Oral administration of the selective GPR120/FFA4 agonist compound A is not effective in alleviating tissue inflammation in mouse models of prototypical autoimmune diseases.

ω3-polyunsaturated free fatty acids (ω3-PUFAs), particularly docosahexaenoic (DHA) and eicosapentaenoic acid (EPA), are thought to exert health promoting effects in metabolic and in inflammatory diseases. The molecular mechanisms of these beneficial effects are only partially understood. DHA and EPA activate Free Fatty Acid receptor 4 (GPR120/FFA4). Recently, the first orally available, synthetic ligand of FFA4, 3-[2-chloro-5-(trifluoromethoxy)phenyl]-3-azaspiro[5.5]undecane-9-acetic acid ("compound A"; cpd A) has been developed. Cpd A exhibits distinctly higher potency, efficiency, and selectivity at FFA4 than ω3-PUFAs and ameliorates insulin resistance and adipose tissue inflammation in the mouse. With GPR120/FFA4 activation believed to also attenuate tissue inflammation in autoimmune diseases, cpd A may also have a beneficial effect in these diseases. We have therefore addressed the therapeutic potential of cpd A in mouse models of three prototypical autoimmune diseases, specifically psoriasis, rheumatoid arthritis, and bullous pemphigoid. The effect of cpd A on the course of Aldara™-induced psoriasis-like dermatitis, K/BxN serum transfer arthritis, and antibody transfer pemphigoid disease-like dermatitis was scrutinized. Cpd A did not alter the course of Aldara-induced psoriasis-like dermatitis, K/BxN serum transfer arthritis, or antibody transfer pemphigoid disease-like dermatitis. Our results suggest that therapeutic regimens solely relying on FFA4 activation do not bear the potential to treat inflammatory diseases. With cpd A distinctly more potent in activating GPR120/FFA4 than ω3-PUFAs, this also suggests that GPR120/FFA4 activation by ω3-PUFAs does not significantly contribute to the health-promoting effects of ω3-PUFAs in autoimmune diseases.

In vivo enzymatic modulation of IgG antibodies prevents immune complex-dependent skin injury.

IgG antibodies are potent inducers of proinflammatory responses by cross-linking Fc receptors on innate immune effector cells resulting in tissue injury. The recently discovered enzymes endoglycosidase S (EndoS) and IgG-degrading enzyme (IdeS) of Streptococcus pyogenes are able to modulate the interaction between IgG antibodies and the Fc receptors, by hydrolysis of the glycan associated with the heavy chain of the IgG molecule (EndoS), or cleavage in the hinge region of the heavy IgG chain (IdeS). In this work, we investigated their ability to inhibit damage mediated by skin-bound antibodies in vivo in two different experimental models, the Arthus reaction, and epidermolysis bullosa acquisita, an autoimmune blistering skin disease associated with autoantibodies against type VII collagen. We demonstrate that both enzymes efficiently interfere with IgG-mediated proinflammatory processes, offering a great asset to specifically target pathological IgG antibodies in the skin and holding great promise for future applications in human therapy.

Blockade of the hedgehog pathway inhibits osteophyte formation in arthritis.

BACKGROUND: Osteophyte formation is a common phenomenon in arthritis. Bone formation by endochondral ossification is considered a key pathophysiological process in the formation of osteophytes. OBJECTIVE: To examine the hypothesis that inhibition of smoothened (Smo), a key component of the hedgehog pathway inhibits osteophyte formation as the hedgehog pathway mediates endochondral ossification. METHODS: Arthritis was induced in 8-week-old C57/BL6 mice by serum transfer (K/BxN model). Mice were then treated by daily administration of either vehicle or LDE223, a specific small molecule inhibitor for Smo, over 2 weeks starting at the onset of disease. Clinical course of arthritis, histological and molecular changes of bone in the affected joints as well as systemic bone changes were assessed. RESULTS: Serum transfer-induced arthritis led to severe osteophyte formation within 2 weeks of onset. Blockade of Smo inhibited hedgehog signalling in vivo and also significantly inhibited osteophyte formation, whereas the clinical and histopathological signs of arthritis were not affected. Also, systemic bone mass did not change. Smo inhibitor particularly blocked the formation of hypertrophic chondrocytes and collagen type X expression. CONCLUSIONS: The data indicate that blockade of hedgehog signalling by targeting Smo specifically inhibits osteophyte formation in arthritis without affecting inflammation and without eliciting bone destruction at the local and systemic level. Blockade of Smo may thus be considered as a strategy to specifically influence the periosteal bone response in arthritis associated with bone apposition.

Antibody isotype-specific engagement of Fcgamma receptors regulates B lymphocyte depletion during CD20 immunotherapy.

CD20 monoclonal antibody (mAb) immunotherapy is effective for lymphoma and autoimmune disease. In a mouse model of immunotherapy using mouse anti-mouse CD20 mAbs, the innate monocyte network depletes B cells through immunoglobulin (Ig)G Fc receptor (FcgammaR)-dependent pathways with a hierarchy of IgG2a/c>IgG1/IgG2b>IgG3. To understand the molecular basis for these CD20 mAb subclass differences, B cell depletion was assessed in mice deficient or blocked for stimulatory FcgammaRI, FcgammaRIII, FcgammaRIV, or FcR common gamma chain, or inhibitory FcgammaRIIB. IgG1 CD20 mAbs induced B cell depletion through preferential, if not exclusive, interactions with low-affinity FcgammaRIII. IgG2b CD20 mAbs interacted preferentially with intermediate affinity FcgammaRIV. The potency of IgG2a/c CD20 mAbs resulted from FcgammaRIV interactions, with potential contributions from high-affinity FcgammaRI. Regardless, FcgammaRIV could mediate IgG2a/b/c CD20 mAb-induced depletion in the absence of FcgammaRI and FcgammaRIII. In contrast, inhibitory FcgammaRIIB deficiency significantly increased CD20 mAb-induced B cell depletion by enhancing monocyte function. Although FcgammaR-dependent pathways regulated B cell depletion from lymphoid tissues, both FcgammaR-dependent and -independent pathways contributed to mature bone marrow and circulating B cell clearance by CD20 mAbs. Thus, isotype-specific mAb interactions with distinct FcgammaRs contribute significantly to the effectiveness of CD20 mAbs in vivo, which may have important clinical implications for CD20 and other mAb-based therapies.