Effects of the I2-imidazoline receptor ligand LSL 60101 on various models of anorexia in rats

Microarray Analysis Revealed Inflammatory Transcriptomic Changes after LSL60101 Treatment in 5XFAD Mice Model

I2-IR have been found dysregulated in patients with neurodegenerative diseases, such as Alzheimer's disease (AD), in which the importance of neuroinflammation in the establishment and maintenance of cognitive decline is well-documented. To research the implication of I2-IR in neuroinflammatory pathways altered in AD, we determined the expression profile of genes associated with inflammation in the 5XFAD model treated with LSL60101, a well-established I2-IR ligand. Thus, we performed a qPCR array containing 84 inflammation-related genes. Hierarchical clustering analysis revealed three gene clusters, suggesting that treatment with LSL60101 affects the gene expression associated with inflammation in the 5XFAD model. Furthermore, we evaluated the functions of the three clusters; thereby performing a pathway enrichment analysis using the GO database. As we expected, clusters 2 and 3 showed alterations in the inflammatory response, chemotaxis and the chemokine-mediated signaling pathway, among others. To validate previous results from the gene profiling analysis, the expression levels of a representative subset of mRNAs were selected according to the intensity of the observed changes and their biological relevance. Interestingly, changes induced by LSL60101 in the 5XFAD model were validated for several genes. These results suggest that treatment with LSL60101 in the 5XFAD model reverses the inflammatory process during the development of AD.

Disease-modifying treatment with I2 imidazoline receptor ligand LSL60101 in an Alzheimer's disease mouse model: a comparative study with donepezil

BACKGROUND AND PURPOSE

The development of effective therapeutic strategies against Alzheimer's disease (AD) remains a challenge. I₂ imidazoline receptor ligands have a neuroprotective role in AD. Moreover, co-treatment of AChE inhibitors with neuroprotective agents have shown better effects on the prevention of dementia. Here, we assessed the potential therapeutic effect of the I₂ ligand, donepezil and their combination in 5XFAD mice.

EXPERIMENTAL APPROACH

5XFAD female mice were treated with low doses (1 mg·kg^-1 ·day^-1 ) of LSL60101, donepezil and donepezil plus LSL60101, during 4 weeks per os. Novel object recognition, Morris water maze, open field, elevated plus maze and three-chamber tests were used to evaluate the cognitive and behavioural status after treatment. The effects on AD-like pathology were assessed with immunohistochemistry, western blot, ELISA and qPCR.

KEY RESULTS

Chronic low-dose treatment with LSL60101 and donepezil reversed cognitive deficits and impaired social behaviour. LSL60101 treatment did not affect anxiety-like behaviour in contrast to donepezil. In the 5XFAD brains, LSL60101 and donepezil/LSL60101 treatments attenuated amyloid-β pathology by decreasing amyloid-β₄₀ and amyloid-β₄₂ levels, amyloid-β plaque number and tau hyperphosphorylation. These alterations were accompanied by reduced microglia marker Iba-1 levels and increased Trem2 gene expression. LSL60101 and donepezil decreased glial fibrillary acidic protein (GFAP) astrocytic marker reactivity. However, only LSL60101 and donepezil/LSL60101 treatments significantly increased the synaptic marker levels of post-synaptic density protein 95 and synaptophysin.

CONCLUSION AND IMPLICATIONS

Chronic low-dose treatment with selective I₂ - ligands can be an effective treatment for AD and provide insights into combination treatments for symptomatic and disease-modifying drugs.

Potential serotonergic and noradrenergic involvement in the discriminative stimulus effects of the selective imidazoline I2-site ligand 2-BFI

The functional significance of imidazoline I2 binding sites is unknown but microdialysis studies have indicated that the administration of I2-site ligands leads to an increase in extracellular levels of monoamines. The specific I2-site ligand 2-(-2-benzofuranyl)-2-imidazoline (2-BFI) generates a cue in drug discrimination, thereby indicating functional consequences of I2-site ligand binding. In the present work, we explored the ability of selective noradrenergic and serotonergic ligands to substitute for 2-BFI. Hooded Lister rats were trained in two-lever operant chambers with condensed milk reward to distinguish 2-BFI (7 mg/kg) from saline vehicle, by pressing the correct lever to a predetermined success criterion. Training sessions were then interspersed with sessions in which animals were administered test substances and the proportion of lever presses on the 2-BFI-associated lever (substitution) recorded. Several agents exhibited significant partial substitution for 2-BFI: The monoamine-releasing agents D-amphetamine and fenfluramine dose-dependently substituted for 2-BFI, while norepinephrine (desipramine, reboxetine) and serotonin (clomipramine, citalopram) reuptake inhibitors substituted at one or more doses. Further investigation using specific receptor agonists and antagonists indicated a possible role for activation of alpha1-adrenoceptors but failed to support involvement of alpha2-adenoceptor, beta-adrenoceptor or 5-HT1A receptor activation. These results support the concept that the 2-BFI cue may contain both noradrenergic and serotonergic components.

Characterization of the discriminable stimulus produced by 2-BFI: effects of imidazoline I(2)-site ligands, MAOIs, beta-carbolines, agmatine and ibogaine

1. The molecular nature and functions of the I(2) subtype of imidazoline binding sites are unknown but evidence suggests an association with monoamine oxidase (MAO). Rats can distinguish the selective imidazoline I(2)-site ligand 2-BFI from vehicle in drug discrimination, indicating functional consequences of occupation of these sites. We have used drug discrimination to investigate the nature of the discriminable stimulus, especially in relation to MAO inhibition. 2. Following training to distinguish 2-BFI 7 mg kg(-1) i.p. from saline vehicle in two-lever operant-chambers, male Hooded Lister rats underwent sessions where test substances were given instead and the proportion of lever presses on the 2-BFI-associated lever (substitution) recorded. 3. 2-BFI; its cogeners BU216, BU224, BU226 and LSL60101; the reversible MAO-A inhibitors moclobemide and RO41-1049; the beta-carbolines harmane, norharmane and harmaline which also reversibly inhibit MAO-A, and the anti-addictive substance ibogaine exhibited potent, dose-dependent substitution for 2-BFI. 4. Agmatine, and LSL60125 substituted at one dose only. The reversible MAO-B inhibitors lazabemide and RO16-1649; the sigma(2)-site ligand SKF10,047 and the I(2A)-site ligand, amiloride, failed to substitute. The irreversible inhibitor of MAO, deprenyl, substituted for 2-BFI while clorgyline did not. 5. These results suggest imidazoline I(2) site ligands produce a common discriminable stimulus that appears associated with reversible inhibition of MAO-A rather than MAO-B, possibly through increases in extracellular concentration of one or more monoamines. Ibogaine exhibits a commonality in its subjective effects with those of I(2)-site ligands.