An improved method for generating human spinal cord neural stem cells

Neural stem cells have exhibited efficacy in pre-clinical models of spinal cord injury (SCI) and are on a translational path to human testing. We recently reported that neural stem cells must be driven to a spinal cord fate to optimize host axonal regeneration into sites of implantation in the injured spinal cord, where they subsequently form neural relays across the lesion that support significant functional improvement. We also reported methods of deriving and culturing human spinal cord neural stem cells derived from embryonic stem cells that can be sustained over serial high passage numbers in vitro, providing a potentially optimized cell source for human clinical trials. We now report further optimization of methods for deriving and sustaining cultures of human spinal cord neural stem cell lines that result in improved karyotypic stability while retaining anatomical efficacy in vivo. This development improves prospects for safe human translation.

Effect of pH and Citrate on Binding of Iron and Gallium by Transferrin in Serum

Although both Al and Fe are bound to transferrin in plasma, they are metabolized differently. Aluminum is less tightly bound to transferrin than is Fe, and might be released in circumstances in which Fe remains bound. The effect of pH ana citrate on the binding of 67Ga (a radiotracer used as an analog of Al) to transferrin in normal human serum was tested in the presence of physiological concentrations of CO2. At pH less than 6.8, Ga started to dissociate from transferrin; at pH 6, greater than 50% of the added 67Ga was present in a low-M(r) form. In contrast, almost all Fe remained bound to transferrin at pH values as low as 4.7. Citrate at concentrations as great as 100 mmol/L had no effect on binding of Fe, but the binding of 67Ga was markedly reduced at citrate greater than 1 mmol/L. Being bound to transferrin less strongly than Ga is, Al could dissociate even more readily, and loss of Al from transferrin in the kidney might explain why Al but not Fe is excreted in urine.

First Report of Phakopsora pachyrhizi, the Causal Agent of Asian Soybean Rust, on Florida Beggarweed in the United States

Phakopsora pachyrhizi Syd. & P. Syd., which causes Asian soybean rust (SBR), was observed on Florida beggarweed, Desmodium tortuosum (Sw) DC., in Attapulgus, GA during late October and early November 2005. Tan to brown lesions (<1.0 mm in diameter) consistent with symptoms of SBR (2) were observed on older leaves of several plants collected near an SBR-infected soybean trial. Dissection (40 to 60×) and compound microscopy (×200 to 400) revealed conical pustules and ellipsoid, echinulate urediniospores (average size 15 × 20 μm) on the abaxial leaf surface. Polymerase chain reaction (PCR) (primers Ppm1 and Ppa2) (1) was conducted on four samples to confirm identification of P. pachyrhizi or P. meibomiae. Three were positive for P. pachyrhizi, and one was negative for both species. Using morphology and real-time PCR, SBR was confirmed as P. pachyrhizi by the USDA/APHIS in Beltsville, MD. Six noninfected Florida beggarweed plants were transplanted to pots during December 2005 and grown at 22 to 24°C in a greenhouse. On 11 January 2006, a water suspension of urediniospores collected from SBR-infected soybeans (1 × 10⁵ spores per ml) was spray inoculated on all leaves to almost runoff and incubated for 48 h in a plastic humidity chamber. Lesions, pustules, and urediniospores consistent with SBR (2) were observed on 3 February 2006. A PCR assay was conducted on six samples from the infected greenhouse plants and all were positive for P. pachyrhizi. Florida beggarweed is widespread in the southern United States and may serve as an additional overwintering source for P. pachyrhizi and a potential inoculum source for the soybean crop. References: (1) R. D. Fredrick et al. Phytopathology 92:217, 2002. (2) J. B. Sinclair and G. L. Hartman. Soybean rust. Pages 25-26 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman et al., eds. The American Phytopathological Society, St. Paul, MN, 1999.

First Demonstration of Koch's Postulates for Lasiodiplodia theobromae Fruit Spot on Eggplant (Solanum melongena)

During October 2004, diseased eggplant fruit from a commercial farm in Colquitt County, Georgia, developed circular, tan, water-soaked lesions. Gray, septate mycelia quickly covered the fruit. Diseased fruit became shriveled, spongy, and mummified. Disease incidence in the field was approximately 1%. Lasiodiplodia theobromae (Pat.) Griffon & Maubl. (synonym Botryodiplodia theobromae Pat.) (2) was isolated from the margins of lesions and cultured on acidified potato dextrose agar. The fungus produced grayish colonies with aerial hyphae and black ostiolate pycnidia massed into stroma. Mature elliptical conidia (25.8 × 15.6 μm) were brown, had a single septation, and longitudinal striations. Isolates obtained from peanut and pecan were included in the pathogenicity tests. Mature fruit cv. Nightshade were surface disinfested for 30 s in 70% ethanol, followed by 60 s in 0.5% sodium hypochlorite, rinsed twice in sterile distilled water, and allowed to dry. Inoculations were made by placing an agar plug containing L. theobromae mycelial side down on the surface of the fruit or wounding with a sterile toothpick containing mycelium of the fungus. Fruit similarly inoculated with agar plugs or sterile toothpicks served as controls. There were a total of three replicates. Fruit were placed in plastic containers lined with moistened paper towels. Containers were placed in a dew chamber and incubated (28°C, relative humidity >95%) for 3 days, and then evaluated. Symptoms identical to those observed on naturally infected fruit developed on inoculated fruit. Controls remained disease free. L. theobromae was reisolated from all symptomatic tissue, satisfying Koch's postulates. Disease damage on wounded fruit was twice that of nonwounded fruit. However, seven of nine inoculations with agar plugs containing L. theobromae resulted in infection. Lesion lengths from wound inoculations were 9.8, 7.3, and 5.2 cm for isolates from peanut, pecan, and eggplant, respectively. Generally, L. theobromae is considered a facultative wound pathogen or a secondary invader (3). However, this study suggests that direct infection can occur. Although fruit spot has been reported previously on eggplant (1), to our knowledge, this is the first report verifying L. theobromae as the causal agent. References: (1) S. A. Alfieri et al. Index of Plant Diseases in Florida. Fla. Dep. Agric. Consum. Serv. Bull. 11, 1984. (2) H. L. Barnett and B. B. Hunter. Illustrated Guide of Imperfect Fungi. 4th ed. The American Phytopathological Society St. Paul, MN, 1998. (3) P. M. Phipps and D. M. Porter. Plant Dis. 82:1205, 1998.

First Report of a Leaf Blight of Onion Caused by Xanthomonas spp. in Georgia

In October of 2001 and 2002, a leaf blight was reported affecting Vidalia onion (Allium cepa) cvs. Pegasus and Sweet Vidalia, respectively, in one field each. Lesions on onion seedlings began as a water-soaked, tip dieback that gradually blighted the entire leaf. Symptoms on onion transplants appeared as elongated, water-soaked lesions that typically collapsed at the point of initial infection. In both cases, disease was very severe on seedlings, and disease incidence was 50% or more in both fields. Warm temperatures combined with overhead irrigation and above average rainfall likely enhanced the severity and spread of disease. Disease was not detected on more mature onions once cool, dry conditions occurred later in the season, and no significant economic loss occurred. Seed was tested from seed lots of the aforementioned cultivars and Xanthomonas spp. were not found. Diseased tissue was macerated in sterile, phosphate-buffered saline, and 10 μl of the resulting suspension was streaked on nutrient agar plates. Yellow-pigmented, gram-negative, rod-shaped bacteria were isolated routinely from diseased tissue. Bacteria were catalase-positive, cellulolytic, oxidase-negative, amylolytic, proteolytic, and utilized glucose in an oxidative manner. Analysis of whole cell, fatty acid methyl esters (FAME) using the Microbial Identification System (MIS, Sherlock version 3.1; MIDI, Inc., Newark, DE) identified four representative strains of the bacterium as a pathovar of Xanthomonas axonopodis (similarity indices 0.75 to 0.83). Known Xanthomonas spp. from onion from Colorado and Texas (1,2) had similar FAME profiles when analyzed by the MIDI system. Onion plants were grown under greenhouse conditions for 2 months and inoculated by injecting the base of a quill with 1.0 ml of bacterial suspensions (1 × 10⁷ CFU ml^-1) of the Xanthomonas sp. isolated from Georgia, and negative controls were inoculated with 1 ml of sterile water. Disease symptoms developed on plants inoculated with bacterial suspensions in 4 to 7 days and Xanthomonas sp. was isolated from the lesions produced. Disease symptoms occurred when the same suspension was sprayed on onion foliage. No symptoms occurred on plants inoculated with 1 ml of sterile water. To our knowledge, this is the first report of Xanthomonas spp. affecting Vidalia onions. References: (1) T. Isakeit et al. Plant Dis. 84:201, 2000. (2) H. F. Schwartz and K. Otto. Plant Dis. 84:922, 2000.

First Report of a Field Outbreak of a Bacterial Leaf Spot of Cantaloupe and Squash Caused by Pseudomonas syringae pv. syringae in Georgia

In March 2000, a leaf spot was reported affecting yellow summer squash (Cucurbita pepo) and cantaloupe (Cucumis melo) in commercial fields in Colquitt, Echols, and Grady counties in Georgia. All of the crops affected were reported within a 10-day period, and average temperatures during that time were 8 to 22.5°C, which is very close to the 50-year normal temperatures for these areas located in southwest Georgia. Incidence in affected fields was 100%. Lesions on squash leaves appeared irregularly shaped, dark, water soaked, somewhat vein restricted, and were 5 to 10 mm in diameter. Lesions on cantaloupe were angular, light tan, and necrotic with a lesion diameter of 2 to 5 mm. A general chlorosis was observed around lesions of both crops. Leaf distortion was observed on squash. Four isolates collected were used in biochemical, pathogenicity, and physiological tests. Gram-negative, rod-shaped bacteria were isolated from diseased tissue from squash and cantaloupes. Bacteria were aerobic, catalase-positive, fluorescent on King's medium B (1), oxidase-negative, nonpectolytic on potato, arginine dihydrolase-negative, utilized sucrose as a carbon source, produced levan, and gave a hypersensitivity response on tobacco (HR). Analysis of fatty acid methyl ester (FAME) profiles using the Microbial identification system (Sherlock version 3.1, Microbial identification system, Newark, DE) characterized representative strains as Pseudomonas syringae (similarity indices 0.65 to 0.80). Upon further characterization, the strains were negative for l (+)-tartarate utilization but utilized l-lactate and betaine and also exhibited ice nucleation activity. These characteristics are consistent with those of Pseudomonas syringae pv. syringae. Squash and cantaloupes were grown in a greenhouse for 4 weeks. Bacteria were grown in nutrient broth, resuspended in sterile tap water, and standardized using a spectrophotometer. Plants were inoculated by infiltrating leaves with 1 ml of bacterial suspensions (1 × 10⁷ CFU/ml) using sterile syringes. Sterile water was used as a negative control, and 1 ml was infiltrated into leaves of squash and cantaloupes. Water-soaked lesions developed in 4 to 6 days on squash and cantaloupes inoculated with bacterial suspensions, and Pseudomonas syringae pv. syringae was isolated from diseased tissue. No symptoms developed on squash and cantaloupes used as negative controls. This outbreak of Pseudomonas syringae pv. syringae did not cause significant economic damage to either crop as symptoms subsided once daily high temperatures reached 28 to 32°C. This disease has been isolated from several cucurbit transplants reared in greenhouses, but to our knowledge, this is the first report of this disease occurring in the field. Reference: (1) E. O. King et al. J. Lab. Clin. Med. 44:301, 1954.

Expression of ferritin, transferrin receptor, and non-specific resistance associated macrophage proteins 1 and 2 (Nramp1 and Nramp2) in the human rheumatoid synovium

OBJECTIVE

To gain a better understanding of how iron accumulates in human rheumatoid synovium.

METHODS

The distribution of ferritin, transferrin receptor, and non-specific resistance associated macrophage proteins 1 and 2 (Nramp1 and Nramp2) in the human rheumatoid synovium was investigated by immunocytochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Both heavy and light ferritin subunit types were detected in the lining layer and the subinitimal zone of rheumatoid synovium, heavy ferritin generally being more abundant than light. Both heavy and light ferritin were detected in isolated synovial macrophages and fibroblasts. Transferrin receptor expression was largely confined to fibroblasts of the synovial lining layer. Nramp2 was detected by PCR in both isolated synovial macrophages and fibroblasts, whereas Nramp1 was detected by PCR and immunocytochemistry in macrophages and neutrophils in the lining and subinitimal zone, and in inflammatory infiltrates, but was absent from fibroblasts.

CONCLUSION

A complex chain of events, perhaps initiated by proinflammatory cytokines, may culminate in a toxic build up of iron in the rheumatoid joint.

Growth inhibition of Bacteroides fragilis by hemopexin: proteolytic degradation of hemopexin to overcome heme limitation

The stimulatory effect of heme on growth of Bacteroides fragilis, an anaerobic human pathogen, was strongly inhibited by hemopexin, an avid (Kd<1 pM) heme-binding plasma protein. Both rabbit and human hemopexins were bacteriostatic for a limited period of time, suggesting an adaptation by B. fragilis to heme-limited growth, and that hemopexin-bound heme can eventually be utilized by the bacteria. The inhibitory effect of hemopexin was lost when heme in the medium was replaced by protoporphyrin IX, which is bound less strongly by hemopexin (Kd approximately 1 microM). Protease activity was detected in the culture supernatant of B. fragilis grown in the presence of heme plus hemopexin but not in the presence of free heme, protoporphyrin IX or protoporphyrin IX plus hemopexin, suggesting that the enzyme(s) is induced by heme macrocycle limitation due to the scavenging effect of hemopexin. This protease activity was able to degrade rabbit hemopexin and human hemopexin, as well as human transferrin and ovalbumin, and may be a due to a serine protease since it was inhibited by phenylmethylsulfonyl fluoride (PMSF) but not by EDTA, leupeptin, pepstatin A or aprotinin. Thus, B. fragilis may overcome hemopexin-mediated heme limitation by secreting inducible protease(s), shown here to make protein-bound heme available to the microorganism.

Bacteriostatic activity of human lactoferrin against Staphylococcus aureus is a function of its iron-binding properties and is not influenced by antibiotic resistance

The in vitro antistaphylococcal activity of lactoferrin and the antibiotic resistance of clinical Staphylococcus aureus isolates obtained from three different sites of infection were examined. Antibiotic, but not lactoferrin resistance correlated with selective antibiotic pressure, and nosocomial and most community isolates were antibiotic resistant, whereas only a third of each group was resistant to lactoferrin. The antimicrobial activity of lactoferrin, both in defined medium and in normal human plasma serum, was dependent upon its ferrochelating properties. Therapeutic approaches based on the use of ferrochelating agents such as lactoferrin combined with antimicrobial drugs may help to counteract the reduced efficacy of current antibiotics.

Liposomes as possible carriers for lactoferrin in the local treatment of inflammatory diseases

Liposomes prepared from naturally occurring biodegradable and nontoxic lipids are good candidates for local delivery of therapeutic agents. Treatment of arthritis by intra-articular administration of anti-inflammatory drugs encapsulated in liposomes prolongs the residence time of the drug in the joint. We have previously shown that intra-articular injection of human lactoferrin (hLf), a glycoprotein that possesses anti-inflammatory and antimicrobial activities, into mice with collagen-induced arthritis reduces inflammation. We have now investigated the possibility of using liposome-entrapped hLf as a delivery system to prolong hLf retention at sites of local inflammation such as the rheumatoid joint. Entrapment of hLf in negatively charged liposomes enhanced its accumulation in cultured human synovial fibroblasts from rheumatoid arthritis (RA) patients, compared with positively charged formulations or free protein. However, in the presence of synovial fluid, positively charged liposomes with entrapped hLf were more stable than the negatively charged formulations. In vivo experiments in mice with collagen-induced arthritis showed that the positive liposomes were more efficient in prolonging the residence time of hLf in the inflamed joint as compared with other liposomes. Thus, the amount of hLf retained in the joint after 2 hr was 60% of the injected dose in the case of positive liposomes and only 16% for negative pH-sensitive liposomes. The results suggest that entrapment of hLf in positively charged liposomes may modify its pharmacodynamic profile and be of therapeutic benefit in the treatment of RA and other local inflammatory conditions.

Staphylococcus aureus fibronectin binding proteins are essential for internalization by osteoblasts but do not account for differences in intracellular levels of bacteria

Staphylococcus aureus is a major pathogen of bone that has been shown to be internalized by osteoblasts via a receptor-mediated pathway. Here we report that there are strain-dependent differences in the uptake of S. aureus by osteoblasts. An S. aureus septic arthritis isolate, LS-1, was internalized some 10-fold more than the laboratory strain 8325-4. Disruption of the genes for the fibronectin binding proteins in these two strains of S. aureus blocked their ability to be internalized by osteoblasts, thereby demonstrating the essentiality of these genes in this process. However, there were no differences in the capacity of these two strains to bind to fibronectin or osteoblasts. Analysis of the kinetics of internalization of the two strains by osteoblasts revealed that strain 8325-4 was internalized only over a short period of time (2 h) and to low numbers, while LS-1 was taken up by osteoblasts in large numbers for over 3 h. These differences in the kinetics of uptake explain the fact that the two strains of S. aureus are internalized by osteoblasts to different extents and suggest that in addition to the fibronectin binding proteins there are other, as yet undetermined virulence factors that play a role in the internalization process.

Cellular and molecular aspects of iron and immune function

Fe plays a critical role in the immune system and defence against infection. However, many aspects of the way in which Fe influences these processes at the molecular and cellular level are unclear. The present review summarizes the role of Fe in lymphocyte activation and proliferation, and discusses how Fe is handled by macrophages.

The effects of local administration of lactoferrin on inflammation in murine autoimmune and infectious arthritis

OBJECTIVE

To determine whether lactoferrin can modify articular inflammation in murine models of autoimmune and septic arthritis.

METHODS

Collagen arthritis was induced in DBA/1 mice and Staphylococcus aureus septic arthritis in Swiss mice. Joints with established inflammation were injected periarticularly with 0.5 mg or 1 mg of human lactoferrin, and arthritis was monitored for 3 days.

RESULTS

DBA/1 mice injected with lactoferrin showed significantly suppressed local inflammation for up to 3 days, achieving up to 71% of the effect of corticosteroid. Periarticular injection of 125I-lactoferrin confirmed that 25% of lactoferrin was retained in paws after 6 hours. Serum levels of interleukin-6, however, were not significantly reduced, suggesting a predominantly local antiinflammatory effect. Similarly, local, periarticular administration of lactoferrin into S aureus-infected Swiss mice significantly suppressed paw inflammation and did not enhance bacterial survival.

CONCLUSION

Lactoferrin may have clinical utility in reducing articular inflammation, particularly in septic arthritis, in which antiinflammatory effects may be achieved without promoting bacterial survival.

A novel endoproteolytic processing activity in mitochondria of erythroid cells and the role in heme synthesis

The erythroid isoform of aminolevulinate synthase (eALAS) protein is a major control point in erythroid heme synthesis and hemoglobin formation. Erythroid cells were extracted from mouse blood and bone marrow and metabolically labeled with (35)S-methionine. This was followed by immunoprecipitation of eALAS protein products. The results show that the N-terminus of the expected full-length 59-kd form of the eALAS protein is truncated in bone marrow erythroid cells by approximately 7 kd. More differentiated erythroid cells in the peripheral blood exhibit very little of this protein truncation. Erythroid cells from the bone marrow were isolated using monoclonal antibody TER-119 and were shown to contain a unique endoprotease activity that could cleave the eALAS protein to the shorter form in vitro. With or without the mitochondrial signal sequence, the eALAS protein could serve as a substrate for the cleavage. This cleavage renders a functional eALAS protein and only removes a domain of unclear function, which has previously been reported to vary in size as a result of alternative RNA splicing. The protease activity was enriched from the membranes of mitochondria from bone marrow cells and was shown to be different from mitochondrial processing peptidase, medullasin, and other known proteases. Apart from the mitochondrial processing peptidase that cleaves the import signal sequence, this is the first description of a mitochondrially located site-specific processing protease activity. (Blood. 2000;96:740-746)

Inhibition of binding of lactoferrin to the human promonocyte cell line THP-1 by heparin: the role of cell surface sulphated molecules

Lactoferrin, an iron-binding protein of the transferrin family, is a highly basic protein which interacts with many acidic molecules, including heparin proteoglycans. Such interactions may modify some of the biological properties of lactoferrin. In the present work we found that heparin caused a dose-dependent inhibition of specific binding of both human and bovine lactoferrin to human monocytic THP-1 cells. Low-affinity binding sites (Kd 500 nM) were more susceptible to inhibition by heparin than the high-affinity sites (Kd 100 nM). The effect was mediated by interaction between lactoferrin and heparin rather than by competition between heparin and lactoferrin for common binding sites on the cells. Pretreatment of cells with NaClO3 to prevent sulphation of surface glycosaminoglycans reduced lactoferrin binding, and de-N-sulphated heparin did not inhibit binding of lactoferrin to THP-1 cells. These results suggest that heparin binding and monocyte/macrophage binding by lactoferrin both involve interactions between basic regions in the N1 domain of lactoferrin and sulphate groups. The N-terminal Arg2-Arg5 sequence of human lactoferrin may be involved, but it does not seem to be the key element in these interactions.

Benefits and dangers of iron during infection

Iron is essential for both human and microbial metabolism, and it is therefore important that iron status is maintained at a level that permits optimal immune responses by the host but does not facilitate availability of iron to microorganisms. This paper reviews the role of iron in resistance to infection, with particular reference to malaria and hepatitis C, and discusses the desirability of iron supplementation of populations at risk of infection.

Regulation of iron metabolism in murine J774 macrophages: role of nitric oxide-dependent and -independent pathways following activation with gamma interferon and lipopolysaccharide

To elucidate the pathways by which nitric oxide (NO) influences macrophage iron metabolism, the uptake, release, and intracellular distribution of iron in the murine macrophage cell line J774 has been investigated, together with transferrin receptor (TfR) expression and iron-regulatory protein (IRP1 and IRP2) activity. Stimulation of macrophages with interferon-gamma (IFN-gamma) and/or lipopolysaccharide (LPS) decreased Fe uptake from transferrin (Tf), and there was a concomitant downregulation of TfR expression. These effects were mediated by NO-dependent and NO-independent mechanisms. Addition of the NO synthase (NOS) inhibitor N-monomethyl arginine (NMMA) partially restored Fe uptake but either had no effect on or downregulated TfR expression, which suggests that NO by itself is able to affect iron availability. Analysis of the intracellular distribution of incorporated iron revealed that in IFN-gamma/LPS-activated macrophages there was a decreased amount and proportion of ferritin-bound iron and a compensatory increase in insoluble iron, which probably consists mainly of iron bound to intracellular organelles. Finally, although NO released by IFN-gamma/LPS-activated macrophages increased the iron-responsive element (IRE)-binding activity of both IRP1 and IRP2, IFN-gamma treatment decreased IRP2 activity in an NO-independent manner. This study demonstrates that the effect of IFN-gamma and/or LPS on macrophage iron metabolism is complex, and is not entirely due to either NO-or to IRP-mediated mechanisms. The overall effect is to decrease iron uptake, but not its utilization.

First Report of Macrophomina phaseolina on Cotton (Gossypium hirsutum) in Georgia

In a field study evaluating the diversity and density of the soilborne mycobiota in a cotton (Gossypium hirsutum L.) production system, Macrophomina phaseolina (Tassi) Goidanich was isolated on potato dextrose agar from dark brown to black lesions on feeder and secondary roots. Multiple proliferations of feeder and secondary roots were also observed. Isolate RB 656 obtained from these lesions was tested for pathogenicity in the greenhouse by mixing 25 ml of 2-week-old cornmeal sand inoculum (3 g of cornmeal, 100 g of sand, and 20 ml of distilled water) with 5 liters of autoclaved soil (Leefield loamy sand, pH 6.2) per pot (40 × 200 cm). Control pots containing autoclaved soil alone were included for comparison. On 17 September, 10 cotton seeds of DPL 90 were sown per pot. Each treatment had five replications. Forty days after planting, plant heights from pots containing M. phaseolina were lower (14.8 cm) than those in the control pots (19.6 cm), but stand counts were similiar. On this date, four plants were left in each pot to allow the remaining seedlings to reach full maturity. On 9 December, the four plants per replicate pot were removed and roots evaluated for damage. Lesions similiar to those seen originally were observed on the secondary and feeder roots of the infested pots, and the characteristic proliferation of feeder and secondary roots was noted. Tap roots in pots containing M. phaseolina were smaller (11.6 cm) than in the control pots (18.6 cm). Isolate RB 656 was reisolated from the damaged roots in the treated pots. This is the first report of M. phaseolina on cotton in Georgia.

Iron, lactoferrin and iron regulatory protein activity in the synovium; relative importance of iron loading and the inflammatory response

OBJECTIVES

To determine the ability of lactoferrin in rheumatoid arthritis (RA) synovial fluid to bind "free" iron, and to study the regulatory mechanisms therein that control iron homeostasis.

METHODS

"Free" iron was determined by the bleomycin assay and lactoferrin concentrations by enzyme linked immunosorbent assay. The activities of iron regulatory protein (IRP) and NF-kappa B in synovial fluid cells were assayed by mobility shift assay.

RESULTS

30% of synovial fluids contained "free" iron and in these, lactoferrin concentrations were significantly lower than in those with no "free" iron (p < 0.01). Addition of exogenous lactoferrin consistently reduced the amount of "free" iron in positive synovial fluids. IRP activity in synovial cells did not correlate with synovial fluid iron concentrations but did correlate with NF-kappa B activation and with serum C reactive protein.

CONCLUSION

Lactoferrin may prevent iron mediated tissue damage in RA by reducing "free" synovial iron concentration when inflammatory stimuli have disregulated IRP mediated iron homeostasis.

Regulation of cellular iron metabolism by erythropoietin: activation of iron-regulatory protein and upregulation of transferrin receptor expression in erythroid cells

Erythropoietin (Epo) is the central regulator of red blood cell production and acts primarily by inducing proliferation and differentiation of erythroid progenitor cells. Because a sufficient supply of iron is a prerequisite for erythroid proliferation and hemoglobin synthesis, we have investigated whether Epo can regulate cellular iron metabolism. We present here a novel biologic function of Epo, namely as a potential modulator of cellular iron homeostasis. We show that, in human (K562) and murine erythroleukemic cells (MEL), Epo enhances the binding affinity of iron-regulatory protein (IRP)-1, the central regulator of cellular iron metabolism, to specific RNA stem-loop structures, known as iron-responsive elements (IREs). Activation of IRP-1 by Epo is associated with a marked increase in transferrin receptor (trf-rec) mRNA levels in K562 and MEL, enhanced cell surface expression of trf-recs, and increased uptake of iron into cells. These findings are in agreement with the well-established mechanism whereby high-affinity binding of IRPs to IREs stabilizes trf-rec mRNA by protecting it from degradation by a specific RNase. The effects of Epo on IRE-binding of IRPs were not observed in human myelomonocytic cells (THP-1), which indicates that this response to Epo is not a general mechanism observed in all cells but is likely to be erythroid-specific. Our results provide evidence for a direct functional connection between Epo biology and iron metabolism by which Epo increases iron uptake into erythroid progenitor cells via posttranscriptional induction of trf-rec expression. Our data suggest that sequential administration of Epo and iron might improve the response to Epo therapy in some anemias.

Iron transport across Caco-2 cell monolayers. Effect of transferrin, lactoferrin and nitric oxide

Differentiated Caco-2 colon carcinoma cell monolayers grown in bicameral chambers have been used as an in vitro model to study the effect of different carrier molecules on mucosal iron transport. Transfer of iron across the monolayers in the apical-to-basolateral direction was greater from ferric lactoferrin than from iron citrate, while very little transport occurred from Fe-transferrin. However, a greater proportion of iron was retained by the cells when Fe-citrate was the donor. Caco-2 cells expressed transferrin receptors (n = 1.3 x 10(5) /cell; Ka = 2 x 10(8) l/mol), but binding of lactoferrin, though substantial in quantity, had an affinity too low to measure. When monolayers were incubated with 125I-labelled lactoferrin or transferrin some 125I-activity was transported, but almost all was TCA-soluble, suggesting that degradation products rather than intact protein were being transported. Addition of 10 microM S-nitroso-N-acetyl-D,L-penicillamine (SNAP), which produces nitric oxide (NO) in solution, caused a significant increase in iron transport from ferric citrate, but not from Fe-lactoferrin or Fe-transferrin. It is concluded that in this in vitro system lactoferrin but not transferrin enhances mucosal iron transport, and that NO may play a regulatory role in iron absorption.

Longitudinal evaluation of peritoneal macrophage function and activation during CAPD: maturity, cytokine synthesis and arachidonic acid metabolism

The release of cytokines and prostaglandins (PG) by peritoneal macrophages (PM luminal diameter of) may influence the cytokine network controlling peritoneal inflammation and in the long-term the function of the peritoneum as a dialysis membrane. In the present study, an evaluation of the long-term effects of peritoneal dialysis on the release of cytokines and prostaglandins, and the expression of surface markers of cellular maturation on blood and mononuclear cells has been performed in patients during their first year on CAPD. Spontaneous release of tumour necrosis factor alpha (TNF alpha) and interleukins 6 (IL-6) by PM luminal diameter of, after 4 or 24 hours in culture, increased significantly with time on CAPD, while there was a small but significant decrease in release of prostaglandin E2 (PGE2). Production of TNF alpha and IL-6 was enhanced following incubation of the cells with lipopolysaccharide (LPS), but the effect of LPS was proportionally greater on blood monocytes than on PM luminal diameter of. There was a significant increase in the concentrations of PGE2 and 6-keto-prostaglandin F1 alpha in overnight dwell peritoneal dialysis effluent with time on CAPD. The levels of TNF alpha and IL-6 in uninfected PDE were below the detection limit of the immunoassay over the whole time period studied. Expression of CD15, which correlates with immaturity, by PM luminal diameter of and blood monocytes increased with time on CAPD, while expression of CD11c, a marker of maturation, decreased on blood monocytes, but did not change significantly on PM luminal diameter of. There was also a slight increase in expression of transferrin receptor in both PM luminal diameter of and monocytes, but this did not reach statistical significance. These findings suggest that peritoneal macrophages and blood monocytes isolated from CAPD patients over a one year period become increasingly immature with time, and this is accompanied by a significant modulation of their ability to secrete inflammatory cytokines. Dysregulation of macrophage function may have important consequences with respect to inflammatory processes and the long-term function of the peritoneal membrane in CAPD patients.

Effect of nitric oxide on expression of transferrin receptor and ferritin and on cellular iron metabolism in K562 human erythroleukemia cells

Nitric oxide (NO) is known to increase the affinity of the intracellular iron-regulatory protein (IRP) for iron-response elements (IREs) in transferrin receptor and ferritin mRNAs, suggesting that it may act as a regulator of cellular iron metabolism. In this study, exogenous NO produced by adding the NO-generator S-nitroso-N-acetyl penicillamine gave a dose-dependent upregulation of transferrin receptor expression by K562 erythroleukemia cells and increased levels of transferrin receptor mRNA. NO did not affect the affinity of transferrin binding by the transferrin receptor. NO alone did not alter intracellular ferritin levels, but it did abrogate the inhibitory effect of the iron chelator desferrioxamine and potentiated the stimulatory effect of additional iron. NO also caused some increase in ferritin mRNA levels, which might mask any IRP-/IRE-mediated inhibitory effect of NO on ferritin translation. Although NO did not affect net iron uptake, it increased release of iron from K562 cells pulsed previously with 59Fe, and subcellular fractionation showed that it also increased the proportion of intracellular iron bound to ferritin. These findings provide direct evidence that NO can affect cellular iron metabolism and suggest that NO produced in vivo by activated bone marrow macrophages might affect erythropoiesis.

Cytokine-mediated regulation of transferrin synthesis in mouse macrophages and human T lymphocytes

Transferrin (Tf) plays an important role during immunologic activation by donating iron to activated lymphocytes. Therefore, synthesis by lymphomyeloid cells has been investigated. Mouse macrophages and macrophage cell lines synthesized Tf, with levels being markedly increased by gamma-interferon (gamma-IFN) and, to a lesser extent, by interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor alpha (TNF alpha). Tf was also produced by phytohemagglutinin-stimulated human T cells and two T-cell lines and was increased by IL-2. Even after appropriate activation, none was synthesized by human macrophages or monocytic cell lines or by mouse T cells, T-cell lines, or thymus cells. In both species, B-lineage cell lines were negative. Tf was also synthesised by macrophages from congenitally hypotransferrinemic mice and was responsive to gamma-IFN, but levels were lower than those from normal controls. Synthesis by human and murine hepatoma cells was increased by IL-6 but unaffected by IL-1, TNF alpha, or gamma-IFN. Iron decreased synthesis by hepatoma cells but had no effect on the lymphomyeloid cells. Tf mRNA levels paralleled protein synthesis, suggesting that regulation was pre-translational. Thus, Tf synthesis by lymphomyeloid cells is regulated differently from hepatic synthesis, which is consistent with the suggestion that Tf may act in a paracrine (mouse) or autocrine (human) manner on activated lymphocytes.

Interaction of lactoferrin with mononuclear and colon carcinoma cells

Lactoferrin is known to bind to macrophages/monocytes and intestinal mucosal cells, but the nature and function of these interactions is not clear. We have therefore examined the interaction of lactoferrin in vitro with the promonocytic cell line U937 and with differentiated human colon carcinoma cells. U937 cells bound more lactoferrin than transferrin, although most of the lactoferrin binding was non-specific. Uptake of iron from transferrin was rapid, but uptake from lactoferrin was slow, and may have been due to prior transfer of iron to transferrin in the culture medium as a result of labilisation of iron from membrane-bound lactoferrin. Unlike transferrin, lactoferrin was not internalised by U937 cells. Lactoferrin significantly reduced uptake of non-transferrin-bound iron by the cells, but had no effect on uptake of transferrin-bound iron. Transport of lactoferrin-bound iron across monolayer cultures of differentiated Caco-2 cells in bicameral chambers was similar to that of ferric citrate, while transport of transferrin-bound iron was lower. Lactoferrin and transferrin themselves were not transported, although some proteolytically degraded material did cross the monolayer. Thus lactoferrin, unlike transferrin, is not an important iron donor to monocytic cells, but may instead serve to regulate iron uptake from other sources. It does not seem to enhance iron transport across mucosal cells.

Effect of transferrin concentration on bacterial growth in human ascitic fluid from cirrhotic and neoplastic patients

Cirrhotic patients with ascites have an unusually high frequency of development of spontaneous bacterial peritonitis. Iron availability is a key factor in bacterial growth and the ability of the host to limit it is associated with resistance to infection. The present study was undertaken to evaluate the influence of iron and transferrin on bacterial growth in ascitic fluid from 25 biopsy-proven cirrhotic and nine neoplastic carcinomatous patients. No significant differences were found when comparing total ascitic fluid iron between the two groups but ascitic fluid transferrin concentration was significantly lower in cirrhotic (29.26 mg dl-1 SD 29.58) than neoplastic (96.57 mg dl-1 SD 76.01) patients. Moreover, a significant negative correlation was found between bacterial growth and transferrin concentration in ascitic fluid (P = 0.039). When the iron concentration in ascitic fluid was experimentally elevated (50 micrograms dl-1 or 150 micrograms dl-1) we observed a progressive increase in bacterial growth. If transferrin concentration is simultaneously elevated (250 mg dl-1) this increase does not occur. These findings indicate that the transferrin level is an important factor in the regulation of bacterial growth in ascitic fluid and that the low concentration found in cirrhotic patients could facilitate spontaneous bacterial peritonitis.

Binding of lactoferrin and transferrin to the human promonocytic cell line U937. Effect on iron uptake and release

We have compared the ability of lactoferrin and transferrin to interact with and donate iron to the monocytic cell line U937. About 10 times more lactoferrin was bound than transferrin, but most lactoferrin bound nonspecifically, and the degree of specific binding was similar for both proteins (2-3 x 10(6) sites/cell). The binding affinity for lactoferrin (83 nM) was about 4-fold lower than for transferrin (21 nM). Lactoferrin did not inhibit binding of transferrin, or vice versa. Binding of lactoferrin was not inhibited by 30 mM glucose or fucose nor by incubating the cells with heparinase. Transferrin, but not lactoferrin, was internalized, and 3 mM primaquine caused intracellular accumulation of transferrin but not lactoferrin. The cells rapidly acquired iron from transferrin, but uptake from lactoferrin was 10-fold slower and probably resulted from transfer of 59Fe from lactoferrin to unlabeled transferrin during culture. Lactoferrin, but not transferrin, released iron to the extracellular medium when bound to U937 cells. Lactoferrin inhibited cellular uptake of iron from Fe-nitrilotriacetate but not from transferrin. It is concluded that transferrin, but not lactoferrin, acts as an iron donor to U937 cells. Lactoferrin may regulate uptake of potentially toxic non-transferrin-bound iron.

Effect of heat treatment and other milk proteins on the interaction of lactoferrin with monocytes

The interaction of lactoferrin from human and bovine milk with the human promonocytic cell line U937 has been studied. Both human and bovine Fe-lactoferrins bound to the cells. Binding of bovine lactoferrin was inhibited by excess bovine lactoferrin but not by human lactoferrin, suggesting that the binding mechanisms for the two proteins are different. Binding of human but not bovine lactoferrin was inhibited by bovine lactoperoxidase, while a 20-fold excess of human IgA inhibited binding of human but not bovine lactoferrin. Human and bovine alpha-lactalbumins, bovine beta-lactoglobulin, and human lysozyme had no effect on binding of lactoferrin from either species. Samples of bovine Fe- and apolactoferrin in capillary tubes were exposed to temperatures of 72 degrees C for 20 s, 85 degrees C for 20 min or 137 degrees C for 8 s. All the heated samples inhibited binding of native Fe- and apolactoferrin, though to a lesser extent than the native proteins. Both heated and native lactoferrins enhanced [3H]thymidine incorporation by U937 cells, except for Fe-lactoferrin heated at 85 degrees C for 20 min, which was inhibitory. These results suggest that heat treatment of lactoferrin under conditions used for industrial processing does not greatly affect its ability to interact with and stimulate monocytic cells, and that other milk proteins in general do not interfere with lactoferrin-monocyte interactions. It may thus be feasible to incorporate biologically active lactoferrin into infant formulas.

Transferrin synthesis by mouse lymph node and peritoneal macrophages: iron content and effect on lymphocyte proliferation

Transferrin is an essential requirement for lymphocyte proliferation, because it supplies activated lymphocytes with iron needed for cell proliferation. However, during inflammation or an immune response, the iron content of circulating transferrin, which is of hepatic origin, decreases. It is hypothesized that activated lymphocytes may therefore obtain transferrin-iron from an alternative source, and we have investigated the possibility that transferrin is synthesized locally in lymphoid tissues. It was found that lymph node cells from mice stimulated in vivo with Freund's complete adjuvant were able to synthesize transferrin, and this was because of the macrophage rather than the lymphocyte population. Transferrin synthesized by mouse lymph node or peritoneal macrophages contained iron and was able to promote mouse lymphocyte proliferation. Peritoneal macrophages activated in vivo synthesized more transferrin, released more transferrin-bound iron, and were more effective than resident macrophages at enhancing lymphocyte proliferation. These results suggest that transferrin synthesized by macrophages acts in a paracrine manner to support lymphocyte proliferation, thus eliminating possible detrimental effect of hypoferremia on the immune system.

Transferrin synthesis by macrophages: up-regulation by gamma-interferon and effect on lymphocyte proliferation

We have investigated transferrin synthesis by human and mouse lymphoid and myeloid cells. It was found that transferrin synthesis is a property of mouse but not human macrophages, whereas in man T lymphocytes synthesised transferrin. Synthesis by mouse macrophages showed a dose-dependent increase in response to gamma-interferon (gamma-IFN), but iron added as ferric nitrilotriacetate had no effect. Macrophage-derived transferrin was found to contain iron already bound to it and was able to support Con A-stimulated mouse lymphocyte proliferation.

Effect of pH and citrate on binding of iron and gallium by transferrin in serum

Although both Al and Fe are bound to transferrin in plasma, they are metabolized differently. Aluminum is less tightly bound to transferrin than is Fe, and might be released in circumstances in which Fe remains bound. The effect of pH ana citrate on the binding of 67Ga (a radiotracer used as an analog of Al) to transferrin in normal human serum was tested in the presence of physiological concentrations of CO2. At pH less than 6.8, Ga started to dissociate from transferrin; at pH 6, greater than 50% of the added 67Ga was present in a low-M(r) form. In contrast, almost all Fe remained bound to transferrin at pH values as low as 4.7. Citrate at concentrations as great as 100 mmol/L had no effect on binding of Fe, but the binding of 67Ga was markedly reduced at citrate greater than 1 mmol/L. Being bound to transferrin less strongly than Ga is, Al could dissociate even more readily, and loss of Al from transferrin in the kidney might explain why Al but not Fe is excreted in urine.

Isolation of a ferritin from Bacteroides fragilis

A ferritin was isolated from the obligate anaerobe Bacteroides fragilis. Estimated molecular masses were 400 kDa for the holomer and 16.7 kDa for the subunits. A 30-residue N-terminal amino acid sequence was determined and found to resemble the sequences of other ferritins (human H-chain ferritin, 43% identity; Escherichia coli gen-165 product, 37% identity) and to a lesser degree, bacterioferritins (E. coli bacterioferritin, 20% identity). The protein stained positively for iron, and incorporated 59Fe when B. fragilis was grown in the presence of [59Fe]citrate. However, the isolated protein contained only about three iron atoms per molecule, and contained no detectable haem. This represents the first isolation of a ferritin protein from bacteria. It may alleviate iron toxicity in the presence of oxygen.

Effect of iron and retinoic acid on the control of transferrin receptor and ferritin in the human promonocytic cell line U937

The effect of changes in iron availability and induction of differentiation on transferrin receptor expression and ferritin levels has been examined in the promonocytic cell line U937. Addition of iron (as 200 micrograms/ml saturated transferrin) or retinoic acid (1 microM) both caused approx. 70% reduction in the average number of surface transferrin receptors, while the iron chelator desferrioxamine caused an 84% increase. Comparable changes also occurred in the levels of transferrin receptor mRNA. Neither iron nor retinoic acid significantly altered the half-life of transferrin receptor mRNA in the presence of actinomycin D (approx. 75 min) but a 10-fold increase in stability occurred in the presence of desferrioxamine. Iron and retinoic acid both caused an increase in intracellular ferritin levels (approx. 4-and 3-fold, respectively), while desferrioxamine reduced ferritin levels by approx. two-thirds. The effect of iron and retinoic acid added together did not differ greatly from that of each agent alone. None of the treatments greatly affected levels of L-ferritin mRNA. Virtually no H-ferritin mRNA was detected in U937 cells. These results show that changes in ferritin and transferrin receptor caused by treatment with retinoic acid are similar to those induced by excess iron, and suggest that changes in these proteins during cell differentiation are due to redistribution of intracellular iron into the regulatory pool(s), rather than to iron-independent mechanisms.

Effect of transferrin, lactoferrin and chelated iron on human T-lymphocytes

The effect of different forms of iron and iron-binding proteins on the proliferative response of human lymphocytes to phytohaemagglutinin (PHA) has been studied. Transferrin enhanced proliferation, the effect being proportional to the degree of iron saturation up to 100%, but decreased if additional iron was present. The lipophilic complex ferric pyridoxal isonicotinoyl hydrazone (FePIH) also enhanced proliferation, but the hydrophilic complex ferric nitrilotriacetate (FeNTA) was inhibitory. Fe-lactoferrin could not substitute for Fe-transferrin, although iron-free (apo) lactoferrin abrogated the inhibitory effect seen when iron levels exceed the binding capacity of transferrin. Lymphocyte ferritin levels increased 4-fold as the iron saturation of transferrin increased from 0 to 90% but no further increase was seen at higher iron levels, suggesting that lymphocytes are poorly equipped to detoxify excess iron through stimulation of ferritin synthesis. The effect of iron on the CD4:CD8 ratio after 72 h culture with PHA was also examined. The ratio was approximately 2:1 for cells cultured with transferrin at iron saturations between 0 and 75%, with FePIH, or without either, but decreased to 1.1:1 when cells were cultured in the presence of FeNTA, regardless of whether or not saturated Fe-transferrin was present. These results show that iron can affect lymphocyte proliferation and subset ratios in different ways according to the form and amount present, and may help to explain some of the immunological disturbances associated with iron overload.

Uptake and intracellular handling of iron from transferrin and iron chelates by mitogen stimulated mouse lymphocytes

The ability of lymphocytes to utilise iron from different sources has been investigated. Iron uptake from transferrin by proliferating lymphocytes gradually increased as saturation of the protein with iron was increased up to 100%, but rose sharply when addition of further iron resulted in the presence of non-transferrin bound iron. Increasing the saturation of transferrin with iron caused an increased rate of proliferation up to about 100% saturation but when the level of iron present exceeded the binding capacity of the protein, proliferation decreased and at high levels of iron it was reduced below that seen in the absence of transferrin. Comparison of the degree of iron uptake from transferrin and from iron chelators showed that the hydrophilic chelator ferric nitrilotriacetate (FeNTA) donated larger amounts of iron to cells than did transferrin or the lipophilic chelator ferric-pyridoxal isonicotinoyl hydrazone (FePIH), but did not promote proliferation, and when present in high amounts caused inhibition. In contrast, FePIH supported proliferation as efficiently as transferrin. In cells cultured with FeNTA, iron was found predominantly in an insoluble form while in the cells cultured with Fe-transferrin or FePIH the largest proportion of iron was found in the non-ferritin high molecular weight fraction, which probably represents iron in enzymes and other metabolically-important proteins. In no case did iron associated with ferritin exceed 15% of the total uptake, and the cells showed no marked increase in synthesis of ferritin in response to any of the forms of iron. These results indicate that different forms of iron are handled in different ways by lymphocytes, and that iron delivered from hydrophilic chelates may be toxic and not readily available for metabolic use. Lymphocytes appear to be poorly equipped to sequester excess iron in ferritin, and this may account for abnormalities in the immune system reported in patients with iron overload.

Expression of transferrin receptors by monocytes and peritoneal macrophages from renal failure patients treated by continuous ambulatory peritoneal dialysis (CAPD)

Approximately 20% of monocytes and peritoneal macrophages from renal failure patients undergoing continuous ambulatory peritoneal dialysis (CAPD) were transferrin-receptor (TfR) positive by immunofluorescence, whereas cells from normal controls were generally TfR negative, as were monocytes from rheumatoid arthritis patients and from renal failure patients treated by haemodialysis. There was a significant correlation between the length of time on CAPD and the proportion of TfR-positive blood monocytes. CAPD peritoneal macrophages possessed 6.7-37.1 x 10(3) transferrin binding sites per cell, with a Ka of 3-25 x 10(7) mol l-1. In culture, monocytes from CAPD patients showed a progressive decrease in TfR expression, while in contrast about 20% of monocytes from normal controls which were originally 100% TfR negative expressed TfR after 3 days in culture. These findings indicate that regulation of TfR in monocytes/macrophages is complex, and that frequent removal of peritoneal cells during dialysate exchange may place a strain on the bone marrow, resulting in the release of an increasingly immature population of TfR positive monocytes to the circulation in CAPD patients.

Interaction of aluminium and gallium with human lymphocytes: the role of transferrin

Aluminium-transferrin (Al-Tf) and gallium-transferrin caused a dose-dependent decrease in proliferation of human peripheral blood lymphocytes cultured for 3 days with phytohaemagglutinin (PHA). Addition of apotransferrin reduced the inhibitory effect. Al added as AlCl3 or aluminium citrate had no effect, and there was no significant difference in the response of cells from renal failure patients with or without high serum Al levels or controls. Lymphocytes cultured in the presence of Al-Tf showed a dose-dependent uptake of Al, whereas uptake from aluminium citrate was low and not dose-dependent. Uptake from AlCl3 was very high but probably involved a nonspecific uptake mechanism. Levels of Al in freshly isolated lymphocytes were approximately 1.6 ng/10(6) cells, there being no difference between cells from patients and controls. It is concluded that Al, when bound to transferrin, may have a detrimental effect on lymphocyte function and might contribute to the decreased immune responsiveness of renal failure patients on haemodialysis. However, lymphocyte Al levels are probably not useful as a marker of Al overload in such patients.