Major depressive disorder (MDD) is associated with the disharmonic functioning of the serotonin system. The serotonin system is mainly modulated by the serotonin transporter (SERT) which regulates serotonin uptake and the metabolism of its precursor, tryptophan and following kynurenine pathway. Currently, there is a lack of research examining both markers concurrently in MDD. This study evaluated the alterations and inter-relationships of both markers in first-episode drug-naïve MDD patients. Thirty-three MDD patients and 33 age- and sex-matched healthy controls (HC) were recruited. The SERT availability were comparable between two groups in the midbrain, thalamus, caudate, and putamen. The kynurenine/tryptophan ratio which indicates tryptophan metabolism was lower in MDD than HC with no group difference in the tryptophan or kynurenine concentration. A negative correlation between the midbrain SERT availability and kynurenine concentration in HC was found. For the subgroup of HC with high kynurenine/tryptophan ratio, the SERT availability was positively associated with the kynurenine/tryptophan ratio and negatively correlated with tryptophan or kynurenine concentration. This study demonstrated the altered tryptophan metabolism and the relationship between tryptophan metabolism and the SERT availability in first-episode drug-naïve MDD patients, which gave a new insight towards the future investigation of the pathophysiology of MDD.

严重的抑郁症（MDD）与5-羟色胺系统的失谐功能有关。5-羟色胺系统主要由5-羟色胺转运蛋白（SERT）调节，该转运蛋白调节5-羟色胺的摄取及其前体，色氨酸和犬尿氨酸途径的代谢。当前，缺乏在MDD中同时检查这两种标记物的研究。这项研究评估了首例未使用过药物的MDD患者中两种标记物的变化和相互关系。招募了33位MDD患者和33位年龄和性别相匹配的健康对照（HC）。SERT的可用性在中脑，丘脑，尾状和壳状核的两组之间具有可比性。表示在MDD中色氨酸代谢的犬尿氨酸/色氨酸比率低于HC，色氨酸或犬尿氨酸浓度没有组差异。发现中脑SERT可用性与HC中犬尿氨酸浓度之间呈负相关。对于犬尿氨酸/色氨酸比例较高的HC亚组，SERT的可用性与犬尿氨酸/色氨酸比例呈正相关，而与色氨酸或犬尿氨酸浓度呈负相关。这项研究表明色氨酸代谢的改变以及色氨酸代谢与未使用过药物的MDD患者中SERT的可用性之间的关系，这为MDD病理生理学的未来研究提供了新的见识。发现中脑SERT可用性与HC中犬尿氨酸浓度之间呈负相关。对于犬尿氨酸/色氨酸比例较高的HC亚组，SERT的可用性与犬尿氨酸/色氨酸比例呈正相关，而与色氨酸或犬尿氨酸浓度呈负相关。这项研究表明色氨酸代谢的改变以及色氨酸代谢与未使用过药物的MDD患者中SERT的可用性之间的关系，这为MDD病理生理学的未来研究提供了新的见识。发现中脑SERT可用性与HC中犬尿氨酸浓度之间呈负相关。对于犬尿氨酸/色氨酸比例较高的HC亚组，SERT的可用性与犬尿氨酸/色氨酸比例呈正相关，而与色氨酸或犬尿氨酸浓度呈负相关。这项研究表明色氨酸代谢的改变以及色氨酸代谢与未使用过药物的MDD患者中SERT的可用性之间的关系，这为MDD病理生理学的未来研究提供了新的见识。