The role of apitoxin in alleviating propionic acid-induced neurobehavioral impairments in rat pups: The expression pattern of Reelin gene

Abstract

The efficacy of apitoxin (bee venom; BV) in ameliorating propionic acid (PPA) −induced neurobehavioral impacts was studied. Sixty rat pups were enrolled in a split litter design to six groups: a control group, a PPA-treated group, a BV-treated group, a BV/PPA protective group, a PPA/BV therapeutic group, and a BV/PPA/BV protective and therapeutic group. Exploratory, social, locomotor, and repetitive/stereotype-like activities were assessed and prosocial, empathy, and acquired behavior were evaluated. Levels of neurotransmitter including serotonin, dopamine, and gamma-aminobutyric acid (GABA) were determined and a quantitative analysis of Reelin gene expression was performed. PPA treatment induced several behavioral alterations, as reduced exploratory activity and social behaviors, increased repetitive/stereotypic behaviors, and hyperactivity. In addition, a marked decline of neurotransmitters and down-regulation of Reelin mRNA expression were observed. BV exhibited high efficiency in ameliorating the PPA-induced neurobehavioral alterations, particularly when applied both before and after PPA administration. Overall, the results implied that BV has merit as a candidate therapeutic treatment to alleviate PPA-induced neurobehavioral disorders.

Introduction

Approximately 3% of neurobehavioral disorders are directly induced by environmental exposures to toxicants and about 25% of these conditions are induced via interactions between inherited susceptibilities and environmental pollutants [1]. Propionic acid (PPA) is a short chain fatty acid and the main end product of numerous enteric gut bacteria [2], [3]. PPA is commonly utilized as a food preservative due to its effective preservative activity, mold inhibition and bactericidal properties. Also, PPA is an additive used in dairy products, poultry litter, livestock rations, and drinking water [4].

By both active and passive means, PPA easily crosses both the gut–blood and blood–brain barriers [5]. Brain exposure to PPA may disturb various neurophysiological processes, including neurotransmitter release, gene expression, mitochondrial function, immune modulation, gap junction gating, and behavior [6], [7]. In rat models, propionic acidemia resulted from either central (i.e., intraventricular) or peripheral (i.e., intraperitoneal or oral) administration of PPA have revealed diverse behaviors and brain markers including repetitive behaviors, impairments in cognition and social behavior, increases in oxidative stress markers, reductions in glutathione, alterations of brain phospholipids/acylcarnitines and neuroinflammation [8], [9], [10], [11], [12], [13].

Therapies have been studied to repair or guard against various neurobehavioral disorders. Various vertebrate and arthropod venoms from snakes, toads, frogs, spiders, scorpions, bees, wasps, and ants have shown pharmacological applications [14]. In particular, apitoxin (bee venom; BV) is a very complex mixture of about 18 active components, including enzymes, active peptides, and amines containing melittin, histamine, polyamines, phospholipase A2, and catecholamines [15]. The radioprotective, antimutagenic, pain relieving, anti-inflammatory, antihyperalgesic, anticancer and antinociceptive effects of BV have been documented [16], [17], [18], [19], [20].

Recently, the BV role in combating neurodegenerative ailments of the central nervous system (CNS) has been documented in many clinical studies [20], [21], [22]. Furthermore, in a 1-methyl-4-phenyl-1,2,3,6-tetrahy dropyridine (MPTP)-induced mouse model, BV acupuncture displayed an obvious neuroprotective action [22]. Moreover, BV might exert a direct neuroprotective effect on SH-SY5Y human neuroblastoma cells against MPP+-induced apoptotic cell death [23]. Yet, there are no studies demonstrating the protective or therapeutic role of BV in PPA-induced neurobehavioral disorders. Our earlier study showed that BV provides beneficial effects by diminishing PPA-induced oxidative stress, neuronal death, and DNA damage in the brains of rat pups [11].

Reelin is a glycoprotein secreted in the cerebral cortex and hippocampus from Cajal-Retzius cells and it acts as a regulator of many phases of laminar formation [24], [25]. Many studies have documented altered Reelin expression in rodents with cognitive dysfunction related to neuropsychiatric disorders [26], [27]. Recent genome screening studies using both a case-control and a family-based design have provided supporting evidence for the linkage/association between Reelin gene variants and either maternal deprivation or autistic disorder [28], [29]. Furthermore, post-mortem autistic brain biochemical analyses have implicated Reelin in the pathogenesis of autism [29], [30].

The specific aims of the current study were to verify whether BV presents a potential protective or therapeutic treatment against PPA-induced neural markers and behavioral performance, and to evaluate the expression pattern of Reelin gene in PPA- intoxicated rat pup brain.