L-carnitine and acetyl-L-carnitine: potential novel biomarkers for major depressive disorder

Abstract Background The lack of biomarkers to identify the target population has greatly limited the precise medical prospects for major depressive disorder (MDD). The endogenous L-carnitine (LC) and its derivative acetyl-L-carnitine (ALC) play different roles in depression, from metabolism and neurochemistry to epigenetic roles. The levels of ALC in people and rodents with depression are significantly reduced. It is necessary to determine whether serum LC and ALC might be used as novel noninvasive biomarkers for the diagnosis of MDD. Methods Ultra-performance liquid chromatography–electrospray–tandem mass spectrometry (UPLC–ESI-MS/MS) was used to determine the concentration of LC and ALC in the serum of healthy controls and patients with MDD; among the latter, in patients who were responsive (effective group) and those who were nonresponsive (ineffective group) after 2–4 weeks of treatment. The diagnostic value of serum LC and ALC for MDD was assessed. Results Serum LC and ALC concentrations were significantly lower in patients with MDD than in healthy controls. The Pearson correlation analysis showed that the HDRS-24 score was positively associated with serum ALC. The ROC analysis revealed an AUC of 0.6943 with 61.0% sensitivity and 74.0% specificity for LC and an AUC of 0.8496 with 67.0% sensitivity and 93.0% specificity for ALC, differentiating patients with MDD from healthy controls. Furthermore, the concentration of LC and ALC in patients with depression was significantly increased in the effective-treatment group and no significant change was observed in the ineffective-treatment group. Conclusion These results suggest that serum LC and ALC might be potential novel biomarkers for the diagnosis of MDD.