Ethika Tyagi

A study of brain insulin receptors, AChE activity and oxidative stress in rat model of ICV STZ induced dementia

In the present study, role of brain insulin receptors (IRs) in memory functions and its correlation with acetylcholinesterase (AChE) activity and oxidative stress in different brain regions were investigated in intracerebroventricular (ICV) streptozotocin (STZ) induced dementia model. Rats were treated with STZ (3 mg/kg, ICV) on day 1 and 3. Donepezil (5 mg/kg po) and melatonin (20 mg/kg ip) were administered in pre- and post-treatment schedules. Morris water maze test was done on day 14 and animals were sacrificed on day 21 from 1st STZ injection. Memory deficit was found in STZ group as indicated by no significant decrease in latency time antagonized by donepezil and melatonin. IR protein level was found significantly increased in trained group as compared to control, whereas STZ decreased IR level significantly as compared to trained rats in hippocampus which indicates that IR is associated with memory functions. STZ induced decrease in IR was reversed by melatonin but not by donepezil. Melatonin per se did not show any significant change in IR level as compared to control. AChE activity (DS and SS fraction) was found to be increased in hippocampus in STZ group as compared to trained which was inhibited by donepezil and melatonin. Increase in MDA level and decrease in GSH level were obtained in STZ group indicating oxidative stress, which was attenuated by donepezil and melatonin. Effectiveness of antioxidant, melatonin but not of anti-cholinesterase, donepezil against STZ induced changes in IR indicates that IR is more affected with oxidative stress than cholinergic changes.

Insulin receptor signaling in rat hippocampus: A study in STZ (ICV) induced memory deficit model

Brain insulin receptors (IRs) have been suggested as an important regulatory factor for cognitive functions but the involvement of IR signaling in memory deficit associated with neurodegenerative conditions is not yet explored. In the present study, IR gene expression was studied by RT-PCR and signaling pathways by immunoblotting in CA1, DG and CA3 subregions of hippocampus in intracerebroventricular (ICV) administered streptozotocin (STZ, 3mg/kg twice) induced memory deficit model in rat. The effect of pre- and post-treatment of donepezil (5mg/kg po) and melatonin (20mg/kg po) on signaling pathways were studied. Effect of LY294002 (ICV), a PI3 Kinase inhibitor, was also investigated on memory functions and Akt phosphorylation. An increased IR expression (both gene and protein), phosphorylation of Shc, Erk1/2, IRS-1 and Akt in CA1 and CA3 region of P2M fraction was observed after training as compared to control. STZ treated rats showed memory deficit and significant decrease in IR expression, phosphorylation of IRS-1 and Akt only in CA3 region as compared to trained group which were reversed by pre and post-treatment of melatonin but donepezil was effective only against memory deficit. LY294002 (3mM) treatment showed delayed learning and decrease in Akt phosphorylation. This study suggests that IR expression and its signaling pathways in hippocampal CA1 and CA3 regions are involved in memory functions and STZ (ICV) induced memory deficit. Hippocampal IR system might be playing an important role in regulation of memory functions, however only IR/IRS-1/Akt pathway in CA3 region is associated with STZ induced memory deficit.

Effect of curcumin on brain insulin receptors and memory functions in STZ (ICV) induced dementia model of rat.

Curcumin, the principal curcuminoid of turmeric, exhibits beneficial role in several neurodegenerative disorders such as dementia of Alzheimer type. Recent evidences suggest the involvement of brain insulin receptors (IRs) in the pathophysiology of dementia disorders. Therefore, the present study was undertaken to investigate the effect of curcumin on memory functions, brain IRs, acetylcholinesterase (AChE) activity and oxidative stress in intracerebroventricular (ICV) administered streptozotocin (STZ) induced dementia in rats. Rats were injected with STZ (3 mg/kg, ICV) bilaterally twice, on day 1 and 3 and curcumin (200 mg/kg, po) was administered in pre- and post-treatment schedules. STZ (ICV) treated group had shown memory deficit as indicated by no significant decrease in latency time in Morris water maze test and significant decrease in IR protein level in both hippocampus and cerebral cortex. Pre- and post-treatment of curcumin in STZ (ICV) treated rats significantly restored the memory deficit and IR protein level in both the regions. Furthermore, STZ (ICV) resulted into enhanced AChE activity in hippocampus and cerebral cortex which was normalized by curcumin pre- and post-treatment. An increase in MDA level and decrease in GSH level were obtained in both hippocampus and cerebral cortex in STZ treated group, indicating state of oxidative stress, which was also attenuated by pre- and post-treatment of curcumin. The results suggest that besides the anticholinesterase and antioxidant activity, effect on brain IR may also be an important factor for protective effect of curcumin against STZ induced dementia model.

Rare dipeptide and urea derivatives from roots of Moringa oleifera as potential anti-inflammatory and antinociceptive agents.

In the course of our studies on the isolation of bioactive compounds from the roots of Moringa oleifera, a traditional herb in southeast Asia, rare aurantiamide acetate 4 and 1,3-dibenzyl urea 5 have been isolated and characterized. And also, this is the first report of isolation from this genus. Isolated compound inhibited the production of TNF-alpha and IL-2; further compound 5 showed significant analgesic activities in a dose dependant manner. These findings may help in understanding the mechanism of action of this traditional plant leading to control of activated mast cells on inflammatory conditions like arthritis, for which the crude extract has been used.

Cholinergic protection via α7 nicotinic acetylcholine receptors and PI3K-Akt pathway in LPS-induced neuroinflammation ☆

The present study was planned to investigate the effect of anti-cholinesterase drugs donepezil and neostigmine on neuroinflammation induced by intracerebroventricular administration of lipopolysaccharide (LPS, 50 microg) in rat. Proinflammatory cytokines (TNF-alpha and IL-1beta), expressions of iNOS and COX-2, acetylcholinesterase activity, malondialdehyde and reduced glutathione were studied in different brain regions at 24h of LPS injection. Donepezil was found to decrease the LPS-induced AChE activity and oxidative stress in all the brain regions. It also inhibited the LPS-induced proinflammatory cytokines and iNOS expression but did not affect the increased COX-2 expression whereas neostigmine treatment had no effect on LPS-induced proinflammatory cytokines. Methyllycaconitine (MLA), a alpha7 nicotinic acetylcholine receptor antagonist, significantly antagonized the donepezil mediated inhibition of LPS-induced proinflammatory cytokines, indicating that alpha7 nicotinic acetylcholine receptor subunit was playing a role in regulation of neuroinflammation. The phosphorylation of Akt, an effector of PI3K, increased with donepezil treatment. These results suggest that increased cholinergic activity in brain by donepezil prevents LPS-induced neuroinflammation via alpha7-nAChRs, followed by the PI3K-Akt pathway and this system may form the basis for the development of novel agents for reversing neuroinflammation or provide new indications for existing drugs.

Influence of LPS-induced neuroinflammation on acetylcholinesterase activity in rat brain

In the present study, neuroinflammation was induced by bilateral intracerebroventricular (ICV) administration of Lipopolysaccharide (LPS). Proinflammatory cytokines (TNF-alpha and IL-1beta), acetylcholinesterase (AChE) activity, malondialdehyde (MDA) and reduced glutathione (GSH) were studied as markers for neuroinflammation, cholinergic activity and oxidative stress respectively in different brain regions at different time points after LPS injection. LPS produced increase in proinflammatory cytokines, MDA and the decrease in level of GSH at 24 h indicating a state of inflammation in brain regions, which was significantly blocked by Ibuprofen, a non steroidal anti-inflammatory drug. Enhanced AChE activity with these inflammatory markers after LPS administration indicates a possible relationship between neuroinflammation and cholinergic system during the development of neurodegenerative diseases.

Effect of melatonin on neuroinflammation and acetylcholinesterase activity induced by LPS in rat brain.

Melatonin, which plays an important role in circadian rhythm regulation, is highly potent endogenous free radical scavenger and antioxidant. To determine the efficacy of melatonin in neuroinflammation induced by intracerebroventricular (i.c.v.) administration of lipopolysachcharide (LPS, 50 microg), pro-inflammatory cytokines (TNF-alpha and IL-1beta), and markers of oxidative stress (malondialdehyde and reduced glutathione) were studied in different brain regions (striatum, cerebral cortex, hippocampus and hypothalamus) of rat. To study the cholinergic intervention during neuroinflammatory conditions acetylcholinesterase (AChE) enzyme activity was taken as marker of cholinergic activity. Melatonin (5 and 10 mg/kg, p.o.) decreased the LPS induced pro-inflammatory cytokines and oxidative stress in different brain regions. It was also found to inhibit the LPS induced increase in AChE activity. These results suggest the therapeutic potential of melatonin for neuroinflammation which is an integral part of neurodegenerative disorders.

Effect of insulin and melatonin on acetylcholinesterase activity in the brain of amnesic mice

Basal forebrain cholinergic neurons and oxidative stress in brain have been suggested to play an important role in the regulation of memory functions. Therefore, the present study was planned to study the effect of donepezil, an anticholinesterase antidementia drug, insulin and melatonin, an antioxidant, on memory deficit and acetylcholinesterase (AChE) activity in brain areas of scopolamine-induced amnesic mice. Memory was tested by passive avoidance (PA) test in Swiss adult male mice. A significant increase in transfer latency time (TLT) in 2nd trial as compared to 1st trial is considered as successful learning. Scopolamine (3 mg/kg i.p.) was administered 5 min prior to 1st trial to induce amnesia. AChE activity in detergent soluble (DS) and salt soluble (SS) fractions was estimated in brain areas after completion of 2nd trial. Scopolamine was effective in producing memory impairment (amnesia) which was reverted by donepezil (5 mg/kg p.o.), insulin (1 IU/kg i.p.) and melatonin (20 mg/kg p.o.). AChE activity in DS fraction of scopolamine amnesic mice was inhibited by donepezil, insulin and melatonin with varying extent in different brain regions, whereas AChE activity in SS fraction was not much affected. The results demonstrate that anti-amnesic effect of donepezil, insulin and melatonin may be mediated through enhancement of cholinergic activity.

Cholinergic influence on memory stages: A study on scopolamine amnesic mice

Objectives: The study was planned to determine cholinergic influence on different stages of memory - acquisition, consolidation and recall in scopolamine-induced amnesia (memory impairment) in mice. Materials and Methods: To study acquision, consolidation and recall stages of memory, we administered scopolamine (0.75, 1.5 and 3 mg/kg ip) 30 minutes and five minutes prior to first trial acquisition and consolidation and 30 minutes prior to second trial recall of passive avoidance (PA) test, respectively, in separate groups. Tacrine (5 mg/kg po) and rivastigmine (5 mg/kg po) were administered one hour prior to first trial in separate groups which received scopolamine (3 mg/kg ip) 30 minutes and five minutes prior to first trial where as the control group received vehicle only. Results: In the control group, there was a significant (P < 0.01) increase in transfer latency time (TLT) in the second trial compared to first indicating successful learning. In scopolamine treated groups, administering scopolamine 30 minutes or five minutes prior to first trial did not show any significant (P > 0.05) change in TLT whereas mice treated with scopolamine 30 minutes prior to second trial showed significant (P < 0.01) increase in TLT in second trial as compared to the first. Both tacrine and rivastigmine administration in scopolamine treated mice showed significant (P < 0.05-0.01) increase in TLT in second trial as compared to first trial while the rivastigmine treated group showed greater percentage retention compared to tacrine treated group. Conclusion: Results show that acquisition and consolidation are more susceptible to the scopolamine effects than recall. Thus, it may be concluded that cholinergic influence is more on acquisition and consolidation as compared to recall.

Involvement of monoamines and proinflammatory cytokines in mediating the anti-stress effects of Panax quinquefolium

Panax quinquefolium (PQ) is well acclaimed in literature for its effects on central and peripheral nervous system. The present study explores the effects of PQ on stress induced changes of corticosterone level in plasma, monoamines (NA, DA and 5-HT) and interleukin (IL-2 and IL-6) levels in cortex and hippocampus regions of brain and also indicate their possible roles in modulating stress. Mice subjected to chronic unpredictable stress (CUS, for 7 days) showed significant increase in plasma corticosterone level and depletion of noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) levels in cortex and hippocampal regions along with an increased level of IL-2 and IL-6 in the same areas. Aqueous suspension of PQ was administered daily at a dose of 100 and 200mg/kg p.o. prior to the stress regimen and its effects on selected stress markers in plasma and brain was evaluated. PQ at a dose of 200mg/kg p.o. was found to be effective in normalizing the CUS induced elevation of plasma corticosterone and IL-2, IL-6 levels in brain. Moreover, it was significantly effective in reinstating the CUS induced depletion of NA, DA and 5-HT in hippocampus, while NA and 5-HT in cortex of brain. However, PQ at a dose of 100mg/kg p.o. was found ineffective in regulating any of these CUS induced changes. Present study provides an insight into the possible role of PQ on hyperactive HPA axis in the regulation of immediate stress effectors like corticosterone, cytokines and brain monoamines. In this study, PQ has emerged as a potential therapeutic in the cure of stress related disorders and needs to be evaluated in clinical studies to ascertain its efficacy.