The toxicity of antiprion antibodies is mediated by the flexible tail of the prion protein.

Prion infections cause lethal neurodegeneration. This process requires the cellular prion protein (PrP(C); ref. 1), which contains a globular domain hinged to a long amino-proximal flexible tail. Here we describe rapid neurotoxicity in mice and cerebellar organotypic cultured slices exposed to ligands targeting the α1 and α3 helices of the PrP(C) globular domain. Ligands included seven distinct monoclonal antibodies, monovalent Fab1 fragments and recombinant single-chain variable fragment miniantibodies. Similar to prion infections, the toxicity of globular domain ligands required neuronal PrP(C), was exacerbated by PrP(C) overexpression, was associated with calpain activation and was antagonized by calpain inhibitors. Neurodegeneration was accompanied by a burst of reactive oxygen species, and was suppressed by antioxidants. Furthermore, genetic ablation of the superoxide-producing enzyme NOX2 (also known as CYBB) protected mice from globular domain ligand toxicity. We also found that neurotoxicity was prevented by deletions of the octapeptide repeats within the flexible tail. These deletions did not appreciably compromise globular domain antibody binding, suggesting that the flexible tail is required to transmit toxic signals that originate from the globular domain and trigger oxidative stress and calpain activation. Supporting this view, various octapeptide ligands were not only innocuous to both cerebellar organotypic cultured slices and mice, but also prevented the toxicity of globular domain ligands while not interfering with their binding. We conclude that PrP(C) consists of two functionally distinct modules, with the globular domain and the flexible tail exerting regulatory and executive functions, respectively. Octapeptide ligands also prolonged the life of mice expressing the toxic PrP(C) mutant, PrP(Δ94-134), indicating that the flexible tail mediates toxicity in two distinct PrP(C)-related conditions. Flexible tail-mediated toxicity may conceivably play a role in further prion pathologies, such as familial Creutzfeldt-Jakob disease in humans bearing supernumerary octapeptides.

A novel in vivo model using immunotoxin in the absence of p-glycoprotein to achieve ultra selective depletion of target cells: Applications in trogocytosis and beyond.

A commonly employed method to determine the function of a particular cell population and to assess its contribution to the overall system in vivo is to selectively deplete that population and observe the effects. Using monoclonal antibodies to deliver toxins to target cells can achieve this with a high degree of efficiency. Here, we describe an in vivo model combining the use of immunotoxins and multidrug resistant (MDR) gene deficient mice so that only MDR deficient cells expressing the target molecule would be depleted while target molecule expressing, but MDR sufficient, cells are spared. This allows targeted depletion at a higher degree of specificity than has been previously achieved. We have applied this technique to study trogocytosis, the intercellular transfer of cell surface molecules, but this principle could also be adapted using technology already available for use in other fields of study.

Treatment of hepatocellular carcinoma in mice with PE38KDEL type I mutant-loaded poly(lactic-co-glycolic acid) nanoparticles conjugated with humanized SM5-1 F(ab') fragments.

We reported previously the development of SMFv-PE38KDEL type I mutant (PE38KDEL-I; Mut-I), a recombinant immunotoxin in which a single-chain antibody derived from mouse SM5-1 monoclonal antibody is genetically fused to PE38KDEL-I. In comparison with the SMFv-PE38KDEL wild-type, Mut-I showed improved therapeutic efficacy and reduced toxicity. To overcome the problems associated with the immune response to the Pseudomonas exotoxin A (PE) component of Mut-I, we have constructed PE38KDEL-I-loaded poly(lactic-co-glycolic acid) nanoparticles conjugated with F(ab') fragments of a humanized SM5-1 monoclonal antibody (PE-NP-S). PE-NP-S specifically bound to SM5-1 binding protein-expressing hepatocellular carcinoma cell lines and was then internalized by these cells, resulting in significant cytotoxic effect. In SM5-1 binding protein-overexpressing tumor xenograft model, administration of PE-NP-S significantly inhibited tumor development and induced tumor regression. Moreover, PE-NP-S was shown to be much weaker in inducing vascular leakage syndrome in mice than Mut-I. The LD(50) of PE-NP-S was about 4-fold higher than that of Mut-I. Remarkably, PE-NP-S was of low immunogenicity in development of anti-PE neutralizing antibodies in vivo and was less susceptible to inactivation by anti-PE neutralizing antibodies compared with Mut-I. In conclusion, the resultant PE-NP-S possessed increased cancer therapeutic efficacy and had reduced nonspecific toxicity and immunogenicity, suggesting that it is a potential candidate in cancer therapy.

The change of the scFv into the Fab format improves the stability and in vivo toxin neutralization capacity of recombinant antibodies.

The antigen-binding fragment (Fab) has been considered a more functionally stable version of recombinant antibodies than single chain antibody fragments (scFvs), however this intuitive consideration has not been sufficiently proven in vivo. This communication shows that three out of four specific scFvs against a scorpion toxin, with different affinities and stabilities, become neutralizing in vivo when expressed as Fabs, despite the fact that they are not neutralizing in the scFv format. A scFv fragment previously obtained from a neutralizing mouse antibody (BCF2) was used to produce three derived scFvs by directed evolution. Only one of them was neutralizing, however when expressed as Fab, all of them became neutralizing fragments in vivo. The initial scFvBCF2 (earlier used for directed evolution) was not neutralizing in the scFv format. After expressing it as Fab did not become a neutralizing fragment, but did reduce the intoxication symptoms of experimental mice. The stability of the four Fabs derived from their respective scFvs was improved when tested in the presence of guanidinium chloride. The in vitro stability of the Fab format has been shown earlier, but the physiological consequences of this stability are shown in this communication. The present results indicate that improved functional stability conferred by the Fab format can replace additional maturation steps, when the affinity and stability are close to the minimum necessary to be neutralizing.

Evaluation of the safety, immunogenicity and pharmacokinetics of equine anti-SARS-CoV F(ab')(2) in macaque.

To warrant potential clinical testing, the equine anti-SARS-CoV F(ab')(2) requires evaluation in as many animal models as possible and a safety test in a primate model. In this study, we evaluated the pharmacokinetics, tolerance and immunity of this kind of antibody in macaques and rats. Results showed that the F(ab')(2) fragments had a normal metabolism in injected animals. The general physiological indexes did not differ between animals injected with anti-SARS-CoV F(ab')(2) or saline. However, a mild inflammatory response in local injection site and a moderate immune response against this antibody in the successively injected animals were observed, which however recovered 3 weeks after the last injection. The antibody titring from 1:100 to 400 against the equine anti-SARS-CoV F(ab')(2) in the inoculated hosts could be detected at week 2 during the successive injections of the equine F(ab')(2). The considerable safety of this antibody used in primates and the fact that the immune system of the host can be motivated by post-injection of the F(ab')(2) indicate that this type of anti-SARS-CoV antibody can be used for prevention and treatment of SASR, especially at the early stage of this virus infection. In addition, it can also provide the precious time for the combined use of other anti-SARS-CoV agents such as antiviral drug and vaccine.

[Anti-rabies immunoglobulin preparation based on F(ab')2 fragments].

Technology of manufacturing of new anti-rabies immunoglobulin preparation based on F(ab')2 fragments has been developed. This preparation is characterized by low reactogenicity, increased virus-neutralizing activity and stability.

Recombinant GPVI-Fc added to single or dual antiplatelet therapy in vitro prevents plaque-induced platelet thrombus formation.

The efficiency of current dual antiplatelet therapy might be further improved by its combination with a glycoprotein (GP) VI-targeting strategy without increasing bleeding. GPVI-Fc, a recombinant dimeric fusion protein binding to plaque collagen and concealing binding sites for platelet GPVI, acts as a lesion-focused antiplatelet drug, and does not increase bleeding in vivo. We investigated, whether GPVI-Fc added in vitro on top of acetylsalicylic acid (ASA), the P2Y12 antagonist ticagrelor, and the fibrinogen receptor antagonist abciximab alone or in combination would increase inhibition of platelet activation by atherosclerotic plaque. Under static conditions, GPVI-Fc inhibited plaque-induced platelet aggregation by 53 %, and increased platelet inhibition by ASA (51 %) and ticagrelor (64 %) to 66 % and 80 %, respectively. Under arterial flow, GPVI-Fc inhibited plaque-induced platelet aggregation by 57 %, and significantly increased platelet inhibition by ASA (28 %) and ticagrelor (47 %) to about 81 % each. The triple combination of GPVI-Fc, ASA and ticagrelor achieved almost complete inhibition of plaque-induced platelet aggregation (93 %). GPVI-Fc alone or in combination with ASA or ticagrelor did not increase closure time measured by the platelet function analyzer (PFA)-200. GPVI-Fc added on top of abciximab, a clinically used anti-fibrinogen receptor antibody which blocks platelet aggregation, strongly inhibited total (81 %) and stable (89 %) platelet adhesion. We conclude that GPVI-Fc added on top of single or dual antiplatelet therapy with ASA and/or a P2Y12 antagonist is likely to improve anti-atherothrombotic protection without increasing bleeding risk. In contrast, the strong inhibition of platelet adhesion by GPVI-Fc in combination with GPIIb/IIIa inhibitors could be harmful.

Protection of mammalian cells from severe acute respiratory syndrome coronavirus infection by equine neutralizing antibody.

The aetiological agent for severe acute respiratory syndrome (SARS) has been determined to be a new type of coronavirus (SARS-CoV) that infects a wide range of mammalian hosts. Up to now, there have been no specific drugs to protect against SARS-CoV infection, thus developing effective strategies against this newly emerged viral infection warrants urgent efforts. Adoptive immune therapy with pathogen-specific heterologous immunoglobulin has been successfully used to control the dissemination of many viral infections. To investigate whether a neutralizing antibody against SARS-CoV raised in an artiodactylous host can have a protective role on primate cells, we prepared serum IgGs and their pepsin-digested F(ab')2 fragments from horses inoculated with purified SARS-CoV (BJ-01 strain). The protective effect of the F(ab')2 fragments against SARS-CoV infection was determined in cultured Vero E6 cells by cytopathic effect (CPE), MTT and plaque-forming assays and in a Balb/c mouse model by CPE and quantitative RT-PCR. The results showed the neutralization titres of F(ab')2 from three horses all reached at least 1:1600, and 50 microg of the F(ab')2 fragments could completely neutralize 1x10(4) TCID50- SARS-CoV in vivo. Additionally, we observed that F(ab')2, against BJ-01 strain could also protect cells from infection by the variant GZ-01 strain in vitro and in vivo. Our work has provided experimental support for testing the protective equine immunoglobulin in future large primate or human trials.

Iodine-131-labeled MAb F(ab')2 fragments are more efficient and less toxic than intact anti-CEA antibodies in radioimmunotherapy of large human colon carcinoma grafted in nude mice.

During one week, beginning 18 days after transplantation, nude mice bearing human colon carcinoma ranging from 115 to 943 mm3 (mean 335 mm3) were treated by repeated intravenous injections of either iodine-131-(131I) labeled intact antibodies or 131I-labeled corresponding F(ab')2 fragments of a pool of four monoclonal antibodies (MAbs) directed against distinct epitopes of carcinoembryonic antigen (CEA). Complete tumor remission was observed in 8 of 10 mice after therapy with F(ab')2 and 6 of the animals survived 10 mo in good health. In contrast, after treatment with intact MAbs, tumors relapsed in 7 of 8 mice after remission periods of 1 to 3.5 mo despite the fact that body weight loss and depression of peripheral white blood cells, symptoms of radiation toxicity, and the calculated radiation doses for liver, spleen, bone, and blood were increased or equal in these animals as compared to mice treated with F(ab')2.

Anti-DNA autoantibodies reveal toxicity to tumor cell lines.

Cytotoxicity of anti-DNA autoantibodies from sera of SLE and CLL patients was assayed on permanent cell lines L929, HL-60, Raji, and K562. L929 cells appeared to be the most sensitive to antibody treatment. DNA-hydrolyzing properties of the same autoantibody preparations were analyzed in parallel. The data obtained outlined the correlation between cytotoxicity and DNA-hydrolyzing properties of these autoantibodies. It was shown that treatment of the cells with cytotoxic anti-DNA autoantibodies induced internucleosomal DNA fragmentation and Annexin V binding to the cell surface characteristic of apoptotic pathway of cell death. A time-dependent profile of antibody-mediated toxicity to L929 cells suggested recruitment of at least two distinct mechanisms of cell death. The first peak of cell death observed in 3 h of incubation was completely inhibited by preincubation of cells with caspase inhibitor YVAD-CHO, while the second increase in cell mortality (18-30 h) persisted. Possible mechanisms for anti-DNA autoantibody cytotoxicity are discussed.

Renal tolerance of digoxin-specific Fab fragments in the rat.

Renal markers were investigated over 96 h in male Sprague-Dawley rats after i.v. administration of 10.7 mg kg(-1) of digoxin-specific Fab fragments (DSFab). The dose was calculated by an allometric equation as equivalent to a high clinical dose. DSFab both alone and pre-incubated with digoxin were tested. None of the markers (creatinine clearance, fractional excretion of sodium, urinary activities of gamma-glutamyl transferase and alkaline phosphatase) were significantly altered in treated rats compared to control rats. Thus no renal toxicity due to DSFab alone or bound to digoxin was observed when administered at 10.7 mg kg(-1) in rats.

Effects of a superantigen-antibody recombinant fusion protein (r-C242 Fab-SEA) on toxicological responses in the anaesthetised rabbit.

The objective was to study toxin-induced effects on physiological parameters in the rabbit and whether these parameters show dose-response and co-variation after administration of a recombinant fusion protein between staphylococcal enterotoxin (SE) and the Fab fragment of an antibody. Rabbits are very sensitive to SE toxins and the cardiovascular and immune effects are similar to those observed in septic shock in man. The test compound, r-C242 Fab-SEA, was administered intravenously to anaesthetised New Zealand white rabbits at doses in the range of 0.00005-50 microg/kg. All rabbits were checked for titres of anti-SEA antibodies before entering the experiment, since they could neutralise the effect of the test compound. Heart rate, blood pressure and body temperature were continuously monitored before and during 6 h after dosing. Immediately before the start of administration and 3 and 6 h during the experiment, blood gases (pO(2) and pCO(2)), pH, haematology, clinical chemistry, cytokine response (TNF-alpha) and trace elements (Mn, Cu, Zn, Se, Ag, Cd, Hg and Pb) were measured. No mortality occurred, but at 50 microg/kg severe adverse clinical signs developed. The decrease in blood pressure was weakly dose-related. Heart rate, ECG, body temperature, pCO(2) and pH were not affected by the treatment. pO(2) tended to increase as a function of time, but not in relation to dose. WBC and PLT decreased dose dependently. TNF-alpha was not affected by the treatment. The major effects on clinical chemistry were a dose-dependent increase in AST and creatinine. Potassium and urea showed dose dependent increases, mainly at higher doses, though these changes were of less value for drug selection purposes. Trace element changes were observed, including an increase in Mn and a decrease of Zn at all doses. The Cu/Zn ratio decreased below normal at low doses, whereas at high doses in which adverse effects developed, it increased above normal. Post mortem examination revealed minimal to moderate dose-related granulocytic infiltrate in the lungs. The present study showed dose-response and co-variation between several changes in cardiovascular, haematology, clinical chemistry and trace element parameters during the initial phase of toxin-induced effects preceding a possible lethal endpoint and associated patho-physiological changes.

Digoxin-specific Fab fragments impair renal function in the rabbit.

A 2 mg kg-1 intravenous bolus dose of digoxin-specific Fab fragments produced a 28% reduction in creatinine clearance in rabbits after 24 h. Urine output was reduced, while plasma and urinary creatinine concentrations were unaffected and increased, respectively. By 5 days the creatinine clearance had returned to normal. The fractional excretion of Na+ was nearly halved, indicating that the tubular reabsorption of Na+ increased to compensate for the reduced glomerular filtration rate, suggesting that tubular (as opposed to glomerular) function was not impaired.

The use of surrogate antibodies to evaluate the developmental and reproductive toxicity potential of an anti-TNFalpha PEGylated Fab' monoclonal antibody.

Certolizumab pegol (CZP) is a PEGylated Fab' fragment of a humanized monoclonal immunoglobulin G (IgG)1 antibody that binds to human tumor necrosis factor alpha (TNFα) with high affinity. As for many monoclonal antibodies (mAbs), nonclinical safety assessment of CZP has been constrained because of its limited species cross-reactivity and recognition of only nonhuman primate and human TNFα, which presents particular challenges for assessing reproductive and developmental safety. To comprehensively assess the potential liability of TNFα suppression on reproductive and developmental processes, a PEGylated Fab' anti-rat TNFα antibody surrogate (cTN3 PF) has been developed and evaluated for reproductive toxicity. Conventional rat fertility and early embryonic development, embryo-fetal toxicity and pre- and postnatal development studies have been shown to be free of maternal, reproductive, or development toxicity effects, following sustained TNFα inhibition with cTN3 PF. Importantly, these studies have also shown that in marked contrast to a whole IgG anti-TNFα antibody, the PEGylated Fab' antibody cTN3 PF homologous to certolizumab pegol demonstrated negligible fetal exposure following maternal administration during the period of organogenesis. In addition to minimal placental transmission, transfer to milk was lower and fetal absorption negligible compared with the whole IgG antibody cTN3 γ1, resulting in little or no detectable antibody in the plasma of lactating pups.

Suppression of antibody-mediated arthritis in mice by Fab fragments of the mediating antibodies.

BACKGROUND AND PURPOSE: Fab fragments (Fabs) of antibodies maintain the ability to bind specific antigens, but lack the binding site for complement as well as the site for binding to receptors on effector cells, such as macrophages that play an important role in inflammation. In the present study, we investigated whether Fabs specific for ovalbumin (OVA) were specifically able to suppress anti-OVA antibody-mediated arthritis (AOA-MA) in mice. EXPERIMENTAL APPROACH: AOA-MA was induced by i.v. injection of purified anti-OVA antibodies into naïve mice followed by intra-articular (left ankle) challenge with the antigen. Anti-OVA Fabs prepared by digestion of anti-OVA antibodies with papain were injected i.v. immediately after administration of the intact antibodies. Normal Fabs were used as a control. Arthritis was assessed by thickness of the joints (caliper) and by histology of paw sections, stained with haematoxylin and eosin. KEY RESULTS: AOA-MA was markedly suppressed by anti-OVA Fabs, but not by control Fabs. Histologically, mice treated with control Fabs showed marked oedema of synovial tissues with a large number of inflammatory cells including neutrophils, whereas animals given anti-OVA Fabs had mild oedema of the synovium and sparse infiltration of such cells. The antigen-specific suppression of joint inflammation by anti-OVA Fabs was associated with reduced consumption of complement. In vitro studies showed that anti-OVA Fabs significantly blocked the binding of intact anti-OVA antibodies to OVA. CONCLUSIONS AND IMPLICATIONS: Antibody-mediated arthritis appears to be specifically down-regulated by Fabs that competitively inhibit the binding of antibodies to antigens.

Development of a universal anti-polyethylene glycol reporter gene for noninvasive imaging of PEGylated probes.

UNLABELLED: A reporter gene can provide important information regarding the specificity and efficacy of gene or cell therapies. Although reporter genes are increasingly used in experimental and clinical studies, a highly specific yet nonimmunogenic reporter that can track genes and cells in vivo by multiple imaging technologies still awaits development. In this study, we constructed a versatile and nonimmunogenic reporter gene to noninvasively image gene expression or cell delivery by optical imaging, MRI, and small-animal PET. METHODS: We cloned and expressed a membrane-anchored anti-polyethylene glycol (PEG) reporter that consists of the Fab fragment of a mouse anti-PEG monoclonal antibody, AGP3, fused to the C-like extracellular-transmembrane-cytosolic domains of the mouse B7-1 receptor. Binding of PEGylated probes (PEG-NIR797 for optical imaging, PEG-superparamagnetic iron oxide for MRI, and (124)I-PEG for small-animal PET) were examined in vitro and in vivo. In addition, we compared the specificity, immunogenicity, and probe toxicity of the anti-PEG reporter with the gold standard reporter gene, type 1 herpes simplex virus thymidine kinase (HSV-tk). Finally, we derived a humanized anti-PEG reporter and evaluated its imaging function in vivo with subcutaneous and metastatic tumor models in mice. RESULTS: The cells or tumors that stably expressed anti-PEG reporters selectively accumulated various PEGylated imaging probes and could be detected by optical imaging, MRI, and small-animal PET. Importantly, the anti-PEG reporter displayed an imaging specificity comparable to the HSV-tk reporter but did not provoke immune responses or cause toxicity to the host. Furthermore, the humanized anti-PEG reporter retained high imaging specificity in vivo. CONCLUSION: The highly specific and nonimmunogenic anti-PEG reporter may be paired with PEGylated probes to provide a valuable system to image gene expression or cell delivery in experimental and clinical studies.

Analysis of the underlying cellular mechanisms of anti-CD154-induced graft tolerance: the interplay of clonal anergy and immune regulation.

Although it has been shown that CD4(+)CD25(+) regulatory T cells (T(reg)) contribute to long-term graft acceptance, their impact on the effector compartment and the mechanism by which they exert suppression in vivo remain unresolved. Using a CD4(+) TCR transgenic model for graft tolerance, we have unveiled the independent contributions of anergy and active suppression to the fate of immune and tolerant alloreactive T cells in vivo. First, it is shown that anti-CD154-induced tolerance resulted in the abortive expansion of the alloreactive, effector T cell pool. Second, commensurate with reduced expansion, there was a loss of cytokine production, activation marker expression, and absence of memory T cell markers. All these parameters defined the tolerant alloreactive T cells and correlated with the inability to mediate graft rejection. Third, the tolerant alloreactive T cell phenotype that is induced by CD154 was reversed by the in vivo depletion of T(reg). Reversal of the tolerant phenotype was followed by rapid rejection of the allograft. Fourth, in addition to T(reg) depletion, costimulation of the tolerant alloreactive T cells or activation of the APC compartment also reverted alloreactive T cell tolerance and restored an activated phenotype. Finally, it is shown that the suppression is long-lived, and in the absence of anti-CD154 and donor-specific transfusion, these T(reg) can chronically suppress effector cell responses, allowing long-lived graft acceptance.

T cell retargeting with MHC class I-restricted antibodies: the CD28 costimulatory domain enhances antigen-specific cytotoxicity and cytokine production.

T cells require both primary and costimulatory signals for optimal activation. The primary Ag-specific signal is delivered by engagement of the TCR. The second Ag-independent costimulatory signal is mediated by engagement of the T cell surface costimulatory molecule CD28 with its target cell ligand B7. However, many tumor cells do not express these costimulatory molecules. We previously constructed phage display derived F(AB), G8, and Hyb3, Ab-based receptors with identical specificity but distinct affinities for HLA-A1/MAGE-A1, i.e., "TCR-like" specificity. These chimeric receptors comprised the FcepsilonRI-gamma signaling element. We analyzed whether linking the CD28 costimulation structure to it (gamma + CD28) could affect the levels of MHC-restricted cytolysis and/or cytokine production. Human scFv-G8(POS) T lymphocytes comprising the gamma + CD28 vs the gamma signaling element alone produced substantially more IL-2, TNF-alpha, and IFN-gamma in response to HLA-A1/MAGE-A1(POS) melanoma cells. Also a drastic increase in cytolytic capacity of scFv-G8(POS) T cells, equipped with gamma + CD28 vs the gamma-chain alone was observed.

Toxicity of high doses of polyclonal drug-specific antibody Fab fragments.

Drug-specific antibody Fab fragments have been used as a treatment for acute drug overdose. For some drugs, the required Fab dose may be very high (up to several g/kg) and may have adverse effects of its own. The current study evaluated the potential toxicity of an affinity purified sheep polyclonal Fab (TFab) directed at the two antidepressants desipramine (DMI) and nortriptyline. TFab 4 g/kg was administered to anesthetized rats i.v. over 10, 25 or 60 min, with or without a toxic dose of DMI. This high dose of TFab, which is in excess of that needed to reduce DMI toxicity, was used in order to exaggerate any adverse effects. In the absence of DMI, TFab produced minimal changes in the electrocardiographic QRS duration, systolic blood pressure and heart rate compared with control animals and was well tolerated. In the presence of DMI, groups receiving TFab as a 10 or 25 min infusion showed a therapeutic effect (lessening of DMI toxicity) over the first 60 min compared with the control group, but one of six animals in each of the TFab groups died prior to the end of the 180 min experiment. No control animals died, but progressive QRS prolongation and decreasing blood pressure toward the end of the experiment suggested that DMI toxicity was increasing over time. These data suggest that, when administered alone, very high doses of rapidly infused TFab are well tolerated. When administered with DMI, TFab is effective in initially reducing DMI toxicity. However, this dose of TFab may later aggravate DMI toxicity and/or the effects of prolonged anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of CAVH to remove digoxin-Fab complex in piglets.

Digoxin toxicity may be associated with renal failure and an inability to excrete the digoxin-Fab (antibody fragment) complex used in detoxification. We are unaware of any previous reports regarding the removal of digoxin-Fab fragment complex by continuous arteriovenous hemofiltration. Continuous arteriovenous hemofiltration allows ultrafiltration of molecules less than 50,000 daltons. Because the digoxin-Fab fragment complex has a molecular weight of 45 - 50,000 daltons, we evaluated the efficiency of continuous arteriovenous hemofiltration in removing the digoxin-Fab fragment complex. Three piglets were given 100 mcg/kg digoxin IM, in divided doses. Animals were anesthetized and continuous arteriovenous hemofiltration was begun using a Diafilter 10 cartridge. A mean ultrafiltration rate of 3.6 +/- 0.4 ml/min was obtained. The system equilibrated for 30 minutes and initial serum and ultrafiltrate digoxin levels were obtained. Mean serum values were total 6.20 +/- 1.74 ng/ml and free 3.72 +/- 0.88 ng/ml. Digibind 40 mg IV was given and then samples of serum and ultrafiltrate were obtained at 30, 60 and 90 minutes for digoxin levels. Mean values were as follows: 30 min serum total 54.23 +/- 26.13 ng/ml and free 0.08 +/- 0.08 ng/ml; 60 min serum total 61.24 +/- 27.31 ng/ml and free 0.07 +/- 0.04 ng/ml; and 90 min serum total 67.63 +/- 26.78 ng/ml and free 0.10 +/- 0.10 ng/ml. Ultrafiltrate levels throughout the experiment were negligible (less than or equal to 0.04 ng/ml). Continuous arteriovenous hemofiltration appears to be ineffective in removing the digoxin-Fab fragment complex.