Teriparatide and clodronate combination as a potential treatment for complex regional pain syndrome type I in delayed consolidation after foot surgery: a case report and review of the literature

BACKGROUND

Complex regional pain syndrome type I is a pathological condition characterized by an exaggerated response of tissues to low or moderate pain stimuli. The exact pathogenesis and optimal medical treatment for complex regional pain syndrome type I are still not fully understood, although bisphosphonates have shown positive effects in reducing pain. Foot surgery can be complicated by the development of complex regional pain syndrome type I, leading to functional decline and difficulties in weight-bearing.

CASE PRESENTATION

The authors present a clinical case involving complex regional pain syndrome type I that developed after surgical foot arthrodesis. The patient, a 42-year-old Caucasian male, did not respond to clodronate treatment but experienced successful outcomes upon the addition of teriparatide, which effectively stimulated the healing of arthrodesis.

CONCLUSION

Teriparatide cannot be considered the primary treatment for complex regional pain syndrome due to insufficient solid clinical data. However, when complex regional pain syndrome is associated with or caused by delayed union, teriparatide can be used to address the underlying cause of complex regional pain syndrome.

Non-purulent myositis caused by direct invasion of skeletal muscle tissue by Leptospira in a hamster model

Myalgia is a common symptom of Leptospira infection in humans. Autopsies have reported that muscle tissue shows degeneration and necrosis of the myofibers and infiltration of inflammatory cells composed mainly of macrophages and lymphocytes. It remains unclear whether Leptospira directly infects the muscle and how the infiltrating inflammatory cells are involved in muscle fiber destruction. This study evaluated the relationship between histopathological changes and leptospiral localization in the muscle tissue of a hamster model. The influence of macrophages in skeletal muscle injury was also investigated, using selective depletion of macrophages by administration of liposomal clodronate. Hamsters infected subcutaneously with Leptospira interrogans serovar Manilae strain UP-MMC-SM showed myositis of the thighs adjacent to the inoculated area beginning at 6 days post-infection. The myositis was non-purulent and showed sporadic degeneration and necrosis of muscle fibers. The degeneration of myofibers was accompanied by aggregations of macrophages. Immunofluorescence staining revealed leptospires surrounding the damaged muscle fibers. Subcutaneous injection of formalin-killed Leptospira or intraperitoneal injection of live Leptospira caused no myositis in hamster thighs. Liposomal clodronate treatment in infected hamsters reduced macrophage infiltration in muscle tissue without impacting bacterial clearance. Muscle necrosis was still observed in the infected hamsters treated with liposomal clodronate, and there was no significant change in serum creatine kinase levels compared to those in animals treated with liposomes alone. Our findings suggest that leptospiral invasion of muscle tissue from an inoculation site leads to the destruction of muscle fibers and causes non-purulent myositis, whereas the infiltrating macrophages contribute less to muscle destruction.

Early macrophage-mediated Bdnf expression in white adipose tissue during high-fat diet feeding

The expression of brain-derived neurotrophic factor (BDNF) is observed not only in the brain, but also in peripheral tissues including white adipose tissues (WATs). Here, we showed that the mRNA expression of Bdnf in inguinal WAT (iWAT) and epididymal WAT (eWAT) increased within 2 weeks of feeding mice with a high-fat diet (HFD). In mice on a 2-week HFD, the induction of Bdnf expression in WATs was significantly correlated with increases in body weight, suggesting that Bdnf expression may increase at an early stage of obesity. The mRNA expression of hypoxia-inducible factor 1α and platelet-derived growth factor, which are involved in neovascularization and the subsequent expansion of adipose tissues, increased in the iWAT of mice on the 2-week HFD. We also found that the expression of macrophage marker F4/80 in iWAT increased under the HFD. Interestingly, HFD-induced Bdnf expression in iWAT was not observed when macrophages were removed by the administration of clodronate liposomes. Accordingly, mice receiving clodronate liposomes also exhibited a significant reduction in the HFD-induced increase in body weight. In conclusion, increased body weight in HFD-induced obese model mice was accompanied by the induction of Bdnf expression in iWAT and was probably mediated by macrophages. Our findings imply a novel function for BDNF in iWAT at an early stage of obesity.

Myeloid Cell Derived IL1β Contributes to Pulmonary Hypertension in HFpEF

BACKGROUND

Pulmonary hypertension (PH) in heart failure with preserved ejection fraction (HFpEF) is a common and highly morbid syndrome, but mechanisms driving PH-HFpEF are poorly understood. We sought to determine whether a well-accepted murine model of HFpEF also displays features of PH, and we sought to identify pathways that might drive early remodeling of the pulmonary vasculature in HFpEF.

METHODS

Eight-week-old male and female C57BL/6J mice received either Nγ-nitro-L-arginine methyl ester and high-fat diet or control water and diet for 2, 5, and 12 weeks. The db/db mice were studied as a second model of HFpEF. Early pathways regulating PH were identified by bulk and single-cell RNA sequencing. Findings were confirmed by immunostain in lungs of mice or lung slides from clinically performed autopsies of patients with PH-HFpEF. ELISA was used to verify IL-1β (interleukin-1 beta) in mouse lung, mouse plasma, and also human plasma from patients with PH-HFpEF obtained at the time of right heart catheterization. Clodronate liposomes and an anti-IL-1β antibody were utilized to deplete macrophages and IL-1β, respectively, to assess their impact on pulmonary vascular remodeling in HFpEF in mouse models.

RESULTS

Nγ-nitro-L-arginine methyl ester/high-fat diet-treated mice developed PH, small vessel muscularization, and right heart dysfunction. Inflammation-related gene ontologies were overrepresented in bulk RNA sequencing analysis of whole lungs, with an increase in CD68+ cells in both murine and human PH-HFpEF lungs. Cytokine profiling showed an increase in IL-1β in mouse and human plasma. Finally, clodronate liposome treatment in mice prevented PH in Nγ-nitro-L-arginine methyl ester/high-fat diet-treated mice, and IL-1β depletion also attenuated PH in Nγ-nitro-L-arginine methyl ester/high-fat diet-treated mice.

CONCLUSIONS

We report a novel model for the study of PH and right heart remodeling in HFpEF, and we identify myeloid cell-derived IL-1β as an important contributor to PH in HFpEF.

Preparation and PET/CT imaging of implant directed 68Ga-labeled magnetic nanoporous silica nanoparticles

BACKGROUND

Implant infections caused by biofilm forming bacteria are a major threat in orthopedic surgery. Delivering antibiotics directly to an implant affected by a bacterial biofilm via superparamagnetic nanoporous silica nanoparticles could present a promising approach. Nevertheless, short blood circulation half-life because of rapid interactions of nanoparticles with the host's immune system hinder them from being clinically used. The aim of this study was to determine the temporal in vivo resolution of magnetic nanoporous silica nanoparticle (MNPSNP) distribution and the effect of PEGylation and clodronate application using PET/CT imaging and gamma counting in an implant mouse model.

METHODS

PEGylated and non-PEGylated MNPSNPs were radiolabeled with gallium-68 (68Ga), implementing the chelator tris(hydroxypyridinone). 36 mice were included in the study, 24 mice received a magnetic implant subcutaneously on the left and a titanium implant on the right hind leg. MNPSNP pharmacokinetics and implant accumulation was analyzed in dependence on PEGylation and additional clodronate application. Subsequently gamma counting was performed for further final analysis.

RESULTS

The pharmacokinetics and biodistribution of all radiolabeled nanoparticles could clearly be visualized and followed by dynamic PET/CT imaging. Both variants of 68Ga-labeled MNPSNP accumulated mainly in liver and spleen. PEGylation of the nanoparticles already resulted in lower liver uptakes. Combination with macrophage depletion led to a highly significant effect whereas macrophage depletion alone could not reveal significant differences. Although MNPSNP accumulation around implants was low in comparison to the inner organs in PET/CT imaging, gamma counting displayed a significantly higher %I.D./g for the tissue surrounding the magnetic implants compared to the titanium control. Additional PEGylation and/or macrophage depletion revealed no significant differences regarding nanoparticle accumulation at the implantation site.

CONCLUSION

Tracking of 68Ga-labeled nanoparticles in a mouse model in the first critical hours post-injection by PET/CT imaging provided a better understanding of MNPSNP distribution, elimination and accumulation. Although PEGylation increases circulation time, nanoparticle accumulation at the implantation site was still insufficient for infection treatment and additional efforts are needed to increase local accumulation.

Cell surface ATP synthase-released H+ and ATP play key roles in cocoa butter intake-mediated regulation of gut immunity through releases of cytokines in rat

Proper food intake is important for maintaining good health in humans. Chocolate is known to exert anti-inflammatory effects; however, the mechanisms remain unclear. In this study, we aimed to investigate the effects of cocoa butter intake on gut immunity in rats and rabbits. Cocoa butter intake increased the lymph flow, cell density, and IL-1β, IL-6 and IL-10 levels in mesenteric lymph. Clodronate, a macrophage depletion compound, significantly enhanced the release of all cytokines. The immunoreactivities of macrophage markers CD68 and F4/80 in the jejunal villi were significantly decreased with clodronate. Piceatannol, a selective cell surface ATP synthase inhibitor significantly reduced the cocoa butter intake-mediated releases of IL-1β, IL-6 and IL-10. The immunoreactivities of cell surface ATP synthase were observed in rat jejunal villi. Shear stress stimulation on the myofibroblast cells isolated from rat jejunum released ATP and carbon dioxide depended with H+ release. In rabbit in vivo experiments, cocoa butter intake increased the concentrations of ATP and H+ in the portal vein. The in vitro experiments with isolated cells of rat jejunal lamina propria the pH of 3.0 and 5.0 in the medium released significantly IL-1β and IL-6. ATP selectively released IL-10. These findings suggest that cocoa butter intake regulates the gut immunity through the release and transport of IL-1β, IL-6, and IL-10 into mesenteric lymph vessels in a negative feedback system. In addition, the H+ and ATP released from cell surface ATP synthase in jejunal villi play key roles in the cocoa butter intake-mediated regulation of gut immunity.

Treatment for osteoporosis in people with beta-thalassaemia

BACKGROUND

Osteoporosis is characterized by low bone mass and micro-architectural deterioration of bone tissue leading to increased bone fragility. In people with beta-thalassaemia, osteoporosis represents an important cause of morbidity and is due to a number of factors. First, ineffective erythropoiesis causes bone marrow expansion, leading to reduced trabecular bone tissue with cortical thinning. Second, excessive iron loading causes endocrine dysfunction, leading to increased bone turnover. Lastly, disease complications can result in physical inactivity, with a subsequent reduction in optimal bone mineralization. Treatments for osteoporosis in people with beta-thalassaemia include bisphosphonates (e.g. clodronate, pamidronate, alendronate; with or without hormone replacement therapy (HRT)), calcitonin, calcium, zinc supplementation, hydroxyurea, and HRT alone (for preventing hypogonadism). Denosumab, a fully human monoclonal antibody, inhibits bone resorption and increases bone mineral density (BMD). Finally, strontium ranelate simultaneously promotes bone formation and inhibits bone resorption, thus contributing to a net gain in BMD, increased bone strength, and reduced fracture risk. This is an update of a previously published Cochrane Review.

OBJECTIVES

To review the evidence on the efficacy and safety of treatment for osteoporosis in people with beta-thalassaemia.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register, which includes references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. We also searched online trial registries. Date of most recent search: 4 August 2022.

SELECTION CRITERIA

Randomized controlled trials (RCTs) in people with beta-thalassaemia with: a BMD Z score below -2 standard deviations (SDs) for children aged under 15 years, adult males (aged 15 to 50 years) and premenopausal females aged over 15 years; or a BMD T score below -2.5 SDs for postmenopausal females and males aged over 50 years.

DATA COLLECTION AND ANALYSIS

Two review authors assessed the eligibility and risk of bias of the included RCTs, and extracted and analysed data. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

We included six RCTs (298 participants). Active interventions included bisphosphonates (3 trials, 169 participants), zinc supplementation (1 trial, 42 participants), denosumab (1 trial, 63 participants), and strontium ranelate (1 trial, 24 participants). The certainty of the evidence ranged from moderate to very low and was downgraded mainly due to concerns surrounding imprecision (low participant numbers), but also risk of bias issues related to randomization, allocation concealment, and blinding. Bisphosphonates versus placebo or no treatment Two RCTs compared bisphosphonates to placebo or no treatment. After two years, one trial (25 participants) found that alendronate and clodronate may increase BMD Z score compared to placebo at the femoral neck (mean difference (MD) 0.40, 95% confidence interval (CI) 0.22 to 0.58) and the lumbar spine (MD 0.14, 95% CI 0.05 to 0.23). One trial (118 participants) reported that neridronate compared to no treatment may increase BMD at the lumbar spine and total hip at six and 12 months; for the femoral neck, the study found increased BMD in the neridronate group at 12 months only. All results were of very low-certainty. There were no major adverse effects of treatment. Participants in the neridronate group reported less back pain; we considered this representative of improved quality of life (QoL), though the certainty of the evidence was very low. One participant in the neridronate trial (116 participants) sustained multiple fractures as a result of a traffic accident. No trials reported BMD at the wrist or mobility. Different doses of bisphosphonate compared One 12-month trial (26 participants) assessed different doses of pamidronate (60 mg versus 30 mg) and found a difference in BMD Z score favouring the 60 mg dose at the lumbar spine (MD 0.43, 95% CI 0.10 to 0.76) and forearm (MD 0.87, 95% CI 0.23 to 1.51), but no difference at the femoral neck (very low-certainty evidence). This trial did not report fracture incidence, mobility, QoL, or adverse effects of treatment. Zinc versus placebo One trial (42 participants) showed zinc supplementation probably increased BMD Z score compared to placebo at the lumbar spine after 12 months (MD 0.15, 95% CI 0.10 to 0.20; 37 participants) and 18 months (MD 0.34, 95% CI 0.28 to 0.40; 32 participants); the same was true for BMD at the hip after 12 months (MD 0.15, 95% CI 0.11 to 0.19; 37 participants) and 18 months (MD 0.26, 95% CI 0.21 to 0.31; 32 participants). The evidence for these results was of moderate certainty. The trial did not report BMD at the wrist, fracture incidence, mobility, QoL, or adverse effects of treatment. Denosumab versus placebo Based on one trial (63 participants), we are unsure about the effect of denosumab on BMD Z score at the lumbar spine, femoral neck, and wrist joint after 12 months compared to placebo (low-certainty evidence). This trial did not report fracture incidence, mobility, QoL, or adverse effects of treatment, but the investigators reported a reduction in bone pain measured on a visual analogue scale in the denosumab group after 12 months of treatment compared to placebo (MD -2.40 cm, 95% CI -3.80 to -1.00). Strontium ranelate One trial (24 participants) only narratively reported an increase in BMD Z score at the lumbar spine in the intervention group and no corresponding change in the control group (very low-certainty evidence). This trial also found a reduction in back pain measured on a visual analogue scale after 24 months in the strontium ranelate group compared to the placebo group (MD -0.70 cm (95% CI -1.30 to -0.10); we considered this measure representative of improved quality of life.

AUTHORS' CONCLUSIONS

Bisphosphonates may increase BMD at the femoral neck, lumbar spine, and forearm compared to placebo after two years' therapy. Zinc supplementation probably increases BMD at the lumbar spine and hip after 12 months. Denosumab may make little or no difference to BMD, and we are uncertain about the effect of strontium on BMD. We recommend further long-term RCTs on different bisphosphonates and zinc supplementation therapies in people with beta-thalassaemia-associated osteoporosis.

Diabetes exacerbated sepsis-induced intestinal injury by promoting M1 macrophage polarization via miR-3061/Snail1 signaling

Background

Macrophages play important roles in diabetes and sepsis-related intestinal injury. Accumulating evidence suggests that microRNAs (miRNAs) act as the fundamental link between macrophage polarization and tissue injury. However, the underlying mechanisms of miRNAs in regulating macrophage polarization–related intestinal injury under diabetes and sepsis conditions remain unclear.

Methods

The cecal ligation and puncture (CLP)–induced sepsis models were established in male wild-type (WT) and diabetic mice. Clodronate liposome was used to deplete macrophage. H&E staining, inflammatory cytokines [tumor necrosis factor–α (TNF-α), interleukin-1β (IL-1β), and IL-6], and intestinal mucosal barrier function markers [occludin, ZO-1, lipopolysaccharide (LPS), and intestinal fatty acid binding protein (iFABP)] were used to assess elevated intestinal damage. miRNA array, RNA-seq, and bioinformatic analysis were performed to detect the miRNA and messenger RNA (mRNA) expression and the potential regulation mechanism. In vitro, RAW264.7 cells were cultured in the absence or presence of high glucose and LPS, miR-3061 mimics, and Snail small interfering RNA stimulation, respectively, for further mechanism studies. Luciferase reporter assay was used to confirm the interplay between miRNA and its target genes.

Results

Compared with WT CLP mice, the diabetic CLP mice showed severe intestinal damage characterized by significant increases in Chui’s scores, expression of inflammatory cytokines (TNF-α, IL-1β, and IL-6), serum LPS and iFABP concentration, and significant reductions in tight junction protein occludin and ZO-1 levels. Macrophage depletion reversed the intestinal damage caused by CLP. The bioinformatic analysis revealed that miR-3061/Snail1 might be a potential regulation axis of macrophage polarization. Furthermore, high glucose and LPS stimulation increased M1 macrophage and reduced the levels of miR-3061, which was negatively associated with Snail1 in RAW264.7 cells. Mechanistic studies demonstrated that miR-3061 regulated macrophage polarization by targeting the Snail1 mRNA 3′‐untranslated region. Moreover, miR-3061 overexpression suppressed Snail1 expression and inhibited M1 macrophage and inflammatory cytokines.

Conclusion

This study elucidated that diabetes exacerbated sepsis-induced intestinal injury by promoting M1 macrophage polarization and further demonstrated that the miR-3061/Sani1 axis may be the potential target of macrophage polarization.

Key role of CCR2-expressing macrophages in a mouse model of low back pain and radiculopathy

Chronic low back pain is a common condition, with high societal costs and often ineffectual treatments. Communication between macrophages/monocytes (MØ) and sensory neurons has been implicated in various preclinical pain models. However, few studies have examined specific MØ subsets, although distinct subtypes may play opposing roles. This study used a model of low back pain/radiculopathy involving direct local inflammation of the dorsal root ganglia (DRG). Reporter mice were employed that had distinct fluorescent labels for two key MØ subsets: CCR2-expressing (infiltrating pro-inflammatory) MØ, and CX3CR1-expressing (resident) macrophages. We observed that local DRG inflammation induced pain behaviors in mice, including guarding behavior and mechanical hypersensitivity, similar to the previously described rat model. The increase in MØ in the inflamed DRG was dominated by increases in CCR2+ MØ, which persisted for at least 14 days. The primary endogenous ligand for CCR2, CCL2, was upregulated in inflamed DRG. Three different experimental manipulations that reduced the CCR2+ MØ influx also reduced pain behaviors: global CCR2 knockout; systemic injection of INCB3344 (specific CCR2 blocker); and intravenous injection of liposomal clodronate. The latter two treatments when applied around the time of DRG inflammation reduced CCR2+ but not CX3CR1+ MØ in the DRG. Together these experiments suggest a key role for the CCR2/CCL2 system in establishing the pain state in this model of inflammatory low back pain and radiculopathy. Intravenous clodronate given after pain was established had the opposite effect on pain behaviors, suggesting the role of macrophages or their susceptibility to clodronate may change with time.

Critical involvement of macrophage infiltration in the development of Sjögren's syndrome-associated dry eye

Lymphocytic infiltration of the lacrimal gland and ocular surface in autoimmune diseases such as Sjögren's syndrome (SS) causes an aqueous-deficient dry eye that is associated with significant morbidity. Previous studies from our laboratory and others have established autoimmune regulator (Aire)-deficient mice as a useful model to examine exocrinopathy and ocular surface disease associated with SS. Consistent with human SS, autoreactive CD4(+) T cells play an indispensible role in the development of exocrine and ocular surface disease in Aire knockout mice. We report that in addition to CD4(+) T cells, a large number of macrophages infiltrate the corneal stroma, limbus, and lacrimal glands of diseased mice. Adoptive transfer of autoreactive CD4(+) T cells from Aire knockout mice led to local infiltration of macrophages and ocular surface damage in immunodeficient recipients. Depletion of local macrophages, through subconjunctival injection of clodronate liposome, attenuated lissamine green staining and improved ocular phenotype. Alternatively, systemic depletion of macrophages had no effect on ocular phenotype but led to significant improvements in lacrimal gland exocrinopathy and tear secretion. Our results suggested that autoreactive CD4(+) T cells provoked macrophage infiltration to the eye and lacrimal gland, where they played a functional role in directing the development of autoimmune dry eye.

The investigation of macrophage infiltration in the early phase of ischemic acute renal failure in mice

BACKGROUND/AIMS

Inflammation plays a key role in ischemic acute renal failure (ARF). The present study investigated the infiltration of macrophages in the early phase of ischemic ARF in mice.

METHODS

Ischemic ARF was induced by renal clamping for 22 min, while the control mice underwent sham surgery (no clamping). The serum creatinine and blood urea nitrogen (BUN) levels were measured in the control and post-ischemia mice. Immunofluorescence staining was used to measure the number of CD 11b-positive cells in the kidney tissue sections to determine the amount of post-ischemic macrophage infiltration. Lipo-Cl2MBP (clodronate) for macrophages depletion was injected via a tail vein 5 d before ischemia induction and again 2 d before ischemia induction.

RESULTS

The study found that the post-ischemia mice had higher levels of serum creatinine and BUN at 16 and 24 h compared to the controls. Immunofluorescence staining showed there were more macrophages in the post-ischemic tissue at 2, 8, 16 and 24 h compared to the control tissue, and that most of these macrophages were located in the outer medulla. The mice treated with clodronate prior to ischemia induction were found to have lower levels of serum creatinine compared to those mice that weren't treated with clodronate.

CONCLUSIONS

There was significant infiltration of macrophages from the early phase of ischemic ARF, and this peaked at 16-24 h. Macrophage depletion using clodronate was protective against ischemic ARF.

Evaluation of liposomal clodronate in experimental spontaneous autoimmune hemolytic anemia in dogs

OBJECTIVES

Liposomal clodronate (dichloromethylene diphosphonate) has been used to deplete macrophages and block clearance of opsonized cells in mouse models of autoimmune disease. However, liposomal clodronate (LC) has not been previously evaluated in a large-animal spontaneous autoimmune disease model. Therefore, the safety and efficacy of LC treatment was assessed in normal dogs and in dogs with spontaneous autoimmune hemolytic anemia (AIHA).

METHODS

LC was administered intravenously first to healthy dogs and then to dogs with spontaneous, severe AIHA to determine if the treatment was safe and could block clearance of opsonized red blood cells (RBCs) in vivo. Studies were also conducted to assess the in vitro effects of LC on dog macrophages and dendritic cells.

RESULTS

Intravenous infusion of low doses of LC was well tolerated and blocked clearance of opsonized RBCs in normal dogs in vivo. LC was taken up by splenic macrophages and dendritic cells in vivo, and induced killing of macrophages and dendritic cells in vitro. Seven dogs with severe, spontaneous AIHA were treated with LC in a pilot study. Treatment was well tolerated, 2 of 7 LC-treated dogs with AIHA had a decrease in RBC clearance, and LC-treated dogs had significantly increased survival times compared to historical control dogs matched for disease severity.

CONCLUSIONS

These results indicate that LC can be safely administered intravenously to dogs and that even relatively low doses are capable of blocking RBC clearance and improving outcomes in a spontaneous large-animal model of AIHA. Therefore, additional studies of LC for treatment of autoantibody-mediated cytopenias in dogs and humans may be warranted.

Macrophages are involved in hexachlorobenzene-induced adverse immune effects

Hexachlorobenzene (HCB) is a persistent environmental pollutant that causes adverse immune effects in man and rat. The Brown Norway (BN) rat is very susceptible to HCB-induced immunopathology and oral exposure causes inflammatory skin and lung lesions, splenomegaly, lymph node (LN) enlargement, and increased serum levels of IgE and anti-ssDNA IgM. T cells play an important role but do not account for all adverse effects induced by HCB. Macrophages are probably also important and the relationship between macrophages and T cells was further investigated. To eliminate macrophages clodronate-liposomes were used. Furthermore, a kinetic study was performed to obtain insight in the early phase of the HCB-induced immune response. Also, experiments were performed to detect specific memory T cells. Therefore, an adoptive transfer study was performed. Our results indicate that macrophages are indeed involved in HCB-induced skin lesions, lung eosinophilia, and elevation of IgM against ssDNA. Kinetics showed that both skin and lung lesions appeared early after exposure. Moreover, immune effects could not be adaptively transferred. Thus, both macrophages and T cells are involved in HCB-induced immune effects but HCB exposure does not lead to specific T cell sensitization. Presumably, HCB exposure induces macrophage activation, thereby generating adjuvant signals that polyclonally stimulate T cells. Together, these events may lead to the observed immunopathology in BN rats.

Role of gut macrophages in mice orally contaminated with scrapie or BSE

While there is a growing consensus on the understanding of the propagation pathways after oral infection of transmissible spongiform encephalopathy (TSE) agents and even if the central role of follicular dendritic cells is identified, little is known about the key players in the first steps of the infection and about the site of the disease development. We investigated the role of gut macrophages, which are capable of capturing aggregates of the prion protein. PLGA particles containing clodronate were designed in order to be orally administered and to target Peyer's patches for inducing gut-associated macrophages suicide in mice. Mice were subsequently infected with scrapie or BSE by the oral route. It was found that the efficacy of macrophage suppression in the Peyer's patches correlated well with an earlier appearance of PrPres in these formations and with a higher amount of PrPres at a later stage of the infection. Thus, the capture of infectious particles that have crossed the epithelial gut barrier and their elimination by macrophages seems to be a key event to restrict the amount of agent initiating the infection.

Renal ischemia-reperfusion injury and adenosine 2A receptor-mediated tissue protection: role of macrophages

The role of monocytes/macrophages in the pathogenesis of ischemia-reperfusion injury (IRI) is unknown. We sought to determine whether activation of macrophage adenosine 2A (A(2A)) receptors (A(2A)Rs) mediates tissue protection. We subjected C57Bl/6 mice infused with clodronate [dichloromethylene bisphosphonate (Cl(2)MBP)] to IRI (32 min of ischemia followed by 24 h of reperfusion) to deplete them of macrophages. IRI induced an elevation of plasma creatinine that was reduced with Cl(2)MBP (26% of control). Adoptive transfer of murine RAW 264.7 cells reconstituted injury, an effect blocked significantly by A(2A) agonists (27% of plasma creatinine from mice reconstituted with macrophages). Macrophages subjected to A(2A) knockout by small interfering RNA were adoptively transferred to macrophage-depleted mice and reconstituted injury (110% of control mice); however, the increase in plasma creatinine was blocked by A(2A) agonists (20% of vehicle treatment). Finally, the A(2A) agonist effect on IRI was blocked in macrophage-depleted A(2A)-knockout mice reconstituted with wild-type RAW 264.7 cells. RNase protection assays 24 h after IRI demonstrated that macrophages are required for IL-6 and TGF-beta mRNA induction. However, A(2A) agonist-mediated tissue protection is independent of IL-6 and TGF-beta mRNA. We conclude that the full extent of IRI requires macrophages and that A(2A) agonist-mediated tissue protection is independent of activation of macrophage A(2A)Rs.

Adoptive transfer of alveolar macrophages abrogates bronchial hyperresponsiveness

Increasing evidence suggests that alveolar macrophages (AM) are involved in asthma pathogenesis. To better understand the role that these cells play, we investigated the capacity of AM from allergy-resistant rat, Sprague Dawley (SD), to modulate airway hyperresponsiveness of allergy-susceptible rat, Brown Norway (BN). AM of ovalbumin (OVA)-sensitized BN rats were eliminated by intratracheal instillation of liposomes containing clodronate. AM from OVA-sensitized SD rats were transferred into AM-depleted BN rats 24 h before allergen challenge. Airway responsiveness to methacholine was measured the following day. Instillation of liposomes containing clodronate in BN rats eliminated 85% AM after 3 d compared with saline liposomes. Methacholine concentration needed to increase lung resistance by 200% (EC200RL) was significantly lower in OVA-challenged BN rats (27.9 +/- 2.8 mg/ml) compared with SD rats (63.9 +/- 8.6 mg/ml). However, when AM from SD rats were transferred into AM-depleted BN rats, airway responsiveness (64.0 +/- 11.3 mg/ml) was reduced to the level of naïve rats (54.4 +/- 3.7 mg/ml) in a dose-dependent manner. Interestingly, transfer of AM from BN rats into SD rats did not modulate airway responsiveness. To our knowledge, this is the first direct evidence showing that AM may protect against the development of airway hyperresponsiveness.

Complete healing of severe osteoradionecrosis with treatment combining pentoxifylline, tocopherol and clodronate

Osteoradionecrosis (ORN) is a late terminal sequela of irradiation that does not resolve spontaneously. In a preliminary study, a combination of pentoxifylline (PTX), tocopherol (Vit-E) and clodonate has been shown to be of clinical benefit with more than 50% regression of progressive ORN observed at 6 months in 12 patients. A 68-year-old woman presenting with severe exteriorized osteoradionecrosis had received radiotherapy for breast cancer 29 years previously. She had palpable breast fibrosis, including the sternum (15 cm x 11 cm) and a painful fistulous track in the upper part of the bone (orifice diameter 10 mm) surrounded by local inflammatory signs, and chronic osteitis with sequestra extrusion. MRI showed deep radiation-induced fibrosis below this area without cancer recurrence, and complete bone destruction over an area of 7 cm x 4 cm. Oral PTX (800 mg day(-1)), Vit.E (1000 IU day(-1)) and clodronate (1600 mg day(-1)) were administered daily for 3 years and were well tolerated. The patient exhibited regular clinical improvement until complete closure of the fistula and total regression of the clinical fibrosis. MRI confirmed the good response and showed heterogeneous restoration of the sternum, which was filled with new tissue. This is the first time that antifibrotic treatment with combined PTX-Vit.E plus clodronate has been shown to have a significant effect on necrosis, by completely reversing severe progressive ORN and the associated radiation-induced fibrosis.

Pig islet xenograft rejection is markedly delayed in macrophage-depleted mice: a study in streptozotocin diabetic animals

The present study aimed to evaluate the effect of depletion of macrophages and/or natural killer (NK) cells on islet xenograft rejection in the pig-to-mouse model. Five microliters (4,000 to 5,000 IEQ, islet equivalents) of adult pig islets were transplanted under the renal capsule of C57BL/6 mice with streptozotocin-induced diabetes. Macrophages were depleted by injection of liposome-encapsulated dichloromethylene diphosphonate (Lip-Cl2MDP) intraperitoneally (i.p.) at a dose of 100 microl/ 10 g body weight (BW) 2 days before transplantation, and 50 microl/10 g BW weekly thereafter. NK cells were depleted by injection of the monoclonal antibody NK 1.1 (anti-NK 1.1 mAb) i.p. at a dose of 100 microg/mouse 1 day before transplantation, and then 25 microg per week thereafter. Islet graft survival was monitored by daily measurements of blood glucose. Graft survival was 8 +/- 1.2 days in untreated controls, 9 +/- 1.0 days with anti-NK 1.1 mAb alone, 22 +/- 4.9 days with Lip-Cl2MDP alone (P<0.01 vs. controls), and 26 +/- 3.8 days with Lip-Cl2MDP plus anti-NK 1.1 mAb (P<0.01 vs. controls). In the last group, two of six animals were killed with functioning grafts 30 days after transplantation. In untreated controls, rejected xenografts were heavily infiltrated by F4/80+ macrophages and CD3+T cells. In Lip-Cl2MDP-treated groups, the number of F4/80+ macrophages was markedly reduced. On the periphery of xenografts, a small number of CD3+T cells were observed. In conclusion, our results suggest that strategies targeting macrophages may facilitate islet xenograft survival. A role for NK cells cannot be excluded, but appears to be of minor importance.

Depletion of blood-borne macrophages does not reduce demyelination in mice infected with a neurotropic coronavirus

Mice infected with the neurotropic coronavirus mouse hepatitis virus strain JHM (MHV-JHM) develop a chronic demyelinating disease with symptoms of hindlimb paralysis. Histological examination of the brains and spinal cords of these animals reveals the presence of large numbers of activated macrophages/microglia. In two other experimental models of demyelination, experimental allergic encephalomyelitis and Theiler's murine encephalomyelitis virus-induced demyelination, depletion of hematogenous macrophages abrogates the demyelinating process. In both of these diseases, early events in the demyelinating process are inhibited by macrophage depletion. From these studies, it was not possible to determine whether infiltrating macrophages were required for late steps in the process, such as myelin removal. In this study, we show that when macrophages are depleted with either unmodified or mannosylated liposomes encapsulating dichloromethylene diphosphate, the amount of demyelination detected in MHV-infected mice is not affected. At a time when these cells were completely depleted from the liver, approximately equivalent numbers of macrophages were present in the spinal cords of control and drug-treated animals. These results suggest that blood-borne macrophages are not required for MHV-induced demyelination and also suggest that other cells, such as perivascular macrophages or microglia, perform the function of these cells in the presence of drug.

The role of Kupffer cells and regulation of neutrophil migration into the liver by macrophage inflammatory protein-2 in primary listeriosis in mice

Depletion of mouse Kupffer cells and splenic macrophages following intravenous administration of liposome-entrapped clodronate severely reduced host resistance to primary infection with Listeria monocytogenes. Infection of clodronate-treated mice with a sublethal dose of L. monocytogenes resulted in death of the mice within 3 days. The macrophage depletion resulted in marked increases in bacterial growth in the liver and spleen, but not in other tissues. The proliferation of L. monocytogenes was observed in a large number of hepatocytes that underwent apoptosis. Infiltration of neutrophils in the liver and rapid formation of microabscesses were observed in the control mice after L. monocytogenes infection. However, there was less accumulation of neutrophils in the liver of Kupffer cell-depleted mice than in the control mice. Expression of macrophage inflammatory protein-2 (MIP-2) was enhanced in the livers of both the control and Kupffer cell-depleted mice after L. monocytogenes infection. MIP-2 was also induced in a murine hepatocyte cell line following L. monocytogenes infection. The administration of neutralizing anti-interleukin-8 receptor homolog antibody severely abrogated neutrophil infiltration into the Listeria-infected mouse liver. Anti-MIP-2 antibody moderately reduced neutrophil infiltration and microabscess formation in the liver. These findings indicate that Kupffer cells protect hepatocytes from L. monocytogenes infection and the resultant apoptosis. Moreover, MIP-2 and its related molecules produced by the infected hepatocytes regulate neutrophil infiltration and microabscess formation in primary listeriosis.

Antigen detection in vivo after immunization with different presentation forms of rabies virus antigen, II. Cellular, but not humoral, systemic immune responses against rabies virus immune-stimulating complexes are macrophage dependent

In this paper we describe the effect of depletion of splenic macrophages on the uptake, and immune response against, different formulations of rabies virus antigen. Splenic macrophages were removed by intravenous injection with clodronate liposomes. beta-propiolacton inactivated rabies virus (RV-BPL) and immune-stimulating complexes (iscom) containing these antigens were given to macrophage-depleted and control mice. In the absence of phagocytic cells in the spleen, antigen is still trapped in the red pulp and to a lesser extent in the peri-arteriolar lymphocyte sheaths (PALS) for both antigen formulations. The localization pattern in the main area of immune response induction, namely the follicles, was unaltered after macrophage depletion. Functionally, the depletion of splenic and liver macrophages had no influence on the induction of specific antibody responses in both RV-BPL or RV-iscom immunized mice, even though the latter presentation form was clearly associated with specific localization in the marginal metallophillic macrophages. In RV-BPL immunized mice, macrophage depletion had no influence on proliferative T-cell responses. However, macrophage-depleted mice that were immunized with RV-iscom showed a significant decrease in proliferative T-cell responses. These results confirm existing ideas on the spleen as a physical filter rather than an induction site for humoral responses and shed new light on the efficient role of iscoms as antigen-presenting moieties in relation to their specific in vivo localization patterns and partial macrophage dependency.

Effect of macrophage depletion by liposomes containing dichloromethylene-diphosphonate on endotoxin-induced uveitis

Footpad injection of lipopolysaccharide (LPS) from Salmonella typhimurium in Lewis rats induces an acute anterior and posterior endotoxin-induced uveitis (EIU). To investigate the role of macrophages in the pathogenesis of EIU, we eliminated macrophages by means of liposomes containing dichloromethylene-diphosphonate (Cl2MDP), a drug which depletes macrophages but not other immunocompetent cells. Intravenous injection of CL2MDP-liposomes clearly inhibited clinical and histological manifestations of uveitis in the anterior segment of the eye (iris/ciliary body) and reduced TNF level in aqueous humor. Specific immunostaining showed that CL2MDP-liposome injections decreased the number of ED2 + resident macrophages in the iris/ciliary body and the choroid. After LPS injection, CL2MDP-liposome treatment reduced the density of infiltrating ED1 + cells (mainly monocytes/macrophages) in the iris/ciliary body but not in the choroid; little or no effect was detected on the OX42 + cellular infiltration (mainly polymorphonuclear leukocytes). The inflammatory cellular infiltration of the retina was not modified by the treatment. These findings suggest that macrophages play a key role in the pathogenesis of ocular inflammation.

Heterogeneity of mouse spleen dendritic cells: in vivo phagocytic activity, expression of macrophage markers, and subpopulation turnover

In the normal mouse spleen, two distinct populations of dendritic cells (DC) are present that differ in microanatomical location. The major population of marginal DC is found in the "marginal zone bridging channels" and extends into the red pulp. The interdigitating cells (IDC) are localized in the T cell areas in the white pulp. The aim of the present study was to characterize these two splenic DC populations with regard to their phenotype, in vivo phagocytic function, and turnover. Both marginal DC and IDC are CD11c+ and CD13+, but only IDC are NLDC-145+ and CD8alpha+. Notably, both populations, when freshly isolated, express the macrophage markers F4/80, BM8, and Mac-1. To study the phagocytic capacity of these cells, we employed the macrophage "suicide" technique by injecting liposomes loaded with clodronate i.v. Marginal DC, but not IDC, were eliminated by this treatment. Phagocytosis of DiI-labeled liposomes by DC confirmed this finding. The two DC populations differed significantly with regard to their turnover rates, as studied in a transgenic mouse model of conditional depletion of DC populations with high turnover. In these mice, marginal DC were completely eliminated, but the IDC population remained virtually intact. From these data we conclude that the marginal DC population has a high turnover, in contrast to the IDC population. Taken together, the present results indicate that marginal DC and IDC represent two essentially distinct populations of DC in the mouse spleen. They differ not only in location, but also in phenotype, phagocytic ability, and turnover.

Interferon-gamma reduces Ia+ dendritic cell traffic to the lung

MHC class II+ lung dendritic cells (DC) increase in number following treatment of animals with interferon-gamma (IFN-gamma) [Kradin et al. (1991) Am. J. Resp. Mol. Biol. 4, 210; Gong et al. (1992)J. Exp. Med. 175, 797]. To test whether this is due to increased sequestration and/or trafficking of DC to the lung, bone marrow DC from BALB/c mice were obtained by culturing bone marrow with granulocyte-macrophage colony-stimulating factor (GM-CSF). Recipient BALB/c mice were injected intraperitoneally (i.p.) for 4 days with one of the following: IFN-gamma, dexamethasone (Dex), or phosphate-buffered saline (PBS). Twenty-four hours after the last dose, they were injected intravenously (i.v.) with carboxyfluorescein (F1) -labeled DC (1 x 10(6)/mouse) and killed 4 h later. DC, double immunostained for Ia and F1, were quantified by morphometry in frozen sections of lung. The number of injected dual-labeled DC/cm2 was reduced by 90% in IFN-gamma-treated mice. By contrast, there was no significant difference between Dex- and PBS-treated animals in the number of double-labeled DC retained in pulmonary capillaries. Biodistribution and imaging studies were conducted on IFN-gamma- and PBS-treated mice using 111In-labeled DC. Reduced radioactivity in the lung was accounted for by an equivalent increase in the liver of IFN-gamma-treated mice; imaging studies confirmed these observations. Removal of >80% of alveolar macrophages (AM) by pretreatment with intratracheally administered chlodronate-loaded liposomes did not change the biodistribution of DC in IFN-gamma- and PBS-injected mice. Serum levels of tumor necrosis factor-alpha (TNF-alpha and nitrite/nitrate in IFN-gamma-treated mice were similar to those of controls. Immunostaining for inducible nitric oxide synthase (iNOS), however, revealed a 1.5-and 6-fold increase in the number of positively stained cells in the lung and liver, respectively, of IFN-gamma-treated mice; the number of iNOS-expressing cells was markedly reduced in Dex-treated animals relative to controls. To test whether the systemic treatment with IFN-gamma stimulated the cytotoxic activity of Kupffer cells, mice were injected with chlodronate liposomes 5 days before death. After treating the mice in the ensuing 4 days with IFN-gamma or PBS, biodistribution and imaging studies with 111In-labeled DC were conducted on the 5th day. After administration of chlodronate liposomes, there was a significant increase in the radioactivity detected in the lungs of IFN-gamma-injected mice but not in those of PBS- injected controls, a finding confirmed by imaging studies. We conclude that IFN-gamma treatment augmented Kupffer cell cytotoxic activity, which, in turn, effectively reduced the number of injected DC in circulation, with the result that fewer of these cells were retained in the lung vasculature. We further conclude that IFN-gamma increases the number of Ia+ lung DC by up-regulating Ia expression of resident Ia- DC precursors and not by promoting the migration of circulating DC to the lung.

The role of macrophages in the pathogenesis of HSV-1 induced chorioretinitis in BALB/c mice

PURPOSE

To examine the effects of modification of immune effector cells, including macrophages, in the pathogenesis of herpes simplex virus retinitis in BALB/c mice.

METHODS

Two intravitreal injections (2 microliters each) of anti-CD11b monoclonal antibody (mAb) [13 micrograms/microliters] were administered to the contralateral eyes of 10 BALB/c mice on days 6 and 8 after HSV inoculation into the right anterior chamber (AC) with HSV-1. A control group consisted of mice injected with anti-HLA-DR mAb in the same fashion. Specific macrophage depletion was performed in an additional group of 12 BALB/c mice by intravenous (i.v.) injection of dichloromethylene diphosphonate (Cl2MDP)-liposomes 7 days before AC HSV-1 inoculation into the eye. Control group consisted of mice receiving i.v. PBS-liposomes. Mice were clinically observed for 14 days postinfection, and the incidence of chorioretinal disease was confirmed by histopathologic studies.

RESULTS

Intravitreal injections of anti-CD11b mAb produced a dramatic suppression of the contralateral retinal necrosis (2 of 10 mice) compared to 9 of 10 controls receiving an irrelevant antibody therapy (P < 0.05). Mice treated with i.v. Cl2MDP-liposomes also showed a significant inhibition of the development of contralateral chorioretinitis, with only 3 of 12 mice developing retinal disease compared to 9 of 12 mice from the control group (P < 0.05). FACS analysis performed on peripheral blood and spleen cells showed a significant depletion of Mac-1+ cells of Cl2MDP-liposome-treated but not of PBS-liposome-treated mice (controls).

CONCLUSION

Intravitreal anti-CD11b mAb therapy, a broadly directed depletion strategy against many effector cells (macrophages, granulocytes, natural killer cells, and even cytotoxic T-cells) was most efficient in suppressing the HSV-1 induced contralateral disease. A more specific technique (i.v. Cl2MDP-liposome therapy) to deplete macrophages also produced a significant inhibition of HSV-1 induced contralateral chorioretinitis. These findings suggest that macrophages are important participants in the effector phase of the destructive inflammatory immune response induced by HSV-1 in the eye.

Macrophage elimination increases bacterial translocation and gut-origin septicemia but attenuates symptoms and mortality rate in a model of systemic inflammation

OBJECTIVE

The central question tested in this study was whether dichloromethylene-diphosphonate (CL2MDP) liposome-mediated elimination of hepatic and splenic macrophages would influence zymosan-induced bacterial translocation and the zymosan-induced generalized inflammatory response.

SUMMARY BACKGROUND DATA

Both an uncontrolled activation of macrophages and the loss of intestinal barrier function have been implicated in the development of adult respiratory distress syndrome and multiple organ failure.

METHODS

Macrophage elimination was accomplished by intravenous injection of 200 microL of CL2MDP-liposome suspension. Control mice received an intravenous injection of 200 microL of phosphate-buffered saline. Two days later, the animals were challenged intraperitoneally with zymosan suspended in paraffin to determine a dose-response curve (0.1, 0.5, or 1.0 mg/g body weight). Twenty-four hours after zymosan challenge, signs of systemic stress were determined, and bacterial translocation to the mesenteric lymph node, liver, spleen, and blood was measured. A separate mortality study was performed with a dose of 1.0 mg/g of zymosan suspension.

RESULTS

The incidence of the systemic spread of bacteria was significantly increased in the macrophage-depleted mice. Although systemic bacterial translocation was promoted by macrophage elimination, the systemic toxic response was significantly decreased in all macrophage-depleted groups (p < or = 0.01). The 12-day mortality rate was 0% in the macrophage-depleted groups and 27% in the control group (p = 0.05).

CONCLUSIONS

The lethal and toxic effects of zymosan appear to be related more to the excessive activation of macrophages than to the systemic spread of bacteria.

Dichloromethylene diphosphonate (Cl2MDP) reduces natural killer (NK) cell activity in mice

Daily administration of dichloromethylene diphosphonate (Cl2MDP) to (C57BL/6 X DBA/2) F1 hybrid mice, from two days of age (10 mg of P/kg body weight), resulted in a marked impairment of natural killer (NK) activity of spleen cells against YAC-1 lymphoma cells. The suppressive effect increased with the duration of the treatment. Cessation of the treatment led to a rapid recovery (in 2 weeks) of NK activity while the osteopetrotic bone lesions persisted. Thus, the loss of natural killing cannot be explained by the simple reduction of bone marrow volume secondary to Cl2MDP-induced osteopetrosis. However, as NK cells are considered to be dependent on the bone marrow because they cannot be sustained by extramedullary production, a direct effect of Cl2MDP on the generation of NK cell precursors by the bone marrow was not excluded. Cl2MDP was not directly toxic to the fully differentiated splenic NK cells, since the addition of Cl2MDP to the in vitro assay (10(-5)-10 micrograms/ml) did not reduce cytotoxicity. These studies suggest that impairment of NK activity during Cl2MDP treatment may have clinical toxicologic implications since NK cells have been suggested to play an important role in natural host defenses against infection and neoplasia.

The effect of diphosphonates on heterotopic ossification in regenerating Achilles tendon of the mouse

Midpoint tenotomy of the mouse Achilles tendon is followed by regeneration with heterotopic ossification at the junction of tendon stump and the regenerated segment. This heterotopic bone formation occurs through a process of endochondral ossification and the cartilage cells appear to arise by a process of fibroblast transformation. Five weeks after tenotomy 60 per cent. of specimens show cartilage and bone formation whilst the remaining 40 per cent. show chondrification only. After 10 weeks all specimens showed bone formation with trabecular bone and haemopoietic marrow. The treatment of tenotomised animals with either disodium ethane-1, 1-diphosphonate (EHDP) or disodium dichloromethylene diphosphonate (Cl2MDP) has no effect on the process of heterotopic ossification which can be detected at the radiological or light microscopical level.

Long-term controlled trial with diphosphonate in patients with osteolytic bone metastases

Thirty-four normocalcaemic women with multiple osteolytic bone metastases from breast cancer were randomly allocated to treatment with disodium dichloromethylene diphosphonate (Cl2MDP) 1600 mg/day orally (17) or placebo (17) for 3-9 months. Fasting urinary hydroxyproline/creatinine and calcium/creatinine ratios declined in the Cl2MDP group but not in the placebo group. Four patients in the placebo group died from hypercalcaemia. New bone metastases were more common in patients on placebo and these patients also required more analgesic drugs than those on Cl2MDP. Cl2MDP seemed to reduce bone pain and bone resorption and prevent the development of hypercalcaemia caused by osteolytic metastases. The formation of new bone metastases and the growth of old ones seemed to be retarded by Cl2MDP.

Effect of dichloromethylene diphosphonate (Cl2MDP) on immune function in breast cancer patients with bone metastases

Immune function was studied in normocalcemic breast cancer patients with bone metastases treated with either dichloromethylene diphosphonate (Cl2MDP) or placebo. The results showed no significant difference between the two patient groups. This suggests that Cl2MDP does not markedly impair the host's defense mechanisms, and in this respect can be safely used in the treatment of patients with resorptive bone disease.

Effects of disodium dichloromethylene diphosphonate on bone loss in paraplegic patients

21 paraplegic patients with recent traumatic spinal cord injury were orally administered 400 (n = 7) or 1,600 (n = 7) mg/d of disodium dichloromethylene diphosphonate (Cl2MDP) and compared with a placebo group (n = 7) to test the preventive effects of the drug on acute bone loss and osteoclastic resorption. Cl2MDP therapy was initiated at a mean of 17.6 d after the onset of paraplegia. The study lasted at least 6 mo, consisting of a 3.5-mo treatment period, and a variable follow-up period. The effects of Cl2MDP were assessed by blood and urine biochemistry, bone histomorphometry on transilial samples, photon absorptiometry of the tibia and fibula, and radiomorphometry of the femur. The elevation in serum and urinary calcium and in urine hydroxyproline observed in the placebo group did not appear under treatment. With both doses of Cl2MDP there was no further decrease in the bone mineral content. In the treated groups, a smaller percentage increase in osteoclastic population was also noted when compared with the placebo group, but this difference was not significant. There was no mineralization defect induced by Cl2MDP, as shown by tetracycline double labeling. It thus appears that at doses ranging between 400 and 1,600 mg, given as early as possible, Cl2MDP can prevent or reduce the development of the acute bone loss of paraplegic patients, without adverse side effects, though it does not prevent the development of heterotopic ossification.

Diphosphonates: history and mechanisms of action

The history of diphosphonates began with studies of inorganic pyrophosphate. This compound was found to occur in many biological fluids and inhibited the precipitation of calcium phosphates. It also slowed the transformation of amorphous calcium phosphate to its crystalline form, and inhibited crystal aggregation and dissolution. These observations suggested that it might be a compound of physiological or pathophysiological significance, perhaps in hypophosphatasia and in renal lithiasis. Diphosphonates are compounds where the P-O-P bond of pyrophosphate is replaced by a P-C-P bond. Many diphosphonates have been synthesized and tested and some relationship of their structure to the spectrum of biological effects has been observed. These analogues have similar properties to pyrophosphate, but unlike pyrophosphate they are resistant to enzymic degradation. Their experimental properties have led to their clinical development as bone scanning agents and in the treatment of disorders of ectopic mineralization and increased bone resorption.