Intranasal administration of neuropeptides as a new therapeutic strategy to treat social and cognitive alterations relevant to schizophrenia
Year: 2016
Type: dissertation
Abstract: Schizophrenia is a chronic enduring disorder ranked among the most debilitating mental illnesses (Mueser & McGurk, 2004; Tandon, Keshavan, & Nasrallah, 2008). Although it has been vigorously studied over the past century, the etiology and pathophysiology of schizophrenia remains largely unknown and currently available treatments, in the form of antipsychotics, are mainly unsatisfactory (Insel, 2010; Tandon et al., 2008). Schizophrenia is characterized by three broad types of symptoms: positive symptoms, negative symptoms, and cognitive deficits. While drugs currently available for the treatment of this disorder are effective for positive symptoms, negative symptoms (including social impairments) and cognitive deficits still remain mainly untreatable.(Keefe et al., 2007; Neill et al., 2010). Negative and cognitive symptoms are more pervasive, fluctuate less over time than psychotic symptoms and are strongly associated with poor psychosocial functioning in community living and work (Kasper & Resinger, 2003; Mueser & McGurk, 2004; Tandon, Nasrallah, & Keshavan, 2009). Although there have been rapid progress in the development of non-invasive technologies to study human brain structure and function in the last two decades, there are still substantial limitations in our ability to investigate details of the physiology and molecular biology of the human brain (Nestler & Hyman, 2010a). To that end, it is imperative to have carefully validated animal models for continued progress in our understanding of pathophysiology and in the development and screening of novel therapeutic agents in order to enhance functional recovery of patients (Davis et al., 2013; Neill et al., 2010). Neuropeptides have an important role in intracerebral signaling and might have the potential to be used as therapeutic agents in many psychiatric and neurological diseases(Bedse, Di Domenico, Serviddio, & Cassano, 2015; Erbaş, Çınar, Solmaz, Çavuşoğlu, & Ateş, 2015; Nishimura, Murayama, & Takahashi, 2015; Reglodi et al., 2015, 2015). Unfortunately, they usually can’t be administered systemically due to the elevated hydrophilicity and molecular weight that prevent them to overcame the blood brain barrier. Intranasal administration might be a promising and non-invasive way of administration of neuropeptides: this administration route enables highly hydrophilic and high molecular weight molecules to bypass the blood-brain barrier permitting them to reach the brain in a non-invasive way. This way has been demonstrated in in humans that permits the delivery of biologically effective concentrations of many peptides to the brain without eliciting significantly eventual systemic hormone-like side effects (Born et al., 2002); This route of administration was tested also in mice and rats (Born et al., 2002; Neumann, Maloumby, Beiderbeck, Lukas, & Landgraf, 2013)and, recently, was successfully used specifically in the context of behavioural studies in in mice (Huang et al., 2014). The aim of the studies described in this thesis is to investigate, through the use of clinically-relevant animal models of schizophrenia, the pharmacogenetics behavioral effects of intranasal administration of two different neuropeptides: - oxytocin (OXT), a neurohypophyseal peptide suggested to have beneficial effects in social behaviors (Meyer-Lindenberg, Domes, Kirsch, & Heinrichs, 2011; Striepens, Kendrick, Maier, & Hurlemann, 2011) and currently in clinical studies for mental disorders characterized by social behavioral alterations such as autism (Anagnostou et al., 2012; Guastella et al., 2010) and schizophrenia (Feifel et al., 2010). - CRF(6-33), a syntetic peptide designed to be an effective competitive antagonist for the binding between the endogenous CRF neuropeptide and its binding protein (CRFbp)(Sutton et al., 1995) suggested in preclinical ICV studies to be an effective pro cognitive agent with potential therapeutic applications (Stephen C. Heinrichs & Joppa, 2001; Stephen C. Heinrichs, 2003; Koob & Bloom, 1985) In previous work from our laboratory (Huang et al., 2014), we already implemented, for the first time, the use of intranasal oxytocin in C57BL/6J mice, checking different behavioral effects. Thus, we now tested the effects of intransal OXT in the schizophrenia-relevant dysbindin-1 knockout mouse model. Genetic variations of the dysbindin-1 gene (DTNBP 1) has been associated with susceptibility to schizophrenia (O’Tuathaigh et al., 2007; Ross, Margolis, Reading, Pletnikov, & Coyle, 2006; Straub et al., 2002) and severity of negative symptoms and cognitive dysfunction in schizophrenic patients (Burdick et al., 2007; DeRosse et al., 2006; Fanous et al., 2005; Straub et al., 2002). Thereafter, using a Dys knockout mutant mouse model, we demonstrated that both the heterozygous and homozygous knockout mice manifested a reduction in social interaction compared to wildtype mice. Similar social deficits in Dys mutant mice have been reported by other groups (Feng et al., 2008; Hattori et al., 2008). Interestingly, both chronic and acute intranasal OXT treatments were able to ameliorate the social deficits observed in the Dys knockout mice. These data suggest that intranasal oxytocin might be beneficial to subjects with genetic modifications relevant to schizophrenia, while administration to healthy subjects has not significant behavioral effect or may eventually be detrimental (Huang et al., 2014). This opens new ways of exploration in relationship to the beneficial effects of OXT treatment and its utility in the clinical setting. The data (aforementioned) correlate well with the molecular data available. As a matter of fact, OXT receptors are downregulated in WT subjects that are chronically IN –OXT treated, and even mutant mice, though treated with the same therapeutic protocol, show that the receptors are not subject to variation , compared to the control subjects treated with the vehicle substance only. Indeed, after being chronically treated, WT mice showed a decrease in social behaviour, while mutant mice (under an equivalent OXT treatment) showed an increase in social behaviour. For the CRF(6-33) part, in order to set the ground for future studies with genetically modified mice, disease-related mouse models and facilitate inter-laboratory comparisons, we first tested the effects of both chronic and acute intranasal CRF treatments in C57BL/6J mice. Considered that OXT did not show significant improvement in cognitive performance, we chose to target these functions with a different peptide that in previous intracerebroventricular studies had shown to improve cognitive functions (Behan et al., 1995; Eckart et al., 1999; S C Heinrichs et al., 1997; Stephen C Heinrichs & Koob, 2004; Stephen C. Heinrichs & Joppa, 2001; Stephen C. Heinrichs, 2003; Koob & Bloom, 1985; Lee, Lee, Wang, & Lin, 1993; Lee & Sung, 1989; Thompson, Erickson, Schulkin, & Rosen, 2004) had shown to improve cognitive functions . To asses cognitive functions we used a modified version of the 5-Choice Serial Reaction Time Task (5-csrtt), a rodent test designed as analog of the Continuous Performance Test (cpt) used to asses quantitatively attentional control in humans (Amitai & Markou, 2011). The modifications are intended to reduce the time needed to train the animals , reduce stressful manipulations as food restriction or single housing. Additionally, several new manipulations have been implemented to investigate various specific cognitive functions such as attention, broad monitoring / compulsivity, response disinhibition/ impulsivity, distractibility and processing speed. We were able to demonstrate that the intranasal administration of CRF(6-33) can produce selective behavioral effects in mice. In particular, acute administration was able to improve accuracy of responses and reduce impulsivity, while chronic administrations produced a delay in correct responses. Gene expression studies with real time PCR are starting to suggest that the CRF(6-33) is able to reach the brain, as both CRFr1 and CRFbp were altered following intranasal CRF(6-33) in different and specific brain areas (i.e. Hippocampus and Prefrontal Cortex ). Subsequent dose-response tests confirmed the ability of evocate behavioral effects with a much lower dose of CRF(6-33). Moreover, we discovered a rebound effect in impulsive behavior the day after administration of higher doses.. This detrimental effect was absent with the lowest doses that was still able to significantly reduce impulsive behavior. Lastly we tested ability of CRF(6-33) to ameliorate an impulsive phenotype in a genetic modified mouse model of schizophrenia. The chosen model was a double mutant for Dysbindin and for the receptor D2. The D2 receptor that had proven in previous test to have an increased impulsive behaviour. The dopamine D2 receptor (D2) gene is another important risk gene identified for schizophrenia. Functional genetic variants in the D2 gene have been found to be differently expressed in patients with schizophrenia (Kaalund et al., 2013) and might modulate schizophrenia-related phenotypes by modifying the ratio of the short isoform (D2S) to the long isoform (D2L) (Bertolino et al., 2009). Heterozigote mutant for D2L has an increased D2S (receptor D2 short form)/ D2L (receptor D2 long form) ratio. From preliminary data CRF(6-33) was not able to significantly affect impulsive behaviour in double heterozygote Dys +/- D2L +/- . Interestigly, in single heterozygote Dys +/- was observed a trend of increased impulsivity il CRF(6-33) group suggesting a detrimental interaction with Dys deficient genotype. From this studies we can conclude that both OXT than CRF(6-33) have the potential to be used for treatment, respectively of social and impulsivity deficits. For OXT so far we observed a positive interaction with Dys deficient genotype , that needs to be confirmed in other schizophrenia relevant mouse models of social deficits. CRF(6-33) so f
Author: Giuliano Gentili
Language: English
Subfield: Psychiatry and Mental health
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2558451992