Activation of melatonin receptor (MT1/2) promotes P-gp transporter in methamphetamine-induced toxicity on primary rat brain microvascular endothelial cells

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Melatonin improves behavioral parameters and oxidative stress in zebrafish submitted to a leucine-induced MSUD protocol

Maple syrup urine disease (MSUD) is an inherited metabolic disorder caused by a deficiency in branched-chain alpha-ketoacid dehydrogenase complex (BCKAC). The treatment is a standard therapy based on a protein-restricted diet with low branched-chain amino acids (BCAA) content to reduce plasma levels and, consequently, the effects of accumulating their metabolites, mainly in the central nervous system. Although the benefits of dietary therapy for MSUD are undeniable, natural protein restriction may increase the risk of nutritional deficiencies, resulting in a low total antioxidant status that can predispose and contribute to oxidative stress. As MSUD is related to redox and energy imbalance, melatonin can be an important adjuvant treatment. Melatonin directly scavenges the hydroxy radical, peroxyl radical, nitrite anion, and singlet oxygen and indirectly induces antioxidant enzyme production. Therefore, this study assesses the role of melatonin treatment on oxidative stress in brain tissue and behavior parameters of zebrafish (Danio rerio) exposed to two concentrations of leucine-induced MSUD: leucine 2 mM and 5mM; and treated with 100 nM of melatonin. Oxidative stress was assessed through oxidative damage (TBARS, DCF, and sulfhydryl content) and antioxidant enzyme activity (SOD and CAT). Melatonin treatment improved redox imbalance with reduced TBARS levels, increased SOD activity, and normalized CAT activity to baseline. Behavior was analyzed with novel object recognition test. Animals exposed to leucine improved object recognition due to melatonin treatment. With the above, we can suggest that melatonin supplementation can protect neurologic oxidative stress, protecting leucine-induced behavior alterations such as memory impairment.

Overview of blood-brain barrier dysfunction in methamphetamine abuse

Methamphetamine (METH) is one of the psychostimulants most widely abused in the world. METH abuse can lead to severe neurotoxicity. The blood-brain barrier (BBB) is a natural barrier separating the central nervous system (CNS) from the peripheral blood circulation, which can limit or regulate the exchange of toxic substances, molecules, ions, etc., to maintain the homeostasis of CNS. Long-term or high dose abuse of METH can cause structural or functional abnormalities of the BBB and increase the risk of neurodegenerative diseases. In this review, we discussed the mechanisms of METH-induced BBB dysfunction, summarized the risk factors that could exacerbate METH-induced BBB dysfunction, and introduced some potential therapeutic agents. It would provide an important basis and direction for the prevention and treatment of BBB dysfunction induced by METH.

Melatonin Alleviates Acute Sleep Deprivation-Induced Memory Loss in Mice by Suppressing Hippocampal Ferroptosis

Objectives: Memory decline caused by insufficient sleep is a critical public health issues and currently lacks effective treatments. This study objective was to explore alleviative effect of melatonin on sleep deprivation (SD)-induced deficiencies in learning and memory.

Materials and Methods: A continuous 72 h SD mouse model, with or without melatonin or Fer-1 supplementation were established. The changes of cognitive function, iron homeostasis, lipid peroxidation and intracellular signal pathways in mice were detected by Morris water maze, antioxidant assay, immunohistochemistry, western blot, RT-PCR and Prussian blue staining. In vitro, we treated HT-22 cells with ferroptosis inducer (Erastin) to further explore the specific mechanism of melatonin in ferroptosis.

Results: Mice subjected to SD had significantly elevated latency and path length to reach hidden platform, as well as a decrease in number of entries and time spent in the target zone when the hidden platform was removed (p < 0.05). Nevertheless, supplementation with ferroptosis inhibitor (Fer-1) mitigated the memory impairment associated with SD. Further evaluation revealed an up-regulation of intracellular iron accumulation, transferrin receptor 1 and divalent metal transporter 1 expression and ROS and MDA production, and a down-regulation of ferroportin and antioxidant enzyme (GPX4 and SOD) expression in SD mice. SD decreased expression of MT2 receptor rather than of MT1, and inhibited ERK/Nrf2 signaling activation in the hippocampus (p < 0.05). In contrast, the aforementioned SD-inductions were reversed by supplementation using 20 and 40 mg/kg melatonin in SD mice. In vitro, melatonin pretreatment reversed Erastin-induced ferroptosis, abnormalities in iron transporter protein and antioxidant enzyme expression and suppression of ERK/Nrf2 signaling in HT-22 cells, however this protective effect of melatonin was blocked by MT2-, ERK- and Nrf2-specific antagonists (p < 0.05).

Conclusion: Our finding suggested SD may induce ferroptosis, in turn leading to cognitive deficits. Melatonin alleviated memory loss and hippocampal ferroptosis caused by acute SD through binding to the MT2 receptor to activate ERK/Nrf2 signaling.

Melatonin, Its Beneficial Effects on Embryogenesis from Mitigating Oxidative Stress to Regulating Gene Expression

Embryogenesis is a complex multi-stage process regulated by various signaling molecules including pineal and extrapineal melatonin (MT). Extrapineal MT is found in the placenta and ovaries, where it carries out local hormonal regulation. MT is necessary for normal development of oocytes, fertilization and subsequent development of human, animal and avian embryos. This review discusses the role of MT as a regulator of preimplantation development of the embryo and its implantation into endometrial tissue, followed by histo-, morpho- and organogenesis. MT possesses pronounced antioxidant properties and helps to protect the embryo from oxidative stress by regulating the expression of the NFE2L2, SOD1, and GPX1 genes. MT activates the expression of the ErbB1, ErbB4, GJA1, POU5F1, and Nanog genes which are necessary for embryo implantation and blastocyst growth. MT induces the expression of vascular endothelial growth factor (VEGF) and its type 1 receptor (VEGF-R1) in the ovaries, activating angiogenesis. Given the increased difficulties in successful fertilization and embryogenesis with age, it is of note that MT slows down ovarian aging by increasing the transcription of sirtuins. MT administration to patients suffering from infertility demonstrates an increase in the effectiveness of in vitro fertilization. Thus, MT may be viewed as a key factor in embryogenesis regulation, including having utility in the management of infertility.

Agomelatine prevents macrophage infiltration and brain endothelial cell damage in a stroke mouse model

Background and purpose: Ischemic/reperfusions are regarded as the clinical consensus for stroke treatment, which results in secondary injury of brain tissues. Increased blood-brain barrier (BBB) permeability and infiltration of inflammatory cells are responsible for the ischemic/reperfusion injury. In the present study, we aimed to investigate the effects of Agomelatine on brain ischemic/reperfusions injury and the underlying mechanism.

Methods: MCAO model was established in mice. The expressions of CD68 and claudin-5 in the cerebral cortex were determined using an immunofluorescence assay. Brain permeability was evaluated using Evans blue staining assay. A two-chamber and two-cell trans-well assay was used to detect the migration ability of macrophages through endothelial cells. The expression levels of claudin-5 and MCP-1 in the endothelial cells were determined using qRT-PCR and ELISA.

Results: CD68 was found to be up-regulated in the cerebral cortex of MCAO mice but was down-regulated by treatment with Agomelatine. The expression level of down-regulated claudin-5 in the cerebral cortex of MCAO mice was significantly suppressed by Agomelatine. Deeper staining of Evans blue was found in the MCAO group, which was however faded significantly in the Agomelatine treated MCAO mice. The migrated macrophages were significantly increased by hypoxia incubation but were greatly suppressed by the introduction of Agomelatine. The down-regulated claudin-5 by hypoxic incubation in endothelial cells was up-regulated by treatment with Agomelatine. Furthermore, the increased expression of MCP-1 in endothelial cells under hypoxic conditions was significantly inhibited by Agomelatine.

Conclusion: Agomelatine prevents macrophage infiltration and brain endothelial cell damage in a stroke mouse model.

Methamphetamine and HIV-Tat Protein Synergistically Induce Oxidative Stress and Blood-Brain Barrier Damage via Transient Receptor Potential Melastatin 2 Channel

Synergistic impairment of the blood-brain barrier (BBB) induced by methamphetamine (METH) and HIV-Tat protein increases the risk of HIV-associated neurocognitive disorders (HAND) in HIV-positive METH abusers. Studies have shown that oxidative stress plays a vital role in METH- and HIV-Tat-induced damage to the BBB but have not clarified the mechanism. This study uses the human brain microvascular endothelial cell line hCMEC/D3 and tree shrews to investigate whether the transient receptor potential melastatin 2 (TRPM2) channel, a cellular effector of the oxidative stress, might regulate synergistic damage to the BBB caused by METH and HIV-Tat. We showed that METH and HIV-Tat damaged the BBB in vitro, producing abnormal cell morphology, increased apoptosis, reduced protein expression of the tight junctions (TJ) including Junctional adhesion molecule A (JAMA) and Occludin, and a junctional associated protein Zonula occludens 1 (ZO1), and increased the flux of sodium fluorescein (NaF) across the hCMEC/D3 cells monolayer. METH and HIV-Tat co-induced the oxidative stress response, reducing catalase (CAT), glutathione peroxidase (GSH-PX), and superoxide dismutase (SOD) activity, as well as increased reactive oxygen species (ROS) and malonaldehyde (MDA) level. Pretreatment with n-acetylcysteine amide (NACA) alleviated the oxidative stress response and BBB damage characterized by improving cell morphology, viability, apoptosis levels, TJ protein expression levels, and NaF flux. METH and HIV-Tat co-induced the activation and high protein expression of the TRPM2 channel, however, early intervention using 8-Bromoadenosine-5′-O-diphosphoribose (8-Br-ADPR), an inhibitor of TPRM2 channel, or TRPM2 gene knockdown attenuated the BBB damage. Oxidative stress inhibition reduced the activation and high protein expression of the TRPM2 channel in the in vitro model, which in turn reduced the oxidative stress response. Further, 8-Br-ADPR attenuated the effects of METH and HIV-Tat on the BBB in tree shrews—namely, down-regulated TJ protein expression and increased BBB permeability to Evans blue (EB) and NaF. In summary, the TRPM2 channel can regulate METH- and HIV-Tat-induced oxidative stress and BBB injury, giving the channel potential for developing drug interventions to reduce BBB injury and neuropsychiatric symptoms in HIV-infected METH abusers.

The protective effect of gastrodin against the synergistic effect of HIV-Tat protein and METH on the blood-brain barrier via glucose transporter 1 and glucose transporter 3

Many individuals infected with human immunodeficiency virus (HIV) are also afflicted with HIV-associated neurocognitive disorders (HANDs). Methamphetamine (METH) abuse puts HIV-1 patients at risk for HANDs because METH and HIV-1 proteins, such as trans-activator of transcription (Tat), can synergistically damage the blood-brain barrier (BBB). However, the underlying mechanism of METH- and HIV-Tat-induced BBB damage remains unclear. In this study, male adult tree shrews and human brain capillary endothelial cells were treated with HIV-Tat, METH, and gastrodin. We used western blotting to examine the expressions of glucose transporters (GLUT1 and GLUT3), tight junctions, and junctional adhesion molecule A (JAMA) and to evaluate the damage and detect Evans blue (EB) and fluorescein sodium in the brain to assess BBB permeability to study the effect of METH and the HIV-1 Tat protein on BBB function in vitro and in vivo. The results showed that the group treated with Tat and METH experienced a significant change at the ultrastructural level of the tree shrew cerebral cortex, decreased protein levels of occluding, claudin-5, Zonula occludens 1 (ZO1), and JAMA in vitro and in vivo, and increased levels of EB and fluorescein sodium in the tree shrew cerebral cortex. The protein levels of GLUT1 and GLUT3 was downregulated in patients with Tat- and METH-induced BBB damage. Pretreatment with gastrodin significantly increased the levels of EB and fluorescein sodium in the tree shrew cerebral cortex and increased the expressions of occluding, ZO1, JAMA, and GLUT1 and GLUT. These results indicate that gastrodin may offer a potential therapeutic option for patients with HANDs.

Up-regulation of P-gp via NF-κB activation confers protection against oxidative damage in the retinal pigment epithelium cells

Dysfunction of retinal pigment epithelial (RPE) cells has been associated with the pathogenesis of age-related macular degeneration in relation to increased oxidative stress, subsequent mitochondrial dysfunction and cell death. Permeability-glycoprotein (P-gp), encoded by the multidrug resistance 1 gene (MDR1), is an active efflux pump involved in cell homeostasis and nuclear factor κB (NF-κB) shows potential involvement in P-gp regulation due to its binding to the promoter domains of MDR1 gene. This study sought to determine the role of P-gp expression regulated by NF-κB in RPE cells during oxidative stress. The human RPE D407 cells were exposed to increasing concentrations of hydrogen peroxide (H₂O₂) for 24 h. The small-interfering RNA (siRNA) transfection was used to down-regulate P-gp and NF-κB, and the expressions of P-gp and NF-κB p65 were determined by quantitative real-time PCR, western blot and immunofluorescence. The activity of NF-κB was detected by luciferase reporter assay. Mitochondrial membrane potential and cell death rate were detected by flow cytometry. We found that H₂O₂ exposure caused increasing rate of cell death and induced an elevated expression of P-gp as well as NF-κB activation and nucleus translocation in D407 cells. Inhibiting or silencing NF-κB led to a decrease in the oxidative-induced expression of P-gp. Down-regulation of P-gp by siRNA transfection further impaired the mitochondrial membrane potential and cell death rate in oxidative cells. Moreover, inhibition/knockdown of NF-κB decreased the high rate of cell death caused by H₂O₂. In conclusion, P-gp can provide moderate cytoprotection for the human RPE cells by ameliorating the mitochondrial dysfunction and NF-κB activation may be a potential regulator of P-gp expression response to oxidative stress.

Melatonin attenuates smoking-induced hyperglycemia via preserving insulin secretion and hepatic glycogen synthesis in rats

Epidemiology survey indicated that cigarette smoking is a risk factor of diabetes. However, the precise mechanisms remain to be clarified. In this study, we found that smoking caused metabolic malfunctions on pancreas and liver in experimental animal model. These were indicated by hyperglycemia, increased serum hemoglobin A1c level and decreased insulin secretion, inhibition of liver glycogen synthase (LGS), and hepatic glycogen synthesis. Mechanistic studies revealed that all these alterations were caused by the inflammatory reaction and reactive oxygen species (ROS) induced by the smoking. Melatonin treatment significantly preserved the functions of both pancreas and liver by reducing β cell apoptosis, CD68-cell infiltration, ROS production, and caspase-3 expression. The siRNA-knockdown model identified that the protective effects of melatonin were mediated by melatonin receptor-2 (MT2). This study uncovered potentially underlying mechanisms related to the association between smoking and diabetes. In addition, it is, for first time, to report that melatonin effectively protects against smoking-induced glucose metabolic alterations and the signal transduction pathway of melatonin is mainly mediated by its MT2 receptor. These observations provide solid evidence for the clinically use of melatonin to reduce smoking-related diabetes, and the therapeutic regimens are absent currently.

Neuroprotective effects of melatonin on amphetamine-induced dopaminergic fiber degeneration in the hippocampus of postnatal rats

Chronic amphetamine (AMPH) abuse leads to damage of the hippocampus, the brain area associated with learning and memory process. Previous results have shown that AMPH-induced dopamine neurotransmitter release, reactive oxygen species formation, and degenerative protein aggregation lead to neuronal death. Melatonin, a powerful antioxidant, plays a role as a neuroprotective agent. The objective of this study was to investigate whether the protective effect of melatonin on AMPH-induced hippocampal damage in the postnatal rat acts through the dopaminergic pathway. Four-day-old postnatal rats were subcutaneously injected with 5-10 mg/kg AMPH and pretreated with 10 mg/kg melatonin prior to AMPH exposure for seven days. The results showed that melatonin decreased the AMPH-induced hippocampal neuronal degeneration in the dentate gyrus, CA1, and CA3. Melatonin attenuated the reduction in the expression of hippocampal synaptophysin, PSD-95, α-synuclein, and N-methyl-D-aspartate (NMDA) receptor protein and mRNA caused by AMPH. Melatonin attenuated the AMPH-induced reduction in dopamine transporter (DAT) protein expression in the hippocampus and the reduction in mRNA expression in the ventral tegmental area (VTA). Immunofluorescence demonstrated that melatonin not only prevented the AMPH-induced loss of DAT and NMDA receptor but also prevented AMPH-induced α-synuclein overexpression in the dentate gyrus, CA1, and CA3. Melatonin decreased the AMPH-induced reduction in the protein and mRNA of the NMDA receptor downstream signaling molecule, calcium/calmodulin-dependent protein kinase II (CaMKII), and the melatonin receptors (MT1 and MT2). This study showed that melatonin prevented AMPH-induced toxicity in the hippocampus of postnatal rats possibly via its antioxidative effect and mitochondrial protection.