Role of glucocorticoid- and monoamine-metabolizing enzymes in stress-related psychopathological processes

Glucocorticoid signaling is fundamental in healthy stress coping and in the pathophysiology of stress-related diseases, such as post-traumatic stress disorder (PTSD). Glucocorticoids are metabolized by cytochrome P450 (CYP) as well as 11-beta-hydroxysteroid dehydrogenase type 1 (11 beta HSD1) and 2 (11 beta HSD2). Acute stress-induced increase in glucocorticoid concentrations stimulates the expression of several CYP sub-types. CYP is primarily responsible for glucocorticoid metabolism and its increased activity can result in decreased circulating glucocorticoids in response to repeated stress stimuli. In addition, repeated stress-induced glucocorticoid release can promote 11 beta HSD1 activation and 11 beta HSD2 inhibition, and the 11 beta HSD2 suppression can lead to apparent mineralocorticoid excess. The activation of CYP and 11 beta HSD1 and the suppression of 11 beta HSD2 may at least partly contribute to development of the blunted glucocorticoid response to stressors characteristic in high trait anxiety, PTSD, and other stress-related disorders. Glucocorticoids and glucocorticoid-metabolizing enzymes interact closely with other biomolecules such as inflammatory cytokines, monoamines, and some monoamine-metabolizing enzymes, namely the monoamine oxidase type A (MAO-A) and B (MAO-B). Glucocorticoids boost MAO activity and this decreases monoamine levels and induces oxidative tissue damage which then activates inflammatory cytokines. The inflammatory cytokines suppress CYP expression and activity. This dynamic cross-talk between glucocorticoids, monoamines, and their metabolizing enzymes could be a critical factor in the pathophysiology of stress-related disorders. Lay summary Glucocorticoids, which are produced and released under the control by brain regulatory centers, are fundamental in the stress response. This review emphasizes the importance of glucocorticoid metabolism and particularly the interaction between the brain and the liver as the major metabolic organ in the body. The activity of enzymes involved in glucocorticoid metabolism is proposed to play not only an important role in positive, healthy glucocorticoid effects, but also to contribute to the development and course of stress-related diseases.