Extracellular and intracellular action of clodronate in osteolytic bone diseases? A hypothesis

Liposomes for specific depletion of macrophages from organs and tissues

A liposome mediated macrophage "suicide" approach has been developed, based on the liposome mediated internalization of the small hydrophilic molecule clodronate in macrophages J Leukoc Biol 62:702, 1997. This molecule has a very short half life when released in the circulation, but does not easily cross phospholipid bilayers of liposomes or cell membranes. As a consequence, once ingested by a macrophage in a liposome encapsulated form, it will be accumulated within the cell as soon as the liposomes are digested with the help of its lysosomal phospholipases. At a certain intracellular clodronate concentration, the macrophage is eliminated by apoptosis. Given the fact that, neither the liposomal phospholipids chosen, nor clodronate are toxic to other (non-phagocytic) cells, this method has proven its efficacy and specificity for depletion of macrophage subsets in various organs. In several cases, organ specific depletion can be obtained by choosing the right administration route for the clodronate liposomes.

Liposomes for targeting of antigens and drugs: immunoadjuvant activity and liposome-mediated depletion of macrophages

Liposomes have proven their use as a tool in various immunological studies. In our own studies, both their application as antigen carriers and as drug carriers appeared to be useful. Immune responses were elicited against free soluble protein antigens and against the same antigens in a liposome-associated (particulate) form, in order to compare both types of response. Since we were especially interested in the role of splenic macrophages in both types of response, we developed a liposome-mediated macrophage suicide approach, based on the liposome-mediated internalization of the small hydrophilic molecule clodronate in macrophages. This molecule has a very short half life when released in the circulation, but does not easily cross phospholipid bilayers of liposomes or cell membranes. As a consequence, once ingested by a macrophage in a liposome-encapsulated form, it will be accumulated within the cell as soon as the liposomes are digested with the help of its lysosomal phospholipases. At a certain intracellular clodronate concentration, the macrophage is eliminated by apoptosis. Given the fact that neither the liposomal phospholipids chosen nor clodronate are toxic to other (non-phagocytic) cells, this method has proven its efficacy for depletion of macrophage subsets in various organs. In several cases, organ-specific depletion can be obtained by choosing the right administration route for the clodronate liposomes.

Bisphosphonate therapy in multiple myeloma: past, present, future

Bone disease characterised by osteolytic lesions, pathological fractures and hypercalcaemia is an important clinical feature in multiple myeloma. Pain, decreased performance status, and the need for palliative radiotherapy and surgical interventions are common sequelae. Bisphosphonates act primarily on osteoclasts to inhibit excessive bone resorption, and have therefore been investigated in myeloma patients to ameliorate the clinical consequences of the bone disease. Bisphosphonates are currently the therapy of choice in myeloma patients with hypercalcaemia. In long-term management, both oral clodronate and intravenous pamidronate are effective in reducing skeletal-related events. Zoledronic acid seems to be as effective as pamidronate. Whether bisphosphonates have antimyeloma activity is currently unknown. Cost-benefit analyses have shown reasonable efficacy with acceptable costs. Bisphosphonate therapy is now accepted as an important part of care in myeloma patients, although much still has to be learned in order to optimise this therapy in multiple myeloma.

Allopathic and complementary alternatives to hormone replacement therapy

Management of the menopause is a rapidly growing concern due to the ageing human population. The overall female lifespan has increased over the last century and up to a third of a woman's life is now spent in menopause. To that end, significant attention has been placed on maximising the quantity and quality of life in the menopausal years. The optimal management strategies are ones that are highly flexible and sensitive to an individual's expectations and concerns. Thus, while traditional oestrogen replacement therapy has been in place for > 20 years, there is now a greater interest in alternatives to this modality for those women who cannot or will not use it. This article reviews some of the alternative therapies that are being incorporated both in the allopathic and complementary medicine arenas.

Suppression of immunoreactive macrophages in atheromatous lesions of rabbits by clodronate

Bisphosphonates inhibit the development of experimental atherosclerosis and decrease the intima-media thickness of human carotid artery. Since arterial macrophages have a key role in atherogenesis, we studied whether clodronate, an antiatherogenic bisphosphonate, will suppress the appearance of macrophages generated by atheromatous process in the rabbit aorta. The atherosclerosis was caused in rabbits by means of a high-cholesterol (1%) diet, and the animals were treated simultaneously with saline (n = 11) or 25 mg/kg of clodronate disodium (n= 12) intravenously twice a week for 6 to 12 weeks. The cholesterol diet for 6 weeks caused no visible atheromatous plaques in the aorta, but feeding for 6 more weeks produced progressively atheromatous lesions. Immunohistochemistry with specific antimacrophage antibody showed an intensive accumulation of macrophages in the subendothelial layer of the aorta in cholesterol-fed rabbits treated with saline or clodronate for 6 weeks. In the aorta of rabbits treated with cholesterol diet + saline for 12 weeks, the area of immunoreactive macrophages extended from the internal elastic lamina up to the luminal surface of the aorta. However, far less immunoreactive macrophages were present in the atheromatous regions of the aorta of rabbits medicated with clodronate for 12 weeks; in the clodronate-treated animals the macrophages were located closer to the luminal surface of the aorta than in controls on saline. No atheromatous lesions and macrophages appeared in the aorta of rabbits on standard diet (n = 7). The results suggest that clodronate suppresses the appearance of cholesterol-phagocyting macrophages in arterial walls during atherogenesis.

Treatment of osteoporosis with bisphosphonates

Bisphosphonates are safe and effective agents for treatment and prevention of osteoporosis. Alendronate and risedronate are the best studied of all agents for osteoporosis in terms of efficacy and safety. They increase bone mass. In patients who have established osteoporosis, they reduce the risk of vertebral fractures. They are the only agents shown in prospective trials to reduce the risk of hip fractures and other nonvertebral fractures. They are approved by the US FDA for prevention of bone loss in recently menopausal women, for treatment of postmenopausal osteoporosis, and for management of glucocorticoid-induced bone loss. Other bisphosphonates (e.g., etidronate for oral use, pamidronate for intravenous infusion) are also available and can be used off-label for patients who cannot tolerate approved agents. Bisphosphonates combined with estrogen produce greater gains in bone mass compared with either agent used alone; whether there is a greater benefit of combination therapy on fracture risk is not clear. Combining a bisphosphonate with raloxifene or calcitonin is probably safe, although data on effectiveness are lacking.

Clodronate: a review of its use in breast cancer

Like other members of its class, the bisphosphonate clodronate (clodronic acid) inhibits bone resorption. The efficacy of oral clodronate 1600 mg/day in reducing the incidence of skeletal complications and metastasis development has been assessed in several clinical trials in patients with breast cancer. Long term use of oral clodronate significantly reduced the total cumulative incidence of skeletal events (including fractures, hypercalcaemia, and the need for radiotherapy for bone pain) compared with that in placebo recipients in 2 randomised double-blind placebo-controlled studies, each involving >100 patients. Significant differences in favour of clodronate were also seen in the frequency of some individual skeletal events in 1 trial. A nonblind trial in 302 patients considered to be at high risk of developing metastases found that, at a 3-year follow-up, significantly fewer patients who received clodronate for 2 years developed skeletal metastases than those in a control group. Clodronate recipients were also significantly less likely than controls to develop visceral metastases, and had significantly higher survival rates. A smaller double-blind placebo-controlled study in women with recurrent breast cancer found that clodronate significantly decreased the total number of new skeletal metastases, but not the number of patients who developed them. In a nonblind trial in 299 patients with node-positive breast cancer, however, the incidence of skeletal metastases did not differ significantly between patients who received clodronate for 3 years and those in a control group. In addition, clodronate recipients had a significantly greater incidence of nonskeletal metastases (local and visceral), and significantly lower survival rates. Intravenous or oral clodronate has been well tolerated in clinical trials. The most common adverse effects reported were mild gastrointestinal disturbances such as nausea, vomiting and diarrhoea. All these events were transient, and usually resolved without stopping treatment.

CONCLUSIONS

Clodronate is a well tolerated bisphosphonate, available in both oral and intravenous forms, that significantly reduces the incidence of skeletal complications associated with breast cancer. Further research is needed to establish more clearly its efficacy in reducing metastasis development, to assess its efficacy compared with other bisphosphonates, and to determine which patients will benefit most from treatment. Currently, clodronate is probably most effective in the treatment and prevention of general skeletal complications in patients with breast cancer.

Treatment of osteoporosis with bisphosphonates

Several bisphosphonates are effective for preventing bone loss associated with estrogen deficiency, glucocorticoid treatment, and immobilization, and for at least partially reversing bone loss in patients with postmenopausal osteoporosis and steroid-induced osteoporosis. The most promising of these agents are etidronate, alendronate, risedronate, and ibandronate. These drugs should have an important role in the prevention and treatment of osteoporosis; however, more research is needed regarding optimal doses and regimens (continuous versus intermittent, oral versus parenteral), comparisons with other agents, and their use in combination with other agents.

Effects of liposome-encapsulated bisphosphonates on acetylated LDL metabolism, lipid accumulation and viability of phagocyting cells

Bisphosphonates, the drugs used for the treatment of e.g. osteoporosis, inhibit the development of experimental atherosclerosis. When encapsulated in liposomes, they also inactivate macrophages, which have a key role in atherogenesis. We studied the effects of three clinically used bisphosphonates, i.e. clodronate, etidronate and pamidronate, on 1) the viability of mouse peritoneal macrophages and macrophage-like RAW 264 cells, 2) the degradation of 125I-labeled acetylated LDL by RAW 264 cells, and 3) the formation of LDL-derived foam cells in vitro. Liposome-encapsulated clodronate and pamidronate, but not etidronate, decreased the fraction of viable peritoneal macrophages in a concentration-dependent manner, whereas RAW 264 cells were much more resistant to the cytotoxic effects of bisphosphonates. Preincubation with liposomal clodronate and etidronate inhibited in a concentration-dependent manner the degradation of acetylated LDL in RAW 264 cells, but non-cytotoxic concentrations of liposomal pamidronate had only a weak inhibitory effect. The inhibition was more pronounced by liposomal clodronate than by liposomal etidronate. At high concentrations (500 microg protein/ml) of acetylated and aggregated LDL, RAW 264 cells transformed to foam cells. Preincubation with liposomal clodronate and etidronate reduced the cellular accumulation of acetylated LDL-derived lipids, but the drugs had no effect on the lipid accumulation caused by aggregated LDL. The results suggest that liposomal clodronate and etidronate inhibit the activity of phagocyting cells in internalizing and degrading atherogenic modified LDL.

Apoptosis of macrophages induced by liposome-mediated intracellular delivery of clodronate and propamidine

Liposomes can be used as vehicles for intracellular delivery of drugs into phagocytic cells. Clodronate and propamidine, delivered into macrophages in this way, will kill these cells as a result of intracellular accumulation and irreversible metabolic damage. The so-called liposome-mediated macrophage 'suicide' approach, which is based on this principle, is now frequently applied in studies aimed at unravelling macrophage function. In the present study, the mechanism of phagocytic cell death induced by liposome encapsulated drugs was investigated 'in vitro'. Peritoneal macrophages and macrophages of the RAW 264 cell line were cultured in the presence of the liposome encapsulated drugs clodronate, propamidine and several forms of ethylenediaminetetraacetic acid (EDTA). The results obtained suggest that apoptotic death is induced in phagocytic cells both by liposomally delivered clodronate and by liposomally delivered propamidine. Although intracellular EDTA did induce apoptosis in a minority of the experiments, the results support earlier findings that EDTA does not deplete macrophages as effectively as clodronate and propamidine.

West Nile virus neuroinvasion and encephalitis induced by macrophage depletion in mice

The encephalitic West Nile virus and its nonneuroinvasive variant, WN-25, were used to study the effect of macrophage depletion on viral invasion of the central nervous system. The in vivo elimination of macrophages was achieved by use of liposome-encapsulated drug dichloromethylene diphosphonate. Depletion of macrophages had an exacerbating effect on the course of the viral infection, exhibited by higher and extended viremia and accelerated development of encephalitis and death. Using a low dose of West Nile virus (5 PFU/mouse), an increase in mortality (from 50% to 100%) due to macrophage depletion was demonstrated. Furthermore, the attenuated noninvasive variant WN-25 showed high and prolonged viremia in the macrophage depleted mice (approximately 5 log 10 PFU/ml versus 2 in control mice), that allowed the penetration of the virus into the central nervous system. The mortality rate caused by the attenuated virus in the macrophage-depleted mice was 70-75%, as compared to complete survival in the control inoculated mice. These results indicate a significant role of macrophages in the non-specific immediate defence system of the organism in case of viral infection.

Effect of liposomal and free bisphosphonates on the IL-1 beta, IL-6 and TNF alpha secretion from RAW 264 cells in vitro

PURPOSE

In order to evaluate the possible antiinflammatory action of bisphosphonates, the effect of the drugs on the secretion of proinflammatory cytokines (IL-1 beta, IL-6 and TNF alpha) from macrophages was studied. Liposomes or high concentration of extracellular calcium was used to enhance the intracellular delivery of bisphosphonates.

METHODS

RAW 264 cells were used as macrophage model, and they were induced with lipopolysaccharide to produce the cytokines. The cytokine concentrations in the culture supernatants were measured with time-resolved fluoroimmunoassay.

RESULTS

As a free drug, clodronate and pamidronate, but not etidronate, inhibited LPS-stimulated secretion of the cytokines from macrophage-like RAW 264 cells. Low concentrations of pamidronate, however, induced the IL-6 secretion, and the cytokine inhibitory action at the higher concentrations of pamidronate was attributed to cytotoxicity of the compound. The cytokine induction or toxic effects were not observed with clodronate or etidronate. When the drugs were encapsulated in negatively charged unilamellar liposomes, the inhibitory potency of both clodronate and etidronate enhanced by a factor of 10-20, while that of pamidronate was not increased. The complex formation of bisphosphonates with extracellular calcium, although enhancing the uptake of the compounds by macrophages, did not considerably increase their cytokine inhibitory potency.

CONCLUSIONS

Bisphosphonates have inhibitory action on cytokine secretion by macrophages. The non-cytotoxic cytokine inhibition by liposome encapsulated clodronate could be beneficial in local inflammatory diseases, where the inflammation is sustained by the excessive amounts of inflammatory cytokines produced by activated macrophages.

Liposome mediated depletion of macrophages: mechanism of action, preparation of liposomes and applications

Selective depletion of macrophages from tissues in vivo can be used to investigate whether these cells are playing a role in defined biological processes. This question is particularly relevant to various host defense mechanisms. We have developed a macrophage 'suicide' technique, using the liposome mediated intracellular delivery of dichloromethylene-bisphosphonate (Cl2MBP or clodronate). The method is specific with respect to phagocytic cells of the mononuclear phagocyte system (MPS) for the following reasons: (1) The natural fate of liposomes is phagocytosis. (2) Once ingested by macrophages, the phospholipid bilayers of the liposomes are disrupted under the influence of lysosomal phospholipases. (3) Cl2MBP intracellularly released in this way does not easily escape from the cell by crossing the cell membranes. (4) Cl2MBP released in the circulation from dead macrophages or by leakage from liposomes, will not easily enter non-phagocytic cells and has an extremely short half life in the circulation and body fluids. In the present review, the preparation of Cl2MBP-liposomes has been described in detail. Furthermore, the mechanism of action of the new approach and its applicabilities are discussed.

Effect of iron on the absorption and distribution of clodronate after oral administration in rats

The effect of iron on the absorption and distribution of disodium clodronate in rats after oral administration was studied. Disodium clodronate (300 mg/25 microCi/kg) was given both alone and with an equivalent amount of ferrous sulphate. The radioactivity in plasma and various tissue was measured. Concentration of clodronate in plasma was also determined with the GC-mass-selective detection method and the values compared with those measured with the isotope method. After administration, clodronate was rapidly cleared from plasma. Most of the dose was taken up by bone and only small amounts were found in non-calcified tissues. Concurrent ingestion of iron caused a marked decrease in the absorption of clodronate.

Liposome mediated depletion of macrophages: an approach for fundamental studies

To study the role of macrophages in immune and non-immune defence mechanisms, a new technique to eliminate macrophages has been developed. This technique uses the capability of macrophages to ingest and digest particulate compounds. As particulate compound liposomes with entrapped clodronate are used. Macrophages will ingest these liposomes and after fusion of their endosomes with their lysosomes the bilayers are disrupted under influence of phospholipases and the clodronate is released into the cytoplasm. If the intracellular concentration of free clodronate reaches sufficiently high values, the macrophage will die. The applications of the approach and some of the results obtained up to now using this macrophage 'suicide' technique are discussed.

Growth inhibition of macrophage-like and other cell types by liposome-encapsulated, calcium-bound, and free bisphosphonates in vitro

Bisphosphonates effectively inhibit osteoclastic bone resorption in diseases characterized by excessive bone loss. Liposome-encapsulated clodronate (dichloromethylene bisphosphonate) also is known to inactivate phagocytic cells in vivo, and inhibit the growth of macrophage-like RAW 264 cells in vitro. The macrophage suppressive effect of liposomal clodronate is of interest in autoimmune diseases, like rheumatoid arthritis, in which phagocytic cells are involved in inflammatory processes. Earlier in vivo studies suggested that liposomal clodronate is a far more potent inactivator of macrophages than liposomal forms of two other bisphosphonate compounds, pamidronate (3-amino-1-hydroxypropylidene bisphosphonate), and etidronate (1-hydroxyethylidene-1,1-bisphosphonate). We examined the growth inhibitory properties of these three bisphosphonates with macrophage-like RAW 264 cells and with other types of cells in vitro. All three bisphosphonates encapsulated in liposomes effectively inhibited the growth of RAW 264 and CV1-P cells, while free drugs were 20-1000 times less potent growth inhibitors. Also, high extracellular calcium concentrations enhanced the potency of bisphosphonates for RAW 264 cells, indicating that, in addition to liposomes, the uptake of bisphosphonates by macrophages is mediated also by calcium. In all formulations, pamidronate was the most potent compound for the cells, with the exception of CV1-P cells, for which liposomal clodronate was the most potent. The effects of liposomal drugs were selective for highly endocytotic cells. The results suggest that liposome-encapsulated bisphosphonates could provide a specific tool to affect the function of macrophages and all three of these bisphosphonates are potentially effective as macrophage suppressors in autoimmune diseases.

Clodronate (dichloromethylene bisphosphonate) inhibits LPS-stimulated IL-6 and TNF production by RAW 264 cells

Effect of liposome-encapsulated and free clodronate on the IL-6 and TNF production by macrophages was studied using RAW 264 cell line as a macrophage model, and dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA) for analysis of secreted cytokines. LPS-stimulated RAW 264 cells proved to produce notable amounts of these two cytokines, and DELFIA was sensitive and reliable method for analysis. Liposome-encapsulated clodronate inhibited the production of both cytokines, IL-6 being affected more than TNF, and the effect was mostly due to the drug itself, not to liposomal lipid. More than ten times higher concentration of free clodronate than liposomal clodronate was needed to inhibit cytokine production. This is the first report on the cytokine inhibitory property of clodronate, and the results support the idea of the use of liposomal clodronate as a macrophage suppressive agent in autoimmune diseases.