Synthesis and iron(III) binding properties of 3-hydroxypyrid-4-ones derived from kojic acid

In an attempt to reduce the toxicity of the 3-hydroxypyrid-4-ones, the more hydrophilic derivatives of kojic acid were explored and compared to the standard, 1,2-dimethyl-3-hydroxypyrid-4-one, L1. The synthesis and iron(III) binding properties of these chelators are described. Neither these compounds nor the clinically effective 1,2-dimethyl-3-hydroxypyrid-4 one is able to completely remove all of the iron(III) from the Fe(III)EDTA complex in sodium acetate buffered solutions, when the 3-hydroxypyrid-4-one: Fe(III) ratio is 6:1. The ability of these compounds to enhance the urinary excretion of iron in rats indicates that the behavior of the 3-hydroxypyrid-4-ones derived from kojic acid is comparable to the analogous derivatives of maltol and ethyl maltol. The structure of the iron(III) complex of 3-hydroxy-6-hydroxymethyl-1-methylpyrid-4-one was determined by x-ray diffraction and found to be similar to the previously reported structure of the iron(III) complex of L1.

Staphylococcal iron requirements, siderophore production, and iron-regulated protein expression

Despite the ability of staphylococci to grow in iron-restricted conditions in vivo, their iron requirements and the mechanisms possessed by them for the uptake of iron are poorly understood. Many bacteria are known to produce siderophores. By using the chrome azurol S universal method for the detection of siderophores, all 14 isolates of Staphylococcus aureus tested grew well under conditions of iron restriction and produced iron-regulated siderophore in large quantities, while all 19 isolates of coagulase-negative staphylococci (CoNS) grew poorly under conditions of iron restriction and produced low levels of iron chelator. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of S. aureus isolates revealed altered protein patterns due to iron restriction, while altered profiles were not seen in the CoNS group. The ability to grow in iron-restricted conditions, possibly with the assistance of siderophore-mediated iron uptake, may contribute to the increased pathogenicity of S. aureus when compared with that of the CoNS.

Age-related phospholipid hydroperoxide levels in gerbil brain measured by HPLC-chemiluminescence and their relation to hydroxyl radical stress

Phosphatidylcholine hydroperoxide (PCOOH) was directly quantified in the hippocampus, cortex and striatum from young (3 months), middle-aged (15 months) and old (20 to 24 months) gerbils by an HPLC-chemiluminescence assay. PCOOH levels in hippocampus and cortex were found between 8.05 to 8.58 pmol/mg tissue and no statistically significant difference was found across the age groups. In striatum, however, PCOOH levels were significantly higher in middle-aged and old gerbils compared to those in young animals. The regional comparison showed that PCOOH levels were significantly higher in striatum than in cortex or hippocampus for all the age groups. Moreover, this regional difference increased with aging, from approximately 20% in young animals to 30% and 40% in middle-aged and old gerbil striatum. PCOOH to phospholipid ratio is approximately the same for all age groups at the level of 1.5/10,000, although it is slightly lower in the cortex. The hydroxyl radical levels in the brain were also measured by the formation of its salicylate trapped product 2,3-DHBA and used as a measure of oxidative stress. The PCOOH levels was used as a measure of oxygen radical-induced lipid peroxidative damage. PCOOH as a function of hydroxyl radical stress was calculated and expressed as PCOOH/2,3-DHBA, representing the oxidative damage as a function of the level of oxidative stress. It also implies the tissue susceptibility to oxidative stress and the efficiency of the antioxidant systems. In hippocampus and cortex, the ratios are high in young gerbils, decrease at middle-age and significantly increase in the old.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary iron excretion depends on the mode of administration of the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one in patients with homozygous beta-thalassemia

OBJECTIVE

To examine the effect of frequency of oral administration of 1,2-dimethyl-3-hydroxypyrid-4-one (L1) on urinary iron excretion.

HYPOTHESIS

Sustained serum concentrations of L1 will cause more iron chelation than the same daily dose given in larger but less frequent amounts.

PATIENTS AND METHODS

Ten patients with thalassemia with a mean age of 20.9 +/- 4.7 years (range, 13 to 27 years), who were receiving regular treatment with 75 to 100 mg/kg/day oral L1, received 75 mg/kg/day L1 orally in equally divided doses: every 6 hours for 3 days and every 12 hours for 3 days. The two study periods occurred 1 month apart immediately after the monthly blood transfusions. Urine was collected for two consecutive 24-hour periods during each of the different schedules. Serial blood samples were collected from six patients over a 6-hour period and analyzed for total L1 and the L1 glucuronide metabolite concentrations.

RESULTS

The patient's mean hemoglobin levels (138.8 +/- 12.5 and 139.0 +/- 11.6 gm/L) and ferritin levels (2856.4 +/- 2207.8 and 2890.0 +/- 2264.4 micrograms/L) were similar during the every-6-hour and every-12-hour L1 administrations, respectively. There was significantly more urinary iron excretion when L1 was administered every 6 hours (0.59 +/- 0.29 mg/kg/day) versus every 12 hours (0.40 +/- 0.26 mg/kg/day; p = 0.0129). Calculated 24-hour area under the plasma concentration-time curve of L1 was similar during the every-6-hour (7023.9 +/- 2637.8 mg.min/L) and every-12-hour (7050.1 +/- 1668.8 mg.min/L) experiments.

CONCLUSIONS

These data suggest that the sustained presence of L1 in the blood results in greater chelation of iron than that observed with larger, less frequent doses.

Alcohol-associated generation of oxygen free radicals and tumor promotion

We discuss evidence indicating how ethanol could generate oxygen free radicals. Recent use of techniques such as spin trapping and EPR spectroscopy have demonstrably confirmed that both acute and chronic alcohol use by laboratory animals would generate free radical intermediates. These radicals are of biological origin and presumably involve lipids. However, an exact identification of the intermediates produced has not been worked out with the currently available methodologies. Also not known is the mechanism whereby ethanol could initiate free radicals. The relationship between generation of free radicals and cell toxicity or carcinogenesis is also not understood. Using a variety of systems that included different species, strains and gender (male Sprague-Dawley and Fisher-344 rats, female C57BL/6 mice, male Syrian golden hamsters) and carcinogens (NMBZA, NNN, NNK, DMBA and LP-BM5 retrovirus) we have shown an association of lipid peroxidation with ethanol tumor promotionability. However, the process of tumor promotion in general is not very clear and the role played by ethanol in this process is still more unclear. Here we are reviewing evidence that could possibly be involved in such promotion processes.

Characterization of regulatory mutations causing anaerobic derepression of the sodA gene in Escherichia coli K12: cooperation between cis- and trans-acting regulatory loci

The genetic loci leading to anaerobic derepression of a sodA::lacZ protein fusion in a UV-generated mutant strain (UV14) of Escherichia coli were identified. The mutant (UV14) was found to harbour two altered loci: one is in the trans-regulatory gene fnr (fumarate nitrate reduction) where leucine-129 was changed to glutamine (fnr14), and the second (sodA14) is in the promoter region (cis) of the sodA gene apparently affecting the binding of the Fur (ferric uptake regulation) protein. Introduction of an fnr+ gene into UV14 restored anaerobic repression of sodA::lacZ and restored the ability of the cells to reduce nitrate. However, when either the fnr14 or the sodA14 mutation was introduced into an otherwise wild-type background, only slight anaerobic derepression of sodA was observed. When both the cis- and trans-acting mutations (i.e. sodA14 and fnr14) were combined simultaneously in an otherwise wild-type background, the specific activity of sodA::lacZ expression was comparable to that of the original mutant strain (UV14). Furthermore, a genetically confirmed fur fnr double mutant was also similarly derepressed in anaerobic sodA::lacZ expression. The data presented suggest that the cis-mutation in UV14 (sodA14) affects the Fur-binding site in the sodA promoter, while having no effect on Fnr or Arc mediated repression. Also, a second putative Fnr-binding site that straddles the ribosomal binding-site was identified in the sodA gene.

Purification of yersiniabactin: a siderophore and possible virulence factor of Yersinia enterocolitica

HPLC analysis revealed that Yersinia enterocolitica WA-C produced two substances under iron-limiting conditions one of which was identified as 2,3-dihydroxybenzoyl-L-serine. The other compound had iron-complexing activity and was called yersiniabactin. The fur mutant H1852 was shown to produce yersiniabactin constitutively in an iron-independent manner. Yersiniabactin was isolated by ethyl acetate extraction from the spent medium of H1852, size-fractionation chromatography and preparative HPLC. A catechol function was demonstrated with different chemical assays and by UV-visible spectroscopy. The molecular mass of yersiniabactin was determined to be 482 Da. Purified yersiniabactin stimulated growth of Y. enterocolitica and Escherichia coli phi under iron-limiting conditions and apparently served as an iron carrier. Transport of 55Fe-yersiniabactin was TonB-dependent, indicating a receptor-mediated uptake across the outer membrane. A pesticin-resistant mutant missing the receptor protein FyuA was unable to transport and use yersiniabactin as a siderophore.

Contrasting interspecies efficacy and toxicology of 1,2-diethyl-3-hydroxypyridin-4-one, CP94, relates to differing metabolism of the iron chelating site

In order to define a predictive animal model for the effects of hydroxypyridinone (HPO) iron chelators in humans, we have compared the 28 d oral efficacy and toxicology of the HPO, 1,2-diethyl-3-hydroxypyridin-4-one (CP94) in rats and guinea-pigs and related the results to the contrasting metabolism of this compound in the two species. CP94 was highly effective at mobilizing liver iron in rats but showed toxicity at higher doses, whereas in the guinea-pig the compound lacked toxicity but was ineffective at mobilizing liver iron. These differences can be explained by the contrasting metabolism of the drug between the two species. In rats, at the top dose of 300 mg/kg intragastrically, all animals died before the end of the study, with no deaths or weight loss at lower doses. At 100 mg/kg, rat liver non-haem iron concentrations were reduced by 53% and 44% in females and males respectively (P < 0.001). At this dose, adrenal medullary cell vacuolation, increased mammary secretory activity, vacuolation of corpora luteal cells and single cell hepatocyte necrosis were seen. There were no reductions in the white cell count. At 50 mg/kg rat liver non-haem iron concentrations were decreased by 50% and 34% in females and males respectively (P < 0.02). In female rats this was associated with increased mammary secretory activity. In iron-overloaded rats given 100 mg/kg by gavage for 28 d, liver non-haem iron concentration was reduced by 39% (P < 0.01) and serum ferritin by 71% (P < 0.001). Ovarian and mammary changes were not influenced by iron loading. In guinea-pigs, CP94 was evaluated at 50 mg/kg, 100 mg/kg or 200 mg/kg by oral insufflation for 28 d. No reduction in liver iron was seen and no systematic dose related histological, biochemical or haematological effects were observed. Whereas in guinea-pigs 99% of urinary recovery following an oral dose of CP94 (100 mg/kg) was as the inactive glucuronide metabolite, in the rat only 23% of the dose was excreted in the urine as the glucuronide with remainder as the free drug or an iron binding metabolite. The lack of both efficacy and toxicity in the guinea-pig may therefore be explained by the rapid inactivation of CP94 by glucuronidation. This metabolism of CP94 in the guinea-pig is closer to humans than the rat, suggesting that both the efficacy and toxicity of this compound in humans may also be limited by glucuronidation.

Chelatable iron and copper can be released from extracorporeally circulated blood during cardiopulmonary bypass

During cardiopulmonary bypass surgery blood is extracorporeally oxygenated and circulated before returning to the systemic arterial circulation. Blood undergoing extracorporeal dilution and circulation is exposed to non-physiological surfaces, which cause the activation of several regulatory cascades. Cells are also subjected to damaging shear stresses. Under such conditions neutrophils can be 'activated' to release reactive oxygen intermediates such as O2- and H2O2, and other cells can release proteolytic enzymes and metalloproteins. Collectively, these events can result in the release of micromolar quantities of redox active iron and copper. Bleomycin-detectable iron and phenanthroline-detectable copper were found in two out of four mock bypass experiments. However, there was no correlation between the presence of chelatable iron and copper and the activation of neutrophils measured as elastase.

Effects of iron loading on uptake, speciation, and chelation of iron in cultured myocardial cells

Accumulation of Fe in the myocardium in circumstances of transferrin saturation is associated with heart failure in Fe-loaded patients. To characterize the underlying causes of this phenomenon, we measured the flux as well as the speciation of Fe in normal and Fe-loaded cultures of rat myocardiocytes. Fe loading with low-molecular-weight Fe (ferric ammonium citrate) promoted a dose- and time-dependent increase in the rate of uptake of non-transferrin-bound Fe (NTBI) that was positively correlated (R = 0.9, p < 0.005) with cellular iron content. At concentrations sufficient to produce this up-regulation, membrane integrity was unaffected but the rate of spontaneous beating of the cells was decreased by 60%. The enhanced rate of NTBI uptake in Fe-loaded cells reverted to control rates after treatment with therapeutic concentrations of Fe chelators deferoxamine, 1,2-dimethyl-3-hydroxypyrid-4-one and 1,2-diethyl-3-hydroxypyrid-4-one under conditions where approximately 80% of the cellular Fe was removed by chelation. Fe loading of cultured myocytes also induced shifts in Fe speciation. Thus the ratio of Fe bound in hemosiderin-like precipitates to ferritin-bound Fe increased twofold, from a range of 0.84 to 1.44 in control cells to 1.96 to 3.3 in iron-loaded cells. This increased ratio was similar to that measured in the heart and liver of a thalassemic patient who underwent a double transplant for the failure of both organs, even though the Fe content of the heart (mean, 5.8 mg Fe/gm dry weight) was much less than that of the liver (28.1 mg/gm dry weight). These results suggest that increased rates of uptake of NTBI may exacerbate iron loading of the heart and contribute to iron-mediated cardiotoxicity, whereas the clinical benefits of chelation therapy may be enhanced by the down-regulation of NTBI uptake.

Iron chelation by deferoxamine in sickle cell patients with severe transfusion-induced hemosiderosis: a randomized, double-blind study of the dose-response relationship

Transfusion-induced hemosiderosis is a serious and potentially life-threatening complication for some patients with sickle cell anemia. The use of high-dose intravenous deferoxamine (DFO) has become widespread in spite of a paucity of published data on safety and efficacy. We report a randomized double-blind study of the dose-response relationship of intravenous DFO in six subjects with sickle cell anemia and severe transfusion-induced hemosiderosis (serum ferritin 4100 to 14,176 ng/ml). Each subject received three different doses of intravenous DFO for 3 days each while consuming a constant diet. Total iron excretion (urine and fecal) was 91% greater at 180 mg/kg/day DFO than at 60 mg/kg/day DFO, and fecal iron excretion became a relatively larger proportion of total excretion at higher doses. Subsequent treatment for 3 months with 150 mg/kg/day DFO caused a 33% to 60% reduction in serum ferritin and demonstrable improvement in hepatic function in all patients. No toxicity was encountered, but DFO at 180 mg/kg/day was associated with a significant increase in fecal zinc excretion when compared with that observed at lower doses.

Iron release and uptake by plant ferritin: effects of pH, reduction and chelation

Ferritins are iron-storage proteins that accumulate in plastids during seed formation, and also in leaves during senescence or iron overload. Iron release from ferritins occurs during growth of seedlings and greening of plastids. Depending on the concentration of the reducing agent ascorbate, either an overall iron release or uptake by ferritins from iron(III) citrate may occur. We have designed methods to measure these simultaneous and independent uptake and release fluxes. Each individual step of the exchange was studied using different iron chelates and an excess of ligand. It is shown that: (i) the chelated form of iron, and not ionic Fe3+, is the substrate for iron reduction, which controls the subsequent uptake by ferritin; (ii) iron uptake by ferritins is faster at pH 8.4 than at pH 7 or 6 and is inhibited by an excess of strongly binding free ligands; and (iii) strongly binding free ligands are inhibitory during iron release by ascorbate. When reactions are allowed to proceed simultaneously, the iron chelating power is shown to be a key factor in the overall exchange. The interactions of iron chelating power, reducing capacity and pH are discussed with regard to their influence on the biochemical mobilization of iron.

Iron sequestration by macrophages decreases the potential for extracellular hydroxyl radical formation

Alveolar macrophages (AM) from smokers contain a much higher quantity of intracellular iron than AM from nonsmokers. Since some forms of iron will catalyze the formation of hydroxyl radical (.OH) from superoxide and hydrogen peroxide, the ability of AM derived from smokers and nonsmokers to generate .OH was assessed. No detectable .OH was produced by AM from either source, suggesting that iron sequestration by AM may limit the potential for .OH-mediated lung injury. Consistent with this hypothesis, the ability of bronchoalveolar lavage fluid (BAL) from smokers and nonsmokers to act as an .OH catalyst decreased after exposure to AM. We found that, like AM, human monocyte-derived macrophages (MDM) have the ability to acquire large quantities of iron from small low molecular weight iron chelates as well as decrease the ability of BAL to act as a .OH catalyst. When MDM or AM were exposed to the iron chelates or BAL they were then able to generate .OH after phorbol myristate acetate stimulation. However, when acutely iron-loaded or BAL-exposed MDM were placed in culture, their ability to produce .OH decreased with time to the level of non-iron-exposed controls. This process correlated with iron translocation from the plasma membrane to the cytosol as well as a 3-9-fold increase in cellular ferritin. No increase in antioxidant enzyme levels or induction of the heat shock response was observed. Iron sequestration by macrophages may protect nearby cells from exposure to potentially cytotoxic iron-catalyzed oxidants such as .OH.

Suppression of colonic cancer by dietary phytic acid

Large differences exist between human populations in the frequency of colonic cancer. Epidemiological evidence indicates that these differences are strongly influenced by country of residence, and a negative correlation has been found between the fiber content of the diet and frequency of colonic cancer. This has prompted the hypothesis that high-fiber diets are in some way protective. However, reanalysis of the dietary data provides equally strong support for the hypothesis that the protective element may be phytic acid (inositol hexaphosphate). This heat- and acid-stable substance is present in high concentration in many food items, including cereal grains, nuts, and seeds. Phytic acid forms chelates with various metals and suppresses damaging iron-catalyzed redox reactions. Inasmuch as colonic bacteria have been shown to produce oxygen radicals in appreciable amounts, dietary phytic acid might suppress oxidant damage to intestinal epithelium and neighboring cells. Indeed, rapidly accumulating data from animal models indicate that dietary supplementation with phytic acid may provide substantial protection against experimentally induced colonic cancer. Should further investigations yield additional support for this hypothesis, purposeful amplification of dietary phytic acid content would represent a simple method for reducing the risk of colonic carcinogenesis.

Mode of action of iron (III) chelators as antimalarials: I. Membrane permeation properties and cytotoxic activity

We have designed two subfamilies of lipophilic iron (III) chelators previously termed reversed siderophores (RSFs). The agents display physicochemical properties that favor extraction of iron beyond membrane barriers of Plasmodium falciparum-infected red blood cells. We studied the in vitro antimalarial potency of RSFs and their relationship to the membrane permeation properties of these agents. The mode of RSF action involves: (1) fast access to intracellular compartments of parasitized cells; (2) selective and high-affinity chelation of iron (III) from parasitized cells; (3) fast exit from cells after iron (III) complexation; and (4) exertion of cell damage on parasites exposed for 3 to 5 hours to drugs, irrespective of the stage of parasite development. These results suggest that on reaching a critical intraerythrocyte target, RSFs induce an iron deficit that parasites in general, and rings in particular, have limited capacity to restore.

Metal regulation of siderophore synthesis in Pseudomonas aeruginosa and functional effects of siderophore-metal complexes

Pseudomonas aeruginosa synthesizes two siderophores, pyochelin and pyoverdin, characterized by widely different structures, physicochemical properties, and affinities for Fe(III). Titration experiments showed that pyochelin, which is endowed with a relatively low affinity for Fe(III), binds other transition metals, such as Cu(II), Co(II), Mo(VI), and Ni(II), with appreciable affinity. In line with these observations, Fe(III) and Co(II) at 10 microM or Mo(VI), Ni(II), and Cu(II) at 100 microM repressed pyochelin synthesis and reduced expression of iron-regulated outer membrane proteins of 75, 68, and 14 kDa. In contrast, pyoverdin synthesis and expression of the 80-kDa receptor protein were affected only by Fe(III). All of the metals tested, except Mo(VI), significantly promoted P. aeruginosa growth in metal-poor medium; Mo(VI), Ni(II), and Co(II) were more efficient as pyochelin complexes than the free metal ions and the siderophore. The observed correlation between the affinity of pyochelin for Fe(III), Co(II), and Mo(VI) and the functional effects of these metals indicates that pyochelin may play a role in their delivery to P. aeruginosa.

The pyocin Sa receptor of Pseudomonas aeruginosa is associated with ferripyoverdin uptake

We have used Tn5 mutagenesis to obtain a mutant resistant to pyocin Sa. When grown in iron-deficient succinate medium this mutant lacked an 85-kDa iron-regulated outer membrane protein (IROMP), and expression of a 75-kDa IROMP was increased compared with that in the parent strain. The mutant was deficient in pyoverdin biosynthesis and showed a 95% decrease in transport of ferripyoverdin purified from the parent strain, suggesting that the 85-kDa IROMP is the specific receptor for ferripyoverdin and pyocin Sa. The mutant compensated for the deficiency in pyoverdin biosynthesis and transport by exhibiting a fourfold increase in ferripyochelin transport. The low-level transport of ferripyoverdin in the Sa-resistant mutant, which extended to heterologous pyoverdins from other strains, suggests that Pseudomonas aeruginosa has a second ferripyoverdin uptake system of lower affinity and broader specificity.

Isolation and partial characterization of a compound with siderophore activity from Vibrio parahaemolyticus

A compound with siderophore activity was purified by successive column and thin layer chromatographic procedures from Dowex 1 x 8 extracts of culture supernatants of Vibrio parahaemolyticus AQ 3354. The strain synthesized the compound in culture media containing less than 2 microM added FeCl3. Hydrolysis of the compound yielded alanine, ethanolamine, citric acid and 2-ketoglutaric acid. The 1H-NMR spectrum exhibited the presence of a residue from each of these components in the intact molecule. The fast-atom bombardment mass spectrum of the methyl ester derivative indicated a prominent ion at m/z 477, probably corresponding to [M + 1] ion. Other strains of V. parahaemolyticus were also found to produce this compound when grown in an iron-limited medium.

The iron uptake mechanisms of enteropathogenic Escherichia coli: the use of haem and haemoglobin during growth in an iron-limited environment

The iron uptake mechanisms of enteropathogenic Escherichia coli (EPEC) were examined and compared with those of control E. coli strains. The incidence of aerobactin production was similar (39% and 37% respectively) in the two groups. The quantities of enterochelin produced by aerobactin-negative EPEC and control strains were similar, as were the quantities of enterochelin produced by aerobactin-positive EPEC and control strains. The ability to use haem or haemoglobin as an iron source in an iron-restricted environment was found in 80.4% and 60.8% of EPEC strains respectively, and in 76.6% and 56.6% of control E. coli strains. The ability of E. coli strains to use these compounds was not related to the production of enterochelin or aerobactin or to the production of haemolysins, and may be an important characteristic of bowel organisms. When growing in an iron-limited environment, the iron contained in haemoglobin was used in preference to ovotransferrin-bound iron. During periods of haemoglobin-stimulated growth, the enterochelin uptake system was shown to be fully expressed and may be involved in transport of haemoglobin-derived iron into the cell. Uptake of ovotransferrin-bound iron took place immediately upon exhaustion of haemoglobin-derived iron. The ability to use iron derived from haem compounds represents an alternative iron uptake mechanism for organisms growing in an iron-limited environment and allows greater flexibility during growth in vivo.

Cloning of the outer membrane high-affinity Fe(III)-pyochelin receptor of Pseudomonas aeruginosa

Pseudomonas aeruginosa produces the phenolic siderophore pyochelin under iron-limiting conditions. In this study, an Fe(III)-pyochelin transport-negative (Fpt-) strain, IA613, was isolated and characterized. 55Fe(III)-pyochelin transport assays determined that no Fe(III)-pyochelin associated with the Fpt- IA613 cells while a significant amount associated with KCN-poisoned Fpt+ cells. A P. aeruginosa genomic library was constructed in the IncP cosmid pLAFR1. The genomic library was mobilized into IA613, and a recombinant cosmid, pCC41, which complemented the Fpt- phenotype of IA613, was isolated. pCC41 contained a 28-kb insert of P. aeruginosa DNA, and the Fpt(-)-complementing region was localized to a 3.6-kb BamHI-EcoRI fragment by deletion and subcloning of the insert. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of IA613 revealed that it lacked a 75-kDa outer membrane protein present in Fpt+ strains. IA613 strains bearing plasmid pRML303, which carries the 3.6-kb BamHI-EcoRI fragment of pCC41, expressed the 75-kDa outer membrane protein and demonstrated a 55Fe(III)-pyochelin transport phenotype identical to that of a wild-type Fpt+ strain. Minicell analysis demonstrated that the 3.6-kb BamHI-EcoRI fragment of pCC41 encoded a protein of approximately 75 kDa. The results presented here and in a previous report (D. E. Heinrichs, L. Young, and K. Poole, Infect. Immun. 59:3680-3684, 1991) lead to the conclusion that the 75-kDa outer membrane protein is the high-affinity receptor for Fe(III)-pyochelin in P. aeruginosa.

Role of aerobactin in systemic spread of an opportunistic strain of Escherichia coli from the intestinal tract of gnotobiotic lambs

To assess the role of the aerobactin-related system in the virulence of bovine opportunistic Escherichia coli, and to determine the stage(s) of the overall infectious process at which it is acting, germfree lambs were mixedly infected orally with two derivative strains of this bacterium differing in their ability (Iut+) or inability (Iut-) to express a functional aerobactin-mediated iron transport system. The Iut- strain was compared with the Iut+ strain for colonization of the gut, translocation to the mesenteric lymph nodes (MLN), and spread to other organs and to the body fluids of diassociated lambs. The Iut- mutant was found in smaller numbers in the duodenum, suggesting that aerobactin conferred a significant selective advantage for colonization of this intestinal segment. Although the two challenge strains translocated to MLN, the population level in the MLN was always higher for the Iut+ strain. Moreover, experimental infections resulted in recovery of only the Iut+ strain in the organs other than the MLN and in the body fluids. These results indicate a role for aerobactin in promoting systemic spread of the bacteria from the intestine. Direct evidence was obtained that aerobactin secretion occurred in vivo at both intestinal and extraintestinal sites of infection. In contrast to enterobactin, aerobactin was detected in the duodenum, jejunum, ileum, cecum, liver, spleen, kidney, urine, cerebrospinal fluid, and bile. The highest concentration of aerobactin was found in the urine, even when the samples were devoid of infecting bacteria. All of these findings suggest that aerobactin is released in vivo in a diffusible form and that it may be an important step in the production of disease by intestinal opportunistic E. coli.

Effects of deferrioxamine on iron-catalyzed lipid peroxidation

The kinetics of iron binding by deferrioxamine B mesylate and the ramifications of this process upon iron-catalyzed lipid peroxidation were assessed. The relative rates of Fe(III) binding by deferrioxamine varied for the chelators tested as follows: ADP greater than AMP greater than citrate greater than histidine greater than EDTA. The addition of a fivefold molar excess of deferrioxamine to that of Fe(III) did not result in complete binding (within 10 min) for any of the Fe(III) chelates tested except ADP:Fe(III). The rates of Fe(III) binding by deferrioxamine were greater at lower pH and when the competing chelator concentration was high in relationship to iron. The relatively slow binding of Fe(III) by deferrioxamine also affected lipid peroxidation, an iron-dependent process. The addition of deferrioxamine to an ascorbate- and ADP:Fe(III)-dependent lipid peroxidation system resulted in a time-dependent inhibition or stimulation of malondialdehyde formation (i.e., lipid peroxidation), depending on the ratio of deferrioxamine to iron. Converse to Fe(III), the rates of Fe(II) binding by deferrioxamine from the chelators tested above were rapid and complete (within 1 min), and resulted in the oxidation of Fe(II) to Fe(III). Lipid peroxidation dependent on Fe(II) autoxidation was stimulated by the addition of deferrioxamine. Malondialdehyde formation in this system was inhibited by the addition of catalase, and a similar extent of lipid peroxidation was achieved by substituting hydrogen peroxide for deferrioxamine. Collectively, these results suggest that the kinetics of Fe(III) binding by deferrioxamine is a slow, variable process, whereas Fe(II) binding is considerably faster. The binding of either valence of iron by deferrioxamine may result in variable effects on iron-catalyzed processes, such as lipid peroxidation, either via slow binding of Fe(III) or the rapid binding of Fe(II) with concomitant Fe(II) oxidation.

An aspartate deletion mutation defines a binding site of the multifunctional FhuA outer membrane receptor of Escherichia coli K-12

The FhuA protein of the outer membrane serves as a receptor for phages T5, T1, and phi 80, for colicin M, for the antibiotic albomycin, and for ferrichrome and related siderophores. To identify protein regions important for the multiple FhuA activities, fhuA genes of spontaneous chromosomal mutants which expressed wild-type amounts of the FhuA protein were sequenced. A mutant which was partially T5 sensitive but impaired in all other functions was missing aspartate residue 348 of the mature protein as a result of a three-base deletion. This aspartate residue is part of the hydrophilic sequence Asp-Asp-Glu-Lys. Replacement by site-specific mutagenesis of each of the Asp residues by Tyr, of Glu by Val, and of Lys by Met reduced FhuA activity but less than the Asp deletion did. Ferrichrome inhibited binding of phage phi 80 and of colicin M to these mutants in an allele-specific manner. A completely resistant derivative of the Asp deletion mutant contained, in addition, a leucine-to-proline substitution at position 106 and eight changed bases, converting at positions 576 to 578 an Arg-Pro-Leu sequence to Ala-Arg-Cys. The latter mutations and the Leu-to-Pro replacement alone did not alter sensitivity to the phages but reduced sensitivity to colicin M and albomycin 10- to 1,000-fold. The proline replacements probably disturb FhuA conformation and, in concert with the Asp deletion, inactivate FhuA completely. It is concluded that the Asp deletion site defines a region of FhuA which directly participates in binding of all FhuA ligands. Growth promotion studies on iron-limited media revealed that certain siderophores of the hydroxamate type, such as butylferrichrome, ferrichrysin, and ferrirubin, are taken up not only via FhuA but also via the FhuE outer membrane receptor protein.

Exogenous siderophore-mediated iron uptake in Pseudomonas aeruginosa: possible involvement of porin OprF in iron translocation

In addition to the two siderophores pyoverdine and pyochelin synthesized by Pseudomonas aeruginosa ATCC 15692 (strain PAO1), several siderophores produced by other bacteria or fungi, namely cepabactin, salicylic acid, desferriferrichrysin, desferriferricrocin, desferriferrioxamine B, desferriferrioxamine E and coprogen, were able to promote iron uptake with variable efficiencies into this bacterium. For most of these siderophores, these results were consistent with the growth stimulation produced by the same compounds in a plate bioassay. Desferriferrichrome A, enterobactin and desferriferrirubin, however, did not promote iron uptake, although enterobactin and desferriferrirubin stimulated bacterial growth. These paradoxical data are discussed in view of siderophore-inducible iron uptake systems, as demonstrated recently for enterobactin. Among the strains tested, including the wild-type PAO1, the pyoverdine-less mutant PAO6606 and the two porin-mutants P. aeruginosa H636 (oprF::omega) and P. aeruginosa H673 (oprD::Tn501), only for the porin-OprF mutant were fewer siderophores able to promote iron uptake compared to the other strains. Such results suggest that beside specific routes for iron uptake P. aeruginosa is also able to take up siderophore-liganded iron through OprF.