Over 50 million persons are living with cognitive deficits worldwide, with over 80% of these individuals living in the developing world. The number of affected persons is projected to go over 152 million by the year 2050. Current drugs used for cognitive impairment are debatably ineffective, costly, inaccessible, and associated with undesirable events that call for the search for alternative and complementary approaches. Plants are arguably affordable, accessible, and efficacious. However, despite the reported healing claims, scientific data validating these claims are lacking.
According to the Alzheimer’s Association [
Various neuromodulators and neurotransmitters, including acetylcholine, nitric oxide,
Oxidative damage to the brain has been implicated as the primary cause of brain dysfunction and cognitive impairment [
Attempts to curb cognitive deficits by the use of psychopharmacologic agents have been made [
Due to the rising statistics of affected subjects and the inefficiency of treatments, the need for alternative mechanisms and agents is imperious. Plants offer a feasible alternative as they are arguably safe, affordable, and accessible, and they contain a myriad of bioactive compounds that exert pharmacologic activity through multitarget sites leading to increased potency, thus ameliorating dementia [
Fresh stem barks of
Swiss albino mice (4-5 weeks, 24 ± 2 g bw) were sourced from the Kenya Medical Research Institute (KEMRI), Nairobi, kept in standard laboratory conditions, and housed in polypropylene rectangular cages measuring 30 cm × 20 cm × 13 cm with softwood shavings as bedding material. They were offered standard rodent pellets and clean water
Extraction was performed according to the method described by Harborne [
On the other hand, the aqueous extract was obtained by warming 50 g of the powdered
The Morris water maze (MWM) method described by Morris [
The maze consisted of a white circular tank (110 cm in diameter and 45 cm in height) with a featureless inner surface. It was filled with clean water, in which 750 g of powdered milk was mixed, to a height of 30 cm, to form an opaque pool, and its temperature was maintained at 26 ± 1°C. A white escape platform (10 cm diameter and 29 cm in height) was placed in the center of the northwest (NW) quadrant of the pool and submerged 1 cm below the water surface to make it invisible at the water level. On the walls of the maze, manila papers of blue, green, pink, and yellow colors were mounted to theWest (W), North (N), South (S), and East (E) quadrants, respectively, as visual cues before introducing the mice. The continuous location of each swimming mouse, from the start position to the top of the platform, was monitored with the help of a digital Sony video camera that was mounted 1.5 meters above the maze [
Before the experiment, each mouse was trained four times to swim for 60 seconds in the presence and absence of a visible escape platform with an intertraining break of 20 minutes.
In the acquisition period, the water level in the maze was adjusted to 1 cm above the escape platform, which was centered in the northwest (NW) quadrant to make it invisible at the water level. Mice were subjected to three sessions each day for three consecutive days with an intertrial break of 20 minutes. The starting point was predetermined (southeast, SE) and remained unchanged for the entire experimental period. A digital video recorder was used to record transfer latency and navigation distance for each mouse. The recorded video clips were fed into Any-Maze software (version 6.05) for quantitative data acquisition.
The experimental mice were introduced into the maze without the escape platform on the fourth day (Day 4) for a single probe trial to assess their learning and spatial memory retention. During this session, the time spent in the target quadrant (NW, the correct location of the escape platform) was recorded (NW quadrant latency).
In this study, a completely controlled, randomized study design was adopted from which an experimental design was derived. For both the aqueous and methanolic stem bark extracts of
Group I (normal control) mice were orally administered with normal saline at a dose of 10 ml/kg bw. On the other hand, Group II (negative control) mice received normal saline (10 ml/kg bw) and scopolamine (1 mg/kg bw), whereas, Group III (positive control) were orally administered with Donepezil at a dose level of 1 mg/kg bw and scopolamine (1 mg/kg bw) intraperitoneally. Besides, Groups IV, V, and VI (experimental) received either the aqueous or the methanolic stem bark extracts of
The Thiobarbituric Acid Reactive Substances (TBARS) assay technique was used to determine the
During the assay, the brain samples were retrieved from the freezer and thawed, and each brain sample was homogenized in 10 ml of ice-cold phosphate buffer (0.1 M: pH 7.4). The reaction mixtures comprised of 1.5 ml of 0.8% thiobarbituric acid, 1.5 ml of 20% acetic acid (pH 3.5), 0.2 ml of 8.1% sodium dodecyl sulphate, and 0.1 ml of the brain tissue homogenates. The reaction mixtures were incubated in a boiling water bath (100°C) for 1 hour and then cooled to room temperature (25°C). After that, 5 ml of
Qualitative tests for various phytochemical compounds in the aqueous and methanolic stem bark extract of
The yields of the studied plant extracts were expressed as a percentage of weights of powders macerated. Quantitative data for the MWM test were obtained from the Any-Maze tracking software version 6.05. The MWM and MDA profile data were tabulated on Excel spreadsheets (Microsoft Office 365), and exported to Minitab version 19.1 statistical software (State College, Pennsylvania) for analysis. In the Minitab platform, descriptive statistics were performed, and resultant values were expressed as
Also, One-Way ANOVA was performed to determine statistical significance among the normal control, positive control, negative control, and the experimental groups at
Following extraction, the percentage yields of the studied plant extracts were determined. In general, the yield of the aqueous stem bark extract of
Percentage of yields of studied plant extracts.
Plant | Percentage yield | |
---|---|---|
Methanol extract | Aqueous extract | |
9.17 | 16.21 |
To appraise the cognitive-enhancing effects of the studied plant extracts in experimental mice that were subjected to the MWM task, the transfer latency, navigation distance, and latency time in the target quadrant (NW) were measured.
The results showed that, on acquisition training day 1, the transfer latency taken by mice that were treated with the aqueous stem bark extract of
Transfer latencies taken by experimental mice treated with the aqueous stem bark extract of
On the second day of acquisition training, we noted significant differences in transfer latencies that were taken by mice to complete the MWM task (
On the third day, no significant differences in transfer latencies taken by mice in the positive control group and negative control group and those that were treated with the aqueous stem bark extract of
On the other hand, during acquisition training day 1, the experimental mice that were administered with the methanolic stem bark extract of
Transfer latencies taken by experimental mice treated with the methanolic stem bark extract of
Moreover, on the second day of acquisition training, the mice which were administered with the methanolic stem bark extract of
On the third day of acquisition training, there were no significant differences in transfer latencies taken by mice that received the methanolic stem bark extract of
Furthermore, a comparison between the effects of the studied plant extracts on experimental mice’s transfer latencies during the acquisition training days (Days 1–3) was done in this study. The results revealed that, on the first day of acquisition training, the mice that received 50 mg/kg bw of the methanolic stem bark extract of
Comparison between the effects of the studied plant extracts on transfer latencies that were taken by mice during the acquisition training period. Bars with the same letter within the same dose level and acquisition training day are not significantly different (
On the other hand, on the second day of acquisition training, the transfer latencies taken by mice which received the methanolic stem bark extract of
Besides, on the third acquisition training day, the latencies taken by mice that were administered with the studied plant extracts, at a dose of 50 mg/kg bw, were not significantly different (
Upon administration of the aqueous stem bark extract of
Effect of the aqueous stem bark extract of
Besides, the transfer latencies taken by mice, which were treated with the methanolic stem bark extract of
Effect of the methanolic stem bark extract of
Moreover, a comparison between the effects of the aqueous and methanolic stem bark extracts of
Comparison between transfer latencies taken by scopolamine-induced cognitive-impaired mice treated with the aqueous and methanolic stem bark extract of
On the first acquisition training day, the mice which received the aqueous stem bark extract of
Effects of the aqueous stem bark extract of
On the second acquisition training day, no significant differences in navigation distances covered by mice treated with 50 mg/kg bw of the aqueous stem bark extract of
The results further revealed that, on the third day of acquisition training, the navigation distance covered by mice treated with 50 mg/kg bw of the aqueous stem bark extract of
On the other hand, the mice that were treated with the methanolic stem bark extract of
Effect of the methanolic stem bark extract of
On the second acquisition training day, there was no significant difference in navigation distance covered by mice that received a 50 mg/kg bw dose of the methanolic stem bark extract of
On acquisition day 3, the results revealed that the mice which received the methanolic stem bark extract of
Furthermore, a comparison between the effects of the aqueous and methanolic stem bark extracts of
The results showed, during acquisition training day 1, the mice that were treated with the aqueous stem bark extract of
Comparison between the navigation distances that were covered by which received the aqueous and methanolic stem bark extracts of
On the other hand, during the second acquisition training day, there was no significant difference in navigation distances recorded between the experimental mice which were administered with the studied plant extracts, at dose levels of 50 mg/kg bw and 200 mg/kg bw (
Besides, on the third acquisition training day, no significant difference between navigation distances was observed in mice, which received 50 mg/kg bw of the studied plant extracts (
The results showed that the mice which were administered with the aqueous stem bark extract of
Effects of the aqueous stem bark extracts of
On the other hand, orally administered methanolic stem bark extracts of
Effects of the methanolic stem bark extracts of
Additionally, a comparison between the effects of the aqueous and methanolic stem bark extracts of
Comparison between the effects of the aqueous and methanolic stem bark extracts of
The results showed that the cognitively impaired experimental mice that were treated with the aqueous stem bark extract of
Effects of the aqueous stem bark extract of
Generally, a dose-dependent increase in latency time in the NW quadrant was observed in cognitively impaired mice, which were treated with the aqueous stem bark extract of
On the other hand, the cognitively impaired mice that received the methanolic stem bark extract of
Effects of the methanolic stem bark extracts of
Furthermore, the times spent in the NW quadrant by mice in the normal and positive control groups were significantly longer than the times spent by the mice in the rest of the groups in the same quadrant (
In this study, a comparison between the effects of the aqueous and methanolic stem bark extracts of
Comparison between the effects of the aqueous and methanolic stem bark extracts of
The MDA profile in the brains of the experimental mice administered with the aqueous stem bark extracts of
Effects of aqueous stem bark extracts of
On the other hand, the experimental mice that were treated with the methanolic stem bark extract of
Effects of the methanolic stem bark extracts of
Moreover, a comparison between the effects of methanolic and aqueous stem bark extracts of
Comparison between the effects of the aqueous and methanolic stem bark extracts of
Upon qualitative phytochemical screening of the aqueous and methanolic stem bark extracts
Qualitative phytochemical profiles of the aqueous and methanolic stem bark extracts of
Phytochemical | Methanolic extract | Aqueous extract |
---|---|---|
Alkaloids | − | + |
Cardenolide glycosides | + | + |
Anthracene glycosides (anthraquinones) | − | − |
Coumarins | + | + |
Tannins | − | + |
Terpenoids | − | − |
Phenols | + | + |
Steroids | + | + |
Saponins | + | + |
Flavonoids | + | + |
+ = present; − = absent.
Alzheimer’s disease is the most common form of dementia, presenting progressive neurodegeneration and brain cell death [
Various factors, including developmental abnormalities, ageing, diabetes mellitus, hypertension, obesity, genetic abnormalities, among others, can either initiate or exacerbate neurodegeneration culminating to cognitive deficits [
In this study, the MWM method was adopted to evaluate the cognitive-enhancing effects of the aqueous and stem bark extracts of
Hyoscine hydrobromide (Scopolamine) is a muscarinic receptor antagonist that inhibits cholinergic transmission in both the peripheral and central nervous systems, resulting in cognitive impairment [
The results reported herein revealed that scopolamine successfully caused cognitive impairment in mice translating to longer transfer latencies and navigation distances in the negative control mice group. The shorter transfer latencies, shorter navigation distances, and longer latencies in the target quadrant recorded by the extract-treated mice were attributed to the cognitive-enhancing effects of these extracts. Overall, the methanolic stem bark extract of
Moreover, a study by Rahimzadegan and Soodi [
Lipid peroxidation is a well-known producer of cytotoxic components in the body as it causes lipid damage, especially those of biological membranes [
Previous studies have implicated scopolamine as a potent inducer of oxidative stress leading to high MDA profiles [
Proper extraction is a crucial stage in the itinerary of medicinal plant processing for purposes of discovering bioactive compounds for drug development [
According to La et al. [
The qualitative phytochemical profile of the aqueous and methanolic stem bark extracts of
Of the full range of plant phytochemicals, phenolic compounds demonstrate the broadest spectrum of pharmacologic bioactivity, which is attributable to their marked antioxidant effects [
The aqueous and methanolic stem bark extracts of
All the data are included within the manuscript. Any additional information is available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding this study.
Gervason Moriasi performed the study and developed the manuscript. Mathew Ngugi and Anthony Ireri supervised the study and reviewed the draft manuscript. All authors read and approved the final manuscript before submission.
The authors wish to acknowledge the Directorate of Research, Mount Kenya University, for granting access and use of Research Laboratory and equipment in this study. Also, much gratitude goes to Mr. Nelson Mandela, Ms. Mary Wachira, Mr. John Nzivo, and Mr. Jared Onyancha of Mount Kenya University (School of Pharmacy) and Mr. Daniel Gitonga of Kenyatta University (Department of Biochemistry, Microbiology, and Biotechnology) for their technical assistance in this study.