Regulation of eicosanoid production in peripheral blood mononuclear cells from patients with systemic sclerosis

Eicosanoids are arachidonic acid-derived mediators that play a key role in the regulation of inflammatory response. 5-Lipoxygenase (5-LOX)-derived leukotrienes are considered proinflammatory while 15-lipoxygenase (15-LOX)-derived products such as 15-hydroxyeicosatetraenoic acid (15-HETE) and lipoxins inhibit proinflammatory mediators including leukotrienes, and actively participate in the resolution of inflammation. It has been demonstrated that a temporal switch of arachidonic acid metabolism from predominant 5-LOX-derived to 15-LOX-derived products is crucial for the resolution of inflammation. We have recently shown that there is an imbalance between proinflammatory leukotrienes and anti-inflammatory lipoxins in the lungs of patients with systemic sclerosis (SSc)-related interstitial lung disease, which may favour chronic inflammation and fibrosis [1, 2].

To further investigate the role of eicosanoids in the pathogenesis of SSc through evaluation of: (1) the basal profile of eicosanoid synthesis, and (2) the pattern of eicosanoid biosynthesis in response to proinflammatory stimuli by peripheral blood mononuclear cells (PBMC) from patients with SSc in comparison with healthy people.

Mononuclear cells were isolated from peripheral blood using density gradient centrifugation on Lymphoprep and cultured in fetal calf serum-supplemented RPMI medium at 37°C under 5% CO₂. Ionophore-stimulated production of 5-LOX-derived leukotriene E₄ (LTE4) and 15-LOX-derived 15-HETE was evaluated by means of enzyme immunoassay at predefined time points in basal conditions (without stimuli) as well as in response to TNFα. Ten patients with SSc (five diffuse and five limited cutaneous SSc) as well as five healthy controls were studied.

There were no significant differences in the basal production of LTE4 or 15-HETE between SSc patients and healthy controls. TNFα induced sequential changes in the production of eicosanoids, with an early (within 1 hour) increase in LTE4 followed by a delayed increase in 15-HETE in both SSc patients and healthy controls. PBMC from SSc patients responded to TNFα with significantly higher production of LTE4 in comparison with healthy controls (P < 0.05 at 1 hour), while there were no significant differences in TNFα-induced production of 15-HETE between SSc patients and controls.

These preliminary results of our study indicate that the TNFα-induced eicosanoid synthesis is altered in PBMC from patients with SSc. Increased production of proinflammatory leukotrienes may contribute to the pathogenesis of SSc.