Nitric oxide modifies glycolytic pathways in cultured human synoviocytes.

Nitric oxide (NO) is a free radical produced during inflammation following activation of an inducible NO synthase by pro-inflammatory cytokines such as IL-1beta. Since both NO and IL-1beta are involved in the physiopathology of inflammatory arthropathies, we investigated the effects of exogenous NO on glycolytic pathways in cultured human osteoarthritic synovial cells. NO generated from S-nitroso-N-acetyl penicillamine (SNAP) or sodium nitroprusside (SNP) inhibited glucose uptake (by 50% after 1 h of incubation) and lactate production by 16% (SNAP) and 8.5% (SNP) after 3 h. Both NO donors also reduced production of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an enzyme of the glycolytic pathway. This effect was reversed by haemoglobin, a NO scavenger with higher affinity for the radical. In contrast, the effect on glucose uptake appeared to be irreversible.

IL-1 modifies system A transport activity in human rheumatoid synovial cells.

Given the importance of interleukin-1 in both rheumatic diseases and the modulation of cell metabolic activities, we studied the action of this cytokine on the neutral amino acid transport A system on rheumatoid synovial cells. In these cells IL-1 (1 ng/ml) induced amino transport stimulation from 5 min to 5 h. This effect was obtained only after a starvation period. No concentration-related effect was found for IL-1-stimulated MeAIB uptake, and the IL-1-mediated MeAIB uptake stimulation is independent of protein synthesis. Neosynthesis or post-translational maturation of protein transport is a prerequisite for obtaining this effect. In conclusion, rheumatoid synovial cells exhibit a higher sensitivity for IL-1 than osteoarthritic ones, probably related to their intense metabolic activity.

System A neutral amino acid transporter regulation by interleukin-1beta in human osteoarthritic synovial cells: evidence for involvement of prostaglandin E(2) as a second messenger.

We studied the long-terms effects of interleukin-1beta (IL-1beta; 3 to 6 h) on alpha-(methylamino) isobutyric acid (MeAIB), a nonmetabolizable amino acid transported by system A. We found that IL-1beta induced a large decrease in MeAIB uptake by human osteoarthritic synovial cells and a concomitant increase in prostaglandin E(2) (PGE(2)) synthesis. Therefore, we investigated whether PGE(2) acts as a mediator for the long-term action of IL-1beta. We found that exogenous PGE(2) inhibited MeAIB uptake, and that AH6809, a PGE(2) receptor antagonist, inhibited IL-1beta-mediated MeAIB uptake. To identify the enzymes involved in the IL-1beta-mediated synthesis of PGE(2) that inhibits MeAIB uptake, we studied the expression of secreted (s) and cytosolic (c) phospholipase A(2) (PLA(2)). Because both were expressed, we selected a broad spectrum of inhibitors to determine which of the two PLA(2)s was involved. We used AACOCF3, a cPLA(2) inhibitor, and dithiothreitol (DTT) and bromophenacyl bromide (BPB), which are sPLA(2) inhibitors. Our results suggest that the PLA(2) involved in the IL-1beta-mediated synthesis of PGE(2) was sPLA(2). We also showed the expression of cyclooxygenase (COX)-2 and its partial involvement using a potent selective COX-2 inhibitor, L-745337. These findings provide insight into the mechanisms underlying the IL-1beta-mediated regulation of transport system A. The Il-1beta-induced inhibition of MeAIB uptake in human osteoarthritic synovial cells thus seems to be essentially mediated by PGE(2) production via the activation of sPLA(2) and the partial activation of COX-2.