Comparative effectiveness of Denosumab vs alendronate among postmenopausal women with osteoporosis

Although clinical trials have shown that denosumab significantly increases bone mineral density at key skeletal sites more than oral bisphosphonates, evidence is lacking from head-to-head randomized trials evaluating fracture outcomes. This retrospective cohort study uses administrative claims data from Medicare fee-for service beneficiaries to evaluate the comparative effectiveness of denosumab versus alendronate in reducing fracture risk among women with postmenopausal osteoporosis (PMO) in the US. Women with PMO ≥ 66 years of age with no prior history of osteoporosis treatment, who initiated denosumab (n = 89 115) or alendronate (n = 389 536) from 2012 to 2018, were followed from treatment initiation until the first of a specific fracture outcome, treatment discontinuation or switch, end of study (December 31, 2019), or other censoring criteria. A doubly robust inverse-probability of treatment and censoring weighted function was used to estimate the risk ratio associated with the use of denosumab compared with alendronate for hip, nonvertebral (NV; includes hip, humerus, pelvis, radius/ulna, other femur), non-hip nonvertebral (NHNV), hospitalized vertebral (HV), and major osteoporotic (MOP; consisting of NV and HV) fractures. Overall, denosumab reduced the risk of MOP by 39%, hip by 36%, NV by 43%, NHNV by 50%, and HV fractures by 30% compared with alendronate. Denosumab reduced the risk of MOP fractures by 9% at year 1, 12% at year 2, 18% at year 3, and 31% at year 5. An increase in the magnitude of fracture risk reduction with increasing duration of exposure was also observed for other NV fracture outcomes. In this cohort of almost half-a-million treatment-naive women with PMO, we observed clinically significant reductions in the risk of MOP, hip, NV, NHNV, and HV fractures for patients on denosumab compared with alendronate. Patients who remained on denosumab for longer periods of time experienced greater reductions in fracture risk.

Cardiovascular Safety in Postmenopausal Women and Men With Osteoporosis Treated With Denosumab and Zoledronic Acid: A Post-Authorization Safety Study

Osteoporosis and cardiovascular disease are common in older adults. Treatment of osteoporosis reduces the burden of debilitating fractures; however, it is important to understand the benefit versus risk of treatment. This study evaluates the risk of stroke (ischemic or hemorrhagic) and myocardial infarction (MI) among postmenopausal women and men initiating osteoporosis treatment with denosumab (receptor activator of nuclear factor κB ligand [RANKL] inhibitor) or zoledronic acid (bisphosphonate) between October 2010 and June 2019. A retrospective cohort study employing the new user/active comparator design was conducted. Analyses were conducted separately in two national US commercial databases, MarketScan® and Optum® for reproducibility. Inverse probability of treatment and censoring weighting was employed to control for confounding and informative censoring. Cumulative risks at 6-month, 12-month, and 36-month time points were calculated and adjusted risk ratios and differences (with 95% confidence intervals [CIs]) were estimated. In MarketScan® and Optum® databases, 96,611 and 73,127 patients met all study eligibility criteria, respectively. At 36 months, the risk ratio estimates (zoledronic acid referent group) were 1.22 (95% CI, 0.77-1.66) and 0.97 (95% CI, 0.63-1.32) for MI and 1.00 (95% CI, 0.61-1.40) and 0.87 (95% CI, 0.56-1.17) for stroke in MarketScan and Optum, respectively. Most of the treatment associations across the other time periods and outcomes also had 95% CIs including the null value. In these large samples of real-world US patients, no increased risk in MI and stroke were identified for up to 36 months of treatment in denosumab users compared with zoledronic acid users. © 2023 Amgen. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Comparability of Osteoporosis Treatment Groups Among Female Medicare Beneficiaries in the United States

It is often difficult to obtain valid estimates of comparative treatment effectiveness and safety owing to differences across patient populations taking different medications in the real world. One approach for assessing comparability between treatment groups in effectiveness studies is to use negative control outcomes (NCOs). NCOs share similar sources of bias with the primary outcomes but have no plausible causal relationship to the treatment of interest. Observing differences in the risk of NCOs thus provides evidence for residual confounding between groups. This retrospective study assessed the comparability of postmenopausal women, treated with osteoporosis medications with various mechanisms of action such as denosumab (RANKL inhibitor), zoledronic acid (bisphosphonate derivative), or oral bisphosphonates including alendronate. Administrative claims data were extracted from the US Centers for Medicare and Medicaid Services' Chronic Condition Warehouse database (May 2010 - December 2016). Propensity scores were used to match denosumab patients 1:1 to comparators. Four non-fracture NCOs and three early fracture NCOs (before substantial biologic effects of treatment would be expected) were assessed over 1-year and 3-month follow-up periods, respectively. According to comparability decision rules established a priori, patients initiating denosumab were comparable to those initiating zoledronic acid or alendronate, irrespective of prior osteoporosis treatment experience. Among new users, new switchers, and in the historical fracture subgroup, no meaningful differences were observed in the cumulative incidence of the 7 NCOs comparing denosumab to zoledronic acid. This empirical examination can assist in the selection of appropriate comparator groups for future comparability research using real-world data. This article is protected by copyright. All rights reserved.

Denosumab in the Treatment of Osteoporosis: 10 Years Later: A Narrative Review

The fully human monoclonal antibody denosumab was approved for treatment of osteoporosis in 2010 on the basis of its potent antiresorptive activity, which produces clinically meaningful increases in bone mineral density (BMD) and reduces fracture risk at key skeletal sites. At that time, questions remained regarding the long-term safety and efficacy of this receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitor; and with clinical experience, new questions have arisen regarding its optimal use. Here, we examine these questions through the lens of data from the FREEDOM trial program and other studies to determine where denosumab fits in the osteoporosis treatment landscape. Clinical consensus and evidentiary support have grown for denosumab as a highly effective anti-osteoporosis therapy for patients at high risk of fracture. In the 10-year FREEDOM Extension study, denosumab treatment produced progressive incremental increases in BMD, sustained low rates of vertebral fracture, and further reduction in nonvertebral fracture risk without increased risk of infection, cancer, or immunogenicity. There was no evidence that suppression of bone turnover or mineralization was excessive, and rates of osteonecrosis of the jaw (ONJ) and atypical femoral fracture (AFF) were very low. It is now recognized, however, that transitioning to another anti-osteoporosis therapy after denosumab discontinuation is essential to mitigate a transient rebound of bone turnover causing rapid BMD loss and increased risk of multiple vertebral fractures (MVFs). Taken together, the available data show that denosumab has a favorable benefit/risk profile and is a versatile agent for preventing osteoporotic fractures in the short and long term.

Treatment patterns and long-term persistence with osteoporosis therapies in women with Medicare fee-for-service (FFS) coverage

Osteoporosis, a chronic disease, requires long-term therapy. In Medicare-insured women, denosumab persistence was higher than oral bisphosphonate persistence over up to 3 years of follow-up. Longer-term persistence was higher among women who persisted in the first year of therapy.

INTRODUCTION

Osteoporosis, a chronic, progressive disease, requires long-term therapy; this study assessed long-term persistence with anti-resorptive therapies in postmenopausal women.

METHODS

This retrospective cohort study used administrative claims for women with data in the 100% Medicare osteoporosis sample who initiated (index date) denosumab, oral/intravenous (IV) bisphosphonate, or raloxifene between 2011 and 2014 and who had ≥ 1 year (zoledronic acid: 14 months) of pre-initiation medical/pharmacy coverage (baseline). Persistence was assessed from index date through end of continuous coverage, post-index evidence of censoring events (e.g., incident cancer), death, or end of study (December 31, 2015).

RESULTS

The study included 318,419 oral bisphosphonate users (78% alendronate), 145,056 denosumab users, 48,066 IV bisphosphonate users, and 31,400 raloxifene users; mean age ranged from 75.5 years (raloxifene) to 78.5 years (denosumab). In women with at least 36 months of follow-up (denosumab N = 25,107; oral bisphosphonates N = 79,710), more denosumab than oral bisphosphonate initiators were persistent at 1 year (73% vs. 39%), 2 years (50% vs. 25%), and 3 years (38% vs. 17%). Persistence decreased over time for all treatment groups, with denosumab users having the highest persistence in every follow-up time interval at or after 18 months. Women using denosumab, oral bisphosphonates, or raloxifene who persisted in a given year were more likely to remain persistent through the subsequent year.

CONCLUSIONS

Denosumab users persisted longer with therapy than women using other anti-resorptive medications, including oral bisphosphonates. Early persistence may predict long-term persistence. Overall persistence with osteoporosis medications is suboptimal and may impact fracture risk. Efforts to improve first year persistence are needed.

The Effect of Discontinuing Denosumab in Patients With Rheumatoid Arthritis Treated With Glucocorticoids

Objective

To evaluate changes in bone turnover and bone mineral density (BMD) in patients with rheumatoid arthritis (RA) receiving glucocorticoids, after discontinuation of denosumab for 12 months.

Methods

We conducted a randomized, double‐blind, placebo‐controlled, phase II study of RA patients. Patients received placebo, denosumab 60 mg, or denosumab 180 mg every 6 months for 12 months and were followed up for an additional 12 months after discontinuation, during which no bone loss prevention therapy was instituted. Changes from baseline in serum C‐terminal telopeptide of type I collagen (CTX), serum procollagen type I N‐terminal propeptide (PINP), and lumbar spine and total hip BMD were evaluated.

Results

In this post hoc analysis of patients treated with glucocorticoids at study baseline (n = 82), levels of CTX and PINP decreased significantly from baseline in both denosumab groups. Following denosumab discontinuation, CTX returned to baseline and was not significantly different from the placebo group 6 and 12 months after discontinuation. Median percentage changes from baseline PINP in those treated with denosumab 60 mg were −0.16% and 15.3% at 6 and 12 months, respectively, after discontinuation (P = 0.062 and P = 0.017, versus placebo); corresponding changes with denosumab 180 mg were 9.0% and 75.8%, respectively (P = 0.018 and P = 0.002 versus placebo). Compared to placebo, lumbar spine and total hip BMD increased in patients receiving denosumab and returned to baseline 12 months after discontinuation. No osteoporotic fractures were reported during treatment or in the off‐treatment period.

Conclusion

In this analysis of short‐term denosumab use in RA patients receiving glucocorticoids, denosumab discontinuation resulted in a gradual increase in bone turnover, which was associated with a return to baseline lumbar spine and total hip BMD.

Bone Mineral Density After Transitioning From Denosumab to Alendronate

CONTEXT

There are few studies on patients transitioning from denosumab to bisphosphonates.

OBJECTIVE

To investigate patient characteristics and changes in bone mineral density (BMD) after transitioning from denosumab to alendronate.

DESIGN

Randomized, open-label, 2-year crossover Denosumab Adherence Preference Satisfaction (DAPS) study (NCT00518531).

SETTING

25 study centers in the US and Canada.

PATIENTS

Treatment-naïve postmenopausal women with BMD T-scores from -2.0 to -4.0.

INTERVENTIONS

This post hoc analysis evaluated women randomized to subcutaneous denosumab 60 mg every 6 months in year 1 followed by once-weekly oral alendronate 70 mg in year 2.

MAIN OUTCOME MEASURE

A 3% BMD threshold identified participants who lost, maintained, or gained BMD in year 2 on alendronate.

RESULTS

Of 126 participants randomized to denosumab, 115 (91%) transitioned to alendronate in year 2. BMD increased by 3% to 6% with denosumab in year 1 and by 0% to 1% with alendronate in year 2. After transitioning to alendronate, most participants maintained or increased BMD; 15.9%, 7.6%, and 21.7% lost BMD at the lumbar spine, total hip, and femoral neck, respectively. Few participants fell below their pretreatment baseline BMD value; this occurred most often in those who lost BMD in year 2. Women who lost BMD with alendronate in year 2 also showed a greater percent change in BMD with denosumab in year 1. The BMD change in year 2 was similar regardless of baseline characteristics or adherence to oral alendronate.

CONCLUSION

Alendronate can effectively maintain the BMD gains accrued after 1 year of denosumab in most patients, regardless of baseline characteristics.

Influence of Duraflo II heparin-treated extracorporeal circuits on the systemic inflammatory response in patients having coronary bypass

Cardiopulmonary bypass generates a systemic inflammatory response, including the activation of leukocytes, contributing to postoperative morbidity. To evaluate whether the use of heparin-treated extracorporeal circuits could reduce the inflammatory reaction in patients undergoing cardiopulmonary bypass, we conducted a prospective clinical study on 14 patients having coronary artery bypass in whom perfusion was done randomly with either Duraflo II heparin-treated circuits or with nontreated circuits. In both groups systemic heparinization was performed before cardiopulmonary bypass. The use of heparin-treated circuits resulted in a reduction of systemic inflammatory activation during cardiopulmonary bypass. This was reflected by lower plasma levels of soluble tumor necrosis factor receptors (p < 0.05) and of interleukin-6 and interleukin-8 (p < 0.05), manifest after release of the aortic crossclamp. Furthermore, 6 and 12 hours after aortic crossclamp release significantly lower levels of the soluble E-selectin (p < 0.05) were observed in the Duraflo II group. In patients in whom noncoated circuits were used, a significant decrease in circulating soluble intercellular adhesion molecule 1 (p < 0.05) was found early during bypass. All these observations suggest that the use of a heparin-treated extracorporeal circuit reduces the systemic inflammatory activation and may after the leukocyte-endothelium interaction.

Differential regulatory effects of adenosine on cytokine release by activated human monocytes

Adenosine is an endogenous nucleoside that can modulate the function of cells involved in the inflammatory response, such as polymorphonuclear leukocytes (PMN) and monocytes. Production and release of cytokines by activated mononuclear phagocytes is an important event in the pathogenesis of ischemia-reperfusion injury, a pathologic phenomenon that is associated with excessive ATP catabolism and subsequent local release of adenosine. The "retaliatory" metabolite adenosine has been shown to interfere with PMN function, thereby attenuating the deleterious consequences of ischemia and reperfusion. In this study, we demonstrate that adenosine inhibits the production of TNF-alpha, IL-6, and IL-8 by LPS-activated human monocytes with a differential potency. The A2 receptor-specific adenosine analogues 2-chloroadenosine and 5'-N-ethylcarboxamidoadenosine (NECA) were most effective in attenuating LPS-induced cytokine production, whereas the A1-selective adenosine analogue N6-cyclopentyladenosine (CPA) was less effective, indicating that inhibition of cytokine production by adenosine is primarily an A2 receptor-mediated event. The observed inhibitory effects were not restricted to endotoxin-induced cytokine production, because adenosine also inhibited TNF-alpha production by monocytes stimulated with the proinflammatory cytokine IL-1 beta. Again, 2-chloroadenosine and NECA reduced IL-beta-induced TNF-alpha production more potently than CPA. In contrast, adenosine enhanced production of IL-6 and IL-8 by monocytes stimulated with IL-1 beta. Furthermore, only 2-chloroadenosine, but not NECA, strongly inhibited cytokine-induced IL-6 and IL-8 production. These results suggest an additional A2 receptor-mediated mechanism of retaliatory action of adenosine under pathologic conditions where cytokine production by activated mononuclear phagocytes is involved, such as ischemia-reperfusion injury and septic shock.

Differential regulatory effects of adenosine on cytokine release by activated human monocytes

Adenosine is an endogenous nucleoside that can modulate the function of cells involved in the inflammatory response, such as polymorphonuclear leukocytes (PMN) and monocytes. Production and release of cytokines by activated mononuclear phagocytes is an important event in the pathogenesis of ischemia-reperfusion injury, a pathologic phenomenon that is associated with excessive ATP catabolism and subsequent local release of adenosine. The "retaliatory" metabolite adenosine has been shown to interfere with PMN function, thereby attenuating the deleterious consequences of ischemia and reperfusion. In this study, we demonstrate that adenosine inhibits the production of TNF-alpha, IL-6, and IL-8 by LPS-activated human monocytes with a differential potency. The A2 receptor-specific adenosine analogues 2-chloroadenosine and 5'-N-ethylcarboxamidoadenosine (NECA) were most effective in attenuating LPS-induced cytokine production, whereas the A1-selective adenosine analogue N6-cyclopentyladenosine (CPA) was less effective, indicating that inhibition of cytokine production by adenosine is primarily an A2 receptor-mediated event. The observed inhibitory effects were not restricted to endotoxin-induced cytokine production, because adenosine also inhibited TNF-alpha production by monocytes stimulated with the proinflammatory cytokine IL-1 beta. Again, 2-chloroadenosine and NECA reduced IL-beta-induced TNF-alpha production more potently than CPA. In contrast, adenosine enhanced production of IL-6 and IL-8 by monocytes stimulated with IL-1 beta. Furthermore, only 2-chloroadenosine, but not NECA, strongly inhibited cytokine-induced IL-6 and IL-8 production. These results suggest an additional A2 receptor-mediated mechanism of retaliatory action of adenosine under pathologic conditions where cytokine production by activated mononuclear phagocytes is involved, such as ischemia-reperfusion injury and septic shock.

Hereditary C6 deficiency in a strain of PVG/c rats

A chance observation has led to the discovery of a strain of PVG rats (PVG/c-) which are deficient in complement (C) component C6. Analysis of total haemolytic activity (CH50) of PVG/c- serum revealed an absent CH50 activity compared with serum of other rat strains and of a PVG/c rat (PVG/c+) that showed normal C activity. Thus, the PVG/c- rat was unable to activate the C5b-9 membrane attack complex. To gain insight into the complement abnormalities, analysis of individual C components was performed. Testing the PVG/c- serum in a C6 haemolytic assay and using deficient human sera showed a deficiency of C6 in the PVG/c- rat. Highly purified human C6 and human sera deficient in other components were able to reconstitute the CH50 activity of the PVG/c- rat. The possibility that an inactivator of C was present in PVG/c- serum was excluded. The deficiency was found to be inheritable and under the control of an autosomal recessive gene. Furthermore, tissue antigens and immunity of the PVG/c- rat were found to be identical to those determined in the PVG/c+ rat. With regard to their health status, the PVG/c- animals seem to have no disadvantages compared with PVG/c+ rats when held under the same conditions within the protected environment of animal facilities. Taken together, both rat strains provide an unique animal model for studying the biological role of C, particularly the C5b-9 membrane attack complex in experimental medicine.

Complement depletion abolishes IgA-mediated glomerular inflammation in rats

Recently, we developed an acute model for IgA-mediated glomerular inflammation in rats in which it was shown that polymeric (p) but not monomeric (m) IgA-containing immune complexes induce acute glomerular inflammation. The glomerular IgA-mediated inflammation is characterized by the activation of complement (C), the presence of intraglomerular macrophages and proteinuria. In the present study, we investigated the role of C in this IgA-mediated nephritis. Rats were pretreated either with cobra venom factor (CVF) to deplete them of circulating C3 or with phosphate-buffered saline followed by introduction of mesangial IgA deposits. Upon deposition of pIgA in the mesangial area, acute proteinuria was observed only in normocomplementemic rats and not in C-depleted animals. Immunofluorescent analysis revealed deposition of C3 and C9 in a pattern identical to that of IgA in the glomeruli of normal rats. Rats pretreated with CVF displayed clear mesangial deposition of IgA in the absence of C3 and C9. In none of the two groups were C4 deposits seen, indicating activation of C via the alternative pathway. In normocomplementemic animals, deposition of IgA together with C3 was associated with an influx of macrophages at day 2. C-depleted rats receiving pIgA also showed an influx of macrophages at 24 h following CVF administration and 1 and 2 days after IgA injection. However, no proteinuria was seen. To obtain insight into the mechanism of macrophage influx in the CVF-treated rats, we also analyzed the number of intraglomerular macrophages in rats receiving only CVF, without introduction of mesangial IgA deposits.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of liver endothelial and Kupffer cells in clearance of human C1q in rats

In the present study the contribution of rat liver endothelial cells (EC) and Kupffer cells (KC) in the clearance of human (hu) C1q in rats was investigated. In untreated rats and rats depleted from KC the clearance kinetics and the tissue distribution of hu C1q were measured. In untreated rats, the clearance of hu C1q occurred in a monophasic manner with a half-life of 66 +/- 26.7 min. The clearance of hu C1q in KC-depleted rats was delayed significantly (p < 0.001) and occurred with a half-life of 217 +/- 78.8 min. Fifteen min after injection, 11 +/- 3.5% of hu C1q was found in the liver of untreated rats and 8 +/- 1.4% was found in the liver of KC-depleted rats. The percentage non-trichloroacetic acid precipitable activity in the circulation, as a measure for degradation of C1q, reached a level of 11.6 +/- 5.6% at 240 min in untreated rats compared with 4.6 +/- 5.8% in KC-depleted rats. Double immunofluorescence staining 5 min after administration of C1q in untreated rats, revealed that C1q was associated with KC and EC in the liver. Fifteen minutes after i.v. injection of hu C1q, there was an uptake of C1q in the hepatocytes. In KC-depleted rats, 5 min after administration of hu C1q, C1q was bound to the EC. Fifteen minutes after injection, C1q was also found in the hepatocytes. Electron microscopical studies revealed that C1q binds to EC, and that it is internalized in the hepatocytes and KC. The clearance of hu C1q in untreated rats was inhibited by preadministration of high concentrations of bovine C1q. These data show that rats depleted from KC are able to bind, internalize and degrade C1q, and that EC may play a role in the handling of C1q and C1q bound to immune complexes.

An acute model for IgA-mediated glomerular inflammation in rats induced by monoclonal polymeric rat IgA antibodies

An acute model for IgA-mediated glomerular inflammation in rats was induced by the in situ deposition of IgA directly into the glomerular mesangium. F(ab')2 anti-Thy1 MoAb was used to anchor an antigen, DNP (2,4-dinitrophenol), in the glomeruli of rats. Subsequent infusion of rat polymeric (p-) or monomeric (m-) IgA MoAb with specificity for DNP resulted in mesangial deposition of IgA in both groups of rats. However, acute proteinuria was observed only in p-IgA-treated rats and not in PBS- or m-IgA-treated rats. Immunofluorescence analysis revealed deposition of C3 in an identical pattern to that of IgA in the glomeruli of p-IgA-treated rats. No mesangial deposits of C4 or C1q were seen in these animals. Rats receiving m-IgA or PBS displayed no detectable C3, C4 or C1q deposition. The amount of proteinuria in p-IgA-treated rats was related to the amount of deposited C3. The presence of intraglomerular monocytes was only observed 2 days after p-IgA injection. By light microscopy, aneurysm formation, mesangial hypercellularity and matrix expansion were seen only in p-IgA-treated rats. However, by 37 days post-injection complete resolution of the lesions was observed. No histological renal changes were observed in PBS- or m-IgA-treated rats. In conclusion, an acute form of IgA-mediated nephritis in rats was induced by p-IgA but not by m-IgA. This reproducible model provides a basis for further study into the mechanisms of IgA-mediated glomerular inflammation.

In vivo activation of complement by IgA in a rat model

In this study we investigated the capacity of rat IgA to activate complement (C) in vivo in a rat model. Rat monomeric (m-), dimeric (d-) and polymeric (p-) IgA MoAbs were injected intravenously and assessed for deposition of C3 and C4 on IgA. By ELISA it was shown that both d- and p-IgA bound C3 whereas no binding of C3 by m-IgA was observed. Polymeric IgA was more efficient in binding of C3 as compared with d-IgA. However, in haemolytic assays no consistent decrease of plasma complement levels was observed except for dimeric IgA which induced a marginal consumption of AP50. When rats were pre-treated with cobra venom factor (CVF) to deplete C3, no C3 deposition was found on m-, d- or p-IgA. Neither m- nor d- or p-IgA was able to bind C4 in vivo. In agreement with the results described above, large sized polymeric IgA was shown to be taken up by Kupffer cells (KC) together with C3. No C3 was detected when rats were depleted of C using CVF. Taken together, the experimental data suggest that d- and p-IgA are able to activate C via the alternative pathway in vivo.

Kupffer cell depletion in vivo results in preferential elimination of IgG aggregates and immune complexes via specific Fc receptors on rat liver endothelial cells

In the present study we have investigated the clearance kinetics and tissue distribution of monomeric (m) IgG and soluble aggregates of IgG (AIgG) and immune complexes (IC) in normal and Kupffer cell (KC) depleted rats. In normal rats, clearance of mIgG occurred in a biphasic manner with a first half-life (T1/2) (T1) of 36.3 +/- 6.3 min and a second T1/2 (T2) of 168.4 +/- 4.7 min. AIgG composed of 20-27 IgG molecules per aggregate were cleared significantly faster than mIgG with a T1 of 2.5 +/- 0.1 min and a T2 of 32.5 +/- 5.6 min. KC depletion did not have a significant effect on the clearance rate of mIgG (T1: 33.4 +/- 8.9 min; T2; 159.5 +/- 12.5 min), while clearance of AIgG was delayed significantly with T1 4.8 +/- 0.7 min and T2 41.2 +/- 3.2 min. Eight minutes after injection, 77% of AIgG was found in the liver in normal rats while 62% was found in the liver of KC-depleted rats. Double immunofluorescence studies indicated that AIgG in the liver was associated with KC and endothelial cells (EC) in normal rats. In KC-depleted rats, AIgG was strongly associated with EC. A similar staining pattern was observed when IgG-immune IC were administered. The clearance of AIgG in KC-depleted rats was inhibited fully by pre-administration of high concentrations of IgG but not by pretreatment with IgA. asialofetuin (ASFe) or ovalbumin (OVA). Aggregated F(ab')2IgG was cleared with a comparable rate to mIgG from the circulation, again suggesting Fc gamma receptor-mediated elimination of AIgG by EC. There was a reduced degradation of AIgG in rats depleted of KC as compared with normal rats. These data suggest binding and degradation of AIgG by EC in vivo.

Deposition of IgA is associated with macrophage influx in the kidney of rats

In the present study we treated rats with N-nitrosodimethylamine (DMN) or D-galactosamine (GALN) to achieve increased circulating IgA levels in rats. GALN-treated rats showed a six-fold increase in serum IgA levels after the first intraperitoneal (i.p.) injection, whereas a 10-fold increase after a second i.p. injection of GALN was seen. DMN-treated rats showed a three-fold increase in serum IgA levels. No differences were observed in IgG and IgM levels between treated and non-treated rats. Sequential renal biopsies analysed by immunofluroescence exhibited mesangial deposits of IgA with different intensities of C3 deposition. Rats treated with GALN showed more IgA deposition in the kidney than DMN-treated rats. The IgA deposition together with C3 was more prominent in rats treated with GALN than in rats treated with DMN. The deposition of C3 together with IgA was associated with an influx of monocytes as detected by ED-1, an antibody directed against a rat monocyte marker. These studies provide evidence that an increase in serum IgA levels is associated with deposition of IgA in the kidney and that IgA has an inflammatory potential.

Kupffer cell depletion in vivo results in clearance of large-sized IgA aggregates in rats by liver endothelial cells

We investigated the clearance kinetics and tissue distribution of different sized IgA in normal and macrophage-depleted rats. Rats were injected iv with liposomes containing dichloromethylene diphosphonate (DMDP). DMDP treatment resulted in complete depletion of liver macrophages 24-48 h after administration. Normal and macrophage depleted rats were injected intravenously with monomeric, dimeric, polymeric or aggregated polymeric IgA (AIgA) and assessed for blood clearance and tissue distribution. In normal rats, clearance of IgA was size dependent, i.e. a faster clearance with increasing size. No differences in clearance kinetics were observed of the different sized IgA between normal and DMDP-treated rats. TCA non-precipitable radioactivity, a measure for degradation of IgA, was found in the circulation of normal and DMDP-treated rats after AIgA administration. The liver was the main organ responsible for the clearance of IgA in normal and DMDP-treated rats. Immunofluorescence studies on liver biopsies indicated that AIgA was associated with Kupffer cells in normal rats. Electron microscopical studies revealed that the AIgA was internalized and located in vesicles in Kupffer cells. In DMDP-treated rats the AIgA was associated with endothelial cells and electron microscopy studies showed that this AIgA was taken up by endothelial cells. These data show that rat liver endothelial cells are able to bind, internalize and degrade AIgA in situations where Kupffer cells are absent, and that these cells may play an important role in the handling of AIgA and IgA-immune complexes.

Complement enhances the clearance of large-sized soluble IgA aggregates in rats

In the present study the involvement of the complement system (C) in the clearance of soluble IgA aggregates in the rat was studied. Monoclonal monomeric IgA (mIgA) antibody (which does not activate C) or aggregated polymeric IgA (aIgA; which activates C) were administered intravenously to phosphate-buffered saline-treated and complement-depleted [Cobra venom factor (CVF)-treated] rats and assessed for clearance from the circulation. In control rats, mIgA was cleared in a biphasic fashion with a first half-life (T1/2) of 29.5 +/- 14.2 min and a second T1/2 of 230 +/- 176 min. No differences were observed in clearance of mIgA in CVF-treated rats as compared to PBS-treated rats. In PBS-treated rats, aIgA with a size between 20 S and 150 S disappeared very rapidly from the circulation with a first T1/2 of 1.1 +/- 0.4 min and a second T1/2 of 23.2 +/- 11.3 min. In CVF-treated rats the clearance of aIgA was significantly delayed as compared to that in control rats, namely with a first T1/2 of 7.3 +/- 2.6 min and a second T1/2 of 64.2 +/- 19.4 min. Immunohistochemical studies of the liver (which is the main site of clearance of aIgA) revealed that Kupffer cells (KC) are mainly responsible for the uptake of aIgA. Furthermore, in PBS-treated rats aIgA deposition was accompanied by C3 deposition in the KC. In CVF-treated rats, the percentage of KC containing aIgA was significantly lower during the first 16 min after aIgA administration as compared to PBS treated rats. In addition no detectable C3 was found in KC of CVF-treated rats. These results indicate that KC play an important role in the clearance of large molecular weight IgA in rats and that C facilitates the clearance of these complexes from the circulation.

Immunoglobulin A: interaction with complement, phagocytic cells and endothelial cells

Deposits of IgA together with complement (C) in different organs support the hypothesis that IgA can trigger inflammatory mechanisms. Some inflammatory mechanisms may be caused by activation of C and phagocytic cells. Therefore, it is essential to understand the interaction of IgA with C and phagocytic cells. Studies will be described demonstrating that polymeric human serum IgA is able to activate the alternative pathway of C and that the activating principle is located in the intact F(ab')2 portion of the molecule. Activation of C is dependent on the molecular composition of IgA, as derived from results obtained with rat monoclonal IgA antibodies. Furthermore, it is demonstrated that polymeric IgA (pIgA) and dimeric IgA (dIgA) are potent activators of C in a homologous rat model, whereas monomeric IgA (mIgA) has a very poor C-activating potential. The interaction of IgA with phagocytic cells induces phagocytosis and release of H2O2 by granulocytes, which may contribute to tissue damage. Little is known about the clearance mechanism of IgA. It is shown in this report that Kupffer cells and C play an important role in the clearance of IgA immune complexes (IC). Clearance of large-sized IgA IC occurs via different receptors present on Kupffer cells. Finally, a new aspect will be described: the interaction of IgA with endothelial cells. Rat liver endothelial cells are able to eliminate IgA IC from the circulation via specific receptors when no Kupffer cells are present. These observations may contribute to our knowledge on diseases such as IgA nephropathy and Henoch-Schönlein purpura. The studies summarized and presented here illustrate the inflammatory potential of IgA.

Enrichment and selection of hybrid hybridomas by Percoll density gradient centrifugation and fluorescent-activated cell sorting

Hybrid hybridomas, producing bi-specific monoclonal antibodies that react with horseradish peroxidase and human IgA1 were isolated by sorting the double-fluorescent cells on single-cell basis after fusion of two hybridomas, previously labelled green or red by octadecylamine-FITC or -TRITC, respectively. The double-fluorescent fused cells were significantly different in AXL (size) and RAS (internal structure) distribution compared with the (non-fused) mono-fluorescent cells. The percentage of double-fluorescent cells and the viability of these cells could be increased by Percoll density gradient centrifugation. As a result, there was an 8-fold increase of total isolated hybrid hybridomas (up to 30% of all tested clones) compared to isolations without Percoll density gradient centrifugation. All the isolated hybrid hybridoma clones had similar amounts of DNA, equal to the sum of the DNA of both parental hybridomas.