Progressive and Concordant Expression of PKC-η and iNOS Phenotypes in Monocytes From Patients With Rheumatoid Arthritis: Association With Disease Severity

Protein kinase C and its inhibitors in the regulation of inflammation: inducible nitric oxide synthase as an example

Protein kinase C (PKC) is a family of ten isoenzymes that play a crucial role in cellular signal transduction. Studies with PKC knockout animals have revealed that many of the isoenzymes are involved in cell growth, proliferation and differentiation. Several PKC isoenzymes have also been shown to be important mediators in inflammation and immunity, particularly in lymphocyte responses. However, less is known about the role of PKC in the regulation of the expression of inflammatory genes. In inflammatory processes, nitric oxide is primarily produced by inducible nitric oxide synthase (iNOS) in inflammatory cells, such as macrophages. In innate immunity, nitric oxide functions as an effector molecule towards the infectious organisms. Increased levels of nitric oxide are also produced by inflammatory and tissue cells in inflammatory diseases, such as asthma and arthritis. In this MiniReview, the role of PKC isoenzymes in the pathogenesis and as a potential drug target in inflammation will be discussed presenting iNOS as an example of an inflammatory gene regulated by the pleiotropic PKC signalling pathway.

Inhibition of Inducible Nitric Oxide Synthase Attenuates Monosodium Urate-induced Inflammation in Mice

The present study elucidated the effect of the selective inducible nitric oxide synthase (iNOS) inhibitor N⁶-(1-iminoethyl)-L-lysine (L-NIL) on monosodium urate (MSU) crystal-induced inflammation and edema in mice feet. L-NIL (5 or 10 mg/kg/day) was administered intraperitoneally 4 h before injection of MSU (4 mg) into the soles of mice hindlimb feet. Twenty-four hours after MSU injection, foot thickness was increased by 160% and L-NIL pretreatment reduced food pad swelling in a dose dependent manner. Pretreatment of 10 mg/kg/day L-NIL significantly suppressed the foot pad swelling by MSU. Plasma level of nitric oxide (NO) metabolites and gene expression and protein level of iNOS in feet were increased by MSU, which was suppressed by L-NIL pretreatment. Similar pattern of change was observed in nitrotyrosine level. MSU increased the gene expression of tumor necrosis factor (TNF)-α and interleukin (IL)-1β and L-NIL pretreatment suppressed MSU-induced cytokines expression. The mRNA levels of superoxide dismutase and glutathione peroxidase1 were increased by MSU and L-NIL pretreatment normalized the gene expression. Phosphorylation of extracellular signal-regulated kinase 1/2 and p38 was increased by MSU, which was suppressed by L-NIL pretreatment. The mRNA levels of iNOS, TNF-α, and IL-1β were increased by MSU in human dermal fibroblasts, C2C12 myoblasts, and human fetal osteoblasts in vitro, which was attenuated by L-NIL in a dose dependent manner. This study shows that L-NIL inhibits MSU-induced inflammation and edema in mice feet suggesting that iNOS might be involved in MSU-induced inflammation.

Divergent effects of infliximab and anakinra therapies on macrophage phenotype from patients with refractory rheumatoid arthritis

Previously, we documented the co-expression of the inducible nitric oxide synthase (NOS2) and protein kinase C-eta (PKC-eta) in peripheral blood-derived macrophages (PBDM) from moderate to severe rheumatoid arthritis (RA) patients with elevated plasma nitric oxide levels but not from those with non-inflammatory osteoarthritis (OA) or normal plasma NO levels. The presence of PKC-eta was found to be required before macrophages could acquire the NOS2-positive phenotype and make copious levels of NO. In the current study, we report the divergent effects of two biological-based RA therapies which target TNFalpha function (infliximab) or IL1 response (anakinra) on the development of the NOS2-positive phenotype by PBDM in patients with refractory RA. Both infliximab and anakinra were effective in improving disease symptoms. However, treatment with anakinra, but not infliximab led to a complete suppression of NOS2 expression in PBDM and consequently, a more pronounced reduction in plasma NO levels. Data also revealed a requirement of both TNF-alpha and IL-1 in the development of the NOS2-positive macrophage phenotype. Finally, the data have shed light on the molecular mechanisms by which NO production may be regulated during disease progression to severe RA, and thus, offer a novel insight into the identification of future therapeutic targets for the treatment of inflammatory diseases.

Inducible nitric oxide synthase activity is increased in patients with rheumatoid arthritis and contributes to endothelial dysfunction

BACKGROUND

Recent in vitro studies suggest that inducible nitric oxide synthase (iNOS) activity mediates endothelial dysfunction. Rheumatoid arthritis (RA) is a chronic inflammatory condition and is associated with endothelial dysfunction and increased risk of cardiovascular disease. The aim of the study was to establish the contribution of iNOS to endothelial function.

METHODS

Forearm blood flow (FBF) was measured during intra-arterial infusions of acetylcholine (ACh), sodium nitroprusside (SNP), N(G)-monomethyl-l-arginine (l-NMMA) and aminoguanidine (AG) in 12 RA patients and 13 healthy control subjects. Levels of C-reactive protein (CRP) and myeloperoxidase (MPO) were assessed. FBF data are presented as mean percentage changes in the ratio (infused/control arm) of FBF + or - SEM.

RESULTS

FBF response to ACh was reduced in patients with RA compared to controls (179 + or - 29 v. 384 + or - 72%, respectively; P=0.01), but SNP response was not (P=0.5). FBF response to AG differed between patients and controls (-15 + or - 2% v. 13 + or - 4%, respectively; P<0.001), whereas the response to l-NMMA did not (P=0.4). In a multiple regression model log CRP, AG response and LDL were found to be independent predictors of endothelial function (R(2)=0.617, P<0.001).

CONCLUSION

RA patients have endothelial dysfunction and increased iNOS activity in comparison to controls. Furthermore, CRP and iNOS activity were independently associated with endothelial function. Our data demonstrates that inflammation is a key mediator in a process of endothelial dysfunction possibly via activation of iNOS and increased production of MPO.