Objective: NLRP3 inflammasome, a multiprotein complex that is located in immune system cells such as macrophages and microglia is formed by the activation of Nod-like receptor protein 3 (NLRP3) via danger signals including stress and is responsible initiating IL-1β and IL-18-mediated inflammatory responses. Since the involvement of cytokine mediated inflammatory responses are well established in depression and stress, the importance of the initiator mechanisms of inflammatory responses have recently been put forward (1). There are promising findings suggesting that the activation of NLRP3 might be interrelated with stress related conditions and inhibition of NLRP3 activation would stand for a novel therapeutic target. Herein, we investigated the effect of Agomelatine (Ago), a new antidepressant acting as an melatonergic receptor agonist and 5-HT2C receptor antagonist with reported immunomodulatory activities (2), on NLRP3 inflammasome activation in a sub-chronic restraint stress model of rats.
Methods: Sprague-Dawley rats weighing 250-350 g were divided into three groups; Control, Stress and Ago+Stress (40 mg/kg; p.o.) (n=6- 8 in each). Rats were subjected to restraint stress using immobilization cages between 08:00 am-12:00 am (4 hours/day) for 7 consecutive days except the control group. Ago was administered via intragastric gavage on the last two consecutive days (Day 6 and 7) and 60 min before the stress procedure. Rats were sacrificed at seventh day immediately after the last stress procedure. Rats’ prefrontal cortex was removed following brain dissection for investigating the NLRP3 inflammasome components and relevant cytokines. qPCR and flow cytometer were used for gene and protein expression analysis, respectively. Statistical analysis was conducted using one-way ANOVA followed by Tukey’s test and p<0.05 value was considered as statistically significance.
Results: In stress group, NLRP3, caspase-1, NF-κB, IL-1β and IL-18 gene expressions levels were significantly increased compared to control group. Acute Ago administration did not show any decreasing effect over these components. Moreover, NLRP3 (2 fold), caspase-1 (3 fold), NF-κB (4 fold) and IL-18 (3 fold) gene expressions were even higher in Ago+Stress group than stress alone. Similarly, protein expression analysis of pro-inflammatory cytokines including IL-1β, IL-6, TNF-α and IL-18 revealed that stress increased the protein levels of these cytokines however, those levels remained high in Ago+Stress group.
Conclusions: According to our preliminary data, acute administration of Ago was not effective on inhibiting NLRP3 inflammasome and relevant pro-inflammatory cytokines induced by sub-chronic restraint stress. Rather, it activated the majority of the NLRP3 components. The activity of melatonergic receptors has been previously reported to be associated with inflammatory processes by a number of studies. However, there is no consensus at present on whether this modulatory effect of melatonergic receptors is negative or positive. Further investigations are needed in order to examine the effect of chronic administration of Ago on NLRP3 inflammasome mediated inflammatory mechanisms in chronic stress conditions. This study was supported by Scientific Research Project Unit of Marmara University (SAG-E-120613-0233).