The effect of Boophone disticha on the regulation of Brain Derived Neurotrophic Factor gene expression in BALB/c mouse model of depression

Abstract

The mental disorder of depression ranks high amongst heterogeneous and disabling conditions on earth. As a complex disease, depression can be characterized by combinations of genetic and environmental factors. The current antidepressants come with adverse side effects and exert their therapeutic action only after prolonged treatment, as a consequence, the significance of developing faster-acting antidepressants cannot be overemphasized. The phytochemical analysis of Boophone disticha has shown to possess alkaloids, an abundance of alkaloids in the leave extracts of the plant contributes to its therapeutic abilities, possibly through interactions of the alkaloids (buphanamine and buphanidrine) to selective serotonin reuptake inhibitor (SSRI) site of the transporter of serotonin having high affinity for SERT.The brain-derived neurotrophic factor (BDNF) is a well-studied neurotrophic factor that is responsible for maintaining neurons and regulating synaptic . The complex gene structure of BDNF, located on chromosome 11 of the human genome, is regulated by multiple promoters. Strong evidence showed that low expression of BDNF can be associated with depression prognosis in patient/animal models. Interestingly, up-regulation of BDNF expression has been seen in response to depression treatment by antidepressants. Also, epigenetic modulation of BDNF gene and its receptor TrkB has been shown to alter BDNF expression profiles. Additionally, chromatin remodelling through acetylation and deacetylation plays an important role in brain associated conditions, with deacetylation resulting in repression of gene expression. histone deacetylase (HDAC), a form of chromatin remodelling is speculated to decrease histone acetylation at the BDNF promoters. The precise promoter responsible for BDNF expression on the onset of depression and response to treatment is yet to be elucidated. Furthermore, the molecular mechanism of epigenetic modulation of BDNF and its association with HDAC is yet to be unravelled. This study, therefore, suggested that the therapeutic benefits of Boophone disticha, ubiquitous plant widely used by indigenous people to treat ailments such as depression and anxiety, could be attributed to regulation of BDNF expression, impacting its activity and association with HDAC.Brain tissue obtained from 60 depressed/ and normal (healthy) male BALB/c mice representing the B .disticha, fluoxetine, non-gavage and normal treatments were used to study the gene expression of five promoters (1-5) of BDNF and HDAC5 using RT-qPCR. The nongavage representing group subjected to the force swim model was the positive control group for depression and the normal group represented by mice not subjected to force swim served as negative control (normal). The experimental group comprised of mice treated with B. disticha. Changes in the expression profiles of BDNF promoter 1-5 and HDAC were measured in relation to GAPDH using RT-qPCR. Furthermore, methylation specific PCR (MS-PCR) was used to assess the regulation and/or the methylation status of promoter 4 of BDNF which has been

described known to be regulated by epigenetics and also the protein expression profiles of BDNF in control and experimental mice were evaluated by ELISA and western blot techniques.It was found that in the fluoxetine (currently prescribed antidepressant) treated mice, BDNF was significantly up-regulated (>2-fold in all promoters), gene and protein levels. This is in contrast to the non-gavage mice, where down-regulation of BDNF was seen. While the 50% methanol and 50% water leaf extracts of B. disticha treatment was also successful in up-regulating BDNF in comparison to the non-gavage, but it did not have a similar effect to fluoxetine. The plant extracts up-regulated the relative expression levels of HDAC5 in relation to fluoxetine and the normal treatment. The observed gene expression of BDNF was correlated to protein expression wherein it was found that fluoxetine treatment enhanced the expression of BDNF protein in comparison to B. disticha.This study found variable promoter activities of BDNF in normal mice and also showed that treatment (fluoxetine and B. disticha) enhanced BDNF expression. However, the variable expression in normal mice indicates that this neurotrophic factor would not serve the therapeutic agent potential significantly. However, BDNF could be thought of as a marker that represents that an individual is responding to antidepressants due to its enhanced expression following treatment.