Cognitive Properties of Coconut Oil Extract Against Aluminum Chloride-Induced Neurotoxicity in Albino Rats

Cognitive dysfunction refers to a decline in cognitive function including impairments in memory, learning, attention and executive function (Harada et al., 2013). It can result from various factors including aging, neurodegenerative diseases, traumatic brain injury and exposure to environmental toxins (Kulkanu and Kaur, 2015). Cognitive dysfunction can have a significant impact on an individual quality of life, daily functioning and overall well-being (Sacdev et al., 2014). The underlying mechanism of cognitive dysfunction involves complex interaction between neurotransmitters, hormones and other signaling molecules (Spiljagic et al., 2022). Oxidative stress, inflammations and neuronal damage are also taught to play a critical role in the development of cognitive dysfunction (Franzoni et al., 2021). Aluminum chloride (AlCl₃) has been widely used in animal models to study cognitive dysfunction as it induces oxidative stress, inflammation and neuronal damage leading to impaired cognitive function (Abbas et al., 2022; Wei et al., 2024). Exposure to AlCl₃ has been shown to disrupt cognitive function by altering neurotransmitters systems impairing synaptic plasticity and promoting neuronal apoptosis (Kawahara and Kato-Negishi, 2011). Coconut oil derived from the pulp of coconut (Cocos nucifera) has been traditionally used for its medicinal and nutritional properties (Intahphuak et al., 2010). The potential cognitive property of coconut oil has been reported particularly its medium chain triglycerides (MCTs) which are metabolized into ketone bodies for providing an alternative energy source for brain cells (Taylor et al., 2018). The MCTs in coconut oils such as lauric acid, capric acid, and caprylic acid have been reported to possess neuroprotective antioxidants and anti-neuro inflammation properties which may counteract aluminum chloride-induced neurotoxicity (Ramesh et al., 2021; Ooi et al., 2022). Despite the reports on cognitive properties of coconut oil extract, experimental evidence particularly in well-established animal model of aluminum chloride-induced cognitive impairment remain scarce. Therefore, this study aims to investigate the cognitive properties of coconut oil extract in aluminum chloride-induced cognitive dysfunction in male albino rats.

Induction of Cognitive Dysfunction

Aluminum chloride (AlCl₃) was used to induce cognitive dysfunction in the experimental rats being a heavy metal that possesses immeasurable neurotoxic properties with ability to impact the brain tissue thereby causing dysfunction in the hippocampus region (Nallagouni et al., 2017). 100 mg/kg of AlCl₃ was administered orally with the aid of canula for 28 days according to the method of Shunan et al., (2021).

MATERIALS AND METHODS

Experimental Animal

Thirty-six male albino rats (200-220g) were obtained from the animal house of the Department of Physiology, Ladoke Akintola University of Technology (LAUTECH), Ogbomoso, Nigeria. They were acclimatized for two weeks before the commencement of the experiment, and kept throughout the experiment in a well-ventilated plastic cages (6 rats per cage) in the animal house under controlled environmental conditions (temperature 28 ± 2 °C; photoperiod: 12-h natural light and 12-h dark: relative humidity: 50-55%) with free access to feed and water ad libitum. The animal handling procedure was done according to guidelines for the use of laboratory animals, as recommended by the animal care and use research ethic committee of Ladoke Akintola University of Technology (LAUTECH), Ogbomoso were followed.

Drugs and Reagents

All drugs and reagents used were of high analytical grade. Aluminum chloride (AlCl₃) was obtained from (Sigma-Aldrich, USA). Donepezil, a manufactured in St. Louis, MO, USA; with Product No. TN00002269 was purchased from a Pharmacy store around Starlight junction, Ogbomoso, Oyo state Nigeria.

Processing of the Coconut

Fresh mature coconuts (Cocos nucifera L.) were purchased from the open market around Recreational Club, Ogbomoso and authentication was carried out in the herbarium of the Department of Pure and Applied Biology, Faculty of Pure and Applied Sciences, Ladoke Akintola University of Technology Ogbomoso (Voucher Number: LHO 903). The coconut fruits were broken and the hard shells removed, and endosperm subsequently rinsed to remove dirt before being cut into smaller pieces in order to ensure proper drying in the oven set at 40°C. The dried coconut was kept in order to employ hydraulic press for the extraction of oil.

Extraction of Coconut Oil

About 5000g of the dried coconut was pressed through the use of manually operated mechanical hydraulic press. The dried coconut was transferred into a metal chamber built in the hydraulic press with subsequent application of pressure, in order to force the oil out through an outlet and the oil was collected by a previously cleaned and dried container. The extracted oil was transferred to hot-air oven set at 40⁰C for 24 hours, so as to eliminate moisture content from the oil. (Gunstone, 2011). After 24 hours, the coconut oil extract was obtained and subsequently transferred into a clean, dried sample bottle to be later used.

Experimental Design

Thirty-six (36) male albino rats were randomly divided into six (6) groups of (n = 6) animal.

Group 1 - Normal Control: Rats given normal feed and water only.

Group 2 - Negative Control: Rats administered with aluminum chloride orally.  (100 mg/kg/ bw).

Group 3 - Positive Control: Rats administered with aluminum chloride (100 mg/kg/ bw) and treated with donepezil (1 mg/kg/ bw).

Group 4 - COE Low Dose: Rats administered with aluminum chloride (100 mg/kg/ bw) and treated with 2.5 ml/kg bw coconut oil extract orally

Group 5 - COE Medium Dose: Rats administered with aluminum chloride (100 mg/kg bw) and treated with 5 ml/kg bw of coconut oil extract orally

Group 6 - COE High dose: Rats administered aluminum chloride (100 mg/kg bw) and treated with 10 ml/kg bw of coconut oil extract orally.

(AlCl₃) was administered for 28 consecutive days to induce neurotoxicity. Donepezil and COE were given concomitantly with AlCl₃ via oral gavage.

Behavioral Assessment                                            

Behavioral tests were performed 24 h after the last treatment in a quiet, controlled environment between 08:00 and 12:00 h. Rats were habituated to the testing room for 30 min before each assessment.

1. Y-Maze Test

Spontaneous alternation behavior was used to evaluate spatial working memory. The Y-maze apparatus consisted of three arms (40 cm length, 12 cm height, 3 cm width at bottom and 10 cm at top) at 120° angles. Each rat was placed at the end of one arm and allowed to explore freely for 8 minutes (Cleal et al., 2021) (Fig 1). An alternation was defined as consecutive entries into all three arms without repetition. Percentage alternation was calculated as:

% Spontaneous Alternation=Number of alternationTotal arm enteries-2 ×100

2. Open Field Test

Locomotor and exploratory activities were assessed in a square arena (100 × 100 × 40 cm) divided into equal squares. After the animals were placed in the apparatus and allowed to explore the environment for five minutes, grooming counts, line crossings, and rearing counts were recorded (Snyder et al., 2021) (Fig. 2).

3. Novel Object of Recognition (NOR) Test

Recognition memory was assessed in an open field box by placing the animals into the apparatus. The habituation phase test was conducted for 10 minutes in empty arena after the training phase involving two identical objects, and testing phase involving one familiar object replaced with a novel object after 1hour. Exploration time of each object by the animals was recorded, and the discrimination index (DI) was calculated as:

DI=Time exploring novel object-Time exploring familiar object Total exploration time

Statistical Analysis

Data were expressed as mean ± standard error of the mean (SEM). Statistical analyses were performed using GraphPad Prism version 7.0 (GraphPad Software, Inc., USA). One-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test was used to determine statistical significance. p<0.05 was considered statistically significant.