Implications of Kynurenine Pathway Metabolism for the Immune System, Hypothalamic-Pituitary-Adrenal Axis, and Neurotransmission in Alcohol Use Disorder.

In recent years, there has been a marked increase in interest in the role of the kynurenine pathway (KP) in mechanisms associated with addictive behavior. Numerous reports implicate KP metabolism in influencing the immune system, hypothalamic-pituitary-adrenal (HPA) axis, and neurotransmission, which underlie the behavioral patterns characteristic of addiction. An in-depth analysis of the results of these new studies highlights interesting patterns of relationships, and approaching alcohol use disorder (AUD) from a broader neuroendocrine-immune system perspective may be crucial to better understanding this complex phenomenon. In this review, we provide an up-to-date summary of information indicating the relationship between AUD and the KP, both in terms of changes in the activity of this pathway and modulation of this pathway as a possible pharmacological approach for the treatment of AUD.

Increased Hippocampal Afterdischarge Threshold in Ketogenic Diet is Accompanied by Enhanced Kynurenine Pathway Activity.

The efficacy of a ketogenic diet (KD) in controlling seizure has been shown in many experimental and clinical studies, however, its mechanism of action still needs further clarification. The major goal of the present study was to investigate the influence of the commercially available KD and caloric restriction (CR) on the hippocampal afterdischarge (AD) threshold in rats, and concomitant biochemical changes, specifically concerning the kynurenine pathway, in plasma and the hippocampus. As expected, the rats on the KD showed higher AD threshold accompanied by increased plasma ß-hydroxybutyrate level compared to the control group and the CR rats. This group presented also lowered tryptophan and elevated kynurenic acid levels in plasma with similar changes in the hippocampus. Moreover, the KD rats showed decreased levels of branched chain amino acids (BCAA) and aromatic amino acids (AAA) in plasma and the hippocampus. No regular biochemical changes were observed in the CR group. Our results are analogous to those detected after single administrations of fatty acids and valproic acid in our previous studies, specifically to an increase in the kynurenine pathway activity and changes in peripheral and central BCAA and AAA levels. This suggests that the anticonvulsant effect of the KD may be at least partially associated with those observed biochemical alternations.

miR-9a-5p expression is decreased in the hippocampus of rats resistant to lamotrigine: A behavioural, molecular and bioinformatics assessment.

The major obstacle in developing new treatment strategies for refractory epilepsy is the complexity and poor understanding of its mechanisms. Utilizing the model of lamotrigine-resistant seizures, we evaluated whether changes in the expression of sodium channel subunits are responsible for the diminished responsiveness to lamotrigine (LTG) and if miRNAs, may also be associated. Male rats were administered LTG (5 mg/kg) before each stimulation during kindling acquisition. Challenge stimulation following LTG exposure (30 mg/kg) was performed to confirm resistance in fully kindled rats. RT-PCR was used to measure the mRNA levels of sodium channel subunits (SCN1A, SCN2A, and SCN3A) and miRNAs (miR-155-5p, miR-30b-5p, miR-137-3p, miR-342-5p, miR-301a-3p, miR-212-3p, miR-9a-5p, and miR-133a-3p). Western blot analysis was utilized to measure Nav1.2 protein, and bioinformatics tools were used to perform target prediction and enrichment analysis for miR-9a-5p, the only affected miRNA according to the responsiveness to LTG. Amygdala kindling seizures downregulated Nav1.2, miR-137-3p, miR-342-5p, miR-155-5p, and miR-9a-5p as well as upregulated miR-212-3p. miR-9a-5p was the only molecule decreased in rats resistant to LTG. The bioinformatic assessment and disease enrichment analysis revealed that miR-9a-5p targets expressed with high confidence in the hippocampus are the most significantly associated with epilepsy. Due to the miR-9a-5p dysregulation, major pathways affected are neurotrophic processes, neurotransmission, inflammatory response, cell proliferation and apoptosis. Interaction network analysis identified LTG target SCN2A as interacting with highest number of genes regulated by miR-9-5p. Further studies are needed to propose specific genes and miRNAs responsible for diminished responsiveness to LTG. miR-9a-5p targets, like KCNA4, KCNA2, CACNB2, SCN4B, KCNC1, should receive special attention in them.

mTOR and HDAC2 are simultaneously activated during electrically induced kindling of seizures.

Although neurotrophic pathways and epigenetic processes are believed to be significant contributors to epileptogenesis and epilepsy, therapies using modulators of these targets are still lacking. BDNF-TrkB-mTOR signalling and the REST/NRSF-coREST-HDAC2 system are critical pathways responsible for neurotrophic and epigenetic processes, respectively. In our study, we assessed whether these two pathways are activated in a kindling model of seizures. We assessed the protein and mRNA levels of BDNF, TrkB, mTOR, REST/NRSF, coREST and HDAC2 in the brain. The study results showed increased expression of BDNF and decreased coREST in rats subjected to electrical kindling compared to control animals. We also revealed increased expression of both mTOR and HDAC2 in the brain tissue of electrically stimulated animals. mRNA production did not follow the intensified mTOR and HDAC2 protein synthesis. Furthermore, increased expression of BDNF, mTOR and HDAC2 was observed in animals that did not fulfil the kindling criteria in comparison to fully kindled rats. In conclusion, our results suggest that during epileptogenesis, the BDNF/mTOR neurotrophic pathway is mainly activated, with TrkB playing a less important role. Furthermore, the epigenetic transcription factor REST/NRSF was not found to be critical for HDAC2 activation. The simultaneous activation of both mTOR and HDAC2 systems during epileptogenesis confirms multifactorial neuronal adaptation, including neurotrophic and epigenetic processes. Our results may indicate that similar to cancer studies, the coadministration of regulators of both system should be considered a new potential strategy for preventing epileptogenesis.

Pro-inflammatory cytokines, but not brain- and extracellular matrix-derived proteins, are increased in the plasma following electrically induced kindling of seizures.

BACKGROUND: The aim of the study was to evaluate the brain-derived proteins, extracellular matrix-derived protein and cytokines as potential peripheral biomarkers of different susceptibility to seizure development in an animal model of epilepsy evoked by chronic focal electrical stimulation of the brain. METHODS: The plasma levels of IL-1ß (interleukin 1ß), IL-6 (interleukin 6), UCH-L1 (ubiquitin C-terminal hydrolase 1), MMP-9 (matrix metalloproteinase 9), and GFAP (glial fibrillary acidic protein) were assessed. The peripheral concentrations of the selected proteins were analyzed according to the status of kindling and seizure severity parameters. In our study, increased concentrations of plasma IL-1ß and IL-6 were observed in rats subjected to hippocampal kindling compared to sham-operated rats. RESULTS: Animals that developed tonic-clonic seizures after the last stimulation had higher plasma concentrations of IL-1ß and IL-6 than sham-operated rats and rats that did not develop seizure. Elevated levels of IL-1ß and IL-6 were observed in rats that presented more severe seizures after the last five stimulations compared to sham-operated animals. A correlation between plasma IL-1ß and IL-6 concentrations was also found. On the other hand, the plasma levels of the brain-derived proteins UCH-L1, MMP-9, and GFAP were unaffected by kindling status and seizure severity parameters. CONCLUSIONS: The plasma concentrations of IL-1ß and IL-6 may have potential utility as peripheral biomarkers of immune system activation in the course of epilepsy and translational potential for future clinical use. Surprisingly, markers of cell and nerve ending damage (GFAP, UCH-L1 and MMP-9) may have limited utility.

The role of REST/NRSF, TrkB and BDNF in neurobiological mechanisms of different susceptibility to seizure in a PTZ model of epilepsy.

Global transcriptional disturbances are believed to play a major role in the course of epilepsy. Due to the high complexity, the neurobiological mechanisms underlying different susceptibility to seizure and epilepsy are not well known. A transcription factor called REST/NRSF (repressor element 1-silencing transcription factor/neuron-restrictive silencer factor) is believed to contribute to processes associated with seizure development. Its downstream genes, those encoding BDNF (brain-derived neurotrophic factor) and TrkB (BDNF receptor; tropomyosin receptor kinase B), are also thought to play a role. To verify this hypothesis, we used a PTZ kindling model of epilepsy and divided animals into groups according to their different susceptibility to seizure. The concentrations of REST/NRSF, BDNF, and TrkB protein and mRNA were measured in hippocampal homogenates. The level of REST/NRSF protein measured 24 h after the last PTZ injection was increased in animals resistant to kindling and was unchanged in groups of rats kindled after 5, 10 and 20 in.ections of PTZ. In contrast, TrkB protein concentration was enhanced in all kindled rats and was unchanged in the resistant rats. There were no changes in the protein concentration of BDNF in rats with different susceptibility to kindling; however, data from the combined kindled groups vs. the resistant group revealed an increased level of BDNF in resistant animals. In sum, the increased level of protein REST/NRSF in resistant animals may reflect its neuroprotective role against seizure development. The increased concentration of TrkB protein in kindled animals indicates its pivotal role in the process of epileptogenesis. We propose that in resistant rats, REST/NRSF could contribute to the prevention of TrkB activation related to seizures.