Dose-dependent effects of isoflurane on TrkB and GSK3β signaling: Importance of burst suppression pattern

Objectives: Deep burst-suppressing isoflurane anesthesia regulates signaling pathways connected with antidepressant responses in the rodent brain: activation of TrkB neurotrophin receptor and inhibition of GSK3 beta kinase (glycogen synthase kinase 3 beta). The main objective of this study was to investigate whether EEG (electroencephalogram) burst suppression correlates with these intriguing molecular alterations induced by isoflurane. Methods: Adult male mice pre-implanted with EEG recording electrodes were subjected to varying concentrations of isoflurane (1.0-2.0% ad 20 min) after which medial prefrontal cortex samples were collected for molecular analyses, and the data retrospectively correlated to EEG ( + /- burst suppression). Results: Isoflurane dose-dependently increased phosphorylation of TrkB(Y816), CREBS133 (cAMP response element binding protein), GSK3 beta(S9) and p70S6k(T412/S424). The time spent in burst suppression mode varied considerably between individual animals. Notably, a subset of animals subjected to 1.0-1.5% isoflurane showed no burst suppression. While p-GSK3 beta(S9), p-CREBS133 and p-p70S6k(T412/S424) levels were increased in the samples obtained also from these animals, p-TrkB(Y816) levels remained unaltered. Conclusions: Isoflurane dose-dependently regulates TrkB and GSK3 beta signaling and dosing associated with therapeutic outcomes in depressed patients produces most prominent effects.Peer reviewe

P11 promoter methylation predicts the antidepressant effect of electroconvulsive therapy

Although electroconvulsive therapy (ECT) is among the most effective treatment options for pharmacoresistant major depressive disorder (MDD), some patients still remain refractory to standard ECT practise. Thus, there is a need for markers reliably predicting ECT non/response. In our study, we have taken a novel translational approach for discovering potential biomarkers for the prediction of ECT response. Our hypothesis was that the promoter methylation of p11, a multifunctional protein involved in both depressive-like states and antidepressant treatment responses, is differently regulated in ECT responders vs. nonresponders and thus be a putative biomarker of ECT response. The chronic mild stress model of MDD was adapted with the aim to obtain rats that are resistant to conventional antidepressant drugs (citalopram). Subsequently, electroconvulsive stimulation (ECS) was used to select responders and nonresponders, and compare p11 expression and promoter methylation. In the rat experiments we found that the gene promoter methylation and expression of p11 significantly correlate with the antidepressant effect of ECS. Next, we investigated the predictive properties of p11 promoter methylation in two clinical cohorts of patients with pharmacoresistant MDD. In a proof-of-concept clinical trial in 11 patients with refractory MDD, higher p11 promoter methylation was found in responders to ECT. This finding was replicated in an independent sample of 65 patients with pharmacoresistant MDD. This translational study successfully validated the first biomarker reliably predicting the responsiveness to ECT. Prescreening of this biomarker could help to identify patients eligible for first-line ECT treatment and also help to develop novel antidepressant treatment procedures for depressed patients resistant to all currently approved antidepressant treatments.Peer reviewe

Ketamine-induced regulation of TrkB-GSK3β signaling is accompanied by slow EEG oscillations and sedation but is independent of hydroxynorketamine metabolites

Subanesthetic rather than anesthetic doses are thought to bring the rapid antidepressant effects of the NMDAR (N-methyl-D-aspartate receptor) antagonist ketamine. Among molecular mechanisms, activation of BDNF receptor TrkB along with the inhibition of GSK3 beta (glycogen synthase kinase 3 beta) are considered as critical molecular level determinants for ketamine's antidepressant effects. Hydroxynorketamines (2R,6R)-HNK and (2S,6S) HNK), non-anesthetic metabolites of ketamine, have been proposed to govern the therapeutic effects of ketamine through a mechanism not involving NMDARs. However, we have shown that nitrous oxide, another NMDAR blocking anesthetic and a putative rapid-acting antidepressant, evokes TrkB-GSK3 beta signaling alterations during rebound slow EEG (electroencephalogram) oscillations. We investigated here the acute effects of ketamine, 6,6-d(2)-ketamine (a ketamine analogue resistant to metabolism) and cis-HNK that contains (2R,6R) and (2S,6S) enantiomers in 1:1 ratio, on TrkB-GSK3 beta signaling and concomitant electroencephalographic (EEG) alterations in the adult mouse cortex. Ketamine dose-dependently increased slow oscillations and phosphorylations of TrkB(Y816) and GSK3 beta(59) in crude brain homogenates (i.e. sedative/anesthetic doses ( > 50 mg/kg, i.p.) produced more prominent effects than a subanesthetic dose (10 mg/kg, i.p.)). Similar, albeit less obvious, effects were seen in crude synaptosomes. A sedative dose of 6,6-d(2)-ketamine (100 mg/kg, i.p.) recapitulated the effects of ketamine on TrkB and GSK3 beta phosphorylation while cis-HNK at a dose of 20 mg/kg produced negligible acute effects on TrkB-GSK3 beta signaling or slow oscillations. These findings suggest that the acute effects of ketamine on TrkB-GSK3 beta signaling are by no means restricted to subanesthetic (i.e. antidepressant) doses and that cis-HNK is not responsible for these effects.Peer reviewe