6-Sulfatoxymelatonin predicts treatment response to fluoxetine in major depressive disorder

BACKGROUND

To date, no biomarker has been able to predict antidepressant response at an early blockade of norepinephrine or serotonin uptake. The transient nocturnal increase in plasma melatonin levels is upregulated by blocking these uptakes. The aim of this study was to test whether fluoxetine increase in urinary 6-sulfatoxymelatonin (aMT6s) is an indicator of serotonin uptake blockade.

METHODS

A total of 20 women (35-45 years of age) recruited from the community had a diagnosis of major depressive disorder confirmed by the Structured Clinical Interview for DSM-IV. Depressive symptoms were evaluated by the Beck Depression Inventory (BDI). Participants were instructed to take 20 mg of fluoxetine every morning. Every 4 weeks, the dose could be increased by 20 mg until symptom remission. The concentration of aMT6s was evaluated in overnight urine samples collected 1 day before and 1 day after the first fluoxetine dose.

RESULTS

An increase in aMT6s correlated to a decrease in BDI score evaluated on day 45 (ρ = -0.67, p = 0.024) was observed.

CONCLUSIONS

Nocturnal increase in urinary aMT6s after the first day of medication use links the early mechanism of action of fluoxetine to its clinical output 45 days later. Thus, the relationship between urinary aMT6s excretion 1 day before/1 day after is a biomarker for predicting clinical output earlier, reducing illness burden and health care costs.

Neurochemical effects of L-pyroglutamic acid

The effect of L-pyroglutamic acid, a metabolite that accumulates in pyroglutamic aciduria, on different neurochemical parameters was investigated in adult male Wistar rats. Glutamate binding, adenylate cyclase activity and G protein coupling to adenylate cyclase were assayed in the presence of the acid. L-pyroglutamic acid decreased Na(+)-dependent and Na(+)-independent glutamate binding. Basal and GMP-PNP stimulated adenylate cyclase activity were not affected by the acid. Furthermore, rats received unilateral intrastriatal injections of 10-300 nmol of buffered L-pyroglutamic acid. Vehicle (0.25 M Tris-Cl, pH 7.35-7.4) was injected into the contralateral striatum. Neurotoxic damage was assessed seven days after the injection by histological examination and by weighing both cerebral hemispheres. No difference in histology or weight could be identified between hemispheres. These results suggest that, although capable of interfering with glutamate binding, pyroglutamate did not cause a major lesion in the present model of neurotoxicity.