A key requirement for synaptic Reelin signaling in ketamine-mediated behavioral and synaptic action

Ketamine is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist that produces rapid antidepressant action in some patients with treatment-resistant depression. However, recent data suggest that ∼50% of patients with treatment-resistant depression do not respond to ketamine. The factors that contribute to the nonresponsiveness to ketamine’s antidepressant action remain unclear. Recent studies have reported a role for secreted glycoprotein Reelin in regulating pre- and postsynaptic function, which suggests that Reelin may be involved in ketamine’s antidepressant action, although the premise has not been tested. Here, we investigated whether the disruption of Reelin-mediated synaptic signaling alters ketamine-triggered synaptic plasticity and behavioral effects. To this end, we used mouse models with genetic deletion of Reelin or apolipoprotein E receptor 2 (Apoer2), as well as pharmacological inhibition of their downstream effectors, Src family kinases (SFKs) or phosphoinositide 3-kinase. We found that disruption of Reelin, Apoer2, or SFKs blocks ketamine-driven behavioral changes and synaptic plasticity in the hippocampal CA1 region. Although ketamine administration did not affect tyrosine phosphorylation of DAB1, an adaptor protein linked to downstream signaling of Reelin, disruption of Apoer2 or SFKs impaired baseline NMDA receptor–mediated neurotransmission. These results suggest that maintenance of baseline NMDA receptor function by Reelin signaling may be a key permissive factor required for ketamine’s antidepressant effects. Taken together, our results suggest that impairments in Reelin-Apoer2-SFK pathway components may in part underlie nonresponsiveness to ketamine’s antidepressant action.

Major depressive disorder (MDD) is a serious disorder that affects ∼20.6% of the US population and is a leading cause of suicide (1). One crucial problem in treating patients with MDD is an incomplete response rate to medications, where a large fraction of patients do not show a response to primary antidepressant medications (2, 3). Recent clinical findings demonstrate that a subanesthetic dose of ketamine, a noncompetitive N-methyl-d-aspartate receptor (NMDAR) antagonist, produces rapid antidepressant effects within hours in some patients with treatment-resistant depression or MDD (4–6). However, ∼50% of patients with treatment-resistant depression do not respond to ketamine (7), and factors involved in the nonresponsiveness to ketamine remain unclear.The hippocampus is a brain region that has been linked to the pathophysiological changes in MDD. Patients with MDD show a decrease in hippocampal volume and function (8–12). In contrast, MDD patients treated with classic antidepressants have a reversal in hippocampal volume changes along with an improvement in hippocampus-dependent cognitive function (13–15). Previous preclinical studies have shown animal models of depression also exhibit a decrease in hippocampal volume and function (13), and hippocampal synaptic functional enhancement is required to mediate antidepressant responses (16–18). This enhancement of hippocampal function has been suggested to be a key requirement to exert an antidepressant response.Ketamine induces rapid molecular changes that elicit synaptic plasticity in the hippocampus (16, 19–22). Specifically, ketamine rapidly generates synaptic potentiation of field excitatory postsynaptic potentials (fEPSPs) in CA3–CA1 synapses in the hippocampus (ketamine potentiation) by inducing the rapid translation of brain-derived neurotrophic factor (BDNF) and trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) onto the postsynaptic surface (16, 19, 23, 24). Recent studies have shown that if key factors for the antidepressant effects of ketamine, such as BDNF (16, 25, 26) or AMPA receptors (16, 27), are deleted or blocked, the synaptic potentiation in the hippocampus concurrently disappears, suggesting that the synaptic potentiation underlies ketamine’s antidepressant effects (16, 19).Ketamine-mediated potentiation of fEPSPs in CA3–CA1 synapses has been shown to require a block of NMDAR activation by spontaneous glutamate release. Ketamine produces synaptic potentiation in the presence of tetrodotoxin, which blocks sodium channels, and thereby the generation of action potentials, suggesting that blocking NMDARs activated by the spontaneous presynaptic release is key to producing the synaptic potentiation (19, 21, 28, 29). In agreement with this premise, deletion of Vps10p-tail-interactor-1a (Vti1a) and vesicle-associated membrane protein 7 (VAMP7), which are soluble N-ethylmaleimide–sensitive factor attachment protein receptor proteins selectively involved in spontaneous neurotransmitter release (30, 31) in the CA3 hippocampal region, occluded the ketamine potentiation (32). Collectively, these lines of evidence suggest spontaneous glutamate release, and NMDARs are important factors for ketamine potentiation. Thus, it is possible that if these pre- or postsynaptic components are impaired, ketamine may not produce the synaptic potentiation and antidepressant effects.Reelin is a secreted glycoprotein and acts as a neuromodulator in the adult brain by regulating pre- and postsynaptic machinery. Reelin binds to its receptors, apolipoprotein E receptor 2 (Apoer2) and very-low-density lipoprotein receptor (VLDLR) and increases tyrosine phosphorylation in Disabled-1 (DAB1) (33–35). The Reelin pathway regulates pre- or postsynaptic function through its downstream signaling pathways in the adult brain. In presynaptic terminals, the Reelin-Apoer2 pathway activates phosphoinositide 3-kinase (PI3K) and increases Ca²⁺ release from intracellular stores, which in turn mobilizes VAMP7-containing synaptic vesicles and augments spontaneous release (31). At the postsynaptic sites, Reelin’s binding to Apoer2 reciprocally activates DAB1 and Src family kinases (SFKs). Subsequently, the activated SFKs increase tyrosine phosphorylation in NMDAR subunits, GluN2A and GluN2B (34–37), and increase NMDAR open probability (37–39). Since pre- and postsynaptic components regulated by Reelin have been suggested to be important for ketamine potentiation (16, 19–21, 32), it is conceivable that disrupted Reelin signaling may abrogate the antidepressant action and synaptic plasticity of ketamine.To examine this premise, we used genetically modified mice with a deletion of either Reelin or Apoer2 and investigated changes in antidepressant-like behaviors and synaptic potentiation in the CA1 hippocampal region following ketamine treatment. We also used pharmacological inhibitors to examine the effects of signaling molecules downstream of Reelin-Apoer2, specifically SFKs and PI3K, on ketamine-induced behavioral changes and synaptic plasticity. Lastly, we investigated whether the disruption of ketamine’s effects is due to a requirement for the activation of Reelin-dependent signaling or the impairment of NMDAR function by the disruption of Reelin-dependent signaling. Our results suggest that disruption of the Reelin-Apoer2-SFKs pathway depresses NMDAR function and diminishes ketamine’s use-dependent NMDAR antagonism, thereby rendering synapses nonresponsive to ketamine’s action as well as subsequent antidepressant responses. Taken together, these results provide insight into understanding the cellular and molecular mechanisms underlying ketamine’s antidepressant effects.     

Management Options for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is associated with diverse pathophysiologic mechanisms. These mechanisms include increased abnormal colonic motility or transit, intestinal or colorectal sensation, increased colonic bile acid concentration, and superficial colonic mucosal inflammation, as well as epithelial barrier dysfunction, neurohormonal up-regulation, and activation of secretory processes in the epithelial layer. Novel approaches to treatment include lifestyle modification, changes in diet, probiotics, and pharmacotherapy directed to the motility, sensation, and intraluminal milieu of patients with IBS. Despite recent advances, there is a need for development of new treatments to relieve pain in IBS without deleterious central or other adverse effects.     

SOD2 genetic polymorphism (rs4880) has no impact on 6‐month response to antidepressant treatment and inflammatory biomarkers in depressed patients

Two thirds of patients suffering from a major depressive episode (MDE) do not reach a complete response with antidepressant drugs. This lack of response is due to several factors, including genetic determinants. Since major depressive disorder is associated with inflammatory and oxidative stress abnormalities, the metabolism of superoxide anions might be involved in non‐response to antidepressant drugs. Superoxide anions are metabolized by manganese‐dependent superoxide dismutase (SOD2) in the mitochondria. A functional genetic polymorphism (SOD2, rs4880), responsible of a 40% reduction in enzyme activity, is associated with anti‐inflammatory response of rosuvastatin. We investigated the association of ala‐allele of SOD2 rs4880 and both antidepressant efficacy and inflammatory parameters in patients treated for a MDE with antidepressant drugs. The Hamilton Depression Rating Scale (HDRS) score and levels of plasma CRP and inflammatory cytokines were assessed at baseline, one month (M1), 3 months (M3) and 6 months (M6) after antidepressant treatment. They were compared according to SOD2 genetic polymorphism. Of the 484 patients studied, 361 (74.6%) carried the ala‐allele (Ala group), 123 (25.4%) of them had Val/Val genotype (Val/Val group). No significant difference was observed between the Ala and Val/Val groups neither for baseline clinical characteristics, nor for HDRS scores, response/remission rates, plasma CRP and cytokine levels throughout the study. The rs4880 SOD2 genetic polymorphism was not associated with the clinical response and cytokines levels after antidepressant treatment. These data suggest that SOD2 is not a major genetic determinant of antidepressant response. Other genes of the oxidative stress pathways should be explored in further studies.     

HPLC-MS/MS法同时测定人血浆中6种抗抑郁药的浓度

目的:建立HPLC-MS/MS同时测定人血浆中西酞普兰、米氮平、曲唑酮、氟伏沙明、氯米帕明、文拉法辛血药浓度的方法。方法:血浆经含内标(伏立康唑)乙腈沉淀蛋白后进样测定,采用Kinetex C18柱(50 mm×2.1 mm,2.6μm)进行色谱分离,以乙腈-0.1%甲酸水为流动相,梯度洗脱,流速0.4 mL·min……-1,柱温40℃,进样量2μL;采用电喷雾离子源,正离子模式,多反应监测进行测定。结果:西酞普兰和米氮平质量浓度范围为4~400 ng·mLmL-1(r>0.9986),曲唑酮、氟伏沙明、氯米帕明和文拉法辛质量浓度范围为10~1000 ng·mL-1(r>0.9984);所有分析物日内、日间精密度(n=6)RSD<11.52%,准确度RE在-3.89%~8.14%,符合生物样品分析要求。氯米帕明在高脂血基质及溶血基质中有明显基质效应,其余待测物无明显基质效应。结论:经方法学考察,该方法灵敏、简便、准确、快速,可用于6种抗抑郁药的临床血药浓度检测。