Suppression of human synovial cell proliferation by dihomo-gamma-linolenic acid.

Prostaglandin E1 (PGE1) and oils enriched in its precursor fatty acids suppress inflammation and joint tissue injury in several animal models. Since synovial cell proliferation is a hallmark of rheumatoid arthritis, we studied the effect of dihomo-gamma-linolenic acid (DGLA), an immediate precursor of PGE1, on the growth of human adherent synovial cells (ASC) in tissue culture. When stimulated by appropriate concentrations of recombinant interleukin-1 beta (rIL-1 beta), ASC proliferate and produce PGE. DGLA-enriched medium suppressed both baseline and rIL-1 beta-stimulated ASC growth fivefold, compared with medium supplemented with arachidonic acid. Indomethacin reduced the effect of the DGLA. Synovial cells incorporated the DGLA, and rIL-1 beta-stimulated cells that were incubated with DGLA exhibited a 14-fold increase in PGE1 (to 25.2 +/- 6.0 ng/ml, mean +/- SD) and a 70% decrease in PGE2 (to 25.2 +/- 4.2 ng/ml) compared with cells in control medium. At equivalent concentrations (5 x 10(-7) M), PGE1 increased the level of cellular cAMP to a greater extent than did PGE2 (16.8 +/- 2.0 pmoles versus 4.3 +/- 1.9 pmoles, mean +/- SEM). Exogenous PGE1 was also a more effective inhibitor of cell growth. Similarly, cAMP concentrations in cells exposed to DGLA for 6 hours were greater than concentrations in arachidonic acid-enriched cultures (17.8 +/- 3.3 pmoles versus 2.1 +/- 2.0 pmoles). These observations suggest that DGLA can restrain ASC growth, an effect which may be due to its capacity to increase PGE1 production and subsequent cellular cAMP concentration.

Prostaglandin E1 inhibits effector T cell induction and tissue damage in experimental murine interstitial nephritis.

Immunosuppressive effects of E-series prostaglandins have been demonstrated in many in vitro assays of immune responsiveness as well as in autoimmune diseases. To explore the mechanisms underlying prostaglandin E1 (PGE1)-associated immunosuppression in autoimmunity, we treated SJL mice immunized to produce immune-mediated interstitial nephritis with PGE1, PGF2 alpha, or vehicle alone. Mice receiving PGE1 treatment do not develop interstitial nephritis, nor do they display delayed-type hypersensitivity (DTH) to the immunizing renal tubular antigen preparation. The observed immunosuppression is critically dependent on PGE1 administration during the period of effector T cell induction. We therefore investigated the effect of PGE1 on the in vitro induction of DTH effector T cells reactive to renal tubular antigens (SRTA). PGE1 inhibits effector T cell induction in a dose-dependent, reversible manner, but has no inhibitory effect on fully differentiated DTH effector cells or SRTA-reactive cell lines. The PGE1 effect is indirect and mediated via nonspecific suppressor lymphokines. This suppression can be overcome by recombinant interleukin 1 (IL-1), which suggests a mechanism related to either diminished IL-1 secretion or target cell sensitivity to IL-1.

Separation and quantification of prostaglandins E1 and E2 as their panacyl derivatives using reverse phase high pressure liquid chromatography.

Separation and quantification of prostaglandin E1 (PGE1) and prostaglandin E2 (PGE2) were achieved using reverse phase high performance liquid chromatography (HPLC). Panacyl bromide (p-(9-anthroyloxy)phenacyl bromide) (PAB) derivatives of PGE2 and PGE1 were prepared. Reverse phase HPLC using a linear gradient of 56% to 80% acetonitrile in water containing 0.10% acetic acid gave baseline resolution of the two derivatives. A 3 um diameter particle, C18 column provided good resolution and reproducible recoveries. Human synovial tissue cells were incubated with the precursor fatty acids for PGE1 or PGE2 and stimulated with a crude Interleukin 1 (IL-1) preparation. Cells grown in the presence of dihomogammalinolenic acid (DGLA), the precursor for PGE1, made significantly more PGE1 than cells grown in control medium or in the presence of arachidonic acid, precursor for PGE2. PGE2 synthesis was reduced when DGLA was added to cells (resting or IL-1-stimulated).

Pinocytosis in human synovial cells in vitro. Evidence for enhanced activity in rheumatoid arthritis.

Human synovial tissue cells in monolayer can be shown to take up and digest a soluble protein, horseradish peroxidase (HRP). Uptake of HRP was linear with increasing concentrations of substrate and cell protein and with time for up to 4 h. Low temperature (4 degrees C), and sodium fluoride, an inhibitor of glycolysis were the most effective metabolic inhibitors of endocytosis. In addition, colchicine, an inhibitor of microtubule assembly, and yeast mannan, an inhibitor of mannose-specific receptors, reduced HRP uptake. Synovial cells from patients with rheumatoid arthritis (RSC) demonstrated a statistically significantly higher rate of endocytosis (247 +/- 107 ng HRP/100 micrograms cell protein per 2 h.) than cells from control, nonrheumatoid patients (NSC) (100 +/- 80 ng HRP/100 micrograms cell protein per 2 h). Thus, it is possible to discriminate RSC from NSC by their quantitatively different rates of endocytosis. Digestion of HRP by synovial cells is statistically significant by 6 h after uptake. A faster initial rate of digestion was seen in RSC. Over the first 6--8 h of incubation 42% of the endocytosed HRP was still cell-associated in RSC and 67% remained in NSC cultures. However, by 24 h 20--30% of endocytosed HRP was found in both types of cultures. These results indicate that endocytosed molecules may accumulate more rapidly in RSC and persist within their lysosomes for a longer time than in NSC. The quantitative determination of enhanced endocytosis by RSC compared with NSC suggests that this increased activity may have a role in the pathological function of synovial tissue in rheumatoid arthritis.