Neurotrophin System as a Complex Set of Potential Biomarkers in Psychiatric Disorders and Therapy—Overview of Recent Advances

The neurotrophin system has numerous regulatory roles in the central nervous system, including the growth, differentiation, and survival of neurons, the control of neurogenesis, synaptic plasticity, and the mediation of neurotransmitter balance, also with proven anti-inflammatory, anti-apoptotic, and antioxidative actions. These functions are seriously affected by numerous pathophysiological processes accompanied by mental illness. The variety of therapeutic protocols (pharmacotherapy, transcranial stimulation, psychotherapy, lifestyle changes, programmed physical activity, dietary interventions), individually or in combination, has been employed in the treatment of psychiatric disorders. To evaluate the effectiveness of therapeutic strategies, specific elements of the neurotrophin system have been quantified to assess their potential as biomarkers. However, data obtained in clinical trials for different psychiatric disorders still do not confirm the reliability of neurotrophin system elements as biomarkers. For this purpose, we aimed this narrative review to explore clinical studies published in the last decade that examined neurotrophin system elements in patients with various psychiatric disorders, with a focus on their association with disease severity, clinical state, and treatment response, which represents a promising avenue for improving our understanding of the underlying mechanisms and for identifying potential clinically relevant biomarkers, as well as sharpening therapeutic protocol outcome analyses.