Mechanism of Antidepressant Action of (2R,6R)-6-Hydroxynorketamine (HNK) and Its Compounds: Insights from Proteomic Analysis

The effects of HNK, I5, and I6 on the expression of protein in hippocampus of depressed mice were studied by isobaric tags for relative and absolute quantitation (iTRAQ) to explore the mechanism of their antidepressant action. HNK, I5, and I6 were administered intragastric administration once a day in the morning for 7 days. The drug was subsequently discontinued for 7 days (without any treatment). On the 15th day, mice in each group were given the drug (1.0, 10.0, 30.0 mg/kg) intragastric stimulation and mouse hippocampal tissues were taken to perform iTRAQ to identify differentially expressed proteins, and bioinformatics was used to analyze the functional enrichment of the differentially expressed proteins. Compared with Ctr group, the number of differentially expressed proteins in HNK, I5, and I6 treatment groups was 158, 88, and 105, respectively. The three groups shared 29 differentially expressed proteins. In addition, compared with HNK group, the number of differentially expressed proteins in I5 and I6 groups was 201 and 203, respectively. A total of 47 and 56 differentially expressed proteins were co-expressed in I5 and I6 groups. Bioinformatics analysis showed that these differentially expressed proteins mainly had the functions of binding, biocatalysis, and transport, and mainly participated in cellular process, biological regulation process, biological metabolism process, and stress reaction process. GO and KEGG pathway analysis found that these differentially expressed proteins were involved long-term potentiation, G13 pathway, platelet activation pathway, and MAPK signaling pathway. HNK, I5, and I6 antidepressants are closely related to sudden stress sensitivity, stress resistance, neurotransmitter, and metabolic pathways. This study provides a scientific basis to further elucidate the mechanism and clinical application of HNK, I5, and I6 antidepressants.

The effects of (2R,6R)-hydroxynorketamine on oxycodone withdrawal and reinstatement

Despite the thousands of lives lost during the ongoing opioid crisis, a scarcity of new and effective clinical treatments for opioid use disorder (OUD) remains. To address this unmet need, some researchers have turned to dissociative and psychedelic drugs to treat multiple psychiatric conditions. In particular, low doses of ketamine have been shown to attenuate opioid withdrawal and drug use in clinical and preclinical studies. However, ketamine has misuse liability and dissociative side effects that may limit its widespread application as a treatment for OUD. More recently, (2R,6R)-hydroxynorketamine (HNK), a ketamine metabolite that lacks misuse potential, has gained attention for its effectiveness in depression and stress models. To uncover its role in OUD, we tested the time-dependent effects of (2R,6R)-HNK on oxycodone withdrawal and reinstatement of oxycodone conditioned place preference (CPP). In male and female oxycodone-dependent mice, we found that 24h pretreatment with (2R,6R)-HNK (10 or 30mg/kg, s.c.) reduced the frequency of withdrawal-like behaviors and global withdrawal scores during naloxone-precipitated withdrawal, whereas 1h pretreatment with (2R,6R)-HNK only reduced paw tremors and the sum of global withdrawal scores but not GWS Z-scores. In other experiments, both 1h and 24h pretreatment with (2R,6R)-HNK (30mg/kg, s.c.) blocked drug-induced reinstatement of oxycodone CPP. Finally, we found (2R,6R)-HNK (30mg/kg, sc) had no effect on locomotor activity and thigmotaxis. Together, these results indicate that acute (2R,6R)-HNK has efficacy in some preclinical models of OUD without producing locomotor or anxiety-like side effects.

Pharmacological features, health benefits and clinical implications of honokiol

Honokiol (HNK) is a natural polyphenolic compound extracted from the bark and leaves of Magnolia grandiflora. It has been traditionally used as a medicinal compound to treat inflammatory diseases. HNK possesses numerous health benefits with a minimal level of toxicity. It can cross the blood-brain barrier and blood-cerebrospinal fluid, thus having significant bioavailability in the neurological tissues. HNK is a promising bioactive compound possesses neuroprotective, antimicrobial, anti-tumorigenic, anti-spasmodic, antidepressant, analgesic, and antithrombotic features . HNK can prevent the growth of several cancer types and haematological malignancies. Recent studies suggested its role in COVID-19 therapy. It binds effectively with several molecular targets, including apoptotic factors, chemokines, transcription factors, cell surface adhesion molecules, and kinases. HNK has excellent pharmacological features and a wide range of chemotherapeutic effects, and thus, researchers have increased interest in improving the therapeutic implications of HNK to the clinic as a novel agent. This review focused on the therapeutic implications of HNK, highlighting clinical and pharmacological features and the underlying mechanism of action.Communicated by Ramaswamy H. Sarma.

Mediation of the behavioral effects of ketamine and (2R,6R)-hydroxynorketamine in mice by kappa opioid receptors

Emerging evidence has implicated the endogenous opioid system in mediating ketamine's antidepressant activity in subjects with major depressive disorder. To date, mu opioid receptors have been suggested as the primary opioid receptor of interest. However, this hypothesis relies primarily on observations that the opioid antagonist naltrexone blocked the effects of ketamine in humans and rodents. This report confirms previous findings that pretreatment with naltrexone (1 mg/kg) just prior to ketamine (10 mg/kg) administration effectively blocks the behavioral effect of ketamine in the mouse forced swim test 24 h post-treatment. Furthermore, pharmacological blockade of kappa opioid receptors prior to ketamine administration with the selective, short-acting antagonist LY2444296 successfully blocked ketamine's effects in the forced swim test. Likewise, the ability of the ketamine metabolite (2R,6R)-hydroxynorketamine to reduce immobility scores in the forced swim test was also blocked following pretreatment with either naltrexone or LY2444296. These data support a potential role of kappa opioid receptors in mediating the behavioral activity of ketamine and its non-dissociate metabolite (2R,6R)-hydroxynorketamine.

Honokiol Inhibits HIF-1α-Mediated Glycolysis to Halt Breast Cancer Growth

Background: Hypoxia-inducible factor-1α (HIF-1α) induces the expression of glycolysis-related genes, which plays a direct and key role in Warburg effect. In a recent study, honokiol (HNK) was identified as one of the potential agents that inhibited the HIF-1α signaling pathway. Because the HIF- 1α pathway is closely associated with glycolysis, we investigated whether HNK inhibited HIF-1α-mediated glycolysis.

Methods: The effects of HNK on HIF-1α-mediated glycolysis and other glycolysis-related genes’ expressions, cancer cells apoptosis and tumor growth were studied in various human breast cancer models in vitro and in vivo. We performed the following tests: extracellular acidification and oxygen consumption rate assays, glucose uptake, lactate, and ATP assays for testing glycolysis; WST-1 assay for investigating cell viability; colony formation assay for determining clonogenicity; flow cytometry for assessing cell apoptosis; qPCR and Western blot for determining the expression of HIF-1α, GLUT1, HK2 and PDK1. The mechanisms of which HNK functions as a direct inhibitor of HIF-1α were verified through the ubiquitination assay, the Co-IP assay, and the cycloheximide (CHX) pulse-chase assay.

Results: HNK increased the oxygen consumption rate while decreased the extracellular acidification rate in breast cancer cells; it further reduced glucose uptake, lactic acid production and ATP production in cancer cells. The inhibitory effect of HNK on glycolysis is HIF-1α-dependent. HNK also downregulated the expression of HIF-1α and its downstream regulators, including GLUT1, HK2 and PDK1. A mechanistic study demonstrated that HNK enhanced the self-ubiquitination of HIF-1α by recruiting two E3 ubiquitin ligases (UFL1 and BRE1B). In vitro, HNK inhibited cell proliferation and clonogenicity, as well as induced apoptosis of cancer cells. These effects were also HIF1α-dependent. In vivo, HNK inhibited tumor growth and HIF-1α-mediated glycolysis.

Conclusion: HNK has an inhibitory effect on HIF-1α-mediated glycolysis in human breast cancer. Our research revealed a new mechanism of HNK as an anti-cancer drug, thus representing a novel strategy to improve the prognosis of cancer.

Ketamine and its metabolite, (2R,6R)-HNK, restore hippocampal LTP and long-term spatial memory in the Wistar-Kyoto rat model of depression

Accumulating evidence implicates dysregulation of hippocampal synaptic plasticity in the pathophysiology of depression. However, the effects of ketamine on synaptic plasticity and their contribution to its mechanism of action as an antidepressant, are still unclear. We investigated ketamine’s effects on in vivo dorsal hippocampal (dHPC) synaptic plasticity and their role in mediating aspects of antidepressant activity in the Wistar-Kyoto (WKY) model of depression. dHPC long-term potentiation (LTP) was significantly impaired in WKY rats compared to Wistar controls. Importantly, a single low dose (5 mg/kg, ip) of ketamine or its metabolite, (2R,6R)-HNK, rescued the LTP deficit in WKY rats at 3.5 h but not 30 min following injection, with residual effects at 24 h, indicating a delayed, sustained facilitatory effect on dHPC synaptic plasticity. Consistent with the observed dHPC LTP deficit, WKY rats exhibited impaired hippocampal-dependent long-term spatial memory as measured by the novel object location recognition test (NOLRT), which was effectively restored by pre-treatment with both ketamine or (2R,6R)-HNK. In contrast, in WKYs, which display abnormal stress coping, ketamine, but not (2R,6R)-HNK, had rapid and sustained effects in the forced swim test (FST), a commonly used preclinical screen for antidepressant-like activity. The differential effects of (2R,6R)-HNK observed here reveal a dissociation between drug effects on FST immobility and dHPC synaptic plasticity. Therefore, in the WKY rat model, restoring dHPC LTP was not correlated with ketamine’s effects in FST, but importantly, may have contributed to the reversal of hippocampal-dependent cognitive deficits, which are critical features of clinical depression. Our findings support the theory that ketamine may reverse the stress-induced loss of connectivity in key neural circuits by engaging synaptic plasticity processes to “reset the system”.

Repeated ketamine treatment induces sex-specific behavioral and neurochemical effects in mice

One of the most striking discoveries in the treatment of major depression was the finding that infusion of a single sub-anesthetic dose of ketamine induces rapid and sustained antidepressant effects in treatment-resistant depressed patients. However, ketamine's antidepressant-like actions are transient and can only be sustained by repeated drug treatment. Despite the fact that women experience major depression at roughly twice the rate of men, research regarding the neurobiological antidepressant-relevant effects of ketamine has focused almost exclusively on the male sex. Importantly, knowledge regarding the sex-differentiated effects, the frequency and the dose on which repeated ketamine administration stops being beneficial, is limited. In the current study, we investigated the behavioral, neurochemical and synaptic molecular effects of repeated ketamine treatment (10mg/kg; 21days) in male and female C57BL/6J mice. We report that ketamine induced beneficial antidepressant-like effects in male mice, but induced both anxiety-like (i.e., decreased time spent in the center of the open field arena) and depressive-like effects (i.e., enhanced immobility duration in the forced swim test; FST) in their female counterparts. Moreover, repeated ketamine treatment induced sustained sex-differentiated neurochemical and molecular effects, as it enhanced hippocampal synapsin protein levels and serotonin turnover in males, but attenuated glutamate and aspartate levels in female mice. Taken together, our findings indicate that repeated ketamine treatment induces opposite behavioral effects in male and female mice, and thus, present data have far-reaching implications for the sex-oriented use of ketamine in both experimental and clinical research settings.