Effects of prostaglandins E1, E2, and F2 alpha on N-acetyl-beta-glucosaminidase activities of human synovial cells in culture

Effects of diclofenac, indomethacin, tolfenamic acid and hydrocortisone on prostanoid production in healthy and rheumatic synovial cells

Prostanoids, found in enhanced concentrations in rheumatic synovial fluid, are involved in the joint destruction seen in rheumatoid arthritis. Adherent cells isolated from rheumatic synovia produce higher amounts of prostanoids in a primary cell culture than cells originating from non-inflamed synovia. In the present study, it was found that exogenous arachidonic acid diminished the differences in prostanoid production between healthy and rheumatic synovial cells. Non-steroidal anti-inflammatory analgesics in clinically relevant concentrations had similar inhibitory effects on arachidonic acid-stimulated prostanoid synthesis in both healthy and rheumatic cells. In the presence of exogenous arachidonic acid, hydrocortisone (0.3-5.0 microM) did not affect prostanoid production in healthy cells. In rheumatic synovial cells hydrocortisone reduced PGE2 and PGF2 alpha synthesis to about half of the control value and the effect was not reversed by adding excess exogenous arachidonic acid. Altered regulation of phospholipase A2 activity in rheumatic synovia could explain the observed differences between healthy and rheumatic synovial cells.

Interleukin-1 beta and interleukin-1 alpha stimulate the N-acetyl-beta-glucosaminidase activity of human synovial cells

The properties of synovial cells are altered in vitro by monocyte-macrophage polypeptides (monokines), and these changes could explain some of the properties of the inflamed synovium in rheumatoid disease. Purified monokines have become available only recently for testing on the target synovial cells. We report here that purified human interleukin (IL)-1 beta and recombinant human IL-1 alpha stimulate the extracellular activity of the lysosomal hydrolase, N-acetyl-beta-glucosaminidase (NAG), of human synovial fibroblast-like cells. In contrast, another monokine, synovial activator, does not increase the NAG activity. Thus NAG is another cellular activity which can be modulated by interleukin-1.

Peripheral blood mononuclear cells stimulate prostacyclin levels of human synovial fibroblast-like cells

Fibroblast-like synovial cells, isolated from intact joints of non-arthritic human donors and from explants of rheumatoid and non-rheumatoid synovial tissue, released prostacyclin (PGI2) when incubated in conditioned medium from human peripheral blood mononuclear cells (MCCM). The effect of MCCM on the rate of PGI2 synthesis (measured by radioimmunoassay as the stable product, 6-keto-PGF1 alpha) was clearly established within 2 h and appeared to require RNA and protein synthesis as judged by inhibition with actinomycin D and cycloheximide, respectively. Low concentrations of dexamethasone suppressed the increase in PGI2 levels. Prostaglandin E2 (PGE2) levels were also raised by the MCCM and reduced by dexamethasone. All-trans retinoic acid did not stimulate the levels of either prostanoid. These findings offer an explanation for some of the inflammatory events occurring in rheumatoid lesions.

Peripheral blood mononuclear cells stimulate N-acetyl-beta-glucosaminidase levels of human synovial fibroblast-like cells

Fibroblast-like synovial cells isolated from intact joints of non-arthritic human donors released up to nine-times higher activity of the lysosomal acid hydrolase N-acetyl-beta-glucosaminidase (NAG) than controls when incubated in conditioned medium from homologous peripheral blood mononuclear cells (MCCM). This increase occurred without decrease in cell numbers or other evidence of cytotoxicity. An increase in cell-associated NAG activity was also suggested, but this was not statistically significant. Indomethacin present during production of MCCM or added with MCCM to fibroblast cultures did not alter the response to MCCM, indicating that the effect of MCCM was not due to the presence of products from the cyclo-oxygenase pathway. At a concentration known to block protein synthesis in most cells (10(-5) M), cycloheximide markedly suppressed the NAG releasing response to MCCM. The secretion of NAG due to MCCM was not affected by all-trans retinoic acid (10(-6) M) but was suppressed by the corticosteroid, dexamethasone.

Stimulation of glycosaminoglycan production and lysosomal activity of human synovial cells in culture by low environmental pH

Glycosaminoglycan production, acid hydrolase activity, proliferation, and morphology were examined in human synovial cells subjected to low environmental pH. The amount and the molecular size of newly synthesised glycosaminoglycan (GAG) were increased without significant change in the rate of cell proliferation. Lowered pH produced an increase in the size of cytoplasmic organelles. Some of these possessed ultrastructural features of lysosomes, but others were clearly nonlysosomal and were of uncertain identity. Intracellular activity of the lysosomal acid hydrolase N-acetyl-beta-glucosaminidase (NAG) was not altered by low pH, but a marked increase occurred in extracellular NAG activity, indicating enhanced release.