1. Introduction
Epilepsy is a persistent neurological brain disorder characterised by abnormal electrical activity in the cerebral neurons. Epilepsy affects approximately 50 million people worldwide. Epilepsy affects all the age groups, especially young people in first two decades of life and elderly [
1]. The importance of oxidative stress being an essential mechanism for understanding seizures caused by epilepsy has been extensively acknowledged. However, there is a lack of clear evidence that free radicals are actively involved in physiological processes during oxidative stress induced by convulsants [
2]. Oxidative stress results a functional cellular disruption and cause cell death via oxidation of bio molecules such as proteins, lipids and nucleotides [
3]. As a result, treating epilepsy through the use of non-pharmacological and antioxidant methods which target oxidative stress may be effective. The commonly used anticonulsant drugs like, sodium valproate, Phenytoin, phenobarbitone and carbamazepine for symptomatic effects not underlying pathological state of epilepsy. About 80 of epileptic patients are adequately controlled with currently available anticonvulsant drugs, while 20 % increase restorative failure and want adjoin on treatment [
4]. The fundamental disadvantage of antiepileptic medications is that they cause undesired side effects and require long-term adherence during the duration of treatment. Both epilepsy and antiepileptic treatments have negative effects on learning and memory. In past few years large number of newer antiepileptic drugs have been has been approved or last phase of development as add on therapy for poorly controlled epilepsy, but safety and tolerability of these drugs needs to be proven [
5,
6]. Although there is no experimental model that could faithfully reproduce all human TLE features, some models are selected to ask a specific set of questions, the pentylenetetrazole (PTZ) kindling model is widely accepted as an experimental animal model for estimating the effectiveness of antiepileptic drugs or studying the pathogenesis of epilepsy [
7].
Kindled seizures have been shown to cause a neuronal loss in limbic systems CA1, CA3, dentate gyrus of hippocampus, amygdala and entorhinal cortex [
8]. The Memory impairment has been attributed to the hippocampus's neurological damage. An increased activity of the glutamatergic transmission has also been found to play a crucial role in neuronal cell death of the PTZ kindling in rats due to free radicals generation [
9]. In order to control epilepsy and its consequences, exogenous dietary supplementation (antioxidants) could serve as a beneficial strategy. The origins of modern medications may be explored in traditional medicine. we have chosen two herbal drugs on the basis of antioxidant properties, one was leaves of
M. oleifera Lam (Moringaceae) and another one is curcumin (isolated compounds) both of the plants is used in African and Indian traditional medicine to treat not only seizures but also leprosy, stroke, anemia, and mental disorders [
10,
11].
M. oleifera Lam. leaves are a good source of nutrition and have anti-tumor, anti-inflammatory, anti-ulcer, anti-atherosclerotic, and anticonvulsant properties due to the presence of polyphenolic and flavonoids compounds such as Querectin, chlorogenic acid, kaempferol, beta-carotene, and amino acids, which contribute to their antioxidant property [
12].
One such medicine is curcumin, which has been shown to ameliorate or even prevent further progression of diseases [
13]. Turmeric has been used for decades in India for its health advantages, as well as a spice and colourant. Curcumin, a principal curcuminoid in turmeric, is obtained from dried rhizomes of the plant
Curcuma longa [
14]. Curcumin has been reported to possess antioxidant, anti-inflammatory, anti-proliferative, anti-apoptotic properties anti-inflammatory, anticancerous, antiepileptic, antidepressant, immunomodulatory, neuroprotective, antiapoptotic and antiproliferative effects [
15]. Curcumin is also an effective scavenger of reactive oxygen species and reactive nitrogen species [
16]. The aforementioned properties of curcumin suggest a potential of using it to treat PTZ-induced kindling while preventing of seizures and memory loss.
Therefore, the combined effect of curcumin and M. oleifera ethanolic extract (MOEE) supplementation on epileptic seizure, cognitive impairment & oxidative stress in PTZ-induced kindling in rats was assessed in the current investigation. The molecular docking investigations are going to provide novel viewpoints on the creation of anti-epileptic drugs.
3. Discussion
The current pharmacotherapy of epilepsy has the limitations of a chronic course, involving unavoidable adverse effects, economical burden, and falls short of the therapeutic goal of a seizure free status in nearly one third of the patients [
17]. Use of plant based products for therapy of convulsions has been a part of long-standing tradition in Asia, Africa, and South America [
18]. Many plant extracts have shown the presence of anticonvulsant activity in animal seizure models, which has been attributed to the action of flavonoids, furanocoumarins, phenylpropanoids, and terpenoids on gamma amino butyric acid (GABA) receptors and voltage gated ion channels [
19]. These phytochemicals facilitate the maintenance of normal physiological function of the major inhibitory neurotransmitters [
20]. Modern laboratory methods and the emphasis on evidence-based medicine have renewed interest in research on herbal items in an effort to discover a safe and effective antiepileptic compound. The present understanding of epilepsy indicates that it may be useful to develop antiepileptic medications with added antioxidant action, and medicinal plants are an excellent source for such an endeavour. Traditional medicinal plants provide a wealth of information for the creation of contemporary pharmaceuticals. The herbal medicine drawn extensive appreciation from the research bases and enterprises lately at the national and international levels. Hence there has been extreme focused with respect to potential phytochemical to protect the neuronal activity and defensive component against epilepsy.
Epilepsy is one of the most common neurological disorders estimated to affect around 50 million people worldwide characterized by epileptic seizures associated with complex molecular, biochemical, physiological and anatomical changes in the brain [
21]. The potential cause of epilepsy includes brain injury, brain tumor, stroke, or inflammation in brain [
22]. Epileptic seizures occur due to abnormal discharge or excessive firing activity of neurons in the brain [
23]. The neuronal death in epilepsy could be attributed to the oxidative stress induced free radical generation in the brain due to lipid peroxidation, protein oxidation and DNA damage [
24]. Both epilepsy and antiepileptic medications have a negative impact on an epileptic patient's ability to learn and remember things. Currently available antiepileptic drugs target only the symptoms but do not prevent the underlying pathology of epilepsy or its associated comorbidities [
25]. Still more than 30% patients experience epileptic seizures after therapy with AED [
26,
27]. It is therefore necessary to find alternative natural remedies (phytoconstituents or nutraceuticals) to the traditional AED that might offer beneficial clinical effectiveness and tolerance with low side effects.
M. oleifera Lam. (Family: Moringaceae) is common culinary plant known as drumstick tree.
M. oleifera Lam is a widely available plant in Southeast Asia which has been evaluated for the presence of antioxidant activity in a few earlier studied
[28]. The most fascinating characteristics of this species are antioxidant [
29], and anti-inflammatory characteristics [
28]. Traditional system of medicine claims to suggest that the leaves of
M. oleifera have the potential in the treatment of epilepsy [
30]. The leaves of
M. oleifera have been reported to contain a number of phytoconstituents including alkaloids, carotenoids, flavonoid, polyphenol, phenolic acids, tannins, saponins & vitamins. The leaves are also said to be rich in Vitamin A and C, beta-carotene, chlorogenic acid, kaempferol, and quercetin which contribute to their antioxidant property [
31,
32]. Curcumin, a principal curcuminoid present in turmeric, is obtained from the dried rhizomes of
Curcuma longa [
33]. Curcumin has been reported to possess antioxidant, anti-inflammatory, antiepileptic, immunomodulatory, and neuroprotective activity [
34]. Curcumin is also believed to be an effective scavenger of reactive oxygen and nitrogen species [
35]. Therefore the characteristics of curcumin propose to enormous prospective as a medicine for treating PTZ-induced kindling that has seizures and cognitive impairment. Due to presence of phenolic group, curcumin acts as a strong antioxidant and inhibit the generation of reactive oxygen species such as superoxide anions and nitrite radical generation both in vitro and in vivo [
36]. The presence of hydroxyl (OH) groups in phenolic compounds may contribute directly to their antioxidant activity and be a significant predictor of their radical scavenging ability [
37]. Pentylenetetrazole (PTZ) kindling model is widely accepted as an experimental animal model for evaluating the effectiveness of antiepileptic drugs or studying the pathogenesis of epilepsy [
38]. Kindling is the process of repeatedly decreasing the seizure threshold in the brain by electrical or chemical stimulation, which results in repetitive seizures. It causes development of seizure gradually that transcribes in generalized tonic-clonic seizures often associated with cognitive impairments [
39]. Pentylenetetrazol on repeated administration with a subconvulsant dose determines the nature and intensity of convulsant activity. Seizure activity of drugs in animals is evaluated on the basis of seizure score gained by the administered drug [
40]. Higher the seizure score lesser is the seizure protective effect and vice versa. As compared to PTZ treated (4.83±0.17) animals, the low dose curcumin (3.33±0.21) and low dose MOEE (3.50±0.50) group animals has significant difference in the seizure score value. The high dose curcumin treated (2.66±0.33) groups has shown highly significant difference whereas high dose MOEE treated (3.00±0.26) group has shown significant difference in their seizure score as compare to PTZ treated groups. The combined low dose MOEE and low dose curcumin treated group has shown highly significant difference in the seizure score (2.50 ± 0.34) as compare to PTZ treated group. The standard (valproic acid) treated groups has highly significant difference in the seizure score (2.16 ± 0.31) as compare to PTZ groups. There were significantly differences initiate in the convulsion score between valproic acid groups and combined Low dose MOEE and Low dose of curcumin, which suggest that the combination treatment exerted excellent antiepileptic activity in reducing the seizure activity. Neurobehavioral assessments were performed to assess cognitive functions such as learning and memory by elevated plus maze (EPM) and passive avoidance (PA) as described by (Sarangi et al
., 2017) [
41]. The biological processes in the brain that contribute to impairment in cognitive function have been reported to be influenced by ongoing seizure activity and antiepileptic drugs treatment [
42]. The reduction in cognitive functions in kindled rats might be caused by an assortment of circumstances. One of several explanation refers to the degenerative processes in the brain structures, secondary to seizure related ischemia and hypoxia [
43]. It has been shown that kindled seizures are associated with a selective degeneration of cortical and limbic structures including hippocampus areas, involving loss of neurons, glial and neuronal growth, and astrocytes hypertrophy [
44]. In addition, the seizure activity and antiepileptic activity have causes increased the level of free radicals & reduced antioxidant scavenging defense activity [
45]. This imbalance in the body's oxidant and antioxidant defence mechanisms may result in seizures and cognitive impairment. Elevated plus maze apparatus were used for evaluating memory in rodents, there was no significantly difference in initial transfer latency between open & closed arms. On the other hand, a significant difference was seen in the retention transfer latency, which was assessed twenty four hour following the initial transfer latency. PTZ kindling induced a highly significantly increase (***p<0.0001) in retention transfer latency as compare with control group, according to post hoc analysis. The dose-dependent effect of Curcumin & MOEE inverted the effect of PTZ-induced kindling on retention transfer latency was observed. The retention transfer latency decrease less significantly (*p<0.01) in the low dosage curcumin and low dose MOEE groups compare with PTZ group. However, when significant amounts of curcumin and MOEE were used, the transfer latency was significantly reduced (**p<0.001) as compare with PTZ groups. When compare with control group, the combined impact of MOEE and Curcumin at doses of 250 mg/kg and 200mg/kg did not showed a highly significant difference (***p<0.0001) in retention transfer latency on EMP tests. When compare with PTZ group, the
per se groups showed a significantly significantly difference (***p<0.0001).The previous study also reported that the 200mg/kg and 300mg/kg dose did not cause any significant in the transfer latency [
46]. When the Pentylenetetrazole groups was compare with control group, the retention latency decreased significantly (***p<0.0001). However, the MOEE & curcumin was combined with PTZ result, substantial dose-dependent increase (**p<0.001) in retention latency as compare with PTZ groups. When compare with PTZ-treated groups, the combined effects of MOEE and Curcumin resulted in a highly significant difference (***p<0.0001) in retention transfer latency of Passive avoidance test. The increase in the locomotor activity reveals the stimulant effect of PTZ on CNS, due to decreased GABA neurotransmitter in brain [
47]. Moreover, kindling process is known to increase the strength of excitatory synaptic connections and decreases the strength of connectivity between inhibitory synapses which could be the reason for an increase in the locomotor activity of PTZ groups [
48]. However, PTZ groups with 300 mg/kg curcumin, 500 mg/kg MOEE, or standard (valproic acid) showed no variation in locomotor activity. In addition, there is no significant change in locomotor activity of the rats treated with MOEE and curcumin compare with PTZ groups. Free radicals are frequently created in the body as a result of aerobic metabolism. Overproduction of these free radicals (ROS/RNS) results in damage to lipids, proteins, DNA in the cells and eventually leading to various neurological disorders [
49]. Moreover, brain is quite susceptible to oxidative damage as it contains high amount of polyunsaturated fatty acids which can be readily per-oxidized [
50]. To counteract excess free radical generation, there are several endogenous antioxidants (catalase, superoxide dismutase, glutathione) they produce protective effect against free radicals geneneration in the brain.
Lipid peroxidation is a process in which free radicals formed react with lipids present in cell membranes leading to cell damage [
51]. Reactive aldehydes such as malondialdehyde (MDA) are the end products of lipid peroxidation. MDA is an end product of free radical generation and is used as an indicator of oxidative stress in biological system [
52]. Malondialdehyde levels were found to be significantly higher (***p<0.0001) in the brains with PTZ treated groups as compare with controls groups. MOEE and Curcumin supplementation substantially reduced PTZ-induced lipid peroxidation in the brain (**p<0.001). The
per se groups of MOEE & curcumin was significantly difference (***p<0.0001) in MDA levels when compared with PTZ treated groups. The MOEE groups, both low dose and high dose have shown less significantly (*p<0.01) difference in MDA level as compare with PTZ treated groups. The combined effect of MOEE + Curcumin showed that the level of MDA was significantly decrease (**p< 0.001) when compare with PTZ treated groups. The combination supplement has shown similar effect to standard valproic acid (**p<0.001) in reducing the MDA level and hence lipid peroxidation in the brain. This antioxidant effect of curcumin in PTZ kindled rats is supported by the finding of recent study [
53] where in oral supplement of curcumin decreases the catalase, MDA & glutathione in rat cerebellum and cerebrum. By scavenging free radicals, GSH serves a crucial function in protecting cells from oxidative damage. It is utilised as an indicator of oxidative stress. The GSH level was significantly decrease in PTZ groups in compare with control group (***p<0.0001). When PTZ-treated group compare with, the
per se groups, standard valproic acid group, and combination of curcumin & MOEE groups all showed a highly significantly (***p<0.0001) increase in brain GSH levels. Low dose MOEE treated group showed non- significant (ns) difference while high dose MOEE and curcumin showed significant difference (**p<0.001) as compare with PTZ treated group. Hence, the combination treatment group was more effective to restoring the depleted GSH level in the brain and it was equally efficacious as standard valproic acid treatment.
The PTZ group had significantly lower brain superoxide dismutase levels in compare with control group (**p<0.001). The per se groups and the combination of MOEE +Curcumin treated group far better than the standard valproic acid groups & have shown significantly difference (**p<0.001) in the level of SOD as compare with PTZ groups. The standard valproic acid, high dose MOEE and curcumin groups were less significantly difference (*p<0.01) in the GSH levels as compare with PTZ groups. The brain catalase level of PTZ treated group have shown highly significantly difference (***p<0.0001) as compare with control group as PTZ causes severe depletion of catalase level in brain. When compare to PTZ treated groups, the per se groups, standard valproic acid group and the combined (curcumin+ MOEE) treated groups have shown highly significantly (***p<0.0001) elevation in the catalase level of brain. The Nitric oxide levels were observed to be increased remarkably and is highly significantly (***p<0.0001) in the brain with PTZ treated groups in comparison with control. The low dose treatments with MOEE or curcumin showed only significantly difference (**p<0.001) whereas the standard valproic acid group, per se groups, high dose MOEE or curcumin groups and the combined MOEE & curcumin treated groups have shown highly significant (***p<0.0001) difference in lowering the nitric oxide levels as compared to PTZ treated group. The present research's results are consistent with the enhanced AChE activity in the PTZ group, suggesting that increased AChE was an additional factor in memory loss. When compared to the normal control group, the PTZ-treated group displays a highly significant difference (***p<0.0001) in higher AChE levels. However, when compare with PTZ-treated groups, AChE activity in all of the other groups showed a highly significant difference (***p<0.0001).
On the above mention result indicate that the combined effect of M. oleifera leaves of ethanolic extract and curcumin has significant protection against PTZ induced kindled epilepsy in Rats. This probably may due to presence of falvonoid and phenolic content. Reduction of free radical as increased expression of antioxidant enzymes in the reduction in lipid peroxidation. The majority of plant extract decreases the significant amount of free radicals. Phenolic compounds are unique secondary metabolites present in the plants and exhibit a number of therapeutic applications such as antioxidant, anticancer and neuroprotective activity etc. The presence of hydroxyl groups contributes significantly to the phenolic compound's scavenging capacity. According to the results, ethanolic extracts of M. oleifera leaves and curcumin have strong antioxidant, free radical scavenging, and antiepileptic actions. The possible mechanism of antiepileptic effects or neuroprotection against PTZ by binding mode analysis of Curcumin, Quercitin and Chlorogenic Acid. Epilepsy is characterized as an aberrant interruption of nerve cell activity in the brain produced by oxidative stress-induced reactive oxygen species (ROS). ROS are unstable molecules containing oxygen and easily interact with other molecules in a cell. Reactive oxygen species in cells can damage genetic materials and proteins that it can lead to cell death. Glutathione Reductase (GR) is an enzyme that regulates reactive oxygen species (ROS) in the cell.
Therefore, activating GR can uplift the antioxidant property, which leads to the inhibition of ROS induced cell death in brain, thus Epilepsy can be prevented after the molecular modeling studies, it has been observed that, the active pocket or, site of Human Glutathione Reductase is “Y” shaped and to get a good a binding activity, it needs long and “Y” shaped ligands and it can also be concluded that if any of the compounds between Chlorogenic acid and Quercetin is treated with the combination of Curcumin can be much more potential.