Ketamine is an injectable anesthetic and recreational drug of abuse commonly used worldwide. Many experimental studies have shown that ketamine can impair cognitive function and induce psychotic states. Neuroinflammation has been suggested to play an important role in neurodegeneration. Meanwhile, ketamine has been shown to modulate the levels of inflammatory cytokines. We hypothesized that the effects of ketamine on the central nervous system are associated with inflammatory cytokines. Therefore, we set out to establish acute and chronic ketamine administration models in C57BL/6 mice, to evaluate spatial recognition memory and emotional response, to analyze the changes in the levels of the inflammatory cytokines interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in the mouse hippocampus, employing behavioral tests, Western blot, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and immunohistochemistry. Our results showed that ketamine at the dose of 60 mg/kg induced spatial recognition memory deficit and reduced anxiety-like behaviors in mice after chronic administration. Moreover, we found that ketamine increased the hippocampal levels of IL-6 and IL-1β after single, multiple and long-term administration in a dose-dependent manner. However, the expression level of TNF-α differed in the mouse hippocampus under different conditions. Single administration of ketamine increased the level of TNF-α, whereas multiple and long-term administration decreased it significantly. We considered that TNF-α expression could be controlled by a bi-directional regulatory pathway, which was associated with the dose and duration of ketamine administration. Our results suggest that the alterations in the levels of inflammatory cytokines IL-6, IL-1β, and TNF-α may be involved in the neurotoxicity of ketamine.

Ketamine has been reported to impair human cognitive function as a recreational drug of abuse. However, chronic effects of ketamine on central nervous system need to be further explored. We set out to establish chronic ketamine addiction models by giving mice a three or six month course of daily intraperitoneal injections of ketamine, then examined whether long-term ketamine administration induced cognition deficits and changed hippocampal post-synaptic protein expression in adult mice. Behavior tests results showed that mice exhibited dose- and time-dependent learning and memory deficits after long-term ketamine administration. Western blot results showed levels of GluA1, p-S845 and p-S831 proteins demonstrated significant decline with ketamine 60 mg/kg until six months administration paradigm. But levels of p-S845 and p-S831 proteins exhibited obvious increase with ketamine 60 mg/kg three months administration paradigm. NR1 protein levels significantly decrease with ketamine 60 mg/kg three and six months administration paradigm. Our results indicate that reduced expression levels and decreased phosphorylation levels of hippocampal post-synaptic membrane GluA1- containing AMPA receptors maybe involved in cognition impairment after long-term ketamine administration. These findings provide further evidence for the cognitive damage of chronic ketamine addiction as a recreational drug.

Si-Miao-Yong-An decoction (SMYAD), a traditional Chinese medicine formula, is mainly used to clear away heat and detoxify and to promote blood circulation and relieve pain. Diabetic retinopathy (DR) is the most common type of microvascular complication caused by diabetes. This study is designed to examine the protective effect of SMYAD against DR and further to reveal the engaged mechanism via integrating network pharmacology and in vivo experimental evidence. Streptozotocin (STZ) was intraperitoneally injected into mice to induce diabetes. The dysfunction of the blood retina barrier (BRB) was observed by conducting Evan’s blue leakage assay, detecting tight junction (TJ) protein expression and counting the number of acellular capillaries in retinas. Our results showed that SMYAD alleviated BRB breakdown in vivo. Network pharmacology results demonstrated that regulating inflammation, immune responses, and angiogenesis might be associated with the efficacy of SMYAD in alleviating DR, in which the tumor necrosis factor (TNF) and hypoxia inducible factor 1 (HIF1) signal pathways were involved. Next, immunofluorescence staining results showed that SMYAD decreased microglia activation in retinas and reduced the enhanced adhesion of leukocytes into retinal vessels. SMYAD reduced the elevated serum TNFα content and retinal TNFα expression. SMYAD abrogated the activation of nuclear factor κB (NFκB) and HIF1α and consequently decreased the enhanced expression of some pro-inflammatory molecules and vascular endothelial growth factor (VEGF) in retinas. These results indicate that SMYAD attenuated DR development through suppressing retinal inflammation and angiogenesis via abrogating NFκB-TNFα and HIF1α-VEGF signal pathways.

As one of the major diabetic microvascular complications, diabetic retinopathy (DR) is mainly initiated by the blood-retinal barrier (BRB) dysfunction. Chlorogenic acid (CGA) is a natural polyphenolic compound in Lonicerae Japonicae Flos, which traditionally has the beneficial function for eyes and is commonly included in many antidiabetic formulas. In this study, the potential protective mechanism of CGA against DR was investigated. Streptozotocin (STZ) was used to induce diabetes in mice. CGA attenuated BRB dysfunction and reversed endothelial-mesenchymal transition (EndoMT) and epithelial-mesenchymal transition (EMT) in retinas in vivo. CGA inhibited microglia activation and reduced tumor necrosis factor (TNF)α release both in vivo and in vitro. CGA promoted nuclear factor erythroid 2-related factor 2 (Nrf2) activation and prevented EndoMT/EMT in TNFα-treated human retinal endothelial cells (HRECs) or retinal pigment epithelial APRE19 cells. CGA alleviated endothelial/ epithelial barrier oxidative injury in HRECs or APRE19 cells stimulated with TNFα, but this effect was disappeared in cells co-incubated with Nrf2 inhibitor. Additionally, the CGA-supplied alleviation on BRB damage and EndoMT/EMT was markedly weakened in retinas from STZ-treated Nrf2 knock-out mice. All results suggest that CGA improves DR through attenuating BRB injury by reducing microglia-initiated inflammation and preventing TNFα-induced EndoMT/EMT and oxidative injury via inducing Nrf2 activation.