The neuroprotective effects of the melatonin receptor agonist agomelatine in a rat model on intracerebral haemorrhage

Abstract

Stroke is a common yet severe disease. Among all forms, intracerebral haemorrhage (ICH) is particularly devastating, often resulted in detrimental outcomes. This dissertation investigated the role of melatonergic receptor-mediated metabolism during ICH and whether administration of agomelatine, an antidepressant and melatonergic receptor agonist, is neuroprotective from damage induced by ICH on a rodent collagenase-induced ICH model. Luzindole, a non-selective melatonergic antagonist was used together with agomelatine for agonist-antagonist study. Right-sided ICH was induced on male Sprague-Dawley rats of 9 weeks of age with burr hole intra-striatal type IV collagenase infusion under general anaesthesia. Intraperitoneal administration of agomelatine 10 mg/kg and 40 mg/kg, and a combination of agomelatine 40 mg/kg with luzindole 30 mg/kg (all homogenized with 1 % hydroxyethylcellulose solution at 2 ml/kg as vehicle) was done at 2 hours, 24 hours and 48 hours post-ICH. Outcomes were measured in terms of expression of inflammatory cytokines TNF-α and IL-1β, apoptotic pathway markers Bax/Bcl-2 in perihaematomal tissues, haematoma volume and sensorimotor deficit in Rotarod test on Neurological deficit scale. Perihaematomal TNF-α level, as established by ELISA, was 33.8 ± 24.2, 24.2 ± 14.2, 46.0 ± 24.4 ng / g protein for vehicle, high-dose agomelatine and luzindole-agomelatine groups (n = 4). Marginal insignificance (p = 0.063) was observed between the agomelatine 40 mg/kg and luzindole-agomelatine group. Similar observation with dose-responsive relationship was seen with IL-1β. No statistically significant results were observed with Bax/Bcl-2 expression by Western blotting and haematoma volume analysis. Functionally high-dose agomelatine group outperformed the other groups in Rotarod test (119.7 ± 91.7 s, vs 87.9 to 97.6 s) (n = 13) at 3 days post-ICH, and luzindole-agomelatine group performed the worst (87.9 ± 38.1 s) (n = 6). A modest benefit not reaching statistical significance was seen in terms of post-ICH sensorimotor function recovery, but interpretation of such observation has been limited by a background of marked individual variability and potentially heterogenicity. In summary, the results from biochemical investigations could suggest existence of post-ICH endogenous melatonergic anti-inflammatory activity, which could be enhanced by agomelatine as an exogenous melatonergic agonist, or inhibited by introduction of an antagonist. This hypothesis correlated with the observations made in functional assessments. Further investigations with greater focus on inflammation pathways and markers over a longer period, and preferably carried in form of melatonergic receptor knock-out study, are indicated to further delineate the clinical significance of any anti-inflammatory effects conferred by melatonergic receptor activity post-ICH.