|Year : 2020 | Volume
| Issue : 4 | Page : 296-305
Mangiferin ameliorates intracerebroventricular-quinolinic acid-induced cognitive deficits, oxidative stress, and neuroinflammation in Wistar rats
Mandeep Kumar Arora, Anglina Kisku, Ashok Jangra
Department of Pharmacology, KIET School of Pharmacy, KIET Group of Institutions, Ghaziabad, Uttar Pradesh, India
|Date of Submission||23-Oct-2019|
|Date of Decision||09-May-2020|
|Date of Acceptance||28-Aug-2020|
|Date of Web Publication||14-Oct-2020|
Dr. Ashok Jangra
Department of Pharmacology, KIET School of Pharmacy, KIET Group of Institutions, Delhi-NCR, Ghaziabad, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
INTRODUCTION: Mangiferin (MGF), a xanthonoid polyphenol, confers neuroprotection via combating oxidative stress and inflammation. The current investigation aimed to assess the neuroprotective potential of MGF on behavioral and neurochemical anomalies evoked by administration of quinolinic acid (QA) through intrastriatal injection in male Wistar rats and to reveal the associated mechanisms.
MATERIALS AND METHODS: QA (300 nm/4 μl saline) was administered intracerebroventricular in the striatum (unilaterally) once. Thereafter, MGF 20 and 40 mg/kg (peroral) was administered to the animals for 21 days.
RESULTS: QA administration caused marked alteration in motor activity (rotatod), footprint analysis, and cognitive function (Morris water maze test, and novel object recognition test). Furthermore, oxido-nitrosative stress (increased nitrite content, lipid peroxidation, with reduction of GSH), cholinergic dysfunction, and mitochondrial complex (I, II, and IV) dysfunction were observed in hippocampus and striatal region of QA-treated rats in comparison to normal control. Pro inflammatory mediators (tumor necrosis factor-alpha TNF-α and interleukin-1β) were noted to increase in the hippocampus and striatum of QA-treated rats. In addition, we observed BDNF depletion in both the hippocampus and striatum of QA-treated animals. MGF treatment significantly ameliorated memory and motor deficits in QA-administered rats. Moreover, MGF treatment (40 mg/kg) restored the GSH level and reduced the MDA, nitrite level, and pro-inflammatory cytokines in striatum and hippocampus. Furthermore, QA-induced cholinergic dysfunction (AChE), BDNF depletion and mitochondrial impairment were found to be ameliorated by MGF treatment.
CONCLUSION: The results suggest that MGF offers the neuroprotective potential that may be a promising pharmacological approach to ameliorate cognitive deficits associated with neurodegeneration.
Keywords: Hippocampus, mangiferin, oxido-nitrosative stress, quinolinic acid, striatum
|How to cite this article:|
Arora MK, Kisku A, Jangra A. Mangiferin ameliorates intracerebroventricular-quinolinic acid-induced cognitive deficits, oxidative stress, and neuroinflammation in Wistar rats. Indian J Pharmacol 2020;52:296-305
|How to cite this URL:|
Arora MK, Kisku A, Jangra A. Mangiferin ameliorates intracerebroventricular-quinolinic acid-induced cognitive deficits, oxidative stress, and neuroinflammation in Wistar rats. Indian J Pharmacol [serial online] 2020 [cited 2021 Jun 24];52:296-305. Available from: https://www.ijp-online.com/text.asp?2020/52/4/296/298155
| » Introduction|| |
Oxidative stress and inflammation elicited by free radical ions are the common factors responsible for cognitive deficits. A previous report expected to rise in the number of dementia patients to 115 million in 2050. In India, 22% of the elder population is combating with cognitive impairment. The elucidation of pathophysiological mechanisms underlying cognitive impairment leads to the development of novel pharmacological interventions.
Quinolinic acid (QA) is one of the potent endogenous neurotoxicants found in the mammalian brain. QA is an intermediate neuroactive metabolite of tryptophan which is produced through the kynurenine pathway in a nanomolar concentration. Previous clinical studies reported the enhanced levels of 3-Hydroxykynurenine (precursor of QA) in depressed and cognitive impaired subjects. The elevated level of QA has been implicated in neuronal degeneration., QA activates the NMDA receptor and increases calcium influx in neurons that activates different key enzymes like phospholipases, constitutive nitric oxide synthase, and protein kinases which are involved in oxido-nitrosative stress. QA enhances the free radical ions induced-lipid peroxidation process by forming the complex with Fe (II) which acts as a prooxidant. These excitotoxic events contribute to the neuronal cell death which in turn leads to cognitive impairment. It has been well documented that intrastriatal injection of QA in the brain causes neuronal damage via activation of microglial cells. Intrastraital injection of QA induces motor and behavioral alterations in the experimental animals.
Mangiferin (MGF) is a xanthanoid polyphenol extracted from Mango fruit, peel, bark, and leaves in Cyclopia species (honeybush tea). MGF has been noted to possess tremendous potential to combat oxidative stress and inflammation that improve behavioral function including cognition., In addition, it possesses cardiostimulating, hepatoprotective, anticancer, antiviral, immunomodulatory properties. Thus, the current investigation was planned to explore the neuroprotective potential of MGF in intracerebroventricular (ICV) QA-induced behavioral and neurochemical alterations into Wistar rats.
| » Materials and Methods|| |
Drug and chemicals
MGF and QA were procured from Sigma Aldrich Chemicals, India. Tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and BDNF kits were procured from Elabscience, India. All other chemicals were freshly prepared and were of analytical grade.
For this investigational study Male young Wistar Rats (200–250 g) were bought from the NIB, Noida, India. The experimental protocol (Approval no. IAEC/KSOP/E/18/07) was reviewed and accepted by IAEC. Under the standard laboratory conditions, animals were kept at 23°C ± 2°C temperature with 70% relative humidity maintained on 12 h light/dark periodic pattern with free access to food and water. To prevent possible chances of infection due to wet cage, animal beddings were changed daily. The animals were sacrificed on scheduled time-interval as per the study plan to assess the various parameters.
Rats were arbitrarily distributed into 5 groups (n = 10): Control group, Sham-operated, QA (300 nM/4 μl QA in Normal saline), QA + MGF-20 mg/kg (300 nM/4 μl QA in Normal saline with MGF: 20 mg/kg), QA + MGF-40 mg/kg (300 nM/4 μl QA in Normal saline with MGF: 40 mg/kg), Drug control (MGF-40 mg/kg). MGF was dissolved in 0.1% dimethylsulfoxide in 0.9% normal saline and given through oral route. Doses selection of MGF was based on our previously designed investigation on MGF.
Normal saline was administered to one group while another group receives QA (300 nM/4 μl in Normal saline) on day 0. The drug treatment was given for the entire study time. No animal mortality was observed during the study period. At the end of study i.e., 21st day, locomotor activity and footprint analysis were performed to analyze the locomotor activity and gait behavior. Spatial learning memory was assessed on the last 5 days of the study. Novel object recognition test (NORT) and Rotarod were performed on the last 3 days of the study period. Biochemical parameters were analyzed in the striatum and hippocampus of the rats after cervical dislocation.
Surgical procedure (intracerebroventricular administration)
All the surgical were sterilized with 70% ethanol. The rat was anesthetized by injecting the ketamine. The rat hairs were shaved from the top of the shoulder to the space between the eyes. The anesthetized rat was positioned on the stereotaxis apparatus. The head was held with the ear bars and disinfected the shaved area with the help of ethanol-dipped cotton swab followed by an iodine-dipped cotton swab. After the incision of the skin, a hole was drilled in the skull according to the coordinates. Hamilton syringe (10 μl) with a needle was cleaned and sterilized for the administration of QA. After the drug administration, the syringe was kept for 5 min to inhibit the oozing of the drug from the hole. Then incision was closed with suturing. The temperature was maintained throughout the surgery to prevent hypothermia. The rats were daily monitored after the surgery for the 1st week. To avoid irritation from the suture thread, 5-0 nylon suture was removed in 7–10 days following surgery.
Morris water maze testing
This maze represents a more specific test of spatial memory. To perform the Morris water maze (MWM) test, a round black water-filled pool of 180 cm in diameter and 40 cm height was taken. The water was filled in the pool up to 30 cm. The temperature of the pool water was maintained at 25°C ± 0.1°C. A 13 cm2 sized platform made up of plexiglass square was positioned in center of one quadrant, ten mm below the water level. The test was performed in two trials: (i) training trial and (ii) probe test. All through the visual cue tests and learning trials, the position of the platform has remained the same but it was removed during the probe test. The learning trial was performed for four successive days. The probe trial was conducted without platform on the 5th day. In the training trial, the location of the platform was changed every time, but the visual pattern of cue remains unchanged. In each trial, rat was allowed to swim till they reached the platform. Once the animal reached the platform, the rat was permitted to halt on this platform for 30 s. The time span utilized by the animal to arrive at platform was noted. During this trial, individual animal was permitted to swim in the MWM for two min. The time consumed in the target quadrant (%) was recorded.
Rotarod test was carried out to determine the grip strength and motor coordination activity of the animal. The training was given to each rat before the test on the final day. 25 rpm was set on the rotatod. The fall-off time was recorded with 180 s cut-off time. Three different trials were carried out with each rat at a 5 min interval.
Novel object recognition test
NORT was used for assessment of recognition memory. Three different phases were carried out to perform NORT i.e., (a) habituation, (b) familiarization, and (c) test phase. The test was executed on a black open box of 50 cm × 50cm × 36 cm. In the first phase, the rat was placed for 5 min in the open box to habituate to the empty open arena. Thereafter, the familiarization phase was conducted in which two objects (a rectangular plastic ball and a wooden rectangle) placed at the box. Freedom was given to the animal for 10 min in the box for area exploration. In the next phase, the wooden rectangular-shaped object was replaced with a pyramid-shaped object. Individual rat was permitted for 180 s. To evade olfactory cues, the objects as well open field box was frequently cleaned with alcohol after each phase of the test. The time taken for exploring the novel and familiar object was recorded. Recognition index was calculated by taking the ratio of time spent by the animal to explore the novel object over the complete time consumed by the animal to explore novel and familiar objects during the 3 min test session. Results were calculated and expressed as percentage recognition index.
A laser beam photoactometer was used to measure the locomotor behavior of each rat to determine horizontal activity. The rat was placed between the beam emitter and detector for one min inside the activity box to get acclimatized so that it could give the normal reading. The activity counts by interrupting the photobeam for 5 min was noted to evaluate the basal activity score.
Foot print analysis
The gait abnormalities in rats were assessed by footprint analysis. Summarily, the footprints of the rats were obtained by dipping their feet in four different colored food dyes and were allowed to run on an inclining gangway with dimensions 80 cm × 10 cm × 8 cm. The runway floor was covered with a white sheet. In order to get a clear footprint, the animals were supposed to walk up the runway into a dim section. Afterward, the rats were cleaned with warm water to remove the dye. The footprints were scanned and the 'stride length' was calculated by using a scale. Stride length was calculated by measuring the distance between sequential placements of the same rat's paw.
Preparation of tissue homogenate
On the last day i.e., 21st day, the rats from each group were killed. The hippocampus and striatum region of the brain was cautiously and speedily isolated on the ice-cold Petri dish More Details. 0.1M PBS of pH 7.4 was used to make 10% tissue homogenate. Homogenate was then centrifuged for 15 min at a low temperature. Finally, the supernatant was separated from homogenate and was stored at −20°C for further biochemical analysis.
Estimation of lipid peroxidation
50 μl of hippocampus/striatum homogenate was mixed thoroughly with 50 μl of SDS (8.1%). Into this mixture, an equal amount (350 μl) of acetic acid (20%) and thiobarbituric acid (0.8%) solution was added and 1.5 ml volume was make up with the water. Afterward, the prepared solution in the test tube was heated at 95°C for 1 h. The solution was kept at 25°C for cooling followed by centrifugation of the tubes for 10 min at 10000 rpm to collect final supernatant. The MDA level was measured at λmax 532 nm. MDA concentration was estimated and represented as μMol of MDA/mg of total protein.
Estimation of GSH level
In brief, the supernatant and 10% (w/v) TCA were taken in a 1:1 ratio, then centrifugation at 1000 g for 10 min (4°C). In the collected supernatant 1 ml of disodium phosphate (0.3M) and 250 μl of DTNB (0.001M) were added. The absorbance (Abs) was recorded through spectrophotometer at λmax 412 nm.
Estimation of AChE level
The AChE was estimated as described previously. Briefly, the mixture was made that contains Acetylcholine Iodide (1 mM), DTNB (2 mM), Monopotassium phosphate (100 mM, pH-7) and homogenate of hippocampus/striatum in 500 μl. This solution was then incubated at 37o C for 10 min. 500 μl of serine hemisulphate (0.5 mM) was incorporated to terminate this reaction. Finally, the Abs of resulted yellow solution measured at λmax 412 nm.
Estimation of nitric oxide
An equal amount of striatal/hippocampal supernatant and the Griess reagent were poured in an Eppendorf tube. At room temperature, the mixture was kept for 10 min in a dark chamber. Finally, the Abs was detected at 540 nm and outcomes were expressed as micromoles per mg of total protein.
Assessment of mitochondrial complexes
Isolation and preparation of mitochondria
The hippocampus and striatum parts were separated out from the brain and mitochondria were recovered as described previously (Rosenthal et al.). The isolation medium containing sucrose (75 mM), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (5 mM), bovine serum albumin (1 mg/ml), mannitol (225 mM), and 1 mM ethylene glycol tetra acetic acid (1 mM) was used to homogenize the hippocampus and striatum sample. The homogenized mixture was centrifuged at 2000 g at 4°C for 3 min. Pellets collection was done after discarding the supernatant and again suspended and centrifuged. Afterward, the synaptosomal layer was resuspended in digitonin (0.02%) and followed by centrifuging for 10 min at 12,000 g for further evaluation.,
NADH dehydrogenase (Complex I) activity
This method includes catalytic oxidation of NADH into NAD+ and subsequently cytochrome C reduction was takes place. 3 ml of glycylglycine (0.2 mM), NADH (6 mM), sodium bicarbonate (0.02 mM) solution, and 1 mM of cytochrome C was mixed and adjusted to pH 8.5. The sample was added in the mixture and the Abs was detected at 550 nm for the subsequent 180 s. The activity was calculated and represented as nMol of oxidized NADH/min/mg of total protein.
Succinate dehydrogenase (Complex II) activity
In this method, a mixture containing butanedioic acid (0.6 M), phosphate buffer (0.2 M), 1% BSA, and potassium ferricyanide (0.03M) of pH 7.8 was taken. The reaction was started after adding the sample into the mixture. The Abs was detected at 420 nm for the subsequent 180 s. The activity was calculated and represented as nMol of succinate dehydrogenase/min/mg of total protein.
Cytochrome c oxidase (Complex IV) assay
Complex IV activity in the sample was assessed as described previously. The reaction mixture was taken that contains reduced form of cytochrome C (0.03 mM) in PBS. Thereafter, mitochondrial sample was added to initiate the reaction. The Abs was detected at 550 nm for subsequent 3 min. The activity was calculated and represented as nMol of oxidized cytochrome c/min/mg of total protein.
Interleukin-1β, tumor necrosis factor-alpha, and BDNF determination
Hippocampus and striatum were quickly isolated from the rat brain on ice-cold petri-dish. Protease inhibitor cocktail was added in the sample during the homogenization process. IL-1β, TNF-α, and BDNF determination was carried out as per the protocol provided in the kit. IL-1β and TNF-α levels represented as pg/mg of total protein. The BDNF level estimated as ng/mg of total protein.
All the data values represented as means ± standard error median. Comparison between different experimental group were performed through one-way analysis of variance, followed by Tukey's post-hoc test (using Graph pad prism software). P < 0.05 was taken into consideration for statistically significance.
| » Results|| |
Effect of mangiferin on intracerebroventricular-quinolinic acid-induced alterations in behavioral parameters
The MWM study was performed from the 17th day of experimental study till the last day. The whole trial was performed in two phases: Acquisition phase and probe trial. In the acquisition phase, significance (P< 0.001, P < 0.01, and P < 0.01) changes in the escape latency time was observed on 2nd, 3rd and 4th day, respectively in the QA-treated group as compared to the control group. Whereas, escaped latency time on 3rd and 4th day showed significant reduction (P< 0.05 and P < 0.01) in MGF (40 mg/kg) treated group [Figure 1]a. In the probe trial, ICV-QA-treated rats spent fewer time in the target quadrant (P< 0.001) as compared to the control group. MGF (20-mg/kg) showed nonsignificant result on the time spent in the target quadrant when compared with the QA-treated group. On another hand, MGF (40 mg/kg)-treated ICV-QA rats spent statistically significant (P< 0.01) longer duration in that target quadrant in comparison with ICV-QA rats [Figure 1]b. Thus, MGF (40 mg/kg) alleviated cognition dysfunction caused due to chronic administration of QA.
|Figure 1: Effect of Mangiferin on quinolinic acid.induced alterations in (a) mean escape latency, and (b) time spent in the target quadrant. The data were assessed at different days of the experimental study. The data were represented as mean ± standard error median (n = 6). ###P < 0.001 and ##P < 0.01 compared to control group. **P < 0.01 and *P < 0.05 when compared with quinolinic acid-administered group|
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Furthermore, the QA-treated group exhibited motor in-coordination as evidenced by rotarod test results. We found that the fall-off time of ICV-QA rats was significantly declined (P< 0.001) as compared to the control group [Figure 2]a. MGF (40 mg/kg) treated ICV-QA rats showed significantly (P< 0.01) longer fall-off spell as compared to ICV-QA rats. No significant effect was observed in MGF (20 mg/kg) group as compared to the ICV-QA-treated group.
|Figure 2: Effect of Mangiferin on quinolinic acid.induced alterations in (a) rotarod activity, (b) in % recognition index, and (c) locomotor activity. The data were represented as mean } standard error median (n = 6). ###P < 0.001, ##P < 0.01, and#P < 0.05 compared to control group. ***P < 0.001, **P < 0.01 and *P < 0.05 when compared with quinolinic acid.administered group|
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NORT results exhibited that ICV-QA rats were unable to distinguish between the familiar and novel objects thereby showed (P< 0.01) lower recognition index in comparison with the control group. MGF (20 mg/kg) treated group exhibited no significant effect on the recognition index in comparison to the ICV-QA-treated group. However, MGF (40 mg/kg) treated ICV-QA rats exhibited significant (P< 0.05) increase in recognition index during comparison with ICV-QA-treated group [Figure 2]b. ICV-QA administration, as well as MGF treatment, did not affect the locomotor activity in comparison to normal control rats [Figure 2]c.
ICV-QA administration significantly altered the stride length during walking in footprint analysis [Figure 3]a. The stride length on day-7, 14, and 21 significantly (P< 0.05, P < 0.01, and P < 0.001) declined in QA administered rats in comparison to normal control rats. MGF (40 mg/kg) treated animal exhibited significant (P< 0.05) increase in stride length as compared to ICV-QA-treated animals on day-21 [Figure 3]b. However, MGF (20 mg/kg) did not produced significant result on stride length in comparison to ICV-QA rats. Thus, our study results indicated that MGF (40 mg/kg) is capable to avert the ICV-QA induced neurotoxicity.
|Figure 3: (a) Illustrative image of footprints from control (A), Sham-operated (B), quinolinic acid-treated rats (C), Mangiferin (20 mg/kg)+ quinolinic acid-treated rats (D), Mangiferin (40 mg/kg)+ quinolinic acid-treated rats (E), and Drug control (F). (b) Effect of Mangiferin on quinolinic acid-induced alterations in footprint analysis by evaluating the alteration in stride length of rats. The data were represented as mean±standard error median (n=6). ###P<0.001, ##P<0.01, and #P<0.05 compared to control group. ***P<0.001, **P<0.01 and *P<0.05 when compared with quinolinic acid-administered group|
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Effect of mangiferin on intracerebroventricular-quinolinic acid-induced differences in MDA level
QA-administered group showed marked (P< 0.001) rise in the MDA level both in striatum and hippocampus in comparison to the normal control rats. On another hand, MGF (40 mg/kg) exhibited significant (P< 0.001) reduction in the MDA level both in the hippocampus and striatum. Nevertheless, MGF (20 mg/kg) treated rats showed significant (P< 0.05) MDA reduction in the hippocampus but no changes were observed in the striatum region in comparison to QA-administered rats [Table 1].
|Table 1: Effect of mangiferin on quinolinic acid -induced oxido-nitrosative stress in hippocampus and striatum|
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Effect of mangiferin on intracerebroventricular-quinolinic acid-induced differences in GSH level
ICV-QA group demonstrated significant (P< 0.01) decline in the GSH level both in the hippocampal and striatal region during comparison with control group. Administration of MGF (40 mg/kg) significantly (P< 0.05) augmented the GSH level in the hippocampus and striatum in comparison to the ICV-QA group. However, no significant effect was observed in MGF (20 mg/kg) group. Similarly, the drug control group failed to show any significant alteration in GSH level in comparison to the control group [Table 1].
Effect of mangiferin treatment on intracerebroventricular-quinolinic acid-induced variation in nitric oxide
We found that ICV-QA administration markedly (P< 0.001) increased the NO levels in the hippocampus and striatal region in comparison to control rats. MGF (40 mg/kg) treated ICV-QA rats exhibited significantly (P< 0.05) decrease of NO level in the hippocampus and striatum as compared to ICV-QA rats [Table 1]. MGF (20 mg/kg) and MGF control group did not exhibit any significant result on NO level in both the brain regions.
Effect of mangiferin treatment on intracerebroventricular-quinolinic acid-induced alteration in AChE activity
ICV-QA administration resulted in the marked (P< 0.001) augmentation of the AChE activity in the striatal as well as hippocampal region in comparison to normal control group. After 21 days of MGF treatment (40 mg/kg), AChE activity was markedly (P< 0.01 and P < 0.05) declined in hippocampus and striatum in comparison to ICV-QA rats [Figure 4]a. MGF (20 mg/kg) failed to exert significant action on AChE activity.
|Figure 4: Effect of Mangiferin on quinolinic acid-induced alterations in (a) AChE activity, (b) interleukin-1β level, (c) tumor necrosis factor-alpha, and (d) BDNF levels in hippocampus and striatum of rat brain. The data were represented as mean ± standard error median (n = 6). ###P < 0.001, ##P < 0.01, and #P < 0.05 compared to control group. ***P < 0.001, **P < 0.01 and *P < 0.05 when compared with quinolinic acid.administered group|
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Effect of mangiferin treatment on intracerebroventricular-quinolinic acid-induced alteration in the mitochondrial complex (-I, -II and -IV)
In the electron transport chain cycle, mitochondrial complex (MC) are involved. Complex I, complex II and complex IV exhibited marked (P< 0.001) reduction in the hippocampus as well as striatum of QA-treated groups as compared to control groups [Table 2]. However, MGF (40 mg/kg) treated ICV-QA group displayed significant (P< 0.01 and P < 0.05) augmentation in the complex I in the striatum and hippocampus. However, the level of complex II was markedly (P< 0.01) increased only in the hippocampal region after administration of MGF (40 mg/kg) in ICV-QA rats. Complex IV was increased significantly (P< 0.05 and P < 0.001) in the hippocampus as well as striatum, respectively in MGF (40 mg/kg) treated ICV-QA rats as compared to ICV-QA treated rats. However, no significant changes in MC activity was noted between the drug control group and normal control rats.
|Table 2: Effect of mangiferin on quinolinic acid -induced alterations in mitochondrial complex activities in hippocampus and striatum|
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Effect of mangiferin treatment on intracerebroventricular-quinolinic acid-induced augmentation of interleukin-1β and tumor necrosis factor-alpha level
Both IL-1β and TNF-α were found to be elevated significantly (P< 0.001) in striatum and hippocampus of ICV-QA administered rats in comparison with control group [Figure 4]b and c]. However, a higher dose of MGF (40 mg/kg) was associated with significant (P< 0.001) reduction in the QA-induced IL-1β level in striatum and hippocampus. Moreover, marked reduction in TNF-α level was noted in the striatum (P< 0.01) and hippocampus (P< 0.001) of MGF (40 mg/kg)-treated ICV-QA rats.
Effect of mangiferin treatment on intracerebroventricular-quinolinic acid-induced BDNF depletion
As shown in [Figure 4]d, the ICV injection of QA significantly (P< 0.001) depleted the level of BDNF in striatal and hippocampal region in comparison with the control group. MGF (40 mg/kg) significantly (P< 0.05) augmented the level of BDNF only in the hippocampus of ICV-QA administered rats. MGF (40 mg/kg) controlled group also demonstrated augmentation of the BDNF level in the hippocampal and striatal region. However, the results were found statistically nonsignificant.
| » Discussion|| |
The current study aims to explore the neuroprotective effect of MGF in QA-administered rats and the possible underlying mechanism. Our findings revealed that MGF significantly alleviated the memory deficits of the QA administered animals. The prevalence of cognitive deficits is very high in neurodegenerative disorders. Moreover, it is associated with a complex and multifactor etiology. It is well well-known from preclinical as well as from clinical studies that cognitive deficit has strong correlation with higher levels of oxido-nitrosative stress and neuroinflammation. The current study results also support the association of oxidative stress with cognitive function. In addition, we found neuroprotective effects of MGF on QA-induced behavioral and neurochemical deficits in rats. Treatment with MGF alleviated the gait abnormalities, motor in-coordination, memory impairment, oxidative stress, neuroinflammation and normalized the mitochondrial function. In the current study, we first demonstrated that MGF exerts a neuroprotective effect in the ICV-QA administered rats and its mechanism may be related to the mitigation of oxidative stress, cholinergic deficits, and mitochondrial dysfunction.
High level of endogenous neurotoxin i.e., QA in the brain associated with behavioral alterations. Intrastriatal administration of QA to experimental animals leads to abrupt and over-stimulation of excitatory NMDA receptors which, in turn causes memory and motor impairments via apoptotic neuronal cell death in different brain regions. The ICV-QA model of behavioral deficits is a well-established experimental model that elicits ROS generation, neuroinflammation, mitochondrial dysfunctioning, and associated apoptotic cell death in the brain. Numerous studies suggested that the ICV-QA administration elicits a vicious cycle of oxido-nitrosative stress and mitochondrial impairment in the brain. NORT and MWM test were employed to evaluate the recognition memory and spatial learning respectively. We found spatial learning impairment and recognition memory deficits in QA-treated rats. Moreover, stride length was measured to assess gait analysis. We found short stride length in QA-administered rats in comparison with normal control and sham-operated groups. The ICV-QA-induced motor coordination impairment was revealed by the rotarod test. Collectively, in the current investigation, we found that intrastriatal injection of QA leads to marked alteration in behavioral function evident by low locomotor activity, gait abnormalities in footprint analysis, impaired motor coordination and memory impairment. Thus, our findings are in concordance with the earlier studies representing behavioral anomalies after the administration of QA in the striatum., Moreover, we found that treatment with MGF significantly ameliorates motor function that clearly indicates an increase in striatum functioning. On the other hand, MGF administration significantly alleviated QA-associate learning as well as memory impairment that reflects the improvement in the hippocampal function. The neuroprotective efficacy of MGF against cognitive function is in accordance with our previously reported investigations.,
Free radicals have been reported to cause oxidative stress and disruption of mitochondrial function. ICV administration of QA elicits oxido-nitrosative damage through the production of free radicals. In this respect, our study results found that the administration of QA in the striatum elicits oxido-nitrosative stress in both striatum and hippocampus. Previous studies also had shown augmentation of oxidive and nitrosative stress indicators in the striatum and hippocampus following ICV administration of QA., QA has been shown to increase lipid peroxidation via QA-Fe2+ complex-generated hydroxyl radical by Fenton reaction. Moreover, QA has the ability to generate peroxynitrite and alter the levels of endogenous antioxidant systems in the brain. Our result also shows an elevated level of MDA, an indicator of lipid peroxidation in the hippocampus and striatum. Moreover, the nitrite level was also found elevated in the hippocampus and striatum of QA-injected rats. In the MGF structure, there is a presence of a catechol ring which enhances the formation of a complex with Fe2+ and Fe3+, thereby inhibiting the lipid peroxidation and Fenton reaction. In addition, MGF enhances the cellular defense system by elevating the superoxide dismutase, and catalase enzymes. MGF has been shown to increase expression of nuclear Nrf2, Nrf2 binding of ARE, and up-regulated its signaling target NAD (P) H dehydrogenase [quinone] 1 (NQO1). In our study, we found that GSH level was significantly elevated by the treatment of MGF in QA-treated rats. The current results suggested that treatment with MGF in QA-treated animals cause significant alleviation of oxido-nitrosative stress suggesting their antioxidant potential. Thus, current findings are in concordance with the aforesaid studies.
Mitochondria are a producer and targets of ROS that can elicit oxidative injury via disruption of oxidative phosphorylation. QA acts as mitochondria toxin which causes mitochondria dysfunction via NMDA receptor-mediated excessive calcium entry in the mitochondria. Previous reports suggested that QA-induced the mitochondrial dysfunction that leads to several damaging effects such as mutation in mitochondrial DNA, augmentation of oxidative as well as nitrosative stress, and an increase in the permeability of mitochondrial membrane., Mitochondrial respiratory chain complexes (I-IV) dysfunctions reflect mitochondria anomalies in the cells that lead to mitochondria energy deficits. Among these complexes, complex II and IV are important because their dysfunction leads to the excessive release of free radical ions which further augments the mitochondrial damage. In our study, we observed that complex I, II, and IV functions were reduced in the hippocampus as well as in striatum of QA-injected rats. These results were corroborated with the previous reports. In the present investigation, MGF treatment significantly ameliorates the MC function in both hippocampus and striatum via inhibition of oxido-nitrosative stress. A previous study reported that MGF alleviates the mitochondrial membrane potential loss and swelling via the free radicals scavenging property of MGF. Thus, it can be inferred that MGF protects the mitochondrial function through its potent anti-oxidant activity.
Several experimental and clinical studies have suggested the crucial role for neuroinflammation in neurodegenerative disorders. The activation of inflammatory mediators like IL-1β and TNF-α during inflammation elicits the vicious mechanism that eventually leads to cell death. Oxido-nitrosative stress increases the levels of pro-inflammatory mediators by the involvement of transcription regulator i.e., nuclear factor-kappa B (NF-κB). Thus, neuroinflammation can be prevented either by oxido-nitrosative stress inhibition or repression of NF-κB. Earlier studies also indicated the NF-κB inhibition property of MGF in different animal models., In our study, QA elicits the neuroinflammation and caused augmentation of IL-1β and TNF-α in both hippocampus and striatum. However, MGF a potent anti-oxidant significantly inhibited the up-regulation of pro-inflammatory cytokines in striatum as well as in hippocampus. Thereby, inhibits the further array of mechanism that can progressed toward neuronal cell injury. The observed anti-inflammatory activity of MGF is well corroborated with our previous published reports. BDNF, a crucial neurotrophic factor has been stated to be dysregulated in oxidative stress and neuroinflammation. However, the effect of intrastriatal administration of QA on BDNF has been found contradictory., In our study, we found BDNF depletion in striatum and hippocampus of ICV-QA rats that is corroborated with a recent study. MGF treatment significantly reestablished the BDNF level in the hippocampal region only.
| » Conclusion|| |
The current outcome of the investigation revealed the neuronal protection of MGF against QA-induced behavioral and neurochemical anomalies. The resulted neuroprotective potential attributed to the mitigation of oxidative as well as nitrosative stress (MDA, GSH as well as nitric oxide), neuroinflammation (IL-1β and TNF-α), protection of MC activities and BDNF content. Thus, MGF may provide an intriguing therapeutic approach for the management of behavioral anomalies. However, additional mechanistic studies are warranted to elucidate a more detailed mechanism of MGF.
The financial support by Dr. A P J Abdul Kalam Technical University, Lucknow under Visvesvaraya Research Promotion Scheme (VRPS) is gratefully acknowledged.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]