-mediated injury. As a defence against such toxicity, upon exposure to free haem, endothelial cells up-regulate haem oxygenase-1 and ferritin. Haem oxygenase is a haem-degrading enzyme that opens the porphyrin ring, producing biliverdin, carbon monoxide and a most dangerous product-free redox-active iron. The latter can be controlled effectively by sequestration within ferritin, a multimeric protein with a very high capacity for storing iron. These homeostatic adjustments have been shown to be effective in the protection of endothelium against the damaging effects of exogenous haem and oxidants. The central importance of this protective system was highlighted recently by the discovery of a child diagnosed with haem oxygenase-1 deficiency, who exhibited extensive endothelial damage.