Apoptotic cell death in activated monocytes following incorporation of clodronate-liposomes

Abstract

The present study was performed to elucidate whether sterically stabilized liposomes laden with clodronate, which lead to depletion of macrophages (Mphis) and amelioration of experimental autoimmune arthritis in vivo, selectively affect cells of the mphi lineage in vitro. The rates of incorporation of drug-free, fluorescent liposomes and the rates of cell death following exposure to clodronate-liposomes were assessed in human peripheral blood monocytes, as well as in polymorphonuclear leukocytes (PMNs), T cells, endothelial cells, and fibroblasts, both at rest and following activation. Gel electrophoresis of nuclear extracts and ultrastructural analyses were performed to identify the modality of cell death. Monocytes, particularly upon activation, were more efficient in incorporating sterically stabilized liposomes than all other cells except PMNs. Twenty percent of resting monocytes and up to 65% of activated monocytes died within 24 h of exposure to clodronate-liposomes, whereas the other cell types, including PMNs, remained unaffected. Activated monocytes exposed to clodronate-liposomes, but not resting or activated monocytes exposed to drug-free liposomes, showed clear signs of apoptotic cell death. In most of the assays, sterically stabilized liposomes were more efficient than conventional phosphatidylcholine-liposomes. Sterically stabilized clodronate-liposomes preferentially affect cells of the mphi lineage, particularly if activated. Selective elimination of activated Mphis by apoptosis may explain both therapeutic efficacy and safety of clodronate-liposomes in experimental models of autoimmunity.

Complementary Adhesion Molecules Promote Neutrophil- Kupffer Cell Interaction and the Elimination of Bacteria Taken Up by the Liver

“…Moreover, the addition of Cl 2 MDP-L had no effect on the viability of hepatocytes in vitro (assessed in terms of aspartate aminotransferase activity released into the culture medium over a 48-h incubation period) or the capacity of cultured hepatocytes to support the intracellular growth of Listeria (21 ; flow cytometric analysis, control listed first). These data are consistent with the results of numerous other studies that failed to show a significant effect of Cl 2 MDP-L on hepatocytes or circulating white blood cells, i.e., lymphocytes, granulocytes (including neutrophils), or mononuclear phagocytes (9,(22)(23)(24)(25) (26 -31). Conjugated mAbs used in flow cytometric analyses to characterize the NPC populations derived from control and Cl 2 MDP-L-treated mice were purchased from PharMingen (San Diego, CA).…”

In vitro cytoreductive effects on multiple myeloma cells induced by bisphosphonates

“…In addition, previous studies detected apoptotic effects of bisphosphonates on isolated osteoclasts 6 and cells of the monocyte-macrophage lineage. 7 Of these targets, osteoclasts appear the most sensitive even in the absence of the concentrating effect of bone material 6 with significant cytotoxic effects seen at concentrations as low as 1 M Pamidronate. The reasons for these relative differences in sensitivity are unknown.…”

“…Since bisphosphonates can induce apoptosis in other cell types, 6,7 we examined MM cells for programmed cell death. Apoptosis was studied in a multiparameter fashion by morphologic examination, DNA electrophoresis and flow cytometry.…”

“…These drugs can also induce apoptosis of monocytes. 7 To further investigate their potential as anti-myeloma agents, we initiated the current study, exposing multiple myeloma cell lines as well as primary MM plasma cell specimens obtained from patients to increasing concentrations of Aredia as well as the third generCorrespondence: A Aparicio; Fax: 310 268 4908 Received 5 June 1997; accepted 1 October 1997 ation, more potent bisphosphonate Zoledronate. The results indicate the ability of these drugs to inhibit growth of myeloma cells.…”

Myeloid progenitors differentiate into microglia and promote vascular repair in a model of ischemic retinopathy

“…We therefore sought to independently confirm these observations by examining whether microglia also play a role in normal retinal vascular development. This was accomplished by manipulating microglia numbers using clodronate-loaded liposomes, which are selectively taken up by, and induce apoptosis in, highly phagocytic macrophages/microglia (24)(25)(26). The specificity of microglial uptake in these experiments was demonstrated using labeled liposomes, which were found to colocalize exclusively within CD11b + microglia 4 days after injection ( Figure 6E, inset).…”