In Vivo Cognitive-Enhancing, Ex Vivo Malondialdehyde-Lowering Activities and Phytochemical Profiles of Aqueous and Methanolic Stem Bark Extracts of Piliostigma thonningii (Schum.)

Abstract

Cognitive impairment (CI) is among the leading causes of disability in humans. It is estimated that over 35.6 million people are suffering from Alzheimer's disease- (AD-) associated cognitive deficits globally with these statistics projected to rise over 115.4 million by the year 2050. There is no specific etiology for this cognitive impairment; however, various contributing factors including advancing age (>60 years old), oxidative stress, cerebral injuries, infections, neurologic disorders, and cancer have been implicated. Despite various attempts to manage CI, no curative medicines are yet available. The current drugs used to manage symptoms of AD-associated CI including Donepezil and Rivastigmine among others are only palliative rather than therapeutic. Furthermore, these agents have been associated with undesirable side effects. This calls for alternative and complementary approaches aimed at either preventing or reverting AD-related CI in a curative way without causing adverse events. It is estimated that over 80% of the world's population utilize herbal medicines for basic healthcare as it is considered safe, affordable, and easily accessible as opposed to conventional healthcare. Various parts of P. thonningii are used in traditional medicine to manage various conditions including CI. However, empirical and scientific data to validate these uses is lacking. In this study, the Morris water maze (MWM) experiment was adopted to evaluate the cognitive-enhancing effects of the studied plant extracts. The malondialdehyde (MDA) profiles in the brains of experimental mice were determined using the thiobarbituric acid reactive substances (TBARS) test. Moreover, qualitative phytochemical profiling of the studied plant extracts was performed using standard procedures. The results showed remarkable cognitive-enhancing activities which were reflected in significantly shorter transfer latencies, navigation distances, longer time spent in platform quadrant, and lower MDA levels compared with those recorded for the negative control mice (p < 0.05). Phytochemical screening of the studied plant extracts revealed the presence of antioxidant phytocompounds, which may have played key roles in the extracts' potency. Based on the findings herein, P. thonningii extracts, especially the aqueous ones have a promising potential for the management of AD-associated CI. Further studies aimed at isolating and characterizing specific active compounds for CI from P. thonningii are recommended. Additionally, specific mode(s) of action of active principles should be elucidated. Moreover, toxicity studies should be done on the studied plant extracts to ascertain their safety.

Figure 1

Effect of the aqueous stem bark extract of P. thonningii on transfer latency. Bars that do not share a letter are significantly different (one-way ANOVA followed by Fisher's LSD; p < 0.05).

Figure 2

Effects of the methanolic stem bark extract of P. thonningii on transfer latency. Bars that do not share a letter are significantly different (one-way ANOVA followed by Fisher's LSD; p < 0.05).

Figure 3

Comparison of the effects of the aqueous and methanolic stem bark extracts of P. thonningii on transfer latency. Bars with the same letter within the same dose level are not significantly different (p > 0.05) while those with different letters within the same dose level are significantly different (p < 0.05) (unpaired Student's t-test).

Figure 4

Effects of the aqueous stem bark extracts of P. thonningii on navigation distance. Bars with different letters are significantly different (one-way ANOVA followed by Fisher's LSD; p < 0.05).

Figure 5

Effects of the methanolic stem bark extracts of P. thonningii on navigation distance. Bars with different letters are significantly different (one-way ANOVA followed by Fisher's LSD; p < 0.05).

Figure 6

Effects of the aqueous and methanolic stem bark extracts of P. thonningii on navigation distance. Bars with different letters within the same dose level are significantly different (unpaired t-test at 95% confidence level; p < 0.05).

Figure 7

Effects of the aqueous stem bark extracts of P. thonningii on spatial memory retention. Bars with different letters are significantly different (p < 0.05) while those sharing a letter are not significantly different (p > 0.05) (one-way ANOVA followed by Fisher's LSD).

Figure 8

Effects of the methanolic stem bark extract of P. thonningii on spatial memory retention. Bars with the same letter are not significantly different (p > 0.5) while those with different letters are significantly different (p < 0.05) (one-way ANOVA followed by Fisher's LSD).

Figure 9

Effects of the aqueous and methanolic stem bark extracts of P. thonningii on spatial memory retention. Bars with different letters within the same dose level are significantly different (unpaired t-test at 95% confidence level; p < 0.05).

Figure 10

Effects of the aqueous stem bark extract of P. thonningii on MDA profile. Bars with the same letter are not significantly different (one-way ANOVA followed by Fisher's LSD; p > 0.05).

Figure 11

Effects of the methanolic stem bark extract of P. thonningii on MDA profile. Bars with the same letter are not significantly different (p > 0.05) while those with different letters are significantly different (p < 0.05) (one-way ANOVA followed by Fisher's LSD).

Figure 12

Effects of the aqueous and methanolic stem bark extracts of P. thonningii on MDA profile. Bars with the same letter within the same dose level are not significantly different (p > 0.05) while those with different letters are significantly different (p < 0.05) (unpaired Student's t-test).