A class of high molecular weight iron chelators has been prepared by covalently attaching deferoxamine (DFO), by its amino group, to a variety of biocompatible polymers such as dextran and hydroxyethyl-starch. The ironbinding properties of DFO are virtually unchanged after the attachment procedure, but the toxicity and circulatory half-life are profoundly altered. Competitive iron-binding experiments indicate that the conjugates retain a high affinity for ferric iron. In addition, the derivatives inhibit iron-driven lipid peroxidation as effectively as the parent drug. However, the LD50 in mice (based on DFO equivalents) is -4000 mg/kg for dextran-DFO as compared to 250 mg/kg for free DFO. Consistent with the greatly decreased LD50, intravenous administration of the conjugates in dogs at a dose of 100 mg/kg (body weight) does not cause the severe hypotension associated with intravenous administration of DFO. The plasma half-lives of these adducts are increased >10-fold for dextran-DFO and hydroxyethylstarch-DFO compared to the free drug. Finally, and most importantly, the conjugates are effective in mediating in vivo iron mobilization and excretion. Because recent evidence implicates iron as an important component of tissue injury in many disease states, these high molecular weight iron chelators may have potential for improved therapy, allowing higher sustained plasma concentrations of the active drug.Deferoxamine B (DFO), a bacterial siderophore isolated from Streptomyces pilosus, is used in a variety of situations in research and clinical medicine where the effective removal of iron is desired (1). In addition to its high affinity (Kd 10-30 M) and specificity for ferric ions (2), DFO renders iron unreactive in free-radical-producing reactions (3, 4) that can damage biomolecules and tissues. For these reasons, DFO is used clinically in cases of acute iron intoxication (5-7) and more commonly to treat iron overload due to chronic transfusion therapy (8, 9). Unfortunately, this chelator has two properties that diminish its usefulness. (i) Its acute (5-7) and chronic (10) toxicity limit the dose that can be safely used. (ii) It has a very short plasma half-life (11) and, since it is not readily absorbed when given orally, it must be administered either by repeated intramuscular injection or by continuous subcutaneous infusion. We have synthesized a class of high molecular weight iron chelators by covalently attaching DFO to biocompatible polymers such as dextran and hydroxyethyl-starch. These DFO-polymer conjugates have not only longer plasma half-lives but also lower toxicity and the same iron chelating properties as the free drug.MATERIALS AND METHODS Chemicals. DFO was obtained as the mesylate salt, Desferal, from CIBA-Geigy; dextran was obtained as Rheomacrodex or Macrodex, as solutions in normal saline from Pharmacia LKB; hydroxyethyl-starch was obtained as HESPAN or modified pentafraction as solutions from DuPont Critical Care (Waukeegan, IL). Gallium was purchased from Johnson Matthey (Seabrook,...

Iron and iron compounds-including mammalian hemoglobinscatalyze hydroxyl radical production and lipid peroxidation. To determine whether hemoglobin-mediated lipid peroxidation might be important in hemorrhagic injuries to the central nervous system (CNS), we studied the effects of purified hemoglobin on CNS homiogenates and injected hemoglobin into the spinal cords of anesthetized cats. Hemoglobin markedly inhibits Na/K ATPase activity in CNS homogenates and spinal cords of living cats. Hemoglobin also catalyzes substantial peroxidation of CNS lipids. Importantly, the potent iron chelator, desferrioxamine, blocks these adverse effects of hemoglobin, both in vitro and in vivo. Because desferrioxamine is not known to interact with heme iron, these results indicate that free iron, derived from hemoglobin, is the proximate toxic species. Overall, our data suggest that hemoglobin, released from red cells after trauma, can promote tissue injury through iron-dependent mechanisms. Suppression of this damage by desferrioxamine suggests a rational therapeutic approach to management of trauma-induced CNS injury.

Mammalian erythrocytes have large amounts of catalase, an enzyme which catabolizes hydrogen peroxide (H202). Because catalase has a low affinity for H202, others have suggested that glutathione peroxidase clears most H202 within the erythrocyte and that catalase is of little import. We hypothesized that erythrocyte catalase might function to protect heterologous somatic cells against challenge by high levels of exogenous H202 (e.g., in areas of inflammation). We find that, whereas nucleated cells (L1210 murine leukemia) are readily killed by an enzymatically generated flux of superoxide (and, therefore, H202), the addition of human and murine erythrocytes blocks lethal damage to the target cells. Inhibition of erythrocyte superoxide dismutase, depletion of glutathione, and lysis of the erythrocytes do not diminish this protection. However, inhibition of erythrocyte catalase abrogates the protective effect and the addition of purified catalase (but not superoxide dismutase) restores it. Furthermore, erythrocytes derived from congenitally hypocatalasemic mice (in which other antioxidant systems are intact) do not protect L1210 cells. Our results raise the possibility that the erythrocyte may serve as protection against by-products of its own cargo, oxygen.

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In select kindreds afflicted with familial idiopathic epilepsy, most individuals suffering seizures also have low levels of the plasma hemoglobin-binding protein, haptoglobin. This hypohaptoglobinemia may be causally associated with a tendency to develop epilepsy. Our experimental results indicate that artificially-induced hypohaptoglobinemia in mice causes retarded clearance of free hemoglobin from the central nervous system, and that such free hemoglobin may engender the peroxidation of brain lipids. We hypothesize that hypohaptoglobinemia, either inherited, or acquired via traumatic processes, may prevent efficient clearance of interstitial hemoglobin from the central nervous system, thereby predisposing these people to encephalic inflammation and the appearance of seizure disorders.