Mouse popliteal lymph node assay for assessment of allergic and autoimmunity-inducing potentials of low-molecular-weight drugs

Complement activation as a bioequivalence issue relevant to the development of generic liposomes and other nanoparticulate drugs

Liposomes are known to activate the complement (C) system, which can lead in vivo to a hypersensitivity syndrome called C activation-related pseudoallergy (CARPA). CARPA has been getting increasing attention as a safety risk of i.v. therapy with liposomes, whose testing is now recommended in bioequivalence evaluations of generic liposomal drug candidates. This review highlights the adverse consequences of C activation, the unique symptoms of CARPA triggered by essentially all i.v. administered liposomal drugs, and the various features of vesicles influencing this adverse immune effect. For the case of Doxil, we also address the mechanism of C activation and the opsonization vs. long circulation (stealth) paradox. In reviewing the methods of assessing C activation and CARPA, we delineate the most sensitive porcine model and an algorithm for stepwise evaluation of the CARPA risk of i.v. liposomes, which are proposed for standardization for preclinical toxicology evaluation of liposomal and other nanoparticulate drug candidates.

Lessons learned from the porcine CARPA model: constant and variable responses to different nanomedicines and administration protocols

Pigs provide a sensitive and quantitative animal model of complement (C) activation-related pseudoallergy (CARPA) caused by liposomes and a wide range of nanoparticulate drugs or drug nanocarriers (nanomedicines). The tetrad of symptoms (hemodynamic, hematological, laboratory and skin changes) that arise within minutes after i.v. injection of reactogenic nanomedicines (RNMs) are highly reproducible among different pigs but the presence, direction and relative severity of symptoms are very different with different RNMs and their administration schedule. Bolus administration of RNMs usually trigger pulmonary hypertension with or without various degrees of systemic hyper- or hypotension, tachy-or bradycardia, arrhythmia, blood cell and inflammatory mediator changes and skin rash. These reactions can be rapid or protracted, and fully tachyphylactic, semi-tachyphylactic or non-tachyphylactic. Slow infusion usually diminishes the reactions and/or entail delayed, protracted and less severe hemodynamic and other changes. The goal of this review is to present some technical details of the porcine CARPA model, point out its constant and variable parameters, show examples of different reactions, highlight the unique features and capabilities of the model and evaluate its utility in preclinical safety assessment. The information obtained in this model enables the understanding of the complex pathomechanism of CARPA involving simultaneous anaphylatoxin and inflammatory mediator actions at multiple sites in different organs.

Characterising vancomycin's immunotoxic profile using Swiss and CFW mice as an experimental model

Immunotoxicology can lead to determining the adverse effects of different compounds on the immune system. Sometimes, many drugs (especially antibiotics) induce immune alterations, mainly auto-immunity. This study was aimed at determining vancomycin's immunotoxic effect by comparing the original molecule to two of the most used copies. Thirty-two mice from two murine strains (Swiss and CFW) were treated with three antibiotic formulations for studying its effect on splenic lymphoid and peripheral blood cell populations by using haemograms, flow cytometry and blastogenesis assays. The results indicated that vancomycin produces neutropenia and lymphocytosis in peripheral populations and that it induces a selective immunomodulatory effect on splenocyte sub-populations, depending on formulation and the strain so treated.

Popliteal lymph node assay: facts and perspectives

The popliteal lymph node assay (PLNA) derives from the hypothesis that some supposedly immune-mediated adverse effects induced by certain pharmaceuticals involve a mechanism resembling a graft-versus-host reaction. The injection of many but not all of these compounds into the footpad of mice or rats produces an increase in the weight and/or cellularity of the popliteal lymph node in the treated limb (direct PLNA). Some of the compounds known to cause these adverse effects in humans, however, failed to induce a positive PLNA response, leading to refinements of the technique to include pretreatment with enzyme inducers, depletion of CD4(+) T cells or additional endpoints such as histological examination, lymphocyte subset analysis and cytokine fingerprinting. Alternative approaches have been used to improve further the predictability of the assay. In the secondary PLNA, the test compound is injected twice in order to illicit a greater secondary response, thus suggesting a memory-specific T cell response. In the adoptive PLNA, popliteal lymph node cells from treated mice are injected into the footpad of naive mice; a marked response to a subsequent footpad challenge demonstrates the involvement of T cells. Finally, the reporter antigens TNP-Ficoll and TNP-ovalbumin are used to differentiate compounds that induce responses involving neo-antigen help or co-stimulatory signals (modified PLNA). The PLNA is increasingly considered as a tool for detection of the potential to induce both sensitization and autoimmune reactions. A major current limitation is validation. A small inter-laboratory validation study of the direct PLNA found consistent results. No such study has been performed using an alternative protocol. Other issues include selection of the optimal protocol for an improved prediction of sensitization vs autoimmunity, and the elimination of false-positive responses due to primary irritation. Finally, a better understanding of underlying mechanisms is essential to determine the most relevant endpoints. The confusion resulting from use of the PLNA to predict autoimmune-like reactions as well as sensitization should be clarified. Interestingly, most drugs that were positive in the direct PLNA are also known to cause drug hypersensitivity syndrome in treated patients. This observation is expected to open new avenues of research.

Diclofenac activates T cells in the direct popliteal lymph node assay and selectively induces IgG(1) and IgE against co-injected TNP-OVA

Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently associated with immune-mediated hypersensitivity reactions. The NSAID diclofenac is associated with several distinct allergic and autoimmune-like reactions including anaphylaxis, idiosyncratic hepatotoxicity and autoimmune hemolytic anemia. The aim of this study was to examine the immunostimulating potential of diclofenac in the direct popliteal lymph node assay (PLNA) and reporter antigen PLNA. In BALB/c mice, diclofenac caused dose-dependent increases in PLN weight and PLN cellularity in the direct PLNA; 0.25 mg was non-immunostimulating whereas 0.50-1.00 mg caused a significant PLN reaction. In the direct PLNA, diclofenac also increased the percent of T cells in the PLN with activated phenotypes (CD44(high)CD62L(low) and CD44(high)CD62L(high)). Finally, the magnitude of the diclofenac-induced direct PLN reaction was significantly reduced when the assay was conducted in T-cell-deficient mice. When co-injected with the reporter antigen TNP-Ficoll (trinitrophenyl Ficoll), 0.50 mg diclofenac caused significant increases in PLN weight, PLN cellularity, and induced IgM and IgG(1) anti-TNP antibody forming cells (AFCs) in the PLN. In a final set of studies, a TNP-OVA PLNA was conducted using diclofenac, phenobarbital (negative control) and streptozotocin (positive control). As expected, phenobarbital (1.00 mg) failed to cause an increase in PLN cellularity or induce AFCs in the PLN. Streptozotocin (1.00 mg) caused significant increases in PLN cellularity, IgM AFCs, and selectively induced IgG(2a) and IgG(2b) AFCs against TNP-OVA. Likewise, diclofenac caused dose-dependent increases (0.25-1.00 mg) in PLN cellularity and IgM AFCs. However, in contrast to streptozotocin, diclofenac caused a selective dose-dependent increase in both IgG(1) and IgE AFCs. Finally, an increase in the intracellular level of IL-4, but not INFgamma, was detected in CD4(+) PLN cells following the injection of diclofenac mixed with TNP-OVA. Collectively, these data suggest that diclofenac: (i) induces a T-cell-dependent direct PLN reaction that; (ii) provides non-cognate help for IgG AFC production when co-injected with TNP-Ficoll, possibly through the formation of neo-antigens; and (iii) possesses intrinsic adjuvant activity that selectively induces IL-4 mediated production of IgG(1) and IgE against co-injected TNP-OVA.

Investigating the TNP-OVA and direct popliteal lymph node assays for the detection of immunostimulation by drugs associated with anaphylaxis in humans

Using current animal models, it is not possible to identify low-molecular-weight compounds (LMWCs) that are likely to be associated with anaphylaxis. It is generally accepted that the ultimate effector mechanism involves drug-induced IgE antibody. The objective of the present study was to determine if diclofenac, zomepirac and glafenine, which are associated with anaphylaxis in humans, have immunostimulating potential in the murine TNP-OVA (trinitrophenyl-ovalbumin) popliteal lymph node assay (PLNA), and more specifically to determine if the immunostimulation caused by these LMWCs results in IgE antibody production. These LMWCs were chosen because both zomepirac and glafenine were removed from the market due to high association with anaphylaxis, and diclofenac, which remains on the market, is frequently associated with anaphylaxis. In addition to conducting a TNP-OVA PLNA, the immunostimulating potential of these compounds was examined in the direct PLNA. When co-administered with TNP-OVA, all three LMWCs caused dose-dependent (0.25, 0.50, 1.00 and 1.25 mg) increases in popliteal lymph node (PLN) weight and cellularity that were observed beginning with the 0.25-mg dose. In addition, beginning with the 0.25-mg dose, all three compounds caused dose-dependent increases in TNP-OVA specific IgM and IgG(1) antibody-forming cells (AFCs). Diclofenac induced an isotype switch and caused a dose-dependent increase in the number of IgE AFCs with no detectable IgG(2a) AFCs and minimal high-dose-only IgG(2b) AFCs. Zomepirac induced IgE, IgG(2a) and IgG(2b) AFCs following the injection of 0.50 mg only, and glafenine induced IgE, IgG(2a) and IgG(2b) AFCs following the injection of 0.50-1.00 mg. In the direct PLNA, diclofenac caused dose-dependent increases in PLN weight and cellularity that were observed beginning with dose of 0.50 mg, whereas zomepirac failed to increase any PLN parameter and glafenine only increased the PLN weight. These results suggest that diclofenac, zomepirac and glafenine are immunostimulating LMWCs in the TNP-OVA PLNA with the potential to induce IgE antibody against a co-administered hapten-conjugate. Furthermore, these results suggest that the TNP-OVA PLNA offered significant advantages over the direct PLNA. Although it is not realistic to suggest that a single assay, based on a low number of test compounds, can identify all LMWCs with the potential to cause anaphylaxis in humans, these observations do demonstrate the potential utility of the PLNAs in examining LMWC-induced immunomodulation and support further development and investigation of the assays.

The popliteal lymph node response to streptozotocin is under type 1, MHC class-I restricted, CD8(+) T-cell control

The popliteal lymph node (PLN) assay has been proposed to predict the 'autoimmunogenic' potential of xenobiotics. A better understanding of the processes involved in PLN responses is needed to establish the value of this assay for preclinical safety evaluation. In order to determine whether PLN responses involve CD4(+) or CD8(+) T-cells, the effects of streptozotocin (STZ), a prototypic immunotoxic compound, were analyzed after injection into the hind footpad of C57 BL/6 mice and major histocompatibility complex (MHC) class I or II deficient mice. The involvement of type 1 or type 2 cell control on the production of cytokine mRNAs was analyzed in lymph node cells by quantitative RT-PCR, together with the analysis of a wide range of cytokine mRNAs after STZ injection (IL-1alpha, IL-1beta, TNF-alpha, IFN-gamma, IL-2, IL-2 receptor, IL-4, IL-5, IL-6, IL-10 and IL-12). We have found that mice depleted in CD8(+) T-cells did not respond to STZ, whereas mice depleted in CD4(+) T-cells exhibited the expected positive PLN responses, with increased weight and cellularity indices. STZ induced a low production of interleukin (IL)-2 mRNAs, a mild increase in IL-1alpha and IL-6 mRNAs production, and a dramatic increase in IFN-gamma, IL-1beta, TNF-alpha, IL-12 and IL-2 receptor mRNAs, which correlated with positive PLN responses. No effects on IL-4, IL-5 and IL-10 mRNAs synthesis were noted. In CD8(+) T-cell deficient mice, there was no production of IFN-gamma or IL-6 mRNAs. These results suggest that PLN responses to STZ are under the control of type 1, MHC class-I-restricted, CD8(+) T-cells. This is in accordance to the known physiopathology of STZ-induced diabetes. Additional studies are necessary to establish the mechanism of CD8+ T-cell activation.