Liposomal clodronate as a novel agent for treating autoimmune hemolytic anemia in a mouse model

Abstract

IntroductionAutoimmune hemolytic anemia (AIHA) is an autoimmune disease in which antibodies directed against the patient's own red blood cells (RBCs) lead to their premature destruction. 1 Anemia can be sudden and life threatening, or more gradual in onset. Although most cases are idiopathic, association with other forms of autoimmunity, malignancy, or infection is common. [2][3][4][5] AIHA occurs in both children and adults, with a wide age distribution.AIHA can be mediated by immunoglobulin G (IgG), IgM, or, rarely, IgA antibodies. 1 Most clinically significant cases, however, are caused by IgG antibodies. 1,3 In these patients, autoantibodies bind to RBCs and promote their uptake by splenic and hepatic macrophages via Fc receptors. 6 Although IgG antibodies can fix complement, the principal means of destruction of RBCs in these cases is via phagocytosis. 1,7-9 Therefore, even though B cells (often with T-cell help) are producing the offending autoantibody, macrophages are the essential effector cells for the development of anemia. This fact is reflected in the therapy for AIHA. Splenectomy and corticosteroids, mainstays of treatment, both ultimately interfere with the phagocytosis of opsonized RBCs. 1 Experimental therapy in animal models has also used the specific blocking of Fc-mediated uptake of RBCs by either genetic means or the use of anti-Fc antibodies. [10][11][12][13][14] Clodronate (dichloromethylene diphosphonate) is a bisphosphonate used for treating osteolytic bone diseases and osteoporosis. Bisphosphonates alleviate these disorders by inhibiting the function of osteoclasts. There is evidence for both a direct blocking effect on these cells as well as an apoptosis-inducing effect. 15,16 Over a decade ago, it was found that incorporation of this drug into liposomes allowed it to become a potent antimacrophage agent both in vivo and in vitro. 17,18 The liposomal drug is taken up by macrophages and rapidly causes apoptosis. 19,20 Its effects in vivo are influenced principally by its route of administration. Injection into tissues leads to the depletion of macrophages from the tissue itself and from draining lymph nodes. Intravenous injection of liposomally encapsulated clodronate leads to nearly complete depletion of splenic and hepatic macrophages as well as marginal zone dendritic cells within 24 hours. 21 Unlike other methods of macrophage depletion, however, this treatment does not lead to the secretion of proinflamatory cytokines by the dying macrophages. 22 Moreover, liposomal clodronate appears to have a very selective effect on macrophages and phagocytic dendritic cells. Neutrophils and lymphocytes have not been found to be directly affected by the drug. 21,[23][24] Due to the well-established, critical role of macrophages in AIHA, we wondered whether the potent and specific antimacrophage effects of liposomal clodronate could be harnessed to treat this disease. To study this question, we generated a model of AIHA in mice. In this model, we treated mice with monoclonal anti-RBC antibodies de...

Gr1+Cells Control Growth of YopM-NegativeYersinia pestisduring Systemic Plague

“…In contrast to the effect of anti-Gr1, treatment of mice with clodronate-liposomes to deplete Ms/DCs curtailed growth of both Y. pestis strains. As reported by other groups (4,24), treatment with clodronateliposomes did not deplete PMNs. Taken together, these data support the hypothesis that PMNs are critical effectors for the in vivo growth defect of YopM Ϫ Y. pestis; in contrast, Ms and/or DCs promote bacterial growth in a YopM-independent manner during the first few days of systemic plague as previously suggested (33).…”

Cell-derived anaphylatoxins as key mediators of antibody-dependent type II autoimmunity in mice

“…Studies with macrophage-depleted mice demonstrated that Kupffer cells are one of the crucial effector cell types in murine AIHA (32). Our results clearly show that in vivo phagocytosis of 34-3C-opsonized erythrocytes by Kupffer cells is strongly impaired in C5aR -/-mice, indicating that this process requires C5aR, which, along with activating FcγR, is expressed on liver Kupffer cells.…”

Exacerbation of autoantibody-mediated thrombocytopenic purpura by infection with mouse viruses

“…This hypothesis was tested by administration of clodronatecontaining liposomes to LDV-infected mice, a treatment known to suppress macrophages with phagocytic activity 10 and, therefore, to cure experimental autoantibody-mediated blood autoimmune diseases that are mediated by phagocytosis. 6,11,12 Administration of these clodronate-containing liposomes resulted in a complete prevention of the increased pathogenicity of both polyclonal and monoclonal antiplatelet antibodies observed in LDV-infected mice (significant difference for all antibodies between mice treated with PBS-and clodronate-containing liposomes: P ϭ .0286; Figure 5A). The hypothesis that LDV enhances thrombocytopenia through Fc receptor-mediated phagocytosis was further supported by administration of total human IgG to mice.…”