Tropisetron inhibits serotonin‐induced PGE2 release from macrophage‐like synovial cells in serum‐free tissue culture

Abstract

Tropisetron has shown potent analgesic and antiphlogistic effects in patients with rheumatic diseases such as osteoarthritis (1) or tendinopathies (2). These observations suggest that serotonin (5-HT) plays an important role in pain and inflammation. Objectives: The objective of our study was to determine if 5-HT stimulates the release of further inflammatory mediators such as prostaglandin E2 (PGE2) and if this effect can be blocked by tropisetron. To resolve these questions, we used a novel serum-free tissue culture technique for dissociated synovial tissue (3). This method permits in vitro experiments without perturbation by serum factors. Our cultures are characterized by 80% synoviocytes expressing the macrophage-specific marker CD68. Methods: Dissociated synovial tissue from osteoarthritis patients (n~5, mean age 67.2i6.2 years) was cultured for 11 days in Iscove’s Modified Dulbecco’s Eagle Medium supplemented with insulin. Cultures were then stimulated with 10, 10, and 10 M 5-HT and antagonized with 50 mg/mL tropisetron. Positive controls consisted of stimulation with 100 U/ml interleukin 1b (IL-1b). Negative controls included unstimulated cells or co-culture with tropisetron alone. After 48 h, PGE2 levels were determined using a conventional enzymeimmunoassay (EIA). PGE2 concentrations/mg protein were expressed as percent of controls and compared using the Mann-Whitney rank sum test. In addition, RT-PCR analyses for 5-HT1A, 5-HT1B, 5-HT2A, 5-HT3, and 5-HT4 receptor subtypes (4) were performed using synovial tissue (n~5). Results: The results (Figure 1) showed an increase of PGE2 in response to 10 25 M 5-HT by 421.8i84.9% (meanistandard error, p~v0.0001), whereas 10 and 10 M did not show significant effects (126.9i28.7%; p~0.37 and 96.8i28.7%; p~0.87, respectively). Stimulation by IL-1b caused an increase of 1347.5i481.4% (p~0.0094). Preincubation with tropisetron completely suppressed the serotonin-induced PGE2 release. RT-PCR showed an expression of the 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT3 but not 5-HT4 receptor subtype. Conclusions: The increase of PGE2 shows that serotonin is a potent proinflammatory mediator. The findings indicate the presence of 5-HT3 receptors and a tropisetron-induced suppression of this response. Additional analyses are necessary to further elucidate the underlying inflammatory mechanisms and inhibitory effect of tropisetron.