Antiretroviral medications disrupt microglial phagocytosis of β-amyloid and increase its production by neurons: Implications for HIV-associated neurocognitive disorders

Up to 50% of long-term HIV infected patients, including those with systemically well-controlled infection, commonly experience memory problems and slowness, difficulties in concentration, planning, and multitasking. Deposition of Aβ plaques is also a common pathological feature of HIV infection. However, it is not clear whether this accumulation is due to AD-like processes, HIV-associated immunosuppression, Tat protein-induced Aβ elevations, and/or the effects of single highly active antiretroviral therapy (ART). Here we evaluated the effects of several ART medications (Zidovudine, Lamivudine, Indinavir, and Abacavir) alone and in combination on: 1) Aβ1-40, 42 generation in murine N2a cells transfected with the human "Swedish" mutant form of APP; 2) microglial phagocytosis of FITC-Aβ1-42 peptides in cultured murine N9 microglia. We report for the first time that these antiretroviral compounds (10 μM) generally increase Aβ generation (~50-200%) in SweAPP N2a cells and markedly inhibit microglial phagocytosis of FITC-Aβ1-42 peptides in murine microglia. The most significant amyloidogenic effects were observed with combined ART (p < 0.05); suggesting certain ART medications may have additive amyloidogenic effects when combined. As these antiretroviral compounds are capable of penetrating the blood brain barrier and reaching the concentrations employed in the in vitro studies, these findings raise the possibility that ART may play a casual role in the elevated Aβ found in the brains of those infected with HIV. Therefore these compounds may consequently contribute to cognitive decline observed in HIV associated neurocognitive disorders (HAND)

Stimulation of cannabinoid receptor 2 (CB(2)) suppresses microglial activation

BACKGROUND: Activated microglial cells have been implicated in a number of neurodegenerative disorders, including Alzheimer's disease (AD), multiple sclerosis (MS), and HIV dementia. It is well known that inflammatory mediators such as nitric oxide (NO), cytokines, and chemokines play an important role in microglial cell-associated neuron cell damage. Our previous studies have shown that CD40 signaling is involved in pathological activation of microglial cells. Many data reveal that cannabinoids mediate suppression of inflammation in vitro and in vivo through stimulation of cannabinoid receptor 2 (CB(2)). METHODS: In this study, we investigated the effects of a cannabinoid agonist on CD40 expression and function by cultured microglial cells activated by IFN-γ using RT-PCR, Western immunoblotting, flow cytometry, and anti-CB(2 )small interfering RNA (siRNA) analyses. Furthermore, we examined if the stimulation of CB(2 )could modulate the capacity of microglial cells to phagocytise Aβ(1–42 )peptide using a phagocytosis assay. RESULTS: We found that the selective stimulation of cannabinoid receptor CB(2 )by JWH-015 suppressed IFN-γ-induced CD40 expression. In addition, this CB(2 )agonist markedly inhibited IFN-γ-induced phosphorylation of JAK/STAT1. Further, this stimulation was also able to suppress microglial TNF-α and nitric oxide production induced either by IFN-γ or Aβ peptide challenge in the presence of CD40 ligation. Finally, we showed that CB(2 )activation by JWH-015 markedly attenuated CD40-mediated inhibition of microglial phagocytosis of Aβ(1–42 )peptide. Taken together, these results provide mechanistic insight into beneficial effects provided by cannabinoid receptor CB(2 )modulation in neurodegenerative diseases, particularly AD

Spirulina Promotes Stem Cell Genesis and Protects against LPS Induced Declines in Neural Stem Cell Proliferation

Adult stem cells are present in many tissues including, skin, muscle, adipose, bone marrow, and in the brain. Neuroinflammation has been shown to be a potent negative regulator of stem cell and progenitor cell proliferation in the neurogenic regions of the brain. Recently we demonstrated that decreasing a key neuroinflammatory cytokine IL-1β in the hippocampus of aged rats reversed the age-related cognitive decline and increased neurogenesis in the age rats. We also have found that nutraceuticals have the potential to reduce neuroinflammation, and decrease oxidative stress. The objectives of this study were to determine if spirulina could protect the proliferative potential of hippocampal neural progenitor cells from an acute systemic inflammatory insult of lipopolysaccharide (LPS). To this end, young rats were fed for 30 days a control diet or a diet supplemented with 0.1% spirulina. On day 28 the rats were given a single i.p. injection of LPS (1 mg/kg). The following day the rats were injected with BrdU (50 mg/kg b.i.d. i.p.) and were sacrificed 24 hours after the first injection of BrdU. Quantification of the BrdU positive cells in the subgranular zone of the dentate gyrus demonstrated a decrease in proliferation of the stem/progenitor cells in the hippocampus as a result of the LPS insult. Furthermore, the diet supplemented with spirulina was able to negate the LPS induced decrease in stem/progenitor cell proliferation. In a second set of studies we examined the effects of spirulina either alone or in combination with a proprietary formulation (NT-020) of blueberry, green tea, vitamin D3 and carnosine on the function of bone marrow and CD34+ cells in vitro. Spirulina had small effects on its own and more than additive effects in combination with NT-020 to promote mitochondrial respiration and/or proliferation of these cells in culture. When examined on neural stem cells in culture spirulina increased proliferation at baseline and protected against the negative influence of TNFα to reduce neural stem cell proliferation. These results support the hypothesis that a diet enriched with spirulina and other nutraceuticals may help protect the stem/progenitor cells from insults

Changes in Brain MicroRNAs Contribute to Cholinergic Stress Reactions

Mental stress modifies both cholinergic neurotransmission and alternative splicing in the brain, via incompletely understood mechanisms. Here, we report that stress changes brain microRNA (miR) expression and that some of these stress-regulated miRs regulate alternative splicing. Acute and chronic immobilization stress differentially altered the expression of numerous miRs in two stress-responsive regions of the rat brain, the hippocampal CA1 region and the central nucleus of the amygdala. miR-134 and miR-183 levels both increased in the amygdala following acute stress, compared to unstressed controls. Chronic stress decreased miR-134 levels, whereas miR-183 remained unchanged in both the amygdala and CA1. Importantly, miR-134 and miR-183 share a common predicted mRNA target, encoding the splicing factor SC35. Stress was previously shown to upregulate SC35, which promotes the alternative splicing of acetylcholinesterase (AChE) from the synapse-associated isoform AChE-S to the, normally rare, soluble AChE-R protein. Knockdown of miR-183 expression increased SC35 protein levels in vitro, whereas overexpression of miR-183 reduced SC35 protein levels, suggesting a physiological role for miR-183 regulation under stress. We show stress-induced changes in miR-183 and miR-134 and suggest that, by regulating splicing factors and their targets, these changes modify both alternative splicing and cholinergic neurotransmission in the stressed brain

Nicotinic Receptors Underlying Nicotine Dependence: Evidence from Transgenic Mouse Models.

Nicotine underlies the reinforcing properties of tobacco cigarettes and e-cigarettes. After inhalation and absorption, nicotine binds to various nicotinic acetylcholine receptor (nAChR) subtypes localized on the pre- and postsynaptic membranes of cells, which subsequently leads to the modulation of cellular function and neurotransmitter signaling. In this chapter, we begin by briefly reviewing the current understanding of nicotine's actions on nAChRs and highlight considerations regarding nAChR subtype localization and pharmacodynamics. Thereafter, we discuss the seminal discoveries derived from genetically modified mouse models, which have greatly contributed to our understanding of nicotine's effects on the reward-related mesolimbic pathway and the aversion-related habenulo-interpeduncular pathway. Thereafter, emerging areas of research focusing on modulation of nAChR expression and/or function are considered. Taken together, these discoveries have provided a foundational understanding of various genetic, neurobiological, and behavioral factors underlying the motivation to use nicotine and related dependence processes, which are thereby advancing drug discovery efforts to promote long-term abstinence

New Pharmacological Agents to Aid Smoking Cessation and Tobacco Harm Reduction: What has been Investigated and What is in the Pipeline?

A wide range of support is available to help smokers to quit and aid attempts at harm reduction, including three first-line smoking cessation medications: nicotine replacement therapy, varenicline and bupropion. Despite the efficacy of these, there is a continual need to diversify the range of medications so that the needs of tobacco users are met. This paper compares the first-line smoking cessation medications to: 1) two variants of these existing products: new galenic formulations of varenicline and novel nicotine delivery devices; and 2) twenty-four alternative products: cytisine (novel outside of central and eastern Europe), nortriptyline, other tricyclic antidepressants, electronic cigarettes, clonidine (an anxiolytic), other anxiolytics (e.g. buspirone), selective 5-hydroxytryptamine (5-HT) reuptake inhibitors, supplements (e.g. St John’s wort), silver acetate, nicobrevin, modafinil, venlafaxine, monoamine oxidase inhibitors (MAOI), opioid antagonist, nicotinic acetylcholine receptors (nAChR) antagonists, glucose tablets, selective cannabinoid type 1 receptor antagonists, nicotine vaccines, drugs that affect gamma-aminobutyric acid (GABA) transmission, drugs that affect N-methyl-D-aspartate receptors (NMDA), dopamine agonists (e.g. levodopa), pioglitazone (Actos; OMS405), noradrenaline reuptake inhibitors, and the weight management drug lorcaserin. Six criteria are used: relative efficacy, relative safety, relative cost, relative use (overall impact of effective medication use), relative scope (ability to serve new groups of patients), and relative ease of use (ESCUSE). Many of these products are in the early stages of clinical trials, however, cytisine looks most promising in having established efficacy and safety and being of low cost. Electronic cigarettes have become very popular, appear to be efficacious and are safer than smoking, but issues of continued dependence and possible harms need to be considered

Inhibition of G Protein-Activated Inwardly Rectifying K+ Channels by Different Classes of Antidepressants

Various antidepressants are commonly used for the treatment of depression and several other neuropsychiatric disorders. In addition to their primary effects on serotonergic or noradrenergic neurotransmitter systems, antidepressants have been shown to interact with several receptors and ion channels. However, the molecular mechanisms that underlie the effects of antidepressants have not yet been sufficiently clarified. G protein-activated inwardly rectifying K+ (GIRK, Kir3) channels play an important role in regulating neuronal excitability and heart rate, and GIRK channel modulation has been suggested to have therapeutic potential for several neuropsychiatric disorders and cardiac arrhythmias. In the present study, we investigated the effects of various classes of antidepressants on GIRK channels using the Xenopus oocyte expression assay. In oocytes injected with mRNA for GIRK1/GIRK2 or GIRK1/GIRK4 subunits, extracellular application of sertraline, duloxetine, and amoxapine effectively reduced GIRK currents, whereas nefazodone, venlafaxine, mianserin, and mirtazapine weakly inhibited GIRK currents even at toxic levels. The inhibitory effects were concentration-dependent, with various degrees of potency and effectiveness. Furthermore, the effects of sertraline were voltage-independent and time-independent during each voltage pulse, whereas the effects of duloxetine were voltage-dependent with weaker inhibition with negative membrane potentials and time-dependent with a gradual decrease in each voltage pulse. However, Kir2.1 channels were insensitive to all of the drugs. Moreover, the GIRK currents induced by ethanol were inhibited by sertraline but not by intracellularly applied sertraline. The present results suggest that GIRK channel inhibition may reveal a novel characteristic of the commonly used antidepressants, particularly sertraline, and contributes to some of the therapeutic effects and adverse effects