Combined treatment with MAO-A inhibitor and MAO-B inhibitor increases extracellular noradrenaline levels more than MAO-A inhibitor alone through increases in beta-phenylethylamine

Perseveration in a spatial-discrimination serial reversal learning task is differentially affected by MAO-A and MAO-B inhibition and associated with reduced anxiety and peripheral serotonin levels

RATIONALE

Impairments in behavioral flexibility lie at the core of anxiety and obsessive-compulsive disorders. Few studies, however, have investigated the neural substrates of natural variation in behavioral flexibility and whether inflexible behavior is linked to anxiety and peripheral markers of stress and monoamine function.

OBJECTIVE

The objective of the study was to investigate peripheral and central markers associated with perseverative behavior on a spatial-discrimination serial reversal learning task.

METHODS

Rats were trained on a reversal learning task prior to blood sampling, anxiety assessment, and the behavioral evaluation of selective monoamine oxidase-A (MAO-A) and MAO-B inhibitors, which block the degradation of serotonin (5-HT), dopamine (DA), and noradrenaline (NA).

RESULTS

Perseveration correlated positively with 5-HT levels in blood plasma and inversely with trait anxiety, as measured on the elevated plus maze. No significant relationships were found between perseveration and the stress hormone corticosterone or the 5-HT precursor tryptophan. Reversal learning was significantly improved by systemic administration of the MAO-A inhibitor moclobemide but not by the MAO-B inhibitor lazabemide. Moclobemide also increased latencies to initiate a new trial following an incorrect response suggesting a possible role in modulating behavioral inhibition to negative feedback. MAO-A but not MAO-B inhibition resulted in pronounced increases in 5-HT and NA content in the orbitofrontal cortex and dorsal raphé nuclei and increased 5-HT and DA content in the basolateral amygdala and dorsomedial striatum.

CONCLUSIONS

These findings indicate that central and peripheral monoaminergic mechanisms underlie inter-individual variation in behavioral flexibility, which overlaps with trait anxiety and depends on functional MAO-A activity.

An adrenal mass and increased catecholamines: monoamine oxidase or pheochromocytoma effect?

Hormonal evaluation in patients with an adrenal incidentaloma can be difficult in patients with comorbidities or in patients using interfering drugs. We present a case of a 54-year-old man who was evaluated for an adrenal mass. The medical history reported treatment with a monoamine oxidase (MAO) inhibitor for recurrent psychoses. Hormonal screening showed elevated levels of normetanephrine and metanephrine in plasma and urine, suggesting a diagnosis of pheochromocytoma (PHEO), and an adrenalectomy was performed. Histologic examination showed that the tumor had an origin of the adrenal cortex. MAO inhibitors are also known to cause elevated levels of catecholamines. In this case, a PHEO seemed more likely the cause due to repeatedly elevated levels of metanephrines and normal levels of catecholamines. Since the tumor had an origin of the adrenal cortex, the use of MAO inhibitors was the most likely explanation for the elevated levels of metanephrines. This case illustrated the difficulties in diagnosing PHEO, especially in patients with comorbidities and interfering drugs.

Xanthoangelol and 4-Hydroxyderricin Are the Major Active Principles of the Inhibitory Activities against Monoamine Oxidases on Angelica keiskei K

Monoamine oxidase inhibitors (MAOI) have been widely used as antidepressants. Recently, there has been renewed interest in MAO inhibitors. The activity-guided fractionation of extracts from Angelica keiskei Koidzumi (A. keiskei K.) led to the isolation of two prenylated chalcones, xanthoangelol and 4-hydroxyderricin and a flavonoid, cynaroside. These three isolated compounds are the major active ingredients of A. keiskei K. to inhibit the MAOs and DBH activities. Xanthoangelol is a nonselective MAO inhibitor, and a potent dopamine β-hydroxylase (DBH) inhibitor. IC₅₀ values of xanthoangelol to MAO-A and MAO-B were calculated to be 43.4 μM, and 43.9 μM. These values were very similar to iproniazid, which is a nonselective MAO inhibitor used as a drug against depression. The IC₅₀ values of iproniazid were 37 μM, and 42.5 μM in our parallel examination. Moreover, IC₅₀ value of xanthoangelol to DBH was calculated 0.52 μM. 4-Hydroxyderricin is a potent selective MAO-B inhibitor and also mildly inhibits DBH activity. The IC₅₀ value of 4-hydroxyderricin to MAO-B was calculated to be 3.43 μM and this value was higher than that of deprenyl (0.046 μM) used as a positive control for selective MAO-B inhibitor in our test. Cynaroside is a most potent DBH inhibitor. The IC₅₀ value of cynaroside to DBH was calculated at 0.0410 μM. Results of this study suggest that the two prenylated chalcones, xanthoangelol and 4-hydroxyderricin isolated from A. keiskei K., are expected for potent candidates for development of combined antidepressant drug. A. keiskei K. will be an excellent new bio-functional food material that has the combined antidepressant effect.

Monoamine Oxidase and Dopamine β-Hydroxylase Inhibitors from the Fruits of Gardenia jasminoides

This research was designed to determine what components of Gardenia jasminoides play a major role in inhibiting the enzymes related antidepressant activity of this plant. In our previous research, the ethyl acetate fraction of G. jasminosides fruits inhibited the activities of both monoamine oxidase-A (MAO-A) and monoamine oxidase-B (MAO-B), and oral administration of the ethanolic extract slightly increased serotonin concentrations in the brain tissues of rats and decreased MAO-B activity. In addition, we found through in vitro screening test that the ethyl acetate fraction showed modest inhibitory activity on dopamine-β hydroxylase (DBH). The bioassay-guided fractionation led to the isolation of five bio-active compounds, protocatechuic acid (1), geniposide (2), 6'-O-trans-p-coumaroylgeniposide (3), 3,5-d-ihydroxy-1,7-bis (4-hydroxyphenyl) heptanes (4), and ursolic acid (5), from the ethyl acetate fraction of G. jasminoides fruits. The isolated compounds showed different inhibitory potentials against MAO-A, -B, and DBH. Protocatechuic acid showed potent inhibition against MAO-B (IC50 300 μmol/L) and DBH (334 μmol/L), exhibiting weak MAO-A inhibition (2.41 mmol/L). Two iridoid glycosides, geniposide (223 μmol/L) and 6'-O-trans-p-coumaroylgeniposide (127μmol/L), were selective MAO-B inhibitor. Especially, 6'-O-trans-p-coumaroylgeniposide exhibited more selective MAO-B inhibition than deprenyl, well-known MAO-B inhibitor for the treatment of early-stage Parkinson’s disease. The inhibitory activity of 3,5-di-hydroxy-1,7-bis (4-hydroxyphenyl) heptane was strong for MAO-B (196 μmol/L), modest for MAO-A (400 μmol/L), and weak for DBH (941 μmol/L). Ursolic acid exhibited significant inhibition of DBH (214 μmol/L), weak inhibition of MAO-B (780 μmol/L), and no inhibition against MAO-A. Consequently, G. jasminoides fruits are considerable for development of biofunctional food materials for the combination treatment of depression and neurodegenerative disorders.

Effects of combined treatment with clorgyline and selegiline on extracellular noradrenaline and serotonin levels

Kitaichi Y, Inoue T, Nakagawa S, Boku S, Koyama T. Effects of combined treatment with clorgyline and selegiline on extracellular noradrenaline and serotonin levels.

Objective Combined treatment with clorgyline, an irreversible monoamine oxidase (MAO)-A inhibitor, and selegiline, an irreversible MAO-B inhibitor, reportedly increases extracellular serotonin levels in the raphe nuclei more than clorgyline does alone. However, the effects of combination of these MAO inhibitors on extracellular noradrenaline have not been reported.

Methods Using in vivo microdialysis, we measured extracellular noradrenaline and serotonin levels after administration of clorgyline and/or selegiline in the medial prefrontal cortex of rats.

Results Administration of clorgyline (10 mg/kg) significantly increased both extracellular serotonin and noradrenaline levels. Combined treatment using clorgyline (10 mg/kg) and selegiline (3 mg/kg) increased extracellular serotonin and noradrenaline levels more than each drug alone did.

Conclusions These findings of this study suggest the augmented antidepressant action of the combination of MAO-A inhibition and MAO-B inhibition. The addition of a MAO-A inhibitor to selegiline or increasing dose of selegiline to achieve full MAO-A inhibition might be the promising strategy for the antidepressant treatment in partial responders or non-responders to selegiline.

Blue again: perturbational effects of antidepressants suggest monoaminergic homeostasis in major depression

Some evolutionary researchers have argued that current diagnostic criteria for major depressive disorder (MDD) may not accurately distinguish true instances of disorder from a normal, adaptive stress response. According to disorder advocates, neurochemicals like the monoamine neurotransmitters (serotonin, norepinephrine, and dopamine) are dysregulated in major depression. Monoamines are normally under homeostatic control, so the monoamine disorder hypothesis implies a breakdown in homeostatic mechanisms. In contrast, adaptationist hypotheses propose that homeostatic mechanisms are properly functioning in most patients meeting current criteria for MDD. If the homeostatic mechanisms regulating monoamines are functioning properly in these patients, then oppositional tolerance should develop with prolonged antidepressant medication (ADM) therapy. Oppositional tolerance refers to the forces that develop when a homeostatic mechanism has been subject to prolonged pharmacological perturbation that attempt to bring the system back to equilibrium. When pharmacological intervention is discontinued, the oppositional forces cause monoamine levels to overshoot their equilibrium levels. Since depressive symptoms are under monoaminergic control, this overshoot should cause a resurgence of depressive symptoms that is proportional to the perturbational effect of the ADM. We test this prediction by conducting a meta-analysis of ADM discontinuation studies. We find that the risk of relapse after ADM discontinuation is positively associated with the degree to which ADMs enhance serotonin and norepinephrine in prefrontal cortex, after controlling for covariates. The results are consistent with oppositional tolerance, and provide no evidence of malfunction in the monoaminergic regulatory mechanisms in patients meeting current diagnostic criteria for MDD. We discuss the evolutionary and clinical implications of our findings.