[Tryptophan metabolism in patients with primary immune thrombocytopenia with high dose of dexamethasone].

Objective

To test whether the tryptophan metabolism was abnormal in newly diagnosed ITP patients as well as in these patients after treatment with dexamethasone.

Methods

Newly diagnosed patients with ITP between Jan 2014 and May 2015 were enrolled, including 14 females and 11 males, with a median age of 57 years and a median PLT count of 16 (0-32) ×10(9)/L. All patients were treated with oral dexamethasone. The expression levels of IDO mRNA and TTS mRNA in peripheral blood mononuclear cells (PBMC) were analyzed by real-time quantitative polymerase chain reaction. ELISA was used to test the concentrations of IDO and TTS in serum. The concentrations of plasma kynurenine and tryptophan were detected by high-pressure liquid chromatography. Samples from healthy individuals were tested as controls.

Results

①After dexamethasone treatment, 17 patients resulted in persistent remission, 2 cases were ineffective, and relapse occurred in 6 cases at a median follow-up of 11 (6-18) months. ②Before and after dexamethasone treatment, the relative expression of indoleamine2,3-dioxygenase (IDO) mRNA and tryptophanyl t-RNA synthetase (TTS) mRNA showed that there were significant decline in persistent remission group (2.54±0.86 vs 19.85±5.36, t=3.188, P=0.003; 0.68±0.19 vs 45.39±15.83, t=2.842, P=0.008) , compared with the normal control group, the difference was not statistically significant (t=2.313, P=0.027; t=1.127, P=0.268) . After treatment, the IDO concentration decreased [ (19.34±0.42) U/ml] and the TTS concentration was markedly increased [ (13.37±0.54) μg/L] in sustained remission group compared with that before treatment [ (21.91±0.37) U/ml] as well as that in normal controls. In particularly, abnormal tryptophan catabolism could be recovered in these 17 patients with persistent remission [Try: (19.85±5.36) μmol/L vs (19.65±4.55) μmol/L, t=1.027, P=0.311; Kyn: (0.56±0.26) μmol/L vs (0.58±0.23) μmol/L, t=2.075, P=0.448]. ③There was no obviously difference in the relative expression of IDO mRNA and TTS mRNA, the concentration of IDO and TTS and the abnormal tryptophan catabolism between before and after treatment of dexamethasone in patients without response and relapsed patients (all P>0.01) .

Conclusion

The tryptophan catabolism was abnormal in ITP patients, and it could be recovered in patients with persistent remission.