RED-BLOOD-CELL L-TRYPTOPHAN UPTAKE IN DEPRESSION .2. EFFECT OF AN ANTIDEPRESSANT TREATMENT

The evolution of the kinetic parameters, maximal velocity (V-max) and Michaelis constant (K-m), of L-tryptophan (L-TRP) uptake into red bloo d cells (RBC) was studied in 30 depressed patients in a drug-free stat e (D0) and after 1 week (D7) and 4 weeks (D28) of a treatment involvin g a variety of antidepressant drugs, including SSRIs and tricyclics. A t D0, 76% of patients exhibited abnormal values of V-max, which were e ither higher (36%) or lower (40%) than the control range (control V-ma x mean +/- 1 S.D.). High and low K-m values were observed in parallel with high and low V-max values. At D7, individual values of V-max vari ed drastically compared to their corresponding value at D0, whatever t he pretreatment value of the parameter. The magnitude of the V-max var iation during the first week of treatment was found to be significantl y larger in the treatment responders than in the non-responders. At D2 8, V-max values of all the responders to treatment were within the con trol range, whatever their pretreatment V-max value. On the contrary, non-responders had V-max values that were significantly lower than tho se of the controls. Changes in K-m followed changes in changes in V-ma x during antidepressant treatment. In conclusion, normalization of L-T RP transport kinetics was concomitant with a clear alleviation of depr essive symptoms, indicating that RBC L-TRP uptake is dependent on clin ical state. Moreover, early reactivity of the V-max as soon as the fir st week of treatment may be useful as a predictive index of clinical o utcome at D28. (C) 1997 Elsevier Science Ireland Ltd.