Minocycline mitigates tau pathology via modulating the TLR-4/NF-Ðºß signalling pathway in the hippocampus of neuroinflammation rat model.

INTRODUCTION: The neuroinflammatory response was seen to impact the formation of phosphorylated tau protein in Alzheimer's disease (AD). This study aims to investigate the molecular mechanism of minocycline in reducing phosphorylated tau protein formation in the hippocampus of lipopolysaccharide (LPS)-induced rats. METHODS: Fifty adult male Sprague Dawley (SD) rats were randomly allocated to 1 of 5 groups: control, LPS (5 mg/kg), LPS + minocycline (25 mg/kg), LPS + minocycline (50 mg/kg) and LPS + memantine (10 mg/kg). Minocycline and memantine were administered intraperitoneally (i.p) for two weeks, and LPS was injected i.p. once on day 5. ELISA was used to determine the level of phosphorylated tau protein in SD rats' hippocampal tissue. The density and expression of Toll-like receptor-4 (TLR-4), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-кß), tumour necrosis factor-alpha (TNF-α), and cyclooxygenase (COX)-2 were determined using Western blot and immunohistochemistry. RESULTS: Minocycline, like memantine, prevented LPS-induced increasein phosphorylated tau protein level suggested via reduced density and expression of TLR-4, NF-кß, TNF-αand COX-2 proteins in rat hippocampal tissue. Interestingly, higher doses were shown to be more neuroprotective than lower doses. CONCLUSION: This study suggests that minocycline suppresses the neuroinflammation signalling pathway and decreased phosphorylated tau protein formation induced by LPS in a dose-dependent manner. Minocycline can be used as a preventative and therapeutic drug for neuroinflammatory diseases such as AD.

Memantine, an NMDA receptor antagonist, protected the brain against the long-term consequences of sepsis in mice.

AIMS: Long-term neuroinflammation and brain dysfunction have frequently been reported in sepsis survivors. In this study, the protective effect of memantine (an NMDA receptor antagonist) on the long-term consequences of sepsis on the brain was investigated in mice. MATERIALS AND METHODS: Eighty-five male C57 mice were included. Memantine was administrated through gavage at 5, 10, and 20 mg/kg three days before sepsis and continued for three days after sepsis induction. Sepsis was induced by intraperitoneal injection of 5 mg/kg LPS. A cohort of mice was sacrificed on the 4th day post sepsis to measure NF-κB, TNF-α, and IL-1ß mRNA expression and oxidative stress markers in the brain. The second cohort was used for behavioral tests one month after sepsis induction and then sacrificed for oxidative stress markers and acetylcholinesterase (AChE) activity measurement. KEY FINDINGS: MDA levels and mRNA expression of NF-κB, TNF-α, and IL-1ß ameliorated by memantine at the early days of sepsis induction, and total thiol content and SOD activity were increased. Post-septic mice showed significant disruption of recognition memory in novel object recognition (NOR) and depressive and anxiety-like behaviors in tail suspension test, elevated plus maze (EPM), and open field tests one month after sepsis. Memantine at 10 and 20 mg/kg dose-dependently ameliorated behavioral abnormalities, reduced AChE activity and MDA levels, and enhanced SOD activity and thiol content one month after sepsis. SIGNIFICANCE: These findings suggest that early treatment of septic mice with memantine could ameliorate brain inflammation and oxidative damage and prevent long-term behavioral consequences of sepsis.

Memantine has a nicotinic neuroprotective pathway in acute hippocampal slices after an NMDA insult.

Memantine is a non-competitive antagonist with a moderate affinity to the N-methyl-d-Aspartate (NMDA) receptor. The present study assessed memantine's neuroprotective activity using electrophysiology of ex-vivo hippocampal slices. Interestingly, a nicotinic component was necessary for memantine's neuroprotection (NP). Memantine demonstrated a bell-shaped dose-response curve of NP against NMDA. Memantine was neuroprotective at concentrations below 3 µM, but the NP declined at higher concentrations (>3 µM) when memantine inhibits the NMDA receptor. Additional evidence that memantine NP is mediated by an alternate mechanism independent of the inhibition of the NMDA receptor is supported by its ability to protect neurons when applied before or after the NMDA insult and in the presence of D(-)-2-Amino-5-phosphonopentanoic acid (APV), the standard NMDA receptor inhibitor. We found several similarities between the memantine NP mechanism and the neuroprotective nicotinic drug, the 4R cembranoid. Memantine's NP requires the release of acetylcholine, the activation of α4ß2, and is independent of MEK/MAPK signaling. Both 4R and memantine require the activation of PI3K/AKT for NP against NMDA-mediated excitotoxicity, although at different concentrations. In conclusion, our studies show memantine is neuroprotective through a nicotinic pathway, similar to the nicotinic drug 4R. This information leads to a better understanding of memantine's mechanisms of action and explains its dose-dependent effectiveness in Alzheimer's and other neurological disorders.

Memantine ameliorates oxaliplatin-induced neurotoxicity via mitochondrial protection.

Oxaliplatin is an effective chemotherapeutic agent for the treatment of malignant tumors. However, severe oxaliplatin-induced neurotoxicity has been well documented. Memantine is a drug for the management of Alzheimer's Disease (AD) due to its promising neuroprotective properties. We hypothesize that Memantine possesses a beneficial role against chemotherapy-induced neuronal damages. In this study, we established an oxaliplatin-induced neurotoxicity assay model in human SHSY-5Y neuronal cells and investigated the protective effect of Memantine. We showed that Memantine treatment ameliorated oxaliplatin-elevated intracellular production of reactive oxygen species (ROS), lipid product malondialdehyde (MDA), and NOX-2 expression. Memantine alleviated impairment of the mitochondrial membrane potential and ATP production by oxaliplatin. As a result, Memantine showed a protective role against oxaliplatin-induced cytotoxicity. Moreover, the terminal deoxynucleotidyl Transferase-mediated dUTP nick end labeling (TUNEL) apoptosis assay revealed that Memantine protected oxaliplatin-induced apoptosis through mitigating the ratio of Bax/Bcl-2 and Caspase-3 cleavage. We concluded Memantine ameliorated the neurotoxicity of oxaliplatin in a mitochondrial-dependent pathway.

Multifunctional memantine nitrate significantly protects against glutamate-induced excitotoxicity via inhibiting calcium influx and attenuating PI3K/Akt/GSK3beta pathway.

Overactivation of N-methyl-D-aspartate (NMDA) receptors has been associated with neurodegenerative disorders such as Alzheimer's disease (AD), cerebral vascular disorders and amyotrophic lateral sclerosis (ALS). We have previously designed and synthesized a series of memantine nitrate and some of them have shown vessel dilatory effects and neuroprotective effects; however, the detailed mechanisms have not been elucidated. In this study, we further demonstrated that memantine nitrate-06 (MN-06), one of the novel compounds derived from memantine, possessed significant neuroprotective effects against glutamate-induced excitotoxicity in rat primary cerebellar granule neurons (CGNs). Pretreatment of MN-06 reversed the activation of GSK3b and the suppression of phosphorylated Akt induced by glutamate. In addition, the neuroprotective effects of MN-06 could be abolished by LY294002, the specific phosphatidylinositol 3-kinase (PI3-K) inhibitor. Ca2+ imaging shown that pretreatment of MN-06 prevented Ca2+ influx induced by glutamate. Moreover, MN-06 might inhibit the NMDA-mediated current by antagonizing NDMA receptors, which was further confirmed by molecular docking simulation. Taken together, MN-06 protected against glutamate-induced excitotoxicity by blocking calcium influx and attenuating PI3-K/Akt/GSK-3b pathway, indicating that MN-06 might be a potential drug for treating neurodegenerative disorders.

Lactoferrin Coupled Lower Generation PAMAM Dendrimers for Brain Targeted Delivery of Memantine in Aluminum-Chloride-Induced Alzheimer's Disease in Mice.

Lower generation PAMAM dendrimers have an immense potential for drug delivery with lower toxicity, but these dendrimers yet need certain basic ameliorations. In this study, the brain delivery potential of the synthesized PAMAM-Lf (lower generation PAMAM and lactoferrin conjugate) loaded with memantine (MEM) was explored and evaluated in vitro and in vivo in the disease-induced mouse model. The developed nanoscaffolds were characterized for size, zeta potential and in vitro release. Increase in the average size from 11.54 ± 0.91 to 131.72 ± 4.73 nm, respectively, was observed for drug-loaded PAMAM (i.e., PAMAM-MEM) and PAMAM-Lf (i.e., MEM-PAMAM-Lf).  Release profile of MEM from MEM-PAMAM-Lf was slow and sustained up to 48 h. In vivo biodistribution in the Sprague-Dawley rat model revealed that the brain uptake of MEM-PAMAM-Lf was significantly higher than that of MEM alone. The behavioral response study in the healthy rats did not result in any significant changes. The in vivo study in an AlCl3-induced Alzheimer's (AD) mice model showed a significant improvement in behavioral responses. Optical density, which reflects the acetylcholinesterase (AChE) activity, was highest in the AL group 0.16 ± 0.01 (higher than the CON group, 0.09 ± 0.02; p < 0.05). No significant suppression of AChE activity was recorded in all the other treated groups. Similarly, the DOPAmine and 3,4 dihydroxyphenylacetic acid (DOPAC) levels were unaffected by the developed formulations. The study reported improved brain bioavailability of MEM in AlCl3-induced Alzheimer's mice leading to improved memory, with the resultant mechanism behind in a descriptive manner. This study is among the preliminary studies reporting the memory improvement aspect of PAMAM-Lf conjugates for MEM in AlCl3-AD induced mice. The formulation developed was beneficial in AD-induced mice and had a significant impact on the memory aspects.

A combination of running and memantine increases neurogenesis and reduces activation of developmentally-born dentate granule neurons in rats.

During hippocampal-dependent memory formation, sensory signals from the neocortex converge in the dentate gyrus. It is generally believed that the dentate gyrus decorrelates inputs in order to minimize interference between codes for similar experiences, often referred to as pattern separation. The proportion of dentate neurons that are activated by experience is therefore likely to impact how memories are stored and separated. Emerging evidence from mouse models suggests that adult-born neurons can both increase and decrease activity levels in the dentate gyrus. However, the conditions that determine the direction of this modulation, and whether it occurs in other species, remains unclear. Furthermore, since the dentate gyrus is composed of a heterogeneous population of cells that are born throughout life, newborn neurons may not modulate all cells equally. We aimed to investigate whether adult neurogenesis in rats regulates activity in dentate gyrus neurons that are born at the peak of early postnatal development. Adult neurogenesis was increased by subjecting rats to an alternating running and memantine treatment schedule, and it was decreased with a transgenic GFAP-TK rat model. Activity was measured by Fos expression in BrdU+ cells after rats explored a novel environment. Running+memantine treatment increased adult neurogenesis by only 17%, but completely blocked experience-dependent Fos expression. In contrast, GFAP-TK rats had a 68% reduction in adult neurogenesis but normal experience-dependent Fos expression. The inconsistent relationship between neurogenesis and Fos expression suggests that neurogenesis does not regulate DG activity during exploration of a novel environment. Nonetheless, running and memantine may benefit disorders where there is elevated activity in the dentate gyrus, such as anxiety and age-related memory impairments.

Memantine prodrug as a new agent for Alzheimer's Disease.

Hydrogen sulphide has recently drawn much attention due to its potent anti-inflammatory and neuroprotective roles in brain functions. The purpose of the current study was to exploit these beneficial properties of H2S to design a new agent for the treatment of Alzheimer's disease (AD). To pursue our aims, we replaced the free amine group of memantine with an isothiocyanate functionality as a putative H2S-donor moiety. The new chemical entity, named memit, was then tested in vitro to determine whether it retains the pharmacological profile of the "native drug", while also providing a source of H2S in the CNS. Indeed, Memit showed the ability to release H2S through a cysteine-mediated mechanism, thus generating memantine. Moreover, the new hybrid molecule exerts protective effects against neuronal inflammation and induces a drastic fall in ROS production. In addition, memit was also able to reduce the Aß(1-42) self-induced aggregation and exerted cytoprotective effect against Aß oligomers-induced damage in both human neurons and rat microglia cells. Finally, similarly to memantine, the new compound promotes autophagy, a complex process required for cellular homeostasis in cell survival that results to be altered in neurodegenerative diseases. In conclusion, our study revealed that memit is a prodrug of memantine. Further in vivo studies will be necessary to fully investigate the synergic or cumulative effects due to the H2S-releasing moiety and the native drug.

Amyloid-beta Interactions with ABC Transporters and Resistance Modifiers.

BACKGROUND/AIM: Failure of cancer chemotherapy caused by multidrug resistance (MDR) of tumor cells is mediated by ABC transporters that reduce the uptake of cytotoxic agents. Similar transporters are responsible for amyloid clearance in nerve cells in Alzheimer's disease (AD). The aim of this study was to compare the biological effects of amyloid complexes of some known ABC transporter inhibitors e.g. disiloxanes. One of the most active fragments of the pathological "endogen" substrate responsible for AD was investigated in the presence of amyloid-beta fragment on the reversal of multidrug resistance and apoptosis induction on multidrug-resistant tumor cells in model experiments. MATERIALS AND METHODS: The efflux pump activity of the cells treated with amyloid-beta complexes was studied by Rhodamin-123 accumulation. Apoptosis induction was measured by staining of treated cells by Annexin-V and propidium iodine. The fluorescent activity FL-1 and FL-2 of the cells was measured and analyzed on a PARTEC FACScan instrument. RESULTS: The resistance modifiers: disiloxanes and memantine complexed with amyloid-beta 1-42 reduced the activity of ABC transporter in MDR tumor cells. Early apoptosis was moderately increased by amyloid-beta complexes. Late apoptosis and the number of total viable cells were not changed. CONCLUSION: Amyloid-beta and its complexes inactivate the efflux pump of tumor cells resulting in accumulation of amyloid. It is supposed that reduced membrane transport can explain the lower incidence of cancer in AD.

GluN2B subunit-containing NMDA receptor antagonists prevent Abeta-mediated synaptic plasticity disruption in vivo.

Currently, treatment with the relatively low-affinity NMDA receptor antagonist memantine provides limited benefit in Alzheimer's disease (AD). One probable dose-limiting factor in the use of memantine is the inhibition of NMDA receptor-dependent synaptic plasticity mechanisms believed to underlie certain forms of memory. Moreover, amyloid-beta protein (Abeta) oligomers that are implicated in causing the cognitive deficits of AD potently inhibit this form of plasticity. Here we examined if subtype-preferring NMDA receptor antagonists could preferentially protect against the inhibition of NMDA receptor-dependent plasticity of excitatory synaptic transmission by Abeta in the hippocampus in vivo. Using doses that did not affect control plasticity, antagonists selective for NMDA receptors containing GluN2B but not other GluN2 subunits prevented Abeta(1-42) -mediated inhibition of plasticity. Evidence that the proinflammatory cytokine TNFalpha mediates this deleterious action of Ass was provided by the ability of TNFalpha antagonists to prevent Abeta(1-42) inhibition of plasticity and the abrogation of a similar disruptive effect of TNFalpha using a GluN2B-selective antagonist. Moreover, at nearby synapses that were resistant to the inhibitory effect of TNFalpha, Abeta(1-42) did not significantly affect plasticity. These findings suggest that preferentially targeting GluN2B subunit-containing NMDARs may provide an effective means of preventing cognitive deficits in early Alzheimer's disease.

Pharmacological implications of two distinct mechanisms of interaction of memantine with N-methyl-D-aspartate-gated channels.

Unlike other N-methyl-D-aspartate receptor (NMDAR) antagonists, clinical trials have shown that memantine is clinically tolerated and effective in the treatment of Alzheimer's disease. The mechanism for memantine tolerability, however, remains contentious but may be partly explained by its uncompetitive antagonism. The specific site of memantine block in the NMDAR channel interacts with magnesium and is assumed to be at or near a narrow constriction representing the channel selectivity filter. A second, very low-affinity site of memantine action has also been reported. Here, using mutational analysis and substituted cysteine accessibility methods on recombinant NR1/NR2A NMDARs expressed in Xenopus oocytes, we precisely localize both the specific and second memantine-blocking sites. Intriguingly, memantine interacts with its specific blocking site in the same fashion as intracellular rather than extracellular Mg(2+). Thus, the N-site asparagine (N) in the M2 region of the NR1 subunit represents the dominant site for uncompetitive antagonism by memantine. The N and N + 1 site asparagines in NR2A produce strong electrostatic interactions with memantine. In contrast, the second (superficial) memantine-blocking site, located at the extracellular vestibule of the channel, appears to be nonspecific and overlaps the site occupied by the nonspecific pore blocker hexamethonium. Residues in the post-M3 segment of the NR1 subunit are not directly involved in memantine binding. The distinct patterns of interaction and the relative degree of affinity of memantine for these two binding sites contribute to the drug's excellent pharmacological profile of clinical tolerability. In the future, these parameters should be considered in searching for improved neuroprotective agents in this class.