Circulating biomarkers of upstream kynurenine pathway and brain-derived neurotropic factor in the diagnosis of type 2 and gestational diabetes mellitus with depression

The kynurenine pathway (KP) is the main catabolic pathway for the essential amino acid tryptophan (TRP). The imbalance between beneficial and harmful kynurenines was concerned with the pathogenesis and biological mechanisms of various disorders such as diabetes mellitus (DM), obesity, dyslipidemia, hypertension, depression, and schizophrenia. The present study aimed to determine the levels of biomarkers—TRP, indoleamine-2,3-dioxygenase (IDO), kynurenine (KYN) and brain-derived neurotrophic factor (BDNF) in type 2 diabetes mellitus (T2DM) and gestational diabetes mellitus (GDM) to find their association with relevant clinical parameters. Further, aimed to shed light on how coordination amongst the metabolites of KP and BDNF may influence the diagnosis of T2DM and GDM comorbid with depression. One hundred eighty participants were divided into six groups based on glycemic index and depression state. TRP, IDO, KYN and BDNF were determined using enzyme-linked immunosorbent assay (ELISA), and their association was examined. The biochemical parameters were analysed by fully automated equipment. The levels of TRP, IDO and KYN were significantly higher in diabetic patients when compared to non-diabetic, whereas the BDNF level was lower. Correlation analyses showed that TRP, IDO and KYN were positively associated, whereas BDNF was negatively associated with glycemic index (p < 0.01). Our study correlated the overall association between KYN metabolites and BDNF in the aetiology of T2DM and GDM with depression as a cofactor. According to our findings, TRP, IDO, KYN and BDNF either individually or in combination have the potential to be an effective diagnostic tool for both diabetes and depression.