Evaluating the neuropsychiatric properties of efavirenz in an inflammatory model of schizophrenia
Since the inception of the human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) epidemic, a collaborative effort between all branches of medicine contributed towards the establishment of highly active antiretroviral therapy (HAART). Efavirenz (EFV), a non-nucleoside reverse transcriptase inhibitor, used in combination treatment as part of HAART, presents with neuropsychiatric effects, possibly contributing towards its abuse potential. The impact of EFV abuse on mental health remains equivocal and holds the possibility of addiction or a substance-induced psychotic disorder (SIPD) development. Drug addiction is a chronic relapsing disorder, primarily characterized by a three-staged cycle, viz. intoxication, withdrawal and craving. Patients with a SIPD experience psychotic symptoms after sudden intoxication or withdrawal of addictive drugs and may develop schizophrenia (SCZ) later in life. SCZ is a debilitating disorder where patients experience a combination of positive-, negative- and cognitive symptoms. Specific brain regions (frontal cortex (FC), striatum and possibly the cerebellum) and neurological pathways implicated in the respective disorders may be partially overlapping which may explain why abusive substances may contribute towards the development of psychotic disorders. EFV exerts a variety of mechanisms which may contribute towards the development of these respective disorders, viz. an affinity for the serotonin 2A receptors and dopamine transporters (DAT) as well as the ability to alter regional brain monoamines and redox-inflammatory pathways. Pre-natal inflammation has been implicated in the pathophysiology of psychotic disorders and may contribute towards drug abuse later in life. Therefore, by simulating maternal infection in rodent dams via a bacterial endotoxin, lipopolysaccharide (LPS), a neurodevelopmental model of SCZ as well as its effects on drug abuse later in life can be established. Moreover, there are, no available treatment platform for EFV abuse (with or without contributary factors i.e. pre-natal inflammation) as well as its sequalae. N-acetylcysteine (NAC), a glutathione (GSH) precursor, may be a viable option as it has the capacity to modulate neurotransmission, inflammation and redox homeostasis. The association between psychotic disorders, EFV abuse and its treatment demands further investigation. This study aimed to investigate addictive- (by utilising the conditioned place preference (CPP) paradigm) and psychotic-like (by measuring locomotor activity and pre-pulse inhibition (PPI)) behaviours in rats after pre-natal exposure to bacterial LPS and/or post-natal EFV exposure, and its response to treatment with NAC. This study was approved (Ethics approval number: NWU-00162-18-S5) by the AnimCare animal research committee (NHREC reg. no. AREC-130913-015) North West University (NWU). All experimental animals used in this study were bred, supplied and housed at the Vivarium (SAVC reg. number FR15/13458; SANAS GLP compliance number G0019) of the Pre-Clinical Drug Development Platform at the NWU. Pregnant Sprague-Dawley rats (12/group) were exposed to either subcutaneous (SC) saline or 100 μg/kg LPS on gestational day 15/16. Male pups (n=96) born from these dams were then randomized into 8 groups (12/group). Starting on post-natal day (PND) 48 all rats were subjected to the CPP paradigm in a drug-free state to establish preference. From PND 49 until PND 54, exposure conditioning (in the CPP paradigm) was performed on alternative days for six days with either olive oil (vehicle) or 5 mg/kg EFV. On PND 55 the first CPP, locomotor activity and PPI were determined. Thereafter, rats received either saline (vehicle) or 100 mg/kg NAC SC for 14 days (PND 56-69). EFV conditioning and behavioural analyses were repeated as per the pre-treatment methodology on PND 70 and 71. The second CPP, locomotor activity and PPI were determined again on PND 72. On PND 73 rats were euthanised and plasma corticosterone (CORT) and GSH, as well as cerebellar c-Fos and striatal and frontal-cortical DAT & phosphoprotein phosphatase-1 regulatory subunit 1B (PPP1R1B)), were analysed. Sub-acute EFV (5 mg/kg) had no addictive-like (CPP) or SCZ-like, (locomotor activity and %PPI) behaviour (PND 55 and 72) compared to control groups. All peripheral (CORT and GSH) and neurochemical (c-Fos, DAT and PPP1R1P) biomarkers were in accordance and remained unchanged in the group exposed to sub-acute EFV alone. Pre-natal LPS (100 μg/kg) exposure significantly decreased the time spent in the drug-paired compartment (CPP), increased locomotor activity and induced significant %PPI deficits compared to control groups on PND 55. Pre-natal exposure to LPS decreased striatal DAT which were in accordance with the positive SCZ-like symptoms (hyper-locomotion and PPI deficits) observed in the respective groups. These alterations became more apparent in the LPS+EFV groups. The LPS+EFV groups presented with hyper-locomotion and aversive behaviour in the CPP paradigm as well as %PPI deficits on PND 55. LPS+EFV also induced a significant decrease in striatal PPP1R1B and DAT and an increase in plasma CORT and cerebellar c-Fos compared to control groups. No differences were observed in frontal cortical PPP1R1B and DAT across all treatment groups. On PND 72, no %PPI deficits were observed in any groups. Furthermore, on PND 72, the locomotor activity and the striatal PPP1R1B level of the LPS+EFV group correlated with the level of the control group. Literature indicate that, NAC’s therapeutic efficacy is based on its capacity to regulate GSH synthesis, however this was not observed in the LPS+EFV group. Therefore, NAC proved to be futile in this study and other mechanisms were considered such as the effects of CORT on dopamine transmission. To conclude, maternal LPS induced psychotic-like behaviour in off-spring, but not addictive-like behaviour, while post-natal EFV did not induce addictive- or psychotic-like behaviour. The behavioural (hyper-locomotion and %PPI deficits), peripheral (hyper-CORT) and neurochemical (decreased striatal PPP1R1B) alterations induced by LPS became more apparent after EFV exposure. NAC was not a viable treatment with regard to any of the bio-behavioural changes following EFV, LPS or LPS+EFV exposure. This study ultimately highlights the risks of EFV abuse in predisposed individuals.
- Health Sciences