Studies on Garcinia mangostana Linn as a therapeutic intervention in an immune-inflammatory model of schizophrenia

Abstract

Schizophrenia is a life-long psychiatric disorder affecting 0.5-1% of the global population. This illness typically presents with severely debilitating clinical features in late adolescence, including positive, negative and cognitive symptoms. It is triggered in a multi-factorial manner by genetic, environmental and neurodevelopmental risk factors, contributing to the complexity of the disease. Prenatal factors are especially prominent in its aetiology, such as obstetric complications, substance abuse and prenatal maternal infection. Although the exact underlying mechanisms of schizophrenia remains unclear, oxidative stress and inflammation pathways have been implicated in its pathophysiology. Since currently-available treatment regimens for schizophrenia are notoriously inadequate for successful management of the clinical syndrome, novel strategies with regards to pharmacotherapy are urgently required. The utility of antioxidant treatment, especially from plant origin, holds substantial interest given the role of oxidative stress in schizophrenia. The pericarp of Garcinia mangostana Linn (GML) or mangosteen, an exotic fruit from Southeast Asia, contains numerous bioactive components including the dominant constituent α-mangostin (AM), that are known for their antioxidant and anti-inflammatory activity. Considering that prenatal inflammation have been associated with an increased susceptibility for schizophrenia, the maternal immune activation (MIA) animal model provides a valuable framework for exploring potential treatment strategies and underlying behavioural and biological deficits in schizophrenia. The rodent MIA model involves exposing a pregnant dam to an infectious agent during gestation to mimic prenatal infection, subsequently inducing a maternal immune response that alters normal neurodevelopment in the offspring and leading to behavioural abnormalities later in life. These altered behaviours bear a striking similarity to many of the positive, negative and cognitive symptoms of schizophrenia. This study aimed to assess the therapeutic effects of GML and AM, as stand-alone or adjunctive treatment to well-known antipsychotic, haloperidol (HAL), on behaviour and plasma and brain immune-inflammatory bio markers related to schizophrenia using a MIA animal model. Animals were bred and housed at the Vivarium of the North-West University (NWU) and all experiments were approved by the AnimCare animal research ethics committee of the NWU (Ethics approval number NWU-00376-16-A5). In the present study, prenatal immune activation was induced by exposing pregnant Sprague Dawley dams (n=18) to a bacterial endotoxin, lipopolysaccharide (LPS) (100 μg/kg) on gestational days 15 and 16. The male offspring from exposed dams were randomly divided into 6 treatment groups viz. vehicle; HAL (2 mg/kg); GML (50 mg/kg); HAL+GML; AM (20 mg/kg) and HAL+AM, consisting of ±12 rats per group. Control dams (n=3) and their offspring (n=8) were treated with vehicle. The offspring were treated via oral gavage with the respective drug treatments for 16 days from postnatal day (PND) 52 — 66. On the last two days of treatment, all groups were subjected to the following behavioural tests: (1) social interaction test (SIT) on day 12 of treatment; (2) prepulse inhibition (PPI) on day 13 of treatment (PND 63); (3) open field test (OFT) on day 14 of treatment (PND 64); (4) forced swim test (FST) on day 14 of treatment (PND 64). 36 hours after the last behavioural test, rats were euthanized by decapitation followed by the collection of trunk blood and brain tissue for peripheral and neurochemical analyses. Frontal cortical, hippocampal and striatal lipid peroxidation as well as plasma levels of pro-inflammatory cytokines, interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α), were measured. The MIA model elicited deficits in all behavioural paradigms studied, including reduced sensorimotor gating in the PPI test, increased locomotor activity in the OFT, depressive-like behaviour in the FST and an increase in social behaviour in the SIT. The MIA-induced deficits in %PPI were only successfully reversed by HAL and HAL+GML treatment. AM was the only treatment to significantly reduce MIA-induced locomotor hyperactivity. MIA-induced depressive-like behaviour was reversed by AM and GML alone and both in combination with HAL, with both combinations being more effective than HAL. Although HAL showed a trend towards antidepressant activity, this did not reach statistical significance. Concerning the SIT, prenatal LPS-challenged offspring showed an uncharacteristic increase in all social behaviours studied, a paradoxical finding when relating this to the well-known social deficits described in schizophrenia. Nevertheless, HAL+GML treatment reversed this finding, suggesting that further study in this regard is necessary. Elevated levels of lipid peroxidation markers were observed in the frontal cortex and striatum (but not hippocampus) of LPS exposed offspring, although only frontal cortical membrane damage was reversed by HAL and AM. Increased plasma concentrations of IL-6 and TNF-α in offspring of immune-compromised dams was reversed by GML, AM, HAL and combinations thereof, although no bolstering effect was observed with the latter. In conclusion, this study confirms that the MIA model is able to induce behavioural deficits akin to schizophrenia symptomology, except social interaction that needs further investigation, together with peripheral and central redox-inflammatory alterations in the offspring later in life. This suggests that prenatal inflammation may affect the normal process of neurodevelopment and result in increased susceptibility for developing schizophrenia during late adolescence. MIA-induced bio-behavioural alterations showed variable responses to treatment, with HAL, GML and AM, with depressive manifestations showing the best response to GML, AM and a bolstering of response when either are combined with HAL, while GML+AM presents with some benefit with respect to sensorimotor gating deficits. AM may be a more effective antioxidant than GML in vivo, although this does not imply improved therapeutic response. Overall, GML displayed superior effects over AM in combination with HAL and may be of clinical value as an adjunctive treatment to antipsychotic agents for improving the therapeutic outcome of schizophrenia.