p38 inhibition and not MK2 inhibition enhances the secretion of chemokines from TNF-α activated rheumatoid arthritis fibroblast-like synoviocytes.

OBJECTIVES: For many years the p38 MAP kinase (MAPK) has been a major anti-inflammatory target for the development of an oral therapy for rheumatoid arthritis (RA). However, disappointing results from Phase II clinical studies suggest that adaptations may occur, which allow escape from blockade of the p38 pathway. In this study we investigated whether p38 inhibition mediated JNK activation represents such an escape mechanism. METHODS: Interaction between the JNK and p38 pathways was studied in TNF-α stimulated THP-1 monocytes, primary macrophages and fibroblast-like synoviocytes from OA and RA patients using pharmacological inhibitors and siRNAs. RESULTS: TNF-α induced phosphorylation of JNK and c-Jun was sustained by p38 inhibitors in monocytes, primary macrophages and FLS. Upregulation of Mip1α, Mip1ß and IL-8 mRNAs and protein were observed upon p38 inhibition. More importantly, inhibition of MK2, the substrate of p38 did not sustain JNK activation upon TNF-α activation and did not elevate Mip1α, Mip1ß and IL-8 chemokines as compared to TNF-α alone. In this study, TNF-α or IL-1ß induced JNK activation is sustained by p38 inhibition, resulting in enhanced chemokine secretion. CONCLUSIONS: Based on the suggested role of these chemokines in RA pathogenesis, the upregulation of these chemokines may provide an explanation for the lack of efficacy of p38 inhibitors in Phase II. The absence of any effect of MK2 inhibition in our models on this mechanism, while coming with similar efficacy on blocking p38, provides support for further investigations to reveal the potential of MK2 inhibition as a novel treatment of RA.

A potent and selective p38 inhibitor protects against bone damage in murine collagen-induced arthritis: a comparison with neutralization of mouse TNFalpha.

BACKGROUND AND PURPOSE: The p38 kinase regulates the release of proinflammatory cytokines including tumour-necrosis factor-alpha (TNFalpha) and is regarded as a potential therapeutic target in rheumatoid arthritis (RA). Using the novel p38 inhibitor Org 48762-0, we investigated the therapeutic potential of p38 inhibition and compared this to anti-mouse (m)TNFalpha antibody treatment in murine collagen-induced arthritis (CIA). EXPERIMENTAL APPROACH: Pharmacological profiles of Org 48762-0 were characterized in kinase assays, cellular assays and in lipopolysaccharide (LPS)-induced inflammation in mice. The effects of Org 48762-0 and of mTNFalpha-neutralization on established arthritis were examined in murine CIA. KEY RESULTS: Org 48762-0 potently inhibited p38alpha kinase with a high degree of kinase selectivity. In cellular assays, Org 48762-0 reduced LPS-induced TNFalpha release. Oral administration of Org 48762-0 in mice showed drug-like pharmacokinetic properties and inhibited LPS-induced cytokine production. These pharmacological characteristics of Org 48762-0 prompted a comparison of therapeutic efficacy with mTNFalpha-neutralization in CIA. Org 48762-0 and anti-mTNFalpha antibody treatment equally inhibited development of arthritis when evaluated macroscopically. Radiological analyses revealed protection against bone damage for both treatments, although statistical difference was reached with Org 48762-0 treatment only. Further, micro-computed tomographical and histopathological analyses confirmed the protective effects of Org 48762-0 on joint damage. CONCLUSIONS AND IMPLICATIONS: Pharmacological targeting of p38 kinase provided good protection against joint tissue damage in CIA. In our experiments, neutralization of mTNFalpha produced less prominent suppression of bone damage. Our data suggest a therapeutic potential for selective and potent p38 inhibitors in RA.

Origin of primordial germ cells, as characterized by the presence of nuage, in embryos of the teleost fish Barbus conchonius.

The presence, location and morphology of cells containing nuage, an ultrastructural characteristic of primordial germ cells (PGCs), is described from the moment of first morphological recognition of PGC (around 100% epiboly) in embryos of the teleost fish Barbus conchonius. Thus characterized cells were studied in relation to their cellular contacts with somatic germ layer cells, possibly involved in the determination of PGCs. The results show that from the very moment that cells, likely to be PGCs, can be light microscopically identified with morphological and positional criteria (from 10 h post fertilization (p.f.) onwards), they contain nuage near the nuclear envelope, which is a strong indication of their PGC-identity. During the studied period (9-12 h and 24 h p.f.) nuage-containing cells seem to translocate from the mesoderm towards the yolk syncytial layer (YSL). These PGCs usually appear not to be directly connected with the YSL but to remain separated from the YSL by one or more endodermal extensions, at least up to 12 h p.f. Also at 24 h p.f. somatic cells separate the PGCs from the YSL.