BDNF and obesity due to melanocortin 4 receptor deficiency: Therefore, plasma or serum BDNF serves as an endocrine molecule and is proposed as a biomarker for various diseases, including hepatic encephalopathy (96), depression (61, 97), Alzheimer's disease (98), mood disorders (99), schizophrenia (100), neuropsychiatric disorders (101), obesity (102), psoriasis (103), cardiometabolic problems (104), and glaucoma (105), among others.