Evaluation of the Protective Effect of Aqueous and Ethanol Fruit Extracts of Phoenix Dactylifera L. On Mercury – Induced Neurotoxicity in Wistar Rats
Chapter One
Aim and Objectives of the Study
Aim
The aim was to evaluate of the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera L on mercury-induced neurotoxicity in Wistar rats.
Objectives
The objectives were to:
- Morphologically, histologically and histochemically investigate the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera L on mercury- induced cerebral, cerebellar and hippocampal neurotoxicity in Wistar
- Investigate the cognitive effects of aqueous and ethanol fruit extracts of dactylifera on mercury-induced hippocampal toxicity in Wistar rats using Elevated Plus Maze test and Morris Water Maze test for spatial memory andlearning.
- Investigate the effect of aqueous and ethanol fruit extracts of dactylifera on mercury-induced cerebellar and cerebral toxicity in Wistar rats using Beam Walking test for motor coordination and balance and Forelimb Grip Strength test for sensory-motoractivity.
- Neurochemically investigate the protective effect of aqueous and ethanol fruit extracts of dactylifera on mercury-induced neurotoxicity in Wistar rats using biochemical analysis for metal (copper, Cu; iron, Fe; manganese, Mn and zinc, Zn) estimation, lipid peroxide levels and antioxidant enzyme activity(malondialdehyde MDA,superoxide dismutase – SOD, catalase – CAT and glutathione peroxidase GPx), and endogenous enzyme (acetylcholinesterase –AchE) activities.
CHAPTER TWO
Literature Review
Mercury
Severe illness and sudden death in human beings have been implicated on environmental pollution, centuries before now. Pollution can be in air, water or on land and can result from mining, automobile exhaust, agricultural and industrial activities among others. Classified among major causes of environmental pollution, are heavy metals.
Heavy metals occur as natural constituents of the earth crust, and are persistent environmental contaminants since they cannot be degraded or destroyed. Although these elements are lacking in abundance they are not lacking in significance (Chen and Chen, 2001). Heavy metals are chemical elements with a specific gravity that is at least 5 times the specific gravity of water (specific gravity of water is 1 at 4°C) (Adedokun et al., 1989; Galadima et al., 2011). Some well-known toxic metallic elements with a specific gravity that is 5 or more times that of water are arsenic, 5.7; cadmium, 8.65; lead, 11.34; and mercury, 13.546 (Galadima and Garba, 2012).
Environmental mercury levels have increased considerably since the on-set of the industrial age. Mercury is now present in various environmental media and food (especially fish) all over the globe at levels that adversely affect humans and wildlife. Widespread exposures are occurring due to human generated sources, and past practices have left a legacy of mercury in landfills, mine tailings, contaminated industrial sites, soils and sediments. Even regions with no significant mercury releases, such as the Arctic, are adversely affected due to the transcontinental and global transport of mercury (United Nations Environmental Programme–UNEP, 2002).
The most significant releases of mercury pollution are emissions to air, but mercury is also released from various sources directly to water and land. Once released, mercury persists in the environment where it circulates between air, water, sediments, soil and biota in various forms. Current emissions add to the global pool– mercury that is continuously mobilized, deposited on land and water, and remobilized (UNEP, 2002).
CHAPTER THREE
Materials and Methods
Materials
Plant Material
Dried Phoenix dactylifera L. (date palm) fruits were obtained from a local market (Samaru Market) in Zaria, Kaduna, Nigeria, and authenticated and deposited in the Herbarium Unit of Department of Biological Sciences, Faculty of Life Sciences, Ahmadu Bello University, Zaria, Kaduna State, Nigeria with the Voucher Specimen Number of 7130.
CHAPTER FOUR
Results
Phytochemical Analysis
Phytochemical analysis of aqueous and ethanol fruit extracts of Phoenix dactylifera produced positive reaction for each of the following secondary metabolites: Alkaloids, Tannins, Saponins, Flavonoids and Carbohydrates. However, a negative reaction was obtained for Anthraquinone and Cardiac glycoside
Discussion
In this study, preliminary phytochemical screening was carried out, and the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera on mercury-induced cerebral, cerebellar and hippocampal neurotoxicity in Wistar rats assessed using morphologic and histometric, histologic and histochemical, neurobehavioural, neurochemical and biochemical investigations.
Phytochemical studies
Phytochemical screening of the plant (Phoenix dactylifera) fruit extracts (aqueous and ethanol), in this study, revealed the presence of flavonoids, saponins, tannins and alkaloids which have been reported to exert neuroprotective actions in animal and cell culture models of neurological disorders (Selvam, 2008; Lobo et al., 2010; Chang et al., 2012; Kumar and Khanum, 2012; Hwang et al., 2015).
Physical Observation
Decreased physical activity exhibited by mercury-treated Wistar rats reflects treatment- related toxicity. This is in concordance with reports on drug-related toxicity; altered physical activity manifesting as sluggishness and loss of appetite indicates drug-related toxicity (Toma et al., 2009; Salawu et al., 2009). Body weight changes serve as a sensitive indication of the general health status of animal (Salawu et al., 2009), and used as an indicator of adverse effect of drugs and chemicals (Mukinda and Syce, 2007). Changes in the body weight of Wistar rats treated with mercury were similar to those of the extract treated. This was at variance with the reports of Jadhav et al. (2007) and Wadaan (2009) who reported remarkable weight changes in rats exposed to mercury.
CHAPTER SIX
Summary, Conclusion and Recommendation
Summary
In this study, evaluation of the protective effect of aqueous and ethanol fruit extracts of Phoenix dactylifera L on mercury-induced neurotoxicity in Wistar rats, the results of phytochemical screening revealed the presence of flavonoids, saponins, tannins and alkaloids which have been reported to exert neuroprotective actions in animal and cell culture models of neurological disorders. Exposure to mercury (HgCl2) resulted in neurotoxicity, which was evident from morphologic, histometric, histologic and histochemical alterations in the brain of the rats. Mercury induced anxiety-related responses, short- and long-term memory impairments and motor deficits in neurobehavioural assessment, and altered the levels of neurochemical and biochemical constituents which could be related, at least in part, by the cortical and hippocampal mercury content that may interfere with local homeostasis. The polyphenolics including flavonoids, found in many plant extracts, have been shown to be strong reactive oxygen species (ROS) scavengers, antioxidants and protectors of neurones from lethal damage (Rice-Evans, 2001; Pujari et al., 2011) and are able to chelate metal ions (Komaki et al., 2015). Flavonoids exert a multiplicity of neuroprotective actions within the brain, including a potential to protect neurones against injury induced by neurotoxins, an ability to suppress neuroinflammation, and the potential to promote memory, learning, and cognitive function. Thus, antioxidant activities of the extracts could be implicated for neuroprotection. Fruit extracts (aqueous and ethanol) of P. dactylifera benefits the brain through neuroprotective property, protecting the brain from the actions of ROS by utilizing its antioxidant property (Wan Ismail and Mohd Radzi, 2013).
Findings of the present study reveal the potentials of the aqueous and ethanol fruit extracts of Phoenix dactylifera as neuroprotective agent in the following studies:
- Morphologic features of the brain and histometric characteristic of brain regions (cerebral and cerebellar cortices and hippocampus) were preserved relative to the control.
- Mercury-induced histologic and histochemical alterations in cerebral and cerebellar cortices and hippocampal regions (CA1 and CA3) were ameliorated relative to the control.
- Mercury-induced anxiety-related responses, short- and long-term memory impairments, and motor coordination and balance deficits in neurobehavioural assessment were ameliorated relative to the control. Thus extracts possess potentials as axiolytics and, cognitive-motor and memory enhancing
- Alterations in the concentration levels of neuro-trace elements (Fe, Mn, Cu and Zn), MDA and endogenous antioxidants (SOD, CAT, GPx), and endogenous enzyme (AchE) activity levels were moderately ameliorated relative to the control, which protect neurones against reactive oxygen species(ROS).
Conclusion
The result of the present study suggests that, the aqueous and ethanol fruit extracts of Phoenix dactylifera may prove efficacious in ameliorating mercury-induced alterations in the brain (cerebral and cerebellar cortices and hippocampus) of Wistar rats.
The neuroprotective property of extracts, relative to the standard (vitamin C), is rather similar, and is attributed to antioxidant properties of constituent phytochemicals, such as flavonoids. Thus, aqueous and ethanol fruit extracts of P. dactylifera are potential candidate for application in the management and treatment of ROS-induced neurodegenerative diseases, such as AD and PD.
Neuroprotective activity is dose dependent; 500 and 1,000 mg/kg doses possessing maximal activity for both extracts (aqueous and ethanol fruit extract of P. dactylifera).
In relation to extracts’ neuroprotective activity, ethanol fruit extract of P. dactylifera is of more efficacy. This could be that, ethanol extract possess certain additional antioxidative and neuroprotective properties or may involve different mechanisms of constituent antioxidant activities.
Recommendation
Further studies are required to fully investigate the mechanisms responsible for the observed neuroprotective activity of aqueous and ethanol fruit extracts of Phoenix dactylifera, and to determine the exact compound(s) or active ingredients responsible for its neuroprotective activity. In depth studies such as, ultra-microscopy, stereology and immunohistochemistry are required to confirm findings of the study.
Further studies are required to investigate the possible neuroprotective activity of other solvents (e.g. organic solvents, such as methanol and chloroform) extract of P. dactylifera fruit and other parts (such as, the pits or seeds) of the plant.
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